Non-aqueous solvent extraction of indium from an ethylene glycol feed solution by the ionic liquid Cyphos IL 101: speciation study and continuous counter-current process in mixer–settlers

摘要

A solvometallurgical process for the separation of indium( III ) and zinc( II ) from ethylene glycol solutions using the ionic liquid extractants Cyphos IL 101 and Aliquat 336 in an aromatic diluent has been investigated. The speciation of indium( III ) in the two immiscible organic phases was investigated by Raman spectroscopy, infrared spectroscopy, EXAFS and ~(115) In NMR spectroscopy. At low LiCl concentrations in ethylene glycol, the bridging (InCl _(3) ) _(2) (EG) _(3) or mononuclear (InCl _(3) )(EG) _(2) complex is proposed. At higher lithium chloride concentrations, the first coordination sphere changes to two oxygen atoms from one bidentate ethylene glycol ligand and four chloride anions ([In(EG)Cl _(4) ] ~(?) ). In the less polar phase, indium( III ) is present as a tetrahedral [InCl _(4) ] ~(?) complex independent of the LiCl concentration. After the number of theoretical stages had been determined using a McCabe–Thiele diagram for extraction by Cyphos IL 101, the extraction and scrubbing processes were performed in lab-scale mixer–settlers to test the feasibility of working in continuous mode. Indium( III ) was extracted quantitatively in four stages, with 19% co-extraction of zinc( II ). The co-extracted zinc( II ) was scrubbed selectively in six stages using an indium( III ) scrub solution. Indium( III ) was recovered from the loaded less polar organic phase as indium( III ) hydroxide (98.5%) by precipitation stripping with an aqueous NaOH solution.