Molecular Diffusion of Chloride Ion through Marl Stone and Sand Stone

Molecular diffusion is one of the important contaminant transport mechanisms through soil and rocks. In this study the molecular diffusion coefficient of marl stone and sand stone from the Urmia City landfill site was determined using the best fit method of the observed laboratory data and the predicted theoretical data. The marl stone and sand stone samples were tested under the conditions of “through diffusion” and “in diffusion”, respectively, and the observed chloride concentrations were determined. The computer code of Pollute was used for theoretical calculations. The average diffusion coefficients of 2.48x10-10 (m2/s) and 2.55x10-10 (m2/s) were obtained for marl stone and sand stone, respectively, which show the similarity of this parameter in both samples due to the compatibility of the effect of physical parameters of the samples such as porosity and density. The results of the sensitivity analysis of the affecting parameters in molecular diffusion in modeled stones showed that the parameters of time and diffusion coefficient have more effect on the concentration of chloride ion at the end of the migration path through stone. The good agreement between the data of the experimental and theoretical models shows the accuracy of the adopted experimental methods and theoretical model. The results of this study could be used in contaminant transport calculations in the design of solid waste landfills situated on bed rocks.