Leaching Characteristics of Fly Ash

from Municipal Solid Waste Incineration

May 2014

Student Investigator: Yibo Zhang, Jiannan Chen, Kevin Perthel

Advisors: Tuncer B. Edil, William J. Likos

University of Wisconsin-Madison

UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE RESEARCH PROGRAM Student Project Report

Leaching Characteristics of Fly Ash from Municipal Solid Waste Incineration

Yibo Zhang

Graduate Research Assistant, Department of Geological Engineering, University of Wisconsin-Madison,

E-mail: zhang579@wisc.edu

Jiannan Chen

Graduate Research Assistant, Department of Geological Engineering, University of Wisconsin-Madison,

E-mail: jchen229@wisc.edu

Kevin Perthel

Undergraduate Research Assistant, Department of Geological Engineering, University of Wisconsin-

Madison, E-mail: kperthel@wisc.edu

Tuncer B. Edil

Professor Emeritus and Research Director, Recycled Materials Resource Center, Department of

Geological Engineering, University of Wisconsin-Madison, E-mail: tbedil@wisc.edu

William J. Likos

Associate Professor, Department of Geological Engineering, Civil and Environmental Engineering,

University of Wisconsin-Madison, E-mail: likos@wisc.edu

ABSTRACT:

Laboratory tests using samples of municipal solid waste incineration fly ash (MSWIFA) indicate that

leachate produced using synthetic precipitation leaching procedures contains heavy metal elements, with

Selenium (Se) and Antimony (Sb) exceeding the USEPA drinking water standard. pH-dependent leaching

tests indicate that MSWIFA releases more metal elements under acidic conditions. Initial results from this

study will be used to develop a characterization of the elements’ leaching behavior and to assess

laboratory leaching methods that best simulate field conditions. The long-term objective is to develop

environmental impact evaluations and recommendations for the treatment and beneficial reuse of

MSWIFA.

KEYWORDS: Municipal Solid Waste incineration fly ash, MSWIFA, leachate, pH, heavy metals.

NTRODUCTION

Ever-increasing municipal construction along with daily garbage generation in the United States (U.S.) is

causing increased demand of MSW landfill space. In 2010, Americans generated approximately 250

million tons of MSW, in which 54.2 % (135.5 million tons) was discarded to landfills and other disposal

facilities (USEPA 2010). To reduce the waste volume, landfill operators implemented controlled burning

processes to incinerate the waste. The incineration of MSW is conducted under combustion and

incineration regulations (40 CFR Part 60), which includes emissions guidelines and compliance times for

municipal waste combustors. Additionally, if properly equipped, the heat generated can be converted into

electrical power (USEPA 2012a).

Currently, the United States has about 872 operational MSW-fired power generation plants, producing

approximately 2,500 megawatts (about 0.3 percent of total national power generation) (USEPA 2013).

The combustion of MSW produces two types of residuals: fly ash and bottom ash. The amount of ash

generated ranges from 15 to 25 percent by weight of the original MSW, and 5 to15 percent of the volume

of the original MSW (USEPA 2012b). Fly ash refers to the fine particles that are removed or captured

from the flue gas by air pollution control devices, such as scrubbers. Fly ash typically amounts 10 to 20

percent by weight of the total ash.

Municipal solid waste incineration fly ash (MSWIFA) may contain toxic materials, e.g., heavy metals,

inherited from the original waste or created during the combustion process, such as Hg, Cd, Cr and As

(Wu and Ting 2005; Shi and Kan 2008). To prevent migration of these substances into the groundwater

and soil, incineration residuals must be analyzed regularly to ensure disposal safety. Hazardous ash must

be managed and disposed of as hazardous waste, while non-hazardous ash, depending on state and local

regulations, may be disposed of in a MSW landfill or recycled for beneficial uses.

1. BACKGROUND

Previous studies from University Wisconsin-Madison Geological Engineering have accumulated a broad

knowledge and database for coal ash leaching characteristics (Bin-Shafique et al. 2006; Li et al. 2008),

and various leaching tests, i.e., column leaching tests, batch leaching tests and serial batch leaching tests,

were conducted on coal ash and other industrial byproducts (Bin-Shafique et al. 2006; Li et al. 2008;

Chen et al. 2012).

In this study, samples of fly ash from waste incineration from LaCrosse Co. Landfill (LaCrosse, WI) have

been investigated for leaching characteristics. The primary contents of the processed waste are wood and

MSW. Batch leaching tests, including synthetic precipitation leaching procedure (SPLP, USEPA method

1312) and pH-dependent leaching tests (USEPA method 1313), have been conducted to characterize the

leaching behavior under simulated precipitation and different pH scenarios. Both testing methods will be

used to more generally assess MSWIFA leaching characteristics. Environmental impact evaluations and

recommendations will be provided for treatment and beneficial reuse of MSWIFA.

The primary objective of this study is to evaluate the environmental concern of leaching elements from

Municipal Solid Waste incineration fly ash (MSWIFA) by investigating the hazardous heavy metal in

leachate using laboratory leaching tests. The testing results will be used as references for MSWIFA

disposal and treatment. The outcomes shall be developing a characterization of the elements’ leaching

behavior and comparing lab leaching methods to find the best way to simulate field conditions.

2. TEST MATERIALS AND METHODS

Four samples of MSWIFA from Lo Crosse Co. landfill (Figure 1) were analyzed in this study. New Ash

Sample 1 and 2 (NA1 and NA2) were sampled from the La Crosse Co. landfill ash monofill at different

locations. Ash was generated during Sep. 2013 and was sampled within 10 days. Old Ash sample 1 and 2

(OA1 and OA2) was sampled from the La Crosse Co. landfill ash monofill at different locations. Ash was

generated in 2013 but was in place for several months in the monofill.

2.1. Physical Properties

The physical and hydraulic properties of materials were tested according to standards of ASTM

International (ASTM) and the American Association of State Highway and Transportation Officials

(AASHTO). The material physical and hydraulic characterization tests including grain size analysis,

water content, dry unit weight, specific gravity and compaction characteristics were performed.

2.1.1. Grain Size Analysis

The grain size distribution of four MSWIFA samples was determined according to ASTM D 422. The

samples were first wet sieved through sieve No. 200 to separate coarse and fine particles. The coarse

portions were oven dried in 105℃ ± 2℃ for 24 hours prior to mechanical sieving, while the distribution of

particle sizes smaller than 75 μm was determined by a sedimentation process using a hydrometer.

2.1.2. Moisture Content.

Moisture content was measured for each sample following ASTM D2216. A representative specimen was

taken from each sample and oven dried in 105℃±2℃ for 24 hours. The mass loss was used to compute

the moisture in the bulk specimen.

2.1.3. Specific Gravity.

The specific gravity of samples was determined by ASTM D854 for soil solids that pass the 4.75-mm (No.

4) sieve using a water pycnometer. Test procedures adopted were exactly as the standard described.

2.1.4. Compaction.

Harvard miniature compactions were performed on the MSWIFA samples with standard effort following

ASTM D 4609 and modified impact by Tastan at University of Wisconsin-Madison. Maximum dry unit

weights and corresponding optimum moisture contents were estimated from the resulting compaction

curves.

2.2. Chemical Properties

The total elemental composition of all four MSWIFA samples was determined by acid digestion

according to EPA 3050B. Tests were conducted in triplicate. A 1:1 nitric acid digestion of 1 g of solid

sample was performed at 90 to 95°C for 2 h, and 30% H2O2 was added to start a peroxide reaction. The

total carbon (TC), total inorganic carbon (TIC), and total organic carbon (TOC) were determined with a

SC144 DR sulfur and carbon analyzer (LECO Inc., St. Joseph, MO, USA) by UW-Madison’s Soil and

Plant Analysis Lab.

2.3. Leaching Tests

Laboratory batch leaching tests including Synthetic Precipitation Leaching Procedure (SPLP) and pH-

dependent leaching were performed to characterize the MSWIFA leaching behavior.

2.3.1. Synthetic Precipitation Leaching Procedure (SPLP).

SPLP testing was conducted following the USEPA method 1312 with two replicate tests for each ash

sample. 50 grams of dry ash was mixed with 1000 mL of SPLP extraction liquid in a 1.5 L LDPE bottle

(Figure 2), and sent into a tumbler for 20 ± 2 h agitation at as speed of 30±2 revolutions per min (rpm)

(Figure 3). Sample pH, electrical conductivity (EC), and oxidation-reduction potential (ORP) were

determined after testing. Eluate was filtered through 0.45 μm filter paper and preserved to pH < 2 with

nitric acid. The #1 SPLP extraction liquid was used to represent the precipitation east of Mississippi River.

Two reasons for selecting #1 SPLP extraction liquid: (1) the monofill of MSWIFA is located at the east

side of Mississippi River, and the projects that potentially involve beneficial use ash are located mostly in

La Cross County. The #1 liquid is also more aggressive than #2 and #3 liquid, and thus is considered

representative of a worst case scenario.

2.3.2. pH-dependent Leaching Test.

pH-dependent leaching tests were performed according to methods outlined in Kosson et al. (2002) and

USEPA method 1313 at a liquid to solid ratio of 10:1 by weight. Batches (Figure 4) were agitated in an

end-over-end tumbler at a speed of 30±2 revolutions per min (rpm). A pH range of 2 to 13 was used for

the pH-dependent leaching tests, with target pH of 13, 12, 10.5, 9, 8, 7, 5.5, 4 and 2. A pre-test titration

was conducted to determine the contact time to equilibrium and the acid/base addition required for each

batch. pH, electrical conductivity (EC), and oxidation-reduction potential (ORP) were determined after

testing. The eluate was filtered through 0.45 μm filter paper, and preserved to pH < 2 with nitric acid. A

chemical model named LeachXS was used to calculate the acid/base addition for each pH target.

2.3.3. Leachate Chemical Analysis

Elemental composition of leachates was determined by inductively coupled plasma optical emission

spectrometry (ICP-OES). The USEPA detect limits and maximum contaminant level (MCL) for drinking

water of each element were listed in Table 1.

A Varian MPX ICP-OES with an axial torch was used to analyze elements summarized in Table 1. Argon

was the fuel source. A Varian Autosampler SPS 3 was utilized for continuous analysis. Prior to analysis,

the ICP was calibrated by diluting certified concentrated standards supplied from High Purity Standards

(Charleston, North Carolina) and Fisher Scientific (Hanover Park, Illinois). The calibration standards

were prepared in nitric acid. Calibration solutions had the same matrix as the samples to prevent

interferences.

The quality control guidelines outlined in USEPA procedure SW-846 were followed. Continuing

calibration verifications (CCV) and continuing calibration blanks (CCB) were analyzed every 10 samples,

and a matrix-spike and sample duplicate were analyzed every 20 samples. Matrix-spiked samples were

spiked prior to digestion. Quality control requirements described in USEPA Method SW-846 were met

for all calibrated wavelengths. These criteria required CCVs within 10% of expected values, CCBs below

detection limits, concentrations of duplicate samples within 20% of the concentration in the original

sample, and spiked samples to have a recovery of 75-125% the non spiked sample.

3. TEST RESULTS

3.1. Physical Properties.

A summary of physical properties of four MSWIFA samples is shown in Table 2. The grain size

distribution curve of all four samples is plotted in Figure 5. Compaction results indicate the the MSWIFA

samples have optimum water content (Wopt) ranging from 37.5 to 50.8%, but similar maximum dry unit

weight (γdmax) from 9.9 to 11.1 kN/m3. Specific gravity ranges from 2.6 to 2.7.

3.2. Chemical Properties.

Results from total elemental analysis by acid digestion and carbon content analysis are shown in Table 3.

Al, Fe, and K are the major constituents in all four samples with more than 1% weight percentage

(>10,000mg/kg). All MSWIFA samples have similar content in the major elements, while sample OA1

has a lower concentration in K. For trace elements, all four MSWIFA samples showed higher

concentration of Cu, Mg, P, Zn, Ba, Mn, Pb, and Ti than other elements, and OA1 also showed a lower

concentration than others. All four samples of MSWIFA had similar total carbon (TC) content with 1.1 to

1.6% wt, total inorganic carbon (TIC) (0.5 to 0.8% wt) and total organic carbon (TOC) (0.5 to 0.9% wt).

Sample OA2 has a lower content than other samples.

3.3. Synthetic Precipitation Leaching Procedure (SPLP) Results

Results from Synthetic Precipitation Leaching Procedure (SPLP), and the concentrations of arsenic (As),

chromium (Cr), lead (Pb), selenium (Se), and antimony (Sb) As in leachate of four MSWIFA samples

were compared with the Maximum Contaminant Level required in the EPA drinking water standard

(Figure 6). As and Sb concentrations exceed the EPA MCL (As10 μg/L, Sb 6 μg/L) for each sample,

while other three elements have concentrations well below the MCL (Cr 100 μg/L, Pb 15 μg/L, Se 50

μg/L). The highest concentration of As is 61.5 μg/L in the NA1 leachate, which is almost 3 times higher

than the lowest concentration in OA1 (22 μg/L). As concentration in samples NA2 and OA2 is a similar

value with around 35 μg/L. Sb concentration in NA2 and OA2 are approximately the same concentration

with 11 μg/L. The peak concentration of Sb occurs in the OA1 leachate with 41 μg/L.

Comparison of pH, electrical conductivity (EC) and oxidation/reduction potential (ORP) between the

SPLP leachate and DI water leaching solution are shown in Table 4. The leachate pH of all four

MSWIFA samples from SPLP fluid was similar with DI leaching solution, with 10.33 to 11.35. The EC

of the SPLP leachate in all samples shown lower value than the DI leaching solution, with OA1 having a

lower value than other samples.

3.4. pH-dependent Leaching Test Results

3.4.1. Acid Neutralization Capacity

Acid Neutralization Capacity (ANC) is a key property of cement/waste systems related to resistance to

acid attack affecting matrix durability and thus leaching of contaminants. Solubility is strongly affected

by the pH conditions and the integrity of the solid matrix depends on its ability to maintain alkaline

conditions (Senden et al. 1997). The acid neutralization capacity (ANC) curve for all four MSWIFA

samples is shown in Figure 7. Negative values represent base addition. The pH (no acid or base added) of

MSWIFA samples ranged from 10.55 to 11.24, with NA1, OA1 and OA2 having similar pH, and

relatively high from sample NA2. Similar ANC curves were observed for all four samples characterized

by a rapid drop in pH, followed by a plateau around pH 1.5 - 4.0. The ANC curves exhibit a rapid

decrease in pH from natural pH (10.55 to 11.24) to around pH 4 over a range of 7 meq/g acid of dry

material, followed by a plateau around pH 4 to pH 1.5 with an acid addition of another 7 meq/g dry

material. The plateau in the ANC can be explained by dissolution of calcium carbonate (carbonation) in

concrete, which is caused by a reaction between portlandite and calcium silicate hydrate with carbon

dioxide from the environment (Garrabrants et al. 2004). A similar plateau width for all four samples can

be coordinated with the similar TIC readings.

3.4.2. Leaching of Trace Metal Elements.

According to total elemental analysis results, four trace metal elements (Pb, Cu, Mn, Zn), were chosen to

be evaluated in this study because they were shown to be the highest concentration trace metal elements

in the MSWIFA (Table3). The release of elements as a function of leachate pH is shown in Figure 8,

reflecting a wide range of pH-dependent leaching behavior with differing release levels.

Lead. The release of lead (Pb) in all four MSWIFA samples exhibits similar behavior, with a significant

decrease at pH values < 5.5, and a minimum concentration (approximately 0.1 mg/kg) between pH 5.5

and 13 (Fig. 7a). At very low pH (pH = 2), the lead concentration (NA1, 2 with 57.5 and 106.4 mg/kg,

OA1, 2 with 76.8 and 71.7 mg/kg) reflected relatively high values.

Copper. The release of copper (Cu) exhibits different leaching behavior between NA and OA samples of

MSWIFA in the pH range 2 to 6 (Fig. 7b), with OA1, 2 having a dramatic decreasing from high

concentration (OA1, 2 with around 2117 and 798 mg/kg at pH 2), while NA1, 2 having a stable

decreasing from relative low concentration (NA1, 2 with around 50 and 39 mg/kg at pH 2). In the pH

range between 6 and 11, the release of all four samples is shown similar behavior with a minimum

concentration of approximately 0.1 mg/kg. A significant increasing release of four samples was detected

for pH values greater than 12.

Manganese. The release of manganese (Mn) of all four MSWIFA samples shown almost the same trend

between pH 2 and 10, with a mild decreasing from high concentration (around 250 mg/kg) at very low pH

(pH=2), then a rapid decline from pH 6 to 10. The concentration of manganese obtained from NA1 and

OA1 are below the recommended detection limit of 0.0013 mg/kg at pH values greater than 11, while

from NA2 and OA2 shown minimum release with approximately 0.01mg/kg.

Zinc. The release of zinc is shown a similar trend for all samples with manganese, with a high

concentration (around 350 to 400 mg/kg) between pH 2 to 5.5, followed by a rapid decreasing (pH 5.5 to

9). However, the release of all four samples is below the recommended detection limit of 0.005 mg/kg in

the pH range 9 to 12, then a rapid increasing for pH values greater than 12.

4. CONCLUSION

In this study, Municipal Solid Waste incineration fly ash (MSWIFA) was evaluated for potential heavy

metal leaching and high alkalinity that has been historically observed surrounding its use in concrete. To

make a comparison, four samples with different histories in the landfill were studied. Laboratory batch

leaching test results have led to the following observations:

1. Heavy metal leaching results from Synthetic Precipitation Leaching Procedure (SPLP) of

MSWIFA samples showed that Antimony (Sb) and Arsenic (As) concentrations exceed the

USEPA drinking water standard. However, contaminants transport modeling to determine the

effects due to soil absorption and dilution have not been evaluated, and thus the impact of

heavy metal leaching on the environment remains unknown.

2. Acid neutralization capacity curves of all four MSWIFA samples showed a pH plateau that

was less obvious, which means all samples have a low acid neutralization capacity.

3. Different leaching characteristics of trace metal elements (Pb, Cu, Mn, Zn) were observed

from the pH-dependent leaching test. All four elements showed highest concentration at

pH2, while lowest leaching at pH>6 for Pb and Cu, with Mn and Zn having lowest release at

pH>9.

Future studies should include: additional mineralogical analysis to better understand the leaching

mechanism using X-ray diffraction, Scanning Electron Microscopy (SEM), and Column leaching tests.

Additionally, a WiscLeach model and Minteq model should be used to simulate the leaching process and

further evaluate contaminant transport and environmental impact.

REFERENCES

Bin-Shafique, S., Benson, C., Edil, T., and Hwang, K. (2006), Leachate Concentrations from Water Leach

and Column Leach Tests on Fly-Ash Stabilized Soil, Environmental Engineering Science, 23(1), 51-65.

Chen, J., Bradshaw, S., Benson, C., Tinjum, J., and Edil, T. (2012), pH-Dependent Leaching of Trace

Elements from Recycled Concrete Aggregate, State of the Art and Practice in Geotechnical Engineering,

GSP No. 225, R. Hryciw et al., Eds., ASCE, Reston VA, 3729-3738.

Garrabrants, A. C., Sanchez, F., Kosson, D. S. (2004). ―Changes in constituent equilibrium leaching and

pore water characteristics of a Portland cement mortar as a result of Carbonation.‖ Waste Manage. 24(1),

19–36.

Kosson, D. S., Van Der Sloot, H. A., Sanchez, F., and Garrabrants, A. C. (2002). ―An integrated

framework for evaluating leaching in waste management and utilization of secondary

materials.‖Environmental Engineering Science, 19(3), 159-204.

Li, L., Benson, C., Edil, T., and Hatipoglu, B. (2008), Sustainable Construction Case History: Fly Ash

Stabilization of Recycled Asphalt Pavement Material, Geotechnical and Geological Engineering, 26, 177-

187.

Senden, G.J., van der Sloot, H.A., Goumans, J.J.J.M. (1997). Waste Materials in Construction: Putting

Theory into Practice, Studies in Environmental Science, vol. 71, Elsevier, Amsterdam, pp. 803–814.

Shi, H. and Kan, L. (2008). ―Leaching behavior of heavy metals from municipal solid wastes incineration

(MSWI) fly ash used in concrete.‖ Journal of Hazardous Materials, Volume 164, Issues 2–3, Pages 750–

754.

USEPA (2010). ―Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts

and Figures for 2010.‖ United States Environmental Protection Agency, Washington, DC.

USEPA (2012a). ―Municipal Solid Waste Combustion.‖ United States Environmental Protection Agency,

Washington, DC. http://www.epa.gov/epawaste/nonhaz/municipal/combustion.htm

USEPA (2012b). ―Municipal Solid Waste – Basic Information.‖ United States Environmental Protection

Agency, Washington, DC. http://www.epa.gov/wastes/nonhaz/municipal/wte/basic.htm

USEPA (2013). ―Clean Energy - Municipal Solid Waste.‖ United States Environmental Protection

Agency, Washington, DC. http://www.epa.gov/cleanenergy/energy-and-you/affect/municipal-sw.html

Wu, H. and Ting, Y. (2005). ―Metal extraction from municipal solid waste (MSW) incinerator fly ash—

Chemical leaching and fungal bioleaching.‖ Enzyme and microbial technology, volume 38, p 839 – 847.

TABLES

Table 1. Elements considered in MSWIFA leaching tests

Element Instrument MCL*(g/L) MDL(g /L)

Aluminum ICP-OES 50-200** 2

Calcium ICP-OES - 31

Iron ICP-OES 300** 2

Magnesium ICP-OES - 1

Potassium ICP-OES - <1000

Silicon ICP-OES - <1000

Sodium ICP-OES - 3

Strontium ICP-OES 4000*** <1

Barium ICP-OES 2000 0.08

Beryllium ICP-OES 4 0.11

Boron ICP-OES 6*** 2.2

Cadmium ICP-OES 5 0.53

Chromium ICP-OES 100 0.3

Cobalt ICP-OES - 0.8

Copper ICP-OES 1000** 2.7

Lead ICP-OES 15 3.8

Manganese ICP-OES 50 0.13

Molybdenum ICP-OES 40*** 3.3

Nickel ICP-OES 100*** 1.8

Vanadium ICP-OES - 0.8

Zinc ICP-OES 5000 0.5

Antimony ICP-MS 6 0.004

Arsenic ICP-MS 10 0.008

Mercury ICP-MS 2 0.03

Selenium ICP-MS 50 0.01

Thallium ICP-MS 2 0.006

*USEPA drinking water standard and Health Advisories

**Secondary drinking water regulation

***Health Advisories - Life time

Table 2. Physical properties of MSWIFA samples

Sample ID NA1 NA2 OA1 OA2

Moisture Content (%) 10.1 20.2 27.0 35.6

Optimum Water Content (%) 37.5 44.2 43.8 50.8

Max Dry Unit Weight (kN/m3) 11.1 9.9 10.5 10.5

Specific Gravity 2.68 2.61 2.68 2.74

Table 3. Total elemental analysis and carbon content analysis results of MSWIFA

Sample Labels NA1 NA2 OA1 OA2

`Al (%) 3.75 3.33 3.18 3.15

Ca (%) 0.48 0.49 0.48 0.48

Cu (%) 0.21 0.23 0.18 0.14

Fe (%) 1.35 1.05 1.10 1.28

K (%) 1.13 1.26 0.44 1.06

Mg (%) 0.22 0.23 0.23 0.22

Na (%) 0.89 0.95 0.53 0.86

P (%) 0.15 0.17 0.17 0.20

Zn (%) 0.17 0.15 0.13 0.14

Ag (mg/kg) 3.40 1.94 4.76 4.39

B (mg/kg) 162.72 187.76 151.51 214.51

Ba (mg/kg) 494.78 555.62 490.22 373.51

Be (mg/kg) nd nd nd nd

Cd (mg/kg) 10.81 9.30 8.24 7.57

Co (mg/kg) 13.90 12.90 10.62 16.72

Cr (mg/kg) 123.71 87.31 80.65 69.85

Li (mg/kg) 15.44 16.70 13.36 13.93

Mn (mg/kg) 737.21 667.78 543.24 692.38

Mo (mg/kg) 14.24 10.12 8.72 11.30

Ni (mg/kg) 60.25 48.85 43.20 49.59

Pb (mg/kg) 375.01 478.67 309.18 218.96

Si (mg/kg) 55.27 51.63 56.30 113.16

Ti (mg/kg) 826.83 504.09 397.00 513.90

As (mg/kg) 22.05 14.27 51.5 30.35

Sb (mg/kg) 47.4 59.1 8.2 14.75

Se (mg/kg) n.d. n.d. n.d. n.d.

Tl (mg/kg) n.d. n.d. n.d. n.d.

Total Carbon (%) 1.507 1.324 1.624 1.114

Total Inorganic Carbon (%) 0.637 0.614 0.795 0.542

Total Organic Carbon (%) 0.870 0.710 0.829 0.573

n.d.: not detected.

Table 4. Comparison of pH, EC and ORP between SPLP and DI leaching

Sample ID pH EC(mS/cm) ORP(mV)

NA1 DI 10.69 6.74 ﹣168.8

NA2 DI 11.28 8.54 ﹣151.7

OA1 DI 10.7 1419(µS/cm) ﹣114.8

OA2 DI 10.74 6.75 ﹣134.5

NA1 SPLP 10.88 5.54 128.8

NA2 SPLP 11.35 6.58 128.7

OA1 SPLP 10.33 814(µS/cm) 108.1

OA2 SPLP 10.49 5.17 116.5

DI: DI water as leaching solution

SPLP: SPLP leaching test

FIGURES

(A) New Ash 1 (NA1)

(B) New Ash 2 (NA2)

(C) Old Ash 1 (OA1)

(D) Old Ash 2 (OA2)

Figure 1. Photographs of MSWIFA samples in this study

Figure 2. Batches used in the SPLP leaching tests

Figure 3. Tumbler used in the batch tests

Figure 4. Batches used in the pH-dependent leaching tests

0

20

40

60

80

100

0.0010.010.1110100

NA1NA2OA1OA2

Perc

ent

Fin

er

(%)

Partical Diameter

Figure 5. Grain size distribution (GSD) curves

100

101

102

103

As Cr Pb Se Sb

NA1

NA2

OA1

OA2

Con

centr

ation (

µg/L

)MCL

Figure 6. Heavy metal concentration in leachate from Synthetic Precipitation Leaching Procedure (SPLP)

0

2

4

6

8

10

12

14

-5 0 5 10 15

NA1

NA2

OA1

OA2

pH

Acid/Base Addition [meq/g-dry]

Base Acid

Figure 7. Acid neutralization capacity (ANC) curve of all four samples from batch leaching tests

10-2

10-1

100

101

102

103

0 2 4 6 8 10 12 14

NA1NA2OA1OA2

Rele

ase (

mg/k

g)

pH

PbIncreasing Release

Minimum Release

(a)

MDL=0.038

10-2

10-1

100

101

102

103

104

0 2 4 6 8 10 12 14

NA1NA2OA1OA2

Rele

ase (

mg/k

g)

pH

Cu Increasing Release

Minimum Release

(b)

MDL=0.027

10-4

10-3

10-2

10-1

100

101

102

103

104

0 2 4 6 8 10 12 14

NA1NA2OA1OA2

Rele

ase (

mg/k

g)

pH

Mn

Increasing Release

Minimum Release

(c)

MDL=0.0013

10-3

10-2

10-1

100

101

102

103

104

0 2 4 6 8 10 12 14

NA1NA2OA1OA2

Rele

ase (

mg

/kg)

pH

ZnIncreasing Release

Minimum Release

(d)

MDL=0.005

Figure 8. Release of trace metal elements as a function of pH for MSWIFA samples NA1, 2 and OA1, 2:

(a) Lead, (b) Copper, (c) Manganese, (d) Zinc.