Abstract
Numerical simulations of solute transport with Ca2+ - Na+ exchange in soil under different solution concentrations and compositions of inflow and initial solutions were performed using the HP1 program (Hydrus1D-Phreeqc) under various solution concentrations and compositions. This research examined partial cation exchange, where only a portion of the exchangeable cations are replaced. When the Ca/Na mixture solutions flow through the soil, they reach equilibrium with the initial charge fraction of exchangeable cations at the midpoint of the concentration front, and no ion exchange occurs below this point. If the permeate concentration is lower than the initial solution concentration, a region emerges where the inflow concentration and a certain solution composition remain unchanged to maintain the initial exchangeable cation composition. In the lower regions, where the solution concentration approaches the initial solution concentration, ion exchange does not occur due to the balance between the effects of the total concentration and solution composition. However, even in the region where ion exchange does not occur, the transport of Ca2+ and Na+ is influenced by the cation-exchange property.
https://ror.org/01529vy56 
