Transport of Cationic Solutes in Sorbing Porous Media

Abstract

A model simulating transport of a cationic solute through soil under steady state water flux conditions is described, and model simulations are reported. Chemical interaction of each cation with the solid soil matrix was assumed to occur by exchangeable adsorption and was described by a general formulation of the Gapon equation. Physical interaction with the soil system was described by lateral diffusion between a mobile and an immobile liquid phase. A mathematical model was derived from the physicochemical model. The resulting system of two algebraically coupled partial differential equations was solved numerically by applying a Crank‐Nicolson time discrete Galerkin approximation. This approximation resulted in a system of nonlinear equations that was solved by Newton‐Raphson iterations. Model simulations indicated the particular and combined effects of the physicochemical processes involved. Model computations were compared with the results of a laboratory experiment employing a cation exchanger column. Considering the uncertainty of some of the parameter estimations, the model simulations and experimental results compared reasonably well.