Dissolution of rare-earth elements (Nd, Dy and Pr) in end-of-life neodymium magnet by an ultrasound-assisted electrochemical process

The development of novel and efficient recycling techniques for rare earth elements (REEs) has prompted widespread interest owing to their limited availability and growing market demand. Herein, the rate of electrochemically assisted dissolution of NdFeB supermagnets in a deep eutectic solvent is improved through the application of ultrasound. Linear sweep voltammetry (LSV) with sonication showed a significant increase in current density for the Fe, Nd and NdFeB-based anodes, resulting in an approximately 10-fold increase in the measured current density as compared to LSV recorded in the absence of sonication. This enhanced rate of electrochemical dissolution, as similarly seen in other ultrasound-assisted dissolution of pure metals, is due to the removal of the passivation layer from the electrode surface. The maximum dissolution rate of the NdFeB in a choline chloride: ethylene glycol with 10 wt% OxA and 10 wt% H₂O reached 5.9 μm min –1 in the presence of ultrasound which is significantly higher than the leaching rate under silent conditions. Furthermore, addition of oxalic acid and water into the eutectic solvent resulted in a selective recovery of the electrochemically dissolved REEs in the form of REE-oxalates, whilst the undesired and cheaper Fe ions remain solubilised to allow ease of separation. Overall, employing sonication with deep eutectic solvents promotes the removal of the passivation layer from NdFeB alloy, which typically forms during electrochemical dissolution.