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Adsorption of Chromium(VI) from Aqueous Solution on a Surfactant Modified Zeolite

Roberto Leyva-Ramos, Paola E. Diaz-Flores, Araceli Jacobo-Azuara, Laura Fuentes-Rubio, and Rosa M. Guerrero-Coronado. Centro de Investigacion y Estudios de Posgrado, Universidad Autonoma de San Luis Potosi, Av. Dr. M. Nava No. 6, Zona Universitaria, San Luis Potosi, 78260, Mexico

The adsorption equilibrium data of Cr(VI) on a surfactant modified zeolite (SMZ) was determined in a batch adsorber. The SMZ was prepared by exchanging the cationic surfactant hexadecyltrimethylammonium on the external surface of the clinoptilolite particles. The surface area, pore volume and average pore diameter were determined by the N2-BET method and it was found that the surface area was reduced due to pore blocking caused by the surfactant molecules adsorbed on the external surface. The Langmuir isotherm model was fitted to experimental adsorption equilibrium data and the isotherm constants were calculated using a least-squares method. It was observed that Cr(VI) did not adsorbed on the natural zeolite but adsorbed considerably on SMZ. The effects of temperature and solution pH on the adsorption isotherm were investigated by measuring the adsorption isotherm at temperatures of 15, 25 and 35C and at pH values from 4 to 8. The maximum adsorption capacity occurred at a pH range of 4-5 and the adsorption capacity was reduced 28.4 and 83.2 % when the pH was increased from 5 to 6 and 5 to 8, respectively. The adsorption capacity was not affected by the temperature in the range from 15 to 35 C. The reversibility of the adsorption of Cr(VI) was investigated by first adsorbing Cr(VI) on the SMZ at pH 6 and then desorbing at pH 4,6 and 8 the Cr(VI) adsorbed. It was found that the Cr(VI) was adsorbed irreversibly on the SMZ but some part of the Cr(VI) was desorbed. The Cr(VI) adsorption capacity of SMZ was compared to those of bone char and organoclay and the adsorption capacity decreased in the following order: organobentonite > SMZ > bone char. It was concluded that the adsorption capacity of the SMZ was very low.