A novel method for scandium recovery is proposed through high-surface area silanol-rich silica sorbents which were prepared with calcium silicate hydrate (C - S - H) as raw material. Two types of silanol - rich silica particles, i.e., LAC-S (silica derived from acid leaching of amorphous C - S - H) and LLC - S (silica derived from acid leaching of low-crystallinity C - S - H) are obtained after calcium ions are removed from both amorphous and low-crystallinity forms of C - S - H through a facile acid leaching process (3 mol/L, 25 °C, 24 h). 29 Si NMR spectroscopy reveals that the proportion of silicon atoms carrying silanol groups increases from less than 43% to over 80% when silica particles are transferred from a dry state to an aqueous solution. Batch adsorption experiments were conducted to evaluate the sorption performance and selectivity of these silica sorbents toward Sc(III).The scandium sorption capacities of LAC - S and LLC - S at an equilibrium pH of 4.2 are 174.45 and 129.57 mg/g, respectively. The separation factors (SF Sc/Ln ) of both silica particles exceed 1000 in the initial pH range of 3.5 to 5. The loaded scandium ions are recovered with 3 mol/L hydrochloric acid and the sorbents exhibit good reusability. This strategy provides an efficient and green method for recovering scandium from aqueous solutions.
The recovery of scandium (Sc) from highly acidic industrial effluents is currently hindered by the use of large quantities of flammable and toxic organic solvents. This study developed an extraction system using ionic liquids (ILs) and phenylphosphinic acid (PPAH) as diluents and an extractant, respectively, to selectively recover Sc from the aqueous phase. The effect of IL chemical structure, aqueous pH and temperature on the extraction of Sc was systematically investigated and the findings revealed that ILs with longer alkyl side chains had reduced Sc extraction ability due to the presence of continuous nonpolar domains formed by the self-aggregation of the IL alkyl side chain. The IL/PPAH system maintained high extraction ability toward Sc across a wide temperature range (288 K to 318 K) and the extraction efficiency of Sc could be improved significantly by increasing the aqueous pH. The extraction process involved proton exchange, resulting in the formation of a metal−ligand complex (Sc(PPA) 3 ).
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