column Code 1: The waste material is below the legislated threshold levels for ARD and/or deleterious materials (note that thresholds will vary by jurisdiction). Code 2: The waste material exceeds the legislated threshold levels for ARD and/or deleterious materials and requires a reasonable level of treatment.
Code 3: The waste material greatly exceeds the legislated threshold levels for ARD and/or deleterious materials and requires an aggressive and prolonged level of treatment. A Qualified Person (QP), as defined in NI 43-101, would make the determination between Codes 2 and 3.
Table 1: Mine and Process Waste Classification System
WASTE CLASSIFICATION -- CHEMICAL PROPERTIES OF MINE WASTE Waste Code Category/Item
0
1
2
3
Neutral
Low Risk
Intermediate Risk
High Risk
Acid rock drainage (ARD, can be mined rock or processing waste)
Non-acid generating
Neutralization Potential Ratio (NPR) >2
NPR = 1-2
NPR < 1
Penalty elements (can include arsenic, mercury, lead, antimony, uranium and asbestos, among others)
No penalty elements
No penalty element exceeds threshold limit
One or more exceeds threshold in the low concentration
One or more exceeds threshold in high concentration
Processing chemicals (can include cyanide, phenols, mercury and flotation agents)
No processing chemicals present
No processing chemical exceeds threshold limit
One or more exceeds threshold in the low concentration
One or more exceeds threshold in high concentration
Comments
May have some commercial value
Threshold limits will vary by jurisdiction
QP determines "low" concentration limit
QP determines "high" concentration limit
Note: NPR is adopted from Price, W.A. “Acid Base Accounting Criteria Used in Prediction of Drainage Chemistry.” International Mine Water Association [IMWA] 2010 Symposium, Sydney, Nova Scotia: September 5-9, 2010
The proposed classification system is illustrated in the table. For the purposes of discussion, the table presents the three broad categories for waste materials: ARD potential; penalty elements in mine waste rock; and chemical substances in processing waste products, such as tailings and residues. However, the list of waste materials can be as detailed as required to identify specific elements, chemicals or characteristics, such as radioactivity, turbidity, etc. We have proposed this mining and process waste classification system to provide the mining industry with a way of
describing mine and process waste in a clear and straightforward manner, both within the industry and to the public. It is an essential step, and one that we should not delay in putting in place, as communicating these ideas clearly is not only necessary but inevitable. CIM
Ljiljana Josic, P.Eng., is a manager of mine waste management for mining and metallurgy at SNC-Lavalin. Lawrence Devon Smith, P.Eng., is the principal consultant at Lawrence, Devon, Smith & Associates.
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May • Mai 2018 | 45