Extraction and separation of iridium(IV) and rhodium(III) from hydrochloric acid media by a quaternary ammonium-based hydrophobic eutectic solvent

Abstract

• Efficient extraction of critical metals by a hydrophobic eutectic solvent. • Efficient separation of iridium(IV) and rhodium(III) in hydrochloric acid media. • Mathematical modeling of the extraction mechanism. • Calculation of the fundamental extraction constants. The extraction and separation of iridium(IV) and rhodium(III) from hydrochloric acid solutions by a hydrophobic eutectic solvent composed of tetraheptylammonium chloride and decanoic acid have been studied for the first time. This eutectic solvent selectively extracts iridium(IV) over rhodium(III), the highest separation factor obtained is approximately 20. The effects of the main experimental factors (shaking time, the volume ratio of aqueous to organic phase, hydrochloric acid concentration, and the initial metal concentration in the aqueous phase) on the extraction behavior of iridium(IV) and rhodium(III) have been investigated. Ultraviolet–visible (UV–Vis) spectroscopy was applied to reveal the [IrCl 6 ] 2− complex to be a predominant species attributed to iridium(IV) extraction. To understand the underlying extraction mechanism, the initial iridium(IV) concentration in the aqueous phase has been varied and a corresponding mathematical model has been developed.