| Fly ash is a large amount of solid waste generated from coal-fired power plants.With the rapid development of China's power industry,fly ash emissions have been increasing year by year.Fly ash not only pollutes the environment but also endanger the health of human beings,turning it into a treasure and increasing its added value is urgently needed.In addition,the alumina content of high-alumina fly ash is as high as 40%or more,which is equivalent to the content of alumina in bauxite and is an important non-traditional aluminum resource.Therefore,utilization of high-alumina fly ash not only solves the environmental problems,but also reduces our dependence on bauxite in other countries and increases our international competitiveness.Based on this,high-aluminum fly ash is used as raw material to prepare hierarchical boehmite,which provides a new way for the utilization of high-alumina fly ash.In this paper,the first step was to find a template-free hydrothermal/solvothermal method for the synthesis of hierarchical structure boehmite by using aluminum chloride hexahydrate as an aluminum source and sodium hydroxide as a precipitating agent.Then,the containing impurities hydrochloric acid leachate and the impurity-free hydrochloric acid leachate were used as the aluminum source,and sodium hydroxide was used as the precipitating agent to prepare the hierarchical structure boehmite.At the same time,SEM,XRD,FT-IR,N2 adsorption and desorption,pore size distribution and adsorption properties of the obtained powders were studied.The main results of the dissertation are as follows:(1).The hierarchical structure of boehmite was successfully prepared by hydrothermal/solvothermal method with sodium hydroxide as precipitator and AlC13·6H2O as aluminum source.And the amount of sodium hydroxide,the volume ratio of water to ethanol,the concentration of aluminum chloride and sodium hydroxide,the type of alcohol,the type of precipitant affect the morphology through the nucleation and growth of boehmite grains.The formation mechanism was as follows:firstly,aluminum hydroxide precipitation converted into boehmite by dissolving and crystallizing under hydrothermal conditions.And boehmite grains grew oriented to produce a sheet-like structure.Finally,the flaky boehmite was assembled into the hierarchical structure of boehmite due to the interaction between the hydroxyl groups on the surface of the flaky structure boehmite.(2).The containing impurities fly ash hydrochloric acid leachate was used as aluminum source,and sodium hydroxide was used as the precipitating agent to prepare hierarchical structure boehmite in water-isopropanol mixed solution.But calcium,silicon of the leachate solution reacted with sodium,aluminum elements to produce sodium aluminosilicate,garnet,zeolite,these impurity phase affect the purity and adsorption properties of the boehmite powder,and the removal rate of Congo red decreased from 97.9%to 30%at the same time.Therefore,it is necessary to purify the leachate to prepare the layered boehmite with good adsorption performance.(3).Using the leached fly ash hydrochloric acid leachate as the aluminum source and the sodium hydroxide as the precipitating agent,the hierarchical purity boehmite with high purity can be prepared by the non-template method.Hierarchical structure boehmite had the best adsorptive effect on Congo red with the water-isopropanol as solvent and the pH was 11.The maximum removal rate of Congo red by the boehmite was 83.8%within 60 minutes and the corresponding adsorption capacity was 83.8 mg/g.The specific surface area of the boehmite is 79.5 m2/g,the pore volume is 0.22 cm3 g and the average pore diameter is 11 nm. |
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