Performance And Mechanism Of Fluoride Adsorption From Aqueous Solution By Granular Ceramic Adsorbent Based On Native Volcanic Rocks

Fluorine is closely related to human health,chronic ingestion of high fluoride can cause dental and skeletal fluorosis.Drinking water is often the main source of fluoride intake by humans,especially in areas where fluoride concentrations in groundwater and/or surface water are high.Adsorption is generally considered as an attractive process because of its efficiency,ease of operation,simplicity of design,and cost-effective.Adsorption materials play a key role in adsorption process.Therefore,it is necessary to develop a adsorbent which is robust and easy to separate from water,having high affinity to fluoride and can adapt to complicated water environment.Firstly,#5 natural volcanic rock was been choosen from five different kinds of volcanic rocks according to the fluoride removal ratio.Fluoride removal performance of the volcanic rock was systematically evaluated under various operating conditions,and the mechanism of defluoridation by the #5 natural volcanic rock was discussed.Secondly,this study developed a novel ceramic adsorbent based on natural volcanic rock for removing fluoride from water.The ceramic adsorbents were prepared by natural volcanic rocks,bentonite,corn starch,and aluminium sulfate.The simplex-centroid mixture design was applied to generate the ceramic proportions and optimize the ceramic proportion for both fluoride removal ratio and ceramic strength.Lastly,fluoride removal potential of the optimized ceramic adsorbent was systematically evaluated under various operating conditions.Also,the characterization of ceamic adsorbent material was carried out.According to the experiment and characterization results,the adsorption mechanisms were discussed.Results showed that the best pH value for defluoridation by volcanic rock was 3.0,and 1 h was enough to reach adsorption equilibrium.With the increase of initial fluoride concentration,the adsorption capacity for fluoride on #5 natural volcano rock increased almost linearly.The adsorption of fluoride on #5 natural volcanic rock could be described by pseudo-second order kenetic model and Freundlich isotherm model.The aluminum sulfate played an important role in fluoride removal on the granular ceramic material.However,corn starch had two-sided influence which was positive to defluoridation while negative to the strength of ceramic adsorbent.The optimum proportions of ceramic adsorbent were 0.40 volcanic rock powder,0.36 bentonite,0.14 corn starch and 0.10 aluminium sulfate.Furthermore,the adsorbent possesses well-defined porous structure,and the BET surface area of the developed optimized ceramic adsorbent was 24.22 m2/g.The ceramic adsorbent was a typical mesoporous material since the pore size mostly distributed between 2~50 nm.Besides,the pores exhibited mainly open and irregular state.The XRD results revealed that the main chemical compositions of ceramic adsorbent were augite,quartz,hematite and corundum.Ceramic adsorbent performed well over a wide pH range of 4.0~11.0.The presence of nitrate,chloride,sulfate had no significant effect on fluoride adsorption except the high concentration of bicarbonate.Adsorption process on ceramic material followed the pseudo-second order kinetic model,and the experimental equilibrium data were fitted well with the Freundlich isotherm model.Therefore,the granular ceramic adsorbent is demonstrated as an effective,pH insensitive and highly selective for removing fluoride from water,which has large potential in the treatment of groundwater polluted by fluoride.