EPA-650/2-74-033
May 1974
Environmental Protection Technology Series
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EPA-650/2-74-033
SOLID WASTE DISPOSAL
FINAL REPORT
by
Nancy P. Phillips and R. Murray Wells
Radian Corporation
8500 Shoal Creek Boulevard
Austin, Texas 78766
Contract No. 68-02-1319 (Task 4)
ROAPNo. 21ADE-10
Program Element No. 1AB013
EPA Project Officer: Charles Chatlynne
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, N. C. 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
May 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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ABSTRACT
This document presents a discussion of available
disposal technologies for nine solid wastes destined for
land disposal. The purpose of the investigation was to
examine the potential applicability of these already developed
technologies to the disposal of sludges generated by flue
gas desulfurization systems. For each material of interest,
including scrubber sludge, the nature of the waste, traditional
disposal procedures, and related environmental effects are
described. Case studies were examined in order to quantify
the problem as much as possible; these results are included
in the report.
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TABLE OF CONTENTS
Page
CONCLUSIONS
EXECUTIVE SUMMARY
REPORT
1.0 INTRODUCTION 1
2.0 MUNICIPAL WASTE DISPOSAL 4
2.1 Nature of Municipal Waste 4
2.2 Disposal of Municipal Wastes 7
2.2.1 Sanitary Landfill 8
2.2.2 Composting 11
2.2.3 Incineration 11
2.2.4 Pyrolysis 13
2.2.5 Resource Recovery 14
2.3 Case Studies of Municipal Waste Disposal 16
2.3.1 Sonoma County Central Solid Waste Disposal Site... 16
2.3.2 Sonoma County Refuse Test Cells 20
3.0 SEWAGE SLUDGE DISPOSAL 32
3.1 Nature of Sewage Sludge 32
3.2 Pre-Disposal Treatment and Handling 37
3.2.1 Sewage Sludge Dewatering 37
3.2.2 Sewage Sludge Handling 40
3.3 Disposal Techniques 42
3.4 Case Study - The Prairie Plan 45
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TABLE OF CONTENTS CONTINUED
4.0 GENERAL ORE WASTES 54
4.1 Nature of the Waste 54
4.2 Disposal Methods 55
5.0 CULM PILES 59
5.1 Nature of the Waste 60
5.2 Conventional Disposal Technology 64
5.2.1 Disposal Site 64
5.2.2 Disposal Procedures 64
5.2.3 Environmental Aspects of Culm Piles 68
5.3 Alternate Disposal Technologies 72
5.4 Case Studies - Culm Pile Reclamation 74
6.0 PHOSPHATE SLIMES 85
6.1 Phosphate Mining and Beneficiation 85
6.2 Nature of Phosphate Rock Slime 88
6.3 Phosphate Slime Disposal Techniques 91
6.3.1 Conventional Method 91
6.3.2 Alternate Disposal Methods 94
6.4 Environmental Aspects of Phosphate Slimes Disposal. 97
6.5 Case Study - Reclamation of Slimes Disposal Area... 99
7.0 TACONITE TAILINGS DISPOSAL 101
7.1 Nature of Taconite Tailings 101
7.2 Disposal Techniques 106
7.2.1 On-Land Disposal 106
7.2.2 Lake Disposal 108
7.3 Case Study - Erie Mining's Tailings Reclamation
Program 108
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TABLE OF CONTENTS CONTINUED
Page
8.0 GYPSUM FROM PHOSPHORIC ACID MANUFACTURE 118
8.1 Nature of By-Product Gypsum 121
8.1.1 Chemical and Physical Properties 121
8.1.2 Production Quantities of Waste Gypsum 125
8.2 Conventional Disposal Practices 126
8.2.1 Description of Methods 126
8.2.2 Environmental Aspects of Phosphogypsum Disposal.... 131
8 = 3 Alternate Disposal Methods 136
8.4 Case Study - Phosphogypsum Disposal 140
9.0 ACID MINE DRAINAGE SLUDGE 142
9.1 Nature of AMD Sludge 143
9.2 Disposal Techniques for AMD Sludge 146
9.2.1 AMD Sludge Conditioning 147
9.2.2 Dewatering Techniques 149
9.2.3 Sludge Handling 151
9.2.4 Ultimate Sludge Disposal 152
9. 3 Alternate Approaches 153
9.4 Case Studies - Consolidation Coal Company 155
9.4.1 Whetstone Portal Treatment Plant 156
9.4.2 Edgell Treatment Plant 159
9.4.3 Levi Moore Treatment Plant 161
10.0 COAL ASH 163
10.1 Nature of Coal Ash 163
10.1.1 Properties 163
10.1.2 Quantities 174
10.2 Disposal Technology 177
10.2.1 Ponding of Coal Ash 177
10.2.2 Landfill 182
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TABLE OF CONTENTS CONTINUED
Page
10.2.3 Deep Mine Disposal 183
10.2.4 Coal Ash Utilization 184
10.3 Case Study - Coal Ash Disposal At TVA's Widow
Creek 195
11.0 SCRUBBER SLUDGE 205
11.1 Nature of the Material 205
11.1.1 Chemical and Physical Properties of Scrubber
Sludge 206
11.1.2 Quantity of Sludge Production 210
11.2 Application of Conventional Disposal Techniques
to Scrubber Sludge 213
11.2.1 Ponding 215
11.2.1.1 Technical Aspects 215
11.2.1.2 Environmental Aspects 218
11.2.2 Disposal by Landfill 222
11.2.2.1 Technical Aspects of Landfilling Sludge 223
11.2.2.2 Environmental Aspects of Landfilling Sludge 234
11.3 Alternate Disposal Techniques 240
12.0 BIBLIOGRAPHY 247
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CONCLUSIONS
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CONCLUSIONS
The results of this case-study type of approach
to the problem of lime/limestone scrubber sludge disposal
are summarized below:
(1) Much of the technology already developed
for ponding of phosphate slimes, by-product
gypsum, taconite tailings, coal ash, and
acid mine drainage sludge is applicable
to scrubber sludge disposal by ponding.
(2) Technologies developed in the area of
land disposal of sewage sludge, coal
ash, and possibly acid mine drainage
sludge that is removed from sludge
ponds during desludging operations may
be applicable to scrubber sludge disposal,
particularly in cases where fixation
technology has been applied.
(3) Alternative disposal methods available
for scrubber sludge, including deep
mine disposal, strip-mined land reclama-
tion, and utilization, possess some degree
of potential. Comparable technologies in
these areas are now under study for AMD
sludge, coal ash, sewage sludge, and
by-product gypsum.
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RADIAN CORPORATION
(4) Sludge handling techniques currently in use
for by-product gypsum, acid mine drainage
sludge, and several other wastes included
in the present study can be applied to
handling scrubber sludge.
(5) Potential leachate problems associated
with scrubber sludge disposal can be
further defined by results of several
in-progress investigations described
in this report.
(6) Reclamation of waste disposal areas is
being conducted by several industries
on a large scale. Techniques have been
developed, or are in the process of
development, for culm piles, taconite
tailings, phosphate slimes, and sanitary
landfills. Much of the experience gained
in these projects may be applicable to
reclamation of scrubber sludge ponds or
landfills. Future work is needed in this
area.
(7) Based on presently available data, there
are no insurmountable technological
problems in disposing of scrubber sludge
in an environmentally acceptable manner.
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EXECUTIVE SUMMARY
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EXECUTIVE SUMMARY
1.0 INTRODUCTION
Disposal of sulfur oxide sludges generated by flue
gas desulfurization systems is currently under investigation
by the Environmental Protection Agency and the utility
industry. Radian Corporation, under contract to EPA, has
been involved in the preparation of several documents dealing
with this issue (Contract Nos. 68-02-1319, Task No. 1,
"Information on the Status of Lime/Limestone Sludge Handling";
68-02-0046, Task No. 12, "Utilization of Stack Gas Cleaning
Equipment in Ohio"; and 68-01-2008, "Prepare a Technology
Transfer Process Design Manual"). The reports generated
from the last two programs listed are to be released shortly.
During the course of those studies, the magnitude of the problem
faced by the electric utility industry was estimated and
briefly compared to similar waste disposal problems encountered
in other areas. This document is an expansion of the comparison
made at that time.
The purpose of the present investigation is to
identify available technologies developed in other industries
that may be applicable to scrubber sludge disposal. The
general nature of the problem, disposal technologies, and
environmental aspects for each of nine solid wastes destined
for land disposal are presented in this document. Those
aspects potentially applicable to the present problem were
emphasized. The quantities, composition, and typical disposal
methods for each material included in this study are summarized
in Table I.
A case study approach was employed to obtain information
related to specific problems encountered, ability of the technique
to meet local environmental standards, and alternatives or
modifications under consideration if the current method has
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TABLE I
SUMMARY OF WASTES AND DISPOSAL TECHNIQUES
Waste
Municipal
Refuse
Typical
Composition
Paper, plastic, glass,
wood, metal, textiles,
garbage etc.
Annual Production
Metric Tons
Disposal Technique
360,000,000 (1973)1'2 Landfllllng, composting,
Incineration, pyrolysls,
resource recovery
Environmental Impact
Aspects Potentially
Related To
Scrubber Sludge Disposal
Potential surface and ground- Leachate Control
water pollution; air pollu-
tion; odor, subsidence; fire;
health hazards In worst cases
Sewage
Sludge
NJ
i
General
ore Wastes
0.1- 15% solids
Typical solids analysis,!
(digested sludge)3:
Volatile matter 45-60
Ash
Insoluble ash
Creases, fats
Protein
55,000,000 (1980)'
NH6N03
P205
KjO
S10,
Fe
Cellulose
40-45
35-50
3-17
16-21
1-4
0.5-3.7
0-4
20-22
5.4
10-13
Rock wastes from
mining operations
1.3 billion*
Land disposal,"composting,
Incineration, pyrolysls,
permanent lagoonlng, ocean
dumping
Surface piles, landfill
Potential surface and ground- Application to reclama-
water pollution; air pollu- tlon of acid mine spoil;
tlon (Incineration) natural leachate fil-
tering system; sludge
handling and transport.
Potential water pollution;
aesthetic considerations
General siting considera-
tions
Culm Piles
Waste coal, slate,
bone, carbonaceous
and pytitle shales,
clay, trace metals
91,000.000 metric
tons or bituminous
waste (1969)5
Surface piles
Surface and groundwater
pollution (acid drainage
and slltatlon) ; air pol-
lution from spontaneous
combustion (SOj, H2S, CO,
partlculates)
Reclamation technique
and economics, espe-
cially use of fly ash
and AMD sludge as soil
conditioners and neutra-
lizing agents.
Phosphate
Slimes
4-67. solids
Solids analysis,
2
CaO
MgO
CO,
LOI7
BFL
8
9-17
31-46
3-7
6-18
14-23
1-2
0-1
0-1
9-16
19-37
38,000,000*
Ponding
Potential surface and
groundwater pollution;
possible permanent bogs
(final settled solids
content 307.) ; potential
dam failures.
Dewaterlng techniques;
reclamation procedures
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JAttlE I (Cont.)
SUMMARY OF VASTCS ANU DISPOSAL TECHNIQUES
I
LO
Waste
Taconltc
Tailings
Gypsum
from
Phosphoric
Acid Manu-
facture
Typical
Composition
6-407. solids
Solids analysis,
Oxygen
Iron
Silicon
Aluninum
Calcium
Magnesium
Manganese
Titanium
Phosphorus
Sodium
Potassium
Sul fur
Carbon
Hydrogen
Lead
Zinc
Nickel
Copper
Molybdenum
Vanadium
Cobalt
Chromium
Cadmium
10
7. :
46.60
14.93
33.03
0.35
1.67
2.55
0.37
0.030
0.026
0.20
0.08
0.03
0.11
0.10
0.005
0.004
0.002
0.004
<0.001
«0.00l
0.002
0.004
0.0003
65-827. solldn as dis-
charged from filter12,
settles to 85-90%
solid13
Solids analysis,
CaSCW'20
CaS04-2H20
Ca3(P04)2
CaF2
S102
Fe2°3
A1203
Other impurities
XU:
Annual Production
Metric Tons
55.000.00011
(dry basta)
25.000.00013
(dry basis)
Negligible
92.84
2.25
2.66
0.95
0.01
0.79
0.50
Plspos.il Technique
Ponding, liike disposal
Environmental Impact
Potential surface and
groundwater pollution
Aspects Potentially
Related To
Scrubber Sludge Disposal
Reclamation techniques
for tailings ponds;
handling and transport
of slurry
Ponding, surface piles,
ocean disposal
Surface and groundwater
pollution; air pollu-
tion (fluoride)
Dewaterlng techniques;
utilization; pond
operation
Acid Mine
Drainage
Sludge
1-57. solids
8,200,00015
Ponding
.15.
Solids analysis, X1
CaSOA. 40
3
20
1
Water pollution potential;
possible permanent bogs
Sludge handling; pond
operation; dewaterlng
technology
CaO
S102
MgO
l2
Tri
ce Metals
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TABLE I (Cent.)
SUMMARY OF WASTES AND DISPOSAL TECHNIQUES
Waste
Coal Ash
Typical
Composition
Annual Production
Metric Tuns Disu
Ash analysis, X16: 38,900,000 (1971)17 Ponding,
Si02
A1203
Fe,03
CaO
K20
MgO
Na20
Ti02
so3
C and volatiles
B
P 0
U + Th
zation
30-50
20-30
10-30
1.5-4.7
1.0-3.0
0.5-1.1
0.4-1.5
0.4-1.3
0.2-3.2
0.1-4.0
0.1-0.6
.01-0.3
0.0-0.1
Disposal Technique
landfill, utill-
Erw Iron-Dental Impact
Potential surface and
groundwater pollution
Aspects Potentially
Related To
Scrubber Sludge Disposal
Potential water pollu-
tion problems, espe-
cially trace metals;
utilities previous
experiences' in disposal
procedures•
Scrubber
S ludge
Typical Limestone Scrub- 113,000,000 (1980)18 Ponding, landfill, possibly
her Sludge: (50% solids) deep mine disposal or utili-
H20 50% zation
CaS03-^H20 187.
CaS04-2H20 27.
CaC03 67.
Ash J 24%
Trace Metals
Potential surface and
groundwater pollution;
possible permanent bogs
2Excluslve of agricultural and mining wastes
-Personal communication, Norbert Schomaker, SHWRL, NERC, Cincinnati
^Source: EN-084
^Source: US-079
^Source: BU-086
^Source: BA-133
jLLoss on ignition
"Bone phosphate of lime
,20ne-third of matrix mined during 1970.
{^Source: RE-093
,,Based on 100 million
^Source: BO-095
,f807, disposed of in Florida.
resource: CO-072
,6Personal Communication, R. D. Hill, NERC. Cincinnati
,,Source: RO-093
JgSource: BR-118
I?"Sl?fi nnn1M5Sh;COn"lnf?8JSlud8e (50% sollds) • Based °" the following assumptions:
a) 116,000 MW of controlled generating capacity by 1980
75% of control by lime/limestone systems
Coal: 3%S; 12% ash
Plant: 6400 hr/yr: 0.4 kg coal/kw-hr
Scrubber: 85% S02 removal; 1.0 CaO/S02(inlet) mole ratio; 1.2 CaC03/so2 (inlet) mole ratio
Source: US-064
annual crude ore Pr°du=ti°". 25% iron content, 607. beneficiation
comn.unication, Mr. Stowalzer, U. S. Bur. Mines, Phosphate Commodity Office
a)
b)
c)
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proven inadequate. This type of approach was used in order
to quantify each problem as much as possible.
The general problem descriptions and case studies
are presented in Sections 2.0 through 10.0 in the Detailed
Report. Section 11.0 presents currently available data
concerning the nature of scrubber sludge and a discussion of
the applicability of disposal technologies developed by
other industries to scrubber sludge disposal. The conclusions
reached in this study are given in Section 12.0.
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2.0 MUNICIPAL WASTE DISPOSAL
Municipal refuse has traditionally been disposed
of by landfilling or open dumping. Alternate methods are now
required because of mounting tonnages of waste being produced,
decreased land availability, higher land costs, and increasing
public concern with environmental issues. Methods now in use
include sanitary landfill, incineration, pyrolysis, composting,
and resource recovery (recycling).
Landfill operations still constitute the major
form of municipal waste disposal. One source estimated that
over 90% of the nation's solid waste is disposed of in this
manner at -12,000 individual sites. The term sanitary landfill
is defined as "a method of disposing of refuse on land without
creating nuisances or hazards to public health or safety, by
utilizing the principles of engineering to confine the refuse
to the smallest practical area, to reduce it to the smallest
practical volume and to cover it with a layer of earth at the
conclusion of each day's operation, or at such more frequent
intervals as may be necessary". This type of operation should
not be confused with open dumping, a practice which involves
none of the above considerations and which is being prohibited
in an increasing number of communities.
Potential environmental hazards associated with a
sanitary landfill operation include groundwater contamination,
gas generation, odor, subsidence, fire, and health hazards.
Proper maintenance and operation of the landfill will effectively
prevent most of these.
Groundwater contamination by landfill leachate has
been the subject of numerous studies. Several experimental
studies were designed to determine quantities, qualities, and
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movement of leachate. In general, climate, temperature, age
of landfill, composition, and original water content are
chief factors affecting leachate characteristics. Prevention
of leachate problems is achieved by careful design in accordance
with the topography and hydrogeology of the area. Currently,
experimentation with sealing of landfills is being conducted;
entrapped leachate is collected and treated, if necessary.
This concept may become important in scrubber sludge disposal
if leachate is shown to pose a hazard.
The aspect of municipal waste disposal having
greatest relevance in the area of scrubber sludge disposal is
leachate formation, migration, and collection. Two case
studies were selected. The first is a full-scale landfill
located in Central Sonoma County, California, where 650 metric
tons of refuse are handled daily. The design feature of interest
is the leachate control system which entails migration to the
surface and subsequent evaporation or recycle through the
refuse. Surface drainage is intercepted and diverted around
the active portion of the site. County officials feel that
this system of refuse disposal/leachate control adequately
complies with all existing water quality standards.
Adjacent to the full-scale landfill at Sonoma
County, a demonstration project is underway to investigate
stabilization of refuse. The study is funded principally
by EPA under Demonstration Grant No. G06-EC-00351 of the
Office of Solid Waste Management Programs. Partial funding
of the three-year project is provided by the County of Sonoma.
The purpose of the investigation is two-fold:
(1) To investigate the stabilization of refuse
in a sanitary landfill by analyzing leachate,
gas, temperature, and settlement parameters.
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(2) To determine the effect on refuse stabiliza-
tion of applying excess water, septic tank
pumpings, and recycled leachate to a sanitary
landfill under various operational modes.
Five clay-lined, earthen test cells were constructed
and are being operated under different sets of leachate
generating conditions. Results to date indicate that the
earth cells are effective in preventing water pollution from
leachate.
This work suggests that techniques for leachate
control which have been developed for municipal refuse
disposal would be applicable to prevention of leaching of
undesirable components from sludge which is disposed of in a
landfill operation, assuming that further characterization
of dewatered sludge shows that it is not subject to regaining
moisture. Even if recycling of leachate is not feasible,
the technology for leachate collection and landfill sealing
would be applicable.
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3.0 SEWAGE SLUDGE DISPOSAL
The disposal technology for sewage sludge having the
greatest potential application to scrubber sludge disposal
is reclamation of devastated land. The best example is the
disposal system used by Chicago since 1971. The Prairie Plan
involves barging 6,800 metric tons of digested sludge, at 3-5%
solids, 300 kilometers from the treatment plant to southern
Illinois. The sludge is spray-irrigated onto the fields at
an appropriate irrigation time after temporary lagooning to
reduce ammonia nitrogen and to allow aging.
A natural filtering system is relied upon to insure
that water reaching surrounding streams is of high quality.
As the sludge filters down through the crop roots, bacteria
convert sludge nutrients to forms usable by the plant. Remaining
liquor continues to pass downward until an impervious stratum
is reached, at which point horizontal movement occurs. Farm
fields are surrounded by hedge rows. Any nutrients seeping
out of the field will be taken up by their extensive root
systems. Monitored field detention basins collect all surface
runoff. If not polluted, the water is released to a nearby
stream. However, if quality is poor, then the entire contents
are recycled through the field. Additional protection is
provided by lines of hedges and trees along banks and streams.
All streams entering and leaving the 7,000-acre (2,800 hectare)
tract are monitored. Additional monitoring stations including
reservoirs, springs, and wells are also checked regularly.
Although no results are yet available from the
water monitoring program at the large scale site, a small
demonstration study to investigate the nature of leachate from
sewage sludge application to highly acidic spoil was conducted
in 1966. Sponsors were the Metropolitan Sanitary District of
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Greater Chicago and the U. S. Forest Service. The results
indicated a need to apply sewage sludge at a rate great
enough to effectively neutralize plot acidity in order to
prevent dissolution of metals added with the sludge.
Disposal of sewage sludge by application to acid
mine spoil thus far appears to be a promising approach to
this problem. Results indicate that crop yields are markedly
improved, that acid stream pollution can be effectively
reduced, and that the devasted land can be returned to productive
use. Future results will provide more detailed insight into
potential contamination of groundwater by trace metals released
from the sewage sludge itself.
The applicability of the technology developed during
these particular projects to scrubber sludge disposal lies in
the potential application of scrubber sludge to acid mine
spoil as a neutralizing agent and possibly a soil conditioner.
Additional information on this subject is presented in the
sections on culm bank reclamation with fly ash and acid mine
drainage sludge. Also of significance in this study is the
extent of effectiveness of a natural filter system to remove
potentially contaminating species from leachate (in this case,
the irrigating water) prior to reaching an aquifer system.
Another aspect of sewage sludge disposal potentially
applicable to scrubber sludge is transport technology (piping
and barging).
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4.0 GENERAL ORE WASTES
The waste material included as general ore wastes
includes both overburden and tunnel rock produced by the mining
industry, exclusive of coal and other fuels. Tailings, the
finely ground rock removed during milling operations, are not
included in this category.
Disposal practices for rock mining wastes are not
very sophisticated. There are three options normally available.
Of 3.0 billion metric tons of overburden produced by the total
surface mining industry in 1966, much was simply redeposited
in the mined-out areas. Approximately 10% was used in the
construction of dams for tailings ponds. The third alternative
involved just heaping the waste in piles near the mine; these
piles are referred to as waste banks or surface piles.
The pertinent environmental aspects associated with
these disposal practices include loss of stability in the
piles, reclamation, and erosion. The biggest problem thus
far is the aesthetic issue. Contamination of groundwater by
leachate has not been studied. One source reported that the
soluble components of waste rock are a minor source of trouble,
the only problem being with heavy metals. If the dump is
properly sited and managed, however, any metal dissolution can
be effectively prevented from leaving the immediate area. The
chief problem in potential surface water contamination is with
siltation and turbidity.
For aesthetic considerations, the pile should be
located away from the main lines of traffic and below the
horizon. The area should be constructed and contoured so
that it blends in with the scenery as much as possible.
Vegetation should be as complete and as rapid as possible.
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Reclamation also prevents wind and water erosion and provides
stabilization. Site surveys prior to placement of the
refuse will locate near-surface water tables and permeable
soil areas, the combination of which should be avoided to
prevent groundwater contamination.
Because of the lack of any highly developed technology
for disposal of this waste, no case study is presented.
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5.0 CULM PILES
The disposal method for coarse preparation coal plant
waste traditionally involves transport to a disposal site where
the material is spread and compacted to achieve stability. The
piles are referred to as culm piles (or banks), gob piles, or
refuse banks. Reclamation techniques are now commonly practiced.
Procedures and costs incurred by the coal-mining industry have
been surveyed by the Bureau of Mines. The results showed that
total costs for reclamation ranged from $1,800 to more $15,000
per acre. Refuse preparation costs ranged from $772 to $5,550
per acre. Soil covering and planting costs ranged from $1,083
to $5,086 per acre. Normal reclamation techniques consist of
spreading and compaction, soil covering, and revegetation.
In an effort to reduce costs associated with providing a soil
cover for the waste, the Bureau is currently investigating
the use of fly ash, acid mine drainage sludge, and other
wastes as soil-substitute for cover. Estimates for reclamation
costs using this new technique are approximately $350/acre,
exclusive of land leveling expenses.
Three such projects were included in the present report
as case studies. Results to date have been very successful both
in reducing reclamation costs and in improving the ability of
the soil to support vegetation.
Several environmental issues exist with respect to
the disposal of coal refuse in conventional culm piles. One
of the most extensively studied problems is air pollution from
burning refuse piles. Also, there is the coal industry's
problem of acid mine drainage. Waste coal refuse containing
pyrite will generate significant amounts of sulfuric acid and
iron sulfate in the presence of air and water. To control
this problem, several approaches are being tested: neutralization
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of waste material; and sealing pile to prevent contact of water
and air with acid-forming materials. Other environmental
problems include physical degrading phenomena such as surface
erosion and bank instability. Aesthetic objections also
must be contended with in many situations; these are related
to land use aspects.
This work suggests that reclamation techniques and
costs developed for culm piles may be applicable to reclamation
of landfills used for the disposal of scrubber sludge. In
addition, a potential exists for utilization of sludge/ash .
mixtures as neutralizing agents and soil conditioners for culm
material and acid mine spoil.
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6.0 PHOSPHATE SLIMES
Phosphate rock slimes are the fine wastes, usually
minus 200 or 150 mesh, discarded from the washer in the
beneficiation process as a 4-6% solids pulp. The phosphorus
content of the solids is often as high as in the original
matrix, 9-177. (BO-074, BA-133). However, because of its
extreme colloidal and hydrophilic nature which greatly hinders
dewatering, attempts to beneficiate this slime have not been
very successful.
The traditional method of slimes disposal is ponding
in dammed, mined-out areas where they settle quite rapidly
to 10-15% solids. However, the rate is so slow beyond this
point that even after two years, the solids content is usually
only 25-35% (BA-133, US-027). For every hectare-meter of matrix
mined, 1.25 hectare-meters are required for slimes disposal.
This means that in order for the mining area to provide sufficient
storage space, dams must be built to increase the site's capacity.
Some dams are constructed to retain slimes up to 12 meters deep.
The ponds are built to rigid specifications normally out of
quartz-sand tailings from the flotation effluent and overburden.
Water recycle is a very important aspect of slimes
disposal and phosphate mining in general. The water leaving
the plant with the slimes accounts for about one-half of the
total water requirements for both the mining and beneficiation
processes. About 10% of the water used in disposal is
retained by the solids even after many years of settling.
This is a tremendous draw on the water resources, thus providing
heavy incentive for maximum water reuse both for environmental
and economic reasons. Water is recycled continuously, but the
rate of drawdown varies with the rate of production of the
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processing plant, pond area, river pollution, rainfall, winds,
amount of freeboard, and possible hurricanes.
Studies of additional methods of phosphate slimes
disposal have centered around improved and novel dewatering
techniques. Investigations have been conducted by industry,
TVA, and the Bureau of Mines. In general, the conclusions of
almost all studies indicate that the dewatering techniques are
not practically applicable to the industry's problem because
(1) they require too much energy (chemical, mechanical, or
thermal) thus making the processes uneconomical, (2) the
dewatered products have no potential utilization, and (3) the
best results obtained still only achieve a 50% solids naterial.
The environmental effects of phosphate slimes disposal
by ponding were studied in several Florida river systems around
1950 (SP-034) and more recently in a North Carolina estuary
(CA-125). In general, no evidence of harmful effects from
clarified slimes liquor have been found with the possible
exception of increase in algae growth which could indirectly
cause eutrophication. Most phosphate mining companies monitor
streams below their plants on a daily basis. The parameters
measured include water flow, suspended solids, phosphate, and
fluorine. No reports of groundwater monitoring were available.
Another potential hazard associated with phosphate
slimes disposal by the conventional method is dam failure.
Loss of the low solids slime over acres of adjacent land
following dam failure has occurred several times in the Florida
phosphate fields generating substantial legal action. Conse-
quently, the dams are monitored constantly so that any structural
weaknesses may be detected early.
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Reclamation of slimes disposal ponds has presented
the only constraint on freely planned development of former
phosphate mining sites since they do not possess the support
necessary for housing. However, they have been successfully
converted to forested parks, greenbelts, and recreational
areas. One reclaimed slimes disposal area visited by Radian
personnel is now an 18-hole golf course. Reclamation procedures
consisted of pumping tailings onto the slimes to achieve
dewatering. Revegetation in this case presented few problems.
The tailing material was contoured and seeded with bermuda
type grasses and native shrubs and trees. Fertilization
requirements were minimial owing to the high phosphate
content in the tailing material.
Even unreclaimed slime ponds are not of zero
value. They generally become heavily vegetated, marshy
areas forming habitat for game birds and animals as well as
a large population of snakes, rodents and predators. The
combination of high fertility, low toxicity, and subtropical
climate encourage verdant growth in all cases.
Several areas of phosphate slimes disposal are
potentially applicable to scrubber sludge. Although the two
materials are chemically dissimilar, the physical properties
appear to be similar in several respects. In both cases,
water recycle is very important, especially for scrubber
sludge if the trend toward closed-loop operation continues.
Both materials have relatively poor settling properties compared
to tailings, for example. This is especially true for
phosphate slimes. Extensive research in dewatering this
material has been conducted and results to date have not
yielded any completely effective method for the colloidal
slimes. The most recent development is the mixing of slimes
and sand tailings to achieve better settling; the mechanism
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is not completely understood, but may prove applicable to
scrubber sludge dewatering. Possibly, fly ash, which possesses
good settling characteristics, may promote sludge dewatering.
Other dewatering technologies developed for testing of
slimes also may be applicable to scrubber sludge.
Another physical property of dewatered slimes is
its relatively low load-bearing capacity. Preliminary
laboratory studies with untreated scrubber sludge, have
produced varying results; however, fixation processes impart
greater material strength properties to the waste. If
scrubber sludge is shown to be a weak structural support,
reclamation techniques and land use plans developed for
slimes areas may be applicable to sludge disposal sites.
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7.0 TACONITE TAILINGS
Two general methods are in use for the disposal of
taconite tailings. The first and most prevalent is ponding
with eventual reclamation of the tailings ponds. The second,
used solely by Reserve Mining, is direct disposal into Lake
Superior.
The taconite plants using on-land disposal generally
use ponds with dams or dikes constructed from tailings. In
the case of the Erie Mining plant, coarse tailings are sluiced
directly to either a 1,300 acre (500 hectare) or a 700 acre
(300 hectare) settling pond. The tailings fines are passed
through thickeners and then discharged to the ponds. Water
is recycled. The Eveleth plant also operates on a closed
loop basis. In this case the coarse tailings containing
17-2070 water are separated and hauled by truck to the pond
site for dike construction. The fines go to a hydroseparator
and then to a thickener before discharging to the tailings pond.
In this case the use of coarse tailings for dike construction
reduces dusting problems. Pond waters are recirculated to the
plant.
The Erie plant has been the subject of rather extensive
experimentation in reclaiming tailings ponds. The company has
instituted a "Multiple Resource Management Plan" designed to
utilize the following resources: minerals, water, wildlife, and
recreational uses. During studies conducted to determine the
optimum methods for stabilization of dikes constructed from
tailings, the conclusion was reached that while the tailings
are not toxic to plant life, their fertility is very low.
Through a planned program of fertilization, seeding and mulching,
it has been possible to revegetate tailings basins within a
single growing season following spring planting. Although the
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revegetation research is still incomplete, it has been noted
that native trees are beginning to reestablish. The main
vegetation is still alfalfa, however. The fine nature of the
tailings have required the planting of low plants with strong
root systems to stabilize the soil. During 1967 and 1971
approximately 100 acres (40 hectares) of basin were reclaimed.
These initial results, although modest, are promising but much
research remains before reclamation of infertile tailings
basins becomes routine.
The relevance of this work to scrubber sludge disposal
lies in the so-far successful reclamation of a disposal site
for a non-vegetative-supporting material. To date, there has
been no investigation of the ability of untreated or stabilized
scrubber sludge to support vegetation or of its phytotoxicity.
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8.0 GYPSUM FROM PHOSPHORIC ACID MANUFACTURE
In the manufacture of phosphoric acid by the wet
process, phosphate ore is contacted with sulfuric acid resulting
in gypsum precipitation. For every metric ton of phosphate
rock processed, 1.5 metric tons of by-product gypsum are
produced. Similarly, for every metric ton of P205 product,
4.5 metric tons of gypsum result. The gypsum is filtered
from the system, and the filter cake is then washed and
discharged from the filter containing 18-357. free moisture.
In most operations in this country, the by-product
gypsum is treated as a waste and traditionally disposed of
in diked ponding areas. The pond area should be 0.5 acres
per daily ton PzOs production (0.2 hectares per daily metric
ton P20s produced). The rate of gypsum accumulation is approxi-
mately one acre-foot per year per daily ton P205 (~0.1 hectare-
meters per year). As the solids settle, the supernatant is
recycled and the settled solids may be used to build up the
height of the dikes. Some dikes have been built up as high
as 30 meters. The disadvantages of this practice include the
necessity of mechanical rehandling and increased slurry pumping
costs. The potential utilization of scrubber sludge in this
capacity has not yet been determined.
Water reuse is a very important aspect of the phosphate
industry because of the huge quantities required in the mining
operations. While -80% water recovery is generally achieved,
some is released to the environment, especially during periods
of heavy rainfall. The composition of the supernatant changes
in the pond until equilibrium is reached, at which time the
results shown in Table II are typical. Prior to discharge,
adjustment of pH, fluoride, and phosphate is necessary. The
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RADIAN CORPORATION
TABLE II
TYPICAL EQUILIBRIUM COMPOSITION OF GYPSUM POND WATER (BA-L33)
Contaminant Concentration, nig/ i
P?0S 6000-12,000
Flouride 3000-5000
Sulfate 2000-4000
Calcium 350-1200
Ammonia 0-100
Nitrate 0-100
pH 1.0-1.5
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exceptions are plants situated where evaporation rates are
very high, regulations are less than stringent, or the subsurface
drainage rate is high. In most cases the treatment consists of
lime neutralization and settling. Double liming, or even triple
liming, is usually required to achieve the necessary degree of
impurity removal
Although groundwater contamination from gypsum pond
leachate and runoff is a potential hazard, no data are available.
However, no harmful effects have been detected to date by state
or federal agencies.
The case studied is typical of the U. S. phosphate
fertilizer industry's practices for disposing of by-product
gypsum. Mobil Chemical's facilities in Polk County, Florida,
were visited by Radian personnel to obtain first-hand informa-
tion in this subject area.
Alternate disposal methods for phosphogypsum entail
various utilization schemes, some of which are quite highly
developed in countries other than the United States Because
of the abundant supply of natural gypsum deposits here, there
has not been as strong an incentive to develop utilization
technology as has been felt in Japan, Europe, and other areas.
Other throwaway procedures used in other countries to varying
extents include ocean- or sea-dumping and truck transport to
landfill sites.
The future of these gypsum piles remains undetermined.
Although the industry is promoting investigation of potential
utilization of this by-product, no schemes appear commercially
feasible at this time. Meanwhile, the gypsum stockpiles are
continuing to build until a time when a feasible scheme is developed.
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For this reason, no attempt has been made by the industry to
reclaim these disposal sites; no information in this area is
available although it would certainly prove very useful in
assessing the reclamation potential of scrubber sludge disposal
sites.
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9.0 ACID MINE DRAINAGE SLUDGE
Acid mine drainage is a significant environmental
problem of the mining industry, especially coal mining. This
water pollution results when naturally occurring pyrite,
FeS2, in the coal seam and wastes is oxidized in the presence
of air and water to form sulfuric acid and soluble iron
[Fe(II) and Fe(III)] sulfates Such mine drainage (AMD) is
typically very acidic (pH 2 to 3) and must be treated for pH
and dissolved iron before release to surrounding water courses.
Most treatment processes are based on neutralization
of the acidity and oxidation and subsequent precipitation of the
iron. Neutralizing agents in common use are lime, hydrated lime,
and to lesser extents, (mostly on an experimental basis) lime-
stone. A sludge with a typical solids content of 1% by weight
results. Under extensive periods in storage basins, final
solids content of 13.97,, has been achieved. Pilot plant data
for clarifier underflow indicate that a solids content of
almost 5% can be achieved. However, results are highly depen-
dent on neutralizing agent used, pH, and aeration. These
results show that AMD sludge possesses poorer settling
properties than scrubber sludge. Information concerning
conditioning, dewatering, handling, and ultimate disposal of
AMD sludge is potentially applicable to scrubber sludge.
The majority of AMD neutralization plants dispose
of their partially dewatered sludges in lagoons where natural
evaporation, freezing, and percolation further reduce the
water content. In the past, a primary settling area and a
permanent sludge impoundment were favored. Now the trend is
toward a single ponding area which receives sludge at one end
and discharges effluent supernatant at the opposite side. The
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volume requirements for a ponding arrangement depend primarily
on the extent of dewatering achieved prior to ultimate disposal.
For example, a 5-670 solids sludge would require approximately
one-third of the volume of drainage water treated. After an
extended period in a secondary settling pond, the resultant
13.9% solids sludge requires only 370 of the volume of drainage
treated. The sludge will continue to settle and compact
until equilibrium is reached; i.e., when the weight of
solids equals the strength of the floes.
There is an increasing use of inactive deep mines as
sludge disposal sites. The waste is either trucked or piped
to boreholes through which it is injected. The alkaline sludge
reportedly remains in solid form; also, little resuspension of
dissolved solids occurs. These areas require further investiga-
tion, however.
Three typical acid mine drainage neutralization plants
owned and operated by Consolidation Coal Company were visited
during the present study. Hydrated lime is employed at all
three sites, and the sludge is contained in earthen impound-
ments where the solids settle and clarified water is pumped to
a stream. In two of the three cases, earth-filled dams were
constructed to retain the sludge. The effluent from each
plant is monitored on a weekly basis using grab sample
techniques, as required by the state of West Virginia. Proposed
effluent limitations for the coal industry as well as West
Virginia limitations are being met by the neutralization treat-
ments employed.
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10.0 COAL ASH DISPOSAL
Basically there are three alternatives available for
the ultimate disposal of solids from fossil fuel fired utilities:
ponding, landfill, and utilization. The first two approaches,
in which the solids are viewed as throw-away wastes, are discussed
with special consideration given to the environmental aspects
of each. Another alternative, deep mine disposal, is also
briefly described.
Ash ponds are typically operated such that the
slurry enters one end of a single pond. As it flows to the
opposite side, the well-settling ash drops out and a pool of
supernatant forms at the far end. The effluent is removed
via weirs or standpipes, thus allowing continuous operation of
the pond until full. In ash pond management, the settled
ash is seldom used to increase the height of the walls because
its spherical form results in a low angle of repose.
A second approach commonly taken by fossil fuel-fired
utilities for solids disposal is landfill. This method eliminates
the need for long distance hydraulic sluicing systems and on-site
ponding facilities. The disposal area may be either on-site
or off, again depending on land availability.
The pollution potential of an ash landfill or ponding
operation is related to the leachate characteristics. To date,
no instances of groundwater pollution by disposed ash have
been reported. Related studies currently are in progress in
which the availability of molybdenum, boron, and other trace
elements to plants is being studied. The results of greenhouse
studies have shown that application of fly ash to soils does
increase the availability of boron, molybdenum, phosphorus,
potassium, and zinc. Whether or not this constitutes a potential
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CORPORim
pollution problem regardless of the beneficial results to some
plants is not yet conclusive.
The case study described in the report is the Widows
Creek Steam Plant, located on the north shore of Guntersville
Reservoir in Jackson County, Alabama. The TVA complex, which has
a total generating capacity of 1968 Mw, consists of eight
boilers fired by pulverized coal. Total consumption rate at
full load is 677 metric tons per hour. Assuming an ash content
of 17%, approximately 115 metric tons of ash are produced hourly;
75% of this is estimated to be fly ash.
Solid wastes generated at Widows Creek are disposed
of by ponding. The original ash pond used for units 1-6, located
inside a railroad loop, was filled and taken out of service
when the existing pond was put into service in February of 1961.
A portion of the first pond has been vegetated, while the other
half is being used as a source of fly ash for mixing with
cement.
The pond now in use is located northwest of the plant
on the southern shore of Widows Creek Embayment. The 65 acre
(2b hectare) area receives ash from all eight units.
A new disposal area is presently under construction.
This project involves relocation of Widows Creek and its
embayment. The site totals 93 hectares (230 acres) which
will be divided into two areas, one for disposal of all ash
from units 1-7 and the precipitator ash from unit 8 and the
other for scrubber waste (sludge plus ash) from unit 8. The
sludge and ash disposal areas will be separated by a divider
dike. The pond bottom will be compacted by heavy equipment
and, according to TVA design engineers, will become impervious
due to early deposition of fly ash. The perimeter and divider
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dikes are being constructed of compacted earth removed from the
pond's interior.
Operation of the new ash pond will be similar to
that used for the existing pond and the effluent is likewise
expected to be similar in composition. The spillway will
discharge to an open channel along the southwest side leading
directly to Guntersville Reservoir. Closed-loop operation of
the scrubber is planned which will eliminate any discharge
from the second waste area.
Monitoring results and environmental studies to
date have not indicated any deleterious effects from ash pond
discharge. Their disposal method effectively meets Alabama's
effluent guidelines.
Coal ash disposal technology is relevant to scrubber
sludge disposal in the following areas. The experience
already gained by the utility industry in ash ponding and
landfill management can be applied. Since ash will be ponded
with sludge in many instances, it is likely that, from the
standpoint of trace contaminants, the problems should be
similar although data available at the present time are not
complete enough to warrant any definite conclusions.
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11.0 SCRUBBER SLUDGE
The sulfur compounds produced by flue gas desulfurization
systems fall into two general categories: throwaway or saleable
products. Lime/limestone scrubbing systems generate a throwaway
sludge with little commercial value at the present time. Lime
scrubbing procejs ;s ordinarily produce sludges containing
CaSOs'^O, Ca(OH)2) CaSCK-ZHzO and CaC03; limestone sludges
generally contain CaS03-JjH20, CaSO^HgO, and CaC03. For coal-
fired installations where efficient particulate removal is not
installed upstream of the wet lime/limestone absorber, such
sludges can also contain large quantities of coal ash
From data available to date, it has been found that
the exact chemical composition of scrubber sludges varies
widely from one system to another, and even within the same
system. Therefore it is not possible to give an analysis
which truly represents all systems.
The amount of sludge generated by a given plant is
a function of the sulfur and ash content of the coal, the coal
usage, the on-stream hours per year (load factor), the mole
ratio of additive to S02, the S02 removal efficiency of the
scrubbing system, the ratio of sulfite to sulfate in the
sludge, and the percent moisture in the sludge. Table III
lists values of these various sludge parameters for a hypo-
thetical plant representing the National average expected
between 1973 and 1980. These values represent a mix of Western
and Eastern plants expected in 1980 based on the trends shown
by present flue gas desulfurization system orders.
Table IV shows the quantities of ash and sludge
produced per year by a 1,000 MW coal-fired generating station
controlled by lime/limestone flue gas desulfurization systems.
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TABLE III
TYPICAL SLUDGE PRODUCTION PARAMETERS
National
Sludge Production Parameters Average*
Coal:
Sulfur Content 3.0%
Ash Content 127.
Plant:
Load Factor 73%
Coal Usage .4 kg/kw-hr
Scrubbing System:
SOS Removal Efficiency 85%
Moisture in Sludge 50%
CaO/S02 (inlet) Mole Ratio 1.0
CaC03/SOa(inlet) Mole Ratio 1.2
Sulfite/Sulfate Mole Ratio 9:1
*The values listed as the National average represent a mix of
Western and Eastern plants expected in 1980 based on the
trends shown by present flue gas desulfurization system orders,
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TABLE IV
TYPICAL QUANTITIES OF ASH AND SLUDGE PRODUCED PER YEAR BY
A 1000 MW COAL-FIRED GENERATING STATION CONTROLLED
WITH LIME/LIMESTONE FLUE GAS DESULFURIZATION SYSTEMS
Coal Ash. dry
Coal Ash. wet (80% solids)
Quantity Produced
2./7.COO Eietric cons/year
384,000 metric tons/year
Volume Required
For Disposal
315,000 cubic meters/yea::
203,000 cubic meters/year
Limestone Sludge, dry
CaCO, Unreacted
TOTAL
264,000 metric tons/year
39,000
99.000
402,000 metric tons/year
N.A
Limestone Sludge, wet
(50% solids)
Limestone Sludge, wet (with
ash)
804,000 metric tons/year
1,418,000 metric tons/year
551,000 cubic meters/year
971,000 cubic meters/year
Lime Sludge, dry
CaS03-%H20
CaO Unreacted
TOTAL
Lime Sludge, wet (50% solids)
Lime Sludge, wet (with ash)
264,000 metric tons/year
39,000
43.000
346,000 metric tons/year
692,000 metric tons/year
1,306.000 metric tons/year
N.A
474,000 cubic meters/year
895,000 cubic meters/year
ASSUMPTIONS
Coal
Plant:
Scrubber
Sludge:
Ash
3.0% S; 12% Ash
6400 hr/yr, 4 Kg Coal/kw-hr
85% S02 Removal
1.0 CaO/S02 (inlet) Mole Ratio
1".2 CaC03/S02(inlet) Mole Ratio
Packing Volume 0 685 cubic meters/metric ton
Packing Voluem 0.53 cubic meters/metric ton
Sulfite/sulfatc ratio based on performance of Chemico scrubbing
unit at Mitsui Aluminum Co., Japan.
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These figures represent the National average sludge and ash
production statistics.
Using the forecast demand for flue gas desulfurization
given in the SOCTAP report (SU-031) and the national average
annual sludge production rates per 1,000 MW of controlled
generating capacity, the amount of wet ash containing sludge
(50% moisture) that will have to be disposed of annually by
1980 is predicted to be 113 million metric tons. This value
is based on the assumption that there will be 116,000 MW of
generating capacity controlled by 1980 and that 75% of the
control will be by lime/limestone scrubbing systems. The volume
required for disposal of this amount of sludge would be
approximately 77.4 million cubic meters.
Ponding and landfilling provide the major mechanisms
of disposal for most solid waste products. In terms of land
use and reclamation, these disposal mechanisms have many points
of similarity for various industries. Land use for waste
disposal may be esthetically objectionable. The wastes could
provide varying degrees of surface and groundwater pollution
depending on chemical composition, solubilities, and the location,
design and operation of the disposal site. For land reclamation,
most of the stable wastes will require only a cover material-to
support vegetation and prevent eventual erosion. However, some
wastes are very resistant to dewatering and could reslurry in
the pond or landfill. If this is shown to be true, it is likely
that fixation will become a necessary practice.
Many of the solid wastes discussed in the preceding
sections are disposed of by ponding These include sewage
sludge, phosphate slimes, taconite tailings, by-product gypsum,
acid mine drainage sludge, and coal ash. Much of the technology
already developed in handling these materials may be applicable
to ponding of scrubber sludge. Those aspects which may be
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compared are settling characteristics of the waste, dimensional
stability, pond construction, open-loop vs. closed-loop operation,
and single-or multi-unit operation.
Potential hazards associated with contamination of
surface and/or groundwaters by sulfur oxide sludges exist in
the following areas:
soluble toxic species (toxic meaning
elements which can cause health problems
even at very low concentrations),
chemical oxygen demand due to sulfite,
excessive total dissolved solids,
excessive levels of specific species,
e.g., sulfate and chloride, not generally
thought of as toxic,
excessive suspended solids.
The nature of the leachate expected from untreated
sludge can be judged by analysis of liquors associated with
scrubber samples, especially clarifier supernatant or scrubber
recycle water in closed-loop operation. Since fly ash will
be collected and/or disposed of together with the scrubber
sludge in many cases, it is likely that many of the potentially
leachable elements originate with the ash. Although ash ponds
have been in operation for years, there has been little concern
with environmental contamination either by high dissolved
solids content or by trace element constituents of the pond
waters. Both have recently been shown to be present in varying
amounts in several ash pond samples. Likewise, this potential
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source of contamination has not been investigated for other
wastes typically disposed of by ponding. This includes
taconite tailings, phosphate slimes, AMD sludge, and phospho-
gypsum. This type of study, if it were available, would prove
very useful in determining potential leachate problems due to
scrubber sludge disposal.
Another potential source of water pollution from sludge
ponds is overflow of supernatant. Disposal ponds have typically
been operated with less than total recycle of pond liquor. Newer
and more stringent regulations on waste water disposal will
likely reduce the practice of overflowing excess liquor into lakes
and streams. This will necessitate the use of closed loop
(total recycle) operation for scrubber sludge disposal by
ponding with treatment of any blowdown streams. Alternatively,
blowdown streams might be disposed of via evaporation or disposal
in the ocean. This sort of operation, combined with proper site
selection, design, and lining of ponds could eliminate contamina-
tion of surface or groundwater by ponded scrubber sludge.
A second approach to the problem of disposal of
waste solids generated by lime or limestone scrubbing systems
is landfill. Currently less than 407., of existing or planned
installations have adopted this alternative, while approximately
60% have included ponding facilities. Several solid wastes
discussed in the previous sections are disposed of by land-
filling; included in this category are municipal waste and
coal ash. Landfill-related technologies are sometimes employed
for sewage sludge and acid mine drainage sludge.
Characterization of lime/limestone scrubber sludge
thus far has revealed a nature not readily applicable to
untreated landfill disposal. The sludge does not settle or
dewater readily, and the results of some experiments have
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CORPORATION
indicated that once dried, the untreated material will
reabsorb moisture to its original water content. This
creates the unattractive possibility of the disposal site
becoming a bog. A second aspect of untreated sludge is its
leachate characteristics. For these reasons, chemical and
physical fixation processes have been proposed and are now
under investigation. The marketing agents for these fixation
techniques claim that conversion to a physically and chemically
stable landfill material is possible. Where leachate is a
problem, leachate control systems developed for sanitary
landfills may be applicable to scrubber sludge landfill
sites.
The technology associated with disposal of waste
scrubber sludges by landfill operations is currently in the
development stage. There are three basic features requiring
discussion to accurately describe the current state of
knowledge regarding this disposal method; dewatering,
fixation, and handling of sludge.
There are numerous techniques available for dewatering
industrial wastes, many of which have been experimentally
and industrially applied to sludges generated by lime or
limestone scrubbing systems. Comparable studies have been
conducted for dewatering other types of waste included in
the present study which bear significance to scrubber sludge
dewatering. Of special interest are phosphate slimes,
gypsum from phosphoric acid manufacture, and acid mine
drainage sludge.
Sludge fixation is the chemical and physical
stabilization of sludge or sludge/fly ash mixtures. The
intent of the processes is to convert the waste to a non-
toxic, load-bearing material via chemical reaction and, in
some cases, aggregate addition. Chemical fixation of scrubber
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sludge and related materials is currently under development
by several commercial groups including Dravo Corporation, I.
U. Conversion Systems, Inc., Chicago Fly Ash, and Chemfix
Corporation. The ability of proposed fixation techniques to
prevent rewatering and leaching from treated sludges is
under investigation. Comparative evaluations of several of
these processes are currently being planned or carried out
in the laboratories of Aerospace Corporation under contract
to EPA (Contract No. 68-02-1010) and in an independent study
by Combustion Engineering, Inc.
Certain aspects of land reclamation following
abandonment of a landfill site or dried up ponds used for
scrubber sludges may lead to potential problems. These
aspects may be assessed by examining the engineering, physical,
and chemical natures of treated and untreated sludge. At
the present time no attempts have been made to reclaim land
committed to scrubber sludge disposal, although disposal
sites for other solid wastes studied including municipal
waste, coal refuse, phosphate slimes, taconite tailings, and
coal ash have been successfully reclaimed. Extensive research
in these areas is being carried out. The degree of reclamation
possible varies with the characteristics of the waste.
Several other possible options are available for
disposal of air pollution control system sludges although
they are not under investigation to the same extent as
landfill and ponding. These alternatives involve direct
deposit of the waste below the surface in subsurface mines
or utilization of the sludge to reclaim strip mine areas.
Another possible solution is commercial utilization. Development
in this area is currently in progress under both government
sponsorship and private industry.
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REPORT
-------
1.0 INTRODUCTION
Disposal of sulfur oxide sludges generated by flue
gas desulfurization systems is currently under investigation
by the Environmental Protection Agency and the utility industry.
Radian Corporation, under contract to EPA, has been involved
in the preparation of several documents dealing with this issue
(Contract Nos. 68-02-1319, Task No. 1, "Information on the
Status of Lime/Limestone Sludge Handling"; 68-02-0046, Task
No. 12, "Utilization of Stack Gas Cleaning Equipment in Ohio";
and 68-01-2008, "Prepare a Technology Transfer Process Design
Manual"). The reports generated from the last two programs
listed are to be released shortly. During the course of those
studies, the magnitude of the problem faced by the electric
utility industry was estimated and briefly compared to similar
waste disposal problems encountered in other areas. This document
is an expansion of the comparison made at that time.
The purpose of the present investigation is to
identify available technologies developed in other industries
which may be applicable to scrubber sludge disposal. The
general nature of the problem, disposal technologies, and
environmental aspects for each of nine solid wastes destined
for land disposal are presented in this document. The
materials under study are listed in Table 1-1.
A case study approach was employed to obtain
information related to specific problems encountered, ability
of the technique to meet local environmental standards, and
alternatives or modifications under consideration if the current
method has proven inadequate. This type of approach was used
in order to quantify each problem as much as possible.
The general problem descriptions and case studies
are presented in Sections 2.0 through 10.0 below. Section
-------
TABLE 1-1
SOLID WASTE MATERIALS
1. Municipal refuse
2. Sewage sludge
3. General ore wastes (rock waste only)
4. Culm piles
5. Phosphate slimes
6. Taconite tailings
7. Gypsum from phosphoric acid manufacture
8. Acid mine drainage sludge
9. Coal ash
10. Sludge generated by flue gas desulfurization
systems
-2-
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11.0 presents currently available data concerning the nature
of scrubber sludge and a discussion of the applicability of
disposal technologies developed by other industries to scrubber
sludge disposal. The conclusions reached in this study are
given in Section 12.0.
-3-
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2.0 MUNICIPAL WASTE DISPOSAL
Disposal of the increasing tonnages of municipal
wastes has traditionally been dealt with by landfilling or
open dumping. Decreased land availability, higher land
costs, and increasing public concern with environmental
issues such as recycling and pollution, however, now demand
alternate practices.
2-1 Nature of Municipal Waste
Municipal refuse can be accurately characterized
by the term heterogeneous. Because of the numerous and
varied sources, domestic, industrial and commercial, the
content of typical refuse is difficult to predict. However,
several attempts have been made to analyze wastes from
specific facilities and to generalize from the results. One
example from the literature is given in Table 2-1. This
includes both a physical materials breakdown and an elemental
analysis. A more detailed analysis of composite municipal
waste was cited by Klass and Ghosh (KL-036); this is shown
in Table 2-2.
Figures quantifying amounts of municipal solid
waste generated annually tend to be in disagreement. Kasper
reported annual urban refuse to be in excess of 123 million
metric tons, while total U. S. refuse production (excluding
industrial, mineral, and agricultural wastes) is approximately
168 million metric tons per year (KA-109). Data from a 1968
national survey indicated that 172 million metric tons of
waste are collected annually by public and private agencies
(HA-183). Kenahan, however, stated that the nation generates
-4-
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CORPORATION
TABLE 2-1
SAMPLE MUNICIPAL REFUSE COMPOSITION -
U. S. EAST COAST (AFTER KAISER, 1967,
AS CITED IN AP-014)
Weight
Physical Percent
Cardboard
Newspaper
Miscellaneous paper
I'l.isiic film
Lc. nher, molded
pl.i»tici, rubber
(i irb.igc
C.r.ibs .ind dirt
Textiles
U/««.l
7
1.4
25
?
2
12
10
3
•9
Weight
Rough Chennciil Percent
Moisture
Carbon
Hydrogen
Ox>gcn
Nitrogen
Sulfur
Glass, ceramics, etc
Metals
A
-------
TABLE 2-2
COMPOSITION OF A COMPOSITE MUNICIPAL REFUSE
(KAISER, AS CITED IN KL-Q36)
Pciccnl
23 38 Corrug paper boxes
9 40 Newspaper
G.SO Magazine paper
557 Brov.n paper
2 75 Mail
2 OG Paper food cartons
1 98 Tissue paper
0 7G Plastic coated paper
076 Wax cartons
2.29 Vegetable food wastes
1 53 Citrus rinds and seeds
2 29 Meal scraps, cooked
2.29 Fried fats
2 29 Wood
229 Ripe tice leaves
1 53 Flower garden plants
1 53 Lawn grass, green
1 53 Evergreens
0 76 Plastics
0 76 Rags
0 38 Leather goods
0 38 Rubber composition
0 76 Paints and oils
076 Vacuum cleaner catch
1.53 Dirt
G 85 Metals
7 73 Glass, ceramics, ash
9 05 Adjusted moisture
10000
-6-
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about 363 million metric tons of urban refuse each year;
this included domestic, commercial, municipal, and industrial
waste products (KE-101). Klass and Ghosh stated that urban
refuse is produced at a rate of 5 pounds (-2.3 kilograms)
per person per day, or ~0.8 metric ton annually per person
(KL-036).
2.2 Disposal of Municipal Wastes
There are two phases of solid waste management:
collection and disposal. The first of these is by far the
most expensive; many estimates for this phase are in the
range of 80% of the total cost (SO-054). It is the second
phase, however, of interest in this investigation. In
general, the following options are available for disposal of
municipal wastes:
sanitary landfill
composting
incineration with or without heat recovery
pyrolysis
resource recovery (i.e., recycling)
In the following discussion, each of these methods will be
described. Information concerning procedures, economics,
extent of use, and environmental aspects will be included.
-7-
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2.2.1 Sanitary Landfill
Landfill operations still constitute the major
form of municipal waste disposal. One source estimated that
over 90% of the nation's solid waste is disposed of in this
manner at ~12,000 individual sites (SO-054). The term
sanitary landfill is defined as "a method of disposing of
refuse on land without creating nuisances or hazards to
public health or safety, by utilizing the principles of
engineering to confine the refuse to the smallest practical
area, to reduce it to the smallest practical volume and to
cover it with a layer of earth at the conclusion of each
day's operation, or at such more frequent intervals as may
be necessary" (WE-095). This type of operation should not
be confused with open dumping, a practice which involves
none of the above considerations and which is becoming
outlawed in an increasing number of communities.
Site selection is often hampered by land availability,
especially in areas of extensive suburban growth. In fact,
many are turning to other methods of disposal for this
reason alone. The criteria that should be considered when
selecting a site are:
relationship to present and planned
development
potential water pollution
availability of suitable cover material
-8-
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hauling routes and distances from
production centers
site development costs
future use of site
topography
The daily operation of a sanitary landfill must
conform to local sanitary codes. The procedures described
below are usually recommended. Dumping should be confined
to well-defined areas in order to facilitate efficiency of
spreading operations. The re-fuse normally is spread in
layers not thicker than two feet to promote maximum compaction.
The purpose of compaction is to conserve landfill space,
minimize potential harborage for rodents and vermin, minimize
subsidence, and reduce oxygen-containing voids which constitute
a fire hazard. This is accomplished in conventional operations
by specialized heavy equipment. Densities achieved by
compaction may range from 300-600 kg/m3 depending on the
type of waste, moisture content, and equipment available.
Several successive compacted layers may be placed until a
lift 2.4-3.0 meters is achieved.
Placement of 15 cm of soil cover over the compacted
waste is the next step. Daily covering is necessary to
prevent insect and rodent infestation and to minimize fire
potential. On completion of a fill area, an additional 0.6
meters of compacted cover should be laid. If multiple lift
layers are planned, an intermediate cover layer 0.3 meter
thick is recommended in place of the thicker cover layer for
-9-
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single lift fill. Vegetation of the final cover will provide
dust control and prevent erosion.
Future use of the landfill site is becoming more
of an important factor in planning and development. Several
highly successful landfill golf courses are already in use
(DU-053). Game preserves, parks, and even building sites
are also potential future uses (RE-092, VI-015). Probably
the most unique solution is development of a ski slope from
layers of compacted refuse. This concept is being realized
in at least two separate instances (ME-072, SK-017).
Potential environmental hazards associated with a
sanitary landfill operation include groundwater contamination,
gas generation, odor, subsidence, fire, and health hazards.
Proper maintenance and operation of the landfill will effec-
tively prevent fires, health hazards, and infestation by
rats and insects. Filling and preventing cracks in the
earth cover largely control odor; placement of activated
carbon in the tops of gas vents is an added means of protection.
Disinfectant application may also be used.
Groundwater contamination by landfill leachate has
been the subject of numerous studies. A recent review by
Heidman and Brunner (HE-063) summarizes published results of
current research. Several experimental studies were designed
to determine quantities, qualities, and movement of leachate
(AN-066, AP-014, TR-031). In general, climate, temperature,
age of landfill, composition, and original water content are
chief factors of leachate characteristics. Initial leachate
concentrations reported in one study were as follows (EM-
006, as cited in EM-003):
-10-
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BOD 20,000 mg/fc
COD 50,000 mg/£
Fe 1,600 mg/X
Cl 2,300
Prevention of leachate problems is achieved by
careful design in accordance with topography and hydrogeology
of the area. Recently, experimentation with sealing of
landfills is being conducted; entrapped leachate is collected
and treated, if necessary (RE-071) . This concept may become
important in scrubber sludge disposal if leachate is shown
to pose a hazard.
2.2.2 Composting
Composting is the decomposition of organic matter
to a relatively stable humus-like material by aerobic thermo-
philic action. This process is used as a disposal method
for municipal solid waste. Its application is limited,
however, by the relatively high costs involved and the
heterogeneous nature of the waste. Although several in-
depth studies of this method have been conducted, a discussion
will not be included here because of its inapplicability to
scrubber sludge disposal.
2.2.3 Incineration
Disposal of municipal waste by incineration is not
a well-accepted disposal technique. In 1968 there were an
-11-
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estimated 300 municipal incinerators in operation taking
care of "8% of the nation's waste; this figure dropped to
only 193 in 1972 (HA-193). Pollution problems, operational
difficulties, and high costs are blamed. Although economic
offsets such as resource recovery and marketing of generated
steam are often cited as advantages for this method, experiences
have been that it is difficult to find markets for the
steam. In addition, recovery of metal value from incinerator
residue is still not feasible. Finally, although incineration
does reduce the bulk of municipal waste by more than half,
the residue must still be ultimately disposed of, usually in
a landfill.
Incinerators generate three forms of potential
pollutants: solid residue (ash); stack gas; aqueous effluent.
Achinger and Daniels reported the results of an evaluation
of seven incinerators from which data were collected describing
refuse, solid waste residue, fly ash, and waste water (AC-
002). They concluded that solid waste was reduced by more
than 94%, thus little residue was produced. Particulate
emissions exceeded most air quality criteria, while aqueous
effluents were found to be contaminated but no treatment was
being applied. The following water streams were analyzed:
incoming water, quench water, scrubber water, and plant
effluent. Detailed results are available in the literature.
In another study, the sulfur balance for incinerators
was determined (KA-110). Typical municipal refuse was found
to contain 0.10-0.15% sulfur. The authors concluded that
during combustion, most of the sulfur remained fixed in the
ash which contains alkaline oxides. Only minor amounts were
released in the stack gas. Observed emissions from four
facilities ranged from 1 to 100 ppm.
-12-
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Particulate emissions from municipal incinerators
must be controlled; usually this is accomplished by electro-
static precipitators or mechanical collectors. Another
approach, however, is controlled air incineration to reduce
the problem (CR-053). The location of the air supply is
also regulated. In this way it is possible to prevent
entrainment of particulates from the refuse bed. This
incinerator design can frequently meet emission standards of
0.23 grams of particulate matter per cubic meter at 50%
excess air when burning general refuse without the aid of
gas washing devices.
2.2.4 Pyrolysis
Pyrolysis is related to incineration in that both
are thermal degradation processes. However, pyrolysis takes
place in the absence of air, produces a different residue
and a different off-gas. It is currently still in the
developmental stages, but it is considered a promising
replacement for the trouble-plagued incineration method.
The advantages of this process over conventional incineration
include (HA-183, LI-061) :
inherently lower pollution potential
potential energy recovery
greater flexibility in that type of
product output and recovery system can
easily be altered
-13-
-------
lower estimated operating costs
relatively low land requirement
The process itself is an endothermic reaction
which converts organic materials into three main component
streams. The gas is composed of hydrogen, methane, carbon
monoxide, and carbon dioxide. This fuel is readily combustible
in conventional furnaces with conventional burners although
the Btu content is lower than that of fossil fuels. The
liquid stream consists of organic chemicals such as acetic
acid, acetone, and methanol at room temperature. The char
produced is basically carbon plus any inerts such as glass,
metal, or rock. The final product mix depends on the heating
rate and ultimate temperature attained.
One of the advantages of this process is its
estimated lower cost. Part of the reason for this is the
low pollution potential involved, thus possibly eliminating
the need for expensive pollution control equipment. This
aspect needs further investigation, however.
2.2.5 Resource Recovery
This approach is perhaps the most widely publicized
method for disposal of municipal wastes. The Council on
Environmental Quality has completed a program in which the
basic feasibility of resource recovery was examined (FR-
070). A second part of their study involved evaluation of
twelve specific recovery processes (MI-081). Energy recovery
was discussed in previous sections of this report (incineration)
Fuel recovery is one feature of pyrolysis processes. One
-14-
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type of materials recovery, composting, was also mentioned
previously.
Materials recovery processes are designed to
remove paper, ferrous and nonferrous metals, and glass from
refuse. All four are recovered in most processes. Paper
can be separated from mixed waste by both wet and dry processes.
Metal recovery processes are under development. Ferrous
metal separation is based on magnetic separations and is
fairly well established technology. Air classification or
flotation is the usual basis for glass separation.
Environmental aspects will of course vary with the
type of recovery system employed. The Aluminum Association's
system, described in reference (SO-056), has installed air
and water controls in all phases of plant operation. Air
pollution control equipment is provided for the incinerators,
pyrolysis unit, and general plant ventilation. This includes
electrostatic precipitators for particulate collection and a
packed tower scrubber for sulfur compounds, chlorides, and
odor. The scrubbing liquor contains sodium carbonate,
sodium hydroxide, or potassium permanganate. A venturi
scrubber is used to remove kiln emissions from the pyrolysis
unit. Other equipment includes baghouse and fabric filter
collectors. For water treatment, provision has been made
for installation of a 650-gpm water treatment facility if
needed.
The extent to which reclamation is currently being
practiced is quite low. Salvage of metal cans from municipal
waste is minimal. Approximately 2% of "tin" cans are reused
in the beneficiation of copper ore, while recycling of
-15-
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aluminum cans amounts to less than 5% of annual production.
The glass content of municipal refuse has increased with
greater use of nonreturnable bottles; collection at reclamation
centers accounts for only 2-3% of annual production. Plastic
reclamation is prevented at the present time by lack of
technology for its separation (HE-061).
2.3 Case Studies of Municipal Waste Disposal
The only one of the five disposal technologies
described above that is being considered for scrubber sludge
disposal at the present time is landfill. While many aspects
of sanitary landfilling of municipal refuse are in no way
related to the present investigation, leachate generation,
migration, and collection are topics of environmental concern
for both types of waste. The following case studies were
selected on the basis of special emphasis given to one or
more of these areas.
2.3.1 Sonoma County Central Solid Waste Disposal Site
The Central Sonoma County Landfill is the largest
of six county disposal sites, handling 60% of the waste
generated in the area, or 650 metric tons of refuse daily
(CO- 166, CO- 167) . The site was opened in July of 1971 and
by the time of completion, estimated at the year 2002, will
fill a canyon of approximately 100 acres (40 hectares) to a
depth of 60 meters. Design features of interest to the
present study is the leachate collection recycle system which
involves migration to the surface and subsequent evaporation
or recycling through the refuse. The disposal site is
located in a large canyon in the southwestern portion of the
county, approximately 70 kilometers north of San Francisco.
-16-
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The area is underlain primarily by marine sediments of the
Franciscan Formation, consisting of sandy clayey shale with
interbedded sandstones and silicic chert beds. Above this
formation on the canyon floor are relatively thin deposits
of poorly consolidated sediments of younger Merced Formation.
These rocks generally consist of gravelly sandstones with
interbeds of sandy clay and silt. Permeabilities of repre-
sentative clay soil samples were less than one foot (0.3
meter) per year.
Groundwater in the disposal area is very limited,
especially in the Franciscan sedimentary rocks. These marginal
supplies of poor to fair quality water do not constitute a
protectable resource. Sediments of the Merced Formation contain
groundwater of moderate to high quality in the more pervious
strata contained in beds of sand, gravels, and occasionally
permeable volcanic rock. Test wells drilled in the canyon
bottom area revealed the presence of an aquifer ranging in
thickness from 0.6 to 3 meters occurring from 4.5 to 7.5 meters
below the surface. In addition to the subsurface water, at
least one perennial and two intermittent springs exist in the
canyon at the upper end of the disposal site. Although
production capacity from wells in this aquifer were marginal,
hydraulic continuity between this aquifer and major production
aquifers to the south established a definite need to prevent
indirect pollution of the latter by refuse leachate.
In addition to construction of access roads, preparation
of the disposal site involved erecting a clay cutoff barrier
across the bottom of the canyon, extending through the aquifer-
containing Merced Formation into the Franciscan Formation. This
barrier provides a physical separation between the canyon ground-
water and any downstream aquifers. A leachate collection system
-17-
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was engineered by which the leachate is brought to the surface
where it is evaporated or recycled through the refuse. Surface
drainage is intercepted and diverted around the active portion
of the site.
The daily operation of the landfill is carried out
by refuse compaction in place by compactors and bulldozers.
A new elevating scraper now on order will soon provide the
capability of a full sanitary landfill operation.
The major bulk of refuse is domestic and light industry
with limited agricultural dumping allowed. Some sorting is
carried out prior to compaction. This consists of removal of
white goods and large metal pieces; recycling of these two
types of refuse is presently the only reclamation effort
planned.
The monitoring program employed at the Central
Sonoma County Landfill, as outlined by the regulatory agency,
the California Regional Water Quality Control Board, consists
of the procedures described in Table 2-3 (CA-139). Three sampling
points are monitored: (1) the main landfill sump (leachate
recycle); (2) collection point near the main cutoff barrier
prior to discharge across the boundary (surface drainage
water); and (3) sand drainage blanket located downgradient
from the cutoff barrier. Monitoring reports are submitted
to the Regional Board on a monthly basis. The local waste
discharge requirements as presented by the California Regional
Water Quality Control Board, North Coast Region, do not cite
specific limits which cannot be exceeded although "neither the
treatment nor discharge of waste shall cause a nuisance or
pollution". The County officials feel, however, that their
present procedures provide compliance with all existing water
quality control standards.
-18-
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TABLE 2-3
WATER MONITORING PROGRAM AT CENTRAL SONOMA COUNTY LANDFILL
Sample Point Constituent
1 COD
TDS
Specific
Units
mg/1
mg/1
Micromhos/cra
Type of
Sample
Grab
Grab
Grab
Frequency
Monthly
Monthly
Monthly
Conductance
Mean Daily
Flow
PH
GPD
Grab
Grab
Daily
Monthly
2
3
COD
TDS
Specific
Conductance
PH
COD
TDS
Specific
Conductance
Iron
PH
mg/1
mg/1
Micromhos/cm
mg/1
mg/1
Micromhos/cm
mg/1
Grab
Grab
Grab
Grab
Grab
Grab
Grab
Grab
Grab
Monthly
Monthly
Monthly
Monthly
*
Semiannually
Semiannual ly
Semiannually
Semiannually
Semiannually
Samples should be collected during the
months of January and July.
-19-
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2.3.2 Sonoma County Refuse Test Cells
Adjacent to the full-scale landfill described in the
previous case study, a demonstration project is underway to
investigate stabilization of refuse. The study is funded
principally by EPA under Demonstration Grant No. G06-EC-00351
of the Office of Solid Waste Management Programs. Partial funding
of the three-year project is provided by the County of Sonoma.
The purpose of the investigation is two-fold:
(1) To investigate the stabilization of refuse
in a sanitary landfill by analyzing leachate,
gas, temperature, and settlement parameters.
(2) To determine the effect on refuse stabiliza-
tion of applying excess water, septic tank
pumpings, and recycled leachate to a sanitary
landfill under various operational modes.
The general geological and hydrological features of the
disposal site were presented in the preceding case study. An
extensive survey was made of the test area which is located
midway up the central canyon in a relatively flat portion of
the valley, just east of the main drainage channel. A small
tributary channel passes through the test area, with three test
cells to the north and two to the south. Little groundwater was
found in the preconstruction survey within twelve feet of the
ground surface in the test area. The native soils in their
natural state were considered generally satisfactory for leachate
retention. Occasional areas of more pervious water-bearing
soils were expected, however, in the excavations. These
areas were over-excavated two feet, then lined with an impervious
-20-
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clay material. Additional details of construction of the cell,
including the leachate collection system, are available in
the Second Annual Report of the Sonoma County Refuse Stabiliza-
tion Study. The cell dimensions are approximately 15 by 15
meters at the base, and 21 by 21 meters at ground level. Each
cell is 2.5 meters deep.
Test procedures included sorting and compaction of
refuse. After placement, the refuse was covered with 0.6
meters of stockpiled sandy clay material from cell excavation.
Some of the test cells also contained a one-foot impermeable
layer between the refuse and cover material. Each of the five
test cells was subjected to different conditions of liquid
recycling; these are summarized in Table 2-4. The monitoring
schedule observed from the period February 1972 through May 1973
is shown in Tables 2-5 and 2-6 for leachate and gas, respectively.
Slightly different schedules were employed during the initial
phase of the study and since May 1973. These details are
available in their Second Annual Report. Although the project
has not yet been completed, preliminary results as reported
in the Second Annual Report are summarized below for each test
cell.
Cell A serves as the control against which the other
four cells are compared in terms of effectiveness of the operation
procedures on refuse stabilization. Monitoring was initiated
in December 1971. However, the first significant quantity of
leachate from the control cell was not obtained until October
1972 when the first winter rainfall occurred. Cracks in the
soil cover permitted considerable access of storm water until
the clay cover swelled, sealing the cracks. Both the volume
and values for compositional parameters of the leachate prior
to November 1972 were very low in comparison with the other
cells, perhaps indicating that the initial leachate samples
-21-
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TABLE 2-4
LIQUID CONDITIONING AND PURPOSE OF CELLS
Initial
Cell
Designation
Liquid
Conditioning
None
Liquid
Used
None
Operation
Daily
Liquid
Application
gal/day
None
Liquid
Used
None
Purpose of Cell
Control Cell
B
Field
Capacity
Water
None
None To determine the effect of high
initial water content on refuse
stabilization.
I
to
to
None
None
700±
(200-1000)
Water To determine the effect of
continuous water through flow
on leachate character.
None
None
1000±
(500-1000)
Recircu- To determine the effect of
lated continuous leachate recircula-
Leachate tion on leachate character.
Field
Capacity
Septic
Tank
Pumpings
None
None To determine the effect of high
initial moisture content, using
septic tank pumpings, on refuse
stabilization.
Field capacity is the condition when a sufficient quantity of
fluid has been added to the refuse to cause a significant
volume of leachate to be produced from the cell.
k
Range of variation in daily application of fluid.
-------
TABLE 2-5
SUMMARY SAMPLING SCHEDULE
FREQUENCY OF ANALYSIS FOR VARIOUS PARAMETERS
COMMENCING FEBRUARY 15, 1972
Parameter
K
Na
Ca
Mg
Rg
Pb
Zn
Cu
Cl
FCB
PH
Alkalinity
COD
BOD
IDS
TSS
Settleable Solids
Nitrogen
Ammonia
Organic N
Nitrate N
Sulphate
Tot. Phosphate
DO
Color
Volatile Acids
Fecal Coliform
Elect. Conductivity
Fecal Streptococci
Leachate
Cells A. B & E
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
6-week intervals
quarterly
6-week intervals
6-week intervals
6-week intervals
6-week intervals
quarterly
6-week intervals
semi-annualy
Cells C & D
monthly
monthly
semi-monthly
semi-monthly
monthly
monthly
monthly
monthly
semi-monthly
quarterly
semi-monthly
semi-monthly
semi-monthly
semi-monthly
semi-monthly
semi-monthly
quarterly
semi-monthly
semi-monthly
semi-monthly
quarterly
semi-monthly
semi-monthly
semi-monthly
monthly
quarterly
semi-monthly
semi-monthly
Groundwater
Hells 1 thru 4
ACE Subdrain
Water Supply
Cell C
quarterly
quarterly
quarterly
quarterly
quarterly
quarterly
quarterly
quarterly
quarterly
semi-annually
monthly
quarterly
quarterly
semi-annually
quarterly
quarterly
semi-annually
semi-annually
quarterly
monthly
semi-annually
monthly
semi-annually
Initial test of Cell A leachate will include all parameters
listed in December 1971 schedule in addition to those listed above.
-23-
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TABLE 2-6
SUMMARY SAMPLING SCHEDULE
Frequency of Gas Analysis
Commencing February 15, 1972
Cell Location
Cell A - Bottom
A - Middle
A - Top
Sampling Frequency
Quarterly
Monthly
Quarterly
Cell B - Bottom
B - Middle
B - Top
Quarterly
Monthly
Quarterly
Cell C - Bottom
C - Middle
C - Top
Quarterly
Monthly
Quarterly
Cell D - Bottom
D - Middle
D - Top
Monthly
Cell E - Bottom
E - Middle
E - Top
Quarterly
Monthly
Quarterly
No gas samples can be withdrawn from these probes
due to fluid interference. Attempts in January 1972
to remove fluids encountered in these probes were
unsuccessful. Attempts will be made periodically
to withdraw samples.
-24-
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were condensate. The following parameters showed marked
increase after November 1972: EC (electrical conductivity),
2+ 2+
TDS, Ca , Mg , SOi,, volatile acids, and alkalinity. The
low pH of 5 was indicative of a high partial pressure of C02.
This in turn meant that biodegradation of organic material
was taking place. Both phosphorus and nitrogen levels were
slightly lower than those from other test cells, however,
some degree of biological activity was evident.
Trace metals data for all five cells are presented
in Tables 2-7 through 2-9. In cell A cadmium never exceeded
the analytical detection limit. However, since the detection
limit was above the 1962 U. S. Public Health Service Drinking
Water Standard (0.01 ppm), no conclusion could be drawn
concerning the potential hazard of this element. Copper was
found to be present in the 0.1-0.2 ppm range which is an
order of magnitude below the USPHS standard (1.0 ppm).
Zinc, lead, and mercury, however, were consistently detected
in amounts greater than or near the USPHS standards of 5
ppm, 50 ppb, and 5 ppb, respectively. Final analysis of
their potential hazards must consider possible interactions
between leachate and soil and potential removal mechanisms
such as ion exchange, absorption, adsorption, and precipitation.
Cell B represented a landfill having reached field
capacity via the addition of 155,000 liters of water prior
to placement of the cover material. No further additional
management procedures were employed on this cell. As in
Cell A, the first winter rains resulted in swelling and
subsequent sealing of the cover material, thus cutting off
infiltration through cracks. Leachate data generated from
the onset of the test until the winter rains in October 1972
were scattered and generally reflected leachate composition
ranges reported in the literature.
-25-
-------
TABLE 2-7
TRACE METAL CONCENTRATIONS IN LEACHATE
CELLS A, B & E
CELL A
Date
2-15-72
9-7-72
10-11-72
11-21-72
4-10-73
CELL B
1-31-72
10-24-72
3-13-73
CELL E
2-15-72
10-24-72
1-23-73
3-13-73
4-24-73
6-5-73
ELEMENT - mg/1
Cu
ND
ND
0.16
0.15
0.22
3.6
0.29
0.18
ND
0.12
0.10
0.19
0.32
0.10
Zn
2.1
0.23
0.58
9.0
3.0
140.0
62.0
10.8
ND
1.67
41.0
5.6
64.0
58.0
Cd
ND
ND
ND
ND
ND
ND
0.19
ND
—
0.09
ND
ND
0.05
0.05
Hg
0.0006
0.0065
0.0035
0.013
ND
0.006
0.0035
0.0044
0.0005
0.0145
0.0112
0.0044
ND
Pb
ND
0.16
0.12
0.44
1.81
3.0
0.95
0.33
ND
0.60
0.60
0.45
0.21
0.42
ND - Not Detected
— - No Analysis Made
-26-
-------
TABLE 2-8
TRACE METAL CONCENTRATIONS IN LEACHATE
CELL C
ELEMENT - mg/1
Date
3-2-72
4-11-72
5-9-72
6-6-72
7-11-72
7-25-72
8-8-72
9-7-72
10-11-72
10-24-72
11-8-72
11-21-72
2-6-73
2-27-73
3-13-73
3-27-73
4-10-73
4-24-73
5-15-73
6-26-73
Cu
0.6
ND
ND
0.15
0.15
0.18
0.13
0.07
0.08
0.06
0.11
0.1
0.06
0.06
0.05
0.06
0.08
0.05
0.04
0.02
Zn
42.0
30.0
30.0
22.0
13.0
10.0
9.5
7.5
6.5
7.5
8.5
8.0
4.6
4.5
4.3
2.8
3.5
3.8
2.5
0.6
Cd
ND
ND
ND
0.1
ND
ND
ND
ND
ND
0.05
0.06
0.04
ND
ND
ND
ND
0.05
0.05
0.05
<0.05
Hg
0.0014
0.0016
0.015
0.0102
0.0065
—
0.018
0.06
0.0065
—
0.035
—
0.0166
0.0123
0.0007
—
0.0034
0.0078
0.0018
0.0002
Pb
ND
ND
ND
0.8
ND
0.1
0.2
0.22
0.15
0.35
0.15
0.17
ND
ND
0.1
--
0.1
0.1
ND
Tr.
ND - Not Detected
— - No Analysis Made
-27-
-------
TABLE 2-9
TRACE METAL CONCENTRATIONS IN LEACHATE
CELL D
ELEMENT - mg/1
Date
1-18-72
3-2-72
4-11-72
5-9-72
6-6-72
7-11-72
7-25-72
8-8-72
9-7-72
10-11-72
10-24-72
11-8-72
11-21-72
1-10-73
1-23-73
2-6-73
2-27-73
3-13-73
3-27-73
4-10-73
4-24-73
5-15-73
6-26-73
Cu
0.4
ND
ND
ND
0.1
0.15
0.16
0.14
0.15
0.25
0.1
0.35
0.32
0.29
0.08
0.11
0.12
0.09
0.12
0.08
0.06
0.04
0.08
Zn
95.0
40.0
40.0
30.0
30.0
28.0
28.0
—
21.5
29.5
28.5
27.5
25.0
21.0
22.5
17.8
17.6
16.9
17.5
14.0
15.0
12.0
8.5
Cd
0.1
ND
ND
ND
0.13
ND
ND
ND
ND
ND
0.16
0.09
0.04
ND
ND
ND
ND
ND
ND
0.05
0.05
0.05
<0.05
Hg
0.003
0.0058
0.0028
0.0066
0.0052
0.009
—
0.012
0.064
0.0055
--
0.0022
—
0.0086
0.0108
0.016
0.0123
0.0047
0.0016
0.0008
0.003
ND
0
Pb
2.0
ND
1.0
ND
0.5
0.18
0.35
0.64
0.36
0.59
0.47
0.32
0.37
0.43
0.40
0.23
0.46
0.24
—
0.1
0.5
ND
0.31
ND - Not Detected
— - No Analysis Made
-28-
-------
Data for the time period from October 1972 on
could be explained in terms of volume flow-through and
biological activity within the cell. In general, anaerobic
biodegradation continues, but no significant activity of
methanogenic organisms has been observed. C02 content
remains high, corresponding to low pH, high alkalinity and
volatile acids. Sulfate content has not yet begun to decrease;
thus apparently cell conditions promoting sulfate reduction
to sulfide have not yet developed. However, the most significant
aspect is the discernible decreasing trend for most parameters
(with the exception of pH and P) during this period. This
dilution mechanism is especially evident for TDS and EC.
The trace metals data for Cell B are similar to those from
Cell A. The only distinct difference was the presence of a
high cadmium level on one occasion (0.19 ppm on 24 October
1972) .
Cell C was subject to continuous flow-through
conditions, with 3,000 liters of water applied daily. This
resulted in an overall flushing action as evidenced by
decreasing concentrations of all parameters except pH with
time. The response of cell temperature to atmospheric conditions
as a function of depth was different in this cell. Whereas
Cells A and B displayed temperature profiles which varied
strongly as a function of depth, the test conditions of Cell
C tended to stabilize the profile through the depth of the
cell.
Vigorous biological activity was indicated by data
on gas composition, BOD, COD and volatile acids. Higher
methane concentrations were evidence of strong methanogenic
organism activity. Increasing proportions of ammonia nitrogen
and corresponding decreasing organic nitrogen concentrations
reflected vigorous biodegradation. Other biological parameters
-29-
-------
were also discussed in the original report. Most of the inorganic
parameters including Na, K, Ca, Mg, Cl, TDS, and EC showed a
rather smooth trend toward lower concentrations with time. The
first six months of data which show high electrolyte concen-
trations reflect the flushing out of readily solubilized
inorganic material, leaving behind those requiring biodegrada-
tion. The only trend noticed in trace metal leachate data
was decreasing zinc concentration. Again zinc, lead, and
mercury were all present at levels higher than the USPHS
standards.
The settling rate for this cell was much greater
than that observed for either Cells A, B, or E. The data
indicate an accelerated rate of compaction compared to the control
cell.
The most significant effect observed with continuous
recycling of leachate in Cell D was the leveling trends of
leachate compositions even though volume of recycled leachate
varied by of a factor of 10 during the test due to rainfall and
other factors. This was especially true for Na, K, Ca, and
Mg during the period October 1972 to March 1973. In addition,
the thermal response of the upper layers was damped by continuous
recycling.
Biological activity was characterized as active
anaerobic. Strong reducing conditions within the cell were
reflected in the relative absence of nitrate, apparent sulfate
reduction, and continually high values for soluble reduced
iron. Substantial amounts of organic matter accumulating in
the leachate is shown by the stable BOD and COD measurement.
Heavy metals showed a tendency to build up in the
recycled leachate. Cadmium was the only one of five measured
-30-
-------
which did not exhibit this pattern, although this may have
been due to the analytical technique employed. The pH of the
liquor was ~5. Additional results are included in the Second
Annual Report.
Cell E has been seeded with septic tank pumpings to
provide microbial seed to accelerate biological degradation
processes. Since this cell was designed to test parameters
not applicable to scrubber sludge disposal, the results are
not discussed here.
Parameters used as indicators to determine extent
of groundwater contamination included Cl, Na, K, Ca, Mg, S0i»,
alkalinity, TDS, and EC. To date, the results indicate that
the earth cells are effective in preventing water pollution
from leachate.
-31-
-------
3.0 SEWAGE SLUDGE DISPOSAL
The bulk of solids present in sewage is separated
as a sludgeous material during primary treatment. This
sludge may either be disposed of directly or in combination
with sludges resulting from secondary treatment processes.
A disposal method extensively used in coastal areas has been
to barge sewage sludge to sea for discharge to the ocean's
depths. Biological investigations have revealed, however,
that ocean biota is adversely affected by this practice (SA-
116). Consequently, in October, 1970, the Council on
Environmental Quality released a policy recommending phasing
out ocean dumping of sludge. For this policy to be enforced,
however, feasible alternatives must be available. Thus, in
1971 EPA established two task forces to investigate possible
alternatives. One group looked at all potential disposal
techniques; the second group examined incineration in depth.
3.1 Nature of Sewage Sludge
A preliminary document describing the composition
and environmental impact of sewage sludge has been published
by Salotto and Farrell as an appendix to the EPA report on
sewage sludge incineration by the EPA Task Force (EN-084).
Much of the following material is a summary of the contents
of that document; the information is augmented in some
instances with additional published results.
The object of primary treatment is the removal of
,the majority of suspended solids from sewage by a settling
process. The resulting waste is referred to as primary
sludge. Secondary treatment usually involves oxidation of
soluble organics by the action of microorganisms. During
this process, the population of microorganisms increases and
-32-
-------
a portion must be wasted, generally as a dilute sludge.
Sludge is designated as "raw" until it has been subject to
stabilization processes such as heat treatment or digestion.
The exact nature of sewage sludge depends on the
source of the waste and the treatment received. The water
content of sludge can range between 85 and 99.9%. Primary
sludge usually consists of 65-75% combustible matter, with
most of the inorganics remaining in the ash residue. After
digestion, the volatile matter drops to ^50% with a corres-
ponding increase in proportion of ash. Most of the ash
occurs as particulate mineral matter (sand and clay). Table
3-1 illustrates the expected ranges of major components of
various types of sewage sludges. Digested sludge contains
nitrogen, phosphorus, and to some extent, potassium, the
three basic components of fertilizer. The liquid phase
contains approximately one-half the nitrogen and smaller
proportions of phosphorus, while the solids contain the bulk
of the phosphorus and the remaining nitrogen (DA-078).
Elemental analyses of 31 elements are presented in
Table 3-2. The major elements found are calcium, magnesium,
sodium, potassium, aluminum, iron, sulfur, and silicon. In
another study, metal contents of sludges from various plants
were analyzed to show typical variations. The authors
commented that it was not possible to predict relative
amounts of metals on the basis of the sludge's origin being
either predominantly industrial or predominantly domestic.
These data are shown in Table 3-3.
The EPA Task Force has estimated the amount of
domestic sewage sludge produced in the United States (EN-
084). For every million gallons of sewage, approximately
one ton of sludge production is estimated. Assuming that
-33-
-------
TABLE 3-1
MAJOR COMPONENTS OF SLUDGE (EN-084)
Constituent
Volatile Matter
Ash
Insoluble Ash
Greases & Pats
Protein
NH^N03
P2°5
K20
Si02
Fe
Cellulose
Types of Sludge
Rav
Pn'unry
60-80
20-1*0
17-35
7-35
22-28
1-3.5
1-1.5
10-13
Digested
U5-60
1*0-1*5
35-50
3-17
15-21
1-U
0.5-3.7
0-U
20-22
5.1*
10-13
Waste
Activated
62-75
25-38
22-30
5-12
32-Ul
M
3-l»
0.86
12
7.1
7.8
Filter Cake
Rav
55-75
25-^5
15-30
5-30
20-25
1.3
1.4
8-10
Digested
1*0-60
1*0-60
30-1*5
2-15
1^-30
1.3-1.6
0.5-3.5
8-12
*A11 data are presented on a dry basis.
-34-
-------
TABLE 3-2
SUMMARY OF MAJOR AND MINOR ELEMENTS IN SLUDGE (EN-084)
(mg/g dried sludge)
Element
Aluminum
Antinior\y
Arsenic
Barium
Berylliim
Boron
Cadmium
Calcium
Chroaiiwa
Cobalt
Copper
Gallium
Iron
Lead
Magnesium
Itoriganece
Mercury
Molybdenum
Nickel
Phosphorus
Potassium
Silicon
Silver
Sodium
Strontium
Sulfur
Tin
Titanium
Vanadium
Zinc
Zirconium
Primry
Sludge
5-1
n.a.-K-
< 1.2
2*2
O.OOC-5
0.10
<0.19
n.n.
2.0
0.22
2.0
0.06
15.1
1.0
10.6
0.78
0.005
0.36
0.52
3-8
n.a.
n.a.
0.2U
k.O
0.13
n.a.
0.95
lJf.8
2.1
6.9
1.7
Activated
Sludge
10.0
n.a.
1.2
1.2
0.0035
0.070
0.35
3.3.0
fc.3
0.002
1.1
0.05
',-0.5
1.5
7.0
0.31
0.02
O.£0
0.38
19.9
k.2
ItO.O
0.15
k.h
O..l£
10.1
0.50
n.8
0.7
3.3
10.0
Digested
Sludge
17-9
0.9
n.a.
1.U
0.0025
o.ote
0.26
33-5
2.3
n.a.
1.6
0.05
30.6
1.9
7-5
0.98
n.a.
0.25
0.38
12.6
2.8
l£2
0.20
6.2
0.26
.12.3
0.60
llf.2
5.2
^.0
2.0
*n.a. - not available.
-35-
-------
TABLE 3-3
CONCENTRATION OF
Tahoc
7/15/71
0.27
13.2
3.0
n n.d.I/
0.18
n.d.
1.0
1.3
8.7
4.5*
s 0.6
n.d.
2.8
n 0.51
n.d.
1.6
Dayton
8/25/71
0.36
12.5
3.0
n.d.
0.8
n.d.
5.9
6.0
20.4
n.a.l/
1.1
n.d.
6.9
n.d.
n.d.
8.4
METALS IN SLUDGES (EN-084)
(mg/g)
Little Mi;imi
Cincinnati
8/20/71
0.03
8.8
0.7
n.d.
n.d.
n.d.
1.7
2.3
16.0
n.a.
1.2
n.d.
2.0
n.d.
n.d.
7.8
Mill Creek
Cincinnati
8/20/71
n.d.
32.2 .
n.d.
n.d.
n.d.
n.d.
1.8
1.6
13.2
n.a.
0.6
n.d.
2.7
n.d.
1.6
4.7
Lor ton
Va.
8/5/71
n.d.
4.4
0.7
n.d.
0.17
n.d.
0.4
0.9
27.4
3.0*
0.5
n.d.
1.1
n.d.
n.d.
0.4
Indianapolis
Plant 1
8/23/71
n.d.
5.2
1.3
n.d.
0.24
n.d.
2.6
2.0
15.3
n.a.
0.6
n.d.
2.8
n.d.
n.d.
1.2
Barst,
7/20/:
0.05
16.2
1.5
n.d.
0.58
n.d.
0.5
1.7
10.6
5.5*
0.18
n.d.
0.8
n.d.
2.1
1.4
Ag, Silver
Al, Aluminum
Ba, Barium
Be, Berylliui
Cd, Cadmium
Co, Cobalt
Cr, Chromium
Cu, Copper
Fe, Iron
Hg, Mercury
Mn, Manganesi
Ni, Nickel
Pb, Lead
Sr, Strontiui
V, Vanadium
Zn, Zinc
* - micrograms/g
1 - n.d.: not detected
2 - n.a.: not analyzed
Analytical determinations on these sludg-js were carried out by 3. Kopp,
Analytical Quality Control Laboratory, Robert A. Taft Water Research Center.
-36-
-------
the per capita sewage production is 400 liters (100 gallons)
per day, 10,000 people will produce 4 million liters (one
million gallons) of sewage and consequently 0.9 metric ton
(one ton) (dry basis) of sludge per day. If thoroughly
digested, the sludge mass will be reduced to 450 kg (1,000
pounds) per day.
On a nationwide basis, municipal sewage sludge
production is estimated to increase from ^265 million liters
(70 million gallons) per day in 1960 to ^640 million liters
(170 million gallons) per day in 1980 (CA-124). Another source
estimates that 55,000,000 metric tons of sewage sludge (0.1-
15% solids) will be produced in 1980 (SC-164).
3.2 Pre-Disposal Treatment and Handling
In this subsection the procedures sometimes employed
in the pre-disposal treatment of sewage sludge will be
discussed briefly. These include dewatering and transport.
3.2.1 Sewage Sludge Dewatering
Volume reduction of sludges prior to actual
dewatering and ultimate disposal is often practiced to
reduce costs. Volume reduction, or sludge concentration, is
defined as the reduction in moisture content in order to
decrease sludge volume while still maintaining its fluid
properties. Maximum solids content typically desired is 10%
since denser sludges are viscous and difficult to pump. For
example, waste activated sludges usually contain 0.5-1.0%
solids. Concentration to 3 or 4% can be significant. Raw
primary sludges, on the other hand, often are already 5-6%
solids; a separate concentration step prior to dewatering or
final disposal is less practical here.
-37-
-------
The conventional gravity sludge concentrator is
equipped with a slowly-turning rake moving over the bottom.
This effects breaking up of the floe bridging, thus allowing
increased particle settling. One example of practical
experience in this area has been described by Alford (AL-
039) .
Vacuum filters are the most common mechanical
dewatering device used (CL-039). Most large treatment
plants which dewater their sludges employ these in their
process. Typical filtration rates achievable for activated
and well-digested primary sludges vary from 12 to 54 kg/m2
/hour (2.5-11 Ib./sq. ft./hr.), respectively. Filter cake
solids contain 60-85% moisture, depending on the nature of
the conditioned sludge. Chemical flocculation usually is
necessary to adapt the sludge to this technique. Factors
that determine the amount of chemical needed are sludge
concentration, type of sludge, and alkalinity. Commonly
used flocculants include ferric chloride and lime or poly-
electrolytes.
Another mechanical dewatering method is centri-
fugation, applied to solid-liquid separations in waste
treatment plants fairly recently. Several types of centri-
fuges are available; details are available in the literature
(AL-032, CL-039, KE-082). Practical experience has been
described by Alford (AL-039). Efficiency of this method
depends basically on the relative densities of the solid and
liquid phases. As a result, the type of sewage treatment
greatly affects the results as illustrated in Table 3-4.
Heat conditioning of the solids is reported to increase the
dewatering capability of this technique (AL-032).
-38-
-------
TABLE 3-4
DEWATERING OF WASTE SLUDGES BY CENTRIFUGING (AL-032)
Loca-
tion
Calif.
Mich.
Conn.
N.J.
Conn
Calif.
Texas
Type
RP
DP
R(P&AS)
R(P&B)
0(P&AS)
U(P&B)
AS
Feed,
%TS
3.83
8.8
3.61
9.57
35
2.79
219
Over-
flow,
% TSS
0.49
1.44
0.06
0.05
030
0.44
0.55
Cake
%TS
35.0
30.0
20.0
22.9
20.0
22.0
19.6
Recov-
ery. %
TS
88.2
882
98.2
99.2
930
95.0
97.9
Chem-
icals,
$/ton OS
0
0
6.40
7.95
15.00
16.00
12.40
TS = total solids, TSS - total suspended solids, DS = dis-
solved solids, R = raw, D = digested, P = primary, B =
biofilter, AS — waste-activated sljdge
-39-
-------
Heat can also be used as a drying technique as
well as a conditioning treatment for sewage sludge (WE-078).
Thermal drying is accomplished by the introduction of hot
gases to rapidly remove moisture from the solids. Some of
the advantages of this method include reduction of harmful
pathogenic microorganisms, odor destruction, and volume
reduction.
3.2.2 Sewage Sludge Handling
The transport of digested sludges by pipeline over
long distances has been growing in importance since 1964
when the idea of piping sludge slurries to strip-mined areas
for land reclamation projects was proposed to the U.S. Public
Health Service. The more conventional function of piping
sludge is short-distance, in-plant transport. Pipelines are
also employed in ocean disposal projects.
The flow characteristics of digested sludge's change
from Newtonian below
-------
TABLE 3-5
PIPELINE SYSTEM DESIGN DATA (RA-075)
i
1 inch = 2.54 cm.
Nominal ! Approximate Annual Dry
Population Served Pipe Size (inches) Sludge Solids (metric tons)^
100,000 1-1.5 -\ , . . , 1,400
idesign chal-
500,000 2.5-3.5Jlenge 7,000
1,000,000 4 14,000
2,000,000 5 29,000
3,000,000 6 42,000
4,000,000 8 58,000
-------
Thompson et al. have studied the economics of
regional waste transport and disposal systems (TH-041).
Total pipeline transport costs ranged from $1.76 per metric
ton ($1.60 per ton) for a 40-km (25-mile), 820 metric ton
(900 ton) per day system to $22 per metric ton ($20 per ton)
for a 160-km (100-mile), 91 metric ton (100 ton) per day
system. These costs include both capital and operating
expenses and are based on a 3.5% solids digested slurry.
The economics of this type of system are very sensitive to
scale; increasing the size from 91 to 820 metric tons per
day reduces total transport costs from $22 to $5.50 per
metric ton.
Comparisons with other modes of transport were also
reported (TH-041). Truck or rail may be used for land
disposal, while barge and tanker are in use for ocean dis-
posal. The economics of each case must be examined in order
to determine which handling method is the most feasible.
Several general conclusions were drawn, however. For ex-
ample, in cases of low tonnages or short distances, trucking
is more economical for land disposal systems. In one case,
costs for barge transport of sewage sludge were reported to
have decreased from $25.25 per metric ton in 1961 to $9.72
per metric ton in 1972 (Guarino as cited in DI-053). Im-
proved unloading techniques, greater quantities, and longer
contract periods accounted for this reduction. The original
literature should be consulted for further details.
3.3 Disposal Techniques
The disposal technology for sewage sludge having
the greatest potential application to scrubber sludge disposal
is reclamation of devasted land. The most well-known example
is the disposal system used by Chicago since 1971 which consists
-42-
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of barging 6800 metric tons of digested sludge at 3-5% solids
300 kilometers from the treatment plant to southern Illinois
(HI-069, DA-078, PR-057, VA-078). The sludge is spray-irrigated
onto the fields after temporary lagooning to reduce harmful
pathogenic microorganism population. Further details are
presented in Section 3.4 in the case study.
Other ultimate disposal technologies for sewage
sludge are more common, but are limited in their potential
application to the scrubber sludge problem. Ocean dumping,
although a major means of sludge disposal in the past, especially
in coastal areas, is being phased out because of possible
environmental hazards (EN-084).
Another alternative fairly recently to come under
development is composting. This process is the aerated micro-
bial decomposition of organic matter during which the tempera-
ture of the pile increases to 140-170°F due to thermophilic
action of microorganisms (US-082). This process begins
within 24 hours after placement of the sludge; as soon as
the action starts, odors do not form. The heat evolution
drives off the moisture, and usually within two weeks a dry
odorless compost material is ready for distribution. Daily
turning of the piles and initial mixing with previously
composted material is recommended for maximum efficiency. A
hectare (10-acre) demonstration project for this disposal
technique was proposed early in 1973. 100-150 tons (dry
weight) of sludge per day from the Washington, D. C.,
area will be transported to the Agricultural Research Center
in Beltsville, Maryland, spread in windrows, mixed with
other bulk materials, and turned by machine once a day.
Approximate yields of 75 tons (dry weight) of compost per
day are expected. Possible environmental hazards will be
studied as well as optimization of the process itself.
-43-
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In 1971 a Task Force was established by EPA to
study the feasibility of incineration as a sewage sludge
disposal technique to replace ocean dumping (EN-084). They
evaluated two types of furnaces: multiple-hearth (2 exist-
ing plants) and fluidized bed furnace (1 existing plant).
All were equipped with particulate scrubbing devices.
Special emphasis was placed on air and water pollution
potential. The results of the study indicated that incin-
eration is capable of achieving low emissions of common
pollutants although lead was found in high concentrations in
the stack particulate. The original literature should be
consulted for further details. The general conclusions were
that a well-designed and -operated incinerator can meet
stringent existing particulate emission control regulation.
Pyrolysis of sewage sludge is also available as a
disposal technique. When powdered dried sludge is heated in
the absence of air, a considerable reduction of mass occurs
due to the production of volatile gases, and the residue is
black containing carbon.
Other methods of sewage sludge disposal include
permanent lagooning and an experimental moisture-reducing
process which converts treated sewage into a nutritious
animal food supplement (SU-037). Lagooning has been in use
for many years, but is currently being phased out in favor
of schemes that require less land and are more appealing to
the public. Potential pollution aspects require further
investigation.
-44-
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3.4 Case Study - The Prairie Plan
The utilization of municipal sewage sludge in
reclamation of devastated mining areas is currently being
tested on a large scale by the Metropolitan Sanitary District
of Greater Chicago in conjunction with the Fulton County,
Illinois, Board of Supervisors. This cooperative venture
began with the purchase of 2800 hectares (7000 acres) of
strip-mined land as a disposal site for Chicago's sewage
sludge. The district serves a residential population of
5.5 million people as well as an industrial population
equivalent to another 4.5 million. On the order of 4.9
billion liters (1.3 billion gallons) of waste water are
processed daily, yielding ^910 dry metric tons of solids
daily (PR-057). Approximately 50% of this quantity is
currently being barged to the site by the Prairie Plan.
The land purchased is located %320 km (200 miles)
south of Chicago in Fulton County, Illinois. Basically, it
is a tract of gently sloping land consisting of spoil bank
soil, with soil textural classifications ranging from silty
clay loam to clay loam. This particular spoil is neither
stony nor acidic, having a surface pH of 7.1-7.6 (HI-069).
The tract is located on the upper reaches of the Spoon River
watershed, virtually a self-contained basin with a creek
ultimately discharging to the Illinois River.
This land is well suited to sewage sludge applica-
tion. Soil analyses have shown that Fulton County spoil
will supply 361-401 kg/hectare of available potassium, 10
kg/hectare available phosphorus, greater than 140 kg/hectare
of reserve phosphorus, and a very low nitrogen value. In
contrast, sewage sludge is low in potassium, but high in
available phosphorus and nitrogen as well as humus content.
The following levels were reported:
-45-
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potassium 3-5 kg/dry metric ton
nitrogen 25-30 kg/dry metric ton
phosphorus 30-35 kg/dry metric ton,
^80% readily available
The trace element content of sewage sludge is
commonly quite high. A typical analysis of Chicago's sludge
is given in Table 3-6. Hinesby, Jones, and Sosewitz pre-
dicted that application of sludge on strip-mined lands could
be accomplished without encountering trace element problems
(i.e., accumulation of toxic levels in the soil) because the
high metal content of the spoil itself "insures some irrever-
sible adsorption of the metals and therefore decreases absolute
amounts available to plants" (HI-069).
In the summer of 1971, the first load of sludge
was barged down the Illinois River to Fulton County.
Currently, about 6810 wet metric tons per day (370 dry metric
tons per day) of the 4% solids sludge are being transported.
Eight barges, each having a capacity of 1450-2800 wet metric
tons, are used to make the 36-hour round trip. The transport
cost is the major item in the reclamation project; estimated
cost is $37 per dry metric ton, or $0.12/dry metric ton/
kilometer ($0.18/dry ton/mile). A pipeline transport system
is now under consideration; this is expected to reduce the
transport cost to $0.03/dry metric ton/kilometer ($0.05/dry
ton/mile) (PR-057), which would greatly improve the overall
economics of the project, recently quoted at $55/dry metric
ton (RE-089).
At Liverpool, the sludge is pumped from the
barges to one of three holding ponds 17 kilometers away.
This is accomplished with a 300 horsepower pump which can
accommodate sludges up to 10% solids (DA-078). Maximum
-46-
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TABLE 3-6
Total Element
N
P
Cd
Cr
Cu
Fe
Pb
Ni
Zn
Mn
Ca
Mg
K
Na
AVERAGE COMPOSITION OF MSDGC LAGOONED
DIGESTED SLUDGE (HI-069)
Concentration
Kg/dry metric ton of Solid
54.0
65.0
0.95
8.4
4.6
95.4
3.0
0.85
14.9
0.5
52.5
14.7
8.0
3.1
-47-
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flow through the 508 mm underground pipeline is 0.2 m3/sec
(3000 gpm). The holding basins have a total capacity of
6 million cubic meters, 1.5-2.3 million cubic meters each.
They are built on tight clay soil and are lined with a 60 cm
(24-inch) thick packed clay blanket (PR-057).
These holding basins serve several purposes.
Their main function is to hold the sludge until the appro-
priate time for application, depending on the season,
rainfall, soil conditions, etc. The retention time will be
a minimum of 30 days and probably more on the order of six
months in order to allow time for the sludge to age. This
will destroy most pathogenic microorganisms that survive the
digestion process; remaining resistant forms will not
present an environmental hazard if soil erosion and sediment
transport are minimized (HI-069). Odor formation will also
be prevented by the lagooning and aging process. Another
purpose is to reduce the nitrogen content of the sludge,
which is the limiting factor in determining sludge applica-
tion rates. Mechanical aerators are being tested in one
holding basin to reduce the ammonia-nitrogen content by
stirring the sludge to the surface where evaporation can
take place.
In 1971, the first tract of land was prepared for
cultivation. This involved leveling to a maximum 5% grade
to prevent rapid runoff of sludge. In addition, earthen
berms were constructed around the edges of the fields to
direct runoff to collecting basins situated in depressions
resulting from the mining operations.
-48-
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RADIAN CORPORATION
In 1972, 320 hectares were planted with corn.
Sludge application was not made until the plants were 20 cm
tall, at which time an application rate of 56 metric tons
per hectare was made several times to approximately one-half
the area while the other half received no fertilization (PR-
057). The treated section yielded 131 bushels per hectare
(53 bushels per acre) compared to only 32 bushels per hectare
(13 bushels per acre) for the control section. It has been
calculated that 168 dry metric tons per hectare (75 tons/
acre) can be applied the first time without exceeding the
nitrogen fixation capacity of the spoil (i.e., no nitrogen
buildup). Decreasing amounts would be applied in subsequent
years until a rate of 18 metric tons per year is reached.
One source suggested a loading rate of 450 dry metric tons
of lagooned sludge per hectare over a four-year period (Hl-
069). This would result in the top surface foot of reclaimed
spoil having a 4-5% humus content to a depth of 0.3 meter at
the end of that period.
The technique used for applying the sludge is
spray irrigation. The settled sludge (^10% solids) is
removed from the bottom of the lagoon by a floating dredge
and pumped to an on-shore holding tank (DA-078). From here
it is pumped to a field distribution system composed of
modular units, each consisting of pumps, an above-ground
header system, and a "big gun" spray vehicle. In the fields,
203 mm pipe brings the "liquid fertilizer" to six self-
propelled irrigation units, each with a spraying capacity of
L3-63 liters per second. The sludge is sprayed outward
within a 52-meter radius of the vehicle which is drawn by a
180-meter cable winch through the fields at 30-213 cm/min
(PR-057). Three or four passes per year should be sufficient
to apply the required volume of sludge. In most cases,
applications will be made before planting and after harvesting.
-49-
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A natural filtering system will be relied upon
to insure that water reaching surrounding streams is of high
quality. As the sludge filters down through the crop roots,
bacteria convert sludge nutrients to forms usable by the
plant. Remaining liquor continues to pass downward until an
impervious stratum is reached, at which point horizontal
movement occurs. Farm fields will be surrounded by hedge
rows. Any nutrients seeping out of the field will be taken
up by their extensive root systems. As mentioned previously,
monitored field detention basins will collect all surface
runoff. If not polluted, the water will be released to a
nearby stream. However, if quality is poor, then the entire
contents will be recycled through the field. Additional
protection will be provided by lines of hedges and trees
along banks and streams. All streams entering and leaving
the 7000-acre tract will be monitored. Additional monitoring
stations including reservoirs, springs, and wells will be
checked monthly for changes in water quality.
Although no results are yet available from the
water monitoring program at the large scale site, a small
demonstration study to investigate leachate from sewage
sludge application to highly acidic spoil was conducted in
1966. Sponsors were the Metropolitan Sanitary District of
Greater Chicago and the U.S. Forest Service. Four 0.05-
hectare plots were treated with Chicago sewage sludge at the
following rates (LE-094):
Plot I 303.7 dry metric ton per hectare
Plot II 178.2 dry metric ton per hectare
Plot III 77.8 dry metric ton per hectare
Control 0.0
-50-
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In each plot a strip two meters wide was tilled to mix the
sludge with the spoil and seeded in April of 1971 with tall
fescue and weeping love grass. By May, all plantings had
germinated and were growing except for those on the control
plot. A direct relationship existed between the rate of
sludge application and the observed growth rates.
Over a 15-month period, subsurface drainage was
collected and analyzed. The results are shown in Table
3-7. Initially from November 1970 through September 1971 a
sharp decrease in metals concentration in the leachate was
observed. These levels rose slightly from October 1971
through January 1972. The results were explained as follows:
during the first winter season, the levels decreased because
of neutralization of plot acidity and because the sludge
acted as a high capacity cation exchanger. Then, during the
growing season evapotranspiration and low rainfall further
decreased acid production, resulting in further decreased
metal solubility. During the second dormant season, the
reverse occurred; heavy rainfall and subsequent high acid
production resulted in increased metal solubility.
In comparing relative effects of sewage sludge
application rates on leachate composition, it was observed
that the heaviest treatment rate resulted in the greatest
reduction in acidity, Al, and Cu before and after treat-
ment. On all three treated plots, acidity, Al, Fe, and Mn
levels were reduced by at least 50% over the course of the
test. Although the leachate results obtained from the con-
trol plot varied so widely that it was not possible to make
meaningful comparisons between treated and untreated plots,
it was generally observed that the average concentrations
of acidity, Fe, Al, and SOu on the treated plots were always
less than on the control.
-51-
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TABLE 3-7
AVERAGE CONCENTRATIONS
RUNOFF
303.7
Before After
OF METALS IN SUBSURFACE
FROM SLUDGE TREATED PLOTS (LE-094)
Treatment (mt
178
Before
per hectare)
.2
After
77.
Before
8
After
0
Average
Element (milligrams per liter)
Al
Cd
Cr
Cu
Fe
Mn
Pb
SO,,
Zn
Acidity
i
U1
M
1,240
1.14
3.5
11.6
3,700
70
0.33
11,000
24.4
22,940
402
1.92
4.8
7.5
1.260
30
0.23
7,740
36.4
8.900
395
0.31
1.3
3.8
1.280
51
0.16
8,400
8.1
7.310
138
1.18
1.6
3.3
320
17
0.18
3,730
24.8
3,320
440
0.70
2.3
4.0
1,000
71
0.42
7,100
14.1
7,040
346
1.13
3.4
3.6
822
42
0.18
6,770
26.0
5,900
548
0.
2.
4.
1,620
36
0.
7,980
13.
9,770
66
1
5
22
3
-------
While the above results tend to indicate the
positive environmental effects of sewage sludge application,
some negative effects were also observed. The levels of
several toxic metals including Cd, Cr, Zn, and in one case
Pb were found to increase over the test period. It was
concluded that the observed increase in heavy metals con-
centration may have been due to insufficient application
rate; i.e., sludge, which is the source of many of the heavy
metals, was applied at a rate which did not effectively
neutralize the plot acidity, thereby promoting dissolution
of metals added with the sludge.
Disposal of sewage sludge by application to acid
mine spoil thus far appears to be a promising approach to
this problem. Results indicate that crop yields are markedly
improved, that acid stream pollution can be effectively
reduced, and that the devastated land can be returned to
productive use. Future results will provide more detailed
insight into potential contamination of ground water by
trace metals released from the sewage sludge itself.
-53-
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4.0 GENERAL ORE WASTES
The mining and milling industry annually handles
over 3.6 billion metric tons (4 billion tons) of materials,
better than half of which is waste. These wastes can be
classified in three categories: waste rock, tailings, and
mine water. Waste rock, which includes overburden, is the
waste developed during exploration, development, and mining
of ore deposits; this is the material of interest in this
study. Both metallic and nonmetallic minerals will be
included with the exception of coal and other fuels which
are excluded from this discussion because of the unique
impact and magnitude of the acid mine drainage problem
associated with the resultant waste.
4.1 Nature of the Waste
Waste rock occurs as discreet pieces which may be
as large as 2 meters in diameter. It may or may not be
mineralized depending on the particular geology of the site.
If minerals are present, however, their levels are below the
point where it would be economically feasible to recover
them. Exact chemical composition cannot be given in a broad
study of this type because the nature of the wastes are so
much a function of each individual case. The waste does not
contain chemical additives, however, with the possible
exception of traces of explosives, fuel oil, gasoline,
lubricants, or other substances lost during the mining
operation (DU-052).
The Bureau of Mines reports that in 1970 the
output of ore and waste at metal and nonmetal mines totaled
3.7 billion metric tons (4.087 billion tons). Wastes for
-54-
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that year totaled 1.3 billion metric tons (1.410 billion tons)
(US-079). Table 4-1 presents a breakdown of materials
handled crude ore vs. waste) on the basis of mineral mined
and type of mining operation for 1970. Table 4-2 compares
amounts of crude ore and wastes handled by various states.
Data presented in Tables 4-1 which was partially estimated
was not included in Table 4-2; this accounts for the seeming
discrepancies in the total tonnages.
4.2 Disposal Methods
Disposal practices for rock mining wastes, over-
burden and tunnel rock, are not very sophisticated. There
are three options normally available. Of 3.0 billion metric
tons (3.3 billion tons) of overburden produced by the total
surface mining industry in 1966, much was simply redeposited
in the mined-out areas (BO-090). Approximately 10% was used
in the construction of dams for tailings and ponds. The
third alternative involved just heaping the waste in piles
near the mine; these piles are referred to as waste banks.
The environmental effects associated with these
disposal practices include loss of stability in the piles,
reclamation, and erosion. The biggest problem thus far is
the aesthetic issue. Contamination of groundwater by leachate
has not been studied. Duncan reported that the soluble
components of waste rock are a minor source of trouble, the
only problem being with heavy metals. If the dump is properly
sited and managed, however, any metal dissolution can be
effectively prevented from leaving the immediate area (DU-
052) .
-55-
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TABLE 4-1
MATERIAL HANDLED AT SURFACE AND UNDERGROUND MINES,
I
Ul
BY COMMODITIES, IN
1970
(US-079)
(Thousand abort tons)
Commodity
METALS
Gold-
Lode -
Lead
Silver -
Oth. r' ---
Total metals
NONMETAL3
Clavs
Fertile
p
Silt .
Stone
Other'
Total nonmetals
Grand total
Crude ore
13,144
232.058
1.564
1,504
221, 1H7
6
269
6,360
1 138
25
23 698
20
2,746
379
4,613
499.000
217
1.595
3.XH6
12,350
53,668
611
1,553
31
7,161
341
636
124.951
3,230
5,898
943 941
833,964
•6.400
7,932
665
1 445
2,078
2,011. COS
2,510,000
Surface
Waste
' 5.417
606,321
8,342
X95
206,451
6
1.773
48.533
600
135
2.946
84,750
244
2,047
963,000
7
1,669
1,660
16.871
•47,000
2,515
559
33
15,307
419
265,128
S8
2
•70,000
•1,900
981
4.108
1,753
431,000
1.399.000
Underground
Total
'8.561
t.38,879
10.306
2,399
427. 6JK
11
2.042
53.8S3
1.738
160
2b.644
20
S7.416
023
6.560
1.467.CtbO
224
3.264
5,0.15
29.221
100.668
3.126
2.112
61
22.468
760
636
390.079
3.318
5.!>00
943.941
903,964
•7,300
7,932
1,546
6.553
3.831
2,442.000
3. 909. 000
Crude ore
W
27.390
2.175
14.791
10,816
173
16.701
737
711
3.6-S3
9,0^9
16
87,000
40
21
107
1.096
7
776
2.258
415
16.604
15,284
4.221
38,693
32
463
72
80,000
167.0CO
Waste
W
8N3
280
2.234
803
24
107
190
1!
1.061
1.650
7
7.000
2
•16
6
132
933
280
2.673
•270
16
4,000
11,000
Total
W
28.273
2.455
17,028
11,619
197
16,808
927
725
4.704
11,279
23
94,000
40
21
109
1.112
7
781
2.390
419
17.537
15.564
6.894
38,963
32
479
72
84,000
178,000
Crude ore
3,144
259,948
4.139
1,504
235, 9.11
10,822
442
22,061
1,138
7C2
23 . 098
731
G.3J.9
10,003
4.529
686,000
257
1.C16
3,993
12.350
54.764
611
1.560
807
9.419
341
640
125.366
16.604
3,230
21.182
943.311
4.221
872.637
6.432
7.932
1.028
1.446
2.150
2,091.000
2,677,000
All mines
Waste
5,417
607,201
8.622
S95
208.685
S08
1.797
48.640
COO
325
2.916
14
85. Ml
1.&94
2.054
975.000
7
1.6G9
1.6C2
16.871
47.016
2,515
559
38
IS. 439
419
265.132
933
88
232
2.673
70,270
1.900
997
4,103
1.753
435,000
1.410,000
Total
8.661
867,152
12,761
2,399
444,666
11,630
2 239
70 ! 701
1.738
1 , OS7
26,644
745
02, -200
11,902
6,583
1,661,000
264
3,285
5,655
29,221
101.780
3,126
2.119
845
24.858
760
640
390,498
17.537
3,318
21,464
943,941
6,894
942,927
7.332
7,932
2,025
6,553
3.903
2,626.000
4.087.000
• Estimated. W Withheld to avoid disclosing Individual company confidential data.
' Includes underground. Burpau of Mines not nt liberty to publish separately.
1 Antimony, beryllium, magnesium, manganese, platinum-group mcUls. rarc-cirth metals, and vanadium.
1 Emery, garnet, and tnpoli. . , .
• Aplitc. graphite, ereci-i^nd marl, iron oxide pigments (crude), kyanite. lithium mineral*, magncslte. olivmc. pyrites, and
wollutanita.
-------
TABLE 4-2
MATERIAL HANDLED AT SURFACE AND UNDERGROUND MINES (INCLUDING SAND AND
GRAVEL AND STONE), BY STATES, IN 1970 (US-079)
(Thousand ahort tonn)
Alaska
Idaho
Krnlucky
New Hampshire
New Jersey
New Mexico
New York
I'onns) Ivama
South Cnrulma
South Dakota
Tennessee ....
Utah
Virginia
Wishing ton —
Went Virginia
Wvo-nine
Other States'
Total
Crude ore
30.072
35,753
157,550
32.209
218.834
26,818
15,476
183,039
39,708
, 20,914
99,534
50.4C4
46,716
, 27.8S7
33,914
32,595
, 14,232
29.9SO
26,315
128,834
208,007
13,051
50,218
46.453
16,499
32,725
6,966
33.895
41,074
82,015
SI, 728
8,280
91,077
24,799
33.318
84,501
2,808
18,007
18,865
43,334
. 92 297
61.848
6 54*
40.951
39.712
12.178
61.09S
18, 2M
8.792
2,507.000
Surface
Waste
23.921
1,251
350.273
6.247
67.205
133
40
220.944
49
16.675
6.966
1
1,039
16.062
106.631
1.162
43,291
64,057
234
122,357
4,016
15,021
6,411
609
975
263
4,649
8,862
11,909
101,558
621
35
1,217
3.692
72.159
22
1,279,000
Underground
Total
61,593
37,004
507,813
38,456
280,039
20,951
16,51 6
403,983
S'J,757
37,5*3
99 534
50,4nt
02,6R2
27,8*7
33,915
32,595
15,271
29,980
26.345
144,896
314,638
13 051
5:.3i>u
89.744
16,499
96.782
6,966
34,129
163,431
86.051
66,749
8,280
91,077
31,210
33,927
85,476
2.808
18.270
23,514
52.196
104.206
163,406
7.169
46.986
40,929
11. ITS
64.790
90.379
8.814
3. 786.000
Crude ore
2.070
5
16.947
830
2.187
18.708
1,008
1,546
2,764
606
1,964
2.818
5.373
6,277
32
126
12,715
21.860
730
87
78
169
19.316
6,302
100
6,087
992
53
6,946
1,994
11.862
628
1.630
191
2,997
299
2,380
837
6,347
167,000
Waste
207
3
625
2
179
894
276
35
56
20
244
1,031
180
36
1
1,423
202
100
1
928
146
705
6
402
6
62K
160
42
2,713
11.000
Total
2. 277
8
17.672
832
2.366
19.602
1,008
1.822
2.764
901
1,964
2.874
5,374
6,297
32
126
12,959
22.941
910
37
114
170
20,739
6,504
100
6,187
992
64
7.874
2,140
12,557
633
2,032
197
3,623
459
2.3M)
879
8,060
178.000
Crude ore
32.742
35,758
174,497
33.039
221.021
46.626
15.476
183,039
40.716
22.460
102.298
61,330
48 680
30.705
39.287
38.872
14.264
30,106
26,345
141.549
20S.007
13.051
72,078
47.183
16,536
32.803
6.966
34.064
60,390
8S.337
51.828
8,280
97.164
25,791
33.371
91.417
2.808
18.007
20.859
65.186
92.925
63.478
6.739
49.943
40.011
14.568
61 .935
23.567
8.792
2.674.000
All mines
Waste
24,128
1,254
350.898
6.249
67,384
1,027
40
220.944
49
16,951
35
5,966
66
2
20
1,039
16,306
106.631
2.243
43.471
64.093
235
123.780
4.218
15.021
100
6.411
610
1.903
263
4.795
9.667
11.914
101 .960
627
663
1.377
3.734
74.S7J
22
1.290.000
Total
56.870
37.012
625.395
89.288
288.405
46.553
15.516
403.983
40.765
39.411
102.293
51.365
54.646
30.761
39.2H9
38.892
15,303
30.106
26.345
107. SI5
314,638
13.051
74.3.11
90.654
1C. 536
96,896
6.966
34.299
184.170
92.555
66.K49
8 J.XO
97.264
32,202
3J.9H1
93,350
2,808
18,270
25.654
64,763
104.839
165,438
7.366
SO. 611
4 1.3." H
14.558
65.669
98.439
8.814
8,964.000
' Partially estimated datn in table 1 not Included In State totals.
' Delaware and Hawaii.
-------
Because of the lack of any highly developed technology
for disposal of this waste, no case study will be presented.
-58-
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5.0 CULM PILES
The coal mining and preparation industry is faced
with several types of solid waste disposal problems. The
mining operations yield a waste consisting of rock and other
impurities removed during the development and working of the
mine. The quantities generated by underground mining are
relatively minor and are generally considered to have little
environmental impact. This type of waste becomes a major
problem in the strip mining industry, however, where vast
amounts of material covering the coal bed are removed and
placed in "spoil banks" adjacent to the strip. Reclamation
of these banks is currently under extensive investigation.
The solid waste of interest in this section is the
refuse generated by the coal preparation processes. To
produce a marketable coal, the raw coal must be crushed,
sized, separated from impurities, and washed. Coarse coal
is usually recovered in a dense-medium process. The coal is
floated off in a suspension of finely divided solids in
water, in aqueous solutions of inorganic salts (e.g., calcium
chloride), or in an organic liquor. A flotation process is
employed to beneficiate the fine coal, often using kerosene
plus pine oil as the flotation agent. These operations are
carried out in plants in the vicinity of the mine. Two
types of waste products result: coarse refuse (>1 mm) and
fines (<1 mm) (MC-096). The fines are typically disposed of
by slurrying to a settling pond. The coarse refuse is often
a major disposal problem, especially if the raw coal is of
low grade. Between 5 and 30% of the coal can be deposited
with the coarse refuse, depending on the efficiency of the
separation process. Most modern techniques seldom leave
more than 5% saleable coal in the refuse, while older culm
piles often contain up to 30%, and in some cases, up to 75%
recoverable coal. This washer plant waste is commonly
-59-
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accumulated in dumps called "culm piles", sometimes referred
to as gob piles, coal refuse banks, or breaker refuse. The
waste contained in older culm piles usually was sorted from
the coal by hand. .These piles may be as high as 200 meters
(700 feet) and over 1.6 kilometers (one mile) long.
5.1 Nature of the Waste
The composition of coal refuse piles depends on
the geological characteristics of the coal seam and over-
burden, efficiency of the beneficiation process, and whether
or not the preparation plant waste is disposed of separately
from mining wastes and settling pond solids.
The culm material generally consists of waste
coal, slate, bone, carbonaceous and pyritic shales, and clay
associated with the coal seam. Thick-seamed coal tends to
have a high proportion of bone, whereas thin-seamed coal
wastes will be low in bone and high in clay shales. Process-
ing plant wastes from strip-mined coal are characterized by
significant amounts of fine sand, silt, and clay. Davies
reported that typical concentration ranges for major compo-
nents were: 15-40% waste coal (except when settling pond
solids are deposited with culm, resulting in up to 60% coal
content); 30-70% carbonaceous and clayey shale; and 10%
sandstone (DA-075). A typical chemical and physical analysis
of culm material and coal fines is given in Table 2-1.
The types and proportions of individual components
affect the physical and engineering properties of the bank
as well as the chemical features. Shale, for example, is
very susceptible to weathering, resulting in fragments that
are resistant to compaction. Sandstone, on the other hand,
weathers into slabs and irregularly shaped plates, presenting
little problem in the bank. Clay either enters the bank as
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TABLE 5-1
CHEMICAL AND PHYSICAL CHARACTERIZATION OF SELECTED
PREPARATION PLANT WASTES (US-055)
Sample description
I
cr\
Culm bank
(gob) material
Coal fines '
Moisture (percent) .. .............................. 0.6 0.9
Ash (percent) .... ............................... 62.6 15.4
Sulfur (percent) ....................................... 3.17 1 56
Carbon (percent) ................................ 23.32 7831
Volatile matter (percent) .. ......................... 15.5 25.2
Loss on ignition ... . .................................. 37 . 2 83. 8
Btu [[[ 4,710 12,320
Ash Anahsis
SiO, (percent) ......................................... 57.60 51.00
Al,0, (percent) ...................................... 28.10 28,10
Fe,Oj (percent) .................................... 8.74 11.20
TiO, (percent) .................................... 1.31 1.22
CaO (percent) ..................................... .59 .89
MgO (percent) .................................... .64 .63
Na2O (percent) ............................................ -53 .44
K2O (percent) ............................................. 2.16 1.80
Fusion Properties
Initial deformation temperature (°F) ................... 1,830 1.620
Softening temperature (spherical) (°F) ................... 2, 900+ 2. 730
Softening temperature (hemispherical) (°F) ............... 2,900+ 2.750
Fluid temperature (°F) ............................ 2, 900+ 2. 770
Physical Propci lies
Water solubility (percent). . .. ........................ 1.4 88
Water nbsoiplion (percent) ........ ................. 2.7 284
Bulk ilcnsitv (Ib/fi3 ) ..................... 69.0 46.5
Ciiinpac-trd bulk density (Ib/ft1) .................. 70.0 53.0
-------
an integral quantity (i.e., not well mixed with other
components) or ultimately winds up in the settling pond.
The overall bulk density of culm material generally ranges
from 1300-1800 kg/m3 (80-110 lb./ft.3) although the extremes
may be 800-2,000 kg/m3(50-125 lb./ft.3).
The particle size range of coal refuse depends on
the period during which the mining and processing took
place. Modern banks contain greater proportions of finer
particles; predominant sizes range from barley [0.24-0.48 cm
(3/32"-3/16")] to egg [6.19-8.25 cm (2 7/16"-3 1/4")] (MA-
222, US-079). Older banks have the following particle size
distribution (DA-075):
30-60% silt or smaller size
30-50% coarser than silt up to
5 cm (2 in.)
20-30% greater than 5 cm
The silt fraction is much larger, of course, if settling
pond solids are included. All of these different fractions
are subject to layering; i.e., as the pile is being formed
and later, as erosion occurs, fines tend to be removed and
larger particles may collect at the base. This phenomenon
is especially evident in poorly engineered projects.
Culm piles occupy many acres of land in coal-
bearing regions of the country. Until the 1950's, they were
considered to be necessary features of the mining industry,
and no attempts were made to reduce them or lessen their
environmental impact. With the passage of the Air Pollution
-62-
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Control Act of 1960, the Clean Air Act and its amendments,
the Air Quality Act of 1967, Solid Waste Disposal Act of
1965, and several state legislations, interest in these
disposal sites began to grow.
In 1965 and 1966 the U. S. Bureau of Mines and the
Pennsylvania Department of Mines and Mineral Industries
surveyed culm piles in Pennsylvania's anthracite region to
determine the extent of that particular problem. The results
indicated that 800 anthracite refuse piles, each containing
at least 7,600 cubic meters (10,000 cu. yd.) of waste material,
occupied a total surface area of 4,872 hectares (12,038
acres) and contained approximately 700 million cubic meters of
solid waste (BU-086). Seventy three percent of the banks
were located within two miles of a population center (>625,000
population). Twenty seven banks were reported to be burning.
An additional 63 banks containing less than 7,600 cubic
meters (10,000 cu. yd.) of waste were also noted but were
not included in the survey because of their relatively small
size.
During 1969, more than 395 million metric tons
(435 million tons) of raw bituminous coal were processed in
the United States, yielding 23% waste on the average (BU-
086) . This amounted to 91 million metric tons (100 million
tons) of bituminous-generated wastes for just one year.
Prior to 1969, 1,677 million metric tons (1,849 million
tons) of bituminous washer plant reject had accumulated (BO-
090) .
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5.2 Conventional Disposal Technology
The disposal method for coarse preparation plant
waste traditionally involves transport to a disposal site.
There the material is spread and compacted to achieve
stability. Reclamation techniques are now commonly practiced.
5.2.1 Disposal Site
Disposal sites, until reclamation regulations were
recently passed, were selected on the basis of size, and
proximity to the preparation plant. Topographical features
are more heavily considered now; valley-filling is advan-
tageous in that two supporting sides are naturally sealed.
Refuse deposits on flat terrain, on the other hand, require
more manpower, equipment, and time since sides must be
terraced, compacted, sealed, and vegetated. This type also
offers more opportunity for spontaneous combustion since
more surface is exposed to air. Active and abandoned strip
mine pits can provide disposal sites for both coarse and
fine preparation plant wastes.
5.2«2 Disposal Procedures
Most sites today receive some sort of preparation
prior to deposition of refuse. Removal of existing vegeta-
t-ion aids in fire prevention. Water drains and diversions
are often installed to prevent storm runoff from eroding the
sides of the pile as well as to reduce acid mine drainage
formation. Existing streams may be diverted from passage
too close to the waste bank. Roads for trucks or other
transport must also be constructed. In some cases, drainage
basins for pile leachate and runoff are provided to collect
water for neutralization treatment.
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TABLE 5-2
REFUSE DISPOSAL (BU-086)
Company
Bethlehem Mines Corp.
Do
Beth-Elkhorn Corp. ...
Do
Eastern Associated
Coal Corp.
Pittsburg & Midway
Coal Mining Co.
Do
U.S. Steel Corp
Mine
location
Barrackville ,
W. Va.
Ellsworth, Pa.
Jenkins , Ky ...
do
Rachel, W. Va.
Cadiz, Ohio...
Hallowell,
Kans.
Madisonville ,
Ky.
Union town , Pa .
Mine name
and type
Idamay mine No. 44
(underground) .
Mine 601
(underground) .
Hendrix No. 22
(underground) .
No. 27 mine
(underground) .
Joanne mine
(underground) .
Georgetown Area
(strip mine) .
Mine 19 (strip
mine) .
Colonial mine
(strip mine) .
Ginger Hill
(underground) .
Refuse
produced,
tons
per day
1,100
2,800
765
1,170
600
4,164
2,400
1,100
4,500
Mode of
transportation
Truck and
aerial tram.
Truck
Conveyor belt
and truck.
Truck
•••••• uo •••••••
Underground
rail mine cars
and carryall.
Distance to Refuse
disposal site disposal
(one way) , cost/
miles ton/mile
1.0 $0.28
1.0 .17
.5 .10
1.0 .13
1.0 .13
1.0 .16
1.0 .25
2.0 .10
2.0 .10
4.0 3 .09
I
Ol
1Abandoned dumps; refuse from Mines 51
2Direct cost only.
and 58 being disposed at Mine 60 dump by aerial tram.
-------
The disposal operation itself consists of several
phases: transport of waste to the site; spreading and
compaction; soil covering; and revegetation. The Bureau of
Mines has recently reported the results of a technical and
economic study of these phases of coal refuse disposal (BU-
086). The following is a summary of their findings.
Transport is most commonly via truck although
aerial trams, conveyor belts, and underground mine cars are
in operation at some facilities. Costs for transport ranged
from 6-19$/metric ton/km (9-28C:/ton/mile) . Table 5-2 gives
further details of the studies from which these figures were
obtained.
Spreading and compacting is usually accomplished
with bulldozers and trucks. Compaction is necessary to hold
the material in place. This procedure also serves to prevent
spontaneous combustion to some extent by reducing the air
supply to the combustible coal in deeper regions of the
pile. It also is effective in preventing air and water
pollution. A relatively new technique now in use is to
sandwich the combustible waste between layers of noncombusti-
ble material such as clay, shale, coal sludge fines, fly
ash, or industrial wastes (gypsum or cement plant by-products)
Terracing is simultaneously done in some cases where simply
sloping the edges does not provide sufficient stability to
the pile. The economics of this disposal phase are rela-
tively inexpensive compared to other phases. The Bureau of
Mines reported handling costs ranging from 3.3-22
-------
TABLE 5-3
REFUSE SPREADING AND COMPACTION (BU-086)
Company
Bethlehem Mines Corp. . .
Do
Beth-Elkhorn Corp
Do
Eastern Associated Coal
Corp.
Pittsburg & Midway Coal
Mining Co.
Do
U.S. Steel Corp
Mine location
Barrackville, W. Va.
Ellsworth, Pa
Jenkins , Ky
do
Rachel, W. Va
Hallowell, Kans.....
Madisonville , Ky....
Mine name
and type
Idairay mine No. 44
(underground).
Mire 601
(underground) .
Hendrix No. 22
(underground) .
No. 27 mine
(underground).
Joanne mine
(underground) .
Georgetown Area
(strip mine).
Mine 19 (strip
mine) .
Colonial mine
(strip mine).
Ginger Hill
(underground).
Spreading
and
compaction
equipment
Trucks and
bulldozer.
(3)
Bulldozer. .
Carryall. . .
Refuse
handled,
t on s pe r
day
1,100
2,800
765
1,170
600
4,164
2,400
1,100
4,500
Handling cost
per ton
$0.03
.05
16
.13
3.11
.10
.20
.12
(*)
I
en
1 Abandoned dumps; refuse from Mines 51 and 58 being disposed at Mine 60 dump by aerial tram.
2Estimated.
3Refuse disposed of in pit areas. No spreading or compacting.
4Included in the cost of refuse disposal, table 2.
-------
hectare ($665 to 10,900 per acre) as shown in Table 5-4; the
latter figure was reported by a company who privately con-
tracted this phase at a fee of $0.55/metric ton ($0.50/ton)
of soil. These figures include soil, transportation, spread-
ing, and compacting. The cost depends on availability of
soil, hauling distance, size of equipment used, and depth of
cover to be placed. In this particular survey, the metric
tons of soil applied per hectare varied from 2,960 to 19,727
(3,263-21,750 tons). This last figure corresponds to the
highest cost per hectare given above. A less costly technique
being developed by the Bureau of Mines involves fly ash
application instead of soil cover. This topic is described
in detail in Section 5.4 where case studies are presented.
After the soil has been spread and compacted,
usually in 20-30 cm layers, soil conditioners, fertilizer,
mulch, and/or seed may be placed. Extensive studies are
underway to determine the species of grasses, legumes,
shrubs, and trees best suited to this growing environment.
Preliminary results are reported in the literature (BU-086).
Costs associated with planting vary widely depending, of
course, on the quantity, variety, and availability of
vegetation to be planted and on the use of soil additives,
if any.
5.2.3 Environmental Aspects of Culm Piles
Several environmental issues exist with respect to
the disposal of coal refuse in conventional culm piles. One
of the most extensively studied problems is air pollution
from burning refuse piles. Also, there is the coal industry's
problem of acid mine drainage. In addition, physically
-68-
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TABLE 5-4
SOIL COVERING AND PLANTING (BU-086)
Company
Bethlehem Mines
Corp.
Do
Beth-Elkhorn Corp.
Do
Eastern Associated
Coal Corp.
Pittsburg & Midway
Coal Mining Co.
Do
U.S. Steel Corp. . .
Mine
location
Barrackville,
W. Va.
Ellsworth, Pa.
Jenkins , Ky. . .
do
Rachel, W. Va.
Cadiz , Ohio. . .
Hallowell,
Kans.
Madisonville ,
Ky.
Uniontown, Pa.
Mine name
and type
Idamay mine No. 44
(underground).
Mine 603
(underground) .
Hendrix No. 22
(underground) .
No. 27 mine
(underground) .
Joanne mine
(underground) .
Georgetown Area
(strip mine) .
Mine 19 (strip
mine) .
ColonxsX ml. nc
(strip mine).
Ginger Hill
(underground) .
Soil cover,
tons per
acre
3,300
21,750
4,350
—
13,235
4,538
8,700
6 525
V f JffJ
3,263
Soil cover,
cost per
acre1
$833
4 10 900
JL v j y \j\j
1,300
—
1,323
1,598
700
700
/ w
665
Vegetation planted
Grasses, black locust,
white pine.
White nine oerennial rve
Kentucky fescue, Serecia
lespedeza.
White pine, annual rye,
Kentucky fescue, Serecia
lespedeza.
White pine short leaf
pine, loblolly pine.
Grasses, locust, white
pine.
Kentucky fescue orchard
grass, crown vetch.
Kentucky fescue , Serecia
lespedeza, locust trees.
If an ^ 1 1 /* If *r f 0sf*ii0 1 n\t&
^CLILUl»lvy ,LCol>UC j XUVC
grass, Serecia kobe,
Serecia lespedeza.
Crown vetch, black locust,
pine trees , perennial rye
grass, Kentucky fescue.
Planting
cost per
acre2
$165
5 AAO
•***A
50
8 60
VU
7 148
48
•TO
50
Cf\
8 455
VO
I
1Includes soil, transportation, spreading, and compacting.
sCosts not footnoted are those for planting grasses and trees on soil cover not conditioned.
3Abandoned dumps; refuse from Mines 51 and 58 being disposed at Mine 60 dump by aerial tram.
4Privately contracted at 50 cents per ton.
6Includes cost of lime, paper mulch, fertilizer, grass seed applied by hydroseeding, and trees planted by hand.
Weighted average cost for 1966, 1969, and 1970-71 projects.
6Soil cover not used. Trees and grasses planted directly on refuse not previously conditioned.
'Includes cost of lime, mulch, fertilizer, seed, and trees.
8Includes cost of soil conditioning, hydroseeding, end tree planting. Direct cost only.
-------
degrading phenomena such as surface erosion and bank
instability are not uncommon. Aesthetic objections also
must be contended with in many situations; these are related
to land use aspects.
In 1968 the Bureau of Mines identified 292 burning
refuse banks in 13 of 26 coal-producing states by visual
signs only (MC-096); a higher number would probably have
been obtained if infrared photography had been used to
detect below-the-surface fires. Coal refuse piles can be
ignited by spontaneous combustion, freak accidents of nature,
or by man. The causes of 66% of the 292 burning piles could
be traced to spontaneous combustion.
The immediate effects of burning refuse piles
entail air pollution by smoke, dust, toxic and noxious
gases; thermal waves; and aesthetic effects. A number of
deaths and accidents have been attributed to burning banks.
In addition, the gases emitted have damaging effects on
nearby vegetation, certain metal surfaces, and lead-based
paint. Some forms of water pollution result from absorption
of some of the gases and fine particulates generated. Smog
can also form in vicinities of these piles during periods of
precipitation.
-70-
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Another important environmental aspect of culm
piles is the acid mine drainage problem which can be des-
cribed by the following set of reactions. Equation 5-1
describes the overall reaction, while Equations 5-2 through
5-4 show the stages through which the phenomenon proceeds.
2 FeS2 + 702 + 2H20->.2 FeSO,, + 2 H 2SO „ (5-1)
4 FeS, + 15 0, + 14 H.O + 4 Fe(OH) , + 8 H ,SO L (5-2)
4 FeS(V+ 2 H2S(\ + 02 + 2 Fe2(S(\)3 + 2 H20 (5-3)
Fe2(SOJ3 + 6 H20 -* 2 Fe(OH)3 + 3 H2S(\ (5-4)
Waste coal refuse containing pyrite will generate
significant amounts of sulfuric acid and iron sulfate in the
presence of air and water. To control this problem, several
approaches are feasible:
prevent acid mine drainage formation
by cutting off supply of air and/or water
remove iron from system by precipitation
as insoluble salt
neutralize acid mine drainage
-71-
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5. 3 Alternate Disposal Technologies
Several possibilities exist for alternate schemes
for coal refuse disposal. These include:
hydraulic backfilling of mine voids
coal recovery from culm pile material
utilization of refuse material in
construction materials
The only one of the above practiced to any extent is coal
recovery; even this approach does not completely solve the
problem since there is still a substantial waste left over
which must be disposed of.
A project was proposed by the Bureau of Mines in
1972 to demonstrate the feasibility of hydraulically inject-
ing crushed coal waste.into deep mine voids (LY-005). The
main thrust of the program is mine subsidence control, not
mine refuse disposal, although 230,000 cubic meters (300,000
cu. yd.) of refuse is involved. The site proposed was the
flooded and dry mine voids in the Clark and New County coal
beds beneath Scranton, Pennsylvania.
A survey taken in 1966 in the anthracite region of
Pennsylvania revealed that contracted costs for backfilling
of mine voids with culm bank material ranged from $1.60 to
4.70 per cubic meter ($1.25-3.60 per cubic yard) (MA-222).
This included crushing, transport, and hydraulic backfilling,
-72-
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RADIAN CORPORATION
During 1970, 31% of the annual anthracite coal
production came from coal recovery from 97 culm and silt
banks (US-079). This is now warranted since the small
particles of coal, for which formerly there was no use and
therefore were disposed of, are now highly useful as fuels and
as lightweight aggregate (MA-222). Recovery of saleable coal
seldom exceeds 20%, or 40% in the case of silt banks. Factors
such as special contaminants in the refuse, location of the
site, and its remoteness from potential markets must be con-
sidered. The processes used for coal recovery are generally
the same as those employed for freshly-mined coal with
modifications to handle larger quantities of dirt. One
process, the Simdex Process, was designed especially for
waste coal recovery. Details of this and other techniques
are available in the literature (HA-186).
The Office of Coal Research and West Virginia
University are currently studying several utilization schemes
for culm pile materials. These include its use as aggregate
in asphalt concrete material for road base construction and
as an admixture in cement for mine stoppings (US-055) . In
this context, the strength and fire resistance of the waste
is being determined. In general, utilization as a light-
weight aggregate is hampered economically by the normally long
distances between the culm piles and the potential market.
Use as landfill in housing and industrial
developments and as backfill for strip mined areas are
closely related. The fire prevention technique commonly
practiced is mixing the waste and covering with a clay
blanket; other methods can also be employed. The costs
vary with each project, as determined by size, shape, and
location of the bank; size and number of equipment required;
-73-
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and distance to the landfill site. No real cost data are
available, but it is estimated that costs should be lower
than for backfilling mine voids (MA-222).
5.4 Case Studies - Culm Pile Reclamation
The Bureau of Mines has been actively engaged in
the disposal and reclamation of mining wastes since passage
of the Solid Waste Disposal Act of 1965. The potential
agricultural uses of fly ash were recognized early, and in
1964 research into its use as a soil conditioner and nutrient
in greenhouse studies was begun. During the next few years
several field tests were initiated employing fly ash in
reclamation of strip mine spoil areas. In 1970 and 1971
the program was expanded to include several coal refuse banks,
or culm piles, in the vicinity of the Morgantown Energy
Research Center (AD-016, CA-112, CA-135). Three such demon-
stration sites were visited during the course of this investi-
gation, and the information obtained is summarized below.
Their first attempt at reclamation of a coal refuse
pile was initiated in 1970 on a one-acre plot at the Bunker
site. This pile, as most in the area, consisted of shale,
rock, bone coal, and quantities of bituminous coal of various
sizes. This refuse was hand-sorted waste from a deep-mining
operation. A section of the pile had at one time been on
fire; consequently, some quantities of "red dog" (oxidized
pyritic materials) were also present.
The reclamation procedure began with a leveling
operation. The plot was then treated with fly ash at a rate
of 340 metric tons per hectare (150 tons/acre).
-74-
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The source of the ash was that collected by electrostatic
precipitators at the Fort Martin power plant, Allegheny Power
System. A typical analysis of this ash is given in Table 5-5.
The ratio of fly ash to refuse was adjusted empirically under
laboratory conditions to obtain a near neutral condition. The
ratio was then used to calculate the fly ash application rate
based on a 15-cm plow layer depth of soil material. Depending
on the extent of refuse acidity and ash alkalinity, these rates
can vary between 170 and 900 kg/hectare. The rate used in this
particular instance corresponded to a 4-5 cm application of fly
ash.
The type of machinery used for leveling, spreading,
and mixing fly ash with the refuse depends primarily on the
terrain. Conventional farm equipment may be suitable in some
cases, but more often heavier equipment is required. The
equipment available to the Bureau of Mines included a bull-
dozer, front end loader, ripper, and rome plow. Large,
powerful dump trucks are usually needed to haul the fly ash
over the rough surfaces.
After the area was prepared, fertilizer and seed
were applied by dry methods. These operations are normally
carried out using a farm tractor and a rotary seeder. A
granular 10-10-10 fertilizer was employed at the Bunker site
at a rate of 1100 kg/hectare (1000 pounds per acre). Equivalent
rates of a triple-16 or triple-12 type fertilizer have been
used at other sites. A typical seed mixture applied in these
projects is shown in Table 5-6; rate of application was
^50 kg/hectare N45 pounds/acre). The birdsfoot trefoil is a
legume which usually gives good results. The symbiotic
nitrogen-fixation activity between legumes and root nodule
bacteria is very beneficial, especially in areas where periodic
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TABLE 5-5
TYPICAL ANALYSIS OF
FORT MARTIN FLY ASH (AD-016)
Constituent
Major elements, wt pel
SiO,
Al,0,
Fe,0,
CaO
MgO
Na,0
K,0
TiO,
PiO,
C
S
Lou on ignition
Trace elements, ppm
B
Cu
Mn
Mo
Zn
Bulk density, g/cc
PH
Fineness, pet through 200 mesh
Average size, micron
46.8
23.3
17.5
5.7
1.1
.8
2.0
.7
.5
1.5
.4
5.1
450
40
200
20
90
MS
11.9
91
19
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TABLE 5-6
SEED MIXTURE TYPICALLY USED IN
BUREAU MINES RECLAMATION PROJECTS (AD-016)
Seed Weight-Percent
Kentucky 31 Fescue 35
(Festuca Arundinacea)
Red Top Grass 14
(Agrostis Alba)
Orchard Grass 18
(Dactylis Glomerta)
Birdsfoot Trefoil 5
(Lotus Corniculatus)
100
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fertilizer application is impractical. Other varieties of
grasses and other plants are being studied to determine their
potential use in such projects. Those that have performed
successfully include: weeping lovegrass, yello sweet clover,
switchgrass, costal panic grass, and common goatsrue. Less
successful results have been obtained with wild rye, deer-
tongue, flat pea, and bluestern.
Procedures normally carried out during later growing
seasons include a light fertilizer application in the spring
equivalent to 225 kg/hectare (200 pounds/acre) of 10-10-10.
Depending on availability of manpower, equipment, etc., some
areas may be reseeded if the first seeding did not produce
satisfactory results.
The results obtained at this site have been very
encouraging. The dominant species, at least during the first
year's growth, was red top; the growth rate of the other
species picked up during the second growing season. While the
first year's production cannot be expected to yield results
comparable to surrounding farmed area, 1971 hay yields at
this site were reported to be 2.2 metric tons/hectare (0.6
dry tons per acre). The average yield of hay grasses for the
West Virginia area is 3.4 dry metric tons per hectare. Better
results were predicted for the following year.
The beneficial effects of fly ash application on
spoil and coal refuse are listed in Table 5-7. The neutraliz-
ing ability is the most important benefit since acidity is
the limiting factor in plant survival in this type of material.
Although detailed results have been reported for spoil areas,
only limited data were available for culm pile treatment.
These are presented in Table 5-8 for the Bunker site and two
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TABLE 5-7
BENEFICIAL EFFECTS OF RECLAIMING SPOIL
AND COAL REFUSE WITH FLY ASH (CA-112)
1. Acidic materials in spoil and refuse are neutralized.
2. Heavy clay and light sandy soils are changed to medium-
texture soils.
3. Moisture-holding capacity increased.
4. Pore-space volume increased.
5. Grasses and legumes established as immediate cover
that resists erosion and reduces stream pollution
potential.
6. Forage yields from fly ash-reclaimed areas compare
favorably with undistributed pastures and fields.
7. Consumption of tonnage amounts of fly ash.
8. Addition of some available major and trace plant
nutrients.
9. Temperature of refuse surface is reduced, thus reducing
moisture loss and preventing plant burning.
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TABLE 5-8
EFFECT OF FLY ASH TREATMENT ON pH OF
BITUMINOUS COAL MINE REFUSE (CA-112)
Site number
and name
A
Bunker
B
Shannopin
C
Cassville
Coal scam
mined
Sewickley
Pittsburgh
Pittsburgh
Area.
acres
1
10
7
pH before
treatment
27-30
40-40
30-38
Fly ad)
rate
tuns/acre
150
Variable1
150-200
pH after
treatment
7 2-7.6
4.0-80
44-76
Years since
fly ash
applied
3
2
2
Average
current
pHfur
area
71
7.4
60
Fly »h was used to cuvei the refuse in order to prevent ipontincoui combustion
-80-
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additional case studies described in this section. It is
generally true that periodic reapplication of fly ash or
other alkaline material is necessary to prevent the reclaimed
area from converting back to its original acid conditions.
The second coal refuse area to be reclaimed by
the Bureau of Mines was the Cassville site, a seven acre
area located in rough, hilly terrain also consisting of hand-
sorted waste from a deep-mining opeation. A great deal of
effort had to be expended in clearing this particular area
of trash before reclamation operations could proceed. Again,
sections of the pile had been on fire at one time. Conse-
quently a great quantity of "red dog" was scattered throughout
the site. Another type of rock formation in abundance here
was sulfur balls; these are pieces of pyritic material which
are worn to this shape by the weathering process.
The initial work was done in 1971 on a 2-acre
portion at the top of the hill. The procedures employed were
similar to those used at the Bunker site. As indicated in
Table 5-8, the fly ash application rate was 340-450 metric
tons/hectare (150-200 tons/acre). The results were success-
ful in that the field was well established with grass. As
at the Bunker site, the dominant species at the end of the
first growing season was red top, with other grasses becoming
established afterwards. The available moisture content
increased from 12.68% for untreated refuse to 18.46% for fly
ash treated Cassville refuse (CA-112). The original pH
.range, 3.0-3.8, had increased to 4.4-7.6 when measured two
years following the original ash application.
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The third area included in this study was a 10-
acre site on the west bank of the Monongahela River near
Poland Mines, Pennsylvania. This site also had been on
fire, but unlike the others described above, had received
fly ash treatment for fire control. No further fly ash was
applied as a reclamation effort; preliminary soil tests
indicated that ripping should sufficiently mix the ash and
refuse beneath to support grasses. However, after seeding
and fertilizing, germination and growth were poor. Although
the 1971 growing season was a dry season, the main reason
for the poor results was attributed to the uneven fly ash
distribution as indicated in Table 5-8. Consequently, the
pH of the site was not favorable in most spots and the
resulting vegetation was very sparse.
The following year, plans were made to treat the
same area with an alkaline sludge resulting from an acid
mine drainage neutralization process. Originally, the
sludge application rate was to have been ^340 metric tons/
hectare (^150 tons per acre); however, only about 20-25
metric tons/ hectare (10 or 11 tons per acre) was actually
applied because of difficulties encountered in obtaining the
sludge. Results at the end of the 1972 growing season were
somewhat disappointing, but since exceptional first year
results are not expected in a project of this nature, the
second year's growth would be more indicative of the extent
of success. Again, an unexpected problem was encountered
when the surface area was almost entirely dug up by the coal
company. The only portion not harmed by the heavy equipment
was a strip approximately six meters long and one or two meters
wide which appeared to have a good growth of grasses established
on it during March of this year (1974). Much of the vegetation
established here was native grasses including barnyard grass,
Johnson grass, and broomsage rather than the seeded species.
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Costs for reclaiming coal refuse piles depend on
many factors such as terrain, soil type and age, acreage,
equipment used, legislative requirements, degree of reclama-
tion desired, fly ash and other materials availabilities,
and hauling distance. Since no soil cover is required and
since most fly ashes could be obtained free of charge or at
least at very low cost, costs would compare favorably
with the usual reclamation procedures. In fact, the Bureau
of Mines has assigned a market value to fly ash based on
equivalent cost of materials found in the ash. These results
are shown in Table 5-9. Estimated cost of reclamation by
this method is $740 per hectare ($300 per acre) of previously
leveled land; the cost of leveling is not included because
it can vary extremely from one site to the next. Although
this estimate has not been confirmed in practice, it appears
that this fly ash technique can compare favorably with most
coal refuse pile reclamation methods.
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TABLE 5-9
EQUIVALENT COST OF MATERIALS
FOUND IN FLY ASH (CA-112)
Material
CiO
K,0
PiO,
Trace dementi
Fine und and
alt1
Priccnl
68
2.0
S-
BCXXppm)
85.6
Amount in ISO-Ion
application
10 2 tons'
6.000 Ib
1.500 Ib1
240 Ib
128 toni4
Total
Mattel value
S 41.60
232.20
256.00
$529.80
'lOO -14.4 percent (tun of Um .fellUar. and lanltion k») • 85.6 pmnd (lot and.
'UimilM/tan.
'hnfltwr il S30/I jOOO pound..
*Rata»diadaUlatSl/iOB.
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RADIAN CORPORATION
6.0 PHOSPHATE SLIMES
The annual U. S. production of marketable phosphate
rock in 1970 was 35 million metric tons (BA-133, US-079).
Florida has been the leading producer for many years, having
74% of the domestic production that year. Approximately 90%
of that yield comes from the land-pebble region of central
Florida (US-027). Other phosphate mining states include, in
order of production capacity, Tennessee, North Carolina,
Idaho, Montana, Utah, Wyoming, and California (BA-133). The
total mine output for 1970 was 114 million metric tons (US-
079) . The difference between this figure and the total U.
S. marketable production figure indicates that a vast amount
of waste is generated during the beneficiation processes.
These wastes take two forms, phosphate slimes and sand
tailings. Close to one-third of the total tonnage of mined
matrix is slime which, after ore processing, occupies approxi-
mately 50% more volume than the original matrix. When the
mined-out area is used as the disposal site, about one-third
more volume is needed than is available (BA-133, US-027).
As of 1968, accumulated phosphate wastes totalled
560 million metric tons covering 3,990 hectares in 16
states (BO-090). In Florida alone there are an estimated
434 million metric tons of slimes containing 56 million
metric tons of P20s, with an additional 3.6 million metric
tons of PaOs being added each year (BO-074). This amounts to
~38 million metric tons of slimes disposed of annually at 4-6%
solids. Approximately one-third of the total tonnage of matrix
mined is slimes.
6.1 Phosphate Mining and Beneficiation
Phosphate rock ore is mined by the open pit method
in all four major production areas (Florida, North Carolina,
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Tennessee, and the western states). Some underground mining
is also conducted in the Western fields. In Florida's land-
pebble deposits, the overburden is stripped and the ore
mined by electric dragline excavators equipped with buckets
up to 38 cubic meters. The matrix is first placed in a
sluice pit, then slurried at 40% solids and pumped through
movable steel pipelines to washing plants, which may be
several miles away (BA-133, US-027). In North Carolina a 55
cubic meter dragline is operating; as in Florida, the ore is
transported hydraulically. This is not the case, however,
in Tennessee and the Western fields where either truck or
rail haul is used.
The ore beneficiation process usually involves
size reduction, washing, desliming, and flotation, although
some ores are marketable as mined, especially those deposits
located in the western states (US-027}. Most of the matrix
from the other regions, however, must be treated prior to
utilization. In the first step of beneficiation, the lumps
of clay are broken up and phosphate nodules freed by hammer
mills, grinding mills, or similar equipment. Clay particles
adhering to the phosphate nodules are removed in log washers.
Separations are then made on the basis of size. The coarsest
fraction, +14 mesh to 1.9 cm (sometimes 16 mesh and 2.5 cm),
is dried and marketed as high grade rock or can be blended
with finer granulated material (-14, +200 mesh) obtained
from other beneficiation steps. Figure 6-1 shows a process
flow sheet for a typical Florida phosphate operation.
The second fraction (-14 or -16 mesh) consisting
of fine clay, silica, and fine phosphates is subjected to
desliming operations using cones or hydroseparators which
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Radian Corporation
8500 SHOAL CREEK BLVD. • P.O. BOX 9948 • AUSTIN. TEXAS 78766 • TELEPHONE 512 -454-4797
Screen
4-5 pel solids-slimes (4 SO mesh)
Hydroseparator and I
\ / cyclones T
Screen
Concentrate
product
Sand tailings
Dam construction
Land reclamation
FIGURE 6-1 - A TYPICAL PHOSPHATE ORE BENEFICIATION
SCHEME (BO-074)
-87-
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perform another size separation at 150-200 mesh. The finer
fraction (i.e., the overflow) is waste slime, and is disposed
of as a 4-6% solids slurry. The underflow is in some opera-
tions further subdivided at 35 mesh (AP-016, BA-133). If
this separation is made, the 14 x 35 mesh material is benefi-
ciated by gravitational separation equipment such as spirals,
tables, belt separator, or coarse flotation devices.
The 35 x 150 (or 200) mesh fraction or the entire underflow
from the desliming is treated in flotation cells. Here,
basically the fine phosphates are floated to the top and the
sand tailings sink. The froth product is then put in a
conditioning tank with sulfuric acid to remove the flotation
agents, is washed, and is then mixed with an amine to
float remaining silica away from the phosphate.
The phosphate losses from the washing and flotation
processes can total up to 40% of the phosphorus in Florida
land-pebble fields, and may be as high as 50% in some Tennessee
areas (US-027). The phosphate concentrates from the beneficia-
tion operations can then be further processed by one of
three basic methods, depending on the ultimate utilization
desired. These methods include acid treatment, thermal
reduction, or thermal treatment without reduction. Further
details of these processes are beyond the scope of this
report.
6.2 Nature of Phosphate Rock Slime
Phosphate rock slimes are the fine wastes, usually
minus 200 or 150 mesh, discarded from the washer as a 4-6%
solids pulp. Tables 6-1 and 6-2 present typical mineralogic
and chemical composition ranges. The phosphorus content of
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asao SHOAL CREEK BLVD • P o BOX994B • AUSTIN TEXAS 78766 • TELEPHONE 512-45«-«797
TABLE 6-1
APPROXIMATE MINERALOGICAL WEIGHT COMPOSITION
OF PHOSPHATE SLIMES SOLIDS*
Mineral Percent
Carbonate fluorapatite 20 - 25
Quartz 30 - 35
Montmorillonite 20 - 25
Attapulgite 5-10
Wavellite 4-6
Feldspar 2-3
Heavy minerals 2-3
Dolomite 1-2
Miscellaneous 0-1
*From BA-133 and BO-074
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Radian Corporation
8500 SHOAL CREEK BLVD • PO BOX 9948 • AUSTIN TEXAS 78766 • TELEPHONE 512 -454-4797
TABLE 6-2
CHEMICAL COMPOSITION OF PHOSPHATE SLIMES SOLIDS
*
Chemical
P2°5
Si02
Fe2°3
A1203
CaO
MgO
co2
F
LOI (1,000°C)
BPL
Typical Analyses,
Percent
9.06
45.68
3.98
8.51
14.00
1.13
0.80
0.87
10.60
19.88
Range ,
Percent
9 -
31 -
3 -
6 -
14 -
1 -
0 -
0 -
Q _
19 -
17
46
7
18
23
2
1
1
16
37
*From BA-133 and BO-074
LOI - Loss on Ignition
BPL - Bone Phosphate of Lime
-90-
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the solids is often as high as in the original matrix, 9-17%
(BO-074, BA-133). However, because of its extreme colloidal
and hydrophilic nature which greatly hinder dewatering,
attempts to beneficiate this slime have not been very successful.
Consequently, slimes are normally sent to settling areas
where they settle quite rapidly to 10-15% solids. However,
the rate is so slow beyond this point that even after two
years, the solids content is usually only 25-35% (BA-133,
US-027).
The Bureau of Mines is currently funding several
programs to examine the basic characteristics of phosphate
slimes. Their purpose is to prevent damage occurring from
slime pond dam failures. The main areas under investigation
include the following (KE-102):
phosphate slimes characterization
surface electronic studies
relationship of thermodynamic properties
to slimes stability
dewatering studies
empirical studies to improve settling rate.
6.3 Phosphate Slime Disposal Techniques
6.3.1 Conventional Method
The traditional method of slimes disposal is
ponding in dammed, mined-out areas (BA-133, BO-074, US-027).
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For every hectare-meter of matrix mined, 1.25 hectare-meters
are required for slimes disposal. This means that in order
for the mining area to provide sufficient storage space,
dams must be built to increase the site's capacity. Some
dams are constructed to retain slimes up to 12 meters deep.
The ponds are built to rigid specifications normally out of
quartz-sand tailings from the flotation effluent and overburden.
Care must be taken to insure that no vegetable matter is
present which could decay and lead to dam weakening. The
top of the dam is sloped to the inside to reduce erosion of
the outside wall. Inclusion of berms are recommended to
prevent erosion on the outer toes of the dam. Spillways
conduct the supernatant back to the fresh water reservoirs
for recirculation or release to nearby streams during periods
of heavy rainfall. Figure 6-2 shows minimum cross sections
recommended for dam construction.
Water recycle is a very important aspect of slimes
disposal and phosphate mining in general. A tremendous
water requirement exists for the overall operation; approxi-
mately 18 x 108 liters are associated with phosphate slimes
daily in the industry as a whole (BA-133). This water
leaving the plant with the slimes accounts for about one-
half of the total water requirements for both the mining and
beneficiation processes. About 10% of the water used in
disposal is retained by the solids even after many years of
settling. This is a tremendous draw on the water resources,
thus providing heavy incentive for maximum water reuse both
for environmental and economic reasons. Water is recycled
constantly, but the rate of drawdown varies with the rate of
production of the processing plant, pond area, river pollution,
rainfall, winds, amount of freeboard, and possible hurricanes.
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ssooSHOAL CREEK BLVD. • P.o BOX 9948 • AUSTIN. TEXAS 78766 • TELEPHONE 512-454-4797
Slope: No jrtjltr
- 5 lilt
Minimum — 25 (eel
NO SCALE
FIGURE 6-2 -
RECOMMENDED MINIMUM CROSS SECTION
OF DAMS (BO-074)
-93-
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The economics of slimes disposal by this method
has been studied by the Bureau of Mines (BO-074). Cost
figures reported were based on production capacity of a
Florida phosphate mining company rather than on actual
company figures. Therefore, the results can be applied to
other phosphate businesses employing similar disposal proce-
dures. Table 6-3 presents a summary of the results; more
detailed information concerning the project is available in
the literature (BO-074). The conclusions were that the net
operating cost was $0.27 per metric ton of phosphate product,
or approximately $0.55 per metric ton of dry slimes solids.
6.3.2 Alternate Disposal Methods
It has become evident in recent years that an
improved method of slimes disposal is needed. The incentives
for this are (1) the desire to avoid adverse effects from
dam failures and (2) potentially lower handling costs if
slimes storage volumes could be reduced and if water recycle
could be improved.
In 1970, American Cyanamid announced that 52 acres
(21 hectares) of slimes disposal area at Chicora Mine had
been successfully reclaimed using a new technique. After
several small-scale tests, a plant-scale project was carried
out in which slimes thickener underflow (3.5% solids) was
used to repulp dewatered sand tailings (CY-001, TI-021, BA-
133, CU-020). This mixture was pumped into a trench 42
meters wide, 1,500 meters long, and 12 meters deep alternately
from opposite sides. The trench was previously filled with
water to a depth of 11 meters. The sand/clay mixture dissoci-
ated when it came in contact with the water in the trench.
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Radian Corporation
8SOO SHOAL CREEK BIVO • PO 60X9948 • AUSTIN TEXAS 78768 • TELEPHONE &12-454-4797
TABLE 6-3.
CAPITAL AMD OPERATING COSTS FOR SLIMES DISPOSAL
Capital Costa
Slime pump stations (3 complete units)
Pond spillways (10 required)
Excavator (for ditching)
Pumps (4 recirculating water)
Pipeline
Plant facilities
Plant utilities
Total cost (tax and insurance base)
Interest during construction
Subtotal (depreciation)
Working Capital
Total capital investment
(1)
Capital
Investment
$700,000
80,000
60,000
160,000
200,000
72,000
76,000
$1,348,000
33,700
1,381,700
280,200
$1,661,900
Operating Costs
Cost per
ton of
Unit cost Total product2
Direct cost:
Raw materials and utilities:
fuel - 13.3 gal x $0.15 x 40 hr x
52 weeks
Power - 2,150 kwhr/hr x 8,760 hr/yr x
$0.01 kwhr
Direct labor:
16 man-hr/day - $3.00/man-hr x 365
day/yr
Supervision - 15 percent of labor
Maintenance:.
5 men - $7,000/yr
Supervision - 20 percent of main-
tenance labor
Material -
$4,100
188,300
17,500
2,600
35,000
$192,400 $0.045
20.100
Payroll overhead - 25 percent of payroll
Operating supplies - 20 percent of maintenance
Total direct cost
Indirect Cost:
40 percent of labor, maintenance, 6 supplies
Fixed Cost:
Taxes and insurance - 3 percent of total cost
Depreciation - 5 percent of subtotal for deprecia-
tion and 10 percent for excavator 72,100
Dam construction 938,000
Total operating cost 1,386,566
Credit for recirculatcd water 358,100
Net operating cost $1,028,400
1From BA-133, BO-074.
2Cost per ton is based on 4,205,000 tons of product.
.005
7,000
17,500
! nance
iplies
cost
59,500
15,500
11,900
299,400
36,600
40,400
.014
.004
.003
.071
.009
.010
.017
.223
-95-
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The sand settled rapidly, and the clay particles settled
slowly over it. With new incoming sand, the gentle motion
of sand encroaching on the clay liberated large volumes of
water which were forced to the surface within a few hours.
Masses of clay settled to a solids content of ^35%. As more
sand was added to this clay, the final settled product was
70-80% solids.
At the start- of this test, the method disposed of
22% of the slimes being, produced; this capacity increased to
45% by the end of the test. Both water circulation and
settling requirements were reduced. A significant savings
in slimes storage volume was also realized; by conventional
method 69 hectare-meters for sand tailings plus 31 hectare-
meters for clay (phosphate slimes, 20% solids) would have
been required. With the new technique, however, only a
total volume of 73 hectare-meters was taken up, or a savings
of ^27%. Handling costs were reduced by one-third. A final
advantage of this new disposal process was that the resulting
fill, 80% solids, possessed excellent load-bearing character-
istics and was easily vegetated.
In a second plant-scale test involving reclamation
of 24 hectares, slimes were made to flow through an existing
settling area to an abandoned, flooded mine where they
settled to 15-25% solids underwater in three months. Then a
sand tailings/slimes underflow mixture was pumped in.
Resultant clarified water was recirculated.
Incorporation of this method into the mining
process would involve allowing the slimes to settle in the
mine cuts. Overburden would be stacked as high as possible
-96-
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along the sides of the cut and would be used as cover material
for the reclaimed slimes areas following solidification with
sand. The problems foreseen in this becoming the accepted
method of slimes disposal are the limited availability of
sand tailings, which is a valuable material for other purposes
as well, and a need to increase dewatering capability. The
latter may possibly be improved by promoting a rolling and
squeezing motion upon sand addition; this may be accomplished
by having spaced retaining walls to keep the clays from
migrating.
Studies of additional methods of phosphate slimes
disposal have centered around improved and novel dewatering
techniques. Investigations have been conducted by industry,
TVA, and the Bureau of Mines. In general, the conclusions
of almost all studies indicate that the dewatering techniques
are not practically applicable to the industry's problem
because (1) they require too much energy (chemical, mechanical,
or thermal) thus making the process uneconomical, (2) the
dewatered products have no potential utilization, and (3)
the best results obtained still only achieve a 50% solids
material. Descriptions of experimental investigations of
various dewatering methods applied to slimes are reported in
the literature (BA-133, BO-074, DE-073, DA-073, DA-074, ST-
151).
6.4 Environmental Aspects of Phosphate Slimes Disposal
The environmental effects of phosphate slimes
disposal by ponding were studied in several Florida river
systems around 1950 (SP-034) and more recently in a North
Carolina estuary (CA-125). Supernatant from the settling
-97-
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ponds, which is sometimes intentionally released to surround-
ing waters, contains high levels of phosphorus (13-40 ug of
P/liter) (CA-125), thus creating the possibility of eutrophica-
tion of the water systems. Specht also monitored other
parameters. Turbidity increased by ^2.5%, but no harmful
effects on fishlife were observed. A beneficial increase in
the dissolved oxygen content was measured, while the biochem-
ical oxygen demand remained unchanged. The alkalinity was
not affected by the pond effluent. The only potentially
toxic species was tall oil, a flotation reagent. However,
none was found in the effluent waters. No increase in algae
growth was noted. Carpenter, however, reported that slime
pond supernatant did account for increased blue-green algae
population in a North Carolina estuary over short periods of
time (44 and 36 days). Effect on phytoplankton was studied,
but no significant effects were observed. In general, no
evidence of harmful effects from clarified slimes liquor
have been found with the possible exception of increase in
algae growth which could indirectly cause eutrophication.
Another potential hazard associated with phosphate
slimes disposal by the conventional method is dam failure.
Loss of the low solids slime over acres of adjacent land
following dam failure has occurred several times in the
Florida phosphate fields generating substantial legal action.
Consequently, the dams are monitored constantly so that any
structural weaknesses may be detected early.
Most phosphate mining companies also monitor
streams below their plants on a daily basis. The parameters
measured include water flow, suspended solids, phosphate,
and fluorine. No reports of groundwater monitoring were
-98-
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found in the literature although this would be another area
of potential environmental concern.
6.5 Case Study - Reclamation of Slimes Disposal Area
In 1972 the Florida phosphate industry produced
more than 29 million metric tons of phosphate, which represented
almost three-fourths of the nation's and one-third of the
world's phosphate output. More than 75% of this was mined
in a single county, Polk County, generally recognized as the
phosphate capital of the world. Reclamation of the mined-
out areas is being accomplished at an accelerated rate. In
the last ten years, the phosphate industry has reclaimed
more than 10,000 hectares of land. An additional 1,300
hectares were in the process of being reclaimed by Florida
mining companies as of June, 1973. In Polk County alone,
over 81,000 hectares of land are owned by the mining industry.
Eventually all of this may be mined although present technology
does not make this feasible. At any rate, these numbers
point out the large effect reclamation of land will have on
the future of that county.
One housing development in this county situated on
a mined-out area, Christina, was visited by Radian personnel.
The area was mined over forty-five years ago, and has just
recently been developed by IMC Development Corporation. The
development is located in a forest, much of which established
itself naturally on the spoil areas after mining operations
had ceased. The old mining pits are now lakes abundantly
populated with fish. The slimes disposal ponds presented
the only constraint on freely planned development since they
did not possess the support necessary for housing. However,
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they were successfully converted to forested parks and
greenbelts.
Near this residential development is the Jekyl-
Hyde Golf Course, originally another project of IMC Development
Corporation for the use of its employees. The area was
mined-out in the late 1930's, with 16 of its 75 hectares
used as slimes disposal area.
IMC began reclamation in March, 1961 and most of
the tailing used for cover material had been pumped to the
site by 1964 when IMC terminated development. Revegetation
in this case presented few problems. The tailing material
was contoured and seeded with bermuda type grasses and
native shrub and trees. Fertilization requirements were
minimal owing to the high phosphate content in the tailing
material. An added note here might be that even unreclaimed
slime ponds are not of zero value. They generally become
heavily vegetated, marshy areas forming habitat for game
birds and animals as well as a large population of snakes,
rodents and predators. The combination of high fertility,
low toxicity, and subtropical climate encourage verdant
growth in all cases.
The reclaimed area was first used as a small par-3
course covering 10 hectares (24 acres). It was later converted
to a conventional course, although incomplete, consisting of
3 holes. In 1969, the land was sold to a private individual
who continued the development of the land to its present 18-
hole configuration, along with a swimming pool and planned
tennis courts. The recreational complex is at the present
time an open (semi-private) club.
-100-
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7.0 TACONITE TAILINGS DISPOSAL
The major fraction of iron ore mined in the United
States is mined in the Lake Superior district encompassing
the states of Minnesota, Michigan, and Wisconsin. The raw
ore is found in several forms. The original formation
consisted of iron oxides, carbonates and silicates in conjunc-
tion with layers of chert. In localized regions enrichment
of the minerals occurred through oxidation and groundwater
leaching. However, a major fraction of the ore remains
unaltered. The iron containing fraction, when it contains
greater than 20% iron as magnetite, is referred to as taconite,
Large reserves of taconite exist in the Mesabi range, north
of Duluth and in the Marquette range in upper Michigan.
Since the mid 1950's when Reserve Mining pioneered the
recovery of usable iron from taconite, the industry has
grown to where over half the usable domestic ore is produced
from taconite or jaspilite (LA-099).
A typical taconite mining and beneficiation plant
will include the following elements:
1. a surface mine
2. a crushing and grinding operation
3. a magnetic separation of iron ore
from tailings
7.1 Nature of Taconite Tailings
Composition of tailings is variable depending on
ore seam being mined and on the mechanical details of the
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beneficiation process. Detailed analyses have been made of
the tailings produced by the Reserve Mining Company's plant
at Silver Bay, Minnesota. A representative analysis is
given in Table 7-1 (RE-093). The composition strongly
resembles a typical silicious sedimentary material.
Tailings are frequently classified as coarse and
fine. Fine tailings generally will pass a 325 mesh screen.
Table 7-2 contains a typical screen analysis for total
tailings, again taken from Reserve Mining data (RE-093).
Calculations performed by Weston (WE-096) indicate that the
fraction 325 mesh or smaller contributes over 90% of the
total surface area available for leaching. This represents
approximately 40 wt. % of the total tailings. Table 7-3
gives the analysis of the particle size-area relationship
(WE-096).
The tailings apparently provide good structural
stability. For example bricks made from tailings demonstrate
compressive strengths of 5,500-7,250 psi (3,800-5,000 new-
tons/cm2) with water absorptivities of about 7% in 24 hours
(WE-096). Representative values for clay brick are 3,000
psi (2,100 new tons/cm2) and 8.2% respectively.
The fact that the Weston report (WE-096) proposes
construction of ski slopes with tailings again attests to
the inherent structural stability of tailings.
The mining industry as practiced today requires
large processing facilities with correspondingly large
quantities of tailings. Over 100 million tons of crude
taconite ore are mined annually (LA-099). If one assumes an
-102-
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TABLE 7-1
TYPICAL
Iron
Silicon
Aluminum
Calcium
Magnesium
Manganese
Titanium
Phosphorus
Sodium
Potassium
Sulfur
Lead
Zinc
Nickel
Copper
Molybdenum
Vanadium
Cobalt
Chromium
Cadmium
Carbon
Hydrogen
Oxygen
Total
ANALYSES OF NATURAL SEDIMENTS AND
RESERVE'S TAILINGS (RE- 09 3)
Tailings
7.
14.93
33.03
0.35
1.67
2.55
0.37
0.030
0.026
0.20
0.08
0.03
0.005
0.004
0.002
0.004
<0.001
<0.001
0.002
0.004
0.0003
0.11
0.10
46.40
99.90
-103-
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TABLE 7-2
TYPICAL TOTAL TAILS SCREEN ANALYSIS (RE- 09 3)
Mesh
3
4
6
8
10
14
20
28
35
48
65
100
150
200
270
325
Micron
6730
4760
3360
2380
1680
1190
841
595
420
297
210
149
105
74
53
45
30
20
10
5
Weight 7,
Finer
96.7
90.4
81.6
72.8
66.3
61.6
57.5
55.5
53.6
51.9
49.6
45.9
41.7
38.0
34.7
32.5
24.7
18.4
9.3
5.3
-104-
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TABLE 7-3
TAILINGS SURFACE AREA DISHCARGED PER DAY DISTRIBUTION
I
I—'
o
Through/On
MICRON SIZES
5/
10/5
20/10
44*/20
MESH SIZES
270/325
200/270
150/200
100/150
65/100
48/65
35/48
28/35
20/28
14/20
10/14
8/10
6/8
4/6
3/4
Total
Average Tailings Density
Average Tuilings Volume
*325 mesh
BY PARTICLE- SIZE RANGE
Average
Particle
Size1
microns
1
1
1
2
7
15
32
48
64
90
125
177
250
355
500
610
.000
,408
,900
.850
4^000
5
,000
Total
Weight
tons/day *
4.350
3,420
7,400
10.600
3,140
3,350
2,750
3,000
2,130
1,670
1 .670
2,000
2,270
2,950
3,550
4,400
4.100
2,750
1,230
Average
Percent
(by \Vt.)
6
5
11
15
4
5
4
4
3
2
2
3
3
4
5
6
6
4
1
.5
.1
.1
.9
.7
.0
.1
.5
2
.5
.5
0
.4
.4
.3
.6
.1
.1
8
Dry Volume
cii.t't./djy 3
66.000
52.000
113.000
144,000
47.500
5 1 .000
41,800
45.500
32,500
25.500
25,500
30,300
34.500
44.700
50,800
67.000
62,300
41,800
18.600
(WE- 09 6)
Unit
Surface
Area
sq ft.
1.84
1.38
6.25
3.0
2.08
1.58
1.06
7 7
5.45
380
2.82
1.80
1.04
8.9
6.8
5.0
3.2
2.5
1.9
./cu ft. *
X
X
X
X
X
X
X
X
X
\
X
X
X
\
\
>:
X
\
X
105
IO5
IO4
IO4
IO4
IO4
IO4
10J
ID*
10?
10°
10^
103
10
K)2
IO2
io2
IO2
IO2
Total
Surface
Are;>
sq tt.
1.21
7.15
7.05
4.30
9.85
8.05
4.42
3.50
1.77
9.7
7.2
5.44
3.59
3 98
3.47
3.47
1.99
1 04
3 54
./day 5
\
X
X
X
X
V
X
X
X
X
X
X
X
X
X
X
X
X
X
IO10
10o
I0o
!09
108
10°
10"
10^
10*
j
IO7
! 0
IO7
IO7
1 0
IO7
io7
IO7
I0r>
66,730
132lbs/cu.ft.
15.2 cu.ft./ton
3376x I08
Percent of
Surface Area
in Size Range
35.84
21.18
20.88
12.73
2.92
2.39
1.31
1.04
.52
.29
.21
.16
.1 1
.12
.10
.10
.06
.03
.01
Cumulative
Surface Area
Distribution
35.84
57.02
77.90
90. (-.3
93.55
95.94
97 25
98 29
98.81
99.10
99.31
99.47
99 58
99 70
9
-------
average iron content of 25% in the ore, with beneficiation
to 60%, the total amount of tailings becomes about 55
million metric tons per year. Examples of tailings rates
from individual plants are (WE-096):
Reserve Mining ~59,000 metric tons per day
Erie Mining -50,000 metric tons per day
Eveleth Taconite -63,000 metric tons per day
Co.
7.2 Disposal Techniques
Two general methods are in use for the disposal of
taconite tailings. The first and most prevalent is ponding
with eventual reclamation of the tailings ponds. The second,
used solely by Reserve Mining, is direct disposal into Lake
Superior.
7.2.1 On-Land Disposal
The taconite plants using on-land disposal generally
use ponds with dams or dikes constructed from tailings. In
the case of the Erie plant, coarse tailings are sluiced
directly to either a 1,300 acre (500 hectare) or a 700 acre
(300 hectare) settling pond. The tailings fines are passed
through thickeners and then discharged to the ponds. Water
is recycled. The Eveleth plant also operates on a closed
loop basis. In this case the coarse tailings containing
17-20% water are separated and hauled by truck to the pond
site for dike construction. The fines go to a hydroseparator
-106-
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and then to a thickener before discharging to the tailings
pond. In this case the use of coarse tailings for dike
construction reduces dusting problems. Pond waters are
recirculated to the plant.
The Erie plant has been the subject of rather
extensive experimentation in reclaiming tailings ponds. The
company has instituted a "Multiple Resource Management Plan"
designed to utilize the following resources: minerals,
water, wildlife, and recreational uses (LA-099, p. 137).
The tailings basins are capable of handling 19 million
metric tons of tailings per year. As mentioned above the
coarse tailings are used for dam and dike construction.
During studies conducted to determine the optimum methods
for dike stabilization the conclusion was reached that while
the tailings are not toxic to plant life, their fertility is
very low. Through a planned program of fertilization,
seeding and mulching, it has been possible to revegetate
tailings basins within a single growing season following
spring planting. Although the revegetation research is
still incomplete, it has been noted that native trees are
beginning to reestablish. The main vegetation is still
alfalfa, however. The fine nature of the tailings have
required the planting of low plants with strong root systems
to stabilize the soil. During 1967 and 1971 approximately
40 hectares of basin were reclaimed. These initial results,
although modest, are promising but much research remains
before reclamation of infertile tailings basins becomes
routine. Additional details are presented in the case study
for this waste material.
-107-
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7.2.2 Lake Disposal
The disposal of tailings directly to Lake Superior
has become the subject of much controversy and a Federal
suit is currently in progress against Reserve Mining.
Reserve Mining now discharges over 60,000 tons per day of
tailings into the lake depending on a "density current" to
carry the material into a deep trough. The actual environmental
effects of this disposal method are the subject of the
litigation and until the court action is complete, they should
probably be discussed only in general terms because of
conflicting data. At any rate problems sited range from
damaging spawning grounds for rainbow trout to eutrophication
to the discharge of "asbestos-like" fibers which enter
drinking waters.
This disposal method clearly would not be approved
for new plant construction and may be altered by court order
before the Reserve plant completes its estimated 10 additional
years of useful life.
7.3 Case Study - Erie Mining's Tailings Reclamation
Program
The beneficiation of taconite ore produces a
tailing material which is generally disposed of by ponding.
Erie Mining Company was chosen as the subject of this case
study on the basis of their extensive research and publications
in the revegetation of tailing basins. An on-site visit was
made to the Erie Mining Company plant and mine on March 13,
1974. The facility is located approximately 65 miles north
of Duluth, Minnesota near the town of Hoyt Lakes. The plant
-108-
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location is shown in Figure 7-1 along with the rail and
harbor facilities for shipment. The capacity of the plant
is some 9.35 million metric tons per year of concentrate
pellets containing approximately 65% iron.
The ore being mined contains approximately 31%
total Fe and 22.5% magnetic iron. The overall mining-
beneficiation process is given schematically in Figure 7-2.
Mining is conducted by the drill and blast method with
electric shovels used to load the raw ore. The ore is then
crushed in gyratory crushers to approximately 17 centimeters
(6 3/4 in.). The coarse ore then passes through a cone
crusher set to 2.9 cm (1 1/8 in.) and shorthead cone crushers
set to less than 0.5 cm. (3/16 in.). This product, termed
fine ore, then passes into the concentrator plant. Rod
mills followed by ball mills are used to obtain a minus 325
mesh product. Three stages of magnetic separation are used;
a rough separation after the rod mills, a cleaner separation
following the ball mills and a finisher section after the
cyclone separator. Tailing is removed from each stage and
flows to a hydroseparator where coarse tailing is separated
for use in dam building. Tailing is pumped at 40% solids to
the tailing basin and allowed to settle.
A map of the plant area is shown in Figure 7-3.
At present there are two tailing basins covering approximately
890 hectares (2,200 acres). Additional area of about 320
hectares (800 acres) will be added by the year 2,000 and is
expected to be sufficient for the plant life.
The plant operates on a total water recycle basis.
Water is reclaimed from the tailing at the concentrations
-109-
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MINNESOTA
ARROWHEAD
ERIE MINING CO.
PLANT, TOWN
RAILROAD 8 HARBOR
FIGURE 7-1
-------
E-1835.3
ERIE MINING COMPANY
COMMERCIAL TAOONITE PLANT
(LONG EN 1 RATO R
——o—
AGGLOMERATING
PLANT
FIGURE 7-2
-------
E-1835.2
ERIE MINING COMPANY
MAP OF
PLANT 8 MINE AREAS
8ASN 2
O
BASIN I
LEGEND
0 COARSE CRUSHER
-------
and from the tailing basins. The plant water usage rate is
9,500 liters per second (150,000 gpm). Approximately 5% of
this is make-up water from an Erie reservoir; 75% is reclaimed
from the thickeners and 20% from the tailing basins.
As mentioned previously, the tailing basin side
walls are constructed primarily from coarse tailing. The
normal slope is 1.5:1-2:1 but stable slopes of ~3:1 are used
in limited areas.
Basin construction is straightforward. Tailings
are sluiced at about 40% solids to the dam site and are
contoured with rubber tired graders. The normal lift is 6
meters with a 48 centimeter rill and 6 meter bench left
between lifts to control erosion. Pumping is through a
multistage system using rubber lined 41 cm pumps. Thirty-six
centimeter pipe is used from the concentrator to the first booster
station; 30 cm. pipe from that point on.
Distribution of tailing to the basin is achieved through
a manifold containing a number of flexible pipes.
During winter operation, only the main pipe is used; this
operating procedure requires frequent moving of the outlet
pipe but reduces freezing problems. Structural stability is
such that machinery can be operated on the material immediately
after deposition. In isolated cases slimes have collected
after a rainfall to form unstable pockets. On covering with
fresh material the instability is eliminated.
Tailing size distribution for the Erie operation
is approximately the following:
-113-
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-325M 48.8%
-200 to +325M 7.0%
-65 to +200M 17.6%
-10 to +65M 18.8%
+10M 7.8%
The material consists of about 75% silica with the balance
mainly iron oxide. Erie studies have shown no plant toxicity
and virtually no plant nutrient value in the tailing.
The major portion of the tailing pond interior is
kept under water. At present about 71 hectares (175 acres)
of the pond interior is vegetated primarily for dust control.
The primary revegetation work is concerned with stabilization
of the back slopes.
Actually, two types of revegetation regimes are
conducted, one for the backslopes and one for the interior.
The primary difference is the necessity for permanence of
the vegetation. A second factor is avoiding encouragement
of algae growth in the water, since the water is recycled
for plant use.
The interior work was approximately 280 kg/hectare
(250 Ib/acre) of a 20-20-0 fertilizer, enough to support 2-3
years of annual growth. By the end of this period fresh
tailing covers the vegetation and the procedure must be
repeated. The primary vegetation for interior work is
annual rye. In addition millet and barley are planted to
provide forage for the geese and ducks which use the ponds.
-114-
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The current rate of revegetation is 40-60 hectares
(100-150 acres) per year, primarily in the,interior. Each
lift of the dam is reclaimed as it becomes available; this
amounts to about 10-12 hectares (25-30 acres) per year.
The more difficult problem is reclamation of the
backslopes. Extensive research has been performed to develop
procedures. Seeding may be done in the spring or summer but
more successful results have been obtained by dormant seeding
in the fall, i.e., the first week was in October. The most
demanding requirement is fertilizer. As mentioned above,
the tailing has no fertility value. For vegetating side
walls, a long lasting application of 1,100 kg/hectare (1,000
Ib/acre) of an 11/4810 fertilizer is applied. The material
requires at least 100 kg N/hectare (9'0 Ib of N per acre) .
Phosphorus presents a unique problem and they attempt to
apply at least 390 kg/hectare (350 Ib/acre).
The problem with phosphorus relates to its mobility
in the tailing. Nitrogen moves through the substrate allowing
root growth to penetrate to a reasonable depth for soil
holding properties. Phosphorus, on the other hand, tends to
remain where it is placed and must be worked into the soil
mechanically. Therefore the fertilizer is applied to the
backslopes and then worked in to a depth of 13-15 centimeters
with a "clodbuster". Then seed is applied at the rate of 50
kg/hectare (45 Ib/acre) with a hydroseeder. Four and a half metric
tons per hectare hay or straw mulch is then applied and an asphalt
task used. South slopes require that the seed be covered to
protect them from lethal temperatures; a chain drag is used
for this purpose.
-115-
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Washouts soon after planting sometimes require a
re-seeding, but the major problem in revegetation is fertilizer
availability. They have had to cut back to 500 kg/hectare
(450 Ib/acre) in some cases because of allocations.
The vegetation used for permanent stabilization
includes at least 50% clover or legume; the most successful
single species is birds foot trefoil. Alfalfa has given
excellent results in providing nitrogen fixation.
The water in the basin is relatively high quality.
Because it is returned to the process, no formal monitoring
program is required. Even seepage is retained within plant
boundaries. Table 7-4 shows a comparison between basin
wastes, seepage and typical waters from the Embarrass River
adjacent to the plant.
Cooperation of the Erie Plant personnel during
this study was outstanding. They are understandably and
justifiably proud of their work with the tailing basin.
Although taconite tailing is perhaps a unique material to
reclaim, the principals followed should be applicable to
many other similar problem areas.
-116-
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TABLE 7-4
WATER QUALITY
Basin Seepage Embarass River
pH 8.1 8.1 6.9
TS, mg/fc 250 189 152
TSS, mg/£ 13 2 2
TDS, mg/f 237 187 150
Turbidity, mg/S, 12 1
-117-
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RADIAN CORPORATION
8.0 GYPSUM FROM PHOSPHORIC ACID MANUFACTURE
Phosphoric acid is an essential intermediate in
the manufacture of phosphate fertilizers. Wet process
phosphoric acid production involves the chemical attack of
phosphate rock by a strong mineral acid, usually sulfuric
acid. The naturally occurring composition of phosphate rock
can be represented by the formula 3Ca3 (POiJz • CaXz where X
may be a halogen, hydroxyl, etc. The most prevalent
form is fluorapatite, 3Ca3 (P0i»)2 • CaF2 . When this calcium
salt reacts with sulfuric acid, the overall reaction products
are phosphoric acid and calcium sulfate, a compound relative-
ly insoluble in phosphoric acid.
Ca3(POO2 + 3H2SCK •* SCaSO., 4- + 2H3POu (8-1)
The reaction between sulfuric acid and fluorapatite is as
follows:
3Ca3 (POu) 2-CaF2(s) + 10H2SOU ( . + 10 x
-»• 6H3PCK(a . + 2HF, . + 10 CaSO,, x H20(s) (8-2)
The value of x may be 0, 1/2, or 2 corresponding to anhydrite,
hemihydrate, or dihydrate (gypsum) , respectively. The form
of the precipitate is determined by process conditions such
as:
extent of P20s recovery from rock,
filtration rate of CaSOit/HsPCU slurry,
-118-
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temperature, and
strength of product acid.
Accordingly, three major process variations are available
based on the form of the by-product. The processes are
referred to as the anhydrite, hemihydrate, and dihydrate
processes. Other variations are also in operation, sometimes
involving two-stage combinations of the above.
The process most prevalent in the United States is
the dihydrate process. A typical flowsheet for this method
is given in Figure 8-1. To assure gypsum formation, the
temperature in the digestor is maintained at 75°C. Since
the reaction is exothermic, the amount of heat generated is
a function of the I^SO,, concentration which is controlled
between 77 and 98% (usually 93%). The efficiency of P205
extraction from the rock is typically >96%, and the acid
product strength is 30-32%. More detailed descriptions of
this and other processes are reported in the literature (BA-
133, CR-052, MA-257, RO-113).
In most operations here, the gypsum by-product is
treated as a waste and traditionally disposed of in diked
ponding areas. In other countries, especially where naturally
occurring deposits of gypsum are scarce, the more common
practice is to market this product for its sulfur value or
for raw material in gypsum wallboard, cement, or plaster of
Paris manufacture.
-119-
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WATER
I
1—I
o
PHOSPHATE
ROCK
RECYCLE
ACID
lit
DIGESTION
VENT TO ATMOSPHERE
FLUORINE
SCRUBBER
-»• WASTE WATER
'FLUORIDE
FUMES
r
WATER
FILTERS
WATER
ACID
CONCENTRATOR
SLURRY TANK
GYPSUM SLURRY
TO GYPSUM POND
WATER
»• VENT TO ATMOSPHERE
FLUORINE
SCRUBBER
•*- WASTE WATER
PHOSPHORIC
ACID PRODUCT
STORAGE
FIGURE 8-1 - WET PROCESS PHOSPHORIC ACID FLOWSHEET FOR DIHYDRATE
PROCESS (BA-133)
-------
8.1 Nature of By-P'roduct Gypsum
8.1.1 Chemical and Physical Properties
The composition of by-product gypsum from phosphoric
acid production (phosphogypsum) is dependent on the phosphate
rock composition and on the process conditions. Table 8-1
compares natural and by-product gypsum. The natural gypsum
is much purer; components of fluorapatite, calcium phosphate
and calcium fluoride, account for the majority of the impuri-
ties present in phosphogypsum. The influence of rock source
on chemical composition is illustrated in Table 8-2, while
Table 8-3 shows the effect of process variations. Note that
in general, the total phosphate content of the gypsum from
the dihydrate process is higher than that from the combina-
tion process in which hemihydrate crystallized during the
first stage is converted to the dihydrate in the second
stage. The phosphate content of the gypsum is important for
several reasons. First, it is an indication of the extrac-
tion efficiency of the process. Secondly, some of the
phosphate crystallizes within the gypsum lattices and adversely
affects the marketing properties of the by-product. This
aspect is dealt with in further detail in Section 8.3 below.
The composition can be altered, if necessary, by washing
operations involving reslurrying and classifying. Typical
results are shown in Table 8-4.
The particle sizes of phosphogypsum is typically
very fine, predominantly minus 100 mesh BSS (British Standard
Sieve) (MU-060). A typical size distribution is presented
in Table 8-5. Gypsum precipitates as needle-like, rhombic-
shaped crystals, twins, and clusters (RO-113) . The* factors
-121-
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TABLE 8-1
COMPARATIVE CHEMICAL ANALYSES OF NATURAL AND
BY-PRODUCT GYPSUM (GO-Q72)
Natural gypsum, % By-product gypsum,
Casoan.0
CaS04-2H,O
Caa(POi}>
CaF,
SiO,
Fe.0,
Al,0,
Other impurities
Total impurities
6.73
92 36
Nil
Nil
0 39
0.15
Nil
0 37
0 91
Nil
92 84
2.25
2.66
0 95
0.01
0 79
0 50
7 16
TABLE 8-2
COMPOSITION OF TYPICAL BY-PRODUCT CALCIUM
SULFATES FROM DIFFERENT ROCK SOURCES (ST-155)
By-product
calcium
aulfivte
A
B
C
D
£
Chemical analysis, wt. %
(anhydrous basis)
Rock source
Flondu
Tennessee
Morocco
Morocco
Kola Peninsula
S
15
20
22
17
18
CaO
9
G
4
1
0
40
39
40
30
30
2
4
9
2
9
SiO<
11 8
7 5
—
1 2
0 7
A1S0,
0
0
1
0
4°
G
7
5
Fc,O,
—
0 4
—
0 7
0 3
P,0,
0 9
1 9
1.5
—
~
F
—
0 4
1 3
—
~
• Total AliO, and Fe,0,.
-122-
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TABLE 8-3
COMPOSITION OF BY-PRODUCT GYPSUM FROM WET-PROCESS
PHOSPHORIC ACID MANUFACTURE3 (MU-060)
Process and
sample no.
Dshydrate
1
2
3»
4»
5»
Hemihydrate-
dihydratc
6
7
S»
9'
10'
11'
12»
Combined
water, %
20
20
19
19
20
20
20
19.
20
07
36
68
41
49
52
23
36
01
SiOt and
insoluble RiOj,
matter, % %
1 35
1 22
2 95
2 02
1 80
—
1 94
0 98
6 43
—
—
3 16
—
0 44
0 27
2 65
0 96
—
0 46
0 25
0.28
—
—
0 36
MgO,
—
0 32
—
—
0 07
—
—
0 44
0 OS
—
—
Tr.
CaO,
32 09
31 28
31,34
31.10
31 73
—
31 30
32 15
29 92
—
—
31 39
Total
SOi, phosphate,
% %
45 13
43 51
43 75
43 04
44 93
—
44 12
44 70
42.73
—
—
43 98
1 08
0 86
0 53
0 77
0 55
0 47
0 60
0.39
0 16
0 36
0 34
0 38
Water-
soluble
phosphate,
0 14
0 36
0 09
008
0 07
0 12
0 33
0 08
0 04
0 02
0 01
0 06
Total
fluorine,
0 41
0 91
—
1 19
0 75
1.25
0 80
0 20
0.1S
0 15
0 17
a 15
Water-
soluble
fluorine,
0 18
0.32
—
—
0 10
0.28
0 38
0 06
0 05
0 04
0.01
0 04
Courtesy of Yoshino Gypsum Company; samples taken during
various periods of plant operation.
3Gypsum repulped and washed again after filtration.
-123-
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TABLE 8-4
COMPOSITION OF BY-PRODUCT GYPSUM AS
AFFECTED BY WASHING (GO-072)
By-product gypsum as By-product gypsum after
received from phosphoric reslurrying and
acid plant, % classifying, %
Loss on ignition at 230°C
SO,
CaO
Total P,0,
SiOj and insolublcs
Fe,0,
A1.0,
MgO
NaCl
Ca,(P04)i
CaSOaH,0
CaSOr2H,0
19 12
45 33
33.08
1 06
1 10
0 009
0 03
0 04
0 92
Probable composition
2 32
6 85
89 33
2025
45.22
32 66
0 76
0 OS
0.005
0.01
0 02
Nil
1.66
0.47
96 65
TABLE 8-5
PARTICLE SIZE OF BY-PRODUCT GYPSUM FROM
PHOSPHORIC ACID PLANT (GO-C72)
Size
BSS
100
150
200
Microns
33
23 1
IS 6
12.3
7.1
4.0
% smaller
than given size
88 2
59 1
4G 2
18 C
7.7
4 1
3 0
2 1
1.5
-124-
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related to particle size and other crystal characteristics
include:
sulfate concentration,
phosphoric acid concentration,
impurities in the rock, and
slurry concentration.
These effects have been studied by several investigators
(RO-113).
8.1.2 Production Quantities of Waste Gypsum
For every metric ton of phosphate rock processed,
1.5 metric tons of by-product gypsum are produced (BA-133,
SC-150). Similarly, for every metric ton of PaOs product,
4.5 metric tons of gypsum result. These relationships
indicate that, for large plants, waste disposal can create a
large-scale problem.
In 1969 wet process acid production in the United
States was estimated to be 5,300,000 metric tons (5,800,000
short tons) P20s (BA-133). This is equivalent to a gypsum
disposal problem amounting to 24-26 million metric tons
(26,000,000 short tons).
-125-
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8.2 Conventional Disposal Practices
In many countries including the United States,
phosphogypsum cannot compete with natural gypsum as a raw
material. Therefore, common practices have developed whereby
it is simply dumped in diked disposal areas or, in some
cases, into the ocean. This section describes common disposal
techniques and associated environmental aspects.
8.2.1 Description of Methods
In a typical phosphoric acid plant, the precipitated
gypsum is separated from product acid by a complex filtration
system. The filter cake is then washed and discharged from
the filter containing 18-35% free moisture (BO-095). In one
type of disposal system, water sprays sluice the material
into a receiving vessel or hopper, from which it either
flows by gravity or is pumped to a gypsum pond. The pond
area should be 0.2 hectares per daily metric ton P205 produced
(0.5 acres per daily ton P205 production). The rate of
gypsum accumulation is approximately 'x.O.l hectare-meters per
year (^one acre-foot per year) per daily ton PaOs.
As the solids settle, the supernatant is recycled although
in some cases it is discharged to the environment following
adjustment of pH, phosphate, and fluorine (see Section
8.2.2).
The design of ponds has been developed through
many years of experience. The Florida Phosphate Council has
adopted certain criteria for dike design, as illustrated in
Figure 8-2. The ponds are usually divided into sections,
which may be filled, drained, and emptied alternately. The
gypsum slurry will flow outward from the point of discharge
-126-
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SLOPF NO GREATER
THAN 2
FREEBOARD.
rMINIMUM 5'
t
I CORE DITCH,
4INIMUM DEPTH 3'
.WATER LEVEL
NO 6REATER THAN 2 I
INSIDE TOE
BERM,?5'MINIMUM
BORROW
FIGURE 8-2 -
RECOMMENDED MINIMUM CROSS SECTION
OF DAM (BO-095)
-127-
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at an angle of repose of only 1°. One unusual feature of
gypsum ponds is that the settled solids may be used to build
up the height of the dikes. Some dikes have been built up
as high as 30 meters (100 feet). The disadvantages of
this practice include the necessity of mechanical rehandling
and increased slurry pumping costs. A typical range of pond
construction costs as a function of plant capacity are shown
in Figure 8-3.
In a few facilities in the United States the
filter cake is removed as a dry cake, and is transferred to
the disposal site via conveyor belt or other solids handling
equipment. This is not a common practice, however, since it
is much more expensive than a slurry handling system (BO-
095) .
While ponding is the most common method of disposal
in the United States, European plants typically dispose of
their waste by ocean- (or sea-) dumping (BE-188). There are
several reasons for this: there is less land area available
for any type of land disposal; since no phosphate mining is
done in Europe, mined-out phosphate areas are not available
as disposal sites; the acid plants are located near sea
coasts, estuaries, rivers; thus the need to recycle water
via ponding wastes is not a strict requirement.
The normal discharge method when ocean-dumping is
used is slurrying with water (sea water if possible) at 5 or
10% solids (BE-188, BO-095). Pumping is usually employed,
although it is much less expensive if gravity flow can be
utilized; the cost for pumping was reported to be $0.30/dry
-128-
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800
600
o
o
o
O
o
o
•—I
»-
o
i-
z
o
o
400
200
I
I
200 400 600 800 1000
PLANT CAPACITY - TONS P«0C PER DAY
1200
FIGURE 8-3 - TYPICAL GYPSUM POND CONSTRUCTION COSTS (BA-133)
-129-
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RADIAN CORPORATION
metric ton compared to only $0.10/dry metric ton for gravity
systems (BE-188). Good dispersion in the ocean must be
assured; this may be achieved by jetting seawater into the
pipelines near point of discharge. In some cases companies
are required to install intermediate dissolution devices;
gypsum is more soluble in seawater than in fresh water. It
is important in this type of operation to avoid hemihydrate
formation because it is difficult to filter and it may cause
scaling in the pipes.
Barges are used for sludge-dumping when distance
to discharge point is too great for pipelining to be feasible.
The slurry is pumped into open barges where it settles; the
resulting supernatant is allowed to overflow the sides.
When full, the barges are hauled out to the outfall of the
estuary and the gypsum is released through bottom hatches.
The most expensive disposal method in use involves
truck transport of dry sludge to abandoned pits, quarries,
and mines. European cost estimates are reported to be as
high as $1.50/dry metric ton (BE-188). This method is only
employed to any extent in Germany, especially in the Ruhr
area.
European land disposal practices involve transport
of the gypsum by conveyor belt, pipe, or ditches to a disposal
site, usually on company-owned land. In regions where
strict environmental regulations are not yet in effect, the
slurry is simply dumped at the site and excess water allowed
to soak into the ground. The cost for this type of disposal
is approximately $0.25/dry metric ton, not including the
cost of the land (BE-188). In some instances, this technique
-130-
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RADIAN CORPORATION
has been utilized in the reclamation of land after flooding
by the seas. The gypsum acts as an ion exchanger, replacing
sodium ions adsorbed by the soil with calcium ions.
8.2.2 Environmental Aspects of Phosphogypsum Disposal
The aspect of gypsum disposal of most interest to
the phosphoric acid industry is water recycle. The gross
water requirements for the wet process acid industry ranges
between 83,000 and 170,000 liters per metric ton P2O5 (20,000-
40,000 gal. per ton P205) (BA-133). While ^80% water recovery
is generally achieved, some is released to the environment,
especially during periods of heavy rainfall. For example, a
540 metric ton P205 per day acid plant may discharge up to 300
liters/sec. (5,000 gpm) during a heavy rainfall period,
while the average over a year is between 2,000 and 4,000
liters/metric ton P205 (500-1,000 gal./ton P205). The
composition of the supernatant changes in the pond until
equilibrium is reached, at which time the results shown in
Table 8-6 are typical. Prior to discharge, adjustment of
pH, fluoride, and phosphate is necessary. The exceptions
are plants situated where evaporation rates are very high,
regulations are less than stringent, or the subsurface
drainage rate is high.
The partial pressure of soluble fluorides can be
significant. Although losses by evaporation on a windy day
have been reported to be as high as 90 kg/day (200 Ib/day),
the corresponding ambient air concentration was only 1 ppb.
Although fluorine present in phosphate rock is essentially
an air pollution problem in wet process acid production, it
becomes a water-related problem since plant gas streams are
-131-
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PORATI
TABLE 8-6
TYPICAL EQUILIBRIUM COMPOSITION OF GYPSUM POND WATER (BA-133)
Contaminant
P205
Fluoride
Sulfate
Calcium
Ammonia
Nitrate
PH
Concentration/ mq/i
6000-12,000
3000-5000
2000-4000
350-1200
0-100
0-100
1.0-1.5
-132-
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scrubbed with dilute fluosilicic acid followed by pond water
for fluorine control. Typical fluoride distribution in wet
process phosphoric acid production is presented in Table 8-
7. Recovery from some of the effluent streams is practical
for fluoride marketing value; for example, 80% recovery from
the acid concentrator gas effluent can be achieved. However,
only 50% removal from the reactor and filter gas streams are
possible. Recovery for resale here would not be warranted.
All scrubbed fluoride not recovered for marketing ultimately
winds up in the gypsum pond where its soluble concentration
builds up until equilibrium is reached.
Pond discharge treatment usually consists of lime
neutralization and settling. In most cases, double-liming
is practiced, while triple-liming is re.quired in a few
instances. A flow sheet for a typical double-liming process
is shown in Figure 8-4. In the first mixing tank, slaked
lime or slaked lime slurry is mixed with pond water for 10-
15 minutes (one hour in some cases). Limestone is not as
reactive, but is used in some processes. The resultant
slurry is transferred to an agitated settling tank or clari-
fier for several hours. During this first stage, the pH is
raised to 3.6-3.8, and fluoride precipitates as CaF2; typical
fluoride concentration at this point is 40-60 mg/£. The
soluble phosphate content is only slightly reduced.
The supernatant from the first clarifier passes to
a second mixing tank where more slaked lime is introduced.
Again, 10-15 minutes in the mixing tank followed by several
hours for clarification is generally required. In this
stage, remaining fluoride precipitates, probably as fluorapa-
tite. Most of the phosphate is precipitated in the second
stage. Final supernate compositions are as follows:
-133-
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TABLE 8-7
FLUORIDE DISTRIBUTION IN WET PROCESS
PHOSPHORIC ACID PRODUCTION (BA-133)
% of Total Fluoride in Rock
Fluoride Disposition
Evolved from Reactor
and Filters
Evolved from Concentrator
Remaining in Gypsum
Remaining in Acid Product
Reference
Typical
Range
4-7
itor 35-45
25-30
luct 20-30
a
Phosphoric Acid
Typical
5
40
30
25
b
, Parts
Values
5.5
41.9
27.8
24.8
a
1 and 2,
ERCO
5
60-65
20-25
10
c
Marcel
Dekker, Inc., New York, New York (1968).
bE. J. Fox, J. M. Stinson, and G. Tarbutton, "Superphosphate,
Its History, Chemistry and Manufacture," United States
Government Printing Office, Washington, D. C. (1964).
CJ. H. Forster, "16th Ontario Industrial Waste Conference
of the Ontario Water Resources Commission," Niagra Falls,
Ontario, June (1969).
-134-
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,_ FRCSH SLAKING
WATER
TRUCK OR CAR
UNLOADING
POND
WATER "Ijjjp DILUTION
=f * NEUTHALIIED
^ WATER TO RIVER
J OR TO CLEAN
WATER POND
LIME WASTE
TO GYPSUM POND
FIGURE 8-4 - POND WATER NEUTRALIZING SYSTEM (BO-095)
-135-
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pH: 6-7
fluoride: 5-20 mg/g,
phosphate: 10-30
The results of a recent survey showed that operating costs
averaged ^$2. 10/metric ton P205 ($1.90/ton), while the range
was $1.00-3.30/metric ton P205 ($0. 90-3. 00/ton P20S) (BA-
133).
Although groundwater contamination from gypsum
pond leachate and runoff is a potential hazard, no data are
available. However, no harmful effects have been detected
to date by state or federal agencies.
8. 3 Alternate Disposal Methods
Alternate disposal methods for phosphogypsum
discussed in this section entail various utilization schemes,
some of which are quite highly developed in countries other
than the United States. Because of the abundant supply of
natural gypsum deposits here, there has not been as strong
an incentive to develop utilization technology as has been
felt in Japan, Europe, and other areas. The Florida Phos-
phate Council has been studying potential uses, but to date
no practical results have been obtained. The following
paragraphs present a summary of progress made in foreign
countries. The majority of the applications have been made
in production of gypsum wallboard, gypsum plaster, plaster
of Paris, cement, stucco, building blocks, ammonium sulfate
fertilizer, and recovery of sulfuric acid or sulfur.
-136-
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Production of ammonium sulfate is based on the
Merseburg Process, treating by-product gypsum or anhydrite
with ammonia and carbon dioxide to form ammonium sulfate and
calcium carbonate (GO-072) . Figure 8-5 is a simplified flow
sheet for this process. Although it was developed for
natural gypsum as a raw material, it has been modified to
work well with phosphogypsum. The residual fluoride and PaOs
do not affect the product (GY-007) , although certain process
operations can be troublesome. Organic impurities may
decompose, releasing C02 which may cause foaming. Phosphates
can result in difficult separation of CaC03 from the product.
Table 8-8 summarizes the industrial application of the
Meresburg Process.
Phosphogypsum1 s utilization in products such as
cement and gypsum wallboard is hampered by the following
parameters :
total
unattacked P20S
syn-crystallized PzOs (dicalcium phosphate
substituted in crystal lattice)
water-soluble
The third parameter listed is the most important one since
it retards setting time and product strength and because
there are no simple means of neutralizing its effects (MA-
257) . The presence of soluble fluorine compounds lowers the
final strength, and also shortens the setting time. Another
-137-
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RADIAN CORPORATION
WASH WATER
GYPSUM
Fl LTER
i
1
T
'ft
WET GYPSUM I (
FROM um-rra 1
PHOSPHORIC *A7 *
ACID PLANT A 8 (OVERFLOW
n " s» • TO
i ' Ti WASTE
O-LO >BM
GYPSUM
TANK
C
vJ
• • cALCiina
[7 CATOONATE
zr
WATER
> DRAI
1HYDI5
JCLA!
SURGE TWK
»-
u
1
AULIC
SiFiER
-0
iYPSUk
CA
k
E
N
LIQUID
AMMONIA
h
(BON
DIOXIDE
J ^
T?
t!
L
_
n
i
CAR3C
M&
GYI
G
J
JEW* "
>SIIM
KE
it'
i
H
-•
E ACTION
p
.f
n
°trr
i— •
Cj
AMMONIUM
SULFATE
SOLUTION
TANKS
S CONOENSATE ' ' '-UUllUJJIilT'
PRESSURE
COOLING FILTERS
,r
kj±
j|e
1
r CARBONATE
OOLER
H
L
ut
cc,
Mill
F
<
NSXTE
WATFB BAROMETRIC
•HIC.K crtNDFtisra
1
LTER
JAKE
STRONG
AWMO.V UM
SULFATE
SOLUTION
EWPORATt
CRYSTALUZ
S ^x
STEAM]
~"*U'
1
1 CALANORIA
HtS04
^\ fr^ ITDAU
••CENTRIFUGE
1MB
v T
BUFFER LIQUOR
TANK COLUMN
I
f
•VM
r
>R
as
^
/
^
1
M
^
f
A
**
f
_n
CATCHER
•^so4
J
* _j
\
'pRE-TMCKEMER
tn
CENTRIFUGE
H»MN1UM
.ULFATE SOLUTION
OMOnCRL-OUOR
Y
AMUONIUM
SULFATE
CRYSTALS
Z
VERTICAl
.0 DRIER
AMMONW
DRAIN
SULFAT
FIGURE 8-5 - SIMPLIFIED FLOW DIAGRAM FOR PRODUCTION OF
AMMONIUM SULFATE FROM PHOSPHOGYPSUM (GO-072)
-138-
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RADIAN CORPORATION
TABLE 8-8
PLANTS MANUFACTURING AMMONIUM SULFATE FROM
CALCIUM SULFATE (GY-007, GO-072)
Operating company
1. BASK (1G J'arben Industrie A/G)
Oppau, Germany
5. BASF (IG Farbcn Industrie A/G)
fauna, Gei many
.1. \ViwiiR-Chcinie StickstofTwcrkc
Krrfelil, Germany
•1. ICI, BilliiiRliam.
U.K. (closed. 1971)
A. ON I A
Toulouse, Frunce
d Kulilninn
Sclziii'tp, Prance
7. Suuln I cililizcrs and Chemicals
Sindn, India
S. I'nki-l.in Industrial Development
Daud Klicl, Pakistan
d. IVrhliicisand Chemicals
Travnncore Limited
Kerala, India
10. Gujarat Slate Fertilizers
India
11. Tuliuku Frrtiluets
Akita, Japan
I1.1. OSAG (Oi».lortirheStickslofr\vcrke)
I.mz, Autlna
13. AN 1C
Kavumn, Italy
l-l Arot S.uuijii
Turkey
15. Fertilizers and Chemicals
Travancore Ltd.
India
16. Fertilizers and Chemicals
Travancore Ltd.
17.Daroda (Farmers' Cooperative
ui fr K .Tn nan AO A ft a a t «*• •HMA\
Date of
installation
1913-1914
1918
195S
1923
—
1942
1947
1957
1947
19G6
Under
construc-
tion, 19C6
1956
1057
195S
Under
construc-
tion, 10C.O
I960
Later than
1960
1967
RAW
materials
Annual
capacity, tons * Evaporation
Engineered
by
Gypsum and Up to 500,000 by — —
anhydrite 192S; later
reduced to
110,000
Gypsum Up to 600, 000 by — —
1943; damaged
by bombs in
1944; believed
Phosphogypsum
Anhydrite
Anhydrite
Phosphogvpsum
Gypsum
Gypsum
Gypsum plus
NH, and H,SO,
Phosphofrypsum
Phosphopypium
Phosphogypsum
Gypsum
Gypsum
Gypsum
Phosphogypsum
Phosphogypsum
Phosphogypsun
rebuilt
45,000
600,000
130,000 in 1951
130, 000 in 1951
200,000 in 195S
300,000
100,000
50,000
100,000
33,000
10,000
45,000
150,000
300,000
100,000
25,000
110,000
155,000
Krystal, triple
effect
Own design
Believed Lurgi
Kryslal, double
Krystul, tnplc
Krystal, triple
Krystal, double:
Kryslal, single
Krystal, triple
—
—
Krystal, triple
Lurgi
Kryslal, triple
Kryslal, triple
— _
__
—
OSAG, Linz
ICI
—
KtiUiutii
Chrinim
nml ICI
DMA iu«l
Sl'I-X'IKM
Inlrrrmili-
ncnl («cn
^^
OSAG
Clirmin>
1 1 / • t
and K I
BASK
—
__
—
1 metric ton =1.1 tons
-139-
-------
disadvantage in using by-product gypsum is the grayish color
of the final product; this is especially a factor in gypsum
wallboard marketing. All of these adverse effects (except
discoloration) can be reduced to some extent by pretreatment
of the phosphogypsum with lime.
The problem can also be approached by examining
the process used in the phosphoric acid manufacture. There
are more disadvantages associated with the by-product gypsum
from the dihydrate process than with the hemihydrate/ dihydrate
process because the former contains greater concentrations
of phosphate and fluorine impurities (refer to Table 8-3).
The phosphogypsum from the two-stage process can be used in
plaster and cement manufacture and requires only a water
wash treatment and sometimes a lime water neutralization
(MU-060). The dihydrate process by-product, on the other
hand, must first be calcined to hemihydrate and soluble
anhydrite, then neutralized with lime water to yield insoluble,
inactive calcium salts. There are several different processes
for manufacturing plaster-type commercial products from
phosphogypsum. Details are available in the literature (SC-
150, EL-039).
8.4 Case Study - Phosphogypsum Disposal
The case studied is typical of the U. S. phosphate
fertilizer industry's practices for disposing of by-product
gypsum from phosphoric acid manufacture. Mobil Chemical's
facilities in Polk County, Florida, were visited by Radian
personnel to obtain first-hand information in this subject
area.
-140-
-------
The acid-contaminated gypsum was being handled by
ponding and storing indefinitely. The pond started out as a
standard unlined pond receiving gypsum pumped at 30% solids.
It is pumped to the top of the pile where, as the material
settles, a small dragline constantly dredges it from the
center outward. This process results in the walls being
built up higher and higher as the dragline "walks" around
the perimeter. The piles in the area were cometimes as high
as 30 meters and more than 1.6 kilometers in length.
Pollution control measures employed at these
facilities included drainage ditches to collect runoff. The
collected water is returned to slurry more gypsum. Each
plant is equipped with a lime treatment facility to neutralize
acidity in the excess drainage. Fluorides in the effluent
are controlled by a two-stage lime process.
Some monitoring of local surface water is being
carried out; groundwater is not being monitored, however.
While release of some slurry liquor to the environment is
almost inevitable, no data are available from the industry
to ascertain whether or not an environmental hazard exists.
No incidents have been detected by state or Federal agencies.
The future of these gypsum piles remains undertemined,
The industry is promoting investigation of potential utiliza-
tion of this by-product. To date, however, no schemes
appear commercially feasible.
-141-
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9.0 ACID MINE DRAINAGE SLUDGE
Acid mine drainage is a significant environmental
problem of the mining industry, especially coal mining.
This water pollution results when naturally occurring
pyrite, FeSa, in the coal seam and wastes is oxidized in the
presence of air and water to form sulfuric acid and soluble
iron [Fe(II) and Fe(III)] sulfates. Such mine drainage
(AMD) is typically very acidic (pH 2 to 3) and must be
treated for pH and dissolved iron before release to
surrounding water courses.
Most treatment processes involve four steps:
neutralization,
aeration,
sedimentation of precipitated solids, and
sludge disposal.
Further details of these processes are available in the
literature (CO-122, CO-121, HI-065, ST-149, KO-107, RE-074).
Neutralizing reagents commonly used are lime, hydrated lime,
or limestone, although sometimes sodium hydroxide or sodium
carbonate is employed. The oxidation step converts the
ferrous ion to the ferric state which precipitates more
readily at a lower pH. Sedimentation traditionally is
allowed to take place in lagoons which are also used as
sludge storage areas. More recently other means of
settling, dewatering, and disposal of the 1% solids sludge
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are being tested. These developing technologies are
discussed in the following subsections of this report
following a brief description of the nature of this waste.
9.1 Nature of AMD Sludge
Sludges resulting from the neutralization of acid
mine drainage are typically non-uniform and vary widely in
composition depending on the make-up of the drainage and the
treatment process and reagents. The Office of Coal Research
is currently funding a project to investigate the chemical
nature of AMD sludges (US-055) an estimated 8.2 million metric
tons of sludge (1-5% solids) are produced annually (HI-074).
Most treatment processes aim at achieving a high
degree of iron oxidation to promote greater stability and
less pollution potential (LO-076). Hydrated oxides of both
iron (II) and iron (III) as well as aluminum are always
present in varying amounts. The sulfate content also varies
widely. Additional constituents include alkalies, silica,
manganese salts, calcium sulfate, etc. A typical analysis
of solids from an AMD treatment process is presented in
Table 9-1. These data are from some preliminary results of
the OCR project (US-055). The type of neutralization
process was not identified.
The precipitation chemistry of the iron system has
an extensive effect on the composition of sludge and on its
settling properties. Both ferrous and ferric salts will
begin to precipitate at pH 4 or 4.5, but the solubilities
are still relatively high in this range. Iron (III) reaches
its minimum solubility at pH 6-7, while the ferrous form
does not reach its minimum until a much more alkaline range
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TABLE 9-1
AMD TREATMENT PROCESS AERATOR
SLURRY ANALYSES (US-055)
Concentration
Slurry water 99.83
Filterable solids (percent)1 .17
Solids analysis (percent):
Fe 10.9
Ca 43.5
Mg .4
Al .6
Si 1.6
50 14.4
'The weight of aerator slurry retained on laboratory filter
paper as a percent of the total slurry.
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(8.5-9.5) (LO-076, DA-077) . Initial aluminum concentrations
in the drainage waters can vary from traces to amounts
greater than the iron content. Aluminum salt precipitation
has not been investigated as thoroughly as the iron system,
although it is known that coprecipitation with iron salts
occurs (LO-076) . Thus, removal of iron salts from solution
by the neutralization treatments also effectively removes
soluble aluminum as long as the pH is not raised
significantly above 6. Above this point, aluminum salts
will be subject to dissolution because of the amphoteric
nature of this element.
The physical properties of greatest interest in an
investigation of AMD sludge disposal are the settling
characteristics. These have been shown to be a function of
the neutralization reagent, pH, and the iron oxidation
state. The results of one study, as summarized by Lovell
(LO-076) , ranked various neutralizing reagents on the basis
of resultant sludge settleability as follows:
-p
•H
•H
XI
(0
4J
JJ
(1)
CO
C
-H
CO
m
cu
u
Q)
Q
Na2C03
CaC0
NaOH
CaO
Ca(OH)2
In another investigation the measured sedimentation and
compression velocities of sludge resulting from Na2C03
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CORPORATION
treatment were 5.28 and 0.218 cm/min., (2.08 and 0.086
in./min.), respectively. Reagents were ranked with respect
to settling rates as follows:
en
C
limestone (CaC03)
-P
•P
Q)
sodium carbonate (Na2C03)
tJ>
-------
ultimate storage site. The problems inherent in this system
are the vast land requirements, the potential danger of mass
slippage, and release of suspended solids to surrounding
water courses if the lagoon becomes full. Therefore, to
relieve these problems, the approach has been to develop
effective, economical dewatering techniques to reduce
storage volume required and to enhance solids settling.
This section presents brief descriptions of the current
state of technology in the following areas: sludge
conditioning; dewatering; handling; and disposal sites.
In Section 9.3 alternate approaches to disposal of typical
AMD sludge will be discussed.
9.2.1 AMD Sludge Conditioning
Sludge conditioning means treating a sludge in
such a way as to enhance the dewatering rate; a conditioning
step is not a dewatering step in itself.
There are two basic types: chemical and physical.
One example of a physical conditioning process is
thickening. This term implies reduction in volume of sludge
to be handled in contrast to sedimentation which is
basically a water clarification function. There are two
mechanisms by which thickening takes place: gravity and
mechanical. Typical results of solids increase in thickener
clarifiers were summarized by Lovell (LO-076). Again, the
results varied with the type of neutralization process.
Clarifier underflow from a pilot-scale hydrated lime process
ranged from 0.9 to 4.98% solids. Better results were
achieved in a limestone system, although quantitative
results were not given; a "rather dense mass" was obtained.
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The best thickening results were from a limestone sludge
neutralized to pH 6.0-7.5. This sludge volume occupied only
one-fourth the volume occupied by the hydrated lime-treated
sludge. The solids content was 12%; this can be compared
with a density of only 1.2% characteristic of a lime process
sludge.
Another type of conditioning is chemical
conditioning. This entails addition of a coagulant and/or
flocculant which promotes destabilization and aggregation of
the dispersed material. In general, chemical conditioning
improves the settling rate of the sludge, but the percent
solids achieved is not affected.
Other conditioning steps for sludge dewatering as
reviewed by Moss include the following (WE-078):
freezing,
ultrasonic,
heating,
artificial seeding, and
miscellaneous processes.
Many of these were investigated to some extent in Germany
during the 1950's by Rummel (RU-030). To summarize his and
other's results, freezing was found to be effective in
achieving up to 7.5% solids; however, the high costs
involved prevented Rummel from following through in that
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area. More recently, this method is now being studied by
the Scientific Control Group of the National Coal Board.
Ultrasonic conditioning, which was proposed as an
aid in the coagulation of hydrous iron (III) oxide, actually
caused dispersion of that precipitate in two separate studies.
Heating was investigated by Rummel with no positive results.
Artificial seeding which involves introduction of a material
which acts as a nucleation site for precipitate growth is cur-
rently applied in several treatment processes as a sludge re-
cycle procedure. These results are discussed in more detail
in Section 9.3.
9.2.2 Dewatering Techniques
The most promising dewatering technique for AMD
sludge is vacuum filtration; in many cases filter aids have
been shown to greatly enhance this method (WE-078, DA-077,
LO-076). Vacuum filtration of lime-treated AMD sludge and
limestone-treated sludge, in the absence of filter aids,
produced up to 29.8 and 45% solids filter cakes,
respectively. Filter aids serve to increase the porosity of
the cake and thus increase the flow rate. They have been
applied both directly to the sludge itself as an additive
and as a precoat on the filter surface. Mixed results
employing bituminous coal as an additive were obtained. The
use of diatomaceous earth as a precoat, however, produced
excellent results in terms of % solids achieved. AMD
treated with hydrated lime, limestone plus lime, and
limestone were dewatered to 22, 45, and 63% solids,
respectively.
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Porous bed drying is a dewatering technique
commonly applied to other types of sludges although experience
with AMD sludge is limited (WE-078). Bed materials which
are used include natural silica sand, crushed anthracite/
crushed magnetite, and garnet sands. This dewatering process
occurs in two phases: drainage and evaporation. Yeh and
Jenkins determined the filter area requirement to achieve
20% solids of a lime neutralized AMD sludge, initially 1%
solids in a bench-scale investigation (YE-005). On a larger
scale at the Hollywood, Pennsylvania, demonstration site a
three-sectioned bed was constructed on a compacted clay
base. The filter bed itself consists of a 0.6-meter (2-
feet) layer of red dog with a 5-cm (2-inch) cover of sand.
A tile drainage system collects the percolate. One of the
three sections is open to the air, a second is covered with
plastic except at the ends, and the third is equipped with a
close-fitting cover (solar dome effect). The results of
these studies have recently been published (LO-080).
Pressure filtration is a technique very seldom
used in the United States because of the high expense
associated with batch-wise processes. However, considerable
experience has been gained in England and other European
countries. Rummel's experiments with this dewatering
technique were of limited success (RU-030). An aged sludge
(1.2% solids) was dewatered to 20-30% solids with the aid of
a pre-conditioner. The general conclusion reached, however,
was that its low capacity, i.e., filter rate, did not
warrant further investigation.
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A pressure filtration device of sorts which has
been tested on bench- and pilot-scales was described at a
recent symposium on coal mine drainage (PA-122). A 25%
solids underflow can be obtained; every 20-30 minutes a
downtime of 20 seconds was required to operate the batch-
wise process.
Other dewatering methods that either have not yet
been tested or have shown poor capability with AMD sludge
include centrifugation, thermal drying, screening, and
flotation. Further details are available in the literature
(WE-078). Lagooning which can also be considered a
dewatering technique is discussed as an ultimate disposal
technique under Section 9.2.4.
9.2.3 Sludge Handling
Transport of AMD sludge from the dewatering device
to the ultimate disposal site is accomplished by either
piping or trucking. Several different piping systems are in
use although detailed descriptions of these are not
available in the literature.
One system utilizes a portable centrifugal pump
located on the sides of the dewatering lagoon. A hose must
be manually positioned in the sludge to operate the system.
There are a number of disadvantages associated with this
practice:
high labor cost,
manually difficult job,
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pumping speed partially controlled by
sludge flowability toward pump suction,
"rat-holing" often occurs when the
supernatant flows faster than the
settled sludge.
A different system employs a pontoon-mounted pump
to achieve better accessibility. Other movable pump set-ups
are also available.
9.2.4 Ultimate Sludge Disposal
The majority of AMD neutralization plants dispose
of their partially dewatered sludges in lagoons where
natural evaporation, freezing, and percolation further
reduce the water content although failure to drain off
supernatant seriously reduces the effects of these natural
processes. The volume requirements for a ponding arrangement
depend primarily on the extent of dewatering achieved prior
to ultimate disposal. For example, a 5-6% solids sludge
would require approximately one-third the volume of drainage
water treated. After an extended period in a primary
settling pond, the resultant 13.9% solids requires only 3%
of the volume of drainage treated. For a plant treating
water at a rate of 13.6 liters/sec, for 16 hours per day,
five days per week (^200,000 liters or 52,000,000 gallons
per year), approximately 0.5 hectare-meters/year (4 acre-
feet/year) are required (WE-078). The sludge will continue
to settle and compact until equilibrium is reached; i.e.,
when the weight of solids equals the strength of the floes.
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There is an increasing use of abandoned or
inactive deep mines as sludge disposal sites (WE-078, ST-
149). The waste is either trucked or piped to boreholes
through which it is injected. The alkaline sludge
reportedly remains in solid form; also, little resuspension
of dissolved solids occurs. These areas require further
investigation, however.
To dispose of dewatered sludge on the land as a
solid, the following land requirements were given (DE-092).
A 2.5-cm (1-inch) layer occupying 0.4 hectare (one acre)
will be sufficient for the sludge generated by lime neutra-
lization of 15 million liters (4 million gallons) of
drainage each year. Land disposal, however, is infrequently
used in comparison to lagooning and deep mine disposal.
9.3 Alternate Approaches
Several variations of conventional neutralization
treatments have been proposed, tested, and applied on
industrial level. One modification is based on sludge
recycling (HI-065). At pH < 4, the rates of coagulation and
settling of ferric sludge were low, but could be increased
significantly by recycling of previously precipitated sludge
to promote growth of better settling particles. At pH > 4,
sludge recycle had no effect on settling and coagulation
rates which were much higher than in low pH ranges.
The High Density Sludge (HDS) Process was
developed and tested by Bethlehem Steel Corp. (KO-107, KO-
109). This is a modified lime neutralization treatment
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which differs from the basic process in the following ways:
controlled sludge recycle
recycled sludge is mixed with lime slurry
in a reaction tank ahead of the neutralization
and separation steps
iron oxidation state desired is the ferrous
(unoxidized) state
Early bench-scale studies produced sludges with at least 40%
solids. However, pilot-scale tests were disappointing in
that only 15% solids could be achieved; only 30% of the iron
was in the ferrous state. Subsequent bench-scale tests
developed basic technology that made 30-35% solids possible
in a demonstration-scale test which operated for over 2.5
years. A full-scale application has been planned.
A modified version of limestone neutralization is
based on production of a well-settling, dense, magnetic form
of ferrous sludge. Details of the process are available in
the literature (BI-014). The settled sludge volume was
reduced by five compared to conventional lime treatment; the
corresponding solids content was ~6 times greater.
Potential utilization of this waste material has
been investigated to some extent, but so far results have
not been practical. Moss has reviewed the major areas of potential
commercial utilization of AMD sludge (WE-078). The chief
categories are:
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soil conditioning agent, especially
for strip mine spoil reclamation,
additive for building material industry,
recovery of iron for use as component
of blast furnace feed,
application of gypsum technology, and
separation of major chemical components
by wet sieving.
Greenhouse studies showed that mixtures of mine spoil, AMD
sludge, and sewage sludge (45, 25, 30%) promoted plant
growth (YE-005). Results obtained were better than those
obtained with sewage sludge alone. The Bureau of Mines has
tested sludge as a soil conditioner for culm pile reclamation
(see Section 5.4).
Since the sludge does not possess cementitious
properties, it cannot be used in cement manufacture or
concrete technology. However, it may be feasible to use for
improvement of color and texture of various building
materials. The Office of Coal Research is investigating its
potential use as a rock-dust substitute in coal mines
because of its high iron, low silica content (US-055).
9.4 Case Studies - Consolidation Coal Company
Consolidation Coal Company mines coal in seven
states and currently operates 19 acid mine drainage treat-
ment plants. Their first facility went on stream in 1967
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in southwestern Pennsylvania. Since then, additional plants
have been built in Ohio and West Virginia as well as Pennsylvania,
Three of these facilities located in West Virginia were visited
by Radian personnel during the course of this study. Case
studies for these are presented below.
9.4.1 Whetstone Portal Treatment Plant
The Whetstone plant went on line in late 1971
to treat acid mine drainage from the Four States Mine (CO-169).
This drainage is characterized as low pH, high acidity, and
large concentrations of iron and other dissolved metals.
Typical chemical analyses of the raw and treated water are
presented in Table 9-2 (LO-079).
The main feature of this facility is its simplicity,
designed to reduce operating problems. Basically, it
consists of a lime slurry mix tank, flash mix tank, aeration
unit, and sludge pond. Water is treated at a rate of 250
gpm (16 liters/sec). The hydrated lime is removed from
a 40-ton bin by a vibrator system and slurried with water
in a 400-gallon (1500-liter) mix tank. The slurry and drainage
are contacted in a 2500-gallon (10,000-liter) flash mix tank
from which the neutralized drainage then flows to a forced
aeration unit of 100,000 gallon (40,000 liters) capacity.
Oxidation of iron (II) to the iron (III) form which is less
soluble in the treated pH range, occurs here. The sludge
then goes to an earthen impoundment where the solids settle
and clarified water is pumped to a stream.
Construction of this impoundment was a major under-
taking; a 14 meter high earth-filled dam was constructed to
retain the sludge. At present, the sludge is estimated
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TABLE 9-2
CHEMICAL ANALYSES OF RAW AND TREATED
WHETSTONE DRAINAGE (LO-079)
Raw Treated
pH 2.4 7.6
Acidity, ppm CaC03 5400 0
Total Alkalinity, ppm CaC03 0 59
Ferrous Iron, ppm 1080 <0.1
Total Iron, ppm 1500 0.5
Aluminum, ppm 310 >0.1
Calcium, ppm 550 750
Sulfate, ppm S04 8400 2050
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to be 4 meters deep in the lagoon. The total capacity
of the pond is 55 million gallons (210 million liters).
This feature accounted for almost two-thirds of the capital
investment. The total cost was $150,000 which included
$25,000-30,000 for the lime slurrying and mixing equipment
and $35,000 for the aeration unit. Most of the remaining
cost was for dam construction. A pH control system was
originally installed on the unit, but has been removed
because gypsum scaling on the electrodes resulted in
ineffective operation. This scale also forms on the shaft
and walls of the mixing chamber, aerator, and inner walls
of all piping. The scale problem is a direct result of the
reduction in sulfate value of the raw water by the system.
The resultant calcium sulfate is very insoluble, and
precipitates rapidly on equipment surfaces, as the dihydrate,
causing scale. Within 4 to 5 months, the scale can, build
up to 20 centimeters in thickness. Consequently, part of the
routine maintenance consists of chipping away built-up scale
from all the equipment. This normally requires two or three
days of plant down-time. Chemical additives were investi-
gated to determine their effectiveness in preventing or
inhibiting scale formation. Those included were long-
chained polymers, coagulant aids, and sequestering agents.
Results were not completely successful; therefore the
approach now being employed is to maintain simplicity in
design of equipment.
The effluent from each of the treatment plants discussed
here is monitored on a weekly basis using grab sampling
techniques, as required by the state of West Virginia.
Proposed Federal EPA effluent limitations for the coal
industry are:
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pH 6-9
Total iron, mg/i 4.0
Alkalinity, mg/l CaCO > acidity
Suspended solids, mg/fl, 30
West Virginia requires that the total iron concentration
not exceed 10 ppm and that pH be within the 5.5-9 range.
Lime neutralization treatment of acid mine drainage is
effective in achieving these limits under normal conditions.
9.4.2 Edgell Treatment Plant
The Mountaineer Division of Consol built and operates
a lime treatment plant near Wyatt, West Virginia, to treat
acid drainage from the western end of the Williams Mine
(AK-006, CO-169). This facility handles 5.7 million liters
per day (1.5 million gallons per day) of relatively neutral,
ferrous-containing drainage. Table 9-3 presents an analysis
of the raw water, including high, low, and mean values.
Also included is an analysis of the treated slurry.
The system operates by automatic addition of
hydrated lime to the slurry mix tank. A pH controller can
be used effectively in this case. The lime consumption
rate is 218 kg/hour (480 Ib/hour). Untreated drainage is
used as the makeup water which, upon addition of the lime,
turns a charcoal or dark green color indicating the presence
of ferrous iron. The lime slurry contacts the bulk of the
drainage in a mixing tank; treatment pH ranges from 8.0
to 8.4. The effluent from this tank flows by gravity to
an earthen aerating lagoon equipped with a 15 horsepower
surface aerator. Two open ditch outlets lead from this unit
downhill to the settling pond. The sludge is retained
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Table 9-3
Edge 11 Treatment Plant Chemical Analysis
PH
Ca (ppm)
Mg (ppm)
Al (ppm)
Si (ppm)
SO^ (ppm)
Fe ppm
Fe ppm
Total Fe (ppm)
Acidity (ppm CaC03)
HCO^ (ppm CaC03)
Ca (ppm)
Mg (ppm)
Al (ppm)
Si (ppm)
SO^ (ppm)
Total Fe (ppm)
Nonfilterable Solids
Analysis of Raw Water
High
6.7
480
150
50
25
5,900 4,
870
80
870
1,700
440
Analysis of Slurry
High
1,400
80
75
20
4,300 4,
340
(ppm) 3,100
(AK-006)
Low
4.6
280
75
2
5
100
210
0
220
50
0
Low
620
70
8
9
200
220
760
Mean
6.0*
370
95
20
15
4,800
460
30
490
660
110
Mean
920
75
35
15
4,200
260
2,200
Median Value
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by a dam'v 6 meters high. Approximately 4 meters of sludge
have accumulated since start-up in 1970. An estimated
6-7 years of capacity remains. As at Whetstone, clarified
supernatant is released to a nearby stream.
9.4.3 Levi Moore Treatment Plant
This facility neutralizes 2.6 million liters per
day (700,000 gallons per day) of drainage from the Williams
Mine; the plant is located in Harrison County near the coal
preparation plan. An important feature of this particular
system is its adaptability to either acid or alkaline
drainage (CO-169).
Incoming drainage is pumped at a rate of 32 liters
per second (500 gallons per minute) and then drops 30 meters
to a holding pond. From here the water flows through a
metal pipe down the side of a hill, across a set of rail-
road tracks, and over Bingamon Creek before it reaches the
lime treatment unit. Again, forced air oxidation is
employed to convert the ferrous iron to the ferric state.
The effluent is fed to one of two settling ponds from which
clarified supernatant is released to Bingamon Creek.
At the present time, a "desludging" operation is
underway. One of the settling ponds is being emptied so
that it may be reused. A rake-type stirring device has
been mounted on a raft capable of moving along the surface
of the pond. The sludge is pumped out of the pond as it is
being stirred. The stirring is necessary to prevent "rat-
holing" , which occurs when the liquid flows at a faster
rate than the solids. Consequently, only the water is
being pumped and the solids remain behind. In this
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desludging operation, the ultimate disposal site for the sludge
is located up the creek bed at a much higher elevation than
the settling ponds. At the time of the visit, this project
was just getting underway.
This facility formerly housed a pilot plant in
which microbiological oxidation of ferrous iron was tested.
The system would have allowed use of the much cheaper reactant,
limestone, instead of lime following iron oxidation. How-
ever, the tests were discontinued because of problems
encountered with the bacteria's inability to withstand
temperature deviations from 25°C.
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10.0 COAL ASH
Coal-fired utilities generate three types of coal
waste. Fly ash accounts for the major tonnages, while dry
bottom ash and boiler slag contribute lesser but still
appreciable amounts. The disposal technologies employed for
these by-products were investigated by Radian Corporation
for EPA under Contract No. 68-01-2008. This is a summary of
much of the information collected during that contract.
Approximately 10-25% of the ash formed during
combustion of pulverized coal drops to the furnace bottom
and is collected as boiler slag or dry bottom ash, depending
on furnace type. The fly ash is suspended in the flue gas
stream and collected either mechanically or by electrostatic
precipitators. A considerable amount of ash is produced
each year and forecast figures shown in Table 10-1 indicate
increasing annual tonnages. In 1971, 38.9 million metric tons
of coal ash were produced (BR-118). Thus the disposal problem
has become critical in some areas. In the past fly ash was
either ponded or dumped in a landfill disposal site. More re-
cently effort has been directed toward development of technically
and economically feasible utilization schemes, although ponding
and landfill remain the prime methods of disposal.
10.1 Nature of Coal Ash
10.1.1 Properties
Chemical analyses of fly ash have shown a high
degree of fluctuation in concentrations of major and minor
constituents. This is a result of several factors:
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RADIAN CORPORATION
TABLE 10-1
CURRENT AND FORECAST ASH PRODUCTION*
1969 1975 1980
Fly Ash 20 26 33
Bottom Ash + Boiler Slag 10 -- 15
Units are million metric tons.
Source: LI-051
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variability of original coal composition,
even from the same field,
degree of pulverization,
type of furnace,
firing temperature and other operating
parameters.
Table 10-2 gives a range of compositions of major
and minor species that might be encountered in average ash
samples. The basic data are from unspecified Government
publications. The uranium and thorium values represent Eas-
tern coals only. Silica and alumina together usually account
for more than 70% by weight of the total fly ash sample,
especially in hard coal (ER-013). The unburned carbon
content is particularly variable, strongly dependent on the
operating parameters and combustion efficiency. The high
boron content is of special interest since this phytotoxic
element could potentially create an environmental hazard.
In Table 10-3 the composition of ashes collected
by mechanical and electrostatic precipitators are compared.
No significant differences are apparent. These data are
from a TVA plant in Alabama. The coal is from Western
Kentucky and Northern Alabama, and averages 17% ash.
Release of trace elements to the environment is
becoming increasingly a matter of concern. Originating in
the coal, a particular element may ultimately wind up either
in the fly ash, bottom ash, flue gas as a gaseous species,
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TABLE 10-2
POWER PLANT COAL ASH COMPOSITIONS*
Constituent 7. by Weight
Silica (Si02) 30-50
Alumina (A1S03) 20-30
Ferric Oxide (Fe803) 10-30
Lime (CaO) 1.5-4.7
Potassium Oxide (KaO) 1.0-3.0
Magnesia (MgO) 0.5-1.1
Sodium Oxide (Na80) 0.4-1.5
Titanium Dioxide (TiOg) 0.4-1,3
Sulfur Trioxide (S03) 0.2-3.2
Carbon (C) and volatiles 0.1-4.0
Boron (B) 0.1-0.6
Phosphorus(P) 0.01-0.3
Uranium (U) and Thorium (Th) 0.0-0.1
From RO-093
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RADIAN CORPORATION
TABLE LO-3
EFFECT OF COLLECTOR TYPE ON FLY ASH COMPOSITION*
% Moisture
% Ignition loss
7. Silica (SiO?)
7. Iron (Fe203)
7. Alumina (Al?03)
7o Calcium (CaO)
7. Magnesium (MgO)
7o Sulfur trioxide (S03)
% Available alkalies
Specific gravity
Elaine fineness (cnf /gram)
7o Passing 200-mesh sieve
70 Passing 325-mesh sieve
Mean particle diameter, microns
Mechanical
Precipitator
0.20
6.60
51.60
13.20
25.00
0.90
1.10
0.10
0.50
2.02
2,250.00
88.50
77.80
13.20
Electrostatic
Precipitator
0.30
2.00
47.50
16 . 10
25.40
1.70
1.10
0.40
0.40
2.14
1,900.00
84.70
78.50
14.80
*From TE-112
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or in the system's water. Therefore the trace element
composition of the coal has a major impact on the composition
of the waste products. Some interesting comparisons for a
Western versus Eastern coal can be seen in Table 10-4.
Relative to the Western coal, the Eastern coal is very high
in zinc, manganese, barium, chromium, and vanadium. The
Western coal is higher in arsenic, antimony, selenium, and
nickel. It also is interesting to compare the trace element
content of fly ash versus bottom ash. Except for manganese
and cadmium the fly ash is significantly higher in every
element measured.
Generally, 2-5% of fly ash is water-soluble. The
resulting solution is usually alkaline due to the effect of
free lime (CaO). The principle soluble species are calcium
and sulfate ions, with limited amounts of sodium, magnesium,
potassium, and silicate also present (BA-169).
One important characteristic of coal fly ash is
its pozzolanic activity. A pozzolan is a substance which
has no cementing property of its own but develops cementitious
properties with lime and water. Some fly ashes possess
limited degrees of self-hardening characteristics when
moistened and compacted. This phenomenon is partly due to
the free lime content of the ash itself, although the results
of some studies have indicated that properties of the insolu-
ble portion of the particulate are involved.
The physical properties of fly ash vary with the
type of collector employed, moisture content, and firing
conditions. A mechanical collector results in a relatively
coarse fly ash, the texture of which is described as a fine
-168-
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TABLE 10-4
SELECTED TRACE ELEMENTS IN COALS AND ASH (ppm)'
Western Coal
Composite
ON
SO
Element
Arsenic
Mercury
Antimony
Selenium
Cadmium
Zinc
Manganese
Boron
Barium
Beryllium
Nickel
Chromium
Lead
Vanadium
Eastern Coal
N.D.
<0.01
<0.05
N.D.
N.D.
180
350
46
1800
<0.01
N.D.
310
30
180
Sample
3
0.05
0.17
1.6
<0.5
0.56
15
15
400
N.D.
25
5
4
9
Fly Ash
15
0.03
2.1
18
<0.5
70
150
300
5000
3
70
150
30
150
Bottom Ash
3
<0.01
0.26
1
<0.5
25
150
70
1500
<2
15
70
20
70
'From RO-084
-------
sand. The ash removed by an electrostatic precipitator is
much finer, having a silt-like grading. The particle size
distribution measured for several Michigan fly ashes, along
with several other index properties, are presented in Table
10-5. The range of specific gravities typically reported is
1.9 to 2.4 (BA-169). A small proportion, 1-3%, of the
particles are hollow spheres called cenospheres which have
an apparent density of 0.4-0.6 g/cm3. Bulk densities of fly
ash vary greatly and maxima are obtained by compaction at
optimum water contents.
Engineering properties of fly ash directly affect
its potential utilization. Those that are commonly associa-
ted with its applicability in structural materials are
unconfined compressive strength, shear strength, age harden-
ing behavior, compressibility, settlement behavior, and
frost susceptibility. Potential environmental hazards,
especially water pollution, can be partially assessed by
determining permeability and drainage characteristics. Of
special interest is the effect of lime addition, which has
been proven to enhance the natural self-hardening characteris-
tics of fly ash through its pozzolanic activity.
Permeabilities of a number of compacted fly ash
samples have been determined experimentally. The results
ranged from 0.5xlO~6cm/sec to 4xlO~6cm/sec (RA-084). These
indicate anywhere from impervious to medium drainage character-
istics, similar to soils having the same particle sizes and
gradings.
Compressibility and settling behaviors are other engineering
properties of importance. The problem associated with these
-170-
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TABLE 10-5
PHYSICAL PROPERTIES OF MICHIGAN FLY ASHES*
Property Sample 1 Sample 2 Sample 3
Specific gravity 2.61 2.48 2,36
Specific surface (cm?/g) 2620 3050 3050
Maximum dry density (g/cm3) 1.19 1.45 1.49
Optimum water content (% HS0) 32.0 23.0 19.5
Particle size distribution:
•> 2mm (gravel size) 000
0.074-2mm (sand size) 12 6.5 10.5
0.002-0.074mm (silt size) 85 88.5 82.5
From GR-087
-171-
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features is not so much the extent of settling and compaction
Observed, but rather its predictability. Laboratory results have
not always been consistent with field behavior. Untreated fly
ash behaves as ordinary soils; aging and loading time intervals
have negligible effect. Lime-treated samples experience varying
amounts of strain depending on the curing time, or age. Similar
behavior is observed under long-term loading.
Bottom ash is the product of coal combustion which
collects in the bottom of the furnace or boiler. The nature
of this material depends on the boiler type. Modern boilers,
which burn pulverized fuel, are usually of the dry bottom type.
The heavier ash falls through open grates at the bottom into
hoppers which usually contain water. The second type of boiler
is the wet bottom variety; the material collected in this
equipment is in the molten state and is generally referred to
as boiler slag. The proportion of total ash produced by coal-
fired utilities categorized as dry bottom ash is approximately
10%.
Chemical analyses are presented in Table 10-6.
The results indicate that the major species present in
bottom ash are silica (SiOz), ferric oxide (Fe2O3), and
alumina (A1203), with minor amounts of the oxides of calcium
(CaO), magnesium (MgO), sodium (Na20), potassium (K20), and
sulfur (SOa). Trace element compositions of bottom ash were
compared to those of fly ash in Table lo-4.
Boiler slag is a black glassy substance composed of
chiefly of angular particles; some of the particles, however,
are rod-shaped. The surface texture is porous although not
to so great a degree as thatof dry bottom ash. Slags tend to
be fairly uniform in grain size distribution, ranging from fine
-172-
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to
TABLE 10-6
CHEMICAL ANALYSIS OF BOTTOM ASH (WT. 7.)
Si02 A1203 Fe2°3 Ca° M8° Na2° K2° S03
Source #1 53.6 28.3 5.8 0.4 4.2 1.0 0.3
Source #2 ' 45.9 25.1 14.3 1.4 5.2 0.7 0.3
?V~'c
Typical Limits 20-60 10-35 5-35 1-20 0.3-4 1-4 0.1-12
*From MO-070 and SE-073
From SE- 075
-------
gravel to fine sand. The specific gravity of boiler slag is
typically higher than that of dry bottom ash, but generally
varies with the iron content. Chemical analyses of several
bituminous slags are presented in Table 10-7. The carbon
content, although not reported here, is usually very low (ER-013)
Engineering properties of boiler slags have also
been investigated. Because of the more porous nature of dry
bottom ash, the optimum moisture contents for slags were
found to be lower than values for bottom ash. Permeability
measurements were approximately 10~6cm/sec which correspond
to typical values for sand. Further details are published
in the open literature '(MQ-070, SE-073) .
10.1.2 Quantities
In 1972 a total of 307 million metric tons of coal
were burned by the electric utility industry in the United
States (BU-087). Assuming a National average ash content of
11% (range 6-20%) , this means that 34 million metric tons of
ash were produced. Other figures (Table 10-1) show that ash
production through 1980 is expected to increase despite
predictions of increasing proportions of nuclear power
generation (LI-055).
The relative amounts of bottom and fly ash depend
on the mode of firing and type of combustion chamber. This
is illustrated by the figures in Table 10-8 based on an
average coal heating value of 13,700 kJ per pound.
-174-
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TABLE 10-7
Ln
I
CHEMICAL ANALYSES OF
Ash*
S-l
S-2
S-3
S-4
S-5
S-6
S-7
S-8
1
2
3
Typical
Limits
Coal Rank
Bituminous
Bituminous
Bituminous
Bituminous
Lignite
Bituminous
Bituminous
Bituminous
Btiuminous
Bituminous
Bituminous
--
SiO,
49.4
48.0
39.9
47.4
33.8
45.6
50.5
53.1
48.9
47.1
53.6
20-60
AUO,
24.8
18.5
22.6
19.0
18.7
23.8
25.8
26.0
21.9
28.3
22.7
10-35
Fe,0,
20.5
17.9
26.3
24.6
6.3
23.4
20.1
20.1
14.3
10.7
10.3
5-35
CaO
10.9
6.0
4.8
6.7
25.2
3.2
4.6
5.5
1.4
0.4
1.4
1-20
BOILER £
HgO
0.8
0.9
1.6
0.5
7.4
0.7
0.6
0.0
5.2
5.2
5.2
0.3-/
Data for samples S-l through S-8 were taken from WE-073.
Analyses for the Michigan samples were reported in MO-070.
Typical limits were published in SE-075.
Na,0
0.7
0.8
1.2
0.1
0.4
0.1
1-4
Acid/Base
7.0
9.6
9.8
9.2
1.6
17.7
14.6
14.3
Source
Kentucky
Wisconsin
New Jersey
Indiana
South Dakota
West Virginia
Tennessee
Ohio
Michigan
Michigan
Michigan
-------
RADIAN CORPORATION
TABLE 10-3
COMPARISON OF PERCENT FLY ASH FROM
DIFFERENT COMBUSTION OPERATIONS*
Type of Operation Fly Ash (7. of Total)
Pulverized Coal Burners
Dry Bottom, regardless of burner
type 85
Wet Bottom, without fly ash
reinjection 65
Cyclone Furnaces 10
Spreader Stokers, without fly ash
reinjection 65
*From BU-087
-176-
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The geographic distribution of coal ash production
within the United States is concentrated in the Great Lakes
and Midwest regions. The five states of Illinois, Indiana,
Michigan, Ohio, and Wisconsin produce more than one-third of
the Nation's fly ash (LI-055). Very limited amounts of coal
ash are produced in the West. This impacts not only the
disposal aspects such as land availability but also the ash
utilization market.
10.2 Disposal Technology
Basically there are three alternatives available
for the ultimate disposal of solids from fossil fuel fired
utilities: ponding, landfill, and utilization. The first
two approaches, in which the solids are viewed as throw-away
wastes, are discussed below with consideration given to the
technical, economic, and environmental aspects of each.
Another alternative, deep mine disposal, is also briefly
described. Commercial utilization is treated in Section
10.2.4.
10.2.1 Ponding of Coal Ash
Ash ponds are typically operated such that the
slurry enters one end of a single pond. As it flows to the
opposite side, the well-settling ash drops out and a pool of
supernatant forms at the far end. The effluent is removed
via weirs or standpipes, thus allowing continuous operation
of the pond until full. In ash pond management, the settled
ash is seldom used to increase the height of the walls
because its spherical form results in a low angle of repose.
-177-
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CORPORATION
In Table 10-9 analyses of ash pond effluent for
TVA's Widows Creek operation are presented. Only metal
analyses for iron and manganese are given, and these are
very low. Total dissolved solids are generally low enough
to meet the U.S. Public Health Service limit of 250 mg/1.
Table 10-10 presents data on ash pond liquor composition for
ten plants in the Ohio Basin Region. Radioactivity data
also are presented. Phosphorus, ammonia, and nitrate are
all very low in concentration for all plants. Boron is very
high for four plants. Regarding the radioactivity, U.S.
Public Health Service limits are 3 pci/1 (picocuries/ liter)
for alpha radiation and 1000 pci/1 for gross-beta-activity;
some of the pond liquors exceed the alpha limit. Table 10-
11 shows results of trace constituents in an unidentified
ash pond. Note the low boron concentration compared to the
values for the Ohio ponds given in th'e previous table.
The major factor contributing to selection of this
disposal method is land availability. For a 1000 megawatt
coal-fired unit over a 20-year lifetime, about 100 hectares
would be required for the ash ponded to a 3-meter depth (JO-
083). This figure is based on a 12% ash. content of coal, an
annual production of 261,000 dry metric tons, a water content
of 20%, and a packing volume of 0.59 m3 dry material/metric
ton. Ponding is a feasible alternative only if sufficient
land is available in close proximity to the utility, preferably
on-site.
The economics of this method of ash disposal indi-
cate that the cost per metric ton of solid is in the range
$0.55 - 2.20. This figure represents an operating cost
which includes transport plus pond management expenses.
-178-
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TABLE 10-9
Type of
Liquor
Ash Pond
Discharge
Sample
Identify
1971 quarterly
samples, TVA's
Widows Creek
VO
I
CHEMICAL ANALYSES
OF ASH POND DISCHARGE FROM TVA ' S WIDOWS
CREEK
Concentration, opm
pH
7.3
9.0
9.8
9.1
Total
Solids
250
190
210
210
Total
Dissolved
Solids
240
190
210
210
Alkalinity,
Total
CJCO,,
54
45
61
75
Total
Hardness
CaCO,
69
99
130
130
Ca
20
34
47
45
Me
4.6
3.4
3.7
4.3
SO.
100
95
70
60
Cl
21
11
19
17
SiO,
5.4
4.4
6.1
5.6
Fe
0.29
0.42
0.27
0.69
Mn
0.44
0.02
<0.01
0.02
Ref.
TE-112
-------
TABLE 10-10
oo
o
POLLUTANT CONCENTRATION IN SEVERAL OHIO
K
Type of Sample in NH3
Liquor Identity pH (ppn)
Ash Pond Ten plants see 0.1
in Ohio Remarks „ ^
Basin region
0.1
1.9
0.1
0.1
-0.1
0.2
0.2
0.2
N
in NO,
(ppm)
-0.1
-0.1
-0.1
-0.1
-0.1
-0.1
-0.1
-0.1
-0.1
-0.1
p
(ppm)
0.1
-0.1
-0.1
-0.1
0.6
0.2
-0.1
0.1
0.5
0.1
B
(ppm)
300
1600
100
500
<100
<100
<100
<100
<100
<100
ASH PONDS
Radioactivity
(pci/0
Alpha Beta Remarks Ref.
1 ± 1
0
0
0
4 i 3
1 ± 1
~ 5
9 ± 4
•* L
«*. 4
7 ± 2 pH ranged from RO-093
15 ±6 6'2 - L1'5- The
ash content of
£ <•> O
the coals ranged
5 s 2 from 11 - 237.,
10 z 4 "ith 13% average.
14 ± 3
78 * 14
44-7
9*5
38 * 11
-------
TABLE 10-11
TRACE ELEMENT CONCENTRATIONS IN ASH POND LIQUOR*
Element Concentration, ppm
Lead .01
Antimony .015
Barium .07
Manganese .075
Mercury <.001
Beryllium .002
Boron .5
Nickel .015
Cadmium .01
Selenium .035
Zinc .03
Arsenic .01
*From RO-084
-181-
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Economics associated with transport of power plant wastes to
off-site disposal areas have been established by experience
with ash disposal. The results of a 1970 nationwide survey
of 22 utilities shows that it.was costing $0.033-1.21 per
metric ton (average of 25 plants, $0.50/metric ton) to
sluice ash to the disposal area (TA-040). Those utilities
employing trucking services were incurring slightly higher
costs ranging from $0.12-1.47 per metric ton or $0.56 per
metric ton on the average (10 plants).
The pond construction cost would depend, of course,
on the nature of the design; i.e., if liners or other pollu-
tion prevention measures are taken. Some approximate cost
figures have been estimated for lined ponds (RO-084).
Factors influencing the price include size and type of
lining required. For a 2-4 hectare pond with no provision
for drainage, $12,000 to $50,000 per square hectare is
estimated for clay or stabilized pozzolan base lining. The
cost of a drained pond fitted with a soil covered plastic
liner can be as much as $62,000 to $75,000 per square hectare.
10.2.2 Landfill
A second approach commonly taken by fossil fuel-
fired utilities for solids disposal is landfill. This
method eliminates the need for long distance hydraulic
sluicing systems and on-site ponding facilities. The disposal
area may be either on-site or off, again depending on land
availability.
The pollution potential of an ash landfill opera-
tion is related to the leachate characteristics. To date,
-182-
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no instances of groundwater pollution by disposed ash have
been reported. Related studies currently are in progress in
which the availability of molybdenum, boron, and other trace
elements to plants is being studied. The results of green-
house studies have shown that application of fly ash to
soils does increase the availability of boron, molybdenum,
phosphorus, potassium, and zinc (MA-218). Whether or not
this constitutes a potential pollution problem regardless of
the beneficial results to some plants is not yet conclusive.
The economics of a landfill operation can vary
widely depending on the amount of waste to be disposed of,
distance to disposal site, type of transport used, and
necessary land reclamation steps. In some instances, there
may be an additional fee charged by the receiving agency if
the site is not utility owned. A typical cost would fall in
the range $0.55-2.20/metric ton. One source reported costs
of $0.88-0.99/metric ton (TO-027). This figure does not
include the cost of reclaiming the area - a factor that is
now becoming more and more of a public issue. This would
add considerably to the cost of the solids disposal.
10.2.3 Deep Mine Disposal
Another possible option available for disposal of
fuel ashes, although not under investigation to the same
extent as landfill and ponding, involves direct deposit of
the waste below the surface in subsurface mines. Deep mine
filling has been used for the disposal of power plant ash
(TO-027). The ash is sluiced into the mine through boreholes,
Normally, gravity is sufficient to create a flow into the
mine. Pumps and additional boreholes were provided in case
-183-
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of hole plugging or increased friction losses. A dewatering
sump and a settling basin were formed by constructing dams
across the mine floor. Overflow from the settling basin
flows to the sump from which it is pumped to an above ground
basin. Further details are available in the literature (TO-
027, HA-158). Investigation of this approach may be worthwhile
to those utilities to which abandoned deep mines are available
as a potential disposal site.
10.2.4 Coal Ash Utilization
Fly Ash
Progress in the area of fly ash utilization i,s
more advanced than other types of waste utilization because
of the greater quantities of fly ash generated compared to
bottom ash or slag and the longer period of experience with
this material compared to sludge. A number of methods have
been developed. Some of these have been successfully prac-
ticed in European countries and the United States, although
the U.S. lags behind other countries in amounts utilized.
In 1969 Britain utilized 42% of its total fly ash production,
France 55%, and the U.S. only 9%. In absolute tonnages,
Britain and Germany each use more than the United States.
More recent figures, however, show that the U.S. is increas-
ing its rate of fly ash utilization, which rose to 12% in
1971 (BR-118). Corresponding increase in total ash utiliza-
tion for the same year rose to 20.1%. This indicates a need
for better market development in this country not only to
realize some economic return for the utility industry for
their by-product, but also to alleviate possible detrimental
environmental aspects of ash disposal.
-184-
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During the recent Third International Ash Utiliza-
tion Symposium, information concerning research progress and
marketing success in this area was exchanged. The following
categories encompass the most pertinent areas in which
effort has been expended:
marketing
fly ash processing
extraction of metals
structural material (highway construction,
structural fill, concrete additive, etc.)
soil additive and conditioner (land reclama-
tion projects and fertilizer)
miscellaneous uses.
Table 10-12 indicates the quantities of ash types used in
various commercial schemes during 1971. Also shown are pro-
jected ash production figures for 1976 (BR-118).
There are several general aspects of marketing of
fly ash which will determine the feasibility of such an
approach. These apply not only to fly ash but other power
plant wastes as well. These were presented recently by a
marketing company official and, although his remarks were
specifically related to its utilization as a pozzolan, they
are broad enough to cover all potential uses (HY-011). The
following must be assured in order to successfully market
fly ash:
-185-
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TABLE 10-12
ASH COLLECTION AND UTILIZATION. 1971 (Tons*)
Fly Ash Bottom Ash Boiler Slag
Ash uses:
1. Mixed with raw material before
forming cement clinker
2. Mixed with cement clinker or mixed
with pozzolan cement
3. Partial replacement of cement in:
a. Concrete products
b. Structural concrete
c. Dams and other mass concrete
4. Lightweight aggregate
5. Fill material for roads, construction
sites, etc.
6. Stabilizer for road bases, parking
areas, etc.
7. Filler in asphalt mix
8. Miscellaneous
Subtotal
Ash removed from plant site (at no cost
to utility, but not covered in
categories listed above, see Table II
below)
Total ash utilized
Ash removed to disposal areas (at
company expense)
Total ash collected. 1971
Estimated 1976 ash production
104,222
16.536
177,166
185.467
71,411
178.895
363.385
36.939
147.655
98,802
-
-
35.377
13,942
533,682
7,880
2.833
475,417
91575
-
76,563
2.628.885
49.564
81.700
428,026
1,380.478
1 ^72.728
1,069,131 3.356,713
542,895
381.775
3.253,206
24,497.848
27.751.054
36^94.436
1.612.026
8,446.941
10.058.967
117.411.603
3.738.488
1.232.298
4570.786
2.517.703
* 1 metric ton = 1.1025 tons (short).
Source: BR-118
-186-
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developed utilization scheme,
distinct technical advantage over other raw
materials,
economically competitive with other raw
materials,
strict quality control,
consistency,
uniformity,
availability.
Electric utilities desiring to place their fly ash on a
commercial market have the option of selling it themselves
or forming a contractual agreement with an ash marketing
firm. The latter alternative offers several advantages
which include, among others, removal of legal responsibility
for quality control. Disadvantages as well as additional
advantages are dealt with by Hyland (HY-011) and Zimmer (ZI-
012).
The majority of fly ash utilization occurs in the
area of concrete addition, serving both as a mechanical fil-
ler (supplementing or replacing fine aggregate) and as a
pozzolan (supplementing or partially replacing cement).
A major application in this utilization area is
pozzolanic pavement. A great deal of interest has been
-187-
-------
shown in constructing road base courses of mixtures of fly
ash, lime, aggregate, and sometimes cement. Several states
including West Virginia, Virginia, Illinois, Maryland, New
Jersey, Ohio, and Pennsylvania have specifications for lime-
fly ash-aggregate base course. Last year approximately one
million tons of fly ash were used in road construction in
the Chicago area alone (SL-041).
Several commercial mixes are being marketed basi-
cally as stabilized road bases. One of these is Poz-0-Pac
developed by what is now I.U. Conversion Systems, Inc., (PU-
017). It consists of a small amount of lime, greater amount
of fly ash, and the bulk being aggregate. A number of other
waste materials can also be incorporated into this basic
mixture. The cost is approximately $3.80/metric ton (approx.
$3.50/ton).
Fly ash is an approved mineral filler for bituminous
or asphaltic concrete; however, application has been limited
(FA-058, ZI-012). Technically fly ash performs well in that
it provides for increased stability and durability. The
characteristics of this by-product important in this applica-
tion are its hydrophobic properties and good void filling
capacity. The economics are based on the availability of
low cost competitive mineral fillers such as limestone dust.
Extensive testing of fly ash/water mixtures as
load-bearing fill has been reported. Various applications
in embankments, road filling, landscaping, grouting, and ash
pond dams have been made. In general, fly ash attains much
greater strengths than soils normally used in compacted
earthworks.. Optimum moisture and compaction are very impor-
tant in this type of utilization. Advantages over alternate
-188-
-------
fill materials include ease of handling and spreading; light
weight; increased compaction strength, cohesion, and angle
of shearing resistance with time; and high pozzolanic action
(RE-073).
Much of the research and utilization in this area
has been done in England where extensive use in highway
embankments, especially as fill behind bridge abutments, is
made. The results have been excellent with minimal differen-
tial settlement between the approach and the structure
itself (LA-085).
Several ash ponds have been constructed in Europe
using fly ash fill to retain the slurried ash. One at Gale
Common, England, will serve as the central disposal site for
five generating stations. The dikes which will have a maxi-
mum height of 100 feet are constructed of compacted fly ash
with no treatment other than dewatering to optimum moisture
content. A second pond, located in Eastern France, has been
sited in a dammed tributory stream of the Saar River. Dam
construction began in 1958 and, as more storage is needed,
the dam height is increased. Maximum height will be 120
feet. Compacted layers of fly ash (18-22% water) are used
in the construction.
Problems associated with use of fly ash in this
application include erosion and liquefaction. Internal
erosion is controlled by properly designed drainage and fil-
ter system. External erosion is prevented by vegetative
cover on the downstream side, slope protection on the upstream
side with clay or similar material, and adequate spillway or
runoff diversion. Liquefaction, or a sudden decrease in
shearing resistance, occurs under the following conditions:
-189-
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material gradation typically in range of fine
sand to coarse silt,
loose material with high percentage voids,
high water table or excess pore water pressure,
shock loading.
The first two cannot be controlled when fly ash is used.
Therefore extreme caution must be taken to prevent water
pressure buildup and shock loading.
The Bureau of Mines is actively investigating the
use of fly ash in mine subsidence prevention and fire con-
trol (SL-041, FA-058, TE-114, MA-247, NA-134). Successful
extinguishment of a mine fire in Pennsylvania has been re-
ported. In addition, fire prevention can be achieved by
either dry pneumatic injection or slurry injection.
A great deal of effort is being made in the use of
fly ash in reclaiming acid mine spoil areas (FA-058, SL-041,
AD-015, CA-112, NA-132). In this capacity fly ash serves as
a neutralizing agent, a diluting agent, a soil amendment,
and enhancer of soil's water retention capacity. The reclaimed
soil has been shown to support a number of grasses (Kentucky
31 fescue, rye, red top) and legumes (birdsfoot trefoil)
although negligible survival of trees and shrubs has been
observed. Reclamation costs depend on terrain, soil type,
age, acreage, equipment employed, legislative requirements,
and degree of reclamation desired. One source estimated a
cost of approximately $740/hectare ($300/acre) for previously
-190-
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leveled land (NA-132). Total costs estimated by another
source, however, are in the range $2000-3000/hectare ($800-
1300/acre) (CA-112). This figure includes a hauling charge
estimate plus the basic reclamation cost ($700-1000/acre for
earthmoving, seeding, fertilization, and soil conditioning).
The factor which accounts for the large difference in the
two estimates is the cost of leveling.
Greenhouse and field experiments have been conducted
to determine the availability and possible adverse effects
of certain elements in fly ash to plants (FA-058, SL-041,
RE-073, MA-218, MA-219, DO-043). Some of the metals of
interest include B, K, Zn, Mo, Al, and Mn. Mechanisms
involved are also under investigation; pH and kinetics are
thought to be strong factors. Results to date indicate that
most fly ashes tested do increase soil availability of these
species. Utilization as a soil nutrient is limited, however,
in that ash does not supply the major plant nutrients such
as nitrogen.
Another promising use for sintered fly ash is as a
lightweight aggregate. Several processes have been developed
for manufacturing fly ash aggregate (BA-169). The product
is a hard cellular material with a bulk density of approxi-
mately 0.89 g/cm3 (approx. 50 Ib/cu ft) (approx. one-half
that of gravel). Although it is not as strong as gravel,
strengths are still high enough to have wide applicability,
especially as a concrete aggregate (RE-073, TE-114, BA-169).
Manufacture of fly ash bricks is currently on an
industrial level. A process developed by the Coal Research
Bureau at West Virginia University is utilized by a Canadian
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manufacturer whose annual production is 35 million bricks.
A Czechoslovakian plant is also planned; approximately
91,000 metric tons (100,000 tons) of fly ash will be utilized
annually. The process itself is based on a composition of
74% fly ash, 23% boiler slag, and 3% sodium silicate (TE-
114). The product is chemically no different from clay-
fired bricks, weighs about one-third less than clay bricks,
and costs approximately one-third less. Another significant
factor is that virtually no seconds are produced in this
process (RE-084).
Another utilization area for fly ash is in water
treatment and sewage conditioning. The properties of ash
which make this use feasible include its absorptive capacity
for organic matter, neutralizing properties for acidic
media, reactivity with inorganic phosphorus, and particulate
characteristics (FA-058, SL-041, TE-114, TE-125, JO-087).
Slag and Dry Bottom Ash
The percentages of boiler slag and dry bottom ash
produced in modern utility boilers are not nearly so high as
fly ash production figures. Therefore, the actual tonnages
to be disposed of are much less. Percentages finding commer-
cial markets have reportedly been greater for the two bottom
ashes than for fly ash in recent years (BO-073, BR-118).
This is mainly due to their extensive use as road and construc-
tion fill. Another potential use is in mineral wool production;
this is still under experimental investigation. Many other
miscellaneous uses for boiler slag have been investigated
(ER-013), but will not be fully described in this report.
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CORPORATION
Processing of dry bottom .ash is not required, at
least in the utilization schemes normally employed. Wet
bottom ash, or boiler slag, is treated in some cases prior
to commercial marketing (ER-013>. One processing technique
involves screening to achieve uniform particle size. The
granules separated by this method show stress-cracking, and
the grain structure of this material seldom meets require-
ments. A second process employs an impingement mill. The
product in this case is a gray to black sand having a parti-
cle size distribution that meets that specified for sand.
All of the granule fractions possess regular cubic form,
high strength, and low bulk weight. The material has a high
melting point and low heat transfer properties.
One of the best examples of application of slag
and bottom ash in road construction is a 9-km long
project carried out during 1971-72 in West Virginia. No
natural aggregates were used, almost all materials being
industrial by-products including approximately 230,000
metric tons of power plant ash and slag (BR-118, MO-070, NA-
130). An expected savings in material costs is estimated at
approximately $500,000.
Experience in using untreated bottom ash as a base
course material was not as successful. If allowed to dry
out after compaction in place, it tended to break up. if
covered immediately with a surface course, this did not
occur. This phenomenon can be prevented by addition of
fines such as fly ash (30-40%) or by addition of blast
furnace slag to the bottom ash.
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The overlying course in the West Virginia Route 2
project was placed in two lifts and compacted to a final
thickness of nine inches. The composition was a mixture of.
80-85% bottom ash and 15-20% blast furnace slag.
The surface course was a two-inch layer of bitumin-
ous concrete containing boiler slag and blast furnace slag
as aggregate. This application is now being investigated to
determine its skid-resistant and wear-resistant properties
(SL-041). It has been reported that boiler slag surfaces
show better than average skid-resistance compared to other
economically available surface materials (MO-071). This is
due to the following characteristics of slag:
hardness and angularity,
affinity to asphalt,
elimination of bleeding and fat spots associa-
ted with other aggregates.
Other advantages of using slag in surface course applications
include:
permanent black color achieved;
when used for shoulders, it offers good color
contrast with Portland cement concrete;
dust free; therefore water absorption is low
resulting in less erosion and higher resis-
tance to freeze/thaw damage;
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faster drying roads because of dark color;
rejects actinic sun rays which damage bitumen;
blendability with other aggregates permits
maximum use of less suitable local aggregate.
10.3 Case Study - Coal Ash Disposal At TVA's Widow
Creek
The Widows Creek Steam Plant is located on the
north shore of Guntersville Reservoir in Jackson County,
Alabama. The complex, which has a total generating capacity
of 1978 Mw, cosists of eight boilers fired by pulverized
coal. The assigned ratings and hourly coal consumption
rates for each unit are shown in Table 10-13.
All eight units are served by the same coal storage
area. Total consumption rate at full load is 677 metric
tons per hour. Assuming an ash content of 17%, approximately
115 metric tons of ash are produced hourly; 75% of this is
estimated to be fly ash. Units 1-6 are equipped with mechanical
collectors rated at 70% efficiency. The electrostatic
precipitator installed on unit 7 is 99% efficient, but that
on unit 8 is only 50-70% efficient. Overall removal on this
unit will be increased to 99% when an SOa scrubbing system
now under construction, goes on stream.
Solid wastes generated at Widows Creek are disposed
of by ponding. The original ash pond used for units 1-6,
located inside a railroad loop, was filled and taken out of
service when the existing pond was put into service in
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RADIAN CORPORATION
TABLE 10-L3
CAPACITY AND FUEL CONSUMPTION RATES
FOR WIDOWS CREEK UNITS
Coal Consumption Rate,
Unit Start-Up Capacity, MW metric tons/hour
1 1952 140 53
2 1952 140 53
3 1952 140 53
4 1953 140 53
5 1954 140 48
6 1954 140 48
7 1961 575 185
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February of 1961. A portion of the first pond has been
vegetated, while the other half is being used as a source of
fly ash for mixing with cement.
The pond now in use is located northwest of the
plant on the southern shore of Widows Creek Embayment. The
26 hectare (65 acre) area receives ash from all eight units.
Ash accumulated in the fly ash hoppers at units 1-6 is
transported to the disposal site by a hydroveyor system.
Water jets create a vacuum which removes the ash from the
hoppers, and the slurry subsequently flows by gravity to the
ponds. A similar ash removal system is employed to remove
the electrostatically precipitated ash from hoppers on units
7 and 8; however, a pumping system is required to transport
the slurry to the pond. The total amounts of fly ash disposed
of in fiscal 1970 were:
Units 1-6 137,806 metric tons
Units 7,8 201,948 metric tons
Bottom ash disposal is handled by a separate
transport system although it ultimately winds up in the same
pond as the fly ash. This waste is washed from hoppers by
high velocity sequential jets and the resulting slurry is
then pumped to the pond. Clinkers from units 7 and 8 are
first ground, then disposed of by this system. In fiscal
1970 units 1-6 generated 65,621 metric tons of bottom ash,
and units 7 and 8 produced 82,697 metric tons. Under full
load conditions, 236 and 277 metric tons per day are generated
daily by units 1-6 and 7,8, respectively.
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Other wastes that are discharged from the plant to
the pond include pyrites that are rejected from the coal
pulverizers, boiler wash solutions, ash slurry sump wastes,
air preheater and economizer dusts, coal scale dusts, and
residue stack dusts.
The clarified effluent is discharged into Widows
Creek Embayment over two spillways located at the southwest
and southeast corners of the pond. Eventually it reaches
the Tennessee River. The effluent averages 76 million liters
per day (20 million gallons per day)of relatively clear,
colorless, alkaline water. Several chemical analyses of the
ash pond water and discharge are presented in Tables 10-14
and 10-15. The first shows a fairly recent analysis of
major and trace components, while Table 10-15 indicates the
variation in parameters measured. The discharge is monitored
on a weekly and quarterly basis for those parameters indicated
in Table 10-16, and continuously for quantities of water re-
leased. In addition, daily patrolling and inspection of
the area provides added protection against possible failures.
Discharges from this pond are in compliance with the Alabama
Water Quality Standards for waters used for public water
supply. These include a limit for dissolved solids of 500 mg/ t..
To date, no significant impact on water quality or
aquatic life has been observed. Biological studies of the
area in 1968 involved sample collection from the bottom of
Widows Creek Embayment near the ash pond outfall. The
results indicated relatively abundant fauna both above and
below the discharge point. Communities of typical benthic
fauna normally associated with fine sediment substrate were
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TABLE 10-14
WIDOWS CREEK ASH POND ANALYSES,
JANUARY, 1973
Quarter January
Date 1-8
pH, units 9.2
Phenol. Alkal., mg/1 11
Total Alkal., mg/1 45
Conductive at 25U C
umhos/cm 120
Chloride, mg/1 6
Sulfate, mg/1 100
Diss. Solids, mg/1 230
Sus. Solids, mg/1 11
Iron, mg/1 0.90
Manganese, mg/1 <0.01
Ammonia as N, mg/1 0.37
Total Phosphate, mg/1 0.19
Silica as SiOP, mg/1 5.6
Cyanide, mg/1 <0.01
Copper, mg/1 <0.01
Zinc, mg/1 0.04
Chromium, mg/1 0.009
Aluminum, mg/1 2.1
Nickel, mg/1 <0.05
Silver, mg/1 <0.01
Calcium, mg/1 44
Magnesium, mg/1 3.9
Hardness, mg/1 130
Lead, mg/1 <0.010
Mercury, mg/1 0.0009
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TABLE 10-14 Continued
WIDOWS CREEK ASH POND ANALYSES,
JANUARY. 1973
Quarter January
Barium, mg/1 <0.1
Arsenic, mg/1 0.036
Cadmium, mg/1 <0.001
Selenium, mg/1 <0.004
Beryllium, mg/1 <0.01
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TABEE 10-15
WIDOWS CREEK STEAM PLANT
NJ
O
Date Time Temp. pH
CT "C.
1967
10/3 0.745 22.0
1968
4/2 0800
6/28 1300
Sept.
1969
L/29
4/3
10/6
1970
1/5
4/8
7/6
10/7
1971
1/4
4/5
7/6
10/4
0800
1000
0830
Alkalinity
Phen. Total
CaC03 CaCO,
mg/l mg/1
0830
8.7
7.1
9.7
9.4
9.1
10. 1
9.8
7.3
9.0
9.8
9.1
3
0
32
14
14
32
21
0
6
52
25
56
33
73
30
61
60
44
54
45
61
75
COD
mg/l
8
ASH POND DISCHARGE
Total
Hard.
CaCO,
mg/l
--
180
110
72
73
100
98
45
69
99
130
130
ANALYSES
(Quarterly Samples)
Ca
mg/l
32
16
23
60
__
--
24
26
35
35
14
20
34
47
45
HE
mg/L
4.0
3.0
3.0
7.0
_ _
--
3.0
2.0
3.0
2.5
2.5
4.6
3.4
3.7
4.3
Cl
mg/l
17
7
9
27
20
--
25
10
7
15
25
21
11
19
17
Fe,
Na Total
mg/l mg/l
10.0 <0.05
6.2 0.05
<0
12.3 0
8.0
--
0
<0
0
0
0
0
0
0
0
.05
.06
--
.05
.05
.53
.28
.26
.29
.42
.27
.69
Mn,
Total
mg/l
0.01
<0.0l
--
0.01
--
<0.0l
<0.01
O.OL
0.03
<0.0l
0.44
0.02
<0.01
0.02
Solids
SQt
mg/l
140
50
75
75
130
45
120
110 •
100
90
50
100
95
70
60
S10.
mg/l
3.6
0.8
3.1
4.5
1.3
5.8
12.0
5.3
6.8
5.2
5.4
4.4
6.1
5.6
Cond.
Dis.
umhos/cm mg/l
350
320
320
410
470
200
320
270
330
380
310
360
300
290
--
--
-.
330
180
250
280
170
240
190
210
210
Tot.
mg/l
_ _
280
400
210
350
210
270
290
180
250
190
210
210
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TABLE 10-16
ANALYSIS OF SAMPLES COLLECTED QUARTERLY
WATER QUALITY MONITORING NETWORK
Temperature
Dissolved Oxygen
Coliforms (fecal and total)
PH
Alkalinity
Hardness
Color (true and apparent)
Turbidity
Conductance
Solids, suspended and
dissolved
Oxygen demand, biochemical
(BOD)
Oxygen demand, chemical
(COD)
Nitrogens (organic ammonia,
nitrite plus nitrate)
Phosphorus (soluble and
total)
Sodium
Potassium
Calcium
Magnesium
Chloride
Fluoride
Sulfate
Silica
Aluminum
Arsenic
Barium
Beryllium
Boron
Cadmium
Cesium
Chromium
Cobalt
Copper
Iron (ferrous, dissolved, and
total)
Lithium
Manganese (dissolved and total)
Mercury
Nickel
Selenium
Silver
Strontium
Titanium
Zinc
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observed on the Creek and Embayment bottoms. Some fly ash
was found, although it did not appear to affect sensitive
fauna species. The conclusion reached was that the discharge
was "not significantly toxic" (TE-101).
A new disposal area is presently under construction.
This project involves relocation of Widows Creek and its
embayment. The site totals 93 hectares (230 acres) which
will be divided into two areas, one for disposal of all ash
from units 1-7 and the precipitator ash from unit 8 and the
other for scrubber waste (sludge plus ash) from unit 8.
The ultimate storage capacity is designed for 2.4 million
cubic meters for ash disposal and an additional 5.0 million
cubic meters for unit 8 wastes. Initially, however, the
capacities will be much less since periodic dike raisings
are planned to gradually increase the capacity.
An impervious dike of compacted earth which will
form the perimeter is being constructed; it will connect to
the dikes at the east and west sides of the existing ash
pond. Material scraped from the interior of the pond will
be used. The outer slope will be no steeper than 2.5:1. A
minimum of 1.2 meters of freeboard will be allowed. The
sludge and ash disposal areas will be separated by a divider
dike of similar construction. The pond bottom will be
compacted by heavy equipment and, according to TVA design
engineers, will become impervious due to early deposition of
fly ash (FA-069).
Operation of the new ash pond will be similar to
that used for the existing pond and the effluent is likewise
expected to be similar in composition. The spillway will
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discharge to an open channel along the southwest side leading
directly to Guntersville Reservoir. The average dilution
effect will be much greater than that presently occurring
into Widows Creek Embayment, even without diffusers or
mixing devices. Closed-loop operation of tke scrubber is
planned which will eliminate any discharge from the second
waste area. The unthickened sludge will be pumped as a 15-
16% solids slurry to the pond. A final settled density of
40% solids is expected, based on pilot plant data showing
57-66% water content after 240 days of settling. The overall
disposal rate is calculated to be 115 cubic meters per hour.
The same monitoring procedures used for the existing
ash pond will be practiced when the new pond goes into
service.
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11.0 SCRUBBER SLUDGE
The disposal of sulfur-containing sludges generated
by lime or limestone wet scrubbing processes is currently
under study by EPA and the electric utility industry. Their
purpose is to determine the extent of potential problems
which may exist with respect to water pollution or land
reclamation aspects of scrubber sludge disposal. Several
reports describing the current state of knowledge in these
areas have been prepared by Radian Corporation under contract
numbers 68-02-1319 Task No. 1 and 68-02-0046 Task No. 12.
These documents are expected to be released shortly. The
information contained in this section summarizes the findings
of those investigations.
11.1 Nature of the Material
The environmental impact of any disposed material
is a function of its physical and chemical properties and of
the quantities involved. Potential water pollution problems
can, in many instances, be predicted by chemical properties
such as solubility, presence of toxic metals, and pH. Land
reclamation is strongly affected by the physical characteristics
of the sludge. The load-bearing capacity is especially
important in this respect. Section 11.1.1 of the report
deals with experimental investigations of properties of
sludge and related materials, while Section 11.1.2 outlines
the method used to predict amounts expected from scrubbing
systems and presents results of the calculations.
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11.1.1 Chemical and Physical Properties of Scrubber Sludge
The sulfur compounds produced by flue gas desulfuri-
zation systems fall into two general categories: throwaway
or saleable products. Lime/limestone scrubbing systems
generate a throwaway sludge with little commercial value at
the present time. Lime scrubbing processes ordinarily
produce sludges containing CaS03*%H20, Ca(OH)2f
and CaCOs; limestone sludges generally contain
CaSOi»'2H20, and CaC03. For coal-fired installations where
efficient particulate removal is not installed upstream of
the wet lime/limestone absorber, such sludges can also
contain large quantities of coal ash.
From data available to date, it has been found
that the exact chemical composition of scrubber sludges
varies widely from one system to another, and even within
the same system. Therefore it is not possible to give an
analysis which truly represents all systems. Factors affecting
the final composition include:
composition of the fuel
composition of the SOz-reactant
(lime or limestone)
composition of the make-up water
operating conditions (e.g., closed- or
open-loop operation)
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RADIAN CORPORATION
settling characteristics, i.e., ease of
dewatering,
rewatering of the dried, aged material,
strength, i.e., load-bearing capability,
ability to support vegetation growth
(chemical properties also are important
here).
Viscosity, particle size, Blaine Index, and several other
physical parameters have been measured for various sludge
materials (SE-066, AE-007, AE-008, AE-009). In addition, it
was reported that the bulk densities of various scrubber
sludges vary similarly as a function of water content. As
the percent of water increases from zero, the bulk density
increases as the pore volume becomes filled. When completely
filled, a maximum bulk density is reached. With greater
percentages of water, a dilution effect is observed as the
bulk density decreases. For clarifier underflow samples
from EPA's Shawnee limestone scrubbing system with simultaneous
fly ash removal, the peak bulk density was reported to be
1.7 g/cm3 at 30% water content. The bulk density of a
packed and dried Shawnee sample was 1.20 g/cm3. These data
are compared to the true density of Shawnee solids equal to
2.48 g/cm3 (AE-008). The peak bulk density for an individual
sludge will depend on the nature of the scrubber system from
which it was obtained. For example, the sludge from a
western power plant employing a limestone system was shown
to have a maximum bulk density of 1.87 g/cm3 at 22% water
content.
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Based on preliminary results of experiments designed
to study settling properties of scrubber wastes produced by
lime/limestone systems, this phenomenon is not expected to
result in extensive separations. From a bench-scale experiment
conducted by TVA, a settling rate of 5 cm/hour was observed
for the first two phases of settling, which were defined as
the induction period during which floe formation occurs and
the second stage, free settling (SL-034). The third phase
is compression settling, i.e., when the floes begin to touch
each other and gel formation occurs. The settling rate
during this stage was greatly reduced. After 48 hours the
settling rate decreased to practically zero and no further
settling was observed, even over a period of several months.
Aerospace reported that limestone sludges with
high sulfate content settle to 45% solids with no drainage
provided. This is compared to final settled solids content
of 50% with underdrainage. Sludges having high sulfite
content settle only to 35% solids regardless of whether
drainage is provided (RO-084). Dravo Corporation compared
solid contents of various power plant wastes after one day
of settling. Results obtained with samples from a lime
system installed on an Eastern coal-burning facility ranged
from less than 30 to 45 weight percent solids. A different
lime scrubber sludge sample obtained from a Western coal-
burning plant equipped with a fly ash removal system up-
stream of the scrubber yielded much poorer results - 21.5%
solids. Two different limestone scrubbing systems were also
sampled. Both samples had no ash present. Results achieved
were 37-40% solids. These sludge samples may be compared to
ash which was reported to settle to 64% solids under the
same experimental conditions.
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Settling characteristics of lime/limestone scrubbing
sludges are directly related to the degree of compaction.
The factors affecting this parameter include the following,
all of which are currently under investigation by TVA (SL-
034).
hydraulic head
ash content
degree of oxidation
stirring
agglomeration
lime vs. limestone
Results of bench-scale studies indicate that
increasing the height of the slurry column increases the
degree of compaction. When the height of an experimental
column was increased from 13 cm to 100 cm, compacting was
increased by 15%. It is predicted that a high ash content
in the sludge would also produce favorable effect on settling
although no data are available to support this point.
Degree of oxidation is under intensive study. It
is known that calcium sulfate crystals, because of their
large blocky nature, settle better than the thin plate-like
calcium sulfite hemihydrate crystals. Thus, oxidation to
sulfate should improve the degree of compaction. It has
been reported that a high degree of oxidation is required,
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however, to produce a noticeable effect. Methods are now
under study to promote oxidation of limestone scrubber
slurries.
Identification of scrubber conditions that promote
agglomeration of sulfite crystals has not been made yet.
Some sulfite crystal agglomeration has been noted. Flocculating
agents are being investigated to determine their effectiveness
in promoting appreciable agglomeration.
11.1.2 Quantity of Sludge Production
The amount of sludge generated by a given plant is
a function of the sulfur and ash content of the coal, the
mole ratio of additive (i.e., lime or limestone) to SOa removal
efficiency of the scrubbing system, the ratio of sulfite to
sulfate in the sludge, and the percent moisture in the sludge.
Table 11-1 lists values of these various sludge parameters for
a hypothetical plant representing the National average expected
between 1973 and 1980. These values represent a mix of
Western and Eastern plants expected in 1980 based on the
trends shown by present flue gas desulfurization system orders.
Most of these parameters will vary from one system
to another. The sulfur and ash contents of coal are a
function of the source of the fuel. The S02 removal' efficiency
will vary from one flue gas desulfurization system to the
next as a function of local requirements.
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RADIAN CORPORATION
TABLE 11-1
TYPICAL SLUDGE PRODUCTION PARAMETERS
Sludge Production Parameters Average^
Coal:
Sulfur Content o Q«
Ash Content
Plant:
Load Factor
C°al
4 kg/kW-hr
Scrubbing System:
S0a Removal Efficiency
Moisture in Sludge
CaO/SOa (inlet) Mole Ratio 1<0
CaC03/SOa (inlet) Mole Ratio 1>2
Sulfite/Sulfate Mole Ratio 9<1
The values listed as the National average represent a mix of
Western and Eastern plants expected in 1980 based on the
trends shown by present flue gas desulfurization system orders.
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coupon
Since unreacted additive is disposed of with the
sludge, the stoichiometry of lime or limestone addition,
that is, the CaO/SOa or CaCOs/SOa mole ratios, greatly
influences the amount of sludge to be handled. The CaO/SCb
and CaCOs/S02 mole ratios vary from system to system at
present but the general trend is toward lower values as
operating experience is gained. It is expected that reasonable
values for this ratio will be 1.0 and 1.2, respectively.
Other factors influencing the amount of sludge to
be handled are the load factor of the plant, the coal use
rate, and the mole ratio of sulfite to sulfate in the sludge.
The amount of sludge produced by a plant is directly propor-
tional to the number of hours per year that the plant operates
and the coal usage of the plant. The 6,400 hr/year and .4
kg/kW-hr (0.88 Ib. coal/ kW-hr) values used for those calcula-
tions are typical of large modern generating stations (DU-
044, SU-031). Obviously if the plant is on line a larger
fraction of the year or more coal is required per kW-hr, the
amount of sludge produced will increase. The sulfite to
sulfate ratio in the sludge effects the weight of the sludge
produced as CaSO.,'2H20 is heavier than CaSO3-%H20. The
ratio assumed in this paper (9:1) is taken from the SOCTAP
report (SU-031). However, some system designers are considering
trying to completely oxidize the sludge to improve settling
characteristics and decrease chemical oxygen demand. If
this were done on a widespread basis the weight of dry
sludge produced per plant would increase but improved settling
characteristics would tend to lower the proportion of water
in the sludge. This would enhance solid/liquid separation
of the waste and thus reduce costs and possibly land reclama-
tion problems associated with sludge disposal.
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Table 11-2 shows the quantities of ash and sludge
produced per year by a 1,000 MW coal-fired generating station
controlled by lime/limestone flue gas desulfurization systems.
These figures represent the National average sludge and ash
production statistics.
Using the forecast demand for flue gas desulfuriza-
tion given in the SOCTAP report (SU-031) and the National
average annual sludge production rates per 1,000 MW of
controlled generating capacity, the amount of wet ash containing
sludge (50% moisture) that will have to be disposed of
annually by 1980 is predicted to be 113 million metric tons
(125 million tons). This value is based on the assumption
that there will be 116,000 MW of generating capacity controlled
by 1980 and that 75% of the control will be by lime/limestone
scrubbing systems.
11.2 Application of Conventional Disposal Techniques
to Scrubber Sludge
Ponding and landfilling provide the major mechanisms
of disposal for most solid waste products. In terms of land
use and reclamation, these disposal mechanisms have many
points of similarity for various industries. Land use for
waste disposal may be esthetically objectionable. The
wastes could provide varying degrees of surface and groundwater
pollution depending on chemical composition, solubilities,
and the location, design and operation of the disposal site.
For land reclamation, most of the stable wastes will require
only a cover material to support vegetation and prevent
eventual erosion. However, some wastes are very resistant
to dewatering and could reslurry in the pond or landfill.
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TABLE 11-2
TYPICAL QUANTITIES OF ASH AND SLUDGE PRODUCED PER YEAR BY A 1000 MW
COAL-FIRED GENERATING STATION CONTROLLED WITH LIME/LIMESTONE FLUE
GAS DESULFURIZATION SYSTEMS
National Average
Coal Ash, dry
Coal Ash, wet (807. solids)
Linestone Sludge, dry*
CaS03 -^HaO
Ca S04 ' 2Ha 0
CaC03 Unreacted
TOTAL
Limestone Sludge, wet
(50% solids)
Limestone Sludge, wet (with
ash)
Lime Sludge, dry*
CaS04'2HB0
CaO Unreacted
TOTAL
Line Sludge, wet (507. solids)
Lime Sludge, wet (with ash)
307,000 metric tons/year
384,000 metric tons/year
264,000 metric tons/year
39,000
99.000
402,000 metric tons/year
804,000 metric tons/year
1,418,000 metric tons/year
264,000 metric tons/year
39,000
43.OOP
346,000 metric tons/year
692,000 metric tons/year
1,306,000 metric tons/year
ASSUMPTIONS:
Coal:
Plant:
Scrubber:
3.07. S; 127. Ash
6400 hr/yr; .4 Kg Coal/kw-hr
85% SOg Removal
1.0 CaO/S08(inlet) Mole Ratio
1.2 CaCOj/SOa(inlet) Mole Ratio
* S'jl f ito/sul fate r.itio based on performance of Chcmico scrubbing unit at Mitsui Aluminum Co., Japan.
-------
If this is shown to be true, it is likely that fixation will
become a necessary practice.
These are the chief methods used by the utility
industry to dispose of ash from fuel combustion. Most
technology available to date is based on experiences with
that material. Technology associated specifically with
sludge is just now under development, thus posing a shortage
of available information in that respect. The following
sections describe the various features of each disposal
operation and, on the basis of available data, present the
potential impact on water pollution. Land reclamation
aspects for both ponding and landfill are dealt with in a
single discussion because of the similarity of an abandoned,
dried-up pond and a completed landfill.
11.2.1 Ponding
11.2.1.1 Technical Aspects
The start-up and day-to-day operation of a disposal
pond involves answering the following questions, as pointed
out by Slack and Potts (SL-034).
Will the pond be operated as a single
unit or divided into sections?
Will the original depth be the limit
or can walls be built up using the settled
material?
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Will the pond be partially filled with
water before operation begins?
Can the pond be filled to the top of the
dike or must some free board be allowed?
The first question is related to the settling
characteristics of the material. In the case of a well-
settling waste (ash, for example), the pond is typically
operated such that the slurry' enters one end of the single
pond. As it flows to the opposite side, the well-settling
solids drop out and a pool of supernatant forms at the far
end. The effluent is removed via weirs or standpipes, thus
allowing continuous operation of the pond until full. In
contrast, waste gypsum from phosphoric acid manufacture is
usually ponded in several units. Since the settling character-
istics of the waste are poor, one pond is allowed to dry and
be emptied while another pond is being filled. Acid mine
drainage sludge possesses especially poor settling character-
istics. The retention time in the cases studied for this
report were on the order of a week to ten days. This provided
sufficient time for clarification of the effluent. The
sludge layer, however, only achieved a solids content of
~10%. In some cases, acid mine drainage sludge receives
preliminary dewatering in a settling pond prior to ultimate
disposal in a second pond.
Scrubber sludge has thus far exhibited poor settling
characteristics as previously discussed in Section 11.1.1.
High sulfite-containing sludges possess worse settling
properties than sulfate (gypsum) type sludges, although in
comparison to AMD sludge, both are relatively better settling.
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Phosphate slime is another example of a poor settling waste
traditionally disposed of by ponding. If ponding is employed
as the disposal technique for scrubber sludge, it is likely
that a multi-unit pond would be most functional. However,
it is still unlikely that high sulfite sludges would achieve
any great degree of dewatering from ponding alone.
The second question deals with the dimensional
stability of the settled material. For some wastes, including
phosphogypsum, this property is great enough to permit its
use in raising the height of the walls. Preliminary data •
for untreated scrubber sludges presented in Section 11.1.1
are not yet sufficient to predict whether this type of
operation could be 'successfully applied.
If the scrubber is operated under closed-loop
conditions, smooth start-up may necessitate partial filling
of the disposal pond before hand. This would provide a
source of recycle water at the onset of operation and eliminate
the need for additional start-up pumping arrangements. This
would produce overall increasing concentrations with respect
to composition of liquor associated with solids until steady
state is achieved.
Gypsum from phosphoric acid manufacture is disposed
of in a closed-loop system. The gypsum is filtered to
separate product acid, and the filter cake is reslurried
with recycle water for transport to the disposal area.
The amount of freeboard required for any particular
pond is chiefly a function of climate. If the area receives
large amounts of precipitation during periods when evaporation
rate is low, then more freeboard would be necessary than for
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ponding operations in hot, dry climates. Ponds which lack
drainage provisions would also tend to require greater
freeboard.
11.2.1.2 Environmental Aspects
Potential hazards associated with contamination of
surface and/or groundwaters by sulfur oxide sludges exist in
the following areas:
soluble toxic species (toxic meaning
elements which can cause health problems
even at very low concentrations),
chemical oxygen demand due to sulfite,
excessive total dissolved solids,
excessive levels of specific species,
e.g., sulfate and chloride, not generally
thought of as toxic,
excessive suspended solids.
These could promote problems via leachate and/or runoff
routes. Although similar in nature, these routes will be
considered separately in the discussion below.
The composition of the leachate formed is a function
of several factors including chemical composition of the
sludge, pH, solubility of the individual species present,
and age of the disposal site. The nature of the leachate
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expected from untreated sludge can be judged by analysis of
liquors associated with scrubber samples, especially clarifier
supernatant or scrubber recycle water in closed-loop operation.
Since fly ash will be collected and/or disposed of together
with the scrubber sludge in many cases, it is likely that
many of the potentially leachable elements originate with
the ash. Although ash ponds have been in operation for
years, there has been little concern with environmental
contamination either by high dissolved solids content or by
trace element constituents of the pond waters. Both have
recently been shown to be present in varying amounts in
several ash pond samples. Likewise, this potential source
of contamination has not been investigated for other wastes
typically disposed of by ponding. This includes taconite
tailings, phosphate slimes, AMD sludge, and phosphogypsum.
This type of study, if it were available, would prove very
useful in determining potential leachate problems due to
scrubber sludge disposal.
A disposal pond provides maximum opportunity for
contamination of groundwater. Unlike a landfill, the sludge
is always saturated with water, and the "head" of liquor in
the pond assures a continuous driving force for percolation.
Underlying strata will also become saturated, and if an
unconfined aquifer exists beneath the pond, the pond site
will act as a "recharge" zone for that aquifer. If no
unconfined aquifer exists, the pond liquor will continue to
seep into the existing strata beneath the pond. Given that
an aquifer does exist, the important factors are the rate at
which pond liquor permeates into the groundwater and the
chemical composition of that liquor as it enters the aquifer;
any suspended material will probably be filtered out by the
-2.19-
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soil. It is also possible that some dissolved species may
be removed from the flow by a group of reactions commonly
referred to as soil attenuation mechanisms. These include
physical adsorption, chemical reaction, and precipitation.
Unfortunately, no data are yet available on this important
topic for scrubber sludge liquors although it is known that
the soil type is significant.
STEAG, a government organization in West Germany,
has instrumented a sludge disposal pond for lime scrubber
sludge to determine effects on groundwater. This group has
been visited and a description of their system obtained. So
far their monitoring system h'as not detected any contamination
of the aquifer which is located only about a meter below
their unlined pond. However, their observation wells are
far enough away from the pond that sufficient time probably
has not elapsed for any contamination to reach the wells.
Combustion Engineering and Kansas Power and Light are also
doing a study of this type, but no results have been released.
Another potential source of water pollution from
sludge ponds is overflow of supernatant. Disposal ponds
have typically been operated with less than total recycle of
pond liquor. The excess liquid has often been permitted to
flow into receiving streams with little treatment beyond
neutralization, settling, or skimming. In the case of acid
mine drainage sludge ponds, this is an inherent feature of
the system in that the purpose of treatment is to improve
the quality of the contaminated streams by removing excess
acidity and iron. Accidental spills have occurred frequently.
Newer and more stringent regulations on waste water disposal
will likely reduce the practice of overflowing excess liquor
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into lakes and streams. This will necessitate the use of
closed loop (total recycle) operation for scrubber sludge
disposal by ponding with treatment of any blowdown streams.
Alternatively, blowdown streams might be disposed of via
evaporation or disposal in the ocean. This sort of operation,
combined with proper site selection, design, and lining of
ponds could eliminate contamination of surface or groundwater
by ponded scrubber sludge.
Pond linings have been finding greater favor in
recent years. In some cases the intent has been to decrease
pollution, in other cases the intent has been to avoid loss
of water which could be recycled. In many areas, clay,
concrete, wood, or metal has been used as a liner. TVA is
planning to have an impervious bottom in their new ash pond
at Widows Creek; this will be a result of deposition of ash
onto the clay bottom. This may prove useful in achieving
impervious bottoms in scrubber sludge ponds, particularly in
those cases where ash and sludge are to be disposed of
together. This would provide a relatively inexpensive means
of achieving a lined pond.
Recently synthetic linings are finding increasing
usage. These materials have been reviewed in the recent
literature (KU-061). At the present time these are used
primarily in ponds handling industrial wastes known to be
hazardous.
Some approximate cost figures have been estimated
for lined ponds (RO-084). Factors influencing the price
include size and type of lining required. For a 2-4 square
hectare (5-10 acre) pond with no provision for drainage,
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$12,000 to $50,000 per hectare ($5,000-20,000/acre) is
estimated for clay or stabilized pozzolan base lining. The
cost of a drained pond fitted with a soil covered plastic
liner can be as much as $62,000 to $75,000 per hectare
($25,000-30,000/acre).
11.2.2 Disposal by Landfill
A second approach to the problem of disposal of
waste solids generated by lime or limestone scrubbing systems
is landfill. Currently less than 40% of existing or planned
installations have adopted this alternative, while approximately
60% have included ponding facilities. Eventually, however,
ponding sites may have to be reclaimed. This possibility
would necessitate future conversion to a landfill type of
operation.
Characterization of lime/limestone scrubber sludge
thus far has revealed a nature not readily applicable to
untreated landfill disposal. The sludge does not settle or
dewater readily, and the results of some experiments have
indicated that once dried, the untreated material will
reabsorb moisture to its original water content (see Section
3.3). This creates the unattractive possibility of the
disposal site becoming a bog. A second aspect of untreated
sludge is its leachate characteristics, discussed to some
extent in the preceding section. For these reasons, chemical
and physical fixation processes have been proposed and are
now under investigation. The marketing agents for these
fixation techniques claim that conversion to a physically
and chemically stable landfill material is possible. In
some cases, a saleable by-product can be made.
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11.2.2.1 Technical Aspects of Landfilling Sludge
The technology associated with disposal of waste
scrubber sludges by landfill operations is currently in the
development stage. There are three basic features requiring
discussion to accurately describe the current state of
knowledge regarding this disposal method: dewatering,
fixation, and handling of sludge.
Dewatering Techniques
The object of any sludge dewatering process is to
recover the solid content of the sludge in a concentrated
form suitable for disposal or further processing. The
liquid content is recovered from suspended solids for recircu-
lation within the process or for safe discharge as a processed
effluent. There are numerous techniques available for
dewatering industrial wastes, many of which have been experi-
mentally and industrially applied to sludges generated by
lime or limestone wet scrubbing systems. These were described
in detail in the EPA/Radian reports. Table 11-3 summarizes
the methods and results.
Comparable studies have been conducted for dewatering
acid mine drainage sludge. Bench-scale tests of several
processes have produced results indicating that all methods
were technically feasible with few exceptions. The energy
requirements and economics, however, were very high (AK-006,
WE-078). Because of the huge volumes of drainage receiving
treatment, it is unlikely that any of the dewatering methods
will be applied on a large scale in the near future. Phospho-
gypsum, on the other hand, is filtered to separate this by-
product acid. The filter cake is M>5-80% solids and must be
reslurried prior to transport to the disposal area.
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TABLE 11-3
SUMMARY OF SLUDGE DEWATERING TECHNIQUES
METHOD
APPLICATION
SLUDGE
RESULTS
COMMENTS
REFERENCE
Clarification Currently used as primary Various lime and Limestone sludges thicken
dewatering device on linestone scrubbing "better" than lime because
full-scale systems. system sludges. of coarse unreacted additive
present.
SE-066
Bench-scale
Limestone system
sludge.
_20% solids achieved
AE-006
Bed Drying Bench-scale column
studies.
Shawnee limestone
system sludge.
Steady state drainage race Air-dried sludge exposed to
was O.C46 cmVmin. Sludge water regained original
with "relatively" high sulfate moisture (51.7%).
content settled to 507. solids
with urderdrainage. High
sulfite sludges settled only
to 357.. Solids under similar
conditions.
AE-007
AE-008
AE-004
N)
-P*
I
Demonstration program,
Hollywood, Penn.
Acid mine drainage Results not available at time
(AMD) neutralization of report.
sludge.
JE-013
Centrifugation Bench-scale tests.
Various lime-scrub- 47-57% find solids content
bing system sludges, (original: 19-44%).
Fly ash was present in the
samples.
SE-066
Bench-scale tests
(short-term).
Linestone scrubbing 53-64% solids achieved
system sludge (feed was 10-29% solids).
SL-034
EL-030
Full-scale
Chiyoda process 85-90% solids achieved.
sludge (high sulfate/
sulfite ratio).
SL-034
Comparative laboratory-
scale.
Various limestone
system sludges.
Shawnee sludge: solids
content increased from
20 to 56%. Mohave sludge:
>65% solids achieved.
Although original water content AE-006
of sludges were similar, better AE-007
results obtained with Mohave AE-010
sludge were believed to be due
to its lower water content at
maximum density.
-------
TABLE 11-3 (Cont.)
Summary of Sludge Dewatering Techniques
METHOD
APPLICATION
SLUDGE
RESULTS
COMMENTS
REFERENCE
Vacuum
Filtration
Bench-scale
Bench-scale
Limestone Scrubbing
system sludges.
~657. solids achieved.
AMD neutralization
sludge.
Solids content increased
from 0.6 to 23%.
Problems with cake blocking
filter were experienced.
AE-007
WE-078
Bench-scale
IS3
Ln
I
Pilot-scale; in
conjunction with
clarification.
Pilot plant limestone 55-607. solids content was
scrubbing system achieved.
samples .'
Compere to 387. solids with
seeding alone. Thixotropic
nature of sludge caused filter
cake to rewacer upon release.
Cake cracking in early stages
prohibited further dewatering.
Removal of cake from filter was
difficult.
SL-034
EL-030
Double-alkali system
(General Motors).
70% solids achieved.
AE-006
Full-scale; in
conjunction with
clarification.
Carbide sludge system
(Louisville Gas and
Electric).
50% solids was achieved.
VA-068
Thenral Commercial
Drying
S0a/fly ash removal
process.
90-95% of original water
content (70%) removed;
i.e., achievement of
90-957. solids is claimed.
EB-003
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Sludge Fixation
Sludge fixation is the chemical and physical
stabilization of sludge or sludge/fly ash mixtures. The
intent of the processes is to convert the waste to a non-
toxic, load-bearing material via chemical reaction and, in
some cases, aggregate addition. Chemical fixation of scrubber
sludge and related materials is currently under development
by several commercial groups including Dravo Corporation, I.
U. Conversion Systems, Inc., Chicago Fly Ash, and Chemfix
Corporation. Information available regarding the chemical
and physical nature of lime/limestone scrubber sludge indicates
a need to investigate potential stabilization techniques.
Quantitative data describing various properties of scrubber
wastes are presented in other sections of this report.
Basically, these data seem to indicate a tendency for untreated,
dewatered sludge to rewater upon contact with an aqueous
environment. In addition, leaching and permeability features
of dried sludges pose potential environmental hazards. The
ability of proposed fixation techniques to prevent rewatering
and leaching from treated sludges is under investigation.
The current status of the fixation techniques now being
marketed has been described in the EPA/Radian reports, and
is summarized here.
I. U. Conversion Systems, Inc., offers several
fixation processes based on the pozzolanic reaction between
®
fly ash and lime (MI-084). Poz-0-Pac , the original process
on which sulfur oxide sludge fixation technology was based,
has been industrially applied to the stabilization of fly
ash for production of structural materials. Poz-0-Tec* is a
commercial process for the stabilization of fly ash using
A service mark owned by I. U. Conversion Systems, Inc.
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sulfur oxide sludges in addition to lime. The chemistry is
comparable to that describing Portland cement technology.
The product, Sulf-0-Poz® , is primarily a disposal material,
but in some instances could be used as a structural material
in land reclamation projects, structural embankments, etc.
after a couple of weeks of curing (FO-018). Further processing
€)
of Sulf-0-Poz is another alternative; utilization of the
treated sludge as synthetic aggregate or road base material
is then possible.
The tail end process itself can be retrofitted to
existing power plant facilities. Application to oil-fired
systems is not feasible, however, since availability of fly
ash is essential to the process. Conditions of relatively
higher pH, as in lime systems compared to limestone, favor
the reactions, although both types of scrubber sludges can
be treated by the IUCS process (AE-007). To date, this
process has not been applied to a flue gas desulfurization
system, but extensive bench-scale testing of that application
and the fixed product is currently being performed in the
IUCS laboratories.
Those factors affecting the cost of this or any
fixation process are given below:
annual tonnages to be handled by the
conversion process,
new boiler installation versus existing
facilities,
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RADIAN CORPORATION
the type of equipment selected for fly
ash removal - for example, electrostatic
precipitators versus wet scrubbers,
the chemical analysis of coal - sulfur,
CaO, and ash contents,
location of plant - on-site versus off-
site,
transportation costs - to and from
conversion plant,
redundancy factor - duplication of
equipment versus emergency holding
basins, etc.
type of scrubber - limestone versus
lime,
acquisition and cost of land, and
type of end-product selected.
Based on estimates for newly installed plants in the range
1,000 - 2,000 MW, burning coal with 3-4% sulfur and 10-15%
ash content, and incorporating a lime scrubbing system, the
cost of sludge disposal is estimated to be $1.65 - 2.76 per
dry metric ton ($1.50 - $2.50/dry ton) to convert the sludge
to a disposable Sulf-0-Poz material. This includes the
cost of chemicals and process services, but no hauling
charges, which can be a major factor.
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The Chicago Fly Ash Company also markets a sulfur
oxides sludge fixation process based on quicklime/fly ash
addition (OB-005). They are currently working with Common-
wealth Edison and the University of Illinois to dispose of
the sludge generated by a limestone wet scrubbing system
installed on a 163 megawatt unit at Will County Station (GI-
017, GI-030, ST-117, JO-083). The spent scrubber slurry
presently receives dewatering treatment by clarification.
Possible secondary treatment, vacuum filtration or thermal
disc drying, is being considered to reduce the volume of
sludge requiring fixation. Clarifier underflow is pumped to
a pond, then to a loading station where the additives and
sludge are blended to produce a stable landfill material.
For every 1,000 kilograms of settled sludge, 100 kilograms
of fly ash and 50 kilograms of lime are added. If higher
water content is present, the proportion of additives required
goes up rapidly (GI-033). The treated sludge (50% solids)
is transported by cement-truck to an on-site sealed basin
about one-half mile away. An off-site location is planned
for the future. At the present time, this fixation process
results in physical but not chemical stabilization of the
sludge (GI-033). The leachate does not meet Illinois water
standards which state that any water entering an aquifer
cannot be of lower quality than water removed from it.
A Chicago fly ash spokesman quoted a cost of
$16.5/metric ton on a dry solid basis for their process (OB-
005). Additional economic information associated with this
disposal method can be derived from estimated operating and
capital investment costs reported by Will County. A utility
spokesman has recently estimated the annual costs for the
disposal system as 1.1 million dollars in addition to the
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initial capital investment of 1.7 million dollars (GI-017).
The annual cost included a sludge disposal figure of $823,000
which is equivalent to $7.70/ metric ton of sludge (dry
basis). Included in the sludge disposal figure are costs
for operating the sludge disposal plant, maintenance, hauling,
and landfill. Actual costs incurred on this project, however,
are reported to be as high as $19/metric ton of dry sludge
(GI-033). Costs possibly may be reduced in the future to
$13.30/dry metric ton.
Dravo Corporation also offers a chemical fixation
process for lime/limestone scrubbing waste products (SE-
066). Much of their technology has been developed using
sludge samples obtained at a pilot-scale lime scrubber
operating at Duquesne Light Company's Phillips Station;
sludge from additional sources has also been examined. The
testing of their process has involved basic chemical and
engineering evaluations of the sludge and treated product on
a bench-scale level; they are currently providing technical
consultation for disposing of Duquesne's lime scrubber
sludge. The chemistry of the process has not been revealed
because of current patent applications on the additive. The
amount of additive required, however, is approximately 3-5%
by weight of sludge solids. The exact amount depends on the
pH of the sludge, % solids desired, and initial solids
content. It is reported that following chemical addition to
the settler underflow (35-40% solids), the sludge can be
pumped 10 kilometers or further to a disposal site, preferably
an area which can be dammed up. Curing time is approximately
30 days; the sludge sets up underwater, forcing excess water
to the surface, where it can then be drained off.
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The economics associated with this process are
quoted by Dravo as $1.10-3.30 per metric ton of sludge (35-
40% solids) as received from the clarifier from the clarifier
underflow (LO-077). This is for a total disposal systems,
including capital and operating expenses for a pumping
situation. Duquesne, however, has estimated their costs for
sludge disposal to be much greater, as high as $16.50 per
dry metric ton (AE-012). The basis of this cost is not
clear.
Chemfix Corporation markets a proprietary fixation
process for conversion of various industrial sludges to
stable landfill using at least two inorganic chemicals, one
liquid and one powder. Little information is available on
the chemistry of the system, although one source reports
that "lime and silicates apparently are not used" (TR-026).
Polyvalent metal ions react with Chemfix process chemicals
resulting in a stable insoluble, inorganic compound within
three days, although gelation time can vary with the system
being treated. Certain species, including chlorides, monovalent
cations, colloidal material and some organics, cannot be
fixed by this treatment. At present, Chemfix is not working
on an industrial scale with any utilities on scrubber sludge
disposal although it has been applied to other types of
problems.
The price range quoted by Chemfix for their services
is 0.5-2.5C/JI or-on the average of K/Jl for a sludge of high
solids content (TR-026). This is equivalent to ~$5.50/metric
ton (30-50% solids) (AE-012). This figure does not include
costs associated with hauling the fixed material to an off-
site landfill.
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Comparative evaluations of several of these processes
are currently being planned or carried out in the laboratories
of Aerospace Corporation under contract to EPA (Contract No.
68-02-1010) and in an independent study by Combustion Engineering,
Inc. Aerospace plans to have sludge samples from four
different power plants conditioned by at least two commercial
processes. Testing of the treated samples will then be
performed by Aerospace to determine the following characteristics:
soluble components
permeability
water retention
compression strength
bulk density
detoxification assessment, if appropriate.
Sludge Handling and Transport
Transport of waste scrubber sludge to the ponding
site can be carried out by sluicing operation, i.e., piping
the slurried solids. This method is also being considered
for transport of sludge to the fixation site. Individual
sludge properties such as viscosity, velocity, temperature,
composition, particle size, and solids concentration affect
the pumping characteristics of the material. Also of major
concern is the distance to be covered. Special problems
specifically related to sulfur oxide sludges such as corrosion
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or erosion potential also require investigation. Dravo
Corporation is investigating the transport of fixed sludges
to the disposal site by pipeline. Acid mine drainage sludge,
sewage sludge, reslurried phosphogypsum, taconite tailings,
and, in many cases, coal ash are transported to the waste
disposal area via pipeline or in some cases, open trenches
where gravity rather than hydraulic pressure is the moving
force.
Transport of sludge to a landfill site via truck
is one of the approaches being considered by utilities if
off-site disposal is used. The results of one study are
available at this time (TA-040). Combustion Engineering
transported 68 metric tons (75 tons) of waste (50% sludge,
50% ash) from the limestone scrubber at Kansas Power and
Light's Lawrence facility to Dulles Airport in Washington,
D. C., a distance of approximately 2,100 km (1,300 miles).
Two types of vehicles, flat- and round-bottomed trucks, were
employed in order to compare the effect of various features
on handling characteristics. Prior to loading, the untreated
sludge had been stored in a settling pond at the utility
site for six months. It was dredged up and allowed to drain
for 24 hours before loading. At various intervals during
the non-stop trip measurements and samples were taken. No
leakage of sludge was observed although excess water drained
from the tailgate while on the road. Unloading problems
were encountered with the flat-bottomed trucks; complete
removal of the sludge necessitated manipulation with a
backhoe. The sludge slid out readily, however, from the
round-bottomed trailers.
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Coal ash is often trucked to the disposal site.
The problems encountered with this waste (fugitive dust,
e.g.) are not the same as those which would be involved in
scrubber sludge transport by truck. Costs, however, may be
comparable.
Conveyor belts and related bucket elevators are
potential modes of transport for dewatered sludge over short
distances. Potential areas of use include conveying of
dewatered solids to a fixation facility, lifting of wastes
to hoppers or mixing devices, and transport of fixed sludge
to landfill sites. The water content of the sludge is the
major factor determining feasibility of this application.
If the nature of the sludge is such that water drains in
large amounts, precautions such as installation of troughs
below the conveyors must be taken to avoid potential water
pollution problems.
Other handling aspects which could be mentioned in
this discussion are alternate methods of transporting the
waste from the scrubber site to the ultimate disposal site.
Encompassed in this category would be barge and rail. Both
would be feasible only in unique situations where geography
and surrounding environment would permit such application.
11.2.2.2 Environmental Aspects of Landfilling Sludge
Water Pollution
Disposal of sludge generated by lime/limestone
scrubbing systems in landfill sites creates two potential
areas of water pollution, leachate to groundwater and runoff
to surface water. Careful evaluation of available research
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CORPORATIOI
results associated with both runoff and leachate must be
made in order to assess any potential environmental hazards
which may exist. In this section, information pertaining to
factors of water pollution and effect of chemical and physical
properties of stabilized scrubber, sludge/fly ash mixtures
are discussed. Also presented here are possible control
measures which have had application in disposal of sludge or
other solid waste materials.
In order to predict leachate characteristics of a
landfill, it is first necessary to describe the general
features of water movement and geological considerations for
this disposal method. Due to the recent surge of ecological
interest in sanitary landfills utilized for solid waste
disposal, there is an abundance of information available.
Emrich's review of research in this field presents an overall
view of progress on this subject (EM-003). The case studies
presented in Sections 2.3 and 3.4 indicate the research
being conducted toward the definition and solution of this
problem. The future results to be obtained from these
projects will shed a great deal of light on the impact of
scrubber sludge leachate. Results available to date, however,
are not sufficient to fully assess the extent of this problem.
The first consideration when looking at the potential
impact of landfill leachate is the volume of leachate that
will be produced. This is a direct function of the amount
of water reaching the landfill. There are two possible
sources of this water: rainfall and naturally occurring
subsurface flow through the landfill site. Subsurface flow
is a natural phenomenon which can seriously interfere with
safe operation of landfills in two ways. First, it is a
source of additional volume of potentially harmful leachate.
The second consideration is that it can serve as a direct
means of groundwater contamination. Prevention can be
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effected by thorough geologic study of the site beforehand
and, if needed, installation of rerouting devices for the
groundwater flow. In a similar vein, coverage of the landfill
area when complete will greatly reduce, if not eliminate,
the amount of leachate produced.
Infiltration and permeability characteristics of
the landfill material determine the relative amounts of
runoff versus leachate as well as the leaching rate. Reductions
in permeability of sludges stabilized by I. U. Conversion
System's process and by Dravo's process have been reported
(AE-006, MI-084). lUCS's results indicate not only the low
permeability values of the fixed scrubber sludges (~10~7
cm/sec after 7 days of curing at 38°C), but also the relatively
great reduction (~2 orders of magnitude) in permeability
compared to freshly prepared sludge/fly ash mixtures. Dravo
Corporation reportedly has obtained permeability values of 2
x 10~8 cm/sec for sludge conditioned in their laboratories
with 3% additive (LO-077). This is compared to high quality
clays having permeation values of 10"7 to 10~8 cm/sec versus
fly ash for which a representative range is 10~2 to 10~3
cm/sec.
For each of the above processes, it is claimed
that soluble components are immobilized in the treatment
process. Specific data to support these claims have been
reported by I. U. Conversion Systems. Chemfix Corporation
has furnished leachate analyses of potentially toxic elements
to Radian for specific treated sludges. No data from Dravo
or Chicago Fly Ash were available for release at this time.
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Land Reclamation Aspects
Certain aspects of land reclamation following
abandonment of a landfill site or dried up pond used for
scrubber sludges may lead to potential problems. These
aspects may be assessed by examining the engineering, physical,
and chemical natures of treated and untreated sludge. At
the present time no attempts have been made to reclaim land
committed to scrubber sludge disposal.
Disposal sites for other solid wastes studied
including municipal waste, coal refuse, phosphate slimes,
taconite tailings, and coal ash have been successfully
reclaimed. Extensive research in these areas is being
carried out. The degree of reclamation possible varies with
the characteristics of the waste. For example, phosphate
slimes areas can support vegetation, but they lack the
strength required for building construction. They are used
with great success, however, as recreational areas. Reclaimed
culm piles have not been evaluated as far as support of
buildings is concerned; all work to date conducted by the
Bureau of Mines has been concentrated on agricultural usage.
These studies have been extremely successful.
Reclamation procedures for municipal waste sanitary
landfills require placement of a cover material since the
refuse itself will-not support vegetation. Phosphate slimes,
on the other hand, provide all the nutrients necessary for
plant life; reclamation of these areas, however, requires
addition of tailings to effect a sufficient degree of dewatering
and to lend support to the material. The taconite industry
reclaims its tailings areas by draining the readily settling
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waste. Since the tailings have no nutrient value of their
own, extensive fertilizer applications must be made. Coal
ash, on the other hand, is currently under investigation to
determine the extent of its ability to support vegetation
with or without addition of fertilizer and soil conditioners.
One consideration is the tendency of dried scrubber
sludge to absorb water with which it comes in contact. As
discussed in previous sections of this report, sulfur oxide
sludges are relatively difficult to dewater. One sludge
sample was observed over a period of several months during
which time little or no settling took place after the first
48 hours. Preliminary results of one TVA study indicated
that dry solids from a limestone scrubber sludge do not
expand when submerged in water or exposed to rainfall (SL-
034). Drainability studies conducted by Aerospace, on the
other hand, resulted in retention of enough water by dried
Shawnee limestone sludge to return to its original water
content. The calculated water retention for sludge with
underdrainage was 51.7% (AE-007). Behavior of chemically
stabilized sludge samples is expected to be greatly improved
although specific tests for rewatering potential have not
been reported. A practical consideration in regard to
rewatering is that for a thick layer of dried sludge, an
accumulation of a few meters of rain might be required for
rewatering. With proper design of the site plus some low
permeability cover material (clay, plastic, or treated
sludge) even untreated sludge might never rewater since the
small amount of water collected during a rain should be lost
by evaporation before the next rain.
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A second consideration in land reclamation of
sludge disposal areas is the weight which can be supported
by the site. This factor can be determined by measuring the
pozzolanic strength, compaction strength, and penetration
resistance of the throwaway product. The strength associated
with any landfill or construction material is a function of
composition, moisture content, and compacted density.
Untreated scrubber sludge has been shown to lack
any appreciable degree of compressive strength based on
studies performed by Aerospace on Shawnee and Mohave samples
(AE-009). Samples subjected to the I. U. Conversion Systems'
fixation process have been tested for various strength
characteristics with good results (MI-084). In addition to
producing greater strengths, the treatment process also
resulted in shorter curing times. Another consideration in
an engineering evaluation is scructural integrity. Experimental
data which can be used to describe this characteristic are
dimensional stability measurements and field testing.
Untreated sludges reportedly have very poor dimensional
stability. On exposure to drying conditions, shrinkage and
cracking was observed (AE-006). This phenomenon can be
prevented by addition of a pozzolanic material such as is
involved in most of the stabilization processes now offered.
Field tests to date have produced good results with regard
to structural integrity.
An additional factor to be considered in reclamation
of abandoned sludge disposal sites is whether growth of
vegetation can be supported on the area. At the present
time no studies are available directly concerning this
aspect.
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11.3 Alternate Disposal Techniques
Several other possible options are available for
disposal of air pollution control system sludges although
they are not under investigation to the same extent as
landfill and ponding. These alternatives involve direct
deposit of the waste below the surface in subsurface mines
or utilization of the sludge to reclaim strip mine areas.
Another possible solution is commercial utilization. Develop-
ment in this area is currently in progress under both govern-
ment sponsorship and private industry.
Deep mine filling has been used for the disposal
of power plant ash (HA-158) and acid mine drainage sludge.
In the first case, ash is sluiced into the mine through
boreholes. Normally, gravity is sufficient to create a flow
into the mine. Pumps and additional boreholes were provided
in case of hole plugging or increased friction losses. A
dewatering sump and a settling basin were formed by constructing
dams across the mine flow. Overflow from the settling basin
flows to the sump from which it is pumped to an above-ground
basin. Acid mine drainage sludge is disposed of in deep
mines in several cases where such sites are available adjacent
to the treatment plant.
This type of approach may not be directly applicable
to disposal of lime/limestone scrubber sludges for several
reasons. First, the viscosity of this waste is such that it
is probable that it would not spread laterally throughout
the mine disposal area. Secondly, the settling characteristics
have been shown to be poor; ready solid/liquid separation is
not expected (Section 11.1.1). This would perhaps decrease
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the attractive features of a mine subsidence operation in
that little geological support would be provided by the
sludge. In addition, some environmental hazard may exist
due to water pollution aspects. Possibly the last two
foreseeable problems could be avoided or reduced by a fixation
treatment. Investigation of this approach may be worthwhile
to those utilities to which abandoned deep mines are available
as a possible disposal site.
Reclamation of strip mine areas with waste sludge
is another possibility. This could be viewed as a specialized
landfill operation; as was discussed in the preceding section/
it is not yet certain whether or not pretreatment of the
sludge will be required for strength development and to
prevent environmental contamination. The benefits of this
type of disposal are obvious, however, if shown to be a
feasible approach. In addition, land availability would not
be a problem in many areas of the nation. Strip mine reclama-
tion with fly ash has been in practice for many years now,
much of it under the development of the Bureau of Mines.
The case study discussed in Section 3.4 is a project utilizing
sewage sludge to reclaim strip-mined areas. Results to date
seem successful, although leachate is under extensive investi-
gation. Acid mine drainage sludge is another potential
candidate for mined land reclamation because of its neutralizing
capacity. As discussed in Section 5.4, preliminary work has
been done in this area. Additional development is needed
for utilization (disposal) of 'Scrubber sludges in this
capacity.
The alternative to disposal of scrubber sludges is
development of commercially applicable utilization processes.
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Numerous programs in this area have been conducted through
government sponsorship and by industry alone. These are
summarized in Table 11-4.
Combustion Engineering and I. U. Conversion Systems
(formerly G&WH Corson), in cooperation with the Research and
Development Division of the Federal Highway Administration,
studied the potential of several industrial sulfate sludges
as highway construction materials (TA-040, BR-112).
In one section of the Dulles Airport in Washington,
D. C., a mixture of lime (3%, dry basis), SOa scrubber
sludge (8%), fly ash (59%), and aggregate (30%) was tested
as a road course material. The sludge was a 50% solids
slurry obtained from Combustion Engineering's limestone
scrubbing system at Kansas Power and Light's Lawrence facility.
The paving mixture was placed in a seven-inch layer over a
compacted subgrade, compacted to five inches, and sealed
with a bituminous material to prevent water infiltration.
Less than completely satsifactory results were obtained,
however, primarily because of excessive rainfall during
construction. Despite these problems, however, the demonstra-
tion project served to firmly establish the feasibility of
this utility scheme.
IUCS offers a process called Poz-0-Tec* to convert
power plant scrubber sludge to stabilize structural fill
material or to usable manufactured by-products. The process
is based on technology of the Poz-0-Pacr process which is
also a fly ash stabilization technique. The product of the
Poz-0-Tec* process, Sulf-0-Poz®, can be used as a stabilized
fill material. It possesses certain structural qualities
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TABLE 11-4
SLUDGE UTILIZATION SCHEMES
I. FILLER MATERIAL
A. Structural Fill
B. Mine Void Fill
C. Filler in Bituminous Concrete
D. Waste Disposal/Sanitary Structural Land Fill
II. Pozzolanic Products
A. Road Base Course
ITI. Autoclave Products
A. Concrete Admixture (Structure and Products)
B. Fired Brick
C. Lightweight Aggregate
IV. Pressure Sintered Products
A. Metal Coatings
B. Pipes
V. Gypsum Products
A. Plaster
B. Wall board
VI. Soil Amendment
VII. Mineral Wool
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TABLE 11-4
(Cont.)
VIII. Mineral Recovery
A. Lime
B. Aluminum
C. Iron
D. PozzoLan (glass particles)
E. Titanium
F. Silicon
G. Rare Elements
IX. Sulfur Extraction
A. Sulfur
B. Sulfuric Acid
X. Polluted Water Treatment
A. Recovery of polluted streams, ponds, lakes
B. Neutralization of: Acid
Polluted Waters
C. Sewage Plant Treatment
B. Neutralization of: Acid Mine Drainage and
Polluted Waters
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permitting its use in some cases as structural embankments,
land reclamation projects, and liners for ponds and reservoirs.
Sulf-0-Poz® can be further processed to produce cementitious
material of other compositions such as synthetic aggregate
suitable for production of structural shapes, portland
cement or asphaltic concrete. Sulf-0-Poz® may also be
supplied directly for use as stabilized road base required
in primary highways, airport runways, trucking terminals,
and similar applications.
Gypsum is one of the solid by-products of the wet
lime/limestone gas desulfurization process. This material
can be recovered although the feasibility of doing so is
limited by the amount of foreign material in the sludge,
i.e., fly ash, unreacted lime or limestone, and calcium
sulfite. Elimination of fly ash can be achieved by burning
oil rather than coal or by installing efficient electrostatic
precipitators upstream of the scrubber unit. Oxidation of
sulfite to sulfate is currently practiced in Japan and is
under investigation in this country as well. The fly ash
elimination and oxidation processes result in a clean grade
gypsum, CaSOi,-2H,,0, which is used in making wallboard, wall
plaster, or as a cement additive for construction use. This
approach has already been taken in Japan. In one plant
sulfite is oxidized to sulfate in special equipment. Similarly,
sulfite oxidation equipment is being installed at the Mitsui
Aluminum Plant in Japan. It was recently predicted, however,
that the Japanese supply of gypsum will soon exceed the
demand (AN-059). The economics of this utilization process
may not be acceptable in the United States where there exist
large natural sources of relatively pure, dry gypsum.
Moreover, if an efficient precipitator is not employed, the
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dark color of gypsum due to fly ash and other impurities
could be a significant problem for a potential gypsum market.
The economics of the utilization are more favorable in the
Chiyoda and Hitachi processes where the gypsum is manufactured
from sulfuric acid and hence the oxidation step is circumvented.
By-product gypsum from phosphoric acid manufacture
has been investigated by the phosphate industry with regard
to potential utilization schemes. Although this research
has been in progress for a number of years, no feasible
method has been found as yet.
The potential utilization technologies described
up to this point are fairly well established in that they
are either commercially practiced or have at least been
successfully demonstrated on a large test scale. A list of
less promising schemes which have been suggested include
autoclaved products (brick, aerated concrete, poured concrete);
mineral wood; soil amendment and stabilizer. Although
several possible markets for scrubber sludge could develop,
it is likely, however, that the growth of these markets will
lag far behind the growth of sludge production, resulting in
the great majority of sludge being disposed of as a throw-
away product.
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GY-007 "Gypsum's Sulphur Values", Ind. Minerals Oct. 1970
(37), 22-25.
HA-158 Halzel, George C., "Ash Disposal", Power Eng. June
1969, 44-6.
-255-
-------
HA-183 "Hard Road Ahead for City Incinerators", Env. S c i.
Tech. §(12), 992 (1972).
HA-186 Hambleton, G. C., "Reclamation from Coal Mine Waste
Dumps", Canadian Mining and Metallurgical Bulletin
£5(722), 83-93 (1972).
HA-193 Harkness, N., et al., "Some Observations on the
Incineration of Sewage Sludge", Water Pollution
Control 71(1), 16-33 (1972).
HE-061 Hershaft, Alex, "Solid Waste Treatment Technology",
Env. Sci. Tech. £(5), 1972.
HE-063 Heidman, James A., and Dirk R. Brunner, "Solid
Waste and Water Quality", J. WPCF 4j>(6), 1198 (1973).
HI-065 Hill, David W., "Neutralization of Acid Mine Drain-
age", J. WPCF 41(10), 1702 (1969).
HI-069 Hinesly, T. D., R. L. Jones, and B. Sosewitz,
"Use of Waste Treatment Plant Solids for Mined
Land Reclamation", Mining Congress J. 5j}(9) , 66
(1972) .
HI-074 Hill, R. D., NERC, Cincinnati, Personal communication,
August 1973.
HY-011 Hyland, Edward J., "Factors Affecting Pozzolan
Marketing", presented at the 3rd International
Ash Utilization Symposium, Pittsburgh, Pa.,
13-14 March 1973.
JE-013 Jennett, J. Charles, and Daniel-J. Harris,
"Environmental Effects on Sludge Drying Bed De-
watering", J. WPCF 45(3), 449 (1973).
-256-
-------
JO-083 Jones, Julian W., and Richard D. Stern, "Waste
Products from Throwaway Flue Gas Cleaning Processes
- Ecologically Sound Treatment and Disposal",
Presented at the Flue Gas Desulfurization Symposium,
New Orleans, 14-17 May 1973.
JO-087 Johnson, Glenn E., Louis M. Kunka, and Joseph H.
Field, "Use of Coal and Fly Ash as Absorbents for
Removing Organic Contaminants from Secondary Municipal
Effluents", IEEC Proc. Des. Develop. 4(3) , 323 (1965).
KA-109 Kasper, William C., Solid Waste and Its Potential
As A Utility Fuel, OER Report No. 18, State of New-
York Public Service Commission, 1973.
KA-110 Kaiser, E. R., "The Sulfur Balance of Incinerators",
J. APCA 18(3), 171-74 (1968).
KE-082 Keith, F. W., Jr., and R. T. Moll, "Matching A
Dewatering Centrifuge to Waste Sludge", CEP 67 (9) ,
55 (1971).
KE-101 Kenahan, Charles B., "Solid Waste-Resources Out of
Place", Env. Sci. Tech. 5(7), 594 (1971).
KE-102 Kenahan, C. B., et al., Bureau of Mines Research
Programs on Recycling and Disposal of Mineral-,
Metal-, and Energy-Based Wastes, 1C 8595, Washington,
D.C., BuMines, 1973.
KE-036 Klass, D. L., and S. Ghosh, "Fuel Gas from Organic
Wastes", Chem. Tech. Nov. 1973, 689.
-257-
-------
KO-107 Kostenbader, P. D., and G. F. Haines, "High-Density
Sludge Treats Acid Mine Drainage", Coal Age 75 (9),
90-97 (1970).
KO-109 Kostenbader, P. D., and G. F. Haines, "High-Density
Sludge Process for Treating Acid Mine Drainage", in
Coal Mine Drainage Research. Preprints of Papers
Presented Before the 3rd Symposium, Pittsburgh, Pa.,
1970, pp. 12ff.
KU-061 Kumar, J., and J. A. Jedlicka, "Selecting and
Installing Synthetic Pond-Linings", Chem. Eng. 80(3)
67 (1973).
LA-085 Lamb, D. William, "Ash Disposal in Dams, Mounds,
Structural Fills, and Retaining Walls", presented
at the 3rd International Ash Utilization Symp.,
Pittsburgh, Pa., 13-14 March 1973.
LA-099 Lawver, James E., and Gordon J. Amundson, eds.,
Thirty-Second Annual Mining Symposium and 44th
Annual Meeting Minnesota Section, AIME Proceedings,
Duluth, Minn., 11-13 Jan. 1971.
LE-094 Lejcher, Terrence R., "Utilizing Treated Municipal
Wastes for Strip Mine Reclamation", Mining Eng. 2J>
(3), 49-50 (1973).
LI-051 Lingard, A. L., and J. H. Cope, The Recovery of
Metal Values In Waste Electric Power Plant Lignite
Ash, Final Report, BuMines Grant SWD-7, Rapid City,
S. Dakota, S. Dakota School of Mines and Technology,
1968.
-258-
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LI-055 Lin, Yen Kuang, Compressibility, Strength and Frost
Susceptibility of Compacted Fly Ash, Ph.D. Disserta-
tion, Univ. of Michigan, 1971.
LI-061 Liebeskind, Judith E., "Pyrolysis for Solid Waste
Management", Chem. Tech. Sept. 1973, 537.
LO-076 Lovell, Harold L., "The Control and Properties of
Sludge Produced from the Treatment of Coal Mine
Drainage Water by Neutralization Processes", in
Coal Mine Drainage Research. Preprints of Papers
Presented Before The 3rd Symposium., Pittsburgh, Pa.,
1970, pp. Iff.
LO-077 Lord, Bill, Dravo Corporation, Private Communication,
26 Feb. 1974.
LO-079 Lombardo, J. L., "State of the Art - Acid Mine
Drainage Control", Presented at the 1973 Mining
Convention Environmental Show, Denver, Colorado,
9-12 Sept. 1973.
LO-080 Lovell, Harold L., An Appraisal of_ Neutralization
Processes to Treat Coal Mine Drainage, Project
14010 EFN, EPA 670/2-73-093. Washington, D.C.,
EPA, 1973.
LY-005 Lyons, William W., "Proposed Project to Demonstrate
Feasibility of Hydraulic Backfilling of Mine Voids",
Fed. Reg. 3J7<4°) • 4222 (1972).
MC-096 McNay, Lewis M., Coal Refuse Fires, An Environmental
Hazard, I.C. 8515, Washington, D.C. BuMines, 1971
(GPO) .
-259-
-------
MA-218 Martens, D. C., and C. 0. Plank, "Basic Soil
Benefits from Ash Utilization", presented at the
3rd International Ash Utilization Symp., Pitts-
burgh, 13-14 March 1973.
MA-219 Martens, David C., "Availability of Plant Nutrients
in Fly Ash", Compost Sci. Nov./Dec. 1971, 15.
MA-222 MacCartney, John C., and Ralph H. Whaite, Pennsyl-
vania Anthracite Refuse. A Survey of Solid
Waste from Mining and Preparation I.e. 8409, Pitts-
burgh, Pa., BuMines, 1969.
MA-247 Magnuson, Malcolm 0., and Wilbert T. Malenka,
"Utilization of Fly Ash for Remote Filling of Mine
Voids", in Proceedings of the 2nd Ash Utilization
Symposium, Pittsburgh, Pa., 10-11 March 1970. BuMines
I.C. 8488, Washington, D.C., BuMines, 1970, pp. 83-
96.
MA-257 Mathew, K. V., "Central Prayon Process for Manufac-
ture of Wet Process Phosphoric Acid", Chem. Age
India 21(1), 78-80 (1970).
ME-072 Metropolitan Sanitary District of Greater
Chicago, Ski Mountain, A Conceptual Feasibility
Study in Solid Waste, PB 213 697, EPA-SW-46D,
Chicago, 111., 1972.
MI-081 Midwest Research Inst., Resource Recovery Processes
for Mixed Municipal Solid Wastes. Part II - Catalogue
of Processes, PB 214-148, Kansas City, Mo., 1972.
-260-
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MI-084 Minnick, L. John, "Fixation and Disposal of Flue
Gas Waste Products - Technical and Economic Assess-
ment" , Paper presented at EPA Flue Gas Desulfuriza-
tion Symposium, New Orleans, La., 14-17 May 1973.
MO-070 Moulton, Lyle K., "Bottom Ash and Boiler Slag",
presented at the Third International Fly Ash
Utilization Symposium, Pittsburgh, Pa., 13-14 March
1973.
MO-071 Morrison, Ronald E., "Application of Boiler Slag",
Charleston, WestVa., American Electric Power
Service Corp.
MU-060 Murakami, Keiichi, and Shoichiro Hori, "Gypsum.
By-Product Recovery - As Raw Material for Plaster
and Cement - Japanese Practice", Phosphoric Acid
1(2), A. V. Slack, ed., N.Y. Dekker, 1968, pp. 519-
528.
NA-130 National Ash Assoc., Inc., Ash At Work £(3), 1972.
NA-132 National Ash Assoc., Inc., Ash At Work. Technical
Bulletin No. 4, Washington, D.C.
NA-134 National Ash Assoc., Inc., "Fly Ash-Cement Grout
Stops Subsidence", Ash At Work. Technical Bulletin
No. 11, Washington, D.C.
OB-005 O'Brien, J. Clayton, Chicago Fly Ash Co., Private
Communication, 3 August 1973.
PA-122 Page, Bruce W., Michael J. Copley, and James M.
Shackelford, "A New Filtration Device for Concentrat-
ing Neutralized AMD Sludges", in Coal Mine Drainage
Research. Pceprints p_f Papers Presented Before 4th
Symposium, Pittsburgh, Pa., 1972, pp. 234ff.
-261-
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PR-057 "The Prairie Plan", Public Works 10.4(4), 64-66
(1973).
PU-017 "Putting Industrial Sludges in Place", Env. Sci.
Tech. 6(10), 874-5 (1972).
RA-075 Raynes, B. C., "Economic Transport of Digested
Sludge Slurries", J. WPCF 42, 1379 (1970).
RA-084 Raymond, Stanley, "Pulverized Fuel Ash as Embank-
ment Material", Proc. Inst. Civil Engr. (London)
19, 515- 36 (1961).
RE-071 "Research Seeks New Ways to Seal Land Fill Against
Leaching", Solid Wastes Management 14(3), 18 (1971).
RE-073 Reeves, E. A., "Cash from Ash", Electrical Engineer-
ing (Melbourne) 48(6), 26-7 (1971).
RE-074 Reid, George W., and Leale E. Streebin, Evaluation
of Waste Waters from Petroleum and Coal Processing,
PB 214-610. EP1.23/2:72.001., Univ. of Okalhoma,
School of Civil Engineering and Environmental
Science, 1972.
RE-084 Reidelbach, John A., Jr., "An Industrial Evaluation
of Fly Ash Bricks", in Proceedings of the 2nd Ash
Utilization Symposium, Pittsburgh, Pa., 10-11 March
1970. BuMines I.C. 8488, Washington, D.C., BuMines,
1970, pp. 193-200.
RE-089 "Recycling Sludge and Sewage Effluent by Land
Disposal", Env. Sci. Tech 6(10), 871 (1972).
-262-
-------
RE-092 "Recycle Land with Refuse", American City September
1972, 97.
RE-093 Reserve Mining Company, Report to the Minnesota
Pollution Control Agency for the Month of August
1971, Silver Bay, Minnesota, 1971.
RO-084 Rossoff, J., R. C. Rossi, and J. Meltzer, "Study
of Disposal and Utilization of By-Products from
Throwaway Desulfurization Processes", Presented at
the Flue Gas Desulfurization Symposium, New Orleans,
La., 14-17 May 1973.
RO-093 Rohrman, F. A., "Analyzing the Effect of Fly Ash
On Water Pollution", Power 115(8), 76-7 (1971).
RO-113 Roy, B. B., "Evaluation of Various Wet Process
Phosphoric Acid Manufacturing Techniques", Chem.
Age India 21(3), 298-309 (1970).
RU-030 Rummel, W., "Production of Iron Oxide Hydrate from
Mine Waters in the Lausitz Region", Wasserwirtschaft-
Wassertechnik I, 344-48 (1957).
SA-116 Sandy Hook Marine Laboratory, U.S. Bureau of Sport
Fishing and Wildlife, The Effects of Waste Disposal
iri the New York Bight., Interim Report for 1 Jan.
1970, Washington, D.C. 1970.
SC-150 Scaife, C. W., and D. Kitchen, "Gypsum. By-Product
Recovery as Raw Material for Plaster and Cement -
European Practice", Phosphoric Acid 1/2), A. V. Slack,
ed., N. Y., Dekker, 531-539 (1968).
SC-164 Schomaker, Norbert, SHWRL, NERC, Cincinnati,
Personal communication, August 1973.
-263-
-------
SE-066 Selmeczi, Joseph G., and R. Gordon Knight,
"Properties of Power Plant Waste Sludges", Paper
#B-7, Presented at 3rd International Ash Utiliza-
tion Symposium, Pittsburgh, Pa., 13-14 March 1973.
SE-073 Seals, R. K., L. K. Moulton, and B. E. Ruth,
"Bottom Ash: An Engineering Material", Proc.,
ASCE, J. Soil Mech. Found. Div. 98(SM4) 311-25
(1972).
SE-075 Selvig, W. A., and F. H. Gibson, Analysis of Ash
from United States Coals, Bulletin 567, Washington,
D.C., BuMines, 1956.
SK-017 "Skiing Down A Garbage Pile", Business Week 6_ Nov.
1971, 90.
SL-034 Slack, A. V., and J. M. Potts, "Disposal and Use
of By-Products from Flue Gas Desulfurization
Processes. Introduction and Overview", Presented
at the Flue Gas Desulfurization Symposium, New
Orleans, La., 14-17 May 1973.
SL-041 Slonaker, John F., and Joseph W. Leonard, "Review
of Current Research on Coal Ash in the U.S.",
Presented at the 3rd International Ash Utilization
Symposium, Pittsburgh, Pa., 13-14 March 1973.
SO-054 "Solid Wastes: Disposal Still Paces Waste Management
Programs", Env. Sci. Tech. £(5), 386 (1970).
SO-056 "A Solid Waste Recovery System For All Municipalities",
Env. Sci. Tech. 5(2), 109 (1971).
-264-
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SP-034 Specht, R. C., "Effect of Waste Disposal of the
Pebble Phosphate Rock Industry in Florida on
Condition of Receiving Streams", AIME Trans. %T_
(July, 1950).
ST-117 Stewart, J. F., "A Review of Babcock and Wilcox
Air Pollution Control Systems for Utility Boilers",
Presented at the Flue Gas Desulfurization Symposium,
New Orleans, La., 14-17 May 1973.
ST-149 "States Make Headway on Mine Drainage", Env. Sci.
Tech. 3(12), 1237 (1969).
ST-151 Stanczyk, Martin H., I. L. Feld, and E. W. Collins,
Dewatering Florida Phosphate Pebble Rock Slime by_
Freezing Techniques, RI 7520, Washington, D.C.,
BuMines, 1971.
ST-155 Stinson, J. M., "Gypsum. By-Product Recovery in
Production of Sulfuric Acid", Phosphoric Acid _1(2) ,
A.V. Slack, ed., N.Y., Dekker, 567-578 (1968).
SU-031 Sulfur Oxide Control Technology Assessment Panel
(SOCTAP), Projected Utilization of Stack Gas
Cleaning Systems by_ Steam-Electric Plants, Final
Report, April 1973.
SU-037 "S02 Hydrolysis Converts Sludge to Animal Feed,
Cuts Plant Cost", Ind. Res. 1^(10), 31 (1970).
TA-040 Taylor-, W. C. , "Combustion Engineering's Experience
in the Disposal and Utilization of Sludge from
Lime-Limestone Scrubbing Processes", Presented at
the Flue Gas Desulfurization Symposium, New Orleans/
La., 14-17 May 1973.
TE-101 Tennessee Valley Authority, Environmental Statement,
Experimental SO2 Removal System and Waste Disposal
-265-
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Pond Widows Creek Steam Plant, (Draft) , Muscle
Shoals, Alabama, 1972.
TE-112 Tennessee Valley Authority, Review of Wastewater
Control Systems . Widows Creek Steam Plant, Muscle
Shoals, Alabama, 1971.
TE-114 Tenney, Mark W. , "Fly Ash Utilization", Compost
Sci. 11. (4) , 25 (1970) .
TE-125 Tenney, Mark W. , and Wayne F. Echelberger, Jr.,
"Fly Ash Utilization in the Treatment of Polluted
Waters", in Proceedings of the 2nd Ash Utilization
Symposium, Pittsburgh, Pa., 10-11 March 1970, BuMines
I.C. 8488, Washington, BuMines, 1970, pp. 237-268.
TH-041 Thompson, T. L. , P. E. Snoek, and E. J. Wasp,
"Economics of Regional Waste Transport and Disposal
Systems", in Water-1970. CEP Symposium Series
1.0_7(67) , 413-22 (1971) .
TI-021 Timberlake, Richard C. , "Building Land wi
Phosphate Wastes", Mining Eng. ,21(12) 38-40 (1969).
TO-027 Tonet, Nelson R. , "Hydraulic Disposal to Mines",
presented at the ASME-IEEE Joint Power Generation
Conf., Pittsburgh, 27 Sept. - 1 Oct. 1970.
TR-026 "Truckloads of Land Fill from Waste Sludge",
Chem. Week 110(4) , 41 (1972).
TR-031 Trattner, R. B., A. J. Perna, and H. S. Kimmel,
"Analysis of Leach Water from a Controlled Sanitary
Landfill", Env. Letters 5(4) , 267-75 (1973).
US-027 U.S. Bureau of Mines, Mineral Facts and Problems,
1970, Washington, U.S. Dept. of Interior, Bureau
of Mines, 1970, Bulletin 650.
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US-055 U.S. Department of Interior, Office of Coal Research,
Clean Energy From Coal—A National Priority, 1973
Annual Report, Washington, D.C., 1973, pp. 19-42.
US-079 U.S. Bureau of Mines, Minerals Yearbook 1970, Vol. 1.
Metals, Minerals, and Fuels, Pittsburgh, Pa., 1972,
(GPO).
US-082 U.S. Dept. of Agriculture, Agricultural Research
Service, Environmental Impact Statement - Research
Demonstration Pilot Study of Municipal Waste
Composting, Beltsville, Md., EIS-MD-73-0030-D,
Washington, D.C., 1973.
VA-068 Van Ness, R. P., Louisville Gas and Electric,
Private Communication, 13 August 1973.
VA-078 "The Value of Sludge", Time, 2J7 Sept. 1971, 93.
VI-015 Villecco, Marguerite, "A Solution to Garbage
Disposal with Park Land as the Bonus", Forum
November 1970, 60.
WE-073 West Virginia Univ. School of Mines, Coal Research
Bureau, Production of Mineral Wool from Coal Ash
Slag, Final Report, Grant SWD-9, Morgantown, W. Va.,
1969.
WE-078 West Virginia Univ., Coal Research Bureau,.Dewater-
ing of Mine Drainage Sludge, Water Pollution Control
Research Series 14010 FJX, Morgantown, W. Va., 1971.
WE-095 Westerhoff, Garret P., "Sanitary Landfill - A
Misleading Name", Public Works December 1970, 72.
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WE-096 Weston, (Roy F.), Environmental Scientists and
Engineers, Concept Evaluation Report. Taconite
Tailings Disposal, Reserve Mining Company, Silver
Bay, Minnesota, West Chester, Pa., 1971.
YE-005 Yeh, Show - Jong, and Charles R. Jenkins, "Disposal
of Sludge from Acid Mine Water Neutralization",
J. WPCF £3, 679 (1971).
ZI-012 Zimmer, F. V., "Fly Ash as a Bituminous Filter",
in Proceedings of the 2nd Ash Utilization Symposium,
Pittsburgh, Pa., 10-11 March 1970, BuMines I.e. 8488,
Washington, D.C., BuMines, 1970.
-268-
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TECHNICAL REPORT DATA
(Please rcail liulrncliun<; on tin- reverse bcjorc completing)
RCPOHTNO.
EPA-65Q/2-74-033
2.
3 RECIPIENT'S ACCESSION-NO.
4 TITLE AND SUBTITLE
Final Report, Solid Waste Disposal
5. REPORT DATE
Mav 1974
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Nancy P. Phillips and R. Murray Wells
8. PERFORMING ORGANIZATION REPORT NO.
200-045-04
g PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
8500 Shoal Creek Boulevard
Austin, Texas 78766
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21ADE-10
11. CONTRACT/GRANT NO.
68-02-1319 (Task 4)
12 SPONSORING AGENCV NAME AND ADDRESS
SPA, Office of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15 SUPPLEMENTARY NOTES
16. ABSTRACT
The report gives results of an investigation of available disposal technologies
for nine solid wastes destined for land disposal. Purpose of the investigation
was to examine the potential applicability of these already developed technologies
to the disposal of sludges generated by flue gas desulfurization systems. For
each material of interest, including scrubber sludge, the nature of the waste,
traditional disposal procedures, and related environmental effects are described.
Case studies were examined in order to quantify the problem as much as
possible; results of these studies are included in the report.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI l-icld/Gioup
Air Pollution
Waste Disposal
Solids
Sludge Disposal
Flue Gases
Desulfurization
Scrubbers
Wastes
Air Pollution Control
Stationary Sources
13B
7D
7A
21B
DISTRIBUTION STATEMENT
Unlimited
19 SECURITY CLASS (Tins Report)
Unclassified
21. NO. OF PAGES
20 SECURITY CLASS (Tinspage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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