Selectively recovering scandium from red mud by a combination process of sulfation roasting and water leaching

Abstract

In order to reduce the environmental pollution caused by red mud and to make full use of the valuable metal resources, a process combining sulfation roasting-water leaching and solvent extraction was proposed to recover Sc from red mud. The phase transition, leaching kinetics and the effects of roasting temperature, concentrated sulfuric acid addition, roasting time on the leaching of Sc and major elements were investigated. The research results indicated that the roasting temperature played a critical role in selective separation of Sc from impurities. Phase transitions and thermal decomposition behaviors of sulfated samples suggested that the decomposition order of various metal sulfates was: TiOSO₄ > Fe₂(SO₄)₃ > NaFe(SO₄)₂ > NaAl(SO₄)₂ > Al₂(SO₄)₃> Na₃Sc(SO₄)₃ > Y₂(SO₄)₃ > La₂(SO₄)₃ > Na₂SO₄ > CaSO₄. Furthermore, the leaching kinetics demonstrated that the leaching process of Sc conformed to a multiphase liquid–solid reaction model with diffusion-controlled. Under the optimized conditions (15°C, 0.5% P507, 0.5 pH and 1:10 O/A ratio), 99.24% Sc and less than 1% Fe, 11% Al were extracted. This approach is efficient and selective, which presents an excellent insight for the recovery of valuable resources from bauxite residue.