Chemical Speciation of Potentially Toxic Trace Metals in Coal Fly Ash

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Chemical Speciation of Potentially Toxic Trace Metals in Coal Fly Ash Associated with the Kingston Fly Ash Spill Nelson A. Rivera, Dean Hesterberg, Navdeep Kaur, and Owen W. Duckworth Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b00020 • Publication Date (Web): 18 Jul 2017 Downloaded from http://pubs.acs.org on July 18, 2017

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Energy & Fuels

Chemical Speciation of Potentially Toxic Trace Metals in Coal Fly Ash Associated with the Kingston Fly Ash Spill

Nelson Rivera,§ Dean Hesterberg,* Navdeep Kaur, and Owen W. Duckworth

Department of Crop and Soil Science, Box 7620, North Carolina State University, Raleigh, North Carolina 27695-7620 USA §

Current Address: Department of Civil and Environmental Engineering, Box 90287, Duke University, Durham, North Carolina 27708, USA

Submitted in revised form Energy and Fuels July 14, 2017

*To whom correspondence should be addressed [email protected] Tel. (919) 513-3035 Fax. (919) 515-1267

ACS Paragon Plus Environment

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Abstract: Coal ash released into the environment may release toxic trace elements into water,

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sediments, and soils. The objective of this study was to characterize the chemical speciation of

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As, Se, Cu, Zn, Cr, and U in coal fly ash samples related to the 2008 Kingston ash spill. Three

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ash samples were analyzed using X-ray absorption spectroscopy (XAS) to determine oxidation

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states or dominant species of trace-elements, which were previously found to range in

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concentration from 8 to 20 mg kg-1. Linear combination fitting (LCF) of X-ray Absorption Near

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Edge Structure (XANES) spectra from ash samples indicated that both reduced and oxidized

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forms of the trace elements were present in the fly ash samples. We used the mineralogical

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composition of the fly ash to select the most relevant standards for LCF fitting of XANES

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spectra, which included metal-doped glasses, trace elements sorbed to iron oxy(hydroxides), and

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pure mineral phases for each element. Arsenic K-edge XANES spectra were best fit as oxidized

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As(V) (95–100%) associated with iron phases or aluminosilicate glass, where selenium K-edge

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XANES spectra were fit as Se(IV) (77–86%) associated with glass, with lesser proportions of

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Se(VI) and a more reduced Se species [fit as Se(0) or Se(II)S2]. Zinc K-edge XANES spectra

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were best fit as Zn associated with ferrihydrite (70–77%), franklinite (ZnFe2O4, 8-12%), and

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ZnO (14-20%). Qualitative assessment of U LIII-edge and Cr K-edge XANES spectra showed

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dominances of U(VI) and Cr(III) oxidation states. Copper K-edge XANES data indicated the

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possibility of both reduced and oxidized species, although our analysis could not fully account

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for all spectral features. Our results revealed multiple species of each trace element in the fly ash

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samples, which is important for predicting environmental mobility and bioavailability under the

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range of geochemical conditions found in aquatic and terrestrial environments.

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1. INTRODUCTION

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Fly ash contains trace elements and radionuclides,1 which has led to longstanding

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concerns about the impacts of ash on aquatic and terrestrial ecosystems due to the large masses

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of materials disposed or released into the environment.2,

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toxicity of trace elements in coal fly ash are partially controlled by their chemical speciation. In

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December 2008, 4.1-million cubic meters of fly ash were released into the Clinch, Emory, and

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Tennessee Rivers from ash impoundment at the TVA Kingston (Tennessee, USA) Fossil Plant.

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Ash samples associated with the release contain 8–200 mg kg-1 of As, U, Cr, Cu, Zn, and Se.4-6

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Following cleanup operations, the total amounts of these potentially toxic trace metals in residual

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ash left in the river sediments were estimated at 5–110 tonnes (Figure 1),5 raising concerns about

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disturbance and redistribution of residual ash.7 Mobilization of these elements into the overlying

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water or uptake into the aquatic food chain may pose a health risk to humans, wildlife, and the

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aquatic ecosystem.4, 6, 8, 9 For example, selenium is an element of specific concern at the TVA

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site, largely due to its potential toxicity to fish and waterfowl.10-12

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The mobility, bioavailability, and

Coal fly ash from differing localities can vary in its composition and trace metal

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concentrations.1,

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transformations.14-21 In addition, trace elements may redistribute spatially in the resulting ash,

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and form discrete solid phases, or adsorb or co-precipitate with major elements associated with

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glassy or mineral matrices.22-25 For example, previous work suggests that fractions of As and Se

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in coal evaporate during combustion, condensing by either heterogeneous nucleation on

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refractory particles or homogeneous nucleation as submicron particles.17,

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understand the chemical species of potentially toxic trace elements that form in fly ash to predict

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their long-term mobility in aquatic environments of varying redox potential and pH.

During coal combustion, elements may undergo both redox and phase

3


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It is important to

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Our previous work5 demonstrated that more abundant Si, Al, Fe, Ca, Na, K, Mg, Ti, S,

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and Ba in fly-ash samples associated with the TVA Kingston release mainly occur in

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aluminosilicate glass, and crystalline phases such as quartz, mullite, anhydrite, and hematite.

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Spatial distributions of trace elements were found to be highly heterogeneous on the sub-

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microscale, with Sr being diffusely distributed and Cr, Zn, Pb, P, and U concentrated into hot

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spots.5 Most of the past research on trace-element speciation in fly ash from the Kingston spill

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has focused on oxidation states and short-range structural order of Hg, As, and Se.26, 27 We lack

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knowledge of speciation of a broader array of environmentally relevant trace metals, including

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their associations with both mineral and glassy phases. The objective of this research was to

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determine the speciation of As, Se, Zn, Cr, U, and Cu in fly ash samples associated with the 2008

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Kingston fly ash release. Synchrotron X-ray absorption spectroscopy was used to determine

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oxidation states and model chemical species of these trace elements in fly ash. Understanding the

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speciation of the trace metals in the fly ash may provide insights into the geochemical processes

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that promote release of these trace metals into the environment, which may in turn help assess

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long-term environmental impacts and public-health risks arising from future releases.

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2. EXPERIMENTAL SECTION

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2.1. Materials. Trace-element speciation was analyzed for three fly ash samples from

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Tennessee Valley Authority (TVA) that were previously characterized for elemental composition

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and macroelement speciation:5 two from the Kingston fossil plant (TVA-KIF-110110-F and

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TVA-122208-7-7-J) and one from the Johnsonville plant (TVA-JVL-101910-A). Herein, we

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refer to these samples as “KIF1”, “KIF2”, and “JVL”, respectively. The KIF1 and JVL samples

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were collected directly from the electrostatic precipitator of each plant, and sample KIF2 was 4


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collected in March 2009 from an intact portion of the failed ash storage cell responsible for the

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2008 ash release into the Clint and Emory Rivers in Kingston, TN. Samples, which were dried

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and stored at room temperature prior to analysis, were provided by TVA personnel as samples of

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fresh and stored ash at the Kingston site, and have been utilized in other studies of ash

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geochemistry to describe the potential heterogeneity of ash at the site.4,

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contained 28–45 mg As kg-1, 6–9 mg Se kg-1, 130–200 mg Zn kg-1, 100–148 mg Cr kg-1, 8.9–12

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mg U kg-1, and 101–194 mg Cu kg-1.5

5, 26-29

The samples

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2.2. X-ray Absorption Spectroscopy (XAS). X-ray absorption near edge structure

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(XANES) spectra for ash samples were collected at the National Synchrotron Light Source

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(NSLS), Brookhaven National Laboratory (Upton, NY) and the Stanford Synchrotron Radiation

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Light Source (SSRL). Spectra were collected at the K-edges of As, Se, Cu, and Zn at room

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temperature in fluorescence mode using a 13-element Ge array detector and a Si(311) double

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crystal monochromator (detuned by 30%) at NSLS Beamline X11A. Uranium M5-edge XANES

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spectra were collected in fluorescence mode at Beamline X15B using a single-channel Ge solid

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state detector, a Si(111) monochromator, and a He flight path. Standards for fitting analyses were

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diluted in boron nitride (BN) to achieve a unit edge step for spectra that were typically collected

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in transmission mode.30 Samples for U were mounted in acrylic holders and covered with 5-µm

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thick polypropylene X-ray film to reduce absorption effects from tape adhesive. Beamline 4-3 at

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SSRL was used to collect Cr K-edge XANES spectra in fluorescence mode using a Si(111)

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variable-exit monochromator and a Vortex-ME4 four element silicon drift detector. Higher-order

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harmonics were rejected by Rh-coated mirrors. Samples were mounted in polycarbonate holders

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and covered with Kapton tape. Multiple spectra collected for each sample were merged to

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improve the signal-to-noise ratio. No evidence for beam-induced sample damage was found in 5


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successive scans. Supporting information Table S1 summarizes the parameters used in collecting

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XAS spectra.

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Details of data collection and analysis are discussed by Kelly et al.30 XANES spectra

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were generally collected over three energy regions of -200 to -50 eV, -50 to 50 eV, and 50 to 300

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eV relative to a given edge energy. Smaller step sizes and larger counting times were used in the

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region bracketing the absorption edge (-50 to 50 eV). Energy calibrations for XANES spectra

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were performed before data collection for each element and energy drift was monitored during

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scans with a reference (see Table S1 for calibrants and energy). XANES data were aligned,

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merged, baseline subtracted using a linear model, and normalized to an edge step of 1 using a

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quadratic model in the IFEFFIT suite of computer programs31 interfaced with the Athena

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software.32 Consistent ranges of energies were used for baseline subtraction and normalization

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for all samples and standards of a given element. Models of chemical speciation of the selected

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trace elements in the fly ash samples were developed using the linear combination fitting (LCF)

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routine in Athena, which calculates the combinations of scaled spectra from our chosen standards

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that sum to a fit to sample spectra.30 The final “best fits” reported here represent the lowest R-

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factor (residual) computed by Athena as a statistical goodness of fit parameter.

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The KIF1, KIF2, and JVL ash samples were predominantly composed of aluminosilicate

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glasses (57–61% w/w) and crystalline phases (39–43% w/w) that included quartz (SiO2), mullite

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(Al6Si2O13), anhydrite (CaSO4), lime (CaO), calcite (CaCO3), and iron (hydr)oxides.5 In addition

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to the mineralogical composition from our previous publication, other characterizations showed

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that the ash samples generally met the requirements of Class F fly ash by the ASTM C618

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classification system.5 In short, class F fly ash has pozzolanic properties with contents of

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aluminosilicates plus iron oxides greater than 70%.33 6


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The above phases were considered to be the main sorbents for trace elements in our

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speciation analysis along with discrete phases containing minerals or non-crystalline solids of a

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given trace element. Based on the mineralogical composition of the fly ash, metal-doped glasses,

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trace elements sorbed to iron oxy(hydroxides), and pure mineral phases for each element were

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used in XANES fitting. A trace metal sorbed to a ferrihydrite phase was used as a proxy for the

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iron phases. All standards used in the LCF fitting are listed in the supporting information.

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3. RESULTS AND DISCUSSION

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3.1. Arsenic. Arsenic in all fly ash samples was predominantly As(V), as shown by the

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alignment of the white-line peaks in K-edge XANES spectra of the samples with that of As(V)

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standards (Figure 2). Linear-combination fitting showed that the combination of our selected

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standards yielding the best fit to the sample data included 62-65% of As(V) co-precipitated with

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aluminosilicate glass and 30-38% of As(V) adsorbed on an iron phase (Table 1), with ~5%

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As(III) present in the KIF2 sample from the failed storage cell. The results suggest that As(V)

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was largely associated with the aluminosilicate glass that constitutes ~60% of these ash samples5,

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and with Fe-(hydr)oxide phases such as hematite, spinels, or Fe(III)-enriched domains in the

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glass (for which we used ferrihydrite as a surrogate sorbent).5 It should be noted that there is

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little distinguishing structure in the white lines of the As(V) standards, and the main difference

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between these spectra is a small energy shift in white line position (ca. 1 eV). These observations

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suggest there may be some ambiguity in the fits with regard to the exact speciation of the As(V)

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fraction. However, all three fits showed similar proportions of As(V)/glass and As(V)/iron oxide,

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and these results agree with published XAS results showing that As(V) was the main oxidation

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state in Class F fly ashes from other sources than used here.21, 34, 35An estimated 50 metric tons of 7


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As remain in Clinch and Emory River sediments following cleanup of the TVA Kingston ash

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spill (Figure 1). Sediment samples collected after the spill showed elevated concentrations of As

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in porewaters.6,

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Kingston ash in aqueous environments, thus posing a risk to the riverine ecosystems.4,

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Arsenic(V), the dominant oxidation state in our samples, is generally less toxic and less mobile

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than As(III) in most environments because it tends to adsorb strongly on Fe(III) and Al(III)

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oxides.8,

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measured at the TVA Kingston site.4, 6, 8, 28, 38

10, 37

8

In addition, leaching studies indicated that As can be mobilized from the 8, 36

However, reduction of As(V) to As(III) in reduced river sediments have been

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3.2. Selenium. A comparison of Se K-edge XANES spectra for samples and standards

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shows that Se(IV) (selenite) was the main oxidation state in our fly-ash samples (Figure 3).

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However, a discernable shoulder on the lower energy side of the white line suggests the presence

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of more reduced species. The XANES spectra of fly ash samples were best fit with spectra for

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standards Se(IV) co-precipitated with glass standard (77–86% of total Se) along with 6–23% of

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spectra from either Se(0) (elemental Se) or Se(II) in selenium sulfide (SeS2), and 90 mol%) form of Cr in our fly ash samples. The apparent lack ( 9,52 providing a pathway for

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increased solubilization of trace elements associated with the glass (namely, Cu, Se, and As, as

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suggested by our XANES results). Elements associated with iron phases may also be influenced

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by the geochemical conditions of this environment. The alkaline pH may also favor the

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desorption of oxyanions such as arsenate and selenite from surface sites of iron (hydr)oxides and

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other sorbents.10 A study of aqueous and solid phase As speciation showed larger total dissolved

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As total concentrations in pore waters (110 µg l-1) than in surface waters (3–13 µg l-1), as well as

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a shift towards As(III) at greater depths in sediments.

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embayments that contain residual fly ash from the spill show As concentrations ranging from

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20–250 µg/L and Se concentrations from 5-40 µg/L when runoff from the surrounding area

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interacts with the fly ash.54 In contrast, cations such as Cu and Zn should be retained at alkaline

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pH, which promotes sorption to minerals or precipitation of insoluble (oxy)hydroxides.40 The

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predicted behavior of this suite of trace elements thus illustrates the differing effects of

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environmental conditions on the mobility of specific elements.

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In fact, data from TVA monitoring of

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4.2. Riverene and Riparian Sediments. Diluted ash mixed with sediments are also

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found in the river or along its banks. In riverine and riparian sediments, we expect to see mildly

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acidic to circumneutral pH and potentially reducing Eh.8 In contrast to concentrated ash deposits,

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the alkaline components in fly ash such as carbonates will solubilize in acidic environments. Our

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XANES fitting results gave no indication of trace elements associated with carbonates, so no co13


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dissolution of carbonate and trace elements is expected. However, any trace element cations such

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as Cu2+ and Zn2+ adsorbed on iron oxides, as suggested by our XANES fits of ferrihydrite-

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associated cations (Table 1), would have a tendency to desorb from ash under increasingly acidic

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sediment conditions. In contrast, oxyanions of As(V) and As(III) that appear to be associated

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with Fe (hydr)oxides, should be less susceptible to desorption under acidic conditions. The

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presence of reduced copper and copper-sulfide species in the fly ash implied by our XANES

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analyses (Table 1) suggests that oxidative dissolution of copper would occur under oxic sediment

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conditions. Chromium as solid-phase Cr(III) (Fig. 5A) should remain stable and insoluble under

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oxid conditions because conversion of Cr(III) to Cr(VI) under oxic conditions is generally

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kinetically slow.10, 57, 58. However, under certain conditions such as in the presence of MnO2 and

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chelators, dissolution of Cr(III) oxide can occur and rapidly convert Cr(III) to Cr(VI).57-61

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Anoxic redox conditions would promote reduction of oxidized trace-element species or

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matrix minerals to which trace elements are bound. Arsenate and selenite are the dominant forms

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of arsenic and selenium in the freshly generated ash, and these species can be reduced in riverine

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sediments.10, 26, 36, 38, 39 Of particular concern would be the reduction of As(V) to As(III), and the

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reductive dissolution of host Fe(III)-phases that may promote concomitant release of sorbed or

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coprecipitated elements. Although our XANES results indicated that the primary solid-phase As

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species is arsenate, pore water extracted from the sediments has been shown to contain arsenite,8,

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38

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arsenite under anoxic conditions.36 In contrast, selenium reduction from selenite to Se(0)/SeS2

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would result in less soluble and less reactive Se forms under reducing conditions.10, 26, 36 Uranium

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exists in the oxidized form of U(VI) (Fig. 5B), and similar to Se, reduction of U(VI) should

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produce less soluble precipitates, mainly uraninite.46 Average dissolved concentrations of Se and

and incubations conducted with sediment/ash mixtures show that arsenate can be reduced to

14


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U in pore water samples of sediments affected by the Kingston ash spill ranged from 0.3–2 µg Se

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L-1 and 0.2–3 µg U L-1.8 Moreover, Cr(III) would not be expected to be mobilized under

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reducing conditions.

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The geochemical complexity of trace elements in the fly ash samples analyzed here

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indicates that direct ecotoxicological assessments of potentially toxic trace elements should

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consider chemical conditions in relation to the chemical speciation of target trace elements of

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concern along with dominant matrix elements such as iron, aluminum, and silicon in oxides or

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glasses with which trace elements are associated. In river sediments and other environmental

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systems, the geochemical conditions in which fly ash resides are important for controlling trace

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metal mobility and potential toxicity.

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Acknowledgments. This work was supported by a Tennessee Valley Authority/Oak Ridge

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Associated Universities Characterization and Environmental Effects of Coal Combustion

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Products Grant (No. 7-22978). We thank Dr. Neil Carriker for valuable discussion and for

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providing ash samples. We thank Dr. David Buchwalter for valuable discussion. We thank Drs.

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Kaumudi Pandya, Paul Northrup, and Maria Hernandez-Soriano for assistance at the National

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Synchrotron Light Source and John Bargar, Erik Nelson, Matthew Lattimer, and Martin Akafia

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for assistance at the Stanford Synchrotron Radiation Lightsource. We thank Dr. Markus Gräfe

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(CSIRO) for providing Cu K-edge XANES data for standards: CuFeS2, CuFe2S3 and CuS2 and

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Paul Northrup for the U standards. Portions of this research were carried out at the National

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Synchrotron Light Source (NSLS), Brookhaven National Laboratory, which is supported by the

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U.S. Department of Energy, Division of Materials Science and Division of Chemical Services.

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Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 15


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is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy

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Sciences under Contract No. DE-AC02-76SF00515.

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SUPPORTING INFORMATION AVAILABLE

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Supporting information includes synthesis details for aluminosilicate glass standards,

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standards used in linear combination fitting, as well as parameters used in collecting XAS

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spectra. . This information is available free of charge via the Internet at http://pubs.acs.org/.

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Energy & Fuels

FIGURES Figure 1. Total mass selected trace elements from fly ash residuum. The total fly ash remaining is estimated to be 380,000 metric tons. Calculations assume a specific gravity of 2.3 and trace element concentrations from previous studies.5, 7 Figure 2. Stacked, normalized As K-edge XANES spectra for coal fly ash samples KIF1, KIF2, and JVL and selected As standards. Best fits to the sample spectra (overlaid solid lines) over the range of 11850 and 11890 eV for As were obtained with linear combinations of As(V) incorporated into glass, As(V) adsorbed to ferrihydrite (Fh), and/or As(III) adsorbed to ferrihydrite (Fh). Figure 3. Stacked, normalized Se K-edge XANES for coal fly ash samples KIF1, KIF2, and JVL and selected Se standards. Best fits to the sample spectra (overlaid solid lines) over the range of 12650 and 12680 eV were obtained with linear combinations of selenite incorporated into glass, selenium sulfide or Se0, and/or Na-selenate. Figure 4. Stacked, normalized Zn K-edge XANES spectra for coal fly ash samples KIF1, KIF2, and JVL and selected Zn standards. Best fits to the sample spectra (overlaid solid lines) over a range of 9650 and 9700 eV included Zn incorporated into glass, ZnO, Sphalerite ((Zn,Fe)S), Zn sorbed to ferrihydrite (Fh), and/or franklinite (ZnFe2O4). Figure 5. (A) Stacked, normalized Cr K-edge XANES and (B) U M5-edge XANES spectra for coal fly ash samples KIF1, KIF2, and JVL and selected Cr and U standards. The Cr oxidation state is predominantly +3 because the fly ash samples lack the prominent pre-edge feature associated with a +6 oxidation state (vertical dashed line). For U, all samples show a peak position consistent with a U in +6 oxidation state. Figure 6. (A) Stacked, normalized Cu K-edge XANES spectra and (B) derivative XANES spectra for coal fly ash samples KIF1, KIF2, and JVL and selected Cu standards. Best fits to the sample spectra (overlaid solid lines) were computed over an energy range of 8970 to 9020 eV for Cu, and included linear combinations of Cu(II) incorporated into glass, Cu2O, chalcopyrite (CuFeS2), and Cu2S. Fitting with our available standards did not account for the pre-white line feature (see dashed vertical line) in fly ash spectra. This feature is indicative of a reduced copper species. Figure 7. Conceptual model of pH and redox conditions favoring leaching and diffusion of trace elements from fly ash.

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Table 1. Results of linear combination fitting (LCF) showing combinations of standards yielding the best fits to arsenic, selenium, copper, and zinc K-edge XANES spectra for fly-ash samples KIF1, KIF2, and JVL. Included are spectral weighting factors on standards (%) ± uncertainties and residuals in the fits (R factors). Fits were performed across energy ranges of 11850-11890 eV (As), 12650-12680 eV (Se), 8970-9020 eV (Cu), and 9650-9700 eV (Zn). Element/Sample Arsenic As(V)/glass KIF1 64 ± 7 KIF2 65 ± 6 JVL 62 ± 8 Selenium Se(0)/SeS2 KIF1 23 ± 1 KIF2 12 ± 3 JVL 6±2 Copper Cu2O KIF1 27 ± 3 KIF2 20 ± 8 JVL 22 ± 8 Zinc ZnO KIF1 14 ± 1 KIF2 20 ± 1 JVL 17 ± 1

XANES Individual components (%)a As(V)/Fh As(III)/Fhb 36 ± 8 30 ± 7 5±2 38 ± 8 Se(IV)/Glass Na-Selenate 77 ± 2 80 ± 2 8±2 86 ± 2 8±2 Cu2S Chalcopyrite Cu-glass CuO 14 ± 3 42 ± 5 17 ± 8 41 ± 8 20 ± 9 19 ± 13 36 ± 8 13 ± 8 29 ± 11 Zn/Fhb Franklinite 77 ± 4 9±3 72 ± 3 8±3 70 ± 3 12 ± 3 b

a

R-factorc 0.01 0.01 0.02 0.01 0.03 0.01 0.02 0.02 0.02 0.001 0.002 0.002

Sum of the data values of individual components (%) are normalized to 100. R-factor = ∑(data – fit)2 / ∑(data2); As(III) , As(V), or Zn sorbed to ferrihydrite; cParameter uncertainties calculated by Athena are given in parenthesis;

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Figure 1.

70 Mass (Metric tons)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

60

60

60

Zn

Cu

50

50 40

40 30

30 20 10 0

5 Se

9 U

Pb

Cr

As


Energy & Fuels

Figure 2.

As(III)/Fh

Normalized XANES

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

As(V)/Fh

As(V)/Glass As2O5 JVL KIF2 KIF1 11860 11870 11880 X-ray Energy (eV) ACS Paragon Plus Environment

Page 28 of 33

Page 29 of 33

Figure 3.

Na-Selenate

Se(IV)/Glass

Normalized XANES

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

SeS2 Se(0)

JVL KIF2 KIF1 12650

12660 12670 X-ray Energy (eV)


12680

Energy & Fuels

Figure 4.

Zn-Glass Sphalerite

ZnO Normalized XANES

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Franklinite Zn/Fh

JVL KIF2 KIF1

9650 9660 9670 9680 9690 9700 X-ray Energy (eV) ACS Paragon Plus Environment

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Energy & Fuels

Figure 5.

A

B

K2Cr2O7

U(IV)

10% Cr(VI)/90% Cr(III)

Cr2O3

JVL

KIF2

Normalized XANES

50% Cr(VI)/50% Cr(III)

Normalized XANES

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

KIF1

U(VI)

JVL

KIF2 KIF1

5980 6000 6020 6040 6060 6080 3540 ACS Paragon Plus Environment X-ray Energy (eV)


Energy & Fuels

Figure 6. A

B

CuO

Cu2S Chalcopyrite Cu2O JVL

First Derivative XANES

Cu2+/Glass

Normalized XANES

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

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KIF2 KIF1


9020



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Energy & Fuels

Figure 7.


Chemical Speciation of Potentially Toxic Trace Metals in Coal Fly Ash

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