Colloid-Facilitated Transport of Lead in Saturated Porous Media.

An improved understanding of colloid and colloid-facilitated contaminant transport in saturated porous media is important to develop best-management practices for groundwater protection and wastewater treatment. I will present findings from laboratory experimentation and mathematical modeling to explore the dynamics of clay colloids and heavy metal contaminants in water-saturated porous media. Batch adsorption experiments were used to obtain the adsorption isotherms of Pb onto kaolinite and quartz sand. Both kaolinite and sand adsorbed Pb from water, but the adsorption capacity of kaolinite was several-fold higher than that of Pb.  Laboratory columns packed with water-saturated quartz sand were used to examine the transport behaviors of kaolinite and kaolinite-Pb complex. Results from the column breakthrough experiments showed that the presence of kaolinite in the saturated porous media enhanced the mobility of Pb. The presence of Pb on kaolinite and grain surfaces, however, reduced the transport of kaolinite through the water-saturated media. Mobile kaolinite scavenged the adsorbed Pb from the sand surface to facilitate Pb transport in saturated porous media. Simulations from the Langmuir model and an advective-dispersive transport model matched well with the experimental data collected from the batch adsorption and column breakthrough studies.