Investigation on Nd Metal Production via Electrolysis of Nd2O3 in NdF3–LiF Molten Salt under Saturated Nd Metal Condition

In this study, the electrolysis of Nd2O3 in a NdF3–LiF molten salt under saturated Nd metal condition was systematically investigated. The saturated Nd metal condition was determined by holding Nd metal in a 70–90 mass% NdF3–LiF molten salt at 1323–1423 K for 9 h under Ar gas atmosphere, and the results revealed that the saturated Nd metal condition corresponded to approximately 1.36–3.77 mass% relative to the salt charge. Electrolysis of Nd2O3 was conducted in NdF3–LiF molten salts containing 10–30 mass% LiF with pre-added Nd metal concentration of 2.5 mass% relative to the salt charge at 1323–1423 K with cathodic current densities of 2.1–10.5 A/cm2 for 2.0–10.0 h. After electrolysis, bulk Nd metal was produced with average cell voltages measured of 1.44–3.19 V, and the highest current efficiency of 55.4% was obtained after the electrolysis in a 90 mass% NdF3–10 mass% LiF molten salt at 1323 K with a cathodic current density of 6.3 A/cm2 for 3.4 h. Further increasing the electrolysis temperature, concentration of LiF, or cathodic current density resulted in a decrease in current efficiency. In addition, no Nd metal was obtained when electrolysis was conducted without establishing the saturated Nd metal condition. This study is expected to provide a practical approach for the reliable evaluation of current efficiency in laboratory-scale Nd2O3 electrolysis by approximating the saturated Nd metal condition formed during continuous industrial operation.