U.S. GEOLOGICAL SURVEY CIRCULAR 932 

Interlaboratory Comparison of 

Mineral Constituents in a 

Sample from the Herrin (No. ·6) 

Coal Bed from Illinois 

Interlaboratory Comparison of 

Mineral Constituents in a 

Sample from the Herrin (No. 6) 

Coal Bed from Illinois 

Edited by Robert B. Finkelman, Faith L. Fiene, 

Robert N. Miller, and Frederick 0. Simon 

U. S. G E 0 l 0 G I C A l S U R V E Y C I R C U l A R 9 3 2 

1984 
Department of the Interior 

WILLIAM P. CLARK, Secretary 

U.S. Geological Survey 

Dallas L. Peck, Director 

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
CONTENTS 

Page 

List of authors and affiliations . . . . . . . . . . . . . . . . . . . . V 

Abstract...................................... 1 

Introduction, by R. B. Finkelman . . . . . . . . . . . . . . . . . . 3 

Experimental design and preparation of a homogeneous sample, by F. L. Fiene . . . . . . . . . . . . . . . 5 

Basic characteristics of the interlaboratory sample 

from the Herrin (No. 6) coal bed, by R. W. 

Stanton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

The methodology of low-temperature ashing, by R.N. 

Miller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Analytical results from the interlaboratory sample 

from the Herrin (No. 6) coal bed 

A. X-ray diffraction analysis, by J. J. Renton, 

R. B. Finkelman and F. L. Fiene . . . . . . . 17 

B. Infrared analysis, by P. C. Painter and N. 

Suhr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

C. Chemical analysis, by R. B. Finkelman..... 21 

D. Quantitative analysis of pyritic sulfur by 

means of Mossbauer spectroscopy, by 

P. A. Montano . . . . . . . . . . . . . . . . . . . . . 24 

E . Qualitative clay mineral analysis, by R. S. 

Dean............................. 24 

Page 

F. Scanning electron microscopy study, by R. 

B. Finkelman . . . . . . . . . . . . . . . . . . . . . . 28 

G. Scanning electron microscopy-automated 

image analysis, by F. E. Huggins, G. P. 

Huffman, and R. J. Lee . . . . . . . . . . . . . . 29 

H. Magnetic contamination of the pulverized 

interlaboratory sample, by F. E. Senftle, 

A. N. Thorpe, C. C. Alexander, and R. B. 

Finkelman . . . . . . . . . . . . . . . . . . . . . . . . 30 

I . Mineralogy of "demineralized" coal, by R. 

B. Finkelman and F. 0. Simon . . . . . . . . 33 

J . Analysis of the low-temperature ash from 

the interlaboratory sample by analytical 

electron microscopy, by N. Guven and 

R. B. Finkelman . . . . . . . . . . . . . . . . . . . . 34 

Interlaboratory study of the Herrin (No. 6) coal bed 

sample: Conclusions and recommendations, by 

R. N. Miller and R. B. Finkelman . . . . . . . . . . . . . . . 39 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 

Appendix.-Participating laboratories . . . . . . . . . . . . . . 41 

ILLUSTRATIONS 

Page 

FIGURE 1. Graph showing example of Fourier transform infrared analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

2. Graph of Moss bauer spectrum at room temperature of the fresh interlaboratory sample . . . . . . . . . . . . . . . . . 25 

3. Graph of pyritic sulfur in coal determined by Mossbauer spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

4. Graph of Mossbauer spectrum at room temperature of the interlaboratory sample after 1 year in a vacuum 

desiccator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

5. Scanning electron photomicrograph of a polished block of the Herrin (No.6) coal depicting kaolinite filling 

veins and inertinite pores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

6. Scanning electron photomicrograph of a polished block of the Herrin (No. 6) coal depicting a large 

inertinite fragment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

7. Scanning electron photomicrograph of ferromagnetic particles extracted from the interlaboratory sample . . . 33 

8. Photomicrograph of illite platelet; irregular morphology suggests a detrital origin . . . . . . . . . . . . . . . . . . . . . . 35 

9. Selected-area electron-diffraction pattern obtained from illite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

10. Photomicrograph of a typical kaolinite particle in the low-temperature ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

11. Selected-area electron-diffraction pattern obtained from kaolinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

12. Photomicrograph of amorphous material consisting of fine-grained particles . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

13. A very high magnification photomicrograph of amorphous material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

iii 
TABLES 

Page 

TABLE 1. Comparison of chemical analyses for six randomly selected subsamples of the interlaboratory sample . . . . . . 6 

2. Comparison of amount of low-temperature ash produced at five laboratories . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3. Mineralogy of low-temperature ash produced at five laboratories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

4. Chemical analyses of whole coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

5. Laboratory carbonization tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

6. Maceral composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

7. Interlaboratory comparison oflow-temperature ashing conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

8. Some inorganic products of low-temperature ashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

9. Quantitative X-ray diffraction results from the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

10. Statistics for major minerals in the interlaboratory sample low-temperature ash as determined by X-ray 

diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

11. Mineral analyses based on peak intensities of the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

12. Clay analysis of the interlaboratory sample by Fourier transform infrared spectroscopy (FTIR) . . . . . . . . . . . 18 

13. Sample preparation techniques for X-ray diffraction analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

14. Mineralogical analysis ofthe interlaboratory sample by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

15. Major-element analyses of the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

16. Trace-element analyses of the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

17. Comparison of normative calculations with X -ray diffraction results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

18. Moss bauer determination of pyritic sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

19. Mossbauer data for the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

20. Results of scanning electron microscopy-automated image analysis of the interlaboratory sample . . . . . . . . . 30 

21. Minerals in the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

22. Magnetic properties of the interlaboratory sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

iv 
LIST OF AUTHORS AND THEIR AFFILIATIONS 

C. C. Alexander 

U.S. Geological Survey 

Reston, VA 22092 

R. S. Dean 

Mineral Sciences Laboratories 

Canada Centre for Mineral and Energy Technology 

Department of Energy, Mines and Resources 

Ottawa, Canada 

Present address: 

Esso Resources Canada Limited 

339-50 Ave SE. 

Calgary, Alberta, Canada T2G 2B3 

Faith L. Fiene 

Illinois State Geological Survey 

Champaign, IL 61820 

Present address: 

Institute for Mining and Minerals Research 

P.O. Box 13015 

Lexington, KY 40583 

Robert B. Finkelman 

U.S. Geological Survey 

Reston, VA 22092 

Present address: 

Exxon Production Research Co. 

P.O. Box 2189 

Houston, TX 77001 

Necip Guven 

Texas Tech University 

Lubbock, TX 79409 

G. P. Huffman 

United States Steel Corporation 

Monroeville, PA 15146 

F. E. Huggins 

United States Steel Corporation 

Monroeville, PA 15146 

v 

R. J. Lee 

United States Steel Corporation 

Monroeville, PA 15146 

Robert N. Miller 

Air Products and Chemicals, Inc. 

Allentown, PA 18105 

Pedro A. Montano 

West Virginia University 

Morgantown, WV 26505 

Paul C. Painter 

Pennsylvania State University 

University Park, PA 16802 

J. J. Renton 

West Virginia University 

Morgantown, WV 26205 

F. E. Senftle 

U.S. Geological Survey 

Reston, VA 22092 

Frederick 0. Simon 

U.S. Geological Survey 

Reston, VA 22092 

R. W. Stanton 

U.S. Geological Survey 

Reston, VA 22092 

Norman Suhr 

Pennsylvania State University 

University Park, PA 16802 

A. N. Thorpe 

Howard University 

Washington, DC 20059 

Interlaboratory Comparison of Mineral Constituents in 

a Sample from the Herrin (No. 6) Coal Bed 

from Illinois 

Edited by Robert B. Finkelman, Faith L. Fiene, Robert N. Miller, and Frederick 0. Simon 

ABSTRACT 

Approximately 20 kg of the Herrin (No.6) coal was collected 

from a strip mine in St. Clair County, Ill. A 10-kg portion was 

ground to -60 mesh, homogenized, and riffled into 128 splits 

of 70-80 g each. Homogeneity of these splits was confinned by 

moisture, ash, and sulfur analyses of six randomly selected 

splits. Results of these analyses were within the ASTM 

(American Society for Testing and Materials) guidelines for interlaboratory precision. Splits of the Herrin (No. 6) coal were 

then transmitted to more than 30 laboratories for analysis. 

Low-temperature plasma oxidation was used to isolate inorganic matter for quantitative chemical and mineralogical 

analysis. Despite a wide variation in ashing conditions, only 

minor variations in ash yields were obtained; these variations 

were attributed to differences in operating temperature and 

moisture content. Mineralogical analyses of low-temperature 

ash (L T A) concentrates prepared by five different laboratories 

indicated variations within the limits of analytical error. The 

mean values, in weight percent, for the major minerals are as 

follows: calcite, 9; quartz, 20; pyrite, 23; kaolinite, 14; and 

illite+mixed-layer clays, 31. Normative mineralogical calculations and Fourier transform infrared analysis (FTIR) yielded 

results similar to those obtained from X-ray diffraction (XRD). 

1 

Choosing appropriate mineral standards was found to be 

critical for the proper use of analytical techniques such as XRD 

and FTIR. 

Good interlaboratory agreement was obtained for most major, minor, and trace elements despite differences in analytical 

procedures and in the type of sample analyzed (coal, hightemperature ash, or L T A). Discrepancies between analyses for 

zinc, strontium, manganese, and iron may be attributed to 

sampling inhomogeneity problems. Mossbauer spectroscopy 

showed that approximately 44 percent of the pyritic sulfur was 

lost through weathering in the first year after preparation of 

the interlaboratory sample. Szomolnokite and possibly coquimbite and jarosite were also identified. Scanning electron 

microscopy studies indicated ubiquitous pyrite framboids and, 

less commonly, euhedral crystals, skeletal grains, irregularly 

shaped particles, and vein fillings. Minor accessory minerals 

such as rare-earth phosphates and possibly silicates, zircon, 

barium sulfate, titanium oxide, and sphalerite were also found. 

The textural evidence indicates that the minerals in the banded 

material are detrital whereas the minerals occurring as vein 

and pore fillings are authigenic. Magnetic measurements indicate that coal crushed in a steel pulverizer is contaminated by 

small quantities of abrasion fragments from the crusher, which 

seriously affect the measured magnetic properties of the coal. 

Interlaboratory Comparison of Mineral Constituents in a Coal Sample from Illinois 

Introduction 

By R. B. Finkelman 

At a conference on mineral matter in coal (held 

in May 1978 at the University of Illinois 

Champaign-Urbana, Ill.), representatives from 

several laboratories described their procedures for 

obtaining X-ray diffraction (XRD) data from lowtemperature ash (LTA). Each laboratory had 

selected or devised procedures for low-temperature 

ashing and XRD analysis to suit its particular 

needs. No two laboratories used the same procedure for preparing and analyzing the samples or 

for reducing the data. Difficulties were encountered in attempting to relate the data of any 

one laboratory to those of another. As a result, the 

conferees felt that a procedure should be developed 

that would permit interlaboratory comparison of 

data One suggestion was to investigate the 

possibility of developing a single or "universal" 

procedure that could be used by all participating 

laboratories. Another suggestion was to have each 

participating group analyze subsamples of the 

same material; the resulting data could then be 

used in developing a basis for relating the data of 

one laboratory to those of another. The latter approach was agreed upon and a committee1 selected 

to devise this X-ray "Rosetta Stone." The sample 

selected for this interlaboratory study was to be 

collected from the Herrin (No. 6) coal bed in St. 

Clair County, Ill. 

The primary purpose of this interlaboratory 

study and this circular is to provide a means for interpreting XRD data on coal minerals reported by 

different laboratories. No attempt was made to 

standardize any of the analytical procedures, nor 

was the interlaboratory study designed to provide 

standard chemical, petrographic, or other types of 

analytical data The data herein are intended to 

provide useful supplementary information and are 

not intended for use as standard values for this 

sample. 

'Committee members: B. Bobar, U.S. Geological Survey, Denver; F. L. 

Fiene, Illinois State Geological Survey (now with Kentucky Institute for 

Mining and Minerals Research); R. B. Finkelman (Chairman), U.S. 

Geological Survey (now with Exxon Production Research Co.); H. J. 

Gluskoter, Exxon Production Research Co.; R. N. Miller, Air Products 

and Chemicals, Inc.; J. J. Renton, West Virginia University; R. W. 

Stanton, U.S. Geological Survey; N. Suhr, Pennsylvania State 

University. 

3 

The maximum value of this study would be realized if every laboratory that is actively engaged in 

research on coal minerals were to participate in 

this comparison. In order to encourage such participation, a supply of the raw coal and the LTA used 

in the interlaboratory study has been reserved for 

future needs. This material may be obtained by 

writing to Frank G. Walthall, U.S. Geological 

Survey, 923 National Center, Reston, VA 22092, 

U.S.A. 

ACKNOWLEDGMENTS 

Many people have made important contributions to the effort represented by this report. The 

editors and committee members express their 

sincere appreciation to these people and the 

organizations that supported their work. 

We are particularly indebted to Jack A. Simon 

and the Illinois State Geological Survey (ISGS) for 

their constant and invaluable support. The following members of the ISGS staff were instrumental 

in the initial collection, preparation, and analysis 

of the Herrin (No. 6) interlaboratory sample: 

Richard Cahill, Richard D. Harvey, Roy J. 

Helfinstine, Larry Kohlenberger, W. John Nelson, 

and Neil Shimp. Norman Suhr and Henry Gong, 

both of the Pennsylvania State University, were 

responsible for the comparison of the preliminary 

LTA mineralogy. Harold J. Gluskoter, Exxon Production Research Co., and John Kuhn, Kentucky 

Institute for Mining and Minerals Research, provided valuable advice and support during the initial stages of this project. The following U.S. 

Geological Survey (USGS) personnel contributed 

analytical data: Edward Dwornik, Joseph L. Harris, Richard R. Larson, and Louis J. Schwarz. 

We are grateful to the many people who improved the manuscript with their constructive 

comments. Foremost in this area are G. R. Belton, 

the Broken Hill Proprietary Co.; Charles Ford, 

Bituminous Coal Research; Richard D. Harvey, 

ISGS; Peter C. Lindahl, Exxon Production 

Research Co.; Suzanne J. Russell and Norman 

Suhr, the Pennsylvania State University; and 

Jean Minkin, Peter Zubovic, and Kathleen Krafft, 

USGS. 

Interlaboratory Comparison of Mineral Constituents In a Coal Sample from Illinois 

Experimental Design and Preparation of a Homogeneous Sample 

By F. L. Fiene 

COLLECTION AND PREPARATION 

OF THE COAL SAMPLE 

The Herrin (No. 6) coal bed was chosen for the interlaboratory sample because it is known to contain a variety of mineral constituents and an ash 

content between 10 and 15 percent. Approximately 20 kg of coal was collected from an active strip 

mine in St. Clair County, Ill., in July 1978. The 

channel sampling procedure described by Schopf 

(1960) was followed. In this procedure, the face of 

the coal bed is sampled, excluding mineral bands, 

partings, and nodules greater than 1 em in thickness. The coal bed had been exposed only a few 

hours prior to collection. There was no evidence of 

clay dikes, faulting, or other sources of contamination nearby. A vertical column of coal approximately 10 em by 10 em was chipped from the bed 

with a steel pick and immediately placed in plasticlined (0.10-mm-thick) burlap bags, which were 

promptly sealed to retain moisture. 

Within one week, the interlaboratory sample 

was prepared for analysis at the Applied Laboratory of the Illinois State Geological Survey, 

Champaign, Ill. The sample was first crushed by a 

roll mill to -10 mesh and air-dried at 85-90°C for 

24 hours. Half of the dried coal (10 kg) was then 

ground to -60 mesh in a hammer mill and homogenized overnight in a V-type blender. Two Jones 

sample splitters with 3/8-in and 1/8-in chutes were 

used to sequentially riffle out 128 individual subsamples. Each subsample, containing 70-80 g 

coal, was put in a 4-oz glass screw-cap bottle and 

sealed in a C02 atmosphere. Six bottles were 

chosen at random for a check on homogeneity, and 

those remaining were randomly assigned numbers 

between 1 and 122. The numbered bottles and the 

remaining 10 kg of the original sample ( -10 mesh, 

stored in plastic-lined cardboard cartons) were 

stored in a freezer. 

HOMOGENIZATION TESTS 

The six subsamples selected for the homogeneity check were subjected to a series of tests considered to be the most reliable indicators of uniformi5 

ty. The six subsamples were first tested for 

moisture, ash, and forms of sulfur (total, pyritic, 

and sulfatic) contents. The results, summarized in 

table 1, are within the repeatability (intralaboratory precision) required for duplicate analyses of 

the same sample according to the American Society for Testing and Materials (ASTM) Annual Book 

of Standards, Part 26 (D2492, D3173, D3174, 

D3177). On this basis, it was concluded that the individual subsamples were representative of the 

original coal sample. Five participating laboratories prepared L T A from the chemically characterized subsamples to monitor the variability in 

both mineral content and composition under the 

ashing procedures used by the individual laboratories. The five laboratories were instructed to ash 

the samples by their routine procedure and to 

return about 1 g of the LTA to Laboratory 4 (participating laboratories are identified by number; 

the identification key is given in the Appendix) for 

mineralogical analysis. The LT A data generated 

by these laboratories are shown in table 2 (see section on methodology of low-temperature ashing for 

discussion). Although there are detectable differences in the L T A percentages, no major differences in mineralogy were detected within the 

experimental error of the analytical procedures 

(table 3). 

The attempts to produce a homogeneous sample 

were not entirely successful. Laboratory 9 

detected some inhomogeneity between two LTA 

samples with respect to calcite and sulfate (see the 

discussion of carbonate distribution, section F, 

and of trace-element data, section C). These inhomogeneities appear to be relatively minor and 

should not adversely affect the use of the interlaboratory sample as a standard for comparing 

X-ray diffraction analyses among laboratories. 

PREPARATION OF LOW-TEMPERATURE ASH 

The five laboratories participating in the 

preliminary homogeneity test prepared the L T A 

used for general distribution. Because the L TA 

was to be homogenized by mixing the LT A from 

all five laboratories, no special precautions were 
TABLE I.-Comparison of chemical analyses for six randomly selected subsamples of the interlaboratory sample 

[All analyses by Laboratory 1. Quantities are given as weight percent; moisture is on an as-received basis, all other analyses on a moisture-free basis. 

ISGS, Illinois State Geological Survey; SD, standard deviation; HT A. high-temperature ash] 

Sample ISGS- ISGS- ISGS- ISGS- ISG8- ISGSNo. C20275 C20276 C20277 C20278 C20279 C20280 Average SD 

Moisture1 6.7 6.9 7.0 7.1 7.0 7.1 7.0 0.14 

Ash2 13.6 13.6 13.7 13.7 13.6 13.7 13.7 .05 

Pyritic sulfur 1.97 1.92 1.95 1.93 1.91 1.91 1.93 .03 

Total sulfu.r4 4.07 3.97 3.88 3.80 3.83 3.78 3.89 .15 

1 ASTM repeatability: > 5% moisture = 0.3% 2

ASTMrepeatability: >5% ash= 0.5% 3

ASTM repeatability: <5%Pyritic sulfur = 0.05% 4ASTM repeatability: > 2% sulfur = 0.1% 

TABLE 2.-Amount of low-temperature ash, in percent, produced at five laboratories 

[SD, standard deviation; LT A. low-temperature ash] 

Laboratory 24 17 4 

Sample ISGS- ISG8- ISGSNo. C20275 C20276 C20277 

LTA 18.4 15.7 16.3 

TABLE 3.-Mineralogy of low-temperature ash produced at five 

laboratories 

[All analyses by Laboratory 4 and given as weight percent. Kaolinite determined by infrared analysis; pyrite, calcite, and quartz determined 

by X-ray diffraction analyses. SD, standard deviation] 

Laboratory 

generating 

LTA 24 17 4 25 1 Average SD 

Pyrite 24 21 17 21 17 20 3 

Calcite 4 6 6 6 5 5 1 

ra:te 

18 17 16 16 15 16 2 

15.6 16.3 15.4 14.7 14.6 15.3 0.7 

taken to minimize the sources of bias resulting 

from the different low-temperature ashing procedures. However, to retard sample deterioration, 

the laboratories were instructed to store the LTA 

in airtight containers in either a vacuum desiccator or a freezer. 

The LTA samples (approximately 100 g each) 

produced by the five laboratories were sent to a 

coordinating laboratory (USGS, Reston, V a), 

where the combined samples were homogenized 

overnight in a V -type blender and then riffled into 

2 equal parts. One part was returned to freezer 

6 

25 1 Average SD 

ISGS- ISG8-

C20278 C20279 

16.7 16.8 16.8 1.0 

storage for reference and reserve purposes, and the 

other part was riffled into 32 1.5- to 2-g subsamples by using a Jones splitter with a 1/8-in 

chute. These subsamples were placed in glass popcap bottles, vacuum-sealed, numbered, and stored 

in a freezer until final distribution. 

DISTRIBUTION 

More than 40 laboratories have participated in 

the interlaboratory study. Each laboratory received a sample of the prepared coal and (or) LTA 

according to its research interests and instrumental capabilities. No restrictions were placed on the 

types of analysis to be undertaken, but laboratories were encouraged to low-temperature ash 

the coal and to analyze the mineralogy of both the 

LTA they produced and the control LT A by X-ray 

diffraction (XRD) and any other analytical method 

at their disposal. The distributed samples were accompanied by a questionnaire requesting written 

documentation of methods and data 
Interlaboratory Comparison of Mineral Constituents in a Coal Sample from Illinois 

Basic Characteristics of the Interlaboratory Sample 

from the Herrin (No. 6) Coal Bed 

By R. W. Stanton 

Data from ultimate and proximate analyses and 

determinations of forms of sulfur for the interlaboratory coal sample are shown in table 4. 

Some differences are evident among the sets of 

data; the differences in the sulfate-sulfur values 

probably are the result of oxidation of pyrite 

before some of the analyses were performed. 

The following list contains the ASTM standards 

for each test and the acceptable reproducibility or 

repeatability value for each specific determination. 

Although each laboratory was not required to 

follow ASTM procedures, these values are presented here to use as a basis for comparison of the 

data 

ASTM standard 

D3177 Total sulfur 

D2492 SuHate sulfur 

D2492 Pyritic sulfur 

D3178 Carbon 

D3178 Hydrogen 

D3179 Nitrogen 

D2015 Calorific value 

D3175 Volatile matter D3174 Ash 

D3302 Moisture 

Reference 

Reproducibility Repeatability (in ASTM, 1981) 

0.15 0.10 p.380-386 . 04 .02 p.319-323 

.30 .10 p.319-323 

100.00 

1.0 

.3 

.50 

.30 p.387-391 

.07 p.387-391 

.05 p.392-395 

50. p.389-397 

.50 p.372-375 

.20 p.370-371 .30 p.410-415 

Some values in table 4 lie outside the acceptable 

differences among laboratories. However, the intent of these data is to provide information on the 

composition of the sample provided for roundrobin laboratory analyses; the sample is not to be 

used as a standard. 

Parr mineral matter values (Parr and Wheeler, 

1909) were calculated from the data by using the 

equation 

Parr = 1.08(A) + .55(8) 

where A = high-temperature ash and S = total 

sulfur. This value includes both minerals and 

organically bound elements and can be compared 

to the LT A values, which average 16.8 percent 

(table 2). 

Carbonization data for this sample appear in 

table 5 . 

PETROGRAPHY 

Five laboratories provided information on the 

TABLE 4.-Chemical analyses of whole coal 

[Moisture-free basis; oxygen determined by difference; all values are in weight percent except calorific value which is in Btu per pound) 

Laboratory 1 9 26 27 Average 

Total sulfur 3.78 4.16 4.19 4.08 4.05 

Sulfate sulfur .06 .23 .08 .19 .14 

Pyritic sulfur 1.91 1.75 1.88 1.76 1.83 

Organic sulfur 1.81 2.18 2.23 2.13 2.09 

High-temperature ash 13.78 13.96 13.40 13.42 13.64 

Moisture (as received) 7.1 7.4 7.21 6.98 7.17 

Volatile matter 39.6 1 37.51 40.4 40.7 39.0 

Carbon 67.64 67.10 68.15 67.63 

Hydrogen 4.89 4.62 4.76 4.69 

Nitrogen 1.24 1.39 1.01 1.20 

Oxygen 8.75 2 7.49 8.51 8.00 

Calorific value 12430 12107 12243 12337 

Parr mineral matter 16.96 17.36 16.78 16.96 16.96 

1Laboratory 9 reported that volatile matter was determined by Australian/British Standard 1038 (Australian Standard, 1979b), which ~ifies 

heating the sample to 900°C rather than 950°C as in ASTM D3175 (ASTM, 1981, p. 372-374). This lower temperature probably accounts for e poor 

agreement of the volatile-matter values. 2

Analytical value. 

7 
TABLE 5.-Laboratory carbonization tests 

[All tests performed by Laboratory 9] 

Crucible Swelling Number (Australian Standards, 1979a) 

CSN = 3.5 

Automatic Gieseler Plastometer (Australian Standards, 1981) 

Initial softening temperature 381 oc 

Maximum fluidity temperature 409°C 

Solidification temperature 434 oc 

Maximum fluidity (dial division per 3 

minute) 

Log10 maximum fluidity 0.4 771 

Plastic range 53 oc 

Audibert-Arnu Dilatometer (International Standards 

Organization, 1983) 

Percentage contraction 

Percentage dilatation 

Temperature T 1 

Temperature T11 

Temperature T 111 

25 

Contraction only. 

325°C 

470°C 

Contraction only. 

petrographic character of the interlaboratory sample. Representative splits of -10 mesh coal were 

obtained from the remaining 10 kg of the original 

sample described previously. Pellets were 

prepared in accordance with ASTM standard test 

D2797 (1981, p. 347-351). 

8 

TABLE 6.-Maceral composition 

[R0 max., mean maximum vitrinite reflectance in percent vitrinite reflectance; all other data in volume percent on mineral-matter-free basis; 

T, trace, less than 5 counts/1000; --,not reported] 

Laboratory number 1 9 25 24 26 Average 

Vitrinite 82 87 90 88 87 

Exinite (liptinite) 4 5 1 2 3 

~orinite 3 2 1 <1 <2 

utinite 1 1 T 2 <1 

Resinite T 2 T <1 <2 

Inertinite 14 9 9 10 10 

Inertodetrinite 1 3 2 

Fusinite 2 2 1 3 2 

Semifusinite 1 4 3 7 4 

Micrinite 7 1 2 <1 2 

Macrinite 3 T T T 2 

Sclerotinite T <1 T 

R0 max. 0.57 0.54 0.55 

Petrographic data reported are presented in 

table 6. The results show good agreement among 

the participating laboratories for most parameters. Because of the low metamorphic rank of this 

coal, there was some difficulty in differentiating 

among the varieties of vitrinite, which included 

abundant desmocollinite and corpocollinite as well 

as less abundant telocollinite and gelocollinite. 
Interlaboratory Comparison of Mineral Constituents in a Coal Sample from Illinois 

The Methodology of Low-Temperature Ashing 

By Robert N. Miller 

The interlaboratory comparison of inorganic 

analytical methods was based on the combined 

subsamples produced in various laboratories by 

low-temperature plasma oxidation. This section of 

the report discusses the L T A methodology, its application in the interlaboratory study, the limitations of the present study with respect to L T A, 

and, finally, the problems associated with L T A 

procedures and possible solutions. 

BACKGROUND 

The initial objective of the interlaboratory study 

was to compare variations among XRD methods 

used on L T A. It soon became apparent that various laboratories used widely different conditions 

for low-temperature ashing. This by itself introduced variations in the composition of the individual ashes. A preliminary screening of the 

interlaboratory sample by XRD showed no gross 

dissimilarities among ashes; however, the X-ray 

method was not capable of detecting minor components or noncrystalline species. Data summarizing the variations among the low-temperature 

ashing conditions used in the different laboratories 

appear in table 7. 

Despite the consistency (coefficient of variation 

= 4 percent) of the LTA results, the ashing conditions used by the participating laboratories obviously lacked standardization. Both mineral and 

chemical analyses of an ash prepared by one L TA 

procedure in one laboratory may differ from the 

analyses obtained on an ash prepared in another 

laboratory using different ashing conditions. 

Recommendations for standardizing low-temperature ashing conditions are necessary before pursuing future interlaboratory comparisons. 

In practice, a researcher will analyze the L T A 

prepared in his laboratory. What is done with the 

ash depends on the specific objectives of the 

research study. On one hand, if a researcher wants 

to analyze major species present in a prepared ash 

and report them as proportions of that ash, then 

the primary concern will be the reproducibility of 

9 

the analytical methods. This aspect was addressed 

as the primary purpose of the interlaboratory 

study-what methods can be used to quantitatively determine major mineral species in LTA? Suppose, however, that a researcher wants to report 

the mineralogical or chemical analysis of the LTA 

on a whole coal basis; that is, he wants to know 

what was in the coal. In this instance, the L T A 

yield must be known accurately. In addition, when 

species are analyzed on the LT A and then calculated back to the coal basis, it must be assumed 

that they were present in the same or a known 

form in the original coal sample. For some 

minerals and especially cations associated with 

organic acids in lower rank coals, this assumption 

may be questioned. Artifacts that are produced by 

ashing can be misinterpreted as being present in 

the original coal. In addition, if a researcher is concerned with the study of the oxidation-reduction 

states of various species, with the analysis of 

minor or trace mineral phases, or with the study of 

the noncrystalline inorganic components in a coal, 

then the question of alteration of the inorganic 

matter during low-temperature ashing of the coal 

becomes an important issue. The interlaboratory 

study dealt with only one sample of a bituminous 

coai and did not address the problems of mineralogical analysis of lignite or subbituminous coal. 

Low-rank coal behaves quite differently in an 

asher and poses its own set of unique problems. In 

the broad context of L T A methodology, the following discussion also pertains to inorganic reactions 

in low-rank coals. 

THE LTA PROCEDURE AND REACTIONS 

OF INORGANIC MAnER 

Gluskoter (1965) introduced plasma oxidation as 

a technique for isolating inorganic materials from 

coal. Earlier methods were unsatisfactory for 

separating major portions of inorganic matter 

from the organic coal matrix. Ashing at high 

temperatures ( > 500°C) or wet-chemical oxidative 

techniques significantly alter the mineral matter 
10 

of most coals; physical separations based on gravity or particle size never succeed in separating 

submicrometer-sized inorganic components from 

the organic particles. Although the LT A technique 

was a significant breakthrough for coal mineral 

matter studies, it is not without problems. Plasma 

oxidation will generate artifacts by changing 

major minerals or forming new inorganic species 

from the breakdown of organic and inorganic 

complexes. 

The plasma oxidation of coal is the combustion 

of organic matter at a relatively low temperature 

( < 200 o C). In contrast to the procedure for hightemperature combustion, the energy required to 

''gasify'' the organic carbon is supplied by exposing the coal surface to oxygen molecules that have 

been "activated" in a radiofrequency (RF) field. 

Organic molecules react with the "RF-activated" 

oxygen releasing carbon, sulfur, and nitrogen oxides and water into the gas phase. Most of these 

combustion products are readily removed from the 

system by the vacuum pump, but some may react 

with the inorganic matter and remain in the ash. 

Thus, as the organic matter reacts, inorganic 

materials are concentrated as a residue. In addition to decomposing the organic matter, the 

ashing procedure may also decompose or alter 

some of the inorganic materials. Therefore, 

depending on the conditions of the experiment and 

on the nature of the starting coal, this residue (the 

LTA) may contain unaltered minerals, minerals 

whose elemental composition is unchanged but 

which have undergone crystallographic change, 

newly formed crystalline phases from gas or solid 

decomposition and oxidation reactions, amorphous inorganic species (see section J), and unburned residual organic matter. Table 8 summarizes some of the changes in the different types of 

inorganic matter. The inorganic alterations and 

the low-temperature ashing conditions that influence them are discussed below. 

THE OXIDATION EFFECT 

The low-temperature asher is basically an oxidizing system, and therefore a species present in a 

reduced state is thermodynamically unstable. 

Hence, organic molecules are rapidly destroyed. 

Likewise, any mineral containing elements in a 

reduced state (such as pyrite) is unstable and can 

undergo reaction in the oxygen plasma. The crystalline surface chemistry of most individual 
TABLE B.-Some inorganic products of low-temperature ashing 

Unaltered minerals 

Altered minerals 

Quartz, kaolinite, illite. 

- alteration of crystallinity 

- alteration by oxidation 

Montmorillonite, mixed-layer clays. 

Ferrous to ferric sulfates. 

Sulfides (Fe82) to oxides or sulfates. 

New _phases - from dehydration Bassanite [Ca804(H20)112] from gypsum. 

- from gas-solid reaction Formation of gypsum and bassanite (from the reac- tion of SOa + CaC03 + H20); alkali nitrates 

and sulfates. 

- from decomposition of organic 

salts 

Alkali and metal oxides, carbonates, nitrates or sulfates. 

- from decomposition of reduced 

minerals 

Amorphous material 

Unburned or charred carbonaceous 

material 

mineral grains is an effective kinetic barrier to oxidation, thus minimizing chemical reactions, but a 

poorly crystalline or defective mineral grain will be 

unstable in the plasma Montano (1977) presented 

unequivocal evidence of the formation of a new 

mineral species [Fe2(SO 4)3] from the oxidation of 

pyrite during the low-temperature ashing process. 

Miller and others (1979) observed that some pyrite 

grains actually ignite in the asher, emitting an obvious red glow, while other pyrite grains are unaffected. Hematite (Fe20 3) was identified as the reaction product under their ashing conditions. During 

the oxidation of pyrite, "hot spots" are formed 

that may cause high-temperature alteration of 

neighboring mineral grains. In addition to the oxidation of discrete minerals, reduced metallic cations ion-exchanged onto clay minerals or coal or 

emplaced isomorphically in certain minerals can be 

oxidized. Montano (1977), using Mossbauer spectroscopy, observed a change from ferrous iron 

(Fe2

+) to ferric iron (Fe3+) after low-temperature 

ashing. 

THE EFFECTS OF TEMPERATURE 

The plasma operates at 100-200 o C (see table 7). 

The heat in the chamber results from the energy 

dissipated during the RF discharge and also from 

the exothermicity of the organic matter combustion. Thus, the higher the RF field power, the 

11 

higher will be the background or normal operating 

temperature in the oxidation chamber. In the normal operating temperature range of the lowtemperature asher, certain hydrated minerals and 

expandable clays that have attained a constant 

weight under normal drying conditions (110°C) 

will gradually lose additional moisture. This effect 

will be more severe the higher the chamber temperature. Gluskoter (1967) demonstrated that certain 

mixed-layer clays lose as much as 20 percent of 

their weight during ashing and attributed this to 

irreversible moisture loss from the interlayer; 

XRD scans indicated a substantial change in the 

c-axis spacing of the clay from 14.9 to 13.6 A. It 

has also been demonstrated that chemical and 

crystal structural changes accompany dehydrations. Certain of the hydrated minerals that lose 

their water between 100 and 250 ° C will alter in the 

LTA. For example, gypsum [CaSO 4(H20)J is readily dehydrated to form bassanite [CaS04(H20)112] at 

temperatures above 100°C but below 170°C; at 

temperatures above 170°C, the hemihydrate is irreversibly stripped of its remaining water to form 

anhydrite. In fact, these specific changes can act 

as a kind of thermometer for monitoring temperatures in the LTA. 

There is yet another temperature-sensitive 

phenomenon that occurs during low-temperature 

ashing-this involves fixation reactions of combusted organic matter with reactive minerals. 

Sulfur, nitrogen, and carbon oxides, all products of 
the organic-matter combustion, are acid gases. In 

the relatively stagnant conditions that prevail in 

the ashing chamber, these gases can react with inorganic bases to form sulfates, nitrates, and carbonates, respectively. The nature and extent of 

reaction depend on the particle size of the inorganic material, the partial pressure of the gas in 

the ashing chamber, and the operating temperature. As chamber temperatures vary, the absolute 

amount of sulfates or nitrates that are formed and 

deposited in the LTA will vary. Miller and others 

(1979) showed that the sulfate ion fixed in the ash 

decreased with increasing RF power. Apparently 

the reaction of a hydrated species of S03 in the gas 

phase with solid carbonate in the ashing dish was 

sensitive to temperature in the normal operating 

range of LTA. Miller and others (1979) also observed that a peculiar ice-like condensate appeared 

on the surface of the ashing equipment when highsulfur coal was ashed at low power but that this 

material evaporated at higher power. The substance was never positively identified but was 

found to be highly acidic upon exposure to air and 

did give a positive test for sulfate ion. Recently, 

F. Stohl (oral commun., 1980) at the Los Alamos 

National Laboratory in New Mexico identified a 

similar condensate found in the L T A at low power 

and obtained an X -ray pattern indicative of a 

hydrogen ammonium sulfate. 

DECOMPOSITION OF ORGANIC SALTS 

It is well known that alkali or alkaline-earth 

metallic ions will catalyze the gasification reactions of coal in oxygen. Alternatively, these same 

cations tend to deactivate the excited oxygen 

molecules during low-temperature ashing and 

therefore inhibit the rate of oxidation. One might 

then predict that coal containing alkali or alkalineearth metals in a dispersed form will be the most 

difficult to ash. Lignite and subbituminous coal 

generally contain a large portion of their so-called 

"mineral matter" in a dispersed form, that is, 

bound as cations to oxygenated, acidic, organic 

functional groups. Therefore, it is not surprising 

that lignite ashes more slowly than do higher rank 

coals. The geochemical literature also suggests the 

presence of organometallic complexes in bituminous coal. The fate of these species during lowtemperature ashing is unknown. 

12 

QUANTITATIVE LOW-TEMPERATURE ASHING 

AND MINIMIZING REACTIONS 

OF THE INORGANIC MAnER 

Miller and others (1979) summarized the reactions that can significantly alter inorganic constituents in coals during low-temperature ashing. If 

reactive species are abundant in the coal, then the 

effect can be serious. Fortunately, many reactions 

can be minimized under carefully controlled experimental conditions, and, at least for bituminous 

coal, a good quantitative approximation of the 

mineral-matter content of a coal can be obtained. 

We propose several criteria for low-temperature 

ashing of bituminous coal that will minimize undesirable reactions due to temperature and oxidation. In addition, the inherent hygroscopic nature 

of coal and coal ash is important in establishing a 

standard experimental ashing procedure. 

THE RF POWER LEVEL 

Widely varying RF power levels (15-125 

W/chamber) were used by the various laboratories 

in this study. Since the RF power level and the 

operating temperature in the ashing chamber are 

correlative, careful control of the RF power level 

should minimize temperature-sensitive reactions. 

In their discussion of quantitative ashing, Miller 

and others (1979) and Frazer and Belcher (1973) 

recommended the use of moderate power settings 

(30-60 W/chamber for their instruments from International Plasma Corp.). Miller and others (1979) 

chose 50 W/chamber as the level where fixation of 

organic sulfur and oxidation of pyrite were 

minimized. A moderate power setting is recommended because low wattage ( < 30 W/chamber) 

tends to greatly increase the fixation of products 

from gas-solid reactions, whereas high power 

levels ( > 70 WI chamber) cause increased dehydration of clay and oxidation of pyrite. Because the 

actual operating temperatures at all power levels 

might vary among instruments, the optimum 

operating conditions for a particular low-temperature asher will have to be determined by trial and 

error. A low-temperature asher can be calibrated 

by using the chemical thermometer method or by 

measuring levels of products from undesirable 

reactions, such as sulfate fixation. Stohl (1980) 

determined the LT A operating temperature by 
using a chromel-alumel thermocouple with a stainless steel sheath inserted into the ashing chamber. 

The temperature can also be read by using a commercially available platinum resistance probe 

within a glass sheath. 

MOISTURE FLUCTUATIONS 

The largest source of variation observed in the 

reported interlaboratory ashing conditions was the 

absence of standardization of the moisture content 

of the prepared ash and coal. Some laboratories 

ashed air-dried coal while others ashed "as received" coal. Further, the moisture content of the 

prepared ash was generally ignored. Since coal is 

extremely hygroscopic, standard procedures have 

been instituted to deal with its moisture determination (ASTM D3173 and D1412) under different conditions. Like coal, a freshly produced LT A 

is extremely hygroscopic and absorbs more than 

90 percent of its moisture within several minutes 

of exposure to air. For the Herrin (No.6) coal bed, 

this can represent as much as 3 percent by weight 

of the coal depending on the relative humidity in 

the laboratory. For example, if a dry LTA yield is 

15 percent of dry coal, then a reported yield on an 

air-equilibrated ash might be 17 percent, a significant difference. This problem can be eliminated if 

one uses either of the following procedures: 

(1) The weight of coal used for the test and the 

final weight of LT A are obtained on dry 

samples. The coal can be dried using the 

standard ASTM procedure. A dry weight of 

L T A is best obtained by initially allowing the 

fresh L T A to equilibrate in lab air and then 

drying it under the same conditions as used 

for the coal. Note that weighing of ash directly out of the asher is not acceptable, since the 

drying conditions in the instrument may differ from the conditions used to dry the coal. 

(2) The weight of coal and the ash can be obtained 

on air equilibrated samples provided an independent determination of moisture is done on 

aliquots from both the coal and ash. 

In either of the above methods, the final L TA 

percentage should be calculated to the dry basis to 

express results free from moisture variability. 

Neavel and others (1980) have obtained data on 

nearly 50 bituminous coal samples which show a 

negligible mean difference (0.05) between dry-basis 

13 

L T A yields and formula-derived mineral-matter 

contents. L T A yields calculated from the weight of 

air-equilibrated ash show a significant bias in the 

mean difference (-1.13). 

STIRRING FREQUENCY AND 

ASHING DURATION 

The longer a sample is exposed to the oxygen 

plasma, the greater the probability of unwanted 

reactions of the unstable materials. Miller and 

others (1979) pointed out that the extent of pyrite 

oxidation increased not only as a function of 

temperature but also as a function of ashing duration. Interlayer alteration of clays due to moisture 

loss may also be enhanced by long-term exposure 

in the plasma Hence, the shorter the ashing time, 

the better. The rate of oxidation of the organic 

matter is relatively slow in the low-temperature 

asher because of the limited surface area of the 

sample. To increase the rate of ashing, a sample 

must be periodically removed from the asher and 

stirred. This is a tedious, time-consuming, but 

necessary operation, as all low-temperature asher 

users are aware. For a typical bituminous coal 

(that is, one with an ash content between 10 and 20 

percent), the rate of oxidation of the organic matter drops after 1-2 hr exposure in the asher. Thus 

longer exposures and, especially, overnight ashing 

do not effectively oxidize much additional organic 

matter. Most of the interlaboratory data refer to 

durations of 2-5 days for complete ashing of the 

Herrin (No.6) coal bed sample. If the sample layer 

density is less than about 30 mg/cm2 (this corresponds to 1.5-2.0 g coal in a standard 6-cm petri 

dish) and if the sample is stirred every 1-2 hr, a 

quantitative ash for a typical bituminous coal can 

be obtained in 12-15 hr. This was verified by 

Neavel and others (1980) on 50 different North 

American bituminous coal samples, for which the 

total duration of ashing by this technique was 

never greater than 20 hours, and the average duration was 17 hours. An added advantage in ashing 

for shorter durations is decreased wear on the 

asher and pump and less subsequent down-time 

for maintenance and repairs. 

The ashing duration also depends on the criteria 

used to determine if ashing is complete. We recommend these approaches: 

(1) The ashing of 1.5-2.0 g of coal can be considered complete when the measured weight 
loss on dry ash is less than 2 mg per 2-hour 

ashing period. 

(2) When ashing a coal, a curve of weight loss 

against time can be plotted. When the weight 

loss levels off, ashing can be considered complete and the final weight recorded. 

(3) Generally the oxidation of organic matter is 

never 100 percent; hence, residual carbon can 

be measured on the ash to correct for incomplete combustion. Refer to the analytical 

tests below for procedures and precautions to 

employ. 

(4) Ashing of low-rank coals (that is, coal with dry 

mineral-matter-free oxygen contents greater 

than 16 percent) is extremely troublesome as 

the carboxylate cations inhibit the oxidation 

of the organic matter. Consequently, weeks 

of ashing may produce only an insignificant 

weight loss. To alleviate the problem, lowrank coals can be first treated with ammonium acetate or dilute hydrochloric acid, to 

remove the organically associated cations, 

and then ashed. Cation removal accelerates 

the ashing and ensures nearly complete combustion of the organic matter. 

ANALYTICAL CHECKS ON PROCEDURES 

Certain standard wet-chemical analyses are 

useful for monitoring the extent of certain inorganic reactions in the low-temperature asher. 

These tests also serve as independent quantitative 

measures of certain minerals or ions in the coal and 

ash. The following tests are recommended: 

(1) Carbon dioxide by acid evolution (ASTM 

D1756; ASTM, 1981, p. 252-254): This 

measures the carbonate contents of coal and 

ash; it will determine the extent of carbonate 

decomposition or formation in the LTA. Because this test serves as a quantitative measure of carbonate in the LTA, it can also be 

used to correct the total carbon value of the 

LTA to obtain the net residual carbon. 

(2) Pyritic sulfur and hydrochloric acid-soluble 

iron (ASTM D2492; ASTM, 1981, p. 319-

322): This test will measure the extent of 

pyrite oxidation in coal and ash. The decrease 

in pyritic sulfur content is proportional to an 

increase in hydrochloric acid-soluble iron 

(Given and Miller, 1978). The test also serves 

14 

as a precise quantitative measure of the 

mineral pyrite in the LTA. 

(3) Sulfate sulfur (ASTM D2492; ASTM, 1981, 

p. 319-322): The amount of sulfate in the coal 

and in the L TA will indicate the extent of 

sulfate ion formation due to either organic 

sulfur fixation or pyrite conversion; this test 

is most useful when setting RF power levels. 

Also, if the organic sulfur fixation is extensive, the LTA can be corrected to a sulfurfree ash, which is a more precise measure of 

yield. 

(4) Moisture (ASTM D3173; ASTM, 1981, 

p. 367 -369): This test measures the moisture 

content of coal and can also be used to 

measure the moisture content of the ash. 

(5) Carbon and hydrogen (ASTM D3178; ASTM, 

1981, p. 387-391): A determination of total 

carbon and hydrogen in the LTA is useful for 

several reasons. Total carbon minus the carbon from carbonate decomposition (determined by the acid evolution test) will measure the residual or unburned carbonaceous 

matter in the LTA. The LTA analyses can 

subsequently be corrected for incomplete oxidation. The hydrogen determination can 

serve as an independent estimate of the 

water of hydration of the clay minerals in the 

LTA, providing a correction is first made for 

absorbed moisture. 

SUMMARY AND CONCLUSIONS 

The low-temperature plasma oxidation technique was selected by the Interlaboratory Committee for isolating the inorganic matter from the 

Herrin (No. 6) coal bed sample for subsequent 

quantitative chemical and mineralogical analysis. 

As part of the interlaboratory study, the experimental conditions of low-temperature ashing 

used by the participating laboratories were 

surveyed and were found to vary considerably. 

Despite this variation in experimental conditions, 

the reported ash yields were reasonably consistent. Nevertheless, some of the variation in results 

among laboratories can be attributed to variations 

in operating temperature and in sample moisture 

content. 

The proposed recommendations for standardization of L TA methodology should allow a quantitative ash yield comparable to the mineral matter 
content of a coal and should minimize many of the 

undesirable side reactions of the inorganic matter. 

The inorganic reactions that can occur during 

plasma oxidation are summarized; certain of these 

reactions are inherent to the technique and cannot 

15 

be avoided. Thus, future investigations using lowtemperature ashing as the method of separation 

must assess the relevance of these factors before 

interpreting the data. 

Interlaboratory Comparison of Mineral Constituents in a Coal Sample from Illinois 

Analytical Results from the Interlaboratory Sample from the 

Herrin (No. 6) Coal Bed 

A. X-RAY DIFFRACTION ANALYSIS 

By J. J. Renton, R. B. Finkelman, and F. L. Fiene 

The results of interlaboratory XRD determinations are presented in tables 9, 10, and 11. 

References describing the sample preparation 

techniques used by the participating laboratories 

are in table 13. As no independent analytical 

technique can determine the absolute composition 

of complex mineral mixtures, there can be no ''correct'' values. Therefore, no value judgements will 

be made, nor will any detailed statistical treatment of the data be offered. The results in table 9 

are from laboratories that considered their data to 

be quantitative. It is evident that there is a 

substantial range of values for each mineral 

species. This wide range undoubtedly reflects differences in sample preparation procedures, 2 in 

equipment and standards, and in the treatment of 

the basic intensity data. In view of all these 

variables, as well as the inherent errors in the 

XRD technique, it is encouraging that so many of 

the laboratories generated similar values for most 

of the mineral species. It is also encouraging to 

note that there was relatively little difference in 

the results between the LT A sent to the laboratories and the L TA that they generated. 

The major nonclay minerals (pyrite, calcite, and 

quartz) were detected or quantified by all reporting laboratories. Clay mineral data were reported 

in a number of different ways (table 9), which made 

direct comparisons difficult. Some basic statistics 

are presented in table 10. Three laboratories 

reported quantitative analyses for clay minerals 

on the basis of a separate analysis of the finer fraction of the LTA (table 12; and see section E). 

However, because of differences between laboratories in grain size of the fractions analyzed, pretreatment methods, and slide preparations, here 

too the results cannot be compared directly. The 

2

As an example, Laboratories 1, 3, 8, and 9 used cavity powder mounts, 

Laboratories 7, 10 and 12 used pressed pellets, Laboratory 4 used a spinner mount, and Laboratory 11 used a slurry mount. 

17 

data are probably a good indication of the bias introduced by using various preparation techniques. 

Marcasite, detected by most of the laboratories, 

was quantified by only three laboratories, probably due to difficulties caused by peak superposition with pyrite. Other minerals detected were 

bassanite (Laboratories 1 and 9), gypsum 

(Laboratories 6 and 23), chlorite (Laboratory 6), 

feldspar (Laboratory 9), and coquimbite and 

possibly siderite (Laboratory 23). Table 11 

presents qualitative mineral analyses based on the 

intensity ranks and intensity percentages of major 

mineral peaks. 

Several laboratories commented on their results. 

Laboratory 1 noted that the discrepancy between 

their first four pyrite values and the remaining two 

values is probably attributable to differences in 

the pyrite standards used. Laboratory 10 attributed their low values for illite to the fact that their 

illite standard had a higher degree of crystallinity 

than the illite in the LT A. They indicated that 

these low values would be omitted in favor of normative calculations. Laboratory 23 reported obtaining good results using Mo radiation on 

powdered whole coal. They stated that they can 

detect 1 percent or less of most major coal minerals and that they can quantify the pyrite content. 

They reported the following minerals in the interlaboratory L T A: illite, coquimbite, gypsum, 

kaolinite, quartz, calcite, pyrite, probably marcasite, and possibly siderite. 

Opinions were solicited from those laboratories 

participating in the study as to the feasibility of 

standardizing the quantification procedure for 

XRD. All those replying believed that a standardized quantitative technique was desirable, 

although few offered suggestions as to how this 

could be accomplished. Skepticism was expressed 

as to the possibility of agreement on any single 

procedure. It is doubtful that one technique could 

be found that would simultaneously satisfy the 
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~~I 10)~~~ 

~~~ :«>~~~~~~ j 

J ~~~ 10)~~~ £ 

~~~ I 

ICX>...-1~ ~cr.l I 

I ] 

~ 

18 

TABLE 10.-Statistics for major minerals in the interlaboratory 

sample LTA as determined by XRD 

[Mean and range in weight percent] 

Number of Range 

Mineral laboratories Mean Minimum Maximum 

Calcite 18 9 6 15 

Quartz 18 20 13 25 

~te 18 23 10 39 

aolinite 7 14 10 18 

Illite + mixed~ 

layer clays 8 31 18 40 

TABLE H.-Mineral analyses based on peak intensities detel'" 

mined by XRD of the interlaboratory sample 

[Comm., LTA supplied to the participating laboratory by the Committee; 

Lab., LT A prepared by participating J.aboratory from Herrin (No. 6) 

coal bed interlaboratory sample supplied by the Committee. Data 

from laboratory 21 total more than 100 percent because of rounding] 

Laboratory 14 16 21 

Comm.. Comm. Comm. Lab. 

Calcite 2 1 36 40 

Pyrite 3 3 19 20 

Kaolinite 4 4 22 20 

Illite + mixed-layer clays 5 5 7 6 

Marcasite 6 6 2 2 

TABLE 12.-Clay analyses, in percent, of the finer fraction ofthe 

interlaboratory LTA sample by FTIR 

[Laboratory 1 reported no chlorite and 64 percent random interlayering] 

Laboratory 1 5 6 

Expandable 

clays 65 50 39 

Kaolinite 14 35 36 

Illite 21 15 25 

Size 

fraction <2~-tm <2~-tm <10~-tm 

Preparation Sedimented glass Ceramic Sedimented 

method slide; ctreatment tile. glass slide; 

descri in Russell no preand Rimmer (1979). treatment. 

need of one laboratory for very precise and accurate data on a few samples and the need of another 

laboratory for high-volume throughput. Finally, 

most laboratories resisted the idea of abandoning 

procedures that have proved to satisfy th~ir own 

particular needs. 

B. INFRARED ANALYSIS 

By Paul C. Painter and Norman Suhr 

Two laboratories submitted data obtained from 

infrared spectroscopic methods. Both prepared 

L T A samples as KBr pellets and used Fourier 
TABLE 13.-Sample preparation techniques for X-ray diffraction analyses 

Laboratory 1. Russell, S. J. and Rimmer, S.M. 1979, Analyses of mineral matter in coal, coal gasification ash, and coal liquefac- tion residues by scanning electron microscopy and X-ray diffraction: in Analytical Methods for Cow and 

Coal Products, v. III, ed. Karr, C. Jr., p. 133-162. 

Laboratory 

Laboratory 

3. 

4. 

Stohl, F. V., 1980, The analysis of minerals in coal: Sandia Laboratories Report No. SAND-79-2016, 43 p. 

Given, P. H., Weldon, D. and Suhr, N., 1980, Investi~ation of the distribution of minerals of coals by normative 

analyses: The Pennsylvania State University Technical Report PSU-TR-22. 

Laboratory 5. Hosterman, J. W., and Loferski, P. J., 1978, Sample preparation for clay-mineral analyses by X-ray diffraction: 

U.S. Department of Energy Morgantown Energy Technology Center, DOE/METC/2287 -112, 9 p. 

Laboratory 6. Schultz, L. G., 1964, Quantitative interpretation of mineralogical composition from X-ray and chemical data for 

the Pierre shale: U.S. Geological Survey Professional Paper 391-C, p. C1-C31. 

Laboratory 7. Renton, J. J., 1979, Use of weighted X-ray diffraction data for semiquantitative estimation of minerals in low 

temperature ashes or bituminous coal and in shale: U.S. Department of Energy, METC/CR-75/5, 22 p. 

Laboratory 9. Used slurry technique. 

Laboratory 10. R. W. Schliephake, 1975, ROntgenographische Untersuchungen an Grubenstauben des deutschen 

Steinkohlenbergbaus: Reproduzierbarkut der Quarzbestimmung und indirekte Ermittlung des Ashegehalten 

Staub-Reinhalt, v. 35, no. 8, p. 295-297. 

Laboratory 11. Used slurry technique (Duco cement and amyl acetate). 

Laboratory 12. Williams, J. M., 1980, Qualitative and quantitative X-ray mineralogy: A layman's approach: Los Alamos Scientific Laboratory Information Report LA-8409-MS, 46 p. 

transform infrared (FTIR) instrumentation. In addition, Laboratory 4 determined kaolinite by 

means of a conventional dispersive infrared (IR) 

spectrometer. Results are shown in table 14. 

Dispersive IR methods depend upon the measurement of the intensity of isolated absorption bands 

characteristic of a specific mineral. Errors and difficulties are introduced by the overlap and superposition of the bands of complex multicomponent 

systems. Computer methods for analyzing such 

multicomponent systems have become routine 

with the introduction of FTIR spectroscopy. 

Painter and others (1978) used the successive subtraction of the spectra of mineral standards from 

the spectrum of the LTA, starting with the most 

strongly absorbing species (usually kaolinite), for 

the analysis of minerals in the LT A. The spectrum 

of the mineral standard is multiplied by a scaling 

factor,_ which is altered on a trial-and-error basis 

until the bands are just removed. As an example, 

figure 1 shows the subtraction of the kaolinite 

component of the spectrum of the interlaboratory 

LT A sample. Provided that the weights of the 

LTA and the mineral standards used to prepare 

the KBr pellets are accurately known, then the 

weight fraction of each mineral in the L T A can be 

calculated from the scaling factor. Painter and 

others (1981) applied least-squares spectral fitting 

methods to the analysis of mineral mixtures. In 

19 

this method, a computer program is used to obtain 

the best fit between the spectra of a set of standards and the spectrum from an LTA. This method 

was used by Laboratory 4. Laboratory 15 synthesized spectra to match the spectrum of the coal. 

There are a number of problems associated with 

FTIR methods, as recently discussed by 

Finkelman and others (1981). The most important 

problem is the choice of standards and is not 

unique to FTIR spectroscopy. A different 

kaolinite standard, used in the preliminary work, 

gave much lower values (7 percent, about half the 

final values) in the analysis of the interlaboratory 

L T A samples. To some extent the problem of 

selecting the appropriate standard has now been 

alleviated by the use of least-squares programs, 

TABLE 14.-Partial mineralogical analysis of the interlaboratory sample by FTIR 

Laboratory 

Kaolinite 

Montmorillonite 

Montmorillonite 

Illite 

Quartz 

Calcite 

[All results in weight percent] 

4 

1

15 

2!3 

310 

1.5 

25 

7 

15 

14 

50 

7 

8.5 

6 

'Kaolinite determined by conventional IR spectroscopy, 12-15 

percent. 2

Standard from Chambers, Ariz. 3

Standard from Amory, Miss. 
1035 

I 

1010 

I 

A. KAOLINITE 

B. LTA 

8-A 

I I 

1400 

I 

1200 1000 

I 

600 

CENTIMETER-1 

FIGURE I.-Example of FTIR analysis. A, spectrum of kaolinite standard; B, spectrum of LTA; B-A, difference spectrum 

obtained by subtracting spectrum A from spectrum B so that the 1035 and 1010 em - 1 bands are just removed. 

which can determine the standard that gives the 

best fit to the spectrum of the LTA (Painter and 

others, 1981). In addition, the use of an entire spectrum rather than a single, usually weak, band in 

the analysis necessitates stringent sample 

preparation requirements. For example, the 

analysis of kaolinite by conventional dispersive 

methods is based on the relatively weak 910 cm-1 

band, so that about 1 mg of kaolinite could be used 

in preparing KBr pellets. However, when this 

20 

much sample is used, other bands absorb so 

strongly that the Beer-Lambert law is no longer 

obeyed. To avoid this problem, about 0.2 mg is required for optimum absorption of the strongest 

band. This necessitates accurate weighings and 

careful and consistent pellet preparation techniques. Finally, most FTIR instruments are set for 

the mid-IR range, where pyrite has no absorption 

bands. Conversion to the far IR is necessary to 

analyze this mineral. 
In spite of these difficulties, FTIR methods appear to be a potentially powerful tool for mineralogical analysis, since all the major components 

(usually anything present to the extent of 3 percent or greater) can, in principle, be determined by 

this one method. 

C. CHEMICAL ANALYSIS 

By R. B. Finkelman 

Chemical analyses of the interlaboratory sample 

were provided by a number of laboratories using a 

variety of analytical techniques. The major- and 

trace-element data are presented in tables 15 and 

16. Despite the differences in analytical procedures and the fact that some laboratories analyzed whole coal whereas others analyzed HTA or 

L TA, there is good agreement for most elements. 

Notable exceptions are iron, zinc, manganese, and 

strontium. The scatter in the analytical results for 

these elements may be attributable to sample inhomogeneity with respect to pyrite, sphalerite, 

and carbonate minerals. The scatter in the manganese analyses may be due to contamination by 

steel (see section H). 

There was a rather serious discrepancy in the 

iron values. Those laboratories analyzing HTA or 

LTA had a range of 18.5 to 21.5 weight percent 

Fe20 3, whereas those laboratories determining Fe 

on whole coal reported values ranging from 13.1 to 

15.0 weight percent Fe20 3• Although the disagreement may have been exaggerated by recalculating 

to an ash basis, it is evident that a serious problem 

existed. Peter Zubovic (oral commun., 1979) suggested that the pyrite particles in the pulverized 

samples had begun to segregate during transportation and handling. Those laboratories analyzing 

whole coal may have just skimmed the top of the 

sample, thereby removing for analysis material 

depleted in pyrite. Those laboratories analyzing 

the ash required about 10 times more material for 

their analysis and would have dug deeper, thus 

removing a more representative sample. To test 

this suggestion, Laboratory 1 was asked to rehomogenize and reanalyze its sample. Their original 

value for Fe20 3 on whole coal by X-ray fluorescence spectroscopy was 13.1 percent; rehomogenization of the sample and reanalysis in duplicate resulted in a value of 16.0 weight percent. A 

rehomogenized sample was resubmitted to Laboratory 22, resulting in a similar increase in Fe20a 

values. Subsequent analysis of whole coal at the 

USGS (Reston) by quantitative de-arc and energydispersive X-ray fluorescence spectroscopy gave 

values of around 20 weight percent for Fe20a. In 

contrast, Laboratory 19 found little difference in 

the iron content of material taken at several intervals from the top to the bottom of their sample 

container. Evidently some segregation of pyrite 

had taken place in many of the interlaboratory 

TABLE 15.-Major-element analyses of the interlaboratory sample 

[--, not reported] 

Laboratory 9 9 9 9 10 10 4 22 

Sample type analyzed LTA LTA LTA LTA HTA:800 HTA:800 HTA:750 HTA:550 

Sample produced by (7) Comm. [20] Comm. [24] Lab. Lab. Lab. Lab. Lab. Lab. 

Mesh -60 -60 -60 -20 -60 -60 -20 -60 

Analytical technique XRF+AES XRF+AES XRF+AES XRF+AES XRF XRF XRF XRF 

Si02 47.2 47.2 47.1 47.2 47 47 47.1 44.51 

Al203 17.2 17.0 17.4 17.5 17 17 17.4 16.96 

Ti02 .88 .90 .88 .93 .9 .9 .83 .81 

Fe20s 21.5 21.3 21.3 21.4 21. 20. 20.1 18.48 

MgO .96 .98 .95 .99 1.01 

CaO 6.3 6.2 6.2 5.6 6.0 5.4 5.71 5.15 

MnO .04 .04 .05 .05 .036 .04 

N~O .61 .65 .60 .68 .71 

K20 1.78 1.80 1.78 1.84 1.8 1.8 1.83 1.73 

80s (1) (1) (1) (1) 3 3 6.5 2.25 

P205 .03 .03 .03 .03 .05(6) 

Total 96.5 96.1 96.3 96.2 96.7 95.1 101.2 90.0 

H2o+ 3.09 3.15 4.28 4.94 

H2o- 6.45 5.75 4.53 4.18 

C02 1.58 1.72 3.55 2.94 

Residual C .95 .86 .10 .08 

Pyritic S 10.1 10.2 9.8 9.5 

21 
TABLE 15.-Major-element analyses of the interlaboratory sample-(Continued) 

Laboratory 28 26 1 

Sample type analhzed HTA:750 HTA:750 we 

Sample produced y (7) Lab. Lab. Comm. 

Mesh -60 -60 -60 

Analytical technique AAS+AES AAS XRF 

Si02 43.6 46.88 49.9 

Al203 18.3 18.1 19.8 

Ti02 .76 1.10 1.0 

Fe20s 20.8 20.3 13.1 

MgO .93 .93 

CaO 5.62 6.07 5.2 

MnO .05 N~O .60 .81 .3(5) 

K20 1.68 1.81 1.5 

SOs 5.4 3.36 

P205 .11 .02 

Total 97.8 99.4 90.8 

Notes: (1) Recalculated based on 3% 803• 

(2) Recalculated based on 17.11% ash. 

(3) Recalculated from submitted analysis. (4) Recalculated based on 13.1% ash. 

(5) Instrumental neutron activation analysis. 

(6) Determined on whole coal. 

(7)Comm.-Sample (LTA or WC) supplied to participating laboratory by the Committee; [ ] indicates split number. 

Lab.-LTA pr::fcared by ~cipating laboratory from Herrin 

( o. 6) inter ratory sample supplied by the 

Committee. 

samples. No differentiation of the trace elements 

was found that corresponded to the differentiation 

of the pyrite, indicating that the pyrite in the interlaboratory sample contains few trace elements. 

Nevertheless, it is evident that extreme care must 

be taken to be certain that the material analyzed is 

representative of the original sample. 

The LT A chemical analysis supplied by 

Laboratory 9 included values for H20+, C02, carbon, and pyritic and sulfate sulfur. The availability 

of these data provided an opportunity to calculate 

the normative mineralogical composition of the 

LTA (see, for example, Pollack, 1979). The following steps outline the procedure: 

(1) Pyritic sulfur was combined with the appropriate amount of iron to form stoichiometric FeS2 (reported as pyrite). 

(2) C02 was combined with CaO to form CaC03 

(reported as calcite). 

(3) Sulfate sulfur was adjusted to account for 

organically bound sulfur. Sulfate sulfur was 

then combined with CaO and H20 to form 

CaSO" · H20 (gypsum). 

(4) Ti02 was reported as rutile. 

(5) MgO was combined with appropriate Si02, 

Al20s, FeO, and H20 to form chlorite (30 percent Si02; 20 percent Al20 3; 30 percent MgO; 

8 percent FeO; 12 percent H20). 

(6) K20 was used to form mixed-layer clays and il22 

13 19 20 

we we we 

Comm. Comm. Comm. 

-60 -60 -60 

Wet Chern. PIXE XRF+AAS Mean S.D. 

43.4 48.2 47.4 48.28 2.01 

20.9 18.3 22.7 18.94 1.58 

.66 .8 .6 .89 .13 

18.3 13.3 19.8 20.08 2.91 

1.46 .8 1.04 .19 

8.2 5.9 5.5 6.11 .81 

.04 .01 

1.39 1.65 .83 .40 

1.58 1.5 1,.80 .14 

3. 8.4 

.04 .03 

98.9 96.4 98.4 

LTA-Low-temperature ash. 

HT A-H~h-temperature ash at indicated temperature in 

~Celsius. WC-Who e coal. 

XRF-X-ray fluorescence spectroscopy. 

AES-Atomic emission spectroscopy. 

AAS-Atomic absorption spectroscopy. 

PIXE-Proton-induced X-ray emission spectroscopy. 

S.D.-Standard deviation. 

lite (50 percent Si02; 25 percent Al20 3; 5 percent K20; 7.5 percent FeO; 2 percent N~O; 

10.5 percent H20). 

(7) Remaining Al20s was used to form kaolinite 

(45 percent Si02; 39 percent Al20 3; 14 percent 

H20). 

(8) Remaining Si02 was reported as quartz. 

About 1.6 weight percent FeO was unaccounted 

for in this procedure. Perhaps it occurred as iron 

sulfates, carbonates, or oxides or in organic 

association. The calculations require about 2 

weight percent more H20 than allowed by analytical data. Perhaps the low H20 values are due to 

dehydration of the clays during low-temperature 

ashing. 

In table 17, the results from the normative calculations are compared with mean values derived 

from the XRD data in table 10. The values are 

very similar. The analytical value for unassociated 

Si02 (quartz) in the LTA is 14.1 weight percent 

(Laboratory 13), suggesting that the XRD value 

may be high. However, Given and others (1980), in 

a critical evaluation of normative analysis, indicated that this procedure tends to underestimate 

quartz content. Laboratory 8, using normative 

calculations and qualitative XRD, obtained the 

following percentages: pyrite, 23; marcasite, 3; 

calcite, 10; kaolinite, 24; illite, 24; and quartz, 16. 

In addition to the trace-element values in table 
TABLE 16.-Trace-element analyses of the Herrin (No.6) interlaboratory sample 

[All values in ppm on a whole-coal basis.---, not reported] 

Laboratory 9 9 22 22 22 22 14 28 19 20 29 

Sample 

type 

analyz¢ we we we we HTA:550 HTA:550 we LTA HTA:750 we we we Sample 

produced 

by (4) Comm. eomm. Comm. eomm. Lab. Lab. Comm. Lab. Lab. Comm. eomm. eomm. 

Mesh -60 -20 -60 -60 -60 -60 -60 -60 -60 -60 -60 -60 

Analytical 

technique XRF XRF NAA NAA AAS AES AES AES AES PIXE NAA NAA 

Ag <0.3 0.02 <0.3 

As 3 3 1.7 1.5 2.3 1.8 1.4 1.8 

Au <.05 <.01 

B >130 460 160 

Ba 54 55 46.8 52 48 47.7 <84 84 

Be 1.3 1.35 

Bi 1 2 

Br 3 3 2.9 2.15 2.8 1.4 2.2 

Cd <4 <4 .18 .08 <4.8 

Ce 19 21 10 9 24.7 9.8 

e1 160 110 

Co 2 2 5 3.9 4.4 5 5.2 4.7 4.32 

er 15 13.8 16.9 20 17.7 20 14.7 13 

es <.5 <.5 .9 .9 1.0 .9 

Cu 3 5 8.7 6.4 13 10.8 7.9 2(5) 

Eu .23 .18 .24 .21 

F 32(1,2) 

Ga 5 4 3.7 4.0 <4 3.4 

Ge 7 8 6.2 16 6.6 

Hf .5 .4 .5 

Hg <2 <2 .042(1) .36 

La <3 <3 6 5 6.5 5.1 5.2 

Li 8.8 

Lu <2 <2 .08 .10 .08 .2 

Mn 45 47 40 36.4 66.3 55 80 42.8 24 24(5) 37 

Mo <1 <1 4 4.6 6 3.6 

Nb 2.0 2.0 

Nd <30 <23 

Ni 17 19 20 16.9 24 16 16.0 17.3 26.0 

Ph 3.8 7.9 6.2 6.4 

Rb 13 13 13 13.2 17.7 12 

Sb <1 <1 .3 .2 .31 .16 .2 

Sc 4 4 2.0 2.37 3.1 3.0 2.68 

Se 2 2 2.0 1.9 2.04 1.8 1.9 2.2 

Sm 1.1 .8 1.0 

Sn 5.5 6.5 

Sr 30 30 11 44.2 20.8 28.2 

Ta .15 .08 .17 .13 

Tb .13 .15 .24 .07 

Th 1.9 1.9 1.8 2.5 .2. 

u 1 <1 1.1 .85(3) 1.5 .8 .9 

v 24 25 19.5 25 16 23.78 13.0 21.3 w <2 <2 .3 .3 

y 6 6 6.0 6.0 

Yb .7 .6 .7 .58 

Zn 38 53 22 27 33.8 312 22.4 33.3 45 65.9(6) 

Zr 23 25 15.6 <23 32 21.2 

Notes: (1) Determined on whole coal LTA-Low-temperature ash. 

(2) Ion-specific electrode. HTA-H~h-temperature ash at indicated temperature in 

(3) Delayed neutron activation analysis. ~Celsius. (4) eomm.-Sample (LTA or We) supplied to participating labora- we-Who e coal 

tory by the Committee. XRF-X-ray fluorescence spectroscopy. 

Lab.-LTA prepared by ~cipating laboratory from Herrin AES-Atomic emission spectroscopy. 

(No. 6) inter ratory sample supplied by the AAS-Atomic absorption spectroscopy. 

Committee. FIXE-Proton-induced X-ray emission spectroscopy. 

(5) Determined bb AAS. 

(6) AAS value: 3 ppm Zn. 

NAA-Neutron activation analysis. 

23 
TABLE 17.-Comparison of normative calculations with XRD 

results from table 10 

Pyrite 

Calcite 

Gypsum 

Rutile 

Chlorite 

Mixed-layer clays + illite 

Kaolinite 

Quartz 

[--, no data] 

Normative 

Calculation 

20.7 

8.3 

1.4 

0.8 

31.0 2.8 l =50.8 

17.0 

16.7 

Mean value 

from XRD 

23 

9 

31 l =45 

14 

20 

16, Finkelman and Aruscavage (1981) obtained the 

following values (whole-coal basis): Pt < 2 ppb; Pd 

< 1 ppb; Rh < 0.5 ppb. 

D. QUANTITATIVE ANALYSIS OF PYRITIC SULFUR 

BY MEAt.!S OF MOSSBAUER SPECTROSCOPY 

By Pedro A. Montano 

Mossbauer spectra and background radiation 

(fig. 2) were recorded for six pellets of different 

thicknesses prepared from the interlaboratory 

sample. Total spectral area is plotted against 

thickness in milligrams per square centimeter in 

figure 3. The amount of pyritic sulfur in each of the 

six pellets was determined from the total spectral 

area These values appear to be very consistent 

(table 18). Other than Fe2

+ in FeS2, only a very 

small amount of Fe2+ (probably in illite) was 

detected. The values are close to those observed 

for Fe2

+ in clays. 

Figure 4 is a spectrum of the interlaboratory 

coal sample taken 1 year after it was received. It 

can be seen that the overall shape of the spectrum 

has changed. Only about 1.1 percent pyritic sulfur 

remains, and there is now very clear evidence of 

weathering; szomolnokite and possibly coquimbite 

are present, as is ferric sulfate. The amount of 

szomolnokite is so large that it almost completely 

covers the contribution of the Fe2+ impurities in 

the clays. The coal was stored in a desiccator, 

which was evacuated to avoid moisture absorption 

by the sample. However, the period of time that 

the sample was exposed to air when being used for 

other studies (from 1 hour to 12 hours) was enough 

to alter the iron constituents. The ferric sulfate is 

probably jarosite. The ferrous sulfate was unequivocally identified as szomolnokite. Care must 

24 

be taken in analyzing the interlaboratory sample 

due to the effects of weathering. LTA of the 

samples was also analyzed, and no other ironbearing mineral was found. 

The pyritic sulfur values determined in 

Laboratory 27 by Mossbauer spectroscopy (Huffman and Huggins, 1978) are very close to the value 

of 1. 76 percent obtained by the ASTM test 

method for forms of sulfur performed in the same 

laboratory (ASTM, 1981). The results of triplicate 

Mossbauer analyses by this laboratory are shown 

in table 19. The Mossbauer spectra consist of three 

absorption doublets arising from pyrite, jarosite, 

and an unidentified ferrous phase. This last absorption doublet is very broad, and its parameters 

are not compatible with any expected mineral 

(closest is melanterite, FeSO 4 • 7H20); it most likely 

arises from two or more very minor ferrous minerals. Scanning electron microscopy-automated image analysis (SEM-AIA, see section G) indicates 

the presence of small amounts of iron sulfate, ironrich clay (chlorite), and possibly siderite, in addition to the clay mineral illite, which may contain 

minor Fe2

+. The combination of melanterite [isomer 

shift (IS) = 1.29, quadrupole splitting (QS) = 3.18 

mm/s], szomolnokite (IS= 1.26, QS = 2.71 mm/s), 

and ferrous clay (IS = 1.13, QS = 2.65 mm/s) 

could well result in such a doublet. 

The QS (0.587 ±0.008 mm/s) measured for FeS2 

in this coal is significantly less than that for pure 

pyrite (0.61 mm/s) and approaches the QS of marcasite (0.51 mm/s), the polymorph of pyrite. This 

reduction suggests that as much as 25 percent of 

the FeS2 absorption may be due to marcasite. 

E. QUALITATIVE CLAY MINERAL 

ANALYSIS 

By R. S. Dean 

A mineralogical analysis of the interlaboratory 

sample was carried out by XRD techniques. The 

basal reflections from the clay minerals were 

studied in oriented mounts prepared from the 

-5-p.m size fraction of the LTA. Clay mineral hk 

reflections and reflections from nonclay minerals 

were examined in the unfractionated and -5-p.m 

LTA by a Guinier-de Wolff powder camera A 

detailed description of the procedures followed and 

results obtained has been reported (Dean, 1979). 
~ 

z 

w 

u 

a: 

w 

a.. 

100 

83 

Fe 2+ FeS2 

.... ~~ t /~--..v--

.. \ /~ 

-1 

\ I 

~ t ~7' F"t'f 

\ (\ f 

\ : \ I 

I l : I 

\ : \ I 

I I I I : i , I I I I ~ : '\ : 

: I : I 

\ ~ \ : 

; I ~ I 

\ : \ : 

: I ; t 

\ : \ : 

1

l v ,, w 

0 1 

MILLIMETERS PER SECOND 

2 

FIGURE 2.-Mossbauer spectrum at room temperature of the fresh Herrin (No. 6) interlaboratory sample. Pyrite (FeS2) is the 

dominant phase. Fe2+ in clays is also indicated. A small amount of Fe3+ may be present, but it is negligible compared to the 

other two species. 

25 
<( 

w 

a: 

<( 

.2-

;i .1 1-

a: 

t; 

w 

a.. 

C/) 

... ······· 

I 

... ······················ 

.. 

I 

100 

I 

.. ··· .. 

.. .. .. .. .. · 

I 

I 

D D 

D 

.... ·· .. .. .... -····· . 

l 

300 

0 

, .. 

0 

•••• •••• 

.. 

I 

0 -2 

.. · ••• • .. ·· 

I 

a: 

:::::> 

u... 

..J 

:::::> 

C/) 

-1 1-

z 

w 

u 

a: 

w 

a.. 

MILLIGRAMS PER SQUARE CENTIMETER 

FIGURE 3.-Pyritic sulfur determination in coal using Mossbauer spectroscopy. The left ordinate indicates the 

spectral area (closed circle) and the right ordinate indicates the weight percent pyritic sulfur (open square) 

determined from the spectral area. 

The mineralogical composition of the unfractionated LTA was found to be as follows: 

Abundant: Quartz, mixed-layer 2:1 layer silicates 

(including chlorite), pyrite 

Moderately abundant: Kaolinite (fairly well 

crystallized), calcite 

Rare: Illite, marcasite 

Trace: Anatase 

The clay minerals are concentrated within the 

-5-J.Lm size fraction of the LTA and consist of 

fairly well crystallized kaolinite, the mixed-layer 

assemblage, and minor illite. Transmission 

(Guinier) powder photographs of the -5-J.Lm LTA 

following NaOH dissolution of dehydroxylated 

kaolinite by the method of Hashimoto and 

TABLE 18.-Mossbauer determination of 

pyritic sulfur in the interlaboratory coal 

sample 

Sample number 

1 

2 

3 

4 

5 

6 

Mean 

Standard deviation 

Weight percent 

pyritic sulfur 

1.97 

1.88 

1.91 

2.08 

1.91 

1.95 

1.95 

0.07 

Jackson (1960) showed no mica polymorph reflections, indicating that the illite is stacking 

disordered (1Md). 

26 
t-.:) 

-l 

1-

z 

w 

u 

0:: 

w 

a.. 

100 

97 

WI • -#!Jtllt .............. i"'•.•-

. ·. -··.,.·.~\ •• •• • • ._. • ....... w lfi*P'W4 • '.-. . 

-1 

i 

' ' ~ 

I 

I 

' ~ 

I 

I 

I 

I 

I 

I 

\ 

I 

v 

·. 

I 

I 

I 

I 

\ -

v 

0 1 

MILLIMETERS PER SECOND 

.. 

2 

FIGURE 4.- Mossbauer spectrum at room temperature of the Henin (No. 6) interlaboratory sample after 1 year in a vacuum desiccator. There is 

strong evidence that pyrite is transformed to szomolnokite and coquimbite. 
TABLE 19.·-Mossbauer ckta for the Herrin (No.6) 

interlaboratory sample 

[Isomer shift (IS) in mm/s relative to Fe foil, quadrupole splitting (QS) in 

mm!s, and percentage of total iron contained in the different minerals 

(Pet). Values in parentheses for samples 1 throu~h . 3 represent 

statistical uncertainties in terms of least significant digit shown; i.e., IS for pyrite of 0.312(1) indicates a vafue of 0.312±0.001. For 

the average, the uncertainties quoted also include variation between 

the three samples and represent approximately one standard deviation in terms of the least significant figure shown. Fe2+, unidentified 

ferrous phases (see text).] 

Mossbauer parameters PctJK;;tic Sample IS QS Pet s 1 

1. Pyrite 0.312(1) 0.587(1) 92(1) 1.75(2) 

Fe2+ 1.22(3) 3.06(5) 3(1) 

Jarosite .40(2) 1.13(4) 5(1) 

2. Pyrite .307(1) .596(1) 94(1) 1.84(2) 

FeZ+ 1.21(2) 3.00(4) 3(1) 

Jarosite .40(1) 1.12(2) 4(1) 

3. Pyrite .306(1) .579(1) 94(1) 1.77(2) 

Fe2+ 1.22(2) 3.05(4) 2(1) 

Jarosite .37(1) 1.13(2) 4(1) 

Average Pyrite .308(4) .587(8) 93(1) 1.79(5) 

of 3 Fe2+ 1.22(2) 3.04(4) 3(1) 

Jarosite .39(2) 1.13(3) 4(1) 

'Weight percent pJ:tic sulfur (as-received coal basis) determined from 

Mossbauer data as escribed in Huffman and Huggins (1978). 

The mixed-layer assemblage consists of two 

mixed-layer systems, each of which is sufficiently 

extensive to diffract X-rays independently. The 

first of these is an interstratified mixture of illite 

and expandable 2:1 layer silicates; the second appears to be a three-component mixed-layer system 

containing illite, expandable 2:1 layer silicates, 

and ferromagnesian chlorite layers. Identification 

of the last phase was facilitated by heat treatment 

at 550°C, the temperature at which chlorite interlayer dehydroxylation occurred. The distribution 

of illite layers within the mixed-layer assemblage 

was studied by using the LiN03 fusion technique 

of Murthy and others (1973). Within the mixedlayer systems, illite and chlorite layers are most 

likely discontinuous and have a "frayed edge" 

relationship with the expandable layers; that is, 

there are continuous compositional gradations between illitic or chloritic "core" areas and crystallite areas rich in expandable layers. 

It is suggested that both mixed-layer systems 

are diagenetic alteration products of a pre-existing 

major smectite-like phase. The minor illite occurring as a separate phase is likely the end product of 

the development of the illite-expandable layerF. SCANNING ELECTRON MICROSCOPY 

STUDY 

By Robert B. Finkelman 

Two coal blocks (cut perpendicular to the bedding, approximately 2 em on edge) were polished, 

carbon coated, and examined with a scanning electron microscope (SEM) equipped with an energy 

dispersive detector. (For details of sample preparation and analysis see Finkelman, 1978; Finkelman 

and Stanton, 1978; Stanton and Finkelman, 1979.) 

In the SEM, the two coal blocks exhibited distinct banding, some bands containing mineral 

grains covering more than 75 percent of the surface area. Inertinite macerals, primarily fusinite 

and semifusinite but also including sclerotinite, 

are common (figs. 5, 6). Globular organic particles 

are common; the low contrast and low relief suggest that they may be corpocollinite. The banded 

mixed layer system. The absence of stacking order FIGURE 5.-SEM photomicrograph of a polished block of the 

within the unmixed illite is consistent with its Herrin (No. 6) coal depicting kaolinite filling veins and merprobably diagenetic origin. tinite pores. Scale bar is 100 JLID. 

28 
FIGURE 6.-SEM photomicrograph of a polished block of the 

Herrin (No. 6) coal depicting a large inertinite fragment. 

Many inertinite pores are filled with kaolinite; others are 

empty, perhaps due to plucking during polishing. Scale bar is 

100 ~tm. 

material consists predominantly of illite, mixedlayer clays, and subrounded to angular quartz particles (most < 10 I-'m). Pyrite framboids are ubiquitous. Other pyrite morphologies, such as 

euhedral crystals, skeletal grains, irregularly 

shaped particles, and vein fillings, are less common. Inertinite pore fillings are exclusively 

kaolinite (fig. 5). Many noncrushed inertinite pores 

are devoid of minerals, probably an indication of 

substantial plucking during polishing (fig. 6). 

Kaolinite also occurs as vein fillings (fig. 5). 

Kaolinite-quartz intergrowths were noted. Contamination of the polished surface by flecks of 

cerium-oxide polishing compound made it difficult 

to detect the micrometer-sized accessory phases. 

Those that were detected include rare-earth phosphates and possibly rare-earth silicates occurring 

in the banded material and in the vitrinite, a zircon 

included within a quartz grain, a barium sulfate 

(association unclear), a titanium oxide particle in 

29 

the banded material, a lens of an iron magnesium 

aluminum silicate (chlorite?), and a sphalerite pore 

filling. The textural evidence indicates that the 

minerals in the bands (quartz, illite, mixed-layer 

clay, zircon, rare-earth minerals, rutile?) are 

detrital, whereas those minerals occurring as vein 

and pore fillings (kaolinite, pyrite, sphalerite) are 

authigenic (Finkelman, 1982). No carbonates were 

observed in the polished blocks. The absence of 

carbonates may indicate that carbonate minerals 

are epigenetic, occurring in veins and cleats, and 

are not intimately associated with the coal. A density separation was made of the interlaboratory 

LTA. Abundant pyrite was found by SEM in the 

L T A fraction that sank in liquid having a specific 

gravity of 3.3. No other heavy minerals 

were observed. 

G. SCANNING ELECTRON MICROSCOPYAUTOMATED IMAGE ANALYSIS 

By F. E. Huggins, G. P. Huffman, and R. J. Lee 

Scanning electron microscopy-automated image 

analysis (SEM-AIA) was performed as described 

by Huggins and others (1980) on two separate 

samples (A and B in table 20), one of which was 

analyzed twice in different areas (A1 and A2). 

More than 3,000 mineral particles were examined 

in the course of these analyses, and 16 individual 

minerals were recognized on the basis of the 

energy-dispersive X-ray spectra The results of the 

three runs, adjusted for pyrite overestimation 

(Huggins and others, 1980), are shown in table 20. 

Excellent agreement among the three determinations is found. The principal minerals found are 

pyrite, quartz, illite, kaolinite, and calcite. The 

mixed-silicate category also makes a sizable contribution; it consists mainly of intimately associated combinations of quartz and illite. Mixed-layer 

clays (for example, illite-montmorillonite) are also 

in this category. The only other significant 

category is the silicate-sulfur category, which 

represents the association of silicate minerals and 

sulfur. The strong sulfur background from the 

high organic sulfur content was sufficient to cause 

some of the silicate minerals to fall in this 

category. 

A summary of the results is presented in table 

21. The left-hand column is an average of the three 

SEM-AIA determinations shown in table 20. The 
TABLE 20.-Results of SEM-AIA analysis of the Herrin (No. 6) 

interlaboratory sample, in weight percent 

[tr, trace, <5 particles] 

Mineral category A1 A2 B 

Quartz 15 16 13 

Kaolinite 4 5 6 

Illite 5 4 5 

Montmorillonite 2 tr tr 

Mixed silicates 26 23 26 

Pyrite 25 28 28 

Calcite 7 5 5 

Siderite-Fe oxide tr 1 tr 

Fe sulfate tr 1 1 

Sulfur tr tr 1 

Others1 3 5 4 

Silicate-sulfur 7 7 7 

Silicate-pyrite 3 2 1 

Unknown 2 2 2 1

Includes chlorite, jarosite, gypsum, K-feldspar, Ti02, apatite, ZnS, 

BaSO •. 

right-hand column is derived from the left-hand 

column and should permit a more direct comparison with XRD and FTIR spectroscopy determinations. These data were obtained by apportioning 

the mixed-silicate, silicate-sulfur, and silicatepyrite categories among the principal minerals. On 

the basis of the average compositions of these 

categories, the silicate fractions were apportioned 

in the ratio illite:quartz:kaolinite = 6:3:1. The 

Mossbauer data (see section D) indicate that as 

much as one-fourth of the pyrite could actually be 

marcasite. Also shown in table 21 are the approximate abundances of the numerous minor phases 

that contribute to the "others" category. 

In conclusion, the mineralogy of this coal is 

dominated by about equal amounts of quartz, illite, and pyrite and lesser amounts of kaolinite, 

calcite, and possibly marcasite. Minor amounts of 

12 other minerals were observed, none of which 

contributes more than 2 weight percent of the 

mineral matter. 

H. MAGNETIC CONTAMINATION 

OF THE PULVERIZED 

INTERLABORATORY SAMPLE 

By F. E. Senftle, A. N. Thorpe, 

C. C. Alexander, and R. B. Finkelman 

Except for some specific studies, most coal 

research is carried out on coal samples that have 

been pulverized in a steel crusher and grinder. It is 

generally recognized that steel pulverizers 

30 

TABLE 21.-Minerals in Herrin (No. 6) interlaboratory sample, 

in weight percent 

[Average is for 3 SEM-AIA analyses from table 20; for adjusted average, 

illite, quartz, and kaolinite values are recalculated to include mixed 

silicates, silicate-sulfur, and silicate-pyrite] 

Mineral category Average Average adjusted 

Quartz 15 24 

Kaolinite 5 8 

Illite 5 23 

Mixed silicates 25 

Pyrite 1

27 1

28 

Calcite 6 6 

Silicate-sulfur 7 

Silicate-pyrite 2 

Others2 6 8 

Unknown 2 2 

1

Mossbauer data indicate that as much as one-fourth of the pyrite (7 wt. pet of mineral matter) may be marcasite. 2

lncludes the following: 1-2 wt. J,>Ct-montmorillonite, iron sulfate, 

sulfur; 0.2-1 wt. pet-chlorite, jarosite, gypsum, K-feldspar, siderite-Fe 

oxide; <0.2 wt. pet-apatite, Ti02, ZnS, BaSO •. 

undergo significant abrasive wear even when soft 

materials such as coal are crushed (Suh, 1978; 

Douglas and Ditchbum, 1980). Therefore, some 

contamination of crushed coal by abraded metal is 

to be expected. In most cases, such as majorelement analysis, the contamination of coal from 

abrasion is negligible. However, for trace analysis 

of specific elements, abrasion can be a serious 

source of contamination. Schultz and others (1975) 

found a twofold increase in the manganese concentration in a coal sample after pulverizing in a 

manganese steel jaw crusher. Although there is 

about 6 to 10 times more iron than manganese in 

manganese steel, the concentration of iron in most 

bituminous coals is generally so high that abrasion 

does not pose a serious contamination problem for 

chemical analysis. Except where trace quantities 

of those elements found in the steel are a problem, 

coal samples can be pulverized in a steel pulverizer 

without significant contamination. 

However, for magnetic studies of coal, abrasion 

particles from the crusher and grinder can conceivably be a problem. Ergun and Bean (1968), for 

instance, noted that magnetic susceptibility 

studies of pulverized coal were meaningless 

because of ferromagnetic contamination. In a more 

recent study of pulverized coal, Jacobs and others 

(1978) found the magnetization was enhanced by 

the pulverization process. They attributed the increase in part to the conversion of pyrite to pyrrhotite but were unable to account for a significant 

fraction of the increased magnetization. In the 

course of a study on the magnetic properties of 

coal (Alexander and others, 1979), we observed, in 
some instances, significant variations in magnetic 

susceptibility among several small samples of 

powdered coal from the same bulk powdered sample. To detennine the significance of possible contamination due to pulverizing coal in a steel 

crusher and grinder, samples of the interlaboratory coal sample were studied in detail. 

EXPERIMENTAL 

Because of the large amount of coal (approximately 20 kg) that was processed for the interlaboratory study, the coal was initially crushed in 

a manganese steel jaw crusher and grinder. The 

magnetic susceptibilities of six powdered samples 

from bottle 2 and one sample from bottle 27 were 

initially measured at room temperature and also at 

liquid nitrogen temperature as a function of the 

magnetic field up to 6 kilo-oersteds (kOe). The 

same samples were then measured as a function of 

temperature at a fixed field strength (1.85 kOe). 

The details of the method of magnetic measurement are given in Alexander and others (1979). 

Because the low field measurements showed the 

presence of abnormally high paramagnetism, additional studies were made on a few selected samples 

at slightly higher magnetic fields (approximately 

10 kOe) using a commercial magnetometer and using a Faraday balance at several fixed temperatures at various field strengths to a maximum of 

4.5 kOe. For comparison, unpulverized single fragments were also measured. A relatively large 

single piece of coal from the interlaboratory coal 

sample was fragmented in a porcelain mortar, and 

five small fragments, each a little less than 100 

mg, were measured under the same conditions as 

the powders. Separates removed from the pulverized interlaboratory sample with a hand magnet 

were examined by the SEM and analyzed with the 

energy-dispersive X-ray analyzer (EDAX). 

RESULTS AND DISCUSSION 

The analytical results on the pulverized coals 

and coal fragments are presented in table 22. The 

room-temperature magnetic susceptibility of all 

the powder is positive in spite of the preponderance of diamagnetic material in the coal. Most 

bituminous coal samples usually have a negative 

(diamagnetic) magnetic susceptibility, as shown 

31 

by the fragments. The positive value of the susceptibility indicates that some part of the 

powdered specimens is making a substantial 

paramagnetic and (or) ferromagnetic contribution 

to the total magnetic susceptibility. 

The specific magnetization of all the samples 

was detennined from an Owen-Honda plot (Owen, 

1912; Honda, 1910), that is, x = Xo + s/H (where x = the magnetic susceptibility, s = the magnetization, and H = the magnetic field strength), at 

fields as high as 6 kOe. If all the ferromagnetic 

minerals or fragments in the samples are completely saturated, this type of plot yields a straight line 

whose slope is the specific magnetization, s. The 

coal fragments yielded normal monotonically increasing straight-line curves indicating complete 

saturation, whereas straight-line relations were obtained for the pulverized samples only at fields in 

excess of 2 kOe. Apparently, a significant fraction 

of the abrasion fragments was not saturated at 

fields less than 2 kOe. Alexander and others (1979) 

gave a more detailed discussion of the type of plot 

relative to coal. In a few cases the plots of the x 

versus 1/H data in the vicinity of 2 kOe showed a 

slight inflection, and the value of s was obtained 

from the best straight-line fit to the data. In these 

cases, the value of s may be slightly lower than the 

true value. The pulverized Herrin (No. 6) coal had 

specific magnetizations that were approximately 

two orders of magnitude larger than the specific 

magnetization measurements of the fragments. 

Again, this indicates the presence of a significant 

amount of a ferromagnetic phase in the pulverized 

samples. The presence of this phase was confirmed 

by washing several pulverized samples in warm 

HCI. Mter washing, this ferromagnetic phase was 

absent, the specific magnetization was reduced 

essentially to zero, and the magnetic susceptibility 

returned to -0.3 X 10-6 emu g-1 (electromagnetic 

units per gram), a value close to that found for the 

single fragments of coal. The only problem with 

this explanation is that the intercept, Xo' on the 

same plot is positive for the powdered specimens 

rather than negative as found for most coal fragments. This suggests that a substantial paramagnetic phase also may have been introduced into the 

ground coal. 

The presence of a paramagnetic phase can best 

be studied by measuring the Curie constant. To 

detennine this constant, the magnetic susceptibility was plotted as a function of the reciprocal 

temperature (1/T) from 77 to 300 K, at a fixed field, 
1.85 kOe. The slope of the resulting straight line is 

the Curie constant, C, and the intercept on the axis 

, is the temperature-independent susceptibility, Xr· 

Xr includes the diamagnetism, the paramagnetism, 

and the sum of the temperature-independent ferromagnetic components ranging from fully saturated to unsaturated phases. Complete saturation could be obtained at higher fields, but at high 

fields the magnetic susceptibility of the saturated 

ferromagnetic components (x1 = s/H) included in 

Xr will necessarily become smaller. To accentuate 

the value of Xr and to obtain a better estimate of 

the saturable and nonsaturable ferromagnetic 

components, the magnitude of the field should be 

below that required for complete saturation. The 

ferromagnetic component, xf' has been subtracted 

from Xr to obtain the temperature-independent susceptibility, x'1

, of the diamagnetic and paramagnetic components only. Thus x'r = Xr- Xf· 

The average value of C for the pulverized coal 

samples was found to be 2 to 3 times larger than 

that for the coal fragments. Ferromagnetic particles from the grinder should not substantially 

change the Curie constant, and therefore this 

result was unexpected. The abnormally high 

values of s and C indicate that a substantial 

amount of both ferromagnetic and paramagnetic 

contamination was introduced during the pulverizing process. Similarly, the pulverized samples had 

values of x'r significantly higher than those of the 

fragments. x'r for most coals is generally less than 

-0.6 X lo-s emu g-1 because of the preponderance 

of diamagnetic hydrocarbon material. 

To determine whether, owing to pulverization, 

some iron mineral had been oxidized to Fe30 4, as 

suggested previously (Ergun and Bean, 1968; 

Jacobs and others, 1978), or to free radicals, three 

of the measured fragments were pulverized in an 

agate mortar and the same magnetic properties 

were remeasured. The results are not very different from the whole-fragment data (table 22). 

These same samples were remeasured approximately a month later to check for oxidation, and 

the results were virtually the same. The large 

values of the magnetic properties observed for coal 

ground in a steel pulverizer thus could not have 

been due to oxidation or to magnetic centers introduced by the grinding process, and the 

suspected contamination must, therefore, have 

come from the grinder itself. 

To confirm that the steel pulverizer was a source 

of contamination, a hand magnet was used to 

separate a ferromagnetic fraction from the 

pulverized samples and also from a coal fragment 

freshly powdered in a porcelain mortar. The 

pulverized samples contained microscopic ferromagnetic fragments (1-20 ~tm) which, under the 

influence of a small hand magnet, formed 

TABLE 22.-Magnetic properties of the Herrin (No.6) interlaboratory sample 

rrhe magnetization, S, the magnetic susceptibility at infinite field, X ' at room temperature (298 K) and at 77 K, and the corrected temperatureindependent susceptibility, x'r' are in electromagnetic units (emu) g-1

; the Curie constant, C, is in emu K g-1

] 

298 K 77K 

s Xo s Xo c Xr Sample Mass 

No. (mg) (Xl0-4) (X lO-s) (Xl0-4

) (Xl0-6

) (Xl0-4) (Xl0-6

) 

Pulverized samples 

H984A 70.65 95.0 .85 86.0 2.80 1.57 - .21 

H984B 71.66 95.0 .85 86.0 2.80 1.57 - .21 

H984H 73.11 95.0 .85 65.5 5.15 2.66 -3.62 

H984J 68.98 99.0 1.0 77.0 5.60 3.12 -3.81 

H984K 66.48 71.0 .90 64.3 5.40 2.27 -2.55 

H984L 64.98 79.5 1.1 81.0 5.15 3.87 -3.02 

Hl007 60.50 67.3 .55 81.0 2.10 1.73 - .39 

Single fragments 

H984C 83.33 .35 -.36 3.65 .29 .73 - .68 

H984D 74.50 .58 -.32 1.55 .52 .82 - .705 

H984E 89.57 .35 -.36 1.55 .51 .89 - .77 

H984F 85.71 0 -.44 .90 .14 .765 - .625 

H984G 93.92 0 -.30 1.50 .89 .92 - .625 

Samples fragmented in agate mortar 

H984C 56.84 0 -.44 0 .44 .91 - .75 

H984E 57.11 0 -.30 0 .58 .90 - .59 

H984G 61.30 0 -.30 -.45 .60 .84 - .57 

32 
magnetic chains of irregularly shaped particles. 

Only a few ferromagnetic particles were recovered 

from the mortar-ground coal. Under the optical 

microscope, no elongated or lustrous metallic 

fragments, such as might be expected from a steel 

pulverizer, could be observed in either sample. 

With the SEM, set at higher magnification, a few 

peeled and knurled fragments were observed in the 

magnetic fraction separate from the pulverized 

sample (fig. 7). EDAX analysis of these fragments 

showed the presence of iron and a small amount of 

manganese. Approximately the same analysis was 

obtained on particles picked up with sticky tape 

from the grinder plate used to process the Herrin 

(No.6) coal sample. An XRD pattern of the ferromagnetic material from the pulverized coal sample 

showed that it was a-iron. In a similar ferromagnetic fraction separated from the single 

piece of coal crushed in the mortar, only iron was 

FIGURE 7.-SEM photograph of ferromagnetic particles exobserved by means of EDAX, and a diffraction 

pattern of magnetite, Fe30 4, was obtained. 

Although the steel particles were smaller than 

expected, the abraded iron as seen by means of the 

SEM had particles that appeared to be larger than 

a single magnetic domain. If we assume that virtually all the steel particles were multidomain, the 

magnetization, s, should be the only seriously affected magnetic property in the powdered coal. 

However, as shown in table 22, the susceptibility, 

Xo• the Curie constant, C, and the temperatureindependent susceptibility, x" which are all primarily paramagnetic properties, were abnormally 

high in the pulverized specimens compared with 

the fragments or mortar-ground samples. A possible explanation of the high paramagnetic properties observed in the pulverized coal samples is the 

presence of superparamagnetic contamination in 

addition to the ferromagnetic steel particles. We 

have examined the superparamagnetic properties 

of the contaminating particles in more detail in a 

separate paper (Senftle and others, 1982). It was 

found that the abraded steel particles were about 

1.5 nm in diameter and that these small particles 

tended to agglomerate into multidomain particles 

in a magnetic field. The clusters significantly 

changed the magnetization of the whole coal. The 

total concentration of contaminating steel from 

the grinder is approximately 2.1 X 10-4 g/g of coal. 

SUMMARY 

The SEM-EDAX results confirm the inferences 

from magnetic measurements; namely, that coals 

crushed in a steel pulverizer are most certainly 

contaminated by abrasion fragments from the 

crusher and that the contamination seriously affects the measured magnetic properties of the coal. 

For a relatively soft material, such as coal, the 

abraded particles are very small compared to 

similar particles formed during the grinding of 

rocks, and therefore they initially were not 

detected by means of an optical microscope. 

I. MINERALOGY OF "DEMINERALIZED" COAL 

tracted from the Herrin (No. 6) interlaboratory sample. By Robert B. Finkelman and Frederick 0. Simon 

Lumps of magnetic particles of knurled and curled shavings 

composed of Fe (major) and Mn (minor) are believed to have Increasing use is being made of "demineralized" 

originated when the sample was powdered in a steel crusher. coals both in laboratory experiments (Kuhn and 

33 
others, 1978) and in technological processes (Jones 

and Rottendorf, 1980). Treating ground coal in 

various mineral acids presumably removes most, if 

not all, of the minerals in the coal, resulting in a 

clean (''demineralized'') coal sample. 

A subsample of the interlaboratory coal sample 

was "demineralized" according to the procedure 

outlined by Kuhn and others (1978). The -60 

mesh coal was separated in a liquid having a 

specific gravity of 1.40. The float fraction was 

refluxed with 10 percent HN03 for 2 hours. The 

HN03 was separated by centrifugation, and the 

coal was washed with distilled water and dried on 

a steambath (at approximately 70°C). The coal 

was then treated with 48 percent HF for 2 hours at 

70°C. After centrifugation and rinsing with 

distilled water, the coal was treated with 1:3 HCl 

for 1 hour at 70°C. The subsample was washed 

with distilled H20 and dried at 70°C. This procedure brought the LT A content of the float fraction 

down from 8 weight percent to 1.5 weight percent 

for the coal washed in HN03 and HF and to 0.5 

weight percent after the HCl wash. 

Polished pellets prepared from these two 

"demineralized" subsamples (1.5 percent and 0.5 

percent LTA) were examined in the SEM. It was 

evident that the demineralization procedure was 

very efficient but very specific. The coal particles, 

most of which appeared to be fractured, were virtually devoid of mineral grains. Essentially all the 

clays and quartz grains had been removed by the 

HF treatment. Only one unfractured coal particle 

contained clay particles. Many of the coal particles 

appeared pitted. These pits were generally alined, 

similar to the banded minerals in the untreated 

coal. These pits probably represented the clays 

and quartz grains that had been leached from the 

coal. Iron sulfides were common. The sulfides (presumably pyrite) occurred in fusinite pores, as 

clusters in vitrinite, and even as isolated massive 

particles. The only carbonate grain detected was a 

large calcite particle completely embedded in an 

unfractured coal particle. Numerous acid-resistant 

minerals were observed in both mounts. These include (in order of decreasing abundance) titanium 

oxides, zircon, laths of an iron aluminum silicate, 

niobium oxide, yttrium phosphate, and a crystal of 

aluminum oxide. There did not appear to be any 

significant difference in the mineralogy of the two 

samples. 

The two "demineralized" coal samples were 

ashed in a low-temperature ashing unit and the 

34 

resultant ash studied in a transmission electron 

microscope (TEM). The residue appeared to be 

structurally amorphous. There was some scattered 

crystalline material, such as cubic clusters, 

spheres, laths, needles, and hexagonal plates. 

Energy-dispersive X-ray analysis of the material 

on the TEM grid indicated that the crystals were 

dominantly zirconium silicates, titanium oxides, 

and iron sulfides. The structurally amorphous 

material, which constituted the bulk of the 

material on the grid, contained aluminum as the 

only major cation. 

Crystals extracted from the L T A of these samples included calcium-aluminum and calcium-iron 

silicates and calcium sulfates (probably formed 

during the ashing process). An XRD pattern of the 

LTA from the sample washed in HN03 and HF 

yielded a pattern of anatase. The sample washed in 

all three acids yielded a pattern containing lines of 

gorceixite [BaAla(P04) 2(0H) · 5H20] and a few spotty lines of zircon. Preliminary chemical analysis indicates that the concentration of chemical 

elements is consistent with the mineralogical 

observations. 

J. ANALYSIS OF THE LOW-TEMPERATURE ASH 

FROM THE INTERLABORATORY SAMPLE BY 

ANALYTICAL ELECTRON MICROSCOPY 

By Necip Guven and Robert B. Finkelman 

LTA of the interlaboratory sample has been examined with a JEM-100 CX3 analytical electron 

microscope (AEM). In the AEM, transmitted electrons are used to form TEM images when the primary electrons are held stationary, and scanning 

transmission electron (STEM) images are formed 

when the primary electrons are scanned. Characteristic X-rays are generated from the individual 

particles in both the stationary ("spot") mode and 

the scanning ("area") mode. These characteristic 

X-rays are detected by an energy-dispersive X-ray 

analyzer. For semiquantitative determination of 

chemical compositions, the X -ray spectra are collected in a given mode for 100 seconds (live time), 

3

Use of trade names is for identification purposes only and does not imply endorsement by the U.S. Geological Survey. 
and the intensities are normalized, usually with 

reference to SiKa line. Elemental intensity ratios 

obtained in this manner are used in this report for 

characterization of the mineral matter in the LT A. 

Transmitted electrons are also used to obtain 

electron-diffraction patterns of the individual particles in the following modes: 

Selected-area diffraction of an area of about 0.5 

t-tm in diameter. 

Micro-diffraction of an area of about 0.2 to 0.1 

t-tm in diameter. 

Micr<rmicro diffraction of an area of about 0.1 t-tm 

to 200 angstroms in diameter. 

SAMPLE PREPARATION 

Samples for AEM were prepared from dilute 

suspensions of the L T A. The suspensions were 

made with the addition of 0.07 percent tertiary 

butyl amine in order to minimize water surface 

tension and allow a satisfactory dispersion of the 

particles. Both copper and beryllium 200-mesh 

grids were used. The grids were coated with a thin 

polycarbonate film upon which a drop of sample 

suspension was dried in air. The grids with the 

sample particles were then coated with carbon and 

gold in a vacuum evaporator. The grids were examined at a 100-keV potential. 

ANALYTICAL ELECTRON MICROSCOPY OF THE LTA 

CLAY MINERALS 

Illite occurs in the form of irregular platelets, as 

shown in figure 8. The irregular morphology of 

these platelets indicates a detrital origin. The 

characteristic X -ray spectrum obtained from these 

platelets (see caption to fig. 8) is in good agreement 

with spectra obtained from the standard illites. 

The selected-area electron-diffraction pattern of 

the illite fragment is given in figure 9. The six 

inner spots (that is, the spots with indices 11, II, 

11, 11, 02, and 02) of this pattern display an intensity distribution in which the 02 and 02 spots are 

much weaker than the other four spots. This pattern is typical for dioctahedral 2M -type micas like 

muscovite. The 2M polymorph of illite is generally 

considered to be detrital in origin. 

Kaolinite occurs in aggregates of irregular 

platelets, as shown in figure 10. These morph<r 

logical features also suggest a detrital origin for 

35 

FIGURE 8.-Illite platelet; irregular morphology suggests a 

detrital origin. Magnification: X6,000. The characteristic 

X-ray spectrum from the particle is given below: 

Intensity Intensity 

Element (counts/100 s) ratio/Si 

AI 3616 0.45 

Si 8040 1.00 

Fe 570 .07 

K 1758 .22 

FIGURE 9.-Selected-area electron-diffraction pattern obtained 

from illite platelet in the previous figure. The intensity relationships of the inner six spots are typical of 2M 

dioctahedral micas like muscovite. This polymorph indicates 

a detrital origin for the illite. 
FIGURE 10.-A typical kaolinite particle in the ash, which consists of an aggregate of small and irregular platelets. 

Magnification: X16,000. The characteristic X-ray spectrum 

is given below: 

Intensity Intensity 

Element (counts/100 s) ratio/Si 

Al 10849 0.65 

Si 16779 1.00 

Fe 866 .05 

the kaolinite. The characteristic X-ray spectrum 

obtained from the kaolinite particle of figure 10 

shows traces of iron contamination (possibly iron 

hydroxides), as indicated in the caption for figure 

10. The selected-area electron-diffraction pattern 

of kaolinite displayed in figure 11 is similar to patterns obtained from standard kaolinites. 

OTHER MINERAL MAnER 

Pyrite and quartz grains were also found along 

with the detrital clay particles. A rather interesting feature of the sample is the amorphous 

material, which is shown in figure 12. At low 

magnification (32,000X), the amorphous material 

seems to consist of fine grains, which give a 

speckled appearance to the aggregate. At higher 

magnifications (to 332,000X), the individual particles are clearly discernible as platy, disklike 

36 

FIGURE 11.-Selected-area electron-diffraction pattern of the 

kaolinite particle in figure 10. 

FIGURE 12.-Amorphous material consisting of fine-grained 

particles. See the following figure for closer view. Magnification: X32,000. The characteristic X-ray spectrum of these 

particles is given below: 

Element 

Al 

Fe 

Ti 

Ca 

Si 

Intensity 

(counts/100 s) 

314 

638 

214 

165 

42 

Intensity 

ratio/Si 

7.48 

15.19 

5.09 

3.93 

1.00 
forms (fig. 13). Some of the platelets have illdefined outlines, but others are disks or doughnuts 

about 200 A in diameter. Neither aggregates nor 

individual particles gave electron diffraction patterns in micro-diffraction and micro-micro diffraction modes with STEM. We therefore assume that 

this material is amorphous. X-ray fluorescence 

spectra have been obtained from these amorphous 

aggregates in "area" and in "spot" modes. The 

X-ray spectra indicate that the amorphous material contains significant amounts of iron, titanium, 

and aluminum. In "spot" mode, the spectra were 

obtained from an individual particle in the aggregate, whereas in "area" mode the spectra were 

obtained from the left-central section of the aggregate. This amorphous material seems to be an 

iron-rich gel with significant concentrations of 

titanium and aluminum. This gel often engulfs 

particles of other minerals, such as kaolinite and 

pyrite. Some amorphous aggregates show rather 

high silicon content suggesting the presence of 

amorphous silica The iron and titanium contents 

of the silica-rich aggregates are also rather high. A 

second type of amorphous material consists of 

crumpled thin films from which acicular units 

grow. This second form of amorphous material is 

less common than the first type, granular-platy aggregates. The X-ray spectra obtained from the 

second type of aggregate (the crumpled films) are 

similar to those from the granular-platy grains, except the titanium and calcium contents are higher 

in the granular-platy particles. 

A preliminary AEM examination of a pulverized 

split of the interlaboratory coal sample was also 

made to find out whether or not the amorphous 

material forms during low-temperature ashing. 

The common mineral particles detected in the 

unashed sample include detrital mica, kaolinite, 

and pyrite. The amorphous material in the coal 

sample is similar to the second type of aggregate 

37 

FIGURE 13.-A very high magnification (X332,0om image of 

the particles in figure 12 reveals that most particles are platy 

disks and some are doughnut shaped. 

found in the L T A (crumpled thin films with 

acicular units growing from them). The X-ray spectra indicate that the titanium content of the amorphous material is lower in the coal sample than in 

the LTA. 

It is probable that the granular amorphous 

material, which makes up more than 10 percent of 

the L T A, is produced during the ashing process. 

The iron, titanium, and aluminum found in this 

material may have originally been associated with 

the organic constituents. The crumpled filmy 

amorphous material found both in the LT A and in 

the unashed coal must have formed prior to the 

low-temperature ashing. It may have been created 

by reaction of the L T A and the coal with distilled 

water. However, additional research is needed to 

confirm this hypothesis. 

Interlaboratory Study of the Herrin (No. 6) Coal Bed Sample: 

Conclusions and Recommendations 

By R. N. Miller and R. B. Finkelman 

The preparation techniques used in this study 

have adequately produced homogenized coal subsamples as determined by a combination of total 

sulfur, pyritic sulfur, ash, and moisture analyses. 

Proximate, ultimate, mineralogical, and chemical 

analyses have produced a precise and thorough 

characterization of the coal sample. Splits of this 

coal sample are now available to the scientific community to provide a basis for the comparison of 

analytical data 

LOW-TEMPERA JURE ASHING 

Different laboratories used widely different conditions to produce LT A. The result of 

nonstandardization of the LTA technique has been 

some variation in the reported LTA yields. The 

principal sources of variation between laboratories 

were operating temperature (RF power) and sample and ash preparation and handling techniques. 

We recommend the adoption of a standard LTA 

procedure that specifies moisture conditions for 

sample preparation and product handling. 

MINERAL ANALYSIS 

There was a substantial range of values for each 

mineral species from XRD data obtained from all 

the participating laboratories. This undoubtedly 

reflected differences in sample preparation procedures, in equipment, in standards, and in the 

treatment of the basic intensity data In spite of 

these differences, many of the laboratories generated similar values for most of the mineral 

species. XRD remains the foremost procedure for 

determining the mineralogical composition of a 

complex mixture. However, consideration should 

be given to techniques such as IR spectroscopy, 

Moss bauer spectroscopy, and differential thermal 

analyses for their superior detection capabilities 

for individual minerals and as corroborative procedures to supplement XRD data 

Clearly more work is necessary to develop 

reliable quantitative XRD procedures for the 

analysis of coal LTA. The use of a uniform set of 

39 

mineral standards and some standardization of 

analytical techniques would go a long way toward 

improving confidence in interlaboratory comparison of XRD data Perhaps we should try to 

develop two standardized XRD procedures: a 

high-throughput, semiquantitative procedure and 

a low-throughput, more quantitative procedure. 

Finally, consideration should be given to the 

amount of X-ray amorphous material generated in 

the low-temperature ashing procedure. 

CHEMICAL ANALYSES 

There is good agreement for most determinations of major, minor and trace elements despite 

differences in analytical procedures and in the type 

of sample analyzed (raw coal, HTA, or LTA). The 

determinations of zinc, strontium, manganese, and 

iron showed serious discrepancies, which can be 

attributed to sampling inhomogeneity problems. 

Mineral-matter determinations by normative analysis are very close to the mean values reported 

from the XRD data With the appropriate analytical data on the LTA (including H20, C02, and 

pyritic S), normative analysis can be a very 

valuable corroborative tool. 

MISCELLANEOUS COMMENTS 

The appropriate choice of mineral standards is 

critical for the proper use of many analytical 

techniques (for example, XRD, FTIR, and differential thermal analysis); this aspect should not be 

minimized. 

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Finkelman, R. B., 1978, Determination of trace element sites in 

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Finkelman, R. B., Fiene, F. L., and Painter, P. C., 1981, Determination of kaolinite in coal by infrared spectroscopy - A 

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Given, P. H., and Miller, R.N., 1978, Determination of forms of 

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APPENDIX.-

PARTICIPATING LABORATORIES 

F. Fiene, S. Rimmer, S. J. Russell 

Illinois State Geological Survey 

Champaign, IL 61820 

Anonymous 

Anonymous 

N. Suhr 

The Pennsylvania State University 

Mineral Constitution Laboratory 

310 Mineral Sciences Building 

University Park, PA 16802 

J. W. Hosterman, P. J. Loferski 

U.S. Geological Survey 

Reston, VA 22092 

R. Dieke, D. Webster 

U.S. Geological Survey 

Reston, VA 22092 

J. J. Renton 

Department of Geology 

West Virginia University 

Morgantown, WV 26505 

S. Pollack 

U.S. Department of Energy 

Pittsburgh Energy Technology Center 

Analytical Chemistry Division 

P.O. Box 10940 

Pittsburgh, PA 15236 

41 

Senftle, F. E., Thorpe, A. N., Alexander, C. C., and Finkelman, 

R. B., 1982, Ferromagnetic and superparamagnetic contamination in pulverized coal: Fuel, v. 61, no. 1, p. 81-86. 

Senftle, F. E., Thorpe, A. N. and Lewis, R. R., 1964, Magnetic 

properties of nickel-iron spherules in tektites from Isabela, 

Philippine Islands: Journal of Geophysical Research, v. 69, 

no. 2, p. 317-324. 

Stanton, R. W., and Finkelman, R. B., 1979, Petrographic 

analyses of bituminous coal, optical and SEM identification of constituents: Scanning Electron Microscopy, 

v.1979, pt. 1, p. 465-470. 

Stohl, F. V., 1980, The analysis of minerals in coal: Sandia 

Laboratories Report SAND-79-2016, 43 p. 

Suh, N. P., 1978, Scientific and technical problems in erosive 

wear during coal utilization, in Cooper, B. R., ed., Scientific 

problems of coal utilization, Conference 770 509: U.S. 

Department of Energy DOE Symposium Series 46, 

p.158-180. 

9. A. C. Knott 

The Broken Hill Proprietary Co. Ltd. 

Central Research Laboratory 

P.O. Box 188 

W allsend, NSW 2287 

Australia 

10. Bergbau-Forschung GMBH 

Abt. Chemie- Analytik 

Postfach 13 01 40 

D-4300 Essen 13 

Federal Republic of Germany 

J. Frigge (XRD) 

L. Kuhn (XRD and IR) 

H. Plogmann (LTA) 

R.W. Schliephake (XRD) 

11. E.S. Erickson 

Mineral and Coal Processes 

Raw Materials and Chemical Processes Division 

Bethlehem Steel Corporation 

Bethlehem, PA 18016 

12. J. M. Williams 

Los Alamos National Laboratory 

Los Alamos, NM 87545 

13. Anonymous 

14. D. Pearson, J. Kwong 

Minerals Resources Branch 

Ministry of Mines 

Parliament Building 

Victoria, BC VSV 1X4 

Canada 
15. P. R. Solomon 23. J. Benson 

Advanced Fuel Research Inc. Ames Laboratory 

87 Church Street Iowa State University 

East Hartford, CT 06108 Ames, lA 50011 

16. C. Robbins, C. Hubbard 24. W. C. Grady 

National Bureau of Standards West Virginia University 

Washington, DC 20234 Morgantown, WV 26505 

17. R.N. Miller, R. C. Neavel 25. R. Stanton 

Exxon Research and Engineering Co. U.S. Geological Survey 

P.O. Box 4255 Reston, VA 22092 

Baytown, TX 77520 

26. J. A. Cavallaro 

18. R. M. Buchanan U.S. Department of Energy 

Mineral Sciences Laboratories Pittsburgh Mining Operations 

Canada Center for Mineral and Energy Technology 4800 Forbes Ave. 

555 Booth Street Pittsburgh, PA 15213 

Ottawa K1A OG 1 

Canada 27. F. E. Huggins 

United States Steel Corp. 

19. P.Simms Monroeville, PA 15146 

Purdue Accelerator Laboratory 

Physics Building 28. C. Ford 

Purdue University Bituminous Coal Research 

West Lafayette, IN 47907 350 Hochberg Road 

Monroeville, PA 15146 

20. A. Bailey 

Department of Geology 29. D. James 

University of Southwestern Louisiana Center for Trace Characterization 

USL Box 44530 Texas A & M University 

Lafayette, LA 70504 College Station, TX 77843 

21. F. T. Dulong 30. P.A. Montano 

U.S. Geological Survey Dept. of Physics 

Reston, VA 22092 West Virginia University 

Morgantown, WV 26506 

22. Branch of Analytical Chemistry 

U.S. Geological Survey 

Reston, VA 22092 

42