Utilization of Coal Fly Ash as CO Gas Adsorbent
a Department of Engineering Physics, Faculty of Industrial Technology,Institut
Teknologi Sepuluh Nopember,
Kampus Keputih ITS Sukolilo
Surabaya 60111 INDONESIA
Abstract :
This
research focused on coal fly ash fabricated as CO adsorbent. Coal fly ash
having grain size of 325 mesh was characterized by XRF, XRD and SEM-EDX.
Physical activation was done at temperatures of 500 0C, 520 0C, 540 0C, 560 0C, 580 0C and 600 0C. Chemical activation was undertaken by
mixing between fly ash and NaOH with mass ratio of 1: 1.2 with subsequent heating at 7500C for 1 h and followed by washing the specimens until pH=7. The samples were dried at 1000C for 1 h. The major constituents of
unactivated coal fly ash are Fe, Ca, K, Si and Al in the form of quatz and
anorthite. The chemical activation led to reduce the amount of quartz or
increase the amount of anorthite. Physical activation does not affect the
amount of minerals.
Keywords: fly ash, adsorbent, activation, characterization
|
1. Introduction
Coal is
one of alternative energy resources. In term of price coal is cheaper than
natural oil. Indonesia has a lot of coal resources, and the utilization of coal
in Indonesia increases every years. It attains
14,1% from total of other energy resources. It is expected that coal usage will
increase until 34,6% at 2025[1]. Utilization
of coal produces waste that can contaminate environment such as CO2, NOX, CO, SO2,
hydrocarbon dan solid waste. The solid
waste is in the form of ash, i.e fly ash and bottom
ash. According to data of Ministry of Environment in 2006, fly ash production
reaches 52,2 ton per day, whereas bottom ash waste production reaches 5,8 ton
per day[1].
Coal fly
ash is exhaust waste was usually released to air without control. Actually fly
ash waste is a kind of hazardous waste. Generally, fly ash can be temporary
saved at coal power plant and further thrown in landfill. Accumulation of this coal fly ash may raise environment al
problem[2]. Coal
fly ash can be used for raw material of cement and construction material[2]. Another utilization of coal is as adsorbent[3]. As adsorbent, fly ash has
advantage in term of economical prices and good for gas and liquid waste
management[4]. Physical and chemical
activation is required to allow coal fly ash for being use as adsorbent.
Physical activation is done by heating at high temperature, whereas chemical
activation is done by mixing of fly ash and acid liquid or alkali.
2.
Materials
and Methods
2.1 Materials
2.1 Materials
2.2
Methods
Two activations were used in this research, namely physical
and chemical activations. The physical activation was done by heating the
sample at temperatures of 500°C, 520°C, 540°C, 560°C, 580°C, and 600°C for 1 hour.
Chemical activation was done by mixing fly ash and NaOH with the mass fractions
of fly ash and NaOH are 1 : 1.2. The mixtures were heated at temperature of 7500C
for 1 hour followed by grinding process. Then, the samples were mixed with distilled
water with L/S of 1/5 in a constant stirring of 400 rpm for 30 minutes. Finally
leaching was done until pH = 7, the samples were then subsequently dried at
temperature of 1000C for 1 hour.
Raw material coal fly ash was characterized by X-Ray Fluorescence
(Minipal4
PanAlytical), X-Ray Diffraction (Brücker AXS D8 Focus) Cu
K-α with λ = 1,5418 Å, and Scanning Electron Microscopy (SEM) Zeiss-EVO MA 10
equipped with Electron Diffraction-X (EDX) of Brücker.
3.
Results and Discussion
3.1 Unactivated Coal Fly
Ash Characterization
Table 1 shows composition
in unactivated fly ash. From Table 1 it is known that the highest contents in
the fly ash are Fe, Ca, K, Si and Al, and the highest oxide are Fe2O3,
CaO, SiO2, Al2O3 and K2O. The
important substance for adsorbent are Si and Al, while Ca is the substance that
has to be remove. Ca can disturb the adsorption process because it may lead the
reaction to become unstable.
Table 1. XRF
analysis of unactivated coal fly ash
No.
|
Substance
|
Concentrate (%)
|
Oxide
|
Concentration (%)
|
1.
|
Al
|
1,8
|
Al2O3
|
2,9
|
2.
|
Si
|
9,3
|
SiO2
|
14
|
3.
|
P
|
0,64
|
P2O5
|
1,0
|
4.
|
K
|
2,19
|
K2O
|
1,84
|
5.
|
Ca
|
30,0
|
CaO
|
29,2
|
6.
|
Ti
|
1,79
|
TiO2
|
2,9
|
7.
|
Mn
|
0,60
|
MnO
|
0,49
|
8.
|
Fe
|
51,23
|
Fe2O3
|
46,51
|
9.
|
Ba
|
0,76
|
BaO
|
0,61
|
Table 2 is mineral composition of unactivated coal fly ash
from XRD analysis. XRD analysis shows that the most
dominant minerals are amorphous structure and crystalline phase of quartz (SiO2).
Fly ash samples consist mainly amorphous aluminosilicate with a less number of
iron-rich part. It is likely that the iron oxide bounds with aluminosilicate to
form amorphous phase. While aluminum and silicon form either as sillimanite, quartz,
or binds with Ca to form anorthite. Calcium was associated with oxygen, sulfur
or with silicon or aluminum. The calcium-rich material is different in
elemental composition from the amorphous alumino-silicate parts. It is clearly
a non-silicate mineral possibly calcite, lime, gypsum or anhydrite[5].
Table 2. XRD analysis of unactivated
coal fly ash
No.
|
Mineral
|
Formula
|
Konsentrasi
(%)
|
1.
|
Quartz
|
21,1
|
|
2.
|
Sillimanite
|
Al2SiO5
|
1,6
|
3.
|
Anhydrite
|
CaSO4
|
0,7
|
4.
|
Magnetite
|
Fe3O4
|
3,3
|
5.
|
Anorthite
|
Ca3SiO5
|
1,7
|
6.
|
Siderite
|
FeCO3
|
1,1
|
7.
|
Arcanite
|
K2SO4
|
2,4
|
8.
|
Periclase
|
MgO
|
6,2
|
9.
|
Hematite
|
Fe2O3
|
0,5
|
10.
|
Maghemite
|
Fe2O3
|
3,9
|
11.
|
Wuestite
|
FeO
|
1,2
|
12.
|
Amorphous
|
-
|
54,9
|
Figure 1 shows
elemental mapping of unactivated fly ash. EDX analysis indicates that the big
particle contains a lot of Si while Fe and Al distribute evenly in all
particles. This evidence indicates intermixing of Fe and Si-Al mineral phases
while Ca may in form non-silicate minerals[5]. These results are supported with XRD
data.
Figure 1 Result SEM of unactivation coal fly ash
3.2 Activation Coal Fly Ash Characterization
Table 3.
XRD Quantitative Data of Coal Fly Ash with Physical Activation
CRYSTAL/MINERAL
|
FORMULATION
|
UNIT
|
PHYSICAL
ACTIVATION
|
|||||
500
|
520
|
540
|
560
|
580
|
600
|
|||
Quartz
|
SiO2
|
%
|
20,0
|
21,1
|
22,0
|
22,2
|
22,3
|
21,0
|
Sillimanite
|
Al2SiO5
|
%
|
4,2
|
2,8
|
3,2
|
2,5
|
3,1
|
2,8
|
Anhydrite
|
CaSO4
|
%
|
0,4
|
0,6
|
0,4
|
0,8
|
1,0
|
0,4
|
Magnetite
|
Fe3O4
|
%
|
2,9
|
3,2
|
3,6
|
3,9
|
3,2
|
3,5
|
Anorthite
|
Ca3SiO5
|
%
|
1,6
|
2,1
|
2,3
|
2,7
|
1,4
|
1,7
|
Siderite
|
FeCO3
|
%
|
1,1
|
0,9
|
1,4
|
1,1
|
1,2
|
1,3
|
Arcanite
|
K2SO4
|
%
|
2,7
|
2,8
|
2,4
|
2,1
|
2,8
|
3,1
|
Periclase
|
MgO
|
%
|
6,7
|
6,3
|
5,9
|
7,4
|
6,6
|
6,4
|
Hematite
|
Fe2O3
|
%
|
0,5
|
0,6
|
0,5
|
0,6
|
0,6
|
0,6
|
Maghemite
|
Fe2O3
|
%
|
3,5
|
3,4
|
2,7
|
2,8
|
3,4
|
3,0
|
Wuestite
|
FeO
|
%
|
0,5
|
1,2
|
0,8
|
0,6
|
0,9
|
0,9
|
Amorphous
|
-
|
%
|
54,0
|
53,7
|
54,1
|
52,5
|
52,7
|
54,3
|
R_wp
|
-
|
%
|
2,9
|
2,9
|
2,9
|
2,9
|
2,9
|
2,9
|
Table 4.
XRD Quantitative Data of Coal Fly Ash with Chemical Activation
CRYSTAL/MINERAL
|
FORMULATON
|
UNIT
|
CHEMICAL ACTIVATION
|
|||||
500
|
520
|
540
|
560
|
580
|
600
|
|||
Quartz
|
SiO2
|
%
|
13,2
|
1,0
|
0,5
|
5,1
|
0,2
|
3,3
|
Sillimanite
|
Al2SiO5
|
%
|
0,0
|
2,6
|
4,0
|
2,5
|
4,3
|
8,4
|
Anhydrite
|
CaSO4
|
%
|
0,0
|
0,0
|
0,1
|
1,2
|
0,3
|
0,0
|
Magnetite
|
Fe3O4
|
%
|
3,1
|
3,4
|
0,1
|
0,0
|
4,3
|
3,5
|
Anorthite
|
Ca3SiO5
|
%
|
35,6
|
14,2
|
7,1
|
20,8
|
17,1
|
24,0
|
Siderite
|
FeCO3
|
%
|
1,3
|
0,0
|
0,0
|
0,2
|
0,2
|
0,2
|
Arcanite
|
K2SO4
|
%
|
14,1
|
18,0
|
16,9
|
18,6
|
15,3
|
14,8
|
Periclase
|
MgO
|
%
|
11,9
|
15,3
|
22,5
|
12,2
|
9,9
|
6,5
|
Hematite
|
Fe2O3
|
%
|
0,2
|
0,0
|
1,4
|
0,1
|
0,1
|
0,1
|
Maghemite
|
Fe2O3
|
%
|
0,0
|
0,0
|
3,0
|
0,0
|
0,0
|
0,0
|
Wuestite
|
FeO
|
%
|
1,0
|
2,8
|
6,2
|
2,7
|
4,6
|
2,0
|
Amorphous
|
-
|
%
|
15,2
|
41,1
|
38,3
|
34,5
|
42,7
|
35,4
|
R_wp
|
-
|
%
|
5,1
|
9,6
|
8,5
|
7,2
|
8,5
|
6,9
|
From Table 3 and 4 one
can observe that amorphous phase and quartz crystalline still dominate in fly
ash after physical activation. There is little changes of mineral composition after
physical activation. On the other hand, the chemical activation changed the
amount of minerals in fly ash. For example, after chemical activation the
amount of quartz decreases while the amount of anorthite increases. Figure 2
exemplifies the change in the amount of mineral of fly ash after physical and
chemical activation. From figure 2 it is known that chemical activation plays
an important in changing the amount of minerals, while the physical activation
does not affect significantly.
Figure
2. Comparison of quartz contents after physical and
chemical activation
Physical activation causes losing water content
(intercrystalline water) in fly ash as indicated by thermogravimetry
experiments[6]. Whereas chemical activation may active the unactivated substances, and finally aids the adsorption process.
4.
Conclusions
Unactivated coal fly ash consist mainly of Fe, ca, K,
Si, and Al, in the form of quartz and amorphous. The mineral contents were
found to change after chemical activation e.g. quartz was reduced, anorthite
was increased. Physical activation does not affect it.
5.
Acknowledgement
The authors would like to thank to DITJEN DIKTI as organizer of Program
Kreativitas Mahasiswa for funding this research, Mr. Heri Purnomo, ST from PT.
Semen Gresik for his assistanship in XRD analysis, Ninit Martianingsih, S.Si
who helps the SEM-EDX characterization, Nurul Faradillah Said, S.Si who helps
the XRF characterization.
6.
References
[1] Setiaka,
Juniawan, Ita Ulfin, Nurul Widiastuti. 2011. Adsorpsi Ion Logam Cu(ii) dalam
Larutan pada Abu Dasar Batubara Menggunakan Metode Kolom. Prosiding Tugas Akhir. Jurusan Kimia, Institut Teknologi Sepuluh
Nopember. Surabaya
[2] Jumaeri,dkk.
2007. Preparasi dan Karakterisasi Zeolit
dari Abu Layang Batubara secara Alkali Hidrotermal. Reaktor, Vol. 11 No.1, Juni 2007, Hal. :
38-44
[3] Ahmaruzzaman M.
2010. A review on the utilization of fly ash. Progress in Energy and Combustion Science, 36: 327–363
[4] Mohan S, Gandhimathi R. 2009. Removal of heavy metal
ions from municipal solid waste leachate using coal fly ash as an adsorbent.
Sience Direct. Journal of Hazardous
Materials, 169: 351-359
[5] Barbara G,
Kutcko, Ann G. Kim. 2006. Fly Ash Characterization by SEM-EDS. Fuel, 85: 2537-2544
[6] Lasryza, Ayu.
2012. Pemanfaatan Fly Ash Batubara sebagai Adsorben Emisi Gas Buang CO pada
Kendaraan Bermotor. Tugas Akhir.
Jurusan Teknik Fisika, Institut Teknologi Sepuluh Nopember. Surabaya
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