Electrochemical Behavior of Neodymium and Formation of Mg–Nd Alloys in Molten Chlorides

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.