Simulation of Inverse Equilibrium of Mineral Dissolution and Precipitation Amounts During Uranium Leaching with CO₂+O₂

CO₂+O₂ uranium leaching process is the third generation of uranium mining and smelting technology in China, in the leaching process of uranium from the ore after the interaction between the leaching agent and the minerals of the ore-bearing layer, the uranium leaches from the ore at the same time, due to the increasing salinity of groundwater, chemical precipitation will generate, resulting in the blockage of the ore-bearing layer. However, in the past, the hydrogeochemical simulation of ore-bearing layer plugging explored the dissolution and precipitation characteristics of minerals through forward simulation, and qualitatively studied the characteristics of ore-bearing layer blockage. In this paper, based on indoor static leaching test (normal temperature and pressure) and the field dynamic leaching test data of the Nalinggou uranium mine with CO₂+O₂ process, PHREEQC software was used to simulate the mineral dissolution and precipitation, the dissolution and precipitation characteristics of ore-bearing minerals were discussed, and the hydrogeochemical mechanism of the ore-bearing layer blockage of Nalinggou uranium mine was explored. The simulation results show that during the leaching process, potassium feldspar, albite and anorthite dissolve during uranium leaching, under indoor leaching conditions, their dissolution amounts for 60-170 d are 0.2-0.26, 2.91-3.26, and 4.58-5.39 mmol/L, respectively. The dissolution amounts under field leaching conditions are 0.14-1.42, 0.27-1.68, and 0.23-0.75 mmol/L, respectively. Illite, calcite, and gibbsite form precipitates, under indoor leaching conditions, the precipitation amounts for 60-170 d are 5.36-5.9, 9.77-11.7, and 0.40-0.53 mmol/L, respectively. Under field leaching conditions, the precipitation amounts are 0.35-2.79, 0.05-1.34, and 0.39-2.84 mmol/L, respectively, and part of CO₂(g) is overflowed. Compared with the indoor leaching test, the dissolution amounts of albite, potassium feldspar and calcite in the rock ore in the field leaching test are relatively lower than that of illite and calcite. The above results indicate that the blocking minerals in the ore-bearing layer in the process of CO₂+O₂ uranium leaching are mainly illite, calcite and gibbsite. The formation of illite is the result of clayification and alteration of feldspar minerals, calcite and gibbsite are mainly affected by the concentration of Ca²⁺, Al³⁺ and pH of the leaching agent, and the higher concentration of Ca²⁺ and Al³⁺ and the increase of pH will lead to the precipitation of calcite and gibbsite. Clayification alteration and calcite precipitation of feldspar are important mechanisms for the ore-bearing layer blockage.