Abstract
The reclamation of potentially acid-generating tailings storage facilities can be achieved by using cover systems aiming to limit oxygen ingress to the tailings, and thus limiting the acid-generating reactions. Reclamation of abandoned, highly oxidized acid-generating tailings represent an additional challenge. Indeed, although limiting oxygen ingress to the tailings decreases sulfide oxidation and acid-generation, it also induces geochemical conditions that are more reducing, destabilizing the accumulated oxyhydroxides and solubilizing the associated contaminants, therefore increasing dissolved metal loadings compared to the pre-reclamation water quality. Consequently, mine water treatment requirements for the contaminated post-reclamation interstitial water are difficult to predict.
The highly oxidized acid-generating tailings of the abandoned Lorraine mine (Québec, Canada), that operated in the 1960’s, were reclaimed in 1999-2000 using a cover with capillary barrier effects that was proven successful in limiting oxygen ingress to the tailings. The evolution of the water quality over the last 23 years will be presented and discussed in this paper. These monitoring results provide a unique opportunity to evaluate the concomitant phenomena controlling post-reclamation water quality of highly oxidized acid-generating tailings. Results suggest that sulfide oxidation gradually decreased following reclamation, and that secondary oxyhydroxide minerals contributed to the release of iron and other dissolved metals.
The results of this study will be useful for practitioners involved in the reclamation of acid-generating tailings and in the planning of water treatment needs for highly oxidized acid-generating sites.