The Study Of Fluoride Removal By Ferric Sulfate Modified Activated Alumina

High fluoride drinking water harms body health. About 70 million people are threated by high fluoride drinking water in China. Therefore it is important to study the removal of fluoride from drinking water. In order to optimize the deflurine performance, batch and column adsorption of fluoride by ferric sulfate modified activated alumina (MAA) were studied in labaoratory. Field demonstration plant was designed and operated.Batch studies showed that the adsorption rate of F- onto MAA was fast in initial four hours and became lower with adsorption going on. Pseudo-second order kinetic model fit kinetic data very well. Diffusion analysis suggested the adsorption rate was controlled by both external diffusion and intraparticle diffusion, and the external diffusion was dominant. Elovich equation studies showed that MAA adsorption energy of the sites was heterogeneous, and the adsorption of fluoride may be chemical adsorption; Sips isotherm could describe the adsorption equilibrium process very well, with the maximum adsorption capacity in 49.4954 mg/g, and coefficient of uniformity y in 0.6019, which also suggested the surface was heterogeneous. D-R equation calculation gave the adsorption energy of E=12.78kJ/mol in lower concentration (Ce<7.86 mg/L), which also showed dominant of chemical adsorption.Single column adsorption study showed that inlet concentration and pH affected adsorption significantly. The breakthrough volume increased 1.9 times when inlet concentration decreased from 5 mg/L to 2 mg/L. The breakthrough volume increased 2.6 times when inlet pH decreased from 7.6 to 6.0. The breakthrough volume decreased with increasing inlet space velocity. When space velocity was in 1.3-2.0 h-1, the breakthrough volume kept steady; but when space velocity was greater than 2.0 h-1, the breakthrough volume decreased greatly. When the space velocity was fixed and unigue, geometric dimension of column did not affect breakthrough volume.Three serial columns adsorption was studied in inlet pH 5.5-7.8, the adsorption capacity and breakthrough volume increased 48-92% and 39-96%, and the adsorption capacity was closed to 87-98% of the end capacity. The adsorption effect of three serial columns was much better than that of single column adsorption.Demonstration project running results showed that for all the running period the outlet water agreeed with drinking water standard. When the inlet pH was in 6.7-7.8, the single adsorption half-cycle can last 8-11 days.The running cost of defluorine was estimated in 0.528-0.658 RMB ￥/T.