United States Industrial Environmental Research EPA-600/7-80-012c
Environmental Protection Laboratory March 1980
Agency Research Triangle Park NC 27711
^•- i . - -.. «. ^^^—^^^—^-^^^^^^^^^— - .. .MI
Waste and Water
Management for
Conventional Coal
Combustion Assessment
Report-1979
Volume III.
Generation and
Characterization
of FGC Wastes
Interagency
Energy/Environment
R&D Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the JNTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide*range of energy-related environ-
mental issues.
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-80-012c
March 1980
Waste and Water Management
for Conventional Coal Combustion
Assessment Report-1979
Volume III. Generation and
Characterization of FGC Wastes
by
CJ. Santhanam, R.R. Lunt, C.B. Cooper,
D.E. Klimschmidt, I. Bodek, and W.A. Tucker (ADL);
and C.R. Ullrich (University of Louisville)
Arthur D. Little, Inc.
20 Acorn Park
Cambridge, Massachusetts 02140
Contract No. 68-02-2654
Program Element No. EHE624A
EPA Project Officer: Julian W. Jones
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
US ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
-------
PARTICIPANTS IN THIS STUDY
This First Annual R&D Report is submitted by Arthur D. Little, Inc.
to the U. S. Environmental Protection Agency (EPA) under Contract No.
68-02-2654. The Report reflects the work of many members of the
Arthur D. Little staff, subcontractors and consultants. Those partici-
pating in the study are listed below.
Principal Investigators
Chakra J. Santhanam
Richard R. Lunt
Charles B. Cooper
David E. Kleinschmidt
Itamar Bodek
William A. Tucker
Contributing Staff
Armand A. Balasco Warren J. Lyman
Janes D. Birkett Shashank S. Nadgauda
Sara E. Bysshe James E. Oberholtzer
Diane E. Gilbert James I. Stevens
Sandra L. Johnson James R. Valentine
Subcontractors
D. Joseph Hagerty University of Louisville
C. Robert Ullrich University of Louisville
We would like to note the helpful views offered by and discussions
with Michael Osbome of EPA-IERL in Research Triangle Park, N. C., and
John Lum of EPA-Effluent Guidelines Division in Washington, D. C.
Above all, we thank Julian W. Jones, the EPA Project Officer, for
his guidance throughout the course of this work and in the preparation
of this report.
iii
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ACKNOWLEDGEMENTS
Many other individuals and organizations helped by discussions with
the principal investigators. In particular, grateful appreciation is
expressed to:
Aerospace Corporation - Paul Leo, Jerome Rossoff
Auburn University - Ray Tarrer and others
Department of Energy - Val E. Weaver
Dravo Corporation - Carl Gilbert, Carl Labovitz, Earl Rothfuss
and others
Electric Power Research Institute (EPRI) - John Maulbetsch,
Thomas Moraski and Dean Golden
Environmental Protection Agency, Municipal Environmental Research
Laboratory - Robert Landreth, Michael Roulier, and Don Banning
Federal Highway Authority - W. Clayton Ormsby
IU Conversion Systems (IUCS) - Ron Bacskai, Hugh Mullen
Beverly Roberts, and others
Louisville Gas and Electric Company - Robert P. Van Ness
National Ash Association - John Faber
National Bureau of Standards - Paul Brown
Southern Services - Reed Edwards, Lamont Larrimore, and Randall Rush
Tennessee Valley Authority (TVA) - James Crowe, T-Y. J. Chu,
H. William Elder, Hollis B. Flora, R. James Ruane,
Steven K. Seale, and others
iv
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CONVERSION FACTORS
English/American Units
Length:
1 inch
1 -!oot
1 fathom
1 mile (statute)
1 mile (nautical)
Area:
1 square foot
1 acre
Volume:
1 cubic foot
1 cubic yard
1 gallon
1 barrel (42 gals)
Weight/Mass:
1 pound
1 ton (short)
Pressure:
1 atmosphere (Normal)
1 pound per square inch
1 pound per square inch
Concentration:
1 part per million (weight)
Speed:
1 knot
Energy/Power:
1 British Thermal Unit
1 megawatt
1 kilowatt hour
Temperature:
1 degree Fahrenheit
Metric Equivalent
2.540 centimeters
0.3048 meters
1.829 meters
1.609 kilometers
1.852 kilometers
0.0929 square meters
4,047 square meters
28.316 liters
0.7641 cubic meters
3.785 liters
0.1589 cu. meters
0.4536 kilograms
0.9072 metric tons
101,325 pascal
0.07031 kilograms per square centimeter
6894 pascal
1 milligram per liter
1.853 kilometers per hour
1,054.8 joules
3.600 x 10^ joules per hour
3.60 x 106 joules
5/9 degree Centigrade
v
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GLOSSARY
Cementitious: A chemically precipitated binding of particles
resulting in the formation of a solid mass.
Fixation: The process of putting into a stable or unalterable
form.
Impoundment: Reservoir, pond, or area used to retain, confine,
or accumulate a fluid material.
Leachate; Soluble constituents removed from a substance by the
action of a percolating liquid.
Leaching Agent: A material used to percolate through something
that results in the leaching of soluble constituents.
Pozzolan; A siliceous or aluminosiliceous material that in
itself possess little or no cementitious value but that in
finely divided form and in the presence of moisture will react
with alkali or alkaline earth hydroxide to form compounds possessing
cementitious properties.
Pozzolanic Reaction: A reaction producing a pozzolanic product.
Stabilization: Making stable by physical or chemical treatment.
vi
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ABBREVIATIONS
BOD biochemical oxygen demand
Btu British thermal unit
cc cubic centimeter
cm centimeter
COD chemical oxygen demand
°C degrees Centigrade (Celcius)
°F degrees Fahrenheit
ESP electrostatic precipitator
FGC flue gas cleaning
FGD flue gas desulfurization
ft feet
g gram
gal gallon
gpd gallons per day
gpm gallons per minute
hp horsepower
hr hour
in. inch
j joule
j/s joule per second
k thousand
kg kilogram
kCal kilocalorie
km kilometer
kw kilowatt
kwh kilowatthour
£ or lit liter
Ib pound
M million
m^ square meter
m cubic meter
mg milligram
MGD million gallons per day
MW megawatt
MWe megawatt electric
MWH megawatt hour
yg microgram
mil milliliter
min minute
ppm parts per million
psi pounds per square inch
psia pounds per square inch absolute
scf/m standard cubic feet per minute
sec second
TDS total dissolved solids
TOS total oxidizable sulfur
TSS total suspended solids
tpy tons per year
yr year
vii
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS
CONVERSION FACTORS
GLOSSARY
ABBREVIATIONS
LIST OF TABLES
LIST OF FIGURES
1.0 INTRODUCTION
1.1 Purpose and Content
1.2 Report Organization
2.0 OVERVIEW ON FGC WASTE GENERATION
2.1 Ash Collection Technology
2.1.1 Mechanical Collectors
2.1.2 Electrostatic Precipitators
2.1.3 Fabric Filters
2.1.4 Wet Scrubbers
2.2 FGD Technology
2.2.1 Introduction
2.2.2 Nonrecovery Processes
2.2.2.1 Wet Processes
2.2.2.2 Dry Processes
2.2.3 Recovery Processes
2.2.3.1 Wet Processes
2.2.3.2 Dry Processes
2.3 Categorization of FGC Wastes
2.4 Dewatering of FGC Wastes
2.4.1 State of the Art
2.4.2 Research and Development Programs
in FGC Waste Dewatering
2.4.2.1 The Aerospace Corporation
2.4.2.2 Auburn University
2.4.2,3 Envirotech Corporation
2.4.2.4 Radian Corporation
Page
iv
V
vi
vii
xii
xvi
1-1
1-1
1-3
2-1
2-1
2-4
2-4
2-5
2-6
2-7
2-7
2-8
2-8
2-15
2-17
2-17
2-20
2-21
2-23
2-23
2-32
2-35
2-38
2-40
2-40
vili
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TABLE OF CONTENTS
(Continued)
Page
3.0 PRODUCTION TRENDS AND HANDLING OPTIONS 3-1
3.1 Coal/Waste Relationships 3-1
3.2 Projected Generation and Trends 3-1
3.3 Waste Stabilization of Technology 3-5
3.3.1 General Stabilization of Wastes 3-5
3.3.2 Stabilization of FGC Wastes 3-11
3.4 Utilization and Disposal Options 3-12
3.4.1 Disposal 3-12
3.4.2 Utilization 3-14
4.0 CHEMICAL CHARACTERIZATION OF FGC WASTES 4-1
4.1 Status of Chemical Characterization 4-1
4.2 Principal Components 4-4
4.2.1 Principal Components in Coal Ash 4-4
4.2.2 Principal Components in
Unstabilized FGC Wastes 4-8
4.2.2.1 Wet Processes 4-8
4.2.2.2 Dry Processes 4-17
4.2.3 Stabilized FGC Wastes 4-20
4.3 Composition Ranges for Trace Components 4-22
4.3.1 Trace Components in Coal Ash 4-22
4.3.2 Trace Elements in Unstabilized FGC Wastes 4-26
4.3.2.1 Total Wastes 4-26
4.3.2.2 Trace Elements in Waste Liquors 4-43
4.3.3 Trace Elements in Stabilized FGC Wastes 4-46
4.4 Leaching Behavior 4-46
4.4.1 Leachates 4-50
4.4.1.1 Coal Ash 4-50
4.4.1.2 Unstabilized FGC Wastes 4-52
4.4.2 Effects of Stabilization on Pollutant
Migration from FGC Wastes 4-72
4.4.3 Soil Attenuation 4-82
4.4.4 Impacts of Weathering on FGC Wastes 4-89
4.4.5 RCRA Implications for FGC Waste Leachates 4-90
ix
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TABLE OF CONTENTS
(Continued)
Page
4.5 Data Gaps and Research Needs -
Chemical Properties 4-93
5.0 PHYSICAL CHARACTERIZATION OF FGC WASTES 5-1
5.1 Introduction 5-1
5.2 Critical Properties 5-1
5.2.1 Handling Characteristics 5-2
5.2.2 Placement and Filling Characteristics 5-3
5.2.3 Long-term Stability 5-4
5.2.4 Pollutant Mobility 5-5
5.3 Status of Physical Testing 5-7
5.4 Available Information 5-9
5.4.1 Index Properties 5-10
5.4.1.1 Fly Ash 5-10
5.4.1.2 FGC Wastes 5-10
5.4.2 Consistency-Water Retention 5-14
5.4.2.1 Fly Ash 5-14
5.4.2.2 FGC Wastes 5-14
5.4.3 Viscosity vs. Water (Solids) Content 5-15
5.4.3.1 Fly Ash 5-15
5.4.3.2 FGC Wastes 5-15
5.4.4 Compaction/Compression Behavior 5-20
5.4.4.1 Fly Ash 5-20
5.4.4.2 FGC Wastes 5-21
5.4.5 Dewatering Characteristics 5-24
5.4.6 Strength Parameters 5-26
5.4.6.1 Fly Ash 5-26
5.4.6.2 FGC Wastes 5-27
5.4.7 Permeability 5-36
5.4.7.1 Fly Ash 5-36
5.4.7.2 FGC Wastes 5-36
-------
TABLE OF CONTENTS
(Continued)
6.0
5.4.8 Weathering
5.4.8.1
5.4.8.2
Fly Ash
FGC Wastes
5.5 Data Gaps and Future Research Needs
RESEARCH NEEDS
6.1
6.2
REFERENCES
Index
Waste Properties Relation to
the Disposal Process
Overview on Research Needs
6.2.1 Field Data
6.2.2 Laboratory Test Procedures
6.2.3 Ash/FGD Waste Co-disposal and
Treatment Requirements
6.2.4 Physical Characterization of
FGC Wastes
6.2.5 Trace Element Focus and Speciation
6.2.6 Anaerobic-Induced Reduction
Reactions/Volatile Species
6.2.7 Radionuclides and Trace Organics
Page
5-40
5-40
5-41
5-43
6-1
6-1
6-5
6-7
6-8
6-8
6-9
6-10
6-10
6-11
R-l
1-1
xi
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LIST OF TABLES
Table No. Page
2.1 Ash Collection and Net Particulate Emissions,1975 2-2
2.2 Largest Ash-Producing Coal-Fired Steam
Electric Power Plants, 1975 2-3
2.3 Summary of FGD Systems Expected to be
in Commercial Operation on Boilers in 1979 2-9
2.4 Summary of FGD Systems Expected to be in
Commercial Operation on Utility Boilers in
1982 (as of February 1979) 2-10
2.5 Matrix of Unstabillzed FGD Waste
Generation-Nonrecovery Solid Waste
Producing Systems 2-24
2.6 Summary of FGC Waste Dewatering Practices
for Operating Utility Scrubbers 2-26
2.7 Dewatering of FGC Wastes at Utility and
Industrial Installations Employing Filters
and Centrifuges 2-30
2.8 Summary of Past/Present Programs Focusing on
the Dewatering of FGC Wastes 2-33
2.9 EPA- and EPRI-Sponsored Projects Focusing on
the Dewatering of FGC Wastes 2-34
2.10 Effects of Fly Ash on the Dewatering
Properties of FGC Waste Samples
(Laboratory Evaluation) 2-37
3.1 Coal/Ash/Sludge Relationships (Typical) 3-2
3.2 Generation of Coal Ash and FGD Wastes 3-3
3.3 Projected Generation of Coal Ash and FGD
Wastes Industrial vs. Utility Breakdown 3-4
3.4 Waste Treatment Processes 3-7
3.5 Waste Types vs. Disposal Scenarios 3-15
3.6 Typical Disposal Scenarios 3-16
xii
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LIST OF TABLES
(Continued)
Table No. page
4.1 Studies on Chemical Characterization
of FGD Wastes 4-2
4.2 Chemical Composition of Fly Ashes According
to Coal Rank - Major Species (Weight Percent) 4-5
4.3 Major Constituents in Fly Ash and Bottom Ash
from Various Utility Plants 4-7
4.4 Major Components in Selected FGC Waste Solids 4-10
4.5 Waste Liquor Phase - Major Constituents 4-14
4.6 Major Dry Solvents Under Investigation in the
United States and Their Reaction Products 4-18
4.7 Chemical Composition of Raw and Spent
Nahcolite Ore 4-19
4.8 Trace Elements in Coal Ash 4-24
4.9 Concentration Range of Trace Species Present
in Coal Ashes 4-25
4.10 Trace Constituents in Fly Ash and Bottom Ash
From Various FGC Units 4-27
4.11 Elements Showing Pronounced Concentration
Trends with Decreasing Particle Size
(ppm unless otherwise noted) 4-29
4.12 Concentrations of Trace Metals in FGC Wastes
and Coal 4-32
4.13 Trace Element Content of Samples from Station 1 4-33
4.14 Trace Element Content of Samples from Station 4 4-34
4.15 Trace Element Content of Samples from Station 5 4-35
4.16 Contents of Various Radionuclides in Coal,
Bottom Ash, and Fly Ash 4-42
4.17 Typical Levels of Chemical Species in FGD Waste
Liquors and Elutriates 4-44
4.18 Principal Programs Funded by the Government
and Utility Industry to Evaluate Leaching
Behavior of FGC Wastes 4-48
xiii
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LIST OF TABLES
(Continued)
Table No.
4.19 Characteristics of Once-Through Fly Ash
Pond Discharges
Page
4.20 Equilibrium Concentrations of Trace
Elements in Coal Ash Leachate 4-53
4.21 Comparision of the Chemical Constituents
in Sludge Liquors with Leachate After 50
Pore Volume Displacements 4-55
4.22 Chemical Analysis - Shawnee Lime Waste
Liquor and Leachates 4-56
4.23 Chemical Analysis Paddy's Run - Carbide Lime
FGC Waste Liquor and Leachates 4-57
4.24 Chemical Analysis - Plant Scholz Dual Alkali
FGD Waste Liquor and Leachates 4-58
4.25 Mass Balance, Charge Balance, and Gypsum
Solubility Ratio of Waste Liquors and Leachates 4-59
4.26 Equilibrium Concentrations of Trace Elements
in FGC Waste Leachate 4-65
4.27 Concentration of Trace Elements in Leachate
from Sulfate-Rich Wastes (First Pore Volume) 4-69
4.28 Summary of Leachate Concentrations from Dual
Alkali Wastes Generated During Prototype Testing
at the Scholz Steam Plant 4-71
4.29 Comparison of the Chemical Constituents in
Eastern Limestone Waste Leachate with Chemfix
Chemically Stabilized Waste Leachate 4-74
4.30 Concentrations of IDS in Leachate from Successive
Shake Tests of Stabilized FGC Waste Sample 4-78
4.31 Chemfix Preliminary Leaching Study on Waste
from Shawnee Plant, TVA, Test No. One 4-83
4.32 Values of K for Spiked Ash Leachate 4-85
4.33 Values of K for Spiked Waste Leachate 4-86
xiv
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LIST OF TABLES
(Continued)
Table No. Page
5.1 Summary of Physical Testing - FGC Wastes 5-8
5.2 Physical Properties of FGC Wastes 5-12
5.3 Standard Proctor Moisture-Density Parameters
for Selected .FGC Wastes 5-22
5.4 Compression Indices for Some FGC Wastes 5-25
5.5 Shear Strength Parameters of FGC Wastes 5-28
5.6 Unconfined Compressive Strength Values as
a Function of Time for Some FGC Wastes 5-29
5.7 Strength Parameters for FGC Wastes 5-30
5.8 Shear Strength and Permeability Values
Waste-Carbide Lime-Fly Ash Impoundments 5-32
5.9 Shear Strength and Permeability Values
Waste-Commercial Lime-Fly Ash Impoundments 5-33
5.10 Coefficients of Permeability for FGC Wastes 5-38
6.1 FGC Wastes Properties and Possible Routes
of Important Environmental Impacts
(Land Disposal) 6-2
6.2 Variables Affecting FGC Waste Properties
and the Resulting Environmental Impact 6-4
6.3 Important Properties of FGC Wastes Affecting
Handling of the Waste Prior to and During Disposal 6-6
xv
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LIST OF FIGURES
Figure No. page
2.1 Flow Diagram of Proposed Dewatering System 2-39
4.1 Enrichment Factors of Various Elements
on Suspended Particles in the Stack with
Respect to the Concentrations in the Ash 4-28
4.2 Correlation of Trace Element Content in
Parent Coal and FGC Wastes 4-37
4.3 Average Trace Element Content of Sludge
Liquor (mg/Jl) 4-38
4.4 Concentration of Major Species and TDS
in Leachate Lime FGD Waste With and Without
Fly Ash from Shawnee, Run F 4-60
4.5 Concentrations of Major Species and TDS in
Filtrate and Leachate FGD Waste from
LG&E Paddy's Run 4-61
4.6 Concentration of Major Species and TDS in
Leachate of FGD Dual Alkali Waste and Mixed
Waste and Fly Ash from GPC Scholz Station 4-62
4.7 Concentration of Major Species in Leachate
from Four Corners Scrubber Waste . 4-67
4.8 Concentration of Major Species in Leachate
from Shawnee Forced Oxidized Scrubber Waste 4-68
4.9 Concentration of Total Dissolved Solids and
Major Species in Pond D Leachate 4-79
4.10 Concentrations of Total Dissolved Solids and
Major Species in Pond B Leachate 4-81
4.11 Removal of Trace Elements from
Pond Leachate by Soil Attenuation 4-88
5.1 Grain Size Distribution Curves for Bottom
Ash and Fly Ash 5-11
5.2 Viscosity of FGC Wastes 5-17
5.3 Viscosity Versus Solids Content 5-19
xvi
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1.0 INTRODUCTION
1.1 Purpose and Content
With increasing coal utilization in industrial and utility boilers,
generation of coal ash (fly ash and bottom ash) and flue gas desulfuriza-
tion (FGD) wastes, which together comprise flue gas cleaning (FGC) wastes,
is expected to increase dramatically in the next twenty years. While
utilization of FGC wastes is also expected to increase, the anticipated
vast increase in generation of FGC wastes indicates that much of the FGC
wastes will be discharged for disposal. In any case, these wastes pre-
sent significant sources of environmental concern and utilization
opportunities.
This is the third volume in a five-volume report assessing tech-
nology for the control of waste and water pollution from combustion
sources. This volume provides an overall review and assessment of genera-
tion of the gas cleaning (FGC) wastes and of the characterization of the
chemical, physical, and engineering properties of FGC wastes. As such,
it serves as the basis for the following two volumes discussing FGC waste
utilization and disposal.
The primary focus of this report is on coal-fired power plants;
however, many of the characteristics discussed would also apply to wastes
from oil-fired boilers. Coal-fired power plants generate the maximum
range of wastes and usually the greatest quantity. Thus, they can serve
as the logical focus for assessing environmental and technological prob-
lems relating to the disposal and utilization of waste materials.
A coal-fired power plant produces two broad categories of coal-
related wastes:
• Coal ash, which includes both fly ash and bottom ash
(or boiler slag), and
• Flue gas desulfurization (FGD) wastes from the con-
trol of sulfur dioxide emissions.
1-1
-------
Together, fly ash and FGD wastes are generally referred to as flue gas
cleaning (FGC) wastes. In many cases, fly ash and SO^ emissions are
separately controlled and represent separate waste streams. In other
cases, fly ash and FGD wastes are combined in a single stream, either
through admixture of these wastes or through simultaneous collection of
fly ash and S02. This review of FGC waste generation and characteristics
includes coal ash, FGD wastes, and their combination both as produced
directly from FGC systems as well as wastes processed for disposal.
The review and assessment has involved two separate efforts as
described below:
(1) Review of the data and information available as of
January 1979 on the generation and chemical, physical,
and engineering properties of FGC wastes. The review
is based upon published reports and documents as well
as contacts with private companies and other organiza-
tions engaged in FGC technology development or involved
in the design and operation of FGC systems and waste
disposal facilities. Much o'f the information has been
drawn from the waste characterization studies and tech-
nology development/demonstration programs sponsored by
the Environmental Protection Agency (EPA) and the
Electric Power Research Institute (EPRI).
(2) Based upon the review of the data and assessment of on-
going work in waste characterization, identification
of data and information gaps relating to waste genera-
tion and properties and the development of recommenda-
tions for potential EPA initiatives to assist in
covering these gaps. The principal purpose of this
effort is to ensure that, ultimately, adequate data
will be available to permit reasonable assessment of
the impacts associated with the disposal and/or
utilization of FGC wastes.
1-2
-------
Throughout this work, emphasis has been placed upon wastes produced by
commercially demonstrated technologies and, where data are available,
by technologies in advanced stages of development that are likely to
achieve commercialization in the United States in the near future. In
terms of FGD wastes, consideration is limited to nonrecovery FGD systems
with focus on those producing solid wastes (rather than liquid wastes).
There are very few recovery systems in operation or under construction
in the United States, and these generally produce a small quantity of
waste in comparison to nonrecovery systems.
1.2 Report Organization
This report presents:
• An overview of FGC technology (Chapter 2.5);
• Production trends and disposal/utilization options
for FGC wastes (Chapter 3)i
• Chemical characteristics of FGC wastes (Chapter 4.0),
• Physical and engineering characteristics of FGC
wastes (Chapter 5), and
• An overview of research needs (Chapter 6).
1-3
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2.0 OVERVIEW ON FGC WASTE GENERATION
2.1 Ash Collection Technology
Coal-fired utility and industrial boilers generate two types of
coal ash—fly ash and bottom ash. (Economizer ash and mill rejects are
lumped into the two major categories here.) Both constitute the non-
combustible (mineral) fraction of the coal and the unburned residuals.
Fly ash, which accounts for the majority of the ash generated, is the
fine ash fraction carried out of the boiler in the flue gas. Bottom
ash is that material which drops to the bottom of the boiler and is
collected either as boiler slag or dry bottom ash, depending upon the
type of boiler.
The total amount of coal ash produced is directly a function of
the ash content of the coal fired. Thus, the total quantity of ash
produced can range from a few percent of the weight of the coal fired
to as much as 35%. The partitioning of ash between fly ash and bottom
ash usually depends upon the type of boiler. Standard pulverized coal-
fired boilers typically produce 80-90% of the ash as fly ash. In
cyclone-fired boilers, the fly ash fraction is usually less. In some
cases bottom ash constitutes the majority of the total ash.
To provide some perspective on ash collected and net particulate
emissions, Table 2.1 summarizes available data on fuel use, ash collec-
tion, and net particulate emission on a state-by-state basis in 1973.
Table 2.2 summarizes data on the 15 largest coal-fired plants in the
United States in 1973.
Collection of bottom ash (or boiler slag) does not involve systems
outside the boiler itself. The key technology issue is the handling
of bottom ash which has been discussed in Volume II.
Fly ash, however, is a major source of particulate emissions and
with increasing regulatory stringency has required major collection sys-
tems. Control of particulate emissions from pulverized-coal-fired steam
generators is rapidly becoming a significant factor in the siting
and public acceptability of coal-burning power plants. The particulate
2-1
-------
Table 2.1
Ash Collection and Net Particulate Emissions, 1975
I
f
N
0
1
2
10
II
. 2
13
14
19
16
IT
16
19
20
23
24
2»
26
27
28
30
31
32
33
35
36
37
38
39
49
41
43
4 *
45
46
47
4S
49
50
SI
52
53
**
55
56
57
9*
54
60
61
62
44
GtMSAPMIC HE&ION ANL SIAIE
HEM E MCI- AND
CONNf CT ICUT
MJ IVP
MASSACHUSETTS
NEK HAMPSHIRE
RHODE ISLAND
VEAKONr
TOTALS
MIDDLE ATLANTIC
NEW JERSEr
NErf *ORK
PENNS»LVAN!A
TOTALS
EAST NORTH CewTIAl
Illinois
INDIANA
MICHIGAN
OH I (3
rfl scn'isiN
TOTALS
•EST MORTK CENTUM
IOUA
KANSAS
NINNFSCTA
HIS5r.JSl
NCBr'ASKA
NORTH 0/-M1TA
SOUTH OAMJTA
TOTALS
SOUTH ATLANTIC
DEL AtrfARE
DISTPItT OF COLUMBIA
fXO»IOA
*«« VLAND
NORTH CAKOt TNA
^JUTH CA«tf3L 1 riA
tinei-ilt
TOTALS
EAST SOUTH CENTRAL
AIAS.'«A
KF.NT'JCKf
MISSISSIPPI
TENNESSEE
TOTALS
KEST SOUTH CENTRAL
AUKA'fSAS
L3UI S t A\'A
OKLAHOMA
TE AAS
TOTALS
MOUNTAIN
ARI ZONt
CHOa *00
I3AH3
MONT1NA
NF VAOA
•*EH IFXICn
ur AM
HtOHIKG
TOTALS
PACIFIC
CALIFORNIA
ORfCr'.l'l
• ASHl'l-.TON
TOTALS
HOH-COMT IGIJOUS U.S.
ALASKA
MAk»AI }
pj£
3,957.57
7i3?5.9i>
2.017.L,
6,90>.dl
ja.»M.i5
4ioo»Iso
141.92
U1.12
402,741.14
VALUF
IbTU/LB.
11,852
1J.138
12.458
11, 691
11.745
10.JS4
10, 980
11,00?
10. 720
10,202
13, 148
9, 07rt
10,iOi
6, 362
4.443
12.77-,
11,354
11.665
ll.'7t.b
11,567
11,762
11,44^
10,740
10,«iJ
11.024
41533
10.724
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12.71
14.92
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2.713.40
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2,213. 92
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128.443.75
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AtflfcAC.1
VALUE
I48i24«
1*>6 ,452
141,, 958
147,161
144.8S1
144,40V
145,715
137,72*
141,890
141,059
142.440
137, Oil
145,1.411
1 4 » , 796
14V,442
i49',175
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> >4t*i 51 4
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i93
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10,752.00
'/b ,4901. 31
69.00
78,548.31
I. .7
8,3/.'5. 40
17,344.54
25.1I1.C1
490. 774.*.*'
144.4..4
14*. £.'7
14»,43.r
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137,377
144. Tie
146, 111
14*il43
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10,455.25
41. 402.2 »
4,649.:^
99,182.4:
41,451.^^
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14.676.40
47,651.50
616. iO
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150,242.88
273,775.62
273,775.65
l.Olt, 41.2.4O
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1,102
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1,031
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1,1.9
1.014
1,033
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1.039
1,013
1 ,0/,9
992
1,150
1 , ; .2
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l' "
WET
»ARTtCULATES
EMISSIONS
f 1,000 TONS)
U«)
* >0
I » Ik
• U3
l*.l»
l^.oO
io>, si
,,
l»..l
U7.9J
1.002^2
1 *. F2
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31.36
6.45
2'.I5
4.9>
314.45
6. 113
*6*
1 '"62
60. 82
52. 46
2 >*•£
12.02
229.75
431.30
3«0.i)5
46.54
5.U
14O. 7*
412.47
• 7<
1.04
sol jo
12 45
57 87
15
6.58
V. 70
52.51
1*3.09
U.62 '
1.02
l>.44
2.67
I.J4
<.40
6.41
2.718.92
MH
COIXECTB)
(1,000 TQMI
».3»
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94, f^
* 7.79
184.41
-43.JO
K«7j'l>*
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472.31
* 'fv.6 1
1.«0».30
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4.321..1
139.1'
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62 7.H I
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SijoIiJ
i* j i
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9. CO
• J4
10*4*
Unit Conversion - .907 metric tons/short ton.
Source: fl!4]
2-2
-------
Table 2.2
Largest Ash-Producing Coal-Fired
Steam Electric Power Plants, 1975
Plant
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Plant Name/Location
Four Corners /New Mexico
Gavin/Ohio
Stuart /Ohio
Paradise/Kentucky
Sammis/Ohio
Monroe/Michigan
Keystone/Pennsylvania
Kingston/Tennessee
Montour /Pennsylvania
Harrison/West Virginia
Con emaugh /Pennsylvania
Shawnee /Kentucky
Monticello/Texas
Marshall/North Carolina
Cumberland/Tennessee
Annual Coal
Consumption
('000 metric tons)
5,510
5,230
4,580
4,280
4,370
5,625
3,780
3,960
3,575
4,105
3,390
4,030
3,240
3,720
3,570
Average
Ash Content
(wt. %)
22.6
16.4
19.2
19.0
17.0
12.9
19.0
18.5
19.2
14.0
18.7
15.5
15.4
15.9
16.7
Annual Ash
Collection
('000 metric tons)
1,240
840
820
800
725
720
710
685
685
655
630
615
600
595
590
Includes bottom and fly ash.
Source: [114]
-------
emission limit set by the EPA for large, new coal-fired boilers is
0.043 grams/10 joules (0.1 lb/10 Btu). Some states have requirements
more restrictive than this.
Fly ash carried in the flue gas stream can be collected in a number
of ways to meet the current particulate emission control limitations as
noted above. Typical methods historically employed include mechanical
collection, electrostatic precipitation, fabric filtration and wet
scrubbing. However, the tightening regulatory requirements support two
criteria for fly ash collection systems [118]:
• The collector must be efficient in removing sub-micron size
particulate matter. This criterion eliminates from consider-
ation all mechanical collectors and many wet scrubber systems
if they are used alone. Mechanical collectors may, however,
function as a first unit followed by a more efficient collector.
• The collector must be available commercially and be proven in
a utility boiler application. This constraint eliminates, for
the immediate future, many hybrid wet scrubber systems and
novel collectors that are now under development. In the
long run, however, it is conceivable that such advanced
systems may be used at least in some instances.
2.1.1 Mechanical Collectors
Settling chambers, cyclones, and impingement separators fall into
this category. For a description of mechanical collectors, the reader
is referred to references 119 and 120. Such devices are rarely more
than 50-80% efficient in particulate collection, particularly at sizes
less than two microns. Mechanical collectors alone are not capable of
meeting present and future New Source Performance Standards (NSPS) in
many cases and in the future are likely to be employed in conjunction
with one of the other three methods.
2.1.2 Electrostatic Precipitators
Electrostatic precipitators (ESP's) have been the dominant particu-
late collection device in the electric utility industry because of their
2-4
-------
low capital and operating cost. However, increasingly stringent emission
standards have led to substantially higher costs for precipitators. These
costs have increased sufficiently that fabric filtration has become a com-
petitive alternative in achieving cost-effective control at least in some
cases.
Three general types of electrostatic precipitators potentially are
applicable to coal-fired boilers:
• Hot-side ESP (U.S.-style) ,
• Cold-side ESP (U.S.-style) , and
• Cold-side ESP (European-style) .
U.S.-style, cold-side ESP's which are designed to treat flue gases
downstream of the combustion air preheater are most suitable for easy-
to-collect low-resistivity ashes typical of eastern and mid-western
medium and high sulfur coals. Hot-side ESP's (which treat flue gases
upstream of the combustion air preheater) and European-style, cold-
side ESP's were developed to handle the high-resistivity fly ashes
typical of low sulfur coals. An alternative to hot-side ESP's and
European-style ESP's for some low sulfur coal applications is the use
of cold-side ESP's in combination with flue gas conditioning. This
usually involves injection of a polar chemical species such as S0_ into
the flue gas to lower the resistivity of the ash through adsorption of
the chemical onto ash particles. However, other conditioning agents
have been developed which, in addition to reducing ash resistivity,
also modify ash particle size and space charge distribution. The
applicability of flue gas conditioning is a function of the coal compo-
sition, type of boiler (and its operating conditions), ESP design and
particulate emissions codes. At present, over 30 different utilities
employ some form of flue gas conditioning at one or more of their
operating plants [115].
2.1.3 Fabric Filters
Fabric filters do not have the years of utility application compared
with ESP's, and only within the past few years have fabric filters been
applied to large pulverized-coal-fired boilers. However, results at
2-5
-------
several full-scale boiler installations are reported to be encouraging
and indicate that high overall efficiency and high sub-micron efficiency
can be obtained, with acceptable maintenance and operating costs. The
experience of fabric filtration in other industries is probably as great
as that of ESP's, and many of the mechanical and process techniques de-
veloped for other applications may be applicable to the utility industry
substantial technology transfer is possible.
At present, two types of fabric filters are proved and commercially
available for boiler flue gas cleaning:
• Reverse-air systems, and
• Combination reverse-air plus gentle shaking systems.
The first involves fully continuous bag cleaning while the latter uses
automatic batch cyclones as a supplementary bag cleaning (i.e., ash
removal) device. Use of fabric filters may make dry handling systems
for fly ash more competitive. Pulse-jet type bag filters using teflon
bags have been tested on boilers [121] but are not commercially proven.
2.1.4 Wet Scrubbers
Most low- and medium-pressure drop scrubbers cannot meet current and
future environmental constraints. However, high-pressure (40-80" water
column) venturi scrubbers can offer particulate collection efficiencies
comparable to ESP's. While these are proven units, the large energy
costs associated with such high-efficiency scrubbers will probably make
them economically unattractive for most boiler applications. Another
possible disadvantage of wet scrubbing is that it necessitates wet
slurry handling systems, and hence either ponding of ash or ash dewater-
ing facilities for ultimate dry disposal. However, one special case of
wet scrubbing will continue to be employed in ash collection. Such
scrubbers use alkalinity of the fly ash to collect SO in the flue gas
X
as is discussed in Section 2.2.
2-6
-------
2.2 FGD TECHNOLOGY
2.2.1 Introduction
The implementation of flue gas desulfurization (FGD) technology
for the control of SCL emissions from the combustion of fossil fuels in
industrial and utility boilers is rapidly growing in the United States.
At present, FGD systems are in operation on over 16,000 megawatts of
utility generating capacity at some 30 different plants throughout the
country, and more than 40 industrial steam plants are equipped with
FGD systems [45,116]. By the end of 1979, the total capacity of FGD sys-
tems in operation on utility and industrial boilers is expected to exceed
25,000 megawatts (equivalent). The degree of S02 control ranges from
less than 50% SO removal efficiency to over 90%, depending upon the
type of FGD system, the sulfur content of the fuel, and the applicable
SO- emissions regulations.
The growth in FGD systems on fossil-fuel-fired boilers in the
United States over the next 20 years will be dependent principally upon
the growth in utility and industrial boiler capacity, current and future
S0? emission regulations, and the impact of alternative desulfurization
approaches to current and developing FGD technology. An important factor
may be the use of existing and enhanced coal-cleaning techniques. In
addition to reductions in sulfur content, the potential benefits of coal
cleaning include: reduction in ash content; increase in heating value;
control of ash fusibility; reduction in quantity (cost) of coal trans-
port; and reduction in boiler operating costs (for coal pulverizing
and boiler maintenance). While in many cases the cost of deep coal
cleaning may not be justified as an alternative to FGD, physical and
low-level chemical coal cleaning may offer substantial overall power
cost savings when employed in conjunction with partial or full FGD
control. The overall cost savings though must be taken into account—
not only the cost of coal cleaning and FGD but also the effects of coal
cleaning on ash properties (relative to particulate control), FGD
waste characteristics, and the attendant disposal costs for all wastes
(coal cleaning, FGD and ash).
2-7
-------
A wide variety of FGD processes have been developed for application
on utility and industrial boilers. In general, the technology can be
grouped into two categories: nonrecovery, or throwaway systems, which
produce a waste material for disposal; and recovery systems, which
produce a saleable byproduct (either sulfur or sulfuric acid) from the
recovered S0_. Nonrecovery processes make up the overwhelming majority
of the technology. Nine different processes and process variations
can be considered to be commercially available, seven of which are
nonrecovery systems. These seven processes constitute more than 95%
of the capacity currently in operation on utility and industrial boilers,
a trend which is expected to continue for the foreseeable future. Table
2.3 summarizes the applications of different FGD process technologies
for systems expected to be in operation by the end of 1979; and Table
2.4 summarizes FGD systems for utility boilers that are expected to be
operational by 1982 (those now in operation and those in design and
under construction).
2.2.2 Nonrecovery Processes
Nonrecovery processes in general can be subdivided into two groups,
wet processes and dry processes. Wet processes involve contacting the
flue gas with aqueous slurries or solutions of absorbents and produce
wastes in the form of solutions or slurries for direct discharge or
further processing prior to disposal. In many cases, waste slurries are
partially dewatered and further processed to produce a soil-like material
for landfill. Dry processes, on the other hand, produce essentially
moisture-free waste solids through the use of dry injection of absorbents
or spray dryers. All nonrecovery processes now in operation as well as
those due to come on line in 1979 involve wet scrubbing. However, a
number of contracts have been signed for the application of dry systems
to utility boilers which will start up in the early 1980's.
2.2.2.1 Wet Processes
Of the seven different types of nonrecovery processes now in
commercial operation on industrial and utility boilers, five involve
conversion of the SO. to some form of solid waste (sludge) for disposal
2-8
-------
VO
Table 2.3
Summary of FGD Systems Expected To Be
in Commercial Operation on Boilers in 1979
Utility
Nonrecovery
Direct Limestone-Conventional and
Forced Oxidation
Direct Lime
Alkaline Ash
Dual Alkali
Once-Through Sodium
Ammonia
Total
Recovery
Wellman-Lord
Citrate
Mag-Ox3
Total
38
2
0
0
21,870
735
735
Industrial
Number
of Plants
19
13
2
3
1
0
Capacity
(MW)
11,780
7,305
1,170
1,105
510
—
Number
of Plants
1
1
0
8
26
7
Capacity
(10* scfm)
50
85
—
1,082
4,954
552
43
0
1
0
xwo systems have been commercially operated on utility coal-fired boilers
but these are not currently in operation.
6,722
(^3000 MW-eq)
104
104
MW-eq)
Source: [45, 116]
-------
Table 2.4
Summary of FGD Systems Expected To Be in
Commercial Operation on Utility Boilers in 1982
(as of February 1979)
Utility
Nonrecovery
Direct Limestone-Conventional and
Forced Oxidation
Direct Lime
Alkaline Ash
Dual Alkali
Once-Through Sodium
Ammonia
Dry Sorbent - Sodium and
Calcium Based
Total
Number
of Plants
28
16
4
3
1
0
53
Capacity
(MW)
21,328
11,445
3,597
1,105
510
450
38,435
Recovery
Wellman-Lord
Citrate
Mag-0xa
Aqueous Carbonate
Total
3
0
0
1
1,855
systems have been commercially operated on utility coal-fired
boilers but these are not currently in operation.
Source: Arthur D. Little, Inc.
2-10
-------
in either wet ponds or landfills:
• Conventional direct lime scrubbing,
• Conventional direct limestone scrubbing,
• Limestone scrubbing with forced oxidation,
• Alkaline fly ash scrubbing, and
• Dual alkali.
Two systems produce a soluble waste which is discharged as an aqueous
liquor to holding ponds or wastewater treatment systems:
• Once-through sodium scrubbing, and
• Ammonia water scrubbing.
As shown in Table 2.3, essentially all utility applications of
nonrecovery technology involves solid waste-producing systems. In
contrast, a large majority of industrial boiler applications of FGD in-
volve the production of liquid wastes.
Both types of wet scrubbing nonrecovery systems can usually with-
stand relatively high levels of particulate, and many in the past have
been designed for simultaneous SC- and particulate removal. Approximately
40% of FGD systems currently in operation on utility boilers and about
80% of those in operation on industrial boilers serve as combined
particulate and SO control systems. However, most systems being installed
today on utility-scale boilers follow high efficiency electrostatic
precipitators in order to ensure reliable service of the FGD system. In
fact, all 7,500 megawatts of FGD capacity scheduled to start up on utility
boilers in 1979 involve SO^ removal only. This trend is expected to
continue as more stringent particulate emissions control regulations make
wet scrubbing for particulates unattractive. For industrial boilers,
however, it is likely that a large number of new FGD systems, at least
for the next few years, will continue to serve as both particulate and
S0_ control systems. Particulate emissions codes tend to be less stringent
at present, and in many cases the range of sizes of particulates encountered is
difficult to reliably control with electrostatic precipitators (such
as that from combined fuel boilers at pulp and paper plants).
2-11
-------
2.2.2.1.1 Solid Waste-Producing Systems
All of the solid waste-producing processes utilize some form of
lime or limestone to produce a mixture of insoluble calcium sulfite and
calcium sulfate salts as the principal waste product. Four of the five
technologies utilize slurry scrubbing (direct lime scrubbing, direct
limestone scrubbing, alkaline ash scrubbing, and limestone scrubbing
with forced oxidation), and their application is almost exclusively
limited to utility boilers. Only one, the dual alkali process, involves
solution scrubbing where spent absorbent solution is regenerated using
lime to produce a waste solid of calcium-sulfur salts. It is being
applied to both industrial and utility boilers.
Conventional direct lime and limestone scrubbing constitute the
majority of FGD systems on utility boilers. In these systems, flue gas
is contacted with a slurry of calcium salts (calcium sulfite/sulfate
and calcium hydroxide or calcium carbonate) and sometimes fly ash at
total suspended solids concentrations of 8-16 wt%. Slurries are recir-
culated through an open venturi or spray-type scrubber at high liquid-
to-gas ratios, and the spent liquor is collected in a delay tank to
allow completion of the precipitation reactions. Fresh alkali makeup
(either slaked lime or a slurry of finely ground limestone) is added to
the delay tank, and a slipstream is removed for solids separation. The
rate of fresh alkali makeup is controlled on pH with lime systems usually
operating at a pH of 6-7, slightly higher than the pH of limestone systems
(5-6). Alkaline ash scrubbing systems, which are similar in scrubber con-
figuration and operation, usually operate in a much lower pH range (3.5-5.0)
to effect good utilization of the ash alkali content. The waste slurry can
be discharged directly to a wet pond (sometimes after thickening) where the
solids are settled out and supernate returned to the scrubber system; or
it can be thickened and filtered for discharge to a dry impoundment. The
latter may require further processing of the wastes.
There are a number of variations on conventional direct lime and
limestone scrubbing systems directed toward improving S02 removal and
overall scrubber system reliability. Many full-scale lime scrubbing
2-12
-------
systems, for example, use either carbide lime or a dolomitic (high
magnesium content) lime rather than commercial lime. (Dravo Corporation
markets a special high magnesium content lime for FGD systems under the
name Thiosorbic lime.) The use of these limes effect lower oxidation
rates and therefore better control of scrubber scaling. Also, the high
magnesium content lime or the addition of magnesium oxide to commercial
lime usually results in higher S0_ removal efficiency and improves lime
utilization for high sulfur coal systems (reducing lime stoichiometries
from typical levels of 1.1-1.3 to 1.0-1.15).
A principal variation on direct limestone scrubbing involves inten-
tional oxidation of the calcium-sulfite salts formed in the scrubber to
calcium sulfate. This is done in order to improve SCL removal efficiency,
minimize scale and plugging potential, improve solids dewatering properties
(by converting the wastes to gypsum), and increase limestone utilization.
It is hoped that use of forced oxidation in high sulfur coal applications
will reduce limestone stoichiometries from the typical levels of 1.25-1.5
to 1.05-1.1. In the simplest form of the forced oxidation process, air
is bubbled through the slurry in a modified delay tank; however, two-stage
scrubbing has also been employed to cause intentional oxidation.
Direct lime, direct limestone, and alkaline ash scrubbing systems
have demonstrated high availability and reliability in many utility-scale
boiler applications. Lime systems have shown good operability in applica-
tions to the full range of coal sulfur contents. In low sulfur coal
applications, commercial-grade lime frequently is used, since the system
chemistry is fairly easy to control and relatively high oxidation rates
exist; however, in high sulfur coal applications, magnesium oxide addition
with commercial-grade lime or special lime such as dolomitic or carbide
lime has been required. Most successful limestone systems to date have
been in low and medium sulfur coal applications, again where oxidation
rates are relatively high. Forced oxidation using limestone scrubbing,
though, offers the potential for broadening the applicability of limestone
scrubbing to high sulfur coals.
2-13
-------
The dual alkali process is a second generation technology which is
just now reaching commercial demonstration in utility-scale applications
although there are a number of successful dual alkali systems in operation
on industrial-scale boilers. In dual alkali systems, SO- removal is
accomplished using solutions of sodium salts which are then regenerated
with lime to produce a waste calcium-sulfur salt that is similar in
chemical composition to the waste produced from direct scrubbing systems.
Dual alkali systems are most appropriate for medium and high sulfur coal
applications where relatively high SO. removal efficiencies are required
and where oxidation rates tend to be relatively low. Waste solids from
dual alkali systems are always discharged as washed filter cake; filters
are used to recover sodium salts in order to minimize sodium carbonate
makeup requirements and reduce the potential adverse environmental impacts
from the high IDS levels in the waste material.
2.2.2.1.2 Liquid Waste Systems
Liquid waste-producing systems have achieved a high degree of utiliza-
tion in industrial-scale boiler applications of FGD technology. Of the
two process technologies, once-through sodium scrubbing is the most widely
used, accounting for over 70% of the total FGD capacity on industrial
boilers. In once-through sodium scrubbing, the flue gas is contacted with
a recirculating solution of sodium salts consisting principally of sodium
sulfite/bisulfite, sodium sulfate, and sodium chloride. The type of
scrubber is dependent primarily upon the degree of S02 control required and
whether or not particulate is being simultaneously controlled. The pH is
controlled in the range of 5-7 through the addition of fresh alkali (e.g.
caustic or soda ash). A slipstream of spent liquor is removed for dis-
charge to holding pond and/or wastewater treatment systems. Frequently,
the waste liquor is treated prior to discharge. Treatment can involve
neutralization and oxidation of sulfite salts to sulfate.
Once-through sodium systems are capable of achieving very high SO
removal efficiencies, approaching 99%. However, the high cost of sodium
makeup and the problem of liquid waste disposal tend to limit the appli-
cability of once-through sodium systems. Most applications are on low
2-14
-------
sulfur fuels (where sodium makeup requirements are relatively low) or
in cases where an inexpensive source of alkaline sodium salts is available.
Instead of soda ash or caustic, some systems utilize brines, trona (impure
soda ash), or other waste process liquors.
There are only a few systems in operation involving ammonia scrubbing.
All are on industrial boilers and all utilize ammonia-laden process water.
Many of these systems have been installed primarily as wet particulate
scrubbing systems where the ammonia water is used to control the pH of
the scrubbing water. Spent liquor is usually sent to a settling pond for
removal of the particulate and the supernate treated prior to discharge.
2.2.2.2 Dry Processes
As previously indicated, dry nonrecovery processes have not yet been
commercially demonstrated in the United States, although at least three
systems for full-scale utility applications are in the early stages of
planning or design.
Three different approaches to dry scrubbing for producing solid
wastes have been actively pursued [57]:
• Injection of solid sorbents into the flue gas stream with
collection of sorbents downstream in a particulate control
device,
• Injection of solid sorbents into the boiler combustion zone, and
• Contacting of flue gas with alkali sorbent slurries in a
spray dryer.
All of these approaches involve simultaneous particulate and S0? control,
and all offer the advantage of not requiring flue gas reheat, which wet
processes generally do require.
The leading approach at present is based on the use of a spray dryer.
An aqueous solution or slurry sorbent is injected as a fine mist into
the ash-laden flue gas in a spray chamber. The hot gas evaporates the
water, and some SO is removed through reaction with the alkali. The
gas then passes to a dry particulate collector (fabric filter or
electrostatic precipitator) where the fly ash and dry sorbent solids are
2-15
-------
removed and further S02 removal is achieved. The flue gas is then
exhausted directly to the stack without reheat. Reheat is not required
since the flue gas is not saturated in the spray dryer.
A number of different sorbents have been tested for dry SC>2 removal
including soda ash, trona, nahcolite, lime, and limestone. Soda ash
generally provides the highest SC- removal capability in excess of 90%
at reasonable stoichiometric ratios. Lower S02 removal is achieved using
lime—60-75% S02 removal at stoichiometries of 1.0-1.5. Higher removal
efficiencies using lime require unrealistically high stoichiometries.
Thus, the application of dry sorbent systems may be limited to low and
medium sulfur coals due to the high costs of reagents.
The wastes are discharged as a dry material. The composition will,
of course, vary according to the type of reagent used. However, it is
expected that the majority of the wastes, aside from fly ash, will
consist of sulfate, sulfite, and chloride salts of either sodium or
calcium, with sulfates being the predominant species.
One spray dryer system utilizing soda ash is now in design for a
utility boiler (a 410-MW unit at Ottertail Power's Coyote Station) and
two other contracts have been awarded by Basin Electric Power Cooperative
[117]. These latter two will utilize lime as the absorbent. All three
of these systems will be installed on low sulfur coal or lignite-fired
boilers.
Testing of the other two approaches, injection of sorbents into the
flue gas and into the boiler combustion zone, has been ongoing at various
levels of activity over the past ten years. Of late, there has been
renewed interest in these approaches for low sulfur coal applications.
Testing of flue gas injection has focused on the use of sodium bicarbonate
nahcolite (impure sodium bicarbonate) and soda ash, all of which have
been shown to be effective for S02 removal for injection/baghouse collec-
tion systems. The most active for S02 removal is apparently nahcolite,
with removal efficiencies of 60-80% for low and medium sulfur coals at
stoichiometries of 0.8-2.0 (based on available alkali). This technology
is now being commercially offered.
2-16
-------
Boiler combustion zone injection is not being commercially offered,
although test work is continuing. The present focus is the mixing of
alkali reagents (e.g., lime, limestone, or soda ash) with the coal prior
to injection into the boiler. Preliminary results indicate appreciable
SCL removal efficiencies.
2.2.3 Recovery Processes
As in the case of nonrecovery processes, recovery processes can
also be categorized into wet and dry according to the mode of S0~ removal.
They can be further classified according to the type of byproduct pro-
duced: concentrated S0~ for conversion to sulfur or sulfuric acid;
sulfur only; or acid only.
At present, only two process technologies have been commercially
demonstrated on large industrial- or utility-scale boilers—the Wellman-
Lord process and magnesium oxide scrubbing. Another, the citrate scrubbing
process, is currently being commercially tested on a large industrial
boiler. All three of these are wet scrubbing processes.
The total capacity attributable to these three technologies (includ-
ing a magnesium oxide system not now in operation) is less than 5% of
the total FGD operating capacity in 1979.
2.2.3.1 Wet Processes
Wet scrubbing recovery processes are similar to nonrecovery systems
in that solutions or slurries are used in contacting the flue gas for SO™
removal. Furthermore, the types of scrubbers used are also similar to
those for nonrecovery systems. As previously noted, three processes have
reached commercial demonstration:
• Wellman-Lord process,
• Magnesium oxide scrubbing, and
• Citrate process.
SCL removal capabilities of each of these processes exceeds 90%; however,
each involves completely different process chemistry.
2-17
-------
The Wellman-Lord process involves absorption of S02 by a concen-
trated aqueous solution of sodium sulfite to produce a solution of sodium
sulfite/bisulfite. The scrubber effluent is recovered thermally with
steam to produce a sodium sulfite solution for recycle to the scrubber
system and a concentrated SO^ gas for further processing. S02 removal
efficiencies in excess of 90% can be achieved easily. A small portion
of the sulfite absorbent (3-15% of the S02 removed) may be oxidized to
sulfate. Since sulfate cannot be thermally regenerated, it is purged
from the system, preferably as a dry solid for sale or disposal.
The magnesium oxide process involves scrubbing with a slurry of
magnesium oxide to produce solid magnesium sulfite and sulfate (from
oxidation of sulfite). The solid is removed from suspension by dewater-
ing equipment, dried and roasted in a reducing atmosphere to decompose
the magnesium sulfite/sulfate into magnesium oxide and sulfur dioxide.
The regenerated magnesium oxide is returned to the scrubbing system, and
the sulfur dioxide is processed into its final byproduct form. The re-
generation step can be performed at the power plant site or at a remote
facility by shipping the magnesium sulfite and oxide, as a dry material,
to and from the regeneration facility. Because of the nature of the
calcining operation, the concentration of SO^ in the product gas is
relatively low (5-10%), so the gas is most suitable for conversion to
sulfuric acid.
In the citrate process the flue gas is scrubbed with a solution of
sodium citrate. The sulfur-laden solution is reacted with hydrogen sul-
fide gas, and sulfur is precipitated. The precipitated sulfur may be
separated from the citrate solution by either a kerosene-additive flota-
tion or an air flotation technique. Two-thirds of the product sulfur is
reacted with reducing gas to form EUS for the Glaus reactor; the rest of
the sulfur is recovered for sale. A bleedstream of the regenerated
absorbent is fed to a crystallizer where sulfate formed by oxidation of
sulfite is removed as gypsum or Glauber's salt. The process has also been
modified to produce concentrated SO^ gas (for conversion to acid) by
thermal stripping of the sulfur-laden citrate solution.
2-18
-------
All of these processes have two features in common: first, they have
limited tolerance to the buildup of impurities in the absorption/regenera-
tion systems (e.g., chlorides and fly ash); and second, there is a practical
limit to the amount of absorbent oxidation that can be tolerated. Thus,
they are most appropriate for high sulfur coal application following high-
efficiency dry particulate removal systems (ESP's). In most applications
to coal-fired boilers, the S0_ absorbers would be preceded by wet scrubbers
to minimize the pickup of fly ash, chloride, and other impurities by the
absorbent liquor. The prescrubbing medium is recirculated water, with the
only makeup requirement being that required to replenish evaporation losses
plus liquor purge. The bleed rate of the purge liquor can be set either
by the level of suspended solids to maintain it below about 5 wt%, or by
the calcium concentration (from fly ash dissolution) to maintain it below
the gypsum solubility product to prevent scaling.
In addition to accomplishing the absorption of chloride and the
removal of fly ash, the prescrubber also absorbs some S02 from the flue
gas. The S(>2 absorption will vary depending upon the liquor bleed rate
and the gas composition, but it conceivably can range from a few percent
of the inlet S02 to as much as 10% or more (especially for low sulfur
coal applications). The prescrubber purge, therefore, will be very acidic
and will require treatment such as neutralization and solids separation
prior to discharge. If neutralization is effected using lime or limestone,
then the solid waste ultimately produced will have a chemical composition
not unlike the wastes produced from nonrecovery systems.
The Wellman-Lord and citrate processes also produce another secondary
waste stream, impure sodium sulfate. The amount will vary according to
the extent of absorber oxidation but will typically correspond to about
5% of the S02 removed. While magnesium oxide scrubbing does not produce
a secondary waste stream of sodium sulfate, it does appear to have an
upper limit of about 15% oxidation based upon the ability of the calcining
operation to regenerate magnesium sulfate. At higher levels it would
probably be necessary to purge some regenerated absorbent to keep magne-
sium sulfate levels down to prevent scaling in the absorber.
2-19
-------
2.2.3.2 Dry Processes
There are presently no dry sorbent systems in operation on utility
or industrial boilers; however, there are four in advanced stage of
development:
• Aqueous carbonate process,
• Shell/UOP copper oxide adsorption,
• Catalytic/Westvaco dry activated carbon, and
• Bergbau-Forschung/Foster Wheeler process.
The aqueous carbonate process is now being installed on an EPA demon-
stration unit on a 100-MW utility coal-fired boiler. The process is
based upon sodium carbonate scrubbing using a spray dryer for gas con-
tacting, analogous to that discussed with regard to dry nonrecovery
processes. Primary particulate removal would be accomplished upstream
of the spray dryer using mechanical collectors. Dryer waste solids
(principally sulfite/sulfate solids, unreacted carbonate, and some fly
ash) are collected and fed to a molten carbonate reactor where the sulfur
is reduced to sulfide by carbon (petroleum coke or coal) at a temperature
of about 1800°F. A portion of the carbon is combusted to provide heat
for the endothermic reduction reactions and system heat losses. The
sodium sulfide melt from the reducer is quenched, and the fly ash and
unreacted carbon are filtered from the resulting green solution. The
C02-rich reducer offgas and the green liquor are then reacted to regen-
erate sodium carbonate. The hydrogen sulfide stream is sent to a Glaus
plant for sulfur production.
Process wastes include wet filter cake containing mostly fly ash
but also residual Na2S and NaHS and a chloride blowdown stream. In order
to achieve a particulate emission of 0.01 gr/scf or less, the process
design specifications may include high efficiency particulate collection
downstream from the spent absorbent collection device (depending upon
the type of device used).
2-20
-------
The other three dry processes noted above use dry adsorbents for
SO* removal. As such, they do not produce any appreciable waste liquor
or solid purges other than spent catalysts or adsorbents. These have all
been operated either in the United States or Europe on boilers up to
about 50 MW in size; however, they have not yet achieved commercial
demonstration in the United States.
2. 3 Categorization of FGC Wastes
The quantity and characteristics of coal ash and FGD wastes produced
from a combustion system depend on a variety of factors including:
• Characteristics (ash and sulfur content) of coal,
• Type of combustion (boiler) system and its operating conditions,
• Type of particulate collection system and its operating conditions,
and
• Type of FGD system and its operating conditions.
Categorization of FGD wastes and coal ash requires an understanding
of the substances making up FGD wastes.
The principal substances making up the solid phase of FGD wastes are
calcium-sulfur salts (calcium sulfite and/or calcium sulfate) along with
varying amounts of calcium carbonate, unreacted lime, inerts, and/or fly
ash. The ratio of calcium sulfite to calcium sulfate is a key parameter
(the latter, usually present as CaSO, • 1/2 H_0 or as gypsum, CaSO, •
2H~0) will depend principally upon the extent to which oxidation occurs
within the system. Oxidation is generally highest in systems installed
on boilers burning low sulfur coal or in systems where oxidation is
intentionally promoted. Fly ash will be a principal constituent of the
waste only if the scrubber serves as a particulate control device in
addition to SCL removal or if separately collected fly ash is admixed
with sludge. The amount of inerts and unreacted raw materials (lime and/
or limestone) in sludges depends on the quality and utilization of raw
materials (system stoichiometry).
When the sulfate content of the waste solids is low, calcium sulfate
can exist with calcium sulfite as a solid solution of hemihydrate crystals
(CaSO • 1/2 H90). Data from pilot plant, prototype, and full-scale FGC
2-21
-------
system operations indicate that up to 25-30% of the total calcium-sulfur
salts can be present as CaSO, • 1/2 H^O in solid solution with GaSO
1/2 1^0. At higher calcium sulfate levels, gypsum (CaSO, • 2H-0) becomes
the predominant form of calcium sulfate. It is expected that at very
high levels of oxidation (greater than 90% oxidation of the S09 removed)
the calcium sulfite can form a solid solution with gypsum (CaSO • 2H 0)
x 2
analogous to the solid solution of hemihydrate salts formed at low
sulfate levels.
Because the differences in the crystalline morphology of hemihydrate and
dihydrate solids not only reflect the chemical composition but also to
a large extent dictate the physical and engineering properties of FGC
wastes, it is convenient to classify FGC wastes on the basis of the
calcium sulfate content. Three such categories have been selected, as
follows:
Category Predominant Crystalline Form
Sulfate-rich (CaSO,/CaSO > 0.90) Dihydrate
^f X
Mixed (0.25 > CaSO,/CaSO * 0.90) Dihydrate and hemihydrate
*4 X
Sulfite-rich (CaS04/CaSOx < 0.25) Hemihydrate
*
where CaSO is the total calcium-sulfur salt content. This categorlza-
X
tion will be employed in the ensuing discussions throughout this report.
Factors which tend to influence the amount of sulfite in FGC wastes
(i.e., the extent of oxidation) are:
• Boiler excess air,
• Type of scrubber,
• Use of forced oxidation,
• Presence of oxidation inhibitors or catalysts in fly ash,
reagents, or water makeup,
• Type of reagent,
• pH in the scrubber loop, and
f Sulfur content of the coal and the degree of S0« removal.
2-22
-------
In general, it is possible to relate the three general categories
of wastes indicated above and their associated crystalline morphologies
with various types of FGC process technologies and their applications
according to the coal sulfur content. Such a matrix relationship is
shown in Table 2.5. As indicated, dual alkali and conventional direct
lime scrubbing systems using either carbide or Thiosorbic lime almost
exclusively produce sulfite-rich wastes. Such systems are generally
applied to medium and high sulfur coal-fired boilers, and attempts are
made to minimize oxidation. On the other hand, alkaline ash and lime-
stone forced oxidation systems produce sulfate-rich wastes almost
exclusively. And conventional direct lime (using commercial lime) and
limestone systems can produce either sulfite-rich, sulfate-rich, or
mixed wastes depending upon the sulfur content of the coal and the
manner in which the scrubber systems are operated.
2.4 Dewatering of FGC Wastes
The following review of FGC waste dewatering is restricted to wastes
produced from SC>2 scrubbing (both systems for S02 control only, and for
simultaneous S02 and particulate control) and wet particulate scrubbing
systems (which also effect a small degree of SC>2 removal) . Bottom ash
and fly ash are relatively easily dewatered materials in relation to
SC>2 scrubbing wastes. Bottom ash and many fly ashes are free drainir?,
and sluiced ash can usually be adequately dewatered to high solids contents
by settling or settling with underdrainage. Only a few coal-fired steam
or power boilers utilize any means of dewatering beyond gravity sedimen-
tation, including those which ultimately use the ash for fill (where the
ash is usually dredged from settling ponds).
2.4.1 State of the Art
Most unthickened slurry wastes produced by FGC systems contain on
the order of 5-15 wt% suspended solids. In order to avoid the unnecessary
discharge of large amounts of process liquor, these wastes frequently are
dewatered mechanically prior to being discharged from the process.
Primary dewatering usually is accomplished using thickener/clarifiers
or settling ponds. Primary dewatering is virtually universally practiced
2-23
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Table 2.5
I
N)
Matrix of Unstabilized FGD Waste
Generation-Nonrecovery Solid Waste Producing Systems
No. Waste Type
1 Sulfite-rich (CaSO • 1/2H 0)
A £
Mixed Sulfite/Sulfate
(CaSO • 1/2H 0 + CaSO • 2H 0
X £. H jf.
Sulfate-rich (CaSO • 1/2H 0
+/or CaS04 • 21^0) 4 Z
Crystalline
Morphology
Needles
Platelets
Agglomerates
Needles or Platelets
Platy1
Needles or Platy
Low Sulfur Coal
DLd/AAeDLSf LSFQ8 DAh
Medium/High
Sulfur Coal0
DL DLS LSFO DA
Sulfite-rich = CaS04/CaSOx <. .25
Sulfate-rich = CaSO,/CaSO >_ .9
b
Low sulfur coal <~2% S.
Medium/high sulfur coal >"2% S.
Conventional direct lime process.
Alkaline ash scrubbing.
Conventional direct limestone process.
^Limestone with forced oxidation.
Dual alkali process.
Resembling rhombohedral cleavage fragments.
Notes; / Refers to the particular waste type as the
common waste product from the type of coal
and process.
? Some question on this.
Source: Arthur D. Little, Inc.
-------
in order to reduce sludge volume and conserve water. Secondary methods
of dewatering are also sometimes employed. These include vacuum filtra-
tion and centrifugation. Secondary dewatering is only employed as a
precursor to dry impoundment in order to improve the handling properties
of the wastes prior to truck transport or stabilization. Table 2.6
summarizes dewatering practices for full-scale FGC systems in operation
on utility boilers as of November 1978.
Table 2.6 shows some interesting trends in dewatering practices in
the utility industry:
• No simultaneous SO,- and fly ash control systems or wet
particulate scrubbing systems employ secondary methods
of dewatering (i.e., filtration or centrifugation) for
FGC waste dewatering, although a number of the plants
do dispose of wastes via dry impoundment of wastes re-
claimed from secondary settling ponds.
• The overwhelming majority of the FGD capacity for S0_
removal only involves thickening and filtration or
centrifugation for dry impoundment of the wastes. This
trend is expected to continue for the foreseeable future.
About 6,700 megawatts of new, nonrecovery FGC capacity
producing solid wastes are expected to be on-line in
1979, all of which will be devoted to SO- control only.
Of this total, approximately 85% will utilize some form
of dry impoundment for waste disposal, and more than
two-thirds of these will employ either filtration or
centrifugation for waste dewatering.
The ease and degree of dewatering FGC wastes, which affects not only
the cost for transportation and chemical treatment but also the manner in
which wastes can be disposed, is highly dependent upon both the chemical
composition and the physical properties of the material. The principal
chemical properties affecting dewatering are the ratio of calcium sulfite
to sulfate, fly ash content, and the presence of unreacted amounts of
lime or limestone. The major physical properties are crystalline
2-25
-------
Table 2.6
to
I
Scrubber System Mode
• SO Removal
Z -i
- Low Sulfur Coal
- High Sulfur Coal°
• SO- + Ash Removal
^ ^
- Low Sulfur Coal
- High Sulfur Coalc
• Wet Particulate Removal
- Low Sulfur Coal
TOTAL
Summary of FGC Waste Dewatering Practices for
Operating Utility Scrubbers3
Dewatering Practices Employed
Pond
Settlingd Thickening
Thickening/
Pond Settling
Thickening/
Filtration
(Number of Plants/Total Capacity, MW)
3/1570
1/550
2/1085
2/885
7/1220
15/5310
2/365
3/185
3/2185
1/1650
3/865 2/1175
12/6250 2/1175
3/1045
6/2515*
__
—
9/3560
Thickening/
Centrifugation
1/1585
1/1585
aBasis: November 1978.
Generally < 1.5% sulfur.
°Generally > 1.5% sulfur.
In addition to dewatering, settling pond acts as final disposal site in 10/3330 of those indicated.
elncludes two plants (totaling 920 MW) whose scrubber system removes ash but have ESP's for primary
ash removal.
-------
morphology and waste particle size distribution. These properties depend
upon a number of factors including:
• Fuel type and composition,
• Boiler type, design, and mode of operation,
• Fly ash and bottom ash removal systems and their
relation to sludge disposal,
• FGD system type, design, and mode of operation, and
• Type of reagent used and overall plant water balance
considerations.
Because of the numerous variables involved, wastes characteristics (i.e.,
chemical and physical properties) can vary over extremely wide ranges.
Consequently the task of developing generalized correlations between
chemical/physical properties of wastes and their degree of dewaterability
is difficult, and there is considerable uncertainty in the design of
dewatering equipment for full-scale systems. In part this is due to the
wide range of operating conditions under which an FGD system must operate;
and in part because of the uncertainty in FGD system performance. Hence,
dewatering equipment, and filters in particular, are designed with large
safety factors.
The dewaterability of FGC wastes can be measured in terms of any
number of parameters. The best measures are those which relate directly
to the dewatering operations involved. If dewatering is to be accomplished
by gravity sedimentation operations—thickening/clarification or pond
settling—then one or all of the following parameters could be used as
a measure of dewaterability:
• Solids settling rate (cm/second),
3
• Settled density (grams/cm ), and
• Weight % solids in the settled waste.
However, where thickeners are used, thickening of the waste solids is not
always the most important concern in design. In many cases, clarification
of the system liquor is the determining factor, and it provides the basis
for design. In this regard, a number of FGC systems employ flocculants
2-27
-------
to ensure acceptable clarity in scrubber return liquors. If the dewater-
ing is accomplished by either vacuum filtration or centrifugation, the
following parameters would be used to design equipment and/or assess
performance:
2
• Filtration rate (kilograms/m hr),
3
• Cake density (grams/cm ), and
• Cake solids content (wt%).
In addition to waste characteristics, the type and design of the
filtration equipment (e.g., belt versus rotary drum, scraper discharge
versus roller discharge) and the manner in which it is operated can
importantly affect the extent of dewatering achieved. In most cases it
is necessary to operate filters with relatively thin cake thicknesses
(on the order of a few centimeters or less) to prevent cake cracking.
Cracking results in loss of vacuum (and thereby poor dewatering) and,
where cakes are washed to recover and return FGD system additives (e.g.,
magnesium or sodium values), loss of wash efficiency. The primary design
and operating parameters that can be used to control cake cracking and
optimize the overall dewatering performance of the filter include:
• Slurry feed concentration,
• Type of cloth,
• Submergence depth (for a rotary drum filter),
• Vacuum applied,
• Drum speed, and
• Drum cycle times (form time, dry time, etc.).
However, even under the best design and operating conditions the solids
content of the filtered cake will still fall short of the optimum dry
density for the waste material (solids content at which maximum dry den-
sity is achieved on compaction).
In an analogous manner, the design and operation of continuous, solid-
bowl centrifuges can importantly affect the extent of dewatering achieved.
Important parameters include:
2-28
-------
• Feed slurry concentration,
• Feed rate,
• Pool depth, and
• Bowl speed.
In general the dewatering achieved with continuous centrifuges and fil-
ters are roughly equivalent, although to some extent, the relative per-
formance is waste-specific. A principal difference is that washing of
the wastes, if required is difficult and inefficient using a centrifuge.
Also, in some cases with sulfite-rich wastes, centrifuges can produce
waste solids contents as much as 5-10% higher than with filters; however,
the centrifuge can tend to "masticate" the wastes resulting in a material
that can be more difficult to handle and transport than a filter cake
even though it has a higher solids content. Thus, to date centrifuges
have only been applied to sulfate-rich and/or high fly ash content wastes
in full-scale systems.
Table 2.7 summarizes the degree of dewatering reported via filtration
or centrifugation for wastes produced by ten full-scale utility FGC sys-
tems, six industrial FGD applications, and three prototype installations.
Drawing from these data as well as information from EPA-funded pilot plant
and laboratory studies [19, 31, 37], some generalizations regarding the
dewatering behavior of different types of FGD wastes are possible.
In most direct scrubbing systems producing calcium sulfite-rich wastes,
the solids consist of extremely thin, fragile platelets that are formed
either as individual crystals or as small clusters or 5-100 crystals. The
degree of clustering and the size of the clusters are generally a function
of the chemical conditions under which the crystals are formed. It has
been suggested that lower sulfur coals form the loosest clusters, so there-
fore these would be expected to be found in wastes from scrubbing systems
on boilers firing low sulfur western coals [21.
Such platelets and small clusters of platelets are generally difficult
to dewater and form a loose, structurally unstable material for disposal even after
filtration. The platelets and loose clusters can form an open structure
of stacked crystals with large voids that trap water. Consequently, such
2-29
-------
Table 2.7
Dewatering of FGC Wastes at Utility and Industrial Installations
Employing Filters and Centrifuges
to
u>
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-------
wastes are not easily compacted by normal settling, nor can they be read-
ily filtered to waste cakes containing high solids contents. Further,
fragile crystals can break under pressure and may clog filter cloths,
resulting in loss of vacuum and poor dewatering [134]. Fracturing also
occurs in centrifugation, and the small fractures result in poor dewater-
ing and cloudy supernates.
As a group, sulfite-rich platelets and platelet clusters produced
in direct slurry scrubbing systems can generally be thickened to 20-35%
solids using conventional open-tank clarifier/thickeners, and can be fil-
tered to 40-55% solids. The degree of dewatering actually achieved within
this range appears to vary according to the general type of scrubbing
system and reagent (alkali) used. For example, wastes produced from direct
lime scrubbing systems using commercial lime tend to fall in the upper end
of the range; wastes produced using Thiosorbic lime tend to fall in the
medium/upper end of the range; and those produced using carbide lime tend
to fall in the low/medium end of the range. Wastes produced from direct
limestone scrubbing systems tend to fall in the medium to medium/upper
end of the range, although the dewaterability of sulfite-rich and mixed
sulfite/sulfate wastes from direct limestone scrubbing systems depend
importantly upon the sulfate content of the wastes and the quantity of
unreacted limestone present. It should be noted that these are general
trends drawn from available data and discussions with FGC equipment sup-
pliers and system operators. Actual dewatering achieved can vary depend-
ing upon the scrubber system operating condition and the design and ope-
ration of the dewatering equipment as discussed earlier.
In contrast to direct slurry systems, dual alkali processes tend to
form needle-like crystals (as opposed to platelets) which generally agglom-
erate into relatively large spherically-shaped clusters. The extent to
which agglomeration occurs depends upon the conditions under which the
regeneration of scrubber bleed liquor is carried out. Important factors
include the composition of scrubber liquor, the design of the reactor
system, and the extent of regeneration (i.e., operating pH). Where a
high degree of agglomeration is effected, the solids tend to exhibit
better settling and filtration properties in comparison to wastes from
2-31
-------
direct slurry scrubbing processes. Using clarifier/thickeners, dual
alkali wastes can typically be thickened to 25-45% solids and can be fil-
tered using standard rotary drum vacuum filters to waste cakes typically
containing 45-70% solids.
Calcium sulfate-rich wastes are generally much more easily dewatered
than are sulfite-rich wastes. The crystalline form of calcium sulfate
present as gypsum is blocky, with some tendency toward elongation. Cry-
stals usually grow individually or as twin crystals to relatively large
sizes in comparison to sulfite-rich crystals. In general, sulfate-rich
wastes thicken to about 40-60% solids via conventional clarifier/thick-
eners and can be filtered to 65-90% solids.
The presence of fly ash in FGC wastes either through simultaneous
collection with SC^ or admixture with FGD wastes may enhance the dewater-
ability of the calcium-sulfur salts. The degree of improvement is
greatest for wastes exhibiting the poorest dewaterability but it is also
dependent on the quantity and properties of fly ash. Fly ash particles
tend to be spherical in nature and, hence, more freely draining than plate-
lets. In combination with sulfite-rich platelets and loose clusters, fly
ash can fill the void spaces and break the surface tension between the
calcium-sulfur particles improving filterability. Laboratory tests per-
formed by Aerospace [31] indicate that more effective dewatering can be
achieved when fly ash is added to a freely drained Shawnee lime waste
sample. However, fly ash has a much less pronounced effect on dewater-
ability of tightly packed, spherical-type agglomerates of sulfite-rich
crystals and large blocky gypsum crystals. (See Section 2.4.2.1.) In
the extreme, fly ash may even slightly decrease dewaterability of
large, well-grown gypsum crystals or sulfite clusters.
2.4.2 Research and Development Programs in FGC Waste Dewatering
At present, there are very few programs, completed or ongoing, which
focus primarily on the dewatering of FGC waste solids. Table 2.8 lists
the major studies having either a principal or limited focus on FGC
waste dewatering, and Table 2.9 summarizes the four major EPA- and EPRI-
sponsored projects which deal directly with dewatering of FGC wastes.
Each of these four programs is discussed briefly below.
2-32
-------
Table 2.8
Summary of Past/Present Programs Focusing on the Dewatering of FGC Wastes
Contractor/Agency Sponsor(s)B
Test-Site
Laboratory/Pilot Testing (Principal Focus on FGC Waste Dewatering)
Aerospace
Auburn University
Envirotech
Radian
EPA
EPA
EPRI
EPA
Aerospace Laboratory
Auburn/ Shawnee
Not Available (NA)
Not Applicable
(study correlated existing
data)
Scrubber System Type
C.D.L. C.D.L.S. F.O.-L F.O.-L.S. P.A. A.A. A.S. Reference No
X X
X
X X
-Not Available
31, 37
134
NA
135
• Pilot/Prototype Testing (Limited Focus on FGC Haste Dewatering)
ADL
Bechtel/TVA
CEA/ADL
CIC
CIC/Radian,
UFA
GFERC
GM/ADL
LG&E/CE
EPA
EPA
EPA/EPRI
EPRI/SCS
EPA/EPRI
EPA
DOE
EPA
EPA
ADL Pilot Plant
Shawnee
Scholz
Scholz
Scholz
RTP
GFERC
CM (Parma)
Paddy's Run
X X
X X
X
X
19
55,
19
X 49
NA
137
20,
18
139
56,
138
136
ADL Arthur D. Little
CE Combustion Engineering
CEA Combustion Equipment Associates
CIC Chiyoda International
DOE Department of Energy
EPA U.S. Environmental Protection Agency
EPRI Electric Power Research Institute
GFERC Grand Forks Energy Research Center
CM General Motors
LG4E Louisville Gas and Electric
RTP Research Triangle Park
SCS Southern Company Services
TVA Tennessee Valley Authority
C.D.L Conventional Direct Lime
C.D.L.S. Conventional Direct Limestone
F.O.-L. Forced Oxidation with Lime
F.O.-L.S. Forced Oxidation with Limestone
D.A. Dual Alkali
A.A. Alkaline Ash
A.S. Acid Scrubbing
Source: [5]
-------
Table 2.9
EPA- and EPRI-Sponsored Projects Focusing on
the Dewatering of FGC Wastes
Project Title
Disposal of by-product from
nonrecovery FGD systems:
final report
Contractor/Agency
Aerospace Corporation
Dewatering of FGC wastes by
gravity sedimentation:
pilot evaluation
Auburn University
N3
Sludge dewatering methods
for FGC processes
Envirotech Corporation
Development of a mathematical
basis for relating sludge
properties to FGD-scrubber
operating variables
Source: [5]
Radian Corporation
Sponsor Project Focus/Status
EPA Determine environmentally sound methods
for the disposal of wastes from nonrecov-
ery FGD systems. This project involved
considerable laboratory testing of FGD
wastes to determine their physical and
chemical characteristics, along with the
evaluation of several dewatering methods
for such wastes. (Completed 1978.)
EPA/TVA Evaluate the performance of a new contin-
uous dewatering system (consisting of a
lamina-type clarifier and conventional
thickener), proposed by Auburn University,
on a pilot scale level on-site at TVA's
Shawnee Power Station. (Ongoing.)
EPRI Evaluate various bench-scale and pilot
dewatering devices such as clarifiers, fil-
ters , and centrifuges to determine what
principal variables in FGD waste affect the
design of such devices. Determine capital
and operating cost data for these dewater-
ing devices as a function of sludge compo-
sition. (Ongoing.)
EPA Develop a mathematical basis for relating
sludge properties to FGD-scrubber operating
variables so as to determine what scrubber
operating parameters will increase the
average particle size of calcium sulfite
enriched sludges in order to increase their
dewaterability. (Completed April 1978.)
-------
2.4.2.1 The Aerospace Corporation
Aerospace has recently completed a four-year study [31, 37] for
the EPA to characterize wastes from nonrecovery FGC systems and evaluate
environmentally sound methods for waste disposal. In this study, chem-
ical and physical properties of waste samples taken from direct lime,
direct limestone, and dual alkali processes at ten different scrubbing
facilities were examined. As a part of the characterization effort,
waste dewatering properties were investigated in laboratory batch testing
using four different methods: settling; settling with underdrainage;
centrifugation; and filtration. Wastes tested included both sulfate-rich
and sulfite-rich materials with a wide range of ash content.
With a few exceptions, simple gravity settling produced the lowest
wet bulk densities (and solids contents), and filtration produced the
highest bulk densities (and solids contents). The solids contents
achieved with simple settling generally ranged from 40 wt% to 50 wt%
solids, while the solids contents achieved with filtration generally
ranged from 50 wt% to 55 wt%. In most cases, filtration resulted in about
a 10 wt% to 15 wt% increase in solids. Dewatering via settling with
underdrainage and-centrifugation usually resulted in solids contents
between these limits; however, the order of these with respect to de-
watering efficiency varied with waste type and composition.
It should be noted that such laboratory testing will not necessarily
produce the same results as full-scale operations. First, batch testing
by its very nature can be considerably different from continuous opera-
tions as would be the case in comparing simple laboratory batch centrifu-
gation versus continuous dewatering using solid bowl centrifuges where
the solid and liquid phases are continuously separated and the solids can
be physically disturbed by the action of the centrifuge. Second, the
small scale of laboratory testing may not account for effects seen in
larger scale field operations such as the consolidation and increased
solids content of settled wastes in deep disposal ponds. Furthermore,
laboratory results may also be affected by sample handling and prepara-
tion (e.g., sample storage and aging, sample reconstitution, etc.). It
2-35
-------
can be difficult, therefore, to accurately predict the relative effective-
ness of different dewatering methods by such tests. However, laboratory
batch tests can usually provide a fairly reliable measure of the relative
ease of dewatering of different types of FGC wastes.
As expected, the wastes with the coarser particle size distributions
were more effectively dewatered by all methods relative to those with
finer particle size distributions. In general, sulfate-rich materials
tended to dewater to higher solids contents than sulfite-rich materials,
although the presence of high concentrations of fly ash and/or unreacted
limestone in many samples make even qualitative comparisons difficult.
In an attempt to assess the effect of simultaneous fly ash removal
on FGD wastes, samples both with and without fly ash from the Scholz dual
alkali prototype system and Shawnee direct lime scrubbing systems were
studied. The laboratory dewatering results are presented in Table 2.10.
As shown, the effect of fly ash varied depending upon the type of waste,
but the effect was generally quite small. The dual alkali waste samples
were obtained from operation of the scrubber system for SO removal only
and for simultaneous ash and SO- removal. The sample of direct lime
scrubbing waste containing 40% fly ash, on the other hand, was manufac-
tured in the laboratory by admixing ash to wastes generated from S0_
scrubbing only. This admixing of ash apparently contributed to the
improved dewatering efficiency, particularly of settling with underdrain-
age. The ash separated from the mix and settled to the bottom of the
column and served as a filtering aid to allow better drainage (possibly
through prevention of blinding of the filter cloth at the bottom of the
column). It is interesting to note that the presence of fly ash in the
dual alkali waste (from simultaneous ash scrubbing) did not improve and,
in fact, decreased slightly the dewatering efficiency measured in the lab-
oratory tests. However, in actual filter operations at the Scholz plant,
the solids content of the waste cake containing ash did increase slightly
relative to that without ash (see Table 2.7).
2-36
-------
Table 2.10
Effects of Fly Ash on the
Dewatering Properties of FGC Waste Samples
(Laboratory Evaluation)
Approximate Solids Content of Dewatered Waste (wt%)
t-0
i
u>
Waste
Direct Lime Scrubbing (Shawnee)
Without Ash
With Ash (40 wt%)
Dual Alkali (Scholz)
Without Ash
With Ash (30 wt%)
Settling
48
45
43
43
Centrifugation
49
53
45
45
Settling with
Underdrainage
51
58
51
47
Filtration
57
61
64
59
Source: [31, 37]
-------
2.4.2.2 Auburn University
Under funding of the EPA, Auburn University is currently conducting
a study to improve the dewatering efficiency achievable with available
thickening and clarification technology. The work has involved laboratory-
scale testing of both batch and continuous thickening using samples of
FGD waste obtained from the direct lime scrubbing system at Louisville
Gas and Electric's Paddy's Run Station. Based upon the evaluation of
several different equipment configurations, a promising dewatering system
has been developed. The system shown in Figure 2.1 consists of two
separate units: a lamina-type (inclined) clarifier and a conventional
(tank) thickener. In this fashion, the clarification and the thickening
functions are decoupled as much as physically possible. Consequently,
the thickener can be designed to produce a sludge with as high a solids
content as possible, without the additional burden of having to produce
a very clear overflow. The role of the clarifier is to produce the clear
overflow which is then recycled back to the system. In addition, the
clarifier produces a moderately concentrated underflow that is returned
to the thickener at any desired tank height. In this way, the clarifier
enhances the performance of the thickener so that FGD wastes can be
thickened to very high solids concentrations with less settling area than
that required by conventional-type thickeners. It has been reported [134]
that the system yields clear overflows and highly concentrated underflows
(30 to 80% solids by weight) as well as offering flexibility of operation,
which allows separation of solids at higher efficiencies and solids
throughput rates than those possible with conventional systems over a range
of scrubber operating conditions.
Auburn University has recently received additional funding from EPA
and TVA to evaluate the performance of this dewatering system on a larger
pilot scale at TVA1s Shawnee facility. This evaluation has a threefold
purpose: (1) to confirm and better establish the results obtained from
the laboratory-scale tests performed at Auburn; (2) to provide design
data for scale-up purposes; and (3) to provide operational data needed
to better estimate the potential cost savings offered by this dewatering
approach.
2-38
-------
N3
I
U>
VO
.Clarified Liquor
for Recycle
Clarifier
Recycle
Feed
Mixer
Feed
Thickener
\'
Underflow
Source: [134]
Figure 2.1 Flow Diagram of Proposed Dewatering System
-------
2.4.2.3 Envirotech Corporation
Envirotech has recently completed a study (yet to be published)
sponsored by EPRI to provide the utility industry with a sound data base
for assisting in selection of dewatering methods for FGC wastes. The
program plan focused on the testing of various bench- and pilot-scale
dewatering equipment (such as clarifiers, filters, and centrifuges) to
evaluate performance and to determine how variations in waste composi-
tion affect the design, and capital and operating costs. A follow-on
second-phase effort is being planned to field-test pilot dewatering
equipment and evaluate the handling and transport properties of the
wastes produced.
2.4.2.A Radian Corporation
Investigators at Radian, under the sponsorship of EPA, examined
prospects for increasing the average size of calcium sulfite particles
in FGD wastes in order to improve dewaterability [141], The purpose was
to correlate pertinent design and operating parameters of SC^ removal
systems producing calcium sulfite-rich wastes with waste quality, that
is, its settling rate, settled bulk density, and particle size distri-
bution. A model for predicting the crystal size distribution of calcium
sulfite produced in conventional direct limestone scrubbing systems was
developed and used to examine the sensitivity of crystal size distribu-
tions to changes in FGD system process variables such as: relative
saturation with respect to calcium sulfite; solids residence time in
the scrubber recirculation tank; and clarifier overflow maximum particle
size. It is believed that the model can be used to interpret actual
experimental results as well as predict process conditions for producing
an optimum waste.
However, more bench- and pilot-scale work has been recommended to
improve the data base for the relationships developed between calcium
sulfite particle size distribution and process variables and to verify
the model's ability to predict conditions conducive to increased particle
size distributions. A pilot-scale test program has been proposed to be
2-40
-------
carried out at RTF's pilot plant facility. The major emphasis of the
program would be to determine the principal locations of calcium sulfite
nucleation in the system. Three possible areas have been identified:
the feed pump; the scrubber; and the hold tank. Tests will be performed
to determine the effect of (1) the feed pump (i.e., pump tip speed,
steel versus rubber-tipped impeller), (2) operating at higher calcium
sulfite saturations within the scrubber liquor, and (3) varying both the
hold tank agitator speeds and its material of construction (steel versus
polypropylene) on the calcium sulfite particle size distribution. Tests
also will be performed to determine and correlate any effect that various
process variables might have on the nucleation and growth rates of cal-
cium sulfite crystals. These include changes in slurry solids content,
scrubbing liquor quality, residence time variations in the scrubber
recirculation tank, and the grinding and recycling of clarifier underflow.
2-41
-------
3.0 PRODUCTION TRENDS AND HANDLING OPTIONS
3.1 Coal/Waste Relationships
Table 3.1 shows typical coal/ash/sludge relationships for six
representative coals and corresponding waste categories according to the
basis set forth in Section 2.0. The coal characteristics reflect
assumption of some coal cleaning prior to combustion.
3.2 Projected Generation and Trends
Projections of the generation of FGC wastes from coal-fired utility
and large-scale industrial boilers (>25 MW-eq) have been estimated
through the year 2000. The basis for these projections were the esti-
mates on coal consumption by type developed by Mitre Corporation [140].
Table 3.2 shows the cumulative generation of coal ash and FGD wastes
(without fly ash) projected to the year 2000, and Table 3.3 shows the
breakdown of ash and FGD wastes by utility and industrial boilers.
The general assumptions used in preparing these estimates were as
follows:
• Consumption of coal based on estimates prior to the National
Energy Act (NBA) of 1978, NEA is expected to impact future
coal utilization.
• All new coal-fired utility boilers are required to meet
standards of 0.258 grams S0?/10 joules (0.6 Ibs/MMBtu) for
^ f
Western coal and 0.516 grams SC^/IO joules (1.2 Ibs/MMBtu)
for all other coals (note that these assumptions were made
prior to the revised NSPS of June 1979).
• Coal properties by region roughly equivalent to those given
in Table 3.3.
• All FGD systems are nonrecovery.
Obviously, all of these assumptions are oversimplifications; however,
the projections do give at least an order of magnitude estimate for
waste production and an overall perspective of waste production trends.
It should be stressed that these projections do not take into
account the passage of the National Energy Act of 1978, nor the passage
3-1
-------
Table 3.1
Coal/Ash/Sludge Relationships (Typical)
Representative Range of Coal Properties*
Coal Type
Appalachian Bituminous
Interior Bituminous
Texas Lignite
Western Subbitumlnous
Western Lignite
Mountain Subbitumlnoua
HHV Sulfur
(Btu/lb) (Ibs/KBtu)
12,500 1.58
11,500 3.5*
7,500 2.0h
9.006 1.0*
6,500 1.0h
11,000 0.58
Ash
(Ibn/HBtu)
9
10
15
8
12
7
Principal Usage by Predominant (dry tons/MWyr)d
EPA Federal Region" FCD Waste Typec FCD Onlye Total FCCf
1,2.3,4.5 Nixed 270 645
4,5,6,7
6
6,7,8
8
7,8
Sulflte-rlch
Mixed
Sulfate-rlch •
Sulfate-rlch
Sulfate-rlch
590
265
200
150
100
1,005
890
530
650
390
In Wast
Due to
70
140
40
60
30
35
Coal properties are typical for each type of coal. Values used are for Illustrative purposes. Actual properties of any specific coal
can vary significantly.
Regions 9 and 10 are not Included due to the very low projections for coal utilization.
CSulfite-rlch: CaSO./CaSO * 0.9O (predominantly CaSO, • 2 H,OJ
Mixed: FCD systems can be operated! to produce a sulflte-rlch or a sulfate-rlch waste, or possibly a vasts with a sulfate content
between these two extremes.
of dry tons of waste produced for each megawatt-year of operation.
'Ash-free waste from S02 removal only. Based upons 85X AS02; 9.SOO Btu/kw hr; 3.0 Ibs sulfate-rlch wastes/lb S02 and 2.4 Ibs
sulflte-rlch wastes/lb SOj.
f Includes all aah.
*95X sulfur release from coal aasused.
6SZ sulfur release from coal aasused.
Source: Arthur D. Little, Inc.
-------
Table 3.2
Generation of Coal Ash and FGD Wastes
Basis: Estimates prior to National Energy Act.
All numbers are cumulative.
Coal Ash
FGD Waste
Federal
Region
1
2
3
4
5
6
7
8
9
10
Total
1975
106 Tons
0.3
1.6
8.4
13.6
19.4
0.6
2.0
1.7
0.3
0.3
48.2
1985 Eat.
106 Tons
(Volume)
8.19
(4.10)
27.31
(13.66)
108.34
(54.17)
156.10
(78.05)
232.54
(116.27)
36.32
(18.16)
36.93
(18.47)
24.48
(12.24)
10.71
(5.36)
0.81
(0.41)
641.73
(320.89)
2000 Eat.
106 Tons
(Volume)
28.29
(14.14)
98.28
(49.14)
317.45
(158.73)
467.57
(233.79)
660.29
(330.15)
253.79
(126.90)
128.84
(64.42)
68.60
(64.30)
84.23
(42.12)
3.62
(1.81)
2,110.95
(1,056.50)
1975
106 Tons
<0.1
0.2
1.2
1.7
3.1
< 0.1
0.5
< 0.1
< 0.1
0.0
6.8
1985 Est.
106 Tons
(Volume)0
4.94
(3.95)
14.82
(11.85)
18.20
(14.56)
38.74
(34.87)
51.62
(46.45)
12.00
(9.60)
14.75
(8.86)
1.29
(0.77)
0.10
(0.05)
0.02
(0.01)
156.48
(130.97)
2000 Est
106 Tons
(Volume)8
21.50
(17.21)
63.98
(51.18)
60.58
(48.46)
156.53
(140.88)
187.90
(169.11)
79.77
(63.81)
56.65
(33.99)
3.83
(2.30)
0.43
(0.26)
0.19
(0.12)
631.36
(527.32)
3 Numbers of 1000's of acre-ft are in parentheses.
Numbers may not add up to the last digit due to rounding.
Source: [1]
-------
Table 3.3
Projected Generation of Coal Ash and FGD Wastes
Industrial versus Utility Breakdown
Annual Rate of Generation
-1985 —, 2000
Coal Ash
10 Tons % of Total 10 Tons %pf Total
Industrial
Utility
Total
9,470
71,010
80,480
12
88
100
21,980
93,450
115,430
19
81
100
FGD Wastes
Industrial
Utility
Total
1,200
23.200
24,200
5
95
100
5,800
32.900
38,700
15
85
100
Source: [1]
3-4
-------
of any more stringent SCL and particulate regulations (NSPS for utility
boilers are now being revised and NSPS for industrial boilers are under
review).
3.3 Waste Stabilization Technology
3.3.1 General Stabilization of Wastes
There are now more than two dozen "stabilization" processes for
solidification/stabilization of many types of wastes. The state of devel-
opment of these processes ranges from laboratory-scale testing to full-
scale, widespread commercialization. Most of the processes have not
been commercially applied although most all have been tested at least
in the laboratory scale on a number of different types of wastes.
There are basically three methods by which "stabilization" processes
can improve the disposability of wastes.
• First, they can improve the physical characteristics of the
wastes to the extent that they are more easily handled. This
frequently leads to better control/management of the disposal
area, resulting in reduced impacts relating to physical stabil-
ity and contamination of ground and surface waters.
• Second, "stabilization" can decrease the exposure of the wastes by
reducing surface area and/or permeability or by encapsulating
the wastes, thus limiting the contact of groundwater (or infil-
tration water) with the waste.
• Finally, "stabilization" can chemically react with the waste,
limiting the solubility of chemical constituents that would
otherwise be readily accessible either through flushing of
interstitial liquor or solubilization.
Different stabilization techniques usually emphasize one or two of these
factors. The applicability and "success" of a particular "stabilization"
process, therefore, will depend importantly upon the chemical and phys-
ical properties of the waste, the disposal site characteristics, and
the waste-handling constraints.
3-5
-------
At the risk of oversimplification, most all stabilieation processes
generally can be categorized into one of about six groups, according to
the manner in which the wastes are treated. These are discussed briefly
below. Table 3.4 lists the principal processes of each type, indi-
cating the vendors and status of the process.
(1) Lime (Cement)-Based; As the name implies, this approach
involves mixing cement or lime with the wastes to produce a
material which will harden with time into a more-or-less
monolithic mass. The extent of hardening and the strength
of the resulting mass will depend importantly upon the waste
properties and the amount and type of additives. A number
of additives including clay and sodium silicate are often
used with cement to increase the curing rate and the ultimate
strength attained, and decrease the permeability of the resulting
mass. The use of lime is similar to the use of cement in that it
relies on the reaction of lime with fine-grained (pozzolanic)
material and water to produce a concrete-like mass. Common
pozzolanic materials used in waste treatment include blast
furnace slag and fly ash from fossil fuel combustion. A poz-
zolan is a siliceous or aluminosiliceous material that in
itself possesses little or no cementatious value, but that in
finely divided form and in the presence of moisture will chem-
ically react with alkali and alkaline earth hydroxides at
ordinary temperatures to form or assist in forming compounds
possessing cementitious properties (ASTM C593-76A, ASTM 1977,
Part 13). The products of the reaction of lime and fly ash or
lime and slag are basically the same, the principal components
being a tobermarite like calcium silicate hydrate with a CaO:S10
ratio varying between 0.8 and 2 with a hexagonal tetrocalcium
aluminate hydrate and ettringite type phases also produced [147]
These products are similar to those formed in the hardening of
Portland cement.
3-6
-------
Table 3.4
Waste Treatment Processes
Process Type
Cement (Llae)-Based
Self -Cement Ing
(plaster of parli)
Silicate-Baaed
Thermoplaatlc
Organic Polymer
Inorganic Precipitation
Unknown
SupDlier/Dtvtiloper
IUCS, Inc.
Oravo Line Co.
TJK. Inc.
Che*-Nucleur System, Inc.
ComBonvealth Cdiaon/ABerican
Adnlxturea, Inc.
Aerojet Liquid Rocket
Sludge Fixation Technology, Inc.
Kesejrch Co tt re 11
Envlrotech (Clieaftx)
Maraton Aaaoclataa
Environmental Technology Corp.
llratlona
FCD, Fly Aah
FCD, Fly Aah, Nine Tailings
Indudtrlal Inorg. , Dredg* Spoila
Utility Hadwaataa
FCD
-
Industrial Heavy Mecal Sludgaa
Ite
-
Metal Hydroxide
OrK- & Inorg. InduHtrl«l, Sewage
Indudcrlal
(HddUaates)
Industrial
RadWutu
-
-
1
7
-
Nuclear Uattet?
7
?
L._vtl of Tesclng/Uperacloo
with FGD Uauteu
Full-Scale
Full-Scale
Full-Scale (Japan)
Unknown
Full-Scale
None
Nune Reported
Field?
Uib?
Field
None Reported
Field
Fl«ld
Hone
Hone Reported
None Reported
None
None
None
Hone
None
Unknown
Lab
(ton.
Notee: 1. Thle la e generic Hating for ill waete
2. The lt«t it m partial Hating
Source: [2.11*1
-------
The products formed in mixing fly ash (or slag) and lime with
partially dewatered wastes will vary somewhat due to inter-
actions with the waste constituents. For example, in treating
FGD wastes, it has been shown [2,146] that the participation
of CaSOx • XH20 salts present in the waste results in the
formation of ettringite (3CaO • A1203 • SCaSO^ • 32H20). The
formation of 3CaO • A1203 • CaS03 . 71^0 has been hypothesized [21
In this regard, it should be noted that some wastes, notably
FGD wastes, may exhibit self-cementing properties. Fly ash
simultaneously collected with SO- and/or admixed with the
calcium sulfur solids can react with the residual lime (either
from the fly ash or calcium sulfur salts), causing hardening
of the waste material.
There are numerous suppliers now offering cement or lime-
based "fixation" processes. Notable are the processes offered
by IUCS (involving the use of fly ash and lime) and Dravo
(which uses furnace slag and lime) commercialized in the United
States, and by TJK commercialized in Japan.
(2) Self-Hardening; Marson Associates has been pursuing develop-
ment of an FGD waste stabilization approach using calcium
sulfate contained in the waste to induce hardening. The pro-
cess involves calcination of a portion of the waste under con-
trolled conditions to produce plaster of Paris. This is then
recombined with the waste in a granulator where it hydrates
into relatively hard, plaster-like pellets.
(3) Silicate Based; At least two processes involving silicate
chemistry are now being commercially offered—by Chemfix, Inc.,
and Ontario Liquid Waste Disposal, Ltd. These processes rely
on the conversion of the wastes into a relatively stable sili-
cate matrix not unlike the formation of sedimentary rocks.
In the case of Chemfix, this is accomplished through the
3-8
-------
addition of a soluble silicate gel and a setting agent
(usually Portland cement). The amount of each additive varies
with the type of waste and its moisture content. The result-
ing material is usually soil-like in consistency and is amen-
able to landfilling. Testing and commercial applications
indicate that such processes can be effective for inorganic
wastes, particularly in tying up heavy metals. However, sili-
cate processes probably are not applicable to most organic
wastes, and they appear to be ineffective in tying up chlo-
rides, monovalent cations, and colloidal materials [2].
(4) Thermoplastic Impregnation/Encapsulation; A number of tech-
niques have been investigated, and a few are being marketed
involving impregnating or encapsulating (coating) the wastes
with thermoplastic materials. A variety of such materials
have been tested including asphalt (or bitumen), paraffin,
polyethylene and vinyl resins, and sulfur. Impregnating the
wastes usually involves drying and heating the wastes and
blending them with the thermoplastic materials at elevated
temperatures. The mix is then allowed to cool and solidify.
In some cases, such as with the use of bitumen, an emulsified
product miscible with the wet sludge is used. Mixing is then
accomplished at convenient temperatures; however, heating and
drying is still required before the mass is in a suitable
form for disposal.
Systems involving the use of bitumen have been actively
researched, particularly for the containment and disposal of
radioactive wastes. However, in many cases, the type of waste
rules out organic-based encapsulation techniques. Wastes
containing organics which are solvents for the encapsulating
material obviously cannot be used, and those containing mater-
ials which react destructively such as strong oxidating salts
cannot be used in the case of bitumen-based encapsulation.
3-9
-------
Thermoplastic materials also have been tested as surface
coatings for wastes, particularly wastes already bound in a
treated/fixed matrix. No surface coating processes are now
being offered for cement-based treated materials due princi-
pally to problems with adhesion of the coatings. Surface
coatings of polyethylene, however, have been successfully
tested in combination with organic polymer and thermoplastic
resin impregnation.
(5) Organic Polymer Impregnation/Encapsulation; A handful of
organic polymer techniques have been developed, mostly in
response to the need for solidification of radioactive wastes
for transportation. These are generally batch processes
involving the addition of prepolymers (or monomers) to the
wastes, followed by polymerization, which encapsulates the
waste particles in a mass rather than chemically combining
with the wastes. The required form of the waste and the
specific processing conditions will depend upon the type of
waste and the specific polymerization technique. When wet
wastes are treated, the liquid usually remains after poly-
merization and requires disposal.
The most thoroughly tested organic polymer solidification
process is the urea-formaldehyde system.
(6) Inorganic Precipitation: An approach to stabilizing sodium
sulfate waste from dry sorbent systems is insolubilization by
coprecipitation with acidic ferric ions to form NaFe_(SO )
(OH)6 (natrojarosite) and Na2Fe(S04)2(OH) • 3H20 (sidero-
natrite) [143]. This would be accomplished by mixing slurried
dry sorbent wastes with sulfuric acid and a source of ferric
ions (such as waste acid and fly ash). The precipitates are
reported to be granular, easily filterable, and relatively
free-draining (not sludge-like). The solubilities of these
sodium ferric hydroxysulfate compounds are less than those of
3-10
-------
calcium sulfate, so the precipitated product may be amenable
to landfill without further processing.
3.3.2 Stabilization of FGC Wastes
A number of the above-listed processes have been tested on FGC
wastes, mostly in the bench scale. Justification of the use of addi-
tives to improve the physical characteristics of FGC wastes has been
based on improvement in strength, reduction in compressibility, and
reduction in permeability caused by an increase in solids content or
the formation of permanent bonds between particles. The additives most
advantageous then would be those available at low cost in large quanti-
ties (e.g., fly ash) and those effective as cementing agents (e.g., Port-
land cement). Combinations of additives may produce both types of
improvement (e.g., fly ash plus lime). A limited amount of study has
been devoted to the evaluation of simple additives such as fly ash, lime,
and Portland cement. These studies are discussed later.
At present, there are two approaches which have achieved commercial
applicability for calcium-based FGD wastes: addition of lime and fly
ash for dry impoundment systems (currently marketed by IUCS); and the
proprietary technology developed by Dravo Corporation involving the use
of processed blast furnace slag as the additive for stabilization in
wet ponds. Other additives and stabilization approaches for calcium-
based wastes have been laboratory- and field-tested but are not being
actively marketed at present.
The economic evaluation of the use of additives for waste stabil-
ization is site specific, at best, and must take into account not only
the applicable disposal regulations, but also the type of waste and the
disposal area hydrogeology. In some cases, for example, dry impound-
ments may be possible to stabilize materials to form containment dikes
and basal layers into which unstabilized materials could be placed.
This would, of course, depend upon the handling properties of the
untreated wastes.
An additive which has received little attention is natural soil.
This neglect is justified generally in the case of cohesive soils. Even
3-11
-------
though cohesive soils usually contain a significant amount of clay
minerals and thus are likely to be almost impervious as well as capable
of attenuation of pollutants in flowing groundwater, mixing cohesive
soils with FGC waste sludges would be very difficult if not impractic-
able. On the other hand, less cohesive soils such as clean sands could
be added to FGC wastes with little difficulty. Such addition would not
decrease the permeability of the wastes or encapsulate it, nor could it
provide attenuation capacity. In this regard it would not be considered
stabilization. However, addition of sand would increase strength and
decrease compressibility.
3.4 Utilization and Disposal Options
Coal ash and FGD wastes together comprising FGC wastes can be
disposed of or utilized. At present, most FGC waste is subject
to disposal; utilization may be expected to grow in the future, but
probably at a rate less than the rate of growth in the total generation
of FGC wastes. Following are brief descriptions of disposal and util-
ization options. These are discussed in more detail in Volumes 4 and 5.
3.4.1 Disposal
There are now a number of methods being employed for the disposal
of FGD wastes and power plant coal ash. The most common method of dis-
posal today is impoundment (ponds), although some mine disposal is also
being practiced. In the future, in addition to impoundments, landfills
(i.e., disposal in which layers of waste are deposited and compacted,
ultimately after full use the disposal area is covered with layers of
soil) would become a major option. The types of impoundments include
both lined and unlined wet ponds and dry pits. In wet impoundments,
sluiced ash or FGD waste (often combined with ash) slurry is piped to the
pond area where the solids settle out. The supernatant is then collected
via overflow weirs and either discharged or recycled to the scrubber or
ash sluicing system. Wet impoundments are used almost exclusively for
on-site disposal at the power plant. In addition to the disposal of
untreated wastes, they are sometimes used for treated materials (admixed
lime and fly ash; or admixed lime, fly ash and FGD wastes).
3-12
-------
Managed fills (sometimes called dry impoundments or managed land-
fills) are used for the disposal of dry ash or dewatered (or treated)
sludges. They can be either offsite or onsite; however, they are usually
located close to the waste source because of the high cost of transporta-
tion. In operating a managed fill, the wastes are collected and usually
trucked to the disposal area. In the disposal area, the waste is spread
on a section of the disposal site at a time in short (1-3 foot or 0.3-0.9
meter) lifts and compacted by wide-track dozer or other conventional com-
paction equipment. Then another layer of waste is placed on top of the
compacted lift and operation proceeds. After filling a section of the
disposal site to a predetermined height, the layering and compaction
shifts to the next section of the disposal site.
There are three options for surface mine disposal of dry wastes:
(1) disposal on the working pit floor prior to return of overburden;
(2) dumping in spoil banks prior to reclamation; and (3) mixing with
overburden. Sludge or ash would be transported to the mine via rail or
truck and then truck-dumped in the disposal area. There is a limited
amount of fly ash and/or FGD waste disposal now being practiced using
the first two options. Disposal of FGD wastes in active mines leads to
fewer fugitive SO emissions because active mines are less acidic than
X
inactive or depleted mines; therefore the sulfur compounds in the wastes
are less likely to be dissolved (releasing SO^) in the less acidic
environment.
In a few instances, fly ash also has been disposed of in underground
mines. The fly ash is sluiced and pumped into mine voids through bore-
holes. Supernatant can be recovered via dams and sump pumps and returned
to a disposal basin or recycled for use in ash sluicing. No commercial
scale FGD waste disposal in underground mines is now being practiced.
All of these options undoubtedly will continue to be used in the
future. However, based upon the impending regulations prohibiting
groundwater contamination, unlined impoundments are expected to decrease
in usage. Mine disposal is expected to increase because of the conven-
ience and the elimination of the large tracts of land required for
impoundments.
3-13
-------
Ocean disposal of treated and sulfate-rich sludges may also be
carried out to a limited extent in regions where there are no mines
available and disposal sites for land impoundments are scarce. Ocean
disposal could take the form of reef construction on the continental
shelf (shallow ocean disposal) using treated material or dumping of
treated or sulfate-rich material off the shelf (deep ocean disposal).
Ocean disposal probably would be more likely to be practiced in Regions
1 and 2. However, should regulations constrain any form of ocean dis-
posal, it is likely that use of regenerable systems would be a strong
possibility in areas where land disposal is impractical.
Table 3.5 lists the potential disposal options and sludge types
appropriate to each disposal option envisioned for the foreseeable
future. Table 3.6 lists the anticipated significance of each disposal
option in each federal region. This disposal scenario was compiled
based on current trends in regulations, existing data on characteristics
of various types of sludges, and expected impacts associated with such
operations.
3.4.2 Utilization
There are numerous uses of coal ash that have been developed both
in the United States and Europe. However, at present, only about 20%
of the total ash produced in the United States is being marketed. Fly
ash, bottom ash and boiler slag, all of which comprise coal ash, are
used in somewhat different applications. Only fly ash appears to be
useful in FGD waste treatment.
Some of the more important markets for ash in the United States
include:
• Manufacture of cement and concrete,
• Light aggregate for construction, and
• Areas where availability of disposal options for nonrecovery
processes is so constrained that the cost of waste disposal
is high.
3-14
-------
Table 3.5
Waste Types versus Disposal Scenarios
Disposal Scenario
1. Land Disposal
a. Wet Ponding
b. Dry Disposal
or Managed
Fillsa
c. Mine Disposal
2. Ocean Disposal
a. Shallow
Dispersed
b. Shallow Concen-
trated
Requirements
Pond
Immediate Workability
Dry, Soil-like
No (or low) COD
availability
Stable, Low CODb avail-
ability, Non-dispersing
c. Deep Condentrated Low TOS Availability
Waste Type'
• Any
Sulfate-Rich
Sulfate-Rich + Ash
Sulfite-Rich + Ash
Treated Soil
Sulfate-Rich
(Dry) Sulfite-Rich
Sulfate-Rich + Ash
Sulfite-Rich + Ash
Treated Soil or Brick
• Sulfate-Rich
Treated, Bricklike
• Sulfate-Rich
• Treated Soil or
Brick
a Dry disposal refers to dewatered and if necessary stabilized
wastes being deposited on ground and compacted.
Chemical oxygen demand (COD) is directly related to sulfite
concentrations.
3-15
-------
Table 3.6
Typical Disposal Scenarios
By Region -r 1985 - 2000
Disposal Methods (Significance)'
EPA Region
1 and 2
3 and 4
5, 6 and 7
8, 9 and 10
FGD Waste
Wet Ponding (H)
Dry Disposal (H)b
Ocean (H)e
Mine (L)
Wet Ponding (H)
Mine (H)
Dry Disposal (M&H)
Wet Ponding (H)
Mine (H)
Dry Disposal (M&H)
Wet Ponding (H)
Mine (H)
Dry Disposal (L)
Ash
Wet Ponding (H)
Dry Disposal (H)
Ocean (L)c
Mine (L)
Wet Ponding (H)
Mine (H)
Dry Disposal (M&H)
Wet Ponding (H)
Mine (H)
Dry Disposal (M&H)
Wet Ponding (H)
Mine (H)
Dry Disposal (L)
a Importance (significance) of each disposal option described in
parentheses: (H) = High in importance in the region; (M) «
Medium in importance in the region; and (L) - Low in importance
in the region. Other options with low importance in a region
are not mentioned.
Also called managed fills or dry impoundments.
£
If regulations preclude all forms of ocean disposal, then it is
likely that ash utilization and the use of regenerable systems
would take up the slack where land disposal is impractical.
3-16
-------
It is important to note that most recovery systems also produce
wastes; e.g., blowdown from prescrubbers (which remove fine particulate
matter and chlorides from the flue gas prior to its entering the sulfur
dioxide absorber) and blowdown of contaminants from the recovery portion
of the process. These were discussed in Section 2 but are not expected
to be major factors in the total waste generation in the next few years.
3-17
-------
4.0 CHEMICAL CHARACTERIZATION OF FGC WASTES
4.1 Status of Chemical Characterization
The Environmental Protection Agency (EPA) , Electric Power Research
Institute (EPRI), and a number of other organizations have sponsored
studies on the chemical characterization of FGC wastes (fly ash and/or
S02 removal wastes). Table 4.1 presents the list of major studies funded
by government agencies or EPRI which have focused on wastes generated by
S02 removal systems (with or without simultaneous fly ash removal). In
addition, a number of private organizations active in commercial fixation
of FGC wastes (for example, Dravo and IUCS and others listed in Table 3.4)
and in the marketing of FGC systems as well as utilities have in-house
data much of which is not available in the open literature.
There are few extensive, generalized studies that have been pub-
lished which focus on the characterization of the chemical and physical
properties of fly ash and bottom ash. However, there have been numerous,
small characterization studies on coal ash, most of which have been tied
to site and system specific utilization or disposal options. Examples
of these are various projects funded by the Federal Highway Works
Administration (FHWA) which emphasize the utilization of coal ash in
conjunction with highway construction. As a result, more emphasis is placed
in these studies on the engineering properties of coal ash-soil/coal ash-cement
road building mixtures than the properties of coal ash alone. One notably
large study entitled, "Characterization of Ash from Coal-Fired Power
Plants," was performed by the Tennessee Valley Authority (TVA) under an
EPA grant [34]. This project involved summarizing existing data from
several small, recent coal/ash studies, on both the chemical and physical
characteristics of ashes produced by coal burning steam-electric generating
plants. The report not only contains information on the physical chemistry
of coal ash, coal ash inorganic trace elements, etc., but also examines
the particular coal and ash analysis methods used in determining such
information.
Attenuation of pollutant concentrations in leachate from deposits
of FGC wastes may occur in natural soil strata below and around sludge
fills. Studies of pollutant attenuation through surface adsorption and
other mechanisms are underway at the U.S. Army Dugway Proving Ground in
4-1
-------
Table 4.1
Studies on. Chemical Characterization of FGD Wastes0
Contractor
Aerospace
ro
•WES
SUHY
Aerospace/TVA
Radian/
AOL/EPA
ADL/HKA
UKD/ADL
DOE/Prlvate
Consortium
ACE(Dugway)
TVA/Bochtel
Plant/
Location
Shawnee/
Kentucky
Phillips/
Pennsylvania
Paddy's Run/
Kentucky
Cholla/Arizona
Mojave/California
Parma/Ohio
Scholz/Alahama
Utah
Not reported
Mot reported
•lot reported
Hoc reported
Not reported
Elrama/Duquesne
Shawnee/
Kentucky
Not citeo
Pilot
SchoIz/Alabama
Pa ma/Ohio
Shawnee/Kentucky
H
L/M
L/M
H
L/M
H
L/M
Eastern
Eastern
Western
Eastern
Western
L/M
H
H
H
NK
L/M.H
H
H
L/M.H
L
DL
DLS/FA
DLS
DA
DA
DA
DLS
DL
DLS
DA
DA
DL
DL
DLS
DL (ox)
NK
DA
DA
DA
DLS
DI.S
DA
Scholt/Alabama
Square Butte/
North Dakota
Square Butte
Pilot/No.Dakota
Six FGD samples and three fly ash a
Shawnce/Kentucky H DLS
DLS (ox)
FA
FA
Was.:e
Tyne
M
SI
SA
H
SI
M
r.A
SI
M
SA
NR
NR
NR
NR
NR
M
SI
M
SA
UK
SI.M.SA
SI.M
M.SA
M
SA
SI
SA
Ash/No
Ash
A/NA
A/NA
A
A
NA
A
NA
NA
NA
NA
NR
NR
NR
NR
NR
A
A/NA
A/NA
A
A/NA
NA
A/NA
NA
N
A
Stabilized/
Unstabllized
U
U
U
U
U
U
U
U
U
U
T/U
T/U
T/U
T/U
T/U
T
T/U
T/U
T/U
U
T/U
U
U
U
U
U
U
SA
U
MO
MO
Studied
MC
MC
TC
TC
MO MC TC
MO
MO
MO
MC
MC
MC
MC
TC
TC
TC
MO MC TC
MC
MC
MC
MC
MC
MC
TC
TC
TC
TC
TC
TC
L
L
L
L
L
L
31,37
16,41
15
TC L (field)
TC L (field)
TC L (field)
L
MO MC TC L
MO MC TC L
MO MC
MC TC L
MC TC L
MC TC L
40
39
19
18
39
46
MO MC TC L (field)21
MC
imples were leached and soil attenuation Measured.
M A U MO MC
SA A U MO MC
20
47
54,55,5«
-------
Table 4.1 (Continued)
Studies on Chemical Characterization of ?GC Wastes'
b
Contractor
LGE/Radian
LGE/CE
SCS
EPA(IERL)
DOE
Radian (EPRI)
Legend
Coal Type:
.e- Process Type:
1
OJ
Waste Type:
aStudies included
research groups
Plant/ Coal
Location Type
Paddy's Run/Kentucky H
Paddy's Run/Kentucky H
Scholz /Alabama L/M.H
Pllot/RTP L/M.H
GFERC/North
Dakota LM
4 FGD samples and 14 fly ash samples
L/M < 22 S
H > 2Z S
DLS; Direct Limestone
DL; Direct Lime
DA; Dual Alkali
FA; Fly Ash
SI; Sulflte Rich
M; Mixed
SA; Sulfate Rich
are those partly or fully funded by
(EPRI).
Process Waste
Type Type
DL SI
DL SI
DA SI ,M
DA(ox) SA
DL,DLS,DL(OX) SI,M
FA, DLS (OX) SA
FA SR
were studied.
Ash /No Ash:
Treated /Untreated :
Parameters Studied:
government agencies (e.g,
Ash/No Stabilized/
Ash Unstabilized Studied
NA U MO MC TC
N* U/T MC,TC,L(field)
NA/A T/U MO MC L
NA/7 T/U MO MC.TC
A/NA U MO
A U MO.MC.TC
A/NA
T/U
MO; Morphology
MC; Major Components
TC; Trace Components
L; Leaching
Ox; Oxidation
EPA, DOE, etc.) and utility
Ref
51
50
14
52
21
146
Key to contractors
ADL
ACE
Aerospace
Bechtel
CE
CEA
DOE
EPA
Arthur D. Little, Inc.
Army Corps of Engineers
The Aerospace Corporation
Bechtel Corporation
Combustion Engineering
Combustion Equipment Associates
Department of Energy
Environmental Protection Agency
EPRI
GFERC
CM
MFC
NEA
Rad ian
SCS
SUNY
TVA
IIND
WKS
Electric Power Research Institute
Grand Forks Energy Research Center
General Motors
Montana Power Company
New England Aquarium
Radian Corporation
Southern Company Services
State University of New York
Tennessee Valley Authority
University of North Dakota
Army Corps of Engineers
(W.iterways Kxperiment Station)
-------
Dugway, Utah. Results from that study are not available at present. No
other comprehensive studies of FGC waste pollutant attenuation in soils
have been identified.
Stabilized FGC wastes can be significantly different from unstabil-
ized wastes in physical and chemical characteristics. Hence, as far
as feasible, characteristics of stabilized FGC wastes will be separately
reported in this chapter.
Data are presented for wastes obtained from non-recovery systems
only.
4.2 Principal Components
4.2.1 Principal Components in Coal Ash
When coal is burned, a significant percentage of the weight of the
parent material (3-30%) does not burn and remains as ash. Depending on
the way in which a particular boiler is fired and the fusion temperature
of the ash, as much as 65-95% of the ash passes out of the boiler with
the flue gases as fly ash and the remainder is removed as bottom ash.
In stoker boilers or other units burning coarsely-ground coal, as little
as 10% of the ash can leave as fly ash.
Each year in the United States, more than 60 million tons of ash
are collected from stationary combustion sources. Approximately, three-
fourths of the collected ash is fly ash. Only about 10% of the collected
fly ash is put to further use; the remainder is discarded [5].
The chemical composition of coal ash (bottom ash, fly ash and slag)
varies widely, in concentrations of both major and minor constituents.
Table 4.2 shows a compilation of chemical composition of fly
ash from the firing of a wide range of different coals [6],
-------
Table 4.2
Chemical Composition of Fly Ashes According
to Coal Rank - Major Species (Weight Percent)
Ui
Eastern Bituminous
Chemical Species3
Sodium Oxide, Na 0
Potassium Oxide, K-0
Magnesium Oxide, MgO
Calcium Oxide, CaO
Silicon Dioxide, S102
Aluminum Oxide, AljO-
Iron Oxide, Fe-0
Titanium Dioxide, Ti02
Phosphorous Fentoxlde
P2°5
Sulfur Trloxlde, S03
Range
0.05-2.04
0.92-4.00
0.50-5.50
0.26-13.15
36.00-57.00
16.25-30.30
3.88-35.40
1.00-2.50
<0. 02-0. 42
0.09-3.30
Median
0.53.
2.53-
1.24 •
2.88 •
48.76 *
23.26 -
16.44 •
1.45 -
2.73 •
0.78 '
Total No. of
Observations
21
20
23
21
22
22
23
19
16
17
Western
Range
0.15-2.14
0.50-1.80
1.10-5.90
1.80-30.40
31.00-64.80
18.70-37.00
3.07-21.50
0.68-1.66
1.19-0.70
0.10-5.23
Bituminous
Western Lignite
Total No. of
Median Observations Range
1.04 "
0.99 '
2.96 '
13.81 •
49.69 '
23.04 '
6.48 •
1.09 •
0.38 .
1.66 '
8
8
12
12
9
12
12
11
6
12
0.60-8.10
0.20-1.02
3.3-12.75
11.7-35.44
2.20-46.1
10.7-25.3
2.9-14.15
0.52-1.60
<0. 02-0. 76
0.32-7.20
Median
1.45
0.50
6.79
22.29
30.69
15.48
8.87
0.74
0.25
3.14
Total No. of
Observations
8
8
10
10
8
10
10
8
5
8
Composition reflects only element breakdown of constituents and reported as their oxides and is
not meant to indicate actual compounds present.
Source: [144]
-------
The principal factor affecting the variation in the composition is the
variability in the mineralogy of the coal. However, differences in
composition can exist between fly ash and bottom ash (or boiler slag)
generated from the same coal due to differences in the degree of pul-
verization of the coal prior to firing, the type of boiler in which the
coal is fired, and the boiler operating parameters and combustion
efficiency. For both fly ash and bottom ash more than 80% of the total
weight of the ash is usually made up of silica, alumina, iron oxide,
and lime.
It should be noted that the compositional breakdown shown in
Tables 4.2 and 4.3 reflects only the elemental breakdown of the con-
stituents reported as their oxides and is not indicative of the actual
compounds present. A sampling of available data on a number of fly ashes
and bottom ashes is presented in Table 4.3.
As much as 20% of fly ash can be water soluble, so the potential
exists for release of contaminants through leaching. The principal
soluble species are usually calcium, magnesium, potassium, sulfate,
and chloride. Leachates resulting from ash are usually alkaline due
to the presence of calcium oxide and other alkaline species, although
some ashes have been found to be inherently neutral or even acidic. A
high, available alkalinity is particularly characteristic of the ash
from low sulfur western sub-bituminous and lignite coals. Coal ash can
also contain sulfate compounds (expressed as percent SOg) which are
partly due to occluded sulfate minerals, but also the result of the
reaction of SC^ produced during combustion with the alkaline cations
and its subsequent oxidation.
An important property of coal fly ash is its pozzolanic potential
The pozzolanic reaction involving fly ash occurs either because of the
lime contained in the fly ash itself or is induced by addition of lime
(and water). The reaction causes the fly ash to aggregate and harden
when moistened and compacted.
Bottom ash can be collected either dry or in a molten state
(generally referred to as bottom slag). Dry collected bottom ash has a
different particle size distribution from fly ash and its bulk density
4-6
-------
Table 4.3
Major Constituents in Fly Ash and Bottom Ash
from Various Utility Plants
a
Compound
or
Element
Si02. Z
A120,. I
T Fe20}, Z
CaO. Z
SOJt f.
HgO. Z
N.20. Z
K20, Z
P2°5' *
T(0,. Z
Plant
FA
59.
27.
3.8
3.8
0.4
0.96
1.88
0.9
0.13
0.43
1
BA
58.
25.
4.0
4.3
0.3
0.88
1.77
0.8
0.06
0.62
Plant
FA
57.
20.
5.8
5.7
0.8
1.15
1.61
1.1
0.04
1.17
2
BA
59.
18.5
9.0
4.8
0.3
0.92
1.01
1.0
0.05
0.67
Plant
FA
43.
21.
5.6
17.0
1.7
2.23
1.44
0.4
0.70
1.17
3
BA
50.
17.
5.5
13.0
0.5
1.61
O.b4
0.5
0.30
0.50
Plant
FA
54.
28.
3.4
3.7
0.4
1.29
0.38
1.5
1.00
0.83
4
BA
59.
24.
3.3
3.5
0.1
1.17
0.43
1.5
0.75
0.50
Plant
.FA
NK
NR
20.4
3.2
NR
NK
NR
NR
NR
NK
5
BA
NR
NR
30.4
4.9
0.4
NR
NK
MR
NR
NR
Plant
FA
42.
17. •
17.3
3.5
NR
1.76
1.36
2.4
NR
1.00
6
BA
49.
19.
16.0
6.4
NR
2.06
0.67
1.9
NR
0.68
aAnalysis is performed for the individual elements and then expressed
as their oxides.
Legend: FA - Fly Ash, BA - Bottom Ash, NR - Not Reported
Source: [112]
-------
is higher than that of fly ash. It has a similar chemical composition
to that of fly ash, although with less pozzolanic activity.
Boiler slag is a black glassy substance composed chiefly of angular
or rod-like particles, with a particle size distrubution ranging from
fine gravel to sand. Boiler slag is porous, although not as porous as
dry bottom ash. It is generally less reactive in terms of its pozzolanic
properties than either dry bottom ash or fly ash. Fly ash is the only
coal ash employed in stabilization of FGC wastes.
Partly because of the historical practice of combined handling,
bottom ash and fly ash have been grouped together in terms of considera-
tions relative to environmental impact assessment. Both bottom ash
and fly ash frequently are disposed of in a pond disposal area. Typically
bottom ash and fly ash are sluiced to a central disposal pond where the
ash is allowed to settle out and the overflow liquor discharged or
returned for sluicing. Analyses of pond liquors indicate total dissolved
solids levels on the order of hundreds of mg/1 (ppm) , with the major con-
stituents being calcium, magnesium, sodium, sulfate, and chloride, and
lesser amounts of silicates, iron, manganese, and potassium.
4.2.2 Principal Components in Unstabilized FGC Wastes
4.2.2.1 Wet Processes
4.2.2.1.1 Solid Wastes
The chemical composition of the wastes produced in any FGC system
will depend upon a variety of factors including:
• the composition of the coal burned,
• the type of boiler and its operating conditions,
• the method of particulate control employed, and
• the type of FGD system and the way in which it is operated.
/
Waste characteristics, and in particular the chemical composition,
can vary over extremely wide ranges. The principal substances making
up the solid phase of FGD wastes are calcium-sulfur salts (calcium sul-
fite and/or calcium sulfate) along with varying amounts of calcium car-
bonate, unreacted lime, inerts and/or fly ash. The ratio of calcium
4-8
-------
sulfite to calcium sulfate (the latter present as CaSO, " 1/2H_0 or as
gypsum, CaSO, • 2H?0) will depend principally upon the extent to which
oxidation occurs within the system.
Oxidation, and consequently, the calcium sulfate-to-calcium sulfite
ratio, is usually greater in systems burning low sulfur western coal.
Less oxidation usually takes place in direct lime than in direct lime-
stone systems. However, it is possible to promote oxidation in either
of these types of systems (or in dual alkali systems) to produce wastes
with a high calcium sulfate-to-calcium sulfite ratio, where essentially
all of the calcium sulfate is present in the form of gypsum. When high
sulfur coal is burned and the boiler and FGD systems are operated in a
conventional manner, the calcium-sulfur salts can consist primarily of
calcium sulfite.
Table 4.4 contains examples of different types of wastes from con-
ventionally operated FGD systems. Some of the wastes contain only very
small amounts of calcium sulfate (Paddy's Run—high sulfur coal, direct
lime scrubbing), and others contain essentially no calcium sulfite
(Mohave—low sulfur coal, direct limestone scrubbing). Scrubbing under
conditions of forced oxidation has been tested at the Shawnee Test
Facility [13] for a direct lime system and a limestone system; and at
both Parma and Gadsby using a dual alkali system.
Fly ash is the other major component which can occur in FGC wastes
and its concentration in the waste can vary over a wide range. Fly ash
will be a principal constituent of the waste only if the scrubber serves
as a particulate control device in addition to S0_ removal or if separ-
ately collected fly ash is admixed with the FGD waste. The amount of
inerts and unreacted raw materials (lime and/or limestone) in the wastes
will depend upon the quality and utilization of raw materials (system
stoichiometry). In some systems, e.g., Paddy's Run, Mojave, or Scholz,
fly ash is collected separately in electrostatic precipitators or in
mechanical collectors ahead of the FGD scrubber. Such fly ash collection
is usually very efficient and little, if any, fly ash is found in the
4-9
-------
Table 4.4
Major Components in Selected FGC Waste Solids
System
Plant Sizea toc«tio.n
Shawnee
Shawnee
Shawnee
Phillips
Paddy's
Run
Cholla
^ Mojave
0
Parma
Scholz
Gadsby
Colstrip
PR
PR
PR
FS
FS
FS
FS
FS
PR
PP
FS
Eastern
Eastern
Eastern
Eastern
Eastern
Western
Western
Eastern
Eastern
Western
Western
Process 2
Limestone
Lime
Lime (Ox.)b
Limestone(0x.)
Lime
Lime
Limestone
Limestone
Dual Alkali
Dual Alkali
Dual Alkali
Fly Ash
I S CaSO»-l/2H,,0
2.9C
2.9C
(2.3)C
1-2.8°
3.5-4c
0.44-lc
<2C
2-3
1-4
0.55C
0.8
19-23
50
(3)
(3)
13
94
11
2
14
65-90
0.2
0-5
CaSO,-2H20
15-32
6
52-65
47-62
19
2
17
95
72b
5-25
82C
5-20
CaCO^
3
4-42
3
2-5
5-10
0.2
0
2.5
0
8
2-10
11
nil
source
Fly Ash Other (Ref. No.)
20-43
41
30-40
30-40 A
60 8.2 Unk.
4
59 10.7 Unk.d
3
7
nil
9
40-70 5-30Z MgSOu
13
13
13,
13,
16
13,
17
18
19
13
20
14
15
15
Full Scale PR = Prototype PP = Pilot Plant
Forced Oxidation
CRef. 45
dPortion (20% of sludge) reportedly CaS04-l/2H20
Portion (18% of sludge) reportedly CaS04
Unknown soluble salt; quantity determined by difference
-------
Table 4.4 (Continued)
Major Components in Selected FGC Waste Solids
Percent by Weight
Plant
Milton
R. Young
Black
Dog
La Cygne
Lawrence
System
Size3
PP
PP
FS
FS
Location
Western
Lignite
Western
Eastern
Western
Process
Fly Ash
Limes tone
(Ox.)b:.
Limestone
Limestone
%o
iD
0.6
0.8
5.4
0.5-1
CaS03. 1/2H2
Nil
Nil
20
0.2-7
0 CaS0^.2H?0 CaCOi Flyash Other
40 - 60
15 41 24
11 - 31 2-22 (40-60)
Source
(Ref. No)
21
22
23
24
FS = Full Scale PR = Prototype PP = Pilot Plant
'Forced Oxidation
-------
waste. In other systems, the S0_ scrubber also functions as a particu-
late control device and the collected fly ash can comprise from 20-60%
of the FGD waste solids. Even in installations where fly ash is
collected separately, it can be admixed with ash-free waste in an
attempt to improve the handling properties of the waste.
Varying amounts of unreacted limestone (CaCO») can be found in the
wastes from direct limestone processes. Direct lime and dual alkali
processes utilizing lime for regeneration usually operate with amounts
of lime only slightly in excess of that required for liquor regeneration.
However, lime is often contaminated with some limestone which passes
through the system unreacted and ends up in the waste, and lime can
also react with CCL forming small amounts of CaCO_. Some dual alkali
processes employ sodium carbonate softening to reduce dissolved calcium
levels in order to minimize scrubber scaling. The softening reaction
produces calcium carbonate, which leaves with the waste.
In certain systems operating with a very tight water balance,
relatively soluble substances, e.g., MgSO^ in the Montana sludge, can
build to sufficiently high levels that they can crystallize out and
appear as solids in the waste. Scrubbers collecting large amounts of
fly ash from low sulfur coals are most likely to produce- such wastes.
The samples characterized in most studies usually consist of a
few samples taken from different FGC systems on particular days. It
must be noted that the compositions of samples taken from any one system
could be quite different on different days. Similarly, the same type
of FGC system installed on another boiler and run under a different set
of operating conditions can produce a waste with entirely different
properties. Thus, the data cited in this section should be viewed as
illustrative of the effects of various considerations which can influ-
ence waste composition rather than as defining the composition of waste
produced by a particular process or process type. Furthermore, in all
cases (fly ash, and stabilized and unstabilized FGC wastes), few data
are available on speciation of various elements reported recently.
4-12
-------
A critical problem in environmental impact assessment is identifying
the chemical form of constituent elements in waste. SCS Engineers
initiated a study for the EPA on chemical speciation of contaminants in
FGD wastes and wastewater [14].
4.2.2.1.2 Liquid Wastes
Waste Liquors
Untreated FGC solid wastes (and some stabilized wastes) carry with
them occluded and/or free liquor which contains a wide variety of dis-
solved substances ranging from trace amounts of various heavy metals,
some of which are toxic at even very low concentrations, to substantial
quantities of commonly occurring species such as sodium, calcium, mag-
nesium, chloride, and sulfate. The amount of liquid phase present
depends upon the degree to which the solids are dewatered prior to dis-
charge and can range from as much as 90% of the total weight of the
waste to as little as 10%.
Early studies on FGC wastes performed by Aerospace [31,37] and the
U.S. Army Waterways Experiment Station (WES) [16,41] under the sponsor-
ship of the EPA, included the compositional analyses of liquors in a
variety of FGC waste samples taken from different pilot, prototype, and
full-scale systems. Table 4.5 summarizes the reported concentrations
of the major constituents measured in the waste liquors and their
principal sources.
The major constituents are considered to be those which can be
present at concentrations up to 100 ppm or more. For commercially
available, calcium-based nonrecovery FGD technology, these include:
calcium, chloride, magnesium, sodium, sulfate and sulfite. Because of
the extensive data on these components from analyses performed in waste
characterization programs and operating data from organizations develop-
ing, testing and operating FGC systems, their concentrations are fairly
predictable.
Broadly speaking, the concentrations of different species in solu-
tion will be dictated either by equilibrium solubilities or, for the
4-13
-------
Species
Calcium
Chloride
Magnesium
Potassium
Sodium
Sulfate
Table 4.5
Waste Liquor Phase - Major Constituents
Concentration (mg/1)
150-3,000
400-50,000
nil-3,000
nil-200
10-30,000
500-30,000
Sulfite nil-3,000
Total Dissolved Solids 2,500-100,000
Principal Source
Process Makeup
Flue Gas
Ash, Process Makeup
Ash, Process Makeup
Ash, Process Makeup
Flue Gas, Ash,
Process Makeup
Flue Gas
Source: [30,37]
4-14
-------
most highly soluble species, by the rate at which they enter the FGC
system. Thus, the levels achieved in the waste liquor will depend upon
the type of FGC system and its operating conditions as well as the coal
composition and reactant impurities.
Compounds of sodium and chloride are generally highly soluble and
their solubilities do not vary appreciably with pH. The concentrations
of these ions in solution tend to rise to a point where the rate at
which they are rejected from the system is in balance with the rate at
which they enter the system from the flue gas, fly ash, (if collected
with FGD waste), and process makeups.
The primary source of chloride is usually the coal, and the soluble
chloride concentration is principally a function of the chloride and sulfur
contents of the coal and the rate of water discharge with the wastes.
Chlorides in coal are highly volatile and enter the system in the flue
gas from which the chloride (present as HC1 vapor) is effectively
scrubbed by relatively alkaline scrubber liquors. While chloride con-
centrations in liquors are generally less than about 5,000 ppm, levels
as high as 43,000 ppm have been reported [37] for systems burning low
sulfur western coal where a very tight system water balance is maintained
(low water discharge rate) and where cooling tower blowdown (a major
source of chlorides) is used for process makeup water.
In most direct lime and limestone scrubbing systems sodium concen-
trations are generally low, less than a few hundred ppm. However, in
alkaline fly ash scrubbing systems where there are high levels of solu-
ble sodium in the fly ash and in sodium based dual alkali systems where
sodium compounds are added to replace losses in the wastes, sodium levels
in waste liquors can range up to 10,000 ppm or more depending on the
degree of dewatering and the extent of washing of filtered wastes [18,
19,20]. For example, during the sampling of the dual alkali systems at
Gadsby (pilot) and Parma, Ohio (industrial full-scale) for the Aerospace
[37] and WES [16] programs, the filter cake was not washed well and
sodium levels (primarily Na.SO, and NaCl) exceeded 20,000 ppm. In con-
trast, during periods of proper cake wash, samples of wastes from the
4-15
-------
Scholz dual alkali system showed 4,000-8,000 ppm of sodium in the
waste liquor [19].
Concentrations of calcium, sulfate, and sulfite are generally
limited by the solubility products of the respective salts and the ion
activities. Ion activities and hence solubilities of these salts depend
importantly upon ionic strength. Thus the ultimate concentrations
achieved in the waste liquors usually vary with the type of system and
the manner in which it is operated.
In general, calcium sulfite and sulfate salts are relatively
insoluble and calcium concentrations usually do not exceed a few thou-
sand ppm (and are typically on the order of 1,000 ppm or less). Sulfate
concentrations are limited by the solubility product of gypsum and the
level of calcium present. In conventional direct lime and limestone
systems where calcium concentrations are also dictated by the solubility
of gypsum (where there is no appreciable sulfite present), sulfate levels
generally do not exceed the range of 5,000-8,000 ppm. However, when
soluble alkali or alkaline earth compounds are added to such systems to
improve performance, and in dual alkali systems where there are high
process liquor IDS levels, the changes in ion activities and the higher
levels of sulfite (which decrease calcium levels) can result in sulfate
concentrations in waste liquors well in excess of 10,000 ppm.
Magnesium sulfite and sulfate are considerably more soluble than
the respective calcium salts and the levels of magnesium achieved are
usually dictated by the rate at which it enters the system. In cases
where it is intentionally added to the system or enters in appreciable
quantities via fly ash significant levels can be attained. The magnes-
ium concentrations are pH sensitive and if the pH is raised to higher
than about 10.5, precipitation of Mg(OH)2 will reduce magnesium levels
to negligible levels.
Lunt £t al. [30] point out that the leaching of sulfite or total
oxidizable sulfur (TOS) from wastes is also of concern. Since it is
readily oxidized to sulfate, TOS represents an immediate oxygen demand
to groundwaters and receiving waters. Total oxidizable sulfur (TOS) may
4-16
-------
also be potentially toxic to aquatic life. The amount of sulfite in
liquor will depend upon the degree of oxidation in the scrubber system
and the manner in which the waste is processed (e.g., further dewatered,
admixed with ash, etc.) and handled prior to and during disposal. Sulfite
levels initially in the liquor phase of FGC wastes as they are discharged
can range from nil to hundreds of ppm, and the amount of sulfite in the
waste solids can vary from nil to greater than 95% of the total calcium-
sulfur salts present. Sulfite levels can change during waste processing
and handling prior to disposal resulting from contact with air and oxida-
tion of the sulfite. Since dissolution of CaSO., • 1/2H20 solids would
normally be relatively low and would be limited by equilibrium conditions
(unless the wastes were acidified), it can be expected that soluble sulfite
levels would not exceed the initial liquor concentrations.
4.2.2.2 Dry Processes
As mentioned earlier in Section 2, a number of dry sorbent processes
are under investigation. These processes can be divided into two cate-
gories. The nonrecovery dry sorbent FGD processes use an alkaline solid
sorbent to react with the SCL and produce a sulfate or a sulfite salt
as a final product. A listing of the chemical compounds being tested
as sorbents and the final waste products is given in Table 4.6. Exten-
sive chemical characterization of any of the waste products has not been
published. Of the sorbents listed in Table 4.6, the use of dry nahcolite
and the spray drying of sodium carbonate and lime slurries have received
greatest attention. The major components present in the final product
may be inferred from the postulated gas-solid reactions. For nahcolite
the reactions which are thought to occur are decomposition of the solid
sodium bicarbonate to solid sodium carbonate, reaction of gaseous S00
with either of these two solids to form solid sodium sulfite and then
partial oxidation of the solid sodium sulfite to sodium sulfate by
oxygen.
The relative chemical compositions of the raw nahcolite and after
exposure to simulated flue gas are shown in Table 4.7 and indicate the
presence of these reactions.
4-17
-------
Table 4.6
Major Dry Solvents Under Investigation in the
United States and Their Reaction Products
Dry Sorbent
Sodium Based
Nahcolite (70% NaHC02>
Commercial NaHCO,)
Trona
Calcium Based
Ca(OH)2
Reaction Process Major Sulfur Products
solid injection
into gas stream
or spray drying
of a slurry
CaSO,, CaSO
Source: [57]
4-18
-------
-Table 4.7
Chemical Composition of Raw and Spent
Nahcolite Ore
Component
NaHC0
Moisture3
Water Insolubles
Organicsa
Wt Ratio Na2S04
to Na2S03
Raw Composition
(% by wt)
77.7-84.7
2.1-2.7
2.0-2.3
8.7-12.3
2.5-5.0
Spent Composition
(% by wt)
1.4-5.9
1.6-32.3
33.4-51.3
8.7-24.5
0.8-1.0
11.4-14.4
3.3-5.9
2.1-5.7
Determined by differential heating and
gravimetric analysis.
Source: [58]
4-19
-------
In some of the processes, fly ash is separated prior to contact of
the flue gas with the dry sorbent. In others, such as the spray-dried
sodium carbonate or calcium hydroxide slurries, the flue gas leaves th
spray dryer containing both the dry reacted sorbent and boiler fly ash
The ash and sorbent are removed simultaneously. Thus, depending on th
system, the waste can contain significant amounts of fly ash.
The solids produced from the calcium hydroxide spray dry system
being mainly CaSO^ and CaS03, are similar to other FGD wastes now dis-
posed. Yet sufficient differences in some properties may occur due to
the different mode of interaction of the SO and the absorbing species
to warrant investigation of the characteristics of this product. Since
the waste is produced from direct reaction of a solid with a gas as
opposed to other FGD systems where absorption and subsequent reaction
occurs in the liquid phase, the morphology of the product may be extreme!
different. In addition, the utilization of Ca(OH) may be quite differe
in these systems and may lead to greater alkalinity in the waste product
An additional difference may occur in the trace element content of the
waste. Since the dry sorbent systems operate at higher temperatures
than other FGD systems, and since no liquid phase exists, some trace
elements which occur as volatile species may not be absorbed as effi-
ciently on the solid sorbent as they would with an aqueous scrubbing
media. Thus, for a dry sorbent system where fly ash is collected separ-
ately, the waste product conceivably could contain fewer trace elements
than other FGD systems.
4.2.3 Stabilized FGC Wastes
As discussed earlier in Section 3, a significant number of generic
and proprietary processes have been proposed whereby FGC wastes would
be "stabilized" by a combination of mechanical or chemical modifications
and the addition of materials to increase strength and decrease perme-
ability and compressibility. A partial listing of such processes was
presented in Section 3. Two of these (offered by IUCS and Dravo) are
now offered commercially for treating FGC wastes from utility plants.
4-20
-------
The alumina and silica which are primary components of coal ash
are slightly soluble in alkaline solutions producing silicate and alum-
inate ions. If a source of calcium is present, a reaction producing
calcium silicate and calcium aluminate can occur. Those reactions also
occur during the setting and curing of Portland cement and tend to form
cementatious bonds in particulate matter that is present. These inter-
mediate products of this pozzolanic reaction reportedly can react further
with sulfate to produce ettringite, (3CaO • Al 0 • 3CaSO, • 32H20) [2].
Ashes that are sufficiently alkaline and contain enough leachable
calcium can be auto-pozzolanic, either alone or in combination with cal-
cium sulfur salts produced during scrubbing. This phenomenon has been
observed for wastes produced in alkaline fly ash scrubbing systems oper-
ating on low sulfur western coal. This same chemistry is the basis of
the treatment process reportedly practiced by IUCS in which lime is
added, and fly ash if necessary, to scrubber wastes in order to stabilize
them.
The Dravo process uses a proprietary material named Calcilox, which
is a product derived from basic, glassy, blast-furnace slag and hydrated
lime. It has been reported [2] that the Chemfix process involves addi-
tion of a soluble silicate, a setting agent such as Portland cement, and
lime, if necessary, to the material being stabilized. In all these
stabilization processes, the formation of cementatious calcium silicates
and aluminates is a key step.
Reduction in waste permeability accompanying the stabilization
reactions is probably the primary factor which reduces pollutant mobil-
ity from treated materials. Such reduction in pollutant mobility is one
of the primary objectives of stabilization. Ease of handling in disposal
is another advantage accruing from stabilization. Inclusion of soluble
sulfate into the insoluble mineral ettringite has been mentioned above,
and the high alkalinity which sometimes results from stabilization theo-
retically should reduce the solubility of trace metals in the waste.
However, very little conclusive data demonstrating the chemical immobi-
lization of pollutants by treatment have been developed.
4-21
-------
At present, some limited data are available in the open literature
concerning complete chemical analysis and mineralogy of wastes treated
by any stabilization process. Limited analysis of some stabilized
materials has been attempted at SUNY [15] and WES [16]. A recent paper
by Weeter [25] reviews results obtained by using several methods includ-
ing scanning electron microscopy (SEM), x-ray diffraction (XRD), and
energy dispersive x-ray analysis (EDXRA). All these methods are useful
in evaluating the structure of stabilized and unstabilized FGC wastes.
IUCS [26] concludes that stabilization leads to a decrease in CaSO •
1/2H.O and increase in ettringite. Other investigators [27] report
formation of calcium sulfoaluminate hydrate in systems with lime, fly
ash and sulfate.
Very limited data are available on stabilization processes and
properties of stabilized wastes produced from dry sorbent processes.
Both sodium sulfate and sodium sulfite produced in the sodium based dry
systems are extremely water soluble and may have significant environ-
mental impact via leaching. Limited laboratory experiments have been
performed [59] which demonstrated how sodium sulfate is rendered insol-
uble by coprecipitation with acidic ferric ion to form insoluble double
salts NaFe3(S04)2(OH)6 (natrojarosite) and Na2Fe(S04>2(OH) • 3H20
(sideronatrite). These experiments were performed with nahcolite filter
cake after separation of the water insolubles and fly ash.
4.3 Composition Ranges for Trace Components
4.3.1 Trace Components in Coal Ash
A variety of trace elements find their way to coal ash waste prin-
cipally from coal and possibly, to a small extent, from water used for
handling. Coal contains a large number of trace elements present either
in minerals occluded within the coal or as organometallic compounds
(compounds of arsenic and selenium, in particular) distributed through-
out the coal itself. The Illinois Geological Survey [28] conducted a
survey of trace elements in coal. From a statistical analysis, they
conclude that:
4-22
-------
1. Elements that have relatively large ranges in concentration and
that have standard deviations larger than the arithmetic means
(for example, As, Ba, Cd, I, Pb, Sb, and Zn) include those that
are found in coals within sulfate and sulfide minerals or those
that would be expected to be found in that association. Elements
that occur in organic combination or that are contained within
the silicate minerals have narrow ranges and smaller standard
deviations. Many of the silicate minerals are thought to be
emplaced in the coal very early in the period of coal formation
as detrital or as syngenetic minerals. The sulfides and some
sulfates, although syngenetic in part, have a major portion
emplaced in the coal by epigenetic mineralization.
2. In general, elemental concentrations tend to be highest in coals
from eastern United States, lowest in coals from western United
States, and intermediate in value in coals from the Illinois
Basin.
3. Many elements are correlated positively in coals. The
most highly correlated are Zn:Cd (r= 0.94 for coals of the
Illinois Basin). Chalcophile elements (As, Co, Ni, Pb, and Sb)
are all mutually correlated, as are the lithophile elements
(Si, Ti, Al, and K). Other significant correlations are Ca:Mn
(r= 0.65) and Na:Cl (r= 0.48) [28].
The above study [28] also concludes that only four elements are, on
the average, present in coals in concentrations significantly greater
than the clarke of those elements (average concentration in the earth's
crust). These are boron, chlorine, selenium, and arsenic. Not all are
concentrated in each of the samples analyzed from the three geographic
groups (eastern U.S., western U.S., and the Illinois Basin).
Typical ranges of concentrations for some trace elements in coal
ash obtained from power plants are presented in Table 4.8. For compar-
ison, ranges for some trace elements in coal ash obtained from ashing
coal samples at 600°C (1140°F) are given in Table 4.9. While the major
constituents of bottom ash and fly ash are generally similar, there is
4-23
-------
Table 4.8
Trace Elements in Coal Ash
Element
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Concentration Range
(ppm)
ND - 200
ND - 1,000
50 - 10,000
ND - 200
15 - 6,000
ND - 0.5
Chromium
Cobalt
Copper
Fluoride
Lead
Manganese
Mercury
Molybdenum
Nickel
Phosphorous
Selenium
5 - 500
5 - 400
20 - 3,000
10
50
.01
5
15
5
1
1,500
10,000
100
1,500
70
10,000
50
Vanadium
Zinc
10 - 1,000
25 - 15,000
Source: [28]
4-24
-------
Table 4.9
Element
Ag
As
B
Ba
Be
Br
Ce
Cl
Co
Cr
Cu
Ga
Ge
La
Li
Mn
Mo
Nb
Ni
Pb
Rb
Sc
Se
Sn
Sr
Th
V
W
Y
Yb
Zn
Zr
Concentration £
Range of Trace Species Present in Coal Ashes'
Concentration Ranges (pptn)
Lignites and Subbituminous Anthracites
1-50
9-45
320-1900
55-13900
1-28
2-3
<95-130
41-90
11-310
11-140
53-3020
16-1000
10-30
20-100
34-90
56-1-0
310-1030
6-11
21-34
20-420
20-165
17-43
2-58
5-16
10-660
230-8000
21-43
20-250
7-14
21-120
2-10
50-320
100-490
63-130
540-1340
6-11
10-165
210-395
30-71
20-20
115-220
58-365
125-320
41-120
50-82
19-4250
80-340
210-310
70-120
5-12
155-350
370-1200
Bltuminous
1-3
11-990
74-2800
96-4660
4-60
2-4
<53-250
76-270
10-440
36-490
30-850
30-380
10-135
20-285
19-270
48-500
31-4400
12-17
31-78
20-610
23-1500
29-<1000
7-155
10-37
10-825
40-9600
26-54
60-860
16-30
29-460
3-23
50-1200
115-1450
aAtomic absorption data on coals ashed at 600°C (1140°F). Concentrations are ppm.
^Elements whose concentration are <2ppm include Ru, pd, Re, Os, Ir,
Rt, Au, Rh, Te, Bi, W, Hf, Lu, I, Cd.
Source: [7, 29, 81, 112]
4-25
-------
usually an enrichment of trace elements in the fly ash as compared with
the bottom ash based upon the total quantity of trace elements in the
coal fired as shown in Table 4.10. A few of the elements originally
present in the coal (notably sulfur, mercury, and chlorine) are almost
completely volatilized and leave the boiler as gaseous species which
are not collected downstream in dry ash collection equipment. However
these can be collected in wet scrubber systems (i.e., FGD system). The
substantial enrichment of fly ash with antimony, selenium, and lead in
comparison to concentrations in the coal (after correcting for weight
loss due to combustion) is shown in Figure 4.1.
It appears that the condensation of elements including volatile
trace elements resulting in a higher concentration of these elements in
the fine particulates of fly ash can occur for two reasons:
1. Condensation occurs either by nucleation or by deposition on
previously formed particles. Since residence times between
volatilization and condensation are relatively low, any nucle-
ation will produce relatively small particles.
2. Deposition occurs on the particle surface and is, therefore
dependent on particle surface area. Since surface area is
greater for finer particles, small particulates display increased
concentrations of elements which tend to recondense [34].
The distribution of various trace elements with fly ash particle
size is shown in Table 4.11 for one sample of fly ash.
4.3.2 Trace Elements in Unstabilized FGC Wastes
4.3.2.1 Total Wastes
The level of trace elements in the FGC waste depends primarily upon
three factors:
• The level of various trace constituents in the coal relative
to its sulfur content and in any FGD process additives;
• The amount of ash, if any, collected with or admixed with the
sludge; and
• The efficiency of the scrubber system in capturing volatile trac
constituents.
4-26
-------
Table 4.10
Trace Constituents in Fly Ash and Bottom Ash
From Various FGC Unitsa
Element Plant 1 Plant 2 Plant 3 Plant 4 Plant 5 Plant 6
As, ppm
Be , ppm
Cd, ppm
Cr, ppm
Cu , ppm
Hg, ppm
•C-
1 Hn. ppn
NJ
'"J Hi. ppm
Pb, ppm
Se, ppm
V. pp.
Zn. ppm
B. pp«
Co. pp»
f, PP"
FA
12.
4.3
0.5
20.
54.
0.07
267.
10.
70.
6.9
90.
63.
266.
7.
HO.
BA
1.
3.
0.5
15.
37.
0.01
366.
10.
27.
0.2
70.
24.
143.
7.
50.
FA
8.
7.
O.i
50.
128.
0.01
150.
50.
30.
7.9
150.
50.
200.
20.
100.
BA
1.
7.
0.5
JO.
48.
0.01
700.
22.
30.
0.7
85.
30.
125.
12.
50
FA
15.
3.
0.5
l'j<>.
69.
0.03
150.
70.
30.
18.0
150.
71.
300.
IS.
610.
BA
j.
2.
0.5
7(1.
33.
0.01
150.
15.
20.
1.0
70.
21.
70.
7.
100.
FA
6.
7.
i.o
3D.
75.
0.()8
100.
20.
70.
12.0
100.
103.
700.
li.
250.
BA
2.
5.
1.0
JO.
40.
0.01
100.
10.
30.
1.0
70.
45.
300.
7.
85.
FA
8.4
8.0
6.44
206.
68.
20.0
249.
134.
32.
26.5
341.
55?.
NR
6.0
624.
BA
5.8
7.3
1 .08
12M.
48.
0.51
229.
62.
8.1
5.6
353.
150.
NX
3.6
10.6
FA
110.
NR
8.0
300.
140.
0.05
298.
207.
8.0
25.
440.
740.
NR
39.
NR
BA
18.
NR
1 . 1
132.
20.
0.028
295.
85.
6.2
0.08
260.
100.
NX
20.8
NR
aFA = Fly Ash, BA = Bottom Ash, NR = Not Reported
Source: [112]
-------
II It
IODINE
! ANTIMONY
! SELENIUM
• ARSENIC
+UAD
mcl
NICKEL!
COBALT!
<
MANGANESE!
CHROMIUM!
i
BARIUM!
STRONTIUM^
4
MAGNESIUM!
RUBIDIUM!
T
II '1 *
BROMINE !
T
• IRON
•VANADIUM
CALCIUM
! POTASSIUM
SODIUM!!
1 !TANTALUM
^RHENIUM
T
1 THORIUM
SCANDIUM!
• TANTALUM
ALUMINUM.'
Ill I 1 1 1 1
» 10 3 5 2 U
ELEMENTS EWRICMFH*-
) 0.8 0.5 0.2 o.
t ELEMENTS DFPI FTFn
Note1 Vertical location hoi no significance.
Source: [34, sic]
Figure 4.1 Enrichment Factors of Various Elements
on Suspended Particles in the Stack with
Respect to the Concentrations in the Ash
4-28
-------
Table 4.11
Elements Showing Pronounced Concentration
Trends With Decreasing Particle Size
(ppm unless otherwise noted)
rartlcla
UO
30-UO
20-30
15-20
10-15
5-10
5
11.3
7.3-H.3
•».7-7.3
3.3-U.7
2.1-3.3
1.1-2.1
0.65-1.1
Tl Sb
CM
Aa
Nl
Cr
A. Fly Ash Retained in Plant
Bl«v«4 fractiona
lUo
160
7
9
1.5 10
7
10
12
20
100
500
100
lUo
100
90
500
Ull
...
1.
3
Aerodynamlcally alzed fractlono
90
300
U30
520
l»30
820
980
5
5
9
1C
15
20
>*5
8
9
8
19
12
25
31
10
10
10
10
10
10
10
15
15
15
30
30
50
50
120
IbO
200
300
Uoo
800
370
300
130
IfjO
200
210
1-30
260
70
mo
150
170
170
160
130
730
7/0
1*80
7?0
770
1100
lUOO
0.
0,
» • 1
• • 1
u.
7.
• • I
,01
,01
,u
,8
»
Analytical method
a
a
a
a
»
B. Airborne
1100
1200
1500
1550
1500
1600
29
62
67
65
76
17
27
3U
37
53
13
15
18
22
26
35
13
11
16
16
19
59
a
b
a
a
Fly Aah
680
800
1000
900
1200
1700
U6o
Uoo
M.O
5**0
900
l£00
7^0
290
U60
U70
1500
3300
8100
9000
6600
3800
15000
13000
n
B ^
7
• *
25
. .
U8
.3
.9
,
.0
.
.6
Fnvc
66.30
22.09
2.50
3'.25
O.flO
0.31
0.33
o.oa
Analytical method
(a)Do arc emi»«ion apectroootry. (b Atonic absorption apectronotry.
(o jpC-n/ fluor««c«nc« ipectronetry. (d)Gp&rlc eourcu raoa
Source: 1112]
4-29
-------
Unlike the data on FGC wastes and those on trace elements in coal
ash (which refer to the solid phases in those wastes), available data
on trace elements in FGC wastes are the stun total of those elements in
the solid and liquid phases of these wastes (or sludges).
Many of the elements are not highly volatile and will be retained
in the ash (fly ash and bottom ash) matrix. The extent to which fly
ash is a part of the waste composition determines the presence of the
least volatile elements in FGD waste but has little impact on the pres-
ence of highly volatile elements. On the other hand, the concentrations
of such highly volatile elements as arsenic, mercury, and selenium which
appear in the waste will depend upon the extent to which they are present
in and released from the coal and, as importantly, the efficiency with
which they are captured in the scrubber. Mercury and selenium are likelv
to be present in the flue gas as elemental vapors that might not be
scrubbed efficiently.
Assuming that the limestone, lime, and process water makeup to the
system are not contaminated with trace elements and that all highly vol-
atile species and fly ash are captured in the scrubber, then the FGC
system would increase the concentration of trace elements proportionate
to the coal weight lost upon combustion. Since the burning of one metri
ton of coal typically produces 0.05-0.20 metric tons of dry scrubber
waste without fly ash (depending upon the sulfur content and SO removal
efficiency) and up to 0.4 tons of scrubber waste with fly ash, theore-
tically it could be expected that many trace element concentrations in
the sludge could increase by a factor of 2.5X to 20X over those found
in coal.
In addition to changes in concentration of trace constituents in
waste as compared to coal, there is also a change in the form and avail-
ability of these constituents. Important differences in trace element
chemistry and availability between the original coal material and the
FGD waste are as follows:
4-30
-------
___ _ Original Coal _ _ FGC Waste _
Trace elements contained in highly Trace elements dispersed in
insoluble mineral matrix. potentially soluble CaSO^ and
matrix.
Undisturbed geological material Sludge composed of fine parti-
compact, relatively non-porous with cles, with finite permeability.
low leaching rates.
Trace elements usually present as On combustion, trace elements
organometallics , sulfides or containing compounds are con-
carbonates [6]. verted to oxides and in certain
cases, elemental forms.
A number of the important trace elements which have been found in FGC
wastes containing up to 60% ash are listed in Table 4.12 along with the range
of concentrations at which they have been detected in conjunction with meas-
urements performed on many samples and a comparative listing of ranges of
trace metal levels which have been measured in a variety of coal samples.
The observed concentrations range over as much as three orders of
magnitude, primarily because the levels of trace elements in coal can
vary by that same extent. The measured concentrations of a given ele-
ment in the waste samples studied generally fall within the same broad
range as do typical concentrations in coal.
Additional data on trace element levels in total FGC wastes are
available from the sampling and testing program performed by Radian for
EPRI [39]. In this program, three power plants with FGC systems (one
with direct lime and two with direct limestone) were studied. Trace
element levels were measured in the coals fired, ash produced (bottom
ash and fly ash), makeup water, reactant feed, total waste, and waste
liquors. The results are given in Tables 4.13, 4.14, and 4.15.
The Radian data indicate that there is no direct general correla-
tion between the levels of a trace element in the coal with those in
the wastes. This is to be expected even in cases where all of the ash
is simultaneously removed with the SO^ or admixed with the waste cal-
cium-sulfur salts. An appreciable quantity can enter the system through
the reactant feed (lime, limestone, soda ash, etc.) and, in some cases,
the process makeup water (concentrations in makeup water can be magnified
by factors as large as ten to twenty in systems with tight water balances) .
4-31
-------
Table 4.12
Concentrations of Trace Metals in FGC Wastes and Coal
Elements
Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Zinc
FGC Waste
Solids (ppm)
0.6-63
0.05-11
0.08-350
3-250
1-76
0.2-21
11-120
0.001-6
6-27
0.2-19
10-430
FGC Waste
Liquor (ppm)
0.09-1.6
<0. 004-1. 8
<0. 001-0. 18
0.004-0.11
0.001-0.5
0.002-0.6
0.001-0.55
<0. 01-90
<0. 001-0. 07
0.9-5.3
0.005-1.5
<0. 001-2. 7
0.01-27
Range in
Coal (ppm)
3-60
0.08-20
2.5-100
1-100
3-35
0.01-30
.
0.5-30
0.9-600
Source: [30, 37]
4-32
-------
Element
Table A.13
Trace Element Content of Samples from Station 1
Coal
(ppm)
Bottom
Ash
(ppm)
Ppt.
Ash
(ppm)
Lime
(ppm)
Waste
(ppm)
Scrubber
Liquor
(mg/D
Makeup
Water
(mg/1)
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Copper
Fluorine
Germanium
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Vanadium
Zinc
.43
.26
300.
.44
27.9
.028
1.5
7.6
54.
<1.0
.90
16.0
.140
<.13
2.3
4.2
<13.
40.
<.48
2.3
2200.
4.6
41.9
.19
3.4
29.
50.0
<.l
2.3
181.
.027
15.
15.6
.36
<24.
35.
1.0
3.2
3600.
5.2
179.
.39
5.6
43.
377. .
1.2
6.4
157.
.126
7.0
34.2
1.7
<50.
92.
5.3
3.0
<30.
3.0
6.45
.28
1.2
5.8
105.
<1.0
1.3
29.8
<.010
150.
4.3
.08
<50.
9.6
4.3
4.0
500.
1.5
68.7
.40
1.6
38.9
1017.
<1.0
1.6
56.
<.010
81.
13.
4.13
<50.
13.9
.02
.011
<.3
.008
11.7
.006
.01
.53
62.7
.015
.015
2.2
<.001
.56
.330
.44
.2
.92
.008
.017
<.5
.001
2.1
.0004
<.001
.35
5.1
.015
.014
.07
.0015
.08
.062
.019
.2
1.0
Co
u>
Note: Values represent the average of duplicate determinations.
Solid samples are reported on a dry basis; water and liquor
samples on an as-sampled basis.
Source: [39]
-------
Element
Table 4.14
Trace Element Content of Samples from Station 4
Coal
(ppm)
Bottom
Ash
(ppm)
Ppt.
Ash
(ppm)
Lime-
stone
(ppm)
Waste
(ppm)
Ash Pond
Liquor
(mg/1)
Scrubber
Liquor
(mg/1)
Makeup
Water
(mg/1)
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Copper
Fluorine
Germanium
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Vanadium
Zinc
.08
.87
440.
.29
37.7
.11
1.8
5.2
78.5
.48
.15
26.2
.131
.87
3.67
,98
<13.
16.2
<1.0
4.4
5600.
.40
83.2
1.1
15.6
68.
44.6
<.l
1.0
56.7
<.010
3.2
14.5
.14
<100.
<8.0
4.4
61.
15,000
5.2
1040.
4.2
8.9
238.
2880.
9.2
4.0
374.
<.010
12.
92.9
16.4
<100.
386.
1.3
.66
<30.
.37
10.8
.90
.57
15.6
103.
<.l
14.
20.3
<.010
8.9
<6.0
.30
<24.
28.0
7.5
12.
4400.
2.0
211.
1.1
4.0
104.
950.
2.4
2.4
147.
.46
8.0
26.0
3.8
<100.
169.
.007
.004
<.3
.002
.41
.001
.004
.090
.43
<.l
.018
.10
<.001
.012
.078
.0030
<.2
.12
.009
.0006
<.3
.002
2.10
.002
.003
.032
3.85
<.l
.009
.21
<.001
.010
.072
.042
<.2
.02
<.002
.006
<.3
.001
.25
<.001
.09
.16
2.72
<.l
.02
.19
.013
.01
.16
.0017
<.2
.40
OJ
Note: Values represent the average of duplicate determinations.
Solid samples are reported on a dry basis; water and liquor
samples on an as-sampled basis.
Source; [39]
-------
Element
Table 4.15
Trace Element Content of Samples from Station 5
Coal
(ppm)
Bottom
Ash
(ppm)
Lime-
stone
(ppm)
Waste
(ppm)
Ash Pond
Liquor
(mg/1)
Scrubber
Liquor
(mg/1)
Makeup
Water
(mg/1)
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Copper
Fluorine
Germanium
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Vanadium
Zinc
.33
4.6
100.
.16
96.9
7.9
.45
41.5
372.
4.5
41.
142.
.322
.41
51.7
3.2
<12.
780.
3.4
3.9
300.
4.5
53.8
1.6
5.5
130.
95.7
.25
21.
491.
<.010
1.4
187.
.51
<24.
798.
3.2
2.7
<30.
.17
17.4
.65
<.80
2.4
117.
.11
13.
290.
.020
12.
6.20
.22
<160.
48.
6.7
6.7
<20.
1.8
41.8
.03
.004
<-3
.001
1.03
25. .04
5.2 <.0002
65. .01
266. 10.4
5.9
290.
340.
0.10
9.6
75.2
2.1
<100. I
2050.
.07
.008
1.1
.0015
.10
.11
.015
.2
2.5
.06
<.0004
<.3
.004
6.17
1 .009
<.0002
.01
15.9
.39
.010
2.0
.002
.27
.25
.18
.2
4.2
.005
.002
<.3
.001
.414
.0007
<.0002
.006
.66
.02
.014 !
.15
<.001
.02
<.01
.0012
.2
.04
I
u>
Note: Values represent the average of duplicate determinations.
Solid samples are reported on a dry basis; water and liquor
samples on an as-sampled basis.
Source: [39]
-------
Furthermore, some elements which are highly volatile may not be efficiently
collected in the scrubber system. Mercury and selenium, for example are
likely to be present in the flue gas as elemental vapors that might not be
effectively scrubbed or completely condensed on fly ash particles.
The fact that a direct generalized correlation does not seem to exist
between trace metal levels in coal and FGC wastes is also confirmed by
analyses performed by Aerospace [31]. Aerospace [31] compared total trace
element content of FGC waste measured in solids with the trace element
content of the parent coal being fired for a large number of waste samples
The samples were taken from wet scrubbing systems with simultaneous SO
and ash removal and the ash content of the samples varied over mile ranee
The relationship between the concentration of trace elements in the coal
and the concentration in the waste solids (corrected for contributions
from the absorbent) is shown in Figure 4-2 when all the elements are taken
into account, inspection of data for individual elements shows varying
degrees of correlation. Of the nine elements studied, general relation-
ships are apparent for only four - beryllium (both 7 data1 points) and
cadmium (6 data points) over the range of 0.1 to 10 ppm, lead (3 data
points) over the range of 1 to 100 ppm and zinc (6 data points) over
the range of 30 to 300 ppm. For arsenic, copper, mercury and selenium,
there is no clear correlation; and for chromium, there appears to be an
inverse relationship. Figure 4.3 shows plots of concentrations of nine
trace elements measured in coals versus concentrations in corresponding FGC
liquors. In no case is a clearcut correlation evident. The lack of correla^
tion for most of the elements is not surprisine in view of the fact that th
amount of fly ash in the samples is variable and that the FGC waste analyzed
in many cases is not obtained from a unit which collects all of the fly aav
produced. Analytical error and in some cases the limited range of the data
may also be contributing factors.
In all of the above cases, trace elements are reported as total values*
no speciation data are available for unstabilized or stabilized FGC wastes
There are no data available on the trace element content of dry sorbent-
FGD wastes. For dry sorbent processes which include simultaneous fly ash
removal, the waste is expected to contain the trace element contribution
from the fly ash.
4-36
-------
"tww
100
1
CX
r- 1
cfl
O
•H
CO
4J
s
§
, __l
w
0)
o
CO
1
o <
i i i I j I 111; | | • i j ,--- T - -i - T | - T i| r
-J
9rj 0
- O V T-. ~
'-' v \7
A
0 J>
B ™ -j
A a
0 S 0
sP
0 D
01
^ LEGEND
O Arsenic * Mercury -j
A • !> D Q Beryllium A, Copper !
A Cadmium w> Lead
V Chromium U Selenium
o.oss an ^ zinc
1 1 n i T 1 1 1 1 1 1 1 | 1 1 1 1 1 ! ! I 1 ill
0,01 0.1 1 10 100 iOOO
Trace elements in FGC waste solids (ppm)
Source: [31]
Figure 4.2 Correlation of Trace Element Content in Parent Coal and FGC Wastes
-------
I
n.
1
55
B
(4
u
1
W
o
too
00
J—1-
0.001
200
100 -
10 —
0.01
0.1
1.0
0 ARSENIC
IOC
r—
-
-
-
§
— i i i-; • i ii'ii i III) • F - F ~ F i — i 1 — r-r
D
Q m •
O —
OBERYLLIUM
DO
i i . 1 i i i « 1 i i i i | . i . i 1 i t i <
(a)
(b)
AMI
0.6'
O.I
1.0
109
200
100
- A
A
OOOI
A CADMIUM
(c)
0.01 0.1 1.0 10 100
Figure 4.3 Average Trace Element Content of Sludge Liquor
(mg/A)
4-38
-------
I
Q.
I
JOO
too
CHROMIUM
(d)
0.001
0.01
0.1
1.0
100
too
D.
O.
8
8
COPPER
(e)
0.001
0.01
0.1
100
I
i
loo
100 -
e e
w
u
LEAD
0.001
0.01
0.1
(f)
1.0
100
Figure 4.3 (Continued)
4-39
-------
z
M
-------
In addition to heavy metals, other chemical constituents that can
potentially cause concern even in small concentrations include polycyclic
aromatics and radionuclides. When coal containing trace radionuclides
is combusted, the radionuclides not volatilized remain with the ash as
do other non-volatilized trace substances. Because of the reduction in
solid mass accompanying combustion, the specific activity of the radio-
nuclides in the ash increases over that observed in the coal. In con-
junction with the evaluations of the environmental impact of radioac-
tivity released from nuclear power plants, a number of comparisons of
radioactive discharges from fossil-fuel plants to those of nuclear power
plants have been made. Radioactive discharges were reviewed in one of
the most recent studies by Coles, e£ al^. [32], where samples of coal and
ash from two power plants burning low sulfur coal were characterized.
One, Plant A, was burning a low ash (9.2%) coal and was equipped with
electrostatic precipitators (ESP's). A second plant, Plant B, was firing
23.3% ash coal and had three boilers equipped with Venturi scrubbers
and two units equipped with ESP's. Measurements of concentrations of
uranium, thorium, and potassium, as well as specific activities for a
number of radionuclides in the coal and samples of bottom and fly ash
are shown in Table 4.16. Also included in the table are ranges of aver-
40 226 9^R
age values for several important radionuclides, K, Ra, and U
taken from Eisembud [33]. An examination of Table 4.16 shows first that
40 226 238
in both coals which were being fired, the K, Ra, and U levels
were in fact within the normal range for various rocks. Observed
increases in specific activity in the ash over the coal are as expected.
Further, an examination of the specific activities of the four size
fractions of post-ESP fly ash shows an enrichment with decreasing par-
ticle size for all of the radionuclides which is typical of the behavior
of the trace elements having significant volatility at combustion temper-
40 228
atures; the possible exceptions to such behavior are K and Th.
o J r
The activity of Ra measured in fly ash is of particular interest
7 9 f\
because Ra activity is one of the measurements specified in Draft
22fi
RCRA methods for assessing waste hazard. ( Ra activity is not to
4-41
-------
Table 4.16
Contents of Various Radionuclides
in Coal, Bottom Ash, and Fly Ash
u
0.71
5.6
4.6
2.6
11
8.4
11
16
20
30
38
ppm
Th
1.6
15
14
5.0
22
19
22
25
31
36
38
K»
860
9440
7900
1660
7400
7200
7200
8200
8600
8600
8100
**K
0.73
8.1
6.8
1.4
6.3
6.2
6.2
. 7.0
7.3
7.4
7.0
•
"«Th
Plant A»
0.17
1.7
1.5
PlantB0
0.56
2.4
2.2
2.5 '
Plant 8°
2.8
3.3
3.3
3.3
aMfU
0.17
1.7
1.5
0.55
2.4
2.1
2.5
2.7
3.5
4.0
4.2
P^rl/Q
210nw
0.26*
1.4*
0.58*
o.ea-
2.2* •
0.84'
2.8*
4.3
10
14
17 ,
»*sRa
0.21
2.3
1.9
0.64
2.9
2.5
3.0
3.3
4.6
5.3
5.9
23»y
0.24'
1.9
1.5
0.85'
3.5'
2.8*
3.6
5.4
6.8
10
. 12
J35y
0.012*
0.093
0.072
0.037
0.14
0.11
0.14
0.17
0.28
0.39
0.50
ESP fly ash (9)
Bottom ash (7)
Coat (3)
ESP fly ash (C)
Bottom ash (JO)
Scrubber ash (7)
Post-£SP (stack)
fy ash (mmd)<*
18.5 urn (2l
6.0 fim(2)
3.7 urn (S)
2.4 pm (2)
• E.TOTS 20% with*. 10% without* (1 v error from the mean or counting statistics, whichever Is larger). * Samples from Plant A; Input coal contains 11.3%
HjO, 9.2% ti'>, and 0.52% sulfur. c Samples from Plant B: Input coal contains 6.8% HjO. 23.2% ash. and 0.46% sulfur, "mmd = mass median dame'.ef determined
by centrifuge I sedimentation.
Range in Rocks
(sedir.entaTry)
2.2-22 — —
— 0.4-1.3 0.4-1.3 —
Source: [32, 33J
-------
226
exceed five pCi/g.) The Ra activities measured in the referenced
[32] work lie between the average range in sedimentary rocks and the
RCRA limits.
Measurements of radioactivity in samples of FGD waste have not
been made or are not readily available from published reports. However,
by analogy with other trace elements, it would be expected that since
the radionuclides are relatively non-volatile and tend to follow fly
ash, they would tend to be found in. FGD waste in proportion to the
amount of ash collected.
One of the measurements that has not been reported is a determina-
tion of the level of radionuclide activity in leachates from fly ash
and/or FGD wastes. Lead and radium are not particularly soluble so one
might expect to find that the mobility of those substances via leaching
would be rather low.
Although the organic matrix of coal itself is primarily a polycyclic
aromatic structure, and copious quantities of polynuclear aromatic com-
pounds (PNA's) are produced when coal is liquefied or destructively
distilled, the amounts of such PNA's on fly ash or in FGD wastes have
not been determined. Certain of the PNA's are known or suspected car-
cinogens. Ray and Parker [34] present results from attempted measure-
ments of PNA's in samples of ash obtained from the Widow's Creek steam
plant. In only a very small proportion of the samples analyzed were
measurable quantities of PNA compounds detected.
Making measurements of PNA's at sub-part-per-million levels has
been possible only recently; and measurements on samples of FGD waste
and fly ash are currently underway in a program being carried out by
TRW [35] for the EPA.
4.3.2.2 Trace Elements in Waste Liquors
The range of trace elements observed for FGC waste liquors are
shown in Table 4.17, and in many cases, the concentrations cover two
4-43
-------
Table 4.17
Typical Levels of Chemical Species in FGD Waste Liquors and Elutriates
___________________________ Western Coals
Range in Median Total No. of Range in
Species
Antimony
Arsenic
Beryllium
Boron
Cadmium
• Calcium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Sodium
Zinc
Chloride
Fluoride
Sulfate
TDS
PH
aLevels of soluble sodium salts in dual alkali sludce (filter cake) depend strongly on the degree of cake
wash. The highest levels shown reflect single measurements on an unwashed dual alkali filter cake.
(See text.)
bLevels of soluble chloride components in sludges are dependent.upon the chloride-to-sulfur ration in the
coal. The highest levels shown are single measurements for a western limestone scrubbing system operating
in a closed-loop using cooling tower blowdown for process makeup water.
Eastern Coals
Range in
Liquor (ppm)
0.46-1.6
<0. 004-1. 8
<0. 0005-0. 05
41
0.004-0.1
470-2 ,600
0.001-0.5
<0. 002-0.1
0.002-0.4
0.02-0.1
0.002-0.55
<0. 01-9.0
0.0009-0.07
5.3
0.03-0.91
<0. 005-2. 7
36-20,000*
0.01-27
470-5,000
1.4-70
720-30,000a
2, 500-70, 000a
7.1-12.8
Median
(ppm)
1.2
0.020
0.014
41
0.023
700
0.020
0.35
0.015
0.026
0.12
0.17
0.001
5.3
0.13
0.11
118
0.046
2,300
3.2
2,100
7,000
— '
Total No. of
Observations
4
15
16
1
11
15
15.
3 .
15
5
15
8
10
1
11
14
6
15
9
9
13
—
Range in Median Total No. of
Liquor (ppm)
0.09-0,22
<0. 004-0. 2
.,. 0006-0. 14
8.0
0.011-0.044
240-0^45, 000)b
0.024-0.4
0.1-0.17
0.002-0.6
0.42-8.1
0.0014-0.37
0.007-2.5
<0. 01-0. 07
0.91
0.005-1.5
<0. 001-2. 2
l,650-(-v9,000)a
0.028-0.88
1,700-4 3, 000b
0.7-3.0
2, 100-18, 500a
5, 000-95, 000b
2.8-10.2
{ppm) Observations
0.16
0.009
0.013
8.0
0.032
720
0.08
0.14
0.20
4.3
0.016
0.74
<0.01
0.91
0.09
0.14
—
0.18
—
1.5
3,700
12,000
—
2
7
7
1
7
6
7
2
7
2
7
6
7
1
6
7
2
7
2
3
7
3
Sourc«: f31,37J
-------
orders of magnitude or more. One may expect that dilution associated
with elutriate tests could have reduced concentration of trace elements
by a factor or as much as five to ten. However, significantly different
concentrations of these elements in elutriates and direct liquors were
not observed. This may be due, at least in part, to the relatively
large reservoirs of trace elements for dissolution from the solids (as
discussed below).
It should be emphasized that only a small fraction of the total
amount of trace elements present in FGC wastes is found dissolved in
the waste liquor; the major portion of trace elements is found in the
solid phase.
The trace element levels in waste liquors measured by Radian,
shown earlier in Tables 4.13 through 4.15, generally agree with the
ranges shown in Table 4.16. The WES/Aerospace and Radian data also
agree on the partitioning of trace elements between the waste liquor
and solids. It is apparent from a comparison of the levels reported
for waste liquors versus total wastes, as given in Tables 4.17 and 4.12,
respectively, and in Tables 4.10 through 4.12, that only a small frac-
tion of the total amount of almost every trace metal is found dissolved
in the sludge liquor. In fact, taking into account the relative quan-
tities of liquor and solids in the waste, in almost all cases well over
90% of the trace elements appear in the solid phase. This is probably
due to the very low solubilities of the trace metal hydroxides, oxides,
and carbonates.
If trace element levels in solution are limited by solubility, as
would be expected by the trace element partitioning, then no direct
generalized correlation would be expected between trace metal levels in
the parent coal and in the waste liquors. The lack of evidence for such
a relationship existing is evident from the Radian data and is also con-
firmed in analyses performed by Aerospace [31] which were discussed
earlier.
4-45
-------
However, the data do not show any upper bound on the soluble con-
centration corresponding to an obvious solubility limitation (as might
be expected based upon the levels of trace elements in the solid phase) .
There could be any number of explanations for this including: data
scatter, displacement of the solution chemistry from actual equilibrium
and changes in solution chemistry made possible by the presence of com-
plexing ions. Unfortunately, there are no data at present on trace
element speciation that could shed some light on the system chemistry.
Work has been initiated in this regard by SCS [14].
4.3.3 Trace Elements in Stabilized FGC Wastes
There are some data on concentration ranges of trace elements in
leachates from treated sludges which will be discussed later.' However,
no data are available on trace elements in treated wastes.
4.4 Leaching Behavior
The potential for groundwater and surface water contamination from
the disposal of FGC wastes varies with the waste characteristics, the
method of disposal, and the site conditions. Potentially, there are
two routes by which such contamination can occur:
• Direct release of occluded waste liquors, and
• Leaching of FGC waste constituents.
Leaching can be envisioned as involving two different mechanisms:
• Surface leaching in which diffusion and waste dissolution are
usually limiting, and
• Flow through waste pores, in which case the mass permeability
strata can be limiting.
In leachate formation via water flow through the wastes, it would
normally be expected that the water will first flush the interstitial
waste liquors from the deposit; and leachate concentrations would be
roughly equivalent to the composition of the occluded liquor, in
successive pore volume displacements, leachate concentration would then
4-46
-------
approach the equilibrium (or steady state) concentrations due to disso-
lution of the solids. The rate of leachate production would be defined
by the limiting mass permeability coefficient (the waste or the surround-
ing strata) and the hydraulic potential (i.e., head of water) present.
The dissolved species in FGC wastes are frequently more readily
available for impacting the environment than are substances associated
with the solid phase which are not highly soluble. The dissolved species
can be released directly, with the waste liquor, via runoff and/or drain-
age accompanying natural settlement, or by forced displacement of liquor
via compaction; and indirectly through flushing or mixing of the liquor
with permeating water. This potential for greater immediate impact and,
perhaps, the fact that undisturbed waste liquors samples are more easily
obtained than pure solid phase samples have resulted in considerably
more detailed analysis of the composition of waste liquors than that
of the solids.
Numerous studies have been undertaken to evaluate the potential
for contamination due to leaching from FGC wastes and to characterize the
leaching behavior of different types of wastes. Most of these have been
laboratory studies involving various leaching column tests at acceler-
ated flow rates and/or elutriate (shake) tests. These tests
attempt to either simulate actual or "worst case" field leaching condi-
tions or to obtain the potential maximum leachate concentrations. A
few programs have included pilot-scale field testing in an attempt to
corroborate laboratory results. However, to date, there has been no
large-scale field monitoring of full-scale, commercial operations,
although a few demonstration projects are now in planning or early
stages of monitoring (as will be discussed later).
Table 4.18 summarizes the major programs funded by the government
and the utility industry which have been undertaken to characterize the
general leaching behavior of FGC wastes. Only those studies and programs
which have been completed, are currently underway, or have been funded,
but not yet started have been included. All of the demonstration
4-47
-------
Table 4.18
Principal Programs Funded by the Government and Utility Industry
to Evaluate Leaching Behavior of FGC Wastes
EPA/IERL
CO
EPA/MERL
EPRI
DOE/ERDA
NYERDA
Contractor
Aerospace
ADL
Aeroapa.ee/TVA
LGE/CE
ADL/UMD
ADL/NEA
LGE/Bechtel
WES
ACE (Dugway)
Radian
Southern Services
(Schola)
Radian
GFERC
SUHY/I7CS
Waate Type
Unstablllzed & Stabilised
Unatablllxed & Stabilised
Unstablllzed & Stabilized
Unstablllzed & Stabilized
Unstablllzed
Unstablllzed & Stabilized
Unatablllzed & Stabilized
Unstablllzed
Unstablllzed
Unstablllzed
Stabilized
Unatablllzed
Stabilized
ProKraa Focua
Laboratory
Laboratory
Laboratory/Pilot (lapoundavent)
Laboratory/Pilot (Impoundment)
Demonstration (Mine)
Laboratory/Pilot (Ocean)
Demonstration (Impoundment)
Laboratory
Laboratory (Land Disposal)
Laboratory
Pilot (Impoundment)
Laboratory
Laboratory
Laboratory/Pilot (Ocean)
Status
Underway
Completed
underway
Underway
Underway
Underway
Planned
Underway
Underway
Completed
Completed
Underway
Underway
Underway
Reference!
31,37
30
40
21
30,48
16
47
39
49
15
Source! Arthur D. Little. Inc.
-------
projects and the pilot work performed by Louisville Gas & Electric and
Combustion Engineering at Paddy's Run involve waste from a single system.
All others involve wastes generated by two or more different systems.
Furthermore, the demonstration programs will include laboratory and
possibly some small-scale field testing to "calibrate" the full-scale
monitoring data and evaluate different waste conditions.
In addition to data obtained in these programs a considerable
amount of data has been developed in testing performed or funded inde-
pendently by specific utilities, FGD equipment suppliers, companies
offering commercial treatment systems, and universities.
Unfortunately, at present no standard laboratory leaching test has
been developed. Testing procedures have varied widely in the method-
ology. Variations have included:
• Sample preparation (dried vs. as received material),
• Degree and method of drying,
• Extent of sample grinding, etc.,
• Characteristics of the leach solution used (distilled
and/or deionized water, simulated groundwater, buffered
solutions, etc.), and
• The manner of contact of leach water and the sample (simple
column leaching, single elutriate, multiple elutriate, etc.).
To compound the problem, few organizations have tested the same waste
sample. In a few cases, though, different methods have been used with
the same samples in an attempt to determine the effects of test methods
on results. A review of the many leaching tests that have been used by
various organizations on many different wastes has been published
recently [113].
This situation has resulted in considerable disagreement and con-
troversy over the proper method(s) for performing leaching tests. At
present, both the EPA (via RCRA) and ASTM are attempting to establish
standardized procedures. However, some argue that the leaching test
most applicable will have to take into account both the waste character-
istics and the disposal scenario. For example, IUCS has developed
4-49
-------
in-house leach tests and advocates the use of a shake test and/or a
combination runoff/leaching test, particularly where treated materials
are concerned.
4.4.1 Leachates
4.4.1.1 Coal Ash
The chemical composition of ash pond effluents varies over a wide
range, depending on the chemical composition of the ash, the variations
in flow and quality of the raw water supply used for sluicing the ash
and the other waste streams discharged into the pond. The concentrations
of the various constituents in the"case where only fly ash is disposed
depend only on the fly ash composition, the flow rate and the quality
of the initial water used for sluicing.
A recent survey of ash pond effluents of over 800 plants has been
performed by Hittman Associates. The data have not been published [118]
The characteristics of coal ash leachate vary greatly since some
ashes, upon contact with water, yield acidic solutions while others
yield neutral or greatly basic solutions. Basic leachates occur when
the metal oxides (primarily Ca, Mg, K, and Na) come in contact with
water. On the other hand, when the metal oxide content of the ash is
very low, an acidic leachate will occur due to hydrolysis of the trans-
3+ 3+
ition metal ions (such as Fe , Al ) and oxidation of sulfides. The
extent of trace element dissolution from the ash will vary greatly,
depending on the leaching media pH. Generally, the greater the acidity
of the liquor, the greater the solubility and rate of solubilization of
most of the trace elements.
The TVA [61] has been monitoring discharges from ash ponds since
1973 for 17 trace elements and 14 other parameters. A typical profile
of a once-through discharge of a fly ash pond is given in Table 4.19.
The values represent not only the materials leached out from the ash
but also include background concentrations of the raw water supply.
Laboratory experiments have been performed on leaching of fly ash.
Radian [62] conducted leaching experiments using deionized water for
4-50
-------
Table 4.19
Characteristics of Once-Through Fly Ash Pond Discharges
TVA Plant A
Parameters 1973 1974
Flow (lit./min.) 23-8 23.2
pH* + 4'5 4'3
Total Hardness (mg/1 as CaC(>3)* 241 280
Conductivity (ymhos/:m)* 807 814
Total Dissolved Solids (mg/1)* 508 508
Suspended Solids (mg/1)* 67 38
Phosphorus (mg/1) 0.07 0.02
Ammonia (mg/1 as N) 0.16 0.70
Sulfate (mg/1) 383 333
Chloride Cmg/1) 8 6
Cyanide (mg/1) <0.01 <0.01
Silica (mg/1) 13.8 11
Calcium (mg/1) 170 102
Magnesium (mg/1) 13.4 14.6
Aluminum (mg/1) 6.6 7.8
Arsenic (mg/1) 0.01 <0.006
Barium (mg/1) 0.2 0.3
Beryllium (mg/1) <0.01 0.01
Cadmium (mg/1) 0.037 0.037
Chromium (mg/1) 0.03 0.11
Copper (mg/1) 0.30 0.30
Iron (mg/1) 0.74 2.13
Lead (mg/1) 0.04 0.08
Manganese (mg/1) 13.38 0.46
Mercury (mg/1) <0.0002 <0.0002
Nickel (mg/1) 0.12 0.09
Selenium <0.002 <0.002
Silver (mg/1) <0.01 <0.01
Zinc (mg/1) 1.4 1.63
* Note: All numbers are averages of quarterly grab samples
collected during the indicated year, except those
parameters shown with an asterisk are averages of
weekly grab samples. The reported values include
background concentrations in the raw water supply.
Source: [61]
4-51
-------
24 hours in 28% slurry samples. The ash samples were various mixtures
of bottom ash and fly ash from five stations. The natural pH of all th
samples was greater than 7. The concentrations of the trace elements
observed are given in Table 4.20. It is difficult to draw conclusions
from these data due to the variability in pH of the final slurry. The
effect of pH on the leachability of the trace elements was also inves-
tigated for the ash obtained from Station 1. The pH was varied between
8.5 and 11.0 by introducing C02 into the slurry. The concentrations of
As, F, Se, Cr and Cu in the leachate were unaffected by variation in this
pH range. Passage of the ash leachates through cation and anion exchange
resins indicated that most of the Cr is present in a cation form and most
of the Se is present in an anion form.
Laboratory experiments on cation solubilities from lignite fly ash
[63] have been made to determine effects of water-to-ash ratio and
leaching percentage with subsequent washings. These results have shown
that between 78~t and 91% of the soluble sodium is leached in the first x
and variations in the water to ash ratio have little effect on the total
leached. A pH effect (over the range 11.8-9.7) on the solubility of Mg
and Fe from the ash was suggested. Laboratory experiments on boron
leaching from southern Illinois fly ash and bottom ash [64] indicate
that up to 50% of the boron in fly ash leaches in the pH region of 6-8.
Leaching was pH independent and occured within two hours. Results of
ESDA indicated that the boron was present in two chemical states. Littl
leaching of boron from bottom ash occurred (<0.1%) where the boron was
present in only one chemical state. Heat treatment (1200°C) rapidly
converted the boron in fly ash to the less leachable form found in
bottom ash.
4.4.1.2 Unstabilized FGC Wastes
One of the earliest programs undertaken to characterize the leach-
ing behavior of different FGC wastes was initiated by the EPA in 1975.
This study, performed by the Aerospace Corporation, is now nearly com-
pleted. At the outset, work focused on untreated FGC wastes. Acceler-
ated leaching column tests were performed on samples of untreated FGC
4-52
-------
Table 4.20
Equilibrium Concentrations of Trace Elements
in Coal Ash Leachate
Station Number
Bottom Ash (wt %)
Precipitator Ash
(wt %)
pH
Element (ppm)
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Fluorine
Germanium
Mercury
Lead
Manganese
Molybdenum
Nickel
Selenium
Vanadium
Zinc
Copper
OH
C03
Cl
S04
Ca
Na
K
Mg
Fe
ran
1
20
80
12.5
.006
<.002
40
.003
.03
<.001
<.001
2.3
<.01
.0006
.0068
<.002
.047
<.05
.009
<.l
.038
<.005
800
70
10
10
900
72
4
1
1
2
2
20
80
9.5
.018
.084
<.3
.00064
16.9
.0025
.21
1.4
<.01
.0005
.0027
<.002
.052
.015
<.0005
<.l
.025
.031
3
20
80
12.2
.033
.015
<.3
.0007
.21
<.01
.11
2.0
<.01
.015
.024
<.002
.05
.025
.033
<.l
.19
.092
4
50
50
12.0
.022
.072
<.3
.001
1.1
<.001
1.0
17.3
<.01
.0003
.0043
<.002
.69
<.05
.47
<.2
<.005
.013
5
100
8.2
.0087
.006
<.3
.00026
.048
.0011
.014
1.4
<.01
.0003
.0063
<.002
.010
.046
< . 0005
<.l
.0175
.015
Source: [62]
4-53
-------
wastes obtained from five pilot and full-scale systems [37]. Columns
containing each waste were leached with acidified, neutral, and basic
solutions saturated with oxygen. A single column containing a portion
of each sample was leached with deaerated, neutral solution to simulate
anaerobic conditions. Leaching was continued until 40-50 pore volume
displacements (PVD's) were collected. In Table 4.21 concentrations of
substances measured in a sample of the leachate collected at the end of
the leaching experiment (40 or 50 PVD's) during aerated leaching tests
on four materials, are compared to the corresponding concentrations in
the liquor occluded within the waste solids when they were discharged
from the FGD process. No significant differences which could be attri-
buted to the pH of the leach solutions were observed, and the values of
final leachate concentration represent the median of the three values
obtained. The results in Table 4.21 show that concentrations of sulfate
and chloride as well as TDS, measured in the leachate after 50 PVD's of
leached liquor had passed through the waste, had reached similar levels
even though the initial concentrations in sludge liquors were signifi-
cantly different. In all cases, TDS had fallen to about 1,500-2,500 mg/1
and sulfate had fallen to about 1,200 mg/1. These levels probably
reflect the equilibrium solubility of the calcium sulfate component of
the waste. The other chemical species showed the same tendency to level
off to similar concentrations after 50 pore volumes of leaching had
taken place.
Recent work reported by Aerospace [31] on additional samples of
unstabilized FGC wastes from three different prototype/test systems is
summarized in Tables 4.22 through 4.25 and corresponding Figures 4.4
through 4.6. Table 4.22 and Figure 4.4 show comparative laboratory
leaching data on waste produced from direct lime scrubbing at the Shawnee
test facility, both with and without simultaneous fly ash removal. Table
4.23 and Figure 4.5 show similar data for waste from a different direct
lime scrubbing system, the Louisville Gas & Electric plant at Paddy's
Run which operates with high efficiency ESP's. Finally, Table 4.24 and
Figure 4.6 provide laboratory data on dual alkali waste filter caJce from
4-54
-------
Table 4.21
Comparison of the Chemical Constituents in Sludge Liquors
With Leachate After 50 Pore Volume Displacements
(Concentrations In mg/liter)
I
Ol
Eastern Limestone
Shawnee
Western Limestone
Cholla
Eastern Dual Alkali
Parma
Western Limestone
Mojave
As
Be
Cd
Cr
Cu
Pb
Hg
Se
Zn
Cl
F
so3
S04
PH
IDS
Liquor"
0.14
0.054
0.003
0.09
0.01
0.25
<0.05
—
—
2,250
6.2
80
10,000
8.3
15,000
Leachate
0.01
0.004
< 0.001
0.003
0.010
0.01
< 0.00005
0.006
0.045
120
< 0.2
25
1,200
5.0
2,400
Liquor"
< 0.004
0.18
0.0009
0.21
0.20
0.01
0.13
2.5
0.07
1,430
0.7
0.9
4,400
4.3
9,100
Leachate
< 0.004
0.004
< 0.001
0.002
0.01
< 0.001
< 0.00005
0.05
0.04
110
6.1
9.0
1,150
5.9
1,900
Liquor"
< 0.004
< 0.005
<0.02
<0.02
0.06
0.52
0.0005
0.075
0.59
5,200
58
140
35,000
12.7
65,000
Leachate"
< 0.002
< 0.004
< 0.001
< 0.001
< 0.01
< 0.01
< 0.00005
0.010
0.04
95
0.2
30
1,100
6.1
1,650
Liquor"
0.03
0.02
0.05
0.25
0.6
0.04
< 0.005
0.12
0.18
28,000
30
1.5
25,000
6.7
92,500
Leachate
< 0 . 004
0.004
< 0.001
0.003
0.010
< 0.001
< 0.00005
0.004
0.045
130
< 0.2
0.3
1,300
4.5
2,100
Liquor analysis for liquor occluded with sludge solid? as disposed.
After 40 pore volume displacements.
Source: [31, 37]
-------
Table 4.22
Chemical Analysis - Shawnee Lime Waste Liquor and Leachates
Constituent3
pH
TDS
Arsenic
Beryllium
Boron
Cadmium
Calcium
Chromium
Copper
Lead
Magnesium
Mercury
Potassium
Selenium
Sodium
Zinc
Chloride
Fluoride
Sulfate
Without Fly Ash
Filtrate
8.0
10260
0.058
<0.001
76
0.013
650
0.011
0.005
0.-010
1730
<0. 00006
24
0.078
137
<0. 001
1320
1 -.9
4500
Leachate
First Pore
Volume
8.3
4480
35
.-_-
690
0. 025
0.011
<0.002
400
14
75
0.007
550
2.6
2150
Fifth Pore
Volume
7.1
1770
0.120
<0.001
3
0.013
450
0.010
<0.002
<0.002
30
< 0.00006
2
<0.0004
47
0.01
1.28
2.5
1100
With 40% Fly Ash
Leachate
First Pore
Volume
7.9
4330
65
600
0.010
<0. 002
<0. 005
310
.
7
72
0.003
400
6
2700
Seventh Pore
Volume
7.4
2430
0. 360
<0. 001
16
0.010
640
0.004
<0.002
<0.005
10
0.00024
4
0. 051
42
0.02
130
1.2
1450
"Sampling date - 9/8/76; concentrations in ag/t BB Appropriate.
-------
Table 4.23
Chemical Analysis Paddy's Run - Carbide Lime
FGC Waste Liquor and Leachates
12% Ash
Leachate
Constituent
PH
IDS
Arsenic
Beryllium
Boron
Cadmium
Calcium
Chromium
Copper
Lead
Magnesium
Mercury
Potassium
Selenium
Sodium
Zinc
Chloride
Fluoride
Sulfate
Filtrate
8.9
24230
0.011
< 0.001
18
0.025
515
0.054
0.0045
< 0.005
3400
0.00006
760
0.0028
260
0.003
5600
<1
15000
First Pore
Volume
7.4
5240
2
410
< 0.0008
0.004
< 0.002
470
125
40
0.015
410
<0.1
2800
Tenth Pore
Volume
8.1
1650
0.023
< 0.001
<0.5
0.004
260
< 0.0008
< 0.002
<0.002
70
0.00006
21
0.006
3
0.005
157
<0.1
920
Concentrations in mg/1 as appropriate.
Source: [31]
4-57
-------
Table 2.24
Chemical Analysis - Plant Scholz Dual Alkali FGD Waste Liquor and Leachates
6/20/76 Run with Ho Ply Ash
6/27/76 Run with 301 Fly Ash
I
in
00
Constituent
pH
TDS
Arsenic
Beryllium
Boron
Cadmium
Calcium
Chromium
Copper
Lead
Magnesium
Mercury
Pol* tiium
Selenium
Sodium
Zinc
Chloride
Fluoride
Sulfate
Lei c hate
Filtrate b
12.1
155700
...
...
;3
...
li
...
0. 1
...
320
53000
5000
24
60000
First Pore
Volume
>2.5
9140
5
1000
—
—
—
<0.01
—
43
2260
1070
•IB
3700
Sixth Pore
Voinmc
12. 3
35 :-0
<0. 004
<0.001
<0.5
0.016
1100
0. 00 IS
<(>. 002
0.005
<0.01
0. 00030
1
<0.0004
12
0.007
310
13
1160
Lcachatc
Filtrateb
li. 0
162700
•10
...
7
...
0.1
380
B5300
—
4900
4
84000
First Pore
Volume
10.4
17330
<0.5
...
550
0.2
74
4720
/050
3
10100
Ninth Pore
Volume
9. t
21-10
0.019
<0. 001
<0.5
0.010
800
0.024
<0.002
<0.002
0.3
0.00024
11
<0. 0004
82
0.013
134
0.9
1415
fl
Concentrations in mg/£ as appropriate
Incomplete analyses for filtrate samples is a consequence of insufficient sample quantity.
Source: [31]
-------
Table 2.25
Mass Balance, Charge Balance, and Gupsum Solubility
Ratio of Waste Liquors and Leachates
Sample Mass Ratio3 Charge Ratiob Ionic Strength Solubility Raiioc
TVA/Sli.Twnr.e Waste
Kun £ Filtrate 1.01 1.29 0.14 0.97
Run F Filtrate 0.68 1.38 0.27 0.85
Run F Lcachatc (No
Fly Ash):
First Pore Volume 0.93 1.18 0.12 1.07
Sixth Pore Volume 1.03 l.OZ 0.05 6.8Z
Run F Leachatc (40-!'o
Fly Ash):
First Pore Volume 1.01 0.87 0.12 1.20
Seventh Pore Volume 0.97 1.03 0.07 1.23
Gulf/Schola Waste
Filtrate (No Fly Ash) 0.91 1.29 2.91 1.19
Leachatc (N'o Fly Ash):
First Pore Volume 1.01 1.08 0.21 1.46
Sixth Pore Volume 0.86 1.08 0.09 1.22
filtrate (30% Fly Ash) 0.90 1.27 3.03 0.91
Lcachiilc W/uFly Ash):
Fir»t Pore Volume 0.98 0.98 0.36 1.17
Ninth Pore Volume 1.17 1.32 0.07 1,36
L. G. &E. /Paddy's Run
Waste
Filtrate 1.19 0.71 0.71 0.86
Lcachate:
Fint Pore Volume 0.85 0.92 0.13 0.80
Tenth Pore Volume 0.91 0.82 0.04 0.48
Avorafle Man Ratio 0. 97{*0. 10)
Average Charge Ratio 1,08(^0.20)
Average Solubility Ratio 1.04(^0.26)
s Ratio - E All Ion Concentrations/TDS (corrected for water in CaCl2 • 2H20 not lost in drying)
Charge Ratio =» I Equivalent Concentrations of Cations/I Equivalent Concentrations of Anions.
CSolubility Ratio - Measured Calcium Concentration x Measured Sulfate Concentration/K
(Solubility Product Constraint Corrected for Ionic Strength).
Source: [31]
-------
*
g
No Fly Ash
O TDS
A SOA
D Cl
0 Ca
O Mg
Ash
2-34- 5 to 7
AVERAGE PORE VOLUME DISPLACEMENT
Source: [31]
Figure 4.4 Concentration of Major Species and TDS in
Leachate Lime FGD Waste with and without
Fly Ash from Shawnee, Run F
4-60
-------
J
T - : I I
O TDS
A SO,
20,000
15,000
e
o
•H
4-1
n)
•u
a
a;
o
c
10,000
a ci
0 Ca
X Mg
Average Pore Volume
Displacement
-
•
Source: [31]
Figure 4.5 Concentrations of Major Species and IDS in Filtrate
and Leachate FGD Waste from LG&E Paddy's Run
4-61
-------
25,000
20,000
»5,000
o
o
•H
•U
W
t-l
4J
c
-------
the Southern Co. Services prototype system at the Scholz Steam Plant.
Again, data are shown for wastes generated from SO- removal only and
from combined fly ash and SO removal.
In general, the results for TDS and sulfate levels for these samples
roughly agree with those of earlier tests. Except for the dual alkali
material without fly ash, TDS levels fell to the range of 1,650-2,430 mg/1.
(The dual alkali materials with their higher initial TDS level may require
a few more displacements to achieve the same steady-state TDS levels.) Sul-
fate concentration levelled off in the range of 920-1,420 mg/1. However,
it is interesting to note that in the case of the Paddy's Run waste (a
material consisting almost entirely of calcium sulfite) the TDS and sul-
fate concentrations did not level off at the saturation concentrations
corresponding to gypsum—they were much lower. This subsaturation with
respect to gypsum is shown in Table 4.25 in which the charge and mass
balances and gypsum solubility ratios for these liquors and leachates
are tabulated.
Presumably, the gypsum subsaturation is due to the almost complete
absence of calcium sulfate in the waste. Dissolution of calcium sulfite
(in conjuncion with oxidation of the dissolved sulfite in the aerated
leach water) may therefore be limiting. This would also be expected in
other sulfite-rich wastes such as the Scholz dual alkali material, par-
ticularly where leaching occurs under anaerobic conditions. Under the
aerated conditions of these tests, though, there may be sufficient sul-
fite oxidation that continuing formation of sulfate combined with the
higher levels of calcium sulfate dissolving results in saturation with
respect to gypsum (the Scholz material contained ^20% calcium sulfate
vs. <5% for the Paddy's Run waste).
The leaching of sulfite from FGC wastes may be a concern, as pointed
out by Lunt, ejt al. , [30]; however, there are very few data on sulfite
levels in leachate under different conditions. As previously noted,
sulfite (or total oxidizable sulfur, TOS) is readily oxidized and there-
fore represents an immediate oxygen demand to groundwaters or receiving
waters. TOS may also be potentially toxic to aquatic life. Under contract
4-63
-------
to the EPA, Arthur D. Little, Inc., is studying the question of sulfite
availability and leaching as a part of their program to evaluate the
disposal of FGC wastes in mines and the ocean [30].
The data on the levels of trace metals in the leachates for comparable
wastes with and without fly ash differ for the Scholz and Shawnee sample
materials. In the Shawnee materials, arsenic, boron, mercury, selenium,
and possibly zinc are significantly higher in the waste containing fly
ash after more displacement washes. The rest of the trace element con-
centrations are about the same except for chromium and magnesium which
are slightly lower in the ash-containing waste. It is also interesting
to note that, of the data reported, arsenic and zinc concentrations in
the leachate are higher than in the original liquor, whereas the con-
centrations of other trace elements in the leachate are about the same
or lower than in the original liquors.
For the Scholz wastes, the concentrations of arsenic, chromium,
magnesium, and possibly zinc in the leachates are higher in the waste
containing ash than in those with no ash, although the wastes containing
ash had undergone more PVD. The higher levels of magnesium in the
leachates of the ash-containing sludge can be attributed to the lower
pH of these leachates. The fluoride concentration in the leachate of
the ash-containing waste is also significantly lower.
Using a different type of test procedure, Radian in a study funded
by EPRI analyzed trace elements in leachates from untreated FGC wastes
produced at three different power plants. The test procedure involved
air-drying the waste followed by 24-hour extraction with deionized water
using 20 wt.% slurries. Results are shown in Table 4.26. The trace
element levels observed generally fall within and to the lower end of
the range of concentrations for waste liquors and elutriates measured
by WES and Aerospace and shown in Table 4.16. The measurements of boron
concentrations range from 1 to 6 ppm compared with the two values of 8 ppm
and 41 ppm in Table 4.17. Fluoride was also found at substantial levels,
but the several measurements of molybdenum were all less than 0.1 ppm—
substantially below the two concentrations reported in Table 4.13.
4-64
-------
Table 4.26
Equilibrium Concentrations of Trace Elements
In FGC Waste Leachate
Station Number
pH
Element (ppm)
Sb
As
B4
B*
B
Cd
Cr
P
Gc
Hg
Pb
Hn
Ho
Hi
Se
V
Zn
Cu
1
8.5
0.014
<0.002
2
0.002
2.6
0.0005
0.001
31.5
<0.01
0.0005
0.0056
<0.002
0.063
<0.05
0.04S
<0.1
0.005
•0.031
4
9.7
0.013
<0.002
<0.3
0.001
6.3
<0.001
0.011
8.7
<0.01
d.ooi
0.0033
-------
Radian noted that the sludge from Station No. 5 contained a substantial amount
of fly ash, whereas the sludges from Stations No. 1 and 4 were quite clean
Interestingly, only arsenic was present at a substantially higher level in
the Station No. 5 ash-containing sludge leachate as compared to the other
two which did not contain ash.
Limited data on leachate concentration of sulfate-rich FGC wastes are
available. Radian [146] has performed laboratory leaching experiments in a
permeability measuring apparatus on the Shawnee forced oxidation scrubber waste
and on waste from the Four Corners fly ash scrubber. The concentration of major
and trace species in these leachates are shown in Figures 4.7 and 4.8 and Table 4.27
These data reported by Aerospace and Radian are representative of the
results obtained in other laboratory studies of the leaching behavior of un-
treated wastes. The changes in leachate concentrations (for most constituents)
with successive PVD'sandthe range of concentrations observed are generally
confirmed in elutriate data reported by Arthur D. Little [19], preliminary
results of leaching column tests performed by WES [16], and many other investi-
gations of leaching with water. While these studies are certainly not con-
clusive, there are definite trends in laboratory leaching behavior:
• The concentrations of major soluble species and trace elements
in waste liquors vary considerably with the type of FGC system
the composition of the coal burned, and other factors including
the impurities in process makeups (reactants and water).
• The initial flush of leachate from the wastes (first pore volume
or less) has concentrations approximating those in the Interstitial
(occluded) liquor.
• Successive displacements of occluded pore water show rapidly
decreasing levels in TDS and certain highly soluble species
(e.g., Na+ and Cl~).
• The initial concentrations of trace elements in leachate are
generally quite low, although many (depending on the waste
characteristics) can exceed levels prescribed in drinking water
standards. Most trace element levels tend to decrease with
successive PVD's. There are a few notable exceptions, such as
4-66
-------
10,000
1,000 —
TDS
SO*
CT»
10
c
O
a
14
*J
C
01
u
o
100
—&-
Cl
10
10
20
Pore Volume Displacements
Source:
[146]
Figure A.7 Concentration of Major Species in
Leachate from Four Corners Scrubber
Waste
4-67
-------
u
e
o
4J
C
0)
u
C
o
fj
10,000 —
1,000 —:
100
10
-o-
TDS
poo
-Q-
A cl
10 15 20
Pore Volume Displacements
25
Source: [146]
Figure A.8 Concentration of Major Species in
Leachate from Shawnee Forced
Oxidized Scrubber Waste
4-68
-------
Table 4.27
Concentration of Trace Elements in Leachate
From Sulfate-Rich Wastes (First Pore Volume)3
Four Corners(yig/ml) Shawnee (ye/ml)
(Fly Ash Scrubber) (Forced Oxide)
Li 0.05 0.002
B 0.9 0.01
F M).5 %2
Na >* 2
Mg 1 0.7
Al 1 0.1
si 3 >10
P 0.5 0.1
S >9 >4
A 0.8 0.2
K 2 0.9
Ca >10 >10
Ti 0.3 0.08
v 0.05 0.04
Cr O-03 0.02
Mn °-01 0.009
Fe 1 0.2
Co <0.002 <0.001
Ni 0.01 0.01
Cu 0.02 0.01
Zn 2 0.06
Ga 0.05 0.002
Ge 0.003 0.007
As 0.01 0.01
Se 0.02 0.02
Rb O-005
Sr 1
Sn 0.01 0.004
ST, 0.02 <0.001
Ba l °-2
pb 0.05 0.009
0.02 0.02
SLiquid sample thermally ashed at 350°C for one hour prior to
analysis by Spark Source Mass Spectrometry.
Source: [146]
4-69
-------
arsenic and zinc, which have been observed to remain relatively
constant, at least over the first ten pore volumes.
• Concentrations of constituents tend to level out after 5-10 PVD's
with IDS concentrations in the range of 1,500 to 2,500 ppm and calcium
and sulfate concentrations, inmost cases, corresponding to the gypsum
solubility product. This suggests that essentially all of the occluded
waste has been displaced and that dissolution of the solid phase
(with the release of any trapped liquor) is controlling.
The results of laboratory leaching tests have yet to be confirmed
by monitoring programs of full-scale field disposal operations. There
are a number of factors which may alter the leaching behavior which have
not been adequately tested, including:
• The effects of microbial activity,
• Variations in the composition of the leaching water and
conditions (e.g., high buffering capacity),
• High TDS levels,
• Anaerobic conditions for sulfite-rich wastes (complete
submersion in seawater, etc.), and
• Management of the disposal sites.
Considering the variations in the types of disposal and disposal
management, and the site conditions, such laboratory leaching studies
need field corroboration.
A limited amount of pilot field testing related to impoundments of
untreated wastes has been performed which has yielded some leaching data.
EPRI funded a study of the impoundment of the wastes generated from two
of the three prototype systems tested at the Scholz Steam Plant [49].
The wastes were dumped in a one-acre, artificially-lined pit with a
leachate collection system. The pond was allowed to sit open without
control of surface water so that the surface of the wastes was covered
with water. Leachate samples were then taken from the pond underdrainage.
Leachate compositions measured from the dual alkali waste pit over
a period of approximately a year and a half (7/75-12/76) are shown in
Table 4.28. Because of the low flow rates through the wastes, there
4-70
-------
Table 4.28
Summary of Leachate Concentrations from Dual Alkali Wastes
Generated During Prototype Testing at the Scholz Steam Plant
Al
As
B
Be
Ca
Cd
Cr
Cu
Fe
Hg
K
Mg
Mn
Na
Hi
Pb
Se
Zn
Concentration Range Measured
in Field Leachate Samplesa
0.12 - 29.0
<0.01 - 0.25
0.9 - 2.5
Laboratory
First PVD
211
<0.01
<0.01
<0.01
0.03
<0.0002
17
0.019
<0.01
2460
<0.01
<0
<0.002
<0.01
- 420
- 0.018
- 0.06
- 0.23
- 4.5
- 0.0026
- 165
- 5.2
- 0.07
- 7880
- 0.11
.01
- 0.190
- 0.07
1000
43
<0.01
2260
Leach Test*5
Sixth PVD
<0.004
<0.5
<0.001
1100
0.016
0.0025
<0.002
0.00030
1
<0.01
12
0.005
<0.004
0.007
IDS
Cl
F
so3
so4
pH
8540 - 24,050
169 - 887
3.6 - 110
54 - 500
5200 - 13,100
11.0 - 12.8
9140
1070
48
3700
12.5
3550
310
13
1160
12.3
^Samples taken from pit underdrain from 7/75 to 12/76, and includes
disposal of waste with inadequate or no filter cake wash. Performed
by Southern Company Services. Source: [49]
^Laboratory leaching test performed by Aerospace on sample taken at
6/20/76.
Source: [31]
4-71
-------
was standing water on the pond at all times. These conditions would
favor a plug flow mechanism (initial flush) for leachate production and
the concentrations in the leachate may be expected to be similar to those
in the liquor.
During the period of testing (3/75-7/76), the system was operated
with a wide range of conditions (including different coals) including
periods where there was no filter cake wash, so that no direct correla-
tions can be made. However, the results are illustrative of the range
of leachate concentration that can be achieved with one type of system
operating under slightly different conditions at one power plant firing
three different coals. For comparison purposes, the leachate data from
laboratory testing performed by Aerospace on one sample of these wastes
is also included in Table 4-28. The concentrations reported for the
pond leachate correspond more closely to the first PVD data than the
sixth.
Aerospace and the TVA are also jointly evaluating leaching from
three small ponds of untreated wastes and a number of ponds containing
treated wastes at Shawnee as a part of the EPA's program to test the
effects of waste treatment. Results of this program are discussed later.
To date there has been no monitoring of full-scale disposal opera-
tions of untreated wastes which provide data on leaching behavior.
However, two demonstration projects funded by the EPA are planned—one
at the Baukol-Noonan mine to evaluate strip mine disposal of wastes from
an alkaline fly ash scrubbing system and one at Louisville Gas & Electric's
Cane Run Station to evaluate the impoundment of dual alkali wastes.
4.4.2 Effects of Stabilization on Pollutant Migration from FGC Wastes
The impact on the environment of the pollutants contained in a mass
of FGC waste depends not only on the concentration of species in the
liquid and solid phases of the waste, but also on the rate that the
materials dissolve from the solid into the interstitial liquor and the
rate that they are transported out of the sludge mass. In earlier sec-
tions, it was noted that chemical stabilization of a waste can affect
4-72
-------
the permeability of the waste in addition to improving its physical
properties for disposal. Reductions in permeability directly reduce
the rate at which interstitial liquor is flushed from the sludge and for
equal concentration in the interstitial liquor, directly reduce the flux
of constituents emerging. Chemical stabilization may also affect the
concentration of substances which are dissolved in the interstitial
liquor by chemical reaction and/or encapsulation. However, in studies
conducted to date it has been difficult to experimentally separate the
effects on solubility and permeability.
In an attempt to evaluate the effect of waste stabilization on
pollutant mobility, Aerospace [40] had samples of waste stabilized chem-
ically by each one of three commercial processors—Chemfix, IUCS, and
Dravo. After the stabilized samples had cured, they were ground into a
fine powder and subjected to accelerated leaching tests similar to those
used for the untreated sludges. Samples were ground to minimize the
effects of restricted diffusion of pollutants from impermeable, large
particles. The results of one such set of tests which is typical of
results obtained for the three stabilization processes are shown in
Table 4.29. With some exceptions, the concentrations of substances in
the first pore volume were somewhat lower for the unstabilized waste
than for the stabilized material. Concentrations of the major soluble
species, sulfate and TDS, were reported to be reduced by 30-50%. A
reduction in chloride concentrations was not observed in this experi-
ment; however, substantial reductions were observed in tests of other
stabilized material. In this experiment, concentrations of lead and
fluoride were substantially lower in the first PVD sample from the
stabilized material. However, levels of copper and chromium in the
first pore volume were somewhat higher for the stabilized materials
than for the unstabilized material.
The accelerated leaching tests were designed primarily to determine
the final equilibrium concentrations of pollutants in leachate after the
major soluble substances had been flushed out. The fact that the first
PVD concentrations in the unstabilized material were somewhat less than
those in the interstitital liquor suggests that perhaps because of the
4-73
-------
Table 4.29
Comparison of the Chemical Constituents in
Eastern Limestone Waste Leachate with Chemfix
Chemically Stabilized Waste Leachate
Waste - Aerobic Chemfix - Aerobic
As
Cd
Cr
Cu
Pb
Hg
Se
Zn
Cl
F
SO,
IDS
PH
1st Pore Vol.
0.06
0.002
0.025
0.007
0.12
0.05
0.03
0.85
1350
2.7
6500
10,500
4.7
50th Pore Vol.
0.01
<0.001
0.003
0.010
0.01
< 0.00005
0.006
0.045
120
<0.2
1200
2400
5.0
1st Pore Vol.
0.04
0.003
0.04
0.05
< 0.035
<0.005
0.01
0.5
1400
0.9
3000
7000
4.70
50th Pore Vol.
0.006
<0.001
<0.001
0.005
<0.001
< 0.0005
0.002
0.065
60
0.2
250
500
6.01
Source: [40]
4-74
-------
rapid rate of elutriation, concentrations of substances measured at
early stages of Leaching may not have been representative of those which
would have been obtained if lower leach rates, more representative of
an actual disposal situation, had been employed.
In 1973, WES [41] began an extended leaching column study of samples
of five unstabilized FGD wastes and corresponding samples treated by
one or more of several commercial treatment vendors. By means of stop-
cocks at the bottom of each leaching column, leachate flow was to be
controlled so that downward flow would approximate permeation through
a sludge mass having a permeability of 10 cm/sec. A large number of
substances, both trace and major constituents, are being monitored in
the leachate collected from the leaching columns. At this time, only
preliminary data are available and the results are inconclusive. In
some cases, there is evidence that treatment may not have reduced the
concentration of dissolved solids in the leachate over the first few
PVD's while in other instances, there appears to be a definite reduction
in leachate concentrations. Preliminary data also suggest that concen-
trations of trace elements are reduced; however, with a few stabilized
wastes, concentrations of some trace elements in the leachate were rela-
tively unchanged or increased, possibly because of the addition of fly
ash or other additives not present in the stabilized wastes.
Jones and Schwitzgebel [42] performed columm leaching studies on
mixtures of fly ash and commercial gypsum or a synthetic calcium sulfite/
sulfate co-precipitate prepared in the laboratory. Leaching tests were
also performed on waste samples obtained from four full-scale FGC systems;
two contained significant amounts of ash. Based on measured permeabil-
ities and unconfined compressive strengths, some of the fly ash containing
sludges had undergone considerable pozzolanic reaction. The compositions
of corresponding fractions of leachate collected from a variety of samples
were quite similar regardless of the nature of the sample. Chloride
ion concentration fell very rapidly to about 10 mg/1. Concentrations of
IDS, calcium, and sulfate fell to equilibrium concentration levels in
the range of 1,000-3,000 mg/1. The similarities in the leaching behavior
4-75
-------
of the materials tested suggested that the curing reactions which
resulted in reduced permeability had not significantly changed the
actual solubility of the solid phase.
Chu, e_t^ alU , [43] studied a number of the physical and chemical
properties of mixtures of fly ash/FGD waste with hydrated lime. They
reported very large decreases in the concentrations of a variety of
substances in leachates from wastes containing lime and fly ash as com-
pared with unstabilized sludges. Ten-fold reductions in the concentra-
tions of major soluble anions like sulfate and choride were reported to
be the result of treatment. The concentrations of certain trace sub-
stances such as boron, fluoride and arsenic were reduced by stabilization-
many were not significantly altered; and a few like molybdenum and
chromium were higher in the treated leachates. The reductions in major
soluble components, in particular,are striking. However, the flow rates
used in the experiments and the extent to which the leach liquor was
forced to pass through the waste matrix were not stated, so the reduc-
tions in concentration might be largely due to reduced diffusion from
within the pieces of stabilized material.
IUCS has been using a "shake test" to characterize the leaching
behavior of the stabilized FGC wastes produced by the IUCS process [44].
Although very few experimental results have been reported in the
literature, these tests provide some evidence that in the IUCS process
pollutant immobilization is probably more a result of physical entrap-
ment than chemical insolubilization. In the IUCS shake test, which is
quite analogous to the elutriate test performed by WES and others, a
quantity of stabilized material, usually 400 grams, is immersed in about
2 liters of doubly distilled water and shaken very gently for two days.
The water is decanted, replaced with fresh water, and shaking is resumed
for two more days. The process is repeated until a total of five "surface
washes" have been performed. The elutriate liquors are then analyzed
for TDS and trace metals. Very few useful data on trace metal analyses
are available. Concentrations of TDS measured by IUCS in five successive
elutriates of a sample of stabilized FGC waste obtained from a Shawnee
4-76
-------
test pond are shown in Table 4.30. The fact that TDS concentrations
declined markedly in the first several leach solutions and then appeared
be levelling off at a constant value is interpreted to mean that the
first wash is really a wash of the surface and the high TDS is due to
the dissolution of solids on or near the surface. Succcessive washes
involved dissolution of solubles from within the relatively impermeable
oieces of material and the amount leached became limited by slow diffu-
irm from within the piece. Unfortunately, IUCS did not report the
amount of sample taken for leaching, or provide an estimate of the total
olubles potentially leachable. Without such data it is not possible
to speculate as to whether or not increased chemical insolubility had
accompanied stabilization.
The best test of the effect of chemical treatment on pollutant
mobility would be a field test conducted on a sufficiently large scale
Od over a sufficient length of time so that actual samples of permeate
and solid cores could be obtained for study and analysis. To that end,
Aerospace, on behalf of EPA, initiated a field study at the TVA Shawnee
power Station at Paducah, Kentucky. Initially, five 0.1-acre contain-
ments were constructed; two were filled with unstabilized FGC wastes and
three with FGC wastes stabilized by Dravo, IUCS, and Chemfix processes,
spectively [36,37]. All of those wastes contained fly ash. During
1976 a program of studies of ash-free lime waste, ash-free limestone
aste, and gypsum waste (produced by forced oxidation in a direct lime-
tone system) in three additional ponds were undertaken. Test samples
f stabilized and unstabilized waste, groundwater, surface water, leachate
d soil cores were analyzed in conjunction with the study.
An example of the behavior of measured values of TDS and three
ther major components in the leachate from one of the ponds containing
stabilized material is found in Figure 4.9. This behavior, which was
orted to be typical of the unstabilized ponds, showed all of the sub-
tance concentrations rising rapidly after filling and reaching concen-
rations approximating those in the interstitial liquor of the dissolved
stes. Although there are temporal variations, after about one year of
4-77
-------
Table 4.30
Concentrations of IDS in Leachate from Successive
Shake Tests of Stabilized FGC Waste Sample3
TDS Grams Grams
(ppm) Leached (in.2)
974 1.948 .046
338 .676 .015
268 .536 .012
194 .388 .009
214 .428 .010
Surface area of sample exposed to leaching solution
273 cm2 (42.4 in2)
Ratio of surface area to volume of leaching solution
137 cm2/ C21.2 in2/
Source: [44]
4-78
-------
I
^J
VO
O ID*
n a
a vij
O c»
fiijure Arrniucr
0|irn Hguit fV»
9/wn
»
SWIM
AIRS flHSI IXKIII MUINT.
l(W/«
CAUNDAR UAIfS
M
in
loom
Source: [37]
Figure 4.9 Concentration of Total Dissolved Solids and Major Species in Pond D Leachate
-------
leaching the concentrations seem to have begun to decline. For compar-
ison, the concentrations of the same substances measured in the leachate
from the same FGC waste after chemical stabilization are shown in Figure
4.10. The general rise in concentration was observed to be similar to
that in the waste from the unstabilized pond. However, the maximum
concentrations observed were only about 60% of those measured for the
unstabilized material.
The general behavior described above was reported by Aerospace to
be typical of the other stabilized or unstabilized materials as well.
Concentrations of major substances in the leachate from unstabilized
materials rose rather rapidly to about the levels present in the inter-
stitial waste liquor. For stabilized materials, concentrations of the
same substances rose to about 1/3-2/3 of the levels observed for the
unstabilized ponds. Significantly, Aerospace reported that levels of
trace substances in pond leachates seemed, for the most part, to be
unaffected by chemical stabilization, probably because the trace elements
do not participate in the fixation reactions.
Another field study of stabilized wastes is being conducted by
Louisville Gas & Electric, Combustion Engineering and the University of
Louisville at the Cane Run Station. This ongoing study focuses on the
effects of stabilizing wastes from a direct carbide lime scrubbing system
with fly ash and lime. Both physical properties and leaching behavior
are being studied.
Testing is also underway to evaluate the disposal of stabilized
wastes in the ocean. Although companion tests on the unstabilized mater-
ial were not performed, Duedall, et^ al_. [15], performed elutriate tests
using seawater to leach four samples of FGC waste treated by IUCS as a
part of its program to study the feasibility of using stabilized FGC
wastes for ocean reef construction. Two of the stabilized materials
had a high sulfate/sulfite ratio. Of particular interest in that work
was the observation that except for a few scattered cases, the concen-
trations of nearly all of the trace substances measured in the elutriates
were less than those measured in the starting seawater, which was used
4-80
-------
5000,
I
oo
1000
O IDS
n c/
a so4
O Ca
Closed Figure-Aerospace Analysis
Open figure-WA Analysis
D
°0
4/14/75
10
ttnin
M
9/1/75
30 40
WEEKS AFTER POND FILLING
11/8/75 1IW/76
CALENDAR DA US
50
3/29/76
60
6(7/76
70
8/16/76
Source: [37]
figure 4.10 Concentrations of Total Dissolved Solids and Major Species in Pond B Leachate
-------
to perform the elutriation. Duedall, et^ a^. [15], attributed the decrease
to adsorption of the trace elements from the seawater onto the stabilized
FGC waste. Additional testing of both unstabilized and stabilized wastes
in regard to ocean disposal is being performed by Arthur D. Little, Inc.
and the New England Aquarium under EPA funding [48].
Data included in a recent EPRI summary of the state of the art of
FGC waste fixation [2] suggest that in other stabilization processes,
such as the Chemfix process, constituents might in fact be chemically
bound within the stabilized material, thus reducing their solubility.
The results of one laboratory leaching study performed by Chemfix are
shown in Table 4.31. Chemfix [15] has observed that their process will
not immobilize certain soluble substances like chloride and monovalent
cations. The details of leaching studies which Chemfix has performed
are not presented; however, a comparison of the concentrations measured
in the first leachate fraction with the concentrations in the unstabilized
waste showed that essentially all of the other constituents were reduced
to a greater extent than was chloride. This suggests that a chemical
insolubilization was probably occurring in addition to possible immobil-
ization due to permeability reductions.
The IUCS shake test is of general interest because a test of that
sort may be a good way to characterize and compare the leaching behavior
of stabilized materials relatively quickly and inexpensively. The
alternative to a shake test is a leaching column test which must be run
for months or years to provide meaningful data.
A recent study on the effect of stabilization on leaching behavior
of dry sorbent FGC waste has been made by the University of Tennessee
[117]. The Extraction Procedure (see Section 4.4.5) was applied
to calcium based dry sorbent process wastes before and after fixation
using commercailly available processes. The results have not been
published.
4.4.3 Soil Attenuation
If the supernatant liquor from a disposal pond is allowed to permeate
4-82
-------
Table 4.31
Chemfix Preliminary Leaching Study on Waste From
Shawnee Plant, TVA
Test Number One
Constituents3
Cadmium
Total Chromium
Copper
Iron
Lead
Nickel
Zinc
Phenol and related
Cyanide and related
Sulfate
Chloride
Alkalinity
Chen. Oxy. Dem.
Unstabilized
Wasteb
1.0
20
24
8,700
54
23
56
< 0.10
0.15
9,000
1,500
600
6,500
Inches of Leachate Water0
0-25
< 0.10
< 0.10
< 0.10
.06
.09
< 0.10
< 0.10
< 0.10
.002
285
110
100
550
25-50
< 0.10
< 0.10
< 0.10
.02
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
250
45
125
500
50-75
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
135
30
75
500
75-100
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< 0.10
< C.10
90
20
65
a
All results in ppm.
Sample from turbulent contact absorber (without upstream fly ash
removal), centrifuged to 56% solids.
'lEach 25" of leachate represents approximately SOOcc of distilled
water.
The above data are supplied for information purposes only. Since unstabilized
wastes vary considerably, other samples of this waste may yield somewhat
different results.
4-83
-------
down through the settled waste and into the underlying soil, the leachate
will carry with it dissolved contaminants, initially, at levels as
high as in the interstitial liquor of the wastes. The same percolation
could occur through a landfill disposal site that was insufficiently
graded and sufficiently permeable so that a significant amount of the
rainfall it received percolated directly down into, and through, the
waste mass. However, if the soil underlying such a disposal site has a
sufficiently high ion exchange capacity or is a sufficiently active
adsorbent for dissolved ions, potential contaminants in the permeate can
be retained by the underlying soil, thereby purifying the permeate and
effecting containment of these species.
Radian [39] studied the retention of a number of trace elements
and species on soil types ranging from sand to loam. Test solutions
were prepared to simulate fly ash leachate and FGC waste leachate by
initially leaching samples of fly ash and waste, and then, because the
levels of trace elements in the actual leachate were quite low, the
leachate samples were spiked with concentrated metal solutions of the
sort used for standardizing atomic absorption spectrometry measurements.
The spiked leachates were allowed to percolate through columns packed
with each of the soil types. Fractions were collected from the effluent
and analyzed for trace element concentrations in order to detect the
breakthrough or point at which the column had become saturated with a
particular trace element. The relative retentions for the trace elements
tested on each of the soil types are shown in Tables 4.32 and 4.33. The
relative retentions are presented as values of a parameter, K, which is
the number of interstitial column volumes of leachate which could pass
through the column before the concentration of the emerging trace element
had risen to 5% of its concentration entering the column. The waste
leachate differed from the ash leachate not only in trace elements and
their levels, but also in pH—the fly ash leachate being very alkaline
(pH = 12), while the waste leachate was nearly neutral. Trace elements
like copper, arsenic, and zinc were uniformly well retained on most
soils from both types of leachate. Conversely, fluoride was poorly
4-84
-------
Table 4.32
Values of K for Spiked Ash Leachate'
.£>
1
oo
Ui
Plant 1
Plant 3
Plant 4
Plant 5
Soil 6
Soil 7
Soil 8
Soil 9
Cu b
(0.075)
>300
>300
>1000
c
>300
>200
c
>300
Cr
(1.0)
VLO-20
^300
550
<20
0
50
200
150
As
(0.4)
>30Q
>3QO
>10QQ
>6QO
>200
>200
>300
Se
(1.0)
25
225
100
200
25
-V300
150
F
(0.9)
0
<20
<20
^25
0
150
Soil T
silt loam
loam
loam
silt loam
K is the number of interstitial column volumes leachate would pass through before 5%
of the initial concentration would emerge from the column.
Concentration (ppm) of element in spiked leachate is in parentheses with each element
'Initial large values, decreasing.
Source: [39]
-------
Table 4.33
Values of K for Spiked Waste Leachate'
oo
Plant 1
Plant 3
Plant 4
Plant 5
Soil 6
Soil 7
Soil 8
Soil 9
Cu .
(1.0) b
1800
>500
>1200
1700
>1000
250
>150
>150
Cr
(i.Q)
10
20
40
20
10
0
0
0
F
(12.6)
. 10
50
25
20
20
<10
10
30
Hg
(1.2)
40
>500
>700
1000
300
20
>150
>150
Zn
(1.0]
1000
>500
>1200
1000
350
>150
>150
Source: [39]
K is the number of interstitial column volumes leachate would pass through before 5%
of the initial concentration would emerge from the column.
Concentration (ppm) of element in spiked leachate is in parentheses with each element,
-------
attenuated in almost every case; chromium was poorly attenuated under
conditions of neutral pH. Retention of selenium was quite variable
depending on the soil type.
The practical significance of soil attenuation in a disposal site
can be seen in Figure 4.11. The capacity of the underlying soil to absorb
elements (determined by soil texture, mineralogy, and organic content),
the concentrations and speciation of the elements and the rate of per-
meation of the leachate through the soil all combine to influence pol-
lutant transport from the pond. The Radian data suggest that if homo-
geneity of the underlying soils is assumed and if the single species
column attenuation tests are representative of the interaction that
would occur for a multi-element leachate then certain elements such as
arsenic, copper, and zinc would be attenuated in most soils within a
depth of 15 meters (50 ft) below the waste pond for as long as ten years
after first deposition of the waste. However, other trace elements
like chromium and fluoride were predicted to penetrate hundreds of feet
below the disposal pond with little attenuation.
Soil attenuation is, as pointed out by Radian, a complex process
composed of both ion exchange and physical adsorption. The speciation
of the elements in the leachate is variable depending upon pH and other
factors as was demonstrated by tests using anion and cation exchange
resins by Radian. Because of the variabilities in the leachate and the
complexity of the interactions with soil, predictions of attenuation
are difficult and column tests are necessary.
One of the most important limitations to the degree to which soil
attenuation can contain pollutants from FGC waste is the fact that major
soluble components like sodium, chloride, and sulfate are very poorly
attenuated and pass readily through the underlying soil into the receiv-
ing groundwater. In addition, the higher concentration of these species
in the FGC waste relative to rainwater may interact with the soil to dis-
place some of the trace elements in the soil and mobilize them.
Under an Interagency Agreement between EPA and the U.S. Army Dugway
Proving Ground, a study of the leaching of trace levels of potential
4-87
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HUB SUIFICf
Source: [39]
Figure 4.11 Removal of Trace Elements from
Pond Leachate by Soil Attenuation
4-88
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pollutants from FGC wastes and their subsequent attenuation by soil
columns has been carried out at Dugway. A series of column tests were
set up to study the leaching of selected trace species from six samples
of FGD wastes and three samples of fly ash. The FGC waste samples were
from limestone scrubbers (low and high sulfur coals), lime scrubbers
(low and high sulfur coal and dolomitic lime), and a dual alkali waste
(medium sulfur coal). All of the fly ash samples were from electrostatic
precipitators (low and high sulfur coals). The leaching column effluents
subsequently were passed through columns filled with six different types
of soil. The experimental design permitted samples of both the influent
to, and effluent from, the soil attenuation column to be taken for
analyses. Preliminary results indicate that the FGC waste leachates
contained little zinc but that a substantial increase in concentration
was observed after the leachate was passed through various soils.
Evidently, displacement and solubilization of the naturally occurring
zinc in the soil occur by passage of the waste leachates. The concen-
trations of boron and fluoride in the wastes and their leachates were
highest compared to all the other trace elements of interest (e.g., As,
Cu, Cd, Cr, Pb, Ni, Zn) and indicate that these two elements deserve
greater attention. These elements were, however, well attenuated by
most of the soils tested. Arsenic was also found in substantial amounts
in some of the wastes but was well attenuated by most soils. Solubil-
ization of in situ arsenic also occurred from one soil by passage of the
leachate solution. The species of Cd, Cr, Cu, Pb, and Ni, which were
found in very low concentrations in the waste leachates, were only partly
attenuated by the soils.
4.4.4 Impacts of Weathering on FGC Wastes
Weathering of FGC wastes, both stabilized and unstabilized, has
been observed to produce several important physical and chemical changes.
Of most importance is the potential for structural deterioration of
stabilized materials which can occur when they are subjected to freeze/
thaw and wet/dry cycling. Increased pollutant mobility may result from
the breakup of the less permeable stabilized structure. WES has carried
4-89
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out some preliminary lab tests of wet/dry and freeze/thaw behavior on
stabilized FGC waste specimens. Breakup has also been noticed on some
of the ponds at Shawnee.
Oxidation of calcium sulfite at the surface of high sulfite wastes
can increase the dissolved solids present in surface runoff following
a rain. Alternate wet/dry cycling can cause recrystallization with the
resultant formation of a hard surface layer which could reduce wind
erosion. Such crustation has been observed at Scholz and by Radian in
their EPRI work.
A further discussion of the effects of weathering on FGC wastes
properties is presented in Section 5.
4.4.5 RCRA Implications for FGC Waste Leachates
Recently, provisions of the Resource Conservation and Recovery Act
(RCRA) of 1976 have raised the possibility that FGC wastes may be declared
hazardous materials. The draft regulations place utility wastes In a
"special" waste category under Section 3004 (hazardous wastes). Until
further data become available, FGC waste disposal will require waste
analysis, monitoring, site selection, recordkeeping, security and
requirements of Section 3004 (Hazardous Wastes) will apply.
The tentative categories under which a waste may be defined as
hazardous are: ignitable, reactive, infectious, corrosive, radioactive,
and toxic, phytotoxic, mutagenic and teratagenic.
Considering the available data on the characteristics of FGC wastes
(fly ash, bottom ash, scrubber sludge, and leachate) there is no evidence
to suggest that any of these wastes are either ignitable or reactive.
The infectious criteria pertain only to health care facilities and, thus,
are not applicable to any of these wastes. The major concern which may
lead to the placement of FGC wastes in the group of hazardous waste is
the toxic category criteria. The pertinent section of the draft regula-
tions determining the potential toxicity is Section 3001 of the draft
regulations. According to the proposed draft regulation [46] a solid
waste is toxic if the elutriate obtained when the waste is applied to
4-90
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the Extraction Procedure (EP) has certain properties as determined by
various testing methods specified in the regulation. The properties
tested include gene mutation, DNA damage, bioaccumulation potential,
presence of "special chemicals" as defined by RCRA, or presence of con-
centrations of various species which exceed various applicable thresholds.
In the latest Extraction Procedure (EP) protocol [46], a sample of
the waste is placed in a polyurethane foam sample holder. The sample
holder is then placed in a compaction tester and subject to a compactive
action. A weight of 0.33 kg is dropped 15 times from a height of 15.2 cm
on the sample. The sample may remain intact or be pulverized by this action.
The sample is then placed together with an amount of water 16 times its
weight in a stainless steel container equipped with a low RPM stirrer.
The pH of the slurry is adjusted to 5.5 using 0.5 N acetic acid and the
sample is stirred for 24 hours wit'u Continual adjustment of pH. Aliquots
of the liquid phases are then taken for biological and chemical testing.
The lack of available data on many of the above specified properties
(mainly due to the need to use specific test methods, some of which have
only recently been defined) prevents the determination of the degree of
hazard of FGC wastes at this time.
Howeverv the available data on characteristics of these wastes suggest
some areas of concern. The presence of many trace metals and sodium u"'-
sulfite (which has been shown to be mutagenic) may yield mutagenic activity
for the waste leachate. In addition, these trace elements are known to
accumulate in the food chain to a significant degree and thus may yield
positive results on the bioaccumulation tests. The presence of compounds
in the wastes which were also on the "special chemicals" list was not
noted [116] so that it is not likely to fall in this category. Concen-
trations of some species in the EP elutriate may exceed threshold values
(such as 10 times the EPA Human Health Water Quality Criteria) since it
is known that the concentrations of some species in waste liquors exceed
these values. FGC waste may also be classified as hazardous under the
corrosive criteria. One such criterion is that of an aqueous waste having
a pH of less than or equal to 3 or greater than or equal to 12. Certain
fly ash slurries may exhibit pH values at these extremes.
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The last criterion by which FGC wastes may be classified as hazar-
dous is radioactivity. The criterion is defined by a waste for which
the Radium-226 concentrations exceed 5pci/gof solid or SOpciA of liquid
waste, or a total of 10 yC for a single discrete source. The single
source of data presented in Section 4.3 on the radionuclide concentra-
tions is fly ash and bottom ash indicating that this criterion may be of
concern.
The applicability of various liquors used in laboratory leaching
experiments towards predicting environmental impact for FGC wastes needs
to be determined. Adjustment of the pH of the final slurry, as is called
for in procedures of ASTM and the Extraction Procedure may produce leach-
ing conditions which are not representative due to the significant buffer-
ing action that some FGC wastes have from their limestone and other
alkali content.
Oak Ridge National Laboratory under contract to the EPA has begun
to evaluate the toxicity of various power plant wastes and the complete
extraction procedure. Initial results have indicated that the procedure
extracts little material with organic character and that the metals
analyses are extremely sensitive to the blank values. Among the samples
being tested are fly ash, bottom ash, and scrubber wastes from the
Shawnee Power Plant. Bioassays using Daphnia magna, mutagenicity assays
using the Ames Salmonella/microsomal activation assay, seedling studies
and chemical characterization of the extracts, including chromatography
after preconcentration on XAD-2 resin, are being carried out. Prelim-
inary results have shown that Shawnee fly ash extracts pass nearly all
of the criteria mentioned above.
A recent assessment on the potential impact of RCRA on utility
solid wastes by Fred Hart Associates for EPRI [108] concludes that ash,
scrubber sludge and other wastes might approach or exceed EPA criteria in
toxicity, radioactivity and corrosiveness. While ash and scrubber sludges
present the most Important issues, other utility wastes including metal
cleaning wastes, both blowdown and coal pipe drainage may also present
4-92
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potential problems. The economic impact of RCRA on utility solid wastes
are under study by the Department of Energy. Results of this study are
expected later in 1979.
4.5 Data Gaps and Research Needs - Chemical Properties
The major data gaps could be subdivided into those relative to
wastes from:
• Dry sorbent systems (whose importance will increase
in the future), and
• Wet scrubber systems.
Dry sorbent systems have not reached significant commercial use now
but are expected to by the early 1980fs. Lack of chemical and physical
data on these wastes are major data gaps.
The following data gaps and research needs for wet scrubbed FGD
wastes and coal ash have been identified:
(1) Field Data - There is an important need to characterize the
chemical and physical properties and behavior of unstabilized and stabil-
ized wastes in actual field disposal operations. Data are needed on
changes in FGC waste composition and properties resulting from waste
aging, weathering (rewetting and freezing/thawing), handling, processing
(stabilizing) and the disposal environment; and the associated changes
in the pollutant mobility. This information is needed covering the
ranges of: basic FGC system types (direct lime, direct limestone, alka-
line ash, and dual alkali) and/or waste types (sulfite-rich vs. sulfate-
rich and pH level); methods of processing (unstabilized, blended, stabil-
ized); and types of handling and disposal (ponding, landfill, mine dis-
posal, ocean). While a limited number of data do exist or are being
developed from EPA-funded projects (e.g., Square Butte demonstration
project, Louisville Gas & Electric/Combustion Engineering, TVA/Aerospace)
or studies are being planned (Louisville Gas & Electric/Bechtel/Combustion
Equipment Associates/Southern Services), more extensive field testing is
recommended. This would involve monitoring of a number of representative
full-scale systems not now studied via waste sampling, corings, and
leachate wells.
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(2) Laboratory Test Procedures - Presently available leachate
(elutriate) and toxicity test procedures do not as yet confidently pre-
dict dissolution and toxicity constituents of FGC wastes. It is impor-
tant to be able to perform tests in the laboratory quickly and cost
effectively, which will characterize the mobility and impact potential
of FGC wastes. A number of different procedures need to be developed
and tested. The current extraction procedure developed under RCRA needs
to be tested on its ability to characterize these properties in FGC wastes.
Limited data in this regard are currently being generated at Oak Ridge
National Laboratory.
(3) Ash/Waste Co-Disposal - There is the distinct possibility that
the practice of co-disposal of fly ash and FGD waste as a mixture currently
done at many locations could have certain advantages over the disposal of
each separately. However, there is a lack of fully definitive data correla-
ting the levels of trace elements in the coal, fly ash and bottom ash, FGD
waste, and ash/waste admixtures - either in the waste materials or their
leachates. More laboratory and field testing needs to be carried out to
determine such correlations if possible and identify and assess pollutant
mobility and toxicity.
(4) Stabilization Requirements - Many fly ashes have appreciable
pozzolanic activity and when admixed with FGD waste (and possibly lime)
will result in a material which hardens with time. The extent of hard-
ening reactions occurring will be dependent to a great extent upon the
ash characteristics but also on the waste type (sulfite vs. sulfate-
rich), the presence of high levels of TDS, and the conditions of ash
mixing (methods and relative quantities). This area still remains some-
what of an art, and more studies are needed to determine the effects of
different types of wastes and waste/ash mixtures not only on physical
properties but also major and trace elements mobility and toxicity.
(5) Trace Element Focus and Speciation - A number of trace elements
present in FGC wastes are of particular interest because they have been
observed in waste liquors at levels which in some situations may deleter-
iously impact on plants or animals. Certain of the elements, e.g., boron
4-94
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fluoride, and molybdenum have been studied in only a few samples. Others,
such as arsenic, antimony, selenium, manganese, and cadmium, are diffi-
cult to measure precisely and accurately at the levels at which they are
present in wastes. This warrants a continuing focus. It is recommended
that as additional samples are obtained from FGC systems for character-
ization, these trace elements in particular should be measured by tech-
niques offering state-of-the-art accuracy and precision in order to
extend the base of good data describing their occurrence in FGC wastes.
That list of key elements should be re-evaluated from time to time based
on an assessment of the potential impacts on plants and animals so that
relatively expensive analytical efforts are focused on the most important
parameters.
Since the chemical form (oxidation state, and existence as a cationic,
neutral or anionic complex) of a pollutant affects its solubility, toxicity,
and attenuation by soil, it is recommended that experimental and theoretical
studies of the chemical species of trace pollutants in FGC wastes and leach-
ates be continued. The trace elements of arsenic, selenium, antimony, chro-
mium, and boron either exhibit amphoterism or highly variable attenuation
by different soils and would be good candidates for speciation studies.
In addition, selenium reportedly can exist as the free element, and as
such its mobility has not been well characterized.
The ability to measure trace (ppm and ppb) levels of pollutants has
only recently been developed and is still an active area of research.
Speciation of a trace constituent into its various chemical forms in a
complicated mixture is still only a research area. Some techniques are
currently available which will allow a limited degree of speciation of
metals in solution. For example, separation of a particular metal into
its kinetically inert anionic, cationic or neutral species is possible
using ion exchange resins and the use of polarographic techniques will
allow determination of oxidation state in solutions under limited con-
ditions. The combination of ion chromatography and electrochemical
detection (conductivity or polarographic) may be a useful tool in the
future.
4-95
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(6) Reactions Producing Gaseous Species - Studies of the reduction
reactions, e.g., Se to I^Se or As to arsines, that might occur in an
anaerobic region of an FGC waste disposal landfill or pond should be
conducted. Tests should also be conducted to determine if any species
which may be present in a volatile state (i.e., elemental Hg and Se) is
released upon exposure of the waste to environmental conditions. These
experiments are important because they would yield data on gaseous pro-
ducts which could be transported into the atmosphere.
Measurement and identification of trace gases in air is a very active
area of research. Measurement of total species in air samples is currently
possible for many species. Separation and quantification of the individual
chemical forms (such as various methylated arsines) of one group of
volatile species is a more difficult problem and still under investigation
for many species.
(7) Radionuclides and PNA's - Although it is not expected that
radionuclides and polynuclear aromatic (PNA) organic compounds will be
present at levels that are of concern, and even more unlikely that they
will leach from the waste at substantial levels, measurements of radio-
9 Of\ 7 1 0
nuclide activity ( Ra, Pb, and U, etc.) should be made for a. repre-
sentative set of FGC wastes and their leachates. The wastes should be
chosen to include those with no ash, those with ash, stabilized mater-
ials and unstabilized materials. In this regard, the results of ongoing
PNA measurements at TRW should be evaluated and additional measurements
made, if necessary, to ascertain if any potential problem could arise
due to their presence.
A measurement of radionuclide activity in FGC wastes and their
leachates is complicated by the expected low level of activity. However
such measurements have been performed for many years and should not
require a substantial research effort. The ability to analyze trace
levels of PNA's, on the other hand, is the result of more recent research
However, techniques are currently available for analyses of these species
at the ppm to ppb region.
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5.0 PHYSICAL CHARACTERIZATION OF FGC WASTES
5.1 Introduction
This section describes the current status of physical testing of
FGC wastes and summarizes the results of appropriate tests conducted to
date on unstabilized and stabilized FGC wastes. The critical properties
which relate to the handling characteristics, placement and filling
characteristics, long-term stability, intrinsic pollution potential,
and potential for stabilization are described. A brief summary of the
status of physical testing is given together with the available data on
important physical properties. Deficiencies in the body of existing
knowledge of these properties are identified and future areas of research
are suggested.
5.2 Critical Properties
It is probable that for some time into the future, the bulk of the
fly ash collected in the United States will be discarded, but the physical
and chemical characteristics of ash (particularly fly ash) make it suitable
for a variety of uses. Such utilization is likely to grow in the future [69]
Disposal of FGC wastes involves handling and transport, field
placement at a disposal site, long-term stability of the deposit, and
the pollutant mobility in the disposal site environment [65]. Each of
these characteristics can be evaluated on the basis of selected parameters
as listed below:
• Handling Characteristics
dewaterability
consistency versus water content
- viscosity versus solids content
compaction parameters
• Placement/Filling Characteristics
- dewaterability
compaction, parameters
compressibility
strength parameters
5-1
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• Long-term Stability in Fills
- erodibility
- durability under weathering
- strength parameters
- compressibility
• Pollutant Mobility
- erodibility
- water retention
- permeability
Some fundamental physical properties importantly govern many of the
characteristics described above. These properties are the grain proper-
ties which include particle size distribution, particle morphology and
specific gravity. The relationship between these and other properties
given above and the characteristics important for FGC waste disposal
are discussed in the following sections.
5.2.1 Handling Characteristics
Handling characteristics have a major bearing on the choice of
transport; e.g., tanker truck vs. pipeline vs. conveyor. It is neces-
sary to develop quantitative parameters to describe handling character-
istics of wastes before alternative transport systems can be evaluated.
The following parameters appear to be diagnostic with respect to
the handling characteristics of FGC wastes:
• The relations between waste consistency and moisture content,
analogous to the Atterburg Limits of natural soils;
• The viscosity of the FGC wastes as a function of water
content (or solids content);
• The dewatering characteristics of the waste as measured by
the equilibrium water content under gravity drainage and as
a function of applied vacuum;
• The compaction characteristics of the waste as quantified
by the compaction moisture—dry density relations for
5-2
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various compactive efforts (Standard Proctor Compaction
Test and Modified Proctor Compaction Tests); and
• The sizes of the waste particles, as determined by a
standard hydrometer grain size analysis.
The tests listed above are not considered sufficient to provide all
the data required for the design of an FGC waste handling system. For
example, pumping tests on various mixes and consistencies of wastes and
additives may be required for selection of transport equipment and design
of pipe networks. Such detailed tests would be required, in any case,
for a site-specific design. However, the tests listed above should be
adequate for comparison and differentiation between various wastes on
the basis of handling characteristics.
5.2.2 Placement and Filling Characteristics
The general feasibility of land disposal of FGC wastes is to a gre^t
extent determined by the economics of disposal compared to FGC waste
utilization. Thus, physical parameters which describe the conditions
of waste placement in fills or ponds need to be identified and related
to economic considerations.
The economics of depositing FGC waste on land depend on the mode of
deposition. Land area required for disposal is directly related to the
weight of FGC waste solids per unit volume of disposal space. The final
dry density of the deposited material depends upon the dewatering and
compaction properties of the wastes. The total amount of waste solids
placed on any unit of area of a disposal site depends not only on the
dry density of the waste, but also on the mode of placement: ponding,
filling inside containment dikes, or construction of a fill composed
entirely of waste. If a fill is to be composed only of waste, or waste
plus stabilizing agent, then material of sufficient strength is needed
for construction of starter dikes. However, starter dikes can be made
of different materials with a general increase in economic considerations.
The physical parameters of greatest significance in evaluation of various
modes of filling include the moisture-density (compaction) properties of
the waste, the compressibility of the placed material, and the strength
5-3
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of the waste to resist slope/bearing failures. The compressibility,
quantified by the results of laboratory consolidation tests, describes
the change in waste density under the influence of its own weight and
any external loads. Compressibility values may be used in settlement
prediction computations. The strength of the waste is described best
by the results of triaxial compression tests. Strength for granular
materials such as waste can be stated according to a Mohr-Coulomb
criterion as:
8 = c + p (tan
-------
the other hand, cycles of freezing and thawing and cycles of wetting
and drying, with consequent swelling, shrinking, and distortion of
deposited material, may have significant effects on grain structure,
intergranular cementation (fixation), and mass stability. Obviously,
stability under loading can be evaluated by means of the strength
parameters c and . However, the stability of deposits of waste under
dynamic loading (machinery vibrations, blast impacts, earthquake vibra-
tions, etc.) will depend upon the relative density, degree of saturation,
and effective confining pressure in the deposit undergoing vibratory
loading, as well as on the strength parameters c and <(>. A loose deposit
under low confining pressure may lose shear strength under dynamic loading.
Thus, long-term stability also is related to compaction characteristics
and placement techniques. Finally, the ability of a waste deposit to
support external loads will be dependent on the compressibility of the
sludge and on the limitations on settlement created by the nature of the
external load source (cover soil, building foundation, roadway sub-base,
etc.). The ability to support external loads will govern future use of
the disposal site; thus, this characteristic has great economic significance.
5.2.4 Pollutant Mobility
Another set of characteristics of great importance are those which
physically govern the mechanisms for pollution of the air and water in
the vicinity of the power plant, transport system, and final disposal
(or reuse) location. For example, an integrated evaluation of FGC waste
permeability, host soil permeability, waste and soil water retention
characteristics, groundwater flow regime and soil-waste interaction
would be required for an assessment of potential groundwater pollution
at a specific disposal site. Such an evaluation could not be made with-
out a knowledge of physical parameters which quantitatively describe
the flow of water through FGC wastes.
In order to evaluate the intrinsic potential of any FGC waste to
cause air or water pollution, it is necessary first to differentiate
between the characteristics of a site which led to pollution and the
characteristics of a waste which would lead to (or inhibit) pollution
5-5
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of any given site. The properties of a waste of interest in this regard
are those which describe the potential for the material itself to be
transported from a disposal site or other location and those which
quantify the potential for toxic constituents to be removed (leached)
from the mass of the waste. Transport of FGC wastes from a disposal
site could occur by erosion caused by wind or water. It is presumed
that erosion would occur only during construction or filling of a dis-
posal site; after filling, the waste deposit would be protected by proper
grading and drainage and by some sort of cover layer. Erosion is often a
relatively minor source of pollution; however, in some cases water erosion
of landfill materials has been significant and design of a collection basin
for runoff is generally considered. Erosion potential can be related to
grain size distribution and interparticle cohesion; an extensive body of
literature exists in which credibility of materials by wind or water has
been expressed in terms of grain size distribution and interparticle co-
hesion. Pollution of surface waters and groundwater by leaching of pollu-
tants from waste deposits is a more important potential problem than
erosion-related pollution. The physical characteristics of an FGC waste
which affect the potential for leachate pollution include the permeability
of the waste, the water retention of the waste, expressed in terms of
water content (i.e., degree of saturation) and any interactions which
occur between the waste and adjacent soil or rock to limit the flow of
leachate from the waste into the surrounding media. Permeability and
water retention will vary with the relative density or void ratio of
the waste. FGC waste-soil interactions will vary from one soil to the
next, and only general indications of possible interactions could be
obtained from laboratory tests using a given FGC waste and soils of
various textures and mineralogical character. Thus, FGC waste perme-
ability and water retention will be the most consistent physical param-
eters for measuring pollution potential of FGC wastes.
The feasibility of land disposal of FGC waste may be affected
seriously by improvements in waste characteristics achieved through
treatment of the waste with some additive or stabilizing agent. Physical
parameters must be selected which describe the ease of waste stabilization
5-6
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with additives and which will provide quantitative indicators of the
effects, on physical properties, of waste stabilization treatment with
additives.
Preliminary evaluations of the physical characteristics of many
FGC waste samples have indicated the desirability of improving the
properties of these materials. It would be advantageous to decrease
waste permeability, increase its strength and decrease its compressi-
bility if these improvements could be made in a cost-effective way.
Some degree of improvement in these parameters can be achieved through
dewatering and/or densification. It appears that further improvements
may be made by adding stabilizing materials to the wastes. In some
instances, other wastes (e.g., fly ash) may be mixed with FGD wastes
to yield materials with characteristics superior to (or no worse than)
the individual constituent characteristics. The physical characteristics
of resultant mixtures may be evaluated by measuring the physical param-
eters mentioned previously in connection with unstabilized, unmixed
wastes. It is appropriate, however, to consider evaluating the FGC
wastes themselves with regard to the relative ease or difficulty of
preparing a "stabilized" mix. In other words, the wastes should be
tested and characterized in some way to indicate the potential for
physical stabilization. The best indications of possible mixing or
handling problems may be obtained from evaluation of waste grain sizes,
grain size distribution (uniformity and texture), and water content-
consistency relationships.
5.3 Status of Physical Testing
A brief summary of the status of physical testing of FGC wastes is
shown in Table 5.1.
The tests listed below with appropriate references/standards have
been standardized on the basis of experience gained in evaluating natural
soils, mineral aggregates, and other particulate materials.
5-7
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Table 5.1
Summary of Physical Testing - FGC Wastes
K«»t« Tnt
gumta-Uch
gulflt./Sulfata
x • 1/ZHjO +
CaS0 • ZHO)
Phralcal Taat.
enla-Sln
Apalyala
Attarbart Llalt.
Proctor Compaction
Paraaablllty
CbuolUatlon
aacanflnad
CoBpraaalon
Trlaxial
Compraaaloo
Dynamic loading
Bawacarinf-
Tlacoilty
Plaid CoBpactlan
Grain Siu
Analyala
Attarbari Lfcalta
Proctor Coap.ctloti
Couolldatlon
Doconflnod
Ipy.«ti«.tor.>
ADL [19], Aatoapac. (37], Dr.vo (93.'
IMC (90,91), UL [71], VES [100]
Dravo 192-94], PMC (90,911, UL (71)
ADL [19], PMC 190,91), UL (71],
MB (100)
A&L (19], Acroapac. (37], UL 171],
KB [100], ladlan [lit]
Bravo 193). IMC 191], OL {ft}
ADL (19), ladlan [146]
PMC [90,91] , UL [71], tedla [146]
01(97]
ADL U9J. A.ri>.p*c. 137,122), DL I»5)
ICS [49,99]
Atro.p.c. [37], UL [*). UD |U],
m. [71], UES 0.00]
BIL (4). UD [Ml. DL [71]
ML (4). UD[M],DL[71],1IZE HOG]
*rro.l>.c« [37], UC [88), VCS (100]
m. [96,98]
»L [4], UE IS8)
B4L|4], UD (M)
AOL [19], Airocvuo [37,122], Dr.yo |»2)
Adoqu.tt covtrig*
lot dUmoiclc
Plold Corr.l.tlon o«*d.d
(•riou. d«t. gap.
PHC: «lJt«d vtth (ly ..h
M>r(iully u*«ful
S«rlou. d.t. gipf
THl« City Taatlng
OL » Onlvoraity of Loulavllla
HES • U.S. Any Uatatvayi ExptrlBODtal Station
Eadl« - tadiag Corporation
5-8
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Test Reference/Standard
Index Properties
• Grain Size Analysis ASTM D422-63
• Specific Gravity ASTM D854-58
• Atterburg Limits ASTM D423-66, D424-59
Soil Classification ASTM D2487-69
Compaction Behavior ASTM D698-70
Field Compaction ASTM D1556-54, D2167-66
Permeability ASTM D2434-66
Consolidation ASTM D2435-70
Unconfined Compression ASTM D2166-66
Triaxial Compression ASTM D2850-70
Available values for critical parameters and other information from
previous studies of physical characteristics of FGC wastes are presented
below.
5.4 Available Information
The properties on which information is available are given in the
following sections:
5.4.1 Index Properties
5.4.2 Consistency-Water Retention
5.4.3 Viscosity vs. Water (Solids) Content
5.4.4 Compaction Behavior
5.4.5 Dewatering Characteristics
5.4.6 Strength Parameters
5.4.7 Permeability
5.4.8 Weathering
The index properties discussed in Section 5.4.1 are in a different
class than the other properties discussed in this chapter since they
are more fundamental to the material and are not dependent, as are the
other properties, on the parameters used in the specific testing procedures.
5-9
-------
5.4.1 Index Properties
5.4.1.1 Fly Ash
Properties of individual fly ash grains include specific gravity,
shape, mean size, and size range. Specific gravity ranges widely, from
about 2.1 to almost 2.9, and is influenced primarily by iron oxide content
increasing with increasing iron oxide content [66].
As much as 70% by weight of a given fly ash may consist of hollow
spherical particles. Typically, fly ashes consist of silt-size particles
with a very narrow grain size distribution [67,81]. Grain size analyses
for fly ashes are given in Table 5.2 and described in detail below. A
comparison of grain size distribution for fly ash and bottom ash is shown
in Figure 5.1.
5.4.1.2 FGC Wastes
The properties of particulate masses most commonly used for purposes
of description are the specific gravity of individual particles and the
sizes of individual grains and grain size distribution.
FGC wastes, as discussed in Chapter 4, are composed mainly of calcium
sulfate and calcium sulfite salts. In stack gas cleaning operations in
which fly ash and sulfur dioxide are removed simultaneously, FGC wastes
may contain significant amounts of fly ash particles. The specific
gravities of typical FGC wastes are also listed in Table 5.2. It may
be seen from this tabulation that specific gravity values of wastes
composed almost entirely of calcium sulfate salts range between 2.30
and 2.40. Specific gravity values of clean calcium sulfite wastes
range between 2.4 and 2.7. FGC wastes containing significant amounts
of fly ash may exhibit specific gravity values below 2.3 or above 2.6,
depending on the specific gravity of the fly ash. As mentioned previously
the specific gravity of fly ash depends mainly on the iron oxide content
and ranges between 2.10 and 2.90, with the high values being those having
a higher iron oxide content [71].
Values of specific gravity for FGC wastes higher than values listed
in the ranges given above have been reported by various investigators.
Many of these anomalous values might be explained by the method used to
5-10
-------
100
U S Stcndord Slew Optnlng in lncti«f U.S. Standard Sim Numb«r«
C 43 2 11/2 ! V4 i/Z V33 4 6 8 TO 1416 20 50 40 SO TO '00 140 ZOO
300
IOO 30
Source: [112]
IOO
10 S I 03
Grain Silt Millrr.»t«r«
0.1 DO'S
001 0.005
O.OCI
Cobblti
Cr9«*l
Coort* | Hr,t
Sond
.».
Caar««
Mtdium
Fin*
SKI «r Cloy
Figure 5.1 Grain Size Distribution Curves for Bottom Ash and Fly Ash
-------
Table 5.2
Physical Properties of FGC Wastes
Ui
WASTE TYPE
FLY ASH
Bltuadnoua
Subbltualnoua
Lignite
Scholz (BltuBlnoua)
LGtt (Bituminous)
Gaeton
SULFITE-RICH
• Without Aah
Harrington Station (Southwestern)
Uk« Vie* (Ontario Hydro)
Faddy'• Run (LC4E)
Scholz (CEA/ADL)
Range
• With Aah
Double Alkali (FMC, 30-501 Ash)
Paddy's Run (SOX Aah)
Paddy'a Run (33X Aah)
Paddy's Run (10Z Aah)
Scholz (CEA/ADL, SOX Ash)
Scholz (CEA/ADL, 33X Aah)
Scholr (CEA/ADL, 10Z Ash)
Elrama
Bruce Mansfield
• With Ash and Lloe
Paddy's Run (SOX Aah, 51 Lime)
Paddy's Run SOX Aah, 10X Lime)
Scholz (CEA/ADL. SOX Aah, 5X Lime)
Seholc (CEA/ADL, SOX Aah, 10X Lime)
Elrana (IUCS Process, Cured)
Range
SULFATE-RICH
• Without Ash
Scholz (CIC)
Japanese Gypsum
German Gypsum
Range
2.86
2.68
2.49
2.56
2.49-2.86
2.54
2.59
2.S8
2.48
2.60
2.57
2.51
2.57
2.55
2.SB
2.56
2.55-2.58
2.35
2.34
2.34
2.34-2.35
2.68
7.24-2.51
>74um
9X
7X
12X
8
38
7
4
4-10
10
3
6
4
7
5
6
9
26
3
4
6
5
3
18
27
30
18-30
38
7-12
2-74um
91X
93X(<74)
88X
88
62
91
93
85-93
85
97
94
96
93
95
94
91
74
97
96
94
95
66
66-96
76
71
66
66-76
62
88-93
<2ina
—
—
~
4
' —
2
3
2-3
5
—
—
—
— .
—
—
—
—
^_
—
~
—
30
6
2
4
2-6
0
—
a With Aah
Caaton (Fly Ash Scrubber)
^erram "jrpsur (50T Ash)
a Wi • Water content where waste transforms to viscous fluid (moisture content dry basis).
b NP - Monplastlc (ASTM D424-59).
c Cu • Coefficient of uniformity.
COEFFICIENT
OF UNIFORMITY
(Cu)
1.3
1.4
1.2
1.5
3.4
1.3
1.5
1.3-3.4
1.3
1.2
1.2
1.2
1.2
1.3
1.2
1.3
1.3
1.3
1.2-1.3
2.5
2.4
2.3
2.3-2.5
1.4
1.5-1.8
ATTERBURG
LIMIT
-
NP
IIP
HP
NP
6SX 48X
IIP
45
36
37
45
DP
HP
56 —
33
33
39
34
HP
NP
HP
NP
NP
REFERENCE
146
146
71
71
71
88
96
95
96
91
71
71
71
71
71
71
145
145
95
95
95
95
145
96
96
96
95
91
Source: [71, 90, 91, 94, 90, 99, 123, 124J
-------
determine specific gravity: the weight and volume of about 40 grams of
FGC waste are experimentally measured. The volume is determined by a
displacement technique, and the weight is determined by oven-drying and
weighing the specimen. In laboratory soils testing, the conventional
drying temperature is 105°C. However, calcium sulfate and calcium
sulfite salts contain chemically bound water which is driven off by
temperatures exceeding 75-80°C [96]. ASTM Specification D2216 states
that soils containing large quantities of gypsum should be dried at
60°C« Drying of calcium sulfate at 105°C yields an apparent specific
gravity of about 3 (CaSO^; Gg = 2.96), while use of the 60° C drying
temperature yields the appropriate specific gravity of gypsum solids
(CaS04 ' 2H20), 2.32.
Grain size analyses of FGC wastes have been performed by a number
of investigators [71,19,4,88,90,95,96]. Particles of any one waste tend
to be extremely uniform in size and morphology [96]. Studies to date
indicate that sulfite wastes resemble in size uniform silts, whereas
sulfate wastes resemble in size sandy silts. Coefficients of uniformity
(C ) of wastes (without additives) listed in Table 5.2 are generally
less than 2.5, which is indicative of the extremely uniform nature of
FGC waste particle size distribution. The coefficient of uniformity
is defined as the particle size corresponding to 60% finer by weight
divided by the particle size corresponding to 10% finer by weight. The
coefficient of uniformity of a waste composed entirely of particles of
a single size is 1. Sulfate-rich FGC wastes appear more well-graded
(containing many different particle sizes) than sulfite-rich FGC wastes.
Specific gravity values and grain size distributions of various
combinations of waste/fly ash and waste/lime/fly ash are also listed
in Table 5.2 [71,95]. It should be noted that these mixtures are also
generally quite uniform in nature, having GU values of 1.2-1.3.
5-13
-------
5.4.2 Consistency-Water Retention
5.4.2.1 Fly Ash
Fly ash Is a non-plastic material; i.e., it is transformed from a
semi-solid granular mass to a viscous slurry over a very narrow range
in moisture content and exhibits no significant plasticity during this
transformation.
Water flow through fly ash occurs more rapidly than through natural
soils of similar grain sizes and water retention in fly ash should be
equal to or less than water retention in fine sands [70,76,81,82,83],
Thus, most fly ashes are freely-draining materials.
5.4.2.2 FGC Wastes
Consistency is generally defined in terms of stiffness or strength
and is a function of water content. The consistency of cohesive soils
(clays) is defined in terms of unconfined compressive strength. For a
given soil type, as the water content increases, the unconfined compres-
sive strength decreases. Clays possessing unconfined compressive strengths
less than 2.4 x 10 Pa (3.5 psi) are termed "soft," whereas strength
values exceeding 1.91 x 10+5 Pa (28 psi) indicate "stiff" materials.
Atterburg Limits tests are of great use in soils engineering because
the results of these simple tests relate to cohesive soil properties used
in design, such as strength and compressibility. That is, Atterburg Limits
tests are a measure of consistency. The liquid limit is defined as the
value of water content above which a material behaves as a viscous fluid.
The plastic limit is defined as the value of water content below which a
material behaves as a semi-solid. For values of water content between
the liquid limit and plastic limit, a material behaves as a plastic, or
remoldable material. The water content of most in-place cohesive soils
is such that they exhibit plastic characteristics.
Granular soils, such as sands and silts, are nonplastic in nature*
that is, at a certain water content value a granular soil transforms
from a friable semi-solid material to a viscous liquid. As mentioned
previously, FGC wastes are similar in size to silts and sandy silts.
Therefore, it is to be expected that FGC wastes would exhibit little
5-14
-------
or no plasticity. As shown in Table 5.2, only one (Paddy's Run) of the
several wastes tested exhibited plastic behavior [90]. Liquid limit
values are tabulated for other wastes in Table 5.2, but these values
indicate water contents at which behavior transforms from that of a
semi-solid to that of a viscous liquid.
Liquid limit and plastic limit values are useful only to the extent
that they correlate with engineering properties used in design. In this
context, Atterburg Limits values apply only to cohesive soils and are
not applicable to silts or sands. The relationship of liquid limit and
plastic limit values to the compressibility and strength of FGC wastes
has not been demonstrated.
5.4.3 Viscosity vs. Water (Solids) Content
5.4.3.1 Fly Ash
The spherical nature of many fly ash particles causes the apparent
viscosity of fly ashes to be much lower than that of soils or mineral
aggregates of similar grain size. This has led to the widespread use
of fly ash in cement grouts to improve penetration of grout into voids
in pervious media. Viscosity tests on one fly ash have been done by
Coones [84]. In general, fly ash viscosity is lower than the viscosity
of other materials at equal solids content and in similar grain size ranges.
5.4.3.2 FGC Wastes
One of the earliest parametric studies of FGC waste viscosity and
pumpability was done by the Colorado School of Mines Research Institute
(CSMKI) for the Dravo Corporation [92], The FGC waste slurries studied
consisted of a basic composition of FGC waste/fly ash to which additional
fly ash, slaked lime, grits and Calcilox were added. The FGC waste/additive
slurry contained approximately 30% solids by weight.
Two waste samples labeled "C" and "D" were tested in preliminary
studies to determine solids concentrations, specific gravities, vis-
cosities, and pH [92].
5-15
-------
Pipeline loop pumping studies were done on the waste/additive slurry
described above using a 6-inch diameter pipe loop. Head loss vs. velocity
and relative pipe wear observations were made. Samples were collected from
the loop for Theological testing and slurry concentration measurements.
On the basis of these studies, CSMRI concluded that FGC waste slurries
are excellent materials for pipeline transport. It was concluded that the
wastes studied behaved as nonsettling slurries. A critical velocity was
found below which turbulent flow could not be maintained. CSMRI recom-
mended that pipelines be designed to give turbulent flow with values of
Reynolds Number greater than 4000. Results of friction head loss tests
were inconclusive since slurry weight percent solids varied in the narrow
range from 28% to 35%. No significant pipe wear was observed in these
tests. Shutdown of the pumping system for 30 to 40 hours did not result
in restart problems; slurry solids concentrations of 30% to 40% were
measured after this time.
The Aerospace Corporation also conducted a series of viscosity
measurements on FGC wastes in an EPA-sponsored study [37]. Viscosity
measurements were conducted on nine FGC waste slurries at varying values
of water content at room temperature using a commercial viscometer (range
3 to 150 poise). The results of these viscosity tests are shown in
Figure 5.2. The Aerospace Corporation suggested that waste slurries
possessing viscosities less than 20 poises could be easily pumped; as
shown in Figure 5.2, one waste (curve 9) could be pumped at solids
contents of up to 70%, whereas another waste (curve 1) could not be
pumped at solids contents exceeding 32%. Results of these tests were
too limited to indicate the effects of particle shape, size, and dis-
tribution on viscosity; however, it was apparent that the addition of
fly ash to waste increases the fluidity of the slurry. Also, high
values of pH appeared to increase viscosity.
In a recently completed study done at the University of Louisville
by Coones [84], viscosity tests, liquid limit tests, and pipe loop pumping
tests were done on a series of sulfite waste, dual alkali FGC waste,
waste, and waste/additive slurries.
5-16
-------
Curve Waste Fly Ash, %
1 GM Parma Dual Alkali 7.4
2 UPL Gadsby Dual Alkali 8.6
3 TVA Shawnee Lime -40.5
4 DLC Phillips Lime 59.7
5 TVA Shawnee Limestone 20.1
6 TVA Shawnee Limestone 40.1
7 TVA Shawnee Limestone 40.9
8 SCE Mohave Limestone 3.0
9 APS Cholla Limestone 58.7
10 LG&E Paddy's Run Carbide Lime 12.4
11 TVA Shawnee Lime <1.0
12 TVA Shawnee Limestone <1.0
13 GPC Scholz Soda Ash Dual Alkali <1.0
14 GPS Scholz Soda Ash Dual Alkali 30.0
15 TVA Shawnee Lime 40.0
10
120
100
—
2
8
40
30
40 50 60
SOLIDS CONTENT, WEIGHT %
70
Source: [37]
Figure 5.2 Viscosity of FGC Wastes
5-17
-------
Viscosity tests were done with a Brookfield Synchrolectric viscometer
(range, 0 to 100 poise). Slurry water contents were varied so that curves
of viscosity vs. percents solids could be plotted. Results of viscosity
testing are shown in Figure 5.3. Test results indicated the following:
1) Paddy's Run and Cane Run sulfite-rich FGC wastes from direct lime
scrubbing have very similar viscosity-solids content relationships;
2) The viscosity characteristics of the dual alkali waste tested are
very similar to those of the other sulfite wastes; however, the dual
alkali waste is less viscous, at a given solids content, than are the
other sulfite wastes; 3) The Scholz CIC (sulfate) waste is much less
viscous, at a given solids content, than either the dual alkali waste
or the other sulfite wastes; 4) At a given solids content, fly ash is
the least viscous of all the materials tested, thus this material could
be tested at much higher solids content than the other FGC wastes.
Various mixtures of wastes and additives were also tested; mixtures
of dual alkali waste and the other sulfite waste with varying propor-
tions were tested for viscosity. Also, a 3:4 mix of dual alkali waste to
sulfite waste was tested; in these tests, the proportion of added fly ash
was varied. Results of viscosity tests on waste/waste and waste/additive
mixtures are shown in Figure 5.3.
Coones performed liquid limit tests on each of the wastes and waste/
additive mixtures tested for viscosity. Atterburg Limits tests were
particularly difficult to perform and gave unreliable results. However,
a modification of the standard liquid limit test was correlated with
viscosity test results. Although this correlation is based on limited
data, it does indicate that results of a relatively simple liquid limit
test might be used as an index to viscosity.
Additional pipe loop pumping tests were conducted in 1978 at the
University of Louisville on sulfite waste/dual alkali waste mixtures
and on other sulfite waste/dual alkali waste/fly ash mixtures. From
limited results of pumping tests it was concluded that FGC wastes may
be pumped at solids contents as great as 60%, as recommended by The
Aerospace Corporation [37], The first pumping tests in this study
5-18
-------
ca
o
at
§
O
O
O
O
Q
4-1
§
t-i
O
p.
800
700
600
500
400
300
200
100
Legend
Dual Alkali Waste
LG&E Fly Ash
Lime Waste
Dual Alkali:Lime,3:4
Dual Alkali:Lime:Fly Ash, 3:4x
Fly Ash Proportion Variable)
"Typical" Mix
Dual Alkali:Lime, Variable Proportions
Dual Alkali:Lime, 0.5:1
Scholz CIC Waste
10
20
30
40
50
60
70
Source: [84]
Solids Content
Figure 5.3 Viscosity Versus Solids Content
5-19
-------
were done using a relatively slow flow velocity with a high viscosity
material. For a material with lower viscosity, pumped at a higher
velocity, the mass handling capacity might be very large. Coones also
noted that, in his tests, the rate of settling of materials was not high;
he suggested that temporary reductions in velocity, which might be ex-
pected in a prototype pumping operation, would not greatly affect the
flow of material. These tests are being continued using different
waste/additive mixtures and pumping velocities.
5.4.4 Compaction/Compression Behavior
5.4.4.1 Fly Ash
Compaction tests yield data on the optimum water content of the
waste, which is an important consideration for placing of the waste
materials at the maximum density in the disposal site. These proper-
ties also influence the degree of settlement, permeability and strength
of the material. Laboratory and field compaction data have been reported
by a number of investigators [68,70,71,72,82,83]. Typically, as disposed
of, fly ash has a bulk dry density of 0.8-1.28 g (50-80 Ib) of dry solid
o o 33
per cm (ft ) with a mean value of about 0.96 g/cm (60 Ib/ft ). Field
compaction may increase the density to an average of 1.12 g/cm (70 Ib/ft )
while controlled compaction may increase the average value to 1.2 g/cm
3
(75 Ib/ft ) [70]. Compaction by vibratory rollers has been shown to be
more effective in increasing fly ash density than that by a static
pneumatic-tired roller or a sheepsfoot roller [68,70]. The optimum
moisture content of fly ash ranges between 16-31% with a corresponding
maximum dry density of 1.14-1.65 g/cm3 (71-103 Ib/ft3) [144], The
3
corresponding values for bottom ash are 14-25% and 1.17-1.87 g/cm
(73-117 Ib/ft3) [144].
•
Volume change under load has been reported for fly ash by several
investigators but test results tend to be highly site specific [68,70,
82,83,86]. Compacted to 90-95% of Standard Proctor maximum dry density
(ASTM D698-70), fly ash has a compressibility similar to that of medium
stiff clays [68,70,82]. The dry density of fly ash is lower than com-
pacted natural soils and thus may cause less settlement when placed
over soft subsoils of equal fill stiffness.
5-20
-------
5.4.4.2 FGC Wastes
The compaction characteristics of some FGC wastes and mixtures of
FGC wastes and fly ash and lime are summarized in Table 5.3. This data,
obtained using Standard and/or modified Proctor compaction test shows a
3 3
range of 1.15-1.36 g/cm (72-83 Ib/ft ) for the maximum dry density of
3 3
ash-free, sulfite-rich wastes with a median of 1.28 g/cm (80 Ib/ft ).
Maximum dry densities for ash-free sulfate wastes are in the 1.12-1.52 g/cm
(70-95 Ib/ft ) range with a median of 1.28 g/cm3 (80 Ib/ft3). The results
of these tests on sulfate-rich materials may not be meaningful since in
some tests (not included in Table 5.3), no well defined maxima appeared [90]
The moisture content at the maximum dry density for sulfate wastes has a
wider and lower range than the sulfite wastes (13-41% vs. 32-43%). The
degree of saturation at the optimum moisture content appears to be lower
for the sulfate wastes. The compaction characteristics of mixtures of
sulfate and sulfite wastes with fly ash and lime are significantly
affected by the particle morphology, grain size distribution and specific
gravity of each of the components in the mixture and, thus, the results
are highly dependent on the characteristics of the materials used. Gen-
erally, however, addition of fly ash to sulflte-rich waste increases
maximum dry density while decreasing the moisture content and percent
saturation at the maximum dry density (Table 5.3). Addition of lime to
the sulfite-rich waste/fly ash mixture generally produces further in-
creases in maximum dry density and further decreases in moisture content
and percent saturation at the maximum dry density.
Addition of fly ash to sulfate-rich wastes also generally increases
their maximum dry density and decreases their moisture content at the
maximum dry density. However, the percent saturation at the maximum
dry density is generally not decreased. Repeated impacts on sulfite-
rich waste appear to cause progressive breakdown In the waste particles
[49,71,99]. The maximum dry density of fresh CEA/ADL waste sample was
1.15 g/cm3 (72 Ib/ft3) vs. 1.28 g/cm3 (80 Ib/ft ) for the same sample
which was subjected to impacts in a previous Proctor compaction test
[71]. The optimum moisture content of the sample was lowered from 33%
to 30% by the previous impacts.
5-21
-------
Table 5.3
Standard Proctor Moisture-Density Parameters
for Selected FGC Wastes
Waste
Sulflte-Rich
• Without Ash:
to
10
Harrington Station
Lakeview
Paddy's Run
Scholz (CEA/ADL)
• With Ash:
Paddy's Run
Paddy's Run (50% Ash)
Paddy's Run (33% Ash)
Scholz (CEA/ADL, 50% Ash)
Scholz (CEA/ADL, 33% Ash)
Will County
• With Ash and Lime:
Range:
Paddy's Run (50% Ash, 5% Lime)
Paddy's Run (50% Ash, 10% Lime)
Scholz (CEA/ADL, 50% Ash, 5% Lime)
Scholz (CEA/ADL, 50% Ash, 10% Lime)
Range:
Maximum Dry
(Ib/ft3)
81-93
91-94
Density
(g/cc)
Optimum
Moisture
Content
a
% Saturation at
Optimum Moisture
Content
1.30-1.49
23-32
1.46-1.50
23-25
79-91
73-85
Reference
Range:
Median:
83
85
80,65
72,80
65-85
80
1.33
1.36
1.28
1.15-1.25
1.15-1.36
1.28
32%
35
33,52
33,43
33-52
33
-
91%
88
69,89
69-91
4
88
96,146
19,71
81,92
82
86
93
87
1.30,1.47
1.31
1.38
1.49
1.39
26,29
32
27
23
29
80,91
86
89
79
-
146
71
71
71
71
146
93,93
94
92,92
91
1.49,1.49
1.50
1.49,1.49
1.46
25
25
23,24
25
81,82
85
73,77
79
71
71
95
95
-------
Table 5.3 (Continued)
Standard Proctor Moisture-Density Parameters
for Selected FGC Wastes
Waste
Maximum Dry
(lb/ft.3)
Density
(g/cc)
Optimum
Moisture,
Content
% Saturation at
Optimum Moisture
Content
Reference
Sulfate-Rich
Without Ash;
Shawnee (Forced Oxide) 82
Scholz (CIC) 95
Dual Alkali Gypsum (ADL Pilot Plant) 79
Range: 79-95
1.32
1.52
1.26
1.26-1.52
32
13
33
13-33
56
89
146
96
19
Ln
N>
co
With Ash:
Milton R. Young
Gypsum (Fly Ash Scrubber)
Gypsum (Fly Ash Scrubber)
Gaston (50% Ash)
Gaston (33% Ash)
Four Corners
Range:
Median:
78-82
86,97,103
97,103
78,89
83
76
76-103
86
1.26-1.32
1.38-1.64
1.55,1.64
1.25,1.42
1.33
1.25
1.12-1.55
1.38
35-41
23
14,17
28,25
31
24
14-41
80
64,72
73,81
85
64-85
89
96
96
71
71
146
«*
Grains of water per gram of dry solid xlOO.
Not aged
-------
Very little information is available on field compaction behavior
of FGC wastes. The limited data available from Scholz on the effect
of four, eight or twelve passes of a rubber-tired roller on mixtures
of waste and fly ash (1:0.75! ratio) and waste, fly ash and lime mix-
ture (1:0.75:0.02 ratio) have indicated no substantial difference in
the dry density of the materials after the various roller passes.
There are no data available to attempt to correlate field and labora-
tory moisture-density relationships.
The compression indices determined at various consolidation loads
of a variety of wastes and waste, fly ash and lime mixtures are shown
in Table 5.4 [93,95,96]. The compression index of sulfite-rich wastes
depends to a. great extent on their water content and degree of compaction
with materials compacted to their optimum moisture content having the
lowest values. Sulfate wastes are much less compressible, due in part
to the different particle morphology, and the compression index is much
less dependent on the water content.
Decrease of the moisture content by addition of a dry filler (e.g.,
fly ash) to sulfite wastes results in a decrease in compressibility with
the most dramatic effect occurring with fly ash added to the sulfite
waste containing the greatest initial water content. Addition of a
small amount of lime to the sulfite waste and ash mixtures causes no
appreciable change in compressibility in the absence of the pozzolanlc
reaction (imaged conditions, Table 5.3). Allowing the samples to cure
for 28 days generally leads to materials which are much less compressible
approaching those properties observed for the sulfate waste.
5.4.5 Dewatering Characteristics
The dewatering properties, like most physical properties, are
primarily a function of the crystalline morphology and distribution of
crystalline phases and the particle size distributions. These, in turn,
are principally dependent upon the type of FGD system (and alkali used),
the calcium sulfite to sulfate ratio in the waste, and the amount of fly
ash and unreacted alkali present.
5-24
-------
WASTE
Table 5.4
Compression Indices for Some FGC Wastes
INITIAL
WATER CONTENT. %
SOLIDS
STRESS RANGE
COMPRESSION INDEX
48-91 (xlOH Pa)
(70-140 psi)
Ln
I
S3
Ul
SULFITE-RICH
• Without Ash
Paddy's Run
Paddy's Run
Paddy's Run
Scholz (CEA/ADL)
Scholz (CEA/ADL)
Lime Scrubber
• With Ash
Paddy's Run (SOZ Ash)
Paddy's Run (SOZ Ash)
Paddy's Run (SOZ Ash)
Will County
200
315 (123-60)
31c
86
27
135
90
128
25c
32
With Ash and Lime (Uncured)
Paddy's Run (50Z Ash, 5% Lime) 77-80
Scholz (CEA/ADL, SOZ Ash, 5Z Lime) 53-54
33%
24 (45-63)
76c
54
79
43
53
44
80
76
56
65
• With Ash and Lime (Aged 28 days Under Light Consolidation Pressure)
Paddy's Run (SOZ Ash, 52 Lime) 77 56
Scholz (CEA/ADL) SOZ Ash, 5Z Lime) 53-54 65
Lime Scrubber 110 48
SULFATE-RICH
• Without Ash
Shawnee (Forced Oxid) 40 71
Scholz (CIC) 33 75
Scholz (CIC) 14 88
• With Ash
Four Corners 45 69
Four Corners 33 75
a Water added to simulate filter coke moisture.
b Water added to simulate thicker underflow moisture.
c Compacted at optimum moisture content (Proctor).
0.3
0.72
0.04
0.12
0.02
0.3
0.18
0.26
0.02
0.13-0.17
0.10-0.23
0.13
0-0.1
0.01
0.01
0.02
0.85
1.12
0.08
0.26
0.06
0.85
0.37
0.50
0.05
0.43-0.48
0.33-0.48
0.43
0.08-0.33
0.02
0.06
0.01
21
21
0.84d 0.66d
0.16
0.58
0.10
1.15
0.62
0.72
0.11
0.14d
0.77-0.87
0.73-0.70
0.83
0.57-0.70
0.04
0.04d
0.12
0.03
0.17d
0.06d
d 3.2-6.4 tons/ft range
Source: [93, 95, 96, 146].
-------
While much of the research and characterization work performed to
date on wastes from FGC systems has not focused on dewatering, some
data are available from pilot and prototype testing [19,49,55,56,125,126]
and full-scale operations [18,123,124,127-133]. A few studies have also
been undertaken sponsored by EPA and EFRI to characterize waste dewater-
ability [1,37,135] and improve dewatering performance [134],
In general, sulfite-rich wastes do not dewater as readily as sulfate-
rich wastes. Sulfite-rich wastes typically can be thickened in conventional
open-tank thickener/clarifiers to 20-45% solids and filtered to 40-70%
solids. Sulfate-rich wastes, on the other hand, typically can be thick-
ened to 40-60% solids and filtered to 65-90% solids. The presence of fly
ash and unreacted alkali (especially limestone) can also affect dewatering.
The presence of these materials can improve the dewaterability of wastes
with initially relatively poor dewatering properties; however, unreacted
alkali and fly ash may even decrease dewaterability for waste with in-
herently good dewatering properties.
A more detailed discussion of waste dewatering characteristics and
a review of studies on waste dewatering are provided in Section 2.4.
5.4.6 Strength Parameters
5.4.6.1 Fly Ash
Unconfined compressive strength measurements of cohesive wastes
and triaxial shear tests of cohesionless wastes are useful in deter-
mining load bearing capacity of these materials. The shear strength
of fly ash depends to a great extent on its density. The angle of
internal friction, a measure of the shear strength, typically ranges
3 3
from 28C to 38° as the density goes from 0.8 g/cm (50 Ib/ft ) to
75 g/cm3 (75 Ib/ft3) [70]. Aged fly ash may exhibit a great deal of
cohesion due to pozzolanic cementation [68,70,82,83,85]. Angle of
internal friction may increase to as much as 43° and cohesion to more
than 6.9 x 10 Pa (100 psi) [68,70,85]. The extent of cementation depends
on the lime content and surface area and is affected detrimentally by un-
burned carbon. Pozzolanic potential of fly ash can be determined by adding
water (and/or lime) and measuring strength parameters of the final cured product.
5-26
-------
5.4.6.2 FGC Wastes
Unconfined and triaxial compression tests on FGC wastes without
additives have been performed by various investigators [4,19,88,89,98,
104-106]. Both sulfite- and sulfate-rich wastes resemble micaceous
silts and very fine sands in shearing behavior and possess insignifi-
cant (^0 Pa> ^0 psi) effective cohesion and angles of internal friction
of from 25° to 35° (Table 5.6). If these wastes are compacted to their
maximum dry density (Proctor compaction) and dried, unconfined compres-
sion strengths on the order of 7-14 x 10 Pa (10-20 psi) are observed.
Liquefaction upon vibration has also been observed for a sulfite-rich
»
waste [27,43]. The values of the unconfined compression strength are
sensitive to changes in moisture content and, depending on the waste,
age of the waste [89,104].
Shear strength parameters for uncured wastes, fly ash and lime
mixtures are shown in Table 5.5. Addition of fly ash and lime generally
results in an increase in shear strength for sulfite-rich wastes derived
both from an increase in the angle of internal friction and in the effec-
tive cohesion. Effective cohesion increases from zero to 2-11 x 10 Pa
(2.4-15.3 psi).
Unconfined compression strength values for uncured and cured
sulfite-rich wastes, fly ash and lime mixtures are given in Table 5.6.
These results illustrate the substantial gain in strength of the waste/
additive mixtures upon curing. Increases in strength of 9-24 x 10 Pa
(10-34 psi) are observed. Addition of only lime to these ash-free sulfite
wastes produces no time-dependent increase in strength.
The effect of admixing various additives with sulfite-rich and fly
ash waste mixtures is shown in Table 5.7. Addition of only soil to the
sulfite waste does not significantly alter its strength initially, but
a gain in strength is observed over a period of time. Addition of soil
and fly ash to sulfite waste produces the same effect but with a marked
increase in strength with time. Addition of cement to sulfite waste
causes an increase of strength with time with highest strengths obtained
for highest percentage of cement added. The strength obtained for cement,
5-27
-------
Table 5.5
Waste
Sulfite-Rich
Shear Strength Parameters of FGC Wastes
Angle of Internal
Friction.
Effective Cohesion,C
(10+5 Pa)
(Ib/in )
Ul
K>
00
• Without Ash;
Paddy's Run
Scholz (CEA/ADL)
• With Ash;
Paddy's Run (50% Ash)
Paddy's Run (33% Ash)
Scholz (CEA/ADL, 50% Ash)
Scholz (CEA/ADL, 33% Ash)
• With Ash and Lime:
Paddy's Run (50% Ash, 5% Lime)a
Scholtz (50% Ash, 5% Llme)a
Elrama (IVCS Process) b
Sulfate-Rich
• Without Ash;
Scholz (CIC)
• With Ash Added;
Gypsum (Fly Ash Scrubber, 50% Ash)
Gypsum (Fly Ash Scrubber, 33% Ash)
30.5°
36
35,32
33
36,33
36
31,35
35
0
0.3
0
0.2,0.6
0.6
0.3,0.7
0.8
0.5,0.3
0.6
1.2
4.6
0
2.4,8.3
8.3
4.9,10.7
11.1
7.6,4.3
7.9
1.6
42
32,37
35
1.1,0
0.8
0
15.3,0
10.9
Uncured
b Cured
Source: [71,95,98]
-------
Table 5.6
Unconfined Compressive Strength Values as a
Function of Time for Some FGC Wastes
Waste
Sulfite-Rich '
• With Lime
Paddy's Run (10% Lime)
Scholz (CEA/ADL, 10% Lime)
Water Content
%
94-98
61-62
Strength
(105 Pa)
0 7 28
0.16 0.16 0.44
0.2 0.2 0.2
(lb/in2)
0 7 28 days
2.4 2.3
3.6 3.2
6.4
3.1
Ui
I
ro
vo
With Lime and Fly Ash
Paddy's Run (50% Ash, 5% Lime) 70
Paddy's Run (50% Ash, 10% Lime) 68
Scholz (CEA/ADL, 50% Ash, 5% Lime)
Scholz (CEA/ADL, 50% Ash, 10% Lime) 50-52
0.05 0.27 0.94
0.22 0.19 1.43
0.4 0.4 1.5
0.4 0.5 2.8
0.8 3.9 13.8
3.2 2.8 21.0
6.1 6.4 21.6
6.7 7.4 41.5
a
FGC wastes without any additives generally flow as viscous fluids
and thus do not have sufficient consistency for an unconfined
compression test.
Source: [95]
-------
Table 5.7
Strength Parameters for FGC Wastes
Ln
to
O
WASTE CATEGORY
(Sulflte-Rich Wastes)
• Without Additives
Double Alkali (Pilot Plant)
Limestone
• With Fly Ash
Limestone
Limestone
(20-662 Ash)
(40-50Z Ash)
1.0-1.8
• With Fly Ash and Lime
Limestone (Shawnee, IUCS)
Limestone (Elrarna, IUCS)
• With Fly Ash and Soilb
Limestone (202 Ash, 50-80Z Soil)
• With Fly Ash and Cement0
Limestone (30-502 Ash, 7-22Z Cement)
Double Alkali (50Z Ash, 33Z Cement)
• With Soil
Limestone (50-802 Soil)
• With Cement
Limestone (7-15Z Cement)
• With Additive
Limestone (Shawnee, Calcilox)
Limestone (Bruce Mansfield, Calcilox)
Limestone (Shawnee, Chemfix)
Strength*1 (x IP*5 Pa)
Cure Tine
7 14
>28 Days
0.7-1.0
1.5
0.7-2 1.3-1.4 1.3-1.6
1.5-2.5
2-18 7.33
1.2-1.8
1.1-1.9 2.5-3.0
>4. 6-7.1
6-57
12-17
1.1-3.5
4.6-5.2
14-16
Strength (pal)
Cure
K6 >28 Days
10-15
22
10-29 19-20
18-36
29-257 100-473
17-26
16-27 34-44
19-23
410;510e
43f
>62-96
93-814
165-244
16-52
62-72
26j33c
24-260*
a Ash Source
b Soil is gravelly, silty clay
c Cement is Portland cement
d Unconflned strength
e Field data
f Cured in tap water
Source: [4, 19, 24, 27, 37, 88, 96]
-------
fly ash and waste mixtures after curing 28 days suggest that at higher
fly ash ratios cement may be more effective than lime in producing in-
creased strengths.
Limited comparison of laboratory and field strength data has been
performed. Field vane shear tests and continuous sampling were done on
ten waste-additive mixtures contained in 15 impoundments (5 pits and
10 pools) at Cane Run Station (LG&E). Laboratory permeability and un-
confined compression tests were done on samples obtained from the field.
In general, it was found from the vane shear measurements that undrained
compressive strength increased with time for all impoundments, and that
measured strength values of commercial lime wastes were much higher than
those of carbide lime wastes. Average vane shear strength values deter-
mined at various times after placement are listed in Table 5.8 for carbide
lime wastes and in Table 5.9 for commercial lime wastes. These values
are considered representative of in-situ shear strength. In other case?
laboratory unconfined compressive strength tests done on field samples
yielded strength values less than 50% of vane shear strength values.
The reason for the differences between vane shear measurements and lab-
oratory unconfined compressive strength values was sample disturbance.
Sample disturbance was severe for frozen waste samples and for frozen-
thawed materials in the summer because the mixture structure was brittle
and sensitive. Many samples were found to be friable and others contained
numerous voids and discontinuities. Thus it was felt that vane shear
strength values were better indicators of in-situ shear strength than
were laboratory unconfined compressive strength values.
Unconfined compressive strength values have been reported for
laboratory-prepared samples of waste/additive mixtures identical to
those contained in the LG&E field impoundments [101]. The unconfined
compressive strength values reported in this reference are for intact
samples cured 60 days under saturated conditions. These values are
also listed in Tables 5.8 and 5.9. Comparison of strength values of
laboratory-prepared samples with strength values measured in-situ
5-31
-------
Table 5.8
Shear Strength and Permeability Values
Waste-Carbide Lime-Fly Ash Impoundments
Untrained Coapreaalve Strength
(In-Sttu Vine Shear Meaaureacnts)
Ui
U)
NJ
Mix Iwoundaenta
O.S Waste: 0.5 Fly Aah
+ 5Z Carbide Ll«e Fit fl
Fool fl
O.S Uaate: O.S Fly Ash
+ SZ Carbide Llae Pit »2
Fool 13
Wast* + St Carbide Lim* Pool 12
O.S Waate: O.S Fly Aab
+ 31 Carbide Lime Fool 14
Negl.
Hegl.
O.SxlO5 Pa
(7 pal)
0.4xU>5 Pa
(5.5 pal)
O.fixlO5 Fa
(8.3 pal)
0.7xl03 Pa
(10.4 pal)
30-Daya
0.3xl05 Fa
(4.2 pal)
Hegl.
0.7xl05 Fa
(10.4 pal)
2.4x103 p.
(34.7 pal)
0.7x105 Fa
(10.4 pal)
23xl05 Pa
(33.3 pal)
90-Dayg
O.SxlO5 Fa
(4.2 pal)
0.7xlOS Pa
2.8x105 Pa
(41.7 p«l)
1.4x105 Pa
(20.8 pal)
O.lxlO5 Pa
(1.4 pal)
Laboratory
Penaablllty of Unconflned Coapreaalve Strength
Flflfl RBffiiBGnt (Laboratorv-PrPDKred SDeclmeasI
180-Daya
O.SxlO5 Pa 3xlO~5 cm/sec
(7 pal)
0.9xl05 Pa 7xlO~* cm/»«c
(13.9 pal) _i
>2.8x!05 Pa 7x10 ca/aec
(>42 pal)
0.9x105 Fa IxlQ"5 caVaec
(13.9 pal)
0.2x10* Pa 2xlO~S ca/aec
(2.8 pal)
Hegl.
Hegl-
7.8xl05 Pa
(114 pal)
7.8xl05 Fa
(114 pal)
4-OxlO5 Fa
(57 pal)
2.4X105 Fa
(349 pal)
uaate la a product of a llae proceaa using carbide lime.
Source: [10]
-------
Table 5.9
Shear Strength and Permeability Values
Waste-Commercial Lime-Fly Ash Impoundments
Mix
Impoundments
Undrained Compressive Strength
(Iti-Situ Vane Shear Measurements)
0-Days 30-Days
Laboratory
Permeability of
Field Specimens
Unconfined Compressive Strength
(Laboratory-Prepared Specimens)
Ul
CO
CO
Waste +0.5 Fly Ash
+ 3Z CaO
0.5 Waste: 0.5 Fly Ash
+ 3Z Ca(OH),
2
0.5 Waste: 0.5 Fly Ash
+ 3Z CaO
0.5 Waste: 0.75 Fly Ash
+ 3Z CaO
0.5 Waste + 0.5 Fly Ash
+ 3Z Portland cement
0.5 Waste + 0.5 Fly Ash
Pit 13
Pool #6
Pit #4
Pool #8
Pit #5
Pool #7
Pool §5
Pool 19
Pool #10
0.4xl05 Pa
(7 psi)
0.9xl05 Pa
(1.4 psi)
1.9xl05 Pa
(27.8 psi)
1.9xl05 Pa
(27.8 psi)
>2.8xl05 Pa
(>42 psi)
0.4xl05 Pa
(7 psi)
0.6xl05 Pa
(8.3 psi)
2.8xl05 Pa
(42 psi)
0.7xl05 Pa
(9.7 psi)
1 ,6
>2.8x:.05 Pa 3x10 cm/sec
(>42 psi)
>2.8xl05 Pa
(>42 psi)
>2.8xl05 Pa ~
(>42 psi) ,
>2.8xl05 Pa 3x10 cm/sec
(>42 psi)
>2.8xl05 Pa 5xlO~ cm/sec
(>42 psi) ,
>2.8xl05 Pa 8x10 cm/sec
(>42 psi)
fi
>2.8xl05 Pa 5x10 cm/sec
(>42 psi)
>2.8xl05 Pa
(>42 psi)
>2.8xl05 Pa —
(>42 psi)
5
6.9x10 Pa
C
6.9x10 Pa
5
12.9x10 Pa
12.9xl05 Pa
S.OxlO5 Pa
S.OxlO5 Pa
s
ll.SxlO3 Pa
S.lxlO5 Pa
2.8xl05 Pa
(100 psi)
(100 psi)
(190 psi)
(190 psi)
(118 psi)
(118 psi)
(174 psi)
(75 psi)
(42 psi)
waste Is a. product of a lime process using carbide lime.
Source: [10]
-------
Indicates that unfavorable curing conditions in the field and field
placement procedures have resulted in in-situ strength values much
lower than those expected on the basis of tests done on laboratory-
prepared samples.
As previously noted, the cohesionless granular nature of FGC wastes
is similar to the character of fine sands and nonplastic silts. Such
materials may be affected by vibrations. If silty or sandy soils in a
loose (low density) condition are subjected to vibratory loading of
appropriate intensity and frequency, they will tend to densify, particu-
larly if they are characterized by a uniform particle size distribution.
If the silt/sand is saturated the tendency for volume decrease creates
positive pressure in the water between particles. The positive water
pressure decreases the contact pressure between particles; a "buoyant"
effect is created. Since the strength of the material (resistance to
distortion) is due to interparticle forces, including friction, the mass
of particles temporarily loses stability. The unstable mass may flow
like a liquid; this behavior is known as liquefaction. Generally, excess
water is expelled and a denser, more stable structure is produced, al-
though this effect may be localized in a liquefaction zone.
Several investigators, including Crowe of TVA [102], Edwards of
Southern Services, Inc. [99], and Twin City Testing [89] have reported
instances of instability of FGC wastes subjected to vibrations. However,
disposal of sulfate (gypsum) slurries (from other industries, not flue
gas cleaning) on land in deposits many feet high has been done for years
with no instability.
To resolve this paradox, a series of tests [36] were carried out in
which model embankments of FGC wastes were subjected to vibratory loading.
A dual alkali process waste and a lime process waste were tested.
The model embankment was approximately 10 centimeters high by 90 centi-
meters long, with a base width of 64 centimeters and a crest width of
21 centimeters (side slope angles of 25°). These dimensions were chosen
to yield a shape stable under static loading. The models were prepared
by compacting the waste in layers about 1 centimeter thick, with a
5-34
-------
compaction energy about 20% of Standard Proctor compaction. Models were
prepared at solids contents bracketing the optimum solids content deter-
mined from compaction tests. Horizontal vibratory motion of the models
was achieved by use of a shake table. The amplitudes and frequencies
used were characteristic of ground motions caused by earthquakes,
blasting, or similar disturbances. All of the results of the tests
cannot be given here. In brief, dual alkali process waste behaved as a
brittle material if compacted at solids contents of 75% or greater.
Frequencies of 15 Ez or greater and accelerations of 1.5g or more were
required to fail models of such material. However, the models compacted
at 70% solids content developed failure planes after several seconds
shaking at a frequency of 1 Hz; 7.5 Hz induced slumping and 10 Hz caused
flow of material. For comparison, a lime process waste model compacted
at 51% solids content failed completely by flow after only a few cycles
of motion at 10 Hz. Since the models were not saturated, cessation of
shaking caused cessation of slumping or flow. Saturated material may
continue to flow after external disturbance ceases.
These results indicate the need for conducting further tests on the
susceptibility of FGC wastes to vibrational instability. The results
may not be as pertinent to the assessment of stability in existing gypsum
waste fills because such fills almost always exhibit a significant degree
of cementation between grains. This cfementation is believed to be caused
by the migration of saturated leachate down through the fills with de-
position of secondary gypsum between grains in the lower portions of the
fill. It appears to be worthwhile, however, to evaluate the dynamic
behavior of fills of sulfate-rich wastes which are placed by dumping
after filtration rather than in a slurry as is done in most existing
waste gypsum disposal operations.
The loss of strength under vibration shown by FGC wastes has led
some investigators to state that these wastes are thixotropic. A truly
thixotropic material would soften and flow under finger pressure. FGD
wastes, when tested for thixotropic behavior by placing a nearly saturated
sample in a small dish and tapping the dish lightly on a table, release
excess water which appears atop of the densified sludge, and when a finger
groove is made in the waste, the material behaves as a stiff mass and breaks
5-35
-------
apart. Renewed tapping of the dish containing the waste which has been
broken apart causes the waste to flow again and close the grove left
by the finger. Extensive testing of FGC wastes has produced no evidence
of true thixotropic behavior or a tendency to "rewet." FGC wastes liquefy
under vibration repeatedly only as long as sufficient water exists in the
waste mass for the creation of positive water pressure and consequent loss
of strength. Drainage of excess water during vibration will prevent or
greatly diminish liquefaction potential for subsequent vibratory loading.
5.4.7 Permeability
5.4.7.1 Fly Ash
The mass permeability of fly ash deposits has been studied by several
investigators [70,82,83]. Typically, values of coefficient of permeability
range from 5 x 10~ cm/sec to 5 x 10 cm/sec. Field permeabilities may be
higher (10 cm/sec) than laboratory values (10 cm/sec) because of compac-
tion problems [83]. Laboratory tests have shown that treatment with lime
is effective in reducing fly ash permeability to values which depend highly
on the treatment conditions [82].
5.4.7.2 FGC Wastes
Permeability tests have been performed on FGC wastes and mixtures
of wastes and additives by a number of investigators [19,37,88,98,100,
145]. The coefficient of permeability for particulate materials (such
as natural soils) varies in magnitude more than any other engineering
property. For example, a sand with no fine particles may have a co-
efficient of permeability of 0.01 cm/sec, while a clay may have a
coefficient of permeability as low as 10'11 cm/sec (one billionth of
the value for the sand). The permeability of material samples tested
in the laboratory is extremely sensitive to sample disturbance. Also,
passage of water around a sample in a laboratory pertneameter is a common
source of erroneous data. Finally, because of sample disturbance,
stratification of deposits, and short-circuiting of water around low-
permeability soils in permeameters, laboratory values of coefficient
of permeability may not relate to field permeability. For these reasons,
permeability determinations should be made by several methods on samples
with minimal disturbance, and should be complemented with field deter-
minations of mass permeability. However, available data can be summarized.
5-36
-------
with minimal disturbance, and should be complemented with field determi-
nations of mass permeability. However, available data can be summarized.
The Aerospace Corporation [37] measured laboratory permeability
values for seven unstabilized FGC waste samples. Laboratory permeability
values were also measured for four FGC wastes stabilized by one or more
of three commercial fixation processes. Results of these tests indicate
that the coefficient of permeability of unstabilized FGC wastes generally
falls in the range of 2 x ICT^ to 1 x 10~5 cm/sec. Similar permeability
values were obtained for samples of crushed stabilized-wastes. However,
permeability values for intact samples of stabilized wastes were two or
more orders of magnitude smaller than those of unstabilized FGC wastes.
The U.S. Army Corps of Engineers-Waterways Experiment Station (WES)
has conducted a laboratory physical characterization study of five FGC
waste samples [100,142]. Unstabilized wastes and wastes stabilized by
use of five procedures were tested for permeability. In general, permea-
bility values of unstabilized wastes were in the range of 1 x 10"^ cm/sec
to 1 x 10"-* cm/sec. Permeability values of stabilized wastes were, in
many cases, several orders of magnitude lower than those of unstabilized
wastes.
The results of a number of laboratory permeability tests on FGC
wastes are shown in Table 5.10. In some instances, the investigators
did not describe the test method they used, but in most cases, the data
in this table were derived from falling-head permeability tests. The
influence of waste composition and morphology is evident from a com-
parison of the values of permeability for the various classes of wastes.
In general, sulfite wastes are less permeable than sulfate wastes
although close control of gypsum formation in a dual alkali plant may
yield a low permeability FGC waste. Addition of stabilization additives
such as fly ash and cement reduce the total waste permeability by about
50%. However, a much more pronounced decrease in permeability was found
for increases in solids contents of the wastes; for example, the addition
of only fly ash may produce a decrease in permeability proportional to
5-37
-------
Table 5.10
Coefficients of Permeability for FGC Wastes
f TL solids by weight for saturated waste.
Cured in the field.
Cured in the presence of tap water.
Source: [19, 37, 88, 98, 145]
WASTE CATEGORY
SULFITE-RICH
Z Solids Permeability Coefficient (cm/sec)
• Without Ash *
Lake View (Ontario Hydro) 77 9xlol«
Paddy's Run 52 8x10"?
Scholz (CEA/ADL) 63 4xlO~3
Range: (0.9-4) x 10~5
• With Ash .
Bruce Mansfield 59 2xl°I«
Elrama 50 7,5x10 ~?
Lake View (Ontario Hydro) -652 Ash 79 7.2x10".!
Paddy's Run -50Z Ash 63 lxlO~3 .
Phillips — .74-1.2x10"?
Mohave — 1.6-5.0x10
Range: (.07-5.0) x 10"4
f • With Additive 5
W Bruce Mansfield + Calcilox (Dravo)0 47 l.SxlO^
Lake View (Ontario Hydro) -39Z Ash, 5Z Cement 75 4.0xlO~° „
Shawnee + Calcilox (Dravo) — 3.8-14.0x10
Rauge: (.4-14.0) x 10"5
• With Ash and Line (Cured) .
Elraaa (IUCS Stabilization) 58 3x10 ,.
Shawnee (IUCS Stabilization) — .5-55.0x10"
Range: (.5-300) x lo"7
SULFATE-RICH
• Without Ash r
Scholz (C1C) 82 5x10
Cholla — 1.1-2.7x10"
Gadshy — 1.2-9.8x10
Shawnee (Forced Oxidation) — .59-2.3 xlO
Range: (0.1-9.8) x 10~*
-------
the resultant decrease in the square of the void ratio. Thacker [98]
also reported substantial decreases in permeability with increasing
values of solids content. As an example, the permeability of Paddy's
Run waste decreased from 1 x 10 cm/sec to 5 x 10~° cm/sec as the
solids content increased from 50% to 55%.
Laboratory permeability tests have been performed by the University
of Louisville on samples of direct-lime FGC waste obtained from field
impoundments at the Louisville Gas and Electric Company Cane Run Station
and those results have been shown in Tables 5.8 and 5.9. Pits 1 and 2 and
Pools 1 through A contained waste/additive mixtures utilizing carbide
lime; Pits 3 through 5 and Pools 5 through 8 contained mixtures utilizing
commercial lime additives. Field vane shear testing and continuous sam-
pling of each impoundment were done on a schedule of 0-days, 30-days,
60-days, 180-days and 360-days after filling.
Laboratory permeability tests were performed on waste/additive samples
obtained from field impoundments by the falling-head technique (ASTM D2434).
Results of permeability tests were quite, variable, mainly because of sample
characteristics. Many of the impounded FGC waste/additive mixtures exhi-
bited distinct layering due to incomplete mixing. In addition, many samples
contained numerous voids and discontinuities due to the compaction proce-
dures used in placement. Non-homogeneity of FGC waste/additive mixtures
placed in impoundments was encountered as a result of freezing and thawing
and because of interruptions in the filling operations. Finally, sample
disturbance was inevitable and severe when frozen FGC waste was sampled;
brittle frozen-thawed materials were also particularly sensitive to sampling.
Therefore, because of these circumstances, changes in field permeability
due to curing were masked by sample variability. However, average permea-
bility values are given for the various impoundments in Tables 5.8 and 5.9;
these values reflect estimates of the maximum in-situ permeability as
determined in laboratory tests performed on disturbed samples. It is
noteworthy that maximum permeability values range between 3 x 10 cm/sec
and 3 x 10~ cm/sec. In-situ values of permeability may be determined by
multiple well pumping tests. Field permeabilities are probably an order
of magnitude lower than maximum values given in Tables 5.8 and 5.9.
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Permeability tests were performed by Combustion Engineering on
intact, laboratory-prepared samples of waste/additive mixtures identical
to those contained in the LG&E field impoundments, [101]. FGC waste
mixtures were cured under saturated conditions before permeability
testing. The permeability values of samples of the various, mixtures
were determined by the falling-head technique. Results of these tests
indicate values of permeability between 2 x 10"' cm/sec and 8 x 10~5
cm/sec. Comparison of permeability values determined on laboratory-
prepared samples with results of permeability tests done on field
samples reveal that field sample values were from one-half to two orders
of magnitude greater than those of laboratory-prepared samples.
—6 — R
IUCS [26,107] has reported permeability values of 10 and 10 cm/
sec for an anonymous FGC waste-lime-fly ash admixture. The samples studied
reportedly exhibited unconfined compressive strength values of (12 - 23) x
10 Pa (180-344 psi). Triaxial compression tests yielded cohesion values of
(0.72 - 23.9)xlO Pa (10.4-347 psi) and an angle of internal friction of >40°.
Some indications have been seen in field studies at the Louisville
Gas and Electric Company Cane Run Plant that physical blinding may occur
at the contact zone between FGC waste and soil layers. Apparently, fine
sludge particles are carried into voids between soil grains to form a
zone of very low permeability. The importance of such action cannot be
evaluated on the basis of the limited data currently available.
Further laboratory determinations of waste permeability are needed
and such determinations must be correlated with field determinations of
mass permeability.
Permeability measurements in addition to all of the physical prop-
erties described in previous sections are planned for Milton R. Young Plant
(fly ash scrubbing) wastes by the University of North Dakota for the EPA
as part of their evaluation of disposal of this high alkalinity fly ash
in a decoaled mine seam.
5.4.8 Weathering
5.4.8.1 Fly Ash
Very little attention has been given to the effects of weathering
(freeze-thaw cycles and/or wet-dry cycles) on fly ash durability because
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the individual grains are highly durable, disposal practices do not
rely on cohesion or cementation between grains, and, when fly ash is
used as a material filler, weather effects are more severe on the material
matrix rather than the filler. Durability of fly ash-stabilized soils
[72] and other media has been investigated because of the frost suscep-
tibility [76] of the fly ash (uniform, silt-size grains), and durability
of waste-fly ash mixtures should be investigated.
Because of its texture (uniform size spherical grains), fly ash is
readily eroded by water and/or wind [68,86]. Fugitive dust emissions
and surface erosion by water are problems in fly ash disposal areas,
particularly in dried sections of disposal ponds.
5.4.8.2 FGC Wastes
Another area of research which has received little consideration is
weather effects on the physical properties of deposits of waste and/or
waste plus additives. Of particular interest are the effects of freeze-
thaw cycles and wet-dry cycles. Freezing of wastes and waste-additive
mixtures soon after placement is certain to occur if land disposal of
FGC wastes is continued year-round in many parts of the United States.
Freezing has been demonstrated to be of some significance in dewatering
of wastes placed in lagoons and ponds (e.g., water treatment wastes).
Field studies at the Louisville Gas and Electric Company Cane Run Plant
have indicated that freezing may cause dewatering of wastes to some
extent (after subsequent thawing), but freezing also produced layering
in waste deposits. Frozen zones that formed on the surface of waste
deposits did not thaw when more waste was added over the surface of
the fills; some layers remained frozen for four to five months. Further,
stabilization of FGC waste with additives was impaired drastically by
freezing. In some deposits, anticipated pozzolanic reactions were
delayed; in other fills such reactions never occurred. In one particular
instance, a mixture of carbide lime process waste, fly ash, and carbide
lime (1:1:0.03 weight proportions) emerged from a mixing truck as spheres
2.5 to 15 centimeters (1 to 6 inches) in diameter. These stiff balls
froze to rock-like hardness within hours after placement, and remained
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rock-like for more than three months. However, with the advent of warm
weather, the balls thawed, dried, and, in many cases, crumbled. Such
behavior indicates the need for more evaluation of freeze-thaw effects.
Of less significance than freeze-thaw effects are the effects of
wet-dry cycles. Field compaction studies at Plant Scholz have shown
that FGC wastes deposited in relatively thin layers 15-45 centimerers
(6-18 inches) may dry appreciably in a hot, dry climate. Experience
with waste sludge disposal at the Reid Gardner Station near Las Vegas,
Nevada also indicated that field drying may be feasible; experience with
the waste from the Trona scrubbing operation at Reid Gardner may not be
directly applicable to disposal of calcium-sulfur salt wastes, but general
behavior may be extrapolated. Drying effects would occur only under
conditions existing at a limited number of sites only during certain
seasons. Intermittent periods of wet weather may increase the potential
for leachate generation and surface erosion of waste deposits. As
mentioned previously, wetting of waste does not appear to cause detri-
mental changes in strength, compressibility, or permeability.
Laboratory tests on the effects of freeze/thaw cycles on fly ash/
laboratory samples of CaS03 and CaSO^/lime mixtures have been performed
by Radian [146]. Twenty-four mixtures were tested for unconfined com-
pressive strengths after freezing and thawing ten times. In general,
slightly higher strengths were observed for the frozen/thawed sample
than those cured at room temperature. Similar effects are also noted
for Calcilox stabilized waste [146].
Erosion of surface layers of waste deposits has been addressed
briefly by Radian Corporation [39]. This problem is not a major hin-
drance to land disposal of wastes since permanent cover layers of soil
probably would be placed over any waste deposit and, during construction
of waste fills, surficial drainage management would minimize area exposed
for erosion as well as prevent contamination of water bodies by eroded
materials. The "silty" nature of FGC wastes, however, makes them prone
to water and air transport. In the Radian study, plots of a clay loam
soil, a fly ash and a scrubber waste were tested. Artificial rainfall
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on plots with varying slopes produced sediment yields 3 to 10 times
as great from the waste plots as from the clay loam soil plots. The
fly ash yielded only about 10-70% as much sediment as did the soil,
depending on slope. Radian investigators applied these results in the
Uniform Soil Loss Equation developed by Wischmeier and Smith [103], for
a hypothetical disposal site location in Central Illinois, assuming exposed
slope lengths of 61 meters (200 ft) at an 8% grade. Their analysis yielded
an estimate of loss of 269 tons/hectare (120 tons/acre) per year. This
figure, four to five times greater than the loss anticipated for silty
soils under natural conditions, indicates that furface erosion must be
considered in the design of disposal areas for FGC wastes. In contrast,
wind erosion experiments showed little susceptibility of waste to wind
transport, because of the protective action of a surface crust on the
waste plots tested. The results of the experiments were not conclusive
and indicate the need for further investigation.
5.5 Data Gaps and Future Research Needs
The major data gaps in physical characteristics of FGC wastes can be
subdivided into those relative to wastes from:
• dry sorbent systems (whose importance will be greater in the
future), and
• wet scrubber systems.
Dry sorbents have not reached significant commercial use now but are
expected to by the early 1980's. Lack of physical characterization data
on these wastes is a major data gap.
A review of the state-of-the-art of FGC wastes characterization in-
dicates that any program to fill deficiencies in existing data should be
structured in the following priority ranking:
(1) Laboratory and Field Permeability Data - A comprehensive
laboratory and field permeability testing program of FGC wastes and waste
additive mixtures (particularly sludge-fly ash mixtures) is needed. These
tests are required since many of the data on permeability which have been
reported are of dubious value, particularly for "fixed" sludges.
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(2) Freeze/Thaw and Dry/Wet Cycles Effects - An aspect of stability
which has emerged as significant as a result of field testing is the pos-
sible deterioration of waste and waste/additive mixtures under influence
of freezing. This behavior requires comprehensive investigation. A
laboratory study of the effects of freezing on waste and waste/additive
mixtures is appropriate. Physical and chemical changes, including cemen-
tation by fixatives, should be studied in tests where mixing and compac-
tion are done in freezing temperatures and in tests where the onset of
freezing is delayed for various time periods. The effects of cycles of
freezing and thawing, with various durations of freezing and thawing,
should be determined. These effects are relevant especially in the case
of mixes of sludges and additives in which chemical reactions are anti-
cipated. These tests should be supplemented with field testing to verify
that field conditions have been simulated accurately in the laboratory.
A limited number of tests should be conducted to determine the
effects of periods of intense heat and low humidity alternating with
periods of heavy rainfall. These tests would be intended to ascertain
if high temperatures and low humidity may accelerate chemical fixation
reactions, and if such acceleration is beneficial or detrimental. Al-
ternating exposure to intense rainfall not only would simulate climate
conditions in some areas of the United States, but also would serve to
test the hypothesis that wastes and mixtures do not reslurry upon re-
wetting.
(3) Laboratory and Field Compaction Tests - Laboratory and field
compaction testing of FGC wastes and mixtures is needed to "calibrate"
the relation between lab and field tests and to determine the most ef-
fective compaction equipment and techniques. Laboratory determinations
of compaction characteristics have been made; these tests must be cor-
related with field studies of waste compaction. Various compaction
methods and equipment should be evaluated: sheepsfoot rollers; pneumatic
rubber-tired rollers; steel drum rollers; and vibratory rollers. Lift
thickness (depth of layer before compaction), number of roller passes
and compaction moisture content are variables to be evaluated. The
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energy and economic trade-offs between dewatering with better subsequent
compaction and poor compaction of wetter materials should be examined.
Optimum compaction conditions may be achieved through addition of dry
solids (e.g., fly ash) and this alternative also merits evaluation. In
any field evaluation of compaction techniques, mixtures of additives
plus waste should be studied, as well as unstabilized wastes.
One additive which has received only limited study is natural soil.
In some locations, cohesionless soils may be available at low cost in
quantities sufficient for use as a waste/additive. Mixing of dry sand
with FGC wastes probably would have minimal effect on the permeability
of the mixed components, but the strength of the mix should be far
superior to that of waste alone, and similar improvements in stiffness
(less compressible) should be realized. Handling and compacting of a
waste-sand mix or a waste-fly ash-sand mix may be easier than similar
processing of raw waste and the resultant fill should be much stronger
and more stable than a mass of ponded waste. Mixing and compacting of
waste-sand and waste-fly ash-sand blends should be evaluated in labora-
tory tests and in field demonstrations.
(A) Dewatering Characteristics - Tests are needed of dewatering
characteristics of FGC wastes and mixtures, including those of drying
with underdrains in field and laboratory. These tests are needed because
of the important connection between dewatering and subsequent mixing
and/or compaction of wastes in land disposal sites. Dewatering techniques
for FGC wastes are being investigated by a team of research personnel at
Auburn University.
(5) Comprehensive Triaxial Compression Tests and Consolidation
Tests - The evaluation of strength and compressibility of FGC wastes and
waste-additive mixtures, although claimed by many, has been accomplished
by few. It is necessary to perform a full suite of triaxial compression
tests and consolidation tests on a representative number of FGC wastes
and waste/additive mixtures after various durations of curing and in
various conditions (compacted, uncompacted, "fixed").
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(6) Mixing Characteristics - Transport and handling characteristics
are extremely important since they are at the beginning point in the
generation-to-disposal route of FGC wastes. To date, it appears that
insufficient attention has been given to the mixing characteristics of
FGC wastes and pertinent additives. Further examination of the mixing
characteristics of FGC wastes, including examination of field deposits
and ponds for evidence of heterogeneity or stratification is needed.
Attention should be given to settling of solids in pipelines and any
changes in apparent pumping characteristics after periods of interrupted
flow. This study should include an examination of the mixing properties
of FGC wastes and likely additives. Field tests have shown that such
mixing may be difficult and that segregation of additives may be a serious
problem under certain conditions. Samples of sludge-additive mixtures
from the EPA-TVA demonstration site at the Shawnee Steam Plant in Paducah
Kentucky, have exhibited distinct stratification of mix components, and
mixing of fixatives in sludge at the Phillips Station of the Duquesne
Light Company has not always been uniform. Mixing tests appear to be
appropriate.
(7) Hydrologic and Soil Attenuation Studies - Field studies also
appear to be required for the evaluation of the water pollution potential
of leachate from FGC waste deposits. Leachate collection and testing has
been done at Plant Scholz, the Phillips Station, the Shawnee Steam Plant
the LG&E Cane Run Plant and elsewhere. However, more attention should
be given to hydrologic studies to quantify water flow in, around and
under waste lagoons and fills. Additionally, attenuation of leachate by
in-situ soils should be studied to provide correlative data for soil at-
tenuation studies being done at the Dugway Proving Ground. Several field
disposal sites should be monitored to determine overall water balance
(net precipitation or evapotranspiration, infiltration, temporary storage
etc.), mass permeability within waste deposits and at soil contact zones
and chemical characteristics of leachate after passage through natural
soil strata.
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(8) Viscosity and Pumping Characteristics - To date, insufficeint
attention has been given to the pumping characteristics of FGC wastes
and pertinent additives. Viscosity tests should be performed on a repre-
sentative number of sludges, and mixtures of wastes and fly ash or other
non-cementing additives. It appears ill-advised to consider pumping
mixtures which could react and cement in pipelines and pumps; however,
non-alkaline fly ash, lime and some soils, used as single additives with
FGC waste, should be examined. The relations between apparent viscosity
and solids content, and between apparent viscosity and flow rate (shear
rate) should be investigated.
Standard tests and equipment are available to determine all of the
properties listed above as current data gaps. With regard to planning
and design of an FGC system for electric power utilities and other
combustion sources, the first five items are of greater ranking than the
last three.
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6.0 RESEARCH NEEDS
6.1 Waste Properties Relation to the Disposal Process
Knowledge of the handling properties and the behavior of FGC wastes
prior to, during and after disposal in relation to their possible environ-
mental impacts are necessary for the design and operation of disposal
systems. The chemical and physical properties discussed previously aid
in determining handling methodology and in assessing possible environ-
mental impacts leading to the choice of the disposal site design.
Determination of these properties may be accomplished by performing
laboratory experiments which are designed to simulate disposal site
conditions or by monitoring disposal sites. Generally, however, labora-
tory experiments cannot always be designed which accurately simulate a
specific disposal environment because of the many possible variables involved.
It is then more beneficial to perform experiments which give insights on
the mechanisms of environmental impact and how specific waste properties
relate to these mechanisms in producing the impact. The relationship
of some of i:he previously discussed waste properties to possible routes
of environmental impact for land disposal is shown in Table 6.1.
The mechanisms of environmental impact (e.g., leaching) are separated
under headings of physical and chemical impact and those related to bio-
logical impacts. The physical and chemical impacts are prerequisites for
any biological impacts to occur, but they may occur without any subsequent
biological impacts. The extent that these mechanisms contribute to the
total impact is governed both by waste properties and site considerations.
Only the properties relating to the waste are included in Table 6.1, and
they are separated into those which affect the identity and concentration
of the spec.ies exiting the waste into the environment and those which
affect the total quantity exiting. For example, the composition of the
leachate exiting the waste depends on the solid and liquid portions of
the waste £nd how much of these species dissolve or mix with the leaching
solution. The total quantity coming out of the waste depends on the rate
that the leachate flows (permeates) through the waste (waste volume, also
a factor it. determining quantities, is not considered to be a waste property),
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Table 6.1
FGC Wastes Properties and Possible Routes of Important Environmental Impacts (Land Disposal)
o\
ho
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The extent of disruption of existing conditions and biological effects
are less defined by quantitative parameters than the other mechanisms
and are not done so in Table 6.1. It is impossible to quantify,
for example, the suitability of the waste for habitation or the impact
of leachate on biological organisms. In this regard, the other FGC
waste properties listed can give insight into the extent of each mechanism
occurring but, at this time, are no substitute for actual exposure tests.
The extent of biological impacts is not only related to specific
waste properties, but is also dependent on the extent with which the
chemical and physical impacts are modified by interaction with the sur-
rounding environment (see below) prior to interaction with the ecology.
Thus, for example, actual biological impact of leachate may occur only
after it has passed through several underlying strata and has been diluted
by underground water flows. These may contribute to modification of both
concentration and species in the leachate with which biological inter-
action may occur.
The waste properties listed in Table 6.1 may be modified during the
course of the disposal process and the lifetime of the disposal site.
These modifications may occur due to the specific site conditions, inter-
action with the environment as well as handling and placement factors. A
listing of these variables is given in Table 6.2. In addition to modifying
the waste properties, some of these variables affect the overall environ-
mental impact by modification of the composition and quantity and resulting
effects of the pollutants that may enter the environment. Specific in-site
conditions such as age of the waste after placement may alter waste proper-
ties for materials which are not at thermodynamic equilibrium (e.g., uncured
stabilized wastes). Interaction of groundwater with the waste may, for example,
produce gaseous products (e.g., acid mine drainage interacting with sulfite
wastes) or deterioration of waste (e.g., reversal of the stabilization process).
Hydrology is also important in determining the final concentration and species
entering the environment (e.g., via leaching). Geological effects may range
from restriction of leachate flow by an impermeable underlying strata and
removal of trace pollutants by soil attenuation to the act of breaking up
a stabilized waste by a seismic disturbance.
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Table 6.2
Variables Affecting FGC Waste Properties
And The Resulting Environmental Impact
TIME (WASTE AGE)
WASTE VOLUME
SITE CONDITIONS
• Hydrology
- Surface Water
- Groundwater
• Geology
- Soils
- Topography
- Seismicity
• Climate
- Wet/Dry Cycles
- Freeze/Thaw Cycles
- Light
- Air Flow
• Ecology
- Biological Interactions
HANDLING/PLACEMENT FACTORS
• Additives
- Stabilization
- Co-Disposal
- Admixing
• Dewatering
- Moisture Content
• Compaction
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Climactic conditions may effect waste properties and quantity of
pollutants. Examples are the possible deteriorating effects of freeze/thaw
cycles and the quantity of rain governing extent of leaching or runoff.
One example of ecological effects is the possible formation of gaseous
products from bacteriological reduction of sulfites and sulfates.
Other variables shown in Table 6.2 involve handling and placement
effects produced during the disposal process. Examples of these effects
include changing initial waste properties by addition of various sub-
stances or chemical reactions and compaction of the vsaste (which may
change the effective permeability).
In addition to their importance in assessing environmental impact
some of the waste properties discussed previously are important in
determining handling methodology in the disposal process. Important
waste properties which affect the handling of the waste are listed in
Table 6.3. These are separated into those which aid in determining
the storage transport process and those relating to placement of the
waste. Properties which relate to the fluid properties of the waste
provide information on the mode of storage and mode of transport. Strength
and compaction properties relate to the ability of the waste to support
compaction equipment. A more detailed discussion of these properties in
relation to handling of the waste was presented in Section 5.0,
6.2 Overview on Research Needs
A number of programs have bave been undertaken sponsored by the EPA,
EPRI and others to develop and demonstrate FGD technology and assess
waste disposal and utilization options. Many of these are still in
progress. Continuation of these programs will provide additional data
and information on the characterization of FGC wastes.
The EPA program for control of waste and water pollution from com-
bustion sources has among its overall objectives development of additional
information on the characterization of FGC wastes, thereby permitting
better environmental assessment. Such characterization studies are part
of the overall environmental assessment program initiated by the EPA
which includes:
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Table 6.3
Important Properties of FGC Wastes
Affecting Handling of the Waste Prior to
and During Disposal
STORAGE/TRANSPORT
• Dewaterability
• Pumpability
- Viscosity
- Density
- Consistency
- Moisture Content
- Atterberg Limits
• Physical Stability
- Consistency
- Density
- Liquefaction Potential
- Atterberg Limits
- Dewaterability
• Compaction Behavior
- Strength
- Compressibility
PLACEMENT
• Volume Related Properties
- Density
- Compaction Behavior
- Dewaterability
- Consolidation
• Strength Parameters
- Compressibility
- Intrinsic Strength
- Compaction
6-6
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• FGC waste characterization studies,
• Laboratory and pilot field studies of disposal techniques
for chemically treated wastes,
• Characterization of coal pile drainage, coal ash and other
power plant effluents, and
• Studies on the attenuation of FGC waste leachate by soils.
Many data gaps in the physical and chemical characteristics of FGC
wastes have been identified in Sections 4.5 and 5.5. These provide a
fairly comprehensive list and could serve as a reasonable starting point
for any program planning in this area. In order to assist in this program
planning in each of the above list of data gaps, a priority rating for
each one of the data gaps has been suggested.
Dry sorbents have not reached significant commercial use now but
are expected to by the early 1980's. Since very little chemical and
physical data is available in wastes from this type of process, this
area represents a major research need.
Testing of FGC wastes should not be limited to solid-producing non-
recovery FGC systems but should also include fly ash and bottom ash,
both dry and wet collected as well as wastes produced from recovery
system prescrubbers and waste liquor producing systems.
Research needs that would be particularly useful are presented
below in the order of priority.
6.2.1 Field Data
There is an important need to characterize:
• Chemical properties and leaching behavior of stabilized and
unstabilized wastes in actual field disposal operations, and
• Permeability of untreated FGC wastes and waste/additive mixtures
(particularly, FGD waste-fly ash mixtures) in the field.
Data are needed on changes in waste composition and the associated
pollutant mobility resulting from waste aging, weathering (erosion,
6-7
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rewetting and freeze/thaw), handling, processing (treatment) and the
disposal environment. Information is needed covering the ranges of:
basic FGC system types (direct lime, direct limestone, alkaline ash,
and dual alkali) or waste types (sulfite-rich vs. sulfate-rich);
methods of processing (untreated, blended,, treated); and types
of handling and disposal (ponding, landfill, mine disposal). While a
limited amount of data do exist or are being developed from EPA funded
projects (e.g., Square Butte mine disposal demonstration project,
Louisville Gas & Electric/Combustion Engineering/University of Louisville,
testing at Paddy's Run, and the TVA/Aerospace Project at Shawnee) or
studies are being planned (e.g., LG&E dual alkali demonstration program),
more extensive field testing is needed. This would involve monitoring of
a number of representative full-scale systems not now studied via sludge
sampling, corings, and leachate wells. Field tests, particularly on
physical characteristics, should be done along with lab tests on a suite
of FGC wastes to "calibrate" the relation between lab and field tests
and to determine most effective compaction equipment and techniques.
6.2.2 Laboratory Test Procedures
Presently available leachate (elutriate) and toxicity test procedures
do not as yet confidently predict dissolution and toxicity of constituents
from FGC wastes. It is important to be able to perform tests in the
laboratory quickly and cost-effectively, which will characterize the
mobility and impact potential of FGC waste components. A number of
different procedures need to be developed and tested. The current
toxicant extraction procedure developed under RCRA needs to be tested
on its ability to characterize these properties in FGC wastes.
6.2.3 Ash/FGD Waste Co-disposal and Treatment Requirements
(a) Ash/FGD Waste Co-disposal
There is the distinct possibility that co-disposal of fly ash and
FGD waste as a mixture could have certain advantages over the disposal
of each separately. However, there is a lack of definitive data corre-
lating the levels of trace elements in the coal ash, fly ash (bottom ash),
6-8
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FGD waste, and ash/waste admixtures—either in the waste materials
or their leachates. More laboratory and field testing needs to be
carried out to determine such correlations if possible and identify/
assess pollutant mobility and toxicity,
(b) Treatment Requirements
Many fly ashes have appreciable pozzolanic activity and when admixed
with FGC waste (and possibly lime) will result in a material which hardens
with time. The extent of hardening reactions will be importantly dependent
upon the ash characteristics but may also depend on the FGD waste type
(sulfite vs. sulfate-rich), presence of high levels of TDS, and the
conditions of ash mixing (methods and relative quantities). This area
still remains an art, and more studies are needed to determine the
effects of different types of sludges and sludge/ash mixtures not only
on physical properties but also trace element mobility and toxicity.
6.2.A Physical Characterization of FGC Wastes
In light of the research needs identified in items (1) and (3)
above, appropriate physical characterization programs need to be under-
taken. This should include:
• Triaxial compression tests on a suite of FGC wastes and
mixtures (after various durations of curing) ,
• Consolidation tests to determine compressibility of wastes
and mixtures at various solids contents and in various
conditions (compacted, uncompacted),
• Further examination of the mixing characteristics of FGC
wastes, including examination of field deposits and ponds
for evidence of heterogeneity or stratification,
• A limited number of tests of the viscosity and pumping
characteristics of FGC wastes, and
6-9
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• Tests of dewatering characteristics of waste and waste mixtures,
including drying with underdrainage.
6.2.5 Trace Element Focus and Speciation
A number of trace elements which are present in FGC wastes are of
particular interest because they have been observed in waste liquors
at levels where a deleterious impact on plants or animals could be
possible in some situations. Certain of them, e.g., boron, fluoride
and molybdenum, have been studied in only a few samples. Others, such
as arsenic, antimony, selenium, manganese and cadmium, are difficult to
measure precisely and accurately at the levels at which they are present
in waste; this warrants a continuing focus. It is recommended that as
additional samples are obtained from FGC systems for characterization,
these trace elements in particular should be measured by techniques
offering state-of-the-art accuracy and precision in order to extend the
base of good data describing their occurrence in FGC wastes. That list
of key elements should be reevaluated from time to time by those assessing
impacts on plants and animals so that relatively expensive analytical
efforts are focused on the most important parameters.
Since the chemical form (cation, neutral, anion, and oxidation
state) of a pollutant affects its solubility, toxicity, and attenuation
by soil, it is recommended that studies of the oxidation state of trace
pollutants in FGC wastes and leachates be continued. The trace elements
arsenic, selenium, antimony, chromium, and boron either exhibit ampho-
terism or highly variable attenuation by different soils and would be
good candidates for speciation studies. In addition, selenium can
reportedly exist as the free element, and as such, its mobility has not
been well characterized.
6.2.6 Anaerobic-Induced Reduction Reactions/Volatile Species
Studies of the reduction reactions, e.g., Se to H_Se or As to
arsines that might occur in an anaerobic region of an FGC waste disposal
landfill or pond should be conducted. Such reactions are important
because they could produce gaseous products which could be transported
6-10
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into the atmosphere. The presence of volatile species (Hg, Se) initially
in the waste material needs to be determined in order to assess if
these species can be released to the atmosphere upon disposal of the
waste.
6.2.7 Radionuclides and Trace Organics
Although it is unlikely that radionuclides and polynuclear aromatic
(PNA) organic compounds will be present at levels that are of concern,
and even more unlikely that they will leach from the waste at substantial
9 1 0 7 *^ft
levels, measurements of radionuclide activity ( Ra, Pb, and U,
etc.) activity should be made for a representative set of FGC wastes
and their leachates. The wastes should be chosen to include those with
no ash, those with ash, treated materials and untreated materials. In
this regard, the results of ongoing PNA measurements at TRW should be
evaluated and additional measurements made, if necessary, to ascertain
if any potential problem could arise due to their presence.
6-11
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for U.S. EPA (Office of Research and Development),
Washington, D.C. , April 1978.
136. Head, Harlan N., "EPA Alkali Scrubbing Test Facility:
First Progress Report," Bechtel Corporation, EPA 600-
2-75-050, prepared for U.S. EPA (Office of Research and
Development), Washington, D.C., September 1975.
137. Borgwardt, R.H., "Sludge Oxidation in Limestone FGD
Scrubbers," U.S. EPA (Research Triangle Park),
EPA 600/7-77-061, June 1977.
138. Ness, H.M. and E.A.Sondreal, "Flue Gas Desulfurization
Using Fly Ash Alkali Derived from Western Coal,"
ERDA-EPA Subagreement No. 77BBV, January 1977.
139. VanNess, R.P., "Scrubber Testing and Waste Disposal
Studies' Interim Report," Louisville Gas and Electric
Company and Combustion Engineering, Inc., prepared for U.S.
EPA (Office of Research and Development), Washington, D.C.,
April 1978.
140. "Annual Environmental Analysis Report," prepared by Mitre
Corporation, Consad Research, Control Data Corporation,
and International Research and Technology; Report to ERDA,
under Contract EE-01-77-0135, September 1977.
141. Edwards, L.O., et al., "Calcium Sulfite Crystal Sizing Studies"
Radian Corporation, under EPA Contract 68-02-2608, Task 30,
Environmental Protection Agency, Washington, D.C., 20460,
Draft Report, December 1971.
142. M. Bartos and M. Palermo, "Physical and Engineering Properties
of Hazardous Industrial Wastes and Sludges," U.S. Army Corps
of Engineers, Waterways Experiment Station, EPA-600/2-77-139,
August 1977.
143. Dulin, J.M., and E.G. Rosar, "Sodium Scrubbing Wastes -
Insolubilization Processes Improve Disposal Options,"
Environmental Science and Technology, Vol. 9, Nov. 7, July 1975.
R-13
-------
144. Jones, B.F., et al., "Study of Non-Hazardous Wastes From
Coal-Fired Electric Utilities," by Radian Corporation to
EPA under Contract 68-02-2608. Draft Final Report,
December 1978.
145. Duvel, W.A., Jr., et al., "Laboratory Investigations:
Interaction of Acid Mine Drainage with FGD Sludge," by
Michael Baker, Jr., Inc. to EPA under Contract ME-76893.
Draft Report, May 1978.
146. Jones, B.F., et al., "Evaluation of the Physical Stability
and Leachability of Flue Gas Cleaning Wastes," by Radian
Corporation to Electric Power Research Institute, Palo Alto,
California, 94302, under Research Project 786-2, January 1979.
147. Lea, F.M. "The Chemistry of Cement and Concrete," 3rd Edition,
Chemical Publishing Company, Inc., 1971, p. 480.
R-14
-------
INDEX
Aerospace Corporation
study on characterization and disposal of FGC wastes 2-35 to 2-37
Alkaline fly ash scrubbing 2-9, 2-10, 2-13
Ammonium water scrubbing 2-9, 2-10, 2-15
Angle of internal friction
see shear strength parameters
Aqueous carbonate process 2-20
Ash collection and net particulate emissions by state 2-2
Ash collection technology 2-1 to 2-7
electrostatic precipitators 2-4, 2-5
fabric filters 2-5,-26
mechanical collectors 2-4
wet scrubbers 2-6
Ash pond discharge
trace elements in 4-51, 4-88
ASTM Standards Methods of Test, physical properties 5-9
Atterberg limits tests 5-9
Atterberg limits values, FGC wastes 5-12, 5-14 to 5-15
Auburn University
thickeners and clarifiers 2-38, 2-39
Bergbau-Forschung/Foster Wheeler process 2-20
Boiler combustion zone injection system 2-17
Bottom ash
grain size distribution 5-11
handling see Vol. II
major constituents in 4-7
radionuclides in 4-42
trace elements in 4-27, 4-33 to 4-35
Calcium sulfate solubility - see ;also gypsum
mass balance in liquor and leachate 4-59
Catalytic/Westvaco dry activated carbon process 2-20
Centrifugation, factors affecting performance 2-28, 2-29
Chemical properties - see also FGC wastes,chemical properties
relationship to environmental impact 6-2
Citrate process 2-9, 2-10, 2-17 to 2-19
Coal
ash in 2-2, 2-3
consumption, regional and state 2-2, 2-3
heating value 2-2
radionuclides in 4-42
sulfur in 2-2, 3-2
trace metals in 4-32 to 4-35
Coal ash, trace elements in 4-24, 4-25
Coal cleaning, benefits 2-7
Coal-fired steam electric power plants, largest ash producing 2-3
1-1
-------
Coal/ash/sludge relationships 3-1, 3-2
FGD waste production as related to coal type 3-2
total FGC waste production as related to coal type 3-2
Coefficient of uniformity, FGC wastes, fly ash, and waste/
additive mixtures 5-12, 5-13
Compaction characteristics, effects of lime/fly ash addition
to FGC waste 5-21, 5-22, 5-23
Compaction test 5-9
field tests, FGC waste and fly ash 5-20, 5-24
laboratory tests, bottom ash and fly ash 5-20
Compaction/compression behavior, fly ash and FGC waste 5-20 to 5-24
Compressibility
effects of compaction on FGC wastes 5-24
effects of lime/fly ash addition to FGC wastes 5-24
FGC waste and fly ash 5-20
Compression index, FGC wastes and waste/additives
mixtures 5-24, 5-25
Consistency-water retention characteristics, FGC waste and
fly ash 5-14 to 5-15
Consolidation test 5-9
Consolidation tests, FGC wastes and waste/additive
mixtures 5-24
Crystalline forms of FGD wastes 2-24
Curing time, effects on strength of FGC waste/additive
mixtures 5-27, 5-29, 5-30, 5-31 to 5-34
Data gaps and research needs, physical properties of
FGC wastes 5-43 to 5-47
Dewaterability, parameters measuring 2^27
Dewatering characteristics, FGC wastes 5-24 to 5-26
Direct lime scrubbing 2-9, 2-10, 2-12
Direct limestone scrubbing 2-9, 2-10, 2-12
Direct limestone scrubbing, with forced oxidation 2-9. 2-in 2-33
Disposal modes for FGC wastes 3-12 to 3-14, 3-15, 3-16 '
Disposal of FGC wastes, Importance of disposal scenarios by
region 3-16
Dravo Corporation
FGC waste stabilization 3-11
high magnesium lime (Thiosorbic Lime) 2-13
Dry density, effects on shear strength of fly ash 5-26
Dry sorbent systems
chemical characteristics 4-18 to 4-20
test reactions 4-18
Dual alkali scrubbing 2-9, 2-10, 2-14
Durability, fly ash stabilized soil 5-41
Effective cohesion see shear strength parameters
Electric power plants, coal-fired steam
annual ash collection 2-3
annual coal consumption 2-3
1-2
-------
Electric Power Research Institute (EPRI) 1-2
FGC waste dewatering projects 2-34
Electrostatic precipitators, for ash collection 2-4, 2-5
Enrichment of elements
on fly ash 4-28 to 4-31
radionuclides (on fly ash) 4-42
Environment impacts, FGC waste properties and disposal mode 6-2
Environmental Protection Agency (EPA)
FGC waste dewatering project 2-34
particulates, specification 2-4
Envirotech Corporation, study of dewatering of FGC wastes 2-40
Erosion, of FGC wastes and fly ash 5-41 to 5-43
Extraction see FGC wastes, research needs, laboratory
test procedures, leaching
Extraction procedure, RCRA, data for FGC wastes 4-90 to 4-92
Fabric filters for ash collection 2-5, 2-6
FGC (Flue Gas Cleaning), waste generation over view 2-1 to 2-40
FGC wastes (see also FGD Wastes)
categories of 2-21 to 2-23
chemical characterization 4-1 to 4-96
bottom ash
major constituents in 4-7
radionuclides in 4-42
trace elements in 4-27, 4-33 to 4-35
coal
radionuclides in 4-42
trace elements in 4-38 to 4-&0
trace metals in 4-32
coal ash
leachates 4-50 to 4-52
trace elements in 4-53
dry sorbent, Nahcolite product composition 4-19
effect of stabilization on waste migration 4-72 to 4-82
leaching studies 4-83
RCRA extraction procedure 4-90 to 4-93
soil attenuation 4-82 to 4-93
weathering 4-89, 4-90
elutriates see FGC wastes and leachates
fly ash
concentration trends with particle size 4-29
major components in 4-5, 4-7
pond discharges, chemicals in 4-51
radionuclides 4-42
trace elements 4-27 to 4-29, 4-33 to 4-35
leachates
composition 4-55 to 4-58
ash 4-56, 4-60 to 4-62
gypsum solubility 4-59
with and without ash 4-56, 4-60 to 4-62
composition vs waste liquor 4-55 to 4-57
1-3
-------
FGC wastes (continued)
concentration of majors vs pore volume displacement 4-67, 4-68
forced oxidized waste (Shawnee) 4-68, 4-69
Four Corners waste 4-67, 4-69
IUCS shake test of treated FGC waste 4-78
Shawnee waste ponds 4-79, 4-81
leaching behavior 4-46 to 4-50
research studies, overview and by agency 4-2, 4-3
trace elements, coal ash 4-53
trace elements equilibrium concentration 4-65
unstabilized wastes 4-20 to 4-22
physical characteristics
bottom ash, grain size 5-11
FGD wastes, with and without ash
coefficient of uniformity 5-12, 5-13
compaction characteristics 5-21, 5-22, 5-23
compression index 5-24, 5-25
grain size distribution 5-12, 5-13
handling and disposal 5-2 to 5-7
long-term stability 5-4, 5-5
placement and filling characteristics 5-3, 5-4
pollutant mobility 5-5, 5-6
permeability 5-36 to 5-40
coefficients of 5-38
physical tests, status of, summary 5-7 to 5-9
shear strength 5-27, 5-28
specific gravity 5-10, 5-12, 5-13
unconfined compressive strength 5-27, 5-29, 5-31 to 5-34
viscosity vs solids content 5-17 to 5-20
weathering, effect on 5-40 to 5-43
fly ash
compaction/compression behavior 5-20 to 5-24
consistency/water retention 5-14, 5-15
grain size distribution 5-10, 5-11, 5-12
permeability (of mass) 5-36
viscosity vs solids content 5-17, 5-19
weathering, effect on 5-40 to 5-43
production 3-1 to 3-5
projections of coal ash and FGD waste generation by
Federal region 3-3
projections of coal ash and FGD waste generation by
utility and industrial source 3-4
related to coal type 3-2
properties of, affecting handling 6-6
properties of, effects on land disposal 6-1 to 6-5
variables and the environment 6-4
relationship to placement and filling operation 5-3, 5-4
research needs 6-5 to 6-11
ash/FGD codisposal 6-8, 6-9
field data 6-7
laboratory test procedures (leaching) 6-8
radionuclides 6-11
1-4
-------
FGC wastes (continued)
reduction reaction/anaerobic 6-10
trace element focus and speciation 6-10
unstabilized FGC wastes 4-52 to 4-72
waste liquors
chemicals in 4-55 to 4-58
chemicals vs coal origin 4-44
major constituents 4-13 to 4-17
trace elements in 4-33 to 4-35
vs in coal 4-37
waste solids, major components 4-10, 4-11
trace elements 4-32 to 4-35, 4-37
FGD systems
commercial operation (1979) 2-9
commercial operation (to 1982) 2-10
FGD technology 2-7 to 2-41
dry processes 2-15 to 2-17, 2-20, 2-21
wet processes, scrubbing 2-8 to 2-15
alkaline ash 2-12
ammonia 2-15
direct lime 2-12, 2-13
direct limestone 2-12, 2-13
dual alkali 2-14
limestone, forced oxidation 2-13
sodium 2-14, 2-15
FGD wastes feee also FGC wastes )
crystal morphology, factors affecting 2-24
dewatering 2-23 to 2-39
chemical and physical properties affecting 2-25, 2-27
effect of fly ash on 2-37 to 2-39
employing filters and centrifuges 2-30
EPA and EPRI sponsored projects 2-34
practices, utility scrubbers 2-26
R&D studies 2-35 to 2-40
Aerospace Corporation 2-35
Auburn University
Envirotech Corporation 2-40
Radian Corporation 2-40
quantity generated 3-3
scrubbing process vs waste type 3-4
stabilization see treatment processes
treatment processes 3-7 to 3-12
effect on 3-5
inorganic precipitation 3-10
lime (cement) based 3-6, 3-7
organic polymer impregnation/encapsulation 3-10
self-handening 3-8
silica based 3-8, 3-9
thermoplastic impregnation/encapsulation 3-9
types vs disposal 3-15
typical disposal in EPA regions 3-16
1-5
-------
Filtration and centrifugation
FGC waste properties affecting equipment design 2-28
performance of installations 2-30
Flue gas injection system 2-16
Fly ash (see also FGC wastes, chemical and physical properties)
collectors, efficiency, specifications 2-4
compaction/compression behavior 5-20 to 5-24
consistency/water retention 5-14, 5-15
grain size distribution 5-10, 5-11, 5-12
permeability (of mass) 5-36
specific gravity 5-10, 5-12
viscosity vs solids content 5-17, 5-19
weathering 5-40 to 5-43
Fly ash collection systems, criteria for 2-4
Four corners
coal ash generated 2-3
coal consumption 2-3
FGC wastes, chemical characterization 4-67, 4-69
Freezing and thawing, effects on physical properties of FGC waste
deposits 5-39, 5-41, 5-42
Freeze-thaw and wet-dry cycles effects, data gaps and research
needs 5-44
Gaseous species product from FGC wastes research needs 4-96
Grain size analysis test 5-9
Grain size distribution
bottom ash 5-11
FGC wastes 5-12, 5-13
FGC waste/fly ash and waste/lime/fly ash mixtures 5-12, 5-13
fly ash 5-10, 5-11, 5-12
Gypsum solubility, waste liquors and leachates 4-59
Handling and disposal, FGC waste 5-1 to 5-7
Hydration forms of FGD wastes 2-21, 2-22
Hydrologic characteristics and soil attenuation studies, data gaps
and research needs 5-46
Index properties, fly ash and FGC wastes 5-10 to 5-13
Inorganic precipitation, stabilization by 3-7, 3-10 to 3-11
Laboratory and field compaction tests, data gaps and research
needs 5-44 to 5-45
Laboratory and field permeability data, data gaps and
research needs 5-4"*
Leachate, FGC wastes (see also FGC wastes, chemical characterization)
FGD waste with/without ash 5-22
fly ash 4-56, 4-58, 4-59, 4-60, 4-62, 4-66
leachate vs liquor composition 4-82, 4-83
Leaching
relationship to waste 6-2
research needs/lab test procedures 6-8
Lime, trace elements in 4-33
Lime scrubbing 2-9 to 2-15
1-6
-------
Lime (cement) based stabilization 4-6 to 3-8
Limestone, trace elements in 4-34 to 4-35
Limestone forced oxidation scrubbing 2-9 to 2-14
Limestone scrubbing 2-9 to 2-14
Liquefaction, FGC wastes 5-27, 5-34 to 5-35
Liquid limit test, as an index to viscosity 5-18
Liquid limits values, FGC wastes 5-12, 5-14 to 5-15
Liquors, FGD waste
chemicals in 4-55 to 4-58
chemicals vs coal origin 4-44
trace elements in 4-33 to 4-35
trace elements in vs in coal 4-32, 4-37 to 4-40
Long-term stability of FGC wastes 5-4 to 5-5
Louisville Gas & Electric Company (LG&E), EPA Cane Run study 5-31 to 5-34
Magnesium oxide process 2-9, 2-10, 2-18
Major components
bottom ash 4-7
FGD wastes liquor 4-14
FGD wastes solids 4-10, 4-11
fly ash 4-5, 4-7
leachates 4-60 to 4-62
Maximum dry density (see moisture-density paramters)
Mechanical collectors, ash collection 2-4
Mixing characteristics, data gaps and research needs 5-46
Moisture-density parameters,standard ASTM compaction test
FGC wastes and waste/additive mixtures 5-21, 5-22, 5-23
fly ash 5-20
Natural gas
ash in 2-2
consumption of 2-2
heating value 2-2
Oil
ash in 2-2
consumption of 2-2
heating value 2-2
sulfur in 2-2
Optimum water content see moisture-density parameters
Organic polymer impregnation/encapsulization. stabilization by 3-7, 3-10
Organics, trace
FGD waste 4-43, 4-96, 6-11
fly ash 4-43
Paddy's Run, FGC wastes generated at
chemical characterization 4-2, 4-3, 4-9, 4-10, 4-57, 4-63
coal ash, generated 2-3
coal consumption 2-3
dewatering 2-30
physical properties 4-59, 4-61, 5-12, 5-17, 5-22, 5-25, 5-28, 5-29, 5-38
Particle size distribution see grain size distribution
1-7
-------
Particulate emission standards, EPA 2-4
Particulate emissions (net) by state 2-2
Permeability
additives, effects on permeability of FGC wastes 5-37
Aerospace Corp. tests on unstabilized and stabilized FGC wastes 5-37
FGC wastes, field values vs laboratory values 5-36
FGC wastes, typical values 5-38
fly ash 5-36
IUCS tests on waste/lime/fly ash mixtures 5-40
LG&E Cane Run study, field values vs_ laboratory values for
FGC wastes 5-32, 5-33, 5-39, 5-40
Waterways Experiment Station,tests on unstabilized and stabilized
FGC wastes 5-37
vs solids content 5-37
Permeability test 5-9
Physical characterization of FGC wastes 5-1 to 5-47
available information 5-9 to 5-43
critical properties 5-1 to 5-7
data gaps and research needs 5-43 to 5-47
status of physical testino 5-7 to 5-9
Physical properties of FGC wastes (see also FGC wastes, physical properties)
critical properties for handling and disposal 5-1 to 5-7
handling characteristics 5-2 to 5-3
long-term stability in fills 5-4 to 5-5
placement/filline characteristics 5-3 to 5t-4
pollutant mobility 5-5 to 5-7
Physical testing of FGC wastes
status of 5-7 to 5-9
summary of previous investigations 5-8
Placement and filling characteristics of FGC wastes 5-3 to 5-4
Placement conditions, effects on mass permeability of FGC waste deposits 5-39
Plastic limits values, FGC wastes 5-12, 5-14 to 5-15
Plasticity, FGC wastes 5-14 to 5-15
Pollutant mobility in FGC wastes 5-5 to 5-7
Pond (test) leachates, TVA, composition 4-79, 4-81
Pore volume displacement
composition of leachate, relation to liquor 4-67 to 4-69
varying of leachate composition with 4-74
Pozzolanic cementation, effects on shear strength of fly ash 5-26
Production trends and handling options 3-1 to 3-17
coal/waste relationships 3-1
projected generation and trends 3-1 to 3-5
utilization and disposal options 3-12 to 3-17
waste stabilization technology 3-5 to 3-12
Pumping tests, viscosity of FGC waste/additive slurries 5-15 to 5-16,
5-18 to 5-20
1-8
-------
Radian Corporation, study of improvement of dewaterability 2-40, 2-41
Radionuclides
bottom ash 4-41 to 4-43
coal 4-42
coal ash 4-41 to 4-43
FGC waste 4-96
FGD waste 4-43
fly ash 4-41 to 4-42
sedimentary rocks 4-42
Resource Conservation and Recovery Act (RCRA) extraction procedure 4-90 to 4-93
Research needs
anaerobic-induced reduction reactions/volatile species 6-10, 6-11
ash/FGD waste codisposal and treatment requirements 6-8, 6-9
chemical and physical characterization of FGC wastes 6-1 to 6-11
file data on chemical and physical propertids of FGC waste and
waste/additive mixtures 6-7, 6-8
laboratory test procedures 6-8
physical characterization of FGC wastes 6-9, 6-10
radionuclides and trace organics 6-11
trace element focus and separation 6-10
'Sanrole disturbance
effects on permeability of FGC waste samples 5-39
effects on unconfined compressive strength of FGC waste samples 5-31
Scrubber liquor, major and trace elements in 4-33 to 4-35
Scrubbing processes
non-recovery, dry
boiler combustion zone injection system 2-17
flue gas injection system 2-16
spray drier systems 2-15, 2-16
non-recovery, wet
liquid waste systems
ammonium water scrubbing 2-15
sodium scrubbing 2-14
solid waste systems
alkaline fly ash scrubbing 2-13
direct lime scrubbing 2-12
direct limestone scrubbing 2-12
direct limestone scrubbing with forced oxydation 2-13
dual alkali scrubbing 2-14
recovery, dry
aqueous carbonate process 2-20
Bergbau-Forschung/Foster Wheeler process 2-20
Catalytic/Westvaco dry activated carbon process 2-20
Shell/UOP copper oxide absorption process 2-20
recovery, wet
citrate process 2-18
magnesium oxide process 2-18
Wellman-Lord process 2-18
Self-hardening stabilization 3-7, 3-8
Shake test, IUCS, FGC waste 4-78
1-9
-------
Shawnee Test Facility
coal,consumption 2-3
coal ash, generated 2-3
FGC wastes
chemical characterization 4-2, 4-10, 4-56, 4-68, 4-69, 4-79, 4-83
dewatering 2-30
physical properties 4-49, 4-60, 5-17, 5-23, 5-25, 5-30, 5-35
pond leachates/total dissolved solids and major species 4-79, 4-81
Shear strength, fly ash and FGC waste 5-26 to 5-36
Shear strength parameters, FGC wastes, fly ash and waste/additive
mixtures 5-26, 5-27, 5-28
Shell/UOP copper oxide adsorption process 2-20
Silicate-based stabilization 3-7, 3-8 to 3-9
Sodium scrubbing 2-9 to 2-11, 2-14
Soil attenuation
mechanism 5-5 to 5-7
studies 4-82 to 4-87, 5-46
Soil classification, Unified system 5-9
Speciation of trace elements in FGC wastes 4-87, 4-94, 4-95
Specific gravity
effects of drying temperature on 5-13
FGC waste 5-10, 5-12, 5-13
fly ash 5-10, 5-12
waste/fly ash and waste/lime/fly ash mixtures 5-12, 5-13
Specific gravity test 5-9
Spray dryer systems 2-15, 2-16
Stabilization of FGC wastes 3-11 to 3-12
Steam electric power plants, largest coal-fired 2-3
Sulfur, in coal and oil 2-2
Thermoplastic impregnation/encapsulization, stabilization by 3-7, 3-9 to 3-10
Thixotropy, FGC wastes 5-35 to 5-36
Trace elements, FGC wastes
bottom ash 4-27, 4-33 to 4-35
coal ash 4-22, 4-24 to 4-26, 4-33 to 4-35
fly ash 4-27 to 4-29, 4-33 to 4-35
research needs 6-10 *
speciation 4-87, 4-94, 4-95, 6-10
waste liquors 4-38, 4-44
waste solids 4-32 to 4-35, 4-37
Trace organics
coal 4-43
FGD wastes 4-43
fly ash 4-43
research needs 4-96, 6-11
Triaxial compression test 5-9
Triaxial compression test data, see shear strength parameters
Triaxial compression tests and consolidation tests, data gaps and
research needs 5-45
1-10
-------
Unconflned compression test 5-9
Unconfined compressive strength
FGC waste and waste additive mixtures 5-27, 5-29, 5-30
freezing, effects on unconfined compressive strength 5-31
LG&E Cane Run study, field vs laboratory values for FGC wastes 5-31 to 5-34
Utilization of FGC wastes 3-14 to 3-17 ( see also Vol. 4)
Vacuum filtration, factors affecting performance 2-28
Vane shear strength, LG&E Cane Run study 5-31
Viscosity
FGC wastes and waste/additive mixtures 5-16 to 5-19
fly ash 5-15, 5-19
Viscosity and pumping characteristics, data gaps and research needs 5-47
Viscosity-solids content relationships fly ash and FGC wastes 5-17, 5-19
Waste stabilization processes 3-5 to 3-11
inorganic precipitation 3-7, 3-10 to 3-11
lime (cement) -based 3-6 to 3-8
organic polymer impregnation/encapsulization 3-7, 3-10
self-hardening 3-7, 3-8
silicate based 3-7, 3-8 to 3-9
thermoplastic impregnation/encapsulization 3-7, 3-9 to 3-10
Waste stabilization technology 3-5 to 3-12
FGC waste stabilization 3-11 to 3-12
overview of processes 3-5 to 3-11
Weathering fly ash and FGC waste 5-40 to 5-43
Wellman-Lord process 2-9, 2-10, 2-17 to 2-19
Wet scrubbers, ash collection 2-6
Wetting and drying, effects on stability of FGC wastes 5-42
1-11
-------
TECHNICAL REPORT DATA
IP/MK read Imttmctiont on the nvene before completing)
1. REPORT NO.
EPA-600/7-80-012C
2.
3. RECIPIENT'S ACCESSION-NO.
4 TITLE AND SUBTITLE Waste and Water Management for
Conventional Coal Combustion Assessment Report--
1979; Volume ffl. Generation and Characterization of
FGC Wastes
6. REPORT DATE
March 1980
6. PERFORMING ORGANIZATION CODE
.santhanam,R.R.Lunt,C.B.Cooper,
D.E.Klimschmidt.I.Bodek, and W.A.Tucker (ADL);
and G.R.Ullrich (Univ of Louis villeT '
B. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc.
20 Acorn Park
Cambridge, Massachusetts 02140
10. PROGRAM ELEMENT NO.
EHE624A
11. CONTRACT/GRANT NO.
68-02-2654
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600 A3
is. SUPPLEMENTARY NOTES T£RL-RTP project officer is Julian W. Jones, Mail Drop 61, 919/
541-2489.
. ABSTRACT
repOrt ? ^e third of five volumes , focuses on trends in generation of
coal ash and FGD wastes (together comprising FGC wastes) and the characteristics
of these wastes. With increasing use of coal, the generation of FGC wastes is expec-
ted to increase dramatically: to about 115 million tons of coal ash and 38. 7 million
tons of FGD wastes by the year 2000. Most of these wastes will be disposed of on
land. Data on the chemical characteristics of fly ash, bottom ash, and both treated
and untreated FGD wastes in this report include data on principal components , com-
position ranges for trace components , and leaching behavior. Based on the charac-
teristics of FGD wastes, a categorization of these wastes is also presented. Ongoing
programs on chemical characterization are assessed. The fundamental physical pro-
perties of FGC wastes are density, size, and crystal morphology. The critical phy-
sical and engineering properties are those relating to handling characteristics , pla-
cement and filling characteristics, long-term stability, and pollutant mobility. The
report includes information on index properties, consistency-water retention, vis-
cosity vs. water content, compaction/compression behavior, dewatering character-
istics, strength parameters , permeability, and weathering characteristics. Further
efforts in this area are recommended: key is data from full-scale disposal sites.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Coal
Combustion
Assessments
Management
Water
Flue Gases
Cleaning
Analyzing
Properties
Ashes
Pollution Control
Stationary Sources
Flue Gas Cleaning
Characterization
Waste Generation
13B
21D
21B
14B
05A
07B
13H
18. DISTRIBUTION STATEMENT
Release to Public
IB. SECURITY CLASS (ThUKtport)
Unclassified
21. NO. OF PAGES
257
20. SECURITY CLASS (TMSpag€)
Unclassified
22. PRICE
CPA Perm 2220-1 (t-73)
1-12
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