Adsorption of fluoride from water by Al3+ and Fe3+ pretreated natural Iranian zeolites

Besides human dental and skeletal fluorosis, drinking water above permissible levels of fluoride is known to cause a wide range of adverse health effects. In this study, the adsorption of Fluoride from aqueous solution onto pretreated zeolite has been studied by using batch test. The large surface area of natural zeolite (i. e., clinoptilolite from Miyaneh region, Iran) was utilized to create active sites for fluoride sorption by exchanging Na+-bound zeolite with Fe3+ and Al3+ ions. In this study, the effects of variables such as contact time, and Fluoride concentration have been investigated. Since the chemistry quality of groundwater varies from point to point, the effects of pH and electrolytes such as bicarbonate, chloride and sulfate on fluoride uptake are studied too. The performances of the Fluoride adsorption with the natural zeolite (i. e., non modified zeolite) were compared with the pretreated zeolite. Factors from the solution chemistry that affected fluoride removal from water were the solution pH and bicarbonate content. Acidic pH was the better condition for fluoride adsorption and the bicarbonate content cause higher pH values and thus diminished the affinity of the adsorption sites for fluoride. Comparing natural and deionized water with each other it was observed that the existence of onions in natural samples has an intervening effect on absorption rate of fluoride. In overall, among the aforementioned Pretreated Zeolites (i. e., Al3+ and Fe3+ -modified zeolites), Al3+ was particularly found to create adsorption media with high capacity and specificity for fluoride.