The size of colloidal particles has long been considered to be a major factor in their mass transport in aquatic environments. In aggregation and deposition reactions, the mass transport rates of colloidal particles are expected to decrease with increasing particle size since thermal diffusion dominates this process. Particle size has also been considered to affect colloid chemical interactions, at least on theoretical grounds, with predicted rates of attachment in aggregation and deposition processes decreasing substantially as colloidal particle size is increased. Observations have failed to confirm this prediction. The situation becomes more complex and predictions more consistent with observations when reversible aggregation and deposition such as can occur in secondary minima are considered. This is done in this paper in simulations using a combination of Brownian dynamics and Monte Carlo (BDMC) techniques. Some experimental observations of virus transport in porous media are presented. The BDMC simulations provide a partial explanation for these results.
