ZIRCONIUM MODIFIED ACTIVATED CARBON MATERIALS FOR WATER DEFLUORIDATION

摘要

Introduction Research in fluoride removal from drinking water has been conducted for several years. The guideline value (permissible upper limit) for fluoride in drinking water has been set at 1.5 mg L~(-1) according to the World Health Organization [1], however, the U.S. Department of Health and Human Services recommended 0.7 mg L~(-1) in January 2011 since recent studies confirmed the hazard of this element for human beings. Unfortunately, many places around the world have high fluoride concentrations, up to 30 mg L~(-1), in water supplies that may cause widespread fluorosis and skeletal illneses among the world population [2]. Many methods have been developed for fluoride removal from water including adsorption, ion exchange, electrodialysis and precipitation. Nevertheless, more efficient and cost-effective processes and materials are needed to fulfill the present regulations. Adsorption has been widely used because is the most cost-effective methodology for removal of ionic contaminants, like fluoride ions, in aqueous streams. Various fluoride adsorbents such as activated alumina, activated carbon, minerals, among others have been tested and have shown that large surface area and the interaction adsorbent-fluoride are important factors for defluoridation process [3,4]. Although activated carbon poorly removes fluoride from water, when it is impregnated with metal ions the adsorption capacity increases [5]. Zirconium and its metal complexes have been used for fluoride monitoring due to their high affinity for fluoride ions. When loaded in activated carbon, zirconium complexes increase the fluoride removal by 3 to 5 times at high fluoride concentrations [6]. The authors consider that the surface area of modified adsorbents is a key factor to increase their fluoride adsorption capacity, however, this is often neglected. The aim of this research is to improve the fluoride adsorption capacity of Zr(IV) modified granular activated carbon by controlling the particle size of the metal ion with a complexing agent such as oxalic acid during the impregnation process.