Recycling of rare earth elements from SmCo_5-Magnets via solid-state chlorination

摘要

The recycling of rare earths from End-of-Life permanent magnets is a widely studied field of research. However, with rare earth prices falling, recycling processes have become increasingly uneconomical. In this context, solid-state chlorination has been intensively studied as this method has the potential to serve as an alternative to acid leaching. Instead of a mineral acid dissolving the magnets, a chlorination takes place by decomposing NH4Cl at temperatures between 225 and 325 degrees C. The resulting dry HCl forms water-soluble chlorides from the magnet material. For rare earth recycling from Fe14Nd2B magnets, the method was found to provide significant advantages in terms of consumption of chemicals as well as and chemical costs. The present work sheds light on another obstacle of magnet recycling, which is the inhomogeneous composition of the starting material. Only 2% of the total end-of-life magnet waste material contains SmCo magnets. Fe14Nd2B magnets account for most of the waste material. SmCo magnets are nevertheless the second most important group of rare-earth-based permanent magnets. However, they are not collected separately, and recycling processes have to focus on recovering both magnet alloys within one process. Therefore, the solid-state chlorination of SmCo5 magnets was examined in detail. The present work focusses consequently on three major issues: (i) Adjustment of solid state chlorination so that SmCo alloys can be chlorinated under the same conditions as Fe14Nd2B magnets. This is the most important requirement for a recycling process that utilizes both types of rare earth magnets. (ii) Examination of the reaction of SmCo with NH4Cl. It was found that the chlorination behaviour differs significantly from that of the Fe14Nd2B magnets. The particles arising from SmCo5 disintegrate more rapidly than expected during chlorination, which eventually enables an almost selective chlorination of samarium. (iii) Furthermore, Sm yields were optimised to reach 99.7% by applying a design of experiments. (C) 2019 Elsevier Ltd. All rights reserved.