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Transport and Retention Mechanisms of Colloids in Partially Saturated Porous Media

^a Department of Biological and Environmental Engineering, Riley-Robb Hall, Cornell University, Ithaca, NY 14853
^b Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996

View larger version (30K): [in a new window]   Fig. 1. Experimental setup. Not shown are the color charged-coupled device camera and computer system.

View larger version (28K): [in a new window]   Fig. 2. Interfacial potential energies for colloids as a function of distance to the grain surface, air–water (AW) interface, and another colloid. Left, hydrophilic colloids; right, hydrophobic colloids.

View larger version (29K): [in a new window]   Fig. 3. Image of the sand layers after application of hydrophobic colloids and water, showing the distribution of the blue-dyed colloids within the preferential (fingered) flow path.

View larger version (16K): [in a new window]   Fig. 4. Colloid breakthrough curves, the solid line represents the mean C/C0 values for regular (hydrophilic) sand, and the dashed line represents the slightly water-repellent sand. (a) Hydrophilic colloids, (b) hydrophobic colloids.

View larger version (18K): [in a new window]   Fig. 5. Distribution of colloids with depth in regular hydrophilic sand. The squares represent the hydrophilic colloids and the circles are the hydrophobic colloids. The open and solid represent the two replicates. The solid line is the average of the two replicates. The triangles represent the water content.

View larger version (121K): [in a new window]   Fig. 6. Four isolated menisci (or a pendular ring of water) between four sand grains associated with static air–water and air–water–solid interfaces. These are the same sand grains that are shown in Videos 1 and 2.

View larger version (59K): [in a new window]   Fig. 7. Various retention mechanisms of hydrophilic colloids: gravitational settling, filtration, colloids collection in bridges, and colloid retention at the air–water–solid interface. The picture was taken at the 10-cm depth at 30 min after the colloid suspension was added.

View larger version (65K): [in a new window]   Fig. 8. (a) Hydrophilic colloids, mainly deposited at the air–water–solid interface. (b) Hydrophobic colloids, mainly deposited within the pendular ring at the solid–water interface with a few at the air–water–solid interface.

View larger version (108K): [in a new window]   Fig. 9. Coagulated hydrophilic colloids forming "bridges" between sand grains at the 13-cm depth 98 min after adding colloid suspension.