ABSTRACT

Recently, studies have been reported based on laboratory column experiments as well as field trials to show that the presence of colloidal fines such as clay particles can facilitate the transport of contaminant species such as heavy metal ions, radionucleides, hydrophobic organic compounds and so on in groundwater flows. We have conducted both experimental and modeling studies to further understand this important phenomenon. Column experiments are conducted to study the effects of mobilization and migration of colloidal fines, kaolin on the transport of a contaminant Ni2+ metal ion through the sand bed containing kaolin particles under  both plugging and non-plugging conditions. It is shown that as reported in literature, colloidal fines can facilitate the transport when they migrate with the flow. In the absence of migration, kaolin-sand bed retard Ni2+ transport as compared to sand bed due to their higher adsorption capacity. However, it is also found that sand-kaolin composite bed acts like an inefficient adsorption column with percentage saturation in general below 25 %. An interesting finding of these column experiments is that under plugging conditions, which can be induced by using lower bead size to particle size ratio, the breakthrough curves are more flattened and delayed at higher kaolin content of the bed. A mathematical model is developed based on relevant basic processes of adsorption, flow through porous media, and release, migration and capture of colloidal fines. This model predicts that the transport of contaminant species can get facilitated as has been observed experimentally, due to the presence of mobilizable fines that adsorb the contaminant species. Significantly, the model also predicts that the transport of contaminant can be prevented  by means of colloidal fines if multiparticle plugging can be induced. Regions of facilitation and prevention have been delineated in terms of parameters relating to the flow through the porous media and to the migration of fine particles. Work on transport of bio-contaminants in presence of colloidal fine is currently underway. Further novel confinement and remediation techniques of contaminants are being developed based on our work.