Comparison of Magnetite Adsorbents for Use in the Separation of Rare Earth Elements from Aqueous Solution

Rare earth elements (REEs) are essential to advanced technologies, yet their separation and recovery remain costly and inefficient. This study evaluated REE adsorption from aqueous solution using unfunctionalized magnetite (Fe₃O₄) and surface-functionalized variants with amine (Fe₃O₄-NH₂) and carboxylic acid (Fe₃O₄-COOH) groups. Single-element tests showed rapid uptake, with >99% removal within minutes. Kinetic modeling of unfunctionalized Fe₃O₄ fit the pseudo-second-order model (R² > 0.99), indicating chemisorption controlled by surface-site availability. Concentration and dosage studies confirmed the importance of the adsorbent-to-adsorbate ratio, as lower REE levels and higher particle loadings improved removal, while multi-element systems showed reduced efficiencies from competitive adsorption. Lanthanum exhibited lower uptake at high concentrations, particularly with functionalized particles, suggesting potential for selective separation. Results demonstrate that unfunctionalized Fe₃O₄ enables efficient bulk REE removal, while functionalization offers opportunities to tailor selectivity. These findings highlight the potential of continuous flow material recovery systems to handle variable-composition feedstocks, such as ore leachates and recycled materials, supporting scalable, solvent-free REE separation for industrial recovery processes.