C. Stinn, Z.K. Adams, A. Allanore
Massachusetts Institute of Technology,
Keywords: magnet recycling, sulfidation, neodymium, dysprosium, iron-neodymium-boron
Summary:With shifting trends towards sustainability and electrification, critical rare earth elements such as neodymium and dysprosium are becoming increasingly foundational across all sectors of industry, manufacturing, and consumption. Green and digital technologies required for electric vehicles, data storage, pollution control catalysts, and infrastructure all rely on these and other rare earth elements to meet modern performance standards. However, growing demand for such critical elements presents technical, sustainability, and logistical challenges. In primary mineral sources, all of the rare earth elements (lanthanides, scandium, and yttrium) coexist and must be co-processed to produce individual, high-demand elements. Due to the chemical similarity of individual rare earth elements, currently employed hydrometallurgical extraction processes are highly water, reagent, and energy intensive, leading to large costs and environmental footprints. Meanwhile, rare earth mineral reserves and refining facilities are geographically concentrated overseas, causing these critical elements to be at risk of geopolitical or supply disruption. Recycled sources of rare earths such as e-waste are alternative avenues to mitigate supply risks and support selective recovery of high-demand elements like neodymium. However, secondary sources of rare earths are generally more dilute than those in primary minerals and exhibit higher rates of ferrous and base metal impurities. These challenges necessitate the design of new rare earth processing and extraction pathways better suited to sustainably and economically manage impurities. Selective sulfidation is a promising new technology and process chemistry to enable targeted rare earth element recycling and recovery. Through the use of simple process controls and readily scalable reactor technology, rare earth elements can be selectively isolated from impurities, enabling efficient remanufacturing of rare earth feedstocks for advanced electronic and sustainability applications. Unlike conventional hydrometallurgical extraction which is dependent on dissolution processes and high rates of water and chemical usage, sulfidation is conducted dry using elemental sulfur as a reagent, reducing costs and environmental impact by 60-90%. Herein, we apply selective sulfidation for the recycling of rare earth elements from magnet e-waste. We present results for laboratory-scale recycling of iron-neodymium-boron magnets using sulfidation chemistry. Through a series of simple sulfidation, thermal treatment, and physical separation steps, we achieve separation efficiencies for critical rare earth elements that exceed conventional hydrometallurgy processing routes by 100x or more. We then discuss the propagation of ferrous and base metal impurities through the sulfidation recycling process, identifying engineering avenues for process refinement. Finally, we discuss the scalability of these process steps and identify a preliminary flowsheet for industrial deployment of rare earth element separation and recovery via sulfidation chemistry.