Nitric acid extraction with monoamide and diamide monitored by second harmonic generation at the water/dodecane interface

Structure of a liquid/liquid interface during solvent extraction combining X-ray and neutron reflectivity measurements

“…The accumulation of the diamide molecules at the water/ oil interface was already evidenced from the surface tension variation as a function of diamide concentration in contact with similar aqueous phases. 33 However, we deduce from the SLD profile simulations an interesting evolution of the interface with significant mixing of oil in water due to the presence of the extractant, a model that seems to be at odds with the current scheme of an amphiphilic monolayer. The formation of a thick interface or an interphase enriched with extractant molecules over several nanometers can be compared to a surface induced pre-transitional effect or a critical adsorption already observed for surfactants close to solid or liquid surfaces.…”

“…Simultaneously, a wider distribution of ion enrichment is observed at the interface. While an excess of molecular complexes at the interface and its dependence on bulk concentration were expected from LL surface tension measurements, which also point out an strong accumulation of amphiphilic extractants at the LL interface with increasing concentration up to the CAC, 33 the distribution of the species at the interface has to date been unknown. Although the studied system is complex, knowledge of the distribution of specific molecular species across the interface would shed light on the ion extraction mechanism.…”

“…31 We present data for a concentration in diamide in dodecane between 0.01-0.1 M, a concentration range below its critical concentration aggregation concentration of about 0.1M in these conditions and for which we have shown in previous work that the separation coefficient is not too high and the rate of ion transfer is maximized. 32 In figure 1, two series of reflectivity profiles varying concentrations of diamide in dodecane are shown: the upper series for x-rays and the lower series for neutrons. The RQ 4 versus Q representation of the x-ray data, where R is the reflectivity and Q the wave vector transfer, was chosen to emphasize the deviation from an ideal Q -4 decay at a sharp interface of the x-ray reflectivity.…”

“…32 We present data for a concentration of diamide in dodecane between 0.01 and 0.1 M, a concentration range below its critical concentration aggregation concentration of about 0.1 M under these conditions and for which we have shown in previous work that the separation coefficient is not too high and the rate of ion transfer is maximized. 33 In Fig. 1, two series of reflectivity profiles at varying concentrations of the diamide in dodecane are shown: the upper series for X-rays and the lower series for neutrons.…”

Molecular Forces in Liquid–Liquid Extraction

“…The transfer of the solute between the phases is driven by the difference in chemical potentials, when the system is not in equilibrium. In practical applications, the industry sometimes cannot wait for the L–L system to reach thermodynamic equilibrium, but the associated slowing down due to the presence of the interphase must nonetheless be taken into account. , Note that here we distinguish the term interphase from the classical liquid–liquid interface (as in extractant-free water/oil (w/o) systems) due to the diffuse and oscillatory character of particle number densities in both directions along the vector normal with respect to the interface …”