PhD defense of Tamir SUKHBAATAR

Abstract:

Solvent extraction is one of the most widely used separation/purification technique in various industries. Its application ranges from a recovery of elements from ores or from waste products in a case of strategic elements, to decontamination of polluted liquids. One of the current challenges in solvent extraction is replacing the traditional organic (diluent) solvents which are usually toxic and volatile by using alternatives such as ionic liquids which are generally non-volatile, non-inflammable and which offer in some cases much higher extraction efficiency. Exploiting this new class of diluent implies however time consuming screening tests to identify the most convenient ionic liquid to use, due to a lack of mechanisms understanding and prediction. Despite a large number of reported mechanistic studies, effect of such diluents on extraction and extractant aggregation has not been studied so far. Therefore, this thesis work has been dedicated to this topic, by focusing on uranium extraction from i) phosphate media and ii) sulfate media, in ionic liquids. First of all, an ionic liquid screening test has been performed with the reference extracting agents (HDEHP/TOPO mixture for extraction from phosphate media, and trioctylamine for extraction from sulfate media) as well as bifunctional compounds of amidophosphonate and aminophosphineoxyde groups. Then, mechanisms of uranium extraction by these extractants in a chosen ionic liquid have been studied at molecular and supramolecular scales. As an analogy to the Critical Micellar Concentration which is related to the Gibbs free energy of Micellization in a case of surfactants, a Critical Aggregation Concentration has been determined by using results obtained by Small-Angle X ray, Neutron Scattering techniques and interfacial tension measurements. Finally, the results obtained in the ionic liquid have been compared to those obtained in a conventional molecular diluent.