Adsorption of chromium(VI) from an aqueous solution on a surfactant-modified zeolite

The adsorption equilibrium data of Cr(VI) from an aqueous solution on a surfactant-modified zeolite (SMZ) was determined in a batch adsorber. The SMZ was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide on the external surface of the zeolite. The surface area and pore volume were determined by the N2-BET method and it was found that the surface area and pore volume were reduced due to pore blocking caused by the surfactant molecules adsorbed on the zeolite. The Cr(VI) was adsorbed considerably on SMZ but not on the natural zeolite. The effects of the temperature and pH on the adsorption isotherm were investigated in this work. The Cr(VI) adsorption capacity of SMZ showed a maximum at pH 6 and diminished 18 and 2.7 times increasing pH from 6 to 10 and decreasing pH from 6 to 4, respectively. The adsorption capacity was reduced by increasing the temperature from 15 to 25 °C since the adsorption of Cr(VI) on SMZ was due to an exothermic reaction. Desorption studies showed that Cr(VI) was irreversibly adsorbed on SMZ corroborating that Cr(VI) was chemisorbed on the SMZ. A comparison of the Cr(VI) adsorption capacities revealed that the capacities decreased in the following order: commercial granular activated carbon > organobentonite > SMZ.