United States
                   Environmental Protection
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
                   Research and Development
EPA/600/S2-89/034 Jan. 1990
4>EPA          Project Summary
                   Cleaning  Excavated  Soil  Using
                   Extraction  Agents:
                   A  State-of-the-Art  Review
                   R. Raghavan, E. Coles, D. Dietz
                    In response to the RCRA Hazardous
                   and Solid Waste Amendments of 1984
                   prohibiting  the  continued  land
                   disposal  of  untreated  hazardous
                   wastes, the U.S. Environmental
                   Protection  Agency (EPA) has
                   instituted  a research and develop-
                   ment program for new technologies
                   to treat RCRA and Superfund wastes.
                   As part of this  research program,
                   technologies  applicable to  cleaning
                   excavated soils were reviewed.
                    This report reviews the state-of-the-
                   art of soil cleaning technologies and
                   their applicability to Superfund sites
                   in  the  United States. The review
                   includes  Superfund  site soil and
                   contamination  characteristics;  as
                   well as soil washing technologies,
                   their  principles  of operation, and
                   process parameters.  The technical
                   feasibility of using  soil washing
                   technologies  at Superfund sites in
                   the United States is assessed.
                    Contaminants  are classified as vol-
                   atile, hydrophilic, or hydrophobic
                   organics;  PCBs;  heavy  metals;  or
                   radioactive material. Soils are classi-
                   fied as either sand, silt, clay, or  waste
                    Three generic  types of extractive
                   treatments are identified for cleaning
                   excavated soils: water washing aug-
                   mented with  a  basic or surfactant
                   agent to remove organics, and  water
                   washing with an acidic or chelating
                   agent to remove organics and  heavy
                   metals; organics-solvent  washing to
                   remove hydrophobic organics and
                   PCBs; and air or  steam stripping to
                   remove volatile organics.
  Although  extraction  of organics
and toxic metal contaminants from
excavated sandy/silty soil that is  low
in clay and humus content has been
successfully demonstrated at several
pilot-plant test facilities,  extraction
from clay and humus soil fractions is
more  complicated  and requires
additional pilot-scale testing before
application at Superfund sites.
  This Project Summary was devel-
oped  by EPA's  Risk  Reduction
Engineering Laboratory, Cincinnati,
OH, to announce key findings of the
research  project  that  is  fully
documented in a separate report of
the same title (see  Project Report
ordering information at back).

  Under  the Comprehensive  Environ-
mental Response,  Compensation,  and
Liability  Act of  1980 (CERCLA)  as
amended by the Superfund Amendments
and Reauthorization Act of 1986 (SARA),
cleanup activities at hazardous waste
sites must reduce the  toxicity, mobility,
and volume  of hazardous substances.
The 1984 Hazardous and Solid Wastes
Amendment  (HSWA) to the Resource
Conservation and Recovery Act (RCRA)
was created in large part in response to
citizen concerns that existing methods of
hazardous waste  disposal,  particularly
land disposal, were not safe.
  The  land  ban provisions of  the  1984
RCRA amendments have given  con-
siderable impetus to developing more
economical  and effective means of
treating hazardous  waste. EPA is  now
sponsoring research on new treatment
technologies to destroy, detoxify, or

incinerate hazardous waste; on ways to
recover and reuse hazardous waste; and
on methods to decrease the volume of
hazardous  waste requiring treatment or
disposal. On-site treatment technologies
that  remove contaminants  or decrease
contaminant levels  may  achieve better
hazard  control  than  containment
techniques.  In addition,  as  landfill
disposal becomes more  expensive and
as hazardous  waste transportation  is
more stringently regulated,  on-site waste
treatment technologies will become more
desirable—if   they  are  technically
demonstrated,  environmentally safe, and
economical. One of the  research  areas
initiated by the EPA is use of extraction
agents for   washing  excavated
contaminated soil.  Washing excavated
soil holds promise for being applicable to
all contaminants.

Soil Washing for Safe On-site
  Soil washing employing  extraction
agents consists of soil excavation, above-
ground  treatment,  isolation and  removal
or destruction of the contaminant, and
redeposit of the cleaned soil. Each of the
above-ground  treatment  techniques  for
separating the contaminant from the  soil
uses  an extraction  agent~a liquid, gas,
chemical additive,  or combination  of
agents-that mobilizes  the  contaminant,
which  is  chemically  or physically
attached to the soil particles.
  This report  reviews  the  technologies
that  may be  applicable for cleaning
excavated soil. Physical  separation and
extraction technologies are examined and
evaluated for their  applicability to soil
  Specifically, this report:
  1.  surveys the contaminants  (by type
and concentration) and soil (by type and
quantity) at the  various National Priority
List  (NPL)  sites to define the  most
frequently occurring problems  at these
  2.  reviews the  extractive treatment
technologies  that  have  potential  for
cleaning the contaminants from soils, and
  3.   recommends  areas for future

Patterns of Contamination at
NPL Sites
  The choice of soil  washing method  will
depend on the type of contaminant and
type of soil at the  site. Therefore, NPL
site  information  files were surveyed  to
determine  the  contaminants and  soil
types prevalent at these sites.
  To determine! the patterns of contam-
ination at NPL I sites, contaminants are
categorized into| major groups from a soil
washing  perspective,  based on  the
following soil washing parameters:
  « water solubjlity
  • vapor pressure
  • octanol/water partition coefficient
  • density
  These parameters are  used  to create
contaminant categories:
 • • hydrophilic organic  compounds
    (volatile and nonvolatile)
  • hydrophobic organic compounds
  • volatile organic compounds
  • heavy metals
  • PCBs     i
  « radioactive hnaterial
  • other organ(cs
  Soil is classified according to its major
particle size fraction as sand, silt, or clay.
Since the soil  and contaminants together
determine  the  effectiveness  of  a
particular  soil! washing  method,  the
contaminant arjd  soil  types are cate-
gorized  under  one of 32 soil-contaminant
type  pairs.  Derived from  soil  and
contaminant data  at 82  NPL sites  in
USEPA's  Region  II (consisting of  New
York,  New Jersjey, Puerto Rico, and the
Virgin  Islands); these  soil-contaminant
type pairs are listed together  with their
frequency of  occurrence. Three  pairs
occur at significantly greater frequency
than do  the remaining 29 pairs. These
are hydrophobic  volatile compounds,
hydrophobic nonvolatile compounds, and
heavy metals-all  of them  in sites with
sandy soil.

  Three major bxtraction  techniques are
used to  clean [soil: water washing with
extractants, solvent extraction, and  air
stripping.      >
  Water washing with extractive agents is
applicable for  cleaning nonvolatile
hydrophilic and hydrophobic  organics
and heavy metals from soil. The solvent
extraction processes show potential  for
cleaning  nonvplatile hydrophilic and
hydrophobic organics from soil. Air strip-
ping processes are  limited  to cleaning
soil of volatile organics.
  Most  of  the
involve  mixing
soil cleaning processes
the extractant with  soil,
followed by solid/liquid separation where
the cleaned so'il  is separated from the
extractant fluid.} The extractant is then
cleaned of the contaminant and recycled
as required.    j

Water Washing
  In water washing with extractive agents,
the washing  solutions can be  basic
aqueous  solutions  (caustic, lime,  slaked
lime,  or  industrial  alkali-based  washing
compounds);  acidic  aqueous  solutions
(sulfuric,  hydrochloric, nitric, phosphoric,
or carbonic  acids);  or solutions with
surfactant or  chelating  agents.  Use  of
hydrogen peroxide, sodium hypochlorite,
and  other oxidizing  agents,  which
chemically change  the contaminants,
often  facilitates the washing process. A
strong (highly ionized) basic or surfactant
solution can be used for some  organics
extraction,  and strong  (highly  ionized)
acidic or chelating agent solutions can be
used for metals extraction.
  In cleaning  soil by  aqueous extraction,
large  objects  -are removed by screening
and then cleaned separately. The soil is
then  mixed thoroughly  with water  and
extraction  agents  to  remove  the
contaminants from  the  soil.  This  is
followed by solid/liquid separation where
the coarse  fraction   of  the   soil  is
separated.  The  extraction  agent with
contaminant and smaller  soil  particles
(clay  and  fine silt)  undergoes further
solid/liquid  separation  where  fine  soil
fractions are  separated  as much  as
possible.  The extraction  agent is cleaned
and recycled. The  separated soil fraction
undergoes  post-treatment where it  is
cleaned of any residual extraction fluid.

Solvent Extraction
  Solvent  extraction  using  organic
solvents  may be  used to clean  soil
contaminated  with  high concentrations of
nonvolatile  hydrophobic organics.
Hydrophilic organics  can be removed by
solvent extraction but are most effectively
removed  by water washing, as discussed
previously. The choice of a  suitable
solvent depends primarily on  chemical
structure of  the  contaminant,   solvent
extractive  capacity,  soil  type,  and
equilibrium  characteristics. In addition to
these, the solvent  should  be stable  and
must  have  favorable  density, viscosity,
and interfacial tension properties. There
should be a sufficient difference  between
the boiling  points  of the  contaminated
solute and  the solvent to  facilitate post-
treatment separation.
  Leaching and immersion extraction  are
the two general extraction  techniques. In
its most typical form, leaching is a batch
extraction operation  in which  the
screened soil  is deposited  in a screened-
bottom tank  inside retaining walls,  and
solvent is sprayed over it. The solvent
leaches the contaminant  from the soil.
  For low-solubility  contaminants,  fine
soils like clay and silt or soils with a very
low residual  contaminant  content,  the
leaching  process  is  unacceptable   be-

cause of slow mass transfer rates. For
these cases,  the solid  is dispersed into
the liquid in an immersion extraction.  In
its simplest form, an immersion extractor
is an agitated tank filled with the solvent,
in  which the soil  is  suspended  and
thoroughly  mixed.  When the extraction
equilibrium  has  been  reached,  the
agitation is  stopped  and  the  solids
allowed to settle.
  The most easily treated soil is a coarse
sand  that  retains, after free gravity
drainage,  approximately  2 to 3 wt%
solvent.  For finer-grained soils,  centrifu-
gation or  thermal desorption may  be
necessary to obtain low solvent residuals.
  Soil/solvent separation  must  be
effected to recycle solvent. For coarse
easy draining soil, solvent is separated
by  gravity  drain.  For hard-to-settle soil
the operation  requires centrifugation  or
filtration.  Residual solvent  is normally
removed  from separated soils by either
solvent displacement  or  gas, steam,  or
vapor stripping.
  Contaminants are generally removed
from the solvent by distillation, assuming
a difference in boiling  point for the sol-
vent and contaminated material;  other-
wise an extractive technique  may first be
needed. Small amounts  of  contaminant
may be recycled  with the  solvent and
may be  present  in a subsequent soil

Air Stripping
  Air stripping is normally used  to
remove  volatile  organic  compounds
(VOCs) from  soil.  To  strip  VOCs from
soil, the VOCs must be  vaporized. The
stripping  may  be done  at ambient
temperatures,  or heat  may  be  used  to
increase the rate of vaporization. Air and
steam are the most  commonly  used
stripping gases.  Adsorption  or  com-
bustion removes VOCs from  a circulating
air  stream. When steam  is used  as the
stripping medium, the  steam  can  be
removed  by  condensation, and  a
relatively  concentrated  vapor  of VOC
remains for disposal.
  In  general, any  system  that  is
employed to dry solids  can also strip
VOCs from soil. These systems consist
of:  a gas/solids  stripping  device;  a
stripping  gas  circulating  device;  and a
means to remove, recover, or destroy the
VOCs in the stripping gas.

Results and Discussion

Water Washing
  To date, several aqueous extraction
systems for cleaning excavated contam-
inated soil have been demonstrated on a
pilot scale; some of these soil pretreat-
ment/extraction  methods  are  listed in
Table 1.

Solvent Extraction
  Large quantities of solids (ores, sugar
beets,  etc.)  have been  extracted using
continuous  countercurrent extractors
such  as  Dravo's Rotocel (rotary-type)
Endless-Belt  Extractor,* Lurgi's  Frame
Belt Extractor, the DeSmet  Beit Extractor,
and the BMA Diffusion Tower. Some of
these solvent extraction  processes  used
for treating soil are listed  in Table 2.

Air Stripping
  When treating soils that adhere  and
form large particles (i.e., are fine-grained
and  tend  to  agglomerate), a  Holo-flite
screw, rotary kiln/dryer,  or  Hereschoff
furnace may be used for stripping.
  When processing granular free-flowing
sandy  soils, which disperse easily, fluid
bed  combustors of  the circulating or
bubbling  types are  applicable. Table  3
describes this  equipment and  states
process operating conditions.

Conclusions and
  The following  conclusions  have
emerged from  this  literature  review of
theoretical, bench-scale, and  pilot-scale
investigations of state-of-the-art tech-
nologies  for  the  extraction  of
contaminants from soil.
  • Pilot-scale tests conducted by TNO,
    Heijmans,  HWZ  Bodemsanering,
    BSN,  and  Ecotechniek show  that
    sand or silt can be washed.
  • Above-ground extraction of organics
    and heavy  metals  from sandy  soil
    containing very low  levels of clay is
  • Above-ground extraction of organics
    and  heavy  metals  from clay  soil
    fractions  has not been demonstrated
    on a pilot scale.
  • Separation of the extractant from the
    soil and regeneration of the  ex-
    tractant  have not  been successfully
    demonstrated for clay soils.
  • Contaminant extraction experience
    does provide enough  information to
    support a decision on the technical
    feasibility of applying soil washing at
    NPL sites.
  • More applied pilot-scale testing must
    be  conducted  to  support any
    statement  on the environmental and
    economic  practicability of  extraction
  • Experience with contaminant removal
    via water washing at the bench, pilot,
    and  prototype  scales   supports
    application of the  technology  for
    cleaning  sandy  and  silty  soils.
    Economic competitiveness  of soil
    washing compared  to other remedial
    technologies such as incineration or
    fixation is  indicated. Further study is
    needed to  establish  fixed and
    operating costs  for  aqueous
    extraction of soil contaminants.
  A  program  is   needed that   would
include the following components:
  • Characterization of  soil at  NPL sites
    from a soil washing perspective. This
    would  include particle  size dis-
    tribution, mineralogical observations,
    physical and chemical analyses, etc.
  • Bench-scale testing to establish the
    required processing configurations
    and operating conditions for the
    various  wastewater treatment and
    regeneration subsystem options.
  • Preliminary process design,  sizing,
    and costing of  a  modular  trans-
    portable  pilot-plant  system  to
    determine process economics  for
    comparison  with  incineration and
    other remedial technologies.
  • Design,  construction, and  operation
    of a modular transportable pilot-scale
    unit to demonstrate its applicability at
    selected NPL sites.
  • Research  and  development efforts
    toward broadening the application to
    washing of high-clay  soils,  if eco-
    nomically justified.
 "Mention of trade names or commercial products
 does  not constitute  endorsement or  recom-
 mendation for use.

Table 1.
Aqueous Phase Extraction Processes
       Aqueous Extraction Process
Netherland's bromide removal from sand   Pilot scale
(Netherlands Organization for Applied       \
Research)                               '
                                          7982    Organic bromide compounds
                                                  removed from sandy soil
                                                  containing less than 10% clay
                                                  and humus. Extract/on agent
                                                  was caustic solution (pH > 11).
                                                  Extractant-to-soil ratio: 2:1.
Heijmans Milieutechniek extractive
cleaning of heavy metals and cyanide
from soils
                            • 10-15        1985    Process has potential for
                            I                      cleaning soil contaminated with
                            I                      cyanides, heavy metals, and
                                                  water-immiscible and low-
                            i                      density hydrocarbons.
HWZ Bodemsanering extractive cleaning
of cyanide-contaminated sandy soils
                               20         1984    The extracting agent used is a
Ecotechniek thermal washing of sandy soil   ,   20
contiminated with crude oil                '
                                          7982    Sands containing 200,000 ppm
                                                  of oil were cleaned to approx.
                                                  20,000 ppm.
Bodemsanering Netherlands (BSN) high-    \   20
pressure washing of sandy soil             \
contaminated with oil                      i
                                          1983    This plant is transportable.
Klockner Umwelttechnik high-pressure       j 75-40
water jet for cleaning contaminated sandy   j
so;7s                                     :
                                          7987    This process is a modified
                                                  version of the BSN process
                                                  and is effective for cleaning
                                                  soils with fines (<63 im) not
                                                  exceeding 20%. Water
                                                  pressure 5,075 psi.
Harbauer soil cleaning system
EWH-Alsen-Breitenburg cleaning of sandy  Pilot scale-
soil contaminated with oil
                            I   40         1987    This wet extraction process
                            I                      uses hydraulically produced
                            :                      oscillation/vibration to achieve
                            I                      initial separation of soil
                            j                      particles and contaminants.
                            I                      So;7 recovery is approximately
                            !                      95% of input volume.

                                          Not     Custom reagents added to
                            8 to 10     Available   water. Water-to-soil ratio is 1:1;
                             m3lhr                cleaning efficiency is 95%.
Lee's Farm lead extraction from soils      Pilot scale-
                                          1985    Crushed soil (lead contarni-
                                       (for short  nated) was washed with a 30%
                                       duration)  EDTA aqueous solution using
                                                  an inclined-screw washing unit.
                                                  Tests were used to specify
                                                  equipment that can handle
USEPA's extraction of spilled hazardous    Pilot scale-
matdrials from excavated soil              !   6
                                          7984    Process using EDTA removed
                                        (limited   97% of the lead in soil
                                       operation)  containing 47,000 ppm. The
                                                  plant is mobile.

Table 2.      Solvent Extraction Processes

  Solvent Extraction Process	Capacity (scale)
                                           Year Operation
CF Systems Corporation
Cambridge, MA
                                    Pilot Scale
              Commercial scale, 1,000
Basic Extraction Sludge
Treatment (BEST)
            Prototype commercial scale,
                WO tons/day design
1984         A kerosene-water solvent removes PCBs from
             soil. The PCB leaching percentage is 84%.
             Kerosene is recovered, decontaminated, and
             recycled. Kerosene residuals in soil have been
             about 25% of the kerosene charged.

1988         Propane at or near its critical point is used to
             dissolve organic contaminants present in a
             sludge-water slurry. Typically, 99% of the
             organics are extracted from the sludge.
             Propane is separated from the organics by
             flashing, and then is recompressed, cooled,
             and recycled to the extractor.

1986         Triethylamine (TEA) extracts oil from oily
             sludges. TEA is soluble in water below 65°F,
             insoluble above 65 "F. Hazardous oil is
             recovered, not destroyed. Operation of this
             multi-step process is highly sophisticated.
  Table 3.
    Volatile Organic Stripping
        Equipment Name
Equipment for Air Stripping VOCs from Soil

                	Equipment Description
                                                                                 Process Operating Conditions
   Holo-Flite™ Screw
   Rotary Kiln/Dryer
   Hereschoff Furnace
   Circulating Bed Combustor
   Bubbling Bed Combustor
               A jacketed trough houses a double-screw
               mechanism. Heat transfer medium enters the
               hollow screw shafts and flights (indirect
               heating). Air contracts soil directly. Removal
               efficiency 99%.

               Rotating Drum. VOCs  can be evaporated
               using direct or indirect heating.
               Soil fed to the center of the top tray is moved
               by rotating flights to the outer edge, falls to
               second tray, moves to center on second tray,
               falls to  third tray, etc.; gas moves counter-
               current to the soil. ID fan required.

               Hot gas flows countercurrent to soil and
               entrains the soil. Entrained soil is separated
               from hot flue gases in a cyclone and
               recirculated to the bed. A solids draw-off is

               Gas is blown from a distributor at bottom of
               bed. Bed is maintained below fluidization.
                                                                         Soil discharge temp. = 50° to 150°C. Soil
                                                                         residence time = 30 to 90 mm. Air inlet temp.
                                                                          = ambient to 90°C. Circulating oil temp. =
                                                                         100° to 300°C.
           Temperature in the kiln controlled at 100° to
           400°C if the character of the soil is to be
           maintained (or to avoid fouling the walls)

           Temperatures to 500°C are attainable.
                                                                         Requires free-flowing soil feed.
                                                                         Residence time controlled by bed height or
                                                                         soil feedrate.
                                                                              U. S. GOVERNMENT PRINTING OFFICE: 1990/748-012/07207



  A Raghavan, E. Coles, and D. Dietz are with Foster Wheeler Enviresponse, Inc.,
        Livingston, NJ 07039.
  Dar/ene Williams is the EPA Project Officer (see below).
  The complete report, entitled "Cleaning Excavated Soil \Using Extraction Agents:
        A State-of-the-Art Review," (Order No. PS 89-212  757/AS; Cost: $15.95,
        subject to change) will be available only from:    \
            National Technical Information Service      '•
            5285 Port Royal Road
            Telephone: 703-487-4650
  The EPA Project Officer can be contacted at:
            Releases Control Branch
            Risk Reduction Engineering Laboratory      :
            U.S. Environmental Protection Agency
            Edison, NJ 08837
United States
Environmental Protection
Center for Environmental Research
Cincinnati OH 45268
   PERMIT No. G-35
Official Business   •
Penalty for Private  Use $300