Organic Solute Uptake from Aqueous Solutions by Soil: A New Diffusion Model

Abstract

A new diffusion model is proposed to describe the uptake of organic solutes from aqueous solutions by soil. The model considers that the uptake process is controlled by the pore diffusion of solutes within the soil pellets, the adsorption of solutes by the mineral fraction of soil, the surface diffusion of solutes along the mineral fraction surfaces, the partition of solutes into the soil organic matter, and the diffusion of solutes within the soil organic matter. An expression, in the Laplace domain, of the solute uptake by a soil pellet is obtained and with appropriate macroscopic conservation equations and standard numerical Laplace transform inversion techniques can be used to describe sorption and desorption as well as transport and distribution of organic solutes under a variety of conditions. On the basis of the uptake expression, a number of calculations are carried out with the objective to identify under which conditions the effect of diffusion into the soil organic matter, as well as the effects of dispersion and mineral adsorption, becomes important. Some comparisons of model predictions with experimental results are also provided to demonstrate the application of the model.