Modeling the sorption and tranport of heavy metals through landfill clay liners

Previous research has emphasized the role of landfill bottom liner as a hydraulic barrier to the hazardous leachate from reaching the subsurface environment. However, the role of the bottom liner as a geochemical barrier has been often neglected. Therefore, this research focused on identifying and modeling the operative geochemical retention mechanisms that contribute to the attenuation of heavy metals in natural liner materials.; This research was divided into five areas of investigation: (1) physical, chemical and mineralogical characterization of the landfill bottom liner materials, (2) sorption equilibrium distribution, (3) combined sorption-sequential extraction isotherm analysis, (4) sorption-sequential extraction rate analysis, and (5) convective-dispersive transport with sorption. The heavy metals selected for this study were cadmium, nickel and lead. The liner materials used for this study were collected from four landfills located in southeastern Michigan.; Results of this research indicate that the liner materials have similar characteristics. These materials were characterized as silty clay with low CEC and high carbonate content. Mineralogical analysis indicate that the clay fraction is dominated by illite and chlorite. Sorption isotherms were found to be nonlinear with Langmuir and Freundlich isotherms providing the best fit to the observed behavior. Sorption maxima was much greater than the CEC value for Ni and Pb while it was smaller for Cd. This indicates that forms other than clay-sized silicates must be playing an important role in the sorption of these metals.; Combined sorption-sequential extraction analysis was successful in determining the isotherms of the individual geochemical forms while together in a natural system. Ion exchange was inferred to be the dominant retention mechanism for cadmium, while nickel and lead were mainly retained by carbonate. The bottom liner can work more effectively as a geochemical barrier if enriched with the geochemical form that has the highest retention capacity.; Two mathematical models were found to reasonably simulate the sorption rate in a completely mixed batch reactor, the First-Order and the First-Order with Equilibrium. The First-Order with Equilibrium was inferred to be more accurate.; It was possible to predict the transport of heavy metals using batch reactor determined parameters. Transport models that incorporate the Freundlich and Langmuir isotherms provided the best predictors over other models. The sorption phase was predicted better than the desorption phase. This was attributed to the effect of sorption-desorption hysteresis.