EPA
600/7
80-172
TVA
United States
Environmental Protection
Agency
Tennessee Valley
Authority
Office of Power
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/7-80-172
October 1980
Energy Demonstrations
and Technology
Chattanooga TN 37401
Coal-Fired Power Plant
Ash Utilization in the
TVA Region
Interagency
Energy/Environment
R&D Program Report
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4. Environmental Monitoring
5. Socioeconomic Environmental Studies
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This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
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EPA-600/7-80-172
Repository Material October 1980
Permanent'Collection
Coal-Fired Power Plant Ash
Utilization in the TVA Region
by
Richard L. Church, Dennis W. Weeter and Wayne T. Davis
(University of Tennessee at Knoxville)
co
g> TVA Project Director
"eg Hollis B. Flora II
—' co ^ ^- TVA, Energy Demonstrations and Technology
"^ ^ . CD o 1140 Chestnut Street, Tower II
•= o ^* < CM <£> Chattanooga, Tennessee 37401
< o> o § c Q u?
Q_ -c "- co .O Q cp Interagency Agreemment No. D5-E721
10 T3 S^^O 3 c co Program Element No. 1NE624A
^ CCD g'-g -^up
co g '"ff § .£ O
tr ^ T- co EPA Project Officer: Julian W. Jones
CO
=30: co^
CTLU T- Industrial Environmental Research Laboratory
co Office of Environmental Engineering and Technology
•T? Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY ?
Office of Research and Development 9
Washington, DC 20460
-------
DISCLAIMER
This report was prepared by the Department of Civil Engineering of
the University of Tennessee under a contract with the Tennessee Valley
Authority (TVA), and has been reviewed by the Emissions/Effluent Technology
Branch of the Utilities and Industrial Power Division of the U.S. Environ-
mental Protection Agency. The contents do not necessarily reflect the
views or policies of TVA or the U.S. Environmental Protection Agency, nor
does the mention of trade names or commercial products constitute endorse-
ment or recommendation for use. TVA makes no warranty or representation,
expressed or implied, concerning the accuracy or usefulness of the
information contained in the report.
11
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ABSTRACT
The objectives of this study were to: (1) summarize the overall national
production of coal ash; (2) summarize the production of coal ash within the
Tennessee Valley Authority (TVA) power plant system consisting of 12 major
ash-producing steam-electric power plants; (3) summarize the physical/
chemical characteristics of coal ash as they affect the potential disposal
and/or utilization of ash; (4) review and summarize existing literature on
the utilization of coal ash with specific emphasis on areas which might be
marketable within the TVA system for TVA coal ash; and (5) make recommenda-
tions on the potential future research and development needs within the TVA
system for utilization of coal ash.
Topics covered included utilization in concrete mixtures, mineral re-
covery, magnetite recovery, lightweight aggregate, utilization of fly ash in
wastewater treatment, utilization as a sanitary landfill liner, cenosphere
reuse, agricultural uses, mineral wool insulation, and use in bituminous
paving mixtures.
Specific data included in this report, relative to the production and
utilization of coal ash in the TVA system, were collected by a combination
of: (1) on-site visits to major power plants with active flyash utilization
programs; (2) TVA data files; and (3) discussions with personnel responsible
for various programs. Data reported on studies outside of the TVA system
were obtained extensively through a literature search and review.
The predominant historical use of fly ash in the TVA region has been as
concrete additives. However, extensive pilot-scale development efforts are
being made to advance ash utilization in the TVA region in such areas as
mineral recovery, magnetite recovery, and mineral wool insulation.
As a result of conducting this study, the authors recommend that the
following studies also be conducted:
1. Conduct a feasibility study of the conversion of existing wet fly
ash collection systems to dry collection and storage. This would lead to
better fly ash utilization options within the TVA system,
2. Since some cenospheres do not float, study the mechanical proper-
ties of ash to learn how to separate nonfloating cenospheres from ash.
3. Conduct a study comparing other process choices and options to see
if a preferred process, if any exists for the TVA region.
4. Conduct an integrated TVA area-wide market study for the potential
uses, markets, generation points, transportation, and feasibility of exten-
sive coal ash utilization.
* • *
m
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CONTENTS
DISCLAIMER 1i
ABSTRACT Hi
FIGURES vi
TABLES vii
ACKNOWLEDGEMENTS viii
CONVERSION TABLE ix
SECTIONS
1. Introduction 1
2. Properties of Coal-Ash 9
3. Ash Disposal 19
4. Fly Ash Utilization in Concrete Mixtures 21
5. Fly Ash and Mineral Recovery 26
6. Fly Ash and Magnetite Recovery 37
7. Sintered Fly Ash as a Lightweight Aggregate 39
8. Fly Ash Utilization in Waste Water Treatment 41
9. Fly Ash and Sanitary Landfill Liners 45
10. Cenospheres from Fly Ash 52
11. Agricultural Uses of Fly Ash 55
12. Bottom Ash and Mineral Wool Insulation 63
13. Bituminous Paving Mixtures 68
14. Recommendations 70
15. References 71
IV
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Appendix A A-l
Appendix B EH
Appendix C C-l
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FIGURES
Number Page
1 Fly Ash Fineness and Type of Collection Process 12
2 Blaine Fineness and Type of Collection Process 13
3 Dry Density vs. Moisture Content for the Fly Ash
Samples 15
4 Curing Conditions and Strength of Portland Cement
Concrete 24
5 Generalized Flowsheet for the Lime-Soda Sinter Process . . 28
6 Generalized Flowsheet for the Salt-Soda Sinter Process . . 29
7 Generalized Flowsheet for the Calsinter Process (36,39). . 30
8 Fly Ash Requirements to Raise Soil pH to 7 61
vi
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TABLES
Number Page
1 Comparative Ash Collection and Utilization in the U.S.
1966 to 1977 2
2 Average Coal Use and Ash Production by TVA Steam Plants
1971-1975 4
3 TVA Ash Production and Sales 1978 6
4 Fly Ash Properties by TVA Power Plant 11
5 Range of Values of Elements in 21 Fly Ashes 16
6 Partition of Elements by Their Tendencies for Distribu-
tion in Coal Combustion Residues 17
7 TVA Ash Generation and Disposal Characteristics 20
8 Estimated Income from Mineral Recovery 34
9 Estimated Annual Operating Costs, Capital Costs, and
Income 36
10 Present and Planned IUCS Installations as of
November 1, 1979 43
11 Sanitary Landfill Laboratory Study Using Kingston Power
Plant Ash 46
12 Sanitary Landfill Laboratory Study Using Gal latin Power
Plant Ash 47
13 Sanitary Landfill Laboratory Study for Coffee County ... 48
14 Sanitary Landfill Laboratory Study for Sumner County ... 49
15 Sanitary Landfill Laboratory Study for Scott County ... 50
16 Increase in Multi-element Uptake of Plants Grown in
Fly Ash Amended Soil 58
17 A Comparison of Mineral Wool Production Factors 66
18 Characteristics of Mineral Wool Made from Coal Ash .... 67
vn
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ACKNOWLEDGEMENTS
The authors are indebted to Mr. Tommy McDaniel and Mr. Frank Parker,
for their assistance during all phases of this project. The efforts of
Mr. McDaniel in providing information on all phases of the TVA system is
ash handling and disposal operations along with suggestions and editorial
assistance in the preparation of this report are gratefully acknowledged.
We would also like to express appreciation to Mr. G. L. Terman and Robert
Cannon of the TVA staff who provided information on several TVA projects
dealing with ash utilization and disposal. We would also like to
acknowledge the assistance of H. Lynn Phillips who provided assistance in
the preparation of this report and to Professor Thomas Bell for his
editorial comments. Earlier drafts of this report were partially reviewed
by various staff members of the U.S. Environmental Protection Agency and
TVA who contributed many useful comments and suggestions in the preparation
of this report.
vm
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CONVERSION TABLE
as
A list of conversion factors for British units used in this report is
follows:
British
1
1
1
1
1
inch
foot
mile
cubic yard
pound
1 ton (short)
1 gallon
1 part per million
1 part per billion
1 British Thermal Unit
per pound
Metric
2.54 centimeters
.3048 meters
1.609 kilometers
.76456 cubic meters
.454 kilograms
.9072 metric tons
3.785 liters
1 milligram per liter
(equivalent)
.001 milligram per liter
(equivalent)
2.325 Joules per gram
IX
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Section 1
INTRODUCTION
PURPOSE AND SCOPE
The passage of local, state, and Federal emissions regulations has re-
sulted in the collection of significant quantities of coal ash which were
historically emitted to the atmospheric environment. Subsequent passage of
the Federal Water Pollution Control Act of 1972, and the Resources Conserva-
tion and Recovery Act of 1976, has placed additional requirements on the
disposal of coal ash collected because of the chemical/physical characteris-
tics of the various ashes. There has been an increasing interest in the
potential utilization of ash due to the increases in total power production
and increasing concern over the environmental impacts of such disposal.
U.S. ASH PRODUCTION RATE
The collection and disposal of coal ash (consisting of fly ash, bottom
ash, and boiler slag) has become a problem of increasing concern in the past
two decades. This concern has been amplified due to (1) the increased con-
cern over the environmental impact of the disposal ash, and (2) the increase
in total amount of ash generated.
Based on a survey conducted by the National Ash Association (NAA) in
1977 and presented at the Fifth International Ash Utilization Symposium of
NAA in 1979, it was estimated that there were 67.9 million tons of coal
ash collected in 1977. Approximately 21% of this ash was utilized for
purposes other than disposal. Table 1 summarizes the U.S. collection and
utilization of coal ash from 1966 to 1977 and illustrates the significant
increase in both production and utilization with time.
NAA has further projected that by the year 1985, the production rate
will be 90 million tons/year with a utilization rate of 40%. By the year
1990, it was estimated that the production rate would be 125 million tons/
year with a 50% utilization.
TVA COAL ASH PRODUCTION
TVA depends upon coal-fired generating plants to produce approximately
80% of its total electrical generating capacity. These 12 steam plants
consume approximately 35 million tons of coal per year and produce 5.6
million tons of coal ash.
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Table 1: COMPARATIVE ASH COLLECTION AND UTILIZATION IN THE U. S. - 1966 to 1977
Ash Collected in
Millions of Tons
Year
1966a
1967
1968
1969
1970
1971
1972
1973
1974b
1975
1976
1977
Fly
Ash
17.1
18.4
19.8
21.1
26.5
27.8
31.8
34.6
40.4
42.3
42.8
48.5
Bottom
Ash
8.1
9.1
7.3
7.6
9.9
10.1
10.7
10.7
14.3
13.1
14.3
14.1
Boiler
Slag
-
-
2.6
2.9
2.8
5.0
3.8
4.0
4.8
4.6
4.8
5.2
Total
Ash
25.2
27.5
29.6
31.7
39.2
42.8
46.3
49.3
59.5
60.0
61.9
67.8
Fly
Ash
1.4
1.4
1.9
1.9
2.2
3.3
3.6
3.9
3.4
4.5
5.7
6.3
Ash
Mill
Bottom
Ash
1.7
2.3
1.8
2.0
1.8
1.6
2.6
2.3
2.9
3.5
4.5
4.6
Utilized in
ions of Tons
Boiler
Slag
-
-
1.5
1.0
1.1
3.7
1.3
1.8
2.4
1.8
2.2
3.1
Total
Ash
3.1
3.7
5.2
4.9
5.1
8.6
7.5
8.0
8.7
9.8
12.4
14.0
Ash Utilization in Percent
Fly
Ash
7.9
8.2
9.6
9.1
8.1
11.7
11.4
11.4
8.4
10.6
13.3
13.0
Bottom
Ash
21.0
25.0
25.0
25.6
18.6
16.0
24.3
21.9
20.3
26.7
31.5
32.6
Bo i 1 er
Slag
-
-
57.8
33.0
39.1
75.2
35.3
44.3
50.0
40.0
45.8
60.0
Total
12.1
13.5
17.6
15.3
13.0
20.1
16.3
16.3
14.6
16.4
20.0
20.7
First year that data was taken.
3In 1974 a more comprehensive data collection program was developed, resulting in a substantial increase
over the previous year.
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Coal ash may be categorized into three types: bottom ash, boiler slag,
and fly ash. Bottom ash and boiler slag are removed from the bottom of a
coal-fired boiler, while flyash exists with exhaust gases and must be removed
by some type of particulate collection device. Current TVA practice is to
grind bottom ash and slag, mix it with water, and convey it to an ash dispo-
sal pond. Similarly, fly ash is removed from the hoppers of mechanical
cyclones, electrostatic precipitators, baghouses, and/or scrubbers and
transported by a water stream to the ash disposal pond. Most of this ash
remains in the disposal area.
Table 2 lists the ash production at the 12 TVA steam plants on a five
year average basis. During calendar year 1978, approximately 0.7 million
tons of coal ash were utilized rather than disposed of.
TVA ASH UTILIZATION PROGRAMS
TVA's ash utilization program began in the 1950's with the use of
flyash as a concrete admixture in the construction of the Wilson Dam Lock
near Muscle Shoals, Alabama. Since that time, TVA has been actively in-
volved in developing specifications for the use of flyash in construction
projects.
The standard procedure in concrete procurement is for TVA to supply
batching facilities and mix designs while the raw materials and equipment
operations are provided by a private contractor. In this way, TVA is able
to require the use of ash in its own construction and to promote the use of
ash by private contractors. TVA experience has been that after using flyash
as an admixture in a TVA construction project, most ready-mix concrete sup-
pliers use ash in other projects.
TVA promotion of ash utilization has included flyash as an admixture in
concrete and boiler slag for roofing materials. Research has been conducted
in other areas of ash use. Bottom ash is extensively used by the TVA power
production staff in the maintenance of ash pond dikes and roads. During
1978, 281,250 tons of bottom ash were used for these purposes.
FLY ASH UTILIZATION
Flyash used as an admixture in concrete must be collected and stored in
the dry state. Four power plants in the TVA system (the Kingston, Colbert,
Allen and Gallatin Steam Plants) are equipped to do this. Visits were made
to each of these plants as a part of this study, and descriptions of the
ash-handling operation at each plant are included as a part of the report.
Flyash is sold by TVA for both TVA and commercial construction uses.
All deliveries are coordinated through the Division of Fossil and Hydro
Power; Chattanooga, Tennessee.
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Table 2. -AVERAGE COAL USE AND ASH PRODUCTION BY TVA STEAM PLANTS 1971-1975.
Plant
Allen
Bull Run
Colbert
Cumberland
Gal latin
John Sevier
Johnsonville
Kingston
Paradise
Shawnee
Widows Creek
Watts Bar
Total
Units
3
1
5
2
4
4
10
9
3
10
8
4
63
Coal Burned
(Million Tons)
per year
1.4
2.3
2.7
3.25
2.2
1.5
2.9
4.0
6.1
4.6
3.9
0.3
35.2
Bottom Ash
(Thousand Tons)
115.3
68.4
80.7
107.3
82.6
46.8
82.5
156.7
867.3
141.4
132.6
23.5
1898
Fly Ash Collected
(Thousand Tons)
47.4
245.4
272.5
425.3
315.7
186.9
333.3
576.5
282.8
557.6
356.8
20.7
3621
Fly Ash Released
(Thousand Tons)
. to Atmosphere
3.8
35.9
1.4
4.3
15.3
0.7
94.2
46.7
6.3
8.9
172.9
1.2
392
Source: Structural Section, Division of Fossil and Hydro Power, TVA
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Kingston
Kingston steam plant is a 9 unit station rated at 1,700 MW(e). Fly ash
collection at the Kingston Steam Plant is accomplished by mechanical collectors
followed by two sets of electrostatic precipitators (the last set was installed
in recent years in order to obtain greater participate collection efficiency).
The fly ash disposal system consists of a vacuum device which empties ash
from the collector hoppers. The ash is then mixed with water and flows
through a pipe to an ash disposal pond. The system serving the newest
precipitators is independent of the previously installed one. A slip-stream
of ash may be diverted from the older ash collection system to a 200 ton
silo for storage. This silo is equipped to discharge ash into trucks. The
dry handling system fills the silo at the rate of 10 to 15 tons per hour,
according to operating personnel.
Table 3 lists the amount of ash sold by Kingston during 1978.
Colbert
Colbert Steam Plant consists of 5 units rated at a total of 1300 MW(e).
The manner of removal of fly ash from the collector hoppers is similar to
that of Kingston except that both the wet and dry handling systems may not
be operated simultaneously and ash is conveyed only from units 3 and 4 by
the dry system. Ash storage is in a 100 ton silo. Because of vacuum losses
and other conveyance problems when fly ash is diverted into the storage
silo, the hopper cleaning system is unable to keep the hoppers emptied.
Therefore, ash may be collected for dry storage for only 4-6 hours before
the wet disposal system must be employed.
Ash is sold only to commercial users from Colbert. The sales during
the year 1978 are listed in Table 3.
Gal latin
Gal latin Steam Plant is a 4 unit station rated at 1,255 MW(e). The
collection system and storage silo are similar to the installation at Kingston.
A new 2,000 ton storage silo is under construction and should be completed
during 1979. This silo is capable of serving both truck and rail carriers.
Table 3 indicates that the majority of ash utilized from Gallatin was
delivered to TVA construction sites, primarily Hartsville Nuclear Plant,
during 1978. Commercial sales from Gallatin are handled through a broker—
Penn-Virginia Materials Company, Eastlake, Ohio. As TVA construction use
declines, commercial markets for the Gallatin ash must be developed in order
for its storage capacity to be fully utilized.
Allen
Allen Steam Plant consists of 3 units rated at 300 MW(e). The boilers
are of the wet bottom type; i.e., the units are operated at temperatures
above the ash fusion point. Molten slag is removed from the bottom of the
furnace and is quenched in water, ground, then pumped with water to the ash
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Table 3. TVA ASH PRODUCTION AND SALES - 1978
ASH PRODUCTION FLY ASH SALES
Bottom Ash Fly Ash TVA Construction Commercial Boiler Slag Sales
Plant (thousand Tons) (Thousand Tons) (Thousand Tons) (Thousand Tons)
Kingston 156.7
Colbert 80.7
Gallatin 82.6
Allen 115.3
576.5 23.8 5.75
272.5 — 3.15
315.7 31.9 19.77
47.4 — — 194. 5a
*Sales rates are greater than production rates because the slag ponds are being mined.
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disposal pond.
The fly ash removal and storage system at Allen has been recently modi-
fied. A vacuum collector manifold empties the collector hopper. Operators
have the option of sending all of the ash collected to two 200 ton silos or
to a conventional wet disposal system. Allen is the only TVA plant able to
remove and store all of the fly ash collected in a dry state.
Slag is removed from the Allen ash pond and sold for further processing.
This is discussed below.
Dry Bottom Ash
As previously mentioned, the majority of the boilers in the TVA system
are of the dry-bottom type producing bottom ash and slag. These materials
are ground when collected and pumped to the ash disposal pond. Bottom ash
and slag are usually discharged into a remote area of the pond where they
may be later mined for use in ground maintenance.
TVA has sought to more extensively use bottom ash and slag as aggregate
in asphalt pavement and as a base coarse material. During the period 1976-
1978, TVA investigated the use of ash obtained from Kingston in asphalt pav-
ing mixtures. A demonstration project was constructed using power plant
ash. The project course appears to be performing well. However, it was
found during the course of the project that the ash was extremely variable,
depending upon the portions of the pond from which it was obtained. High
asphalt contents were required to produce an optimum mixture.
Wet Bottom Slag
As previously described, the term "wet bottom" applies to those boilers
producing molten slag. The Allen and Paradise steam plants are of this
design. Slag from these boilers has commercial value because of its consis-
tent composition and uniform gradation.
The H.B. Reed Company is a manufacturer of blasting grit and roofing
granules derived from boiler slag. As a part of the visit to the Allen
Steam Plant, a tour was made of the Reed Company installation at Memphis,
Tennessee.
H.B. Reed Company
The Reed plant at Memphis processes approximately 800 tons of raw slag
per day. The manufacturing process is basically a size-fractionating opera-
tion. Material greater than 0.5 in. and less than a number 100 seive is not
used but is sold to cement manufacturers as a raw material for Portland
cement. After drying, the remaining material is fractionated into blasting
grit (20%) and roofing granules (80%).
Fly ash is not suitable for this application because of its small par-
ticle size. Slag and bottom ash from the dry bottom boilers are also unsuit-
able since the small amount of carbon still present could combust during
drying. Table 3 lists the sales of slag from Allen during 1978. Note that
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more slag was sold than was produced because previous years' productions of
slag are being mined from the pond.
Reed Company has recently entered into an agreement with TVA to buy at
least 150,000 tons per year of slag fromvthe Paradise Steam Plant. The slag
would be processed at the Memphis plant. The agreement includes an option
to build a processing plant at Paradise and to process up to 500,000 tons per
year.
Cenpspheres
Cenospheres, commonly referred to as "floaters," are hollow fly ash
particles that float in ash ponds because of their low density (see Section
2 for cenosphere properties). Floaters have been collected for some time at
TVA plants by skimmers to prevent them from exiting the pond with the effluent.
Cenospheres are being removed from TVA ponds on a limited basis by Porter
Warner Industries, Inc., this company is developing and evaluating various
markets for Cenospheres.
8
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Section 2
PROPERTIES OF COAL ASH
PHYSICAL CHARACTERISTICS OF FLY ASH AND BOTTOM ASH
With respect to the utilization of coal ash, physical and chemical
characteristics must be considered prior to using ash for any purpose—whether
it be on-site disposal or for commercial purposes such as aggregate in
concrete, asphalt, or soil. The ash is a result of unburned organic material
and non-volatilized inorganic materials present after the combustion of coal
in the furnace of a combustion unit. During the combustion phase, the ash
is distributed into two parts: the bottom ash and the fly ash. The bottom
ash is collected from the bottom of the furnace (a boiler unit) and may be
dry bottom ash or wet bottom ash (commonly referred to as boiler slag—the
molten state of the bottom ash).
The distribution of ash between the bottom and fly ash fractions is a
function of the boiler type and coal type. In cyclone furnace/boilers (wet
bottom units), up to 85% of the ash may be collected as bottom ash (slag);
while in the pulverized coal-fired boiler, up to 85% may be emitted as
flyash.
4 5
(Ray and Parker and Furr and Parkinson have conducted thorough reviews
of the physical ahd chemical characteristics of ashes in the United States.
The reader is referred to these for in-depth information).
In general, the flyash makes up 15 to 85% of the ash and ranges in dia-
meter from 0.5 to 100 microns. Typically, the mass-median diameter is in
the range of 8-30 microns and is dependent upon the type of boiler and type
of flyash collector utilized. The particles are generally spherical and
solid in nature, with a light tan to gray appearance. The presence of sig-
nificant alkaline materials results in a lighter color; those processes
burning inefficiently result in excess carbonaceous material and a blacker
appearance due to excess carbon. Also, the presence of excess alkaline ma-
terials or excess carbon generally produces ashes with a smaller fraction of
spherical particles.
Fly ash may also contain very lightweight particles called cenospheres
which consist of silicate glass spheres filled with N2 and C02. These^particles
may comprise as much as 5% by weight, or 20% by volume of the flyash.
These spheres, although a problem for wet disposal due to their tendency to
float, have a commercial value and will be discussed in Section 10 in more
detai1.
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The actual physical characteristics of an ash cannot be predicted
accurately but must be measured experimentally after a power plant is on-line.
Discussions with commercial users of ash revealed that frequent analyses of
both physical and chemical characteristics of ash were required to insure
that the ash was acceptable for the intended use. Changing operating condi-
tions can result in undesirable characteristics (such as increased carbon
content) significantly different from the average characteristics of the
ash.
Summary of Physical Characteristics of Coal Ash in the TVA System
Several studies which summarize the physical characteristics of coalfi -,
ash produced in the Tennessee Valley Region have recently been conducted. '
These studies included tests to determine one or more of the following char-
acteristics:
1. Particle size and fineness
2. Specific gravity
3. Compaction
a. Maximum dry density
b. Optimum moisture content
4. Loss on ignition
5. Surface area (Blaine fineness)
Table 4 is a summary of typical data for fly ash taken at 10 TVA power
plants. The variations in these properties are a function of the type of
collector employed on each plant (cyclone-mechanical collector or electro-
static precipitator). Appendix A includes detailed data sheets typical of
the analyses conducted on each coal fly ash.
A similar series of tests were conducted by Rose, et al., in 1979 for
the 24 power plants located in Kentucky (several of which are in the TVA
system). In this study, the authors related the various parameters and
identified the point of collection of the flyash and/or bottom ash. Figure
1, taken from that study, illustrates the relationship between the percent
of fly ash passing the 325 mesh by the "wet wash" method used in hydraulic
cement (ASTM C 430). The percent passing the 325 mesh generally ranges from
75-95+% for flyash collected by precipitators; for mechanical collectors the
percent passing the 325 mesh is significantly less (40-75%) illustrating the
coarser characteristic of this latter ash.
Blaine fineness, as measured by ASTM C 204, was also found to be affected
by the type of collector and specifically related to the percent passing a
No. 325 mesh sieve. As shown in Figure 2, the Blaine fineness, a measure
of the surface area per unit mass, varies significantlypWithin a single
particle collector category with ranges of 2500-6500 cm /gr for precipitator
fly ash and 1500-2000 cm /gr for mechanical collector ash.
The specific gravity of the flyashes collected in the TVA system and in
Kentucky ranged from 2.0-2.9.
10
-------
Table 4. FLY ASH PROPERTIES BY TVA POWER PLANT
Plant
Colbert
Shawnee
Gallatin
Kingston
Widows Creek
Paradise
Johnsonville
John Sevier
Cumberland
Bull Run
%
-200
75.0
94.7
97.5
93.6
70.1
91.8
94.0
90.3
91.0
83.9
%
-325
63.15
(56 - 91)
90.8
96.0
(77 - 99.3)
92.0
(84.1 - 99.4)
66.3
90.1
89.44
(94.8 - 99.6)
87.2
(95 - 99.8)
87.7
81.4
Blaine
cm /gm
1940
4173
3920
3770
1750
2620
2810
3675
2620
2200
Surface Area
cm2/crn3
4830
10440
8630
8715
3510
7290
7113
8705
6560
5105
Mean Dia.
Microns
16.1
7.7
7.0
7.05
17.1
8.2
9.2
7.8
9.2
11.9
Specific
Gravity
2.45
2.48
2.34
2.31
2.01
2.78
2.53
2.35
2.50
2.30
LOI (%)
1.05
(1.56 - 13.6)
3.27
2.0
(1.7 - 4.2)
3.0
(1.6 - 9.0)
1.4
2.65
.88
(.5 - 8.5)
3.55
(1.9 - 4.2)
.30
3.60
( ) = 1971-1975 Range. Data on the point of collection (electrostatic or cyclone) is not available.
Watts Bar and Allen plants were not analyzed.
-------
100
90
M- Mechanical
P -Precipitator
C -Combined
1
1
i L
1
10 20
30 40 50 60 70 80 90
% Finer (325 Washed Sieve)
100
Figure 1. Fly Ash Fineness and Type of Collection Process
12
-------
^JM>
CM
a
09
CO
C
•S
S
•s
a
7000
6000
5000
4000
3000
2000
1000
IHM
M - Mechanical P»
P - Precipitator 7
"" C - Combined /
/
P /
/
PP /
— /
M*
./P P
M Cp^'^ M
- ^— — -"^'* —
C^ • M
—
1 1 1 1 1 1 1 Jr L J-
10
20
30 40 50 60 70
% Finer (No. 325 Sieve)
100
Figure 2. Elaine Fineness and Type of
Collection Process
13
-------
Compaction tests were also conducted on the Kentucky flyashes. Both
maximum dry density and optimum moisture content (OMC) tests were performed
(ASTM D 698, Method A ). These data are shown in Figure 3 illustrating
a range of values of dry density of 70-125 pounds/CF and OMC's of 10-35%.
Typically the moisture content of the bulk flyash samples ranged from 0.03%.
The loss on ignition7(LOI) of the flyashes for the Kentucky plants
ranged from 0.95 to 9.34% , while the TVA system LOI's ranged from 0.3-3.27%.
The boiler bottom ash/slag LOI's ranged from 0-33.14% for the Kentucky
plants, showing a significantly larger variation than for the flyash. Also,
the moisture content of the boiler slag ranged from 0.04 to 1.14%.
The size characteristics of boiler ash/slag were reported to range from
0.69-13.3% less than 200 mesh (74 microns).
CHEMICAL CHARACTERISTICS OF FLY ASH AND BOTTOM ASH
The chemical composition of ash is a function of the geological and
geographical location of the coal deposit, the combustion conditions, and
the air pollution control devices controlling the emissions. The inorganic
constituents of ash are those typical of rocks and soils, primarily Si, Al,
Fe, Ca, Na; the oxides of these elements comprise 95-99% of the ash. Ash,
however, may5also contain small quantities of almost every other element.
Furr, et aj. , in a study of flyashes collected in 21 different states in
the U.S., summarized the elemental content of each ash for 45 different
elements. Their results are summarized in Table 5. The ranges in con-
centration are included in Table 5 as well as the pH range from 4.7 to 11.8.
In the previous section it was shown that the particle size of the ash
was significantly different for the boiler bottom ash/slag and the fly ash.
Similarly, it has been found that the chemical content of the ash is fre-
quently related to the size of the particles.
A
As shown in Table 6, Ray and Parker summarized the tendency of elements
to be distributed by size. Further studies conducted on the chemical analy-
sis of flyash collected by mechanical versus high efficiency collectors have
also shown partitioning of elements by size. Kaakinen, et al_. , found that
Mo, As, In, Sb, Pb, and Cn significantly increased in concentration (referred
to as enrichment) as the flyash proceeded through the boiler and control
devices. In general, the degree of enrichment increased as the flyash pro-
gressed downstream from bottom ash to mechanical collector ash to electro-
static precipitator ash to ash emitted from the stack. The concentrations
at the precipitator outlet were approximately 15 times those found in the
bottom ash. The observed enrichment was attributed to the fact that the
particle size decreased as the flyash progressed downstream due to preferential
removal of the larger particles in the control devices. Specific chemicals
tend to accumulate on smaller particles due to absorption, adsorption, and
condensation phemonena due to the increased surface area per unit volume of
the smaller particles.
14
-------
*-All numbers are reference to Index 1
10
15 20 25 30 35
W%,,Moisture Content
40
Figure 3. Dry Density vs. Moisture Content for the
Fly Ash Samples
15
-------
Table 5. RANGE OF VALUES OF ELEMENTS IN 21 FLY ASHES5
El ement
Al
As
Au
B
Ba
Br
Ca
Cd
Ce
Cl
Co
Cr
Cs
Cu
F
Fe
Ga
Hg
I
In
K
La
ppm (dry
59,100
11
.004
10
618
.3
7,250
.1
74
13
4.9
43
7.7
45
.9
27,130
13
.02
.6
.1
1,534
33
weight basis)
- 135,100
- 312
- .08
- 600
- 6,917
- 21
- 163,300
- 3.9
- 300
- 460
- 73
- 259
- 18
- 616
- 46
- 289,900
- 230
- .7
- 20
- 1.1
- 34,700
- 104
El ement
Lu
Mg
Mn
Mo
Na
Ni
Pb
Rb
Sb
Sc
Se
Sm
Sn
Sr
Ta
Th
Ti
U
V
U
Yb
Zn
ppm (dry weight basis)
.5 -
11,500 -
58 -
6.5 -
1,180 -
1.8 -
3.1 -
36 -
2.6 -
6 -
1.8 -
5.4 -
27 -
59 -
.5 -
22 -
2,758 -
.8 -
68 -
2.9 -
1.7 -
14 -
1.5
60,800
460
41
18,400
115
241
300
13.0
28
17
24
334
3,855
2.6
68
8,310
19.0
442
21
7.0
406
16
-------
Table 6. PARTITION OF ELEMENTS BY THEIR TENDENCIES FOR DISTRIBUTION
IN COAL COMBUSTION RESIDUES4
Group I
Elements Comparably Concentrated
in Bottom Ash and Flyash
Al
Ba
Ca
Ce
Co
Eu
Fe
Hf
K
La
Mg
Mn
Rb
Sc
Si
Sm
Sr
Ta
Th
Ti
Group II
Elements Preferentially concentrated in the Flyash
As
Cd
Cu
Ga
Mo
Pb
Sb
s
Z?i
Group III
Elements Tending to be Discharged to Atmosphere as Vapors
Hg Cl
S.,. Br"
t Majority of S is discharged as vapor; however, a significant portion
of fly ash content also contains S.
17
-------
Studies have also been conducted to measure the radiochemical characteris-
tics of coal and coal ash. Specifically, measurements have been made of the
concentrations of radium, thorium, and uranium. ' Radiochemical analyses
reported by Krieger and Jacobs showed that radioactive emissions from both
flyash and bottom ash were significantly greater than for the coal. The
gamma ray activity for Louisville, Kentucky, power plant flyash was found to
be as folIowa,.(where the activity is.listed in parenthesisrbeside each
element): "bRa (3.8-2,0 pCi/g); ^U (4.2-6,3npCi/g); "DU (.2-.3 pCi/g);
"pU (4.4-8.6 pCi/g); ^8Th (1.8-1.9 pCi/g); "uTh (4.5-6.5 pCi/g); and
Th (1.6-1.8 pCi/g). The range of values represented radiochemical
analyses obtained on two different dates approximately one year apart. Analy-
ses of the bottom ash showed radioactivity levels ranging from 0-36% less
than the flyash, dependent on the element.
18
-------
Section 3
ASH DISPOSAL
There are three types of coal burning furnaces: stoker, cyclone, and
pulverized coal. Stoker furnaces are generally not used for large utility
systems, and no stoker furnaces are in operation in the TVA power network.
In both the cyclone and pulverized coal furnaces, exhaust gases carry
fly ash which is removed from the exit gas stream via the air pollution
control system. Due to higher operating temperatures and ash fusion in the
furnace, cyclone furnaces generate less fly ash than do pulverized coal
furnaces.-.Inversely, cyclone furnaces generate larger amounts of bottom ash
and slag.
Fly ash removal in the air pollution control system is either wet or
dry. Wet systems include wet scrubbers which are designed to remove fly ash
simply or in conjunction with sulfur dioxide. Dry systems include dry air
pollution control systems (cyclones, bag filters, electrostatic precipita-
tors) which either remove fly ash by themselves or in combination with dry
additive (lime, sodium, ammonia) sulfur dioxide removal systems. Wet systems
obviously generate wet ash for disposal. Dry collection systems can gener-
ate either a wet (sluiced) or dry ash for disposal. Dry ash disposal sys-
tems generally involve either some reuse or recycle, or the dry
wetted down to control dust and taken to a designed landfill area.
Bottom ash is characterized as to the type of boiler used. Pulverized
coal furnaces are either wet bottom type (molten ash) or dry bottom (solid
ash) type. Cyclones create a molten ash on the walls of the cyclone. This
molten ash runs out of the burner onto the furnace floor. In the wet bottom
boiler, the molten ash is quenched in water, crushed, and then sluiced to
the disposal area. In the dry bottom boiler, ash is crushed, and juiced to
the disposal area. Therefore, in both cases, a "wet" ash results. Generally,
this "wet" ash is ponded either separately or in the same pond with the fly
ash or scrubber sludge. When the pond volume is exhaus|gd, either the ponds
are excavated for subsequent disposal or covered over.
Table 7 presents a summary of the ash generation and disposal charac-
teristics of plants in the TVA region. The discussion in Section 1 on the
TVA ash utilization program presents details on specific ash disposal systems.
19
-------
Table 7. TVA ASH GENERATION ADN DISPOSAL CHARACTERISTICS
PO
o
Plant
Allen
Bull Run
Colbert
Cumberland
Gal latin
John Sevier
Johnsonville
Kingston
Paradise
Shawnee
Widows Creek
Watts Bar
Boiler Type
Cyclone
Pulverized Coal
Pulverized Coal
Pulverized Coal
Pulverized Coal
Pulverized Coal
Pulverized Coal
Pulverized Coal
Cyclone
Pulverized Coal
Pulverized Coal
Pulverized Coal
Bottom Type
Generation
Wet Bottom
Dry Bottom
Dry Bottom
Dry Bottom
Dry Bottom
Dry Bottom
Dry Bottom
Dry Bottom
Wet Bottom
Dry Bottom
Dry Bottom
Dry Bottom
Fly Ash
Collection
Dry
Wet
Dry & Wet
Wet
Dry & Wet
Wet
Wet
Dry & Wet
Wet
Wet
Wet
Wet
Bottom Ash
Conveyance
Wet
Wet
Wet
Wet
Dry& Wet
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Ash Disposal
Bottom Ash Fly Ash
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Wet
Dry
Wet
Dry & Wet
Wet
Dry & Wet
Wet
Wet
Dry & Wet
Wet
Wet
Wet
Wet
-------
Section 4
FLY ASH UTILIZATION IN CONCRETE MIXTURES
INTRODUCTION
The use of fly ash in ready-mix concrete is considered to be one of the
most promising areas for ash utilization. This is due to the fact that fly
ash can be used to partially replace cement, which is the highest cost
ingredient of concrete. Because the market for ready-mix concrete is stable
and growing, long term utilization of fly ash can be assured as long as
there is an economic savings in using fly ash as a fine aggregate as well as
cement substitute. At this time, with the increasing cast of energy, the
cost of cement production will undoubtedly increase since energy is a principal
ingredient of cement production. It should be recognized that because of
the varying properties of fly ash, and because the source of fly ash must be
economically transportable to the concrete batching operation, the economics
of fly ash utilization in concrete is site specific. In some places, fly
ash is currently being transported up to 500 miles for utilization. Thus,
in many cases fly ash utilization in concrete will represent a cost savings
as well as a potential for increased concrete production.
The ingredients used in producing conventional Portland Cement concrete
are PortlandrCement, water, gravel, sand, and a variety of chemicals called
admixtures. The amounts of each of these ingredients affect the properties
of the resulting concrete. Admixtures are materials that are added to con-
crete at some stage in its production. They give the concrete new properties
either when in a fluid and/or in the set or cured condition. Admixtures
differ from additives in that additives are materials which are added during
its manufacture as an aid to production or to give the concrete some special
property.
Admixtures are generally classified into eight categories: (1)
Accelerating, (2) Retarding, (3) Water-Reducing/Plasticising, (4) Air Entrain-
ing, (5) Waterproofing, (6) Pumping, (7) Superplasticisers, and (8) Miscel-
laneous. In the miscellaneous category, one subcategory is called "finely
divided materials." Among the finely divided materials, one can consider
two types: inert and pozzolanic. Of special interest here are finely
divided pozzolans (i.e., pozzolanic material).
Pozzolans are materials which by themselves have no strength-producing
properties or cementing properties. Basically, they are siliceous and alum-
inous materials that, when finely divided, will react chemically with calcium
hydroxide,-4lime) in the presence of water to form an adequate cementing
material.
21
-------
Pozzolans can be either natural or artificial, such as pulverized fuel
or fly ash. Pozzolans are added for increased strength, improved workability
of the concrete mix, and reduced bleeding and segregation. (Bleeding occurs
when the mix water tends to rise to the surface of fresh concrete as solids
constituents settle downward. Bleeding tends to lead toward weak concrete
subject to disintegration.) Other advantages associated with pozzolans are
greater resistance to freezing and thawing and resistance to attack by
sulphates. In addition, pozzolans can be used to replace a proportion of
the cement, thereby leading to lower concrete costs whenever the additional
pozzolan costs are offset by the saving associated with lower cement content.
The main justification for using pozzolans is the possibility of reduc-
ing costs. Unless a worthwhile reduction in cost can be made by a savings
in the amouniQof cement used, it is doubtful whether a case can be made for
general use. However, economic incentives by utilities to concrete batchers
may make the use of a pozzolan-like fly ash economically justifiable in
concrete, at a cost that is less than that of ultimate disposal by the
utility even when the savings in concrete reduction do not justify its use.
Fly ash normally contains a silicon dioxide (Si02), aluminum oxide
(AlpOO, carbon in the form of unburnt fuel, calcium oxide (CaO), and small
quantities of magnesium oxide (MgO) and sulfur trioxide (SOO. When using
fly ash as an admixture in concrete to serve as a pozzolanic material, sev-
eral properties are important. First, the material should be finely divided.
Fly ash obtained from electrostatic precipitators is generally finer than
Portland Cement; therefore, it is very suitable without considerable process-
ing. Second, the carbons-content of the ash plays an important role in the
amount of entrained air. Generally, the amount of entrained air is de-
pressed with the use of fly ash. Since the amount of entrained air is
important for strength and other properties, the control of entrained air in
fly ash concrete is important.
Concrete containing small air bubbles (.05 mm/1.25 mm) spaced at gaps
less than or equal to .4 mm evenly distributed throughout its bulk is more
durable to freeze/thaw action than normal concrete. Air entrained concrete
in the plastic state is more workable. It can usually be placed with less
segregation and bleeding. However, air entrainment does result in some
strength loss. All air-entraining agents are surface active and reduce the
surface tension at the water/air interface. This means that minute bubbles
that form remain as stable bubbles and do not collapse.
Controlling the right amount of an air-entraining agent is very important.
Since the carbon residue in fly ash has the ability to absorb most air
entraining admixtures, usually more air entraining agent needs to be added
when fly ash is included in the concrete. It has been stated that concrete
made with a fly ash that has a four percent carbon contentrneeds twice the
amount of air entraining agent than needed conventionally. This plays a
role in the economics of fly ash utilization in concrete.
22
-------
VARIATIONS IN STRENGTH DUE TO FLY ASH
Concrete can be classified as either non air entrained (natural air
content .3 to 3 percent by volume) or air entrained (air content ranges from
3.5 to 8 percent). As mentioned previously, air entrained concrete tends
to have a higher resistance to freezing and thawing damage. Most industrial
and commercial structures today are built with air entrained concrete.
Unfortunately some loss of compressive strength occurs with increasing air
volume above that level naturally occurring in a mixture.
Figure 4 depicts the relationship between the compressive strength and
the curing age of the concrete when Type I Portland Cement is used. In
order for the concrete to develop to its full strength, it is necessary for
moisture to remain in contact with the cement. If this is not the case,
full strength is not realized. The early strength of the concrete is important
in that it determines the time necessary before loads can be placed on the
concrete. Bloem has shown that curing conditions affect fly/sash concrete in
a manner similar to that of plain Portland Cement concrete.
The general trend is that replacement of up to 30 percent of the cement
by fly ash tends to lower the compressive strength during the period of 7 to
28 days and raise the compressive strength at ages beyond 90 days as compared
to normal portland cement concrete. This is due to the fact that pozzolanic
action is slow to develop. Elevated temperatures speed up the pozzolanic
action, so fly ash concrete placed in warm weather will have higher earlier
strengths as compared to that placed in colder weather. However, the general
approach used to assure early strength that is comparable to Portland Cement
concrete for a fly ash concrete is to have a slightly higher 28 or 90 day
design strength. In many cases the lower strength during the 7 to 28 day
period should not be of great concern, since it is usually within 85% of the
strength of the comparable Portland Cement concrete.
ECONOMICS OF FLY ASH CONCRETE
In order to estimate the cost of fly ash concrete, a number of factors
need to be assumed. First, the cost of fly ash at a batching facility is a
function of the cost of the fly ash as well as the cost of the transportation
and handling. Second, fly ash utilization in concrete requires special equip-
ment for storage and handling at the batching plant. Third, the savings in
cement in making fly ash concrete is a function of the type of concrete and
desired properties. In order to make some estimates, let's assume that the
fly ash is available at $4/ton and that the batching facility is 50 miles
from the power plant. If it costs $6/ton to handle and transport, then the
fly ash at the batching site would be $10/ton. If the extra handling equip-
ment costs an additional $5,000 per year, if there is an additional maintenance
of $2,000 per year at the batching plant, and if we assume a use of 2000
tons per year of fly ash, then the cost per ton at the batching plant (in-
cluding handling) is $10 plus $3.50, which equals $13.50 per ton.
Currently, cement costs $47/ton plus transportation. To estimate the
savings, if any, the type and strength of the concrete must be specified.
23
-------
150
125
100
bo
e _.
g 75
•w
GO
&
Q
8 50
25
Type I Cement |
37 28
.moist-cured
in air after 7 daya
in air after 3 days
in air entire time
90
Age, days
18C
Figure 4. Curing Conditions and Strength of Portland
Cement Concrete
24
-------
If a 3000 psi air entrained concrete was specified, then one could use the
following amounts for one cubic yard:
Cement
Fly ash
Air entraining agent
Aggregates
Air Entrained
Concrete
470 Ib.
5 Ib.
3200 Ib.
For the cost side, we can estimate:
Cement
Fly ash
Air entraining agent
Aggregates
Air Entrained
Concrete
$11.05
.05
3.20
$14.30
Air Entrained
Fly Ash Concrete
400 Ib.
125 Ib.
10 Ib.
=3200 Ib.
Air Entrained
Fly Ash Concrete
$ 9.40
.85
.10
3.20
$13.55
From this calculation we can see that a difference of 75 cents per yard ex-
ists. Thus, a savings of greater than 5 percent can be achieved by utilizing
fly ash in this case. Obviously, costs are a function of the cost of fly
ash, and any savings would be based on the cost of fly ash.
It should be realized that the costs can change considerably based on
the total transportation costs of both fly ash and cement. The transporta-
tion cost of cement was not considered in the above example, and would more
than likely add an additional differential of 25 cents per cubic yard. It is
safe to state that future differentials are likely to be larger and in favor
of fly ash utilization because the cost of cement manufacture is a function
in large part to energy costs. In the early 1970's energy cost accounted for
only 10 percent of total cement manufacturing costs. However, energy costs
are now close to 30 percent of total costs and are likely to be even higher
with new source performance standards on cement plant emissions.
25
-------
Section 5
FLY ASH AND MINERAL RECOVERY
BACKGROUND
It has been recognized that coal ashes contain large concentrations of
aluminum and iron as well as lower concentrations of Ti, U, Th, Cr, V, Ni,
Co, and In. Concepts for recovering these materials existed 50 years ago
but were not economic.
Three facts today may make recovery more feasible. First, the cost of
mining, extraction, and transportation of primary metals is rising rapidly.
Second, many metals used in United States industry are imported in high per-
centages and tba concern over international cartel control of these minerals
is increasing. Third, the recovery of metals may reduce the volume of re-
sidual solids that require disposal.
RECOVERY TECHNIQUES
Presently seven techniques have been proposed for recovery of metals.
Each technique will be discussed. Comparison of the techniques will not be
made as only two (lime sinter and lime soda sinter) have been demonstrated
on an engineering scale. Finally, a discussion will be presented related to
product recovery techniques:
1. Lime Sinter: Fly ash is first sintered at 1200-1300°C with powdered
limestone where the silica is fixated and soluble aluminate compounds are
formed. The aluminates are then dissolved from pulverized sinter in an aqu-
eous soda ash solution, which is then precioitated as aluminum trihydrate
which is separated and calcined to alumina. Magnetic separation of iron
prior to fly ash processing is recommended as a means of increasing aluminum
yield. 8
2. Lime-Soda Sinter: When soda ash is also in the sinter with lime-
stone, sodium aluminate is formed along with calcium silicate and calcium
aluminate. In the sinter reaction the lime combines with silica to form
dicalcium silicate:
2 CaC03 + Si02 -» 2 CaO • Si02 + 2 C02 (1)
This reaction frees the aluminum which was combined with the silica. This
alumina reacts with soda ash or limestone to form soluble aluminates:
26
-------
12 CaC03 + 7 A1203 -> 12 CaO - 7 A1203 + 12 C02 (2)
NaC03 + A1203 -» Na20 • A1203 + C02 (3)
The aluminates are then dissolved via a soda ash solution, and treated with
lime to precipitate silica. The tailings from the leaching steg are sintered
and mixed with gypsum during grinding to form Portland Cement.
Magnetic separation of the fly ash is again advisable to increase alumi-
num yield. The CaOrSiCL mole ratio should be 2 with excess CaO to give
a CaO:A«U°3 mole ratio of 12:7 or enough Na?CO. to give a Na?0:Al?0~ mole ratio
of 1:1. Figure 5 presents a flow diagram of the lime-soda-sintef process.
Studies at the Department of Energy's Oak Ridge NationalqLaboratory (ORNL)
indicated aluminum recoveries were in the 60-70% range.
3. Direct Acid Leach: Samples of fly ash were leached, at ambient tem-
peratures, with HC1 , HNOo, and-nhLSC.. Low recoveries were observed to be: 15%
Al, 60% fe, 35% U, and 17% Ti. ^ 4
The same ashes were treated with the same acids under reflux conditions
for sixghours and recoveries were observed to be: 56% Al , 73% Fe, 40% Ti ,
74% U. Low recoveries on fly ash can be expected since the ash consists
of iron and aluminum silicates along with silica which is fused into re-
fractory glassy material.
4. Salt-Soda Sinter: ORNL developed a modified sintering egocess
(Figure 6) to recover aluminum and other metals from fly ash. ' A fusion
mixture of NaCl-Na2C03 (weight ratio of 2:1) is mixed with fly ash on a weight
ratio of 3:1, heated to 800°C to sinter, quenched in water, and leached in
diluted HNO.,-pr-QH9SOA. Fe, Ti , and U are solubilized and aluminum recovery
exceeds
5. Cal sinter: ORNL also studied a sinter process (Figure 7) where
fly ash was sintered at 1000-1300°C with a mixture of gypsum and limestone.
The sinter is followed by leaching with ^SO.. Using 1:1:1 weight ratio of
fly ash,-gyD§um, and limestone and 4NH9SOA, the following recoveries were
observed"30'33: Al-97%, Fe-90-95%, Ti-90-95%, U-80%, Mn-70%.
Studies have been conducted to substitute FGD scrubber sludge for gyp-
sum and some of the limestone in the Calsinter process. As the sintering
temperature increased to 1200°C and the ratio of sludge3§olids to fly ash
ratio increased, Al recovery improved to more than 95%. Figure 7 presents
options for product recovery which include either extraction or continuous
ion exchange.
6. Hi-Chlor: DOE's Ames Laboratory has developed a process utilizing
the non-magnetic fraction of fly ash where upon carbon is added as a reduct-
ant to react with oxygen released from oxides and is then chlorinated at
800-900°C :
Si02 + 2C + 2 Cl2(g) -> SiCl4(g) + 2 CO (g)
27
-------
Soda Aah( solid or solution.)
Limestone
Concentrated solution
from soda ash recovery
Lime
Waahed FhieGas
»Jron Oxide
Desilication Residue
Flue Gas
Filtrate
» Tailings
interingl— *-Flue Gas
IGindingj*- Gypsum
[Settling & Filtration!
—>-fCarbonation] < Seed
Cement
1
[Classification & Thickening! ** Carbonated solution
™*^ soda as!
[Filtration! ^Filtrate
-»-Stack Gas
Figure 5. Generalized Flowsheet for the Lime-Soda
Sinter Process^°»39
28
-------
Fly Ash Binter
1800' C
Evaporate
recovery
HNO3 | Tb HN03
Leach I recovery
Figure 6. Generalized Flowsheet for the Salt-Soda
Sinter Process-^", .39
29
-------
Fly
Palletize]
| Sinter at 1100 -1200 *C |
Grind 40 Mean {-
Pugging
Leach
36NH,SO.
Dilution
Leach
H,0
Filter
B
Solids
Figure 7. Generalized Flowsheet for the Calsinter
Process (36,39)
30
-------
§
•s
2
i
Alternative*
Bi^
£
a
A
o
£
1
Minor metal*
•
Amine
Regeneration
aqueous 1
(Evaporation"] Fe,Ti,U,Th,Re
To recovery
if desired
A1,(S(X>,
Al A
ICalclnej product
I t
j. jCalcine]
Al,0, \"-
rj,,:, AJ,(S04),
(NH.XSQ+H.SO. {
| 1 Evaporation
T
, Continuous AI3(SO4)f
Ion Ercnange fraction
__.„ Pe fraction , Tri rnrriirnrir
if desired
Figure 7. (Continued)
31
-------
AlpOo + 2C + 3 Cl2(g) -> 2AlCl3(g) + 3 CO (g)
Fe203 + 3C + 3 C_l2(g) •* 2FeCl3(g) + 3 CO (g)
TIP, + 2C + 2 Cl2(g) -» TiCl4(g) + 2 CO (g)
Although difficult, this process is proposed to remove the metal chlorides
from the off-gas by absorption into fused salts followed by serial phased
distillation for recovery of relatively pure FeCU, A1C1,, TiCl., and SiCl..
SiCl* would be recycled to the reactor to control formation of this probably
undesirable product.
The principal product, A1C1-,, can be used for production of Al metal.
TiCl. can be converted to Ti09 wnich has a market value of $900/ton.n Re-
coveries have been 70-80% for^Al, 80-90% for Fe, and 70-80% for Ti.
Since some iron will remain in the non-magnetic fraction, and since
iron has a strong affinity for Clp, it is recommended that the remaining
iron be removed as volatile FeCU at 400-600°C whereas Al, Si, and Ti do
not react until 800°C. J
7. Mineral Gas Company (MGC): MGC of Memphis, Tennessee.-.has a patent
on a mineral recovery process which can be applied to fly ash.
The process at its present level of development consists of five primary
steps:
1. Precondition the ash at 90°C with a solution of sodium hydroxide.
2. Solubilize the aluminum, iron, and other metals in a bath of
hydrochloric acid.
3. Remove 60-65 percent of the iron via an electrical plating process.
4. Precipitate the remaining iron with the recycled sodium hydroxide
from step 1.
5. Precipitate the aluminum oxide with a solution of hydrochloric acid.
All reagents used are recycled and the process uses a relatively low heat in-
put when compared with other recovery processes. Laboratory test results
indicate that iron, iron oxide, and aluminum oxide can be removed economically.
MGC has also developed a second process to extract aluminum sulphate
(alum) directly from fly ash.
39
8. End Product Options: ORNL has summarized end product options as
follows:
1. Recovery of the aluminum as ammonium alum from Calsinter leach solu-
tions by neutralization of the acid with ammonium hydroxide.
32
-------
2. Crystallization of aluminum chloride by evaporation of the leach
solution to approximately 72% sulfuric acid followed by saturation
of the liquid with anhydrous HC1.
3. Extraction of the iron, titanium, manganese, and uranium into an
organic compound containing 30% primary amine in a suitable diluent,
and crystallizing the aluminum sulfate left in the raffinate by
evaporation.
4. Separation of the iron and aluminum by continuous ion exchange
chromatography using gradient elution.
5. Precipitation of hydrous aluminum oxide which can be sintered
to yield anhydrous alumina.
All of these methods should be capable of producing materials suitable
for producing aluminum metal by electrolytic methods. Other product options
are possible utilizing conventional hydrometallurgical techniques.
MARKETABLE EXTRACTED MATERIALS
39
The end products from some of the recovery processes include, as follows:
Lime-Soda Sinter: Fe, Alumina, Cement
Salt-Soda Sinter: Fe, Alumina, Mn02, Ti02, Silica Gel
Acid Leach: Fe, Alumina, MnOp, Ti02
Calsinter: Fe, Alumina, MnOp, TiOp, Cement
TVA SUPPORT OF PROCESS DEVELOPMENT
TVA will be cooperating with Mineral Gas Company, Inc. (MGC) and the City
of Lawrenceburg, Tennessee, in the construction and operation of a one ton
per hour pilot plant to study the,technical and economical feasibility of
the MGC process discussed above.
MGC has also proposed to build an alum.extraction facility at the
Bull Run Steam Plant using another process.
ECONOMICS
No information was available on the MGC extraction process in the litera-
ture. Murtha and Burnet project that for a 1000 ton per day alumina output, fly
ash could be processed via the HiChlor process for an 8% return on investment
even if fly ash were purchased at $6/ton.
39 42
Table 8 ' presents the estimated income per ton of alumina for
several processes as presented by ORNL.
33
-------
Table 8. ESTIMATED INCOME FROM
MINERAL RECOVERY
Process products
Lime-soda sinter
Iron
Al umi na
Cement
Salt-soda sinter
Iron
Al umi na
MnO~
TiO?
Silica gel
Nitric acid
Iron
Al umi na
MnO?
TiOg
Cal sinter
Iron
Alumina
MnOo
TiOo
Cement
Bayer
Alumina
Production
(103 tons/year)
110
208
1526
149
217
2.6
15.3
227
138
157
1.8
5.8
144
261
1.5
13.9
1550
350
Income
($/ton A1203)
15.8
155.0
(322.1)
170.8
16.1
155.0
2.4
37.5
(292.7)
211.0
21.9
155.0
2.0
19.8
198.7
16.5
155.0
1.1
28.2
(327.2)
200.8
155.0
Income
($ 106/year)
3.29
32.30
(83.95)
35.59
3.49
33.61
0.51
8.12
(63.47)
45.73
3.45
24.27
0.32
3.10
31.12
4.31
40.39
0.29
7.35
(85.26)
52.34
54.25
34
-------
The process may produce salable materials from fly ash in addition to
alumina, some of them in substantial quantities. Cement and silica values
are excluded from the totals because the volume of production is so large
that market conditions could be drastically affected. Some of the plants
could sell Portland Cement at reduced prices, some at prices near present
values,oWhile other plants use different processes which do not produce
cement.
For these calculations, the following selling prices were assumed: iron
oxide pellets, $30/ton; iron oxide powder, $5/ton; alumina, $155/ton; man-
ganese dioxide, $200/ton; titanium dioxide, $530/ton; cement, $55/ton; and
silica gel, $280/ton. The possibility of recovering other metal values,
such as magnesium, exists for the salt-soda or Calsinter processes but hag
not been explored. No account was taken for reduction in disposal cost.
39 42
Table 9 ' presents a summary of estimated annual operating costs,
capital costs, and income for five processes. If cement can be sold, some
processes are economically viable while others are not. Other processes,
such as the salt-soda process, appear to be economically attractive. How-
ever, the costs for nitrate cleanup, which could be significant, were not
included in either the salt-soda or the acid-leach process.
The capital costs of the processes include equipment facilities, engi-
neering, contractor's fee, construction, interest, contingency, and working
capital. These costs show that, although the Calsinter process may be the
most economical on the basis of alumina produced, it requires a high capital
investment. Cost figures for this type of estimate are useful in predicting
relative costs of similar processes. All of these processes show economic
potential and deserve further study and development.
35
-------
Table 9. ESTIMATED ANNUAL OPERATING COSTS, CAPITAL COSTS, AND INCOME
CO
en
Operating costs ($/ton alumina)
Raw materials
Utilities
Labor ($25,000/man-year)
Maintenance (10% of fixed cost)
Taxes and insurance (2% of fixed cost)
Depreciation (5% of fixed cost)
Total
Income from products ($/ton alumina)
Capital Costs
Total capital for plant {.$ 106)
Capital cost per annual ton of alumina ($)
Lime-soda
118.70
56.76
4.80
92.74
5.94
14.88
230.82
170.80
62
297
Slat-soda
85.01
30.32
4.61
30.44
6.08
15.22
171.68
211.00
66
304
Nitric Acid
55.17
39.86
6.39
37.04
7.40
18.52
167.38
198.70
58
370
Cal sinter
56.83
65.11
4.41
27.62
5.52
13.82
173.31
200.80
72
276
Bayer
34.72
22.55
3.00
25.72
5.14
12.86
103.99
155.00
90
257
-------
Section 6
FLY ASH AND MAGNETITE RECOVERY
INTRODUCTION
A review of the literature indicated that Minnick in 1961 developed a
procedure for magnetic ash separation that was used for concrete addition
(43). In 1962, Joppa received a patent for magnetic fractionation of fly
ash for use in coal preparation (44). A facility, which is presently not in
operation, was built at Lakeview station of Ontario Hydro to remove the
magnetite fraction from fly ash (45).
Few industrial installations have been built for magnetic recovery; and
the only high volume installation in the U.S.A. to date is at Penn Virginia
Materials Corp., in Cleveland, Ohio. This facility is now closed. The fly
ash was separated magnetically dry on a series of three permanent magnet
rotary separators and was then air classified. About 800 tons of magnetic
fractions were removed per month and 60% of this material (=40 micron size)
was marketed as fine grade magnetite (43-47).
Researchers at Iowa State were the first to examine the use of the
separated magnetic fraction of fly ash as a substitute for commercial mag-
netite in coal washing (46, 47) by using a device similar to that devised by
Minnick (43). The Iowa State researchers (46, 47) found that 10-15% by
weight of bituminous coal fly ash may be recovered as a magnetic fraction.
The particles were spheroid in shape (commercial magnetite is angular) and
65-85% by weight passed a 325 mesh (44 micron) screen (this is similar to
commercial magnetite). It is recommended that further processing via ball
mill grinding and washing be conducted to remove the clay-like materials.
The density of the ground and washed material was 3.5 g/cm , whereas com-
mercial magnetite has a density of 4.7 g/cm . The viscosity of ground and
washed magnetic fractions was lower than that of commercial magnetite and re-
sulted in lower mixing energy requirements for stirring. Also, ground and
washed magnetic fly ash fractions settled slower than commercial magnetite
samples indicating that the magnetic fraction was more stable. Finally, the
Iowa State researchers found that a ground and washed magnetic fraction was
a good heavy medium material capable of washing coal.
HISTORY OF TVA INTEREST
TVA has initiated a research program related to magnetite recovery for
coal washing. Phase I has begun and involves investigation of the economic
and efficiency limits on the percent of magnetite that can be recovered from
37
-------
coal ash. Phase II will evaluate whether the magnetite fraction can
be used in a heavy media coal cleaning process. Phase III will involve a
technical and economic comparison of the magnetic fraction to commercial
grade magnetite. Phase III intends to design, construct, and operate a
magnetic separation facility on coal ash. The project is to be completed
by January 1982 (41).
The long term need for the magnetic fraction can be projected to the
TVA system. A coal cleaning facility is already being constructed at
Paradise Steam Plant and it will process 2000 tons per hour. Assuming
1.5 Ib. magnetite per ton of coal and an availability factor of 0.85, this
one facility will require 8000 tons of magnetite per year. Iowa State (47)
estimates that magnetite is worth between $70-100/ton. Therefore, the Para-
dise coal washing facility could spend between $600,000-$800,000 per year
to buy magnetite. TVA estimates that a fly ash magnetite recovery facility
could be built at Paradise for $250,000 (to generate 8000 ton/year magnetite).
Excluding operating costs, this could save $310,000-550,000 per year in
commercial magnetite costs (41).
The general impact on the TVA region can be indicated by comparing
estimated national coal cleaning demands with coal burned. For example, in
1979, about 500 x 10 metric tons of coal was burned in the USA. In 1985,
this number could be 700 x 10 metric tons. It is estimated that by 1985,
365 x 10 metric tons of coal will be cleaned in the USA or roughly (365/
700) 50% of that burned (47). TVA was burning, in 1975, 35.1 x 10° tons.
If it is assumed that this tonnage holdSgConstant through 1985 and if 50%
is cleaned, then at a minimum 17.55 x 10 tons could be expected to be
cleaned per year in 1985. At $100 per ton fog magnetite, and at 1.5 Ibs.
magnetite/ton, this could cost TVA $1.32 x 10 annually to purchase mag-
netite.
38
-------
Section 7
SINTERED FLYASH AND LIGHTWEIGHT AGGREGATES
Almost any material can be obtained with the required particle size and
grading, provided it has the required strength and can be used as an aggre-
gate for concrete provided it does not contain any substance-.liable to lead
to unsoundness or to react in a harmful way with the cement. Aggregates can
be classified by weight as heavy, normal, or lightweight. Normal weight
aggregates have a specific gravity of about 2.6, while heavy-weight aggregates
have a specific gravity that is greater than 2.8. Light-weight aggregates
have a specific gravity of less than 2.4.
The unit weight of concrete can be effectively controlled by the type
of aggregate used. Concrete with a weight of less than 115 Ibs/cubic ft.
is classified as a lightweight concrete. Lightweight concrete is produced by
using various types of lightweight aggregates that are either natural or
artificial or by keeping the fines out of the mix design.
The advantages of having a lightweight, structural concrete are based
on the difference in weight between that and normal concrete. Lightweight
structural concrete provides flexibility in designing longer spans, larger
floor areas, added height or simpler foundations.
Many types of lightweight aggregate can be used in producing a light-
weight structural concrete. These include: expanded slag; sintered shale,
clay or flyash; and kiln expanded shale, clay and slate. Other lightweight
aggregates, such as vermiculite and pumice, produce only low to moderate strength
concrete because when the aggregate is below a certain density, the attained
28 day compressive strength is usually less than 2500 psi.
Producing lightweight aggregate from slate, shale, clay, or flyash re-
quires either a sintering process or a heat expanded process. When certain
clays, shales, and slates are heated to 1300-1400°F, they expand as a result
of the formation of gas within the material. This develops a cellular struc-
ture of lower density.
For flyash, a lightweight aggregate can be produced by sintering.
Usually the flyash is wetted and formed into pellets. The pellets are then
placed on a grate in a firing chamber at about 2600°F. At this temperature
the pellets soften and agglomerate into larger particles. The internal
structure of the sintered flyash is filled with voids caused by evaporation
of the pellet water and by the combustion of the residual carbon in the flyash.
The sintered flyash is then cooled and crushed to desired sizes.
39
-------
The carbon content of the flyash plays a large role in the sintering
process as a source of heat during combustion. If the carbon content of the
flyash falls below 4%, it is probably necessary to add pulverized coal to
the pellets before sintering. If the carbon content is more than 6%, it
may be necessary either to mix it with ash with a lower carbon content, or
to fire the carbon and use an external source of heat. This is important
because the sintering process must be closely controlled. The production of
a suitable lightweight aggregate from flyash also appears to.be a function
of the size of the particles of the flyash before sintering.
A number of facilities have been built for producing lightweight aggre-
gate from flyash; however, at this time only a few are in operation. Major
problems include deficiencies in design, excessive wear, as well as the
quality of the flyash being sintered.
The facilities that are currently operating in the U.S. are apparently
not able to market the product for a profit. This fact is due in large part
to institutional barriers to the use of flyash as a lightweight aggregate.
Predictions that demands for lightweight aggregate will increase are based
on the adoption of codes like those in Europe which allow the use of light-
weight concrete and the use of sintered flyash.
Since sintered flyash is stable, easily handled and transported, it ap-
pears that the best place for a lightweight aggregate plant is next to a
power facility. This would mean that any storage facilities could be in
terms of sintered flyash instead of flyash. In addition, the handling of
flyash would be minimized.
TVA has indicated that the Bull Run Steam Plant has been considered for
a lightweight aggregate facility; however, at this time no serious plans have
been made.
40
-------
Section 8
FLY ASH UTILIZATION IN WASTE WATER TREATMENT
FLYASH APPLICATION IN WASTEWATER TREATMENT
Numerous researchers have evaluated the use of fly ash in aspects of
wastewater treatment. These applications and their present problems with
potential field scale systems will be discussed.
Deb, et al_., studied the removal of COD from wastewater using fly ash.
COD removal decreased after 10 minutes of contact time. It was found that
50 mg/1 of activated carbon was as effective as 1000 mg/1 of fly ash.fi?Above
3000 mg/1, COD removal became independent of further flyash addition.
Eye and Basu studied COD removal as well as sludge conditioning.
COD removal decreased after 10 minutes contact time. With an initial COD
of 60 mg/1 and fly ash concentrations varying from 778-2570 mg/1, removals
ranged from 15-40% and averaged about 30%. The authors project that 50-80%
cost savings can be achieved via use of limegnlus fly ash and fly ash alone
as wastewater sludge conditioning chemicals.
In a study by Tenney and Echelberger, fly ash was evaluated for these
possible applications: lake restoration, sludge conditioning, and treatment
of acid mine drainage. In studying fly ash addition to eutrophic lake
waters, phosphorus and organic matter were removed. Organics (65-10%) were
adsorbed; and it was surmised that due to extraction of lime and gypsum from
the fly ash, phosphorus was precipitated. Dry, unreacted fly ash was more
effective than washed fly ash. In the studies on sludge conditioning at
greater than 50 grams/1, fly ash improved dewaterability and increased fuel
value. The authors also found fly ash at greater than 100 grams/1 to be
effective in neutralizing acid mine drainage.
Chu, et aJL , studied the capability of fly ash to remove a copper-ammonia
complex whTchTs discharged to ash ponds. It was surmised that copper is
both adsorbed and precipitated by alkaline fly ash. Copper adsorption to fly-
ash is dependent upon the amount of flyash added, up to 40 grams/1. Removal
ranged from 94-99%. D
Finally, Gangoli, et al., studied the removal of heavy metals (from
3-100 mg/1) from aqueous solutions with fly ash. The following metals were
removed fairly,successively0using0as high as.a 40 OKams/Kfly ash dose: 0
Al+o, Cr . Mn . Fe • Ni . Cu % Zu Z, Zn Z, Cd *, Sr % Pb Z, Cr20 ~i.
Hg was not effectively removed. Experiments indicated that prior acid
treatment of fly ash was detrimental to metal removal. The authors
41
-------
proposed the following mechanisms for metal removal:
Precipitation occurs at high pH probably as metal hydroxides.
Cr anion is removed by reduction of Cr+^ to Cr+3 or by ion exchange.
Adsorption is probably due to the presence of silica and
alumina available in flyash.66
Although in some respects, fly ash addition to wastewater and sludge
for metals, organics, phosphorus, neutralization benefits, and dewatering
improvements, has been demonstrated, there are three problems that need to
be addressed as well.
First, flyash has exhibited the ability to desorb heavy metals upon water
contact.6' Several authors have evaluated this effect.62' °3> °^ With a
future emphasis on priority pollutants, this may create problems in utiliz-
ing fly ash to aid wastewater treatment.
Second, if fly ash is added to the wastewater then the ash will ulti-
mately end up in the sludge. Given concerns addressed to more proper man-
agement of solid wastes, this could present a problem because the sludge
could become a hazardous waste following fly ash addition.
Third, most fly ash is not generated near a wastewater plant. The
logistics of handling and economics of use would need to be studied.
SCRUBBER SLUDGES
Fly ash is used in some stabilization processes to aid pozzolanic
reactions or to serve as a fly ash disposal technique. It is estimated
by one commercial vendor, IU Conversion System (IUCS), that by 1982,
2.5 x 10° tons of ash will be used annually in that vendor's stabiliza-
tion process, the Poz-0-Tec** process.^ This represents the largest
fly ash utilization by any commercial vendor. Existing IUCS operations
or those under contract with utilities are shown in Table 10.
The Poz-0-Tec material is formed by the addition of lime, flyash
and other materials to FGD sludge to accomplish fixation. The. flyash
to sludge ratio is approximately 0.5 : 1, although a 1:1 ratio can be
achieved. The fly ash serves as the pozzolan for the reaction. The
largest installation in operation is at Columbus and Southern Ohio
Electric Compan's Conesville Station and is designed to treat FGD
sludge and flyash from two units totalling 830 MW.
Dravo has also patented a fixation process through the addition of
CalciloxR which is a cementitious product obtained from blast furnace
slag. Flyash may or may not be added to the mixture, but in this
fixation process, flyash is not a necessary ingredient for accomplishing
the reaction. At the Bruce Mansfield Plant operated by the Pennsylvania
Power Company, flyash and FGD wastes are treated from two units with a
capacity totalling 1834 MW.
42
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Table 10
PRESENT AND PLANNED IUCS INSTALLATIONS AS OF
November 1, 1979
Big Rivers Electric
Central Illinois Public Service
Cincinnati Gas & Electric
Columbus & Southern Ohio
Commonwealth Edison
Duquesne Light
Duquesne Light
East Kentucky Power Coop
Hoosier Energy
Indianapolis Power & Light
Lakeland Utilities
Louisville Gas & Electric
Louisville Gas & Electric
Public Service of Indiana
Southwestern Electric Power
Texas Municipal Power
Station/UniUs)
Green 1, 2
Newton 1
East Bend 2
Conesville 5, 6
Powerton 51
Elrama
Phillips
Spurlock 2
Merom 1, 2
Petersburg 3, 4
Me In tosh 3
Cane Run 4, 5, 6
Mill Creek 1, 2, 3, 4
Gibson 5
H. W. Pirkey 1
Gibbons Creek 1
MW
480
615
600
800
450
500
400
500
980
1060
350
670
1580
650
720
410
Source: FGD Sludge Disposal Manual. Second Edition, Michael Baker, Jr., Inc.
EPRICS-1515, September 1980.
43
-------
Other propietary stabilization/fixation processes include ones
by American Admixtures, Inc. and the Stablex Corporation. The
Sealosafe^ process patented by Stablex is commercially available in
Europe and combines portland cement or cement dust, flyash, industrial
waste, and sometimes lime, other companies also offer cement processes,
but commercial applications have not been made for flyash utilization.
Physical stabilization of scrubber sludge has been proposed and
received limited application. At the Southwest Station of Springfield
City Utilities, FGD sludge is processed by thickening, followed by
vacuum filtration. The filter cake is then blended with flyash. The
mixture is achieved with a non-alkaline flyash hence a pozzolanic
reaction is not made, and care must be taken to keep the disposed
material dry.
44
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Section 9
FLY ASH AND SANITARY LANDFILL LINERS
Fly ash can be used for improving the properties of the soils used to
line cells in sanitary landfills and the properties of the soil used for the
final cover. TVA has conducted several tests to determine the conditions
under which fly ash can be used as either a soil extender or amender. Public
Law 94-580 directs the U.S. Environmental Protection Agency to determine the
regulations associated with the approval and operation of sanitary landfills.
Because of the concern for leachate from sanitary landfills polluting aquifers
or nearby surface waters, the current promulgated regulations require that
location of landfills, along with the operation, must insure that no appreci-
able impacts occur to surface or groundwaters. This means that whenever
ground waters could be impacted, the lining of the landfill must be close to
impervious. In addition, to reduce the potential for leachate, the surface
must be graded and swelled to remove any large potential for infiltration.
EPA has issued criteria for the protection of groundwater which should be
consulted in this regard.
Utilizing fly ash in both lining soil material and covering soil mater-
ial can help in attaining the desired properties. In 1972 and 1978, TVA
blended ash to soil samples from landfills of Coffee, Scott, and Sumner
counties in Tennessee to determine whether ash can be easily used and to
what degree the ash amended soil can be impervious. For the TVA studies,
the ash was taken from the spoil area at the Gal latin and Kingston Steam
Plants. Both fly ash and bottom slag were used in the study. The sizing of
the two ashes are given in Tables 11 and 12.
The soils from each of the two landfills were blended with both types
of ashes under several conditions of moisture. When the soil was moist and
mixed with the fine fly ash, the absorption rates were slow for ranges of
soil to ash of 1:1 to 1:3. When similar soil was mixed with the slag, the
absorption rates were medium to rapid under the same mixture ratios. When
the soil moisture was increased about 4% above normal moisture to represent
wet weather conditions, the soil and flyash blends were hard to mix. When
the soil was mixed with wet fly ash or a mixture of wet fly and bottom ash,
the absorption rates were slow for the soil to ash ratio of 1:1. The results
are given in Tables 13, 14 and 15 for the tests made.
It appears that when the soil has a normal moisture content, it is
feasible to mix either fly ash or a mixture of fly and bottom ash with the
soil to reduce permeability. The easiest blending ratio to produce is a 1:1
under normal operating conditions according to TVA results.
45
-------
Table 11. SANITARY LANDFILL LABORATORY STUDY
USING KINGSTON POWER PLANT ASH
Particle Sizes - Percent Passing
1-Inch Sieve No. 4 Sieve No. 200 Sieve
Ash type: Fly ash (fine bottom) 100 92
Plasticity: None
Natural moisture content (sample): 27%
Compacted wet unit weight: 95 pcf
pH: 4.8
Particle Sizes - Percent Passing
1-Inch Sieve No. 4 Sieve No. 200 Sieve
Ash type: Coarse ash (slag) 100 81 32
Plasticity: None
Natural moisture content (sample): 14%
Compacted wet unit weight: 115 pcf
pH: 2.8
46
-------
Table 12. SANITARY LANDFILL LABORATORY STUDY USING
GALLATIN POWER PLANT ASH
Particle Sizes - Percent Passing
Ash type: Fly ash (fine bottom)
Plasticity: None
Natural moisture content (sample):
Compacted wet unit weight: 90 pcf
55%
No. 4 Sieve
100
No. 200 Sieve
90
Particle Sizes - Percent Passing
1-Inch Sieve No. 4 Sieve No. 200 Sieve
Ash type: Coarse ash (slag)
Plasticity: None
Natural moisture content (sample): 12.5%
Compacted wet unit weight: 120 pcf
100
70
20
47
-------
Table 13. SANITARY LANDFILL LABORATORY STUDY
FOR COFFEE COUNTY
Particle Sizes
Sand Silt Clay
T" % %
Soil type: Fat clay 20 40 40
Plasticity: Medium to high (plasticity index 33)
Natural moisture content (sample): 28%
Blend Ratios (By Volume)
Soil: Fine Ash
1
2
3
Soil: Wet Fine Ash
1 1
Wet Soil: Fine Ash'
1 1
*
Soil: Coarse Ash
**
1
2
3
Soil: Wet Coarse Ash
1 1
Wet Soil: Coarse Ash
1 1
*
Soil: Mixed Ash
1 1
**
Rate of Absorption
Slow
Slow
Slow
Slow
N.A.
Medium
Rapid
Rapid
Medium
N.A.
Slow
**
Soil and ash tested at natural moisture contents.
k
The wet soil has poor blending characteristics.
48
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Table 14. SANITARY LANDFILL LABORATORY STUDY
FOR SUMMER COUNTY
Particle Sizes
Sand Silt Clay
Soil type: Medium clay 15 40 45
Plasticity: Medium (plasticity index 24)
Natural moisture content (sample): 25.5 percent
Blend Ratios (By Volume) Rate of Absorption
Slow
Slow
Slow
Slow
N.A.
Rapid
Rapid
Rapid
Soil: Wet Coarse Ash
1 1 Medium
**
Wet Soil: Coarse Ash
1 1 N.A.
Soil: Mixed Ash*
1 1 Slow
*
Soil and ash tested at natural moisture contents.
**
The wet soil has poor blending characteristics.
49
Soil
1
1
1
Soil
1
Wet
1
Soil
1
1
1
*
: Fine Ash
1
2
3
: Wet Fine Ash
1
Soil: Fine Ash
1
: Coarse Ash
1
2
3
-------
Table 15. SANITARY LANDFILL LABORATORY
STUDY FOR SCOTT COUNTY
Particle Sizes
Gravel Sand Silt Claj
y~v ~~°i °/
h la To h
Soil type: Medium clay 16 16 29 39
Plasticity: Medium (plasticity index 25)
Natural Moisture content (sample): 21.7%
Blend Ratios (By Volume) Rate of Absorption
*
Soil: Fine Ash
1 1 Medium
Soil: Coarse Ash
1 1 Fast
Soil: Mixed Ash
1 1 Slow
**
Wet Soil: Mixed Ash N.A.
*
Soil and ash tested at natural moisture contents.
**
The wet soil has poor blending characteristics.
50
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The use of fly ash in landfills depends on the accessibility of a good
source of ash as well as the overall need. In addition, the use is also a
function of weather conditions, since blending cannot be easily done when
soil moisture is high. One of the nicest features of this alternative is
that the ash can be utilized when it is wet. In fact, this means that
ponded ash could be used when most alternatives require that the ash be dry.
One point should be mentioned here: the potential for utilization is a
function of specific site characteristics and accessibility. At this
time, the utilization of fly ash as a material for landfill liners re-
mains an alternative that looks good if the fly ash is not being put to
alternative use.
51
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Section 10
CENOSPHERES
BACKGROUND AND DESCRIPTION
A small portion of fly ash typically consists of small microscopic
hollow spheres referred to as cenospheres. These spheres are frequently
referred to as floaters, resulting from the property that they exhibit in
ash settling ponds; all cenospheres do not, however, float. The uniqueness
of cenospheres is their light weight, coupled with their ability to with-
stand hydrostatic pressures in excess of 100,000 psi. They are relatively
non-grindable and inert when cleaned. The floaters tend to have tiny pin-
holes in their walls which decrease their strength in comparison to "sinker"
cenospheres. Also, cenospheres are able to withstand temperatures up to
2000°F making them a desirable fire insulation material.
Although the floaters may be only a small percentage of the total fly
ash, the "sinkers" may be a relatively large portion of the total ash.
32
Zeeuw and Abresch reported that Northern States Power Company s fly
ash from a pulverized fuel plant contained 50-70% cenospheres. The wall
thickness of the floaters was found to be 5-8% of the diameter, whereas the
remainder of the cenospheres (sinkers) had wall thicknesses of up to 30%
of the diameter of the spheres and higher strengths. Typically, the floaters
are skimmed and collected from fly ash sluice ponds.gWhile the sinkers and
floaters are collected in a dry separation process. They are frequently
separated by size into the "minus to 5 micrometer," "5-50 micrometer," and
"greater than 50 micrometer" ranges dependent on their potential use.
Chemically, the cenospheres are composed3of SiOp, AlpO,, Fe^O^, and
traces of other compounds. Ashby and Carroll reported on Australian ceno-
spheres which were 55% Si09, 36% Al?0~, 2.2% Fe?0, and 1.5% K20. At
Northern States Power Plant (Minnes&tS) the content was 52% ST09, 39%
A1203, 1% Fe203, and 5% K20. *
A series of tests were conducted by3golorado School of Mines Research
Institute on a TVA total fly ash sample. Ceno Science Research, Inc.,
separated the material to be tested into magnetic material, carbon black,
floater cenospheres (specific gravity Sl.O), and cenospheres with specific
gravity ^1.0. These later spheres were then ber.eficiated into plus 50 urn,
minus 50 plus 5 urn, and minus 5 urn products. The results were as follows:
1. The fly ash can be separated into desired plus 50 urn, 5 to 50 urn,
and minus 5 urn cenospheres by wet methods.
52
-------
2. Removal of iron to an acceptable level, 2% or less, by low-
intensity magnetic separation was not possible.
3. Carbon black removal to the desired level of 1.0% or less was
possible using froth flotation.
4. Soluble salts in the minus 5 u cenospheres were removed to a level
of 0.02% by washing.
5. The specific gravity of both the minus 50 plus 5 [j and minus 5 p
products was 2.48.
6. The specific gravity of the floating cenospheres was 0.74.
7. The pH of the minus 5 pm pulp was 6.0.
8. The products from the total fly ash sample had the following
weights and distribution:
Product Weight (g) Distribution Weight (%)
Floating Cenospheres 32.6 0.2
Magnetic Concentrate 919.5 4.3
Magnetic Cleaner Tailing 1,513.4 7.1
+50 pm 983.0 4.6
5 to 50 urn 15,892.8 74.1
-5 pm 2,070.5 9.7
Total 21,411.8 100.0
9. The 5 to 50 pm cenospheres had the following chemical analysis:
Na?0, 0.3%; MgO, 1.3%; A1.0-, 28.2%; Si09, 49.5%; SO,, 0.5%;
K26, 0.2%; CaO, 1.1%; TiO^, 1.1%; Fe203/6.0%. 6
10. The minus 5 (jm cenospheres had the following chemical analysis:
Na90, 0.3%; MgO, 1.2%; Al«0,, 25.4%; Si00, 49.1%; SO,, 0.3%; K.O,
0.4%; CaO, 1.0%; TiO, l.i%? Fe0, 5.4%f d Z
APPLICATIONS
At the present time several markets exist for cenospheres, dependent on
the characteristics of the spheres. Areas under evaluation include:
a. plastic extenders g. foams
b. aluminum h. coatings
c. paints i. rubber compounds
d. tapes j. sprays
e. sands k. fire proofing
f. insulation
30
Turner reported a successful application of cenospheres as a filler
in flexible polyurethane foam where up to 48% by weight was utilized. The
53
-------
market involved the use of foam in products such as carpet padding, mattresses,
and cushions. Carpet industry officials have expressed considerable interest
in this type of rebound padding. Since the carpet padding industry utilizes
close to one billion pounds of rebounding padding per year and rebound l
material availability is decreasing, a strong market for cenospheres exists.
Studies have also been conducted on the use of cenospheres as a paint
filler. The potential advantages of the less than 5 urn fraction are the
wearing capability, retention of high gloss under corrosion, and weathering
tests. It was estimated that tbe primary use of minus 5 urn cenospheres :
would be in the paint industry. >
30 32
Investigations are currently being conducted ' on-the use of ceno-
spheres as a plastic binder. In Australia, Ashby, et aJL , reported that the
main use of cenospheres was in plastics because of the light weight and low
resin demand; cenospheres were found to require less resin per unit volume
of product than talc.
Ashby, et al. , also studied the use of cenospheres as a concrete addi-
tive for replacing sand. When compared to a blended cement/sand cement (1:1.8
by volume) which had 7 day and 28 day compressive strengths of 2465 psi and
6160 psi, a mixture of 1:1:1 cement/sand/cenospheres had 7 day and 28 day
compressive strengths of 2175 and 5438 psi. A mixture of h cement/cenospheres
had 7 day and 28 day compressive strengths of 1810 and 4495 psi. Although
strength was reduced by the addition of cenospheres, it was concluded that
there was still a potential use for the cenospheres in lightweight construction
such as for ferro-cement boat construction.
54
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Section 11
USE OF FLYASH IN AGRICULTURE
INTRODUCTION
Previous sections of this report have indicated that flyash may be an
important source of specific elements required as nutrients in the growth of
plants as well as animals. It has been shown that although the bulk of fly-
ash consists of Si02, Fe^O-j, ^2^3 (common^y greater than 85%), fly ash also
contains various amounts of elements considered to have nutrient and/or lim-
ing value when used as a soil conditioner. Unfortunately, while many useful
nutrients may be present, some elements in specific flyashes may be present
in concentrations that could potentially cause an undesirable side effect
due to their toxicity to vegetative matter and/or foraging animals. EPA has
issued criteria concerning the application of solid waste to land used for
the production of food crops.
The properties of flyash have been summarized in Section 2. One of the
most significant properties is the property of many fly ashes to have a lim-
ing value, a quality very important in strip mined areas and in soils of an
acidic nature. Furr, et al_. , showed that for flyash obtained from 21 states
(23 sites), 16 of these had pH values in excess of 7.0 with a maximum of
11.8. In general, the lignite coals have high pH due to the.presence of
substantial concentrations of alkali oxides. Ray and Parker have summarized
data from which it was concluded that significant variations in CaQ, MgO,
Na20 and K20 exist within coals found in the USA. Fail and Wochok reported
the neutralizing power of bituminous coal to rangeQfrom 15 to 200 tons of
ash equivalent to one ton of lime. Phung, et aJL , in a study on Western
flyashes, concluded that many western coals were strongly alkaline and that
Pb, Co, Ni, Cd, Mo, Se, and As existed in concentrations higher than in most
mineral soils. However, due to the higher pH of the flyashes, the solubility
of these trace elements was reduced.
FLY ASH AS A SOURCE OF NUTRIENTS*
As a Source of K and P
Total K content of fly ash from 21 power plants in the U.S. ranged from
0.15 to 3.47%. Eight of the eastern sources and one from Minnesota were
^Section taken from TVA report written by G.L. Terman, Agronomist, Soils
and Fertilizer Research Branch, National Fertilizer Development Center, TVA.
55
-------
evaluated In a plot experiment as sources of K for corn grown on acid Davidson
clay loam by Martens, et al_. Dry matter and K uptake were increased
significantly, presumably as a result of the liming effect of the fly ash on
the acid soil. Concentrations of K in the corn were not increased appre-
ciably by eight of the fly ashes applied at rates to supply 158 and 474 mg
of K/plot. The Minnesota source applied at lower K rates had a greater lim-
ing effect and resulted in higher K concentrations and uptake by corn.
Although elemental composition of fly ash is quite variable, it usually
contains higher,concentrations of essential plant nutrients (except N) than
do soils.12'13'14
15
Martens found that P deficiency of corn grown in a pot experiment on
Landisburg silt loam was corrected by application of 210 mg of P as a soluble
phosphate, but only partially by the same amount of P in fly ash (125 g/pot
containing 0.17% P) from Maidsville, West Virginia. Soil pH was increased
from 5.6 to 7.2 by this application, which may have reduced P availability.
As a Source of S
Elseewi, et al. found the 0.4% S in ash from a western U.S. coal was
readily available to alfalfa (Medicago sativa L.) and other crops.
As a Source of B and Other Micronutrients
cTotal B concentrations in fly ash (Table 4) ranged from 10 ppm to 600
ppm. Fly ash samples from 11 TVA power plants ranged in total B from 120
to 480 ppm; water-soluble B increased with total B (r = 0.96). An average
of 72% of the total B was water-soluble (TVA data).
Mulford and Martens evaluated the availability of the B in three fly
ashes containing 319, 415, and 618 ppm of total B for alfalfa grown on Tatum
soil. Availability of the B in fly ash was equal to that in borax. The
higher rates of the Montanta fly ash (618 ppb of B) decreased yields, prob-
ably as a result of its liming effect which decreases availability of Mn
and Zn. Soil pH was increased from 5.9 to 7.7 by the highest rate (21.6 mg
of B, or 350 g of fly ash/pot of 2.1 kg of soil). Plank and Martens15 found
that dissolution of B in hot water was a good index of crop availability of
B in soil-fly ash mixtures.
FRESH VERSUS WEATHERED FLY ASH
As mentioned previously, most sources of fresh fly ash from the collec-
tors are highly alkaline (pH 9-10) and contain varying amounts of soluble B.
On contact of the alkali metal oxides with moisture, hydroxides are formed,
which undergo further reaction with C0? in the air to form carbonates (pH
7.5-8.5). Thus, on exposure to moisture and air, initial toxicity to plants
due to high alkalinity soon decreases.
Soluble B in fresh fly ash is also toxic to plant growth at disposal
rates of application. If the fly ash is conveyed to drained waste pond
56
-------
sites, leaching by water will soon remove soluble B and reduce alkalinity.
As a result, a ponded area will usually sustain vegetative growth within a
year or two under natural rainfall in humid climates if needed nutrients
(largely N and P) are provided.
19 ?n ?i
Holliday, et al_. , and Rees and Sidrak ' suggested that fresh fly ash
caused Al and Mn toxicity in plants. Holliday, et a]_. , however, concluded
that B, rather than Al or Mn, was the toxic element.
FLYASH AS A SOURCE OF MULTIELEMENT SOIL AMENDMENT AND/OR ANIMAL RATION
Although the use of flyash as a source of nutrients has been studied rig-
orously, many of the earlier studies (1950-1975) did not review in depth the
uptake of non-nutrient elements with potential toxic side effects. These
earlier studies concentrated on the positive benefits of soil enrichment by
flyash by addition of appropriate elements such as K, P, B, Mn, and Zn.
Since 1976 several significant studies have been conducted to investigate
the multielement uptake of (1) plants grown on fly ashgamended soils ' ,
and (2) animals either fed rations containing fly ash or fed food grown
on flyash ammended soil.
23
Furr, et a_L , conducted a study in which 42 elements were determined
in beans, cabbage, carrots, millet, onions, potatoes, and tomatoes grown on
soil amended by addition of 10% by weight flyash. Thirty-two elements were
present in higher total concentrations in the fly ash than in the soil.
Thirteen elements were found to be in higher concentration in the edible
portions when grown on flyash amended soil, compared to the control soils.
Because of the 9:1 ratio of soil to flyash, there were only three elements
for which the average ppm of the elements in the amended soil was increased
by more than a factor of 2. (These were Arsenic, Selenium, and Molybdenum
with relative increases in concentration of factors of 5.7, 6.5, and "un-
known," respectively.) The data are presented for these three in Table 17.
The uptake of both arsenic and selenium Were significantly greater in some
cases than the relative increase in concentration of the element in the soil.
A study was also conducted using a 5% flyash ammended soil. It was con-
cluded that the uptake9gf Selenium was roughly proportional to the rate of
application of flyash. Ehlig has noted that dietary Se concentrations
necessary for preventing Se-deficient disease syndromes in livestock feed
diets is between .02 and .10 ppm, and that above 5 ppm Se-toxicity occurs.
Although the data in Table 16 are less than 5 ppm (1.9 ppm in the amended fly-
ash), they are significantly greater than the level required to satisfy a
Selenium deficiency. Further, Ehlig has shown that a thorough knowledge of
both Selenium concentration and plant type is required since the Selenium
uptake is affected to a measurable extent by the plant species.
In more recent studies, Stoewsand, et a]_.24, have studied the uptake and
response of Japanese quail fed wheat grown on flyash. In this study a winter
wheat was grown to maturity on a deep bed of flyash, harvested, and fed as
60% of a complete diet to quail for 112 days. The wheat contained 5.7 ppm
(dry wt.) of selenium, compared to .02 ppm for the control wheat grown on
57
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Table 16. INCREASE IN MULTI-ELEMENT UPTAKE OF PLANTS GROWN
IN FLY ASH AM ENDED SOIL
in
oo
Beans
Cabbage
Carrots
Millet
Onions
Potatoes
Tomatoes
Soil
Control
.01
.1
.01
.2
.1
.1
.1
2.9
As
Ammended
Soil
.2
.2
.2
1.0
.03
.1
.1
13.9a
16.5C
Ratiob
20
2
20
5
.3
1
1
—
5.7
Control
.02^
.01
.00
.02
.00
.01
.01
.3
Se
Anmended
Soil
.47«>
.95
.19
.90
.30
.49
.20
16. 8a
1.95
Ratio
24
95
20
45
30
49
20
—
6.5
Control
.9<0
1.0
.2
.3
.7
.2
.5
—
Mo
Ammended
Soil
3.2
-------
soil. The tissues and eggs of the quail contained greatly elevated levels
of selenium compared to the control quail. The average ppm (dry wt ) found
in the quail fed flyash was 3.4, 4.4, 9.4, 11.2, and 3.9 ppm in the brain,
heart, kidney, liver, and muscle, respectively; the control ppm levels were
0.8, 0.4, 1.4, 0.7, and 0.2, respectively. The primary effect of the in-
creased selenium was to increase the egg shell thickness by roughly 7%. It
was concluded that flyash high in selenium, but low in toxic elements, might
be a desirable amendment to low selenium soils.
25
Furr, et al_. , studied the uptake and elemental content of tissues and
excreta of lambs, goats, and kids fed white sweet clover grown on flyash
found to contain high concentrations of selenium, bromide, molybdenum, rubi-
dium, strontium, and others. The harvested clover containing 66 ppm of
selenium was fed as 23.5% of a dry pelleted ration to lambs and goats for
173 days. High concentrations of selenium were found in tissues, blood,
goats milk, and excreta. In excess of 6.0 ppm was found in the goat's milk.
Although no toxic effects were reported in the animals studied, it was
stated that 0.5 ppm of selenium in milk is considered unsafe for human con-
sumption. Molybdenum in liver, strontium in bone, and bromine and rubidium
in animal tissues were also elevated in the animals fed the fly ash amended
ration.
26
In a similar study by Furr, et al_. , sheep, fed a 7.5% by weight of
fly ash in pelleted rations (with a selenium concentration in the ration
of 0.6 ppm), were found to be fairly resistant to the Se uptake compared to
a control group. It was concluded that although no adverse effects were
observed, the practice would appear to have limited value as a means of in-
creasing selenium content in deficient animals.
DISCUSSION
Based on a review of the literature, it can be concluded that Se has
been studied extensively. Both Arsenic and Molybdenum have been studied to
a lesser extent. Although many factors such as application procedure, soil
condition, plant species, and animal species have been found to cause signi-
ficant variations in uptake of metals, it can be concluded that a key factor
in determining the suitability of flyash as a soil conditioner or ration
conditioner for any specific constituent is a complete analysis of all other
constituents. In particular, a thorough knowledge of the ratio of the level
of each constituent in the flyash amended soil to the original soil is neces-
sary. In the studies reviewed, a significant increase in concentration of
any constituent (generally greater than two) resulted in an observable in-
crease in that constituent in the crops being produced and in the livestock
fed those crops.
Furr and Parkinson conducted a national survey of the fly ashes from
21 states in 1975-1976 in which 45 elements were evaluated for chemical con-
tent as reviewed in a previous chapter of this report. It is significant
to note that the range of concentrations of elements varies widely from
state to state as shown in Table 4. For many of the elements, the range
is greater than 2 orders of magnitude. A brief comparison of these ranges
59
-------
23
with the typical soil used by Furr, et al. , reveals that at a 9:1 mix-
ture of soil to flyash that As, B, Ba, Ca, Cd, Cu, Fe, I, Mo, Pb, Sb, Se,
Sn, Sr, and U could potentially exist at concentrations greater than a factor
of 2 times the concentration in the soil. Although only three elements were
found in Purr's study with the particular ash used, sufficient evidence
exists to indicate that a case by case evaluation might be required for de-
termining the feasibility of flyash as an amendment to soil.
A final factor which further complicates the analysis of feasibility is
that the trace elements generally are preferentially found in discrete size
particles in the flue gas. As a result, the concentration of any given element
may vary significantly. Kaakinen, et al. , compared the ash collected in the
bottom ash centrifugal collectors, electrostatic precipitator, and wet scrubber
for Public Service of Colorado's Valmont Station, Unit No. 5, near Boulder,
Colorado. For example, selenium was found to be 1.9, 7.7, and 62 ppm for the
coal, mechanical collector ash, and electrostatic precipitator outlet ash,
respectively.
In conclusion, "the safe use of flyash in agriculture would therefore
require careful and persistent monitoring of the complete elemental composi-
tion of flyashes, that^Qf plants grown on them, and the tissues of foraging
animals" (Furr, et al_. ).
APPLICATION OF FLY ASH TO MINE SOILS
In recent years, studies have been conducted to determine if fly ash
might be used as a soil amendment in highly acidic strip mine soils where
vegetative reclamation is difficult. The acidic nature of strip mine spoil
has generally prevented rapid reclamation due to nutrient deficiencies re-
sulting from the low pH of the acid-mine spoils. The use of certain fly-
ashes has been found to aid the revegetation. Experiments have shown that
flyash mixed with mine spoils may raise the pH of acid soil as well as add
additional calcium, magnesium, and other needed elements. Further, the fly-
ash application may enhance the moisture0reiention ability, increase the
air capacity, and improve soil texture. ' However, flyash does not
normally contain sufficient phosphorus or nitrogen; therefore, a fertilizer
may be required. Although generally beneficial for vegetative reclamation,
the negative aspects of flyash addition (i.e. boron toxicity, selenium toxi-
city of vegetative cover to foraging animals) must still be considered.
FLY ASH NEUTRALIZATION CAPACITY
The primary benefit of flyash application to acid mine spoils is the
neutralization capacity of the ash. McLean, et al. , performed a series
of labortory tests on various samples of strip mine spoils by mixing them
with various percentages of flyash. For a flyash (pH = 10.6) the relation-
ship between application rate required to neutralize to pH = 7 and the ini-
tial spoil pH is shown in Figure 8 illustrating typical application rates.
Of several plants studied, it was noted that the neutralization capacity
varied significantly. The "neutralization capacity" (NC) was measured in
60
-------
...
"
"H,
i
£
-
c
£
:
c
7
20
30
40
50
%flv ash bv dry weight in spoil-fly ash mixture
I I I I I I I I
100 200 300 400
APPLICATION RATE Tons/Acre*
spoil sample number * To convert Tons/Acre to Metric Tons/Hectare
multiply by 2.2416
Figure 8. Fly Ash Requirements to Raise
Soil pH to 7
61
-------
terms of the number of mi Hi equivalents of HLO per 100 grams of flyash.
For the Mitchell Power Plant flyash (pH = 10:7), the NC was 45; whereas for
another plant's (Phillips Power Plant with a pH of 9.0) flyash, the NC was
only 3. Thus, the flyash application rate required to neutralize an acid
mine spoil would be approximately 15 times greater than with the pH = 10.6
ash. This represents a substantial increase,™ the cost of reclamation due
to shipping costs of flyash. McLean, et aJL , have also documented that the
NC of a single source of flyash may vary significantly. For instance, the
Mitchell Power Station NC was 9-99 at the 95% confidence level with 54 as
an average over a 9 month period. It was further noted that the use of
average spoil pH was not a good value to use for determination of the appli-
cation rate of flyash; rather,the extreme low pH was preferred due to the
logarithmic properties of the pH scale.
29
Keefer, et al_. , studied the application of flyash, sewage sludge, and
chicken manure to barren mine spoils to determine the effects of individual
applications versus various mixtures of three additives. Application of
flyash alone resulted in poor legume growth. Although pH was increased, the
nutrients were not present. Both alfalfa and lespedeza ground covers grew
well where all three wastes were supplied. Flyash combined with other waste
materials increased soil pH and P levels, and decreased levels of toxic ele-
ments such as Al, Mn, Ni. Typical application rates used with success were
22.4 metric tons/ha, 27 tons/ha and 45 tons/ha of manure, flyash. and sewage
sludge,2Eespectively. The conclusion reached by McLean, et a_[. , and Keefer,
et aj. , was that flyash alone had no significant effect due to nutrient
deficiencies; however, in combination with fertilizer it produced desirable
results. Further, it was recommended that test plot studies should be con-
ducted to determine the proper combination of the additives.
62
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Section 12
MINERAL WOOL INSULATION
BACKGROUND
With increasing shortages of energy and price increases associated with
home, office, and industrial heating and cooling, considerable emphasis is being
placed on insulation. Mineral wool is a competitive insulation product. Making
mineral wool from ash would result in decreased ash waste volumes and thereby
decrease waste disposal problems.
Research conducted at the Coal Research Bureau (CRB), West Virginia
University, from 1966-1970, indicated that it is possible to manufacture
mineral wool insulation from bottom ash, from fly ash, and from limestone
modified bottom ash and fly ash. At the-^iiyjs^owever, energy costs did not
make the alternative appear competitive. ' *
The primary raw material for conventional mineral wool production is
waste blast furnace slag from the steel industry. Sometimes fluxing agents
such as Ca and Mg salts are added to maintain proper chemical composition.
The slag is generally heated in a coke-fired cupola furnace to a molten
state (2600-2800°F). The slag is discharged to a concave metal wheel spin-
ning at 1000-1500 rpm which forces the slag off the edge in thin sheets.
Fine steam spray jets then cause the fibers to form. The fibers are col-
lected and then either granulated and bagged or resin treated and pressed
into batts. To use coal ash, it is recommended that a reverberating fur-
nace be used ratheg than a cupola due to the small particle size associated
with coal wastes.
In general, the viscosity of the molten ash and the "temperature of
critical viscosity" (TCV) determine whether a given slag can be used to manu-
facture mineral wool. TCV is defined as the point where the viscosity of
the liquid begins to increase rapidly with a small decrease in the liquid
temperature. Other conditions being the same, both fiber length and diam-
eter will increase with an increase in slag viscosity. Conversely, if the
viscosity is lowered below a given point^thgre will be an absence of fiber
with only spherical solids being formed. '
Most manufacturers use the acidity modulus, usually referred to as the
acid/base ratio (wt % S109 + wt % Al?0,/wt % CaO + wt % MgO), of the raw
materials as a guide in attaining th5 proper TCV. Generally, the ratio is
maintained between 0.8 and 1.2. The addition of a limestone or dolomite
flux i9/,the proper proportion is generally used to adjust the acid/base
ratio.74'75
63
-------
The CBR studies investigated limestone, dolomite, and modified fly ash
as fluxing agents. )/:>'/D
TVA has expressed an interest in producing mineral wool insulation from
wet bottom ash generated at Allen and Paradise Steam Plants. Since both
plants are wet bottom boilers, energy savings result from using molten slag
tapped from the furnace as compared to having to remelt slag. The tempera-
ture of the molten slag must be raised in order to produce mineral wool.
TVA has conducted bench §c,ale and pilot scale work and found the process to
be technically feasible. At the present time, implementation has been
halted due to the question of radioactivity associated with fly ash and
bottom ash.
QUALITY OF MINERAL WOOL
Table 17 presents a comparison of mineral wool production factocs for
the CBR coal ash studies and for the primary mineral level industry.
Table 18 presents characteristics of mineral wool made from coal and those
of commercial mineral wool. Table 18 summarizes slag for bituminous and
lignite ash as well as for modified (limestone) ash.
Commercial wool is generally brown in color, whereas most of the other
wools are lighter in color. Also, the average coal ash wool has a smaller
fiber diameter than commercial wool. The corrosion characteristics are only
slightly different. The quality of coal ash wool is similar to commercial
wool.'8
MARKET CONDITIONS
The mineral wool industry7growth was from a sales value of $100 x 10
in 1950 to6$5QO x 10° in 1968./0 In 1976, the industry sales volume was
$1335 x 10 . With rising energy prices, decreases in supply, and available
tax credits, the national increase in insulation sales is a certainty.
Since most commercial mineral wool is made from steel slag, if coal ash
mineral wool can be economically competitive, the future demand could be
met by coal ash mineral wool. Also, since fiberglass insulation is petroleum-
based, coal ash mineral wool would provide an opportunity to reduce petro-
leum use. On a national basis, coal ash usage for insulation may reduce the
cost of insulation due to the somewhat limitless resource base of ash.
Economics
The Coal Research Bureau presented the following advantages and dis-
advantages of using coal ash for mineral wool production:
Advantages
(1) No mining costs are incurred as compared to use of wool rock.
64
-------
(2) Little raw material preparation is required as compared to use of
blast furnace slag.
(3) Raw materials costs are markedly reduced because fluxing agents
are not required.
(4) Raw materials are available near virtually all major markets,
thus minimizing transportation costs.
(5) Some forms of coal and ash wool retard corrosion of piping, thus
reducing piping maintenance costs.
(6) High silica and alumina content of coal ash wool improve its
insulating and heat duty properties as compared to other types
of mineral wool.
Disadvantages
(1) Fine-particle size of coal ash required use of reverberatory
furnaces for melting on a batch or semi-batch basis. Continuous
cupolas, which are thermally more efficient, cannot be used.
(2) Due to color of the finished mineral wool, bituminous and anthra-
cite ashes are not suitable for use in exposed surfaces (eg,
acoustic tile). Lignite and sub-bituminous ashes are, however,
suitable.
TVA estimated that a 4 ton per hour plant built at Allen Steam Plant
could manufacture coal ash mineral wool insulation at $132 per ton. It was
also indicated that the 1978 market price was $200 per ton.-^TVA's cost
estimate included capital amortization and operating costs.
Summary
Mineral wool insulation can be produced from coal ashes. Properties of
coal ash mineral wool are similar to those of commercial wools. Research
has indicated that not only bottom ash, but fly ash and limestone modified
fly ash can be processed into mineral wool insulation as well. With a
rapidly expanding demand for insulation, coal ash mineral wool can supple-
ment the existing market, but it will not substitute for the existing commer-
cial wools. In a study by TVA, coal ash mineral wool can be produced at a
cost significantly below commercial wools.
65
-------
Table 17. A COMPARISON OF MINERAL WOOL PRODUCTION FACTORS
Raw Material
Furnace
Fuel
Melting Temp.
Blowing Temp.
Steam
*
Air
Recovery
Industry
Wool rock-(calcareous sandstone
or shale) or blast furnace slag +
CaC03 + Si02
Cupola-water jacketed and/or
reverberatory furnaces
Coke
Gas or oil in the reverberatory
2550 - 3400°F
2600 - 3200°F
85 - 125 psig
50-125 psig
35 - 75% by weight of charge
Coal Research Bureau
Coal-ash slag and/or flyash
Carbon arc
Electricity
2700 - 3200°F
2800 - 3150°F
60 - 100 psig
**
50 - 65%
A spinner arrangement may be used and may be combined with an annular gas nozzle
system.
**
Percent recovery varies with the individual slags or flyashes and with individual
test runs. The numbers reported are the range of averages for four or more
test runs on each slag or ash. With industrial equipment and techniques, higher
recoveries can reasonably be expected.
66
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Table 18. CHARACTERISTICS OF MINERAL WOOL MADE FROM COAL ASH
Pouring
Temp.,
Ash
•>
j
Modified
Ash
Commercial
Wool
A
B
C
D
*E
F
G
H
J
K
L
M
N
3020
3100
3000
3050
3050
3100
3100
3000
2300
2600
2600
2500
3000
Air Pressure,
psig
95
95
90
90
90
95
95
95
80
85
80
80
100
Acid/Base
Ratio
6.15
10.04
10.01
9.20
1.61
17.8
14.6
14.4
1.27
1.00
1.32
1.40
9.03
Average
Fiber
Diameter
Microns
7
6
8
6
5
11
6
12
7
12
9
9
14
11
Fiber
Color
Light Gray
White
Brown
Light Gray
White
Light Gray
Gray
Light Buff
Light Brown
Light Gray
Whi te
Light Gray
Gray
Brown
Corrosion Retarding Tests
Rusting Etching
Very Slight
Very Slight
Slight
Less Than
Control Strips
Slight
Very Slight
Slight
Slight
Very Slight
Very Slight
Very Slight
Very Slight
Not Tested
Less Than
Control Strips
None
5%
5%
5%
None
5%
None
5%
None
5%
None
5%
Not Tested
10%
Lignite Ash
-------
Section 13
BITUMINOUS PAVING MIXTURES
INTRODUCTION
Poweg plant bottom ash has been utilized in both base and surface
courses. In this use, bottom ash is used as a full or partial substitute
for conventional aggregates in bituminous mixtures. In order to insure
that a particular bottom ash is a potential substitute for a conventional
aggregate, the properties of the bottom ash need to be measured. The impor-
tant properties include: (1) particle size distribution; (2) relative density;
(3) soundness. Of these factors, size distribution is considered to be
the most important. Soundness is defined as^the ability of the aggre-
gate to withstand abrasion and/or crushing. As a general rule, aggregates
with a percentage loss equal to or less than 40 percent in the Los Angeles
abrasion machine are satisfactory. Durability of the aggregate under freez-
ing and thawing conditions is also very important.
81
Majidzadeh, et a_L , has shown that a number of different bottom ashes
meet the specifications of conventional aggregates.
ASPHALT MIX DESIGN
The design of an asphalt mix can be based upon one of several methods.
The two most widely used techniques are the Marshall and Hveem methods.
The Marshall method consists of making specifications of aggregate and bitum-
inous mix by varying the amounts of asphalt. Typical amounts might be 4,
4*2, 5, 5h percent, and so on. Specimens are compacted using a compact!ve
effort applicable to the desired loading conditions. The best mix results
when the stability is at a maximum and where the voids between the grains
are almost full. After the optimum asphalt content is selected, the specimen
must then fulfill a specific design criteria.
TVA INTEREST
During the past two years, TVA has conducted several tests associated
with bottom ash. (See Appendix A for specific details of tested samples using
the Marshall method.) The Marshall method was used in testing bottom ash
from the Watts Bar Steam Plant and the Kingston Steam Plant. The binder
used in the tests was an asphalt cement obtained from Volunteer Asphalt
Company in Knoxville.
68
-------
For the Watts Bar samples, the bottom ash was not considered suitable
as a base aggregate. For a surface course aggregate, the material larger
than the 3/8 inch sieve had to be removed. The optimum blend for asphalt
content was estimated at 8.5 percent. This is considered too high to be
economical.
For the Kingston Steam Plant samples, the bottom ash was extremely
variable in terms of particle size. For a base course, the best asphalt
cement content was estimated at between 6.0 and 6.5 percent by weight. The
samples could produce a base course that meets all requirements for a Ten-
nessee Department of Transportation grading B, base course.
For surface course tests, the optimum asphalt content is higher than
8.5 percent by weight. Although a surface course material can be made which
meets all requirements (with the possible exception of the minimum flow
requirement), the necessary asphalt content is too high to be considered
economical.
At this time, one test in utilizing ash for road surface aggregate is
underway by TVA. A 1.4 mile section of Swan Pond Road near the Kingston
Steam Plant has been resurfaced utilizing bottom ash as an aggregate.
The use of bottom ash is a function of economics. With increasing
asphalt costs and higher required contents for bottom ash, it appears that
bottom ash will continue to be a marginal material except in the case of
areas which lack an adequate supply of aggregate.
69
-------
Section 14
RECOMMENDATIONS
As a result of conducting this study, the authors recommend that the
following studies be conducted:
1. Conduct a feasibility study of the conversion of existing wet fly
ash collection systems to dry collection and storage. This would lead to
better fly ash utilization options within the TVA system.
2. Since some cenospheres do not float, study the mechanical proper-
ties of ash to learn how to separate nonfloating cenospheres from ash.
3. As well as proceeding with Mineral Gas Co. in the area of mineral
recovery, TVA should compare other process choices and options to see if a
preferential process would exist for the TVA region.
4. Conduct an integrated TVA-wide market study for the potential uses,
markets, generation points, transportation, and feasibility of extensive
coal ash utilization.
70
-------
Section 15
REFERENCES
1. Personal communication with Mr. R.W. Cannon, Materials Design Section,
Tennessee Valley Authority, March 16, 1979.
2. TVA Ash Use Data Summary, Power Division, TVA, Chattanooga, Tennessee.
3. Personal communication with Mr. Jerry Chumley, Structural Section,
Division of Power Production, Tennessee Valley Authority, May 25, 1979.
4. Ray, S.S. and F.G. Parker. Characterization of Ash from Coal-Fired
Power Plants, EPA-600/7-77-010, January 1977.
5. Furr, A.K. and T.F. Parkinson. "National Survey of Elements and Radio-
activity in the Fly Ashes: Absorption of Elements by Cabbage Grown in
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6. TVA data summary supplied by Mr. Frank Parker, TVA, Chattanooga, TN.
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Kentucky Power Plant Ash," Fifth International Ash Utilization Sympo-
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8. Kaakinen, J.W., R.M. Jorden, M.H. Lawasani and R.E. West. "Trace
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71
-------
13. Engle, C.F. alnd J.P. Capp. "Fly Ash: New Hope for Strip Spoil,"
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15. Martens, D.C. "Availability of Plant Nutrients in Fly Ash," Compost
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17. Mulford, F.R. and D.C. Martens. "Response of Alfalfa to Boron in
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18. Plank, C.O. and D.C. Martens. "Boron Availability as Influenced by
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19. Holliday, R., W.N. Townsend and D. Hodgson. "Plant Growth on Fly
Ash," Nature (London), Vol. 176, pp. 983-984, 1955.
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23. Furr, A.K., et al_. "Multi-Element Uptake vy Vegatables and Millet
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24. Stoewsand, G.S., W.H. Butenmann and D.J. Lisk. "Wheat Grown on Fly
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25. Furr, A.K., T.F. Parkinson, C.L. Heffron, J.T. Reid, W.M. Hashek, W.H.
Gutenmann, C.A. Bache, L.E. St. John, Jr., and D.J. Lisk. "Elemental
Content of Tissues and Excreta of Lambs, Goats, and Kids Fed White
Sweet Clover Grown on Fly Ash," Journal of Agriculture and Food Chemistry,
Vol. 26, No. 4, pp. 847-851, 1975:
26. Furr, A.K., T.F. Parkinson, C.L. Heffron, J.T. Reid, W.M. Hashek,
W.H. Gutenmann, I.S. Pakkala and D.J. Lisk, "Elemental Content of Tis-
sues of Sheep Fed Rations Containing Coal Fly Ash," Journal of Agricul-
ture and Food Chemistry. Vol. 26, No. 6, pp. 1271-1274, 1978.
72
-------
27. Ehlig, C.F. , W.H. Allaway, E.E. Gary and J. Kubota. "Differences
Among Plant Species in Selenium Accumulation from Soils Low in Avail-
able Selenium," Agronomy Journal, Vol. 60, pp. 43-47, 1968.
28. McLean, E.T. and M.T. Dougherty. "Hillman State Park: Final Assess-
ment of Fly Ash as a Solid Modifier for Acid Strip Mine Spoil," pre-
sented at 5th International Ash Utilization Symposium, Atlanta,
Georgia, sponsored by National Ash Association, February 1979.
29. Keefer, R.F. , R.N. Singh, F. Doonan, A.R. Khawaja and D.J. Horvath.
"Application of Fly Ash and Other Wastes to Mine Soils as an Aid in
Revegetation," presented at 5th International Ash Utilization Sym-
posium, Atlanta, Georgia, sponsored by National Ash Association,
February 1979.
30. Turner, C.J., Letter of Communication with TVA, July, 1977, from Ceno-
Science Research, Inc.
31. Ashby, J.B. and J. Carroll. "Australian Cenospheres," presented at the
5th International Ash Utilization Symposium, Atlanta, Georgia, February
1979.
32. Zeeuw, H.J. and R.V. Abresch. "Cenospheres from Dry Fly Ash," Ceno-
Science Research Inc., Minneapolis, Minnesota.
33. Faber, John H., "A U.S. Overview of Ash Production and Utilization,"
Paper A-l, Fifth International Ash Utilization Symposium of National
Ash Association, Atlanta, Georgia, February 1979.
34. Gulp, A.W., Jr., Principles of Energy Conversion, McGraw Hill, New
York, NY, 1979.
35. Weeter, D.W., J. Niece and A.M. Digioia. "Water Quality Management for
Coal Fired Power Plant Solid Wastes," Proceedings 34th Purdue Industrial
Waste Conference, Lafayette, Indiana, 1974.
36. Seely, F.G., R.M. Cannon and W.J. McDowell. "Chemical Development of
New Processes for the Recovery of Resource Materials for Coal Ash,"
Proceedings of the Fifth International Ash Utilization Symposium,
Atlanta, Georgia, February 25-27, 1979 (available through National
Ash Association, Washington, D.C.).
37. National Association of Recycling Industries (NARI), "Recycling
Resources," Washington, D.C., August 1979.
38. Murtha, M.J. and G. Burnet. "New Developments in the Lime-Soda System
Process for Recovery of Aluminum from Fly Ash," Proceedings of the
Fifth International Ash Utilization Symposium, Atlanta, Georgia,
February 25-27, 1979 (available through National Ash Association,
Washington, D.C.).
73
-------
39. Canon, R.M., et aJL "Metal Removal from Coal Ashes and Wastes," Pro-
ceedings of the ASCE/EPRI Workshop on Solid Waste R & D Needs for
Emerging Technologies, San Diego, California, April 25-27, 1979
(available through the American Society of Civil Engineers, New York).
40. Murtha, M.J. and G. Burnet. "Processes to Increase Utilization of Power
Solid Waste," Proceedings of the ASCE/EPRI Workshop on Solid Waste R & D
Needs for Emerging Technologies, San Diego, California, April 25-27,
1979 (available through the American Society of Civil Engineers, New
York).
41. Personal Communication with T.L. McDaniel, TVA, Energy Research,
Chattanooga, Tennessee, June 12, 1979.
42. Canon, R.M., F.G. Seeley and J.S. Watson. "Engineering Analysis and
Comparison of New Processes for the Recovery of Resource Materials
from Coal Ash," Proceedings of the Fifth International Ash Utilization
Symposium, Atlanta, Georgia, February 25-27, 1979 (available through
National Ash Association, Washington, D.C.).
43. Minnick, L.J. "The Application of the Roto-Flux Magnetic Separator
for Pulverized Coal Fly Ash," American Society of Mechanical Engineers,
Paper 61-WA-313. 1961.
44. Joppa, E.L. "Heavy Medium for Gravity Separation," U.S. Patent 3021,
282, February 1962.
45. Baux, J.J., "Canadians Pioneer New Fly Ash Processing System," Mineral
Processing. March 16, 1979.
46. Murtha, J.J. and F. Burnet. "The Magnetic Fraction ofCoal Fly Ash:
Its Separation, Properties and Utilization," Proceedings of the Iowa
Academy of Science. 85(1). 1978, pp. 10.
47. Roy, N.K., M.J. Murtha and G. Burnet. "Use of the Magnetic Fraction
of Fly Ash as a Heavy Medium Material in Coal Washing," Proceedings
of the 5th Sympgs ium on j\sh Utl1ization. Atlanta, Georgia, February,
1978, (National AsTi Association, Washington, D.C.).
48. Klotten, Rudolph, "Lightweight Aggregate from Sintered Ash," Fourth
International Ash Utilization Symposium, St. Louis, Missouri, March,
1976.
49. Moss, Derek, "Lightweight Aggregate Production and Utilization from
Fly Ash in the United Kingdom," Fourth International Fly Ash Utiliza-
tion Symposium, St. Louis, Missouri, March, 1976.
50. Technical and Economic Factors Associated with Fly Ash Utilization,
Final Report to U.S.E.P.A., Aerospace Corporation, El Segundo,
California.
74
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51. Poporics, Sandor. Concrete-Making Materials, Hemisphere Publishing
Corporation, Washington, 1979.
52. American Concrete Institute Standards 1966, ACI, Inc., Detroit, Mi-
chigan, 1966.
53. Orchard, D.F. Concrete Technology, Applied Science Press, London,
1979.
54. Lyden, F.D. Concrete Mix Design, Applied Sciences Publishers, LTD,
London, 1972.
55. Taylor, W.H. Concrete Technology and Practice, American Elsevier,
New York, 1969.
56. Principles of Qua!ity Concrete, Portland Cement Association, John Wiley,
New York, 1975.
57. Morrison, R.J. "Marketing and Economics, Technology and Utilization
of Power Plant Ash," Arizona State University, 1978.
58. Lovewell, C.E. and George W. Washa. "Proportioning Concrete Mixtures
Using Fly Ash," American Concrete Institute Journal, June, 1958.
59. Cannon, R.W., "Proportioning Fly Ash Mixes for Strength and Economy."
American Concrete Institute Journal, November, 1968.
60. Bloem, D.L. "Effect of Fly Ash in Concrete National Ready Mix Associ-
ation," Publication No. 48, January 1954.
61. David, R.E. "Properties of Cements and Concrete Containing Fly Ash,"
American Concrete Institute Journal, June, 1979.
62. Deb, P.K., et ah "Removal of COD from Wastewater by Fly Ash," Pro-
ceedings 21st Purdue Industrial Waste Conference, Lafayette, IN,
p. 848, May 1966.
63. Eye, J.D. and T.K. Basu. "The Use of Fly Ash in Wastewater Treatment
and Sludge Condition," Journal of the Water Pollution Control Federation,
42(5), Part 2, R125 (1970).
64. Tenney, M.W. and W.F. Echelberger, Jr. "Fly Ash Utilization in the
Treatment of Polluted Waters," Third International Ash Utilization
Symposium, 1974.
65. Chu, et al_. "Removal of Complex Copper-Ammonia Ions from Aqueous
Wastes wth Fly Ash: Journal of the Water Pollution Control Federation,
50(9), 2157 (1978).
66. Gangoli, N. , et al^. "Removal of Heavy Metal Ions from Aqueous Solutions
with Fly Ash^Third International Ash Utilization Symposium, 1974.
75
-------
67. Weeter, D.W., et aJL "Water Quality Management—Power Station Ashes,"
Proceedings, 29th Purdue Industrial Waste Conference, Lafayette, In.,
1974.
68. Michael Baker, Jr., Inc. "State of the Art of FGD Sludge Fixation,"
FP-671, Electric Power Research Institute, Palo Alto, California,
January 1978.
69. Phillips, H.L. "An Evaluation of the Waste Product from a Calcium
Based Dry Flue Gas Desulfurization System," M.S. Thesis, University of
Tennessee, Knoxville, Tennessee, Agust 1979.
70. Smith, C.L. "The Largest Use of Fly Ash-Scrubber Sludge Disposal,"
presented at the Fifth International Ash Utilization Symposium,
Atlanta, Georgia, February 25-27, 1979.
71. Chen, D.Y.G. "The Stabilization of Flue Gas Desulfurization Sludge
by Addition of Lime and Fly Ash," M.S. Thesis, University of Tennessee,
Knoxville, Tennessee, 1977.
72. TVA Memorandum to O.W. Kochtitzley from Gener Farmer, March 20, 1978.
73. TVA Memorandum to O.W. Kochtitzley from Gener Farmer, February 21, 1978.
74. Humphreys, K.K. and W.F. Lawrence. "A Promising Possibility: Production
of Mineral Wool from Coal-Ash Slag," Report No. 20, Coal Research Bureau,
West Virginia University, Morgantown, WV, October, 1966 (also published
October 1966 in Coal Mining and Processing).
75. Humphreys, K.K. and W.F. Lawrence. "Production of Mineral Wool Insulat-
ing Fibers from Coal Ash Slag and Other Serviced Waste Materials,"
Report No. 53. Coal Research Bureau, West Virginia University, Morgantown,
WV, March, 1970.
76. Humphreys, K.K. and W.F. Lawrence. "Producing Mineral Wol from By-
Products," Mineral Processing (March, 1970).
77. Parker, F.G. and T.L. McDaniel. "Production of Mineral Wool from Coal
Slag," Preliminary Report, TVA, Energy Research, Chattanooga, Tennessee,
November, 1978.
78. Lawrence, W.F. "Mineral Wool Production from Coal Ash-A Progress
Report," Report No. 38, Coal Research Bureau, West Virginia University,
Morgantown, WV, 1968.
79. U.S. Department of Commerce, Bureau of the Census, "Annual Survey of
Manufacturers," 1972.
80. Yoder, E.J. and M.W. Witczak. Principles of Pavement Design, 2nd Edi-
tion, John Wiley and Sons, Inc., New York, 1975.
76
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81. Magidzadeh, K., et aL "Material Characteristics of Power Plant Bottom
Ashes and Their Performance in Bituminous Mixtures: A Laboratory In-
vestigation," Fifth International Ash Utilization Symposium, Atlanta,
Georgia, 1979.
82. Sargious, M. Pavements and Surfacing for Highways and Airports,
Hal stead Press, New York, 1975.
83. Eisenbud, M. and H. Petrow. "Radioactivity in the Atmosphereic Effluents
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77
-------
Appendix A
A-l
-------
Table A-l. FLY ASH TEST DATA*
Steam Plant
Unit No.
Date
RS-413
Gallatin
#1
3-13-78
RS-414
Gallatin
#2
3-13-78
RS-415
Gallatin
#3
3-13-78
RS-41 6
Gallatin
#4
3-13-78
Physical Properties
Specific gravity 2.43 2.43 2.33 2.40
Available alkali, %
% passing 325 sieve (wet) 86.1 85.0 75.2 89.4
Loss on ignition, % 1.60 1.55 1.69 3.56
Pozz. index with cement, % 83 77 74 88
Pozz. index with lime, psi 1008 955 939 955
Water Requirement, % 95 96 98 94
Multiple Factor, %
(L01x325 % retained) 22.2 23.3 41.9 37.7
pH of fly ash 11.60 11.50 11.60 11.40
pH of mortar „ - 12.00 12.25 12.25 12 25
Elaine-fineness,, cmVcrn 8011 6721 7036 3251
Job Sand Mortar Data
% cement by volume 11.43 11.47 11.40 11.57
% fly ash by volume 8.89 8.92 9.25 9.11
Flow at IS drops 136 129 135 133
Water/cement ratio .615 .629 .643 .522
% entrained air 10.67 10.12 10.68 9.61
Compressive strength, psi
3 day 2962 2771 2580
7 day 3973 3790 3568 3997
28 day 6099 5271 5621 6417
90 day 8694 8556 8222 9352
Percent of control
3 day 127 119 111
7 day 128 122 115 129
28 day 144 126 133 152
90 day 174 171 165 187
Chemical Properties
Silicon Dioxide, SiO?,% 49.45 49.87 49.68 50.72
Calcium oxide, CaO,% 5.80 5.45 5.00 5.38
Ferric oxide, Fe-0,,,% 14.90 15.40 15.40 15.40
Aluminum oxide, A1~0V% 19.48 18.80 18.35 18.35
Magnesium oxide, MgO?% 0.98 1.02 1.02 1.05
Sulphur trioxide, SO.,% 1.42 1.57 1.58 1.54
Moisture content,% •* 0.37 0.32 0.29 0.28
A-2
-------
Table A-l (continued)
Steam Plant
Unit No.
Date
RS-413
Gall a tin
#1
3-13-78
RS-414
Gallatin
#2
3-13-78
RS-41
Gallatin
#3
3-13-78
RS-41 6
Gallatin
#4
3-13-78
CL, ppm 52.0 60.0 46.0 60.0
N03> ppm 0.4 0.5 0.4 0.3
Cement Properties
Brand and type Marquette type II
C A,% 4.50
Specific gravity 2 3.15
Blaine fineness, cm /gm 4171
*
Tennessee Valley Authority - Singleton Materials Engineering Laboratory
A-3
-------
Appendix B
REPORT ON ASPHALT MIX DESIGN
By A.B. Moore
B-l
-------
FINAL REPORT
Prepared by
A.B. Moore, Consultant
February 24, 1977
Subject: Bituminous Mix Design Utilizing Bottom Ash from Kingston Steam
Plant.
I. Introduction:
This report presents the results of laboratory testing to determine the
mix design and optimum asphalt content utilizing aggregate obtained from the
Kingston Steam Plant. Two aggregate gradings were investigated. The first
grading utilizes a sample of material conforming to the gradation require-
ments of the TDOT, Grading B for base courses. The second grading evaluated
was obtained by scalping the material above the 3/8 in. sieve from the first
grading. This sample conforms to the TDOT, Grading D for surface courses.
II. Materials:
The binder used in these tests was an asphalt cement obtained from Volun-
teer Asphalt Company. The viscosity grading was AC-20, and the specific gravity
was 1.000.
The table below presents the gradations of both fractions included in
the tests. The sieve analysis was performed in the TVA labs.
Sieve Size % Passing, D Specifications % Passing, B Specification
1-1/2
I
3/4
1/2
3/8
4
8
16
30
50
100
200
100.0
100.0
100.0
100.0
90.6
72.1
53.1
-
23.5
14.9
9.2
3.0
100.0
100.0
100.0
100.0
88 - 100
56 - 80
40 - 60
-
18 - 38
8-26
5 - 15
2-10
100.0
94.5
86.2
73.3
66.4
52.8
38.9
25.9
17.2
10.9
6.7
3.0
100.
-
65 -
-
-
30 -
20 -
-
8 -
-
1 -
0 -
0
90
55
45
25
12
7
Eff. S.G. (Bulk) for D grading = 2.34 for B grading =2.42
B-2
-------
III. Procedures:
Test procedures were as described in the following ASTM Designations:
D-70, Specific Gravity of Semi-Solid Bituminous Materials
D-1559, Resistance to Plastic Flow of Bituminous Mixtures Using
the Marshall Aparatus
D-2726, Bulk Specific Gravity of Compacted Bituminous Mixtures
Using Saturated Surface-Dry Specimens
Since the proposed use for these bituminous mixes is on the secondary road
system, a 50 blow compactive effort (Traffic Category - Medium) was used in
preparing the specimens for test.
IV. Specification Requirements for the Compacted Samples:
Surface Mix Base Mix
Test Property Min. Max. Min. Max.
Stability, Ibs.
Flow, 0.01 in.
Percent air voids
500
,8
3
-
18
5
500
8
3
-
18
8
Percent voids in mineral aggre-
gate 16 - 12
V. Test Results:
The results of all tests are summarized in Figures B-l and B-2. Figure B-l
presents the results of tests on the Base mixture, and Figure B-2 presents the
results of tests on the surface mixture.
VI. Discussion of Results:
The bottom ash produced by the Kingston Steam Plant is extremely vari-
able. Specific gravity measurements vary with each fraction of particle size
as well as within each particle size. The Value measured depends on how much
of the expanded clinker type particle and how much of the heavy slag type
particle is included in the sample being tested. This variation produced a
considerable problem during the Density-Voids analysis phase of the evalua-
tion. Samples with the same asphalt content, by weight, had considerable
variation in asphalt content, by volume. The analysis of results was made
on a weight as well as a volume basis. However, only the weight basis analy-
sis is presented since the effect of the volume analysis was to shift the
plotted points slightly in a lateral direction. No appreciable error in the
determination of optimum asphalt content is introduced by using this type of
analysis.
B-3
-------
1) Grading B, Base Course Analysis:
By referring to Figure B-l, it may be observed that the optimum asphalt
content with respect to stability and unit weight appears to be be-
tween 6.0 and 6.5 percent asphalt, by weight. The voids curves in-
dicate that an asphalt content of 6.5 percent will provide a percent
voids in the compacted mix of approximately 4.5% and a percent voids
in the mineral aggregate of approximately 17%. As stated above the
voids analysis is subject to question, due to the variable aggre-
gate specific gravities. The flow value in all samples was quite
low, even though all samples met the minimum requirement of 8. This
is attributed to the highly textured surface of the aggregate par-
ticles, which will prevent the particles from moving easily under
load. The effect of this low flow value may be to produce a mix-
ture which does not posess a high degree of workability as it is
being placed and compacted.
2) Grading D, Surface Course Analysis:
The analysis curves for the surface course mixture, shown in Fig-
ure B-2, indicate that an asphalt content as high as 8.5 percent is
still below optimum. In designing the experiment it was believed
that the finer graded aggregate of the surface course would re-
quire a higher asphalt content than the base course aggregate,
but the test results indicate that it was even higher than expected.
Since this high asphalt content borders on being uneconomical, fur-
ther testing of samples with higher asphalt contents was regarded
as unwarranted at this time. The results which are presented in-
dicate that a surface mixture can be produced from this material
that will meet or exceed all requirements with the possible excep-
tion of the minimum flow requirement. All samples tested had flow
values less than 7, which does not comply with the specification.
Again, it appears that the coarse textured particles are concen-
trated in the finer particle size range, and consequently the lower
flow values are appearing in the finer mixtures.
VII. Conclusions and Recommendations:
1) The Kingston Steam Plant ash can be utilized to produce a satis-
factory base mixture conforming to the TDOT, Grading B. The asphalt
content required to produce the optimum properties is 6.5 percent,
by weight.
2) If an emulsified asphalt is used as the binder in the proposed
demonstration section, the amount of emulsion to be used will de-
pend on the residue from distillation to indicate the asphalt
cement content of the emulsion, which would be equivalent to 6.5
percent, by weight.
3) It is recommended that some type of travel plant be utilized for
the mixing of materials rather than a blade type mixing operation.
This will insure a more thorough coating action and will reduce
segregation.
4) Testing of the ash should also involve a determination of whether
an anionic or cationic emulsion should be used as the binder. Some
B-4
-------
UNIT WEIGHT Ibs/ft3
O GJ U> CJ U U> *
00 O ** *• O- 00 C
L
/
^
i
i
^s
i
N
QQ
I
14
12
10
8
6
4
2
567
%Bitumen. Weight
IOUU
1600
1400
1200
1000
800
600
X
^ri
r
\
t
f~~
\
~N>
\
\
567
% Bitumen. Weight
567
% Bitumen, Weight
fc VOIDS, COMPACTED MIX
O N> *• O- 0> O *
^
^1
^
/
i
^-~,
k
k
^-—^
567
% Bitumen, Weight
22
20
< 18
# 16
14
n
-*=l
—L
r™^— ^—I
2
J
^
\
L
^
X
/
567
% Bitumen. Weight
Bituminous Mix Design
MARSHALL METHOD
Asphalt. AC-20
Aggregate. TVA - Kingston Ash
Gradation: TDOT, Grading B (Ba*a)
Compaction: 50 Blow
Tested: 2-18 & 19-77
Tested by: A.B. Moore
Figure B-l. Bituminous Base Mix Design Using Kingston Ash
B-5
-------
[T WEIGHT -Iba /ft3
- — Jo N> »0 C
J O O *- 00 K,
— »-
g
irto
f**"^ t
^^4
t
k
^
<
**'^ ^
^- '
k
A
1800
14
12
7 8
% Bitumen,Weight
7 8
% Bitumen,Weight
7 8
Bitumen,Weight
1— I
i
% VOIDS.COMPACTED
•J *. O- CD O K
N
N
\
L
A
\
I
i
"X
t
\
t
VS.
678
%Bitumen, Weight
7 8
% Bitumen.Weight
Bituminous Mix Design
MARSHALL METHOD
Asphalt: AC-20
Aggregate: TVA- Kingston Ash
Gradation : TDOT, Grading D 'Surface
Compaction: 50 Blow
Tested: 2-18&19-77
Tested by: A.B.Moore
Figure B-2. Bituminous Surface Mix Design Using Kingston Ash
B-6
-------
of the particles resist coating, either from the fly ash dust ad-
hering to the larger particles or due to the presence of other
minerals, such as pyrite.
5) Solely on an experimental basis, the B Grading mixture might be
used as a surface mix. The gradation does not comply with any of
the specified TDOT mixes for surface use, but the other properties
of the mix do meet the requirements for a surface mixture. How-
ever, two precautions should be taken if it is utilized in a
surface mix:
a) First, the large maximum particle size (1-1/2 in.) will re-
quire that the surface layer before compaction should not be
less than 2 inches thick and preferably 2-1/4 in. thick.
b) Second, this mixture is relatively porous, and a fairly heavy
tack coat should be used to seal the underlying layers from
moisture penetration.
6) Although the D Grading mixture has not been fully evaluated, it
could be utilized, again on an experimental basis in the proposed
demonstration project, to produce a satisfactory surface mix. The
recommended asphalt content for such a mix would be 8.5 to 9.0 per-
cent, by weight. This asphalt content should produce a mix meeting
all the requirements with the exception of the flow requirement.
However, this high asphalt content will probably not produce a
very economical mix. However, due to the low density of the mix-
ture, utilizing this aggregate will provide an increased coverage
of approximately 20 percent when compared to a mix utilizing nor-
mal weight aggregate. The equivalent asphalt content for a normal
weight aggregate mixture would be about 7 percent.
7) Finally, the properties of the mixes utilizing the recommended
asphalt contents should be as follows:
Property Surface Mix Base Mix
Density, lbs/ft3 124 135
Stability, Ibs 1400 1500
Flow, 0.01 in. 7 9
% Voids, compacted mix 4 4.5
% Voids in the mineral aggre-
gate 22 17
B-7
-------
FINAL REPORT
Prepared by
A.B. Moore, Consultant
January 12, 1978
Subject: Bituminous Mix Design Utilizing Bottom Ash from Watts Bar Steam
Plant.
I. Introduction:
This report presents results of laboratory testing to determine the mix
design parameters and optimum asphalt content utilizing aggregate obtained
from the Watts Bar Steam Plant. Tests were conducted using the facilities
of the Department of Civil Engineering, The University of Tennessee, Knox-
vilie. Two aggregate gradings were investigated—first, the bottom ash as
received from Watts Bar; and second, this same ash after the material re-
tained on the 3/8 inch sieve had been removed. Neither of these fractions
were graded to meet a paving specification, but since further aggregate pro-
cessing would result in additional cost on a commercial basis, it was de-
cided to evaluate the possibilities of the material on an "as received" basis.
II. Materials:
The binder used in the tests was an asphalt cement, AC-20, obtained from
the Volunteer Asphalt Company in Knoxville. Lab tests indicate the specific
gravity is 1.015.
The table below shows the gradations of both aggregate fractions tested.
The sieve analysis and aggregate specific gravities were furnished by TVA.
The specification referred to as "D" is that specified by the TDOT for a
surface course, and the specification "B" is that specified by the TDOT for
a base course material. This information is furnished for comparative pur-
poses, only.
As Received +3/8 Scalped
Sieve Size Spec. "D" % Passing Spec. "B" % Passing
1-1/2 100 100.0 100 100.0
1 100 100.0 - 99.2
3/4 100 100.0 65-90 98.2
1/2 100 100.0 - 95.1
3/8 88-100 95.4 - 90.7
4 56-80 82.0 30-55 78.0
8 40-60 66.5 20-45 63.3
16 - 33.8 - 32.1
30 18-38 18.2 8-25 17.2
B-8
-------
(Con't.)
Sieve Size
50
100
200
Spec. "D"
8-26
5-15
2-10
As Received
% Passing
11.2
7.2
5.0
Spec. "B"
_
1-12
0-7
+3/8 Scalped
% Passing
10.6
6.8
5.0
Effective SG (Bulk): "D" Grading = 2.56 "B" Grading = 2.51
III. Procedures:
Test procedures were as described in the following ASTM Designations;
D-70, Specific Gravity of Semi-Solid Bituminous Materials
D-1559, Resistance to Plastic Flow of Bituminous Mixtures Using
the Marshall Apparatus
D-2726, Bulk Specific Gravity of Compacted Bituminous Mixtures
Using Saturated Surface-Dry Specimens
Since relatively low stability values were expected, due to the aggregate
grading problems, it was decided to use a 75 blow compactive effort in pre-
paring the Marshall samples for test.
IV. Specification Requirements for the Compacted Samples (Medium Traffic):
Surface Mix Base Mix
Test Property Mm. Max. Mm. Max.
Stability, Ibs.
Flow, 0.01 inches
Percent air voids
500
8
3
-
18
5
500
8
3
-
18
8
Percent voids in min. aggre-
gate 16 - 12
V. Sample Preparation:
Three samples were prepared at each asphalt content. Test results re-
flect the average of three samples, except that one of the 6 percent "B"
grading samples was dropped and destroyed prior to testing. The asphalt con-
tents to be investigated were estimated to encompass the optimum for both
gradings and were taken at 0.5 percent intervals betweeen the maximum and
minimum levels shown below:
B-9
-------
Grading "D": 6.5 - 8.5 percent
Grading "B": 5.0 - 7.0 percent
VI. Test Results:
The results of all tests are summarized in Figures B-3 and B-4. Figure
B-3 presents the results of the tests conducted on the surface mixture, ||D.(|
Figure B-4 presents the results of the tests conducted on the base mix, B.
VI. Discussion of Results:
The variations in specific gravity of the Kingston Steam Plant bottom
ash, noted in a previous report, were not as severe in the bottom ash obtained
from the Watts Bar Steam Plant. Therefore, the density-voids analysis of the
Watts Bar material produced somewhat more meaningful results. The major prob-
lem with the Watts Bar ash is in the gradation. The surface gradation D test
results were quite uniform, which is a result of the fact that this gradation
varies only slightly from the TDOT specification for a surface aggregate. The
results of tests on the base gradation "B" material were quite variable due
mainly to the extreme variation from the TDOT specification, particularly in
the percent passing the 3/4-in., No. 4 and No. 8 sieve sizes. As noted be-
low, this gradation will not provide a suitable material for a base mix.
1) Grading "D", Surface Course Analysis:
Analysis of the data shown in Figure B-3 indicates that a satisfactory
surface mix could be constructed with this material at an asphalt
content of 8.5 percent, by weight. This asphalt content would op-
timize the stability and density of the mix. However, this asphalt
content is not sufficient to provide the required voids in the com-
pacted mix. The data indicate a voids content of 5.5 percent, as
compared to the required maximum of 5.0 percent. An asphalt con-
tent of 9.0 percent would probably produce a mix that would meet
all requirements of the specifications. An asphalt content of 85
percent does not meet the minimum flow requirement either, but it
would produce a mix with^flow of approximately 7 which is only
one below the required minimum.
A minor adjustment in the aggregate gradation might be more eco-
nomical than using this relatively high asphalt content. The addi-
tion of aggregate particles in the size range of the No. 4 sieve
would have the effect of closing the void structure, which would
result in a lowered asphalt content to produce a mixture to meet
the specification requirements. Analysis of this possibility was
not an objective of this investigation.
2) Grading "B", Base Course Analysis:
The normal range of asphalt content in a base mixture is 3-5 per
cent. Test results, shown in Figure B-4 indicate the optimum as-
phalt content for this aggregate gradation is in excess of 7.0 per-
cent. An asphalt content of 7.0 percent P™duces3a mix w th the
following properties: unit weight - 128.4 Ibs/ft , stability
B-10
-------
194
"c: 133
.9 i .j0
1
ffi 1
5t 130
S 129
13
128
1500
1400
d? 1300
E 1200
§ 1100
05 1000
onn
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/
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/
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/
z
j
/
cd
)—
25
S
Q
W
H
% VOIDS, COMPAC
789
% Bitumen, Weight
/
y {
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7
:
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^
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k
s
14
12
10
8
6
A
2
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^
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S
i,
N
k
7 8 9
22
20
18
16
14
% Bitumen, Weight
7 8
%Bitumen , Weight
6 8
%Bitumen, Weight
I
9
6
7
6
5
4
a
^
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r~
s
s
y^
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<_
7 8
% Bitumen, Weight
Bituminous Mix Design
MASHALL METHOD
Asphalt Grade: AC-20
Aggregate Type: Watts Bar Ash
Gradation Surface: TDOT "D"
Compaction: 75 Blow
Date Tested: December 22, 1977
Tested by : A.B.Moore
Figure B-3. Bituminous Surface Mix Design Using Watts Bar Ash
B-ll
-------
• •
a
a
\
IJU
129
128
127
126
125
\")A
(
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9
B
% VOIDS , COMPACTED MIX
(k. O> 00 O K> K C
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^v
567
% Bitumen, Weight
567
%Bitumen, Weight
I/W
1100
£ 1000
I
fc 900
§ 800
700
Ann
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567
% Bitumen, Weight
567
% Bitumen, Weight
Bituminous Mix Design
MARSHALL METHOD
Asphalt Grade: AC-20
Aggregate Type:Watts Bar Aah
Gradation Base: TDOT "B"
Compaction: 75 Blow
Date Tested: December 22,1978
Tested by: A.B.Moore
567
% Bitum»n Weight
Figure B-4. Bituminous Base Mix Design Using Watts Bar Ash
B-12
-------
990 Ibs., flow - 6.5 and voids - 9.5 percent. These values indi-
cate that an economical mix cannot be produced using this aggre-
gate gradation. The major problem with this mixture may be ob-
served by referring to the table on page I of this report. This
gradation is excessively different from the requirement of the
following sieves; 3/4 in., No. 4 and No. 8.
VII. Conclusions and Recommendations:
1) The Watts Bar bottom ash may produce a satisfactory surface agg-
regate after the material larger than the 3/8 inch sieve is removed.
However, the high asphalt content (8.5 percent) required to pro-
duce an optimum mixture may not be economical.
2) The voids in the compacted mix at an 8.5 percent asphalt content
surface mixture would be approximately 5.5 percent, which exceeds
the required maximum of 5.0 percent. However, it is my opinion
that this would not have a large adverse effect on the durability
of the mix.
3) The Watts Bar bottom ash, as received, will not produce a satis-
factory base aggregate.
B-13
-------
Appendix C
"Fly Ash Concrete Mix Design Procedures"
C-l
-------
PRINCIPAL METHODS USED TO DETERMINE MIX RATIOS
Cannon has stated that many concrete mix designers substitute fly ash
for cement on a one-for-one basis either by volume or weight. Most fly
ash concretes developed with this mix proportioning will usually have a com-
pressive strength greater than a comparable all cement portioned concrete at
ages beyond 90 days. However, the compressive strength between 3 to 28 days
for the fly ash concrete is usually lower than that of a comparable non-fly
ash concrete. Because of this difference in strengths at early ages, many
have concluded in the past that fly ash concrete should be used only where
strength is not the principal requirement.
Several different mix design methods have been developed for fly ash
concrete where comparable strengthSrgre assured between fly ash concrete and
a typical Portland Cement concrete. Lovewell and Washa have developed a
procedure for proportioning fly ash in a concrete mix which results in ,-Q
approximately equal compressive strength during the period of 3 to 28 days.
Their proportioning method is based on the mixture of flyash and Portland
Cement having a total weight greater than the cement used in a comparable
straight Portland Cement.
Cannon has,-|lso developed a mix design based upon a number of investi-
gations at TVA. His approach is readily adaptable to different qualities
of fly ash as well as meeting standards for Type I or Type II cement. This
design approach is as follows:
STEP I: Select the volumerQf coarse aggregate per unit volume of
concrete from Table 6 of ACI 613-54. In making this selection the fineness
modulus of the sand should be reduced by 20% to allow for the effect of the
larger volume of the cementitious material in the fly ash mix.
STEP 2: Estimate the water requirements for the maximum size of
aggregate to be used and the required slump (use ACI-613-54 as a guide).
Slump is a measure of workability and represents the distance that an un-
supported cone of concrete will settle in height below the form used to form
the cone of concrete.
STEP 3: Select from Figure C-l the water-cement ratio required for
a given strength concrete.
STEP 4: Select the fly ash proportion to be used by either Figure
C-2 or Figure C-3. The selection is based on the relative cost of fly ash and
required strength in order to select the lowest cost blend of fly ash and
cement.
STEP 5: Using the water-cement ratio of step 3 and fly ash propor-
tion of step 4, determine the water reduction from Figure C-4 or Figure C-5.
STEP 6: Using the estimated water requirements of step 2 for the
control mix, determine the water requirements of the fly ash mix by using
the water reduction of step 5.
C-2
-------
7UW
(490)
6000
(420)
1 5000
jy (350)
a
.s
je 4000
•& (280)
e
co
I 3000
| (210)
i
0 ,-y
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ngths
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itg/c
V.
3 0.4 0.5 0.6 0.7 0.8 0.9
^7
^
^ —
^
.0
w/c
Water-Cement Ratio
Figure C-l. Water-Cement Ratios and Compressive
Strengths
C-3
-------
1.00
0.95
decrease
in water
increase
in water
Fly ash content as a
percent of the cement
content by weight.
7 8 9 10 11 12 13
030
Percent increase or decrease in water content of fly ash concrete
Figure C-2.
Comparison of Water Requirements of
Concrete With and Without Fly Ash for
Identical Slump, Air contents and 28
Day Strength
C-4
-------
decrease
in water
Fly ash content as a
percent of the cernem
content by weight.
34 5 678 9 10 11 12
0.40
Percent increase or decrease in water content of fly ash concrete
Figure C-3.
Comparison of Water Requirements of
Concrete With and Without Fly Ash for
Identical Slump, Air Contents and 90
Day Strength
C-5
-------
JS
bO
PQ
Note:Proportion fly ash
the nearest 5%
20
0 10% 20% 40% 50% 60%
Cost of fly ash as a percent of cost of cement
by weight
Figure C-4. Economic Proportions of Fly Ash
for 28 Day Strength Concrete
C-6
-------
I
u
4J
a
c
u
§
-•
o
od
od
=
Oi
O 00
0 'S
co
*
140
Note:Proportion fly ash to
the nearest 10%.
10%
20%
30%
40%
50%
Cost of fly ash as a percent of cost of cement
by weight
*Required minimum strength
at 90 days of age.
Figure C-5. Economic Properties of Fly Ash for 90
Day Strength Concrete
60%
C-7
-------
STEP 7: Determine the cement requirements of the control mix by
dividing the control mix water requirements by the water-cement ratio of
step 3.
STEP 8: Select the proportionate cement requirement of the fly
ash mix from Figure C-6 or C-7 (depending on the age strength requirements)
using the water-cement ratio of step 3 and the fly ash proportion of step 4.
cp
STEP 9: Using methods in ACI-613-54 , determine the solid volume
of sand for the mix by subtracting the solid volumes of coarse aggregate,
cement, fly ash and water, plus the required volume of air from the unit
volume of concrete in the mix.
STEP 10: Check the mix for the slump and air content and repeat
the procedure for the actual water required to provide the desired slump and
air contents.
STEP 11: If trial mix strengths differ significantly from the
required strength an adjustment in cement and fly ash contents will be re-
quired. This adjustment is in direct proportion to the water-cement ratio
of Figure C-l corresponding to the trial mix strength divided by the original
water-cement ratio used in design.
Let us assume we wanted to design a 28 day, 3000-psi concrete with Ih
in. maximum size aggregate, five percent air content, 2h in. slump, no water
reducing agent, and fly ash cost at 25 percent of cement cost.*
STEP 1: Using Table 6 of ACI-613-5452 and a fineness modulus of
2.6, the volume of aggregate to volume of concrete is .74. If the aggregate
has a specific gravity of 1.6 then
.74 x 27 ft3/yd x 1.6 x 62.5 lb/ft3 = 2000 Ibs. of aggregate
STEP 2: With an air entrainment of 5 percent, and an aggregate
size of 1% in., one can see from Table 3 of ACI-613-54 that between 29
and 32 gallons of water are required for a slump of 2.5 inches. We will
use 30 gallons or 250 Ibs. of water.
STEP 3: Concrete is tested3for compressive strength according to
ASTM specifications. For each 150 yd of concrete, two to 3 test cylinders
are made. From the compressive strengths of the test cylinders, a coefficient
of variation can be determined. From the coefficient of variation, and a
specification that the design strength be met in a certain percentage of
cylinder tests, a required strength for a mix can be determined. For example,
for a coefficient of variation of 15% and no more than ope weak test cylinder
in 10, the required strength to design strength is 1.23. Thus, the required
strength of the concrete is 3000 x 1.25 = 3700 psi. Using Figure C-l the water-
cement ratio for a 28 day strength 3700 psi is .59.
STEP 4: From Figure C-4, and a fly ash cost of 25 percent of the
cement cost, the most economical mix would utilize a ratio of fly ash to
cement of 50 percent.
C-8
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O
inimum cement content
30 40 5O 60 /O 8U 90
Fly ash content as a percent by weight of the
cement content of the fly ash mil
Figure C-6. Cement Requirements for Various Fly Ash
Proportioned Concretes for 28 Day Strength
C-9
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minimum cement content
20 40 60 80 1
Fly ash content as a percent by weight of the
cement content of the fly ash mix
Figure C-7. Cement Requirements for Various Fly Ash
Proportioned Concretes for 90 Day Strength
C-10
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STEP 5: From Figure C-2, a fly ash to cement ratio of .5 by weight
and a water-cement ratio of .59, the water reduction should be about 4%.
STEP 6: The water content of the fly ash concrete is less than
250 Ibs (.96) = 240 Ibs.
STEP 7: Since the water-cement ratio is w/C = .59 and the water
content is 240 Ibs, then the control mix concrete has
= 425 Ibs. of cement
STEP 8: From Figure C-6, the fly ash mix cement content equals 80
percent of the cement content of the control mix when the water-cement
ratio is 50 percent. This means that the cement in the fly ash concrete
equals:
.80 x 425 = 340 Ibs. of cement
STEP 9: We need to calculate the volume of sand given the specific
of 2.65 for sand.
Ingredient Weight (Ibs.) Volume (cu.ft.)
Aggregate 2000 12
Cement 340 1.71
Fly ash 170 1.14
Water 240 3.84
Air (5%) - 1.35
Subtotal - 20.04
Sand needed 1149 6.94
Total 3899 27
STEP 10: Assume slump is within ±% in. of design slump.
STEP 11: Assume trial mix had an average 28 day strength of .3750
psi., then no adjustment is necessary.
After calculating a total for flyash and cement contents, it is
easy to calculate the overall economics of the fly ash concrete as opposed
to an all -cement cost without the cost of aggregates. The comparisons are
given in Table C-l. The above analysis is made without adjusting for the cost
of equipment needed for fly ash handling equipment. This will be discussed
further in the economics of fly ash. In addition, the use of any admixtures
for keeping air entrainment at suitable levels is not included here but will
be discussed later.
EFFECT OF FLY ASH ON WATER CONTENT
It is generally agreed that the use of fly ash in limited amounts as a
C-ll
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TABLE C-l. ECONOMICS OF FLY-ASH MIX
Ingredient
Fly Ash Mix
Weight
Ibs.
Cost
Unit
Total
Weight
Ibs.
Cost
Unit
Total
Cement
Fly Ash
Water
Added Sand
Total
340 $47/2000
170 $10/2000
240
0
7.99
.85
8.84
373
250
100
$47/2000 8.77
$2/2000 .10
8.84
C-12
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replacement for cement or as an addition to the cement, or in replacement of
some sand, does not appreciably affect the water requirement for maintenance
of the same slump. Slump is a measure of workability and represents the dis-
tance that an unsupported cone of concrete will settle in height below the
form used to form the cone of concrete. Although the water needed for a
given slump and maximum size aggregate remains relatively unchanged when fly
ash is included, some controversy still exists as to the water requirement
when the fly ash is coarse and has a high carbon content.
The water-to-cement ratio has a great influence on the overall strength
of concrete. Since the workability is a function of aggregate size and water
content, it is necessary to determine a water requirement based on aggregate
size and desired workability and then translate the water requirement to a
cement content based on a design strength. After the cement content and
fly ash content are calculated, it is important to recalculate the needed
water as done in the Cannon mix method.
REDUCTION IN CEMENT CONTENT
The reduction in cement content must be based on the relative costs of
cement and fly ash and the design compressive strength. Figure C-4 gives the
relationship between the fly ash to cement ratio and the ratio of fly ash
to cement cost as a function of the 28;day design compressive strength. For
example, for a fly ash-to-cement cost ratio of .36 and a design strength of
3000 Ibs. per square inch, the fly ash-to-cement ratio (by weight) is 34
percent. This gives us the economical ratio of amounts in the fly ash con-
crete. The reduction in cement is based on the ratio of a fly ash to cement
ratio and the water-cement ratio needed for desired workability and aggre-
gate size. This relationship is given in Figure C-6. For example, if the
weight ratio of fly ash to cement is 34 percent and the water to cement ratio
was .5, then the cement in the fly ash mix would be 85 percent of the amount
in a non fly ash mix. This would represent a reduction of 15%.
C-13
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
.. REPORT NO.
EPA-600/7-80-172
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Coal-Fired Power Plant Ash Utilization in the TVA
R E PORTO ATE _
v rober 1980
Region
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Richard L. Church, Dennis W. Weeter, and
Wayne T. Davis
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
TVA, Energy Demonstrations and Technology
1140 Chestnut Street, Tower H
Chattanooga, Tennessee 37401
1O. PROGRAM ELEMENT NO.
1NE624A
11. CONTRACT/GRANT NO.
IAG-D5-E721
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
Task Final; 3/78-10/79
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES JERL-RTP project officer is Julian W. Jones, MD-61, 919/541-
2489.
16. ABSTRACT Tne repo^ giV6s results of a study: (1) to summarize (a) production of coal
ash nationally and by TVA's 12 major ash-producing steam/electric power plants,
and (b) the physical/chemical characteristics of coal ash that affect ash disposal
and/or use; (2) to review reported methods of coal ash use, emphasizing potential
markets in the TVA system; and (3) to recommend potential R and D for coal ash use
in the TVA system. Uses discussed include: concrete mixtures, mineral and magne-
tite recovery, lightweight aggregate, wastewater treatment, sanitary landfill liners,
cenosphere reuse, agriculture, mineral wool insulation, and bituminous paving mix-
tures. The TVA region's predominant historical use of fly ash has been as a concrete
additive; however, extensive pilot scale development is underway to advance ash use
in the TVA region in such areas as mineral and magnetite recovery, and mineral
wool insulation. Recommended studies include: (1) the feasibility of converting exis-
ting wet fly ash collection systems to dry collection and storage; (2) mechanical
properties of ash to learn how to separate nonfloating cenospheres from ash; (3)
other mineral recovery process choices (in addition to the one with Mineral Gas Co.);
and (4) the potential uses, markets, generation points, transportation, and feasi-
bility of extensive coal ash utilization in the TVA area.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Concretes
Ashes Bituminous Concretes
Ash Content Minerals
Physical Properties Magnetite
Electric Power Plants
Coal Aggregates
CombustionEarth Fills
Pollution Control
Stationary Sources
Ash Utilization
Cenospheres
13B
21B
07D
14G
10B
21D
13C
11B
08G
10A
11G
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
125
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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