Passive treatment of alkaline drainage from iron and titanium metallurgical slag

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Mining and metallurgy generate, among other waste, alkaline drainage (AlkD) producing tailings. AlkD is characterized by a pH above 9 and variable concentrations of metals and sulfate. Passive treatment is often used for the rehabilitation of mine drainage generating mine sites. However, there is a critical lack of knowledge on passive treatment of AlkD. The 3-year applied research project focuses on the passive polishing of an AlkD generated by iron and titanium (Fe-Ti) slag tailings from an active metallurgical site impoundment. As systematic monitoring data shows mostly a high pH-related issue, with inconsistent exceeding concentrations of other contaminants, the project attempts to evaluate the feasibility of AlkD passive polishing using locally available materials, including the responsible processes for pH decrease and system stability over time. Precisely, the long-term general objectives of this project are to (i) generate novel knowledge and relevant tools for accurate environmental characterization of Fe-Ti slag tailings from the Sorel-Tracy metallurgical plant, and (ii) design passive treatment for AlkD generated from the waste. The specific objectives are to: SO1) Evaluate the contaminant leaching potential of Fe-Ti slag tailings; SO2) Predict the evolution of drainage water chemistry, based on historical field monitoring data and laboratory setting test results; SO3) Evaluate the impact of influence factors and propose design criteria for passive treatment of AlkD using materials available on or near the site. Results on the efficiency of selected materials and the associated costs will benefit the Canadian mining companies and governments facing similar contamination issues to improve the selection of the most appropriate materials.