Simulated Transport of Multiple Cations in Soil Using Variable Selectivity Coefficients

Abstract

AbstractA chromatographic model for describing the transport of multiple cations in soil was modified to include both mobile‐immobile flow regions and variable ion exchange selectivity coefficients Kij for each binary combination of cation species in a ternary soil‐water system. The model was evaluated by comparing simulated results with published breakthrough curves (BTC) for Na+ and Mg2+ concentrations in effluent from columns of Yolo loam soil initially saturated with Ca2+ ions. Experimental BTC for the relatively uncompetitive Na+ species were adequately described when either constant or variable values of Kij were used in the model. For the more competitive Mg2+ species however, simulations using constant Kij coefficients described the relative location for maximum concentration but underestimated tailing for the BTC. When all of the soil solution was assumed to be mobile, description of tailing for Mg2+ BTC was improved by the use of variable Kij values in simulations, but retardation for Mg2+ transport tended to be overestimated. The combined use of mobile‐immobile liquid regions and of variable selectivity coefficients provided the observed tailing in Mg2+ BTC but minimized overestimation of retardation.