Molten salt/liquid metal extraction: Electrochemical behaviors and thermodynamics properties of La, Pr, U and separation factors of La/U and Pr/U couples in liquid gallium cathode

Abstract

The electrochemical behavior of lanthanides (La, Pr) and actinide (U) on inert W and liquid Ga electrodes in LiCl-KCl molten salt as well as their related thermodynamic properties were experimentally determined for further Lns/Ans separation. The results indicate that the reductions of La³⁺ and Pr³⁺ in LiCl-KCl melts are both one-step process with three electrons exchanged, and the reactions are quasi-reversible processes at low scan rate. Temperature dependencies of apparent standard redox potentials of La(Ga), Pr(Ga) and U(Ga) alloys were determined by open-circuit chronopotentiometry versus Cl^-/Cl₂ reference electrode. The activity and activity coefficients of lanthanum, praseodymium and uranium on the liquid Ga electrode in the temperature interval 723-813 K were calculated. The separation factors for La/U and Pr/U on the liquid Ga electrode in the molten salt were determined by logθ_U/La=-10.39+11440.69T±0.0125 and logθ_U/Pr=-5.84+7763.27T±0.07. The separation factors of La/U and Pr/U on the liquid Ga electrode indicate that lower temperature should be more effective for separating uranium.

Keywords: Lanthanides; Liquid Ga; Separation factor; Thermodynamic properties; Uranium.