Recycling of Waste NdFeB Magnets by Supergravity-enhanced Impurity Removal

NdFeB magnets are the most widely used rare earth permanent magnet materials at present. The increasing number of the waste NdFeB magnets and their high rare earth content motivate a search for technologies to allow their cost-effective and environmental-friendly recycling. In this study, removal of oxide inclusions from waste NdFeB magnets by supergravity technology was investigated and the separating conditions were optimized for maximum oxide removal. Under the optimized conditions of G = 800 and t = 15min, the total oxygen of the sample decreased from 410 ppm to 28 ppm, with the oxide removal efficiency of 96.8%. The theoretical time to remove inclusions with different sizes was calculated by Stokes' law, and the experimental phenomena were in good agreement with the calculated ones. The supergravity technology has been demonstrated highly efficient in removing oxide from waste NdFeB magnets for the recycling. A design for an industrial reactor was presented to pave the way for future commercial processing and utilization of waste NdFeB magnets.