Study On Adsorption Of Fluorine From Water By Coated Filter Media

The fluorine is an important micronutrient for the production and maintenance of healthy bones and teeth, but when the concentrations of F^-1 in drinking water higher than 1.0mg/L, it could lead to fluorosis. The traditional method of removal F from water, such as chemistry-precipitation, coagulation-precipitation, adsorption removal, RO process, ion exchange process, electrical flocculation techniques, liquid-film technique, co-distillation process and so on, are applied widely around the world. The most economical sorbent for F removal from drinking water, for small community water supply, is activated alumina (AA), but sorption capacity and sorption kinetics of AA is poor for treating large quantity of water. Therefore, it is very necessary to develop a high cost-efficient F sorbent.Based on the principle and techniques of surface treatment for water material, adsorption potential of four type modified filter media, such as iron-coated-sand(IOS), manganese oxide-coated sand(MOCS), manganese-oxides-coated-alumina(MOCA) and manganese-oxides-coated ceramicist(MOCC), were investigated for defluoridation of drinking water using batch and continuous model experiment. The effects of different parameters such as pH, initial fluoride concentration and contact time were studied to understand the adsorption behavior of the sorbent under various conditions.The analysis by SEM revealed that manganese-oxide-coated sand (MOCS) and manganese-oxide-coated alumina (MOCA) was covered with aciculate MnO₂, iron-oxide-coated sand (IOCS) was cover with compact Fe₂O₃. The experiment results showed that the fluoride sorption on preparing coated media followed pseudo-second kinetics with a correlation coefficient greater than 0.96.The Langmuir equilibrium model was found to be suitable for describing the fluoride sorption with a correlation coefficient greater than 0.98. Adsorption of fluoride is governed by the combined effect of surface and intraparticle diffusion. Based on adsorption capacity, reaction rate and reuse potential from batch and column experiments, the iron oxide was found to be suitable for fluoride adsorbing. pH affected remarkably the performance of fluoride sorption on preparing coated media. Optimum removal of fluoride ions occurred in a pH range of 5～8. A bed depth service time (BDST) approach was adopted to describe the continuous flow system. The saturation concentration of the MOCA bed was found to be 1.6 g/l, which is around 2 times greater than that of activated alumina. Coated treatment with manganese oxide could improve efficiency of fluoride adsorption on activated alumina.