Performance of Insulation Covers to Control Acid Mine Drainage in Cold Environments

Performance of a 1.2 m thick insulation cover constructed on the Xstrata Nickel Raglan Mine tailings storage facility was assessed in situ. The mine is located in the Northern part of the province of Quebec, Canada, in the continuous permafrost zone. The methods used in this study to quantify the performance of the insulation cover include oxygen consumption tests to assess the tailings reactivity and temperature measurements at various depths in the cover material and sulfide tailings. The oxygen consumption test consists of measuring the decrease in oxygen concentration in a sealed chamber and, using fundamental gas diffusion laws, to calculate the oxygen flux through the tailings surface, the oxygen consumption can be related to the tailings oxidation. Three stations were installed directly in the tailings without insulation cover and three under the 1.2 m insulation cover. Oxygen consumption reached a maximum value of 544 moles⋅m^-2⋅year^-1 for the non-covered stations during August when the tailings temperature was 12.8°C. Oxygen consumption drops with temperature and is close to zero at about -4 °C. For the covered stations, oxygen consumption is low in August and tends to increase from September to the end of October, to reach a maximum value of 444 moles⋅m^-2 ⋅year^-1. Tailings reactivity decreases in December when tailings temperature drops to approximately -5°C. These results show that, when the tailings are not preserved from freeze-thaw cycles, even with a granular insulation cover of 1.2 m, the sulfide contained in the tailings can oxidize. Moreover, the tailings can still oxide at subzero temperature.