Numerical modelling of ion exchange reactions in sedimentary rocks and its application to natural systems

Abe, Takeyasu  ; Ishii, Eiichi   

Understanding of diagenesis is important for engineering use of underground environments for example industrial and radioactive waste management, CO storage, and so on. Authors have been developing numerical model of reactive transport in sedimentary rocks. In order to analyse ion exchange reactions during freshening process of fossil seawater in Horonobe mudstones, active fraction model was adopted. Exchangeable cationic composition was simulated under the assumption of static exchange reactions. Our calculation revealed that Na-desorption and Ca-adsorption will occur when exchange parameters of the rocks are assumed to be those of soils. This result is qualitatively consistent with observed depth profile of bulk composition. We try to calculate bulk compositional profiles by coupled modelling between ion exchange reactions and advective-dispersive transport of solutes, and will quantitatively discuss ion exchange parameters inherent in Horonobe mudstones.