Removal Of Fluoride From Aqueous Solution On Ca-Al-La Composite Adsorbent

Presence of fluoride in drinking water can be beneficial or harmful effects on human health depending on its concentration. An appropriate concentration of fluoride is required to prevent dental cavities. However, excess ingestion of fluoride with high concentration can induce mottling of teeth, softening of bones, even neurological damages. According to the World Health Organization standards, the permissible limit of fluoride in drinking water is between0.5and1.5mg/L. In China, the standard of fluoride concentration in drinking water is below1.0mg/L. Among some treatment technologies, adsorption because of its simplicity of operation, cost-effectiveness, selectivity, high efficiency and the availability of a wide range of adsorbents, is still one of the most extensively used methods for the fluoride removal from water. Unfortunately, low adsorption capacities, slow adsorption processes and narrow optimum pH ranges of the most materials, though cheap, limit their practical applications. Therefore, an inexpensive adsorbent with high fluoride adsorption capacity, fast adsorption processes and wide optimum pH ranges is desired. In order to solve the above-mentioned technique problems, in the present paper, Ca-Al-La adsorbent was prepared by simple method.The as-prepared sample was characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area measurement. A series of batch sorption experiments were conducted to study the influence of various factors such as pH, adsorbent dose, initial fluoride concentration, temperature, equilibrium contact time and co-existing anions on the sorption of fluoride. Using batch methods, we studied the adsorption-desorption-regeneration behavior of fluoride onto the adsorbents. According to the FT-IR and XPS analysis, the mechanisms of fluoride removal by the adsorbent and its regenerations were suggested.XRD analysis indicated that the Ca-Al-La composite was not a simple mixture of the CaO, Al2O3and La2O3. FT-IR analysis indicated that the hydroxyl groups on the adsorbent surface were involved in the fluoride adsorption. XPS analysis demonstrated that the hydroxyl groups bonded to metal (M-OH) were involved in fluoride adsorption.The fluoride adsorption data on the Ca-Al-La adsorbent agreed well with the Langmuir mode. The adsorption process followed the pseudo-second-order model for fluoride. The effects of co-existing anions on the sorption of fluoride followed the decreasing order of HCO3-> SO42-> NO3-> Cl-. The Ca-Al-La adsorbent still showed high adsorption capacity after five regeneration cycles. The results of desorption and reuse experiments indicated that the Ca-Al-La adsorbent could be employed as a promising adsorbent for fluoride adsorption from drinking water.