Coupled Effect of Input Concentration and Solution Ionic Strength on Colloid Transport in Saturated Porous Media

The objective of this study is to investigate the coupled role of colloid input concentration and ionic strength on the fate and transport of colloidal particles in saturated porous media. For this purpose, transport experiments were conducted in a well-controlled packed-bed system using 1 �‰ m carboxylate fluorescent latex over a range of ionic strengths (1-200 mM KCI) at a constant Darcy velocity of 0.5 cm/min. Column experiments with two different input colloid concentrations (i.e., 10 7 colloids/ml and 10 8 colloids/ml) were also conducted to examine the coupled role of colloid input concentration and ionic strength. The experimental results showed that colloid deposition was almost identical for very low and high solution ionic strength conditions; however, at an intermediate condition (i.e., 50 mM in this study) colloid deposition was enhanced for low input colloid concentration than for high colloid concentration, suggesting strong coupling influence between solution ionic strength and input colloid concentration. Derjaguin-Landau-Verwey- Overbeek (DLVO) interaction calculation results suggested that colloids may be retained at 50 and 100 mM solution ionic strength conditions via secondary energy minimum. Hence, the above results imply that the balance between the attraction energy for colloids-quartz surfaces and the colliding energy for suspending colloids-retained colloids likely played an important role on colloid deposition in porous media.