United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/018 Feb. 1990
&EPA Project Summary
Evaluation of Solidified
Residue from Municipal Solid
Waste Combustors
Danny R. Jackson
The study summarized here evalu-
ated the effectiveness of commercial
solidification techniques to immobil-
ize inorganic and organic constitu-
ents in five municipal refuse inciner-
ator ash (MRIA) samples. Although
the ash samples were analyzed for
selected organic and inorganic
constituents, the organic character-
ization was deleted from the
analytical scheme because of the low
organic composition of the ash.
The ash samples were also ana-
lyzed for elemental content, including
arsenic, barium, boron, cadmium,
calcium, chromium, copper, lead,
mercury, nickel, selenium, sodium,
and zinc. The most prevalent ele-
ments in the ash samples were
calcium (2.2%-8.8%), copper (0.04%-
0.17%), lead (0.07%-0.17%), sodium
(0.28%-1.8%), and zinc (0.15%-6.69%).
Extracts obtained by use of the
toxicity characteristic leaching pro-
cedure (TCLP) were made from the
unsolidified ash samples. Analysis of
the TCLP extracts showed that con-
centrations of metals in the ash were
well below regulatory limits.
Three solidification techniques
were performed on the ash samples:
chemical fixation, cementation with
kiln dust, and cementation with fly
ash, with all of the ash samples
solidified by the chemical fixation
technique. A combined-ash sample
and a fly-ash sample were also
solidified by cementation techniques.
The TCLP and static leach test
(SLT) procedures were performed on
solidified ash samples, and extracts
generated from the fly ash and the
combined ash were analyzed for
elemental content Concentrations of
all metals in the ash extracts were
well below regulatory limits.
This Project Summary was devel-
oped by EPA's Risk Reduction
Engineering Laboratory, Cincinnati,
OH to announce key findings of the re-
search project that is fully docu-
mented in a separate report of the
same title (see Project Report order-
ing information at back).
Introduction and Objectives
This study was performed to evaluate
the effectiveness of commercial solidi-
fication techniques to immobilize TCLP-
extractable hazardous constituents of ash
from five municipal refuse incinerators.
Combined ash samples (a mixture of
bottom ash and fly ash) were collected
from four facilities and fly ash as well as
combined ash samples were collected
from a facility in Dayton, Ohio, for a total
of six ash samples from five facilities.
All ash samples were solidified by
chemical fixation. Two of these ash
samples (a combined ash and a fly ash)
were also solidified by cementation with
kiln dust and with fly ash.
Concentrations of inorganic constitu-
ents in the ash samples and their extracts
were compared before and after the
solidification procedures. TCLP extracts
of the ash samples were not analyzed for
organic constituents because concentra-
tions of organic compounds were equal
to or below the quantifiable method
detection limits.
Methods
To determine the pH and electrical
conductivity (EC) of the ash samples, a
slurry of equal volumes of sample and
deionized water was prepared and the pH
of the decanted liquid was measured. A
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slurry of one part fly ash to five parts
water was used to generate enough
volume for pH and EC analysis of the
Dayton fly ash sample.
The distribution of particle sizes in the
ash samples was quantitatively deter-
mined: particle sizes larger than 75 iim,
by sieving, and particle sizes smaller
than 75 urn, by sedimentation with a
hydrometer.
Before analysis, the ash and leachate
samples were subjected to acid digestion
procedures. Inductively coupled argon
emission spectroscopy (ICP) was used to
analyze for boron, barium, cadmium,
calcium, chromium, copper, nickel, silver,
sodium, and zinc in the ash and leachate
samples. Furnace atomic adsorption
spectrophotometry was used to analyze
samples for arsenic, lead, and selenium
by the procedures outlined in EPA
Methods 7060, 7421, and 7740,
respectively. Cold vapor atomic adsorp-
tion spectroscopy was used to determine
mercury in the ash and leachate samples.
The solidified ash samples were pre-
pared according to specifications in
ASTM Method C-192-81 entitled, "Stand-
ard Method of Making and Curing
Concrete Test Specimens in the Labora-
tory." The unconfined compressive
strength (UCS) of the solidified samples
was measured as a way of estimating the
maximum shear strength developed by
solidified ash samples. The permeability
coefficients for cured solidified ash
samples were measured with the use of
flexible-wall membrane triaxial cell.
The ash and solidified ash samples
were extracted according to the TCLP, a
procedure which is designed to assess
the presence of organic and inorganic
contaminants in liquid, solid, and multi-
phase wastes.
Solidified ash samples were also ex-
tracted by the SLT, a test that measures
the maximum credible concentrations of
elements in quasi-static groundwater that
has been in contact with a stabilized
waste. Sequential SLT's were also per-
formed on each solidified ash sample.
Each extract was filtered through a 0.60-
to 0.80-Hm glass-fiber filter to remove
solids.
Results
Because of the very low levels of
organics found in the MRIA samples,
organic characterization of the ash leach-
ates, the solidified ashes, and the
leachates of the solidified ashes was
deleted from the experimental scheme.
The most prevalent__inprganic species
found in the samples were c'a1cTuTfr(2:2%^
to 8.8%), copper (0.04% to 0.17%), lead
(0.07% to 0.17%), sodium (0.28% to
1.8%), and zinc (0.15% to 0.69%).
Metal concentrations in TCLP extracts
of ash and solidified ash were below the
regulatory levels defined in the TCLP.
The low levels of trace elements found in
the TCLP extracts indicated that the
metals in the MRIA samples were not
soluble in the extraction fluid. Because
the TCLP extracts of the Marion com-
bined ash and the Dayton fly ash
contained the largest concentrations of
metals, the leachates of these two solid-
ified samples were submitted for inor-
ganic analyses.
Permeability coefficients of solidified
cured waste materials ranged from 1.0 x
10-s to 1.4 x 10-6 cm/sec. UCS results
ranged from 18 psi in the Marion com-
bined ash solidified by chemical stabiliza-
tion to 97 psi in the Dayton combined ash
solidified by cementation with kiln dust.
For materials to be disposed of in a
landfill, minimum strengths of 50 psi or
greater are desired.
Conclusions and
Recommendations
Because organic compounds were
either not detected or were found in low
parts-per-billion levels in the ash
samples, these compounds were not
determined in the TCLP extracts. The
most prevalent elements found in the ash
samples were calcium, copper, lead,
sodium, and zinc.
, Permeability coefficients for solidified
ash samples showed that the solidified
ash samples would have low to moderate
permeability as disposed waste. UCS for
the solidified ash samples ranged from
.t8_to^7i_gs[1_ which_jndjcated a high
degree of variability in "com(5ressive"
strength.
Results of the analysis of TCLP
extracts showed that extractable metal
concentrations in all the ash samples
were well below regulatory limits both
before and after the ash samples were
solidified. Similarly, concentrations of
metals in extracts from the SLT pro-
cedure were extremely low for all of the
solidified ash samples.
Additional ash samples, known to be
relatively high in metals and possibly
organics, should be solidified and ana-
lyzed. Because of the extreme hetero-
geneity in metals concentrations in ash
from MSW facilities, time-averaged
samples should be obtained that would
give a more accurate representation of
ash characteristics.
The full report was submitted in
fulfillment of Contract No.68-01 -6999 by
Radian Corporation under the sponsor-
ship of the U.S. Environmental Protection
Agency.
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Danny Ft. Jackson is with Radian Corporation, Austin, TX 78720-1088.
Charles I. Mashnl is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Solidified Residue from Municipal
Solid Waste Combustors," (Order No. PB 89-190 284/AS; Cost: $15.95, 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
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EPA/600/S2-89/018
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