Effects Of MSWI Fly Ash Characteristics On Dioxin Formation

Since the characteristics of municipal solid waste incineration (MSWI) fly ashes have an important influence on dioxin generation,14fly ash samples from different type of MSWIs were collected and analyzed by SPSS. Results indicated that Si, Al, Fe, O revealed a strong positive correlation, and Na, K, Cl, S were the same, but there was a negative correlation between the two groups. There were more Si, Al, Fe, O and less Na, K, Cl, S in circulating fluidized bed (CFB) than in grate incinerator. The concentration of international equivalence quantity (I-TEQ) of fly ash samples ranged from0.02to2.53ng I-TEQ/g, OCDD and HpCDD were main contributors for congener concentration fingerprint of CFB fly ashes, while low chlorinated furan were main contributors of grate fly ashes, but2,3,4,7,8-PeCDF was the major contributor for total I-TEQ nomater which type the fly ashes were.The major elements in different depth of six fly ashes and their leachabilities are discussed. Results indicated that Si, Al, Fe, Ti and Ca, with high boiling point, are more easily taken into the core of fly ash particles mechanically in the forms of stable oxides. While elements with low boiling point, such as Na, K, Zn, are mostly adsorbed on the surface of fly ash particles by "evaporation-condensation" process. At the outermost layer of fly ash surface, the C has different species, such as graphitic-C, aliphatic-C and O-functional groups(C-O/C=O/O-C=O); The Cl consists of both inorganic and organic functionalities, and the proportion of them is60%and40%, respectively. For the reason of low concentration of Chlorine and oxidizing atmosphere in CFB incinerator, the enrichment of Na and K on the surface of fly ash particles in CFB incinerator is not as high as that in grate incinerator.Ca(H2PO4)2and CaO were added to modle fly ashes to change pH of them, and experiments were conducted on a tube furnace for dioxin generation by de-novo synthesis. The result suggested that the acid additives may transfer congener concentration fingerprint from low chlorinated congeners to high chlorinated congeners, and basic additives may inhibit dioxin generation effectively.