Study On The Cement Kiln Co-processing Of Waste Incineration Fly Ash

The cement kiln co-processing of waste incineration fly ash can realize harmless disposal and resource utilization of fly ash and reduce the input of raw materials in the cement industry.However,the presence of chlorine and heavy metals in fly ash not only limits the disposal capacity of the cement kiln,but also affects its operating conditions,and has a profound impact on the surrounding environment.Therefore,based on the optimization of fly ash dechlorination process and clinker calcination process,the migration and transformation law of heavy metals in the whole process was explored,providing technical support for the safe and efficient disposal of waste incineration fly ash.Firstly,the physical and chemical properties of waste incineration fly ash were explored through physical testing and chemical analysis.The results show that the chemical composition of fly ash is similar to that of cement raw materials,and its recyclable component accounts for about 61.99%of its total.The total chlorine content in the fly ash is 12.04%,of which the soluble chlorine content is 11.46%and the insoluble chlorine content is 0.58%.Fly ash has a higher content of heavy metals and a higher risk of leaching.Secondly,the influence of relevant factors on the dechlorination of fly ash during the process of water washing dechlorination,high-temperature calcination dechlorination and synergistic dechlorination by water washing and high-temperature calcination were explored.On this basis,the fly ash dechlorination process and the clinker calcination process were optimized.The results show that the synergistic dechlorination treatment of water washing and high-temperature calcination can significantly improve the dechlorination effect of fly ash.It is suitable to wash the fly ash with liquid solid ratio of 3m L/g for three times and then calcination at 1200℃for 60 min.After the synergistic dechlorination treatment,the chlorine content in the fly ash is reduced to 0.48%,the chlorine removal rate is 93.69%,and the maximum mixing amount in the raw meal is4.58%.In terms of calcination process,the optimal calcination temperature is 1400℃,the optimal calcination time is 30 min,and the optimal cooling method is quenching.The fly ash treated by synergistic dechlorination can obviously improve the burnability of the raw meal,and has no adverse effect on the chemical composition,mineral composition and hydration performance of the clinker,and the chlorine content in the burnt clinker is only0.01%.Finally,the distribution,migration and transformation of Zn,Cu,Cr,Cd and Mn during calcination and hydration were investigated by clinker phase extraction,continuous chemical extraction（BCR）and microwave digestion.The results show that in the calcination process,the volatilization rate of heavy metals is generally low,and most of the heavy metals can enter the clinker minerals,and the clinker minerals are selective for the solution of heavy metals due to the differences in chemical composition and crystal structure.In the hydration process,the heavy metals extracted by weak acid are mainly distributed around Ca（OH）₂,the heavy metals in reducible state are mainly distributed in Ca（OH）₂and partially hydrated calcium silicate（C-S-H）,and the heavy metals in oxidized state are mainly concentrated in C-S-H,ettringite（AFt）and unhydrated cement clinker.With the development of hydration reaction,all heavy metals have a tendency to transform from the form with weak migration ability to the form with strong migration ability,among which Cr and Cd are more obvious.The co-disposal of cement kiln has obvious effect on the solidification of heavy metals in fly ash,the proportion of heavy metals with strong migration ability decreases obviously,and the leaching toxicity of heavy metals decreases obviously.