Evaluation of sorption and diffusion behavior of selenium in crushed granite by through-diffusion column tests

Distribution coefficients (K _d), apparent diffusion coefficients (D _a) and retardation factor (Rf) in this work obtained by batch and through-diffusion experiments have been performed, respectively. The accumulative concentration method developed by Crank (The mathematics of diffusion, 12) was applied to realize apparent and effective diffusion coefficient (D _a and D _e) of Se. Besides, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K _d) obtained by batch tests in 14 days under aerobic and anaerobic systems were 6.98 ± 0.35 and 5.21 ± 0.25 mL/g. Moreover, Rf^cal and K _d ^cal of Se obtained from accumulative concentration’s method in through-diffusion test showed an obvious discrepancy with the increase of length/diameter (L/D) ratio. However, it presented an agreement of Rf^H/Se and K _d ^H/Se in a various L/D ratio by comparison of apparent diffusion coefficient’s (D _a) between HTO and Se. It appears that the Rf^H/Se and K _d ^H/Se obtained from the through-diffusion experiments are lower than those derived from the batch experiments. Therefore, it demonstrates that reliable Rf and K _d of Se by through-diffusion experiments could be achieved at a non-reactive radiotracer (HTO) prior to tests and will be more confident in long-term performance assessment of disposal repository.