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 NdCl 3 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 cm 2 s –1 . After MgCl 2 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 Mg 3 Nd, Mg 2 Nd, and MgNd observed in open circuit chronopotentiometry curves are transformed to thermodynamically more stable Mg-rich phases of Mg 12 Nd and Mg 41 Nd 5 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, Mg 12 Nd, Mg 41 Nd 5, 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–MgCl 2 –NdCl 3 melts.