Influence of desulfurized tailings cover heterogeneity and variability on long term performance of mine site reclamation

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Reclamation of acid generating mine tailings storage facilities is a challenge for the mining industry. Traditional methods are revisited to incorporate issues such as climate change, resource scarcity, and responsible mining. The reuse of inert tailings, or tailings made unreactive by desulfurization, as cover material in a reclamation scenario, has been a focus of research for the past decade. Mining companies now seriously consider desulfurization for reclamation as part of responsible mine development. However, desulfurization is not often used in operating mine sites for production of cover material. Full-scale implementation of desulfurized tailings as monolayer covers was performed on a few sites in Canada. Challenges were identified on full-scale covers, mainly related to variability of desulfurized tailings sulfur content and particle size distribution. Indeed, on a cover deposited hydraulically as a slurry, significant particle size segregation occurs, which could affect the performance of the cover. Furthermore, desulfurized tailings may evolve over their service life as cover material. Geochemical evolution may occur because of residual sulfide consumption within the cover. Other elements may be released over time from the cover and affect effluent quality (e.g. Zn, As). The new conditions in the covered sulfidic tailings, while preventing sulfides oxidation, may trigger other reactions leading to the release of metals. Previous numerical modeling provided preliminary evaluation of cover performance using estimated average cover properties that did not change with time. A long-term perspective on cover performance needs to include variability in cover material properties, and specifically for desulfurized tailings used as cover material, since reclaimed sites have an indefinite service life. Desulfurized tailings as cover material is close to being implemented at the full-scale level as a successful reclamation scenario. The research program aims to fill the knowledge gaps related to the effect of cover heterogeneity and evolution on long term performance through three main objectives: (1) Establish a numerical model of the hydrogeochemical behaviour of a desulfurized tailings cover system in 2 and 3 dimensions, considering heterogeneity and spatial variability in chemical composition and particle size distribution; (2) Evaluate the mid and long term performance of a desulfurized tailings cover system considering the evolution of geochemical conditions in the acid-generating tailings and in the desulfurized tailings cover; (3) Compare the behaviour of a desulfurized tailings cover system from laboratory results and numerical predictions to full scale cover. The methodology that will be used include laboratory experiments, field instrumentation and measurements, and numerical modeling. It is expected to train 1 PhD, 1 MSc, 1 PDF and 3 internship students over the course of this research program.