Study On Preparation Of Molecular Sieves And Extraction Of Silicon And Aluminum From Fly Ash Of Huainan Power Plant

Fly ash is a solid waste discharged by coal-fired power plants.China is the world’s largest producer and user of coal.Coal-fired power generation has long been the main way of electric power production.The piling of a large amount of fly ash not only occupies land and farmland,wastes land resources,but also pollutes soil,air and water,and affects human health.Therefore,how to deal with the fly ash emitted by coal-fired power plants has been a hot topic concerned by the industry and researchers.At present,the utilization of fly ash in China mainly focuses on construction,building materials and road building.Although this simple way of utilization reduces the stacking of fly ash,it wastes the silicon and aluminum resources rich in ash.Therefore,to develop new ways of utilization and realize the resource utilization of alumina and silica in fly ash is not only of great practical environmental significance,but also of certain economic value.In this master’s thesis,three aspects of resource utilization of fly ash from a power plant in Huainan were studied,namely:（1）13X molecular sieve was prepared by alkali fusion hydrothermal method by adjusting the Si/Al ratio;（2）extracting aluminum from fly ash;（3）Extracting silicon from fly ash.The main contents of this paper are as follows:The first chapter is a literature review,which briefly summarizes the chemical composition of fly ash,its adverse impact on the environment and the current utilization situation of fly ash.It mainly introduces the structure,properties and synthesis mechanism of molecular sieves,the research progress in the synthesis of molecular sieves from fly ash,and the technologies of aluminum extraction and silicon extraction.The purpose and content of this paper are put forward.The second chapter discusses the technological conditions for preparing 13X molecular sieve from fly ash from Huainan power plant.NaOH was used as roasting reagent,and through single factor analysis of experimental conditions,the best preparation conditions were obtained as follows:alkali melting temperature 700℃,alkalinity[n（Na₂O）/n（SiO₂）]2.0,aging time 24h,crystallization temperature 80℃,crystallization time 8h.The calcium ion exchange capacity of the synthesized 13X molecular sieve is 281.68mg/g,which is higher than 236.30mg/g of the commercial molecular sieve of the same type,and is much higher than the value of 15.27mg/g of the original fly ash.In the third chapter,13X molecular sieve was prepared by using the mixture of NaOH and Na₂CO₃ as roasting reagent.The best preparation conditions are as follows:mass ratio of alkali to salt is 1∶0.5,mass ratio of ash to alkali is 1∶1.8,alkali melting temperature is 500℃,seed crystal dosage is 8mL,aging time is 24h,crystallization temperature is 80℃,crystallization time is 8h.Under these conditions,13X molecular sieve with single crystal phase and high crystallinity was prepared,with specific surface area of 574.5m²/g,pore volume of 0.44mL/g,pore size of 3.36nm and Ca2+exchange capacity of 290.18mg/g.The fourth chapter discusses the experimental conditions for extracting aluminum from fly ash.Aluminum was extracted by roasting NH4HSO4.The optimum technological conditions were as follows:n（Al₂O₃/NH₄HSO₄）was 1∶8,roasting temperature was 400℃,roasting time was 90min.The extraction rate calculated by EDTA back titration is 63.7%.Orthogonal experiments show that the order of influence degree of aluminum ion extraction rate from large to small is roasting temperature>roasting time>n（Al₂O₃/NH₄HSO₄）.As a comparative experiment,aluminum was extracted by using a mixed roasting reagent of H₂SO₄ and NH₄HSO₄.The optimum technological conditions were as follows:(SO₄^2-/Al₂O₃)in the roasting reagent was 4,n（H₂SO₄/NH₄HSO₄）was 1.5,the roasting temperature was300℃,and the roasting time was 90min.The extraction rate calculated by EDTA back titration is 85.4%.Orthogonal experiments show that the order of the influence of experimental conditions on the extraction rate of aluminum ions is:roasting temperature>roasting time>n（H₂SO₄/NH₄HSO₄）>n(SO₄^2-/Al₂O₃).The fifth chapter discusses the experimental conditions of extracting silicon from fly ash.The fly ash after aluminum extraction was used as raw material,and NaOH was used to extract silicon from it.The optimum technological conditions were as follows:the ratio of alkali to lime was 1.8∶1,the roasting temperature was 600℃,and the roasting time was 60 min;The liquid-solid ratio was 2.2∶1,the dissolution temperature was 60℃,and the stirring time was 2 h.Under these conditions,the extraction rate of silicon was 82%calculated by potassium fluoride titration.Figure[55]table[21]reference[80]...