Effectiveness of various cover scenarios on the rate of sulfide oxidation of mine tailings

ong term environmentally sound disposal of the millions of tons of mining residue is a serious hallenge to the international mining industry. This paper evaluates, through a numerical nvestigation, the potential performance of desulfurized tailings as a cover material for the eduction of acidic drainage from sulfidic tailings. This evaluation is facilitated through a omparison of various cover types as decommissioning options. The cover types considered onsist of a desulfurized tailings material cover exposed to ambient climate conditions, a water over (flooded tailings), and a combination cover type. As part of the evaluation of cover erformances, the effect of climatic variability on the potential rate of sulfide oxidation in tailings ith an open ground surface, was also assessed. The numerical analysis was conducted using he model PYROX, which was modified to allow for variably-saturated conditions, time arying moisture contents, and to account for the temperature dependence of Henryʹs law and as diffusion. In the case study presented here, the benign cover material consists of a low ulfide waste stream (cassiterite float tails, CFT), a by-product of the production of tin oncentrate (cassiterite, SnO2). Modelling results after a simulation period of 100 years ndicate that a water cover alone or an exposed CFT cover alone are both less effective ptions than the combined cover type. A water cover alone leads to a reduction of pproximately 99.1%, in the oxidation rate relative to uncovered tailings while the combined over type results in the lowest potential extent of sulfide oxidation after mine closure-an pproximately 99.8% reduction. Importantly, a CFT cover exposed to ambient environmental onditions can still substantially reduce the sulfide oxidation rate, by approximately 75–82% ver a 100-year time period, relative to uncovered tailings. Variability in precipitation (and ence percent saturation of the surface layer) had less of an effect on the potential sulfide xidation rate than did the cover type. The performance of the exposed CFT cover varied by ess than 10%, within the range of climatic conditions expected at the Renison Bell mine site in outhwest Tasmania, Australia. Although the modelling results indicate that the combined water nd CFT cover is the best option, this approach achieves only a minor improvement over the ater cover alone.