Electrochemical deposition of alkaline-earth elements (Sr and Ba) from LiCl-KCl-SrCl2-BaCl2 solution using a liquid bismuth electrode

Abstract

Electrochemical deposition of Sr and Ba into liquid Bi metal was investigated in LiCl-KCl-SrCl2-BaCl2 electrolytes at 500 °C as a means to separate stable alkaline-earth ions from the molten salts (eutectic LiCl-KCl) utilized for recycling used nuclear fuel, by leveraging the strong chemical interactions between alkaline-earth metals and liquid Bi. The liquid Bi electrodes were subjected to cathodic discharge up to 270 C g–1 at a constant current density of 50 mA cm−2 in eutectic LiCl-KCl with the addition of 5 mol% total of SrCl2 and/or BaCl2. The use of Bi resulted in complex electrode reactions, leading to co-deposition of Sr (2.0–6.5 mol%), Ba (4.1–12.8 mol%), and Li (5.9–16.2 mol%), and coulombic efficiencies of 63–67% were achieved. The observed co-deposition was also supported via thermodynamic analyses of electrode potentials by incorporating the experimentally determined activity values of each alkali/alkaline-earth metal in Bi. The results of this work suggest that alkaline-earth fission products accumulated in molten salts (Sr2+ and Ba2+) can be recovered into liquid Bi by electrochemical separation, which could be employed as a critical step for recycling the process salt (LiCl-KCl) in order to minimize the generation of additional nuclear wastes.