Electrochemical properties and separation of uranium from lanthanide (Eu, Sm, Yb, La, Ce, and Ho) fluorides in FLiBe molten salt

Abstract

BackgroundMolten salt electrochemical separation of spent fuel in molten salt medium is one of the most widely studied technologies in pyroprocessing. It is based on the use of electrolysis to achieve the separation.PurposeThis study aims to investigate the separation of actinides and lanthanides in situ using high-temperature molten salt media.MethodsCyclic voltammetry (CV), square wave voltammetry (SWV), and constant potential electrolysis were employed to study the electrochemical behavior and separation feasibility of UF4 and LnF3 (Ln=Eu, Sm, Yb, La, Ce, and Ho) in FLiBe molten salt. Firstly, the eutectic salt was prepared, followed by the precise measurement and mixing of FLiBe molten salt and UF4 or LnF3 powder in accordance with the desired concentration ratio. Then, the electrochemical behavior of uranium and lanthanide elements in FLiBe molten salt was experimentally studied using electrochemical CV and SWV. Subsequently, the constant potential electrolysis method was employed to achieve the electrochemical deposition of uranium or lanthanide elements. Finally, the feasibility of separating uranium and lanthanide elements in FLiBe molten salt was evaluated through X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analysis of the electrolysis products.ResultsExperimental results show that U4+ undergoes two electron transfer reductions on an inert tungsten electrode, namely U4++e-→U3+ and U3++3e-→U0, while Yb3+, Sm3+, and Eu3+ have only one electron transfer reduction, leading to the +2 valence state of Yb2+, Sm2+, and Eu2+ ions, respectively. In addition, La3+, Ce3+, and Ho3+ ions do not exhibit significant electrochemical signals within the electrochemical window of FLiBe molten salt. The findings from XRD and EDS analyses verify that the electrolysis products presented on the W electrode consist of metal U, UF3, and entrain molten salt, with no lanthanide (Ln=Eu, Sm, Yb, La, Ce, and Ho) electrolytic deposition product detected.ConclusionsThe suitable electrolytic separation method developed in this study provides basic data to separate actinides and lanthanides from molten salts.

Keywords

• flibe molten salt
• uranium
• lanthanide elements
• molten salt electrochemistry
• electrolytic separation