Geochemical Assessment of Desulphurized Tailings as Cover Material in Cold Climates

It is essential to develop effective mine waste management approaches and mine site reclamation techniques to curtail the adverse effects of mining processes on the natural environment. This study focuses on the use of partially desulphurized tailings as a moisture-retaining layer in an insulation cover with capillary barrier effects (ICCBE). Tailings were obtained from a nickel ultramafic ore processing plant at a mining company located in a continuous permafrost region of northern Québec, Canada. The geochemical response of tailings at two different sulphur contents (0.4 and 0.8 wt%), with and without ICCBEs, was tested by applying eight freeze-thaw and wetting cycles. Desulphurization of the tailings allowed to reduce the content of sulphide minerals by about 90%, from ~22 wt% to around 1.2–2.2 wt%. Column kinetic geochemical tests showed that Ni leaching was significantly reduced to concentrations ranging between 0.01–0.22 mg L−1 compared to 0.63–1.92 mg L−1 from the raw tailings (thanks to the desulphurization process). Zinc release was maintained around 0.04–1.72 mg L−1 compared to 0.4–3.69 mg L−1 from the raw tailing. Although all the columns produced leachates displaying circumneutral to slightly alkaline pH, the columns with ICCBE are expected to prevent acid mine drainage generation longer than the other columns due to reduced sulphide content and a constantly high degree of saturation maintained by capillary barrier effects.