Cathodic processes of neodymium(iii) in LiF–NdF3–Nd2O3 melts

Abstract

In this paper, cyclic voltammetry and square wave voltammetry are applied to characterize the cathode processes of neodymium ions on a W electrode in LiF–NdF₃ melts with or without the metal Nd. The results indicate that neodymium ions in the LiF–NdF₃ (2 wt%) melt are reduced in two steps, i.e. Nd³⁺ → Nd²⁺ and Nd²⁺ → Nd⁰, corresponding to starting reduction potentials of 0.35 V vs. Li⁺/Li and 0.1 V vs. Li⁺/Li, respectively. The Nd³⁺ → Nd²⁺ process is controlled by mass transfer and the Nd²⁺ → Nd⁰ process is controlled by both an interfacial step and mass transfer. But in the LiF–NdF₃ melt with excess metal Nd equilibrium, the kinetics of the above two processes are controlled by mass transfer. After potentiostatic electrolysis at 0.35 V in the LiF–NdF₃–Nd₂O₃ melt NdF₂ is formed on the Mo cathode, and metallic Nd is obtained by potentiostatic electrolysis at 0.1 V in the LiF–NdF₃–Nd₂O₃–Nd melt, which validates the above electrochemical reduction results.