United States
Environmental
Protection Agency
Office of Solid Waste and
Emergency Response
Washington, DC 20460
Office of
Research and Development
Cincinnati, OH 45268
Superfund
EPA 540/2-91/009
April 1991
&EPA Superfund
Engineering Issue
Treatment of Lead-Contaminated Soils
Index
Introduction
Soil Characterization
Treatment Technologies for Lead-Contaminated Soils
Extraction
Solidification/Stabilization
Vitrification
Electrokinetics
Flash Reactor Process
Technology Contacts
References
Introduction
This bulletin summarizes the contents of a seminar on
treatment of lead-contaminated soils presented on August 28,
1990, to Region VSuperfund and RCRA personnel by members
of EPA's Engineering and Treatment Technology Support Center
located in the Risk Reduction Engineering Laboratory (RREL)
in Cincinnati, Ohio. This bulletin is intended to summarize
the information presented during the seminar and it should not
be viewed as a definitive treatise on lead treatment technologies.
The seminar was sponsored through EPA's Technical
Support Project (TSP). The Office of Solid Waste and Emergency
Response (OSWER) and the Office of Research and
Development (ORD) established the Superfund Technical
Support Project in 1987 to provide technical assistance to
Regional Remedial Project Managers (RPMs) and On-Scene
Coordinators (OSCs). The TSP consists of a network of Regional
Forums, four specialized Technical Support Centers (TSCs)
located in ORD laboratories, and one TSC at OSWER's
Environmental Response Team.
Technical presentations were made by David Smith and
Paul de Percin of EPA's RREL in Cincinnati, Ohio; Michael Royer
of RREL in Edison, New Jersey; and Radha Krishnan, P.E., of
PEI Associates, Inc., in Cincinnati, Ohio. The seminar was
coordinated by Louis Blume and Steve Ostrodka of EPA Region
V.
Lead is one of the most common contaminants at
Superfund sites across the Nation. Region V alone has over
100 sites on the National Priorities List (NPL) where lead
contamination is found. The magnitude of the problem
increases when emergency response sites and RCRA corrective
action sites are taken into account. Lead is a common
contaminant at sites where past industrial activities include
battery breaking and recycling, oil refining, paint manufacture,
metal molding and casting, ceramic manufacturing, and primary
and secondary smelting. Several technologies have been
implemented for treating lead-contaminated soils. Research
and evaluation of other treatment technologies is ongoing.
The seminar summarized in this bulletin was developed
to provide RPMs and OSCs with an overview of the state of the
art for treatment of lead-contaminated soils. More detail on
specific technologies can be obtained from the referenced
reports and from consultation with technology contacts.
The seminar was organized to address site characterization
issues and actual treatment technologies. The treatment
technologies were divided into two categories: "demonstrated"
and "emerging." Extraction processes (e.g., soil washing and
acid leaching) and solidification/stabilization techniques have
been evaluated where lead was a contaminant of concern. The
emerging technologies discussed were in situ vitrification,
electrokinetics, and flash smelting.
Printed on Recycled Paper
echnical
reject
*Ch
Superfund Technical Support Center
for Engineering and Treatment
Risk Reduction and Engineering
Laboratory
Technology Innovation Office
Office of Solid Waste and Emergency
Response, U.S. EPA, Washington, DC
Walter W. Kovalick, Jr., Ph.D.
Director
-------
The remainder of this bulletin summarizes information
concerning data needs for sile and soil characterization and
the applicability of the discussed treatment technologies.
general, the contaminated soil is excavated before treatment.
The washing agent is chosen depending on the contaminant
type and particle size distribution of the soil.
Determining the appropriate treatment techniques to be
used to clean up a particular soil requires knowledge of the
chemical and physical nature of the contaminated soil.
Potential treatment technologies must be identified early in the
phased remedial invesligation/leasibility study (RI/FS) process
as shown in Figure 1. This is to ensure the data required to
evaluate a technology's applicability to a site is collected during
the remedial investigation or as part of a treatability study.
Solids Handling
Figure 1. The role of treatability studies in the RI/FS
and RD/RA process (USEPA 1989a)
Table 1 provides a list of soil characterization parameters
related to treatment technologies that may aid the RPM/OSC
in developing sampling and analysis plans and treatability
studies.
Treatment Technologies for Lead-
Contaminated
Extraction
FUNCTION: Extraction refers to several processes that separate
the contaminants from soil particles. Often the goal of the
process is to reduce the volume of contaminated soil that
ultimately must be treated or disposed or to transfer the
contaminants from the soil medium to an aqueous medium
where they can be more easily treated.
PROCESS: There are two general extraction processes interest:
soil washing and acid leaching. Soil washing used a washing
solution (e.g., water, surfactant, chelating agent) and mechanical
agitation to extract the contaminant from the soil particles.
Figure 2 is a generalized process diagram for soil washing. In
Extraction/Washing
Dewatering
Lead Recovery
Figure 2. General block diagram of soil washing process
The acid leaching process (under development by the
Bureau of Mines specifically for lead-contaminated soil and
battery casings) converts lead sulfate and lead dioxide to lead
carbonate, which is soluble influosilicic acid. Lead is recovered
from the leaching solution by electrowinning and the acid is
recycled back to the leaching process. Further leaching with
nitric acid may increase lead movement. Figure 3 is a process
flow diagram of the Bureau of Mines' process.
APPLICATION: Soil washing experiments have shown that a
significant fraction of the contaminants are attached to the
fines (sill, humus, and clay) and that the coarse material can
be cleaned by physically separating and concentrating the fines.
Addition of a chelate solution (e.g., EDTA) has been shown to
be effective in improving metal removal efficiencies. Surfactant
solutions have shown high organic removal (compared with
water wash) for the fines particles. Water appears to be more
effective in mobilizing organics than metals, probably because
some organic compounds are slightly hydrophilic.
A number of bench-scale studies were conducted to
evaluate soil washing for treating lead-contaminated soils
(USEPA 1989b). The purpose of these screening trealability
studies, which were conducted under a give set of operating
conditions, was to determine if soil washing can reduce the
levels of lead contamination in the soil and to examine the
partitioning of lead relative to soil particle size. The results of
these tests, expressed as percent reduction of total lead, are
presented in Table 2. The data indicate that limited removal of
lead occurs, particularly in the course and medium fractions.
The concentration of TCLP-leachable lead also was signilicantly
reduced, as shown in Table 3. Additional bench-scale studies
are required to determine the optimum operating parameters
and to verify that site-specific cleanup goals can be achieved.
Further data on these tests are contained in the referenced
reports.
The acid leaching procedure using fluosilicic acid is
specifically applicable to lead-contaminated soils and battery
casings. This leaching process was developed with the purpose
Treatment of Lead-Contaminated Soils
-------
Table 1. Site and Soil Characterization Parameters for Treatment Technology Evaluation
TREATMENT
TECHNOLOGY
MATRIX
PARAMETER
PURPOSE AND COMMENTS
General
Soils/sludges
Physical:
Type, size of debris
Chemical:
Dioxins/furans, radionuclides, asbestos
To determine need for pretreatment
To determine special waste-handling procedures
Extraction
Soils/sludges
Physical:
Particle-size distribution
Clay content
Moisture content
Chemical:
Organics
Metals (total, teachable and species)
Contaminant characteristics
-vapor pressure
-solubility
-Henry's Law constant
-partition coefficient
-boiling point
-specific gravity
Total organic carbon (TOC), humic acid
Cation exchange capacity (CEC)
PH
Cyanides, sulfides, fluorides
To determine volume reduction potential, pretreatment needs, solid/liquid separability
To determine adsorption characteristics of soil
To determine conductivity of air through soil
To determine concentration of target or interfering compounds, pretreatment needs
extraction medium
To determine concentration of target or interfering compounds, pretreatment needs
extraction medium, and mobility of target constituents and posttreatment needs
To aid in selection of extraction medium
To determine presence or organic matter, adsorption characteristics of soil
To determine adsorption characteristics of soil
To determine pretreatment needs, extraction medium
To determine potential for generating toxic fumes at low pH
Solidification/
Stabilization
Soils/Sludges
In situ
Physical:
Description of materials
Particle size analysis
Moisture content
Oil and grease
Halides
Soluble metal salts
Phenol
Density testing
Strength testing
-Unconfined compressive strength
-Flexural strength
-Cone index
Durability testing
Chemical:
PH
Alkalinity
Interfering compounds
Indicator compounds
Leach testing
Heat of hydration
Presence of subsurface barriers
Depth to first confining layer
To determine waste handling methods
To determine surface area available for binder contact and leaching
To determine amount of water to add/remove in mixing process
Greater than 10% weakens bonds between waste particles and cement when using
cement based technology
May retard setting
Can affect strength of final product
Greater than 5% may decrease compressive strength
To evaluate changes in density between treated and untreated waste
To evaluate changes in response to overburden stress between untreated and treated wastes
To evaluate material's ability to withstand loads over large area
To evaluate materia's stability and load bearing capacity
To evaluate durability of treated wastes (freeze-thaw and wet-dry durability)
To evaluate changes in leaching as a function of pH
To evaluate changes in leaching as a function of alkalinity
To evaluate visibility of S/S process
To evaluate performance of S/S
To evaluate performance of S/S
To measure temperature changes during mixing
To assess feasibility of adequately delivering and mixing the S/S agents
To determine required depth of treatment
Vitrification
Soils/sludges (in situ)
Physical:
Depth of contamination and water table
Moisture content
Soil permeability
Organic carbon
Metal content of waste material and
placement of metal within the waste
Combustible liquid/solid content of waste
Rubble content of waste
Void volumes
Technology is applied in unsaturated soils
To estimate energy required in driving off water
Dewatering of saturated soils may be possible
To design off-gas handling systems
Greater than 5 to 15% by weight or significant amounts of metal near
electrodes interfere with process
Greater than 5 to 15% by weight interferes with process
Greater than 10 to 15% by weight interferes with process
Large, individual voids (greater than 150 ft3) impede process
Electrokinetics
Soils/sludges
Physical:
Hydraulic conductivity
Depth to water table
Areal extent of contamination
Electroosmotic permeability
Cation exchange capacity (CEC)
Chemical:
Presence of soluble metal contaminants
Salinity
Technology applicable in zones of low hydraulic conductivity
Technology applicable in saturated soils
To assess electrode and recovery well placement
To estimate the rate of contaminant and water flow that can be induced
Technology most efficient when CEC is low
Technology applicable to soluble metals, but not organics and insoluble metals
Technology most efficient when salinity is low
Adapted from; USEPA1989a
Treatment of Lead-Contaminated Soils
-------
Water
NH OH.
4 ' '
Water
MVO
Water
Contaminated Soil
i
Grizzly *- +4 inch
U
r i
-i»j Trommel j— 4- f/2 inch — •*• Hammer Mill
1
-* (Ifsrhnnattnn ^ "" fin.'? Xt-nragni
I
f Tr
~J i/Vas/? »> Wastetvafer
|
_J Leach -«
BUj
1
fiVfer |— Rffrate >• Elect/manning
I
-N Leac^i
1
Filter
I
-*J Looc^ »- M/as/ew/atef
C/ean So/7 e
ad
of reclaiming lead for secondary smelting. It has not been
widely Icsted for general application al Supcrlund sites;
however, the technology has been tested on several lead-
contaminated soils. Table 4 summarizes the bench-scale test
results.
LIMITATIONS:
SOIL WASHING
• Effectiveness of treatment is highly dependent on
particle size.
• Fine particles have high adsorption capacity for
contaminants and can be difficult to remove from
washing fluid.
« Aqueous waste stream and fines fraction require
subsequent treatment.
« Materials handling issues are critical to treatment
effectiveness.
« Wash solution must be tailored for the site.
• Difficulty and costs in recovering chelating agents.
Figure 3. Block diagram of Bureau of Mine's fluosillclc
acid system to leach and electrowin lead from
contaminated soils.
Table 2. Results of Bench-Scale Evaluations of Soil Washing
Site/Waste
Old Man's Township
C&R Battery
Sen uyl kill
Gould Soil
Gould Casings
J&L Fabricating
SARM III
UNTREATED SOIL
Predominant Avg.Tot. EPTox.
Lead Species Lead, mg/kg mg/L
PbCO, 48,000 300
Pb3(C03)2jOH)2 68,400 418
PbCO, 4,700 55.5
PbS04 27,600 148
PbS04 209,000 1,830
Pb02
Pb4S04(C03)2jOH)2 4,194 N/A
PbS04 12,776 N/A
Pb02
%LEAD REDUCTION IN TREATED SOIL
Wash Solns.
Tested
Water
EDTA(1)
Water
EDTA(1)
Water
EDTA(1)
Water
EDTA(1)
Water
EDTA(1)
Water
EDTA(2)
EDTA(3)
EDTA(4)
EDTA(5)
Water
EDTA(1)
>2
NR
NR
26.7
NR
81.0
98.1
NR
67.5
82.9
79.7
NR
NR
NR
74.2
NR
99.4
99.5
250^m
to 2mm
53.5
48.9
23.7
16.2
54.0
50.2
53.6
68.6
-
51.8
67.3
35.2
63.9
69.5
97.9
98.9
<250,um
(fines)
4.38
14.1
27.6
64.7
37.3
15.0
NR
44.7
34.1
44.3
NR
NR
NR
NR
NR
N/A
N/A
NR = no reduction N/A = not available (1) 3:1 molar ratio for EDTA to total chelatable metals, pH = 7-8
(2) 0.0160M, pH = 7-8
(3) 0.0148M, pH = 7-8
(4) 0.021 OM, pH = 7-8
(5) 0.0210M, pH = 11-12
Source: USEPA1989b
Treatment of Lead-Contaminated Soils
-------
Table 3. TCLP Lead for Bench-Scale Soil Washing Studies
Site Name
Gould Soil
J&L Fabricating
Pesses Chemical Co,
Wash
Solution
Water
EDTA
Water
EDTA(a)
EDTA(b)
Water
EDTA(a)
EDTA(b)
Untreated
Soil, mg/L
657
657
225
225
225
0.297
0,297
0.297
>2mm,
mg/L
96.0
177
83.6
130
153
0,864
<0.062
<0.062
%
Reduction
85.4
73.1
62.8
42.2
32.0
NR
>79.1
>79.1
250,um to
2 mm, mg/L
273
241
51,1
37.2
48.1
<0.103
0.305
0.730
%
Reduction
58.4
63.3
77,3
83,5
78.6
>65.3
NR
NR
<25Q/,im
mg/L
700
323
163
38.4
79.9
0.0670
0.297
0.465
%
Reduction
NR
50.8
27,6
82.9
64.5
NR
NR
NR
(a) pH = 7-8
ipH =
NR = no reduction
Source: USEPA1989b
Table 4. Results of the Bureau of Mines' Treatabllity Tests on Lead-Contaminated Soils
UNTREATED
TREATED MATERIAL
Site/Waste
United Scrap Lead
"Soil
United Scrap Lead
°Soil
Arcanum
°Soil
Arcanum
°Soil
C&R Battery
"Soil
Predominant
Lead Species
Pb, PbSCX
Pb02
Pb(2%), PbSO,
PbO,
Pb(6.6%)
PbSO,
Pb(6.6%), PbS04
Pb, PbSO,
PbCO,, Pb02
Average Total
Lead, ppm
8,000-18,000
8,000-18,000
71,000
71,000
17,000
Leach
Method
HNO,
H2SiFs/HN03
H2SiF6/HN03
HN03
HN03
Total Lead,
ppm
200
203
330
<250
29
EP
tox, mg/L
<1
<1
0,26
<1
<0.1
Source: Schmidt 1990
ACID LEACHING
« Acid handling requires special handling procedures and
construction materials.
« Residual waste streams require subsequent treatment.
• Process has not been widely tested at Superfund sites.
« Lead sulfate sludge requires further treatment before
disposal.
RESIDUALS:
SOIL WASHING - The aqueous wasle slream (wash
solution) will require treatment for contaminant removal. The
resulting fines will likely need to be treated (e.g., using
solidification/stabilization) before disposal.
ACID LEACHING - Several aqueous waste streams are
generated during this process that require treatment. The treated
soil must be analyzed to determine the options for either
additional treatment or disposal. Lead can be reclaimed from
this process.
Solidification/Stabilization
FUNCTION: Solidification/stabilization (S/S) reduces the
hazardous potential of contaminated sites by converting the
contaminants into their least soluble, mobile, or toxic lorm,
thus minimizing their potential migration off site. The process
has been well developed for above-ground application. The
unique aspect of in situ application is the means of mixing S/S
agents within the soil. Many mixing agents are not effective in
immobilizing organic contaminants. However, recent studies
indicate that modified clays, silicates, and some organic binders
can be used to immobilize organic contaminants.
PROCESS: The S/S process, often referred to as fixation or
immobilization, involves mixing the contaminated soil with
an appropriale ratio ol binder/stabilizer and waler. Binding
and hardening material ties up the free water in the matrix.
Reactions with hydroxides and carbonates form insoluble metal
compounds. Potential binders include pozzolan-portland
cement, lime-fly ash, thermoplastic binders (asphalt), and
sorbents such as activated carbon, clays, zeolites, and
anhydrous sodium silicate.
Treatment of Lead-Contaminated Soils
-------
For the in situ process, the binding agents (e.g., cement,
lime, kiln dusl, fly ash, silicates, clay, and zeolites or
combinations thereof) used for contaminated wastes are mixed
with the contaminated material by the surface area, injection,
or auger method. In situ S/S has been applied at contaminated
sites.
Solidification/stabilization has been widely tested and
implemented at Superfund sites and is considered a reliable
treatment technology for many metal-contaminated soils and
sludges. Generally, immobilization by the solidification/
stabilization technique has lower costs than other treatment
options.
APPLICATION: Solidification/stabilization is highly suited for
soils, sludges, or slurries contaminated with metals. The
treatment is applicable to slurries after the solids content of the
matrix has been adjusted. It is a required treatment for several
metal-containing hazardous wastes prior to land filling.
Many of the additives are not effective in immobilizing
organic contaminants. Modified clays, however, are currently
being studied for application in the S/S of organic contaminants.
Recent tests with some silicate binders and some organic
binders have shown success in immobilizing and perhaps
treating some semivolatile and heavier organic contaminants.
Solidification/stabilization has been demonstrated through
the SITE program by several vendors. HAZCON, inc., uses a
proprietary binder with cement to immobilize organic and
inorganic contaminants in soils by bind ing them in a concrete-
like mass. Table 5 and 6 summarize the results of treatment ol
lead-contaminated soils using the HAZCON process.
Soliditech, Inc., also uses a proprietary reagent and additives
with fly ash, kiln dust, or cement to immobilize metals and
organics. Table 7 shows some results of the Soliditech process
on lead, arsenic, and zinc.
The most significant challenge in applying solidification/
stabilization treatment in situ for contaminated soils is achieving
complete and uniform mixing of the solidifying/stabilizing agent
with the soils. In situ surface area mixing of solidifying/
stabilizing agents with contaminated sludges in a lagoon is
typically accomplished by use of a backhoe, clamshell, or
dragline. Other in situ mixing techniques are the injection
system, the auger/cassion system, and the auger system. These
application techniques are generally limited to depths of less
than 1 00 feet.
LIMITATIONS:
« The volume of treated material will increase with
addition of reagent.
« Organics are usually not effectively treated using
standard binding/stabilizing agents. If organics are of
concern, special proprietary binding agents will be
necessary.
« Delivering reagents to the subsurface and achieving
uniform mixing and treatment in situ may be difficult.
« Volatilization and emission of volatile organic
compounds may occur during mixing procedures and
emissions control may be warranted.
Table 5. Lead Analysis of Untreated and Treated
Soils—Hazcon S/S Process
Location
Code
DSA
LAN
FSA
LFA
PKA
LAS
Untreated,
ppm by Wt.
3,230
9,250
22,600
13,670
7,930
14,830
Treated, ppm
(28-day Results)
830
2,800
10,300
1,860
3,280
3,200
Source: USEPA1989c.
Table 7. Chemical Properties of Untreated and
Treated Wastes—Soliditech, Inc. S/S Process
OFFSITE AREA ONE
Leachate Leachate
from from
Chemical Untreated Treated Untreated Treated
Parameter (a) Waste Waste(b) Waste(c) Waste(c)
Arsenic
94
92
0.19
ND
Table 8. Concentration of Metals in TCLP Leehates-
Hazcon S/S Process, mg/L
Location
Code
DSA
LAN
FSA
LFA
PKA
LAS
Untreated
Soil
1.5
31.8
17.9
27.7
22.4
52.6
7-Day
Cores
0.015
<0.002
0.07
0.04
0.01
0.14
28-Day
Cores
0.007
0.005
0.400
0.050
0.011
0.051
Lead
Zinc
650
120
480
95
0.55
0.63
0.012
ND
(a) Analyte concentration units for the untreated and treated waste
are mg/kg. Analyte concentration units for the leachate from
untreated and treated waste are mg/L.
(b) Treated wastes were sampled after a 28-day curing period.
(c) Leachate values refer to results from TCLP test.
ND = not detected
Adapted from: USEPA1989d.
Source: USEPA1989c.
Treatment of Lead-Contaminated Soils
-------
• The permeability of the treated area is significantly
reduced. Revegetation may require placement of a soil
cover of sufficient depth. However, properties of
stabilized material can be engineered to produce an
excellent sub-base or slab for subsequent industrial use
at the site.
• Runoff controls may be required.
RESIDUALS:
• The solidified/stabilized product is the principal
residual.
• Vapors or gaseous emissions may be released in some
cases, requiring capture and subsequent treatment.
Vitrification
FUNCTION: Contaminated soils are converted into chemically
inert and stable glass and crystalline materials by a thermal
treatment process.
PROCESS: Large electrodes are inserted into soils containing
significant levels of silicates. The electrodes are usually arranges
in 30-foot squares. Graphite on the soil surface connects the
electrodes. A high current of electricity passes through the
electrodes and graphite. The heat causes a melt that gradually
works downward through the soil. Volatile compounds are
collected at the surface by a negative pressure hood for
treatment. After the process is terminated and the ground has
been cooled, the fused waste material will be dispersed in a
chemically inert and crystalline form that has very low
leachability rates. Figure 4 is a schematic diagram of the
process.
This technology is currently slated for demonstration as
part of the SITE program. It has been chosen as a remedy at
several site cleanups such as Northwest Transformer in
Washington and Crystal Chemical in Houston, Texas. Bench-
scale testing has been conducted for the New Bedford Harbor
site in Massachusetts and the Jacksonville, Arkansas, Water
Treatment Plant site. The Department of Energy (DOE) has
evaluated in situ vitrification at several locations in its Hanford,
Washington, facility.
APPLICATION: Vitrification was originally tested as a means
of immobilizing low-level radioactive metals. The process
destroys nitrates and partially decomposes sulfate compounds
in the wastes. Fluoride and chlorine compounds are dissolved
into the glass materials up to their limits of solubility. Wastes
containing heavy metals, PCBs, process sludges, and plating
wastes are amenable to treatment by the vitrification process
because they will either fuse or vaporize. Contaminant organics
and some metals are volatilized and escape from the soil surface
and may be collected by a vacuum system. Inorganics and
some organics are trapped in the melt that, as it cools, becomes
a form of obsidian or very strong glass. The treatment rate is 3
to 5 tons/hour.
Vitrification may also be useful for forming barrier walls
(e.g., similar to slurry walls), however, this concept has not
been proven.
LIMITATIONS:
• The process is energy intensive and often requires
temperatures up to 2500°F for fusion and melting of
the waste-silicate matrix.
• Special equipment and trained personnel are required.
• Water in the soils affects operational time and increases
the total costs of the process.
• The technology has the potential to cause some
contaminants to volatilize and migrate to the outside
boundaries of the treatment area instead of to the surface
for collection.
• A substantial amount of time may be needed for cool-
down of the melt.
• The technology has not been demonstrated at depths
over 20 feet.
• The boundary between successive melts may require
special attention to assure that an impermeable bond
is formed.
RESIDUALS:
• Resulting vitrified mass is effectively inert and
impermeable.
• Soil cover material is needed to allow for vegetative
growth and support.
Support
Moiling Zonft
WaK» BurtaJ
Coin Cap
Vilrftod Sol.Wasle
Figure 4. The in situ vitrification operating sequence (USEPA 1990a)
Treatment of Lead-Contaminated Soils
-------
Electrokinetics
FUNCTION: Electrokinetic technology can remove heavy
metals and other contaminants from the soil and groundwater
when the soil is electrically charged with direct current. The
movement of ions, particles, and water are transported under
the influence of an electrical field.
PROCESS: An electrokinetic phenomenon occurs when liquid
migrates through a charged porous medium underthe influence
of a charged electrical field. The charged medium is usually
some kind of clay, sand, or other mineral particle that
characteristically carries a negative surface charge. The
electrical field is applied through anodes. Cations bound in
the soil will migrate toward the negatively charged cathode.
Concentration gradients in the soil solution are established
between the cathode and anode. The concentration gradients
cause diffusion from areas of low concentration to areas of
high concentration (see Figure 5). The spacing of wells
containing the cathode and anode depends on site-specific
factors. Both the cathode and anode housing have separate
circulation systems filled with different chemical solutions. The
contaminants are captured in these solutions and brought to a
purification system.
This technology has been field demonstrated in the United
States and Europe.
APPLICATION: Ionic metal species that are subject to ionic
reaction and migrate in the soil system appear to be the types
of contaminants that can be effectively treated. Also, a nearly
static groundwater regime and saturated, moderately permeable
soils at a shallow depth are favorable conditions for applying
this technology.
LIMITATIONS:
• This technology is confined to sites contaminated with
metals.
• Electrical power requirements could be excessive, thus
the technology might not be cost effective.
• Further treatments would be required for sites
contaminated with organics or other waste types.
• Precipitation of salt and secondary minerals could
decrease the effectiveness of this technology.
• The technology may raise the soil pH to levels that result
in the mobilization of metallic contaminants. The high
pH levels could also inhibit or destroy microbial
populations present within the soil.
• Chlorine gas may be formed from the reduction of
chlorine ions in the vicinity of the anode.
RESIDUALS:
• Nonmetallic contaminants would not be affected and
would remain in the soil matrix.
• Precipitated salts and secondary minerals need to be
removed from the collection points to increase the
effectiveness of the technology.
• Metallic contaminants would need to be removed from
the collection points and treated at the surface.
Flame Reactor Process
FUNCTION: The flame reactor process (patented by Horsehead
Resource Development Co., Inc.) Is a flash smelting system
that treats residues and wastes containing metals.
PROCESS: The reactor processes wastes with a very hot (greater
than 2000°C) reducing gas produced from the combustion of
solid or gaseous hydrocarbon fuels in oxygen-enriched air. In
a compact low-capital cost reactor, the feed materials react
rapidly allowing a high waste throughput. The end products
are a nonleachable slag (a glasslike solid when cooled) and a
recyclable, heavy metal-enriched oxide. The volume reduction
achieved (of waste to slag) depends on the chemical and
physical properties of the waste. Figure 6 shows a process
flow schematic for the Horsehead Development Co. flame
reactor.
Figure 5. Diagram of a typical electrokinetic operation (USEPA 1990a)
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Treatment of Lead-Contaminated Soils
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Figure 6. Horsehead Resource Development Company
flame reactor process flow schematic (USEPA 1989d)
The flame reactor technology can be applied to granular
solids, soil, flue dusts, slags, and sludges containing heavy
metals. The volatile metals are fumed and captured in a product
dust collection system, and the nonvolatile metals are
encapsulated in the slag. At the elevated temperature of the
flame reactor technology, organic compounds should be
destroyed. In general, the process requires that wet
agglomerated wastes be dry enough (up to 1 5% total moisture)
to be gravity-fed and fine enough (less than 200 mesh) to react
rapidly. Larger particles (up to 20 mesh) can be processed,
however, a decrease in the efficiency of metals recovery usually
results.
APPLICATION: Electric arc furnace dust, lead blast furnace
slag, iron residues, zinc plant leach residues and purification
residues, and brass mill dusts and fumes have been successfully
tested. Metal-bearing wastes previously treated contained zinc
(up to 40%), lead (up to 10%, cadmium (up to 3%), and
chromium (up to 3%), as well as copper, cobalt, nickel, and
Technology Contacts
The following individuals can be contacted with technical
questions concerning the treatment technologies:
Extraction:
Soil washing and soil flushing
Hugh Masters (201) 321-6678, FTS 340-6678
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Edison, New Jersey
Acid leaching
William Schmidt (202) 634-1823
Bureau of Mines
Washington, DC
Solidifica tion/Stabiliza tion
Inorganics
Carlton Wiles (513) 596-7795, FTS 684-7795
Paul de Percin (513) 569-7797, FTS 684-7797
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
Organ ics
Edward R. Bates (513) 569-7774, FTS 684-7774
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
In Situ Vitrification
Teri Shearer (513) 569-7949,
FTS 684-7949
Jonathan Herrmann (513) 569-7839,
FTS 684-7839
Donald Oberacker (513) 569-7510, FTS 684-7510
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
LIMITATIONS:
This technology is currently being demonstrated as part
of the Superfund Innovative Technology Evaluation (SITE)
program. It has not been widely tested for use at Superfund
site cleanups.
RESIDUALS:
An iron-rich aggregate is formed from the molten slag.
The metal contaminants (e.g., lead) are recovered as a crude,
heavy metal oxide, which may be marketable. Air pollution
controls are required to handle the off-gas.
Electrokinetics
Jonathan Herrmann (513) 569-7839, FTS 684-7839
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
Treatment of Lead-Contaminated Soils
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Flash Smelters
Donald Obcrackcr (513) 569-751 0, FTS 684-751 0
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
Acknowledgments
The efforts of many people were necessary in order to
present the workshop that preceded this bulletin. Many of
these same people also provided comments useful in
preparation of this bulletin. The efforts of the following
individuals are recognized:
Paul de Percin, Mike Royer, Hugh Durham, Ernst
Grossman, Joan Colson, Don Obcrackcr and David Smilh ol
RREL, USEPA; Lou Blume, Tony Holoska and Steve Ostrodka
of Region V, USEPA and Shahid Mahmud of OSWER, USEPA;
Catherine Chambers and Radha Krishnan of IT Corp.
References
Schmidt, VV.B. 1990. Assessment of Current Treatment
Techniques at Superfund Battery Sites. Proceeding of the 1 990
EPA/A&WMA International Symposium, February, Cincinnati,
OH.
U.S. Environmental Protection Agency. 1989a. Guide to
Conducting Trcatability Studies Under CERCLA. EPA/540/2-
89/058. Office of Solid Waste and Emergency Response,
Washington, DC and Office of Research and Development,
Cincinnati, OH.
U.S. Environmental Protection Agency. 1989b. Lead Battery
Site Treatability Studies. Prepared under Contract No. 68-03-
3413 by PEI Associates, Inc.
U.S. Environmental Protection Agency. 1989c. HAZCON
Solidification Process, Douglassville, PA, Applications Analysis
Report. EPA/540/A5-89/001 Office of Research and
Development, Cincinnati, OH.
U.S. Environmental Protection Agency. 1 989d. The Superfund
Innovative Technology Evaluation Program: Technology
Profiles. EPA/540/5-89/013. Office of"Solid Waste and
Emergency Response and Office ol Research and Development,
Washington, DC.
U.S. Environmenlal Protection Agency. 1990a. Handbook on
In Situ Treatment of Hazardous Waste-Contaminated Soils. EPA/
540/2-90/002. Office of Research and Development,
Cincinnati, OH.
U.S. Environmental Protection Agency. 1990b. Technology
Evaluation Report: SITE Program Demonstration Test Soliditech,
Inc. Solidification/Stabilization Process, Volume I. EPA/54 0/5-
89/005a. Office of Research and Development, Cincinnati, OH.
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