Greening the supply chain: Sustainable approaches for rare earth element recovery from neodymium iron boron magnet waste

The increasing demand for modern technologies has led to a growing reliance on rare earth elements (REEs). To address this issue, recycling used products such as permanent magnet waste containing REEs. However, this approach necessitates the development of advanced extraction and separation techniques to ensure high yields and purity of the REEs extracted. This review provides an overview of the latest extraction and separation technologies, with a particular focus on the hydrometallurgical approach for extracting REEs from secondary sources, notably permanent magnets. Hydrometallurgy, which involves leaching followed by solvent extraction for purification, has gained widespread use for obtaining REEs from secondary sources, as evidenced by its reported high recovery efficiencies. We found that the recovery of REEs using chemical leaching varied between 80% and 99%, influenced by factors such as type of source material, leaching solvent, leaching conditions, impurities, reaction kinetics and solid-liquid ratio. However, effectively employing this process on a larger scale still faces certain challenges due to the excessive use of corrosive solvents for leaching magnet waste and the generation of toxic chemicals as end products in the form of leachate. Additionally, the current process exhibits deficiencies in the targeted recovery of REEs from magnet waste, specifically in achieving purity and selectivity by eliminating iron impurities. This article concludes that the future prospects for the selective recovery of REEs from neodymium iron boron magnet waste lie in green and environment-friendly solvents. One such approach revolves around the utilization of biodegradable organic acids and salt aqua regia for leaching. These solvents are less corrosive and have high dissolution efficiency, which results in less chemical consumption and an overall environment-friendly and cost-effective recovery process.