Diffusion behavior of Re(VII) in compacted illite-, hematite- and limonite-montmorillonite mixtures

A through-diffusion method was used to investigate the Re(VII) (as a surrogate to Tc-99(VII)) diffusion in compacted illite-, hematite- and limonite-montmorillonite mixtures. The effective diffusion coefficient D (e) values were in the range of (4.29-6.71) x 10(-11) m(2)/s at pH 3.0 and (3.44-5.72) x 10(-11) m(2)/s at pH 9.0, respectively. Compared to montmorillonite, both D (e) and alpha values enhanced at least three-folds in montmorillonite mixtures, indicating that the impurities changed the diffusion path. Interestingly, the K (d) values of (0.63-3.94) x 10(-4) kg/m(3) were found in montmorillonite mixtures. However, the change of D (a) value was less than two-folds, indicating that the illitization and iron corrosion of a back-fill material had no obvious influence on Re(VII) diffusion velocity.