Accepted Manuscript Title: Effect of Ferrous Metal Presence on Lead Leaching in Municipal Waste Incineration Bottom Ashes Author: Wesley N. Oehmig Justin G. Roessler Jianye Zhang Timothy G. Townsend PII: DOI: Reference:
S0304-3894(14)00778-X http://dx.doi.org/doi:10.1016/j.jhazmat.2014.09.040 HAZMAT 16288
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
23-5-2014 14-8-2014 3-9-2014
Please cite this article as: W.N. Oehmig, J.G. Roessler, J. Zhang, T.G. Townsend, Effect of Ferrous Metal Presence on Lead Leaching in Municipal Waste Incineration Bottom Ashes, Journal of Hazardous Materials (2014), http://dx.doi.org/10.1016/j.jhazmat.2014.09.040 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Research Highlights:
te
d
M
an
us
cr
ip t
Addition of iron to WTE ash reduced lead leaching Removal of ferrous metals from WTE ash increased lead leachability Advanced metals recovery may increase potential for WTE ash to be hazardous for lead
Ac ce p
• • •
1
Page 1 of 27
Effect of Ferrous Metal Presence on Lead Leaching
cr
ip t
in Municipal Waste Incineration Bottom Ashes
us
Wesley N. Oehmig1, Justin G. Roessler1, Jianye Zhang2, and Timothy G. Townsend1* 1
Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450,
an
Gainesville, FL. 32611-6450, USA. 2
M
PO Box 678, Department of Natural Sciences, Voorhees College, Denmark, SC 29042.
Ac ce p
te
d
* Corresponding author. Phone: 352-392-0846, Fax: 352-392-3076; email: [email protected]
ABSTRACT:
2
Page 2 of 27
The recovery of ferrous and non-ferrous metals from waste to energy (WTE) ash continues to advance as the sale of removed metals improves the economics of waste combustion. Published literature suggests that Fe and Fe oxides play a role in suppressing Pb leaching in the Toxicity
ip t
Characteristic Leaching Procedure (TCLP); further removal of ferrous metals from WTE ashes may facilitate higher Pb leaching under the TCLP. Eight WTE bottom ash size-fractions, from
cr
three facilities, were evaluated to assess the effect of metallic Fe addition and ferrous metal
us
removal on TCLP leaching. Metallic Fe addition was demonstrated to reduce Pb leaching; the removal of ferrous metals by magnet resulted in a decrease in total available Pb (mg/kg) in most
an
ash samples, yet Pb leachability increased in 5 of 6 ash samples. The research points to two chemical mechanisms to explain these results: redox interactions between Pb and Fe and the
M
sorption of soluble Pb onto Fe oxide surfaces, as well as the effect of the leachate pH before and after metals recovery. The findings presented here indicate that generators, processors, and
d
regulators of ash should be aware of the changes ferrous metal that removal may have on Pb
Ac ce p
management of WTE ashes.
te
leaching, as a substantial increase in leaching may have significant implications regarding the
Keywords:
3
Page 3 of 27
Solid waste; incineration; ash; ferrous; lead; iron; TCLP; leaching Abbreviations: AMR, advanced metals recovery; CFR, code of federal register; FMR, ferrous metals removal;
ip t
HDPE, high density polyethylene; ICP-AES, inductively coupled plasma atomic emission spectrometry; LDPE low density polyethylene; MSW, municipal solid waste; RCRA, resource
cr
conservation and recovery act; RDF, refuse derived fuel; SEM-EDS, scanning electron
us
microscopy - energy-dispersive X-ray spectroscopy; TCLP, toxicity characteristic leaching
an
procedure; WTE, waste to energy
M
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval
te
Funding Sources
d
to the final version of the manuscript.
Ac ce p
This research was conducted with support from the Hinkley Center for Solid and Hazardous Waste Management.
Acknowledgements
The authors would like to thank the waste to energy facilities that allowed for the collection of samples during this study as well as undergraduate research assistants Stephanie Nevadunksy and Ashley Walsh.
4
Page 4 of 27
1. Introduction The combustion of municipal solid waste (MSW) for power generation, or waste to energy
ip t
(WTE), accounted for nearly 12% of MSW managed in the United States in 2011. This equated to 26 million metric tonnes of MSW combusted, and the generation of approximately 6.6 million
cr
metric tonnes of combustion residuals[1]. Management of these residuals (WTE fly and bottom
us
ashes) is a considerable expense associated with this process. In the United States, commingled ash typically undergoes ferrous and non-ferrous metals recovery and is then disposed of in a
an
secure landfill[2]. The sale of recovered ferrous and non-ferrous metals is a significant cost offset in this process, and advanced metals recovery (AMR) techniques (electromagnetic and
M
electrostatic separation) to remove these metals with greater efficacy are being tested and applied[3]. The implementation of AMR techniques will continue to increase in the future
d
because of their cost benefit. The beneficial use of WTE bottom ash has been well
te
researched[2,4-10] and in certain reuse applications metals recovery can facilitate the production
Ac ce p
of a more structurally sound material[4]. Changes in trace pollutant behavior in disposal and recycling of WTE ash as a result of AMR merits exploration. In the United States, hazardous waste management is regulated at the federal level by the Environmental Protection Agency (EPA), generally resulting in more costly treatment, storage and disposal; the EPA has set definitions for hazardous waste (40 CFR 261) under the authority of the Resource Conservation and Recovery Act (RCRA) of 1976. Wastes not specifically listed as hazardous (including residuals from the WTE process), may still be classified as such if they exhibit a characteristic of toxicity (TC), ignitability, reactivity, or corrosivity. The TC is evaluated by assessing the leaching concentrations of Ag, As, Ba, Cd, Cr, Hg, Pb, and Se with the Toxicity Characteristic Leaching Procedure (TCLP) and comparing to prescribed TC limits
5
Page 5 of 27
(40 CFR 261.30) [11]. Commingled WTE ash in the United States has been routinely demonstrated to be non-hazardous with respect to the toxicity characteristic. For WTE ash, the element most commonly approaching its TC limit is Pb[2]; that limit is 5 mg/L. While regularly
ip t
leaching below the (TC) limits, the total concentrations (mg/kg) of several elements in WTE ash (including Pb) are sufficiently large enough to cause the ash to exceed TC limits if enough is
cr
leached[11,12]. The fraction of an element that leaches from a waste in the TCLP will be
us
influenced by waste characteristics and the resulting chemical conditions in the leaching test (pH, redox conditions, reactive surfaces, organic carbon presence, ect.) [13-18]. Therefore changes to
an
ash composition (such as additional ferrous metal removal) may alter the chemical nature of the processed ash and would be expected to affect TCLP leaching; if such changes increased the
M
leachability of Pb, the likelihood of WTE ash being designated a TC hazardous waste might increase.
d
The presence of Fe has long been recognized to influence the leachability of Pb in TCLP
te
testing. In the past, some industries would add Fe filings to Pb-bearing foundry sands to reduce
Ac ce p
TCLP Pb leaching; Kendall [13] demonstrated that some treatment did not result in true stabilization of the Pb. He cited three potential mechanisms for metallic Fe interaction with Pb: reduction by metallic Fe, sorption by hydrous ferric oxide, and precipitation of hydroxides. Musson et al., found electronic devices to leach less Pb in the presence of ferrous metal components, and Vann et al., concluded that reduction by metallic Fe (as well as Zn in galvanized plating) was a major responsible mechanism[14,15]. The standard electrode potentials (versus Standard Hydrogen Electrode) for the reduction of divalent Pb and Fe to zerovalent state are -0.13 and -0.44 V, respectively[16]. 2+ The sorption of Pb on Fe oxide surfaces is a wide studied phenomenon in a variety of
disciplines[17-20] and has been cited as a mechanism affecting Pb leaching in several studies
6
Page 6 of 27
related to WTE ash[21-23]. Kim et al.[21], found that pulverized WTE bottom ash was shown to have an adsorption capacity of 10 to 20 mg-Pb/g-bottom ash, and that Pb was also seen to be sorbed by Fe powder. Meima et al.[22], conducted leaching experiments and geochemical
ip t
modeling that demonstrated leachate concentrations of Pb in weathered bottom ash were under saturated with respect to the solubility controlling mineral forms. Meima hypothesized that Pb
cr
leaching was again influenced by sorption to Fe/Al oxides[23] and identified the association of
us
Pb particles with Fe oxides through scanning electron microscopy - energy-dispersive X-ray spectroscopy (SEM-EDS)[22].
an
Given the role that the presence of metallic Fe, steel, and other ferrous metal materials have been shown to play in Pb leaching, and the effect of Fe oxides on Pb solubility, the impact that
M
AMR on WTE ash might have on Pb leaching in the TCLP warrants investigation. It is hypothesized that as ferrous metal presence in WTE ashes is reduced, Pb concentrations in the
d
TCLP extract may increase such that the TC limit is exceeded. Exceeding the TC limit would
te
have severe management implications since classification of WTE ash as a hazardous waste
Ac ce p
would trigger federal regulation under RCRA. While the TCLP is not an ideal test for assessing true behavior in an ash disposal or reuse setting [24], it is a required test in the United States and carries regulatory consequences if TC limits are exceeded. To examine this issue, research was conducted to evaluate the effect of ferromagnetic metal presence in WTE bottom ash on Pb leachability. In the first part of this study, WTE bottom ashes (having already undergone ferrous metal removal) were spiked with metallic Fe and TCLP leaching was assessed. In the second part, additional WTE bottom ashes were subject to a laboratory-scale AMR treatment for ferrous metals and the effect on Pb leachability in the TCLP observed. The results are discussed with respect to the framework of US hazardous waste policy, and potential management implications for generators and processors of WTE ash. Additionally
7
Page 7 of 27
these results serve to demonstrate that metals removal from other waste products could alter its leaching characteristics, and that processors of wastes should take precautions to ensure that the post-processed residuals are appropriately characterized.
ip t
2. Materials and Methods 2.1 Ash Sampling
cr
WTE bottom ash was sampled from three separate facilities (A, B, and C) in Florida, United
us
States. Facility A is a mass burn facility; bottom ash was sampled following screening and both ferrous (belt magnet) and non ferrous (eddy current) metals recovery. The ash was screened at
an
9.5 mm, resulting in two samples: < 9.5 mm and > 9.5 mm bottom ashes, referred to as samples A9.5 respectively; approximately 200 kg of each size fraction was sampled over the
M
course of one week. Facility B is a mass burn facility; one large (~200 kg) grab sample of bottom ash was collected from a conveyor following the boiler and quench. Sampling was conducted
d
over approximately 6 hours, and occurred prior to any ferrous or non-ferrous metals recovery.
te
This sample is referred to as sample B. Facility C is a refuse derived fuel (RDF) plant,
Ac ce p
employing a flail mill, ferrous and non-ferrous metals recovery, screening, and final shredding to produce the RDF. A grab sample of bottom ash (~200 kg) was collected immediately following the boiler and quench. This sample is referred to as sample C. All samples were mixed thoroughly in a pre-cleaned drum mixer for homogenization and then placed into sealed 20 L high-density polyethylene (HDPE) containers until preparation and analysis; the headspace in the HDPE containers was minimized to avoid excess sample contact with atmospheric CO2. 2.2 Preparations and Initial Characterization The particle size distribution of sample ashes was determined by sieving three replicates, of approximately 5 kg each, with the following U.S. standard sieve sizes: ½” (12.5 mm), 3/8” (9.5 mm), No. 4, No.10, No. 20, No. 50. Mass retained on each sieve was recorded. Size-separated
8
Page 8 of 27
samples of bottom ashes were desired for this study because AMR often fractionates ashes based on size. Samples B and C were separated with sieves into four size fractions: > 12.5 mm, 12.5 to 9.5 mm, 9.5 to 4.75 mm, and < 4.75 mm. The >12.5 mm size fraction was not used in the
ip t
experiments described here. The subsamples are denoted with the subscripts 12.5/9.5, 9.5/4.5, and 9.5, were size reduced through crushing and cutting. In a large aluminum bowl, approximately 0.5 kg of ash was struck with a 1 kg hammer 5-8 times. The
an
resulting ash was sieved through a 9.5 mm standard U.S. sieve. The portion of the sample passing the sieve was set aside and that retained on the sieve was again struck with the hammer
M
5-8 times. This process was repeated until no ash was retained on the sieve. For uncrushable, malleable, or metallic pieces, a bolt cutter was used to cut the material to pass a 9.5 mm sieve;
d
these pieces did not account for a significant portion of the material (99.9%) metallic form, and was obtained as a 1 mm diameter wire from a scientific supply vendor; it was cut into 10 mm lengths prior to being added to A9.5. 5Fe Nomenclature for these additions is: “ A>9.5” representing the A>9.5 sample dosed with 5% Fe by
mass.
9
Page 9 of 27
2.4 Ferromagnetic Metal Content and Removal In a second experiment bottom ashes were processed to remove ferrous metal, and leaching from these was compared to unprocessed samples. For each subsample from Facilities B and C
ip t
(B12.5/9.5, B9.5/4.5 B
S0304-3894(14)00778-X http://dx.doi.org/doi:10.1016/j.jhazmat.2014.09.040 HAZMAT 16288
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
23-5-2014 14-8-2014 3-9-2014
Please cite this article as: W.N. Oehmig, J.G. Roessler, J. Zhang, T.G. Townsend, Effect of Ferrous Metal Presence on Lead Leaching in Municipal Waste Incineration Bottom Ashes, Journal of Hazardous Materials (2014), http://dx.doi.org/10.1016/j.jhazmat.2014.09.040 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Research Highlights:
te
d
M
an
us
cr
ip t
Addition of iron to WTE ash reduced lead leaching Removal of ferrous metals from WTE ash increased lead leachability Advanced metals recovery may increase potential for WTE ash to be hazardous for lead
Ac ce p
• • •
1
Page 1 of 27
Effect of Ferrous Metal Presence on Lead Leaching
cr
ip t
in Municipal Waste Incineration Bottom Ashes
us
Wesley N. Oehmig1, Justin G. Roessler1, Jianye Zhang2, and Timothy G. Townsend1* 1
Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450,
an
Gainesville, FL. 32611-6450, USA. 2
M
PO Box 678, Department of Natural Sciences, Voorhees College, Denmark, SC 29042.
Ac ce p
te
d
* Corresponding author. Phone: 352-392-0846, Fax: 352-392-3076; email: [email protected]
ABSTRACT:
2
Page 2 of 27
The recovery of ferrous and non-ferrous metals from waste to energy (WTE) ash continues to advance as the sale of removed metals improves the economics of waste combustion. Published literature suggests that Fe and Fe oxides play a role in suppressing Pb leaching in the Toxicity
ip t
Characteristic Leaching Procedure (TCLP); further removal of ferrous metals from WTE ashes may facilitate higher Pb leaching under the TCLP. Eight WTE bottom ash size-fractions, from
cr
three facilities, were evaluated to assess the effect of metallic Fe addition and ferrous metal
us
removal on TCLP leaching. Metallic Fe addition was demonstrated to reduce Pb leaching; the removal of ferrous metals by magnet resulted in a decrease in total available Pb (mg/kg) in most
an
ash samples, yet Pb leachability increased in 5 of 6 ash samples. The research points to two chemical mechanisms to explain these results: redox interactions between Pb and Fe and the
M
sorption of soluble Pb onto Fe oxide surfaces, as well as the effect of the leachate pH before and after metals recovery. The findings presented here indicate that generators, processors, and
d
regulators of ash should be aware of the changes ferrous metal that removal may have on Pb
Ac ce p
management of WTE ashes.
te
leaching, as a substantial increase in leaching may have significant implications regarding the
Keywords:
3
Page 3 of 27
Solid waste; incineration; ash; ferrous; lead; iron; TCLP; leaching Abbreviations: AMR, advanced metals recovery; CFR, code of federal register; FMR, ferrous metals removal;
ip t
HDPE, high density polyethylene; ICP-AES, inductively coupled plasma atomic emission spectrometry; LDPE low density polyethylene; MSW, municipal solid waste; RCRA, resource
cr
conservation and recovery act; RDF, refuse derived fuel; SEM-EDS, scanning electron
us
microscopy - energy-dispersive X-ray spectroscopy; TCLP, toxicity characteristic leaching
an
procedure; WTE, waste to energy
M
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval
te
Funding Sources
d
to the final version of the manuscript.
Ac ce p
This research was conducted with support from the Hinkley Center for Solid and Hazardous Waste Management.
Acknowledgements
The authors would like to thank the waste to energy facilities that allowed for the collection of samples during this study as well as undergraduate research assistants Stephanie Nevadunksy and Ashley Walsh.
4
Page 4 of 27
1. Introduction The combustion of municipal solid waste (MSW) for power generation, or waste to energy
ip t
(WTE), accounted for nearly 12% of MSW managed in the United States in 2011. This equated to 26 million metric tonnes of MSW combusted, and the generation of approximately 6.6 million
cr
metric tonnes of combustion residuals[1]. Management of these residuals (WTE fly and bottom
us
ashes) is a considerable expense associated with this process. In the United States, commingled ash typically undergoes ferrous and non-ferrous metals recovery and is then disposed of in a
an
secure landfill[2]. The sale of recovered ferrous and non-ferrous metals is a significant cost offset in this process, and advanced metals recovery (AMR) techniques (electromagnetic and
M
electrostatic separation) to remove these metals with greater efficacy are being tested and applied[3]. The implementation of AMR techniques will continue to increase in the future
d
because of their cost benefit. The beneficial use of WTE bottom ash has been well
te
researched[2,4-10] and in certain reuse applications metals recovery can facilitate the production
Ac ce p
of a more structurally sound material[4]. Changes in trace pollutant behavior in disposal and recycling of WTE ash as a result of AMR merits exploration. In the United States, hazardous waste management is regulated at the federal level by the Environmental Protection Agency (EPA), generally resulting in more costly treatment, storage and disposal; the EPA has set definitions for hazardous waste (40 CFR 261) under the authority of the Resource Conservation and Recovery Act (RCRA) of 1976. Wastes not specifically listed as hazardous (including residuals from the WTE process), may still be classified as such if they exhibit a characteristic of toxicity (TC), ignitability, reactivity, or corrosivity. The TC is evaluated by assessing the leaching concentrations of Ag, As, Ba, Cd, Cr, Hg, Pb, and Se with the Toxicity Characteristic Leaching Procedure (TCLP) and comparing to prescribed TC limits
5
Page 5 of 27
(40 CFR 261.30) [11]. Commingled WTE ash in the United States has been routinely demonstrated to be non-hazardous with respect to the toxicity characteristic. For WTE ash, the element most commonly approaching its TC limit is Pb[2]; that limit is 5 mg/L. While regularly
ip t
leaching below the (TC) limits, the total concentrations (mg/kg) of several elements in WTE ash (including Pb) are sufficiently large enough to cause the ash to exceed TC limits if enough is
cr
leached[11,12]. The fraction of an element that leaches from a waste in the TCLP will be
us
influenced by waste characteristics and the resulting chemical conditions in the leaching test (pH, redox conditions, reactive surfaces, organic carbon presence, ect.) [13-18]. Therefore changes to
an
ash composition (such as additional ferrous metal removal) may alter the chemical nature of the processed ash and would be expected to affect TCLP leaching; if such changes increased the
M
leachability of Pb, the likelihood of WTE ash being designated a TC hazardous waste might increase.
d
The presence of Fe has long been recognized to influence the leachability of Pb in TCLP
te
testing. In the past, some industries would add Fe filings to Pb-bearing foundry sands to reduce
Ac ce p
TCLP Pb leaching; Kendall [13] demonstrated that some treatment did not result in true stabilization of the Pb. He cited three potential mechanisms for metallic Fe interaction with Pb: reduction by metallic Fe, sorption by hydrous ferric oxide, and precipitation of hydroxides. Musson et al., found electronic devices to leach less Pb in the presence of ferrous metal components, and Vann et al., concluded that reduction by metallic Fe (as well as Zn in galvanized plating) was a major responsible mechanism[14,15]. The standard electrode potentials (versus Standard Hydrogen Electrode) for the reduction of divalent Pb and Fe to zerovalent state are -0.13 and -0.44 V, respectively[16]. 2+ The sorption of Pb on Fe oxide surfaces is a wide studied phenomenon in a variety of
disciplines[17-20] and has been cited as a mechanism affecting Pb leaching in several studies
6
Page 6 of 27
related to WTE ash[21-23]. Kim et al.[21], found that pulverized WTE bottom ash was shown to have an adsorption capacity of 10 to 20 mg-Pb/g-bottom ash, and that Pb was also seen to be sorbed by Fe powder. Meima et al.[22], conducted leaching experiments and geochemical
ip t
modeling that demonstrated leachate concentrations of Pb in weathered bottom ash were under saturated with respect to the solubility controlling mineral forms. Meima hypothesized that Pb
cr
leaching was again influenced by sorption to Fe/Al oxides[23] and identified the association of
us
Pb particles with Fe oxides through scanning electron microscopy - energy-dispersive X-ray spectroscopy (SEM-EDS)[22].
an
Given the role that the presence of metallic Fe, steel, and other ferrous metal materials have been shown to play in Pb leaching, and the effect of Fe oxides on Pb solubility, the impact that
M
AMR on WTE ash might have on Pb leaching in the TCLP warrants investigation. It is hypothesized that as ferrous metal presence in WTE ashes is reduced, Pb concentrations in the
d
TCLP extract may increase such that the TC limit is exceeded. Exceeding the TC limit would
te
have severe management implications since classification of WTE ash as a hazardous waste
Ac ce p
would trigger federal regulation under RCRA. While the TCLP is not an ideal test for assessing true behavior in an ash disposal or reuse setting [24], it is a required test in the United States and carries regulatory consequences if TC limits are exceeded. To examine this issue, research was conducted to evaluate the effect of ferromagnetic metal presence in WTE bottom ash on Pb leachability. In the first part of this study, WTE bottom ashes (having already undergone ferrous metal removal) were spiked with metallic Fe and TCLP leaching was assessed. In the second part, additional WTE bottom ashes were subject to a laboratory-scale AMR treatment for ferrous metals and the effect on Pb leachability in the TCLP observed. The results are discussed with respect to the framework of US hazardous waste policy, and potential management implications for generators and processors of WTE ash. Additionally
7
Page 7 of 27
these results serve to demonstrate that metals removal from other waste products could alter its leaching characteristics, and that processors of wastes should take precautions to ensure that the post-processed residuals are appropriately characterized.
ip t
2. Materials and Methods 2.1 Ash Sampling
cr
WTE bottom ash was sampled from three separate facilities (A, B, and C) in Florida, United
us
States. Facility A is a mass burn facility; bottom ash was sampled following screening and both ferrous (belt magnet) and non ferrous (eddy current) metals recovery. The ash was screened at
an
9.5 mm, resulting in two samples: < 9.5 mm and > 9.5 mm bottom ashes, referred to as samples A9.5 respectively; approximately 200 kg of each size fraction was sampled over the
M
course of one week. Facility B is a mass burn facility; one large (~200 kg) grab sample of bottom ash was collected from a conveyor following the boiler and quench. Sampling was conducted
d
over approximately 6 hours, and occurred prior to any ferrous or non-ferrous metals recovery.
te
This sample is referred to as sample B. Facility C is a refuse derived fuel (RDF) plant,
Ac ce p
employing a flail mill, ferrous and non-ferrous metals recovery, screening, and final shredding to produce the RDF. A grab sample of bottom ash (~200 kg) was collected immediately following the boiler and quench. This sample is referred to as sample C. All samples were mixed thoroughly in a pre-cleaned drum mixer for homogenization and then placed into sealed 20 L high-density polyethylene (HDPE) containers until preparation and analysis; the headspace in the HDPE containers was minimized to avoid excess sample contact with atmospheric CO2. 2.2 Preparations and Initial Characterization The particle size distribution of sample ashes was determined by sieving three replicates, of approximately 5 kg each, with the following U.S. standard sieve sizes: ½” (12.5 mm), 3/8” (9.5 mm), No. 4, No.10, No. 20, No. 50. Mass retained on each sieve was recorded. Size-separated
8
Page 8 of 27
samples of bottom ashes were desired for this study because AMR often fractionates ashes based on size. Samples B and C were separated with sieves into four size fractions: > 12.5 mm, 12.5 to 9.5 mm, 9.5 to 4.75 mm, and < 4.75 mm. The >12.5 mm size fraction was not used in the
ip t
experiments described here. The subsamples are denoted with the subscripts 12.5/9.5, 9.5/4.5, and 9.5, were size reduced through crushing and cutting. In a large aluminum bowl, approximately 0.5 kg of ash was struck with a 1 kg hammer 5-8 times. The
an
resulting ash was sieved through a 9.5 mm standard U.S. sieve. The portion of the sample passing the sieve was set aside and that retained on the sieve was again struck with the hammer
M
5-8 times. This process was repeated until no ash was retained on the sieve. For uncrushable, malleable, or metallic pieces, a bolt cutter was used to cut the material to pass a 9.5 mm sieve;
d
these pieces did not account for a significant portion of the material (99.9%) metallic form, and was obtained as a 1 mm diameter wire from a scientific supply vendor; it was cut into 10 mm lengths prior to being added to A9.5. 5Fe Nomenclature for these additions is: “ A>9.5” representing the A>9.5 sample dosed with 5% Fe by
mass.
9
Page 9 of 27
2.4 Ferromagnetic Metal Content and Removal In a second experiment bottom ashes were processed to remove ferrous metal, and leaching from these was compared to unprocessed samples. For each subsample from Facilities B and C
ip t
(B12.5/9.5, B9.5/4.5 B
