Final Report to the Air Pollution Control Office of
the U.S. Environmental Protection Agency under Con-
tract Number CPA 22-69-65 July 15, 1971
Petrographic and Mineralogical
Characteristics of Carbonate Rocks
Related to Sulfur Dioxide Sorption
in Flue Gases
Richard D. Harvey
ILLINOIS STATE GEOLOGICAL SURVEY, Urbana, Illinois
-------
STATE OF ILLINOIS
DEPARTMENT OF
REGISTRATION AND
EDUCATION
WILLI.AM H. ROBINSON,
DIRECTOR, SPRINGFIELD
BOARD OF NATURAL
RESOURCES AND
CONSERVATION
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CHAIRMAN WILLIAM H. ROBINSON
GEOLOGY LAURENCE L. SLOSS
CHEMISTRY ADGER ADAMS
ENGINEERING FtOBEAT H. ANDIiRSON
BIOLOGY - . THOMAS PARK
FORESTRY CHARLE. IE OLMSTED
UNIVERSITY Oil' ILLINOIS
DI:AN WILLIAM L. EVRAITT
SOUTHERN ILLINOIS UNIVI£RS'TY
DEAN ROGER IE SEYLER
ILLINOIS STATE GEOLOGICAL SURVEY
NATURAL RESOURCES BUILDING, URBANA, ILLINOIS 61801
TELEPHONE 217 344-1481
JOHN C. FRYE, CHIE~
Ju1.tj 15, 1971
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ContJtaet No. CPA 22-69-65
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-------
Petrographic and Mineralogical Characteristics
of Carbonate Rocks Related to
Sulfur Dioxide Sorption in Flue Gases
Richard D. Harvey
Final report to the Air Pollution Control Office of the u.s. Environmental
Protection Agency under Contract Number CPA 22-69-65
July 15, 1977
IlliNOIS STATE GEOLOGICAL SURVEY, Urbana, Illinois
-------
CONTENTS
Abstract. . . . . . . . . . . . . . . . .
Conclusion and recommendation. . . .
. . . . .
. . . . .
. . . . .
. . . . .
Introduction
. . . . .
........
. . . . . . . . .
Petrographic studies of selected types of carbonate
rocks (phase I) . . . . . . . . . . . . . . . . . . . . . . . .
Mineral and chemical analyses . . . . . . . . . . .
Petrographic classification and source of samples. .
Mineralogy- . . . . . . . . . . . . . . . . . . . . .
Chemical analyses. . . . . . . . . . . . . . .
Petrographic characterization of carbonate rocks. . . . .
Description of type samples. . . . . . . . . .
Type 1 - Iceland spar calcite. . . . . . . . .
Type 2 - Calcite spar. . . . . . . . . . . . .
Type 3 - Coarse-grained calcitic limestone. . .
Type 4 - Fine-grained calcitic limestone. . . .
Type 5 - Reef dolomite. . . . . . . . . . . . .
Type 6 - Nonreef dolomite. . . . . . . . . . .
Type 7 - Magnesite. . . . . . . . . . . . . . .
Type 8 - Oolitic aragonite. . . . . . . .
Type 9 - Calcitic-limonitic dolomite. . . . . .
Petrographic characterization of pore structure. . .
The Quantimet and its operation. . . . . . . .
Measurements. . . . . . . . . . . . . . .
Results of pore studies with the Quantimet . . .
Petrographic grain-size distribution. . . . . . . .
Characterization of the calcined samples. . . . . .
Description of the calcined samples. . . . . . . . .
Discussion of the calcines. . . . . . . . . .
Petrographic studies of samples of certain commercial
carbonate rocks (phase II) ..................
Samples and methods . . . . . . . . . .
Petrographic characterization of samples. . . . . . . . .
Marls and chalks. . . . . . . . . . . . . . . . . . . . .
Grain and pore size distributions. . . . . . . . . . . .
Mineralogy- . . . . . . . . . . . . . . .
Chemical analyses . . . . . . . . . . . . . . . . .
Discussion of results related to sulfur dioxide
sorption tests. . . . . . . . . . . . . . . . . . . . . . . .
Petrography related to S02 sorption. . . . . . . . . . .
Grain size and pore structure related to sorption. . . .
Chemical analyses and sorption. . . . . . . .
Reaction products. . . . . . . . . . .
. . . .
. . . . .
Page
1
2
2
3
3
3
5
6
7
9
9
9
9
11
11
11
11
13
13
14
14
15
15
17
17
19
25
28
28
28
39
39
41
43
43
47
47
51
51
-------
Petrographic studies of limestone-modified fly ash and
boiler deposits. . . . . . . . . . . . . . . . . . . . .
Mineral analyses. . . . . . . . . . . . . . .
Chemical analyses. . . . . . . . . . . . . .
Grain size distribution . . . . . . . . . . . . . .
Electron microscopy of limestone-modified fly ash. . . .
Studies of boiler deposits. . . . . . . . . . . . .
Deposits collected September 1970 . . . .
Inner layer material. . . . . . . .
Outer layer material. . . . .
Deposits collected June 1970 .. . . . . . . .
Concluding remarks on boiler deposits. .
Summary and conclusions. . . . . . . . . . . . . . . . .
Petrography and reactivity. . . . . . . . . .
Fly ash and boiler depos its. . . . . . . . . . . . . . .
Acknowledgments. . . . . . . . . . . . . . . . . .
References
Glossary
Figure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
2l.
22.
23.
24.
25.
. . . .
. . . . . .
. . . . . .
. . . .
. . . . "
. . . . . .
. . . .
. . . .
. . . . .
ILL US T RA T ION S
Type 1; Iceland spar calcite. . . . . . . .
Type 2; calcite spar. . . .
Type 3; coarse-grained limestone
Type 3; coarse-grained limestone
Type 4; fine-grained limestone. . . .
Type 4; fine-grained limestone. . . .
Type 5; dolomite . . . . . . . . . . . . . . . . .
TYIJe 5; dolomite. . . . . . . . . . . . . . . . . . . .
Type 6; impure dolomite . . . . .
Type 6; impure dolomite. . . . . . . . . . . . . . . . .
Type 7; magnesite. . . . . . . . . . .
Type 7; magnesite. . . . . . . . . . . . . . . . .
Type 8; oolitic aragonite . . . . . . . . . . . . .
Type 8; oolitic aragonite . . . . . . . . . . . . .
Type 8; oolitic aragonite. . . . . . . . . . . . .
Type 9; limonitic dolomite. . . . . . . . . . . . . . .
Type 9; limonitic dolomite. . . . . . . . .
Type 9; limonitic dolomite. . . . . . . . . . . . . . .
Type 1 calcine. . . . . . . . . . . . . . .
Type 1 calcine. . . . . . . . . . . . . . . . . . . . .
Type 1 calcine. . . . . . . . . . . . . . . . . .
Type 1 calcine. . . . . . . . . . . .
Type 1 calcine. . . . . . . . . . . . . . .
Type 1 calcine. . . . . . . . . . . . . . . . . . . . .
Type 2 calcine . . . . . . . . . . . . . . . . . .
. . . .
. . . . . . .
. . . . .
. . . .
......
. . . . . .
Page
55
57
62
65
65
71
71
77
79
79
84
85
85
86
87
89
91
Page
8
8
8
8
8
8
10
10
10
10
10
10
12
12
12
12
12
12
20
20
20
20
20
20
22
-------
Figure
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
4l.
42.
43.
44.
45.
46.
47.
48.
49.
50.
5l.
52.
53.
54.
55.
56.
57.
58.
59.
60.
6l.
62.
'l'y"pe 2 calcine. . . . . . . . . . . . . . . . . .
'l'y"pe 2 calcine. . . . . . . .
'l'y"pe 2 calcine
'l'y"pe 2 calcine. . . . . . . . . . . . . . .
'l'y"pe 2 calcine. . . . . . . . . . . . . . .
'l'y"pe 3 calcine . . . . . . . . . . . . . . . . . .
'l'y"pe 3 calcine . . . . . . . . . . . .
'l'y"pe 3 calcine. . . . . . . . . . . . . . .
'1'ype 3 calcine. . . . . . . . . . . . . . . . . . . . .
'l'y"pe 4 calcine . . . . . . . . .
'l'y"pe 4 calcine. . . . . . . . . . . . . . . . . . . . .
'l'y"pe 4 calcine . . . . . . . . .
Type 4 calcine . . . . . . . . . . . . . . .
'l'y"pe 5 calcine. . . . . . . . . . . . . . . . . .
'l'y"pe 5 calcine. . . . . . . . . . . . . . . . . . . . .
'l'y"pe 5 calcine. . . . . . . . . . . . . . . . . . . . .
'l'y"pe 5 calcine. . . . . . . . . . . . . . . . . . . . .
Type 6 calcine . . . . . . . . . . . . . . .
'l'y"pe 7 calcine. . . . . . . . . . . . . . . . . .
'l'y"pe 8 calcine. . . . . . . . . . . . . . .
'l'y"pe 8 calcine. . . . . . . . . . . . . . . . . .
'l'y"pe 9 calcine. . . . . . . . . . . . . . . . . .
'l'y"pe 9 calcine. . . . . . . . . . . . . . . . . . . . .
Photomicrographs of limestone and marble (phase II)
Photomicrographs of dolomites (phase II) ........
Photomicrographs of marls and chalks (phase II) . . . . .
S02 capacity versus mean grain size. . . . . . . .
S02 capacity versus volume of pores larger than 0.9 ]l . .
S02 capacity versus volume of pores 2 to 16 ]l . . . . . .
S02 differential reactivity versus volume of pores
larger than 0.9 ]l . . . . . . . . . . . . . . . .
S02 differential reactivity versus pore projection
S02 capacity versus Na20 . . . . . . . . . . . . .
Distribution of S in S02-reacted calcines. . . . .
Exterior surface of S02-reacted calcine of dolomite
Exterior surface of S02- reacted calcine of limestone. .
Cross section of the quarry of Fredonia Valley Quarries.
X-ray diffraction patterns of limestone-modified
. . . .
. . . . . .
fly ash . . . . . . . . . . . . . . .
......
63.
64.
65.
66.
67.
68.
Particle size of limestone-modified fly ash from
planes AA and CC . . . . . . . . . . . . . . . .
Normal fly ash particles. . . . . . . . . . . . . . . .
Limestone-modified fly ash, mechanical hopper. . . . . .
Limestone-modified fly ash, mechanical hopper. . . . . .
Limestone-modified fly ash, plane AA . . . .
Limestone-modified fly ash, plane CC and
electrostatic hopper. . . . . . . . . . . . . . . . .
Reheat section of boiler and cross section of
boiler deposit. . . . . . . . . . . . . . . . . . . .
Specimens of boiler deposit. . . . . . . . . . . . . . .
Specimen of boiler deposit showing inner layer material .
69.
70.
71.
Page
22
22
22
22
22
23
23
23
23
24
24
24
24
26
26
26
26
27
27
27
27
27
27
33
35
37
48
49
49
50
50
50
52
53
54
56
59
67
68
69
70
72
73
74
76
78
-------
Figure
Table
Page
72.
Photomicrographs of boiler deposits collected
September 1970 . . . . . . . . . . . . . . . . . . . . . 81
Photomicrographs of boiler deposits collected June 1970 . 83
73.
TABLES
Page
Type Carbonate Rocks (phase I)
1-
2.
3.
4.
5.
6.
7.
Petrographic description and source of samples 4
Mineralogy of type samples. . . . . . . . . . . . . 5
Chemical analyses. . . . . . . . . . . . . . . . . . . . 6
Trace element analyses. . . . . . . . . . . . . . . . . . 7
Quantimet analyses of pore structure of phase I samples. 16
Grain size distribution. . . . . . . . . . . 18
Description of the calcines. . . . . . . . . . . . . . . 19
Commercial Carbonate Rocks (phase II)
8.
9.
10.
11.
12.
13.
14.
Petrographic description and source of samples . . . 29
Grain size analyses. . . . . . . . . . . . . . . . . . . 40
Quantimet analyses of pore structure. . . . . . . . 42
Void inclusions in dolomite grains. . . . . . . . . 43
Mineral analyses. . . . . . . . . 44
Chemical analyses. . . . . . . . . . . 45
S02 reactivities. . . . . . . . . . . . . . . . . . 46
Fly Ash and Boiler Deposits (phase III)
15.
16.
17.
18.
19.
Fly ash samples studied. . . . . . . . . . . . . . 57
Mineralogy of fly ash samples. . . . . . . . . . . 58
Chemical analyses of fly ash materials. . . . . . . 61
Chemical analyses of normal fly ashes. . . . . . . . . . 63
Chemical analyses of limestone-modified fly ash
samples from planes AA and CC . . . . . . . .
Particle size analyses of fly ash samples from
planes AA and CC . . . . . . . . . . . . . .
Chemical and mineral analyses of fire-side boiler
depos its. . . . . . . . . . . . . . . . . . . . . . . . 75
. . 64
20.
. . . 66
21.
-------
PETROGRAPHIC AND MINERALOGICAL CHARACTERISTICS
OF CARBONATE ROCKS RELATED TO
SULFUR DIOXIDE SORPTION IN FLUE GASES
Richard D. Harvey
ABSTRACT
Detailed petrographic, mineralogical, and chemical analyses of
26 carbonate rocks were made and compared with the capacity (3t hr. re-
action period) and differential reactivity (120 sec. reaction period) of
calcined specimens for sorption of sulfur dioxide (S02)' The study also
included petrographic and chemical examination of limestone-modified fly
ashes and boiler deposits obtained from the Tennessee Valley Authority1s
limestone injection tests at their Shawnee Plant, Paducah, Kentucky. Im-
age analysis and scanning electron microscope methods were employed to
examine limestones, dolomites, and a variety of other types of carbon-
ates and their calcines. A wide range of petrographic and S02 sorptive
properties were revealed.
Three petrographic and chemical properties appear to be useful
indexes of the S02 sorption capacity: the pore volume, the grain size,
and the sodium oxide content of the rocks. The larger the pore volume
(determined by image analysis of polished sections of limestones and
dolomites), the greater was the sorption capacity of the rock. Pores
with a maximum chord length between 2 and 16 ~ appear to have the most
influence on this behavior. In general, the finer the grain size of the
rock, the higher was the sorption capacity, although certain limestone
samples showed the opposite correlation owing to the positive effect of
the intracrystalline pores in the crinoidal fossil fragments abundant in
some of these samples. Of the chemical elements analyzed, only sodium
showed a correlation trend with the S02 test data. The sodium present
in the samples increased with increasing sorption capacity.
- 1 -
-------
- 2 -
Unlike
ity tests showed
properties.
the sorption capacity tests, the differential react iv-
little or no correlation with petrographic and chemical
The reaction products of the samples calcined at 9800 C for 2
hours and exposed to sulfur oxides in laboratory tests are solid grains
of anhydrite (CaS04)' Electron microscopy shows two types of behavior.
The calcines of the Iceland spar calcite absorbed sulfur on the outer
surface of its particles, whereas in calcines of a porous limestone ab-
sorption took place throughout tne particles. Sulfation occurred on the
outer surfaces of particles by multiple nucleation of anhydrite crystal-
lites, which enlarged until they abutted each other to produce a tightly
interlocking texture of subrounded grains.
Anhydrite was the only sulfur-bearing compound positively de-
tected in S02-reacted calcines and limestone-modified fly ashes. Limited
X-ray diffraction data suggest also the presence of trace amounts of
CaS03 in the coarse fraction of dust from the 6500 F position behind the
reheat section in the TVA boiler. Anhydrite crystallites in the fly
ashes are subrounded in shape and submicron to about 2 ~ in diameter.
The growth of anhydrite on surfaces of large lime particles results in
notable percentages of anhydrite in the coarse fractions of the ash. A
nonporous and interlocking grain texture similar to that of laboratory-
reacted specimens was observed on a few lime-rich particles in the ash,
although many such particles appeared to retain a porous structure.
Conclusion and Recommendation
The relatively high S02 reactivity observed for chalks, cal-
careous marls, and oolitic aragonite sand samples is believed due mainly
to the high pore volume and fine grain size of these carbonate rocks.
Geologically, high pore volume is indicated by the relatively unconsoli-
dated nature of these rock materials. It is recommended that further
studies be made of these rock types. Detailed geologic and petrographic
investigations should be made of widely distributed deposits of chalk,
calcareous marl, and calcareous shell (similar to the oolitic sand dis-
cussed in this paper). A representative number of deposits should be
examined in the field and samples taken to determine the natural varia-
bility of pore volume and grain size within the deposits. Further, re-
lations between the pore structure of the samples and that of their cal-
cined products should be examined for possible aids to prospecting for
highly reactive limestones.
INTRODUCTION
Air pollution due to emission of sulfur dioxide (802) from power
plants is a major environmental concern, especially in highly industrialized
areas. One of the current areas of research on this problem is concerned with
the limestone injection process for control of 802 that is formed during com-
bustion of fuels containing sulfur. This process, if it can be shown to be
-------
- 3 -
technically feasible. is of considerable importance because it involves the
minimum capital and operating costs of any prospective process for S02 control.
The basic procedure for this method of S02 control is injection of
pulverized carbonate rock, composed chiefly of calcite (CaC03) or dolomite
(CaMg(C03)2), into a high-temperature zone of a coal-fired boiler, where it is
converted to lime (CaO) and carbon dioxide (C02). The lime then combines with
S02 from the flue gas to form anhydrite (CaS04), which is removed as solid par-
ticles from the flue gases.
This investigation was jointly supported by the Illinois State Geolog-
ical Survey and the Air Pollution Control Office (APCO), U. S. Environmental
Protection Agency, under Contract No. CPA 22-69-65. The study was made to de-
termine the basic mineralogic and petrographic reasons for the wide variation in
S02 sorption by various types of carbonate rocks that had been observed in lab-
oratory and pilot-plant tests. Phase I of the project involved the study and
testing of a number of samples representative of a wide diversity of naturally
occurring carbonate rock types. The samples were analyzed for their mineral and
chemical components, including certain trace elements, and subjected to detailed
petrographic examinations. Correlations were observed between the grain size,
pore structure, and sodium oxide content of the samples and their capacity to
absorb S02.
In phase II, samples of commercially available crushed carbonate rocks
were examined and tested to evaluate the above-mentioned criteria developed in
phase I. Phase III involved the study of fly ash from the Tennessee Valley
Authority's full-scale limestone injection project at their Shawnee Steam Plant,
Paducah, Kentucky.
PETROGRAPHIC STUDIES OF SELECTED TYPES OF CARBONATE ROCKS (PHASE I)
Mineral and Chemical Analyses
Petrographic Classification and Source of Samples
Nine types of carbonate rocks and minerals were selected for detailed
study and testing of their capacity to react with S02. Specific petrographic.
mineralogic, and chemical analyses of several provisional samples were made so
that samples could be selected that would represent a wide diversity of naturally
occurring carbonate rocks and minerals that possibly could be used for control-
ling S02 emission. The samples selected for study included two limestones (one
coarse grained and one fine grained), two calcite spars (one Iceland spar and the
other bearing numerous crystal imperfections), an oolitic aragonite sand. three
dolomites (a reef, a nonreef. and one rich in limonite), and a magnesite. The
petrographic rock types and sources of the samples are listed in table 1. as are
the distinguishing characteristics for which the samples were selected.
-------
TABLE I--PETROGRAPHIC DESCRIPTION AND SOURCE OF SAMPLES
:-;~lt\ple
type
no.
1
2
3
4
5
6
7
3
Rock or
mineral
classification
Calcite
( Iceland
Calcite
spar
Limestone
Limestone
Dolomite
Dolomite
Magnesite
Aragonite
Dolomite
spar)
Dis tinguishing
characteristics
Nearly perfect
crystals
Abundant crystal
defects
Coarse-grained,
high purity
Fine-grained,
high purity
Reef type,
high purity
Nonreef type,
clayey and
sil ty
Fine-grained,
high purity
Oolitic and
strontium-
bearing
Limonite- and
calc i te-
bearing
Color
Clear
Milky
Gray
Gray
Gray
Buff
Milky
Light
buff to
milky
Brown &
gray
Grain
shape
Cleavage
rhombs
Cleavage
rhombs
Anhedral
Anhedral
Anhedral
Anhedral &
rhomb ic
Anhedral &
rhomb ic
Fibrous &
bladed
Anhedral &
rhomb ic
Degree of
grain
interlocking
None
None
High
High
High
Low
Low
High
Low
Other textural features
Abundant intracrystalline voids,
solid inclusions, twin lamellae;
subgrains present in some
specimens.
Inequigranular; crinoid and
bryozoan fossil fragments;
intragranular voids abundant.
Equigranular; dense; a few
veinlets occur with medium-
sized grains of clear calcite.
Recrystallized granular; porous;
abundant intragranular voids.
Equigranular; microporous; grains
adjacent to pores are rhombic.
Clay along bedding planes; iron
oxide along dolomite grain
boundaries.
Equigranular and microporous.
Elliptical and cylindrical re-
mains of marine organisms abun-
dant; very smooth exterior
surfaces; most microporous.
Equigranular and microporous;
rhombic grains along pores;
fibrous limonite (?) occurs
along dolomite grain boundaries;
abundant intragranular voids.
Source of samples
Location
Ecjungo,
Mexico
Hillside
Durango,
Geologic
formation
Kimmswick
Subgroup
Davenport
Member of
Wapsipinicon
Racine
Waukesha
Recent
mar ine
deposit
mine
dump, Rosiclare,
Ill.
Columbia Quarry
Co. mine, Val-
meyer, Ill.
Allied Stone Co.
Quarry, Milan,
Ill.
Midway Stone
Quarry, Osborne,
Ill.
Abandoned quarry
near Bourbon-
nais, Ill.
Red Mountain
Dist., Santa
Clara Co., Cal.
North Cat Cay,
Bahama Islands
Jeffrey Limestone
Co. Quarry)
Parma, Mich.
-------
- 5 -
TABLE 2-MINERALOGY OF TYPE SAMPLES IN WEIGHT PERCENTAGE
Major
SaJIlple component (%)
Type 1 100 calcite
Type 2 100 calcite
Type 3 91 calcite
Type 4 98 calcite
Type 5. 99 dolomite
Minor and trace
components
Insoluble
residue (%)
None detected
0.0
Traces of soluble
salts of Cl and S03
0.1
8% dolomite and < 1%
limonite
0.2
< 2% quartz
0.9
< 1% calcite; approxi-
mately 0.3 mole %
FeC03 is present in
the dolomite
0.1
Type 6
81 dolomite
9% quartz; 4% calcite;
5% clay; apprQximately
0.8 mole % FeC03 is
present in the dolomite
14.4
Type 7
99 magnesite
< 0.5% quartz and clay;
approximately 0.26 mole
% FeC03 and 4.51 mole %
CaC03 are present in the
magnesite
0.1
Type '8
96+ aragonite
Approximately 3%, Mg-calcite
and < 1% clay;. approximately
1.38 mole % SrC03 is present
in the aragonite
0.4
Type 9
70 dolomite
18% calcite; 4% quartz;
< 2% clay; 5% limonite
4.2
Mineralogy
The samples were subjected to X-ray analysis with a diffractometer
equipped with a recording potentiometer output, to acid treatment, and to study
under an optical microscope for quantitative identification of their mineralogy.
The results are listed in table 2. The mole fractions of the various carbonates
present in some of the samples were calculated from chemical analyses. X-ray.
data verified the. presence of magnesium carbonate in solid solution in calcite
impurities in the oolitic aragonite (sample type 8).
-------
- 6 -
TABLE 3-CHEMICAL ANALYSES IN WEIGHT PERCENTAGE
(Analyses by Analytical Chemistry Section of the Illinois State Geological Survey)
Oxides
1
2
3
Sample type number
4
5
6
7
8
9
Si02
Ti02
A1203
Fe203
FeO
MnO
MgO
CaO
Na20
K20
P205
C02
S03
SrO
Cl
Ign. loss
NDa
ND
ND
ND
0.13
ND
ND
55.3
0.003
0.02
traceb
43 . 95
0.01
0.014
ND
43.49
ND
ND
0.01
0.19c
0.06
ND
55.5
0.015
0.02
43.35
0.17
0.002
0.04
43.15
ND
ND
ND
0.20c
0.10
1.86
53.4
0.015
0.02
43.75
0.20
0.009
0.03
43.67
1.53
ND
0.01
0.31 c
0.09
ND
54.8
.0.047
0.04
43.35
0.15
0.019
ND
43.15
0.03
ND
0.02
0.34c
0.02
21.40
30.30
0.008
0.03
47.30
0.13
0.019
0.09
47.24
H.8
0.02
1. 77
0.13
0.41
0.02
17.4
26.5
0.040
0.90
0.02
40.27
0.03
0.04
trace
0.47
ND
0.08
ND
0.07
ND
44.2
2.93
0.026
0.03
trace
50.96
0.01
0.01
40.46d 51.56e
ND
0.19
ND
0.27
ND
0.01
ND
ND
55.2
0.53
0.03
0.01
42.10
0.37
0.10
0.24
43.33
5.88
0.15
0.69
2.82
1. 75
0.21
15.33
30.82
0.16
0.22
0.10
40.68
0.42
0.04
ND
41. 85
a ND - not detected: Limits of detection for Si02' 0.03; Ti02 and MnO, 0.01; A1203' 0.05; Fe203' 0.01;
MgO, 0.10; Cl, 0.02.
b Trace of P205' approximately 0.005%.
c Percentage of total iron expressed as Fe203.
d Includes 0.3% H20+.
e Includes 0.61% H20+.
Chemical Analyses
The results of chemical analyses of the major and minor elements pres-
ent in the samples are listed in table 3. Flame photometry was used to determine
the K20 and some of the SrO results; gravimetric methods were used to determine
the FeO, C02, P20S, and S03 results; and neutron activation methods were used to
determine the Cl, Na20, and the remaining SrO results. All other oxides were
determined by X-ray fluorescence. Neutron activation methods were used to de-
tect the trace element content of the samples. The results are shown in table 4.
-------
- 7 -
TABLE 4-TRACE ELEMENT ANALYSES OF CARBONATE
ROCKS DETERMINED BY NEUTRON ACTIVATION METHODS
(Analyses by Dr. R. R. Ruch of the Analytical Chemistry Section
of the Illinois State Geological Survey)
Element (ppm)
Sample
type Cu Br La Sc Eu As Ga Cr Hg
1 15 < 2 < 0.3 0.03 < 0.03 2 < 1 < 2 0.06
2 44 < 2 3.3 0.35 5.2 < 2 < 7 <11 0.06
3 5.7 < 3 1.6 0.16 < 0.07 2 < 2 < 5 0.06
4 < 3 17 < 1 0.10 < 0.2 a < 6 < 2 0.04
5 11 < 1 1.2 0.23 < 0.05 < 0.8 < 2 <4 o. 03
6 ~ 25 ~5 9.6 1.4 < 0.3 < 4 < 6 35 0.07
'1 <8 < 0.9 < 0.2 0.06 < 0.1 < 0.7 < 3 127 0.03
8 b 17 < 1 0.05 b a b < 12 0.02
9 25 < 1 3.4 1.0 < 0.7 < 2 < 14 < 31 0.23
a Not determined, excessive interference from Br.
b Not determined, excessive interference from Na.
Petrographic Characterization of Carbonate Rocks
The petrographic studies were focused primarily on the textural rela-
tions between the grains. the grain shape and size distribution, and the pore
structure of the samples. Many of the geologic terms used in this paper are
defined in a glossary at the end of the report. The petrographic descriptions
that follow are based on studies made with a scanning electron microscope and a
Quantimet, an image-analyzing computer with a polarizing microscope. The scan-
ning electron microscope (SEM) permits direct examination of the surface of a
solid specimen about 1 x 1 x ~ em at magnifications from 20 to over 20,000 times.
Two to four specimens of each sample were selected as representative.
and polished and etched surfaces were prepared for petrographic analyses. Frac-
tured surfaces also were examined to determine the nature of the surface exposed
to the S02' The specimens were studied at both low and high magnifications to
determine their most typical and representative textural features. From a total
of 158 scanning electron micrographs of the specimens, two or three of each type
were selected that showed the most typical textural characteristic, and these
pictures are reproduced in figures 1 through 18.
-------
- 8 -
TYPICAL SURFACE TEXTURES, TYPES 1 THROUGH 4
Fig. 1. Type 1; Iceland spar calcite; cleaved
and etched.
Pig. 3. Type 3; coarse-gpained limestone;
polished and etohed.
Fig. 5.
'l'ype 1t;
fine-grained limestone; polished
and e tch(;.~d "
Fig. 2.
Type 2; caloite (spar); cleaved and
etched.
Fig. 4. Type 3; coarse-grained limestone;
extension fracture.
Fig. 6. 'Type 4; fine-grained lImestone;
sian :rracture.
exten-
-------
- 9 -
Interpretation of the electron micrographs is direct; that is, knolls
on the specimen appear as knolls on the photographs. Edges of grains are high-
lighted in such a way that they appear as though the "lighting" is directed at
a high angle from the top of the photographs. Intragranular voids and cleavage
steps, thought to be sites of high chemical activity during calcination, were
noted. The descriptions of the samples that follow are summarized in table 1.
Description of Type Samples
Type 1 - Iceland Spar Calcite
The Iceland spar sample consists of clear, transparent cleavage rhombs
as much as 1 inch across (very coarse-grained). Few cleavage steps occur on the
surfaces of the rhombs (fig. 1), which the electron microscope revealed as es-
sentially free of crystal imperfections or dislocations. Fresh cleavage surfaces.
lightly etched in 0.02 N RCI for 5 seconds and thoroughly rinsed, up to magnifi-
cations of X5000. show no intracrystalline voids or dislocation etch pits. Sev-
eral polygonal and flat-bottomed pits vaguely detected in figure 1 are interpreted
as the result of random dissolution of a perfect crystal rather than as sites of
dislocations.
Type 2 - Calcite Spar
The calcite spar sample consists of colorless or milky white. trans-
lucent, and irregular cleavage rhombs as much as 1 inch across. Some of the
specimens contain numerous twin lamellae and several subgrains, each of which
has a crystal orientation slightly different from those of neighboring subgrains.
The sample is characterized by the abundance of intracrystalline voids and cleav-
age steps (fig. 2). Many solid inclusions also are present, such as the one at
the top of figure 2. These crystal inclusions are possibly Ca and Na precipi-
tated as chlorides and sulfates that were previously trapped in the calcite crys-
tal as fluids under high temperatures. The chemical composition of the inclu-
sions cannot be determined with the scanning electron microscope, although they
probably contain the trace amounts of Na. Cl. and S present in the sample (table
3). The nature of the cleavage surfaces of certain crystal inclusions suggests
they may be calcite.
Type 3 - Coarse-Grained Calcitic Limestone
The coarse-grained calcitic limestone is gray with a few dark gray,
very thin seams of carbonaceous stylolites. It consists of fragments of crinoid
and bryozoan fossils with minor amounts of fine-grained calcite and a few rhombic
grains of dolomite scattered between them. The crinoids are very coarsely crys-
talline broken plates and stems (frequently single crystalline grains). The
bryozoans are finely crystalline and polygranular particles that have a matted
and/or net structure. The limestone has an inequigranular texture characterized
by tightly interlocking anhedral grains of calcite. The grains vary in size
from approximately 2 ].l to over 5,000].l. The grain boundaries are predominantly
curvilinear (fig. 3). The crinoid grains contain numerous intragranular voids
(fig. 4). Fractured surfaces, especially on the large grains. show numerous
cleavage steps. as shown in the linear features in figure 4. Fracture surfaces
of the fine-grained particles. which form a minor fraction of the sample, are
-------
- 10 ":"
TYPICAL SURFACE TEXTURES, TYPES 5 THROUGH 7
Fig. 7.
Type 5; dolomite; polished and etched.
Fig. .9. Type 6: impure dolomite: polished and
etched.
Fig. 11.
Type 7; magnesite; polished and etched.
Fig. 8.
Type 5;
dolomite; extension fracture.
Fig. 10.
Type 6; impure dolomite; extension
fracture.
Fig. 12.
Type 7: magnesite; extension fracture.
-------
- 11 -
generally free of cleavage steps and appear to have propagated along grain
boundaries. The sample is typical of the Kimmswick Limestone Subgroup in south-
western Illinois.
Type 4 - Fine-Grained Calcitic Limestone
The fine-grained calcitic limestone is uniformly gray and equigranular.
A few small veinlets of clear, sparry calcite occur in some specimens. Studies
indicate the anhedral grains are tightly interlocked, and grain boundaries are
distinctly curvilinear (fig. 5). The fractured surfaces show the equigranular
nature of the sample, abundant sharp edges on the broken grains, cleavage steps
on a few grains, and highly irregular surfaces with abundant tiny nooks and
crevices (fig. 6). The mode of the fracture is transgranular. The sample is
typical of the Davenport Member of the Wapsipinicon Limestone Formation in the
vicinity of Davenport, Iowa.
Type 5 - Reef Dolomite
The sample of reef dolomite was obtained from the core area of a large
recrystallized reef. It is gray, hard, and porous, has abundant fossil fragments,
and is of high purity. The grains are generally medium in size. The shape of
the grains is anhedral and highly irregular, as shown by the grain boundary in-
dicated by the arrow in figure 7. As a rule, the grains have curvilinear bound-
aries and are tightly interlocking. Intragranular voids are abundant throughout
the sample (figs. 7 and 8). The light-colored grain on the left in figure 7 is
harder and less soluble in acid than the surrounding dolomite, and it is proba-
bly chert. Fracture surfaces show transgranular mode (fig. 8), except when the
fracture passes through a pore space. The sample is typical of the reef dolomite
in the Racine Formation in northern Illinois.
Type 6 - Nonreef Dolomite
The nonreef dolomite is uniformly buff and is fine grained, equigranu-
lar, and microporous. It is clayey and silty. Polished and etched surfaces of
the sample show small pore spaces adjacent to nearly every grain. The grains
are frequently rhombic along the pore surfaces and anhedral elsewhere (fig. 9).
A high percentage of grains contain intragranular voids.
Clay particles are concentrated along bedding planes and can be seen
on a few surfaces broken normal to the bedding, as shown by the tiny, light-
colored flakes near the edge of the rhombic dolomite grain in the center of
figure 10. X-ray data indicate the clay mineral is predominantly illite. Iron
oxide occurs along boundaries of the dolomite grains. The fracture surfaces of
the rock are highly irregular and show more particles of less than 5 ~ than are
seen on polished surfaces of the sample, suggesting that the fracture tends to
follow the boundaries of the smaller particles. The sample is typical of much
of the Waukesha Formation of northeastern Illinois.
Type 7 - Magnesite
The magnesite sample is of high purity and is colorless or milky and
has a very fine-grained and microporous texture (figs. 11 and 12). The grain
size of the sample is uniform, ranging from 1 to 10 ~, and the grains are both
-------
- 12 -
TYPICAL SURFACE TEXTURES, TYPES 8 THROUGH 9
Fig. 13. Type 8;
two oolites.
oolitic aI'agonite; surfaces of
Fig. 15. Type 8; 001 i tic aragonite; polished
and etched.
Fig. 17. Type 9; limonitic dolomite; polished
and etched.
Fig. 14. T~~e 8; oolitic aragonite; polished
and etched.
Fl,g. 16. 1'ype 9; limonitic dolomite; extension
l'racture.
Fig. 18. Type 9; limonitic dolomite; polished
and etched,
-------
- 13 -
anhedral and rhombic. The polished surfaces show pore spaces around parts of
nearly every grain. A few small areas in the sample have unusually large pores
that contain traces of brown iron oxide stains and magnesite grains up to 40 ~.
The fractured surfaces of the magnesite (fig. 12) show that a very high percen-
tage of the grains have a distinct rhombic shape.
Type 8 - Oolitic Aragonite
The aragonite sample is an oolitic sand composed of light buff to
milky elliptical oolites and remains of marine organisms. many of which are cy-
lindrical. The oolites and other particles have a median size of 400 ~ and are
predominantly aragonite. The exterior surfaces of the oolites and fossils are
very smooth. Many of the oolites contain pore spaces just underneath the outer-
most layer of aragonite. as is shown by the oolite on the left in figure 13.
Some of these porous areas are now exposed because of attrition between the
particles.
The oolites consist mainly of fibrous aragonite. as shown in figure 14.
Aragonite (orthorhombic structure) is an unstable form of CaC03 and it inverts
to calcite (rhombohedral structure) with time and heat. The strontium present
in the s~ple (0.10%) is thought to occur by substitution for calcium in the
aragonite structure. The fibers are approximately 0.1 ~ in diameter, range from
approximately 0.5 to 2 ~ long, and show a slight tendency for preferred orienta-
tion in the southwest to northeast direction (fig. 14). This orientation is about
45 degrees from the direction of the radius vector of the oolite. The fibrous
habit of the aragonite is the most common form of aragonite in nature.
Very small gray patches that contain a bladed form of aragonite (fig.
15) occur on the surface of the oolite. as can be seen on the right side of fig-
ure 13. They possibly also contain the minor amounts of magnesium-calcite grains
detected in the sample by X-ray diffraction. In some cases, the aragonite blades
show preferred orientation normal to the outer boundary surface of the gray areas.
The size of the bladed aragonite particles averages about 2~ ~ long and one-half
~ wide.
Type 9 - Calcitic-Limonitic Dolomite
Sample 9 consists of limonite-coated gray and brown
dolomite. The texture of the dolomite is fine, equigranular,
(figs. 16 and 17). As is true of type 6. the dolomite grains
the pores have rhombic crystal surfaces; others are anhedral.
numerous intragranular voids in the dolomite grains.
particles of crushed
and microporous
that occur next to
Some specimens show
Certain brown weathered particles (as distinguished from the buff-gray
unweathered particles) contain equigranular dolomite grains rimmed along the pores
by platy minerals (light colored in fig. 17). Close examination reveals that the
structure of this material is fibrous (fig. 18). Chemical and mineralogical anal-
yses suggest that these fibrous bands are limonite and/or clay. The clay that
is present in the sample is mainly illite, with lesser amounts of kaolinite.
Observations of thin sections with the petrographic microscope indicate both
limonite and clay occur along the carbonate grain boundaries. The effect of the
fibrous layer on the S02 reaction of the calcine of the dolomite is not known.
-------
- 14 -
If the layer is clay, it may have an adverse effect; if it is lim~nite, such
a close association with the carbonates should enhance the catalyt~c effect of
the iron oxide on the reaction with S02'
Calcite occurs in patches within the dolomite and consists of tightly
interlocking anhedral grains with curvilinear grain boundaries.
Petrographic Characterization of Pore Structure
The pore volume and pore-size distribution are fundamental properties
of carbonate rocks and are basic to the physical and chemical behavior of rock
materials. The porosity and pore-size distribution can be measured on cross-
section surfaces on the basis of the principle that the volume fraction and the
area fraction of a phase occupied on a random cross-section surface are equal
(Sorby, 1856). This principle has been verified in a number of studies, includ-
ing those of Rosiwal (1898), Thomason (1930), and Chayes (1956).
The Quantimet and Its Operation
The instrument used in this work is an image analyzing computer, called
a Model B Quantimet by the manufacturer.* It was described in detail by Fisher
and Nazareth (1968). The instrument has several components--a polarizing micro-
scope, a television camera and monitor, a detector, a computer, and an output
meter. The microscope accommodates vertically reflected illumination, as well
as transmitted polarized and ordinary light. A large specimen holder and assoc-
iated illumination system (epidiascope) can be substituted for the microscope
for analyzing photographs.
An image of the specimen is produced on the vidicon tube of the tele-
vision camera through the microscope or epidiascope. This electronic image is
scanned by a detector that responds to changes in voltage as the scanner passes
over contrasting features. A discriminator (threshold control) sets the lower
level of the voltage detected. Signals thus accumulated in the detector are fed
to the computer, which counts and makes area summations. The output from the
detector is fed into the television monitor for visual check by the operator
that the desired features are being detected. Quantitative data are read out
of the computer by means of a multiscale meter.
Briefly, three basic measurements, or modes, may be made: area, pro-
jection, and count. An additional mechanism is provided that permits the deter-
mination of the cumulative sizing of the projection and count measurements.
Basic to the operation is the detection of the desired features, such as pores.
Relatively good and uniform contrast must exist between the features to be meas-
ured and the other components in the specimen image. The image of the specimen
and a rectangular area, called the blank frame, over which features are detected
and measured, are displayed on the monitor. The highest intensity areas of the
image are detected first by use of the threshold control. As the control is in-
creased, more and more of the image is detected. The specific areas detected
are clearly indicated on the monitor by extra-high intensity flooding. Adjust-
ments of the level of flooding are made with the threshold control until the
flooded (detected) areas and the features to be measured exactly match on the
* Metals Research Limited, Melbourn, England.
-------
- 15 -
television monitor. The polarity of the detection can be reversed. i.e., the
lowest intensity areas, or black areas, are detected first and progressively
higher intensity areas are detected by increasing the threshold control setting.
Measurements
With the mode selector switch in the area position. the area of the
detected features within the entire image in the blank frame is read from the
meter as a fraction of the total blank frame area. When the projection is
measured, the edges or boundaries of the detected features are indicated on the
monitor by white dots at the intercepts of each television scan line and the
features. The meter gives the projected length in terms proportional to the
height of the blank frame. With the minimum chord control set at zero. the
total projection. Pt, of the image features is
Pt = P HIM
where P is the meter reading, H the blank frame height, and M the image magni-
fication. The units of the total projection value are those that are used to
measure the height of the blank frame on the television screen.
The size distribution of the projected chord intercept lengths of the
features detected is obtained from meter readings with the minimum chord con-
trol set at various minimum chord values. As the setting of the minimum chord
control is increased to various positive values, progressively longer intercept
chords of the features are disregarded by the detector. In this way the cumu-
lative frequency of the chords greater than selected chord lengths is determined.
The number of features in the image of the specimen is obtained by the
count mode. The total number of features detected is indicated on the meter when
the minimum chord control is set on zero. As the setting is increased, the num-
ber of features detected (counted) decreases, depending on the size distribution.
The cumulative size distribution of features is found by noting the count on the
meter at increasing settings of the minimum chord control.
Results of Pore Studies with the Quantimet
Quantimet (QTM) measurements of the pore structure of the type samples
were made on specimens polished with 0.05 ~ alumina on an open, silk-covered lap.
The surfaces were coated with a film of chromium 200 to 400 Angstroms thick under
high vacuum. Examined under vertical illumination, the surfaces show good con-
trast between the highly reflective solid areas and the nonreflective areas. or
pores.
One to three carefully selected specimens considered to be represen-
tative of each sample were analyzed within 30 to 90 different rectangular areas.
The area analyzed in each field of view by the Quantimet with the 20-mm objective
lens used in this analysis is 0.195 by 0.136 mm. The lens provided a specimen-
to-monitor magnification of X1300 and a resolution of approximately 0.9~. The
volume of pores larger than 0.9 ~ (QTM pore volume), the pore boundary projection
lengths, and the pore volume distribution are listed in table 5 for all type sam-
ples except magnesite (type 7). The values listed in table 5 are averages of the
output obtained from 30 or more areas (fields of view) chosen at random on each
-------
TABLE 5--QUANTIMET ANALYSES OF PORE STRUCTURE OF PHASE I SAMPLES*
Pore volume distributiont
Mean Pore (nun3/gram) Predominant
Sample pore volume projection occurrence of
type (nun3/g) (nun) 0.9-2 2-2.8 2.8-3.9 3.9-5.5 5.5-7.8 7.8-11 11-16 16-22 22-32 (11) poresT
1 1.4 0.03 0.7 0.1 0.1 0.2 0.1 0.0 0.1 0.0 0.0 Within crystals
\
2 8 0.18 4.1 1.6 0.6 0.6 0.4 0.3 0.1 0.0 0.0 Within crystals
3 30 0.38 13.7 4.7 2.8 2.5 2.1 1.4 1.2 0.8 0.5 Within and be- I-'
tween grains 0\
4 13 0.45 8.2 3.2 1.0 0.4 0.2 0.0 0.0 0.0 0.0 Between grains
5 24 0.72 13.5 5.3 2.4 1.6 0.7 0.3 0.1 0.1 0.1 Within and be-
tween grains
6 54 0.99 21. 6 9.4 6.0 7.0 4.4 2.8 1.7 0.7 0.1 Between grains
8 18 0.22 6.2 3.0 1.7 2.2 1.8 0.9 0.9 0.7 0.2 Between grains
9 63 0.79 18.8 8.1 5.9 8.5 7.5 5.4 4.5 2.8 1.3 Between grains
* Image analyses of pores larger than 0.9 11 (Quantimet magnification 1300X) exclusive of type 7.
t The intervals, in microns, corresponds to a constant interval of 1/2 phi units.
T Determined by scanning electron microscopy.
-------
- 17 -
sample. The predominant occurrence (within or between the grains) of pores also
is indicated in table 5.
Petrographic Grain-Size Distribution
The grain sizes of the type samples were individually determined in
thin sections with only the polarized light microscope on the Quantimet. Spec-
imen preparation methods attempted to date have failed to produce sufficient con-
trast between the grains and the grain boundaries to enable the automatic sizing
feature of the Quantimet to be used. One to four thin sections of each of the
type samples were examined, and 300 to 700 grains. were measured in each sample.
Standard point-counting methods were used to select the grains for measurement.
The measurements were grouped into eight to ten logarithmic size intervals (phi
units. where phi = -10g2D and D is the apparent diameter in millimeters). Math-
ematical analyses of the observed size frequency were made, with minor modifica-
tions, according to the method presented by Rose (1968). This analysis makes a
statistical correction on the bias that occurs in the observed frequency data.
The bias results from two factors - large grains have a greater chance
of being counted than do small grains; and grain diameters observed in cross sec-
tion rarely are as large as the true diameter of the grain. The analysis assumes
the grains are spherical, which is a reasonable first approximation of the shape
of calcite and dolomite grains. Cumulative curves and histograms of the cor-
rected data were drawn. The graphic mean size, equal to one third of the sum
of the 16th, 50th, and 84th cumulative percentiles of the distribution (Folk and
Ward, 1957), were computed. The arithmetic mean of the distribution (Krumbein
and Pettijohn, 1938) also was computed for the samples. The percentiles were
computed by linear interpolation between the cumulative data points. The dis-
tribution and means of the samples are shown in table 6.
Characterization of the Calcined Samples
As part of the petrographic characterization of the carbonate rocks.
a study was made of the calcined products of the samples. These observations are
pertinent to the over-all project because these products are the main material
that reacts with S02 in the test.
Approximately 180 grams of rock sample was calcined while being rotated
in a laboratory furnace, at a preset temperature. for 2 hours by personnel in
the Process Research Section of APCO. The temperature of calcination for all
samples was 18000 F, except for a few specific test runs on the samples of cal-
cite (types 1 and 2). Each calcine was subdivided into three size grades for
tests and microscope studies: 12 by 16, 42 by 65, and 150 by 170 Tyler mesh
grades. A portion of each sample was placed in a glass vial immediately after
its removal from the furnace, was sealed with an air-tight cap and melted paraf-
fin to prevent absorption of moisture. and was shipped to the Illinois Geological
Survey for microscope study. The samples were stored in a dessicator until just
prior to examination.
Because the grain size of the calcined samples is mainly in the range
of 0.1 to 10 microns, a scanning electron microscope was used for the study. In
-------
TABLE 6-GRAIN SIZE DISTRIBUTION
Frequency of grains (%)
(Number of grains X midpoint of interval)
Size interval
(~) Sample: Type 3 Type 4 Type 5 Type 6 Type 7 Type 8 Type 9
1000-4000 5.8 0 3.2 0 0 0 0
500-1000 26.7 0.3 5.7 0 0 0 0
250-500 19.4 2.0 6.7 0 0 0 2.3
125-250 9.2 0.9 32.4 0 0 0.4 0.5
63-125 9.8 1.2 13.8 11. 9 0 1.7 2.2
32-63 4.8 0.2 30.0 7.4 0 2.4 6.7
16- 32 6.6 49.6 0.6 I-'
0.7 7.5 4.5 44.7 CX>
8-16 29.6 I
9.2 11. 9 0.5 21.2 13.2 4.2
4-8 7.1 46.1 0.3 9.5 44.2 3.3 1l.4
1-4 1.3 36.7 0.1 0.4 42.0 83.5 2.6
Mean (arith.*) ~ 31.6 4.2 69.0 16.7 4.0 2.8 13.1
Mean (graphict) ~ 138.0 4.1 101.0 20.0 4.0 2.3 16.0
Graphic standard
deviation* (log
units) 2.6 1.2 1.4 1.2 1.1 1.2 1.0
* Krumbein and Pettijohn (1938, p. 240).
t Folk and Ward, 1957.
-------
- 19 -
addition~ each sample was subjected to X-ray diffraction analysis to determine
the mineral phases present. Each was also examined with the Quantimet under
polarized light while immersed in oils of various indices of refraction. The
descriptions of the calcined samples that follow are briefly summarized in
table 7.
Description of the Calcined Samples
Type 1 ~ calcined at 1700° F ~ was found by X-ray and opti cal analyses
to be entirely lime (CaO). The lime retains the rhombic shape and size of the
original I-mm Iceland spar calcite rhombs. At high magnification. the exterior
and broken surfaces of the rhombs are covered with angular granules. or sub-
grains~ averaging about 0.25 ~ in diameter (figs. 19 and 20). The subgrains
are closely packed. and little or no porosity is observed in SEM photographs.
TABLE 7-DESCRIPTION OF THE CALCINES
Sample Temperature Minerals Particle size t Relative
type (oF) present ( IL ) Texture poros ity
*
1 1700 Lime 0.1 to 0.5 Granular Very low
1800 Lime 1 to 2 Rounded Moderate
2 1700 Lime and 2 to 4 Partly spongy Low to moderate
minor calcite
1800 Lime 2 to 5 Spongy Low
1900 Lime 2 to 10 Blocky Low
3 1800 Lime, minor 1 to 2 Spongy, partly Moderate to
periclase rounded high
4 1800 Lime 0.5 to 1 Granular, partly Low to moderate
spongy
5 1800 Lime and 0.2 to 1 Granular- Moderate
periclase agglomeratic
6 1800 Lime. peri- 0.2 to 1 Granular- High
clase, and agglomeratic
quartz
7 1800 Periclase 0.1 to 0.5 Granular Very low
8 1800 Lime 2 to 10 Spongy, partly Low to moderate
blocky
9 1800 Lime and 0.5 to 2 Granular- Moderate
periclase agglomeratic
t Determined from scanning electron micrographs.
* These particles are subgrains of 1 mm grains that
other samples are isotropic limes.
are anisotropic and laminated.
All
-------
- 20 -
LIMES FROM ICELAND SPAR CALCITE,
Fig. 19. Type 1 calcine; 1'700°
par.ticles; angular grains of
XJ.O. 000.
F, 42/65-mesh
lime; SEN,
Fig. 21. T;ype 1 c.alcine; 1700c F, crushed 12/16
mesh; each l:iJnc parti,c.le has a po}ygranular
surfaoe, as in fig. 19; in transmitted light,
Xlc:l{. .
Fig. 23. Type 1 calcine; 1800° F, 10/28 mesh;
rounded granu.les of 1.ime; SE~1. X2240..
TYPE 1,
CALCINED AT 1700 AND 1800° F
;.,J,t 'WI
':'-i'~:1
Fig. 20. Type 1 calcine; 1700° F, 150/170-
mcsh particles; angular grains of l:iJne; SEM,
X15 ,000.
Fig. 22~ Same as fig. 21; laminated structure
probably due to internal strain; in crossed
polarized transmitted light, X575.
" T,';' ."~'.1it),, . '. .':.;-.. ,;,., ,)I':~!';!i~
A'~ ;..~~..7~~~~ ;);~t:'.(~ ". " ~.:1~ ~~~~;',?1 ,t,j
, n< ,;'"""z) '-"}'A ~ ~."""'~4' ~ ii,<, ~ ~~
,.'t(~~; ;t '~'r';«.,' ':--::.:: ".~~?~.i:\;;'~l:)
,,;,,:: ..e~, ,f ~~:. ~;~;~ ;.,,0. ~~~'~iij
:~~~'.;..., ~'l':...~ :~;!" +.~" >. ~cl':';~.k.~~
. ? fr ~h."1; .~ '..' . ,". .." ff ,,>' 1'j", ->.;:;'"
's,. ,~" t. .., ,w ",,, . ~,'
" 't'~I'.3>~ . ~, ".,,: ''',j~:;£'b4
":~.",f~.:',::~~~~~~~,~), ~.~;,~~,~,~f;,.~
;. ,..;"':",~ ,"~f-i" .~, »,':'5,,',;> "P "'..'!.. ..
~, .t:..~.,~':f~,'~;~Y'~~,~:;::,,'~,'~>',"':;1':'!"~' ~,:>,;'( ~.'i;= ..? 2 OJL
" .~:.t"~,~>J1~,~:f;.~."~:, :;J:,:_!~l~'::i~~'~"!~~ c;J L-:......J
,: '~-)!;~~:.'~' 0 . "
;,:~ '~~'.)~~ ~~: ~~'~' i::~
~t~~1 ,1;1~..i '~ f,::.
;"~"., , .c."
~..!:.~. .. ,."..
I<'ig. 24. Same
granules of
X550.
as fig. 23; partly dispersed
l:iJno; in transmitted light,
-------
- 21 -
In reflected light the particles are colorless, but in transmitted
light most are brown to tan (fig. 21). Nearly all grains are distinctly aniso-
tropic and are revealed in crossed polarized light to be laminated (fig. 22),
which results in an anomalous wavy exinction as the grains are rotated. Aniso-
tropism is not a normal characteristic of lime. All other samples of calcines
described below are more than 95 percent isotropic particles of lime and peri-
clase (MgO). Also, the 1700° calcine of type 1 is the hardest to crush in a
mortar and pestle of all the samples studied.
Type 1 calcined at 1800° F consists of isotropic and rounded grains
of lime (figs. 23 and 24). The grains average about 1 ~ in size. The 18000 F
calcine is essentially the same color as the 17000 F material. but it is not as
hard.
Calcination of type 2 at 17000 F yields lime and approximately 5 per-
cent unburned calcite. The material is slightly porous and granular in texture
as observed with the SEM (fig. 25); it breaks up easily into angular particles
about 2 to 4 ~ in diameter (fig. 26). Samples calcined at 18000 F are typified
by their spongy texture (fig. 27) and show a three-dimensional configuration of
lime particles that are very irregular in shape. The calcine has a complex
maze of void spaces throughout. Patches of blocky lime of low porosity and con-
sisting of interlocking grains also occur in the sample (fig. 28). Samples cal-
cined at a still higher temperature, 1900° F, have more areas of blocky, inter-
locking texture (fig. 29). In figure 29 the presence of joints or cracks in
certain raised material that occurs mainly along edges of several lime grains
can be seen. This material is thought to be portlandite (Ca(OH)2) formed by
reaction of the calcine with moisture sometime after its removal from the fur-
nace. The joints were probably formed by desiccation during high-vacuum pro-
cessing of the specimen for SEM study. Incipient cubic (010) crystal surfaces
on a few lime grains are indicated by arrows in figure 29. The 20400 F calcine
(fig. 30) appears to have a dense interlocking texture of equant grains of lime,
although much of the surface is coated with jointed material, probably port-
landite.
Type 3 calcines (1800° F) are mainly spongy textured lime (figs. 31
to 34). Figure 31 is a typical view of the sample at low magnification. Many
areas of the specimens are highly porous and have elongated lime particles
(fig. 32), while in other areas the particles are rounded and granular (fig.
33). Figure 34 shows the lime and periclase (MgO) that were derived from a
single dolomite rhomb. The obtuse angle of the rhomb is shown in the upper part
of the figure. The larger highlighted particles in the lower left and upper
part of the figure are dust particles.
Type 4 calcines are illustrated in figures 35 to 38. The stone is a
high-purity limestone composed of equant calcite grains that average about 4 ~
in diameter. The texture of the limestone is faintly preserved in the calcine
by the distribution of the lime particles (fig. 35). The texture of the lime
is typically granular (figs. 35 and 36), although certain parts of the sample
are spongy (fig. 37) and others are mixtures of the two types (fig. 38). The
grain size of the lime is mainly between 0.5 and l~. Type 4 calcined at 18000 F
is relatively hard compared with other samples.
-------
LIMES FROM CALCITE SPAR, TYPE 2,
Fig. 25. T~~e 2 calcine; 1700° F, 42/65 mesh;
partly calcined to lime; low pore volume;
SEK, nooo.
Fig. 27. Type 2 calcine; 1800°
t;ypical view, sho\dng spongy
high porosity; SEM, X2000.
F, 42/65 mesh;
texture and
Fj,g. 29. 'r:v~e 2 calcine; 1900c F, 12/16 mesh;
j,nterlocking grains 01' lime with incipient
crystal faces (arrows); note cracks in sur-
ficial material, possibly portland:J,te,
Ca(OU)2; SEM, X5000.
- 22 -
CALCINED AT VARIOUS TEMPERATURES
6;" r/" (~}; . " " .: \'1
"', ,. 0 "~I ~<; ~'\'~ ,',
~\. ~).>.. {r. {.::.......-;; 1'1,'... ."""J ~"1 .."~
.',' ,," . - - -~- ., -~ ;;"-',--
~- E-t../ I' f) _f>;';:-' ";n,-jf".:' - -~ ...,-~- "''t,
~\?~.t",.~p'ftJ~9'~{ J, (;':/-" "i""
~"t. . L q!'.rt::~ ,sj {;,.!J ~~ P'7f.. :,~~,.~- ~". not
1i" ~ : c:;',.;:'", ~,. .;p.' ,
'}:.~,:.-~,i:,.- ,,'\. H.: .;<:~, - I" --" -!~- "v.
."li ". '. <;;", ~- '. " ~. :i.r::3, ,"'Z~'"
::~..:~ ~" , tH.~~>.- ~ -.- f,~:' '.f.~'~'"
>; (" - "f;'{ 1I"(,~";C.~~..fI: t:.'t.:'~".~- < .~~?:. '.r
0Jtl': ~'"J:,t ;.~ .,. D~ - (} 1.h:~
):- :rft~~," ~%~fZS. Q"{~".
Fig. 26. Same as fig. 25. dispersed granules
of lime and calcite; in transmitted light,
X550.
Fig. 28. Same as fig.
porosity and partly
nooo.
27; an area of low
sintered lime; SEM,
Fig. 30. Type 2 calcine; 20400 F. 42/65 mesh;
sintered lime. low-pore-volume lime with
interlocking grains; pronounced surface
cracking; SEM, X~330.
-------
- 23 -
LIME FROM COARSE-GRAINED LIMESTONE, TYPE 3, CALCINED AT 1800° F
Fig. 31. 'l'ype 3 calcine; 12/16 mesh; typical
view of specimen, showir~ spongy texture;
SEM, X1l00.
:"1g. 33. 'fype 3 calcine; !Lz/6::; mesh; rounded-
granular texture; SEN, X5000.
Fig. 32. Close-up of specimen in fig. 31,
showing detail of spongy textured lime;
SEN, 1(541+0.
Fig. )i.!.. Type 3 calcine; 150/170 mesh; mix-
tm'c of) l:i.me and pe:riclase (medium gray)
ded.vcd from a dolomite grain in the lime-
st;one; SEM, X5000.
-------
- 24 -
LIME FROM FINE-GRAINED LIMESTONE, TYPE 4, CALCINED AT 1800° F
Fig. 35.
T~~e 4 calcine; 12/1£ mesh; shows
general char'acter of the material
at 10w
rnagnif:toat:i.on: SEE:. X1100.
Fig. 37. Another area of spec:tmen in fig. 35,
showing spol~:Y texture; SEM, X4890.
Fig. .~6. Close-up of fig. 35, showing gran-
u.lar character of much of the lime; SEI-1,
:<':5100.
Fi.g. 38. T;ype 4 calcine; 1;;>/65 mesh; shows
m:i.xed granular and spongy texture; SEN,
X5000.
-------
- 25 -
Type 5 calcines consist of lime and periclase in nearly equal propor-
tions and crush very easily in the mortar and pestle. The texture of the orig-
inal dolomite is commonly preserved in the calcined product (fig. 39). However,
the calcines are very finely granular (figs. 40 and 41). Distinction between
the lime and periclase in the electron micrographs cannot be made positively,
but two groups of particle sizes can be seen in the calcine. One group is ap-
proximately 1 ~, the other is near 0.2~. As the magnesium carbonate of the
dolomite loses C02 at a lower temperature than the calcium carbonate, the larger
particles are probably periclase. In the electron micrographs. the larger par-
ticles appear to underlie the submicron grains. Most of the 0.2 ~ particles,
probably lime, appear to be attached individually to the surface of the larger
particles (figs. 40 and 42). The term "sub grain" may be applicable to these
attachments. or appendages.
Type 6 calcines consist of lime and periclase with quartz and other
constituents derived from the small amounts of clay in the original dolomite.
The texture of the calcine is uniformly finely granular and porous (fig. 43).
The particles of calcine are found to be fairly soft in the mortar and pestle
and consist of lime granules 1 ~ or less in size.
Type 7 calcines are derived from fine-grained magnesite and are quite
uniform in surface texture (fig. 44). The material consists entirely of peri-
clase. The texture is finely granular. and resembles that of the 1700° F cal-
cine of type 1 (fig. 19). The calcine particles of type 7 are moderately hard
when ground in the mortar and pestle.
Type 8 (oolitic aragonite) calcines consist of lime. The lime is
typified by its spongy texture (fig. 45); however, small areas of the samples
have an interlocking grain texture (fig. 46). The figure also shows solid ma-
terial, probably lime. occurring along some of the grain boundaries. Most of
the calcined particles are colorless in reflected light, but many are pale green
and are generally composed of grains about 5 ~ in diameter. The colorless par-
ticles are generally in the range of 0.5 to 2 ~ in diameter.
Type 9 calcines consist of lime and periclase derived from the orig-
inal calcitic dolomite. The calcines are distinctly buff in color because they
contain iron oxide. The calcines (figs. 47 and 48) are composed of 1 to 15 ~
agglomerate particles and retain much of the granular character of the original
stone. A highly magnified view of the larger particles (fig. 48) shows they
have a granular texture much like the calcine of type 5 dolomite. and that the
occurrence of many 1 ~ grains (probably lime) are partly fused to, or incorpor-
ated in, larger "underlying" grains that are probably periclase.
Discussion of Calcines
These studies do not show consistent or significant differences between
the three grades, 12 by 16, 42 by 65, and 150 by 170 Tyler mesh sizes, of the
calcined materials. The 1700° F calcine of Iceland spar calcite (type 1) has a
low sorption capacity for 802, which will be discussed later. This low capacity
probably is due to the large size and density of the lime particles. The aniso-
tropism of this lime is unique and no doubt results from a high degree of strain
in the Ca-O bonds of the lime's crystal structure. When the calcine is heated
-------
- 26 -
CALCINES FROM REEF DOLOMITE, TYPE 5, 1800° F
Fig. 39. Type 5 calcihe; 12/16 mesh; original
grain texture of the dolomite is pr'cserved
in the lime and periclase; SEM, X520.
Fig. 41. Type 5 calcine; 150/170 mesh; gen-
eral view, shewing granular nature of the
lime and pericl.ase; SEM, X5000.
Fig. 40. Close-up of the center of fig. 39;
nlli~eroUS grains, 0.1 to 0.2 ~, are fused
to form agglomerate particles about 1 to
2 ~ in diameter; SEM, XIO,240.
Fig. 42. Close-up of granular particles of
sample in fig. 41; SEM, X20,OOO.
-------
- 27 -
CALCINES fROM TYPES 6 THROUGH 9. 1800° F
Fig. 43. T;,,'pe (, calcine of interreef doJ.o-
mite; 12/16 mesh; typical vie\>I of very
fj.nely granular lime and pex~iclase; SEK..
no,ooo.
Fig. 4'5. Type 8 calcine of oolit:Lc aragonite;
the lime is typi.fied by its spongy texture;
SEr.j., Xl 000.
Fig. 47. T:yrpe 9 calc.inc of calc:i.tic doJ..ornite;
12/J6 mesh; general view. show:lng texture
of the calc ine, which stron.gly resemble:::
the texture
of' the orig:i,nal stene; SE.~~1,
X:LOOO.
}"if:. I,.!i. Type '/ calcine of magr,csitc; typical
view shQwi:115 granular cr."aracter of the
p0riclasc; SEMJ X10,OOO.
Fig. 1+6. S~~e as fig. 45;
an interlocking texture
thl:.~ sample; SEJ~i, XJ.OOO.
sinteJ.'ed lime fo::'IT\s
in small
patcbes in
Fig. ;.,.8. Close-up of a g!'ain in center~ of
fir;. '+7, showing partial fusion of :Lime
and perj.clase gran1.l:Les; SE14 , X10,000.
-------
- 28 -
further to 1800° F, the
1700° F calcine becomes
lime becomes isotropic.
shape of the angular subgrains on the surface of the
rounded, the grain size is greatly reduced, and the
When the temperature of calcination is changed from 1700° to 2040° F,
the SEM observations of types 1 and 2 calcines show porosity increases, then de-
creases. These porosity changes are accompanied by a series of changes in tex-
ture, starting from granular (with submicron angular grains), altering to rounded
granular, then to spongy. and finally to an interlocking granular texture with
blocky grains of lime.
It is postulated that the lime particles formed by calcination of dolo-
mite are prevented from coalescing because of the presence of masses of periclase
formed earlier, which tend to physically separate the nuclei of the lime and
thereby produce a sub grain structure with a very high CaO surface area.
PETROGRAPHIC STUDIES OF SAMPLES OF
CERTAIN COMMERCIAL CARBONATE ROCKS (PHASE II)
Samples and Methods
Seventeen commercially available crushed stone samples were examined
and studied in the second phase of the project. Included in these samples are
five poorly lithified and unconsolidated marls and chalks, each rich in calcite,
a calcitic marble, six limestones, and five dolomites. All the limestones and
dolomites contain more than 93 percent carbonates. One of the samples (2061)
was the limestone injected into unit 10 of the Shawnee Steam Plant of TVA during
the first stage of the dry limestone injection project.
The samples studied during this phase of the project were obtained from
the Division of Process Control Engineering of APCO. They consist of crushed
particles, most less than an eighth of an inch in diameter, considered to re-
present a commercial product. Representative sample splits were analyzed for
their mineral content by HCl residue, X-ray diffraction, and microscope methods;
they were also subjected to chemical analysis and petrographic studies. For the
petrographic studies, 30 to 60 specimens, 12 to 16 mesh, were cast in epoxy
molds. Three to six petrographic thin sections and two or more polished sec-
tions were then prepared for examination with the Quantimet. Also, selected spec-
imens were examined with a scanning electron microscope (SEM). Grain and pore
size measurements were made with both the Quantimet and electron microscope.
Petrographic Characterization of Samples
Petrographic descriptions and source of the samples are given in table
8. Typical photomicrographs from the polarizing and scanning electron micro-
scopes are shown in figures 49 to 51. In table 8, the term granularity refers
to the degree of uniformity of the grain size of the rock as observed micro-
scopically. The term inequigranular is used for a sample in which the majority
-------
1359
2060
2061
2065
2071
1336
TABLE 8--PETROGRAPHIC DESCRIPTION AND SOURCE OF SAMPLES
Granularity
LIMESTONES
Inequigranular
Equigranular
Inequigranular
Inequigranular
Inequigranular
Inequigranular
MARBLE
Single crystal
particles
Relative
grain size
Fine to
medium
Fine
Fine to
coarse
Fine and
coarse
Fine to
medium
Very fine
and
medium
Very
coarse
Grain
shape
Anhedral
Anhedral
Anhedral
Anhedral -
subhedral
Anhedral
Anhedral
and
rhombic
Cleavage
rhombs
Degree of
grain inter-
locking
Other textural features
High
Micro-fossiliferous and fragmental: algal,
foraminifera, brachiopod shells etc.,
also pelletoidal.
High
Few veinlets of medium-grained sparry
calcite. Few specimens are inequigranu-
lar, others limonite bearing.
Moderate
Fossiliferous and fragmental; abundant
coarse crinoid plates, other fine-
grained fossils (see 2061), dolomite
and quartz silt (24 ~) set in very
fine calcite matrix.
Low
Oolitic and fossiliferous and fragmental:
fine-grained brachiopods, echinoids,
bryozoans, ostracods, and foraminifera
fragments; and few coarse single
grained crinoid plates.
Moderate
Pelletoidal, with sparry calcite
cement; also irregular patches
medium-grained sparry calcite.
(10 ~)
of
High
Mostly very fine-grained even textured
with scattered dolomite rhombs through-
out the stone particles. Few patches
of sparry calcite in some specimens.
Sparry calcite, intracrystalline inclu-
sions and twin lamellae. Scattered
grains of tremolite surrounded by
calcite in some specimens.
Source
Hooper Bros., Weeping
Water, Nebraska
(1/8" down aglime)
Grove Lime
Stephens
(aglime)
Company,
City, Virginia
Fredonia Valley Quarries,
Fredonia Valley,
Kentucky (Blue Ledge)
Fredonia Valley Quarries,
Fredonia Valley,
Kentucky
(Upper white ledge)
Longview Limestone (TVA)
Marble Cliff, Carntown,
Kentucky (TV A)
Georgia Marble Company,
Tate, Georgia
(#2 crushed marble)
-------
""""
TABLE 8-PETROGRAPHIC DESCRIPTION AND SOURCE OF SAMPLES (Continued)
::';c11i1]'1 e
t llUnber
Granularity
Relative
grain size
Grain
shape
Degree of
grain inter-
1 oc king
Other textural features
Source
1337
1378
1380
1688
2069
2080
:1
DOLOMITES
Equigranular
Coarse
Inequigranular
Coarse,
medium
and fine
Equigranular
Medium
Inequigranular
Coarse
and
medium
Equigranular
Medium
and
fine
MARLS AND CHALKS
Inequigranular
friable
Fine
Inequigranular
friable
Fine
Rhombic
Sub-
rhombic
Sub-
rhombic
Rhombic
Rhombic
and
anhedral
Anhedral
and
fibrous
Anhedral
High
High
High
High
High
Moderate
Low
Granular mosaic, microporous; few
specimens are fine-grained.
Granular mosaic; grain boundaries tend
to be stairstepped in many particles,
others are curvilinear.
Granular mosaic; grain boundaries tend
to be stairstepped.
Granular mosaic
Mixture of fine-grained (anhedral) and
medium-grained (rhombic) stone
particles.
Banded algal (?) structures and forami-
nifera, also globular and irregular
shaped agglomerates. Sparry calcite
cement partly surrounding banded par-
ticles. The latter crystallites are
generally parallel to one another
(fibrous) .
Variety of thin fossil shells and other
microfossils and woody organic matter.
Thin bands of organic-rich matter sur-
rounds many dense very fine-grained
calcite globules. Also some specimens
with abundant quartz silt (20-50 ~).
Pores largely in microfossil cavities.
Scattered limonite grains.
Chas. Pfizer Company,
Gibsonburg, Ohio
(#10 Glasshouse stone)
Verplanks Coal and Dock
Fettysburg, Michigan
(Fluxing fines)
Rockwell Lime Company,
Manitowoc, Wisconsin
Marblehead Lime Company,
Chicago, Illinois
James River Limestone,
(TVA)
Ohio Geological Survey
Columbus, Ohio
(NE, OH)
Soil Conservation Ser-
vice, Syracuse, New
York (Canastota,
Madison County,
New York)
-------
mple
mber
Granularity
TABLE 8-PETROGRAPHIC DESCRIPTION AND SOURCE OF. SAMPLES (Conciudea.)
I '
Relative
grain sizec
Grain
shape
D~gree of
grain inter';'
locking
Other textural features
Source
29
~)
77
ustin
halk)
81
ansas
halk)
Equigranular
friable
Inequigrariular
friable
Inequigranular
friable
Fine
Anhedral
Low
Low
Moderate
Predominantly fine, even te~tured
calcite (1 ~); few scattere~ thin
shelled fossils and limonite-
organic-rich,particles ari
-------
- 32 -
EXPLANATION OF FIGURE 49
1343 -- TPL (Thin-section in transmitted crossed-polarized light); shows inequigranular
and fossiliferous nature of the limestone. A foraminifera test is shown in the lower
left and clear sparry calcite is scattered throughout the fine-grained calcite. The
dark grains, near center and in upper left, are calcite oriented at optical extinction
in crossed-polarized light.
1359 -- SEM (Fracture surface in scanning electron microscope); shows equigranular char-
acter of the limestone sample and high degree of grain-interlocking.
2061 -- TPL; shows oolitic and fossiliferous nature of the limestone. The dark areas are
very fine-grained and the light areas are medium- to coarse-grained (crinoid fossil
fragments) sparry calcite.
2061 -- SEM; shows detail of the main components in the limestone: (1) large single
crystal grain of calcite (crinoid fossil fragment) with intracrystalline voids on left,
(2) very fine-grained and poorly interlocking calcite grains that form the outer bands
of the oolites and fossil fragments (see 2061-TPL), and (3) the medium-sized and tightly
interlocked grains of clear sparry calcite on the right.
2065 -- TPL; shows the inequigranular character of the irregular patches of'sparry calcite.
SEM photographs of the pelletoids that occur in this sample appear as in 1359 above.
The dark grains are mainly crystalline grains of calcite oriented at optical extinction
and a few grains of opaque pyrite.
1336 -- SEM; shows cleavage surface of a large grain of calcite in the marble. Note the
presence of eight voids, approximately 0.5 to 2 microns across, shown in this micrograph.
-------
131.:.3 - Limestone
X130
- 33 -
1359 -
Limestone
X3310
206J - L:L'"l1es t;one
2065 - Limestone
X30
206: - Limestone
X1+30
-~_..,
X130
1336 - Marble
X990
, Fig. 119.
Typical textures and gr'ain oharactcrisi;ics of.' lblestenes and maJ'ble.
I
q. r ' :'/'. r
/1e.D',' '\ L
:... v jl!i 0')'"
I '
-------
- 34 -
EXPLANATION OF FIGURE 50
1337 -- TPLj equigranular and coarse-grained dolomite.
extinction show very small crystallite inclusions.
rhombic angles by intersection of grain boundaries.
Dark grains oriented at optical
Several grains show characteristic
1378 -- TPLj inequigranular dolomite showing few occurrences of "stairstep" grain boundaries.
The dark inclusions abundantly shown in the grains are intragranular voids such as are
shown in the SEM photograph of 1688 below. The larger dark areas are dolomite grains.
1380 -- TPLj equigranular dolomite showing typical granular
to be less linear than those in the other samples. Note
and dark-appearing inclusions (voids) within the grains.
mosaic. Grain boundaries tend
also t.he abundance of very small
1688 -- TPLj inequigranular dolomite.
1688 -- SEMj shows detail of the type of intragranular voids common in all of the dolomite
samples.
2069 -- TPLj mosaic of equigranular dolomite.
-------
- 35 -
J':~~'
....~.,':.'~
~.~;,.>,;..:~-
'4"'~\~ 0,1 m m
;~~!~., I I
1337 - Dolomite
X130
ly(8 - Dolomite
Xl30
1380 - Dolomite
X130
J.688 - Dolomite
X130
1688 - Dclomij",
X99C
2069 - Dolomite
X130
Fig. 50.
rrypica1. tex.tures and gralrJ r~haracte:t'Jstj.c~ of dolomites.
-------
- 36 -
EXPLANATION OF FIGURE 51
2080 -- SEM; shows fine-grained, partly fibrous, and porous character of the marl.
2109 -- SEM; shows general texture of the marl.
pared with those of 2080.
Note the uniformity of grain sizes com-
2129 -- SEM; shows the fine-grained and agglomerated character of the marl (x2800).
2129 -- SEM; close-up view of one agglomerate particle showing the platy crystallites of
calcite and the highly porous nature of the particle.
2077 -- SEM; shows the granular nature
grains 1 to 2 ~, or agglomerates of
less than those in 2129.
of the chalk. The particles are single subrhombic
interlocking grains whose porosity appears to be
2081 -- SEM; shows the character of the chalk. Note the presence of fibrous particles of
calcite and the polygranular nature of the particles.
-------
- 37 -
(~ ~)B 0
- Karl
X21.;OO
2109 - Hay'l
X240n
2129
- J"'larl
x,sooo
?12C) - !VIarI
lI0,GOO
2iJ7'7
- Chalk
X~)lO()
2081 - r;ba1k
X5600
S':'i.g. 51.
Typical tCAt;lH'(H~ and
gr'1.:"rl (;h2;.ractet'J.stic5 of ma.r
-------
- 38 -
of the chip specimens (crushed particles) observed contains
grain sizes. Grain shapes are qualitatively referred to as
and anhedral. The two-dimensional granular fabric produced
anhedral grains is termed a mosaic texture.
a wide range of
rhombic, subrhombic,
by interlocking of
Petrographically, limestone samples 1343 and 2060 are very similar,
being high-purity fossiliferous fragmental rocks with a micritic type of calcite
matrix that is very fine grained (2 to 8 ~), dense, and anhedral. The fossil
fragments consist of interlaminated grains of calcite (brachipods), large single
crystalline grains (crinoid fossil plates), and fine-grained calcite (other re-
mains of marine invertebrates). Abundant patches of clear (sparry) anhedral
calcite grains occur in former fossil voids and in other irregular areas in the
stone (fig. 49, 1343). In some cases the clear calcite has replaced parts of
the original fossil material.
Sample 2061 is a soft, oolitic, and porous limestone. The oolites are
mainly of a normal type in that they consist of spherical or ellipsoidal bodies
0.5 to 1 mm across, with a nucleus and concentric rings. Most nuclei are single
crystals of calcite (crinoid fossil fragment); rarely, they are quartz sand
grains. The concentric rings consist of very fine-grained calcite (poorly de-
fined in 2061 of fig. 49 by the dark bands shown magnified 30 times (X30), and
in the center area of 2061 at x430). Few of the oolites show radial structure
in the outer rings. Many superficial oolites occur that have only one ring
around the nucleus. Several oolites in 2061 are flattened, and others have de-
formed or ruptured outer rings. Fossils occurring in 2061 are mainly crinoid,
brachiopod, bryozoan, and ostracode fragments. In addition, irregularly shaped,
fine-grained intraclasts occur. The oolites, fossils, and intraclasts are ce-
mented (lithified) together by clear, sparry, anhedral calcite (light-colored
areas surrounding oolites in fig. 49. 2061, at X30; also shown on right side of
2061 at x430). The geologic occurrence and additional information on the source
of sample 2061 is given in a later section, as this stone was used as limestone
additive in the TVA tests.
Sample 1359 is a very fine-grained, even-textured, and dense limestone,
which is almost entirely micritic calcite. This limestone is essentially the
same as type 4 of phase I. The high degree of grain interlocking and the char-
acter of the grains are shown in figure 49. 1359.
Sample 2065 is a pelletoidal limestone. It consists predominantly of
ellipsoidal pellets up to 0.5 mm across that are composed of a mixture of micri-
tic and sparry calcite. Figure 49, 2065, shows detail of the interior structure
of a pellet. The pellets are surrounded by sparry calcite.
Sample 2071 is dominantly micritic calcite (similar to 1359); however,
rhomb-shaped crystals of dolomite, 35 to 40 ~ in size, are scattered throughout
the rock.
The marble, sample 1336 (fig. 49), is uniformly very coarse-grained
calcite spar, and the crushed sample consists almost entirely of cleavage
rhombs or irregularly broken fragments of a single crystal of calcite. Scat-
tered through the particles are a few grains of tremolite (ideal composition:
Ca2MgsSis022(OH)2). a mineral commonly associated with marbles. Few intragran-
ular voids or inclusions were observed in specimens of the marble with the SEM
(fig. 49. 1336).
-------
- 39 -
The dolomite samples described in table 8 also are petrographically
very similar. They all cons ist of more than 98 percent dolomite, and each ap-
pears to have a similar geologic origin: replacement of original limestones.
Their textures are similar (fig. 50), each resulting from the replacement and
recrystallization processes. and they differ mainly in grain size distribution
and pore structures. Samples 1378 and 2069 are more inequigranular than the
other samples, and 1337 has the highest porosity. These samples. with the ex-
ception of 1337, are quite similar to type 5, phase I.
Marls and Chalks
The marls and chalks are grouped together because these two types of
carbonate rocks are very similar in mineralogy and texture. Marl is defined
as a "semifriable mixture of clay materials and lime carbonate" (Pettijohn,
1957, p. 369). The mineral composition of marls may vary greatly, and various
limits of the carbonate and clay contents have been proposed, ranging from 25
to 75 percent carbonate and a complementary content of clay (Gillson. 1960).
Quartz silt and organic matter are usually present. and in some deposits of
marl calcite occurs only in fossil shells.
Chalk is a porous, fine-textured, and somewhat friable carbonate
rock. Normally, it is light buff to white and consists almost wholly of cal-
citic shells of microfossils (Pettijohn. 1957, p. 400). Most chalks are 90 or
more percent calcite, although. according to Gillson (1960), rocks that are
classified as chalks may be as much as 25 percent noncalcite.
Most literature on the deposition of fresh-water lake marls of New
York through Minnesota describes the importance of an alga (Chara) that causes
CaC03 to precipitate on its surfaces. The carbonate, as very fine-grained cal-
cite, is eventually sloughed off the alga and accumulates on the bottom of the
lake where it forms marl.
The samples of marls and chalks studied in this phase are described in
detail in table 8. and typical SEM micrographs are shown in figure 51. The sam-
ples are composed of a variety of microfossils, mainly shells (up to 0.5 mm) of
foraminifera. plus a few gastropod shells and other fossil remains. The Kansas
chalk (2081) and Ohio marl (2080) are petrographically very similar, as is
shown in table 8 and figure 51. The marls 2109, 2129, and the Austin chalk
(2077) also are similar, although the Austin chalk contains more coarse sparry
calcite than do the marls. All the chalks and marls investigated here are
characterized by their high calcite content, poor consolidation, high porosity,
and very fine grain structure.
Grain and Pore Size Distributions
The grain sizes of the limestone, marble, and dolomite samples were
determined fro~ thin sections with the polarized light microscope on the Quanti-
met, by methods described earlier. The grain size data are summarized in table
9. The modes listed in the third column of the table were determined by inspec-
tion of the histograms.
-------
- 40 -
TABLE 9--GRAIN SIZE ANALYSES
Sample
MOdes*
(~)
Distribution
major; minor
Graphic
meant
(~)
Graphic
standard
deviation
(in log units)
Ar ithme tic
meanT
(~)
1343
1359
2060
2061
2065
2071
1336
1337
1378
1380
1688
2069
2080
2109
2129
2077
2081
LIMESTONES
Fine skew
2
6.2
2.7
12.2
10.2
6.2
4.1
1300 **
126.9
119.0
117.2
119.0
52.9
0.9
0.8
0.4
1.1
1.6
2.0
1.2
2.2
2.9
2.2
0.3
0.9
1.1
0.9
0.8
0.8
1.1
1.1
1.2
1.0
1.4
4
3
7
5
4
3
107
89
94
108
45
1.1
1.1
0.6
1.4
2.9
Bimodal
2; 20
20, 2; 180
* As observed from histogram plots of equal logarithmic size intervals.
t Folk and Ward, 1957.
T Krumbein and Pettijohn (1938, p. 240).
** Single grained particles (12 by 16 mesh).
size = 1300 ~.
Irregular
Bimodal
2; 90
Irregular
2; 10, 45
Fine skew
2
MARBLE
Normal
DOLOMITES
Coarse skew
150
210, 50; 25
Irregular
Normal
(with very minor
second mode)
105; (25)
Bimodal
125; 50
50
Normal
MARLS AND CHALKS
Fine skew
0.8; 25
0.8; 5
Fine skew
Fine skew
0.4; 10
1; 15
Fine skew
Fine skew
2; 10
Average grain size = average particle
-------
- 41 -
Grain size measurements of the marls and chalks were made from elec-
tron micrographs. As the diameters were determined predominantly from whole
grains, no corrections due to cross section effects are necessary. In thin
sections, small patches consisting of grains up to 0.3 mID across are widely
scattered throughout the marl and chalk samples.
The results (table 9) indicate the limestones are predominantly fine
grained. Sample 2060 is the only limestone that does not have a major mode at
2 microns. The dolomites are much coarser than the limestones and show a wider
range of major modes. Rowever, four of the five dolomites have a graphical
mean (geometric mean) near 120 microns. The fifth dolomite (2069) has a mean
of 53 microns.
The marls and chalks are the finest grained samples, and of these the
Michigan marl (2129) is the finest grained, having a graphic mean diameter of
0.4 microns. The Kansas chalk (2081) is the coarsest of this group. with a
graphic mean diameter of 1.6 microns.
The volume of pores greater than 0.9 ~ (QTM pore volume) and their
size distribution were determined for the phase II samples by using the same
methods described earlier for the phase I samples. The particle size of the
phase II samples analyzed with the Quantimet was 12 by 16 mesh. The results
in volumetric units (table 10) are the means of image analyses of 60 to 240
areas within different particles and are essentially equal to the total pore
volume of the samples of limestones, dolomites. and marble. The QTM pore vol-
ume of two of the marls (2080 and 2109) and one chalk (2081) are thought to be
erroneously low owing to the filling of several large pores with epoxy during
preparation of the specimens and to the presence of many pores less than 0.9 ~.
The electron microscope showed abundant voids within dolomite grains
in each of the dolomite samples. Image analyses with the Quantimet were made
of scanning micrographs taken of cleaved rock surfaces of four samples (for
example, fig. 50, SEM 1688) with the epidiascope and the Quantimet. The abun-
dance and size distribution of void inclusions were measured, and the results
are listed in table 11. Sample 1380 appears to contain about half as many
inclusions as the other dolomites. Time did not permit the analyses of a suf-
ficient number of specimens to determine haw representative the data are.
Mineralogy
Mineral composition of the samples was determined by the methods de-
scribed earlier. The results are listed in table 12. The RCI-insoluble resi-
dues from 20-gram samples of the limestones and dolomites proved to be mainly
quartz and clay in various amounts plus smaller amounts of organic matter and
a grain or two of opaque minerals, mainly pyrite. Sample 2060 has the highest
residue (5.92 percent) found in the limestones and dolomites. The residues
from samples of the marls and chalks make up as much as 13 percent of the sam-
ple. Much of the residue from 2109 and 2129 is woody organic matter. In addi-
tion, RCI-soluble organic matter occurs in the marls and chalks. The calcite
ranges from 76 to 98 percent by weight in the marls.
-------
TABLE lO-QUANTlMET ANALYSES OF PORE STRUCTURE
Pore volume distributiont
Mean Pore (nun3/g) Predominant
pore volume projection position
Sample (mm3/g) (nun) 0.9-2 2-2.8 2 . 8- 3 . 9 3.9-5.5 5.5-7.8 7. 8-11 11-16 16+ (IJ.) of poresf
LIMESTONES
1343 22 0.22 11.7 5.1 2.4 1.8 0.6 0.2 0.1 < 0.1 Between grains
1359 10 0.09 6.9 2.2 0.5 0.3 < 0.1 < 0.1 < 0.1 0 Between grains
2060 9 0.29 5.3 2.0 1.0 0.6 0.2 0.1 < 0.1 0 Between grains
2061 21 0.32 12.8 4.7 1.5 1.0 0.4 0.4 0.1 < 0.1 Variable
2065 9 0.09 5.1 2.5 0.8 0.6 0.2 < 0.1 < 0.1 < 0.1 Between grains
2071 18 0.52 12.1 3.7 1.2 0.6 0.1 < 0.1 < 0.1 < 0.1 Between grains
MARBLE
1336 8 0.18 5.0 1.4 0.6 0.5 0.4 0.2 0.2 0.1 Within grains
~
I\)
DOLOMITES I
1337 51 0.46 30.9 11.2 4.5 4.6 3.9 1.3 1.3 0.8 Variable
1378 14 0.22 7.5 2.8 1.4 0.9 0.8 0.4 0.1 < 0.1 Within grains
1380 18 0.38 11.5 3.4 2.2 0.9 0.5 0.2 0.2 < 0.1 Within gra ins
1688 2!j. 0.55 14.5 5.2 1.9 1.4 0.5 0.3 0.1 < 0.1 Within grains
2069 15 0.40 8.4 2.8 1.3 1.1 0.6 0.4 0.1 0.1 Within grains
MARLS AND CHALKS
2080 21 0.42 13.9 3.2 1.0 1.4 0.7 0.4 0.3 0.2 Between grains
2109 9 0.17 5.6 1.6 0.7 0.5 0.3 0.1 < 0.1 < 0.1 Between grains
2129 73 1.34 29.2 14.4 8.7 9.1 5.3 3.7 1.7 1.0 Between grains
2077 56 0.19 28.0 14.9 6.9 4.0 1.6 0.4 0.1 < 0.1 Between grains
2081 17 0.36 10.8 2.8 1.4 0.9 0.6 0.3 0.1 . 0.1 Between grains
* Image analyses of pores larger than 0.9 IJ.. Quantimet magnification of 1300X.
t The intervals, in microns, correspond to a constant interval of 1/2 phi units.
+ Determined by scanning electron microscopy.
-------
- 43 -
TABLE Il--VOID INCLUSIONS IN DOLOMITE GRAINS
Frequency percentage of voids larger than (1-1)
No. of Median
Sample 0.1 0.2 0.4 0.8 1.6 3.3 4.9 vOids/mm2 size (11)
1378 90.3 78.9 65.4 43.6 19.7 5.3 0.2 17,400 0.65
1380 92.5 79.3 64.2 30.2 13.2 1.9 0 8,000 0.53
1688 * 83.4 69.1 50.7 26.1 7.4 2.6 17,300 0.82
2069 87.6 68.8 53.2 34.4 15.6 0 0 16,760 0.45
* Not determined.
Chemical Analyses
The results of analyses of the major and minor elements present in
the samples are listed in table 13. The methods of analyses used were described
earlier in this report. The data show that. of the limestone samples, 2060
contains the most silica (4.42 percent) and the least CaO (49.2 percent). The
composition of the dolomite mineral as calculated from the chemical analyses is
given in table 12. The analyses indicate there is slightly more calcium than
magnesium in all samples except 1688, which has the ideal dolomite composition
(Ca/Mg = 1/1).
Chemical analyses of the marls and chalks show a wide range of or-
ganic matter and silica content. Sulfur contents range from 0.01 to 0.62 per-
cent. The sulfur occurs mainly in very rare, small grains of pyrite. Less
than 0.1 percent of the sulfur is organic in these samples. The marl from
Michigan (2129) has high Na20 and H20 contents.
DISCUSSION OF RESULTS RELATED TO
SULFUR DIOXIDE SORPTION TESTS
The samples of carbonate rocks investigated were tested for their S02
reactivity by personnel of the Division of Process Control Engineering, APCO,
Cincinnati, Ohio. Two methods were used to evaluate the relative reactivity
of carbonate rock samples with S02 in flue gases. Their capacity for reaction
was measured in a fixed-bed reactor (Potter, 1969), and an indirect assessment
of the rate of reaction was made with a differential reactor, according to the
Borgwardt method (1970a).
grams of
flue gas
For the capacity test a weight of uncalcined sample equivalent to 20
calcine, 16 to 20 Tyler mesh, was exposed in a fixed-bed reactor to a
containing 2700 ppm S02 for 3~ hours at 1800° F. The gain in weight
-------
- 44 -
TABLE 12-MINERAL ANALYSES
Sample
Major
component (%)
Minor and trace
components
RCI insoluble
residue (%)
LIMESTONES
134-3
98 Calcite
1.4-% kaolinitic clay:
trace of quartz
1.65
1359
99 Calcite
Traces of illitic clay
and dolomite
0.65
2060
81 Calcite
12% dolomite: 3.5% quartz:
2% illitic clay: trace
of limonite
5.92
2061
98+ Calcite
2065
94- Calcite
< 1% kaolinitic clay:
< 1% quartz sand
5% dolomite: trace of
quartz as sand and silt:
trace of clay
loll
0.95
2071
95 Calcite
3.8% dolomite: < 1% quartz:
traces of feldspar and clay
1. 73
MARBLE
1336
98 Calcite
1+ % tremolite: < 1% mica
1.95
DOLOMITES
1337
99+ Dolomite*
Cal.14-Mg.86(C03)2
98 Dolomite
Cal.03Mg.97(C03)2
Traces of quartz and clay
0.34-
1378
1% quartz sand; < 1% clay
1.88
1380
99 Dolomite
Cal.03Mg.97(C03)2
99+ Dolomite
Cal.0~1.00(C03)2
98 Dolomite
Cal.08Mg.92(C03)2
< 1% cherty quartz; < 1% clay
0.76
1688
Traces of quartz and clay
0.35
2069
1.5% kaolinitic clay:
trace of limonite
1. 94-
MARLS AND CHALKS
2080
98 Calcite
1% organic matter: 1% illitic
clay: < 1% silty quartz
5% woody and RCI-soluble
organics: 2% clay:
2% dolomite
1.19
2109
92+ Calcite
2.58
2129
76+ Calcite
11% organics, mainly woody:
3% illitic clay: 4-% silty
quartz: 4-% dolomite
6% glauconitic clay: 3% quartz:
1% limonite: trace of feldspar
13.07
2077
87+ Calcite
8.11
2081
92+ Calcite
2% organic matter: 1% clay:
1% quartz: trace of feldspar
2.82
* The proportions of Ca++ and Mg++ in the dolomite, calculated from analyses in table 13, are as shown.
Ideal dolomite is Cal.OMgl.0(C03)2.
-------
TABLE l3-CHEMICAL ANALYSES IN WEIGHT PERCENTAGE
(Analyses by Analytical Chemistry Section, Illinois State Geological Survey)
Organic
Sample Si02 A1203 Fe203 MnO MgO CaO Na20 K20 S H20+ C02 C Total
LIMESTONES
1343 O.ll 0.57 0.14 * * 54.8 0.031 0.06 0.04 * 43.10 * 98.8
1359 * 0.14 0.07 0.01l trace 55.5 0.007 0.01 * 0.25 43.27 0.15 99.5
2060 4.42 0.64 0.23 0.016 2.79 49.2 0.047 0.15 trace 0.26 41.58 * 100.3
I 2061 0.29 0.47 0.14 0.013 * 55.0 0.012 * * 0.22 43.63 * 99.8
2065 0.25 0.04 0.28 0.009 * 55.0 0.004 0.14 0.01 * 43.48 * 99.2
2071 0.56 0.33 O.ll 0.005 0.92 54.3 0.034 0.06 0.03 * 43.52 * 99.9
MARBLE ~
1336 t \J1
0.08 0.40 0.12 0.005 1. 01 54.1 0.01l 0.03 * * 43.25 * 99.0
DOLOMITES
1337 * 0.15 0.19 0.004 18.0 33.2 0.044 O.ll < 0.01 0.04 47.17 * 98.9
1378 * 0.43 0.02 * 20.82 30.7 0.066 0.01 0.01 0.01 46.42 * 98.5
1380 * 0.27 0.19 * 20.67 30.5 0.044 0.02 < 0.01 0.23 46.97 * 98.7
1688 * 0.21 0.02 * 21.57 30.0 0.048 0.01 < 0.01 1.10 47.09 0.01 101.1
2069 0.44 0.61 0.23 0.020 19.2 31.4 0.031 0.22 0.04 0.84 44.93 0.60 98.6
MARLS AND CHALKS
2080 * 0.67 0.03 * * 54.8 0.024 0.05 0.62 1.23 40.99 0.35 98.8
2109 * 0.84 0.01 * 1.88 51.7 0.033 0.02 0.55 1.47 40.16 2.77 99.4
2129 t 5.10 0.88 0.47 0.01 3.08 43.9 0.160 0.01 0.19 4.66 35.38 6.18 100.0
2077 6.34 2.17 0.82 0.01 * 49.2 0.035 0.49 0.01 1.13 38.31 0.19 98.8
t 2.48 1. 09 0.15 * 1.41 51.4 0.060 O.ll 0.57 1.16 39.44 0.95 98.8
2081
* None detected.
t Mercury in 1336 = 0.19 ppm, in 2129 = 0.07 ppm, and in 2081 0.77 ppmj not determined in other samples.
-------
- 46 -
TABLE 14--s02 REACTIVITIES
(S02 tests by Division of Process Control Engineering, APCO)
Rock
Sample classification
Type 1 Iceland spar
(calcite)
Type 2 Calcite spar
Type 3 Limestone
Type 4 Limestone
Type 5 Dolomite
Type 6 Dolomite
Type 7 Magnesite
Type 8 Aragonite
Type 9 Dolomite
1343 Limestone
1359 Limestone
2060 Limes tone
2061 Limes tone
2071 Limestone
1336 Marble
1337 Dolomite
1378 Dolomite
1380 Dolomite
1688 Dolomite
2069 Dolomite
2080 Marl
2109 Marl
2129 Marl
2077 Chalk
2081 Chalk
Sorption capacity,
fixed bed (gj20 g)
Reactivity, differential
(mg SOy30 mg calcine)
5.46 8.3
11.65 9.6
10.73 13.9
6.97 14.0
9.03 17.0
13.68 12.1
1.78
18.30 7.1
14.91 15.8
6.06 5.08
4.94
12.25 8.98
9.52 4.84
7.40 4.42
7.50 3.86
11.53 9.28
11.90 7.08
8.70 6.53
11.35
9.08 8.82
15.60 6.60
15.38 7.12
14.83 14.92
12.54 8.62
13.37 11.73
of the sample after the test period was taken as the measure of the sample's
S02 sorption capacity. The results of the fixed-bed capacity tests of the
samples appear in table 14.
For the differential reactor tests, the stone was precalcined at
1800° F for 2 hours, and a 150- to 170-mesh calcine was exposed at 18000 F for
various periods of time to a flue gas containing 2700 ppm S02. The plot of "the
amount of S03 sorbed by the sample versus time was constructed and evaluated at
120 seconds to give the differential reactivity. These values, supplied by the
Division of Process Control Engineering, for the samples investigated are given
in table 14.
In the discussions that follow, samples of all the carbonate rocks
studied will be considered.
-------
- 47 -
Petrography Related to S02 Sorption
No consistent correlation is apparent between the results of fixed-bed
and differential S02 reactivities and the mineralogy of the samples. A clayey
and silty nonreef-type dolomite~ selected for study because of its impurity~
contains about 25 percent inert oxides in its calcine~ yet this sample was among
the highest in S02 capacity. On the other hand, Borgwardt (1970b) found the
rate of reaction of this sample notably reduced, compared to rates of high-
purity calcines ~ at a particular degree of sulfation. Considered in terms of
capacity for sorption of S02~ the textural properties of the calcine and, pre-
sumably, the raw stone outweigh a moderate degree of impurity.
In the fixed-bed capacity tests, the dolomites averaged 11.27 grams
per 20 grams of calcine and the limestones averaged 6.84. The marls and chalks
had a high average of 14.34 g/20 g. The oolitic aragonite (type 8) adsorbed the
largest amount of S02 (18.3 g/20 g) and the magnesite (type 7) the least
(1.78 g/20 g). The limestones containing abundant crinoidal fossil fragments
had higher S02 sorption capacities than other limestones. The crinoid fragments
are generally the coarser crystalline grains in limestones and the abundance of
crinoids is generally reflected in the mean grain size of the stone.
In differential reactivity tests the dolomites averaged 10.9 mg of S03
per 30 mg of calcine, whereas. the limestones averaged 8.5 mg of S03/30 mg of
calcine. The comparable values for the marls and chalks are 9.55 and 10.68 mg,
respectively. Two of the marls had rather low differential reactivities, while
sample 2129 had a high value (14.9 mg of S03/30 mg of calcine). The reef dolo-
mite, type 5, had the highest differential reactivity (17.0) and the marble~
sample 1336. the lowest (3.86). The very fine-grained limestone with scattered
dolomite rhombs (2071) tested very low (4.42); limestone sample 2061, very sim-
ilar to 2071 but lacking the dolomite rhombs, also had a very low differential
reactivity. However~ the fine-grained, type 4 limestone, which is similar petro-
graphically to 2061 and 2071, had a rather high reactivity (14.0 mg of S03/30 mg
calcine). Such diverse differential reactivities are thought to result from
slight differences in pore structure of the calcines of these samples. which
gives rise to differences in the rate of reaction during the first few tens of
seconds of exposure to S02, with a resultant significant difference in the de-
gree of sulfation after a reaction period of 120 seconds. Determination of the
rate of reaction of calcines at a constant degree of sulfate loading enabled
Borgwardt (1970b) to correlate the differential reactivity with the surface
area measurements of the calcines. As the surface area of the calcine increased,
a linear increase in the differential reactivity was observed for calcines having
a constant degree of sulfation.
Grain Size and Pore Structure Related to Sorption
The interim report on this project gave results on the nine type sam-
ples that showed the S02 capacity tended to increase with increasing pore volume
and decreasing grain size of the stone. These relations are more conclusively
demonstrated by the data on all samples studied except the magnesite. Graphs
of the various petrographic parameters showing notable correlations appear in
figures 52 to 56.
-------
::t
-
u
.s::
a.
~
C7'
Q)
N
"(jj
C
~
C7'
C
o
~ 10
1000
I
I
~
A
M
M
Fig. 52. 802 capacity as measured
in fixed-bed tests versus mean
grain size of carbonate rocks.
L = limestones, D = dolomites,
8 = calcite spars, C = chalks,
and M = marls.
s
s
s
100
"
~
~
I!
I!
l!
l!!!
I!
~
1.0
~
o
M
I I I
5 10 15
502 capacity, g/20g calcine
tion. Other petrographic
ential reactivity.
- 48 -
-
The finer grained rocks, in general,
tend to have greater 802 capacities (fig. 52).
The measure of the grain size plotted is the
graphic mean from table 9; a similar distri-
bution is apparent when the arithmetic mean
is substituted for the graphic mean. In fig-
ure 52 four clusters of data points occur.
The cluster of points near 10 ~ are for the
micritic limestones and two petrographically
similar dolomites (types 6 and 9). This clus-
ter shows increasing 802 capacity as grain
size increases. This behavior, which is con-
trary to the general trend, is related to the
occurrence of crinoid grains in the limestones
as discussed above. The coarse-grained cri-
noidal limestone (type 3) is associated with
the coarse-grained dolomites near 100 ~ on the
graph (fig. 52), and each of these samples con-
tain abundant intragranular voids. The chalks
and marls and the oolitic aragonite samples
constitute the cluster (fig. 52) with the
finest grain size and show the highest aver-
age 802 capacity of the various groups. The
three coarsest samples (top of fig. 52) are
calcite spar and related types. The grain
size of the carbonate rocks shows no signi-
ficant correlation with their differential re-
activity (120-second reaction period).
-
20
Measurements of the mean QTM pore volume
(tables 5 and 10) show certain correlations
with 802 capacities (fig. 53). With exception
of the aragonite sample and the chalk and marl
samples that had pore volumes thought to be er-
roneously low (2080, 2109. and 2081, each cir-
cled in fig. 53), there is a significant linear
increase in pore volume with increasing sorption
capacity- The correlation coefficient is 0.71.
The pore volume (QTM) within the 2 ~ to 16 ~
size interval plotted against the 802 capacity
(fig. 54) also shows increasing sorption capac-
ity as pore volume increases. The 2 ~ to 16 ~
pore volume has a correlation coefficient of
0.97 with the QTM pore volume.
The differential reactivity data plotted
against the QTM pore volume of the uncalcined
samples (fig. 55) and against the pore projec-
tion (fig. 56) show little significant correla-
properties show even less correlation with differ-
-------
. .
.
. I l
18 @
.
16
@
Q) @
co . .
u
0 14
u .
@ I
0"'
0 +=-
N . . \()
'- 12 .
0"' .
. .
>.
.
u
0 10
a. .
0
u . .
.
N
0 8
U)
. .
.
6 .
.
.
4
0 5 10 15 20 25 30 35 40 45
Volume of 2- 16 fL pores. m m3/ 9 roc k
Fig. 54. 802 capacity in fixed-bed tests versus volume of
2 to 16 l-L in "diameter" pores of carbonate rocks, as
determined by Quantimet methods.
20
@
18
16 @
@
14
Q) @
c
u
0 12 .
.
u .
.
0"'
0 .
C\J
'- 10
0"' .
. .
>- . .
"'::
u 8
0 . .
a. .
0
u
",6 .
~. .
4
2
o
10
20 30 40 50
Mean pore volume (QTM),mm3/g rock
Fig. 53. 302 capacity as measured in fixed-bed
tests versus volume of pores larger than 0.9 l-L
in diameter (tables 5 and 10) in carbonate rocks,
determined by Quantimet methods. The pore volumes
of samples that are circled are believed to be
erroneously low. Correlation coefficient, dis-
regarding circled samples, is 0.71.
-------
20 1.0 I 1
I
>,W D
- c:: . D
.~ ~ 15 . M
L L . .
u u . .
0
~ C1> C D
E . .
00 10 5 D
~r<> .L D C
c::, 5 . . . .
w ", . M DAM
~O
'+-Cf) . . DI . ,
~ry L L
.., E 5 5 ...
a . L
0.1 -
Cf)
0 ' I I .
0 10 20 30 40 50 60 70 .
Meon pore volume(QTM), mm'/g rock . . ..
~ .
Fig. 55. 802 reactivity in differential tests volume .
versus ~ . .
of pores larger than 0.9 ~ in diameter 0", . . .
in carbonate rocks, 0
as determined by Quantimet methods. L = limestones, D = z .
dolomites, 8 = Iceland spar, calcite spar, and marble,
C = chalks, M = marls, and A = aragonite. Correlation ..
coefficient is 0.48. . V1
. 0
0.01 -
I
.
.
0.4 06 0 B 1 0
Pore projection, mm rock
Fig. 56. 802 reactivity in differential tests versus pore
(boundary) projection of carbonate rocks, as determined by
Quantimet methods. L = limestones, D = dolomites, 8 = Ice-
land spar, calcite spar, and marble, C = chalks, M = marls,
and A = aragonite. Correlation coefficient is 0.67.
i~
:~~ 15
u8
o
~o>
E
~ ~ 10
C, 5
w '" .
~O
;~
.., E 5
a
Cf)
20
I
L
L .
.
C
.
5 D
.c L D .
M.A . .
. 'D D M
..
L i
s. L
.
.
D
. D
.
M
.
D
.
.
0.002
1
5 10 15
502 Capacity, g/20g calcine
20
Fig. 57. 802 capacity in fixed-bed
tests versus Na20 content of car-
bonate rocks. Correlation coef-
ficient is 0.78.
00
0.2
I 2
1.4
-------
- 51 -
Chemical Analyses and Sorption
Graphic plots of the weight percentages of the chemical elements
present in the samples versus the S02 reactivities show no correlations. ex-
cept for the plot of the sodium content. The capacity to react with S02 tends
to increase with the am01mt of sodium (measured analytically as Na20) in the
sample (fig. 57). The figure shows the logarithm of Na20~ determined by neu-
tron activation methods~ plotted against the S02 capacity test results. The
correlation coefficient is 0.78. Sodium is considered only as an index~ not
as a reactant with S02; however ~ it may be acting as a catalytic or fluxing
agent to produce a more reactive calcine. For all the type samples except
types 6 and 9. the sodium is thought to be in the form of soluble salts rather
than inert clays; analysis shows that 77 percent of the Na20 of type 6 is a
soluble salt~ as is 97 percent of the Na20 of type 9. Similarly high propor-
tions of the minor amounts of Na20 present in the phase II samples are probably
also in the form of soluble salts. These salts are probably located along
grain boundaries and in void inclusions in the dolomite samples (Lamar and
Shrode~ 1953). Sodium salts of chloride and carbonate were reported by Murray
(1956) to result in decreased shrinkage of limestone and dolomite particles
during calcination.
Comparison between the two calcite spar samples (types 1 and 2) shows
that type 2 contains the highest concentration of all trace elements (table 4).
These impurities may have contributed to the higher sorption capacity observed
for type 2.
REACTION PRODUCTS
Fundamental differences in the reactions of calcines with S02 were
observed by analyses of the X-ray spectrum of sulfur from reacted specimens
examined in the SEM (fig. 58). The 1700° F calcine of Iceland spar calcite
(type 1) exposed to S02 for 600 seconds was converted to anhydrite (CaS04)
only at the edges of the particles (fig. 58B)~ whereas~ under the same condi-
tions. the calcine of the coarse-grained crinoidal limestone reacted to form
anhydrite throughout the particles (fig. 58D). This difference in behavior is
thought to be due to the difference in porosities of the calcined particles.
Anhydrite was the reaction product in every reacted sample studied. No magnes-
ium-sulfur compounds were detected in any of the samples. but periclase (MgO)
was abundant in the reacted calcines of the dolomite samples.
The anhydrite on the exterior surfaces of S02-reacted particles (3~
hours at 1800° F) is granular ~ with grains ranging from about 1 to 6 microns.
The particles of anhydrite are smooth surfaced~ and their boundaries tend to
be linear in reacted dolomites (fig. 59). Examination of the SEM micrographs
of reacted type 5 dolomite indicates a moderate number of pore channels lead
from the external surfaces into the particles. SEM studies of reacted calcines
of type 4~ an example of the limestones, show larger grains (up to 30 ~) of
anhydrite that are generally smooth and anhedral and have a tightly interlocking
granular fabric that is essentially impervious (fig. 60).
-------
A..
(:POSS sec tior.. of a calcined par'ticle of
Icelar~ spar (type 1) reacted with 302
for 600 seconds; embedded in expoxy.
Polished section of particle is 0.67
by 0.25 mffi; S~~, X120.
~
".
G!'oss section of a calcined particle of
Doar'se 1:L'11ostone (type :5) reacted with
802 for 600 seconds. Polished section
of particle is o.lj.8 by 0.25 IrJn; SEM, X200.
Fig. 58.
- S2 -
B.
Sulfur X-ray scan of' A, showing sulfated
lime on outer rim.
, . .
. ..,.. Jt1 .
" " ,', .' ' . l;~':.:r' '
, " ' ~. .......,- ..c.' ' . '
, ., ".," ' ..:..,~~"..;!t'~". '
:"" ',' ,""..: ", ",.': ..,~>i:<;'!tJ~~lf~J . -' ,.::'
. ,.",: , ,"~ ,.'
, "" .:: ..~~,....::;:.t;,~,; ttM~'))!f": ' " ,'. '
/:i,~.\-14f~""''';.(>;'-~;'':: :. , ' ',' .
, .. ,~."'i~R~~,(:,~r '1'1,' \ , ..
. ... -';~~¥.G-.' ':',
D.
Suli~r X-ray scan of C, showing complete
sulfate permeati.on.
Dh1tribution of sulfur i.n two types of carbonate rocks showing dii'feront reaction behavior.
-------
- 53 -
Fig. 59. Exterior surface of SOz-reacted calcine of a high-purity reef dolomite (type.5),
showing blocky texture of anhydrite (gray). The highlighted grains are dust particles
derived from the sample. SEM, X9350.
-------
- 54 -
Fig. 60. Exterior surface oi' SOz-reacted calcine of' a fine-grained limestone (type
dense mosaic of anhedral grains of anhydrite (gray). The highl~~ted grains are
cles derived from the sample. SEM, x2080
1+ ). showing
dust parti-
-------
- 55 -
PETROGRAPHIC STUDIES OF LIMESTONE-MODIFIED
FLY ASH AND BOILER DEPOSITS
The limestone injected into boiler number 10 of the Tennessee Valley
Authority's (TVA) Plant. Paducah, Kentucky, was taken from the "Upper white
oolitic limestone" ledge in the quarry of Fredonia Valley Quarries, Inc.,
located about one mile south of Fredonia, Kentucky. During the summer of
1969, three distinct ledges of stone were being exploited in the quarry, an
"Upper white oolitic limestone" ledge 35 to 40 feet thick, a middle "Blue
limestone" ledge 29 to 30 feet thick. and a "Lower white oolitic limestone"
about 33 feet thick. These units are diagrammed and a field description of
the upper strata are given in figure 61. The limestone beds exposed in the
quarry are geologically classified as part of the Fredonia Member of the Ste.
Genevieve Formation (Dever and McGrain, 1969). This member consists mainly of
oolitic, gray, fossiliferous limestone. which occurs in the western parts of
Kentucky and Tennessee, in the southern parts of Indiana and Illinois, and in
southeastern Missouri (Keroher and others, 1966). The oolitic beds in the
Fredonia Member are characteristically high-calcium limestones. Sample 2061.
previously described, was taken from the upper white oolitic limestone beds,
and sa;mpl_e 2060 was taken from the "blue," fossiliferous limestone beds that
underlie the upper oolite in the quarry.
Recently, TVA has been injecting oolitic aragonite into the boiler.
Sample type 8, described earlier, was taken from the same source as the stone
used in the TVA tests.
Samples of the normal fly ash were obtained from the mechanical hopper
of the test boiler so that the constituents derived from the coal consumed in
the boiler could be identified and characterized. Limestone-modified fly ash
samples were obtained from the various positions in the boiler.
Sample plane AA is nearly horizontal across the upper part of the
boiler at an elevation of 376 feet and about 20 feet above the points of lime-
stone injection. Plane CC is horizontal across the down-draft section of the
boiler. behind the exchanger section. Samples from these two planes across the
gas stream were collected by special probes introduced into the planes to various
sampling points. Samples were also taken from the mechanical and electrostatic
hoppers (dust collectors). Details of the boiler and sampling procedures were
given by Womble and Reese (1970). The samples for the following petrographic
studies were supplied by personnel of TVA and APCO. Identifications of the sam-
ples of fly ash materials studied are given in table 15.
The injection test conditions were:
Injection temperature
Particle size of injected limestone
Average temperature at plane AA
Average temperature at plane CC
Stoichiometry (number of molecules
of CaO injected divided by num-
ber of atoms of S in coal)
3000 ° F
70% < 200
2190° F
650° F
mesh
1. 3 to 1. 5
-------
Bed
designation
Operating
ledges
A
" T
Upper white
oolitic limestone"
35 to 40ft.
-8 SS
-c
-0
-E
F
-G
H
"Slue limestone"
29 to 30 ft .
, I
- shale bed, 2 to 2 fl.
-clayey NmeslonT
shale I
"Lower white
oolitic limestone"
Dark gray limestone underlies (
the lower white limestone ledge.
Scale
[
~ 20
Feet
Fig. 61.
- 56 -
DESCRIPTION OF BEDS
Overburden consists of 2 to 14 feet of clay,
silt, and soil. A gray limestone ledge up to 40
feet thick has been quarried from above the upper
oolitic limestone ledge currently being produced.
On the face of the quarry that was examined in
detail there was 1 to 2 feet of the gray limestone
remaining (sample A).
A.
Gray limestone with calcite spar nests in mi-
crite, biomicrite thin shell-oolitic, stylo-
litic, irregular patches of lithographic beds
interbedded--irregular thickness 1-2 feet.
B.
White limestone highly oolitic, fossilifer-
ous, few sparry cement patches. Soft porous,
homogeneous stone sample 5-6 feet from top of
unit. Varies slightly laterally to somewhat
harder stone--sample BB--crinoidal, brown,
coarse crystalline.
C.
2-3 feet below B; same as B.
D.
2 feet below C. Contains
soidal fossils of unknown
to iron-stained beds.
3 mm gray ellip-
type. 18 inches
E.
White oolitic limestone, as in B, with iron-
stained beds about 4 feet thick; iron stain
most intense along vertical joints.
F.
White oolitic limestone as in B.
G.
White oolitic limestone, mixture of fine- and
coarse-grained stone with notable porosity in
some beds.
H.
White oolitic limestone; porous adjacent to
joints, fine-grained and non-porous a few
feet laterally from the joints.
Floor of upper ledge
Cross section of the quarry of Fredonia Valley Quarries, Inc., Fredonia. Kentucky.
-------
- 57 -
TABLE 15--FLY ASH SAMPLES STUDIED
Sample
identification
Type of fly ash
Boiler locations and test date
45
66-71
92-3, 97-8
104-
106
Test 2, I-rv
Test 4, I-rv
Test 6, I-rv
Test 8, I-rv
Test 2, V-VI
Test 4, V-VI
Test 6, V-VI
Test 8, V-VI
Test 25, I-IV
Test 25, V-VI
Test N
I
II
III
Normal
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Limestone-modified
Normal
Normal
Normal
Normal
Mechanical hopper
Plane AA, probe 5AW
Plane ee, composite of 3 probes
on the east side of boiler
Mechanical hoppers 1-3
Electrostatic hoppers 5-8
Plane AA. 4 composite samples in
each test from certain probes
taken during 4 different tests:
2(5-13-70), 4(5-21-70). 6(5-27-
70), and 8(6-2-70).
Plane ee. 2 composite samples each
from certain probes during same
tests as above.
Plane AA. 4 composite samples each
from certain probes taken on
8-31-70.
Plane ee, 2 composite samples each
from certain probes taken on
8-31-70.
Taken on 6-1-70
Electrostatic hopper 7
Electrostatic hopper 3
Mechanical hopper 3
Mineral Analyses
The minerals occurring in the fly ash samples were identified by X-ray
diffraction methods. The iron-rich particles were removed from the nonmagnetic
fraction in the samples by repeated use of a very strong hand magnet. Most sam-
ples were further separated into eight size classes with sieves of the following
mesh: 100. 140, 170, 200, 230, 325. and pan. Each class was further pulverized
and mixed with a small amount of mineral oil. and the mixture was spread on a
glass slide and X-rayed. The results are tabulated in table 16, and two partial
X-ray tracks are shown in figure 62.
The only sulfur-bearing compound positively detected that is believed
to have formed in the boiler by reaction with limestone-derived materials is
anhydrite (CaS04). Some calcium sulfite (CaS03) may have formed. but, if so,
most of it must have been converted to the sulfate form prior to analysis of the
-------
TABLE 16-MINERALOGY OF FLY ASH SAMPLES DERIVED BY X-RAY DIFFRACTION
Nonmagnetic fraction Magnetic fraction
Total
mag.
Sample Relative abundance'; High Medium Low High Medium Low (%)
45 Quartz Lime Portlandite Magnetite Hematite Periclase (?) 51. 6
(normal ash) Anhydrite
Pyrite (?)
66-71 Lime Quartz Portlandite Magnetite Lime 8.1
(plane AA) Anhydrite Anhydrite Vl
Periclase (?) CD
I
92-3, 97-8 Lime Anhydrite Quartz 6.6
(plane CC) Portlandite
Calcite
Periclase (?)
104 Lime Anhydrite Quartz Magnetite Hematite Anhydrite (?) 17.5
(mec hanic al portlandite (?) Pyrite (?)
hopper)
106 Lime Anhydrite Quartz 0.4
(electrostatic Portlandite
hopper)
-------
35
- Portlandite
- Lime
o - Anhydrite
(b 30
OQ
t1 calcite
(b -
(b Portlandite
(II -
N - Co C03 (?)
II) - Quartz
25 - Anhydrite
45
40
V1
\0
- Periclase (?)
- Anhydrite
- Quartz
- Anhydrite
- Lime
20
- Quartz
- Port1andite
CD
15
»
Fig. 62. X-ray diffraction tracks of nonmagnetic fraction of limestone-modified fly ash from plane CC.
(A) sample 92-3, 97-8; (B) the +100 mesh of test 25, probes 8E-l,2,3, showing possible trace occurrence of CaS03'
-------
- 60 -
samples. The identification of very small amounts of CaS03 is complicated by
the partial masking of the main diffraction peak of CaS03 by a moderate peak of
portlandite (Ca(OH2)), a very small peak from anhydrite, and a peak from mag-
netite. The main peak of CaS03 occurs at 28.6 degrees, and secondary peaks
occur at 30.8 and 35.4 degrees. The small anhydrite peak also occurs at 28.6
degrees, the main peak of magnetite occurs at 35.4 degrees, and one peak of
Ca(OH2) occurs at 28.7 degrees. To add to the difficulty, anhydrite, portlan-
dite, and magnetite occurred to some extent in nearly every sample. Four sam-
ples had X-ray tracks that suggest the possible occurrence of CaS03: the 100-
to 140-mesh and the +lOo-mesh samples from probes 8E and 8W, all from plane CC
(test 25, 8-31-70). One of these tracks is shown in figure 62B. Portlandite
appears to be absent in this sample (fig. 62B), the anhydrite content is low
(small peak at 25.5 degrees), and the peak at 28.8 degrees appears too large to
be accounted for solely from anhydrite. Therefore, the 28.8 degree peak indi-
cates a minor amount of CaS03 is present. However, the 30.8 degree peak of
CaS03 is absent, and the 35.4 peak on the sample track could be produced from
a small amount of magnetite that remained in the sample.
The X-ray peak heights from the samples indicate anhydrite occurs in
nearly the same abundance in both electrostatic and mechanical hoppers; less
anhydrite was found in the CC plane, and the least occurs in samples from
plane AA.
The separation of magnetite and hematite from the ashes by repeated
passing of the sample through the magnetic field was successful in that no iron
oxides were detected by X-ray diffraction in the nonmagnetic fraction. Small
amounts of lime and traces of anhydrite were captured by the magnetic particles
and were detected in the magnetic fraction. The weight percentage of the mag-
netic fraction separated from the samples is given in table 16. Microscope
examination reveals numerous glassy and spherical particles in both magnetic
and nonmagnetic fractions. Those in the magnetic fraction were dark gray to
black, while most of the nonmagnetic spherulites were colorless. These glassy
and amorphous particles account for the broad hump in the base line of the X-ray
pattern between 15 and 22 degrees 2 Q (fig. 62).
The mineral composition of the fly ash samples taken from plane AA in
test 25 differed from that of the first series (66-71). Calcite was abundant
in the coarse fractions in plane AA samples taken during test 25, whereas it
was not detected in samples 66-71. The amount of limestone injected into the
boiler or the temperature of injection probably differed for the two tests.
Certain mineralogical changes in the fly ash apparently occurred dur-
ing cooling. The occurrence of portlandite in the fly ash is the result of the
reaction of small amounts of moisture with the lime, probably during handling
of the sample. The X-ray data suggest that pyrite is present in trace amounts
in samples 45 and 104. This pyrite either survived combustion or reformed dur-
ing cooling of the ash-gas mixture by reaction of gaseous S02 and certain Fe-
rich particles. The increase of approximately 0.5 percent of sulfate sulfur
in the samples from the electrostatic and mechanical hoppers over that of plane
CC (table 17) indicates some growth of anhydrite occurs in the dust below
plane CC.
Studies were made of samples of the normal fly ash of test N (I, II,
and III) to develop a method for rapid analysis of anhydrite-lime relations in
-------
- 61 -
TABLE 17-CHEMICAL ANALYSES OF FLY ASH MATERIALS IN WEIGHT PERCENTAGE*
(Analyses by Analytical Chemistry Section, Illinois State Geological Survey)
Limestone-modified fly ash Normal fly ash
Electrost. Mech. Mech.
Boiler position: AA CC hopper hopper hopper
92-3
Oxide Sample number: 66-71 97-8 106 104 45
Si02 31.2 33.4 46.5 38.8 39.0
A1203 11.19 15.0 18.99 13.94 15.63
Fe203 8.62 8.75 8.07 14.89 31.68
CaO 39.8 30.7 17.1 24.5 10.8
C02 0.49 1. 90 0.93 1.00 0.28
Organic C 4.29 1.00 1.19 0.66 1.32
Sulfate S 0.26 1.52 1. 65 1.68 0.43
Pyritic S 0.07 0.03 0.05 0.10 0.09
Organic S 0.03 0.32 0.33 0.07 T
TOTALt 95.95 92.62 94.81 95.64 99.23
Calculated compounds (%)
Anhydrite (CaS04) 1.1 6.46 7.0 7.1 1.8
Calcite (CaC03) 1.1 4.3 2.1 2.3 0.6
* CaO was determined by X-ray, C02 by gravimetric methods, total C by hi-temp methods,
total S by ESCHKA, sulfate S by dilute HCl treatment, pyritic S by measurement of Fe
in nitric acid solution, organic Sand C by difference.
t Minor amounts of Ti02' MnO, MgO, and K20 probably are present and account for the low
totals.
T None detected.
limestone-modified ash. Oil-immersed, powdered samples were examined in crossed-
polarized light with the Quantimet. Under these conditions, the glassy compo-
nents (isotropic) of the ash appear black. and anhydrite and a few other aniso-
tropic components (principally quartz) appear in their characteristic interference
colors. Image analysis of the quantity and size of anisotropic particles in
normal and limestone-modified samples should provide a means of determining the
content and particle size of anhydrite in limestone-modified ash samples. How-
ever, the amount of quartz and other anisotropic grains varied greatly in the
normal ashes, and the anhydrite grains in modified ashes were too small for
rapid identification and accurate analysis by this method.
-------
- 62 -
Chemical Analyses
Chemical analyses of the fly ash samples are shown in table 17, along
with the percentage of anhydrite in the samples, as calculated from the chem-
ical data. These values for anhydrite are in close agreement with the X-ray
diffraction data. Calcite percentages also were calculated (table 17). The
presence of small amounts of C02 in the samples substantiates the presence of
calcite, especially in sample 92-3, 97-8.
The percentages of the sulfur as S04 and of the organic sulfur in un-
burned coal particles are related to the total sulfur in the ash samples, as
follows:
Percentage of total S as:
Sample
66-71 (plane AA)
92-3, 97-8 (plane CC)
106 (electrostatic hopper)
104 (mechanical hopper)
45 (normal ash, mechanical
hopper)
Organic S
8
17
16
4
o
S04
72
81
81
91
83
The reason for the relatively low proportion of organic sulfur in
plane AA compared to that in the other limestone-modified ash samples is not
lmown. Because of fairly wide variation in these figures, detailed analyses
of the various species of sulfur in fly ash samples, including organic S,
should be made in future studies.
The average of the analytical results of the nonmagnetic and magnetic
fractions of normal fly ash samples from mechanical hopper 3, test N, III (table
18) show only slight differences in composition from sample 45. Two samples from
electrostatic hoppers 3 and 7 also were analyzed (table 18). The particles from
the electrostatic hoppers were too fine for a good magnetic separation. The
analyses of these two samples are very similar; none of the elements differ sig-
nificantly. The magnetic fraction in the sample from mechanical hopper 3 was
found to contain 66.5 percent iron oxide, which is equivalent to 46.5 percent
iron.
Another series of limestone-modified fly ash samples (tests 2 through
8) was selected to evaluate the characteristics of the lime-anhydrite particles.
Initially, special attention was to be given to the differences in crystal mor-
phology of particles obtained from the AA and CC planes within the TVA boiler;
however, the X-ray diffraction data indicated much of the lime in the samples
had been hydrated to portlandi te. Therefore, only chemical analyses were per-
formed on these samples. These data (table 19) were subjected to statistical
analyses to evaluate the dispersion of particles in planes AA and CC because
various areas in the two boiler planes were sampled by a number of different
probes.
Statistical analyses of the results from standard analysis of variance
methods (Snedecor, 1946) led to the following conclusions:
1.
There was no significant differences in CaO in plane AA
between tests 2, 4, 6, and 8, as evaluated by the means
of the various probe samples.
-------
- 63 -
TABLE 18-CHEMICAL ANALYSES OF NORMAL FLY ASHES (TEST N)
TAKEN FROM SHAWNEE UNIT 10, JUNE 1, 1970
(Analyses by Analytical Chemistry Section, Illinois State Geological Survey)
Test N: I II III
Mechanical hopper 3
Electrostatic Electrostatic
Oxide hopper 7 hopper 3 Magnetic Nonmagnetic Average
Si02 50.8 52.1 19.7 50.6 35.1
Ti02 1.10 1.10 0.4-0 0.85 0.6
A1203 23.5 23.3 8.4-6 20.8 14-.7
Fe203 12.0 12.1 66.5 5.38 36.0
MnO 0.15 0.15 0.80 0.07 0.4-
MgO 0.4-4- 0.83 0.53 0.17 0.4-
CaO 4-.98 3.89 2.17 15.3 8.8
K20 2.61 2.61 0.77 2.29 1.5
P205 0.23 0.34- 0.09 0.01 0.05
C02 0.19 0.10 0.23 0.50 0.4-
Organic C 3.4-6 2.90 0.35 3.89 2.1
S03 0.01 0.03 0.03 0.03 0.03
Pyritic S 0.11 0.10 0.17 0.01 0.09
Organic S 0.32 0.4-5 0 0.32 0.16
TOTAL 99.90 100.0 100.2 100.22
2.
There was no significant difference in CaO as sampled at
the various probe positions in plane AA at the 99 percent
confidence level. At the 95 percent confidence level the
difference between probes 6AE + 7 AE and 4AE + 5AE may be
important, for it implies there may be some degree of non-
uniformity of CaO in plane AA as sampled by the probes.
3.
There was a significant increase in the sulfur content in
plane AA between test runs 2 and 8. test run 8 being high
in sulfur.
4.
No significant differences were found in the sulfate sul-
fur from various probes in plane AA.
5.
No significant differences in level of sulfate sulfur was
found to occur in probes 8w 1. 2. 3 and 8E 1, 2, 3.
6.
Plane CC contains significantly higher levels of sulfate
sulfur and C02 than plane AA.
-------
TABLE 19-CHEMICAL ANALYSES OF LIMESTONE-MODIFIED FLY ASH SAMPLES
FROM PLANES AA AND CC FROM UNIT 10, SHAWNEE STEAM PLANT
(Analyses by Analytical Chemistry Section, Illinois State Geological Survey)
Sample Weight percentage
identification
and date Plane Probes CaO C02 S03 Organic C Total S* S as 304 Organic S
Test 2 (5-13-70)
I AA 6AE + 7AE 34.6 3.56 1.30 5.77 0.87 0.52 0.24
II 6AW + 7AW 37.7 2.57 1.20 2.82 0.78 0.48 0.30
III 4AW + 5AW 41. 0 2.38 1.12 4.58 0.73 0.45 0.28
IV 4AE + 5AE 36.7 2.18 0.80 5.02 0.58 0.32 0.26
V CC 8w 1,2,3 31.3 3.56 5.04 2.52 2.64 2.02 0.62
VI 8E 1,2,3 36.6 3.96 4.72 2.71 2.39 1.89 0.50
Test 4 (5-21-70)
I AA 6AE + 7AE 37.8 3.56 0.87 4.95 0.54 0.35 0.19
II 6AW + 7AW 36.6 3.37 0.87 4.91 0.57 0.35 0.22
III 4AW + 5AW 42.9 2.57 0.82 7.61 0.63 0.33 0.30
4AE + 5AE 44.6 3.56 3.60 0.47 0.36 0\
IV 0.90 0.11 +:-
V cc 8w 1,2,3 32.8 4.36 2.80 3.51 1.90 1.12 0.78
VI 8E 1,2,3 35.6 4.16 3.15 2.71 1. 66 1.26 0.39
Test 6 (5-27-70)
I AA 6AE + 7AE 34.7 2.18 0.80 4.53 0.44 0.32 0.12
II 6AW + 7AW 39.7 1.98 0.60 4.67 0.29 0.22 0.06
III 4AW + 5AW 37.3 1. 98 0.80 9.00 0.63 0.32 0.30
IV 4AE + 5AE 45.1 1. 78 0.47 4.10 0.44 0.19 0.24
V cc 8w 1,2 39.9 2.77 2.07 1. 34 1.16 0.83 0.33
VI 8E 1,2 29.4 2.77 2.07 5.08 1. 07 0.83 0.23
Test 8, run 2 (6-2-70)
I AA 6AE + 7AE 35.1 1.58 0.57 3.84 0.33 0.23 0.09
II 6AW + 7AW 40.3 1.98 0.70 4.07 0.39 0.28 0.10
III 4AW + 5AW 39.4 1.39 0.75 6.02 0.51 0.30 0.20
IV 4AE + 5AE 47.2 1.98 0.90 5.24 0.66 0.36 0.30
V CC 8W2 + 8W3 43.9 2.57 2.00 2.05 1.51 0.80 0.70
VI 8E2 + 8E3 24.9 2.97 2.87 3.31 1.19 1.15 0.03
* S as pyritic sulfur was found to be less than 0.01% in all samples except Test 4-1, in which none was detected.
-------
- 65 -
7.
The ratios of the mean sulfate sulfur in planes CC to
AA in tests 2. 4. 6, and 8 indicate the order of increas-
ing amount of reaction between lime and S02 in the
boiler:
test 6 < test 4 = test 8 < test 2.
Thus the conditions in the boiler were most favurable
for sorption of sulfur during test 2.
Grain Size Distribution
Particle size analyses of the samples taken during test 25 are given
in table 20. The samples were sieved by ultrasonic vibration. and the weight
percentage of the various intervals was determined. The size distribution of
particles smaller than 44 ~ were analyzed by number of particles with the
Quantimet.
Differences in the particle size distribution from the various probes
in plane AA are not significant, but the difference between the distribution of
probes in planes AA and CC are considerable. The data in table 20 indicate
there is nearly twice as much material in the range 44 to 63 ~ in plane CC as
in plane AA. This fact is more clearly shown by the histograms in figure 63.
In CC samples. 37.5 percent (by weight) of the material is coarser than 44 ~,
whereas in AA samples, 25.5 percent is coarser than 44~. This enlargement of
grains is likely due to agglomeration of normal fly ash dust particles (fig. 64)
and possibly also to the conversion of the surface of some of the lime particles.
However, the average frequency (by number) of particles less than 4 ~ in the
CC plane is somewhat larger than in the AA plane (table 20).
The anhydrite content of the samples taken during test 25 varies accord-
ing to particle size of the ash. In plane CC the anhydrite-to-lime ratio is high
for the particles greater than 149 ~ and for those less than 63 ~. compared with
those in the 63 to 149 ~ range. The anhydrite grains are mainly submicron to,
possibly, 2 microns in size. The high anhydrite content in the coarser sieve
fraction is due to the adherence of very small particles to the surfaces of
large particles of lime.
Electron Microscopy of Limestone-Modified Fly Ash
Observations from scanning electron microscope studies of limestone-
modified fly ash samples, in connection with phase III of the project. were made
from approximately 130 micrographs, 25 of which were selected and reproduced
herein (figs. 64-68) to show the surface character of typical particles and cer-
tain special features. The discussion and interpretation of the micrographs are
partly based on recent results obtained from the X-ray spectrometer attached to
the scanning electron microscope. However, the specific samples illustrated
were not analyzed with the X-ray apparatus.
Figure 64 shows typical particles found in normal fly ash obtained
from the mechanical hopper (sample 45). They consist of very small spheru-
lites with a fairly smooth-textured outer surface and some larger spherulites
-------
TABLE 20--PARTICLE SIZE ANALYSES OF FLY ASH SAMPLES FROM VARIOUS PROBES INTO PLANES AA AND CC.
TEST 25, AUGUST 31, 1970, SHAWNEE PLANT, KENTUCKY.
6AE-7AE 4-AE-5AE 5 AW-4-AW 6AW-7 AW BE-l,2,3 SW-l,2,3
Screen and AA Plane AA Plane AA Plane AA Plane CC Plane CC Plane Average
particle size
(1-1) Weight percentage retained on screen AA cc
+14-9 1.36 1. 68 2.55 3.21 2.09 0.70 2.20 1.4-
+105 1.68 2.07 2.4-6 2.57 2.71 1.11 2.20 1.9
+ 88 2.38 3.34- 3.16 3.74- 3.93 5.20 3.2 4-.6
+ 74- 2.77 4-.30 4.18 3.89 5.4-1 4-.4-2 3.8 4-.9
+ 63 2.13 2.93 3.11 2.50 3.84- 2.30 2.7 3.1 I
0'\
+ 4-4- 10.58 13.80 10.85 10.55 22.55 20.67 11.4- 21.6 0'\
I
Pan 79.10 71.88 73.69 73.54- 59.47 65.60 74-.6 62.5
Size intervals
(1-1) Number of particles in percent
4-4--31 2 4 4- 4- 1 1 3.5 1
31-16 9 7 15 11 6 8 10.5 7
16-8 27 24- 27 28 20 35 26.5 28
8-4- 50 4-6 4-3 4-7 53 37 4-6.6 4-5
4--0 12 19 11 10 20 19 12.9 19
-------
74.6%
40
~
~
~ 30
c:
Q)
:3
~ 20
~
LL..
Plane AA
10
62.5%
50
~ 40
~
>.
o
~ 30
:3
0-
Q)
~
LL.. 20
Plane CC
10
210
149 105 88 74 63
Particle size. fL
44
Fig. 63. Particle-size distribu-
tion of limestone-modified fly
ash in boiler planes AA and CC.
test 25.
- 67 -
with scattered pits and small holes
(fig. 64A, B, and C). Larger spheres
are hollow and usually contain smaller
particles of fly ash (fig. 64B, C,
and D). Many spheres of various sizes
have a granuJ.ar-textured surface, best
shown in figure 64B. The iron content
of these particles probably varies
considerably, as their color in ordi-
nary light ranges from colorless to
dark black. Qualitative chemical anal-
yses of a number of relatively smooth
and spherical fly ash particles indi-
cate they are mainly Si, AI, and Fe,
in order of relative abundance.
o
The next most abundant type of
particle is one characterized as vesic-
ular slag (fig. 64D and fig. 65A and B).
These particles are irregular in shape.
but broken shells of the smooth spheru-
lites may also be vesicular, as shown
by the large particle in the lower right
quarter of figure 64D. Figure 65 shows
typical micrographs of limestone-modi-
fied fly ash from the mechanical hopper
(sample 104). Over 90 percent of this
sample appears to consist of normal ash
particles. A few black and vesicular
particles were observed in sample 104
(fig. 65A) that closely resemble slag,
but because of their color it is thought
these are unburned coal fragments. A
variety of surface textures occur on par-
ticles in the limestone-modified fly ash
samples that were not observed on normal
particles (fig. 65C, D. and E).
Positive identification of the crystallites shown as epitaxial growths
on spherulite surfaces in these pictures cannot be made at this time; however,
the crystallites may be anhydrite. Figure 65F is a close-up view of a portion
of a spheruli t e that is partly smooth and partly granular. The granularity may
be due to the presence of lime and/or sulfated lime. The cavity in the center
of this sphere contains platy and spherical fly ash particles. The two large
spherulites (fig. 65H) have granular coatings that might be sulfated lime; how-
ever, the larger one resembles others observed in normal ash (fig. 64B).
Figure 66 shows particles in modified fly ash (sample 104). Micrographs
B and C are typical views of the sample; C is mainly slag-type ash and B is mainly
spherulites. Micrographs A and D are of particles thought to consist of lime and
sulfated lime. Figure 66 A indicates some degree of sintering of the constituent
grains on the surface of the particle; D shows less sintering and a more porous
particle with normal ash spherulites attached to it.
-------
r- jr~~~"
~...~
~
t :~
~".
., ..,
f' w ~
~
i
V-~
~" :iJJ
~
'"
....
Fit"';. 64.. No r'ffi,J.l f:!.y ash paI.ti(~:;. es t ~p-chanical hopper' (sample l.~5)..
Q")
=
-------
.ji!'J"~T-~,
--\
!L'<
. '.:1' ~ L..-.I 0 fl ---1
*">~ ",'
Pig.. 65..
- ---
,,'
J
*
.Jil'.1-,
(J')
LD
LiITleston2-modii'ied fly ash, mechanical hopper (sample J ~-)"
-------
. ,,~.{
,~k,~
~t~
./~'; ij...
~.4 ~....:I'
':'\
.... .. \"t \"
,. t,."
" /f.",'i 1 ...
B .
Fig. 66,
1:Lc,c:,stvne-no<'1ii'Jed f'l;y ash, ",>echmJeal t,,)PP'2~' (sa'.~.ple l:YL).
'oJ
o
I
-------
- 71 -
Figure 67 shows particles that occur in limestone-modified ash from
plane AA inside the boiler (sample 66-71). The granular (nonspherical) parti-
cles in A and B may be limestone-derived material. Micrographs C and D show
mainly siliceous spherulite material; however, the coating on the lower part
of the 10 ~ spherulite near the center of C shows evidence of chemical activity,
possibly sulfation. The large spherulites shown in C and D prove that pitting
and complex cavities in fly ash spherulites develop very early in the formation
of the ash, plane AA being at the top of the fire box in the boiler.
Figure 68A and C show particles taken from plane CC, probes 8E-l, 2,
and 3, during test 2 of limestone injection on May 13, 1970. The micrographs
are close-up pictures of particles that appear to contain sulfated lime. The
granular and partly sintered texture is the basis of this interpretation. None
of the particles from the CC plane could be identified from SEM observations as
CaS°3. The insert in A shows fibrous portlandite (CaOH) in the sample. Moisture
was permitted to react with the lime in this sample prior to examination.
Figure 68B and D show typical particles that occur in samples taken
from the electrostatic hopper (sample 106). They consist mainly of alumina-
silica spherulites. Sulfated lime particles (anhydrite) are known from X-ray
diffraction data to occur in this sample. but none could be positively identi-
fied under the scanning electron microscope. Possibly the very fine particles
that are attached as granular dust on larger spherulites, shown in the lower
half of figure 68D, are anhydrite.
Studies of Boiler Deposits
During the course of injection of pulverized limestone into the boiler
at the Shawnee Steam Plant i ~ was noted in May 1970 by TVA engineers that a build-
up of deposits was occurring. Inspection of the boiler in June showed consider-
able deposits had formed on the fire side of the reheat section. Petrographic
examination of a few specimens of these deposits was made by the author. Since
the specific orientation of the specimens relative to the steam pipes was not
known and was considered important to the interpretation of the data, additional
specimens were collected from the boiler during the next scheduled shut-down in
September 1970. The results of petrographic and chemical studies of the speci-
mens follow.
Deposits Collected September 1970
The spatial relation of the pipes in the reheat section is indicated
in figure 69A. By and large, the front side of the pipes was as free of deposits
as the back side shown in the photograph. However. a few areas on the front
and rear sides of the reheat section, about midway from the s ides of the boiler,
did have a hard material deposited on the fire side of the pipes. Eleven sam-
ples of these deposits were taken. Several specimens were separated into sub-
samples after preliminary microscope study, and chemical and mineralogical anal-
yses were made of these subsamples. The results of these tests are given in
table 21.
The deposits extended along the axis of the pipes for several feet
and were triangular in cross section, as shown in figure 69B. Their shape is
-------
I. ,-
~ ,"~;J .. ..
... .J. ......"
- J.""""
.,.. I i,l...'1-
.. \.
..
All< ." ~
....
..
.;
~~ ,.
~,...
..
.,.
1<
~
r
.
!'
"Hr >
,
o
..~
~
~
"-J
N
.,
"
I
.'
i:ig.. 67.
lJll!1.€s,:;one-re1id:Lfied fly 8.SQ, plan€ Aft. (sa.rnp:u:: 66-71) ~
- - - - - --
-------
- -:-- -..:J
...
- r:.~ ~.., ." ,,', ft'...' ...-.,,' ' ,~- r,,-.
l '.. \
. . '..... , \
. ~.. 'A .,., I
, ~
,
51"
1- ._-_J
,t#
~
,
-..J
W
Hi!!.. 6tL A 3.n<1 G - L1.mesto:nQ-~oclified fly aBh, r1 ~ne CO (sample 92-"), 97-8}; 13 and D >- Li;,:t~st0De-rnodi;t'ied
:f.']y ;1811, e.Le()l.~'o8t2,~ir; hi.JppoI' (88.1:\pJe l()6).
...
<'.J
10"
L._,.-1
-------
- 74 -
,
... -
layer
c:
Direction of
gas flow
Fig. 69. A. View of the back side of the reheat section through
an entry port. B. Cross section of a steam pipe with its
attached deposit, showing the shape and layered structure of
the deposit. Note the location of zones I and II in relation
to the inner layer deposits.
-------
TABLE 21-CHEMICAL AND MINERAL ANALYSES OF FIRE-SIDE BOILER DEPOSITS IN WEIGHT PERCENTAGE
Inner layer Outer layer Mixed layer Dark
White (Zone I) Reddish brown (Zone II) Buff + brownt Buff Brownt gray
front
Position: * F B B F screenT
F F' F F F F F F' B
Sample: 4A 1 2 3A-l 5A-l 8B 3A-2 4B 3B-2 3B-l 5B 8A 6 7B
3i02 8.73 10.50 9.91 22.73 17.20 16.68 8.20 7.12 7.16 8.96 27.22 45.70 43.36 42.15
A1203 3.93 4.16 3.89 10.57 7.50 7.57 lJ-.50 2.89 2.90 lJ-.20 10.6lJ- 17.28 19.4lJ- 18.07
Fe203 2.74 2.42 2.04 6.37 7.42 5.23 2.29 2.01 2.43 2.60 10.69 14.90 14.81 17.18
MgO 0.05 0.52 0.25 1.08 0.54 0.29 0.55 1.19 1.12 0.83
CaO 36.26 35.96 35.26 22.95 25.63 31.lJ-0 36.7lJ- 41. 23 36.79 36.34- 18.52 7.4-0 6.11 14-.33
K20 0.44 0.62 0.56 1.40 0.97 0.96 0.43 0.28 0.39 0.47 1.56 2.27 2.61 1.84
Na20 0.31 0.15 0.56 0.50 0.46 0.38 0.09 0.22 0.20 0.27 0.66 1.13 1. 24- 1.20
303 4- 6.73 43.27 45.51 33.66 35.74- 31. 06 lJ-2.69 lJ-lJ-.73 4-7.4-8 4-1. 4- 0 26.28 8.67 7.89 1. 99
TOTAL 99.4-1 97.13 98.25 98.18 95.17 94-.36 94-.94 99.02 97.35 94-.53 96.12 98.54- 96.58 97.59
**
Anhydrite XXX XXX XXX XX XX XX XXX XXX XXX XXX XX X X X
Quartz X X X X X X X X XX XX XX XX
Hematite X X X X X X X X XX XX XX
Magnetite (?) X XX X
Calcite X X X X
Lime X X X X X X XX
* Samples from the front of the reheat section of the boiler are indicated by F, those from the back side by B. F' indicates the sample
came from the second row of pipes in the front of the reheat section.
t The brown material is the outermost crust of the deposit.
f The section of pipes in front of the reheat section. This sample is vesicular slag.
** The number of XIs indicate the relative abundance based on X-ray data, XXX is the most abundant and X the least.
-------
lONE I
~ ZDNE. :II
, "<
\
INNER
LA Yf: R
- .
.....
"
"
- 76 -
--
----.
I
...~}
,';'" .
.'
,:
6
~;~,
-------
- 77 -
essentially isosceles, with the apex pointing toward the fire side of the boiler,
opposite to the direction of gas flow. The base of the triangle is attached to
the pipe and is concave, owing to the curvature of the pipe. The typical shape
of the samples is illustrated in figure 70. The specimen in the lower right of
the figure shows a small double ridge on the apex of the triangle. This shape
was observed by Bishop (1968) in laboratory tests simulating boiler deposition
within a period of one hour after start of the test.
The deposits are characterized by two layers: an inner layer (Anderson
and Diehl, 1955), also known as the primary layer (Bishop. 1968), which occurs
adjacent to the steam pipe (fig. 69B), and an outer layer that forms the main
body of the deposit. The outer layer is itself finely laminated and the outer-
most surface of the outer layer forms a brown and relatively hard crust. The
inner and outer layers are distinguished by differences in color. The inner
layer is primarily off-white, whereas the outer layer is mainly buff. Distinc-
tion between the two layers is not obvious on the sides of the pipes where the
deposit is thinnest. and the boundary between the two layers grades from about
1 to 2 mm on the front side of the pipe where the deposit is thickest.
Inner Layer Material
The composition of the material adjacent to the pipe depends on its
position on the surface of the pipe. The various positions of the pipe surface
were divided into zones (fig. 69B). The actual distribution of the materials
deposited in the various zones can be seen on the specimens (figs. 70 and 71).
Zone I is on the front side of the pipe and generally extends through an arc
of about 100 degrees. The inner layer material in zone I is white to light
gray, soft, microporous, and granular. X-ray studies indicate it is largely
anhydrite. Electron microscopy of the inner white material shows irregularly
shaped anhydrite grains 0.2 to 1 ~ across and spherical ash particles (fig. 72A).
Many anhydrite particles occur as individual grains and others are agglomerates
of 2 to 10 grains. The surfaces of the glassy fly ash spheres (fig. 72A) are
coated with a granular material. probably anhydrite. The electron micros cope
examination also shows the white material has a relatively high porosity, which
accounts for the observed softness. The white layer was not observed on one
sample (3A), which was collected on the front of the reheat section, just l~
feet below sample 4, which had a well developed white layer. In sample 3A, an
iron-rich scale occurred partly on the front side of the pipe.
The chemical analyses and mineral components of three different sam-
ples of the white inner layer are given in table 21. The X-ray and chemical data
show these samples consist of 74 to 80 percent anhydrite (CaS04) and traces of
quartz, hematite. calcite, and lime. The spherical particles of fly ash occur-
ring in this zone account for the alumina and most of the silica in the chemical
analyses. Sodium and potassium oxide contents are low in zone I.
Zone II of the inner layer is characterized by a deposit of a mottled,
reddish brown, scale-like material about 1 mm thick (fig. 71), or by small blebs
of reddish brown material interspersed with white anhydrite, as shown on the
two upper fragments in figure 70. It may be significant that the iron-rich scale
was not observed in samples that had the white inner layer, whereas iron blebs
were always associated with the white layer. Electron microscope studies show
the reddish brown scale has a matted appearance (fig. 72B). Observations at
-------
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~.~ ~.....'
I .~
. . ~-!&
I ..,;,",\'
ZONe .Jr
iti ...~,;~
>- "-".t.
...~,
':11
-"
r;
" J
~ .~
'"
ZDNE I
>-
I'
Fie:. {1.
- 78 -
..
14
~
1
~~
~_k;j'Or;
f"
.
,
,
. 'I"
J ,.
.
~
""
,
~
J:J. !
\oJ"
~
Inner layer of Qcposit showine the iron-cxide scale in zone II.
,.
--- -
-------
- 79 -
ultra-high magnifications (not illustrated) show a high degree of interlocking
of grains within these matted areas. The matted and interlocked grains may be
anhydrite or hematite. and the texture indicates notable sintering of the
material has occurred. Figure 72B shows that normal fly ash spherulites also
occur in zone II of the inner layer.
Chemical analyses of the reddish brown scale are listed under sam-
ples 3A-l, 5A-l, and 8B in table 21. This material is characterized by its
high iron oxide, silica, and alumina contents. Anhydrite represents only 53
to 61 percent of the brown scale in zone II.
Examination of the brown blebs in zone II shows the material has dis-
tinct. platy grain shape (fig. 72C), and X-ray data suggest the main constituent
in these blebs is hematite. The white areas around the iron blebs in zone II
are essentially the same as those in zone I. The hematite blebs are observed
in samples from both the front and back of the reheat section.
Outer Layer Material
The outer layer grades from a light buff next to the inner layer
through deepening shades of buff to a brown on the outer surface. The contact
between the inner white and the outer buff layers is gradational for a distance
of about 2 mm in the center of the fire side of the steam pipe. The contact of
the outermost brown crust and the main "buff material is quite sharp. The outer-
most crust of the outer layer is relatively hard, but chemically does not differ
significantly from the buff material (compare chemical data on samples 3B-l.
3B-2, 3A-2, and 4B). The outer layer is porous and composed of agglomerates of
individual 1 ~ grains of anhydrite (fig. 72D and E). Few of the grains have
well formed crystal surfaces (fig. 72E), most are subrounded, and little fusion
of grains (sintering) occurred.
Deposits Collected June 1970
Several specimens were obtained from the boiler during the shut-down
period in June 1970. By comparison with the oriented specimens, the June sam-
ples, with few exceptions, are judged to consist of only the outer layer. The
specimens are a buff to brown, very fine grained, soft, porous mixture of anhy-
dri te and normal fly ash components. Thin sections examined in transmitted light
and magnified 25 times appear in figure 73A. Interlayered with these particulate
materials are a few very thin dark gray bands composed of ultrafine-grained or
amorphous matter (upper left corner of fig. 73A). These thin dark gray bands
may consist of hematite or, possibly, carbonaceous matter. A few specks of
transparent fly ash particles are enclosed in the dark bands (fig. 73A). Two,
three, or four such bands could be recognized in cross sections of the specimens
examined. The main body of the buff material is finely laminated, as in the
outer layer in samples obtained in September.
The outermost crust of several of the specimens has a corrugated surface
coated with a dark gray material that appears identical to the interior bands.
Under the microscope this surface has a smooth texture and the anhydrite grain
boundaries are very indistinct (lower right corner in fig. 73B). The upper left
of figure 73B shows the edge of one of several pits that occur on the corrugated
surfaces. Fly ash spherulites can be recognized in these pits.
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- ~ -
EXPLANATION OF FIGURE 72
A.
Broken surface of the light gray inner layer of zone I showing
the fine granularity of the anhydrite (0.2 to 1 ~ diameter) and
spherical fly ash particles coated with anhydrite. Electron
micrograph of sample 4A, X5500.
B.
Innermost surface of reddish brown scale showing mixture of normal
fly ash components and recrystallized iron mat in center, probably
compound of hematite and anhydrite. Electron micrograph of sample
3A-I, X4500.
C.
Innermost surface of a reddish brown bleb showing platy form of
the iron, probably hematite. Electron micrograph, specimen sep-
arated from sample 4 (see fig. 69), X4680.
D.
Broken surface of the buff-colored outer layer showing the gran-
ular character of the anhydrite grains that constitute 80 percent
of the specimen. CaS04 occurs mainly as individual grains and as
a few small agglomerated grains. The specimen also has considerable
porosity. Electron micrograph, sample 4, X1300.
E.
Close-up view of same specimen as in D showing the occurrence of
individual grains and small agglomerates of several grains. Elec-
tron micrograph, X4760.
F.
Broken surface of white anhydrite adjacent to hematitic bleb in
zone II. Note the presence of several agglomerate particles show-
ing little or no porosity. This is probably due to incipient sin-
tering of the anhydrite in this area of the deposit. Electron
micrograph, x1870.
-------
- 81 -
i'c
?ig. 72
- ScanXJ.i.ng 6'~ec t~or" m:.eI'og::'
-------
- 82 -
EXPLANATION OF FIGURE 73
A.
Finely laminated structure in the buff outer layer. The
dark bands probably contain some hematite and possibly
carbonaceous matter. The small light grains are anhydrite
and transparent fly ash particles. Few opaque fly ash
particles are embedded in anhydrite in the lower left.
The two circles in the upper right are air bubbles in the
immersion oil. Transmitted light, x26.
B.
Outer surface of a corrugated outer crust s.howing a smooth
surface in the lower right and the edge of a pit in the
upper left with normal fly ash particles coating the pit
surface. Electron micrograph, X5525.
c.
Fracture surface of buff outer layer showing
lized and interlocking grains of anhydrite.
is indicative of sintering action. Electron
x2660.
well crystal-
This texture
micrograph,
D.
Same specimen as figure 13, showing the variability of the
porosity and grain size of the recrystallized anhydrite.
Electron micrograph, X2465.
E.
Anhydrite crystal on a fracture surface of a glassy area,
probably in inner layer, zone II. Electron micrograph,
X2465.
F.
Detail of same specimen as figure 15, showing
and partly granular character of the iron-rich
Electron micrograph, X5355.
the smooth
inner layer.
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- 83 -
-- - -- -
- -- --
73 - Micrographs sho;!i.ng the natuI"-) of' bo:L1.er deposits collected June 1970.
Fig.
!
,\
.tIf!.
,.'"
,."'"
'-'>,
:S#:~;'/
"
h", 11
.-11
2fL
L-!...-l
~.
:f~
,,," ~
"
-------
- 84 -
Broken surfaces of the buff material (outer layer) consist of well
crystallized and tightly interlocking anhydrite grains (fig. 73C and D). The
grain size of the anhydrite, where distinct grains could be recognized, ranges
from about 1 to 10~. From the electron microscope observations, the porosity
appears to vary considerably from point to point in any given specimen. One
specimen thought to represent zone II of the inner layer showed patches of
brown, glas sy material surrounded by the soft, brown anhydrite. At high mag-
nification, these glassy areas are very smooth, as illustrated in the background
of figure 73E and F. Bladed crystals of anhydrite were observed on broken sur-
faces of the glassy areas (fig. 73E).
Concluding Remarks on Boiler Deposits
The fire side boiler deposits observed September 14, 1970, in the re-
heat section of Unit 10 of the Shawnee Steam Plant were not large enough to sig-
nificantly deter the passage of flue gases. The deposits that were present had
distinct inner and outer layers. The inner layer contains two types of materials,
a reddish brown, iron-rich material and a light gray to white, soft, granular
material. The iron material occurs in an arcuate zone on both sides of the pipes
and near the thin edges of the deposit. Two forms of iron occur, (1) small red-
dish brown blebs of platy hematite embedded in white, fine granular anhydrite,
and (2) a thin scale. The light gray to white material is the most abundant
constituent in the inner layer, occurs on the front side of the pipe, and is com-
posed mainly of 1 ~ granular anhydrite particles mixed with siliceous spherulites,
which are common in normal fly ash. The range of chemical and mineralogical data
of the gray to white inner layer overlaps that of the buff outer layer. The iron
oxide content of the white inner layer is about the same as that in the outer
buff layer. The mean concentration of K20 of the inner zone I (0.83 percent) is
higher than in the outer layer (0.39 percent). and a similar relation holds for
the Na20 values. However, these oxides are most abundant in samples containing
the most normal fly ash constituents--quartz, hematite, and magnetite (samples 6
and 8A). Anderson and Diehl (1955) observed much higher enrichments of sodium
and potassium in the inner layer in their studies than those reported here.
The apparent porosity and grain shapes of the September anhydrite sam-
ples (fig. 72D and E) are quite different from those observed (fig. 73C and D)
in the June samples. The outer layer in the June samples contained well crystal-
lized and tightly interlocking grains of anhydrite, indicative of considerable
sintering and grain growth.
The observed enrichment of iron oxide in zone II of the inner layer
appears to be unique in these deposits. Furthermore, the iron-rich blebs are
definitely associated with a well developed white to light gray inner layer,
whereas the iron-rich scale occurred in no samples containing a distinct white
inner layer. Anderson and Diehl noted significant amounts of iron oxide in the
inner layer on several fire side deposits. Basing their conclusions on the weight
gained in laboratory experiments designed to simulate the boiler conditions,
Anderson and Diehl concluded that sodium-potassium-iron sulfates had formed in
fly ash and flue gas mixtures at temperatures ranging from 1000 to 1200° F. Like
them, we detected no iron sulfates by X-ray diffraction. Calculation of the
CaS04 content from the chemical analyses of the inner layer samples (table 21)
shows excess CaO in all samples except 3A-l. In that sample a deficiency was
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- 85 -
found, leaving 0.9 percent S03 that may be combined with iron. In contrast.
the other two iron-rich samples from the inner layer (samples 8B and 5A-l)
yield excess CaO with respect to S03. The interlocking granular texture of
the iron-rich specimens from the inner layer (fig. 12B and C) supports the
conclusion that hematite is the predominant form of iron; however. the possi-
bility that small amounts of very poorly crystalline or glassy masses of iron
sulfates occur in the samples is not ruled out.
SUMMARY AND CONCLUSIONS
Petrography and Reactivity
Petrographic properties of the various carbonate rocks observed in
this study reveal correlations with the S02 sorption capacity (3~ hr. reaction
period) -
The pore volume of carbonate rocks appears to be an important index
property to the sorption capacity of a rock. The greater the total pore volume
of the carbonate rock, especially when pores are between 2 and 16 ~ in diameter,
the greater its capacity for reacting with S02 in the fixed-bed tests. In sup-
port of this conclusion. the data on two porous dolomite samples show that they
had high S02 reactivity in spite of moderate amounts of inert clay and quartz
impurities. Six high-purity dolomites, each consisting for the most part of
tightly interlocking rhombic to anhedral grains of dolomite containing many
intergranular voids, had an average S02 sorption capacity of 10.3 grams per 20
grams of calcine, whereas two dolomites containing 10 to 15 percent clay and
quartz had an average reactivity of 14.3 g/20 g of calcine. The pore structure
of these samples appears to be more influential in their S02 behavior than does
their degree of mineral or chemical purity.
Of the limestones tested, those containing crinoidal fossil fragments
had the highest S02 sorption capacity. The positive influence of the crinoidal
grains is probably due to the presence of voids wi thin the grains that make the
calcine more porous. These voids probably also contain most of the sodium-
bearing soluble salts.
Comparison between the crystallographically "perfect" Iceland spar
calcite (type 1) and the calcite spar sample, which contains abundant intra-
crystalline voids and twin lamellae (type 2), also supports the positive influ-
ence of voids on sorptive capacity, type 2 having more than twice the capacity
for S02 sorption of type 1. The pores in carbonate rocks are believed to re-
main as pores through the early, and possibly the middle, stages of calcination.
Two samples of marl, a chalk, and the aragonite proved to be excep-
tions to the pore volume-capacity rule. However, the pore volume measurements
in these high-capacity samples are probably erroneously low, for 20 other sam-
ples of carbonate rocks conform to this rule.
The grain size of carbonate rocks is also a useful index of S02 sorp-
tion capacity. In general. the finer the grain size the higher the S02 capacity.
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- 86 -
The coarsest grained samples--Iceland spar, calcite spar, and marb le--h ad an
average capacity of 8.2 g/20 g calcine, whereas the very fine-grained marls,
chalks, and oolitic aragonite have an average capacity of 15 g/20 g. However,
the limestones are an example of an opposite but explainable trend related to
the occurrence of void inclusions in crinoid fragments present in the lime-
stones.
Of particular importance is the observed tendency of the samples with
high sodium content to have high sorption capacities. Minor to trace amounts
of sodium, frequently present in carbonate rocks as soluble salts and located
along grain boundaries and in fluid inclusions within grains (Lamar and Schrode,
1953), may act as a catalytic or fluxing agent to produce a more porous calcine.
Petrographic interpretations of the differential reactivities (120-
second reaction period) are not clear. Of the five high-purity dolomites that
are nearly identical petrographically, four have differential reactivities rang-
ing from 6.3 to 9.3 mg S03/30 mg calcine. The fifth (type 5) has a reactivity
of 17.0 mg S03/30 mg calcine. In addition, although the very fine-grained and
dense limestone (type 4) is completely different from the coarse crinoidal lime-
stone (type 3) in texture, their S02 differential reactivities are nearly iden-
tical. Differential reactivities are thought to result from slight differences
in pore structure of the calcines that result in changes in rate of reaction
during the first few tens of seconds of exposure to S02' These changes give
rise to notable differences in the degree of sulfation after a reaction period
of 120 seconds. Evaluation of reacted calcines at a constant degree of sulfate
loading enabled Borgwardt (1970b) to correlate the differential reactivity with
the surface area measurements of the calcines.
The product of the reaction of calcines of carbonate rocks with S02
in laboratory tests conducted at 1800° F was found to be anhydrite (CaS04)'
Two types of reactions were observed by a scanning electron microscope equipped
with an X-ray spectrum analyzer. The calcines of the nonporous Iceland spar
calcite (type 1) absorbed sulfur only on the outer surface of the particles,
while the calcines of a porous limestone (type 3) absorbed sulfur throughout
the particles. This supports the conclusion that the pore structure of the rock
is maintained through the reactive stage of the calcine.
Fly Ash and Boiler Deposits
Anhydrite was the only sulfur-bearing compound positively detected in
the fly ash samples that is believed to have been formed by reaction of S02 in
the flue gas with CaO derived from the limestone that was injected into the
boiler. Some evidence also suggests the presence of trace amounts of CaS03 in
the coarse particles in plane CC in the boiler; no evidence for CaS03 in plane
AA was observed. The size of the anhydrite particles is submicron to about 2
microns in diameter. However, X-ray data show notable percentages of anhydrite
in the coarse sieve sizes owing to sintering of crystallites of anhydrite on
surfaces of large lime particles. The crystal structure of the anhydrite, as
evidenced by X-ray diffraction patterns, is essentially identical to that of the
naturally occurring mineral.
-------
- 87 -
The character of limestone-derived and normal fly ash particles in
limestone-modified fly ash samples was documented by scanning electron micro-
scope methods. Little development of crystal faces was observed on the anhy-
drite grains. Sintered textures formed by grain growth on the exterior surfaces
of a small number of ash particles are similar to the texture of laboratory-
reacted specimens (compare figs. 66A and 60). Several epitaxial growth struc-
tures on ash particles were observed, but their significance is not known.
Samples from mechanical hoppers proved better than those from the electrostatic
hoppers for the recognition and study of lime and anhydrite with microscope
techniques. Attempts to concentrate the lime-anhydrite particles in fly ash
samples from the mechanical hoppers by magnetic separation to facilitate their
study were successful.
Studies of boiler deposits that formed in the rehe~t section were re-
vealed to have inner and outer layers that could easily be observed with the
naked eye. Detailed chemical and mineral analyses showed minor differences
between the white inner layer and the buff to brown outer layer. Both layers
consist largely of anhydrite mixed with less abundant normal fly ash particles.
Sintering and interlocking growth textures of anhydrite grains were observed
in the largest and hardest deposits. Iron oxide present in the inner layer
is concentrated in blebs and scales on both sides of the steam pipes. The
scale deposit was not observed where the white inner zone was well developed,
but the blebs, composed of platy hematite, occurred with the white inner zone
material. The data suggest K20 and Na20 are concentrated to a minor extent in
the inner zone. adjacent to the steam pipe. Poorly crystalline or glassy masses
of iron sulfates, reported in the fire side boiler deposits by other workers,
were not observed in the samples studied but may exist in small amounts.
Acknowledgments
Melvin C. Stinson of the California Division of Mines and Geology,
Marshall T. Hunting of the Washington Division of Mines and Geology, and Edward
P. Pearson of Basin Chemicals Incorporated, Cleveland. Ohio. kindly supplied
samples of magnesite for this study. Ocean Industries Incorporated provided
the sample of oolitic aragonite.
The analytical chemical data reported herein were determined by per-
sonnel of the Analytical Chemistry Section of the Illinois State Geological
Survey.
The scanning electron microscope used in this study is located in the
Center for Electron Microscopy, University of Illinois, Urbana. This instrument
was obtained by a grant from the Geology Division of the National Science Foun-
dation. The opportunity to use the scanning electron microscope and other
equipment in the Center is gratefully acknowledged.
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- 89 -
REFERENCES
Anderson. C. H., and E. K. Diehl, 1955, Banded fireside deposits in coal-fired
boilers, in Studies relative to ash fouling when burning central
Illinois coals: The Babcock and Wilcox Co., Alliance, Ohio, 23 p.
Bishop. R. J., 1968. The formation of alkali-rich deposits by a high-chlorine
coal: Jour. Inst. Fuel, v. 51. Feb., p. 51-65.
Borgwardt, R. H., 1970a, Kinetics of the reaction of S02 with calcined limestone:
Environmental Science & Technology, v. 4. no. 1. p. 59-63.
Borgwardt. R. H., 1970b, Isothermal reactivity of selected calcined limestones
with S02: NAPCA Limestone Injection Process Symposium Proc., Gilberts-
ville. Kentucky, June 22-26.
Chayes. Felix, 1956, Petrographic modal analyses:
109 p.
John Wiley & Sons, New York,
Dever, G.
R., Jr.. and Preston McGrain, 1969, High-calcium and low-magnesium
limestone resources in the region of the lower Cumberland, Tennessee
and Ohio Valleys, western Kentucky: Kentucky Geol. Survey Bull. 5,
192 p. .
Fisher. C., and L. J. Nazareth, 1968, Classified treatments for the application
of the Quantimet to stereological problems: The Microscope, v. 16.
2nd quarter, p. 95-104.
Folk. R. L., and W. C. Ward, 1957, Brazos River bar: A study in the significance
of grain-size parameters: Jour. Sed. Petrology, v. 27, p. 3-26.
Gillson, J. L., 1960. The carbonate rocks, in J. L. Gillson [ed.], Industrial
minerals and rocks: Am. Inst. Mining & Metall. Engrs., New York,
p. 123-201.
Keroher, G. C., and others, 1966, Lexicon of geologic names of the United States
for 1936-1960: U. S. Geol. Survey Bull. 1200, pt. 1, p. 1424.
Krumbein, W. C., and F. J. Pettijohn, 1938. Manual of sedimentary petrography:
D. Appleton - Century Co., New York. p. 240.
Lamar, J. E., and R. S. Shrode. 1953, Water soluble salts in limestones and dolo-
mites: Econ. Geology, v. 48. no. 2, p. 97-112.
Murray, J. A., 1956, Summary of fundamental research on lime:
Assoc., Washington, D. C.
National Lime
Pettijohn, F. J., 1957, Sedimentary rocks:
p. 368-369, 400, 410-411.
2nd ed., Harper & Brothers, New York.
Potter, A. E., 1969, Sulfur oxide capacity of limestones:
v. 48, no. 9. p. 855-858.
Am. Ceramic Soc. Bull.,
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- 90 -
Rose, H. E., 1968, The determination of the grain-size distribution of a spher-
ical granular material in a matrix: Sedimentology, v. 10, p. 293-309.
Rosiwal, A., 1898, Ueber geometrische Gesteinsanalysen u.s.w.:
k.-k. Geolog. Reichsanstalt Wien, p. 143-175.
Verhandl. der
Snedecor, G. W., 1946, Statistical methods:
Ames, Iowa, 485 p.
4th ed., Iowa State College Press,
Sorby, H. C., 1856, On slaty cleavage as exhibited in the Devonian limestones
of Devonshire: Philos. Mag., v. 11, p. 20-37.
Thomason, E., 1930, Quantitative microscopic analysis:
no. 3, p. 193-222.
Jour. Geology, v. 38,
Womble, T. D., Jr., and J. T. Reese, 1970, The dry limestone injection process
for S02 control, unit full-scale evaluation: NAPCA Limestone Injection
Process Symposium Proc., Gilbertsville, Kentucky, June 22-26.
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- 91 -
GLOSSARY
Algae
Seaweeds and related primitive (aquatic)
plants. Some species secrete laminated
crusts of calcium carbonate, forming spher-
ical or irregularly shaped fossils composed
of very fine-grained calcite.
Anhedral
A term applied to mineral grains that
are not bounded by any characteristic crys-
tal face. Contrasted in this paper with
rhombic and subrhombic grains.
Anisotropic
A term applied to describe an optical
property of nonopaque mineral grains or
crystals that transmit light at different
velocities along different crystallographic
directions. Such grains show double re-
fraction. Contrasts with "isotropic."
Brachiopods
Marine animals with two unequal shells,
each of which is bilaterally symmetrical.
The shells are common as fossils. Most are
composed of fine, interlaminated grains of
calcite.
Bryozoans
Colonial marine invertebrates that secrete
a calcareous, horny or membranous covering.
The calcareous bryozoans have a variety of
shapes and are common as fossils. Many are
branching or lacelike, some are encrusting,
and others form massive growths.
Chert
A very fine-grained variety of silica
(Si02), typically composed of quartz in
grains less than 10 microns in diameter.
Crinoi ds
Marine invertebrates characterized by a
radially symmetrical calyx attached to a seg-
mented stem. Most fossils are fragmented
calyx plates and stem discs. They consist
of relatively coarse-grained calcite.
Echinoids
Sea urchins and closely related marine
invertebrates (echinoderms). The shell is
composed of a number of small, calcareous
plates and is covered by numerous movable
spines.
Equigranular texture
A descriptive term applied to rocks that
have a granular (as opposed to glassy or
amorphous) texture and mineral grains that
are all of one order of size.
Foraminifera
Single-celled
characterized by
composed of very
animals, usually minute,
a perforated shell commonly
fine-grained calcite.
Gas tropods
Gastropods, or snails, have a single
spirally coiled or cap-shaped shell. A
-------
- 92 -
Gastropods (Continued)
few have no shell at all. They live in shal-
low marine waters, in fresh water, and on dry
land. The mineral content of the shell is
aragonite, which alters to calcite on fossil-
ization.
Grain
An individual crystalline unit bounded by
an optical discontinuity in rocks.
Granularity
The degree of uniformity of grain size of
rock specimens as observed with a petrographic
microscope. A relative term useful for de-
scribing carbonate rocks.
Illi te
A clay mineral commonly occurring in sed-
imentary rocks (such as limestones) that is
composed of a complex hydrous silicate of
potassium and aluminum in a layered structure;
similar to muscovite mica.
Intraclast
A fragment of consolidated carbonate sedi-
ment that has been reworked and redeposited
within a sedimentary environment to form a
part of a new sediment within the same for-
mation.
Isotropic
An optical property of nonopaque crystals
or grains that belong to the isometric crystal
system and amorphous substances. Light passes
through these materials at the same velocity
in all directions, and they have one character-
istic index of refraction. Contrasts with
"anisotropic."
Kaolinite
A clay mineral that occurs in sedimen-
tary rocks, such as limestones. A hydrous
aluminum silicate in a layered structure.
Micritic calcite
Calcite (CaC03) that is less than 10 mi-
crons in grain size, generally 1 to 4 microns;
subtranslucent with a faint brownish cast in
thin section.
Os tracodes
Minute bivalve crustaceans, mostly marine,
abundant as fossils. The shells are gener-
ally somewhat bean-shaped. In many species
the surface of the shell has a characteristic
ornamentation.
Pelle toi dal
Refers to pellet-shaped particles in some
limestones. The pellets are spherical or
ellipsoidal in shape and consist mainly of
fine-grained calcite with traces of clay and
organic matter.
Reef dolomite
A type of dolomite rock found in reefs
(large mounds or ridges) built by marine or-
ganisms and characterized by abundant fossils
and lack of bedding. Reef dolomites are fre-
quently high-purity dolomite, very porous but
of low permeability. The dolomite is gener-
ally of secondary origin, formed by replacement
of calcite in a former limestone reef.
Rhombic
A term applied to ~rbonate (usually dol-
omite) mineral grains that have two or mOre
sides with characteristic rhombic crystal faces.
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- 93 -
Sparry calcite
Calcite (CaC03) that is translucent (some-
times transparent) and more than 10 microns
in grain size. Frequently in grains larger
than 50 microns. In thin section, sparry cal-
cite is distinctly clear, compared to micritic
calcite.
Subrhombic
A term applied to carbonate mineral grains
that have one side of the characteristic
rhombic outline present as a grain boundary.
Thin section
A fragment of rock ground to a thickness
of approximately 30 microns for examination
with a petrographic microscope in transmitted
and polarized light.
TWin lamellae
Parallel lines on the surface or cross
section of a grain (or crystal) that has
multiple twinning along parallel planes
through the grain.
TWinned crystal
Composite crystals of a single substance,
in which the individual parts are related to
one another in a definite crystallographic
manner--usually a plane through the crystal
or grain. The plane represents a discontinu-
ity in the crystallographic structure of the
material.
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