Field-Scale Reactive Transport Modeling of CO2+O2 In-Situ Uranium Leaching: Impacts of Development Conditions on Flow Behavior and Recovery Efficiency

The CO2+O2 in-situ leaching (ISL) mining process has been widely applied in the exploitation of sandstone-type uranium deposits; however, evaluating leaching efficiency remains a challenging issue. In this study, a sandstone-type ISL uranium deposit was selected, and based on comprehensive investigations of hydrogeological conditions and mineral geochemistry, a multi-physics coupled numerical model of uranium solute reactions during CO2+O2 leaching was established. The model fully accounts for variations in the groundwater flow field between injection and production wells and, on this basis, couples the chemical reaction field between the ore and the leaching solution. The model simulates the evolution of uranium concentration in the leaching solution and further calculates the leaching efficiency of the ore. The results indicate that groundwater flow velocity is highest between injection and production wells, where groundwater dynamics are strongest, and gradually decreases toward the interwell zones as hydrodynamic intensity weakens. Uranium concentration in the leaching solution is closely related to the groundwater flow field. In the early stage, high-uranium-concentration zones are mainly concentrated between injection and production wells. As time progresses, ore reactions in high-flow regions become more complete, leading to a decline in uranium concentration, while residual uranium ions within the formation diffuse outward under concentration gradients, causing high-concentration zones to expand outward. Sensitivity analysis shows that increasing CO2 and O2 concentrations significantly enhances uranium leaching concentrations, with increases of approximately 22.1% and 11.3%, respectively. Lower injection-production flow rates reduce dilution and promote more complete reactions, but may also introduce risks such as ore layer clogging. These results provide a theoretical basis and scientific guidance for flow-field regulation in situ leaching uranium mining.