Preparation Of Metal Modified Chitosan Composite Adsorbent And Performance Of Fluoride Removal From Water

Fluoride in drinking water is a double-edged sword for human health: On the one hand,Fluoride is one of the essential trace elements in the human body.Appropriate amount of fluoride can be used to prevent dental caries.On the other hand,fluorine is a pro-bone element.Excessively intaken,it will affect the human body's metabolism of calcium and phosphorus,so that the body's material metabolism and physiological dysfunction are abnormal.Long-term consumption of high fluoride water can lead to dental fluorosis,bone disorders and other diseases.Fluoride poisoning caused by drinking water is distributed in 29 provinces,autonomous regions and municipalities in China of 72 million sick population,mainly in northeast,north and northwest area.There has a number of high fluoride water area in Guangdong Province found a total of 448 water fluoride disease area of natural villages.Acoording to the majority of rural areas scattered residents,it is difficult to focus on water supply.Local fluoride poisoning has without special drug treatment,the fundamental preventive measures is to use low fluoride drinking water to replace high fluoride water to reduce the intake of fluoride.The use of adsorbents to remove fluoride can effectively reduce the fluoride concentration,and currently the use of chitosan preparation of adsorbents has been widespread concern and research.Chitosan is derived from chitosan deacetylated,which has good biocompatibility,biodegradability,non-toxic side effects,and be approved by the US Environmental Protection Agency as a drinking water purification agent.Chitosan-NH₂ adsorbs F-by electrostatic attraction to achieve the purpose of fluoride removal,but the saturated adsorption capacity is too low,unmodified chitosan is not suitable directly for drinking water F^-adsorbent.By modifying chitosan,different functional groups are bound to chitosan to improve the chitosan capacity of scavenging.In the different adsorbents reported for the removal of fluoride,it has been found that rare earth or transition metal based adsorbents are potential materials for fluoride ion removal.Chitosan can be modified by some selected metal elements,these metal elements must have two aspects of the quailty,first it can chelate with chitosan;Second,it is a strong affinity with the fluorine.Such as titanium,cerium,zirconium can be chelated with chitosan,which can be made adsorbent whose performance of removing fluoride is better.The transition metal Ti ?Zr always possesses a full d-orbit that can accept a pair of electrons,which plays an important role in the attack of amino hydroxyl groups and can be the central ion of the complex.Transition metals often have a full d-orbit,and can also be the central ion of the complex,and the F-bound to the central atom to achieve the purpose of fluoride removal.And stability coefficient of TiO²⁺ ?ZrO²⁺and F-are higher,it is shown that Ti and Zr modified chitosan has strong affinity with the fluorine and is good for fluoride removal..Rare earth ions such as Ce are hard acid,it have a strong coordination capacity with coordination atoms,such as oxygen,fluorine,nitrogen,all of them belong to the hard alkali.Therefore,Ce can also be coordinated with amino or hydroxyl of chitosan to be formation of cerium modified chitosan,chitosan loaded cerium and fluoride have a strong affinity,can be used to remove fluoride ions in water.In this study,chitosan be modified by titanium,cerium and zirconium were used to prepare composite adsorbents and observe the efficiency of fluoride removal and quality of absorbtion.The specific research contents and results are as follows:1.Preparation of Titanium Modified Chitosan Adsorbent?Ti-CH?and Study on Defluorination PerformanceTo prepare titanium modified chitosan adsorbent,take 1.00 g chitosan into the beaker,add 60 m L of 5% acetic acid,stir for 1h to completely dissolve,add 8m L of 0.15ml/L titanium sulfate solution,chase a slow drop join 1:5 ammonia adjust pH to 3,mixing 30 min,chase a slow drop join ammonia?1:5?to p H 7.2 to precipitate,let stand for 1 h,and the titanium-modified chitosan adsorbent solid was repeatedly washed with single distilled water until the pH was close to 7,and dried at 80 ? for 24 h.The adsorbent was applied to the static fluoride removal of fluorine-containing water.The effects of fluoride removal and adsorption were observed.The amount of adsorbent was 3.0 g/L,and the temperature was 160r/min.The adsorption was carried out at room temperature for 60 min,pH 4⁷?5⁶ is best?,the concentration of fluoride was 0.37mg/L after 100 ml concentration of 4.99mg/L,the removal rate of fluoride was 83.27%,which accorded with GB 5949-2006 "drinking water health standard" Fluorine limited requirements.Coexisting anions HCO₃^-,CO₃^2- have a great effect on the adsorption of fluoride ions on Ti-CH.The adsorption isotherm is well fitted to the Freundlich and Langmuir isotherms,and the maximum adsorption capacity is 9.80 mg/g at 30°C.The adsorption kinetics data are better fitted to the secondary adsorption kinetic model and the particle diffusion model,and the adsorption rate is faster.Thermodynamic studies have shown that the fluoride ion adsorption process of Ti-CH adsorbent is inherently spontaneous and endothermic.The adsorption of fluoride on Ti-CH adsorbent mainly includes physical adsorption and ion exchange.Titanium modified chitosan adsorbent has good stability and static scavenging can obtain satisfactory results,and it has a good application prospect in drinking water.2.Preparation of cerium modified chitosan adsorbent?Ce-CH?and study on fluoride removal performanceTo prepare cerium modified chitosan adsorbent,take 1.00 g chitosan dissolved in 60 mL 5% acetic acid,to be completely dissolved by adding 5mL 0.15mol/L cerium ammonium nitrate solution,continue stirring for 30 min,chase a slow drop join ammonia?1:4?to adjust the pH 8.0 to precipitate cerium modified chitosan adsorbent and let it stand for 1h filter,the solid repeatedly washed with single distilled water until the pH was close to 7.0,and dried at 80 ? for 24 h.The adsorbent was applied to the static fluoride removal of fluorine-containing water.The removal efficiency and adsorption performance of the adsorbent were observed.The amount of adsorbent was 1.5 g/L,and the adsorption was carried out at a temperature of 160 r/ min for 90 min at room temperature,pH 4⁷?Water neutral is best?,the concentration of 100 ml of 5.03mg/L of high fluoride water,fluoride ion concentration after adsorption less than 1mg/L,to meet GB 5949-2006 "drinking water health standards" on the fluorine limit requirements.Coexisting anions HCO₃^-,CO₃^2-have a great effect on the adsorption of fluoride ions on Ce-CH adsorbent.The adsorption isotherm is well fitted to the Freundlich and Langmuir isotherms,and the maximum adsorption capacity is 8.62 mg/g at 30°C.The adsorption kinetics data are better fitted to the secondary adsorption kinetic model and the particle diffusion model,and the adsorption rate is faster.Thermodynamic studies have shown that the fluoride ion adsorption process of Ce-CH adsorbent is inherently spontaneous and endothermic.The adsorption of fluoride on Ce-CH adsorbent mainly includes physical adsorption and ion exchange.The static scavenging of Ce-CH adsorbent can obtain satisfactory results,and it has a good application prospect in drinking water.2.Preparation of zirconium modified chitosan-zeolite-kaolin?Zr-CZK?composite adsorbent and study on fluoride removal performancePreparation of zirconium modified chitosan-zeolite-kaolin?Zr-CZK?composite adsorbent for fluoride removal from water: 0.60 g chitosan was dissolved in 36 m L 5 % acetic acid solution,20.00 ml 0.15 mol/L dichlorooxozirconium solution was added,adjusted pH 5.0 with 5% ammonia water and zirconium incorporated chitosan for stirring 60 min,then 1.40 g zeolite and 0.50 g kaolin were added for stirring 60 min,adjusted pH 7.5 with 5% ammonia water for Zr-CZK composite adsorbent precipitation,let stand for 1 h,and Zr-CZK composite adsorbent solid was repeatedly washed with single distilled water until the pH was close to 7,and dried at 70 ? for 24 h..The suitable adsorption conditions in static adsorption test:pH value was 4⁷?the best pH 5⁶?,contact time was 120 min by oscillating 158 r/min at room temperature;The suitable adsorption conditions in dynamic adsorption test:pH value was 5⁶?the best pH 6?,adsorbent particle size of 1² mm,water samples with 3⁴ ml/min through the adsorption column.The equilibrium adsorption capacity was 3.07 mg/g at the dosage of 1.5 g/L Zr-CZK adsorbent against the water containing F-of 5.24 mg/L in static adsorption test;The treated water volume was 1800 ml and adsorption capacity was 2.71 mg/g at the dosage of 2.00 g adsorbent against the water containing F-of 5.24 mg/L in dynamic adsorption test;The water containing 5.24 mg/L Fwas reduced to F-less than 1.0 mg/L after treated with Zr-CZK in both static adsorption and dynamic adsorption.The adsorption of fluoride ions on the composite adsorbents followed pseudo-first-order kinetics and pseudo-second-order kinetics.Particle diffusion and particle diffusion are all involved in the control of adsorption process.The results showed that the adsorption isotherms of fluoride fitted Freundlich and Langmuir equation,and the maximum adsorption capacity was 10.75 mg/g at room temperature.The adsorption thermodynamics function indicates that the adsorption is spontaneous,endothermic and entropy increasing.The Zr-CZK composite adsorbent did not cause secondary pollution in water treatment and showed high adsorption capacity and efficiency in both static and dynamic adsorption fluoride.