The use of an organic carbon cover system at a Cu-Ni mine in Sudbury, ON McAlary, Mason; Ptacek, Carol J.; Blowes, David W.; McGarry, Samantha
Acid rock drainage (ARD) occurs when sulfide minerals oxidize, generating low pH water and the release of dissolved metals. This phenomenon is one of the most significant concerns in the mining industry, where the future loading of dissolved metals from inactive mine sites could continue for decades to centuries. Traditionally, remediation of ARD is focused on collection of water from surface-water bodies and treatment through pH neutralization using lime (CaO). While this approach improves water quality, it represents a recurring cost for mining companies. Therefore, numerous approaches have been developed over the past few decades to passively mitigate and remediate ARD by limiting the supply of O₂(g) and water to tailings rich in sulfide minerals. For example, some cover systems utilize organic carbon material such as biosolids, wood-waste, peat and compost. A two-layer cover system was studied at an active Cu-Ni mine site located near Sudbury, ON and comparisons were made between sites with a two-layer cover system, a one-layer cover of desulfurized tailings only, and no cover. Pore-gas results show that the organic layer consumes a portion of the O₂(g) ingress from the atmosphere, with most of the O₂(g) depletion occurring in the desulfurized tailings layer. Pore-water results show that the organic carbon layer increases the alkalinity and that the presence of the desulfurized tailings vastly improves water quality. Thus, the re-use of waste products within a cover system has the potential to sustainably manage ARD in the near term and further study on their use as a land reclamation measure is warranted.
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