Recovery of Alkaline-Earths into Liquid Bi in Ternary LiCl-KCl-SrCl₂/BaCl₂ Electrolytes at 500 °c

Electrochemical reduction of Sr²⁺ and Ba²⁺ into liquid Bi was investigated in dilute concentrations of SrCl₂/BaCl₂ (05 mol%) in LiCl-KCl electrolytes at 500 °C to ascertain the limit of liquid Bi electrodes for alkaline-earth recovery. Analysis of the electrodes after constant current electrolysis to the specific charge of 270 C g^-1 showed Sr²⁺ ions consuming 29% of charge at 5 mol% before dropping to 8%10% of the total charge at 0.450.72 mol% SrCl₂. Ba²⁺ ions consumed 54% at 5 mol% BaCl₂ before decreasing to 22%24% at 0.420.89 mol% BaCl₂; substantial co-deposition of Li was observed in all chemistries, consuming up to 53% of charge. Considering only 1% of the total charge was consumed for depositing Ba²⁺ and Sr²⁺ ions in ∼0.1 mol% SrCl₂/BaCl₂ electrolyte, the lower recovery limit of Bi for alkaline-earth elements is suggested to be at ∼0.4 mol% SrCl₂/BaCl₂ to achieve appreciable deposition of alkaline-earths (>1.5 mol% Ba/Sr in liquid Bi). The overpotentials of liquid Bi at 5 mol% of SrCl₂/BaCl₂ were evaluated by electrochemical impedance spectroscopy. The co-deposition of Sr and Li exhibited the largest increase in charge transfer resistances implying sluggish charge transfer kinetics whereas the co-deposition of Ba and Li exhibited a large increase in mass transport resistances due to the slow diffusion of Ba²⁺ ions in the electrolyte.