Study On Solidification Technology For MSWI Fly Ash With Geopolymer

With the advantages of remarkable volume-reduction, weight-reduction and energy-recovery, in recent years, disposal of MSW byincineration is becoming applicated and promoted rapidly in China.However, MSWI fly ash concentrates toxic substances such as heavymetals, if treated improperly it would lead to secondary pollution.Therefore, MSWI fly ash is considered as hazardous waste, and needspecial treatment.Geopolymer is a new kind of inorganic polymer, the molecularityconsists of Si, O, Al and mainly connected by electrovalent bond andcovalent bond, it is able to solidify heavy metal ion effectively because ofits cage shape like zeolite.A lot of research works has been done on solidification of heavy metalsin MSWI fly ash with geopolymer. The characterization of MSWI fly ashinvolve mineral, chemical compositions and leaching toxicity, wereobserved under X-ray diffraction analyses, energy-dispersive X-rayspectroscopy （EDS）, Toxicity Characteristic Leaching Procedure tests. Itwas studied that the effect of oxide proportion, the volume of fly ash,curing time and curing conditions on geopolymerization reaction.Conclusion: （1） When oxide proportion was confirmed as n（Na₂O）/n（SiO₂）=0.30,n（SiO₂）/n（Al₂O₃）=4.7, the compressive strengths ofthe solidfied matrices which 40% MSWI fly ash was added-reached31.25MPa after 7d of curing, and could meet the strength requirements inconstruction. （2） The compressive strengths continued to strengthen withthe increase in curing time. The compressive strengths of solidfied matriceswhich cured for 7d could achieve about 90% of what cured for 28d. （3）Lower humidity was beneficial for the compressive strength. （4） Theleaching characteristics of heavy metals of solidified matrices were muchlower than our criteria for hazardous waste toxicity leaching standards. （4）The use of solidified matrices was promising potential when the amount ofMSWI fly ash did not exceed 40%.The synthesizing mechanism of solidification of MSWI fly ash withgeopolymer was sicussed in the end. FTIR analyses of metakaolin, MSWIfly ash, geopolymer and solidified matrices confirmed geopolymerization.