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Characterization of Vapor Phase Mercury Released from Concrete
Processing with Baghouse Filter Dust Added Cement
Jun Wang,
†,§
Josh Hayes,
†
Chang-Yu Wu,*
,†
Timothy Townsend,
†
John Schert,
‡
Tim Vinson,
‡
Katherine Deliz,
†
and Jean-Claude Bonzongo
†
†
Department of Environmental Engineering Sciences, Engineering School of Sustainable Infrastructure & Environment (ESSIE),
University of Florida, Gainesville, Florida 32611, United States
‡
The Bill Hinkley Center for Solid and Hazardous Waste Management, University of Florida, Gainesville, Florida 32611, United
States
§
Department of Occupational and Environmental Health, University of Oklahoma Health Sciences Center, Oklahoma City,
Oklahoma 73126, United States
*
SSupporting Information
ABSTRACT: The fate of mercury (Hg) in cement processing
and products has drawn intense attention due to its
contribution to the ambient emission inventory. Feeding Hg-
loaded coal fly ash to the cement kiln introduces additional Hg
into the kiln’s baghouse filter dust (BFD), and the practice of
replacing 5% of cement with the Hg-loaded BFD by cement
plants has recently raised environmental and occupational
health concerns. The objective of this study was to determine
Hg concentration and speciation in BFD as well as to
investigate the release of vapor phase Hg from storing and
processing BFD-added cement. The results showed that Hg
content in the BFD from different seasons ranged from 0.91−
1.44 mg/kg (ppm), with 62−73% as soluble inorganic Hg,
while Hg in the other concrete constituents were 1−3 orders of magnitude lower than the BFD. Up to 21% of Hg loss was
observed in the time-series study while storing the BFD in the open environment by the end of the seventh day. Real-time
monitoring in the bench system indicated that high temperature and moisture can facilitate Hg release at the early stage. Ontario
Hydro (OH) traps showed that total Hg emission from BFD is dictated by the air exchange surface area. In the bench simulation
of concrete processing, only 0.4−0.5% of Hg escaped from mixing and curing BFD-added cement. A follow-up headspace study
did not detect Hg release in the following 7 days. In summary, replacing 5% of cement with the BFD investigated in this study
has minimal occupational health concerns for concrete workers, and proper storing and mixing of BFD with cement can
minimize Hg emission burden for the cement plant.
1. INTRODUCTION
Fly ash from coal-fired power plants is one of the main raw
materials in the pyroprocess of the Portland cement kiln,
1
and
it provides the desired plasticity, permeability, sulfate resistance,
and durability for cement and concrete.
2,3
However, as a result
of utilizing activated carbon injection in the power plant flue
gas treatment system,
4
coal fly ash now contains mercury (Hg)
loaded carbon material. The addition of coal fly ash to the raw
mill therefore leads to an undesired Hg emission from the
cement kiln stack.
5
The Environmental Protection Agency
(EPA) established the National Emission Standards for
Hazardous Air Pollutants (NESHAP) and the New Source
Performance Standards (NSPS) for Portland cement kilns, with
a limit of 55 or 21 lb Hg emission per million tons of clinker
production for the existing or new cement kiln, respectively.
6
To control dust emission and to address the Hg emission issue,
afiltration baghouse is typically used downstream in the
cement kiln to remove the Hg-loaded dust from the flue gas.
7
A
material flowchart in a typical cement plant is illustrated in
Figure 1. The collected kiln’s baghouse filter dust (BFD) is
either landfilled or recycled back into the cement production
loop.
8,9
Although there is no adverse effect to the cement kiln
and the product, the accumulated Hg in the kiln may eventually
increase the Hg emission from the stack to the ambient air.
10
As
the cement demand and production continue to grow
11
in the
United States with potential economic revival and increasing
construction activities, the excessive contribution to the Hg
emission inventory from cement plants becomes an important
issue to the environment and ecosystem.
Received: October 10, 2013
Revised: January 11, 2014
Accepted: January 21, 2014
Published: January 21, 2014
Article
pubs.acs.org/est
© 2014 American Chemical Society 2481 dx.doi.org/10.1021/es4044962 |Environ. Sci. Technol. 2014, 48, 2481−2487
In lieu of recycling BFD to the kiln, some cement plants in
the State of Florida have been practicing to directly add BFD to
the final cement product in the ball mill. The practice is based
on the hypothesis that the concrete made from the BFD-added
cement can immobilize the Hg. BFD has similar property to
lime, and research showed adding BFD up to 5% mass of the
cement has no significant effect on the mechanical properties of
concrete.
12
While this practice theoretically may reduce the Hg
emission to the ambient air, no study has yet investigated the
environmental consequences of storing the BFD-added cement
and the exposure of the workers processing the BFD-added
cement. In addition, the ball mill mixing the BFD and cement
may not have a dust filtration device as the rotary kiln has. This
may consequently increase the Hg emission from the cement
plant, due to the unfiltered flue gas.
It was reported that the total Hg concentration in the BFD is
similar to the coal fly ash added to the cement kiln.
9
However,
the recent popularity of selective noncatalytic reduction
(SNCR) devices employed in coal-fired power plants has
changed the composition of the fly ash, with more ammonia
and possibly Hg.
13−15
Information about Hg concentration for
the other concrete constituents is also scarce. These concrete
constituents may have trace level Hg due to the possibility for
Hg entering these materials either in the kiln (cement) or by
natural occurrence (aggregates). In addition, it is difficult to
determine the speciation of Hg due to the fact that the amount
of total Hg present in these materials is at a trace level.
However, the environmental mobility, bioaccumulation, and
toxicity of Hg all depend on the speciation (see Table 1). Alkyl-
Hg and soluble inorganic-Hg (SI-Hg) are much more mobile
and toxic than the nonsoluble inorganic-Hg (NSI-Hg) that is
predominantly elemental Hg.
16
Among the studies with the Hg-contained cement, most
focused on the leaching characteristics of curing the concrete,
while very few focused on the vapor phase Hg release. A
headspace study
17
showed that vapor phase Hg was released
from the Hg-doped (0.2 wt %/wt) solidified cement monolith.
The release rate of Hg was a function of time and temperature.
The study also prompted that the vapor phase Hg release from
cement monolith was possibly due to moisture and temperature
increase during mixing and curing. However, the study was
carried out with a very high concentration of doped Hg (0.2 wt
%/wt) in cement which is not likely to happen in the industrial
setting. Another study
18
demonstrated that about 0.31% of total
Hg was released from curing concrete, with 55% of the cement
replaced by coal fly ash. A study
19
in New Jersey revealed that
the total Hg contribution to the atmosphere from cement-
stabilized waste was negligible (<4%), although the release rate
(130 kg/y) was on par with other industrial sources.
The objective of this study was to characterize the Hg
concentration and speciation in the BFD as well as other
concrete constituents, by using different extraction methods
and high sensitivity analytical equipment. A bench system was
built to simulate the storage, mixing, and curing of the BFD-
added cement, under different environmental conditions. Both
real-time monitoring and the Ontario Hydro (OH) method
were used to examine the amount of vapor phase Hg released.
The environmental impact and occupational hazard of adding
BFD to cement were assessed.
2. EXPERIMENTAL SECTION
2.1. Material Characterization. Fresh BFD was sampled
from different running seasons (Oct, 2011; Dec, 2011; Feb,
2012, Aug 2012) of one cement kiln in the State of Florida.
Commercially available Portland cement, coarse aggregate
(rocks), and fine aggregate (sands) were acquired from local
retail stores. All the materials were stored in either desiccators
or desiccated buckets. The materials were homogenized by a
rotatory drum prior to the experiment.
The digestion procedure for materials followed the
sequential extraction procedure described in EPA Method
3200,
20
while the analyses of the materials were based on EPA
Method 7474.
21
The samples were extracted using different
solvent and acids using a microwave digestion system (CEM
MDS 81D, Matthews, NC) and analyzed by a hydride
Figure 1. Material flow of a typical cement kiln. The BFD from the baghouse filter was either recycled back to the raw mill or added to the final
cement product.
Table 1. Hg Classification in This Study
Hg species environmental
mobility toxicity
soluble inorganic
Hg (SI-Hg) Hg2+ (HgCl2, HgSO4,
HgO, Hg(NO3)2,
Hg(OH)2)
mobile toxic
alkyl Hg methyl Hg, ethyl Hg mobile highly
toxic
nonsoluble
inorganic Hg
(NSI-Hg)
Hg0semimobile less
toxic
HgS, Hg2Cl2nonmobile less
toxic
total Hg all of the above
Environmental Science & Technology Article
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generation - atomic fluorescence spectrometer (HG-AFS)
(Aurora Biomed 3300, Vancouver, BC, Canada). Details of
the digestion and analysis are available in the Supporting
Information.
In addition to the characterization, a 7-day time-series study
was carried out on two batches of the BFD (Oct, 2011; Dec,
2011) to evaluate the Hg loss from the BFD, by exposing them
to natural weather in Florida (∼30 °C, 60−70% relative
humidity). The BFD was laid down on a flat surface as a thin
layer (<1 mm) to ensure homogeneous exposure and left
outdoors. A small portion of the sample was fetched on a daily
basis during the 7-day period. The retrieved sample was dried
in the desiccator to remove excessive water absorbed on the
BFD, digested, and analyzed by HG-AFS. The condition was
used to simulate storing the BFD in an open area with
indefinite headspace.
2.2. Bench System. Real-time measurement of vapor phase
Hg release from the materials and concrete processing were
performed separately in a small enclosed cylindrical tube and an
airtight glovebox (Plas Lab 818-GB, Lansing, MI) with an
interior volume of 489 L. The conceptual illustration of the
bench system is shown in Figure 2. In Figure 2a, gas flows from
two air cylinders were mixed at a mixing chamber to create a
total flow of 1−2 L per minute (Lpm). The ratio of flow rates
between water saturated air and dry air was used to control the
relative humidity (RH), which was monitored by a hygrometer
(Omega HX94C, Stamford, CT) inside the mixing chamber.
The gas stream then went through either apparatus in Figure 2b
or 2c, depending on whether measuring vapor phase Hg release
from the materials or concrete processing. The small enclosed
cylindrical tube with heating tape wrapped around (Figure 2b)
was used to test vapor phase Hg release from the BFD, cement,
and BFD/cement mixture under given flow rate, RH, and
temperature. This limited head space study was to simulate
storing the BFD in an enclosed environment. Simulation of
concrete processing was carried out in the glovebox shown in
Figure 2c. Thermometers mounted in the cylindrical tube and
inside the concrete were used to monitor the temperature
during the earlier stage of mixing.
The gas stream carrying any released vapor phase Hg was
sent through a Hg transformation unit (Figure 2d) developed
in previous studies.
22,23
The unit is able to measure the
concentration of nonsoluble inorganic Hg (NSI-Hg) and total
Hg in the gas stream, respectively. The concentration of soluble
inorganic Hg (SI-Hg) was calculated from the mass difference.
Details of the unit are available in the Supporting Information.
The vapor phase Hg passed the Zeeman atomic absorption
spectrometer in the real-time Hg analyzer and then entered the
Ontario Hydro (OH) trap. Since SI-Hg was either removed or
reduced by the Hg transformation unit, the original OH
sampling train
24
was modified to skip the 10% KCl solution
impingers. 100 mL of a hydrogen peroxide (H2O2) solution
Figure 2. Breakdown schematic diagram of the bench system: (a) controlled humidified air generator; (b) temperature controlled tube; (c) glovebox
with concrete processing inside; (d) Hg transformation unit, real-time Hg analyzer, and OH trap.
Environmental Science & Technology Article
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and 100 mL of a potassium permanganate (KMnO4) solution
with acids were used to collect Hg0. 10% KCl solution was
added to the KMnO4trap solution after the sampling to
remove any acid. The OH trap was diluted and immediately
analyzed by a cold vapor - atomic fluorescence spectrometer
(CV-AFS) (Tekran 2600, Toronto, ON, Canada). The CV-
AFS with a detection limit of 1 pg/mL was capable of detecting
trace amount of Hg in the OH traps.
2.3. Test Conditions. 500 g each of BFD, cement, and 5%
BFD/95% cement was weighed and laid on the bottom surface
of the cylindrical tube in Figure 2b. Two flow rates (1 and 2
Lpm) and four RHs (0%, 25%, 75%, 100%) were employed.
The temperature in the tube was either room temperature
(∼23 °C) or elevated by the heating tape (∼80 °C). This
experiment was designed to identify the potential effect of
environmental parameters on storing BFD and cement prior to
processing. In addition to 500 g of BFD, 100 g of BFD was also
tested, which had a similar surface area exposed to the air flow
in the cylindrical tube (Figure 3), under 100% RH.
Simulation of concrete processing was conducted in the
glovebox in Figure 2c using the Feb, 2012 BFD sample. The
mixing ratio of different constituents followed the original
recipe for Portland cement concrete.
25
The recipe of concrete
was scaled down to fit the size of the glovebox and is listed in
Table 2. Different from the simulation of storage, the gas
stream’s RH was fixed at 50%. During concrete processing, a
large amount of water was supplied to the mixture and the
relative humidity was already at 100%. The air exchange rate of
the glovebox was set to 1.5 Lpm. The stirring of BFD, cement,
water, and aggregates using a hand mixer lasted about 3 min,
while the concrete remained undisturbed and became
completely solidified in 8 h. The concrete processing was
repeated five times using a 5%BFD/95% cement mixture and a
10% BFD/90% cement mixture, respectively. After 24 h of
curing, one of the concretes from each mixing ratio was
subjected to a 7-day headspace study with an OH trap.
The bench system was used for the first 24 h due to two
reasons: the data record length limit of the real-time Hg
analyzer and instability of Hg in the OH trap while feeding
continuous air.
26
A long-term headspace experiment was
therefore performed using the glovebox as a supplement to
the 24 h study. The solidified concrete was put into the box
without air exchange. After a preset period, vacuum was used to
pull 20 L air from the glovebox through the OH trap. The
concentration in the OH trap was used to calculate the Hg
vapor released from the solidified concrete.
2.4. Quality Control and Statistics. Details of quality
control and statistical analysis are available in the Supporting
Information.
3. RESULTS AND DISCUSSION
3.1. Hg Concentration and Speciation in the
Materials. Table 3 lists the Hg concentration and speciation
in the BFD, cement, and other constituents in the concrete
processing. Alkyl-Hg was below the detection limit in all the
samples and therefore was eliminated from the following
studies. The high temperature and combustion condition in the
cement kiln might have decomposed any organic phase
compounds.
The total Hg concentration in the BFD ranged from 0.91−
1.52 mg/kg (ppm) and was consistent in each season. More
mobile and toxic SI-Hg counted 62−73% of total Hg in the
samples, while the rest was in the NSI-Hg phase. The total Hg
concentration in the BFD was higher than the 0.66 mg/kg
(mean) in the cement kiln dust reported by Portland Cement
Association (PCA).
27
It should be noted that Hg concentration
in the kiln dust measured by PCA has a large deviation with
some samples having up to 25.50 mg/kg total Hg. The BFD
from different cement kiln plants does not have the same
characteristics. The variance of total Hg concentration in fed
coal fly ash, raw materials, wastes, and fuels could contribute to
the difference among different seasons of the same cement
plant.
The total Hg concentration was 74.51 μg/kg (ppb) in the
commercial cement. It was about 1 order of magnitude lower
than the BFD. When mixing 5% of BFD with 95% of cement,
the significance of Hg contributed from BFD diminished due to
the small proportion. The concentration in the cement was also
higher than those in the available studies
2,27
in past decades; the
latter showed Hg in the cement was averaging below 14 μg/kg
with the highest to be 39 μg/kg.
Figure 3. Cross sectional and lateral view of the cylindrical tube loaded
with 500 and 100 g of BFD.
Table 2. Recipe of the Portland Cement Concrete (kg) Used
in This Study
constituent 5% BFD/95% cement 10% BFD/90% cement
water 0.54 0.54
BFD 0.05 0.10
cement 0.95 0.90
coarse aggregates 1.82 1.82
fine aggregates 1.45 1.45
total 4.81 4.81
Table 3. Hg Concentration (Mean ±Standard Deviation)
a
and Speciation in the Concrete Constituents
material total Hg
(μg/kg) SI-Hg (μg/kg) percentage of SI-Hg
(%)
BFD Oct 2011 910 ±60 560 ±20 61.5
Dec 2011 1430 ±70 1050 ±40 73.4
Feb 2012 1520 ±90 990 ±100 65.4
Aug 2012 1440 ±230 1030 ±100 71.5
cement 74.51 ±6.24 47.02 ±8.94 63.1
coarse aggregates
(rocks) 4.32 ±1.52 2.63 ±1.16 60.8
fine aggregates
(sand) 0.44 ±0.06 0.33 ±0.04 73.2
a
Five replicates.
Environmental Science & Technology Article
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The aggregates in the concrete processing showed much less
Hg presence compared to the BFD and the cement. The coarse
aggregates (rocks) and the fine aggregates (sands) had 4.32 μg/
kg and 0.44 μg/kg of total Hg, respectively. Hg in the sands was
just slightly above the detection limit of CV-AFS. Those
constituents were naturally occurring materials, and the
characteristic can substantially vary from different geological
locations. All the constituents had a relative constant SI-Hg/
total Hg ratio of 0.6−0.7.
3.2. Vapor Phase Hg Released from the BFD and
Cement (Bench System). Figure 4 shows the change of Hg
concentration in the 7-day time-series study in the open area
using the BFD. The vaporization of NSI-Hg loss was significant
on the first day, from 0.36 mg/kg to 0.27 mg/kg for the Oct,
2011 sample and from 0.25 mg/kg to 0.15 mg/kg for the Dec,
2011 sample. The concentration of NSI-Hg stayed relatively
unchanged afterward. The SI-Hg remained constant during the
7-day period. The total Hg loss was 13.83−17.52% on the first
day, while 20.21−21.16% during the 7-day period, mostly
contributed from NSI-Hg vaporization due to its higher
volatility than SI-Hg. This corresponded to 30.77−57.14% on
the first day and 43.59−65.71% during the 7-day of the total
NSI-Hg in the samples.
Figure 5 shows the total Hg concentration in the gas stream
as a function of time in 24 h in the bench system for the BFD
samples. Generally, significant Hg release was detectable only in
the first 2 h by the real-time analyzer after the experiment
started. The concentration was at the background level (2 ng/
m3) afterward. High RH and temperature facilitated the Hg
release at the earlier stage, while the gas flow rates did not affect
the release pattern. High temperature increased the diffusion
activity while lowering the adsorption affinity between Hg and
the dust. Water in high moist air may compete with Hg on the
adsorption surface.
28
Hg speciation results are not presented in
Figure 5, due to the fact that early detectable release was mostly
NSI-Hg, i.e. switching the channel in the Hg-transformation
unit gave an identical result. The Hg analyzer could not detect
any significant release from the cement and the 5% BFD/95%
cement mixture under all experimental conditions. This was
due to the lower total Hg concentration in these materials.
Averagely, 1.6 ±0.4% of Hg in the 500 g of BFD was
released as vapor phase, while almost all released Hg was in the
NSI-Hg phase (p< 0.05). The amount of total Hg released
from the BFD and consequently captured by the OH trap in
different experimental conditions is listed in Table 4. There was
no statistical correlation found between total Hg released with
any environmental parameter. This indicated the total Hg
released in 24 h were independent of gas flow rate,
temperature, and RH in a limited headspace environment.
Furthermore, the amount of Hg released from 500 and 100 g
BFD were identical, regardless of the mass difference in total
Hg. It was possibly due to their similar area of air exchange
(Figure 3). This suggests the release was limited to the top
layer. This implies that the release of Hg from BFD can be
correlated to the degree of contact between air and dust. More
experiments with different exposure surface areas will help
quantify the dependence of loss on air exchange surface area.
The amount of Hg released from the cement was below the
detection limit at most environmental conditions, due to the
low Hg concentration in the cement. Similarly, the 5% BFD/
95% cement mixture did not show any detectable vapor phase
Hg released. The higher concentration of Hg and porous
structure of the BFD likely contributed to the higher vapor
phase Hg released and captured by the OH traps.
3.3. Vapor Phase Hg Release during Concrete Curing.
The release of Hg from mixing and curing cement was more
complicated than the BFD and the cement. The mixing process
involved several minutes of high speed blending and numerous
bubbles were created in the mixtures. A considerable amount of
water was added into the mixture during this process. In this
study, the BFD and the cement contributed 1% and 20% mass
balance to the concrete mixture, respectively. The rest of the
concrete mixture was coarse and fine aggregates, which
contained much less Hg. The total mass of concrete
constituents was 4.8 kg for each batch of experiment and the
material contained about 0.15−0.22 mg of total Hg, from the
calculation using mass fraction in Table 2 and Hg concentration
in Table 3.
During the mixing and curing of the 5% BFD/95% cement
and the 10%BFD/90% cement, there was no detectable Hg
release activity from the real-time monitoring. It may be due to
the lower total Hg content in the concrete mixture (3.4 times
less) than the 100% BFD. Total Hg released from the 10%
BFD/90% cement mixture captured by the OH trap was 0.8 ±
0.09 μg, slightly higher than 0.7 ±0.07 μg from the 5% BFD/
95% cement mixture (p< 0.05). Again, all total Hg released was
in the NSI-Hg phase (p< 0.05). The total Hg released from the
concrete mixing was about 0.4−0.5% of the total Hg in the
concrete constituents. This was higher than that in the study
29
using coal fly ash-added cement, while the latter had 0.1% of
Hg escaped. Powdered activated carbon in coal fly ash was
usually not saturated with Hg due to low Hg-carbon ratio,
30
and it increased the ability of retaining Hg in the dust, thus
possibly leading to the difference between study results. There
was no detectable Hg in the OH trap for the 7-day headspace
study on solidified concrete. It indicated that the majority of Hg
release occurred in the first 24 h.
3.4. Impact on the Ambient and Occupational
Environment. From the experimental results, storing BFD
in an open area contributed the highest Hg loss up to 21%. The
Hg loss is related to the degree of contact between air and
BFD, i.e., area of air exchange surface. Hence, it is
recommended that the cement kiln plant store unused BFD
Figure 4. Total Hg, SI-Hg, and NSI-Hg concentration in the 7-day
time-series study.
Environmental Science & Technology Article
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in a closed area to avoid additional Hg emission from the plant.
The ball mill where clinkers are ground and BFD is added to
the final product is in constant action. Thus, it creates good
mixing between air and BFD. All the volatile Hg (NSI-Hg) can
be possibly released from rotating and feeding air. However,
there will be likely minimum oxidized Hg (SI-Hg) loss due to
the low temperature profile (∼240 °F/116 °C) of the ball mill.
Based on mass balance, there would be maximum 30 lb of
additional Hg emitted from the ball mill per million ton of
cement produced, by adding 5% of BFD containing 1 mg/kg of
Hg content to the ball mill, assuming conservatively all the 30%
NSI-Hg is released. This is above the EPA limit of 21 lb per
million tons of clinker produced.
6
Therefore, it is recom-
mended that the plant direct the flue gas from the ball mill to a
Hg-removal device to prevent undesired emission of Hg to the
ambient air. The worst case scenario is if the 73 million tons of
cement US produced
31
in 2012 all contained 5% BFD and
there were no Hg-removal device attached. This would create
2190 lb additional Hg emission. This conservative estimate is
significant compared to the total Hg emission of 9658.2 lb in
2008
32
from the cement industry as estimated by EPA.
During concrete curing and after being solidified, less than
0.5% of Hg was released in the vapor phase. Assuming 5% of
the cement is replaced with the BFD containing 1 mg/kg of
Hg, about 0.05 mg Hg per ton of concrete could be released. In
a typical scenario of workers placing and finishing the concrete
floor (about 16.5 ton concrete) in an enclosed room (6.72 m in
length, 5 m in width, 3 m in height), the maximum ceiling
concentration of Hg is less than 0.01 mg/m3, if no ventilation at
all. This is much lower than the permissible exposure limit
(PEL) of 0.1 mg Hg/m3ceiling concentration set by the
Occupational Safety and Health Administration (OSHA).
33
For an outdoor concrete curing scenario, the Hg will be
instantly diluted by ambient air and should cause no violation
to the PEL.
In summary, caution should be exercised how the BFD
should be stored and mixed to minimize Hg emission to the
environment. Meanwhile, the occupational exposure is minimal
while replacing 5% of the cement with the BFD containing Hg
concentration around 1 ppm. It should be noted that the total
Hg concentration in the concrete constituents may vary from
geological location, hence affecting the released amount.
Understanding the mechanism how Hg is trapped in the
concrete will provide knowledge how to avoid potential release
from concrete in the long term. Field study is also essential to
Figure 5. Hg released from the BFD as a function of time: (a) 1 Lpm gas flow rate and room temperature; (b) 1 Lpm gas flow rate and elevated
temperature; (c) 2 Lpm gas flow rate and room temperature; (d) 2 Lpm gas flow rate and elevated temperature.
Table 4. Total Hg (μg) Released from the BFD under
Different Experimental Conditions, in the OH Trap
amount
of BFD
air
flow
rate temp dry air 25% RH 75% RH 100%
RH
500 g 1 Lpm 23 °C18
(2.4%)*
9 (1.2%) 10
(1.3%) 15
(2.0%)
80 °C 11 (1.5%) 5 (1.3%) 13
(1.7%) 7 (0.9%)
2 Lpm 23 °C 13 (1.7%) 18 (2.4%) 14
(1.8%) 13
(1.7%)
80 °C 11 (1.5%) 11(1.5%) 11
(1.5%) 13
(1.7%)
100 g 2 Lpm 80 °C13
(8.7%)
*
The percentage in the parentheses denotes total Hg released versus
total Hg in the 500 or 100 g Feb, 2012 BFD.
Environmental Science & Technology Article
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validate the laboratory study of vapor phase Hg release in the
cement plant and concrete processing site.
■ASSOCIATED CONTENT
*
SSupporting Information
Additional text, Table S1, and Figure S1. This material is
available free of charge via the Internet at http://pubs.acs.org.
■AUTHOR INFORMATION
Corresponding Author
*Phone: 1-352-392-0845. Fax: 1-352-392-3076. E-mail: cywu@
ufl.edu. Corresponding author address: University of Florida,
P.O. Box 116450, Gainesville, FL 32611-6450, USA.
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
The study was funded by the Florida Department of
Transportation (FDOT) through contract BDK75-977-50.
The authors would like to thank Mr. Oliver H. Sohn and Mr.
Eduardo R. Ferrer of Cemex for assisting the sample and data
collection. The authors are also grateful to Mr. Al Linero and
Mr. David Read of Florida Department of Environmental
Protection for their valuable input.
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