Mass Transfer of Hazardous Organic Compounds in Soil Matrices Experiment and Model

Thermal processes for cleaning or removing organic contaminants from soil matrices include complete incineration applied to the soil mass and thermal desorption with purge at temperatures lower than incineration. We have performed several types of experiments to determine mass transfer parameters of volatile organic contaminants in soil matrices relevant to the above techniques and we have developed an initial model to describe the mass transfer. The experiments consist of: (1) plug deposition of the contaminant at the head of a well characterized soil column, (2) continuous, uniform exposure of the soil bed to organic vapor and subsequent removal (desorption) at varied temperatures and (3) equilibrium measurements of the target organic compounds on soil. The plug deposition experiments yielded equilibrium constants, heat of adsorption, axial dispersion coefficients and intraparticle diffusion coefficients. The continuous flow and the equilibrium tests on soil demonstrated that adsorption isotherms show good linearity at lower concentration and that the linear zone extended to higher concentrations with increasing temperature. Chromatographic response analysis and transient adsorption/desorption equations have been utilized incorporating: intra and inter particle diffusion, heat of adsorption and equilibria, in addition to normal mass transfer parameters, in developing the initial model. Equilibrium constants were strongly dependent on temperature and showed good linearity in van'l HofT plots for temperatures above the Minimum Allowable Temperature (MAT).