Selective recovery of indium from iron-rich solutions using an Aliquat 336 iodide supported ionic liquid phase (SILP)

Abstract

Selective recovery of valuable metals from secondary (waste) sources is essential for better resource efficiency. However, low-grade waste streams typically have complex and variable compositions and low concentrations of valuable metals. Therefore, development of novel technologies, able to deal with these complex and variable waste streams, is necessary. In this work, we present a process for the separation and purification of indium from iron-rich matrix solutions making use of a supported ionic liquid phase (SILP). The SILP used in this study was synthesized by impregnating AmberliteXAD–16N with the iodide form of the quaternary ammonium salt Aliquat336. The SILP was characterized by infrared spectroscopy, elemental analysis, density, specific surface area and porosity and it was tested for the selective recovery of indium. Adsorption was preceded by the addition of an excess of iodide anions to the solution, to form indium iodide species, which were extracted to the ionic liquid of the SILP. A high selectivity for indium over iron could be achieved because iron iodide species are not stable in aqueous medium. The reaction kinetics and several adsorption parameters, including anion concentration, adsorbent mass, stripping and reusability of the adsorbent were investigated, using synthetic binary iron-indium solutions containing iron in large excess in comparison with indium, as is typically the case in low-grade ores or industrial process residues. Finally, the developed indium recovery process was validated on a real leachate of goethite residue. A pure indium solution of 49 mg L–1 was obtained with an indium-over-iron mass ratio of 7.9 and a selectivity factor equal to 5400.