Effects of ionic strength and humic acid on 99TcO4 − sorption and diffusion in Beishan granite

Abstract

In terms of pre-safety assessment of a potential site for high-level radioactive wastes disposal in China, the geochemical behavior of key radionuclides which tend to be released from the repository must be thoroughly investigated. 99Tc is a long-lived fission product with appreciable productivity in nuclear fuel, and Tc (+7) has unlimited solubility in near-field geochemical environments. In this study, the effects of ionic strength and humic acid on 99TcO4 − sorption and diffusion in Beishan granite were investigated with through-diffusion and batch sorption experiments. Results indicated that the effective diffusion coefficients (D e) of 99TcO4 − in Beishan granite varied from 1.07 × 10−12 to 1.28 × 10−12 m2/s without change with ionic strength, while the distribution coefficients (K d) negatively correlated with ionic strength of the rock/water system. This study also indicates that there is no evident influence of humic acid concentration on the diffusion behavior of 99TcO4 − in Beishan granite, due to the limited interaction between humic acid and 99TcO4 −.