Geochemical study of deep groundwater in the Horonobe area; Estimation of a reaction controlling the NH concentration in groundwater

Sasamoto, Hiroshi

no journal, , 

Cs has been considered as an important radionuclide for performance assessment of high-level radioactive waste disposal. It is expected that migration of Cs in rock would be retared by sorption on clay minerals. Sorption of Cs on clay minerals, however, might compete with other cations such as NH and K in groundwater. Therefore, it would be quite important to estimate the reaction controlling the NH concentration in groundwater for evaluation of Cs migration in rock. In the present study, thermodynamic calculations were conducted to estimate the reaction controlling the NH concentration in the Horonobe groundwaters. As the results, the Horonobe groundwaters were plotted on the mineral stability field of muscovite similar to illite which was dominant clay mineral in the Horonobe sedimentary rocks, and additionally an activity ratios of Hfor NH and K for groundwaters were plotted on the line of slope 1. These results suggest that the NH concentration in the Horonobe groundwaters could be controlled by an ion exchange reaction between NH and K on illite in the sedimentary rocks.