Nowadays NdFeB magnets are widely used in many applications such as electric two-wheelers, air conditioners, hybrid and electric cars, MRI scanners, wind generators, HDD, acoustic transducers, magnetic separators, etc. Thus, the global demand for NdFeB magnets is expected to continuously increase in the near future.
However, the supply of rare earth elements including neodymium, praseodymium and dysprosium for NdFeB magnets does not meet this growing demand, so rare earth elements are regarded as critical elements. Despite their criticality, less than 1% of rare earths are being recycled from end-of-life rare earth permanent magnets. Moreover, during the manufacturing process of NdFeB magnets, approximately 20~30% of rare earth alloy are lost and stockpiled as industrial waste. Therefore, development of an efficient recycling process for separation and recovery of rare earths from end-of-life products and magnet waste is an important issue.
Rare earth double sulfate precipitation is a traditional method for separation of rare earths from non-rare earths, which has advantages such as simple operation, low reagent cost, easy filtration of rare earth precipitates, high recovery of rare earths, etc. However, recovery of rare earths from NdFeB magnet waste by the rare earth double sulfate precipitation has not been reported.
Kim Sok Chol, a section head at the Faculty of Chemical Engineering, has succeeded in applying the rare earth double sulfate precipitation to the separation and recovery of rare earths from the solution obtained by leaching NdFeB magnet waste with sulfuric acid on a laboratory scale. He has also conducted a pilot plant test in order to investigate and optimize the various steps of the whole process for its application on an industrial scale.
The process includes leaching of NdFeB magnet waste by sulfuric acid, precipitation of rare earths in the form of double sulfate by sodium chloride, and conversion of rare earth double sulfates into hydroxides.
The yields of neodymium and dysprosium in the whole process were 92.3% and 90.8%, respectively. In the final rare earth hydroxides, the total rare earth oxides (TREO) content was 79.8%, where the contents of neodymium and dysprosium were 94.2% and 5.8%, respectively.
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