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Recycling 2017, 2(4), 22;

Hydrocyclone Separation of Hydrogen Decrepitated NdFeB

School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
Author to whom correspondence should be addressed.
This paper is an extended version of our paper published in 6th International Conference Quo Vadis. Recycling, High Tatras, Slovak Republic, 6–9 June 2017.
Received: 23 August 2017 / Revised: 31 October 2017 / Accepted: 13 November 2017 / Published: 14 November 2017
(This article belongs to the Special Issue Quo Vadis Recycling 6)
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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. View Full-Text
Keywords: hydrocyclone; centrifugal separation; fine particle separation; NdFeB; recycling; rare earth elements hydrocyclone; centrifugal separation; fine particle separation; NdFeB; recycling; rare earth elements

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Awais, M.; Coelho, F.; Degri, M.; Herraiz, E.; Walton, A.; Rowson, N. Hydrocyclone Separation of Hydrogen Decrepitated NdFeB. Recycling 2017, 2, 22.

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