| Coal fly ash(CFA), a solid waste formed in the process of coal combustion and transformation, has caused a seriously environmental pollution by the large-scale emissions and accumulation. The 70 percent of components of CFA are silicon and aluminum. Synthesizing zeolite by using CFA as the raw materials decreases the production cost and the pressure to be green. The significance obviously is there for establishing resource circulation and economic sustentation.In this work, coal fly ash-one of the industrial solid wastes, was selected as a source of silicon and aluminum components to synthesize microporous NaP zeolite and analcite with low Si/Al ratio through hydrothermal synthesis after activated and purification. The process parameters of the hydrothermal system are optimized and the influences of different types of organic steric agent, such as circulating strain, short strain and long strain, on crystal growth was studied. At last, the adsoption of metal ions was performed to test the properties of zeolite products and the mechanism was preliminary analyzed. The results of the studies are as follow:(1) CFA calcinated with active addition at a high temperature could increase the extraction rate of silicon and aluminum and the utilization of CFA. After calcinated CFA was dipped in HCl solution, the silicon and aluminum of CFA could be extracted successfully. The impurities such as Fe, Ca and Mg could be removed by segment adjusting the p H value of solution. The extraction rate of aluminum of CFA was 80.89%.(2) The optimum condition of synthesizing pure NaP zeolite by using CFA as raw materials was as follows: the n(H2O)/n(SiO2) ratio was 116, the reaction temperature was 120℃ and the reaction time was 8 h. The addition of circulating strain organic steric agents had good effect on growth regulatory and decrease the crystal size, and the change of yield was little. When the ratio of n(H2O)/n(SiO2) was 1:3, the minimum average crystal size is 1.85 μm. The NaP zeolite with cyclohexanol addition has the best adsorption capacity. The highest removal rate of Zn2+ was 98.15% at 35℃ at 30 min and that after desorption regeneration was 96.57%.(3) The optimum condition of synthesizing pure analcime by using CFA as raw materials was as follows: the n(SiO2)/n(Al2O3) ratio was 10, the reaction temperature was 210℃ and the reaction time was 12 h. The short strain addition could decrease the crystal size effectively with little change on yield, and the crystal morphology was more regular. Larger BET surface area and pore volume could be obtained with the DEA addition and the ion exchange capacity of K+ could be improved. The maximum removal amount was 57.75mg/L at 10 min.(4) The addition of different types of organic steric agents in zeolite precursor solution had good effect on crystal growth regulatory. The regulation degree of different types of organic steric agents had different function and had selectivity on the types of zeolites. The organic addition could decrease the crystallization size and improve the properties of zeolite and obtain larger BET surface area and pore volume.(5) Preliminary analysis proved that during the adsorption process, the forms of adsorption were not single, but physical adsorption, chemical adsorption and electrostatic adsorption are all present. During the physical adsorption process, 5%-11% ion exchange also occurred due to the site of zeolite framework and different zeolite properities. During the chemical adsorption(ion exchange) process, 6%-13% physical adsorption also occurred due to the different surface area and pore volume of zeolite. |
PDF Full Text Request