Electrochemical behavior of Neodymium and formation of Mg-Nd alloys in molten Chlorides

Abstract

The electrochemical behavior of Nd(III) and its coreduction with Mg(II) were investigated on a molybdenum electrode at 1023 K in eutectic NaCl-KCl melts. The results indicate that the reduction of NdCl₃ in NaCl-KCl melts is a one-step process with three electrons exchanged, and the reaction is an irreversible diffusion-controlled process at low scan rate with the calculated diffusion coefficient of about 6.8 × 10^-5 cm² s^-1. After MgCl₂ is introduced to the melts, the reduction of Nd(III) takes place at a more positive potential value due to the formation of Mg-Nd intermetallic compounds through electrochemical co-deposition and chemical reduction of Nd(III) ions by preferentially deposited Mg. The solid intermetallic compounds of Mg₃Nd, Mg₂Nd, and MgNd observed in open circuit chronopotentiometry curves are transformed to thermodynamically more stable Mg-rich phases of Mg₁₂Nd and Mg₄₁Nd₅ when potentiostatic electrolysis at -2.10 V. It has been confirmed by X-ray diffraction and SEM-EDS microscopy that the cathodic deposits are composed of Mg, Mg₁₂Nd, Mg₄₁Nd₅, and Nd. The present results confirm that it is an effective method for recycling of neodymium from waste NdFeB magnets by means of electrochemical formation of Mg-Nd alloys from NaCl-KCl-MgCl₂-NdCl₃ melts.