Adsorption Of Fluoride Ions From Aqueous Solutions By Ce(Ⅲ)-impregnated Activated Alumina

Ce(Ⅲ)-impregnated activated alumina (Al2O3/Ce), a new adsorbent, was prepared for the adsorption of fluoride ions from aqueous solution in this paper’s research.Its adsorption effect and mechanism was examined by comparation with original activated alumina (OAA) and La(Ⅲ)-impregnated activated alumina (Al2O3/La). These two materials have been studied by former researchers. In this paper, based on such experiences, the experimental conditions will be uniformed to make sure the results convincing.The surface properties of the three adsorbents were measured by FTIR mothed. The result shows that impregnation with La(Ⅲ) and Ce(Ⅲ) can provide much more enhanced activate sites than OAA. OAA, Al2O3/La and Al2O3/Ce show a typically mesoporous structure.OAA, Al2O3/La and Al2O3/Ce show a typically mesoporous structure. The calculated BET surface areas of OAA, Al2O3/La and Al2O3/Ce in this study are137.59m2/g,121.42m2/g and137.23m2/g respectively.The adsorption ability changes significantly with solution pH. With increasing pH, the removal of fluoride decreases. Considering the hydrolysis of Al(Ⅲ), La(Ⅲ) and Ce(Ⅲ), the optimal pH value is3.5.The pH at the point of zero charge (pHpzc) was also estimated in this paper. It is a pH value when the quantity of positive charges on a sorbent surface just equals that of negative charges. The pHpzc for OAA, Al2O3/La and Al2O3/Ce was found to be7.41,5.35and5.82respectively.The adsorption isotherms and kinetics of fluoride removal in aqueous solution were studied. For all the three adsorbents, equilibrium data fit well to the Langmuir isotherm model and the pseudo-second-order kinetics model.The Langmuir isotherm model equation assumes that the adsorption process is performed by monolayer adsorption on specific activate sites which have no effect on each other. And the pseudo-second-order model assumes that the sorption rate is controlled by chemical interaction and the sorption capacity is proportional to the number of active sites on the sorbent.Al2O3/Ce can show a much better performance than OAA in adsorption of fluoride ions, and with comparation to Al2O3/La, this new adsorbent has similar character and adsorption effect.