Microstructured silicon substrates impregnated with bis(2,4,4-trimethylpentyl) phosphinic acid for selective scandium recovery

Abstract

The recovery of trace amounts of scandium from process tailings represents a challenging yet critical task for the growing demand for sustainable and renewable technologies. As an important step toward addressing the environmental and technical concerns related to current scandium separation approaches, we developed novel extractant-impregnated surfaces (EIS) that held a thin layer of extractant within a micropillar texturized substrate. Compared with traditional solvent extraction, the EIS requires significantly less volume of extractant and no agitation. About 95 % of scandium is separated from the complex feedstock prepared from industrial waste bauxite residue, and the selectivity of scandium is more than 200 times higher than that of aluminum. Adsorption isotherm and kinetic studies are performed, and the experimental data are in good agreement with the Langmuir isotherm model and indicate pseudo-second-order kinetics. Cryo time-of-flight secondary ion mass spectrometry depth profiling is conducted on post-extraction EIS to unveil the scandium ions transport behaviour. Moreover, it is confirmed the EIS scheme and its underlying principles can be applied to sandblasted polytetrafluoroethylene substrates, which proves the potential of using EIS design at larger scales.