Abstract
Ion separation using liquid-liquid extraction (LL) or solvent extraction is a key process used in various industrial hydrometallurgy applications, particularly for the nuclear fuel re-processing. In order to better understand the ion transfer between an aqueous and an organic phase in this type of process it is important to understand i) the speciation of the different ionic and molecular species in each of the two phases in contact and which defines the differ-ences in chemical potential between the two phases but also ii) all the phenomena of molecu-lar and supramolecular interactions at the interface, which are at the origin of the potential barriers that can influence the kinetics of ion transfer. Numerous results of volume phase ex-periments exist and can now be interpreted structurally from molecular dynamics simulations. However, this same experimental/simulation correlated approach at the interface containing ligands and in equilibrium with adjacent volumes has been little explored. In this thesis work, we first synthesized a diamide extractant containing a chromophore (MAD) in order to be able to exalt the nonlinear optical signal in a second harmonic generation experiment which has been proved to be a relevant technique for probing buried fluid interfaces. The different physicochemical and extracting properties of this molecule were studied as well as its re-sponse in nonlinear optics. In parallel, molecular dynamics simulation boxes were built on a reference diamide but also with the new chromophore ligand allowing us to visualize as a function of time the equilibrium of ligand distributions between the organic phase and the LL interface. The objective of comparing the experimental and simulated SHG signal from the simulation boxes has not been achieved because the SHG response of this new ligand proved to be more complex by revealing a chiral response dependent on the interfacial concentration of the ligand. Nevertheless, it was possible to suggest that for a more amphiphilic extractant and therefore more capable of surface organization and aggregation in solution, a depletion layer close to the interface could generate a potential barrier, source of an ionic transfer more kinetic than diffusive.