Geoscience Reference
In-Depth Information
Fig. 8.36 Fluoride
adsorption from aqueous
suspensions as affected by pH
a on K
+
-montmorillonite and
b on six soils (Bar-Yosef
et al.
1989
)
of soils (clay, 4-61 %; OM, 2-7 %), as affected by solution pH. The fluoride
adsorption isotherms are shown in Fig.
8.36
. In all cases, fluoride adsorption is a
function of its concentration at the selected pH values. Soil pH is correlated
inversely to the maximum number of fluoride adsorption sites, and this correlation
stems from the effect of pH on the charge density of the clay edges. No significant
correlation was found between the OM content and the maximum fluoride
adsorption. Fluoride partitioning between solid and liquid phases of neutral and
high pH is in accord with the earlier results of Flühler et al. (
1982
). The time
needed to attain quasi-equilibrium in fluoride sorption reactions is satisfactorily
described by a Langmuir adsorption isotherm model.
Cesium is a radionuclide found in radioactive wastes intended for storage in
underground repositories; it is used as a standard marker for highly radioactive and
long-lived materials. Argillaceous or clay media are considered potential earth
materials for inclusion as barriers in radioactive waste repositories, due to their
favorable properties for confinement: low permeability, high retention capacity,
