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 99Tc(VII)) diffusion in compacted illite-, hematite- and limonite-montmorillonite mixtures. The effective diffusion coefficient De values were in the range of (4.29–6.71) × 10−11 m2/s at pH 3.0 and (3.44–5.72) × 10−11 m2/s at pH 9.0, respectively. Compared to montmorillonite, both De and α values enhanced at least three-folds in montmorillonite mixtures, indicating that the impurities changed the diffusion path. Interestingly, the Kd values of (0.63–3.94) × 10−4 kg/m3 were found in montmorillonite mixtures. However, the change of Da 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.