Recovery of valuable metals from NdFeB magnets by mechanochemically assisted ferric sulfate leaching

A new hydrometallurgical method for the recovery of rare-earth elements and Co from permanent NdFeB magnets by mechanochemically assisted ferric sulfate leaching was developed. The overall process consists of the following steps: (1) activation of the NdFeB magnet powder and ferric sulfate powder by grinding, resulting in a mechanochemical conversion of the metals to their corresponding water-soluble sulfates; (2) recovery of the rare-earth elements and cobalt by leaching the activated powder in water, with sequential removal of the solid residue by filtration; (3) precipitating the rare-earth elements by oxalic acid, removing the mixed rare-earth oxalates by filtration; and (4) calcining the rare-earth oxalates to form the corresponding oxides. This hydrometallurgical process excludes the necessity of using mineral acids or pyrometallurgical pre-treatments steps, avoiding the production of hydrogen gas or pollutants (e.g. NOx or SO2). A low-intensity grinding operation was sufficient to improve both the leaching yield of the rare-earth elements and the selectivity against iron. In addition, the complete leaching process could be carried out at room temperature. The remaining acidic leachate, rich in Fe(II) can be reused after conversion of Fe(II) in Fe(III). In this way, the process consumes only minor amounts of the cheap ferric sulfate, oxalic acid, water and is low energy intensive providing a green and novel perspective for metal recovery from NdFeB magnets.