Adsorption Of Fluoride Ions From Water By Activated Carbon Supporting Alumina

Fluorine is an important trace element for human body, fluoride are widelydistributed in nature in fluoride ion forms. Fluorine is an indispensable component ofteeth and bone. A small amount of fluoride can promote, strengthen tooth enamelresistance to bacteria acidic corrosion, and be very good to prevent decayed teeth,strong bones. But the harm of excessive fluoride absorption to animals and plants andthe human body, has far exceeded the fluorine deficiency effects on human health.Excessive intake will lead to "fluorosis", dental fluorosis can even lead to serious acutefluorosis, resulting in cardiac or respiratory failure and death. In China there are fluorinecontent in groundwater in many areas are exceed the standard, especially the highfluorine pollution in the north of the vast rural area.Adsorption is the most widely used method to remove Fluoride. It has manyadvantages such as high efficiency, stable effluent, simple process and convenientoperation, economical. Properties of adsorbent is a key factor affecting the adsorptionprocess, economic, efficient agent become the constant pursuit of the goal. According tothe low adsorption capacity of fluoride and great specific gravity of the traditionalalumina adsorption exist is not high enough, than the major problems, this papercombined with activated carbon with high specific surface area, developed porestructure, light and other characteristics, the activated carbon impregnated withaluminum chloride solution, drying, calcination of aluminum were loaded active carbonas adsorbent in this research. Adsorption kinetics and isothermal adsorptioncharacteristics as well as how the loading and operation conditions of the adsorbentaffects the removal of fluoride in the water were studied through the batch experiment.Then combined with X ray photoelectron spectrum analysis of surface elements, thediscussion studied on the adsorption process mechanism. The followings are the mainconclusions:â‘ The best conditions of the preparation of activated carbon loaded aluminumis:the concentration of nitric acid of pretreatment is1%, aluminum ion concentration0.3mol/L, calcination temperature is300℃;â‘¡The adsorption capacity of aluminum loading activated carbon based on Al₂O₃was much higher than Al₂O₃, removing fluoride ions from water by activated carbonsupported of aluminum, aluminum developed a greater role in this process. When reached a equilibrium concentration of1mg/L, for aluminum loading activated carbon,the fitting results of Freundlich adsorption isotherm model shows: fluorine ionadsorption capacity of unit equivalent of alumina is40times as single Al₂O₃.â‘¢The adsorption of aluminum loading activated carbon of fluoride ion followstwo order reaction kinetics model of dC/dt=-k（C-Ce）², the adsorption rate isproportional to the square of the difference of the concentration of fluoride ion systemand the equilibrium concentration,in the initial fluoride ion concentration is5-20mg.L^-1,the reaction rate constant of0.1095-0.2555L/（h.mg）^-1. Isothermal adsorption obeys theLangmuir model, and there is a good linear relation between the load of aluminumcontent and the saturation adsorption capacity;â‘£Too low or too high, pH have adverse effects on the adsorption of fluoride ion,aluminum loading activated carbon saturated adsorption capacity reached a maximumwhen the pH=8; Compared to the Freundlich model, the effect of PH on the adsorptionprocess was more suitable described by Langmuir isothermal adsorption model.⑤Coexist ions have a certain effect of adsorption of fluoride ions, when saltconcentration increased,the adsorption performance reduced, but the degree wassmaller. The effect of ionic strength on the adsorption of fluorine ion is not veryprominent, static electricity in the process of adsorption played a limited role;â‘¥Activated carbon supported aluminum has abundant chemical surfacecomposition. Under different conditions, there are more factors that may play a role.There not a single surface morphology of Al, it might play an important effect on theadsorption of fluoride ions.