Geoscience Reference
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Fig. 8.37 Cs
+
adsorption
isotherm on Na
+
-loess clay.
Reprinted from Bergaoui
et al. (
2005
). Copyright 2005
with permission of Elsevier
and chemical buffering effect. Bergaoui et al. (
2005
) studied cesium adsorption on
aNa
+
-loess clay, where batch experiments were analyzed by X-ray diffraction and
infrared and far-infrared measurements. The adsorption isotherm (Fig.
8.37
) 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 int-
erstratified illite-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 spectroscopy shows the presence of
very selective adsorption sites that correspond to internal collapsed layers. At high
concentration, 133 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 con-
tent, is reported by Melkior et al. (
2005
); the study aimed to test the efficiency of a
host rock for radionuclide confinement. Mudrock samples were collected from
Callovo-Oxfordian layers in Bure (France), at depths between -422 and -478 m.
The total clay content increases with depth by a factor of two to three between the
measured depths. Figure
8.38
depicts the K
d
of Cs
+
as a function of its concen-
tration in solution at equilibrium.
Soil and sediment samples collected from Fukushima prefecture were investi-
gated for Cs content using a sequential extraction (EXAFS) procedure by Qin et al.
(
2012
). The investigations revealed that 94 % of
137
Cs was retained in the inter-
layer of the phyllosilicate mineral (Fig.
8.39
). The k
3
v(k) spectra of vermiculite,
soil, and sediments showed significantly different oscillations in frequency and
amplitude compared to those for the CsCl solution, suggesting that inner-sphere
complexes were formed on contaminated vermiculate and soil-sediment materials
were formed on vermiculite. However, the Cs-soil/sediment complexes were
smaller than those formed on vermiculite. The authors attribute these differences to
the OM content of the soil-sediment samples.