DoE
United States
Department of Energy
Division of Environmental
Control Technology
Washington, DC 20545
LA-8773-SR
EPA
US Environmental Protection Agency
Office of Research and Development
Industrial Environmental
Research Laboratory
Research Triangle Park.NC 27711
EPA-600/7-81-07
April 1981
Leaching Experiments on
Coal Preparation Wastes:
Comparisons of the EPA
Extraction Procedure
With Other Methods
Interagency
Energy/Environment
R&D Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
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RESEARCH AND DEVELOPMENT series. Reports in this series result from the
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tems. The goal of the Program is to assure the rapid development of domestic
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-------
DoE LA-8773-SR
EPA-600/7-81-072
April 1981
UC-90i
Leaching Experiments on Coal
Preparation Wastes: Comparisons
of the EPA Extraction Procedure
With Other Methods
by
R.C. Heaton, P.L. Wanek, E.F. Thode,*
E.J. Cokal, and P. Wagner
Los Alamos National Laboratory
University of California
Los Alamos, New Mexico 87545
EPA/DoE Interagency Agreement No. IAG-D5-E68I
Program Element No. INE825
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
*Los Alamos Short-Term Visiting Staff Member. New Mexico State University, Department of
Management, P.O. Box 3DJ, Las Cruces, NM 88003.
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460 rr c _
?'
and -.-
Division of Environmental Control Technology
Washington, DC 20545
lljra;rl'' (5PL-16)
-------
LEACHING EXPERIMENTS ON COAL PREPARATION WASTES:
COMPARISONS OF THE EPA EXTRACTION PROCEDURE WITH OTHER METHODS
by
R. C. Heaton, P. L. Wanek, E. F. Thode,
E. J. Cokal, and P. Wagner
ABSTRACT
Mineral wastes from seven coal preparation plants, located in
the Illinois Basin, the Appalachian Region, and the West have been
leached in accordance with the EPA extraction procedure published in
the Federal Register dated May 19, 1980. This is one of the tests
required for the classification of solid wastes under RCRA. When ex-
amined according to the procedures set forth in the Federal Register,
all of the coal waste leachates had trace element concentrations
below the maximum set by EPA. Results of the EPA leaching procedure
compare favorably with those of our own leaching experiments for
those elements which were analyzed (Ag, As, Ba, Cd, Crs Hg, Pb, Se).
However, we note that coal wastes release substantial quantities of
other trace elements not included in the protocols at the present
time (Fe, Al, Ni, Mn, Zn, Cu). In addition, the requirement that
the test leachate be maintained at pH < 5 has the effect of estab-
lishing an abnormal environment for those wastes that are neutral
or alkaline.
I. INTRODUCTION
The United States Congress, in the fall of 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 Environmental Protection Agency (EPA) to promulgate a series of regulations
which classify solid wastes as hazardous or non-hazardous and which set forth
various protocols for disposing of these wastes. Among the criteria used to
determine whether a solid waste is to be considered hazardous, by virtue of
its ability to contaminate aqueous drainages, are the results of a standard
-------
leaching procedure. This test is set forth in detail in the Federal Register
(1), but in essence involves leaching the solid material with deionized water
under rigidly defined conditions. In past work on coal preparation wastes,
we at the Los Alamos Scientific Laboratory (LASL) have used similar procedures
for scientific studies of the environmental weathering and leaching of these
wastes. Because of this experience we are in a unique position to make com-
parisons between the RCRA leaching procedure and our own environmental simula-
tion studies on coal cleaning wastes. This report summarizes our recent re-
searches in this area.
In the following discussion we first present the results of RCRA leaching
tests carried out on refuse from seven different coal cleaning plants. We then
compare these results with those obtained using related procedures which we
have developed during the course of our own work and, finally, we offer some
comments regarding the RCRA procedures as they relate to coal wastes.
II. RESULTS OBTAINED USING THE EPA EXTRACTION PROCEDURE
Seven mineral wastes from coal preparation plants in the Illinois Basin,
the Appalachian Region and the West were leached in accordance with the EPA ex-
traction procedure published in the Federal Register dated May 19, 1980. (1)
This, in essence, amounts to using lOOg of waste, ground to pass through a 9.3
mm standard sieve (-3/8"), adding 1600 m£ of deionized water to the waste and
agitating for 24 hours in an extractor designed to insure that all sample sur-
faces are continuously brought into contact with well-mixed extraction fluid.
The pH values of the mixtures must be monitored during the course of the
extraction and, in those cases in which the pH is greater than 5, adjustment
must be made by addition of 0.5N acetic acid. At the end of the 24 hour ex-
traction period, the solids are removed by filtration, and the concentrations
of eight elements (Ag, As, Ba, Cd, Cr, Hg, Pb, Se) in the filtrate are deter-
mined. The results of these determinations with seven coal preparation wastes
are presented in Tables I and II, while the analytical details may be found in
the Experimental Section of this report.
Table I shows the initial and final pH values for each of the samples stud-
ied. The pH was well below 5 in all cases except for plant D, which is locat-
ed in the western U. S. A comparatively small amount (35 m£) of 0.5N acetic
acid was sufficient to maintain the required pH of 5 throughout the course of
the extraction for this sample. This imposed acidic pH probably represents
-------
TABLE I
INITIAL AND FINAL pH VALUES FOR COAL
WASTE LEACHATES USING THE EPA EXTRACTION PROCEDURE
Plant3
3.1
-
4.2
2.8
-
2.2
3.3
-
3.2
9.6
35 mS,
5.0
4.1
-
3.8
3.1
-
2.6
3.3
-
2.7
pH, initial
Acetic Acid added
pH, final
aPlants 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.
an abnormal circumstance for the western coal waste sample, but is certainly
typical of many coal wastes from the eastern part of the country.
The results of the elemental analyses are presented in Table II A cursory
examination of this table reveals that many of the elements are present at
TABLE II
CONCENTRATIONS (ppm) OF TOXICITY INDICATOR
ELEMENTS IN COAL WASTE LEACHATES FROM SEVEN COAL PREPARATION
PLANTS
Plant A B C D G I K HDWSa
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
<0.006
0.024
<0.06
<0.003
<0.005
<0.001
<0.012
0.0015
<0.006
0.100
0.14
<0.004
0.023
<0.001
<0.012
0.0035
<0.006
0.007
0.08
<0.003
0.010
<0.001
<0.012
0.0011
<0.006
<0.001
1.4
<0.003
<0.005
<0.001
<0.012
0.0016
<0.006
<0.001
0.08
<0.003
<0.005
<0.001
<0.012
0.0020
<0.006
0.016
<0.06
<0.003
<0.017
<0.001
<0.012
0.0017
<0.006
0.096
<0.06
<0.003
<0.005
<0.001
<0.012
0.0038
5.0
5.0
100
1.0
5.0
0.2
5.0
1.0
100 x Primary Drinking Water Standard.
-------
levels below the detection limits of the analytical methods used. In only
three instances do any of the values exceed the primary drinking water stand-
ards. 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 non-
hazardous wastes are 100 times the primary drinking water standards (1) and all
of the values in Table II are at least an order of magnitude below these.
Statistical analyses were carried out in order to determine the prob-
abilities, based on the analytical data, that the true concentrations of the
various elements equal or exceed either the primary drinking water standard or
the "Hazardous Waste" limit defined in the Federal Register (1). These were
done by calculating the so-called "p errors", using the one-sided t-test with
a 95 percent confidence interval. The methodology for doing this has been
published elsewhere (6). Some of the results of these calculations are shown
in Table III.
TABLE III
PROBABILITIES THAT THE TRUE CONCENTRATIONS
OF TOXICITY INDICATOR ELEMENTS EQUAL OR EXCEED
THE FEDERAL PRIMARY DRINKING WATER STANDARDS
Plant
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
A
<0.01
<0.01
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
B
<0.01
>0.99
<0.01
<0.8
0.02
<0.5
<0.4
<0.01
C
<0.01
<0.01
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
D
<0.01
<0.01
>0.99
<0.5
<0.01
0.99
<0.01
<0.5
<0.01
<0.5
<0.4
<0.01
These results show that the probabilities for exceeding the drinking water
standards are significant only for Cds Hg and Pb generally, and for As and Ba
in specific cases. The probabilities for exceeding the "Hazardous Waste" lim-
its, which are 100 times the drinking water standards, are less than 0.01 in all
cases.
-------
III. COMPARISONS AMONG DIFFERENT LEACHING PROCEDURES
Let us first consider static leaching experiments. These are experiments
in which a fixed amount of liquid phase is maintained in contact with the solid
sample throughout the duration of the extraction, as opposed to cases in which
the liquid phase is allowed to flow through the solid. There are a number of
independent variables in such static experiments. These are the geometric sur-
face 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
what components are determined in the final leachate. All of our static leach-
ing experiments have been carried out using deionized water as the liquid phase
and fairly vigorous agitation (90 strokes/min, 3 inches/stroke). In addition,
the vast majority have been done at room temperature with the extractor open
to air. With the exception of the presence of air, these conditions are compar-
able to those called for in the EPA procedure when applied to acidic coal wastes.
Consequently we are left free to examine the effects of the liquid to solid
ratio, the mesh size and the extraction time. The other variables still deserve
comment but that will be reserved for Part IV of this report.
The one-day static leach experiments which we have routinely carried out
in the past are directly comparable to the EPA extraction procedure. The only
difference is that we have used liquid to solid ratios of either 4 to 1 or 5 to
1, whereas the EPA test calls for a ratio of 16 to 1 during the extraction, and
20 to 1 in the final samples. The concentrations of the toxicity indicator
elements in the leachates are presented in Table IVa for the EPA test and in
Table Va for our own one-day static leach. (The values in Table IVa are closely
related to those in Table II, but have been adjusted to represent the concen-
trations in the original leachate at a 16 to 1 liquid to solids ratio. This is
necessary in order to eliminate the effects of the dilution of the leachate
before the filtration and analysis.) If equilibrium were reached during the
extraction, then one would expect the concentrations of the elements in the
leachate to 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 IVa and Va reveals that these extractions are not at equilibrium. There-
fore, the concentrations of the elements in the leachates are at least partially
kinetically controlled. Under these circumstances it becomes advantageous to
-------
use a low liquid to solids ratio, because this leads to more concentrated leach-
ates which are usually easier to analyze.
A more direct comparison can be made by converting the leachate concen-
trations to the total amounts of each element leached per unit of solid waste.
These results are presented in Tables IVb and Vb. If the release of an element
is strictly kinetically controlled, these data should be exactly comparable.
The elements Cr and, to a lesser degree, Cd seem to compare fairly well between
these two methods. However, much more As was leached using the EPA method,
while our own procedure seemed to yield higher Pb values. The As results might
be explained by noting that the analytical methods used for As were different,
however the Pb results remain unexplained.
Table IVc and Vc show the leachate compositions expressed as the fraction
of each element originally present in the solid which is dissolved in the
leachate. These results exactly parallel those in Tables IVb and Vb. However
it is interesting to note that Cd seems to be highly mobile, with large per-
centages being extracted, whereas other elements are extracted to much lesser
degrees.
Results of extractions done on 20 mesh samples are shown in Tables Via, VIb,
and Vic. In general there is little change between these and the -3/8" samples
described in Tables Va, Vb and Vc. Since reduction of the particle size from
3/8" to 20 mesh represents a substantial increase in the geometric surface area,
one must conclude that the actual effective surface area is much larger than the
geometric surface, or that the surface area does not affect the leaching be-
haviors of the various elements. The former conclusion seems more likely. Note
that cadmium, which does not seem to fit this analysis, is highly mobile and
may be much more sensitive to minor changes in accessible surface area than
the other, less mobile elements.
Longer term static leaches are summarized in Tables Vila, Vllb, and VIIc.
In most cases, the amounts of leached elements can be seen to remain constant
or increase with the duration of the extraction. While this agrees with our
conception of how the leaching process works, it is useful to note that the
differences between the one-day leaches and the multi-day leaches are not very
large. This suggests that most of the action, at least for As, Cd, Cr and Pb,
takes place in the early part of the experiment (the first 24 hours).
While our static leaching experiments were designed primarily to determine
what might be leached from a coal waste, our dynamic (column) leaching experi-
-------
TABLE IVa
ADJUSTED* LEACHATE COMPOSITIONS OBTAINED USING THE RCRA
LEACHING PROCEDURE FOR COAL WASTE SAMPLES (ppm)
Plant A B C D G I
Element
Ag <0.008 <0.008 <0.008 <0.008 <0.008 <0.008
As 0.030 0.125 0.009 <0.001 <0.001 0.020
Ba <0.075 0.175 0.100 0.075 0.100 <0.075
Cd <0.004 <0.005 <0.004 <0.004 <0.004 <0.004
Cr <0.006 0.029 0.012 <0.006 <0.006 <0.021
Hg <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Pb <0.015 <0.015 <0.015 <0.015 <0.015 <0.015
Se 0.0019 0.0044 0.0014 0.0020 0.0025 0.0021
pH 4.2 2.2 3.2 5.0 3.8 2.6
^Adjusted to reflect the original leachate composition at a 16 to 1
solids ratio, before dilution to the final 20 to 1 ratio.
TABLE IVb
LEACHATE COMPOSITIONS OBTAINED USING THE RCRA LEACHING
PROCEDURE FOR COAL WASTE SAMPLES. RESULTS EXPRESSED AS
mg ELEMENT LEACHED PER Kg SOLID WASTE
Plant A B C D G I
Element
Ag <0.120 <0.120 <0.120 <0.120 <0.120 <0.120
As 0.480 2.00 0.140 <0.020 <0.020 0.320
Ba <1.20 2.80 1.60 1.20 1.60 <1.20
Cd <0.060 <0.080 <0.060 <0.060 <0.060 <0.060
Cr <0.100 0.460 0.200 <0.100 <0.100 <0.340
Hg <0.020 <0.020 <0.020 <0.020 <0.020 <0.020
Pb <0.240 <0.240 <0.240 <0.240 <0.240 <0.240
Se 0.030 0.070 0.022 0.032 0.040 0.034
pH 4.2 2.2 3.2 5.0 3.8 2.6
TABLE IVc
K
<0.008
0.120
<0.075
<0.004
<0.006
<0. 001
<0.015
0.0048
2.7
liquid to
K
<0.120
1.92
<1.20
<0.060
<0.100
<0.020
<0.240
0.075
2.7
LEACHATE COMPOSITIONS OBTAINED USING THE RCRA LEACHING PROCEDURE
FOR COAL WASTE SAMPLES. RESULTS EXPRESSED AS THE PERCENT OF THE
ORIGINALLY PRESENT THAT APPEARS IN THE LEACHATE
Plant A B C D G I
Element
Ag - - - <32
As 0.86 2.1 0.64 - <0.11
Ba
Cd <25 <20 <5.4 <9.7 <18
Cr <0.17 0.74 0.29 <0.07 <0.11
Hg - - - .
Pb <0.49 <0.71 <0.48 <0.86 <1.0
Se 0.32 1.1 0.26
PH 4.2 2.2 3.2 5.0 3.8 2.6
ELEMENT
K
2.7
-------
Plant
TABLE Va
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER LEACHES
OF COAL WASTE SAMPLES (-3/8"). RESULTS EXPRESSED AS ppm
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
-
0.008
-
0.0014
0.001
-
0.048
-
7.1
-
-
-
0.024
0.060
-
0.300
-
2.2
-
0.004
-
0.020
0.032
-
0.32
-
3.5
-
.054
-
.015 .010
.094
-
0.15
0.002
2.6 3.0
TABLE Vb
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY LEACHES
OF COAL WASTE SAMPLES (-3/8"). RESULTS EXPRESSED AS mg
ELEMENTS LEACHED PER Kg SOLID WASTE
Plant
B
D
Element
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
-
0.04
-
0.0068
0.005
-
0.240
-
7.1
-
-
-
0.12
0.30
-
1.5
-
2.2
-
0.02
-
0.10
0.16
-
1.6
-
3.5
-
0.270
-
0.075 0.050
0.470
-
0.750
0.010
2.6 3.0
Plant
TABLE Vc
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER
LEACHES OF COAL WASTE SAMPLES (-3/8"). RESULTS EXPRESSED
AS THE PERCENT OF THE ELEMENT ORIGINALLY PRESENT
THAT APPEARS IN THE LEACHATE
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
pH
-
0.07
-
2.8
0.008
-
0.49
-
7.1
-
-
-
30
0.48
-
4.4
-
2.2
-
0.09
-
8.9
0.23
-
3.2
-
3.5
-------
TABLE Via
LEACHATE COMPOSITIONS OBTAINED FROM ONE-DAY SHAKER LEACHES
OF COAL WASTE SAMPLES (-20 MESH). RESULTS EXPRESSED AS ppm
Plant
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
A
<0.008
<0.008
2.9
<0.001
<0.20
0.048
7.1
LEACHATE
OF COAL
B
-
-
48
0.156
-
0.320
2.2
COMPOSITIONS
WASTE SAMPLES
C
<0.008
<0.004
8.9
0.032
<0.20
0.320
3.5
TABLE VIb
OBTAINED FROM
(-20 MESH).
ELEMENT LEACHED PER Kg
A
<0.040
<0.040
0.0070
<0.005
<1.00
0.24
B
-
-
0.190
0.780
-
1.60
C
<0.040
<0.020
0.100
0.160
<1.00
1.60
D G I K
-
-
9.3
.0018 0.080
-
-
4.3 3.2
ONE-DAY SHAKER LEACHES
RESULTS EXPRESSED AS mg
SOLID WASTE
D G I K
-
-
0.031 0.10
0.007 0.40
-
-
Plant
Ag
As
Ba
Cd
Cr
Hg
Pb
Se -
pH 7.1 2.2 3.5 4.3 3.2
TABLE Vic
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
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
<0.07
-
2.9
<0.008
-
0.49
-
7.1
_
-
48
1.2
-
4.7
-
2.2
<0.09
-
8.9
0.23
-
3.2
-
3.5
-
-
9.3
0.008
-
-
-
4.3
-------
TABLE Vila
LEACHATE COMPOSITIONS OBTAINED FROM LONG TERM SHAKER LEACHES
OF COAL WASTE SAMPLES (-3/8"). RESULTS EXPRESSED IN ppm
Plant
Days
Ag
As
Bg
Cd
Cr
Hg
Pb
Se
PH
A
28
-
0.008
-
0.0003
0.0012
-
0.006
-
7.6
LEACHATE
B
22
-
-
-
0.035
0.116
-
0.280
-
1.9
COMPOSITIONS
C D G I
28 25
-
0.175
-
0.124 0.01
0.240 0.10
-
0.360
-
1.9 2.2
TABLE Vllb
OBTAINED FROM LONG TERM SHAKER LEACHES
K
25
-
3.0
-
0.041
-
-
0.004
0.036
2.0
OF COAL WASTE SAMPLES (-3/8"). RESULTS EXPRESSED AS mg
Plant
Days
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
pH
OF COAL
A
28
-
0.04
-
0.0014
0.006
-
0.030
-
7.6
LEACHATE
ELEMENT
B
28
-
-
-
0.18
0.58
-
1.40
-
1.9
COMPOSITIONS
WASTE SAMPLES (-3/8").
LEACHED PER Kg SOLID WASTE
C D G I
28 25
-
0.88
-
0.62 0.05
1.20 0.50
-
1.80
-
1-9 2.2
TABLE VIIc
OBTAINED FROM LONG TERM SHAKER LEACHES
K
25
-
15.0
-
0.205
-
-
0.020
0.180
2.0
RESULTS EXPRESSED AS THE PERCENT OF THE ELEMENT
ORIGINALLY PRESENT THAT APPEARS IN THE LEACHATE
Plant
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 D G I
28 25
-
4.0
-
55.4
1.74
-
3.60
-
1.9 2.2
K
25
2.0
10
-------
TABLE Villa
LEACHABILITIES OF SELECTED ELEMENTS FROM COAL WASTE SAMPLES
(-3/8") OBTAINED FROM CONTINUOUS COLUMN LEACHING EXPERIMENTS.
RESULTS EXPRESSED AS ppm FOR 162 WATER PER Kg SOLID
Plant A B
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
-
0.016
-
0.0048
0.031
-
0.014
-
2.9-7.7
-
0.34
-
0.016
0.021
-
0.022
-
1.7-3.4
-
0.50
-
0.0072
0.050
-
0.0075
-
2.4-3.8
-
-
-
0.0026
0.0080
-
-
-
2.9-40
TABLE VHIb
LEACHABILITIES OF SELECTED ELEMENTS FROM COAL WASTE SAMPLES
(-3/8") OBTAINED FROM CONTINUOUS COLUMN LEACHING EXPERIMENTS.
RESULTS EXPRESSED AS mg ELEMENT LEACHED PER Kg SOLID WASTE
Plant A B
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
-
0.26
-
0.077
0.49
-
0.22
-
2.9-7.7
-
5.3
-
0.26
0.39
-
0.35
-
1.7-3.4
-
0.80
-
0.12 0.042
0.80 0.13
-
0.12
-
2.4-3.8 2.9-4.0
TABLE VIIIc
LEACHABILITIES OF SELECTED ELEMENTS FROM COAL WASTE SAMPLES
(-3/8") OBTAINED FROM CONTINUOUS COLUMN LEACHING EXPERIMENTS.
RESULTS EXPRESSED AS THE PERCENT OF THE ELEMENT
ORIGINALLY PRESENT THAT APPEARS IN THE LEACHATE
Plant
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
PH
-
0.46
-
32
0.82
-
0.44
-
2.9-7.7
-
5.7
-
66
6.4
-
1.0
-
1.7-3.4
-
3.6
-
10 13
1.2 0.14
-
0.24
-
2.4-3.8 2.9-4.0
11
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merits have been attempts to simulate the weathering of an exposed waste pile.
We were primarily interested in studying the leaching of elements as a function
of time and the effects of intermittent leaching. Thus these experiments are
more difficult to compare to the EPA procedure than the static leaches. How-
ever, a comparison can be made by integrating the concentration versus volume
curve in each element out to a volume representing a 16 to 1 liquid to solids
ratio. This gives the total amount of a given element extracted in that volume.
These results were then used to calculate the amounts extracted per unit solids
shown in Table VHIb. The values shown in Tables Villa and VIIIc were then de-
rived from those in Table VHIb. One should note that most of the extraction
takes place 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.This is especially so for As and to lesser degrees for Cd
and Cr. Pb shows the reverse trend. This might be due to reprecipitation
caused by the increase in pH with time, but this is speculation.
In summary, the EPA leaching procedure compares well with those procedures
which we have been using in our work on coal preparation wastes for the last
several years, at least to the extent to which these various methods can be
compared. The major difference between our procedures and the EPA procedure,
in the case of acidic coal preparation wastes, is the higher liquid to solids
ratio used in the EPA method. This high ratio has the effect of diluting the
leachate and rendering the chemical analyses more difficult. In the case of
non-acidic coal wastes, there is the additional difference that acetic acid is
added to the extraction mixture in the EPA method. For coal wastes which
are not naturally acidic this creates an artificial environment and complicates
the scientific interpretation of the results.
IV. THE EPA LEACHING PROCEDURE AS APPLIED TO COAL WASTES
One must remember that the EPA leach test is designed to satisfy a regula-
tory 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 substantially. It
seems unlikely that any single test can be entirely appropriate in all these
different types of waste, and thus it is important for one to understand what
the limitations of the test are for various types of waste. In the following
12
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discussion we shall record our observations on the applicability of the EPA
leaching test to coal preparation wastes. The most important question is
whether the leaching test is an accurate indicator of the potential of a given
waste to harm the environment and our considerations have been carried out with
this in mind.
Past studies have revealed that the elements with the highest discharge
severities in leachates from coal preparation wastes are Fe, Al, Ni, Mn, Zn,
Cu and Cd as well as the acidity (2,3,4). The elements addressed in the EPA
leaching test are those included in the Federal Primary Drinking Water Standards,
namely Ag, As, Ba, Cd, Cr, Hg, Pb and Se. The only element common to these two
groups is Cd. 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 Ag, Hg and Ba, are typi-
cally 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 only
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 EPA leaching test in its present form does not address the
elements of real concern. If the elements in the secondary drinking water
standards were included in the EPA leaching test, then the situation would be
markedly improved, since Fe, Mn, Zn and Cu would be covered. This would leave
only Al and Ni as elements of potential concern not considered in the leaching
test.
When acidic coal wastes are considered, the leachates are sufficiently
acid so that no acetic acid additions are called for. Under these circumstances
the EPA test is essentially a water leach and reasonably simulates the acid-base
conditions one might expect in a more or less stagnant coal waste pile. Since
acidic coal wastes are the most abundant type and since they represent the
wastes of most concern in the eastern coal fields of the United States, this
type of test seems entirely appropriate. However, alkaline coal wastes, typi-
cally from the western United States, are treated differently under the EPA
test. When acidified to a pH of five with acetic acid, these wastes are sub-
jected to an artificial environment which they are not likely to encounter under
normal circumstances. We believe that this test becomes unnecessarily severe
for those elements which are mobilized under acidic conditions while ignoring
13
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the possible effects on elements which may be alkaline mobile such as selenium
and arsenic.
At first glance, one would expect the results of a leaching experiment to
depend on the size of the particles in the solid sample. This is because small
particles have a higher geometric surface area per unit mass than large ones.
However, our experience with coal wastes has been that the particle size does
not strongly affect the results of our leaching experiments. Since the mesh
size seems unimportant, one might as well choose one that is convenient. The
9.3 mm (-3/8") size is probably the most convenient for this type of waste.
Agitation of the sample during the leaching procedure is most important.
The EPA test procedure calls for vigorous agitation. In our opinion such
vigorous agitation is preferred over stagnant leaching because a vigorous
agitation is easier to define and to reproduce from one experiment to the next
and among different laboratories.
The matter of time is necessarily a compromise. The time needs to be long
enough so that whatever chemical reactions are involved can proceed to a reason-
able degree and yet short enough to complete the experiment in a timely fashion.
With high sulfur coal wastes that do not have any self-neutralizing capacity, the
24 hour extraction time seems reasonable. However, some materials may not be-
come severely acidic for several days or even weeks. Such a delay can be
caused by the presence of carbonate minerals acting as i_n situ neutralizing
agents, which must be used up before the pH can become very acidic. Whatever
the cause, such a delay in the acid-releasing character of a coal waste could
result in a rather toxic material being erroneously classified as non-hazardous.
The only straightforward way to avoid this problem is to run leaching experiments
for longer periods of time.
One factor which is important in the case of coal wastes, but which may
not matter for other types of solid wastes, is the presence of air during the
leaching process. The leachates from coal wastes are acidic because the oxi-
dation of pyrite yields sulfuric acid as a by-product. If access of air to the
solid is restricted, then less oxidation occurs and the leachates are less
acidic. In the case of a 24 hour leaching experiment, most of the acid in-
volved was generated before the actual leach was begun, so that access to air
may not be important. However, in longer leaching experiments, the generation
of acid during the experiment may be significant and restriction of the air
intake may lead to artifically low results.
14
-------
With reference to coal waste samples, liquid to solid ratios of 20 to 1
for the final analysis tax the detection limits of the analytical procedures.
Use of 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 would like to offer one comment on the mechanical aspects of
the extraction procedure. In order to facilitate the rapid separation of the
leachate from the solid residue, thus eliminating long contact times of leach-
ate and residue following the 24-hour agitation period, we have found it advan-
tageous to use a pre-filtaring step with a hard, ashless filter paper (Whatman
#541) and a Buchner porcelain funnel prior to final filtration through a Mini-
pore 0.45u filter. Even a glass fiber pre-filter, as mentioned in the ex-
traction procedure, offers little relief from prolonged separations of mate-
rials containing clays, and the pre-filtering with the paper is much more rapid
than the centrifuge method described in the EPA test procedure.
V. 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
procedure published in the Federal Register dated May 19, 1980 (1). When
judged according to the toxicity criteria set forth in this procedure, all of
the coal wastes are non-hazardous. The probabilities that any of the eight
elements examined might actually exceed the levels set forth in the procedure
are all less than one percent. The probabilities of the elements exceeding the
federal primary drinking water standards are significant only for Cd, Hg and Pb.
When compared to leaching tests which we have used over the past several
years in our research on coal wastes, the EPA test gives comparable results for
those elements which are examined. The primary differences between our pro-
cedures and that prescribed in the Federal Register is the use of a higher
liquid to solids ratio in the EPA test and the requirement that alkaline sys-
tems be acidified with acetic acid.
With respect to coal preparation wastes we can make the following comments
concerning the EPA extraction procedure. First, the elements Fe, Al, Ni and
Mn, which have the highest discharge severities in coal waste leachates, are not
addressed by the method. Second we believe that the acidification of non-
acidic materials is inappropriate in the case of coal wastes. Third, the time
15
-------
of filtration can be significantly shortened by introducing a pre-filtering step
before filtration through the Millipore filer. In addition to these concerns
there remains the question of whether longer extraction times should be con-
sidered and whether the extraction vessel should be left open to the air.
REFERENCES
1. Federal Register, 45 (98), 33127 (May 19, 1980).
2. Wewerka, E. M. , Williams, J. M. , "Trace Element Characterization of Coal
Wastes - First Annual Report" EPA-600/7-78-028 (March 1978).(NTIS # =
LA-6835-PR)
3. Wewerka, E. M., Williams, J. M., Vanderborgh, N. E., Harmon, A. W. ,
Wagner, P., Wanek, P. L. and Olsen, J. D., "Trace Element Characterization
of Coal Wastes Second Annual Progress Report", EPA-600/7-78-028a (July 1978).
(NTIS # = PB-284-450)
4. Wewerka, E. M., Williams, J. M. Wangen, L. E., Bertino, J. P., Wanek, P. L.,
Olsen, J. D., Thode, E. F. and Wagner, P., "Trace Element Characterization
of Coal Wastes - Third Annual Progress Report", EPA-600/7-79-144 (June 1979).
(NTIS # = PB-80-166150)
5. Cleland, J. G. and Kingsbury, G. L. , "Multimedia Environmental Goals for
Environmental Assessment. Vols. I an II" Environmental Protection Agency
reports EPA-600/7-77-136a and EPA-600/7-77-136b (November 1977).
6. Natrella, M. G., "Experimental Statistics", National Bureau of Standards
Handbook 91, U. S. Government Printing Office (1966) pp. 3-13.
EXPERIMENTAL
A. RCRA Leaching Experiments
The procedure published in the Federal Register of May 19, 1980 (1)
was carried out with the following modifications. First, we used pre-dried
samples, since no fresh (wet) material was available. Second we modified the
filtration procedure, as described below. Finally we allowed the pH of the
Plant D sample to become a little lower than the specified value when making
the initial addition of acetic acid.
16
-------
Short-term pre-tests were made on all samples by adding 400 ml. deionized
water to 25g solid, thereby determining initial pH values. For those samples
with a pre-test pH value less than 5 and a history, according to prior LASL
leaching procedures, of producing highly acidic leachates, no recording pH
meter was used during the 24-hour test period, thus allowing simultaneous
leaching of several samples. Refuse from Plants B, C, G, K and I met those
criteria. Accordingly, lOOg of -3/8" (9 mm) material was put into a 1/2-gallon
(2-liter) polyethylene bottle, 1600 ml deionized (Milli-Q) water was added, the
bottle capped, and the sample was swirled by hand to assure thorough wetting of
the solid. The initial pH was then recorded. The bottle was placed on a plat-
form shaker on its side, and agitation was begun at 90 3-in strokes per minute.
Since 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 pre-test 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 which was covered with plastic wrap to pre-
vent 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 0.5N acetic
acid. An initial 10-ml increment of acid lowered the pH from 9.6 to 4.1. Four
more additions of acid were made at 2.5 hr, 3.75 hr, 18.5 hr, and 20 hr after
agitation was begun to maintain the pH below 5.2. A peak value of 5.75 was
reached overnight. A total of 35 ml acetic acid was added.
After the samples were removed from the shaker, final pH values were re-
corded for those samples not monitored continuously. Vacuum filtration was
begun according to the Federal Register procedure on Plant B and C samples and
the remaining unfiltered samples were refrigerated. After 4 hours filtering
was only partially complete. The vacuum was shut off overnight. After 19
hours (5 hours with vacuum turned on) filtering was still incomplete, though
several changes of pre-filters as well as final 0.45u filters had been made.
At that time a pre-filtering step using a Buchner funnel with Whatman #541
paper was added. Remaining samples were filtered without incident, using the
Buchner pre-filter step. 400 ml water was added to bottles as a rinse, and
that water added to the filter, except for Plant D, in which 365 ml was added,
making the final volume of liquid 2000 ml in all cases. Aliquots of each
17
-------
sample were poured into polyethylene bottles for analysis and all samples were
stored in the refrigerator prior to analysis. (No acid was added for preser-
vation).
Table IX summarizes the methods used to analyze the leachates. The result-
ant analytical data are shown in Table X. In Table X, X is the mean of n in-
dependent measurements for the sample. The letter "t" represents the student's
t for a = 0.05 based upon pooled standard deviations for the sample set. The
calculations of the p errors are described in Part II 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.
B. LASL Leaching Experiments
1- Static (Shaker) Leaches. Representative samples were obtained by
splitting from barrels of pre-dried refuse. All samples leached were no great-
er 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 50g. The amount of water added was 200 ml for Plants A, B,
C, and G (4:1 liquid: sol id) and 250 ml for Plants K and I (5:1 liquid: sol id).
The container used was a 500-ml 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. 1). The refuse/water mixtures were placed
on a platform shaker and agitated at 90 3-in strikes per minute. All leaching
referred to in this report was done at room temperature, generally around
22° C. After various leaching times, samples were removed from the shaker and
filtered by vacuum filtration, using Whatman #541 paper for the first step,
followed by either gravity filtration through a fine filter paper (Whatman
#42), as with Plant A, B, C, and G samples or through a Millipore 0.45|j filter
(vacuum filtration), as with samples from Plants K and I. Leachates then were
diluted by addition of 10% 6N HN03 for preservation of sample prior to anal-
ysis.
2. 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
18
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TABLE IX
ANALYTICAL METHODS USED FOR THE RCRA LEACHING EXPERIMENTS
ELEMENT
AA,
AA,
METHOD
Arsenic
Barium
Cadmi urn
Chromium
Lead
Mercury
Selenium
Silver
(1) Borohydride Reduction.
(2) 1000 ppm Na instead of K.
(3) Air/C2H2 Flame.
(4) Persulfate oxidation not used.
AA, Hydride (1)
AA.
AA, Flame
N£0 flame (2)
Flame (3)
Flame
AA, Cold vapor (4)
AA, Hydride (1)
AA, Flame
1979 Methods Manual
EPA EQUIV. METHOD
206.3
208.1
213.1
218.1
239.1
245.1
270.3
272.1
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 sediments 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 experiments (Plants A, B, C) employ 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. Measurements 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.
19
-------
3. Analytical Methods. Cd, Pb and Cr were determined in the acidified
leachates by atomic absorption spectrophotometry. In the case of Cr, an air
acetylene flame was used. As was determined by neutron activation analysis.
20
-------
TABLE X
ANALYTICAL RESULTS OF EPA EXTRACTION PROCEDURES
FOR SEVEN COAL WASTE LEACHATES
SELENIUM ppm
SILVER ppm
tUMLNI
Sample
HpO. Control
Plant A
Plaiit B
Plant C
Plant 0
Plant G
Plant I
HOAc, Control
Sample
H;0, Control
Plant A
Plant B
Plant C
Plant D
Plant G
Plant 1
Plant K
HCAc, Control
X ±
<.001
.024 ±
.100 i
00 / t
-..001
<.001
.016 ±
' 001
X ±
^.003
<.003
«. . 004
v.003
•- . 003
v . 003
«. 003
v.003
<.003
ts//n n
3
.001 3
. 004 3
.001 3
3
3
001 3
3
CADMIUM
ts//n n
3
3
3
3
3
3
3
3
3
O_£ _~— «^^_^_
p error
DWS RCRA
<.01 <.01
<.01 '.01
>.99 <.01
•, 0] <- 01
<.01 <.01
'.01 <.01
<.01 < 01
<.01 <.01
ppm
p error
DWS RCRA
<.50 <.01
<.50 <.01
< . 80 < . 0 1
<.bO <.01
<.50 <.01
<,50 <,01
<.50 < 01
<.50 <.01
<.50 <.01
X ± ts//n
<.06
<.06
.14 ± .06
.03 ± .06
.08 ± .06
<.06
.08 + .06
CHROMIUM
X ± ts//n
<.005
<.005
.023 ± .006
.010 ± .005
<.005
<.005
.017 ± .006
<.005
<.005
P error
n DWS RCRA
4 < . 01 <. 01
4 <. 01 '.01
4 < . 01 < . 01
4 < . 01 <. 01
8 '.99 <.01
4 <.01 '.01
4 < . 01 <. 01
4 <. 01 < . 01
ppm
p error
n DWS RCRA
3 < 01 <.01
4 <.01 <.01
3 .02 <.01
3 <. 01 < . 01
5 <. 01 <. 01
5 <.01 <.01
3 < . 01 '.01
3 <. 01 <. 01
4 <.01 <-01
X ± ts//n
.0014 i .0006
.0015 ± 0006
.0035 ± .0007
.0011 + .0006
'.0016 ± .0006
.0020 ± .0006
.0017 ± .0006
.0038 ± .0007
.0009 ± .0006
LEAD
X ± ts//n
<.012
<.012
<.012
<.012
<.012
<.012
<.012
<.OI2
<.012
p error
n DWS RCRA
3 <.01 <.01
3 '.01 '.01
3 ' . 01 <. 01
3 <. 01 < . 0 1
3 '.01 '.01
3 <. 01 < . 01
3 '.01 <. 01
3 <.01 <.01
3 '.01 ' . 01
ppm
p error
n DWS RCRA
5 '.40 '.01
5 '.40 '.01
5 <.40 '.01
5 <.40 '.01
5 '.40 '.01
5 <.40 <.01
5 <.40 '.01
5 <.40 <.01
5 <.40 <.01
X ± ts//n
' 006
'.006
'.006
'.0(16
'.00
' . 006
'.006
'.006
< . 006
n
3
3
3
3
3
3
3
3
3
MERCURY
X ± ts//n
'.001
'.001
'.001
<.001
'.001
<.001
'.001
'.001
'.001
n
4
3
3
3
3
3
2
3
2
p error
DWS RCRA
'.01 '.0,
'.01 '.01
'.01 '.01
'.01 '.01
'.01 '.01
' 01 '.01
'.01 '.01
'.01 '.01
< 01 '.01
ppm
p error
DWS RCRA
'.4 '.01
'.5 '.01
'.5 '.01
'.5 '.01
'.5 '.01
<.5 <.01
'.7 <.01
<.5 <-01
<.7 <.01
-------
24/40
JOINT
1.9 -cm i.d.
11.4cm
ERLENMEYER
FLASK,500 ml.
18.7cm
Fig. 1. Extraction Vessel Used for
LASL Shaker Leaching Experiments
22
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO
EPA-600/7-81-072
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Leaching Experiments on Coal Preparation Wastes:
Comparisons of the EPA Extraction Procedure with
Other Methods
6. REPORT DATE
April 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R.C.Heaton, P.L.Wanek, E.F.Thode,
E.J. Cokal, and P.Wagner
B. PERFORMING ORGANIZATION REPORT NO
LA-8773-SR
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Los Alamos Scientific Laboratory
University of California
Los Alamos, New Mexico 87545
10. PROGRAM ELEMENT NO.
INE825
11. CONTRACT/GRANT NO
IAG-D5-E681
12 SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 6-12/80
14. SPONSORING AGENCY CODE
EPA/600/13
— j — — — ^j A **f V \J\f / AW
is. SUPPLEMENTARY NOTES IERL-RTP project officer is David A. Kirchgessner, Mail Drop
61, 919/541-4021.
is. ABSTRACT j,^e rep0rt gives results of leaching experiments on mineral wastes from
seven coal preparation plants (in the Illinois Basin, the Appalachian Region, and the
West), in accordance with the EPA extraction procedure in the Federal Register of
May 19, 1980. (This is one of the tests required for classifying solid wastes under
RCRA.) All of the coal waste leachates had trace element concentrations below the
maximum set by EPA. Results of the EPA leaching procedure compare favorably
with those of the authors' leaching experiments for the elements that were analyzed
(Ag, As, Ba, Cd, Cr, Hg, Pb, and Se). However, coal wastes release substantial
quantities of trace elements not included in the protocols (Fe, Al, Ni, Mn, Zn, and
Cu). In addition, the requirement that test leachate be maintained at pH < or = 5
establishes an abnormal environment for neutral or alkaline wastes.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Pollution
Coal Preparation
Coal
Waste Treatment
Leaching
Minerals
Extraction
Chemical Analysis
Pollution Control
Stationary Sources
Mineral Wastes
Solid Waste
Trace Elements
13B
081
08G
07D,07A
13H
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
27
20. SECURITY CLASS (Thispage/
Unclassified
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