The stepwise extraction strategy for selective recovery of scandium from hydrochloric acid leachate of bauxite residue based on reactivity of metal ions

The recovery of Sc from secondary resources such as bauxite residue has received considerable interest. As the main elements in bauxite residue, Fe and Al exhibit significant interference in the selective separation of Sc. Herein this work, a stepwise extraction strategy of Sc from the hydrochloric acid leachate of bauxite residue was proposed based on the differences in reactivity of metal ions. The results show that Fe(III) and Sc(III) can be extracted sequentially with Aliquat 336 and Cyanex 272 from hydrochloric leachate. The separation factors of Fe/Sc, Fe/Al and Sc/Al were up to 4.3 × 104, 4.1 × 104 and 2.6 × 103, respectively. The results of spectroscopic characterization indicate that a cation exchange and coordination occur during the extraction of Sc(III) with Cyanex 272. The Sc(III) complex with Cyanex 272 (H2A2) is presented as ScClA2(HA)2¯. The loaded Aliquat 336 and Cyanex 272 can be stripped with acidified sodium sulfite and oxalic acid, respectively. The extraction-stripping performance of the stepwise separation route was investigated and the extraction efficiency of Fe(III) and Sc(III) can be remained above 97 % after 5 cycles. The proposed strategy has the potential to be considered industrially for the recovery of Sc from bauxite residue and other secondary resources.