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

Abstract

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 ¹¹⁵In NMR spectroscopy. At low LiCl concentrations in ethylene glycol, the bridging (InCl₃)₂(EG)₃ or mononuclear (InCl₃)(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)Cl₄]^-). In the less polar phase, indium(iii) is present as a tetrahedral [InCl₄]^- 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.

Fig. 1. (a) Distribution ratios of indium(iii) (D_In) and (b) percentages extraction of indium(iii) (%E_In) as a function of LiCl concentration for the EG + (5 vol% Cyphos IL 101 in toluene) system (■) and EG + (5 vol% Aliquat 336 in toluene) system (▲). Conditions: volume MP : LP = 1 : 1, room temperature, 600 rpm, 1 h. Initial In(iii) concentration = 5 g L⁻¹.

Fig. 2. Raman spectra at 0 M LiCl as a function of the indium concentration. EG (1), 5 g L⁻¹ indium (2), 10 g L⁻¹ indium (3), 20 g L⁻¹ indium (4), 40 g L⁻¹ indium (5), 60 g L⁻¹ indium (6), 100 g L⁻¹ indium (7), 150 g L⁻¹ indium (8), 200 g L⁻¹ indium (9). λ_laser = 532.0 nm.

Fig. 3. Tentative chemical structures of the lithium complex in EG.

Fig. 4. Raman spectra at 60 g L⁻¹ indium as a function of the LiCl concentration. EG (1), 0 M LiCl (2), 1 M LiCl (3), 2 M LiCl (4), 3.5 M LiCl (5). λ_laser = 532.0 nm.

Fig. 5. Tentative chemical structures of indium(iii) complexes formed at low (left + middle) and high (right) LiCl concentration.

Fig. 6. k ⁴-Weighed EXAFS function (a) and Fourier transform (b) of the indium complex in the more polar phase consisting of 3 mol L⁻¹ LiCl and 30 g L⁻¹ indium (from InCl₃) dissolved in EG. The fitted model is indicated with a red dashed line.

Fig. 7. k ⁴-Weighed EXAFS function of the indium complex in the less polar phase after extraction of a EG solution containing 5 or 60 g L⁻¹ dissolved as InCl₃ and 0 or 3 mol L⁻¹ LiCl with Cyphos IL 101 or Aliquat 336 (5 or 60 vol%) dissolved in toluene. The fitted model is indicated with a red dashed line.

Fig. 8. (a) Distribution ratios of indium(iii) (D_In) and (b) percentages extraction of indium(iii) (%E_In) as a function of LiCl concentration for the EG + (5 vol% Cyphos IL 101 in toluene) system (■) and the EG + (5 vol% Cyphos IL 101 in p-cymene) system (▲). Conditions: volume MP : LP = 1 : 1, room temperature, 600 rpm, 1 h. Initial metal concentrations: [In(iii)] = 5 g L⁻¹.

Fig. 9. (a) Distribution ratios (D) and (b) percentages extraction (%E) of indium(iii) (■) and zinc(ii) (▲) as a function of LiCl concentration for the EG–2.56 vol% Cyphos IL 101 in p-cymene system. Conditions: volume MP : LP = 1 : 1, room temperature, 600 rpm, 1 h. Initial metal concentrations: [In(iii)] = 5 g L⁻¹, [Zn(ii)] = 5 g L⁻¹. Modifier: 1 vol% 1-decanol.

Fig. 10. (a) Distribution ratios (D) and (b) percentages extraction (%E) of indium(iii) (■) and zinc(ii) (▲) as a function of LiCl concentration for the water–2.56 vol% Cyphos IL 101 in p-cymene system. Conditions: volume MP : LP = 1 : 1, room temperature, 600 rpm, 1 h. Initial metal concentrations: [In(iii)] = 5 g L⁻¹, [Zn(ii)] = 5 g L⁻¹. Modifier: 1 vol% 1-decanol.

Fig. 11. (a) Distribution ratios (D) and (b) percentages extraction (%E) of indium(iii) (■) and zinc(ii) (▲) as a function of Cyphos IL 101 concentration for the EG–Cyphos IL 101 in p-cymene system. Conditions: volume MP : LP = 1 : 1, room temperature, 600 rpm, 1 h, [LiCl] = 3.5 M, [1-decanol] = 1 vol%. Initial metal concentrations: [In(iii)] = 5 g L⁻¹, [Zn(ii)] = 5 g L⁻¹.

Fig. 12. McCabe–Thiele diagram for the extraction of indium(iii) from EG using Cyphos IL 101 diluted in p-cymene. Conditions: room temperature, 600–1000 rpm, 3 h, [Cyphos IL 101] = 2.56 vol%, [LiCl] = 3.5 M, [1-decanol] = 1 vol%. Initial metal concentrations: [In(iii)] = 5 g L⁻¹, [Zn(ii)] = 5 g L⁻¹.

Fig. 13. McCabe–Thiele diagram for the scrubbing of zinc(ii) from the loaded more polar phase. Conditions: room temperature, 600–1000 rpm, 3 h, [LiCl] = 3.5 M. Metal concentration scrubbing solution: [In(iii)] = 5 g L⁻¹.

Fig. 14. Concentration profile of indium(iii) (black) and zinc(ii) (red) in the extraction (top) and scrubbing (bottom) mixer–settler experiment. Conditions: volume MP : LP = 1 : 2, room temperature, 1000 rpm. Initial metal concentrations for extraction experiment: [In(iii)]_MP = 5 g L⁻¹, [Zn(ii)]_MP = 5 g L⁻¹ in EG; initial scrub feed concentration: [In(iii)]_MP = 5 g L⁻¹ in EG. LP phase: 2.56 vol% Cyphos IL 101, 1 vol% 1-decanol in p-cymene.