Enrichment of Sc₂O₃ and TiO₂ from bauxite ore residues

As a major byproduct generated in the alumina industry, bauxite ore residue is an important reserve of scandium and titanium. In this study, the feasibility and mechanism of enriching Sc₂O₃ and TiO₂ from a non-magnetic material, which was obtained from carbothermal reductive roasting and magnetic separation of bauxite ore residue, were investigated based on a two-step (acidic and alkali) leaching process. It was revealed that approximately 78% SiO₂ and 30-40% of CaO, FeO and Al₂O₃ were removed from a non-magnetic material with 0.0134wt.% Sc₂O₃ and 7.64wt.% TiO₂ by phosphoric acidic leaching, while about 95% Al₂O₃ and P₂O₅ were further leached by subsequent sodium hydroxide leaching of the upper-stream leach residue. A Sc₂O₃-, TiO₂- rich material containing 0.044wt.% Sc₂O₃ and 25.5wt.% TiO₂ was obtained, the recovery and the enrichment factor of Sc₂O₃ and TiO₂ were about 85% and 5, respectively. The enrichment of Sc₂O₃ was attributed to higher pH (>3.3) of phosphoric acid solution than its dissolution pH⁰, and the enrichment of TiO₂ was mainly associated with the insoluble perovskite (CaTiO₃) in the acidic solution at ambient temperature. As Sc₂O₃ and TiO₂ cannot be dissolved in the alkali solution, they were further enriched in the leach residue.