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Most metal extraction studies focus on the kinetics, the maximum loading and the extraction equilibrium, while structural information on the extracted complexes has been limited. This paper concerns the nature of the indium(III) chloride complexes, present in the organic and aqueous phase during the solvent extraction of indium(III) from an aqueous HCl solution by undiluted ionic liquids Cyphos® IL 101 and Aliquat® 336. In an aqueous HCl solution (0–12 M), indium(III) exists as octahedral mixed complexes, [In(H2O)6−nCln]3−n (0 ≤ n ≤ 6). EXAFS and 115In NMR were used to characterize these species. The stoichiometric composition of the extracted complexes, which is estimated from viscosity and maximum loading studies and confirmed by EXAFS, is unaffected by the HCl concentration in the aqueous phase. Indium(III) is present in the ionic liquid phase as the tetrahedral [InCl4]− complex. Based on the speciation results an extraction mechanism is proposed. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Koen Binnemans (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal history: Received 19 February 2017; Accepted 8 March 2017; Accepted Manuscript published 8 March 2017; Advance Article published 15 March 2017; Version of Record published 27 March 2017 ispartof: Dalton Transactions vol:46 issue:17 pages:4412-4421 ispartof: location:England status: published

Aqueous waste streams of the metallurgical industry often contain considerable concentrations of metal salts. Previous research showed that the metal chloride salts of zinc(ii), manganese(ii) and iron(iii) can be recovered by solvent extraction using a sustainable and renewable fatty acid based ionic liquid as the extractant. In this paper, the extraction mechanism of Zn(ii), Co(ii) and Ni(ii) from chloride media has been studied systematically. The metal extraction performances of the precursors, sodium oleate and tetraoctylammonium chloride, were compared to the extraction performance of the ionic liquid tetraoctylammonium oleate. Slope analysis experiments were performed to determine the number of ionic liquid molecules involved in the extraction. The experimental data showed that Co(ii) and Ni(ii) were extracted in the pH range from 6 to 8 by the formation of negatively charged metal carboxylate complexes with tetraalkylammonium counter ions. In contrast, Zn(ii) gets extracted as a mixed metal chloride carboxylate anionic complex with tetraalkylammonium counter ions. This extraction mechanism was supported by EXAFS measurements.