MODELING ADSORPTION/DESORPTION KINETICS OF PESTICIDES IN A SOIL SUSPENSION

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Abstract
We studied the adsorption/desorption kinetics (time scale: 0 to 24 h) and the reversibility of the sorption process of the herbicides cyanazine and metribuzin in a suspension of a loamy sand soil. Mathematical models of pesticide sorption kinetics based on Langmuir and Freundlich isotherm equations were considered in attempts to descibe measured adsorption kinetics. We found a Freundlich model to be most suitable for description. In this model, the sorption kinetics of two classes of site are considered. The sites of the first class equilibrate at a time scale of minutes, those of the second at a time scale of hours. Measured desorption kinetics and equilibria were found to be explained well, quantitatively, by the Freundlich model whose parameters were based on adsorption kinetics and equilibria. Thus, no hysteresis was found in the isotherms, and desorption kinetics was found to proceed as fast as adsorption kinetics.