Abstract:Acid in-situ leaching of uranium is the preferred process for recovering uranium resources, some uranium will inevitably flow into groundwater and pollute the ecological environment. However, the reduction and fixation of free uranium with the reductant Na2S2O4 can effectively solve this problem. Therefore, the mechanism of Na2S2O4 reduction and fixation of soluble uranium in the groundwater of a decommissioned uranium mine in the acid leaching method was simulated and analyzed using PHREEQC, and the influence of NaHCO3 on Na2S2O4 reduction of fixed soluble uranium was discussed. The simulation results show that: 1) U(Ⅵ) is the dominant uranium in the groundwater of this area, in which UO2SO4, UO22+ and UO2(SO4)22- are the dominant species, accounting for 63.60%, 32.35% and 3.89% respectively. 2) The reduction of fixed soluble uranium by Na2S2O4 can reduce the Eh value and Fe(Ⅲ) concentration of groundwater, enhance the reducibility of groundwater, and promote the precipitation of uraninite and pyrite, but cause acidification and high SO32- concentration of groundwater. 3) When reducing fixed soluble uranium, NaHCO3 + Na2S2O4 alleviates groundwater acidification, enhances the removal of U(Ⅵ) and SO32-, and has little effect on the reduction of fixed soluble uranium by Na2S2O4. The optimum remediation effect is achieved when the concentration ratio of Na2S2O4 to NaHCO3 is between 1︰1 and 1︰1.5.