Experimental and modeling study of fission products and minor actinides extraction with N,N-dialkylamides

International audienc

Electrostatic Relaxation and Hydrodynamic Interactions for Self-Diffusion of Ions in Electrolyte Solutions

The concentration dependence of self-diffusion of ions in solutions at large concentrations has remained an interesting yet unsolved problem. Here we develop a self-consistent microscopic approach based on the ideas of mode-coupling theory. It allows us to calculate both contributions which influence the friction of a moving ion: the ion atmosphere relaxation and hydrodynamic interactions. The resulting theory provides an excellent agreement with known experimental results over a wide concentration range. Interestingly, the mode-coupling self-consistent calculation of friction reveal a nonlinear coupling between the hydrodynamic interactions and the ion atmosphere relaxation which enhances ion diffusion by reducing friction, particularly at intermediate ion concentrations. This rather striking result has its origin in the similar time scales of the relaxation of the ion atmosphere relaxation and the hydrodynamic term, which are essentially given by the Debye relaxation time. The results are also in agreement with computer simulations, with and without hydrodynamic interactions

Condensation d'ion sur une surface chargee analyse par dynamique moleculaire de la couche de Stern pour une interface eau-silice

National audienceNous etudions la couche de Stern a l'interface eau-silice chargee en calculant l'interaction ion-surface a partir de simulations de dynamique moleculaire biaisee de type umbrella-sampling [1] permettant ainsi de determiner les profils d'interaction des ions avec les surfaces d'ou decoulent les constantes d'association. Nous avons fait varier l'hydrophilicite d'une surface de silice en faisant varier le nombre de silanols en surface (Fig.1). Chaque surface comporte une charge unique portee par un oxygene deprotone qOc = -1 e

Ion dynamics in compacted clays: Derivation of a two-state diffusionreaction scheme from the lattice Fokker-Planck equation

We show how a two-state diffusion-reaction description of the mobility of ions confined within compacted clays can be constructed from the microscopic dynamics of ions in an external field. The diffusion-reaction picture provides the usual interpretation of the reduced ionic mobility in clays, but the required partitioning coefficient K-d between trapped and mobile ions is generally an empirical parameter. We demonstrate that it is possible to obtain K-d from the microscopic dynamics of ions interacting with the clay surfaces by evaluating the ionic mobility using a novel lattice implementation of the Fokker-Planck equation. The resulting K-d allows a clear-cut characterization of the trapping sites on the clay surfaces and determines the adsorption/desorption rates. The results highlight the limitations of standard approximation schemes and pinpoint the crossover from jump to Brownian diffusion regimes

Condensation at a charged surface: a molecular dynamics investigation of the Stern layer for water-silica interfaces

National audienc