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Modélisation multi-échelles du comportement de l'eau et des ions dans les argiles

Abstract : Predicting the fate of radioactive waste stored in a clay formation requires a good understanding of the transport properties of water and ions in clays. Their diffusion in this charged porous medium is described by empirical parameters such as their partioning coefficient Kd which accounts for the interactions with the mineral surfaces. The present work deals with the relevance of this concept and its definition based on microscopic grounds.

We have first modeled the ionic contribution to the dielectric properties of clays and suggested an experimental determination of Kd from dielectric spectroscopy measurements.

Using microscopic simulations (Monte-Carlo and Molecular Dynamics), we then have computed the Gibbs free energy and enthalpy for ionic exchange in the case of alkaline cations. They control the value of Kd and its evolution with the temperature. The results for cesium are in good agreement with both microcalorimetric measurements and the determination of Kd at different temperatures.

We have participated in the development of a new lattice simulation method (Lattice Fokker-Planck), which we have then used to link explicitely the microscopic dynamics of ions to the diffusion-reaction model underlying the definition of Kd.

Finally, we have used Molecular Dynamics to investigate the kinetics of exchange of water and ions between clay particles (interlayer) and the extra-particle porosity. The results confirm the generally admitted idea that water and ions can explore the whole porosity, whereas anions are excluded from the interlayers.
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https://tel.archives-ouvertes.fr/tel-00181433
Contributor : Benjamin Rotenberg <>
Submitted on : Tuesday, October 23, 2007 - 5:37:54 PM
Last modification on : Tuesday, December 8, 2020 - 3:39:25 AM
Long-term archiving on: : Sunday, April 11, 2010 - 11:57:29 PM

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  • HAL Id : tel-00181433, version 1

Citation

Benjamin Rotenberg. Modélisation multi-échelles du comportement de l'eau et des ions dans les argiles. Matériaux. Université Pierre et Marie Curie - Paris VI, 2007. Français. ⟨tel-00181433⟩

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