Adsorption potential for the concentration and recovery of rare earth metals from NdFeB magnet scrap in the hydrometallurgical route: A review in a circular economy approach

Rare earth metals (REM) are critical resources, and future supply concerns governments, economy experts, and scientists worldwide. Neodymium and dysprosium metals are paramount for the rise of clean energy technologies due to their use in NdFeB magnets in electric vehicles and wind turbines. Scarcity, supply risk, and importance to the renewable energy field motivate the recovery of Nd and Dy from secondary sources, moving the typical production chain towards a circular economy. Diverse approaches have been investigated to recuperate Nd and Dy; among them, adsorption has grown in interest due to the simplicity, low cost, ability to concentrate the metals, and high efficiency. This Review aims to present the potential, challenges, and prospects of adsorption in hydrometallurgical routes of REM recovery from spent NdFeB magnets. The current literature has been extensively reviewed, and the adsorbent properties, kinetics, equilibrium, thermodynamics, selectivity, reusability, multicomponent adsorption, and fixed-bed applications have been critically discussed concerning the potential to concentrate and recover REM from magnet scraps. Thus, this work reports state-of-the-art recovery of Nd and Dy from a residue rich in REM through the incorporation of the adsorption and desorption in hydrometallurgical routes contributing to the REM circular economy.