materials
Article
The Characterization of Fixation of Ba, Pb, and Cu in
Alkali-Activated Fly Ash/Blast Furnace Slag Matrix
Jan Koplík *, Lukáš Kalina, Jiří Másilko and František Šoukal
Materials Research Centre, Faculty of Chemistry, Brno University of Technology, Purkyňova 118,
Brno 61200, Czech Republic; kalina@fch.vut.cz (L.K.); masilko@fch.vut.cz (J.M.); soukal@fch.vut.cz (F.Š.)
* Correspondence: koplik@fch.vut.cz; Tel.: +420-541-149-426
Academic Editor: Claudio Ferone
Received: 13 April 2016; Accepted: 24 June 2016; Published: 30 June 2016
Abstract: The fixation of heavy metals (Ba, Cu, Pb) in an alkali-activated matrix was investigated.
The matrix consisted of fly ash and blast furnace slag (BFS). The mixture of NaOH and Na-silicate
was used as alkaline activator. Three analytical techniques were used to describe the fixation of heavy
metals—X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with
energy dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD). All heavy metals
formed insoluble salts after alkaline activation. Ba was fixed as BaSO4 , and only this product was
crystalline. EDS mapping showed that Ba was cumulated in some regions and formed clusters. Pb
was present in the form of Pb(OH)2 and was dispersed throughout the matrix on the edges of BFS
grains. Cu was fixed as Cu(OH)2 and also was cumulated in some regions and formed clusters. Cu
was present in two different chemical states; apart from Cu(OH)2 , a Cu–O bond was also identified.
Keywords: fixation; alkali-activated materials; X-ray photoelectron spectroscopy; heavy metals
1. Introduction
Heavy metals are a significant part of various industrial and chemical waste materials, which can
be a serious environmental threat. Waste materials with heavy metal content are processed by the set
of procedures called stabilization/solidification. During these procedures, many different materials
such as concrete and glass are used. In the past few decades, a new material for the inhibition of
hazardous materials was used—alkali-activated material (AAM) [1,2].
The history of AAMs began in 1940s, when Kühl [3] and later Purdon [4] used an alkali
activator for the activation of blast furnace slag. Nowadays, AAMs include broad types of
materials—blast furnace slag, metakaolin, fly ash, etc. However, AAMs can vary in chemical or
phase composition, and an alkali activator (high pH) is always used during the preparation of them.
The main difference among AAMs is the content of calcium. AAMs can be divided into the groups
of high-calcium alkali-activated materials (HCAAMs) and low-calcium alkali-activated materials
(LCAAMs). HCAAMs are represented by alkali-activated blast furnace slag (BFS) or other types
of slag (steel, phosphorus, copper, nickel, etc.). The C–S–H and C–A–S–H gels are assumed to be
the main hydration products of alkali activation of HCAAMs. This gel has a similar structure like
disordered tobermorite-like C–S–H(I) type and AlO4 tetrahedra enable the extension or crosslinking of
the silicon chains. The secondary hydration products are formed depending on the composition of blast
furnace slag and used activator. AFm type phases were identified when using NaOH as the activator,
hydrotalcite was identified in activated slags with a high amount of MgO, and zeolites were identified
in BFS with a high amount of Al2 O3 [5–10]. A considerably different structure is present after the alkali
activation of LCAAMs. The structure can be described as a disordered cross-linked aluminosilicate
network, which consists of SiO4 and AlO4 tetrahedra linked by oxygen atoms. The negative charge
of AlO4 is balanced by the presence of a positive ion in the structure. Usually Na+ or K+ serve as
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Materials 2016, 9, 533
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the charge-balancing ions, but Ca2+ , Ba2+ , Mg2+ , and NH4+ can also occur. In fact, the structure of
LCAAMs is very similar to the structure of zeolites [5,11,12]. The main reaction product of the alkali
activation of the mixture of both types of AAMs (BFS and fly ash) is the N–A–S–H type gel. The gel is
actually of a C–S–H type with a high concentration of tetrahedrally coordinated Al and an interlayer
of Na ions incorporated into its structure [13].
The ability of AAMs to immobilize heavy metals and other hazardous materials in their structure
has been investigated since the second half of the last century. The efficiency of the inhibition of
heavy metals and other hazardous materials within AAMs depends on more factors including the
type of immobilized material, its dosage, the type of matrix, the nature of alkaline activator, and its
concentration. In general, Pb, Zn, Cr, and B reach a high efficiency of immobilization in AAMs, as
opposed to Cu, Cd, and As, which have worse inhibition results. There are two different ways of
how to fix heavy metals in the matrix—physical and chemical. Often, both of these types occur at the
same time. The physical immobilization of heavy metals is the same in AAMs as in other binders
(e.g., ordinary Portland cement). The physical immobilization is linked with the mechanical properties
of matrix and its porosity. The chemical fixation means bonding with newly formed alumino-silicate
phases. Some metals are fixed by forming insoluble salts, mainly hydroxides or silicates [14–29].
The aim of this study was to describe, how heavy metals (Ba, Pb, Cu) are fixed within the matrix
based on the alkali-activated mixture of fly ash and BFS, what their chemical state is, and how they
are distributed in the matrix. The description of form and chemical state of heavy metals after the
activation was enabled by using a modern analytical method—X-ray photoelectron spectroscopy.
2. Materials and Methods
2.1. Sample Preparation
Blast furnace slag and high-temperature fly ash were used as raw materials. Their chemical
composition is shown in Table 1. The mixture of NaOH and Na-silicate (weight ratio SiO2 :Na2 O—3.1;
wt % SiO2 —27.3) was used as the alkaline activator. Heavy metals were used in the form of Ba(NO3 )2
p. a., Pb(NO3 )2 p. a., and CuCl2 ¨2H2 O p. a. They were added as solids in the dosage of 2.5 wt % of
binder. Finally, three matrices with added heavy metals were prepared—one matrix for each heavy
metal. Demineralized water was used throughout. The composition of matrices is listed in Table 2.
The preparation of the matrix started with the mixture of all solid compounds together for 5 min,
followed by the adding of the alkaline activator and mixing for another 5 min. After mixing, the
samples were cast in steel molds measuring 20 ˆ 20 ˆ 100 mm3 and vibrated for 90 s. All analyses
were performed after 28 days of open curing at ambient conditions.
Table 1. Chemical composition of fly ash and BFS (wt %).
Fly Ash
SiO2
50.30
Al2 O3
27.70
CaO
3.84
Na2 O
0.76
K2 O
2.67
MgO
1.15
SO3
0.87
Fe2 O3
10.40
TiO2
1.45
P2 O 5
0.28
SO3
1.46
Fe2 O3
0.25
TiO2
0.96
MnO
0.55
Blast Furnace Slag
SiO2
34.70
Al2 O3
9.05
CaO
41.1
Na2 O
0.41
K2 O
0.90
MgO
10.5
Table 2. Composition of matrices (wt %).
Slag
Fly ash
NaOH
Na2 O.SiO2
Water
Ba, Pb, Cu
15.6
57.4
6.1
6.2
12.2
2.5
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2.2. Methods
The X-ray photoelectron spectroscopy (XPS) analyses were carried out with an Axis Ultra DLD
spectrometer (Kratos Analytical Ltd., Manchester, UK) using a monochromatic Al Kα (hν = 1486.7 eV)
X-ray source operating at 150 W (10 mA, 15 kV). The spectra were obtained using the analysis area of
~300 ˆ 700 µm. The Kratos charge neutralizer system was used for all analyses. The high-resolution
Remote Sens. 2016, 8, 533
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spectra were measured with the step size of 0.1 eV and 20 eV pass energy. The instrument base
8 Pa. The spectra were analyzed using the CasaXPS software (version 2.3.15)
pressure
was 2source
ˆ 10´operating
eV) X-ray
at 150 W (10 mA, 15 kV). The spectra were obtained using the analysis
of ~300Ltd.,
× 700Teignmouth,
μm. The Kratos
charge
system was used
for all
analyses.
(Casaarea
Software
UK)
and neutralizer
were charge-corrected
to the
main
line ofThe
thehighcarbon C
resolution
spectra were
measured
the284.80
step size
0.1 eV andShirley
20 eV pass
energy. Thewas
instrument
1s spectral
component
(C–C,
C–H) with
set to
eV.ofStandard
background
used for all
base
pressure was 2 × 10−8 Pa. The spectra were analyzed using the CasaXPS software (version 2.3.15)
sample
spectra.
(Casa Software Ltd., Teignmouth, UK) and were charge-corrected to the main line of the carbon C 1s
The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses
spectral component (C–C, C–H) set to 284.80 eV. Standard Shirley background was used for all
were performed using a JEOL JSM-7600F (JEOL Ltd., Tokyo, Japan) scanning electron microscope
sample spectra.
equippedThe
withscanning
X-Max electron
80 mm2 microscopy
SDD detector
in back-scattering
mode.X-ray
The working
distance
(SEM)
and energy dispersive
spectroscopy
(EDS)for all
samples
was
15
mm,
the
accelerate
voltage
was
15
kV,
and
the
probe
current
was
1
nA.
Prior
analyses were performed using a JEOL JSM-7600F (JEOL Ltd., Tokyo, Japan) scanning electronto the
SEM microscope
analysis, allequipped
sampleswith
wereX-Max
polished
for2 6SDD
h bydetector
a cross-section
polisher JEOL
Ltd., Tokyo,
80 mm
in back-scattering
mode.(JEOL
The working
distance
for all samples
was 15 mm,
accelerate
voltage
15 kV,
and the probe current was 1
Japan).
All samples
were sputtered
by the
gold
to obtain
good was
surface
conductivity.
nA. Prior
the SEM diffraction
analysis, all samples
were were
polished
for 6 h by
a cross-section
polisher Empyrean
JEOL
The
X-raytopowder
(XRD) data
obtained
using
a PANanalytical
(JEOL
Ltd.,
Tokyo,
Japan).
All
samples
were
sputtered
by
gold
to
obtain
good
surface
conductivity.
(PANanalytical B.V., Almelo, The Netherlands) diffractometer with CuKα radiation (1.54 Å) operating
The X-ray powder diffraction (XRD) data were obtained using a PANanalytical Empyrean
at the voltage of 40 kV, and the current of 30 mA and equipped with 3D detection system PIXcel3D
(PANanalytical B.V., Almelo, The Netherlands) diffractometer with CuKα radiation (1.54
Å)
(PANanalytical B.V., Almelo, The Netherlands). All samples were step-scanned from 5˝ to 90˝ 2θ
operating at the voltage of 40 kV, and the current of 30 mA and equipped
with
3D
detection
system
˝ 2θ. Time per step was 96 s.
usingPIXcel3D
vertical(PANanalytical
high-resolution
goniometer
a step size
of 0.013were
B.V.,
Almelo, Thewith
Netherlands).
All samples
step-scanned from 5° to
The variable
slitsvertical
with an
irradiated length
of 10 with
mm awere
used.
Presented
X-ray
an
90° 2θ using
high-resolution
goniometer
step size
of 0.013°
2θ. Time
perpatterns
step was have
96
original
background
that
has
been subtracted.
s. The
variable slits
with
annot
irradiated
length of 10 mm were used. Presented X-ray patterns have an
original background that has not been subtracted.
3. Results and Discussion
3. Results and Discussion
3.1. XPS
3.1. XPS
The XPS results show the chemical state of examined elements (Pb, Ba, Cu). In the case of lead,
The XPS results
show the
chemical
state ofenergy
examined
elements
Ba,4f
Cu). In
the case of lead,
the high-resolution
spectrum
gives
the binding
of 138.6
eV (Pb,
for Pb
7/2 line (Figure 1), typical
the high-resolution spectrum gives the binding energy of 138.6 eV for Pb 4f7/2 line (Figure 1), typical
for Pb(OH)2 . The conversion of primary phase Pb(NO3 )2 to hydroxide will probably take place in the
for Pb(OH)2. The conversion of primary phase Pb(NO3)2 to hydroxide will probably take place in the
same way as in the hydration of Portland cement. This salt forms insoluble hydroxide in an alkaline
same way as in the hydration of Portland cement. This salt forms insoluble hydroxide in an alkaline
solution
and and
maymay
form
a coating
ononthe
furnaceslag)
slag)
particles,
which
can
be observed
solution
form
a coating
thecement
cement (blast
(blast furnace
particles,
which
can be
observed
in Figure
6.
There
is
no
evidence
that
the
lead
compound
creates
highly
insoluble
Pb
SiO
as in the
in Figure 6. There is no evidence that the lead compound creates highly insoluble Pb3SiO35 as in5 the
system
of alkali-activated
flyfly
ash
ininPalomo
study[29].
[29].
system
of alkali-activated
ash
Palomoet
etal.’s
al.’s study
Figure
1. X-ray
photoelectron spectroscopy
spectroscopy (XPS)
spectrum
of Pb.
Figure
1. X-ray
photoelectron
(XPS)
spectrum
of Pb.
The Ba 4d spectrum (Figure 2) demonstrates the creation of BaSO4 with a binding energy of Ba
3d5/2 of 780.0 eV, which is consistent with the EDS analysis.
Materials 2016, 9, 533
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The Ba 4d spectrum (Figure 2) demonstrates the creation of BaSO4 with a binding energy of Ba
3d
of 780.0
which is consistent with the EDS analysis.
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Remote Sens. 2016, 8, 533
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Figure
2. XPS spectrum
of Ba.
Figure
Figure2.2. XPS
XPSspectrum
spectrumof
ofBa.
Ba.
Finally, the XPS spectrum of Cu 2p (Figure 3) shows two different chemical states. The first Cu
Finally,
Finally,the
theXPS
XPSspectrum
spectrumof
ofCu
Cu2p
2p(Figure
(Figure3)
3)shows
showstwo
twodifferent
differentchemical
chemicalstates.
states. The
The first
first Cu
Cu
2p3/2 component at 934.8 eV with a strong shake-up satellite belongs to Cu(OH)2. Shake-up peaks may
2p
componentatat934.8
934.8eV
eVwith
with
a strong
shake-up
satellite
belongs
to Cu(OH)
peaks
2p3/2
3/2 component
a strong
shake-up
satellite
belongs
to Cu(OH)
2. Shake-up
peaks
may
2 . Shake-up
occur
when the outgoing photoelectron simultaneously interacts with a valence electron
and excites
may
the outgoing
photoelectron
simultaneously
interacts
a valence
electron
and
occuroccur
whenwhen
the outgoing
photoelectron
simultaneously
interacts
with awith
valence
electron
and excites
it to a higher-energy level. The kinetic energy of the shaken-up core electron is then slightly reduced
excites
it to a higher-energy
level.
The energy
kinetic of
energy
of the shaken-up
core electron
is then reduced
slightly
it to a higher-energy
level. The
kinetic
the shaken-up
core electron
is then slightly
giving the satellite structure a few eV below (higher on the calculated binding energy scale) the core
reduced
giving
the satellite
few eV(higher
below on
(higher
on the calculated
energy
giving the
satellite
structurestructure
a few eVabelow
the calculated
binding binding
energy scale)
thescale)
core
level position [30]. It should be noted that the determination of Cu(OH)2 also depends on the peak
the
core
level position
[30]. Itbe
should
noted
the determination
of 2Cu(OH)
also
depends
on
level
position
[30]. It should
notedbe
that
the that
determination
of Cu(OH)
also depends
on
the
peak
2
shape and main peak to shake up peak separation. The second Cu 2p3/2 peak at 932.7
eV represents
the
peak
shape
main
peak to
up peak separation.
TheCu
second
Cu 2p
peak
932.7 eV
shape
and
mainand
peak
to shake
upshake
peak separation.
The second
2p3/2 peak
at3/2
932.7
eVatrepresents
the bond of Cu with O. That can be interpreted as the formation of copper oxide or the formation of
represents
with
can be interpreted
as theofformation
of copper
or the
the bond ofthe
Cubond
withof
O.Cu
That
canO.
beThat
interpreted
as the formation
copper oxide
or the oxide
formation
of
the bond with the matrix.
the bond with
matrix.
formation
of thethe
bond
with the matrix.
Figure 3. XPS spectrum of Cu.
Figure3.3. XPS
XPSspectrum
spectrumof
ofCu.
Cu.
Figure
3.2. SEM
3.2. SEM
The microstructure of prepared matrices with heavy metals was characterized by the SEM
The microstructure of prepared matrices with heavy metals was characterized by the SEM
analysis. The regions containing heavy metals were investigated with EDS analysis. In all images,
analysis. The regions containing heavy metals were investigated with EDS analysis. In all images,
remaining particles of fly ash and grains of BFS are evident. High-temperature fly ash consists of
remaining particles of fly ash and grains of BFS are evident. High-temperature fly ash consists of
spherical particles of various sizes. Some of them can be hollow, and smaller particles are
spherical particles of various sizes. Some of them can be hollow, and smaller particles are
encapsulated in bigger ones in many cases. BFS is represented by grains of irregular shape. The
encapsulated in bigger ones in many cases. BFS is represented by grains of irregular shape. The
remaining space is filled by alumino-silicate gel.
remaining space is filled by alumino-silicate gel.
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3.2. SEM
The microstructure of prepared matrices with heavy metals was characterized by the SEM analysis.
The regions containing heavy metals were investigated with EDS analysis. In all images, remaining
particles of fly ash and grains of BFS are evident. High-temperature fly ash consists of spherical
particles of various sizes. Some of them can be hollow, and smaller particles are encapsulated in bigger
ones
in many cases. BFS is represented by grains of irregular shape. The remaining space is filled
by
Remote Sens. 2016, 8, 533
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alumino-silicate gel.
Figure
shows the
the SEM
SEMimage
imageofofthe
theprepared
preparedmatrix.
matrix.
The
light
structure
in the
middle
of
Figure 44 shows
The
light
structure
in the
middle
of the
the
image
represents
the
area
with
a
high
amount
of
barium.
Performed
EDS
analysis
determined
image represents the area with a high amount of barium. Performed EDS analysis determined
barium,
barium, sulfur,
sulfur, and
and oxygen
oxygen as
as the
the main
main components
components of
of the
the structure
structure (Table
(Table 3).
3). Their
Their molar
molar ratio
ratio of
of
1:1:4
responds
to
BaSO
.
These
results
correspond
with
the
XPS
analysis.
BaSO
was
also
identified
by
4 4 was also identified
1:1:4 responds to BaSO4 4. These results correspond with the XPS analysis. BaSO
the
analysis.
Subsequently,
the mapping
of chemical
elementselements
within thewithin
matrixthe
wasmatrix
performed.
by XRD
the XRD
analysis.
Subsequently,
the mapping
of chemical
was
The
mapping
(Figure
7)
showed
that
Ba
cumulated
in
some
bigger
areas
such
as
BaSO
,
rather
than
4
performed. The mapping (Figure 7) showed that Ba cumulated in some bigger areas such as BaSO4,
being
the matrix. the
Unlike
Cu and
Pb,Cu
Ba and
did Pb,
not Ba
form
rather dispersed
than beinguniformly
dispersedthroughout
uniformly throughout
matrix.
Unlike
didhydroxide
not form
because
of the
goodofsolubility
Ba(OH)2of
. The
sulfates
originated
from raw materials
to the due
fact
hydroxide
because
the goodofsolubility
Ba(OH)
2. The
sulfates originated
from rawdue
materials
that
the
chemical
composition
of
both
fly
ash
and
blast
furnace
slag
contained
a
sufficient
amount
of
to the fact that the chemical composition of both fly ash and blast furnace slag contained a sufficient
sulphur
to
form
BaSO
.
amount of sulphur to 4form BaSO4.
Figure 4.
4. Scanning
Scanningelectron
electron
microscopy
(SEM)
image
ofregion
the region
with barium,
fixed barium,
magnitude
Figure
microscopy
(SEM)
image
of the
with fixed
magnitude
2000ˆ.
2000×.
Table 3. Energy dispersive X-ray spectroscopy (EDS) analysis of the Ba cluster (atom %).
Table 3. Energy dispersive X-ray spectroscopy (EDS) analysis of the Ba cluster (atom %).
O
62.86
ONa
0.59
62.86
SS
Na Si Si
0.591.961.96 14.44
14.44
ClCl
K K Ca CaFe
1.76 1.121.12 0.32 0.32
1.76
0.59
Fe
Ba
Ba
0.59
16.36
16.36
In Figure
Figure 5,
5, the
the SEM
In
SEM image
image of
of the
the area
area with
with cumulated
cumulated Cu
Cu is
is displayed.
displayed. It
It can
can be
be seen
seen as
as “foggy”
“foggy”
lighter
structure
of
irregular
shape
in
the
central
part
of
image.
The
prevailing
components
are are
Cu
lighter structure of irregular shape in the central part of image. The prevailing components
and
O
(Table
4).
The
molar
ratio
of
1:1.6
shows
Cu(OH)
2 as a possible reaction product of Cu. This
Cu and O (Table 4). The molar ratio of 1:1.6 shows Cu(OH)2 as a possible reaction product of Cu.
assumption
was was
proved
by the
analysis.
No No
Cu(OH)
2 was identified by the XRD analysis. It
This
assumption
proved
by XPS
the XPS
analysis.
Cu(OH)
2 was identified by the XRD analysis.
indicates
a
non-crystalline
character
of
Cu(OH)
2. The mapping showed similar results as in the case
It indicates a non-crystalline character of Cu(OH)2 . The mapping showed similar results as in the case
of barium.
barium. Cu
tends to
to cumulate
cumulate in
in small
small areas
areas of
of Cu(OH)
Cu(OH)2 rather
rather than
than being
being dispersed
dispersed throughout
throughout
of
Cu tends
2
the matrix.
matrix. The
of distribution
distribution between
that copper
copper forms
forms aa higher
higher
the
The difference
difference of
between barium
barium and
and copper
copper is
is that
number
of
smaller
clusters.
number of smaller clusters.
Figure 6 shows the detail of a grain of BFS. A coating of small particles are visible on the edges
of the grain. The EDS analysis proved that the coating contained Pb (Table 5). The particles are
supposed to be formed of Pb(OH)2 according to XPS analysis. Unlike both previous elements, Pb did
not cumulate in larger clusters of Pb(OH)2, but it seems to be dispersed throughout the matrix (Figure
7). The reason that Pb did not form bigger clusters could be caused by the smaller amount of Pb atoms
in the matrix. All metals were added in wt %, so the amount of Pb atoms in the matrix is the lowest,
Materials 2016, 9, 533
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Figure 5.
5. SEM
SEM image
image of
of region
region with
with fixed
fixed Cu,
Cu,magnitude
magnitude7000ˆ.
7000×.
Figure
Table 4. EDS analysis of the Cu cluster (atom %)
Table 4. EDS analysis of the Cu cluster (atom %)
O
Al
55.8
O
Al
Si
Si
0.87 6.91
55.8
0.87
6.91
Cl
Cl
1.31
1.31
Ca
Fe
Cu
Ca
Fe
0.34 0.28 33.79
0.34
0.28
Pb
Cu
0.38
Pb
33.79
0.38
Figure 6 shows the detail of a grain of BFS. A coating of small particles are visible on the edges of
the grain. The EDS analysis proved that the coating contained Pb (Table 5). The particles are supposed
Figureaccording
5. SEM image
of region
with fixed
Cu, magnitude
7000×.elements, Pb did not
to be formed of Pb(OH)
to XPS
analysis.
Unlike
both previous
2
cumulate in larger clusters of Pb(OH)2 , but it seems to be dispersed throughout the matrix (Figure 7).
Table 4. EDS analysis of the Cu cluster (atom %)
The reason that Pb did not form bigger clusters could be caused by the smaller amount of Pb atoms
in the matrix. All metals were
O added
Al inSiwt %,Clso the
Caamount
Fe of Pb
Cuatoms
Pbin the matrix is the lowest,
because of its superlative55.8
molar0.87
weight.
6.91 1.31 0.34 0.28 33.79 0.38
Figure 6. SEM image of Pb coating on the BFS grain, magnitude 4000×.
Table 5. EDS analysis of the Pb coating (atom %).
O
58.36
Mg
5.48
Al
5.64
Si
20.08
S
0.58
K
3.29
Ca
4.25
Ti
0.28
Fe
0.57
Cu
0.42
Pb
1.04
Figure 6.
6. SEM
SEM image
image of
of Pb
Pb coating
coating on
on the
the BFS
BFS grain,
grain, magnitude
magnitude 4000ˆ.
4000×.
Figure
Table 5. EDS analysis of the Pb coating (atom %).
O
58.36
Mg
5.48
Al
5.64
Si
20.08
S
0.58
K
3.29
Ca
4.25
Ti
0.28
Fe
0.57
Cu
0.42
Pb
1.04
Materials 2016, 9, 533
7 of 9
Table 5. EDS analysis of the Pb coating (atom %).
O
Mg
Al
Si
S
K
Ca
Ti
Fe
Cu
Pb
58.36
5.48
5.64
20.08
0.58
3.29
4.25
0.28
0.57
0.42
1.04
Remote Sens. 2016, 8, 533
Remote Sens. 2016, 8, 533
7 of 9
7 of 9
Figure 7. EDS mapping of Ba, Cu, and Pb in the matrix.
Figure 7.
7. EDS
EDS mapping
mapping of
of Ba,
Ba, Cu,
Cu, and
and Pb
Pb in
in the
the matrix.
matrix.
Figure
3.3. XRD
3.3. XRD
XRD
3.3.
The XRD analysis identified only one crystalline compound of fixed heavy metals—BaSO4. The
The XRD
XRD analysisidentified
identifiedonly
only
one
crystalline
compound
of fixed
heavy
metals—BaSO
4.
one
crystalline
compound
of fixed
heavy
metals—BaSO
XRDThe
patterns analysis
of the alkali-activated
matrix
are shown
in Figure
8. The
patterns
of BaSO4.4 The
are
The
XRD
patterns
of
the
alkali-activated
matrix
are
shown
in
Figure
8.
The
patterns
of
BaSO
are
4
XRD
patterns
of the
alkali-activated
matrix
are phases
shown of
in the
Figure
8. (quartz,
The patterns
of merwinite,
BaSO4 are
described,
the rest
of the
patterns belongs
to the
matrix
mullite,
described, the
the rest
rest of
of the
the patterns
patterns belongs
belongs to
to the
the phases
phases of
of the
the matrix
matrix (quartz,
(quartz, mullite,
mullite, merwinite,
merwinite,
described,
calcite, magnetite) and to NaCl. No compounds of Pb and Cu were identified by XRD, since they are
calcite, magnetite)
magnetite) and
and to
to NaCl.
NaCl. No compounds of Pb and Cu were identified by XRD, since they are
calcite,
fixed in the amorphous
phases. No compounds of Pb and Cu were identified by XRD, since they are
fixed
in
the
amorphous
phases.
fixed in the amorphous phases.
Figure 8. X-ray powder diffraction (XRD) patterns of the alkali-activated material (AAM) matrix with
Figure
8.
Figure
8. X-ray
X-ray powder
powder diffraction
diffraction (XRD)
(XRD) patterns
patterns of
of the
the alkali-activated
alkali-activated material
material (AAM)
(AAM) matrix
matrix with
with
heavy metals.
heavy
metals.
heavy metals.
4. Conclusions
4.
4. Conclusions
Conclusions
The fixation of three heavy metals—Ba, Pb, and Cu—in alkali-activated matrices based on blast
The
fixation
heavy
metals—Ba,
and
Cu—in
alkali-activated
matrices
based
on
The
fixation
of
three
heavy
metals—Ba,
Pb,
and
Cu—inproved
alkali-activated
matrices
basedinsoluble
on blast
blast
furnace slag
and of
flythree
ash was
examined.
ThePb,
XPS
analyses
that all metals
formed
furnace
slag
and
fly
ash
was
examined.
The
XPS
analyses
proved
that
all
metals
formed
insoluble
furnace
slag4,and
fly ash
wasCu(OH)
examined.
Thealkaline
XPS analyses
proved
that
metals
formed
insoluble
salts—BaSO
Pb(OH)
2 and
2—after
activation.
Only
Cuall
was
present
in matrices
in
salts—BaSO
4, Pb(OH)2 and Cu(OH)2—after alkaline activation. Only Cu was present in matrices in
salts—BaSO
,
Pb(OH)
and
Cu(OH)
—after
alkaline
activation.
Only
Cu
was
present
in
matrices
in
two different
chemical
states;
apart
from
Cu(OH)
2
,
a
Cu–O
bond
was
also
identified.
Both
Pb(OH)
2
4
2
2
two
different
chemical
states;
apart
from
Cu(OH)
2, a Cu–O bond was also identified. Both Pb(OH)2
two
different2 chemical
states;
apart
from Cu(OH)
was
also could
identified.
Pb(OH)
and Cu(OH)
were present
in an
amorphous
or semicrystaline
form,
which
not beBoth
identified
by2
2 , a Cu–O bond
and
Cu(OH)
2 were present in an amorphous or semicrystaline form, which could not be identified by
XRD.
The distribution
of heavy metals within the matrices was quite different. Ba and Cu were not
XRD.
The distribution
of heavy
within
the matrices
wasinquite
different.
were
not
dispersed
throughout the
matrixmetals
evenly
and were
cumulated
some
regions.Ba
Onand
theCu
other
hand,
dispersed
throughout
evenly
and clusters
were cumulated
some as
regions.
On the
other
hand,
EDS mapping
showedthe
thatmatrix
Pb did
not form
and was in
present
a coating
on the
edges
of
EDS
mapping
showed
that
Pb
did
not
form
clusters
and
was
present
as
a
coating
on
the
edges
of
grains of the blast furnace slag in the whole matrix. The results show that the metals were fixed
grains
blast furnaceinslag
in the whole
matrix.insoluble
The results
show
the case
metals
were
fixed
mainlyofbythe
encapsulation
the matrix
and forming
salts.
Onlythat
in the
of Cu
can
the
mainly by encapsulation in the matrix and forming insoluble salts. Only in the case of Cu can the
Materials 2016, 9, 533
8 of 9
and Cu(OH)2 were present in an amorphous or semicrystaline form, which could not be identified by
XRD. The distribution of heavy metals within the matrices was quite different. Ba and Cu were not
dispersed throughout the matrix evenly and were cumulated in some regions. On the other hand, EDS
mapping showed that Pb did not form clusters and was present as a coating on the edges of grains
of the blast furnace slag in the whole matrix. The results show that the metals were fixed mainly by
encapsulation in the matrix and forming insoluble salts. Only in the case of Cu can the formation of
some chemical bond with newly formed phases after alkali activation be assumed.
Acknowledgments: This work was financially supported by the project “Materials Research Centre at FCH
BUT”—Sustainability and Development, REG LO1211—with financial support from National Programme for
Sustainability I (Ministry of Education, Youth and Sports).
Author Contributions: Jan Koplík and František Šoukal conceived and designed the experiments; Jan Koplík
performed the experiments; Jiří Másilko and Lukáš Kalina performed the analysis; Jan Koplík wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
The following abbreviations are used in this manuscript:
BFS
XPS
SEM
EDS
XRD
AAM
HCAAMs
LCAAMs
blast furnace slag
X-ray photoelectron spectroscopy
scanning electron microscopy
energy dispersive X-ray spectroscopy
X-ray powder diffraction
alkali-activated material
high-calcium alkali-activated materials
low-calcium alkali-activated materials
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