Factors influencing in-situ leaching of uranium mining in a sandstone deposit in Shihongtan, Northwest China

The Shihongtan uranium deposit in northwest China is a sandstone-type deposit suitable for alkaline in-situ leaching exploitation of uranium. Alkaline leaching tends to result in CaCO₃ precipitation there by affecting the porosity of the ore-bearing aquifer. CaCO₃ deposits can also block pumping and injection holes if the formulation parameters of the leaching solution are not well controlled. However, controlling these parameters to operate the in-situ leaching process is challenging. Our study demonstrates that the dissolved uranium concentration in the leaching solution increases as HCO₃^－ concentration increases. Therefore, the most suitable HCO₃^－ concentration to use as leaching solution is defined by the boundary value of the HCO₃^－ concentration that controls CaCO₃ dissolution-precipitation. That is, the dissolution and precipitation of calcite is closely related to pH, Ca²⁺ and HCO₃^－ concentration. The pH and Ca²⁺ concentration are the main factors limiting HCO₃^－ concentration in the leaching solution. The higher the pH and Ca²⁺ concentration, the lower the boundary value of HCO₃^－ concentration, and therefore the more unfavorable to in-situ leaching of uranium.