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

Abstract

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. Nd₂O₃ and Gd₂O₃ are chlorinated using NH₄Cl, with electrochemical measurements demonstrating the electrodeposition and dissolution currents of Nd³⁺ and Gd³⁺ ions. Th and Np chlorides are prepared using AlCl₃ as a reactant. The reaction between ThO₂ and AlCl₃ produces ThCl₄, as evidenced by the electrodeposition-dissolution currents of Th⁴⁺. For the chlorination of NpO₂, NpO₂Cl is first prepared by dissolving NpO₂ in acidic solutions and then drying. Subsequently, the reaction of NpO₂Cl and AlCl₃ in molten LiCl-KCl yields NpCl₄. Electrochemical and UV–Vis spectroscopic measurements confirm the redox reactions of Np⁴⁺/Np³⁺/Np⁰ and the presence of NpCl₄ in the molten LiCl–KCl, respectively.