Selective recovery of indium via continuous counter-current foam separation from sulfuric acid solutions II – Optimization of operational parameters on separation performance

Abstract

Continuous counter-current foam separation under the simultaneous injections of metal and surfactant solutions into rising foam bed was applied to recover In(III) from a sulfuric acid solution. In this system, an anionic organophosphate surfactant containing a similar structure to a phosphoric acid extractant, D2EHPA, was employed as the metal collector with addition of a nonionic co-surfactant as a foam stabilizer. Among the various commercial products available, A219B/POOE20 was elucidated as the optimum combination of anionic/nonionic surfactants. In this study, the effects of the experimental parameters such as the aqueous pH, air flow rate, and injection rates of metal and surfactant solutions were discussed in terms of the percent recovery and separation factors of In(III) over the other metals. The results were successfully obtained under the optimized conditions with a dose of ascorbic acid as a reductant for Fe(III); the percent recoveries of indium and iron; the separation factors of In/Fe, In/Cu, and In/Zn; and the enrichment ratio of indium were 97%, 1.1%, 93, 1300, 1300, and 5.5, respectively. The mixture mol ratio of mono- and di-esters of anionic A219B was derived as 35:65 by a slope analysis, and the mono-esters would influence the separation performance in the case of rich A219B concentration in foam bed. The performance comparison of this method with solvent extraction using D2EHPA or the conventional foam separation was also presented.