Evaluating the Role of the Secondary Energy Minimum in Colloid Deposition and Release in Saturated Porous Media
Year: 2011
Type: article
Abstract: Transport and release of carboxylate-modified polystyrene microspheres of two sizes (36nm and 490nm) in saturated quartz sand under steady flow conditions were investigated in this study.The interaction energy profiles and classic DLVO framework were set up based on measurements and characterization of both particles and sand grains to evaluate and explain the colloidal behavior in the porous media.Emphasis was focused on the roles of the secondary energy minimum and effects of solution chemistry.It was found that the deposition of both colloids displayed apparent ionic strength dependence, and generally the higher ionic strength values were, the more deposition occurred.All the breakthrough curves had extended tailing, which was ascribed to the reversible colloid deposition (release from the secondary minimum) under hydrodynamic drag interactions.The 36nm colloids were observed to have retarded initial breakthrough at high ionic strength, similar to the reversible adsorption of solute species.This was interpreted to result from readily reversible deposition in the secondary minimum.The 490nm colloids did not have such delayed breakthrough and instead displayed slight size exclusion effects indicative of straining.The influence of heterogeneities on colloid deposition and release was also considered.For example, surface roughness appeared to be an important mechanism for 36nm colloid deposition at low ionic strength.At high ionic strength, however, the secondary and even primary minima dominate colloid deposition and release.Both straining and the secondary minimum were enhanced at greater ionic strength.The profile of retained colloids measured for the 490nm colloids transitioned from hyper-exponential to non-monotonic styles as the ionic strength increased.This reflects a transition from straining-dominated deposition to deposition involving both straining and the secondary minimum.Plausible release mechanisms were deduced based on experimental observations.The final release step, which involved the transition from the existence of the secondary minimum to no secondary minimum, was the most important step.During this transition, no secondary minimum association sites were available for colloid retention, and the only colloid retention iii sites left were likely straining sites such as grain-grain contact points.The release behavior indicated that global release was the net of local release and subsequent redeposition.A conceptual model was developed to include the assumptions of non-contacting deposition, critical ionic strength ranges, distributed nature of interaction energies, as well as squeezing-induced local colloid release mechanisms.
Author: Qing Ye
Institution: The Ohio State University
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2595886031