Study On Synthesis Of Zeolites From Fly Ash And Removal Of Lead Ions

Fly ash is an industrial by-product which generated during the combustion of coal for energy production. Thus, the amount of coal waste (fly ash), released by factories and thermal power plants have been increasing with the ever increasing energy needs. At present, some fly ash is mainly used for cement production, building materials and filler. However, most of fly ash is mainly openpiled, which not only takes up a lot of land but also brings serious environmental pollution to our production and life. Therefore, It is necessary to develop resources utilization technology of fly ash.Zeolite has large specific surface area, powerful absorption capacity and good exchange prosperities owing to its unique structure and composition. It has been widely applied to chemical industry, petrochemical industry and environmental protection. Due to the fly ash and the precursor of natural zeolites own similar composition, synthesis of zeolite with fly ash was not only a feasible method in theory, but also a new way for resources utilization of fly ash. Furthermore, Wastewater was treated with these zeolite materials and achieved the aim of waste control by waste. Synthesis process of zeolite A by direct hydrothermal crystallization of Alkali-melting fly ash was systematically investigated. Meanwhile, the study of synthesis of ZSM-5and13X from Silicon-Aluminum extraction liquid which was prepared from solid-liquid mixture of alkali-melting fly ash by centrifugal separation was also performed. The structure, specific surface area and morphology of the samples were characterized with X-ray diffraction (XRD), Nitrogen adsorption-desorption, infrared (IR) and Scanning electron microscopy (SEM).Firstly, zeolite was prepared by alkali-melting-hydrothermal method, which was investigated on the structure and performance, the main effects of the melted-alkaline temperature, the sodium hydroxide to fly ash ratio, alkalinity, aging time, crystallization temperature and time on zeolite type and crystallinity were studied. Experimental results showd that zeolite A can be synthesized with fly ash without adding silicon and aluminum sources. The Key Factors affecting the process were NaOH/fly ash molar ratio and temperature, One process was that alkali fusion temperature was850℃and NaOH/fly ash molar ratio was1.2whlile the other was350℃and2.8respectively, the same as other technological Processes were showed as follows:alkali concentration=2.14mol/L, aging time=6h, reacting temperature=90℃and reacting time=12h, the same high grade of zeolites A were prepared using two methods which were denoted as ZFA1and ZFA2.Secondly, Pure zeolites and13X zeolites can be synthesized from obtained from alkali fusion fly ash by centrifugal separation, The extraction potential of alkali fusion fly ash under different fusion process condition was investigated by X-ray diffraction (XRD). The results showed that when fusion temperature was650℃and mass ratio of FA/NaOH was2.4, the silica and alumina extracts was white and reached its max amount,158.63g/kg ash and62.73g/kg ash respectively which through second separation. Then the pure ZSM-5and13X zeolites were synthesized using these silica and alumina extracts. Alkalinity, ratio of n(Si) to n(Al) in the feed, aging time, crystallization temperature and time were investigated either, the synthesis conditions are showed as follows: when SiO2/Na2O molar ratio=7.3, SiO2/Al2O3ratio=40, crystallization temperature and time were180℃and72h, zeolite ZSM-5was synthesized by only adding silicon source, when SiO2/Na2O was1.0, SiO2/Al2O3was3.7, aging time was5h and crystallization time was17h, Zeolite13X was synthesized by adding right amount of silica source and aluminum source, these zeolites synthesis from the Al-Si-bearing extracts were characterized by X-ray diffraction(XRD), IR and N2absorption-desorption, which were equal to commercial zeolite on the quality and colour.The adsorption performance of ZFA1and ZSM-5zeolites to lead ion in aqueous solution was studied, which contained solution pH、adsorption time、 adsorption isotherm and kinetics models. The results showed that the adsorption isotherm of both ZFA1and ZSM-5zeolites were well in accordance with Langmuir isotherms and the greatest adsorption capacity were90mg/g and 4mg/g, respectively. The adsorption process on ZSM-5correlated well with a pseudo-second-order kinetic model.