Date of Publication :31st July 2024

Abstract:Contaminated mine drainage results from the interaction between the running water and the components of a mine site. The treatment of mine drainage is mandatory, with respect to its long-term environmental impacts. For the case of closed mines, passive treatment of mine waters is generally the viable option. Passive treatment involves chemical, physical, and biological processes found in the environment, which is cost-effective and require little maintenance. Dolomite (CaMg(CO3)2) is often employed for passive mine water treatment. Dolomite dissolves and therefore neutralizes and reduces acidity, increases alkalinity; dolomite also remove metals, non-metals, and metalloids in contaminated mine waters. Moreover, its activation by half-charring enhances its performance for mine water treatment. Compared to raw dolomite, half-charred dolomite (CaCO3·MgO) is more soluble (due to change in chemical composition), has a larger specific surface area (0.7 versus 23.0 m2 /g) and higher paste pH (7.9 versus 11.6), which contribute to enhance its performance in mine drainage treatment. In this study, half-charred dolomite will be prepared and evaluated for the treatment of mine drainage, sampled on the previously restored mining site of Normétal, Quebec, Canada. Dolomite will be characterised by X-ray diffraction, elemental chemistry (acid digestion followed by ICP-MS scan), and thermogravimetric analysis. Specific surface, pores volume and paste pH will be also investigated. Characterization will be performed before and after dolomite charring (temperatures 700 to 800°C, for one to six hours), with the aim to investigate chemical and mineralogical modification of dolomite through heating, as well as the origin of the improved performance of half-charred dolomite for the mine water treatment. Thereafter, batch scale experiments will be performed in 2L bottles, filled with mixture of dolomite and half-charred dolomite in various ratios. Two representative temperatures will be considered (4°C and 20°C) for kinetics (to determine the hydraulic residence time) and isotherms study (to predict the lifespan of the treatment system). Pilot scale test will be performed in 1m3 container manufactured from recycled high-density polyethylene. The results will be therefore used for the design of the field scale treatment system. Dolomite regeneration for reuse will be evaluated, aiming a zero-waste process.

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