Pertechnetate diffusion in GMZ bentonite

99 Tc is an important radionuclides related to repository safety assessment. The mobility pertechnetate (TcO 4 − ) can be reduced to immobility technetium(IV) hydrous oxides (TcO 2 · n H 2 O) by Fe(II)-bearing minerals. In China, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for the HLW repository, which is contained some FeO. The diffusion behavior of 99 Tc was investigated in GMZ bentonite by through- and out-diffusion methods. The effective diffusion coefficient ( D e ), the accessible porosity (ε acc ), apparent diffusion coefficient ( D a ) and distribution coefficient ( K d ) were decreased with the increasing of dry density. The D e values were (2.8 ± 0.2) × 10 −11 m 2 /s and (3.5 ± 0.2) × 10 −12 m 2 /s at dry density of 1,600 and 1,800 kg/m 3 , respectively. It was indicated that the dominating species was TcO 4 − during the diffusion processing. While, out-diffusion results showed that part of TcO 4 − may be reduced by Fe(II). The relationship of D e and ε acc could be described by Archie’s law with exponent n = 2.4 for 99 Tc diffusion in GMZ bentonite. Furthermore, the relationship between D a and dry density (ρ) was exponential.