Sorption behaviour of lead onto montmorillonite in the presence of carbonate

Sugiura, Yuki  ; Ishidera, Takamitsu ; Suyama, Tadahiro*; Okazaki, Mitsuhiro*; Hamamoto, Takafumi*; Ishida, Keisuke*; Tachi, Yukio  

Pb-210 is one of the important radionuclides for the performance assessment of geological disposal. In this study, we investigated the sorption behaviour of Pb onto montmorillonite in the presence of carbonate. Kd values decrease with the increase of DIC concentration in pH8-11 region. Data from the carbonate-free and conditions of 2.5 and 25 mM DIC can be fitted using surface complexation constants determined from carbonate-free condition dataset. However, the model underestimated the data at DIC concentrations of 100 and 250 mM. Therefore, the formation of a ternary complex was assumed and its surface complexation constant was determined by fitting the experimental data at DIC concentrations of 100 and 250 mM. The results succeeded in fitting all experimental data well. Spectroscopic studies on the ternary complexation system will be required to enhance the reliability of the present results.