Development of solid phase extraction process for selective separation of scandium and iron from aqueous solutions

Scandium (Sc) is a rare earth element with critical applications in aerospace, solid oxide fuel cells, and laser crystals. It is often extracted from secondary sources, such as waste streams generated in titanium, aluminum, and nickel production processes. However, its separation is challenging due to the presence of impurities, especially iron (Fe), which exhibits similar chemical behavior in aqueous solutions. Traditional separation methods, including solvent extraction and precipitation, are chemically intensive and often lack selectivity. This study investigates a selective separation strategy based on induced speciation differences between Fe and Sc by introducing excess chloride ions through the addition of CaCl₂, enabling their separation using solid-phase extraction. At a chloride concentration of 9 M, Fe primarily presented as FeCl₄⁻ and FeCl₃, while Sc existed as ScCl₂⁺ , as confirmed by spectroscopy and speciation modeling, facilitating selective Fe adsorption using anion exchange resins. The performance of three anion exchange resins (MTA 5011, MTA 1930, MTA 5013), containing tertiary and quaternary amine functional groups, was evaluated. Thermodynamic studies indicated that Fe adsorption was feasible and spontaneous. Kinetic studies revealed that Fe adsorption is primarily chemically controlled, with high adsorption capacities observed for MTA 5011 (120.95 mg/g) and MTA 1930 (106.55 mg/g). Under optimized conditions, the process achieved a maximum selectivity factor of 998 for Fe over Sc, and ∼ 95 % desorption efficiency using deionized water within two cycles. The resins retained their performance over repeated cycles, highlighting their industrial potential for Sc separation and broader rare earth element applications. This approach offers an environmentally friendly and efficient alternative to traditional Sc separation methods.