C adsorption

Na -loess clay, where batch experiments were analyzed by X-ray diffraction and infrared and far-infrared measurements. The adsorption isotherm (Fig. 8.36) shows that loess clay is selective for cesium cations. The raw material contained a large amount of quartz, and the clay material was a mixture of kaolinite and an interstrati-fied iUite-smectite mineral as a result, equilibrium Cs" adsorption data are not consistent with a single site Langmuir model. Cesium adsorption on this particular soil clay occurs by cation exchange on sites with various cesium affinities. At low concentration, far-infrared spechoscopy shows the presence of very selective adsorption sites that correspond to internal collapsed layers. At high concentration, Cs MAS-NMR shows that cesium essentially is adsorbed to external sites that are not very selective. 

Variation of Cs adsorption with depth, as a function of changes in clay content, is reported by Melkior et al. (2005) the study aimed to test the efficiency of a host rock for radionuclide confmement. Mudrock samples were collected from Callovo-Oxfordian layers in Bure (France), at depths between 22m and 78m. The total clay content increases with depth by a factor of two to three between the measured depths. Figure 8.37 depicts the of Cs as a function of its concentration in solution at equilibrium. 

Fig. 8.36 Cs+ adsorption isotherm on Na+-loess clay. Reprinted from Bergaoui L, Lambert JF, Prost R (2005) Cesium adsorption on soil clay macroscopic and spectroscopic measurements. Applied Clay Science 29 23-29. Copyright 2005 with permission of Elsevier...

Bostick et al. (2002) studied Cs+ adsorption onto vermiculite and montmorillonite with EXAFS and found that Cs+ formed both inner-and outer-sphere complexes on both aluminosihcates. The inner-sphere complexes bound to the siloxane groups in the clay structure. Combes et al. (1992) found that NpOj adsorbed onto goethite as a mononuclear surface complex. Waite et al. (1994) were successful in describing uranyl adsorption to ferrihydrite with the diffuse layer model using the inner-sphere, mononuclear, bidentate surface complex observed with EXAFS. 

Guivarch, A., Hinsinger, P., and Staunton, S. (1999). Root uptake and distribution of radiocaesium from contaminated soils and the enhancement of Cs adsorption in the rhizosphere. Plant Soil 211, 131-138. 

Staunton, S., and Levacic, P. (1999). Cs adsorption on the clay sized fraction of various soils effect of organic matter destruction and charge compensating cation. J. Environ. Radioact. 45, 161-172. 

Kj is related to the previously discussed K, of cation exchange. The general form of equation for Cs adsorption, assuming that the soil exchange sites are occupied mostly %is... 

The missing row reconstruction may be induced in ordinarily unreconstructed fee metals by driving electrons into the surface region, either electrochemically or by alkali-metal adsorption. For example, a (1x2) missing row reconstruction of Cu(110) and Pd(110) may be created by K and Cs adsorption (Barnes et al., 1985 Hu et al., 1990). The structural parameters of these surfaces are included in table 2 and show the smaller normal relaxations that are qualitatively similar to the stable missing-row forms of Ir(110). 

Fig. 2. The heat of Cs adsorption on Ru(0001) as a function of the coverage as derived from TPD measurements [96P1, 9802]. The open points are from theory and the arrow on the right indicates the calculated cohesive energy of Cs [96P1].

Figure 2. Measurements and 2- and 3-box model predictions of Cs adsorption and desorption on K-saturated illite (top) and Ca-saturated illite (bottom). Solutions were lO M in either or Ca. Clo concentration of Cs in solution at t = 0 Cl = concentration of Cs in solution at time t (i.e. Cl/Clo = fraction of total Cs in solution) particle concentration 100 mg/L. The arrow indicates the start of desorption. (Adapted from ref. 15)...

Figure 4a. Kinetic data of Cs adsorption on K-saturated illite (top) and Ca-saturated illite (bottom), linearized according to the method of Jannasch et al. (17), Data are taken from (14). The ordinate represents the left hand side of equation (9) Ctot total Cs concentration of the suspension lines (linl, lin2) indicate distinct first order processes identified by the linearization method.

---