Dry Stack Tailings Management
Meticulous Planning, Desired Output A specialist from Knight Piésold Africa states that detailed planning and thorough implementation of key elements in the dewatered tailings disposal process is essential to achieving the expected moisture content.
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n the present mining atmosphere, cost, environment, and reputation are the primary factors influencing decisions on the tailings disposal technique employed. Regarding meeting these requirements, mounting evidence indicates that theviability of dry stack disposal (dewatered tailings) is increasing. However, attaining the desired residual moisture content threshold in dewatered tailings can be a complex task. Therefore, meticulous planning and effective implementation are crucial. This insight comes from Andrew Copeland, Technical Director (Mining) at Knight Piésold Africa, as part of the company’s regular updates to mining companies in a changing regulatory environment. Knight Piésold is a highly regarded international consulting company that offers
engineering and environmental services across the mining, power, water, transportation, and construction sectors. Achieving the Desired Moisture Content Drawing from Knight Piésold’s extensive experience in developing sustainable solutions for clients, Copeland is eager to advise mining companies on the practical approach of achieving the desired moisture content in dewatered tailings. Specifically, he highlights the following aspects: the impact of the fine fraction on dewatering; the significance of sampling tailings; evaluating dewatering systems during pre-feasibility; and the business case for dry tailings. 1. Fine Fraction (Clay Fraction) The fine fraction, particularly the clay fraction (presence of clay in tailings), determines the moisture content in dewatered tailings. Two common scenarios arise with tailings: one without clay presence and another with clay presence.
No Clay Presence Relating to moisture content in tailings without clay presence, Copeland expounds, “In tailings from hard rock sources where no clay is present, consistently achieving a filter cake moisture content of as low as 15% should be achievable with well-operated equipment.” • Clay Presence On the other hand, in cases such as weathered rock-originated tailings, kimberlite, or mineral sands ore bodies, clays can result in a moisture content of 30 to 40%. Generally, with these materials, achieving a filter cake moisture content of 30% residual moisture can be highly challenging, as Copeland indicates. Inevitably, this can lead to a substantial volume of water remaining in the tailings and being deposited on a dry stack. Given this challenge, some argue that the industry should refrain from labelling dewatered tailings as “dry stacks,” as liquefaction might still be possible. Thus far, this remains the bone of contention within the industry. 2. Sampling Tailings Due to the effect of the fine fraction on moisture content, Copeland emphasises the importance of obtaining tailings samples before designing the filter plant, transport system, and dry
www.knightpiesold.com 14 Mining Business Africa | September - October 2023
