Electrochemistry of Neodymium in an Equimolar NaCl-KCl Melt without and with Addition of Fluoride Ions

Abstract

The paper presents the results of neodymium electrochemical behavior in chloride and chloride-fluoride melts. It was shown that the process of neodymium electroreduction in the NaCl-KCl-NdCl3 melt proceeds in two stages. By diagnostic criteria of voltammetry it was established that the discharge process of Nd(III) to Nd(II) at a sweep rate in the range of 0.6 ≤ ν ≤ 1.0 V s−1 is not complicated by disproportionation reaction. In this study diffusion coefficients, activation energy of diffusion for Nd(III) chloride complexes and standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple in the NaCl-KCl melt were determined. The nature of the working electrode on the standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple has been studied by cyclic voltammetry and electrochemical impedance spectroscopy. The formal redox potentials E * Nd(III)/Nd(II) in the NaCl-KCl melt were obtained from the cyclic voltammetry data. It was shown that the addition of fluorine anions into the NaCl-KCl-NdCl3 melt leads to stabilization of the higher oxidation state of neodymium in chloride-fluoride melts and the intermediate oxidation state Nd(II) does not exist in these melts.