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ABSTRACT
The distribution coefficient (Kd) value of radionuclides is an important parameter in the radionuclide migration analysis in the safety assessment of the geological disposal of high-level radioactive waste. To improve the reliability of safety assessment, the Kd values must be extensively evaluated, particularly under conditions where they might be decreased. In this study, the pH dependence of the Kd values for Sn and Nb on montmorillonite was evaluated using batch sorption experiments at neutral to alkaline pH, which might be caused by the leaching of cementitious materials and the corrosion of carbon steel. The Kd values were determined in the range 8 < pH < 12 by the experiments and were found to decrease with increasing pH. A model calculation using a thermodynamic sorption model was conducted on the measured pH dependence of the Kd values. Two different sorption sites were required to describe the pH dependence of the Kd values of Sn in the model calculation, whereas one sorption site was considered predominant in the sorption of Nb.
Graphical abstract
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1. Two studies [Citation15,Citation16] are not open to the public at present. The reported Kd values by these studies can be referred to in JAEA-SDB, which compiled reported Kd values in bentonites, rocks, and cementitious materials [Citation23].