The use of thermal hydrogen decrepitation to recycle Nd-Fe-B magnets from electronic waste

Abstract

Rare earth magnets based upon neodymium-iron-boron (NdFeB) are employed in many high tech applications, including hard disk drives (HDDs). The key elements in manufacturing NdFeB magnets are rare earth elements (REEs) such as neodymium. This element has been subject to significant supply shortfalls in the recent past. Recycling of NdFeB magnets contained within waste of electrical and electronic equipment (WEEE) could provide a secure and alternative supply of these materials. Various recycling approaches for the recovery of sintered NdFeB magnets have been widely explored. Hydrogen decrepitation (HD) can be used as a direct reuse approach and effective method of recycling process to turn solid sintered magnets into a demagnetised powder for further processing. In this work, sintered Nd-Fe-B magnets were processed without prior removal of the metallic protective layer using the thermal HD process as an alternative recycling method. The gas sorption analyzer was used to determine the quantity of the hydrogen absorbed by a samples of magnets, under controlled pressure (1, 2, 3, and 4 bar) and temperature (room, 100, 300, and 400?C) conditions, using Sieverts? volumetric method. The composition and morphology of the starting and the extracted/disintegrated materials were examined by ICP, XRD, and SEM-EDS analysis.

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

“…Finally, they found that the overall hydrogenation process accelerates, and the blasting power reduces with increasing pressure. Despite the results found by Li, Piotrowicz et al reported a slight increase in maximum hydrogen uptake by increasing the pressure from 2 to 4 bar. It was reported that complete decomposition occurs at an operating pressure of 2–4 bar.…”

“…The HPMS is based on the difference in reactivity of the Nd-rich phase and the matrix of Nd 2 Fe 14 B grains upon exposure to hydrogen gas. Due to the formation of neodymium hydride in the Nd-rich phase and induced expansion, the entire structure of the magnet is collapsed and converted into powder form. , Due to some differences between the two existing hydrogenation methods (HD and HDDR) and the similar terminology, it is necessary to present them separately.…”

“…The common nickel coating with a thickness of about 13 μm can be easily removed or damaged manually or by electrochemical technology. ,,, Damaging the coating by bending and breaking the magnets is preferable to complete decoating, as this provides sufficient free surface area for hydrogen diffusion and prevents a higher degree of oxidation . Piotrowicz et al reported that the optimal pressure of hydrogenation decreases from 2–4 bar to 1–2 bar by removing the coating layer before hydrogenation. Michalski et al reported that some damage occurred to EoL NdFeB magnets collected from hard drives during magnet separation without intentional intervention.…”

“…They attributed this phenomenon to grain growth. In addition, Piotrowicz et al 49 reported that the maximum hydrogen uptake into the magnet’s bulk decreases significantly with increasing hydrogenation temperature. This group of researchers stated that the temperature should be less than 100 °C to achieve complete decrepitation and that samples subjected to hydrogenation at higher temperatures partially decrepitated, and the lowest degree of decrepitation occurs at 400 °C.…”

“… 51 The common nickel coating with a thickness of about 13 μm can be easily removed or damaged manually or by electrochemical technology. 28 , 49 , 53 , 74 Damaging the coating by bending and breaking the magnets is preferable to complete decoating, as this provides sufficient free surface area for hydrogen diffusion and prevents a higher degree of oxidation. 28 Piotrowicz et al 49 reported that the optimal pressure of hydrogenation decreases from 2–4 bar to 1–2 bar by removing the coating layer before hydrogenation.…”