Sorption of Sn and Nb on montmorillonite at neutral to alkaline pH

ABSTRACT

The distribution coefficient (K_d) 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 K_d values must be extensively evaluated, particularly under conditions where they might be decreased. In this study, the pH dependence of the K_d 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 K_d 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 K_d values. Two different sorption sites were required to describe the pH dependence of the K_d values of Sn in the model calculation, whereas one sorption site was considered predominant in the sorption of Nb.

Graphical abstract

KEYWORDS:

• Geological disposal
• high-level radioactive waste
• montmorillonite
• Nb
• Sn
• sorption

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1. Two studies [15,16] are not open to the public at present. The reported K_d values by these studies can be referred to in JAEA-SDB, which compiled reported K_d values in bentonites, rocks, and cementitious materials [23].