Reactive transport numericalmodeling of CO₂+O₂ in-situ leaching based on COMSOL-PHREEQC

Uranium resource is important strategic resource in the world. How to develop and utilize coal-uranium resources safely and efficiently is of great significance for ensuring national energy supply and national strategic security.The CO₂+O₂ in-situ leaching of uranium is the main way of mining and smelting sandstone-type uranium mines. Studying the coupling mechanism of hydrodynamic field and chemical field during the CO₂ + O₂ leaching process is the key to predicting the dynamic leaching of uranium in the process of CO₂+O₂ in-situ leaching. In this study, a coaluranium coexisting deposit in Inner Mongolia is taken as the object, the convection and dispersion model of solute migration in the in-situ leaching process is constructed by COMSOL, and the thermodynamic database of the CO₂+O₂ dissolution process of sandstone-type uranium ore is constructed by PHREEQC. Using the iCP platform (Interface COMSOL-PHREEQC), a numerical model of the reaction and migration of CO₂ +O₂ in-situ leaching of uranium in the COMSOL-PHREEQC coupling framework is established, and the dynamic leaching process of uranium ore during CO₂+O₂ in-situ leaching is simulated. Meanwhile, the importance of different parameters on the uranium leaching effect is quantitatively compared based on parameter sensitivity analysis. The results show that this model can simulate and predict the reaction and migration of uranium in the process of CO₂+O₂ leaching. The simulation results show that in the process of in-situ leaching of uranium with CO₂+O₂, the hydrodynamic force around the pumping and injection wells is strong, and the leaching solution has a strong chemical reaction with uranium minerals, forming a high concentration uranium area, while in the place with weak hydrodynamic action, the leaching solution cannot reach in time, forming low concentration uranium areas. The migration process of leached uranium is mainly controlled by convection and dispersion. The leached uranium can enter the working face and goaf through the mining fractures in the lower coal seam, affecting the safe mining activities of the coal mine. The results of parameter sensitivity analysis reveal that the extraction flow rate, CO₂, and O₂ concentration are the key control factors of the uranium leaching rate, while the uranium leaching rate is not monotonously increasing with formation permeability and groundwater flow rate. The research results have a certain guiding role in the CO₂+O₂ in-situ leaching mining of sandstone-type uranium deposits.