United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-F-96-003
April 1996
vvEPA
A Citizen's Guide to
Solvent Extraction
Technology Innovation Office
Technology Fact Sheet
What Is solvent extraction?
Solvent extraction is a treatment technology that uses a
solvent (a fluid that can dissolve another substance) to
separate or remove hazardous organic contaminants
from sludges, sediments, or soil. (Sludge is a mud-like
material produced from industrial or sewage waste, and
sediment is fine-grained rock and mineral fragments
which have settled to the bottom of a water body such
as a river or lake.) Solvent extraction does not destroy
contaminants. It concentrates them so they can be more
easily recycled or destroyed by another technology.
When the soil enters an extractor (a tank where the con-
taminated soil is mixed with the solvent), the soil is
separated into three components, or "fractions." The
three fractions are: solvent with dissolved contami-
nants, solids, and water. Different contaminants con-
centrate into different fractions. For example, polychlo-
rinated biphenyls (PCBs) concentrate in the contami-
nated solvent, while metals are left behind in the solids
and water. Each fraction can be individually treated or
disposed of more cost effectively. A simplified drawing
of the solvent extraction process is illustrated in Figure
1 on page 2.
The solvent extraction process involves five steps:
• Preparation (sorting the contaminated material)
• Extraction
• Separation of concentrated contaminants from solvent
• Removal of residual solvent
• Contaminant recovery, recycling, or further treatment.
How does it work?
Treatment of contaminated soil is discussed in this
guide, but the method would be basically the same for
treatment of sludges or sediments.
The entire process is conducted on-site and begins by
excavating the contaminated soil and moving it to a
staging area where it is prepared for treatment. The soil
is then sifted to remove debris and rocks. The soil may
be processed in either a batch, a semi-batch, or a con-
tinuous mode. In the semi-batch mode, the material is
cycled through the extraction unit in increments. If the
soil is processed continuously, it may need to be made
more fluid so it can move easily through the process by
pumping. This is accomplished by adding water or, in
the case of oily sludges, adding solvents to the material.
A Quick Look at Solvent Extraction
Separates contaminants so they may be treated individually.
Is a transportable technology that can be brought to the site.
Reduces the volume of contaminated material.
Processes up to 125 tons of waste per day.
Is designed to operate without air emissions.
Printed on Recycled Paper
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The soil is placed in the extractor. Extractors can vary
in size. Some process 25 tons per day, while others
may treat over 125 tons daily and require setup areas of
1,500 to 10,000 square feet or more. (For comparison,
a tennis court covers about 4,000 square feet.) The sol-
vent is added to the extractor, and the soil and solvent
are mixed together. Consequently, the organic con-
taminants dissolve into the solvent.
A number of factors control the speed with which con-
taminants are dissolved from the soil. Some of these
controlling factors include temperature, moisture con-
tent, and the level of contamination. Each is critical to
the design of the treatment. Treatability studies per-
formed in a laboratory are required to determine how
much solvent is needed and how long the material must
remain in the extractor in order to assure maximum ef-
fectiveness. Since some solids may contain contami-
nants that require more than one cycle in the extractor,
this step of the process may need to be repeated.
The extraction process produces three fractions which
require separation:
• The contaminated solvent mixture.
• The treated soil which, depending on the concentra-
tions of contaminants present, may require a repeat
cycle or further treatment by some other technique.
• The water, which must be analyzed to determine if
further treatment is necessary before discharge to ei-
ther a publicly-owned treatment plant or other ap-
proved discharge area.
The separation process occurs next. The contaminants
are separated from the solvent either by changing the
pressure and temperature, by using a second solvent to
pull the first solvent out of the solvent/contaminant
mixture, or by other physical separation processes. At
the completion of this step, concentrated contaminants
result. Concentrated contaminants are removed during
the separation process, and the solvent is sent to a hold-
ing tank for reuse. The contaminants are then analyzed
to determine their suitability for recycle/reuse, or need
for further treatment before disposal.
Solvent extraction units are designed to operate with-
out giving off contaminated vapors or air emissions.
However, at some sites, air emissions could occur dur-
ing excavation or preparation of contaminated soil. If
air emissions exceed levels allowed by law, waste
preparation and handling procedures at the site must be
modified.
Figure 1
The Solvent Extraction Process
\
Contaminated Soil
Extractor
Treat
Again If
Necessary \ <
Recycled Solvent
Solvent with
Organic |
Contaminants
Concentrated
Contaminants
Separator
Water
(Further Treatment
or Disposal)
Oversized Debris
Treated Solids
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Why consider solvent extraction?
Solvent extraction can be both an effective and cost ef-
ficient process for separating hazardous contaminants
from non-hazardous materials and concentrating the
hazardous materials for further treatment. Because the
contaminants are separated, the treatment selected can
be targeted to the contaminant. As a result of solvent
extraction, some contaminants may be recycled or re-
used in manufacturing, thus minimizing disposal re-
quirements. The process has been effective in removing
organic contaminants from paint wastes, synthetic rub-
ber process wastes, coal tar wastes, drilling muds, wood
treating wastes, pesticide/insecticide wastes, and oily
wastes.
What contaminants can it treat?
Solvent extraction has been shown to be effective in
treating sediments, sludges, and soils containing prima-
rily organic contaminants, such as polychlorinated bi-
phenyls (PCBs), volatile organic compounds (VOCs),
halogenated solvents (solvents containing halogens,
which are bromine, chlorine, or iodine), and petroleum
wastes. These contaminants typically come from metal
degreasing, printed circuit board cleaning, gasoline, and
wood preserving manufacturing processes. Table 1 lists
the different solvents that are used. This technology is
generally not used for removing inorganics (i.e., acids,
bases, salts, and heavy metals) as these materials do not
readily dissolve in most solvents. Other treatment
methods exist to treat these contaminants.
• If the waste contains detergents or strong acids or
bases, solvent extraction may not be effective. Their
presence can reduce the amount of contamination
removed and slow the speed with which they are
removed.
• The presence of lead and other inorganics may inter-
fere with the removal of organic materials.
• Implementation can require complex engineering
considerations. For example, some systems include
compressed butane and propane, which require strict
management to prevent them from vaporizing and
igniting.
• Extensive pretreatment of the waste may be required
to remove or break up large clumps.
Where is solvent extraction being used?
Table 2 on page 4 lists some Superfund sites at which
solvent extraction has been selected as a treatment
method. In addition to using this technology at Super-
fund sites, solvent extraction is commonly used by
manufacturers in their day-to-day operations. Since sol-
vents are expensive raw materials that can be reused,
manufacturers, such as the dry cleaning and perfume
industries, regularly recycle the solvents used in their
manufacturing processes.
Will it work at every site?
Solvent extraction can be effective at separating hazard-
ous organic contaminants from some contaminated
soils, sludges, and sediments. It does not reduce the tox-
icity of the contaminants and, therefore, the final prod-
uct of the process (the concentrated residuals) still re-
quire treatment or disposal. Some of the limitations of
this technology include:
Table 1
Solvents Used in the Solvent Extraction Process
Liquid Carbon Dioxide
Propane
Butane
Triethylamine
Acetone
Methanol
Hexane
Dimethyl Ether
What Is An Innovative Treatment
Technology?
Treatment technologies are processes applied to
hazardous waste or contaminated materials to
permanently alter their condition through chemical,
biological, or physical means. Treatment
technologies are able to destroy or change
contaminated materials so they are less hazardous
or not hazardous at all. This may be done by
reducing the amount of contaminated material, by
recovering or removing a component that gives the
material its hazardous properties, or by immobilizing
the waste.
Innovative treatment technologies are those that
have been tested, selected, or used for treatment of
hazardous waste or contaminated materials but lack
well-documented cost and performance data under a
variety of operating conditions.
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Table 2
Examples of Superfund Sites Using Solvent Extraction
Name of Site Status** Type of Facility Contaminants
Carolina Transformer, NC In design Transformer repair Polychlorinated biphenyls (PCBs)
United Creosoting, TX In design Wood preserving Polyaromatic hydrocarbons (PAHs)
Arrowhead Refinery Co., MN Operational Waste oil refining Volatile organic contaminants (VOCs),
PCBs, PAHs, metals, solvents
Idaho Nat'l Engineering Lab (Pit 9), ID In design Nuclear research VOCs, PCBs
For a listing of Superfund sites at which innovative treatment technologies have been used or selected for use, contact
NCEPI at the address in the box below for a copy of the document entitled Innovative Treatment Technologies:
Annual Status Report (7th Ed.), EPA 542-R-95-008. Additional information about the sites listed in the Annual
Status Report is available in database format. The database can be downloaded free of charge from EPA's Cleanup
Information bulletin board (CLU-IN). Call CLU-IN at 301-589-8366 (modem). CLU-IN's help line is 301-589-8368. The
database also is available for purchase on diskettes. Contact NCEPI for details.
Not all waste types and site conditions are comparable. Each site must be individually investigated and tested.
Engineering and scientific judgment must be used to determine if a technology is appropriate for a site.
*As of August 1995
For More Information
Publications with "EPA" document numbers can be ordered free of charge by faxing your request to 513-489-8695
or writing to NCEPI at the address below. If NCEPI is out of stock of a document, you may be directed to other
sources.
National Center for Environmental Publications and Information (NCEPI)
P.O. Box42419
Cincinnati, OH 45242
Publications with "PB" document numbers are available by contacting the National Technical Information Service
(NTIS) at 1-800-553-6847. There will be a charge for these documents. Mail orders can be sent to:
National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161
Selected Alternative and Innovative Treatment Technologies for Corrective Action and Site Remediation: A
Bibliography of EPA Resources, EPA 542-B-95-001. A bibliography of EPA publications about innovative
treatment technologies.
Physical/Chemical Treatment Technology Resource Guide, EPA 542-B-94-008. A bibliography of publications
and other sources of information about soil flushing, soil washing, solvent extraction, and other
innovative treatment technologies.
Engineering Bulletin, Solvent Extraction, EPA 540-S-94-503, PB94-190477.
EPA Engineering Issue: Technology Alternatives for the Remediation of PCB-Contaminated Soil and Sediment,
EPA 540-S-93-506, PB94-144250/XAB.
WASTEd-P Monograph on Solvent/Chemical Extraction, ISBN #1-883767-05-9. Available for $49.95 from the
American Academy of Environmental Engineers, 130 Holiday Court, Annapolis, MD 21401. Telephone 410-266-
3311.
NOTICE: This fact sheet is intended solely as general guidance and information. It is not intended, nor can it be relied upon, to create any rights enforceable by any
party in litigation with the United States. The Agency also reserves the right to change this guidance at any time without public notice.
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