A reactive transport model for in-situ leaching of weathered crust elution-deposited rare earth ores using ammonium sulfate

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This study presents a reactive transport model for the in-situ recovery of weathered crust elution-deposited rare earth ores and aims to provide predictive and optimization techniques for rare earth recovery. The model integrates Kerr's selection coefficient, dynamic reversible shrinking core model, and transport model to capture the dynamics of leaching fraction, rare earth elements (REEs), and exchangeable ions during in-situ leaching. The proposed model was validated through bench-scale equilibrium, kinetic, and column experiments, as well as numerical simulation. The results indicate that the deviation from using a single selection coefficient (referred to as 4.26 L2 mol−2 in this study) for modeling is acceptable. Both Darcy velocity and concentration of leaching solution mainly affect the peak value and bending degree of the post-peak leaching curve. Optimal cessation of leaching solution injection, such as substituting water after the peak of the leaching curve, enables effective conservation of leaching solution and reduction of environmental pollution. Differences of at least two orders of magnitude were observed between dynamic parameters derived from kinetic experiments (1.46 and 4.34 L mol−1 min−1) and those obtained from column experiments (2.60 × 10−3 and 1.71 × 10−2 L mol−1 min−1). This finding carries substantial implications for in-situ recovery and mineralization processes, highlighting the need for further investigation at the pore scale.