Abstract
Extracting scandium (Sc) from red mud facilitates the comprehensive management of this solid waste, mitigating its environmental impact, while securing a sustainable supply of this critical metal. Two ionic liquids (ILs), [lauryl betaine]-[bis-(trifluoromethanesulfonyl)-imide] ([HLaur]-[Tf(2)N]) and [cocamidopropyl betaine]-[bis-(trifluoromethanesulfonyl)-imide] ([HCoca]-[Tf(2)N]) were used to separate Sc(3+) from Al(3+) in H(2)SO(4) aqueous solution. At pH 3.0, [HLaur]-[Tf(2)N] showed higher Sc(3+) extraction efficiency (44.4 vs 36.4%) and better selectivity over Al(3+) compared to [HCoca]-[Tf(2)N]. The optimal conditions for [HLaur]-[Tf(2)N] extraction were determined as follows: a [HLaur]-[Tf(2)N]-to-Sc(3+) molar ratio of 5.8:1, an extraction time of 40 min, 0.5 mol·L(-1) Na(2)SO(4), and pH ≥ 3.0. The extraction process was found to follow a cation exchange mechanism involving sulfate ions. Quantitative stripping of the loaded Sc(3+) was achieved using a 0.035 mol·L(-1) H(2)SO(4) solution. FT-IR analysis and recycling tests indicated that [HLaur]-[Tf(2)N] maintained its structural integrity over six cycles. Even in a simulated red mud leachate with high Al(3+) and low Sc(3+) concentrations, [HLaur]-[Tf(2)N] exhibited strong Sc(3+) selectivity, and a total extraction efficiency of 94.4% was achieved after five extraction stages, with the residual Sc(3+) concentration as low as 0.26 mg·L(-1).