Colloid-associated contaminant transport in porous media: 1. Experimental studies

Abstract

Many studies have identified colloid-associated transport of contaminants as an important mechanism of contaminant migration through groundwater. It is a complex phenomenon in porous media involving several basic processes such as adsorption of contaminants, release and migration of colloidal fines, and entrapment of fines at the pore constrictions. The effects of these basic processes on the contaminant transport are studied. Column experiments are conducted to study the effects of the mobilization and migration of colloidal fines, kaolin on the transport of contaminant, and Ni2+ metal ion through the sand beds containing kaolin particles under both nonplugging and plugging conditions. As reported in literature, colloidal fines can facilitate the contaminant transport when they migrate with the flow. In the absence of migration, kaolin-sand beds retard Ni2+ transport in comparison to sand beds due to their higher adsorption capacity, but the sand-kaolin composite bed acts like an inefficient adsorption column with percentage saturation (which is in general below 25%). It is interesting to note that under plugging conditions, which can be induced by using a lower bead size to particle-size ratio, the breakthrough curves are more flattened and delayed at a higher kaolin content of the bed.