Passive treatment of As-contaminated neutral mine drainage from gold mine tailings in cold climate

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Mining can entail the release of As towards natural waters. At the rehabilitation stage, passive treatment is common practice for active, closed and abandoned AMD-generating mine sites. However, there is a critical lack of knowledge on NMD, especially on As treatment efficiency in cold climates (low temperature and high salinity). In cold climate, water recycling and reuse reduces freshwater consumption but increases the contaminant load salinity and As concentrations. This leads to major issues related to As removal from saline and cold water. The project focuses on As-NMD in tailings from an active mine and a rehabilitated site, after a 45-year abandonment. With respect to the rehabilitated site, the project attempts to elucidate As retention mechanisms and stability within the contaminated wood residuals of the Wood Cadillac passive biofilter. The latter proved efficient for over 20 years but the identification-quantification of biogeochemical processes responsible for As immobilisation are still to be confirmed. Such knowledge is needed for potential replication on the Éléonore mine. The general objective of the project is to generate novel knowledge and tools to improve the passive treatment of As in NMD. The focus is on cold climate and high salinity conditions. The specific objectives are: O1) Evaluate the efficiency of selected natural and residual materials for As removal; O2) Evaluate the impact of influence factors on the performance of passive As-NMD treatment under low temperature and high salinity; O3) Evaluate As removal mechanisms and stability in a 20-year passive biofilter (Wood Cadillac); O4) Evaluate the upscaling effects on the efficiency of As-NMD passive treatment (Newmont-Éléonore); O5) Conduct a techno-economic assessment and propose specific design criteria for passive As-NMD treatment. Results on the efficiency of selected materials and the associated costs will benefit the Canadian mining companies and governments facing similar As contamination issues to improve the selection of materials in cold climates and to apprehend potential adjustments in the treatment systems in the context of adaptation to climate change.