Significant efforts have been put into the recycling of bulk sintered NdFeB magnet wastes around the world in the past decade because bulk Nd–Fe–B sintered magnet wastes are valuable secondary rare-earth resources. There are two major facts behind the efforts. First, the waste magnets contain total rare-earth content as high as more than 30 wt.%, which is higher than most natural rare-earth mines. Second, the waste magnets maintain the physical and chemical properties of the original magnets even with deterioration of the properties on surfaces due to corrosion and contamination. In this review, various techniques for recycling bulk NdFeB sintered magnet wastes, the overall properties of the recycled NdFeB sintered magnets, and the mass production of recycled magnets from the wastes are reviewed.
Either researchers or magnet manufacturers have been put many efforts into the recycling of bulk sintered Neodymium magnet wastes due to the concerns of environmental protection and rare-earth resource supplies. The total rare-earth content in waste magnets is certainly around 30wt% which much higher than most natural mines. In the meanwhile, waste magnets are usually maintaining original magnet’s physical and chemical properties even with deterioration of the properties on its surface due to corrosion or contamination.
Sintered Neodymium magnet wastes are mainly come from industrial wastes and end-of-life wastes. Industrial wastes are produced through the entire production process of sintered Neodymium magnets, especially furnace slag during melting and strip casting, ultrafine powder during jet milling, defective parts during compaction and sintering, and scraps or sludge during the machining process. The machining process yields most of the industrial wastes of sintered Neodymium magnets. On the other hand, end-of-life wastes are come from the out-of-service devices which contain sintered Neodymium magnets.
Numerous solutions have been developed to recycle bulk sintered Neodymium wastes which contain machining scraps and end-of-life waste magnets. The main recycling techniques can be divided into waste magnets to recycle sintered magnets and waste magnets to magnetic powder or bonded magnets.