Chemical characteristics of banded ingredients of coal

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1

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REPORT OF INVESTIGATIONS — NO. 132

CHEMICAL CHARACTERISTICS OF
BANDED INGREDIENTS OF COAL

By

O. W. Rees, W. F. Wagner, and W. G. Tilbury

Reprinted from Industrial and Engineering Chemistry,
Vol. 39, No. 11, pp. 1516-1520, November 1947

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CHEMICAL CHARACTERISTICS OF BANDED INGREDIENTS

OF COAL

BY

O. W. Rees, W. F. Wagner, and W. G. Tilbury

Abstract

Data are presented on certain fundamental chemical characteristics for
four sets of banded ingredients and whole coals from Illinois representing
three ranks — high volatile bituminous A, B, and C. Evidence is shown of
variation by rank of the banded ingredients, vitrain, clarain, and durain.
Evidence of variations by rank of fusains is more erratic. Comparison of
characteristics of Hsiao fusains with those of hand-picked fusains indicates
that the hand-picked samples contain rather large proportions of more
reactive materials. Variations in reported analyses of banded ingredients
appear to be due partially to the influence of varying rank, but also to
variations in the selection of samples.

IN THE work on Illinois coals in this
laboratory, considerable attention has
been given to studies of the physical and
chemical characteristics of the banded in-
gredients, vitrain, clarain, durain, and fu-
sain. The Stopes classification (15) of
banded ingredients is based on macrovisual
appearance. It is of interest, therefore, to
compare these visually selected ingredients
to learn whether each shows more or less
specific chemical characteristics. It is also
of interest to learn whether each ingredient,
secured from coals of different ranks, varies
in chemical characteristics as do the source
whole coals.

Published analyses for the banded ingredi-
ents show wide differences in chemical
composition for each ingredient. Probably
the composition of each ingredient, at least
of vitrain, clarain, and durain, is influenced
by the degree of metamorphosis undergone;
but how far this may account for reported
differences and how much may be due to
variation in the selection of ingredients,
source plant materials, etc., is a question.
Recently Lowry (6), in summarizing chem-
ical information on the banded ingredients,
showed clearly the wide differences in re-
ported analyses for each ingredient. Mar-
shall (7) attempted to correlate analyses of
anthraxylon with type and rank variation in
coal seams. Fisher et al. (3) studied hydro-
genation characteristics of the ingredients.
Sprunk (13) summarized the influence of
physical constitution of coal upon its chemi-

cal properties. Many other investigators
have contributed information on various
phases of this problem, but space does not
permit a complete summary.

This report presents the results of studies
of certain chemical characteristics on four
sets of banded ingredients from the three
ranks of coal — high volatile bituminous A,
B, and C — represented in Illinois. The
work represents an effort to obtain infor-
mation on variations of chemical character-
istics of ingredients as related to rank of
source coals, and in addition to secure in-
formation on differences due to variability
in visual selection, particularly of the fu-
sains.

Tests on Coal Samples

Four sets of samples, including whole
coals and banded ingredients from Gallatin,
Franklin, Macoupin, and Henry counties
were studied. These represent coals of high
volatile bituminous ranks A, B, C, and C,
respectively. The whole coals were channel
samples, cut down, crushed to pass a 4-mesh
sieve, and sealed in sample cans in the mines.
The banded ingredient samples were hand-
picked in the mines, the selection being made
macroscopically. These samples were
crushed to pass a 4-mesh sieve and were
sealed in sample cans in the mines. In the
laboratory, samples were air-dried, crushed
to -20 mesh size in a Braun type 6CP pul-
verizer, and further pulverized to smaller
sizes in a ball mill.

[5]

BANDED INGREDIENTS OF COAL

Several tests were used to compare chem-
ical characteristics of the banded ingredi-
ents. Proximate analysis, calorific value,
and total sulfur were determined on -60
mesh samples according to standard A.S.
T.M. procedures (1). Reactivity index
was determined by the C.R.L. reactivity
test (11, 12). Determinations were made
on -40 +60 mesh samples in both oxygen
and air, and results were indicated as T15
and T75, respectively. Free swelling index
tests were made on —60 mesh samples ac-
cording to a tentative A.S. T.M. method
(2). Moisture characteristics were deter-
mined by the equilibration method described
by Stansfield and Gilbart (14) and later
used in this laboratory (10).

Further studies were made on the hand-
picked fusains. Fusain determinations were
made on these samples by the Hsiao method
(■/). The inert portions (Hsiao fusains)
remaining after nitric acid oxidation of the
hand-picked fusains were studied for re-
activities by the C. R. L. method, and mois-
ture characteristics were studied by the
equilibration method. Proximate and ulti-
mate analyses were made according to
A.S. T.M. standard methods.

Analyses

Proximate analyses, total sulfur, and cal-
orific values for whole coals and hand-picked
ingredients are summarized in table 1. In
general, analytical values for the vitrains,
clarains, and durains vary in the same way
as do those for the corresponding whole
coals. Moisture and calorific values are of
particular interest in considering variations
due to rank. As-received moisture values
for vitrain, clarain, and durain increase with
decrease in rank, as do those for the whole
coals. Moisture values for the fusains show
an exception in regular increase with de-
crease of rank of the corresponding source
coals; that for the Franklin County fusain
is higher than that of the fusain from the
lower rank Macoupin County coal. Fusain
moisture values are distinctly higher than
those for other ingredients.

Calorific values on the moist mineral-
matter-free basis, for all ingredients, de-

crease with decrease in rank of the source
whole coals. In general, calorific values on
the dry mineral-matter-free basis for vitrain,
clarain, and durain show this same trend,
although values for vitrain and clarain from
Henry County are higher than those for
the same ingredients from Macoupin
County. This is also true for the corre-
sponding whole coals. Fusain from the
Franklin County rank B coal showed the
highest calorific value on the dry mineral-
matter-free basis. With the exception of
the fusain from the Gallatin County rank
A coal, calorific values (dry mineral-matter-
free) for fusains are higher than for other
banded ingredients and whole coals. This
is in accord with the findings of Parr, Hop-
kins, and Mitchell (8) in a study of Illi-
nois fusains. However, the work reported
by these authors covered fusains from high
volatile bituminous B and C coals but not
for fusain from high volatile bituminous A.

Reactivity and Free Swelling Indices

Table 1 gives reactivity indices for the
samples studied. The T15 and T75 values
for the whole coals decrease with decrease
in rank. This same trend is exhibited also
by the banded ingredients. Reactivity in-
dices for ingredients and whole coals from
the same source are similar. Results ob-
tained by the C.R.L. test are probably more
nearly a measure of the reactivity of the
most reactive portion of mixed samples.
Sherman et al. (12) gave evidence of this.
Macroscopically picked ingredients may be
mixtures containing portions of various
other ingredients as impurities. This may
account for the similarity of the values for
samples from the same source. The fact
that ingredient reactivity indices decrease
with decrease in rank of corresponding
whole coals is further evidence of variation
of ingredients with rank.

Table 1 also gives free swelling indices
for whole coals and banded ingredients.
These values do not show progressive de-
crease with rank as do the reactivity indices.
Samples from the highest rank coal from
Gallatin County show the highest free
swelling indices. Samples from the next

BANDED INGREDIENTS OE COAL

Table 1. — Analyses of Hand-Picked Sample:

Whole coal

Moisture (as-received), %

Gallatin

Franklin

Macoupin

Henry

Ash (dry), %

Gallatin

Franklin

Macoupin

Henry

Volatile matter (dry, ash-free), %

Gallatin

Franklin

Macoupin

Henry

Fixed C (dry, ash-free), %

Gallatin

Franklin

Macoupin

Henry

Total S (dry), %

Gallatin

Franklin

Macoupin

Henry

Calorific value, B.t.u.

Moist mineral-matter-free

Gallatin

Franklin

Macoupin

Henry

Dry mineral-matter-free

Gallatin

Franklin

Macoupin

Henry

Free swelling index

Gallatin

Franklin

Macoupin

Henry

Reactivity indices, °C.
Tis (in oxygen)

Gallatin

Franklin

Macoupin

Henry

Tib (in air)

Gallatin

Franklin

Macoupin

Henry

5.1

8.0

14.0

19.3

10.0
10.3
11.9
11.0

43.1
40.6
45.0
44.0

56.9
59.4
55.0
56.0

3.19
1.69

5.23
4.77

14,098
13,377
12,022
11,486

14,989
14,701
14,349
14,694

7.0
3.0

4.5
4.5

207
182
160
164

254
229
188
186

Vitrain

4.4

9.2

15.3

17.2

8.1
4.3
3.4

7.5

42.8
34.1
43.3
41.6

57.2
65.9
56.7
58.4

2.42
1.04
3.32
4.76

14,371
13,170
11,920
11,667

15,108
14,576
14,194
14,383

6.5
4.0

3.5

210
184
160

258
245
190

Clarain

3.6

8.0

13.4

18.2

10.3
4.9
4.3

11.0

41.1
37.3
47.0
44.9

58.9
62.7
53.0
55.1

2.74
1.37
4.16
4.32

14,361
13,386
12,248
11,633

14,975
14,633
14,284
14,644

6.5
3.0

3.5
3.5

211
187
159
163

254
240
190
185

Di

6.0
16.2

11.4

'7 '.5

43.2
43^6

56'8
56 '.4

i!i6

3*85

13 ',827
12,131

14,849
14,739

To

3*.5

180

175

218
193

17.8
21.1
20.3

25.2

18.9

8.6

10.0

14.1

28.6
15.2
19.6
26.9

71.4
84.8
80.4
73.1

4.26

4.20

6.20

10.46

11,719
11,634
11,428
10,397

14,985
15,155
14,812

14,847

1 +
1.0
2.0
1 +

211
186
179
170

258
228
222
208

I 10

tl 8
O

2

BANDED INGREDIENTS OF COAL

GALLATIN COUNTY
FRANKLIN COUNTY
MACOUPIN COUNTY
HENRY COUNTY

i^

//

/

/

{.'*}

2-

,*y

30 40 50

RELATIVE HUMIDITY-

60 70

PER CENT

80

ig. 1.

Moisture characteristics of whole
coals

CALLATIN COUNTY
FRANKLIN COUNTY
MACOUPIN COUNTY
HENRY COUNTY

. — •""•

S

'?

**"

30 40 50

RELATIVE HUMIDITY

60 70

-PER CENT

Fig. 2. — Moisture characteristics of vitrains

BANDED INGREDIENTS OF COAL

u
a.

O

5

GALLATIN COUNTY
FRANKLIN COUNTY
MACOUPIN COUNTY
HENRY COUNTY

/ /

) 20 30 40 50 60 70 80

RELATIVE HUMIDITY— PER CENT

Fig. 3. — Moisture characteristics of clarains

90

100

highest rank coal from Franklin County
show the lowest. Values for the two C rank
coals appear to be similar for both whole
coals and banded ingredients. Fusain is non-
swelling, and values greater than 1 shown
in table 1 indicate the presence of small
amounts of swelling ingredients in the
hand-picked fusains.

Moisture Characteristics

Figures 1 to 5 show graphically the re-
sults obtained. Samples, ground to pass a
14-mesh sieve, were brought to equilibrium
at different humidities, and moisture con-
tents were then determined by heating in a
vacuum oven at 105° C. for 3 hours. These

a.

I 8
u
cr

H
in 6

O

FRANKLIN COUNTY
HENRY COUNTY

20 30 40 50

RELATIVE HUMIDITY-

60 70

PER CENT

Fig. 4. — Moisture characteristics of durains

10

BANDED INGREDIENTS OF COAL

20

W Q
O

5

-"-

GALLATIN COUNTY

FRANKLIN COUNTY

MACOUPIN COUNTY

HENRY COUNTY

20 30 40 50

RELATIVE HUMIDITY

60 70

PER CENT

Fig. 5. — Moisture characteristics of hand-picked
fusains

values were plotted against the correspond-
ing relative humidities. For the four sets of
samples studied, the interrelations of mois-
ture-humidity curves are similar. In gen-
eral, vitrain curves are highest, clarain and
whole coal are next, durain is somewhat
lower, and fusain is decidedly lower up to
high humidities where the curves rise steep-
ly. Comparisons of the moisture-humidity
curves for the four whole coals studied, as
well as for the corresponding handed in-
gredients, show wide differences. Curves

for vitrains, clarains, and durains have the
same general shape and occupy the same
relative positions as do curves for the dif-
ferent rank whole coals. The fusain curves
(fig. 5) do not occupy the same relative
positions.

These comparisons appear to show that
moisture characteristics indicate variations
by rank in vitrain, clarain, and durain as
in the whole coals. Indications of variation
by rank of fusains are not clear.

ui 6
Q.

I

GALLATIN COUNTY
FRANKLIN COUNTY
MACOUPIN COUNTY
HENRY COUNTY

30 40 50

RELATIVE HUMIDITY

60 70

-PER CENT

Fig. 6. — Moisture characteristics of Hsiao
fusains

BANDED INGREDIENTS OF COAL

11

Further Studies on Fusains

The question of purity of banded ingredi-
ent samples made it desirable to study the
characteristics of more carefully purified
samples. The relative inertness of fusain
to nitric acid (-/) makes possible its purifica-
tion, whereas no such means of purifica-
tion of the other ingredients is available.
Therefore further studies were made on the
fusains in an effort to learn whether dis-
tinct differences in chemical characteristics
of the hand-picked fusains were due to the
presence of various amounts of other in-
gredients or to the influence of rank varia-
tion of the source coals.

Determinations were made by the Hsiao
method (-/) on the hand-picked fusains.
Furthermore, since fusain is quite friable,
similar tests were made on the close-sized
reactivity samples (-40 +60 mesh) to de-
termine the loss of fusain in sizing between
close limits:

% Hsiao Fusain in

Hand-picked

-40+60 mesh

fusains

fusain

61.5

31.6

79.3

46.8

65.0

44.1

49.0

28.2

County

Gallatin . .
Franklin. .
Macoupin
Henry. . . .

This tabulation shows that the hand-picked
samples fall far short of being 100% fusain,
as judged by the Hsiao fusain determina-
tions. Close sizing further reduces the
fusain content of -40 +60 mesh samples.
The question then arose as to whether re-
sults obtained on samples selected according
to the Stopes classification by visual appear-
ance are to be interpreted as representative
of fusain or of mixtures in which fusain may
in some cases be the lesser constituent as
judged by chemical characteristics.

Hsiao Fusains

Since the Hsiao determinations on the
four hand-picked fusains showed the pres-
ence of considerable amounts of oxidizable
material, it was thought that residues from
nitric acid treatment might be more similar
in characteristics. Accordingly, such inert
portions were prepared from the four sam-

ples of fusain available. Five 10-12 gram
portions of each sample were refluxed in
200-240 ml. of 8 N nitric acid for 7 hours.
The inert residues were purified by remov-
ing alkali-soluble material with 1 N sodium
hydroxide, followed by repeated centrifug-
ing and final washing with dilute hydro-
chloric acid and water. The samples were
then dried by exposure to the laboratory
atmosphere (with frequent stirring) for 8
or 9 hours, and then various determinations
were made. The nitric acid inert residues
prepared as outlined are referred to here as
Hsiao fusains.

Analyses. — Table 2 presents the results
of proximate, ultimate, total sulfur, and
calorific value analyses. Samples available
were too small to permit duplicate determi-
nations in most cases. These analyses show
much closer agreement than did those for
the hand-picked fusains. However, certain
differences are apparent even in these sam-
ples. The ash for the Gallatin County sam-
ple is higher than for the others. The car-
bon value for the Henry County sample
was distinctly lower than those for the other
three. Nitrogen values are similar. Sulfur
values for three of the samples are not very
different ; that for the sample from the low
sulfur Franklin County coal is definitely
lower than for the others.

Dry ash-free volatile matter and fixed
carbon values and dry mineral-matter-free
(unit coal) calorific values for the samples
from Gallatin, Franklin, and Macoupin
counties are very similar. The sample from
Henry County shows higher volatile matter,
lower fixed carbon, and lower calorific val-
ues than the other three.

To summarize, it is evident that the vari-
ations of analytical results for the hand-
picked fusains were due, in large part, to
the presence of other more reactive materials
in the samples. Although the Hsaio fusains
show comparatively small variations in cer-
tain characteristics, these variations do not
appear to correlate with the ranks of the
corresponding coals.

Reactivity index and specific surface. —
Table 2 shows that reactivity indices for
these samples are decidedly higher than for
the corresponding hand-picked samples.

12

BANDED INGREDIENTS OF COAL

Table 2. — Analyses of Hsiao Fusains

County

Hsiao
Fusains

Hand-picked
Fusains

Ash (Dry), %

Gallatin 5.1 18.9

Franklin 2.3 8.6

Macoupin 3.8 10.0

Henry 2.4 14.1

Volatile Matter
(Dry, Ash-Free), %

Gallatin 13.6 28.6

Franklin 13.5 15.2

Macoupin 13.8 19.6

Henry 14.8 26.9

Fixed C (Dry, Ash-Free), %

Gallatin 86.4 71.4

Franklin 86.5 84.8

Macoupin 86.2 80.4

Henry 85.2 73.1

Total S (Dry), %

Gallatin 0.42 4.26

Franklin 0.21 4.20

Macoupin 0.52 6.20

Henry 0.46 10.46

B.t.u. (Dry Mineral-
Matter-Free)

Gallatin 14,103 14,985

Franklin 14,076 15,155

Macoupin 14,145 14,812

Henry 13,969 14,847

T ° C

Gallatin 285 ~' 211

Franklin 263 186

Macoupin 243 179

Henry 266 170

T,6i °C.

Gallatin 326 258

Franklin 310 228

Macoupin 319 222

Henry 313 208

Hsiao

Fusains

C (Dry, Ash-Free), %

89.64
89.56
89.13
87.62

H (Dry, Ash-Free), %

2.47

2.44
2.57
2.43

N (Dry, Ash-Free), %
0.68
0.66
0.55
0.87

O (Dry, Ash-Free), %

6.77
7.13
7.21
8.61

Sp. Surface
Sq. Cm. Gram
5490
4610
4170
5310

Earlier in this report attention was called
to the fact that reactivity indices for ingredi-
ents and whole coals from the same source
are quite similar. This is true even for the
fusains. Since fusain is considered the most
inert of the ingredients, its reactivity index
would be expected to be higher. It was sug-
gested that, since the C.R.L. method prob-
ably measures more nearly the reactivity of
the most active constituent of a mixture, the
values found were representative of the
most reactive constituent in mixed samples
and not of the particular banded ingredient
supposedly being tested. If this were true

in the case of the fusains, removal of the
more reactive material should have given
residues whose reactivity indices were defin-
itely higher. This is exactly what happened
in the Hsiao fusains.

Some differences in reactivity indices for
the four samples are apparent. T15 and T1:>
values are highest for the sample from the
highest rank coal. The T15 value is lowest
for the sample from Macoupin County, and
the T75 value lowest for the Franklin
County sample. No definite correlation
with rank is apparent.

BANDED INGREDIENTS OF COAL

13

It was thought that differences in re-
activity indices might he due to differences
in specific surface of the samples. Sherman
et al. {12) showed that increasing the spe-
cific surface results in lowering reactivity
index when studying the same coal. Accord-
ingly, specific surface determinations were
made by the Lea and Nurse method (5).
Table 2 shows that the sample from Galla-
tin County with the highest T15 and T75
values had the highest specific surface; the
sample from Macoupin County with the
lowest T15 value showed the lowest specific
surface. Although a study of the relation of
surface to reactivity should be made on the
same coal, the authors wished to determine
whether there might be such a correlation
for these samples. As the relation here is
the reverse of that to be expected, it seems
reasonable to assume that differences in
reactivity index for these samples are due
to more fundamental causes.

Moisture characteristics. — Results ob-
tained by the equilibration method are
shown graphically in figure 6. Comparison
of figures 5 and 6 indicates that moisture-
humidity curves for the Hsiao fusains are
more similar than are the curves for the
hand-picked fusains. All samples (fig. 6)
show a gradually increasing moisture con-
tent with increasing humidity, but there is
practically no indication of high moisture
take-up at high humidities such as that
exhibited by the hand-picked fusains.

At present there is no definite explanation
for this difference between the Hsiao and
hand-picked fusains. Previous data (9)
indicate that the differences in moisture
characteristics cannot be due to the presence
or absence of water-soluble salts. It seems
reasonable to suppose that possible changes
in porosity or surface characteristics, or
both, resulting from nitric acid oxidation
might account for the differences in moisture
characteristics between hand-picked and
Hsiao fusains.

In an attempt to secure further informa-
tion regarding banded ingredients of Illi-
nois coals, some work has been done with

the electron microscope. Through the co-
operation of G. L. Clark, of the University
of Illinois, electron microscope pictures at
various magnifications were made for one
set of banded ingredients and for the four
Hsiao fusains. This work appears promis-
ing but has not progressed far enough to
permit definite conclusions to be drawn.

Acknowledgment

Appreciation is expressed to F. H. Reed,
G. H. Cady, and G. R. Yohe for helpful
suggestions, to F. K. Bursack for assistance
in making chemical analyses, and to C. C.
Boley, B. C. Parks, and J. M. Schopf for
help in securing samples.

Literature Cited

(1) Am. Soc. for Testing Materials, 1943 Sup-

plement to Standards, ft. Ill, pp. 1-26,
Method D271-43.

(2) Ibid. Pt. Ill, pp. 154-7, Tentative Method

4720-43T.

(3) Fisher, C. H., Sprunk, G. C, Eisner, A.,

O'Donnell, H. J., Clarke, L., and
Storch, H. H., U. S. Bur. Mines, Tech.
Paper 642 (1942).

(4) Fuchs, W., Gauger, A. W., Hsiao, C. C,

and Wright, C. C, Pa. State College,
Mineral Indus. Expt. Sta., Bull. 23 (1938).

(5) Lea, F. M., and Nurse, R. W., J. Soc.

Chem. Ind., 58, 277 (1939).

(6) Lowry, H. H., J. Geol, 50, 357 (1942).

(7) Marshall, C. E., Fuel, 22, No. 6, 140

(1943).

(8) Parr, S. W., Hopkins, H. C, and

Mitchell, D. R., Ibid., 10, No. 4, 181
(1931).

(9) Rees, O. W., Land, G. W., and Reed, F.

H., Ind. Eng. Chem., 33, 416 (1941).

(10) Rees, O. W., Reed, F. H., and Land, G. W.,

111. State Geol. Survey, Rept. Invest. 58
(1939).

(11) Sebastian, J. J. S., and Mayers, M. A.,

Ind. Eng. Chem., 29, 1118 (1937).

(12) Sherman, R. A., Pilcher, J. M., and

Ostborg, H. N., A.S.T.M. Bull. 112, 23
(1941).

(13) Sprunk, G. C, J. Geol., 50, 411 (1942).

(14) Stansfield, Edgar, and Gilbart, K. C,

Trans. Am. Inst. Mining Met. Engrs.
101, 125-43 (1932).

(15) Stopes, M. C, Proc. Roy. Soc. (London),

B90, 470 (1919).

Illinois State Geological Survey

Report of Investigations No. 132

1948