PhD: Characterization of aqueous biphasic systems for metal recycling - Gautier Meyer

The need for metal ion recycling, which is omnipresent in many industrial applications such as batteries or microelectronics, is prompting an intense search for non-polluting chemical processes. For liquid-liquid extraction, aqueous and acidic biphasic solutions, AcABS (Acidic Aqueous Biphasic Systems) offer a promising alternative. In this thesis, we characterized the physicochemical properties of ABS composed of an ionic liquid, tributyltetradecylphosphonium chloride and strong acids.

The phase separation is promoted here by the addition of salt or acid in the solution and the increase in temperature. The separation mechanisms could be highlighted from the structural organization of the solution and the precise titration of ionic species: the solution is characterized by the formation of spherical micelles, whose electrostatic repulsion is more or less skimmed by the presence of ions in solution and by the adsorption of these to the surface of the micelles following an increase in temperature. The interface between the two aqueous phases has a very low surface tension and spreads over more than 60 Angstrom, showing that the ionic liquid does not form a monolayer at the interface as would be expected for a surfactant.

The last particular point of these systems is the particularly long separation kinetics. By simple models derived from the Cahn-Hilliard equation, we were able to predict the characteristic time of the phase separation, dominated by the forces of gravity on the drops of one phase in the other and dependent on the viscosity and the surface tension.

Finally, the migration of metal ions in solutions can be studied thanks to the experimental setup and the analysis of the results developed during this work, allowing the characterization of the diffusion processes of metal ions in each phase and through the interface.

Jury :

Emmanuelle Dubois (PHENIX, Paris), Damien Bourgeois (ICSM, Marcoule), Mathieu Salanne (PHENIX, Paris), Jean-Michel Andanson (ICCF, Clermont-Ferrand) et Elisabeth Charlaix.

Direction de thèse: Marie Plazanet et de Isabelle Billard