J Mater Cycles Waste Manag (2008) 10:93–101 DOI 10.1007/s10163-007-0204-y
SPECIAL FEATURE: ORIGINAL ARTICLE
© Springer 2008
4th I-CPEC, Part 2
Morihiro Osada · Nobuhiro Tanigaki · Shin Takahashi Shin-ichi Sakai
Brominated flame retardants and heavy metals in automobile shredder residue (ASR) and their behavior in the melting process
Received: March 15, 2007 / Accepted: November 1, 2007
Abstract The End-of-life Vehicles Recycling Act went into effect on January 1, 2005, in Japan and requires the proper treatment of airbags, chlorofluorocarbons (CFCs), and automobile shredder residue (ASR). The need for optimal treatment and recycling of ASR, in particular, has been increasing year after year because ASR is regarded as being difficult to treat. Dioxin-related compounds, brominated flame retardants (BFRs), heavy metals, chlorine and organotin compounds are all present in high concentrations in ASR. The authors conducted ASR melting treatment tests using a 10-tons/day-scale direct melting system (DMS), which employs shaft-type gasification and melting technology. The results obtained showed that dioxin-related compounds and BFRs were decomposed by this melting treatment. The high-temperature reducing atmosphere in the melting furnace moved volatile heavy metals such as lead and zinc into the fly ash where they were distributed at a rate of more than 90% of the input amount. This treatment was also found to be effective in the decomposition of organotin, with a rate of decomposition higher than 99.996% of the input amount. Via the recovery of heavy metals concentrated in the fly ash, all the products discharged from this treatment system were utilized effectively for the complete realization of an ASR recycling system that requires no final disposal sites. Key words Direct melting system (DMS) · ASR · Brominated flame retardants · Heavy metal M. Osada (*) Nippon Steel Engineering Co., Ltd., Tokyo Head Office, 6-3 Otemachi 2-chome, Chiyoda-ku, Tokyo 100-8071, Japan Tel. +81-3-3275-6079; Fax +81-3-3275-5983 e-mail:
[email protected] N. Tanigaki Nippon Steel Engineering Co., Ltd., Tobata Technical Center, Kitakyushu, Japan S. Takahashi Ehime University, Center for Marine Environmental Studies, Matsuyama, Japan S. Sakai Kyoto University, Environment Preservation Center, Kyoto, Japan
Introduction The number of automobiles disposed of as end-of-life vehicles (ELVs) in Japan today is of the order of approximately 5 million cars/year. About 4 million of this total, excluding automobiles exported as secondhand cars, were recycled as secondary materials and disposed of as waste.1 The recycling rate of ELVs ranges from 75% to 80%. In previous flows of recycling and disposal procedures, ELV bodies were crushed and the automobile shredder residue (ASR) remaining after the recovery of metals was mainly managed in landfills. However, with landfills for industrial waste becoming increasingly scarce, the conventional recycling system has become dysfunctional today, and illegal dumping and the improper handling of industrial waste have become major social issues.2 Under these circumstances, the ELV Recycling Act went into effect on January 1, 2005, in Japan and the proper treatment of airbags, chlorofluorocarbons (CFCs), and ASR has become compulsory.1 Moreover, the need for optimal recycling and ASR treatment in particular has been increasing year after year. ASR has the following characteristics: (1) it has a high calorie and ash content; (2) it contains many fine particles of diameter 5 mm or smaller as well as considerable crushed waste of diameter 50 mm or larger, resulting in a low bulk specific gravity; and (3) it contains large amounts of heavy metals, brominated flame retardants (BFRs), and chlorine. Due to these characteristics, ASR is considered to be a type of waste that is very difficult to treat. In Europe, as well as in Korea, several ASR recycling methods, including thermal treatment, have been investigated to meet future expected restrictions on ASR landfill.3–5 Subsequently, in Japan, of all the ASR recycling technologies, for which thermal recycling technology utilizing nonmetal refineries6 has become the mainstream method, increasing attention has recently been directed at gasification and melting technology. To increase the ASR recycling rate, not only is thermal recycling technology with power generation important but also the effective utilization of molten slag and the reuse of heavy metals by
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returning fly ash to mines is crucial.7 However, the articles mentioned above have mainly covered the material composition of ASR and its thermal behavior in the lab; they have not investigated the distribution behavior of heavy metals during ASR treatment. In addition, problems related to BFRs and brominated dioxins (PBDD/DFs) contained in nonflammable plastics have also been attracting attention.8–12 ASR treatment will involve evaluation of the technology to decompose and control emissions of the substances mentioned above. Treatment and recycling of municipal solid waste and other industrial waste using high-temperature melting technology started substantially in the 1990s, and there are currently around 70 high-temperature melting units in operation.13,14 Melting furnaces with different furnace designs have been developed, including shaft furnaces, kilns, and fluidized beds.15–17 Direct melting furnaces are shaft-type gasification and melting furnaces and have proved effective in many municipal solid waste applications. In this system, combustible waste is gasified and then incinerated in the combustion chamber, while incombustible waste is completely melted in the coke-bed of the melting furnace at a high temperature, allowing it to be reused as slag or metal. In this study, an ASR melting test was conducted using a shaft-type direct melting furnace to identify the behavior of BFRs, PBDD/DFs, and organotin and the distribution behavior of heavy metals in slag and fly ash. To date, there have been no reports indicating the behavior of BFRs, PBDD/DFs, organotin, and the distribution behavior of heavy metals during ASR treatment by gasification and melting processes.
a gas cooler, a bag filter, an induced draft fan, and a catalytic reactor. The capacity of the test facility is 10 tons/day (when 100% ASR is processed). ASR introduced into the melting furnace is gradually dried and preheated in the upper section. Subsequently, combustible waste is thermally decomposed and pyrolysis gas is discharged from the top of the melting furnace. Pyrolysis gas is transferred to the combustion chamber and is then completely burned. Meanwhile, incombustible waste and remaining residues descend to the bottom of the melting furnace and melt completely, with the heat generated by burning coke. Finally, molten materials are discharged from the tap hole, quenched with water, and magnetically separated into slag and metal. The shaft-type gasification and melting furnace used in this study employed the cyclone dust injection method via a tuyere. This technology includes processes whereby after the separation and collection of the combustible dust from the pyrolysis gas via the dust-removal system (cyclone) installed between the melting furnace and the combustion chamber, the dust is cooled, sieved, and then injected into the hottest coke bed layer through a tuyere for combustion and slag production. This technology can significantly contribute to increased combustibility in the combustion chamber and to reduced total weight of the final residues via the production of slag from combustible dust.9,18,19 The evaluation period of the data obtained in the 100% ASR test was 24 h. Operational data were recorded and slag, metal, fly ash, and exhaust gas were also sampled. As for the exhaust gas, samples were taken from three positions: the respective outlets of the combustion chamber, the gas cooler, and the catalytic reactor shown in Fig. 1. Approximately 15 tons of ASR was collected from a shredding and recycling company and stored in the ASR stockyard of the testing plant. For the material component and chemical analysis, a total of 107 kg of ASR samples was collected by a sampling shovel (35 l in volume) from 15 different locations. These samples were reduced and homogenized in accordance with JIS K0060, the Sampling Method of Industrial Waste. Subsequently, the ASR sample was
Materials and methods Outline of the test facility Figure 1 shows the test facility flow diagram. The test facility consisted of a melting furnace, a combustion chamber, Fig. 1. Test facility flow diagram
Waste charging crane
Outlet of combustion chamber Outlet of catalytic reactor Coke Limestone
ASR
Catalytic reactor
Ca(OH)2 Bag filter
Waste pit
Capacity : 10tons/day (100%-ASR)
Melting furnace
Combustion Gas chamber cooler Cyclone Induced draft fan
Fly ash Melt
Slag and metal
O2
Granulating equipment Forced Combustion draft fan draft fan
Outlet of gas gas cooler cooler
Stack
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sieved using a 5-mm-mesh screen and manually separated into individual components such as plastics, rubber, polyurethane foam, textiles, wire, and metals. Each component was weighed and crushed to less than 1.0 mm, and subsamples from each component were mixed together based on the weight percent of each component in the original ASR. This remixed sample was again crushed to less than 0.25 mm and subjected to chemical analysis.
Chemical analysis ASR was analyzed with respect to its physical components, bulk specific gravity, material type composition, and lower calorific value. As for the main elements, such as Cl, Br, S, Ca, Si, Al, Na, and K, and heavy metal elements, such as Pb, Cd, As, Se, Fe, Cu, Zn, and Sb, analysis was conducted using bomb combustion-ion chromatography (Dionex, DXAQ, CA, United States), an Inductivity Coupled Plasma (ICP) atomic emission spectrophotometer (SII Nanotechnology, SPS-5000, Tokyo, Japan), and an ICP mass spectrometer (SII Nanotechnology, SPQ-9000). This analysis was carried out on the ASR and the slag, metals, fly ash, and exhaust gas at the outlet of the catalytic reactor. Mercury analysis was conducted using reduction-vaporization atomic absorption spectrometry (AAS) (Nippon Instruments, RA1, Tokyo, Japan) and Cr (VI) was analyzed using absorption spectrometry (Hitachi, U-1500, Tokyo, Japan). Sampling was conducted in compliance with JIS Z8808, and Pb, Cd, As, Se, and Cr analysis was conducted in compliance with JIS K0083. Heavy metals that are not subject to special treatment according to JIS, such as Fe, Cu, Zn, and Sb, were also analyzed in accordance with JIS K0083, and mercury was analyzed in compliance with JIS K0222. In addition to the heavy metals, analysis of the concentration of dust, HCl, SOx, NOx, Cl2, HBr, CO, and HCN was conducted at the outlet of the catalytic reactor in compliance with JIS K0107, JIS K0103, JIS K0104, JIS K0106, JIS K0085, JIS K0098, and JIS K0109, respectively. BFRs such as polybrominated diphenyl ethers (PBDEs), tetrabrombisphenol-A (TBBP-A), and dioxin-related compounds including polychlorinated dioxins (PCDD/DFs), polybrominated dioxins (PBDD/DFs), monobromopolychlorinated dibenzo-p-dioxins (MoBrPCDD/DFs), and Polychlorinated biphenyls (PCBs) were analyzed in the
ASR, slag, metal, fly ash, and exhaust gas at the outlet of the catalytic reactor following the method described elsewhere.20 These compounds were analyzed by using a gas chromatograph/mass spectrometer (GC-MS) (Micromass MS, AutoSpec-ULTIMA, MA, United States, and JOEL, JMS-700, Tokyo, Japan). Organotin compounds, mono- to trisubstituted butyltins [monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT)] and octyltins [monooctyltin (MOT), dioctyltin (DOT), and trioctyltin (TOT)] in ASR, slag, metal, fly ash, and exhaust gas samples were also analyzed following the method described by Iwamura et al.21 with slight modifications. Analysis was conducted using GC-MS (Agilent Technologies, Agilent HP-5973, CA, United States). Furthermore, slag was examined by leaching and content tests (in compliance with JIS K 0058) to identify the stability of heavy metal components such as Pb.
Results and discussion Operating data of the ASR treatment test Table 1 shows the operating data during the ASR treatment test. The amount of coke used in the test was 170 kg/tonASR, while that of the limestone was 75 kg/ton-ASR; the processing load was 390 kg/h (9.4 tons/day). The melt discharged was 390 kg/ton-ASR, 260 kg/ton-ASR of which was slag and the remainder was in the form of metals. The temperature of the melt was about 1700°C, which allowed smooth delivery of the melt during the test period. Fly ash was generated at 44 kg/ton-ASR (including injected calcium hydroxide). As shown in Fig. 2, the temperature at the outlet of the combustion chamber was 960°C and the exhaust gas from the stack amounted to 11 000 m3 N/tondry. Furthermore, the CO concentration of the exhaust gas was only 4 ppm, which proved that complete combustion of the pyrolysis gas generated from the melting furnace was possible. As for the balance of discharged materials, about 90% of the charged ash content of ASR was discharged as melt. The concentrations of dust, HCl, SOx, NOx, Cl2, HBr, CO, and HCN in the exhaust gas were less than 0.001 g/m3 N, 13 ppm, less than 2 ppm, 111 ppm, less than 0.2 ppm, less than 2 ppm, 4 ppm, and less than 2 ppm, respectively.
Table 1. Operational data Amount of waste processed Amount of coke used Amount of limestone used Amount of melt produced Amount of slag produced Amount of metals produced Amount of fly ash generated Temperature in combustion chamber Amount of exhaust gasa Oxygen concentration in exhaust gas a
(ton/24 h) (kg/ton-ASR) (kg/ton-ASR) (kg/ton-ASR) (kg/ton-ASR) (kg/ton-ASR) (kg/ton-ASR) (°C) [m3(12%O2dry)/ton] (%-dry)
9.4 170 75 390 260 120 44 960 11 000 14
Calculated on the basis of the water content (24%), the exhaust gas measurement, and the flow rate of the pitot tube
96 Outlet Temperature of Combustion Chamber
CO Concentration at Exhaust Gas 300
1000
250
800
200
600
150
400
100
200
50
Outlet Temperature of CC (°C)
1200
0 0:00
3:00
6:00
9:00
12:00
15:00
18:00
21:00
CO Concentration at Exhaust Gas (ppm)
Fig. 2. Combustion conditions in the ASR processing plant. CC, combustion chamber
0 0:00
Table 2. Composition of ASR Analysis item Three contents
Physical composition
a
Water content Combustible contenta Ash contenta Smaller than 5 mm Plastics Rubber Urethane Textiles Paper Wood Metals Glass Electric wire Others (nondetachable substances) Others (polystyrene foam, etc.) Miscellaneous substances
Net calorific value Bulk specific gravity
Unit
Measurement
%-wet %-wet %-wet %-dry %-dry %-dry %-dry %-dry %-dry %-dry %-dry %-dry %-dry %-dry %-dry %-dry kJ/kg ton/m3
1.2 68.1 30.7 30.07 29.09 9.35 4.96 3.65 0.94 0.02 2.22 N.D. 3.52 14.59 0.19 1.4 21 500 0.164
a
Respective properties excluding metals N.D., not detected
ASR properties Table 2 shows the results of the analysis of ASR. The water content was as little as 1.2%, while the combustible and ash content were confirmed at 68% and 31%, respectively. The lower calorific value was as high as 21 500 kJ/kg and the bulk specific gravity was 0.164 ton/m3. The physical composition included plastics at 29.1% and rubber at 9.35%, with these two types of material making up about 38% of the ASR, followed by nondetachable substances at 14.6%, urethane at 4.96%, textiles at 3.65%, electric wire at 3.52%, and metals at 2.22%. Others materials included paper at 0.94% and wood at 0.02%, both of which were present at extremely low values. The content of fine particles smaller than 5 mm in diameter as they were sieved was 30.1%. According to the Japan Environmental Sanitation Center,22 the composition of Japanese ASR varies. They showed that the water content, combustible content, and ash were 9.7% (3.5%–27.1%), 59.8% (41.4%–73.4%), and
30.5% (22.6%–38.1%), respectively. Compared with this result, the water content in our ASR was rather low. Our ash content was almost same as that in previous reports. Generally, there are two types of ASR selection methods: wet and dry types. As our ASR was pretreated by the dry selection method and we carried out the analysis soon after ASR selection, this explains why the water content was lower than that in According to the Japan Environmental Sanitation Center, the concentrations of plastics, rubber, urethane, textiles, paper, woods, metals, glass, other nondetachable substances, and particles smaller than 5 mm in ASR were 34.2% (24.1%–44.0%), 9.7% (5.2%–16.8%), 7.5% (3.3%–12.2%), 7.0% (3.1%–12.0%), 1.2% (0.4%– 3.7%), 1.4% (0.0%–4.0%), 2.9% (0.8%–5.7%), 0.1% (0.0%–0.3%), 10.7% (6.4%–18.5%), and 20.7% (10.4%– 36.6%), respectively. There are some differences between these results and our own: especially, our value for the items smaller than 5 mm is much higher than the average of the previous report. They had different operating conditions for
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the air-jet selection in the selection process and the recovery of parts before shredding for metal recovery, and these operation conditions are thought to affect the physical composition of ASR. Although there are some differences between the previous reports and our results, the ASR that we have analyzed in this study is thought to be representative ASR in Japan because it was within the ranges of previous report.22 Kim et al.4 showed that the light and heavy fluff of ASR ranged from 0.142 to 0.258 ton/m3; our results in this study gave lighter values than these. Kim et al.4 also showed that the concentrations of plastics, textiles, sponge, rubber, glass, soil/sand, and wire in ASR were 20%–24%, 31%, 6%–16%, 6%–8%, 9%–17%, 2%–3%, 4%–5%, respectively. Meanwhile, Nourreddine3 showed that the concentrations of plastics, textiles, and glass in ASR were 41%, 10%, and 16%, respectively. Some differences do remain between this study and the previous studies mentioned above; the ratio of textiles in our study was lower than that of previous studies, but those of plastics, rubber, and wire were almost the same. These results indicate that these differences may depend on the manufacturer, the kind of cars, and the pretreatment system of ASR such as recovery of parts before shredding or types of selection.
Concentrations and behavior of dioxin-related compounds and brominated flame retardants It is pointed out that PVC and catalysts in ASR affect the formation of PCDDs, PCDFs, and dioxin-like PCBs in the thermal treatment of ASR.5 In this study, not only PCDDs, PCDFs, and dioxin-like PCBs, but also dioxin-related compounds and BFRs were investigated in the ASR melting process. Table 3 shows the results of the analysis of dioxin-related compounds and BFRs. The ASR contained 0.97 ng/g of PCDD/DFs, 30 ng/g of Co-PCB, and 270 ng/g of PCBs. The
ASR also contained 30 ng/g of PBDD/DFs, but MoBrPCDD/ DFs were not detected. High concentrations of BFRs were detected: PBDEs at 310 000 ng/g and TBBP-A at 15 000 ng/g. Among the congeners of PBDEs and PBDD/ DFs detected in ASR, higher brominated congeners such as decabromodiphenylethers (DeBDEs) and octabrominated dibenzofurans (OBDFs) showed the highest proportions: 94% and 60%, respectively. Such congener patterns of BFRs and PBDD/DFs in ASR were similar to those reported in BFR-treated plastics such as those in waste TV sets in Japan.8,12 In addition, a relatively high concentration of PCBs and its congener profile (higher proportions of tetra- and pentachlorobiphenyls) in ASR suggests that its potential sources are technical PCB mixtures (i.e., KC-400 and KC-500) used in electrical equipment such as capacitors. Compared with municipal solid waste and waste TV sets that the authors previously investigated, the amount of BFRs such as PBDD/DFs, PBDEs, and TBBP-A in ASR was found to be higher than that in the municipal solid waste and lower than that in waste TV sets.8 The exhaust gas sampled at the outlet of the combustion chamber and that sampled at the outlet of the gas cooler were found to contain few dioxin-related compounds or BFRs. Meanwhile, the exhaust gas sampled at the outlet of the catalytic reactor contained 0.15 ng/m3 N of PCDD/DFs, 0.20 ng/m3 N of PBDD/DFs, and 28 ng/m3 N of TBBP-A. Neither MoBrPCDD/DFs nor PBDEs were detected in the exhaust gas sampled at the outlet of the catalytic reactor. The slag and metals discharged from the melting furnace contained few dioxin-related compounds or BFRs. The concentration of PCDD/DFs in the fly ash was 99 ng/g (1.6 ng-TEQ/g), with the concentrations of PBDD/DFs and MoBrPCDD/DFs at 0.26 ng/g and 44 ng/g, respectively. On the other hand, the concentrations of PBDEs and TBBP-A were 2.8 ng/g and 0.29 ng/g, respectively, which were much lower than their concentrations in the ASR. Table 4 shows the behavior of dioxin-related compounds and BFRs. Although the ASR contained 30 000 μg/ton of PBDD/DFs, this was reduced to 1.3 μg/ton at the outlet of
Table 3. Concentration of dioxin-related compounds and brominated flame retardants (BFRs) ASR (ng/g)
PCDDs/DFsa Co-PCBs PCDDs/DFs + co-PCBs PBDDs/DFsb MoBrPCDDs/DFsc Brominated diphenyl ethersd Tetrabromobisphenol A PCBse
0.97 (0.0043) 30 (0.023) (0.027) 30 N.D. 310 000 15 000 270
Slag (ng/g)
0.27 (0.00086) 0.027 (0.00023) (0.0011) N.D. N.D. 0.1 0.07 0.091
Metals (ng/g)
1.1 (0.0038) 0.03 (0.00019) (0.0040) N.D. 0.03 0.2 0.05 0.15
Fly ash (ng/g)
99 (1.6) 4.6 (0.070) (1.7) 0.26 44 2.8 0.29 22
Exhaust gas (conversion for O2 at 12%) Combustion chamber (ng/m3 N)
Gas cooler (ng/m3 N)
Catalytic reactor (ng/m3 N)
0.28 (0.0016) 0.17 (0.000019) (0.0017) 0.12 N.D. 2 14 1.5
– – – N.D. (0.09)f – 24 13 –
0.15 (0.0014) 0.16 (0.000026) (0.0014) 0.2 N.D. N.D. 28 2.6
The values indicated in parentheses are WHO-TEF (1998) conversion values; the units are ng-TEQ/g or ng-TEQ/m3 N PCDDs/DFs, chlorinated dioxins; PCBs, polychlorinated biphenyls; PBDD/DFs, brominated dioxins; MoBrPCDDs/DFs, monobromopolychlorinated dibenzo-p-dioxins; –, not analyzed; N.D., not detected a 4–8 chlorinated, b 4–8 brominated, c 3–7 chlorinated, d 1–10 brominated, e 1–10 chlorinated f Including those lower than the lower limit of determination and those higher than the detection limits
98 Table 4. Input and emissions of dioxin-related compounds and BFRs
PCDDs/DFs Co-PCBs PBDDs/DFs MoBrPCDDs/DFs Brominated diphenyl ethers Tetrabromobisphenol A PCBs
Charged
Outlet of each section
Emissions
ASR
Exhaust gas at outlet of combustion chamber
Exhaust gas at outlet of gas cooler
Exhaust gas at outlet of catalytic reactor
Fly ash at bag filter
Slag discharged from melting furnace
Metals discharged from melting furnace
3.1 1.9 1.3 N.D. 22 156 17
– – N.D. – 270 150 –
1.7 1.8 2.2 N.D. N.D. 310 29
4300 200 11 1900 120 13 960
71 7.1 N.D. N.D. 26 18 24
140 3.7 N.D. 4.0 25 6.1 18
970 30 000 30 000 N.D. 310 000 000 15 000 000 270 000
Total emissions
4500 210 14 1900 170 350 1000
Values are mg/ton of waste
the combustion chamber, indicating that the gasification and combustion process had decomposed more than 99.99% of PBDD/DFs. The cooling process showed almost no resynthesis, unlike the behavior of PCDD/DFs. With the total emission at 14 μg/ton, 99.9% of the input amount had been decomposed, with 79% of the emission discharged as fly ash. No PBDD/DFs were detected in the slag or metals; similarly, MoBrPCDD/DFs were not detected in the exhaust gas or slag. Since MoBrPCDD/DFs were detected in the fly ash, resynthesis during the cooling process might have taken place. PBDEs at the outlet of the combustion chamber showed 22 μg/ton, indicating that more than 99.99999% of the input amount had been decomposed by the gasification and combustion process. The total emission was 170 μg/ton, which means that 99.9999% of the input amount was decomposed, with 71% of the emission discharged as fly ash. The TBBP-A at the outlet of the combustion chamber was 160 μg/ton, indicating that more than 99.99% of the input amount had been decomposed by the gasification and combustion process. The total emission was 350 μg/ton, which means that more than 99.99% of the input amount had been decomposed, with about 89% of the emission discharged as exhaust gas. The concentration at the outlet of the combustion chamber was low for all compounds. Some of the char discharged from the melting furnace was removed by a cyclone and this is thought to cause an improvement in combustibility in the combustion chamber. Furthermore, the temperature at the outlet of the combustion chamber was more than 900°C, as shown in Fig. 2, and this kept residence time of Combustion gas in the Combustion Chamber at a figure of more than 2 s; these facts seem to contribute to the low level of generation of BFRs and other compounds. Compared to the amounts in ASR, the emissions of PCDD/DFs and MoBrPCDD/DFs increased. Since they were hardly detected in the exhaust gas sampled at the outlet of the combustion chamber, the emissions are considered to have increased by de novo synthesis during the cooling process. This trend was found to be the same as in the treatment of MSW and waste television sets by the direct melting system (DMS).8 As mentioned above, the distribution behavior of TBBP-A is different from those of other compounds. We have presumed the
causes of the high emission rate of TBBP-A as exhaust gas to be related to the difference in sorbability to activated carbon or the difference in vapor pressure; however, details of the causes were not clarified. Based on the abovementioned results, the DMS method is proven to be effective in the decomposition of Persistent Organic Pollutants (POPs) such as PBDEs, TBBP-A, PBDD/DFs, and PCBs.
Concentrations and behavior of major elements and heavy metals Table 5 shows the concentrations of the major elements and heavy metals in the ASR. The ASR contained 29 000 mg/kg of Cl, 1700 mg/kg of Pb, 2.8% of Fe, 3.4% of Cu, and 0.86% of Zn, which are generally high concentrations. Compared to the results presented in a report by Masuda, such slag components as Si, Ca, and Al were higher in this report but the concentrations of heavy metals such as Fe and Cu were at almost equivalent levels in that report.7 Compared to the results for fluff in another previous report by Nourreddine,3 our concentrations of Zn, Pb, and Si were higher, but that of Fe was much lower than the result of the previous report. Of these elements, the concentrations of Cl, Pb, and Zn was highest in the fly ash: 36%, 1.62%, and 8.0%, respectively. On the other hand, iron and copper were contained in large quantities in the metal fraction: 33.5% and 41.2%, respectively. As mentioned above, differences in the heavy metal concentrations in ASR may depend on the pretreatment system. Figure 3 shows the distribution rates of chlorine, bromine, and heavy metals. For the distribution rates, the rate of each element against the total emission level was calculated. More than 90% of Cl and more than 80% of Br were distributed in the fly ash. Pb, Zn, and Cd, comprising low-boiling-point compounds, were mostly distributed in the fly ash. The concentration of Pb in the fly ash was 16 000 mg/kg, with a high 91% distribution rate in the fly ash. However, the concentration in the slag was as low as 19 mg/kg. It is now confirmed that most of the Pb was distributed within the fly ash, with a little distributed in the melt. For Zn as well, 97% of total emissions were
99 Table 5. Concentrations of major elements and heavy metals in ASR, fly ash, slag, and metals Element/compound
Unit
ASR
Fly ash
Slag
Metal
Total chlorine (Cl) Total bromine (Br) Total sulfur (S) Calcium (Ca) Silica (Si) Aluminum (Al) Sodium (Na) Potassium (K) Lead (Pb) Mercury (Hg) Cadmium (Cd) Arsenic (As) Selenium (Se) Chromium-VI (Cr-VI) Iron (Fe) Copper (Cu) Zinc (Zn) Antimony (Sb)
mg/kg mg/kg mg/kg % % % % % mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg % % % %
29 000 300 3 600 12.4 12.9 5.3 1.89 0.53 1 700 0.08 6.2 3.5 0.2
