ADSORPTION OF SURFACTANTS ON CRISTOBALITE ROCKS IN AQUEOUS-SOLUTIONS

The adsorption behavior of surfactants on cristobalite rocks, siliceou s hard shales found in Aomori Prefecture, Japan, was investigated at 2 5 degrees C to clarify the surface properties of the rocks and to asse ss possible use as an adsorbent for the processing of waste water cont aining surfactants. Two kinds of rocks tested here were found to have a comparatively large Nz BET surface area of 56 similar to 67 m(2)/g w ith a negatively charged surface in aqueous solutions. Therefore, the rocks selectively adsorbed cationic surfactants such as hexadecyltri m ethylammonium ion and 1-dodecylpyridinium ion by electric attraction, whereas anionic surfactants such as aerosol OT were not highly adsorbe d. The cationic surfactants were thought to adsorb on the surface of t he rocks by the formation of a double layer. The first layeris formed by the adsorption of the polar head of the surfactant to the surface o f the rocks and the second layer is physically adsorbed on the first l ayer with the polar heads directed towards the solution. Anionic surfa ctants were adsorbed in aggregate form only at Al2O3 or Fe2O3 sites of the rocks. The amount of the adsorbed surfactant increased with the s urfactant concentration of bulk solutions, following Freundlich isothe rm. The zeta potential and the preference property of dispersion of th e rocks with various adsorbed amounts of surfactant,were used to predi ct the adsorption mechanism. It was concluded that rocks with high sur face area and high crystallinity of silica adsorb more surfactants.