Purification of scandium from concentrate generated from titanium pigments production waste

Abstract

Nowadays 80% of scandium in China is obtained from titanium pigments production waste through a complex purification process. The study mainly focused on the purification of Sc from its concentrate generated from titanium pigments production waste by solvent extraction. Several extractants have been tried and 10% D2EHPA - 5% TBP - 85% sulfonated kerosene exhibited the best extraction performance towards Sc in 7 mol/L H2SO4 solution, so it was selected as the oil phase. 0.5% of H2O2 was added into the concentrated solution which can effectively inhibit the extraction of Ti. Both the extraction and back extraction parameters are optimized. The preferred extraction conditions were obtained, i.e., acidity: 7 mol/L H2SO4, the phase ratio A/O: 10, room temperature, mixed contact time: 30 min, Sc concentrate: 10 g/L, that the extraction rate of Sc in the above conditions was nearly 100%. NaOH was used for back extraction with the stripping rate 99% on the following conditions: 5 mol/L NaOH stripping for 30 min at a phase ratio A/O: 1 at 90 °C. Finally, H2C2O4 was used to further purify the back extraction product and Sc2(C2O4)3 precipitant formed. The final product Sc2O3 with a purity over 99.5% was obtained by calcining Sc2(C2O4)3 at 1000 °C for 2 h. A conceptual process for Sc purification was put forward and proved. The total recovery yield of Sc in the whole process is 95%.