Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite.

Natural zeolite was modified by loading cetylpyridinium bromide (CPB) to create more efficient sites for humic acid (HA) adsorption. The natural and CPB modified zeolites were characterized with X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and elemental analysis. The effects of various experimental parameters such as contact time, initial HA concentration, solution pH and coexistent Ca2+, upon HA adsorption onto CPB modified zeolites were evaluated. The results showed that natural zeolite had negligible affinity for HA in aqueous solutions, but CPB modified zeolites exhibited high adsorption efficiency for HA. A higher CPB loading on natural zeolites exhibited a larger HA adsorption capacity. Acidic pH and coexistent Ca2+ were proved to be favorable for HA adsorption onto CPB modified zeolite. The kinetic process was well described by pseudo second-order model. The experimental isotherm data fitted well to Langmuir and Sips models. The maximum monolayer adsorption capacity of CPB modified zeolite with surfactant bilayer coverage was found to be 92.0 mg/g.