Optimum conditions for extracting rare earth metals from waste magnets by using molten magnesium

Liquid-metal extraction using magnesium as a medium was studied to examine its suitability as an environmentally friendly process for recycling rare earth (RE) metals from magnets. To determine the optimum conditions for extracting RE metals, RE extraction experiments were conducted under various conditions. Effects of extraction period, temperature, and magnesium/magnet mass ratio on RE extraction efficiency were investigated. As these parameters were increased, extraction efficiency for neodymium increased and reached almost 100%. The efficiency for dysprosium increased as well but was limited to 60%, and some dysprosium remained in the magnet. It was found that RE metals partially exist as oxide in the initial magnet. It was also found that neodymium oxide was reduced by magnesium but that dysprosium oxide was not reduced completely. RE extraction experiments with calcium added as a reducing agent were therefore conducted, and result showed that extraction efficiency for dysprosium was improved to 74%. All tolds, the optimum conditions for RE extraction (with calcium added to a magnesium/calcium mass ratio of 20) are the extraction time of six hours, the extraction temperature of 1000 °C, and the magnesium/magnet mass ratio of 10.