Study On The Characteristics Of Improved Reaction During Melting Of Muncipal Solid Waste Incineration Fly Ash With Solid Waste

With the development of modernization,the amount of municipal waste collected and transported is increasing year by year.At present,the mainstream treatment method for municipal solid waste is incineration,which can achieve waste reduction,harmlessness and resource utilization.However,municipal solid waste incineration(MS WI)fly ash produced by incineration,contains heavy metals and dioxins with high leaching toxicity,and is classified as hazardous waste.The thermal treatment method of MS WI fly ash can remove and solidify heavy metals and decompose dioxins at the same time,which is an efficient MSWI fly ash treatment method.However,due to the high melting temperature of MSWI fly ash,it is necessary to add silicon-aluminumcontaining glass forming additives during the melting process to form a SiO2-CaOAl2O3 ternary system of vitrification to improve the melting characteristics and leaching properties of MSWI fly ash.Based on the concept of "using waste to treat waste",three industrial solid wastes with high content of silicon and aluminum were selected as glass forming additives for thermal treatment of MSWI fly ash as follows.First,silica fume,generated in the flue gas of electric furnace smelting ferrosilicon,mainly consists of amorphous SiO2.Second,coal gangue,discharged in the process of coal mining and washing,mainly consists of mullite(2Al2O3·SiO2).Third,blast furnace slag,discharged from the blast furnace for smelting pig iron,mainly consists of amorphous phases of SiO2,Fe2O3 and Al2O3.The effect of the melting characteristics and properties of products of MSWI fly ash with different additives were studied.The optimal addition amount range was given.The main conclusion are as follows:(1)The effect of three solid waste additives on the melting characteristics of MSWI flyash was investigated.The quaternary basicity was used as an index to evaluate the content of the molten material(R4=[m(CaO)+m(MgO)]/[m(SiO2)+m(Al2O3)]).R4 of MSWI fly ash was 9.45 of highly alkaline.R4 of silica fume,coal gangue,blast furnace slag was acidic 0.02,0.05,0.19 respectively.The results showed that,when the mixed ash was neutral around R4=1,the melting characteristic temperature reached the lowest value.The flow temperature FT was used as the evaluation index of melting characteristics.When the mass fractions of silica fume,coal gangue,and blast furnace slag were 20%-30%,about 30%,and about 40%respectively,the lowest FT was 1300℃,1260℃,and 1200℃ respectively.(2)The characteristics of co-thermal treatment process of solid waste additives and MSWI fly ash were investigated.Compared with no addition,MSWI fly ash with addition of industrial solid waste after thermal treatment had lower melting temperature,reduced weight and volume of solid products,improved mineral composition into glass,and greatly reduced leaching concentration of heavy metals and chlorine.At 1300℃,when the mass fraction of silica fume was 20%～30%,a green homogeneous amorphous calcium silicate glass was formed;At 1300℃,when the mass fraction of coal gangue was about 30%,the brown glass ceramics were formed,and the crystal composition was Gehlenite;At 1200℃,when the mass fraction of blast furnace slag was about 40%,brown red glass ceramics were formed,and the crystal composition is Akermanite.(3)The leaching toxicity of solid waste additives and MSWI fly ash co-thermal products was investigated.After the removal of most volatile heavy metals in thermal treatment,the residual heavy metals such as Zn,Cr and Ni were encapsulated and solidified by glass matrix,which reduced the leaching toxicity and had high potential value.In this process,the reduction,harmlessness and resource disposal of MSWI fly ash were achieved.