Metal Leaching and G-METS Distillation for Neodymium Magnet Scrap Recycling

Chinwego, Chinenye

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Metal Leaching and G-METS Distillation for Neodymium Magnet Scrap Recycling

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The importance of rare earth metals for clean energy technology and the threat to their supply has prompted several researchers to consider alternative techniques to mining. One strategy that is gaining traction in this area is recycling. Recycling has been proposed as a promising potential supply source to meet some of the US rare-earth demand for use in permanent magnets. Besides reducing the environmental impact of mining for rare earth metals, recycling offers manufacturers a commercially viable alternative. Studies show that the concentration of rare earth in end-of-life devices and waste streams is higher than in ores. The high growth rates of products that use rare-earth magnets, particularly wind turbines and electric and hybrid vehicles, highlight that their stock in use is on the rise and, in the near term, will become available as scrap feed for recycling. Various studies have shown that the magnet-to-metal recycling method, in which rare earth metals such as neodymium, praseodymium, and some traces of dysprosium and terbium can be leached from the magnet and obtained as recycled mixed rare earth metal which may be used as a precursor for the manufacturing of rare earth magnets. This thesis provides an introduction to magnet recycling technologies. It evaluates the techno-economic analysis of liquid metal leaching and distillation, including the effect of a new continuous gravity-driven multiple effect thermal system (G-METS) metal distillation technology on energy use and overall cost. The G-METS system can potentially reduce the energy consumption of the overall process to 64 kWh/kg, which is about 30% less than metal production from ore and 61–67% less than the conventional process distillation. A commercialization study is also presented. It suggests that the commercial viability of rare earth magnet scrap recycling depends on a consistent supply of high-quality scrap material, the demand for rare earth magnets, and the cost of virgin rare earth metals from primary production. Incentivizing the collection of rare earth magnet scraps and their recycling can foster the development of viable recycling technologies. This study further assesses the leaching and distillation of rare earth magnets using magnesium. It demonstrates magnesium’s effectiveness as a leaching agent for rare earth metals. It further presents a reduced-order model that predicts a three-effect distiller's distillation temperatures and production rates. The effect of neodymium activity on the distillation of Magnesium-neodymium alloy compared to pure magnesium is presented. The results of the reduced-order model were benchmarked using a third-party distillation model for magnesium-aluminum-zinc alloys. Models of distillation for magnesium and bismuth can be used for scale-up reactor engineering.

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