Influence of freeze-thaw cycles on the performance of covers with capillary barrier effects made of crushed rock-bentonite mixtures to control oxygen migration

In temperate climates, covers with capillary barrier effects (CCBEs) are being used successfully to prevent oxygen fluxes from reaching covered potentially acid mine drainage (AMD) generating mine tailings. In northern climates, the more attractive option for mine site reclamation is insulation covers, which are designed to keep reactive materials frozen. This article suggests that CCBEs can simultaneously control oxygen migration and mine waste temperature to inhibit AMD generation. However, in northern conditions, where natural fine-grained materials needed for the CCBE moisture-retaining layer are not always available, soil-bentonite mixtures could be used instead. This laboratory study assessed-using instrumented columns-the effects of freeze-thaw cycles on the performance of three CCBEs made with crushed rock-bentonite mixtures. An oxygen diffusion test was developed to determine the effective diffusion coefficient of oxygen (De) and its sensitivity to freeze-thaw cycles. The results show good initial performance for the saturated CCBEs. However, the tested CCBEs are significantly affected by freeze-thaw cycles and have limited oxygen-limiting ability.