Preparation And Adsorption Properties Of Fly Ash-based Multi-porous Molecular Sieve ZSM-5

Fly ash is the main solid waste discharged from coal-fired power plants,with SiO₂,Al₂O₃,Fe₂O₃and CaO as the main components.In 2021,China’s annual production of fly ash was 827 million tons.A large number of fly ash pile and discharge not only occupy a lot of land resources,but also cause pollution to the soil and groundwater,therefore,the resource utilization of fly ash is very necessary,of which,the use of fly ash synthesis molecular sieve The use of fly ash to synthesize molecular sieve is one of the ways of resource utilization.In this thesis,fly ash from the power plant of Xuzhou Jinshanqiao Thermal Power Co.,Ltd.was used as raw material,and firstly,the available elements Si and Al were extracted through graded treatment,and then the multi-stage pore ZSM-5 molecular sieve was prepared by double template-hydrothermal method.The results obtained in this thesis are as follows:（1）Grinding is limited for improving the activity of fly ash,and the grinding time is appropriate at 75 min.Na₂CO₃as activator can further stimulate its activity after high temperature roasting with fly ash,and the optimal activation conditions were determined through orthogonal experiments:roasting time of 3h,roasting temperature of 900°C,and the ratio of fly ash to sodium carbonate is 1:0.8.（2）Through single-factor experiments,the optimum conditions for the extraction of Si and Al from hydrochloric acid were determined as follows:hydrochloric acid concentration of 3 mol/L,solid-liquid ratio of 1:12,acid leaching at 75°C for 1.5h.The p H of the acid leach solution was adjusted with NaOH to further remove impurities such as Fe,Ca and Mg,and the optimum p H value for centrifugal removal was 3.4.The extraction rate of silicon could reach 94.36%.（3）The optimum synthesis conditions for the preparation of multi-stage pore ZSM-5 molecular sieve by double template-hydrothermal method:the molar ratio of each substance is SiO2:Al2O3:CTAB:TPABr:H2O=1:0.01:0.05:0.18:50,the crystallization temperature is 160℃,the crystallization of 36h,successfully synthesized fly ash-based multi-stage pore ZSM-5 molecular sieve,its mesoporosity is 61%.（4）The adsorption experiment results of ZSM-5 molecular sieve on typical macromolecular dye methylene blue show that the adsorption effect is best at p H=10,with an adsorption capacity of 36.21mg/g for methylene blue at a concentration of50mg/L,and a removal rate of 98.2%.The adsorption kinetics are more in line with the pseudo second-order kinetic equation,and the adsorption isotherm equation fits better with the Langmuir equation.The adsorption thermodynamics indicates that the adsorption process is endothermic and spontaneous,and heating is beneficial for the adsorption of methylene blue.（5）The regeneration experimental results of ZSM-5 molecular sieve showed that after 6 cycles of adsorption,the adsorption capacity remained at 30.78 mg/g,and the specific surface area and adsorption capacity decreased to a certain extent,but the degree of decrease tended to level off gradually,indicating that the stability of the adsorbent was great.