Leaching behaviour and mechanism of U, ²²⁶Ra and ²¹⁰Pb from uranium tailings at different pH conditions

A large number of radionuclides remain in uranium tailings, and U, ²²⁶Ra and ²¹⁰Pb leach out with water chemistry, causing potential radioactive contamination to the surrounding environment. In this paper, uranium tailings from a uranium tailings pond in southern China were collected at different depths by means of borehole sampling, mixed and homogenised, and analysed for mineral and chemical composition, microscopic morphology, U, ²²⁶Ra and ²¹⁰Pb fugacity, static leaching and dynamic leaching of U, ²²⁶Ra and ²¹⁰Pb in uranium tailings at different pH conditions. The variation of U, ²²⁶Ra and ²¹⁰Pb concentrations in the leachate under different pH conditions with time was obtained, and the leaching mechanism was analysed. The results showed that the uranium tailings were dominated by quartz, plagioclase and other minerals, of which SiO₂ and Al₂O₃ accounted for 65.45% and 13.32% respectively, and U, ²²⁶Ra and ²¹⁰Pb were mainly present in the residue form. The results of the static leaching experiments show that pH mainly influences the leaching of U, ²²⁶Ra and ²¹⁰Pb by changing their chemical forms and the particle properties of the tailings, and that the lower the pH the more favourable the leaching. The results of dynamic leaching experiments during the experimental cycle showed that the leaching concentration and cumulative release of U, ²²⁶Ra and ²¹⁰Pb in the leach solution were greater at lower pH conditions than at higher pH conditions, and the leaching of U, ²²⁶Ra and ²¹⁰Pb at different pH conditions was mainly from the water-soluble and exchangeable states. The present research results are of great significance for the environmental risk management and control of radioactive contamination in existing uranium tailings ponds, and are conducive to ensuring the long-term safety, stability and sustainability of uranium mining sites.