Crucial factors controlling the formation of halogenated organic compounds during high-temperature combustion proc esse s

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Six dust samples recovered from bag filters of electric arc furnaces for steelmaking or six fly ashes recovered from electrostatic precipitators in pulverized coal-fired power plants are characterized by use of XRD, SEM-EPMA, XPS and TPD techniques to examine several factors controlling the formation of organic halogen compounds in the steelmaking or coal combustion process, respectively. The dust samples contain 2. 1-6. 4 wt%-dry of carbon element, and some of the C can release CO_2 in the TPD up to 300℃to provide carbon active sites. The number is related closely to hexachlorobenzene(HCB) concentration of each dust. Further, it is suggested that the Zn present in the samples consists of ZnFe_2O_4, ZnO and surface ZnCO_3, and the dust with a larger content of the ZnCO_3 has a higher concentration of HCB. On the other hand, the ashes include 20-130цg/gg-dry and 0. 5-4. 2 wt%-dry of F and C elements, respectively, and these components are enriched at the outermost layer of the ash surface. The F consists of both inorganic and organic functionalities, and the proportion of the latter is as high as 84-93 mol%. The C has different types of surface oxygen species, such as carboxyl, lactone/acid anhydride and phenolic groups, and most of these groups decompose into CO_2 or CO up to 800℃to give carbon active sites. When the amount of the O-functional forms increases, the content of organic CF forms tends to increase almost linearly.