SREL Reprint #2471

Selective colloid mobilization through surface-charge manipulation

John C. Seaman and Paul M. Bertsch

Advanced Analytical Center for Environmental Sciences, Savannah River Ecology Laboratory,
The University of Georgia, Drawer E, Aiken, South Carolina 29802

Abstract: The objective of the current study was to evaluate the use of amine hexadecyltrimethylammonium bromide (HDTMA) to enhance the mobilization and subsequent transport of colloidal iron oxides by selectively blocking negatively charged sites within soil or aquifer sediments. Two materials were used in a series of column leaching studies, a surface soil (Orangeburg Series) and an iron oxide-rich subsurface sediment (Tobacco Rd. Formation) both from Aiken, SC. For comparison, the same materials were leached with sodium hexametaphosphate (Na—P) as a nonselective dispersing agent. As a cationic surfactant, HDTMA is generally considered a strong flocculent for soils because of its ability to shield the electrostatic repulsion on opposing negatively charged clays, which was observed in leaching experiments for the surface soil material. Leaching HDTMA solutions through the iron oxide-coated aquifer sediments resulted in the selective dispersion and transport of iron oxides, relative to the more abundant kaolinite. Despite effluent colloid levels in excess of 6 g L-1, no column plugging was observed for the HDTMA treatments. The Na—P treatment, however, produced effluent turbidity levels that were less than HDTMA but induced rapid column plugging. Thermal characterization of the Na—P-derived colloids indicated that they were similar to the same as the bulk clay fraction of the aquifer sediment, indicating that dispersion was nonselective. HDTMA appears to block negatively charged filtration sites that limit iron oxide transport, thus enhancing colloid dispersion without inducing column plugging observed for nonselective dispersants. Iron oxides have been demonstrated to be the resident phase for many inorganic and organic contaminants within highly weathered, organic matter-poor systems. This suggests that selective mobilization of colloidal iron oxides and their associated contaminants can potentially enhance subsurface remediation activities via implementation of pump-and-treat technologies.

SREL Reprint #2471

Seaman, J.C. and P.M. Bertsch. 2000. Selective colloid mobilization through surface-charge manipulation. Environmental Science & Technology 34:3749-3755.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).