Solidification/Stabilization Of MSWI Fly Ash By CFBC Fly Ash

Municipal Solid Waste Incineration(MSWI)fly ash,with large output,high leaching toxicity of heavy metal,dioxin and other persistent organic pollutants(pops)and degradation difficulty,is clearly classified as hazardous solid waste.Therefore,we urgently need to safely deal with the MSWI fly ash with effective technology.This paper presents a technical process for the safe treatment of MSWI fly ash,which used to activate the Circulating Fluidized Bed Combustion(CFBC)fly ash by the mechanochemical method.The optimizing the parameters which solidified MSWI fly ash with CFBC fly ash were optimized.And this paper explored the effect and mechanism on solidified MSWI fly ash with CFBC fly.Through the comparison on which solidified MSWI fly ash with CFBC fly ash and the cement,and the following creative results have been achieved:Firstly,the present research explored the role played by mechanochemical method on immobilization of the MSWI fly ash.And the most important influence parameters including the MSWI fly ash/(MSWI fly ash+CFBC fly ash)ratios,ball-milling frequency and time on the performance of the solidified wastes were investigated.As results indicated,the mechanochemical method substantially promoted pozzolanic activity of CFBC fly ash and resulted in a higher compressive strength to the solidified waste.Under the optimized conditions that velocity of milling was 600 r/min,milling time was 5 h,the compressive strength of the ball-milling solidified wastes(BM solidified wastes)were 15.6 MPa and 17.9 MPa by curing after 28 d and 56 d at 60 ?,respectively.Meanwhile,the comparison experiment on which solidified wastes without activated CFBC fly ash(NBM solidified wastes)with the mechanochemical method was carried out.The result showed,the compressive strength of NBM solidified wastes were 14.4158 MPa and 17.8169 MPa,respectively.Nevertheless,the compressive strength of BM solidified wastes were 35.4094 MPa and 36.8325 MPa by curing after 28 d and 56 d at 60?,respectively.When the MSWI fly ash and CFBC fly ash mixing ratio increased to 60%,NBM solidified wastes occurred the phenomenon of cracking expansion by curing after 28 d and 56 d at 60?.As indicated that,mechanochemical method was very significant to enhance the activity of CFBC fly ash,and reduced the expansion of the performance of CFBC fly ash,which greatly enhanced the activity of CFBC fly ash and the compressive strength of the solid wastes.Secondly,the effect of CFBC fly ash on BM solidified wastes and NBM solidified wastes was compared.The results show that the effect of BM solidified wastes was much better than that of NBM solidified wastes,and the leaching amount of BM solidified wastes was much lower than the national standard value(GB 5085.3-2007).Indicating that BM solidified wastes with CFBC fly ash had excellent anti-leaching performance stabilize the heavy metals from MSWI fly ash.The results show that hydration products of BM solidified wastes were the calcium silicate hydrate(C-S-H),gismondine and ettringite(AFt),And the heavy metals from MSWI fly ash mainly were physically encapsulated in C-S-H and chemically absorbed in the structure of AFt respectively.Thirdly,the research which based on the optimized parameters,which further explored the anti-leaching performance and the thermogravimetric,porosity,the phase structure and the molecular structure of the solidified wastes with CFBC fly ash and solidified wastes with cement were analyzed and compared.The further research explored the role played on effect and immobilization of the MSWI fly ash.The results showed,under the optimized conditions that velocity of milling was 600 r/min,milling time was 5 h,MSWI fly ash and CFBC fly ash mixing ratio increased to 70%,by curing after 56 d at 60?,the compressive strength of solidified waste with CFBC fly ash was 36.8966 MPa.Moreover,the compressive strength of solidified waste with cement was 36.8966 MPa.Indicating that solidified wastes with CFBC fly ash had strong compressive properties.Furthermore,when MSWI fly ash adding rate was 70%.The leaching amounts of Zn,Pb,Cu,Cd and Cr from solidified waste with CFBC fly ash were 0.5086 mg/L,0.0519 mg/L,0.6462 mg/L,0.1222 mg/L,respectively.Simultaneously,The leaching amounts of Zn,Pb,Cu,Cd and Cr from solidified wastes with CFBC fly ash were 0.0358 mg/L?0.0939 mg/L?0.1097 mg/L,0.0998 mg/L?0.8734 mg/L,respectively.And that were much lower than the national standard value(GB 16889—2008).Thermogravimetric analysis showed that A7 and B7 materials were heated from 85 to 250? have endothermic peaks,which are attributable to the dehydration evaporation of the free water,calcium silicate hydrate and Ettringite;from 900 to 950?,the endothermic peaks are attributable to the decomposition of the calcium carbonate.When the heating temperature rises to 600 ~700?,the thermal stability of A7 was better than that of B7;when the cement was heated from 30 to 1000?,the change of the weight loss rate of B7 bcame much larger and the overall instability wasn't stable.The porosity analysis showed that the densification of A7 was much better than that of B7,and the compressive properties of A7 were much higher than that of B7.As results showed,the increase of the densification was beneficial to the improvement of the compressive strength of the solidified waste,and was helpful to the solidification and stabilization of heavy metals from MSWI fly ash.The XRD and FTIR analysis showed that,during the hydration process,the solidified wastes with CFBC fly ash was basically the same as the hydration products of the solidified wastes with cement,which were the calcium silicate hydrate(C-S-H),gismondine and ettringite(AFt),and solidified MSWI fly ash with CFBC fly ash can also achieved the stabilization of heavy metal from the MSWI fly ash,and attained to the effect on treatment of wastes with processes of wastes against one another.Finally,the technology and the benefit analysis which solidified MSWI fly ash with CFBC fly ash and the solidified wastes with cement were analyzed by comparing.The analysis shows that the cost of solidification of MSWI fly ash with CFBC fly ash is 245.71 yuan/ton,and the process cost is lower than that of cement solidification.And technology of solidification of MSWI fly ash with CFBC fly ash has certain guiding significance for environmental protection and comprehensive utilization of wastes resource.Meanwhile,it has certain engineering application value and has potential economic benefits for the enterprise.