Ion Transport across a Liquid-Liquid Interface for metal extraction – ITALLIX

Recycling without polluting is one of the current challenges addressed to chemistry, requesting innovative systems for liquid-liquid extraction. Moreover, an optimal separation in a large-scale continuous process of flowing solutions, rather than static baths, needs to be examined when new chemical systems are proposed. Following a recent breakthrough with the obtaining of acidic aqueous biphasic systems enabling the selective extraction of metallic ions, we propose with ITALLIX a combined experimental and theoretical project that will address fundamental questions about ionic transport across the interface of two co-flowing non miscible but yet aqueous solutions. We will both examine static and flowing conditions. The origins of the chemical potential difference felt by the ions between the two phases and naturally driving the transport from one phase to another, strongly dependent on acidity and ionic strength of the solution, are to be clarified. In addition, we expect in flowing conditions a subtle interplay between different effects: viscosity, surface tension, slippage, advection or concentrations polarization, to be coupled with liquid-liquid interface instabilities.
We propose here to address these entangled questions in studying three different systems that will enable to address separately the effect of electrostatic interactions, entropy and molecular packing. These selected ternary solutions all undergo phase separation upon temperature rise, i.e present a Lower Solution Critical Temperature (LCST). First, a complete characterization of the structure, ion dynamics and nucleation kinetics will be performed. Second, in order to make the experiment handable in a laboratory length and time scale, we will use a co-flow microfluidic setup equipped with optical (UV/vis spectroscopy) and X-ray (SAXS, XAS) profile characterization. The channel surfaces will enable to address the nucleation origin in different conditions. We will then characterize the structure of the solution and of the interface, the concentration profiles and diffusion coefficients. Eventually, combining the geometric parameters and viscosity conditions (solution composition) will offer the possibility to create surface instabilities and determine their role on ionic transport across the interface.
In parallel, a theoretical description of the systems will be given by MD simulation and mesoscopic modelling, providing a complementarity of the two scales of description. This includes the all-atom simulation of the liquid/liquid interface, and non-equilibrium molecular dynamics simulations to model transport phenomena (hydrodynamics, slip length, diffusion) at the mesoscopic level. All the theoretical results will be systematically compared both with each other and with the experiments. Such an approach will provide the prediction of the different thermodynamic contributions and microscopic interactions driving the ionic transport.
ITALLIX will allow a proper understanding of the influence of physico-chemical parameters (acidity, charges, hydrophobicity…) and of the various hydrodynamic effects (slippage, advection vs diffusion, surface instabilities…). Each of these effects can potentially be turned at the advantage of an enhanced transport, i.e. an increased extraction efficiency. The aim of the project is to develop a new pathway for separation chemistry via liquid-liquid interfaces with a very low surface tension.