The effect of copper speciation on the formation of chlorinated aromatics on real municipal solid waste incinerator fly ash

Degradation and regeneration inhibition of PCDD/Fs in incineration fly ash by low-temperature thermal technology

Low-temperature thermal degradation of PCDD/Fs for incineration fly ash (IFA), as a novel and emerging technology approach, offers promising features of high degradation efficiency and low energy consumption, presenting enormous potential for application in IFA resource utilization processes. This review summarizes the concentrations, congener distributions, and heterogeneity characteristics of PCDD/Fs in IFA from municipal, medical, and hazardous waste incineration. A comparative analysis of five PCDD/Fs degradation technologies is conducted regarding their characteristics, industrial potential, and applicability. From the perspective of low-temperature degradation mechanisms, pathways to enhance PCDD/Fs degradation efficiency and inhibit their regeneration reactions are discussed in detail. Finally, the challenges to achieve low-temperature degradation of PCDD/Fs for IFA with high-efficiency are prospected. This review seeks to explore new opportunities for the detoxification and resource utilization of IFA by implementing more efficient and viable low-temperature degradation technologies.

Incineration of carbon nanomaterials with sodium chloride as a potential source of PCDD/Fs and PCBs

The incineration of waste carbon nanomaterials will become an inevitable waste management strategy following the disposal of products containing carbon nanomaterials. We investigated the formation of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) during the incineration of selected carbon nanomaterials [fullerene (C₆₀), single-walled carbon nanotubes (SWNTs), and graphene], with sodium chloride and trace copper at 850 °C in air using a laboratory-scale electric furnace. Most PCDD/Fs and PCBs were concentrated in particulate fly ash post-incineration, and in low-temperature zones in the furnace (54-670 °C). Notably, C₆₀ had a specific thermal behavior leading to the formation of high concentrations of high chlorinated PCDD/Fs and toxic 2,3,7,8-tetra-CDD/F (2,3,7,8-T4CDD/F). SWNTs had a lower potential to generate such compounds than C₆₀, but had a higher potential than graphene and graphite. Temperature, solid/gas phases, chlorine sources, and the thermal stability of carbon nanomaterials were the key controlling factors. There is a need to consider the generation of PCDD/Fs and PCBs during the incineration of waste streams containing carbon nanomaterials.

Quantitative speciation of insoluble chlorine in E-waste open burning soil: Implications of the presence of unidentified aromatic-Cl and insoluble chlorides

Open burning of electronic waste (E-waste) produces numerous organochlorine compounds (OCs). Although the presence of unidentified OCs has been suggested, the mass balance of identified and unidentified OCs in E-waste open burning soils (EOBSs) still remains unknown. In this study, the concentrations of Cl bonded with aromatic carbon (aromatic-Cl) and aliphatic carbon (aliphatic-Cl), and inorganic Cl in EOBSs were determined by focusing on chlorine (Cl) in water-insoluble fractions (insoluble Cl) and applying Cl K-edge X-ray absorption spectroscopy in conjunction with combustion ion chromatography. The concentrations of identified Cl (Cl in five individual OCs: polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, chlorinated polycyclic aromatic hydrocarbons and chlorinated benzenes) were calculated from the concentrations previously reported for the same samples. The proportions of identified Cl were less than 1% to aromatic-Cl, indicating the abundance of unidentified OCs. The concentrations of both aromatic-Cl and identified Cl were highest in the sample collected from the site in Vietnam (VN), where wires and cables were mainly burned, suggesting that unidentified aromatic-Cl were produced through pathways similar to those of identified OCs, and the pathway could be related to burning of wires and cables. Further, insoluble Cu (II) compound, Cu₂(OH)₃Cl were assumed to be present in EOBSs and the concentration was highest in VN, implying that insoluble inorganic chlorides could be related to the formation of aromatic-Cl and identified Cl.

Electrophilic Chlorination of Naphthalene in Combustion Flue Gas

Naphthalene chlorination is an important formation mechanism of polychlorinated naphthalenes (PCNs) in combustion flue gas. In this study, a total of 21 metal chlorides and oxides were screened for their activities in the electrophilic chlorination of naphthalene. Copper(II) chloride exhibited the highest activity at 200-350 °C, followed by copper(I) chloride. Copper(II) chloride primarily acted as a strong chlorinating agent to facilitate chlorine substitution on naphthalene. Iron (II and III) chlorides were only highly active at 200-250 °C. At 250 °C, the average naphthalene chlorination efficiency over CuCl₂·2H₂O was 7.5-fold, 30.2-fold and 34.7-fold higher than those over CuCl, FeCl₃·6H₂O and FeCl₂·4H₂O, respectively. The other metal chlorides were less active. Under heated conditions, copper(II) and iron(III) chlorides were transformed to copper(I) and iron(II) chlorides via dechlorination, and then transformed to oxychlorides and oxides, thereby forming dechlorination-oxychlorination cycles of copper and iron species, respectively. The results obtained suggest that electrophilic chlorination of naphthalene in combustion flue gas is primarily driven by dechlorination-oxychlorination cycles of copper and iron species, and the reaction produces a selective chlorination pattern at 1 and 4 positions of naphthalene.

Chemical and mineral composition of fly ashes from home furnaces, and health and environmental risk related to their presence in the environment

The study presents the results of an analysis of fly ashes produced from burning of solid fuels mixed with municipal waste and assesses the environmental and health risk associated with infiltration of the selected metals to the environment. The phase composition suggests that the material is extremely mixed and diverse. Low-temperature components were mixed with substances formed in high temperatures. The variable composition of waste from different home furnaces with high content of the amorphous phase (which dissolves in water more easily than its crystalline equivalents) may be harmful to the environment and for the people. The dominant elements were silicates and aluminosilicates, such as: quartz, feldspar and plagioclase (albite). Clay minerals (kaolinite and mullite), carbonates (calcite), oxides/oxidehydroxides of iron and sulfate minerals (gypsum and anhydrite) were also abundant. The particles' major constituents were Si, Al, Ca and Fe oxides (85.5%), while S, Mg, Na, K and Ti oxides accounted for 12.6% of the total content. The risk assessment code suggested: Low Risk for As, Co, Cr, Ni, Medium Risk for Cd, Cu and Pb, and High Risk for Zn. Hazard Index (HI) calculated for non-cancerogenic substances for children was 2.35E+00. The total Risk index for children was 4.88E-05. As for adults, HI was 2.42E-01 for women, and 2.89E-01 for men, while the Risk index value was 6.85E-05 for women, and 8.48E-05 for men. The value HI > 1 points to the risk of adverse health impact on children exposed to fly ashes.

Uranium speciation in coal bottom ash investigated via X-ray absorption fine structure and X-ray photoelectron spectra

Similar to chromium contamination, the environmental contamination caused by uranium in radioactive coal bottom ash (CBA) is primarily dependent on the chemical speciation of uranium. However, the relationship between uranium speciation and environmental contamination has not been adequately studied. To determine the relationship between uranium speciation and environmental contamination, X-ray absorption fine structure (XAFS) and X-ray photoelectron spectra (XPS) analyses were performed to determine the uranium speciation in CBA exposed to different chemical environments and simulated natural environments. The leachability of the different forms of uranium in the CBA was studied via a simulated acid rain leaching experiment, and the results showed that 57.0% of the total uranium was leached out as U(VI). The results of a linear combination fit (LCF) of the X-ray absorption near edge structure (XANES) spectrum revealed that in the raw CBA, the uranium mainly occurred as U₃O₈ (71.8%). However, in the iron-rich particles, the uranium mainly occurred as UO₂ (91.9%) after magnetic separation. Magnetite is a ubiquitous ferrous-bearing oxide, and it was effective for the sorption of U(IV). The result of FeSO₄ leaching experiment indicated that 96.57% of total uranium was reduced from U(VI) to U(IV) when infiltrated with the FeSO₄ solution for 6months. This result clearly demonstrated the changes in chemical valence of uranium in the coal ash and provided a conceptual principle for preventing uranium migration from ash to the surrounding soil and plants.

Effects of the addition of municipal solid waste incineration fly ash on the behavior of polychlorinated dibenzo-p-dioxins and furans in the iron ore sintering process

Raw materials were co-sintered with municipal solid waste incineration (MSWI) fly ash through iron ore sintering to promote the safe treatment and utilization of MSWI fly ash. To assess the feasibility of this co-sintering method, in this study, the effects of the addition of MSWI fly ash on the formation and emission of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) were estimated via iron ore sintering pot experiments. During co-sintering, most of the PCDD/Fs in the added MSWI fly ash were decomposed and transformed into PCDD/Fs associated with iron sintering, and the concentrations of lower- and mid-chlorinated congeners increased. As there was a sufficient chlorine source and the sintering bed permeability was decreased by the addition of MSWI fly ash, the PCDD/F concentration in the exhaust gas increased. The mass emission of PCDD/Fs decreased; however, the emission of toxic PCDD/Fs increased beyond the total emissions from the independent MSW incineration and iron ore sintering processes due to the transformation of PCDD/F congeners. The co-sintering may be an important solution after technological improvements in the flue gas cleaning system and PCDD/F formation inhibition procedures.

Iron chloride catalysed PCDD/F-formation: Experiments and PCDD/F-signatures

Iron chloride is often cited as catalyst of PCDD/F-formation, together with copper chloride. Conversely, iron chloride catalysis has been less studied during de novo tests. This paper presents such de novo test data, derived from model fly ash incorporating iron (III) chloride and established over a vast range of temperature and oxygen concentration in the gas phase. Both PCDD/F-output and its signature are extensively characterised, including homologue and congener profiles. For the first time, a complete isomer-specific analysis is systematically established, for all samples. Special attention is paid to the chlorophenols route PCDD/F, to the 2,3,7,8-substituted congeners, and to their relationship and antagonism.

PCDD/F catalysis by metal chlorides and oxides

Model fly ash (MFA) samples were composed of silica, sodium chloride, and activated carbon, and doped with metal (0.1 wt% Cu, Cr, Ni, Zn and Cd) chloride or oxide. Each sample was de novo tested at 350 °C for 1 h, in a flow of gas (N2, N2 + 10% O2, +21% O2 or +10% H2) to investigate the effect of metal catalyst and gas composition on PCDD/F formation. Total PCDD/F yield rises rapidly with oxygen content, while the addition of hydrogen inhibits the formation and chlorination of PCDD/F. The amount of PCDD on average rises linearly with the oxygen concentration, while that of PCDF follows a reaction order of about 1/2; thus the PCDF to PCDD ratio drops when more oxygen becomes available. Some samples do not follow this trend. Chlorides are much more active than oxides, yet there are marked differences between individual metals. Principal component analysis (PCA) was applied to study the signatures from all samples, showing their unique specificity and diversity. Each catalyst shows a different signature within its individual homologue groups, demonstrating that these signatures are not thermodynamically controlled. Average congener patterns do not vary considerably with oxygen content changing from oxidising (air) to reducing (nitrogen, hydrogen).

Mechanism of unintentionally produced persistent organic pollutant formation in iron ore sintering

Effects of temperature, carbon content and copper additive on formation of chlorobenzenes (CBzs) and polychlorinated biphenyls (PCBs) in iron ore sintering were investigated. By heating simulated fly ash (SFA) at a temperature range of 250-500°C, the yield of both CBzs and PCBs presented two peaks of 637ng/g-fly ash at 350°C and 1.5×10(5)ng/g-fly ash at 450°C for CBzs, and 74ng/g-fly ash at 300°C and 53ng/g-fly ash at 500°C. Additionally, in the thermal treatment of real fly ash (RFA), yield of PCBs displayed two peak values at 350°C and 500°C, however, yield of CBzs showed only one peak at 400°C. In the thermal treatment of SFA with a carbon content range of 0-20wt% at 300°C, both CBzs and PCBs obtained the maximum productions of 883ng/g-fly ash for CBzs and 127ng/g-fly ash for PCBs at a 5wt% carbon content. Copper additives also affected chlorinated aromatic formation. The catalytic activity of different copper additives followed the orders: CuCl2∙2H2O>>Cu2O>Cu>CuSO4>CuO for CBzs, and CuCl2∙2H2O>>Cu2O>CuO>Cu>CuSO4 for PCBs.

Amino Compounds as Inhibitors of De Novo Synthesis of Chlorobenzenes

The inhibitory effects of four amino compounds on the formation of chlorobenzenes (CBzs)--dioxin precursors and indicators, and the inhibitory mechanisms were explored. The results show NH4H2PO4 can decrease the total yields of CBzs (1,2di-CBz, 1,3di-CBz, 1,4di-CBz, penta-CBz and hexa-CBz) by 98.1%±1.6% and 96.1%±0.7% under air and nitrogen flow. The inhibitory effects indicated by the total yields of CBzs follow the order NH4H2PO4 > NH4HF2 > (NH4)2SO4 > NH4Br under air flow and NH4H2PO4 ≈ (NH4)2SO4 ≈ NH4HF2 >NH4Br under nitrogen flow. The inhibition mechanism revealed by thermal analysis that CuCl2 was converted to CuPO3 by reacting with NH4H2PO4 below 200 °C, which can block the transfer of chlorine and formation of C-Cl bonds at 350 °C. The effects of the other three inhibitors were weaker because their reactions with CuCl2, which form other copper compounds, and the reaction of CuCl2 with carbon, which forms C-Cl bonds, were almost simultaneous and competitive. Oxygen influenced the yield of CBzs obviously, and the total yield of five CBzs sharply increased with oxygen. Because of their high efficiency, low environmental impact, low cost, and availability, amino compounds--especially NH4H2PO4--can be utilized as inhibitors of CBzs during incineration.

Iron and copper catalysis of PCDD/F formation

The formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) was explored during de novo tests designed to compare the catalytic activity of copper (II) chloride (CuCl2) with that of iron (III) oxide (Fe2O3) and to test some synergistic effect between these two catalytic compounds. Both copper chloride (CuCl2) and iron oxide (Fe2O3) were earlier proposed as catalysts to explain the PCDD/F emissions from, e.g. municipal solid waste incineration (MSWI). In addition, haematite (Fe2O3) is the main iron ore and could be responsible for the typical iron ore sintering plant fingerprint. A total of nine model fly ash (MFA) samples were prepared by mixing and grinding of sodium chloride (NaCl), activated carbon and a powder matrix of silica (SiO2) with the selected metal compound(s). The conditions of these de novo tests were 1 h in duration, 350 °C in a flow of synthetic combustion gas (10 vol.% oxygen in nitrogen). The effect of Fe-Cu catalyst concentration on yield and distribution pattern of PCDD/F was systematically explored; three strongly differing ratios of [Fe]:[Cu] were considered (1:1, 10:1 and 100:1) to study the potential interactions of Fe2O3 and CuCl2 suggested earlier. The results show some slight rise of PCDD/F formed with raising iron concentration from 0 to 10.1 wt% (no Cu added; 0.1 wt% Cu), as well as strong surging of both amount and average chlorination level of PCDD/F when rising amounts of copper (0 to 1.1 wt%) are introduced. The resulting fingerprints are compared with those from sintering and from MSWI.

Interplay of metals and bromine with dioxin-related compounds concentrated in e-waste open burning soil from Agbogbloshie in Accra, Ghana

Open burning of electronic waste (e-waste) releases various metals and organohalogen compounds in the environment. Here we investigated the interplay of metals (Cu, Pb, Zn, Fe, Co, and Sr) and bromine (Br) in the formation of dioxin-related compounds (DRCs), including polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs), as well as non-regulated DRCs such as polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) and their monobrominated PCDD/Fs in soils sampled from open burning e-waste sites at Agbogbloshie in Accra, Ghana. The predominant DRCs were PBDFs, PCDFs, PCDDs, and DL-PCBs. Statistical analyzes, X-ray absorption spectroscopy, and the PCDF/PCDD ratio suggested possible formation paths of PCDD/Fs and DL-PCBs by catalytic behaviors of copper chlorides (CuCl, CuCl2, and Cu2(OH)3Cl) and thermal breakdown of polyvinyl chloride. Predominant formation of brominated furans may be derived from electron transfer from intermediates of PBDE to copper, Cu(II) → Cu(I). Lead chloride also contributed to generate DRCs and may become highly bioaccessible through the open burning of e-waste. The main zinc species (ZnCl2 and ZnS) suggested a possible relationship to generate DRCs and specific zinc source such as tire burning. Cu, Pb, Zn, and Br contained in various e-wastes, wires/cables, plastics, and tires strongly influenced generation of many DRCs.

Removal of toxic and alkali/alkaline earth metals during co-thermal treatment of two types of MSWI fly ashes in China

This study aims to vaporize heavy metals and alkali/alkaline earth metals from two different types of fly ashes by thermal treatment method. Fly ash from a fluidized bed incinerator (HK fly ash) was mixed with one from a grate incinerator (HS fly ash) in various proportions and thermally treated under different temperatures. The melting of HS fly ash was avoided when treated with HK fly ash. Alkali/alkaline earth metals in HS fly ash served as Cl-donors to promote the vaporization of heavy metals during thermal treatment. With temperature increasing from 800 to 900°C, significant amounts of Cl, Na and K were vaporized. Up to 1000°C in air, less than 3% of Cl and Na and less than 5% of K were retained in ash. Under all conditions, Cd can be vaporized effectively. The vaporization of Pb was mildly improved when treated with HS fly ash, while the effect became less pronounced above 900°C. Alkali/alkaline earth metals can promote Cu vaporization by forming copper chlorides. Comparatively, Zn vaporization was low and only slightly improved by HS fly ash. The low vaporization of Zn could be caused by the formation of Zn2SiO4, ZnFe2O4 and ZnAl2O4. Under all conditions, less than 20% of Cr was vaporized. In a reductive atmosphere, the vaporization of Cd and Pb were as high as that in oxidative atmosphere. However, the vaporization of Zn was accelerated and that of Cu was hindered because the formation of Zn2SiO4, ZnFe2O4 and ZnAl2O4 and copper chloride was depressed in reductive atmosphere.

Leaching for recovery of copper from municipal solid waste incineration fly ash: influence of ash properties and metal speciation

Recovery of metals occurring in significant amounts in municipal solid waste incineration fly ash, such as copper, could offer several advantages: a decreased amount of potentially mobile metal compounds going to landfill, saving of natural resources and a monetary value. A combination of leaching and solvent extraction may constitute a feasible recovery path for metals from municipal solid waste incineration fly ash. However, it has been shown that the initial dissolution and leaching is a limiting step in such a recovery process. The work described in this article was focused on elucidating physical and chemical differences between two ash samples with the aim of explaining the differences in copper release from these samples in two leaching methods. The results showed that the chemical speciation is an important factor affecting the release of copper. The occurrence of copper as phosphate or silicate will hinder leaching, while sulphate and chloride will facilitate leaching.

Coexistence of Cu, Fe, Pb, and Zn oxides and chlorides as a determinant of chlorinated aromatics generation in municipal solid waste incinerator fly ash

We investigated chemical determinants of the generation of chlorinated aromatic compounds (aromatic-Cls), such as polychlorinated biphenyls (PCBs) and chlorobenzenes (CBzs), in fly ash from municipal solid waste incineration. The influences of the following on aromatic-Cls formation in model fly ash (MFA) were systematically examined quantitatively and statistically: (i) inorganic chlorides (KCl, NaCl, CaCl2), (ii) base materials (SiO2, Al2O3, CaCO3), (iii) metal oxides (CuO, Fe2O3, PbO, ZnO), (iv) metal chlorides (CuCl2, FeCl3, PbCl2, ZnCl2), and (v) "coexisting multi-models." On the basis of aromatic-Cls concentrations, the ∑CBzs/∑PCBs ratio, and the similarity between distribution patterns, MFAs were categorized into six groups. The results and analysis indicated that the formation of aromatic-Cls depended strongly on the "coexistence condition", namely multimodels composed of not only metal chlorides, but also of metal oxides. The precise replication of metal chloride to oxide ratios, such as the precise ratios of Cu-, Fe-, Pb-, and Zn-chlorides and oxides, may be an essential factor in changing the thermochemical formation patterns of aromatic-Cls. Although CuCl2 acted as a promoter of aromatic-Cls generation, statistical analyses implied that FeCl3 also largely influenced the generation of aromatic-Cls under mixture conditions. Various additional components of fly ash were also comprehensively analyzed.

X-ray absorption fine structure study of multinuclear copper(I) thiourea mixed ligand complexes

X-ray absorption fine structure spectra of five copper(I) thiourea complexes [Cu4(thu)6 (NO3)4 (H2O)4] (1), [Cu4(thu)9 (NO3)4 (H2O)4] (2), [Cu2(thu)6 (SO4) H2O] (3), [Cu2(thu)5 (SO4) (H2O)3] (4), and [Cu(thu)Cl 0.5H2O] (5) have been investigated. Complexes 1 and 3 are supposed to have one type of copper centers in trigonal planar and tetrahedral environment, respectively. Complexes 2 and 4 are supposed to have two types of copper centers, one center having trigonal planar geometry and another center having tetrahedral geometry. The aim of the present work is to show how extended X-ray absorption fine structure (EXAFS) spectra of these complexes, having different types of coordination environment, can be analyzed to yield the coordination geometry around one type of copper centers present in complexes 1 and 3, and two types of copper centers present in complexes 2 and 4. The crystal structure of complex 5 is unavailable due to inability of growing its single crystals, and hence the coordination geometry of this complex has been determined from EXAFS. The structural parameters determined from the EXAFS spectra have been reported and the coordination geometry has been depicted for the metal centers present in all the five complexes. Also, the chemical shifts have been used to determine the oxidation state of copper in these complexes. The X-ray absorption near edge spectra features have also been correlated with the coordination geometry. Also, the presence of both three and four coordinated Cu(I) centers in complexes 2 and 4 has been suggested from a comparison of the intensity of the feature at 8984 eV with those of 1 and 3. Further, in case of complex 5, the high intensity of peak A at 8986.5 eV is found to correspond to the presence of Cl coordinated to the copper center.

Thermochemical behavior of lead adjusting formation of chlorinated aromatics in MSW fly ash

In this study, we examined the thermochemical role of Pb in the formation of chlorinated aromatics (aromatic-Cls) in MSW fly ash at 300-400 °C, a key temperature window for maximum yield. In the presence of lead oxide alone, aromatic-Cls formation was suppressed. One of the mechanisms of suppression was partial chlorination of PbO by an inorganic chlorine source in the solid phase, based on in situ Pb L3-edge X-ray absorption near-edge structure (XANES) data. In contrast, quantitative GC/MS measurements revealed that PbCl2 promoted aromatic-Cls formation to an extent that depends on the Pb concentration, the heating temperature, and the presence of other metal catalysts. We identified two mechanisms of aromatic-Cls formation triggered by PbCl2 in MSW fly ash. First, promotion can occur by the thermochemical partial oxidation of PbCl2. More specifically, real complex solid phase increases the thermochemical oxidation reactivity of PbCl2, based on in situ Pb L3-edge XANES data. Second, Cl K-edge X-ray absorption spectroscopy revealed a coexistent effect of PbCl2 with other metal catalysts such as CuCl2 and FeCl3. The presence of PbCl2 influences the balance of the bonding state of chlorine with Cu and Fe atoms at various temperatures. Thus, Pb in real MSW fly ash functions as an "adjuster" in the generation of aromatic-Cls, the nature of which depends on the lead oxide/chloride ratio and the presence of other metal catalysts.

Dioxins and their fingerprint in size-classified fly ash fractions from municipal solid waste incinerators in China--mechanical grate and fluidized bed units

The distribution of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), in brief dioxins, has seldom been addressed systematically in fly ash from municipal solid waste incinerators (MSWIs). This study shows the amount and fingerprint of PCDD/Fs in fly ash from four different Chinese MSWIs, that is, three mechanical grate units and one circulating fluidized bed unit. In these fly ash samples, dioxins-related parameters (international toxic equivalent quantity, total amount of PCDD/Fs, individual isomer classes, and 17 toxic 2,3,7,8-substituted congeners) all tend to increase with decreasing particle size for mechanical grate incinerators, yet only for the finest fraction for fluidized bed units. Moreover, the fluidized bed incinerator seems superior to grate incineration in controlling dioxins, yet a comparison is hampered by internal differences in the sample, for example, the fluidized bed fly ash has much lower carbon and chlorine contents. In addition, the presence of sulfur from mixing coal as supplemental fuel to the MSW may poison the catalytic steps in dioxins formation and thus suppress the formation of dioxins. With more residual carbon and chlorine in the fly ash, it is easier to form dioxins during cooling. Nevertheless, there is no apparent relation between Fe, Cu, and Zn contents and that of dioxins in fly ash.

Thermochemical chlorination of carbon indirectly driven by an unexpected sulfide of copper with inorganic chloride

Unintentional anthropogenic thermal chlorination of carbon is known to be a contributor to global environmental pollution of organochlorine compounds. We found unexpected, serious chlorination of carbon promoted by a "sulfide" of copper, which has been generally thought of and studied as an inactive metal catalyst. Our quantitative and X-ray spectroscopic results show that a fraction of cupric sulfide indirectly promoted thermochemical solid-phase formation of a large quantity of organochlorine compounds such as polychlorinated dibenzo-p-dioxins, dibenzofurans, biphenyls, and benzenes that used inactive inorganic chloride as chlorine storage, which partly caused environmental pollution by organochlorine compounds.

Role of zinc in MSW fly ash during formation of chlorinated aromatics

In this study, we determined the thermochemical role of zinc in municipal solid waste (MSW) fly ash. Zinc's role depended on its chemical form and the presence of other metal catalysts. When only zinc was present or it dominated other metal elements, chlorinated aromatic compound (aromatic-Cl) formation was promoted by zinc chloride but blocked by zinc oxide. When only zinc was present, such as in zinc metallurgical plants, some aromatic-Cls were generated and contaminated the environment. When zinc coexisted with other metal promoters in a thermal postcombustion solid phase, such as MSW incineration, Fourier-transform Zn K-edge extended X-ray absorption fine structure (EXAFS) analysis showed that the chemical forms of zinc were primarily chloride and/or oxide, and zinc chloride (ZnCl(2)) was thermally stable in the solid phase. Thus, we used ZnCl(2) in coexistence experiments as a promoter to generate aromatic-Cls. Zinc chloride acted as a coexistent inhibitor of metal catalysis and precursor dimerization to generate aromatic-Cls. There were two coexistent inhibition mechanisms. First, a low-temperature transition of chlorine to the gas phase (low-Cl(g)) occurred with metal catalysts such as CuCl(2) and FeCl(3), confirmed by Cl K-edge near-edge X-ray absorption fine structure (NEXAFS) analysis. Second, X-ray photoelectron spectroscopy (XPS) analysis of the surface or near-surface concentration of ZnCl(2) indicated weak reactivity between the catalysts and the carbon matrix.

The behavior of PCDD and PCDF during thermal treatment of waste incineration ash

The polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) content of three fly ash samples with different elemental compositions from different municipal waste incinerators were analyzed before and after thermal treatment at 300 °C or 500 °C. Gas phase emissions during the treatments were also collected and analyzed. Substantial reductions in the total PCCD/F content of the ashes were observed after treatment at 500 °C, seemingly due to degradation rather than dechlorination. Treatment at 300 °C resulted in an increase in the PCDD/F content of the three ashes. Initial concentration of PCDD/F in the untreated ashes did not reflect the outcome of the treatment at the different temperatures. In addition, the composition of the ash was found to influence the rate of decomposition and formation of PCDD and PCDF during thermal treatment; the results showed that Cu, Fe, Ca and S play important roles in these processes.

Real-time gas-phase analysis of mono- to tri-chlorobenzenes generated from heated MSWI fly ashes containing various metal compounds: application of VUV-SPI-IT-TOFMS

We measured sensitive real-time change of low-chlorinated (Cl(1)-Cl(3)) benzenes in gas phase from heated model and real solid samples using the recently developed vacuum ultraviolet (VUV) single-photon ionization (SPI) ion trap time-of-flight mass spectrometer (VUV-SPI-IT-TOFMS). Model solid samples that contained activated carbon, potassium chloride, silicon dioxide, and trace metallic compounds (copper, iron, lead, and zinc) were used to simulate fly ash at a municipal solid waste incinerator (MSWI). The concentrations of chlorobenzenes determined by integrating the area for 30 min using VUV-SPI-IT-TOFMS were correlated with gas-phase concentrations analyzed by GC/MS. Real-time changes had characteristic patterns dependent on metal species and compounds. Comparing gas-phase real-time patterns of low-chlorinated benzenes between real and model fly ashes, copper chloride- and oxide-like compounds in real fly ash at the postcombustion zone in a MSWI may play key factors in the formation of low-chlorinated benzenes. Lead and zinc compounds and iron oxide in solid phase did not affect the formation of low-chlorinated benzenes in gas phase. VUV-SPI-IT-TOFMS can be applied to the time-dependent characterization of volatile low-chlorinated benzenes in gas phase in various artificial and environmental processes.

Formation of chlorinated aromatics in model fly ashes using various copper compounds

Various copper compounds found in fly ash are related to the formation of chlorinated aromatics. The formation potentials of chlorinated aromatics in different model fly ashes containing various copper compounds and the chemical behavior of such copper compounds were investigated. In model fly ash with copper metal, hydroxide, carbonate, or oxides, the generated amounts of chlorobenzene (CBz) and polychlorinated biphenyls (PCBs) and the average chlorination numbers were low and at the same level, respectively. The maximum generated amounts of chlorinated aromatics were observed at 300 degrees C. Although X-ray absorption near edge structure (XANES) spectra indicated that the chemical form of copper compounds changed little, they were found to promote the formation of chlorinated aromatics. Therefore, these copper compounds play the same role as CuO. On the other hand, in model fly ash with copper chloride, the generated amounts of CBz and PCBs were quite high and the average chlorination numbers was high. Dynamic changes were observed in XANES spectra, and the pre-edge peak attributed to monovalent copper compounds appeared at around 300 degrees C. A large difference was observed between these two groups in the amount of CuCl generated and the homologs of chlorinated aromatics present, indicating that CuCl played an important role in the formation of chlorinated aromatics.

Investigating the speciation of copper in secondary fly ash by X-ray absorption spectroscopy

Although some researchers have reported that chlorides may play an important part in the evaporation of copper during heat treatment of municipal solid waste incinerators (MSWI) fly ash (1, 2) , details on the copper speciation in volatile matters (secondary fly ash, SFA) are still lacking. In this work, we used in situ X-ray absorption spectroscopy (XAS) experiments involving three types of SFA, which was collected from a high-temperature tubular electric furnace by thermal treatment of municipal solid waste incinerator (MSWI) fly ash at 1000, 1150, and 1250 degrees C. The results obtained by a linear combination fit (LCF) of X-ray absorption near edge structure (XANES) spectra revealed that in MSWI fly ash copper mainly exists as CuO and CuSO(4).5H(2)O while chloride almost dominated all the content of the SFA conformation, which was more than 80%. Extended X-ray absorption fine structure (EXAFS) data analysis indicated the presence of both Cu-O and Cu-Cl bonds in the first coordination shell of Cu ions in all SFA, while only Cu-O bonds occur in the MSWI fly ash. Consequently, in the MSWI fly ash during heat treatment copper evaporated as chloride, and the latter plays an important role in the formation of copper chloride.

Influence of Cu, Fe, Pb, and Zn chlorides and oxides on formation of chlorinated aromatic compounds in MSWI fly ash

Model fly ashes containing admixed Cu, Fe, Pb, and Zn chlorides and oxides were heated at a temperature corresponding to the postcombustion zone of a municipal solid waste incinerator (MSWI), resulting in the formation of chlorinated aromatic compounds, including polychlorinated dibenzo-p-dioxins (PCDDs) and furans (PCDFs), polychlorinated biphenyls (PCBs), and chlorobenzenes (CBzs). The concentrations of these compounds were measured and compared with those occurring in real fly ash. The order with respect generative capacity of each metal additive was calculated from principal component analysis of the concentrations of the different chlorinated aromatic compounds as CuCl(2)*2H(2)O > Cu(2)(OH)(3)Cl > FeCl(3)*6H(2)O > FeCl(2)*4H(2)O > CuO > Fe(2)O(3) > PbCl(2) > blank (no metal added) > ZnCl(2) > PbO > ZnO. From hierarchical cluster analysis of the concentrations and congener distribution patterns of the PCDDs, PCDFs, PCBs, and CBzs, the metallic compounds were divided into five groups: Group A (CuCl(2)*2H(2)O and Cu(2)(OH)(3)Cl), B (FeCl(3)*6H(2)O and FeCl(2)*4H(2)O), C (CuO and PbCl(2)), D (Fe(2)O(3), blank, and ZnCl(2)), and E (PbO and ZnO). Cluster analysis showed the congener distribution patterns of model fly ashes to be similar to the pattern of real MSWI fly ash. The formation of PCDDs was influenced mainly by group B, blank, and PbO; PCDFs, mainly by CuO, Fe(2)O(3) and ZnCl(2); PCBs, mainly by groups B and C; and CBzs, mainly by groups A and B. Thus, the multiple promotion of chlorinated aromatic compound formation by metallic chlorides and oxides in the fly ashes of MSWIs and other thermal processes has considerable importance for the environment.

Potential formation of PCDD/Fs and related bromine-substituted compounds from heating processes for ashes

Thermal experiments were conducted using real boiler ash and fly ash samples from three types of municipal or industrial solid waste incineration plants to understand the formation reactions of polychlorinated dibenzo-p-dioxin and furans (PCDD/Fs) and related bromine compounds that were chlorinated-brominated dibenzodioxins and furans (PXDD/Fs) and polybrominated dibenzo-p-dioxin and furans (PBDD/Fs). The results obtained were as follows: The formation of PCDD/Fs was clearly shown, and fly ash containing abundant carbon matter had a significant potential for de novo synthesis. The homologous distribution change apparently showed that the formation of PXDD/Fs occurred from the substitution of a bromine atom with a chlorine atom in the PCDD/F molecules. This suggests that PXDD/Fs are usually formed with PCDD/Fs on the ash. PBDD/Fs might be formed from any reaction mechanism different from that of PXDD/Fs. The existence of carbonaceous matters always does not mean the potential formation of PCDD/Fs. However, any addition of catalytic copper may influence the nature of ash to increase the formation potential. The findings suggest that there are many instances that result in the unintended production of trace hazardous pollutants in the incineration process and show that careful and sophisticated control is required to prevent the formation of pollutants.

Relationship between dynamic change of copper and dioxin generation in various fly ash

Only limited information on the chemical forms of copper in municipal solid waste incinerator (MSWI) fly ash is available in the literature. Therefore, we performed in situ X-ray absorption near-edge spectroscopy (XANES) experiments involving two types of real fly ash to confirm the behavior of copper in fly ash at secondary formation temperatures for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). CuCl(2).3Cu(OH)(2) was detected in both fly ash types before heating experiments. Cupric compounds in real fly ash were reduced to cuprous compounds or elemental copper at approximately 200 degrees C. The changes in the Cu XANES spectra observed for the two fly ash samples were similar to those observed previously. We also examined the behavior of copper in model fly ash using SiO(2) to investigate the effect of supporting materials and copper content in fly ash on the dynamic changes of copper and amount of dioxins generated. There was little difference between the use of boron nitride (BN) and SiO(2) as a supporting material. The formation mechanisms of PCDDs and PCDFs in both of the model fly ash types were basically the same. Thus, we conclude that the dynamic change of copper in MSWI fly ash during heating is a commonly observed feature, and no simple relationship between the composition of fly ash and the amount of PCDD/PCDF generated or dynamic change of copper is apparent. The dynamic change of copper explained the generated amount and homologue distribution of PCDDs and PCDFs.

Catalytic effects by metal oxides on the formation and degradation of chlorinated aromatic compounds in fly ash

Polychlorinated benzenes, dibenzo-p-dioxins (PCDD), and dibenzofurans (PCDF) may be formed below the combustion temperature in fly ash from municipal solid waste incinerators (MSWI). Copper catalyzes this formation, possibly by the Deacon reaction. Many other elements are also Deacon catalysts or promoters, and here we report results from a statistically designed experiment with 15 metal oxides added to fly ash and heated at 300 degrees C for 2h in an air atmosphere. A resolution IV fractional factorial design with four replicates was completed in 36 runs with the oxides of magnesium, yttrium, titanium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, and tin. All samples were analyzed for chlorinated benzenes and the results were evaluated by analysis of variance. The addition of copper significantly increased the amounts of the chlorinated benzenes, while cobalt, chromium and vanadium decreased the net formation. The oxides of zinc and iron seemed to have a slightly positive and negative effect respectively. The findings in this study seem to corroborate our previously reported results regarding the different catalytic effects of copper and chromium, and lack of a significant effect by nickel. Besides chromium, it also identifies cobalt and vanadium as potent catalysts for oxidative degradation of the chlorinated aromatic compounds found in MSWI fly ash.

Characterization of residual carbon influencing on de novo synthesis of PCDD/Fs in MSWI fly ash

Using 19 samples of fly ash collected from various MSW incineration facilities, residual carbon was characterized by gasifiable fraction at 450 degrees C (C450), and the correlations with de novo synthesis of PCDD/Fs were experimentally examined. Fly ashes were classified into three groups by the ratio of C450 to total residual carbon. By comparison of CO and CO2 generation patterns with those of reference materials, unburnt carbon of solid waste and activated carbon powder injected into flue gas were identified as a carbon source in fly ash. In the experiment of de novo synthesis of PCDD/Fs, the content of PCDD/F synthesis depended on C450 regardless of the origin of carbon. In addition, the model to predict the content of PCDD/F synthesis, DeltaPCDD/F=0.989.Cu.C450, fitted well with experimental values.

Tracking of copper species in incineration fly ashes

Speciation of copper in the incineration waste heat boiler (HB) and the down stream electrostatic precipitator (EP) fly ashes during the flue gas cooling down (1123-->473 K) has been studied by X-ray absorption near edge structural (XANES) spectroscopy in the present work. Copper species such as Cu(OH)(2) (59-67%), CuCl(2) (5-12%), CuO (24-26%), and a small amount of CuS (3-4%) in fly ashes were determined by semi-quantitative analyses of the XANES spectra. In the toxicity characteristics leaching procedure (TCLP) tests, about 83 and 20% of copper were leached from the EP and HB fly ashes, respectively. The relatively high leachability of copper for the EP fly ash might be due to the fact that CuCl(2) was enriched on the surfaces as observed by X-ray photoelectron spectroscopy (XPS). On the contrary, CuCl(2) was mainly encapsulated in the HB fly ashes.

PCDD/F and related compounds in solid residues from municipal solid waste incineration--a literature review

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) from waste incineration into the air have been a major focus of interest during the last two decades. An integrated approach to clean waste disposal has to take the occurrence of PCDD/F in all residues into account. This paper compiles published data on concentration ranges of PCDD/F and the related compounds polychlorinated biphenyls (PCB), chlorinated benzenes and phenols, as well as polyaromatic hydrocarbons (PAH) in solid residues from waste incineration in grate furnaces and their development since 1985. A short description of inertization processes for PCDD/F loaded materials is added.