Recovery of scandium from spent sulfuric acid solution in titanium dioxide production using synergistic solvent extraction with D2EHPA and primary amine N1923

High-efficiency and good-selectivity extraction systems are very attractive in the solvent extraction process. A synergistic extraction of scandium (III) from a spent sulfuric acid solution of titanium dioxide production by using a mixture of bis-2-ethylhexyl phosphoric acid (D2EHPA, P204) and primary amine (N1923) has been proposed in this study. The effect of the molar fraction of N1923 in the mixed extractants on the extraction of scandium was studied and the synergistic enhancement coefficient R was calculated. The maximum synergistic coefficient was found to be 12.50 when the H2SO4 concentration was 0.5 mol.L-1 and the molar fraction of N1923 was 0.5. The synergistic extraction mechanism was also discussed. Appropriately 90% scandium could be stripped from the loaded organic phase in the synergistic extraction system when the nitric acid was 6 mol.L-1. The result of FT-IR spectra well verified the conclusion that the synergistic effect owed to the formation of hydrogen bond N-H+ center dot center dot center dot O=P, causing a much easier dissociation of proton H of P204. Finally, after three-stage counter-current extraction and stripping, Sc2O5 product with a high purity of 90% was obtained from spent sulfuric acid solution by precipitation and calcination.