Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-12

Classification of Fly Ash based on Physical and Chemical Characterization for
The Usage of Acid Mine Drainage Prevention
Sendy Dwiki ,1 Hideki Shimada,1 Takashi Sasaoka,1 Akihiro Hamanaka,1 Rudy Sayoga
Gautama,2and Ginting Jalu Kusuma2
1Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Fukuoka
819-0395, Japan
2Institute Technology Bandung, Bandung 40191, Indonesia

Abstract
Fly ash, as the excessive waste material from coal-fired steam power plant, has advantages tobe used as an additional cover layer in a dry cover method which can increase the pH of waterand also physically cover sulfide mineral as well as decrease permeability of the water andoxygen infiltration so that acid mine drainage generation could be minimized. Unfortunately,
the usage of this material is not widely well-known despite its abundant availability as
by-product. Recent studies also have not investigated the characteristics of fly ash and its
difference among fly ash itself in detail. Therefore, this study intends to investigate
characteristic of fly ash, from geochemical and physical behavior that has advantages in AMD
prevention. Moreover, this study also aims to establish a simple classification of fly ash inorder to make the usage of this material easier to be implemented.
economical to be applied, due to the highamount that is needed, which make it
expensive, or because of unavailability of
those materials around the mining site,which increase the transportation cost thus
impossible to be used. In coal mines, one ofinteresting material to be applied as anadditional cover layer is fly ash, as aby-product of thermal combustion of coal inpower stations that has alkalinity matterfrom unburned coal.
In the world, 780 Mt coal fly ash is
produced annually, that estimated only
utilized under 50%, mostly for cement or
construction industries (WWCCPN, 2011).
The rest of fly ash ends up in the disposal.
This causes more serious problem to theenvironment due to the alkalinity of it, thatneeds specific treatment only for disposing.
Moreover, numerous countries classify flyash as a hazardous material. Therefore, thefly ash usage is beneficial, not only forcontrolling AMD generation, but also
increases its utilization thus reducing its
number in disposal. A lot of coal mines havemine-mouth coal-fired steam power plant,suggests its availability to be used in AMD

1. Introduction
Acid mine drainage (or also known as
ARD for ore mining, etc.) is an infamousenvironmental problem in mining site. Thisissue is prominent due to its large scaleeffect that can pollute the surrounding water
environment in mind, thus negatively alter
the adjacent water bodies in the same watersystem. The mine water can flow out
through river or groundwater, whichcontaining acidity and high concentration ofheavy metals and/or cation-anion. It could
endanger the living organism around theflowing acid mine water, because
over-consuming this water up to thethreshold can affect their health and causing
severe diseases, for example cancer, which
likely lead to death.
Various alkaline materials have been
widely investigated in order to improve dry
cover, as an additional layer that able toreduce acid mine drainage (AMD)generation. This includes limestone, lime,
sodium bicarbonate, etc. that prospectively
might control the pyrite oxidation, as themain sulfide minerals in AMD generation.
However, those materials can be not32

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

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prevention method.
Regarding the usage of fly ash in AMDcontrol, various studies attempt tocharacterize its chemical and physicalproperties in order to understand the mainprocess, side effects and also efficiency of it
for preventing AMD. However, those studiesof fly ash mainly focus only on the specified
available type of fly ash in the coal mine(site specific) even though physical andchemical properties of a particular fly ash
are dependent on the composition of parent
coal, conditions of coal combustion,
efficiency of emission control and storage
and handling practices (Adriano et al., 1980).
Therefore, this research intends toinvestigate various of fly ash properties inorder to know the difference based on
physical and geochemical properties, thus
knowing the main effect of fly ash to AMD
prevention. Moreover, due to the lack ofcomparative study of fly ash in regard toAMD, this research also aims to establish asimple classification that can be used inchoosing the suitable fly ash for different
condition of the mines.
2. Material and Experimental Methods
2.1. Material
5 fly ashes and 2 bottom ashes fromlocations are collected. 6 samples are basedin Indonesia coal-fired steam power plant
while only 1 samples that is originallysourced from Fukuoka coal-fired steam
power plant, Japan. However, the source ofJapan coal-fired steam power plant is fromIndonesia and Australia. Further details
about the fly ash and bottom ash samples
can be seen in Table 1.
SampleFA AI
FA ADRFA KYUFA KPCFA ICABA ICA
FA BA
BA BA

treatment prior the experiments. Fly ash andbottom ash were dried in the ovencompletely before start analysis at 105oC.
After that, the certified amount of samples
wasanalyzedforits
physicalcharacterization while the other amount wasanalyzed for geochemical characterization.
Physical characterization is carried out by
conducting several experiments, including
experiments for analyzing specific gravity,
particle size distribution, morphology ofparticles, and specific surface area by using
method of water pycnometer, the sieve
analysis (for particle size above 0.075 mm)
and hydrometer analysis (for particle size
below 0.075 mm), scanning electron
microscopy energy dispersive X-ray(SEM-EDX), and Brunauer-Emmet-Teller(BET), respectively.
Geochemical characterization was
carried out together with chemicalcharacterization, by conducting static tests,
bulk chemical analysis and element
composition by using chemical reactions asmentioned in AMIRA 2002, X-ray
Fluorescence (XRF) and elemental digestion
with acid sequential extraction. In order tosupport the result, mineralogical analysis
was also conducted by using X-ray
diffraction (XRD) technique.
3. Result and Discussions
2.1. Physical Characterization
Particle size distribution was analyzed
by two methods, for the particle size above
0.075 mm using sieve analysis and particle
size below 0.075 mm using hydrometer
analysis. The result can be seen in Figure 1.
From the result, it can be seen that finerparticle size was owned by mostly fly ash,
except for FA KPC. This result isunderstandable since fly ash is coal
combustion product that are driven out ofthe boiler with the flue gases, while that ashthat falls to the bottom of the boiler is called
as bottom ash. The difference in size is thereason why such segregation happens
However, in FA KPC, it gives different
trend of particle size. This might happen
because of the handling during the storage

Table 1. List of samples
SourceSouth Kalimantan
East Kalimantan
Fukuoka
East Kalimantan
West Kalimantan
West Kalimantan
South Sumatera
South Sumatera

2.2. Experimental Method
All of the samples received similar

33

Proceedings of International Forum for Green Asia 2017Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-12
where agglomeration of particle occurs andaffect the overall particle size. In order tounderstand this, further analysis isconducted by using the SEM-EDX result.

100.000

Weight Percentage Passing (%)

90.00080.000FA AI

70.000FA KPC60.000FA ADR

50.000FA KYU

40.000FA BA

30.000FA ICA

20.000BA BA

10.000BA ICA

0.000
0.001

0.010

0.100

1.000

Particle Size (mm)Figure 1 Particle size distribution of fly ash and bottom ash
Microstructure of fly ash and bottom
ash can be observed from the result ofSEM-EDX techniques. Based on its opticalmorphology, the particles of fly ash can bedefined into 11 classes: (1) amorphous,nonopaque; (2) amorphous, opaque; (3)amorphous, mixed opaque and nonopaque;(4) rounded, vesicular, nonopaque; (5)rounded, vesicular, mixed opaque andnonopaque; (6) angular, lacy opaque; (7)nonopaque, cenosphere (hollow sphere); (8)nonopaque, pleroshpere – sphere packed
with other spheres; (9) nonopaque, solidsphere; (10) opaque, sphere; and (11)nonopaque sphere with either surface orinternal crystals (Fisher, et al., 1978).
Therefore, based on SEM-EDX result, forsimplification, fly ash according to theirshapes and structures can also be classified
spherical particles, plerosphere and irregularparticles (Chengfeng, et al., 2005).
Generally, spherical particles existed inall samples (see Figure 2). However, there
are significant difference in the structure thatcan differ fly ash into two groups.
FA KYU, FA ADR and FA AI were
dominantly consist of spherical particles andalso plerosphere. Moreover, the sphericalparticles were also seen to be attached to thebigger sphere, or sometimes agglomerated
between similar size of particles. Meanwhile,FA KPC, FA ICA and FA BA were shared
the similar particles that dominantly have an
irregular shape with small amount ofspherical particles. Furthermore, all of theirregular particles have coarse surface.
Irregular particles are particles with irregularshapes and various sizes. Some irregularparticles in this research look like solids (FAICA and FA BA) that. Some have holes on
their surfaces as can be seen in FA KPC.
Interestingly, the hollow surface in FA KPC
was seen obviously porous that indicates its
high capacity in holding the water.
So far, the studies of fly ash conclude
that difference in boiler types may be themain reason for different particle types,
resulting in different formation of particles.
2.2 Geochemical Characterization
Bulk chemical analysis was measured
by using the XRF technique for total 7
samples of fly ash and bottom ash. The
result of XRF measurement is provided inTable 2. As can be seen, the primarychemical components were SiO2, Al2O3,FeO and CaO. All of samples are mainlycomposed by SiO2, indicates that most of
unburned material from coal is the silicate
minerals. Moreover, samples of FA ADR, FAKYU, FA BA and FA AI were high in theCaO concentration, suggest its higher
capacity in producing alkalinity compare to34

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-12
the rest of the samples. The main inorganic
elements found in samples are Si and Al,suggesting the high amount of quartz andaluminosilicates.

Figure 2 SEM-EDX for fly ash (1000x) and bottom ash (40x) particles
Except for FA KPC, based on ASTM
only for raw of calcined natural pozzolan.
C-618 (standard specification for coal fly
Even though can be referred to, thisash and raw or calcined natural pozzolan forclassification is difficult to be implemented
use in concrete) all of samples are classified
in AMD prevention since no further
into class F, ASTM C-618 classification.
explanation for the capacity in neutralizing,
Class F in this classification means that thetherefore it is important to observe its
number of silicon dioxide, aluminum oxide
neutralization as well as acid production
and iron oxide has minimum 70% in masspotential and also further physicalpercentage, while class C only 50%. Class N
characteristic that has beneficial to theis also available, however this class specificprevention of AMD.
Table 2 Bulk chemical analysis by XRF
SampleSiO2(%)TiO2(%)

Al2O3(%)

FeO
(%)

MnO
(%)

MgO
(%)

CaO
(%)

Na2O
(%)

K2O
(%)

P2O5(%)FA ADRFA KPCFA ICABA ICA
FA KYU
FA BA
BA BA
FA AI

36.2
33.1
50.6
73.5
67.4
46.5
68.8
42.1

1.1
0.8
1.2
0.8
1.1
0.9
0.7
0.6

20.4
14.3
23.3
15.6
18.7
21.1
18.5
9.9

21.4
5.8
10.9
5.5
4.2
5.3
3.9
25.0

0.3
0.1
0.1
0.0
0.0
0.1
0.0
0.4

4.9
1.4
1.9
1.1
1.1
2.8
2.1
7.7

10.7
1.7
1.9
1.4
2.9
3.0
1.7
11.5

0.6
0.7
0.6
0.5
0.7
0.9
0.9
0.5

0.8
1.5
2.0
1.0
1.2
0.8
0.8
0.5

0.3
0.1
0.1
0.1
0.3
0.2
0.1
0.0

Result of static test shows an interesting
result that able to differ the fly ash into two
main groups. From acid neutralizing
capacity (ANC) test (see Figure 3) shows asignificant result of neutralization from FAAI, FA ADR and FA KYU, which reacheduntil more than 100 kg H2SO4/ton. It is also

Loss onIgnition
(%)
1.4
39.8
5.3
0.2
2.0
16.4
2.5
0.2

supported by the result of NAG pH of those
3 samples that have high value, for FA AI,FA ADR and FA KYU, 11.93, 11.01 and11.77, respectively. On the contrary, FA BA,
FA ICA and FA KPC has a low result of theANC and also NAG pH. This suggests thatthe latter group has the insignificant capacity

35Total(%)
98.1
99.2
97.9
99.7
99.5
98.0
99.9
98.6

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-12in producing alkalinity. Meanwhile, bottom
ash samples show inconsiderable value ofANC therefore can be ignored.
14.05. Conclusion
Physical characterization shows that mostly
the fly ash can be distinguished from thebottom ash. Microstructure of fly ash also
shows that there are two groups, the one that
dominantly by spherical particles anddominantly by irregular particle structure.
Based on the geochemical characterization,
this classification can be more clearlydistinguished. With the support of physicalcharacterization, Type 1 fly ash (highalkalinity) and Type 2 fly ash (lowalkalinity) classification can be established.
Further experiments are needed in order tomake this classification is reliable.

12.0200

8.0
6.0100NAG pH

10.0150

4.050

BA BABA ICAFAKPCFA ICA

FA BAFAKYU

FAADR02.0

FA AI

Acid Neutralizing Capacity (kg H2SO4/ton)

250

geochemical characterization can differ thefly ash into two general types, Type 1 andType 2.

0.0

Figure 3 Acid neutralizing capacity (ANC) test
Figure 4 shows the result of NAG tests withvarious ration of fly ash addition to the PAF
samples. In this test, quantified amount offly ash is added to the powdered PAF rocks
sample (less than 0.0075 mm), at thepercentage of 0%, 25%, 50% and 100%.
This result also supports previous result,where classification of a group that has highalkalinity and low alkalinity can beestablished. To make it easier, fly ash groupwith high alkalinity an be named as Type 1
meanwhile fly ash group that has low
alkalinity named as Type 2.
When the fly ash of the high alkalinity groupis added to the PAF sample, the value of
NAG pH increases dramatically along withthe amount of fly ash addition. On thecontrary, when fly ash of the low alkalinity
group is added to the PAF rock, the increaseof pH is not really high.
14.00
12.00

FA BA

NAG pH

10.00

FA AI

8.00

FA KYU

6.00

BA BA
FA KPC

4.00

FA ADR

2.00

0.00

FA ICABA ICA
0 10 20 30 40 50 60 70 80 90 100

Percentage of FA

Figure 4 NAG
withvariousfly ash andOverall,the test
resultof physicalandPAF
samplesAcknowledgment
The first author wishes to extend
gratitude to ITB for the full support of thisresearch to visit mining sites andcooperation in providing the samples andmaterials used in this study. First author
would like also to thank to Green Asia forresearch financial support.Text
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Email: sendy12r@mine.kyushu-u.ac.jp37