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 betwe en the pore gas phase and the solid phase in the soil, axially dispers ed flow pattern in the column, and mass transfer resistances in the pa rticle and in the film around the particle. Data are taken on volatile organic compounds adsorption/desorption using frontal analysis chroma tography, and the breakthroughs are predicted by the model without the use of any data-adjusted parameters. It was observed that the desorpt ion breakthrough profiles exhibit a plateau section if the initial soi l loadings of the volatile organic compounds exceed a certain limit. T hese profiles cannot be predicted by the model using the adsorption is otherm for the volatile organic compound on soil. The plateau obtained in the desorption profiles was linked to the existence of a desorptio n hysteresis phenomena, which is present even at loadings close to the amount corresponding to monolayer coverage that is then known as the ''scanning curve'' The desorption hysteresis is experimentally determi ned, and its effect is ascertained by comparing desorption curves obta ined following the adsorption and desorption branches of the isotherm.