Geochemical behavior of amended and non-amended mine tailings as cover materials for acid mine drainage control: Column tests and reactive transport modeling

Mining companies generate large volumes of waste rock and tailings every year. To reduce these volumes, mining companies can valorize them as construction materials for cover systems such as cover with capillary barrier effects (CCBE). However, questions remain related to the geochemistry of the leachate that percolates through CCBEs made from mining materials. Limestone amendment can be used for increasing the neutralizing potential (NP) of mining materials in the case where the materials have a risk to generate contaminants. This study aims at assessing the performance of low-sulfide tailings, amended or not, and non-acid generating waste rock as components of CCBEs. To do so, five column tests were conducted in the laboratory to assess the long-term geochemical evolution of waste-rock, low-reactive tailings (2 % pyrite), tailings amended with 8 wt% of limestone, CCBE with the moisture-retaining layer (MRL) made of low-reactive tailings (CCBE-T), and CCBE with the MRL made of amended tailings (CCBE-TA). The geochemical evolution of leachates from the different column tests was simulated with MIN3P, a multicomponent reactive transport model. The numerical model was calibrated using results from the column tests. Long-term simulations using the short-term calibrated models suggested that low-reactive tailings could produce AMD when exposed to laboratory conditions, while limestone amendments effectively neutralized the generated acidity and stabilized the pH. Furthermore, incorporating tailings as a MRL in a CCBE reduced sulfide oxidation in the long-term due to the high degree of saturation that limited oxygen diffusion and sulfide reactivity.