6.3.3 Fixation of Cesium Ion by Soil
The mechanism of radiocesium fixation by weathered biotite is similar to that for
potassium, which is shown in Fig. 3.11. Although a large amount of cesium was
added, the fixed cesium can be detected by EDX. Figure 6.23a shows examples of
partially weathered biotite particles. The particles still include potassium. After
washing the weathered biotite particles twice with 2 mol L
À1 CsCl solution,
followed by washing with water, and air-drying, X-ray counts from Cs(Lα) are
detectable in the EDX spectrum (Fig. 6.23b). The Cs(Lα) peak is not detected in the
EDX spectrum of the untreated sample (Fig. 6.23c). The fixed Cs is also detectable
in a Cs element map (Fig. 6.23d). Cs is distributed over the whole area of the
weathered biotite particles, where K is also detected (Fig. 6.23e). Under the accelerating voltage of 15 kV, X-rays from the depth of about 1 μm, which is much
thicker than the basal spacing (1 nm) of biotite, are detected (see Sect. 1.4).
a
d
e
b
c
Si
Al
Mg
K CsL
Ti
Fe
Energy (keV)
0
2
4
6
8
Cs
K
Fig. 6.23 Fixation of cesium ion by weathered biotite. (a) SEM image of weathered biotite
particles picked up from a side bar deposit (2nd layer, Fig. 6.25a) of the Utsushi River, (b and c)
EDX spectra of Cs-sorbed and untreated weathered biotite, respectively, (d and e) element maps of
Cs and K, respectively, of the Cs sorbed weathered biotite particles. The EDX spectrum (b) was
obtained from the dashed square in (a)
158
6 Role of Inorganic Soil Constituents in Selected Topics