United States Energy
Research and Development
Administration
United States
Environmental Protection
Agency
Office of Assistant Administrator
for Environment and Safety
Washington. D.C. 20545
LA-6600-MS
EPA-600/7-76-007
Industrial Environmental lPA-600/7-7
Research Laboratory
Research Triangle Park. N.C. 27711 AllQUSt 1976
ENVIRONMENTAL
CONTAMINATION FROM
TRACE ELEMENTS IN
COAL PREPARATION WASTES
A Literature Review
and Assessment
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 seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The seven 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
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
Research 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 systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses 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-related environmental issues.
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 recommen-
dation for use.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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ERDA LA-6600-MS
EPA-600/7-76-007
August 1976
ENVIRONMENTAL CONTAMINATION
FROM TRACE ELEMENTS
IN COAL PREPARATION WASTES
A Literature Review and Assessment
by
E.M. Wewerka, J.M. Williams, P.L. Wanek,
and J.D. Olsen
Los Alamos Scientific Laboratory
University of California
Los Alamos, New Mexico 87544
EPA/ERDA Interagency Agreement No. IAG-D5-E681
Program Element No. EHB527
EPA Project Officer: J.D. Kilgroe ERDA Project Officer: Myron Gottlieb
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. ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION
Office of Assistant Administrator for Environment and Safety
Washington, DC 20545
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CONTENTS
ABSTRACT 1
I. INTRODUCTION 1
II. LITERATURE SEARCH FORMAT .=>
III. TRACE ELEMENTS AND MINERALS IN COAL-PROCESSING WASTES . 8
IV. TRACE ELEMENTS AND MINERALS IN RAW COALS .... ... 10
V. TRACE-ELEMENT BEHAVIOR DURING COAL PREPARATION . . . . 18
VI. WATER CONTAMINATION FROM TRACE ELEMENTS IN
COAL-PROCESSING WASTES 22
VII. TRACE-ELEMENT EMISSIONS FROM BURNING COAL REFUSE .... 34
Vffl. TRACE ELEMENTS OF ENVIRONMENTAL CONCERN IN
COAL-PROCESSING WASTES 35
IX. PREVENTION AND TREATMENT OF CONTAMINATION
COAL-PROCESSING WASTES 36
X. RECOVERY OF TRACE ELEMENTS AND MINERALS FROM
COAL-WASTE MATERIALS 42
XI. SUMMARY AND CONCLUSIONS 45
REFERENCES 47
iii
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LIST OF FIGURES
1-1. a) ANNUAL PRODUCTION OF COAL REFUSE;
b) FRACTION OF TOTAL COAL PRODUCTION WHICH
IS MECHANICALLY CLEANED AND FRACTION
DISCARDED AS WASTE OR REFUSE
V-l. HISTOGRAMS SHOWING THE CONCENTRATIONS OF
BORON, PHOSPHORUS, SELENIUM, AND ZINC IN THE
FLOATING PORTION VERSUS THE SOLVENT SPECIFIC
GRAVITY USED IN A FLOAT-SINK TEST 20
VI-1. RAINFALL AND SPOIL LEACHING BEHAVIOR DURING
AN 8-YEAR PERIOD (FOR MARGINAL SPOIL) 30
VI-2. LEACHING OF TOTAL SALTS (a) AND SULFATE (b)
FROM VARIOUS SPOIL TYPES AS A FUNCTION OF TIME
NORMALIZED TO CONSTANT RAINFALL (35 INCHES) 30
VI-3. AMOUNTS OF CALCIUM (a) AND MAGNESIUM (b) LEACHED
FROM VARIOUS SPOIL TYPES AND THEIR RATIOS (c) AS A
FUNCTION OF WEATHERING TIME UNDER NORMALIZED
RAINFALL CONDITIONS 30
VI-4. AMOUNT OF IRON (a), ALUMINUM (b), AND MANGANESE
(c) LEACHED FROM VARIOUS SPOIL TYPES VERSUS EXPOSURE
TIME UNDER NORMALIZED RAINFALL CONDITIONS 31
IV
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LIST OF TABLES
I-I. SIZES OF COAL-REFUSE PILES IN THE U.S 4
I-H. BURNING REFUSE PILES NEAR RESIDENTIAL AREAS 4
II-I. ELECTRONIC DATA BASES SEARCHED 6
II-H. KEYWORDS FOR LASL'S ELECTRONIC
LITERATURE SEARCH 7
KEYWORDS IN EPA/BATTELLE'S ELECTRONIC
SEARCH
HI-I. MINERALS IDENTIFIED IN COAL REFUSE FROM
SEVERAL WEST VIRGINIA SITES 9
in-n. ELEMENTAL ANALYSES OF WEST VIRGINIA
COAL REFUSE 10
IV-I. MINERALS IDENTIFIED IN AMERICAN COALS 13
IV-H. AVERAGE TRACE-ELEMENT CONTENTS FOR COALS
FROM VARIOUS REGIONS OF THE U.S 13
IV-IH. AVERAGE TRACE-ELEMENT CONTENTS OF THE ASH
FROM U.S. COALS OF VARIOUS RANK 14
IV-IV. TRACE-ELEMENT CONTENTS OF EIGHTY-TWO COALS
FROM THE ILLINOIS BASIN 15
IV-V. RANGE OF TRACE ELEMENTS IN U.S. COALS 16
IV-VI. RANGE OF TRACE-ELEMENT CONCENTRATIONS IN
ASHES FROM U.S. COALS 17
IV-VH. TRACE ELEMENTS MINERAL CORRELATIONS 18
V-I. COAL-CLEANING METHODS 19
V-E. DISTRIBUTION OF TRACE ELEMENTS DURING
FLOAT-SINK WASHING 21
V-m. REDUCTION OF TRACE ELEMENTS IN COALS
BY FLOAT-SINK WASHING 21
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V-I. QUALITY OF SURFACE AND GROUND WATER IN A
PENNSYLVANIA COAL-MINING REGION 25
VI-II. WATER QUALITY ALONG A FLOODPLAIN BELOW
A MINED AREA 26
VI-IH. TRACE ELEMENTS IN EXTRACTS OF LABORATORY
LEACHED KENTUCKY COAL SPOILS 26
VI-IV. LEACHABILITY OF EASTERN KENTUCKY
COAL REFUSE 26
VI-V. ANALYSES OF EFFLUENTS FROM PENNSYLVANIA
GOB PILES 28
VI-VI. ANALYSES OF EFFLUENTS FROM WEST VIRGINIA
COAL-REFUSE BANKS 28
VI-VH. ANALYSES OF DRAINAGE FROM KENTUCKY
SPOIL BANKS 28
VI-VIII. ANALYSES OF EFFLUENTS FROM INDIANA
COAL REFUSE 29
VI-IX. ANALYSES OF EFFLUENTS FROM ILLINOIS
COAL-REFUSE PILES 29
VI-X. EFFECT OF SURFACE MINING ON WATER QUALITY
OF SOME EASTERN KENTUCKY STREAMS 32
VI-XI. WATER QUALITY OF RUNOFF OR LEACHATES
FROM WESTERN COAL SPOILS 32
VI-XII. EPA PROPOSED EFFLUENT LIMITATIONS FOR
COAL REFUSE 33
VIM. GASEOUS POLLUTANTS EMANATING FROM
BURNING REFUSE BANKS 35
K-L METHODS FOR PREVENTING OR CONTROLLING ACID
DRAINAGE FROM COAL-REFUSE MATTER . . . .' 37
LX-H. EFFECTIVENESS OF ALKALINE NEUTRALIZATION
FOR IMPROVING QUALITY OF MINE DRAINAGE 40
IX-m. TYPICAL WATER ANALYSES FROM ION-EXCHANGE
TREATMENT OF ACID MINE DRAINAGE 40
IX-IV. SUMMARY OF QUALITY OF ACID MINE DRAINAGE
AFTER TREATMENT BY REVERSE OSMOSIS UNIT 41
vi
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ENVIRONMENTAL CONTAMINATION FROM TRACE ELEMENTS IN
COAL PREPARATION WASTES: A REVIEW AND
ASSESSMENT OF THE LITERATURE
by
E. M. Wewerka, J. M. Williams,
P. L. Wanek, and J. D. Olsen
ABSTRACT
The purpose of this review of the literature is to collect and evaluate the
available information on the chemistry and behavior of trace elements in
coal processing wastes, and to utilize this information to assess the potential
for environmental contamination from the trace elements in these wastes.
Only limited attention has been given previously to the chemistry of trace
elements in coal waste materials; however, most of the growing body of
knowledge concerning trace elements and minerals in raw coals can be ap-
plied directly to coal wastes. The consensus from analytical studies is that
nearly every naturally occurring element is likely to be present in coal and
coal refuse. The fate of these elements during coal preparation is poorly
defined; however, large concentrations of trace elements are discarded in
the washing refuse. Toxic or harmful quantities of elements, such as Fe, Al,
Mn, Co, Ni, and Zn, are released into the environment in the drainage from
coal mineral wastes, but, in general, the behavior of trace elements during
refuse weathering, leaching, and burning is not well understood. Although
the mineral and inorganic matter in coal wastes is an acknowledged major
contributor to both air and water pollution, without the benefit of further
research, a comprehensive assessment of the full potential for environmen-
tal contamination from the trace elements in these wastes cannot be made.
I. INTRODUCTION
Coal, as mined, contains a great deal of extraneous rock and mineral matter. The inorganic
constituents of coals often represent as much as 50% of run-of-the-mine products (Hanna et al.
1963). These rock and mineral impurities are expensive to ship, dilute the caloric content of the
coal, and produce undesirable gaseous and paniculate pollutants when the coal is burned or
utilized. Consequently, much of the more highly mineralized coals—about one-half of the total
mined in the U.S.—is cleaned or processed to remove some of the unwanted mineral and rock
materials. The discarded rock, mineral, and coaly matter from coal processing, together with
other coal mine refuse constitute the gob piles and culm banks, which are scattered over thou-
sands of acres in coal-producing regions.
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Recent estimates are that nearly 3 billion tons* of carbonaceous mineral wastes have ac-
cumulated in the U.S. as a result of coal processing and mine development (National Academy of
Sciences 1975). Increased coal production, wider use of indiscriminate mining techniques,
improved cleaning methods, and greater emphasis on clean fuels will undoubtedly increase the
rate at which wastes accumulate. A vivid example of this trend—a 10-fold increase in the rate at
which wastes have been produced since 1940—is shown in Fig. I-la (National Academy of
Sciences 1975). Although there has been a recent trend by utilities to use larger amounts of un-
cleaned coal, as detailed by Fig. I-lb, a committee studying the underground disposal of these
wastes estimated that the current rate of waste production of 100 million tons per year will dou-
ble by 1980 (National Academy of Sciences 1975). Added to the present accumulation, this
material can no longer be merely discarded in convenient places. Indiscriminate disposal of coal
wastes will not be accepted by a concerned populace.
Most of the current waste disposal areas are on private land (McNay 1971). Generally, the
refuse is deposited in piles, in canyons, or stripped-out areas. The material is transported to the
dumping areas primarily by truck, but aerial trams, mine cars, and conveyor belts are also used.
Refuse piles can cover from one to over 100 acres, and may range from 20 to more than 300 feet in
height or depth (McNay 1971). Most refuse piles are small, less than 500 000 cubic yards, but the
bulk of the refuse, as shown in Table I-I, resides in the very large piles, those greater than 1.5 mil-
lion cubic yards. The total number of sizeable active or abandoned refuse piles or impoundments
is 3000-5000. Of the 961 refuse piles studied by the Department of Interior in 1968, over one-half
posed some form of health, safety, or environmental problem (National Academy of Sciences
1975).
Most of the coal refuse is produced by cleaning or preparation facilities. These preparation
plants generally crush the run-of-mine coal to minus 6-inch pieces prior to processing. The finer
material, less than 1 mm, is often cleaned by froth-flotation techniques. The waste from this
process is deposited in slurry ponds. The larger pieces of coal are separated from the heavier
mineral matter by some form of density separation. This is accomplished primarily by oscillating
water washers, jigs, cyclones, or baths with heavy-media solutions of magnetite or calcium
'Although it is the policy of EPA and ERDA to report measurements in the international system of metric units, for
clarity of presentation, the units used in this report are given as they appear in the references. A conversion table is
provided.
CONVERSION FACTORS: 1 Ib = 0.45 kg, 1 ton = 0.91 metric ton, 1 ft = 0.30 m, 1 in = 2.54 cm and 1 cu yd =1.3] m3.
60
20
1970
1930
1940
19SO
1960
1970
Fig. 1-1.
(a) Annual production of coal refuse, (b) fraction of total coal production which is
mechanically cleaned and fraction discarded as waste or refuse. Source: National Academy
of Sciences 1975.
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chloride (Deurbrouck and Jacobsen 1974). The fine residue obtained when the cleaned coal is
dried, either by cyclones, centrifuges, or vacuum driers, also goes to the slurry pond. The bulk of
the mineral refuse comes out of the plant looking like dark concrete which is deficient in cement
and water, and whose rock filler is too big for adequate packing. This reject material constitutes
about 25% of the run-oi'-mine coal and is the largest single contributor to coal waste piles
(McNay 1971). (It is not uncommon also to find garbage, trash, abandoned equipment, tires, and
other items in these piles.)
Coal-waste piles are generally formed from preparation (tipple) plant refuse and mine-
development wastes by dumping them in a disposal area. The dumping may be down the side of
an embankment, in which case the larger rocks roll to the bottom, and the finer refuse stays at
the top, producing a segregated mass. Often refuse dumps are graded after disposal. The current
trend is to use grading to produce a more uniform and compacted deposit. Frequently, in the
past, refuse piles grew in a rather helter-skelter fashion (Harrington and East 1948). Wastes have
been piled on vegetation near stream and residential areas, often on slopes having greater than
50% grades (Davies 1973; Coalgate et al. 1973). These conditions sometimes produced gob slides
like those which caused the 1972 disaster at Buffalo Creek, \VV (Busch et al. 1974). and the
tragedy at Aberfan, Wales, a few years ago (Taylor 1973). Such haphazardly formed waste piles
also create conditions which play havoc with water resources.
Water quality has always been a difficult problem where coal-mining activity is high. Water
pollution from refuse piles arises from two main sources: siltation and acid drainage. Siltation is
caused by finely divided coal ("blackwater"), minerals (silt), and disturbed soil (primarily from
surface mining). This form of contamination is generally controllable in impoundment areas
where the particles settle or are filtered as the water passes through a retaining barrier. Acid
drainage is not so easily handled. In Appalachia alone, more than 10 500 miles of streams are af-
fected by acid drainage from coal mines and refuse dumps (Appalachian Regional Commission
1969). It is estimated that 3.5 million tons of sulfuric acid entered the inland waterways in 1962
from coal-mine-related sources (Reid and Streebin 1973). The major portion of the acidity (75%
in Appalachia) is supplied by inactive, underground mines (Foreman 1974). Coal-processing
plants and refuse areas supply the remainder of the acid to stream systems. More than 2000 coal-
waste piles are thought to be contributing to stream pollution (National Academy of Sciences
1975). Over half of the active refuse piles in Pennsylvania are within one-quarter mile of stream
banks. The percentage of abandoned waste heaps this close to waterways is probably even higher.
Acid drainage occurs when iron sulfides (pyrite or marcasite) are exposed to air and water. The
sulfur oxidizes to sulfuric acid and the iron is liberated as iron sulfate. Typically, 1.5 to 2 pounds
of acid and 0.5 to 0.7 pounds of soluble iron are produced per acre of refuse per day, but, in some
highly mineralized areas, acid has formed at a rate of more than 300 pounds per acre per day
(National Academy of Sciences 1975). The acids formed in refuse dumps run off into drainage
areas or percolate through the pile, where considerable mineral matter is dissolved. Some of the
flow from refuse dumps eventually reaches subsurface water systems. Acid drainage lowers the
pH of lakes and streams, making the growth of aquatic life, which functions best under slightly
basic conditions, difficult (Kimmel and Sharpe 1976). The dissolved iron in refuse or mine
drainage reduces the oxygen content in the water and forms ferric hydroxide, "yellow-boy." which
settles out on the stream bottom. This material often covers wide swathes in drainage areas.
Quite effective in smothering life-forms, yellow-boy leaves a desolate terrain of yellow-orange
streams and soil.
Air pollution from refuse piles is also a major problem. Fires in gob piles have been occurring
for more than 100 years (Sussman and Mulhern 1964). Some piles have burned continuously for
over 20 years as timbers, clinging coal, and oxidizing sulfides provide fuel. This particular
problem has received considerable attention in recent years, but as of 1968 it was estimated that
there were still approximately 300 coal-waste piles burning (National Academy of Sciences
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TABLE I-I TABLE MI
SIZES OF COAL-REFUSE PILES IN THE U.S. BURNING REFUSE PILES NEAR
RESIDENTIAL AREAS
Size of Fraction of Fraction of
Refuse Pile Piles this Size8 Total Yd3 b Number of Population Near
(103yd3) (%) (%) Refuse Piles % of Total Refuse Bank
<100 33 2 138 47 <1000
100-500 29 10 123 42 1-10000
500-1000 13 14 25 9 10-100000
1000-2000 10 21 6 2 > 100 000
>2000 15 53
Source: McNay 1971.
"Source: McNay 1971.
"Our estimate.
1975). Of the burning waste piles, 99% were on private land; 25% were in Pennsylvania. Also,
42% of the piles were less than half burned, 36% were more than three-quarters burned, and 28%
were receiving new wastes at the time of the survey (McNay 1971). Burning waste piles are quite
noxious and are generally located close to small communities (Spicer and Luckie 1970). Twenty-
two sites were immediately adjacent to municipal, residential, or commercial lands and 89%
were within 5 miles of a community with 200 or more people; 45%, within less than 1 mile
(McNay 1971). Some were in an area populated by more than 100 000 people, as shown in Table
I-II.
In recent years, attempts have been made to circumvent some of the major environmental
problems associate with coal-refuse disposal (Boyer and Gleason 1972). To prevent exposure to
water and air, waste materials have been crushed, carefully compacted, and then covered with
top soil or sealed with sludge, clay, or other materials. Often coal debris is sealed into abandoned
mines or placed in stripped-out areas. Substantial effort to stabilize waste piles and banks by
revegetation has been undertaken, and much work has gone into methods of neutralizing acidic
effluents. Although these measures appear to solve the immediate problem of stabilizing the
structures of gob piles, and they seem to slow the environmental processes somewhat, it is not
clear how effective they will prove to be in the long run.
In addition to these well-recognized problems, however, another potential environmental
hazard is beginning to gain attention. Coals, and undoubtedly coal wastes, contain a broad array
of trace or minor elements (Gluskoter 1975). Many of these trace elements, such as lead, cad-
mium, arsenic, selenium, mercury, etc., are of considerable concern because of the low tolerances
of plants and animals for them (Piperno 1975). Undoubtedly many of these trace elements are
carried into the environment by weathering, leaching, and burning of refuse. Although the
relative amounts of these components per unit of waste is usually small, the total absolute
amount of each available in a large waste bank could cause grave consequences in water, soil, or
air if they were concentrated by natural processes.
The purpose of this review of the literature is to collect and evaluate the available information
about the chemistry and behavior of trace elements in coal-processing wastes, and to assess the
potential for environmental contamination from the trace elements in these wastes. Trace ele-
ments are defined here to include all elements except carbon, hydrogen, oxygen, nitrogen, and
sulfur. For convenience, these trace elements have been subdivided into major (those forming the
major minerals in coal) and minor classes. As a base, previous works on coal-cleaning processes
and coal wastes were considered. Particular attention was focused on literature describing the
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fate of trace elements during cleaning processes, and the chemical forms and associations of these
trace elements in coal and coal-processing wastes. Information on specific trace-element/mineral
correlations was sought. Literature on weathering, leaching, oxidation, or burning of coal refuse
was also considered. And, finally, some insight into the economic utility of this material, which
undergoes such considerable handling, was also sought. The details of the search and the results
obtained are addressed in the following sections.
II. LITERATURE SEARCH FORMAT
An extensive and thorough search of the open literature on environmental pollution by trace
elements in coal-processing wastes has been completed both by manual and computer searches of
the literature.
The literature on coal and its related disciplines was found to be widely scattered and poorly
catalogued. For example, many studies by state geological surveys and university research
groups were picked up as secondary references from the bibliographies of more widely quoted ar-
ticles. Nevertheless, it is believed that the search objectives have been achieved and that the
references compiled accurately represent the available literature through mid-1975 on trace ele-
ments in coals and coal-processing wastes and trace-element contamination from these wastes.
The literature search was conducted in three phases:
1. All data bases were searched either electronically or manually.
2. All of the primary references from the data bases were examined through either their
abstract or the complete article where available.
3. Secondary references found in the bibliographies of the primary articles, but not in the data
base searches, were evaluated.
The three phases required about equal portions of a 6-month period.
The electronic search was carried out using the bases which are listed in Table II-I. These data
bases were searched through CHEMCON (Chemical Abstracts), which is available through
several commercial suppliers, and RECON (all others), which is available through ERDA from
Oak Ridge National Laboratory. The number of references found in each data base is also in-
cluded in Table II-I. An extensive list of key words was used to comb the data bases. This is given
in Table II-H.
The electronic search of Chemical Abstracts was done somewhat differently. LASL had
limited access to CHEMCON at the time of the search, so this part was restricted to literature on
the chemistry and mineralogy of coal(s) for the period 1972 to mid-1975. However, as will be dis-
cussed, Chemical Abstracts was covered completely by the manual search. In addition, parts of a
broad survey emphasizing the desulfurization of coal (CHEMCON, 1970 to early 1975) was made
available by EPA-Research Triangle Park and Battelle, Columbus (see Table II-III). The
references from the electronics searches were screened through their abstracts to give approx-
imately 300 primary sources which were relevant to the subject at hand.
The manual search of the literature was made using several data bases—the major source be-
ing Chemical Abstracts, volumes 1 through 83 (1907 - mid-1975). Abstracts dealing with the sub-
jects listed in Table II-II, but slanted toward coal wastes, were pulled from four major Chemical
Abstracts listings: (1) coal, (2) lignite or brown coal, (3) waste and wastes, and (4) waste pollu-
tion. (The electronic search had already covered most of the articles from 1972 1975.) Other
bases searched manually were ERDA Report Abstracts (1975), EPA Bibliography (1971 -1973),
EPA Report Abstracts (1975), and LASL's "What's New in Reports" (1974 1975), a weekly
listing of reports mailed to LASL's library from throughout the country. This latter base listed
several papers which had been too recently published to be covered by the abstracting services.
In a final effort to secure primary references on trace elements in coal-processing wastes, the
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TABLE II-I
' ELECTRONIC DATA BASES SEARCHED"
Data Base
Chemical Abstracts
Nuclear Science Abstracts (NSA)
Water Resources Abstracts (WRA)
Metals Abstracts (MEX)
Energy R & D Projects (ERl)
Energy Data Base (ENG)
Energy Data Base (EDB)
Toxic Materials Data Base (TOX)
Total references selected
for visual review
References
1678"
387
83
0
356
647
Comments
804
462
4417°
Compendium of private and govern-
ment projects compiled by ORNL from
questionnaires sent to project authors.
Subject matter covering the use,
generation, distribution, environ-
mental effects of energy as compiled
by ORNL.
Major ERDA energy data base: in-
cludes nonnuclear ERDA Research
Abstracts (ERA), Energy Abstracts for
Policy Analysis (EAPA), NSF-RANN
Energy Abstracts, and other publica-
tions representing similar interests
as compiled by ORNL.
Subject matter includes effects
on the environment of numerous toxic
substances, including heavy metals,
as compiled by ORNL.
•Most of the data bases are restricted to post-1972 articles. Chemical Abstracts and NSA are relatively liirge, WRA.
KDB and MKX are of moderate size (50 000-150 000 items) and ERl, TOX and ENN are small (<. 10 CMH) items) in
"•Includes 1511 items from Battelle (1970-early 1975 literature, see lext) and 167 by l.ASL (1972-micl 1975} using a
narrower scope.
'Estimate 20-:i()% duplicates as some articles were covered by nearly all data bases.
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TABLE II-II
KEYWORDS FOR LASL'S ELECTRONIC LITERATURE SEARCH
Filel
File 2
File3
Coal
Coals
Pollution
Environment
Environmental Impact
Environmental Effects
Environmental Quality
Geology
Geochemistry
Land Reclamation
Ecology
Revegetation
Solid Wastes
Residues
Waste Disposal
Wastes
Waste Water
Liquid Wastes
Mining Wastes
File 4
File 5
Chemical Composition
Chemical Analysis Minerals
Minerals
Trace Amounts
Trace Elements
Metals
Mining
Processing
Chemical Preparation
Cleaning
Crushing
Preparation
Flotation
Enrichment
Extraction
Washing
Sampling
Separation Processes
Roasting
Dem ineralization
TABLE IMII
KEYWORDS IN EPA/BATTELLE'S ELECTRONIC SEARCH
Filel
File 2
Coal
Cleaning
Washing
Leaching
Chemical Treatment
Hydrogenation
Desulfurization
Hydrodesulfurization
Sulfur Removal
Preparation
Beneficiation
Liquefaction
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agenda of recent meetings of regularly scheduled symposia, such as the Symposium of Coal Mine
Drainage Research and the Symposium on Mine and Preparation Plant Refuse Disposal were
considered. A few references did not show up in any of the standard places but were obtained by
word of mouth from colleagues working at several other institutions. The manual search
produced about 300 relevant, primary sources—a number equal to that of the electronic search.
The second phase of the search involved an extensive review of the primary sources. For this
review the list was reduced to include only those articles dealing with studies of U.S. coal or coal
refuse. This substantially reduced the number to be given closer scrutiny, since both the English
and Russians have published widely on these topics. iSome foreign references are considered in
Sec. X, however.) The selected sources were obtained in full form from numerous libraries. With
these in hand, the bibliographic section of each article was searched for references related to rele-
vant works, which had not previously appeared.
The final phase of the search was devoted to obtaining and reviewing the secondary
references—approximately 50 in number. These were mostly publications from state geological
surveys and universities, which appeared well known to the authors of the primary sources, but
not to the public at large. The time needed to secure these secondary references was generally
much longer than that needed to secure the primary sources.
The net result of this search is the list of 200 references which appears at the end of this review.
Although selective, it represents the state of the art concerning trace elements and minerals in
coal wastes—their identities, problems of disposal, and possible uses. Frequently, when a subject
or author appeared in several related references, only the most pertinent one was listed in the
bibliography. When references were part of a continuing or updated series, only the final article
was usually listed.
An adjunct to this endeavor is the establishment of a computer-interactive storage system
which includes all of the pertinent references pulled in the search. Presently there are about 650
references in this data base, and the list will be updated periodically. A computer search and
retrieval system, based on key word identification, will be used to comb the file. This data base
will be available upon request.
III. TRACE ELEMENTS AND MINERALS IN COAL-PROCESSING WASTES
Only a few studies of the minerals and trace elements in coal-processing wastes have been
reported. Most of this work has concerned the composition and structure of the major minerals;
only limited attention has been given to identifying or characterizing the minor or trace elements
in these wastes. This is not to say that information about the character of the trace elements in
coal wastes is nonexistent, however. There is an ever-expanding base of knowledge about the
trace elements and minerals in raw coals, and, considering that coal refuse is primarily con-
centrated mineral wastes derived from coals, it is reasonable to assume that most of the pertinent
information from studies of raw coals can be applied directly to coal refuse. Undoubtedly, the
small number of direct studies of the composition of coal refuse stems from this emphasis on raw
coals.
Several reviews concerning the structure and composition of coal-refuse materials have ap-
peared in recent years (Coalgate 1975; Moulton et al. 1974; Coalgate et al. 1973; Sun et al. 1971).
These included information about the engineering properties of the material, and about well-
recognized problems such as acid drainage from the wastes, but there was little reported about
trace elements and minerals in these wastes. Nonetheless, the few studies which have touched
upon the subject of the mineralogy of coal refuse are of interest and are reviewed first.
-------
TABLE III-I
MINERALS IDENTIFIED IN COAL REFUSE FROM
SEVERAL WEST VIRGINIA SITES
Quartz8 Calcite
Chlorite Feldspar
Illite Pyrite
Kaolinite Muscovite
"Predominant species.
Source. Bu4i et al. 1974. 197.r>.
One of the more detailed investigations of coal-refuse composition was completed recently un-
der the sponsorship of the U.S. Bureau of Mines (Busch et al. 1975; 1974). Since this work was in-
itiated in the aftermath of the Buffalo Creek disaster, the main purpose of the study was to col-
lect engineering and physical-properties data, which could be applied to waste-bank construc-
tion. As part of the study, however, the major minerals and some of the trace elements were iden-
tified in samples of both fine and coarse bituminous-coal refuse from several sites in West
Virginia. Quartz was the predominant mineral species identified in these refuse samples, as seen
from the data in Table III-I.
Emission spectroscopy and atomic absorption spectrometry were utilized to determine the
elemental composition of the waste samples. A compilation of the elements identified and the
probable composition ranges appear in Table III-II. The data show that many of the minor ele-
ments in the coal-refuse samples can be attributed to the major minerals. For example, Al and Si
are the main components in clays, Si is found in quartz, Fe in pyrite, and Ca and Mg compose
much of the structure of calcite and chlorite, respectively. The specific sources or mineral as-
sociations of the less abundant elements, however, are more difficult to surmise.
In another study, Barnhisel and Massey (1969) examined the mineralogy of spoil-bank
materials from three locations in eastern Kentucky. Qualitative analyses were obtained by x-ray
diffraction and other techniques. Clay minerals (kaolinite and illite) and quartz were the most
abundant constituents of these wastes. Lesser quantities of chlorite and pyrite were present, also.
The character of the mineral matter in anthracite coal refuse was studied by Augenstein and
Sun (1974) of Penn State University. X-ray diffraction and infrared techniques were used to
identify the minerals in samples of weathered refuse from inactive disposal sites as well as sam-
ples of fresh materials from active operations. All of these wastes were found to have similar
mineralogical compositions. The clay minerals, kaolinite, illite, and pyrophyllite, made up about
70 to 80% of the rock in these samples; quartz made up 10 to 30%, while rutile and pyrite were
generally present at less than 2% each. Waste composition did not vary greatly with the size of
the material.
This small, but impressive, group of studies is the total extent of what was found in the
literature from direct studies of trace elements and minerals in coal refuse. However, as discussed
earlier, the relatively large volume of information on the inorganic constituents of raw coals can
ordinarily be applied directly to coal wastes. The available information on trace elements and
minerals in raw coals is reviewed in the next section.
-------
TABLE III-II
ELEMENTAL ANALYSES OF WEST VIRGINIA COAL REFUSE"
Element Min Value Max Value
Be 0.2 3
Na 150 375
Mg 500 8000
Al (%) >2.5
Si(%) >2.5
K 500 1200
Ca 50 2000
Sc 3 25
Ti 300 3000
V 25 250
Cr 3 25
Mn 65 1300
Fe (%) 0.75 4.1
Co 3 25
Ni 25 250.
Cu 12 50
Zn 30 85
Ga 3 25
Y 3 25
Zr 3 25
Ag 0.3 2.5
Cd 0.25 1.0
Pb 20 150
•All values ppm unless otherwise indicated.
Sniiri-i-: Bush et al. 1974, 1975.
IV. TRACE ELEMENTS AND MINERALS IN RAW COALS
While there is a paucity of data dealing with the composition and mineralogy of coal refuse, an
abundance of information is available from many studies of the trace elements and minerals in
raw coals. Coal-refuse piles are simply accumulations of the rock and inorganic debris separated
from the coals during mining or preparation, hence, most of the data about coal mineralogy can
be directly extrapolated to coal-refuse materials.
Knowledge of coal mineralogy has generally kept pace with the development of modern
analytical instrumentation and techniques, but recent concern about environmental contamina-
tion resulting from coal production or utilization has sparked a new flurry of interest in the
chemistry of the inorganic coal constituents. The identities of the major minerals and many of
the trace elements in coals are now fairly well established. The more recent studies have begun to
concentrate on elucidating the associations among trace elements and major minerals in coals,
and understanding the details of the chemistry and behavior of these constituents during mining,
processing, or utilization.
A comprehensive review of the available information concerning trace elements and minerals
in raw coals, of course, is outside the scope of this endeavor. However, the following information,
10
-------
culled from some of the more prominent works on this subject, will serve to illustrate the present
state of knowledge in this area.
Mineral and Trace-Element Analyses
To identify the minerals and trace elements in coals or coal refuse, it is usually necessary first
to separate the inorganic components from the carbonaceous matrix. This is done to concentrate
the mineral matter and remove background interferences from the organic fractions. Removal of
the organic material can be accomplished in several ways, which include heavy-media separation
(float-sink) and oxidation by high- or low-temperature methods. Low-temperature oxidation or
ashing (LTA) is now almost universally used for this purpose, because the reaction temperature
is low enough «150°C) that the minerals and inorganic compounds in most cases are not
significantly altered or lost (Gluskoter 1975). In the LTA method, oxygen is passed through a
radiofrequency discharge to produce active species at low temperature, which then pass over the
coal to oxidize the organic material.
Following the separation of the mineral matter from the coal or retuse. the minerals and minor
elements can be more readily identified (Babu 1975). X-ray diffraction, electron microprobe, in-
frared spectroscopy, and differential thermal analysis are among the useful techniques used to
identify major-mineral phases in coaly materials. Neutron activation analysis, emission
spectroscopy, and atomic absorption spectrometry are the most widely used techniques for iden-
tifying coal-associated trace elements, although spark-source mass spectrometry, x-ray
spectroscopy, and electron spectroscopy are becoming increasingly popular for certain applica-
tions.
Major Minerals in Coals
Many distinct types of rocks and minerals have been identified in close association with coals
and coaly deposits. In spite of some variations from locality to locality and even within individual
seams, certain classes of major minerals are present in nearly all coals. These are the
aluminosilicates or clay minerals, silica, carbonates, sulfides, and sulfates.
The clay minerals are present in coals in greatest abundance. The principal ones are kaolinite,
illite, and mixed-layer illite/montmorillonite. It is not unusual for more than 90% of the coal-
associated mineral matter to be composed of these clay mineral types (Thiessen et al. 1936). Rao
and Gluskoter (1973) report an average of 52% clays in the mineral matter of 65 Illinoin Basin
coals. The mineral matter in 57 coal samples of various ranks and from many parts of the country
were studied by O'Gorman and Walker (1972; 1971). They report that clay-mineral contents
ranged from about 10 to more than 70% in these coals.
The main sulfide and sulfate minerals in coals are pyrite and its dimorph marcasite. and gyp-
sum. These minerals compose about 25% of the mineral matter in Illinois coals (Rao and
Gluskoter 1973). For American coals, in general, pyrite and marcasite will range from essentially
none to as high as 40% of the total inorganic matter (O'Gorman and Walker 1972). Gypsum may
represent as much as 60% of the minerals in some coals, although such high quantities are un-
usual (O'Gorman and Walker 1972).
Carbonate minerals are found in coals in a wide range of compositions, usually as mixtures of
calcite, dolomite, and siderite. These average about 9% of the mineral matter in Illinois coals
(Rao and Gluskoter 1973), and when present, do not often exceed 10% of the total inorganic
material of most American coals (O'Gorman and Walker 1972; 1971).
11
-------
Quartz (silica) is very seldom found in coals in large amounts. Generally, about 20% of the
mineral constituents is the maximum present (O'Gorman and Walker 1972). Rao and Gluskoter
(1973) report that quartz represents about 15% of the minerals in Illinois coals.
In addition to these major minerals, there have been various other less abundant minerals
identified in coals. The range of the mineral types identified in coals and coal deposits is il-
lustrated by the list of major and minor coal minerals presented as Table IV-I.
Trace Elements in Coals
Studies of trace elements in coals have been conducted for more than 100 years (Gluskoter
1975). However, the advent of modern work in the field is attributed to Goldschmidt, who first
applied instrumental techniques to the problem in the mid-1980s.
Many trace or minor elements are present in coals; in all about 40 such elements have been
identified and undoubtedly others are present. Several excellent studies have been conducted in
recent years on this subject.
Zubovic and his coworkers at USGS have studied selected trace elements in coals on a regional
basis (1967, 1966, 1964, and 1961). These investigations included coals from the Appalachian,
Eastern Interior, Western and Southwestern Interior, and Northern Great Plains regions. Emis-
sion spectroscopic analyses were used to determine the concentrations of 15 minor elements in
these coals. The average trace-element contents for the variety of coals studied appear in Table
IV-II.
A group at Penn State University, headed by O'Gorman and Walker, considered the trace-
element contents of coals by ASTM rank (1972, 1971). A total of 57 samples ranging from lignite
to anthracite was analyzed by atomic absorption spectrometry and emission spectroscopy. The
average trace-element concentrations of the ashes obtained from the various coals are given in
Table IV-III.
Work conducted at ISGS has resulted in the identification of many of the elements present in
Illinois coals (Gluskoter 1975; Ruch et al. 1974). The trace elements in over 80 Illinois Basin coals
were analyzed by neutron activation analysis, emission spectroscopy, atomic absorption
spectroscopy, x-ray spectroscopy, and ion-selective electrode. The averages for the elements
found in these coals are reported in Table IV-IV.
In addition to these efforts, there have been several other excellent studies or reviews about
trace elements in coals (Averitt et al. 1976; Sather et al. 1975; Ayer 1974; Magee et al. 1973; Sun
et al. 1971; Zubovic 1966; Abernethy and Gibson 1962; Headlee and Hunter 1953; Gibson and
Selvig 1944). Information from these sources and those discussed earlier was compiled into
listings of the ranges of concentration of the various trace elements found in American coals and
the ashes from these coals. These lists appear in Tables IV-V and IV-VI.
Except for a few elements, which are thought to be almost exclusively associated with the
organic coal components, most of the trace elements in coals are distributed among or within the
major-mineral constituents (Gluskoter 1975; Ruch et al. 1974; Zubovic 1966). The actual associa-
tions or relationships among the various trace elements and coal minerals have been explored in
only a few instances. Miller (1974) has studied the distribution of certain trace elements and
minerals in 15 Illinois coals. As illustrated in Table IV-VII, a positive correlation was found
between some of the trace elements in the coals and specific mineral types. Ruch and his
coworkers (1974) statistically analyzed a large volume of data on trace elements in coals. They
noted positive geochemical associations among groups of trace elements which have common
tendencies to associate with or form certain mineral types. Results from washability studies also
suggest preferred associations among certain minerals and trace elements (Ruch et al. 1974;
Deurbrouck and Jacobsen 1974; Schultz et al. 1975). Si, Ti, Al and K were found in clay-rich
12
-------
TABLE IV-I
MINERALS IDENTIFIED IN AMERICAN COALS
Major Minerals
Aluminosilicates
Silica Sulfates Sulfides Carbonates
Illites Quartz Gypsum Pyrite Calcite
Kaolinite Marcasite Dolomite
Illite/montmorillonite Siderite
Minor Minerals
Sulfides Oxides
Micas
Sulfates Feldspar Alunites
Carbonates
Sphalerite Hematite Muscovite Thenardite Pla«ioclase -larosite
(ialena Rutile Chlorites
Source: Rao and (iluskoter. 197:*,
Source: O'Clorman and Walker 1971. 1972.
Aragonite
Ankerite
TABLE IV-II
AVERAGE TRACE-ELEMENTS CONTENTS FOR COALS
FROM VARIOUS REGIONS OF THE U.S."
Element
SWP
B
Be
Co
Cr
Cu
(ia
(u>
La
Mo
Ni
Sn
Ti
V
Y
7,n
33
1.1
4.6
13
11
2.0
5.9
6.5
3.1
14
1.3
250
18
7.4
108
EP
96
2.5
3.8
20
11
4.1
13
5.1
4.3
15
1.5
450
44
NGPd
116
1.5
2.7
7
15
5.5
1.6
9.5
1.7
7.2
0.9
591
16
13
59
APP*
25
2.5
5.1
13
15
4.9
5.8
9.4
3.5
14
0.4
350
21
14
7.6
"ppm.
hS\Vl = Forty-eight coals from Western and Southwestern Inti-rior Region.
"Kl ~ Kastern Interior Region. ;Vi coals.
''>.' .1' Northern (Ireat Plains Ki-sion. ."il samples.
'AIM' = Seventy-three roals iroin Appalachian resjion.
Snurt-e: /uhovic el al. UKH. 1964. I9«i. 19B7.
13
-------
TABLE IV-IH
AVERAGE TRACE-ELEMENT CONTENTS OF THE
ASH FROM U.S. COALS OF VARIOUS RANK"
Element Anthb LVBC MVBd HVBe L(SB)r
Ag <1 <1 <1
-------
TABLE IV-IV
TRACE-ELEMENT CONTENTS OF EIGHTY-TWO COALS
FROM THE ILLINOIS BASIN"
Element Average Element Average
As 14.9 K(%) 0.16
Al(%) 1.22 Mn 53.2
B 113.8 Mg(%) 0.05
Be 1.7 Mo 8.0
Br 15.3 Na(%) 0.05
Ca(%) 0.74 Ni 22.4
Cd 2.9 P 62.8
Cl(%) 0.15 Pb 39.8
Co 9.2 Sb 1.4
Cr 14.1 Se 2.0
Cu 14.1 Si(%) 2.4
F 59.3 Sn 4.6
Fe(%) 2.06 Ti(%) 0.06
Ga 3.0 V 33.1
Ge 7.5 Zn 313.0
Hg 0.2 Zr 72.1
"All values in ppm unless otherwise indicated.
Somvi1: (lluskoter 1975.
Soun-e: Rui-h et al. 1974.
Although there are variations in composition, it must be concluded from considering the
available information that most coal-refuse materials will be composed mainly of clay minerals,
pyrite, quartz, carbonate minerals, and gypsum. Some of these minerals, such as quartz and the
clays, are chemically quite resistant to weathering and other natural processes, whereas, the
pyrites and carbonates notably lack such resistance.
Another major conclusion from the studies referenced is that a great many inorganic elements
are present in coals. In all, about 40 elements have been identified in coal and coal refuse, and
undoubtedly others are present. With few exceptions, most of the trace or minor elements in
coals reside in or among the inorganic constituents as discrete mineral phases, solid solutions, or
polymorphs of other minerals. This intimate and recurring association of specific trace elements
with specific mineral components leads to the conclusion that the behavior of many trace ele-
ments in coal-waste materials during weathering, leaching, or burning will be linked directly to
the behavior of the major-mineral phases. Therefore, it is anticipated that the trace elements as-
sociated with the more labile minerals in the refuse will be those most likely to be released into
the environment by weathering or burning. This suggests that an understanding of the
relationships among minerals and trace elements will be a key factor in developing control
methods for environmental contamination from trace elements in coal refuse.
The next topics of interest concern the fate of trace elements during coal washing or prepara-
tion, and how the minerals and trace elements in coal-refuse materials are affected by the proces-
ses occurring in waste dumps. These subjects are addressed in the following sections.
15
-------
TABLE IV-V
RANGE OF TRACE ELEMENTS IN U.S. COALS8
Major Elements"
Element
Na
Mg
Al
Si
Cl
K
Ca
Ti
Fe
Znc
Range(%)
-0.20
-0.25
-3.04
-6.09
-0.56
-0.43
-2.67
0.002 - 0.32
0.32 -4.32
0 - 0.56
0
0.1
0.43
0.58
0
0.02
0.05
Minor Elements
Element
Be
B
F
P
Sc
V
.Cr
Mn
Co
Ni
Cu
Ga
Ge
As
Se
Br
Y
Zr
Mo
Cd
Sn
Sb
La
Hg
Pb
U
Range (ppm)
0
1.2
10
5
10
0
0
6
0
0.4
1.8
0
0
0.5
0.4
4
<0.1
8
0
0.1
0
0.2
0
0.01
4
<10
31
356
295
1430
100
-1281
610
181
43
104
185
61
819
106
8
52
59
133
73
65
51
9
98
1.6
218
1000
•References used were Ruch et al. (1974, Abernethy and Gibson (1962), Zubovic et al.
(1961-1967), Sun et al. (1971) and Magee et al. (1S73). (Data by Deul and Annell in these
references have been omitted.)
"Elements present in .0.2% in coals.
cZinc is not normally considered a major element in coal;..
16
-------
TABLE IV-VI
RANGE OF TRACE-ELEMENT CONCENTRATIONS IN
ASHES FROM U.S. COALS"
Major Elements"
Minor Elements
Element
Na
Mg
Al
Si
K
Ca
Ti
Fe
Znc
Sr
Ba
Range(%)
Range (ppm)
0.71
0.
5.3
9.3
0.66
0.58
0.1
2.09
0.
0.009
0.01
2.72
2.4
-21.2
-28
1.32
14
2.6
-24.4
1.6
- 0.96
1.39
Element
Li
Be
B
P
Sc
V
Cr
Mn
Co
Ni
Cu
Ga
Ge
As
Rb
Y
Zr
Mo
Ag
Sn
Sb
La
Yb
W
Hg
Pb
Bi
•References used were O'Gorman and Walker 11971 & 197'J). Sun et a\. (19711. Mac1* ci
al. (197M), Ahernethyand Gibson (1962). Headlee and Hunter H9oHi and Zubovic el al.
(1961-1967). (Data by Deul and Annell in these references have been omitted.!
"Elements present in >0.7%.
cZinc is not normally considered a major element in coals.
<20
0
30
<440
2
6
<1
30
0
0
10
0
0
21
<91
0
100
0
<1
0
<40
0
<2
<10
<70
10
1
-3100
-1100
-6500
-3360
- 15.-)
- 3800
1800
-1800
- 600
-1200
-°0'0
- 540
-1500
570
-- 1100
- 620
-1450
-2900
84
-4250
- 230
- 820
- 23
- 182
259
-1420
900
17
-------
TABLE IV-VH
TRACE ELEMENTS - MINERAL CORRELATIONS"
As, Be, Cu, Sb Pyrite
B, Cd, Zn, Hg Sphalerite
B, Cd, Mn, Se, Mo, V Calcite
B, Cr, Mn, Cd, Mo, Se, V, Zn Quartz
B, Cu, F, Hg, Sn, V Clays
"Correlation i-nel'fifients >O.S.
Simrc-e: Miller 1974.
V. TRACE-ELEMENT BEHAVIOR DURING COAL PREPARATION
Cleaning of run-of-the-mine coals to remove some of the unwanted mineral matter has been
done for more than a half-century (Deurbrouck 1961). Environmental concern about air pollution
from sulfur dioxide has focused attention on the removal of sulfur from the coal. Indeed, many of
the recent studies on the washability of coals have centered on this aspect: notable are the reports
from the Illinois State Geological Survey (Helfinstine et al. 1974), the Bureau of Mines at Pitt-
sburgh (Deurbrouck and Jacobsen 1974), Bituminous Coal Research, Inc. (1972), and Mitre Cor-
poration (Hoffman et al. 1974). The general conclusion from these studies is that coal cleaning
represents a viable short-term solution to providing a low-ash and low-sulfur coal. The newer
preparation plants can recover about 90% of the BTU content of coals, while reducing medium-
sulfur (1-3%) coal to less than 1% sulfur (Deurbrouck and Jacobsen 1974).
The fate of trace elements during coal preparation has received limited, but dedicated, atten-
tion in recent years. Concern for the environment has increased efforts to insure that toxic
materials will not spew out of power plants in sufficient quantities to contaminate the environ-
ment. More recently, the catalytic and corrosive properties of these chemicals have received at-
tention, as new coal conversion processes are being developed. At every turn, the emphasis is on
reducing the metal (ash) content of the coal before use. Granting that coal is full of undesirables
(See Sec. IV), the next few paragraphs will briefly describe what is known about the behavior of
trace elements during coal washing, and to what extent trace elements are likely to be removed
by this process and, consequently, concentrated in the discarded refuse.
The most widely used washing techniques (representing 75% of the total commercial produc-
tion) utilizing density separation methods, as Table V-I reveals. Production equipment is
generally too large and the feedstock too variable to easily determine what happens to trace ele-
ments during large-scale cleaning of coal. To simulate these processes on a laboratory scale, in-
vestigators use static vats of organic solvents with varying densities. The float portion of a sample
in a solvent of some given density is scooped out and the sink fraction is drained and subjected to
the next solvent mixture. When analyzed, these float-sink samples provide a histogram which
depicts the behavior of the property measured as the density of the sample (washing medium)
changes.
Histograms illustrating the float-sink behavior of B, P, Se, and Zn are shown in Fig. V-l (Ruch
et al. 1974). Some elements, such as B, are not readily removed from coal by density gradient
means. Other elements, Zn, for example, are more completely removed from the lighter coal.
Many elements (P and Se) show intermediate behavior. The tendency of specific trace elements
18
-------
TABLE V-I
COAL-CLEANING METHODS
Fraction of coal cleaned
by equipment type (7r)
Washer
Type 1942 1952 1962 1972
Jigs 47.0 42.8 50.2 43.6
Dense-medium processes 8.8 13.8 25.2 31.4
Concentrating tables 2.2 1.6 11.7 13.7
Flotation --- -- 1.5 4.4
Pneumatic 14.2 8.2 6.9 4.0
Classifiers 7.4 8.5 2.1 1.0
Launders 13.1 5.2 2.2 1.0
>.-'irrc 1 h'libruiu k ;uid -liioihsi-ii lilTl.
to concentrate in the sink fraction has been the subject of studies at i'SGS (Xubovic 196(>i. ISCS
(Gluskoter 1975). and the Bureau of Mines at Pittsburgh (Deurbrouck and -Jacobsen 1974). A list
of the findings from these investigations is given in Table V-II.
A completely satisfactory picture of trace-element behavior during washing is still not
available. A wide array of variables complicate the problem. For example, trace elc inents almost
certainly do not exist as pure minerals on a macroscale, especially those elements present at the
ppm level. Also some minerals, such as pyrite, are present in a wide arra> of particle sizes in the
coal matrix, ranging from lenses greater than 6 inches in diameter to microscopic fragments
deposited in the tiny cells of carbonized plant life. Very fine grinding is required to release these
minute particles (Deubrouck and Jacobsen 1974; Sun and Savage 1968). Another point to con-
sider is the possibility that certain elements are intricately interwoven as polymorphs or solid
solutions through one of the major-mineral phases. Considering these and other questions, it
must be concluded that more definitive work is needed.
Some semiquantitative data on trace-element removal during float-sink washing is tabulated
in Table V-IJI. From these data it is seen that significant reductions in the trace-element content
of coals are achieved by washing. Likewise, significant quantities of these elements will be dis-
carded by a washing plant. If these data are representative, then, the refuse will contain greater
than 2.5 times the trace-element level present in the raw coal. A similar conclusion can be drawn
from the following list of elements which are reduced in Illinois coals by more than 50% when
20% of the raw coal is removed by float-sink (Miller 1974).
Al As Ca Cd Co Cr Cu
Fe Ga Hg K Mn Mo Ni
Pb Sb Se Si Ti Zn Zr
In summary, the understanding of trace-element removal from coal by washing or preparation
is in its infancy, but several things are clear. Trace elements differ in their susceptibility to be
removed from coal by density separation. While the reasons for this phenomenon are not entirely
clear, one can draw from the reported data the fact that significant amounts of these elements
will be discarded in the washing refuse and that this refuse will have a higher concentration of
these elements than was present in the feed coal.
19
-------
35 0-
30.0-
2" K-°-
PM
CM
s3- 20.0-
7-'
*•?
pd
PM
cn
O 9.6
sa
PH
M.3
n.n
1.2B
1.29 1.31 1.40 1.60
SPECIFIC GRRVITT FRRCTION
1.28
1.29 1.31 I. 10 I.EO
SPECIFIC GRPVITT FRPCTION
>1.6
18.0
15.0
s
S 12-°
g 6.0
1 30
en
n.n
• ,
T1 ' , ' ' , '
1 S •
1.3
/~x 1.1 .
8-S
o
o.u .
0.2 •
o.o -1
1 1
1.25
1.28 1.33 l.UO 1.60 2.89
SPECIFIC GRRVITY FRRCTION
>2.9
1.25
1.28 1.33 l.UO 1.60 2.89 >2.9
SPECIFIC GRflVITY FRflCTION
Fig. V-L
Histograms showing the concentrations of boron, phosphorus, selenium, and zinc in the
floating portion versus the solvent specific gravity used in a float-sink test. Source: Ruch et
al 1972.
20
-------
TABLE V-II
DISTRIBUTION OF TRACE ELEMENTS DURING FLOAT-SINK WASHING
Source
USGS*
ISGSb
PERO
Summary"
Increasing Concentration in Sink Fraction
GeBe
GeBeB
GeBe
GaTiBV
P Ga Sb Ti V
Ga B Ti V
Ni Cr Co Y Mo Cu
Co Ni Cr Se Cu
Ni Cu S Cr
CoNiCrCuMo
Sn La Zn
Hg Zr Zn As Cd Pb Mn Mo
FHgCdPbMn
HgZnCdPbMn
•Zuliovic (19<><>).
"(Jliiskmer (1975).
cSc-hultz ct al. (197.r)) and Deurhrouck and Jacohsen (19741.
dHascd mi observations from at least two laboratories.
TABLE V-III
REDUCTION OF TRACE ELEMENTS IN COALS
BY FLOAT-SINK WASHING
Source A"
Source Bb
Trace
Element
Level Remaining
in Coal
(ppm)
No Samples
Tested
Level of
Reduction
(%)c
Level of
Reduction
(%)
No Samples
Tested
Mn
Pb
Cd
Hg
F
Cr
S
Cu
Ni
7- 68
3-8
0.02 - 0.10
0.17
26-65
10-20
10- 22
11-27
2
3
3
1
3
2
2
2
50-78
42 -53
0-97
47
14 77
28-60
24-41
20-27
50-75
56
0
24-47
6-42
29 - 56
18-r,n
29 - 4:?
28 - 30
2
1
1
3
3
2
7
2
2
"Ihu-rbrouck and -lacobsen (1974).
bSi-bult/. i-t al. 11975).
-2:i<>o (if total sample removed as sinK fraction.
SoluMon densities for both studies = l.fiO K/m\.
21
-------
VI. WATER CONTAMINATION FROM TRACE ELEMENTS IN COAL-PROCESSING
WASTES
The contaminated runoff from coal-processing wastes and mining activities is one of the most
serious water-pollution problems in many parts of the country. Often the drainage is highly
acidic and will contain large quantities of dissolved or suspended materials. The actual
magnitude of the pollution problem from acid runoff and drainage from coal mineral wastes can
only be estimated, but the total amount is staggering. The U.S. Fish and Wildlife Service reports
that some 10 000 miles of waterways, located mainly in the eastern half of the country, are being
degraded by acid drainage (Appalachian Regional Commission 1969). Under the worst of circum-
stances, such waters are nearly devoid of aquatic life, but even slightly acidic waters are far less
productive than neutral or alkaline streams or lakes (Kimmel and Sharpe 1976; Sykora et al.
1972; Rehwoldt et al. 1971; Boccardy and Spaulding 1968; Morgan 1942). In addition to waterway
damage, some 200 x 103 acres of land lay barren or noticeably infertile as a result of refuse dis-
posal and acid runoff (National Academy of Sciences 1975).
The major source of acid from coal mineral materials is thought to be abandoned or neglected
mines. About 70% of the total of this type of contamination is attributed to mines; the other 30%
results from coal-refuse materials (National Academy of Sciences 1975; Foreman 1974). This in-
formation is somewhat misleading, however. The bulk of acid drainage comes from coal mines
only because there are more of them than there are refuse piles (National Academy of Sciences
1975). (There are approximately 70 000 abandoned or inactive underground coal mines in the
U.S. versus about 5 000 abandoned waste piles.) Taken on a local level, a single refuse pile of ma-
jor proportions has far more potential for producing acid and mineral contaminants than does an
abandoned mine. Because coal refuse is relatively finely divided and well exposed, the weather-
ing and leaching processes that produce acid drainage and mineral dissolution can work more ef-
fectively (Good et al. 1970). For these reasons, refuse-pile drainage is often considered to be a
more serious pollution hazard than mine drainage.
Acid drainage either from coal refuse or from coal mines—both of which are lumped under the
generic term acid mine drainage (AMD)—typically contains substantial amounts of dissolved
and suspended mineral matter (see below). In the ensuing paragraphs, it will be shown that the
major part of the water-borne contaminants in AMD results from the dissolution and degrada-
tion of the major coal minerals. Considering the high degree of mineral dissolution, many of the
trace elements associated with the minerals in coals must also be present in the contaminated
runoff from coal wastes. Not a great deal is known about this latter topic, but enough analytical
work has been done on the character of waste pile runoff to establish that a significant potential
exists for pollution by trace elements from waste runoff or drainage.
Before getting into a discussion of the available literature on the composition of refuse
drainage, it will be informative to consider first some of the factors responsible for the formation
of sulfuric acid in coal mineral wastes.
Formation of Sulfuric Acid in Coal-Processing Wastes
The chemistry of the formation of acids in coal-processing wastes has been studied extensively
(Williams 1975; Forges et al. 1966; Hanna et al. 1963; Lorenz 1962; Hoffert 1947). The initial step
in acid production is the air oxidation of pyritic substances (pyrite, marcasite) in the wastes to
form FeSO4 and SO2,
FeS4 + 302 - FeSO4 + SO2 . (D
22
-------
Further oxidation in the presence of water results in the formation of sulfuric acid,
2S02 + ()2 + 2H20 - 2H2SO< . (2)
Under some circumstances, the acid concentration in the drainage from coal mineral wastes can
run as high as 5 wt% (Hoffert 1947). The most facile formation of sulfuric acid occurs where the
pyrites are very finely divided (Caruccio 1970; Barnes and Romberger 1968; Nelson et al. 1933),
and where waste pile structure and climatic conditions are conducive to a good flow of air and
water through the waste materials (Moebs 1966; Hanna et al. 1963).
Overall, the stoichiometry of the formation of sulfuric acid from pyritic wastes can be written
as Eq. (3). Actually, this situation,
2FeS2 + 7()2 + 2H20 - 2FeS04 + 2H2SO, . (3)
is much more complex than it appears; accordingly Eq. (3) is very simplified, and it does not
reflect the mechanism of the reaction. There is strong evidence, for example, that iron- or sulfur-
oxidizing bacteria are involved in the process (Smith et al. 1968; Lorenz and Tarpley 1963;
Hebley 1953; Temple and Colmer 1951) and, although the chemical dynamics of the acid-
forming reactions have been studied by many researchers, the details of the rate-determining
step are still not known with certainty (Singer and Stumm 1970: 1969; 1968; Morth et al. 1970;
Lau et al. 1970; Shumate et al. 1969; Smith et al. 1968; Burke and Downs 1937). There is some
evidence that marcasite is more easily oxidized than pyrite (Barnes and Romberger 1968; Hoffert
1947), and that certain inhibitors or accelerators affect the acid-forming reactions (Hanna et al.
1963). Some of the other variables which have been found to influence the rates of the acid-
forming processes include: pH, presence of water, oxygen partial pressure, and Fe~ " ' concentra-
tion (Oaruccio 19(58). Because of the enormous complexity of the pyrite oxidation/acid-forming
reactions, it is extremely difficult to sort out the essential steps from the subsidiary reactions.
Unfortunately, time alone does little to help alleviate the intensity of acid formation in coal
mineral wastes. In fact, the older materials seem to be far more prolific acid producers than new-
ly worked materials (Hoffert 1947). Perhaps this is due to the acceierative effects of bacterial
agents, which have not had sufficient time to flourish in the newer wastes. Rate differences for
pyrite oxidation of more than 10* have been observed between sterile laboratory conditions and
field conditions where bacteria readily multiply (Singer and Stumm 1970).
The complete story of acid drainage does not end with its formation, however. The acidic solu-
tions produced by the weathering of pyrites will affect many of the other minerals present in the
waste piles (Grube et al. 1971; Lorenz 1962). Certain of the clay minerals will be dissolved by the
acidic agents (Barnhisel and Rotromel 1974; Grim 1968). This will add Al and other ions to the
solution, along with the Fe and So< ions already present from pyrite degradation (Struthers
1964). In addition, calcites and dolomites are known to be readily attacked by acids, with the
resultant production of Ca and Mg ions. Undoubtedly, the trace elements associated with these
acid-soluble mineral phases will also be brought into solution. The net effect of all this is the
production of waste drainage or runoff that contains high concentrations of both dissolved salts
and sulfuric acid (-)asinski and Gaines 1972; Dugan 1970).
Trace Elements in Coal-Waste Drainage
The present state of knowledge concerning the major and minor elements present in coal-waste
drainage is amply illustrated by the studies detailed in the following text. For the purposes of
23
-------
completeness, drainage from coal mines, coal-mine-development wastes (spoil heaps) and coal-
preparation wastes (gob piles) are all considered in this section. As pointed out earlier, the latter
two materials compose the bulk of what is known as coal-processing wastes. There is no apparent
difference in the composition of the drainage from these sources, as all involve the same minerals;
and hence, no attempt is made by workers in the field to differentiate among the various drainage
sources.
The effects of drainage from coal-mining activity on surface and ground water in Pennsylvania
was the subject of a recently reported study (Gang and Langmuir 1974). The mineral and trace-
element contents of the water from several springs and a number of surface waters were analyzed.
Among the constituents considered were Fe, Mn, Al, Zn, Co, Ni, Cu, Cr, Cd, Ag, and Pb. Fe and
Mn were found to be greatly in excess of local drinking water standards for all of the water sam-
ples; the contents of Zn, Cr, and Cd exceeded these standards in some of the ground waters.
(ienerally, the trace-metals concentrations were higher in ground-water samples than in the sur-
face waters. A compilation of the ranges of concentrations of dissolved species for all of the water
samples studied is given in Table VI-I.
Blevins and his coworkers (1970) at the University of Kentucky studied the effects of acid
drainage from coal-mining activities on the soils in the flood plains below the mined areas. As
part of this study water samples were collected from various places along the flood plain and
analyzed. These results appear in Table VI-II. In all instances significant quantities of dissolved
ions are present in the water samples; however, particularly noteworthy are the relatively high
concentrations of the plant-toxic ions Fe and Mn in the soil water table.
Massey (1972) has studied the dissolved components in drainage solutions from eastern Ken-
tucky coal spoils. He found that the concentrations of Fe, Al, and Mn in leachates from the coal
wastes are roughly a function of the pH of the solution. Under the most acidic conditions Fe is the
dominant dissolved ion. Concentrations of Zn, Cu, and Ni as high as 145, 85, and 122 ppm,
respectively, were found in aqueous extracts from the spoil materials. Massey could not deter-
mine whether these heavy elements were originally present in the sulphide minerals or if they
resulted from secondary dissolution of some of the other mineral types present in the wastes. The
concentrations of Zn and Cu in spoil leachates decreased significantly with increasing pH, but Ni
concentrations were not greatly affected by the solution acidity.
Results similar to Massey's were obtained in another study of weathered coal spoils from six
eastern Kentucky areas (Cummins et al. 1965). The pH of aqueous extracts of these materials
ranged from 2.2 to 5.7. The concentrations of some specific elements detected in the extracts are
reported in Table VI-HI. The highest concentrations of dissolved ions were found in the extracts
from the most highly acidic spoils.
In a similar study, Massey and Barnhisel (1972) investigated the character of the dissolved
mineral matter in aqueous solutions extracted from samples of acid spoil materials from eastern
Kentucky coals. Successive extractions with water were made over a 35-week period. Listed in
Table VI-IV are the maximum concentrations observed for selected ions from each of the spoil
materials. These results are a startling illustration of the potential for water contamination from
acid coal refuse. Of particular interest in this study were the concentrations of Ni, Zn, and Cu
ions, as there is some indication that these elements can be geochemically enriched in certain
rocks or soils. In one case, concentrations as high as 5000 ppm Zn, 700 ppm Ni, and 200 ppm Cu
were reported in a shale commonly associated with coal beds (Vine).
Lowry (1961) investigated the identities of some of the leachable components from 19 different
Ohio coal spoils, which had been subjected to various degrees of weathering. The content of total
soluble salts in aqueous leaching solutions, which in one case was 7 wt%, was found to be a func-
tion of the pH of the leachate. High concentrations of Fe, Al, Mn, Ca, and Mg ions and lesser
amounts of Na and K ions were detected in the more highly acidic solutions.
A research group from West Virginia University determined the concentrations of several trace
elements in the drainage from a number of West Virginia coal-mining areas (Corbett et al. 1967).
24
-------
TABLE VI-I
QUALITY OF SURFACE AND GROUND WATER
IN A PENNSYLVANIA COAL-MINING REGION
Mean8
Variable
*pH
V
Monovalent Cations
Na
K
Ag
Divalent Cations
Mg
Ca
*Fe(II)
*Mn
Zn
Ni
Co
Cu
Cr
Cd
Pb
Trivalent Cations
*Fe(ni)
Al
Neutral
SiO2
Monovalent Anions
Cl
HCO8
Divalent Anion
*S04f
PPM
4.24d
1625e
15.9
4.8
120
104
61.5
29
1
0.69
0.5
PPB
Range"
19.7
13.2
10.3
204
13.9
985
0.54
29.6
10.8
3.6
1.8
2.69
222
0.8
1.5
0.0
5.8
3.0
0
0
0.001
0.04
0.01
1.5
0
0.3
0
0
0
2.9
0
0
-6.78
7000
70
11.4
3.1
985
312
510
281
- 14.5
7.5
4.98
410
120
13.1
7.0
102
201
70
129
122
28 - 6230
<>!' this variable exceeds the water standard.
"I'I'M -• pan* per million. H'B = parts per liillion.
'Hiinjsi1 units same as lor mean.
'"Krroiumendi'd local drinking water standards (units same a> lor meani.
Jpll units.
"Micrumhos at -~i ('.
'Much as HS()4.
Source: liann «"d Lan«muir 1974.
Water
Standard6
6.0-8.5
<625
<50
<0.3
<0.05
<5
<1000
<50
<50
<0.3
<250
<250
25
-------
TABLE VI-II
WATER QUALITY ALONG A FLOODPLAIN
BELOW A MINED AREA"
Sample
Source
pH Fe Al Mn Ca Mg
1
2
3
5
Stream Channel
Soil Water Table
Pond (middle)
Pond (bottom)
3.7
3.7
3.8
3.9
1
137
1
9
22
11
17
1
5
26.
21.
3
152
104
156
52
56
32
88
20.
"Concentrations in ppm.
Source: Blevins et al. 1970.
TABLE VI-III
TRACE ELEMENTS IN EXTRACTS OF LABORATORY
LEACHED KENTUCKY COAL SPOILS8
Elements SO4 Fe Al Mn Cu Zn
B
Mo
'Concentrations listed in ppm.
Source: Cummins et al. 1965.
TABLE VI-IV
LEACHABILITY OF EASTERN KENTUCKY COAL REFUSE" b
Sample pH Fe
Al
Mn
Ca
Mg
Na
K
Zn
•Concentration in ppm.
"Maximum observed concentrations.
Source: Massey and Barnhisei 1972.
Cl
Mean
High
Low
1313
6500
50
104
619
13
6.1
26.6
0.2
37
205
2.
18.2
27.8
1.3
14.2
18.1
9.0
32
170
1
0.17
0.20
0.15
0.058
0.188
0.005
2.3
33.2
0.2
Ni
Cu
1
2
3
4
5
6
7
1.0
1.6
2.2
2.2
2.4
2.8
5.2
37500
19500
11000
2800
86
15
7
29700
15200
16000
11600
200
470
1
375
220
1800
324
80.
95
47
1100
1000
650
1075
670
1325.
1800
800
595
2050
615
300
530
700
55
95
355
83'
91
91
130
50
62
320
65
170
165
225
59
46
145
55
44
24
1
122
28
97
16
17
10
1.
85.
10
11
11
15.
3
1
26
-------
Most of the water samples were acidic but a few were nonacidic. B, Ba, Cr, Mn, and Sr were
detected in all of the samples, while Be, Cd, Co, Cu, Ni, Ag, Pb, and V were found only in the
acid waters. Unfortunately the concentrations of these elements were not reported. These
researchers attributed the greater number of trace elements in the acidic samples to the much
higher solvating power of the acid solutions.
In a 1974 report, Martin summarized a large accumulation of data on the quality of aqueous ef-
fluents from coal-refuse piles located in many of the coal-producing regions of the country. Sam-
ples were collected and analyzed from direct runoff, seeps, ponds, and swamps in or near refuse
disposal sites. The results from Martin's report are reproduced here (as Tables VI-V to VI-IX)
almost in their entirety because they represent one of the most comprehensive assessments of the
quality of the natural drainage waters from coal-refuse materials.
From the tables, it is seen that the total acidity (free acid, acid salts, and dissolved C02) of
these refuse effluents varied from alkaline to an acid equivalent (as CaCOs) of 34 x 103 mg/jfc. The
pH values (free hydrogen ions) of the samples ran between 2.1 and 6.9. The most general observa-
tion that can be made from this valuable collection of information is that the concentrations of
metals and sulfate ions generally relate to the acidity of the effluents. Surprisingly, however,
total acidity and total ion concentration are only casually related. This observation implies that
the total amount of materials dissolved from refuse piles is dependent on local conditions such as
particle sizes, mineralogy and waste composition, and disposal area drainage patterns, and that
relatively high concentrations of dissolved species can accumulate in the effluents from non-
acidic waste materials.
There are obvious variations in the amounts of contaminants released by the various refuse
materials. Undoubtedly, much of this can be attributed to the types of coals and methods of min-
ing and preparation. In addition, the total quantity of water-borne contaminants produced by
waste piles will be a function of the hydrology of the area. However, the data reported in Tables
VI-V to VI-IX amply demonstrate the general character and quantity of the dissolved mineral
material in effluents from coal refuse.
The high concentrations of Fe, Al, Ca, Mg, and SO4 ions in most of the refuse water samples
are undoubtedly produced by dissolution of the major minerals (clays, pyrites, and carbonates).
The information for the less abundant trace elements is limited to just a few elements. However,
considering the overall extent of mineral dissolution in most of the effluents, it must be con-
cluded that many other of the trace elements associated with the minerals are present in solu-
tion, also.
Vimmerstedt and Struthers (1968) conducted a long-term study of the chemical products in
the leachates from weathered Ohio coal spoils. The spoils investigated were from 19 different
sites, and they were classified according to their acid-forming tendencies in the following way.
Toxic pH <4 on more than 75% of the refuse surface.
Marginal pH <4 on 50 to 75% of the refuse surface.
Acid pH 4.0 to 6.9 on more than 50% of the surface area.
Calcareous pH >7 on more than 50% of the refuse surface.
The spoils (1-ft-diam by 4-ft-deep columns) were allowed to weather under natural climatic
conditions, and each year for a total of 8 years the leachate percolating through the spoil columns
was analyzed for total dissolved salts and several ionic species. The results of this study are
reproduced as Figs. VI-1 to VI-4.
Although the rates of formation of dissolved products are generally slowing with time, the main
conclusion to be drawn from this work is that significant quantities of mineral matter will con-
tinue to dissolve from refuse dumps for many years after initial disposal. The data in the figures
show, as have the other studies discussed so far, that the concentrations of total dissolved salts
27
-------
TABLE Vl-V
ANALYSES OF EFFLUENTS FROM PENNSYLVANIA GOB PILES"
Sample Location" Aridity5 pH
Conduct"
SO.
Fe
1
2
3
4
5
6
7
8.
9
10
Drainage
Drainage
Drainage
Drainage
Drainage
Drainage
Drainage
Drainage
Drainage
Drainage
34300
24400
23100
15600
6100
1330
1300
690
325
250
3.1
2.2
2.1
2.7
2.6
3.7
3.5
3.0
3.6
4.0
13600
10000
10400
12400
5600
3500
3700
4400
926
3000
40500
29760
27600
17750
5750
1125
1485
3000
420
1600
6168.
3737
3758
3197
1265
130
176
30
6
1
999
668
948
1014
353
68
40
87
28
50
63
69
545
31
86
15
9
60
4
90
AI Mn Ca Mg Na
Zn Cu Nl
340 250
180 140
100
2.8 0.14 1.7
60 16 2.4 0.18 1.1
'Acidity and elemental concentrations in ppm.
bDrainage includes seepage from the refuse pile, pile drainage and runofT and streams at the base of gob piles.
Titratable hydrogen ion.
'Micromhoa.
Source: Martin 1974.
TABLE VI-VI
ANALYSES OF EFFLUENTS FROM WEST VIRGINIA COAL-REFUSE BANKS'
Sample Location" Aridity0 pH
Conduct4
SO,
Fe
Al
Mn Ca
Mg Na
Zn Ni
1
2
3
4
5
6
Drainage
Drainage
Drainage
Drainage
Pond
Drainage
6940
4090
300
150
85
11
3.0
2.9
3.1
4.9
3.4
6.2
9300
16500
6200
6000
3200
640
9660
10054
3300.
3800
2400
310
2940
2240.
120
260
170
45
220
50
20
4
4
1
70
67
26
9
10.
3
380
145
310
415
460
30
680
664
230
146
105
28
600
780
250
14
25
22
8
10
1.5
0.2
0.1
0.1
•Acidity and elemental concentrations in ppm.
'See drainage definition in Table VI-V, a pond is a drainage impoundment.
Titratable hydrogen Ion.
'Micromhos.
Source: Martin 1974.
TABLE VI-VII
ANALYSES OF DRAINAGE FROM KENTUCKY SPOIL BANKS'
Sample Location" Aridity* pH
Conduct
SO.
Fe
Al
Mn
Ca Mg ' Na
Zn
Ni
1
2
3
Swamp
Drainage
Drainage
2380
210
7
2.4
3.8
6.9
4200
1200
880
3629
1066
690
630
2
6
244
70
2
26
8
4
200
74
50
90
86
26
150
22
116
1
42
3
2.9
1.1
0.1
0.46
0.25
•Acidity and elemental concentration in ppm.
•See drainage definition to Table VI-V.
Titratable hydrogen Ion.
"MicTorohos.
Source: Martin 1974.
28
-------
TABLE VI-VIII
ANALYSES OF EFFLUENTS FROM INDIANA COAL REFUSE"
Sample Location" Acidity' pH Conduct" SO, Fe
16200 5500
1500 4500
10400 4180
9513 2600
1711 100
1700 160
850 25
•Acidity and elemental concentration! in ppm.
'See drainage definition in Table VI-V, subsurface is underground flow near a spoil heap.
Titratahlc hydrogen ion.
'Micromhos.
Source: Martin 1974.
1
2
3
4
5
6
7
Subsurface
Subsurface
Subsurface
Drainage
Lake
Lake
Lake
16400
13600
10300
6500
800.
760
160
2.2
2.3
2.5
2.4
2.8
2.6
3.2
15000
1200
9800
6400.
2600.
2400
1480
Al Mn Ca Mg Na
Zn Cu
Ni
Pb
340.
52
50
6
36
56
40
120
25
24
11
342
360
200
160.
ISO
185
285
100
100
75
200
30
18
40
7.2 0.16 1.6 0.30
1.7
0.4 0.14
TABLE VMX
ANALYSES OF EFFLUENTS FROM ILLINOIS COAL-REFUSE PILES"
Sample Location" Acidity* pH Conduct" SO4
Fe
Total
Solids
1
2
3
4
5
6
Drainage
Drainage
Drainage
Drainage
Drainage
Drainage
14400
8700
4600.
6100
5900
640
•Acidity and elemental concentrations in ppm.
"Si'p drainage definition in Table VI-V.
Tilralable hydrogen ion Ippmi.
"Micromhos.
Sourer: Martin 1!)74.
2.4
2.8
2.9
3.3
3.1
3.6
3540
3500
3200
2800
1950
1200
13500
4600
1400
50
1200
55
35320
13860
14420
16830
11060
8570
29
-------
30 t
4000
3000
- 2000
a 40
20
10
0
234 36
WEATHERING PERIOD C
SALT CONCENTRATION 3
IS LEACH4IE (PPM) §
I 1
RAINFALL (INCHES) 3
3 •
(INCHES) *
SALTS TfATRFD
(TOSS/ACRE)
Fig. VI-1.
Rainfall and spoil leaching behavior during an
8-year period (for marginal spoil). Source:
Vimmerstedt and Struthers 1968.
son.
Cm)
12343
masaaa ration
3
1.1
.03
ciLcinaas
tea
o»
1234317
cauonac.2niao ml
V7-2.
Leaching of total salts (a) and sulfate (b) from
various spoil types as a function of time—nor-
malized to constant rainfall (35 inches).
Source: Vimmerstedt and Struthers 1968.
1000
« 100
10
ACID
I I
1 234567
EXPOSURE TIME (YR)
1000
100
10
QXIC
MARGINAL
^CALCAREOUS
ACID'
(b)
SOIL
J
2 345 67
EXPOSURE TIME (YR)
I
id
U
CALCAREOUS
TOXIC
I I I I I I
1234567
EXPOSURE TIME (YR)
Fig. VI-3.
Amounts of calcium (a) and magnesium (b) leached from various spoil types and their ratios
(c) as a function of weathering time under normalized rainfall conditions. Source: Vim-
merstedt and Struthers 1968.
30
-------
4000
1000
100
10
.1
sTOXIC
MARGINAL
(a)
. _ ACID
CALCAREOUS
4000
1000
100
10
1 234S678
WEATHERING PERIOD (YR)
4000
1000
MARGINAL
(b)
- — _ __ ACID
a
ui
s
100
;o
CALCAREOUS
SOIL
Jill
12 34567
WEATHERING PERIOD (YR)
TOXIC
MARGINAL
(c)
^CALCAREOUS
1234 5 678
WEATHERING PERIOD (YR)
ig. V7-4.
Amount of iron (a), aluminum (b) and manganese (c) leached from various spoil types versus
exposure time under normalized conditions. Source: Vimmerstedt and Struthers 1968.
are highest in the effluents from the most acidic spoil materials, but significant amounts of
materials were dissolved from nonacidic spoils.
The results of Vimmerstedt and his colleagues are substantiated by Curtis (1972), who con-
ducted a 4-year study of the water quality in several watersheds in coal-mining areas of eastern
Kentucky. His work shows that significant dissolution of the mineral matter from coals can con-
tinue for many years after exposure to natural climatic conditions. Curtis observed that ap-
preciable contamination of drainage water occurs even for nonacidic spoil materials, although
the total quantities of dissolved and suspended matter appear to be much lower than is usually
the case for acid spoils. A "before-and-after" comparison of stream water quality in four different
watershed locations where nonacid spoils have been produced is given in Table VI-X. Ca and Mg,
probably produced from limestone and dolomites, are the most significant contaminants,
although the concentrations of several other ions increased by more than an order of magnitude
after mining in the area was commenced. The relatively low concentrations of Al in the coal-field
drainage waters likely indicates a resistance of clay minerals to dissolution by neutral water.
Finally, the results from an interesting study of the water-pollution potential of mine spoils
from the coals of the southern Rocky Mountain region were reported by a Colorado State Univer-
sity group in 1974 (McWhorter et al.). Western coals generally contain low amounts of pyritic
materials, so the wastes from these coals are usually nonacidic. Accordingly, this study provides
an interesting contrast to the major body of work on refuse-pile contaminants, which has been
done principally with acidic waste materials.
Mine spoils from two locations were studied. The quality of typical runoff and leachates from
these spoils is illustrated by the data in Table VI-XI.
These results correspond quite closely to those obtained by Curtis (see above) in his study of
nonacidic spoils from eastern Kentucky coals. The total salt content is low, pH is high, and the
concentrations of metallic elements are modest compared to those found in acid-spoil drainage.
31
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TABLE VI-X
EFFECT OF SURFACE MINING ON WATER QUALITY
OF SOME EASTERN KENTUCKY STREAMS
Stream Sample8 pH Cond.b SO4 Fe Al Mn Ca Mg Zn Cu
1
2
3
4
Before
After
Before
After
Before
After
Before
After
7.3
7.8
7.1
8.1
7.0
7.5
7.0
7.5
55
407
151
522
73
334
95
264
12
178
18
176
12
132
10.
61
0.38
4.00
0.31
1.55
0.27
3.80
1.38
3.50
0.07
0.44
0.07
0.25
0.05
0.15
0.06
0.19
0.08
1.85
0.00
1.80
0.12
1.20
0.30
0.70
4.8
45.0
4.5
50.4
6.2
30.0
6.6
18.3
3.6
35.5
2.4
36.0
4.4
24.3
3.8
17.6
0.90
1.80
0.10
2.20
0.80
1.20
0.90
1.26
0
0
0
0
0
0
0
0
"Before or after surface mining.
"Conductivity) in micromhos. concentrations in ppm.
Source: Curtis 1972.
TABLE VI-XI
WATER QUALITY OF RUNOFF OR LEACHATES FROM WESTERN COIL SPOILS"
Sample pH Cond. SO4 Fe Mn Ca Mg Na K Zn Cu Cl
1
2
3
4
7.4
7.4
7.5
2510
3160
4700
>460
>800
>450
610
<0.05
<0.05
<0.05
0.07
0.34
<0.01
<0.01
<0.01
370
340
250
388
160
240
150
41
21
92
1180
1290.
48
13
17
80
0.09
0.04
0.02
0.09
<0.01
<0.01
<0.01
0.03
5
4
9
22
•Conductiviiy is in microinhos. concentrations in ppm.
Source: MiAVhorter et al. 1974.
Here, too, Mg and Ca are the dominant observed water contaminants, although as in most other
instances, only a limited number of elemental constituents was considered.
An interesting sidelight to this study is the observation by these researchers that the quantity
of annual precipitation is so limited at some Southwestern sites that the chances of significant
drainage of water through those waste materials is remote.
Other notable work in this area includes studies by Barnhisel and his colleagues (1974; 1969)
on the weathering of clay minerals and of the extractability of Kentucky spoil materials. Beyer
and Hutnik (1969) have investigated the exchange behaviors of certain ions in Pennsylvania spoil
banks. Maneval (1975) has reported on the composition of waters associated with several mining
sites, and the effects of AMD on the quality of a Missouri reservoir were studied by Brezina et al.
(1970). The hydrology and chemistry of coal-mine drainage in Indiana is the subject of a report
by Agnew and Corbett (1969).
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In addition to the works cited above, other studies have been conducted on the quality or-com-
position of the drainage, runoff, or leachates from coal mineral wastes or spoils. However, those
discussed or referenced here were considered to be the most informative and the most useful for
demonstrating the present state of knowledge in this area.
Throughout this section, the nature and magnitude of the trace element releases in the ef-
fluents from coal refuse and mineral wastes were discussed. It is. of course, difficult at this time
to assess the overall seriousness of this type of discharge because suitable data are generally lack-
ing on the behavior&nd effects of the various trace elements in the environment. EPA. however.
recently published a set of proposed effluent limitations that apply to discharges from coal-refuse
materials. These guidelines are listed in Table VI-XII. Although only a few elements and effluent
characteristics are covered by the proposed regulation, these data, nonetheless, serve as a useful
point of reference. Significantly, it is seen that nearly all of the waste effluents discussed earlier
exceed the proposed EPA effluent limitations—some by orders of magnitude.
There are a number of observations and conclusions which can be drawn from the foregoing
concerning the nature of the dissolved contaminants in the drainage from coal-processing wastes.
There seems to be little doubt that the runoff or drainage from coal waste disposal areas will be
contaminated to some degree with dissolved or suspended mineral matter. Generally the highest
concentrations of contaminants are found in the more highly acidic effluents, although the runoff
even from nonacidic wastes contains enough added material to be notable and based on this
criterion to be of possible concern. The acid drainage from coal-processing refuse and mining ac-
tivities typically contains high concentrations of Fe, Al, Ca, Mg, and 864 ions. These are derived.
apparently, from the major minerals in the wastes.
Little is known about the effects of weathering and leaching on the less abundant or minor ele-
ments in coal-processing wastes. Many of these elements have been identified in the effluents or
leachates from wastes, but a comprehensive assessment of the behavior ;>f the full spectrum of
trace elements which are present in the wastes has not yet been made. It is more than likely that
the minor elements associated with the soluble mineral phases will also be solubilized during
waste-bank leaching. Quite obviously, many questions remain to be answered concerning the
fate of trace elements in weathering coal wastes and waste drainage, particularly if and how these
elements enter into the surrounding environment. Of added concern is the possibility that some
TABLE VI-XII
EPA PROPOSED EFFLUENT LIMITATIONS FOR COAL REFUSE
Average of daily values
Effluent Maximum for any for 30 consecutive days
Characteristic 1 day (mg/l) shall not exceed (mg/£)
Iron, total 7.0 3.5
Iron, dissolved 0.60 0.30
Aluminum, total 4.0 2.0
Manganese, total 4.0 2.0
Nickel, total 0.40 0.20
Zinc, total 0.40 0.20
TSS 70 35
pH Within the range 6.0 to 9.0
*-.iur. i<: Kcileral KejjUter. 40. Nn. J02. October 17. 197.V
33
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of the more toxic elements will be concentrated by chemical or biological processes to produce
even greater hazards.
Finally, it has been shown that abandoned coal-waste materials will continue to produce
water-borne contaminants for years after their disposal. Several investigators have pointed out
that older refuse is an even more prolific producer of acid drainage than recently discarded
material. The inescapable conclusion is that exposed coal mineral wastes are environmentally in-
nocuous only where water is absent or severely limited.
VII. TRACE-ELEMENT EMISSIONS FROM BURNING COAL REFUSE
Under certain circumstances, the oxidation of residual coal or other mineral matter in coal-
refuse piles can produce sufficient concentrations of heat to ignite the interior of the pile. In the
late 1960s, there were approximately 300 to 500 such piles burning in the U.S. (Magnuson and
Baker 1974; McNay 1971; Anon. 1965; Stahl 1964; Sussman and Mulhern 1964). These burning.
wastes are an acknowledged source of gaseous contaminants from the combustion of residual coal
and minerals (carbon and sulfur oxides and hydrocarbons); however, whether or not emissions of
volatile trace elements from burning wastes pose a substantial environmental threat has not yet
been assessed.
The cause of gob pile fires is not known with certainty. Some, of course, are caused by care-
lessness or are deliberately set, but most appear to result from the spontaneous generation of heat
by reactions occurring within the waste mass. Fires occur most frequently in wastes containing a
lot of finely divided coal and pyrite materials, and in those which are poorly compacted so that
good air circulation is maintained in the pile (Magnuson and Baker 1974; McNay 1971; Sussman
and Mulhern 1964; Hebley 1956; Zimmerman 1952; Harrington and East 1948). Most authorities
consider the heat from the oxidation of the residual coal to be the major cause of coal-refuse fires,
but they recognize that the oxidation of pyritic materials is an important contributing factor
(Magnuson and Baker 1974; Coalgate et al. 1973; Harrington and East 1948; Jones and Scott
1939; Scott and Jones 1937).
Only a limited effort has been made to identify the air-borne pollutants from burning refuse
(Coalgate et al. 1974; McNay 1971; Sussman and Mulhern 1964; Harrington and East 1948). An
estimate of the amounts of gaseous pollutants released by all of the burning coal refuse in the
U.S. was made by Hoffman in 1968, and is given in Table VII-I. Of course, the total load of con-
taminants originating from burning coal wastes is small compared to national totals;
nevertheless, coal-refuse pollutants are highly concentrated in the vicinity of the sources, where
they can have considerable local impact.
It is widely known that coals contain a number of trace elements which are volatilized or con-
verted to volatile forms during combustion and subsequently released in the gaseous products
(Ruch et al. 1974; Magee et al. 1973). Only one study concerning trace elements in burning coal
refuse was found in the literature. Finkelman and his colleagues (1974) at USGS have shown that
a large number of trace elements, many of which are toxic, are transported from the hot zone and
subsequently deposited in cooler areas by the vapors generated within the burning refuse. Clear-
ly, trace-element emissions from burning refuse have the earmark for being a potentially serious
environmental problem, particularly at the local level. However, this is an area which still needs
to be comprehensively assessed.
It is not likely that aqueous leaching of burning waste piles presents any additional problems
with trace elements (to those already recognized), unless the leach zone extends into areas of the
refuse mass where concentrations of trace elements have been deposited by vapor transport from
the burning area. So little is known about the chemistry and mineralogy of burning coal refuse,
however, that further speculation about leaching behavior is unwarranted. Likewise, there is
34
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TABLE VII-I
GASEOUS POLLUTANTS EMANATING FROM
BURNING REFUSE BANKS"
Total Amount Portion of Total Emitted
Gas Emitted (19' tons) From All U.S. Sources (%)
Sulfur Oxides 0.6 1.8
Particulates 0.4 1.4
Carbon Monoxide 1.2 1.2
Nitrogen Oxides 0.2 1.0
Hydrocarbons 0.2 0.6
"i!MiS ilatll.
••mure: Hulimun 197U.
practically nothing on which to judge the particular vulnerability of burned-out wastes to
weathering and leaching.
Most of the interest in burning coal wastes has concerned the prevention and control of refuse
fires (Magnuson and Baker 1974; Coalgate et al. 1974; McNay 1971: Maneval 1969; Stahl 1964;
Hebley 1956; Zimmerman 1952; Harrington and East 1948). Preventive measures include proper
grading and compacting or sealing of the waste-pile perimeters to reduce the flow of air through
the bank. With care, and attention to sound engineering practices, waste-pile fires can be almost
entirely prevented. To control or extinguish refuse fires once they have begun is another matter.
Success in this area has been rather limited. The most effective method for extinguishing coal-
refuse fires has been to dig out the burning materials and allow them to cool at the surface. A few
of the more successful methods of waste fire control include sealing the piles with soil or other
materials to control air circulation or injecting slurries, usually of water and finely divided in-
combustible materials, to essentially smother the burning waste.
The best overall practice, though, is to prevent the fires in the first place. When ignited, gob
pile fires can smolder or burn for years, in spite of the efforts to extinguish them.
VIII. TRACE ELEMENTS OF ENVIRONMENTAL CONCERN IN COAL-PROCESSING
WASTES
One of the main reasons for conducting this search of the literature was to determine if the
available information could provide a guide as to whether potentially toxic trace elements are
released into the aqueous or atmospheric environments from discarded coal-processing wastes.
This information is, of course, essential to assess the threat of environmental contamination from
the trace elements and mineral matter in these wastes, and to map adequate preventative or con-
trol measures should they be necessary. Unfortunately, as detailed in the previous sections, there
are large gaps in the body of knowledge on this subject. Therefore, a satisfactory judgement of the
hazards posed by the inorganic constituents of coal mineral wastes really cannot be made at this
time.
Very certainly there is a host of potentially toxic or harmful inorganic elements present in the
wastes from coal preparation and mine development, and it is known that some of these can find
their ways into the environment. Fe, Al, and Mn, which often leach out of these wastes in large
35
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amounts, can be detrimental to soils and destructive to plant and aquatic life. For example,
Lowry (1961) reports that as little as 400 ppm of Fe or Al ions in soils result in the complete mor-
tality of pine seedlings, and it has been reported that fish may be killed by concentrations of
these same ions of less than 0.5 ppm each (Massey and Barnhisel 1972). Solutions containing 2.5
ppm Ni, 5 ppm Cu, 25 ppm Zn, or 250 ppm Mn were found to be toxic to oat plants (Hunter and
Vergnano 1953), and concentrations of Cu ranging from 1.5 to 11.6 ppm have been reported by
Rehwoldt et al. (1971) to kill several species offish in 24 h. All of these effects are caused by quan-
tities of trace elements that are known to sometimes be present in the effluents from coal-waste
materials or in the waste dumps themselves (see earlier sections). In fact, the notorious inability
of many of the acidic waste materials to support any substantial plant life at all is thought to be
the result of toxic amounts of Fe, Al, and Mn present in these materials (Coalgate et al. 1973;
Massey and Barnhisel 1972; Beyer and Hutnik 1969).
In addition to these documented cause-and-effect relationships, of concern also are the highly
toxic heavy metals present in coal wastes; little about the waste-bank behavior of this group of
elements is known. Such elements as Pb, Se, Cd, As, and Hg have been singled out as being bad
actors in coal-combustion systems (Piperno 1975; Magee et al. 1973). But, this is largely because
these elements are volatile or tend to form volatile compounds and, therefore, can rather easily
escape from the burning coal along with the stack gases. Undoubtedly, many of these same ele-
ments are also released from burning waste banks, but whether or not these volatile trace ele-
ments will so readily escape into the drainage from weathered refuse remains to be seen. In addi-
tion to these volatile heavy elements, many other elements, which have been implicated as being
generally harmful or injurious, are also thought to be present in most coal refuse. These include
Be, Ni, Co, Cu, and Y (Piperno 1975; Anon. 1971). Here again, little has been reported about the
behavior or fate of this class of trace elements under the dynamic conditions in waste dumps.
Another aspect of trace-element behavior which merits attention concerns the possibility that
toxic elements can be chemically concentrated or accumulated either in the waste banks or in the
surrounding environment. There are many instances of this kind of behavior reported in t he
geochemical literature (Randama and Bahama 1950). For example, Vine as previously noted has
observed extremely high concentrations of Zn, Cu, and Ni in shales of a type found in close as-
sociation with coals. This phenomenon has been attributed to biogeochemical enrichment.
Within the waste dump, both the clay minerals and carbon residues are known to have con-
siderable ion exchange capacity (Coalgate et al. 1973; Grim 1968; Reese and Lovell 1966;
Broderick and Bogard 1941; Broderick and Hertzog 1941), and such processes as coprecipitation
and selective dissolution can concentrate or deplete certain elements or compounds from solution
(Massey 1972). Also, many of the soils in the areas surrounding the waste disposal sites can ac-
cumulate toxic ions, presumably via an ion exchange mechanism (Beers et al. 1974; Beyer and
Hutnik 1969; Rankama and Sahama 1950).
As can be readily seen from the foregoing discussion, considerably more research needs to be
done to provide a less fragmented picture of the behavior of the more toxic coal-related trace ele-
ments under the conditions prevailing in coal-refuse dumps. Until such work is conducted, it will
be difficult if not impossible to assess the full potential for environmental contamination from
trace elements in coal refuse and mineral wastes. Likewise, a determination of which trace ele-
ments are of most concern from an environmental standpoint is equally difficult.
IX. PREVENTION AND TREATMENT OF CONTAMINATION FROM COAL-
PROCESSING WASTES
Trace elements may be released into the environment from coal-processing wastes by two
plausible routes: as volatile components from burning wastes or as dissolved or suspended
36
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materials in the effluents or drainage from waste dumps. The control of trace-element emissions
from burning wastes can be dismissed rather briefly by stating that the best method is to ex-
tinguish the fire; this subject was discussed sufficiently in a previous section and is. therefore, not
belabored here. Actually, nothing a great deal more profound can be said about controlling trace
elements in the drainage from coal-refuse materials either, because so very little is known about
the extent or nature of such elements in waste effluents. However, especially in recent years,
much attention has been given to various methods for preventing, reducing, or controlling acid
drainage from coal mines and refuse dumps. (The amount of acidic contaminants allowed in the
drainage from coal-mining activities is now regulated in most places by federal, state, or local
laws.) These techniques are directed primarily at neutralizing the acidic refuse and mine ef-
fluents, and at reducing the large quantities of dissolved and suspended mineral matter in them.
Although these control measures are often only peripherally directed at trace elements, the trace-
element contents of acidic waters will be affected to varying degrees by the control methods used.
Consequently, some of the methods used to prevent or treat AMD may also be useful for controll-
ing or removing environmentally harmful trace elements. The following paragraphs address this
subject.
Acid drainage from coal mineral matter is essentially indentical in character, whether it
originates from refuse piles or abandoned mines. Therefore, methods for treating or preventing
acids apply equally to either source of contamination, and generally no distinction is made
regarding the origin of the drainage. However, in the literature all acidic effluents are referred to
by the generic term "acid mine drainage," so, this terminology has been adopted here. also.
Basically acid mine drainage (AMD) control methods can be divided into two groups: Those
directed primarily at preventing the formation of AMD and those concerned with treating AMD
once it has formed. A list of the various techniques used to prevent or treat AMD from coal-refuse
materials is given in Table IX-I. In addition, many other control or treatment methods have been
proposed, but these are yet to be proven technically or economically feasible under field condi-
tions.
TABLE IX-I
METHODS FOR PREVENTING OR CONTROLLING ACID
DRAINAGE FROM COAL-REFUSE MATTER
Preventative Measures
Control of air influx
Control of water influx
Disposal in underground or
strip mining sites
Treatment Methods
Neutralization
Flash Vaporization
Ion Exchange
Reverse Osmosis
-•uirri1: Str te\l.
37
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Prevention and Control of Acid Drainage
Sulfuric acid is formed when the pyritic material in coal refuse is oxidized by air in the
presence of water (see Sec. VI). Therefore, the most effective means of preventing the generation
of acids in acid-forming coal mineral wastes is to restrict or prevent the influx of air and flow of
water through the waste pile (Foreman 1974; Coalgate et al. 1973; Robins and Troy 1971; Bell
and Escher 1969). The circulation of air or water through waste materials can be markedly
reduced by carefully sizing and compacting the waste to reduce permeability, or by sealing the
edges of the pile with clay or some other suitable agent (National Academy of Sciences 1975; Loy
1974; Lorenz 1962). Mixing coal wastes with water glass, silica gel, or fly ash has been reported as
an effective means for reducing permeability and sealing the waste pile (Capp and Gillmore 1974;
Capp and Adams 1971; Walitt et al. 1970; Jones and Ruggeri 1969). These substances not only
help to reduce waste pile porosity, but they also help to neutralize acids as they are formed.
Possibly the most widely used method for controlling water and air influx in coal-refuse
materials involves grading the wastes and covering them with top soil (Brundage 1974; Kosowski
1972; Krause 1972; Hill 1969). In addition to reducing the seepage of water and air through the
underlying wastes, the added soil will often support vegetation, which further contributes to the
structural stability of the pile (Coalgate et al. 1973; Grube et al. 1971; Limstrom 1964).
Another method for preventing acid build up in coal wastes, which is a variation of the above
technique, is to bury the refuse back into the mining sites (National Academy of Sciences 1975;
Foreman 1974; Loy 1974; Poundstone 1974; Hill 1969; Moebs 1968, 1966). This is fairly easily ac-
complished for strip mines and indeed has now become a standard practice. However, to place
coal wastes back into underground mines is not so easy to do because of high costs and safety and
drainage control problems. In either case, when properly done, the formation of AMD from the
buried wastes is substantially reduced or alleviated entirely.
A very effective approach to prevent acid drainage is to direct the flow of incoming surface and
subsurface water away from refuse disposal areas (Loy 1974; Coalgate et al. 1973; Krause 1972;
Ramsey 1970; Hanna et al. 1963; Lorenz 1962). This is accomplished by the use of aqueducts,
diversion ditches, barriers, and impoundments, but the proper placement and grading of the
waste piles is also an important factor in preventing the influx of water (Maneval 1975).
Treatment of Acid Drainage
By far the most widely used method for treating AMD once it has formed and drained out of
the coal refuse or mine area is by neutralizing with alkaline materials (O'Brien et al. 1974; Mc-
Donald et al. 1974; Bhatt 1974; Wilmoth et al. 1972; Kemmer and Beardsley 1971). Agents which
have been used for this purpose include limestone, lime, caustic soda, or a combination of these.
In the neutralization process, the acid drainage is brought into contact with the neutralizing
agents, and as the pH of the water rises, iron and aluminum hydroxides precipitate. Although at
first glance this seems like a straightforward process, there are-many complicating factors which
limit the choices of neutralizing agents and operating conditions.
Lime or caustic soda are soluble in water throughout a broad pH range and will rapidly reduce
acidity and effect the precipitation of iron and aluminum salts (Bhatt 1974; Holland 1970, 1969:
Girard and Kaplan 1966). But, these agents are relatively expensive, careful control of reaction
conditions is required, and they are dangerous materials to store and handle. Proper disposal of
the large volumes of sludge produced by the use of lime or caustic is also a problem (Lovell 1970;
Kostenbader and Haines 1970).
Limestone, on the other hand, is a much cheaper neutralizing agent for AMD compared to lime
or caustic soda, and it is easier to use and safer to handle (Ford 1972; Mihok et al. 1968; Calhoun
38
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1968; Reidl 1947). Also the volumes of sludge produced by limestone treatment are smaller than
for caustic or lime. There are also several disadvantages of using limestone. Limestone has a" low
solubility in neutral solutions, so a pH of about 7 is all that can be practically achieved with this
agent. This is not a particular problem if the iron present in solution is principally in the form of
Fe+++, which rapidly precipitates as the hydroxide at a pH of 6.5 (Wilmoth and Scott 1970).
However, if a substantial amount of Fe"1"1" is present, additional processing steps are required to
completely remove iron from solution. Fe+* hydroxide does not precipitate until the solution pH
is increased to about 9, a value unattainable in a practical sense with limestone. Consequently,
the usual practice is to oxidize the Fe** to Fe before or during limestone neutralization. This
oxidation step is often accomplished by direct aeration (Selmeczi 1972; Holland 1970; Stauffer
and Lovell 1969), but many other methods have also been used in conjunction with the limestone
process (Gaines et al. 1972; Jasinski and Gaines 1972; Streeter et al. 1971; Beller et al. 1970;
Mihok 1969; Steinberg et al 1968). In addition to these problems, the low solubility of limestone
in water requires that the acidic effluents remain in contact with the limestone for relatively long
times to complete neutralization. This severely limits the volume effectiveness of limestone
treatment facilities. Another general disadvantage of using either hydrated lime or limestone for
neutralizing AMD is that water hardness is increased (Ca and Mg ions) during treatment. In
spite of these drawbacks the economy, ease of operation, and safety of handling still make
limestone a popular and widely used agent for neutralizing acid drainage from coal mine wastes.
There are now about 300 plants in operation in the U.S. for treating AMD with the various
alkaline neutralizing agents. Most of these plants utilize hydrated lime; but many of the
problems with limestone are being overcome, and it is expected that a higher proportion of
limestone treatment facilities will begin to appear in coming years. Regardless of the neutralizing
agent used, it must be pointed out that these processes are designed primarily to treat solution
acidity. Only those ions, such as Fe, Al, and Cl, whose solubilities are sensitive to pH in the acid
to neutral range, will be removed by the alkaline neutralization process (McDonald et al. 1974).
The solubilities of other ions (Ca, Mg, and Pb, for example) are not highly dependent on solution
pH, and thus will probably not be affected, but may be even increased in AMD by alkaline
neutralization. Typically, waters treated by alkaline agents tend to retain relatively high con-
tents of dissolved salts as indicated by the specific conductance values given in Table IX-1I.
Under certain circumstances, the utilization of ion-exchange technology offers a more highly
refined method of treating AMD than does direct neutralization with alkaline agents. Ion ex-
change is a method where specific ions are removed from solution by exchanging them with other
ions of like charge at the surface of an adsorbent. This accumulates the removed ions on the ad-
sorbent, but releases the ions originally held by the adsorbent into solution. The newly adsorbed
ions are removed from the adsorbent by flushing it with a regenerating solution. The adsorbents
used are either natural ion-exchange materials, like clays or zeolites, or, increasingly, various
types of synthetic resins.
Ion-exchange treatment of acidic effluents reduces both the total acidity and a substantial part
of the dissolved ions. For example, Kunin et al. (1974) have reported the effectiveness of a 1 x 106
gal/day ion-exchange, AMD treatment facility located in Pennsylvania. This facility utilizes
weakly basic, bicarbonate anion exchange columns. As the acidic coal mine drainage water is
passed through the ion-exchange column, the metal sulfates in solution are converted to soluble
metal bicarbonates. Aeration releases C02 and raises the pH of the solution, precipitating Fe,
Mn, and Al as hydrous oxides. Part of the Ca and Mg also precipitates, but to produce the
highest quality water, further treatment with lime will precipitate more of the latter ions as the
less soluble carbonates. The ion-exchange resins are regenerated by backflushing with NH4OH
followed by CO2. Typical results from the treatment of AMD with this ion-exchange facility are
recorded in Table IX-III.
39
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TABLE IX-II
EFFECTIVENESS OF ALKALINE NEUTRALIZATION FOR
IMPROVING QUALITY OF MINE DRAINAGE"
Feed Water Lime Limestone Limestone - Lime
Parameter11 Range Treatment Treatment Treatment
PH 2.4-3.1 7.1 6.0 7.1
Total acidity 1700-9200 7.6 107 33
Alkalinity 0-93 10.3 93 35
Specific Conductance 2800-7900 5200 4600 2900
Sulphate 2200-6600 3500 4200 3000
Iron, total 145-1130 1.94 3.40 1.75
Aluminum — 1.80 2.65 1.00
Magnesium — 135 282 82
Calcium — 900 965 170
"Kn>in McDonald el al. U974).
"i
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Reverse osmosis is a technique in which special types of semipermeable membranes are
utilized to selectively remove disssolved ions from the acidic waste waters (Blackshaw et al. 1974:
Wilmoth et al. 1972; Kremen et al. 1970; Mason 1970). The membranes used are permeable to
water but relatively impermeable to dissolved ions. High pressures are used to force the con-
taminated solutions through the membrane. The ions removed from the drainage solutions,
which are concentrated in a brine on the fore-side of the membrane, must be collected for dis-
posal or further processing. Typical before-and-after results from a reverse-osmosis AMD proces-
sing facility are given in Table IX-IV.
Although reverse osmosis does an excellent job of removing dissolved salts from solution, ad-
ditional treatment of some kind is necessary to adjust the pH of the solutions. Also, some trouble
has been experienced with fouling of the membranes by iron precipitates at low pK. causing a
reduction in efficiency. In spite of these difficulties, reverse osmosis is considered feasible for
treating AiMD, and several pilot-scale plants have been built and tested.
Flash distillation is a simple and highly effective method to clean up AMI) which is highly con-
taminated O1000 ppm) with dissolved salts (B'hatt 1974; Maneval and Lemezis 1972). With this
method, the contaminated feed water is heated to the vaporization point in a series of enclosed
chambers. The product water is condensed in another part of the cell in a highly purified state.
Residual salts are collected for disposal.
A pilot plant utilizing flash distillation has been constructed to treat AMD. Initial estimates
are that this method is expensive, but it is still one of the more promising techniques for up-
grading the quality of the most highly contaminated waste waters.
In addition to the methods described above, there are many other techniques that may be
feasible for cleanup or prevention of AMD. These include: sulfide precipitation (Streeter 1970);
antibacterial agents (Shearer et al. 1970); microbial polymers (Dugan 1970); foam separating
agents (Hanson 1972); biological treatment (Rice and Rabolini 1972); deep-well injection
(Stefanko 1969: Linden and Stefanko 1966); sewage treatment (Pearson and Nesbitt 1974;
Morgan 1942); and metal-hydroxide precipitation (Evans 1966). Most of these methods,
however, have not been carried beyond the laboratory stage. Consequently, their general
economic or technical feasibility for large-scale work is unproven.
TABLE IX-IV
SUMMARY OF QUALITY OF ACID MINE DRAINAGE
AFTER TREATMENT BY REVERSE OSMOSIS UNIT"
Variable" Feed Water Product Water
pH 4.7 3.8
Conductivity 3800 48
Total acidity 930 132
Total dissolved salts 4850 23
Total iron 393 1.5
Aluminum 29 0.22
Calcium 427 1.5
Magnesium 137 0.5
Sulfate 3400 16
"From lilackshaw et al. (197-ii.
"i inn-rniraiion* in ppm. conductivity in micrnmhns.
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At this point, then, several observations can be made regarding the possible effectiveness of the
various methods used to prevent or treat AMD for removing or controlling the trace-element con-
tents of the waste waters.
It is fairly well established that the highest contents of dissolved and suspended materials in
the effluents from coal wastes are carried in the most highly acidic solution. Therefore, the
techniques for initially preventing the formation and buildup of AMD by excluding oxygen and
water from coal-processing wastes should also be effective for keeping the levels of dissolved or
suspended trace elements to a minimum in the waste runoff.
The situation becomes more complex after acid has been generated in the waste material and
the runoff has become contaminated with large quantities of acid and dissolved salts. Un-
doubtedly, many of these solutions carry large amounts of trace elements in addition to the major
elemental components, but the effectiveness of AMD treatment methods at removing these trace
elements can, at this point, only be surmised.
The methods for neutralizing AMD with alkaline agents are particularly nebulous with regard
to the fate of trace elements during processing. It has been seen that, although certain elements
are precipitated as a result of the treatment, others are unaffected and remain in solution. The
almost universal use of these neutralization techniques for treating AMD makes it imperative
that a careful assessment of the chemistry and behavior of the trace elements in coal-refuse
drainage be made within the context of the treatment parameters. This will be especially neces-
sary if some of the more toxic trace elements are eventually identified in AMD in appreciable
quantities.
Ion exchange, reverse osmosis, and flash distillation have all been shown to be effective for
removing a substantial part of the dissolved mineral matter for AMD. Accordingly, these techni-
ques should be fairly effective at removing many of the minor- or low-abundance elements as
well. Again though, it will be necessary to evaluate each method of treatment on a case-by-case
basis to establish the effectiveness for removing the specific elements of concern.
The main conclusion to be drawn from this section is that the methods now being utilized to
prevent or treat contaminated runoff or drainage from coal mineral wastes are directed mainly at
the control of acidity and only in some instances at removing disssolved constituents. Should the
removal of particular trace elements prove necessary or desirable, a reassessment of the specific
treatment methods will be needed to determine their suitability for this purpose. Undoubtedly,
in many cases, additional steps or modifications of existing methods will be necessary to ac-
complish the desired objective. Apparently, there has already been some concern about these lat-
ter aspects, as laboratory studies concerning the removal of specific ions from treated waste
waters are now being reported (Swain and Roselle 1974; Huck et al. 1974).
X. RECOVERY OF TRACE ELEMENTS AND MINERALS FROM COAL-WASTE
MATERIALS
Workers have experimented for many years with various processes for utilizing the material in
coal-waste piles with the idea of reducing the enormous areas occupied by such piles, and subse-
quently, their contamination of air and water. An additional incentive has been the desire to
retrieve some of the minerals or other economically valuable products contained in the coal
wastes. A partial review of the literature on this subject has been written by Coalgate (1975);
and, Kenahan et al. (1973) conducted a survey for the Bureau of Mines on possible uses of wastes.
Generally, coal-waste utilization falls into one of three categories: coal salvage, building or con-
struction materials, and metals or minerals recovery.
The use of coal refuse as a direct fuel source was discussed recently by Leonard and Lawrence
(1973). Effective utilization of this resource requires a knowledge of a past history of the bank's
42
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deposition, since suitable deposits of coaly waste must be located within the refuse dump. There
is a large potential for using the residual coal in refuse for power plant applications. Of particular
interest are the low- to medium-energy coals, which were discarded along with the %vastes at
times when consumers demanded higher energy coals. With beneficial ion, 10% of the waste piles
studied could qualify for presently available power generation processes. The recovery of salable
coal from these banks seldom exceeds 20% of the total waste material (MacCartney and Whaite
1969), but one large steel company has seriously engaged in a program to obtain steam coal from
the refuse produced by its metallurgical coal plant (Charmbury 1970).
The use of coal wastes for building and construction materials has shown promise of economic
success (McNay 1970). Products which have been considered are road aggregates, non skid
materials, and building materials (Spicer and Luckie 1970). Several processes have been studied
to make lightweight aggregate building materials (e.g., cinder blocks) from coal wastes (Myers et
al. 1964; 1962). The fusion heat required was supplied by the residual carbon in the refuse. Pel-
letization of the refuse before fusion produces a stronger, more uniform product. However, one of
the two plants studied required many modifications of the original design because flat slate par-
ticles did not easily form pellets; also, the process used may be impractical for some refuse. In
later studies. Utley et al. (1965) related washability data to aggregate production and concluded
that the ideal refuse, which resulted in a finished product with greatest compressive strength and
best expansion characteristics, was that which sank at 2.60 specific gravity and contained 12-
25% pyrites. Two much carbon decreased expansion, and excess alumina required high fusion
temperatures. Clearly, much work will be needed to adapt a variable source, like coal waste, to
the manufacture of finished products like those mentioned above.
Interest in recovering metals from coal wastes has flourished since the forties, when wartime
conditions threatened to cut off supplies. Current interest is also stimulated by the realities ol ex-
ternal dependence, as more than one-half of the total U.S. requirements of 20 strategic metals
and minerals are imported, and much of these from "Third World" suppliers (Falkie 1975). Trace
metals and minerals in coal and, hence, in coal waste, could supply much of the U.S. demands if
they were to be recovered from these materials. The problems encountered in utilizing these
sources—low-quality ore and a widely scattered resource—are not small, however. The following
paragraphs will briefly describe some of the technical solutions which have been reported on
securing materials from coal wastes.
Sulfuric acid is the major chemical produced in the U.S. A constant supply is vital to the na-
tion's economic health. Mitchell (1944) attempted to recover pyrite from coal waste to be used for
sulfuric acid production. The method used was mechanical separation with jig tables. Although
borderline quality raw materials could be obtained from coal waste by this method, the economic
picture at the time was not optimistic, particularly in view of the capital outlay required for con-
centrating the pyrite.
Stimulated by a shortage of sulfur and sulfuric acid, and an increased interest in environmen-
tal contaminants in the late 1960s, more workers turned their attention to pyrite recovery from
• •<>al waste. Sun and Savage (1968) developed a comparatively successfully dotation process, in
which separation took place in stages. The process involved dual notation, using collectors and
Irothers, first to separate the coal from mineral matter, then pyrite from the remaining clay
minerals in the waste.
A magnetic pyrite separation process, aimed generally at pollution control via sulfur reduction
of coals .for electric utility use, was developed by Krgun and Bean (1968). This process was also
thought useful for the recovery of iron or sulfur. An attempt was made to increase the magnetic
susceptibility of pyrite above its normal value by using heat to rapidly convert a part of the iron
into a ferromagnetic state. The most promising result was obtained using dielectric heating of the
co;il. A study of Brazilian raw coals indicated a potential for the use of magnetism to effect the
separation of the mineral constituents of coal, other than pyrites (Trindade 197:5).
43
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Many processes have been used for alumina extraction from coal wastes. Kelley et al. (1946)
present a detailed study of the thermodynamics of the conversion of various aluminum-
containing compounds to alumina. These included a high-alumina clay (20% available alumina
as kaolinite) and alunite. Also, coal waste has been burned in the presence of alkaline-earth com-
pounds to solubilize the silicates in the ash, from which alumina could be extracted (Freling and
Dorren 1937). Muller and Oversohl (1951) patented a method in which coal tailings were treated
with chlorine at temperatures between 600 and 1000°C in rotary kilns or shaft furnaces to recover
iron and aluminum. Another method was employed by Sukhanova and Ponomarev (1969), who
used sulfuric acid to extract alumina from coal wastes by countercurrent leaching. Korshunov
and Shmuk (1957) obtained alumina by extracting coal flotation tailings with nitric acid, but
they obtained some iron impurities in the final product. By treating coal ash with sodium oxide,
Ni (1973) succeeded in separating alumina from the other products and achieved a 93-97%
recovery of the alumina present.
Less has been done on the technology of the recovery of specific trace elements from coal.
Mitchell (1944) reported that copper, zinc, lead, silica, alumina, phosphorous, manganese, and
additional elements were associated with the mineral, pyrite, and that these elements could be
separated from the pyrites in coals, should their quantity and concentration make separation
economically feasible. Sun et al. (1971) indicated that perhaps the most generally useable por-
tions of the coal waste are silica (30-60% of most coals) and alumina (10-40%), from which gal-
lium or germanium might be by-products.
Manganese and molybdenum have also received attention. Molybdenum has been extracted
with hydrochloric acid from tailings of the sulfuric-acid treatment of coal ash, yielding 85% of the
metal present (Mirzakarimov 1970). Ozone, hypochlorite ion, and chlorine gas have been used to
remove manganese as MnO2 from acid mine drainage (Swain and Rozelle 1974). The
hypochlorite ion worked best, but all had the disadvantage that iron in the acid drainage had to
be removed from the water first, since it was preferentially oxidized.
In other studies, the mineral portions of coal, containing various metals, were enriched using
horizontal cyclone burners in a process described by Gol'dina (1968). A foam separation techni-
que, using sodium dodecyl sulfate as a surfactant, was applied to acid mine drainage. This
process removed only 6% of the metals per pass through the foam column. Because the acid
drainage did not foam easily, and the foaming agent was not readily recovered, the method was
not concluded to be economically advantageous. Finally, ion-exchange methods have been used
to recover germanium from coal ash (Adamenko et al. 1972). Germanium was removed from the
exchange column by elution with hydrochloric acid.
The carbon left in the coal refuse might also be of use. Experiments have been conducted using
bone coal and high-carbon refuse as materials for water purification (Broderick and Hertzog
1941). In most cases, the product contained too much ash to meet federal water purification stan-
dards. Combined with other techniques, this problem might be overcome.
As the above suggest, there are many possible ways to utilize coal refuse and recover useful
materials from it. However, most of the processes investigated require modifications for adapta-
tion to the various types of wastes, and often the other components in the wastes interfere with
the recovery operation. Many of the processes are not adaptable to large-scale, commercial
operations. Nonetheless, there is little doubt that coal mineral wastes represent a resource of
fuel, metals, and minerals of enormous magnitude. Research is needed to develop suitable
utilization and recovery methods and to establish the feasibility of these processes within the
context of today's rapidly evolving economics.
44
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XI. SUMMARY AND CONCLUSIONS
The major conclusions from this review of the literature are:
• Few studies of the trace elements in coal-processing 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 the contribu-
tions of trace elements to this form of environmental contamination, let alone the effects of these.
are not 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-processing 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 could themselves produce undesirable effects.
• 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 this review.
Introduction
The mineral wastes from coal processing and mine development constitute a major en-
vironmental problem. Over 3 billion tons of these materials have accumulated in the U.S., and
the current annual rate of waste production (100 million tons per year) is expected to double
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 or cave-
ins. Coal-waste piles are also the source of highly mineralized, often acidic drainage, which af-
fects 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 environmental contamination from the trace elements in coal mineral wastes. The pur-
pose of t his review is to utilize the available information in the literature to assess the potential of
this latter possibility.
Literature Search Format
An extensive search of the open literature on trace elements in coal processing 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.
45
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Trace Elements and Minerals in Coal-Processing Wastes
Only a few studies of the minerals and trace elements in coal-processing 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
A large volume of data on this subject is available, and most of the information can be applied
to coal-processing 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 is
still not well defined. Laboratory investigations of elemental behavior utilizing float-sink techni-
ques have been conducted. These studies reveal that trace elements differ in their susceptibilities
to be removed from coals by density separation, but significant reductions of these elements in
coals can be achieved. Therefore, large quantitites of trace elements are discarded in the washing
refuse.
Water Contamination from Trace Elements in Coal-Processing Wastes
The aqueous drainage from coal refuse is usually contaminated by acids and dissolved or
suspended mineral matter. The highest concentrations of dissolved species are found in the more
highly acidic solutions. Typically, the acid drainage from coal refuse contains high concentra-
tions of Ke, Al, Ca, Mg, and SO< 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 were burn-
ing in 1968. The cause 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.
46
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Trace Elements of Environmental Concern in Coal-Processing Wastes
There are numerous potentially toxic trace elements in coal wastes, and many of these find
their way into the environment. Ions, such as Fe, Al, and Mn. 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 ele-
ments can accumulate or concentrate within the waste pile, or in the surrounding environment,
warrants attention. Based on the available information, an adequate assessment of the total
potential for environmental contamination from trace elements in coal-processing wastes cannot
be made.
Prevention and Treatment of Contamination from Coal-Processing 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.
Preventative measures include grading, compaction, 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 utilization 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 ele-
ments 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.
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60
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO. ERDA LA-6600MJ
EPA-600/7-76-007
?•
4. TITLE AND SUBTITLE
ENVIRONMENTAL CONTAMINATION FROM TRACE
ELEMENTS IN COAL PREPARATION WASTES
A Literature Review and Assessment
7. AUTHORS E> M> Wewerkaj j
and J. D. OJsen
M Wflliqms J-
>.L. Wanek,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Los Alamos Scientific Laboratory
University of California
P.O. Box 1663
Los Alamos , New Mexico 87544
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development*
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
is. SUPPLEMENTARY NOTES (*) Cosponsored by ERDA as part of ]
tal Research and Development Program. ERDA project
EPA project officer is J D Kilgroe
3. RECIPIENT'S ACCESSION- NO.
5. REPORT DATE
August 1976
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
EHB527
11. CONTRACT/GRANT NO.
EPA/ERDA IAG-D5-E681
13. TYPE OF REPORT AND PERIOD COVERED
FInalL_7/75-8/76
14. SPONSORING AGENCY CODE
EPA-ORD
Federal Energy /Environmen-
officer is Myron Gottlieb;
16. A ACT The report gives results of collecting and evaluating available information
on the chemistry and behavior of trace elements in coal preparation wastes , and
assessing the potential for environmental contamination from the trace elements in
these wastes. Only limited attention has been given previously to the chemistry of
trace elements in coal waste materials; however, most of the knowledge concerning
trace elements and minerals in raw coals can be applied directly to coal wastes.
Nearly every naturally occurring element is likely to be present in coal and coal
refuse. The fate of these elements during coal preparation is poorly defined; but,
large concentrations of trace elements are discarded in the washing refuse." Although
the behavior of trace elements during refuse weathering, leaching, and burning is not
well understood, sufficient data exists to show that toxic or harmful quantities of
elements (e.g. , Fe, Al, Mn, Co, Ni, and Zn) are often released to the environment.
A comprehensive assessment of the full potential for environmental contamination
from the trace elements in these wastes cannot be made without further extensive
research.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Pollution Weathering
Coal Preparation Leaching
Wastes Combustion
Trace Elements
Chemical Reactions
Washing
13. DISTRIBUTION STATEMENT
Unlimited
b. IDENTIFIERS/OPEN ENDED TERVS C. COSATI Field/Group
Pollution Control 13B
Stationary Sources 081
21B
07D
13H, 07A
19. SECURITY CLASS (This Report) 31. NO. OF PAGES
Unclassified 67
20. SECURITY CLASS (This page) 22. PRICE
Unclassified
EPA form 2220-1 (9-731
•frU.S. GOVERNMENT PRINTING OFFICE 1977—777-018/47
61
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