EPA/600/D-86/028
January 1986
STABILIZATION/SOLIDIFICATION
OF
HAZARDOUS WASTE
Presented by
Ronald D. Hill
U.S. Environmental Protection Agency
Hazardous Waste Engineering Research Laboratory
Cincinnati, Ohio 45268
Based on a Technical Handbook Prepared for the U.S. EPA
by
M. John Cul1 inane
Larry W. Jones
U.S. Army Engineer Waterways Experiment Station
Vicksburg, Mississippi
and a Summary
by
Philip A. Spooner
Science Applications International Corporation
McLean, Virginia
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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NOTICE
This document has been reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or recommendation for use.
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FOREWORD
'•Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased generation of
solid and hazardous wastes. These materials, if improperly dealt with, can
threaten both public health and the environment. Abandoned waste sites and
accidental releases of toxic and hazardous substances to the environment also
have important environmental and public health implications. The Hazardous
Waste Engineering Research Laboratory assists in providing an authoritative and
defensible engineering basis for assessing and solving these problems. Its
products support the policies, programs, and regulations of the Environmental
Protection Agency, the permitting and other responsibilities of State and
local governments, and the needs of both large and small business in handling
their wastes responsibly and economically.
This paper presents a summary of the EPA Handbook on Stabilization/Solidi-
fication Alternatives for Remedial Action and was developed as a resource
document for a joint USEPA/Spain Seminar on the treatment and disposal of
hazardous waste to be held in Spain in May 1986.
For further information, please contact the Land Pollution Control Division
of the Hazardous Waste Engineering Research Laboratory.
William A. Cawley, Acting Director
Hazardous Waste Engineering Research Laboratory
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ABSTRACT
A technical handbook for stabilization/solidification of hazardous waste
has recently been developed for EPA by the U.S. Army Engineer Waterways Experi-
ment Station, This document is intended to serve as a guide to stabilization/
solidification technologies for individuals responsible for preparing and
reviewing remedial action plans. The handbook provides detailed discussion of
the chemistry of commonly used stabilization/solidification techniques, high-
lighting their advantages and disadvantages. It provides suggested methodolo-
gies for waste and site characterization, as well as for laboratory and bench/
pilot-scale testing. Planning and executing of full-scale treatment operations
are also discussed, along with four different treatment scenarios from which
cost and other comparisons can be made. The handbook also provides guidance on
site safety, site cleanup, and site closure and monitoring.
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TABLE OF CONTENTS
Foreword .................................
Abstract . i
Introduction .............. . ...
Stabilization/Solidification Techniques
Sorption ............. ...........
Lime-Fly Ash Pozzolan Process
Pozzolan-Portland Cement Processes ...
Thermoplastic Microencapsulation . . ...
Macroencapsulation
Other Techniques . . . ....... . ......
Pretreatment ..... .
Waste Character!zation
Physical Characterization ... ....
Chemical Characterization » , . .
Process Selection ....
Process Screening . . . .
Process Operation . . .............
Summary
Reference . ,
Tables
1. Typical Physical and Chemical Properties of Commonly Used Natural
Sorbents ,
2. Synthetic Sorbents Used With Hazardous Wastes .............
3. Hazardous Waste Consistency Classification .........
4. Summary¦Comparison of Relative Cost of Stabilization/Solidification
Alternatives .. .......
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7
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10
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17
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4
9
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STABILIZATION/SOLIDIFICATION OF HAZARDOUS HASTE
INTRODUCTION
Over the last decade, there has been an increased interest in the
stabilization and solidification of hazardous wastes and contaminated soils and
sediments. In response to this growing interest, the Land Pollution Control
Division of EPA'a Hazardous Waste Engineering Research Laboratory has produced
a technical handbook on the subject. This handbook provides details of the
materials and equipment in common use, and outlines methodologies for applying
these techniques to hazardous waste problems. Among the subjects covered are
waste and site characterization, laboratory testing and leaching protocols,
bench and pilot scale testing, and full-scale operations. Four stabilization/
solidification scenarios are presented to illustrate advantages and disadvan-
tages of different mixing techniques. Cost factors for the four techniques are
also presented and discussed.
For this handbook, the terminology associated with these techniques is
defined as follows: (1) Stabilization refers to those techniques which reduce
the hazard potential of a waste by converting the contaminants into their least
soluble, mobile, or toxic form. The physical nature and handling characteristics
of the waste are not necessarily changed by stabilization. (2) Solidification
refers to techniques that encapsulate the waste in a monolithic solid of high
structural integrity. The encapsulation may be of fine waste particles
(microencapsulation) or of a large block or container of wastes (macroencapsu-
lation). Solidification does not necessarily involve a chemical interaction
between the wastes and the solidifying reagents, but may involve mechanically
binding the'wastes into the monolith. Contaminant migration is restricted by
vastly decreasing the surface area exposed to leaching, and/or by isolating the
wastes within an impervious capsule.
Considerable impetus has been given to stabilization/solidification by
both the Resource Conservation and Recovery Act (RCRA), including the 1984
amendments, and by the Comprehensive Environmental Response, Compensation and
Liability Act (CERCLA). These techniques are often the basis for delisting*
petitions under RCRA, and can be employed to satisfy the prohibition on the
landfilling of liquids. Under CERCLA, solidification and encapsulation are
specifically cited in the NCP (40 CFR 300) as methods to be considered during
the feasibility study for remedying releases from contaminated soils and
sediments.
STABILIZATION/SOLIDIFICATION TECHNIQUES
Most stabilization/solidification systems available today are proprietary
processes involving the addition of absorbents and solidifying agents to a
waste. Often the process is changed to accommodate specific types of wastes.
~Delisting. The approval given by the U.S. EPA that a waste is no longer
hazardous following a specific treatment process.
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Most processes fall within a few generic types with proprietary additives added
by different companies. The exact degree of performance observed in a specific
system may vary widely from its generic type, but the general characteristics
of a process and its products can be discussed.
Waste stabilization/solidification systems that have potentially useful
application for hazardous waste to be discussed in detail here include:
0 Sorption
° Lime-fly ash pozzolan processes
° Pozzolan-portland cement processes
° Thermoplastic microencapsulation
° Macroencapsulation
Sorption
Sorption involves the adding of dry, solid substance to a liquid or semi -
liquid waste to take up free liquid and improve waste handling characteristics.
The sorbent may hold the fluid as capillary liquid, or react chemically with
it. Common natural sorbents include:
° Soil
0 Fly ash
0 Bottom ash
0 Cement kiln dust
0 Lime kiln dust
Physical and chemical properties of these and other natural sorbents are
shown in Table 1.
A number of synthetic sorbents are also available, but due to their
relatively higher cost, are less commonly used as presolidification agents.
Table 2 lists some synthetic sorbents and the wastes that are effectively
treated by them.
Sorbents, especially natural ones, are in wide use at hazardous waste
landfills to eliminate free liquid and improve waste handling characteristics.
In many cases, however, the sorbed wastes remain subject to leaching, and the
landfill liner and leachate collection system are relied on to prevent contami-
nant migration. Sorbents that act like sponges and only soak up the liquids
are not recommended.
Mixing requirements and equipment for sorption are job specific. For many
jobs, a mixing pit and backhoe will suffice. If greater control of sorbent/
waste ratios or mixing thoroughness is required, pug mills or ribbon blenders
may be used. In any case, each batch of natural sorbent should be tested with
the waste to ensure optimum mix ratios are employed.
Lime-Fly Ash Pozzolan Process
This process involves mixing wastes with natural or artificial silicic
material and hyd rated lime. Natural pozzol ana include some volcanic tuffs and
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TABLE 1. TYPICAL PHYSICAL AND CHEMICAL PROPERTIES OF
COMMONLY USED NATURAL SORBENTS
Sorbent
Bulk
density
(kg/m3)
Cation-
¦ exchange
capacity
(meq/100
gms)
Am'on-
exchange
(meq/100
gms)
Slurry
. pH "
Major
mineral
species
present
Fly ash,
acidic
1187
—
—
4-5
Amorphous
silicates,
hematite,
quartz,
mullite,
free carbon
Fly ash,
basic
1187
9-10
Calcite, amor-
phous sili-
cates, quartz,
hematite,
mullite, free
carbon
Kiln dust
641-890
9-11
Calcite,
quartz,
lime (CAO)
anhydrite
Limestone
screenings
—
—
—
6-7
Calcite,
dolomite
Clay minerals
(soils)
1519
—
--
Various, e.g.,
illite
Kaolinite
"¦
5-15
6-20
Can be rel ac-
tively pure
kaolinite
Ve rnricul ite
100-500
4
—
Can be rela-
tively pure
Bentonite
100-120
Smectite,
quartz illite,
gypsum, feld-
spar, kaoliniti
calcite
Zeolite
. 1543
100-300
Zeolite (e.g.,
heulondite,
laumonite,
stilbite,
chabazite,
etc.)
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TABLE 2. SYNTHETIC SORBENTS USED WITH HAZARDOUS WASTES
Waste treated effectively
Sorbs fluoride in neutral wastes
Sorbs dissolved organics
Sorbs water and organics
Reportedly effective with oil
emulsions
Reportedly useful in spills of
inert spirits-type liquids
(cyclohexane)
Sorbent
Activated alumina
Activated carbon
Hazorb* (foamed glass)
Locksorbt (treated clay)
Imbiber beads# (cross-linked polymer)
* Product of Diamond Shamrock Corporation.
t Product of Radecca Corporation, Austin, TX.
# Product of Dow Chemical Company, Midland, MI.
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diatomaceous earth. Artificial pozzolana include blast furnace slag, ground
brick, and some fly ashes from the burning of powdered coal. The wastes, often
prestabilized, are mixed with the pozzolanic material to a pasty consistency.
Calcium hydroxide (hydrated lime) is then blended into the fly ash-waste mixture.
In order to produce a mechanically strong solid, from 20 to 30 percent lime is
often required, depending on the wastes and type of fly ash "used. The fly ash-
wast e-1 ime mixture is then placed in a landfill and compacted to increase its
density. Alternately, the moist mixture may be compacted into molds and allowed
to cure and pass specific tests prior to disposal.
Lime-fly ash solidification has several advantages. The materials and
equipment required are readily available at relatively low cost. The resultant
waste-lime-fly ash mixture sets into an easily handled solid product with
reduced permeability. Among the disadvantages of this technique are the
increased volume of material requiring disposal, and a relatively high leaching
loss of potential contaminants from the solidified wastes, thus requiring secure
disposal. A number of compounds, including sodium borate, calcium sulfate,
potassium bichromate, and carbohydrates, can interfere with the setting reaction.
Also, high oil and grease in the wastes can physically coat waste, fly ash, and
lime particles, preventing them from reacting.
Pozzolan-Portland Cement Processes
A number of waste treatment processes employ portland cement as the
solidifying agent, often with a pozzolanic material (such as fly ash) added to
improve strength and increase durability. A variety of other additives, such
as other forms of silica, and clays, may also be employed to alter the performance
of. these processes.
The type of portland cement can be selected to favor particular cementation
reactions, thus avoiding interference from incompatible compounds. The five
major types of portland cement include:
G
O
O
C
0
Due to its relatively low cost and wide availability, Type I is the most
commonly used for solidification of.wastes. Types II and V are used to a much
lesser extent. Subject to availability, lower cost cement kiln dust may also
be used, but larger quantities are generally required.
Many types of water-based waste-fly ash slurries may be mixed directly
with cement using conventional cement mixing equipment. Large solidification
projects may make the use of concrete batch mixing plants advantageous.
Extremely hazardous waste may require the use of controlled, in-drum mixing
equipment.
Type I: Common portland cement
Type II: Low alumina cement, moderately sulfate resistant
Type III: Rapid set cement, high early strength
Type IV: Long set cement for large mass pouring
Type V: Very low alumina cement, sulfate resistant
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The suspended solids in a waste slurry become incorporated into the hardened
concrete matrix. Most multivalent toxic metals will be transformed into their
low solubility hydroxides or carbonates by the high pH of the cement mixture.
Some metal ions may become integrated into the mineral crystals within the
cement. Some materials in a waste can increase the strength and durability
of a waste. These include sulfides (except sodium sulfide),"asbestos, and latex.
A number of compounds can interfere with the solidification process.
Some, such as soluble salts of manganese, tin, zinc, copper, and lead, can
increase setting times and greatly decrease physical strengths. Impurities
such as organic matter, silts, and some "clays, can cause significant delays in
setting. These impurities and other insoluble materials, fine enough to pass a
No. 200 mesh sieve, can coat larger particles and weaken the waste/cement bond.
Cement-fly ash solidification techniques, with or without waste-specifi c
additives, are among the most common offered by solidification vendors. Due to
their relatively higher cost, they are less commonly used than lime-fly ash
techniques.
Thermoplastic Microencapsulation
Thermoplastic microencapsulation involves mixing dried wastes with materials
such as bitumen (asphalt), paraffin, polyethylene, polypropylene, or sulfur
amended asphalt, and placing the mixture in some sort of container or mold.
The most commonly employed material is asphalt. These techniques, developed
originally for radioactive waste disposal, are adaptable to highly soluble
toxic substances which are not amenable to lime or cement-based techniques.
Many waste types should not be considered for asphalt microencapsulation.
Combustible materials such as solid hydrocarbons or sulfur, can ignite or
explode at the elevated temperatures (130° to 260°C) employed for mixing.
Borate salts can cause sudden hardening and clog equipment. Some solvents can
prevent hardening while others, such as toluene and xylene, can readily migrate
from the asphalt mixture. For wastes that are compatible with these techniques,
however, the resultant product has a very low loss of contaminants to leaching
fluids.
The greatest limitations to use of these techniques are relatively high
cost, and the need for specialized mixing equipment and trained operators.
Also, the wastes must be dried before mixing with the heated thermoplastic.
Consequently, these techniques are generally used to achieve complete contain-
ment of special waste types in cases where costs are not a seriously limiting
factor.
Macroencapsulation
Macroencapsulation, often referred to as jacketing, is a technique for
isolating wastes by completely surrounding them with a durable, impermeable
coating. One such technique involves sealing the wastes in a polyethylene, or
polyethylene-lined, drum. Another involves drying the wastes, mixing them with
polybutadiene, and compressing the mixture into a block. The block is then
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placed in a mold, surrounded by powdered polyethylene, and heated under pressure.
The resultant product is a block with a thin polyethylene coating fused to it.
These techniques may be employed to contain very soluble toxic wastes,
such as nonoxidizing mineral acids. The containment of the wastes is complete
and assured for the life of the coating material. The polyethylene drum sealing
technique can be used to over-pack damaged or leaky drums during both immediate
removals and remedial actions.
The disadvantages of this technique include the expense of materials,
specialized equipment, and energy, especially for fused-coating systems.
Skilled labor is required and volatilization and combustion are an important
consideration for wastes considered for these techniques.
Other Techniques
Other less common specialty systems are briefly discussed in the following
paragraphs:
Two other solidification techniques show promise for selected wastes and
situations. Self-cementation can be applied to wastes containing large amounts
of calcium sulfate or calcium sulfite, such as flue-gas cleaning sludges or
desulfurization sludges. A portion of the waste, usually 8 to 10 percent by
weight, is calcined and then remixed with the waste along with proprietary
additives. Fly-ash may be used to absorb excess moisture. The resultant
product is an easily handled stable solid. The major drawbacks of this technique
are waste specificity, energy and equipment expenses, and the need for skilled
labor. • ¦ » ' .
Another solidification technique is vitrification. Wastes are mixed with
silica and heated to extremely high temperatures, and allowed to cool Into a
glass-like solid. A variation of this technique, using graphite electrodes
driven into buried wastes, allows in-situ vitrification. All vitrification
systems employ some type of hood to capture and treat the fumes and vapors
given off during operation. Because these systems are very energy intensive,
thus costly, they are generally considered only for radioactive or extremely
dangerous wastes.
PRETREATMENT
Pretreatment systems, which overlap with stabilization and sorption
processes, can be used to achieve a number of results that condition the waste
to ensure better and more economical containment after the remaining materials
have been stabilized and solidified. These include:
° Destruction of materials (such as acids or oxidizers) that can react
with solidification reagents (lime or portland cement)
° Reduction of the volume of waste to be solidified (using processes such
as settling or dewatering)
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° Chemical binding of specific waste constituents to solid phases added
to scavenge toxic materials from solution and hold them in solids
° Techniques for improving the scale on which waste processing can be
done, for example, bulking and homogenizing waste to allow a single
solidification system to be used without modification"on a large volume
of waste
Neutralization, oxidation or reduction, and chemical scavenging stabilize
the waste in that they bring the chemical waste into an inert or less soluble
form. Dewatering, consolidation, and waste-to-waste blending are also useful
pretreatment methods which reduce the waste volume or numbers of different
waste forms requiring treatment,
WASTE CHARACTERIZATION
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A thorough physical and chemical characterization of a waste is essential
to determine the most suitable stabilization/solidification method, as well as
any special pretreatment or material handling methods that may be required.
Physical characterization focuses mainly on transport, storage, and mixing con-
siderations, while chemical characterization focuses mainly on interfering com-
pounds, hazard assessment, and compatibility. These issues are discussed below.
Physical Characterization
Tests performed to characterize the physical properties of a waste will
vary with the specific wastes and the stabilization/solidification techniques
proposed for them. The physical determinations most commonly employed for
stabilization/solidification are:
° Moisture content
° Suspended solids content
° Bulk density
° Grain-size distribution
° Atterberg limits
° Cone index
0 Unconfined compressive strength
Moisture content is the ratio of the weight of water to the weight of
solids expressed as percent. This value is used to determine if pretreatment
is necessary, and for designing the stabilization/solidification process to be
employed. A standard method for making this determination is given in ASTM
method D 2216-80.
Suspended solids content is used to determine the best method for handling
the waste and for estimating the amount of volume decrease due to consolidation
or dewatering. Table 3 gives general consistency categories based on approximate
suspended solids content. The EPA Standard Method for Settleable Matter is
often used for this determination.
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TABLE 3. HAZARDOUS WASTE CONSISTENCY CLASSIFICATION
Consistency Category
Characteristics
.Liquid waste
Pumpable waste
Flowable waste
Nonflowable waste
<1% suspended solids,* pumpable liquid, generally
too dilute for sludge dewatering operation
<10% suspended solids,* pumpable liquid, generally
suitable for sludge dewatering
>10% suspended solids,* not pumpable, will flow or
release free liquid, will not support heavy equip-
ment, may support high flotation equipment, will
undergo extensive primary consolidation
Solid characteristics, will not flow or release free
liquids, will support heavy equipment, may be 100%
saturated, may undergo primary and secondary
consolidation
*Suspended solids ranges are approximate.
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Bulk density of a waste is defined as the weight of a known waste volume to
the weight of the same volume of water. This weight per unit volume, or bulk
density, expressed in grams per cubic centimeter (g/cc) is used to convert waste
weight to volume for materials handling calculations.
Because fine-grained wastes can cause problems with several solidification
techniques, grain-size distribution measurements are important. These are made
using ASTM Standard Method for Particle-size Analysis of Soils (ASTM D 422-63[72]).
Atterberg limits are the moisture contents which mark the boundaries
between a materials liquid and plastic states. The liquid limit of a material
is the moisture content below which it wi11 flow as a viscous 1icuid. This is
determined by ASTM Standard Method for Liquid Limit of Soils {ASTM D 423-66[72]).
The plastic limit is the moisture content at the boundary between the plastic
and semisolid states. It is determined by ASTM Standard Method for Plastic
Limit and Plasticity Index of Soils (ASTM 0 424— 59[71]). The plasticity index
is the difference of moisture content between the liquid limit and the plastic
limit. These data are used to estimate such properties as compressibility,
strength, and swelling characteristics, to provide an indication of how the
waste material will behave when stresses are applied.
The cone index test involves forcing a standard cone-shaped device into
the material to be tested, and measuring the penetration resistance offered by
the material. This test is used to measure the in-situ strength of the wastes.
ASTM Standard Method for Deep, Quasi-Static, Cone and Friction-Cone Penetration
Tests for Soils (ASTM D 3441-79), may be used.
Unconfined compressive strength tests are used to measure shear strength
of cohesive soils. These, in turn, may be used to predict the stability and
ultimate bearing capacity of the wastes. ASTM Standard Method for Unconfined
Compressive Strength of Cohesive Soil (ASTM D 2166-66[79]), is used for this
determination.
Chemical Characterization
The purposes of chemical characterization are to determine the hazards
associated with waste handling, to determine if interfering materials are
present, and to examine waste/waste and waste/process compatibilities. The
hazard potential, used to develop worker health and safety plans and equipment
requirements, may be determined by analysis for hazardous pollutants. Tests to
determine the presence of compounds deleterious to the intended stabilization/
solidification processes may be used to identify necessary pretreatment
measures. Compatibility testing is used to determine if wastes can be mixed
into larger bulks for treatment, and to determine if the wastes are amenable to
various stabilization/solidification techniques.
PROCESS SELECTION
The first measure taken in determining the feasibility of a stabilization/
solidification technique as a remedial alternative, is to complete a thorough
characterization of the wastes, and to calculate their volume. From this, a
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determination of the need to pretreat the wastes can be made. Flammable,
corrosive, reactive, and infectious wastes are among those that should not be
considered for solidification without some form of pretreatment. If more than
one pretreatment measure is required, as may be the case with complex wastes,
some method other than solidification may become more cost-effective.
Another use for the waste characterization is to assess the degree of
hazard associated with handling the wastes. The equipment and time needed to
protect workers and nearby residents while extremely hazardous wastes are being
processed, may become prohibitively expensive.
An additional process selection measure is to characterize the site where
the solidified wastes will be disposed. Because all solidification techniques
result in increased volumes for disposal, and transportation costs are signifi-
cant, wastes are usually solidified at the site where they will be disposed.
Consequently, wastes are either excavated and hauled to a suitable site (often
first stabilized), or the existing site is made suitable through modifications.
Many uncontrolled sites can be made suitable to accept solidified wastes through
the installation of a liner, leachate collection system, or other engineered
measure. As with the costs'of pretreatment processes, the costs of site
modifications for secure burial may become limiting.
Another step in selecting a suitable process is to develop the specifica-
tions the solidified wastes must meet. Such specifications should include:
0 Leachabil ity
° Free liquid content
0 Physical stability and strength
0 Reactivity
° Ignitability
0 Resistance to biodegradation
° Permeability
Standards for testing stabilized/solidified wastes have not yet been developed.
The specifications and testing procedures outlined below constitute a minimum
suggested program.
There are essentially three types of Teachability tests performed on
hazardous materials intended for landfilling: tests for regulatory compliance,
tests for maximum hazard assessment; and tests for landfill and landfill facility
design.
The regulatory compliance test most commonly applied to stabilized/solidified
wastes is the Extraction Procedure (EP) toxicity test required under RCRA (40
CFR Part 261.24). This involves subjecting a waste sample to leaching by dilute
acetic acid for 24 hours, and analyzing the resultant leachate for eight toxic
metals and six pesticides. The allowable level of these toxics in the leachate
is 100 times their Interim Primary Drinking Water Standard level. If this
limit is exceeded, the stabilized waste is still considered hazardous and must
be disposed of in a licensed hazardous waste facility.
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A number of tests to assess the maximum hazard of a solidified waste have
been proposed. Most involve subjecting finely-ground waste to leaching by
water, followed by successive leaching of fresh waste with recycled leachates.
This results in a solution that is saturated with respect to the component
contaminants. Although no specific levels of contaminants in the leachate have
been established for guidance, levels of concern can be identified and possibly
counteracted by alternation to the treatment process,
Leachability tests conducted for engineering purposes are generally for
use in the design of leachate collection and treatment systems. The most
commonly employed is the Uniform Leaching Procedure (ULP) developed for assessing
solidified low-level radioactive wastes. This procedure involves leaching a
set volume of wastes with a set volume of leaching medium (usually water) which
is changed regularly. Based on the surface area of the waste sample and
contaminant concentrations in the leachate, contaminant losses by diffusion
from the mass may be calculated. These values may be used"to predict the degree
of containment required of the disposal site.
The free liquid content of solidified waste is an important consideration.
USEPA regulations currently prohibit landfilling of wastes containing free
liquids. Several tests have been developed for measuring the free liquid
content of solidified materials. Most involve placing a block or cylinder of
waste of specific dimensions and weight between two filters. This sample is
then loaded to pressures equal to the anticipated landfill overburden pressures.
Any exudate collected on the filters is weighed to calculate its amount.
Physical stability and strength are important for solidified wastes intended
for landfilling. The .wastes must be able to support the weight of construction
equipment without significant consolidation and settling. The amount of
allowable settlement is largely governed by landfill design. Flexible membrane
covers, for example, are less tolerant of settlement than earthen covers. The
most commonly used tests for physical stability and strength are unconfined,
triaxial shear, or plate loading, compressive strength tests. Often these
tests are run on saturated and unsaturated samples to determine if saturation
results in lower strength.
Samples of solidified waste should be tested for both reactivity and
ignitability if there is a possibility that they would exhibit these properties.
Reactivity testing is employed to assess the compatibility of the solidified
wastes with landfill liner material and with other wastes. Ignitability testing
is generally reserved for wastes that are solidified with thermoplastics or
biodegradable wastes which could generate methane.
An assessment of a solidified waste's ability to support biologic activity
may be important. Microbial activity can produce acids which can attack and
weaken lime and cement. ASTM Standard Methods G 21 and G 22 can be used for
this purpose.
Measuring the permeability of solidified wastes can yield predictions of
the rate at which contaminants could be leached out of the solid. Low
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permeability equates to low contaminant mobility. Typically, a falling head
permeability test conducted in a back-pressured triaxial chamber is used. The
normal range of permeabilities for solidified wastes ranges from 10-4 to 10-8
cm/sec.
- PROCESS SCREENING
Assuming that one or more stabilization/solidification processes are
identified as feasible by the selection procedures described above, bench-scale
or pilot-scale studies can be used to choose and refine the most suitable
technique. Areas of concern investigated by these studies include:
° Safe waste handling procedures
° Waste uniformity
° Mixing and pumping properties
° Processing parameters
° Process control procedures
° Volume increases
A large stabilization/solidification operation has the potential to present
many safety concerns. Heat generation, volatilization, and dust propagation
are among the potential hazards. Also, the rapid addition of a reactive
pretreatment or solidification agent such as lime, could cause a flash fire by
rapid volatilization of organic chemicals. Many solidification reactions are
exothermic, and an evaluation of the heat transfer characteristics of the
treatment system is essential. The effects of heat transfer on reaction rates
as the system is scaled up must also be evaluated. ASTM Standard Method C
186, Test for Heat of Hydration .of Hydraulic Cements, is often, employed in these
evaluations. Like many of the tests used to assess stabilization/solidification
processes, modifications may have to be made to assess the generation of fumes
during treatment.
Waste uniformity and the mixing and pumping qualities at various points
within the treatment system should also be studied. Serious problems can be
caused by rapid viscosity increases within the system and must be evaluated,
along with performance evaluations of the pumps, mixers, or other equipment to
be used.
Process parameters, including mix ratios, mix and set times, and volume
increases, are among the most important results of bench- or pilot-scale testing.
Due to the heterogeneity of wastes and many commom treatment materials (such as
fly ash), many of the process parameters will be determined by trial and error.
Moisture content of wastes or treatment agents can show wide variability and
significantly alter mix ratios.
There is no substitute for a pilot study to evaluate a solidification
program and develop production techniques in large-scale solidification projects.
Pilot studies also provide large samples of material required for more accurate,
realistic testing, and permit resolution of equipment and material handling
problems. Pilot studies can also be used to train equipment operators on the
characteristics of the waste and the solidified product. Although quite
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expensive and time-consuming, pilot studies can reduce the possibility of a
major accident, reduce work stoppages, and increase product consistency and
process reliability, paying for themselves many times over in large-scale
projects.
PROCESS OPERATION
Full-scale operation of a solidification process requires detailed plan-
ning and cost comparisons. The first planning step involves the characteriza-
tion, testing, and process selection efforts described above. The second phase
of planning involves the development of the operations plan, including equipment
requirements, work sequence and scheduling, and cost estimation for the specific
site. These are briefly discussed below.
Equipment requirements are largely determined by the type of mixing to be
employed in the process. For the purpose of this discussion, four types of
mixing are discussed: in-drum, in-situ, plant, and area.
In-drum mixing is best suited for application to highly toxic wastes that
are present in relatively small quantities. This technique may also be appli-
cable in cases where the waste is stored in drums of sufficient integrity to
allow rehandling. In-drum mixing is typically the highest cost alternative
when compared to in-situ, mobile plant, and area mixing scenarios. Quality
control also presents serious problems in small batch mixing operations; com-
plete mixing is difficult to achieve and variations in the waste between drums
can cause variations in the characteristics of the final product.
In-situ mixing is primarily suitable for closure of liquid or slurry
holding ponds. In-situ mixing is most applicable for the addition of large
volumes of low reactivity, solid chemicals. The present state of technology
limits application of in-situ mixing to the treatment of low solids content
slurries or sludges. Where applicable, in-situ mixing is usually the lowest
cost alternative. Quality control associated with in-situ mixing is limited
with present technology.
Mobile mixing plants can be adapted for applications to liquids, slurries,
and solids. This technique is most suitable for application at sites with
relatively large quantities of waste materials to be treated. It gives best
results in terms of quality control. Mobile plant mixing is applicable at
sites where the waste holding area is too large to permit effective in-situ
mixing of the wastes or where the wastes must be moved to their final disposal
area.
Area mixing consists of spreading the waste and treatment reagents in
alternative layers at the final disposal site and mixing in place. It is
applicable to those sites where slurries with high solids content or where
contaminated soils or solids must be treated. Area mixing requires that the
waste materials be handled by construction equipment (dumptrucks, backhoes),
and is not applicable to the treatment of liquids. Area mixing is land-area
intensive in that it requires relatively large land areas for mixing. Area
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mixing presents the greatest possibility for fugitive dust, organic vapor, and
odor generation. Area mixing ranks below in-drum and plant mixing in terms of
quality control.
Project sequencing and scheduling is largely determined by the type of
mixing technique employed. The first step generally involves" preparation of
the site and construction of any necessary facilities. These could include
excavation of an inground mixing pit9 or construction of a disposal site to
receive the processed waste. This is often followed by any needed evaluation
of the wastes including such things as drum integrity or phase separation. The
actual processing of the wastes then takes place, along with the process control
monitoring. This is followed by waste curing and final disposal. Variations
to these sequences are likely due to process and site-specific factors.
Cost estimations for a full-scale processing operation must take into
account costs for:
° Treatment reagents
0 Labor
0 Materials
e Equipment (and mobilization)
° Cleanup
° Overhead and profit
These will depend on the solidification technique employed, the amount of wastes
to be processed, and many other site-specific constraints. For comparative
purposes, Table 4 shows the costs for solidification of 500,000 gallons of
waste with 30 percent¦port!and cement and 2 percent sodium silicate, based on
the four mixing methods described above. As shown, in-situ mixing is the least
costly, and in-drum mixing is nearly an order of magnitude more costly. This
illustrates why in-drum mixing and disposal is generally reserved for highly
toxic wastes where the secondary containment in drums is needed to lower the
migration potential.
The number of waste processing, handling, and mixing technologies is highly
varied, as is the number of treatment reagent-waste formulations. Waste and
site characteristics, and reagent cost and availability are the major factors
which must be weighed in project planning to ascertain the most cost-efficient
and reliable containment strategy. This section has discussed a sampling of
possible stabilization/solidification scenarios, all of which are commercially
available. This is intended to give the reader an appreciation of the wide
diversity of applicable technology now in use.
SUMMARY
A technical handbook for stabilization/solidification of hazardous waste
has recently been developed for EPA by the U.S. Army Engineer Waterways Experi-
ment Station. This document is intended to serve as a guide to stabilization/
solidification technologies for individuals responsible for preparing and
reviewing remedial action plans. The handbook provides detailed discussion of
the chemistry of commonly used stabilization/solidification techniques,
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TABLE 4. SUMMARY COMPARISON OF RELATIVE COST OF STABILIZATION/
SOLIDIFICATION ALTERNATIVES
(U.S. Dollars)
Plant Mixing
Parameter
In-drum
In-situ
Pumpable
Unpumpabl e
Area Mixing
Metering and
mi xi ng
efficiency
Good
Fai r
Excellent
Excellent
Good
Processing
days
requi red
374
4
10
14
10
Cost/ton
Re agent
$23.58
(9%)*
$20.50
(63%)
$20.50
(53%)
$20.50
(42%)
$20.50
(49%)
Labor and
Per Diem
58.88
(231)
1.36
(4%)
3.83
(10%)
6.93
(1«)
6.35
(15%)
Equipment
Rental
42.82
(17%)
1.38
(4%)
3.93
(10%)
7.54
(16%)
4.07
(10%)
Used drums
§ $ll/drum
55.55
(21%)
—
__
—
Mobilization-
demobilization
18.08
0%)
1.58
(5%)
1.43
(4%)
2.25
(5%)
1.20
(3%)
Cost of
treatment
processes
$198.91
$24.82
$29.69
$37.23
$32.12
Profit and
overhead
(30%)
59.67
(23%)
7.45
(23%)
8.91
(23%)
11.17
(23%)
9.63
(23%)
TOTAL
COST/TON
$258.58
$32.27
$38.60
$48.40
$41.75
* % of total cost/ton for that alternative.
NOTE: In all cases, 500,000 gal (2,850 tons) of waste treated with 302 Portland
cement and 2% sodium silicate with on-site disposal; costs include only those
operations necessary for treatment. All costs are per ton of waste treated.
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highlighting their advantages and disadvantages. It provides suggested methodolo-
gies for waste and site characterization, as well .as for laboratory and bench/
pilot-scale testing. Planning and executing of full-scale treatment operations
are also discussed, along with four different treatment scenarios from which
cost and other comparisons can be made. The handbook also provides guidance
on site safety, site cleanup, and site closure and monitoring.
REFERENCE
Cullinane, M. J., Jr. and L» W. Jones, "Draft Technical Handbook for Stabiliza-
tion/Solidification of Hazardous Waste," Environmental Laboratory, U.S. Army
Engineer Waterways Experiment Station, Vicksburg. MS., under contract to the
Land Pollution Control Division, Hazardous Waste Engineering Research
Laboratory, Office of Research and Development, U.S. Environmental Protection
Agency, Cincinnati, OH, September 1984.
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technical report data
(Please read Instructions on the reverie before completing!
1. REPORT NO.
EPA/600/D-86/028
2.
3. RECIPIENT'S ACCESSION NO.
PBS 6 1 5 ft 3 1 2 7K
4. TITLE AND SUBTITLE
STABILIZATION/SOLIDIFICATION ALTERNATIVES
REMEDIAL ACTION .
FOR
5. REPORT DATE
January 1986
6. PERFORMING ORGANIZATION CODE
7. AUTHORCS)
Ronald D. Hill
8. PERFORMING ORGANISATION REPORT NO.
9. performing organization name and address
U. S. Environmental Protection Agency
10. PROGRAM ELEMENT NO.
TEJY1A
26 ¥. St. Clair Street
Cincinnati, Ohio ^5268
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Hazardous Waste Engineering Research Laboratory
13. TYPE OF REPORT AND PERIOD COVERED
Office of Research and Development
U. S, Environmental Protection Agency
Cincinnati5 Ohio 45268
14. SPONSORING AGENCY CODE
EPA/600/12
1 5- SUPPLEMENTARY NOTES
Project Officer: Ronald D.
Hill, Phone (513) 569-7861
16. ABSTRACT
In"response to the growing interest in stabilization and solidification of hazardous
wastes and contaminated soils and sediments, the Land Pollution Control Division of
EPA's Hazardous Waste Engineering Research Laboratory has produced a technical hand-
book on the subject. This handbook provides details of the materials and equipment
in common use, and outlines methodologies for applying these techniques to.hazardous
waste problems. Among the subjects covered are waste and site chacterization, labora-
tory testing and leaching protocols, bench and pilot scale testing, and full-scale
operations. Four stabilization/solidification scenarios are presented to illustrate
advantages, disadvantages and costs for different nixing techniques.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.lOENTIFIEKS/OPSN ENDED TERMS
c. COSATJ Field/Group
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport;
UNCLASSIFIED
21. NO. OF PAGES
20. SECURITY CLASS (Thispose!
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Re*. 4-77) previous edition is obsolete
1
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