Electrochemical properties and extraction of erbium on liquid gallium electrode in the 3LiCl-2KCl molten salt

Liquid metallic gallium demonstrates a great potential as a reactive cathode with an excellent characteristic for the effective separation of fission products in the recovery of spent nuclear fuel in the “liquid metal-salt melt system”. Advanced electrochemical methods were utilized to investigate the deposition mechanism of Er(III) ions, along with the kinetic and thermodynamic properties of Er(III) ions on both an inert molybdenum (Mo) electrode and a liquid gallium (Ga) electrode. The results indicate that the reduction reaction of Er(III) belongs to a one-step of process involving the transfer of three electrons and the process is reversible within the range of scanning rates investigated on an Mo electrode. The diffusion coefficients at different temperatures were calculated on inert Mo electrode, and the activation energy of diffusion process was calculated to be 33.38 kJ mol-1. Subsequently, the electrochemical co-deposition of Ga(III) and Er(III) ions on an inert Mo cathode and the reduction of Er(III) ions on reactive Ga cathode were investigated, and the electrochemical mechanisms of the two reaction types were determined. Additionally, the oxidation-reduction potentials of the Er-Ga intermetallic compounds that may be appeared during the reaction were determined. The main thermodynamic properties of Er-Ga alloy were obtained by open circuit potentiometry, then the separation factors of U/Er couple were explored. Meanwhile, Er was effectively extracted as ErGa6 through potentiostatic electrolysis at -2.0 V for 12 h, achieving an extraction rate of approximately 98.3%.