With rapid growth in the use of NdFeB magnets and growing concerns for environmental protection as well as conservation of rare earths (REs), the recycling of NdFeB magnet scrap is becoming a hot issue for current society. In this study, it is demonstrated that the rare earths in a NdFeB magnet can be selectively extracted using molten MgCl 2 −KCl salts at temperatures of 600−1200°C. After crushing to granules, the scrap was subjected to molten chlorides in a dry argon atmosphere. The reaction process between NdFeB scrap and molten MgCl 2 −KCl was directly observed using a high-temperature contact angle measuring instrument to clarify the phenomena that occur when rare earth chlorides are formed in situ. Furthermore, the effects of reaction temperature, holding time, and mass ratio of MgCl 2 / NdFeB were investigated to transform REs in the scrap to RECl 3 as completely as possible. The reaction products were examined with the necessary analytical techniques including SEM, EDS, XRD, and ICP. The overall extraction efficiency for REs was found to be more than 90% under the optimum operating conditions. The obtained RECl 3 in the molten MgCl 2 −KCl can be processed with molten salt electrolysis for the direct production of Mg−Nd alloy.
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 onestep 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.
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