Study On The Preparation Of Zolites From Coal Fly Ashes By Alkaline Fusion Followed By Hydrothermal Crystallization

The pollution of heavy metal waste is increasingly fearful with the development of industrialization,and straight threaten the environment and human health.Coal fly ash is a kind of waste from the thermal power plant and occupy a large amount of space every year.Using fly ash as raw material to synthesis zeolite molecular sieve and the products can be applied to purification of heavy metal waste.This technology of waste water treatment by synthesized zeolite from fly ash shows the method of waste reutilization with high environmental and economical benefits.Firstly,alkaline fusion followed by hydrothermal treatment was adopted to fabricate zeolites from coal fly ash.In order to obtain the precursors for hydrothermally synthesizing zeolites,the mixtures of coal fly ash,sodium carbonate and sodium hydroxide according to a certain mass ratio were calcined at high temperature.The as-calcined precursors were then hydrothermally treated to prepare zeolites.X-ray diffraction(XRD)and scanning electron microscopy(SEM)were employed to characterize crystal phase compositions and micorstructures of the obtained precursors and zeolites.The orthogonal tests were used to design the raw of alkali melting and hydrothermal treatment.The HCl acid corrosion ratio of the precursors and the methylene blue decolorization rate of zeolite were studied to optimize the material compositions and experimental conditions.The optimized process conditions were selected,and most of silicium and aluminium contained in coal fly ash can be melted to be aluminiu,silicates,the precursor of zeolites.The results show that the optimum conditions of alkali fusion are the mass ratio of coal fly ash to mixtured alkali of 1:1.5,the NaCO3to NaOH mass ratio of 1.2:1 and the calcining temperature of 800 ℃.The zeolites with the highest methylene blue decolorization rate were fabricated by hydrothermally treating at 110℃ for 8h with the conditions of NaOH concentration of 2mol/L and the liquid-solid ratio of 8:1.Secondly,based on the research result of process conditions on zeolites synthesized from fly ash by alkali fusion followed by hydrothermally treatment method.The aging time,liquid-solid ratio,alkali concentration,hydrothermal temperature,holding time,filling degree,stage heating and other process conditions on the synthetic products were explored.The adsorption of methylene blue(Methylene blue adsorption effect)on the zeolited coal fly ashes was used to simulate the adsorption of water.Crystalline phase composition of the synthesized products were characterized by XRD.The results showed that:a short aging time,the higher the degree of filling,higher hydrothermal temperature,a longer holding time and a higher concentration of NaOH are conducive to the formation of the sodalites.On the contrary,it is more conducive to the formation of zeolite NaA.Finally,Based on the last two experiments,a suitable alkali fusion and hydrothermally treatment conditions were selected.And the effects of adding different amounts of NaF;CaF2,CTAB(cetyl trimethyl ammonium bromide),PEG400(polyethylene glycol 400),SDS(sodium dodecyl sulfate)and F127(tri-block polymer)on the zeolite synthesis were studied.XRD and FESEM were employed to characterize the crystal structure and microstructure of the synthesized products.Adsorption of methylene blue was tested.Experimental results show that the additive of NaF promote the forming of NaA zeolite,CaF2 with low concentrations is conducive to generate CaA zeolite,and zeolite NaA is formed with adding CTAB at the critical micelle concentration.Adding PEG400 and F127 has little affect on the crystal compositions.But PEG400 prevented and F127 promoted the growth of the sodalite crystals.