Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Abstract

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For 99TcO4 − in present of EDTA, the D e values was (1.2 ± 0.1) × 10−11 m2/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between 99TcO4 − and EDTA might be formed. By contrast, the D e values of ReO4 − remained unchanged in present or absent of EDTA, indicating that ReO4 − could not complex with EDTA. However, the diffusion of ReO4 − could be increased in present of EDTA, the D a value was found to be increased from 1.8 × 10−10 to 5.4 × 10−10 m2/s. It demonstrated that ReO4 − need more drastic conditions to form the Re(VII)–EDTA complexes than those used for 99TcO4 −. For both ReO4 − and 99TcO4 −, the rock capacity factor α is less than the total porosity e tot, indicating that they has little retention/sorption on the surface of bentonite.