Effect of Organic Matter on the Flocculation of Colloidal Montmorillonite: A Modeling Approach

FURUKAWA, Y. and WATKINS, J.L., 2012. Effect of organic matter on the flocculation of colloidal montmorillonite: A modeling approach. Journal of Coastal Research, 28(3), 726-737. West Palm Beach (Florida), ISSN 0749-0208. The effect of organic matter (OM) on the flocculation of colloidal montmorillonite was investigated through a complementary use of laboratory experiments and computational flocculation modeling. The model, based on Smoluchowski's coagulation model and population balance equation (PBE), was established with two key flocculation parameters: sticking efficiency and breakup parameter. The laboratory flocculation experiments tracked the temporal evolution of the mean floc sizes for aqueous systems with colloidal bare montmorillonite as well as those with montmorillonite and OM (humic acid, chitin, or xanthan gum). The key flocculation parameters were derived and calibrated through the interactive optimization of the model results by juxtaposing against the laboratory results. The calibrated flocculation parameter values revealed that OM has a complex influence on the flocculation behavior of montmorillonite. They also showed that the effect of OM on flocculation depends on the types of OM. For example, xanthan gum does not significantly modify the flocculation behavior of montmorillonite that is primarily determined by the electrical double-layer repulsion (i.e., zeta-potential) and van der Waals attraction [i.e., Derjaguin and Laudau, Verwey and Overbeek (DLVO) interaction energies], whereas chitin modifies both the sticking efficiency and breakup parameter. This study illustrates that there is no universally predictive correlation between DLVO energies or zeta-potential and flocculation parameters, as some OM has little effect on the DLVO interaction of montmorillonite colloids whereas other types of OM exert significant non-DLVO interactions such as repulsive hydration, steric repulsion, and polymer bridging. Further understanding of the physical-chemical properties of OM is needed in order to predict the flocculation behaviors of estuarine and coastal suspended colloids.