United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/007 May 1985
SEPA Project Summary
Assessment of Fluidized-Bed
Combustion Solid Wastes for
Land Disposal
T. W. Grimshaw, R. A. Minear, A. G. Eklund, W. M. Little,
H. J. Williamson, and J. E. Dunn
Fluidized-bed combustion (FBC) is
an emerging energy technology that
holds promise for both high efficiency
of energy conversion and minimiza-
tion of adverse air quality impacts. A
major advantage of FBC is that high-
sulfur coal can be burned without the
use of flue-gas desulfurization equip-
ment to meet air quality standards.
During combustion in a fluidized bed,
sulfur in the coal is oxidized to sulfur
oxides (SOX) as in conventional
boilers, but these SOX then react with
a sorbent that is injected into the
fluidized bed with the coal. During
steady state conditions, the sorbent
constitutes more than 95% of the bed
material. The sorbent, typically lime,
limestone, or dolomite, usually forms
calcium sulfate compounds, such as
anhydrite, when reacting with the
SOX. The solid residues that are
generated in an FBC unit are usually
larger in volume and have different
properties than the typical bottom ash
from a conventional boiler.
The objectives of this investigation
were to obtain and analyze represent-
ative samples of FBC wastes, assess
the characteristics of leachates
generated from the wastes under
laboratory and field (landfill) condi-
tions, and characterize the attenua-
tion of the leachates by earth mater-
ials that are typical of disposal set-
tings. An attempt was made to devel-
op a means of predicting the leachate
generation behavior of FBC wastes
under landfill conditions on the basis
of laboratory test results by estab-
lishing a rigorous statistical relation-
ship between the laboratory and field
leaching results. In addition, the com-
patibility of commonly used landfill
liner materials with FBC waste
leachates was assessed.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Re-
search Triangle Park, NC, to an-
nounce key findings of the research
project that is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
FBC is an emerging energy technology
that holds promise for both high efficien-
cy of energy conversion and minimization
of adverse air quality impacts. A major
advantage of FBC is that high-sulfur coal
can be burned without the use of flue-gas
desulfurization equipment to meet air
quality standards. During combustion in a
fluidized bed, sulfur in the coal is oxidized
to SOX as in conventional boilers, but
these SOX then react with a sorbent that
is injected into the fluidized bed with the
coal. The sorbent, typically lime, lime-
stone, or dolomite, usually forms calcium
sulfate compounds, such as anhydrite,
when reacting with the SOX. The solid
residues that are generated in an FBC unit
are usually larger in volume and have dif-
ferent properties than the typical bottom
ash from a conventional boiler.
Although FBC wastes can be used as
soil conditioners or disposed of in im-
poundments or at sea, it is likely that
-------
most wastes that will be generated in the
future will be landfilled. The objective of
this investigation was to assess the
suitability of FBC wastes for landfill
disposal and to determine several char-
acteristics of the waste important to land-
fill considerations. The procedures were
to obtain and analyze representative
samples of FBC wastes, determine the
composition of the wastes, assess the
characteristics of leachates generated
from the wastes under laboratory and
field (landfill) conditions, and characterize
the chemical interaction of the leachates
with earth materials that are typical of
disposal settings.
The investigation included both exten-
sive laboratory studies and large field cells
to simulate actual landfill conditions. An
attempt was made to develop a means of
predicting the leachate generation be-
havior of FBC wastes under landfill condi-
tions on the basis of laboratory test
results by establishing a rigorous sta-
tistical relationship between the laboratory
and field leaching results. In addition, the
compatibility of commonly used landfill
liner materials with FBC waste leachates
was assessed. The laboratory studies
were performed at Radian Corporation
laboratories in Austin, TX, and the field
investigation took place at the former EPA
mine drainage control facility, about 9 mi*
south of Morgantown, WV.
Sources of Samples
Sources of FBC wastes were selected
to be as representative of future FBC
waste streams as possible while, at the
same time, being capable of providing
enough sample for laboratory and field ex-
periments. The waste source selected for
pressurized FBC (PFBC) was the Exxon
Miniplant at Linden, NJ. Two atmospheric
FBC (AFBC) sources were selectedthe
EPRI/B&W unit at Alliance, OH, and the
Georgetown University boiler in Washing-
ton, DC. Both AFBC units were operating
in the recycle mode when wastes were
collected.
Several types of geological substrate
materials (termed "disposal media") were
obtained from the vicinity of the field cells
in northern West Virginia and eastern
Ohio. They were selected as represen-
tative of substrate materials at future
disposal sites in the eastern U.S. and in-
cluded shale, coal mine interburden, sand-
stone, glacial till, alluvium, and limestone.
These samples were used in the lab-
oratory and field studies to investigate the
interaction (contaminant attenuation and
mobilization) of the FBC waste leachate
with typical substrate materials.
Overview of Procedures
The principal component of the
laboratory investigation was a six-step se-
quential batch equilibration protocol for
assessing the characteristics of leachate
after both generation from FBC wastes
and exposure to samples of the disposal
media (Figure 1). The leaching steps of
the batch equilibration protocol consisted
of initial leaching of the waste (at a liquid-
to-solid mass ratio of 10:1) with deionized
water, secondary leaching of leached
waste with additional deionized water
(Step 2) for up to seven repetitions; and
secondary exposure, sequentially for up to
seven repetitions, of leachate to fresh
waste in Step 3.
The leachate was exposed to the dis-
posal media to assess the tendency of
contaminants to be attenuated by (or
mobilized from) the media. Step 4 of the
protocol assessed the initial attenuation of
*1 mi = 1.609 km.
I
to
X)
i
Fi&
I
%
*
Step 1
Waste
(for A
repetition) ,
Sfep2
Waste
«,
^
Step 2
Leachate
(repeat as necessary)
*»
I
to
f
Step 4
Disposal
Medium
i j
(fr \ A
repetition)
StepS
Disposal
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Step 1
Leachate
\
Step 5
Leachate
Fresh
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/_
Step 1
Waste
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Step 1
Leachate
i
I
Fresh
Disposal
Medium
A
Step 4
Disposal
Medium
Step 1
Leachate
\
Step 4
Leachate
\
-------
leachate from Step 1 when exposed to a
sample of disposal medium. Step 5
evaluated the ability of a disposal medium
sample to continue to attenuate fresh
leachate from Step 1. In Step 6, the
leachate from Step 4 was repeatedly ex-
posed to new samples of disposal medium
to evaluate the progressive attenuation of
the leachate by exposure to fresh media.
Step 5 was repeated up to nine times and
Step 6 was repeated five times.
Samples of the FBC waste and disposal
media were analyzed in the laboratory for
a variety of parameters. Physical proper-
ties that were determined included grain
size distribution, specific surface area, and
particle surface characteristics. The solids
composition was investigated by X-ray
diffraction to determine the crystalline
phases present and by sample digestion
and analysis to determine the chemical
composition.
The laboratory studies also included
two sets of leaching columns, one set
containing only disposal media, and
another set containing layers of waste and
disposal media. In addition, the FBC
waste samples were subjected to the Ex-
traction Procedure test for hazardousness
(toxicity category) as set forth in regula-
tions developed pursuant to the Resource
Conservation and Recovery Act. Another
component of the laboratory studies was
the assessment of the compatibility of
various landfill liner materials with FBC
waste leachate.
The main feature of the field investiga-
tion was the design, installation, and
operation of several large (4 ft* diameter,
7 ft long) cylindrical field cells. Field cells
containing Exxon PFBC and Alliance
AFBC waste were constructed and oper-
ated below ground surface. These field
cells were open at the land surface to
natural precipitation and isolated from the
subsurface environment. The field cells
were intended to simulate actual landfill
conditions in the field as closely as prac-
ticable. The cells contained layers of
waste and disposal media arranged sim-
ilarly to a landfill configuration, with an
upper layer of disposal medium to
simulate landfill cover material, a layer of
waste, and a lower layer of medium to
simulate landfill substrate (Figure 2).
Leachate sampling points were included
at the base of the waste layer (upper sam-
ple point) for collection of unattenuated
leachate and at the base of the lower
layer of disposal medium (lower sample
point) for collection of attenuated
leachate. Excess leachate was removed
from the bottom of the field cells and not
allowed to escape into the subsurface en-
vironment.
The field studies also included two
large-diameter permeameters containing
FBC wastes. These permeameters were
used to determine the permeability of un-
compacted waste initially after emplace-
ment and again after several months of
exposure to weathering processes and
chemical changes in the wastes.
1 ft = 30.48 cm.
Field Cell
Equipment
r- Shell
Connector
Pipes
Cross-Section
Schematic
Drum
a. Layout
Figure 2. Field cell layout and geometry.
Cross Section through
Sampling Array-
Not to scale
Disposal
4 ft Diameter Gutter Medium1
FBC Waste 1%'ft':.
O Porous Cup Samplers
8 in. centers along 2
diameters, connected
by manifold to vacuum
flask
D Moisture Sensing Device
.Sand'/2ft'':
\« !«.!.. ..
Filter Cloth
Disposal
Medium3 ft
Porous
Cup
Sand'
7 ft Freeboard
Land Surface
Baffle
\- Baffles
Upper
- Sampling
Array
\-Baffles
^- Baffle
Lower
Sampling
Array
Impermeable
Membrane
b. Geometry
-------
FBC Waste Composition:
Mineralogy and Major
Chemistry
The principal crystalline phases found in
the unleached Exxon PFBC waste were
anhydrite, periclase, and quartz. The most
significant components found in the solids
analysis were calcium (22%), magnesium
(12%), and sulfate (23%). After leaching
in Steps 1 and 2 of the batch equilibration
protocol, the most prominent minerals
were gypsum, brucite, calcite, and quartz.
Field cell leaching produced similar
crystalline materials and also ettringite.
The solids composition of both the
laboratory- and field-leached PFBC waste
showed a reduction in calcium, sulfate,
and magnesium. The leached waste from
the laboratory protocol had 12% calcium,
20% sulfate, and 8% magnesium. The
field-leached waste contained 14%
calcium, 18% sulfate, and 8% mag-
nesium. Both the crystalline and chemical
composition data indicated that the
minerals were hydrated during leaching.
Both the unleached and leached (Pro-
tocol Steps 1 and 2) Alliance AFBC waste
contained quartz, calcite, portlandite, and
hematite. The unleached and leached
waste differed: the former had anhydrite
and lime, and the latter had gypsum and
ettringite. The leached waste from the
field cells had the same crystalline com-
position as the protocol-leached waste.
Unleached Alliance waste had 31-35%
calcium and 10-13% sulfate. Laboratory
leaching resulted in a reduction of the
calcium content to 20-21 % and of sulfate
to 1.4%. Field cell leaching lowered the
calcium to 21-24%, but sulfate remained
at 11%. These results again indicate a
hydration of minerals during the leaching
process.
X-ray diffraction analysis of the
unleached Georgetown AFBC waste re-
vealed the presence of portlandite, an-
hydrite, quartz, calcite, lime, and
hematite. Leaching in the laboratory pro-
tocol (Steps 1 and 2) resulted in the for-
mation of ettringite and gypsum and the
hydration of lime. Before leaching, the
Georgetown waste was composed of 38%
calcium and 8.5% sulfate. Laboratory pro-
tocol leaching reduced the calcium to
15-23%, and the sulfate content was
about 7%. Field cells containing George-
town AFBC waste were not constructed.
Physical Properties of
FBC Waste
Scanning electron micrographs were
obtained for each of the three wastes.
both unleached and leached. The un-
leached Exxon PFBC waste consisted of
irregularly shaped particles covered with
fine material. A few spherical particles
were also present. The leached PFBC
waste also consisted mostly of irregular
particles, but it also contained lath-shaped
crystals (probably precipitated calcite or a
hydration product of calcium sulfate,
possibly gypsum).
The unleached Alliance AFBC waste
also consisted mostly of irregular particles
and a few spheres. The leached waste
consisted of generally smaller particles
than the unleached waste, including laths
similar to those in the PFBC waste.
Unleached Georgetown AFBC waste con-
tained two different groups of particle
sizes, one from the bed draw and one
from the fly ash component of the waste.
The leached waste contained little of the
original fine fraction, but had small
needles adhering to the coarser grains.
Mixed (composite) samples of Exxon
PFBC, Alliance AFBC, and Georgetown
AFBC wastes were dry-sieved to deter-
mine the particle size distribution of the
as-received wastes. The mean grain sizes
of these wastes were 195 /tm for the Ex-
xon waste, 270 /tm for the Alliance waste,
and 230 /tm for the Georgetown waste.
The grain size distributions for the Exxon
and Alliance waste were quite similar,
although the Exxon waste was consistent-
ly finer grained. The Georgetown waste
had a different grain size distribution than
the other two wastes: there was a higher
percentage of material below 100 /*m.
The specific gravities of the Exxon
PFBC, Alliance AFBC, and Georgetown
AFBC wastes (after sample grinding) were
2.49, 2.65, and 2.42, respectively. The ap-
parent bulk densities (after sample grind-
ing) were 1.10, 1.29, and 1.21 g/cm3, re-
spectively. The specific surface area for
the ground Exxon PFBC waste was 0.9
mVg.
The field permeabilities of Alliance
AFBC and Georgetown AFBC waste were
determined by constructing large (4 ft
diameter and 4 ft long) cylindrical
permeameters at the field site. Permeam-
eters were constructed above ground,
separate from the field cells. The waste
was emplaced in the cells without com-
paction. The permeability of the waste
was determined initially, at an interim
point in the program, and at the conclu-
sion of the field studies. The Alliance
AFBC permeameter was operated about
19 months, and the Georgetown AFBC
permeameter was in place for about 13
months. Data are given for the initial
permeability and the permeability after
comparable periods of operation.
The initial permeabilities of the two
wastes were quite similar: 1.1 x 10~3
cm/sec for the Alliance AFBC waste and
1.7 x 10'3 cm/sec for the Georgetown
AFBC waste. These initial permeabilities
are within the range typical of a sandy
loam soil. After 15.5 months of operation,
the permeability of the Alliance AFBC
waste decreased to 1.1 x 1Q-« cm/sec.
The permeability of the Georgetown
waste decreased to 1.7 x 10~6 cm/sec
after 13 months of operation. These per-
meabilities are comparable to a silty clay
soil.
Composition of FBC Waste
Leachate
The leaching properties of the FBC
wastes were evaluated in the laboratory
sequential batch equilibration protocol
(Steps 1-3), in laboratory leaching col-
umns, and in the large field cells. The Ex-
xon PFBC and Alliance AFBC waste were
investigated in all three sets of studies;
the Georgetown AFBC waste was evalu-
ated in the batch equilibration protocol.
All three wastes were also subjected to
the Extraction Procedure (EP) toxicity test
set forth in regulations developed pur-
suant to the Resource Conservation and
Recovery Act (RCRA) of 1976. The con-
centrations reported below are mean
values from analysis of aliquots from
several repetitions of the protocol steps
and sample replicates. The interpretation
included here is based on overall averages
and trends observed from about 65,000
individual analytical determinations.
Exxon PFBC Waste Leachate
Leaching of Exxon PFBC waste for 7
days (Step 1) produced leachates that had
calcium and sulfate in the highest concen-
trations. The pH of the leachate was
about 12. The calcium concentration was
about 1670 mg/L, and the sulfate concen-
tration was about 1600 mg/L. Also pres-
ent in relatively high concentrations were
potassium (250 mg/L), sodium (17 mg/L),
and boron (11 mg/L). Other significant
species were chloride (4 mg/L), strontium
(2.8 mg/L), molybdenum (2.5 mg/L),
magnesium (1.4 mg/L), and silicon (1.3
mg/L). Other species were present in
concentrations less than 1 mg/L. Com-
parison of the mass of each of the major
species leached to the mass in the bulk
solids of the PFBC waste showed that
chloride was as much as 26% leached,
boron was 20% removed, strontium about
-------
13%, calcium about 7%, sodium about
5%, and sulfate about 6%.
Repeated leaching of the Exxon PFBC
waste in Step 2 of the protocol resulted in
constant or decreasing concentrations of
all species except silicon and aluminum,
which showed an increase. Repetition of
Step 3, where the same leachate was ex-
posed to fresh waste, resulted in increas-
ing concentrations. Only aluminum, iron,
and silicon showed decreases. Magnesium
remained constant.
Two small, 3-in? diameter leaching col-
umns containing layers of Exxon PFBC
waste and disposal media were used to
evaluate the characteristics of leachate
generated under laboratory column condi-
tions. These columns contained an upper
layer of shale (to simulate natural cover
material) and a lower layer of PFBC
waste. Leachate was collected from the
bottom of the columns, so the composi-
tion of the leachate reflected the com-
bined effect of exposure to the layers of
shale and PFBC waste.
The leachates from these columns
again had calcium and sulfate as the
species of highest concentration: as high
as 1000 mg/L for calcium and 3000 mg/L
for sulfate. The pH was again very high
(11-12). Potassium and chloride ranged as
high as 3500 mg/L and 410 mg/L, respec-
tively. The total dissolved solids (TDS)
reached 8500 mg/L. Boron was as high as
25 mg/L, lithium reached 4 mg/L, and
molybdenum was as high as 2.8 mg/L.
Aluminum and barium reached 1.7 and
1.2 mg/L, respectively.
The leaching behavior of Exxon PFBC
waste under field (landfill) conditions was
evaluated by collecting and analyzing
leachates from the upper sample point of
the field cells. This leachate reflected the
combined effects of exposure of infiltra-
ting precipitation to an upper layer of
disposal medium (to simulate landfill cover
material) and an 18-in. layer of PFBC
waste. Two of the six PFBC field cells
had shale in the upper layer, and the re-
maining four cells had glacial till, alluvium,
limestone, and sandstone. The cells were
operated for about 27 months, including a
6-month period during which they were
covered and not operated. A total of 30
leachate samplings occurred during this
period.
In general, many of the species in the
upper sample point leachates had high
concentration in the initial samples, but
the concentrations showed considerable
fluctuation. After the first month of
*1 in. = 2.54 cm.
sampling, the concentrations oscillated
much less, and smoother trends were
observed. The concentration ranges in
leachates from the more stable period of
operation, when concentrations were
more stable, were highest for sulfate and
TDS (generally 1000 to 10,000 mg/L),
calcium and potassium (100 to 1,000
mg/L), and chloride, silicon, sodium,
magnesium, and potassium (10 to 100
mg/L). The pH of the field cell leachates
was generally much lower (7-8) than in
the laboratory protocol or laboratory leach
column leachates. There was little cell-to-
cell variation in the concentration ranges
of the various species, indicating that the
upper layer of disposal medium ("natural
cover material") did not have a domi-
nating influence on the composition of
the leachate.
The Extraction Procedure (EP) set forth
to determine the hazardousness of waste
(toxicity category) under the provisions of
RCRA was performed on the Exxon PFBC
waste. The EP extractant was analyzed
for the eight metallic ions specified by the
regulations (Ag, As, B, Cd, Cr, Hg, Pb,
and Se). None of these elements had a
concentration higher than the limits
specified in the RCRA regulation, so the
PFBC waste would likely be classed as
nonhazardous in the toxicity category.
Alliance AFBC Waste Leachate
Leaching of Alliance AFBC waste in the
batch equilibration protocol (Step 1)
yielded leachates with a mean calcium
concentration of 1340 mg/L and a mean
sulfate concentration of 1110 mg/L. The
pH was also very high (12.3 to 12.5).
Other species having somewhat elevated
concentrations were chloride (51 mg/L),
potassium (44 mg/L), and sodium (13
mg/L). Step 1 leaching resulted in
removal of 63% of the chloride, 25% of
the strontium, and 13% of the molyb-
denum from the Alliance AFBC solids.
Calcium and sulfate, which had the
highest leachate concentrations, were
4.5% and 8.5% removed by leaching,
respectively.
With continued leaching in repetitions
of Step 2 of the protocol, the leachate
concentrations of the major species,
calcium and sulfate, generally decreased,
although sulfate decreased only slightly.
For the other species examined, 14 in-
creased in concentration and 7 decreased.
The pH remained constant. Repetitions of
Step 3, where the same leachate sample
was repeatedly exposed to fresh waste
samples, resulted in increasing concentra-
tions for almost all parameters, except pH
and magnesium, which remained con-
stant. Aluminum, beryllium, and silicon
showed a decrease followed by an in-
crease.
A laboratory leaching column contain-
ing Alliance AFBC waste was constructed
and operated. It had an upper layer of
sandstone (to simulate landfill cover
material) and a lower layer of waste.
Calcium and sulfate were again the
predominant species in the leachate
samples, with concentrations up to 1300
and 2000 mg/L, respectively. Chloride
(levels up to 1200 mg/L) and potassium
(levels up to 950 mg/L) also had elevated
concentrations. The pH was again very
high (12).
Five field cells containing Alliance
AFBC waste were constructed and oper-
ated. Two of the cells contained alluvium
in the upper layer, and the other three
cells contained shale, interburden, and
limestone. The cells were operated for 21
months, from March 1980 to November
1981. During the period of operation, 24
samples were collected from the upper
sample point and analyzed.
Leachates from the upper sample points
for all the cells had highest concentrations
(1000 to 10,000 mg/L) for sulfate and
TDS. Next highest were calcium and
potassium, with concentrations generally
of 100 to 1000 mg/L. Also significant,
with concentrations of 10 to 100 mg/L,
were silicon, sodium, and strontium.
Chloride ranged from 10 to 100 mg/L in
some cells and from 100 to 1000 mg/L in
others. The pH values were at or near
neutral.
The RCRA Extraction Procedure was
performed on the Alliance AFBC waste,
and the extracts were analyzed for the
eight metallic ions specified by the RCRA
regulations. The results of these analyses
showed that the waste is likely to be clas-
sified as nonhazardous in the RCRA tox-
icity category.
Georgetown AFBC Waste
Leachate
Steps 1 and 2 of the laboratory protocol
were used to determine the leaching char-
acteristics of the Georgetown AFBC
waste. The species with the highest con-
centration in the Step 1 leachate were
calcium and sulfate, with mean values of
1500 and 1400 mg/L, respectively. Other
species with lower but still substantial
concentrations were chloride (24 mg/L),
potassium (18 mg/L), and strontium (13
mg/L). The mean pH value was 12.5.
Comparison of the mass leached to the
mass originally present in the solids for
each species showed that chloride and
-------
strontium were leached the most, with
63% and 52% removed, respectively.
Sulfate and calcium, the highest concen-
tration species, were leached 17% and
5%. About 13% of the lithium was
leached from the Georgetown AFBC
waste.
Successive repetitions of Step 2 on the
Georgetown AFBC waste resulted in
decreasing leachate concentration trends
for most species. No species showed a
consistent increase in concentration with
increased leaching, although barium
showed an initial increase followed by a
decrease. Fluoride remained constant dur-
ing the Step 2 repetitions.
Extraction and analysis of the George-
town AFBC waste by RCRA procedures
showed that the waste is nonhazardous in
the toxicity category.
Attenuation of FBC Waste
Leachate
The attenuation of leachates from each
of the three FBC wastes was evaluated
separately for each of the six types of
disposal media. Attenuation was studied
in the laboratory and field for the Exxon
PFBC and Alliance AFBC waste and in
the laboratory for the Georgetown AFBC
waste. In general, attenuation was evalu-
ated by reference to a derived parameter
termed "fractional attenuation" (A). For
the laboratory protocol results, fractional
attenuation is defined as:
AL = C' ~
d
where: AL = laboratory fractional at-
tenuation,
C| = initial leachate concentra-
tion (before exposure to
the disposal media, pro-
tocol Step 1), and
Cf = final leachate concentra-
tion (after exposure to
the disposal media, pro-
tocol Step 4).
For the field cells, fractional attenuation is
defined as:
where: AF = field fractional attenua-
tion,
Cu = concentration in leachate
from upper sample point,
and
CL = concentration in leachate
from lower sample point.
The attenuation of FBC waste leachate
was found to be quite variable for dif-
ferent wastes, for different disposal
media, and for laboratory and field condi-
tions (Table 1). Overall, strong attenuation
was observed for more species in the
laboratory protocol than in the field cells.
More parameters were found to exhibit
strong mobilization in the field cells than
in the protocol. In the laboratory protocol,
about the same number of parameters ex-
perienced strong attenuation and strong
mobilization.
Table 1. Comparison of the Attenuation of Leachates from Three FBC Wastes Resulting from Exposure to the Disposal Media'1
Element/
Species
Al
B
Ba
Ca
Cl
Cr
F
Fe
K
Shale
EP*
AA'
GA'
EP
AA
GA
EP
AA
GA
EP
AA
GA
EP
AA
GA
EP
AA
GA
EP
AA
GA
EP
AA
GA
EP
AA
GA
Lab1
SA
N
7
SA
SM
*
WA
WA
WA
WA
WA
*
WA
SA
WA
WA
*
EM/SM
#
WA
N
N
N
Field3
WM
SM
#
WA
N
tt
WA
N
It
N
WM
It
tt
N/WA
SM
tt
#
N/WA
SM
tt
N/WA
WA
t.
Interburden
Lab
WA
WA
SA
WA
WA
WA
WA
WA
WA
WA
SM
N
WA
*
WA
WM
SM
SM
WA
SA
N
N
Field
tt
SM
tt
tt
SM
tt
tt
WA
tt
tt
SM
»
#
It
tt
SM
tt
tt
It
tt
SM
It
tt
WA
tt
Sandstone
Lab
*8
WA
SA
WA
#
SA
WA
WA
WA
WA
*
WA
WA
WA
WA
WM
WM
WA
WA/SA
WM
WM
Field
SM
tt
It
N
tt
It
N
tt
It
N
tt
it
tt
It
SM
tt
tt
tt
»
WA
tt
It
M
tt
tt
Glacial Till
Lab
WM
WA
SA
SA
*
WA/SA
WA
WA
WA
WA
_
N
WA
WM
WA
WA
WM
SM
WA
»
WA
WA
Field
SM
It
It
WA
tt
tt
N
It
It
N
tt
It
_
tt
tt
N
tt
tt
tt
tt
WA
tt
It
WA
#
tt
Alluvium
Lab
WM
WA
SA
WA/SA
WM
N
N
WA
WA
WA
_
N
WA
WM
WA
WA
SM
WM
SM
SM
N
WA
Field
SM
SM
tt
N
SM
tt
N
WM
It
N
»*10
tt
tt
WM
WA
W
tt
N
N/WM
It
WA
SA
9
Limestone
Lab
SM
WA
SA
SA
WM
WA
WA
WA
WA
WA
N
WA
WM
SA
N
SM
SM
WA
SA
SM
SM
Field
SM
SM
tt
N
SM
It
WA
WM
It
N
N
It
_
tt
WM
WM
tt
#
WM
SM
#
N
WA
tt
-------
Table 1. (Continued)
Element/
Species
Li EP
AA
GA
Mg EP
AA
GA
Na EP
AA
GA
Ni EP
AA
GA
Si EP
AA
GA
SO4 EP
AA
GA
Sr EP
AA
GA
TDS EP
AA
GA
Zn EP
AA
GA
Shale
Lab2 Field3
SA WA
WA SA
SA tt
SA WM/SM
SM
WA tt
**
WM N
WM It
WM SM
N tt
N/WA
SM WA
SM It
WA N/WM
WA WM
WA #
WA N/WM
WA WA
WA «
WA
WA
WA It
NA/WM
WM SM
It
Interburden
Lab
SA
WA/SA
WA
SA
WA
WM
WM
WM
SA
SA
SA
WA
SM
N
NA
WA
NA
*
WA
WA
WA
WA
WA
*
SA
-
Field
tt
SM
tt
tt
SM
tt
It
WA
tt
tt
SM
It
It
SM
It
tt
SM
It
tt
WA
It
#
tt
tt
SM
tt
Sandstone
Lab
SA
WA
SA
SA
*
SA
WM
WM
WA
SA
WA
SM
N
WA
WA
NA
N
N
WA/SA
WA
WA
WA
SA
WA
-
Field
WM
tt
tt
SA
tt
tt
WM
It
It
9
tt
WA
tt
tt
WM
tt
it
WM
tt
9
tt
tt
WM
»
tt
Glacial Till
Lab
SA
WA
WA/SA
SA
WA
SA
WM
WM
SM
SA
WM
WM
SM
SM
WA
WA
WA
WA
WA
WA
WA
WA
WA
SA
SA
Field
WA
It
It
SA
It
It
WM
It
tt
tt
It
WA
tt
tt
N
tt
tt
WA
tt
tt
9
9
WM
tt
tt
Alluvium
Lab
WA
SA
SA
SA
WA/SA
SA
N
N
SA
SA
SA
WM
SM
N
WA
WA
WA
WA
N
WA
WA
WA
WA
SA
SA
-
Field
WA/SA
SA
tt
SA
SM
It
N
WA
It
WM/SM
tt
WA
WA
It
N
WA
tt
WA
WA
tt
tt
SM
It
Limestone
Lab
WA
WA
WA
SA
WA
WA
SM
SM
SM
SA
WA
WM
SM
N
WA
WA
WA
N
N
N
WA
WA
WA
WA
SA
-
Field
WM
N
tt
SA
SM
tt
SM
SM
It
SM
tt
WA
N
tt
WM
WM
tt
SM
WA
tt
tt
SM
SM
tt
'SA = Strong Attenuation (A a 0.9)
WA = Weak Attenuation (0.2 < A < 0.9)
N = No Attenuation or Mobilization (-0.2 < A
WM = Weak Mobilization (-0.9 < A <
-0.2)
< 0.2)
SM = Strong Mobilization (A £ -0.9).
*Lab Protocol Steps 1 and 4.
3Field Cell Upper and Lower Sample Point. Last Few Months of Operation.
EP
'AA
'GA
J(-)
*(*)
'(It)
10**
= Exxon PFBC.
= Alliance AFBC.
= Georgetown AFBC.
= Step 7 concentration was at detection limit.
= One value of duplicate pairs was negative and one was positive so no mean value is reported.
= No field cell.
_ oifferent results from duplicate field cells.
Assessment of FBC Waste
Leachate Quality
An overall assessment of the en-
vironmental "acceptability" of the FBC
wastes for land disposal was performed
by comparing: (1) the bulk composition of
FBC wastes with that of the disposal
media; (2) the quality of FBC waste
leachate with similar leachate derived
from the disposal media; and (3) the con-
centrations of various parameters found in
FBC waste leachate with accepted water
quality reference values. The third com-
parison is presented here.
Opinion concerning "safe" ambient
concentrations as well as "safe" concen-
trations in leachates and other discharges
to the environment is quite varied. Several
authoritative sources were surveyed to
form the basis of comparison for the FBC
waste leachates. These sources include
the Primary and Secondary Drinking
Water Regulations, the Resource Conser-
vation and Recovery Act Regulations, and
the Quality Criteria for Water.
From these sources, the most stringent
reference value was selected for purposes
of the comparisons. In some instances,
the most stringent value may not be
directly applicable to likely avenues of
FBC waste leachate discharge to the en-
vironment. The purpose of drawing a
-------
comparison in those instances is to em-
phasize that some of the FBC leachate
concentrations do not exceed even the
most stringent value. For many of the
parameters, the most stringent criterion
possibly is too low and could be increased
to allow for dilution and dispersion of
FBC leachate in the environment.
A comparison of the leaching and at-
tenuation results showed that several
parameters exceeded the reference values
in almost all phases of the study (both
laboratory and field), including boron,
calcium, chromium, sulfate, and TDS
(Table 2). The reference value for pH was
exceeded in all phases of the laboratory
investigation, and potassium, manganese,
and nickel generally exceeded the ref-
erence value for all phases of the field
study. Barium, fluoride, iron, molyb-
denum, strontium, and titanium were
generally below the reference values for
all phases of the investigation. Mag-
nesium was below the reference value for
the laboratory studies. In the field studies.
only pH was consistently within the
reference value (besides the parameters
mentioned above for both the laboratory
and field studies). There was little or no
difference between the laboratory and
field results in terms of parameters which
were consistently above or below the
reference value.
For the field cells, there appeared to be
no significant difference between cells
containing disposal media only and cells
containing both waste and disposal
media.
Table 2. Summary of Parameters Which Consistently Exceeded or Were Consistently Below the Most Stringent Reference Value
Laboratory Investigations
Field Investigations
Exxon PFBC
Genera-
tion
£'
B
Ca
Cr
pH
SO,
TDS
Zn
B1
As
Ba
Cd
Cl
Co
Cu
F
Fe
K
Mg
Mn
Mo
Pb
Se
Sr
Ti
V
Attenua-
tion
E
B
Ca
Cr
Co
Cu
Ni
K
SO,
pH
TDS
B
Ba
Cl
F
Li
Mg
Sr
Ti
Alliance AFBC
Genera-
tion
£
At
B
Ca
Cd
Cr
Cu
K
Ni
PH
SO,
TDS
V
B
Ba
Co
F
Fe
Mg
Mn
Mo
Ti
Zn
Attenua-
tion
E
B
Ca
Cd
Cr
Cu
Ni
K
SO,
V
PH
TDS
B
Ba
Cl
Co
F
Fe
Mg
Mo
Sr
Ti
Zn
Exxon
Georgetown AFBC Upper
Genera- Attenua- Sample
tion tion3 Point
E B E
Ca Al SO.
pH Cl
TDS Co
Cu
F
Fe
K
Mg
Mn
Mo
Sr
Ti
Zn
B E
Ba e
Cd Co
Cr Cr
Mg
Mn
Ni
K
S0t
V
TDS
B
Ba
F
Fe
Mo
Sr
Ti
pH
PFBC
Alliance AFBC
Lower
Sample
Point
E
Al
B
Ca
Cr
Mg
Mn
Ni
K
SO,
V
TDS
B
Ba
Cl
F
Fe
Li
Mo
Sr
Ti
PH
Upper
Sample
Point
E
B
Ca
Cl
Cr
Li
K
SO,
fi
Ba
Co
F
Mo
Sr
Ti
Zn
Lower
Sample
Point
E
Al
B
Ca
Cl
Mn
Ni
K
SO,
TDS
B
Ba
Co
F
Li
Mo
K
Sr
Ti
pH
Field
Control
Cells
E
Ca
Cr
Mg
Mn
K
SO,
V
Zn
TDS
B
Ba
Cl
F
Fe
Li
Mo
Sr
Ti
PH
'£ = Consistently exceeds the most stringent criterion or standard (approximately 50% or more).
*B = Consistently below the most stringent criterion or standard I approximately 10% or less).
3Based on only two data points.
Prediction of Field Leaching
Behavior of FBC Wastes
Based on Laboratory
Results
One of the goals of this investigation
was to determine the feasibility of
developing a method of reliably predicting
the leachate generation (and attenuation)
behavior of FBC wastes under landfill
disposal conditions. The hope was that
the field behavior might be predicted on
the basis of simple and relatively inexpen-
sive laboratory tests of the waste. Two
empirical but rigorous statistical ap-
proaches were taken to predict the chem-
ical behavior of FBC wastes after disposal
in landfills. Both approaches involved the
development of statistical models from
laboratory leaching data to predict field
leachate properties. An extensive sta-
tistical analysis of leaching and attenu-
ation data for Exxon PFBC and Alliance
AFBC waste was performed in the first
approach. A feasibility study for the sec-
ond approach employed leaching data for
the PFBC waste.
The two methods differed in the steps
used to develop the statistical models. In
the first approach, the "direct" method, a
model was developed directly to predict
the concentrations of a particular species
as a function of volume of leaching solu-
tion per mass of waste leached. The con-
centrations of other species did not come
into play. In the second approach, the
"indirect" method, a regression model
was first developed in which the concen-
tration of a chemical species was pre-
dicted in terms of the concentrations of
itself and other chemical species at the
preceding batch equilibration protocol
leaching step and possibly pH at the
preceding or current leaching step.
Subsequently, transformations were made
through a set of mathematical steps tc
produce models which predicted concen-
tration as a function of leachate volume
per mass of waste leached.
Direct Method
In the direct method of analysis,
leaching behavior was first analyzed.
Models were developed from laboratory
data to predict field leachate concentra-
tions. When these models were devel-
oped, those chemical species whose con-
centrations were predominantly near oi
below detection limits were excluded.
Subsequently, an analysis was performec
to quantify the agreement between ob-
served field concentration and corres-
ponding values predicted from the
-------
laboratory models. It was found that, for
the 13 species investigeated in leachates
from the Exxon PFBC waste, the mean
agreement between the observed field
values and the laboratory-predicted field
values was within a factor of 10 in 11
cases, a factor of 5 in 8 cases, and a fac-
tor of 2 in 3 cases. For 19 species in-
vestigated in leachates from the Alliance
AFBC waste, the mean agreement was
within a factor of 10 in 17 cases, a factor
of 5 in 16 cases, and a factor of 2 in 10
cases. Thus, laboratory models are
capable of predicting field trends within
an order of magnitude in most cases. The
difference between the laboratory-
predicted and field-observed values was
statistically significant for most species,
however.
The prediction of field data involved an
extrapolation, since the laboratory
volumes of leachate per unit mass of
waste leached were much larger than
those for the field cells. Further investiga-
tion showed, however, that the differ-
ences between field-observed and
laboratory-predicted values are not at-
tributable wholly or predominantly to the
extrapolation. Actual differences between
the behavior of the laboratory and field
chemical systems are believed to explain a
significant part of the discrepancies be-
tween observed and predicted values.
It was found that prediction of field
fractional attenuation (AF) values by
models developed from laboratory (AL)
values was not possible in most cases.
The reasons were the scatter in the frac-
tional attenuation data and the dissimilari-
ty in the trends observed in the field and
the laboratory.
Indirect Method
For the indirect method, more limited
investigation was undertaken to assess
the overall feasibility of the approach.
Only leaching (no attenuation) data were
used, and only the Exxon PFBC waste
data (not the data from the two AFBC
wastes) were used. The analysis was per-
formed using laboratory protocol Steps 1
and 2 data and upper sample point
leachate data from the PFBC field cell
containing shale in the upper layer.
The principal finding of the modeling by
the indirect method was that the species
fell into two groups. In the first group,
consisting of sulfate, silicon, chromium,
barium, sodium, iron, calcium, zinc, and
strontium, the species were self-
controlled; that is, the concentration (at a
given extraction step) of one of these
species was related to concentrations (in
the preceding step) of species within the
group. Sulfate and silicon were individual-
ly self-controlled. Concentrations for the
second group (magnesium, boron, fluor-
ide, chloride, and aluminum) were largely
controlled by the first group. That pH did
not play a crucial role as a predictor
variable is not surprising, since pH varied
between only 11.0 and 12.0 during the se-
quence of laboratory extractions for the
Exxon PFBC waste.
For predicting field observed values
from the laboratory, the indirect method
was close for barium and strontium and
nearly as close for zinc. Sulfate was
predicted within a factor of two, and
calcium and chromium were predicted
within a factor of three. Except for
sulfate, silicon, and sodium, the predicted
values were higher than the observed
values.
Compatibility of Landfill Liners
with FBC Waste Leachate
If some future FBC wastes are disposed
of in secure landfills with liners, the com-
patibility of commonly used landfill liner
materials with FBC waste leachate was in-
vestigated. Under certain conditions (e.g.,
in shallow water table conditions or where
ground water is used as a nearby drinking
water source) even nonhazardous FBC
waste landfills may utilize liners.
The objective of the liner investigation
was to determine if the liner integrity is
reduced as a result of exposure to FBC
waste leachate by using several chemical
and physical tests. Six synthetic liner
materials and one clay were tested: Neo-
prene, polyvinyl chloride (PVC), chlori-
nated polyethylene (CPE), chlorosul-
fonated-polyethylene (Hypalon), butyl rub-
ber, ethylene propylene diene monomer
(EPDM) rubber, and sodium bentonite
clay.
Leachate from protocol Step 1 leaching
of the Exxon PFBC waste was used in the
experiment. For the synthetic liners,
uniformly sized strips of the liner material
were attached to a rack and immersed in
a tank containing the leachate. The ben-
tonite clay was suspended in with the
leachate, and the mixture was con-
tinuously agitated. Degradation of the
synthetic liner materials with time was
monitored by removing samples of the
liner strips monthly and testing them for
tensile strength. The leachate was also
sampled monthly and analyzed for total
organic carbon (TOO concentration to in-
dicate the release of liner carbon consti-
tuents to the leachate. In addition, the
liner surfaces were examined by scanning
electron microscope for direct visual
evidence of liner degradation.
For the clay liner material, degradation
was monitored by monthly sampling and
analysis of the clay by X-ray diffraction to
detect clay mineral breakdown. Also, the
leachate was analyzed for aluminum as a
means of detecting the release of clay
mineral components to the leachate solu-
tion. The investigation of both the syn-
thetic liner and the clay liner continued for
18 months.
For the synthetic liners, Hypalon was
the strongest overall. Four of the six
(EPDM rubber, butyl rubber, Neoprene,
and CPE) had very similar strengths, all
lower than Hypalon's. PVC had a strength
intermediate between Hypalon and the
other four. All liners showed a decrease in
strength with increasing time of exposure
to the leachate. In terms of percentage of
the maximum tensile strength observed,
the greatest drop in strength was ob-
served for CPE, with a decrease to 50%
of maximum. The least decrease in
strength was seen for the Hypalon and
EPDM rubber liners (to 70% of
maximum).
Under SEM magnification, only two of
the six liners showed evidence of signifi-
cant deterioration resulting from exposure
to the Exxon PFBC waste leachate. Most
of the liners could not be easily observed
because of the formation of a precipitate
on their surfaces. The TOC concentration
trends showed the greatest gain in carbon
content in the leachates containing the
Hypalon and CPE liners. EPDM rubber
and Neoprene showed the lowest in-
creases in TOC content in these
leachates.
In general, the liner showing the least
compatibility with the Exxon PFBC waste
was CPE, which showed the clearest sign
of chemical degradation under SEM ob-
servation and by the TOC analysis. Its
tensile strength was in the group of four
liners having the lowest strength. Hy-
palon, on the other hand, showed signs
of chemical degradation in the SEM and
TOC studies, but its strength (which was
initially high) remained the highest of all
the liners for the duration of the experi-
ment.
X-ray diffraction analysis of the ben-
tonite clay that was suspended in the
PFBC waste leachate revealed that one of
the first changes to occur was a change
in the clay from 'a sodium- to a calcium-
montmorillonite as the calcium in the
leachate replaced the sodium ions in the
surface positions of the montmorillonite.
Although one of the peaks on the XRD
-------
patterns changed slightly as the experi-
ment progressed, which may have been
an indication of incipient breakdown of
the aluminosilicate structure of the clay,
the patterns in ^general showed no major
structural change in the clay. -After the
first month, a new mineral, ettringite, was
identified in the XRD pattern, which in-
dicated a possible change in the basic
structure of some of the initial clay
material.
Throughout the experiment, the con-
centration of aluminum in the leachate
was at or below the levels found in the
leachate prior to interaction with the clay.
Thus, the aluminum concentration data
did not substantiate breakdown of the
aluminosilicate structure of the clay over
the 18 months of the test.
In general, the liner materials tested
were found to be quite compatible with
Exxon PFBC waste leachate insofar as
could be determined in this relatively short
and simple investigation. If there had
been strong incompatibility of the liners
with the leachate, then the degradation
would have been readily detected in this
program. Although no strong incompati-
bility was observed, some of the polymer
liners did show a significant loss of tensile
strength during the 18 months of leachate
exposure. The formation of a new mineral
phase, ettringite, as a possible reaction
product of the montmorillonite and the
high-calcium leachate, could also lead to
eventual breakdown of the effectiveness
of the clay or a liner material.
Conclusions
Overall, this investigation shows that,
with proper consideration of waste- and
site-specific factors and with good
engineering practice, the disposal of
wastes should not be an inhibitive factor
in the development and use of the FBC
energy conversion technology. The
wastes do not contain (or release to
leachate) large concentrations of highly
toxic species or other species that are
hazardous to human health or the en-
vironment. There is some potential con-
cern for certain species, such as calcium
and sulfate, which will need to be ad-
dressed at future disposal sites, but prop-
er design and operation should allay these
concerns. It appears feasible to use readi-
ly available liner materials when necessary
in the design of FBC landfills.
T. W. Grimshaw, R. A. Minear, A. G. Eklund. W. M. Little, H. J. Williamson. T. S.
Gibson, D, L Heinrich, and R. C. South are with Radian Corporation, Austin, TX
78766; J. E. Dunn is with the University of Arkansas, Fayetteville, AR 72701.
John O. Milliken is the EPA Project Officer (see below).
The complete report consists of eight volumes, entitled "Assessment ofFluidized-
Bed Combustion Solid Wastes for Land Disposal:" (Set Order No. PB 85-175
859/AS; Cost: $130.50)
"Volume 1. Final Report," (Order No. PB 85-175 867'/AS; Cost: $22.00)
"Volume 2. Appendices A thru C, "(Order No. PB 85-175 875/AS; Cost: $ 16.00)
"Volumes. Appendices D andE, "(Order No. PB 85-175 883/AS; Cost: $28.00)
"Volume 4. Appendix F," (Order No. PB 85-175891 /AS; Cost: $ 13.00)
"Volume 5. Appendix G," (Order No. PB 85-175 909/AS; Cost: $22.00)
"Volume 6. Appendix H," (Order No. PB 85-175 917/AS; Cost: $13.00)
"Volume 7. Appendix I," (Order No. PB 85-175 925/AS; Cost: $14.50)
"Volume 8. Appendix J," (Order No. PB 85-175 933/AS; Cost: $25.00)
The above reports will be available only from: (costs subject to change)
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
W
U. S. GOVERNMENT PRINTING OFFICE: 1985/559 111/10832
-------
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