Selective Precipitation of Strontium and Barium from Molten MgCl2 Following Chlorination Using Carbonate and Sulfate Reagents

Growing interest has focused on separation technologies that selectively dissolve high heat–generating fission products (FPs), such as strontium (Sr), in molten salts via direct chemical reactions with used nuclear fuel (UNF) without electrochemical processes, thereby reducing disposal volume. Separated FPs can be precipitated using suitable reagents and converted into stable waste forms for final disposal. Previous studies have shown that SrO in simulated nuclear fuel can be separated through chlorination with molten MgCl 2 , producing SrCl 2 that dissolves into the salt phase. This study investigates the precipitation behavior of Sr and Ba dissolved in MgCl 2 using two precipitants, K 2 CO 3 and MgSO 4 , following chlorination reactions between MgCl 2 and SrO or BaO. K 2 CO 3 preferentially reacted with MgCl 2 to form MgCO 3 , which decomposed into MgO and CO 2 (g), rendering it unsuitable for this system. In contrast, MgSO 4 reacted with Sr- and Ba-containing MgCl 2 melts to form SrSO 4 and BaSO 4 without generating additional Mg-containing by-products through reaction with the MgCl 2 solvent salt, although MgO originating from the preceding chlorination step may remain in the recovered solid products. When MgSO 4 was added to MgCl 2 containing both Sr and Ba, a mixed sulfate phase (Ba 0 . 75 Sr 0 . 25 SO 4 ) formed. These results demonstrate that sulfate-based precipitants are suited for the separation of Sr and Ba from molten MgCl 2 salts and offer a viable strategy for managing high heat–generating FPs.