Guijin Su

Atmospheric Emission of PCDD/Fs, PCBs, Hexachlorobenzene, and Pentachlorobenzene from the Coking Industry

The coking process is considered to be a potential source of unintentionally produced persistent organic pollutants (UP-POPs). However, intensive studies on the emission of UP-POPs from the coking industry are still very scarce. Emission of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), hexachlorobenzene (HxCBz), and pentachlorobenzene (PeCBz) covered under the Stockholm Convention were investigated for the coking process in this study. Stack gases from some typical coke plants in China were collected and analyzed to estimate the emission of UP-POPs from the coking industry. Emission factors of 28.9 ng WHO-TEQ tonne(-1) for PCDD/Fs, 1.7 ng WHO-TEQ tonne(-1) for dl-PCBs, 596 ng tonne(-1) for HxCBz, and 680 ng tonne(-1) for PeCBz were derived based on the investigated data. The annual emissions from the global coking industry were estimated to be 15.8 g WHO-TEQ for PCDD/Fs, 0.93 g WHO-TEQ for dl-PCBs, 333 g for HxCBz, and 379 g for PeCBz, respectively (reference year 2007). According to the distribution of PCDD/Fs, we argued for the de novo synthesis to be the major pathway of PCDD/F formation. With regard to the characteristics of dl-PCBs, the most abundant congener was CB-118, and the most dominant contributor to the total WHO-TEQ of dl-PCBs was CB-126.

Estimation and Congener-Specific Characterization of Polychlorinated Naphthalene Emissions from Secondary Nonferrous Metallurgical Facilities in China

Secondary nonferrous production is addressed as one of the potential sources of the unintentionally produced persistent organic pollutants (UP-POPs) due to the impurity of raw material. Although there are inventories of dioxin emissions from secondary nonferrous metallurgical facilities, release inventories of polychlorinated naphthalenes (PCNs) are scarce. This study selected typical secondary copper, aluminum, zinc, and lead plants to investigate the emissions of PCNs in secondary nonferrous production in China. The toxic equivalency (TEQ) emission factor for PCNs released to the environment is highest for secondary copper production, at 428.4 ng TEQ t(-1), followed by secondary aluminum, zinc, and lead production, at 142.8, 125.7, and 20.1 ng TEQ t(-1), respectively. PCNs released in secondary copper, aluminum, lead, and zinc production in China are estimated to be 0.86, 0.39, 0.009, and 0.01 g TEQ a(-1), respectively. Analysis of stack gas emission from secondary nonferrous production revealed that less-chlorinated PCNs are the dominant homologues, with mono- to tri-CNs making the most important contributions to the concentration. However, for fly ash, the more highly chlorinated PCNs such as octa-CN are the dominant homologues.

Estimation and characterization of PCDD/Fs, dl-PCBs, PCNs, HxCBz and PeCBz emissions from magnesium metallurgy facilities in China

Magnesium production is considered to be one potential source of unintentional persistent organic pollutants (unintentional POPs). However, studies on the emissions of unintentional POPs from magnesium metallurgy are still lacking. Emissions of unintentional POPs, such as polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), polychlorinated naphthalenes (PCNs), hexachlorobenzene (HxCBz) and pentachlorobenzene (PeCBz) are covered under the Stockholm Convention. In this study, these emissions were investigated through a magnesium smelting process. Stack gas and fly ash samples from a typical magnesium plant in China were collected and analyzed to estimate the emissions of unintentional POPs from magnesium metallurgy. Emissions factors of 412 ng TEQ t(-1) for PCDD/Fs, 18.6 ng TEQ t(-1) for dl-PCBs, 3329 μg t(-1) for PCNs, 820 μg t(-1) for HxCBz, and 1326 μg t(-1) for PeCBz were obtained in 2009. Annual emissions from magnesium metallurgy in China were estimated to be 0.46 g WHO-TEQ for PCDD/Fs and dl-PCBs, 1651 g for PCNs, 403 g for HxCBz and 653 g for PeCBz, respectively.

A preliminary investigation of unintentional POP emissions from thermal wire reclamation at industrial scrap metal recycling parks in China

Thermal wire reclamation is considered to be a potential source of unintentional persistent organic pollutants (unintentional POPs). In this study, unintentional POP concentrations, including PCDD/Fs, dioxin like PCBs (dl-PCBs), polychlorinated naphthalenes (PCNs), hexachlorobenzene (HxCBz) and pentachlorobenzene (PeCBz), were quantified in flue gas and residual ash emissions from thermal wire reclamation at scrap metal dismantling parks in Zhejiang Province, China. The total average TEQ emissions of the investigated unintentional POPs from flue gas and residual ash in two typical scrap metal recycling plants ranged from 13.1 to 48.3ngTEQNm(-3) and 0.08 to 2.8ngTEQg(-1), respectively. The dominant PCDD/F congeners were OCDD, 1,2,3,4,6,7,8-HpCDD, OCDF and 1,2,3,4,6,7,8-HpCDF, while PCB-126 and PCB-169 were the main contributors to the toxicity of the dl-PCBs. There were clear differences in the distribution dl-PCBs congeners contributing to the TEQ concentrations in the flue gas samples from the two plants. The PCN TEQs were dominated by PCN-66/67 and PCN-73. Although thermal wire reclamation in incinerators has been proposed as an alternative to open burning, there are still considerable environmental risks associated with regulated incinerators, and unintentional POP emissions from thermal wire reclamation sites need to be controlled by local government agencies.

Estimation and characterization of PCDD/Fs and dioxin-like PCB emission from secondary zinc and lead metallurgies in China

Secondary zinc and lead production is addressed as one of the potential sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) due to the impurity of the raw material. However, the release inventory of PCDD/Fs and dioxin-like PCBs is very scarce for these secondary nonferrous metallurgies. This study selected typical secondary zinc and lead plants to investigate the emissions of PCDD/Fs and dioxin-like PCBs released from such plants in China. The toxic equivalent quantity (TEQ) emission factor of PCDD/Fs and dioxin-like PCBs released into the environment is higher for secondary zinc production, at 52 298.02 ng TEQ ton(-1) than for secondary lead production, at 646.05 ng TEQ ton(-1). The most abundant congeners of PCDD/Fs are 2,3,4,7,8-PeCDF and 1,2,3,4,6,7,8-HpCDF for the secondary zinc and lead metallurgies, respectively. The most abundant congener of dioxin-like PCBs in the samples collected from both metallurgies is CB-126 . According to the distribution of PCDD/Fs (PCDF/PCDD >> 1) and the dominant contribution of higher chlorinated congeners, the de novo synthesis is assumed to be the main formation pathway of PCDD/Fs in the secondary zinc metallurgies. For the secondary lead metallurgies, the role of precursor formation is also very important. Based on the emission factor and production level, the total estimated emission amounts of PCDD/Fs and dioxin-like PCBs in both stack gas and fly ash released into the environment from secondary zinc and lead production is estimated to be at least 2.76 and 0.42 g TEQ yr(-1), respectively. The dioxin-like PCBs contribute 2.8% and 0.6% of the total emission from secondary zinc and lead plants, respectively.

The degradation of 1,2,4-trichlorobenzene using synthesized Co3O4 and the hypothesized mechanism.

Co(3)O(4) was synthesized with cabbage-like, plate-like and sphere-like morphologies. The effect of different morphologies on the degradation of 1,2,4-trichlorobenzene (1,2,4-TrCB) was evaluated, and the cabbage-like Co(3)O(4) exhibited the highest reactivity. The degradation of 1,2,4-TrCB on the cabbage-like Co(3)O(4) is hypothesized to act competitively via hydrodechlorination and oxygen-attacking pathways. By the hydrodechlorination pathway, 1,2,4-TrCB is successively dechlorinated into the three dichlorobenzenes (DCBs) and then monochlorobenzene (MCB). The yield of the DCBs was in the order of p-DCB>m-DCB>o-DCB, which can be explained by the calculated C-Cl bond dissociation energies in 1,2,4-TrCB and DCBs. Derivatization and electron spin resonance experiments identified that lattice oxygen and superoxide anions may take part in the oxidation pathway. The lattice oxygen initiated a partial oxidation of 1,2,4-TrCB, leading to the formation of chlorinated phenols. The superoxide anions caused ring-cracking oxidation of 1,2,4-TrCB, possibly producing some low-molecular-weight products, thus explaining a mass imbalance in the chlorine atoms and total organic carbon.

Occurrence and characteristics of polybrominated dibenzo-p-dioxins and dibenzofurans in stack gas emissions from industrial thermal processes.

The occurrence and characteristics of 2,3,7,8-substituted polybrominated and polychlorinated dibenzo-p-dioxins and dibenzofurans (PBDD/F and PCDD/F) from various combustion and metallurgic industrial thermal processes were investigated. PBDD/F levels from metallurgic processes (TEQ) concentrations from 0.14 to 1.5 ng Nm(-3), mass concentrations from 0.56 to 5.8 ng Nm(-3)) were markedly higher than those from combustion processes (TEQ) concentrations from 0.010 to 0.054 ng Nm(-3), mass concentrations from 0.025 to 0.15 ng Nm(-3)). This indicated that metallurgic processes could be important sources of PBDD/F. Consequently, more attention should be paid to the metallurgical emission sources in addition to combustion of brominated flame retardants (BFRs) and related products. Specific isomeric patterns for PCDD/F from various industrial sources were highly consistent, while PBDD/F patterns were not. This revealed that PCDD/F might form through a common mechanism such as de novo synthesis mechanism, while PBDD/F might form by different mechanisms in thermal processes such as precursor mechanisms. Finally, an approach to identify the PBDD/F sources in ambient air by using the PBDD/F to PCDD/F ratio was developed.

Mixed Polybrominated/chlorinated Dibenzo-p-dioxins and Dibenzofurans in Stack Gas Emissions from Industrial Thermal Processes

Very little is known about mixed polybrominated/chlorinated dibenzo-p-dioxins and dibenzofurans (PBCDD/F) in industrial thermal processes. In this study, the occurrences and characteristics of PBCDD/F from various incineration and metallurgical processes were investigated. In addition, PBCDD/F analytical protocols based on HRGC/HRMS were developed and optimized. The sum of isomer group concentrations ranged from 1.7-3740 pmol Nm(-3) for PBCDF and 0.2-582 pmol Nm(-3) for PBCDD. For some metallurgical industries, the amounts of PBDD/F and PBCDD/F emitted were similar to or even higher than the amounts of PCDD/F. The sources of bromine and brominated-precursors in these processes should be evaluated. The PBCDD/F characteristics investigated included isomer group patterns, ratio of bromine and chlorine incorporated in PBCDD/F, and ratio of halogenated furans to dioxins. Lower brominated PBCDD/F were binomially distributed. But in some cases, the concentrations of higher brominated PBCDD/F were much higher than predicted from the binomial distribution. The formation mechanisms of PBDD/F, PBCDD/F, and PCDD/F in these processes were also evaluated.

Degradation of polychlorinated biphenyls using mesoporous iron-based spinels

A series of mesoporous iron-based spinel materials were synthesized to degrade polychlorinated biphenyls (PCBs), with CB-209 being used as a model compound. The materials were characterized by X-ray powder diffraction (XRD), pore structure analysis, and X-ray photoelectron spectroscopy (XPS). A comparison of the dechlorination efficiencies (DEs) of the materials revealed that NiFe2O4 had the highest DE, followed by Fe3O4. Newly produced polychlorinated biphenyls, chlorinated benzenes, hydroxyl species and organic acids were detected by gas chromatography-mass spectrometry, high performance liquid chromatography-mass spectrometry and ion chromatograph. Identification of the intermediate products indicates that three degradation pathways, hydrodechlorination, the breakage of CC bridge bond and oxidative reaction, accompanied by one combination reaction, are competitively occurring over the iron-based spinels. The relative amounts of produced three NoCB isomers were illustrated by the CCl BDEs of CB-209 at meta-, para- and ortho-positions, and their energy gap between HOMO and LUMO. The consumption of the reactive oxygen species caused by the transformation of Fe3O4 into Fe2O3 in the Fe3O4 reaction system, and the existence of the highly reactive O2(-) species in the NiFe2O4 reaction system, could provide a reason why the oxidation reaction was more favored over NiFe2O4 than Fe3O4.

Thermal Degradation of Octachloronaphthalene over As-Prepared Fe3O4 Micro/Nanomaterial and Its Hypothesized Mechanism

Decomposition of octachloronaphthalene (CN-75) featuring fully substituted chlorines was investigated over as-prepared Fe3O4 micro/nanomaterial at 300 °C. It conforms to pseudo-first-order kinetics with kobs = 0.10 min(-1) as comparable to that of hexachlorobenzene and decachlorobiphenyl. Analysis of the products indicates that the degradation of CN-75 proceeds via two competitive hydrodechlorination and oxidation pathways. The onset of hydrodechlorination producing lower chlorinated naphthalenes (CNs) is more favored on α-position than β-position. Higher amounts of CN-73, CN-66/67, CN-52/60, and CN-8/11 isomers were found, while small content difference was detected within the tetrachloronaphthalene and trichloronaphthalene homologues, which might be attributed to lower energy principle and steric effects. The important hydrodechlorination steps, leading to CN-73 ≫ CN-74 in two heptachloronaphthalene isomers contrary to that in technical PCN-mixtures, were specified by calculating the charge of natural bond orbitals in CN-75 and the energy of two heptachloronaphthalene radicals. On the basis of the molecular electrostatic potential of CN-75, the nucleophilic O(2-), and eletrophilic O2(-) and O(-), present on the Fe3O4 surface, might attack the carbon atom and π electron cloud of naphthalene ring, producing naphthol species with Mars-van Krevelen mechanism, and formic and acetic acids.