Study On Modification Of Fly Ash And Solidification Of Heavy Metals By Nano-montmorillonite And Bottom Ash

Municipal solid waste fly ash（MSWI FA）is the product of waste incineration at high temperature,and its main components are Ca O,Si O₂and Al₂O₃.As the fly ash contains heavy metals such as Cr,Cu,Ni,Pb and Zn,how to treat the fly ash correctly to avoid pollution is particularly critical.In this paper,mechanical grinding and nano-materials are used to modify fly ash to solidify heavy metals.The purpose of mechanical grinding is to reduce the particle size of bottom ash,which is one of the raw materials,so that it can participate in the reaction better by increasing the specific surface area.Compared with traditional building materials,nano-materials have larger specific surface area,stronger surface tension and good modification ability.As the nano-materials selected in this paper,nano-montmorillonite is cheap and easy to manufacture.In this paper,the mechanical properties and microstructure of heavy metals solidified by modified fly ash are preliminarily tested,and the main conclusions are as follows:（1）Through the uniform design of three factors and four levels,the influences of different content of nano-montmorillonite,the ratio of fly ash to bottom ash and the content of nano-montmorillonite on the mechanical properties of the prepared specimens were investigated,and the optimum ratio of the test was as follows:nano-montmorillonite content was 2%,sodium silicate content was 0%,the mixing ratio of fly ash to bottom ash was 6:4,and the bottom ash was mechanically ground for 30min before the test.The 28d compressive strength and the 28d flexural strength of the specimen thus obtained are 38.49MPa and4.99MPa,respectively.Meet the standard of safe use of some projects,and because it is made of waste materials,it has better economic benefits.（2）Through the regression equation and model of predicting strength by multiple regression analysis,it is concluded that the mechanical properties are more prominent when the ratio of fly ash to bottom ash is 6:4,and the compressive strength of the specimen at 28days is increased by about 20%compared with the control group.（3）Analyzing the modification mechanism of nano-materials,choosing different content of nano-montmorillonite to analyze the optimal ratio,it is found that when the content of nano-montmorillonite is 0-2%,the effect of nano-montmorillonite on the specimen is positive,and the strength of the specimen is increased by about 32%,which is due to its own characteristics,such as tiny particle size and large specific surface area,which means that tiny holes and pores can be filled in the reaction process;However,when the content exceeds 2%,it has a negative effect.When the content is 6%,the strength decreases by 23%.This is because the strong water absorption of nano-montmorillonite makes the sample less easy to prepare,which affects the water-cement ratio of the reaction,and leads to insufficient hydration reaction.In addition,excessive nano-montmorillonite swelled excessively in the process of filling pores,which destroyed the original structure.Therefore,2%of nano-montmorillonite is a more suitable content.（4）Heavy metal leaching test was carried out on the best group,and the concentrations of Cr,Cu,Ni,Pb and Zn were found to be 1.02,2.99,0.28,1.08 and 9.20（unit:mg/L）.The limit concentrations in the specification are 5,100,5,5 and 100（unit:mg/L）.The results show that the content of harmful elements leached by the specimen is far lower than the limit concentration of the code,which can be safely applied to engineering.