Synthesis Of Zeolites From Coal Fly Ash And Their Applications In Removing Heavy Metals From Wastewaters

Coal fly ash is a kind of granule material by combustion, which mostly comes from the coal-firing power plant. Coal fly ash, owing to being discharged fields and rivers at random, poses a serious threat to thermal power industries specifically. Because it not only occupies large space but also pollutes the environment on which the life of people relies.Coal fly ash utilization methods include extraction of alumina/magnetite, fly ash bricks, pozzolan cement, and concrete which are all low value utilization. Currently, synthesis of zeolites from fly ash, a high value added product, is receiving increasing attention.To better exploiting coal fly ash, we elected the coal fly ash from the Yangluo Thermal Power Plant located in Wuhan city in China, from which zeolites were synthesized by microwave and autoclave heating. It was amorphous material with some crystalline phases such as quartz and mullite. By scanning electron micrograph method, we can see the coal fly ash was of pearl morphology. Chemistry analysis indicated that the contents of SiO₂ and Al₂O₃ in the fly ash sample are higher than 75%, and the ratios of SiO₂/ Al₂O₃ are 1.52. It belong to high Al and low SiO₂/ Al₂O₃ rate fly ash and can be used as the material of synthesizing zeolite from fly ash.Through matter analysis of XRD, observation of SEM and infrared spectral analysis, on the condition that we can synthesize zeolites by heating the coal fly ash and making it produce hydrothermal synthesization reaction with high-pressure kettle. In this test, we get the three types of zeolites: NaPl zeolite, analcime and chabazite. Moreover in the common, each zeolite can produce 1³ zeolites which mentioned above, the most transforming rate from the coal fly ash to zeolite of each sample can amount to 40-75%, the total that of each group can amount to 60⁸0%, the sample, which its transformation rate is close to and larger than 75% and is retested with the same parameters, have more recurrence, its transforming rate also have more stability.By adjusting the parameters, we make large amount of hydrothermal test with the high-pressure kettle. And we get two groups of the relatively best test parameters by optimization method: in one group the rate of solute and coal fly ash is 2.0, the concentration of NaOH is 1.0mol/L, the synthesization time is 48 hours, the synthesization temperature vary from the 90 ℃ to 190℃, the synthesization pressure is less than 10 Mpa, In anther group, the rate of that vary from 1.25 to 2.50, the average is 2.0, the concentration of that is 2.0 mol/L, the time is 24 hours , the temperature vary from the 90℃ to 190℃, the pressure is less than 10Mpa.(The temperature and pressure is the same as that of one group.)Laumontite, Chabazite and NaPl zeolite can be synthesized from coal fly ash that producethe hydrothermal synthesizing reaction by radiation heating with microwave oven, each sample only produce a kind of zeolite in the synthesized sample, its transforming rate vary 20% to 40%. The zeolite can be got in ten minutes in reaction, the transforming rate amounts to the max at the 30 minutes. The kind of synthesized zeolite is different under the different parameters and the same condition; but the kind of synthesized zeolite is same when the parameters and condition is same and the synthesized time is different. The kind of synthesized zeolite is also different under the condition of the same parameters and the different experiment condition. The relatively best synthesized parameters are that the rate of solute and coal fly ash is more than 2.5 , the concentration of NaOH varies from 1 mol/L to 2 mol/L, the temperature varies from the 76 ℃ to 94℃ , the synthesized time are 30 minutes.It is disadvantageous for the zeolite to form nucleus and react completely by microwave heating in short time, the formation of the crystal, the growth rate of crystal and the transformation rate are affected by several factors in the reaction system, the reaction have the biggish randomicity, uncertainness and unprediction.When treating the wastew...