Journal of Colloid and Interface Science 294 (2006) 155–164 www.elsevier.com/locate/jcis Coating of silica sand with aluminosilicate clay Jorge Jerez a,b , Markus Flury a,b,∗ , Jianying Shang b , Youjun Deng b a Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164, USA b Department of Crop and Soil Sciences, Center for Multiphase Environmental Research, Washington State University, Pullman, WA 99164, USA Received 2 June 2005; accepted 6 July 2005 Available online 8 August 2005 Abstract The objective of this work was to coat aluminosilicate clays on an inert silica support, and to characterize the properties and stability of the clay–silica coating. Two polymers, polyacrylamide (PAM) and polyvinyl alcohol (PVA), were used to bind kaolinite, illite, and smectite onto silica grains. The clay–polymer composites were studied by X-ray diffraction, FTIR, and electrophoretic mobility. Clay coatings on silica grains were characterized by mass coverage, scanning electron microscopy, specific surface area, and pH stability. Silica sand was successfully coated with clays by using the two polymers, but with PVA, the clay coating had a greater mass coverage and was more stable against pH variations. Less polymer was needed for the clay coating using PVA as compared to using PAM. Clay–polymer complexes and pure clay minerals had similar cation exchange capacities and electrophoretic mobilities, indicating that overall surface charge of the clays was little affected by the polymers. Some decrease in hydrophilicity was observed for illite and smectite when clays where coated with the polymers. The methodology reported here allows the generation of a clay-based porous matrix, with hydraulic properties that can be varied by adjusting the grain size of the inert silica support.  2005 Elsevier Inc. All rights reserved. Keywords: Silica sand; Smectite; Illite; Kaolinite; Polyacrylamide; Polyvinyl alcohol; Cation exchange capacity; Contact angle 1. Introduction Clay minerals are important constituents of soils and sed- iments, and are used ubiquitously in industrial applications. Clay minerals can be used in environmental remediation and waste water treatment. For some of these applications, it would be desirable to pack clay minerals into columns and use the columns as filters or flow reactors. However, the use of clay minerals as filters or flow reactors is limited by the low hydraulic permeability of packed clay. In addition, pos- sible compaction and clogging of pores due to migration of clay particles will further reduce the already low perme- ability. Clay minerals can be mixed with sand particles to increase hydraulic permeability, but clay particles can mi- grate and clog up pores [1]. * Corresponding author. Fax: +1 509 335 8674. E-mail address: flury@mail.wsu.edu (M. Flury). Alternative approaches have been proposed to overcome the limitation of the low permeability. Kocherginsky and Stucki [2] reported a procedure to immobilize clay min- erals between two cellulose membranes to produce a clay filter membrane. Clay minerals can be attached to silica sur- faces by using polymers as binding agents [3]. Phillips and co-workers [3,4] developed a methodology to coat clay min- erals onto inert silica grains. They used natural polymers to bind clay minerals to silica surfaces. The polymers are mixed with a solid support (silica sand or beads), and then clay minerals are added and thoroughly mixed. After dry- ing and rinsing with water, a composite clay–silica material is obtained which can be used as a clay-based porous mate- rial [3,4]. Phillips and co-workers applied these clay–silica composites as flow through reactors to remove lead [3] and organic contaminants [4] from water. Mucilage and carboxymethylcellulose polymers were used to bind clay to silica surfaces [3,4]. Other polymers seem to be promising candidates for clay–silica bonding 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.07.017