DoE
United States
Department of Energy
Division of Environmental
Control Technology
Washington, D.C. 20545
LA-6835-PR
EPA
U.S. Environmental Protection Agency
Office of Research and Development
Industrial Environmental Research
Laboratory
Research Triangle Park, North Carolina 27711
EPA-600/7-78-028
March 1978
TRACE ELEMENT
CHARACTERIZATION
OF COAL WASTES--
FIRST ANNUAL REPORT
-NVlRONMfcNTAk
PROTECTION
AGENCY
DALLAS. TEXAS
UBRMW
Interagency
Energy-Environment
Research and Development
Program Report
*********
*********
*********
*********
*********,
*********,
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RESEARCH REPORTING SERIES
* *****
******
******
******
:*****
;*****
*****
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
-1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Researcn and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-reiated environ--
mental issues.
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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DoE LA-6835-PR
EPA-600/7-78-028
March 1978
UC-901
TRACE ELEMENT
CHARACTERIZATION
OF COAL WASTES--
FIRST ANNUAL REPORT
JULY 1, 1975 TO JUNE 30, 1976
by
Eugene M. Wewerka and Joel M. Williams
Los Alamos Scientific Laboratory
University of California
Los Alamos, New Mexico 87545
An Affirmative Action/Equal Opportunity Employer
EPA/DoE Interagency Agreement No. IAG-D5-E681
Program Element No. EHE623A
EPA Project Officer: David A. Kirchgessner DoE Project Officer: Charles Grua
Industrial Environmental Division of Environmental
Research Laboratory Control Technology
Research Triangle Park, NC 27711 Washington, DC 20545
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
and
U.S. DEPARTMENT OF ENERGY
Division of Environmental Control Technology
Washington, DC 20545
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CONTENTS
ABSTRACT 1
SUMMARY OF TASK PROGRESS 1
TASK PROGRESS DESCRIPTION 3
Task 1 3
Task 2 5
Task 3 32
Personnel 33
APPENDIX A. Summary and Conclusions from Literature Survey 37
APPENDIX B. Sample Preparation, Analytical Procedures, and
Analytical Results for Standard Coal and Ash Samples 39
APPENDIX C. Procedures for Collection of Coal Cleaning
Waste Samples 50
w
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TABLES
I. Task Breakdown. Trace Elements Characterization and
Removal/Recovery 2
II. Preferred LASL Methods for Elemental Analyses of
Coals and Coal Wastes 6
III. Summary of LASL Coal and Refuse Sample Analyses 13
IV. Trace Element and Mineral Content of Coal Waste
Materials from Illinois Basin Plant B 14
V. Trace Element and Mineral Content of Low-Sulfur
Coal and Coal-Waste Materials from Plant D 16
VI. Tendency of Trace Elements to Remain with Coal
Fractions During Washing 19
VII. Relative Concentrations of Trace Elements in Coal
Preparation Wastes of Differing Sulfur Contents 19
VIII. Trace Element and Mineral Content of Weathered
Coal-Waste Materials from Illinois Basin Plants A and B 22
DC. Relative Trace Element Contents in Coal Preparation
Wastes as a Function of Waste Dump Depth 24
X. Distribution of Trace Elements and Minerals Between
Slurry and Gob for Illinois Basin Cleaning Plant B 24
XI. Distribution of Trace Elements Between an Eight-Year-Old
Gob Pile and an Adjacent Dry Stream Bed 25
XII. Trace Element and Mineral Content of Weathered and
Sized Coal-Waste Materials from Illinois Basin Plant B 26
XIII. Pyrite Oxidation: Relative Concentrations of Trace
Elements in Pyrite and Iron Sulfate 28
XIV. Trace Elements Leached from Coal Refuse Collected
from Plant B 28
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XV. Trace Element and Mineral Content of Sized Coal-
Waste Materials from Illinois Basin Plant B 34
XVI. Segregation of Trace Elements and Minerals According
to Particle Size of Illinois Basin Coal Waste 36
FIGURES
1. View of the landscape at an Illinois Basin
coal-waste dump
2. Freshly dumped coal cleaning waste 8
3. Graded surface of an active coal refuse dump 9
4. Eroded face of an 8-yr-old coal refuse pile 9
5. Graded surface of a coal-waste dump illustrating
profuse formation of iron sulfate 11
6. Concentration of iron sulfate in the drainage
channels of a coal refuse pile 11
7. Water-filled drainage channel between two coal
refuse banks 12
8. Photomicrograph showing areas analyzed on a sample of
refuse from Cleaning Plant D 20
9. Scanning electron micrograph showing typical fibers
from the surface of oxidized pyrite 29
10. Size fractions of Illinois Basin coal refuse 31
11. Size distribution of coal cleaning wastes from
the Illinois Basin 32
VI
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TRACE ELEMENT
CHARACTERIZATION
OF COAL WASTES-
FIRST ANNUAL REPORT
Eugene M. Wewerka and Joel M. Williams
ABSTRACT
The literature search on the chemistry and environmental behavior of
trace elements in coal cleaning wastes has been completed, and an inter-
pretive report of the findings from the literature has been written. Techni-
ques and methods for analyzing trace elements and minerals in coals and
coal cleaning wastes have been developed and are documented in this
report. Standard coal and ash samples were used to establish the precision
and accuracy of these methods. High-sulfur coal-waste materials have been
collected from three coal cleaning plants in the Illinois Basin, and cleaning
wastes from a low-sulfur coal have also been collected. Analytical studies of
the trace elements and minerals in these wastes are progressing, and in-
vestigations of the effects of weathering and leaching on the trace elements
in the refuse have been started.
SUMMARY OF TASK PROGRESS
The major objective of this research program is to assess the potential for environmental pollu-
tion from trace or minor elements that are discharged or emitted from coal preparation wastes,
and to identify suitable environmental control measures should they be needed. An additional
objective is to investigate methods to economically recover useful trace elements or minerals
from coal refuse matter. The technical accomplishments in each of the main areas of the
program for the period July 1, 1975, to June 30, 1976, are presented in this report.
As outlined in the Work Plan, the technical activities of this program for the current fiscal year
are broken into major tasks and subtasks. These are shown in Table I. Generally, we succeeded
in accomplishing the project objectives and milestones as outlined.
The activities under Task 1, Literature Search and Program Planning, have been completed.
An extensive literature search on the chemistry and environmental behavior of trace elements in
coal preparation wastes has been completed, and a report and commentary on the literature as it
pertains to the present work has been written (Subtask 1.1). Subtasks 1.2 through 1.5 concern
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TABLEI
TASK BREAKDOWN
TRACE ELEMENTS CHARACTERIZATION
AND REMOVAL/RECOVERY
TASKl
LITERATURE SEARCH
AND
PROGRAM PLANNING
TASK 2
LABORATORY PROGRAM
FOR TRACE ELEMENTS
CHARACTERIZATION
TASK3
LABORATORY PROGRAM
FOR TRACE ELEMENTS
REMOVAL/RECOVERY
1.1 LITERATURE SEARCH
ON TRACE ELEMENT
CHEM. AND COAL
CLEANING PROCESSES
2.1 STANDARDIZE ANA-
LYTICAL TECHNI-
QUES AND DEVELOP
METHODS
3.1 EVALUATE NEW
CHEMICAL OR
PHYSICAL REMOVAL
PROCESSES
1.2 EVALUATE PREVIOUS
WORK ON CLEANING
PROCESSES AND
WASTES
2.2 COLLECT COAL
AND WASTE
SAMPLES
3.2 SUGGEST NEW OR
MODIFIED STEPS TO
EFFECT REMOVAL
1.3 RE VIEW TECHNOL-
OGY OF COAL
CLEANING
PROCESSES
2.3 DETERMINE TRACE
ELEMENT DISPOSI-
TION IN CLEANING
PROCESS
1.4 REVIEW CHEMISTRY
OF TRACE ELEMENTS
IN RESIDUES
2.4 IDENTIFY TRACE
ELEMENTS OF
CONCERN
1.5 IDENTIFY
TRACE ELEMENTS
OF INTEREST
2.5 CHARACTERIZE
CHEMISTRY OF
WASTES
1.6 CHOOSE CLEANING
PROCESS AND
RESIDUES
2.6 CHARACTERIZE
ENVIRONMENTAL
BEHAVIOR OF
WASTES
2.7 DEVELOP PROCE-
DURES FOR TRACE
ELEMENT
SEPARATIONS
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topics which were addressed in the literature search, and a commentary about each is given in
the following section on task progress and in the literature search report. Subtask 1.6 was com-
pleted when the decision was made to initially concentrate our studies on coal preparation
wastes from the Illinois Basin.
We have also made considerable progress on Task 2—Laboratory Program for Trace Elements
Characterization. Methods for analyzing trace elements in coals and coal refuse have been
developed and standardized (Subtask 2.1). Also, representative samples of both fresh and
weathered coal preparation wastes have been collected (Subtask 2.2). We did not conduct a com-
plete trace element balance of a coal cleaning plant, as was originally planned in Subtask 2.3;
however, a preliminary indication of the fate of trace elements in the cleaning plants studied can
be obtained from the analyses of the feed and cleaned coals and reject waste materials from each
plant. Work on Subtask 2.4 is progressing. A preliminary identification of the trace elements of
environmental concern in coal preparation wastes will be made on the completion of the initial
characterization work, it is hoped, early in FY 77. As outlined in Subtask 2.5, analytical studies
to determine the chemical forms, mineralogy, and associations of the trace elements in the coal
waste samples are being conducted and laboratory investigations of the effects of weathering and
leaching on the trace elements in coal refuse (Subtask 2.6) are under way. Regarding Subtask
2.7, we are initially investigating the segregation of trace elements according to particle size in
coal refuse, and the possibility that particle size can be used as an effective method for
separating certain trace elements from coal wastes.
Although we have begun exploring methods to remove or recover specific trace elements from
coal preparation wastes as outlined in Task 3—Laboratory Program for Trace Elements
Removal/Recovery—it is not likely that we can make a great deal of progress in this area until
specific environmental problems are defined by our initial studies. However, some of our work
(for example, the separation of trace elements by waste particle size, and the removal or recovery
of specific trace elements by aqueous leaching techniques) directly applies to this phase of the
program.
TASK PROGRESS DESCRIPTION
TASK 1-LITERATURE SEARCH AND PROGRAM PLANNING
Subtask 1.1—Literature Search
A literature search on the chemistry and environmental behavior of trace elements in coal
preparation wastes has been completed. A comprehensive report and commentary on the
literature, as it pertains to the present program, has been written. The general content of the
literature search report is too broad to be adequately discussed here; however, a summary of the
main conclusions which were drawn from our studies of the available literature appear in Appen-
dix A. The literature report is now being reviewed by ERDA and EPA, and preprints should be
available during the next quarter.
In addition, a computer interactive storage system, which includes all pertinent references ob-
tained from the literature search has been established. At present, there are about 450 references
in the data base, and the list will be updated periodically. A computer search and retrieval
system, based on key-word identification can be used to comb the file. Use of this data base by
interested individuals or organizations can be arranged upon request.
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Subtasks 1.2 and 1.3—Review Previous Work and Technology of Trace Elements in Coal
Cleaning Processes
These subtasks, as well as Subtasks 1.4 and 1.5, were addressed as subjects in the literature
search. As detailed in the literature report, we found little to guide us concerning either the ef-
fects of the various types of coal cleaning methods on the trace elements in raw coals, or the fate
of trace elements in general during coal cleaning. Only a few studies in this area have been repor-
ted, and most of these are based on laboratory float-sink work.
Subtask 1.4—Review Chemistry of Trace Elements in Coal Preparation Wastes
Only preliminary work on the chemistry of trace elements in coal preparation wastes has been
reported. Available information is mainly devoted to the identification of the major minerals in
the wastes. Some insight into the chemistry and behavior of trace elements in coal mineral
wastes was obtained from studies of raw coals. But here again, little actual chemistry has been
investigated; the bulk of the attention has focused on identifying the minerals and trace ele-
ments present in coals.
Subtask 1.5—Identify Trace Elements of Interest
Based on available information, an adequate assessment of the extent or seriousness of en-
vironmental contamination from coal preparation wastes cannot be made. Certain ions, such as
iron, aluminum, and manganese, leach out of coal refuse dumps in toxic amounts; however,
there is little information available about the teachability or environmental behavior of most
trace elements present in coal refuse. A preliminary identification of the trace elements of en-
vironmental concern in coal wastes will be made when our initial characterization work is com-
pleted early in the next fiscal year. A more complete assessment of the total potential for en-
vironmental pollution from trace elements in coal wastes will be made near the end of the next
fiscal year.
Subtask 1.6—Choice of Cleaning Processes and Wastes
Based on the literature search and discussions with authorities in the field of coal chemistry
and mineralogy, we have decided to concentrate our initial laboratory work on coal waste
materials from the Illinois Basin (U.S. Eastern Interior Region). This area was chosen for several
reasons:
• The coals from the Illinois Basin are widely used; they represent about 25% of the total US
production.
• Illinois Basin coals are highly mineralized—ROM coals typically contain 10-40 wt% mineral
matter—and they contain a broad array of trace elements.
• The coals from this basin contain relatively high amounts (3-5 wt%) of pyritic sulfur.
In addition, there is ample rainfall and surface-water drainage in the region so that extensive
waste pile weathering and leaching can be expected. All things considered, we believe that the
waste materials from the Illinois Basin present nearly maximum possibilities for environmental
contamination, as well as great potential for mineral or trace element recovery, and that they
come as close as possible to what could be called "typical" or "representative" coal cleaning
wastes.
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TASK 2—LABORATORY PROGRAM FOR TRACE ELEMENTS
CHARACTERIZATION
Subtask 2.1—Develop and Standardize Analytical Techniques and Methods
During the past year, a substantial effort was devoted to developing and standardizing
methods for analyzing trace elements and mineral matter in coals and coal cleaning wastes.
Evaluation of these techniques was based upon analyses of NBS-SRM and other standard coal
and ash samples. The results obtained clearly demonstrate that the LASL analytical methods
are both suitable and reliable for the analysis and characterization of coal and coal waste
materials. The details of specific procedures and methods, and the results of the standard coal
and ash analyses, are given in Appendix B, and are only briefly described in this section.
Procedures were established for reducing the considerable bulk of coal and waste materials
collected from the field to a quantity suitable for laboratory work. This process, which involves a
series of crushing, dividing, and blending steps, is based on the ASTM methods for preparing
analytical samples from coals (D-2013) and aggregates (C-702).
Methods for both low- and high-temperature ashing of coal and waste samples were developed.
Low-temperature ashing is particularly useful for concentrating the mineral matter in coals or
coaly substances without significantly altering the character or structure of the minerals.
The extensive analytical capabilities at LASL were tapped to establish methods for identify-
ing and characterizing trace elements and minerals in coals and coal cleaning wastes. For trace
and minor element analyses, neutron activation analysis (NAA) is used extensively because raw
coal and waste materials can be analyzed directly with a minimum of sample preparation, many
elements can be observed simultaneously, and the method is reliable and accurate (Appendix
B). A number of elements are not readily determined by NAA, and other techniques are used for
these characterizations. These techniques include optical emission spectroscopy (OES), atomic
absorption spectrophotometry (AA), x-ray fluorescence (XRF), electron microprobe (EM), ion
microprobe (IM) and wet-chemical methods. Most of the remaining analyses are done by AA or
OES. AA and OES methods have been widely used to analyze coals and mineral materials; the
general usefulness, reliability, and precision of both methods are well established. A compilation
of preferred LASL methods for analyzing various major and minor elements in coals and coal
cleaning wastes appears in Table II. Where more than one technique can be applied to a specific
analytical task, the method or combination of methods used will provide the necessary speed,
sensitivity, and precision with the least expense.
The characterization of the crystalline mineral phases in the samples of interest is done largely
by x-ray diffraction (XRD). Both qualitative and quantitative XRD analyses can be done direc-
tly on the highly mineralized coal-waste samples. However, because of dilution and interference
from the organic components, quantitative results for most of the common minerals in raw coals
are best obtained by examining the low-temperature ash. In some instances mineral phases are
undetectable by XRD, particularly when they are amorphous or present in low concentrations.
For this circumstance, the more sensitive electron microprobe may provide the necessary infor-
mation.
Wet-chemical methods are used to determine the carbon, hydrogen, nitrogen, and sulfur con-
tents of the coal and waste samples. Also, wet chemistry is used to prepare samples for chlorine
and fluorine analyses using ion specific electrodes. Other properties of coals and wastes, such as
moisture, volatile matter, and ash, are also determined using ASTM techniques.
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TABLE II
PREFERRED LASL METHODS FOR ELEMENTAL ANALYSES
OF COALS AND COAL WASTES
Element
Method
NAA—Neutron Activation Analysis.
AA—Atomic Absorption Spectrophotometry.
OES—Optical Emission Spectroscopy.
C—Chemical Methods.
Element
Method
Li
Be
B
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
AA, OES
AA, OES
OES
C
NAA
NAA, OES
NAA, OES
AA, OES, C
AA, C
C
NAA,C
NAA, OES
NAA
NAA, OES
NAA, AA
NAA, AA, OES
NAA, AA, OES
NAA, AA, OES
NAA, AA
NAA, AA, OES
AA, OES
AA, OES
NAA, AA
NAA, OES
OES
NAA, AA
NAA
Br
Rb
Sr
Y
Zr
Mo
Ag
Cd
Sn
Sb
I
Cs
Ba
La
Ce
Sm
Eu
Tb
Yb
Lu
Hf
Ta
W
Hg
Pb
Th
U
NAA
NAA, OES
NAA
OES
OES
OES
AA
AA
OES
NAA
NAA
NAA
NAA
NAA, OES
NAA
NAA
NAA, OES
NAA
NAA, OES
NAA
NAA
NAA
NAA
NAA, AA
AA, OES
NAA
NAA
Subtask 2.2—Collect Coal and Waste Samples
Samples of cleaning wastes from high-sulfur coals were collected from three coal preparation
plants in the Illinois Basin and from a cleaning plant for a low-sulfur coal located in another
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region. In addition to fresh waste materials, we also obtained samples of feed coal and cleaned
coal from each plant. In two instances, we collected materials from aged and weathered gob
(refuse) piles.
Gob and coal sampling procedures had to be improvised somewhat for each cleaning plant
depending on the accessibility of the various coal and waste streams. However, in all cases, the
procedures adopted were based on ASTM methods for collecting field samples of coal (D-2234)
and aggregates (D-75). To reduce the possibility of sampling errors due to size segregation,
whenever it was logistically possible, materials were collected from moving belts or streams.
A more complete description of the cleaning plants that were sampled, the materials collected,
and the techniques and methods used, is given in Appendix C.
While collecting the samples from the Illinois Basin, we took a few photographs of waste dump
areas, and particularly, weathered wastes. These photographs vividly illustrate what appears to
us to be typical landscape in and around coal-waste disposal sites.
Figure 1 is a panorama of a coal-waste dump, which is similar to those we saw in many parts of
the Illinois Basin. This is an area that has been used continuously for about the last 15 yr for the
disposal of wastes from a coal preparation plant. The older waste material is at the lower level in
the center of the picture. The photograph was taken from another newer waste pile which had
just been graded. The edge of the graded area can be seen in the foreground of the figure.
Figure 1 illustrates an interesting aspect of waste dumps that we often observed in this coal
region. Disposal sites are frequently located in low-lying areas, often in or near swamps and
waterways. Although such sites are undoubtedly convenient to dump into, it would seem from
the standpoint of water contamination to be the worst possible circumstance. Also noteworthy is
the milky-looking consistency of the water immediately to the left of the older waste pile. This is
a common occurrence in the drainage from coal refuse dumps, and is probably due to an acidic
suspension of iron oxides and hydroxides called "yellow boy."
A view of freshly dumped coal cleaning waste is shown in Fig. 2. These are materials that
had been deposited within the previous hour and each of the piles represents one truckload of
waste. The larger pieces of waste in the foreground are about 15 cm (6 in.) across. It can be seen
that the larger material is segregated at the lower edge of each pile, while the finer waste is found
at the apex of the pile. This size-separation phenomenon, which is typical of aggregate materials,
illustrates why it is so difficult to collect representative samples from accumulations dumped
from trucks or hoppers. Another feature worthy of note is the general appearance and consistency
of the new job. It looks much like fresh concrete that has been prepared with a broad distribution
of aggregate.
Figure 3 depicts an active waste dump in which the recently deposited refuse has been graded
and smoothed. More waste will be deposited on the graded surface.
The eroded face of an 8-yr-old coal refuse pile is shown in Fig. 4. Over the years, the con-
sistency of the gob has been changed considerably. Very few distinct "hard" particles remain.
Nearly all of the material has been degraded to a fine powder, and the remaining particles are
very friable or weak. Undoubtedly, with time, the exposed waste will disintegrate completely to a
sand or silt-like consistency.
Figure 5 is a photograph of the graded surface of an active disposal area. The white material
dispersed on the surface is iron sulfate produced by the oxidation of pyrite or marcasite. The ox-
idation of iron sulfides to iron sulfate is the first step in the formation of sulfuric acid; the
presence of water is necessary to complete acid formation. During and after rain storms, the iron
sulfate is dissolved and carried away from the surface, again leaving fresh sulfide exposed. Rain-
fall had been sparse just previous to the time the photograph was taken; however, our discussions
with people working in the area lead us to believe that the iron sulfate illustrated in the figure
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Fig. 1.
View of the landscape at an Illinois Basin coal-waste dump.
Fig. 2.
Freshly dumped coal cleaning waste.
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Fig. 3.
Graded surface of an active coal refuse dump.
Fig. 4.
Eroded face of an 8-yr-old coal refuse pile.
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was produced in a period of less than 3 months. Figure 6 shows how the sulfate concentrates in
the natural drainage paths off the surface of the waste pile. Undoubtedly, much of the dissolved
product is carried down into the waste pile by water seepage.
Finally, a drainage channel between two coal refuse banks is shown as Fig. 7. In this in-
stance, the water is relatively static, so much of the suspended matter has settled out. Although
it is difficult to detect from the photograph, the whole bottom of the watercourse is coated with a
layer of yellow boy. As an aside, we have seen streams and waterways in the Illinois Basin that
are located miles away from coal-waste dumps or mines, but are so clogged with yellow slime and
mud that the rocks or debris on the stream bottom cannot be distinguished.
Subtask 2.3—Determine Trace Elements Disposition in Coal Cleaning Processes
We have begun to identify the trace elements in the feed coal, cleaned coal, and reject waste
materials for the four coal cleaning plants under consideration. From these analyses, we will be
able to ascertain, in a broad sense, the fate of trace elements in these commercial coal cleaning
facilities. To maintain continuity in our reporting of waste analyses, the results obtained thus far
in this endeavor are discussed below in the subtask on waste characterization (2.5). In addition,
we are characterizing samples collected from each of the output streams of the three cells of a
commercial jig or washing table; analytical results on these materials will appear in a future
report.
Subtask 2.4—Identify Trace Elements of Concern
A preliminary identification of the trace elements of environmental concern in coal cleaning
wastes will be made sometime in early FY 77, after the completion of the rather extensive initial
waste characterization work now under way (see below). A more complete assessment of the
trace elements in coal refuse, which may cause the greatest environmental problems, will be
forthcoming near the end of the second year of this program.
Subtask 2.5—Characterization of Coal Preparation Wastes
We are now characterizing coal and waste samples from four different coal cleaning opera-
tions. Three of these, Plants A, B, and C, are from the Illinois Basin. The types of samples collec-
ted from these cleaning plants, and the procedures used, are described in Appendix C. In addi-
tion to the Illinois Basin samples, all of which are high-sulfur coal and wastes, we have collected
some low-sulfur feed coal and waste from a cleaning plant located in another coal basin (Plant
D). Because these latter materials represent a compositional contrast to the high-sulfur wastes
from the Illinois Basin, we have included them in our initial studies. Samples of weathered coal
refuse were also collected from two of the Illinois-Basin facilities.
Since we collected these samples, many of them have been divided according to particle size.
We have 67 coal and waste samples in various stages of analysis. Quite obviously some of these
materials will be characterized somewhat more extensively than others. A listing of these sam-
ples is given in Table HI, together with information about the analyses which have, or will be,
performed on each.
10
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-^ '• ^t^*
Fig. 5.
Graded surface of a coal-waste dump illustrating profuse formation of iron sulfate.
Fig. 6.
Concentration of iron sulfate in the drainage channels of a coal refuse pile.
11
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Fig. 7.
Water-filled drainage channel between two coal refuse banks.
The results obtained thus far on the coal and waste samples have been compiled by a com-
puter interactive method so that additional analytical information can be added as it is ob-
tained. In addition, the use of a computer storage system facilitates the rapid retrieval of
analytical results about any particular sample or set of samples. An attempt has been made to
assemble the information in the tables into categories or groupings according to plant location or
sample type. The symbols and abbreviations used in the tables are explained by footnotes which
appear at the end of Table IV. A discussion and interpretation of the data for related waste sam-
ples follows.
Analysis of Coal Preparation Wastes from Illinois Basin Cleaning Plant B
Fresh coal refuse from Illinois Basin coal cleaning Plant B was collected from the dump itself
where it was being deposited by trucks. Three 50-kg increments—designated in chronological or-
der Gob A, B, and C—were successively collected over a 4-h period. About nine separate
truckloads of refuse were sampled. The mineralogical and trace element analyses completed so
far for these wastes appear in Table IV.
The data in Table IV reveal that the composition of the waste material was reasonably cons-
tant over the duration for which we collected the samples, although the later sample (Gob C) ap-
pears to contain a slightly greater amount of illite and lesser amount of pyrite than the earlier
sample (Gob A). This trend is also reflected in the iron, aluminum, and silicon values.
This refuse, we believe, is fairly typical of the high-sulfur, mineral waste that is produced from
the major coal types in the Illinois Basin. It contains about 20 wt% residual carbon and around
14 wt% sulfur. Typically, the bulk of the waste material is distributed among the clay minerals
12
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TABLE III
(i)
SUMMARY OF LASL COAL AND REFUSE SAMPLE ANALYSES
5-15-76
LOCALE
STD VALUE
LASL DATA
PLANT A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
PLANT B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
PLANT C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
PLANT D
D
D
(2)
IDENTITY
S NbS 1M2 CQ«,L
NDS 1632 COAL
FEED COAL A
FEED COAL B
CLEAN COH
GOB A-FRESH
GOB B-FPJESH
GOB C-FRFSH
GOB D-FRESH
GOB E-FRESH
GOB A,C,E AVE
GOB OCCAS LG PC
GOB 1Y TOP 3IN
GOB 1Y 2«N BELO SURF
FEED COAL
PRODUCT COAL-FINE CUT
PRODUCT COAL-COAREE CUT
GOB A FRESH-DUMPED
GOB B FRESH-DL'MFED
GOB C FRESH-DUKPED
GOB A,B,C AVE
GOB A TYPE 2
GOB B TYPE 2
DRY STREAM AT 8Y GOB PILE
GOB PILE.-8Y AT FOOT
GOB WHITE-1Y
SLURRY POND
FEED COAL A
FEED COAL B
CLEAN COAL
FEED COAL TYPE 2
GOB A COARSE-FRESH
GOB B COARSE-FRESH
GOB C COARSE-FRESH
GOB A,B,C, AVE
GOB FINE-FRESH
GOB VERY FINE-FRESH
FEED COAL
BREAKER REJECTS +6IN
FRESH GOB AT DUMP
(3)
SIZE
28KG
30KG
6KG
65KG
73KG
71KG
73KG
70KG
-1/t
-1
-1 ID
-2
+2
20KG
31KG
37KG
30KG
29KG
29KG
t7KG
H9KG
51 KG
-I/1*
-1
-1 ID
-2
+ 2
61KG
5UKG
10KG
16KG
-6
-10
-20
-35
-60
-115
-250
+6
10KG
30KG
34 KG
27KG
33KG
51KG
5 3 KG
55KG
-l/i*
-1
-1 ID
-2
+ 2
M8KG
-1/K
-1
-1 ID
-2
2tKG
-1/t
-1
-1 ID
-2
8KG
11KG
10KG
SAMPLE
STD
STD
13
It
15
25
11
12
10
28
25B
25C
25D
25E
25F
16
8
9
30
31
29
2t
17
23
24 B
2tC
2UD
24E
2>*F
26
27
S
6
7A
7B
7C
7D
7E
7F
7G
7H
it
32
33
3t
35
18
21
22
18B
18C
18 D
18E
18 F
20
20B
20C
20D
20E
19
19 B
19C
19 D
19E
3
1
2
LTA
NA
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NA
NA
NA
NA
NA
NA
NA
YES
YES
YES
YES
YES
CHN
ANAL
NA
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
"YES"
YES
NA
NA
NA
NA
NA
NA
NA
YES
YES
YES
MINE-
RALOGY
NA
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NA
NA
NA
NA
NA
NA
YES
YES
YES
YES
YES
YES
TRACE
ELEMENTS
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
FLOAT
SINK
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
TOTAL NUMBER OF SAMPLES = 67
FOOTNOTES
(1) YES=ANALYSIS DONE, NA=NO ANALYSIS IS TO BE DONE, BLANK=ANAYLSIS YET TO BE DONE
(2) DESIGNATIONS A,B,C, ETC INDICATE ThE ORDER IN WKICR SAMPLES WEP.E COLLECTED: A, FIRST;
B, SECOND; ETC. Y=AGE OF MATERIALS IN YEARS
(3) SAMPLE WEIGHTS IN KILOGRAMS; SAMPLE PARTICLE SIZE IN MINUS(-) OR PLUS(t) MESH (SAMPLE 7)
AND INCHES (ALL OTHERS); -1 ID INDICATES MINUS 1 INCH IN ONE DIRECTION AND -2 INCHES IN
THE OTHERS
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(kaolinite, illite, mixed-layer clays), the sulfides (pyrite and marcasite), and quartz. In addition,
small amounts of carbonate minerals and gypsum have been identified in this gob. There are also
undoubtedly many minor or trace mineral phases present in this material as evidenced by the
relatively high concentrations of such trace elements as lithium, sodium, manganese, zinc, ar-
senic, and cerium. From an environmental standpoint, there are disturbingly high quantities of
the trace elements vanadium, chromium, zinc, arsenic, lead, and thorium distributed in this
waste; however, the extent to which these elements are, or may be, released by environmental
processes has not been determined. We believe that the behavior of the individual trace elements
in coal preparation wastes will be dictated largely by the behavior of the major minerals in which
the trace components reside. Labile or unstable minerals, such as pyrite or limestone, will un-
doubtedly release greater amounts of the associated trace elements into the environment at a
faster rate than will the more stable minerals, such as quartz.
Analysis of Coal and Waste from Cleaning Plant D
Trace element and mineralogical analyses have been completed for samples of low-sulfur feed
coal, breaker rejects, and fresh refuse from coal cleaning Plant D. The breaker reject is the rock
and mineral matter that was too large (>15 cm) to be processed by the cleaning plant even after
passing through a crusher. Results are given in Table V for both the raw or as-received coal and
waste samples and for the residue produced by low-temperature ashing (LTA basis). The latter
information provides a carbon-free direct basis on which to compare the trace elements and
minerals in the various samples.
The major minerals present in the coal and refuse from cleaning Plant D are the clays, calcite,
and quartz. The absence of pyrite or marcasite, and the relatively higher concentration of sulfur
in the feed coal as compared to the waste, suggests that most of the sulfur present in the coal is
organically bound. The waste materials from this coal cleaning plant contrast with those repor-
ted above for Plant B in that pyrite is a major consitituent in the latter refuse, but is absent
altogether from Plant D waste.
The elemental composition of Plant D refuse reflects to a large degree the types of minerals
present in the waste. The relatively high percentages of aluminum and silicon can, of course, be
attributed to the high clay and quartz contents. Predictably, in the absence of pyrite, the iron
content of Plant D coal and wastes is fairly low compared to the Illinois Basin waste discussed
earlier. There are several toxic trace elements present in relatively high concentrations in the
low-sulfur waste; notably iron, aluminum, manganese, copper, nickel, zinc, yttrium, and lead.
As we point out in Appendix C, only relatively small amounts of the coal and waste materials
were collected from Cleaning Plant D. We were somewhat concerned about whether we had
collected enough of each to provide statistically representative samples. The general correspon-
dence and consistency between the relative quantities of each element present in the coal and
refuse samples collected from this plant suggests that our samples are indeed representative of
the short-term operation of the plant.
By comparing the trace element composition of the feed coal going into the preparation plant,
and of the mineralized waste material discarded from the plant, we were able to categorize the
elements according to their tendency to remain with the cleaned coal or to drop out with the
heavier mineral matter during the washing operation. This information appears in Table VI. For
comparison, we have included in the table corresponding data obtained by other laboratories
from float/sink studies of high-sulfur coals. Table VI reveals some interesting differences bet-
ween these two coal types. Cobalt, nickel, chromium, and copper, for example, tend to preferen-
tially associate with the mineral matter in the high-sulfur coals; whereas, these elements in the
18
-------
low-sulfur coals showed a positive tendency to remain with the coal fraction. This behavior may
be due in part to the differences in pyrite contents of the two coal types. Copper, nickel, and
cobalt are chalcophile elements that commonly occur as sulfide minerals, and perhaps these are
present as sulfide phases or components in the dense pyrite fractions of the high-sulfur coals. In
the absence of much pyrite in the low-sulfur coal, these elements must be present in some other
mineral phase, and therefore, their behavior during density separation would be expected to
deviate from that of the pyritic samples. Another possible factor, which could explain some of
the deviations between the two sets of data in Table VI, is the scale-up factor between the
laboratory float/sink studies used elsewhere and the commercial preparation plant products in-
corporated into our study.
An interesting comparison can be made between the relative concentrations of trace elements
in the low-sulfur coal wastes and the high-sulfur Illinois Basin refuse considered earlier. It is seen
from Table VII, perhaps as would be expected from the diverse geology of the two coal types, that
only a few trace elements are present in both waste types in nearly equal amounts. Most of the
elements found in the high-sulfur coal wastes in greatest relative abundance are those expected
to form sulfides or to be associated with pyrite or marcasite, while those present in highest
relative amounts in the low-sulfur coal refuse appear to be those most preferentially associated
with the clay minerals, quartz,and the carbonates.
The characterization of the mineralogy and chemistry of trace elements in coals and coal
wastes is one of the more important aspects of this project. At present, we are using both electron
TABLE VI
TABLE VII
TENDENCY OF TRACE ELEMENTS
TO REMAIN WITH COAL
FRACTIONS DURING WASHING
RELATIVE CONCENTRATIONS OF
TRACE ELEMENTS IN COAL
PREPARATION WASTES OF DIFFERING
SULFUR CONTENTS8
LOW SULFUH COAL
CLEANING PLANT D
F, r. s
Li. B. Cf, Cu. Y. Zr
Ti, V, Co. Ni, Afl, Sb, U
Be. Na. Mg. Al. K. Ca
Sc, Cs, La, Ce, Sm, Eu,
Dy, Lu. Hf. Th
Si. ft. Zn, Mo. Cd
HIGH SULFUR COALS
OTHER STUDIES
Ge, Bt
G«. B. Ti. V
Co, Ni, Cr, Cu. Mo
nQ. Zu, Cd, Pb, Mn
"Correlation based on data in Table V.
"Information collected from float/sink studies by Zubovic (Adv.
in Chem. Ser. 55, 221-30, 1966), Gluskoter (Chap. 1, Adv. in
Chem. Ser. 141, 1975), Duerbrouck ("Coal Cleaning: State of the
Art," Conf. Coal and the Environment, Louisville, Kentucky,
October 22, 1974), and Schultz (Chap. 11, Adv. in Chem. Ser.
141, 1975).
HIGHER CONCENTRATION
IN LOW-SULFUR WASTE
>100%1 F. Na. Al. Si, P. Ca. T«
APPROXIMATELY EQUAL
IN BOTH WASTES
HIGHER CONCENTRATION
IN HIGH-SULFUR WASTE
50-100%) Mg, Cr, Th
10-50%) Be, K, Ti, V, Mn, Zr, Hf, U
Sc. Y, Cd, Sb, Cs, La. Ce, Eu
10-60%) B, Rb. As, Sm
Yb
Li, Fe, Co, Ni, Cu, Zn, Mo, Dy
"Correlations based on data in Tables IV and V.
19
-------
and ion microprobes as scanning devices to gain general information about the compositions of
both the major and minor mineral phases present. Once we have more completely characterized
the waste materials of interest, we will begin to use the microprobes to search for particular
micromineral phases containing specific trace elements. This information is necessary to es-
tablish the spatial associations of trace elements within the waste structure.
Figure 8 is the photomicrograph of a sample of crushed refuse from Plant D that was examined
with the electron microprobe. The elemental compositions of the particle at position A show
evidence of three major phases: (1) calcium, carbon, and oxygen, probably as calcite; (2)
aluminum, silicon, and oxygen with low concentrations of krypton, most likely a clay area; and
(3) calcium, iron, magnesium, carbon, and oxygen, likely a dolomite or iron-rich dolomite. In
area B, the large smooth particle near the top, which appears gray on the photograph, contains
only silicon and oxygen, and is probably quartz. The black-appearing particle to its left contains
silicon, aluminum, krypton, magnesium, iron, and oxygen, and is likely a mixture of clay
minerals. The large particle at the bottom of area B, which appears to be much the same color as
the mounting plastic, is residual coal because only carbon was detected. In the large gray particle
labeled C, the light-gray part of the circular area at the lower left contains predominantly
calcium, carbon, and oxygen, with some iron and magnesium, again defining a dolomitic or
sideritic carbonate mineral, while the dark-gray portion contains aluminum, silicon, and oxygen
(a clay?). In addition, this circular area contained carbon and trace amounts of sulfur, fluorine,
Fig. 8.
Photomicrograph showing areas analyzed on a sample of refuse from Cleaning Plant D
(-100X).
20
-------
chromium, rubidium, strontium, and barium. The strontium and barium are present in the car-
bonate phase.
Microprobe studies, such as that just described, amply demonstrate the structural and
morphological complexity of the rocks and minerals present in these coals and coal wastes. These
materials tend to be very fine grained and they are highly interspersed with each other. There are
few pure mineral phases that extend over major areas of the waste particles. This, of course,
makes it more difficult to sort out the mineralogy of the trace constituents.
Characterization of Weathered Coal Preparation Wastes
We have begun to characterize the trace elements and minerals in samples of aged or
weathered coal cleaning wastes that we collected from the Illinois Basin. A description of the
weathered waste material collected appears in Appendix C.
Refuse, which was about 1 yr old, was collected at a dump site near Cleaning Plant A. Some
material was picked up near the surface and another increment was collected about 62 cm (24
in.) below the surface from a fresh cut. The analyses for these two weathered wastes are given in
Table VIII.
A comparison of the data for the waste samples collected from the two depths reveals an in-
teresting fact: certain minerals and trace elements are substantially depleted from the exposed
or surface layer of waste material. This information is presented in Table IX. In particular,
pyrite and marcasite (iron and sulfur values) are clearly less abundant in the surface material
than in the interior of the pile. Also, as Table IX reveals, many of the trace elements which have
strong tendencies to form sulfide minerals (cobalt, nickel, arsenic, copper, zinc, and cadmium)
are also appreciably depleted from the surface layer. In fact, of all the elements studied, only
phosphorus is present in the surface layer in substantially greater abundance than in the interior
of the waste bank. A final judgment on this issue must be deferred until quantitative
mineralogical analyses are completed; nonetheless, the behavior just described strongly implies
that some of the labile minerals and many of the trace elements have been removed from the
waste surface by the weathering and leaching processes.
Analysis of a Slurry Pond Residue
A sample of residue was collected at the inlet of the slurry pond near Cleaning Plant B. This
material is composed of the very fine residual waste that is left in the process water from the
cleaning operations. The sample we obtained is thought to represent the settled accumulation of
1 yr or more of plant operation. Analytical results for this material appear in Table VIII.
A listing of the relative abundances of trace elements in the slurry sample as compared to the
fresh gob from the same cleaning plant is given in Table X. This information reveals a strong
tendency of certain trace elements to segregate by particle size. Particularly interesting is that
many of the sulfide-forming elements, such as zinc, cadmium, and copper, are found in greater
relative amounts in the finer slurry particles, while the iron and sulfur analyses indicate that
pyritic materials in general do not exhibit much of a bias toward either coarse or fine waste.
21
-------
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en
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23
-------
TABLE IX
TABLE X
RELATIVE TRACE ELEMENT CONTENTS
IN COAL PREPARATION WASTES AS A
FUNCTION OF WASTE DUMP DEPTH8
DISTRIBUTION OF TRACE ELEMENTS
AND MINERALS BETWEEN SLURRY
AND GOB FOR ILLINOIS BASIN
CLEANING PLANT Ba
HIGHER CONCENTRATION
IN SLURRY
>100%) Ca, Zn, Br, Ag, Cd
APPROXIMATELY EQUAL
CONTENT AT BOTH LEVELS
Be, K, Se. La. Ce. Lu
B, F, N., Al, Si. C«, Sc, V. G«.
Cr. Zr, Ci, EU, Hf, Th
10-50X) Li, Ma. Ti, ft, Cu, Y, Mo, Cd. Oy, Yb
50-100%) S, Mr). Zn. Rb, A6, Sb, Sm. T.
Co, Mi, At
50-100%) Al, Cu, Rb, Sb
10-60%) Mn, Si, U
APPROXIMATELY EQUAL
LEVELS IN BOTH
"Correlations based on data in Table VIII.
HIGHER CONCENTRATION
IN GOB (WASTE)
B, Na, Mg, CI, K, ft. Ni, Y
Zr, Cs. Hf
F, Si, S, V, Cr, As, Ce, Sm,
Eu, DV, Th
(50-100%) UBe,Sc,T,,Co,Mo,U.
>100%) Yb
"Correlations based on data in Tables IV and VIII.
Characterization of Refuse From a Highly Weathered Waste Dump
Samples of coal refuse were collected from the base of an 8-yr-old waste bank, and along a dry
stream bed located immediately adjacent to the bank at Plant B. The stream is apparently ac-
tive only during periods of heavy precipitation, carrying surface water away from the dump area.
The elemental and mineralogical analyses for these two weathered waste materials appear in
Table VIII.
The results for the two sample locations are compared in Table XI. Most of the elements are
fairly equally distributed between the weathered waste bank and the stream sediment. However,
the higher content of carbon, hydrogen, and nitrogen in the stream samples suggests that the
lighter coal particles have been preferentially washed out of the waste pile. Based on the elemen-
tal composition of the samples, the waste bank appears to have a relatively higher content of the
denser pyritic material than the stream bed. Elements such as aluminum, sodium, krypton, and
silicon, associated primarily with the medium-density clays and quartz, are found about equally
distributed in both the waste bank and stream sediment samples. These observations suggest
that the mechanical action of running water, rather than dissolution/precipitation phenomena,
is the prime force for moving material from the waste bank into this stream bed.
24
-------
TABLE XI
DISTRIBUTION OF TRACE ELEMENTS
BETWEEN AN EIGHT-YEAR-OLD GOB PILE
AND AN ADJACENT DRY STREAM BED8
HIGHER CONCENTRATION
IN STREAM BED
P, Ga
Be, Cd, Cs. (C,H,N)
10-50% ) V, Cr, Sb
APPROXIMATELY SAME
LEVEL IN BOTH
HIGHER CONCENTRATION
IN WASTE PILE
Li, B, Na, Mg, Al, Si, K. Sc,
Ti, Cu, Zn, As, Se, Y, La, Ce •
Sm, Eu, Dy, Yb. Lu. Hf, Ta
Ni, Rb, Zr, Mo, Th
>100%) S, Ca, Mn, Fe, Co. Ag
"Correlations based on data in Table VIII.
Analysis of Oxidized Pyritic Coal Refuse
Samples of oxidized pyritic waste were collected from the surface of a refuse dump in the Il-
linois Basin. The exterior surfaces of these samples were coated with a white crystalline material,
which was later determined to be iron sulfate.
During shipment of these samples from the field to our laboratory, much of the white
crystalline material fell off the sample surfaces and accumulated at the bottom of the shipping
container. Subsequently, these waste materials were graded according to particle size in the
range of +6 to —250 mesh in an attempt to recover the fine powder. The coarsest sample was
found to be relatively rich in matrix material (unoxidized pyrite and marcasite), and the finest
particle fraction was mostly iron sulfate (rozenite) as demonstrated by the mineralogical data
presented in Table XII.
A comparison of the elemental analyses for the various samples of oxidized and unoxidized
materials reveals an interesting and perhaps important trend. As Table XIII illustrates, most of
the trace elements investigated were present in higher concentrations in the sulfate when com-
pared to their original abundance in the pyritic matrix. At present, we don't have an explanation
for this rather startling phenomenon. However, it will be important to delineate the mechanism
by which the concentration of trace elements is increased in the highly soluble, surface layers.
Because of our particular interest in these oxidized pyritic wastes, we examined them further
with SEM to observe their microstructures and the growth patterns of the white surface layers.
25
-------
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This material appeared as fine whiskers or fibers deposited on the surfaces of the sample.
Typical fibers are shown in the photomicrograph, Fig. 9. All the fibers that were examined con-
tained iron, sulfur, aluminum, and oxygen, although the aluminum was present only in minor
quantities. The interior of the matrix material was composed principally of pyrite, but narrow
channels were found within the pyrite that contained iron, sulfur, oxygen, and a small amount of
aluminum, and these may be the source from which the sulfate whiskers grew.
Subtask 2.6—Characterize Environmental Behavior of Coal Preparation Wastes
Studies of the effects of aqueous leaching on the trace elements and minerals in Illinois Basin
coal refuse have been started. Several waste materials have been leached for various times with
neutral and acidic solutions, but so far, the analyses have been completed for only one sample.
A 10-g sample of crushed coal refuse (-20 mesh) from Cleaning Plant B was leached with 100
ml of 0.01 M sulfuric acid solution for 5 days at ambient temperature. During the experiment,
the waste sample and leachate were contained in a sealed Pyrex flask and agitated with a
horizontal shaker. After the completion of the experiment, the acidic leachate (pH 2.3) was
removed from the residue by filtration and analyzed for a core group of 13 trace elements.
The concentration of the trace elements in solution, and the percentage of each extracted
(based on the content in the original sample) are reported in Table XIV. The high percentage of
TABLE XIII
TABLE XIV
PYRITE OXIDATION: RELATIVE
CONCENTRATIONS OF TRACE
ELEMENTS IN PYRITE
AND IRON SULFATE8
TRACE ELEMENTS LEACHED FROM COAL
REFUSE COLLECTED FROM PLANT B
HIGHER CONCENTRATION
IN IRON SULFATE
APPROXIMATELY EQUAL
LEVELS IN BOTH
Ni, Ca, Hf
Al, Sc, Ti. V, Co, U,
Sm, Dy, U
50-100% ) Sb. Eu. Lu. Th
Cl, Mn, Ta
HIGHER CONCENTRATIONS
IN PYRITE
"Correlations based on data in Table XII.
Trace
Element
Ca
Co
Ni
Zn
Cd
Mn
Fe
Mg
As
Cu
Cr
Al
K
ppmm
Solution
71
1.8
3.2
4.7
0.02
4.0
1650
22
0.67
0.27
0.10
58
8.8
Per Cent
Extracted8
83
60
45
38
35
29
15
9
8
5
1.4
1.2
0.7
"Based on the original content of each element in the refuse
sample.
28
-------
(500X)
(1000X)
(2000X)
Fig. 9.
Scanning electron micrograph showing typical fibers from the surface of oxidized pyrite.
29
-------
some of the elements that were removed from the waste material by dissolution is indeed strik-
ing. Based on the available information, it can be surmised that the carbonate and sulfide
minerals were leached to the greatest degree. Although the experiment involved a relatively high
concentration of leachate, and relatively small particles of waste, the other conditions (pH, tem-
perature, and time) were not greatly out of line with conditions often encountered in nature.
Subtask 2.7—Development of Procedures for Trace Element Separations
A major goal of this program is to begin to identify methods for removing or separating trace
elements of environmental concern from coal processing wastes. Toward this end, one of the
areas we are considering is whether specific mineral or trace element types concentrate in certain
of the various size fractions produced by coal cleaning operations. The removal or treatment of a
specific range of particle sizes to control toxic or harmful trace elements in coal wastes would be
one of the easiest and most convenient operations to perform. Therefore, each of the Illinois
Basin refuse materials (Plants A, B, and C) was classified according to size, both to characterize
the distributions of sizes present and to determine whether mineral or trace element separations
could possibly be made by this technique.
After drying, the samples were screened and hand separated into five size categories: —1/4 in.,
—1 in., —1x2 in., -2 in., and +2 in. Representative samples of waste in each of these size ranges
is shown in Figs. lOa through e. Occasionally, pieces larger than 15 cm (6 in.) in width or
length appear; these were included in the +2 in. material, but are shown separately in Fig. lOf.
The relative amount of each size fraction was determined by weighing. The particle size distribu-
tions for each of the three Illinois Basin coal refuse types are shown in Fig. 11. Two of the plants
(A and C) have similar size materials, whereas the other (B) has a finer blend.
Following size analyses, each fraction was crushed, blended, and further reduced in prepara-
tion for further characterization. While doing the sample size separations, we noted visually that
certain mineral types had tendencies to accumulate in certain size ranges. For example, the
clays were very friable and showed a marked tendency to disintegrate into small particles. On
the other hand, much of the heavier mineral matter, presumed at the time to be pyritic material,
congregated in the larger size fractions. The analytical results obtained thus far on the size frac-
tions, for the most part, substantiate these observations. The mineralogical data are incomplete,
but referral to the iron and sulfur values for Plant B wastes, found in Table XV, confirms that
the largest waste particles (>1 in.) contain substantially greater proportions of pyrite and mar-
casite than the smaller fractions. Consideration of the aluminum values suggests that the clay
minerals are more uniformly spread over all the size ranges, but there does appear to be some
bias toward greater aluminum (clay mineral) content in the smaller size ranges. A clearer picture
of this situation will be provided when the quantitative mineral analyses are completed.
A very interesting picture emerges from a consideration of the tendencies of some of the trace
elements to preferentially segregate in the various particle sizes. The relatively high contents of
iron, sulfur, arsenic, and molybdenum in the largest waste fragments is rather striking, as are the
enriched concentrations of such elements as lithium, phosphorus, copper, zinc, and lead in the
smaller size fractions. A compilation of the trace element compositions as a function of waste
particle size appears in Table XVI.
Although it is not yet clear why certain trace elements are preferentially found in certain waste
size ranges, nor is it yet certain that this phenomenon is universal, the implication of such
behavior is important because it suggests that it may be possible to separate or remove certain
trace elements from coal preparation waste solely on the basis of waste particle size.
30
-------
t.o* Alamos Scientific
Of Wt «*HVtWW5f «W
I i1. i»i ,1 ,^ iS.aAj'i ^ 1*1
Fig. 10.
Size fractions of Illinois Basin coal refuse, a, -1/4 in.; b, -1 in.; c, -1x2 in.; d, -2 in.; e, +2
in.; f, +6 in.
31
-------
40
35
30
z
I
g
20
15
10
I I
\
-1/4
-1 -1x2
SIZE (in.)
-2
Fig- 11-
Size distribution of coal cleaning wastes from
the Illinois Basin.
TASK 3—LABORATORY PROGRAM FOR TRACE ELEMENTS
REMOVAL/RECOVERY
Work on this task was begun as scheduled during the second half of the fiscal year. Progress in
this area has been slow, however, due to the necessity of having first to identify specific environ-
mental problems from trace elements in coal wastes before control or removal measures can be
defined. Nonetheless, some of the activities described above, for example, the separation of trace
elements according to waste particle size and the removal or recovery of trace elements by
aqueous leaching, apply directly to the goals of this task. Greater emphasis can be given to Task
3 after we are further along with our studies of coal refuse composition and environmental
behavior.
32
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Personnel
A large number of LASL personnel contributed to the programmatic effort during the past
year. Their work and continued interest is essential to the success of this program and is deeply
appreciated.
Advisors: R. D. Baker, R. J. Bard, and R. C. Feber
Analytical Advisors: G. R. Waterbury, M. E. Bunker, and N. E. Vanderborgh
Sample Preparation: J. M. Williams and P. L. Wanek
Neutron Activation Analyses: E. S. Gladney, W. K. Hensley, J. Bubernak, and G. M. Matlack
Spectrochemical Analyses: O. R. Simi, J. V. Pena, and D. W. Steinhaus
Atomic Absorption Spectrophotometry and Wet Chemistry: R. D. Gardner, J. E. Troxel, and
W. H. Ashley
X-ray Fluorescence, Electron Microprobe, and Ion Microprobe: E. A. Hakkila, J. M. Hansel,
W. B. Hutchinson, and N. E. Elliot
X-ray Diffraction/Mineralogy: J. A. O'Rourke
Mass Spectrometry: E. D. Loughran
Literature Search: E. M. Wewerka, J. M. Williams, P. L. Wanek, and J. D. Olsen
33
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TABLE XVI
SEGREGATION OF TRACE ELEMENTS
AND MINERALS ACCORDING TO
PARTICLE SIZE OF ILLINOIS
BASIN COAL WASTE"
MINERALS
ILLITE. KAOLINITE
PYRITE, MARCASITE
TRACE ELEMENTS
Li. Na, Mg. P. K. C.. Sc, Ti,
Ni, 2n. 8r, Rb, Y. Cl, L«. Ce
Lu. Th, U
Be, Al. Si, V, Cr, Co, Cu,
Zr, Sm, Eu, Dy. Yb, Hf
B, f. Cl. Mn, Sc.Ag.Sb
S. Fe, A.
"Correlations based on samples 24B, C, and F in Table XV.
36
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APPENDIX A
SUMMARY AND CONCLUSIONS FROM LITERATURE SURVEY
The major conclusions from the review of the literature are that
• Few studies of the trace elements in coal preparation wastes have been conducted.
• There is a considerable body of knowledge about trace elements and minerals in raw coals,
which, in most instances, can be applied directly to coal wastes.
• The fate of trace elements during coal washing or preparation is poorly defined.
• The drainage and runoff from coal refuse is a serious polluter of waterways, but neither the
contributions nor the effects of trace elements to this form of environmental contamination is
well understood.
• Combustion of coal-waste materials is a major source of air pollution; however, the fate of
trace elements during waste-dump burning is unknown.
• Based on the available information, a comprehensive assessment of the seriousness of en-
vironmental contamination from trace elements in coal preparation wastes cannot be made.
• Some of the methods used to prevent or treat acidic effluents from coal wastes may also be
useful for controlling trace element releases, but these may lead to undesirable secondary effects
in some cases.
• Significant quantities of important minerals and materials are present in coal refuse, but
methods for recovering them have not been extensively investigated within the context of today's
economics.
The following paragraphs provide brief summaries of the highlights of each of the major sec-
tions included in the review.
Introduction
The mineral wastes from coal preparation and mine development constitute a major environ-
mental problem. Over 3-billion metric tons of these materials have accumulated in the U.S., and
the current annual rate of waste production (100-million metric tons per year) is expected to dou-
ble within a decade. The total number of active and abandoned refuse dumps is estimated to be
between 3000 and 5000. About one-half of these pose some type of health, environmental, or
safety problem. Structural weaknesses in coal refuse banks have led to tragic landslides. Coal
waste piles are also the source of highly mineralized, often acidic drainage, which affects more
than 10 000 miles of streams and waterways, and the 300 or so burning refuse dumps are a major
source of air pollution. In addition to these problems, there is growing concern about possible en-
vironmental contamination from the trace elements in coal mineral wastes. The purpose of this
review is to use the available information to assess the potential of this latter possibility.
Literature Search Format
An extensive search of the open literature on trace elements in coal preparation wastes and en-
vironmental contamination from these elements was completed both by computer- and manual-
search techniques. Over 4400 references on the general topics of coal, coal wastes, the elemental
and mineralogical composition of coal and its wastes, and the environmental behavior of these
materials, were reviewed. This major collection of background information was culled to 200 of
the most pertinent references, on which this review is based.
37
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Trace Elements and Minerals in Coal Preparation Wastes
Only a few studies of the minerals and trace elements in coal preparation wastes have been
reported. Most of these have concerned the identification and structures of the major minerals;
only limited attention has been given to the trace elements present in these wastes.
Trace Elements and Minerals in Raw Coals
Much information on this subject is available, and most of it can be applied to coal prepara-
tion wastes. Clay minerals, silica, carbonates, sulfides, and sulfates constitute the major
minerals in most coals. Nearly all of the naturally occurring elements have been identified in
coals—most in trace or minor amounts. With few exceptions, the less-abundant elements are
associated with the major mineral phases. This leads to the conclusion that the behavior of many
of the trace elements in coal wastes during weathering, leaching, or burning will be dictated by
the behavior of the major minerals.
Trace Element Behavior During Coal Preparation
The fate of trace elements during coal preparation has received only limited attention, and
still is not well defined. Laboratory investigations of elemental behavior using float-sink techni-
ques have been conducted. These studies reveal that trace elements differ in their suscep-
tibilities to be removed from coals by density separation, but significant reductions of these ele-
ments in coals can be achieved. Therefore, large quantities of trace elements are discarded in the
washing refuse.
Water Contamination from Trace Elements in Coal Preparation Wastes
The aqueous drainage from coal refuse is usually contaminated by acids and dissolved or
suspended mineral matter. The higher concentrations of dissolved species are found in the more
highly acidic solutions. Typically, the acid drainage from coal refuse contains high concentra-
tions of Fe, Al, Ca, Mg, and So4 ions, which are derived from the major minerals. Little is known
about the minor or less abundant trace elements in coal waste drainage. Some of these elements
have been identified in the drainage or leachates from coal refuse or spoils, but a thorough assess-
ment of this subject has not been made. There is considerable evidence that coal refuse dumps
will continue to produce significant quantities of water-borne contaminants for many years after
their disposal.
Trace Element Emissions from Burning Coal Refuse
The gaseous products from the combustion of residual carbon and minerals in coal refuse are
significant atmospheric contaminants. Approximately 300 to 500 of these waste piles are now
burning. The causes of refuse fires are varied, but once started they can burn for many years. By
analogy with other coal-combustion systems, volatile trace elements are undoubtedly released
by burning refuse, but this problem has not been addressed.
38
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Trace Elements of Environmental Concern in Coal Preparation Wastes
There are numerous potentially toxic trace elements in coal wastes, and many of these find
their way into the environment. Ions, such as iron, aluminum, and manganese, which leach out
of coal refuse in large amounts, can be harmful to soils, waterways, and plant and animal life.
Little information exists on the behaviors of toxic heavy metals in coal refuse banks. The
possibility that toxic elements can accumulate or concentrate within the waste pile, or in the sur-
rounding environment, warrants attention. Based on the available information, an adequate
assessment of the total potential for environmental contamination from trace elements in coal
preparation wastes cannot be made.
Prevention and Treatment of Contamination from Coal Preparation Wastes
Much attention has been given to methods for preventing or controlling contamination from
coal refuse materials. These techniques have been directed primarily at preventing or neutraliz-
ing acidic effluents and reducing the dissolved or suspended mineral matter in waste waters.
Preventive measures include grading, compacting, and sealing of wastes to reduce the influx of
air and water. Treatment of acid drainage is done by alkaline neutralization, ion exchange,
reverse osmosis, or flash distillation. Some of the methods for preventing or treating acid
drainage may also be useful for controlling or reducing environmentally harmful trace elements.
Recovery of Trace Elements and Minerals from Coal Waste Materials
Some work has been reported on the use of coal refuse materials. Of primary interest is the
recovery of residual coal, but the use of these wastes for building and construction products and
as a source of metals or minerals has also been reported. Among the major materials that have
been sought from coal wastes are sulfur and aluminum. Processes for recovering minor elements
such as gallium, germanium, manganese, and molybdenum have been developed. Magnetic
separation, ion exchange, and roasting and leaching methods are among the most promising
techniques for recovering useful materials from coal refuse. Coal mineral wastes could supply
much of the U.S. demand for certain metals and minerals if the economic and technological
problems of recovery could be solved.
APPENDIX B
SAMPLE PREPARATION, ANALYTICAL PROCEDURES,
AND ANALYTICAL RESULTS FOR STANDARD COAL AND ASH SAMPLES
Sample Preparation and Reduction
Raw coal and waste samples are crushed to less than 2 in. with a hammer. The material is
spread thinly in ceramic-coated pans and dried for 24 h at 60°C in a forced-draft oven. The dried
39
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sample is further crushed to -3/8 in. with a jaw crusher, and then is reduced to a 0.5-kg lot with a
cone or riffle splitter. In the final step, the reduced coal or waste samples are pulverized to —20
mesh with a rotary grinder (equipped with ceramic plates).
Low- and High-Temperature Ashing
Low-temperature ashing (LTA) is done in an oxygen-plasma asher according to the following
procedure.
Five powdered (-20 mesh) and blended samples of coal or waste material (0.7-g each) are
dried for 24 h at 60°C after having been placed into ceramic boats. Then the dried samples are
ashed at 75°C until all of the organic matter has been removed (constant weight). This usually
requires 72 to 96 h to complete. During ashing, the samples are stirred frequently to expose new
material to the oxygen plasma. The three sample boats with ash values closest to the mean of all
five samples are selected for analytical work.
High-temperature ashing (HTA) is done by a procedure similar to that used for LTA, except
that the ashing step is done at 500°C in an electric muffle furnace. About 2 h is required to com-
pletely ash a sample at high temperature.
Neutron Activation Analysis
Neutron activation analysis (NAA) is one of the most accurate and reliable methods of assay-
ing for trace elements in natural materials. The method relies on the production of radioactive
nuclides in a sample and the subsequent detection and measurement of the associated gamma
radiation with a Ge(Li) detector. It is a nondestructive technique in most applications, and has
the advantage that many elements can be observed simultaneously. Although the method is
"blind" to a number of elements, this is often advantageous. Among those that cannot be obser-
ved (or are very difficult to observe) are carbon, oxygen, silicon, and lead.
The present program involves the trace element assay of large numbers of samples of coal and
waste residues. For this work, we have developed a computer code that will scan the gamma-ray
spectrum of a neutron-bombarded sample and produce a list of all elements identified and their
concentrations (in ppm). The method involves matching each gamma-ray energy against a com-
puter "library" of possible gamma rays that can result from neutron capture. The library con-
tains the principal gamma rays from 67 elements, involving 124 separate isotopes. However, it
should be recognized that in routine NAA analyses of natural materials (coal, rock, soil, etc.), it
is unusual to observe more than about 30 elements unless postbombardment chemistry is em-
ployed.
We have tested our system by assaying several standard NBS materials. Table B-I includes
the NAA results for NBS coal (SRM-1632), and Table B-II contains the NAA results on the NBS
standard fly ash (SRM-1633). Eight elements (titanium, manganese, magnesium, vanadium,
aluminum, sodium, calcium, and barium) were determined using 15-mg samples which were
irradiated for 20 s in a thermal neutron flux of 7 x 1012 n/cm2 s. These samples were permitted to
decay for 10 min following the irradiation and were then counted for 10 min with a 55-cm3 Ge(Li)
detector. The remaining elements were determined using 3-g samples and an irradiation time of
5 min. These samples were permitted to decay for 10-14 days and were then counted for 10 min.
Additional elements could be determined, if deemed necessary, by lengthening the counting
periods or by modifying the decay times. Based on the two-count procedure described above, the
40
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TABLE B-I
ANALYTICAL RESULTS FOR COAL SRM 1632
Element
Li
Be
B
F
Na
Mg
Al
Si
P
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Rb
Sr
Y
Zr
Nb
Mo
Ru
Rh
Ag
Cd
Sn
Sb
Cs
Ba
La
Ce
Pr
SRM-1632 Coala'b
Elemental
Concentrations
1.5
414 ± 20
0.20 ± 0.05%
1.85 ± 0.13%
3.2%
0.28 ± 0.03%
0.43 ± 0.05%
3.7 ±0.3
1040 ± 110
[35 ± 3]
[20.2 ± 0.5]
[40 ± 3]
[8700 ± 300]
5.7 ±0.4
[15 ±1]
[18 ± 2]
[37 ± 4]
Emission"'0
Spectroscopy
24 ± 1.1
1.2 ± 0.07
30 ±1.1
1200*
0.16%*
2.1%
2.1%*
0.31%*
0.51%*
3.6 ± 0.08
900*
32 ±1.3
16 ±1.2
36 ± 1.8
6500*
4.7 ± 0.32
15 ±1.1
17 ±7. 5
45 ±17
6.2 ±0.3
2.7 ± 0.22
Atomica'd
Absorption
and Wet
Chemistry
25
1.5
100
3.2%
71
800
36
19
40
8730
7
15
21
37
Neutron"
Activation
415 ± 42
0.20 ± 0.04%
1.80 ± 0.18%
0.28 ± 0.05%
0.44 ± 0.09%
3.8 ±0.4
1100 ± 110
36 ±4
21.6 ±2
40 ±4
9800 ± 1000
5.8 ±0.6
34
[5.9 ± 0.6]
[2.9 ± 0.3]
21 ±2
161 ± 16
0.06 ± 0.03
[0.19 ± 0.03]
3.9 ± 1.3
1.4 ±0.1
352 ± 20
10.7 ± 1.2
19.5 ± 1
22 ± 2.9
280*
7,6 ±0.81
25 ±3
3.6 ±0.16
<5
<5
<0.15
0.7
2-10
410*
6.0 ± 0.17
30
46
0.08
0.31
6.6 ±1.3
3.1
19 ±6
170 ± 17
4.1 ± 1.2
1.4 ± 0.3
345 ± 70
19.7 ± 0.2
41
-------
TABLE B-I (cont)
Element
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ir
Pt
Au
Hg
Tl
Pb
Bi
Th
U
SRM-1632 Coal8 b
Elemental
Concentrations
1.7 ±0.2
0.33 ± 0.04
0.23 ± 0.05
0.7 ±0.1
0.14 ± 0.01
0.96 ± 0.05
[0.12 ±0.02]
[0.59 ± 0.03]
[30 ± 9]
3.2 ±0.2
[1.4 ±0.1]
Atomic8'"
Absorption
Emission8'0 and Wet
Spectroscopy Chemistry
<15
<15
0.41 ± 0.06
<15
<15
<5
<1.5
<15
<5
0.91 ± 0.07
<7
<50
<15
<5
<5 <1
12-120 30
<1.5 <1
<15
6
Neutron8
Activation
0.37 ± 0.04
0.20 ± 0.04
0.55 ± 0.08
0.15 ±0.02
1.15 ±0.12
0.16
3.2 ±0.3
"All values are expressed in ppm unless otherwise indicated.
"Values in brackets are certified NBS results. Other values are NBS uncertified or from J. M. Ondov et al., Anal.
Chem. 47, 1102 (1975).
"Emission spectrochemical results followed by an asterisk have an estimated precision of ±20% RSD (relative standard
deviation), otherwise the precision is estimated to be ±50% RSD. A result with a standard deviation indicates the
average of six replicate analyses.
"Atomic absorption values have an estimated precision of ±2.0% RSD unless the value is at the detection limit of the
method.
sensitivity of our NAA counting setup for selected elements is as shown in Table B-III. As an ex-
ample, if a 3-g sample containing 0.5 ppm arsenic were analyzed, the strongest arsenic gamma
ray would produce a peak with an area of ~100 counts, which is about as small a peak as we have
confidence in measuring.
Spectrochemical Analysis (Optical Emission Spectroscopy)
Three spectrochemical methods were used for the analysis of coal and coal ash samples: (1) a
high-temperature ashing (HTA) method for trace elements, (2) an improved low-temperature
ashing (LTA) method for trace elements, and (3) a method for major and minor elements. In the
42
-------
TABLE B-II
ANALYTICAL RESULTS FOR COAL ASH SRM 1633
Element
Li
Be
B
F
Na
Mg
Al
Si
P
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Rb
Sr
Y
Zr
Nb
Mo
Ru
Rh
Ag
Cd
Sn
Sb
Cs
Ba
La
Ce
Pr
SRM- 1633" b
Coal Ash
Elemental
Concentrations
12
0.32 ± 0.04%
1.8 ±0.4%
12.7 ± 0.5%
,21 ± 2%
1.61 ± 0.15%
4.7 ± 0.6%
27 ±1
0.74 ± 0.03%
[214 ± 8]
[131 ± 2]
[493 ± 7]
6.2 ± 0.3%
41.5 ±1.2
[98 ± 3]
[128 ± 5]
[210 ± 20]
[61 ± 6]
[9.4 ± 0.5]
125 ± 10
0.17 ± 0.03%
62 ±10
301 ± 20
[1.45 ± 0.06]
6.9 ± 0.6
8.6 ±1.1
0.27 ± 0.02%
82 ±2
146 ± 15
Emission"'0
Spectroscopy
140 ±9
14 ± 0.95
500 ± 29
0.97%*
1.6%*
13%*
17%*
3.3%*
4.8%
23 ± 2.3
0.72%*
230 ± 12
150 ± 13
460 ± 26
5.6%
38 ± 0.96
120 ± 7.5
110 ± 11
210 ± 36
68 ±14
25 ± 1.4
110 ± 22
0.23%
44 ± 4.2
160 ± 34
<100
37 ± 1.3
<30
<30
<1
<5
10
<100
0.30%*
45 ± 4.5
200
<100
Atomicttd
Absorption
and Wet
Chemistry
80
12
20
880
0.87%
410
130
506
7.0%
39
78
129
250
0.35
1.53
Neutron8
Activation
0.34 ± 0.03%
1.5 ± 0.3%
12.3 ± 0.5%
5.1 ± 0.6%
24 ±1
0.70 ± 0.07%
225 ± 20
118 ±8
504 ± 25
5.6 ± 0.2%
41 ±3
308 ± 75
68 ±15
10.1 ±2.2
112 ± 20
1.0
9.8 ±2.1
7.7 ±1.3
0.25 ± 0.03%
86 ±2
145 ±6
X-ray"
Fluorescence
3.5%
0.30%
6.0%
0.8%
0.18%
43
-------
TABLE B-II (cont)
Element
SRM-1633a'b
Coal Ash
Elemental
Concentrations
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Er
Pt
Au
Hg
Tl
Pb
Bi
Th
U
12.4 ±0.9
2.5 ± 0.4
1.9 ±0.3
7±3
1.0 ±0.1
7.9 ± 0.4
[0.14 ± 0.01]
4
[70 ± 4]
24.8 ± 2.2
[11.6 ±0.2]
Emission*'0
Spectroscopy
<100
<100
2.8 ±0.13
<100
<100
<30
Atomic*'"
Absorption
and Wet
Chemistry
Neutron*
Activation
12.8 ± 0.6
2.6 ±0.2
X-ray*
Fluorescence
<100
<30
5.7 ± 0.56
<50
<300
<90
<30
<30
74 ±9
4.8 ± 0.6
1.0 ±0.2
6.5 ± 0.7
0.55
5
82
<100
22.5 ± 0.6
"All values are expressed in ppm unless otherwise indicated.
"Values in brackets are certified NBS results. Other values are NBS uncertified or from J. M. Ondov et al., Anal.
Chem. 47, 1102 (1975).
°Emission spectrochemical results followed by an asterisk have an estimated precision of ±20% RSD (relative standard
deviation) otherwise the precision is estimated to be ±50% RSD. A result with a standard deviation indicates the
average of six replicate analyses.
"Atomic absorption values have an estimated precision of ±2.0% RSD unless the value is at the detection limit of the
method.
HTA method for trace elements, the coal is ignited at a high temperature (~750°V), the ash is
mixed with an equal weight of high-quality graphite powder, and precisely weighed portions of
the mixture are analyzed by de-arc excitation. In the LTA method, the sample is ignited at
<100°C in an oxygen plasma, the ash is mixed with four parts of sodium carbonate-graphite
powder buffer, and weighed portions of the mixture are excited by dc arc. When the method for
major and minor elements (sodium, magnesium, aluminum, silicon, krypton, calcium, titanium,
iron, strontium, barium) is applied, HTA or LTA is mixed with 40 parts of copper oxide-graphite
powder buffer and weighed portions are analyzed by de-arc excitation.
Results were obtained by visual comparison of standards and samples exposed on the same
spectrographic plate or by photometry of those plates. A visual comparison result has a precision
estimated at ±50% relative standard deviation (RSD). A result obtained by photometry has an
estimated precision of ±20% RSD.
44
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TABLE B-III
ESTIMATED 100-COUNT PEAK-AREA
DETECTION LIMITS IN TYPICAL
NAA ANALYSIS OF 3-g SAMPLES
Element ppm Element ppm
Ba 45 Lu 0.04
Sr 45 Th 0.5
Cu 2 Cr 5
K 450 Hf 0.7
As 0.5 La 2
Ti 500 Sb 1
Mn 4 Cs 2
Mg 6000 Sc 0.09
Na 100 Fe 900
V 6 Zn 10
Al 300 Co 2
Ca 5000 Eu 0.3
W 0.5 Yb 0.5
Sm 0.07 Rb 50
Ce 2 Ta 0.5
The emission spectrochemical results for the coal (NBS SRM-1632) and the coal ash (NBS
SRM-1633) are presented in Tables B-I and B-II, respectively, with the results obtained by other
methods. The spectrochemical results agree very favorably with the NBS certified values.
Atomic Absorption Spectrophotometry
One of the main techniques used for determining trace elements and minor constituents in the
NBS coal and fly ash samples was atomic absorption spectrophotometry with a carbon-rod
atomizer.
The coal samples were dry-ashed at a high temperature (~500°C). The resulting ash and the
NBS fly ash were dissolved in 5 ml 12M Hcl at 300°C in a sealed quartz tube. The SiO2 was
filtered for gravimetric determination, and the solutions were analyzed for specific trace ele-
ments by atomic absorption spectrophotometry. The results of these analyses are also given in
Tables B-I and B-II.
Two wet-ashing techniques were investigated: one using a HN03-HC104 mixture and one us-
ing HF. Both techniques left a slight amount of insoluble residue indicating incomplete dissolu-
tion.
A small sample of low-temperature ash from the NBS coal was analyzed, and the results were
compared with the high-temperature ash results. Zinc, lead, copper, cadmium, and silver gave
higher results (10-30%) on the low-temperature ash with the titanium result being lower.
45
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X-Ray Fluorescence and Ion Microprobe
X-ray spectroscopy, electron microprobe, and ion microprobe techniques were evaluated for
examination of coal and fly ash. In x-ray spectrographic analysis, the powdered samples were ex-
amined using an energy dispersive spectrograph without sample dissolution or separation
procedures.
Energy dispersive x-ray spectroscopy was evaluated for determining major constituents in the
ash sample, NBS SRM-1633. Zinc was used as an internal standard, but only linear background
corrections and no correction for absorption or fluorescence were employed. Results (Table B-II)
were in fair agreement with other methods, but probably could be improved with better excita-
tion of the sample and with a mathematical treatment of the data.
The NBS coal ash sample also was analyzed with the ion microprobe (IMMA) using a com-
puter program CHARISMA for quantitative data reduction (Table B-IV). Data were uncorrec-
ted for overlapping oxide peaks. A mathematical correction for overlapping peaks is being
developed as time permits, and application of corrections should improve results and enable
determination of more elements.
X-Ray Diffraction
Both qualitative and quantitative x-ray studies are under way on raw coals and ash. It now ap-
pears that quantitative results can be obtained for most of the common mineral constituents in
the raw coals by examining the low-temperature ash fractions.
The method used is essentially that developed at the Mellon Institute by Klug, et al.1"3 for the
analysis of quartz in industrial and community dusts, which was subsequently extended by Rao4
and Miller6 to the evaluation of mineral constituents in coals. For this purpose 1 (i a-A!203, of
high purity, is being used as an internal standard. The values of the proportional constants, the
R-factors, given by Miller for such components as illite, kaolinite, and pyrite are being reex-
amined and various methods of preparing truly unoriented samples are being explored.
Hopefully the R-factors for the unoriented or reproducibly oriented clay minerals will soon be
known with greater accuracy.
In an initial application of the quantitative method, a sample of the standard NBS coal, SRM-
1632, was evaluated. In the raw coal sample only "illite," kaolinite, and a-quartz were detected
above the high background radiation, but after 75°C ashing (LTA) most of the expected mineral
constituents were observed. Using the Miller R-factors, quantitative analysis of the LTA fraction
gave the following percentages of minerals as present in the raw coal:
4.46% Kaolinite
7.9% Illite Group Minerals
2.08% a-Quartz
<0.1% Sphalerite
1.59% Pyrite
0.52% Calcite
The percentages listed for the clay minerals must be considered at present as only approx-
imate. It would appear however, that once good R-factors are available, and with isotropic sam-
ples, the kaolinite content can be established with appreciably better accuracy. The illite in-
dicial peak appeared to be from a composite of two or more illite-group minerals, therefore any
measurements assuming pure illite can only be relative. Separation of the minerals of this group
by methods developed at the USBM6 seems feasible, thus permitting analysis of the individual
components; however, the accuracy of such analyses will probably never be as great as with the
other components.
46
-------
TABLE B-IV
COMPARISON OF IMMA VALUES FOR
SRM-1633 COAL ASH WITH OTHER TECHNIQUES"
Element
H
Li
Be
B
C
N
0
F
Na
Mg
Al
Si
P
Ca
K
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
As
Sr
Ba
U
NBS Value
Certified
214 ±8
131 ±2
493 ±7
98 ±3
128 ±5
210 ± 20
61 ±6
11.6 ±0.2
Round Robin
Anal. Chem. 47,
1102 (1975)
0.32 ± 0.04%
1.8 ± 0.4%
12.7 ± 0.5%
21 ± 2%
4.7 ± 0.6%
1.61 ±0.15%
27
0.74 ± 0.03%
235 ± 15
127 ±6
496 ± 19
6.2 ± 0.3%
41.5 ±1.2
98 ±9
216 ± 25
58 ±4
0.17 ±0.03%
0.27 ± 0.5%
12 ± 0.5
IMMA
1.25%
1.4
5
180
1%
20
10.8%
60
0.44%
1.2%
10.2%
22.9%
325
Interference
4.9%
Interference
0.75%
370
361
480
Interference
Interference
Interference
230
Interference
87
0.19%
0.48%
"All values are given in ppm unless otherwise specified.
Wet-Chemical Analyses
Several standard ASTM methods were used to characterize the SRM-1632 coal and SRM-1633
fly ash for moisture, volatile matter, ash, fixed carbon, hydrogen, total carbon, and nitrogen.
Total sulfur, pyritic sulfur, carbonate carbon, chloride, and fluoride were measured using
methods not available as ASTM procedures.
These analyses were performed on a 125-g sample that was pulverized in a diamond mortar to
pass a No. 60 sieve. The material was allowed to equilibrate, and weighed portions were taken for
47
-------
the following analyses by ASTM (D-271) methods. The precision valves are based on these
replicate analyses.
Moisture: A 10-g portion was heated for 1 h at 110°C, and the weight loss calculated as moisture.
Estimated precision was about 0.02%.
Volatile matter: A 1-g portion of sample was heated for 6 min at 600°C, then for 6 min at 950°C,
excluding air. After correcting for moisture, the weight loss was calculated as volatile matter.
Precision was about 0.05%.
Ash: The residue from the moisture determination was heated in air at 750°C to constant weight
and the residue calculated as ash. Precision was about 0.02%.
Fixed carbon: Fixed carbon was calculated by subtracting from 100 the sum of moisture,
volatile matter, and ash.
Hydrogen: A 50-mg sample was burned in 02 at 900°C. The weight of water formed was
calculated as H2. The precision was about 2% relative.
Total carbon: Total carbon was determined by igniting a 25-mg sample in 02 at 900°C. Carbon
was calculated from the weight of C02 obtained. The precision was about 0.3%.
Nitrogen: Nitrogen was determined by the Kjeldahl procedure. After dissolving the sample in
18M H2S04 with suitable catalysts, the solution was made basic, and the nitrogen was distilled
as ammonia and titrated. Precision was about 1% relative.
ASTM methods were not available for the following analyses that were made by established
LASL methods:
Total sulfur: Sulfur was determined with a LEGO Titrimetric Sulfur Analyzer. A 50-mg sample
was burned in O2 and the combustion gases bubbled through a solution of HC1. The S02 was
titrated with a KIOa-KI solution as evolution occurred, using a starch indicator. Precision was
about 2% relative.
Pyritic sulfur: Pyritic sulfur was determined by leaching first with HC1 to dissolve readily solu-
ble iron; then with HNO8 to dissolve FeS2. In the latter solution, iron was determined by atomic
adsorption and the sulfur was calculated.
Carbonate carbon: The sample was treated with acid and the evolved C02 absorbed and
weighed for calculation of carbon.
Chloride and fluoride: The sample was pyrohydrolyzed, and chloride and fluoride were deter-
mined in the distillate using specific ion electrodes.
The analytical results for the SRM-1632 and -1633 samples are presented in Table B-V for
future reference and standardization. The analyses of the lignite coal from the Beulah Mine in
North Dakota, which had been analyzed by the Bureau of Mines, are shown in Table B-VI.
48
-------
TABLE B-V
WET-CHEMICAL ANALYSES OF STANDARD REFERENCE
MATERIALS 1632 AND 1633
SRM-1632
Moisture
Ash
Total C
Fixed C
Organic C
COa carbon
H2
Total S
Pyritic S
Oi-diff.
Volatile Matter
Organic S
N2
Cl
F
As
Received
2.74%
13.41%
68.9%
55.2%
13.6%
0.07%
4.46%
1.43%
0.51%
8.03%
28.62%
0.92%
1.03%
3.8%
100 ppm
H2O/Mineral-
Free
Basis
82.4%
66.1%
16.3%
0.08%
5.34%
1.71%
0.61%
9.69%
34.25%
1.10%
1.23%
SRM-1633
As
Received
0.17%
96.10%
3.05%
1.07%
1.92%
0.06%
0.10%
0.29%
0.20%
0.25%
2.66%
0.09%
0.04%
0.08%
20 ppm
TABLE B-VI
ANALYSIS OF LIGNITE FROM BEULAH MINE, MERCER COUNTY, NORTH DAKOTA
LASL Analyses
Moisture
Vol. Matter
Fixed C
Ash
Total
Hydrogen
Carbon
Nitrogen
Oxygen
Sulfur
Ash
Total
As Received
13.6%
38.0
39.8
8.6
100.0
4.5%
54.4
1.7
29.9
0.87
8.6
100.00
(Calculated)
Dry Basis
44.0
46.0
10.0
100.0
3.5%
63.0
2.0
20.5
1.01
10.0
100.00
Bureau of Mines Analyses
Dry Sample As Received Dry Sample
43.7
46.2
10.1
100.0
4.1%
62.0
1.8
21.0
0.96
10.1
100.00
25.30%
33.02
34.29
7.39
100.00
6.18%
46.55
0.64
38.47
0.77
7.39
100.00
44.21
45.89
9.90
100.00
4.51%
62.32
0.86
21.33
1.03
9.90
100.00
49
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APPENDIX C
PROCEDURES FOR COLLECTION OF COAL CLEANING WASTE SAMPLES
Illinois Basin Coal Cleaning Plant A
The first coal preparation plant that we sampled has a throughput of about 20 x 103 tons of raw
coal per day. The feed coal, which is a mixture of strip-mined varieties, is highly mineralized.
The coal washing is done with a battery of six-cell McNally jigs. The coarse coal product is
screen dried, and the finer coal is dewatered in a series of cyclones and is further dried in a rotary
drier. The washing plant removes about 40% of the input material, and produces a cleaned coal
containing approximately 10 wt% ash.
Fresh gob samples were obtained from a moving conveyor belt at the outlet of the washing
plant. An approximately 11-kg sample was taken with a shovel every 600 s until a total of 30 in-
crements (340 kg) were collected. As much as possible, a complete cross-belt sample was
removed each time.
Four separate samples of feed coal, each weighing about 14 kg were collected at 1-h intervals
from a stopped conveyor belt at the inlet of the plant. Also, 6 kg of cleaned coal, representative
of an 8-h plant output, was obtained. This was collected from an automated sampling device
located at the exit of the plant.
Finally, about 70 kg of weathered gob was retrieved from a waste pile which was approx-
imately 1 yr old. Samples were collected at the surface and from a fresh cut about 24 in. deep
produced by a bulldozer.
The samples collected at this plant, like all others gathered elsewhere, were sealed in plastic-
lined drums for shipping and storage.
Illinois Basin Coal Cleaning Plant B
The input coal for this cleaning plant is also a mixture of strip-mined types. The coal is
cleaned with one of two McNally jig boxes. The coarser coal (>0.25 cm) is screen-dried after
passing through the jig table. Drying of the fine product is accomplished by a succession of
screens, dewatering cyclones, and centrifugal driers. This plant produces about 4 x 103 tons of
clean coal (~10 wt% ash)/day.
There was no convenient place to collect the waste material at this cleaning plant, so we ob-
tained the gob samples from the dump where they were being continuously deposited by trucks.
Nine separate truckloads of waste, representing about 4 h of plant output, were sampled. Three
separate 7-kg samples were taken from each truckload: one at the top, one at midside and one at
the bottom-side of the pile. This procedure was used to obtain representative materials from
each size range.
Five samples of feed coal ~7 kg each were collected from a moving belt at the entrance to the
plant. These were taken at random over a 3-h period. The cleaned coal was sampled randomly
eight times over the same 3-h period. About 60 kg total of this material was collected.
In addition to the fresh gob dump, we were given access to several older waste disposal areas.
These ranged in age from about 2 to 10 yr old. We collected a quantity of weathered rocks,
minerals, and finely divided materials from the surfaces and drainage areas of these waste heaps.
50
-------
Illinois Basin Coal Cleaning Plant C
The day we visited this Illinois-Basin preparation plant, coal from a single underground seam
was being washed. The plant contains two 3-cell jig boxes, although only one was operating when
we were there. The cleaned coals are dried before shipping by techniques similar to those used in
the other plants we visited: that is, by the use of screens, centrifugal dewatering devices, and
rotary driers. The daily output of the washing plant is about 8 x 103 tons of coal containing about
11 wt% ash.
At this plant, we collected waste samples from the output streams of each of the cells of the jig
box. By collecting the samples in this way, we were able to obtain unmixed quantities of fine,
medium, and coarse gob. Eighteen total increments of each waste size were collected at 450-s in-
tervals over 4 h. The amount of each size collected was in proportion to the relative output of
each cell. A total of about 225 kg of wastes were obtained, of which ~90% was coarse material. It
should be noted that our sampling sequence was interrupted several times because of a lack of
coal.
About 70 kg of feed coal was collected semi-randomly from a moving belt over a 4-h period.
The cleaned coal was collected during the same time in a random manner from railroad hopper
cars. A total of about 27 kg of this material was obtained.
Low-Sulfur Coal Cleaning Plant D
The feed coal for this plant was furnished equally by an underground mine and a strip mine
using the same coal seam. The major portion of the coal (>0.12 cm) is cleaned by heavy media
flotation and hydrocyclones, while the finer material is cleaned by froth flotation. After the
mineral matter is reduced from 20 to 7 wt% at an output of 2 x 103 tons of cleaned coal per day,
the product is mechanically dewatered before storage to await shipping. The coarse waste is
dumped by truck to form a dam behind which the slurry is drained.
Samples of approximately 10 kg each were collected at this coal cleaning plant. These in-
cluded the feed coal, breaker rejects (+15 cm), and fresh gob, which had just been dumped at the
disposal site. This material was collected over a short period of time from available storage piles.
REFERENCES
1. H. P. Klug, L. Alexander, and E. Kummer, J. Ind. Hyg. Toxicol., 30 (1948), p. 166.
2. H. P. Klug, L. Alexander, and E. Kummer, Anal. Chem., 20 (1948), p. 607.
3. H. P. Klug, Anal. Chem., 25 (1953), p. 704.
4. C. P. Rao, and H. J. Gluskoter, 111. Geol. Survey Circ. 476.
5. W. G. Miller, "Relationships Between Minerals and Selected Trace Elements in Some
Pennsylvanian Age Coals of Northwestern Illinois," (Thesis), Univ. of Illinois, 1971.
6. D. Carroll, "Clay Minerals: A Guide to Their X-Ray Identification," Geol. Soc. Am. Special
Paper 126.
51
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-800/7-78-028
3. RECIPIENT'S ACCESSIOf*NO.
;. TITLE AND SUBTITLE Trace Element Characterization of
Coal Wastes--First Annual Report
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHORiS)
Eugene M. Wewerka and Joel M. Williams
8. PERFORMING ORGANIZATION REPORT NO.
DoE LA-6835-PR
9. PERFORMING OROANIZATION NAME AND ADDRESS
Los Alamos Scientific Laboratory
University of California
Los Alamos, New Mexico 87545
10. PROGRAM ELEMENT NO.
EHE623A
11. CONTRACT/GRANT NO.
EPA/DoE IAG-D5-E681
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development*
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Annual: 7/75-6/76
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES(*) Cosponsored by DoE. Project officers are Charles Grua (DoE)
and David A. Kirchgessner (EPA).
is. ABSTRACT
repOr^. gjves the status of B. program to assess the potential for environ-
mental pollution by trace elements discharged from coal storage piles and coal clean-
ing wastes. Mineralogic and trace element analyses on raw coal and wastes from
three Illinois Basin preparation plants are nearly complete. Aqueous leaching studies
are in progress to determine the release potential of pollutants from coals and coal
wastes. The work will lead to the recommendation of removal/recovery methods for
controlling trace element release to the environment.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group
Pollution
Coal
Coal Preparation
Wastes
Coal Storage
Trace Elements
Leaching
Chemical Analysis
Pollution Control
Stationary Sources
Coal Wastes
13B 07D,07A
08G,21D
081
06A
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS fT/UJ Report!
Unclassified
20. SECURITY CLASS (Thispage/
Unclassified
21. NO. Or PAGES
58
22. PRICE
EPA Form 2220-1 (9-73)
52
U S. GOVERNMENT PRINTING OFFICE 1978—777-089/25
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