Highly effective and selective recovery of scandium using high-surface area silica prepared from calcium silicate hydrate

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.