Chemical behavior of grey oxide phases in MgCl2-based molten salts for Sr nuclide separation

•Leaching technique with MgCl2-based salts is tested for Sr nuclide separation.•Varying reaction time, temperature, and salt composition, Sr is separated.•Sr in Sr oxides is efficiently converted to a chloride form in MgCl2 molten salts. To reduce the burden of storage and disposal of high-level radioactive waste, in this study, molten salt leaching was employed using several Sr oxides, grey oxide phases (SrZrO3, SrMoO4, and U2SrOy), and MgCl2-based molten salts for Sr nuclide separation. The reaction time, temperature, and salt composition were varied to effectively separate Sr in chloride forms. The Sr removal efficiency, structure, and morphology were analyzed via ICP-AES, XRD, and SEM. For SrZrO3, a Sr removal efficiency above 99% was achieved for all experiments with MgCl2 at 800 °C for reaction times of 5, 10, and 20 h, and MgO and ZrO2 were found to be produced. In LiCl-KCl-MgCl2 and NaCl-MgCl2 molten salts at 500 or 600 °C, a Sr removal efficiency above 97% was obtained, with the production of MgO and Zr2O as reaction products. For SrMoO4, a Sr removal efficiency above 99% was obtained using a Mg/Sr molar ratio of 7, and MgO and Mg2Mo3O8 (predominant component) were obtained as reaction products. U2SrOy was also tested with MgCl2 molten salt at 800 °C, and a Sr removal above 99% was obtained, with the production of MgUO4 as a reaction product. Based on the work presented in this study, molten salt leaching using MgCl2-based molten salts has been identified as a viable approach for efficient Sr separation from oxides.