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

Abstract

Liquid metallic gallium demonstrates great potential as a reactive cathode with its excellent ability for the effective separation of fission products during the recovery of spent nuclear fuel in the “liquid metal-salt melt system”. In this study, 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. Results indicated that the reduction reaction of Er(III) belonged to a one-step process involving the transfer of three electrons, and the process was reversible within the range of scanning rates investigated on the Mo electrode. The diffusion coefficients were calculated at different temperatures on the inert Mo electrode, and the activation energy of the diffusion process was calculated to be 35.575 kJ mol⁻¹. Subsequently, the electrochemical co-deposition of Ga(III) and Er(III) ions on the inert Mo cathode and the reduction of Er(III) ions on the reactive Ga cathode were investigated, and the electrochemical mechanisms of the two reactions were determined. Additionally, the oxidation–reduction potentials of the Er–Ga intermetallic compounds that appeared during the reaction were determined. The main thermodynamic properties of Er–Ga alloy were obtained using open circuit potentiometry, and the separation factors of the 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%.