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Solvent-based liquid-liquid extraction and stripping is the key separation method at the basis of all hydrometallurgical processes, such as those used to retrieve strategic metals from ores or waste material. During formulation of an efficient extraction system, chemical engineers often encounter instabilities and the formation of undesired phases. In order to avoid the appearance of those in practice, we propose a simple and convenient approach of the phase diagram, based on mole ratio of cations as the variable that controls interfacial curvature. The proposed formulator’s cut through the Gibbs phase prism is more adapted than fish-cuts or similar ones in the case of extraction and stripping formulation optimized against variation in the feed composition.

International audience; We develop a minimal model of weak aggregation in water in the case of neutral extractant in a Winsor II regime, i.e. dispersed microemulsions in thermodynamic equilibrium with concentrated brine. All the terms involved in the free energy associated with the transfer of ions from a concentrated aqueous to an organised organic phase have been estimated: supramolecular effects, bulk terms, extractant film bending and electric polarisation terms. This allows the rationalization of the paradoxical observation of apparent stoichiometry: “constant” associated with the phase transfer that varies with the nature of the solvent and the bending properties of the surfactant. The extractant film is characterized by its spontaneous packing parameter (of the order of 4) and its intrinsic rigidity of the order of 6.25 kJ mol$^{−1}$ (2.5 $k_BT$). This multi-scale study combining supramolecular chemistry and mesoscale modelling approach allows a large reduction of the number of parallel apparent equilibria currently used for dimensioning extraction devices. Prediction power versus variations of water activity and temperature is in reasonable agreement with observations made in typical pilot cascade

The influence of the corrosion on the evaporation of sessile droplet of sodium chloride solution was quantitatively investigated at a relative humidity of 0%. On planar surface, sessile saline droplets evaporated in the pinned, constant contact area mode. The time of evaporation of a sessile saline droplet is much longer on iron substrate than on silicon. This is due to the initiation of corrosion phenomenon. At low and intermediate salt concentrations, the inverse of the classical Evans model is observed due to the evaporation time which is fast and the hydrodynamic flows linked to evaporation. Increasing salt concentration leads to the same evaporation rate for iron and silicon. This study shows that the conditions of evaporation will influence both the evaporation itself and the corrosion phenomenon.

The theoretical description of systems with soft interfaces requires a precise definition of the interfaces that are present. Such definitions are common for interfaces of simple liquids and for surfactant assemblies like micelles, membranes, and microemulsions. Here, we focus on several possible rigorous definitions in a recently described surfactant-free microemulsion that consists of octanol, ethanol, and water, in which micelle-like aggregates are in dynamic equilibrium with the surrounding pseudo phase. We test different definitions that are based on the radial distribution functions of the components with respect to the center of these surfactant-free micelles. All definitions result in experimentally indistinguishable locations of the interface within the limits of resolution of light, X-ray, and neutron scattering experiments, since their locations differ by at most 0.4 nm, which corresponds to roughly 2-3 bond lengths.

The effect of adding salts to micelles made of a sugar based surfactant, n-octyl-beta-glucoside, has been investigated using small angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. It was shown that adding salts leads to change the outer shell hydration of the micelles i.e. where the glucose moieties are situated. No ion adsorption at the micelle surface was detected. Three regimes have been determined as a function of the ionic strength (IS): (i) at low IS (

a b s t r a c t There is a still growing interest in the recovery of rare earth elements due to their manifold industrial and technological applications. We present here a simple and effective method for the enrichment of micrometer sized La2O3 particles via microparticle stabilized foams. By using the short chain amphiphile (1-hexyl)trimethylammonium bromide (C6TAB) foam that is generated by surface modified particles only can be generated. This technique allows a more selective and specific particle transport mechanism. The results are discussed in terms of surface charges and transport mechanisms. Furthermore, the effects of particle concentration, pH and amphiphile concentration are studied and evaluated. © 2012 Elsevier B.V. All rights reserved.

Single particle light scattering (SPLS) has been extended towards sizes near 100 nm to measure particle size distributions with high precision and model free and thus to establish a diagnostic about the stage of aging emulsion properties. SPLS measurements on emulsions stabilized with catanionic crystals allowed to follow the evolution of droplet size distribution as a function of surface charge upon aging in the absence of Oswald ripening. Small angle neutron scattering (SANS) experiments allowed identification of the crystalline nature of the solids stabilizing these Pickering emulsions. The remarkably stable Pickering emulsions stabilized via catanionic microcrystals were in addition characterized by confocal microscopy and by ζ-potential measurements.

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.

Osmotic pressure is a key parameter to understand the thermodynamics and the interactions in colloidal systems. We present here four examples to demonstrate the variety of information that can be extracted from it. The equation of state, i.e. the osmotic pressure versus concentration curve, could be established using analytical ultracentrifugation in binary clay–water mixtures. This method allows a quick and efficient determination of the phase boundaries, and the equation of state shows a good agreement with a Poisson–Boltzmann model. In ternary mixtures of water–anionic surfactant–cationic surfactant, phase separation with a different partitioning of the surfactant in both phases could be evidenced. In the monophasic domains, the surface charge density of the objects could be estimated from the equation of state. In mixtures of polyelectrolytes, different behaviours of the osmotic pressure with respect to the composition could be interpreted in terms of microphase separation, or homogeneous complexation, depending on the composition in polyelectrolyte. Finally, in a colloidal dispersion of spheres coated with polyelectrolytes, three different colloid–colloid interaction regimes could be identified, depending if the polyelectrolyte shells are collapsed onto the colloid, swollen, or non-overlapping. These examples illustrate the variety of information that osmotic pressure can give in a large variety of situations, making this technique an indispensable tool for the physico-chemist.

In this overview, some new applications of micelles, vesicles and lyotropic phases used for mineralization are described. Special focus is put on cases where a complex fluid built from “stiff” structures is used as a scaffold for mineralization events in the aqueous phase. Various minerals and metals have been successfully crystallized in these templates showing that it is possible to mimic the natural vesicle archetypes in biomineralization processes, although colloidal interactions can also well over compensate the templating effect of the organic matrix.

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.

The effect of a hydrophobically modified polysaccharide, cholesteryl-pullulan (CHP), on the swelling of the DMPC L α lamellar phase has been investigated by small angle neutron scattering. The CHP derivative can be introduced in the aqueous layers of the lamellar phase by anchoring lateral cholesterol groups into the bilayers. The resulting lamellar phase (L p ) is stabilized at large membrane separations by the introduction of a new repulsive and long range contribution in the force balance of the system. We emphasize here the temperature dependence of two coexisting lamellar phases (L α + L p ) differing in their polymer content and in their periodicities. At low polymer content (DMPC:CHP=99:1 by weight), the two lamellar phases at thermodynamic equilibrium change into a single phase on heating from room temperature to 50°C. The new phase (L p ′) is characterized by a very large correlation peak whose position is consistent with a lamellar structure following an ideal dilution law. The transition L α + L p → L p ′ is reversible on cooling, indicating that the observed coexistence of the two lamellar phases at room temperature is a true thermodynamic equilibrium. At higher polymer content (DMPC:CHP=95:5 by weight) the critical behaviour has not been observed. The periodicity of the L p phase slightly decreases on heating indicating a reduction in the miscibility gap and a possible critical point at temperatures higher than 50°C. However, in the investigated temperature range, the thermodynamic coexistence of the two lamellar phases is not affected in this case.