- Copyright ©2003. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.
The use of surfactant-modified zeolites and clay minerals as sorbents to remove multiple types of contaminants from water has attracted great attention recently. Sorption of cationic surfactants onto negatively charged zeolite and clay mineral surfaces is controlled by cation exchange and hydrophobic interactions. When surfactant loading is less than the cation exchange capacity (CEC) of the substrate, the retention of surfactant is via cation exchange. Once the surfactant loading exceeds the CEC of the substrate, further retention of surfactant is governed by hydrophobic interactions among surfactant tail groups, and the sorbed surfactant molecules form a bilayer on mineral surfaces, which is responsible for retention of anionic contaminants. To evaluate the feasibility of using surfactant-modified clays and zeolites for environmental remediation, the desorption of sorbed surfactant from these mineral surfaces needs further study, particularly from column flow-through desorption tests.
In this study, batch and column experiments were performed to evaluate desorption of hexadecyltrimethylammonium, a cationic surfactant, from zeolite and clay mineral surfaces. The results indicate that the sorbed surfactant is subject to slow desorption (on the order of 0.0001–0.003 per pore volume), depending on initial surfactant loading, the type of mineral substrate, and the flow rate. Desorption of surfactant showed a two-stage behavior, with the first stage likely corresponding to desorption from the outer layer of the surfactant bilayer and the second stage corresponding to desorption from the inner layer of the bilayer electrostatically bound to the mineral surface. Each stage of the desorption was well described by a first-order kinetic model.
Zhaohui Li is an associate professor of geology at the University of Wisconsin—Parkside. He has been working on using innovative materials for ground water and soil remediation for the past eight years. He is currently focusing on combining the superior solubilization power of surfactants with broad reactivity of zero valent iron and permanganate to achieve faster degradation of environmental recalcitrant contaminants.Cari Willms is a senior student at University of Wisconsin—Parkside. She has been involved in experiments using zero valent iron and surfactant-modified minerals for environmental remediation for the past two years. She is graduating in May 2003 and is currently seeking a professional career in environmental geosciences.
Stephen Roy received his bachelor's degree in geology from the University of Maine in 1996, and his master's degree in hydrology from New Mexico Tech in 1999. He has been a hydrologist with Sanborn, Head, and Associates in Portland, Maine since 1999.
Robert Bowman is professor of hydrology and director of the Hydrology Program at New Mexico Tech. He has been investigating the properties and applications of surfactant-modified zeolites (SMZ) for more than ten years. Current research includes sorption and inactivation of microorganisms and viruses by SMZ and mechanisms of SMZ-contaminant and SMZ-particle interactions.