Reactive transport model of uranium by CO₂ + O₂ in situ leaching

Uranium is an important strategic resource, and its safe and efficient development and utilization are of great significance to ensuring a nation's energy supply and strategic security. Sandstone-type uranium ore is commonly mined by CO₂ + O₂ in situ leaching, for which understanding the coupling mechanism between the hydrodynamic and chemical fields is key to predicting uranium leaching. This study focused on a coal-uranium ore deposit in China. A convection and dispersion model of the solute transport by in situ leaching was constructed in COMSOL, and a thermodynamic model of CO₂ + O₂ in situ leaching in sandstone-type uranium ore was constructed in PHREEQC. The two models were coupled to simulate the reactive transport and dynamic leaching processes of uranium by CO₂ + O₂ in situ leaching. A sensitivity analysis was performed to quantitatively analyze the effects of different model parameters on the uranium leaching efficiency and uranium contamination remediation. The results showed that the coupled model could simulate and predict the reaction and transport of uranium. The sensitivity analysis indicated that the production rate and the injected CO₂ and O₂ concentrations are the key parameters that control the uranium leaching efficiency, followed by the formation permeability and injection rate. The uranium leaching efficiency does not increase monotonically with the formation permeability and production rate. The results also indicated that natural dilution is insufficient for remediating uranium-contaminated groundwater, but the remediation efficiency can be improved by increasing solution extraction. The results of this study can be used to develop guidelines for the safe and efficient development and utilization of uranium ore while protecting the ecological environment.