EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Since the NdFeB magnets are easily oxidated, it can lead to enhance rapidly oxygen concentration, and it can be directly related to the REE-extraction efficiency. Thus, the control of the oxygen concentration is a significant role in the process of pulverizing for recycling. In this study, the effect of hydrogen decrepitation and disproportionation are investigated in the liquid metal extraction (LME) process. Through the differential thermal analysis (DTA) in a hydrogen atmosphere, it is observed that the temperature dependence of phase decomposition reaction behavior and hydrogen decrepitation. Based on the results, the samples are prepared by the hydrogen spraying vacuum furnace with increasing temperature and time. For the characterization of microstructure and phase distribution, the Field Emission Scanning Electron Microscopy (FE-SEM) and X-Ray diffraction (XRD) measurement is carried out. It shows that the hydrogen is easily desorbed in the Nd-rich phase and it is possible to be completely crushed while effectively preventing oxidation even at low temperature. With increasing temperature, there is phase decomposition of NdFeB magnet with hydrides. In optimized condition, it is observed that the 82% of heavy rare earth is extracted from the REE magnets in the LME process. On the contrary, in the mechanically milling process as the control group, it is observed that the residual Nd2O3 and Dy2O3 are attributed to the relatively low amount of REE-extraction (maximum 75%) due to the high oxygen concentration of the powder before the reaction.