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Due to their amphiphilic properties, malonamide molecules in alkane are organized in reverse micelle type aggregates, composed of a polar core formed by the malonamide polar heads and the extracted solutes, and surrounded by a hydrophobic shell made up of the extractant alkyl chains. The aggregates interact with one another through an attractive potential, leading to the formation of a third phase. This occurs with the splitting of the organic phase into a light phase composed mostly of diluent, and a heavy third phase containing highly concentrated extractant and solutes. In this article, we show that the aggregation (monomer concentration, domain of stability, and attractive potential between micelles) greatly depends on the nature of the extracted solute, whereas the size of aggregate (aggregation number) is only slightly influenced by this. We describe the extraction of water, nitric acid, neodymium nitrate and uranyl nitrate. Strongly polarizable species induce consistently large attraction potentials and a small stability domain for the dispersion of nanodroplets in the solvent. Highly polarizable ions such as lanthanides or uranyl induce more long-range attractive interactions than do protons.

We show that solubilization in microemulsion droplets is best described as a combination of interfacial adsorption and internal absorption. We progressively add solute to a Winsor type I system, and simultaneously measure the amount of solute at the oil–water interface and its effect on the interfacial curvature. We determine the relationship between the effective packing parameter and the amount of solute adsorbed at the oil–water interface. For four solutes, a significant amount of oil is co-extracted with solute into the interfacial film. Moreover, we show that solubilization in microemulsions can be characterized by two physical quantities with precise meaning: (1) the increase in interfacial area per molecule of adsorbed solute and (2) the number of oil molecules co-extracted with each solute molecule into the interfacial film. To quantify these effects, we introduce the constant interfacial thickness (CIT) model. It provides a general relationship between curvature, packing and interfacial composition in oil/water/surfactant/solute mixtures. Finally, we show that these results can be used to calculate the free energy of transfer of solute and oil from the droplet core to the interface.

For future back-end of the nuclear fuel cycle, the partitioning of minor actinides: Np, Am and Cm, followed by their transmutation will minimize importantly the radiotoxicity of nuclear glass waste. In this paper, the research done in France and in Europe will be presented: (i) partitioning of Np by modified PUREX process, (ii) partitioning of Am and Cm by the DIAMEX and SANEX hydrometallurgical processes. (c) 2007 Published by Elsevier B.V.

We show that liquid–liquid extraction can be described as the equilibrium between two pseudophases of ions: the hydrated state in the water phase and the solvation state when the ions are adsorbed on an organized interface. The extractant is considered as a potential surface where the ions can adsorb. Unlike phenomenological binding “constants”, ion extraction/stripping can be seen as the sum of Langmuir isotherms. The number of aggregated extractants in one reverse micelle in the solvent is at least equal to or higher than the number of extracting molecules complexed at a given instant to the ion to be extracted. Considering extraction equilibrium as a sum of isotherms corresponding to the different states of aggregation of extractant molecule in the solvent, the resulting constant is representative of both the efficiency of the extraction and the structure of the solution. This is a first step toward the development of predictive models for the apparent distribution coefficients.

Some general principles of surfactant self-assembly are rationalised in order to give a short introduction to the use of phase diagrams for binary (two components) and ternary (three components) systems. Finally models for solubilisation are considered to be understood within the frame of those general packing principles: volume, surface and curvature conservation.

Our aim is to give a short introduction of the use of phase diagrams in order to rationalise general principles of surfactant self-assembly. These can be rationalised in terms of geometrical constraints: volume, surface and curvature. Binary (two components: surfactant and water) and ternary systems (surfactants, water, oil) are considered separately. Models for solubilisation, to be understood within the general principles and not as tabulated data, are presented. Finally, some examples of application of solubilisation in formulation are given. To cite this article: F. Testard, T. Zemb, C. R. Geoscience 334 (2002) 649–663.