E. Alhajji

Ce travail s’inscrit dans le contexte du stockage des dechets radioactifs dans les couches geologiques profondes. Le but etait d’etudier les proprietes de retention de la bentonite MX-80 vis-a-vis de Cs(I), Ni(II) et Se(IV) pour les etats compactes. Ce travail etait divise en quatre parties : La premiere etude concernait la mise en place d’une methodologie de type « batch » pour etudier la retention des elements d’interet dans le systeme compacte. Une nouvelle methode a ete developpee et implique l’utilisation de capillaires. Nous avons montre que la technique de RMN du proton a bas champ est une methode de choix : elle est quantitative et permet une speciation de l’etat de l’eau dans les materiaux poreux satures en eau. La troisieme etude avait pour but de rendre compte des interactions de surface des elements d’interet dans le systeme bentonite MX-80/eau. Nous avons montre par une approche « bottom up » que la phase argileuse gouverne la retention. Finalement, le quatrieme travail a consiste a evaluer l’applicabilite du modele de retention deduit des experiences realisees pour les etats disperses aux etats consolides. Les resultats de l’etude montrent, que la compaction n’affecte pas la capacite de retention des argiles lorsque le mecanisme d’echange cationique domine la sorption. Lorsque l’interaction est gouvernee par les sites de bordure, l’effet apparait variable suivant l’element etudie : pour Ni, la compaction a pour consequence une legere diminution de la retention alors que pour Se(IV), aucun effet n’etait observe. L’origine de la diminution de retention de Ni peut etre expliquee quantitativement par une modification de la constante d’affinite du site.

The goal of the paper is to assess the applicability of sorption models to describe the retetention of contaminants on clay materials both in dispersed and compacted states. A batch method is used to characterize the sorption equilibria between Cs, Ni and MX-80 bentonite for solid to liquid ratios varying from 0.5 to 4200 kg/m3. For compacted bentonite (dry density of 1100 kg/m3), a new method is presented where the material compaction is performed in PEEK capillaries. Sorption edges and isotherms were measured in the presence of a synthetic groundwater. A model considering cation exchange reactions with interlayer cations and surface complexation reactions with edge sites was used for the dispersed state. Montmorillonite was shown to be the dominant interacting phase in MX-80 bentonite. The applicability of the model to compacted bentonite was tested. The results indicate that under conditions where the cation exchange mechanism is dominant, there is no difference between the dispe...

ABSTRACT Low field (0.54 T) proton nuclear magnetic resonance spectroscopy (H-1 NMR) was used in order to determine the water adsorbed on porous silica and nano-powder alumina, between 0 and 36% of water content by analyzing free induction decay (FID) and Carr-Purcell-Meiboom- Gill (CPMG) relaxation curves at room temperature. The main objective of this study is to demonstrate the usefulness of NMR relaxation times in characterization of the state of water in silica and alumina, the first results showed that the CPMG sequence detected all added adsorbed water and very probably the few residual water molecules of dry samples. A short apparent transverse relaxation time T-2* of 50 mu s was observed for silica and a very short one of 15 mu s for alumina.

The goal of the paper is to assess the applicability of sorption models to describe the retention of contaminants on clay materials, both in dispersed and compacted states. A batch method is used to characterize the sorption equilibria between Cs, Ni, and MX-80 bentonite for solid-to-liquid ratios varying from 0.5 to 4200 kg/m3. For compacted bentonite (dry density of 1100 kg/m3), a new method is presented where the material compaction is performed in PEEK capillaries. Sorption edges and isotherms were measured in the presence of a synthetic groundwater. A model considering cation exchange reactions with interlayer cations and surface complexation reactions with edge sites was used for the dispersed state. Montmorillonite was shown to be the dominant interacting phase in MX-80 bentonite. The applicability of the model to compacted bentonite was tested. The results indicate that under conditions where the cation exchange mechanism is dominant, there is no difference between the dispe...