Study of the Interaction of Ni²⁺and Cs⁺ on MX-80 Bentonite; Effect of Compaction Using the “Capillary Method”

Abstract

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/m 3 . For compacted bentonite (dry density of 1100 kg/m 3 ), 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 dispersed and compacted states. For the degree of compaction studied, all exchange sites are available for sorption. For Ni, when surface complexation is the dominant sorption mechanism, a decrease of the Kd values by a factor of about 3 was observed (pH=7-8, trace concentrations). This could be explained quantitatively by a diminution of the conditional interaction constant between Ni and the edge surface site in the compacted state. One consequence of this decrease is that the contribution of the organic matter content of MX-80 bentonite to the total sorption becomes significative.2

Self-Diffusion of Water and Ions in Clay Barriers

“…In at least one clay-rock, however, direct measurements of Cs þ adsorption in intact and crushed rock yielded identical results (Figure 6.2;Van Loon et al, 2009;Chen et al, 2014), and a values obtained by adsorption on crushed rock and by diffusion in intact rock could be reconciled by using Eqn (6.10) to account for the nonlinearity of the adsorption isotherm (Appelo et al, 2010). In the case of bentonite, adsorption experiments indicate that the K d value for Cs þ adsorption is independent of the solid-water ratio at low degrees of compaction (Montavon et al, 2006) but increases with the solid-water ratio in highly compacted clay (Van Loon and , a change in behavior that may reflect the higher affinity of Cs þ for clay mineral surfaces at lower levels of interlayer hydration (Laird and Shang, 1997;Bourg and Sposito, 2011b). In short, the use of adsorption parameters obtained for dispersed clay to describe diffusion in compacted systems requires careful consideration of the species, material, and conditions of interest.…”

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

“…They were prepared for both microscopic (NMR experiments) and macroscopic (isotopic dilution experiments) measurements. The compacted medium was prepared in capillaries according to the method given in Montavon et al (2006) (see next part). The percentage water was determined according to eq.…”

“…Both model mineral phases of interest (synthetic montmorillonite, illite) and MX-80 bentonite were used. The results were compared with accessible porosities estimated for iodide and HTO using an isotopic dilution method (Montavon et al, 2006).…”

Effect of Water Saturation on the Diffusion/Adsorption of 22Na and Cesium onto the Callovo-Oxfordian Claystones

“…The experimental conditions were identical to those previously used in Savoye et al [13,14]: (i) rock samples issued from a core in the immediate vicinity and (ii) use of the same four suction values (up to 9 MPa) generated by osmosis process. The cationic adsorption values were acquired using the principle of the diffusive method developed by Montavon et al [20]. However, in our case this method was adapted to partially saturated conditions.…”