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 co lloids onto heterogeneously charged mineral grains is developed and ap plied to column experiments. The model characterizes mineral grain sur faces according to a patchwise charge distribution, with individual pa tches being either favorable or unfavorable for deposition depending o n their electrostatic charge. Separate rate expressions are used in th e model to depict favorable and unfavorable deposition kinetics. Decli ning deposition kinetics that ape produced when previously retained pa rticles block subsequent attachment of colloids are quantified in the model by dynamic blocking functions, Column experiments involving coll oid transport in geochemically heterogeneous porous media were perform ed using silica colloids and quartz sand. Surface charge heterogeneity was introduced into the porous medium by coating a fraction of the qu artz sand with iron oxyhydroxide. Theoretical breakthrough curves gene rated 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 b ehavior of colloidal particles in heterogeneous aquatic environments.