Multicomponent solute transport model with cation exchange in a redox subsurface environment

In order to clarify the behaviour of chemical species under reducing condition in a subaqueous soil similar to a paddy field, a column experiment was carried out. As Mn- and Fe-(hydr)oxides were dissolved by microbially mediated reduction, Na⁺, K⁺, Mg²⁺, Ca²⁺, Mn²⁺, and Fe²⁺ existed in the pore water as major cations. The Ca²⁺ concentration had a tendency to decrease in the layer at 5-25 cm depth in the column, whereas the Ca²⁺ concentration increased with time below 45 cm depth. This phenomenon can be assumed to be due to the desorption of Ca²⁺, by Mn²⁺ and Fe²⁺, and its infiltration. Therefore, it is necessary to develop a solute transport model which takes into account both biochemical and cation exchange reactions. In this paper, a simulation model that considers both reactions is described and applied to simulate the results of the column experiment. The reliability of this model was evaluated by comparing the calculated results with the result of the experiment.