Note: Descriptions are shown in the official language in which they were submitted.
CA 02260611 1999-01-27
1
TITLE:
TREATMENT OF SOIL
CONTAMINATED WITH HAZARDOUS RESIDUES
Field of the Invention
The present invention relates to a method for the
treatment of soil materials contaminated with hazardous
hydrophobic organic substances or residues, and in
particular to a method for removal of such hazardous
hydrophobic organic substances in which the soil material
is substantially comprised of clay and/or sand.
Hazardous organic substances or residues are referred to
herein as "organic contaminants". As noted herein,
organic contaminants may include hydrocarbon materials
e.g. oil, provided such materials are present in a minor
amount.
Reference is made herein to the use of adsorbent
materials. However, it is to be understood that those
materials might also exhibit absorbent properties with
respect to the organic contaminants or combinations of
the contaminants with oil or other mobilizing agents. In
addition, as used herein, soil includes clays and sands.
Background of the Invention
Owners of sites containing soils contaminated with
hazardous substances may be required by governmental or
other regulations to remediate these materials. Examples
of known methods of doing so include application of
biological, physical or chemical methods to remove or
stabilize/destroy the substances, or to transfer the
contaminated material to approved off-site landfills.
The methods used to remediate solid materials include
bioremediation, aqueous soil washing including use of
surfactants, soil extraction with organic solvents,
thermal desorption and incineration. Although such
methods may be effective, they also tend to be expensive.
CA 02260611 1999-01-27
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There is substantial interest in development of cost
effective methods for removing or remediating organic
contaminants from solid particulate materials such as
soil. Because of the low solubility of these organic
contaminants in water, such contaminants tend to tightly
adsorb on or absorb into the solid materials and
consequently are less amenable to biodegradation by
microorganisms, which normally requires an aqueous phase
for growth and metabolism.
It has been observed that the degree of difficulty
of extracting or remediating organic contaminants from
soil increases with an increased content of clay and/or
humic substances or organic carbon in the soil.
More economic methods for removal of hazardous
contaminants from soils are required for purposes of
remediating the soil and to prevent contaminants from
spreading through the soil and/or to prevent
contamination of groundwater.
Summary of the Invention
A method for remediating soils containing hazardous
organic contaminants has now been found.
Accordingly, one aspect of the present invention
provides a method for remediating soil containing organic
contaminants, comprising:
a) forming an aqueous slurry of a mixture of a
hydrophobic adsorbent selected from foamed synthetic
materials with said soil in the presence of water, the
adsorbent having a density less than water;
b) mixing said slurry for a period of time; and
c) effecting a gravity separation of the adsorbent
from the aqueous admixture thus obtained.
In another aspect, the present invention provides a
method for removal of organic contaminants from solid
particulate soil contaminated with the organic
contaminant, comprising:
a) forming an aqueous slurry of a mixture of a
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hydrophobic adsorbent selected from natural materials
which entrap gas, and cellular or foamed materials
prepared by synthesis or modification of natural fibres
with said soil in the presence of water, the adsorbent
having a density less than water;
b) mixing said slurry for a period of time; and
c) effecting a gravity separation of the adsorbent
and sorbed organic contaminant from the aqueous admixture
thus obtained.
In a preferred embodiment, the adsorbent is a
natural material with entrapped gas-containing pores.
In preferred embodiments of the methods of the
present invention, the slurry is subjected to a step to
permit settling of soil and other particulate prior to
effecting separation of the adsorbent.
In further embodiments, the admixing of the slurry
effects contact between the adsorbent and the soil.
In a further embodiment, a mobilizing agent may be
added to the aqueous slurry to promote better
mobilization of the contaminant from the soil particles
to the adsorbent and/or for better sorption.
In a still further embodiment, the hydrophobic
liquid may be added and mixed with the soil prior to
addition of water to form an aqueous slurry.
In another embodiment, a surfactant is added to the
slurry to effect separation of the organic contaminant
from the soil, said surfactant being selected in an
amount that does not inhibit adsorption of the organic
contaminant on the adsorbent.
In yet another embodiment, the water content of the
aqueous slurry is at least 25% by weight of the soil,
especially 25-100% by weight.
In a further embodiment, the soil is comprised of
clay and/or sand.
Detailed Description of the Invention
The method of the invention involves mixing the
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soil, water, with or without any other agents e.g. oil
material, and the adsorbent, thereby forming a slurry.
These components may be added and mixed with the soil in
a single operation or by adding and mixing individual
components in any sequence. Mixing may be accomplished
using processes known in the art, including using
reactors, tanks with air spargers, impellers, rakes,
screw assemblies or stirrers, rotating drums e.g. similar
to a cement mixer, tumblers, reactors on reciprocating or
orbital shaking machines, vibration or sonication mixers
and screw or other conveyor equipment.
The slurry is preferably directed to a settling
step, which may be accomplished in the mixing vessel or a
following conveyance, including by pouring or other
transfer of the slurry to a separating vessel. The
separating vessel may or may not contain additional water
to promote separation of soil and adsorbent. The mixing
and/or separation stages may be carried out in a batch or
continuous mode.
The separated floating organic contaminant/adsorbent
material is recovered and may be further processed by a
variety of methods e.g. compression, heating or washing.
The adsorbent binding the organic contaminant may be
volume reduced by thermal or solvent treatment or by
using other physical or chemical methods which melt the
polymer and destroy the cellular structure or
depolymerize or otherwise modify the polymer, or the
adsorbed organic contaminant or the mixture.
In the method of the present invention, an aqueous
slurry is formed from a mixture of a hydrophobic
adsorbent and soil. The soil may be obtained from a wide
variety of sources, and is soil that has been
contaminated with an organic contaminant. The soil is a
solid particulate, which may be in a variety of forms.
Hazardous organic contaminants that may be treated
by the method of the invention include aliphatic,
aromatic, polycyclic aromatic, heterocyclic and other
CA 02260611 1999-01-27
cyclic compounds, and derivatives of such compounds,
especially derivatives containing halogen, nitrogen,
sulphur and/or oxygen atoms. Examples of toxic compounds
include polycyclic aromatic hydrocarbons (PAHs);
5 polychlorinated biphenyls (PCBs); phthalate esters;
phenols and chlorinated phenols; pesticides and
herbicides and related structures; chlorinated ethanes,
ethylenes and methane; monoaromatics including BTEX
compounds; dioxins and furans; nitrotoluenes and
nitrobenzenes. BTEX is a mixture of benzene, toluene,
ethyl benzene and xylene. The method of the invention
may also be used to treat other known hazardous organic
contaminants, unidentified toxic substances and mixtures
of toxic organic components.
A variety of adsorbent materials may be used, which
as discussed above may also exhibit absorbent properties
towards the organic contaminants. Examples of adsorbents
are given below. The preferred adsorbents are
hydrophobic and float in water e.g. have a density of
less than one, and are particularly effective in
promoting flotation of the hydrophobic adsorbent with
associated organic contaminant.
The adsorbent materials are foamed synthetic
materials, especially polymeric foams or cellular
polymers, which contain a large number of pockets or
pores which entrap gas and substantially decrease the
apparent density of the material. When the cells or
pores are interconnected, the material is described as
open-celled, whereas when cells are discreet, they are
termed closed celled. The foamed synthetic materials,
which may be rigid or flexible, are produced by
production methods including methods including extrusion,
expansion, froth foaming, compression and injection
moulding and sintering.
Examples of foamed synthetic materials are foams of
synthetic materials of polystyrene, polyvinylchloride,
polyethylene, polyurethane, epoxy and phenolic and urea-
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formaldehyde resins, silicones, cellulose acetate,
polytetrafluoroethylene, ebonite, natural and foam
rubber. Other foamed polymers include novel biodegradable
foam materials incorporating modified polysaccharides,
including starches. The foamed synthetic materials, may
be mixtures of polymers or copolymers. For example, the
susceptibility of polystyrene foams to attack by some
petroleum solvents led to the development of styrene-
acrylonitrile copolymers which are resistant to these
materials.
The foamed synthetic materials may be in a variety
of shapes and sizes including sheets, discs, spheres,
other shapes, extruded cylindrical fibres (spaghetti), as
well as in other various forms including irregular shapes
produced by disintegration of larger moulded materials.
Key properties for the invention are the hydrophobic
properties of the foam surfaces promoting selective
sorption of hydrophobic oil components and their low
apparent densities which when coupled with moisture
resistance provides high buoyancy or flotation
characteristics. This facilitates separation of the
particles containing sorbed organic contaminants from the
heavier solids and aqueous liquid phases. Closed-cell
structures tend to maximize flotation characteristics.
Foams can also be classified as rigid or flexible.
In general, more rigid foams are preferred for flotation
applications.
Example of ranges of densities of some rigid foam
plastics are polystyrene, 32-160 kg/m3; polyvinyl
chloride, 32-64 kg/m'; polyurethanes 32-128 kg/m3;
cellulose acetate 96-128 kg/m3 phenolic forms, 32-64
kg/m3. Polystyrene foams produced by the decompression
expansion process have a density in the range of 23-53
kg/m3.
In addition, adsorbents that may be used in the
method of the invention include natural materials having
pockets which entrap gas, for example, particles of
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lignocellulose, cellulose or other plant materials which
contain gas filled pores. In addition, cellular or
foamed materials prepared by synthesis or modification of
natural fibres or polymers including cellulose,
lignocellulose, starches, proteins and lipids,
combinations of these and mixtures of natural polymers
and synthetic chemicals or copolymers may be used.
The choice of preferred adsorbents will be
determined by a variety of considerations, including
flotation and sorption properties. Highest flotation
efficiency is observed with adsorbents having limited or
no external pores, e.g. expanded polystyrene beads with a
surface "skin". Maximum sorption is observed with
cellular adsorbents which have an external open pore
structure. Materials which have external pores allowing
effective binding of contaminant and/or penetration into
the adsorbent but which retain some gas filled cells will
promote high efficiencies of both sorption and
contaminant separation by flotation.
The adsorbent is not, however, limited to foamed
materials and may involve use of non-foamed adsorbent
particles which have a density of less than one. The
adsorbent may also be polymeric particles, both
hydrophobic and non-hydrophobic, which may be coated with
a hydrophobic surface layer.
The aqueous slurry used in the method of the present
invention preferably contains at least 25% by weight of
water, based on the weight of soil material, and
especially 25-100% by weight of water. Higher amounts of
water may be used, but such higher amounts tends to lead
to additional costs in the forming of the slurry. In the
subsequent separation of the adsorbent from the aqueous
mixture, the amount of water should be sufficient to
effect efficient floating of sorbent/contaminant above
the soil in the mixture. Thus, higher amounts of water
may be preferred e.g. at least 100% by weight of water
based on the weight of the soil material, and especially
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100-200% by weight, although higher amounts may be used.
The time period for mixing of the aqueous slurry of
adsorbent and soil may be varied, depending on the mixing
method.
Effective separation may normally be achieved by
gravity separation (flotation), but supplementary methods
may be used to improve the rate of separation, reduce
water content and/or reduce residual water content in the
soil.
Transfer of the organic contaminant from the sand or
soil particles to the added polymers in an aqueous medium
may be accelerated or facilitated by addition of a
mobilizing agent of a suitable oil or other solvent or
chemical capable of extracting or solubilizing the
organic contaminant. An amount of less than 20% by
weight of the soil is preferred. Such addition may be
before or after the aqueous slurry is formed. The type
and concentration of any solvent or chemical used should
promote contaminant mobilization from the sand or soil
particles but not inhibit adsorption of the contaminant
to the polymer. The mobilizing agent may consist of
natural oils from animal, microbial or vegetable oil
sources, hydrocarbon oils or other organic solvents which
can assist in transfer of the contaminant to the
adsorbent. Up to 25% by weight, especially up to 15% by
weight, of organic solvent may be added as part of the
mobilizing agent.
In a preferred embodiment, the mobilizing agent
added is a contaminant-solubilizing solvent or chemical,
or an animal or vegetable oil, or any combination
thereof, which is added to promote better contaminant
mobilization from the soil.
The method of the present invention may be operated
as a continuous process or as a batch process.
The method may involve a single extraction process
or a multiple extraction process where, following removal
of the separated organic contaminant-sorbent material,
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the soil is again treated with additional adsorbent. The
method of the invention may also be used as part of a
soil treatment train, where other physical, chemical or
biological methods are used as a pre-intermediate or
post-treatment to remove a portion of the organic
contaminant.
While the present application refers to the presence
of oil in the soil that is treated, it is understood that
the amount of any hydrocarbon contaminant e.g. oil is
intended to be a minor amount. In the event that the
hydrocarbon contaminant is not a minor amount, the method
of treatment is covered by a separate patent application
of Owen Ward and Ajay Singh filed concurrently herewith.
The present invention is illustrated by the
following examples.
EXAMPLE I
In this example, different kinds of foamed
polystyrene adsorbents were used, optionally in the
presence of peanut oil as a mobilizing agent, for the
removal of polyaromatic hydrocarbons (PAHs) from
contaminated soil. Garden soil, contaminated with
different polyaromatic hydrocarbons (about 2000 ppm of
total PAHs), was used in the form of a 50% (w/v) slurry.
The following adsorbents were tested:
Sorbent A. Foamed polystyrene (broken packing,
skinless, 4-6 mm)
Sorbent B. Foamed polystyrene (broken packing,
porous, 4-6 mm)
Sorbent C. Polystyrene beads (with skin, 4 mm)
Sorbent D. Polystyrene beads (with skin, 1.5 mm)
To 10 g contaminated soil were added 10 ml water,
0.25% (w/v) of adsorbent and 0.5% (v/v) of peanut oil and
the resultant mixture was put on a rotary shaker at 200
rpm for 24 hr. An additional 10 ml water was added and
the adsorbent was separated after settling of soil for 10
CA 02260611 1999-01-27
min.
Residual polyaromatic hydrocarbons in the soil were
measured using gas chromatography with a flame ionization
detector (GC-FID) (Shimadzu, Japan).
5 The residual PAHs in soil was determined by
extracting with 10 ml dichloromethane and centrifuging at
4,000 rpm for 5 min. The dichloromethane extract was
passed through a column containing florisil and sodium
sulphate to remove any residual oil and water. A one
10 microlitre sample was injected into the GC-FID system to
measure the concentration of individual PAHs.
The results obtained are given in Table 1.
CA 02260611 1999-01-27
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CA 02260611 1999-01-27
11
The results indicate that up to 90% of PAHs can be
extracted out of contaminated soil using a single
extraction, particularly when the polystyrene adsorbents
were used in the presence of the mobilizing agent.
Different adsorbent types performed similarly.
EXAMPLE II
Foamed polystyrene adsorbent A of Example I was used
in the presence of different concentrations of the
mobilizing agent (peanut oil) for the removal of
polyaromatic hydrocarbons (PAHs) from the contaminated
soil described in Example I. To 10 g contaminated soil
(about 2000 ppm of total PAHs) were added 10 ml water,
0.25% (w/v) of adsorbent and different concentrations of
peanut oil and the resultant mixture was put on a rotary
shaker at 200 rpm for 24 hr. An additional 10 ml water
was added and the adsorbent was separated after settling
of soil for 10 min.
Residual polyaromatic hydrocarbons in the soil were
measured using the procedure of Example I and the results
are shown in Table 2.
CA 02260611 1999-01-27
r-A
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CA 02260611 1999-01-27
13
The results indicate that PAHs were removed
efficiently at vegetable (peanut) oil concentrations of
0.5-1.0% by weight. While 71% of the naphthalene was
removed by the sorbent in the absence of mobilizing
agent, removal of other PAHs was less efficient under
these conditions.
EXAMPLE III
Foamed polystyrene adsorbent A was used in the
presence of different concentrations of peanut oil for
the removal of polyaromatic hydrocarbons (PAHs) from
weathered soil. To 10 g contaminated soil (- 1600 ppm of
total PAHs), 10 ml water, 0.25% (w/v) of adsorbent and
different concentration of peanut oil were added and put
on a rotary shaker at 200 rpm for 24 hr. An additional
10 ml water were added and the adsorbent was separated
after settling of soil for 10 min.
Residual polyaromatic hydrocarbons in the soil were
measured using gas chromatography with a flame ionization
detector (GC-FID) by Biorem Technologies Inc., Guelph,
Ontario.
Results are shown in Table 3.
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14
Table 3.
Components Peanut Oil 0.5% Peanut oil 1.0%
Acenaphthylene 40 61
Acenaphthene 41 97
Fluorene 55 70
Phenanthrene 23 37
Anthracene 59 62
Fluoranthene 29 29
Pyrene 51 90
Benzo(a)anthracene 71 74
Chrysene 81 76
Benzo(k)fluroanthene 74 82
Benzo(a)pyrene 70 83
Indeno & Dibenzo 62 95
Benzo(ghi)perylene 93 85
Total PAHs 58 73
About 58% and 73% total PAHs were removed in the
sorbent system containing the mobilizing agent peanut oil
at 0.5% and 1% concentrations, respectively. Removal
efficiencies of different PAHs ranged from 29% to 97%
with 1% peanut oil.
EXAMPLE IV
In this example, the effect of mobilizing agents (i)
peanut oil, (ii) a non-ionic surfactant Igepal CO-630 and
(iii) a combination of peanut oil and surfactant, were
tested using adsorbent A of Example I for the removal of
the volatile organic compounds, benzene, toluene, ethyl
benzene and xylenes (BTEX) from contaminated soil.
To 10 g contaminated soil (about 1000 ppm of total
BTEXs) were added 10 ml water, 0.25% (w/v) of adsorbent
and different concentrations of the mobilizing agent and
the resultant mixtures were put on a rotary shaker at 200
rpm for 4 hr. An additional 10 ml water was added and
the adsorbent was separated after settling of soil for 10
min.
CA 02260611 1999-01-27
Residual BTEX compounds in the soil were measured
using gas chromatography with a flame ionization detector
(GC-FID), using the procedure of Example I.
CA 02260611 1999-01-27
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CA 02260611 1999-01-27
17
The maximum BTEX removal (84%) was observed with
0.5% peanut oil. Increasing concentrations of surfactant
resulted in a decreased percentage removal of the BTEX.
A combination of peanut oil and surfactant was
ineffective.
EXAMPLE V
In this example, the effect of mobilizing agents (i)
peanut oil, and (ii) a non-ionic surfactant IgepalTM CO-
630, were tested using sorbent E (foamed polyolefin,
skinless, 4 mm) for the removal of trichloroethylene
(TCE) from contaminated soil.
To 10 g contaminated soil (containing up to 100 ppm
trichloroethylene) were added 10 ml water, 0.25% (w/v) of
adsorbent and different concentrations of peanut oil or
surfactant Igepal CO-630 and the resultant mixture was
put on a rotary shaker at 200 rpm for 4 hr. An additional
10 ml water was added and the polyolefin adsorbent/oil
was separated after settling of soil for 10 min.
Residual TCE in soil was measured using gas
chromatography with a flame ionization detector (GC-FID),
using the procedure of Example I, and results are shown
in Table 5.
Table S. Percentage removal of TCE from soil
Mobilizing agent TCE conc. TCE removal
(%) (ppm) (%)
None 100 58
None 40 70
None 20 65
None 10 53
0.1% Peanut oil 100 35
0.2% Peanut oil 100 37
0.2% Peanut oil 20 71
0.05% Igepal CO-630 20 72
0.05% Igepal CO-630 100 40
0.1% Igepal CO-630 100 33
At different concentrations of TCE, up to 70%
removal of TCE from contaminated soil was obtained by the
sorbent in the absence of any mobilizing agent. No
CA 02260611 1999-01-27
18
significant effect of mobilizing agent on TCE removal was
observed.
EXAMPLE VI
In this example, the effect of mobilizing agents
peanut oil, a non-ionic surfactant Igepal CO-630 and a
short chain fatty acid tributyrin were tested with
polystyrene adsorbent A for the removal of
pentachlorophenol (PCP) from contaminated soil.
To 10 contaminated soil (250 ppm PCP), 10 ml water,
0.25% (w/v) of adsorbent and different concentrations of
mobilizing agents were added and put on a rotary shaker
at 200 rpm for 24 hr. An additional 10 ml water was
added and the adsorbent/oil was separated after settling
of soil for 10 min.
Residual PCP in the soil were measured using gas
chromatography with a flame ionization detector (GC-FID)
after extraction of DCM:acetone (1:1) and results are
shown in Table 6.
Table 6. Percentage removal of PCP from soil
Sorbent type Mobilizing agent PCP removal
(%)
A None 35
A 0.2% Peanut oil 41
A 0.5% Peanut oil 77
A 0.05% Igepal 62
A 0.2% Igepal 67
A 0.5% Igepal 19
E 0.5% Tributyrin 78
Maximum removal of 77% and 78% PCP was achieved with
mobilizing agents peanut oil and tributyrin,
respectively.
EXAMPLE VII
In this example, the effect of mobilizing agents
CA 02260611 1999-01-27
19
peanut oil, a non-ionic surfactant Igepal CO-630 and a
combination of peanut oil and surfactant were tested with
polystyrene adsorbent A for the removal of dioctyl
phthalate (DOP) from contaminated soil.
To 10 g contaminated soil (up to 5000 ppm DOP), 10
ml water, 0.25% (w/v) of adsorbent and different
concentrations of peanut oil or surfactant Igepal CO-630
were added and put on a rotary shaker for 200 rpm for 24
h. An additional 10 ml water was added and the
adsorbent/oil was separated after settling of soil for 10
min.
Residual DOP in soil were measured using gas
chromatography with a flame ionization detector (GC-FID)
and results are shown in Table 7.
Table 7. Percentage removal of DOP from soil
DOP conc. Mobilizing agent DOP removal
(ppm) (%) (%)
2000 None 67
2000 1% Peanut oil 77
2000 0.1% Igepal 74
5000 None 17
5000 0.5% Peanut oil 50
5000 1.0% Peanut oil 63
5000 0.1% Igepal 41
5000 0.5% oil + 0.05% 39
Igepal
Maximum DOP removal by sorbent obtained with
vegetable oil and surfactant was 77% and 74%,
respectively. A combination of peanut oil and surfactant
was ineffective.
EXAMPLE VIII
The efficiency of removal of polychlorinated
biphenyls (PCBs) from contaminated soil by the mobilizing
agent (i) vegetable (canola) oil and (ii) mineral oil,
CA 02260611 1999-01-27
was tested.
Foamed polystyrene (broken packing, skinless, 2-4
mm) was used as adsorbent. The effect of mixtures of 90%
mobilizing agent with 10% acetone (w/w) was also tested.
5 To 475 g contaminated soil containing 250-440 ppm of
Aroclor 1260, 18% mobilizing agent (w/v) was added;
Aroclor 1260 is a mixture of PCB's with 60% chlorine
content, obtained from Monsanto. After mixing for 1 h,
the admixture was left stationary for 24 h. 200 ml water
10 and 0.5% (w/w soil) of adsorbent were added and mixed for
1 h. Separation and removal of the adsorbent was
facilitated by the addition of 50 ml of water. Another
0.5% (w/w soil) of adsorbent was added, mixed for 1 h,
and removed after separation.
15 Residual PCBs in the soil were measured using gas
chromatography. Results are shown in Table 8.
Table 8.
Mobilizing agent % Removal of PCBs from soil
Canola oil 75
90% Canola oil/10% acetone 85
Mineral oil 78
90% Mineral oil/10% acetone 93
20 The mobilizing agent containing mineral oil proved
to be the more effective. The presence of acetone in the
mobilizing agent increased the efficiency of PCB removal
from the soil.
EXAMPLE IX
The most efficient mobilizing agent was selected
from Example VII and used in a scaled-up test to monitor
the removal PCBs from contaminated soil using industrial
mixing equipment.
20 kg of soil contaminated with 250-440 ppm of
AroclorTM 1260 was mixed at 75 rpm for 1 h with 20%
mobilizing agent (w/w) made up of 90% mineral oil with
10% acetone (w/w) in a 6 ft3 mortar mixer. The mixture
was left stationary for 24 h. 5 kg of water and 0.5%
CA 02260611 1999-01-27
21
(w/w soil) broken foamed polystyrene were added and mixed
for 1 h. Another 5 kg of water was added to effect
separation of the polystyrene.
Analysis of the treated soil showed 90% removal of
the PCBs.
