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Volume# 3 (2011)

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Suggested Citation format for this article:

Silva, L.F.O., Oliveira, M.L.S., Serra, C., Hower, J.C., 2011, Zinc Speciation in Power Plant Burning Mixtures of Coal and Tires. Coal Combustion and Gasification Products 3, 41-50, doi: 10.4177/CCGP-D-11-00008.1

I S S N 1 9 4 6 - 0 1 9 8

j o u r n a l h o m e p a g e : w w w . c o a l c g p - j o u r n a l . o r g

Zinc speciation in power plant burning mixtures of coal and tires

Luis F.O. Silva1, Marcos L.S. Oliveira2, Carmen Serra3, James C. Hower4,*1 Environmental Science and Nanotechnology Department, Catarinense Institute of Environmental Research and Human Development – IPADHC, Capivari de Baixo,

Santa Catarina, Brazil. felipeqma@yahoo.com.br2 Development Department of Touristic Opportunities, Catarinense Institute of Environmental Research and Human Development – IPADHC, Capivari de Baixo, Santa

Catarina, Brazil3 Servicio de Nanotecnologıa y Analisis de Superficies C.A.C.T.I., Universidade de Vigo, Vigo, Spain4 University of Kentucky Center for Applied Energy Research, Lexington, KY, 40511, USA. james.hower@uky.edu

A B S T R A C T

Fly ash from the cyclone-boiler co-combustion of high-S, high volatile bituminous coal and tire-derived fuel (tdf) was studied

using a variety of chemical, optical, and microbeam techniques. Fly ash, dominated by Al-Si glass with lesser amounts of coal-

derived carbons, Fe-spinels, and tire-derived carbons, has Zn concentrations ranging from 2200 ppm (1st ESP row) to 6900 ppm

Zn (3rd ESP row). Zinc occurs in Zn-rich nanoparticles in the Al-Si glass phases and as ZnO in amorphous and crystalline

nanominerals, Fe- and Zn-sulfides, Pb-Al-Fe sulfates, and Zn sulfates. Iron-rich, Al- and Ti-bearing spinels contain accessory

Zn2+, Cr3+, Mn2+, and Pb2+. Fe-sulfates and phosphates nanoparticles incorporate As, Cr, V, Ni, and Zn. Fullerenes were not

detected in this fly ash, potentially due to the higher temperature of combustion in the cyclone boiler. Zinc was detected by

XPS, but the low binding energies mitigated against the determination of the speciation of the element.

f 2011 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association

All rights reserved.

A R T I C L E I N F O

Article history: Received 03 May 2011; Received in revised form 05 July 2011; Accepted 14 July 2011

Keywords: zinc; tires; coal combustion; fly ash; fullerenes

1. Introduction

Humans are increasingly exposed to anthropogenic ultrafine

particles and nanominerals, increasing the urgency to explore

toxicological impact and other adverse health effects arising from

the exposure to ultrafine particles and nanominerals from coal

power plants and spontaneous coal combustion (Hower et al.,

2008; Silva et al., 2009; Silva and Da Boit, 2011). Our previous

studies have concentrated on coal-combustion-derived particles,

but there are a number of power plants burning mixtures of coal

and non-coal fuels, such as petroleum coke and tires. Tire-derived

fuel has attracted attention as a high-heating value replacement for

small percentages of feed coal, typically 1–3% of the total feed,

and as a means of averting disposal of a large percentage of waste

tires (Hower et al., 2001, 2007; Hower and Robertson, 2004).

In this study, the first on the detection and complex

characterization of ultrafine/nano-particles assemblages in a

power plant burning mixtures of coal and tires, we investigate

the forms of nanocarbons, nanominerals, and others compounds

containing hazardous trace elements (in particular Zn) in fly ashes

(FA) from the combustion of high-S coal and tire-derived fuel, the

latter about 2–3% of the total fuel feed, in a 100-MW cyclone

utility boiler.

2. Methods

Coal and FA were sampled at a western Kentucky power plant in

the course of the pentannual sampling of Kentucky power plants

by the University of Kentucky Center for Applied Energy Research

(CAER) (Hower et al., 2009). The coarse coal + tire-derived fuel feed* Corresponding author. Tel: 1-859-257-0261. Email: james.hower@uky.edu

doi: 10.4177/CCGP-D-11-00008.1

f 2011 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association. All rights reserved.

was sampled at two feed hoppers. The FA was sampled in one

hopper for each of the three electrostatic-precipitator (ESP) rows.

Fly ash petrology was analyzed on Sudan Black-laced epoxy-

bound pellets prepared to a final 0.5-mm polish with 503 oil-

immersion optics and polarized white light following procedures

initially defined by Hower et al. (1995) and refined and expanded

since that publication.

Basic FA chemistry was conducted following ASTM procedures.

Major and minor elements were determined by X-ray fluorescence

at the CAER following procedures outlined by Hower and Bland

(1989) and by a variety of methods at the US Geological Survey’s

Denver Laboratories following procedures after Meier et al. (1996).

Mercury was analyzed at the CAER on a LECO AMA 254 Advanced

Mercury Analyzer absorption spectrometer.

Inductively coupled plasma mass spectrometry (ICP-MS, Xseries

II), in a pulse counting mode (three points per peak), was used to

determine most trace elements. Arsenic and Se were determined by

ICP-MS using collision cell technology (CCT) in order to avoid

disturbance of polyatomic ions. For ICP-MS analysis, samples were

digested using an UltraClave Microwave High Pressure Reactor

(Milestone). The basic load for the digestion tank was composed of

330-ml distilled H2O, 30-ml 30% H2O2, and 2-ml 98% H2SO4.

Initial nitrogen pressure was set at 50 bars and the highest

temperature was set at 240uC for 75 mins. The reagents for 50-mg

sample digestion were 5-ml 65% HNO3, 2-ml 40% HF, and 1-ml

30% H2O2. The procedures of sample digestion and ICP-MS

analysis were outlined by Dai et al. (2011).

The major crystalline mineral composition of the FA samples

was determined by means of a Siemens D5005 X-ray diffraction

(XRD). The samples were ground by hand in a ceramic mortar and

pestle, dry mounted in aluminum holders, and scanned at 8–60u 2h

with Cu K-a radiation.

Electron beam methods included Field Emission Scanning

Electron Microscope (FE-SEM) with energy-dispersive X-ray

spectrometer (EDS) capabilities and high-resolution transmission

electron microscope (HR-TEM) with SAED (selected area

electron diffraction) or MBD (microbeam diffraction), and

scanning transmission electron microscopy (STEM). Time of

flight secondary ion mass spectrometry (TOF-SIMS) was used

to investigate the elemental and molecular structure of the

samples. Surface composition for zinc speciation was deter-

mined by X-ray photoelectron spectroscopy (XPS). Details of

Fig. 1. A/ Anisotropic coke (a) showing interference colors, with included inertinite (i). B/ Anisotropic coke (a) with pyrrhotite (s) in lumens. C/ Carbon from tire-derived

fuel (tdf). D/ Carbon from tire-derived fuel (tdf), some of it showing development of anisotropic (a) domains.

42 Silva et al. / Coal Combustion and Gasification Products 3 (2011)

the microbeam procedures and nanominerals detection follow-

ing sequential extraction have been published by Silva et al.

(2011a, b, c).

3. Results and Discussion

3.1. Petrology

The FA petrology is dominated by Al-Si glass, with secondary

amounts of anisotropic coke with included inertinite (Figure 1a)

and pyrrhotite (Figure 1b). Overall, the amount of glass increases

from the first to the third ESP row as the amount of FA carbons

decreases (Table 1). Isotropic coke and Fe-spinels are also among

the fly ash constituents. Tire-derived fly ash carbons are present in

trace to minor amounts (Figures 1c, d).

3.2. Chemistry

The feed coal + tire-derived fuel (tdf) chemistry is presented on

Table 2. The tires, however, being more difficult to grind than the

coal, are not proportionately represented in the analysis.

The FA chemistry is presented on Table 3. The contribution of

the tires to the fly ash is reflected in the amount of Zn. As known

from previous studies of both strictly coal- and coal + tdf – derived

ashes, the concentration of volatile trace elements increases

towards the back rows of the ESP array as a function of both the

cooling of the flue gas and the decreased particle size, therefore,

greater surface area, of the FA from the 1st to the 3rd row. This is

well expressed in the increase of the Zn concentration from about

2200 to 6900 ppm. The tdf-derived fly ash carbon also increases in

the same direction. Based on many observations of strictly coal-

derived FA, we know that Zn, As, and other elements tend to

partition towards the back rows of ESP arrays (Mardon and Hower,

2004), therefore, we suspect that some of the Zn, both coal- and

tdf-derived, enters the volatile phase in the boiler.

Mineral nanoparticles (nanoscale versions of bulk minerals) and

nanominerals (minerals or mineraloids that occur only in

nanoscale forms (e.g., hematite and magnetite) are important

major constituents in coal power plants (Chen et al., 2004; Hower

et al., 2008; Silva et al., 2010a,b) and spontaneous coal combustion

processes (Ribeiro et al., 2010; Silva et al., 2011c). In the present

research, the incidental/anthropogenic Zn-nanopartices, Zn-ultra-

fine particles (e.g. Figure 2), and Zn-nanominerals (e.g. Figures 3–

5) detected collectively have immense surface areas relative to

mm-sized and larger particles.

The amount of Zn in the FA was relatively high (Table 3), and

the Zn-rich nanoparticles and nanominerals occurred in complex

aggregates in the non- and/or silicate minerals (Fe-, Si-, and Al-

oxides and phosphates) that preferentially embedded in the Al-Si

(with lesser Ca, Fe, K, Mg, P) glass matrix (Figure 2).

Glass phases are the main constituents of studied fly ash

(Figure 2), entrapping several assorted crystalline ultrafine and

nanomineral phases or melt clusters (spinels and metallic

inclusions with Zn). The glasses have numerous discrete vesicles

and fractures that resulted from rapid quenching in the transit from

the boiler to the ESPs. The particles are spherical, highly

aggregated, and can significantly affect the geochemical cycling

of metals and the dissolution of redox-sensitive metal oxides,

promoting potential environmental impacts. Generally, the studied

CFA comprises spherical solids (Figures 2–5) and hollow ceno-

spheres with sizes ranging from ,5 nm to .500 mm with a

maximum of the particle size distribution in the 0.003- to 250-mm

interval and have a heterogeneous chemical composition and

different morphologies. While some particles are completely

spherical, others have an elongate-elliptical morphology (Fig-

ure 2A). The occurrence of elongate-elliptical Al-Si ash particles

indicates that the residence time in the high temperature zone of

the furnace was too short for complete sphere formation/

Table 2

Feed coal chemistry. Proximate, ultimate, and S forms on a weith % basis. Minor elements on ppm ash basis; with exception of Se, Hg, and Cl on ppm whole coal basis

sample Ash Moisture VM FC C H N S O Spy Ssulf Sorg HV (MJ/kg)

93443 13.99 3.41 36.9 45.7 63.77 4.69 1.41 4.85 11.29 2.76 0.11 1.98 26.81

93444 12.33 3.82 37.61 46.24 65.9 4.93 1.44 3.95 11.45 2.05 0.07 1.83 27.31

sample SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O P2O5 TiO2 SO3

93443 37.13 14.93 25.68 8.53 0.73 0.53 1.87 0.11 0.76 12

93444 40.4 16.5 22.44 8.38 0.77 0.58 1.99 0.09 0.87 11.22

sample V Cr Mn Co Ni Cu Zn As Rb Sr Zr Mo Cd Sb Ba Pb

93443 159 95 443 65 36 dl 53 87 dl dl 186 dl 1 11 262 23

93444 186 93 365 58 50 dl 57 78 1 dl 175 dl 1 10 305 25

sample Se Hg Cl

93443 1.4 0.3 9

93444 1.38 0.24 29

Table 1

Fly ash petrology. All units are in volume %. Trace 5 t

sample no. 93446 93447 93448

ESP row 1 2 3

glass 66.5 88.5 93.0

mullite 0.0 0.0 0.0

spinel 8.5 3.5 2.5

quartz 0.0 0.0 0.0

sulfide 1.0 0.0 0.0

sulfate 0.0 0.0 0.0

crystalline silicate 0.0 0.0 0.0

lime 0.0 0.0 0.0

rock fragment 0.0 0.0 0.0

isotropic coke 6.5 1.5 2.0

anisotropic coke 13.5 5.5 0.5

inertinite 4.0 1.0 1.0

pet coke 0.0 0.0 0.0

tire-derived carbon t 0.0 1.0

unburned coal 0.0 0.0 0.0

Silva et al. / Coal Combustion and Gasification Products 3 (2011) 43

Fig. 2. FE-SEM general illustration. (A) Completely spherical particles and resemble an elongate-elliptical morphology; (B and D) Cenospheres; (C) Complex association

between amorphous Al-Si-minerals, mullite, Fe-oxides and Zn-sulfates particles.

Table 3

Fly ash chemistry. Samples 93446, 93447, and 93448 correspond to the first, second, and third electrostatic precipitator (ESP) rows, respectively. The first through third

row path also corresponds to the decrease in flue gas temperature. Ultimate analysis on a weith % basis. Minor elements on ppm ash basis; with exception of Se and Hg

on ppm whole ash basis.

sample Ash Moisture C H N S O

93446 81.27 0.4 12.59 0.12 0.17 1.24 4.61

93447 85.77 0.77 7.22 0.3 0.13 1.64 4.94

93448 89.39 0.88 4.3 0.24 ,0.01 1.95 4.12

sample SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O P2O5 TiO2 SO3

93446 42.28 17.59 26.8 5.15 0.86 0.87 3.25 0.17 1.15 1.59

93447 39.36 16.65 28.63 4.6 0.87 1.09 3.37 0.23 1.25 2.01

93448 38.32 16.07 28.73 4.37 0.87 1.18 3.43 0.25 1.3 2.72

sample V Cr Mn Co Ni Cu Zn As Rb Sr Zr Mo Cd Sb Ba Pb

93446 310 133 375 74 96 135 1370 183 dl dl 176 3 1 11 406 54

93447 383 165 394 82 119 224 3520 301 dl dl 181 3 1 12 461 85

93448 412 174 402 83 141 137 6579 323 dl dl 176 14 1 11 484 91

sample Se Hg

93446 16.12 0.16

93447 30.44 0.49

93448 46.58 0.59

44 Silva et al. / Coal Combustion and Gasification Products 3 (2011)

generation (Goodarzi and Sanei, 2009) and/or gas flow was

turbulent, also quite likely.

In addition, Zn was detected as ZnO (Figure 3), imbedded in

amorphous and/or crystalline Fe nanominerals (Figure 4); with

sulfides (e.g. sphalerite, Figure 5); in Pb-Al-Fe-sulfates, some in

association with glass (e.g. anglesite [PbSO4]); and with pure

complex sulfates in minor abundance (gunningite [ZnSO4 N H2O];

zinkosite [ZnSO4]; bianchite, ZnSO4 N 6H2O; and goslarite, ZnSO4 N7H2O). For these hydrated Zn-nanosulfates, the composition may

change during sample processing or in the HR-TEM vacuum.

However, these minerals (after solubilised by water and before

crystallized) were easily identified by FE-SEM/EDS/SAED study

after water extraction. These results were interesting for under-

stand of Zn-sulfates leaching in the environmental during FA

deposition.

Massive ZnO with different morphologies (Figure 3) was

detected by HR-TEM/EDS/SAED. ZnO nanominerals have received

broad attention due to their value in electronics, antibacterial

agents, optics, in pigments, in sun screens, in photonics, and in

polymers or tires as stabilizers (Liu et al., 2009). Of course, the

latter use is one of the vectors for Zn incorporation into the fuel

blend and, subsequently, the FA under investigation. Despite the

excellent advantages, the ecological risk arising from their release

during the production and application process has received

increasing attention in many reports. Nano-ZnO has been found

to be toxic to algae (Aruoja et al., 2009; Wong et al., 2010),

Fig. 3. (A) crystaline zinc oxide contain amorphous carbonaceous particles. (B) nanowires growing from a thin platelet base and parallel to each other to form a bundle;

(C) General ZnO agglomerate.

Silva et al. / Coal Combustion and Gasification Products 3 (2011) 45

crustaceans (Blinova et al., 2010), fish (Wong et al., 2010), bacteria

(Zhang et al., 2010), nematodes (Wang et al., 2009), plants (Lin et

al., 2008) under aquatic and aerosol exposure modes (Wu et al.,

2010) at various levels. Deleterious human health effects resulting

in pulmonary changes from inhaled ZnO have only been

documented in connection with acute high or long-term occupa-

tional exposure at coal power plants workers.

Fe-nanominerals with magnetite, hematite, goethite (Figure 4),

as well as a series of Al-substituted and Ti-substituted varieties, are

commonly identified in the studied FA. Varying amounts of Zn2+,

Cr3+, Mn2+, and Pb2+ are incorporated into these spinels. Therefore,

there is no single, uniform alteration path upon exposure to the

environment. However, the composition of FA from different tdf- +coal-fueled plants are similar (Hower et al., 2001, 2007; Hower and

Fig. 4. Zn-bearing Fe-nanominerals detected by EDS (white zones). (A) Goethite; (B) Hematite; (C) Magnetite; (D) Jarosite pseudomorph after pyrite.

46 Silva et al. / Coal Combustion and Gasification Products 3 (2011)

Robertson, 2004), which suggests that high-temperature processing

of solid waste produces more-or-less uniform outcomes in view of

both chemical and mineralogical characteristics. These findings are

consistent with the fact that Zn2+, Cr3+, Mn2+, and Pb2+ have

relatively high free energies (|DGfu|) of oxidization, indicating

their easily oxidable properties (Wei et al., 2011). In the

nanoparticulate hematite, surface Fe sites are also under coordi-

nated relative to Fe in the bulk structure and may explain an

increased sorptive capacity for aqueous Zn2+ relative to larger-

sized hematite particles (Ha etal.,2009) and its potential leaching

risk this FA. In addition, Fe-sulfates (e.g. jarosite, Figure 3D) and

phosphate nanoparticles typically incorporate other elements such

as As, Cr, V, Ni, and Zn. Based on the HR-TEM/EDS/MBD analyses,

composite (Zn, Fe)3(PO4)2 could be present.

The nanosphalerite grains (Figure 5) have been the focus of

several structural studies. A pioneering study of nano-ZnS

nanoparticles (Gilbert et al., 2004) reported the structure is stiffer

than that of bulk ZnS, based on a higher Einstein vibration

frequency in the nanoparticle (Brown and Calas, 2011). In the

present study, the surface region of the detected ZnS nanoparticle

is highly strained. In a similar study of ZnS nanoparticles in

contact with aqueous solutions containing various inorganic and

organic ligands, stronger surface interactions with these ligands

resulted in a thicker crystalline core and a thinner distorted outer

shell (Zhang et al.,2010).

The TOF-SIMS scan of the 550–900 mass/u range detected some

heavy hydrocarbons, but none corresponding to fullerenes. This is

contrast to the abundant fullerenes in the fly ash carbons from the

stoker boiler combustion of a bituminous coal as reported by Silva

et al. (2010a). The coal feed in the latter case is high volatile a

bituminous, slightly high that the high volatile C bituminous rank

of the coal burned at this plant. Rather than the coal rank, the

difference in the nature of the ashes may be attributable to the

combustion process, with the cyclone boiler used at the plant in

this study operating at higher combustion temperatures than the

stoker boiler, in excess of 1650uC (Kitto and Stultz, 2005, chapter

14) compared to about 1300 uC for a stoker boiler (Kitto and Stultz,

2005, chapter 16).

The binding energy of selected elements is listed in Table 4 and

the binding energies of Zn, based on the literature, are given on

Fig. 5. Sphalerite nanoparticles detected by HR-TEM/EDS/MB.

Table 4

XPS binding energies and chemical state assignments

Experimental / Binding energy B.E. (eV)/ Chemical state assignments

Carbon Zinc Iron Silicon Aluminum Sulfur

Samples

‘‘As received’’ C1s Zn2p3/2 Fe2p3/2 Si2p Al2p S2p3/2

46 C1: 285/C-C,CH 1022.46 (Ni2+) 710.8 (Fe3+) 103.44 75.16 163.78(5.7%)

C2:286.52/C-O 712.58FeOOH Si 4+ Al 3+ 169.26(94.4%)

C3:288.87/ O5C-O 715.54 Fe2p Satellite

47 C1: 285/C-C,CH 1022.72 (Ni2+) 710.68 (Fe3+) 103.5 75.28 164.4(4.6%)

C2:286.7/C-O 1021.51 712.38FeOOH Si4+ Al3+ 169.24(95.4%)

C3:289.3/ O5C-O 715.03 Fe2p Satellite

48 C1: 285/C-C,CH 1022.6(Ni2+) 710.83 (Fe3+) 103.48 75.25 169.29(100%)

C2:286.76/C-O 712.48FeOOH Si4+ Al3+C3:289.05/ O5C-O 714.54 Fe2p Satellite

Silva et al. / Coal Combustion and Gasification Products 3 (2011) 47

Table 5. The Binding energy of Zn detected in the samples is

between 1022.5–1022.7 eV, this value is mostly attributed to Ni2+

in the databases. However, the published binding energies for

different Zn2p3/2 compounds, such as metallic Zn, ZnO, or ZnS are

quite similar. To identify metallic Zn or ZnO by the Zn2p3/2 peak

presents some difficulties. The chemical shifts of Auger peaks are

usually more pronounced than photoelectron peaks, therefore, they

can be used to identify the chemical states of elements as the

complements to photoelectron peaks. However, in this study, due

the low concentration of this element, the Auger peaks are not

detected. The Zn signals are very low, close to detection limit of the

XPS instrument and, therefore, the conditions are not optimal for

determining the chemical state of these species. The third-row ESP

sample does show stronger Zn signals than the first row ESP

sample (Figure 6 and 7), but, at these low binding energies, it is not

possible to draw conclusions about any relation between the flue

gas temperature and the chemical state of the Zn. The sulfur

detected in the samples is mainly (94%–100%) due to sulfate.

4. Conclusions

Fly ash from the cyclone-boiler co-combustion of high-S high

volatile bituminous and tire-derived fuel (tdf) was studied using a

variety of chemical, optical, and microbeam techniques. The fly

ash is dominated by an Al-Si glass with lesser amounts of coal-

derived carbons, Fe-spinels, and tire-derived carbons. Owing to the

Zn in the tdf, the ESP fly ash contains from 2200 ppm (1st ESP row)

to 6900 ppm Zn (3rd ESP row). As with other volatile trace

elements, the increase in concentration of Zn from the 1st to 3rd

ESP rows is a function both of the decrease in flue gas temperature

and the decrease in particle size (therefore, greater surface area) in

the same direction.

Microbeam analysis showed that Zn-rich nanoparticles were

associated with the Al-Si glass phases. Zinc also occurs as ZnO

associated with amorphous and crystalline nanominerals, Fe- and

Zn-sulfides, Pb-Al-Fe sulfates, and Zn sulfates. Iron-rich nano-

minerals, generally identified as spinels in the optical character-

ization, are present. Varieties with Al and Ti are present, and Zn2+,

Cr3+, Mn2+, and Pb2+ are present as accessory elements in the

spinels. Fe-sulfates and phosphates nanoparticles incorporate other

elements such as As, Cr, V, Ni, and Zn.

In contrast to the carbons from a stoker boiler studied by Silva et

al. (2010a), fullerenes were not detected in this fly ash, potentially

due to the higher temperature of combustion in the cyclone versus

stoker boilers.

Fig. 6. Comparison of Zinc XPS binding energy for fly ash sample 93446, the

1st-row ESP fly ash, and fly ash sample 93448, the 3rd-row ESP fly ash.

Table 5

Binding energy values from references (1 – Bar et al., 2006; 2 – Chen et al., 2010;

3- Fiedler & Bendler, 1992; 4- Olivella et al., 2002; 5- Castano et al., 2007)

Zn2p3/2 references S2p3/2 references

1022.4 ZnO (Zn2+) 1 ,164 organic non oxidized

(sulfur)

3

,168 sulfoxides S(O)

168 sulfone SO2

169.2 sulfonic acid SO3H

1021.7 ZnS (Zn2+) 1 158.7–159.6 pyritic 4

161.2 162.5 sulfidic

163.7–164 thiophenes,

thioethers, mercaptanes

166 sulfoxides

168 sulfone SO2

169.2 sulfonate

174.8–175.8 sulfates

1021.7 Zn metallic 2 167.4 eV sulfite ion (SO322) 5

169.2 eV sulfate ion (SO422)

48 Silva et al. / Coal Combustion and Gasification Products 3 (2011)

Zinc was detected by XPS, but the low binding energies

mitigated against the determination of the speciation of the

element.

Acknowledgements

The work performed by the group from Brazil (FE-SEM, HR-

TEM, and XRD) was carried out with support from the Catarinense

Institute of Environmental Research and Human Development –

IPADHC.

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