Abstract
To the best of our knowledge, the formation mechanisms of PBDEs in the combustion system, fly ash, as well as their relation with temperature, have never been investigated. In this study, the formation mechanisms of PBDE soccurring in the processes of heating fly ash have been investigated using a laboratory furnaceand graphite crucibles in order to clarify the effects of temperature. A dramatic increase in total PBDE content in the heated water-washed fly ash (3.33 ng/g) occurred, 17.7 times higher than that of the unheated one (0.188 ng/g), when the heating temperature reached 400°C. We speculate that at this temperature, PBDEs form through de novo synthesis as well as heterogeneous solid-phase reactions of the precursor mechanisms. Another dramatic increase in PBDE content in the water-washed fly ash occurred in the range 650°C–850°C, due to the enormous amounts of brominated aromatic precursors that are formed, and then condensed or are adsorbed onto the surface of the fly ash during the cooling down to 400°C, where PBDEs form through de novo synthesis and precursor mechanisms. The raw fly ash contains more alkaline compounds such as sodium and calcium compounds than the water-washed fly ash, which are inhibitors for the formation of precursors and PBDEs. Consequently, the water-washed fly ash has much greater PBDE formation potential than the raw fly ash.
Highlights
Polybrominated diphenyl ethers (PBDEs), structurally similar to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs), have been extensively used as brominated flame retardants (BFRs) in a large variety of consumer products
The PBDE content decreased from 0.750 ng/g to 0.188 ng/g after water washing treatment, revealing the PBDE reduction resulted from the finer ash being dissolved or suspended in the water, and later being removed
The contents of inorganic bromide and calcium in the raw fly ash reduced from 1.61 and 26.3 mg/g to 0.0483 and 1.32 mg/g after water washing treatment, that is, there was about 97% and 95% removal of the original contents, respectively. (Zhu et al, 2008) found that approximately 15% of the chlorine in the raw fly ash of municipal solid waste incinerators (MSWIs) was in the form of NaCl, 10% was in the form of KCl, 51% was CaCl2, and the remainder was in the form of Friedel’s salt
Summary
Polybrominated diphenyl ethers (PBDEs), structurally similar to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs), have been extensively used as brominated flame retardants (BFRs) in a large variety of consumer products. Due to health risks, commercial penta-BDE and octa-BDE mixtures were banned within the European Union in 2004. Our recent study found that besides controlling PBDE mixtures in commercial products, mitigation of PBDE emissions from combustion sources is required to reduce environmental PBDE levels and human exposure (Wang et al, 2010b). The PBDE concentrations in the stack flue gases of combustion sources, including waste incinerators, metallurgical processes, power-heating systems and so on, range from 8.07 to 469 ng/Nm3 (Wang et al, 2010b). Combustion sources possess highbred concentrations, huge flow rates of stack flue gases and in great numbers, revealing that they are major PCDD/F emission sources, and important PBDE emitters to the
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
