International Journal of Coal Geology 94 (2012) 337–348

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International Journal of Coal Geology

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Leaching of elements from bottom ash, economizer fly ash, and fly ash from twocoal-fired power plants

Kevin B. Jones ⁎, Leslie F. Ruppert, Sharon M. SwansonU.S. Geological Survey, Mail Stop 956, Reston, VA 20192, USA

⁎ Corresponding author. Tel.: +1 703 648 6448; fax:E-mail address: kevinjones@usgs.gov (K.B. Jones).

0166-5162/$ – see front matter. Published by Elsevier Bdoi:10.1016/j.coal.2011.10.007

a b s t r a c t

a r t i c l e i n f o

Article history:Received 25 July 2011Received in revised form 4 October 2011Accepted 8 October 2011Available online 15 October 2011

Keywords:Coal combustion productsFruitland FormationLeachingPittsburgh coalTCLPSGLP

To assess how elements leach from several types of coal combustion products (CCPs) and to better under-stand possible risks from CCP use or disposal, coal ashes were sampled from two bituminous-coal-firedpower plants. One plant located in Ohio burns high-sulfur (about 3.9%) Upper Pennsylvanian Pittsburghcoal from the Monongahela Group of the Central Appalachian Basin; the other in New Mexico burns low-sulfur (about 0.76%) Upper Cretaceous Fruitland Formation coal from the San Juan Basin, Colorado Plateau.The sampled CCPs from the Ohio plant were bottom ash (BA), economizer fly ash (EFA), and fly ash (FA);the sampled CCPs from the New Mexico plant were BA, mixed FA/EFA, FA, and cyclone-separated coarseand fine fractions of a FA/EFA and FA blend. Subsamples of each ash were leached using the long-term leach-ing (60-day duration) component of the synthetic groundwater leaching procedure (SGLP) or the toxicitycharacteristic leaching procedure (TCLP, 18-hour duration). These ashes were all alkaline. Leachate concen-trations and leachabilities of the elements from the CCPs were similar between corresponding CCP types(BA, EFA, and FA) from each plant. The leachabilities of most elements were lowest in BA (least leachable)and increased from EFA to FA (most leachable). Ca and Sr were leached more from EFA than from eitherBA or FA. Leachability of most elements also increased as FA particle size decreased, possibly due in part toincreasing specific surface areas. Several oxyanion-forming elements (As, Mo, Se, U, and V) leached moreunder SGLP than under TCLP; the opposite was true for most other elements analyzed.

Published by Elsevier B.V.

1. Introduction

Coal combustion by coal-fired power plants, cement plants, andsteel plants produces large quantities of coal combustion products(CCPs), which include ashes, slag, and flue-gas desulfurization resi-dues. Coal-fired power plants in the USA produced 135 million tonsof CCPs in 2009 (ACAA, 2011); bottom ash (BA) and fly ash (FA)make up about 60% (80 million tons) of these. Combustion of coalconcentrates many of its minor and trace elements in the resultingCCPs. Some of the elements that are concentrated in CCPs relative tothe source coal (e.g., As, Cd, and Pb) are potentially hazardous tohuman health or the environment, and may enter the environmentunder some CCP use or disposal conditions.

Coal ashes can be classified as BA, FA, or a specific kind of FA calledeconomizer fly ash (EFA). BA is noncombustible material that is tooheavy to be entrained in the flue gas stream and falls to the bottomof the furnace during coal combustion. Particles of BA are typicallyangular, irregularly shaped, and sand- to gravel-sized (Meawad etal., 2010). FA is composed of vaporized and combusted materialentrained in theflue gas stream. At least someof this vaporizedmaterial

+1 703 648 6419.

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condenses, as flue gases cool, into mainly fine-sand-sized and smaller,glassy, hollow silicate spherules called cenospheres. A portion of theFA can be captured by electrostatic precipitators (ESPs) or by fabricfilters in baghouses (Meawad et al., 2010). Economizer fly ash (EFA)is FA that is captured at the economizer unit, located along the flue gaspathway between the furnace and the ESPs or baghouses. As a result,EFA contains some small, angular, non-volatilized particles entrainedin the flue gas stream and some spherules that condensed from fluegas at higher temperatures than those at the ESPs or baghouses. EFA isalso coarser than FA collected at ESPs or baghouses. Of the BA and FAproduced in the USA, about 80% is FA and 20% is BA (ACAA, 2011).

About 32 million tons, or 40%, of BA and FA produced in the USAare used, for example, as agricultural soil amendments, abandonedmine fill, or in wallboard, concrete, or highway construction (ACAA,2011). The remaining 48 million tons are stored in piles, landfills,monofills (landfills that contain only ash), or holding ponds (ACAA,2011). Use rates of CCPs elsewhere in the world range from about30% in India and China (Asokan et al., 2005; Pei-wei et al., 2007) tonear 100% in Germany and the Netherlands (Barnes and Sear, 2006).

In the USA, CCPs are classified as non-hazardous solid wastes underSubtitle D of the Resource Conservation and Recovery Act (RCRA, PublicLaw 94-580, 1976), so CCP disposal in lined impoundments is allowed.However, in June 2010, theU.S. Environmental Protection Agency (EPA)proposed two options to regulate CCPs destined for impoundments,

flue gas and fly ash

boiler economizerelectrostaticprecipitator

BA EFA FA

coal

exha

ust

Fig. 1. Schematic diagram showing CCP sampling locations at the Ohio power plant.This plant also contains a flue gas desulfurization system (not pictured) that capturesadditional trace elements in the flue gas. Abbreviations: BA = bottom ash, EFA =economizer fly ash, FA = fly ash.

338 K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

including storage, settling, and aeration pits, ponds, and lagoons; theproposed rule does not include mine fills or beneficial use (e.g., as wall-board or cement additives) of CCPs. The first option is to list CCPs asspecial wastes under the more stringent RCRA Subtitle C, which essen-tially labels them as hazardous. Under this option, all CCPs, from thepoint of generation through the closing of any landfill, alongwith relatedsurface water run-on and run-off controls, dust controls, groundwatermonitoring, financial assurance, and post-closure care would requirepermits and inspections (U.S. EPA, 2010). The second option is forCCPs to remain listed as RCRA Subtitle D non-hazardous solid waste,but to establish national standards to ensure that landfills are properlysited, constructed, monitored, and closed: composite liners, ground-water monitoring, corrective action for any releases, and closure andpost-closure care standards would be required.

Many researchers (e.g., de Groot et al., 1989; Gitari et al., 2009;Jankowski et al., 2006; Karuppiah and Gupta, 1997; Kosson et al.,2002; Popovic et al., 2005; Praharaj et al., 2002; Sheps-Pelleg andCohen, 1999; Wang et al., 1999, 2009; Ward et al., 2009) have inves-tigated the possible leaching of elements from CCPs into the environ-ment under various CCP use or disposal scenarios. Many leachantshave been used in these studies, from pure water to strong acidic andalkaline solutions. However, as several researchers have discussed(Hassett, 1994; Hassett et al., 2005; Kim and Hesbach, 2009; Kosson etal., 2002; Zandi and Russell, 2007), some of these leachants are unreal-istic, simulating conditions atypical for CCP use or disposal and theseleaching results should be interpreted cautiously.

For example, researchers sometimes use the toxicity characteristicleaching procedure (TCLP; U.S. EPA, 2004) to investigate CCPs. Thisprocedure quantifies the “toxicity characteristic” of elements in a waste,used by the EPA to assess whether a waste is considered hazardous dueto its toxicity. The TCLP uses a buffered acetic acid solution as the leachantto simulate disposal intermixedwith garbage in amunicipal landfill. CCPsare rarely, if ever, disposed in such a setting, although this low-pH leach-ing could be relevant to CCPs used to remediate acid mine drainage. Infact, water mixed with some CCPs forms alkaline solutions, in contrastto the acidic leachant used in the TCLP (Hassett, 1994). AlthoughTCLP results regarding CCPs are informative, they are unlikely to providean analog for most environmental conditions in which CCPs are used ordisposed.

To better understand CCP leaching and its possible environmentalimpacts, we investigated the leaching of trace metals from severalkinds of ash resulting from combustion at two power plants of bitu-minous coals, one high-sulfur (about 3.9%) and one low-sulfur (about0.76%). We used two standard batch leaching procedures. The first wasthe synthetic groundwater leaching procedure (SGLP; Hassett, 1998),which simulates the interaction of ash with groundwater, using as theleachant reagent water, sampled groundwater, or a solution similar togroundwater. Such an interaction could occur as a result of disposal ofash in a monofill if its walls or liner failed. The second was theTCLP, selected to allow direct comparison of our results with similarTCLP-based studies by others. The primary goal of our research wasto assess the extent to which trace elements leach from coal ashes,in order to understand possible risks from their use or disposal. Asecondary objective was to assess differences in leaching betweenashes from high-sulfur and low-sulfur coals and between differenttypes and particle sizes of coal ashes.

2. Materials and methods

Coal combustion products were sampled from two pulverized-coal-fired power plants in Ohio and New Mexico, USA. The Ohioplant burns bituminous high-sulfur (about 3.9%) locally availableUpper Pennsylvanian Monongahela Group Pittsburgh coal from thecentral Appalachian Basin. Tewalt et al. (2001) discuss the geologyof this coal in detail. From this plant, feed coal, bottom ash (BA), econ-omizer fly ash (EFA), and fly ash (FA) were collected as separate

composite samples twice weekly over an eight-week period in 2007for a total of 16 coal samples and 48 ash samples. In this study, weleached two of these BA, EFA, and FA sample suites (the fourth andthe tenth), a total of 6 samples, and characterized the correspondingfeed coals. These two sample suites were chosen randomly from thesuites in which all samples were complete and were successfully col-lected on the same day. Fig. 1 schematically shows the sampling loca-tions for the Ohio plant. BA was collected from a storage pond. EFAwas collected from the economizer unit. FA was collected from allESP hoppers and combined into a single sample. Flue gas temperatureat the ESPs is about 160 °C (330 °F) in this power plant.

The New Mexico plant burns a bituminous low-sulfur (about0.76%) coal blend from three locally available coal beds in the UpperCretaceous Fruitland Formation, San Juan Basin, Colorado Plateau.Fassett (2000) discusses the geology of this formation. Feed coal,BA, FA mixed with EFA, and FA without EFA were collected from theplant on 18 consecutive days in July and August, 2007. In this study,we used two days of samples, collected on 27 July and 8 August.These dates were selected randomly from the days on which all sam-ples were successfully collected. Fig. 2 schematically shows the sam-pling locations for this plant. During plant operation, BA is dumpedinto a storage area, and still-warm BA samples were collected fromthe center of this area. At this plant, FA is captured in two baghouses;one collects solely FA and the other collects roughly equal amounts ofFA and EFA. Ash samples were collected from each baghouse. At thepower plant, a blend of ashes from the two silos undergoes cycloneparticle-size separation so that the fine portion can be sold, primarilyfor use in concrete. We sampled the coarse (generally>40 μm) andfine (generallyb40 μm) fractions of the FA/EFA mixture that resultedfrom this separation. In all, five kinds of ash samples were collectedfrom the New Mexico plant: 1) BA, 2) a FA and EFA mixture, 3) FA, 4)the coarse fraction of a mixture of types 2 and 3, and 5) the fine fractionof a mixture of types 2 and 3. Flue gas temperature in this power plant isabout 430–450 °C (800–850 °F) at the economizer unit and about 105 °C(220 °F) at the baghouses.

Proximate analyses (moisture, volatilematter, ash, and fixed carbon)of the feed coals were performed using ASTM method D3172 (ASTMInternational, 2007). Total S contents of the feed coals were measuredusing the direct combustion and infrared absorption method (ASTMmethod D4239, ASTM International, 2007). These and all other analysesand leaching procedures in this study were performed at a single com-mercial laboratory.

Total concentrations (all valences) of Al, As, Ba, Be, Ca, Co, Cr, Cu,Fe, K, Li, Mg, Mn, Mo, Ni, Pb, Sr, Ti, V, and Zn in subsamples of each

boiler baghouse

BA mixed EFAand FA

FA

coal

cycloneseparator

coarse EFA/FA

fine EFA/FA

exha

ust

baghouse

flue gas and fly ash

Fig. 2. Schematic diagram showing CCP sampling locations at the New Mexico power plant. This plant also contains an inhibited oxidizing scrubber (not pictured) that capturesadditional trace elements in the flue gas. The fine fraction from the cyclone separator is sold for use in concrete. Abbreviations: BA = bottom ash, EFA = economizer fly ash,FA = fly ash.

Table 1Proximate analyses of feed coals from the Ohio and New Mexico power plants.

Ohio day 4feed coal

Ohio day 10feed coal

New Mexico22 July 2007feed coal

New Mexico8 August 2007feed coal

Moisture (%) 3.22 5.69 11.2 11.7Volatile matter (%) 38.9 38.0 31.4 31.4Fixed carbon (%) 48.2 46.7 34.3 34.2Ash (%) 9.64 9.61 22.5 23.3Total (%) 100.0 100.0 99.4 100.6

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dry, unleached ash were measured by inductively coupled plasma–atomic emission spectroscopy (ICP–AES), and total concentrations(all valences) of Ag, Cd, Cs, Ge, Rb, Sb, Sc, Se, Th, Tl, and U in subsam-ples of each dry, unleached ash were measured by inductively coupledplasma–mass spectrometry (ICP–MS); both these techniques usedASTM method D6357 (ASTM International, 2007). P and Si in subsam-ples of each ash were measured by ICP–AES (ASTM method D6349;ASTM International, 2007); C and S in subsamples of each ash weremeasured by the combustion and infrared absorption method (ASTMmethods D5373 for C and D4239 for S; ASTM International, 2007);and Hg in subsamples of each ash was measured by cold-vaporatomic absorption spectroscopy (AAS; ASTM method D6722; ASTMInternational, 2007).

A 10.0-gram (g) subsample of each ash from each plant was sub-jected to the toxicity characteristic leaching procedure (TCLP), i.e.,EPA method 1311 (U.S. EPA, 2004), which specified a buffered aceticacid solution (Extraction Fluid #1 of TCLP section 5.7.1, pH=4.93) asthe leachate, and a leaching duration of 18 h. The TCLP procedure wasmodified to use 10-g samples rather than the stipulated 100-g sam-ples because of the limited quantity of ash available to us. NaturalpH values of the ashes were determined by mixing 5.0 g of ash with96.5 mL of reagent water as specified in TCLP section 7.1.4. A second10.0-g sample of each ash was leached using the long-term leaching(LTL) component of the synthetic groundwater leaching procedure(SGLP; Hassett, 1998). The synthetic groundwater used as the SGLPleachate was prepared by adding 0.50 g of sodium sulfate and 1.00 gof sodium bicarbonate to 1 L of Type IV reagent water, producing apH of ~8.5, and concentrations of approximately 436 mg/L Na and113 mg/L S. This preparation was outlined by Pflughoeft-Hassett etal. (2005), and simulates typical North Dakota, USA groundwater.The leaching duration, specified by the LTL SGLP, was 60 days. A200-mL aliquot of extraction liquid was used in both TCLP and SGLP,resulting in a liquid-to-solid (LS) ratio of 20 mL/g. The TCLP and SGLPboth used 30-rpm end-over-end agitation for their full durations.

Total concentrations (all valences) of the elements Al, Ba, Ca, Co,Fe, K, Li, Mg, Mn, Mo, Na, P, S, Si, Sr, Ti, V, and Zn in each leachatewere measured by EPA method 6010B, ICP-AES (U.S. EPA, 2004);Ag, Be, Cd, Cr, Cs, Ge, Ni, Pb, Rb, Th, Tl, and U in each leachate weremeasured by EPA method 6020, ICP–MS (U.S. EPA, 2004); Hg ineach leachate was measured by EPA method 7470, cold-vapor AAS(U.S. EPA, 2004). The elements As, Cu, Sb, Sc, and Se in the leachateswere measured by either ICP–AES or ICP–MS; the type of analysis isindicated in the tables showing the element concentrations in theleachates, in the Results section.

3. Results

Results of proximate analyses of the feed coals from the Ohio andNew Mexico power plants are shown in Table 1. Feed coals from theOhio plant contained 3.66% and 3.67% total S on days 4 and 10, respec-tively. Feed coals from theNewMexico plant contained 0.71% and 0.76%total S on 22 July and 8 August 2007, respectively.

Element concentrations in the dry ashes from the Ohio and NewMexico power plants are shown in Tables 2 and 3, respectively.Abundance of most elements in the ashes from each plant is generallyleast in BA and increases from EFA to FA — the relationship expectedby Clarke (1993)— for As, C, Cd, Cu, Ge, Pb, S, Sb, Se, Tl, U, V, Zn, and pos-sibly Hg. Element abundance in ash also increases from coarse FA to fineFA for most elements analyzed: Al, As, Be, Cd, Co, Cr, Cs, Cu, Ge, Hg, Li,Mg, Mo, Na, Ni, P, Pb, Rb, Sb, Sc, Se, Sr, Th, Ti, Tl, U, V, and Zn.

Element concentrations in the SGLP and TCLP leachant blanks areshown in Table 4. Concentrations in the SGLP leachant blank werebelow quantitation limits for all elements except Ca (0.2 mg/L) andZn (0.03 mg/L). Concentrations in the TCLP leachant blank werebelow quantitation limits for all elements except Ba (0.6 mg/L), Ca(4.2 mg/L), K (3.2 mg/L), Mg (0.5 mg/L), and Zn (0.15 mg/L).

The natural pH values of the Ohio plant ashes were 8.4 and 8.5 forthe BA, 10.4 and 10.8 for the EFA, and 10.1 and 10.3 for the FA(Table 5). The New Mexico plant ashes were slightly more alkaline;the BA pH was 9.5, and pH values for the various FAs were 11.0–11.8(Table 6). After adding 3.5 mL of 1 N HCl to these solutions as speci-fied in TCLP section 7.1.4, pH values were all reduced to less than2.0 (Tables 5 and 6), stipulating the use of the 4.93-pH ExtractionFluid #1 in the TCLP (U.S. EPA, 2004).

SGLP leachate concentrations for the Ohio plant ashes are in Table 7and for the New Mexico plant ashes are in Table 8. TCLP leachateconcentrations for the Ohio plant ashes are in Table 9 and for the

Table 2Element concentrations (mg/kg) in ashes from the Ohio power plant. Italicized values were measured by ICP–MS; C and S were measured by combustion and infrared detection; Hgwas measured by cold vapor AAS; all others were measured by ICP–AES. Quantitation limits: a1000 mg/kg, b100 mg/kg, c50 mg/kg, d10 mg/kg, e5 mg/kg, f1 mg/kg. g0.5 mg/kg,h0.25 mg/kg. i0.2 mg/kg. j0.1 mg/kg. k0.01 mg/kg. Abbreviations: BA = bottom ash, EFA = economizer fly ash, FA = fly ash.

Element Day 4 Day 10

BA EFA FA BA EFA FA

Agj 0.93 0.91 1.05 0.94 0.93 1.04Ale 92,400 90,900 81,400 76,000 80,700 86,000Asf 4.8 70.3 58.2 4.5 42.6 51.2Bag 296 428 284 211 337 224Bej 9.9 10.7 9.9 8.4 11.4 9.6Cb 3800 3900 10,000 3600 4500 6700Cae 9100 18,600 9070 7560 9890 7910Cdj 0.23 0.74 1.04 0.30 0.54 0.76Coh 48.6 50.4 47.4 47.7 52.0 48.1Crh 348 263 146 284 262 140Csi 6.54 6.18 7.39 5.01 6.67 5.44Cug 62.3 69.4 74.4 55.5 64.6 66.7Fef 197,000 242,000 155,000 189,000 243,000 194,100Gei 29.4 51.6 38.3 30.1 40.5 42.5Hgk b0.01 b0.01 0.03 b0.01 b0.01 0.02Kd 13,800 12,800 15,600 8280 7840 14,000Lig 97.5 81.0 103 81.4 78.3 97.1Mge 2260 2650 1970 1650 2080 1510Mng 284 306 213 308 303 221Mog 5.6 5.0 6.4 4.6 4.8 4.2Nae 2480 2420 13,400 2120 2020 10,700Nig 201 142 94 180 159 94Pc 740 1220 1180 830 1090 960Pbf 15.0 24.1 36.1 15.2 19.3 31.7Rbi 88.0 74.4 92.6 64.2 83.1 78.1Sa b1000 3000 6000 b1000 1000 6000Sbi 0.88 2.43 1.94 0.90 1.79 1.64Sci 26.8 20.7 28.3 18.5 20.8 22.5Sei 2.46 1.10 8.85 0.78 1.41 6.72Sic 201,000 173,000 204,000 192,000 184,000 188,000Srg 422 529 491 320 403 416Thi 16.2 12.1 13.8 13.0 13.4 11.8Tih 5070 4660 5420 5040 4910 5140Tlj 0.77 2.09 4.36 0.60 1.55 3.70Ui 5.94 7.10 6.87 5.87 6.65 6.72Vh 204 236 242 206 225 224Zng 57.0 75.6 110 54.0 67.1 91.5

340 K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

New Mexico plant ashes are in Table 10. The elements Ag and Hgwere not measured in any leachate above their quantitation limitsof 0.001 mg/L and 0.0002 mg/L, respectively. The elements Be, Co, Cs,Li, and Th were below quantitation limits (0.001 mg/L, 0.005 mg/L,0.001 mg/L, 0.2 mg/L, and 0.001 mg/L, respectively) in most leachatesand never exceeded 2.5 times the quantitation limit in any leachatesample. These elements will not be discussed further.

Most trace elements detected in the leachates at concentrationsgreater than a few times the quantitation limit are least abundant inBA leachates and most abundant in FA leachates. Similarly, coarse-FA leachate contains less of these elements than does fine-FA leach-ate. This pattern generally applies for As, Cr, Cs, Ge, Mo, P, Rb, S, Sb,Se, Tl, U, and V.

4. Discussion

4.1. Leachate concentrations and toxicity

The TCLP simulates municipal landfill disposal and is used by theU.S. EPA to determine whether a waste is classified as hazardousbased on its toxicity (40 CFR 261.24); it was used in this study mainlyto facilitate comparisons with previous leaching studies by othersusing the TCLP. Element concentrations in all of our TCLP ash leach-ates (Tables 9 and 10) were below toxicity characteristic thresholds(Table 11). The TCLP is, however, a poor predictor of leaching underalkaline conditions (U.S. EPA, 1996), such as those resulting from

water contacting any of the ashes discussed in this paper. The toxicitycharacteristic (i.e., the concentration resulting from the TCLP) forelements in CCPs may therefore be a poor indicator of possible envi-ronmental risk from the leaching of ashes under many disposal con-ditions, although it may be useful in a situation where coal ashes areused to neutralize acid mine drainage.

Using a leachant with a pH similar to that of groundwater orsurface water where CCPs are used, stored, or disposed (such as theSGLP), rather than the acetic acid of the TCLP, in many instances couldbe a more representative test for whether a CCP might be hazardousbased on its toxicity. The pH of the synthetic groundwater used in thisstudy was ~8.5; the median pHs of surficial or near-surface aquiferslocated near (within tens of km) the Ohio and New Mexico powerplants are 7.6 (range 6.3–8.9; Brown, 2008) and 7.3 (range 6.6–8.5;Ohio EPA, 2008), respectively. Because the coal ashes studied herewere observed to create alkaline solutions (pH 8.4–11.8) when mixedwith water, the slight alkaline bias of the SGLP leachant as comparedto local waters is probably overshadowed by the natural alkalinity ofthe ashes (e.g., see leachate pH data in Jankowski et al., 2006).Other differences in water chemistry between the two sites and thesynthetic North Dakota groundwater used could affect the leach-ability of some elements, however, so we caution against using theresults of this study as a direct analog for either the Ohio or NewMexico environments.

To provide context for the element concentrations in SGLP leach-ates, we compared them to EPA national (USA) recommended water

Table 3Element concentrations (mg/kg) in ashes from the New Mexico power plant. Italicized values were measured by ICP–MS; C and S were measured by the combustion and infraredabsorption method; Hg was measured by cold vapor AAS; S was measured by combustion and infrared absorption; all others were measured by ICP–AES. Quantitation limits: a1000mg/kg, b100 mg/kg, c50 mg/kg, d10 mg/kg, e5 mg/kg, f1 mg/kg. g0.5 mg/kg, h0.25 mg/kg. i0.2 mg/kg. j0.1 mg/kg. k0.01 mg/kg. Abbreviations: BA= bottom ash, EFA= economizer flyash, FA = fly ash.

Element 22 July 2007 8 August 2007

BA EFA+FA FA Coarse FA/EFA Fine FA/EFA BA EFA+FA FA Coarse FA/EFA Fine FA/EFA

Agj 0.85 0.99 1.04 0.85 1.15 0.88 1.00 1.06 0.88 1.21Ale 115,000 122,000 118,000 118,000 124,000 118,000 122,000 124,000 110,000 113,000Asf 3.0 9.5 11.4 5.0 16.2 3.5 10.1 11.0 5.7 17.8Bag 489 350 645 619 504 751 460 484 359 790Bej 4.0 4.7 4.7 3.8 5.4 4.7 5.4 5.6 4.4 6.5Cb 8600 3600 3500 4700 3200 7300 3800 4700 6300 3200Cae 9640 8180 10,800 12,300 10,200 12,100 10,100 11,000 9740 8950Cdj 0.15 0.47 0.54 0.29 0.77 0.16 0.39 0.42 0.23 0.65Coh 19.5 21.0 21.6 19.2 22.9 20.9 20.4 21.2 18.4 24.3Crh 20.4 24.0 24.7 18.7 27.4 29.6 26.7 28.2 21.1 32.4Csi 3.03 2.79 3.14 3.05 3.19 7.90 3.70 3.74 3.62 4.98Cug 42.1 53.7 54.0 41.0 63.2 40.8 49.2 46.4 39.8 59.8Fef 25,100 21,500 20,400 24,100 21,600 29,100 25,200 23,200 27,900 23,900Gei 4.53 6.41 7.06 5.16 9.63 5.14 7.55 8.56 6.13 12.5Hgk b0.01 0.016 0.127 0.065 0.118 b0.01 0.023 0.100 0.068 0.089Kd 7540 7140 7080 7490 7420 12,600 9240 8920 8910 9160Lig 92.5 89.6 90.4 86.5 97.8 80.7 117 121 108 110Mge 1610 2350 2130 1880 2180 4020 2500 2160 1710 1960Mng 244 190 179 257 174 169 201 180 244 152Mog 1.5 4.8 5.3 3.1 7.4 0.7 4.0 4.9 2.0 8.9Nae 7250 7930 6900 6600 9270 9340 9870 9210 7850 8320Nig 12.1 15.8 15.9 11.1 18.2 17.8 16.4 16.2 12.6 18.5Pc 790 920 1000 830 1050 520 740 740 700 830Pbf 22.0 37.7 38.8 22.7 57.0 14.6 34.2 39.0 20.7 57.2Rbi 31.8 30.5 32.6 32.1 32.8 73.0 41.1 41.6 40.6 50.5Sa b1000 b1000 b1000 b1000 b1000 b1000 b1000 b1000 b1000 7000Sbi 0.86 2.19 2.39 1.18 3.48 1.17 2.47 2.57 1.40 3.92Sci 10.5 15.2 14.6 11.0 15.7 16.8 20.4 16.0 14.8 15.7Sei 0.73 6.69 7.50 4.88 5.74 1.33 8.48 9.91 6.33 11.3Sic 303,000 308,000 309,000 314,000 299,000 309,000 292,000 293,000 297,000 292,000Srg 215 172 217 206 266 207 276 275 176 231Thi 21.8 19.7 21.3 15.5 21.5 25.3 18.7 21.6 16.1 23.4Tih 4800 5280 5340 4800 5450 4790 5260 5400 4820 5590Tlj 0.35 0.68 0.77 0.38 1.04 0.51 0.94 1.01 0.59 1.49Ui 8.25 9.83 9.77 7.94 11.5 9.83 10.2 10.4 8.89 12.3Vh 76.4 91.1 93.3 77.2 105 93.0 90.0 92.6 77.0 110Zng 22.8 53.8 56.4 28.3 80.7 28.4 51.7 53.5 29.4 80.1

341K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

quality criteria (U.S. EPA, 2009; Table 11). These criteria are thefreshwater criteria maximum concentration (CMC), to which aquaticlife can be exposed briefly without unacceptable effects, and thefreshwater criteria continuous concentration (CCC), to which aquaticlife can be exposed indefinitely without unacceptable effects. The CMCsand CCCs are less than the toxicity characteristic levels. In an environ-mental coal-ash disposal scenario, some dilution of leachates wouldlikely occur during any subsurface flow, by dilution with groundwa-ter or possible precipitation or sorption. The extent of this dilutionand attenuation depends on many factors, making a general-casedilution-attenuation factor (DAF) difficult to quantify effectively.However, some regulators (e.g., U.S. EPA, 1990) have accounted forthe dilution and attenuation of contaminant concentrations by using ageneral DAF of 100 (i.e., contaminant concentrations at a site of interestsuch as a well or a waterway are assumed to be 1% of those at a nearbycontaminant source).

No elements in the SGLP leachates from the CCPs from eitherpower plant (Tables 7 and 8) exceed the CMCs or CCCs (Table 11)after applying a DAF of 100. Without applying this DAF and consider-ing only undiluted, unattenuated leachates, As, Cr, and Se in someSGLP leachates exceed the CMC and/or CCC. No CMC exists for Se,but SGLP FA leachate from the Ohio plant (Table 7) contains about32 times as much Se as the CCC. SGLP fine FA leachate from theNew Mexico plant (Table 8) contains Se at up to 66 times the CCC,and all types of EFA and FA SGLP leachate from this plant contain at

least 24 times the CCC. The recommended water quality criteria forCr are specific to the less toxic Cr(III) and more toxic Cr(VI), but thisstudy assessed only total Cr. In a worst-case scenario, if all the leachedCr is hexavalent (see Sheps et al., 1999), SGLP FA leachates from theOhio plant (Table 7) contain up to about 5 times the Cr as the Cr(VI)CMC and about 7 times the Cr(VI) CCC. Similarly, some SGLP FA leach-ates from the New Mexico plant (Table 8) contain up to about 8 timesthe Cr as the Cr(VI) CMC and about 12 times the Cr(VI) CCC. Arsenicalso exceeds the CMC and CCC: As concentrations in SGLP FA leachatesfrom the Ohio plant (Table 7) are more than double the CMC, and Asconcentrations in some SGLP FA leachates from the New Mexico plant(Table 8) are five times the CMC and more than double the CCC.

For comparison with waters near the two power plants, a surficialaquifer near (tens of km from) the New Mexico power plant contains0.003–1.2 mg/L As (median 0.0335 mg/L), up to 0.37 mg/L Cr (median0.12 mg/L) and up to 0.037 mg/L Se (median 0.0025 mg/L) (Brown,2008). A near-surface aquifer near (about 8 km from) the Ohio powerplant contains b0.002 mg/L As and Se and up to 0.05 mg/L Cr (OhioEPA, 2008). The concentrations of As in most ash SGLP leachates forthe New Mexico power plant, then, exceed the median As concen-tration in a nearby aquifer (by an order of magnitude for fine FA)but do not exceed the maximum concentration measured there. Atthe Ohio plant, on the other hand, As concentrations in all ashSGLP leachates exceed those in a nearby near-surface aquifer; FASGLP leachates contain hundreds of times the concentration of As

Table 4Blank element concentrations (mg/L) for SGLP and TCLP. Italicized values were measuredby ICP–MS; Hg was measured by cold vapor AAS; all others were measured by ICP–AES.Quantitation limits: a1 mg/L, b0.5 mg/L, c0.3 mg/L. d0.2 mg/L, e0.1 mg/L. f0.05 mg/L.g0.02 mg/L. h0.01 mg/L, i0.005 mg/L, j0.002 mg/L, k0.001 mg/L, l0.0002 mg/L. Abbrevia-tions: NA = not analyzed, SGLP = synthetic groundwater leaching procedure, TCLP =toxicity characteristic leaching procedure.

Element SGLP blank (mg/L) TCLP blank (mg/L)

Agi b0.005 b0.005Ale b0.1 b0.1Asg b0.02 b0.02Bac b0.3 0.6Bek b0.001 b0.001Cad 0.2 4.2Cdj b0.002 b0.002Coi b0.005 b0.005Crh b0.01 b0.01Csh b0.01 b0.01Cuh b0.01 b0.01Fef b0.05 b0.05Geh b0.01 b0.01Hgl b0.0002 b0.0002Kb b0.5 3.2Lid b0.2 b0.2Mge b0.1 0.5Mnh b0.01 b0.01Mog b0.02 b0.02Nih b0.01 b0.01Pa b1 b1Pbg b0.02 b0.02Rbh b0.01 b0.01Sa NA b1Sbg b0.02 b0.02Sch b0.01 b0.01Seg b0.02 b0.02Sib b0.5 b0.5Srh b0.01 b0.01Tii b0.005 b0.005Tlg NA b0.02Uh b0.01 b0.01Vi b0.005 b0.005Znh 0.03 0.15

Table 5pH values for ash leachates from the Ohio power plant. Abbreviations: BA = bottomash, EFA = economizer fly ash, FA = fly ash.

Day 4 Day 10

BA EFA FA BA EFA FA

TCLP initial pH 8.4 10 10 8.5 11 10TCLP pH with HCl 1.6 1.7 1.8 1.6 1.6 1.8TCLP final pH 5.0 5.1 5.5 5.0 5.1 5.4SGLP final pH 8.6 8.0 9.5 8.6 8.4 9.6

Table 7Element concentrations (mg/L) in SGLP ash leachates from the Ohio power plant. Theelements Agj, Bac, Bem, Cdj, Coi, Hgk, Pbj, Scj, Thj, and Znh were not measured abovetheir quantitation limits in any of these leachates. Italicized values were measured byICP–MS; Hg was measured by AAS; all others were measured by ICP–AES. Quantitationlimits: a1mg/L, b0.5 mg/L, c0.3 mg/L, d0.2 mg/L, e0.1 mg/L, f0.05 mg/L, g0.02 mg/L, h0.01 mg/L,i0.005 mg/L, j0.001 mg/L, k0.0002mg/L, l0.01 mg/L for ICP–AES and 0.001 mg/L for ICP–MS,m0.005 mg/L for BA and 0.001 mg/L for EFA and FA. Abbreviations: BA = bottom ash,EFA = economizer fly ash, FA = fly ash.

Element Day 4 Day 10

BA EFA FA BA EFA FA

Ale 0.5 0.2 3.0 0.8 0.4 1.9Asl 0.006 0.12 0.78 0.011 0.17 0.79Cae 3.5 78.7 6.1 3.3 25.3 4.6Crm b0.005 0.007 0.080 0.005 0.009 0.073Csj b0.001 b0.001 0.002 b0.001 b0.001 0.002Cu 0.013i 0.009j b0.01h 0.015i 0.009j b0.01h

Fef b0.05 b0.05 0.07 1.72 0.08 0.10Gem b0.005 0.009 0.017 b0.005 0.007 0.026Kb 1.0 6.3 10.8 0.8 2.5 7.4Lid b0.2 b0.2 0.3 b0.2 b0.2 b0.2Mge 0.6 3.0 4.2 0.3 1.5 2.0Mnh b0.01 0.01 b0.01 0.03 b0.01 b0.01Mog b0.02 0.07 0.19 b0.02 0.05 0.16Nad 407 403 1060 402 415 957Nim b0.005 0.006 0.001 0.044 0.004 b0.001Pa b1 b1 2 b1 b1 3Rbj 0.003 0.016 0.023 0.003 0.008 0.016Sa 106 250 426 107 177 386Sbl b0.001 0.001 0.007 b0.001 b0.02 0.006Sel 0.002 0.002 0.16 0.002 0.003 0.15Si 2.4b 4a 1.6b 3.5b 3.3b 2.6b

Srh 0.03 0.78 0.07 0.03 0.38 0.06Tii b0.005 b0.005 b0.005 0.022 b0.005 b0.005Tlm b0.005 0.001 0.005 b0.005 b0.001 0.005Uj b0.001 0.008 0.016 b0.001 0.005 0.015Vi b0.005 0.036 0.387 0.009 0.045 0.436

342 K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

in the near-surface aquifer. Concentrations of Se in SGLP FA leach-ates from the Ohio plant are greater than about 80 times the maxi-mum measured in a local near-surface aquifer. Concentrations ofSe in SGLP leachates from the various FAs and EFAs from the NewMexico plant are up to about 9 times the maximum measured in alocal near-surface aquifer. Concentrations of Cr in SGLP FA leachatesfrom the New Mexico plant do not exceed the maximum measured

Table 6pH values for ash leachates from the New Mexico power plant. Abbreviations: BA = bottom

Element 22 July 2007

BA EFA+FA FA Coarse FA/EFA Fine F

TCLP initial pH 9.5 11 11 11 11TCLP pH with HCl 1.6 1.7 1.7 1.6 1.6TCLP final pH 5.1 5.4 5.3 5.5 5.3SGLP final pH 8.7 10.6 10.3 11.4 9.9

in the near-surface aquifer; concentrations of Cr in SGLP FA leach-ates from the Ohio plant (up to 0.08 mg/L) only slightly exceed themaximum concentration (0.05 mg/L) in the near-surface aquifer.

4.2. Mobility of elements

Element concentrations in leachates were greater when waterwas the leachant (SGLP) than when the acetic acid solution was theleachant (TCLP) for the oxyanion-forming elements As, Mo, Se, U,and V. The opposite was the case for most other elements, includingCd, Co, Cu, Ge, Mn, Ni, Tl, and Zn. In general, transition metals will besorbed at high pH due to negatively charged surface sites; more sorp-tion of oxyanions will occur at low pH due to positively chargedsurface sites. The behavior of trace elements in ash over varying pHis complex, however: some elements have been observed to leachmore from CCPs as pH increases, some leach more as pH decreases,and some amphoteric or oxyanion-forming elements leach more inboth acidic and alkaline environments than in neutral ones (Dellantonioet al., 2010; Kosson et al., 2009; Zandi and Russell, 2007). This complexbehavior makes it difficult to assess the modes of occurrence of traceelements in CCPs using only SGLP and TCLP, as these two leachingprocedures provide only two pH-points to characterize potentially

ash, EFA = economizer fly ash, FA = fly ash.

8 August 2007

A/EFA BA EFA+FA FA Coarse FA/EFA Fine FA/EFA

9.5 12 12 12 111.5 1.8 1.7 1.8 1.75.1 5.8 5.6 7.1 5.58.7 11.8 11.6 12.0 11.1

Table 8Element concentrations (mg/L) in SGLP ash leachates from the New Mexico power plant. The elements Agk, Bek, Cdk, Coj, Csk, Hgl, Lie, Pbk, Thk, and Tlk were not measured abovetheir quantitation limits in any of these leachates; Zni was not measured above the SGLP blank concentration of 0.03 mg/L. Italicized values were measured by ICP–MS; Hg wasmeasured by AAS; all others were measured by ICP–AES. Quantitation limits: a5 mg/L, b1 mg/L, c0.5 mg/L, d0.3 mg/L, e0.2 mg/L, f0.1 mg/L, g0.05 mg/L, h0.02 mg/L, i0.01 mg/L,j0.005 mg/L, k0.001 mg/L, l0.0002 mg/L, m0.01 mg/L for ICP–AES and 0.001 mg/L for ICP–MS. Abbreviations: BA = bottom ash, EFA = economizer fly ash, FA = fly ash.

Element 22 July 2007 8 August 2007

BA EFA+FA FA Coarse FA/EFA Fine FA/EFA BA EFA+FA FA Coarse FA/EFA Fine FA/EFA

Alf 0.6 5.2 4.6 10.2 4.5 0.9 12.1 12.4 7.9 10.6Asm 0.007 0.20 0.21 0.088 0.34 0.003 0.13 0.19 0.02 0.35Bad b0.3 b0.3 b0.3 b0.3 b0.3 b0.3 b0.3 b0.3 0.4 b0.3Caf 6.2 4.2 3.5 3.4 4.2 5.3 11.4 4.9 35.3 2.7Crk 0.001 0.059 0.056 0.016 0.087 0.001 0.077 0.072 0.023 0.13Cum 0.008 0.020 0.014 0.014 0.034 0.009 0.010 0.011 0.008 b0.01Feg 0.13 0.05 0.07 0.11 b0.05 0.11 0.05 0.07 0.07 0.06Gek 0.001 0.011 0.027 0.001 0.043 0.001 b0.001 b0.001 b0.001 0.006Kc 0.7 b0.5 b0.5 b0.5 b0.5 0.8 0.8 0.6 0.6 0.7Mgf 0.4 0.1 0.3 b0.1 0.5 0.7 b0.1 b0.1 b0.1 b0.1Mni 0.01 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01Moh b0.02 0.16 0.18 0.07 0.27 b0.02 0.16 0.16 0.06 0.28Nae 400 397 400 398 397 404 398 382 396 389Nik b0.001 b0.001 0.001 b0.001 0.001 b0.001 b0.001 b0.001 b0.001 b0.001Pb b1 1 2 b1 3 b1 b1 b1 b1 b1Rbk 0.001 0.001 0.001 0.001 0.002 0.002 0.003 0.002 0.002 0.002Sb 110 121 121 110 129 109 122 118 106 134Sbk b0.001 0.020 0.018 0.011 0.029 b0.001 0.023 0.002 0.009 0.035Scm b0.001 b0.001 b0.001 0.002 b0.001 b0.001 0.002 0.002 0.002 b0.01Sem 0.002 0.15 0.23 0.15 0.29 b0.001 0.16 0.24 0.12 0.33Si 4.4c 8.4c 5.7c 30a 3.1c 3.1c 27a 25a 18a 13a

Sri 0.04 0.02 0.02 0.01 0.02 0.04 0.09 0.04 0.13 0.02Tij 0.014 b0.005 0.007 b0.005 b0.005 0.010 b0.005 b0.005 b0.005 b0.005Uk 0.001 0.025 0.026 0.003 0.041 0.001 0.001 0.003 b0.001 0.022Vj 0.008 0.269 0.272 0.124 0.382 0.009 0.337 0.403 0.111 0.394

Table 9Element concentrations (mg/L) in TCLP ash leachates from the Ohio power plant. Theelements Agk, Hgl, Pb, and Thk were not measured above their detection limits in anyof these leachates; Bad was not measured above its TCLP blank concentration of0.6 mg/L. Na was not analyzed. Italicized values were measured by ICP–MS; Hg wasmeasured by AAS; all others were measured by ICP–AES. Quantitation limits: a5 mg/L, b1 mg/L, c0.5 mg/L, d0.3 mg/L, e0.2 mg/L, f0.1 mg/L, g0.05 mg/L. h0.02 mg/L.i0.01 mg/L. j0.005 mg/L, k0.001 mg/L, l0.0002 mg/L, m0.01 mg/L for ICP–AES and0.001 mg/L for ICP–MS, n0.02 mg/L for ICP–AES and 0.001 mg/L for ICP–MS. Abbrevia-tions: BA = bottom ash, EFA = economizer fly ash, FA = fly ash.

Element Day 4 Day 10

BA EFA FA BA EFA FA

Alf 0.7 1.6 1.3 0.5 0.6 1.2Ask b0.001 0.014 0.043 b0.001 0.020 0.051Bek b0.001 0.002 0.001 b0.001 0.001 0.001Caf 8.7 269 259 10.9 164 255Cdk b0.001 0.005 0.016 b0.001 0.003 0.007Coj b0.005 0.009 0.011 b0.005 b0.005 0.007Crk 0.009 0.072 0.067 0.014 0.030 0.063Csk b0.001 b0.001 0.002 b0.001 b0.001 0.002Cui 0.02 0.10 0.33 0.04 0.06 0.08Feg 0.65 15.9 b0.05 5.62 5.72 b0.05Gek b0.001 0.028 0.110 b0.001 0.017 0.107Kc b3.2 9.4 18.0 b3.2 4.6 13.5Lie b0.2 b0.2 0.5 b0.2 b0.2 0.4Mgf 1.3 5.0 12.9 1.0 2.9 9.0Mni 0.16 1.18 0.51 0.44 0.74 0.42Moh b0.02 b0.02 0.11 b0.02 b0.02 0.10Nii 0.024 0.062 0.21 0.031 0.071 0.043Pbk 0.001 b0.001 b0.001 0.006 b0.001 b0.001Rbk 0.003 0.017 0.025 0.003 0.008 0.019Sb 5 173 439 6 82 362Sbn b0.001 b0.02 0.005 b0.001 b0.02 0.004Sck b0.001 0.002 0.003 b0.001 0.001 0.003Sem b0.001 0.021 0.11 b0.001 0.002 0.10Si 1.5c 8.8c 19a 1.2c 7.5c 19a

Sri 0.06 2.05 1.46 0.08 1.16 1.26Tij b0.005 0.010 b0.005 b0.005 0.006 b0.005Tlk b0.001 0.003 0.018 b0.001 0.002 0.017Uk b0.001 0.009 0.006 b0.001 0.004 0.007Vj b0.005 0.007 0.044 b0.005 0.029 0.048Zni 0.19 0.16 0.53 0.16 b0.15 0.24

343K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

complex pH-leachability relationships. The fact that several elementsleachmore using SGLP than TCLP, however, demonstrates that althoughthe acidic conditions of the TCLP are sometimes thought to reveal themaximum leachable amounts of elements in a substance, other leachingtests, such as the SGLP, allow more of some elements to leach.

Because some of an element may be leached from a CCP but thenbe immobilized by sorption or precipitation, we make a distinctionbetween the fraction of an element that was mobilized from a CCPand the possibly smaller fraction that then remained mobile in theleachate. Determining the fraction of an element that leached froman ash and remained mobile is straightforward. We calculated thisby dividing the mass of an element in leachate (the concentration ofan element in leachate multiplied by the 200 mL of leachant used inthe leaching procedures) by its mass in the unleached ash (the con-centration of an element in ash multiplied by the 10.0 g mass of theash samples used in the leaching procedures). Calculated fractionsof each element that remained in solution in CCP leachates are inTables 12–15. Using SGLP, Se, Mo, and As are the most mobile ele-ments in the coal ashes analyzed in this study (up to 100%, 80%, and42% of these elements, respectively, were leached and remained mo-bile). Using TCLP, Ca, Se, Mo, Cd, and As are the most mobile elements(up to 100%, 52%, 46%, 31%, and 18% of these elements, respectively,were leached and remained mobile).

Other researchers report various groups of trace elements withhigh mobilities or leachabilities from coal ashes: Br, I, Mo, and Sr fromGreek lignite FA using SGLP (Georgakopoulous et al., 2002); B, Mo, Cr,V, and Se from 23 European coal FAs using deionized water as theleachant (Moreno et al., 2005); As, Mo, and Se (leachabilities>50%)from coal FA from two United Kingdom power plants using TCLP anda water-based leaching procedure (Zandi and Russell, 2007); andMo, Se, B, Sr, Cr, and Sb from coal FA in decreasing order of watersolubility (Dellantonio et al., 2010). These studies tend to show, andour results agree, that the oxyanion-forming elements As, Mo, Sb, Se,and V are highly leachable (up to tens of percent mobilized in thisstudy), particularly from FAs; Cr and Sr leached from FAs at ~10% orless in this study. The work of Eary et al. (1990), Jankowski et al.

Table 10Element concentrations (mg/L) in TCLP ash leachates from the New Mexico power plant. The elements Agk, Coj, Csk, Hgl, Lie, Pbk, Sbh, and Thk were not measured above theirdetection limits in any of these leachates; Kc and Zni were not measured above their TCLP blank concentrations of 3.2 and 0.15 mg/L, respectively. Na was not analyzed. Italicizedvalues were measured by ICP–MS; Hg was measured by AAS; all others were measured by ICP–AES. Quantitation limits: a5 mg/L, b1 mg/L, c0.5 mg/L, d0.3 mg/L, e0.2 mg/L,f0.1 mg/L, g0.05 mg/L. h0.02 mg/L. i0.01 mg/L. j0.005 mg/L, k0.001 mg/L, l0.0002 mg/L, m0.01 mg/L for ICP–AES and 0.001 mg/L for ICP–MS. Abbreviations: BA = bottom ash,EFA = economizer fly ash, FA = fly ash.

Element 22 July 2007 8 August 2007

BA EFA+FA FA Coarse FA/EFA Fine FA/EFA BA EFA+FA FA Coarse FA/EFA Fine FA/EFA

Alf 0.8 0.3 0.4 0.4 0.4 0.9 0.3 0.3 b0.1 0.5Asm 0.023 0.059 0.080 0.013 0.147 0.001 0.018 0.030 0.010 0.068Bad 1.4 1.1 1.3 2.3 0.9 2.5 1.1 1.4 2.6 1.1Bek b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 0.002Caf 63.4 280 261 351 252 49.5 482 410 643 360Cdk b0.001 0.002 0.003 0.001 0.004 b0.001 0.002 b0.001 b0.001 0.004Crk 0.006 0.047 0.035 0.011 0.062 0.006 0.061 0.045 0.012 0.130Cui b0.01 0.04 0.03 0.01 0.04 b0.01 0.03 0.03 b0.01 0.04Feg 0.07 b0.05 b0.05 b0.05 b0.05 0.07 b0.05 b0.05 b0.05 b0.05Gek 0.001 0.048 0.051 0.014 b0.001 0.002 0.066 0.070 0.018 0.157Mfd 2.6 2.8 2.7 2.3 3.0 2.9 3.5 3.3 2.9 3.7Mn? 0.49 0.77 0.75 1.12 0.66 0.26 0.98 0.87 0.90 0.73Moh b0.02 0.09 0.10 0.03 0.17 b0.02 0.09 0.10 0.05 0.17Nik 0.006 0.008 0.015 0.007 0.010 0.015 0.010 0.013 0.013 0.021Pb b1 b1 1 b1 2 b1 b1 b1 b1 b1Rbk 0.002 0.002 0.002 0.002 0.003 0.003 0.003 0.003 0.002 0.004Sb 8 21 20 11 29 7 28 26 14 37Sck 0.001 0.004 0.003 0.003 0.003 0.001 0.003 0.003 0.003 0.004Sem b0.001 0.073 0.14 0.071 0.15 0.001 0.075 0.13 0.081 0.141Si 5.0c 20a 22a 20a 22a 4.3c 25a 23a 24a 26a

Sri 0.24 0.44 0.44 0.48 0.49 0.22 0.86 0.77 0.96 0.77Tij b0.005 0.011 0.006 b0.005 0.006 b0.005 0.008 0.005 0.009 0.009Tlk b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 0.001Uk b0.001 0.006 0.004 0.002 0.006 0.001 0.008 0.007 0.003 0.010Vj b0.005 0.113 0.146 0.025 0.271 0.008 0.087 0.131 0.032 0.289

Table 12Element mobilization (%) in SGLP ash leachates from the Ohio power plant. Ag, Ba, Be,Cd, Co, Hg, Pb, Sc, Th, and Zn were not detected in the SGLP leachate from this plant.Abbreviations: BA = bottom ash, EFA = economizer fly ash, FA = fly ash.

Element Day 4 Day 10

BA EFA FA BA EFA FA

Al 0.01 0.004 0.07 0.02 0.01 0.04As 2.5 3.4 27 4.9 8.0 31Ca 0.8 8.5 1.3 0.9 5.1 1.2Cr b0.03 0.05 1.1 0.04 0.07 1.0Cs b0.3 b0.3 0.5 b0.4 b0.3 0.7

344 K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

(2005), andWard et al. (2009) shows that oxyanion-forming elementstend to bemostmobile in alkaline solutions. Our results support this as-sertion; As, Mo, Se, and V were more mobile in the ultimately alkalineleachant of the SGLP than the ultimately acidic leachant of the TCLP.We did not analyze the elements B, Br, and I.

Considering each power plant independently because of differ-ences in ash chemistry, the fractions of elements that were leachedfrom the ashes and remained mobile using either leaching procedureshow patterns similar to those noted for element concentrations inthe leachates. Most trace elements are least mobile from BA andmost mobile from FA, with EFA in between; the fraction mobilizedis also greater from fine FA than from coarse FA, possibly due to greaterspecific surface area in finer FA. These patterns generally hold for As,Cd, Cr, Ge, Mo, P, Sb, Se, U, and V. Among the ashes from the Ohiopower plant, Cs, K, Mg, Rb, and Tl also follow the BAbEFAbFA mobi-lization pattern. These patterns may also reflect changing modes ofoccurrence for these elements, ranging from more-refractory modesin BA to more-leachable modes in FA. Two elements that clearly donot follow these patterns at either plant are Ca and Sr, which are

Table 11U.S. EPA toxicity characteristic levels, freshwater criteria maximum concentrations(CMCs), and freshwater criteria continuous concentrations (CCCs) for elements ana-lyzed in this study (U.S. EPA, 2004, 2009).

Element Toxicity characteristic(mg/L)

Freshwater CMC(mg/L)

Freshwater CCC(mg/L)

Ag 5 0.0032As 5 0.34 0.15Cd 1 0.002 0.00025Cr(III) 0.57 0.074Cr(VI) 0.016 0.011Hg 0.2 0.0014 0.00077Ni 0.47 0.052Pb 5 0.065 0.0025Se 1 0.005Zn 0.12 0.12

generally more mobile in EFA than in either BA or FA, and more mobilein coarse FA than in fine FA. This may reflect a different, more-leachablemode of occurrence for Ca (and Sr, which often substitutes readily forCa) in EFA than in the other types of ashes, and a relatively less-leachable mode in FA, particularly the fine fraction.

To further assess the relationship between ash type and leachingof elements, we created scatter plots (e.g., Figs. 3 and 4) of element

Cu 0.4 0.3 b0.3 0.5 0.3 b0.3Fe b0.007 b0.0004 0.0009 0.02 0.0007 0.001Ge b0.3 0.3 0.9 b0.3 0.3 1.2K 0.1 1.0 1.4 0.2 0.6 1.1Li b4.1 b4.9 5.8 b4.9 b5.1 b4.1Mg 0.5 2.3 4.3 0.4 1.4 2.6Mn b0.07 0.07 b0.09 0.2 b0.07 b0.09Mo b7.1 28 59 b8.7 21 76Ni b0.05 0.08 0.02 0.5 0.05 b0.02P b2.7 b1.6 3.9 b2.4 b1.8 6.0Rb 0.06 0.4 0.5 0.09 0.2 0.4Sb b2.3 0.8 7.2 b2.2 b22 7.3Se 1.6 3.6 36 5.1 4.3 45Si 0.02 0.04 0.02 0.04 0.04 0.03Sr 0.1 2.9 0.3 0.2 1.9 0.3Ti b0.002 b0.002 b0.002 0.009 b0.002 b0.002Tl b13 1.0 2.3 b17 b1.3 2.7U b0.3 2.3 4.7 b0.3 1.5 4.5V b0.05 0.3 3.2 0.09 0.4 3.9

Table 13Element mobilization (%) in SGLP ash leachates from the New Mexico power plant. Ag, Be, Cd, Co, Cs, Hg, Li, Pb, Th, and Tl were not detected in the SGLP leachate from this plant.Abbreviations: BA = bottom ash, EFA = economizer fly ash, FA = fly ash.

Element 22 July 2007 8 August 2007

BA EFA+FA FA Coarse FA/EFA Fine FA/EFA BA EFA+FA FA Coarse FA/EFA Fine FA/EFA

Al 0.01 0.09 0.08 0.2 0.07 0.01 0.2 0.2 0.1 0.2As 4.6 42 37 35 42 1.7 26 35 7.0 39Ba b1.2 b1.7 b0.9 b1.0 b1.2 b0.8 b1.3 b1.2 2.2 b0.8Ca 1.3 1.0 0.6 0.6 0.8 0.9 2.3 0.9 7.2 0.6Cr 0.1 4.9 4.5 1.7 6.4 0.07 5.8 5.1 2.2 8.0Cu 0.4 0.7 0.5 0.7 1.1 0.4 0.4 0.5 0.4 b0.3Fe 0.01 0.005 0.007 0.009 b0.005 0.008 0.004 0.006 0.005 0.005Ge 0.4 3.4 7.6 0.4 8.9 0.4 b0.3 b0.2 b0.3 1.0K 0.2 b0.1 b0.1 b0.1 b0.1 0.1 0.2 0.1 0.1 0.2Mg 0.5 0.09 0.3 b0.1 0.5 0.3 b0.08 b0.09 b0.1 b0.1Mn 0.08 b0.1 b0.1 b0.08 b0.1 b0.1 b0.1 b0.1 b0.08 b0.1Mo b27 67 68 45 73 b57 80 65 60 63Ni b0.2 b0.1 0.1 b0.2 0.1 b0.1 b0.1 b0.1 b0.2 b0.1P b3 2 4 b2 6 b4 b3 b3 b3 b2Rb 0.06 0.07 0.06 0.06 0.1 0.05 0.1 0.1 0.1 0.08Sb b2.3 18 15 19 17 b1.7 19 1.6 13 18Sc b0.2 b0.1 b0.1 0.4 b0.1 b0.1 0.2 0.3 0.3 b1.3Se 5.5 45 61 61 101 b1.5 38 48 38 58Si 0.03 0.05 0.04 0.2 0.02 0.02 0.2 0.2 0.1 0.09Sr 0.4 0.2 0.2 0.1 0.2 0.4 0.7 0.3 1.5 0.2Ti 0.006 b0.002 0.003 b0.002 b0.002 0.004 b0.002 b0.002 b0.002 b0.002U 0.2 5.1 5.3 0.8 7.1 0.2 0.2 0.6 b0.2 3.6V 0.2 5.9 5.8 3.2 7.3 0.2 7.5 8.7 2.9 7.2Zn b0.9 b0.4 b0.4 b0.7 0.2 b0.7 b0.4 b0.4 b0.7 b0.2

345K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

concentrations in dry ash and element concentrations in TCLP or SGLPleachates for the ten NM power plant samples (2 days×5 ash types).The six Ohio plant samples were not lumped with the New Mexicosamples because of differences in ash chemistry, and were not ana-lyzed independently because of a greater risk of spurious correlations

Table 14Element mobilization (%) in TCLP ash leachates from the Ohio power plant. Ag, Hg, P,and Th were not detected in the TCLP leachate from this plant. Abbreviations: BA =bottom ash, EFA = economizer fly ash, FA = fly ash.

Element Day 4 Day 10

BA EFA FA BA EFA FA

Al 0.02 0.04 0.03 0.01 0.01 0.03As b0.4 0.4 1.5 b0.4 0.9 2.0Ba 3.0 2.7 2.9 4.7 2.8 4.1Be b0.2 0.4 0.2 b0.2 0.2 0.2Ca 1.9 29 57 2.9 33 64Cd b8.7 14 31 b6.7 11 18Co b0.2 0.4 0.5 b0.2 b0.2 0.3Cr 0.05 0.5 0.9 0.1 0.2 0.9Cs b0.3 b0.3 0.5 b0.4 b0.3 0.7Cu 0.6 2.9 8.9 1.4 1.9 2.4Fe 0.007 0.1 b0.0006 0.06 0.05 b0.005Ge b0.07 1.1 5.7 b0.07 0.8 5.0K 0.4 1.5 2.3 0.6 1.2 1.9Li b4.1 b4.9 9.7 b4.9 b5.1 8.2Mg 1.1 3.8 13.1 1.2 2.8 11.9Mn 1.1 7.7 4.8 2.9 4.9 3.8Mo b7.1 b8.0 34 b11 b8.7 48Ni 0.2 0.9 4.5 0.3 0.9 0.9Pb 0.1 b0.08 b0.05 0.8 b0.1 b0.06Rb 0.07 0.5 0.5 0.09 0.2 0.5Sb b2.3 b16 5.2 b2.2 b22 4.9Sc b0.07 0.2 0.2 b0.1 0.1 0.3Se b0.8 38 25 b2.6 2.8 20Si 0.01 0.1 0.2 0.01 0.08 0.2Sr 0.3 7.8 5.9 0.5 5.8 6.1Ti b0.002 0.004 b0.002 b0.002 0.002 b0.002Tl b2.6 2.9 8.3 b3.3 2.6 9.2U b0.3 2.5 1.7 b0.3 1.2 2.1V b0.05 0.06 0.4 b0.05 0.3 0.4Zn 6.7 4.2 9.6 4.4 5.9 3.6

due to their lower number of samples. A strongpositive linear correlation(often r>0.9) exists among the New Mexico power plant ash samplesbetween element concentrations in dry ash and element concentrationsin TCLP or SGLP leachates. Themost correlative of these—As, Cr, Cu,Mo,Se, and V — are shown in Figs. 3 and 4. For Cr, Cu, and V (Fig. 3), theregression line crosses the x-axis substantially to the right of the origin:element concentrations of up to tens of mg/kg in the original ashcorrespond to element concentrations of zero in leachate.

The linear relationships we observe might represent mixing of atwo-component system, where many trace elements in one compo-nent tend to be immobile or of very low leachability (e.g., in the re-fractory forms typical in BA) and these trace elements in the otherhave leachabilities closer to those observed in fine FA, as discussedabove. The relative contribution of the more leachable phase to anash and to its leachate would increase away from the furnace, andcould indicate highly oxidized, relatively soluble chemical species.The inert phase would contain little of elements such as As, Mo, andSb (Fig. 4), but greater amounts of Cr, Cu, and V (Fig. 3).

An alternative explanation for these linear relationships is thatthey may show post-leaching immobilization of some elements (par-ticularly Cr, Cu, and V). It is possible that an element may persist inleachate only after the leaching of a certain initial quantity, sufficientto fill all sorption sites or reach equilibrium with a precipitate. Theamount of each element that may have leached from the ash but thenbeen immobilized in this case would be shown by the x-intercept ofthe regression line. For a given element, this quantity is similar inboth SGLP and TCLP leachates. This effect is apparent to a lesser extent(element concentrations of 3 mg/kg or less in the original ash) in Asand Mo (Fig. 4).

Ettringite, a hydrated calcium aluminum sulfate (Ca6Al2(SO4)3(OH)12·26H2O) that commonly forms in alkaline ash leachates (deGroot et al., 1989; Gougar et al., 1996; Hassett, 1994; Jankowski etal., 2005; Saikia et al., 2006; Zhang and Reardon, 2003), is a knownash leachate precipitate that immobilizes some of these trace ele-ments. By substitution, it can incorporate oxyanions of elementsincluding As, B, Cd, Cr, Mo, Se, and V (Gougar et al., 1996; Jankowskiet al., 2005; Zhang and Reardon, 2003). Ettringite precipitation occursat high pH and may have occurred during our SGLP leaches. However,

Table 15Element mobilization (%) in TCLP ash leachates from the New Mexico power plant. Ag, Co, Cs, Hg, Li, Pb, Sb, and Th were not detected in the TCLP leachate from this plant. Abbre-viations: BA = bottom ash, EFA = economizer fly ash, FA = fly ash.

Element 22 July 2007 8 August 2007

BA EFA+FA FA Coarse FA/EFA Fine FA/EFA BA EFA+FA FA Coarse FA/EFA Fine FA/EFA

Al 0.01 0.005 0.007 0.007 0.006 0.02 0.005 0.005 b0.002 0.009As 15 12 14 5.2 18 0.6 3.6 5.5 3.5 7.6Ba 5.6 6.2 4.1 7.3 3.8 6.6 4.8 5.8 14.6 2.7Be b0.5 b0.4 b0.4 b0.5 b0.4 b0.4 b0.4 b0.4 b0.5 0.6Ca 13 68 48 57 49 8.2 95 75 132 80Cd b13 8.5 11 6.9 10 b13 10 b4.8 b8.7 12Cr 0.6 3.9 2.8 1.2 4.5 0.4 4.6 3.2 1.1 8.0Cu b0.5 1.5 1.1 0.5 1.3 b0.5 1.2 1.3 b0.5 1.3Fe 0.006 b0.005 b0.005 b0.004 b0.005 0.005 b0.004 b0.004 b0.004 b0.004Ge 0.4 15 14 5.4 b0.2 0.8 17 16 5.9 25K 0.7 0.6 0.6 0.6 0.6 0.5 0.5 0.5 0.5 0.5Mg 3.2 2.4 2.5 2.4 2.8 1.4 2.8 3.1 3.4 3.8Mn 4.0 8.1 8.4 8.7 7.6 3.1 9.8 9.7 7.4 9.6Mo b27 35.8 37.4 16.5 45.9 b57 46.1 39.2 44.5 37.8Ni 1.0 1.0 1.9 1.3 1.1 1.7 1.2 1.6 2.1 2.3P b3 b2 2 b2 4 b4 b3 b3 b3 b2Rb 0.1 0.1 0.1 0.1 0.2 0.08 0.1 0.1 0.1 0.2Sc 0.2 0.5 0.4 0.5 0.4 0.1 0.3 0.4 0.4 0.5Se b2.7 22 37 29 52 1.5 18 26 26 25Si 0.03 0.1 0.1 0.1 0.1 0.03 0.2 0.2 0.2 0.2Sr 2.2 5.1 4.1 4.7 3.7 2.1 6.2 5.6 10.9 6.7Ti b0.002 0.004 0.002 b0.002 0.002 b0.002 0.003 0.002 0.004 0.003Tl b5.8 b3.0 b2.6 b5.2 b1.9 b3.9 b2.1 b2.0 b3.4 1.5U b0.2 1.2 0.8 0.5 1.0 0.2 1.6 1.3 0.7 1.6V b0.1 2.5 3.1 0.6 5.2 0.2 1.9 2.8 0.8 5.3Zn 11 5.2 3.2 8.5 2.7 4.9 4.3 4.5 2.7 3.7

346 K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

the final pH values for the TCLP leachates are too low for ettringitestability. Ettringite precipitation is, therefore, unlikely to account forthe positive x-intercepts common to both the SGLP and TCLP regressionlines (Figs. 3 and 4).

4.3. Variability

Leachate concentrations, when compared between the two sam-pling dates from a single ash type at a single power plant, generallyvaried by up to tens of percent. Isolated exceptions for single ele-ments in individual ashes varied by 10 times or more: iron in TCLPleachate from Ohio BA varied by 78 times, As in TCLP leachate fromOhio BA varied by 18 times, and Se in TCLP leachate from Ohio EFAvaried by 10 times. This day-to-day variability may result from feedcoal or ash heterogeneity or possibly contamination, and it suggeststhat leaching tests of several additional CCP samples collected atdifferent times or on different days could provide a better understand-ing of leachate variability. Leaching larger samples of ash (e.g., 100 grather than 10 g) could also reduce any variability caused by ashheterogeneity.

Concentrations of elements in leachates from similar ash typesderived from the two different source coals (New Mexico BA vs. OhioBA and New Mexico FA vs. Ohio FA) were generally similar within afactor of 2, and almost all were similar within a factor of 4. TheNew Mexico power plant, burning Fruitland Formation coal, pro-duced TCLP FA leachates containing about 4 times the V as thosefrom the Ohio plant. TCLP FA leachates from the Ohio plant, burningMonongahela Formation Pittsburgh coal, contained about 4 timesthe As as the corresponding leachates from New Mexico. The Ohioplant SGLP and TCLP leachates also generally contain several timesthe Fe, K, Mg, Ni, Rb, and Tl of the corresponding leachates fromthe New Mexico plant. Much of this variability can be explained bydifferences in the compositions of the CCPs. The Ohio plant CCPs,for example, contain more As, Fe, K, Ni, Rb, and Tl, and less V, thanthose from the New Mexico plant. Magnesium, however, is of similar

abundance in the CCPs from both power plants, so its greater abun-dance in leachates from the Ohio plant may be due to differences inoverall ash chemistry.

5. Conclusions

For both the low- andhigh-sulfur coals analyzed here, leachates fromBA generally contained the lowest concentrations and FA leachates gen-erally contained the highest concentrations of most trace elementsanalyzed, with EFA intermediate between BA and FA in its leachingproperties. The elements Ca and Sr, however, were leached morefrom EFA than from either BA or FA. Leachates from the coarse FA/EFA mixture from the New Mexico power plant contained lowerconcentrations of most elements than leachates from the fine FA/EFA mixture from this plant, possibly due to the greater specific sur-face area of the finer ash. FA, and in particular fine FA, is thus theash of greatest concern with respect to leaching of some potentiallyharmful elements. In this study, no TCLP leachates exceeded the EPAtoxicity characteristics and no SGLP leachates exceeded the EPA recom-mended water quality criteria for aquatic life using a DAF of 100. With-out using a DAF, however, Se, Cr, and As in leachates from both powerplants exceeded the aquatic life criteria.

SGLP leachates of FA from the Ohio power plant exceeded the EPAprimary drinking water MCLs for As, Sb, and Tl; SGLP leachates of FAfrom the New Mexico power plant exceeded the MCLs for As, Sb, andU; suggesting that these elements may be of the most environmentalconcern in leachates from Pittsburgh coal FA and from FruitlandFormation coal FA, respectively.

The CCPs sampled from the two power plants discussed here werequite heterogeneous, with a several-times variation in element con-centrations in ash and ash leachates between the two sampling daysat each plant. This variability, combined with the low number (two)of each type of sample analyzed in this study, made outlier identi-fication and interpretation of leaching trends difficult. Because ofCCP heterogeneity, and if time and resources permit, we recommend

0 10 20 30 40

Cr in dry ash (ppm)

0.00

0.05

0.10

0.15

Cr

in le

ach

ate

(mg

/L)

a. Cr

0 20 40 60 80

Cu in dry ash (ppm)

0.00

0.01

0.02

0.03

0.04

0.05

Cu

in le

ach

ate

(mg

/L)

b. Cu

0 20 40 60 80 100 120

V in dry ash (ppm)

0.0

0.2

0.4

0.6

0.8

V in

leac

hat

e (m

g/L

)

c. V

SG

LP

SG

LPSG

LP

TCLP

TCLP

TCLP

BAEFA/FACoarse FA and EFA/FAFAFine FA and EFA/FA

Fig. 3. Plots of a) Cr (all valences), b) Cu, and c) V concentrations in dry ash (mg/kg) vs.concentrations in leachates (mg/L) from NewMexico power plant CCPs. Filled symbolsrepresent SGLP leachates; open symbols represent TCLP leachates. The BA sample col-lected on 8 August was considered a too-high outlier for Cr and V concentrations in dryash and is not plotted. For Cr after discarding the BA outlier, SGLP r=0.97, TCLPr=0.92. For Cu, SGLP r=0.86, TCLP r=0.91. For V after discarding the BA outlier,SGLP r=0.93, TCLP r=0.98.

0 5 10 15 20

As in dry ash (ppm)

0.0

0.1

0.2

0.3

0.4

As

in le

ach

ate

(mg

/L)

a. As

0 5 10 15Se in dry ash (ppm)

0.0

0.1

0.2

0.3

0.4

Se

in le

ach

ate

(mg

/L)

c. Se

SGLP

0 2 4 6 8 10

Mo in dry ash (ppm)

0.0

0.1

0.2

0.3

Mo

in le

ach

ate

(mg

/L)

b. Mo

SGLP

SGLP

TCLP

TCLP

TCLP

BAEFA/FACoarse FA and EFA/FAFAFine FA and EFA/FA

Fig. 4. Plots of a) As, b) Mo, and c) Se concentrations in dry ash (mg/kg) vs. concentra-tions in leachates (mg/L) from NewMexico power plant CCPs. Filled symbols representSGLP leachates; open symbols represent TCLP leachates. For As, SGLP r=0.96, TCLP r=0.77.For Mo, SGLP r=0.96, TCLP r=0.94. For Se, SGLP r=0.79, TCLP r=0.77.

347K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

sampling and leaching several days of ash samples, which shouldproduce the most useful and interpretable results in future studies.Although a single leaching test such as the SGLP may provide a rea-sonable approximation of environmental leaching behavior of CCPs,several leaching tests at different pHs would allow a better under-standing of how elements leach from CCPs under a wide range of dis-posal or use conditions.

Acknowledgments

We thank the operators of the NewMexico and Ohio power plantsfor allowing collection of samples and publication of our analyses. We

also thank Harvey Belkin (U.S. Geological Survey), Jim Coleman (U.S.Geological Survey), Mark Engle (U.S. Geological Survey), Colin Ward(University of New South Wales), and two anonymous reviewers forconstructive comments on an earlier draft of this manuscript.

References

ACAA (American Coal Ash Association), 2011. Corrected 2009 Coal CombustionProduct (CCP) Production & Use Survey. 1 pp.

Asokan, P., Saxena, M., Asolekar, S.R., 2005. Coal combustion residues — environmentalimplications and recycling potentials. Resources, Conservation and Recycling 43,239–262.

ASTM International, 2007. Annual Book of ASTM Standards, ASTM International. WestConshohocken, PA.

Barnes, D.I., Sear, L.K.A., 2006. Ash utilisation from coal-based power plants. In: Pro-ceedings of the International Coal Ash Technology Conference, AshTech 2006,

348 K.B. Jones et al. / International Journal of Coal Geology 94 (2012) 337–348

Birmingham, UK, 15–17 May 2006, United Kingdom Quality Ash Association, Wol-verhampton, UK.

Brown, J.B., 2008. Review of available water-quality data for the Southern ColoradoPlateau Network and characterization of water quality in five selected parkunits in Arizona, Colorado, New Mexico, and Utah, 1925 to 2004. U.S. GeologicalSurvey Scientific Investigations Report 2008–5130. 119 pp.

Clarke, L.B., 1993. The fate of trace elements during coal combustion and gasification:an overview. Fuel 72, 731–736.

de Groot, G.J., Wijkstra, Jan, Hoede, Dirk, van der Sloot, H.A., 1989. Leaching characteristicsof selected elements from coal fly ash as a function of the acidity of the contactsolution and the liquid/solid ratio. In: Côté, P.L., Gilliam, T.M. (Eds.), EnvironmentalAspects of Stabilization and Solidification of Hazardous and Radioactive Wastes.American Society for Testing and Materials, Philadelphia, pp. 179–183.

Dellantonio, A., Fitz, W.J., Repmann, F., Wenzel, W.W., 2010. Disposal of coal combustionresidues in terrestrial systems: contamination and risk management. Journal ofEnvironmental Quality 39, 761–775.

Eary, L.E., Rai, D., Mattigod, S.V., Ainsworth, C.C., 1990. Geochemical factors controllingthe mobilization of inorganic constituents from fossil fuel combustion residues: II.Review of minor elements. Journal of Environmental Quality 19, 202–214.

Fassett, J.E., 2000. Geology and coal resources of the Upper Cretaceous Fruitland Formation.In: Kirschbaum,M.A., Roberts, L.N.R., Biewick, L.R.H. (Eds.), San Juan Basin,NewMexicoand Colorado, Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado,New Mexico, and Utah. U.S. Geological Survey Professional Paper, Report 1625-B, pp.Q1–Q132.

Georgakopoulous, A., Filippidis, A., Kassoli-Fournaraki, A., Iordanidis, A., Fernández-Turiel,J.-L., Llorens, J.-F., Gimeno, D., 2002. Environmentally important elements in fly ashesand their leachates of the power stations of Greece. Energy Sources 24, 83–91.

Gitari, W.M., Fatoba, O.O., Petrik, L.F., Vadapalli, V.R.K., 2009. Leaching characteristics ofselected South African fly ashes: effect of pH on the release of major and tracespecies. Journal of Environmental Science and Health. Part A, Toxic/HazardousSubstances and Environmental Engineering 44, 206–220.

Gougar, M.L.D., Scheetz, B.E., Roy, D.M., 1996. Ettringite and C–S–H Portland cementphases for waste ion immobilization: a review. Waste Management 16, 295–303.

Hassett, D.J., 1994. Scientifically valid leaching of coal conversion solid residues topredict environmental impact. Fuel Processing Technology 39, 445–459.

Hassett, D.J., 1998. Synthetic groundwater leaching procedure. In: Meyers, R.A. (Ed.),Encyclopedia of Environmental Analysis and Remediation. John Wiley & Sons,Inc., Hoboken, NJ, pp. 4797–4803.

Hassett, D.J., Pflughoeft-Hassett, D.F., Heebink, L., 2005. Leaching of CCBs: observationsfrom over 25 years of research. Fuel 84, 1378–1383.

Jankowski, J., Dubikova, M., Ward, C.R., French, D.H., 2005. Formation of ettringite inleaching solutions from alkaline fly ashes: evaluation using hydrogeochemicalmodeling. Proceedings of Twenty-Second Annual International Pittsburgh CoalConference, Pittsburgh, PA, 12–15 September 2005. 23 pp.

Jankowski, J., Ward, C.R., French, D., Groves, S., 2006. Mobility of trace elements fromselected Australian fly ashes and its potential impact on aquatic ecosystems. Fuel85, 243–256.

Karuppiah, M., Gupta, G., 1997. Toxicity of and metals in coal combustion ash leachate.Journal of Hazardous Materials 56, 53–58.

Kim, A.G., Hesbach, P., 2009. Comparison of fly ash leaching methods. Fuel 88, 926–937.Kosson, D.S., van der Sloot, H.A., Sanchez, F., Garrabrants, A.C., 2002. An integrated

framework for evaluating leaching in waste management and utilization ofsecondary materials. Environmental Engineering Science 19, 159–204.

Kosson,D., Sanchez, F., Kariher, P., Turner, L.H., Delapp, R., Seignette, P., 2009. Characterizationof coal combustion residues from electric utilities— leaching and characterization data.U.S. EPA Document EPA-600/R-09/151. . 215 pp.

Meawad, A.S., Bojinova, D.Y., Pelovski, Y.G., 2010. An overview of metals recovery fromthermal power plant solid wastes. Waste Management 30, 2548–2559.

Moreno, N., Querol, X., Andrés, J.M., Stanton, K., Towler, M., Nugteren, H., Janssen-Jurkovicová, M., Jones, R., 2005. Physico-chemical characteristics of Europeanpulverized coal combustion fly ashes. Fuel 84, 1351–1363.

Ohio EPA (Environmental Protection Agency), 2008. Inorganic Ground Water WellSummary Report, Middleport Wellfield, STU #2. http://wwwapp.epa.ohio.gov/ddagw/Documents/sitesum/MEI02142ssf.pdf. Retrieved 22 July 2011.

Pei-wei, G., Xiao-lin, L., Hui, L., Xiaoyan, L., Jie, H., 2007. Effects of fly ash on the propertiesof environmentally friendly dam concrete. Fuel 86, 1208–1211.

Pflughoeft-Hassett, D.F., Hassett, D.J., Buckley, T.D., Heebink, L.V., Zacher, E., 2005.Laboratory methods for the evaluation of potential release of mercury from coalutilization by-products. Topical report prepared for U.S. Department of Energy.Energy and Environmental Research Center, University of North Dakota, GrandForks. 29 pp.

Popovic, A., Radmanovic, D., Djordjevic, D., Polic, P., 2005. Leaching of selected elementsfrom coal ash dumping. In: Lichtfouse, E., Schwarzbauer, J., Robert, D. (Eds.), Environ-mental Chemistry: Green Chemistry and Pollutants in Ecosystems. Springer-Verlag,New York, pp. 145–151.

Praharaj, T., Powell, M.A., Hart, B.R., Tripathy, S., 2002. Leachability of elementsfrom sub-bituminous coal fly ash from India. Environment International 27,609–615.

Saikia, N., Kato, S., Kojima, T., 2006. Behavior of B, Cr, Se, As, Pb, Cd, and Mo present inwaste leachates generated from combustion residues during the formation ofettringite. Environmental Toxicology and Chemistry 25, 1710–1719.

Sheps, S., Finkelman, R.B., Councell, T.B., Cohen, H., 1999. Leaching of chromium fromcoal fly ash. Proceedings of the 3rd European Coal Conference, 1997, pp. 475–479.

Sheps-Pelleg, S., Cohen, H., 1999. Evaluation of the leaching potential of trace elementsfrom coal ash to the (groundwater) aquifer. Abstracts from the 1999 InternationalAsh Utilization Symposium. Center for Applied Energy Research, University ofKentucky, Lexington. 12 pp.

Tewalt, S., Ruppert, L., Carlton, R., Bresinski, D., Wallack, R., Bragg, L., 2001. A digitalresource model for the Upper Pennsylvanian Pittsburgh coal bed, MonongahelaGroup, Northern Appalachian Basin Coal Region. U.S. Geological Survey ProfessionalPaper 1625-C. 102 pp.

U.S. EPA, 1990. Environmental fact sheet: toxicity characteristic rule finalized. DocumentEPA/530-SW-89-045. 4 pp.

U.S. EPA, 1996a. Hazardous Waste Characteristics Scoping Study. http://www.epa.gov/osw/hazard/wastetypes/wasteid/char/scopingp.pdf. Retrieved 22 July 2011, 276 pp.

U.S. EPA, 2004. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods(SW-486). Government Printing Office, Washington DC.

U.S. EPA, 2009. National Recommended Water Quality Criteria. http://water.epa.gov/scitech/swguidance/standards/current/upload/nrwqc-2009.pdf. Retrieved 22 July2011, 22 pp.

U.S. EPA, 2010. Hazardous and solid waste management system: identification and listingof special wastes; disposal of coal combustion residuals from electric utilities. Docu-ment EPA-HQ-RCRA-2009-0640-0352, 40 CFR Parts 257, 261, 264, 265, 268, 271,and 302: Federal Register, Vol. 75, pp. 35,128–35,264. No. 118.

Wang, Y., Ren, D., Zhao, F., 1999. Comparative leaching experiments for trace elementsin raw coal, laboratory ash, fly ash, and bottom ash. International Journal of CoalGeology 40, 103–108.

Wang, T., Wang, J., Tang, Y., Shi, H., Ladwig, K., 2009. Leaching characteristics ofarsenic and selenium from coal fly ash: role of calcium. Energy & Fuels 23,2959–2966.

Ward, C.R., French, D., Jankowski, J., Dubikova, M., Li, Z., Riley, K.W., 2009. Elementmobility from fresh and long-stored acidic fly ashes associated with an Australianpower station. International Journal of Coal Geology 80, 224–236.

Zandi, M., Russell, N.V., 2007. Design of a leaching test framework for coal fly ashaccounting for environmental conditions. Environmental Monitoring and Assessment131, 509–526.

Zhang, M., Reardon, E.J., 2003. Removal of B, Cr, Mo, and Se from wastewater byincorporation into hydrocalumite and ettringite. Environmental Science and Technology37, 2947–2952.