Recovery of Rare Earths from Magnet Sludge by FeCl<SUB>2</SUB>

Abstract

A large amount of neodymium magnet sludge is generated during the manufacture process. Because the sludge is considerably contaminated by oxygen, it is difficult to reuse it as it is. The present basic study has been carried out to establish efficient recycling process of the sludge. The rare earths in the neodymium magnet sludge were extracted by chlorination with FeCl2. An activated carbon was used as a de-oxidation reagent. Metallic iron in the sludge was not chlorinated because the iron monochloride is not stable. The extracted rare earth chlorides were easily separated from Fe-alloy and the excess of FeCl2 by vacuum distillation. In this study, 96% of neodymium and 94% of dysprosium in the sludge were extracted into chloride phase. By the vacuum distillation, a mixture of neodymium and dysprosium trichlorides of 99.2% purity was recovered with the rare earth element’s yield of 76% for the charged sludge. In addition, it was confirmed that the rare earth chlorides can be converted to the corresponding oxides by a pyrohydrolysis reaction accompanied by a formation of HCl gas. The HCl gas can chlorinate metallic iron to FeCl2. Therefore, a new recycling process for rare earth magnet waste can be realized as a chlorine circulation type process. During the process, only carbon and water are consumed, and there are no toxic pollutants. Moreover, the obtained rare earth oxide can be directly used as raw material in the oxide electrolysis, which is the conventional industrial reduction process for rare earth metal production.