United State?
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/035 Feb. 1987
SEPA Project Summary
Leaching and Hydraulic
Properties of Retorted Oil
Shale Including Effects from
Codisposal of Wastewater
David B. McWhorter and Deanna S. Durnford
The purpose of this project was to
develop methods and data on the \
leaching and hydraulic properties of
solid residues resulting from the proc-
essing of oil shale. A column test, called
the Equilibrated Soluble Mass (ESM)
test, was developed as an aid to charac-
terization of the chemical quality of the
first leachate that would issue from a
disposal pile of spent oil shale. Water
added for cooling, compaction, and
dust control will develop a chemical
composition dictated by chemical reac-
tion between the solution and solid
phases. In the ESM column test, this
process is simulated by moisturizing
the solid to the expected field water
content, followed by an equilibration
period. After packing the moistened
material into a column, the antecedent
pore solution is displaced by injection
of distilled water. Both theoretical and
experimental results indicate that the
first effluent from the column is dis-
placed antecedent pore water, the
chemical composition of which has
been unaffected by the displacement
process. The chemical characteristics of
the first effluent are expected to be a
reasonable index to the quality of first
leachate generated from a disposal pile.
The ESM test was used to assess the
effect on leachate quality of codisposal
of process water with the solids. This
was accomplished by conducting one
set of tests with distilled water as the
moisturizing fluid and another set of
tests with process waters as the mois-
turizing fluid. These tests indicate an
overall negative effect on leachate qual-
ity as a result of adding process water
to the solids.
A variety of hydraulic properties were
measured in addition to leachate qual-
ity. Spent shales tested included those
from the Lurgi-Ruhrgas, TOSCO II, Allis
Chalmers Roller Grate, Paraho Direct
Mode, Chevron STB, and Hytort retort-
ing processes. One comprehensive data
set, including measurements of the
vapor diffusion coefficient, was devel-
oped for the Lurgi spent shales. This
was accomplished by a new technique
that utilized an iodine solution and a
dual source of gamma rays to measure
simultaneously the iodine and water
distributions. These data permit distin-
guishing water that has been trans-
ported by vapor diffusion from that
which moves as bulk liquid flux.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report or-
dering information at back}.
Introduction
The total identified shale oil resources
in the U.S. are estimated by the U.S.
Geological Survey to be over 270 billion
metric tons, with a major source in the
Green River formation of Colorado,
Wyoming, and Utah. Possible future
commercial exploitation of this vast re-
source warrants careful consideration
of the effects that a commercial oil shale
operation might have on the other natu-
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ral resources of an oil shale region. Al-
though a great deal of attention has
been focused on these effects, data
gaps still exist. The report provides in-
formation pertinent to the estimation of
the quantity and quality of leachate
from a spent shale disposal pile. These
data will contribute to the eventual as-
sessment and alleviation of potentially
undesirable impacts on the water re-
sources that will receive this leachate.
Oil shale facilities will produce large
volumes of solid wastes, and the poten-
tial for recycling these wastes is small.
Therefore, establishing environmen-
tally acceptable methods for disposing
of spent shale residues is an important
objective for the oil shale industry.
In addition to the solid wastes, a sig-
nificant amount of liquid waste will be
generated by the various retorting proc-
esses. One method being proposed for
disposing of this liquid waste is to
codispose it with the solid waste. Spent
shale leaves the retort at elevated tem-
peratures, and various liquid waste
streams could be used to help cool it
before it is transported to a disposal
site. Moisture is also needed for com-
paction at the disposal site and for dust
control. Codisposal of the liquid and
solid wastes, however, may change the
impact of the disposal pile on the envi-
rons compared to using higher quality
water for moisturization.
The project reported in this paper ad-
dresses the components needed for the
prediction of disposal pile leachate
quality and quantity. The primary objec-
tives of the research are to provide a
column leaching methodology and lab-
oratory data base that will contribute to
the eventual prediction and assessment
of the quantity and quality of leachates
from retorted shale disposal piles.
Soecific objectives are to:
1. Develop a viable column leaching
test for spent shales.
2. Develop and verify the theory for
the column leaching test so that re-
sults can be compared and gener-
alized.
3. Compare the chemistry of leachate
from the column test with the re-
sults from batch tests using the
water shake test proposed by the
ASTM and EPA's RCRA acetic acid
test.
4. Conduct a study of the hydraulic
and physical properties of spent
shales, including both its saturated
and unsaturated properties.
5. Quantify the effects on leachate
quality of codisposing of the
wastewaters from the retort proc-
ess with the solid wastes.
This report describes: 1) two column
leach test procedures, 2) the mathemat-
ical theory required for interpretation of
the leach test data, 3) the results of
chemical analyses of column leachate
and comparison of these with the re-
sults of batch tests, 4) the hydraulic and
physical properties of the retorted
shales, and 5} the chemical differences
in leachate quality if process waters, in-
stead of higher quality water, are used
for moisturizing the retorted shales.
While the data reported here are be-
lieved valid for the particular material
tested, the relationship of these data to
those for materials produced by the
same process under different operating
conditions (e.g., at a different tempera-
ture or at commercial scale) remain
largely unknown.
Summary and Conclusions
This report summarizes the develop-
ment of methods for determining the
leaching and hydraulic properties of
solid residues resulting from the proc-
essing of oil shale. The activities, re-
sults, and conclusions can be divided
into three major categories: 1) solid
leaching, 2) hydraulic properties, and
3) codisposal of solid and liquid wastes.
Category 3 is actually an application of
the methodology developed in Cate-
gory 1.
Solid Leaching
The difficulty in establishing an ini-
tially saturated condition without caus-
ing some leaching led to a test in which
the leachant (distilled water) was in-
jected at a constant rate into the bottom
of an initially dry column of solid. The
salient feature of this test is incorpora-
tion of easily dissolved chemicals into
the advancing wetting front upon con-
tact by the leachant. An approximate
mathematical model for this test was
developed, applicable to conservative
species instantaneously dissolved at
the wetting front. For this reason, the
test was called the Instantaneously Sol-
uble Mass (ISM) test.
Several data sets collected from the
ISM test are presented in this report.
While it was determined that the test
was reproducible and amenable to a
reasonably simple mathematical analy-
sis (for conservative species), important
shortcomings remained. First, the injec-
tion of leachant into an initially dry
medium did not simulate the expected
field conditions in which the material
would be disposed of in a moist condi-
tion. Also, the results of the test were
highly sensitive to the length of the
column, an undesirable feature because
it was not possible to construct the
columns long enough to approach the
depth of a field pile.
These shortcomings were eliminated
by another type of column test, called
the Equilibrated Soluble Mass (ESM)
test developed by researchers under the
project. In this procedure, the solid was
moistened by distilled water (process
water in the case of codisposal tests)
until the water content was that ex-
pected to be a reasonable value for dis-
posal under commercial operations.
The moisturizing process was carried
out by sprinkling the solid, spread on a
plastic sheet, with frequent mixing and
respreading. The moisturized material
was then placed in a closed container
and allowed to approach chemical equi-
librium. The material, thus prepared,
was packed into the leach column, and
constant-rate injection into the bottom
was started.
Both theoretical and experimental ev
idence was developed that indicates
that the pore solution existing in the
column antecedent to injection is dis
placed ahead of the invading solution
This is the salient feature of this test
Because of the displacement process
the first effluent from the column is thf
antecedent pore solution and exhibit!
the chemical composition thereof. Be
cause the chemical composition re
suited from equilibration of the wate
with the solid at a liquid-to-solid rati<
approximately that expected durinc
field disposal operations, the quality o
the first effluent should be a reasonabli
index to the quality of the pore solutic
in the field. Furthermore, the firs
leachate generated in the field will b
the antecedent pore solution, regard
less of whether the leachate result
from drainage or from net infiltratior
Net infiltration will displace the an
tecedent pore solution in the field, jus
as does the injected water in the colum
test.
A degree of mixing exists betwee
the injected water and the displaced ar
tecedent water due to hydrodynami
dispersion. When this mixing zon
reaches the outflow end of the columi
the chemical composition of the effli
ent is no longer that of the antecedet
pore solution. The subsequent breal
through curve is affected by such expe
-------
Jmental parameters as column length,
Jnjection rate, particle size, and initial
' moisture content.
Examples of the chemical composi-
tion of the first effluent from ESM
column tests are summarized in Table 1.
Such data are expected to be reason-
able indices to the quality of the first
leachate that would occur from these
materials. The two experiments on
Lurgi ULG and on TOSCO II indicate the
reproducibility of the test. Additional
data relating to the assertion that the
antecedent pore solution is displaced
and to reproducibility are contained in
the report.
Batch leaching tests, details of which
are presented in the report, were also
performed. The salient features of the
batch tests, both RCRA and ASTM, are
the violent agitation and the very large
liquid-to-solid ratios that are utilized.
Neither feature is remotely similar to
field conditions. Nevertheless, batch
tests can be used to assess the maxi-
mum quantity of extractable chemicals
in a given quantity of raw or retorted
shale. However, concentrations of most
chemical components of leachate from
disposal piles greatly exceed the con-
centrations observed in the batch tests,
because the liquid-to-solid ratios that
will exist in the waste piles will be much
smaller than in the batch tests.
Hydraulic Properties
The permeability at saturation, the
moisture characteristic, and the perme-
ability as a function of water content
were measured on materials by recog-
nized methods. These data are pre-
sented in the report. During the project,
it became apparent that water transport
at very low water contents would be an
important consideration in the question
of leachate generation. Extensive meas-
urements of the hydraulic properties
were made for one Lurgi retorted shale
provided by the Rio Blanco Oil Shale
Company.
A method was developed for measur-
ing the hydraulic diffusivity down to
practically zero water content. In this
method, a horizontal column of the
spent shale is injected at a very low rate
with a syringe pump. The water content
distribution is measured as a function of
time and position in the column using
gamma attenuation. These data permit
the direct calculation of the hydraulic
diffusivity.
As expected, the data indicated a
range of water contents on the dry end
of the water-content scale in which flow
was dominated by vapor transport. The
measurements were repeated using an
iodine solution for injection and a dual
source of gamma rays which permitted
the simultaneous measurement of the
concentration distribution of iodine and
the water content distribution. It was
observed that iodine-free water indeed
moved ahead of water containing
iodine. The iodine-free water moved by
vapor diffusion. Further, it was ob-
served that the plane separating the
iodine-free water from the other liquid,
while moving progressively farther into
the medium, always occurred at a con-
stant, characteristic water content. This
characteristic water content was inter-
preted as being the value below which
bulk, Darcian-type flow of liquid water
could not occur. It is likely that liquid
water at or below this characteristic
value existed in adsorbed films not ca-
pable of bulk flow.
In the material on which these meas-
urements were made, the critical water
content was about 7% (by volume). This
means, for example, that water con-
tents up to about 7% in this material can
be regarded as being nondrainable.
Other materials are expected to have
different values. Detection of the critical
water content permitted separation of
Table 1. First Effluent Concentrations for ESM Tests
Run No.
EC(dS/m)a
Fb
Cl
SO4
Na
Ca
Mg
Mo
K
Fe
Mn
Sr
B
Lurgi ULG TOSCO II
33 34 29 35
15.81
17.8
355
9,650
3,830
519
0.619
5.53
14.91 38.90
13.0 29.2
341
9,840 23,300
3,680
466 397
0.478 483
7.24 56.4
36.50
24.9
218
28,510
9,910
368
695
26.3
109
Allis Chalmers
4
8.50
-
298
6,820
194
644
1,380
1.41
340
32.20
31.90
4.10
5.64
Lurgi RB-II
3
24.6
-
145
6,480
3,190
683
0.03
1.41
629
0.02
0.01
31.90
2.25
Paraho II
7
43.7
-
240
35,300
11,400
583
2,100
10.10
1,440
0.14
0.05
5.3
1.92
Chevron
9
10.8
8.2
234
2,400
738
1,150
0.13
5.3
130
0.07
0.03
32.9
1.96
'Electric conductance in deci-siemens per meter.
bAII concentrations in milligrams per liter.
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the diffusivity data into regions of
vapor-dominated and liquid-dominated
contributions. The method permits
measurement of vapor diffusion coeffi-
cients.
Codisposal
The ESM column test was used to as-
sess the effect of codisposing process
water with the solid. This was accom-
plished by utilizing distilled water as the
moisturizing fluid in one set of tests and
process water as the moisturizing fluid
in an otherwise identical set of tests.
Table 2 summarizes the results of
these codisposal trials. It is evident that
moisturizing these materials with these
waters tended to result in greater TDS
concentration in the first effluent as
compared to the tests in which the ma-
terial was moisturized with distilled
water. Even in the tests with distilled
water moisturization, the TDS concen-
trations were quite large; therefore, the
additional increment due to the process
water may not be too significant.
The total organic carbon (TOC) con-
centration in the first effluent from ma-
terials moisturized with process water is
markedly greater than from materials
moisturized with distilled water. The
data indicate significant adsorption of
organic carbon by the solid, but adsorp-
tion is not sufficient to reduce the TOC
in the first effluent to that observed in
tests with distilled water moisturization.
D. B. McWhorter and D. S. Durnford are with Colorado State University's
Engineering Research Center, Fort Collins. CO 80523.
Edward P. Bates is the EPA Project Officer (see below).
The complete report, entitled "Leaching and Hydraulic Properties of Retorted
Oil Shale Including Effects from Codisposal of Wastewater," (Order No. PB
87-120 507'/AS; Cost: $18.95. subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC 27711
Table 2. Summary of Results of Codisposal Tests
Total Dissolved Solids, mg/l
Total Organic Carbon, ppm
Lurgi RB-II
Paraho-ll
Chevron
Run
No.
1
2
3
5
6
7
8
9
Moisturizing
Fluid
Unstripped
Retort Water
Stripped Retort
Water
Distilled Water
Retort Water
Gas Condensate
Distilled Water
Process Water
Distilled Water
Moisturizing
Fluid
48,900
8,430
-
14,250
79,200
-
3,790
-
First
Effluent
32,700
18,200
13,200
59,700
65,900
52,900
9,300
5,680
Last
Effluent
3,900
4,020
38,200
5,020
5,150
4,770
2,690
3,900
Moisturizing
Fluid
5,470
3,700
-
2,960
4,140
-
660
-
First
Effluent
4,380
2,660
<5
1,950
1,820
531
565
380
Last
Effluent
36
54
<5
56
118
12
20
18
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Environmental Protection
Agency
Center for Environmental Research
Information
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