Non-aqueous solvent extraction of cobalt and nickel using undiluted ionic liquids in milliflow contacting devices
Jonas VAN OLMEN1, Koen BINNEMANS2, Jinu Joseph JOHN1, Van Gerven TOM1
1KU Leuven - Department of Chemical Engineering (ProcESS), Leuven, Belgium
2KU Leuven - Department of Chemistry (SOLVOMET Group), Leuven, Belgium
Over the last years, industry has shown interest in more efficient production techniques and intensified resource management.1,2 Specific for the metallurgical processing industry, the strive for greater efficiency and sustainability is often heavily associated with the concepts of process intensification and green chemistry. Amongst the various technologies available to achieve these principles, the use of highly-performant extractants in combination with micro- or millifluidic reactors for solvent extraction has shown to provide a compelling solution.3
Materials & methods
This work investigates the possibility of using undiluted ionic liquids in milliflow contacting devices to perform non-aqueous solvent extraction of cobalt and nickel.
An elaborate experimental campaign was conducted to characterise the extraction performance at different temperatures and metal concentrations, both from a batch and continuous perspective. The first system that was investigated, consisted of 1-ethyl-3-methylimidazolium chloride (EMIMCl) as the feed solution using trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) as extractant.4 The second system that was investigated, consisted of ethylene glycol (EG – containing 0.75 M of sodium chloride) as the feed solution and employed trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) as extractant.5 Physicochemical parameters such as density, viscosity and interfacial tension were also measured to assist the interpretation. The hydrodynamics of the system were captured using high-speed imaging.
Selectivity towards extraction of cobalt to the less polar phase was observed regardless of the employed system. Extraction performance of the system involving ethylene glycol and trihexyl(tetradecyl)phosphonium chloride was found to be the most promising during batch trials reaching percentages extraction up to 94% (30 min stirring at 850 rpm), which is why it was selected for additional experiments using the continuous milliflow setup. Depending on the processing conditions such as tube diameter (0.08” or 0.04” ID) and flow rate (0.25 mL/min to 4 mL/min), different flow regimes were attained. It was found that across the range of temperatures (20°C to 140 °C), comparable percentages extraction of up to 86% could be obtained in flow.
This study has shown that non-aqueous solvent extraction using undiluted ionic liquids in milliflow at elevated temperatures is a feasible and attractive approach to critical metal recovery. The case study was applied to the separation of cobalt and nickel, obtaining highly selective separation across the entire range of temperatures, with percentages extraction up to 94% and 86% in batch and continuous modes respectively.
(1) Duflou, J. R. et al. CIRP Annals, 61(2):587–609 (2012)
(2) Hall, G. M. et al. Edu. for Chem. Eng., 5(4):100–107 (2010)
(3) Park, J. et al. Int. J. Mol. Sci., 15(9):15320–15343 (2014)
(4) Wellens, S. et al. Phys. Chem. Chem. Phys.,15, 9663–9669 (2013)
(5) Cool, V. et al. [Manuscript in preparation
: The authors acknowledge support from the Research Foundation – Flanders (FWO), project G0D7421N.