title: Coupled effect of extended DLVO and capillary interactions on the retention and transport of colloids through unsaturated porous media.
abstract: Colloids are potential vectors of contaminants in the subsurface environment. The knowledge of transport and retention behaviors of colloids is of primary importance for assessment and prediction of subsurface pollution risks. In this study, sand column experiments were conducted to investigate the coupled effects of various interfacial forces on the retention and transport of a hydrophilic silica colloid and a relatively hydrophobic latex colloid. Water column experiments were performed to observe the movement of colloids with air bubbles. Extended DLVO interaction energies and capillary potential energy were calculated to analyze colloid retention at air-water interface (AWI), solid-water interface (SWI), and air-water-solid interface (AWS). Results show that colloid retention decreases due to increase in electrostatic repulsion and Born repulsion as well as decrease in Lewis acid-base attraction and hydrophobic interactions. Water content effect and hydrophobic effect on colloid retention become more predominant in the solution of higher ionic strength. Colloid retention at AWI is minimal (i.e., due to nonexistence of primary and secondary minima) at the ionic strengths <75mM. Capillary potential energy (107-108KBT) of colloids is 4-5 orders of magnitude greater than the extended DLVO interaction energy (~103KBT), suggesting that capillary retention at AWS is the primary mechanism controlling colloid retention in unsaturated porous media. Results from this study show that immobile solid phase (e.g., soil) could be much more important than air phase in determining colloid retention in unsaturated porous media under unfavorable conditions, especially in the solutions of high ionic strengths.
authors: Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; University of Chinese Academy of Sciences, Beijing 100039, China.
authors: Shuang
authors: S
authors: Xu
authors: Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA.
authors: Jun
authors: J
authors: Qi
authors: Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China.
authors: Xijuan
authors: X
authors: Chen
authors: Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA.
authors: Volha
authors: V
authors: Lazouskaya
authors: Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; Department of Biosystems Engineering and Soil Science, The University of Tennessee, Knoxville, TN 37996, USA. Electronic address: jzhuang@utk.edu.
authors: Jie
authors: J
authors: Zhuang
authors: Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA. Electronic address: yjin@udel.edu.
authors: Yan
authors: Y
authors: Jin
keywords: Capillary forces; Colloid mobilization; Unsaturated flow; XDLVO