Extraction of scandium from scandium-rich material derived from bauxite ore residues

In our previous study, it has been proven that the content of scandium could be enriched to about 0.04 wt% in a solid product after proper pretreatment of bauxite ore residue. The extraction of scandium from this scandium-rich material was investigated in the present study, with emphasis on both acid leaching of various components and solvent extraction of scandium from acidic leachate. It showed that more than 90% of Sc2O3 was leached out from this material with 6-8 mol/L phosphoric acid at 120-140 °C for 60-90 min and liquid-solid ratio of 10-12 mL/g. The presence of phosphoric acid promoted the leaching of scandium due to increased dissolution of perovskite, which converted to CaHPO4 and (TiO)3(PO4)2 and then TiO2 precipitates through TiO2+ hydrolysis precipitation. In the subsequent solvent extraction step, about 98% of Sc3+ was further extracted from the acidic leachate with 2% D2EHPA (P204) at pH 1.8 and aqueous-organic ratio of 3:1. Compared with hydrochloric acid, sulfuric acid and nitric acid, phosphoric acid had much higher selectivity in separation of Sc from the other main constituents, as demonstrated by its large separation coefficient (β) between scandium and other elemental species (e.g., for iron, βSc/Fe = 2703).