Mathematical modeling of adsorption and desorption of volatile contaminants from soil : Influence of isotherm shape on adsorption and desorption profiles

A mathematical model is presented for the prediction of adsorption and desorption profiles of volatile organic contaminants from oven-dried soil in a packed-bed column. The model assumes local equilibrium between the pore gas phase and the solid phase in the soil, axially dispersed flow pattern in the column, and mass transfer resistances in the particle and in the film around the particle. Data are taken on volatile organic compounds adsorption/desorption using frontal analysis chromatography, and the breakthroughs are predicted by the model without the use of any data-adjusted parameters. It was observed that the desorption breakthrough profiles exhibit a plateau section if the initial soil loadings of the volatile organic compounds exceed a certain limit. These profiles cannot be predicted by the model using the adsorption isotherm for the volatile organic compound on soil. The plateau obtained in the desorption profiles was linked to the existence of a desorption hysteresis phenomena, which is present...