Abstract
Hydrogen decrepitation (HD) is an effective and environmentally friendly technique for recycling of neodymium-iron-boron (NdFeB) magnets. During the HD process, the NdFeB breaks down into a matrix phase (Nd2Fe14BHx) and RE-rich grain boundary phase. The grain boundary phase in the HD powder is <2 μm in size. Recycled NdFeB material has a higher oxygen content compared to the primary source material. This additional oxygen mainly occurs at the Rare Earth (RE) rich grain boundary phase (GBP), because rare earth elements oxidise rapidly when exposed to air. This higher oxygen level in the material results in a drop in density, coercivity, and remanence of sintered NdFeB magnets. The particle size of the GBP is too small to separate by sieving or conventional screening technology. In this work, an attempt has been made to separate the GBP from the matrix phase using a hydrocyclone, and to optimise the separation process. HD powder, obtained from hard disk drive (HDD) scrap NdFeB sintered magnets, was used as a starting material and passed through a hydrocyclone a total number of six times. The X-ray fluorescence (XRF) analysis and sieve analysis of overflows showed the matrix phase had been directed to the underflow while the GBP was directed to the overflow. The optimum separation was achieved with three passes. Underflow and overflow samples were further analysed using an optical microscope and MagScan and matrix phase particles were found to be magnetic.
Highlights
The growing need for sustainable technologies is resulting in an increasing emphasis on the recycling of materials
Magnets—possess the highest energy product of all permanent magnets, which makes them highly efficient and suitable for lightweight mobile applications [1]. They are widely used in computer hard drives (HDDs), loudspeakers, medical imaging, household electrical appliances, hybrid and electric vehicles (HEVs and EVs), wind turbines, and many other small consumer electronic devices
A VCM magnet was mounted in conductive bakelite, and the microstructures were analysed using using software and Joel electron microscope (SEM)
Summary
The growing need for sustainable technologies is resulting in an increasing emphasis on the recycling of materials. This development is important in the case of rare earth elements (REEs). Magnets—possess the highest energy product of all permanent magnets, which makes them highly efficient and suitable for lightweight mobile applications [1]. They are widely used in computer hard drives (HDDs), loudspeakers, medical imaging, household electrical appliances, hybrid and electric vehicles (HEVs and EVs), wind turbines, and many other small consumer electronic devices. The amount being used varies between a few grams (e.g., loudspeakers) to tonnes of materials (e.g., wind turbines) [2]
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