Progress in recycling of Nd–Fe–B sintered magnet wastes*

Abstract

Significant efforts have been put into the recycling of bulk Nd–Fe–B sintered 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 Nd–Fe–B sintered magnet wastes, the overall properties of the recycled Nd–Fe–B sintered magnets, and the mass production of recycled magnets from the wastes are reviewed.

Green and Sustainable Rare Earth Element Recycling and Reuse from End-of-Life Permanent Magnets

“…Currently, recycling practices focus more on the recycling of sintered NdFeB magnets than on the recycling of resin-bonded ones, as they occupy the main market and also concentrate more resources [32,33]. Sources of NdFeB sintered magnet waste are industrial waste and end-of-life waste from decommissioned devices containing NdFeB sintered magnets [28,32]. For example, during the shaping and finishing process, up to 30% of the raw materials are wasted as scraps during NdFeB production [24].…”

“…Thus, the rising opportunity for recycling a variety of products containing NdFeB magnets allows a systematic approach to recycling scrap magnets as a potential secondary resource [8]. Different treatment approaches for recycling REE-containing spent magnets [27] or scrap have been extensively investigated [28][29][30].…”

Direct Recycling of Hot‐Deformed Nd–Fe–B Magnet Scrap by Field‐Assisted Sintering Technology

“…Sintered magnets are produced through a conventional powder metallurgy method, in which Nd-Fe-B single-crystal microcrystalline powders are magnetically aligned by applying a strong magnetic field when compacted into a green body, and freely sintered. [13] Hot-deformed Nd-Fe-B magnets also start from nanocrystalline powders, but they are instead hot pressed and subsequently hot deformed or backextruded to obtain a fully dense magnet with a pronounced texture and anisotropic microstructure. [14] Bonded magnets are formed from the combination of fine Nd-Fe-B powders with small crystallite size, typically prepared with melt spinning or hydrogenation-disproportionation-desorption-recombination (HDDR), with a polymer binder, such as epoxy.…”

“…The crushing of sintered Nd-Fe-B magnets for recycling has been performed with the primary goal of producing anisotropic polymer bonded magnets. [13,28,29] However, in a polymer bonded magnet, the remanence, which is the amount of magnetic induction that remains after magnetization, and energy product would be compromised relative to a sintered magnet, as binder volume, pore volume, and misorientation of the grains/powder. [30][31][32] To achieve the highest possible B r , recycled magnets would have to be reformed into a fully dense sintered or hot-deformed magnet.…”