COAL STRUCTURAL CHARACTERISTICS OF BAYAH FORMATION BASED ON X-RAY DIFFRACTION ANALYSISAhmad Helman Hamdani 1, Agus Didit
Haryanto 1, Muhamad Iqbal 1 1 Department of Geology, University of Padjadjaran, Indonesia |
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Received 06 January 2022 Accepted 12 February 2022 Published 28 February 2022 Corresponding Author Ahmad Helman Hamdani, ahmad.helman@unpad.ac.id DOI 10.29121/granthaalayah.v10.i2.2022.4495 Funding: This research
received no specific grant from any funding agency in the public, commercial,
or not-for-profit sectors. Copyright: © 2022 The
Author(s). This is an open access article distributed under the terms of the
Creative Commons Attribution License, which permits unrestricted use, distribution,
and reproduction in any medium, provided the original author and source are
credited. |
ABSTRACT |
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The coal of Bayah Formation in Lebak
Regency, Indonesia have been subjected to attenuated to X-ray diffraction
(XRD), to study their chemical and structural characteristics. X-Ray
Diffraction (XRD) has been widely used throughout the world and has high
accuracy in identifying the molecular structure of coal. Curve-fitting
analysis was employed to characterize coal structural. Based on ASTM, the
coal rank from this area is high-volatile bituminous B. The research results
show all coals have the similar coal structural crystallite characteristics.
The value of d002 is in the range of 3.87 to 3.96, reflecting the
coals have a low content of crystalline structure. The crystallite height
(Lc) and diameter (La) were increase, while d002 decrease in
relation of more mature coals. Due to structural parameters (d002,
Lc and La) the coals of Bayah Formation dominantly
by disordered amorphous structure, with small amount crystallite structure. |
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Keywords: Coal, Structural, XRD, Curve Fitting, Bayah
Formation 1. INTRODUCTION
During coalification process, various kinds of inorganic, organic and
water materials are involved together, so coal is heterogeneous; and provides
diverse physical and chemical characteristics which are reflected in the
values of the heterogeneous crystalline structural parameters in coal.
Therefore, study on the crystal coal structure is important; with knowledge
of molecular structure of coals; physicochemical reactions during the coal
combustion, gasification, and pyrolysis can be controlled. Singh et al. (2015), Sonibare et al. (2010), Saikia et al. (2007).
XRD is a non-damage method that is often used to study the crystallite
structural of materials containing carbon, such as coal Haenel (1992), Lu et al. (2001), Vivek et al. (2016). Several indicators of crystal structure in coal
measured by XRD are stacking height of crystallite (Lc), average lateral
sizes (La), interlayer spacing of the crystalline structure (d002),
aromaticity (fa). The coal rank was controlled the development of coal
crystal structure parameter. An increase in coal maturation will be followed
by a decrease in the value of d002, and an increase in the value of La and
Lc, but the value of Lc gradually decreasing. In the throughout the
coalification process, an increase crystal structure of coal and a decrease
in the amorphous structure Jiang et al. (2019). Hirsch (1979), Watanabe et al. (2002). Qualitatively, the structure in coal generally
consists of crystalline carbon and amorphous carbon Lu et al (2015). In
Banten Province the |
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occurrence of coal is reported
found within Bayah Formation of Eocene strata Sujatmiko and Santosa (1992) Investigation
of the Bayah Formation coal was limited to the analysis of
proximate, ultimate and maceral compositions. However, research on the structure of coal has not been
investigated. The aim of this research is the use of XRD technique to study the
structural characteristics of the Bayah Formation
coal.
2. MATERIALS AND METHODS
2.1. Sample and Sample Preparation
Five bituminous coals from Bayah
Formation, Banten Province were selected for this investigation. Several
analyses were carried out to obtain the chemical molecular structure
characteristics of bituminous coal, such as proximate, ultimate, XRD analysis.
2.2. Experimental Methods
Proximate, Ultimate Analysis. The
series measurement of moisture, ash, fixed carbon, and volatile matter in coal
which is grouped in Proximate Analysis. The ASTM Standard of moisture, ash, fixed carbon,
volatile matter was used, such as D-3173, D-3174, D-388, D-3175, respectively. The
ultimate analysis was measured carbon and hydrogen, nitrogen, sulphur, and
oxygen based on ASTM Standard of ASTM D-3178, ASTM D-3179, ASTM D-3177, and
ASTM D-3176, respectively. The result of all analysis was presented in Table 1.
XRD. An X-ray
diffractometer device (BrukerAXSD8) was used to obtain the spectral
characteristics of the XRD. The operational conditions used are as follows: CuKa radiation (40Kv, 40mA) in the angular range of 100
–800 (2θ) with 0.020 step interval and a scanning rate of increments from
50 to 900 (2θ) at intervals of 0.02 and counted for 0.5 sec per step. The Bragg’s
and Scherrer equations were used calculated the structural parameters Equation 1, Equation 2, Equation 3, Equation 4 Equation 5, Iwashita
et al. (2004), Okolo et al
(2010), Robert
et al. (2015), Baysal et al. (2016), Li et al. (2013), Li and Zhu (2014)
ƒa = Car/ (Car + Cal) = A002/ (A002 + Aƴ) Equation 1
La = 1.84λ/(β002cosϴ002) Equation 3
Lc = 0.89λ/(β100cosϴ100) Equation 4
N Equation 5
Where Car is the sum of the aromatic carbons, and the value of Cal is the sum of the aliphatic carbons. A002 and Aƴ are areas of peak 002 and peak ƴ which are around the 26° and 20° x coordinates respectively on the XRD graph. λ =1.54056 for copper Ka radiation; λ is the wavelength of the radiation used. ϴ002 and ϴ100 are the diffraction angles from peak 002 and peak 100. β002 and β100 are full width half at maximum values (FWHM) of peak 002 and peak 100.
To determine coal rank from XRD from the formula Equation 6, Yoshizawa
et al. (2002)
Coal rank = (I26/I20) Equation 6
3. RESULTS AND DISCUSSIONS
3.1. PROXIMATE AND ULTIMATE ANALYSIS
Result of analysis of Bituminous coals from Bayah Formation, Banten Province was shown in Table 1. The average atomic ratios of H/C, O/C, were calculated to be 0.86, 0.08, respectively. The moisture is low in all coals (1.8–2.4wt%), and low ash yield (, 5% wt.%). The coals have a high volatile matter, and fixed carbon, i.e., 45.7% to 46.1%, 47.5% to 51.1%., respectively. The sulfur in samples is low (0.76–n1.21 wt.%). Measurement of C-H-O elements in coals showed that the carbon content was very high, which was followed by oxygen and hydrogen as presented in Table 1.
Table 1 Result of proximate and ultimate measurement of coal samples |
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Parameters |
ST-11.2 |
ST-14 |
ST-17 |
ST-21 |
ST-24 |
|
Proximate
(ad) |
Moisture |
4,13 |
4.21 |
4.73 |
3.92 |
4.28 |
Ash |
5.81 |
4.21 |
3.78 |
2.61 |
2.17 |
|
Volatile
Matter |
39.31 |
40.12 |
41.42 |
42.18 |
42.51 |
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Fixed
Carbon |
50.75 |
51.46 |
50.07 |
51.29 |
51.03 |
|
Ultimate
(daf) |
Carbon |
79.64 |
78.49 |
80.05 |
78.43 |
78.34 |
Hydrogen |
3.35 |
4.19 |
4.2 |
4.54 |
5.23 |
|
Oxygen
(by diff) |
15.31 |
14.82 |
14.4 |
16.18 |
15.44 |
|
H/C |
0.5 |
0.64 |
0.62 |
0.69 |
0.8 |
|
O/C |
0.14 |
0.14 |
0.13 |
0.15 |
0.15 |
3.2. XRD
In the XRD graph Figure 1, it is clear that
the peaks of XRD spectral intensity of 002, 10, and 100 are identified.
These three peaks are at diffraction degrees of 2ɵ at 26°, 42° and 47°, respectively. In addition, to the left
of peak γ is identified peak, both of which are Gaussian peaks.
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Figure 1 XRD
spectra of Bayah coal samples |
To get the peak area,
diffraction angle 2Ɵ, intensity value and FWHM (Full Width Half Maximum)
value; Curve fitting analysis (Gaussian method) was performed on all coal
samples. Figure 2 shows the results of the Curve fitting sample no. ST. 17, and ST. 21, which
represents all coal samples. Table 2 tabulated the results of the calculation of the structural parameters
of coal with the XRD method of Bayah Formation coal
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Figure 2 Gaussian’s curve fitting XRD Spectral from coal samples of Bayah Formation |
Table 2 Structural parameters of coal by XRD |
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Sample |
d002 (Ǻ) |
La
(Ǻ) |
Lc
(Ǻ) |
ƒa |
N |
n2 |
I26/I20 |
Ro
(%) |
ST
11_2 |
3.96 |
15.3 |
7.3 |
0.76 |
2.85 |
2.61 |
2.61 |
0.72 |
ST
14 |
3.94 |
13.16 |
5.81 |
0.64 |
2.49 |
1.98 |
2.01 |
0.71 |
ST
17 |
3.94 |
14.9 |
3.01 |
0.73 |
1.76 |
1 |
1.98 |
0.68 |
ST
21 |
3.86 |
15 |
3.12 |
0.67 |
1.79 |
1.03 |
1.69 |
0.74 |
ST
24 |
3.91 |
14.1 |
3.31 |
0.68 |
1.84 |
1.09 |
1.93 |
0.65 |
Where:
D002: Interlayer spacing fa: aromaticity
Lc: Crystallite height N: Average Number of aromatic
layers
La: Crystallite diameter n: average total carbon atoms in the
aromatic layer
I26/I20: Coal rank
From
the results of measurement of coal structural parameters by XRD analysis Table 2, it can be seen that the value of the interlayer distance
(d002) is in the range of 3.86 to 3.96 Å , the average diameter of
crystallite (La) is in the diameter of 13.16 to 15.30 Å , the average size of
crystallite height is (Lc) in the range 3.01 to 7.30 Å, carbon aromaticity (ƒa) in the range 0.64 to 0.76, coal rank (I26/I20)
in the range 1.69 to 2.61, and carbon layer (N) in the range of 1.76 to 2.85,
and the value of n is between 1.00 - 2.61.
4. DISCUSSION
Based on the analysis of
proximate and ultimate analysis; ratio of H/C and O/C indicated that all coals
were classified as the High Volatile Bituminous-B coal.
The results of the
observation of coal XRD spectral peaks show that peak 002 is higher compared to
peak 10 or 100; apart from structured; it was clearly found at 26°, 42° and 47°,
respectively. Generally, in coals the XRD spectral consists of 002 and 100
peaks, which peak 002 has the position in areas between 15–30°: and peak 100 in
the range of 40–50°. Smȩdowski et al. (2011), Baysal et al. (2016). This reflects that the coal studied have a structure like graphite
(crystallite carbon). However, with the high detected background, the coal also
contains an amorphous material structure (highly disordered materials). Therefore,
based on the appearance of the peak of the spectral XRD; Therefore, Bayah coal is composed of amorphous and crystalline
material Lu et al. (2001), Okolo et
al. (2015).
The
values of coal crystallite structures such as d002, La, and has a relation
with coal maturity (%Ro). For all the coal samples were shown that with an
increase of %Ro, the variation of La increase
slightly for coal from 13.16 – 15.30 Ǻ;
d002 decrease slightly of 3.86-3.96 Ǻ,
while Lc decreasing from 3.91 – 3.86 Ǻ. In
high rank coal, graphite structure is more likely to form compared than in low
rank coal. The interlayer distance (d002)
in all samples showed a higher range (3.86 to 3.96 Å) than d002 pure
graphite (d002= 3.36-3.37Å), reflecting the low degree of crystal
regularity in coals. Bhupati et al (2017).
The interlayer spacing (d002)
in the high mature bituminous coal (Ro =0.74%) of the Bayah
Formation was small (3.86 Å); associated with a lower carbon element content
value (79 - 80%) compared to that contained by pure graphite Singh et
al. (2015), Singh et al (2017). Besides
that, it is also related to the aromatic ring in the coal continues to solidify
as the coal matures.
Overall, the findings in this
study indicate that the more mature (high %Ro), the smaller the amorphous
structure, which is followed by an increase in crystallite height and diameter;
but the interlayer spacing is getting smaller. The same finding was also
conveyed by other researchers. Shike et al. (2021), Takagi
et al. (2004)
5. CONCLUSIONS AND RECOMMENDATION
A total of 5 coal sample from
Bayah Formation, Indonesia have been identified the
structural characteristic based on XRD measurement. Following conclusion are
drawn:
1) The coals are classified as the High Volatile Bituminous B
2) The XRD investigations show the highly disordered amorphous
and crystallite structure were identified in coals.
3) The crystalline carbon in coals having the sizes of La,
(Lc), and d002 ranging from 13.16-15.30 Å, 3.01 to 7.30 Å, and 3.86
to 3.96Å, respectively.
We, recommend XRD study to be
used to indicate coal maturity level
ACKNOWLEDGEMENTS
The authors would like to expression of gratitude was conveyed to the Chancellor of the University of Padjajaran who has funded this research through the 2021 ALG scheme.
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