Issue 15, 2018

Mechanism of ionic-liquid-based acidic aqueous biphasic system formation

Abstract

Ionic-liquid-based acidic aqueous biphasic systems (IL-based AcABS) represent a promising alternative to the solvent extraction process for the recovery of critical metals, in which the substitution of the inorganic salt by an acid allows for a ‘one-pot’ approach to the leaching and separation of metals. However, a more fundamental understanding of AcABS formation remains wanting. In this work, the formation mechanisms of AcABS are elucidated through a comparison with traditional aqueous biphasic systems (ABS). A large screening of AcABS formation with a wide range of IL identifies the charge shielding of the cation as the primary structural driver for the applicability of an IL in AcABS. Through a systematic study of tributyltetradecylphosphonium chloride ([P44414]Cl) with various chloride salts and acids, we observed the first significant deviation to the cationic Hofmeister series reported for IL-based ABS. Furthermore, the weaker than expected salting-out ability of H3O+ compared to Na+ is attributed to the greater interaction of H3O+ with the [P44414]+ micelle surface. Finally, the remarkable thermomorphic properties of [P44414]Cl based systems are investigated with a significant increase in the biphasic region induced by the increase in the temperature from 298 K to 323 K. These finding allows for the extension of ABS to new acidic systems and highlights their versatility and tunability.

Graphical abstract: Mechanism of ionic-liquid-based acidic aqueous biphasic system formation

Supplementary files

Article information

Article type
Paper
Submitted
08 Feb 2018
Accepted
08 Mar 2018
First published
08 Mar 2018

Phys. Chem. Chem. Phys., 2018,20, 9838-9846

Mechanism of ionic-liquid-based acidic aqueous biphasic system formation

N. Schaeffer, H. Passos, M. Gras, V. Mogilireddy, J. P. Leal, G. Pérez-Sánchez, J. R. B. Gomes, I. Billard, N. Papaiconomou and J. A. P. Coutinho, Phys. Chem. Chem. Phys., 2018, 20, 9838 DOI: 10.1039/C8CP00937F

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