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

authors	Schaeffer, N; Passos, H; Gras, M; Mogilireddy, V; Leal, JP; Perez-Sanchez, G; Gomes, JRB; Billard, I; Papaiconomou, N; Coutinho, JAP
nationality	International
journal	PHYSICAL CHEMISTRY CHEMICAL PHYSICS
keywords	MOLECULAR-DYNAMICS SIMULATIONS; HOFMEISTER SERIES; MUTUAL SOLUBILITY; WATER-STRUCTURE; PALISADE LAYER; LITHIUM IONS; EXTRACTION; DENSITY; EXCHANGE; MICELLE
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 ([P-44414] 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 [P-44414](+) micelle surface. Finally, the remarkable thermomorphic properties of [P-44414] 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.
publisher	ROYAL SOC CHEMISTRY
issn	1463-9076
year published	2018
volume	20
issue	15
beginning page	9838
ending page	9846
digital object identifier (doi)	10.1039/c8cp00937f
web of science category	Chemistry, Physical; Physics, Atomic, Molecular & Chemical
subject category	Chemistry; Physics
unique article identifier	WOS:000430537600015