Abstract
Carbothermal reduction technique was applied to extract rare earth elements from the machined powders of R-Fe-B based magnets, where R is Nd, Pr, Dy etc., generated as waste from the manufacturing process. After the oxidizing process to oxidize the powders and the reduction process to reduce iron oxide to iron metals by carbon, the powders were separated to the pig iron which mainly contained Fe and the slag which mainly contained rare earth elements. During the oxidizing process, the rare earth elements in the machined magnet powders needed to be oxidized, which could be achieved by heat-treatment at more than 1173 K for 1 hour under an air atmosphere. During the reduction process, the oxidized powders needed to be heat-treated at more than 1323 K under an argon atmosphere to separate them into the pig iron and slag. However, to separate these phases mechanically, the powders needed to be heat-treated at more than 1673 K, which is higher than the melting points of these two substances. And though the melting points of most of rare earth oxides are over 2173 K, the existence of B in the slag makes the melting point lower, which enables to separate to pig iron and slag at a temperature under 2173 K. Using this technique 93.6% of the rare earth elements were extracted from the machined magnet powders.
