DoE
EPA
United States
Department of Energy
Division of Environmental
Control Technology
Washington, DC 20545
LA-8826-PR
US Environmental Protection Agency
Office of Research and Development
Industrial Environmental
Research Laboratory
Research Triangle Park, NC 27711
EPA-600/7-81-087
May 1981
Trace Element
Characterization
of Coal Wastes -
Fifth Annual
Progress Report
Interagency
Energy/Environment
R & D Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment 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 sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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DoE LA-8826-PR
EPA-600/7-81-087
May 1981
UC-90i
Trace Element Characterization
of Coal Wastes -
Fifth Annual Progress Report
October 1, 1979 — September 30, 1980
by
R. C. Heaton, L E. Wangen, P. L. Wanek, J. M. Williams, E. F. Thode,*
M. M. Jones, A. M. Nyitray, P. Wagner, and J. P. Bertino**
Los Alamos Scientific Laboratory
University of California
Los Alamos, New Mexico 87545
EPA/DoE Interagency Agreement No. IAG-D5-E681
Program Element No. INE825
'Short-Term Visiting Staff Member. Department of Management, New Mexico
State University, P.O. Box 3DJ, Las Cruces, NM 88003.
""Consultant. 1079 Mansion Ridge Road, Santa Fe, NM 87501.
EPA Project Officer: David A. Kirchgessner
Industrial Environmental
Research Laboratory
Research Triangle Park, NC 27711
DoE Project Officer: Charles Grua
Division of Environmental
Control Technology
Washington, DC 20545
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
and
U.S. DEPARTMENT OF ENERGY
Division of Environmental Control Technology
Washington, DC 20545
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CONTENTS
ABSTRACT 1
EXECUTIVE SUMMARY 2
I. ENVIRONMENTAL CONTROL TECHNOLOGIES 2
IL ASSESSMENT OF HIGH-SULFUR APPALACHIAN COAL WASTES 5
HI. LEACHING PROCEDURES 7
RESULTS AND DISCUSSION 8
I. ENVIRONMENTAL CONTROL TECHNOLOGIES 8
A. Codisposal Techniques 8
1. Treatment and Lime and/or Limestone 8
2. Codisposal with Soils or Process Wastes 19
a. Experiment A 19
b. Experiment B 25
B. Coal Waste Effluent Neutralization 32
C. Calcination of Coal Wastes 35
D. Summary and Conclusions 37
IL ASSESSMENT OF HIGH-SULFUR APPALACHIAN COAL WASTES 38
A. Introduction 38
B. Mineralogical Analyses 38
C. Chemical Composition 40
D. Micromineralogy 42
E. Leaching Behavior 44
1. Static Leaching 44
2. Dynamic Leaching 47
F. Conclusions 49
III. COMPARISONS OF EPA EXTRACTION PROCEDURE AND PAST WORK
AT LOS ALAMOS 55
A. Background 55
B. Results Obtained Using the EPA Extraction Procedure 55
C. Comparisons Among Different Leaching Procedures 56
D. EPA Leaching Procedure as Applied to Coal Wastes 63
E. Summary and Conclusions 64
REFERENCES 64
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APPENDIX A. RESULTS OF LIME AND LIME/LIMESTONE TREATMENT
EXPERIMENTS 65
APPENDIX B. PROCEDURES AND RESULTS FOR EXPERIMENTS ON CODISPOSAL OF
COAL WASTES WITH SOILS OR PROCESS WASTES 71
APPENDIX C. TRACE ELEMENT CHEMISTRY OF ACIDIC COAL CLEANING WASTE
LEACHATES 78
APPENDIX D. GENERAL INFORMATION ON COAL PREPARATION PLANTS I AND K
91
APPENDIX E. RESULTS OF STATIC AND DYNAMIC LEACHING EXPERIMENTS WITH
COAL AND COAL WASTE SAMPLES FROM PLANT K 92
APPENDIX F. PROCEDURES AND RESULTS FOR COMPARATIVE LEACHING
EXPERIMENTS 96
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TABLES
I. Physical and Chemical Properties of Materials Used in Attenuation and Codisposal
Experiments 22
II. Effluent pH Observed in Experiment B During the First Liter of Eluent, After
Attainment of Near Steady State and After Oxidation by Air 26
HI. Summary of in situ Attenuations of Aluminum Resulting from Codisposal of Coal
Waste with Finely Ground Subsoils and a Quarry Limestone 27
IV. Summary of in situ Attenuations of Iron (II) Resulting from Codisposal of Coal Waste
with Finely Ground Subsoils and a Quarry Limestone 27
V. Summary of in situ Attenuations of Manganese Resulting from Codisposal of Coal
Waste with Finely Ground Subsoils and a Quarry Limestone 28
VI. Summary of in situ Attenuations of Fluorine Resulting from Codisposal of Coal Waste
with Finely Ground Subsoils and a Quarry Limestone 28
VII. Summary of in situ Attenuations of Nickel Resulting from Codisposal of Coal Waste
with Finely Ground Subsoils and a Quarry Limestone 29
VIII. Summary of in situ Attenuations of Arsenic Resulting from Codisposal of Coal Waste
with Finely Ground Subsoils and a Quarry Limestone 29
IX. Total Solution Concentrations of Thirteen Chemical Components in Coal Waste
Leachates as Measured After Additions of Calcium Hydroxide and as Predicted by a
Chemical Equilibrium Model 33
X. Trace Element Leachabilities of Calcined Coal Preparation Wastes With and Without
Selected Chemical Additives 36
XI. Discharge Severities for the Leachates from Calcined Coal Preparation Wastes 37
XII. Mineralogical Compositions of Coal Waste Samples from Plant K 40
Xm. Elemental Compositions of Coal Waste Samples from Plant K (Dry Basis) 41
XIV. MEG/MATE Analysis of Static Leachates from Plant K Materials 48
XV. Initial and Final pH Values for Coal Waste Leachates Using the EPA Extraction
Procedure 56
XVI. Concentrations (ppm) of Toxicity Indicator Elements in Coal Waste Leachates 56
XVII. Probabilities that True Concentrations of Toxicity Indicator Elements Equal or Exceed
Federal Primary Drinking Water Standards 57
Vll
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XVIIIa. Adjusted Leachate Compositions Obtained Using the RCRA Leaching Procedure for
Coal Waste Samples ...................................
XVIIIb. Leachate Compositions Obtained Using RCRA Leaching Procedure for Coal Waste
Samples. Results Expressed as Milligrams Element Leached per Kilogram Solid Waste . 58
XVIIIc. Leachate Compositions Obtained Using RCRA Leaching Procedure for Coal Waste
Samples. Results Expressed as the Percent of the Element Originally Present that
Appears in the Leachate ................................. ^°
XDCa. Leachate Compositions Obtained from One-Day Shaker Leaches of Coal Waste Samples
(-3/8-in.) (ppm) ...................................... 59
XlXb. Leachate Compositions Obtained from One-Day Shaker Leaches of Coal Waste Samples
(-3/8-in.). Results Expressed as Milligrams Element Leached per Kilogram Solid Waste
.............................................. 59
XIXc. Leachate Compositions Obtained from One-Day Shaker Leaches of Coal Waste Samples
(-3/8-in.). Results Expressed as the Percent of the Element Originally Present
that Appears in the Leachate ............................... 59
XXa. Leachate Compositions Obtained from One-Day Shaker Leaches of Coal Waste Samples
(-20 Mesh) (ppm) ..................................... 60
XXb. Leachate Compositions Obtained from One-Day Shaker Leaches of Coal Waste Samples
(-20 Mesh). Results Expressed as Milligrams Element Leached per Kilogram Solid Waste
................. ; ............................ 60
XXc. Leachate Compositions Obtained from One-Day Shaker Leaches of Coal Waste Samples
(-20 Mesh). Results Expressed as the Percent of the Element Originally Present that
Appears in the Leachate ................................. 60
XXIa. Leachate Compositions Obtained from Long-Term Shaker Leaches of Coal Waste
Samples (-3/8-in.) (ppm) ................................. 61
XXIb. Leachate Compositions Obtained from Long-Term Shaker Leaches of Coal Waste
Samples (-3/8-in.). Results Expressed as Milligram Element Leached per Kilogram Solid
Waste ................................... 61
XXIc. Leachate Compositions Obtained from Long-Term Shaker Leaches of Coal Waste
Samples (-3/8-in.). Results Expressed as the Percent of the Element Originally Present
that Appears in the Leachate ...... ,
....................... ol
XXIIa. Leachabilities of Selected Elements from Coal Waste Samples (-3/8-in.) Obtained from
Continuous Column Leaching Experiments. Results Expressed as ppm for 16/ Water
per Kilogram Solid Waste .............
....................... 62
Vlll
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XXIIb. teachabilities of Selected Elements from Coal Waste Samples (-3/8-in.) Obtained from
Continuous Column Leaching Experiments. Results Expressed as Milligram Element
Leached per Kilogram Solid Waste 62
XXIIc. teachabilities of Selected Elements from Coal Waste Samples (-3/8-in.) Obtained from
Continuous Column Leaching Experiments. Results Expressed as the Percent of the
Element Originally Present that Appears in the Leachate 62
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FIGURES
1. Discharge severities (leachate concentration/ 100 X Mate) for selected trace elements in
drainages from high-sulfur coal preparation wastes ......................
2. Discharge severities (leachate concentration/ 100 X Mate) for selected trace elements in
leach ates from Plant K coal preparation wastes as determined by dynamic leaching
experiments .....................................
3. Dependence of effluent pH on time for six treated coal waste samples
4. Concentrations of iron in the effluents from six treated coal waste samples as functions
of time ............................................. 11
5. Concentrations of nickel in the effluents from six treated coal waste samples as functions
of time ............................................. 12
6. Concentrations of aluminum in the effluents from six treated coal waste samples as functions
of time ............................................. 13
7. Concentrations of manganese in the effluents from six treated coal waste samples as
functions of time ....................... ' ................. 14
8. Concentrations of copper in the effluents from six treated coal waste samples as functions
of time ............................................. 15
9. Concentrations of zinc in the effluents from six treated coal waste samples as functions
of time ............................................. 16
10. Concentrations of cobalt in the effluents from six treated coal waste samples as functions
of time ............................................. 17
1 1 . Concentrations of calcium in the effluents from six treated coal waste samples as functions
of time ............................................. 18
1 2a. Concentrations of selected trace elements in treated coal waste effluents vs pH ....... 20
12b. Concentrations of selected trace elements in treated coal waste effluents vs pH 21
13a. Behaviors of pH, Fe(Il), Al, Mn, F, and As vs effluent volume for the four treatments
of Experiment A .......................... « .
13b. Behaviors of Ni, Fe(III), and specific conductance vs effluent volume for the four treatments
of Experiment A .................
14a. General Patterns of pH, Al, Fe(II) in effluents from columns containing coal waste alone
coal waste plus an acidic soil, and coal waste plus calcareous soils ........... '. 30
14b. General patterns of Mn, F, Ni, and As in effluents from columns containing coal waste
alone, coal waste plus an acidic soil, and coal wastes plus calcareous soils ........ 3]
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15. Concentrations of Fe(II), As, and Zn in coal waste leachates vs pH—comparisons of
values predicted by thermodynamic calculations with those experimentally observed
after additions of calcium hydroxide to coal waste leachates 34
16. Scanning electron micrographs of selected coal waste samples from Plant K 45
17. Results of static leaching experiments with coal preparation wastes from Plant
K—concentrations of selected trace elements in the leachates plotted as functions
of time 46
18. Results of static leaching experiments with feed coal from Plant K—concentrations
of selected trace elements in the leachates plotted as functions of time 46
19. Results of static leaching experiments with cleaned coal from Plant K—concentrations
of selected trace elements in the leachates plotted as functions of time 47
20. Results of dynamic leaching experiments with coal waste from Plant K—pH vs eluent
volume 47
21. Results of dynamic leaching experiments with coal waste from Plant K—specific
conductance vs eluent volume 50
22a. Results of dynamic leaching experiments with coal waste from Plant K—concentrations of
selected trace elements in the leachate vs eluent volume 51
22b. Results of dynamic leaching experiments with coal waste from Plant K—concentrations of
selected trace elements in the leachate vs eluent volume 52
23a. Results of dynamic leaching experiments with coal waste from Plant K—concentrations of
selected trace elements in the leachate vs pH 53
23b. Results of dynamic leaching experiments with coal waste from Plant K—concentrations of
selected trace elements in the leachate vs pH 54
XI
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FIFTH ANNUAL PROGRESS REPORT
TRACE ELEMENT CHARACTERIZATION OF COAL WASTES
October 1, 1979—September 30, 1980
by
R. C. Heaton, L. E. Wangen, P. L. Wanek, J. M. Williams,
E. F. Thode, M. M. Jones, A. M. Nyitray, P. Wagner, and J. P. Bertino
ABSTRACT
During the past year we continued our research on environmental control technolo-
gies as they relate to coal preparation wastes and extended our assessments to include
studies of high-sulfur Appalachian coal cleaning wastes.
The most promising control technology for dealing with high-sulfur coal wastes
consists of sequential slurry coating of the waste with lime and limestone. In the
configuration tested (0.35% lime and 1.1% limestone), this technique controlled the
waste effluent quality for 4 months; the effluent pH remained between 7.3 and 7.6, and
the trace element concentrations (Al, Ca, Mn, Fe, Co, Ni, Cu) were within acceptable
limits according to the Environmental Protection Agency Multimedia Environmental
Goals/Minimum Acute Toxicity Effluent system of evaluation. Codisposal of coal
wastes and alkaline soils or mine overburdens is partly effective in controlling the
leachate quality under steady-state conditions. However, none of the materials tested
could control the highly acidic effluents obtained under intermittent leaching conditions.
Comparisons between trace element concentrations predicted by chemical
equilibrium models and those obtained in experiments with coal waste leachates yielded
good agreements for the major cations (Al, Ca, Fe) but, except for fluoride, the major
anions were not well accounted for. The observed trace element concentrations were all
significantly lower than predicted.
Calcination experiments have shown that high-sulfur coal waste from Appalachia
(Plant K) behaves differently than other wastes we have studied. The high cost of this
technology ($1.39 to $9.84/ton product) places it outside the realm of economic
feasibility at this time.
We have also completed an assessment of the Plant K coal wastes. These materials
are similar to those from the Illinois Basin and their leachates are often very acidic, with
pH values sometimes less than 2. Several trace elements have shown discharge severities
greater than unity (Fe, As, Ni, Mn, Al), but iron is by far the worst offender, with values
sometimes greater than 100.
Results of the EPA Extraction Procedure, used to classify solid wastes under the
Resource Conservation and Recovery Act, compare favorably with those of our own
leaching experiments for those elements analyzed (Ag, As, Ba, Cd, Cr, Hg, Pb, Se).
However, coal wastes release substantial quantities of other trace elements not included
in the protocols at present (Fe, Al, Ni, Mn, Zn, Cu).
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EXECUTIVE SUMMARY
In the past, our research on coal and coal wastes
focused on identifying trace elements released in hazard-
ous amounts during weathering and leaching of high-
sulfur coal refuse from the Illinois Basin, and on
evaluating control technologies for this problem. Present
efforts are directed toward further development of these
control technologies and extension of trace element
assessments to the drainages from high-sulfur coals and
coal wastes from Appalachia. Technical highlights and
accomplishments during FY 1980 are summarized in
this section and more detailed discussions are contained
in the main body of this report.
The drainages from many coal waste dumps are often
highly contaminated with trace or inorganic elements.
However, until recently there has been little concrete
information on the quantities released, the controlling
chemistry involved, or the ways to control these releases.
Accordingly, the principal objectives of our program are
to
(1) assess the nature and magnitude of trace element
releases of environmental concern.
(2) reveal experimentally the chemistry controlling
trace element releases.
(3) evaluate and recommend appropriate pollution
control technologies or necessary research and
development programs.
The studies under way are a continuation of experimen-
tal efforts begun in 1976, which were directed toward
identifying and quantifying the trace element releases
from high-sulfur coal wastes from the Illinois Basin. We
now have a good quantitative understanding of the
environmental concerns associated with these wastes and
their drainages. In FY 1979 we began in-depth ex-
perimental evaluations of various technologies for con-
trolling them. Among the methods considered were
codisposal of the coal waste with neutralizing or at-
tenuating agents, containment of waste leachates coupled
with water treatment techniques, and alteration of the
waste to yield an environmentally inert material. Cost
analysis showed the last of these technologies to be too
costly, while the first two were only partially effective, at
least in the configuration studied. In FY 1980 we have
continued to evaluate and improve these technologies,
emphasizing those we consider to be the most promising,
namely, sequential slurry treatment of the coal waste
with lime and limestone and certain codisposal tech-
niques. We also extended our trace element assessments
to include coals and coal wastes from Appalachia.
Technical accomplishments of FY 1980 fall into three
general areas: (1) studies of control technologies for
high-sulfur coal wastes from the Illinois Basin, (2)
evaluation and assessment of coal wastes from Ap-
palachia, and (3) continuing development of procedures
and techniques.
I. ENVIRONMENTAL CONTROL TECHNOLO-
GIES
Studies performed over the past several years show
that the drainages from uncontrolled piles of high-sulfur
coal wastes typically are very acidic (pH values less than
2 have been observed) and contain environmentally
significant concentrations of several trace elements.1"4
This contamination is caused by sulfuric acid generated
within the waste by oxidation of pyrite. In order to
eliminate the contamination one must either prevent the
formation of the acid within the waste, neutralize the acid
in situ after it is formed, or allow the leaching to take
place and treat the effluents to remove the acid and trace
element contaminants. Each of these approaches has
advantages and disadvantages.
In situ neutralization of acid formed within a waste
pile can be accomplished by mixing the coal refuse with
alkaline materials either before or during disposal. We
have demonstrated that if the pH of the waste effluents is
maintained in the proper range, the trace element
concentrations also stay within acceptable limits. The
initial pH of the waste effluent can be easily controlled
by adding hydrated lime to the waste, but this treatment
is only temporary because any excess lime is quickly
washed out of the solid refuse. Ground limestone is more
durable, since it is not soluble in neutral solutions, but it
cannot control the high initial acidities of high-sulfur coal
waste. Although neither the lime treatment nor the
limestone treatment alone is an adequate control technol-
ogy, a combination of the two, using a small amount of
lime to control the initial acidity and a larger amount of
limestone to control the slowly generated acid within the
pile, promises the advantages of both without the
limitations of either. Experiments completed during FY
1980 show that this approach is very effective in
controlling coal waste effluents for periods of up to 4
months.
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Leachates from high-sulfur coal wastes obtained from
the Illinois Basin (Plant B) typically have pH values of
approximately 2.0 or less when subjected to long-term
laboratory weathering experiments. However, when the
same wastes were sequentially treated with 0.35% lime
and 1.0% limestone and subjected to artificial weathering
conditions equivalent to intermittent rains totaling 39 in.
per year, the waste effluents had pH values between 7.3
and 7.6 for nearly 4 months. In addition the trace
element releases were all within acceptable limits accord-
ing to the EPA MEG/MATE (Environmental Protection
Agency Multimedia Environmental Goals/Minimum
Acute Toxicity Effluent) system of evaluation.5 Figure 1
shows the effectiveness of this treatment in controlling
trace element releases from this waste. Cost analyses
carried out in 1978 show that sequential lime/limestone
slurry treatment would cost between 22 and 50$ per ton
of cleaned coal (1978 dollars), which is competitive with
the technologies already in use.
Although the lime/limestone slurry treatment has
provided some very encouraging results, it lasts for only
about 4 months under the conditions of the laboratory
weathering tests. In fact, because the amount of
limestone added is chemically equivalent to only about
10% of the pyrite in the waste, this treatment cannot be
permanent unless oxidation of the waste is somehow
prevented. However, we believe this treatment of the
waste, followed by disposal in an anaerobic environment,
would be useful as a comprehensive waste disposal
strategy. The lime/limestone treatment would neutralize
the acid initially present in the waste and control the
trace element releases until the permanent anaerobic
disposal could be implemented.
Some uncertainties remain concerning the
lime/limestone treatment. Because this treatment has
been evaluated with only one coal waste, we must
determine whether the observed performance is a general
phenomenon or whether it is unique to the material we
tested. In addition, no attempt was made to optimize the
treatment parameters. The effects of compaction of the
waste pile or freeze-thaw cycles have not been studied.
Finally, the mechanism by which this process works is
only partially understood. All of these questions warrant
study and will be addressed in the coming year.
Another way to effect in situ acid neutralization in
coal wastes tis to mix the refuse with alkaline soils or
mine overburdens either before or during deposition in
the waste dump. Alkaline process wastes, such as fly ash,
could also be used. This possibility is attractive because
it would be easy to implement and the required materials
0.001 0.01 0.1 1 10 100
Discharge Severity
Fig. 1.
Discharge severities (leachate concentration/100 X MATE) for selected trace elements in drainages from high-
sulfur coal preparation wastes—untreated wastes (unshaded) and lime/limestone treated wastes (shaded).
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are inexpensive and readily available. Laboratory studies
conducted this year with a variety of soils and process
wastes show that alkaline materials are partly effective in
controlling effluent quality when mixed in with the coal
waste or placed downstream of the waste. Concentra-
tions of aluminum, nickel, fluorine, and arsenic (and the
acidity) were all lower in the leachates for those samples
treated with the alkaline materials. Furthermore, the
concentration decreases coincided with the increases in
pH. However, the concentrations of manganese and iron
were higher in the leachates from the treated samples,
probably because these elements were leached from the
codisposed materials themselves. None of the materials
tested could produce acceptable leachates during the
initial leaching of the sample. The same was true after
regeneration of the waste pile by the passage of air
through the waste. Therefore, codisposal of coal waste
with these types of materials, at least by itself, is not
likely to constitute a workable control technology.
However, information gained from these studies will be
useful in evaluating the effects of the mineralogy and
underlying structure of potential disposal sites on the
waste effluents. We are continuing these investigations in
order to determine which types of soils or underburdens
are the most beneficial and which are the most harmful
to effluent quality.
The most widely used control technology for coal
waste effluents is collection of the acidic drainages
coupled with water treatment, usually alkaline neutral-
ization. This approach is simple and uses proven technol-
ogy. Also, cost analyses carried out in 1978 showed that
this approach typically costs between 7 and 55$ per ton
of cleaned coal, so it is also relatively inexpensive. The
obvious disadvantage is that the water treatment must be
continued as long as the waste pile retains any acid-
generating potential, which can be hundreds of years.
Nevertheless, because this technique is so widely used,
and because its principle, alkaline neutralization, is the
same as that behind the best control technologies so far
devised, additional investigation is warranted.
To study the chemistry of the neutralization process,
we titrated a coal waste leachate with calcium hydroxide
to various pH values and determined the concentrations
of the trace elements left in solution. We then calculated
the expected concentrations using a complex equilibrium
code.6 The calculated and experimental values compare
well for the major cations [calcium, aluminum, Fe(II)
and Fe(III)]. However, the behaviors of the anions of
major interest (sulfate, arsenate, borate, and fluoride) are
not well accounted for in the thermodynamic model,
except for fluoride. In addition, the important trace
element concentrations are all lower than the calculated
values. We speculate that these elements (arsenic, cad-
mium, cobalt, chromium, copper, manganese, nickel, and
zinc) are adsorbed on the hydrated iron and aluminum
hydroxide precipitates. This behavior suggests that
alkaline neutralization of coal waste leachates may
actually be more effective in controlling the release of
trace metal cations than thermodynamic calculations
predict. Although these theoretical calculations cannot
yet describe such complex chemical systems, they are
valuable in identifying the factors controlling the
solubilities of potential pollutants. Therefore, we will
continue this line of investigation next year.
The formation of acid within the coal waste can be
prevented in two ways. One is to dispose of the waste in
an anaerobic environment (nonoxidizing) so that oxida-
tion of the pyrite cannot occur. This is essentially a
return of the coal waste to the type of environment from
which it originally came. Disposal of the waste in this
way is simple in principle, and once the anaerobic
conditions are established, no further treatment is re-
quired to control the waste effluents as long as the
disposal site is not disturbed. However, it takes a
significant length of time to properly structure such a
disposal site, and during this time, the acid generated
within the pile must be controlled. We believe that
combination of anaerobic disposal with a short-term
method, such as the lime/limestone treatment, offers an
acceptable solution to coal waste disposal.
The second way to prevent acid generation is to
destroy the pyrite so that, even under oxidizing condi-
tions, the waste has no acid-generating capability. In past
studies we have shown that calcining, which destroys
pyrite, is effective in controlling the leachabilities of the
trace elements in high-sulfur coal wastes from the Illinois
basin.2"4 Calcining is a one-time, permanent treatment.
Thus, the treated materials can be disposed of by
conventional means without concern for their potential
behavior in the distant and unforeseeable future. How-
ever, the calcining process merely exchanges one prob-
lem for another. The coal wastes are rendered innocuous
because the calcining process drives off the sulfur, which
eliminates the acid-generating capacity of the waste. The
solids are left inert, but the evolved sulfur must be dealt
with, either by flue gas desulfurization or by some
technique of retaining the sulfur in the solid waste. Also,
costs are high-not only for the control of the evolved
sulfur, but also for the energy required to heat the
mineral matter to the required temperatures In fact
our
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cost studies show that the cost of calcining coal wastes
can be as high as $10.00 per ton of cleaned coal (March
1978), clearly placing this technology beyond the realm
of economic feasibility. Nevertheless, we recently con-
ducted some experiments to determine whether waste
from Plant K calcines in the same manner as that from
Plant B. We found that trace element releases from Plant
K mineral wastes, when calcined at the optimum condi-
tions for Plant B, are not as well controlled. The
discharge severities for manganese and nickel remained
larger than unity after calcining, and significant dis-
charge severities (0.1 < DS < 1.0) were observed for
aluminum, copper, and iron. These results were quite
unexpected in view of the similarity of the mineral make-
up of the wastes. Conditions may have not been
optimum for these wastes, or other factors may be
involved, but we have not initiated the experimental
program required to determine the reasons. We believe
that, because the treatment is very expensive, additional
intensive study is unwarranted.
II. ASSESSMENT OF HIGH-SULFUR AP
PALACHIAN COAL WASTES
During the past year we have systematically studied
the refuse from two coal cleaning plants located in
western Pennsylvania. These plants, designated Plants I
and K, process high-sulfur Appalachian coal, although
they use different processes. The laboratory work has
been completed for both plants, but because the data are
complete only for Plant K, the results for Plant K are
presented in this report; results for Plant I will be
presented in the next annual report. Plant K is a jig
operation and is unusual among the plants we have
studied because the fines are not cleaned, but are sent
straight through the plant and combined with the clean
coal. Consequently, the plant output consists of cleaned
coal, coarse mineral matter, and a 60-mesh slurry
effluent. In this study, we have examined only the coarse
refuse, the cleaned coal^ and the raw feed coal.
In general, the mineral content of the waste from Plant
K is comparable to that previously studied from the
Illinois Basin. The Plant K material has a slightly lower
sulfur content, but slightly higher concentrations of
lithium, chlorine, arsenic, cadmium, antimony, and
lutetium. Except for zinc and rubidium, which are
slightly lower in the Plant K waste, all the remaining
elements are present in comparable concentrations. No
marcasite was detected, but the pyrite concentrations
(~25%) are typical of the high-sulfur coal wastes we
have studied. In addition we identified the presence of
siderite (FeCO3). This is the first time we have found this
mineral in coal wastes. The calcium content of the Plant
K refuse is low, which suggests that little or no calcite is
present. This material has little or no self-neutralizing
capacity.
Before chemical and mineralogical analyses, the refuse
from Plant K was separated into seven fractions, based
on the gross external appearances of the various pieces.
Examination of these fractions along with the composite
waste permitted us to derive some very useful informa-
tion about the relationships between some of the trace
elements and the various mineral phases. Most of the
leachable trace elements tend to concentrate in those
fractions containing the highest concentrations of clays
and other silicate minerals. However, certain elements
(selenium, arsenic, antimony, cadmium, and iron) are
associated with the pyritic minerals. These elements are
undoubtedly present in the form of sulfides (or selenide)
and some of them are important because of their
toxicological properties. Leaching studies (described
below) suggest that the chemistry of these elements in the
waste pile effluents is somewhat different than that of the
rest of the trace elements.
We performed micromineralogical studies of these
coal wastes, using electron microscopy coupled with
energy dispersive spectrometry. Because this technique
observes such a small fraction of the sample at any one
time, the results must be interpreted carefully. Never-
theless, one can perform elemental analyses while retain-
ing the spatial resolution of the microscope. This is
difficult, if not impossible, with other techniques. These
studies confirmed our observations that most of the trace
elements are associated with various types of clays. In
addition, the trace elements seem to be present as
discrete mineral phases, rather than in chemical associa-
tions with the gross minerals.
We performed static leaching experiments in which the
coal waste was shaken with deionized water for varying
lengths of time ranging from 1 to 50 days. The mixtures
were then filtered and the filtrate was analyzed for
acidity, specific conductance, and trace element content.
All these measurements increased with leaching time. In
many cases, the leachates were very acidic, with pH
values less than 2, indicating that this waste could
generate drainages of environmental concern. Iron,
arsenic, nickel, manganese, and aluminum had discharge
severities greater than unity, indicating sufficient concen-
trations in the waste effluents to be of environmental
-------
concern. Zinc, cadmium, and copper had discharge
severities between 0.5 and 1.0, suggesting that these
elements may be cause for concern under certain circum-
stances.
The concentrations of several trace elements increase
sharply with increased time, and they continue to
increase even after most of the other elemental concen-
trations have reached steady-state values. These ele-
ments, arsenic, selenium, and cadmium, are associated
with sulfide mineral phases, possibly as sulfides (or
selenide). We surmise that the mobilization of these
elements depends not only on the pH of the leachate, but
also on the rate at which the respective mineral phases
are oxidized.
In addition to the static leaching experiments, we also
performed a series of dynamic leaching experiments with
the coal wastes by placing the coal waste into glass
columns and pumping deionized water through the
columns at a slow and constant rate. The effluents from
the columns were sampled and analyzed periodically for
acidity, specific conductance, and trace element concen-
trations. After all these values had reached steady state,
the leachate flows were stopped for 2 weeks and air was
forced through the columns. The leachate flows were
then resumed and the experiment continued as before
until the trace element concentrations in the effluents
again reached steady state. This experiment is designed
to simulate the weathering of an uncontrolled waste pile
that is intermittently exposed to wet (rain) and dry
cycles. The initial leachates are very acidic when they
emerge from the waste column, with pH values from 1.9
to 2.2. As the leachate flow continues, these decay to
more moderate values (~4). After the columns are
"regenerated" by passing air through them, the initial pH
values are again very low (~2.3 to 2.4). Continuation of
the leachate flow also causes these values to decay to
moderate steady-state values (~4). Trace element con-
centrations behave in exactly the same way as the
solution acidity (Fig. 2). This behavior can be explained
in the following way. Before the experiment the coal
waste is exposed to air in the normal course of handling
and sample preparation. This causes some oxidation to
take place. The oxidation of pyrite within the waste leads
to the formation of sulfuric acid, which accumulates in
the waste until it is washed out by the leachate early in
the leaching experiment. As the leaching proceeds, both
the acidity and the trace element concentrations decay to
more moderate steady-state values. However, when the
leachate flow is interrupted and air is forced through the
column, oxidation again takes place and the resulting
acid accumulates in the waste until leaching is resumed.
Thus when water is again allowed to flow through the
column, the initial effluents are very acidic and the trace
element concentrations are very high. Our observations
Al
Mn
Fe
Ni
Cu
Zn
Cd
0.001
0.01
0.1 1 io
DISCHARGE SEVERITY
Fig. 2.
100
~l—I I I 11
1000
Fig. 2.
Discharge severities (leachate concentration/100 X MATE) for selected trace elements in leachates from PI
K coal preparation wastes as determined by dynamic leaching experiments—initial values (un«h,>H A\ *",
steady-state values (shaded). (unsnaaea) and
-------
of very acidic leachates after air regeneration of the
waste column suggest that this waste has strong acid-
generating tendencies, and that the acid-drainage prob-
lem associated with this waste, significant even under
steady-state conditions, is aggravated when the leaching
is done intermittently.
The initial discharge severities of iron, nickel, and
manganese were all greater than unity, but iron, with a
discharge severity of more than 100, was by far the
worst offender. In addition, zinc, cadmium, aluminum,
and copper had initial discharge severities between 0.5
and 1.0. These elements may pose problems of environ-
mental concern under certain weathering conditions. In
past reports in this series, we showed that trace element
concentrations in the leachates are controlled by the pH.
However, in certain cases (lead, arsenic, and possibly
cobalt and aluminum), other factors are involved. The
most important of these is probably oxidation of the
respective minerals containing these elements.
In summary, the experimental evidence seems to
indicate that the high-sulfur waste from Plant K may
pose problems with serious environmental consequences
unless it is properly disposed of. These problems are
caused by the high acidities and the high concentrations
of several trace elements in the waste effluents. Although
our laboratory leaching conditions may be somewhat
more severe than those encountered in a large waste pile,
it is clear from our field work that there is cause for
concern in the disposal of these solid wastes. The
behaviors of these materials exactly parallel those of the
high-sulfur wastes from the Illinois Basin.1"4 While there
is every reason to believe that the same control technolo-
gies will work for each of these coal wastes, we plan to
test some of the more promising techniques with this
waste as well as that from plants in the Illinois Basin.
in. LEACHING PROCEDURES
Throughout our investigation of coal waste, we have
attempted to devise leaching tests that provide mean-
ingful information on the environmental behavior of
these materials. Accordingly, we have developed several
procedures and have used the results of these tests as the
basis for our predictions on the weathering behaviors of
coal cleaning wastes. However there remains the ques-
tion of how these procedures compare with those used by
other researchers and, in particular, how they relate to
the EPA extraction procedure used to classify wastes
under the Resource Conservation and Recovery Act
(RCRA). We addressed this question by comparing the
results of our leaching procedures to those obtained
using the EPA extraction procedure.
Seven mineral wastes from coal preparation plants in
the Illinois Basin, the Appalachian region, and the
Western US were leached in accordance with the EPA
extraction procedure published in the Federal Register
dated May 19, 1980.7 This amounts to using 100 g of
waste, ground to pass through a 9.3-mm standard sieve
(-3/8 in.), adding 1600 mt of deionized water to the
waste, and agitating for 24 h in an extractor designed to
ensure that all sample surfaces are continuously brought
into contact with well-mixed extraction fluid. The pH
values of the mixtures are monitored during the extrac-
tion and, if the pH is greater than 5, adjustment must be
made by addition of 0.5N acetic acid. After 24 h, the
solids are removed by filtration, and the concentrations
of eight elements (Ag, As, Ba, Cd, Cr, Hg, Pb, Se) in the
filtrate are determined.
The primary differences between our leaching pro-
cedures and that prescribed by EPA are the use of a
higher liquid-to-solids ratio in the EPA test, the examina-
tion of a different set of elements by the EPA test, and
the requirement that alkaline systems be acidified in the
EPA procedure. Compared to leaching tests that we
have used over the past several years in our research on
coal wastes, the results of the EPA procedure compare
favorably with those of our procedures for elements
examined by both.
Among the samples that we leached according to the
EPA procedure, only the western coal waste required
addition of acetic acid to maintain the pH below 5.
Judged according to the criteria in the Federal Register,
all the coal waste leachates had trace element concentra-
tions below the maximum values set by EPA. However,
two factors should be noted. First, iron, aluminum,
nickel, and manganese, the most important elements in
coal waste leachates, are not included in the protocols at
the present time. Second, we believe that the acidification
of neutral or alkaline materials simulates an abnormal
environment for these samples, and is inappropriate for
coal wastes.
-------
RESULTS AND DISCUSSION
I. ENVIRONMENTAL CONTROL TECHNOLO-
GIES
A. Codisposal Techniques
1. Treatment with Lime and/or Limestone. One ma-
jor conclusion from our earlier studies of the environ-
mental behavior of coal refuse materials concerned the
importance of pH in controlling trace element releases
during refuse leaching. In every case in which leachate
pH was maintained at or near the neutral point, only
minimal amounts of trace elements were solubilized by
the leachates. Conversely, when oxidative degradation of
the pyritic materials in the refuse caused leachate
acidities to build up, substantial quantities of aluminum,
manganese, iron, cobalt, nickel, and copper were re-
leased in the acid leachates. This marked dependence of
trace element contamination on ieachate pH suggested
that a potentially valuable way to prevent trace element
releases from discarded refuse materials might be to add
neutralizing agents to the refuse before disposal to negate
leachate acidity as it is formed. We performed several
experiments in which lime or crushed limestone was
mixed with or placed adjacent to high-sulfur coal waste
to observe the leaching behavior. These experiments,
described in Ref. 3, showed this approach to be effective
under the right conditions.
We showed that the use of hydrated lime can control
the effluent pH and is only moderately costly.1 For
example, levels of 0.5 or 1.5% of lime were too low to
neutralize the acid in high-sulfur coal waste from Plant
B. However, levels of 3 and 10% yielded acceptable
leachates over the duration of the experiment. Long-term
effectiveness was not addressed in this experiment.
Similar experiments were done to assess the use of
crushed limestone. Limestone crushed to —3/8 in. was
only partly effective in raising the pH of the leachates
from high-sulfur coal waste. Two possible reasons are (1)
limestone alone cannnot elevate solution pH to very
alkaline levels because of its insolubility and because,
once solubilized as bicarbonate, it tends to form a buffer
system at slightly acid pH. (2) More important, however,
is that calcium carbonate is insoluble except under acid
conditions, so that its neutralization of the leachate is
slow unless the leachates are very acidic. If, in fact, the
effectiveness of limestone is limited by its rate of
dissolution, results should be improved by using pow-
dered limestone instead of crushed limestone because of
the greater surface area.
In addition to direct admixture of lime or limestone to
the coal waste, we also added excess lime (5% in water)
and then neutralized it with CO2. The rationale was that
the excess lime should neutralize the acid initially present
while CO2 precipitates the remainder as a durable
coating of CaCO3 on the coal waste particles. This
coating would then serve the dual purpose of neutralizing
any new acid generated and also act as a barrier to
incoming oxygen, so that further oxidation of the waste
and the resulting acid generation would be retarded. This
procedure was successful in controlling both the acid and
the trace element contents of the leachates.1 However,
the need to add large amounts of gaseous CO2 to a coal
waste slurry makes this scheme impractical on any
realistic scale.
A simpler neutralization and coating scheme would be
to sequentially add a small amount of lime, followed by a
large amount of powdered limestone as a slurry. This
could achieve control of leachate acidity and should be
much easier to implement on a large scale than any
scheme requiring neutralization by CO2. We performed a
long-term experiment in which we examined the
leachates from high-sulfur coal wastes mixed with vari-
ous levels of lime and one mixed sequentially with lime
and limestone. Preliminary results of this experiment are
reported in Ref. 4, which includes partial results from the
first 12 weeks of the experiment. In the following
discussion, we detail complete results of the 10-month
experiment.
A highly acidic Illinois Basin coal waste was mixed in
plastic-lined 55-gal. barrels with wet slurries containing
lime in amounts from 0.17 to 3.3 wt% of the waste. In
one case, 1.1% limestone slurry was mixed in after
0.33% lime had been used. These slurries were screened
to remove excess water and placed in specially designed
disposal boxes. Six boxes of each of the six
lime/limestone/waste mixes were then placed in a pattern
to await wet and dry weathering cycles.
The weathering cycles consisted of weekly additions of
water equivalent to 3/4 in. of rain, which was drained
from each box 24 h later and immediately analyzed for
PH, specific conductance, and iron species. Sample
ahquots were acidified and retained for trace element
-------
analyses to be conducted after the completion of the
experiment. The procedural details of this experiment are
reported in Ref. 4.
Figure 3 shows the pH values of the effluents as a
function of the weathering time. The lime added raised
the initial pH above 5 in all cases; however, the pH
values all dropped to below 4 after only 3 weeks, except
for the sample with the most lime and that containing
limestone. In the sample with the most lime, pH values
were unacceptably high in the beginning. Clearly, lime is
an effective neutralizing agent, but it does not maintain
high pH values for extended times because, first, excess
lime is washed out of the system by water percolating
through the waste, and second, oxidation of the coal
waste is not retarded in any way. As soon as the
neutralizing capacity of the resident lime has been
exhausted the pH drops to levels typical of untreated
coal waste effluents.
Treatment of the waste with lime followed by a
limestone slurry was much more effective in controlling
the effluent pH: the pH remained between 7.3 and 7.6 for
nearly 4 months. The inability of the limestone to
generate strongly alkaline pH values is a distinct advan-
tage, and because it is insoluble, it does not wash out of
the waste easily. Whether the limestone coating actually
retards the oxidation of the waste or whether it simply
neutralizes the acid as it is generated is debatable; it is
effective in controlling pH, whatever the mechanism, for
a significant period of time. Although this treatment is
not permanent, it may be useful as part of a more
comprehensive disposal scheme.
Figure 4 shows the total iron contents of the effluents
as functions of time. The iron values closely parallel the
effluent acidities; that is, when the acidity is high (low
pH) the iron contents of the leachates are high. When the
acidity is low (high pH) the iron concentrations in the
leachates are also low. Sample 6, the lime/limestone-
treated material, is particularly interesting because the
iron levels remain low as long as the pH is maintained in
the neutral region. Consequently, this treatment effective-
ly controlled the pH and the release of iron for nearly 4
months.
In addition to iron, a number of other elements must
be considered. Figures 5 through 10 show the behaviors
of nickel, aluminum, manganese, copper, zinc, and
cobalt. Note that these plots are logarithmic; the actual
concentration ranges involved are much larger than they
appear. In every case, the behavior is the same. When
acidities are low, the concentrations of these elements in
the leachates are also low. Again, control of the pH is a
key to control of the leachate quality. More important,
however, the lime/limestone slurry treatment maintained
acceptable effluent quality for a period of months.
Figure 11 shows the calcium contents of the leachates
as functions of time. The calcium concentrations are
consistently high in all samples. Presumably, the acid
generated within the waste dissolves the calcium com-
pounds, thereby releasing the calcium. Because the
major calcium components, lime or limestone, were
added in substantial amounts, the calcium releases are
predictably large. The behavior of sample 6 is again very
interesting. If retarding the oxidation of the pyrite in the
coal waste (by the formation of a coating around the coal
particles) is a major factor in controlling the acidity of
the leachates, there should be a substantial reduction of
the calcium release from the sample while this mecha-
nism was operative. In fact, sample 6 does show a
reduction in the calcium release during the first 4
months, but this reduction is not very large, so other
important factors must be involved. We conclude that
the major factor in controlling the effluent pH is
probably the neutralization of acid as it is formed in the
waste. If this is true, the major difference between the
lime/limestone treatments and the simpler lime treat-
ments is that the limestone is more durable and not easily
washed out of the system. Thus the treatment should be
effective for a longer period of time than a simple lime
treatment.
Although the degree of control offered by the
lime/limestone slurry is certainly encouraging, the main
point is whether the leachates are harmful to man or the
environment. To determine this, we compared the trace
element contents of the leachates to the Multimedia
Environmental Goals (MEG) that have been set forth by
the Environmental Protection Agency.5 Discharge sever-
ities were calculated by finding the ratio of the observed
trace element concentration to its corresponding ad-
justed ecology Minimum Acute Toxicity Effluent
(MATE) value.5 The MATE values, derived from vari-
ous types of toxicological data, are meant to represent
levels of various chemical moieties above which deleteri-
ous health or ecological effects might occur. The MATE
values were adjusted to account for dilutions of the waste
effluent by multiplying the published MATE value by
100 before calculating discharge severities.* Thus, very
*This dilution factor was recommended by Garrie Kingsbury
of Research Triangle Institute.
-------
Sample No 1
(0 17% CaO)
20
Time (weeks)
Sample No 2
(033% CaO)
30
Time (weeks)
I
D.
Sample No 3
(053% CaO)
20
Time (weeks)
Sample No 4
(1.1% CaO)
20
Time (weeks)
£• 6
Sample No 5
(33% CaO)
20
Time (weeks)
a:
D.
Sample No 6
(0 35% CaO + 1 1% CaCOj)
20
Time (weeks)
Fig. 3.
Dependence of effluent pH on time TOT six treated coal waste samples.
10
-------
Iff
104
?lrf
o.
"-' vS
a
*~ ~i
1,*
10-
in~2
c
! ^
= OS = 1
Sample No. 1
[ (0.175! CaO)
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Time (weeks)
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Sample No. 2
(0.335! CaO)
1 .... 1 .... 1 , i
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Time (weeks)
106
10'
20
Time (weeks)
10°
10"'
Sample No. 4
(1.1% CaO)
10
20
Time (weeks)
30
40
105 r
Sample No. 6
(0.35% CaO + 1.1% CaCO,)
20
Time (weeks)
20
Time (weeks)
Fig. 4.
Concentrations of iron in the effluents from six treated coal waste samples as functions of time.
11
-------
icf
icf
r 10f r
10°
10
10
20
Time (weeks)
Sample No 1
(0 17% CaO)
30
40
itf
icf
_ 10"
10°
10"'
10
20
Time (weeks)
Sample No 2
(0.33% CaO)
30
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1C?
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10"
10
20
Time (weeks)
Sample No- 3
(053% CaO)
30
40
10' r
Iff r
r 101 r
10
10
20
Time (weeks)
Sample No- 4
(1.1% CaO)
30
40
10"
20
Time (weeks)
103
icf
10°
10
10
Sample No 6
(035% CaO 1 1% CaCO,)
20
Time (weeks)
30
40
Fig. 5.
Concentrations of nickel in the effluents from six treated coal waste samples as functions of time.
12
-------
Irf
_lrf
A
| Irf
B
3 Irf
irf
10
20
Time (weeks)
Sample No. 1
(0.17% CaO)
30
40
irf
I Irf T
Irf f
Irf
10
20
Time (weeks)
Sample No. 2
(0.33% CaO)
30
40
irf
irf
| Irf
irf
10
20
Time (weeks)
Sample No. 3
(0.53% CaO)
30
40
103
102
101
10°
10
20
Time (weeks)
Sample No.
(1.1% CaO)
30
40
irf F-
Sample No. 6
(0.35% CaO 1.1% CaCOj)
20
Time (weeks)
20
Time (weeks)
Fig. 6.
Concentrations of aluminum in the effluents from six treated coal waste samples as functions of time.
13
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icf
icf
a 10°
10"
10
20
Time (weeks)
Sample No. 1
(0 17% CaO)
30
40
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Sample No 2
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20 30
Time (weeks)
40
icf
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10"
10
20
Time (weeks)
Sample No 3
(0.53% CaO)
30
40
10?
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10"'
10"
10
20
Time (weeks)
Sample No 4
(1.1% CaO)
30
40
103
icf
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I 10°
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10"
10
20 30
Time (weeks)
40
103
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10"
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Sample No 6
(0.35% CaO 1.1% CaCOs)
20 30
Time (weeks)
40
Fig. 7.
Concentrations of manganese in the effluents from six treated coal waste samples as functions of time.
14
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a
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Sample No. 1
(0.17% CaO)
10
20
Time (weeks)
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a.
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Sample No. 6
(0.35% CaO 1.1% CaCOs)
10
20
Time (weeks)
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40
Fig. 8.
Concentrations of copper in the effluents from six treated coal waste samples as functions .of time.
15
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icf
101
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20
Time (weeks)
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Sample No 3
(0.53% CaO)
20 30
Time (weeks)
10°
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10
20
Time (weeks)
Sample No 4
(1.1% CaO)
30
40
10"
20
Time (weeks)
Irf
irf
6
o,
D-
10"
10"
Sample No 6
(0.35% CaO 1.1% CaCO,)
10 20
Time (weeks)
30
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Fig. 9.
Concentrations of zinc in the effluents from six treated coal waste samples as functions of time.
16
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8
10-
10
20
Time (weeks)
Sample No. 1
(0.17% CaO)
30
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10
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Time (weeks)
Sample No. Z
(033% CaO)
30
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20
Time (weeks)
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(0.53% CaO)
30
40
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r 10°
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10 20
Time (weeks)
30
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Sample No. 5
(3.3% CaO)
20 30
Time (weeks)
40
10°
id
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10
Sample No. 6
(0.35% CaO 1.1% CaCOs)
20
Time (weeks)
30
40
Fig. 10.
Concentrations of cobalt in the effluent from six treated coal waste samples as functions of time.
17
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r
-
-
-
• Sample No. 4
: (11% CaO)
. . . , I . . , , 1 . . . . 1 . . . . -
3 10 20 30 4C
Time (weeks)
; DS i
^ e o
: "• e e
-------
small discharge severities are desirable, whereas those
near one or larger may be cause for concern. The
horizontal dashed lines in Figs. 3 through 11 show the
levels at which the discharge severities are equal to unity,
a simple way to note when the leachates are of accep-
table quality. (A complete table of discharge severities is
included in Appendix A.) The lime/limestone treatment
maintained .acceptable discharge severities for all trace
elements for 4 months. The sample treated with the most
lime also had acceptable discharge severities for a longer
period, but the leachates from this sample were strongly
alkaline during the early parts of the experiment.
Because the pH seems to be the major controlling
factor in trace element leachability, we examined the
functional dependence between the concentration in the
leachate and the pH for each element. The results of
these comparisons are shown in Fig. 12. All data from
the six samples are plotted, regardless of the time or the
treatment process. In spite of the large variations in
conditions among the samples, the correlations are very
good, particularly for the elements present in high
concentrations, which permit better analytical precision.
These results should be compared with calculated values
derived from complex equilibrium codes, but at present,
the solution pH is apparently the major controlling
factor for the effluent quality.
In summary, the lime/limestone sequential treatment
of high-sulfur coal wastes has some attractive features. It
seems to be very effective, at least for some months, and,
as we showed in our previous annual report,4 it is among
the less expensive options. Its major negative aspect is
that it is not permanent. Also, there are several un-
answered questions. For example, is this treatment
effective with different types of coal wastes? What are
the effects of freeze-thaw cycles? What about the
possible effects of compaction of the waste pile? Are
there better treatment conditions: what are they? In spite
of these limitations and uncertainties, we consider this
type of treatment to be one of the best options available
at present, particularly as a part of a more com-
prehensive disposal strategy. We are continuing to
investigate this approach to more thoroughly understand
its limitations and to optimize its performance.
2. Codisposal with Soils or Process Wastes. Previous
batch experiments have shown that natural materials,
such as subsurface soils and mine overburden, have a
considerable potential for reducing acidity and contami-
nant concentrations in leachates from coal cleaning
wastes.4 Another possible disposal scheme that could
mitigate the escape of contaminated leachates from coal
cleaning waste disposal sites is disposal along with
natural or process waste materials. This might involve
dumping coal cleaning waste and alkaline material
together and mixing them by conventional tillage pro-
cedures. The acidity of the waste would be neutralized in
situ, thereby producing a less contaminated leachate by
precipitation of insoluble solids. In addition, because
many soils have significant adsorption capacities, secon-
dary control by adsorption of chemical species not
precipitated by alkaline neutralization is probable. A
variation of this procedure consists of preparing or
selecting a site that can be underlain by subsurface soil
or mine overburden materials with desirable physical and
chemical properties. Such materials, with adequate per-
meability, alkalinity, and adsorption capacities, could
greatly reduce contaminant concentrations in leachates
from coal waste piles, if the leachate were made to
percolate slowly through them.
Two sets of experiments were completed during FY
1980 to investigate the possibility of soil-waste
codisposal as a control measure. The first was a
preliminary experiment using mine overburden. In the
second experiment, several soils were mixed with coal
cleaning waste and leached in columns with water to
determine contaminant concentrations compared with a
control column containing only waste. The geologic
materials used and some of their physical, chemical, and
mineralogical properties are listed in Table I and Appen-
dix B, Table B-I. The materials were all collected from
the Illinois Basin at or near active coal mines. The
materials were air dried, crushed to —3/8 in. with a jaw
crusher, and subsampled using a sample splitter.
a. Experiment A: Attenuation of Acidity and Trace
Elements by a Calcareous Mine Overburden. This ex-
periment was designed to investigate three possible
treatments for acidity and trace element attenuation by a
mine overburden collected above Kentucky coal seam
11.
For the first treatment, we used a mixture of 422 g of
—3/8-in. coal cleaning waste and 278 g of —3/8-in. soil.
We used enough soil to neutralize 150% of the acidity hi
the coal waste. Acidity was determined by titration of
19
-------
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Iff
1U
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Fig. 12b.
Concentrations of selected trace elements in treated coal waste effluents vs pH.
21
-------
TABLE I
PHYSICAL AND CHEMICAL PROPERTIES OF
MATERIALS USED IN ATTENUATION AND
CODISPOSAL EXPERIMENTS
Cation Free Particle
Carbonate" Organic Exchange Iron Clay' Sizeg
pHa (%) Matterc(%) Capacityd(meq/100g) Oxidese(%) (%) (mm)
Seam 11
Overburden 7.6 3.8 3.2 9.8
Seam 12
Overburden 7.8 1.4 3.2 7.5
Acidic Loess
Subsoil (OKA W) 4.8 0.5 1.5 24.1
Calcareous Till
Subsoil (BS3) 7.9 7.1 0.1 14.5
Quarry
Limestone (HI) 7.5 - - —
1.4 0 0.21
2.5 9.5 0.18
0.8 22.0 <0.074
3.5 28.6 0.17
0 - 0.15
apH made on filtrate after 16 h water-soil equilibration on shaker at 2:1 watensoi) ratio.
bCarbonate by rapid titration method.
°Walkley-Black.
dAmmonium acetate extraction following saturation with sodium acetate.
'Sodium-dithionite extraction.
fPipet sedimentation.
'Mass-median diameter by sieve analysis.
-------
waste leachate. Soil alkalinity was based on titratable
carbonate (Table I). Codisposal with —3/8-in. soil should
be feasible because such sizes can be realized at field
sites.
For Treatment 2, we used the same mixture and
capped it with 92 g of the same soil ground to a mass
median diameter (MMD) of 0.21 mm. Water first flowed
through the soil-waste mixture and then through the
finely ground soil cap.
Treatment 3 consisted of 422 g of —3/8-in. waste
topped by a 278-g layer of ~20- to 50-mesh soil (MMD
= 0.21 mm). (No soil was mixed with the waste for this
case.) Water first flowed through the waste and then
through the finely ground soil.
Treatment 4 consisted of 422 g of —3/8-in. waste as a
control.
All columns were leached for 21 days with deionized
(Milli-Q) water at 10 m//h until 5 f had passed through
each. Flow was directed upward. The column, influent
water, and effluent leachate were maintained under an
argon atmosphere throughout in an attempt to prevent
oxidation of Fe(II) to Fe(III). We monitored Eh, pH,
conductivity, Fe(II), and total dissolved Fe throughout.
After leaching stopped, water-saturated air was forced
through each column for 2 weeks to promote pyrite
oxidation in an attempt to regenerate acidity and high
trace element levels. After oxidation, each column was
leached with about 1 t of deionized (Milli-Q) water and
analyzed as above. Selected aliquots were analyzed for
iron, aluminum, manganese, nickel, and arsenic. This
subset of elements was selected as being indicative of
general trace element behavior.
Complete results of this experiment are listed in
Appendix B, Tables B-II through B-V. Results are shown
in Figs. 13a and b. Concentrations of hydrogen,
aluminum, nickel, fluoride, and arsenic were generally
lower in the effluents from the three columns containing
soil than in those of the control. In contrast, manganese
concentrations were much higher and Fe(II) slightly
higher in the soil-treated column leachates compared
with those of the coal waste control. Treatment 1 is the
least effective overall, at least during the initial leaching
by the first liter of effluent water. However, none of the
treatments alone produced an acceptable leachate during
initial leaching by the first liter. Arsenic is the only
contaminant satisfactorily controlled, but only by treat-
ments 2 and 3.
After regeneration by oxidation with water-saturated
air, effluent pH values of all four treatments decreased to
low levels for the first few hundred milliliters. However
the soil-treated columns exhibited more rapid pH in-
creases than did the control. Iron concentrations were
quite high after regeneration. Surprisingly, aluminum,
manganese, nickel, and fluorine concentrations were
higher in the effluents from soil-treated waste columns
than from the control after oxidation. Arsenic was also
higher, except in treatment 3. Except for manganese,
these higher concentrations in soil-treated columns after
regeneration are probably a result of acid leaching or
dissolution of elements previously attenuated by ion
exchange or precipitation at higher pH. In general,
effluent trace element concentrations after air regenera-
tion were quite high for all elements compared with initial
effluent concentrations from the control, showing that
considerable pyritic oxidation occurs with soil treated
coal waste.
This experiment was designed to test the three soil
treatments for effectiveness in reducing contaminant
levels in the effluents from coal cleaning wastes. Treat-
ment efficacy can be judged by three criteria:
(1) ability to reduce the high contaminant levels in the
first few volumes of effluent to environmentally
acceptable levels,
(2) ability to maintain steady-state concentrations at
low levels, and
(3) ability to prevent oxidation of pyrite during post-
burial air infiltration.
Regarding the first criterion, contaminant concentra-
tions for all treatments are not reduced enough to use
any of these as a primary control. In only one case
(arsenic in treatment 3), was the initial effluent concen-
tration sufficiently low.
These treatments also fail to meet the third criterion.
That is, if air contacts the treated materials, appreciable
pyritic oxidation occurs, resulting in the production of
considerable additional soluble acidity and chemical
elements.
Only the second criterion was met with some success.
Steady-state concentrations of aluminum, arsenic,
fluoride, and nickel are generally maintained at levels low
enough to satisfy most environmental concerns. (Nickel
and fluoride concentrations in treated columns are the
same as those in the control.) Treated columns also
maintain high effluent pH (> 6), compared with the
control containing coal waste only. However, "steady-
state" concentrations of manganese and ferrous iron are
too high in all treated columns.
In the present experiments, treatments 1 and 2 used
—3/8-in. soil mixed with the coal waste because this size
would most likely be used in a practical application
23
-------
LEGEND
n= CONTROL
o = TREATfl
A = TREAT|2
« = TREATI3
0.0 1.0
2.0 3.0 4.0 5.0 6.0
Volume (Liters)
Detection Lim
LEGEND
t> = CONTROL
° = TREAT|1
» = TREATJ2
«=TREAT|3
2.0 3.0 4.0 5.0 6.0
Volume (Liters)
7.0 8.0
0.0 10 2.0 3.0 4.0 5.0 6.0 7.0 8.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
LEGEND
o = CONTROL
o = TREAT*!
A=TREAT|2
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Volume (Liters)
9
T-
So
1/1^
<2:
O,
'o
^~
9
' ^\ i
A \ a
'V ^
'•. V Detec t'o" 1 !T»J
\ '- \
LECOC
a . CONTROL
o . TREAT! 1
> A . TREAT12
1 . . TREAT}]
Volume (Liters)
Fig. 13a.
Behaviors of pH, Fe(II), Al, Mn, F, and As vs effluent volume for the four treatments of Experiment A.
24
-------
0.0
1.0
2.0 3.0 4.0 5.0 6,0
Volume (Liters)
7.0
8.0
Detection ^Limi
LEGEND
o - CONTROL
o = TREAT»1
» = TREAT02
o = TREAT^3
0.0
1.0
2.0 3.0 4.0 5.0 6.0
Volume (Liters)
8.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Volume (Liters)
Fig. 13b.
Behaviors of Ni, Fe(ni), and specific conductance vs
effluent volume for the four treatments of Experiment A.
where overburden is codisposed with waste. However,
we know that limestone, to be an effective treatment of
acidity, should be ground to a small particle size because
of the low solubility of limestone at high pH (> 6), and
because limestone particles are deactivated by coating
with sulfates and hydroxides formed as the coal refuse
leachate is neutralized. Nevertheless, we hypothesized
that, under water-saturated conditions, —3/8-in. soil
might disperse, thereby providing ample surface area for
neutralization.
Apparently the soil did not disperse and create enough
additional available soil alkalinity to maintain a high pH
during the production of initial leachate. However, there
was sufficient alkalinity to eventually increase pH of the
—3/8-in. soil-treated columns to a value above 6 after
passage of 1.25 ( of leachate. This compares to a pH
value of 2.1 for the control at a corresponding volume.
The two columns capped with finely ground soil reached
a pH of 6 after passage of only 0.5 (. After removal of
most Fe(II) and Al from the leachate, there was ap-
parently adequate alkalinity available to produce a near-
neutral leachate. It is possible that a slower leachate flow
rate could provide more significant attenuation of
hydrogen ion by this soil. Also, codisposal by mixing soil
and waste might be more effective if the soil is finely
ground. The next set of experiments addresses these
possibilities.
These experimental results indicate that none of these
soil-waste codisposal methods is adequate for controlling
acidity and contaminant levels in leachates likely to be
produced from water percolating through coal cleaning
waste disposal piles.
b. Experiment B. Codisposal of Coal Cleaning Waste
with Finely Ground Subsoils. This experiment was
designed to test the effectiveness of codisposing soil and
coal cleaning waste by mixing and burying them togeth-
er. To ascertain whether such a procedure would be
useful, finely ground soils (Table I) were completely
mixed with —3/8-in. waste. Such mixing with finely
ground soils is probably the optimum procedure possible
but is probably unattainable in the field. However, we
chose this procedure because a definitive answer to the
technical feasibility of this control was desired. Also, if
the results were unfavorable, no method practical in the
field could be expected to be successful.
An amount of soil or overburden material having
enough carbonate content to neutralize 150% of the coal
waste acidity was mixed with the waste material in each
25
-------
column. One column (seam 11 overburden) was dupli-
cated and left open to air to determine any difference in
its behavior compared with columns maintained under
argon (anoxic conditions).
About 4 ( of distilled water was passed through each
column (upward flow) at a rate of 4-6 mif/h. Then the
soil-waste mixtures were removed from the columns,
allowed to air-oxidize for several days, and batch-
leached using a 5:1 water-to-solid-mass ratio. Column
influent, effluent, and batch leachates were monitored for
pH, specific conductance, total iron, Fe(II), aluminum,
arsenic, fluoride, manganese, and nickel. Ferric iron was
determined by the difference between total iron and
ferrous iron.
Raw results of this experiment are listed in Appendix
B, Tables B-VI through B-XII. The results are sum-
marized in Tables II-VIII and Figs. 14a and b. The
behavior of eluent pH is discussed first because it is of
principal importance to the chemistry of the other
measured components. The pattern of eluent pH vs
volume falls into the three patterns shown in Fig. 14a.
The waste alone gives an initial eluent pH value of about
2.0, which slowly rises to about 2.5 after passage of 3 (
of water. (This quantity of water corresponds to an eight-
fold water-to-waste ratio). The eluent from the waste
treated with acid soil varies from an initial pH of 3.7 to
3.5 after 3 f of water is added. Thus, the acid soil does
not raise leachate pH adequately and very little contami-
nant control is expected by the precipitation of solids. In
contrast, alkaline soil treatment results in initial pH
values between 4 and 5, rising fairly quickly to > 6 after
passage of 1.4 t of eluent. Thus, some control by alkaline
neutralization would be expected for these calcareous
materials.
General patterns of eluent concentrations for Al,
Fe(II), Mn, F, Ni, and As are also illustrated in Figs. 14a
and b for the control and for acid and alkaline soils.
These patterns show that, for treated wastes, the concen-
trations of most of the measured species decrease rapidly
with increasing eluent volume to values far below those
of the control coal waste. Manganese is the major
exception; it is apparently leached from the soil materi-
als, themselves. These concentration decreases appear to
coincide with pH behavior for the most part. These
curves also show that air oxidation, after leaching,
regenerates the low pH and high contaminant concentra-
tions, once again pointing out the necessity for prevent-
ing air infiltration into abandoned coal waste dumps.
Quantitative aspects of these control experiments are
discussed with reference to Tables II-VIII. In Tables III-
VIII, we have listed the total amount of contaminant
released per gram of coal waste in the first 3 f of eluent,
TABLE H
EFFLUENT pH OBSERVED IN EXPERIMENT B DURING
THE FIRST LITER OF ELUENT, AFTER ATTAINMENT OF
NEAR STEADY STATE AND AFTER OXIDATION BY AIR
Sample
Soil:
Waste
Ratio
Initial8
pH
Steady -
State
pH
After
Oxidation
pH
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS 3
Quarry
Limestone
-
0.67
0.67
1.78
5.38
0.36
0.087
1.9 -
4.2 -
4.1 -
4.0 -
3.6 -
4.2 -
3.8 -
2.4
6.4
5.0
5.2
3.9
6.2
5.4
2.7
7.9
8.0
7.3
3.3
8.0
8.0
2.3
3.0
2.9
2.8
3.0
2.4
6.4
'Initial pH over first liter of effluent.
26
-------
TABLE III
SUMMARY OF in situ ATTENUATIONS OF ALUMINUM
RESULTING FROM CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS AND A QUARRY LIMESTONE
Al Concentration (mg/l)
Sample
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS3
Quarry
Limestone
Soil:
Waste
Ratio
0.67
0.67
1.78
5.38
0.36
0.087
Al Released "
Total
(mg)
360
0.36
1.32
24
23
0.10
0.29
per gram
of Waste
0.99
0.0010
0.0037
0.113
0.242
0.0002
0.0005
Avb Cone
120
0.12
0.44
8
7.7
0.03
o.iq
Steady
State
-19
<0.2
<0.2
<0.2
2.5
<0.2
<0.2
After
Oxidation
44
28
34
1.6
11
84
0.3
'Milligrams of Al released into first 3 ( of eluent.
""Average concentration in first 3 (.
TABLE IV
SUMMARY OF in situ ATTENUATIONS OF IRON (II)
RESULTING FROM CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS AND A QUARRY LIMESTONE
Sample
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS3
Quarry
Limestone
Soil:
Waste
Ratio
0.67
0.67
1.78
5.38
0.36
o.oa7
Feui)
Total
(g)
3.73
1.82
1.70
2.40
0.254
1.68
2.76
neieasea -
per gram
of Waste
0.0100
0.0050
0.0047
0.0111
0.0027
0.0038
0.0050
revii; ^
Avb Cone
(mg/D
1240
607
567
800
85
560
920
'Unueniruu
Steady
State
200
<0.02
<0.02
<0.02
30
<0.02
<0.02
ion vi«S/*;
After
Oxidation
640
156
198
152
36
566
4
"Grams of Fe(II) released into first 3 ( of eluent.
bAverage concentration in first 3 (.
27
-------
TABLE V
SUMMARY OF in situ ATTENUATIONS OF MANGANESE
RESULTING FROM CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS AND A QUARRY LIMESTONE
Mn Concentration (mg/l)
AvB Cone Steady After
(mg/,6) State Oxidation
Sample
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS3
Quarry
Limestone
Soil:
Waste
Ratio
0.67
0.67
1.78
5.38
0.36
0.087
Mn Released0
Total
(rag)
7.4
40.4
59.7
46.4
104
149
16.4
per gram
of Waste
0.020
0.112
0.166
0.215
1.11
0.339
0.030
2.5
13.5
19.9
15.5
34.7
49.7
5.5
0.6
0.8
20
<2
<0.2
1.4
28
21
6.4
31
11.3
0.8
"Milligrams of Mn released into first 3 ( of eluent.
bAverage concentration in first 3 (.
TABLE VI
SUMMARY OF in situ ATTENUATIONS OF FLUORINE
RESULTING FROM CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS AND A QUARRY LIMESTONE
Sample
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS3
Quarry
Limestone
Soil:
Waste
Ratio
0.67
0.67
1.78
5.38
0.36
0.087
F Released8
Total
(mg)
7.75
-0.2
-0.2
1.52
1.48
c
c
per gram
of Waste
0.021
-0.0005
-0.0005
0.0071
0.016
c
c
F Concentration
Avb Cone
(mg/J!)
2.6
<0.2
<0.2
0.5
0.5
C
C
Steady
State
0.4
<0.2
<0.2
<0.2
-0.25
<0.2
<0.2
(rag/*)
After
Oxidation
0.68
2.6
2.9
1.6
0.9
3.3
<0.2
"Milligrams of F released into first 3 ( of eluent.
bAverage concentration in first 3 (.
CA11 concentrations less than detection limits (0.2 mg/V).
28
-------
TABLE VII
SUMMARY OF in situ ATTENUATIONS OF NICKEL
RESULTING FROM CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS AND A QUARRY LIMESTONE
Sample
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS3
Quarry
Limestone
Soil:
Waste
Ratio
0.67
0.67
1.78
5.38
0.36
0.087
Ni Released a
Ni Concentration
Total
(mg)
7.41
6.68
6.32
8.04
2.13
2.41
4.45
per gram
of Waste
0.020
0.018
0.017
0.037
0.023
0.005
0.008
Avb Cone
2.5
2.2
2.1
2.7
0.7
0.8
1.5
Steady
State
0.5
<0.01
<0.01
0.02
0.2~
<0.01
<0.01
After
Oxidation
1.1
2.0
2.5
0.47
0.51
3.0
0.44
'Milligrams of Ni released into first 3 ( of eluent.
bAverage concentration in first 3 (.
TABLE VIII
SUMMARY OF in situ ATTENUATIONS OF ARSENIC
RESULTING FROM CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS AND A QUARY LIMESTONE
As Concentration (mg/£)
Sample
Control
Seam 11
(Argon)
Seam 11
(Air)
Seam 12
OKAW
BS3
Quarry
Limestone
Soil:
Waste
Ratio
0.67
0.67
1.78
5.38
0.36
0.087
As
Total
(mg)
1.15
0.0064
0.0051
0.0110
0.0117
0.0021
Released a
per gram
of Waste
0.0032
1.8E-5
1.4E-5
5.1E-5
1.2E-4
4.8E-6
8.0E-4 1.5E-6
'Milligrams of As released into first 3 ( of eluent.
bAverage concentration in first 3 (.
Av" Cone
(mg/l)
0.38
0.0021
0.0017
0.0037
0.0039
0.0007
2.7E-4
Steady
State
0.08
<0.001
<0.001
<0.001
0.003
<0.001
<0.001
After
Oxidation
0.14
0.004
0.007
0.005
0.004
0.052
0.001
29
-------
II
9
8
7
6
5
4
"2
2
1
°
1 1 1 — 1
rniMTnni —
ACID SOIL °
CALCAREOUS SOILS <
AND o-
LIMESTONE x
o
^^^ \ x.
.,' \
s' \
^ \
./ \
_ ,/
—
—
^— -— "
1 1
31234
-
UJ
Xx Z ~
•»*-
UJ —
\
\
\
\ —
\
~^^
~**
—
ELUENT VOLUME (£)
1000
ACID SOIL
CALCAREOUS
SOILS
AND
LIMESTONE
234
ELUENT VOLUME U)
ELUENTVOLUMEU)
Fig. 14a.
General patterns of pH, Al, and Fe(II) in effluents from columns containing coal waste alone, coal waste plus
an acidic soil, and coal waste plus calcareous soils.
30
-------
100
10
o>
1.0
O.I
CONTROL
• ACID SOIL
CALCAREOUS SOILS
AND
LIMESTONE
I i
1234
ELUENT VOLUME (I)
o>
IUU
10
1.0
a'c
z ' 1 ' |
CONTROL
ACID SOIL
:
CALCAREOUS SOILS
AND
LIMESTONE
r\ -
I \ OXIDATION -^
_ \
\ \
r\N^-_________ ,
-\ "-^ ;
- \ ^-—y/
V, i , i/
31234
-
r _
/ _
/ :
ELUENT VOLUMEU)
ACID SOIL
CALCAREOUS SOILS
AND
LIMESTONE
1.0 —
0.01
234
ELUENT VOLUME (jj)
O.I
0.01
0.001
\
- CONTROL
ACID SOIL
-CALCAREOUS SOILS
AND
LIMESTONE
OXIDATION
1234
ELUENT VOLUME (£)
Fig. 14b.
General patterns of Mn, F, Ni, and As in effluents from columns containing coal waste alone, coal waste plus
an acidic soil, and coal wastes plus calcareous soils.
31
-------
the approximate concentrations at which a near steady
state was attained after passage of several volumes of
water, and the concentrations measured after oxidation
by air. Each soil material should be compared with the
control (no treatment).
Three criteria determine the efficacy of these environ-
mental controls:
(1) control of initial large quantities of contaminant,
(2) control of steady-state concentrations at accep-
table levels, and
(3) control subsequent to oxidation after leaching of
initial contaminants.
Based on criterion (1), fluoride, aluminum, and arsenic
are adequately controlled by some of the materials. The
elements Fe(II), Mn, and Ni are not controlled and their
concentrations remain unacceptably high. The pH values
may not be acceptable depending on the water quality
criteria used.
Steady-state concentrations are quite low in general,
and thus, would be acceptable by most standards of
water quality. The only exceptions are in the acidic
OKAW soil where concentrations remain high for all
contaminants except arsenic.
Trace element concentrations and pH after oxidation
caused by allowing air to penetrate the soil-waste
mixtures are, in general, not well controlled. Arsenic is
an exception for several of the materials. Also the
limestone treatment appears to be effective at main-
taining lower concentrations and a high pH (6.4) after
oxidation.
For each soil material, some codisposal mixture would
probably maintain relatively low contaminant levels.
However, to be practical in the field (using attainable
ratios of soil to waste, mixing of materials, particle sizes
reasonably obtained by conventional tillage procedures),
we must conclude that codisposal of calcareous soil
materials with die coal waste will not adequately control
levels of several soluble chemical species present in coal
waste. It will be necessary to provide a more readily
soluble alkaline substance, such as Ca(OH)2, than the
carbonate minerals present in soils to control the large
quantities of contaminant initially present in freshly
disposed coal waste (or prevent their release by some
other method). At present, our belief is that
lime/limestone codisposal is a better control method than
codisposal with soils.
B. Coal Waste Effluent Neutralization
Previous laboratory experiments in this program have
shown the effectiveness of alkaline neutralization for
limiting concentrations of inorganic chemical compo-
nents in acidic leachates from coal cleaning wastes.
Although it is generally assumed that these controls are
caused by precipitation of insoluble carbonates, hydrox-
ides, or other solids at the higher pH values attained, this
assumption has not been investigated either experimen-
tally or theoretically. As a result, we investigated the
chemistry of a coal waste leachate system as a function
of pH using MINEQL, a complex chemical equilibrium
model designed for aqueous systems.6 This study was
made to test the applicability of chemical
thermodynamic principles in understanding factors con-
trolling the solubility of trace elements in a complex coal
waste leachate. Results of the calculations were com-
pared with the results of laboratory neutralizations of a
waste leachate with Ca(OH)2. In addition, the speciation
of solution components and their controlling solids as
predicted by the chemical equilibrium model were de-
termined. Appendix C gives details on this investigation,
including figures that compare empirical and theoretical
(calculated) values. The most significant results of this
work are summarized below.
Equilibrium concentrations were calculated using
MINEQL for 24 chemical components, including the 11
elements identified as potential problems in coal waste
leachates.3 These were done at incremental pH values
from 1 through 14 and for the specific pH obtained after
the Ca(OH)2 additions in the laboratory experiments.
From these, total solution concentrations were calculated
for comparison with experimental results. [After
Ca(OH)2 additions, chemical analyses were performed
only for the 13 components listed in Table IX.] For
thermodynamic predictions, multivalent species were
assumed to be as follows; arsenic as AsO43~, chromium
as Cr(III), copper as Cu(II), and manganese as Mn(II).
These assignments are consistent with a system con-
trolled by the oxidation potential of an Fe(II)-Fe(III)
couple. Because the experiments were performed under
an argon atmosphere to prevent oxidation of Fe(II) to
Fe(III), this reaction was not allowed in the
thermodynamic calculations. The argon atmosphere also
eliminated the need to consider CO2(g) exchange with
our solutions.
32
-------
TABLE IX
TOTAL SOLUTION CONCENTRATIONS OF THIRTEEN CHEMICAL COMPONENTS IN COAL WASTE
LEACHATES AS MEASURED AFTER ADDITIONS OF CALCIUM HYDROXIDE AND AS PREDICTED BY A
CHEMICAL EQUILIBRIUM MODEL
Lime
Added
(mmole)"
0
2.16
4.75
5.8
6.7
8.11
pH
2.25
2.73
5.82
6.49
8.09
10.18
Data
Source
rneas.
calc.
meas.
calc.
meas.
calc.
meas.
calc.
meas.
calc.
meas.
calc.
Final Element Concentration (mg/f)'
Ca
350
350
540
393
430
447
450
523
500
573
490
664
Al
370
370
370
370
0.46
0.30
<0.1
0.002
<0.1
0.001
1.1
0.17
Fen
1680
1680
1800
1680
1350
1260
620
1200
2.2
14.7
<0.02
0.01
Fein AsOj-
1630 0.76
1550 0.76
160 0.26
70 0.76
<0.02 <0.02
0.002 0.76
<0.02 <0.02
0.0004 0.76
<0.02 <0.02
l.E-5 0.76
<0.02 <0.02
0.0006 0.46
Cd
0.21
0.21
0.23
0.21
0.08
0.21
<0.03
0.21
<0.003
0.21
<0.009
0.21
Co
3.5
3.5
3.7
3.5
2.8
3.5
0.5
3.5
<0.02
0.042
<0.02
0.04
Cr
0.43
0.43
0.28
0.43
<0.01
0.43
<0.01
0.13
<0.1
0.086
<0.01
0.43
Cu
0.09
0.09
0.11
0.09
0.01
0.09
<0.01
0.09
<0.01
0.09
<0.01
0.0003
F
81
81
86
81
2.0
4.0
4.2
3.1
10
2.9
12
2.6
Mn
9.9
9.9
10.1
9.9
10.8
9.9
8.1
9.9
0.3
8.3
<0.02
0.30
Ni
7.5
7.5
7.7
7.5
3.8
7.5
0.5
7.5
<0.02
0.15
<0.02
0.0001
Zn
16
16
17
16
3
16
0.5
11.4
<0.02
1.2
<0.02
0.10
"Speciation used for equilibrium calculations: Ca, Cd, Co, Cu, Mn, Ni, and Zn divalent cations; Al, Cr as trivalent cations; F; AsOj .
bmmoles added to leachate (final volume 75 ml).
-------
Comparisons of measured and predicted total soluble
species concentrations after lime additions show good
agreement for fluoride and the major cations Ca, Al,
Fe(II), and Fe(III), but very poor agreement for trace
elements As, Cd, Co, Cr, Cu, Mn, Ni, and Zn. These
comparisons are shown in Table IX and illustrated for
Fe(ni), AsO4~3, and Zn(II) in Fig. 15.
Total solution concentrations of ferric iron (Fig. 15)
were maintained at low levels by the precipitation of
Fe(OH)3(s) in this system from pH 4-12. No significant
solid forms of arsenate are predicted below a pH of 9 in
this coal waste leachate. Laboratory measurements show
arsenic concentrations to be lower than the detection
limit of 0.01 mg/( at pH 8.09 and 10.18. This is an
approximate 500-fold discrepancy between measured
and predicted concentrations (Fig. 15), indicating that
some very important factor controlling AsO43~
chemistry in this system is not accounted for by the
thermodynamic model. The comparison between meas-
ured and predicted concentrations for Zn(II) is in-
termediate between the extremes shown by Fe(III) and
AsO43~. Predicted zinc concentrations decrease from 16
mg/( at pH 4.0 to a minimum of ~0.02 mg/f at pH 9.0,
followed by a rapid increase to 10 mgj( at pH 12.
Predicted zinc chemistry is almost completely controlled
by the formation of soluble free cation and ZnSO4 ion
pairs below pH 7. By pH 7, nearly half the zinc is
precipitated as the silicate, which, together with the
insoluble hydroxide, limits soluble zinc to low concentra-
tions between pH 7 and 10. Above pH 11, the formation
of the negatively charged Zn(OH)3 complex begins to
return zinc to a soluble form in appreciable quantities.
Measured zinc concentrations, after addition of
Ca(OH)2, begin to decrease at pH 5.82 and drop to
values significantly lower than predicted (Fig. 15) be-
tween pH 6 and 10.
Similar to arsenic and zinc, measured concentrations
of cadmium, cobalt, chromium, copper, manganese, and
nickel are comparable to predicted concentrations at pH
2.73. In general, measured values of these elements begin
to diverge to values lower than predicted at pH 5.82 and
above. Of these, measured concentrations of nickel are
substantially lower than predicted at pH 6.49, whereas
measured values of manganese are substantially lower
than predicted only at pH 8.09. Thus for all the trace
elements except fluoride, measured concentrations fall
below predictions, often by a considerable amount.
That the two major cations (aluminum and iron) are
well accounted for in these calculations and that a charge
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
10°
O
<
00 20 40 60 8.0 10.0 120 140 16.0
pH
00 20 40 60 8.0 10.0 130 140 160
2 x I O"3
Fig. 15.
Concentrations of Fe(II), As, and Zn in coal waste
leachates vs pH—comparisons of values predicted by
thermodynamic calculations with those experimentally
observed after additions of calcium hydroxide to coal
waste leachates.
34
-------
balance to within 10% is obtained suggests that all of the
significant ligands have been included in the
thermodynamic calculations. Consequently, we do not
believe that some unknown solid phase can be invoked to
account for the lower measured concentrations. The
major cationic components (aluminum and iron) in these
solutions form amorphous hydrous solid phases at all
measured pH values. At pH > 5.5, virtually all of the Al
and Fe(in) exist in the form of colloidal hydrous oxides.
In addition, substantial quantities of other solid phases,
CaSO4(s), Fe(OH)2(s), FeCO3(s), and CaF2(s), are pres-
ent, which may very well serve as sorbing sites for trace
elements. Several investigators8"10 have shown that sub-
stantial quantities of various trace components are
removed from solution by adsorption onto the surfaces
of hydrous oxides; we postulate that such a mechanism
is responsible for the discrepancy between experimental
and predicted trace element concentrations in this work.
In general, chemical speciation is controlled by the
major cations and anions and pH (Appendix C). The
only anions present in substantial quantities are CO32~,
S042~, and F~. At low pH, CO32~ is not present in an
unprotonated form, thus, at pH 2.73, the only solid
phases involve Fe(III) and Ca, which are present in high
concentrations. Soluble cation species are dominated by
free ions and sulfate or bisulfate complexes. At low pH,
weakly acidic anions, CO32~, SiO32-, B(OH)~ and
AsO33~, exist primarily as uncharged completely pro-
tonated species, whereas the strongly acidic anions are
either complexed with Al, in the case of F~, or pre-
cipitated as solids, in the case of PO43~.
As pH increases, hydroxide and anions of weak acids
become increasingly abundant, and therefore, important
in solution chemistry. Solubility products of several
carbonates and hydroxides involving both major and
trace cations are exceeded. For example, at pH 6.49, Al
has been removed from the solution by precipitation as
A1(OH)3, 70% of Cr exists as Cr(OH)3, and 30% of
Fe(II) is precipitated as the carbonate. Such trends
continue as pH increases until most cations are main-
tained at relatively low concentrations at pH 8.09
because they precipitate as carbonates or hydroxides, or,
in the case of zinc, as the silicate. At still higher pH
(>10), many cations return to soluble forms as a result of
the formation of negatively charged hydroxy species.
The anions of major interest (SO42~, F~, B(OH)4~,
As043~) are not well controlled by precipitation as solid
phases except for F~. Predicted concentrations of F~ are
maintained below 4 mg/f at pH > 5.82. No solid phases
of AsO43~ are indicated before the formation of
Ca3(AsO4)2 (s) at pH > 10. Solid phases involving boron
are nonexistent according to the calculations. A con-
siderable amount of CaSO4(s) is predicted at ill pH
values between 2.73 and 10.18, but because of its large
abundance (12 000 mg// in the initial leachate), SO42~
concentrations remain high at all pH.
In summary, these results show that application of
chemical thermodynamic principles to problems in en-
vironmental control can assist in the understanding of
factors controlling the solubility of potential contami-
nants. Alkaline neutralization is even more effective than
anticipated, based on solubility controls alone. We
believe this to be due to adsorption of trace components
onto the surfaces of solids formed as the pH increases.
Adsorption itself is a sensitive function of pH and might
be maximized by proper selection of final pH.
C. Calcination of Coal Wastes
In previous reports, we demonstrated that calcination
can convert high-sulfur coal wastes to innocuous
forms2"4 because, at high temperatures (600-1000°C),
the sulfur is driven off in the form of SO2, and thus the
acid-generating potential of the waste is drastically
reduced.4 In addition to sulfur, however, other volatile
elements (bromine, cadmium, and lead) are driven off in
appreciable quantities. Consequently, the calcining of
coal wastes is a conversion process in which the problem
of acid drainage is alleviated while incurring an air
pollution problem caused by SO2 and volatile trace
elements. We reported some attempts at controlling the
sulfur emissions in such a process, but the cost of these
controls will be high, regardless of the method used.
In the past year, we completed calcination studies of
coal wastes from Plant K. Plant K, hi Pennsylvania,
processes high-sulfur Appalachian coal. In Sec. II.B we
show that this waste is mineralogically quite similar to
high-sulfur coal wastes from the Illinois Basin. The
calcining behaviors of these wastes, however, appear to
be somewhat different as shown by the data in Table X.
Table X shows the trace element teachabilities for
calcined coal wastes from Plant K, along with those for
the same wastes combined with selected chemical ad-
ditives before calcination. Previously reported values for
Plant B are also included for comparison.3 These calcina-
tions were all done at 1000°C for 2 h. Although this
treatment does dramatically reduce the trace element
leachabilities of Plant K refuse, it is evident that the
calcined refuse from Plant K is considerably more
35
-------
TABLE X
TRACE ELEMENT LEACH ABILITIES OF CALCINED COAL
PREPARATION WASTES WITH AND WITHOUT SELECTED
CHEMICAL ADDITIVES
Refuse Type
Additive
Plant K
(Appalachian Region)
CaC03
5 wt%
CaCOa
10 wt%
KNO,
5 wt%
KN03
10 wt%
Plant B
(Illinois Basin)
Element
Al
Mn
Fe
Co
Cu
Ni
Zn
Cd
38.5
34.1
5.7
0.57
1.37
0.87
0.67
<8
<0.6
<0.03
<0.3
<0.03
0.17
<0.03
0.08
<0.003
<0.6
<0.03
0.31
<0.03
0.17
<0.03
0.16
<0.003
122
34.1
17.1
1.17
0.36
1.19
4.53
0.003"
397
56.4
267
1.83
0.50
2.5
7.28
0.003"
0.4
0.03
<0.03
<0.01
0.01
0.01
0.05
<0.001
pH
TDS, wt%c
3.9
0.21
11.51
0.40
11.33
0.52
"Concentrations are in ng/cm3 in the leachates.
b±0.003.
CTDS = total dissolved solids.
4.05
0.70
4.00
1.60
8.0
0.2
teachable than other calcined wastes that we have
previously studied. This is surprising in view of the
similar mineral compositions of these materials.
We carried out several experiments in which chemicals
were added to the refuse before calcining, hoping to
accelerate the sintering and oxidation of the various
mineral phases. The results of these experiments are also
shown in Table X. Addition of limestone (CaCO3)
elevates the pH and reduces the trace element concentra-
tions of the leachates; however, it is not apparent from
this experiment that addition of calcium carbonate
followed by calcining is any different than simple addi-
tion of calcium oxide to the refuse. Nitrate salts might be
expected to promote the oxidation of sulfur-containing
minerals, but such behavior was not observed in this
experiment. In fact, many of the trace elements show
much increased teachability in the presence of nitrates.
Table XI contains the same data as Table X, but they
are expressed in terms of discharge severities. These were
determined by finding the ratios of the elemental concen-
tration to 100 times the ecology MATE values for the
corresponding elements. In certain respects, the dis-
charge severities are more useful than the elemental
concentrations because they reveal the extent to which
each element in the leachate might threaten the environ-
ment. Table XI shows that calcined waste from Plant K
still has appreciable discharge severities for manganese,
nickel, and, to a lesser extent, aluminum, copper, and
iron. Under these conditions, calcination of Plant K
wastes does not produce an entirely innocuous waste.
It is not clear why the wastes from Plant K behave
differently than those previously studied. We believe that
calcination conditions can be devised to control these
materials. However, the cost of the calcination process is
36
-------
TABLE XI
DISCHARGE SEVERITIES FOR THE LEACHATES FROM
CALCINED COAL PREPARATION WASTES
Refuse Type
Additive —
CaCOa
5 wt%
(Appalachian Region)
CaC03 KN03
10 wt% 5 wt%
" KNOa
10 wt%
Plant B
(Illinois Basin)
Element
Al
Mn
Fe
Co
Cu
Ni
Zn
Cd
0.38
3.4
0.23
0.023
0.27
0.87
0.067
<80
<0.006
<0.003
0.012
<0.001
0.034
<0.03
0.008
<0.03
<0.006
<0.003
0.012
<0.001
0.034
<0.03
0.016
<0.03
12.2
3.41
0.68
0.047
0.072
1.2
0.45
0.03
40
5.6
11
0.073
0.10
2.5
0.73
0.03
pH
3.9
11.5
11.3
4.0
'Discharge Severity = (Concentration)(0.01)-i- (Ecology MATE).
4.0
0.004
0.003
<0.001
<0.0004
0.002
0.01
0.005
<0.01
8.0
so high that it may never be used on any commercial
scale.3'11 Thus, though pyrolysis of coal wastes is
important to our research in control technology and to
our understanding of the behavior of the mineralized coal
wastes, it does not have a high priority in our research
program at this time.
D. Summary and Conclusions
During the past year, we have addressed four types of
environmental control strategies. These include disposal
of the waste after treatment with lime and limestone,
codisposal of the waste with alkaline soils or other
process wastes, neutralization of the coal waste effluents,
and calcination of coal wastes, with and without
chemical additives. The most effective of these treat-
ments is the lime/limestone treatment.
Coal waste that has been sequentially slurry-coated
with lime and then limestone results in leachates of
acceptable environmental quality for periods of at least 4
months. This treatment is not permanent, but it is cost
effective and may be useful as part of a more com-
prehensive strategy that will provide for ultimate disposal
of the treated coal wastes under anaerobic conditions. At
present, several unanswered questions remain. The most
important is whether results of our studies with one coal
waste are representative of all coal wastes, or at least
coal wastes of certain mineral compositions. We must
also determine the optimum treatment conditions.
Furthermore, several environmental factors, such as
freeze-thaw cycles, compaction of the waste pile, and
permeability of the waste pile, must be evaluated.
Finally, the mechanism by which this process works
needs to be understood so that its limitations can be
determined and improvements made. In spite of these
issues, the HmeAimestone treatment is the most promis-
ing control strategy investigated so far, and we will
continue intensive studies during the coming year.
Alkaline soils or process wastes, mixed directly with
the coal waste or placed in series with the effluent flow, is
partly effective in controlling trace element releases from
the waste pile. However, none of the materials tried gave
an entirely acceptable leachate. The main difficulties
arose after air regeneration of the acid within the waste.
The high initial acid contents of the resulting leachate
37
-------
overwhelmed the capacity of the soils or process wastes
to deal with it, although the treated wastes recovered
more quickly than those which were not treated. In
addition, because many of the materials mixed with the
waste contained leachable forms of manganese and iron,
they were ineffective in controlling these elements. Nev-
ertheless, the information obtained from these experi-
ments is very useful in assessing potential effects of the
mineralogy and structure of hypothetical waste disposal
sites. For example, this information can suggest the
optimum structure of a waste disposal site in terms of the
underlying soil layers and location of the site. Future
emphasis in this area will be on determining the effects of
natural soils and mine overburdens on the effluents of
coal waste piles.
Neutralization of acid mine drainages and coal waste
effluents is the most widely practiced environmental
control for these types of problems because of its
simplicity and low cost. For this reason and also because
acid neutralization is the basis of our most effective
control efforts, we have investigated this process and its
limitations. Comparisons of experimental results with
those from thermodynamic calculations reveal that the
major cation concentrations are controlled by solution-
precipitation chemistry, which is reasonably well under-
stood. However, the trace element concentrations are
significantly lower than theory predicts. As expected, the
speciations of most of the elements is controlled by the
major ions in solution, but the anion behavior is not well
accounted for except for fluoride. We believe that the low
trace element concentrations are caused by adsorption of
ions on the highly dispersed colloidal precipitate formed
during the neutralization process. Understanding these
phenomena would allow us to extrapolate our ex-
perimental results to other systems and would add to our
predictive powers.
Calcining coal wastes reduces the starting material to
an innocuous form, but this exchanges one problem for
another because large amounts of sulfur and trace
elements must be removed from the gaseous by-prod-
ucts. Coal wastes from Plant K behave differently than
those studied before. Specifically, calcined waste from
Plant K still yields leachates containing environmentally
significant amounts of manganese and nickel, and, to a
lesser degree, aluminum, copper, and iron. We believe
successful calcining conditions could be found to reduce
waste from Plant K to innocuous form, but previous cost
studies show that this approach is costly in comparison
with other methods. Consequently, we will not study this
technique further at this time.
II. ASSESSMENT OF HIGH-SULFUR AP-
PALACHIAN COAL WASTES
A. Introduction
Our early studies were with high-sulfur coal wastes
from the Illinois Basin, and most of our reported work
has dealt with these materials.1"3 Last year, we reported
assessments on low-sulfur Appalachian coal wastes
(Plant G).4 We are now investigating high-sulfur coal
wastes from Appalachia (Plants I and K) and have
obtained some pertinent information on these wastes.
Some of the particulars regarding Plants I and K are
summarized in Appendix D. Both plants are in western
Pennsylvania and process coal from the Kittanning and
Freeport seams. Plant I uses cyclones to clean the coal.
All incoming coal is reduced to —3/4 in. with a rotary
breaker so that the refuse consists of —3/4-in. waste and
the breaker reject. We have completed most of the
experimental work, but the data are incomplete and have
not been reduced to a usable form. Results for Plant I
will appear in our next annual progress report. Plant K is
a jig operation in which only the coarse coal (+3/8 in.) is
cleaned. The fine coal goes directly through the plant and
is combined with the cleaned coal. Waste streams consist
of coarse refuse and a slurry containing -60-mesh fines.
In the present assessment, we consider only the coarse
waste. The results for Plant K are mostly complete. The
only missing data are the atomic absorption analyses for
the solid starting materials. Available results from neu-
tron activation and emission spectroscopy are reported
here; complete assessments on both plants will be
included in our next annual report.
B. Mineralogical Analyses
Coal waste samples were dried at 60°C. Each of four
barrels was sorted separately into fractions according to
gross mineralogical appearance. All the — 1/2-in. materi-
al was first screened out. This unsorted (< 1/2-in.)
material constitutes sample 52G. The larger pieces were
sorted in piles according to appearance. Because fine
coal dust covered most of the material, properties such
as apparent density also had to be accounted for. Luster,
color, and form were all factors in the sorting. No
quantification of hardness or density was attempted. In a
few cases, rocks were broken to reveal their features
more clearly, and all the fragments were placed in the
same appropriate piles. The numbers and types of piles
38
-------
were not predetermined; a pile was formed as a signifi-
cant number of similar rocks were placed together.
The material from Plant K naturally divided into
seven fractions that can be characterized as follows:
Sample 52B (13.9%) looks like coal, with block
cleavage, but has a resinous rather than a vitreous luster.
In general, the pieces were cubic with 1- to 2-in. sides.
Sample 52C (27.6%) contained pieces, some quite
large (2 to 6 in.), that had black, vitreous, coaly material
adhering to whitish or dull metallic pyrite. The weight of
these pieces compared to similarly sized coal or clay was
a distinguishing feature.
Sample 52D (25.3%) contained pieces, generally less
than 2 in. across, of roundish, whitish clay, that often
broke into layers. The pieces were typically coated with a
yellowish, powdery substance.
Sample 52E (4.0%) pieces were dark, hard, heavy, and
coated with a thin layer of rust-colored substance.
Sample 52F (5.8%) labeled "miscellaneous +1," con-
sisted mainly of large slabs of shale-like material, typi-
cally ~ 1/2 in. thick.
Sample 52G (20.2%) was a collection of all the
original material that passed through a 1/2-in. screen.
Sample 52H (3.2%) was material that could not be
classified into any of the above fractions. The sample
included chunks of orange-colored sandstone, small clay
balls with unidentified inclusions, and a few pieces of
granite, a material not known to be indigenous to coal
deposits.
We also generated a composite sample, 52A, by
recombining representative samples split from each of
the seven fractions described above.
These fractions, as well as the composite waste
material, a feed coal, and a clean coal from the same
plant were plasma-ashed at 150°C. The resultant low-
temperature ash was ground to -200 mesh in a mechani-
cal mortar and pestle. A portion of each was mixed with
1 urn alumina powder as an internal standard (to
approximately 20 wt% alumina). A lightly compacted
sample was then examined by x-ray diffraction. Relative
peak heights of the major minerals were determined by
direct measurements of the diffraction tracings. The
quantitative mineral composition was obtained by means
of a computer program that converts the raw digitized
peak-height data to percent mineral present, using pre-
determined standard calibration curves for the minerals
in the program library.2-12'13 Results of the analyses of
mineral content are shown in Table XII. Because of
uncertainties in the measurement of the diffraction
intensities and the many assumptions involved in deriv-
ing the quantitative values, errors for the major mineral
components may be ~20%, and those for the minor
components could be larger.
Unlike the Illinois Basin wastes previously examined,
this waste has little or no marcasite. However, the pyrite
content in composite sample 52A, is comparable to that
in the high-sulfur Illinois Basin coal wastes that we have
studied. The fractions containing clays also contain
relatively large amounts of illite compared with the
Dlinois Basin waste; however, the illite content (16%) of
composite sample 52A is comparable to that in the
composite samples for both Plant G (low-sulfur Ap-
palachian) material (19%) and Illinois Basin waste from
Plants A (14%) and C (16%). Kaolinite varies from 10 to
16% throughout the samples of average waste analyzed
from both the Illinois Basin and Appalachian region,
except for Plant B, with 7% kaolinite in the average
waste samples. Mixed-layer clays of statistically signifi-
cant amounts were found only in fraction 52B and in the
cleaned coal of the Plant K samples. Montmorillonite
was not positively identified in any sample. The quartz
content seems'to vary little in the average samples from
plant to plant, but was highly concentrated in fraction
52H, a piece of granite-like rock of unknown origin.
Quartz is also concentrated in fraction 52D, a clay
fraction.
One component of the Plant K waste, not observed in
any other coal preparation waste that we have studied, is
siderite (FeCO3). It could not be quantified by our
computer program, but we estimate it to be present hi the
greatest concentrations in fraction 52E (rusty material),
in moderate concentrations in fraction 52B (smooth,
block cleavage fraction), in lesser amounts hi fraction
52A (composite waste) and 52G [miscellaneous -25-mm
(~l-in.) fraction], decreasing in fractions 52F, 52H, and
52D, and absent in fraction 52C (pyrite with adhering
coal fraction). Small amounts are also present hi both the
feed and cleaned coal samples. The type of siderite
identified might have 1-2% manganese in its structure, as
an iron replacement in the crystal.
Another component of the material could not be
identified as belonging to any major mineral group
mentioned, which may indicate the presence of
amorphous noncrystalline matter undetectable by x-ray
diffraction analyses. (This and the siderite compose the
quantity labeled "unknown" hi Table XII.)
The mineralogical information reported here will be
used to determine the trace element and mineral associa-
tions in the plant K coal waste. In turn, that information
may be used to develop models to aid our understanding
39
-------
TABLE XII
MINERALOGICAL COMPOSITIONS OF COAL WASTES SAMPLES
FROM PLANT K
52Aa
52B
52C
52D
52E
52F 52G 52H
53
LTA
76.4
62.2
68.7 92.5
86.1
54
Pyrite
Marcasite
Quartz
Calcite
Gypsum
Illite
Kaolinite
Montmoril—
lonite
Mixed Clay
Unknown
25
Trace
19
0
1
16
10
0
0
7
8
Trace
15
0
Trace
6
9
0
9
15
53
0
5
0
0
3
3
0
Trace
4
4
0
28
0
Trace
29
15
0
0
17
23
Trace
16
0
2
15
7
0
0
24
13
0
16
0
1
19
12
0
Trace
19
23
0
16
0
1
12
8
0
0
16
2
0
(51)b
0
1
28
15
0
0
0
6
Trace
7
0
Trace
7
7
0
0
4
2
0
5
0
0
4
6
0
3
8
79.6 76.2 97.0 31.1 28.0
"52A: Composite waste sample.
52B: Smooth, block cleavage fraction.
52C: Pyrite with adhering coal fraction.
52D: Whitish, roundish clay fraction.
52E: Black fraction having rust-colored coating.
52F: Miscellaneous +25 mm (+1 in.) fraction.
52G: Miscellaneous —25 mm (—1 in.) fraction.
52H: Fraction largely consisting of granite, sandstone, etc.
53: Average feed coal +9.5 mm (+3/8 in.).
54: Average cleaned coal +9.5 mm (+3/8 in.).
bThe quartz value was too high to be calculated directly; the 51% was obtained by difference.
of trace element mobilities and leaching behaviors of
coals and their mineral wastes.
C. Chemical Composition
Elemental analyses were performed on each fraction.
Lithium, beryllium, silicon, silver, cadmium, sodium, and
calcium were determined by optical emission spec-
troscopy and the remaining elements were measured by
neutron activation analysis. The one exception is sulfur,
which was determined by chemical means. The results of
these analyses are displayed in Table XIII. This table
shows that, in general, these samples have low calcium
contents, consistent with the mineralogical observation
that little or no calcite is present. In general, the samples
have slightly less sulfur than appears in similar samples
from the Illinois Basin. The levels of lithium, chlorine,
arsenic, cadmium, antimony, and lutetium are higher
than in samples from the Illinois Basin. Among these,
arsenic, antimony, and cadmium may be significant if
they are mobilized in the waste leachates. In general, zinc
and rubidium levels are lower than those observed in
other high-sulfur coal wastes.
Because the sample fractions are substantially dif-
ferent mineralogically, we can derive some information
about the tendencies of various trace elements to as-
sociate with certain minerals. Silicon is predictably
highest in those fractions containing the most quartz and
clays, and lowest in the fractions containing large
amounts of pyrite. Sodium, magnesium, aluminum, and
potassium show the same trends. Calcium is uniformly
smeared through all the fractions. Sulfur is markedly
more concentrated in the phases with the most pyrite,
40
-------
TABLE XIII
ELEMENTAL COMPOSITIONS OF COAL WASTE SAMPLES
FROM PLANT K (DRY BASIS)
Sample
Li
Be
B
F
Na(%)
Mg(%)
Al(%)
Si(%)
P
S(%)
Cl
K(%)
Ca(%)
Sc
Ti(%)
V
Cr
Mn
Fe(%)
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Rb
Mo
Ag
Cd
Sn
Sb
I
Sr
Ca
Ba
La
Ce
Sm
Eu
Tb
Dy
Yb
Lu
Hf
Ta
W
Hg
Pb
Th
U
52A
Composite
Waste
100
<1
0.28
0.51
6.2
14
9.74
250
1.0
0.34
11.8
0.49
75
77
300
13.7
16.6
<100
11.7
<20
320
10.9
17
<70
<0.8
21
5.2
<10
<200
4.6
330
40
78
<0.06
0.9
<2
4.7
1.2
4.9
<0.7
1.1
0.07
13.3
3.1
52B
92
<1
0.27
0.34
5.6
14
4.40
195
1.1
0.31
12.1
0.45
69
62
720
7.4
14.3
<200
118
<10
123
10.9
'22
<50
<0.7
10
3.3
<20
<300
3.8
330
34
62
12.8
0.8
<2
6.6
1.2
4.6
<0.6
3.9
<0.02
11.1
3.3
52C
18
<1
0.04
0.08
1.7
5.1
23.6
320
0.22
0.23
3.0
0.17
28
20
43
30
14.3
<70
<4
<30
800
13.8
19
<60"
<0.8
39
19.9
<6
100
<0.8
92
17
29
5.9
0.4
<0.9
2.1
<0.2
1.2
<0.6
<1
0.07
3.1
1.1
52D 52E 52F
Coal Waste Fractions
69
2.3
0.30
0.86
12.2
30
1.30
76
2.8
0.27
22
0.84
130
127
103
3.0
16.9
<100
<3
33
28
2.3
4.3
177
<0.9
14
2.3
<9
500
8.3
540
65
144
13.2
1.5
2.1
7.9
1.9
7.5
1.1
1.6
<0.02
21.1
5.2
42
<1
0.26
0.58
4.0
14
10.75
<100
0.76
0.47
8.4
<0.10
38
37
1360
24
21.0
<400
<50
<20
196
27
7.8
<80
<0.9
15
3.5
<40
<500
2.8
<200
22
48
10.5
0.8
<2
<1
<0.4
3.0
<0.7
<0.007
0.10
7.3
1.7
52
0.8
0.55
0.68
8.8
20
4.04
140
1.8
0.19
16.8
0.58
113
78
183
7.2
18.3
<100
97
21
115
7.4
12
147
<0.8
9
4.3
<10
<200
7.2
380
50
103
5.6
1.4
1.8
7.1
0.6
5.2
<0.5
<1
0.03
14.4
4.4
52G
89
<1
0.39
0.52
6.4
19
11.46 .
210
1.2
0.24
10.5
0.41
79
56
270
12.4
16.9
<100
71
<20
280
11.7
18
118
<0.8
20
9.7
<10
<200
4.1
340
50
71
21.0
0.9
1.8
5.2
<0,2
3.6
<0.4
3.3
0.04
9.8
3.0
52H
54
1.4
0.36
0.66
6.1
>37
0.58
<20
1.6
0.47
9.9
0.55
74
54
250
4.0
8.9
<100
71
12
24
5.4
3.3
87
<1.0
<8
1.2
<10
<200
2.6
270
34
69
5.7
0.8
1.2
5.3
1.0
9.0
0.8
3.6
<0.01
10.0
3.3
53
Feed
Coal
23
2.0
0.08
0.18
3.3
6.1
2.9
990
0.50
0.21
7.7
0.21
48
49
74
3.3
11.7
<100
<100
<10
114
<3
54
<40
<0.5
8
3.4
18
<100
2.1
200
22
46
10.3
0.6
1.6
4.2
1.0
2.2
<0.6
<0.01
<0.02
7.5
2.1
54
Cleaned
Coal
19
2.4
0.09
0.07
2.5
6.1
1.64
1030
0.32
0.19
6.1
0.17
41
28
54
1.6
9.0
<100
102
<10
26
4.8
50
<30
<0.5
<8
1.7
17
240
1.5
130
15
32
6.5
0.5
<0.8
3.3
<0.2
1.2
<0.4
<0.6
<0.01
4.8
1.8
41
-------
which agrees with our perception that pyrite is the major
sulfur-bearing component in the coal waste. Iron is most
concentrated in the fractions with the most pyrite, but it
is also abundant in the fractions with large unknown
components and in certain clay fractions. This suggests
that the unknown component may contain micro-
crystalline pyrite, but it may also indicate that some of
the clays contain significant amounts of iron. Titanium
seems most concentrated in the phases with the most
quartz and clays, and least concentrated in the high-
pyrite phases. Thus, the titanium is probably present as
the oxide, either in a discrete mineral phase, or as a
component of the quartz or some of the clays.
The alkali metals and alkali earths tend to concentrate
in the fractions with the highest clay contents and in
those with the highest quartz values; the lowest amounts
are found in the fraction that is mostly pyrite. These
findings agree with our understanding of the chemistries
of these elements, since we expect these elements to be
associated with various aluminosilicates. In group VIIA
(halogens), we have experimental data on only chlorine
and bromine. Similarly, in group VIA, we have data only
for sulfur and selenium, and in VA, we have data for
arsenic and antimony. However, these elements all show
the same trends. They tend to be most concentrated in
the pyrite phases and least concentrated in the quartz
phases. Some of these (selenium, arsenic, and antimony)
may have serious environmental implications. In group
IVA, we have data only for silicon, and in group IHA,
our information is restricted to aluminum, which is
predictably associated with the clays.
Among the transition metals, most are associated with
clay-bearing fractions and are least concentrated in the
pyrite-containing fractions. These include titanium, scan-
dium, vanadium, chromium, thorium, and uranium.
Manganese seems to be somewhat different because it
tends to associate with the fractions containing large
unknown components and may be associated with the
iron there. Manganese is least concentrated in the pyrite
fractions. It is hard to draw conclusions about cobalt,
except that it is least abundant in the pyrite fractions.
The same is true for zinc. Cadmium is notably different
because it tends to associate with the high-pyrite frac-
tions and presumably is present as the sulfide. The rare
earth elements that we have determined, with the possible
exception of samarium, are associated with the fractions
having high contents of clays and other silicates, and are
least evident in the fractions with the most pyrite.
Notably absent from this analysis are mercury and lead.
The lead analyses are not available yet, and the data for
mercury are of insufficient quality to draw conclusions.
We expect both elements to be associated with the sulfide
(pyrite) phases.
In general, the materials from Plant K are comparable
to those from the Illinois Basin. The sulfur levels are
slightly lower, and the concentrations of a few of the
trace elements are higher in the Plant K materials
(lithium, chlorine, arsenic, cadmium, antimony, and
lutetium) and others are slightly lower (zinc and
rubidium). The Plant K waste has little or no calcite and,
hence, should have correspondingly little self-neutralizing
capacity. Trace metals likely to cause concern because of
water quality tend to be associated with the clays and
silicates in the samples. However, several important
elements (selenium, arsenic, antimony, cadmium, iron,
and possibly others) are associated with the sulfide
phases (pyrite). In our samples, the trace element and
mineral associations essentially agree with our under-
standing of the chemistries of these elements.
D. Micromineralogy
To determine the structural relationships of trace
elements and minerals, fractions of waste (sorted accord-
ing to gross mineral appearance) and feed and cleaned
coals from Plant K were examined by a scanning
electron microscope (SEM) equipped with an energy
dispersive spectrometer (EDS). Procedures for sample
preparation, techniques for distinguishing mineral forms,
and photomicrographs of typical coal/coal waste mineral
forms have been published in Ref. 14. Microscopic
examination of bulk mineralogical samples is subject to
severe sampling errors because so little of the sample is
studied at any one time. The situation is analogous to the
fable of the six blind men and the elephant. In this story,
each of the blind men, after examining only a small part
of the beast, draws completely erroneous conclusions
about the nature of the animal. Only by pooling their
knowledge can the six observers reach the correct
conclusions. Similarly, with our coal waste samples, a
very large number of random microscopic examinations
must be made to complete a representative analysis of
the bulk sample. Unfortunately, microscopists tend to
concentrate on those particles that are either easily
observed (high atomic number) or that are particularly
interesting (unique). Since neither of these particle types
is likely to be representative of the sample as a whole,
one can be easily misled by these observations. In spite
of these limitations, the SEM/EDS combination can
42
-------
perform elemental analysis while retaining spatial resolu-
tion. This allows conclusions to be drawn about the
elemental associations within the sample—very difficult
to do by other means except in indirect ways.
Certain assumptions must be made in order to derive
the mineral composition of the particles observed by the
scanning electron microscope. Because SEM/EDS
analyses cannot detect elements below sodium in atomic
number, many references to mineral types reported here
are conjecture, based on their known presence as
determined by x-ray diffraction analysis for major min-
erals, or, as in the case of microminerals, on the
probability of the existence of a particular element in that
form. For example, if titanium is detected alone, it is
probably as TiO2, but whether it is of the anatase or
rutile or other crystallographic form cannot be de-
termined.
Although a few trace elements may be chemical
constituents of a major mineral phase, such as calcium in
calcite or gypsum, they usually are found in what
appears to be a physical, rather than chemical, associa-
tion with the major minerals. In general, the trace
elements in coal wastes are found in particles of elemen-
tal compositions that seem to indicate discrete mineral
phases and that can be identified by direct observation
with the scanning electron microscope. However, the
amounts of these phases relative to the total mineral
matter in the waste are too low to be detected by bulk
analytical techniques such as x-ray diffraction.
Clays are the most prevalent minerals identified in
Plant K materials, both by x-ray diffraction analysis and
by micromineral analysis, as is typical of all coal waste
samples studied. The number of occurrences of illite-type
clays (identified by aluminum, silicon, and potassium
peaks on the EDS) in the immediate environment of
trace-element-containing particles is larger than that for
kaolinite (identified by aluminum and silicon peaks but
no potassium peak) in the SEM analyses. Most of the
trace elements identified were found in the large matrix
of clay. Nearly all the micromineral constituents identi-
fied were associated with illite-type clays. This may
occur because exchange sites between the layers of such
clays allow the "capture" of elements that might have
passed in solution through the material at one time.
Perhaps these elements later recrystallize to form the
particles seen in the SEM photomicrographs.
Rare earth elements identified in these Plant K
samples were lanthanum, cerium, dysprosium, and
gadolinium, and always seemed to occur with phos-
phorous, and were apparently always in the proximity of
illite-type clays. Thorium and uranium were also found
in occasional particles, possibly as rare earth phosphates.
Calcium occurred with phosphorous (associated with
illite-type clay) and with iron and manganese. The latter
occurrence could be explained if some siderite (FeCO3) -
dolomite [ C a M g ( C O ,) 2 ] - a n k e r i t e
[CA(Mg0 67Fe0 33XCO3)2] transition were involved, espe-
cially since manganese-rich siderite was identified in
several fractions by x-ray diffraction.
Iron was identified in most particles in the ratio of 1
Fe:2 S, as in pyrite, but it was also observed with no
sulfur and with manganese, magnesium, or calcium
instead, as in a carbonate phase. Iron also occurred with
sulfur in approximately equal proportions in a few
particles. This could represent either a monosulfide phase
or an iron sulfate phase, which is indistinguishable by
SEM/EDS.
Probable sulfates present were gypsum (CaSCy2H20)
and barite (BaSO4). The latter was predominantly in the
illite-type clay.
Sulfides were present in all fractions examined. Sample
52C, sorted by gross mineral appearance as being coal
with adhering pyrite, contained very "pure" pyrite and
only small amounts of clay. No microminerals were
noted in that fraction. Other fractions, however, con-
tained mostly pyritic sulfides, but also contained parti-
cles of PbS, ZnS, and CuS. One particle was half PbS,
half ZnS; others were mixed sulfide forms of, for
example, ZnS and CuS.
Probable oxide minerals included silicon (as quartz,
SiO2), titanium (as TiOj), and zirconium (as ZrO2,
zirconia). The common coexistence of titanium and
silicon in single particles indicates the possible presence
of rutilated quartz. Titanium and vanadium were found
together, but the actual mineral that contained these
elements could not be determined.
With a few exceptions, there were no noticeable
differences in the trace minerals found from one fraction
to another. The exceptions were 52C, which had numer-
ous pyrite particles but few trace minerals, 52E, which
had an abundance of siderite-type iron compared with
the other fractions, and 52H, which had more rock-type
(feldspathic) silicates as opposed to the clays normally
found in SEM analyses of coal waste. The large pieces of
granite in that fraction, atypical of coal waste material,
could account for the rock silicates. (Because 52H
43
-------
represented only 3.2 wt% of the total waste, its atypical
composition is not expected to have a significant in-
fluence on the behavior of the waste.) Samples 52D and
52F had the greatest frequency of occurrence of trace-
element-containing microminerals and particles with
zinc, copper, and lead. This was expected because these
fractions had the most clay. However, these trace
minerals were also found in other fractions, in composite
sample 5 2A, and in the coal samples. As expected, the
coals had many occurrences of organic sulfur. Although
gross mineral separations greatly facilitate the concentra-
tion of the major minerals for examination by x-ray
diffraction analysis, they have little effect on the micro-
scopic particles examined by the SEM technique. This is
especially true when the samples are scanned by hand,
and those particles having a high density or unusual
morphology (generally indicating the presence of ele-
ments with a higher atomic number than the background
sea of aluminosilicate clay material) are picked for
elemental analysis by the EDS. Because the particles and
their immediate surrounding matrix are so small, the
equivalent of dust-size particles, they could easily sift
through or adhere to any type of rock, and could be in
any sorted pile.
Except for the frequent occurrence of manganese-rich
siderite and the atypical feldspathic material in the Plant
K samples, there were no notable differences between
these and other coal waste materials we have examined.
Because siderite could be considered a major mineral in
at least two of the Plant K fractions, the behavior of any
trace element associated with siderite, which, therefore,
might be affected by the leachability or reactivity of
siderite, might be altered from the behavior of those
elements in wastes not containing iron carbonates. The
elements most likely to be affected in the Plant K waste
because of their association with siderite are iron,
manganese, calcium, and magnesium.
The difficulty in obtaining correlations between zinc
and copper and any mineral fraction separated by size or
density in coal wastes studied previously is substantiated
by finding ZnS and CuS in very small particles in the
Plant K waste. Such particles probably are distributed
randomly among any physically separated materials.
The photomicrographs in Fig. 16 illustrate the complexi-
ty of the trace element and mineral associations and the
difficulty of sorting any micromineral into a "pure state."
E. Leaching Behavior
1. Static Leaching. Coal wastes, clean coal, and feed
coal from Plant K were subjected to standard static
leaching procedures using 5 cm3 water/g solid.2 The
duration of these experiments ranged from 1 to 50 days. *
The compositions of the leachates obtained are displayed
in Appendix E and in Figs. 17-19. In general, the results
are consistent with those obtained from similar materials
from the Illinois Basin.
The tables in Appendix E show that the pH decreases
with time in all cases and that the specific conductance
undergoes corresponding increases. Both trends are
expected with high-sulfur coals and coal wastes and
indicate that these materials have strong acid-generating
tendencies. The fact that the final pH of the coal waste
leachate was less than 2 suggests that this material may
cause a serious acid-drainage problem if not properly
disposed of.
Figure 17 shows how the element concentrations in
the coal waste leachates depend on time. All the elements
being studied are mobilized under acid conditions, so it is
not surprising that the leachate concentrations increase
with time as the pH drops. However, note that some
elements show much stronger time dependences than
others. In particular, arsenic, selenium, and, to a lesser
degree, cadmium, increase much more rapidly in concen-
tration than the others, and they continue to increase
even after most of the other elements seem to approach
equilibrium values. This suggests that the rates of
dissolution for these elements are controlled by some
process other than that for the remaining elements. Each
of these elements tends to be associated with the pyrite-
(sulfide-) containing fractions of the coal wastes. Presum-
ably, both cadmium and arsenic are present as sulfides,
and selenium is in anionic form (selenide). In each case,
oxidation is required to convert the element to a water-
soluble form: leaching of these elements may be con-
trolled by the oxidation rate of the corresponding mineral
instead of (or in addition to) the acidity of the leachate.
Behavior should be similar from other elements in the
sulfide minerals (lead, mercury, and antimony), but the
importance of this mechanism depends on the solubility
of the sulfide in acidic solutions, the rate of the oxidation
reaction, the rate at which the ionic reactions approach
equilibrium, and the fraction of the element present as
44
-------
1 Fe, Mn (siderite?)
2 Pyrite
3 (KAISi) clay
4 Si (quartz?)
188X
I
Rare earth (Gd, Dy, Er) Th
Phosphate in a (KAISi) clay.
3750X
\
*
"^ -*
3
£*_ - - , ^g,
Rare earth (Gd, Dy) phosphate in gypsum. 3750X
The (KAISi) clay is outside the picture.
?
f*r*
• .
4 «
2 Pyrite
3 (KAISi) clay
4 Si (quartz?)
Fig. 16.
M. l^. «V.
Scanning electron micrographs of selected coal waste samples from Plant K.
-------
10
20 30 40
TIME (DAYS)
50
60
Fig. 17.
Results of static leaching experiments with coal prepara-
tion wastes from Plant K—concentrations of selected
trace elements in the leachates plotted as functions of
time.
10
20 30 40
TIME (DAYS)
50
60
Fig. 18.
Results of static leaching experiments with feed coal
from Plant K—concentrations of selected trace ele-
ments in the leachates plotted as functions of time.
the sulfide versus other chemical forms. Iron, pre-
dominantly in the form of pyrite, also falls into this
category. There may be two classes of trace elements
present in these wastes. Many of the elements associated
with the clays and silicates may be mobilized by simple
contact with acidic leaching media. However, although
acidic media may be necessary to mobilize the elements
in the sulfide mineral phases, acidity alone may not be
sufficient, and oxidation of these minerals may be
required to solubilize the trace elements because many
sulfides are insoluble even in acidic media.
In Figs. 18 and 19 leaching results for the feed coal
and the cleaned coal show the same general trends. The
feed coal might be considered a mixture of the coal waste
and the cleaned coal, so that its behavior should be
between the two. This is true with regard to the time
dependence of the elemental concentrations in the
leachates. The coal waste has the strongest time depen-
dence, the cleaned coal has the weakest, and the feed
coal is intermediate. Concentrations of arsenic and
selenium show stronger than average time dependences
in the feed coal and the cleaned coal: cadmium does not.
However, these experiments show that the cleaned coal
46
-------
10'
I01
10'
UJ
o
10"
10
IO"3
-Al -
Pb-
10 20 30 40
TIME (DAYS)
50
60
Fig. 19.
Results of static leaching experiments with cleaned coal
from Plant K—concentrations of selected trace ele-
ments in the leachates plotted as functions of time.
and the coal waste give leachates with higher trace
element concentrations than the feed coal. The cleaning
process may affect (increase) the teachability of these
trace elements, or it may be an artifact caused by the
sampling process. Since the feeds to most cleaning plants
vary in composition, it is difficult to know whether the
outflowing process streams at a given time actually
correspond to the incoming coal at the same time. This
observation must be confirmed by other means before
drawing conclusions.
The final element concentrations were compared with
the MATE values for liquids to identify elements of
environmental concern. In these comparisons, the
leachate concentrations were divided by 100 to account
for the effluent dilution that would occur at a disposal
site.1 The final (50-day) values were used to provide a
worst-case analysis. Discharge severity factors were
calculated by finding the ratio of the adjusted leachate
concentration to its MATE value. Table XIV shows the
results of this analysis for the Plant K materials. Iron,
arsenic, nickel, manganese, and aluminum have dis-
charge severity factors greater than unity. In addition,
zinc, cadmium, and copper have discharge severity
factors between 0.5 and 1.0. Any of these elements may
be cause for concern under specific conditions, although
iron is, by far, the worst case.
2. Dynamic Leaching. Column leaching experiments
were carried out using the coal waste from Plant K. Each
of four 30-cm glass columns was filled with 500 g of coal
waste, previously crushed to — 3/8-in. particle size.
Deionized water was pumped upward through the col-
umns at 0.5 ntf/min. All four columns were stopped at
approximately 4 f total volume of effluent. Two columns
were dismantled, and air was forced through the other
two for 2 weeks. These columns were leached again with
deionized water to collect an additional 3 ( of effluent
from each. The specific conductance and pH of the
effluents were measured as they were collected. Samples
were then acidified and saved for later analysis. At the
end of the experiment, selected samples were analyzed to
determine their trace element contents. The results of
these experiments are tabulated in Appendix E, and
shown in Figs. 20 through 22.
These experiments were designed to simulate the
weathering of a waste pile. For example, as coal is
processed in a preparation plant and while it is being
handled and transported to the waste disposal site,
oxidation of the pyritic minerals and generation of acid
within the waste occurs. Because water does not flow
through the waste at this time, the acid accumulates until
leaching occurs as the result of rain or other natural
processes. Thus, the initial leachates should be much
more highly contaminated than those produced after a
steady state is reached. When there is no water flow (rain
or other natural water) through the pile, leaching stops
and accumulation of acid resumes. Subsequent leaching
will again result in initially high contaminant levels. In
our dynamic leaching experiments, alternating leaching
and air regeneration cycles are designed to simulate this
process, to provide information on the kinetics of the
processes involved, to determine the relative concentra-
tions of those contaminants released, and to identify the
areas of most concern.
47
-------
TABLE XIV
MEG/MATE ANALYSIS OF STATIC LEACHATES FROM
PLANT K MATERIALS
Element Concentration in Leachate (ppm)a
Coal
Waste
Cleaned
Coal
Feed
Coal
MATE Discharge Severity Factors
Value Coal Cleaned Feed
Waste Coal Coal
Fe
As
Ni
Mn
Al
Zn
Cd
Cu
Se
Co
Be
Pb
9250
18.0
2.8
23
110
6.5
0.059
2.60
0.57
1.56
0.043
<0.01
890
1.4
1.3
4.7
49
6.1
0.032
1.15
0.04
0.92
0.024
0.01
580
0.4
1.0
2.6
16
3.1
0.028
1.07
0.01
0.68
0.012
0.05
0.250
0.050
0.010
0.10
1.0
0.10
0.001
0.050
0.025
0.25
0.055
0.050
370
3.6
2.8
2.3
1.1
0.6
0.6
0.5
0.2
0.06
0.008
<:0.002
36
0.3
1.3
0.5
0.5
0.6
0.3
0.2
0.02
0.04
0.004
0.002
23
0.08
1.0
0.3
0.2
0.3
0.3
0.2
0.004
0.04
0.002
0.01
"Static leach, 50 g solids with 250 cm3 water for 50 days.
"Discharge Severity Factor = (Concentration in Leachate)
(O.Ol)-HMATE VALUE).
Figure 20 shows the dependence of the effluent pH on
the eluent volume. Initial acid contents of the leachates
are very high, but they decay to more moderate values as
leaching continues (consistent with the above descrip-
tion). Under steady flow conditions, the final acid
concentration should be determined by the relative rates
of acid generation within the pile and the effluent flow.
Unfortunately, the leachate flow does not remain con-
stant in a real waste pile unless the pile is in an
underground aquifer. In most cases, the flow is intermit-
tent. The air regeneration cycle shows what happens
under intermittent leachate flow. Because of the large
acid-generating potential of this waste, the pH of the
effluent drops drastically when the leachate flow is
interrupted and air flows through the waste. The only
conclusion possible is that this waste may pose an acid-
drainage problem of grave environmental concern unless
it is disposed of in an environmentally acceptable
manner.
The dependence of conductance on effluent volume is
shown in Fig. 21. Conductance is a measure of the total
ionic concentrations of the solution. In the case of high-
sulfur coal waste leachates, the dissolved salts may
depend strongly on pH, and if this is true, the conduc-
tance and the pH should behave the same. In fact, the
conductance is a virtual image of the pH, clearly
demonstrating that pH is a major controlling factor for
the salt concentration in these leachates.
The dependences of solution concentrations of several
trace elements on effluent volume are shown in Figs. 22a
and b. The vertical line in each graph labeled "air
regeneration" indicates the effluent volume at which the
flow was interrupted and air was forced through the
column. The horizontal line labeled "DS=1" shows the
concentration at which the discharge severity is unity.
Data points plotted above this line show contaminant
levels of ecological concern. Figures 22a and b show that
iron, nickel, and manganese have initial discharge severi-
ties greater than one. Of these, iron is by far the worst
offender, with an initial discharge severity of nearly 100.
Nickel follows with a value of 5, and manganese has a
value of 2. These discharge severities decay to acceptable
values, but they rise again after regeneration. Zinc,
cadmium, aluminum, and copper form a group of
elements having initial discharge severities between 1 and
0.5. Although this group is worthy of concern, the
48
-------
ac
ex
6
a GL-30
A GL-31
v GL-32
o GL-33
6
g
8
Waste
10
12
14
Fig. 20.
Results of dynamic leaching experiments with coal waste from Plant K—pH vs eluent volume.
discharge severities would probably not become large
unless the waste underwent an unusually long regenera-
tion cycle. Arsenic, cobalt, lead, beryllium, and selenium,
with initial discharge seventies less than 0.5, probably
would never exceed a value of unity except under very
unusual circumstances, although the highest of these,
arsenic, may occasionally approach this value. Beryllium
and selenium have very low discharge severities (0.02)
and are unlikely to pose an environmental problem. In
fact, the concentrations of these elements were near
detection limits of our analytical methods.
Figures 23a and b show element concentrations in the
leachates plotted as functions of pH. Circles show
measurements taken before air regeneration of the col-
umns; squares show measurements taken after regenera-
tion. Concentrations of cadmium, lead, selenium, and
beryllium are near or at the detection limits, so measure-
ment precision is poor. Other studies of coal wastes
suggest that pH is the major controlling factor in their
leaching behavior. Therefore, if the system is at
equilibrium, all the points should fall on a smooth curve.
However, for lead, arsenic, and perhaps cobalt and
aluminum, the values obtained before and after regenera-
tion fall on different curves. Therefore, other factors, in
addition to pH, control the leaching of these wastes.
Some possibilities are depletion of the element in the
waste, irreversible changes in the structure of the waste,
or the effect of some kinetic process such as oxidation of
certain minerals. Nevertheless, pH is still the major
controlling factor in determining the leachate composi-
tion.
F. Conclusions
In general, wastes from Plant K are comparable to the
high-sulfur coal wastes that we have examined from the
Illinois Basin. Plant K materials are slightly lower in total
sulfur and slightly higher in lithium, chlorine, arsenic,
cadmium, antimony, and lutetium. They have no ob-
servable marcasite, but are high hi pyrite. In addition,
some of the iron is in the form of siderite, which we have
49
-------
^_^
6
o
o
(-<
H
d
^_i.
0)
0
c
cd
0
•d
c
0
0
o
«4— (
• ^^
O
D
CO
101
10°
10"
io-2
irr3
^
?^5 Ao So
- A °^rP
CL
^ ^%H O
*P ^ ° D
- ^^ ^ °n
- "v a O D
" ^ 0^ °0 D
rf) n o
^D Rn'-'
VOIA SQ
A
PU. O
P A
: ' ft
: II
0? S
iji
00
4> QJ
: a GL-30 -g-S
u C
: A GL-31 gg
t •)
f
r - UL.-OO "
1 1 1 , 1 ._...
0
468
g HzO/g Waste
10
12
14
Fig. 21.
Results of dynamic leaching experiments with coal waste from Plant K—specific conductance vs eluent
volume.
not previously observed in coal wastes. The calcite
content is low and, as a result, these wastes have little or
no self-neutralizing capacity.
The coal waste was separated into seven fractions
based on the gross external appearances of the individual
pieces. Elemental and mineralogical analyses of each
fraction revealed some interesting correlations. Most of
the trace elements with high discharge severities tend to
be associated with the clay- and silicate-containing
fractions. Selenium, arsenic, antimony, cadmium, and
iron were predominantly found in the fractions with high
pyrite contents. Several of these elements are important
because of their high toxicities. Their presence in the
sulfide mineral phases was expected.
Micromineralogical examination using SEM/EDS
showed little difference among the fractions regarding
micromineral contents, but this may have been a result of
the difficulty of sampling the materials in a representative
way. In general, the trace elements seem to be present as
distinct micromineral phases, rather than as chemical
associations with the gross minerals.
Static leaching experiments showed that acidity, spe-
cific conductivity, and trace element concentrations
increase smoothly with time. Because the pH values of
the leachates were very low, sometimes less than two,
these wastes may pose a serious acid-drainage problem
unless they are dealt with properly. Iron, arsenic, nickel,
manganese, and aluminum have discharge severities
greater than unity and may pose environmental problems
in uncontrolled waste pile drainages. Similarly, zinc,
cadmium, and copper have discharge severities between
0.5 and 1.0 and may be cause for concern under some
circumstances. Concentrations of arsenic, selenium, and
cadmium have much stronger time dependences than
those of the other elements. Factors other than pH may
control the leaching of these elements. These elements
are associated with the sulfide mineral phases and
probably exist as sulfides (or selenide). Consequently,
their dissolution and mobilization may be limited by the
oxidation rate of these minerals. Similar behavior may
occur with other elements that tend to form insoluble
sulfides, for example, lead and mercury.
50
-------
10*
Ji
a
£
1-1 ~2
c l(j
£
1
§ Irf
3
0 g
°o i
£
f °oo j
0 .fc
: o
o
I.I.I.
0
0
0
DS=1
°o
1,1,
1U
1
o.
^
o
S
c
o
£ -i
"c ^
S
1
irr2
»o 1
D B
: o
; o
: o
o
°o DS=1
o
o
I.I,
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
g HzO/g Waste g HzO/g Waste
1 rP * *""^
1U
?
a
S
g ,
M
{0
S
c
_o
? 10°
'S
1
6
i
c
: 5
• €
°n *
o .fa
Q
; o
o
: °
; o
1.1.1.
o
°o DS= 1
o
o
a0
I.I,
1U
6 ..a
^
O
C
§ 10°
^J
£
c
D
S 10-
S
irf~z
!
QO.
• ° o ° §
"a
• = o 1
: i
: <
o
.
I.I.I.;
DS=1
0
o
QO
I.I.
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
g HzO/g Waste g HjO/g Waste
Iff "^
J.V/
e""*"
ex
3
6 -i
e
•o
m
O
|
£ 10'"
'c
8
S
in-3
; j
£
1
£
:°o
oo
0
o o 0
I.I.I.
DS=1
o
0,0
0 « 00
I.I.
i\j
g* Iff
Q. 1U
E
I 1^
C
5
I 10°
I
C!
2 10-
3
2
?°° 1
° 1
o g
1
o
o
(
1,1.1,
DS=1
0
o
0
0
oo
,1,1,
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
g HzO/g Waste g HjO/g Waste
Fig. 22a.
Results of dynamic leaching experiments with coal waste from Plant K—concentrations of selected trace
elements in the leachate vs eluent volume.
51
-------
1U
IT
ex
d,
"i io°
0)
<
c
o
a ,
i 10
c
S
C
o
o
in"2
0 J
c
a
0
1.1,1,
DS=1
0
0
do
0
oo
1,1.
0 2 4 6 8 10 12 1'
g fWg Waste
ICf
10° ,
ID"
ID"
.0.5=1-
4 6 8 10 12 14
g HzO/g Waste
ICf
JlO°
10"
101
Q-
- 10°
10"
10-
g HzO/g Waste
4 6 B
g Hifl/g Waste
10 12
14
10 12
14
101
10°
10"
10"
10"
itf
10°
m 10
10
1
B
0
- 0
- O 0
DS=1
| OOO O QQ
I.I.
3 2 4 6 8 10 12 14
g HsO/g Waste
C
2
1
r c
: |
N
•
0
1 , 1 |
DS=1
0
00
i ° 0 OO
3 2 4 6 8 10 12 1'
g HjO/g Waste
Fig. 22b.
Results of dynamic leaching experiments with coal waste from Plant K—concentrations of selected trace
elements in the leachate vs eluent volume.
52
-------
10°
D.
O.
| 10-
—
tT
m
c
0
i io~2
"c
o
c
3
_.,
~ O
I O
D
00
an o
^ ° » » 0 0* 0 0
I.I.I.
io3
1 icf
E
1 lo1
§
<•
c „
o icr
1
c
S 10"
C
a
-------
10°
Itf
101
10-t
10°
10
10
10
3
pH
10
3
PH
Itf
10°
S 10°
10-
10
10
3
pH
10"
8
I
10
3
PH
10-
10
10
10
10
3
PH
10
Fig. 23b.
Results of dynamic leaching experiments with coal waste from Plant
elements in the leachate vs pH.
2 3 4
pH
f
-concentrat»ons of selected trace
54
-------
Dynamic leaching experiments show that initial waste
leachates are very acidic. This acidity decays to more
moderate values under steady leachate flow, but high
acidity recurs when the leachate flow is stopped and air
is forced through the waste. Therefore, intermittent
leaching of the waste can aggravate an already serious
acid-drainage problem. Iron, nickel, and manganese have
initial discharge severities greater than unity, but iron,
with a discharge severity sometimes greater than 100, is
by far the worst offender. In addition, zinc, cadmium,
aluminum, and copper, with discharge severities between
0.5 and 1.0, may be cause for concern in some cases.
Correlations between the element concentrations and the
solution pH reveal that the pH is the major controlling
factor, but that in some cases other factors are involved.
IH. COMPARISONS OF EPA EXTRACTION PRO-
CEDURE AND PAST WORK AT LOS ALAMOS
A. Background
The United States Congress, in 1976, enacted the
Resource Conservation and Recovery Act (RCRA),
designed to establish a comprehensive program for
management of solid industrial and urban wastes. This
act requires the EPA to promulgate a series of regu-
lations that classify solid wastes as hazardous or non-
hazardous, and that regulate disposal of these wastes.
One criterion that determines whether a solid waste is
considered hazardous because it may contaminate
aqueous drainages is the results of a standard leaching
procedure. This test, described in the Federal Register,7
essentially involves leaching the solid material with
deionized water under rigidly defined conditions. In the
past, we have used similar procedures to study environ-
mental weathering and leaching of these wastes; there-
fore, we are in a unique position to compare the RCRA
leaching procedure with ours. This discussion sum-
marizes our recent research in this area.
B. Results Obtained Using the EPA Extraction Pro-
cedure
Seven mineral wastes from coal preparation plants in
the Illinois Basin, the Appalachian Region, and the
Western US were leached according to the EPA extrac-
tion procedure published in the Federal Register, May
19, 1980.7 This calls for 100 g of waste to be ground to
pass through a 9.3-mm standard sieve (—3/8 in.); 1600
mf of deionized water is added to the waste, and the
mixture is agitated for 24 h in an extractor designed to
ensure that all sample surfaces are continuously brought
into contact with well-mixed extraction fluid.
The pH values of the mixtures must be monitored
during the extraction and, if the pH is greater than 5,
adjustment must be made by addition of 0.5N acetic
acid. After 24-h extraction, the solids are removed by
filtration, and the concentrations of eight elements (sil-
ver, arsenic, barium, cadmium, chromium, mercury,
lead, and selenium) in the filtrate are determined. The
results of these determinations with seven coal prepara-
tion wastes are presented in Tables XV and XVI
(analytical details are presented in Appendix F).
Table XV shows initial and final pH values for each
sample. The pH was well below 5 in all cases except for
Plant D, located in the Western US. A comparatively
small amount (34 ml) of Q.5N acetic acid maintained the
required pH of 5 throughout the extraction for this
sample. This imposed acidic pH is probably abnormal
for the western coal waste sample, but it is typical of
many coal wastes from the Eastern US.
The results of the elemental analyses, Table XVI,
reveal that many of the elements are present at levels
below the detection limits of the analytical methods. In
only three instances do any of the values exceed the
Federal Primary Drinking Water Standards. These cases
are the arsenic values for Plants B and K and the barium
value for Plant D. However, the limits specified for these
elements in nonhazardous wastes are 100 times the
Primary Drinking Water Standards,7 and all the values
of Table XVI are less than 1/10 of these.
Statistical analyses were made to determine whether
the analytical data could fail to detect an actual
equivalence between the concentrations of the various
elements and either the Primary Drinking Water Stan-
dard or the "Hazardous Waste" limit defined in the
Federal Register.7 These were done by calculating the so-
called p errors, using the one-sided t-test with a 95%
confidence interval. The method for this was published in
Ref. 15. Some of the results of these calculations are
shown in Table XVII.
Probabilities for exceeding the drinking water stan-
dards are significant only for cadmium, mercury, and
lead generally, and for arsenic and barium in specific
cases. The probabilities for exceeding the Hazardous
Waste limits, which are 100 times the drinking water
standards, are less than 0.01 in all cases.
55
-------
TABLE XV
INITIAL AND FINAL pH VALUES FOR COAL WASTE
LEACHATES USING THE EPA EXTRACTION PROCEDURE
Plant"
B
D
K
pH, initial 3.1 2.8 3.3 9.6 4.1 3.1 3.3
Acetic acid added — — — 35 mt — — —
pH, final 4.2 2.2 3.2 5.0 3.8 2.6 2.7
"Plants A, B, C: high-sulfur, Illinois Basin waste
Plant D: low-sulfur, western waste
Plant G: low-sulfur, Appalachian waste
Plants I, K: high-sulfur, Appalachian waste
TABLE XVI
CONCENTRATIONS (ppm) OF TOXICITY INDICATOR ELEMENTS IN COAL WASTE LEACHATES
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
A
<0.006
0.024
<0.06
<0.003
< 0.005
<0.001
<0.012
0.0015
B
<0.006
0.100
0.14
<0.004
0.023
<0.001
<0.012
0.0035
C
<0.006
0.007
0.08
<0.003
0.010
< 0.001
<0.012
0.0011
D
<0.006
<0.001
1.4
<0.003
<0.005
<0.001
<0.012
0.0016
Plant
G
<0.006
<0.001
0.08
< 0.003
<0.005
<0.001
< 0.01 2
0.0020
I
<0.006
0.016
<0.06
<0.003
<0.017
<0.001
<0.012
0.0017
K
<0.006
0.096
<0.06
<0.003
<0.005
< 0.001
<0.012
0.0038
HDWS"
5.0
5.0
100
1.0
5.0
0.2
5.0
1.0
"100 X Primary Drinking Water Standard.
C. Comparisons Among Different Leaching Procedures
In static leaching experiments, a fixed amount of liquid
phase is kept in contact with the solid sample throughout
the extraction, as opposed to allowing the liquid phase to
flow through the solid. Independent variables in static
experiments include the geometric surface area of the
solid (mesh size), the liquid-to-solids ratio, the duration
of the extraction, the degree and type of agitation used,
the composition of the liquid phase, the temperature,
whether the reaction mixture is open to air, and the
components determined in the final leachate. Our static
leaching experiments used deionized water as the liquid
phase with fairly vigorous agitation (90 strokes/min, 3
in./stroke). In addition, most were done at room tem-
perature with the extractor open to air. Except for
exposure to air, these conditions are comparable to those
of the EPA procedure for analysis of acidic coal wastes.
56
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TABLE XVII
PROBABILIUIES THAT TRUE CONCENTRATIONS OF TOXICITY INDICATOR ELE-
MENTS EQUAL OR EXCEED FEDERAL PRIMARY DRINKING WATER STANDARDS
Element
Plant
B
K
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
<0.01
<0.01
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
<0.01
>0.99
<0.01
<0.8
0.02
<0.5
<0.4
<0.01
<0.01
<0.01
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
<0.01
<0.01
>0.99
<0.5
<0.01
<0.5
<0.4
<0.01
<0.01
<0.01
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
<0.01
<0.01
<0.01
<0.5
<0.01
<0.7
<0.4
<0.01
<0.01
>0.99
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
Consequendy, we have only to examine the effects of the
liquid-to-solid ratio, the mesh size, and the extraction
time. The other variables are discussed in Sec. III.D.
Our 1-day static leach experiments are directly com-
parable to the EPA extraction procedure, except that we
use liquid-to-solid ratios of either 4 to 1 or 5 to 1,
whereas the EPA test uses a ratio of 16 to 1 during the
extractions, and 20 to 1 in the final samples. The
concentrations of the toxicity indicator elements in the
leachates are listed in Table XVIIIa for the EPA test and
in Table XlXa for our 1-day static leach. (The values in
Table XVIIIa are closely related to those in Table XVI,
but we adjusted them to represent the concentrations in
the original leachate at a 16-to-l liquid-to-solids ratio to
eliminate the effects of the dilution of the leachate before
the filtration and analysis.) If equilibrium had been
reached during the extraction, the concentrations of the
elements in the leachate would be independent of the
liquid-to-solid ratio, provided that the supply of the
original elements in the sample was not exhausted.
Comparison of Tables XVIIIa and XlXa reveals that
these extractions are not at equilibrium. Therefore, the
element concentrations in the leachates are at least partly
kinetically controlled. Under these circumstances a low
liquid-to-solids ratio should be used to yield more
concentrated leachates, which are easier to analyze.
A more direct comparison can be made by converting
the leachate concentrations to the total amount of each
element leached per unit of solid waste. These results are
presented in Tables XVfflb and XlXb. If the release of
an element is strictly kinetically controlled, these data
should be the same. Chromium and, to a lesser degree,
cadmium compare fairly well between these two meth-
ods. However, much more arsenic was leached using the
EPA method, and our procedure yielded higher lead
values. We used different analytical methods for arsenic,
which may explain the difference in those results, but the
lead results remain unexplained.
Tables XVIIIc and XIXc show the leachate composi-
tions as the fraction of each element in the solid before
dissolution. These results exactly parallel those in Tables
XVIIIb and XlXb. However, it is interesting that
cadmium is highly mobile, with large percentages being
extracted, whereas other elements are extracted to much
lesser degrees.
Results of extractions done on 20-mesh samples are
shown in Tables XXa-c. In general, these results are
much the same as those of the —3/8-in. samples describ-
ed in Tables XlXa-XIXc. Reduction of the particle size
from 3/8 in. to 20 mesh means a substantial increase in
the geometric surface area, so either the actual effective
surface area is much larger than the geometric surface,
or the surface area does not affect the leaching behaviors
of the elements. The former conclusion seems more
likely.
Longer term static leaches are summarized in Tables
XXIa-XXIc. In most cases, the amounts of leached
elements remained constant or increased with duration of
extraction. Although this agrees with our concept of the
way leaching works, the differences between the 1-day
57
-------
TABLE XVIIIa
ADJUSTED' LEACHATE COMPOSITIONS OBTAINED USING THE RCRA LEACHING
PROCEDURE FOR COAL WASTE SAMPLES (ppm)
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
pH
A
<0.008
0.030
<0.075
<0.004
< 0.006
<0.001
<0.015
0.0019
4.2
B
<0.008
0.125
0.175
<0.005
0.029
<0.001
<0.015
0.0044
2.2
C
<0.008
0.009
0.100
<0.004
0.012
<0.001
<0.015
0.0014
3.2
Plant
D
<0.008
<0.001
0.075
<0.004
<0.006
<0.001
<0.015
0.0020
5.0
G
<0.008
<0.001
0.100
<0.004
<0.006
<0.001
<0.015
0.0025
3.8
I
<0.008
0.020
<0.075
<0.004
<0.021
<0.001
<0.015
0.0021
2.6
K
<0.008
0.120
< 0.075
<0.004
<0.006
<0.001
<0.015
0.0048
2.7
"Adjusted to reflect original leachate composition at 16-to-l liquid-to-solids ratio, before dilution to the final 20-
to-1 ratio.
TABLE XVIIIb
LEACHATE COMPOSITIONS OBTAINED USING RCRA LEACHING PROCEDURE FOR
COAL WASTE SAMPLES. RESULTS EXPRESSED AS MILLIGRAM ELEMENT LEACHED
PER KILOGRAM SOLID WASTE
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
pH
A
-------
TABLE XlXa
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER
LEACHES OF COAL WASTE SAMPLES (-3/8-in.) (ppm)
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
A
0.008
—
0.0014
0.001
—
0.048
—
7.J
B
—
—
0.024
0.060
—
0.300
—
2.2
Plant
C D
0.004
—
0.020
0.032
—
0.32
—
3.5
G I
—
—
0.015
0.094
—
—
—
2.6
K
0.054
—
0.010
—
—
0.15
0.002
3.0
TABLE XlXb
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER
LEACHES OF COAL WASTE SAMPLES (-3/8-in.). RESULTS EXPRESSED
AS MILLIGRAMS ELEMENT LEACHED PER KILOGRAM SOLID WASTE
Element
Ag
As
n_
Da
Cd
Cr
Hg
Pb
Se
PH
A
0.04
0.0068
0.005
—
0.240
—
7.1
B
—
0.12
0.30
—
1.5
—
2.2
C
0.02
0.10
0.16
—
1.6
—
3.5
Plant
D G I
—
0.075
0.470
—
—
—
2.6
K
0.270
0.050
—
—
0.750
0.010
3.0
TABLE XIXc
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER
LEACHES OF COAL WASTE SAMPLES (-3/8-in.). RESULTS
EXPRESSED AS THE PERCENT OF THE ELEMENT ORIGINALLY
PRESENT THAT APPEARS IN THE LEACHATE
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
ph
A
0.07
—
2.8
0.008
—
0.49
—
7.1
B
—
—
30
0.48
—
4.4
—
2.2
Plant
C D G I K
0.09
—
8.9
0.23
—
3.2
—
3.5
59
-------
TABLE XXa
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER
LEACHES OF COAL WASTE SAMPLES (-20 MESH) (ppm)
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
pH
A
<0.008
<0.008
—
2.9
<0.001
<0.20
0.048
—
7.1
B
—
—
48
0.156
—
0.320
—
2.2
Plant
C D
<0.008
<0.004
—
8.9
0.032
<0.20
0.320
—
3.5
G I K
, —
— —
— —
9.3
0.0018 0.080
— —
— —
— —
4.3 3.2
TABLE XXb
LEACHATE COMPOSITIONS OBTAINED FROM ONE DAY SHAKER
LEACHES OF COAL WASTE SAMPLES (-20 MESH). RESULTS
EXPRESSED AS MILLIGRAMS ELEMENT LEACHED
PER KILOGRAM SOLID WASTE
Element
Ag
As
Dn
Ha
Cd
Cr
Hg
Pb
Se
pH
A
<0.040
<0.040
0.0070
<0.005
<1.00
0.24
—
7.1
B
_
—
0.190
0.780
—
1.60
—
2.2
Plant
C D
<0.040
<0.020
0.100
0.160
-------
TABLE XXIa
LEACHATE COMPOSITIONS OBTAINED FROM LONG-TERM SHAKER
LEACHES OF COAL WASTE SAMPLES (-3/8-in.) (ppm)
Plant
Element
Days
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
A
28
—
0.008
—
0.0003
0.0012
—
0.006
—
7.6
B
22
—
—
—
0.035
0.116
—
0.280
—
1.9
C D
28
0.175
—
0.124
0.240
—
0.360
—
1.9
G I
25
—
—
—
0.01
0.10
—
—
—
2.2
K
25
—
3.0
—
0.041
—
—
0.004
0.036
2.0
TABLE XXIb
LEACHATE COMPOSITIONS OBTAINED FROM LONG-TERM
SHAKER LEACHES OF COAL WASTE SAMPLES (-3/8-in.)
RESULTS EXPRESSED AS MILLIGRAMS ELEMENT LEACHED PER
KILOGRAM SOLID WASTE
Plant
Element
Days
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
A
28
—
0.04
i
C.0014
0.006
—
0.030
—
7.6
B
28
—
—
—
0.18
0.58
—
1.40
—
1.9
C
28
—
0.88
—
0.62
1.20
—
1.80
—
1.9
D G I
25
—
—
—
0.05
0.50
—
—
—
2.2
K
25
—
15.0
—
0.205
—
—
0.020
0.180
2.0
TABLE XXIc
LEACHATE COMPOSITIONS OBTAINED FROM LONG-TERM SHAKER
LEACHES OF COAL WASTE SAMPLES (-3/8-in.) RESULTS EXPRESSED AS THE
PERCENT OF THE ELEMENT ORIGINALLY PRESENT THAT APPEARS IN THE
LEACHATE
Plant
Element
Days
Ag
As
Bg
Cd
Cr
Hg
Pb
Se
PH
A
28
—
0.071
—
0.583
0.010
—
0.061
—
7.6
B
28
—
—
—
45.0
0.935
—
4.12
—
1.9
C
28
—
4.0
—
55.4
1.74
—
3.60
1.9
D G I K
25 25
2.2 2.0
61
-------
and the multiday leaches are small. This suggests that
most of the action, at least for arsenic, cadmium,
chromium, and lead, occurs in the early part of the
experiment (the first 24 h).
Our static leaching experiments were designed to
determine materials that might be leached from a coal
waste: our dynamic (column) leaching experiments were
designed to simulate the weathering of an exposed waste
pile. We wanted to study the leaching of elements as a
function of time and to discover the effects of intermit-
tent leaching. Although these experiments are more
difficult to compare with the EPA procedure than the
static leaches, we compared them by integrating the
concentration-versus-volume curve in each element to a
volume representing a 16-to-l liquid-to-solids ratio. This
gives the total amount of an element extracted in that
volume. From these results, we calculated the amounts
extracted per unit solids shown in Table XXIIb, and
from those values, we derived the results shown in Tables
XXIIa and c. Most of the extraction occurs early in the
experiment, so that the choice of the upper volume limit
to the integration does not drastically affect the results.
In general, the column leaching experiments show higher
extraction efficiencies than the static experiments, espe-
cially for arsenic and, to lesser degrees, for cadmium and
chromium. Lead shows the reverse trend, possibly be-
cause of reprecipitation caused by the increase in pH
with time.
In summary, results of the EPA leaching procedure
agree with results of our procedure to the extent to which
TABLE XXIIa
LEACHABILITIES OF SELECTED ELEMENTS
FROM COAL WASTE SAMPLES (-3/8-in.) OB-
TAINED FROM CONTINUOUS COLUMN
LEACHING EXPERIMENTS.
(ppm for 16 I water per kg solid)
Plant
Element A
Ag - - _ _
As 0.016 0.34 O.JO —
Ba — — — _
Cd 0.0048 0.016 0.0072 0.0026
Cr 0.031 0.021 0.050 0.0080
Hg - — _ _
Pb 0.014 0.022 0.0075 —
Se — — — _
pH 2.9-7.7 1.7-3.4 2.4-3.8 2.9-4.0
TABLE XXIIb
LEACHABILITIES OF SELECTED ELEMENTS FROM
COAL WASTE SAMPLES (-3/8-in.) OBTAINED FROM
CONTINUOUS COLUMN LEACHING EXPERIMENTS.
RESULTS EXPRESSED AS MILLIGRAM ELEMENT
LEACHED PER KILOGRAM SOLID WASTE
Plant
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
A
0.26
—
0.077
0.49
0.22
—
2.9-7.7
B
5.3
—
0.26
0.39
0.35
—
1.7-3.4
C
0.80
—
0.12
0.80
0.12
—
2.4-3.8
G
—
—
0.042
0.13
—
—
2.9-4.0
TABLE XXOc
LEACHABILITIES OF SELECTED ELEMENTS FROM
COAL WASTE SAMPLES (-3/8-in.) OBTAINED FROM
CONTINUOUS COLUMN LEACHING EXPERIMENTS
RESULTS EXPRESSED AS PERCENT OF THE ELEMENT
ORIGINALLY PRESENT THAT APPEARS IN THE
LEACHATE
Plant
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
pH
A
0.46
—
32
0.82
—
0.44
—
19-7.7
B
5.7
66
6.4
—
1.0
1.7-3.4
C
3.6
10
1.2
0.24
2.4-3.8
G
13
0.14
_
2.9-4.0
these methods can be compared. The major difference
between the procedures (in the case of acidic coal
preparation wastes) is the higher liquid-to-solids ratio
used m the EPA method. This high ratio dilutes the
leachate and makes chemical analyses more difficult.
With nonacidic coal wastes, another difference is that
acetic ac,d ,s added to the extraction mixture in the EPA
method. For coal wastes that are not naturally acidic,
to creates an artificial env.ronment and complicates
interpretation of the results.
62
-------
D. EPA Leaching Procedure as Applied to Coal Wastes
The EPA leach test is designed to satisfy a regulatory
need to classify solid wastes as hazardous or not. As
such, it must apply to a wide variety of wastes, including
municipal, chemical, and industrial by-products, whose
properties and chemical behaviors may differ substantial-
ly. It is unlikely that any single test can be entirely
appropriate in all cases, and thus, it is important to
understand the limitations of the test for various types of
waste. The following discussion concerns our observa-
tions on the applicability of the EPA leaching test to coal
preparation wastes. The most important question is
whether the EPA leaching test accurately indicates
whether a given waste can harm the environment.
Studies have revealed that the chemical components
with the highest discharge severities in leachates from
coal preparation wastes are iron, aluminum, nickel,
manganese, zinc, copper, and cadmium, as well as the
acidity.1"3 The elements addressed in the EPA leaching
test are those included in the Federal Primary Drinking
Water Standards (silver, arsenic, barium, cadmium,
chromium, mercury, lead, and selenium). The only
element common to these two groups is cadmium. Iron
has by far the highest discharge severity, based on the
MEG/MATE system,5 followed roughly in order by the
other elements listed. Some of the elements included in
the EPA procedure, notably silver, mercury, and barium
are typically present at levels below the detection limits
of the methods used for the analysis of the leachates.
Furthermore, the parent coal waste materials often
contain these elements in such minimal quantities that we
have rarely attempted to determine them in our research
on coal waste leaching behavior. Consequently, in the
case of typical coal preparation wastes, we conclude that
the present EPA leaching test does not address the
elements of real concern. If the elements in the Secon-
dary Drinking Water Standards were included, the test
would be markedly improved because iron, manganese,
zinc, and copper would be covered. Only aluminum and
nickel, elements of potential concern, would not be
analyzed in the EPA leaching test.
In analysis of acidic coal wastes, the leachates are
sufficiently acid so that no acetic acid additions are
needed. Under these circumstances, the EPA test is
essentially a water leach and reasonably simulates the
acid-base conditions expected in a stagnant coal waste
pile. Acidic coal wastes are the most abundant type and
represent the wastes of most concern in the Eastern US
coal fields, so this test is appropriate. However, alkaline
coal wastes, typically from the Western US, are treated
differently in the EPA test. These wastes are acidified to
a pH of 5 with acetic acid and subjected to an artificial
environment that they are unlikely to encounter under
normal circumstances. We believe this test is unneces-
sarily severe for those elements mobilized under acidic
conditions, and it ignores the possible effects of elements
such as selenium and arsenic, which may be alkaline
mobile.
Because small particles have a higher geometric
surface area per unit mass than large particles, the results
of a leaching experiment should depend on the size of the
particles in the solid sample. However, our experience
with coal wastes shows that particle size does not
strongly affect the results of leaching experiments. There-
fore, we chose the most convenient size for this type of
waste [9.3 mm (-3/8 in.)].
Agitation of the sample during the leaching procedure
is most important. The EPA test procedure calls for
vigorous agitations, which, in our opinion, is preferable
to stagnant leaching: a vigorous agitation is easier to
define and reproduce from one experiment to the next
and among different laboratories.
Duration of leaching, necessarily a compromise, must
be long enough to allow any chemical reactions to
proceed to a reasonable degree, and yet short enough to
complete the experiment in a reasonable time. With
high-sulfur coal wastes with no self-neutralizing capacity,
the 24-h extraction time seems reasonable. However,
some materials may not become severely acidic for
several days or even weeks. This delay may be caused by
the presence of carbonate minerals acting as in situ
neutralizing agents, which must be used up before the pH
can become very acidic. Such a delay in the
acid-releasing character of a coal waste could result in a
toxic material being erroneously classified as non-
hazardous. The only straightforward way to avoid this is
to run leaching experiments for longer periods of time. In
addition, there is the question of how the aging of a
refuse pile might affect its leaching behavior. This may
be outside the purview of a regulatory test procedure,
and is a problem that can only be addressed by careful
research and understanding of the chemistry of the
refuse material.
One factor important in the case of coal wastes (but
possibly unimportant for other types of solid wastes) is
the presence of air during the leaching process. The
leachates from coal wastes are acidic because the
oxidation of pyrite yields sulfuric acid as a by-product. If
access of air to the solid is restricted, less oxidation
63
-------
occurs and the leachates are less acidic. In a 24-h
leaching experiment, most of the acid involved was
generated before the actual leach was begun, so access to
air may not be important. However, in longer leaching
experiments, the generation of acid during the experi-
ment may be significant and restriction of the air intake
may lead to artificially low results.
With reference to coal waste samples, liquid-to-solid
ratios of 20 to 1 for the final analysis often tax the
detection limits of the analytical procedures. A lower
liquid-to-solids ratio, for example, 4 or 5 to 1, would
allow greater confidence in the analytical results and
their implications concerning pollution potentials.
Finally, we offer one comment on the mechanical
aspects of the extraction procedure. To facilitate the
rapid separation of the leachate from the solid residue,
thus eliminating long contact times of leachate and
residue after the 24-h agitation period, we have found it
advantageous to use a prefiltering step with a hard
ashless filter paper (Whatman 541) and a Buchner
porcelain funnel before final filtration through a Milli-
pore 0.45-um filter. Even a glass fiber prefilter, as
mentioned in the extraction procedure, offers little relief
from prolonged separations of materials containing
clays, and the prefiltering with the paper is much more
rapid than the centrifuge method described in the EPA
test procedure.
E. Summary and Conclusions
Mineral wastes from seven coal preparation plants,
located in various parts of the country, have been
leached in accordance with the EPA extraction pro-
cedure published in the Federal Register dated May 19,
I960.7 According to the criteria set forth in this pro-
cedure, all the coal wastes are nonhazardous. The
probability that any of the eight elements examined
might exceed the levels set forth in the procedure is less
than 1 %. The probabilities of the elements exceeding the
Federal Primary Drinking Water standards are signifi-
cant only for cadmium, mercury, and lead.
Compared with leaching tests we have used over the
past several years on coal wastes, the EPA test gives
similar results for those elements examined. The primary
differences between our procedure and that of the EPA
are the use of a higher liquid-to-solids ratio in the EPA
test and their requirement that alkaline systems be
acidified with acetic acid.
64
With respect to coal preparation wastes we can make
the following comments concerning the EPA extraction
procedure.
• Iron, aluminum, nickel, and manganese, which
have the highest discharge severities in coal waste
leachates, are not addressed by the method.
• We believe that the acidification of nonacidic
materials is inappropriate in the case of coal
wastes.
• Filtration time can be significantly shortened by
introducing a prefiltering step before filtration
through the Millipore filter.
We also question whether longer extraction times should
be considered and whether the extraction vessel should
be left open to the air.
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9. E. A. Jenne, "Controls on Mn, Fe, Co, Ni, Cu and
Zn Concentrations in Soils and Water: The Signifi-
cant Role of Hydrous Mn and Fe Oxides," in Trace
Inorganics in Water, R. F. Gould, Ed. (American
Chemical Society, 1968), Chap. 21, pp. 337-387.
10. R. O. James and T. W. Healy, "Adsorption of
Hydrolyzable Metal Ions at the Oxide-Water In-
terface I. Co(H) Adsorption on SiO2.and TiO2 as
Model Systems," J. Colloid Interface Sci. 40, 42
(1972).
11. E. F. Thode, J. M. Williams, E. M. Wewerka, and P.
Wagner, "Costs of Coal and Electric Power Pro-
duction—The Impact of Environmental Control
Technologies for Coal-Cleaning Plants," Los
Alamos Scientific Laboratory report LA-8039-MS
(October 1979).
12. E. M. Wewerka, J. M. Williams, N. E. Vanderborgh,
P. Wagner, P. L. Wanek, and J. D. Olsen, "Trace
Element Characterization and Removal/Recovery
from Coal and Coal Wastes: Progress Report for
the Period October 1, 1976 to December 31, 1976,"
Los Alamos Scientific Laboratory report
LA-6933-PR (October 1977).
13. J. M. Williams, "Qualitative and Quantitative
X-Ray Mineralogy: A Layman's Approach," Los
Alamos Scientific Laboratory report LA-8409-MS
(June 1980).
14. J. M. Williams, N. E. Elliott, E. A. Hakkila, W. B.
Hutchinson, L. S. Levinson, R. D. Reiswig, W. O.
Wallace, E. M. Wewerka, and W. F. Zelezny, "Coal
Preparation Waste Micromineralogy," Los Alamos
Scientific Laboratory report LA-8474-MS (August
1980).
15. M. G. Natrella, "Experimental Statistics," National
Bureau of Standards Handbook 91, US Government
Printing Office (1966), pp. 3-13.
APPENDIX A
RESULTS OF LIME AND LIME/LIMESTONE TREATMENT EXPERIMENTS
Detailed descriptions of the procedures used in this
experiment were published in Ref. 4 (main text); however
a brief summary is provided here. Results are presented
in Tables A-I through -VII.
Three 55-gal. drums of Plant M, high-sulfur, Illinois
Basin coal preparation waste were crushed to —3/8 in.
without prior drying. Scoops of material from each
barrel were placed in sequence into six empty barrels
fitted with plastic liners until each barrel held 250 Ib of
material. We added 30 ( of deionized water to 'each
barrel and tumbled the barrel for 5 min at 15 rpm. After
the barrels stood for several days, excess water (approx-
imately 8 I) was siphoned off and analyzed for acidity.
The leachates had pH values from 2.8 to 2.9 and were
0.045 molar in acid. We added a slurry (38 to 50%
solids) of lime to each barrel. This slurry was blended
into the waste slurry by tumbling the barrel at 15 rpm for
2 min. In one case, limestone was later added and
blended. (Each mixture settled for 4 to 9 days while other
barrels were being prepared and used.) After settling,
excess water was siphoned off, and the slurry was sieved
through a muslin filter into a 90- by 150- by 25-cm-deep
polyethylene tub and spread evenly to allow further
water drainage.
The drained lime/limestone/waste slurries were por-
tioned into several groups. The first six portions (1/10
65
-------
TABLE A-I
RESULTS OF LABORATORY WEATHERING EXPERIMENTS USING
HIGH-SULFUR COAL PREPARATION WASTE
TREATED WITH 0.17% LIME
Time
(Weeks)
3
4
5
6
7
8
9
10
11
12
13
15
19
23
27
31
35
39
Volume
(I)
0.65
0.75
1.06
0.92
1.04
1.04
1.00
0.80
1.10
1.03
0.88
4.08
3.71
3.45
2.57
2.98
2.76
2.88
Cum
Volume
U)
0.65
1.40
2.46
3.38
4.42
5.46
6.46
7.26
8.36
9.39
10.27
14.35
18.06
21.51
24.08
27.06
29.82
32.70
Cum VolV
Mass Waste
(cm'/g)
0.057
0.123
0.216
0.296
0.388
0.479
0.567
0.637
0.733
0.824
0.901
1.26
1.58
1.89
2.11
2.37
2.62
2.87
pH
2.37
2.23
2.16
2.17
2.18
2.17
1.96
1.73
1.98
1.84
1.77
1.84
1.72
1.65
1.53
1.53
1.60
1.63
Cond
(mmho/cm)
6.80
7.50
8.70
9.35
12.0
12.5
12.8
19.0
11.0
13.0
16.0
12.2
14.6
15.8
20.0
17.4
20.7
18.8
Total Fe
(rag/cm")
3.75
5.18
8.47
8.50
9.70
12.3
14.4
21.4
11.6
11.8
12.8
14.1
14.6
14.7
15.3
-
-
~
Fe (II)
(mg/cm')
2.00
2.25
2.95
3.94
3.64
3.72
4.86
7.98
3.84
3.45
4.42
3.62
4.30
2.09
2.28
-
-
~
"11.4 kg waste per experiment.
TABLE A-II
RESULTS OF LABORATORY WEATHERING EXPERIMENTS USING
HIGH-SULFUR COAL PREPARATION WASTE
TREATED WITH 0.33% LIME
Time
(Weeks)
3
4
5
6
7
8
9
10
11
12
13
15
19
23
27
31
35
39
Volume
w
0.50
0.65
0.91
0.86
1.04
1.02
1.01
0.83
1.10
1.06
0.86
4.12
3.89
3.59
2.87
3.26
3.03
3.21
Cum
Volume
w
0.50
1.15
2.05
2.92
3.96
4.98
5.99
6.82
7.92
8.98
9.84
13.96
17.85
21.44
24.31
27.57
30.60
33.81
Cum VolV
Mass Waste
(cm'/g)
0.044
0.101
0.180
0.256
0.347
0.437
0.525
0.598
0.695
0.788
0.863
1.22
1.57
1.88
2.13
2.42
2.68
2.97
pH
2.47
2.19
2.19
2.21
2.23
2.22
1.99
1.77
1.99
1.86
1.82
1.85
1.76
1.71
1.59
1.58
1.64
1.61
Cond
(mmho/cm)
5.10
7.50
7.75
8.75
11.8
11.6
12.0
18.5
11.0
12.5
15.3
12.2
13.4
14.5
18.5
15.5
16.1
17.6
Total Fe
(mg/cm')
1.66
4.29
4.72
10.1
10.4
11.3
13.0
22.1
14.3
10.3
11.8
10.0
16.2
15.0
19.9
Fe (II)
(mg/cm3)
0.67
1.65
2.03
3.30
3.12
2.90
3.85
7.87
4.75
2.93
4 4^
t.fU
3.30
q 71
O. / J.
2.01
3.07
a!1.4 kg waste per experiment
66
-------
TABLE A-III
RESULTS OF LABORATORY WEATHERING EXPERIMENTS USING
HIGH-SULFUR COAL PREPARATION WASTE TREATED WITH 0.53% LIME
Time
(Weeks)
3
4
5
6
7
8
9
10
11
12
13
15
19
23
27
31
35
39
Volume
w)
0.75
0.65
0.82
0.77
0.73
0.89
0.95
0.81
1.11
1.05
0.94
4.12
3.85
3.52
2.87
3.07
2.82
2.96
Cum
Volume
W
0.75
1.40
2.22
2.99
3.72
4.61
5.56
6.37
7.48
8.53
9.47
13.59
17.44
20.96
23.83
26.90
29.72
32.68
Cum VolV
Mass Waste
(cm'/g)
0.066
0.123
0.195
0.262
0.326
0.404
0.488
0.559
0.656
0.748
0.831
1.19
1.53
1.84
2.09
2.36
2.61
2.87
PH
3.80
2.75
2.58
2.38
2.25
2.29
2.02
1.88
2.02
1.87
1.81
1.79
1.63
1.54
1.43
1.49
1.52
1.49
Cond
(mmho/cm)
2.05
2.85
4.00
6.70
11.3
12.0
12.6
175
11.7
13.5
16.0
14.0
17.0
19.3
23.0
20.0
17.9
22.0
Total Fe
(mg/cm')
0.004
0.121
1.34
3.55
6.97
13.1
14.5
21.9
18.9
22.9
18.3
20.0
15.7
22.7
21.6
—
-
-
Fe (II)
(mg/cm')
0.002
0.010
0.610
1.42
3.52
2.90
3.94
7.79
3.56
4.02
5.35
3.66
2.85
2.28
3.15
—
-
-
"11.4 kg waste per experiment.
TABLE A-IV
RESULTS OF LABORATORY WEATHERING EXPERIMENTS USING
HIGH-SULFUR COAL PREPARATION WASTE TREATED WITH 1.1% LIME
Time
(Weeks)
3
4
5
6
7
8
9
10
11
12
13
15
19
23
27
31
35
39
Volume
(1)
0.60
0.60
0.82
0.84
0.72
0.80
0.69
0.51
0.97
0.80
0.58
3.26
3.03
3.35
2.64
3.10
2.80
2.85
Cum
Volume
W
0.60
1.20
2.02
2.86
3.58
4.38
5.07
5.58
6.55
7.35
7.93
11.19
14.22
17.57
20.21
23.31
26.11
28.96
Cum VolV
Mass Waste
(cmVg)
0.053
0.105
0.177
0.251
0.314
0.384
0.445
0.489
0.574
0.645
0.696
0.982
1.25
1.54
1.77
2.04
2.29
2.54
PH
2.22
3.76
3.41
4.15
3.71
3.65
3.01
2.92
3.04
2.82
2.55
2.37
2.07
1.97
1.76
1.61
1.59
1.51
Cond
(mmho/cm)
7.70
3.15
2.16
2.05
2.15
2.30
2.50
2.85
3.05
3.29
6.40
5.50
11.0
13.1
17.3
16.2
18.5
20.5
Total Fe
(mg/cm')
0.001
0.001
0.006
0.001
0.001
0.001
0.004
0.003
0.030
0.029
1.22
—
14.4
22.7
29.1
-
_
-
Fe (II)
(mg/cm')
0.001
0.001
0.006
0.000
0.000
0.000
0.001
0.001
0.006
0.004
0.469
-
2.76
2.09
4.32
-
_
-
•11.4 kg waste per experiment.
67
-------
TABLE A-V
RESULTS OF LABORATORY WEATHERING EXPERIMENTS USING
HIGH-SULFUR COAL PREPARATION WASTE
TREATED WITH 3.3% LIME
Time
(Weeks)
3
4
5
6
7
8
9
10
11
12
13
15
19
23
27
31
35
39
Volume
(/)
0.40
0.50
0.70
0.59
0.60
0.70
0.68
0.46
0.88
0.73
0.60
2.88
2.19
1.20
0.60
0.51
0.43
0.04
Cum
Volume
(I)
0.40
0.90
1.60
2.19
2.79
3.49
4.17
4.63
5.51
6.24
6.84
9.72
11.91
13.11
13.71
14.22
14.65
14.69
Cum Vol"/
Mass Waste
(cm'/g)
0.035
0.079
0.140
0.192
0.245
0.306
0.366
0.406
0.483
0.547
0.600
0.853
1.04
1.15
1.20
1.25
1.28
1.29
pH
11.70
11.60
11.47
11.27
11.09
10.76
9.3
8.0
7.3
7.1
7.1
4.8
4.6
3.6
3.6
3.6
3.04
2.52
Cond
(mmho/cm)
4.20
3.00
2.57
2.58
2.45
-
2.38
2.55
2.53
2.50
2.32
2.89
2.51
2.45
2.50
2.65
3.30
a.oo
Total Fe
(mg/cm')
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.002
0.002
0.003
0.004
-
-
—
Fe (II)
(mg/cm')
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.000
0.000
0.000
-
-
—
"11.4 kg waste per experiment.
TABLE A-VI
RESULTS OF LABORATORY WEATHERING EXPERIMENTS USING
HIGH-SULFUR COAL PREPARATION WASTE
TREATED WITH 0.35% LIME AND 1.1% LIMESTONE
Time
(Weeks)
3
4
5
6
7
8
9
10
11
12
13
15
19
23
27
31
35
39
Volume
w
0.50
0.60
0.77
0.73
0.67
0.96
0.72
0.63
0.99
0.83
0.59
3.36
2.41
1.97
2.08
3.12
3.09
2.94
Cum
Volume
(I)
0.50
1.10
1.87
2.60
3.27
4.23
4.95
5.58
6.57
7.40
7.99
11.35
13.76
15.73
17.81
20.93
24.02
26.96
Cum VolV
Mass Waste
(crn'/g)
0.055
0.121
0.205
0.286
0.359
0.465
0.544
0.613
0.722
0.813
0.878
1.25
1.51
1.73
1.96
2.30
2.64
2.96
PH
7.35
7.34
7.34
7.40
7.63
7.31
7.54
7.51
7.53
7.43
7.68
7.49
4.44
2.35
1.90
1.66
1.70
1.56
Cond
(mmho/cm)
2.20
2.20
1.93
2.02
2.01
2.00
1.85
2.08
1.82
1.82
2.00
1.80
2.40
7.11
15.0
_
16.0
19.0
Total Fe
(mg/cm8)
0.000
0.000
0.001
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.011
4.19
10.9
-
Fe (II)
(mg/cm8)
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.002
0.283
4.51
-
•9.1 kg waste per experiment.
68
-------
TABLE A-VII
TRACE ELEMENT CONCENTRATIONS IN THE LEAC HATES FROM TREATED
HIGH-SULFUR COAL PREPARATION WASTES
Experiment ID
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 5; 3.3% CaO
No. 5; 3.3% CaO
No. 5; 3.3% CaO
No. 5; 3.3% CaO
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCOs
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
Time
(Weeks)
3
5
10
15
27
39
3
5
10
15
27
39
3
4
5
12
15
27
39
3
10
12
15
19
27
39
3
15
23
39
3
15
19
23
27
31
39
pH
2.37
2.16
1.73
1.84
1.53
1.63
2.47
2.19
1.77
1.85
1.59
1.61
3.80
2.75
2.58
1.87
1.79
1.43
1.49
2.2
2.92
2.81
2.37
2.08
1.76
1.51
11.7
4.77
3.61
2.52
7.35
7.49
4.44
2.35
1.90
1.66
1.56
Ni
(ppm)
26
28
60
51
45
45
14
25
53
34
33
45
2.3
4.4
9.5
22
30
27
15
0.18
1.64
3.1
11.6
50
50
29
0.36
0.34
0.19
4.1
0.37
0.40
6.4
33
57
65
56
Al
(ppm)
190
270
460
370
420
410
97
220
450
330
390
390
3.4
18.1
58
340
380
380
370
2.9
10.2
18.7
97
460
460
420
1.11
1.35
1.63
62
1.35
1.21
31
210
400
420
390
Mn
(ppm)
53
57
72
41
32
21
39
55
70
43
31
22
7.9
14.1
28
56
52
36
21
0.17
5.8
10.0
27
62
70
37
0.04
0.06
0.13
16.13
1.55
1.62
19.8
51
85
75
46
Cu
(ppm)
1.2
2.2
12.9
4.3
3.7
<3
1.4
2.9
6.6
3.4
3.6
5.0
0.03
0.18
0.56
8.6
6.1
<3
<3
0.03
0.06
0.30
1.3
<3
5.4
<3
<0.02
<0.02
<0.02
1.3
<0.02
0.03
0.66
<1
5.2
<3
<3
Zn
(ppm)
18.4
13.6
<3
<3
<3
<3
13
19.7
<3
<3
<3
<3
1.15
4.0
9.7
<3
4.6
<3
<3
<0.02
1.54
3.3
10.1
8.4
<3
<3
<0.02
<0.02
0.02
4.5
<0.02
<0.02
5.6
9.4
18.1
<3
<3
Co
(ppm)
7.9
9.4
19.2
6.4
<4
<4
5.6
7.6
7.8
<4
5.5
<4
0.6
1.9
3.9
11.6
5.0
7.4
6.4
0.03
0.64
1.2
3.3
5.0
8.8
<4
<0.03
<0.03
<0.03
1.4
<0.03
0.08
2.8
8.6
12.6
12.6
<4
Ca
(ppm)
510
460
820
610
720
710
490
490
830
620
700
700
440
390
430
780
780
820
790
1480
400
450
410
920
900
830
700
520
470
510
470
380
410
560
770
860
850
K
(ppm)
190
220
340
380
260
160
94
151
196
<200
<200
<200
40
48
75
250
177
300
<200
71
57
37
93
420
<200
<200
25
29
26
44
28
17
26
<50
<100
<200
<200
Na
(ppm)
<6
<10
<30
<30
<30
<30
<2
<6
<30
<30
<30
<30
7.9
8.2
<2
<30
<30
<30
<30
19.2
10.6
7.4
<2
<30
<30
<30
7.7
5.0
3.7
6.0
5.2
1.05
1.63
<10
<20
<30
<30
Cd
(ppm)
<1
<2
<5
<5
<5
<5
<0.3
<1
<5
<5
<5
<5
<0.03
<0.03
<0.3
<5
<5
<5
<5
<0.03
<0.03
<0.03
<0.3
<5
<5
<5
<0.04
<0.03
<0.03
<0.04
<0.04
<0.03
<0.03
<2
<3
<5
<5
H,O, Control
0.05
<0.3
0.01 <0.02 <0.02 <0.02
2.3
<0.9
<0.2
<0.02
69
-------
TABLE A-VIII
DISCHARGE SEVERITIES FOR TRACE ELEMENTS IN THE LEACHATES FROM
TREATED HIGH-SULFUR COAL PREPARATION WASTES
Experiment ID
No 1, 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0.17% CaO
No. 1; 0 17% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 2; 0.33% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 3; 0.53% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 4; 1.12% CaO
No. 5; 3.3% CaO
No. 5; 3.3% CaO
No. 5; 3.3% CaO
No. 5; 3.3% CaO
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6; 0.35% CaO 1.1% CaCO,
No. 6, 0.35% CaO 1 1% CaCO,
No. 6; 0.35% CaO 1 1% CaCO,
No. 6; 0 35% CaO 1 1% CaCO,
Time
(Weeks)
3
5
10
15
27
3
5
10
15
27
39
3
4
5
12
15
27
39
3
10
12
15
19
27
39
3
15
23
39
3
15
19
21
23
27
31
39
pH
2.37
2.16
1.73
1.84
1.53
2.47
2.19
1.77
1.85
1.59
1.61
3.80
2.75
2.58
1.87
1.79
1.43
1.49
2.22
2.92
2.81
2.37
2.08
1.76
1.51
11.7
4.77
3.61
2.52
7.35
7.49
4.44
3.05
2.35
1.90
1.66
1.56
Fe
150
339
856
564
612
66.4
189
884
400
796
-
0.156
4.84
53.6
916
800
864
-
0.056
0.103
1.16
-
576
1160
0.011
0.075
0.120
—
0.0004
0.432
168
436
Ni
26.0
28.0
60.0
51.0
45.0
14.0
25.0
53.0
34.0
33.0
45.0
2.30
4.40
9.50
22.0
30.0
27.0
15.0
0.180
1.64
3.10
11.6
50.0
50.0
29.0
0.360
0.340
0.190
4.10
0.370
0.400
6.40
14.8
33
57
65.0
56.0
Al
1.90
2.70
4.60
3.70
4.20
0.97
2.20
4.50
3.30
3.90
3.90
0.034
0.181
0.580
3.40
3.80
3.80
3.70
0.029
0.102
0.187
0.970
4.60
4.60
4.20
0.0111
0.0135
0.0163
0.620
0.0135
0.0121
0.310
1.00
2.10
4.00
4.20
3.90
Mn
5.30
5.70
7.20
4.10
3.20
3.90
5.50
7.00
4.30
3.10
2.20
0.79
1.41
2.80
5.60
5.20
3.60
2.10
0.017
0.980
1.00
2.70
6.20
7.00
3.70
0.004
0.006
0.013
1.613
0.155
0.162
1.98
4.10
5.10
8.50
7.50
4.60
Cu
0.240
0.440
2.58
0.860
0.740
0.280
0.580
1.32
0.680
0.720
1.00
0.006
0.036
0.112
1.72
1.22
<0.600
•C0.600
0.006
0.012
0.060
0.260
<0.600
1.080
<0.600
<0.004
<0.004
<0.004
0.260
<0.004
0.006
0.132
0.360
<0.200
1.04
<0.600
•C0.600
Zn
1.84
1.36
<2.300
<0.300
<0.300
1.30
1.97
<0.300
<0.300
<0.300
<0.300
0.115
0.400
0.970
<0.300
0.460
<0.300
<0.300
<0.002
0.154
0.330
1.01
0.840
<0.300
<0.300
<0.002
<0.002
0.002
0.450
<0.002
<0.002
0.560
1.36
0.940
1.81
•C0.300
<0.300
Co
0.316
0.375
0.768
0.256
<0.160
0.224
0.304
0.312
<0.160
0.220
<0.160
0.024
0.076
0.156
0.464
0.200
0.296
0.256
0.001
0.026
0.048
0.132
0.200
0.352
<0.160
<0.001
<0.001
<0.001
0.056
<0.001
0.003
0.112
0.252
0.344
0.504
0.504
<0.160
Ca
0.319
0.288
0.512
0.381
0.450
0.306
0.306
0.519
0.388
0.438
0.438
0.275
0.244
0.269
0.488
0.488
0.512
0.494
0.925
0.250
0.281
0.256
0.575
0.562
0.519
0.438
0.325
0.294
0.319
0.294
0.238
0.256
0.256
0.350
0.481
0.538
0.531
K
0.044
0.051
0.079
0.088
0.060
0.022
0.035
0.046
<0.046
< 0.046
<0.046
0.009
0.011
0.017
0.058
0.041
0.070
<0.046
0.016
0.013
0.009
0.022
0.098
<0.046
<0.046
0.006
0.007
0.006
0.010
0.006
0.004
0.006
0.010
<0.012
•C0.023
<0.046
<0.046
Cd
<10
<20
<50
<50
<50
<3
<10
<50
<50
<50
<50
<0.3
<0.3
<3
<50
<50
<50
<50
<0.3
<0.3
<0.3
<3
<50
<50
<50
<0.4
<0.3
<0.3
<0.4
<0.4
<0.3
<0.3
<0.7
<20
<30
<50
<50
70
-------
barrel each) were placed in molded plastic pans previous-
ly fitted with Tygon drains, then covered with glass wool
and a layer of sand. The pans were then placed in a
6-column by 6-row grid for weathering by wet and dry
cycles.
The weathering cycles consisted of weekly "rain
showers" of 1650 mf deionized water (equivalent to 39
in./yr), with the drains stoppered. The following day the
drains were opened and the leachates collected. The pH,
specific conductance, volume, and ferric and ferrous ion
concentrations were measured weekly and the trace
element concentrations were determined later. The
drained boxes of lime/limestone/waste were allowed to
dry until the following week and the cycle was started
again.
APPENDIX B
PROCEDURES AND RESULTS FOR EXPERIMENTS
ON CODISPOSAL OF COAL WASTES WITH SOILS OR PROCESS WASTES
I. EXPERIMENT A. ATTENUATION OF ACIDITY
AND TRACE ELEMENTS BY A CALCAREOUS
MINE OVERBURDEN
This experiment was designed to investigate three
possible treatments for in situ attenuation of acidity and
trace elements with mine overburden from Kentucky
coal seam 11. Seam 11 overburden has a moderate
amount of carbonaceous minerals and cation exchange
capacity as shown in Tables I (main body of the report)
and B-I, and therefore, is reasonably typical of material
found at many active mining locations.
The three disposal treatments were described by the
experimental procedure in the main body of this report
(Sec. I.A.2.a).
Treatment columns 1 and 2 had —3/8-in. soil mixed
with coal waste because we felt that this material was the
most practical size for field applications of codisposal of
TABLE B-I
MINERALOGY OF SUBSOILS AND QUARRY LIMESTONE USED IN
ATTENUATION AND CODISPOSAL EXPERIMENTS
Mixed
Mont- Layer
Quartz Calcite Hike Kaolinite morillonite Clays
Seam 11
overburden
Seam 12
overburden
Acid Loess
subsoil (OKAW)
Calcareous Till
subsoil (BS3)
Quarry*
limestone (111.)
33.0
55.6
48.2
39.4
4.1
3.6
0.6
0.0
6.5
70.0
22.2
22.2
5.1
7.3
7.8
9.9
0.7
1.2
2.2
0.0
0.0
0.0
0.0
0.0
12.3
17.4
71
-------
overburden and waste. Treatment 1 tested the effective-
ness of codisposing coal cleaning waste and a mine
overburden by conventional tillage procedures with no
additional control measures. Treatment 2 simply added
the control of a semipermeable soil liner below the waste
to take advantage of a calcareous soil's natural capabili-
ty for neutralizing and sorbing contaminants. Treatment
3 uses only the soil liner, although much more of it than
treatment 2.
The columns were leached with distilled water for 21
days at 10 ntf/h until about 5 ( had passed through.
Direction of flow was upward. Column, influent water,
and effluent leachate were maintained under an argon
atmosphere throughout leaching to retard pyrite oxida-
tion and conversion of Fe(II) to Fe(III). Eh, pH, specific
conductance, Fe(II), and total dissolved Fe were
monitored throughout. After cessation of leaching, col-
umns were dried and water-saturated air was forced
through them for 2 weeks to promote pyrite oxidation in
an attempt to regenerate acidity and high trace element
levels. This was done to test the efficacy of the soil
treatment at retarding pyrite oxidation. After the oxida-
tion procedure, each column was leached again with
about 1 ( of deionized (Milli-Q) water and analyzed as
above. Selected aliquots were also analyzed for fluorine,
aluminum, manganese, nickel, and arsenic. This subset
of elements was selected as indicative of general trace
element behavior. Raw data from these experiments,
listed in Tables B-II through B-V, show that none of the
treatments completely controlled contaminants from this
coal cleaning waste.
II. EXPERIMENT B. CODISPOSAL OF COAL
CLEANING WASTE AND FINELY GROUND SUB-
SOILS
This experiment was a follow-up to treatment 1, which
indicated that codisposal of —3/8-in. soil with coal
cleaning waste was unsatisfactory for mitigating the
water pollution potential of the waste.
In this experiment, finely ground soils were mixed with
—3/8-in. coal cleaning waste to test the efficacy of
codisposing soils and wastes under near optimal condi-
tions. If effective, ways to attain such mixtures in the
field could be investigated. Earlier experiments showed
that limestone (CaCO3) is more effective at neutralizing
acidic waste leachates when present as smaller particles.
Materials used in this experiment and some of their
properties are shown in Tables I (main body of the
report) and B-I. These materials were collected at or near
active coal mining sites in the Illinois Basin.
TABLE B II
RESULTS FOR TREATMENT 1 OF EXPERIMENT ON ATTENUATION OF ACIDITY AND
TRACE ELEMENT CONCENTRATIONS BY MINE OVERBURDEN
Sample
Vol (/)
pH
Cond (umho)
Fe(II)
Fe(IH)
F
Al
Mn
Ni
As
1
0.195
2.6
13 200
6 166
1 257
15.3
870
116.4
25
2.2
6
0.5
3.29
7 000
3 857
165
7.6
105
57.9
13
0.09
12
0.993
4.74
2 800
1 190
15
2.4
2.7
24
4
0.014
19
2.39
6.48
2 300
160
2.0
<0.5
0.06
5.1
0.4
<0.001
33
4.49
6.50
1 300
23
<0.02
<0.5
0.05
1.5
<0.02
<0.001
35-36
4.89
2.0
7 600
3 801
7 349
38.2
406
99
9.6
2.8
72
-------
TABLE B-m
RESULTS FOR TREATMENT 2 OF EXPERIMENT ON ATTENUATION OF ACIDITY AND
TRACE ELEMENT CONCENTRATIONS BY MINE OVERBURDEN
Sample
Vol (t)
PH
Cond (nmho)
Fe(H)
Fe(in)
F
Al
Mn
Ni
As
1
0.094
4.4
8 300
3 396
700
4
52.9
140
19
0.033
6
0.526
6.14
3 400
1 236
68
1.6
0.6
25.7
4
0.020
12
0.956
6.39
2 800
652
6.0
<0.5
0.05
15.8
2.1
<0.002
18
2.378
6.35
3 100
435
<0.02
<0.5
0.06
11.4
1.1
<0.001
34
4.411
6.80
1 600
48
<0.02
<0.5
<0.04
2.3
0.1
<0.001
35-38
5.87
2.33
7 600
1 900
6 498
31.7
343
79
7.5
3.7
TABLE B-IV
RESULTS FOR TREATMENT 3 OF EXPERIMENT ON ATTENUATION OF ACIDITY AND
TRACE ELEMENT CONCENTRATIONS BY MINE OVERBURDEN
Sample
Vol (/)
PH
Cond (ixmho)
Fe(II)
Fe(III)
F
Al
Mn
Ni
As
1
0.140
4.6
9 600
5 895
305
8
45.4
101
23
<0.005
5
0.486
5.0
5 900
3 097
341
2.7
9.1
35
8
<0.001
11
0.976
6.4
2 800
997
19
<0.5
<0.04
10.4
1.5
<0.001
20
2.557
6.7
2 250 1
65
1
<0.5
<0.08
2.1
0.05
<0.001
36
4.934
7.0
100 5
17 1
<0.02 6
0.6
<0.04
0.7
<0.02
<0.001
38-41
5.40
2.5
400
384
782
22.5
331
37
5.4
0.9
73
-------
TABLE B-V
RESULTS FOR TREATMENT 4 OF EXPERIMENT ON ATTENUATION OF ACIDITY AND
TRACE ELEMENT CONCENTRATIONS BY MINE OVERBURDEN
Sample
voi (e)
pH
Cond (umho)
Fe(II)
Fe(III)
F
Al
Mn
Ni
As
1
0.093
1.40
34 000
12 876
3 473
19.4
793
36.7
33
2.2
6
0.450
1.67
13 950
4 754
234
11.9
210
9.5
9.0
0.85
12
0.958
2.10
3 600
690
<0.02
3.5
22.4
2.1
1.5
0.32
19
2.3
2.80
640
33
<0.02
<0.5
0.4
0.05
0.04
0.14
35
4.78
3.45
300
10
<0.02
<0.05
0.2
0.04
<0.02
0.09
36-38
5.24
1.59
15 700
4 696
3 123
5.9
142
7.5
3.5
2.5
Six glass columns, 6-cm i.d. by 38 cm long, were filled
with these soils as follows:
Mixture
Column (g)
(g)
1A,1B
2
3
4
5
6
240
384
506
160
48
Ky. Seam 11,
Ky. Seam 12,
Acidic Loess,
Calcareous Till,
Quarry Limestone,
360 waste
216 waste
94 waste
440 waste
552 waste
365 waste
The quantity of soil or overburden used was based on
providing enough titratable carbonate to neutralize
150% of the leachable waste acidity. Waste acidity was
determined by titration after extraction of the waste with
an H2O2 solution (ASTM Method D 1067E). Column 1
was duplicated and IB was maintained under an air
atmosphere to determine whether air had any effect on
the results. All other columns were maintained under
argon to prevent oxidation of Fe(II) to Fe(III).
About 4 ( of deionized water was passed through each
column (upward flow) at a rate of 4-6 nnf/h. Then the
soil-waste mixtures were extruded from the columns,
allowed to air-oxidize for several days, and
batch-leached using a 5:1 water-to-solid mass ratio.
Column influent, effluent, and batch leachates were
monitored for pH, specific conductance, total dissolved
Fe, Fe(II), Al, As, F, Mn, and Ni. Ferric iron was
determined by the difference between total iron and
ferrous iron. Iron, pH, and conductance measurements
were performed on virtually all samples. The remaining
parameters were determined from aliquots selected by
pH and iron results to obtain sufficient data points for
definition of contaminant concentration versus volume
profiles. These results are completely listed in Tables
B-VI through B-XII and are discussed in Sec. I.A.2.b. in
the main text.
74
-------
TABLE B-VI
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR
EXPERIMENTS ON CODISPOSAL OF COAL WASTE WITH FINELY GROUND SUB
SOILS—CONTROL
Cumulative
Volume (()
0.142
0.306
0.676
1.026
1.308
1.633
1.739
1.881
2.251
2.389
2.614
3.269
3.391
3.577
3.826
REG
Conductivity Fe2
pH (limbo) rag/t
1.9
1.9
2.4
2.4
2.4
2.4
2.5
2.4
2.4
2.6
2.5
2.7
2.7
2.6
2.7
2.3
17000
11000
7700
5400
4100
3700
3200
3700
3100
2600
2450
2150
1500
1000
6600
4750
1930
880
850
770
870
790
610
540
340
560
370
280
200
640
Fe'ot
mg/(
8510
5730
2170
1010
880
830
880
860
660
600
480
690
440
320
260
1100
F Al Mn Ni As
mg/( mg/( mg/V mg/( mg/(
14 570 2.4 7.7 1.68
1.0 62 2.3 1.91 0.19
0.61 32 1.3 1.06 0.13
0.7 26 1.2 0.89 0.078
0.27 10.8 0.6 0.45 0.078
0.68 44.4 1.4 1.08 0.144
TABLE B-VII
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR EXPERIMENTS
ON CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS—SEAM 11 OVERBURDEN (AIR)
Cumulative Conductivity Fe2 Fetot
Volume (m() pH (umho) (mg/l) (mg/0
F Al Mn Ni As
(mg/0 (mg/Q (mg/Q (mg/f) (mg/()
0.158
0.268
0.448
0.878
1.258
1.595
1.955
2.075
2.238
2.638
2.808
3.088
3.250
3.420
3.670
REG
4.1
4.9
4.1
4.9
5.5
5.8
6.9
7.7
7.6
7.7
7.8
8.0
8.0
8.0
8.1
2.9
7500
5400
3500
2800
2600
2300
2200
1950
2150
2300
2100
2100
2050
2050
2100
3980
2180
1516
810
320
140
2
1
0.22
0.05
0.05
0.03
<0.02
<0.02
<0.02
200
4200
2430
1620
800
380
140
27
4
1.9
0.7
0.3
<0.02
<0.02
<0.02
<0.02
240
0.4 5.9 82
17.8 0.014
<0.02 <0.02 17 0.46 <0.001
<0.2 <0.2 5.7 <0.01 <0.001
<0.2 <0.2 3.3 <0.01 <0.001
<0.2 <0.2 1.6 <0.01 <0.001
<0.2 <0.2 5.0 <0.01 <0.001
2.9 33.5 20.7 2.53 0.007
75
-------
TABLE B VIII
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR EXPERI
MENTS ON CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS—SEAM 11 OVERBURDEN (ARGON)
Cumulative
Volume (0
0.142
0.266
0.448
0.888
1.328
1.708
2.108
2.238
2.418
2.888
3.081
3.371
3.565
3.775
4.075
REG
Conductivity Fe2
pH (umho) (mg/0
4.8
4.9
4.3
6.4
6.2
6.7
7.7
8.1
8.1
7.7
7.8
7.9
7.8
7.9
8.0
3.0
9000
5700
4800
3100
2200
2100
2250
1950
2000
2250
2100
2000
2000
2000
6570
2416
1413
543
106
49
3
0.4
0.7
0.9
0.8
1.4
<0.02
<0.02
156
Felw
(mg/0
6964
2577
1549
594
127
56
22
2
2
3
2
1.5
<0.02
<0.02
188
F Al
(mg/0 (mg/0
0.21 1.5
<0.2 <0.2
<0.2 <0.2
<0.2 <0.2
<0.2 <0.2
<0.2 <0.1
t
2.6 27.8
Mn Ni
(mg/0 (mg/0
55 23.7
21 1.55
5.2 0.02
2.7 <0.01
0.9 <0.01
<0.01
18.7 2.01
As
(mg/0
0.02
0.002
<0.001
<0.001
<0.001
<0.001
0.004
TABLE B-IX
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR EXPERI-
MENTS ON CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS—SEAM 12 OVERBURDEN
Cumulative
Volume (0
0.188
0.316
0.511
0.941
1.356
1.685
2.053
2.173
2.343
2.793
2.961
3.251
3.441
3.641
3.931
REG
pH
4.0
4.3
4.0
5.2
5.2
6.0
5.4
5.9
6.0
6.5
6.8
7.4
7.4
7.2
2.8
Conductivity
(umho)
8800
6500
5400
3200
2900
2200
1600
1600
1775
1500
1200
1275
880
Fe2
(mg/0
4620
3490
2560
820
310
170
71
61
39
18
8
<0.02
<0.02
<0.02
<0.02
150
Fe""
(mg/0
5140
3770
2740
910
360
180
74
63
41
18
9
<0.02
<0.02
<0.02
<0.02
190
F
(mg/0
6.3
<0.2
<0.2
<0.2
<0.2
1.6
Al
(mg/0
130
<0.2
<0.2
<0.2
<0.2
16.1
Mn
(mg/0
78
9.1
3.6
1.4
1.0
6.4
Ni
(mg/0
16.3
1.1
0.26
0.02
0.03
0.47
As
(mg/0
0.019
0.002
0.001
<0.001
<0.001
0.005
76
-------
TABLE B-X
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR
EXPERIMENTS ON CODISPOSAL OF COAL WASTE WITH
FINELY GROUND SUBSOILS—ACID LOESS SUBSOIL (OKAW)
Cumulative Conductivity FeJ Fe"" F Al Mn Ni As
Volume (0 pH (umho) (mg/0 (mg/0 (mg/0 (mg/0 (mg/0 (mg/0 (mg/0
0.123
0.247
0.597
1.067
1.442
1.777
1237
2.417
2.605
3.095
3.289
3.589
3.889
4.389
REG
3.6
3.8
3.7
3.6
3.7
3.7
3.7
3.8
3.8
3.4
3.7
3.4
3.2
3.3
3.0
2400
1850
1240
960
980
1300
840
680
800
840
880
800
690
310
230
62
81
62
110
57
60
52
48
46
18
23
58
36
370
250
80
80
77
110
60
62
56
64
47
20
29
73
48
1.4
0.43
0.3
<0.2
0.3
0.9
23.1
6.6
3.9
1.7
2.1
11
80
39
31
21
19
31
1.62
0.67
0.47
0.3
0.21
0.51
0.008
0.002
0.003
0.003
<0.001
0.004
TABLE B-XI
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR
EXPERIMENTS ON CODISPOSAL OF COAL WASTE
WITH FINELY GROUND SUBSOILS—CALCAREOUS TILL SUBSOIL (BS#3)
Cumulative
Volume (()
0.134
0.444
0.884
1.234
1.572
1.987
2.157
2.331
2.781
2.971
3.256
3.636
3.916
REG
PH
5.1
4.3
6.3
5.8
6.4
6.3
6.6
6.8
7.5
7.6
7.8
8.0
8.0
2.4
Conductivity
(nmho)
6300
4400
2700
3000
2300
1900
2000
2200
2300
2300
2300
2200
Fe2
(mg/0
3120
2510
680
260
160
24
17
7
2
2
2
<0.02
<0.02
570
Fe""
(mg/0
3300
2680
740
290
180
29
20
20
36
21
4
<0.02
<0.02
1000
F
(mg/0
<0.2
<0.2
<0.2
<0.2
<0.2
3.3
Al
(mg/0
0.2
<0.2
<0.2
<0.2
<0.2
84
Mn
(mg/0
200
40
12
4.4
2.3
11.3
Ni
(mg/0
8.3
0.55
<0.01
<0.01
<0.01
3.05
As
(mg/0
0.002
0.002
<0.001
<0.001
<0.001
0.052
77
-------
TABLE B XII
VALUES OF MEASURED PARAMETERS AT VARIOUS EFFLUENT VOLUMES FOR EXPERIMENTS
ON CODISPOSAL OF COAL WASTE WITH FINELY GROUND SUBSOILS—QUARRY LIMESTONE
Cumulative
Volume (0
0.126
0.426
0.856
1.206
1.546
1.961
2.131
2.301
2.751
2.931
3.221
3.416
3.886
REG
Conductivity
pH (nmho)
4.8
4.0
5.2
5.8
6.8
7.3
7.3
7.3
7.8
7.8
7.8
8.0
8.0
6.4
10400
4700
2600
2200
2000
2200
1950
2100
2100
2100
2100
2100
Fe2
(mg/0
10800
3660
480
95
97
50
5
3
2
2
3
<0.02
<0.02
4
Fe'ot F Al
(mg/0 (mg/0 (mg/0
11000 <0.2 1.1
3970 <0.2 <0.2
540
120
100
55
12 <0.2 <0.2
3
6
6
5
<0.02
<0.02 <0.2 <0.1
4 <0.2 0.3
Mn Ni As
(mg/0 (mg/0 (mg/0
43 21.0 0.004
15 4.6 0.001
0.7 <0.01 <0.001
0.2 0.01 <0.001
0.8 0.44 0.001
APPENDIX C
TRACE ELEMENT CHEMISTRY OF ACIDIC
COAL CLEANING WASTE LEACHATES
Lawrence E. Wangen and Joel M. Williams
ABSTRACT
We investigated the chemistry of an acidic leachate from coal cleaning wastes as a
function of pH after neutralization with Ca(OH)2. The distribution of the chemical
components between solid and liquid forms was determined using a chemical
equilibrium model designed for aqueous systems. Major focus is on the use of alkaline
neutralization as a technology to control potential contamination by trace elements in
acidic coal waste leachates. Results for major components show good agreement
between equilibrium model predictions and laboratory measurements. However,
predicted concentrations are substantially higher than those measured for most trace
elements. Adsorption onto amorphous oxides is suggested as an explanation.
78
-------
I. INTRODUCTION
TABLE C-I
Recent research at Los Alamos National Laboratory
has shown that, in addition to acid, aluminum, iron, and
manganese, many trace inorganic chemical species are
present in leachates from the mineral by-products of coal
cleaning in excessive concentrations according to water
quality criteria.1 These results led to research aimed at
developing methods for reducing leachate concentrations
of these elements. In view of the popularity of alkaline
neutralization for acidity control in such leachates,2 its
effect on the concentrations of trace species in these
waters has been investigated. This report presents results
of chemical equilibrium calculations on a coal waste
leachate as a function of pH and compares predicted
solution concentrations with those obtained by labora-
tory neutralization of an acidic coal waste leachate with
calcium hydroxide. In addition, the speciation of compo-
nents and controlling solids as predicted by the chemical
equilibrium model are presented.
In recent years, several computerized chemical models
have been designed to calculate equilibrium concentra-
tions of chemical species in complex aqueous systems.3
Some models include gas-solution, solid-liquid, complex
formation, and oxidation-reduction chemistry, and thus
are quite sophisticated in terms of the types and complex-
ity of species modeled. We used a version of MINEQL
developed by Morel and Morgan,4 which contains a
fairly extensive data base that includes most of the
inorganic species thought to be important in natural
water systems. MINEQL uses equilibrium constants at
25 °C and 1 bar pressure, the Davies procedure for
correction of activity coefficients according to ionic
strength,5 and includes a check for precipitation of any
solid species contained hi the program's library that
could possibly be formed from the list of chemical
components input by the user.
COMPONENT CONCENTRATIONS AND
SPECIATIONS OF LEACHATE FROM A
COAL CLEANING WASTE
II. EXPERIMENTAL
CHEMICAL ANALYSES
PROCEDURE AND
Table C-I contains a list of components with initial
element concentrations in a coal cleaning waste leachate
used as input to MINEQL and as starting material for
laboratory titrations with Ca(OH)2. A stock coal clean-
ing waste leachate was obtained by extraction from a
quantity of coal waste by deionized water for 30 days at
a 5:1 water-to-solid ratio. The resultant slurry was
filtered through Whatman 42 filter paper and the filtrate
Component moles//
mg/f
Ca(II)
Mg(II)
K(I)
Na(I)
Fe(III)
Fe(II)
Mn(II)
Cu(II)
Cd(II)
Zn(II)
Ni(II)
Pb(II)
Co(II)
Cr(III)
Al(III)
CO32~
so42~
Cl
F-
po43-
SiO32-
B(OHfc
MoO42~
As043-
8.73E
2.20E
4.77E
1.45E
2.92E
3.0 IE
1.80E
1.42E
1.86E
2.45E
1.28E
1.61E
5.94E
8.21E
1.37E
8.73E
1.23E
2.07E
4.26E
2.46E
1.78E
1.42E
2.08E
5.47E
-03
-03
-04
-02
-02
-02
-04
-06
-06
-04
-04
-07
-05
-06
-C
-03
-01
-04
-03
-06
-04
-04
-06
-06
3.50E
5.35E
1.86E
3.33E
1.63E
1.68E
9.89E
9.02F
2.09E
1.60E
7.5 IE
3.34E
3.50E
4.27E
3.70E
5.24E
1.18E
7.34E
8.09E
2.34E
1.35E
1.12E
3.33E
7.60E
+ 02
+ 01
+ 01
+ 02
+ 03
+ 03
+ 00
-02
-01
+ 01
+ 00
-02
+ 00
-01
+ 02
+ 02
+ 04
+ 00
+ 01
+ 00
+ 01
+ 01
-01
-01
was stored in an argon atmosphere to prevent oxidation
of iron from the ferrous to the ferric state. Chemical
analyses of the stock leachate throughout several months
gave comparable results indicating no appreciable
change in major or trace chemical components during
storage. Hydrogen ion activity of the stock leachate was
1.0 X 10~2 mole// (pH = 2.00). The stock leachate was
diluted (2 parts leachate with 1 part water) during the
lime additions, including the control sample.
Different amounts of hydrated lime [Ca(OH)2] were
added to each of six 250-ntf, 24/40 opening, Erlenmeyer
flasks. Each flask was fitted at the top with a gas
entry/exit adapter through which argon flowed at ~7.5
l/min. Each flask was connected in series and contained
a stirring bar that was turned from below. Purified
79
-------
(Milli-Q) water (25 mf) was added to each flask and a
slurry was made with the lime while stirring 2 h in argon
atmosphere. Stock leachate (50 m() was transferred by
pipet with argon purging to each flask beginning with the
first in the series. After stirring for 24 h and measuring
the pH, the contents of each flask were filtered under
argon through a 0.45-um millipore filter. The filtrates
were stored in argon in polyethylene bottles. Aliquots
were taken to evaluate the Fe(II)/Fe(III) ratios and the
remaining filtrates were acidified to 5% concentrated
nitric acid for trace element analyses.
Flame or flameless atomic absorption spectrometry
was used to analyze most elements; an ion-selective
electrode was used to determine F~ ion. Fe(III) was
calculated as the difference between total iron and Fe(II),
which were determined by the orthophenanthroline pro-
cedure. Moles of lime added, equilibrium solution pH,
and total solution concentrations of species measured, as
well as those predicted by MINEQL, are listed in Table
C-II.
Equilibrium Model Calculations
Equilibrium speciations were calculated using
MINEQL for all 24 chemical components listed in Table
C-I at incremental pH from 1 through 14 and for the
specific pH obtained after the Ca(OH)2 additions. From
these, total solution concentrations were calculated for
comparison with experimental results. (Chemical
analyses after Ca(OH)2 additions were performed only
for components listed in Table C-II.) Oxidation states
and assumed speciation of all initial components are
listed in Table C-I. For thermodynamic predictions,
multivalent species were set as follows: arsenic as
As043~, chromium as Cr(III), copper as Cu(II), and
manganese as Mn(II). These assignments are consistent
with a system controlled by the oxidation potential of an
Fe(II)-Fe(III) couple. Since the experiments were
performed under argon atmosphere to prevent oxidation
of Fe(II) to Fe(III), this reaction was not allowed in the
thermodynamic calculations. The argon atmosphere also
negated the need to consider CO2(g) exchange with our
solutions.
III. RESULTS
A. Comparison of Equilibrium Modeling and Ex-
perimental Results for Total Soluble Species
Comparison of measured and predicted total soluble
species concentrations after lime additions shows good
agreement for F~ and major cations, Ca, Al, Fe(II), and
Fe(in), but very poor agreement for trace components,
As, Cd, Co, Cr, Cu, Mn, Ni, and Zn. These comparisons
are shown in Table C-II and illustrated for Fe(ni),
AsO4~3, and Zn(II) in Fig. C-l. Additional comparisons
are shown in Fig. C-2a-d.
Total solution concentrations of ferric iron (Fig. C-l)
are maintained at low levels by the precipitation of
Fe(OH)3(s) in this system from pH 4-12. In contrast, no
Lime
Added
(mmole)"
0
2.16
4 73
5 8)
b 76
8.11
TABLE C-II
MEASURED AND CALCULATED TOTAL SOLUTION CONCENTRATIONS (mg/0"
Final Element Concentration (mg/e)
PH
2.25
2.73
5.82
6.49
8.09
10.18
Data
Source
meas
Calc.
meas.
calc.
cal.
meas
calc.
meas.
calc.
350
350
540
393
430
447
450
523
500
573
370
370
370
370
0.46
0.30
<0 1
0.001
1680
1680
1800
1680
1350
1260
620
1200.
meas
calc.
490
664
a) speciation used for equilibrium calculations.
b) mmoles added to leachate (final volume 75m£)
1630
1550
160
70
3.5
3.5
<0.02
0.002
<0.02
0.0004
<0.02
l.E-5
0.26
0.76
<0.02
0.76
<0.02
0.76
<0 02
0.76
0.23
0.21
0.08
0.21
<0.03
0.21
<0.003
0.21
0.43
0.43
0.28
0.43
<-02
0.042
<0.02
0.01
<0.02 <0.02
0.0006 0.46
<0.009 <0.02
0.21 0.04
<0.01
0.13
.
0.086
<0.01
0.43
0.09
0.09
0.01
0.09
<0.01
0.09
<0 01
0.09
<0 01
81
81
Ca, Cd, Co, Cu, Mn, Ni, and Zn divalent cations
Al, Cr as trivalent cations
10.1
9.9
4.2
3.1
10
2.9
12
0.0003 2.6
8. 1
9.9
<0.02
0.30
<0.02
0.15
<0.02
0.0001
17
16
3
16
0 5
11.4
<0.02
1.2
<0.02
0.10
80
-------
IOZ
10'
)0o
ltf'
1
)
_
Iff*
l
-------
00 20 40 6.0 80 10.0 120 140 160
I02
10'
10°
: 10'
n
' ID'2
)
" ID'5
IO'4
IO'5
10"
0 THEORY
o EXPER
BET LIM
J l_
OO 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
pH
IO'2
T 1 r
\
o THEORY
o EXPER
DET LIM
00 20 40 60 80 100 120 140 16.0
pH
8.0 10.0 12.0 140 16.0
I03
O 10
O
a THEORY
o EXPER
DET LIM
-8-8-
2.0 4.0 60 8.0 10.0 12.0 14.0 16.0
pH
00 20 40 6.0 8.0 10.0 12.0 140 16.0
Fig. C-2a.
Total solution concentration vs pH for selected chemical components as predicted by a chemical equilibrium
model and/or as measured following additions of Ca(OH)2 to coal waste leachates.
82
-------
ID''
IO"
\
D THEORY
o EXPER
DET LIM
0.0 2.0 4.0 6.0 8.O 10.0 12.0 14.0 16.0
pH
00 2.0 4.0 6.0 8.0 10.0 12.0 140 16.0
2xlO"3
10'
10°
lO'l
IO'2
IO'8
IO'9
n THEORY
o EXPER
— DET LIM
10'
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
pH
10 '
2x IO"4
n THEORY
o EXPER
— DET LIM
I I i_
0.0 2.0 40 6.0 8.0 10.0 12.0 I4.O 16.0
PH
10°
-ID''
ZxlO"3
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
pH
10''
IO'2
IO
'3
lO'8
ID'9
a THEORY
o EXPER
DET LIM
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
pH
Fig. C-2b.
Total solution concentration vs pH for selected chemical components as predicted by a chemical equilibrium
model and/or as measured following additions of Ca(OH)2 to coal waste leachates.
83
-------
00 20 40 6.0 80 10-0 12.0 140 16.0
10'
10"
a THEORY
o EXPER
DET LIM
00 20 40 60 8O IO.O 12.0 140 16.0
pH
00 20 40 60 80 100 120 140 160
e
c\r^-
'O
4x I03
"00 20 40 6.0 8.0 100 120 140 160
pH
40.Kf" ,Blln-7
00 20 40 60 80 100 120 140 160
pH
o
m
4 x 10°
00 20 4° 60 80 10.0 120 140 160
pH
Fig. C-2c.
Total solution concentration vs pH for selected chemical components as predicted by a chemical equflibri
model and/or as measured following additions of CafAHV *„ „„„! ..,„... ,._... numun
following additions of Ca(OH)2 to coal waste leachates.
84
-------
10'
v 10°
o>
E
O
in
1 1 1 1 1 T
10'
2 x I0~'l L_
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
pH
2x 10°
n THEORY
00 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
pH
7« 10°
J I I I L
0.0 2.0 4.0 6.0 8.O 10.0 12.0 14.0 16.0
pH
10'
D THEORY
0.0 2.O 40 6.0 8.0 10.0 12.0 140 16.0
pH
10-'
-IO'2
N
V
9
ja
a.
ID'3
THEORY
I02
IO1
10°
IO"2
IO'3
IO'4
2 i IO"4
0.0 2.0 4.0 6.0 8.0 10.0 12.0 140 16.0
PH
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
PH
Fig. C-2d.
Total solution concentration vs pH for selected chemical components as predicted by a chemical equilibrium
model and/or as measured following additions of Ca(OH)2 to coal waste leachates.
85
-------
above. Of these, measured concentrations of nickel are
substantially lower than predicted at pH 6.49, but
measured values of manganese are substantially lower
than predicted only at pH 8.09. Thus, in all cases except
F~, measured concentrations fall below those predicted,
often by a considerable amount.
B. Chemical Speciation of Ca(OH)2-Treated Coal Re-
fuse Leachate
Predicted equilibrium thermodynamic distributions of
various initial components at acidic, near-neutral, and
alkaline pH values, that is, pH of 2.73, 6.49, 8.09, and
10.18, are listed in Tables C-III through -VI. "Total
Cone" values are those measured in the initial coal
cleaning waste leachate, and for anion species, constitute
the sum of unprotonated and protonated forms. "^
Soluble'' values refer to the total concentrations of all
soluble forms of that component. "Free Cone" values
are the predicted solution concentrations of the un-
associated free cation or anion. Predominant speciation
of soluble forms is evident in the tables.
At pH 2.73 (Table C-IH), three solids have pre-
cipitated, removing from solution a large fraction of the
total Fe(ni) and Ca and nearly all PO43~. Solution
concentrations of the generally quite soluble cation
calcium are maintained at lower levels by the presence of
high sulfate (0.123A/) concentrations. Free ions and
sulfate ion-pairs tend to dominate soluble forms of
cations.
At pH 6.49 (Table C-IV), several more solid phases
have appeared, effectively removing most aluminum
from solution and reducing concentrations of CO32~, Cr,
F, Fe(II), PO43~, SiO32~, and Zn by varying amounts. At
this pH all ferric iron is present as Fe(OH)3(s) and about
30% of the ferrous iron has precipitated as the
carbonate. As at pH 2.73, cation soluble forms are
dominated by free ions and sulfate complexes.
TABLE C-III
CALCULATED EQUILIBRIUM DISTRIBUTION OF CHEMICAL
COMPONENTS IN COAL WASTE LEACHATE AFTER ADJUSTING TO
pH 2.73 WITH Ca(OH)2''b
B(OH)4
Cations
Ca(II)
Ng(II)
K(I)
Nad)
Fe(III)
Fe(II)
Hn (II)
Cu (II)
Cd (II)
Zn (II)
Ni (II)
Pb (II)
Co (II)
Cr (III)
Al (III)
H
H2
H3
Comment
Total
Cone
1 43
2 66
3 32
1 84
1 53
1 52
3. 74
5 85
5.73
3 61
3.89
6 79
4 23
5 09
1 86
Free
Cone
2.23
2.93
3.39
1.87
4.25
1 75
3.97
6.07
5 96
3.84
4 12
7 23
i 55
6 90
2 47
i Soluble
2.01
2.66
3.32
1.84
2.90
1.52
3.74
5 85
5 73
3 61
3 89
6 79
4 23
5 09
1 86
0.91
1.21
1.02
2.40
2.99
4 13
3.01
3 01
1.91
4 It
6.24
6.12
4.00
4.28
6.99
4 51
5 09
2 17
2 37
2.06
12 16
2.06
6.78
7.47
13.45
8 01
12 79
16 17
13 24
5 32
2 06
99 9%
as H2CO,
4.61
18 72
5 82
11.29
11.48
7.83
11.43
13 12
22 67
11 79
9 90
5 86
6.90
93 8% as
FeP04(s)
2 37
6.04
2 37
7.80
7.80
5 24
11 45
11.53
9 21
9 69
8.69
2 46
6 10
99 T%
complexed
with Al
3 68 3.75 3.85
3.70 20 07 9 91
3.68 J 75 3.85
7.49 5.11 6.20
5.17
7.2-0
9.80 9.51
8.28
8 66
7.95
985 12.56
8 37
10.32 3.85
3.77
95 7% as 99.6 as
«2SiO, HB(OH)4
5.26
17. 03
5 26
12.02
11 71
3.74
7.93
1 1 66
11 56
12. 54
10 92
11 91
1 1 33
8 10
4.87
8.90
5.26
100% as
pFeP04 = 4 64
pFe(OH)3 - 1.55
pCaS04 1.56
a All values given as negative logarithms of component in moles/1,ter, blank indie
b Cation - an,on comple.es include all poss.ble combinations of the components
86
-------
TABLE C-IV
CALCULATED EQUILIBRIUM DISTRIBUTION OF CHEMICAL
COMPONENTS IN COAL WASTE LEACHATE AFTER ADJUSTING TO
pH 6.49 WITH CA(OH)2"'b
B(OH),
Total Free
Cations
Ca(II)
Ng(II)
K(I)
Nad)
Fe(III)
FeCII)
Hn(II)
Cu (II)
Cd(II)
Zn(II)
Ni(II)
Pb(II)
Co(II)
Cr(III)
Al(III)
H
H2
H3
Comnent
Cone
1.06
2.66
3.32
1.84
1.53
1.52
3.74
5.85
5.73
3.61
3.89
6.79
4.23
5.09
1.86
Cone
2.04
2.85
3,37
1.86
15.53
1.83
3.90
6.42
5.89
3.92
4.05
7.17
4.46
8.93
11.13
I Soluble
1.89
2.66
3.32
1.86
8.19
1.79
3.74
5.85
5.73
3.75
3.89
6.79
4.32
5.59
7.07
0.91
1.39
1.28
2.40
3.10
4.29
3.17
14.73
2.19
t.25
6.76
6.24
4.26
4.40
7.12
4.61
7.30
11.06
6.30
58% as
CaS04(s)
2.06
7.12
3.89
5.30
6.11
8.40
6.67
8.09
11.06
8.14
4.03
4.54
95.9% as
FeC03(s)
4.61
11.55
6.00
7.68
7.99
15.70
7.95
10.06
15.4
8.46
6.48
6.21
11.01
95.9% as
Fe3(P04)20
2.37
3.80
3.78
5.39
5.48
13.9
9.55
9.22
7.04
7.38
8.37
7.07
7.60
96.2% as
0 CaF2(s)
3.68 3.75 3.85 5.26
3.69 13.3 6.15 9.88
3.68 4.55 3.85 5.26
18.76 13.42 13.35
5.25
7.13
10.14 6.07
8.22
8.74
7.88
9.80 8.65
8.28
7.35 3.85 5.51
t.55 5.63
84% as 99% as
ZnS103(s) HB(OH)4
or A12(S103)2
OH (s)
= 2.69;
= 2.07;
= 1.53
= 1.87;
= 4.15
= 5.25
pCaS04 =1.15
PFe3(P04)2 = 4.93
PAl2(Si03)2(OH)2 = 4.40
p FeC03
P Fe(OH)3
P A1(OH)3
pZnS103
P Cr(OH)3
a All values given as negative logarithms of component in moles/liter, blank
Indicates species not present
b Cation - Anion complexes include all possible combinations of the components
8.08
7.88
82.5% as CaS04(s)
8.19
4.25
7.83
8.14
8.72
7.24
6.58
8.10
7.48
5.60
8.84
All as
29% as
29% as
Fe(OH)3(s)
FeC03(s)
ZnSi03 (s)
69% as Cr(OH)3 (s>
99.4% as A1(OH)3 (s)
At pH 8.09 (Table C-V), all phosphate is now present
as Caj(P04)3OH(s). Ferrous iron concentrations have
been lowered even further because of the formation of
Fe(OH)2(s) at this concentration of OH~. MnCO3(s) and
MnS04(s) have appeared for the first time, removing a
fraction of manganous ion from solution. Several other
insoluble phases appear or become increasingly impor-
tant, for example, CoCO3(s), and the hydroxides of Zn,
Ni, Pb, and Cr. No solid phases are indicated for
B(OH)4 or AsO43~ at this pH. In addition to soluble
sulfate complexes, hydroxy complexes become important
at this pH,
At pH 10.18 (Table C-IV), insoluble hydroxides are
the dominant solid phase for all cations except calcium
and zinc. No solid phases containing boron, cadmium, or
chromium are predicted at this pH. Predicted total
solution concentrations are quite low for all components
except calcium, arsenic, boron, cadmium, and chromium
compared with initial values. The precipitation of
Ca3(AsO4)2 at this pH accounts for 37% of the total
AsO43~. At this pH, Cr(III) is soluble as the Cr(OH)4~
complex, whereas at pH 8.09, it was present as insoluble
Cr(OH)3(s). Negatively charged hydroxy complexes are
important in speciation of soluble components at this
pH. Sulfate complexes are no longer very important.
IV. DISCUSSION
These laboratory and theoretical results have shown
some reasons that lime addition is a most effective
method for controlling contaminant levels in acidic
waters from coal mine and coal cleaning residue
drainages. Added hydroxide ions are consumed by the
87
-------
TABLE C-V
CALCULATED EQUILIBRIUM DISTRIBUTION OF CHEMICAL
COMPONENTS IN COAL WASTE LEACHATE AFTER ADJUSTING TO
pH 8.09 WITH Ca(OH)2"'b
Total
Cone
Cations
Ca (II) 1 00
Hg (II) 2.66
K (I) 3.32
Na (I) 1 84
Fe(III) 1.53
Fe(II) 1.52
Hn(II) 3.74
Cu(II) 5.85
Cd(II) 5 73
Zn(II) 3.61
Ni(II) 3.89
Pb(II) 6 79
Co(II) 4.23
Cr(IIl) 5.09
Al(III) 1.86
H
H2
H3
Comment
Solid Phases
pCa5(P04)3OH =
pFe(OH)2
pFe(OH)3
pPb(OH)2
pNI(OH)2
PZnSl03
pAl(OH)3
pCoC03
pCr(OH)3
pMnCO^ -
a All values
b Cation-anin
Free
Cone
1.99
2.83
3.36
1 86
20.33
3.77
3.82
8 21
5.89
4.87
5 77
8.57
6 37
13.73
15.93
5 09,
1 67
1.53
7.03
3 90
3.75;
1.86
4 23
5.18
4.54
given as
n comple
SO,2' CO2' PO,3- F- el' SiO/- B(OH)4' AsO, '
0.91 2 06 4 61 2 37 3.68 3.75 3.85 5.26
1.46 518 1201 3.83 368 12.38 4.63 8.04
ISoluble 1.39 3.65 847 3.81 368 6.78 3.85 5.26
1 84
2 66
3.32
1 84
9.62
3.58
3.82
5.85
5.73
4.72
5.59
7 16
6.15
5 78
7 30
pCi
2 40 4.90 9 69 5.35
3.14 5.58 10.03 5.48
4.35
3 24 6.47
19.39 22.55 18.96 23.55 18.87 15.35
4.18 7-18
,.38 6 39 10 06 7 18
8 62 7.94 13.91 11.37 11.92 5.86
6.31 9 13 15.89 9.26 8.21
5.28 11 46 8.03 9.68
6.18 9-13 9.58
8.58 7.60 11-18 7-62
6.58 10.18
12.17 13 20
15.94 11 96
7 97 3.70 8.54 9.24 8.00 3.93 5.27
5.80 9 86 6.80 6.99
16. j
67 1 % as 96 4% as 100% as 96% as 99.9% 99 9% as 98.3% as 99.9%
CaS04(s) FeC03(s) Ca5(OH) - CaF2
-------
TABLE C-VI
CALCULATED EQUILIBRIUM DISTRIBUTION OF CHEMICAL
COMPONENTS IN COAL WASTE LEACHATE AFTER ADJUSTING TO
pH 10.18 WITH Ca(OH)2"-b
8(OH)
Total
Cone
Cations
Ca(II) 0.93
Hg(II) 2.66 •
K(I) 3.32
Na(I) 1.84
Fe(III) 1.53
Fe(II) 1.52
Hn(II) 3.74
Cu(II) 5.85
Cd(II) 5.73
Zn(II) 3.61
Ni(II) 3.89
Pb(II) 6.79
Co(II) 4.23
Cr(III) 5.09
Al(III) 1.86
H
H2
H3
Comment
Solid phases
pFe(OH)2= 1.52
pFe(OH)3 =1.53
pAl(OH)3 =1.86
pCaC03 =2.06
pHn(OH)2= 3.76
pHg(OH)2 = 2.73
pPb(OH)2 = 6.80
pCu(OH)2 = 5.85
pNi(OH)2 = 3.89
pCo(OH)2 = 4.23
pZn(OH)2 = 4.18
Free
0.910
1154
Conc I Soluble 1.48
1 . 90 1 . 78
3.65 3.48
3.36 3.32
1.86 1.84
26.60 8.01
7.95 6.65
5.55 5.27
12.05 8.28
7.01 5.73
9.05 5.80
9.95 8.74
12.75 8.99
7.95 6.15
21.36 5.09
22.20 5.21
; pCaF2 =2.69
; pZnSiOj = 3.
2.40
4.04
4.43
3.32
25.76
8.44
6.04
12.54
7.50
9.54
10.44
12.84
8.24
19.90
22.32
10.15
72.9% as
CaS04(s)
; PCaSO, =
75
2.06 4.61
5.14 12.85
4.83 11.41
5.29 12.53
6.84 13.77
6.42
31.75
10.02 14.57
11.73 20.67
10.20 17.84
18.57
11.73
5.75 11.47
9.94 14.88
23.37
99.8% as 100% as
CaC03(s) Ca5(P04)3
OH(s)
1.05; PCa6(P04)3 OH
2.37 3.68 3.75 3.85 5.26
3.88 3.68 8.20 3.86 6.24
3.86 3.68 5.85 3.85 5.49
5.31 4.24 85.8% bound in solid phases
6.35 4.98 85.1% as Mg(OH)2(s)
25.76 29.82 23.05 20.10 8.01 100% as Fe(OH3(s)
11.36 6.68 100% as Fe(OH)2(s)
8.76 5.78 97.0% as Mn(OH)2(s)
15.25 15.76 8.29 8.32 99.6% as Cu(OH)2(s)
10.41 9.32 5.76
12.25 13.86 5.80 72. 1% as ZnSiOjfs) ;27. 3% as
13.35 13.76 8.78 100% as Ni(OH)2(s)
15.36 10.31 9.08 99.4% as Pb(OH)2(s)
11.76 0.20 98.8% as Co(OH)2 (s)
20.90 5.09 100% as Cr(OH)~
18.33 5.21 100% as A1(OH)3 (s)
11.37 5.91 5.26 5.56
6.80 9.37
96.8% as 99.2% as 96.1% as
CaF2(s) ZnSi03(s) B(OH)4~ 37% as
Ca3(As04)2
= 5.09; PCa3(As04)2 = 5.99
a All values given as negative logarithms of component in moles/liter, blank indicates species not present
b Cation - anion complexes include all possible combinations of the components
all pH values from 5.82 through 10.18. The predicted
cadmium values are nearly 100-fold too high at pH 6.49
and 8.09.
In view of what is known about coal cleaning waste
leachates, the facts that the two major cations (aluminum
and iron), are well accounted for in these calculations,
and that a charge balance within 10% is obtained, make
it unlikely that any significant ligands have been omitted
from the thermodynamic calculations. Consequently, we
do not believe that some unknown solid phases can be
invoked to account for the lower measured concentra-
tions. The major cation components in these solutions
form amorphous hydrous solid phases at all measured
pH. In fact, at pH greater than ~2.5, most of the Fe(III)
present in the initial leachate occurs as Fe(OH)3(s). The
analogous situation is true for aluminum at pH greater
than ~5.5. Thus at pH > 5.5, 2.92 X 10~2 moles of
Fe(OH)3(s) and 1.37 X 10~2 moles of Al(OH)3(s) are
available per liter of leachate in a finely dispersed form
for adsorption of other components in solution. Removal
of trace species from solution by adsorption onto these
hydrous oxides seems highly probable. In addition to
ferric and aluminum hydroxides, substantial quantities of
other solid phases, CaSO4(s), Fe(OH)2(s), FeCO3(s), and
CaF2(s), are present. The adsorption properties of these
solids may also aid in removing minor and trace species
from this experimental solution.
89
-------
Different investigators7"9 have shown that substantial
quantities of various trace components are removed from
solution by adsorption onto the surfaces of hydrous
oxides. For example, Ref. 7 shows that at pH 7.0, 6.25
mmole/^ of hydrous ferric oxide removes more than 10%
of the Zn(II) and Cd(II) from solutions containing 1.0
mmole/^ of these species. These adsorption values in-
creased rapidly to 60-70% adsorption at pH 8. Our
solution contained 0.24 mmoles of Zn(II), 1.86 X 10~3
mmoles Cd(II) and 29.2 mmoles of Fe(OH)3(s) per liter
of solution. Thus, sufficient adsorption capacity is ap-
parently available to have a significant effect on solution
concentrations of trace or minor species, such as cad-
mium and zinc.
Sufficient available adsorbing surface does not neces-
sarily mean that all or even a large fraction of a certain
species will be adsorbed. The quantity adsorbed is
dependent on, among other things, the equilibrium
concentration of the adsorbed species. Thus, adsorption
can be treated in a manner analogous to the
thermodynamic approach used in MINEQL by including
an equilibrium expression between sorption and desorp-
tion. Such models incorporating sorption/desorption
have recently been added to computer equilibrium codes
based on the original MINEQL program.10'11 Analysis
by such a program of the coal cleaning waste leachate
system presented here is planned as a part of future work
in this area.
In summary, these results show that application of
chemical thermodynamic principles to a problem in
environmental control can assist in understanding mech-
anisms and factors controlling the solubility of compo-
nents. Although the equilibrium assumption was not
explicitly tested, kinetic arguments are not needed to
explain discrepancies between laboratory and calculated
concentrations.
REFERENCES
1. E. M. Wewerka, J. M. Williams, N. E. Vanderborgh,
A. W. Harmon, P. Wagner, P. L. Wanek, and J. D.
Olsen, "Trace Element Characterization of Coal
Wastes—Second Annual Progress Report," Los
Alamos Scientific Laboratory report LA-7360-PR,
US Environmental Protection Agency report
EPA-600/7-78-08 (July 1978).
2. Roger C. Wilmouth, "Limestone and Lime Neutral-
ization of Ferrous Iron Acid Mine Drainage," US
Environmental Protection Agency report
EPA-600/2-77-101 (May 1977).
3. D. K. Nordstrom, L. N. Plummer, T. M. L. Wigley,
T. J. Wolery, J. W. Ball, E. A. Jenne, R. L. Bassett,
D. A. Crerar, T. M. Florence, B. Fritz, M. Hoffman,
G. R. Holdren, Jr., G. M. Lafon, S. V. Mattigod, R.
E. McDuff, F. Morel, M. M. Reddy, G. Sposito, J.
Thrailkill, "Comparison of Computerized Chemical
Models for Equilibrium Calculations in Aqueous
Systems," in Chemical Modeling in Aqueous Sys-
tems, E. A. Jenne, Ed. (American Chemical Society,
1979), Chap. 38, pp. 857-892.
4. Francois Morel and James Morgan, "A Numerical
Method for Computing Equilibria in Aqueous
Chemical Systems," Environ. Sci. Technol. 6, 58-67
(1972).
5. C. W. Davies, Electrochemistry (Philosophical Li-
brary, London, 1967).
6. Darrell K. Nordstrom, Everett A. Jenne, and James
W. Ball, "Redox Equilibria of Iron in Acid Mine
Waters," in Chemical Modeling in Aqueous
Systems, E. A. Jenne, Ed. (American Chemical
Society, 1979), Chap. 3, pp. 51-79.
7. R. Rao Gadde and Herbert A. Laitinen "Studies of
Heavy Metal Adsorption by Hydrous Iron and
Manganese Oxides," Anal. Chem. 46, 2022-2026
(1974).
8. Everett A. Jenne, "Controls on Mn, Fe, Co, Ni, Cu,
and Zn Concentrations in Soils and Water: the
Significant Role of Hydrous Mn and Fe Oxides," in
Trace Inorganics in Water, R. F. Gould, Ed.
(American Chemical Society, 1968), Chap. 21, pp.
337-387.
9. Robert O. James and Thomas W. Healy, "Adsorp-
tion of Hydrolyzable Metal Ions at the Oxide-water
Interface I. Co(II) Adsorption on SiO2 and TiO2 as
Model Systems," J. Colloid Interface Sci. 40, 42-52
(1972).
90
-------
10. Sara E. Ingle, James A. Kemiston, and Donald W.
Schultz, "REDEQL. EPAK: A Chemical
Equilibrium Computer Program," Corvallis En-
vironmental Research Laboratory, Corvallis, Ore-
gon, US Environmental Protection Agency report
EPA-600/3-80-049 (May 1980).
11. Shas V. Mattigod and Garrison Sposito, "Chemical
Modeling of Trace Metal Equilibria in Contaminated
Soil Solutions Using the Computer Program
GEOCHEM," in Chemical Modeling in Aqueous
Systems, E. A. Jenne, Ed. (American Chemical
Society, 1979), Chap. 37, pp. 837-856.
APPENDIX D
GENERAL INFORMATION ON COAL PREPARATION PLANTS I AND K
TABLE D-I
INFORMATION ON PREPARATION PLANT I
Date sampled: 5/1/79 for 4 h
Location: Western Pennsylvania
Coal seams: Purchased coal that is blended
Old piles and seconds
Deep mines-Lower Kittanning
Strip mines-Upper Kittanning
-Lower Freeport
37%
29%
7%
27%
Feed coal properties:
Company data, March 1979
Moisture (%)
Ash (%, dry)
Sulfur (%, dry)
Btu
% Float
Cleaning equipment: — 3/4-in. rotary breaker
Cyclones
—3/4-in. clean coal
4.53
13.96
2.89
12 500
65
Feed rate:
Sampled:
Waste disposal:
500 ton/h
Raw coal before breaker
Cleaned and dried
Refuse and breaker reject
Conveyored; thin-layered in shallow valley;
clay-lined with drainage ditches;
effluent collected and treated with
mine water at lime plant.
500 X 1500 ft pile, 20 ft. high.
Uncovered without evidence of intermittent cover.
4 X 13 gal.
4 X 13 gal.
4 X 13 gal.
91
-------
TABLE D-II
INFORMATION ON PREPARATION PLANT K
Date sampled:
Location:
Coal seams:
Cleaning equipment:
Feed rate:
Sampled:
Observations:
Waste disposal:
5/3/79 for 3 h
Western Pennsylvania
Purchased coal that is blended
Upper and Lower Kittanning
Upper and Lower Freeport
—5-in. crusher
1 cell, Jeffery jig
—2-in. clean coal
—3/8-in. bypass
150 ton/h
Raw coal (5 X 3/8)
Raw coal/"clean" coal (3/8 X 0)
Clean coal (2 X 3/8)
Refuse (5 X 10)
60/40 fine/coarse split
pH adjusted in washing water with soda ash
Trucked back to strip mine
4 X 13 gal.
2 X 13 gal.
4 X 13 gal.
4 X 13 gal.
APPENDIX E
RESULTS OF STATIC AND DYNAMIC LEACHING EXPERIMENTS
WITH COAL AND COAL WASTE SAMPLES FROM PLANT K
TABLE E-I
AVERAGE LE AC HATE COMPOSITIONS FROM STATIC LEACHING
EXPERIMENTS WITH COAL PREPARATION WASTES FROM PLANT K
Time
(Days)
1
50
pH
3.0
2.9
1.6
Cond
( ^mho/cm )
1140
1520
5200
14400
Be
(ppm)
0.012
0.023
0.046
0.043
Al
(ppm)
4.7
9.9
72
110
Mn
(ppm)
3.3
3.1
24
23
Fe
(ppm)
181
295
1940
9250
Co
(ppm)
0.63
0.84
1.22
1.56
Ni
(ppm)
1.0
1.3
1.8
2.8
Cu
(ppm)
0.66
0.82
3.74
2.60
Zn
(ppm)
1.0
2.0
5.7
6.5
As
(PPm)
0.05
0.06
3.0
18.0
Se
(PPm)
0.002
<0.002
0.04
0.57
Cd
(ppm)
0010
0.017
0.041
0.059
Pb
(ppm)
0 15
<0.01
•C0.01
<0.01
92
-------
TABLE E-II
Time Cond Be Al Mn Fe Co Ni Cu Zn As Se Cd
(Days) pH (mmhB/cm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)
-------
TABLE E-V
RESULTS OF DYNAMIC LEACHING EXPERIMENT GL-31
ON COAL WASTE FROM PLANT K
Sample
31- 1
31- 2
31- 3
31-4
31- 5
31- 6
31- 7
31- 8
31-9
31- 10
31- 11
31- 12
31- 13
31- 14
31- 15
31- 16
31- 17
31- 18
31- 19
Time
(hrs)
17.0
20.5
23.5
39.5
43.5
46.5
64.1
67.5
-
93.0
136.4
140.0
143.5
160.2
162.8
164.5
166.5
168.0
183.5
CumVol
(m/)
86
174
257
465
552
633
1183
1270
1351
1941
2681
2757
2845
3180
3267
3353
3437
3536
4316
gH20/
g waste
0.172
0.347
0.513
0.928
1.10
1.26
2.36
2.54
2.70
3.87
5.35
5.50
5.68
6.35
6.52
6.69
6.86
7.06
8.62
pH
2.00
2.05
2.12
2.21
2.50
2.58
2.90
3.11
3.14
3.33
3.62
3.71
3.78
3.81
3.98
3.99
4.03
4.06
4.01
Cond
(mmho/cm)
8.80
7.80
6.90
5.80
3.68
3.12
1.70
0.84
0.71
0.45
0.24
0.24
0.20
0.17
0.12
0.11
0.11
0.07
0.08
TABLE E-VI
RESULTS OF DYNAMIC LEACHING EXPERIMENT GL-32
ON COAL WASTE FROM PLANT K
Sample
32- 1
32- 2
32- 3
32- 4
32- 5
32-6
32-7
32- 8
32- 9
32- 10
32- 11
32- 12
32- 13
32- 14
32- 15
32- 16
32- 17
Time
(hrs)
16.0
18.5
21.0
23.5
39.5
43.0
48.0
63.5
65.5
68.5
72.0
88.1
91.0
-
117.0
160.6
163.5
CumVol
-------
TABLE E-VII
RESULTS OF DYNAMIC LEACHING EXPERIMENT GL-33
ON COAL WASTE FROM PLANT K
Qamnlp
sample
33- 1
33- 2
33— 3
33— 4
33- 5
33- 6
33— 7
33— 8
33— 9
33- 10
33— 11
33- 12
33— 13
33- 14
33-15
33-16
33-17
33-18
33— 19
33- 20
33- 21
33- 22
33-23
33- 24
33-25
33-26
33- 27
33
Tine
(hrs)
17.2
20.5
23 8
39.5
43.0
46.8
63.5
67.5
70.5
OQ 1
oo.A
91.8
117.0
160 7
164.7
519.5
522.0
523.0
525.5
527.5
543.5
545.5
550.0
551.5
567.5
570.0
573.0
575.5
CumVol
(mf)
105
203
301
576
676
786
1001
1114
1991
1441
1761
1873
1976
2651
3991
4111
4695
4770
4849
4972
5064
5629
5715
5833
5960
6550
6634
6749
6861
gH,0/
g waste
0.205
0.396
0.588
1.12
1.32
1.54
1.96
2.18
2.38
3.49
3.66
3.86
5.18
7.80
8.03
9.17
9.32
9.47
9.71
9.89
11.0
11.2
11.4
11.6
12.8
13.0
13.2
13.4
pH
2.14
2.20
2.27
2.51
2.81
2.89
3.04
3.19
3.29
3.45
3.47
3.50
3.80
3.93
4.03
2.36
2.44
2.50
2.57
2.73
2.97
3.18
3.23
3.29
3.43
3.54
3.59
3.62
Cond
mmho/cm
6.80
6.00
5.20
3.60
2.15
1.82
1.32
1.02
0.840
0.510
0.350
0.295
0.200
0.124
0.100
4.60
3.65
3.23
2.67
1.93
1.09
0.650
0.550
0.450
0.345
0.237
0.210
0.195
Fe
(ppm)
-2410
1920
1600
980
510
420
300
53
30
13
970
690
570
440
340
49
19
17
Ni
(ppm)
4.8
4.1
3.3
2.0
1.0
0.8
0.59
0.10
0.08
0.02
2.06
1.50
1.25
0.95
0.71
0.10
0.02
0.02
Mn
(ppm)
20.0
17.2
14.9
10.4
6.4
5.4
4.2
1.12
0.74
0.37
20.5
14.7
12.5
9.7
7.3
1.35
0.60
0.56
Zn
(ppm)
10.5
10.0
7.8
6.3
2.7
8.0
2.6
0.30
0.26
0.08
17.1
6.1
5.2
3.9
5.6
0.35
0.12
0.11
Cd
(ppm)
0.10
0.07
0.06
0.03
0.03
0.02
0.01
0.01
<0.01
<0.01
0.04
0.02
0.02
0.02
0.01
0.01
<0.01
<0.01
Al
(ppm)
95
79
65
36
15.2
11.3
6.2
0.4
0.2
<0.1
50.4
35.5
28.2
19.9
13.8
0.8
0.1
0.1
Cu
(ppm)
3.38
2.64
1.99
0.94
0.32
0.23
0.13
0.03
0.02
0.01
1.70
1.10
0.83
0.57
0.39
0.02
0.01
<0.01
As
(ppm)
2.2
1.6
1.1
0.66
0.34
0.30
0.25
0.09
0.05
0.04
0.58
0.34
0.26
0.19
0.17
0.05
0.03
0.03
Co
(ppm)
3.14
2.81
2.31
1.39
0.72
0.60
0.41
0.08
0.03
0.01
1.27
0.92
0.75
0.56
0.43
0.05
0.01
0.02
Pb
(PPm)
0.60
0.43
0.30
0.17
0.08
0.06
0.04
0.01
0.01
<0.01
0.02
0.03
0.01
0.01
0.01
0.01
<0.01
<0.01
Be
(ppm)
0.09
0.08
0.07
0.03
0.02
0.01
0.01
<0.01
<0.01
<0.01
0.04
0.03
0.02
0.02
0.01
<0.01
<0.01
<0.01
Se
(ppm)
0.02
0.01
0.02
<0.01
<0.01
<0.01
<0.004
<0.004
<0.004
<0.004
0.01
0.02
0.01
0.01
<0.01
<0.004
<0.004
<0.004
•
Ag Ba
(ppm) (ppm)
<0.01 <0.1
<0.01 <0.1
0.06 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
<0.01 <0.1
-------
APPENDIX F
PROCEDURES AND RESULTS FOR COMPARATIVE LEACHING EXPERIMENTS
I. RCRA LEACHING EXPERIMENTS
The procedure published in the Federal Register of
May 19, 1980 [Federal Register 45 (98), 33127] was
followed with modifications: (1) we used predried
samples because fresh (wet) material was unavailable; (2)
we modified the filtration procedure as described below;
and (3) we allowed the pH of the Plant D sample to
become a little lower than the specified value during the
initial addition of acetic acid.
Short-term pretests were made on all samples by
adding 400 m( deionized water to 25 g solid, thereby
determining initial pH values. For those samples with a
pretest pH value less than 5 and a history, according to
prior Los Alamos leaching procedures, of producing
highly acidic leachates, no recording pH meter was used
during the 24-h test period, thus allowing simultaneous
leaching of several samples. Refuse from Plants B, C, G,
K, and I met those criteria. Accordingly, 100 g of —3/8-
in. (9-mm) material was put into a 1/2-gal. (2-()
polyethylene bottle, 1600 mt deionized (Milli-Q) water
was added, the bottle was capped, and the sample was
swirled by hand to assure thorough wetting of the solid.
The initial pH was recorded. The bottle was placed on its
side on a platform shaker and agitation was begun at 90
3-in. strokes per min. Because prior analysis had shown
Plant A waste to have some self-neutralizing capacity in
the form of calcite and Plant D waste had an initial
pretest pH value over 5, those wastes were leached
separately, and the test was monitored with a recording
pH meter. No automatic titrator was used. The pH
electrode was fitted through a rubber stopper that was
covered with plastic wrap to prevent contamination from
the rubber. Thus, the system was essentially sealed, as
were the samples not monitored with the recording pH
meter. The pH of the Plant A refuse leachate remained
below 5 for the test period, and no addition of acid was
necessary. For Plant D waste, the pH was adjusted
manually with 0.57V acetic acid. An initial 10-m/ incre-
ment of acid lowered the pH from 9.6 to 4.1. Acid was
added at 2.5 h, 3.75 h, 18.5 h, and 20 h after agitation
was begun to maintain the pH below 5.2. A peak value
of 5.75 was reached overnight. A total of 35 m( acetic
acid was added.
After the samples were removed from the shaker, final
pH values were recorded for those samples not
monitored continuously. Vacuum filtration was begun
according to the Federal Register procedure on Plants B
and C samples and the remaining unfiltered samples
were refrigerated. After 4 h, filtering was only partially
complete. The vacuum was shut off overnight. After 19 h
(5 h with vacuum turned on), filtering was still in-
complete, though several changes of prefilters and final
0.45-um filters had been made. At that time, a prefilter-
ing step using a Buchner funnel with Whatman 541
paper was added. Remaining samples were filtered
without incident, using the Buchner prefilter step. We
rinsed the bottles with 400 ml water and added that
water to the filter, except for Plant D, to which 365 m(
was added, making the final volume of liquid 2000 m( in
all cases. Ahquots of each sample were poured into
polyethylene bottles for analysis and all samples were
stored in the refrigerator before analysis. (No acid was
added for preservation).
Table F-I summarizes the methods used to analyze the
leachates. The resultant analytical data are shown in
TABLE F-I
ANALYTICAL METHODS USED FOR RCRA
LEACHING EXPERIMENTS
Element
Method
1979 Methods Manual
EPA Equiv. Method
As
Ba
Cd
Cr
Pb
Hg
Se
Ag
AA, Hydride"
AA, N2O flame"
AA, Flame
AA, Flame0
AA, Flame
AA, cold vapord
AA, Hydride"
AA, Flame
206.3
208.1
213.1
218.1
239.1
245.1
270.3
272.1
"Borohydride reduction.
b!000 ppm Na instead of K.
cAir/C2H2 flame.
dPersulfate oxidation not used.
96
-------
Table F-II. In Table F-II, X is the mean of n independent
measurements for the sample and "t" represents the
student's t for a = 0.05, based on pooled standard
deviations for the sample set. The calculations of the p
errors are described in Sec. Ill of the main body of this
report. The p error (DWS) represents the probability,
based on the analytical data, that the true concentration
of the element equals or exceeds the Interim Drinking
Water Standard. The P error (RCRA) represents the
same probability relative to 100 times the Interim
Drinking Water Standards.
II. LOS ALAMOS LEACHING EXPERIMENTS
A. Static (Shaker) Leaches
Representative samples were obtained by splitting
from barrels of predried refuse. All samples leached were
no greater than 3/8 in. (9 mm) in particle size. In some
cases, the samples were pulverized by alumina shell
plates to —20 mesh. Previously split samples were
tumbled to mix; portions were weighed into flasks and
deionized water was added. The sample size was 50 g.
The amount of water added was 200 mf for Plants A, B,
C, and G (4:1 liquid:solid) and 250 mf for Plants K and
I (5:1 liquid:solid). The container used was a SOO-ntf
Erlenmeyer flask with a ground-glass neck, fitted with a
glass chimney to allow air access without allowing liquid
to splash out during agitation (Fig. F-l). The re1
fuse/water mixtures were placed on a platform shaker
and agitated at 90 3-in. strokes per minute. All leaching
referred to in this report was done at room temperature
(~22°C). After various leaching times, samples were
removed from the shaker and filtered by vacuum filtra-
tion, using Whatman 541 paper for the first step,
followed by either gravity filtration through a fine filter
paper (Whatman 42), as with Plants A, B, C, and G
samples, or through a Millipore 0.45-um filter (vacuum
filtration), as with samples from Plants K and I.
Leachates were diluted by addition of 10% 6N HNO3 for
preservation of the sample before analysis.
B. Dynamic (Column) Leaches
Coal or refuse material (0.5 kg) crushed to —3/8 in.
was packed into a Pyrex column 70 cm long by 4.6 cm
diam in a vertical position. The leaching column was
equipped with a necked-down inlet at the bottom for
introducing the leachates. A side arm located 5 cm below
the open top served as an effluent outlet, Both the upper
and lower ends of the coal or refuse bed were retained in
the column with loosely packed glass-wool plugs. An
upward or countercurrent leachate flow was used in
most of the experiments to prevent flow blockage from
fine sediment that might settle to the bottom of the
column.
The leachate, usually deionized water, was fed through
the packed column in one of two ways. Early experi-
ments (Plants A, B, C) used a gravity feed from a
reservoir elevated above the column inlet. The flow was
regulated by a valve located between the reservoir and
the column inlet. Later experiments used a peristaltic
pump to feed the effluent through the column. Flow rates
used were typically between 0.5 and 1.0 m//min. Meas-
urements of leachate flow and pH were made at the
column outlet. Periodically, samples of leachate were
collected for analysis of total solids and trace element
composition.
C. Analytical Methods
Cadmium, lead, and chromium were determined in the
acidified leachates by atomic absorption spec-
trophotometry. An air acetylene flame was used for
chromium. Arsenic was determined by neutron activa-
tion analysis.
97
-------
TABLE F II
ANALYTICAL RESULTS OF LEACHING TESTS CARRIED OUT ON SEVEN COAL
WASTE SAMPLES ACCORDING TO THE EPA EXTRACTION PROCEDURE
Arsenic
Sample
H20,
Plant
Plant
Plant
Plant
Plant
Plant
Control
A
B
C
D
G
I
X
<0
0
0
0
<0
<0
0
± ts//n
.001
.024 ±
.100 ±
.007 ±
.001
.001
.016 i
0.001
0.
0,
0.
.004
.001
001
(ppm)
n
3
3
3
3
3
3
3
Beta
DWS
<0.01
<0.01
>0.99
<0.01
<0.01
<0.01
CO. 01
Error
RCRA
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
UOAc, Control <0.001
<0.01
Cadmium
(ppm)
HO, Control
Plant A
Plant B
Plant C
Plant D
Plant G
Plant I
Plant K
HOAc, Control
X t ts//n
<0.003
<0.003
<0.004
<0.003
<0.003
<0.003
< 0.003
<0.003
<0.003
n
3
3
3
3
3
3
3
3
3
Beta
DWS
<0.50
<0.50
<0.80
<0.50
<0.50
<0.50
<0.50
<0.50
<0.50
Error
RCRA
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
Chromium
(ppm)
X ± ts//n
<0.005
<0.005
0.023 ± 0.
0.010 ± 0,
<0.005
<0.005
0.017 ± 0,
<0.005
<0.005
n
3
4
.006 3
.005 3
5
5
.006 3
3
4
Lead
(ppm)
Beta Error
DWS
<0.01
<0.01
0.02
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
RCRA
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
X ± ts//n
<0.012
<0.012
<0.012
<0.012
<0.012
<0.012
<0.012
<0.012
<0.012
n
5
5
5
5
5
5
5
5
5
Beta
DWS
<0.40
<0.40
<0.40
<0.40
<0.40
<0.40
<0.40
<0.40
<0.40
Error
RCRA
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
X ± ts//n
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
Mercury
(ppm)
n
4
3
3
3
3
3
2
3
2
Beta Error
DWS
<0.4
<0.5
<0.5
<0.5
<0.5
<0.5
<0.7
<0.5
<0.7
RCRA
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
-------
1.9 -cm i.d.
24/40
JOINT
11.4cm
ERLENMEYER
FLASK.500 ml.
18.7cm
Fig. F-l.
Extraction vessel used for Los Alamos shaker leaching experiment.
99
-------
TECHNICAL REPORT DATA .
(Htm rtad Inunctions on the reverse before completing)
REPORT NO
EPA-600/7-81-087
3. RECIPIENT'S ACCESS
TITLE AND SUBTITLE
Trace Element Characterization of Coal Wastes
Fifth Annual Report
6. REPORT DATE
Mav 1981
6. PERFORMING ORGANIZATION CODE
AUTHORS R c Heaton.L. E. Wangen,P. L. Wanek, J. M.
Williams,M. M. Jones,A. M.Nyitray,P. Wagner, and
J. P. Bertino
1. PERFORMING ORG
LA-882 6-PR
PERFORMING ORGANIZATION NAME AND ADDRESS
os Alamos Scientific Laboratory
University of California
Alamos , New Mexico 87545
10. PROGRAM ELEMENT NO.
INE825
'11. CONTRACT/GRANT NO.
IAG-D5-E681
2. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Annual: 10/79-9/80
14. SPONSORING AGENCY CODE
EPA/600/13
5. SUPPLEMENTARY NOTES IERL_RTp project officer is David A. Kirchgessner, Mail Drop
61, 919/541-4021. Previous reports in this series are EPA-600/T-81-073, -79-144,
-78-028a, and -78-028.
e. ABSTRACT rp^g rep0rt summarizes work during the 5th year of a trace element charac
:erization of coal wastes. Basically, research was continued on environmental con-
trol technologies relating to coal preparation wastes; assessment efforts were exten-
ded to include high-sulfur Appalachian coal cleaning wastes. The most promising
technology for controlling high-sulfur coal wastes is sequential slurry coating of the
waste with lime and limestone. As tested (0. 35% lime/1.1% limestone), this tech-
nique controlled waste effluent quality for 4 months; effluent pH remained at 7. 3-7. 6
and trace element concentrations (Al,Ca,Mn,Fe,Co,Ni,Cu) were within acceptable
limits according to the EPA MEG/MATE evaluation system. Codisposal of coal
wastes with alkaline soils or mine overburdens is partially effective in controlling
leachate quality under steady state conditions. However, none of the materials tested
could control the highly acidic effluents during intermittent leaching. Comparisons
between trace element concentrations predicted by chemical equilibrium models and
those observed in coal waste leachates yielded good agreement for the major cations
(Al,Ca,Fe); but, except for F, the major anions were not well accounted for. Obser-
ved trace element concentrations were all significantly lower than predicted.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
COSATl Field/Croup
Pollution
oal Preparation
Wastes
Waste Treatment
Chemical Analysis
Leaching
Pollution Control
Stationary Sources
Trace Elements
Characterization
Coal Cleaning
13B
081
14G
07D
07A
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
20_ SECURITY CLASS IThtl p^e)
Unclassified
21. NO. OF PAGES
111
100
*U.«. GOVERNMENT PR.NT.NG OFF.CE: , 98 1 -0-576-OEO/1 65
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