Submitted to: Annual Colloid and Surface Science Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 2/10/2006
Publication Date: 6/18/2006
Citation: Bradford, S.A., Torkzaban, S., Walker, S. 2006. Coupling of physical and chemical mechanisms of colloid deposition. Annual Colloid and Surface Science Symposium. Paper No. 63. Interpretive Summary:
Technical Abstract: Considerable research suggests that colloid deposition is frequently not consistent with filtration theory predictions under unfavorable attachment conditions. Filtration theory does not include the potential influence of pore structure on straining deposition. Conversely, previous research on straining has not considered the potential influence of chemical interactions. Experimental and theoretical studies were therefore undertaken to explore the coupling of physical and chemical mechanisms of colloids deposition under unfavorable attachment conditions (pH=10). Negatively charged latex microspheres and quartz sands were used in packed column studies that encompassed a range in suspension ionic strengths and Darcy water velocities. DLVO calculations and batch experiments suggest that attachment of colloids to the solid-water interface was not a significant mechanism of deposition for the selected experimental conditions. Breakthrough curves and hyperexponential deposition profiles were strongly dependent on the solution chemistry and system hydrodynamics, with increasing deposition occurring for increasing ionic strength and lower flow rates. For select systems, the ionic strength of the eluant solution was decreased to 1 mM following the recovery of the breakthrough curve. In this case, only a portion of deposited colloids was recovered in the effluent and the majority of the deposited colloids were still retained in the sand. These observations suggest that straining is strongly coupled to solution chemistry. Increasing the solution ionic strength is believed to increase the force (secondary minima) holding colloids in pores and at grain-grain junctions, or promotes colloid-colloid interactions at these locations.