Alternative materials for engineered covers used to control acid mine drainage

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One of the most serious environmental challenges facing the mining industry today is the reclamation of mine waste disposal areas, especially when they contain sulphide minerals that can produce acid mine drainage (AMD). The proposed research program seeks to improve cover technologies through the use of alternative materials as cover components, and is divided into two distinct projects: 1) assessment of paste rock as cover material; 2) assessment of bentonite based fine grained materials in engineered covers. In Project 1, paste rocks with different waste rock to tailings ratios will be prepared, characterized, and tested. The performance of the paste rock mixtures will be compared, in terms of hydrogeological properties, with theoretical predictions made using Mixture theory. The results of large-scale column tests, in which paste rocks are used as cover material, will be compared with the results from existing field experimental cells. Both set-ups will be instrumented to measure unsaturated water movement and gas migration, and will allow for leachates to be recovered. Results obtained from the physical models (column tests and field experimental cells) will be compared with those from hydrogeochemical numerical models. Bentonite-based fine-grained materials (soil-bentonite or geocomposite clay liner (GCL) are interesting options as cover materials when traditional fine-grained materials are not available near the mine site. Recent work performed by the candidate demonstrated that rock-bentonite mixtures are efficient in controlling oxygen migration over short periods, but are significantly influenced by freeze-thaw cycles. In Project 2, a detailed characterization of different soil bentonite mixtures will be performed in the lab. Based on the results of the characterizations, instrumented column tests in a temperature-controlled chamber will be performed to assess the performance of bentonite-based covers in controlling oxygen and water migration when exposed to freeze-thaw cycles. GCL will also be investigated in this project as a fine-grained layer used in engineered covers. The candidate has access to a mine site where GCL is used as an existing cover material. Laboratory tests (e.g., water and air permeability, microstructural characterization) on intact, post-freeze-thaw cycles, and in situ samples will be performed to evaluate the capacity of GCL to control fluid (water and gas) movement when installed at AMD-generating mine sites. The proposed research program will provide new or improved techniques for the reclamation of AMD-generating mine waste disposal areas. The work will be performed by HQP, who will benefit from this training by becoming highly-valued specialists with the knowledge and ability to reduce the environmental impacts of mining, while supporting the industry's goal of sustainable exploitation of metal resources.