Experimental and modelling studies of caesium sorption on illite

Reversibility of radiocaesium sorption on illite

“…Adsorption of 137 Cs on Na-illite decreases somewhat after 800 h of reaction time and is probably related to a slow release of potassium from the illite edge interlayers, causing a noticeably greater competition for Cs adsorption. This hypothesis is corroborated by the findings of Poinssot et al (1999) who reported the release of potassium from Na-saturated illite at near-neutral pH. Although the trace Cs adsorption-desorption data on the Na-saturated illite are probably influenced by a slow potassium release, they clearly show the effect of a less competitive environment on the adsorption of Cs.…”

“…These authors (Poinssot et al, 1999) position this site at the planar clay surfaces, supported by 133 Cs MAS NMR data of Kim et al (1996). Based on a three-site ion-exchange model similar to that of Poinssot et al (1999), but including a low affinity/high capacity Site III on the planar illite surfaces, Bradbury and Baeyens (2000) have derived a consistent set of selectivity coefficients for Cs relative to K, NH 4 , Rb, and Na from the analysis and modelling of a wide range of published Cs sorption data on pure illites. Cs sorption on Fithian illite (Comans et al, 1991), which is used in the present study, was also analysed and well described by their model and parameter set.…”

“…The lower affinity sites (so-called Site II) made up 90.9% of the highly Cs-selective sites, with a log K Cs K C of 1.4. A somewhat different approach was used by Poinssot et al (1999) who modelled Cs adsorption at initial Cs concentrations in solution between 2 ϫ 10 -8 M and 7 ϫ 10 -5 M, using a two-site model. Site I was considered as the FES and Site II was interpreted as an intermediate site.…”

“…Stable Cs concentrations in fresh waters are generally below 0.15 nmol.L -1 (Hilton et al, 1997), thus our laboratory experiments were performed with Cs concentrations ϳ20 times those found in the natural environment. However, Cs sorption experiments with a range of Cs concentrations have shown that below a Cs concentration in solution of 10 -8 -10 -9 M, sorption to illite occurs at the sites with the highest affinity for caesium (Brouwer et al, 1983;De Preter et al, 1991;Poinssot et al, 1999), and these sites are assumed to control caesium partitioning in the natural environment.…”

Comportement de radionucléides (Cs, I, Sr, Se, Tc) dans le sol : proposition de valeurs de Kd par défaut

“…Le travail présenté ci-après repose sur l'établissement d'une base de données de Kd ; celle-ci comporte l'ensemble des valeurs « sources » qui ont servi à définir les valeurs génériques de l'AIEA en 1994 et du DOE auxquelles ont été adjoints les résultats de publications récentes, en général postérieures à 1994. Yu et al, 2001 ; Valeur fausse, la valeur de la publication qui fait référence Liu et al, 1995 ;Poinssot et al, 1999). Ce mécanisme concerne surtout les montmorillonites (illite ou vermiculite) dans lesquelles les charges négatives sont compensées par les cations majeurs du sol (en particulier K + ).…”