Thermal Formation of Polybrominated Diphenyl Ethers in Raw and Water-Washed Fly Ash

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.

Distribution of Polybrominated Diphenyl Ethers (PBDEs) in a Fly Ash Treatment Plant

“…The higher PBDE emissions from the stack of the SAF could be related to precursor formation and de novo synthesis that occurred during the cooling process of the flue gas due to using coke as an auxiliary fuel and deploying GSC as one of the APCDs (Lin et al, 2008;Wang et al, 2010a;Artha et al, 2011). The PBDE emission factor to the atmosphere of the whole system, that is, the EAF fly ash treatment plant, was 0.318 mg/tonne-feedstock.…”

“…In our previous study, the effects of temperature on the formation mechanisms of PBDEs occurring in the processes of heating fly ash were investigated. Compared to PBDE contents of the fly ashes during the temperature window of formation, the PBDE contents during the heating temperature at 900°C-1450°C dramatically decreased, and remained at the level of 0.253-0.389 ng/g (Artha et al, 2011). Fig.…”

“…This is because the fly ash from the pelletizer only underwent the mixing process, and the PBDEs of the EAF fly ashes were retained. For the other ash samples, the extremely high temperature in the processes leads to effective PBDE destruction (Artha et al, 2011). In our previous study, the effects of temperature on the formation mechanisms of PBDEs occurring in the processes of heating fly ash were investigated.…”

PBDE Emissions during the Start-up Procedure of an Industrial Waste Incinerator by the Co-Combustion of Waste Cooking Oil and Diesel Fuel

“…The PBDEs would start to be released from the combustion residues, when the melting points (64-306°C) of congeners were approached during S1 (101-236°C) and S2 (226-450°C). Artha et al (2011) also indicated the first temperature with higher PBDE emission during fly ash heating-up processes was around 400°C. On the other hand, the decomposition temperature of each PBDE congener was increased with the substitution of bromine and up to 425°C of BDE-209, which was the dominant species of PBDE emissions.…”

“…Temperature Stage A (< 250°C) displayed the PBDEs concentrations before chamber temperature reached the first temperature range of higher PBDE emission, which was around 400°C (Artha et al, 2011). Furthermore, Stage B was ranged 250-450°C, representing the temperature of PCDD/F and PBDE formation resulted from de novo synthesis.…”