Study on efficient extraction of indium from complex sulfuric acid solution by “ionic liquid + di(2-ethylhexyl)phosphoric acid + tributyl phosphate”

Abstract

For low indium ion concentration, high Fe/Zn ions concentration of acid leaching solution of wet zinc smelting waste slag, it was challenging to efficiently separate indium because iron ion was usually extracted simultaneously with indium ion by sulfonated kerosene and acid-phosphate-type extractants. It was found that the extraction system of“hydrophobic ionic liquid and acid-phosphate-type extractants and tributyl phosphate (TBP)”(i.e. “IL + P204 + TBP”) could extract indium ion exclusively and indium ion could be stripped efficiently with HCl. Research results indicated that the best extraction conditions by “IL + TBP + P204” were sulfur acid solution pH = 0.9 ∼ 1.1, IL:TBP:P204 = 2:3:1, A/O = 3:1, t = 5 ∼ 10 min. The indium extraction rate was 98.11% and Fe 0.0% under the optimal extraction conditions. The best indium stripping conditions of “IL + TBP + P204” system were HCl 1.5 ∼ 2 mol/L, O/A = 1:1, t = 15 min. The indium stripping efficiency was 100% under the optimal stripping conditions. Mechanism investigations showed that indium ions in sulfuric acid solution were extracted into the organic phase as InSO4+, and also showed that TBP and [BMIm]PF6 (IL) together inhibited the P-OH activity of P204, which made the extraction performance of Fe3+ was completely suppressed. Thus, “IL + TBP + P204” extraction system had an exclusive extraction of indium ions from sulfuric acid solution and avoided iron ions cyclic accumulation in organic phase.