From Trace to Pure: Pilot-Scale Scandium Recovery from TiO2 Acid Waste
Abstract
Scandium (Sc), officially classified as a critical raw material by the European Union (EU), is increasingly threatened by supply risks, as current availability depends almost exclusively on imports from China, Russia, and Ukraine. This dependency highlights the urgent need for alternative recovery methods that can secure a more resilient European supply chain. In the present study, we developed and piloted an integrated process combining tandem nanofiltration with solvent extraction for scandium recovery from titania (TiO2) acid waste, and further enhanced the system through the incorporation of antisolvent crystallization.
The newly designed approach involved a sequence of advanced separation techniques, including hydroxide precipitation, microfiltration, ultrafiltration, nanofiltration, solvent extraction, and final purification by antisolvent crystallization. The process was evaluated in terms of both material and energy requirements, with performance benchmarks based on scandium trifluoride (ScF3) production. From approximately one cubic meter of European TiO2 acid waste containing scandium at a concentration of 81 mg L−1, a total of around 13 grams of scandium was successfully recovered. The recovery yield reached 43% after nine operational stages, and the final product, ammonium hexafluoroscandate ((NH4)3ScF6), achieved a purity of about 95%, demonstrating the technical viability of this integrated recovery route.
Economic analysis revealed that the estimated production costs per kilogram of ScF3 using this method were below current reported market prices, underscoring the competitive potential of the process at industrial scale. While several technical bottlenecks remain—particularly challenges related to solid–liquid separation and relatively high electricity consumption—the combination of advanced filtration, solvent extraction, and antisolvent crystallization offers a promising pathway for scandium recovery from secondary European sources. This approach not only contributes to reducing dependence on external suppliers but also aligns with circular economy principles by valorizing industrial waste streams into valuable critical raw materials.