Zeolite Synthesis From Coal Fly Ash And Its Application In Environment

In China's primary energy,coal accounted for more than 70%.A large amount of solid waste of coal fly ash was produced each year,causing serious environmental problems.Therefore,using the fly ash from coal fired boiler as test subject,the pretreatment methods,hydrothermal synthesis and characterization of zeolite,the performance and mechanism of heavy metals removal from wastewater by synthetic zeolite were studied in detail through experiments and theory methods in this paper.The pretreatment included sieving,grinding,high temperature calcination,acid leaching and alkali fusion to improve the content and reaction activity of silicon and aluminum.The high temperature calcination conditions were 750?,1.5h,with15.2%carbon removal.Acid leaching conditions were 4mol/L hydrochloric acid,solid-liquid ratio of 1:5,90?,and reaction time of 2h.The impurity of iron,calcium,sulfur,and magnesium can be removed about 64%,87%,80%,78%,respectively,the molar ratio of silicon to aluminum increased from 4.01 to 11.70.Besides,the alkali fusion step can improve the reactivity of fly ash under the conditions of the sodium hydroxide and fly ash mass ratio of 1.2:1,at 550?for1.5h.The effects of alkali concentration,crystallization temperature,and time,the ratio of Si/Al ratio,alkali melting and ultrasonic field on the zeolite species were investigated through synthesis experiments.The zeolites of P(PDF#80-0699),X(PDF#83-2319),Y(PDF#75-1860)and analcime(PDF#76-0905)were successfully synthesized.The zeolites were characterized and analyzed by scanning electron microscopy(SEM),X-ray powder diffraction(XRD),fourier transform infrared spectroscopy(FTIR),thermogravimetric-differential scanning calorimetry analysis(TG-DSC),specific surface area and pore size analysis(BET-DFT).The results showed that the pore volume and specific surface area of Y zeolite were the largest,which were 0.348cm~3/g and 573m~2/g,respectively;it was followed by X zeolite,whose pore volume and specific surface area were 0.180cm~3/g and 181m~2/g,respectively;the pore volume and specific surface area of analcime were the smallest,with 0.028cm~3/g and 6m~2/g,respectively.The zeolites through hydrothermal synthesis from coal fly ash have good thermal stability.Ultrasonic physical field is conducive to promoting zeolite synthesis.The effects of temperature,reaction time,dosage of zeolite,initial concentration of solution,p H on the purification efficiency of copper and nickel ions in simulated wastewater were investigated using the synthetic P-type and Y-type zeolites.The isothermal adsorption of copper ions on the two zeolites is in accordance with the Langmuir model,and the isothermal adsorption of nickel ions conforms to the Freundlich model.Y zeolite is better than P type zeolite in purifying copper and nickel ions in wastewater,and the purification process is in accordance with the secondary adsorption kinetics model.The adsorption of heavy metal ions on the zeolite can be promoted by increasing the temperature,which may be related to the ion exchange process of zeolite.Moreover,the experimental results showed that P zeolite,X zeolite,Y zeolite and analcime have a certain purification effect on the phenol in simulated wastewater.