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United States Department of Agriculture

Agricultural Research Service

Title: Colloid Transport in Unsaturated Porous Media: the Role of Water Content and Ionic Strength on Particle Straining

item Torkzaban, S.J. - U.C. RIVERSIDE, CA
item Bradford, Scott
item Walker, S.K. - U.C. RIVERSIDE, CA

Submitted to: Annual Colloid and Surface Science Symposium
Publication Type: Abstract Only
Publication Acceptance Date: February 10, 2006
Publication Date: June 18, 2006
Citation: Torkzaban, S., Bradford, S.A., Walker, S. 2006. Colloid transport in unsaturated porous media: the role of water content and ionic strength on particle straining. Annual Colloid and Surface Science Symposium. Paper No. 21.

Technical Abstract: Packed column and mathematical modeling studies were conducted to explore the influence of water content, pore-water ionic strength, and grain size on the transport of latex microsphere colloids (1 ƒÝm) in unsaturated conditions. Experiments were conducted under unfavorable conditions in terms of colloid attachment to the solid-water interface (SWI) and the air-water interface (AWI) by using hydrophilic-negatively charged colloids and a bicarbonate buffer at pH 10. DLVO calculations and/or batch experiments demonstrated that attachment of colloids to the solid-water or air-water interfaces was insignificant across the range of considered ionic strengths. The effluent concentration data and the deposition profile of retained colloids were highly dependent on the suspensions ionic strength, water content, and grain size. Mathematical modeling of the colloid transport experiments was also conducted to deduce the underlying mechanisms of unsaturated colloid deposition. Results suggest that straining is the primary mechanisms of colloid retention under both saturated and unsaturated conditions for the selected experimental conditions. The role of straining increased with decreasing water content due to the more presence of flow stagnation zones. Increasing the solution ionic strength is also believed to increase straining by stabilizing the entrapped colloids in stagnation regions and at grain-grain junctions.

Last Modified: 4/22/2015
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