Coal utilization byproducts (CUBs)—pubs.awma.org/gsearch/em/2005/5/murphy.pdf · Mercury Adsorption Capacity of CUBs NETL in-house Table 2. Other DOE/NETL CUB environmental research

awma.org may 2005 em 19

emfeature

Coal utilization byproducts (CUBs)—also known as coal combustion (by)products—are producedby the combustion or gasification of coal and include flyash, bottom ash, boiler slag, gasifier ash and slag, and fluegas desulfurization (FGD) solids. The American Coal AshAssociation estimates that 129 million tons of CUBs wereproduced in the United States in 2002,1 of which approxi-mately 83 million tons (65%)were disposed of in landfillsand approximately 46 milliontons (35%) were recycled.Some of the most successfulapplications for recycledCUBs include use as a partialsubstitute for cement inconcrete (fly ash), structuralfill material (bottom ash andfly ash), blasting grit (boilerslag), and in the manufactureof wallboard (FGD gypsum).Several types of CUBs are used in mine reclamation applica-tions, in particular fluidized-bed combustion ash, whosealkaline properties make the ash useful in the remediation ofacidic mine backfills. Other applications for fly ash includeuse as mineral filler for paints, roofing shingles, carpet back-ing, ceiling and floor tiles, and many other building materi-als and industrial products.2

CUBs generated from coal-fired power plants are composedprimarily of benign mineral components, but also contain trace

elements of aluminum, arsenic, boron, cadmium, lead, mer-cury, and selenium. Tests conducted by the U.S. Departmentof Energy’s National Energy Technology Laboratory (DOE/NETL) and others indicate that there is minimal potential re-lease of these trace elements from CUBs through leaching—leaching is a chemical process in which water or other liquidpercolates through a material that results in the separation of

soluble components from thematerial to the liquid. The U.S.Environmental ProtectionAgency (EPA), under the Re-source Conservation and Re-covery Act (RCRA), regulatesCUBs from coal-fired powerplants. Wastes defined as “haz-ardous” are federally regulatedunder RCRA Subtitle C, while“nonhazardous wastes” arestate-regulated under RCRASubtitle D. In its 1999 Report

to Congress, EPA determined that CUBs did not generally ex-hibit the characteristics of hazardous waste.3 Consequently,CUBs are currently categorized as nonhazardous wastes underRCRA. The continued regulatory categorization of CUBs as anonhazardous solid waste is obviously an important factor inminimizing the cost of disposal and is critical to CUB market-ability for beneficial use applications.

According to EPA estimates, in 1999, U.S. power plantsburned 786 million tons of coal containing approximately75 tons of mercury. It is estimated that approximately 48tons of mercury were emitted to the atmosphere, while theremaining 27 tons, along with 107 million tons of CUBs,were captured by air pollution control devices, such as elec-trostatic precipitators (ESPs) and FGD systems.4 Recentlyissued EPA regulations to reduce mercury from U.S. coal-fired power plants will increase the capture of mercury inthese devices resulting in higher concentrations of mercury

William W. Aljoe ([email protected]) is a projectmanager, Thomas J. Feeley, III, is a technology manager, and

Lynn A. Brickett is a project manager for the U.S. Departmentof Energy’s National Energy Technology Laboratory (DOE/

NETL) in Pittsburgh, PA. James T. Murphy is a seniorenvironmental engineer for Science Applications

International Corp. in Pittsburgh, PA.

Tests conducted by DOE/

NETL and others indicate that

there is minimal potential

release of trace metals,

including mercury, from CUBs

through leaching.

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20 em may 2005 awma.org

in the corresponding CUBs that lead to greater concernover their environmental characteristics in both disposal andutilization applications. For example, the use of activatedcarbon injection for mercury capture would increase themercury concentration in fly ash collected by ESPs.

DOE/NETL’S CUB RESEARCH PROGRAMDOE/NETL is conducting a comprehensive research anddevelopment program to enhance the environmental per-formance of coal-based power plants. The goal of the CUBresearch activity is to increase coal byproduct use in theUnited States from current levels of approximately 35% to50% by 2010. However, achieving this goal will be challeng-ing for several reasons. First, increasing concern over thefate of mercury and other trace metals captured inbyproducts will bring about increased scrutiny as to how thesematerials are to be used and disposed. Second, the installa-tion of FGD technology to comply with sulfur dioxide (SO2)regulations could significantly increase the number of CUBsgenerated by coal-fired power plants. Third, the injection ofsorbents such as activated carbon to control mercury couldnegatively impact the sale of fly ash and FGD gypsum forcement and wallboard. Fly ash with a high level of activatedcarbon may not be acceptable as a substitute for Portland

cement in concrete because the carbon interferes with theperformance of air entraining admixtures, which are used inconcrete to improve workability and freeze/thaw attributes. Theconcern with FGD gypsum is that mercury could be releasedto the atmosphere during a heating step in the wallboard manu-facturing process. Fourth, nitrogen oxides (NOx) controls couldalso negatively impact the beneficial use of fly ash due to exces-sive levels of unburned carbon and/or ammonia.

The focus of this article is DOE/NETL’s research on thefate of mercury in CUBs. The research includes testing vari-ous CUB materials for potential environmental releasemechanisms, such as leaching (chemical dissociation ofmercury caused by water percolation through the CUB),volatilization (thermal dissociation of mercury caused byheating the CUB), and microbiological transformation (mi-crobiological dissociation of mercury caused by bacterialprocesses in the CUB). Table 1 lists ongoing research projectswhose focus is on the environmental fate of mercury in CUBs.Test results to date indicate there is minimal potentialrelease of mercury from CUBs in either disposal or benefi-cial use applications. While much of the current research isfocused on the fate of mercury, the impact of other tracemetals, such as arsenic, boron, and selenium, and other con-stituents like ammonia and activated carbon are also being

Table 1. DOE/NETL CUB research projects focused on the fate of mercury.

Project Title Lead Company

CUB Analysis from Activated Carbon Injection Mercury Control Field Demonstrations ADA-ES and Reaction EngineeringCUB Analysis from Wet FGD Reagent Mercury Control Field Demonstrations Babcock & WilcoxCharacterization of Coal Combustion Byproducts for the Re-Evolution of Mercury into Ecosystems Consol EnergyMercury and Air Toxics Element Impacts of Coal Combustion Byproduct Disposal and Utilization UNDEERCThe Effect of Mercury Controls on Wallboard Manufacture CBRC—TVAFate of Mercury in Synthetic Gypsum Used for Wallboard Production USG Corp.Column Leaching Tests NETL in-houseRapid Leaching Protocol NETL in-houseMercury Adsorption Capacity of CUBs NETL in-house

Table 2. Other DOE/NETL CUB environmental research projects.

Project Title Lead Company

Water Quality Monitoring at an Abandoned Mine Site CBRC—USGSVarra Coal Ash Burial Project CBRC—CGRSEnvironmental Performance Evaluation of Filling and Reclaiming a Surface Coal Mine with CBRC—Ish Inc. Coal Combustion ByproductsEffects of Large-Scale CUB Applications on Groundwater: Case Studies CBRC—West Virginia UniversityBoron Transport from Coal Combustion Product Utilization and Disposal Sites CBRC—Southern Illinois UniversityEffects of Ammonia Absorption on Fly Ash Due to Installation of SCR Technology CBRC—GAI ConsultantsSpeciation and Attenuation of Arsenic and Selenium at Coal Combustion Byproduct Management Facilities EPRIThe Impact of Adsorption on the Mobility of Arsenic and Selenium Leached from Coal Combustion Products CBRC—Southern Illinois UniversitySoil Stabilization and Drying by Use of Fly Ash CBRC—University of WisconsinEnvironmental Evaluation for Utilization of Ash in Soil Stabilization CARRC—UNDEERCEnvironmental Effects of Large-Volume FGD Fill CBRC—GAI ConsultantsFlue Gas Desulfurization By-products Provide Sulfur and Trace Mineral Nutrition for Alfalfa and Soybean CBRC—Ohio State UniversityQuantifying CUBs for Agricultural Land Application CBRC—UNDEERCCUBs as Capping Material NETL in-house



evaluated. Table 2 lists DOE/NETL’s other CUB environ-mental characterization research projects. In addition, DOE/NETL directs a significant research effort toward thedevelopment of market applications for CUBs. Additionalinformation on all DOE/NETL CUB projects can befound online at www.netl.doe.gov/coal/E&WR/cub.

Many of the DOE/NETL CUB research projects are beingconducted through two consortia. Since 1998, DOE/NETLhas sponsored the Coal Ash Resources Research Consortium(CARRC; www.undeerc.org/carrc), an international consor-tium of industry and government representatives, scientists,and engineers working together to advance coal ash utiliza-tion, which is administered by the University of North DakotaEnergy & Environmental Research Center (UNDEERC). Alsoformed in 1998, DOE/NETL’s own Combustion By-ProductsRecycling Consortium (CBRC; wvwri.nrcce.wvu.edu) is admin-istered through West Virginia University’s Water ResearchInstitute. Academia, industry associations, federal and stateregulatory agencies, and power generators provide assistanceto CBRC through an advisory steering committee.

The following sections provide a brief description andsummary of results on the fate of mercury in CUBs fromseveral DOE/NETL research projects. Further details on thetest procedures, conditions, and results for other trace met-als can be found in the referenced technical reports andconference papers.

CUB Analysis from Activated Carbon InjectionMercury Control Field Demonstrations

In 2001 and 2002, ADA-ES Inc. and Reaction Engineer-ing International conducted field demonstrations ofactivated carbon injection (ACI) for mercury control at fourcoal-fired power plants: Alabama Power’s E.C. Gaston,PG&E’s Brayton Point, We Energies’ Pleasant Prairie, andPG&E’s Salem Harbor.5-8 Results of leaching tests con-ducted on the CUBs produced during these demonstra-tions are described below.

E.C. Gaston. The particulate collection configuration at theGaston power plant was unique because it included both ahot-side ESP for primary particulate collection and a com-pact hybrid particulate collector (COHPAC) fabric filterbaghouse downstream of the ESP. During mercury con-trol testing, activated carbon was injected downstream ofthe ESP and upstream of the COHPAC to prevent carboncontamination of the ESP ash. Mercury concentrations inthe baseline (pre-ACI injection) ash from the COHPACmeasured 0.2–2 microgram per gram (µg/g); whereas, atan ACI feed rate of 1.5 lb per million actual cubic feet (lb/MMacf) of flue gas, mercury concentrations in the com-bined activated carbon/fly ash byproduct ranged from 10to 50 µg/g. Since most of the fly ash was captured in thehot-side ESP, total mercury concentration in the COHPAC

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byproduct was significantly higher than it would be in appli-cations with ACI located upstream of the primary particulatecontrol device.

Brayton Point. The Brayton Point particulate collection sys-tem was also somewhat atypical because two cold-side ESPswere used in series. Most of the fly ash was collected in theupstream ESP; during mercury control testing, activated car-bon was injected between the upstream and downstreamESPs. The baseline ash from both the upstream and down-stream ESPs contained 0.2–0.53 µg/g of mercury; whereas,at an ACI feed rate of 10–20 lb/MMacf, the downstreamESP ash contained 0.4–1.4 µg/g of mercury. The reasonfor the relatively low mercury content of the downstreamESP ash at Brayton Point (compared to the GastonCOHPAC ash) is that most of the mercury in the flue gaswas not captured by the activated carbon, but was insteadcaptured by the fly ash in the upstream ESP. Apparently,the unburned carbon in the fly ash was sufficient on itsown to achieve a high degree of mercury capture acrossthe upstream ESP, leaving only a small amount to be col-lected by ACI and the downstream ESP. However, becausethe mercury captured by the upstream ESP was dilutedwith the bulk of the ash product, total mercury concentra-tions in the ash were very low.

Pleasant Prairie and Salem Harbor. The particulate collec-tion systems at Salem Harbor and Pleasant Prairie were moretypical of the current fleet of coal-fired power plants in theUnited States, one cold-side ESP unit at each plant, exceptthat the specific collection areas of the ESPs (i.e., the collec-tion plate area divided by flue gas flow rate) at both plantswere comparatively large. Baseline ash from the Pleasant Prai-rie ESP contained less than 0.5 µg/g of mercury; whereas, atan ACI feed rate of 10 lb/MMacf, the ash byproduct con-tained 0.5–5 µg/g of mercury. At Salem Harbor, mercury con-centrations ranged from 0.1 to 0.7 µg/g during both baseline

and ACI testing conditions. Like Brayton Point, much of themercury in the flue gas at Salem Harbor was collected by thecarbon in the baseline fly ash, thereby minimizing the addi-tion of mercury to the ash as the result of ACI.

Leaching Test Descriptions and Results. Leaching analyses wereconducted using the standard toxicity characteristic leachingprocedure (TCLP) and a procedure developed by UNDEERCknown as the synthetic groundwater leaching procedure(SGLP) on the combined activated carbon/fly ash byproductsthat were collected during ACI tests. The TCLP method wasdesigned to simulate leaching in an unlined sanitary landfillusing an acetic acid as the leaching solution. UNDEERC de-veloped the SGLP method to more realistically simulate CUBleaching in typical disposal environments. For the SGLP analy-sis, deionized water was used as the leaching solution with a20:1 liquid-to-solid ratio.

Table 3 summarizes the leaching test results at the fourACI test plants. For the Gaston and Pleasant Prairie ash samples,the amount of mercury in the leachate was at or below themeasurement detection limit of 0.01 microgram per liter (µg/L). For Salem Harbor, only one sample exceeded the detec-tion limit (0.034 µg/L); this sample came from the baselineash (i.e., no ACI). For Brayton Point, leachate of samples fromboth the nontreated (upstream) ESP and the ACI-treated(downstream) ESP contained detectable amounts of mercury(0.01–0.07 µg/L). However, no discernable differences inleachate concentrations were found between the upstream anddownstream ESPs, or at different levels of ACI injection. Thisappears to be related to the fact that most of the mercury re-moval at Brayton Point occurred as the result of high carbonlevels in the baseline ash. It should be noted that the leachatemercury concentrations at all four plants were more than anorder of magnitude lower than the 0.77-µg/L freshwatercriterion continuous concentration and 1.4-µg/L freshwatercriterion maximum concentration for mercury under thefederal water quality criteria for protection of aquatic life.

Table 3. ADA-ES leaching test results for ACI ash byproducts.

ACI Rate Mercury in Solid Mercury in Leachate (µg/L)Plant Sample Location (lb/Mmacf) (µg/g) TCLP SGLP

Gaston COHPAC B-Side 1.5 10 – 50 0.01 BDLa

Gaston COHPAC B-Side 1.5 10 – 50 N/Ab BDLGaston COHPAC B-Side 1.5 10 – 50 BDL BDLPleasant Prairie ESP Hopper Composite 10 0.5 – 5 BDL BDLPleasant Prairie ESP Hopper Composite 10 0.5 – 5 BDL BDLPleasant Prairie ESP Hopper Composite 10 0.5 – 5 BDL N/ABrayton Point Downstream ESP 0 0.2 – 0.53 BDL 0.01Brayton Point Upstream ESP 0 0.2 – 0.32 0.02 0.05Brayton Point Downstream ESP 10 0.4 – 1.4 0.07 0.03Brayton Point Upstream ESP 10 N/A 0.03 0.01Brayton Point Downstream ESP 20 0.4 – 1.4 BDL 0.01Brayton Point Upstream ESP 20 N/A 0.02 0.02Salem Harbor ESP Row A 0 0.1 – 0.7 0.034 BDLSalem Harbor ESP Row A 10 0.1 – 0.7 BDL BDLSalem Harbor ESP Row A 10 0.1 – 0.7 BDL BDL

aBDL = below detection limit of 0.01 µg/L. bN/A = not available.



Ash byproduct samples from Gaston and Pleasant Prairiewere also tested using other leaching procedures for com-parison. Samples from Gaston were analyzed using a sulfuricacid leaching solution with a pH of 2, using procedures simi-lar to TCLP and SGLP to simulate use in an acid mine drain-age environment. Ash byproduct samples from PleasantPrairie were analyzed using the ASTM water leaching proce-dure (ASTM D-3987). The Pleasant Prairie samples were alsoleached over longer periods of 30 and 60 days using SGLP,due to concerns that potentially slower reactions can take placewith high-calcium ashes. All of the additional test results werebelow or equal to the 0.01-µg/L detection limit.

CUB Analysis from Wet FGD ReagentMercury Control Field Demonstrations

In 2001, Babcock & Wilcox (B&W) and McDermott Tech-nology Inc. (MTI) carried out joint full-scale field testing of aproprietary liquid reagent to enhance mercury capture incoal-fired power plants equipped with wet FGD systems.9 Thefield tests were conducted at two power plants: Michigan SouthCentral Power Agency’s 60-MW Endicott Station and CinergyCorp.’s 1300-MW Zimmer Station. Both plants burn Ohiohigh-sulfur bituminous coal and use cold-side ESPs for par-ticulate control. Endicott uses a limestone wet FGD systemwith in-situ forced oxidation; while Zimmer uses a magne-sium-enhanced lime wet FGD system with ex-situ forced

oxidation. Table 4 presents a summary of the average mer-cury concentrations for the coal and process byproduct streamsamples for both Endicott and Zimmer. For both plants, themajority of mercury was found in the wet FGD slurry fines,rather than in the gypsum. Although not shown in Table 4,the majority of liquid stream samples were “nondetects” formercury (i.e., measuring less than 0.5 µg/L), with a fewsamples measuring 1–3 µg/L.

B&W and MTI also evaluated the byproduct streamsamples for their potential to volatilize mercury at elevatedtemperatures using a thermal dissociation test (TDT) de-veloped by MTI. The TDT method involves the gradual heat-ing of a CUB test sample in an oven while measuring the

Table 4. Mercury concentration in B&W and MTIprocess samples.

Mercury (µg/g; dry)Process Sample Endicott Zimmer

Coal 0.21 0.15ESP ash 0.32 0.016Gypsum 0.70 0.055Wet FGD slurry 0.76 0.49Wet FGD fines 38 (by TDT) 13.3

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September 14-16, 2005 | The Westin CalgaryCalgary, Alberta, Canada

With the Kyoto Protocol coming into force in February 2005, countries thathave ratified the Protocol are implementing plans to meet their requirementsunder the international agreement. Since the Protocol is a small, yetimportant, first step aimed at reducing greenhouse gas emissions fromanthropogenic sources, there is considerable interest in the changes neededto address long-term global climate change. This conference examinessome of these fundamental changes through four half-day sessions:

• Transforming international and domestic policy to address long-term climate change

• Energy sector modifications needed to address long-term climate change

• The role of markets in encouraging solutions to climate change

• Process, product, and technology innovation to address climate change



Table 5. CONSOL fly ash mercury volatilization test results.

Mercury in Solid CUB (µg/g)As 3 Month 6 Month

Plant ID CUB Type Control Equipment Coal Source Received 100EF 140EF 100EF 140EF

3 Bottom ash Mg Lime FGD Ohio high-sulfur bituminous 0.09 0.09 0.10 0.12 0.17

6 Fly ash ESP IL/W.KY blend bituminous 0.29 0.34 0.32 0.38 0.34



4 Fly ash ESP Illinois No.6 bituminous 0.08 0.11 0.12 0.13 0.12

4 Fly ash ESP Illinois No.6 bituminous 0.08 0.09 0.10 0.11 0.13

off-gas mercury concentration. Results of TDC tests forEndicott and Zimmer FGD gypsum indicated that there wasminimal mercury volatilization below 140 °C (284 °F) andpeak mercury volatilization at 250 °C (482 °F). The 140 °Chold temperature was chosen as representative of tempera-tures FGD byproducts are likely to encounter when used asfeedstock during the manufacture of wallboard. However,some wallboard manufacturing processes may expose FGDbyproducts to temperatures higher than 140 °C; conse-quently, DOE/NETL is sponsoring additional research (de-scribed later in this article) to determine the fate of mercuryin wallboard manufacturing facilities.

One of the significant findings from the B&W and MTItest program was that the mercury in the wet FGD wasteslurry from both plants was associated primarily with smallparticle size impurities in the slurry (fines) and not boundto the larger gypsum particles. Therefore, it may be possibleto use particle separation techniques and provide separatelandfill disposal of the fines, if necessary, for use in applica-tions where mercury release is a concern.

CUB Analysis from Ash and FGD Byproduct Disposaland Beneficial-Use Applications

CONSOL Energy Study. CONSOL Energy conducted an ex-tensive evaluation of mercury in CUBs from 14 coal-firedpower plants from August 2000 to October 2004.10,11 The plantsrepresented a range of coal ranks and air pollution controldevice configurations and the evaluation included leachingand volatilization tests of bottom ash, fly ash, wet and dry FGDscrubber solids, and products from ACI tests. Testing was alsoconducted on products made from CUBs, such as cement,gypsum wallboard, and manufactured aggregates. In addition,groundwater-monitoring wells at two CUB disposal sites wereevaluated for mercury on a quarterly basis over one year.

Mercury leaching rates from eight CUBs were measuredusing modified TCLP tests with leaching solutions at threepH values: 2.8, 4.9, and 7.0 (distilled water). Mercury con-centrations in all leachates were less than the 1-µg/L detec-tion limit. (Note: These leaching tests were conducted forscreening purposes; the detection limit was relatively high,

but was below the drinking water standard of 2 µg/L.) Sixleachate samples from fly ashes at two sites (three samplesper plant) were tested at a lower mercury detection limit of0.0002 µg/L. The mercury concentrations from these sixsamples ranged from 0.0075 to 0.084 µg/L.

Mercury volatilization tests were conducted using a pro-cedure developed by CONSOL. The CUB samples were splitinto two ovens and held at constant temperatures of 38 °C(100 °F) and 60 °C (140 °F) for six months. Some prelimi-nary results from the fly ash volatilization tests are shown inTable 5. The results indicate a slight increase in mercuryconcentration in the CUB solids over time, suggesting thepossibility that the ash samples could have adsorbed addi-tional mercury from the ambient air.

Groundwater monitoring wells at an active wet FGD dis-posal area and an active fly ash slurry impoundment wereevaluated quarterly for one year for possible mercury releases.Preliminary results for the first and second quarter samplesfrom the FGD disposal site indicate less than 1 µg/L mercuryconcentration for all six monitoring wells and two seepagesites. Likewise, the first quarter results for the ash impound-ment site indicate less than 1 µg/L mercury concentrationsfor all 11 monitoring wells and a leachate collection site.

UNDEERC Studies. UNDEERC is conducting a multifacetedset of experiments to determine the level of mercury thatmay volatilize from CUBs and the potential for microbio-logical activity in the release of mercury from CUBs.12,13 Mer-cury vapor release tests were conducted on six fly ash samplesat ambient and near-ambient temperatures (37 °C/99 °F)and microbiological tests were conducted on two samples.The fly ash samples were taken from two Powder River

The amount of mercury leached from C

significantly lower than the federal d

quality criteria for the protection of aqu



Basin (PRB) coals, two eastern bituminous coals, and twoSouth African coals. They were selected because of their rela-tively high mercury concentrations, ranging from 0.112 to0.736 µg/g, and their corresponding potential for releasingmeasurable amounts of mercury vapor. However, as with theCONSOL volatilization experiments, five of the six samplesacted as mercury sinks (i.e., the mercury content of the ashesincreased over time); for the sixth sample, its behavior as amercury source or sink could not be determined.

Results from the microbiological tests are not yet availablebecause the testing protocols have recently been redesignedto take advantage of improved analytical procedures for de-termining organomercury and methyl mercury species that

may be produced via microbiological processes. Preliminaryresults suggest that microbiologically mediated vapor releasesof mercury from CUBs may be somewhat greater than innonmicrobiologically mediated experiments, but are still verylow (i.e., less than 60 × 10-12 g/g). Microbiologically mediatedmercury releases appeared to be enhanced when aerobic con-ditions and a ready food source for bacteria were present.

Fate of Mercury in Synthetic GypsumUsed for Wallboard Production

TVA Study. The Tennessee Valley Authority (TVA) is con-ducting a CBRC-funded laboratory study to examine ther-mal decomposition profiles and leaching characteristics ofmercury in wet FGD byproduct materials and gypsum wall-board. The study includes mercury measurements usinga laboratory-scale wallboard manufacturing process. Dueto the relatively low mercury concentrations, analysis ofthese materials will be accomplished using cold vapor

atomic fluorescence (CVAF) spectroscopy. Results from thisstudy are currently under review.

USG Study. In July 2004, USG Corp. signed a cooperativeagreement with DOE/NETL to perform a two-year study tomeasure potential releases of mercury from synthetic FGDgypsum during the wallboard manufacturing process. Test-ing will be conducted at three wallboard manufacturingplants using synthetic FGD gypsum produced from fourpower plants. The four power plants represent a broad cross-section of synthetic gypsum sources, including bituminous-and Texas lignite-fired boilers, with and without selectivecatalytic reduction (SCR) controls, and limestone- and lime-FGD processes. The field tests include mercury measure-ments of all input and output process streams to obtaincomplete mercury balances for the wallboard manufactur-ing plants. Samples of the synthetic FGD gypsum will be evalu-ated in laboratory simulation tests as a means of comparisonto the field measurements. In addition, TCLP leaching testswill be conducted on the wallboard products to determinepotential mercury releases in landfills. Testing at the firstwallboard plant began in July 2004; the project is scheduledfor completion in October 2005.

CUB Analysis for Mercury Control Technology FieldTesting in 2004 and 2005

DOE/NETL issued a competitive solicitation in July 2004for one or more contractors to conduct independent labo-ratory analysis of CUBs generated during DOE/NETL’smercury control technology field tests conducted at 14 coal-fired power plants in 2004 and 2005. The purpose of thesolicitation was to ensure accurate and consistent labora-tory procedures are used to determine the environmentalfate of mercury in CUBs. DOE/NETL expects to award thecontract in April 2005.

DOE/NETL In-House CUB ResearchAn important part of the CUB research program are theevaluations performed by DOE/NETL’s in-house research

Table 6. DOE/NETL column leaching test results for mercury.

Cumulative Leached Mercury (ng/g)Ash Mercury Leachant SolutionSample # Source (ng/g) LOI % H2O HAc Na2CO3 SP H2SO4

FA50 NETL pilot 1156 1.31 0.259 0.410 0.130 0.094 0.148combustor



FA52 Carbon injection 88,100 28.66 0.003 0.047 0.026 0.003 0.004ash— Gaston

FA55 Carbon injection 1527 16.08 0.846 0.043 1.263 0.465 0.083ash—Brayton Point

FA51 Power plant 1587 6.46 0.012 0.754 0.007 0.009 0.020FA58 NETL pilot 87 1.79 0.015 0.045 0.517 0.0005 0.012

combustor

CUB samples tested by DOE/NETL is

drinking water standards and water

uatic life.



team, which are directed atproviding an unbiasedsource of data on the envi-ronmental characteristics ofcoal byproducts and devel-oping new applications forCUBs. Recent research hasfocused on the developmentof a short-term leaching testthat can be used by industryand state regulatory agenciesto inexpensively develop ap-propriate coal byproductmanagement strategies.DOE/NETL’s current in-house CUB research projectsrelated to mercury are sum-marized below.

Column Leaching Tests. DOE/NETL has been conductingcolumn leaching tests onCUB samples using sevenleachant solutions: deion-ized water, synthetic ground-water, synthetic precipitation,acetic acid, sodium carbon-ate, sulfuric acid, and ferricchloride.14-16 In one study,leaching tests were con-ducted on 38 fly ash samplescollected from pulverizedcoal-fired power plantsacross the United States.Leachate samples were ana-lyzed for iron, aluminum,manganese, magnesium, cal-cium, sodium, potassium,sulfur, arsenic, barium, beryl-lium, cadmium, cobalt, chro-mium, copper, nickel, lead,antimony, selenium, andzinc. Table 6 presents a sum-mary of the test results. Thedata are presented in termsof cumulative leached mer-cury measured in nanogramper gram (ng/g; ng is equiva-lent to 10-9 g). Leaching testswere completed onceleachant concentrationsdropped below the measure-ment detection limit. As a re-sult, the leaching tests varyin duration from 30 to 180days. Although the data mayappear to vary, all of theleaching results, with one

REFERENCES1. 2002 Coal Combustion Product Survey;

American Coal Ash Association: Au-rora, CO, 2002; available online atwww.ACAA-USA.org.

2. Buyer’s Guide to Coal Ash ContainingProducts; Energy & Environmental Re-search Center, University of North Da-kota: Grand Forks, ND; availableonline at www.undeerc.org/carrc/BuyersGuide/default.asp.

3. Report to Congress—Wastes from the Com-bustion of Fossil Fuels; EPA-530-S-99-010;U.S. Environmental ProtectionAgency, Washington, DC, March 1999.

4. Control of Mercury Emissions from Coal-Fired Electric Utility Boilers: Interim Report;EPA-600/R-01-109; U.S. Environmen-tal Protection Agency, Washington,DC, April 2002.

5. Senior, C. et al. Characterization of FlyAsh from Full-Scale Demonstration ofSorbent Injection for Mercury Controlon Coal-Fired Power Plants. Presentedat the Air Quality III Conference, Ar-lington, VA, September 2002.

6. Senior, C. et al. Characterization of FlyAsh from Full-Scale Demonstration ofSorbent Injection for Mercury Controlon Coal-Fired Power Plants. Presentedat the Mega Symposium, Washington,DC, May 2003.

7. Senior, C. et al. Characterization of FlyAsh from Full-Scale Demonstration ofSorbent Injection for Mercury Controlon Coal-Fired Power Plants. Presentedat the Air Quality IV Conference, Ar-lington, VA, September 2003.

8. Feeley, T.J.; Murphy, J.T.; Hoffmann,J.W.; Granite, E.J.; Renninger, S.A.DOE/NETL’s Mercury ControlTechnology Research Program forCoal-Fired Power Plants; EM 2003,October, 16-23.

9. Full-Scale Testing of Enhanced MercuryControl Technologies for Wet FGD Systems;Final Report to the U.S. Departmentof Energy under Contract No. DE-FC26-00NT41006. Prepared byBabcock & Wilcox Co., Barberton,OH, and McDermott Technology Inc.,Houston, TX, August 2002.

10. Withum, J.; Schwalb, A.; Statnick, R.Characterization of Coal CombustionBy-Products for the Re-Evolution ofMercury into Ecosystems. Presentedat the Air Quality III Conference, Ar-lington, VA, September 2002.

11. Schwalb, A.M.; Withum, J.A. The Evo-lution of Mercury From Coal Combus-tion Materials and By-Products. Pre-sented at the DOE/NETL MercuryControl Technology Research andDevelopment Program Review Meet-ing, Pittsburgh, PA, August 2003.

12. Hassett, D.J. et al. Potential for Mer-cury Release from Coal CombustionBy-Products. Presented at the Air Qual-ity III Conference, Arlington, VA, Sep-tember 2002.

13. Hassett, D; Heebink, L. Long-TermMercury Vapor Release from CCBs.Presented at the Air Quality IV Confer-ence, Arlington, VA, September 2003.

14. Kim, A. NETL CUB Characterization.Presented at the DOE/NETL MercuryControl Technology Research andDevelopment Program Review Meet-ing, Pittsburgh, PA, August 2003.

15. Kazonich, G.; Kim, A.; Dahlberg, M.Comparison of Leaching Results forThree High Mercury Fly Ash Samples.Presented at the Air Quality IV Confer-ence, Arlington, VA, September 2003.

16. Kim, A.; Kazonich, G. Coal Combus-tion By-Products: Major Cation Solu-bility. Presented at the InternationalAsh Utilization Symposium hosted bythe University of Kentucky Center forApplied Energy Research in 2001.

exception, indicate less than 0.001% of the mercury leachedfrom the ash samples. The exception is Sample #FA58, whichleached approximately 0.006% of the mercury using thesodium carbonate leachant.

Mercury Adsorption Capacity of CUBs. DOE/NETL is also con-ducting tests to measure the mercury adsorption capacity offly ash.14 The adsorption tests are conducted by mixing flyash in a water solution that is spiked with a known amountof mercury. Adsorption isotherms are calculated for eachfly ash sample that plot the amount of mercury adsorbedversus the amount of mercury in solution. Based on adsorp-tion tests of two bituminous fly ash samples, it appears thatcarbon content affects adsorption, with high-carbon ash hav-ing a higher mercury adsorption capacity than low-carbonash. For example, with a pH of 2 and 1,000 µg/L of mer-cury in solution, the high-carbon ash (5.2% loss-on-ignition,LOI) adsorbed approximately 20,000 µg/kg of mercury,compared to only 2,500 µg/kg of mercury adsorbed by thelow-carbon ash (1.3% LOI).

SUMMARYDOE/NETL’s research has helped to further scientific un-derstanding of the environmental characteristics of CUBsin both disposal and beneficial utilization applications. Thefollowing general observations can be drawn from results ofthe research that has been carried out to date:

• There appears to be only minimal mercuryrelease to the environment in typical disposal orutilization applications for CUBs generated usingACI control technologies.

• There appears to be only minimal mercury releaseto the environment in typical disposal and utiliza-tion applications for CUBs generated using wetFGD control technologies. The potential release ofmercury from wet FGD gypsum during themanufacture of wallboard is still under evaluation.

• The amount of mercury leached from CUBsamples tested by DOE/NETL is significantlylower than the federal drinking water standardsand water quality criteria for the protection ofaquatic life; in many cases, leachate concentra-tions were below the standard test methoddetection limits.

DOE/NETL will continue to partner with industry andother key stakeholders in carrying out research to betterunderstand the fate of mercury and other trace elements inthe byproducts from coal combustion.

ACKNOWLEDGMENTSThis article would not have been possible without the ef-forts of the DOE/NETL project managers and researcherswho provided valuable technical input. In particular, theauthors would like to acknowledge the contributions of AnnKim, Swenam Lee, Chuck Miller, and Bob Patton. Disclaimer:References in this article to any specific commercial prod-uct or service are to facilitate understanding and do not im-ply endorsement by the U.S. Department of Energy. em


Documents

Coal utilization byproducts (CUBs)—pubs.awma.org/gsearch/em/2005/5/murphy.pdf · Mercury Adsorption Capacity of CUBs NETL in-house Table 2. Other DOE/NETL CUB environmental research