Reactive transport modeling of the geochemical behavior of highly reactive tailings in different environmental conditions

The hydrogeochemical behavior of highly reactive tailings with no or very low neutralizing capacity and their hydrogeochemical response when covered by a cover with capillary barrier effects (CCBE) were evaluated in laboratory columns. The hydrogeochemical response of highly reactive tailings under wetting-drying cycles and saturated conditions was also simulated using the MIN3P code, a finite volume model for coupled groundwater flow, oxygen diffusion and multi-component reactive transport. Laboratory tests were conducted for approximately 18 wetting and drying cycles, over a period of one and a half years. A numerical simulation model was validated using laboratory results of uncovered highly reactive tailings under wetting and drying cycles conditions. The acceptable agreement between the geochemical observations in the laboratory and the numerical simulations shows that MIN3P can simulate the hydrogeochemical response of highly reactive tailings (initially very acidic) under laboratory experimental conditions and can make realistic predictions. The laboratory hydrogeochemical response of highly reactive tailings covered by a CCBE and the numerical modeling results of highly reactive tailings under saturated conditions (an equivalent CCBE oxygen barrier) indicated a decrease in the concentration of sulfate and most metals in the leachate compared to uncovered highly reactive tailings, indicating that both scenarios decreased sulfide oxidation. The simplified approach for geochemical modeling of saturated reactive tailings evaluated in this paper could be used to determine the required oxygen barrier efficiency to reach the target effluent geochemistry as a preliminary stage of reclamation design.