Colloid transport in geochemically heterogeneous porous media: Modeling and measurements

The transport of colloids in geochemically heterogeneous porous media is investigated. A model describing the transport and deposition of colloids onto heterogeneously charged mineral grains is developed and applied to column experiments. The model characterizes mineral grain surfaces according to a patchwise charge distribution, with individual patches being either favorable or unfavorable for deposition depending on their electrostatic charge. Separate rate expressions are used in the model to depict favorable and unfavorable deposition kinetics. Declining deposition kinetics that ape produced when previously retained particles block subsequent attachment of colloids are quantified in the model by dynamic blocking functions, Column experiments involving colloid transport in geochemically heterogeneous porous media were performed using silica colloids and quartz sand. Surface charge heterogeneity was introduced into the porous medium by coating a fraction of the quartz sand with iron oxyhydroxide. Theoretical breakthrough curves generated by the model using experimentally determined parameters compared quite well to the experimental results, demonstrating the importance of geochemically heterogeneous surfaces in determining the transport behavior of colloidal particles in heterogeneous aquatic environments.