Among the many solvent extraction technologies, those used for metal recovering are quite challenging due to the poor solubility of inorganic ions in oils. Metal extraction thus requires the use of lipophilic extractant molecules to complex the cations and solubilize the complex in the oil phase. In practice, there is a trade-off between selectivity, kinetics and efficiency, in keeping with cost constraints. Despite all the attention solvent extraction has received, however, the molecular structure of the Liquid/liquid (LL) interface remains quite elusive and, as a result, the mechanisms of complexes (ion + extractant molecules + counterions) formation and transfer, that influence the kinetics of extraction, are not well understood. Ion-extraction can be referred to as a diffusion-limited or a reaction-limited process depending on how high is the energy barrier at the LL interface. To tackle this highly challenging problem, we will buckle down by seeking for coherent structural information of the interface at the nanometer scale, at equilibrium in a first step. X-ray AND neutron reflectivities were used to show the evolution of the interfacial structure and to determine the ion potentials at the LL interface [1,2]. In parallel second harmonic generation (SHG) signal can be recorded from the LL interface during a ion transfer highlighting some intense intensity fluctuations. SHG is indeed an very promising and specifiic technique to study LL interface static and dynamic evolution in a solvent extraction process. However, the quantification of this signal is not so simple and a deep analysis of the second order susceptibility components is required. This second part of the presentation will be dedicated to molecular dynamic approach on a simple LL interface, without ligand molecules, to demonstrate how we can correlate the interfacial structure and its evolution with the variation of the SHG signal [3].

Solvent extraction: Structure of the liquid/liquid interface containing a diamide ligand

254th National Meeting (2017)

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