United States
Environmental Protection
Agency
EPA/540/SR-94/513
August 1994
&EPA
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology
Summary
Acid Extraction Treatment
System for Treatment of Metal
Contaminated Soils
Stephen W. Paff, Brian E. Bosilovich, and Nicholas J. Kardos
The Acid Extraction Treatment Sys-
tem (AETS) is intended to reduce the
concentrations and/or teachability of
heavy metals in contaminated soils so
the soil can be returned to the site
from which it originated. The objective
of the project was to determine the
effectiveness and commercial viability
of the process. The report summarized
here is an account of the activities con-
ducted during the project, the experi-
ments performed, results and
conclusions.
A pilot-scale AETS system was used
to treat 5 different soils containing dif-
ferent combinations of seven heavy
metals. The study showed that AETS is
capable of treating a wide range of
soils, and reducing the TCLP metals to
below the RCRA limits. The AETS can,
in most cases, treat the entire soil, with
no separate disposal or stabilization of
the clay fines needed. The estimated
treatment costs are between $80 and
$240/yd3.
This project summary was developed
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).
Introduction
Through a Cooperative Agreement with
the U.S. Environmental Protection
Agency's (USEPA) Risk Reduction Engi-
neering Laboratory (RREL), the Center for
Hazardous Materials Research (CHMR)
developed the Acid Extraction Treatment
System (AETS). The project was con-
ducted with support from Interbeton bv
and The Netherlands Organization for Ap-
plied Scientific Research (TNO), located
in the Netherlands. AETS is intended to
reduce the concentrations and/or leach-
ability of heavy metals in contaminated
soils to render the soils suitable to be
returned to the site from which they origi-
nated. Additional applications may include
treatment of contaminated sediments,
sludge and other heavy metal-containing
solids.
The objective of the project was to de-
termine the effectiveness and commercial
viability of the AETS process in reducing
the concentrations and. leachability of
heavy metals in soils to acceptable levels.
This report represents an account of the
activities conducted during the project, the
experiments performed, and the results.
A pilot scale system was designed, con-
structed, and used to test different soils.
Five soils were tested, including EPA Syn-
thetic Soil Matrix (SSM), and soils from
Printed on Recycled Paper
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four Superfund sites (NL Industries in
Pedricktown, NJ; King of Prussia site in
Winstow Township, NJ; smelter site in
Butta, Montana; and Palmerton Zinc site
in Palmerton, PA). These soils contained
elevated concentrations of arsenic, cad-
mium, chromium, copper, lead, nickel, and
zinc.
Process Description
A simplified block flow diagram of the
AETS process is shown in Figure 1. Full-
scale units are anticipated to be able to
process between 10 and 30 tons/hr. The
first step in the full-scale AETS process is
screening to remove coarse solids. These
solids, typically greater than 4 mm in size,
are anticipated to be relatively clean, re-
quiring at most a simple rinse with water
or detergent to remove smaller attached
particles. If the soil contains a high per-
piped to the rinse system, while the cy-
clone overflow (extractant) are treated us-
ing a proprietary technology which
removes the metals and regenerates the
acid.
The soils are rinsed with water to re-
move entrained acid and metals. The met-
als are removed from the rinsate using
the same technology that regenerates the
acid. After rinsing, the soil is dewatered
using hydrocyclones and (if required) de-
watering screens. In the final step, the
soils are mixed with lime and fertilizer to
neutralize any residual acid and return the
soil to natural conditions.
Test Procedures
This section describes the experimental
procedures used with the pilot-scale AETS
unit, which is capable of processing be-
tween 20 and 100 kg of soil per hour.
Contaminated
soil
Make-up
acid
Rinse water
Classification
(Screening)
Coarse soil
particles
Extraction unit
Extractant
\
Rinse/Dewater
^Rinsate
Entrained
soils
Acid
regeneration
3 J
Heavy metals
Neutralization &
stabilization
Treated soil
Figure 1. AETS block flow diagram.
cantage of clays, these may be removed
as well for treatment separately.
After coarse particle removal, the re-
maining soil is scrubbed in an attrition
scrubber to physically remove the metals
and break up agglomerations. Then it is
contacted with acid (HCI) in the extraction
unit.
The residence time in the unit may vary
depending on the soil type, contaminants
and contaminant concentrations, but is
anticipated to range between 10 and 40
min. The soil/extractant mixture is con-
tinuously pumped out of the mixing
tank, and the soil and extractant are sepa-
rated using hydrocyclones. The solids are
The soils were initially characterized for
total and TCLP metals content. The soils
were screened to remove the +8 mesh
fraction on a mechanical shaker prior to
being placed in the lab-scale attrition scrub-
ber, where the soil was slurried with water
or regenerated hydrochloric acid from pre-
vious experiments.
Next, the soil was contacted with hydro-
chloric acid for residence times between
10 and 40 min. in the extraction tank. The
pH of the mixture was maintained be-
tween 1.8 and 2.2. Figure 2 shows the
flow diagram for the extraction step. Dur-
ing extraction, the solids were separated
using two hydrocyclones, and returned to
the extraction tank. The extractant was
pumped to the acid regeneration system,
and then returned to the extraction tank.
At the end of the: experiment, the soil
was dewatered using two cyclones and a
mechanical shaker with a 200 mesh screen
to separate the solids and the extractant.
The extractant was then regenerated to
be used as the acid in the next experi-
ment, and the solids were prepared for
the rinsing step.
The solids were rinsed in water to re-
move any residual acid. The metals were
removed from the rinse water using a
separate regeneration system than the one
used during the extraction. The clean sol-
ids and all liquids were then analyzed for
total and TCLP metals to form a material
balance. The rinse water was ready for
the next experiment, so no waste streams
were generated.
Experimental Soils
This section gives a brief discussion of
the five soils used during the laboratory-
and pilot-scale investigations.
Synthetic Soil Matrix
The Synthetic Soil Matrix (SSM) is pro-
duced by EPA specifically for use in re-
search and development of emerging or
innovative technologies. The soil is a mix-
ture of clay, silt, sand, gravel, and topsoil
that is blended together to form the soil
matrix. Organic and inorganic contami-
nants are added based on typical hazard-
ous materials at Superfund sites. Table 1
lists the total and TCLP metals concentra-
tions in the initial SSM.
NL Industries Site
The NL Industries site, located in
Pedricktown, NJ, was an integrated bat-
tery breaking and lead smelting facility.
The soil is contaminated with copper, lead,
and zinc, but was chosen for this project
due to the high levels of lead. The total
lead concentrations ranged from 23,200
to 29,200 mg/kg and TCLP concentra-
tions ranged from 500 to 520 mg/L.
King of Prussia Site
This site, in Winslow Township, NJ, was
used to neutralize acid streams from an
adjacent site. The soil is contaminated
with chromium, copper, and nickel, and it
is not hazardous by RCRA standards. The
site was placed on the National Priorities
List (NPL) because of high levels of chro-
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Figure 2. Extraction flow diagram.
Table 1. Synthetic Soil Matrix Contaminant Levels
Metal
Total Range (mg/kg)
Table 2. King of Prussia Contaminant Levels
Metal
Total Range (mg/kg)
Cr
Cu
Ni
1,020 to 1,390
1,240 to 2,030
335 to 518
TCLP Range (mg/L)
As
Cd
Cr
Cu
Pb
Ni
Zn
620 to 730
970 to 1, 130
1,320 to 1,640
10,900 to 12,400
10,040 to 10,800
980 to 1,410
20,500 to 26,300
4.0 to 4.2
41.0 to 48.9
<0.05
297 to 298
26.0 to 27. 1
35.6 to 35.9
669 to 719
TCLP (mg/L)
0.20
7.10
27.6
mium. Table 2 describes the extent of
contamination in the initial soil.
Silver Bow Creek Site
This site, in Butte, MT, contains a very
sandy soil, with very little clay. The soil is
contaminated with copper and zinc, with
total metals ranging from 98 to 127 mg/
kg, and 1,170 to 1,350 mg/kg, respec-
tively. The TCLP range was from 1.4 to
1.7 mg/L for copper, and 2.6 to 7.1 mg/L
for zinc. The Butte soil was non-hazard-
ous soil, but still contained metals that
needed removal.
Palmerton Zinc Site
This site, located in Palmerton, PA, was
an old zinc smelting facility. Only one ex-
perimental extraction was conducted on
this material, due to a lack of the soil. This
soil was chosen due to its high levels of
zinc, but also because it contained lead,
cadmium, and copper. Table 3 summa-
rizes the concentrations of the metals in
the initial soil.
Results
Table 4 and Table 5 summarize the
results of tests using the five different
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Tab/o 3. Palmerton Soil Contaminant Levels
Metal
Total Metals (mg/kg)
TCLP Metals (mg/L)
Cd
Cu
Pb
Zn
137
166
898
9,150
2.60
0.16
0.66
71.0
soils, containing seven separate metals.
The results Indicate that the AETS pro-
cess can reduce the concentrations of
heavy metals and reduce the TCLP leach-
ability levels to below current regulatory
limits.
Table 4 summan'zes the soil treatability
across the soils and metals tested. Where
individual soil fractions were separated
during the extraction, and analyzed sepa-
rately, the table shows the composite re-
sults if the entire soil had been remixed.
The results show that AETS treated virtu-
ally all the soils tested to both reduce the
total metals concentrations to below cur-
rently regulated concentrations and reduce
the TCLP to below the currently regulated
concentrations. The only exceptions were
cadmium, which consistently failed the
TCLP for SSM soil, and lead, which failed
both the TCLP and total metals require-
ments for SSM soils.
Table 5 shows the results obtained from
the lead contaminated soil from the NL
Industries Superfund site in Pedricktown,
NJ. The table shows over 90% reductions
in total metals concentrations, and a 99%
reduction in TCLP. Further work indicated
that the TCLP and total lead in the soil
could be reduced to below 5 mg/L and
1000 mg/kg, respectively.
The experimental work was completed
during January 1993, and the final report
has recently been issued.
Process Economics
Table 6 below shows the cost summary
for AETS at several different process con-
figurations. The table shows the effects of
varying six critical parameters (feed rate,
extraction time, percent fines, metals con-
centrations, site size and the number of
sites treated with each set of equipment).
Note that the table includes costs for
mobilization, pilot plants, excavation, re-
placing soil, and reseeding the ground as
well as soil treatment. Thus, the costs
represent the total costs of treatment us-
ing the Acid Extraction Treatment System.
Also note that the table conservatively as-
sumes that the capital costs of the AETS
system are amortized over only 1 or 2
sites, and that the plants operate only one
8 hour shift per day. Finally, the economic
calculation assumes that the metal sludge
is stabilized and disposed, and not re-
claimed. The metals in many sites may be
reclaimable. Relaxing all of these conser-
vative assumptions will reduce the esti-
mated treatment costs by 20 to 30%.
Conclusions
The results of the study are summa-
rized below:
• AETS is capable of treating a wide
range of soils, containing a wide range
of heavy metals to reduce the TCLP
below the RCRA limit and to reduce
the total metals concentrations below
the California-mandated total metals
limitations.
• In most cases, AETS is capable of
treating the entire soil, with no
separate stabilization and disposal for
fines or clay particles, to the required
TCLP and total limits. The only
exception to this among the soils
tested was with the SSM, which may
require separate stabilization and
disposal of 20% of the soil because
of lead. This soil was successfully
treated for other metals, including
arsenic, chromium, copper, nickel and
zinc.
• Costs for treatment, under conser-
vative process conditions, range be-
tween $80 and $240/yd3 of soil,
depending on the site size, soil types
and contaminant concentrations.
Tab/8 4. Qualitative Results of Extractions
Metal
As
Cd
Cr
Cu
Ni
Pb
Zn
Soil
SSM
*, T.L
", T
',T,L
*,T,L
*.T,L
*
*,r,L
Butte
*.T,L
*,T,L
*,T,L
*,T,L
King of Prussia Pedricktown
*, T, L *,T,L
*,T,L
*, T,L
*,T,L
*, T,L
Palmerton
*, T,L
*, T, L
*,T,L
", T,L
* - Metal is present in the soil
T • Successful treatment for total metals
L • Reduction in teachability to below standards
Bold and large fonts indicate high initial metals content (at least double regulatory standards)
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Table 5. NL Industries Soil
Total Metals (mg/kg)
Metal
Pb
Initial
29,200
Final
1,310
% Removal
95.5%
TCLP (mg/L)
Metal
Pb
Initial
520
Final
5.1
% Removal
99.0%
Table 6. AETS Cost Summaries Under Various Conditions
Process and Site Parameters
Feed
Rate
(ycP/hr)
30
20
20
20
15
15
15
10
Extraction
Residence
Time (mm)
24
24
36
24
24
36
36
36
% Fines
(<50u.m)
15
15
30
15
15
30
15
30
Metals
Cone.
(mg/kg)
5,000
5,000
15,000
15,000
5,000
15,000
5,000
15,000
Site Size
(1000yd3)
150
100
60
80
60
30
30
20
Amortized
Capital and
Operating Costs
($/m3)
77
96
138
118
122
193
168
241
The following notes apply to this table:
1. Plant is operating for only 1 eight hour shift per day.
2. No metal recovery value is assumed. All metal sludge is disposed.
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Stephen W. Paff, Brian E. Bosilovich and Nicholas J. Kardos are with the
Center for Hazardous Materials Research, Pittsburgh, PA 15238
Naomi P. Barkleyis the EPA Project Officer (see below).
The complete report, entitled "SITE Emerging Technologies: Acid Extraction
Treatment System for Treatment of Metal Contaminated Soils," (Order No.
PB94-188109/AS; Cost: $19.50, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
. Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penally for Private Use
$300
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EPA/540/SR-94/513
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