Environ. Sci. Technol. 2009, 43, 8053–8059

Influence of Cu, Fe, Pb, and Zn Chlorides and Oxides on Formation of Chlorinated Aromatic Compounds in MSWI Fly Ash T A K A S H I F U J I M O R I , * ,† MASAKI TAKAOKA,† AND NOBUO TAKEDA‡ Department of Urban and Environmental Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nisikyo-ku, 615-8540, Kyoto, Japan, and Eco-Technology Research Center, Ritsumeikan University, Noji Higashi 1, 1-1 Kusatsu, 525-8577, Shiga, Japan

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Received June 23, 2009. Revised manuscript received September 17, 2009. Accepted September 28, 2009.

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 occurringinrealflyash.Theorderwithrespectgenerativecapacity of each metal additive was calculated from principal component analysis of the concentrations of the different chlorinated aromatic compounds as CuCl2 · 2H2O > Cu2(OH)3Cl > FeCl3 · 6H2O > FeCl2 · 4H2O > CuO > Fe2O3 > PbCl2 > blank (no metal added) > ZnCl2 > 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 (CuCl2 · 2H2O and Cu2(OH)3Cl), B (FeCl3 · 6H2O and FeCl2 · 4H2O), C (CuO and PbCl2), D (Fe2O3, blank, and ZnCl2), 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, Fe2O3 and ZnCl2; 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.

Introduction Many chlorinated aromatic compounds are emitted by thermal processes and subsequently persist in the environment. Of particular note are those produced from municipal solid waste incinerators (MSWI) (1), which are known to be major sources of polychlorinated dibenzo-p-dioxins (PCDDs) and furans (PCDFs). PCDDs and PCDFs become concentrated * Corresponding author e-mail: [email protected]. media.kyoto-u.ac.jp. † Kyoto University. ‡ Ritsumeikan University. 10.1021/es901842n CCC: $40.75

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 2009 American Chemical Society

in fly ash by postcombustion processes, forming in the presence of oxygen, their precursors, unburned carbon, and chlorine sources (2, 3). Chlorobenzenes (CBzs) and polychlorinated biphenyls (PCBs) also concentrate in fly ash. Hexachlorobenzene is one of the more persistent organic pollutants, and PCBs are known toxins. An understanding of the postcombustion mechanism that generates chlorinated aromatic compounds, including PCDDs, PCDFs, PCBs, and CBzs, is essential for protecting human health, given the persistence of these compounds in the environment. However, there are far fewer accounts of the formation of CBzs (4) and PCBs (5), compared with PCDDs and PCDFs, in fly ash. Some metal species promote the formation of chlorinated aromatic compounds in fly ash. Of particular note is copper, which has been reported to have high affinity for chlorine and to serve a catalytic role when admixed in model fly ashes (6-9). Iron chlorides and oxides are also known to promote the development of chlorinated organic compounds in model systems (10-13), and zinc in real fly ashes has been associated with the occurrence of PCBs and CBzs (14). Nonetheless, the effects of only a few metal species or their compounds have been compared systematically under similar experimental conditions. Furthermore, real fly ash is complex and contains many elements (14-16), making it difficult to determine the specific components responsible for producing chlorinated aromatic compounds. In this report, we describe the influence of different Cu, Fe, Pb, and Zn chlorides and oxides on the formation of chlorinated aromatics, including PCDDs, PCDFs, PCBs, and CBzs, under the same experimental conditions. The metallic compounds were divided into groups using hierarchical cluster analysis, and comparisons were made among the congener distribution patterns of PCDDs, PCDFs, PCBs, and CBzs in both model fly ashes and MSWI fly ash. The contribution for formation path of each chlorinated aromatic was determined, and the role of each metallic compound was assessed.

Materials and Methods Real and Model Fly Ashes. Five real fly ashes were collected from the inlets or outlets of electrostatic precipitators and bag filters, involving no lime injection, at four stoker-type MSWIs in Japan. Model fly ash was prepared from activated carbon. Any organic compounds were removed by heating at 500 °C for 60 min under a stream of 100% nitrogen gas (100 mL/min). The product is referred to as “AC” in this paper. The model fly ash was admixed with different metal species by grinding in a mortar for about 10 min in the proportions: AC (3.0 wt %), potassium chloride (KCl; 10 wt % Cl), metal compound (0.2 wt % metal), and silicon dioxide (SiO2; remainder). A blank model fly ash (blank) without any metal compound was prepared from a mixture of AC, KCl and SiO2. Details are shown in the Supporting Information (SI). Detection of Chlorinated Organic Compounds in Real and Model Fly Ashes. In our earlier study, the concentrations of PCDDs and PCDFs in real fly ash were analyzed by highresolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS) (17). In the current work, PCBs and CBzs were analyzed by HRGC/low-resolution MS (HP-6890/ HP-5973). Sample pretreatment for the determination of chlorinated aromatic compounds was according to Japanese Industrial Standards (JIS) K 0311 and 0312. We placed 5 g of model fly ash into a quartz boat contained within a quartz tube (120 × 4 cm internal diameter), which was then placed in a preheated electronic furnace at 300 °C VOL. 43, NO. 21, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. (a) Concentrations and (b) average number of chlorines [n(Cl)] for polychlorinated dibenzo-p-dioxins (PCDDs; Cl4-Cl8), furans (PCDFs; Cl4-Cl8), PCBs (Cl2-Cl8), and chlorobenzenes (CBzs; Cl2-Cl6) in residues of model fly ashes to which various metal species had been added before heating at 300 °C for 30 min. for 30 min under a flow of 10% oxygen/90% nitrogen delivered at 50 mL/min, to simulate the postcombustion zone of a MSWI (SI Figure S1). After heating, the concentrations of chlorinated aromatic compounds in the model fly ash residue and in the gas phase collected in an impinger containing 100 mL of toluene were analyzed separately. Experimental details are shown in the SI. Multiple Classification Analyses. The data set obtained in this study (SI Table S1) was analyzed by multiple classification analyses, i.e., principal component analysis and hierarchical cluster analysis, using the add-in software Mulcel supplied by Excel (Microsoft Corp.) (18). The hierarchical cluster analysis obtained by Mulcel showed the same results as those obtained by an SPSS-based procedure using the same data. Details of these analyses are given in the SI.

Results and Discussion Formation of Chlorinated Aromatic Compounds by Cu, Fe, Pb, and Zn Chlorides and Oxides. The amounts of chlorinated aromatic compounds generated in the model fly ashes by Cu, Fe, Pb, and Zn chlorides and oxides clearly differed among the metals. For all metal species, the concentrations of PCDDs, PCDFs, PCBs, and CBzs were higher in the model fly ash solid residue than in the gas phase contained in the toluene impinger. The ratios of solid/ gas concentrations of the chlorinated aromatic compounds ranged from the single digits to greater than 100 (SI Tables 8054

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S1 and S2). Of note, the solid/gas concentration ratios of PCDDs and PCDFs derived using Cu and Fe chlorides were in excess of 103. In contrast, the ratios of CBzs ranged from 2 to 10. This trend reflects the variation in the volatility of the chlorinated aromatic compounds. The concentrations of chlorinated aromatic compounds in the ash residue ranged from 0.1 to 104 ng/g ash (Figure 1a), with CBzs having the greatest concentration of all the aromatic compounds. Principal component analysis of the PCDDs, PCDFs, PCBs, and CBzs contents was performed to combine all of the information affecting the generation of chlorinated aromatic compounds (see SI). The concentrations were combined using weighting coefficients in a single component, the contribution rate () 95%), and interpreted as the “total” amount of PCDDs, PCDFs, PCBs, and CBzs. Based on the scores of the main component, the “total” amounts of chlorinated aromatic compounds formed were ordered according to admixed metal species as follows: CuCl2 · 2H2O > Cu2(OH)3Cl > FeCl3 · 6H2O > FeCl2 · 4H2O > CuO > Fe2O3>PbCl2 > blank(only KCl) > ZnCl2 > PbO > ZnO (1) The chlorination effect arising from macro-carbon was promoted primarily by copper chlorides. In Figure 1b, the average number of chlorines, described as n(Cl), was highest for the copper chlorides (CuCl2 · 2H2O and Cu2(OH)3Cl): 7.7

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FIGURE 2. Grouping of metallic compounds by hierarchical cluster analysis of the contents and distribution patterns of PCDDs, PCDFs, PCBs, and CBzs in the model fly ash residues. (PCDDs), 7.3 (PCDFs), 5.5 (PCBs), and 4.1 (CBzs). The second greatest chlorination occurred using FeCl3 · 6H2O and FeCl2 · 4H2O. In contrast, CuO, Fe2O3, the Pb and Zn compounds, and the blank yielded low levels of chlorinated organic compounds, with n(Cl) values of 4.4-6.6 (PCDDs), 5.2-6.4 (PCDFs), 3.5-4.1 (PCBs), and 2.2-3.1 (CBzs). The concentrations of chlorinated organic compounds were positively correlated with the average chlorine numbers (r values: PCDDs, 0.62; PCDFs, 0.77; PCBs, 0.93; and CBzs, 0.78). Grouping of Cu, Fe, Pb, and Zn Compounds. Each metallic compound was classified by cluster analysis using the hierarchical clustering procedure of Ward (19) (SI). In this method, the square sum of data in the cluster is minimized. For this purpose, we considered the concentrations and congener distribution patterns of the PCDDs, PCDFs, PCBs, and CBzs in the model fly ash residue. These data were standardized by Z ) (X - µ)/σ,

(2)

where X is a variable, µ is the average, and σ is the standard deviation. The amounts of PCDDs, PCDFs, PCBs, and CBzs were changed to logarithmic base before standardization, i.e., X ) log10 (chlorinated aromatic compound concentration), to neutralize the distance bias between clusters. Figure 2 shows the dendrogram resulting from the cluster analysis. The metallic compounds have been divided into five groups, A-E. The order of the chlorinated aromatic compounds is given in SI Table S3, along with the relevant n(Cl) values. In the distance between clusters where the dendrogram divided into two, group A and B and group C, D, and E had similarities between the groups. Although the concentrations of chlorinated aromatic compounds and the n(Cl) value were high in the former, they were low in the latter. Group A included the copper chlorides, CuCl2 · 2H2O and Cu2(OH)3Cl, which gave the highest concentrations and n(Cl) values for PCDDs, PCDFs, PCBs, and CBzs. We have reported elsewhere that copper chlorides directly chlorinate the carbon matrix to generate chlorinated aromatic compounds in the solid phase (9), and it is the distribution patterns of these compounds that show the highest levels of chlorination (Figure 3). The congener distribution pattern for each chlorinated aromatic compound in heated model fly ash containing Cu2(OH)3Cl was the same as that in heated model

FIGURE 3. Normalized distribution patterns of chlorinated aromatic compounds, PCDDs, PCDFs, PCBs, and CBzs, found in fly ashes, classified according to five groups of metallic compounds that were admixed with the model fly ash prior to heating. fly ash containing CuCl2 · 2H2O. We have also previously reported that most copper in MSWI fly ash is present as Cu2(OH)3Cl (8) and that the formation of PCDDs, PCDFs, PCBs, and CBzs in MSWI fly ash is probably promoted primarily by Cu2(OH)3Cl and similar copper compounds. Group B consisted of the iron chlorides, FeCl3 · 6H2O and FeCl2 · 4H2O and is responsible for the second highest concentrations of chlorinated aromatic compounds and n(Cl) values. The contents of PCDDs, PCDFs, PCBs, and CBzs in model fly ash residue with added Fe(III) chloride were 3-6 times those with added Fe(II) chloride, presumably because of the difference in chlorine content between the two iron chlorides. Irrespective of iron valence, the contribution for path of formation was the same for PCDDs, PCDFs, PCBs, and CBzs, as shown by the congener distribution patterns for group B (Figure 3). Group C comprised CuO and PbCl2. The contents of PCDDs and PCDFs in heated model fly ash with added CuO were 11 and 39 times, respectively, those in the blank ( SI Table S1). The formation of low-chlorinated PCDDs and PCDFs (CuO in Figure 3) was catalyzed by CuO in the solid phase, using KCl as a chlorine source. The concentrations of PCDDs, PCDFs, and PCBs in model fly ash with added PbCl2 and the concentrations of PCBs and CBzs in model fly ash with added CuO were the same as the respective concentrations in the blank. In contrast, the concentration of CBzs in the PbCl2-containing model fly ash was only one-third that in the blank, suggesting that PbCl2 may chemically or physically inhibit the formation of CBzs in the ash residue. Group D included Fe2O3, ZnCl2 and the blank. This group had the lowest n(Cl) values (SI Table S3), which were reflected VOL. 43, NO. 21, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. Normalized distribution patterns of PCDDs, PCDFs, PCBs, and CBzs in real fly ashes from general municipal solid waste incinerators. Error bar is standard error. in the low chlorination apparent in the congener distribution patterns (Figure 3), with the exception of PCDFs in the blank. The contents of PCDDs, PCDFs, and PCBs were the similar as those in the blank (PCDDs: 6.1, PCDFs: 0.89, PCBs: 21 ng/g). The concentration of CBzs in model fly ash residue with added Fe2O3 was about twice that in the blank (CBzs: 510 ng/g), whereas the concentration of CBzs in ZnCl2containing model fly ash was one-third that in the blank. Thus, the formation of CBzs in fly ash residue may be promoted by Fe2O3 and inhibited by ZnCl2. Group E consisted of the Pb and Zn oxides. These formed the lowest concentrations of PCDDs, PCDFs, PCBs, and CBzs. Compared with the respective compounds in the blank, model fly ash with added ZnO produced 1/15 the PCDDs, 1/2 the PCDFs, 1/2 the PCBs, and 1/8 the CBzs; fly ash with added PbO generated 1/30 the PCDDs, 1/5 the PCDFs, and 1/6 the CBzs (SI Table S1). PbO is thought to have suppressing effect of PCDDs formation from precursors (20). PbO and ZnO promote dechlorination reaction of CBzs (21). Therefore, PbO and ZnO appear to impair oxidation of the carbon matrix and/or block formation of PCDDs and CBzs by a mechanism involving inorganic chloride (KCl). Chlorinated Aromatic Compounds in Fly Ash from Various MSWI. The concentrations of PCDDs and PCDFs in real fly ash produced between 1987 and 2008 have been documented from MSWIs in Europe (Czech Republic, Germany, Sweden, and Switzerland), Asia (Japan and Taiwan), and North America (United States of America). There are a total of 39 MSWI fly ashes (17, 22-30), including those discussed in our previous report (17). The concentrations of PCDDs and PCDFs for each congener, including those from the present study, have a wide range (SI Table S4). However, the normalized distribution patterns of congeners from tetra- (T4) to octa- (O8) chlorinated dioxins and furans in MSWI fly ash had very small errors (Figure 4). For higher chlorination of PCDDs, the mean n(Cl) was 6.5 ( 0.05; for lower chlorination of PCDFs, the mean n(Cl) was 5.4 ( 0.07. Normalization was performed by dividing each congener by the total concentration of each chlorinated aromatic compound. The PCDD/PCDF ratio (weight based) of fly ash was 1.1 ( 0.18. The normalized distribution patterns, n(Cl) values, and PCDD/PCDF ratio were scarcely influenced by regional variation, year of measurement, or fly ash collection method. The standard errors were small enough to determine specific values. We concluded that these distribution patterns and values were general numerical values characterizing the properties of PCDDs and PCDFs in fly ash from MSWIs. The PCBs and CBzs of the five MSWI fly ashes analyzed in this study are also shown in SI Table S4. The normalized distribution patterns of PCBs, from di (D2)- to octa (O8)-, 8056

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and CBzs, from di (D2)- to hexa (H6)-, had errors equally as small as those for the patterns of PCDDs and PCDFs (Figure 4). The n(Cl) values of PCBs and CBzs reflected lower chlorination (4.2 ( 0.14 in Cl2-Cl8) and medium chlorination (4.2 ( 0.23 in Cl2-Cl6), respectively. The PCB/ CBz ratio (weight based) was 0.049 ( 0.0098. The normalized distribution patterns, n(Cl) values, and PCB/CBz ratio showed little effect owing to the fly ash collection method, as is the case for general PCB and CBz properties in MSWI fly ash. Influence of Cu, Fe, Pb, and Zn Compounds on the Generation of Chlorinated Aromatic Compounds in MSWI Fly Ash. Figure 3 shows the normalized distribution patterns of PCDDs, PCDFs, PCBs, and CBzs in 11 model fly ashes, and those of a general MSWI fly ash are shown in Figure 4. The similarities can be objectively described by hierarchical cluster analysis, which can clarify the relative influences of the Cu, Fe, Pb, and Zn oxides and chlorides. Clustering results for each chlorinated aromatic compound are shown in Figure 5. All data have been standardized by eq 2. Where one distribution pattern lies in the same cluster as MSWI fly ash, we regard the distribution pattern as similar. Similarity levels were both high (H) and medium (M). High similarity was indicated by shorter distances between clusters (s in Figure 5) compared with the longest distance (l). For medium similarity, the distance between clusters (m) was comparatively longer than that for high similarity. In the present study, we described the conditions for each similarity level by s/l and m/s ratios as shown below: H: high similarity, s/l < 1/10, M: medium similarity, s/l > 1/10 andm/s > 2, L: low similarity, i.e., different clusters.

(3)

The similarity levels of PCDDs, PCDFs, PCBs, and CBzs between model fly ashes with added metallic compounds and general MSWI fly ashes are shown in Table 1. The normalized distribution patterns of PCDDs in the blank and model fly ashes with added iron chlorides (group B) and with added PbO showed high similarity (Figure 5a and Table 1). From the formation concentrations and congener distribution patterns, it is apparent that the iron chlorides in group B play one of the more important roles in forming PCDDs in MSWI fly ash, although PCDDs may also form by chlorination of the carbon matrix by inorganic chlorides such as KCl in the solid phase. The destructive effect on PCDDs exerted by PbO, as described above, resulted in a distribution pattern similar to that of MSWI fly ash. Copper chlorides (group A) showed medium similarity for the distribution patterns of PCDDs because of elevated chlorination (SI Table S3). In contrast, group

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FIGURE 5. Similarity of normalized distribution patterns generated by hierarchical cluster analyses of (a) PCDDs, (b) PCDFs, (c) PCBs, and (d) CBzs, comparing model fly ashes with added metallic compounds and MSWI fly ash.

TABLE 1. List of the Similarity of Normalized Distribution Patterns between Model Fly Ashes with Added Metallic Compounds and MSWI Fly Ash. H: High Similarity, M: Medium Similarity, and Blank: Low Similarity (See Text for Details) distribution pattern group

metal compound

PCDDs

A

CuCl2 · 2H2O Cu2(OH)3Cl

B

FeCl3 · 6H2O FeCl2 · 4H2O

C

CuO PbCl2

D

Fe2O3 blank ZnCl2

E

ZnO PbO

PCDFs

PCBs

CBzs

M M

M M

H H

H H

H H

H H

H H

M M

H H H H H

C (CuO and PbCl2) and Fe2O3, ZnCl2 and ZnO displayed low similarity. The distribution patterns of PCDFs in fly ashes with added CuO, Fe2O3 and ZnCl2 have high similarity (Figure 5b and Table 1). In contrast, other metallic compounds

display low similarities. When thinking about the similarity of the distribution patterns, it is concluded that metallic compounds except CuO, Fe2O3 and ZnCl2 exercise only a slight influence on the contribution of formation path of PCDFs in the solid ash residue. Studies of PCDF formation report that CuO or Fe2O3 can catalyze the dimerization reaction on the surface of the carbon matrix of gas phase precursors (7, 13). In the present study, KCl provided the sole solid-phase chlorine source. Therefore, precursors such as gas-phase CBzs generated by KCl in the blank might have been catalyzed the dimerization reaction by CuO or Fe2O3. Only Fe2O3 and PbCl2 in group D displayed high similarity for PCDFs among the chlorinated aromatic compounds. The distribution patterns of PCBs in groups B (iron chlorides) and C (CuO and PbCl2) showed high similarity (Figure 5c and Table 1). A comparison of PCB formation by solid phase reactions in groups B and C indicates that iron chlorides are probably more effective than CuO or PbCl2 in generating PCBs. By analogy with the formation of PCDFs, CuO might have catalyzed the dimerization of precursors in the gas phase. Copper chlorides in group A showed only medium similarity, principally because n(Cl) at >5.3 exceeded that of MSWI (4.2). Groups D and E have low similarity. The highest congener from their distribution patterns was the tri (T3)-chlorinated biphenyls, which differed from T4-chlorinated biphenyls in MSWI fly ash (Figure 3). VOL. 43, NO. 21, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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The distribution patterns of CBzs in model fly ashes with added copper chlorides (group A) and iron chlorides (B) both have high similarity (Figure 5d and Table 1). Traces of copper and iron chlorides exercise a dramatic effect on the formation of CBzs in MSWI fly ash, as indicated by the concentrations and distribution patterns, with the formation of hexa (H6)-chlorobenzene, a persistent organic pollutant, showing a comparatively high ratio in groups A and B (Figure 3). As a result of lower chlorination levels, group C (CuO and PbCl2) showed only medium similarity with MSWI fly ash. Groups D and E had low similarity, with relatively low chlorination [n(Cl) ) 2.2-2.5] (SI Table S3). The PCDD/PCDF and PCB/CBz ratios also had characteristic values dependent on the groupings and metallic compounds involved. Both ratios showed the same values in groups A (1.2-1.3 and 0.043-0.046, respectively), B (0.6-0.8 and 0.017-0.018, respectively), and E (1.0-1.3 and 0.020-0.024, respectively), as shown in SI Figures S2 and S3. The PCDD/PCDF ratio of MSWI fly ash is 1.1, which is about the same that in groups A, B, and E. The PCB/CBz ratio of MSWI fly ash is 0.049, which is similar to that of group A and the blank (0.040). These ratios are presumably influenced mainly by the copper chlorides of group A. In contrast, groups C and D had higher PCDD/PCDF ratios than that of MSWI (SI Figure S2). In brief, the selective formation of PCDDs may occur. We conclude that the formation of chlorinated aromatic compounds is strongly influenced by traces of metallic compounds in real fly ash of MSWIs. The formation paths depend on the metallic compounds in the fly ash and vary among PCDDs, PCDFs, PCBs, and CBzs. High chlorination is affected by Cu and Fe chlorides. Low chlorination and inhibition of the reactions result from Pb and Zn oxides. In the formation of PCDFs in real fly ash, CuO and Fe2O3 act as catalysts in gas-phase reactions of precursors. The interactions among the different metallic compounds in fly ashes are unknown, although studies of other relevant thermal processes can contribute useful information. For example, iron sintering provides a major source of chlorinated aromatic compounds (31). Using the same analysis methods as used here, estimates can be made of the influences of metallic compounds on the formation of chlorinated aromatic compounds in solid phases other than fly ash via other thermal processes.

Acknowledgments We thank Y. Tanino, A. Shiono, K. Oshita, S. Morisawa, and J. S. Komatsu for supporting this study; Shimadzu Techno-Reseach, Inc. for helping with dioxins measurement. We greatly acknowledge the financial support by a Grand-in-Aid for Waste treatment Research from Ministry of the Environment, Japan (Proporsal No. K1514 and K1632).

Supporting Information Available Information concerning the materials and method, principal component analysis, hierarchical cluster analysis, and four tables and four figures. This material is available free of charge via the Internet at http://pubs.acs.org.

Literature Cited (1) Olie, K.; Vermeulen, P. L.; Hutzinger, O. Chlorodibenzo-p-dioxins and chlorodibenzofurans are trace components of fly ash and flue gas of some municipal incinerators in The Netherlands. Chemosphere 1977, 6, 455–459. (2) Addink, R.; Olie, K. Mechanisms of formation and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans in heterogeneous systems. Environ. Sci. Technol. 1995, 29, 1425– 1435. 8058

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