The physiochemical properties and heavy metal pollution of fly ash from municipal solid waste incineration

Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 333–341

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Process Safety and Environmental Protection journal homepage: www.elsevier.com/locate/psep

The physiochemical properties and heavy metal pollution of fly ash from municipal solid waste incineration Tian Zhipeng, Zhang Bingru ∗ , He Chengjun, Tang Rongzhi, Zhao Huangpu, Li Fengting College of Environmental Science and Engineering, State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, 1239 Siping Rd, Shanghai 200092, China

a r t i c l e

i n f o

a b s t r a c t

Article history:

Fly ash originating from municipal solid waste incineration (MSWI) is potentially hazardous

Received 28 April 2015

waste and is harmful to the surrounding area once it enters the environment. In this study,

Received in revised form 18 August

we measured the physiochemical properties of fly ash derived from domestic waste incin-

2015

eration as well as the leaching toxicity of heavy metals in fly ash was contained. The

Accepted 4 September 2015

results suggested that the porosity of fly ash is relatively high, and the leaching concen-

Available online 18 September 2015

tration of heavy metals can be greatly reduced through densification strategies in which fly ash is stabilized by chemical agents. The adsorption–desorption curve of fly ash had an

Keywords:

obvious hysteresis loop that belongs to the H2-type hysteresis loop. Fly ash was typically

Fly ash

mesoporous, and the silicate in fly ash was relatively stable. Its glass phase contents were

Characteristics

higher—this allowed it to be used in ceramic tile decoration. In addition, Pb and Cd were the

Heavy metals

major heavy metals in fly ash. These heavy metals were mainly distributed in the residue.

Leaching toxicity

Heavy metals were easily leached out under strong acid or alkaline conditions. © 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1.

Introduction

There were 0.172 billion tons of municipal solid waste generated in China in 2013 (CSY, 2014). The capacity of harmless diposal was 0.154 billion tons. The harmless diposal rate was 50.8% in 2003, and rose to 89.3% in 2013. In the past ten years, the capacity for harmless diposal has increased markedly (Fig. 1) (CSY, 2014). This was most significant since 2006. The main processes for harmless diposal were sanitary landfill, incineration and compost. In recent years, incineration has been favored more than sanitary landfills because of limited land resources in China, especially in the first-tier cities. As shown in Fig. 2 (CSY, 2014), the amount of waste in sanitary landfills is still high, but has been gradually decreasing as incineration becomes more popular. The propotion of incineration was 4.9% in 2003 and 30.1% in 2013. In contrast, the

∗

use of sanitary landfill and composting has been decreasing. Hence, the incineration process has a huge space for additional development. Municipal solid waste incineration (MSWI) is popular because of its superior performance at lowering the volume (∼90%) of domestic waste while also generating heat. This can be recycled for electricity (Lin, 2006). However, secondary pollution can accompany incineration. The fly ash generated by the flu-gas cleaning system is a major carrier of secondary pollutants, and the production of fly ash accounts for 3–5% of waste from incineration. Therefore, fly ash is accepted as a hazardous material that has high amounts of heavy metals and dioxin (Quina et al., 2008). Many treatment methods of MSWI fly ash before disposal have been developed: cement solidification (Aubert et al., 2004, 2006; Lin et al., 2003), chemical reagent solidification (Quina et al., 2010; Bontempi et al.,

Corresponding author. Tel.: +86 21 65980567; fax: +86 021 65985059. E-mail address: [email protected] (Z. Bingru). http://dx.doi.org/10.1016/j.psep.2015.09.007 0957-5820/© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

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Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 333–341

Fig. 1 – diposal capacity of MSW.

2010) and melting solidification (Monteiro et al., 2006; Sakai and Hiraoka, 2000; Ito, 1996). In Taiwan, the characteristics of three incinerator bottom ash and fly ash was studied (Chang and Wey, 2006). They found that the characteristics and surface structures depend on the difference between the transportation and hybrid systems. The size of the fly ash directly affected its sintering character (Wang et al., 2001). It was found that the larger size fly ash has a lower compressive strength after sintering. The sintered fly ash had sufficient compressive strength to be considered a non-hazardous material when the sintering temperature is 600–800 ◦ C and the grain size is 43–73 ␮m. Aubert et al. (2006) analyzed physical, chemical, and mineral properties of two pre-treated MSWI fly ash samples that were applied to the composite concrete. They found that calcium–aluminum borosilicate was the main component of fly ash. This type of ash can is used as an additive for cinders and as a substitute for concrete in cement-based materials. Liu et al. (2009) suggested that the concentration of aluminum borosilicate increased with incineration temperature. Moreover, the leaching behaviors of heavy metals significantly affect the treatment and disposal of fly ash. The heavy metals in the fly ash could be released under acidic conditions, which threaten the quality of groundwater.

TCLP(Toxicity Characteristic Leaching Procedure) (Kim et al., 1998), HVEP (Horizontal Vibration Extraction Procedure) (GB 5086.2-1997) (solid waste-extraction procedure for toxicity of solid waste in China, 1997), ALT (Available Leaching Toxicity), and SEP (Sequential Extraction Procedure) (Jin et al., 2013; Shi and Kan, 2009; Shim et al., 2005; Chou et al., 2009; Van Herck et al., 2000) were used to assess the leaching toxicity of heavy metals in fly ash. Lin and Chang (2006) studied the leaching characteristics of slag ash, and found that the leaching values of Pb and Cd exceeded the standard. Shim et al. (2005) discovered that the neutralizing capacity of fly ash from Japan was four-fold higher than that in South Korea. In addition, the leaching value of both ashes also exceeded the standard. At pH 6–9, the leaching amount of heavy metals was relatively small. Thus, it is important to understand the leaching behavior of heavy metals on the treatment and disposal of fly ash. Herein, we studied fly ash morphology, specific area, elemental composition, and mineral ingredients. The leaching toxicity, specification, and leaching characteristic of the heavy metals were also determined.

2.

Materials and methods

2.1.

Samples

The fly ash in this study was sampled from a municipal solid waste incinerator in the Jinshan (Shanghai) MSWI plant that handles 800 t of solid waste per day.

2.2.

Physical characterization

Scanning electron microscope (XL-30ESEM) was used to characterize the morphology of the fly ash. The size distribution was examined by dynamic light scattering (DLS) on a Malvern Zetasizer (Ms3000h, Britain). Specific surface area was measured by adsorption–desorption of ultrapure N2 on a Quantachrome Instruments system via Brunauer–Emmett–Teller (BET) method. The X-ray diffraction (XRD) patterns were obtained on an Advanced-D&X diffractometer with Cu-K␣ radiation (40 kV, 40 mA). This employed a scan rate of 2◦ /min in the 2Â range of 0–90◦ to interpret the mineral composition of fly ash. Elemental composition was analyzed by Energydispersive X-ray spectroscopy (EDS, type INCA). The elemental concentrations and chemical ingredients of the fly ash were quantified with X-ray fluorescence (XRF, AXIOSmAX).

2.3.

Leaching toxicity of heavy metals

Leaching toxicity analysis was performed according to TCLP and ALT standards. And the liquid to solid ratio (L/S) was 20:1 for the former and 100:1 for the later. Leaching results were analyzed by ICP (Inductively Coupled Plasma).

2.4. Specification analysis of heavy metals and XRD analysis of residue after each step

Fig. 2 – change of three treatment method.

Sequential chemical extraction has always been used as a method to study the specification of heavy metals. In this research, the sequential chemical extraction was according to a five-step sequential extraction method (Tessier et al., 1979)

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Table 1 – The sequence extraction procedures of a solution containing fly ash. Species Water soluble Exchangeable Acid soluble Organic binding Iron and manganese oxides Residual

Reagents

Conditions

Deionized water 1 mol/L MgCl2 1 m mol/L NaAc (pH = 5) 0.1 mol/L Na4 P2 O7 0.175 mol/L (NH4 )2 C2 O4 + 0.1 mol/L H2 C2 O4 HCl + HNO3 + HF + HClO4

Continuous Stirring for 3 h Continuous Stirring for 3 h Continuous Stirring for 3 h Intermittent stirring for 3 h at 85 ◦ C Intermittent stirring for 3 h at 95 ◦ C Digestion

(Table 1). One difference was that we added one more species of water. Heavy metals from each step were determined by ICP.

2.5.

Leaching characteristics analysis of heavy metals

Leaching behavior was studied according to the horizontal vibration method. Various concentrations of extractants were used at different pH values to extract heavy metals in the fly ash.

3.

Results and discussion

3.1.

Physical properties of fly ash

The high porosity of fly ash is illustrated in Fig. 3. This porosity facilitates enrichment of volatile heavy metals such as Pb and Hg on the fly ash surface and leads to environmental pollution. Thus, heavy metals leaching would be greatly reduced if the ash could be denser. Fly ash stabilized by chemical agents can offer significant densification that can greatly reduce the leaching of heavy metals. These morphology differences are shown in Fig. 4 at 10,000× magnification. Hence, chemical stabilization is an important method to treat MSWI fly ash. Specific areas of fly ash before and after ultrasonification are shown in Table 2. The results indicate that the surface area is 6.44 m2 /g, and the maximum adsorption capacity is 9.75 cm3 /g before ultrasonification. After 5 min of ultrasonification, the surface area and maximum adsorption capacity

Table 2 – Morphology and specific area of fly ash. Category

Specific area (m2 /g)

Pore volume (cm3 /g)

Original ash Ultrasonicated ash

6.44 7.28

0.015 0.044

increased to 7.28 m2 /g and 28.52 cm3 /g, respectively. We noted that larger surface areas resulted in increased leaching of heavy metals. Thus, ultrasonic pretreatment of fly ash can increase the leaching of heavy metals from fly ash. Fly ash absorption–desorption curves are shown in Fig. 5. There is an obvious hysteresis loop that belongs to the H2 model hysteresis loop—this is likely caused by the porous adsorption mass or particle accumulation. The fly ash was typically a mesoporous material. In addition, the absorption–desorption of fly ash before and after ultrasonic treatment can be depicted by the П adsorption isotherm, which indicated that the fly ash has unevenly distributed mesoporous materials. Laser particle size analysis of fly ash is shown in Fig. 6. The fly ash particle size distribution is roughly normally distributed from 1 to 100 ␮m. By volume, particle size at 1.65–64.5 ␮m of fly ash accounts for 80% of the total, and 90% of the fly ash is less than 64.5 ␮m. 50% fly ash is below 15.7 ␮m. The fly ash, therefore, can be seen as fine powder with regard to particle size. It is critical to carefully monitor particle size in studies of fly ash.

Fig. 3 – SEM micrographs of fly ash at different magnification values.

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Fig. 4 – SEM micrographs of fly ash stabilized by chemical agents.

3.2.

Chemical properties

3.2.1.

Elemental composition

The EDS spectrum of fly ash is shown in Fig. 7. The data shows that the elemental contents of fly ash are different at different analysis spots. One limitation of EDS is poor sensitivity. It is also a qualitative method.

3.2.2.

Fig. 5 – Isotherm desorption/absorption curve of raw and ultrasonic fly ash.

3.2.3.

Fig. 6 – Particle size distribution of fly ash.

Mineral components

The XRD spectrum of MSWI fly ash is shown in Fig. 8. The high amount of glass phase in the ash is because of higher levels of molten glass phase due to the heat of incineration. The ingredients of ash are NaCl, KCl, CaCl2 , CaCO3 , CaSO4 , CaO, Al2 O3 , Fe2 O3 , CaSO4 ·0.15H2 O, Ca3 (Si3 O9 ), and Ca2 SiO4 ·H2 O. The high level of chloride is because of the formation of chloride salts in fly ash including NaCl, KCl, and CaCl2 . The CaCO3 , CaSO4 , and CaSO4 are due to the use of lime in the gas purification system that removes HCl, HF, H2 CO3 , SOX and other acidic gases. No heavy metals phases were detected because of their low contents and even coverage by crystals.

Chemical components

The main components of MSWI fly ash are shown in Table 3. The Ca content in fly ash was 178,600 mg/kg and could be divided into two parts. One part is from fine particles produced during incineration, and the other is CaSO4 or Ca(OH)2 formed by limewater that was sprayed into the tower. The Si and Al contents were 23,330 and 5000 mg/kg, respectively—they formed Si O and Al O. Sodium was the most concentrated element at 296,700 mg/kg. This was primarily in the form of NaCl, which increased the content of soluble salts in fly ash. The Cl content in fly ash was 157,200 mg/kg and was mainly as soluble salts such as NaCl, KCl, and CaCl2 . This promoted leaching of heavy metals from fly ash due to the ion exchange. Therefore, soluble salts in fly ash contribute to the toxicity of MSWI fly ash.

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Fig. 7 – EDS spectra of fly ash. Table 3 – The elemental contents in fly ash. Elements Content (mg/kg) Elements Content (mg/kg)

Ca

Na

K

Fe

Si

Cl

S

P

Mg

Al

178600 Zn 3487

296700 Pb 2370

31530 Cr 133

11260 Cd 62

23330 Cu 603

157200 Hg 99

55420 Mn 198

5600 Sr 150

8500 As 64

5000 Ni 24

3.3.

Leaching characteristics of heavy metals in fly ash

3.3.1.

Leaching toxicity of fly ash

Heavy metal leaching data are shown in Table 4. In this study, the leaching toxicity of heavy metals used the acetic acid buffer solution method. We noted slightly different leaching

concentrations of heavy metals with HVEP. The leaching concentration of Pb was far below the level that determined by HVEP. This is because the leaching liquid pH value of acetate buffer is close to neutral, and Pb leaches at strong acidic or alkaline conditions. In addition, the pH value of the oscillation solution was strongly basic. Here the leaching level of Pb was high. Table 4 shows that the leaching concentration of heavy metals did not exceeded the standard limit except for Pb and Cd.

3.3.2.

The availability of heavy metals from fly ash

Available leaching toxicity reflects the maximum leaching level of heavy metals in the most adverse environmental

Table 4 – Leaching toxicity of heavy metals in fly ash (mg/L).

Fig. 8 – XRD analysis of fly ash.

Type

As

Cd

Cr

Cu

Ni

Pb

Zn

Raw ash Standard limits

ND 0.3

0.18 0.15

0.15 4.5

1.05 40

ND 0.5

0.47 0.25

5.14 100

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Fig. 9 – The availability of heavy metals. conditions. The maximum leaching concentration of the heavy metals are shown in Fig. 9. The leaching maximum of heavy metals exceeded the standard limits except for Cd and Pb. The maximum leaching amount of Pb was far beyond the standard limit (0.005 mg/kg). Under acidic conditions, Cd and Pb leaching may cause water and soil pollution. Therefore, Cd and Pb are the main heavy metal pollutants in fly ash.

3.3.3.

Specification distribution of heavy metals

Data from fly ash sequential extraction are depicted in Fig. 10. The soluble heavy metals were barely detectable (<5%). Thus, there is little potential environmental harm for aqueous fly ash. Under acidic conditions, the leaching proportion of Cu was the highest. It can easily be released into the environment. There are low environmental risks due to the low toxicity of Cu and the high leaching toxicity of the standard. In addition, the total amount of Cd in the fly ash was only 62 mg/kg, and thus the leaching concentration of Cd was low. There was no obvious leaching toxicity. However, the acid soluble state content of Pb was around 45%, and the total amount was

2369 mg/kg. Thus, the leaching concentration of Pb went far beyond the landfill standards (GB 16889-2008) (Standard for Pollution Control on the Landfill Site of Municipal Solid Waste in China). The risk of pollution will significantly increase in acidic environments. In the organic combination forms (or reductive state), heavy metal leach out under strong acidic or oxidant conditions. These rarely occur naturally. Therefore, the organic combination state is also known as the stable state. Fig. 8 shows that in this condition, only some of the heavy metal ions can be leached. These heavy metals are difficult to leach, and their leaching toxicity need not be considered under natural conditions. In the Fe Mn oxidation state, the leaching amount of Ni and Cr were relatively high. This implies that they are more easily released into the environment. The lower concentration of other heavy metals is due to high chemical stability. In this residual state, heavy metals generally exist in the mineral crystal lattice and are not easily released—this is known as the unavailable state. Fig. 8 shows that the residual levels of Cr, As, and Zn were high with residue content over 50%.

3.3.4.

Mineral components of residue from each step

We used XRD to study the residuals from each step and understand the mineral forms of fly ash. The XRD spectrum of residual from the first step is shown in Fig. 11. Versus the XRD of the original ash, NaCl, KCl, and heavy metal salts were dissolved. There were no soluble salts except for silicates and sulfates that were abundant in fly ash. Therefore, the toxicity of heavy metals will be greatly reduced after immersing fly ash in water. The Ca(OH)2 peak in the XRD spectrum can be observed because Ca(OH)2 does not dissolve completely. The XRD spectrum of the exchangeable residue is also shown in Fig. 11. Silicate such as CaSi2 O5 and Ca3 SiO5 as well as the hydrate forms abundant in the ash. We also saw Mg(OH)2 diffraction peaks. This is because the exchange interaction is between metal ions with Mg2+ that form Mg(OH)2 . The diffraction peak of CaSO4 hydrate disappeared due to ion exchange and dissolution of CaSO4 . The XRD spectrum of the acid-soluble residues and the diffraction peak of hydroxides

Fig. 10 – Species distribution of heavy Metals.

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Fig. 11 – XRD analysis of residue derived from the first to fourth step. could not be seen because they dissolved in the acidic conditions (Fig. 11). The XRD peak of CaCO3 is because of incomplete dissolution. The XRD spectra show iron and manganese oxide (Fig. 11). The abundant silicates and their hydrates could be obtained in the fly ash, which indicates their strong stability and insolubility. Fly ash may have utility as ceramic tiles because of the stability of the residues and high levels of glass phase material present in the ash (XRD data; Figs. 11 and 12).

3.3.5.

Leaching characteristics of heavy metals

Heavy metals are sensitive to environmental conditions, especially pH. The leaching characteristics of heavy metals in fly ash are shown in Fig. 13. The Zn release was 42 mg/L at pH < 5. From pH 7.5–11.5, Zn leaching was 0.3 mg/L due to the precipitation of Zn(OH)2 and the lower levels of Zn in solution. At pH > 11.5, a sharp rise in the amount of Zn leaching Zn was seen. It reached a maximum of 18 mg/L. This is because of

Fig. 12 – XRD analysis of residue derived from the fifth step.

dissolution of the precipitates as [Zn(OH)3 ] , [Zn(OH)4 ]2− in extremely alkaline conditions. Below pH 2.5, the change in Pb leaching was not obvious. Concentrations reached 66 mg/L indicating that Pb was easily released in strong acidic conditions. From pH 2.5–11.5, the Pb leaching first declined, but then stabilized. This is because Pb gradually precipitated as Pb (OH)2 , but remained constant when the precipitate saturated. At pH > 11.5, the Pb leaching rapidly increased to 30 mg/L due to dissolution of the [Pb(OH)3 ] and [Pb(OH)4 ]2− precipitates. Below pH 5, the leaching amount of Cu was high, suggesting that Cu leached easily under acidic condition. Between pH 7–12.5, the leaching amount was nearly zero due to the generation of CuS, Cu2 S, CuO, and Cu2 O.

Fig. 13 – Leaching characteristics of heavy metals.

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findings suggested that under acidic conditions, the release of heavy metals from fly ash into the environment is a threat to the environment. However, heavy metals generally exist in the mineral crystal lattice form, which is stable under natural conditions. Only at strong acidic conditions do the heavy metals leach out. This is in accordance with the results of the specification distribution. In strong alkaline conditions, the dissolution of heavy metals precipitates caused a gradual increase in the leaching of heavy metals.

Acknowledgements

Fig. 14 – Leaching characteristics of heavy metals. Below pH 2, the leaching amount of Ni was 0.45 mg/L. This indicated that Ni was not released at low pH values. Between pH 7 and 13, Ni leaching was essentially zero. This is because of Ni(OH)2 and Ni(OH)3 precipitates. Fig. 14 shows that at pH < 5, the leaching amount of Cd was constant at about 2.3 mg/L. Cd leached more easily under acidic conditions. At pH > 7, Cd leaching was reduced due to the formation of Cd(OH)2 and CdCO3 . Cr leaching was 1.8 mg/L below pH 2. The Ni leaching rapidly decreased from pH 2–5. It is hard to dissolve Ni in mildly acidic conditions. From pH 5–12.5, the Ni leaching was essentially zero because of the formation of Cr(OH)3 and Cr(OH)6 . When pH > 12.5, the Cr leaching was 0.3 mg/L. This indicates the dissolution of precipitates. At pH < 1, the leaching amount of As was 1.4 mg/L. This is far beyond the landfill leachate concentration limit. At pH > 5, no As2+ was seen in the leaching liquid due to the formation of precipitates. In outdoor conditions, fly ash is in a weakly acid state. Thus, the effects of As from fly ash on the environment are negligible because it does not leach. In strong acidic conditions, the leaching amount of Hg was about 0.12 mg/L, far beyond the landfill leachate concentration limit (0.05 mg/L) too. Between pH 5–7, Hg leaching amount rapidly reduced, indicating that in weak acid environment, Hg was difficult to dissolve.

4.

Conclusions

The fly ash had a high porosity that made it possible for volatile heavy metals such as Pb and Hg to easily be enriched on the surface. Chemical agents that caused the surface to be denser stabilized the fly ash. This greatly reduced heavy metal leaching. In addition, the specific area of fly ash is relatively small. Fly ash has an obvious hysteresis loop that belongs to the H2 model hysteresis loop. This is typical of mesoporous materials. The fly ash contains large amounts of salts such as NaCl, KCl, and CaCl2 . These all promote heavy metal leaching from fly ash. Therefore, soluble salts in fly ash contribute to the toxicity of MSWI fly ash. The leaching values of Pb and Cd in fly ash were beyond the safety limits. According to the hazardous waste identification standard of China, fly ash is a hazardous waste. Our

This work was funded by the National Natural Science Foundation of China through program No. 21577100. We sincerely thank the State Key Laboratory of Pollution Control and Resource Reuse and Key Laboratory of Yangtze River Water Environment, Ministry of Education, for assisting with the experimental work.

References Aubert, J.E., Husson, B., Vaquier, A., 2004. Use of municipal solid waste incineration fly ash in concrete. Cem. Concr. Res. 34 (6), 957–963. Aubert, J.E., Husson, B., Sarramone, N., 2006. Utilization of municipal solid waste incineration (MSWI) fly ash in blended cement. Part 1: Processing and characterization of MSWI fly ash. J. Hazard. Mater. 136 (3), 624–631. Bontempi, E., et al., 2010. A new method for municipal solid waste incinerator (MSWI) fly ash inertization, based on colloidal silica. J. Environ. Monit. 12 (11), 2093–2099. Chang, F.-Y., Wey, M.-Y., 2006. Comparison of the characteristics of bottom and fly ashes generated from various incineration processes. J. Hazard. Mater. 138 (3), 594–603. Chou, J.D., Wey, M.Y., Chang, S.H., 2009. Evaluation of the distribution patterns of Pb, Cu and Cd from MSWI fly ash during thermal treatment by sequential extraction procedure. J. Hazard. Mater. 162 (2–3), 1000–1006. CSY, 2014. China Statistic Almanac, http://www.stats.gov.cn/tjsj/ndsj/2014/indexch.htm. Ito, T., 1996. Vitrification of fly ash by swirling-flow furnace. Waste Manage. 16 (5-6), 453–460. Jin, Y.-q, et al., 2013. Effects of hydrothermal treatment on the major heavy metals in fly ash from municipal solid waste incineration. Energy Fuels 27 (1), 394–400. Kim, Hooper, et al., 1998. Toxicity characteristic leaching procedure fails to extract oxoanion-forming elements that are extracted by municipal solid waste leachates. Environ. Sci. Technol. 32 (23), 3825–3830. Lin, K.L., Chang, C.T., 2006. Leaching characteristics of slag from the melting treatment of municipal solid waste incinerator ash. J. Hazard. Mater. 135 (1–3), 296–302. Lin, K.L., Wang, K.S., Tzeng, B.Y., Lin, C.Y., 2003. The reuse of municipal solid waste incinerator fly ash slag as a cement substitute. Res. Conserv. Recycl. 39 (4), 315–324. Lin, K.L., 2006. Feasibility study of using brick made from municipal solid waste incinerator fly ash slag. J. Hazard. Mater. 137 (3), 1810–1816. Liu, Y.S., Zheng, L.T., Li, X.D., Xie, S.D., 2009. SEM/EDS and XRD characterization of raw and washed MSWI fly ash sintered at different temperatures. J. Hazard. Mater. 162 (1), 161–173. Ministry of Environmental Protection of the People’s Republic of China, 1997. Solid waste-extraction procedure for toxicity of solid waste—horizontal vibration extraction procedure. GB 5086.2-1997 (in Chinese). Ministry of Environmental Protection of the People’s Republic of China, 2008. Standard for pollution control on the landfill site of municipal solid waste. GB 16889-2008 (in Chinese).

Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 333–341

Monteiro, R.C.C., et al., 2006. Development and properties of a glass made from MSWI bottom ash. J. Non-Cryst. Solids 352 (2), 130–135. Quina, M.J., Bordado, J.C., Quinta-Ferreira, R.M., 2008. Treatment and use of air pollution control residues from MSW incineration: an overview. Waste Manage. 28 (11), 2097–2121. Quina, M.J., Bordado, J.C.M., Quinta-Ferreira, R.M., 2010. Chemical stabilization of air pollution control residues from municipal solid waste incineration. J. Hazard. Mater. 179 (1–3), 382–392. Sakai, S., Hiraoka, M., 2000. Municipal solid waste incinerator residue recycling by thermal processes. Waste Manage. 20 (2–3), 249–258. Shi, H.S., Kan, L.L., 2009. Leaching behavior of heavy metals from municipal solid wastes incineration (MSWI) fly ash used in concrete. J. Hazard. Mater. 164 (2–3), 750–754.

341

Shim, Y.S., Rhee, S.W., Lee, W.K., 2005. Comparison of leaching characteristics of heavy metals from bottom and fly ashes in Korea and Japan. Waste Manage. 25 (5), 473–480. Tessier, A., Campbell, P.G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51 (7), 844–851. Van Herck, P., Van der Bruggen, B., Vogels, G., Vandecasteele, C., 2000. Application of computer modelling to predict the leaching behaviour of heavy metals from MSWI fly ash and comparison with a sequential extraction method. Waste Manage. 20 (2–3), 203–210. Wang, K.S., Sun, C.J., Liu, C.Y., 2001. Effects of the type of sintering atmosphere on the chromium leachability of thermal-treated municipal solid waste incinerator fly ash. Waste Manage. 21 (1), 85–91.