United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/540/S2-86/001 Dec. 1 986
&EPA Project Summary
Handbook for Stabilization/
Solidification of
Hazardous Waste
M. John Cullinane, Jr., Larry W. Jones, Philip G. Malone, Philip A.
Spooner, and Terry M. Bliss
In response to the growing interest in
stabilization and solidification of haz-
ardous wastes and contaminated soils
and sediments, the Land Pollution Con-
trol Division of EPA's Hazardous Waste
Engineering Research Laboratory has
produced a technical Handbook on the
subject. This Handbook provides de-
tails of the materials and equipment in
common use and outlines methodolo-
gies 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 scenar-
ios are presented to illustrate advan-
tages, disadvantages, and costs for dif-
ferent mixing techniques.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The terminology associated with sta-
bilization/solidification technology is
not rigidly defined and is often confus-
ing. For this Handbook, stabilization
refers to those techniques that reduce
the hazard potential of a waste by con-
verting the contaminants into their least
soluble, mobile, or toxic form. The
physical nature and handling character-
istics of the waste are not necessarily
changed by stabilization. Solidification
refers to techniques that encapsulate
the waste in a monolithic solid of high
structural integrity. The encapsulation
may be of fine waste particles (microen-
capsulation) or of a large block or con-
tainer of wastes (macroencapsulation).
Solidification does not necessarily in-
volve chemical interaction between the
waste and the solidifying reagents, but
may involve mechanically binding the
waste into the monolith. Contaminant
migration is restricted by vastly de-
creasing the surface area exposed to
leaching, or by isolating the waste
within an impervious capsule.
Considerable impetus has been given
to stabilization/solidification by both the
Resource Conservation and Recovery
Act (RCRA) and by the Comprehensive
Environmental Response, Compensa-
tion and Liability Act (CERCLA). These
techniques are often the basis for delist-
ing petitions under RCRA, and can be
employed to satisfy the prohibition on
the landfilling of liquids. Under
CERCLA, solidification and encapsula-
tion are specifically cited in the NCR (40
CFR 300) as methods to be considered
during the feasibility study for remedy-
ing releases from contaminated soils
and sediments.
Stabilization/Solidification
Techniques
Most stabilization/solidification sys-
tems being marketed are proprietary
processes involving the addition of ab-
sorbents and solidifying agents to a
waste. Often the marketed process is
changed to accommodate specific types
of wastes. Since it is not possible to dis-
cuss completely all potential modifica-
tions to a process, discussions of most
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processes are related directly to generic
process types. The exact degree of per-
formance observed in a specific system
may vary widely from its generic type,
but the general characteristics of a proc-
ess and its products can be discussed.
Waste stabilization/solidification sys-
tems that have potentially useful appli-
cation in remedial action include:
• Sorption
• Lime-fly ash pozzolan processes
• Pozzolan-portland cement processes
• Thermoplastic microencapsulation
• Macroencapsulation
Other less common techniques include:
• Self-cementation
• Vitrification
Pretreatment systems, which overlap
with stabilization and sorption proc-
esses, can be used to achieve a number
of results that condition the waste to en-
sure better and more economical con-
tainment 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 port-
land cement)
• Chemical binding of specific waste
constituents to solid phases added to
scavenge toxic materials from solu-
tion and hold them in solids
• Techniques for improving the scale
on which waste processing can be
done, for example bulking and ho-
mogenizing waste to allow a single
solidification system to be used with
modification on a large volume of
waste.
Neutralization, oxidation or reduc-
tion, and chemical scavenging stabilize
the waste, in that they bring the chemi-
cal 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 differ-
ent waste forms requiring treatment.
Waste Characterization
A thorough physical and chemical
characterization of a waste is essential
to determining the most suitable stabi-
lization/solidification method, as well as
any special pretreatment or material
handling methods that may be re-
quired. Physical characterization fo-
cuses mainly on transport, storage, and
mixing considerations. Chemical char-
acterization focuses mainly on interfer-
ing compounds, hazard assessment,
and compatibility.
Tests performed to characterize the
physical properties of a waste will vary
with the specific wastes and the stabi-
lization/solidification techniques pro-
posed for them. The physical determi-
nations most commonly employed for
stabilization/solidification are:
• Moisture content
• Suspended solids content
• Bulk Density
• Grain size distribution
• Atterberg limits
• Cone index
• Unconfined compressive strength
The purposes of chemical characteri-
zation are to determine the hazards as-
sociated with waste handling, to deter-
mine 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 deter-
mined by analysis for priority pollu-
tants. Tests to determine the presence
of compounds deleterious to the in-
tended stabilization/solidification proc-
ess may be used to identify necessary
pretreatment measures. Compatibility
testing is used to determine if wastes
can be mixed into larger bulks for treat-
ment, and to determine if the wastes are
amenable to various stabilization/solidi-
fication techniques.
Process Selection
The first measure taken in determin-
ing the feasibility of a stabilization/solid-
ification technique as a remedial alter-
native, is to complete a thorough
characterization of the wastes, and to
calculate their volume. From this a de-
termination of the need to pretreat the
wastes can be made. Flammable, corro-
sive, reactive, and infectious wastes are
among those that should not be consid-
ered 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 characteri-
zation is to assess the degree of hazard
associated with handling the wastes.
The equipment and time needed to pro-
tect workers and nearby residents while
extremely hazardous wastes are being
processed may become prohibitively
expensive.
An additional process selection meas-
ure is to characterize the site where the
solidified wastes will be disposed. Be-
cause all solidification techniques result
in increased volumes for disposal, ano
transportation costs are significant,
wastes are usually solidified at the site
where they will be disposed. Conse-
quently, wastes are either excavated
and hauled to a suitable site or the exist-
ing site is made suitable through modi-
fications. Many uncontrolled sites can
be made suitable to accept solidified
wastes through the installation of a
liner, leachate collection system, or
other engineering measure. As with the
costs of pretreatment processes, the
costs of site modifications for secure re-
burial may become limiting.
Another step in selecting a suitable
process is to develop the specifications
the solidified wastes must meet. Such
specifications should include:
• Leachability
• Free liquid content
• Physical stability and strength
• Reactivity
• Ignitability
• Resistance to biodegradation
• Permeability
Standards for testing stabilized/solidi-
fied wastes have not yet been devel-
oped. A suggested program of specifi-
cation and testing procedures arr
outlined in the Handbook.
Process Screening
Assuming that one or more stabiliza-
tion/solidification processes are identi-
fied as feasible by the selection proce-
dures, bench-scale or pilot scale studies
can be used to choose and refine the
most suitable technique. Areas of con-
cern investigated by these studies in-
clude:
• Safe waste handling procedures
• Waste uniformity
• Mixing and pumping properties
• Processing parameters
• Process control procedures
• Volume increases
A large stabilization/solidification op-
eration 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 pretreat-
ment 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 treat-
ment system is essential. The effects of
heat transfer on reaction rates as th,
system is scaled up must also be evalu
ated.
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Waste uniformity, and the mixing and
pumping qualities at various points
within the treatment system should also
be subject to study. Serious problems
can be caused by rapid viscosity in-
creases 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 ra-
tios, mix and set times, and volume in-
creases are among the most important
results of bench or pilot-scale testing.
Due to the heterogeneity of wastes and
many common treatment materials,
many of the process parameters will be
determined by trial and error. Moisture
content of wastes or treatment agents
can show wide variability, and signifi-
cantly alter mix ratios.
Process Operation
Full-scale operation of a solidification
process requires detailed planning and
cost comparisons. The first planning
step involves the characterization, test-
ing and process selection efforts de-
scribed above. The second phase of
planning involves the development of
*he operation plan, including equip-
lent 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. The four types
of mixing commonly used are in-drum,
in-situ, plant and area.
Project sequencing and scheduling
are largely determined by the type of
mixing technique employed. The first
step generally involves preparation of
the site and construction of any neces-
sary facilities. These could include exca-
vation of an inground mixing pit, or con-
struction 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 separations. The actual proc-
essing of the wastes then takes place,
along with the process control monitor-
ing. 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 proc-
essing operation must take into account
costs for:
Treatment reagents
- Labor
• Materials
• Equipment
• Cleanup
• Overhead and profit
These will depend on the solidification
technique employed, the amount of
waste to be processed, and many other
site-specific constraints.
The number of waste processing,
handling, and mixing technologies is
highly varied, as is the number of treat-
ment reagent-waste formulations.
Waste and site characteristics, and
reagent cost and availability are the
major factors which must be weighted
in project planning to ascertain the most
cost-efficient and reliable containment
strategy.
The full report was submitted in par-
tial fulfillment of Interagency Agree-
ment No. AD-96-F-2-A145 by the U.S.
Army Engineer Waterways Experiment
Station under the sponsorship of the
U.S. Environmental Protection Agency.
M. John Cullinane, Jr., Larry W. Jones, and Philip G. Ma/one are with the
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS 39180;
the EPA author Terry M. Bliss is with the Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH 45268.
Janet M. Houthoofd is the EPA Project Officer (see below).
The complete report, entitled "Handbook for Stabilization/Solidification of
Hazardous Waste," (Order No. PB 87-116 745/AS; Cost: $18.95, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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