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Chemosphere ; 226: 809-816, 2019 Jul.
Article in English | MEDLINE | ID: mdl-30965252

ABSTRACT

The correlation between the content and morphology of Fe2O3 and the yields of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) was studied in this work. Three fly ash surrogates containing 1%, 2.5%, and 4% of Fe2O3 were prepared and their effects on PCDD/Fs formation were investigated and compared to our previously studied 5% iron oxide sample using 2-monochlorophenol precursor model. As the intermediate of PCDD/Fs, environmentally persistent free radical formation propensity was correlated with the PCDD/Fs formation yields for different iron oxide samples. PCDD/Fs yield increases exponentially with the increasing iron content under pyrolytic conditions. On the contrary, low iron oxide content promotes oxidation and lowers yields of PCDD/Fs. Changing iron oxide clusters' morphology (crystallinity and cluster size) affects the mechanism of PCDD/Fs formation - on larger crystallites, a bidentate chemisorption of precursor is preferred leading to lower chlorinated congeners, while smaller clusters promote formation of PCDFs through mixed monodentate-bidentate surface species, resulting in formation of congeners with 1 chlorine more. This study further confirms the propensity of iron oxide to predominantly form PCDFs. The iron content also defines PCDDs:PCDFs ratio.


Subject(s)
Chlorophenols/chemistry , Coal Ash/chemistry , Dibenzofurans, Polychlorinated/chemical synthesis , Ferric Compounds/chemistry , Polychlorinated Dibenzodioxins/chemical synthesis , Dibenzofurans, Polychlorinated/analysis , Incineration , Oxidation-Reduction , Polychlorinated Dibenzodioxins/analysis
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