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Mechanism of ionic liquid-based acidic aqueous biphasic systems formation


Ionic liquid-based acidic aqueous biphasic systems (AcABS) represent a promising alternative to solvent extraction process for the recovery of critical metals in which the substitution of the inorganic salt by an acid allows for the ‘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 ionic liquids identifies the charge shielding of the cation as the primary structural driver for the applicability of an ionic liquid in AcABS. Through a systematic study of tributyltetradecylphosphonium chloride ([P44414]Cl) with various chloride salts and acids, we observed the first significant deviations 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 AcABS to new acidic systems and highlights their versatility and tuneability.

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Publication details

The article was received on 08 Feb 2018, accepted on 08 Mar 2018 and first published on 08 Mar 2018

Article type: Paper
DOI: 10.1039/C8CP00937F
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Mechanism of ionic liquid-based acidic aqueous biphasic systems formation

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

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