Selective recovery of indium via continuous counter-current foam separation from sulfuric acid solutions I – Application of anionic organophosphate surfactant as metal collector

Abstract Continuous counter-current foam separation (CCFS) with simultaneous injections of metal and surfactant solutions respectively into rising foam bed was applied to In(III) recovery from sulfuric acid solutions containing ternary metal ions of In/Cu/Zn. Through the screening tests of the surfactants in both conventional batch foam separation and CCFS, anionic organophosphate surfactant which has similar structure to phosphoric acid extractant (D2EHPA) was selected as the metal collector, with an addition of a nonionic co-surfactant as the foam stabilizer. The optimized surfactant combination was shown anionic A219B/nonionic POOE20 in this study; the complete recovery of In(III) was attained with the enrichment ratio of 5.5, whereas those of the other metals were suppressed in trace level, resulting in the excellent selective recovery. Moreover, metal solutions of quaternary In/Fe/Cu/Zn were also examined, and a dose of reductant for interfering Fe(III) into the metal solution was executed for improving the separation efficiency; the dose of ascorbic acid could invert the affinity order of A219B from Fe > In to In > Fe. The percent recovery and enrichment ratio of In(III) were 97% and 5.5, while the separation factors of In/Fe, In/Cu and In/Zn were 93, 1300 and 1300 respectively. This is our first favorable case for expanding the choice range of target metal ions in CCFS using anionic surfactants.