Molecular recognition approach to REE extraction, separation, and recycling

Rare earth elements (REE) are highly requested by modern industry, being indispensable for construction of electric vehicles and environmentally friendly energy sources. Challenge in their production lies in their joint occurrence and similar chemical properties. It can be answered by using solid phase extraction, applying highly selective nanostructured adsorbents. The latter are bearing organic ligands with high specific affinity to particular REE grafted on their surface via covalent bonding. This work is a comparative study to demonstrate the ligand properties in relation to distinct REE as a function of various operating conditions, such as concentration of solutions and pH. Mechanisms of adsorption are elucidated with a variety of techniques including FTIR (Fourier-transform infrared spectroscopy), solid-state NMR spectroscopy (Nuclear Magnetic Resonance), and EXAFS spectroscopy (extended X-ray absorption fine structure) in combination with analysis of particles bearing adsorbed cations by SEM-EDS (scanning electron microscopy/energy dispersive X-ray spectroscopy) and of solutions by complexometric titration. Recommendations are elaborated for specific choice of ligands and adsorption–desorption conditions for improved separation of single REE. The results are verified in separation of REE from complex leachates both by magnetic nanoadsorbents and by mesoporous microparticles applied as a sorbent in High Performance Chelation Ion Chromatography (HPCIC).