Electroleaching of NdFeB Matrix from Spent Permanent Magnets in Organic Acids

Student report (2023)

Authors

J. Li Mechanical Engineering

Contributors

S.T. Abrahami Team Shoshan Abrahami (mentor)
Faculty
Mechanical Engineering
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Published Date

08-12-2023

Language

English

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Faculty

Mechanical Engineering

Abstract

Neodymium (Nd) recycling plays a significant role in rare earth elements (REEs) reproduction and spent neodymium-iron-boron (NdFeB) permanent magnets is a crucial resource for Nd. This study aims at investigating the anodic behaviour and dissolution properties of NdFeB magnets during electroleaching in four biodegradable organic acids to indicate a suitable environmentally friendly and safe reagent that promotes electroleaching. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) characterization revealed that the metallic coating of the magnet was made of zinc. SEM-EDS analysis of polished sample surface showed the Nd-rich phases were surrounded by the matrix. Then open circuit potential (OCP) and linear scanning voltammetry (LSV) measurements were carried out to study the anodic behaviour of NdFeB. The comparison among the four organic acids at 1 M resulted in that citric acid and tartaric acid achieved the highest corrosion current with least negative OCP, as they have more carboxylic groups and higher acidities, while the lower OCP of formic acid compared to acetic acid which shows the lowest acidity revealed that the chemical leaching properties are not only dominated by acidity. But the higher corrosion current density of formic acid stated that the external potential reduced the influence of the factors other than acidity. Next, citric acid and formic acid were selected for studying the impact of concentration on anodic behaviours for their high corrosion current density and low price. Along the test that monitored the concentrations, 0.25 M citric acid was selected as the desired electrolyte for the higher corrosion current density compared to all groups of formic acid and low difference between citric acid at higher concentrations. The chronopotentiometry experiment for observing the influence of applied current density on the dissolved mass of NdFeB was failed to carry out due to the limited voltage range of the potentiostat. SEM-EDS characterization displayed that the NdFeB matrix formed a rough and porous surface after electroleaching, and the increase in test time and acid concentration promotes dissolution. The semi-quantitative composition analysis showed good dissolution properties of Nd-rich phases and praseodymium (Pr) when undergoing electroleaching in citric acid.

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