Synthesis Of Bimetal (hydr-) Oxides And Its Application On Removal Of Arsenic And Fluoride

The living standard was increased with the development of the economy in China,while a series of environmental problems arose slowly and affected the human lives.Among these problems,water pollution attracted more and more attention due to the close connection with the safty of the drinking water.For example,people in northeast of China were facing the problem of concentration over-standard of arsenic and fluoride in drinking water.Besides,the extraction of arsenic and fluoride ore caused the fact that the concentration of arsenic and fluoride exceeded the standard seriously in water.Extensive arsenic and fluoride were transferred to the underground water through the way of nature migrate endangering the safty of the drinking water and making it urgent for us to develop a method for the removal of arsenic and fluoride from waterboday.Adsorption is a common method to remove pollutants including arsenic and fluoride due to low cost and reusability.Adsorbent with higher adsorption amount is a key part of adsorption method.In this thesis,two kinds of adsorbents were synthesized and used on arsenic and fluoride removal.Detailed experimental results were discussed as followed:(1)Ca-Al layered double hydroxides(LDHs)with different Ca/Al molar ratios were composited at different pH values were synthesized by co-precipitation method.A series of Fe–Ti bimetal oxides with different Fe/Ti mole ratios were also synthesized through a co-precipitation method.The composite materials were characterized with X-ray diffraction(XRD),scanning electron microscopy(SEM),Thermogravimetric analysis(TGA)and p Hpzc.The results showed that different synthesis conditions of Ca-Al LDHs had a significant effect on their morphology,layered structure,and particle size distribution.(2)Synthesied Ca-Al LDHs and Fe-Ti bimetal oxides were used to remove As(Ⅲ)and As(Ⅴ)form waterbody.The adsorption experiment result showed the maximal adsorption capacity of As(Ⅲ)and As(Ⅴ)were 41.08 mg/g and 94 mg/g,the Freundlich model and pseudo second model hava been proven more appropriate than other models for fitting As(Ⅲ)and As(Ⅴ)adsorption.The pH values influenced the amount of adsorption obviously due to the existing form of As(Ⅴ)could be affected and the electronic bonds were weakened among these layers in the Ca-Al LDHs.The removal of arsenic by Fe-Ti bimetal oxides was a combination of the fast and slow adsorption process.The bimetal oxide with a Fe/Ti molar ratio of 0.8:0.2 showed the best performance in As(Ⅲ)removal and the maximal adsorption capacity of As(Ⅲ)and As(Ⅴ)were 111mg/g and 31mg/g,respectively.The reason can be investigated that the adsorption capacity of As(Ⅴ)was significantly increased with the decreaed pH value and the increased ionic strength with Fe-Ti bimetal oxides and the presence phosphate inhibited the arsenic removal significantly while the coexisting sulfate and bicarbonate showed little effect on arsenic removal.The adsorption-desorption experiment indicated that Fe-Ti bimetal oxides can be reused.(3)The removal of the fluoride in aqueous was carried out with Ca-Al LDHs and Fe-Ti bimetal oxides and the kinetic,isotherm and effects of the adsorption were also studied.The LDHs had the highest capacity for the fluoride removal(149mg/g)with the synthized condition of Ca/Al molar ratio of 2 and the pH of 12 and the equilibrium could be reached within 30 min.investigating the high adsorption efficiency using this material.The result of the effect of pH value indicated that the fluoride could be effectively removed in a wide pH range by Ca-Al LDHs.As for fluoride removal form waterbody by Fe-Ti bimetal oxides,Langmuir model showed the maximal adsorption amount was 76mg/g and the pseudo second order model has been proven fitting well with fluride adsorption kinetics with the equilibrium time of 200 min.The large surface area of Fe-Ti bimetal oxides ensures the high adsorpent amount of fluoride and the pH affected the adsorption amount slightly.