Study of Extractant Molecules as Cosurfactant at the Water- Oil Interface in Microemulsions

In the present work specific adsorption phenomena of metal ions at the water –oil interface are studied. Bicontinuous microemulsions were chosen as a model system because of their high specific surface between water and oil phases. Mixing an extremely hydrophobic extractant considered here as the co-surfactant with an extremely hydrophilic sugar surfactant we succeed to formulate microemulsion that can be described with the classical Winsor formalism for multiphasic microemulsions. From the so-called “fish-cuts” inside the phase tetrahedron we observe the phase transition WI-WIII-WII by only increasing the extractant concentration. We were particularly interested in the WIII-type microemulsions and their two excess phases. Chemical analysis of these excess phases gives us the exact film composition. Neutron scattering experiments of the microemulsion inform about the microemulsion structure as well as characteristic length scales and specific area. Finally, highly precise analytical techniques like ICP-AES permit to determine adsorption isotherms for various ions of interest in nuclear industry, like Nd, Eu, Fe, UO2 , at this water oil interface. These results lead to a better understanding of interfacial effects taking place in liquid/liquid extraction processes used for the nuclear fuel reprocessing. Ultimately this paves the way for the design of new selective ion extraction processes.