Sustainable Geoenvironmental Engineering Practice - Sustainable Practices in Geoenvironmental Engineering - page 494

100 2.0

90 1.8

80 1.6

Specific surface area

70

1.4

60 1.2

50 1.0

40

0.8

30 0.6

Grain size distribution

20 0.4

10 0.2

0

0

0.001 0.01 0.1 1 10

Grain size (mm)

FIGURE 13.12
Grain size distribution and ideal speciic surface area of the sample soil.

It is well known that more radioactive cesium can be adsorbed on the inest soil par-
ticles such as montmorillonite clay than on coarse soil particles (Maes et al., 1985) due to
the surface characteristics and speciic surface area of the particles. The sorption char-
acteristics of the particles can be used for removing radioactive cesium (Karamanis and
Assimakopoulos, 2007). If the sorption characteristics of radioactive cesium are similar to
other metal ions, the sorption quantity is thus considered to be function of the speciic sur-
face area. In the example shown in Figure 13.12, the relationship between speciic surface
area and grain size distribution is obtained by calculating the ideal speciic surface area of
spherical particles with a density of 2.65 g/cm 3 . The graph shows that speciic surface area
increases rapidly with a decrease in grain size, and that speciic surface area of particles
greater than 0.1 mm can be neglected (for this sampled soil). Furthermore, the speciic
surface area of particles smaller than D 10 , grain size (10% iner), possesses approximately
90% of the total speciic surface area. Therefore, if we remove the particles smaller than D 20
(grain size that is 20% iner; approximately 0.07 mm in Figure 13.12), most adsorbates can
be removed. It is noted that this can be achieved by removing the silt and clay fractions.

13.6.3 Segregation of Particles in Water

Smaller particles can be segregated by suspension of soil particles in water under forced
convectional low, as explained by Stoke's law.

2

D ( ρρ

η

− ) g

p w

v = (13.1)

w

18

where v w is the forced convectional upward low velocity, D is the diameter of the spherical
particle (m), ρ p is the density of the particle (kg/m 3 ), ρ w is the density of water (kg/m 3 ), g is