Hydrocyclone Separation of Hydrogen Decrepitated NdFeB

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 (Nd 2 Fe 14 BH x ) 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.

Leaching and Recovery of Rare-Earth Elements from Neodymium Magnet Waste Using Organic Acids

“…No clusters with higher concentration of certain elements than in the bulk material were found. Some locations on the powder-like the one represented by Line 1 in Figure 1a and point 2 in Figure 1b-showed higher amounts of oxygen, which can be attributed to the fact that the REE-rich grain boundary phase oxidizes fast when exposed to air during the HD process [33].…”

The Future of Permanent-Magnet-Based Electric Motors: How Will Rare Earths Affect Electrification?

“…This additional oxygen is mainly trapped in the REE-rich materials; e.g., this is a huge problem as they do not sinter at the low temperatures of regular magnet sintering. This produces low-density parts with low hard magnetic values [51,52]. Additions of either several wt.% NdH 2 [53] to the recycled powder or extra Dy [54] are thus needed to induce an increase in the coercivity to the original values.…”

High-effective magnetic hydrocycloning equipment for magnetite ore processing

“…Efficiency of sizing in such ma chines is governed by the milling circuit efficiency and also by the performance of all subsequent process flows at a concentration factory. The studies aimed at reduction of size of particles effectively separated by hydrocyclones are in progress [2,3]. Magnetic field allows separating even submicron particles [4].…”