Preparation Of Zeolite Modified By Zirconium And Its Ability For Fluoride Removal

There are many natural zeolites in China, As zeolite has a strong adsorption because of its structure, and Zirconium oxides and hydrous oxides has a strong affinity for fluoride and unique specifications such as large specific surface areas and high adsorption, heat resistance and radiation, they were used to make the composite adsorbents for fluoride:conditions of static, dynamic adsorption, the adsorption properties, and Fluoride removal applied research, adsorbent regeneration, and the reserach of thermodynamics and Kinetics of the adsorption of fluoride. The results are as follows:The optimal conditions of preparation of zeolite were:modified with10%HCl, Zr(Ⅳ) concentration of0.15mol/L, bath temperature of70℃and soaking time of2h,placed for24h and modified for3times. After modified, the optimized static adsorption conditions of zeolite were:pH=7, oscillation temperature is40℃; oscillation time is60min; initial concentration is10μg/mL; solid-liquid ratio is1:100. Under optimized adsorption condition, The absorption rate of fluoride by modified zeolite reach to96%, it is much better than original zeolite(32.94%) and modified zeolite with acid (57.05%). which suggested the natural zeolites modified by zirconium have excellent performance in fluoride adsorption.XRD analysis and scanning electron microscopy shows that a certain amount of zirconia are imported into the surface and pore of zeolite, and it’s the main reason that adsorption significantly increased.In the condition of optimized adsorption, when the fluoride concentration is less than10μg/mL, the absorption rate of fluoride by modified zeolite can reach to96%, after treated fluorinated water, the fluoride concentration were below1.0μg/mL, reached the stipulation by the national purifielc water standard.Dynamic test results showed that:the concentration of fluoride and bed height has a great influence on fluoride by zirconium modified zeolite, and pH was not significantly. When the fluoride dosage was5.0g, maximum flow was10.0mL/min. When the flow rate of raw water was6.0mL/min, fluoride concentration of20.0mg/L could be handled within the reach of national fluoride standards.After adsorption of fluoride on the modified zeolite, desorption studies have shown that:static conditions with0.5mol/L NaOH and dynamic conditions with0.05mol/L NaOH can desorb fluoride effectively, desorption rate can reach to90%.Adsorption equilibrium and adsorption kinetics were studied, results showed that with increasing equilibrium concentration of fluoride adsorption capacity increased rapidly; in the low equilibrium fluoride concentration,can reached a high adsorption capacity, indicating that the adsorbent has a strong affinity to fluoride.It’s a significant feature of this defluorinating agent. Adsorption equilibrium fit better with Freundlich adsorption isotherm. Adsorption rate is in line with the two dynamic equations. And calculate the thermodynamic functions:△H(35.226kJ/mol),AS(0.129kJ/k.mol), AG(-2.676,-3.744,-5.268kJ/mol).The results showed that the adsorption is an endothermic reaction(△G<0), the chemical adsorption(△H>35kJ/mol).The fluoride removal mechanism of the modified zeolite studies have shown that:The OH-of zirconia play an important role in adsorption capacity of fluoride ions on fluoride removal agent.The OH" more load on the zeolite surface,the fluoride removal capacity there will be some growth. But when the zeolite surface zirconium hydroxy saturated surface load coincide with each other, fluoride removal reached a certain degree after no longer increase.