Recovery of scandium from red mud by leaching with titanium white waste acid and solvent extraction with P204

Abstract

Recovery of scandium (Sc) from various wastes is generally one strategy to solve potential supply shortage problems of Sc. This work proposes a synergistic process for co-recovery of Sc by using the acid titanium white waste acid (TWWA) to leach the basic red mud, to which the acidity was adjusted with concentrated sulfuric acid when necessary. First, the effect of adjusted acidity of TWWA on Sc leaching from red mud was studied when the acidity of TWWA was adjusted to 5 mol/L H2SO4, which inhibited the formation of silica gel in the leachate with a Sc recovery of 70%. Then, the volume fraction of 10% P204 (di-(2-ethylhexyl) phosphate)-5% TBP (tributyl phosphate)-85% sulfonated kerosene was used to extract Sc from the leachate under the most suitable conditions. Specifically, at an A/O (volumetric liquid phase over oil phase) ratio of 10 for 30 min at room temperature, over 99% Sc was extracted and almost no Fe and Al were co-extracted. The selective scrubbing of 99% Ti was achieved via 5 mol/L H2SO4–1% H2O2 at 60 °C with almost no scrubbing towards Sc. A solution of 3 mol/L NaOH was then used as the stripping agent, which resulted in solid Sc enrichment with a high stripping efficiency of 99%. The process generated a final Sc-enrichment product with a purity of 17.4% and a total recovery yield of 68.6%.