United States
Environmental Protection
Agency
EPA/540/MR-92/010
March 1992
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
Solidification/Stabilization of
Organic/Inorganic Contaminants
Silicate Technology Corporation
Technology Description: Silicate Technology Corporation's
(STC's) technology for treating hazardous waste utilizes silicate
compounds to stabilize organic and inorganic constituents in
contaminated soils and sludges. STC has developed two groups
of reagents: SOILSORB HM for treating wastes with inorganic
constituents and SOILSORB HC for treating wastes with organic
constituents. These two groups of reagents can be combined to
treat wastes containing both organic and inorganic contaminants.
These silicate reagents adsorb organic and inorganic contami-
nants prior to encapsulating the waste in a cementitious material.
This process results in a high-strength, leach-resistant monolith.
Treatability studies and site investigations are conducted to de-
termine the necessary type and dosage of reagents required
depending on the waste characteristics and treatment objectives.
Treatment of contaminated soil (Figure 1) begins with separation
of coarse and fine waste materials, and the crushing of coarse
material which reduces it to the size required (<%") for the
solidification technology. The pretreated waste is weighed and
predetermined amounts of silicate reagents are added. The mix-
ture is conveyed to a pug mill mixer where water is added and
the mixture is blended.
Sludges may be placed directly into the pug mill for addition of
reagents and mixing. The amounts of reagents required for stabi-
lization can be adjusted according to variations in organic and
inorganic contaminant concentrations determined during treat-
ability studies. Treated material is placed in confining pits for
onsite curing or cast into molds for transport and disposal offsite.
Waste Applicability: This technology is designed to treat
contaminated soils and sludges where semi- or non-volatile or-
ganics, inorganics, or a combination of these contaminants exist.
Demonstration Results: The STC technology was demon-
strated at the Selma Pressure Treating (SPT) wood preserving
site in Selma, CA, during November 1990. Approximately 16 tons
of waste were treated. The SPT site waste was contaminated
with organics, predominantly pentachlorophenol (PCP), and with
inorganics, primarily arsenic, with lesser amounts of chromium,
and copper. Extensive sampling and analyses performed on the
waste before and after treatment compared physical, chemical,
and leaching characteristics of the raw and treated waste. The
objective of the demonstration was to assess the STC process
effectiveness in treating the PCP and AS.
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Printed on Recycled Paper
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SITE demonstration results indicate that the STC process chemi-
cally stabilized contaminated soils containing organic and inor-
ganic contaminants. Specific findings of the STC demonstration
are summarized below. It should be noted that post treatment
data have been mathematically adjusted to eliminate any appar-
ent reductions due solely to dilution.
• POP was successfully treated by the STC process. Initial
raw waste concentrations of PCP as high as 10,000 ppm
were reduced 91% to 97% to values as low as 53 ppm as
measured by total waste analysis (EPA Method SW 846-
8270 for semi-volatiles using methylene chloride extraction
on ground sample passing 100 mesh). This complies with
EPA draft policy guidance on stabilization of organics which
states that total waste analyses should be used to assess
the effectiveness of stabilization processes for treating semi-
volatile and non-volatile organics: (OSWER Directive No.
9200.5-220). Leaching tests for PCP using toxicrty charac-
teristic leaching procedure (TCLP 55FR26986 June 1990),
but using distilled water instead of acetic acid, indicated
reductions up to 97% (from 40.0 ppm to 0.58 ppm). Treat-
ment of other toxic organic compounds could not be evalu-
ated because of the very low concentrations of such com-
pounds.
• Arsenic was successfully immobilized. Standard TCLP tests
(TCLP 55FR26986 June 1990) using acetic acid produced
reductions up to 92% (from 1.82 ppm to 0.086 ppm). TCLP
procedures .using distilled water in place of acetic acid
produced reductions up to 98% (from 1.25 ppm to 0.012
ppm). Arsenic analyses were by EPA Method 7060 using
GFAAS. Copper and chromium were also present at the
site but in lower concentrations that were not targeted for
treatment.
• After a 28-day curing period (open air, ambient site tem-
perature), the treated wastes exhibited high physical stabil-
ity. Testing is scheduled for 6, 18, and 36 months following
the demonstration to determine long-term stability.
Unconflned compressive strength (UCS) of the treated
wastes was moderately high, averaging 260 to 350 psi
(ASTM D1633-34).
Permeability of the treated waste was low (<1.7 x 10'7 cm/
sec by TMSWC-13). The relative, cumulative weight loss
after 12 wet/dry (ASTM D4843-88) and 12 freeze/thaw
(ASTM D4842-90) cycles was negligible (less than 1%).
Treatment of the wastes resulted in volume increases
ranging from 59% to 75% (68% average), with slight
increases in bulk density.
The STC process successfully solidified contaminated soils
that contained less than 2% oil and grease (EPA Method
413.2), and initial moisture contents of up to 6%.
Petrographic (ASTM 856) analyses including microscopi-
cal, X-ray diffraction, scanning electron microscopic, and
fourier transform infrared analyses indicated good binder-
to-aggregate bonding. Metal containment was good.
The process equipment used during the technology evalu-
ation was observed to be mechanically reliable. The 5-yd3
pug mill mixer was provided by Texas Industries Incorpo-
rated of Dallas, TX. The remainder of the equipment was
rented locally. No equipment-related problems occurred
during the 6-day demonstration.
The process equipment used during the demonstration
-produced a homogenous, solidified product, after pretreat-
ment screening and size reduction of surface hardpan
material down to 1 to 2mm.
The STC process has been estimated to cost approxi-
mately $200/yd3 when used to treat large amounts (15,000
yd3) of waste similar to that found at the STC demonstra-
tion site.
For Further Information:
EPA Project Manager:
Edward R. Bates
U.S. EPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7774 (FTS: 684-7774)
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
,= BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/540/MR-92/010
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