Reactive Solute Transport with a Variable Selectivity Coefficient in an Undisturbed Soil Column

Abstract

The spatial distribution of major ion concentrations limits the pre‐dictability of solute transport processes in field soils. Therefore, it is important to analyze solute transport with chemical reactions based on results obtained from field soils and numerical simulation. A simulation model with cation‐exchange reactions was developed and applied to solute‐transport analysis of an undisturbed field soil. Chemical reaction terms in the convective‐dispersive equation were estimated by the Levenberg‐Marquardt nonlinear least‐squares regression technique to satisfy physical and chemical processes simultaneously. The reliability of the model was tested with liquid‐phase and solid‐phase concentrations of measured spatial distributions of Ca2+, Mg2+, Na+, and K+ after continuous infiltration of KCl solution into an undisturbed soil column. The experimental results revealed that the selectivity coefficients for Ca‐Na and Ca‐Mg exchange could be kept constant, while those for Ca‐K exchange increased with the equivalent fraction of K+ in the solid phase. The effects of the exchange selectivity coefficient on reactive solute transport are discussed based on the simulation results. When a constant selectivity coefficient was used, the model failed to predict the spatial distributions of cation concentrations in the solid phase. Thus, model predictions can be improved by use of variable instead of constant selectivity coefficients.

Modelling reactive solute transport from groundwater to soil surface under evaporation

“…Accurate estimation of the reaction term in Equation (5) will lead to concentrations of cations in the liquid phase simultaneously satisfying physical and chemical processes such as convection, dispersion and reactions. In this study, the following procedure proposed by Momii et al (1997) was employed.…”

“…After being released into the liquid phase, the front for these cations started to move towards the soil surface. At the evaporation stage of the experiment, all cations had high concentration gradients Momii et al, 1997). Initial condition of soil water distribution and initial concentration distributions in liquid phase should also be given more accurately in order to obtain better results.…”

“…The model considers cation exchange and anion adsorption as chemical reactions. The solution algorithm for reactive transport follows the theory outlined by Momii et al (1997). The calculation results are compared to the laboratory experiments.…”

Modeling of Biologically Mediated Redox Processes Using Sawdust as a Matrix

“…In this study, the finite difference method and the method of characteristics were used as numerical solution techniques to solve the model equations 9) . The model for the biologically mediated redox processes is highly complex, as it needs to involve a large number of parameters.…”

Soil heterogeneity effects on acid flushing of lead-contaminated soil

“…As mentioned, numerical studies on reactive and advective dispersive transport processes also need to include related chemical reactions (surface complexation, adsorption, dissolution, and precipitation). The sequential iteration approach (SIA) as a general calculation procedure has been used to solve governing equations in a wide range of studies (e.g., [11,19,39,42,43], amongst others). For this approach, coupling the reaction and transport terms is accomplished by an iteration procedure.…”