REMOVAL OF FLUORIDE FROM WATER SOLUTIONS BY NATURAL ZEOLITE MODIFIED WITH CATIONIC SURFACTANT

摘要

The removal of fluoride from an aqueous solution by natural zeolite modified with a cationic surfactant was studied in a batch system. Hexadecyltrimethylammonium (HDTMA) bromide was used for zeolite modification. In the current study, the influence of several variables including pH of solution, initial concentration of fluoride, dose of surfactant-modified zeolite (SMZ), contact time, effects of competing ions, and effect of temperature were investigated. SMZ was characterized using XRD, XRF and SEM analyses. The equilibrium isotherm for fluoride uptake corresponded to the Langmuir model, and maximum fluoride adsorption capacity was found to be 0.96 mg/g. Kinetic studies have shown that the adsorption followed the pseudo-second-order model. When the pH was increased from 3 to 9, the fluoride removal efficiency decreased significantly. By increasing the concentration, the adsorption capacity of fluoride was increased. The best dosage of SMZ was found to be 0.2 g. The anion competition effect on fluoride adsorption by SMZ was very significant, as defluoridation in solutions containing Cl~-, I~-, and HCO_3~-ions was higher than in those containing H_2PO_4~-, NO_3~-and SO~(2-)_4 ions, and they were in the order of C~-＞ I~-＞ HCO~-_3＞ H_2PO~-_4＞ NO~-_3＞ SO~(2-)_4.