Numerical modelling of column experiments to investigate in-situ bioleaching as an alternative mining technology

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This publication investigates indirect in-situ bioleaching as an alternative mining technology for minimizing waste production, environmental impact, and chemical consumption. The process consists in injecting a leaching solution into a targeted ore body for dissolving base metal bearing minerals, while iron-oxidizing microorganisms regenerate the solution. In this contribution, we present laboratory column experiments that investigate the impact of grain size on the action of an acidic oxidizing solution in contact with ore samples crushed at different grain sizes. These results are used for developing a one-dimensional reactive transport model based on PhreeqC software. In this model, porous and fractured media are approached by a dual porosity reactive transport model where dissolution reactions are described by kinetics. Column experiments are used as a reference for calibrating the key parameters of the numerical models, which include the relative volume of mobile and immobile zones within the dual porosity medium and the exchange rate between these two volumes. This model is then adapted to in-situ conditions by considering the preferential flow of fluids through natural or artificial fractures of enhanced hydraulic conductivity. These models are used to discuss key elements affecting the feasibility of coupling bioleaching and in-situ recovery for improving the sustainability of mining, especially for deep and complex ore deposits.