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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                                 Batch Plant
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Figure 1. Flow Diagram for STC Treatment Process
                                                                                             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
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 EPA/540/MR-92/010

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