Electrochemical study of reduction Ce(III) ions and production of high purity metallic cerium by electrorefining in fused LiCl-KCl eutectic

The electrode reactions of the Ce³⁺/Ce couple in molten LiCl–KCl eutectic in the temperature range 723–823 K on solid Mo electrodes were investigated by electrochemical techniques. The mechanism of deposition of metallic cerium has been established. It was found that the cathode reaction is irreversible and proceeds in one stage. The apparent standard Gibbs energy of CeCl₃ formation from the elements was calculated. The values of enthalpy and entropy were equal: ΔH* = − 1000.2 kJ/mol, ΔS* = 166.0 J/mol·K. The conditions of high-purity cerium production have been studied. The chemical structure of cathode deposits as well as the surfaces of the crucible were investigated by XRD, ICP and SEM-EDS methods. It was established that the best results for purification of the cathode product from impurities were achieved in the range 40–60 mA/cm² using a two-stage electrolysis. The amounts of the main impurities in the final product were 0.005 wt% Al, 0.0021 wt% Fe, and 0.003 wt% Si. The total purity of metallic cerium after cleaning was increased up to 99.971 wt% if a vitreous carbon crucible was used.