CONSIDERATION ON EFFECTIVE DIFFUSIVITY OF STRONTIUM IN GRANITE

Diffusive behavior of strontium and certain kinds of divalent cations in Inada granite were studied by a through-diffusion method. In order to examine the effect of sorption onto overall diffusive behavior, two kinds of solutions were used: 0.1 M KCl solution and deionized water. The effective diffusion coefficient (D(e)) and rock capacity factor (alpha) were (2.0-3.6) x 10(-13) m2/s and less than 0.022 in 0.1 m KCl solution and (0.32 approximately 1.7) X 10(-11) M2/s and 1.5 approximately 2.4 in deionized water respectively. The D(e) and alpha in deionized water were much larger than those in 0.1 M KCl solution. These results are well explained by taking into account the diffusion of sorbed ion or the surface diffusion. In support of this mechanism, most D(e) values of Sr reported for various rocks are found proportional to the sorptivity (rhoR(d)). In the case that the sorptivity is low, D(e) of Sr depends on porosity like that of nonsorbed iodide. The effective diffusion coefficient of Sr in rocks was well explained by taking into account pore and surface diffusion and was expressed as D(e) = 2.1 x 10(-10)epsilon1.3 + 3.5 x 10(-12)rhoR(d). The effective diffusion coefficient of divalent cations in the granite was found proportional to their diffusion coefficients in bulk solution.