1. R.H. Matjiea,b, Zhongsheng Lic, Colin R. Wardc
DETERMINATION OF MINERAL MATTER AND ELEMENTAL COMPOSITION OF INDIVIDUAL MACERALS IN COALS FROM HIGHVELD MINES
R.H. Matjiea,b, Zhongsheng Lic, Colin R. Wardc
a Sasol Technology (Pty) Ltd, P.O. Box 1, Sasolburg, Free State 1947, South Africa
b Department of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria 0002, South Africa
c School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia

2. OUTLINE
Introduction and background
Objectives
Experimental
Results
Conclusions
Acknowledgements

3. BACKGROUND

5. OUTLINE
Introduction and background
Objectives
Experimental
Results
Conclusions
Acknowledgements

6. Objectives
Characterise coals from mines in the Highveld coalfield, in order to gain a better understanding of the mineralogical and chemical properties of the individual components in the feedstocks used for coal conversion processes;
Improve the understanding of problems (e.g. abrasion, stickiness, slagging, sintering, corrosion and pollution) associated with coal handling and use.
BACKGROUND

7. OUTLINE
Introduction and background
Objectives
Experimental
Results
Conclusions
Acknowledgements

8. Conventional and advanced analytical
techniques employed to analyse coals
Chemical Analysis:
Proximate analysis (percentages of moisture, ash and volatile matter)
Ultimate analysis (C, H, N, O and S)
XRF – analysis of inorganic elements in whole-coal or coal ash
Low-temperature Ashing:
Determine the mineral matter percentage in the coal samples
Isolate the minerals for XRD analysis (including clay fraction)
Mineralogical Analysis:
XRD – identify the minerals and quantify the mineral phases in the LTA using the Rietveld-based SIROQUANT technique

9. Low-temperature ashing X-ray diffraction
Petrographic Analysis:
Determine the types and proportions of maceral groups in each of the coals, and the rank by vitrinite reflectance
Electron Microprobe Analysis:
Detemine the elemental composition of the individual macerals in each coal sample

10. Cameca SX-50 Electron Microprobe
Element Line Crystal Count Standard
Time (s)
C Kα PC Anthracite
N Kα PC BN
O Kα PC Sanidine
Al Kα TAP 10 Sanidine
Si Kα TAP 10 Diopside
S Kα PET 10 Marcasite
Ca Kα PET 10 Diopside
Fe Lα PC Marcasite
Ti Kα PET 10 Rutile
Mg Kα TAP Diopside
K Kα PET 10 Sanidine
Accelerating voltage 10 kV
Beam current nA
Beam diameter µm

11. Sampling from the coal mines

12. OUTLINE
Introduction and background
Objectives
Experimental
Results
Conclusions
Acknowledgements

13. Proximate analyses of coals tested (air-dried basis)
Sample Number 1 2 3 4 5 6
Moisture (%)
3.3
2.9
3.2
3.4
3.0
3.8
Ash (%)
24.5
29.0
29.7
27.2
26.8
22.1
Volatile matter (%)
21.7
22.9
21.3
21.5
22.4
23.1
Fixed carbon (%)
50.5
45.2
45.8
47.9
47.8
51.0
Total sulphur (%)
1.1
1.0
0.8
0.7
Volatile matter (daf basis, %)
30.1
33.6
31.7
31.0
31.9
31.2

14. Ultimate analyses of coals tested (dry, ash-free basis)
Sample Number 1 2 3 4 5 6
Carbon (%)
79.9
78.5
77.1
77.8
79.0
77.9
Hydrogen (%)
4.36
4.55
4.07
4.12
4.59
4.29
Nitrogen (%)
2.12
2.00
1.97
2.08
Total sulphur (%)
1.55
1.41
1.15
1.50
1.62
0.92
Oxygen (% by difference).
12.1
13.5
15.7
14.6
12.7
14.9

15. X-ray diffractograms of low-temperature ashes

16. Mineralogical analyses of LTA from coal samples1 2 3 4 5 6
LTA
31.9
43.9
33.6
24.6
36.2
34.5
Quartz
17.6
21.5
20.1
18.3
15.2
20.6
Kaolinite
51.4
50.4
50.8
47.6
44.0
49.5
Illite
bld
5.7
5.3
2.2
Mica
10.4
7.4
4.5
6.9
7.0
Calcite
2.1
1.2
1.8
4.6
9.8
2.7
Dolomite
10.3
6.4
10.2
10.0
11.7
Siderite
0.0
1.3
0.3
1.4
0.4
0.9
Pyrite
2.4
2.6
2.0
1.6
Bassanite
1.9
2.5
Goyazite
1.0
1.7
3.0
Anatase
1.5
0.8

17. Inferred ash chemistry (inorganic oxides, wt%) from mineral percentages and mineral compositions
Sample 1 2 3 4 5 6
SiO2
55.2
59.3
56.2
51.3
57.6
54.0
Al2O3
28.9
29.1
27.5
28.2
28.5
26.6
Fe2O3
1.9
2.0
1.5
2.3
2.7
TiO2
3.2
1.7
1.2
1.0
P2O5
0.4
0.7
1.1
1.3
0.6
CaO
6.3
3.9
7.3
12.2
6.0
10.3
MgO
1.6
3.1
4.1
Na2O
0.0
K2O
0.9
Total
100.0

18. Measured inorganic oxide percentages (wt %) from normalised XRF analysis of whole-coal samples
Sample Number 1 2 3 4 5 6
SiO2
57.16
55.38
55.91
52.20
57.43
55.68
Al2O3
24.96
30.21
27.78
29.40
26.70
25.31
Fe2O3
5.13
2.34
1.88
2.42
3.58
2.59
TiO2
1.21
1.26
1.42
1.64
1.17
1.33
P2O5
0.32
0.76
0.53
0.86
0.89
0.68
CaO
7.49
6.54
8.26
9.27
7.03
10.60
MgO
1.67
2.02
1.84
1.23
2.06
Na2O
1.06
1.07
0.85
K2O
0.95
1.02
1.29
1.13
0.54

19. Mineralogy of <2 micron fraction of LTA by oriented aggregate XRD
Sample Number
Kaolinite %
Illite %
Expandable Clay %
Nature of Expandable Clay 1 93 6
Mainly smectite 2 92 3 5
Mainly irregular I/S 4 96
Regular to irregular I/S 90 8
Smectite + regular I/S

21. Petrographic analysis of coal samples (volume %, mineral free)
Maceral Group 1 2 3 4 5 6
Vitrinite (%)
19.2
25.8
20.5
20.6
31.6
27.1
Liptinite (%)
3.5
3.7
3.2
3.4
5.4
Inertinite (%)
77.3
70.6
76.3
76.1
64.0
67.5
Rvmax (%)
0.72
0.70
0.75

22. Elemental composition of macerals in coal samples
by electron microprobe analysis
Maceral
Points C% N% O%
Mg%
Al%
Si% S% K%
Ca%
Ti%
Fe%
Sample 1 TC 23
73.24
2.38
18.97
0.01
0.06
0.65
0.00
0.10
0.55
0.02
DSC 12
74.82
2.46
17.39
0.11
0.67
0.44 SF 15
84.40
0.98
10.21
0.04
0.30
0.07
FUS 16
85.73
0.84
8.68
0.03
0.09
0.25
0.13
Sample 2
74.34
2.29
18.00
0.79
0.38 22
78.56
1.94
14.71
0.12
0.58
0.22 7
88.28
0.23
7.07
0.24
89.28
0.75
6.31
0.36
0.15
Key: TC = telocollinite, DSC = desmocollinite, SP = sporinite, CUT = cutinite, SF = semifusinite, FUS = fusinite, IDT = inertodetrinite.
Pts = number of points analysed for indicated maceral.

23. Elemental composition of macerals in coal samples
by electron microprobe analysis
Maceral
Points C% N% O%
Mg%
Al%
Si% S% K%
Ca%
Ti%
Fe%
Sample 4 TC 23
77.32
1.93
16.02
0.01
0.10
0.39
0.03
0.06
0.42
0.00
DSC 17
77.67
2.10
15.24
0.17
0.16
0.40
0.02
0.07
0.45 SF 12
85.46
0.81
9.16
0.19
0.09
FUS 14
86.36
0.99
8.43
0.04
0.18
Sample 5 33
75.39
17.96
0.24
0.80 19
76.47
2.19
16.80
0.87
0.08 SP 1
79.70
1.89
15.00
0.54
0.53
1.14 6
86.26
0.94
9.48
0.34 8
89.22
0.43
7.39
0.37
0.12
IDT 2
90.90
1.52
5.77
0.13
0.33
Key: TC = telocollinite, DSC = desmocollinite, SP = sporinite, CUT = cutinite, SF = semifusinite, FUS = fusinite, IDT = inertodetrinite

24. Elemental composition of macerals in coal samples
by electron microprobe analysis
Maceral
Points C% N% O%
Mg%
Al%
Si% S% K%
Ca%
Ti%
Fe%
Sample 3 TC 15
73.17
2.41
19.83
0.01
0.41
0.33
0.76
0.05
0.06
0.38
0.00
DSC 12
74.49
2.31
18.62
0.40
0.25
0.77
0.08
0.07 SF 10
81.04
1.66
13.03
0.02
0.22
0.42
FUS 14
83.11
1.00
11.41
0.36
0.11
Sample 6 29
69.51
2.67
23.38
0.19
0.46
0.12 21
70.06
2.55
22.06
0.20
0.47
0.17
CUT 2
76.49
1.61
16.03
0.18
0.35 SP 4
77.04
1.84
14.28
0.29
0.09
0.93 18
80.39
1.25
12.64
0.04
0.03
0.14
85.05
0.72
9.40
0.10
0.26
IDT 5
90.13
0.68
4.23
0.43
Key: TC = telocollinite, DSC = desmocollinite, SP = sporinite, CUT = cutinite, SF = semifusinite, FUS = fusinite, IDT = inertodetrinite

25. Elements in Coal Macerals
Element Vitrinite Inertinite
Carbon % %
Oxygen % %
Nitrogen % %
Organic sulphur % %
Titanium up to 0.4% < 0.02%
Notes:
Carbon more abundant in inertinite; oxygen more abundant in vitrinite
Organic sulphur, nitrogen and titanium are more abundant in vitrinite than inertinite

26. Comparison of microprobe data (maceral composition and maceral percentage) and dry, ash-free ultimate analysis data
Ultimate (dry ash-free) 1  2  3  4  5  6 
Carbon (daf %)
79.9
78.5
77.1
77.8
79.0
77.9
Oxygen (daf %)
12.1
13.5
15.7
14.6
12.7
14.9
Nitrogen (daf %)
2.12
2.00
1.97
2.08
Total sulphur (daf %)
1.55
1.41
1.15
1.50
1.62
0.92
Hydrogen (daf %)
4.36
4.55
4.07
4.12
4.59
4.29
 Total
100.0
Whole coal inferred from probe 1 2 3 4 5 6
Carbon (%)
82.1
84.4
80.3
84.2
83.3
Oxygen (%)
11.9
10.1
13.7
10.2
11.8
Nitrogen (%)
1.3
1.0
1.5
1.1
1.2
Organic sulphur (%)
0.4
0.5
0.2
0.3

27. OUTLINE
Introduction and background
Objectives
Experimental
Results
Conclusions
Acknowledgements

28. Conclusions
A range of conventional and advanced analytical techniques, including whole-coal X-ray fluorescence, low-temperature ashing, quantitative X-ray diffraction and electron microprobe analysis, have been used to evaluate the mineral and organic matter in coals from the different Highveld coal mines, used as feedstock to combustion and gasification processes.
The combination of techniques allows better evaluation of the proportions of fluxing minerals (pyrite, dolomite and calcite) and organically-bound inorganic elements that are responsible for clinker formation, as well as for volatilisation of inorganic elements, during coal conversion processes.