Ligand-Assisted Discrimination of Nd³⁺ and Dy³⁺ Ions: Toward Rare Earth Recycling from NdFeB Magnets

The global shift toward sustainable and green technologies has created an urgent demand for new materials and systems that minimize our environmental impact. Rare Earth Elements (REEs) are fundamental in this transformation due to their unique magnetic, luminescent and catalytic properties [1]. They are crucial components in a wide array of modern technologies, including lighting systems, catalysts, medical diagnostics, as well as the manufacturing of ceramic and glass materials [2]. One particularly important REE-based material is the neodymium-iron-boron (NdFeB) permanent magnet, which is extensively employed in electronic devices, wind turbines, rechargeable batteries, and electric vehicles [3]. However, the increasing reliance on REEs presents significant geopolitical, economic and environmental challenges. The Global REE production is concentrated in a few countries, leading to supply chain vulnerabilities and market imbalances [4]. In addition, the extraction and processing of REEs from natural ores generate large amounts of environmental pollutants and hazardous waste [5]. As a result, the recovery and recycling of REEs from end-of-life (EOL) products is gaining increasing importance as a sustainable strategy to ensure the supply security and reduce the reliance on mining. In this context, our work explores a ligand-assisted method for selectively precipitating REEs from spent NdFeB magnets, which typically consist of approximately 65% iron, 20% neodymium (Nd), and 1% dysprosium (Dy). A set of Salpen-based ligands were synthesized and designed to modify the steric hindrance and lipophilicity near the metal coordination sites, thereby affecting the solubility and precipitation behaviour of the corresponding Nd³⁺ and Dy³⁺ complexes in different organic solvents. Structural characterization of the resulting compounds was performed using Single-Crystal X-ray Diffraction (SCXRD), providing insight into the coordination environments and speciation of these metal-ligand systems. Five distinct Dy complexes were successfully isolated and characterized, revealing different stoichiometries and nuclearities. Promising results for the selective separation of rare earth cations were obtained by exploiting the ligand steric hindrance in combination with the subtle chemical differences between Nd3+ and Dy3+, such as their ionic radii and coordination number. Overall, this ligand-controlled separation approach offers a promising pathway toward a more efficient and scalable recycling of REEs from waste products. [1] S. Cotton, Lanthanide and Actinide Chemistry. 2nd edition, Wiley, 2024. [2] M. M Nkiawete, R. L Vander Wal J. Rare Earths, 2025, 43, 1-8. [3] J. J. Croat, J. F. Herbst, R. W. Lee, F. E. Pinkerton, Appl. Phys. Lett., 1984, 44, 148–149. [4] K. Binnemans, P. T. Jones, K. Van Acker, B. Blanpain, B. Mishra, D. Apelian, Jom, 2013, 65, 846–848. [5] K. Binnemans, P. T. Jones, B. Blanpain, T. V. Gerven, X. Yang, A. Walton, M. Buchert, J. Clean. Prod., 2013, 51, 1-22.