Electrochemical Extraction of Nd from NaCl-KCl Melt by Formation of Cu-Nd Alloys

Abstract

Electrochemical behavior of Nd was studied in NaCl-KCl melt on W and Cu electrodes via cyclic voltammetry and chronopotentiometry. Generally, the reduction of Nd³⁺ takes place in two consecutive steps in molten chlorides, such as LiCl-CaCl₂, LiCl-BaCl₂, CaCl₂-NaCl, LiCl-KCl melts. However, the reduction of Nd³⁺ ions was found to be through a one-step process: Nd³⁺ + 3e⁻ → Nd. The co-reduction behavior of Nd³⁺ and Cu²⁺ ions and the mechanisms of alloy formation were investigated in NaCl-KCl melt on W electrodes at 988 K (715 °C). Four potential plateaus corresponding to four different kinds of Cu-Nd intermetallic compounds were detected. Cu-Nd alloys were prepared on Cu electrodes at 988 K (715 °C) and 1143 K (870 °C). At 988 K (715 °C), Cu₅Nd phase was identified by X-ray diffraction. The morphology and micro-zone chemical analysis of the alloys were characterized by scanning electron microscopy equipped with energy-dispersive spectrometry. The alloy film was observed on the Cu electrodes. Moreover, at 1143 K (870 °C), a globate bulk Cu-Nd alloy with Cu₅Nd, Cu₄Nd, Cu₂Nd, CuNd, and Cu phases, as liquid in the melt, was obtained at the bottom of the crucible.