| The pollution of heavy metal waste water including Cd2+and Ni2+is increasingly fearful with the development of industrialization, and straight threaten the environment and human health. Using fly ash as raw material to synthesis zeolite molecular sieve and the products can be applied to to purification of heavy metal wastewater including Cd2+and Ni2+. This technology of wastewater treatment by synthesized zeolite from fly ash shows the method of waste control by waste with high environmental and economical benefits.In this paper, Single-Phase zeolites NaA and NaX are synthesized by using fly ash as raw materials and sodium hydroxide as activator respectively in the alkali fusion-hydrothermal method. In the synthesis process, the influence of various factors on the fly ash zeolite is studied. The optimum conditions of the fly ash zeolite is that the calcining temperature is650℃, the calcining time is2hours, the alkali ash ratio is1.2, the aging time is24hours, the liquid solid ratio is6, the hydrothermal time is4hours and24hours respectively. Analysis of SEM shows that the crystals were of regular shape, good dispersivity, and uniform particle size. The crystallites of NaA and NaX zeolites form fine cubic and octahedron particles respectively; XRD analysis shows that the synthetic products are NaA zeolite and NaX zeolite without the presence of other phases; Analysis of IR spectra corresponded to peaks of corresponding zeolitic structural formation; Analysis of TG-DSC shows that synthesized products have good thermal stability. Their CEC values reached92%and90%of the eonunereial zeolite respectively.We have chosen Cd2+and Ni2+in solution as indicators, batch method is employed to study the influential parameters including initial pH value and initial concenteation of the solution, and adsorbents dosage etc on the adsorption process. The results show that the removal rate and adsorption capacity of Cd2+and Ni2+is getting higher with the increase of initial pH value. The removal rate of Cd2+and Ni2+is getting higher with the increase of initial concentration and the dosage of zeolite while the adsorption capacity is gradually decreaseing.The suitability of and isotherms to the equilibrium data are studied in the solid-liquid system while the Langjmuir model produces the best results. The adsorption kinetic characteristics of Cd2+and Ni2+on synthesized zeolites are studied. The results show that the adsorption process is confirmed to pseudo-second-order kineties equation very well. The suitability of Langrnuir and Freundlich isotherms to the equilibrium data are studied in the solid-liquid system while the Langjmuir model produces the best results. The removal performance of Cd2+and Ni2+in aqueous solution are investigated by adsorption process on the different samples, the result show that the adsorptive capacity of NaA zeolite is relatively higher; the adsorptive capacity of zeolites synthesized is obviously higher than raw fly ash; the samples exhibit a relative ability to adsorb Cd2+The two kinds of synthesized zeolites are applicable in eliminating heavy metals(Cu2+Zn2+、Cd2+、Ni2+etc)under low concentration. The removal rate can be achieve about99%after120min adsorption handing under25℃and pH=6.0. The concentration of Cd2+and Ni2+is lower than the waste letting standard of our country. NaAand NaXzeolites synthesized by using alkali fusion-hydrothermal method have an potential industrial application on removeing heavy metals in wastewater. |
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