Chlorination pathways of lanthanide and actinide oxides in LiCl-KCl molten salt: Electrochemical and spectroscopic studies

Pyroprocessing is a critical technology for recycling spent nuclear fuel, which enhances the sustainability of nuclear power generation. This process begins with metal oxides, which must be converted into metal chlorides to facilitate further processing, including electrorefining and electrowinning. In this work, we investigate the chlorination of lanthanide (Nd, Gd) and actinide (Th, Np) oxides in LiCl-KCl molten salt and confirm the chlorination through electrochemical and spectroscopic analyses. Nd 2 O 3 and Gd 2 O 3 are chlorinated using NH 4 Cl, with electrochemical measurements demonstrating the electrodeposition and dissolution currents of Nd 3+ and Gd 3+ ions. Th and Np chlorides are prepared using AlCl 3 as a reactant. The reaction between ThO 2 and AlCl 3 produces ThCl 4 , as evidenced by the electrodeposition-dissolution currents of Th 4+ . For the chlorination of NpO 2 , NpO 2 Cl is first prepared by dissolving NpO 2 in acidic solutions and then drying. Subsequently, the reaction of NpO 2 Cl and AlCl 3 in molten LiCl-KCl yields NpCl 4 . Electrochemical and UV–Vis spectroscopic measurements confirm the redox reactions of Np 4+ /Np 3+ /Np 0 and the presence of NpCl 4 in the molten LiCl–KCl, respectively.