Speciation of indium(iii) chloro complexes in the solvent extraction process from chloride aqueous solutions to ionic liquids

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 46; no. 13; pp. 4412 - 4421
• Main Authors: Deferm, Clio, Onghena, Bieke, Vander Hoogerstraete, Tom, Banerjee, Dipanjan, Luyten, Jan, Oosterhof, Harald, Fransaer, Jan, Binnemans, Koen
• Format: Journal Article
• Language: English
• Published: England 27.03.2017
• Subjects: Aqueous solutions; Chlorides; Concentration (composition); Ionic liquids; Nuclear magnetic resonance; Solvent extraction; Speciation; Viscosity
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt00618g

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(H O) Cl ] (0 ≤ n ≤ 6). EXAFS and In 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 [InCl ] complex. Based on the speciation results an extraction mechanism is proposed.