Microwave-Assisted Carbothermic Reduction of Discarded Rare Earth Magnets for Recovery of Neodymium and Iron Values
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https://doi.org/10.1007/s11837-020-04409-9 2020 The Minerals, Metals & Materials Society
ADVANCES IN THE CIRCULAR ECONOMY OF LANTHANIDES
Microwave-Assisted Carbothermic Reduction of Discarded Rare Earth Magnets for Recovery of Neodymium and Iron Values HIMANSHU TANVAR1 and NIKHIL DHAWAN
1,2
1.—Metallurgical and Materials Engineering, Indian Institute of Technology, Roorkee, Roorkee, Uttarakhand 247667, India. 2.—e-mail: [email protected]
IIT-
Neodymium-iron-boron (NdFeB) waste magnets consist of approximately 28% rare earth values in the form of the Nd2Fe14B phase. According to the results, carbothermic reduction through microwave irradiation of crushed magnets was observed to be promising for the separation of metallic iron and rare earth values. The effect of microwave exposure time and charcoal addition on the formation of different phases was evaluated. Carbothermic reduction (10% C) for 1.2 min raised the temperature of the sample to 990C and resulted in the formation of iron balls with more than 85% purity. Higher exposure time favors the formation of the NdFeO3 phase, thereby encapsulating the rare earths, resulting in limited dissociation. Rare earth oxides with purity of more than 98% were recovered via a leaching and precipitation route. The microwave route was found to be superior to the conventional muffle furnace heating route with low energy consumption and metallic iron formation.
INTRODUCTION Neodymium-iron-boron (NdFeB) magnets are extensively used in electronic devices (laptops, music players, cell phones, hard drives), wind turbines, electric vehicles, magnetic cooling systems, etc.1,2 NdFeB magnets are comprised of 25– 35% rare earth elements (REEs) (Nd, Dy, Pr), with the rest being Fe, while modification of some physical and magnetic properties as per application can be done by adding Al and Co.3 An approximately 400-kg NdFeB magnet is required in a wind turbine for production of 1 MW electrical energy, and an electric vehicle motor uses an approximately 2-kg magnet, reflecting a considerable quantity of NdFeB waste to be considered as a potential source, which can be procured easily.4 The increasing demand for and limited production of REEs, including Nd and Dy from primary sources, draws attention to the recovery of REEs from secondary sources.1,2 It has been reported that recycled magnets have greater energy efficiency (75%) compared with magnet production from primary resources (60%).5 The REE content in the sorted magnet ( 25%) is quite high compared with primary deposits (0.15–3%).6,7
(Received July 14, 2020; accepted September 22, 2020)
Magnets collected from discarded instruments provide a potential REE source with several advantages such as reducing landfill problems and environmental impact.8,9 Hydrometallurgical and pyrometallurgical processing routes provide various opportunities to extract REEs from waste NdFeB magnets. Pyrometallurgy based routes are energy-intensive with high reaction temperatures (1000–1500C), duration (6– 24 h), and excess flux dosage (S
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