Basic Research On Process Of Preparing Zeolite4A By Using High-alumina Coal Fly Ash

With the rapid development of electric power industry in our country, the amount of fly ash discharged is growing day by day, which brings a great harm to the production of industry and people’s living conditions. The content of alumina and silica in high-alumina fly ash from Power Generation Company in Inner Mongolia of Datang International Group is more than80%.In order to diminish the harm caused by a lot of stacked fly ash and make full use of it, this article has put up methods such as hydro-thermal method and alkali fusion-hydro-thermal method that could prepare zeolite4A which meets the requirement of industry using high alumina fly ash as the main raw material, and has discussed the effects of the different ratio of silicon to aluminum in raw material, alkalinity, aging time, crystal temperature, crystal time and washing process on the structure and state of zeolite4A from hydrothermal synthesis to get optimum synthesis technologies of zeolite4A with fly ash, and has investigated the prepared zeolite4A by x-ray powder diffraction, scanning electron microscopy, laser granularity analysis, differential thermal analysis and thermal-gravimetric analysis nitrogen adsorption-desorption. The main research contents and conclusions are as follows:(1) This paper presents the study of calcinations of fly ash including the removal of carbon by calcination, alkali fusion and removing iron by acid washing. The optimum conditions are:the calcination and activation temperature is850℃, the calcination time is2h, the concentration of HCl is20%, the acid washing temperature is85℃, the ratio of liquor and solid is5:1, the stirring time of washing temperature is60min.(2) This paper presents the study of the effects of the different ratio of silicon to aluminum in raw material, alkalinity, aging time, crystal temperature, crystal time and washing process on the structure and state of zeolite A from direct hydrothermal synthesis. The experimental results show that zeolite A can not be prepared by direct hydrothermal synthesis, because the content of mullite in fly ash from Datang Group produced by traditional pulverized coal boilers reaches to70%, which can not be activated by calcinations effectively. In addition, higher temperature and alkalinity are not in favor of the generation of zeolite A, despite of accelerating the dissolution of mullite, and thus no zeolite A appears.(3)This paper presents the study of the effects of the different calcination temperature, the ratio of silicon to aluminum in raw material, alkalinity, aging time, crystal temperature, crystal time and washing process on the structure and state of zeolite4A from alkali fusion-hydrothermal synthesis. The optimum conditions are as follows:the calcination temperature is850℃, the ratio of silicon to aluminum in raw material is0.8, the alkalinity of NaOH is2.5mol/L, the aging time is6h, the crystal temperature is90℃, the crystal time is6h.(4) Sample of zeolite4A prepared by alkali fusion-hydrothermal synthesis was investigated by using X-ray powder diffraction, scanning electron microscopy, laser granularity analysis, differential thermal analysis and thermal-gravimetric analysis nitrogen adsorption-desorption. The results indicate that the zeolite4A prepared by optimum conditions has uniform and single size, narrow distribution, good thermal stability. Its shape is cube and in rules, and its all properties are close to zeolite4A sold in the market.