Experimental Data of Bentonite Diffusivity

Diffusion experiments of bentonite are classified into transient methods and steady-state methods (Sato and Shibutani 1994 Kozaki et al. 1999). 

A typical transient method is the in-diffusion method (i.e., concentration profile method) shown in Fig. 9.9 After the species is allowed to diffuse into the onedimensional specimen, it is sliced into segments of approximate thickness of 0.5 1 mm, and the amount of the species in each slice is measured. The diffusivity is then determined using this concentration profile. The diffusivity determined by this method is referred to as the apparent diffusion coefficient, which is denoted by Da. 

A typical steady-state method is the through-diffusion method shown in Fig. 9.10, where the concentration of species from the sampling cell is measured at each time interval. At its steady-state the concentration is linearly increased, and the time-rate corresponds to the mass flux, thus we obtain the diffusivity from the slope of the mass flux. This diffusivity is referred to as the effective diffusion coefficient, which is denoted by Dg. 

The apparent values of the diffusion coefficient obtained by the in-difftision method are shown in Tables 9.1 and 9.2, and the effective diffusion coefficients obtained by the through-diffusion method are shown in Table 9.3. The effective 

From Tables 9.2 and 9.3 we recognize a difference in the apparent diffusion coefficient Da and the effective one It is known that both are represented in terms of the diffusion coefficient in bulk water Do as 

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