Saimm 202203 mar

VOLUME 122 NO. 3 MARCH 2022

Beyond Bricks and Mortar

A Future Beyond Bricks and Mortar

T

he COVID-19 pandemic has changed the world of work forever, as it catalyzed and brought forward changes to work arrangements for all companies. The Minerals Council as a progressive and agile organization also adapted to the ‘new normal’ by shifting to work-from-home office arrangements with a shift to virtual meeting platforms.

For the last 132 years the Minerals Council (previously known as the Chamber of Mines) has had a leading presence in the inner city anchored in the Minerals Council building, which was constructed in 1921. It was a six-storey building, constructed in the Renaissance style with the Minerals Council taking occupancy at the end of 1921 and holding its first AGM in the building on 27 March 1922.

Over the next three decades the building was expanded on the vacant land adjacent to the building and then in 1956 the various sections additions and extensions were united by cladding the building with precast stone and breaking though the various sections of the building to form a cohesive unit.

COVID 19 brought to light the simple fact that the 100-year-old building is no longer appropriate for the Minerals Council and for the foreseeable future world of work especially as the building was established to house a much larger centralized function than that of lobby and advocacy which the Minerals Council provides today.

The COVID-19 pandemic brought forward significant changes to the way that organizations work and function which catalyzed new thinking on the world of work. After two years of working from home, we have a better understanding that in our circumstances and given the nature of the Minerals Council activities, work is an activity and not a physical location. Simply stated, team members have been equally and more effectively operating from home than in the traditional office-based work arrangements.

The Minerals Council is in a process of moving out of the Inner City to a smaller building that is more in keeping with an agile modern organization – a building that is fit-for-purpose, adaptable and flexible. And although we do so with a certain nostalgia, we are looking forward to an exciting new chapter in our 132 year old existence.

Jeannette Hofsajer

The Southern African Institute of Mining and Metallurgy OFFICE BEARERS AND COUNCIL FOR THE 2020/2021 SESSION Honorary President

Nolitha Fakude President, Minerals Council South Africa

Honorary Vice Presidents

Gwede Mantashe Minister of Mineral Resources, South Africa Ebrahim Patel Minister of Trade, Industry and Competition, South Africa Blade Nzimande Minister of Higher Education, Science and Technology, South Africa

President

I.J. Geldenhuys

President Elect Z. Botha

Senior Vice President W.C. Joughin

Junior Vice President E. Matinde

Incoming Junior Vice President G.R. Lane

Immediate Past President V.G. Duke

Honorary Treasurer W.C. Joughin

Ordinary Members on Council Z. Fakhraei B. Genc K.M. Letsoalo S.B. Madolo F.T. Manyanga T.M. Mmola G. Njowa

S.J. Ntsoelengoe S.M. Rupprecht A.J.S. Spearing M.H. Solomon S.J. Tose A.T. van Zyl E.J. Walls

Co-opted to Members M. Aziz M.I. van der Bank

Past Presidents Serving on Council N.A. Barcza R.D. Beck J.R. Dixon R.T. Jones A.S. Macfarlane M.I. Mthenjane C. Musingwini

S. Ndlovu J.L. Porter S.J. Ramokgopa M.H. Rogers D.A.J. Ross-Watt G.L. Smith W.H. van Niekerk

G.R. Lane–TPC Mining Chairperson Z. Botha–TPC Metallurgy Chairperson A.T. Chinhava–YPC Chairperson M.A. Mello––YPC Vice Chairperson

Branch Chairpersons Johannesburg Namibia Northern Cape Pretoria Western Cape Zambia Zimbabwe Zululand

D.F. Jensen N.M. Namate Jaco Mans Vacant A.B. Nesbitt Vacant C.P. Sadomba C.W. Mienie

PAST PRESIDENTS *Deceased

* W. Bettel (1894–1895) * A.F. Crosse (1895–1896) * W.R. Feldtmann (1896–1897) * C. Butters (1897–1898) * J. Loevy (1898–1899) * J.R. Williams (1899–1903) * S.H. Pearce (1903–1904) * W.A. Caldecott (1904–1905) * W. Cullen (1905–1906) * E.H. Johnson (1906–1907) * J. Yates (1907–1908) * R.G. Bevington (1908–1909) * A. McA. Johnston (1909–1910) * J. Moir (1910–1911) * C.B. Saner (1911–1912) * W.R. Dowling (1912–1913) * A. Richardson (1913–1914) * G.H. Stanley (1914–1915) * J.E. Thomas (1915–1916) * J.A. Wilkinson (1916–1917) * G. Hildick-Smith (1917–1918) * H.S. Meyer (1918–1919) * J. Gray (1919–1920) * J. Chilton (1920–1921) * F. Wartenweiler (1921–1922) * G.A. Watermeyer (1922–1923) * F.W. Watson (1923–1924) * C.J. Gray (1924–1925) * H.A. White (1925–1926) * H.R. Adam (1926–1927) * Sir Robert Kotze (1927–1928) * J.A. Woodburn (1928–1929) * H. Pirow (1929–1930) * J. Henderson (1930–1931) * A. King (1931–1932) * V. Nimmo-Dewar (1932–1933) * P.N. Lategan (1933–1934) * E.C. Ranson (1934–1935) * R.A. Flugge-De-Smidt (1935–1936) * T.K. Prentice (1936–1937) * R.S.G. Stokes (1937–1938) * P.E. Hall (1938–1939) * E.H.A. Joseph (1939–1940) * J.H. Dobson (1940–1941) * Theo Meyer (1941–1942) * John V. Muller (1942–1943) * C. Biccard Jeppe (1943–1944) * P.J. Louis Bok (1944–1945) * J.T. McIntyre (1945–1946) * M. Falcon (1946–1947) * A. Clemens (1947–1948) * F.G. Hill (1948–1949) * O.A.E. Jackson (1949–1950) * W.E. Gooday (1950–1951) * C.J. Irving (1951–1952) * D.D. Stitt (1952–1953) * M.C.G. Meyer (1953–1954) * L.A. Bushell (1954–1955) * H. Britten (1955–1956) * Wm. Bleloch (1956–1957) * H. Simon (1957–1958) * M. Barcza (1958–1959)

* R.J. Adamson (1959–1960) * W.S. Findlay (1960–1961) * D.G. Maxwell (1961–1962) * J. de V. Lambrechts (1962–1963) * J.F. Reid (1963–1964) * D.M. Jamieson (1964–1965) * H.E. Cross (1965–1966) * D. Gordon Jones (1966–1967) * P. Lambooy (1967–1968) * R.C.J. Goode (1968–1969) * J.K.E. Douglas (1969–1970) * V.C. Robinson (1970–1971) * D.D. Howat (1971–1972) * J.P. Hugo (1972–1973) * P.W.J. van Rensburg (1973–1974) * R.P. Plewman (1974–1975) * R.E. Robinson (1975–1976) * M.D.G. Salamon (1976–1977) * P.A. Von Wielligh (1977–1978) * M.G. Atmore (1978–1979) * D.A. Viljoen (1979–1980) * P.R. Jochens (1980–1981) * G.Y. Nisbet (1981–1982) A.N. Brown (1982–1983) * R.P. King (1983–1984) J.D. Austin (1984–1985) * H.E. James (1985–1986) H. Wagner (1986–1987) * B.C. Alberts (1987–1988) * C.E. Fivaz (1988–1989) * O.K.H. Steffen (1989–1990) * H.G. Mosenthal (1990–1991) R.D. Beck (1991–1992) * J.P. Hoffman (1992–1993) * H. Scott-Russell (1993–1994) J.A. Cruise (1994–1995) D.A.J. Ross-Watt (1995–1996) N.A. Barcza (1996–1997) * R.P. Mohring (1997–1998) J.R. Dixon (1998–1999) M.H. Rogers (1999–2000) L.A. Cramer (2000–2001) * A.A.B. Douglas (2001–2002) S.J. Ramokgopa (2002-2003) T.R. Stacey (2003–2004) F.M.G. Egerton (2004–2005) W.H. van Niekerk (2005–2006) R.P.H. Willis (2006–2007) R.G.B. Pickering (2007–2008) A.M. Garbers-Craig (2008–2009) J.C. Ngoma (2009–2010) G.V.R. Landman (2010–2011) J.N. van der Merwe (2011–2012) G.L. Smith (2012–2013) M. Dworzanowski (2013–2014) J.L. Porter (2014–2015) R.T. Jones (2015–2016) C. Musingwini (2016–2017) S. Ndlovu (2017–2018) A.S. Macfarlane (2018–2019) M.I. Mthenjane (2019–2020) V.G. Duke (2020–2021)

Honorary Legal Advisers M H Attorneys

Auditors

Genesis Chartered Accountants

Secretaries

The Southern African Institute of Mining and Metallurgy Fifth Floor, Minerals Council South Africa 5 Hollard Street, Johannesburg 2001 • P.O. Box 61127, Marshalltown 2107 E-mail: journal@saimm.co.za

Editorial Board S.O. Bada R.D. Beck P. den Hoed I.M. Dikgwatlhe R. Dimitrakopolous* M. Dworzanowski* L. Falcon B. Genc R.T. Jones W.C. Joughin A.J. Kinghorn D.E.P. Klenam H.M. Lodewijks D.F. Malan R. Mitra* H. Möller M. Mullins C. Musingwini S. Ndlovu P.N. Neingo M. Nicol* S.S. Nyoni P. Pistorius P. Radcliffe N. Rampersad Q.G. Reynolds I. Robinson S.M. Rupprecht K.C. Sole A.J.S. Spearing* T.R. Stacey E. Topal* D. Tudor* F.D.L. Uahengo D. Vogt* *International Advisory Board members

Editor /Chairman of the Editorial Board R.M.S. Falcon

Typeset and Published by The Southern African Institute of Mining and Metallurgy P.O. Box 61127 Marshalltown 2107 E-mail: journal@saimm.co.za

VOLUME 122 NO. 3 MARCH 2022

Contents Journal Comment: From Acronyms to Energy

by D. Tudor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

President’s Corner: “Making the invisible visible”

by I.J. Geldenhuys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

iv v-vi

PROFESSIONAL TECHNICAL AND SCIENTIFIC PAPERS Implications of credit constraint on the formalization of artisanal and small-scale mining (ASM) in sub-Saharan Africa

by O.D. Eniowo, L.D. Meyer, S.R. Kilambo, and L.J. Gerber . . . . . . . . . . . . .

97

This paper explores the concept of formalization as it relates to the artisanal and small-scale mining (ASM) subsector and how it is being affected by the funding situation. The paper seeks to address the question as to whether formalization of artisanal mining operations can achieve the desired results with the lingering credit constraints. It is recommended that focus should be placed not only on access to credit in ASM, but also towards optimizing the credit-worthiness of ASM firms.

Void filling and water sealing in a decline in the Kalahari Manganese Field

by I. Serepa and N.C. Steenkamp . . . . . . . . . . . . . . . . . . . . . . . . . . . .

107

As part of a strategy to modernize the operations of a mine in the Kalahari Manganese Field in South Africa’s Northern Cape Province, the condition of the existing decline was investigated. Voids were identified behind the concrete lining of the hangingwall and water was flowing into the decline, causing softening of the concrete lining and deterioration of the surrounding rock mass. Remedial work comprising void filling and water sealing was completed successfully, and all voids were filled and stability achieved without compromising the concrete lining.

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Directory of Open Access Journals

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THE INSTITUTE, AS A BODY, IS NOT RESPONSIBLE FOR THE STATEMENTS AND OPINIONS ADVANCED IN ANY OF ITS PUBLICATIONS. Copyright© 2022 by The Southern African Institute of Mining and Metallurgy. All rights reserved. Multiple copying of the contents of this publication or parts thereof without permission is in breach of copyright, but permission is hereby given for the copying of titles and abstracts of papers and names of authors. Permission to copy illustrations and short extracts from the text of individual contributions is usually given upon written application to the Institute, provided that the source (and where appropriate, the copyright) is acknowledged. Apart from any fair dealing for the purposes of review or criticism under The Copyright Act no.

98, 1978, Section 12, of the Republic of South Africa, a single copy of an article may be supplied by a library for the purposes of research or private study. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means without the prior permission of the publishers. Multiple copying of the contents of the publication without permission is always illegal.

U.S. Copyright Law applicable to users In the U.S.A. The appearance of the statement of copyright at the bottom of the first page of an article appearing in this journal indicates that the copyright holder consents to the making of copies of the article for personal or internal use. This consent is given on condition that the copier pays the stated fee for each copy of a paper beyond that permitted by Section 107 or 108 of the U.S. Copyright Law. The fee is to be paid through the Copyright Clearance Center, Inc., Operations Center, P.O. Box 765, Schenectady, New York 12301, U.S.A. This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale.

MARCH 2022

VOLUME 122

The Journal of the Southern African Institute of Mining and Metallurgy

PROFESSIONAL TECHNICAL AND SCIENTIFIC PAPERS A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine

by L. Scheepers and D.F. Malan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

115

The seismic response to mining is expected to differ according to rock type and geotechnical conditions. As a case study of this behaviour, the seismicity at Mponeng Mine was investigated. Moment-tensor analyses indicated that the majority of the large-magnitude events are not related to geological structures, but are face-related, implying that shear failure of intact rock is occurring ahead of the mining front. Preliminary modelling indicated that the closure volume for the shale footwall may be higher than for the quartzite footwall, providing a possible explanation for the observed difference in seismic response.

Development and beneficiation technology of rare earth ores in China

by Y. Chen, D. He, and J.H. Potgieter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

125

The ore characteristics of four typical rare earth element (REE) deposits in China are introduced. The conventional beneficiation techniques, including gravity separation, magnetic separation, flotation, and hydrometallurgical processing, are discussed. Some of the latest laboratory findings and industrial applications are presented, as well as the development of novel reagents for REE processing in China.

Climate impacts of fossil fuels in today’s electricity systems

by L. Schernikau and W.H. Smith . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

133

The authors examined airborne CO2, which is less than half of emitted CO2, as well as reported CH4 emissions, and the global warming potential of CH4 as published by the IPCC for coal and natural gas. The surprising conclusion is that surfaced-mined coal appears better for the climate’ than the average natural gas, and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to unintended consequences. Switching from coal to natural gas, especially LNG, will not have the desired effect of reducing predicted future global warming, in fact, quite the contrary.

Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks

by M.Z. Emad, Y. Majeed, and G. Rehman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

147

The current practices in rock salt mining include drilling and blasting, which introduces undesired fractures in the product blocks. The current research focuses on the extraction of rock salt blocks by applying conventional cuboid-shaped block mining techniques from quarries, including wedges and feathers, expansion chemicals, and controlled blasting. The results of laboratory as well as in-situ testing showed that the wedges and feathers technique is the most suitable method for mining rock salt blocks of the desired size and shape, while minimizing cracking.

Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine, Sweden

by S. Manzoor, M. Danielsson, E. Söderström, H. Schunnesson, A. Gustafson, H. Fredriksson, and D. Johansson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

155

This research investigated whether measurement while drilling (MWD) can be used to predict rock fragmentation in sublevel caving (SLC). The results show a stronger correlation for fine and medium fragmented material with rock type (MWD) data than coarser material. A model is presented for prediction of fragmentation, and correlation test results show that MWD data can be used to predict fragmentation in an SLC mine.

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al

Journ

From Acronyms to Energy

ent Comm

T

he first thing that struck me when I read through the abstracts of the papers in this edition was that they are all the work of authors who are based in South Africa. This is a wonderful illustration of the capabilities that exist in South Africa to serve the mining and metallurgical industry.

A wide range of subject matter makes for some challenging reading, with topics that cover artisanal mining, continuous casting in steelmaking, mine design, procurement, exploration drilling, and tailings storage facilities.

I have become increasingly aware of the use of abbreviations and acronyms when reading any technical literature and I illustrate this with information that comes from Drax, a power generating facility near Selby, North Yorkshire, not too far from where I live in the UK. Drax Power Station (https://www.drax.com) was constructed in the late 1960s and it produces about 6% of the UK’s electricity. It has six boilers, four of which have now been converted to burn biomass instead of coal. The biomass is wood pellets that are sourced from the USA and Canada and shipped to the UK and then railed to the power station. Drax burns in the region of 8 Mt/a of wood pellets.

Drax is the home of the largest decarbonization project in Europe and is now the site of innovation for bioenergy with carbon capture and storage (BECCS), a negative emissions technology essential for fighting the climate crisis.

It was the BECCS acronym that hit me when I looked at the Drax website while I was trying to gain a better understanding of Drax’s biomass operations. I have since been drawn into a state of confusion!

A press release dated 15 December 2021 states that: ‘ Drax has approved a further investment in the development of its Yorkshire carbon capture project that will see Worley commence work on the Front-End Engineering and Design (FEED) phase. ‘ [The] Contract is part of a 2022 capital investment programme of around £40m that includes site preparation works for BECCS and decommissioning of coal infrastructure following the end of Capacity Market obligations at the end of September 2022. ‘ BECCS is seen as an essential technology to tackle climate change with the project at Drax set to capture and permanently lock away at least eight million tonnes of CO2 a year ... ’ The UK’s largest power station is looking for a new subsidy. Drax’s £10 billion of subsidies to burn wood for power will come to an end In 2027, and with it Drax’s means of generating profit. In order to continue operating past 2027, Drax plans to build the world’s first bioenergy with carbon capture and storage (BECCS) plant. By capturing the carbon emissions of wood burned for electricity and storing them under the North Sea, Drax intends to generate the negative emissions the UK is reliant upon to reach national climate targets, and would seek to be rewarded for this through new public subsidy.

Drax received more than £800 million in biomass subsidies from the UK government (British taxpayer) in 2020 - with no obvious climate benefit. However, critics suggest that the scientific consensus on ’sustainable’ biomass may soon change. ‘ Recent science demonstrates that burning forest biomass for power is unlikely to be carbon neutral – and there’s a real risk that it’s responsible for significant emissions.’ Ember Chief Operating Officer Phil MacDonald stated. https://ember-climate.org/ ‘ Before the government spends more taxpayer money on biomass, we should make sure we know we’re getting the emissions reductions that we’re paying for.’

It would be interesting to see an energy balance that details the energy consumed for the production of the wood pellets plus the energy required to transport, ship, and rail the pellets to Drax. In other words the energy input cost to Drax and compare it to the energy output cost.

It seems to me that the Drax story has a long way to go, and all this because of my interest in an acronym!

D. Tudor

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nt’s

de Presi

er

“Making the invisible visible”

Corn

T

he United Nations World Water Development Report is a flagship report on water and sanitation issues, focusing on a different theme in each issue.

The report provides insight on main trends concerning the state, use and management of freshwater and sanitation, and is launched in conjunction with World Water Day. The intent of this report is to provide decision-makers with knowledge and tools to formulate and implement sustainable water policies.

Groundwater has always been critically important to human society and ecosystems, but it has not always been fully recognized as part of water security.

The most recent UN World Water Development Report, launched on 21 March 2022, highlighted how countries with high water security risks should make groundwater the heart of sustainable development policymaking. Making the invisible visible was the key message as the UN and many other organizations globally marked World Water Day on 22 March 2022.

The UNESCO report is available online (https://unesdoc.unesco.org/ark:/48223/pf0000380721).

According to the UN water report, groundwater accounts for 99% of all liquid freshwater on Earth, and has the potential to provide societies with social, economic, and environmental benefits and opportunities. Groundwater already provides half the volume of water withdrawn for domestic use by the global population, including drinking water for most of the rural population, who do not get their water delivered to them via supply systems. Furthermore, around 25% of all water withdrawn for irrigation is extracted from groundwater sources. It is noteworthy however that this natural resource is often poorly understood, and consequently undervalued, mismanaged and even abused.

While South Africa is not listed as one of the 30 driest countries in the world, there are significant water challenges in the country. Rankings aside, there are regions where there is water stress due to regional climate and climate variances.

This vulnerability to water distress was particularly in the spotlight during the drought that caused Cape Town’s water crisis in 2017, with many residents of Cape Town lining up day and night to fill containers with water from the city’s few natural springs. After months of warnings through an anomalously long drought, Cape Town was on the verge of becoming the world’s first major city to run out of water. Freshwater dams had dipped below 25% of capacity, and levels continued to fall. If the dams fell to 13.5% of capacity, the municipal water network would shut down, and millions of residents would face severe water restrictions. The dams fortunately never reached that critical 13.5% level, dubbed Day Zero. Four months later, the rains returned, and dam levels rose. The shadow of Day Zero however still lingers over Cape Town, and the memory of this continues to impact the city, with the average daily water use in the city still between 700 and 800 million litres, about half what it was in 2014 (www.technologyreview.com, 23 December 2021).

But even if consumption remains low, the next drought could yet again challenge the city’s continued efforts. Scientists believe that Cape Town will face more sustained droughts over the next 100 years

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President’s Corner (Continued) because of climate change. The drought of 2017 serves as a great example of the impact climate change can have on society and how crucial it is to plan for these impacts. Cape Town’s planned mitigations include diversifying water sources to include groundwater from wells and boreholes, but also includes recycled stormwater, treated wastewater, and household grey water, which could be reused for gardening and other applications. There are also plans for more desalination, controls on water use, leak reduction, and infrastructure investment. All of these coming at a significant infrastructure investment cost.

In the driest, and more remote parts of South Africa, groundwater may be the only water people have access to, and it is crucial to integrate groundwater management into our water plans, both as policymakers and as an industry. Despite being invisible, the impact of groundwater on our daily lives is visible all around us. Our drinking water and sanitation, our food supply and natural environment all rely on groundwater stability and quality. A healthy and stable groundwater system is also critical in the balance of ecosystems, such as wetlands. In deltas and coastal areas, groundwater ensures the stability of the ground and prevents seawater intrusion underground.

The new UN report highlights that groundwater is therefore seen as central to the fight against poverty, and key to food and water security on a global scale. Reliance on groundwater will only increase in the future, mainly due to growing water demand by all sectors, combined with an increasing variation in rainfall patterns. The report describes the challenges and opportunities associated with the development, management, and governance of groundwater across the world, and is worth reviewing as we remind ourselves of the importance of water.

Understanding the role that groundwater plays in our daily lives and how we can use this largely available, yet fragile resource sustainably is critical. Unfortunately, human activities frequently overuse and pollute groundwater, and, in many instances, we do not even know how much water is down there.

Groundwater is out of sight, but it should not be out of mind. What we do on the surface matters underground and will matter tomorrow.

I.J. Geldenhuys President, SAIMM

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Implications of credit constraint on the formalization of artisanal and small-scale mining (ASM) in subSaharan Africa

by O.D. Eniowo1, L.D. Meyer1, S.R. Kilambo1, and L.J. Gerber1 Affiliation:

University of Pretoria, South Africa.

1

Correspondence to: O.D. Eniowo

Email:

od.eniowo@up.ac.za

Dates:

Received: 2 Jul. 2021 Revised: 5 Jan. 2022 Accepted: 24 Jan. 2022 Published: March 2022

How to cite:

Eniowo, O.D., Meyer, L.D., Kilambo, S.R., and Gerber, L.J. 2022 Implications of credit constraint on the formalization of artisanal and small-scale mining (ASM) in sub-Saharan Africa.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 97-106 DOI ID: http://dx.doi.org/10.17159/24119717/1665/2022 ORCID: O.D. Eniowo https://orcid.org/0000-00016173-7709 L.D.Meyer https://orcid.org/0000-00019004-3610 S.R. Kilambo https://orcid.org/0000-00019433-9846 L.J. Gerber https://orcid.org/0000-00023536-7406

Synopsis Artisanal and small-scale mining (ASM) operations continue to grow across sub-Saharan Africa and serve as a source of livelihood to many rural communities. Owing to safety, health, environmental, and social concerns, the occupation has been regarded as a menace in several sub-Sahara African countries.

Recent studies in the field of ASM prescribe formalization as a way to tame its excesses while enhancing its potential. This paper explores the concept of formalization as it relates to ASM and how it is being affected by the funding situation. The paper seeks to address the question as to whether formalization of artisanal mining operations can achieve the desired results in view of the lingering credit constraints in this mining subsector. It is recommended that, as a way of extending the scope of formalization, focus should be placed not only on access to credit in ASM but also towards optimizing the creditworthiness of ASM firms, with the goal of improving the viability of the operations.

Keywords artisanal and small-scale mining, credit facilities, formalization.

Introduction Artisanal and small-scale mining (ASM), which is characterized by low-tech, labour-intensive extraction and processing, has continued to grow in sub-Saharan Africa, serving as a source of livelihood to many communities. ASM activities are carried out by individuals, groups, families, or cooperatives with minimal or no mechanization, usually by those in the informal sector (Hentschel, Hruschka, and Priester, 2003), and involve in many instances illegal operations like the ‘zama-zamas’ in South Africa and the ‘galamsey’ in West Africa. Public commentary on ASM has largely been negative, dominated by reports of gold smuggling, money laundering, child labour, and links with organized crime (Planetgold, 2020a), poor safety and health, environmental pollution, and incidences of mercury and lead poisoning (Clement and Olaniyan, 2016; Owolabi and Opafunso, 2017; Hilson, Hilson, and Maconachie, 2018). Because of these aspects, mineral-rich countries around the world consider that ASM should be discouraged to create space for large-scale mining (LSM) companies (Cuvelier, 2019).

Nonetheless, the relevance of ASM is not in doubt. The occupation is attractive, especially for rural communities, for several reasons. One selling point is that it involves lower labour and technical costs.

ASM operators can explore sites that are difficult for large mining companies to access and can excavate deposits with lower volumes (Geenen and Radley, 2014). The occupation plays key roles in opening up remote areas to development and can significantly reduce rural-urban migration (Hilson and McQuilken, 2014). It has been argued that local economies are primarily sustained by ASM and not LSM (Yankson and Gough, 2019). At the economic level, ASM contributes 15 to 20% of the global output of minerals and metals, in particular producing up to 20% of all diamonds, 20% of gold, and 80% of all sapphires (Buxton, 2013). The importance of ASM, especially for the sustenance of rural communities, explains its widespread proliferation across sub-Saharan Africa in recent history (See Table I for estimates of employment generated by ASM across the region).

ASM is usually practiced by people who are poor, and because the miners are mostly untrained, they sometimes do not realize that the methods they use for mining and processing of ores pose a great danger to their health and the environment. Most ASM operators would like to semi-mechanize to upgrade production capacities or develop new reserves. While there may be a reasonable concern

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Implications of credit constraint on the formalization of artisanal and small-scale mining Table I

Estimate of ASM employment showing minerals mined in selected sub-Saharan African countries (Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development (IGF), 2018) Country

Angola Burkina Faso Central African Republic Chad Côte D’ivoire DRC Eritrea Ethiopia Ghana Guinea Liberia Madagascar Malawi Mali Mozambique Niger Nigeria South Africa Sierra Leone South Sudan Tanzania Uganda Zimbabwe

Directly working in ASM

Estimated number of dependents

Main minerals mined by ASM

150 000 200 000 400 000 100 000 100 000 200 000 400 000 500 000 1 100 000 300 000 100 000 500 000 40 000 400 000 100 000 450 000 500 000 20 000 300 000 200 000 1 500 000 150 000 500 000

900 000 1 000 000 2 400 000 600 000 600 000 1 200 000 2 400 000 3 000 000 4 400 000 1 500 000 600 000 2 500 000 2 400 000 1 200 000 2 700 000 2 500 000 1 800 000 1 200 000 9 000 000 900 000 3 000 000

Diamonds Gold Gold, diamonds Gold Gold, diamonds Diamonds, gold, coltan Gold Gold Gold, diamonds, sand Gold, diamonds Gold, diamonds Coloured gemstones, gold Coloured gemstones, gold Gold Coloured gemstones, gold Gold Gold Gold Gold, diamonds Gold Gold Gold Gold, diamonds, coloured gemstones

in some quarters that artisanal miners lack the skills required to operate better technology (as expressed in Saldarriaga-Isaza, Villegas-Palacio, and Arango, 2013), there are instances where they are quite knowledgeable in the use of technology and may have perhaps seen its use in neighbouring mine sites (Perks, 2016). Yet, without financial resources, they are forced to make do with what is readily available. Thus, in this case, the main bottleneck is the lack of resources to be able to adapt and replicate better mining techniques and equipment.

Given the potential of ASM, academic discussion as to the way forward has been largely on the formalization of the industry.

Formalization, in this context, includes efforts to legalize ASM activities, where ASM is conducted on an illegal basis. It typically involves demanding that miners secure the required permits, in line with the law, and launching programmes which foster technical and/or financial support for licensed miners, among others (Hilson, 2020). There have been genuine attempts by governments across sub-Saharan Africa to formalize ASM operations (Siwale and Siwale, 2017). These efforts have yielded some progress, with widespread granting of licenses to artisanal and small-scale miners and reports of some governments designating and allocating mineralized land specifically for ASM operations (Fold, Jønsson, and Yankson, 2014). There are instances, as is the case in South Africa, where the ASM sector was profiled by the national government as an intervention to develop local economies. Nevertheless, the question of the viability and sustainability of ASM operations still persists (Perks, 2016; Planetgold, 2020a). Along this line, this article examines access to credit for ASM operations and its implication for attempts at formalization across sub-Saharan Africa.

This paper is a review of literature that covers selected articles on ASM in the past four decades, which is generally regarded as 98

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the period of widespread proliferation of ASM operations in subSaharan Africa and across the developing world1. Specifically, the review focuses on selected articles that discuss access to credit for artisanal miners2 in relation to formalization of the ASM sector within the stated timeframe. Its purpose is to draw attention to the gap in the funding mechanism of ASM. This is achieved by first exploring the existing funding mechanisms for ASM, then using these lessons to discuss the need to expand the scope of formalization efforts to capture access to credit and enhance the ability of ASM operators to attract forming lending. Thus, the major themes in this paper include a review of the existing funding mechanism for ASM operations, implications of ASM credit constraint, the concept of formalization, access to credit, and discussion of the findings.

Existing funding mechanisms for ASM operations A review of empirical findings on available funding for ASM activities indicates that the bulk of the operations are selffinanced. They also obtain funding from other sources. The funding sources, their structure, benefits, and drawbacks are further explored below.

External informal financing One of the most common sources of funding for artisanal mining across sub-Saharan Africa and other developing countries is what can be termed ‘external informal financing’. It typically involves This review paper forms the background to a doctoral research programme being carried out in the Mining Engineering Department at the University of Pretoria While different forms of classification are used in the literature, in this article, ‘artisanal mining’, ‘small-scale mining’, and ‘artisanal and small-scale mining’ (ASM) are all used interchangeably

1

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Implications of credit constraint on the formalization of artisanal and small-scale mining miners receiving funds for investment from external sponsors who have interest in the mineral to be mined. Mostly, these sponsors are buyers who provide investment capital to miners in exchange for an agreement that the miner will sell the mineral produced to them, usually below the market price.

Varying viewpoints have been expressed in the literature about external informal financing. The perception of its importance in sub-Saharan Africa seems to deviate from the view in some other developing countries. As an illustration, Verbrugge (2014) provides a positive impression based on his experience exploring informal financing arrangements in Southern Philippines. In this financing arrangement, described in the study as ‘back-financing’, the financier retains about two to three shares of the ore proceeds after deducting operational expenses and the landowner’s share, then leaves the remaining share to the miner. Verbrugge (2014) argues that artisanal gold mining is a dangerous operation and miners may follow the veins of gold deeper into the earth, which increases the risks of flooding or collapse of the tunnel. At this point, the ability to continue with the operation usually depends on the availability of cash to provide reinforcement and other equipment. The intervention of external financiers therefore becomes very helpful. In this case study, it is further argued that the benefit of such arrangement is that the risks are shared among the participants in the investment, and this enables the miners to continue with their operation, focusing on the mining activities and not needing to worry about subsistence needs.

However, across sub-Saharan Africa, the findings of empirical studies on informal financing arrangements are rarely positive.

For example, Perks (2016), who looked at informal financing arrangement in Tanzania and Rwanda, asserts that the way such finance and trade relations are structured usually leads to artisanal miners receiving less than the market value for their products. In this case study, it is argued that the absence of formal financing opportunities and technological support has pushed miners to adopt short-term mineral extraction strategies which rely on informal arrangements with outside financiers, traders, and sometimes large-scale mining companies in order to access the global mineral market.

Hilson and Ackah-Baidoo (2011) document how artisanal miners in Ghana rely on sponsors for loans to acquire crushers, pumps, and generators. These sponsors usually require high interest rates from the miners, in addition to the precondition that miners agree to sell their produce to the sponsors on ‘inequitable terms’. There are instances where sponsors (who are also buyers) ask for a price cut of up to 10–15% less than the market rate (ibid.).

Consequently, the report of the Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development (2018) asserts that the financiers, which the study described as ‘power holders’ in ASM, make the largest share of profit, while those doing the work on the ground barely make enough to survive.

This led Perks (2016) to argue that such a form of capitalization prevents the miners from having the decision-making power to plan far into the future on their business. Fold et al., (2014) used these lessons to justify why interventions downstream in the gold value chain, on access to mineral markets, could facilitate the formalization efforts upstream for artisanal miners.

The body of literature further discusses the potential for vested interests of financiers to subvert ASM formalization by governments and funding agencies such as the World Bank. Perks (2016) again illustrates how middlemen and financiers opposed technical and financial assistance by the World Bank to artisanal miners in Tanzania in 2014. These actors, who pre-finance a large The Journal of the Southern African Institute of Mining and Metallurgy

majority of the gold mines in the country, considered outside assistance as damaging to their monopoly on gold supplies from the artisanal mine sites.

While some documented cases expose the opportunistic tendencies of financiers to exploit the informal nature of ASM, there are instances where legitimate license-holders who are not able to acquire the funds needed to advance their operations willingly make way for artisanal miners on their concession areas, just so they can have access to the mineral to be mined. Based on experience in Uganda, Siegel and Veiga (2009) provide a tale of how a small-scale license holder who could not afford to employ a formal mining crew allowed ‘illegal’ miners to trespass on his concession area, while supporting them with tools and meals, with the agreement to purchase the gold they produce. The study argues that such a scenario underscores the flaw in formalization efforts where the licensee ‘remains unable to access technical and financial resource(s) to advance his operation beyond the liveand-go-on artisanal stage’ (Siegel and Veiga, 2009, p. 54).

Donor interventions Another major source of funding for ASM operations is through grants by international and domestic donor agencies. Some of these grant schemes are carried out by the donor agency in collaboration with the host government. A typical example of such donor initiatives is the World Bank support in Nigeria, which has a budget of US$120 million under the Sustainable Management of Mineral Resources Project (SMMRP), of which US$10 million was earmarked for ASM (Oramah et al., 2015). According to the Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development (IGF, 2018), the SMMRP ran from 2004 to 2012 in Nigeria, provided 245 grants to 147 ASM cooperatives and 98 community entities, and included projects to enhance granite, gravel, sand, and laterite quarrying. A similar World Bank SMMRP scheme in Uganda is documented in IGF (2018), which ran from 2003 through 2011. To access this grant, miners only needed to form groups and be further trained on financial management and procurement. The IGF (2018) noted that the scheme motivated several ASM groups to start village savings and loans associations that could provide small loans to members in times of need (e.g. to pay children’s school fees, build houses, etc.).

In Tanzania, Pedersen et al. (2019) examined a World Bank intervention programme, again through SMMPR, and identified its positive contributions. The donor intervention supported current efforts to upgrade the ASM industry, which also fits into the current resource nationalism agenda of the country. Some previous donor initiatives targeting ASM in Tanzania include the Global Mercury Project (GMP) and initiatives by domestic NGOs. It is noted that ‘by systematically working with the state institutions that control the sector, the SMMRP has been by far the most far-reaching and potentially impactful support programme’ (Pedersen et al., 2019, p. 343). This argument underscores the role of the state in intervention programmes and why any such programme must be captured along the line of formalization.

It is noteworthy, that donor grant funding is helpful in the short term, but it usually fails to align with a business-led approach to develop sustainable long-term solutions. Additionally, as expressed in Siegel and Veiga (2009), donor interventions by international development agencies often come in the form of limited-term ‘grants’ and not ‘loans’. It has been suggested that a more sustainable approach would be for development agencies to VOLUME 122

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Implications of credit constraint on the formalization of artisanal and small-scale mining actually lend to miners as a way of addressing the capital shortfall.

This can better enhance the viability of such operations. Another drawback is that competition for grants is very stiff. Thus, even when a miner manages to present every requirement, a grant is still not assured.

Government loan facilities Siegel and Veiga (2009) drew evidence from Namibia and Mozambique on the implementation of government loan facilities to ASM. In Namibia, the government provided US$92 million in loans through the Mineral Development Fund for projects, with emphasis on the sinking of shafts, exploration, and mine expansion. The loans were provided at low interest rates, with generous repayment periods and minimal bureaucratic overheads.

The loan scheme has recorded a 92% repayment rate. A similar fund was provided in Mozambique which offered credit facilities, provided miners could show a mining license, feasibility study, plan for repayment, and proof of collateral (20% of the loan amount) (Siegel and Veiga, 2009). The key takeaway from these loan schemes is that they were relatively successful.

Planetgold (2020b) reports a similar loan scheme in Ghana, circa 2005, where the government provided loans to small-scale miners amounting to US$500 000. The loan was provided through the government’s Mineral Development Fund and coordinated by officials of the Minerals Commission, which is the country’s major mining policy-making body. The loans were provided primarily to gold and salt miners. To access a loan, the miners were required to form cooperatives and were collectively bound by the terms of the loan. The loans were provided in the form of cash, tied to equipment and consumables, and beneficiaries were required to repay the loan in agreed instalments at a subsidized interest rate.

Another feature of the scheme is that miners were required to share the mine machinery purchased such as crushers, pumps, and generators. Findings on the impact of the scheme are mixed.

Nevertheless, a key takeaway is that the programme was relatively successful despite the initial teething problems, as borrowers agreed to the terms of the loan and the requirements in relation to repayment (Planetgold, 2020b).

There are recorded attempts in the literature of government loan interventions that were not so successful. An example is a South African government loan scheme to provide support for small-scale mining projects, managed by the National Steering Committee (NSC) under the supervision of the South Africa Department of Mineral Resources (DMR) – now the Department of Mineral Resources and Energy (DMRE). The funding structure was 90% loan, and applicants were required to source the remaining 10% themselves. The funds were provided for equipment purchases, operational costs, and for rehabilitation guarantees. Findings on the performance of the loan scheme indicate that borrowers were unable to repay their loans, and that led to the programme’s cancellation in 2005 (ibid.). However, it was argued that one possible reason for the scheme’s failure is that the bulk of the loans were provided to those in the industrial minerals sector, which has a relatively small profit margin. Perhaps interventions in small-scale gold mining, which has much higher profit margins, could have led to different outcomes. Another reason for the failure of the scheme was the inability of the DMR to monitor borrowers or pre-screen their applications (ibid.).

Apart from direct funding of ASM operations, there are documented cases in the literature where the state became involved in a section of the value chain of ASM mineral production 100

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to enhance formalization efforts. An example of this scenario was reported by Fold, Jønsson, and Yankson (2014), where in 1990 the Tanzanian government (through the Bank of Tanzania) legalized the selling of gold to government-appointed banks. The state’s policy aimed to reduce illegal trading and smuggling of gold in the country. With this policy, no questions were asked about the origin of the gold. Thus, the system became popular among ASM operators who suddenly had access to legal and locally available gold purchasers. Consequently, the official gold exports rose rapidly from just above a million US dollars in 1989 to more than 40 million US dollars in 1992, reflecting a significant reduction in illegal gold exports (Fold, Jønsson, and Yankson, 2014).

The observed limitation of government loans in the ASM industry is in its sustainability. Even when government loan schemes are successful, they are often short-lived. Also, the criteria set out for access to government loans sometimes place them out of reach for most artisanal miners.

Miners’ cooperatives and village savings and loans associations Mining cooperatives (sometimes called associative entrepreneurships) are local associations set up by miners to provide savings facilities and easy access to credit as a service for their members (Chaparro Avila, 2003). Mining cooperatives represents an alliance between individual interests to achieve collective benefits for all those involved. Alves, Ferreira, and Araújo (2019) asserted that alliance via cooperatives can be a key element in improving sustainability in the ASM sector. They argued that, as a business model, the use of cooperatives has not been fully explored in the mining sector compared with other sectors such as agriculture, health, credit, and consumerism.

Some successful cases of cooperatives, however, have been documented. Perks (2016) reports a successful cooperative model adopted in Rwanda, where cooperatives are obliged to employ an administrator/accountant whose role is to formalize the cooperative’s dealings and ensure better accountability of their financial resources. Under the term ‘associative entrepreneurship’, the collaboration between mining cooperatives and government regulating agency has produced some successes in Rwanda.

The cooperatives are obliged by the government to pay social insurance and pensions to their members.

With the assistance of the state regulating agency, cooperatives have managed to hire the services of geologists to evaluate potential reserves (Perks, 2016). This underscores the potential of self-regulation in the ASM sector (Eniowo and Meyer, 2020). Saldarriaga-Isaza, Arango, and Villegas-Palacio (2015) therefore recommend that governments need to strengthen associative entrepreneurship as a way of formalizing the ASM industry.

Another initiative that is increasingly in use in some subSaharan African countries is that of village savings and loans associations (VSLAs). Reichel (2019) reports the results from a community-led savings and credit project implemented by the Canadian nongovernmental organization IMPACT in artisanal gold mining communities in the Democratic Republic of Congo (DRC). The scheme recorded very encouraging repayment rates (98%). More importantly, it is believed that such saving groups can contribute to local formalization efforts, since they can significantly increase the financial literacy of their members, which is one of the requirements for a formalized ASM operation.

It must be noted, that VSLAs are not able to address all financial The Journal of the Southern African Institute of Mining and Metallurgy

Implications of credit constraint on the formalization of artisanal and small-scale mining problems in ASM, e.g. major capital investment. However, they can contribute to cover the basic financial needs of miners, such as medical bills, children's school fees, food security, and housing needs, before banks or other formal lenders step in (ibid.).

Commercial bank loans Despite the potential of ASM, the absence of formal bank investment in the sector is worrisome. The few recorded attempts to fund ASM operations through commercial bank loans usually have challenges. A typical illustration of this was an initiative to supply credit to emerald miners in Zambia, documented in Siwale and Siwale (2017). To access the fund, which was made available by the European Investment Bank (EIB), miners were required to provide bankable documents with requisite technical documents if their applications were to be considered. Siwale and Siwale (2017, p. 197) assert that ‘due to the low educational levels among these miners, none were able to submit an application deemed acceptable to the EIB’. More appalling was that in this case, the technical assistance unit of the bank that was meant to assist loan applicants to design bankable documents required miners to pay 30% of the cost of designing the documents. Where applications for a loan were successful, miners were asked to pay the balance of 70%. In effect, artisanal miners could not afford these costs, and the project completely failed to fund any ASM operation.

Microfinance loans To close the funding gap for artisanal miners, another reasonable option would be the creation of microfinance institutions specifically for artisanal mining operations, similar to the agricultural microfinance banks and other trade microcredit agencies in developing countries. Blore (2015) noted that, remarkably, only a few attempts have been made to create alternative financing networks specifically for artisanal mining, despite the rise of the microcredit movement. More recent literature, however, provides evidence of microcredit initiatives in sub-Saharan Africa that brings glimpses of hope for formal lending

in the industry. A typical example is the microfinance initiative used to support an equipment lending model based on a ‘group sharing’ arrangement, in the Bolgatanga and Tongo communities in Ghana. In this model, participants in a group rank their fellow group members according to their financial strength. This rank is used to determine who receives the loan first, and to elect a chairperson who coordinates the repayment. One useful feature of this financing arrangement is that the risk is shared across the group’s members (Planetgold, 2020b).

While microfinance funding may be quite helpful as a funding option for ASM activities, the funding provided by such schemes is usually not enough to cater for efficiently mechanized small-scale mining operations. Thus, there is a need for ASM operations to be able to access commercial loans to acquire mining equipment in order to scale up their operation, improve their performance, and more importantly, ensure that their operation is safer and more environmental-friendly.

A snapshot of the major credit schemes used to fund artisanal and small-scale mining operation in selected sub-Saharan African countries and their successes and failures is shown in Table II.

Implications of ASM credit constraints As shown, ASM operators usually suffer from a lack of access to formal lending, which fuels the perpetuity of the poverty in ASM operations on the one hand, and increases the adverse consequence for safety, health, and the environment on the other.

It has been shown that the primary factor responsible for the problems caused by ASM is the inability of operators is to obtain capital for investment to advance their operations (see Figure 1). This leads to the use of inadequate techniques for mining and processing, resulting in low recoveries and productivity and traps them into crude and inefficient mining and processing. A consequence of this is the poor health, safety, and environmental record attributed to the occupation (Barry, 1996). Richard Noetstaller, in his keynote address at a World Bank round table on ASM. asserts that ‘most of the harmful effects of artisanal mining

Table II

Credit schemes used to fund ASM in selected sub-Saharan African countries (author’s compilation) Authors

Credit scheme

Country

Remarks

Planetgold (2020b) Siegel and Veiga (2009) Siegel and Veiga (2009) Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development (2018) Planetgold (2020b) Perks (2016) Reichel (2019)

Government loan facilities Government loan facilities Government loan facilities Government loan facilities

South Africa Namibia Mozambique Zimbabwe

Unsuccessful, borrowers were unable to repay Successful: 92% repayment rate recorded Successful, but out of reach for most miners Successful, but short-lived

Government loan facilities Mining cooperatives Village savings and loans associations (VSLAs) Donor grants - World Bank Donor grants – World Bank

Ghana Rwanda Democratic Republic of Congo (DRC) Nigeria Uganda

Successful, though had initial teething problems Successful Successful

Donor grants – World Bank Informal finance Informal finance Commercial loan Microfinance loan

Tanzania Ghana and Tanzania Rwanda Zambia Ghana

The scheme is just emerging.

Unfavourable to miners Unfavourable to miners Unsuccessful Successful

World Bank (2012) Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development (2018) Fold, Jønsson, and Yankson (2014) Fold et al. (2014) Perks (2016) Siwale and Siwale, (2017) Planetgold (2020b)

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Satisfactory Successful

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Implications of credit constraint on the formalization of artisanal and small-scale mining Thus, proponents of formalization argue that the acquisition of mineral properties benefits the miners by providing them with a form of collateral through which they could access support to upgrade their operations. They argue that poor people possess assets, but because these assets exist in the informal sector, they lack legal representation that can help generate adequate capital or value. It is therefore believed that formalization will give informal miners a face and more visibility that can bring about financial intervention from the state and financial organizations (Siwale and Siwale, 2017).

Figure 1—Negative circle affecting artisanal miners (Noetstaller, 1995)

is directly related to the technical and financial limitations typical for the subsector’ (Noetstaller, 1995, p. 5).

A typical illustration of the offshoot of the ASM poverty circle is that of tin ore (cassiterite) artisanal mining in Jos, Nigeria carried out by groups of community peasants using a local method of mining called loto3. Mallo (2011) examined loto mining and argued that miners using this technology lead a hard, insecure, unhealthy, and dangerous life while their earnings remain low.

Each miner receives an average income of less than US$1 a day, placing them squarely in the broad category of ‘absolute poverty’.

Apart from that, the loto mining technique results in large-scale environmental degradation which adversely affects the land, waters, and other aspects of the ecosystem.

Noetstaller (1995) states that, given the crude processing techniques typically employed in ASM, usually only about 50% of the valuable minerals is recovered, the remainder being lost in the tailings and thus wasting non-renewable resources. This argument, among others, fuels the recent efforts to prioritize the issue of formalization of artisanal mining. What it involves, and why is important to do so, are discussed in the next section.

Formalization of ASM – The major discussions The concept of formalization, for the development of informal economic activities, such as artisanal mining, has its origin in the study of Hernando de Soto, a Peruvian economist, who argued that property rights are the key to overcoming poverty in the developing world. He opined that the issue of formalization is ultimately about a clash between what can be termed the ‘mainstream legal economy’ and the ‘informal or extra-legal economy’ (De Soto, 2000). As much as 80% of economic activities are part of the informal (extra-legal) economy . Thus he argues that by not extending rights to the informal economy, government institutions are denying economic freedom to an overwhelming majority of the world’s population, who exist in a state of ‘legal apartheid’ (Siegel and Veiga, 2009). As a result, there is now a consensus among scholars that the foundation of intervention in ASM lies in formalization. Formalization, in the context of ASM, involves governments and other stakeholders demanding that ASM operators obtain necessary permits, in line with the law, with the goal of attracting support to their operations. The expected benefits that formalization would bring to the ASM industry, as documented in the literature, are discussed below.

Collateral security It has been established that the lack of collateral security4, occasioned by the peasant nature of ASM operators, is a major impediment to formal lending in ASM (Eniowo and Meyer, 2020).

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Access to mineralized land Regarding access to land with mineral deposits, the issue discussed in the literature relates to how ASM operators could have easy and affordable access to mining licenses. Studies have documented instances where local populations and artisanal miners have discovered rich mineral deposits that ended up in the hands of large-scale mining companies (Hentschel, Hruschka, and Priester, 2002). Similarly, the regulatory bottlenecks involved in artisanal miners’ access to mining licenses are well documented (Siegel and Veiga, 2009). To tackle these challenges, in line with formalization, legislation for ASM ‘designated mining spaces’ has been recommended. Examples of this form of legislation can be seen in the DRC, Mali, Mozambique, and Tanzania (Mutemeri et al., 2016; Corbett, O’Faircheallaigh, and Regan, 2017; Hilson et al., 2021).

Attraction of credit Proponents of formalization argue that it would provide the necessary exposure to ASM operations, which would help the operators to access formal lending. They argue that having informal mining formalized will give the miners more visibility, which can bring about financial intervention from the state and financial organizations (Eniowo and Meyer, 2020). Recently, attention has been placed on how to upgrade artisanal mining operations to a more sustainable form of small-scale mining enterprise (Marin et al., 2016). The goal is to improve the artisanal miners’ access to formal lending, which is in line with the formalization drive. The relationship between access to credit and formalization will be further expanded in later sections of this paper.

Stemming the tide of clashes More expediently, formalization presents an opportunity to abate the dangerous clashes between the informal and formal mining sectors. Informality breeds chaos. The clashes caused by illegal miners entering established large-scale mines make a case for the formalization of informal ASM. These intrusions are sometimes carried out violently. A reported case is a gold mine owned by AngloGold Ashanti in Ghana, which was overrun by thousands of illegal miners in 2016, and the mine was forced to evacuate employees (Jamasmie, 2016). Another reported case is an intrusion at the copper mine operated by Glencore in Congo, Loto mining involve group of community peasants numbering 10 to 15 who form clusters by separating themselves into groups consisting of those who extract the cassiterite and those who process it. The cycle of operation involve manual digging of pits to an average depth of 30 m and sluicing water over the ore, sun-drying it, and marketing the product.

4 Collateral security is defined as an asset which a borrower is required to deposit with, or pledge to, a lender as a condition of obtaining a loan, which can be sold off if the borrower defaults on the loan (Pass, Lowes, and Davies, 2005).

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Implications of credit constraint on the formalization of artisanal and small-scale mining where 43 deaths, including those of several illegal miners who broke into the mine site, were caused by a landslide (ibid.).

The unsafe investment environment created by these clashes puts doubt in the mind of investors in several would-be mining destinations in Africa. Furthermore, as illegal miners operate without consideration for safety, there is usually a record of high casualties in their operations, which brings into question the issue of safety. A typical example is an accident that occurred in the shaft of an unused gold mine in South Africa in 2017 where over 30 illegal miners died in an explosion (Bloomberg, 2019). It has been argued that while effective policing of the ASM industry may sometimes be unavoidable, formalization presents a more sustainable solution and a win-win situation for policy-makers and artisanal miners in addressing the major conflicts linked to ASM. By capturing informal miners to the formal domain, and designating mine spaces for them, it has been perceived that the clashes between the formal and informal mining sectors would be abated.

Improving working conditions Advocates of formalization argue that it would help miners to receive the necessary support through which their working conditions can be improved (Fold, Jønsson, and Yankson, 2014).

It is expected that the support that miners would receive will help improve their health and safety conditions, working environment, and enhance access to better equipment. It would also create an avenue for the state to check issues such as child labour, prostitution, drug abuse, and other social menaces associated with the occupation. Thus, formalization makes it easier to trace those who abuse the vulnerable sections of the population.

Generation of tax For governments, the issuance of legal documents, in particular licenses to miners, provides the benefit of taxation. As such, the formal system can therefore be described as a win-win for both the state and the miners (Siegel and Veiga, 2009). Several studies have examined the issue of taxation of the informal economy such as the ASM sector. Some suggest that increased taxation, along with burdensome regulation, is counterproductive to the formalization drive (Ihrig and Moe, 2004). Others argue that the relationship between taxation and formalization is not a direct one, claiming that what motivates firms to formalize, register, and/ or pay tax is the availability of credit markets and the potential for greater productivity (McKenzie and Sakho, 2010).

Protection of the environment While the granting of mining rights bestows benefits on artisanal miners, it also imposes duties on them to conform to environmental, human rights, and labour standards. The negative impact of ASM on the environment is well documented in the literature (Clement and Olaniyan, 2016; Owolabi and Opafunso, 2017; Omotehinse and Ako, 2019). Advocates of formalization therefore argue that it makes it easier to identify operations that harm the environment and to monitor compliance to environmental, safety, and health standards. In line with formalization efforts, studies have recommended vocational training courses for miners and capacity-building, provision of mining-related extension services, and adequate institutional support in order to tackle environmental damage traced to the occupation (Hilson, 2002; Hinton, Veiga, and Veiga, 2003; Spiegel and Veiga, 2005).

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Access to credit in ASM and implications for formalization Recent United Nations guidelines on artisanal mining formalization describe access to finance as ‘one of the most pressing needs’ in ASM (Reichel, 2019). Table III provides illustrations of how poverty and lack of access to credit impede the formalization drive in some sub-Saharan African countries.

One essential for access to credit is financial inclusion5. The link between formalization and financial inclusion in ASM is quite complex. Hilson and Ackah-Baidoo (2011) regard formalization as a prerequisite for access to finance for ASM operators. However, Reichel (2019) opined that the absence of formal financial services is a major obstacle to the development and formalization of ASM, especially in areas that are affected by conflict. In places where there are available formal financial institutions, there is often that challenge of ease of access to funds for ASM operators. The reasons for this will be discussed next.

The associated financial risks involved in ASM operations are a primary cause of difficulties in accessing formal finance. Previous studies such as Binks, Ennew, and Reed (1992) reveal that it is harder for small businesses to obtain credit than for larger firms.

Binks Ennew, and Reed argue that small businesses have trouble in obtaining loans since they can experience a debt gap caused by insufficient business collateral. Perks (2016) cites local banks’ lack of experience in translating geological assets into collateral that is familiar to them as the reason why artisanal miners may not enjoy bank lending. Holistically, for ASM, the reasons for poor financial services can be attributed to a long list of credit risks, some of which are itemized under the next subheading. Reichel (2019) suggested that these factors could contribute to actual or perceived challenges in making loan repayments.

Predicting ASM viability As highlighted, the inability of formal lenders to predict the viability of ASM operations by quantifying and pricing the credit risks of such investments limits the ability of artisanal miners to access formal bank financing. Hilson and McQuilken (2014) identified the concern of government-sponsored ‘mining banks’ in supporting ASM operations in developing countries. It is believed that ASM has high technical and financial risks; funding the operations is hence difficult and expensive. It is a fundamental principle that recipients of loans must be creditworthy companies with technically and financially viable operations and projects (Bosson and Varon, 1978). For ASM operations to be technically viable, efficient and safe types of machinery are required. As such, financial viability is a prerequisite for the technical viability of ASM companies.

A nuanced study into the inability of ASM firms to obtain capital for their operations by Seccatore et al. (2014) reveals that the high-risk nature of the investment, occasioned by the lack of guarantee of return or fiscal success, is a cause. As a result, there is little attraction for investors in the occupation.

This situation is further compounded by the absence of proper geological exploration. As such, artisanal miners restrict their operational planning to instinct and rely on experience based on previous operations (Marin et al., 2016). Any meaningful upgrade The World Bank (2018) defined financial inclusion as a term used to describe individuals and businesses’ access to useful and affordable financial products and services that meet their needs – transactions, payments, savings, credit, and insurance – delivered in a responsible and sustainable way

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Implications of credit constraint on the formalization of artisanal and small-scale mining Table III

Summary of findings on the effect of financial constraint on the attempt to formalize ASM in some case studies Publication

Case study

Spiegel (2012) Zimbabwe

Van Bockstael Liberia (2014)

Reichel (2019) Democratic Republic of Congo (DRC)

Hilson (2020) Sierra Leone

Hilson (2020) Ghana

Kinyondo and Tanzania Huggins (2020)

Hilson et al., Mozambique (2021)

Observation

Recommendations

Government banned ASM activities, then demanded that artisanal miners submit an Environmental Impact Assessments (EIA) before they could resume work. The costs for the EIA were prohibitive (up to US$4000) and the miners could not afford this.

Advanced artisanal miners who wish to improve their production capacity by using earthmoving equipment complained that they are required to apply for a different license, which costs up to US$10 000, and which is more than they could afford.

Majority of ASM sector is still shut out of financial inclusion programmes, which affects their access to credit.

Small-scale license costs a whopping US$1000, requires an annual fee of US$800 per hectare for plots, and a renewal fee of US$1000. Fewer than 10 individuals have been able to afford these costs over the 3-year period of the study.

Considering the levels of payments that must be made before an application can be reviewed, the costs of obtaining a license to mine on a small scale are so high that only a small group of individuals can consider moving towards legality.

Training centres set up to enhance capacity-building of ASM workers and other professionals in the mining sector offer courses at a rate too expensive for an average ASM worker. The fees are between US$260 and US$434, which is quite a high sum in a nation with a per capita GDP of US$1050.

Miners have spent huge sums in attempts to get licensed but to no avail. A respondent recounts ‘I have spent around 200 000 MZN (US$3000) to gather all the required documents but still have no license. It’s too much money, I don’t have a salary’.

The poverty situation affects the ability of miners to pay for licenses.

Decentralized and ‘assistance-oriented’ ASM sector management policies should guide future political decisions.

of ASM should therefore be accompanied by optimization of the creditworthiness of ASM companies.

To tackle this limitation, some recent studies have proposed methodologies for creating mineral deposit certainty that can help boost the confidence of formal lenders in investing in ASM operations. For example, a recent approach was developed in Marin et al. (2016) which simplifies the method for the determination of the feasibility of a new ASM operation. In this approach, there is no need for a large investment to ascertain the feasibility of a small-scale mining operation like that required for large-scale mineral exploration. Instead, only proof of ‘minimum reserve and replication’ is needed for the project start-up (Seccatore et al., 2014; Marin et al., 2016 ).

Marin et al. (2016) defined ‘minimum reserve’ as a reserve whose exploitation allows for the payback of the capital expenditure (CAPEX), operational costs of the mining business, provides capital for another round of exploration to extend the proven reserve, and desired profit. ‘Replication’ is the exploitation in several volumes of minimum reserves (Marin et al., 2016).

When applied to a real case, it was shown that the reserve required to prove the feasibility of a responsible small-scale operation is of the order of 1/1000 of that required for large-scale mining. The ‘minimum reserve and replication’ technique could help boost investors’ confidence in ASM operations, specifically 104

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Top-down regulatory policies should be avoided.

Laws should be made attractive to encourage ASM operators to willingly opt-in.

Miners’ village savings groups can contribute to closing the capital gap for ASM operators, especially at the basic personal level.

No recommendation.

No recommendation.

Government is advised that affordability of the training courses is essential for formalization.

Also, it is argued that if the state uses the training centres primarily to generate profit rather than serve miners’ needs, they will become less relevant over time.

Government should simplify the licensing system for ASM. This, among other steps, would help individuals in ASM to expand their operations.

because orebody risk is the single most important characteristic that potential lenders focus on for their due diligence (Benning, 2000 ).

However, it is also true that proof of economic feasibility through a Proved Mineral Reserve alone is not a guarantee of the sustainability of an ASM operation. It is equally essential that ASM operators can service loans obtained for investment.

This re-echoes the need for strengthening of the technical and financial capabilities of artisanal miners, which was identified by Sinding (2005). The study stressed that in some cases artisanal miners may only have enough to cover subsistence and operating costs. Still, a miner is continuously faced with the choice between current consumption (whether for subsistence or operating) and investment. The choice made in this regard may ultimately determine whether the miner will be able to break free from the poverty circle.

Discussion and concluding remarks Formalization is conceived as an avenue through which government could enhance the economic fortunes of indigenes, protect the environment, and generate tax by regularizing the operations of artisanal miners. ASM, whether formal or informal, cannot simply be wiped out through heavy-handed measures. This could result in a more dangerous social menace being created.

The Journal of the Southern African Institute of Mining and Metallurgy

Implications of credit constraint on the formalization of artisanal and small-scale mining Rather, the operations must be formalized and their performance upgraded to meet global best mining practices. However, for a sustainable formalization drive, the limited availability of formal lending in the ASM industry is a challenge. It has been shown that the persistence of informality in the ASM sector can be traced to the lack of sustainable finance mechanisms for operators (Fold, Jønsson, and Yankson, 2014; Siwale and Siwale, 2017; Eniowo and Meyer, 2020 etc.).

A body of knowledge has attempted to unravel the mystery behind ASM’s lack of credit access. Fold, Jønsson, and Yankson (2014) argue that ASM operators face difficulty in accessing formal loans due to a lack of collateral and insecure production outcomes. The question that arises here is, can all ASM operations vaguely be classified as having insecure production outcomes?

Perhaps a more robust argument for the justification of formal lenders’ apathy in ASM is the point emphasised in Ledwaba (2017), that ASM lacks access to funding due to poor knowledge of the economic potential and lifespan of the mineral resource, economic value of the deposit, market availability, and recording of cash flows .

Other studies such as that of the Environmental Law Institute (2014) question the technological capabilities of miners and cite the unavailability of adequate geological knowledge that can improve lenders’ confidence in the deposit. Theoretically, the essence of ore reserve estimation carried out before mining operations commence is to provide proof of the existence of the orebody. Typically, this should be followed up by documented feasibility studies that provide evidence of financial viability of the business – which is what formal lenders want to see, but which ASM operators may not be able to provide. Thus, a reasonable direction for intervention aimed at optimizing the ability of ASM operators to access loans must focus on closing the gap between the requirements of formal lenders and the inadequacies of ASM operators.

In line with this, recent studies on ASM concentrate on how to strengthen and upgrade ASM companies with the goal of tackling the challenge of undercapitalization. Some of the strategies put forward include the creation of ASM designated areas (formalization of ASM spaces) (Corbett, O’Faircheallaigh, and Regan, 2017); provision of revolving loans for ASM companies (Spiegel and Veiga, 2005); establishing village savings and loans associations (VSLAs) (Reichel, 2019); and creation of mineral buying centres (Adesugba, 2018). Likewise, some authors suggest the provision of community-led microfinance schemes, increasing the financial literacy of ASM operators (Reichel, 2019), and training ASM operators on economic sustainability (StocklinWeinberg, Veiga, and Marshall, 2019) .

Other studies prescribe emerging alternative forms of project financing such as metal streaming and offtake agreements (Perks, 2016). Specifically, Perks (2016) argues that considering the constraint faced by ASM operators in accessing formal domestic financing sources, which has hindered the capacity of the ASM subsector to move from opportunistic activity to sustainable growth, formal streaming, and offtake agreements could provide a further push for the small-scale mining sector to effectively develop and mature.

However, one key initiative that may play a more sustainable role in enhancing ASM operators’ access to credit is the strengthening of associative entrepreneurship movements such as miners’ cooperatives. First, this form of association would help miners to accumulate enough capital with which they could engage in more viable and safer operations (Saldarriaga-Isaza, The Journal of the Southern African Institute of Mining and Metallurgy

Villegas-Palacio, and Arango, 2013). Additionally, considering the low tendency of miners to save, which is partly due to the burden of the informal arrangements through which their operation is usually funded, associative entrepreneurship provides an option for artisanal miners to increase their financial capital.

Furthermore, due to the perceived itinerant nature of artisanal mining, such associations provide a face for artisanal miners, a governing structure, and an avenue through which miners could be held accountable for excesses in their operations.

As efforts are being made to capture artisanal and small-scale mining operations into the formal economy, as is the case in South Africa and other sub-Saharan Africa nations, attention must now be placed towards upgrading ASM operations economically to sustainable enterprises. In the long run, there is need for ASM companies to be able to operate sustainably without grants from governments and international donors. In this regard, this paper argues that future research and policy frameworks need to focus on optimizing the creditworthiness of ASM firms, with the goal of enhancing their ability to attract formal funding from banks and microfinance institutions. To achieve this, a mechanism must be developed to assist miners in acquiring adequate knowledge of the orebodies as this would improve the confidence of would-be investors and formal lenders.

Again, it has been shown that recipients of loans should be creditworthy companies with financially viable operations. ASM, as is practiced, has been unable to attract formal lending, partly because there is no standard, specific to ASM, for estimation of viability or creditworthiness. It is therefore recommended that future study should also consider creating simplified tools and methods to estimate the viability of ASM operations – such methodology should be void of the encumbrances seen in banks’ due diligence for large mining companies. It is equally important that the scope of the current ASM formalization efforts is expanded to familiarize ASM operators with the credit risks inherent in their operations and train operators on mechanisms with which such risks can be reduced.

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Void filling and water sealing in a decline in the Kalahari Manganese Field

by I. Serepa1 and N.C. Steenkamp1 Affiliation: 1

Worley.

Correspondence to: I. Serepa

Email: ikza87@gmail.com

Dates:

Received: 27 Nov. 2018 Revised: 20 Nov. 2020 Accepted: 27 Jan. 2022 Published: March 2022

How to cite:

Serepa, I. and Steenkamp, N.C. 2022 Void filling and water sealing in a decline in the Kalahari Manganese Field.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 107-114 DOI ID: http://dx.doi.org/10.17159/24119717/480/2022

Synopsis Investigations were conducted to determine the condition and stability of the existing decline at a mine in the Kalahari Manganese Field, Northern Cape Province, South Africa. During the inspection of the decline, voids were identified behind the concrete lining on the hangingwall and sidewalls over a total linear distance of 230 m. The voids did not provide confinement and, as a result, self-mining was occurring behind the lining. Water was flowing into the decline, over a total linear distance of 100 m, at areas where the decline intersected incompetent rock units, causing softening of the concrete lining and deterioration of the surrounding rock mass. Further damage to the concrete lining was caused by expansion and contraction of the wet red clay unit.

Remedial work comprised void filling and water sealing to prevent further deterioration of the decline and ensure that it remained operable for the remainder of the life of mine. Void filling was accomplished by drilling rows of holes along the decline to access the voids and filling the voids with foam. This was followed by the sealing with polymer fluids. Telescopic pipes were also installed to allow water to drain off.

A visual inspection was conducted and check-holes were drilled to assess the quality of the remedial work. The void filling material had penetrated cracks in the concrete lining, and areas where voids were intersected by check-holes were re-filled. Additional holes were drilled to re-seal areas that were still wet. The remedial work was completed successfully, as all voids were filled and stability achieved without compromising the concrete lining. The ingress of groundwater was also reduced to some residual dampness.

Keywords ground support, decline, concrete lining, void filling, sealing.

Introduction Background The decline under study was developed during the late 1970s and commissioned in the early 1980s. It is currently the primary means of accessing the mine. The decline intersects unconsolidated sediments and highly weathered material before entering competent rock. The condition of the decline in the upper portion deteriorated over the last 30 years and remedial action needed to be taken to ensure safe use for the remainder of the life of mine. The decline has a total length of 770 m. The first 240 m from the portal is supported with steel arches spaced at 1 m and 0.50 m thick concrete slabs. The remainder of the decline is located in hard rock and supported with rockbolts.

A variety of investigations, including in-decline geotechnical mapping and a surface electrical resistivity imaging (ERI) survey were conducted to determine the factors affecting the stability of the decline. Voids were identified behind the concrete lining. The voids occurred on the hangingwall and sidewalls from approximately 10 m to 240 m into the decline. The extent of the voids was determined using a borehole camera. The width of the voids varied from 0.3 m to 1 m and their length was limited to 1 m, which is the spacing between the steel arches. No voids were identified in areas where the decline is located in hard rock.

Water ingress into the decline was observed from 120 m to 220 m where the decline intersects calcrete, gravel, and red clay units. The water had deteriorated the rock mass and washed out fines from

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Void filling and water sealing in a decline in the Kalahari Manganese Field the calcrete, unconsolidated gravel units, and highly weathered tillite. In addition, the water caused softening of the concrete lining and deterioration along the red clays due to the expansion and contraction of the wet clay. It was suggested that the flow of groundwater can initiate void formation through self-mining and that the size of the voids would increase over time. A secondary problem was that during winter the water on the roadway froze due to wind chill. This caused the decline to be closed until it was safe to access again.

Recommendations were made to prevent further damage to the decline. These included filling all voids with material that would provide confinement without compromising the integrity of the concrete lining and creating an impenetrable curtain around the decline to seal the water. The aim of the project therefore was to stabilize the ground conditions behind the concrete lining of the decline and to effectively manage the groundwater ingress into the decline.

Location of the project The mine is located within the Kalahari Manganese Field (KMF).

The KMF is located 60 km northwest of Kuruman in the Northern Cape Province of South Africa (Figure 1) and hosts 1350 Mt of manganese ore resources, making it the largest manganese ore basin in the world in terms of ore resources (Kuleshov, 2012).

Geological setting The KMF is the largest known preserved land-based manganese deposit on Earth. It has been traced by boreholes and mining works over 15 km in the longitudinal direction and 35 to 40 km in the meridional direction (Kuleshov, 2012). The KMF is hosted by the Transvaal Supergroup in the Griqualand West area. The Transvaal Supergroup is overlain by the Karoo Supergroup, followed by the Kalahari and Gordonia formations (Steenkamp, 2014).

Figure 2 illustrates the rock units that are intersected by the decline. The decline is developed through the red Kalahari sand

at the portal and then progresses through several sequences of alternating calcrete and gravel horizons. The decline then passes through the red clay unit before re-entering the alternating sequence of calcrete and gravel. The gravel is clast-supported and has a weak interstitial calcrete matrix. There are sharp contacts at the top and bottom of the highly weathered tillite interval. A highly weathered bostonite dyke marks the transition to the hard rock lithologies. The top manganese seam (MN2), which is partially eroded away by the tillite, is followed by the banded ironstone formation (BIF) middling, and then the lower manganese seam (MN1).

Problem statement The long-term stability of the decline was compromised due to the continual water damage to concrete lining. The damage was occurring because of the following issues: ➤ Self-mining of the hangingwall and sidewalls, which was promoted by the existence of voids behind the concrete lining ➤ The inflow of water into the decline, which was causing softening of the concrete lining and deterioration of the rock mass. Further damage was incurred due to the expansion and contraction of the wet red clay unit against the concrete lining.

Formation of voids A borehole camera was used to inspect the condition of the voids behind the concrete lining, as well as to estimate their size. It was observed that the hangingwall of the voids showed a possible original hangingwall of the decline (Figure 3). The possible original hangingwall was supported by shotcrete and, in some areas, cribbing made up of gumwood planks and metal beams (Figure 4). The voids were not backfilled. In some areas the voids were filled with loose rocks that seemed to have been derived from the collapsed hangingwall (Figure 5).

Figure 1—Location of major mines in the Kalahari Manganese Field (after Steenkamp, 2014) 108

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Void filling and water sealing in a decline in the Kalahari Manganese Field

Figure 2—The lithology that is intersected by the decline

Figure 3—Void behind the concrete lining of the decline

The initial voids were formed when the gap between the original excavation and the concrete lining was not filled. This interpretation is supported by the fact that no voids were identified in areas where the concrete lining is not installed. The size of the voids increased due to self-mining and exposure of the rock to groundwater.

Inflow of water into the decline The stratigraphy which the decline is developed through is

Figure 4—View inside a void showing cribbing support along the red clay section of the decline

comprised predominantly of calcrete. The calcrete is underlain by gravel and red clay units (Figure 6). The red clay, unlike the calcrete and the gravel, is not permeable. As a result, laminar flows of groundwater occur in the gravel and calcrete units and the red clay unit is kept damp. Figure 6 shows groundwater ingress into the decline at sections where the decline intersects the aforementioned rock units.

Figure 5—Loose rocks from the collapsed hangingwall The Journal of the Southern African Institute of Mining and Metallurgy

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Figure 6—Section of the local stratigraphy where the decline is developed

Table I

Areas requiring void filling and water sealing in the decline Remedial work

From (m)

To (m)

Distance (m)

10 120

240 220

230 100

Void filling Water sealing

The flow rate of the ingress water was measured in the gutter along the decline roadway. The flow rate was variable over time (0.9 - 8.7 L/minute) over time and could be correlated to seasonal changes . The volumes of the water ingress also dictated the start of the project.

filling and a water-sealing product. The exact composition of the polymers cannot be disclosed due to confidentiality agreements.

The void-filling material that was recommended is pumped as two polymer fluids that are mixed in the nozzle prior to injection. The mixture of the two components is exothermic and produces ‘foam’ that rapidly expands to fill the void and then harden (see Figure 8). The setting time is estimated to be one minute. Considering that the void-filling material would flow down-dip, the filling of voids commenced from the bottom of the decline and progressed up-dip. One row of holes was filled at a time, starting with the holes on the sidewalls and followed by the hole in the hangingwall.

Objectives and scope of the project The purpose of the project was to carry out remedial work to prevent further damage to the concrete lining of the decline. The remedial work comprised filling of the voids behind the lining to prevent further self-mining of the hangingwall and sidewalls, and sealing to prevent groundwater ingress into the decline.

The scope of the remedial work was limited to the areas highlighted in Table I. Void filling was limited to filling cavities in the hangingwall and sidewalls of the decline, and water sealing was done around the decline, including the footwall.

Figure 7—Drilling layout for void-filling holes

Methodology Void filling Access to voids The voids were accessed by drilling rows of holes along the hangingwall of the decline. The rows were spaced 3 m apart and a total of 77 rows were drilled. Each row comprised three holes as depicted in Figure 7. Hole 2 was drilled in the centre of the hangingwall and the side holes (holes 1 and 3) were drilled 0.5 m from the sidewall and 2.0 m from hole 2. The length of the holes was not fixed, but was determined by the intersection depth of a void or water loss during the drilling process.

Filling of voids ISO (Industrial Synthetic Oils) developed a proprietary void110

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Figure 8—Void-filling material The Journal of the Southern African Institute of Mining and Metallurgy

Void filling and water sealing in a decline in the Kalahari Manganese Field

The holes were filled in this order to build the void fill from the sidewalls up to the hangingwall. A hole was considered to be completely filled when void-filling material started seeping out of the hole being pumped or another hole in the same or an adjacent row.

to speed up the reaction. The setting time in this case varied between 10 seconds and one minute, depending on the quantity of catalyst added.

Water sealing commenced once void filling was completed.

Water sealing was started by grouting the five rows of holes that were drilled down-dip of the water area. One row was sealed at a time; starting with the footwall holes (holes 1, 7, and 8) followed by the sidewall holes (holes 2 and 6) and then the hangingwall holes (holes 3, 4, and 5). A hole was considered to be completely grouted when the water-sealing fluids started seeping out of the hole being grouted or another hole that had not yet been grouted.

Once the bottom barrier had been completed, water sealing was undertaken in the water area. It commenced at the top of the decline and progressed down-dip so as to direct the water down the decline to the bottom barrier. Two telescopic pipes were installed in the water area to allow water to drain off. The telescopic pipes are connected to flexible pipes which direct the water into a drainage pipe, as illustrated in Figure 10. The water is then fed along the water drainage channel to the bottom of the decline, from where it is further handled by the underground water management system.

Quality assessment of the void filling

Quality assessment of the water sealing

The quality of the void filling was assessed by drilling check-holes on the hangingwall of the decline. The position of check-holes was determined based on the quantity of void-filling material pumped through hole 2. A check-hole was drilled if the void-filling material pumped was less than 32 kg or greater than 500 kg. Random check-holes were also drilled in areas where there was no visible evidence of the void-filling material penetrating cracks in the concrete lining. Each check-hole was surveyed with a borehole camera for cavities. If cavities were observed, these holes were re-filled.

The quality of the water sealing was assessed by conducting visual inspections of the decline. If excessive groundwater ingress was observed, additional holes were drilled and grouted in the area concerned.

Figure 9—Drilling layout for water-sealing holes

Water sealing Drilling of holes

A total of 40 rows of holes were drilled along the decline, each spaced 3 m apart. Thirty-five rows were drilled in the water area, and five rows down-dip of the water area to create a barrier that would prevent the water from progressing to the lower areas of the decline. Each row was drilled 1.5 m from a row of void-filling holes and comprised eight holes as depicted in Figure 9. The holes in one row were drilled and spaced as follows: ➤ Holes 1 and 7 on the sidewall 0.5 m from the footwall ➤ Holes 2 and 6 on the sidewall 1.8 m from the footwall ➤ Holes 3 and 5 on the hangingwall 0.5 m from the sidewall and 2 m from hole 4 ➤ Holes 4 on the hangingwall 2.5 m from the sidewall ➤ Hole 8 on the footwall 2.5 m from the sidewall.

The length of the holes was limited to 3 m as it was planned to create a seal with an effective thickness of at least 2 m around the decline.

Results and discussion The depth of the holes drilled to intersect the voids behind the concrete lining depends on the lithology intersected by the decline and the lining. It is suggested that the overbreak in the gravel units during excavation was greater than in the calcrete and red clay units. The concrete lining is 0.50 m thick and the average depth of holes drilled to access the voids was calculated to be 0.96 m. The minimum depth drilled was 0.56 m, and the maximum 1.30 m.

Figure 11 shows the consumption of void fill and water-sealing grout. The consumption of void fill was generally low around the portal and increased towards the groundwater ingress areas. This would suggest that the void fill material is affected by the presence of flowing groundwater. The challenge therefore was to apply correct batching of the void fill material. The mixture needed to remain fluid enough to migrate throughout the required volume

Grouting of holes The recommended grouting material consists of a mix with two polymer fluids that are mixed in the injection nozzle while being injected. The fluids infiltrate cracks and joints before setting as an impermeable rubber coating. Cementing powder can be added to adjust the viscosity of the pumped fluid. The setting time for the water sealant is estimated to be about 20 minutes. In the presence of groundwater that may wash the fluids away, a catalyst is added The Journal of the Southern African Institute of Mining and Metallurgy

Figure 10—Telescopic pipe installed in the decline VOLUME 122

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Figure 11—Sectional consumption of void fill and water-sealing grout

Figure 12—Void filling that has penetrated cracks on the concrete lining of the decline

Figure 13—Void filling on row 71

of the void behind the lining, but to react and expand before being diluted too much by groundwater, which would reduce the efficiency of the reaction. From a comparison of the void fill and grout consumption per section, the correlation between high consumption of void fill material and water sealing grout consumption is evident. The main challenge in water sealing in unconsolidated material is that there is no specific point of water ingress that can be targeted for sealing, unlike for example a joint or fracture in a hard, impermeable rock. The groundwater has a tendency to migrate to the unsealed portion and create a new point of ingress, but to a very limited extent.

Void filling was completed successfully. Stability was achieved without affecting the integrity of the concrete lining. Evidence of the effectiveness of the void filling is visible in the decline. The void-filling material penetrated cracks in the concrete lining as illustrated in Figure 12.

Figure 13 shows photographs of one of the voids before and after being filled.

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Water sealing was also completed successfully. The water volumes after the completion of the project were found to have decreased compared to the same period the prior year. Figures 14 and 15 show the ingress surface areas along the decline before and after completion of the project. The ingress of groundwater into the decline has been reduced to some residual dampness. Figure 16 shows photographs of a portion in the main water ingress area before and after water sealing and grouting.

Conclusions and recommendations The remedial work was recommended following detailed investigations of the condition of the decline, which highlighted two main issues that were compromising the stability of the decline: ➤ Voids were identified behind the concrete lining of the decline. Self-mining was occurring on the hangingwall and sidewalls as the voids were not filled with any material to provide confinement The Journal of the Southern African Institute of Mining and Metallurgy

Void filling and water sealing in a decline in the Kalahari Manganese Field

Figure 14—The main water area before grouting. The white arrows indicate wet sidewall

Figure 15—The main water area after grouting. White arrows indicate wet sidewall positions

Figure 16—Row 16 before and after grouting

➤ Water was flowing into the decline at areas where the decline intersected calcrete, gravel, and red clay units. The water was softening the concrete lining and deteriorating the rock mass.

The remedial work that was completed included void filling and water sealing. The void filling involved filling voids with void-filling foam to provide confinement and prevent further self-mining of the hangingwall and sidewalls. Water sealing was undertaken to create a seal around the decline in areas where groundwater inflows were observed. The water sealing was supported with a groundwater ingress management system.

A quality assessment of the remedial work indicated that the void filling and water sealing succeeded in meeting the aim of the project – to produce a near-dry decline with stabilized ground conditions behind the concrete lining.

Melamu, who gave permission on behalf of the client. We also acknowledge Gerrie Bezuidenhout and Raymond Mateveke for their contribution, and Donovan Munro for the review of the final draft. This paper is based on a presentation at given at the 3rd Young Professionals Conference, 9-10 March 2017 at the innovation hub in Pretoria.

Acknowledgements

Tsikos, H. 2000. Petrographic and geochemical constraints on the origin and post-depositional history of the Hotazel iron-manganese deposits, Kalahari Manganese Field, South Africa. PhD thesis, Rhodes University. Grahamstown, South Africa. 292 pp. u

We would like to thank Worley for permission to publish this paper, as well as Christo Kuhl, Henk Gouws, and Christopher The Journal of the Southern African Institute of Mining and Metallurgy

References Kuleshov, V.N. 2012. A superlarge deposit - Kalahari manganese ore field (Northern Cape, South Africa): Geochemistry of isotopes and genesis.

Lithology and Mineral Resources, vol. 47. p. 217.

Steenkamp, N.C. 2014. Challenges of developing a ventilation shaft in Kalahari and Karoo Formations, Northern Cape, South Africa. Proceedings of the 12th AusIMM Underground Operators’ Conference. Australasian Institute of Mining and Metallurgy, Melbourne. pp. 81-88.

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SAIMM HYBRID CONFERENCE

Void filling and water sealing in a decline in the Kalahari Manganese Field

SDIMI 2022 SUSTAINABLE DEVELOPMENT IN THE MINERALS INDUSTRY

15-17 SEPTEMBER 2022 CONFERENCE 17-20 SEPTEMBER 2022 TOURS AND TECHNICAL VISITS

10TH INTERNATIONAL CONFERENCE

WINDHOEK COUNTRY CLUB & RESORT, WINDHOEK, NAMIBIA

Making economies great

through sustainable mineral development

It is my pleasure to invite you to SDIMI (Sustainable Development in the Minerals Industry) 2022, the 10th of a series of conferences whose objective is to assist the global mining and minerals industries in their transition to sustainable development. The conference will take place from (15-20 September 2022) in Windhoek and will run under the theme (Making Economies Great through Sustainable Mineral Development). This will be a hybrid conference entailing a real-time, face-to-face component as well as a virtual component.

We celebrate a journey that commenced in 2003 in the historic town of Milos, Greece, when the landmark MILOS DECLARATION was adopted. The MILOS DECLARATION represents a statement of our collective contribution to a sustainable future using scientific, technical, educational, and research skills and knowledge in minerals extraction and utilization that was endorsed by the leading global professional and scientific organizations and institutes representing the minerals professionals. SDIMI 2022 aims to continue with our noble journey by building on the progress we have made since 2003.

T H E CO N F E R E N C E TO P I C S A R E A S L I S T E D B E LO W • Mining industry’s response to covid-19 : Impact and learning points • Artisanal and Small-scale mining • Mining in Africa and its Unique Challenges • Social Licence to Operate • Circular Economy • Mining in Protected Areas • Uranium Mining • Marine Mining • Mining towards a renewable future – lithium, rare earths, strategic minerals etc.

• Precious gems • Fair Trade of raw materials (Minerals) • Critical Minerals • Advances in life cycle and sustainability assessment in the industry • Integration of sustainability thinking into professional education • Economic sufficiency • Water Stewardship • Policy and Regulatory Framework • Mine Closure and repurposing case studies • Tailings management • Mineral Beneficiation and value chains • Energy Efficiency • Space mining

FOR FURTHER INFORMATION, CONTACT: Gugu 114 Charlie MARCH 2022 Conference Coordinator SAIMM

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The Journal of the Southern African Institute of Mining and Metallurgy

A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine

by L. Scheepers1 and D.F. Malan1

Affiliation:

Department of Mining Engineering, University of Pretoria, South Africa.

1

Correspondence to: F. Malan

Email:

francois.malan@up.ac.za

Dates:

Received: 9 Feb. 2021 Revised: 17 Jan. 2022 Accepted: 31 Jan. 2022 Published: March 2022

How to cite:

Scheepers, L. and Malan, D.F. 2022 A case study of geotechnical conditions affecting mininginduced seismicity in a deep tabular mine.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 115-124

Synopsis Seismic risk in the deep gold mines of South Africa has been studied for many decades. A clear understanding of the effect of geotechnical conditions on the seismic hazard nevertheless remains elusive. Certain reef types seem to be associated with a higher risk of rockbursts. The stability and deformation behaviour of excavations on the different reef horizons are affected by the rock types and the varying strength properties. The seismic response to mining is therefore also expected to differ according to the geotechnical conditions. As a case study of this behaviour, the seismicity at Mponeng mine was investigated. On the VCR (Ventersdorp Contact Reef) horizon, two areas can be delineated.

On the eastern side of the mine, the footwall is shale, and on the western side it is a strong brittle quartzite. More large-magnitude events occur in the area with the shale footwall than the area with the quartzite footwall. Moment tensor analyses indicated that the majority of the large-magnitude events are not related to geological structures, but are face-related, implying that shear failure of intact rock is occurring ahead of the mining front. Preliminary modelling indicated that the closure volume for the shale footwall may be higher than that for the quartzite footwall, providing a possible explanation for the observed difference in seismic response.

Keywords seismic risk, deep mining, shear failure, rock type.

DOI ID: http://dx.doi.org/10.17159/24119717/1511/2022 ORCID: F. Malan https://orcid.org/0000-00029861-8735

Introduction Damaging rockbursts, associated with the high incidence of mining-induced seismic events, are a major hazard in the deep-level gold mines of the Witwatersrand Basin in South Africa. Research on rockbursts has been conducted since the early days of mining (e.g. see Durrheim, 2010). Surprisingly, little work has being done to compare the rockburst hazard and the nature of the seismicity for the different reef types. This is a difficult problem to study as typically the depths, layouts, and support standards also vary in the different mining areas. Denkhaus et al. (1958) described the differences in rock properties and speculated that the variation in rockbursts along a line on strike running through Blyvooruitzicht and West Driefontein may be related to a variation in rock properties along this line. They considered a laboratory-determined parameter termed ‘relative violence of fracture’ in this regard. Other well-known historical rockburst studies, such as Cook et al. (1966), focused mainly on aspects such as stope span, abutment size, excavation size, depth below surface, geological structure, and stoping width. No mention is made of the role of different reef types and rock types in the hangingwall and footwall. Jager and Ryder (1999) analysed accident data for the Department of Mineral Resources’ (DMR’s) SAMRASS database and produced the graph shown in Figure 1. The risk of rockburst fatalities in mining on the Carbon Leader Reef seemed significantly higher than for the other reefs for the period from 1990 to 1997. Note that the risk in terms of fall-of-ground fatalities seems comparable for the different reef types. The data should be treated with caution as the role of other factors, such as different depths and mining layouts, could not easily be quantified. However, these results pose the question as to whether different reef types present a higher risk in terms of damaging rockbursts. Jager and Ryder (1999) also emphasised that layouts and

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A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine support strategies play an important role, and illustrated this by means of data for neighbouring mines with similar geotechnical conditions but significantly different rockburst fatality rates.

Anecdotal evidence is available from the industry regarding the seismic risk of different reef types. For example, experienced production personnel in the Westonaria region believe that the seismic hazard for the Middelvlei Reef is substantially less than for the Ventersdorp Contact Reef (VCR). This has never been scientifically quantified, and the reason for the difference is not clear. Esterhuyse and Malan (2018) stated that the remnants and abutments for some reef types are easily under- or overstoped.

The classical example is that of VCR remnants, which are easily understoped by mining on the Kloof or Libanon reefs in areas where the middling is small (< 20 m). In contrast, when highly stressed Carbon Leader Reef abutments are overstoped by mining on the Middelvlei Reef, where the middling is approximately 50 m, seismic events of magnitude M3.0 are a common occurrence.

Mponeng mine provides a rare opportunity to study the effect of different geotechnical conditions on seismic behaviour. At the mine, two geotechnical areas can be delineated for the VCR based on the footwall lithology. The immediate footwall on the eastern side of the mine consists of shale, and at the western side of the mine it is a brittle quartzite. The depth, layout, mining method, and support methodology are comparable for the two areas and a meaningful comparison of the seismic response is therefore possible.

Mining method and geotechnical conditions at Mponeng The mining method at Mponeng is a modified ‘sequential grid mining’ (Appelgate, 1991; McGill et al., 2007). It consists of a development grid from where the reef is accessed (Figure 2). Raiselines are spaced 220 m apart. This allows for partial extraction, leaving 30 m wide regional dip stability pillars between

Figure 1—Fatality rates caused by rockbursts and falls of ground for different reef types for the period 1990 to 1997 (after Jager and Ryder, 1999)

Figure 2—Typical sequential grid layout in a small portion of Mponeng mine. The coloured lines are the grid tunnels developed ahead of the stoping operations 116

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the mining blocks. The stope spans are 180 m on strike and several hundred metres on dip. More recently, 30 m wide strike pillars were left in addition to the dip pillars. The motivation was to further reduce the extraction ratio and to reduce the closure volume and associated seismic response.

Owing to the mining depth (currently in excess of 3600 m), the stress levels are high and mining-related seismicity and possible rockburst damage is the biggest risk at the mine. Meticulous mine design is required to manage the seismic hazard and ensure safe mining. Over the years a number of seismic hazard management strategies have been included in the mine design strategy. Most of these strategies aim at reducing excess shear stress on the seismically active geological structures and minimizing volumetric closure in the stopes. The current seismic hazard management strategies are as follows (see Figure 3): ➤ Partial extraction with a low extraction ratio of less than 60% ➤ Limiting the mining spans to a maximum of 180 m on strike ➤ Large regional stability pillars, 30 m wide on dip and strike ➤ Bracket pillars on major geological structures, typically 20 m wide both sides of the structure ➤ Overhand face configuration with controlled lead/lags of 7 m to 10 m ➤ A 35° approach angle onto minor structures if mined through ➤ Face preconditioning ➤ Mine-wide backfill using classified tailings in approximately 70% of the stoping area. Areas where travelling or transport are done (gullies) are not filled, so 100% backfill is not possible ➤ Rockburst-resistant support.

These strategies are based on a combination of guidelines stated in historical codes of practice, guidelines in rock engineering textbooks and research documents, interactions with experienced rock engineers, and personal experience. Most of these guidelines have also been verified with modelling and seismic response observations.

The near-reef lithology associated with the current mining on the VCR is a thick strong Alberton lava hangingwall, conglomerate VCR reef, and shale or quartzite footwall. On the western side of the mine, the footwall is quartzite of the Elsburg Series. On the eastern side of the mine the footwall is a thick shale of the Booysens Series. This shale at Mponeng must not be confused with the weak and soft shale associated with some of the reefs in the Welkom area. The shale at Mponeng is a siltstone that is metamorphosed to a relatively high strength and is brittle. The strength (UCS) of the shale ranges between 155 MPa and 195 MPa with an average of 173 MPa. The average Young’s modulus (E) of this rock is 64 GPa. This strength is nevertheless significantly lower than the strength of the quartzite, which ranges from 160 MPa to 332 MPa with an average of 252 MPa. The average Young’s modulus is 83 MPa. This difference in footwall rock strength is an important consideration in this study as the seismic response to mining on the shale footwall is compared to that on the quartzite footwall.

In Figure 4, a plan view of the footwall lithology transition is overlain with the mining outlines. The Booysens zone refers to the Booysens Shale that forms the direct footwall of the VCR in that area. All the other zones refer to quartzite as the direct footwall of The Journal of the Southern African Institute of Mining and Metallurgy

A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine

Figure 3—Plan view of the western side of Mponeng mine illustrating the partial extraction and the dip and strike pillars

Table I

Footwall rock properties in the study areas Area

Footwall rock type

Footwall UCS (MPa)

Footwall E (GPa)

Western side Eastern side

Quartzite Shale

252 173

83 64

Figure 5—West-east section (east on the right), showing a simplified model of the hangingwall, reef, and footwall lithology

quartzite footwall. In this study, the seismic response in the area with thick shale footwall is compared with that in the area with thick quartzite footwall. The data from the transition zone is not used or discussed further in this paper.

Seismic data analysis

Figure 4—Plan view of the mining outlines and footwall lithology of the VCR at Mponeng

the VCR. In Figure 5, a simplified sectional view of a model of the footwall lithology associated with the VCR is shown. From these diagrams, it is clear that only in the far eastern side of the mine is the shale the immediate footwall. On the far west, the immediate footwall is quartzite. The thickness of the quartzite in the footwall gradually increases from east to west. A zone can be identified where the quartzite in the footwall is relatively thin, followed by the shale layer. This is the transition zone, where the seismic response to mining may be influenced by both the shale and the The Journal of the Southern African Institute of Mining and Metallurgy

For the period 2016–2018 (see Figures 6 to 8), the mining activity and yearly production were comparable between the shale area and the quartzite area. Although the mining production below 120 Level, on the quartzite footwall, increased year-on-year, this was excluded from the seismic comparison. The focus of this study is therefore on the three-year period from 2016 to 2018 for data above 120 Level. This was deemed necessary to enable a seismic comparison that was mostly affected by the footwall rock type and minimize the effect of other parameters. The polygons for data comparison were selected to suit the appropriate data to be used in each year.

Figure 9 compares the number of large events in the magnitude bins 2.0 ≤ ML ≤ 3.0 and ML ≥ 3.0 for the two areas analysed. It is clear that there are significantly more large events on the shale footwall compared to the quartzite footwall for every year from 2016 to 2018. The year-on-year increase in each area is attributed to the increase in mining spans during this period.

The mining span increases were approximately similar in the two areas.

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Figure 6—Recorded seismic events for 2016

Figure 7—Recorded seismic events for 2017

It is interesting to note that there is a tendency for more large events in mining areas with shale footwall compared to mining areas with quartzite footwall for similar mining depth and mining spans. Even though the tendency for large events is controlled by the existence of shale as opposed to quartzite in the footwall, the large events generally occur in the lava hangingwall. This may be associated with non-seismic deformation in the footwall shale as opposed to the brittle response in the lava hangingwall.

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In terms of the smaller events in the magnitude bins 0.0 ≤ ML < 1.0 and 1.0 ≤ ML < 2.0, the opposite behaviour was recorded, with a larger number of small events on the quartzite footwall (Figure 10).

Frequency-magnitude graphs, also known as GutenbergRichter graphs, are used to display the number of seismic events recorded in magnitude bins/magnitude ranges. The GutenbergRichter graphs for the study data are shown in Figures 11 and The Journal of the Southern African Institute of Mining and Metallurgy

A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine

Figure 8—Recorded seismic events for 2018

Figure 9—Annual numbers of events for 2016 to 2018 for the magnitude bins 2.0 ≤ ML < 3.0 and ML ≥ 3.0 for the quartzite footwall polygon (top) and the shale footwall polygon (bottom)

12. The slope of the graph of cumulative number of events per magnitude is called the b-value. This describes the relationship between the number of large events and small events. When two graphs are compared, a lower b-value (flatter slope) represents a higher seismic hazard as it indicates a tendency for more large events to occur in relation to the number of smaller events compared to a data-set with a higher b-value (steeper slope). From the frequency-magnitude graphs of the two areas (Figures 11 and 12), the b-value for the shale footwall is 0.846 compared to 0.917 for the quartzite footwall area. This again indicates that more The Journal of the Southern African Institute of Mining and Metallurgy

Figure 10—Annual numbers of events for 2016 to 2018 for the magnitude bins 0.0 ≤ ML < 1.0 and 1.0 ≤ ML < 2.0 for the quartzite footwall polygon (top) and the shale footwall polygon (bottom)

large events can be expected on the shale footwall compared to the quartzite footwall, where the smaller events dominated.

A study to determine the location of the large events in the vertical direction indicated that most of the large events occurred in the stronger lava hangingwall and not in the footwall. The reason for this is not clear. It is postulated that the failure in the shale may occur non-seismically, resulting in more events in the stronger lava hangingwall rock owing to the resulting rock mass deformation. This requires additional study to understand the mechanism of deformation and resulting seismicity.

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Figure 11—Gutenberg-Richter graph for the shale footwall for 2016 to 2018, with the fit point at ML 0.0.

Figure 12—Gutenberg-Richter graph for the quartzite footwall for 2016 to 2018, with the fit point at ML 0.0 120

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The Journal of the Southern African Institute of Mining and Metallurgy

A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine Moment tensor analysis can be used to identify and distinguish between potential source mechanisms of complex seismic events (Malovichco, 2020). The quality of moment tensor analysis is dependent on the layout of sensors in the seismic network. For high-quality moment tensors, the sensors should be geometrically well distributed so that the event location is surrounded by sensors. A quality factor is assigned to each moment tensor, and only moment tensors with a quality factor of 0.5 or more should be deemed of sufficient quality to be used in seismic analysis. In the study area the network density and geometrical distribution (36 × 4.5 Hz geophones) is favourable for good-quality moment tensor analysis.

The moment tensor solutions of all events with magnitudes exceeding ML = 1.5 and with quality factor of 0.5 or more, that occurred in the period 2015 to 2018 in the shale footwall area as well as the quartzite footwall area, were studied. Each moment tensor solution has two possible slip plane orientations (nodal planes) for the DC component as the numerical technique cannot distinguish between two conjugate nodal planes (Malovichco, 2020). It can be argued that the steeper plane is the more likely, as the stress orientation is such that the orientation of the maximum shear stress is steep and the damage observed underground is consistent with steep sources rather than shallow-dipping event sources. For this assessment, only the steeper one of each pair of nodal planes was used.

For the diagrams in this paper, the moment tensor solution source planes are shown in the lower hemispherical stereonet plot as poles, where the pole is orthogonal to the source plane and the position of the pole in the plot area represents the orientation of the source plane. A pole close to the centre of the plot area represents a shallow-dipping plane while a pole near the edge of the plot area represents a steep-dipping plane. As an example, where this pole (near the edge of the plot area) is at the three o’clock position in the plot area, the plane it represents has a north-south orientation and steep dip, and where it is in the twelve o’clock position, the plane that it represents has

an east-west orientation and steep dip. The program also uses density contouring of poles with a similar position. Where several poles cluster in the plot area, red density contours are formed to highlight the clustering.

Figure 13 illustrates the steepest nodal planes of each moment tensor solution of 56 events with magnitudes in excess of ML = 1.5 in the shale footwall polygon on the eastern side of the mine. The black lines in the stereonet plots represent the plane of maximum excess shear stress (ESS) associated with the pre-mining stress state, according to the Mohr-Coulomb failure criterion.

The pre-mining stress state was interpreted from field stress measurements in appropriately selected areas on the mine, using the strain cell overcoring technique. The major principal stress is proportional to the weight of the overburden and orientated approximately orthogonal to the reef plane, the intermediate principal stress k-ratio is approximately 0.7 and is orientated in the strata dip direction, and the minor principal stress k-ratio is approximately 0.4 and is orientated in the strike direction. The plane of maximum ESS associated with this stress field will then be oriented in the intermediate stress field direction with dip determined by the k-ratio between the maximum and minimum principal stresses as well as the rock mass friction angle. This plane of maximum ESS is also the plane of most likely failure in an isotropic and homogenous rock mass; that is, the most likely orientation of a shear fracture is represented by the black lines in the stereonet in Figure 13 (conjugate plane orientations).

Figure 14 illustrates a similar plot for events in the quartzite footwall area. The high-density contours confirm the previous observation that a large number of event source planes have similar orientations. The purple lines in the stereonet in Figure 14 are the two most common nodal plane orientations of the moment tensor solutions of the 52 events in this data-set. These lines have similar strike orientations, but opposite dip directions – namely northeast and southwest. The southwest dipping source planes are likely associated with events on west mining faces and the northeast dipping source planes with events on east mining

Figure 13—The nodal plane orientations of the moment tensor solutions of 56 seismic events in the shale footwall polygon in plan view (left) and in stereonet plot (right). The purple lines represent the planes associated with the densest area and the black lines represent the ESS planes associated with the pre-mining stress state The Journal of the Southern African Institute of Mining and Metallurgy

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Figure 14—The nodal plane orientations (steepest only) of moment tensor solutions of 52 seismic events in the quartzite footwall polygon on the western side of the mine and in the magnitude range ML ≥ 1.5.

faces. The general northwest-southeast orientation of these planes confirms the observation that most of the event source planes are orientated in a relatively narrow envelope around the northwestsoutheast direction. This provides an important new insight into the seismic sources on Mponeng mine, not observed before. It appears that the majority of events in the data-set are face-related and oriented along the stope abutments rather than related to and oriented along the geological structures.

Numerical modelling of stope convergence Numerical simulation of stope convergence was useful to compare the layouts at the eastern and western sides of the mine. The simulated peak value of stope convergence seemed to be a useful criterion to compare different areas at the mine. This is supported by the work of McGarr and Wiebols (1977), which indicated that the cumulative seismic moment ΣM0 is proportional to the stope convergence according to: [1] where G is the modulus of rigidity and ΔVc is the volume of stope closure. As a consequence, control of the volumetric convergence was long considered an important strategy to control the rate of energy release and the risk of rockbursting (see e.g. Budavari, 1983). Of particular interest is the relationship between the maximum closure recorded in the stope and the volumetric closure. This is explored by considering the convergence solution for a single parallel-sided stope. The two-dimensional plane strain convergence solution for such a parallel-sided stope is given by (Salamon, 1968): [2] where Sz is the vertical convergence, ν is Poisson’s ratio, q is the 122

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vertical virgin stress, G is the modulus of rigidity of the rock mass, l is the excavation half-span, and x is the distance from the excavation centre-line. Convergence is a maximum at the centre of the excavation (x=0) and based on Equation [2] can calculated from: [3] The volume of convergence (m3) for this geometry can be calculated by integrating Equation [2] along the length of the stope from –l to l with the out-of-plane dimension given by b: [4] The solution of Equation [4] after integration is: [5] Substituting Equation [3] in Equation [5] we get: [6] For this 2D geometry, the volumetric closure is therefore proportional to the maximum closure. The benefit of maximum closure is that it is a very simple modelling parameter and useful as a first-order comparison of different layouts. It is, however, not without drawbacks as the simulated closure is dependent on the calibrated value of Young’s modulus. Jooste and Malan (2020) illustrated the effect of this elastic parameter on the simulated closure and the stress values on remnants in high-extraction areas where total closure occurred. They warned that: ‘Reducing Young’s modulus has been discussed for many years in order to reduce the disparity between underground closure and simulated closure, but the concept has also been widely criticized.’ Simulated elastic The Journal of the Southern African Institute of Mining and Metallurgy

A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine convergence is nevertheless valuable to give some preliminary insights when comparing different layouts, provided the limitations are clearly understood and recorded. Similarly, the elastic ERR concept should also be treated with caution as it does not consider the dissipative failure mechanisms occurring in the rock mass (Napier and Malan, 2014).

For the two geotechnical areas discussed in this paper, it was useful to compare maximum convergence for mining on the shale footwall with that for mining on the quartzite footwall. Modelling was done with the MAP3D code. For this preliminary modelling, modelling parameters were the same for both sides of the mine to investigate the effect of the layout geometries. The difference between quartzite and shale footwall was not explicitly simulated and a Young’s modulus of 70 GPa was used throughout the model.

Figure 15 illustrates the convergence for the western side of the mine with the quartzite footwall. The red colours represent higher convergence values. Convergence values exceeding 270 mm are shown in grey. This maximum convergence value was adopted based on a study by Scheepers et al., (2012) which found that the seismic response to mining increased significantly at mining spans where the modelled maximum closure of 270 mm is exceeded.

For the last four raiselines to the west, the simulated convergence does not exceed the adopted maximum convergence of 270 mm, while it was exceeded in nearly all the older raiselines.

Figure 16 illustrates the simulated convergence for the eastern side of the mine with the shale footwall. The last six raiselines to the east at the bottom of the figure also do not exceed the convergence criterion. Owing to low-grade patches in this area, some ground has not been mined and the extraction ratio is less than the design. The associated simulated maximum convergence (for constant input parameters) is lower than the values on the western side of the mine (smaller mining spans). The seismic activity on the eastern side of the mine is therefore expected to be lower than the western side. The opposite behaviour is shown in Figure 9, however, with more large-magnitude seismic events on the east. This further supports the hypothesis that the difference in footwall type (which was not simulated in this model) plays a role in the observed seismic response.

The convergence simulations illustrated above are only used to investigate the effect of mining spans and geometries and not to investigate the effect of different footwall rock types. Inelastic failure is also not simulated in these codes.

As a preliminary experiment to investigate the influence of

different footwall rock types, numerical modelling, using MAP3D, was used to simulate the convergence volume for a conceptual raiseline at Mponeng mine at the same depth as 116 to 120 Level (approximately 3500 m below surface). In the model the maximum mining span is limited to 180 m (separated by 30 m wide dip pillars). The dip span is limited to 300 m.

For the model, Young’s modulus was changed from 77 GPa for the quartzite to 63 GPa for the shale. These are rather crude assumptions as these values are assumed everywhere in the model and not only in the footwall. The simulated volume of convergence versus the mining span for the two modelling scenarios is plotted in Figure 17. As expected, the value is higher for the shale material and according to Equation [1], a larger cumulative seismic moment is expected. This does not, however, explain the occurrence of larger magnitude events and further work is required. Inelastic modelling and underground observations of closure needs to be conducted to explore this aspect further.

Conclusions The behaviour of the mining stopes in deep gold mines is affected by the different rock types and the varying rock mass strength properties. The role of geotechnical conditions in the seismic hazard in deep-level gold mines is, however, not clearly

Figure 16—Simulated maximum convergence for the east side of the mine with the shale footwall. This is for the stope face positions during December 2018. The mining area of interest was the six raiselines at the bottom right

Figure 15—Simulated maximum convergence for the west side of the mine with the quartzite footwall. This is for the stope face positions during December 2018 The Journal of the Southern African Institute of Mining and Metallurgy

Figure 17—Conceptual model of a raiseline between 116 and 120 Level at Mponeng mine. The strike span was increased in steps from ledging (green) to maximum (orange). The dip span remained constant VOLUME 122

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A case study of geotechnical conditions affecting mining-induced seismicity in a deep tabular mine and dykes, improving the layouts to minimize the seismic risk, and the risk associated with pillars and remnants. The data in this paper is valuable as it demonstrates that seismic hazard can also be affected by aspects such as the footwall rock type. This implies that a more adaptable approach in terms of seismic hazard assessment may be required and that a ‘one-size-fits-all’ approach may not work best for different geotechnical areas.

Acknowledgements Figure 18—Simulated volume of convergence versus strike mining span for the simplified model shown in Figure 17

understood and it has never been properly quantified. The seismic response to mining is expected to differ according to different rock types. To investigate this behaviour, the seismicity at Mponeng mine was studied. Two distinct geotechnical areas can be identified for the VCR horizon based on the difference in footwall lithology. On the eastern side of the mine, the footwall is shale and on the western side the footwall is quartzite. There is a gradual transition from thin quartzite footwall to thick quartzite footwall in the centre of the mine.

Careful seismic data selection for the east and the west sides of the mine was done to enable a comparison of the seismic response to mining between the two geotechnical areas. All mining areas or time periods with a significant difference in mining depth, mining geometry, and frequency of geological structures were excluded. Based on the selection criteria, only the data for the period 2016 to 2018 was used. During this period, mining on the shale footwall and the quartzite footwall took place on the same levels and the depths were comparable. The mining spans and mining geometries were also considered similar.

The study indicated that for the area with the shale footwall, there is tendency for more large-magnitude events to occur for a similar mining volume and span compared to the quartzite footwall area. The b-values of the frequency-magnitude distribution of events also confirmed that the seismic hazard for mining on the shale footwall appears to be higher, as more largemagnitude events can be expected for this area. By considering the moment tensor solutions for seismic events in the magnitude range ML ≥ 1.5, it appears that the majority of these events are related to the face orientations and stress orientation, and not the geological structures.

The difference in seismic response for the two areas requires additional work. It can be hypothesised that the closure rates are higher in the area with the softer shale and the additional deformation results in an increase in seismic hazard. As shown in this paper, this can be easily demonstrated using simple elastic modelling and the postulate that cumulative seismic moment is proportional to convergence volume. Further work is nevertheless required using inelastic numerical modelling to represent the different rock types and failure in these rocks. Underground closure measurements are also required to confirm if higher closure rates are indeed occurring on the areas with the shale footwall.

This study emphasised an important, but hitherto neglected area of research, namely the effect of different geotechnical areas on the seismic risk in deep mines. Most research to date has focused on aspects such as the hazard associated with faults 124

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This work forms part of the MSc study of Lourens Scheepers at the University of Pretoria.

References Applegate, J.D. 1991. Rock mechanics aspects of sequential grid mining. M.Eng dissertation, University of the Witwatersrand.

Budavari, S. 1983. Rock mechanics in mining practice, Monograph series M5.

Southern African Institute of Mining and Metallurgy, Johannesburg.

Cook, N.G.W., Hoek, E., Pretorius, J.P.G., Ortlepp, W.D., and Salamon, M.D.G. 1966. Rock mechanics applied to the study of rockbursts. Journal of the South African Institute of Mining and Metallurgy, vol. 66. pp. 435-528.

Denkhaus, H.G., Hill, F.G., and Roux, A.J.A. 1958. A review of recent research into rockbursts and strata movement in deep-level mining in South Africa. Papers of the Association of Mine Managers of South Africa, 1958–1959. pp. 245–269.

Durrheim, R.J. 2010. Mitigating the risk of rockbursts in the deep hard rock mines of South Africa: 100 years of research. Proceedings of Extracting the Science: 100 Years of Mining Research, Phoenix, AZ. Brune, J.F. (ed.). Society for Mining, Metallurgy, and Exploration, Littleton, CO. pp. 156-171.

Esterhuyse, J.C. and Malan , D.F. 2018. Some rock engineering aspects of multireef pillar extraction on the Ventersdorp Contact Reef. Journal of the Southern African Institute of Mining and Metallurgy, vol. 118, no. 12. pp. 1285-1296.

Jager, A.J. and Ryder, J.A. 1999. A Handbook on Rock Engineering Practice for Tabular Hard Rock Mines. Safety in Mines Research Advisory Committee, Johannesburg.

Jooste, Y. and Malan, D.F. 2020. The need for improved layout design criteria for deep tabular stopes. Journal of the Southern African Institute of Mining and Metallurgy, vol. 120, no. 1. pp. 23-32.

Malovichco, D. 2020. Description of seismic sources in underground mines: Theory. Bulletin of the Seismological Society of America, vol. 110, no. 5. pp. 2124-2137.

McGarr, A. and Wiebols, G.A. 1977. Influence of mine geometry and closure volume on seismicity in a deep-level mine. International Journal of Rock Mechanics and Mining Sciences, vol. 14, no. 3. pp. 139-145.

McGill, R.B. 2007. Strategies to manage seismicity in a deep VCR environment on Mponeng (1995-2003). Challenges in Deep and High Stress Mining. Potvin, Y., Hadjigeorgiou, J., and Stacey, D. (eds). Australian Centre for Geomechanics, Perth. pp. 217-223.

Napier, J.A.L. and Malan, D.F. 2014. A simplified model of local fracture processes to investigate the structural stability and design of large-scale tabular mine layouts. Proceedings of the 48th US Rock Mechanics/Geomechanics Symposium, Minneapolis, MN. American Rock Mechanics Association, Alexandria, VA. Salamon, M.D.G. 1968. Two-dimensional treatment of problems arising from mining tabular deposits in isotropic or transversely isotropic ground.

International Journal of Rock Mechanics and Mining Sciences, vol. 5. pp. 159-185.

Scheepers, L.J., Hofmann, G., and Morkel, I.G. 2012. The study of seismic response to production for a grid mining layout. SHIRMS 2012. Proceedings of the Second Southern Hemisphere International Rock Mechanics Symposium.

Australian Centre for Geomechanics, Perth. pp. 387-406. u The Journal of the Southern African Institute of Mining and Metallurgy

Development and beneficiation technology of rare earth ores in China

by Y. Chen1,2, D. He3, and J.H. Potgieter4

Affiliation:

School of Materials and Chemical Engineering, Hunan Institute of Engineering, Xiangtan, China.

2 Hunan

Huaqi Resource and Environment Science and Technology Development Co., Ltd, Zhuzhou, China 3 School

of Xingfa Mining Engineering, Wuhan Institute of Technology, Wuhan, China.

4 School

of Chemical and Metallurgical Engineering, University of the Witwatersrand, South Africa.

1

Correspondence to: Y. Chen

Synopsis The demand for rare earth elements (REE) is increasing rapidly owing to the emergence of new cleanenergy and defense-related technologies. China’s dominates the world production of REE. In this paper, we review the ore characteristics of four typical REE deposits in China and discuss the conventional beneficiation techniques, including gravity and magnetic separation, flotation, and hydrometallurgical processing of these ores. Some of the latest laboratory findings and industrial applications, as well as the development of novel reagents for REE processing in China are presented. The REE beneficiation technologies developed and employed in China could constitute a good case study for many other emerging projects being explored around the world.

Keywords rare earth elements, mineralogy, flotation, processing technology.

Email: chenyunhn@hotmail.com

Dates:

Received: 21 Jan. 2020 Revised: 27 Oct. 2021 Accepted: 1 Feb. 2022 Published: March 2022

How to cite:

Chen, Y., He, D., and Potgieter, J.H. 2022 Development and beneficiation technology of rare earth ores in China.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 125-132 DOI ID: http://dx.doi.org/10.17159/24119717/1098/2022

Introduction China has the largest resources of rare earth elements (REE) in the world, with an estimated 30% of global reserves (Hurst, 2010). China has dominated the world’s REE market in the last two decades, accounting for 57.6% of the total global rare earth mine production in 2020 (Garside, 2021). With the rapid increases in the consumption of rare earths owing to the emergence of new clean-energy and defense-related technologies, there is increasing interest among governments, industry, and academics in the exploration of REE resources and expansion of new applications. China has several state key laboratories and research centres funded by the government and industry, such as the State Key Laboratory of Rare Earth Materials Chemistry and Applications, the State Key Laboratory of Rare Earth Resource Utilization, Baotou Research Institute of Rare Earths, and the General Research Institute for Nonferrous Metals (Mancheri, 2013), which focus on the comprehensive exploitation and utilization of REE as well as research on rare earth metallurgy, environmental protection, new rare earth functional materials, and rare earth applications in traditional industry.

This paper is designed to give the reader a brief introduction to China’s REE resources, conventional technologies used in representative plants for beneficiating different ores, and recent progress in the processing of REE in China, which could be good references for many other emerging projects being explored around the world.

Current situation of China’s rare earth industry The REE are strategic materials for hi-tech products and military application in modern society. The conventional processing technology and applications for REE are shown in Figure.1 (Hurst, 2010). Since the introduction of reform and open policy in late 1970s, China's rare earth industry has been developed rapidly. Major progress has been made in research and development of mining, processing, and REE applications. The increasing expansion of industrial production has basically satisfied the needs of the nation's economic growth and social development (Chen, 2011).

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Figure 1—Conventional REE processing technology and REE applications

After several decades of development, China has established four major rare earth production areas, i.e., the light rare earth production areas in Baotou of Inner Mongolia, Shandong Weishan, Liangshan of Sichuan, and middle and heavy rare earth production areas in five southern provinces. Currently, six state-owned miners are in charge of China’s rare earth industry, in theory allowing the country to keep a strong handle on production, as China is constantly expediting reform in the rare earth industry.

The rapid development of China's rare earth industry has not only satisfied domestic demand for economic and social development, but also made important contributions to the world's rare earth supply. Despite its rapid development in the past decades, China's rare earth industry still faces many challenges and problems, including smuggling and illegal mining activities, environmental damage due to poor mining practice, and the growing challenge of meeting domestic needs for rare earths (Chen, 2011). A major concern surrounding China’s REE industry is the negative impact it has on the environment due to lax mining practices. There is overproduction of low-end products and overflow for exporting, while high-end products are in short supply and the local market is dependent on imports (Wang, 2009). These challenges need to be addressed by researchers, engineers, and policy-makers.

little or no beneficiation (Ni et al., 2012; Ren and Song, 2000). This part explores the current physical beneficiation of REE -bearing minerals, the unit operations employed, and some processes currently utilized at the major rare earth mines and processing plants in China.

Bayan Obo REE−Fe−Nb deposit The rare-earth resources in Bayan Obo were discovered in 1927 and industrial production of rare-earth concentrates started from 1957. Though Bayan Obo is the largest REE deposit, it is a polymetallic Fe-(REE, Nb) deposit where iron is the primary product and REEs are the by-products. Bayan Obo is also the second largest niobium (Nb) deposit in the world. Table I shows the typical chemical composition of the ore. More than 80% of the light REE resources in China are distributed in the Bayan Obo region, Inner Mongolia, Northern China (Wu et al., 1996; Fan et al., 2010).

The Bayan Obo ore is mineralogically complex, containing 71 elements and 170 distinct minerals, More than 90% of the REE occur in discrete minerals, and about 4–7% are dispersed in iron minerals and fluorite. A total of 15 rare earth minerals are found, the principal ones being bastnaesite and monazite in a ratio of 7:3 or 6:4. Magnetite and haematite are the dominant Fe ore minerals (Li and Yang, 2014).

The mineralogical characteristics of REE-bearing minerals is a key parameter impacting beneficiation. Most of the Bayan Obo minerals, particularly in the banded ore, are very fine or extremely fine grained, particularly the Fe−REE−Nb minerals. The grain sizes of the REE minerals are in the range of 0.01–0.074 mm, with 70–80% falling in the < 0.04 mm size fraction.

The separation process for bastnaesite ores may employ numerous unit operations including gravity and magnetic separation. However, the Bayan Obo minerals are beneficiated

Typical REE plants and beneficiation technology in China The processing of REE-bearing minerals, including beneficiation, downstream metallurgical processing for the separation of the individual rare earths, and purification based on end-product applications, requires a great deal of investigation to fill the knowledge gaps surrounding the developing of rare earth projects. There are only three major REE-bearing minerals that are currently exploited commercially (bastnaesite, monazite, and xenotime), excluding ion-adsorbed clays, which currently undergo

Table I

Typical chemical composition of Bayan Obo REE−Fe−Nb ore (wt%) La2O3

CeO2

Pr6O11

Nd2O3

Sm2O3

Eu2O3

Gd2O3

(Tb-Lu)2O3

Y2O3

24-26

50

3-5

16-18

1.5

0.2

0.4

0.2-0.3

0.3

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Development and beneficiation technology of rare earth ores in China primarily by flotation using a fatty acid or hydroxamate-based collector system (Chi et al., 2010). Bayan Obo ores are difficult to beneficiate due to their physical and chemical properties, and the close association of the REE with iron and gangue minerals.

A great deal of work had been done in China on the beneficiation of the Bayan Obo REE deposits since the 1950s, and more than 20 beneficiation techniques have been reported. Significant progress on the processing of REE minerals was made in the early 1990s (Yu, 2000).

A flow sheet comprising low-intensity magnetic separation (LIMS), high-intensity magnetic separation (HIMS), and flotation, developed by Changsha Metallurgical Research Institute in 1990, was considered the most suitable to be used in industrial plants, and which is shown in Figure 2.

Initially, cyclic alkyl hydroxamic acid and alkyl hydroxamic acid were chosen as collector, although the selectivity was poorer than that of H205 (aromatic hydroxamic acid, developed in 1986).

The concentrate grade and recovery of REE could be improved significantly by using the new-generation collector H205 with water-glass, while the sodium fluoride activator was not required (Zhu et al., 2000). By the end of 2012, the Bayan Obo flotation concentrator had achieved an annual throughput of 250 000 t of REE Concentrates (50% rare earth oxides, REO).

Sichuan Mianning REE deposit Mineralogy The Mianning REE deposit, which was discovered in the mid1980s, is an alkaline pegmatite carbonate-type deposit. The industrial reserve is 1 × 106 t, with an average grade of 3.7% REO. It contains both light and heavy REE. A typical chemical analysis is shown in Table II. Bastnaesite is the main rare earth mineral; chevkinite and parisite are found in the ore as well. Other associated minerals are barite, fluorite, iron and manganese minerals, as well as small amount of galena. The ore can be classified into granular and powder types. The granular ore has a coarse grain size, > 1 mm. The grain size of the bastnaesite is between 1 and 5 mm.

The powder ore is the weathered product of the original ore and accounts for about 20% of the total reserve. The grade is about 3−7% REO and the grain size is 80% < 325 mesh (Li and Yang, 2014).

Beneficiation techniques A combination of conventional physical separation operations – gravity concentration, magnetic-gravity separation, and gravity separation-flotation – is used: The flow sheet is shown in Figure 3. The presence of weathered amorphous Fe-Mn aggregates in the form of massive and powdered black sludge greatly influences the floatability of the REE minerals.

Rare earth minerals are good candidates for gravity separation as they have relatively high specific gravities (4–7) and are typically associated with gangue material (primarily silicates) that are significantly less dense. The ore is ground to 62% passing 200 mesh and wet-classified into four size fractions. Shaking tables are used to process the fractions separately. Three different grades of bastnaesite concentrates are obtained with grades of 30%, 50%, and 60%. The overall recovery is around 75% (Ni et al., 2012) Magnetic separation techniques are a common separation step in rare earth mineral beneficiation to eliminate highly magnetic gangue, or to concentrate paramagnetic REE-bearing minerals such as monazite or xenotime. After grinding, the ore is concentrated by LIMS and HIMS and a magnetic concentrate with a grade of 5.64% is obtained. The recovery in the magnetic circuit

Table II

Chemical composition of Mianning REE ore Constituent

wt%

Constituent

wt%

REO TFe SiO2 Al2O3 FeO

3.70 1.12 41.00 4.17 0.43

F CaO MgO S P

5.50 9.62 1.10 8.33 0.24

Constituent wt %

Na2O MnO BaO K2O Pb

1.39 0.73 21.97 1.31 0.23

Figure 2—Beneficiation flow sheet of the Bayan Obo ore The Journal of the Southern African Institute of Mining and Metallurgy

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Figure 3—Gravity separation–flotation process at Mianning REE mine

is 74.2% with a yield of 42%. The magnetic concentrate is then classified into four size fractions that are processed separately by shaking tables. The final concentrate has a grade of 52.3% REO, with an overall recovery of around 55%.

Froth flotation is commonly applied to the beneficiation of rare earth ores since it is able to process a wide range of fine particle sizes and can be tailored to the unique mineralogy of a given deposit. As shown in Figure 3, the ore is ground to 50% passing 200 mesh and wet-classified into four size fractions. The classified fractions are concentrated on shaking tables. The overall grade of gravity concentrate is 30% REO with a REE recovery of 74.5%. The gravity concentrate is reground to 70% passing 200 mesh for flotation. C5−9 hydroximic acid (H205) and phthalate in the ratio of 1:1, sodium carbonate, and sodium silicate are used as the flotation reagents at pH 8–9. By using one rougher, one cleaner, and one scavenger stage a concentrate with a grade of 50−60% REO is acquired with a REO recovery of 50−60%.

Shandong Weishan REE deposit Mineralogy The Shandong Weishan deposit was discovered in 1958 and exploration was completed in 1975. The reserve of REE was about 2.55 × 106 t and the average geological grade was 3.13%. This is a quartz−barite−carbonate type REE ore deposit. The main rare earth minerals are bastnaesite and parasite, and the main associated minerals are barite, calcite, quartz and fluorite. The

grain size of the rare earth minerals is in the range of 0.04– 0.5 mm. The chemical composition is shown in Table III.

Beneficiation techniques The Weishan REE flotation plant had been in operation since the beginning of the 1980s. Many technological flow sheets and reagent suites have been tested to optimize the metallurgical performance. For the typical conventional processing flow sheet, the ore was ground to 65-75% passing 200 mesh and the REE minerals were floated with one rougher stage followed by three cleaner and three scavenger stages. In the 1980s oleic acid and kerosene were used as collectors at pH5, adjusted by sulphuric acid. Since 1991, as the ore grade dropped to 3-4%, a specific collector with the formula C6H4OHCONHOH has been used with the addition of sodium silicate and L101 frother. The flotation is operated at weak alkaline conditions of pH 8−8.5. The flotation concentrate has a grade of >60% REO at a recovery of 60–70%. A secondary REE concentrate with the grade of 32% REO at a recovery of 10–15% is also obtained. The conventional beneficiation process applied in this ore is shown in Figure.4.

Weathered crust elution-deposited rare earth ores (ion-w adsorption clays) Mineralogy Ion adsorption rare earth ores consist of aluminosilicate minerals (e.g. kaolinite, illite, and smectite) and contain 0.05-0.3 wt% REE

Table III

Chemical composition of Shandong Weishan REE ore (wt%) REO

TFe

SiO2

Al2O3

F

CaO

MgO

S

Na2O

Th

BaO

K2O

3.17

2.81

47.92

22.48

0.70

1.09

1.18

2.1

3.53

0.002

11.99

1.85

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Figure 4—Typical flow sheet applied at Shandong Weishan REE mine

that are physically adsorbed at sites of permanent negative charge.

These deposits are the result of in-situ lateritic weathering of rare-earth-rich host rocks (granitic or other igneous rocks). The very fine-grained clay particles have the capability of adsorbing lanthanide ions released/dissolved during weathering. Subtropical climates present ideal conditions for this lateritic process to occur (Papangelakis and Moldereanu, 2014).

The ion-adsorption clay deposits of REE were first discovered in 1969 in the Jiangxi Province (southern China) and were recognized as a novel type of exogenous rare earth ore. Since then, further deposits have been discovered and mined throughout the south of China. The known reserve of weathered crust elution− deposit rare earth ores in China is over 1 × 106 t REO, which constitutes over 80% of the world total heavy REE reserve. China currently produces about 1 × 104 t concentrate (REO>60%) from this type of ore annually.

Although ion-adsorption clay deposits are substantially lower grade than other types of lanthanide resources, the lower grade is largely offset by the lower mining and processing costs and the very low content of radioactive elements (normally associated with yttrium). These deposits are mined by open-pit methods and no ore beneficiation is required. A simple leaching by monovalent sulphate or chloride salt solutions at ambient temperature can produce a high-grade REO product. Because of their abundance in surface layers and simple mining and processing these clays warrant a detailed study as important sources of rare earths (Chi and Tian 2008).

Extraction techniques The ion-adsorption clays contain anywhere between 0.05 and 0.3 wt% rare earths, 60–90% of which occur as physically adsorbed species that are recoverable by simple ion-exchange leaching. In the typical procedure, the ores are leached with concentrated inorganic salt solutions of monovalent cations. During leaching, the REE are selectively desorbed and substituted on the substrate by the monovalent ions, and transfer into solution as soluble sulphates or chlorides, following a 3:1 stoichiometry. Solubilized REE are usually selectively precipitated with oxalic acid to form oxalates that are subsequently converted to REO by roasting at 900°C. Finally, the mixed REO are separated by dissolution in HCl followed by fractional solvent extraction. Approximately 99% of The Journal of the Southern African Institute of Mining and Metallurgy

Figure 5—REE extraction technique for weathered crust elution deposit REE ore

the REO can be recovered by a five-stage countercurrent leaching process (Chi and Tian 2008).

China has been at the forefront of research and development for these unique deposits, applying the ion-exchange leaching procedure for the extraction of lanthanides via three successive generations of technology. The first-generation leaching technology employed batch leaching with NaCl, The secondgeneration technology used batch and heap leaching with (NH4)2SO4, and the third generation comprised in-situ leaching with (NH4)2SO4, which has been summarized by Chi et al. (2013).

The conventional flow sheet is shown in Figure 5.

The in-situ leaching technique is also currently applied in China for the recovery of residual REE from the tailings of older batch and heap leaching operations. The implementation of in-situ leaching requires comprehensive geological surveys in order to determine the hydrogeological structure of the area, ore characteristics, grade, orientation and the permeability of the host rock. The procedure can only be applied to an orebody with suitable permeability and underlain by solid bedrock without fissures. Failure to conduct diligent geological surveys may result in serious environmental degradation such as underground water contamination, mine collapse, and landslides, as well as unsustainable REE recoveries (Tian et al., 2010).

Technology developments Development of flotation reagents A major difficulty in the separation of REE by flotation is due to their surface characteristics being similar to the two main contaminants: carbonates and silicates. Oxalic acid is one of the organic acids most widely used to depress the gangue minerals (carbonates and haematite) during flotation of ores that containing oxide minerals (Jordens et al., 2013; Chehreh et al., 2015). The development of REE separation techniques is often closely linked to flotation reagent development. Mineral processing researchers have synthesised and/or modified many kinds of reagents aiming at improving the metallurgical performance of REE flotation since the 1960s, such as reagents VOLUME 122

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Development and beneficiation technology of rare earth ores in China containing nitrogen, phosphorus, carboxylic acid etc., some of which have been successfully applied in industry (Jordens et al., 2013). Recently, more work has been done to synthesise or modify collectors and flocculants for fine particles to enhance the metallurgical performance of existing plants (Li et al., 2018; Fan et al., 2017). Since China is the world’s largest producer of REE, it is interesting to follow the development of leaching reagents for REE flotation in China.

Nitrogen-containing reagents Based on the type of non-polar groups, nitrogen-containing reagents can be classified as alkyl, cyclo-alkyl, and aromatic types.

Generally speaking, hydroxamic acid has a stronger chelating capacity with many metal ions – however, it has a weaker chelating capacity with alkaline earth metal ions and superior chelating capacity with REE, tungsten, and niobium metal ions (Wang, 1981). Since the 1960s, the synthesis of hydroxamate reagents has been extensively studied in China. Alkyl, cycloalkyl, aromatic, and other hydroxamates were developed and successfully commercialized for flotation at the Baotou and Sichuan REE mines, and good results were obtained. Currently, C5-9 alkyl hydroximate, H205, and H316 are widely applied in commercial REE flotation plants in China (Yu, 2000; 1998). Theoretical studies indicated that H205 attaches to bastnaesite surfaces mainly by chemisorption, as an O–O type 5-membered chelated ring is formed by chemical reaction, with multilayer and inhomogeneous physical adsorption. Reagent H316 is a modification of H205, with better selectivity, stability, and fluidity, which does not require saponification by aqueous ammonia, and is an effective collector for REE flotation. The combination of H316 with H103 and water glass has been successfully applied at Baotou Steel (Ren et al., 2000; 2003).

Phosphorus-containing reagents Traditionally, phosphorus-containing reagents were widely used in the flotation of oxide minerals such as cassiterite, scheelite, and wolframite. This kind of reagent has been investigated for the beneficiation of REE minerals in China since the 1980s.

The reaction mechanism of the alkyl phosphate ester on the surface of REE minerals (bastnaesite and monazite) has been studied in detail. Alkyl phosphate ester has good selectivity for bastnaesite over monazite due to its structural characteristics.

The hydrophobic group is aromatic and its centric atom is phosphorus instead of carbon. IR spectra test work indicated that styrene phosphinic acid could form special species with REE cations, which can be explained by the electronic theory of organic chemistry as the interaction between atoms in the organic conjugated system results in the delocalization of bonds, leading to a reduction in the energy of the system, which will strengthen the stability of the dissociated negative ions of styrene phosphinic acid, thus improving the flotation selectivity (Zhang et al., 1982).

Organic phosphoric acids were applied in combination with auxiliary kerosene at the REE beneficiation plant at Weishan in Shandong Province in the mid-1980s, with satisfactory results.

Synergistic effect of mixed reagents It is well known that mixtures of various flotation collectors are often more effective than would be expected from their individual characteristics. This phenomenon is a classic example of synergism in flotation in which the combined effect exceeds the sum of the weighted individual effects (Bradshaw et al., 1998).

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Normally, mixed reagents can enhance the selectivity, decrease the reagent consumption, reduce the reagent costs, and improve metallurgical performance.

Aromatic hydroxamic acid has good selectivity for rare earth minerals, although its collecting ability for bastnasite is relatively poor. The combination of aromatic hydroxamic acid and a small amount of strong cycloalkyl hydroxamic acid can overcome the shortcomings and enhance the recovery of bastnasite (Che et al., 2004). Hydroxamic acid collectors have good performance but are somewhat expensive. A mixture of hydroxamic acid, isooctyl alcohol, and kerosene was tested at one REE plant and showed a marked synergistic effect, with enhanced collecting ability and good selectivity, and which not only reduced the consumption of hydroxamic acid, but also reduced the cost of industrial production (Zhu et al., 2000). In order to meet increasing market demand and lower the reagent costs for REE beneficiation, further work has been done to identify a co-collector to be combined with hydroxamic acid for REE flotation. New developments in reagent combinations generally have a rapid effect on production.

Practical experience has proved that the combined use of reagents is an effective way to reduce reagent costs and is undoubtedly important direction for research.

Industrial applications Usually, rare earth minerals are finely disseminated (sometimes < 10 μm) and intimately associated with gangue minerals, thus fine grinding is necessary in order to obtain effective liberation. Also, rare earth minerals are brittle and easily become slimed in the grinding process, which makes it difficult to get a good flotation recovery (Yu et al., 2014). Yin (2013) tested different physical separation processes such as gravity separation, electrostatic separation, magnetic separation, and flotation to recover REE from Baotou Bayan Obo tailings containing 6.70% REO , 12.94% total iron, 11.7% silicon oxide, 12.50% fluorine, and 30.34% calcium oxide. The main minerals of economic interest are bastnaesite and monazite. A single rougher stage (high-intensity magnetic separation) followed by three flotation cleaner stages produces a final concentrate with a rare earth grade of 19.87% at a recovery of 7.10%.

Xiong and Chen (2009) studied the beneficiation of bastnaesite from Mianning Sichuan, using water glass as depressant and a modified hydroxamic acid as collector. The pH of the pulp was controlled within 7.5-8 in order to improve the metallurgical performance. A concentrate with REO grade of 62.10% and recovery of 86.98% was achieved in bench scale test work.

Processing of alkaline hard-rock rare earth deposits The alkaline hard-rock rare earth ores are located in Maoniuping Sichuan Province, and constitute the second largest REE reserve in China after Bayan Obo. In the past, only the rare REEbearing minerals could be recovered by conventional processing technology, while large amounts of barite, fluorite, and other associated minerals were discarded as tailings.

Wang et al. (2013) and Cao et al. (2013) carried out comprehensive tests to compare different separation process and a novel flow sheet was developed and applied on site. The nonmagnetic gangue, including large amounts of slimes, is discarded via WHIMS, then gravity separation is used to discard any low specific gravity gangue and produce a final concentrate.

The middling stream from the shaking tables is processed by flotation to increase the recovery of fine particles.

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Development and beneficiation technology of rare earth ores in China

Figure 6—Flotation flow sheet for Maoniuping REE ore

The effect of various parameters, including grinding fineness, type and dosage of regulators, collectors, and promoters, pulp density, conditioning time, and temperature were studied systematically by comparative trials. A selective hydroxamic acid collector, known as GSH, and sodium silicate as regulator are used to produce a REO flotation concentrate with grade of 65.11% at 17.05% recovery. The two concentrate streams from the shaking tables and flotation are combined to form the final REO concentrate with a grade of 65.08% at an overall recovery of 84.61%. The reagent suite and flotation flow sheet are shown in Figure 6 (Cao et al., 2013).

Table IV

R esults of locked cycle test on the flotation of ultrafine rare earth minerals Item

Yield (%) REO grade (%) REO recovery (%)

De-carbon product Concentrate Tailings ROM

0.55 2.08 97.37 100.00

1.57 27.41 0.09 0.71

1.36 80.23 18.41 100.00

Flotation separation of ultrafine rare earth minerals Yu (2014) tested many kinds of depressant for their effectiveness in separating bastnasite from fluorite and calcite, which are the main gangue minerals in low-grade refractory rare earth ore from Hubei Province. The results showed that fluorite and calcite were completely depressed at a sodium citrate dosage of 140 mg/L, although bastnasite was depressed as well. At a sodium silicate dosage of 40 mg/L, fluorite and calcite were completely depressed, while bastnasite was partly depressed. The floatability of the three minerals remained unchanged with increasing dosages of sodium fluosilicate, and fluorite and calcite could not be completely depressed. However, sodium silicate showed better selectivity when H205 was used as collector at a pH around 9.

Based on the laboratory studies, good metallurgical performance could be obtained using sodium silicate as depressant, H205 as collector, and BY-10 as auxiliary collector.

The feed could be upgraded from 0.69% REO to 43% with 48% recovery in the open circuit test, while in locked cycle testing the grade of the final concentrate was 27% with a recovery of 80%.

Further tests were carried out on site at the pilot scale (Yu et al., 2014; Yin, 2013). The results are listed in Table IV, and the flow sheet for the locked cycle test and pilot-scale test is shown in Figure 7.

Conclusions Rare earths are an important, non-renewable natural resource The Journal of the Southern African Institute of Mining and Metallurgy

Figure 7—Flotation flow sheet for ultrafine REE at Hubei VOLUME 122

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Development and beneficiation technology of rare earth ores in China with increasingly wide applications in economic and social development. The REE comprise elements of the lanthanide series as well as yttrium, and are found in over 250 different minerals.

China is among the countries with relatively rich rare earth reserves, and since the 1950s remarkable progress has been made in the country’s rare earth industry. After many years of effort, China has become the world's largest producer, consumer, and exporter of rare earth products.

Globally, rare earths are not that rare, but they are not found in economically exploitable concentrations, thus they are quite expensive to extract if they are to be processed with smaller footprints and less harm to the environment. Companies have to now engage in more costly and less environmentally harmful mining and metallurgical processes and make efforts to develop a real ‘green economy’ in the long chain of REE mining and downstream applications.

After many years of development, China has established a relatively complete R&D system, pioneered numerous advanced technologies in rare earth mining and processing, and laid a solid foundation for efficient exploitation and utilization of rare earth resources. The REE beneficiation technologies developed and employed in China could be a good reference for many other emerging projects being explored around the world.

Acknowledgements The authors would like to thank the Ministry of Land and Resources for providing funding to Dr Dongsheng He via the Research Fund Programme of the Key Laboratory of Rare Mineral (grant no.KLRM-KF201801).

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Li, M., Gao, K., Zhang, D.L., Duan, H.J., Ma, L.L., and Huang, L. 2018. The influence of temperature on rare earth flotation with naphthyl hydroxamic acid. Journal of Rare Earths, vol. 36, no. 1. pp. 99-107 [in Chinese].

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The Journal of the Southern African Institute of Mining and Metallurgy

Climate impacts of fossil fuels in today’s electricity systems

by L. Schernikau1 and W.H. Smith2

Affiliation: 1 2

TU Berlin, Germany.

W ashington University of St. Louis

Synopsis Correspondence to:

Oil, coal, and gas account for approximately 80% of global primary energy, but only a portion of total airborne CO2eq (approx. 35% at GWP20 to 65% at GWP100), even though they account for 95% of total measured CO2 emissions. The benefits of these energy sources, as well as their related costs, are not all incorporated in current energy policy discussions. Global greenhouse gas policies must include documented changes in measured airborne CO2eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies.

The authors examined airborne CO2, which is less than half of emitted CO2, as well as reported CH4 emissions and the global warming potential of CH4 as published by the IPCC for coal and natural gas. The surprising conclusion is that surfaced-mined coal appears ‘better for the climate’ than the average natural gas, and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to unintended consequences and the switch from coal to natural gas, especially LNG, will not have the desired impact of reducing predicted future global warming; in fact, quite the contrary. A large portion of anthropogenic global warming is attributed by the IPCC and IEA to CH4, but it must be noted that CH4 emissions from natural sources and from agriculture account for approximately 40% and 25% of annual global CH4 emissions respectively. Energy accounts for about 20% of documented CH4 emissions.

CO2 contributes only approximately 35% of annual airborne anthropogenic GHG emissions after accounting for CH4, over a 20-year horizon. At a 100-year horizon, the contribution of CO2 increases to approximately 60%. Energy policies that do not consider all GHG emissions along the entire value chain will lead to undesired economic and environmental distortions. All carbon taxation and CO2 pricing schemes are incorrect and need to be revised.

At IPCC’s GWP20 an approximately 2%1 higher loss of CH4 across the value chain prior to combustion of natural gas versus coal will lead to ‘climate parity’ of coal with natural gas. According to public data, natural gas value chains have high CH4 and undocumented CO2 losses. On a global average, using only IEA-documented CH4 data, natural gas emits approximately 15% more CO2eq than surface-mined coal, over a 20-year horizon. This difference will increase as the use of shale gas and LNG expands.

Investors should support all energy systems in a manner that avoids an energy crisis, including intermittent renewable energy systems where they make sense. If CO2 emissions need to be reduced, one of the most effective ways would be to install ultra-supercritical power plants with CCUS technology.

However, the undisputed benefits of increased CO2 concentrations in the atmosphere because of its promotion of photosynthesis and plant growth effects (fertilization) need to be considered in energy policy decisions as well. The authors suggest that future research and development should concentrate on reducing net emissions from fossil fuel power plants and providing cost-effective and reliable new conventional power generation capacity, utilizing clean coal and clean natural gas technology.

L. Schernikau

Email: lars@lali.com

Dates:

Received: 26 Oct. 2021 Revised: 31 Jan. 2022 Accepted: 2 Feb. 2022 Published: March 2022

How to cite:

Schernikau, L. and Smith, W.H. 2022 Climate impacts of fossil fuels in today’s electricity systems.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 133-146 DOI ID: http://dx.doi.org/10.17159/24119717/1874/2022 ORCID: L. Schernikau https://orcid.org/0000-00016469-0117 Smith, W.H. https://orcid.org/0000-00019839-7023

Keywords fossil fuels, GHG, greenhouse gases, energy policy, climate change potential, clean coal technology.

Introduction In 2019, fossil fuels – in order of importance oil, coal, and gas – made up approximately 80% of global primary energy (PE) production totalling approximately 170 000 TWh or 600 EJ. Despite the covid pandemic and significant wind and solar capacity additions, the percentage did not change much in 2021.

1

his coal/gas break-even number increases from approximately 2% to 5,5% loss of methane using IPCC’s 100-year Global Warming Potential T (GWP) instead of the 20-year GWP. Detailed calculations can be found in footnote4

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Climate impacts of fossil fuels in today’s electricity systems This proportion has also been largely constant since the 1970s, when energy consumption was less than half what it is today.

The same three fossil fuels made up over 60% of global gross electricity production, totalling approximately 27,000 TWh in 20202. It is important to note that global electricity production makes up about 40% of PE, with transportation, heating, and industry accounting for the remaining approximately 60% (see also Figure 1).

Renewables in the form of wind and solar – while not the subject of this paper – accounted for approximately 3% of global PE and 8% of global gross electricity production in 2019, and this was largely unchanged in 2020 and 2021 (refer to Schernikau and Smith, 2021, for more details on solar energy). For comparison, coal and gas combined accounted for approximately 50% of global PE and 60% of global gross electricity production.

The UN projects that global population will rise from the current 8 billion to 10 billion in the next 30 years (Roser, Ritchie, and Ortiz-Ospina, 2013), and may peak around 11-12 billion by the end of the century. Despite continued improvements in energy efficiencies, rising living standards in developing nations are forecast to increase global average annual per capita energy consumption from 21,000 kWh to 25 000 kWh by 2050 (Lomborg, 2020; BP, 2020). As a result, global PE consumption could rise by as much as 40% to 60% by 2050 (a 25% population increase and a 20% PE/capita increase translates to 50% PE demand increase).

Energy demand growth is fuelled by developing nations in Asia, Africa, and South America. Developed nations are expected to consume less energy in the decades to come, owing to population stagnation or decrease, and increases in energy efficiency.

However, it should be noted that recent models by McKinsey (McKinsey Energy Insights, 2019, 2021) estimate that global PE demand will only increase by 14% by 2050, while the International Energy Agency’s (IEA’s) 2021 Net-Zero Pathway (IEA, 2021) models a reduction by approximately 10% by 2030 to reach ‘net zero’ CO2emissions (not CH4 emissions) by 2050, although this is questioned by the authors. The same reports estimate that global power generation will almost double from 2020 to 2050 (McKinsey Energy Insights. 2019), also driven by the projected electrification of transportation. The Institute for Energy Economics in Japan (IEEJ) predicts global PE demand to increase by 30% by 2050, while the American Energy Information Agency (EIA) predicts a 50% increase (IEEJ, 2019; EOA, 1019, 2021) in line with the authors’ analysis.

It is prudent to assume that wind and solar alone will not be able to generate enough energy to match the expected demand

2

0% of 170 000 is not 27 000; the difference comes from energy lost during electricity 4 production. Only a fraction of energy put into a system is usable after conversion, the remainder is lost as heat. Authors’ Research and Analysis based on the following sources: IEA. 2019. Installed power generation capacity in the Stated Policies Scenario, 2000-2040. https://www.iea.org/data-and-statistics/charts/installed-power-generationcapacity-in-the-stated-policies-scenario-2000-2040 [accessed 25 October 2021].

IEA. 2021b. Key World Energy Statistics 2021. https://iea.blob.core.windows.net/ assets/52f66a88-0b63-4ad2-94a5-29d36e864b82/KeyWorldEnergyStatistics2021.pdf [accessed 25 October 2021].

BP. 2021. Statistical Review of World Energy. 70th edition.https://www.bp.com/content/ dam/bp/business-sites/en/global/corporate/pdfs/energy-economics/statistical-review/ bp-stats-review-2021-full-report.pdf [accessed 25 October 2021].

BP. 2020. Statistical Review of World Energy. 69th edition.https://www.bp.com/content/ dam/bp/business-sites/en/global/corporate/pdfs/energy-economics/statistical-review/ bp-stats-review-2020-full-report.pdf [accessed 25 October 2021] REN21. 2021. Renewables 2021 Global Status Report (GSR). https://www.ren21.net/ reports/global-status-report/ [accessed 25 October 2021].

Smil, V. 2017: Energy Transitions: Global and National Perspectives. Praeger, Santa Barbara, CA.

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Notes: (1) Only the portion of industry/transport/building that is not included under electricity (2) Assumed worldwide net efficiency of about 33% for nuclear, 37% for coal, 42% for gas, assume average.~40% efficiency => 27 000TWh becomes 68 000 TWh or 40% of 170 000 TWh Sources: Schernikau, analysis based on IEA Energy Technology Perspectives 2020

Figure 1—Overview of global primary energy and electricity

increase to 2050. This is confirmed by the IEEJ’s October 2020 report (IEEJ, 2019; EIA. 2019, 2021) forecasting an absolute increase in fossil fuels’ share in PE in its reference case by 2050.

In July 2021, the IEA (2021) confirmed that ’…[renewables] are expected to be able to serve only around half of the projected growth in global [electricity] demand in 2021 and 2022’. Over 60% of global electricity growth during 2021 was fuelled by coal and natural gas (NG), and only 30% from renewables. For PE growth, the renewable share will be only a fraction, about 20%, as about 2/5th of PE is for electricity. Schernikau, Smith, and Falcon (2022) provide more details on the global energy landscape, including a discussion on the pros and cons of using PE with increased penetration of renewable energy.

Even if wind and solar were to fulfill all future increases in PE demand, it becomes clear that for the next 30 years and beyond we will continue to depend on conventional energy resources for a large portion, if not the vast majority, of our global energy needs.

Therefore, given the relevance of coal and natural gas to the future energy scene, this paper examines the global warming impact of such fossil fuels.

Which fossil fuel is ‘best for the climate’?

Coal and natural gas are the main fuels for electricity generation, while oil is the main fuel for transportation. Nuclear’s share reaches about 10-11% for electricity and 5-6% for PE (see Figures 1 and 2). Nuclear energy is not discussed further in this paper despite its many benefits and challenges. Given the importance of coal and NG, especially for electricity but also for energy as a whole (approx. 60% of electricity and 50% of PE), the authors review the impact of both coal and NG on global warming, relying on reported data by the IPCC, the IEA, and Our World in Data.

Introducing greenhouse gases and global warming potential It is undisputed that (1) the average global temperature has increased since the 1800s – the end of the Little Ice Age, and that (2) humans have contributed to global warming in the past and will continue to do so. It is also undisputed that (3) CO2 is a greenhouse gas (GHG) and that increasing airborne CO2 levels contribute to global temperature change, in concert with other climate forcings.

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Climate impacts of fossil fuels in today’s electricity systems In addition, it is undisputed – though less well known – that the global warming impact of CO2 or any GHG declines logarithmically, thus each additional ton of CO2 airborne has less capacity to increase temperatures (Wijngaarden and Happer, 2020). CO2 is active in the wavelength band from about 12-18 μm, which has been essentially saturated. This works in such a way that additional CO2 molecules can only slightly widen the wavelength band in which the molecule can impact outgoing thermal radiation. In the absence of GHGs, the Earth’s surface temperature would be on average about -18°C; but with GHGs the surface reaches a temperate and livable 15°C. The 33K difference is ascribed to the so-called ‘greenhouse effect’ of the atmosphere (World Meteorological Organization, 2021).

The IPCC in its 5th Assessment Report AR5 gives the global warming potential (GWP) of several of GHGs over both a 20and a 100-year horizon. These GWPs are little changed in AR6, published in August 2021. The IPCC (2014a) defines GWP as ‘An index measuring the radiative forcing following an emission of a unit mass of a given substance, accumulated over a chosen time horizon, relative to that of the reference substance, carbon dioxide (CO2)’. There remains scientific uncertainty and debate about the global warming potential, but for the sake of this paper the authors choose to use the official reported IPCC data3 (Cain, 2018; Derwent, 2020; ClimateAnalytics. 2017; Kleinberg, 2020; Lynch et al., 2020). For instance, the IPCC notes the large uncertainties in the GWP of CH4 – between about 32% and 40% (see IPCC, 2021, Table 7.SM8) The definition of GWP is given in many sources, but explained well by Kleinberg (2020). Equation [1] shows that the GWP of a particular molecule j is the ratio to CO2, denoted by i in the equation, integrated over time following an initial pulse of gas at t = 0. This metric implies that a gas which decays quickly will have a greater initial GWP than a gas which decays more slowly.

Kleinberg’s academic paper places the GWP in the correct physics perspective while pointing out its shortcomings.

[1] Considering the urgency of addressing global warming as well as the declared climate crisis by the UN, governments, and institutions, the authors use the IPCC’s 20-year GWP20 metric for CH4 of 84× and illustrate the implication on energy policy if one were to accept the IPCC’s GWP. For comparison, IPCC’s 100-year GWP100 metric for CH4 is 28×. The reader can adjust from GWP20 to GWP100 by dividing or multiplying any relevant CH4 number by 3 = 84 / 28. The GWP index is not radiative forcing but is a ‘metric’ intended to indicate how much ‘worse’ or ‘better’ a greenhouse gas is compared to CO2 (GWP of 1) and its impact on global warming (IPCC. 2014). The following six main GHGs and their respective GWPs are mentioned by the IPCC (2014b, 2014c): ➤ Water vapour (H2O): The most important and most abundant GHG, but not further detailed by the IPCC. The

The authors stipulate the IPCC GWP numbers for the purpose of our energy illustrations based on data used by governments and institutions. The authors’ detailed objection to GWP, as well as the scientific debate and uncertainty on GWP, cannot be detailed here due to space constraints (refer also to Cain, 2018; Derwent, 2020; ClimateAnalytics, 2017; Kleinberg, 2020; Lynch et al., 2020). For instance, Wijngaarden and Happer (2020) have analysed GHG forcing in detail and conclude significantly lower climate sensitivities than those used by the IPCC. 3

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authors are concerned that the greenhouse effect of water is not included in the IPCC analysis, apparently due to its complicated variability and energy transport effects. ➤ Carbon dioxide (CO2): GWP20 = 1, GWP100 = 1, no lifetime defined by IPCC ➤ Methane (CH4): GWP20 = 84, GWP100 = 28, lifetime 12,4 years ➤ Nitrous oxide (N2O): GWP20 = 264, GWP100 = 264, lifetime 121 years ➤ Perfluoromethane (CF4): GWP20 = 4880 years, GWP100= 6630 years, lifetime 50 000 years ➤ Hydrofluorocarbon (HFC-152a): GWP20 = 506, GWP100 = 138, lifetime 1,5 years

The misconception of reported global CO2 emissions and error in carbon taxing A recent survey identified over 1,200 different climate laws and policies (Grant et al., 2020). The vast majority of reports on global CO2 emissions as well as most proposed climate policies, laws, and regulations, and global carbon-tax discussions centre on measured-human-energy CO2 emissions. This is despite recent efforts by the IEA and other institutions to understand other GHGs better, primarily the shorter-lived GHG CH4. The National Oceanic and Atmospheric Administration (Tans, 2021; Dlugokencky, 2021) notes that atmospheric concentrations of CH4 increased from about 1630 ppb (parts per billion mole-fraction CH4) in 1984 to 1880 ppb in 2021, an increase of 15% or 0,4% per annum. During the same time, the atmospheric concentration of CO2 increased from approximately 345 ppm to 415 ppm, a 20% or 0.5% annual increase (Tans, 2021; Dlugokencky, 2021).

The IEA found that in June 2021, 73% of the world’s countries had announced net-zero pledges for CO2, but only 28% had policies to reduce CH4, with no zero-CH4 pledge. Governmental discussions on the ‘social cost of carbon’ (SCC) or any CO2 tax have led to significantly distorted policies as they entirely ignore natural CO2 uptake and other GHG emissions. GHG emission measurements should at least include CO2eq emissions from all sources, including but not limited to CH4 emissions from livestock agriculture, energy production, or natural causes (see Table I).

GHG emissions from changes in land use, nitrous oxides (N2O), or fluorinated gases (F-gases), which together may add another 5-10% of total anthropogenic GHGs (Olivier and Peters, 2020), are not discussed in this paper.

The omission to include at least CH4 emissions may be driven primarily by the simplicity of measuring or easily calculating human-energy CO2 emissions. The chemistry and physics are simple for CO2, assuming a certain efficiency of a given power plant as well as measuring the tons of fossil fuel combusted. From this data, one can relatively easily estimate CO2 emissions from such a plant. For instance, 1 t of carbon equals 3,67 t of CO2, purely based on the molecular mass. Thus, the complete combustion of coal with a 50% carbon content (as-received basis) will simply result in 50% of 3,67 t, or 1,8 t, of CO2 per ton of coal burnt.

These CO2 emissions are detailed by country, by application, by fuel source, by income, even by activity type, and in many other ways in quite an elaborate process at a global scale. For example, recently, credit cards have become available that can manage and limit your spending based on the ‘CO2 footprint’ of your purchases’.

One misguided result of limiting efforts on measured-humanenergy CO2 emissions is the widely accepted government policy of switching from coal to NG (in most cases to LNG) to slow or VOLUME 122

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Climate impacts of fossil fuels in today’s electricity systems limit global warming. Consequently, many international banks, institutions, and conglomerates, e.g., the Tesla gas-fired power plant in its new Berlin Gigafactory (Randall, 2020) or the EU’s plan to label natural gas as green (Abnett and Jessop, 2022), are withdrawing from coal but are actively supporting NG as a ‘bridge fuel’. Another recent example, the world’s leading coalto-liquids company Sasol in South Africa was applauded for its announcement in August 2021 to develop NG. Global LNG export terminal capacity is also expected to more than double from 440 Mt in 2020 to over 1,000 Mt in 2030.

Most scientific studies, government reports, or any carbon tax for that matter, consider solely CO2 emissions from combustion when recommending NG or LNG as a bridge fuel towards a netzero future (see Figure 4). This is indisputably wrong and leads to distorted policies, as will be explained in the following pages. A wider selection of additional studies, reports, and press releases on CH4 emissions is given in the Appendix.

Reported CO2 and CH4 emissions

For the purpose of this paper, the authors rely on reported CO2 and CH4 emissions from the IEA and Our World in Data, which in turn rely on the Global Carbon Project, the Carbon Dioxide Information Analysis Centre (CDIAC), and Saunois et al. (2020).

The IEA notes, however, that estimates of CH4 emissions are subject to a high degree of uncertainty. Top-down estimates used by the IEA are lower than bottom-up estimates, and estimates have been increasing steadily. The IEA’s reported CH4 emissions data is summarized in Table I. In addition, the authors rely on the IPCC’s confirmation that about half of the CO2 emitted to the atmosphere disappears annually into global ecological and physical sinks, i.e., taken up by plants through photosynthesis, fertilization, and by oceans. In fact, IPCC AR6 (IPCC, 2021) states with high confidence that 54% of CO2 is removed and 46% remains airborne in the atmosphere.

During the period 2010-2019, 31% of the emitted CO2 was taken up by ecosystems (e.g., plants) and 23% by the oceans.

Several other studies (e.g. Knorr, 2009) also confirm that less than half of CO2 emissions remain airborne. Logically, only

airborne CO2 can contribute to the greenhouse effect. This ‘natural CO2 uptake’ is highly relevant when comparing CO2 to other GHG emissions that do not contribute to plant growth.

Thus, governments and institutions should switch from ‘measured-human-energy CO2 emissions’ toward the more correct metric that the authors call ‘changes in airborne CO2eq’. Figure 2 and the following section illustrate this process.

Documented CO2 and CH4 emissions are detailed in Table I and Figure 3. Because IPCC’s 20-year global warming potential (GWP20) for CH4 is 84 times higher than that for CO2, the calculations are straightforward and as follows (Ritchie and Roser, 2020a, 2020b): ➤ Global measured-human-energy CO2 emissions totalled 36 Gt in 2019 (95% from fossil fuels), of which 40% or 14 Gt stem from coal, 34% from oil, and 21% from NG. Approximately 54% of all CO2 emissions disappear annually, reducing 36 Gt of emission in 2019 to about 17 Gt of airborne CO2 increase that year (6,6 Gt from coal). ➤ Documented anthropogenic CH4 emissions total approximately 360 Mt at GWP20, resulting in 30 Gt CO2eq – 12 Gt from agriculture, 3,4 Gt from NG, 3,5 Gt from underground coal mining, 3 Gt from oil, and 8 Gt from other sources. An additional 230 Mt of CH4 result in 19,5 Gt CO2eq from natural sources. ➤ As a result, global changes in airborne CO2eq from anthropogenic sources of CO2 and CH4 at GWP20 are approximately 47 Gt (17 Gt from CO2 and 30 Gt from CH4). Fossil fuels accounted for approximately 60% of total anthropogenic CO2eq. Coal itself contributed just over 20%, oil just below 20% and NG 15%. For comparison, at GWP100 fossil fuels accounted for approximately 75% of total anthropogenic CO2eq. ➤ Total measured-human-energy airborne CO2 accounted for approximately 35% of the total changes in airborne anthropogenic CO2eq from both CH4 and CO2 at GWP20.

When considering CH4’s 100-year global warming potential GWP100 this increases to 65%.

Source: Schernikau, based on IPCC (2021), AR6 – Physical Science Basis, p. 89, and IEA methane tracker (IEA, 2021)

Figure 2—Less than half of CO2 emissions remain airborne – Illustrative comparison to anthropogenic CH4 at GWP20 136

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Climate impacts of fossil fuels in today’s electricity systems Table I

Summary of global CO2, CH4, and CO2eq emissions at GWP20 and GWP100

Note: all numbers were updated in December 2021 based on the latest IEA-reported CH4 data Previous data was based on end of 2020 IEA figures. The IEA adjustments slightly favoured gas over coal. All figures are based on 2019 except for IEA CH4 figures, which are best estimates per annum Source: IPCC, IEA, author’s calculations

Notes: (1) @ GWP20 means 20-year GWP defined by the IPCC; (2) anthropogenic 30 Gt at GWP20 become 10 Gt at GWP100.

Source: Schernikau, 2021 based on (left) Our World in Data based on Global Carbon Project: CO2 emissions by fuel (https://ourworldindata.org/emissions-by-fuel) and CO2 emissions (https://ourworldindata.org/CO2-emissions?country=https://ourworldindata.org/CO2-emissions?country=); (right) IEA methane tracker database analysis (https://www.iea.org/articles/ methane-tracker-database)

Figure 3—2019 Global changes in anthropogenic airborne CO2eq

Air pollution from coal versus gas

Coal production, transportation, and combustion adversely affect the environment in many ways, including but not limited to particulate emissions and air pollutant emissions. However, air pollution from combustion of coal is reduced to a bare minimum The Journal of the Southern African Institute of Mining and Metallurgy

in modern coal-fired power plants utilizing clean coal technology where the newest filter and waste product management systems are employed. For example, the United Arab Emirates commissioned one of the world’s most advanced and newest 2,4 GW ultra-supercritical (USC) coal-fired power plants in 2021 VOLUME 122

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Climate impacts of fossil fuels in today’s electricity systems (Power Technology Energy News and Market Analysis, 2021). Such modern coal-fired power plants emit virtually only water vapour and CO2. Much investment and effort are needed to upgrade all global power plants with the newest technologies to increase their efficiency and further reduce particulate matter, SOx, and NOx emissions.

The 10-15% concentrated CO2 stream from coal plants could, in principle and if required, be captured and utilized, or stored (Tramošljika et al., 2021). Carbon capture utilization and storage (CCUS) at fossil power plants would be more effective than any direct air capture (DAC) from the 0,04% CO2 content of the atmosphere or reducing CO2 through other means. Qvist et al.

(2020) present a case study for Poland.

Coal mine methane (CMM) leakages are associated primarily with underground coal mining. This is the CH4 which is released during exploitation of coal seams and is vented to the atmosphere.

Coalbed methane (CBM) can be extracted for commercial utilization from unmined coal seams. This extraction is usually done either by drilling vertically into the seam (SIS methane drainage) or drilling directionally along the seam (UIS methane drainage) (Zheng et al., 2019). CBM projects that utilize the CH4 are supported under the Kyoto Protocol and investors can claim CO2 credits, either using them to offset their own emissions or by selling them on the open market.

Underground coal mines, once production is halted and the mine is abandoned, may continue to leak CH4. This leakage is referred to as abandoned mine methane (AMM) (Kholod et al., 2020). CH4 migrates into the abandoned mine from connected coal deposits. If not prevented by an adequate sealing, the liberated gas will migrate to the surface and escape to the atmosphere through natural and mining-related fractures and other conduits. On average, the CH4 content per ton of coal mined increases with increasing depth.

It is important to note that surface coal mines rarely emit CH4. Even if the coal seams had collected, emitted, or stored CH4 during burial, when the pressure is reduced or at shallower depths, the gas escapes. As a result, CH4 from coal seams closer to the surface was vented over the past millions of years. Hence, irrespective of coal quality, coal seams closer to surface and mined by opencast methods will not normally emit CH4 (Lloyd and Cook, 2005; Cook, 2013).

Much effort and investment are required to further reduce the negative environmental impact of coal production, processing, transportation, and combustion; although the technology mostly exists today. Generally, the combustion of coal causes more air pollution than NG, due to the emission of particulate matter, SOx, and NOx. Coal ash may be useful for certain industrial processes such as cement manufacturing, but is often of significant environmental liability. Also, the production and transportation of coal usually effects the environment more than NG does (other than CH4). Any unutilized leaked or ‘fugitive’ CH4 from coal mining can be considered a component of air pollution and contributes to the GWP of CH4.

Pollution from natural gas other than CH4 also includes SOx and NOx. Unconventional gas production generally affects the environment more than conventional gas, e.g., from chemicals used during fracking and/or drilling. Furthermore, it is understood that CH4 does not only have climate impacts but also affects air quality because it is an ingredient in the formation of groundlevel ozone, a dangerous air pollutant that can cause respiratory and cardiovascular diseases. Other toxic gases and hazardous air pollutants are also emitted along with CH4; these can lead 138

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to long-term health effects or even death (CATF, 2021). CO2, on the other hand, does not affect human health unless average ambient concentrations continuously reach levels 10 to 100 times higher than current atmospheric concentrations of about 420 ppm, at which may then cause drowsiness, tiredness, and headaches. Humans exhale about 40 000 ppm (4%) of CO2. CO2 concentrations in buildings vary from 400 to 2 000 ppm (author’s own measurements).

Comparison of coal and natural gas GHG emissions Surface-mined coal versus natural gas With the introduction of a new metric, anthropogenic ‘changes in airborne CO2eq’ using IPCC’s GWP metric and IEA data, it is necessary to summarize and re-assess discussions on energy policy. Both coal and NG have benefits and issues. When choosing coal versus NG, all economic and environmental benefits and problems should be compared appropriately based on available data. NG is an important and favourable energy resource and is much needed for a stable and affordable energy system, as are coal, nuclear, hydro, and other resources.

Applying changes in airborne CO2eq, the authors calculated the following GHG impacts, with and without CH4 emissions, using the IPCC’s GWP20 and IEA primary energy data (see Tables I and II): ➤ Pure combustion with zero energy-related fugitive CH4 emissions: 0,09 Mt CO2 per TWh for NG versus 0,15 Mt CO2 per TWh for coal. NG emits about 40% less CO2 than coal.

This is the typical global ratio. ➤ With fugitive energy-related CH4 emissions: 0,18 Mt CO2eq per TWh for NG versus 0,23 Mt CO2eq per TWh for coal.

NG emits about 20% less CO2eq than coal. This is the actual global ratio based on known data. ➤ NG versus surface-mined coal: 0,18 Mt CO2eq per TWh for NG versus 0,15 Mt CO2eq per TWh for surface-mined coal. NG emits about 15% more CO2eq than surface-mined coal.

Based on the calculations above and the fact that surface coal mines rarely emit CH4, it can be demonstrated that at GWP20, on a global average, surface-mined coal emits about 15% less CO2eq than NG. This figure increases as the use of shale gas and LNG expands. For completeness, at a 100-year horizon, at GWP100 surface-mined coal still emits about 25% more CO2eq than average NG when comparing primary energy supply. However, for LNG the situation does not look as favourable even at GWP100 where coal is on par with NG at approximately 5% additional CH4 loss prior to LNG combustion (see Table I and calculations in Ritchie and Roser, 2020a). It must be noted that if one were to use electricity production, rather than primary energy, as the basis for comparison, the ratios further improve in favour of coal since gas causes higher CH4 emissions for less electricity produced.

However, it is difficult to detail the non-electricity energy contributions of gas and coal, and therefore the authors chose to use PE only, which is also more conservative and relevant to this analysis.

In addition to CH4, CO2 is also emitted during NG (and especially LNG) production and processing. These CO2 emissions are currently not considered in the life-cycle analysis of the gas chain; neither are they included in the reported global CO2 emission data nor in the analysis herein. The Institute for Energy Economics and Financial Analysis (IEEFA, 2020) presented a detailed analysis of the Australian LNG industry and associated CO2 emissions with the subtitle ‘Increased Emissions The Journal of the Southern African Institute of Mining and Metallurgy

Climate impacts of fossil fuels in today’s electricity systems Table II

Comparison of coal and NG global measured CO2eq emissions

Note: PES = Primary Energy Supply Source: Schernikau Illustration and calculations based on IEA, Our World in Data, IPCC (Ritchie and Roser, 2020a, 2020b)

[from LNG] Have Offset Any Gains From Renewables' Rise in Electricity Generation’. The IEFFA reports that new Australian LNG projects emit on average 0,7 t CO2 per ton LNG during production only. For example, according to the report, the Darwin LNG Barossa field may even emit 2,4 to 3,6 t CO2 per ton LNG, thus ‘the total project could become a CO2 venting factory with an LNG by-product’. Another documented example is the CO2 emissions of the Western Australian Gorgon LNG project. The Conservation Council of Western Australia (2019) documented in 2019 that Western Australian LNG operations emit on average approximately 0,6t CO2 per ton LNG produced. The CO2 streams stem from the raw feed gas extracted from the oceans that is vented to the atmosphere. This stream of CO2 was planned to be captured but this was not fully implemented by 2021(Milne, 2019; Morton, 2021) (see also Figure 4).

We reiterate, the analysed CO2eq figures in this paper do not consider any CO2 emissions associated with LNG production, processing, or transportation and thus underestimate the total CO2eq emissions of natural gas.

Total global natural gas versus coal It is important to keep in mind that fugitive CH4 must include all CH4 sources and not only those from energy. Sources of CH4 must include agriculture, wetlands, waste disposal, thawing permafrost, and others as documented by the IEA (see Figure 3). Natural CH4 emissions amount to about 40%, and agriculture to about 25%, of total annual fugitive CH4 (see Table I). The GWP then dictates the global warming potential of CH4 from all sources other than from energy. These non-energy CH4 emissions dominate CO2eq emissions from all coal. The competition is not even a close race, and little can be done to alter this ratio since wetlands and agricultural sources are inviolate in the global ecology and in the sustenance of human populations. Ocko et al. (2021) conclude that CH4 accounts for ‘at least a quarter of today’s gross warming’ and also detail estimates of natural CH4 sinks. The IEA (2021) stated The Journal of the Southern African Institute of Mining and Metallurgy

in 2021 that ‘Methane has contributed around 30% of the global rise in temperature today’.

In addition, using the GWP20 metric it can now be demonstrated that marginally, NG emits more CO2eq than the average coal as soon as more than about 2%1 of CH4 is lost prior to gas combustion compared to coal along the value chain of production, processing, and transportation of pipeline natural gas (PNG) or LNG. For comparison, using GWP100 coal reaches climate parity with NG at about 5% additional CH4 loss prior combustion4. This figure is principally confirmed by Ladage et al. (2021), who estimate a break-even CH4 leakage rate of 2,7% for the USA and 4,1% for Germany. However, Ladage et al. do not consider the natural CO2 uptake as confirmed by the IPCC, and thus overestimate the break-even CH4 leakage rate by about 50%.

The exact relationship of natural gas or LNG to coal depends on the origin of the gas, the distance and efficiency of the gas logistics, as well as the technology used for refining, liquefaction, transportation, and regasification (Figure 4 and Appendix). It is relatively certain and the authors’ understanding, though unproven due to lack of data, that the global LNG supply chain on average results in CH4 leakages greater than 5% (see Appendix).

Costs and benefits of carbon dioxide and methane The value chain for production, transport, and use of oil, PNG, and LNG is illustrated in Figure 4. Current CO2 taxation and related policies primarily target the combustion stage (right side)

The numbers vary and are assumed as follows: 375 g CO2/kWh at partial load combined cycle PNG (48% efficiency), 825 g CO2/kWh partial load coal (41% efficiency); Δ450 g CO2/kWh becomes 207 g after 54% natural CO2 uptake; 26,400 kJ/ kg CH4 and 1,47 m3/kg CH4 translate to 200,5 m3/MWh; 1% methane loss translates to 2 m3/MWh or 1,4g CH4 per kWh or 115 g CO2eq/kWh @GWP20; therefore at 1,8% methane leakage coal and gas are on par; @GWP100, coal and gas are on par at 5,4% methane leakage.

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Climate impacts of fossil fuels in today’s electricity systems

Source: Schernikau (2021), own Illustration

Figure 4—Illustration of GHG emissions from production, transportation/processing and combustions of gas

only. Based on annual global CH4 emissions of approximately 590 Mt and total anthropogenic emissions of about 360 Mt, anthropogenic CO2eq emissions from CH4 are about four times higher than CO2 emissions from coal alone, at GWP20 (see Table I). LNG and shale gas production, processing, and/or transportation increase fugitive CH4 emissions per unit of energy produced and make the situation even less favourable for gas.

This conclusion is a surprise and one that was not anticipated by the authors. When we factored in the GWP20 value from the IPCC AR5 and AR6 reports, the GWP for CH4 – from all sources – dominates the equation. CH4, until combusted, is a far more potent greenhouse gas (for caluclations see footnote4 on page 139) than CO2, and it lacks the beneficial role of CO2 in photosynthesis which compensates at least part of other possible effects of CO2 on the climate.

As discussed earlier, both CO2 and CH4 are GHGs that contribute to global warming. For this reason, both the costs and the benefits of CO2 and CH4 should be considered in any cost and benefit analysis of each hydrocarbon (coal, natural gas, and oil) compared to renewable sources of power. Readers are invited to consider the general practice in Western Europe to couple intermittent wind or solar with natural gas (see new gas firedpower plants in Germany or the EU’s plan to put gas on the ‘green’ list (Abnett and Jessop, 2022; Independent, 2021).

Disregarding any benefits from CO2, Nobel Prize winner Professor William Nordhaus (2018) calculated a GDP cost of 2,8% in 2100 from global warming, assuming his optimal scenario with 4,1°C warming. For comparison, the UN announced (UNFCC, 2021) that their current climate trajectory is in line with about 2,7°C warming from pre-industrial times (1850-1900) until the end of century, of which 1,1°C to 1,2°C has already occurred.

Based on his work, Nordhaus earned the Nobel Prize for ‘Climate Economics’ in 2018. He estimates the GDP cost of global warming under different scenarios using his DICE model (the merits of using the GDP metric will not be elaborated in this paper). Suffice to say that Nordhaus makes the following important statements confirming that reduced use of fossil fuels will lead to reduced growth and therefore wealth: ➤ ‘… the revised DICE model shows more rapid growth of output in the baseline or “no-[climate]-policy” path compared to earlier DICE versions and most other models.

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‘ … the international target for climate change with a limit of 2°C appears to be infeasible with reasonably accessible technologies even with very ambitious abatement strategies. This is so because of the inertia of the climate system, of rapid projected economic growth in the near term, and of revisions in several elements of the model. ➤ ‘A target of 2,5°C is technically feasible but would require extreme and virtually universal global policy measures in the near future.’

Professor Nordhaus’ optimal DICE scenario corresponds to a peak in CO2 emissions (not airborne CO2eq) around 2050 at approximately 40 Gt and a global warming of 4,1°C using the implausible IPCC RCP8,5 climate scenario. For comparison, it is predicted that covid-19 will cause up to a 10% drop in GDP by 2050; in line with the 10% drop in GDP after 3 years during the Great Depression (IEEJ , 2020). Lomborg (2020) and Kahn et al.

(2021) principally confirm Nordhaus’ calculations.

The potential effects of climate changes may be considerable and should not be discounted. However, the benefits of increased CO2 concentrations in the atmosphere because of their undisputed fertilization effects on plants are confirmed by numerous peer-reviewed studies, a selection of which is listed

by Idso (2021). In addition to adjusting for CO2 fertilization, the modelled economic impact of global warming – to be fair and complete – should be compared to the costs and impacts of prematurely forcing energy systems away from conventional fuels prior to having a truly sustainable energy solution.

Carbon, oxygen, hydrogen, and nitrogen are the four most important elements for life. CO2 is a key building block for all life on Earth as all plant life depends on CO2, water, and solar radiation for photosynthesis. In fact, atmospheric CO2 is the sole source of carbon contained in plants, and therefore in human and animal bodies.

The CO2 concentration in the atmosphere increased by a little more than 0,01% or 100 ppm (by over 30%) in the past 100 years, apparently due mainly to combustion of carbon-rich oil, coal, and NG. The release of this additional CO2 has contributed to warming and to noticeable greening of our planet. NASA and the World Economic Forum confirm that elevated CO2, slight warming, and precipitation increases contribute to the overall net greening of the Earth over the past decades (NASA Earth Observatory. 2019, Dunne, 2019). The increase in the Leaf Area Index (LIA) and ➤

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Climate impacts of fossil fuels in today’s electricity systems Vegetation Index due to CO2 fertilization has been confirmed by several researchers, e.g., Zaichun et al. (2016) and Wang et al.

(2020). This greening is crucial in providing sufficient food to the growing population and its benefits have not been properly calculated. Zhu et al. (2016) point out that vegetation increased by about 14% from 1981 to 2014, about 70% of which is due to CO2 fertilization. The growth equals an area twice as large as the USA. Deforestation counteracts CO2 fertilization and needs to be further reduced; however, at a global scale, more biomass is added than is lost by deforestation.

Atmospheric CH4, in contrast, has no benefit to the environment but only costs. CH4 needs to be captured to have value for energy generation. CH4 that ends up in the atmosphere, according to the IPCC, is a far more potent GHG causing global warming (see footnote4, p.139). Additionally, it is understood that CH4 does not only have climate impacts but also affects air quality because it is an ingredient in the formation of ground-level ozone, a dangerous air pollutant.

In summary, higher CO2 emissions such as those from fossil fuel combustion are more beneficial for plant life relative to lower CO2 emissions (the emphasis is on plant life). Higher CH4 emissions have no benefit to the environment, are a potential health hazard, and have a larger GHG effect. These undisputed facts also need to be considered in energy policy.

Conclusions This paper has sought to raise awareness that oil, coal, and natural gas account for approximately 80% of global PE and 95% of measured-human-energy CO2 emissions, but a smaller portion of total anthropogenic airborne CO2eq (about 55% at GWP20 to 70% at GWP100). The benefits of these energy sources as well as their related costs are not all incorporated in current energy policy discussions. Anthropogenic CO2 emissions account only for about 35% of total anthropogenic airborne CO2eq at GWP20 (60% at GWP100) after accounting for CH4.

It is evident that global GHG policies at least need to include documented changes in anthropogenic measured airborne CO2eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies. Nowadays many governments, most global funds, international banks, conglomerates, and insurers have publicly announced they will abandon coal but will continue to support LNG and PNG projects, which are required to power human life.

The authors recommend that energy policies be reviewed taking all available information into account. Policies that focus only on combustion but leave out the true and full life-cycle emissions of all types from mining, processing, transportation, and utilization will lead to environmental surprises and potentially very large economic costs. The authors strongly support the fact that energy from all sources, including natural gas, oil, coal, nuclear, and renewables, is required to eradicate poverty.

Increased wealth translates to increased resilience against illness and natural disasters.

Applying the IPCC’s 20-year global warming potential GWP20, measured CH4 emissions significantly outstrip global anthropogenic airborne energy-related CO2, or coal’s total CO2eq emissions (see Tables I and II). Moreover, the dominant CH4 emissions are not from human energy-related sources, which contribute only about 20%, but they arise from natural wetlands, agriculture, and waste handling. Elimination of those CH4 sources would mean eliminating biologically productive areas, food resources, and the waste products of billions of people (Figure 3).

The Journal of the Southern African Institute of Mining and Metallurgy

Using UN-funded IPCC and IEA data sources, it can be calculated that at GWP20, on a global average, surface-mined coal emits about 15% less CO2eq than natural gas. This figure increases as the use of shale gas and LNG expands. At a 100-year horizon (GWP100) surface-mined coal still emits 25% more CO2eq than average NG. However, for LNG the situation does not look as favourable, even at GWP100 where coal is on a par with NG at 5% additional CH4 loss prior to combustion. Additional CO2 releases from NG or LNG production are not measured nor accounted for.

These observations make the case that investors should not favour NG over coal for electricity production but should support all energy systems in a manner that avoids an energy crisis, including variable renewable energy systems where they make sense. If CO2 emissions need to be reduced, one of the most effective ways would be to install CCUS technology (Tramošljika et al., 2021) However, the benefits of CO2 through fertilization need to be fairly considered and evaluated.

The authors suggest that future research and development should concentrate on reducing net emissions of fossil fuel power plants and providing cost-effective and reliable conventional new power generation projects. This should be dedicated to ultra-supercritical (USC) power plants for increased efficiency, whether fossil fuel-fired or biomass-fired. The introduction of USC technologies is already growing in China and other countries and should be introduced – possibly at no cost to accelerate their deployment – to all developing countries, such as Bangladesh, Pakistan, Vietnam, Indonesia, South Africa, Kenya, Nigeria, and countries in South America. China, instead of forswearing support for coal-fired plants outside its borders, could then justify support for construction of efficient USC plants worldwide. Such advanced high-efficiency and low-emission (HELE) plants could replace less efficient existing power plants or even provide new facilities, all of which would support increasing economic activity, reduce emissions, and improve the quality of life for the growing population.

USC technology would have an immediate positive effect on nature (Tramošljika et al., 2021) at a lower cost than installing grid-scale intermittent renewable energy systems with the required backup or storage. Fossil fuels, including natural gas and coal, require investment, not divestment, in the interest of our planet’s health and to eradicate (energy) poverty.

Acknowledgement The authors declare that they did not receive any financial or other support from any company or organization for this paper.

Key abbreviations CCUS Carbon capture utilization and storage CO2eq CO2 equivalents incorporating IPCC’s Global Warming Potential of CH4 GHG Greenhouse gas GWP Global Warming Potential (specified over 20 years or 100 years) IEA International Energy Agency IPCC Intergovernmental Panel on Climate Change LNG Liquified natural gas NG Natural gas PE Primary energy USC Ultra-supercritical VOLUME 122

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Climate impacts of fossil fuels in today’s electricity systems Appendix International studies and press releases on methane A number of international studies and press releases, mostly funded by environmental organizations and even the gas industry itself, confirm that for ‘the climate’, LNG and shale gas are at best on a par with coal or will emit higher relevant GHG emissions.

In the past few years there has been a shift to more focus on methane, as illustrated by IEAs Methane Tracker and various reports (Ritchie and Roser, 2020a, 2020b; IEA, 2021; Saunois et al.

2020; October 2021).

The studies do not typically consider the points made above, namely (1) the higher GWP20 for methane compared with coal or (2) the natural CO2 uptake of about 50%. The authors do not disagree with these studies on the comparisons made for gas versus coal, but their calculation shows the situation to be less favourable for natural gas than suggested, due to the fugitive methane from other identified sources. This conclusion is equally valid for GWP100 and even for fugitive methane arising from methane produced for combustion alone.

The following references provide support for the authors’ views, namely, that natural gas in various forms is likely to generate higher emissions than coal. ➤ Bloomberg (2021), Sarah Smith, programme director for super pollutants at Clean Air Task Force, ‘World leaders are starting to recognize that curbing methane is the only clear strategy to cut warming over the next two decades’. ➤ CNN (2021), after the release of the IPPC AR6 Report: ‘… for the first time, the UN climate change report emphasized the need to control a more insidious culprit: methane, an invisible, odor-less gas with more than 80 times more warming power in the near-term than carbon dioxide’. ➤ Clean Energy Wire (2021): ‘The advantage of natural gas in terms of climate change is disputed. It not only emits CO₂ when burned, but is mainly composed of methane, making it a powerful greenhouse gas itself’. ➤ IEA World Energy Outlook (2021), p. 41: ‘Methane has contributed around 30% of the global rise in temperature today’. ➤ German Ministry for the Environment, (2020): ‘LNG from shale gas does not contribute to climate goals’.

➤ Washington Post (2020), Chris Mooney, ‘Methane is a hardhitting greenhouse gas. Now scientists say we’ve dramatically underestimated how much we’re emitting’. ➤ Dan Gocher, Director: Australasian Centre for Corporate Responsibility (ACCR, 2020): ‘BHP . . . is still betting heavily on gas — which is proven to have the same, if not worse emissions than coal once fugitive methane emissions are factored in’. ➤ Environmental Council, Australia (2019): ‘… a major international review of LNG infrastructure released in July 2019 found the threat to the climate from LNG is as large or larger than coal’. ➤ EnergyWatchGroup, Germany (2019 (see Figure 5): ‘ … the switch from coal and oil to natural gas in power plants and heating systems even increases the greenhouse effect of energy consumption by around 40%’. ➤ Bill Gates, Stanford (Stanford Energy, 2018): ‘ … forcing function is sooner on natural gas, converting coal to natural gas for the next 50 years and then shutting it down, that’s a net addition [to emissions]. ➤ Total Gas study (CIRAIG, 2016): ‘With 95% confidence interval, US shale gas may emit more greenhouse gases than Colombian hard coal systems’.

Additional resources in English and German are referenced below.

Howarth (2019) points out that ‘While methane emissions are often referred to as “leaks”, some of the emissions include purposeful venting, including the release of gas during the flowback period immediately following hydraulic fracturing, the rapid release of gas from blowdowns during emergencies but also for routine maintenance on pipelines and compressor stations, and the steadier but more subtle release of gas from storage tanks and compressor stations to safely maintain pressures’.

Scientific studies and reports (last accessed 25 October 2021) Alvarez, R.A. et al. 2018. Assessment of methane emissions from the U.S. oil and gas supply chain. https://www.science.org/doi/10.1126/science.aar7204 CCWA. 2019. About LNG in Australia: “Gas is not ‘cleaner’ than coal”. p. 43. https://apo.org.au/sites/default/files/resource-files/2019-11/apo-nid266691.pdf

Source: Energy Watch Group Germany, 2019 (https://energywatchgroup.org/wp-content/uploads/EWG_Natural_Gas_Study_September_2019.pdf)

Figure 5—EnergyWatch - Switch from coal to gas increase GHGs 142

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Climate impacts of fossil fuels in today’s electricity systems Cornwall, W. 2018. Natural gas could warm the planet as much as coal […].

Science. https://www.science.org/news/2018/06/natural-gas-could-warmplanet-much-coal-short-term Etminan, M., Myhre, G., Highwood, E.J., and Shine, K.P. 2016. Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing. https://doi.org/10.1002/2016GL071930 Energy Watch Group. 2019. Natural gas makes no contribution to climate protection. http://www.energywatchgroup.org/wpcontent/uploads/EWG_ Natural_Gas_Study_September_2019.pdf Global Energy Monitor. 2019/2020. The new gas boom by coal swarm. http://www.europeangashub.com/wp-content/uploads/2019/08/ NewGasBoomEmbargo.pdf [accessed 25 October 2021]; Tracking LNG infrastructure. https://globalenergymonitor.org/wp-content/uploads/2020/07/ GasBubble_2020_r3.pdf Hmiel, B., Petrenko, V.V., Dyonisius, M.N., Buizert, C., Smith, A.M., Place, P.F., Harth, C., Beaudette, R., Hua, Q., Yang, B., Vimont, I., Michel, S.E., Severinghaus, J.P., Etheridge, D., Bromley, T., Schmitt, J., Faïn, X., Weiss, R.F., and Dlugokencky, E. 2020. Preindustrial CH4 indicates greater anthropogenic fossil CH4 emissions. Nature. https://www.nature.com/articles/ s41586-020-1991-8 Howarth, R.W. 2014. LCA – oil and gas with higher greenhouse gas emissions than coal. https://onlinelibrary.wiley.com/doi/10.1002/ese3.35 Howarth, R.W. 2019. Ideas and perspectives: Is shale gas a major driver of recent increase in global atmospheric methane? https://bg.copernicus.org/ articles/16/3033/2019/

CNN. 2021. Scientists say this invisible gas could seal our fate on climate change. https://edition.cnn.com/2021/08/11/us/methane-climate-change/index.html Economist. 2021. Those who worry about CO2 should worry about CH4, too. https://www.economist.com/leaders/2021/04/03/governments-should-settargets-to-reduce-methane-emissions and https://www.economist.com/ leaders/2021/03/31/governments-should-set-targets-to-reduce-methaneemissions Financial Times. 2020. BHP targets 30% cut in carbon emissions by 2030. https:// www.ft.com/content/9cffdac1-aba9-407d-a236-7560ab2e0554?

Gas Strategies Group. 2021. Gas matters today news on methane pledge from EU and the US. www.gasstrategies.com/information-services/gas-matters-today/ gas-matters-today-news-roundup-wc-13-september-2021 Guardian. 2019. Fracking causing rise in methane emissions, study finds. https:// www.theguardian.com/environment/2019/aug/14/fracking-causing-rise-inmethane-emissions-study-finds?

New York Times. 2019. It’s a vast, invisible climate menace. We made it visible. https://www.nytimes.com/interactive/2019/12/12/climate/texas-methane-superemitters.html? searchResultPosition=1 Stanford Energy. 2018. Cheap renewables won’t stop global warming, says Bill Gates. https://energy.stanford.edu/news/cheap-renewables-won-t-stop-globalwarming-says-bill-gates Washington Post. 2020. Methane is a hard-hitting greenhouse gas. Now scientists say we’ve dramatically underestimated how much we’re emitting. https:// www.washingtonpost.com/climate-environment/2020/02/19/were-vastlyundercounting-methane-emissions-fossil-fuels-scientists-say/

IEA. 2020. Comprehensive IEA study on methane gas flaring. https://www.iea.org/ commentaries/putting-gas-flaring-in-the-spotlight

West Australian. 2019. Future emissions shock for WA’s major LNG players. https://thewest.com.au/business/energy/future-emissions-shock-for-wasmajor-lng-players-ng-b881143493z?

IEEFA 2020, Report on the growth of Australia's LNG industry and the decline in greenhouse gas emission standards. https://ieefa.org/ieefa-brief-the-australianlng-industrys-growth-and-the-decline-in-greenhouse-gas-emissionsstandards/

Selected press/sources in German (last accessed 25 October 2021)

Ladage, S., Blumenberg, M., Franke, D., Bahr, A., Lutz, R., and Schmidt, S. 2021.

On the climate benefit of a coal-to-gas shift. https://www.nature.com/articles/ s41598-021-90839-7 Lechtenböhmer, S. and Dienst, C. 2009. Future development of the upstream greenhouse gas emissions from natural gas industry, focusing on Russian gas fields and export pipelines. https://doi.org/10.1080/19438151003774463 McKinsey. 2021. Curbing methane emissions: How five industries can counter a major climate threat. https://www.mckinsey.com/business-functions/ sustainability/our-insights/curbing-methane-emissions-how-five-industriescan-counter-a-major-climate-threat?cid=other-eml-dre-mip-mck&hlkid=a774e 1a8976d4a078406df70a8406fd5&hctky =11701123&hdpid=6bc90219-24ea-4ea9bad2-299f795342c3 Poyry Study. 2016 Gas ist klimaschädlicher als Kohle. https://www.energatemessenger.ch/news/165477/studie-gas-ist-klimaschaedlicher-als-kohle?

Schiermeier. 2020. Methane levels soar to record high. Nature. https://www. nature.com/articles/d41586-020-02116-8 CIRAIG. 2016: p. 5. https://www.ciraig.org/pdf/CIRAIG_LCA_gas_vs_coal_final_ report_version.pdf

Selected additional press releases in English (last accessed 25 October 2021) Bloomberg. 2020. Gas exports have dirty secret [...]. https://www.bloomberg.com/ news/articles/2020-01-23/gas-exports-have-dirty-secret-a-carbon-footprintrivaling-coal-s?

Bloomberg. 2021. Methane plumes spotted near Central Asia pipes to China, Russia on methane plumes in turkmenistan. https://www.bloomberg.com/ news/articles/2021-09-16/methane-plumes-spotted-near-turkmenistan-pipesto-china-russia Bloomberg. 2021. The cheap and easy climate fix that can cool the planet fast. https://www.bloomberg.com/graphics/2021-methane-impact-on-climate/ The Journal of the Southern African Institute of Mining and Metallurgy

Deutsche Umwelthilfe. 2021. Rechtsgutachten über LNG. https://www.duh.de/ presse/pressemitteilungen/pressemitteilung/rechtsgutachten-der-deutschenumwelthilfe-belegt-klimaschaedliches-lng-terminal-bei-stade-ist-nicht/ Deutsche Welle. 2019. Methan: Der böse Zwillingsbruder von CO2. http://www. dw.com/de/methan-der-böse-zwillingsbruder-von-CO2/a-49208882?

DIW. 2021. Interview mit Prof. Claudia Kemfert in der TAZ. https://www.diw.de/ de/diw_01.c.810797.de/nachrichten/pipeline_setzt_geld_in_den_sand.html?

Energate|messenger. 2016. Gas ist klimaschädlicher als Kohle. https://www. energate-messenger.ch/news/165477/studie-gas-ist-klimaschaedlicher-alskohle?

Spiegel. 2020. Methanlecks aus Gasnetzen: Kleine Löcher, großer Klimaschaden. https://www.spiegel.de/wissenschaft/mensch/klimawandel-durchmethanlecks-kleine-loecher-grosser-schaden-a-e381a23d-ddf6-4c40-b420bf91d334f610?

Wallstreet-Online. 2020. Flüssigerdgas ähnlich klimaschädlich wie Kohle. https://www.wallstreet-online.de/nachricht/13019432-umweltministeriumfluessigerdgas-klimaschaedlich-kohle

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HYBRID CONFERENCE

Climate impacts of fossil fuels in today’s electricity systems

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A B O U T T H E CO N F E R E N C E The Southern African Institute of Mining and Metallurgy (SAIMM), in collaboration with the University of the Witwatersrand through the DSI/NRF SARChI chair in Hydrometallurgy and Sustainable Development, and Mintek, will be hosting a hybrid conference on mineimpacted water including acid mine drainage (AMD) in October 2022. With a theme of “impacting the circular economy, closing the water loop”, the conference will run over a period of two days. This second SAIMM AMD themed conference will provide an excellent opportunity for industry, researchers and other global stakeholders to share their knowledge, new processes and technologies that can be used to advance the implementation of sustainable solutions to the challenges associated with mine-impacted water. The conference, with its extensive program, will also offer notable keynote speakers and, the popular student session, all with the purpose of giving a unique view into novel solutions and industry progression on the issue of mine-impacted water.

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CO N F E R E N C E TO P I C S Presentations related, but not limited to the following mine-impacted water related topics are invited: • Sustainable and innovative mine-impacted water treatment technologies • Waste to resource: remediation, reuse and resource recovery • Prediction and mitigation • Case studies • Mine closure practices • Legislation and policy drivers for sustainability • Novel and emerging strategies for sustainable management of mine-impacted water • Circular economy concepts, closing the water loop

FOR FURTHER INFORMATION, CONTACT: Camielah Jardine E-mail: camielah@saimm.co.za MARCH 2022 VOLUME 122 11 834-1273/7 The Journal of the Southern African Institute of Mining and Metallurgy Head of Conferencing Tel: +27 SAIMM Web: www.saimm.co.za

Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks

by M.Z. Emad1, Y. Majeed1, and G. Rehman2 Affiliation: 1 Department

of Mining Engineering, University of Engineering and Technology, Lahore, Pakistan.

2 Department

of Mining Engineering, Karakoram International University, Gilgit, Pakistan.

Correspondence to: M.Z. Emad

Email:

zaka@uet.edu.pk

Dates:

Received: 7 Oct. 2021 Revised: 8 Feb. 2022 Accepted: 9 Feb. 2022 Published: March 2022

How to cite:

Emad, M.Z., Majeed, Y., and Rehman, G. 2022 Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 147-154 DOI ID: http://dx.doi.org/10.17159/24119717/1780/2022 ORCID: M.Z. Emad https://orcid.org/0000-00018537-8026 Y. Majeed https://orcid.org/0000-00015479-8466 G. Rehman https://orcid.org/0000-00025744-3529

Synopsis Massive deposits of rock salt are mined in the Salt Range area of Pakistan. The main export products of rock salt include salt lamps, blocks, and tiles, while local consumption includes the chemical industry and domestic use. The profitable production of salt for value addition depends on the quality, size, and shape of the block. Salt processing for value addition is easier when very few cracks are present in the blocks.

The current salt mining practice involves drilling and blasting, which introduces undesired fractures in the material. This paper focuses on the extraction of rock salt blocks by applying conventional cuboidshaped block mining methods used in quarries. The techniques include wedges and feathers, expansion chemicals, and blasting with low-yield explosives. Experimental work involved both laboratory-scale and in-situ field testing. Laboratory experiments assisted with the determination of splitting force, loaddeformation curves, and other rock mechanics parameters. Regression analysis proposes a relationship for the estimation of radial strain from the load in the case of the wedges and feathers method. The splitting force obtained from the laboratory tests was used to confirm the accuracy of the already published empirical relationship. The results of the laboratory as well as in-situ tests showed that the wedges and feathers technique is the most suitable method for mining rock salt blocks of the desired size, shape, while minimizing cracking.

Keywords rock salt block, stope and pillar mining, splitting force, radial strain, Young’s modulus, tensile strength, wedge and feather, expansion chemicals, controlled blasting.

Introduction Rock salt mining is carried out by both underground mining and quarrying operations using conventional drill and blast techniques. Generally, mechanized mining techniques enable the extraction of minerals using mechanical excavators, pumping brines, and evaporation methods. However, the oldest and most popular technique for mining salt is conventional underground mining of massive deposits by the roomand-pillar method. About 40% of the salt is extracted, while the remaining 60% is left for supporting the roof (Hustrulid, 2001).

Pakistan is a rock salt producing country with an annual production of around 2.16 Mt (Department of Mines & Minerals, 2015). It is estimated that only 15% of the salt produced is export quality, while the remainder is of low value due to cracks produced during mining. Himalayan rock salt is a very popular product globally. Many items are in demand, including salt block slabs, blocks, salt lamps, tiles, and material for making medical slabs (Naz and Haleem, 2010; Rashleigh, Smith, and Roberts, 2014).

Salt exports from Pakistan could be increased if the local salt industry produces high-quality products. This requires larger, regular-shaped blocks free from undesirable micro- and macro-flaws.

The industry can produce larger flawless blocks of salt by adopting unconventional mining techniques.

In dimension stone quarry operations, rock splitting techniques like wedges and feathers, expansion chemicals, and controlled blasting are very common. These rock splitting methods can be adapted for underground salt deposits. The current research work includes the application of simple rock-splitting techniques for mining regular-shaped cuboid blocks of salt. The aim is to carry out a comparative analysis of the abovementioned three techniques based on block shape, size, and crack density.

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks Salt mining in Pakistan Vast reserves of rock salt are located in the Salt Range Formation (Precambrian) of the northern Punjab province (Baloch et al., 2012; Shah, 1980), and salt mining and associated businesses are key elements in the local economy. The Salt Range Formation extends from Tilla Jogian in the east through Warchha to Kalabagh in the west, and is located on an active frontal thrust zone of the Himalayan mountain range. Interpretation of seismic data reveals that the offset of the basement resulted in the formation of the central Salt Range, now known as the Potwar Plateau (Leathers, 1988; Wynne, 1878). Wynne (1878) and Gee (1948) called the Salt Range the ‘Saline Series’ and ‘Punjab Saline Series’. Asrarullah (1967) named the same rock unit the ‘Salt Range Formation. The lithology of this formation includes the Sahwal Marl Member, Bhandar Kas Gypsum Member, and Billianwala Salt Member. Red marl and ferruginous content are indications of the Billianwala Salt Member (650 m thick). This is found along the southern escarpment of the Salt Range where underground salt mining takes place in Khewra, Warchha,, and Kalabagh (Shah 1980). The rock salt reserves occur in large deposits, with the Khewra mine alone containing 82 Mt (Asrarullah, 1967).

Salt Mines Khewra The Salt Mines Khewra are located near Khewra City (32°39'N 73°03'30"E), district Jhelum, Punjab (Batth, 2018). This is the second-largest salt mine in the world and the largest underground mine in Pakistan. The annual production of the mine is about 465 kt and the expected mine life is 350 years (Baloch et al., 2012).

The rock salt deposit at Khewra forms an irregular dome-like lenticular structure. It is a massive deposit comprising many seams having a combined thickness of 150 m. Pakistan Mineral Development Corporation (PMDC) is operating the Khewra mine, which is a multilevel operation (having 17 levels) developed by regular stope and pillar mining methods. Rock salt of excellent purity occurs in different colours including semi-transparent, whitish, pink, reddish, and beef-red. In certain horizons, salt appears in the form of crystalline structures. The current mining technique is the conventional drill and blast method using black powder. Production is mainly for the chemical industry and consumer market, but some large blocks of rock salt are also extracted, which add value in the form of exports. These salt blocks are of irregular shape and low quality due to the presence of cracks from the blasting process. Fine quality crack-free blocks are used in decorative items such as salt lamps and tiles). Typical salt mining practice is depicted in in Figure 1.

Rock splitting techniques Dimension stone mining employs wedges and feathers, expansion chemicals, controlled blasting, laser cutting, jet piercing, chain-

Figure 1—Salt mining practice at Khewra: (a) Mining front, (b) manual auger for drilling holes­ 148

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and wire saws, and other methods for extraction of crack-free blocks. In this study, three simple, non-mechanized and lowcapital methods – wedges and feathers (WF), expansion chemicals (EC), and controlled blasting (CB) – were selected for extracting crack-free, regular shaped salt blocks. The details of the chosen techniques and their application in dimension stone mining are described below:

Wedges and feathers This is one of the most common techniques of obtaining dimension stone, which involves either drilling closely spaced holes or carving a V-shaped groove with a hand tool (chisel and hammer) followed by wedging into the rock. For the wedging action different methods have been practiced, including plugs and feathers, wooden wedges that expand when wet, and for cold climates, filling the groove or holes with water (Kirby et al., 1990; Dougan 2018). The cold temperature expands water during the night, thus inducing a split in the rock (Dunda and Kunjundžić, 1998; Changyou, 2017). According to Kirby et al. (1990), different variations of WF have been practiced since ancient times. The Egyptians used bronze plugs and feathers for mining limestone and sandstone cubes. Smith (1999) noted that many factors control the performance of the WF method, including the number and size of holes, the size of wedge and feathers, and the type of stone. The drill-holes may be coplanar to produce a clean crack.

The WF method works on the principle of transformation of vertical stress into normal or horizontal stress. Hammering of many sets of wedges and feathers in the same orientation produces a tensile splitting stress in a plane. The tensile stress produced must overcome the strength of the rock to create a splitting plane.

Expansion chemicals Non-explosive expansion material (NEEM) is a controlled cracking method for mining good quality blocks of rock (Gholinejad and Arshadnejad, 2012). This method is safe, quiet, and free of vibrations compared to conventional techniques. It involves drilling several holes in a rock block with a fixed length, diameter, and spacing between the holes (centre-to-centre distance). NEEM slurry generates an incremental static load in the holes within 24 hours. Cracks appear between the coplanar holes if the design specifications are correct, and merge to form a clean splitting surface. It is important to adhere to the manufacturer’s recommendations to achieve the desired results. In general, the closer the holes are spaced, the faster the material will crack. The results produced by NEEM are dependent on the diameter of the holes. A smaller hole diameter results in no split plane, while a very large diameter develops a blowout from the collar.

Another important parameter is the reaction time of the chemical, which ranges from 24 hours to 76 hours. A longer time affects production scheduling. The range is a function of many factors such as the type of material, hole diameter and spacing, and the temperature on-site (Hoek and Bieniawski, 1963; Konik et al., 2007; Ahn and Hu, 2015; Yu et al., 2018). According to Gomez and Mura (1984) expansion chemicals can exert a peak expansion stress of up to 11 000 psi (75 842 kN/m2). EC works similarly to WF, creating the splitting surface by the development of tensile stress. The radial force generated within the drill-holes produces high compressive stress perpendicular to the split surface, which generates cracks in the rock matrix. These cracks are not desirable, and care must be taken to minimize their formation.

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks Modified controlled blasting Drilling and blasting is one of the cheapest methods (low initial and operational costs, fast production rate, and site area flexibility). Block extraction is also possible through the blasting of holes with small spacing and using a low-power explosive.

The conventional blasting process creates both desirable and undesirable cracks and fissures in the rocks, while the CB method generates micro-fissures in the desired direction and reduces the development of microcracks in the remaining rock matrix (Rao et al., 1997; Bhandari and Rathore, 2006). The extraction of rock blocks using a CB has been discussed by various researchers.

Olsson and Bergqvist (1996) emphasised the crack-free extraction of dimension stone by decoupling of holes and sympathetic detonation. According to Khoshrou (1996) and Ahmadinejad (2009), the propagation of cracks in the rock mass is generally controlled by the quantity of explosive charge. Detonating cord with lining is another useful technique for mining dimension stone.

The working mechanism of the CB technique for rock splitting is like that of the WF and EC methods. It involves the development of radial stresses in drill-holes due to the instantaneous production of shock waves accompanied by gas pressure. This radial force is a dynamic impact load, which is then converted to tensile stress, creating a split plane. Some of the radial stress creates a compressive stress, which leads to the development of undesirable cracks.

Figure 2—Block diagram showing the adapted methodology

Experimental Majeed et al. (2019) confirmed the quality of rock salt blocks excavated in situ through conventional quarrying techniques.

The physicomechanical laboratory testing programme validated the results of block mining techniques studied. The current study envisaged a comprehensive testing programme including both laboratory-scale and in-situ field experiments to assess the selected techniques from the dimension stone industry (WF, EC, and CB). Laboratory testing on rock salt blocks paved the way for in-situ experimentation. The laboratory compression machine helped with establishing the splitting force required to produce a split plane in a rock salt block using the WF method, and also helped with the generation of rock properties data for validation.

Figure 2 illustrates the entire testing scheme and a summary of the stepwise method.

Figure 3 shows the manufacturing of wedges and feathers for this research. Each set comprises a tapered tool-metal wedge (plugs, 10 inches or 25.4 cm long), and bi-metal shims (feathers, 8 inches or 20.32 cm long). The feathers are wider at the bottom than at the top.

The ambient temperature (10–25°C) of the Khewra salt mine and laboratory conformed to the specifications the SCA-1 chemical. Gunpowder paper cartridges assisted with carrying out CB.

Laboratory-scale experiments Laboratory-scale testing of WF (samples 1 and 2) and EC (samples 3 and 4) methods was carried out on rock salt blocks from the Khewra mine. Rock properties were determined in the laboratory for validation of crack formation. The CB method was not used in the laboratory for obvious reasons. For each method (QF and EC) a single row of 1 inch (2.54 cm) diameter holes with both spacing and depth of 4 inches (10.16 cm) was drilled into the boulders. The results of these experiments are shown in Figures 4 and 5. The The Journal of the Southern African Institute of Mining and Metallurgy

Figure 3—Development of wedges and feathers: (a) Wooden models, (b) cast iron tools (after Majeed et al., 2019)

Figure 4—Results of preliminary laboratory experiments with wedges and feathers at 4 inches (10.16 cm) centre-to-centre hole spacing: (a) sample 1, (b) sample 2

flatter lower part is oriented along with the anticipated orientation of the splitting plane. In the WF method, the plugs were placed and the wedges hammered until the appearance of a crack along the hole. As shown in Figure 4, the technique produced a regular split line between the holes. For the EC experiments, a mixture of expansion chemical (5 kg chemical per 1.5 litres water) was poured into the pre-drilled holes within ten minutes of mixing. The boulders were then cured for a period of 24 hours. An irregular split line was formed between the holes and the boulders were split into three pieces (see Figure 5).

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks rock salt samples as per ISRM suggested methods (ISRM, 1978, 1979). The area of the splitting surface (A) was acquired by considering split plane dimensions at 4, 6, 8, and 10 inches (10.16, 15.24, 20.364, cm), and 25.4 cm) centre-to-centre hole spacing.

Table I outlines the input parameters required for Equation [1] along with the computed splitting force (Fr) for each block size. It is worth noting here that the splitting force of 14.4 kN (at 4 inches or 10.16 cm spacing in Table I), computed by using Equation [1], is quite close to the actual splitting force of 11 kN determined through direct experimentation (Figure 7b).

In-situ experiments In-situ experiments were carried out at Khewra salt mines by adopting the three selected rock splitting techniques according to a pre-defisned programme as explained in Table II. For this purpose, a suitable location in the mine was selected based on the availability of a bench face (two free faces normal to each other). This was required to perform four experiments using each technique for extracting blocks of rock salt. As per plan (Table II), a total of eight holes (diameter 2.54 cm) were drilled vertically to form a square shape. Four horizontal holes were drilled from the bench face to form a square prismatic block. The inter-hole spacing at the upper face was varied at 4 inches (10.16 cm), 6 inches (15.24 cm), 8 inches (20.32 cm), and 10 inches (25.4 cm).

The centre-to-centre hole spacing at the bottom of the block was kept at 4 inches (10.16 cm).

Figure 5—Results of preliminary laboratory experiments with expansion chemical method at 4 inches (10.16 cm) centre-to-centre hole spacing: (a) sample 3, (b) sample s4

Determination of splitting force The rock splitting technique produces radial compressive stress (σr) around the drill-hole and a radial strain (ε). When the drillholes are aligned to form a split plane, a splitting force (Fr) is produced perpendicular to the splitting plane (Figure 6). The radial stress is responsible for generating a crack in the rock block when it exceeds the tensile strength (σt) of the material (i.e., σr≥σt).

In the first phase, a laboratory experiment on a rock salt block was designed to find the actual splitting force and strain by using the WF. For this purpose, three drill-holes of 1 inch (2.54 cm) diameter were drilled into the block at 4 inches (10.16 cm) centre-to-centre spacing up to a depth of 4 inches (10.16 cm).

An electrical resistance strain gauge was fixed at the anticipated split plane approximately midway between two adjacent drillholes (Figure 7a). The prepared block was then loaded through wedges between the platens of a universal testing machine until a split plane appeared. The strain values at prefixed load intervals of 2 kN were recorded using a Vishay digital strain recorder. The test results are presented in Figure 7b, where a linear increasing relationship can be seen between splitting force and strain.

In the second phase, efforts were made to compute the force required to produce a split plane in a rock salt block indirectly, using routine rock mechanics parameters, with the help of the following empirical relationship (Atanackovic and Guran, 2000; Salmi and Hossainzadeh, 2014): Fr=AE ℇ

Figure 6—Diagram showing the application of splitting force required for producing a split plane

[1]

where Fr is the splitting force; A is the area of splitting surface, E is the Young’s modulus, and ε is the strain.

The mechanical rock properties [tensile strength (σt) and Young’s modulus (E) were determined on prepared cylindrical

Figure 7—(a) Rock salt block showing wedges and feathers and electrical strain gauge, (b) test results (force versus strain curve)

Table I

Values of force required for splitting a plane in rock salt blocks Sample no.

Block size / centre-to-centre hole spacing

1 2 3 4 150

4 in (10.16 cm) 6 in (15.24 cm) 8 in (20.32 cm) 10 in (25.4 cm) MARCH 2022

Area (cm2)

Rock mechanics parameters

103.22 E = 2.9 GPa 232.26 st = 1.4 MPa 412.90 me (strain) = 0.48 645.20 VOLUME 122

Splitting force (kN)

14.4 32.3 57.5 89.8

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks In the case of the WF rock splitting technique, four blocks of rock salt (WF4, WF6, WF8, and WF10) were extracted. The numbers 4, 6, 8, and 10 are assigned based on inter-hole spacing as per the experimental plan (Table II). Figure 8 shows the stepwise procedure adopted for block extraction. The results are shown in Figure 9. Some undesirable cracks were observed in the walls of mined-out blocks WF4 and WF6 when the inter-hole spacing was kept at 4 inches (10.16cm) and 6 inches (15.24 cm).

In contrast, blocks WF8 and WF10, extracted with 8 inches (20.32 cm) and 10 inches (25.4 cm) spacing showed promising results.

Field experiments were performed with the EC method according to the pre-defined experimental plan. In general, it was observed (Figure 10) that the EC technique produced more undesirable cracks (especially in blocks EC4 and EC6) compared to the WF method. The best result was obtained in the case of block EC8, extracted at 8 inches (20.32 cm) centre-to-centre hole spacing, while at 10 inches (25.4 cm) hole spacing the salt block (EC10) was not extractable due to the improper formation of the splitting plane. A 10 inch (25.4 cm) hole spacing is thus not practicable in the given experimental conditions.

The CB method was applied by using explosive (gunpowder) paper cartridges 0.87 inches in diameter (2.21 cm), and 4 inches (10.16 cm) in length. The holes, drilled according to the experimental plan (Table II), were bottom-charged using 4-inch (10.16cm) long cartridges and primed with 2.5 ft long safety fuses.

The remaining 8 inches (20.32 cm) of the holes were filled with the drill cuttings as stemming material. To reduce the explosive quantity per blast, the holes were charged alternately (one charged and one uncharged), so that one drill-hole acted as a free face for the other one. This technique produced shattered and irregularshaped salt blocks CB4 and CB6 at inter-hole spacings of 4 inch (10.16 cm) and 6 inches (15.24). Regular shaped blocks (EC8 and EC10) with fewer undesirable cracks were obtained from 8 inch (20.32 cm) and 10 inch (25.4 cm) hole spacings. The results of the

Figure 8—In-situ application of wedges and feathers method: (a) Drilling, (b) installation of tools, (c) extracted block (after Majeed et al., 2019)

Figure 9—Results of block extraction for different centre-to-centre hole spacings with wedges and feathers method. (a) WF4, (b) WF6, (c) WF8, (d) WF10

CB experiments are shown in Figure 11. The results of the field experiments performed with all three techniques are summarized in Table III.

Core quality assessment The rock salt blocks retrieved by in-situ testing (Table III) were

Table II

Experimental plan for in-situ tests Wedges and feathers

Expansion chemical Experiment 1

Controlled blasting

Centre-to-centre hole spacing 4” (10.16 cm) Centre-to-centre hole spacing 4” (10.16 cm) Hole depth 12” (30.48 cm) Hole depth 12” (30.48 cm) Hole diameter 1” (2.54 cm) Hole diameter 1” (2.54 cm) No of holes 12 (8 on top, 4 at bottom No of holes 12 (8 on top, 4 at bottom of bench face) of bench face) Block name EC4 Block name WF4

Centre-to-centre hole spacing 4” (10.16 cm) Hole depth 12” (30.48 cm) Hole diameter 1” (2.5 4cm) Charging 4” (10.16 cm) Stemming 8” (20.32 cm) No of holes 12 (8 on top, 4 at bottom of bench face) Block name CB4

Experiment 2

Centre-to-centre hole spacing 6” (15.24cm) Block name WF6 (Other parameters same as in exp. 1)

Centre-to-centre hole spacing 6” (15.24 cm) Block name EC6 (Other parameters same as in exp. 1)

Centre-to-centre hole spacing 8” (20.32 cm) Block name WF8 (Other parameters same as in exp. 1)

Centre-to-centre hole spacing 8” (20.32 cm) Block name EC8 (Other parameters same as in exp. 1)

Centre-to-centre hole spacing 6” (15.24 cm) Block name CB6 (Other parameters same as in exp. 1)

Experiment 3

Centre-to-centre hole spacing 8” (20.32cm) Block name CB8 (Other parameters same as in exp. 1)

Experiment 4

Centre-to-centre spacing 10” (25.4 cm) Block name WF10 (Other parameters same as in exp. 1)

Centre-to-centre spacing 10” (25.4 cm) Block name EC10 (Other parameters same as in exp. 1)

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks Table IV

Summary of core quality assessment Block no.

Length of core

Core quality (%)

recovered from Near split plane split plane (cm)

Figure 10—Results of block extraction for different centre-to-centre hole spacing with expansion chemical method: (a) EC4, (b) EC6, (c) EC8, (d) EC10 (block not extracted)

WF4 WF6 WF8 WF10 EC4 EC6 EC8 EC10 CB4 CB6 CB8 CB10

13.9 15.5 16.9 18.1 14.2 14.6 15.1 2.0 2.2 3.3 3.9

Centre of block

50.1 68.0 75. 9 78.2 45.2 47.0 63.1 6.7 13.4 45.8 60.5

71.1 75.3 80.0 89.4 62.1 69.7 72.5 7.4 14.1 54.9 64.0

IV. The core quality is very like the rock quality designation or RQD, and is computed by the following relationship: Core quality (%) = Length of core obtained ×100 Total length drilled

[2]

Discussion

Figure 11— Results of block extraction for different centre-to-centre hole spacings with controlled blasting method. (a) CB4 (irregular shaped block), (b) CB6 (irregular shaped block), (c) CB8 (d) CB10

assessed for the development of cracks along the splitting plane.

The assessment involved drilling NX-sized cores and measuring rock quality along the perimeter and from the centre of the blocks.

The cores obtained had both natural fractures and fresh cracks created by the three splitting techniques. The crack formation is represented by the core quality and the results are shown in Table

The laboratory work was conducted to develop an understanding of rock splitting mechanisms and determine the splitting force, load-deformation curve, and rock parameters (Young’s modulus, tensile strength, and strain). The laboratory experiments also helped to determine the diameter, centre-to-centre spacing, and depth of holes. The preliminary laboratory experiments conducted on rock salt boulders with 1 inch (2.54 cm) diameter holes drilled at 4 inch (10.16 cm) centre-tocentre spacing showed that a regular split surface can be produced with both the WF and EC techniques. Laboratory experiments was also performed on rock salt blocks extracted by the WF4 method to determine the peak splitting force and to record the strain during splitting using an electrical resistance strain gauge (Figure 7). The experiment helped with developing a load-deformation curve and the strain along a splitting plane can be determined using the equation proposed in Figure 7b. Finally, the splitting force was also determined (Equation [1]), using simple rock mechanics

Table III

Summary of in-situ test results Experiment no.

Wedges and feathers

Expansion chemical

1 [Centre-to-centre hole spacing 4”]

Prismatic block (WF4) extracted Prismatic block (EC4) extracted with successfully with few undesirable more undesirable radial cracks all around cracks. Clear and smooth splitting plane the holes. This was attributed to reduced was not found. hole spacing.

2 [Centre-to-centre Block (WF6) extracted successfully with Block (EC6) extracted with few unwanted hole spacing 6”] very minor undesirable cracks. A clear cracks (comparatively more than at 4 inche split was formed. or 10.16 cm). This was due to increased

centre-to-centre hole spacing.

3 [Centre-to-centre Block (WF8) extracted successfully Block (EC8) extracted with fewer hole spacing 8”] with no undesirable cracks. A fine split undesirable crack than the previous block surface was obtained. (with 6 inch or 15.24 cm spacing) 4 [Centre-to-centre Square prism block (WF10) extracted Block (EC10) not extractable because hole spacing 10”] smoothly without undesirable cracks of minor hole-to-hole crack formation, due to increased hole spacing. A smooth probably due to greater confinement. and clear break was observed.

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Controlled blasting

Irregular shaped block (CB4) obtained with many undesirable cracks due to shattering. The required size of block was not obtained.

Once again, block (CB6) was extracted with undesirable cracks as well as s irregular shape. The size of the block was fairly close to that planned.

Block (CB8) extracted with fewer undesirable cracks, and moderately regular shape and size.

A relatively larger size block (CB10) was extracted containing fewer undesirable cracks than other blocks extracted with CB. The shape was also improved.

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks parameters like area of splitting plane, Young’s modulus, and strain. It was found that the value of the splitting force calculated from Equation [1] is close to the actual value found in the experiment.

The subsequent in-situ experiments showed that regular prismatic blocks can be produced by the WF technique (Figure 9). The shape and size of blocks and the split surface produced at all four centre-to-centre spacings were of good quality (Table III) with no undesirable cracks. The WF technique was found to be much better than the EC and CB methods. This is due to the controlled static radial load around the wedge and feather tools. The parametric study performed (for centre-to-centre hole spacing) with the WF method showed that blocks extracted with a hole spacing of 8 inches and 10 inches (20.32 cm and 25.4 cm) conform to the desired product. Extraction with WF is also friendlier as it produces no vibrations, dust, gases, or fly-rock.

Moreover, this technique is simple, and labourers can be trained within a couple of hours.

Experiments on the extraction of blocks with expansion chemicals (Figure 10) showed that irregular cracks are produced, leading to an irregular splitting surface and unwanted fractures.

The effect was prominent in blocks with smaller hole spacings (10.16 and 15.24 cm). The expansion chemicals performed much better with greater spacings but the results were not as good as with wedges and feathers. Blocks with a hole spacing of less than 6 inches (15.24 cm) contained undesirable cracks, while a spacing of 8 inches (20.326 cm) produced more regularly shaped and sized blocks. This is because a low splitting force is required to split the blocks with smaller spacing. The extra energy provided by expansion chemicals generates fractures in the blocks. A block with a hole spacing of 10 inches (25.4 cm) could not be extracted since separation from the host rock was incomplete. Many undesired cracks were found around the drill-holes. There are two issues with this technique. Firstly, it takes 24 hours before a full split surface is obtained, and secondly, the technique is sensitive to temperature. In a mining cycle, this technique is too slow compared to WF or CB. This will affect mine scheduling and mine planning.

The results of the modified CB technique (Figure 11) showed that it is an unsatisfactory technique. The blocks obtained were of irregular shape and unsuitable size. The loss of block shape and size was noticeable for blocks produced with hole spacings of 4 and 6 inches (10.16 cm and 15.24 cm). This is because a low splitting force is required to split the blocks along holes drilled with smaller spacing. The energy provided by the explosive is far more than is required for generating the splitting plane. The blocks with hole spacings of 8 and 10 inches (20.32 cm and 25.4 cm) were also irregular and improperly sized with many unwanted cracks. The failure of this technique to produce regular shaped and sized blocks is attributed to uncontrollable blasting parameters including a low-quality initiation system, inappropriate delay detonation, low-quality explosive, the intrinsic properties of rock salt, local geology, and skill of the operator. The technique can be further studied to optimize many factors before adoption to block extraction.

The core quality test results (Table IV) show that the cores drilled near the splitting plane obtained by the WF technique have a quality of 50% to 80%, followed by EC (45% to 64%), and CB techniques (6% to 60%). Core retrieved from the block centre for the WF technique has a higher core quality percentage (70% to 89%) in comparison to the EC (60% to 70%) and CB (50% to 60%) techniques. It is evident from the test results (Table IV) that WF The Journal of the Southern African Institute of Mining and Metallurgy

techniques can produce higher-quality salt blocks, with minimal fractures, than the other two techniques. Furthermore, the design adopted for the wedges and feathers can be improved.

All three techniques are labour-intensive and need skilled operators to produce rock salt blocks without undesirable cracks. A comparative study is required incorporating further block extraction techniques such as laser cutting, jet piercing, and wire saw and chainsaw cutting. Economic analysis of all these techniques is also required, along with performance evaluation. An optimization study to identify the best techniques for underground salt mining is to be investigated. A salt block processor is also required by the mining industry which can cut and polish larger blocks into tiles or slabs.

Recommendations and future work Wedge and feather techniques can be used for salt block extraction in the salt mining industry. The main recommendations are: (1) W edges should be prepared according to the specification of the holes (diameter and length).

(2) T he feathers and wedges should be oriented along the direction of the intended split.

(3) T he expansive cement must be chosen in accordance with the temperature on site.

(4) A high-resolution camera should be used for photography.

A lot of research can be carried out in the future in this field related to economic analysis, experiments with new techniques, optimization of techniques, and the design of new mechanized cutters for flawless salt block extraction. Research can be conducted on developing salt block processors to produce quality products that can be exported around the world.

Conclusions Salt block extraction techniques are very important for the growing ornamental rock salt industry of Pakistan. A good rock salt block extraction technique can help to produce good quality exportable products. We have presented the results of laboratory and in-situ experiments using three techniques from dimension stone mining – wedge and feather (WF), expansion chemicals (EC), and controlled blasting (CB). The parameters for the in-situ experiments were determined through laboratory tests. A loaddeformation curve was developed during experimentation on an actual rock salt block for the WF method. A prediction equation has been proposed for the estimation of deformation for a given value of the applied load. The actual value of the splitting force was found to be close enough to the theoretical value computed using the empirical correlation.

The in-situ experiments showed that the WF method produces regular shaped, and proper sized blocks with minimal undesirable cracks, provided an appropriate drill-hole spacing is used. A hole spacing of 8 inches (20.32 cm) and 10 inches (25.4 cm) produces good quality blocks. The blocks extracted with expansion chemicals were regularly sized and shaped, but contained some unwanted cracks. No block could be extracted with expansion chemicals for the 10-inches (25.4 cm) centre-to-centre spacing.

The CB technique produced irregular-shaped and impropersized blocks with a good number of undesired cracks, owing to the energy provided by the explosive being far more than is required for splitting. Only with a wider drill-hole spacing was a more regular block with fewer unwanted cracks produced.

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Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks The quality of the salt blocks produced was assessed from core quality checks. Even in the worst scenario (cores from near the split plane), the test results showed that the WF technique produced the best quality blocks with a core quality value of 50% to 80%, followed by the EC technique (45% to 64%) and CB (6% to 60%).

The WF technique is promising for producing larger sized rock salt blocks. This technique can be further studied to optimize the drill-hole diameter, depth, and spacing. The production of larger blocks will enable the manufacture of good quality products.

Acknowledgements The authors would like to acknowledge the support and assistance of the management of Salt Mines Khewra (PMDC), especially Engineer Irfan Chaudhry (Project Manager), Engineer Azghar Iqbal Khattak (Assistant Manager), and Engineer. Hafiz Muhammad Saeed (Assistant Manager) for their continued support, guidance, and dedicated help during the in-situ work.

The authors are also thankful to the Department of Mining Engineering, University of Engineering, and Technology, Lahore, for facilitating this project.

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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine, Sweden

by S. Manzoor1, M. Danielsson2, E. Söderström3, H. Schunnesson1, A. Gustafson1, H. Fredriksson3, and D. Johansson1 Affiliation:

Division of Mining and Geotechnical Engineering, Luleå University of Technology, Sweden.

2 Ramböll,

Sweden.

3 AFRY, Sweden.

1

Correspondence to: S. Manzoor

Email:

sohail.manzoor@ltu.se Dates:

Received: 2 Apr. 2021 Revised: 1 Feb. 2022 Accepted: 2 Feb. 2022 Published: March 2022

How to cite:

Manzoor, S., Danielsson, M., Söderström, E., Schunnesson, H., Gustafson, A., Fredriksson, H., and Johansson, D. 2022 Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine, Sweden.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 122, no. 3, pp. 155-166 DOI ID: http://dx.doi.org/10.17159/24119717/1587/2022 ORCID: Sohail Manzoor https://orcid.org/0000-00033791-4431

Synopsis Fragmentation analysis is an essential part of the optimization process in any mining operation. The costs of loading, hauling, and crushing the rock are strongly influenced by the size distribution of the blasted rock. Several direct and indirect methods are used to analyse or predict fragmentation, but none is entirely applicable to fragmentation assessment in sublevel caving mines, mainly because of the limitations imposed by the underground environment and the lack of all the required data to adequately describe the rock mass. Over the past few years, measurement while drilling (MWD) data has emerged as a potential tool to provide more information about the in-situ rock mass. This research investigated if MWD can be used to predict rock fragmentation in sublevel caving. The MWD data obtained from a sublevel caving mine in northern Sweden were used to find the relationship between rock fragmentation and the nature of the rock mass. The loading operation of the mine was filmed for more than 12 months to capture images of loaded load-haul-dump (LHD) buckets. The blasted material in those buckets was classified into four categories based on the median particle size (X50). The results showed a stronger correlation for fine and medium fragmented material with rock type (MWD data) than coarser material.

The paper presents a model for prediction of fragmentation, which concludes that it is possible to use MWD data for fragmentation prediction.

Keywords rock fragmentation, measurement while drilling, quick rating system, partial least squares regression, sublevel caving.

Introduction Rock fragmentation is defined as the size distribution of blasted rock. It is influenced by such factors as blast design, rock strength, and discontinuities already present in the rock mass (Hunter et al., 1990; Latham and Lu, 1999; Azimi et al., 2010). Fragmentation is a key indicator of blast performance and is significantly affected by the drilling and charging of the boreholes. Good fragmentation facilitates the loading and hauling operation as well as minimizes energy consumption in the comminution process (Silva, Amaya, and Basso, 2017). It plays an important role in controlling the costs of any mining operation (Monjezi, Rezaei, and Varjani, 2009; Faramarzi, Mansouri, and Ebrahimi Farsangi, 2013; Zhang et al., 2020). Fragmentation-related costs can be divided into pre-blast costs, i.e., the costs related to drilling, charging, and blasting the rock mass, and post-blast costs, i.e., the costs related with loading, hauling, and crushing the blasted rock. In general, reduced post-blast costs and increased pre-blast costs are the result of finer fragmentation, and the opposite for coarser fragmentation (Mackenzie, 1967 in Morin and Ficarazzo, 2006).

Fragmentation is a very important aspect of sublevel caving (SLC) as it affects the gravity flow of the blasted material, the loading at the drawpoints, the efficiency of load-haul-dump (LHD) operations, the orepass efficiency, and the energy requirements of crushers (Wimmer, 2010; Danielsson et al., 2017).

Wimmer (2010) found that finer fragmentation increased the mobility of the material and resulted in more uniform gravity flow from the blasted ring. Meanwhile, coarser fragmentation, especially oversize fragments, hinders the material flow and may cause hangups in the ring, resulting in reduced ore recovery if the hangups cannot be released. An unsafe working environment is another possible consequence of coarse fragmentation and boulders (Danielsson et al., 2017). An oversize fragment is defined by Singh

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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine and Narendrual (2010) as ‘any fragment produced from primary blasting, which cannot be adequately handled by the standard loading, hauling and crushing equipment used in an operation’.

Fragmentation variation is an inherent characteristic of an SLC operation (Shekhar et al., 2016), depending on the design of the blast ring (Dustan and Power, 2011), the confined nature of blasting (Johansson, 2011), and the specific charge (Hustrulid and Kvapil, 2008). The design of the blast ring is important, as holes are concentrated at the bottom and more widely spread in the upper part of the ring (Dunstan and Power, 2011) (see example in Figure 2). The upward drilling of long holes will also increase the probability of borehole deviation in the upper part of the ring (Ghosh, Schunnesson, and Gustafson, 2017). This design of the blast ring and the probable borehole deviation lead to an uneven burden and specific charge, resulting in an uneven energy distribution along the boreholes. Consequently, variations in fragmentation are observed at different stages of material loading from the blasted ring (Power, 2004; Brunton, Fraser, and Hodgins, 2010; Wimmer, Nordqvist, and Ouchterlony, 2012).

The chargeability of SLC rings is another key factor influencing fragmentation and boulder generation. The actual charged length of a borehole can be less than the planned one because of borehole collapse or other blockages. The actual vs planned charging length of a borehole can be defined as the chargeability (Ghosh, Gustafson, and Schunnesson, 2018). Danielsson et al.

(2017) found that a decrease in chargeability will cause a lower local specific charge and, thus, coarser material. In a study at LKAB’s Malmberget mine, Andersson (2016) found that chargeability, on average, was below 90%. However, individual areas had chargeability rates of approximately 70%, and individual rings in those areas occasionally had chargeability rates as low as 44%. Ghosh, Schunnesson, and Gustafson (2017) also showed that borehole stability is an important consideration when analysing fragmentation, as it is directly linked to the amount of explosives that can be charged into the borehole. If the borehole is blocked at some point by caving, it may not be possible to restore or redrill the borehole, leading to insufficient charging to break the rock mass effectively (Lundin, 2020). Borehole instability is also likely to be worsened by high stress states, production blasting, rockbursts, or mine seismicity (Zhang, 2016).

The assessment of rock fragmentation has some practical limitations. There are several direct and indirect techniques for fragmentation assessment, including sieving, observational methods, and image-based analysis, but they are all limited in their ability to continuously monitor fragmentation, especially in an underground environment (Campbell and Thurley, 2017). Rock fragmentation is often estimated before blasting using different empirical formulae developed by various researchers. Ouchterlony and Sanchidrian (2019) presented a comprehensive review of these formulae. Fragmentation models help to target the required rock size distribution after blasting (Morin and Ficarazzo, 2006), but the uncertainty and even unavailability of correct rock properties causes errors. Another limitation of fragmentation models is their origin, i.e., they are mostly developed for surface mines (Ouchterlony and Sanchidrian, 2019) and lack application in underground environments. For example, they do not incorporate several essential factors relevant to fragmentation in SLC mining, such as the shape of the blast fan, confined nature of blasting, drilling accuracy, chargeability etc.

Application of modern technologies like laser scanning and borehole scanning in the mining industry is enabling the acquisition of more accurate rock mass data. One of these 156

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technologies is measurement while drilling (MWD), a method that monitors the drilling process. It does not require additional equipment like laser scanners or cameras to collect data, and it does not disturb the mining operation. During production drilling, it records various parameters, for example, depth of the hole, penetration rate, percussive pressure, feed pressure, rotation pressure, rotation speed, flushing pressure at specified intervals along the length of the borehole (Schunnesson, 1996; van Eldert et al., 2019). The MWD technique has been used to improve blast design (Leighton, 1982), assess the chargeability of boreholes (Ghosh, Gustafson, and Schunnesson2018; Navarro et al., 2019), estimate rock strength (Rodgers et al., 2018), estimate the blast sill thickness (Vezhapparambu and Ellefmo, 2020), and detect discontinuities in the rock mass (Schunnesson, 1996; Khorzoughi, 2013; Manzoor et al., 2020). MWD provides a fingerprint of the penetrated rock mass and increases the information available on the hidden volume of rock surrounding boreholes (Segui and Higgins, 2002; Khorzoughi, 2013). Ghosh, Zhang, and Nyberg (2015) have shown that MWD data can assist in estimating the borehole stability after a hole has been drilled.

In this paper, the possibility of using MWD data to predict fragmentation in sublevel caving is studied. MWD data and fragmentation data from two different orebodies in LKAB’s Malmberget mine were collected and analysed. Correlation analysis and partial least squares (PLS) regression are used to identify the relationship between MWD-based rock mass characteristics and fragmentation.

Methodology This research comprised a literature review, acquisition of MWD data from production drilling, and filming of the loading operation. Data processing involved MWD data filtering and extraction of relevant images from the filmed data. The data analysis involved the classification of rock mass based on MWD data, classification of fragmentation of the blasted material based on median fragment size, and the correlation of these data types.

Site description LKAB’s Malmberget iron ore mine is located in Gällivare municipality in northern Sweden. The mine consists of around 20 orebodies which spread over a large underground area of 2.5 by 5 km (Lund, 2013). Of these, 13 are currently being mined (Shekhar, 2020). The annual production in 2019 was 16 Mt of ore.

The mining operation is carried out from several main haulage levels located at 600 m, 815 m, 1000 m, and 1250 m. To achieve high productivity, large-scale sublevel caving is the current method of ore extraction. Blasted rock from the drawpoints is hauled by load-haul-dump (LHD) machines to orepasses that transfer the ore from the production level down to the haulage level. The ore is transported to underground crusher stations by trucks, and after primary crushing, the ore is hoisted to the processing plant at the surface. A general layout of the complete operation is shown in Figure 1. In the Malmberget mine, trucks are used instead of a train at stage four.

Data collection The required data was collected from two orebodies of the mine: orebody A and orebody B. The selected drift from orebody A was drift 7870 at 1074 m level, and selected drifts from the orebody B were drifts 4960 and 4990 at 1052 m. In Malmberget mine, drilling is done in a fan-shaped pattern (Figure 2). The shortest The Journal of the Southern African Institute of Mining and Metallurgy

Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine Data processing

Figure 1—Layout of sublevel caving operation at LKAB mines (LKAB, 2020)

The data collected from drill monitoring and film data was processed prior to analysis. Drill monitoring or MWD data often contains data values that are out of range of what can be considered as normal drilling behaviour. An example of this is very high or negative values, e.g. a negative penetration rate that indicates an impossible backward movement of the drill string.

Furthermore, the drilling process in itself may generate data that is not related to rock mass variations but rather to the drill or control system, such as data recorded during collaring or when a new rod is added to the drill string. These examples suggest that initial filtering of data is essential for the final outcome of the analysis. Therefore, a new filtering method was developed to potentially improve the quality of data. The developed filtering method was compared with a previously known filtering method (Ghosh, Gustafson, and Schunnesson 2018) to find the one best representing the characteristics of the rock. A brief description of both methods is given below.

MWD data filtering (method A)

Figure 2—Schematic layout of drilling pattern in SLC

holes are less than 20 m long, and the longest are close to 50 m.

The number of boreholes is mostly eight per ring, but there can be nine or ten per ring especially near the footwall. The mine site uses a fixed blasting configuration with a borehole diameter of 115 mm and a ring-to-ring distance (burden) of 3.5 m. MWD data from 17 rings with a total of 141 boreholes, including a complete film record of all LHD buckets loaded from those rings, was used for this study.

Drill monitoring data was collected from Simba WL6C drill rigs used in the Malmberget mine. The recorded data included time (YYYY-MM-DD hh:mm:ss), depth (m), rotation pressure (bar), penetration rate (m/min), feed pressure (bar), and percussive pressure (water pressure measured in bar). The sampling interval along the borehole was set to 3 cm.

To monitor fragmentation, cameras were installed in the selected drifts to record each LHD bucket. Cameras were configured to record a short video whenever there was movement in the recording area. Filming underground in a production environment is always challenging. Commonly dust tends to reduce the quality of the recordings. To ensure better quality videos, cameras were assisted with good lighting. Another challenge during the recordings was that the headlights of the LHD machines sometimes distorted the frame pixels. The recordings took place during two time periods. During the first period, data was collected from orebody A; during the second period, from orebody B. The collected data cover more than 12 months.

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This method of MWD data filtering is adopted from Ghosh, Gustafson, and Schunnesson (2018) and is based on frequency analysis and practical experience. The recorded samples are filtered using predefined intervals for each parameter. Outside these threshold limits the drilling is assumed unrealistic or faulty.

The predefined intervals used in this study are given in Table I. Thus, all samples having any of the MWD parameters outside the corresponding filter limit were removed from the data-set.

The lower limit of percussive pressure in Table I was adjusted from 5 bar, the limit used by Ghosh, Gustafson, and Schunnesson (2018) to 20 bar based on the data-set for the mining areas used in this study.

MWD data filtering (method B) The second filtering method (B) is based on the time difference between the consecutive samples of MWD data. For normal drilling, with a logging interval of 3 cm, a new sample is recorded approximately every 2 to 3 seconds. Longer time intervals between samples will indicate irregularities in the drilling process such as rod changes or other types of stoppages. After such stoppages, the applied forces will only gradually regain their normal values and it will take some time before drilling is stable again. This means that several data-points surrounding stoppages are not reliable and should be removed from the data-set.

In Figure 3, the borehole depth vs the time between the samples is presented for a particular borehole. In this case, the drilling process stops for 50-60 seconds every time a new rod is added to the drill string (at every 2.1 m, which is the length of each rod).

Table I

P re-defined intervals for MWD data filtering (Ghosh, Gustafson, and Schunnesson, 2018) Recorded parameters

Selected intervals as filter limits

Penetration rate (m/min) Percussive pressure (bar) Feed pressure (bar) Rotation pressure (bar)

≥ 0.1 and ≤ 4 ≥ 20 and ≤ 200 ≥ 35 and ≤ 100 ≥ 25 and ≤ 125

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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine

Figure 3—Time difference for MWD samples along a borehole

Table II

MWD parameters before applying any data filtering Sample Time Depth (m)

1 2 3 4 5 6

00:36:17 00:36:17 00:37:14 00:37:21 00:37:25 00:37:30

Penetration rate (m/min)

Percussive pressure (bar)

Feed pressure (bar)

Rotation pressure (bar)

0.70 0.64 0.00 0.27 0.41 0.41

163.11 165.68 70.03 116.57 114.86 116.57

64.52 64.95 55.86 60.19 60.19 58.02

53.32 57.19 59.34 57.62 53.75 52.89

4.18 4.19 4.22 4.25 4.28 4.31

Table III

MWD parameters after applying the developed filter method based on time series Sample Time Depth (m)

1 2 3 4 5 6

00:36:17 00:36:17 00:37:14 00:37:21 00:37:25 00:37:30

Penetration rate (m/min)

Percussive pressure (bar)

Feed pressure (bar)

Rotation pressure (bar)

0.70 0.64 0.59 0.53 0.47 0.41

163.11 153.81 144.50 135.19 125.88 116.57

64.52 63.22 61.92 60.62 59.32 58.02

53.32 53.23 53.15 53.06 52.98 52.89

4.18 4.21 4.23 4.26 4.28 4.31

Table II shows the raw MWD data when a new rod is added.

The rod addition occurs between samples 2 and 3 and has a time length of 57 seconds. In the table it can be seen that the percussive pressure is reduced after the rod addition to protect the drilling system. This will affect the penetration rate. Therefore, it is important to remove not only the data sample during rod addition, where penetration rate is zero, but also surroundings values which are influenced by the stoppage.

In this newly developed filtering method, the threshold time between two consecutive samples was set to 10 seconds to exclude both rod changes and other stoppages but include all normal drilling. For all identified stoppages the samples closest to the high time-step were assumed to be outliers and were removed.

To reconstruct a complete MWD log, the removed samples were replaced by interpolated values from samples before and after the stop, assuming similar rock characteristics before and after the stoppage. Practically, the removed sample parameters are replaced by linearly interpolated data based on two samples 158

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before and three samples after the removed samples. In Table III, an example of the data after filtering is shown.

After applying the time-based filtering method on the data-set, the threshold filter limits in Table I were applied to further refine the MWD data.

Rock mass classification based on MWD After filtering the MWD data, the quality of the rock mass surrounding the boreholes was characterized using principle component analysis (PCA). As input to the PCA analysis, not only the recorded and filtered MWD parameters were used, but also the variability of penetration rate and rotation pressure, and a fracturing parameter which is calculated using the following equation developed by Schunnesson (1996):

The Journal of the Southern African Institute of Mining and Metallurgy

Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine where PRV is penetration rate variability and RPV is rotation pressure variability, while σ shows the variance of the corresponding parameter. A detailed description of the PCA calculations can be found in Ghosh, Schunnesson, and Gustafson, (2018).

Based on the PCA analysis the rock mass is classified into five categories, ‘Solid’, ‘Slightly fractured’, ‘Highly fractured’, ‘Minor cavities’, and ‘Major cavities’ (Ghosh, Schunnesson, and Gustafson, 2018). A similar rock mass classification based on MWD data was also used by Navarro et al. (2019) to assess chargeability in sublevel caving. Finally, the percentage of each category was calculated for every included ring.

Processing film data To monitor the fragmentation, HD surveillance cameras were utilized to collect videos of every passing bucket/loading sequence through built-in motion detection applications. The film data from the cameras was processed before the analysis to convert the raw video data into a usable form. Since the cameras were sensitive to motion, any movement in the filming area was recorded.

Movements were caused by LHDs, personnel cars, drifters, water sprinklers, dozers etc., or by the oscillating ventilation duct during blasting activities. A MATLAB code was developed to extract the relevant images (frames) from the videos. From 500 to 1200 frames were extracted from each video depending on the length of the videos, yielding too many images. Most of the frames did not contain images of buckets with the blasted material.

Instead, they showed different machine parts from when the machine was entering or leaving the filming area or no machines at all. Few of the extracted frames from each video (about 5-10 frames) contained LHD buckets filled with material. Some frames showed partial buckets as the videos were recorded during LHD motion. Only frames with full LHD buckets were forwarded to fragmentation analysis; all the rest were discarded. Figure 4 shows examples of frames with relevant and irrelevant data.

Quick rating system (QRS) A total of 5908 images of LHD buckets filled with blasted rock were selected for fragmentation assessment. These types of images can be analysed using commercially available software, e.g., Split-Desktop® (Kemeny, 1994), WipFrag™ (Maerz, Palangio, and Franklin, 1996), GoldSize (Kleine and Cameron, 1996), FragScan (Schleifer and Tessier, 1996), TUCIPS (Havermann and Vogt, 1996), CIAS® (Downs and Kettunen, 1996), PowerSieve (Chung and Noy, 1996), IPACS (Dahlhielm, 1996), Fragalyst (Raina et al., 2002) etc. Image analysis using these software packages is normally time-consuming; for example, analysing a single image using Split-Desktop® can take two to three hours depending on the quality of the image (Petropoulos, 2015). Therefore, the analysis using commercial software was considered impractical,

Figure 4—Frames with irrelevant (A, B, C, D, E, F and G) and relevant data (H, I) (Manzoor et al., 2022)

or even impossible considering the large number of images. The study used an observational method called quick rating system (QRS) as reported by Petropoulos (2015), Wimmer et al. (2015), Danielsson, Johansson, and Schunnesson (2019), and Danielsson et al. (2017) to assess the median fragment size, X50, of the material in the LHD buckets. In the QRS method, the actual images of fragmented rock are manually compared to reference fragmentation images (Wimmer et al., 2015). It is similar to the ‘Compaphoto’ method (Cunningham, 1996), but is here modified to estimate fragmentation in LHD buckets. Since QRS is an observational method, it can be significantly influenced by the observer’s experience and bias and therefore carries a risk of low accuracy (Babaeian et al., 2019). However, similar and consistent results can be achieved as for Split-Desktop® if QRS classification is carried out carefully (Wimmer et al., 2015).

In this study, the fragmentation was categorized into four classes based on X50. Class 1 referred to fine fragmentation, X50 < 50 mm; class 2 was medium fragmentation, X50 = 50-400 mm; class 3 was coarse fragmentation, X50 = 400-1000 mm; class 4 was oversize fragmentation, X50 > 1000 mm. Malmberget mine defines oversize fragments as rock blocks bigger than 1 x 1 x 1 m (Gustafson et al., 2016; Danielsson et al., 2017). An example of the fragmentation classes is shown in Figure 5.

Correlation analysis This study used correlation analysis to examine the relationship between rock mass quality determined from MWD data and the fragmentation estimated from QRS. Correlation analysis is a statistical approach used to assess the association between two variables e.g., independent and response variables, where the correlation coefficient ‘R’ quantifies the strength of the relationship (Franzese and Luliano, 2019). Values range from −1 to

Figure 5—Frames showing four classes of fragmentation based on X50 The Journal of the Southern African Institute of Mining and Metallurgy

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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine +1; in this rating system, –1 shows a perfect negative correlation, +1 a perfect positive correlation between the pair of variables, and 0 indicates a complete independence and absence of any correlation (Franzese and Luliano, 2019). The intermediate values from 0 to ±1 represent a partial correlation of variables; the correlation can be significant or weak (Franzese and Luliano, 2019). In practical applications visible correlations can have a value as small as ±0.4 (Kleinbaum et al., 1998).

In this study, multivariate regression analysis was used to model the relationship between rock mass types and fragmentation categories. Multivariate regression has the ability to handle multiple variables and consider all the associations between variables simultaneously (GeiB and Einax, 1996). Some of the most commonly used multivariate methods are PCA, discriminant analysis (DA), multiple regression analysis, factor analysis, logistic regression, PLS regression, cluster analysis, log-linear models, and multivariate analysis of variance. This study used PLS because of its minimal demands on measurement scales and sample size, as well as its ability to suggest where relationships might or might not exist. PLS helps to build models predicting more than one dependent variable (Lorber, Wangen, and Kowalsk, 1987). PLS regression was introduced by Wold in 1966; it generalizes and combines features from PCA and multiple regression (Colombani et al., 2012). It is particularly useful when it is needed to predict a set of dependent variables from a large set of independent variables (Colombani et al., 2012). PLS does not assume that the predictors are fixed, unlike multiple regression; this means the predictors can be measured with error, making PLS more robust to measurement uncertainty (Cramer, 1993). A detailed description of the strengths and weaknesses of the PLS method is given by Cramer (1993).

percentage of solid rock mass increases, and decreases for all other rock mass types. Similarly, medium sized rock fragments decrease when solid rock mass increases and increase for all other rock mass types.

Correlation tests – linear or monotonic relationship To further investigate the relationship between rock mass and fragmentation, Pearson and Spearman correlation coefficients were calculated and analysed. Initially, the Pearson correlation coefficients (R), p-values, and coefficients of determination (R2) were calculated (shown in Table V). The null hypothesis in this study states there is no relationship between the variables under observation, while the alternative hypothesis states there is a relationship. A significance level of 0.05 is used to reject the null hypothesis, i.e., a p-value less than 0.05 (typically ≤ 0.05) demonstrates strong evidence against the null hypothesis, as there is a probability lower than 5% that the null hypothesis is correct (and the results are random). R2 shows the amount of variability captured by the model and represents the goodness of fit for the model. Dogruoz, Rostami, and Keles (2017) reported R2 values as low as 0.40 in rock engineering applications.

The p-value for fine and medium fragmentation is <0.05 (with one exception) which means that the null hypothesis can be rejected and that there could be a correlation between the MWD readings and the fine and medium fragmented rock. For coarse and oversize material, the p-value suggests a statistically non-significant correlation. The values of R, p-value, and R2 for fine and medium categories indicate a better correlation between fragmentation and rock type than for coarse and oversize categories.

A Pearson correlation coefficient measures the extent to which two variables tend to change together, i.e., linearly. If the relationship is not strictly linear, the Spearman correlation coefficient can be used (Hauke and Kossowski, 2011). The Spearman correlation evaluates the monotonic relationship between two continuous or ordinal variables. In a monotonic relationship, the variables tend to change together, but not necessarily at a constant rate. Table VI lists a comparison of Pearson and Spearman correlation coefficients. It indicates a higher correlation for Spearman than for the Pearson correlation coefficient. This suggests a monotonic relationship between the variables under observation. More importantly, both coefficients suggest the same relationship, i.e., fine and medium categories have better correlation than coarse and oversize fragmentation categories.

Results and discussion Correlation tests – filtering methods To evaluate any quality differences between filtering methods A and B, the correlation coefficients for the two methods were compared (see Table IV).

Since the correlation coefficients generally are higher for filtering method B, this method is selected for the following analysis.

Correlation tests – rock mass type vs fragmentation To initially study the relationship between rock mass classes (from MWD) and fragmentation (from QRS), scatter plots with linear regression lines are presented for each category (Figure 6).

Each data-point in the figure represents one ring. In most cases a clear visible correlation can be seen, but the scatter is higher for coarse and oversize fragmentation than for fine and medium fragmentation. The amount of fine material increases when the

Partial least-squares regression The rock mass categories extracted from MWD analysis are not independent variables but relates to each other, so if some

Table IV

Comparison of correlation coefficients for the two filtering methods Variables Method A

Solid Slightly fractured Highly fractured Cavities Major cavities 160

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0.444 -0.197 -0.586 -0.573 -0.508

Fine Method B

0.531 -0.396 -0.658 -0.574 -0.516

Method A

-0.549 0.362 0.668 0.617 0.499

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Medium Method B

-0.622 0.542 0.714 0.615 0.501

Coarse Method A Method B

-0.080 -0.180 0.228 0.279 0.314

-0.158 -0.018 0.317 0.263 0.325

Oversize Method A Method B

0.228 -0.378 -0.201 -0.089 0.071

0.178 -0.326 -0.121 -0.038 0.097

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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine

Figure 6—Scatter plots and linear regression lines corresponding to percentages of different fragmentation classes from QRS (x-axis) and rock mass classes from MWD (y-axis)

category is bigger, the other one is reduced. The parameters from the fragmentation analysis have a similar relationship. That means that multicollinearity exists between the explanatory and the response variables. Therefore, PLS regression was used since it has the ability to handle multiple variables and consider all the associations between variables simultaneously as well as deal with multicollinearity. The PLS components are linear combinations of the explanatory (MWD) variables that maximize their covariance with response (QRS) variables.

Figure 7 illustrates the quality indices of the PLS regression model for the first two model components. The figure shows the The Journal of the Southern African Institute of Mining and Metallurgy

Q2 cumulative index, which represents the global goodness of fit and predictive quality of the model. R²Y cumulative and R²X cumulative measure the cumulative fraction of the variation of the Y (QRS) and X (MWD) variables, respectively. The cumulative Q2 has a relatively low value, suggesting the quality of fit is weak. The R²X for comp. 1, however, shows a very high value (88.2%) that indicates that the variance in the explanatory variables (MWD) is well captured by the first component and the second component increases the explained variance to 97.5%.

Figure 8 shows the variable importance projection (VIP) for each independent variable for the first component. Values above VOLUME 122

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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine Table V

Summary of correlation test using Pearson correlation method Variables R

Solid Slightly fractured Highly fractured Cavities Major cavities

0.531 -0.396 -0.658 -0.574 -0.516

Fine p-value R2 R

0.028 0.116 0.004 0.016 0.034

0.28 0.16 0.44 0.32 0.27

Medium p-value R2 R

-0.622 0.542 0.714 0.615 0.501

0.008 0.025 0.001 0.008 0.040

0.38 0.29 0.50 0.38 0.25

-0.158 -0.018 0.317 0.263 0.325

Coarse p-value R2 R

0.545 0.946 0.214 0.308 0.203

0.01 0.03 0.05 0.08 0.10

0.178 -0.326 -0.121 -0.038 0.097

Oversize p-value

R2

0.495 0.202 0.644 0.886 0.711

0.03 0.11 0.01 0.002 0.01

Table VI

Comparison of correlation coefficients using Pearson and Spearman correlation methods Variables Pearson

Solid Slightly fractured Highly fractured Minor cavities Major cavities

0.531 -0.396 -0.658 -0.574 -0.516

Fine Spearman

0.689 -0.463 -0.718 -0.699 -0.652

Medium Pearson Spearman

-0.622 0.542 0.714 0.615 0.501

-0.738 0.632 0.703 0.730 0.627

Pearson

-0.158 -0.018 0.317 0.263 0.325

Coarse Spearman

-0.301 0.056 0.365 0.346 0.321

Oversize Pearson Spearman

0.178 -0.326 -0.121 -0.038 0.097

0.272 -0.400 -0.245 -0.260 -0.238

Figure 8—VIPs (first component with 95% confidence interval) Figure 7—PLS regression model quality for first and second components

or close to unity are considered important and therefore those variables cannot be excluded from the model. Values significantly less than unity are less important and the corresponding variables can be excluded from the model. It can be seen in the figure that all variables are above or relatively close to unity and can therefore be considered as important for the model.

In order to predict fragmentation, four regression models were made in PLS. The model parameters are presented in Table VII together with the R2 values for the respective models. R2 values for the models of fine and medium fragmentation suggest a better model fit compared to coarse and oversize fragmentation, which supports the results from the Pearson and Spearman correlation tests. That concludes that fine and medium rock fragmentation can be better predicted than coarse and oversize fragmentation.

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The four regression models defined in Table VII are visualized in Figure 9, where the comparison of actual versus predicted fragmentation values for different categories is shown.

Figure 9 shows a more visible correlation for fine and medium fragmentation than for coarse and oversize fragmentation.

This agrees with the correlation results, that solid rock tends to produce more fine fragmentation. In solid rock and rock with low fracturing the charging and blasting procedures face fewer challenges and uncertainties. Hence, the corresponding fragmentation will be better predicted for such rock mass types.

This agrees with Akbari et al. (2018), who showed a positive correlation between discontinuities and fragmentation size, which means that an increase in fractures or discontinuities spacing, increases fragmentation size.

This study shows that it is possible to predict fragmentation in an SLC mine using MWD data, which can therefore be a very The Journal of the Southern African Institute of Mining and Metallurgy

Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine Table VII

Model parameters and R2 values for different predictive models Variables

Fine Medium Coarse Oversize

Intercept

Solid

Slightly fractured

Highly fractured

Minor cavities

Major cavities

R2

25.250 66.669 5.927 2.378

0.157 - 0.255 0.049 0.044

0.279 0.465 - 0.449 - 0.247

- 3.100 2.080 0.759 0.181

- 1.822 1.120 0.506 0.142

- 2.203 0.757 0.960 0.384

0.36 0.42 0.21 0.23

Figure 9—Comparison of actual and predicted fragmentation based on model parameters given in Table VII

useful tool for mine productivity improvement. The model may be further improved using chargeability data, which is known to have a major impact on the blasting result.

time series was, in the correlation analysis, found to better reject unrealistic drilling behaviour and therefore better represent the true characteristics of the rock mass.

Conclusions

Acknowledgments

Drilling is an integral part of sublevel caving operations, and it is done before the rock mass is charged and blasted. This means that MWD data is available for interpretation purposes well before charging and blasting take place. The correlation test results presented in this paper shows that MWD data can be used to predict fragmentation in an SLC mine and can therefore be a very useful tool for fragmentation control and in the material handling processes.

The study showed that a solid rock mass tends to produce more fine fragmentation. This may be explained by better and more optimal charging and blasting conditions in solid rock.

In a disturbed rock mass, however, the analysis shows that less fines can be expected. In this case, poor rock conditions that may cause charging and blasting problems can be expected to result in coarsely fragmented material.

Compared to traditional MWD filtration based on fixed threshold limits, the newly developed filtering method based on The Journal of the Southern African Institute of Mining and Metallurgy

The authors acknowledge LKAB and the staff and management of Malmberget mine for their valuable input and support during field studies. Vinnova, the Swedish Energy Agency and Formas are acknowledged for financing this project through the SIP-STRIM programme. Finally, the authors would like to acknowledge the support from the Centre for Advanced Mining and Metallurgy (CAMM2), Sweden and the illuMINEation project funded by the European Union’s Horizon 2020 research and innovation programme under the grant agreement no. 869379.

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Dunstan, G. and Power, G. 2011. Sublevel caving. SME Mining Engineering Handbook. 3rd edn. Darlin, P. (ed.). Society for Mining, Metallurgy and Exploration, Littleton, CO. pp. 1417-1437.

Faramarzi, F., Mansouri, H., and Ebrahimi Farsangi, M.A. 2013. A rock engineering systems based model to predict rock fragmentation by blasting.

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Ghosh, R., Gustafson, A., and Schunnesson, H. 2018. Development of a geological model for chargeability assessment of borehole using drill monitoring technique. International Journal of Rock Mechanics and Mining Sciences, vol. 109. pp. 9-18.

Ghosh, R., Schunnesson, H., and Gustafson, A. 2017. Monitoring of drill system behavior for water-powered in-the-hole (ITH) drilling. Minerals, vol. 7, no. 121. https://doi.org/10.3390/min7070121 Ghosh, R., Zhang, Z., and Nyberg, U. 2015. Borehole instability in Malmberget underground mine. International Journal of Rock Mechanics and Rock Engineering, vol. 48. pp. 1731-1736.

Gustafson, A., Jonsson, K., Johansson, D., and Schunnesson, H. 2016. From face to surface - A fragmentation study. MassMin 2016. Proceedings of the Seventh International Conference & Exhibition on Mass Mining, Sydney, Australia, 9-11 May 2016. Australasian Institue of Mining and Metallurgy, Melbourne. pp 555-562.

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Havermann, T. and Vogt, W. 1996. TUCIPS - A system for the estimation of fragmentation after production blasts. Measurement of Blast Fragmentation: Proceedings of the Fragblast-5 Workshop on Measurement of Blast Fragmentation, Montreal, Quebec, Canada, 23-24 August 1996. Franklin, J.A. and Katsabanis, P.D. (eds). Balkema, Rotterdam. pp. 59-65.

Hunter, G.C., McDermott, C., Miles, N.J., Singh, A., and Scoble, M.J. 1990. A review of image analysis techniques for measuring blast fragmentation. Mining Science and Technology, vol. 11. pp. 19-36.

Hustrulid, W. and Kvapil, R. 2008. Sublevel caving – past and future. Proceedings of the 5th International Conference and Exhibition on Mass Mining, Luleå, Sweden. https://www.u-cursos.cl/ingenieria/2009/2/MI58B/1/material_docente/ bajar?id_material=257763 Johansson, D. 2011. Effects of confinement and initiation delay on fragmentation and waste rock compaction. Doctoral thesis, Luleå University of Technology, Luleå, Sweden.

Kemeny, J.M. 1994. Practical technique for determining the size distribution of blasted benches waste dump and heap leach sites. Mining Engineering, vol. 46, no. 11. pp. 1281-1284.

Khorzoughi, M.B. 2013. Use of measurement while drilling techniques for improved rock mass characterization in open-pit mines. Masters thesis: University of British Columbia, Vancouver, Canada. doi: 10.14288/1.0073823 Kleinbaum, D.G., Kupper, L L., Muller, K.E., and Nizam, A. 1998. Applied Regression Analysis and Other Multivariable Methods. 3rd edn. Duxbury Pres, Pacific Grove, CA. Kleine, T.H. and Cameron, A.R. 1996. Blast fragmentation measurement using Goldsize. Measurement of Blast Fragmentation: Proceedings of the Fragblast-5 Workshop on Measurement of Blast Fragmentation, Montreal, Quebec, Canada, 23-24 August 1996. Franklin, J.A. and Katsabanis, P.D. (eds). Balkema, Rotterdam. pp. 83-89.

The Journal of the Southern African Institute of Mining and Metallurgy

Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine Latham, J.P. and Lu, P. 1999. Development of an assessment system for the blastability of rock. International Journal of Rock Mechanics and Mining Sciences, vol. 36. pp. 41-55.

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Navarro, J., Schunnesson, H., Ghosh, R., Segarra, P., Johansson, D., and Sanchidrián, J.A. 2019. Application of drill-monitoring for chargeability assessment in sublevel caving. International Journal of Rock Mechanics and Mining Sciences, vol. 119. pp. 180-192.

Ouchterlony, F. and Sanchidrian, J.A. 2019. A review of development of better prediction equations for blast fragmentation. Journal of Rock Mechanics and Geotechnical Engineering, vol. 11. pp. 1094-1109.

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Power, G.R. 2004. Modelling granular flow in caving mines: large scale physical modelling and full scale experiments. PhD thesis, University of Queensland, Brisbane, Australia.

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The Journal of the Southern African Institute of Mining and Metallurgy

Schunnesson, H. 1996. RQD prediction based on drill performance. Tunnelling and Underground Space Technology, vol. 11, no. 3. pp. 345-351.

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Shekhar, G., Gustafson, A., Boeg-Jensen, P., and Schunnesson, H. 2016. Draw control optimisation along the production drift in sublevel caving. Proceedings of the Seventh International Conference & Exhibition on Mass Mining, Sydney, Australia. Australasian Institute of Mining and Metallurgy, Melbourne. https:// www.onemine.org/document/document.cfm?docid=234536&docorgid=2 Silva, J.D., Amaya, J.G., and Basso, F. 2017. Development of a predictive model of fragmentation using drilling and blasting data in open pit mining. Journal of the Southern African Institute of Mining and Metallurgy, vol. 117. pp. 1087-1094.

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Analysis of rock fragmentation and its effect on gravity flow at the kiruna sublevel caving mine. Proceedings of the International Symposium on Rock Fragmentaion by Blasting, Sydney, Australia, 24-26 August 2015. Australasian Institute of Mining and Metallurgy, Melbourne. pp. 775-791.

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Zhang, Z.-X., Qiao, Y., Hou, D-F., and Chi, L. 2020. Experimental study of surface constraint effect on rock fragmentation by blasting. International Journal of Rock Mechanics and Mining Sciences, vol. 128.j http://jultika.oulu.fi/files/nbnfife2021063040635.pdf u VOLUME 122

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THE 8th INTERNATIONAL CONFERENCE

Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine 2-3 NOVEMBER 2022 - CONFERENCE 4 NOVEMBER 2022 - TECHNICAL VISIT VENUE - SUN CITY, RUSTENBURG, SOUTH AFRICA

The Platinum conference series has covered a range of themes since its inception in 2004, and traditionally addresses the opportunities and challenges facing the platinum industry.

This prestigious event attracts key role players and industry leaders through: • High quality technical papers and presentations • Facilitating industry networking • Having large, knowledgeable audiences • Global participation, and • Comprehensive support from industry role players.

WHO SHOULD ATTEND • • • • • • • • • • • • • • • • •

Academics Business development managers Concentrator managers Consultants Engineers Exploration managers Explosives engineers Fund managers Geologists Hydrogeologists Innovation managers Investment managers Market researchers and surveyors Marketing managers Mechanical engineers Metallurgical consultants Metallurgical managers

• • • • • • • • • • • • • • •

Metallurgists Mine managers Mining engineers New business development managers Planning managers Process engineers Product developers Production managers Project managers Pyrometallurgists Researchers Rock engineers Scientists Strategy analysts Ventilation managers

The 8th International PGM Conference will, under the guidance of the organising committee, structure a programme which covers critical aspects of this continually evolving and exciting industry.

The success and relevance of this event to the industry really depends on your participation and support.

You can participate in this event as an organising committee member, author/ presenter, delegate or sponsor.

COVID-19 Protocols

The SAIMM is committed to the safety and wellbeing of our members and the industry. We will take all necessary precautions to ensure that we adhere to protocols and guidelines. Sun International has strict COVID-19 protocols in place to ensure the safety of guests at all their facilities. Social functions will be arranged in open spacious venues. The vast open spaces and outdoor activities like golf, swimming pools and game drives all make for a top class and safe conference venue.

ABOUT THE VENUE The Sun City resort lies in a tranquil basin of an extinct volcano in the Pilanesberg adjacent to South Africa's rich platinum belt. It boasts four hotels, an award-winning golf course and many other attractions.

Nestled in the rolling hills of the Pilanesberg, one of South Africa’s most scenic locations, Sun City is a world unto itself and has earned its reputation as Africa’s Kingdom of Pleasure.

Finally re-discovered and now part of Sun City, the Lost City and the Valley of Waves, fabled to be the ruins of a glorious ancient civilisation, celebrate and bring to life the legends of this mystical city.

166 FURTHER MARCH 2022 122 FOR INFORMATION,VOLUME CONTACT:

Camielah Jardine, Head of Conferencing

E-mail: camielah@saimm.co.za Web: www.saimm.co.za

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NATIONAL & INTERNATIONAL ACTIVITIES 2022 4–8 April 2022 — Ex Mente Pyro Week 2022 Casa Toscana Lodge, Pretoria Tel: +61 8 9389 1488 E-mail: info@ex-mente.co.za Website: https://ex-mente.co.za/pyroweek/ 20–27 May 2022 — 26th ALTA 2022 Nickel-Cobalt-Copper, Uranium-Rare Earths, Gold-PM, In-Situ Recovery, Lithium & Battery Technology Online Conference & Exhibition Perth, Australia, Tel: +61 8 9389 1488 E-mail: alta@encanta.com.au Website: www.encanta.com.au 23–26 May 2022 — Mine Planning and Design Online School Contact: Gugu Charlie Tel: 011 538-0238 E-mail: gugu@saimm.co.za Website: http://www.saimm.co.za 13–16 June 2022 — EXPONOR Chile 2022 International Exhibition of Technologies and Innovations for the Mining and Energy Industry Chile Website: https://www.aia.cl/ Website: https://www.exponor.cl/ 14–16 June 2022 — Water | Managing for the Future Online Conference Vancouver, BC, Canada Website: https://www.mineconferences.com Website: http://www.saimm.co.za 20–23 June 2022 — International Exhibition of Technologies and Innovations for the Mining and Energy Industry Chile Website: https://www.aia.cl/ 21–24 June 2022 — Mine to Mill Reconciliation: Fundamentals and tools for productivity improvement Online Short Course Contact: Camielah Jardine Tel: 011 538-0238 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 21–23 August 2022 — International Mineral Processing Congress Asia-Pacific 2022 (IMPC) Melbourne, Brisbane + online Website: https://impc2022.com/ 21–25 August 2022 — XXXI International Mineral Processing Congress 2022 Melbourne, Australia + Online Website: www.impc2022.com 24–25 August 2022 — Battery Materials Conference 2022 Misty Hills Conference Centre, Muldersdrift, Johannesburg, South Africa Contact: Gugu Charlie Tel: 011 538-0238 E-mail: gugu@saimm.co.za Website: http://www.saimm.co.za

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8–14 September 2022 — 32nd Society of Mining Professors Annual Meeting and Conference 2022 (SOMP) Windhoek Country Club & Resort, Windhoek, Namibia Contact: Camielah Jardine Tel: 011 538-0238 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 15–20 September 2022 — Sustainable Development in the Minerals Industry 2022 10th Internationl Hybrid Conference (SDIMI) ´Making economies great through sustainable mineral development´ Windhoek Country Club & Resort, Windhoek, Namibia Contact: Gugu Charlie Tel: 011 538-0238 E-mail: gugu@saimm.co.za Website: http://www.saimm.co.za 28–29 September 2022 — Thermodynamic from Nanoscale to Operational Scale (THANOS) International Hybrid Conference 2022 on Enhanced use of Thermodynamic Data in Pyrometallurgy Teaching and Research Mintek, Randburg, South Africa Contact: Camielah Jardine Tel: 011 538-0238 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 4–6 October 2022 — 18th MINEX Russia Mining and Exploration Forum Moscow Website: https://2021.minexrussia.com/en/contact-forumorganisers/ 12–13 October 2022 — Mine-Impacted Water Hybrid Conference 2022 ´Impacting the Circular Economy´ Mintek Randburg, South Africa Contact: Camielah Jardine Tel: 011 538-0238 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 2–4 November 2022 — PGM The 8th International Conference 2022 Sun City, Rustenburg, South Africa Contact: Camielah Jardine Tel: 011 538-0238 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 13–17 November 2022 — Copper 2022 Santiago, Chile Website: https://copper2022.cl/ 28 November –1 December 2022 — South African Geophysical Association’s 17th Biennial Conference & Exhibition 2022 Sun City, South Africa Website: https://sagaconference.co.za/ 13-16 December 2022 — 4th International Conference on Science and Technology of Ironmaking and Steelmaking Indian Institute of Technology Bombay (IIT Bombay) Website: http://stis2022.org/

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Company affiliates The following organizations have been admitted to the Institute as Company Affiliates 3M South Africa (Pty) Limited AECOM SA (Pty) Ltd AEL Mining Services Limited African Pegmatite (Pty) Ltd Air Liquide (Pty) Ltd Alexander Proudfoot Africa (Pty) Ltd Allied Furnace Consultants AMEC Foster Wheeler AMIRA International Africa (Pty) Ltd ANDRITZ Delkor(Pty) Ltd Anglo Operations Proprietary Limited Anglogold Ashanti Ltd Arcus Gibb (Pty) Ltd ASPASA Aurecon South Africa (Pty) Ltd Aveng Engineering Aveng Mining Shafts and Underground Axiom Chemlab Supplies (Pty) Ltd Axis House (Pty) Ltd Bafokeng Rasimone Platinum Mine Barloworld Equipment -Mining BASF Holdings SA (Pty) Ltd BCL Limited Becker Mining (Pty) Ltd BedRock Mining Support (Pty) Ltd BHP Billiton Energy Coal SA Ltd Blue Cube Systems (Pty) Ltd Bluhm Burton Engineering (Pty) Ltd Bond Equipment (Pty) Ltd Anglo Operations Proprietary Limited Castle Lead Works CDM Group CGG Services SA Coalmin Process Technologies CC Concor Opencast Mining Concor Technicrete Council for Geoscience Library CRONIMET Mining Processing SA (Pty) Ltd CSIR Natural Resources and the Environment (NRE) Data Mine SA Digby Wells and Associates DRA Mineral Projects (Pty) Ltd DTP Mining - Bouygues Construction Duraset Elbroc Mining Products (Pty) Ltd eThekwini Municipality Ex Mente Technologies (Pty) Ltd

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Expectra 2004 (Pty) Ltd Exxaro Coal (Pty) Ltd Exxaro Resources Limited Filtaquip (Pty) Ltd FLSmidth Minerals (Pty) Ltd Fluor Daniel SA (Pty) Ltd Franki Africa (Pty) Ltd-JHB Fraser Alexander (Pty) Ltd G H H Mining Machines (Pty) Ltd Geobrugg Southern Africa (Pty) Ltd Glencore Gravitas Minerals (Pty) Ltd Hall Core Drilling (Pty) Ltd Hatch (Pty) Ltd Herrenknecht AG HPE Hydro Power Equipment (Pty) Ltd Huawei Technologies Africa (Pty) Ltd Immersive Technologies IMS Engineering (Pty) Ltd Ingwenya Mineral Processing (Pty) Ltd Ivanhoe Mines SA Joy Global Inc.(Africa) Kudumane Manganese Resources Leica Geosystems (Pty) Ltd Loesche South Africa (Pty) Ltd Longyear South Africa (Pty) Ltd Lull Storm Trading (Pty) Ltd Maccaferri SA (Pty) Ltd Magnetech (Pty) Ltd Magotteaux (Pty) Ltd Malvern Panalytical (Pty) Ltd Maptek (Pty) Ltd Maxam Dantex (Pty) Ltd MBE Minerals SA (Pty) Ltd MCC Contracts (Pty) Ltd MD Mineral Technologies SA (Pty) Ltd MDM Technical Africa (Pty) Ltd Metalock Engineering RSA (Pty)Ltd Metorex Limited Metso Minerals (South Africa) (Pty) Ltd Micromine Africa (Pty) Ltd MineARC South Africa (Pty) Ltd Minerals Council of South Africa Minerals Operations Executive (Pty) Ltd MineRP Holding (Pty) Ltd Mining Projections Concepts Mintek MIP Process Technologies (Pty) Limited MLB Investment CC

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Modular Mining Systems Africa (Pty) Ltd MSA Group (Pty) Ltd Multotec (Pty) Ltd Murray and Roberts Cementation Nalco Africa (Pty) Ltd Namakwa Sands(Pty) Ltd Ncamiso Trading (Pty) Ltd Northam Platinum Ltd - Zondereinde Opermin Operational Excellence OPTRON (Pty) Ltd Paterson & Cooke Consulting Engineers (Pty) Ltd Perkinelmer Polysius A Division Of Thyssenkrupp Industrial Sol Precious Metals Refiners Rams Mining Technologies Rand Refinery Limited Redpath Mining (South Africa) (Pty) Ltd Rocbolt Technologies Rosond (Pty) Ltd Royal Bafokeng Platinum Roytec Global (Pty) Ltd RungePincockMinarco Limited Rustenburg Platinum Mines Limited Salene Mining (Pty) Ltd Sandvik Mining and Construction Delmas (Pty) Ltd Sandvik Mining and Construction RSA (Pty) Ltd SANIRE Schauenburg (Pty) Ltd Sebilo Resources (Pty) Ltd SENET (Pty) Ltd Senmin International (Pty) Ltd SISA Inspection (Pty) Ltd Smec South Africa Sound Mining Solution (Pty) Ltd SRK Consulting SA (Pty) Ltd Time Mining and Processing (Pty) Ltd Timrite Pty Ltd Tomra (Pty) Ltd Traka Africa (Pty) Ltd Ukwazi Mining Solutions (Pty) Ltd Umgeni Water Webber Wentzel Weir Minerals Africa Welding Alloys South Africa Worley

The Journal of the Southern African Institute of Mining and Metallurgy

0.1 CPD points for every 1 hour event attended online or contact

2 DAY HYBRID CONFERENCE

THANOS PROJECT

THERMODYNAMICS FROM NANOSCALE TO OPERATIONAL SCALE

INTERNATIONAL CONFERENCE

ON ENHANCED USE OF THERMODYNAMIC DATA IN PYROMETALLURGY TEACHING AND RESEARCH 28-29 SEPTEMBER 2022 - CONFERENCE VENUE - JOHANNESBURG (MINTEK)

BACKGROUND Fundamental knowledge of thermodynamic principles and data is important in understanding and improving processes used in the production of metals as well as in the design and development of new processes. This is particularly so given the fact that the production of metals from ores and/or secondary resources using pyrometallurgical processes involve complex thermochemical phenomena as a result of high temperatures and application of energy to materials. In most cases, however, pyrometallurgists do not fully appreciate the immense potential of thermodynamics to the design and operation industrial processes. This trend is worrying so as the engineering society is moving towards competencies focusing on a wide area of knowledge. The shift towards “Wikipedia knowledge” is a natural consequence of availability of huge amounts of information, but invariably, tends to occur at the expense of fundamental knowledge which forms the backbone of high quality thermodynamics teaching and research. In some instances, students and researchers tend to regurgitate derivations of thermodynamic equations with no indication of how such thermodynamic principles and data are to be put to practical use. To keep the interest and the dedication to the teaching, learning and application of thermodynamics principles and data, new teaching methods must continuously be developed with emphasis on how the fundamental knowledge is used in the research, design and operation of pyrometallurgical processes.

CONFERENCE OBJECTIVES The broad objective of the International Conference on enhanced use of Thermodynamic Data in Pyrometallurgy Teaching and Research is to enhance the use of thermodynamic data in pyrometallurgy teaching and research. The ultimate goal is to increase competitiveness of the South African pyrometallurgical industry by demystifying thermodynamics and equipping the industry to use thermodynamic principles and data in metal production. Hosted by the Metallurgy Technical Programme Committee of the Southern African Institute of Mining and Metallurgy, this conference will focus on two main pillars: (a) the enhanced use of thermodynamic tools and data and the understanding the fundamental reaction mechanisms in metal production, and (b) developing methods for teaching thermodynamics and enhancing the teaching and learning and availability of thermodynamic methods and data. The project is funded by the Research Council of Norway through the Programme for International Partnerships (INTPART) under the project “Thermodynamic from Nanoscale to Operational Scale” (THANOS).

FOR FURTHER INFORMATION, CONTACT: Camielah Jardine, Head of Conferencing

E-mail: camielah@saimm.co.za Tel: +27 11 538-0238 Web: www.saimm.co.za

CONFERENCE | 2023 13 MARCH 2023 - WORKSHOP

Sulfuric Acid Catalysis - Key Parameters to Increase Efficiency and Lower Costs

14-15 MARCH 2023 - CONFERENCE 16 MARCH 2023 - TECHNICAL VISIT THE VINEYARD HOTEL, NEWLANDS, CAPE TOWN, SOUTH AFRICA

BACKGROUND The production of SO2 and sulphuric acid remains a pertinent topic in the Southern African mining and metallurgical industry, especially in view of the strong demand for, and increasing prices of, vital base metals such as cobalt and copper.

OBJECTIVES •

The electric car revolution is well underway and demand for cobalt is rocketing.

New sulphuric acid plants are being built, comprising both smelters and sulphur burners, as the demand for metals increases. However, these projects take time to plan and construct, and in the interim sulphuric acid is being sourced from far afield, sometimes more than 2000 km away from the place that it is required.

The need for sulphuric acid ‘sinks’ such as phosphate fertilizer plants is also becoming apparent.

All of the above factors create both opportunities and issues and supply chain challenges.

To ensure that you stay abreast of developments in the industry, the Southern African Institute of Mining and Metallurgy invites you to participate in a conference on the production, utilization, safe transportation and conversion of sulphur, sulphuric acid, and SO2 abatement in metallurgical and other processes, to be held in March 2023 in Cape Town.

FORMAT OF THE EVENT At this point in time, the event is planned as a full contact conference with international participation through web links. It is also planned to hold technical visits to nearby facilities.

The situation will be constantly reviewed, and if it appears that the effects of the pandemic are still such as to pose a threat to the health and safety of delegates, this will be changed to a digital event.

•

•

•

To expose delegates to issues relating to the generation and handling of sulphur, sulphuric acid, and SO2 abatement in the metallurgical and other industries.

Provide an opportunity to producers and consumers of sulphur and sulphuric acid and related products to be introduced to new technologies and equipment in the field.

Enable participants to share information about and experience in the application of such technologies.

Provide an opportunity for role players in the industry to discuss common problems and their solutions.

WHO SHOULD ATTEND

The Conference will be of value to: Metallurgical and chemical engineers working in the minerals and metals processing and chemical industries Metallurgical/chemical/plant management Project managers Research and development personnel Academics and students Technology providers and engineering firms Equipment and system providers Relevant legislators Transportation

EXHIBITION AND SPONSORSHIP There are a number of sponsorship opportunities available. Companies wishing to sponsor or exhibit should contact the Conference Co- ordinator.

FOR FURTHER INFORMATION, CONTACT: Gugu Charlie, Conference Co-Ordinator E-mail: gugu@saimm.co.za Web: www.saimm.co.za

WORKSHOP SPONSOR