COMPETITIVE ADSORPTION DURING SOLUTE TRANSPORT IN SOILS

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Abstract
Computer simulations of the effects of Langmuir and Freundlich-type competition, in binary systems under equilibrium and dynamic (time-dependent) conditions, were presented and discussed. These simulations indicate that during competitive adsorption (for both Langmuir and Freundlich-type competition), the presence of a competing species can have a marked effect in depressing (lowering) the equilibrium isotherm of an adsorbing species to an extent determined by the relative solution concentrations, distribution and selectivity coefficients, etc. In Langmuir-type competitive dynamic (time-dependent) adsorption, the amount of adsorption can exceed the equilibrium value during some periods. In binary competition, the experimental conditions, such as solution-to-solid ratio, can have significant influence on the shape of the isotherm and thus on the isotherm parameters estimated. Freundlich and Langmuir-type competitive adsorption isotherms in binary systems may resemble the isotherms in single-species systems. Thus, with limited experimental data, one may easily overlook the presence of competitive adsorption, even when it has significant influence on the equilibrium adsorption isotherms, and the adsorption parameters may change from one set of experimental conditions to another. Accounting for competition should allow the estimation of correct parameters.

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