United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-84-156 Nov. 1984
Project Summary
Evaluation of an
ESCA/Leachate Analytical
Scheme to Characterize
Process Stream Wastes
Barbara M. Myatt
An ESCA/leachate analytical scheme
was evaluated for its ability to charac-
terize solid waste from combustion
processes and hazardous waste incin-
erators. Samples were analyzed for
surface elemental composition by elec-
tron spectroscopy for chemical analysis
(ESCA) before and after aqueous leach-
ing. Selected elements were subjected
to oxidation state studies by ESCA, and
leachates were analyzed for anions by
ion chromatography and for trace met-
als by inductively coupled plasma spec-
trometry. The results of ESCA before
and after leaching compared favorably
with leachate data. Although aqueous
leaching did not significantly affect the
metal species present in the samples
used in this study, it did extract con-
siderable amounts of water-soluble
ions: sodium, calcium, chloride, sulf ate.
Essentially all samples showed an in-
crease in oxygen after leaching that was
attributed to hydration by the aqueous
extraction medium.
ESCA can successfully speciate chro-
mium, lead, and zinc when these ele-
ments are sufficiently abundant in the
sample. The technique is limited, how-
ever, by its ability to detect only those
elements present at greater than 0.1 to
1.0 percent atomic. Most process
wastes contain very low concentrations
of metals, thereby minimizing the suit-
ability of ESCA for process waste
characterization. However, municipal
and hazardous waste incinerators pro-
duce bottom and baghouse ashes con-
taining significant amounts of hazard-
ous trace metals. ESCA in conjunction
with process data could prove useful in
determining metal species present and
their potential for release from partic-
ulate.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory, Research Triangle"
Park, NC, to announce key findings of
the research project that is fully doc-
umented In a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Solid waste from refuse incineration
presents a landfill disposal problem owing
to its potentially hazardous nature. Signif-
icant leaching from fly ash and bottom
ash has been shown to occur when these
materials are exposed to neutral or slight-
ly acidic solutions simulating rainwater.
In a landfill disposal situation, ground
water quality would be affected by the
amounts and types of compounds thus
leached.
Incinerator residue leachates and acid
digestions have been characterized for
anion and cation content, but the actual
solid waste has not been studied before
and after leaching to determine changes
in its composition. Electron spectroscopy
for chemical analysis (ESCA or XPS) is a
surface analysis technique and was ex-
pected to be useful for obtaining such
information. With ESCA, only the top 20
to 100 A of the solid or paniculate surface
are analyzed, and in leaching studies, it is
this part of the sample that is of interest.
ESCA provides elemental composition
data for all elements except hydrogen and
helium. In addition, for a number of
elements, ESCA can be used to determine
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oxidation state and bonding information.
This project was designed to evaluate a
combined ESCA/leachate analytical
scheme for characterizing the leachability
of wastes from process streams. ESCA
was used to analyze waste samples (fly
ash, bottom ash) before and after leach-
ing, and to provide an estimate of oxida-
tion state (speciation) for several ele-
ments. Chemical analyses of the leach-
ates were used to provide supporting data
for the ESCA/leachate results. '
Experimental Program
The experimental program for evaluat-
ing the utility of an ESCA/leachate
analytical scheme consisted of replicate
analyses of actual source particulate
samples using ESCA, Level 1 aqueous
leachate generation, ion chromatography,
and inductively coupled plasma emission
spectroscopy.
Conclusions
Several conclusions were drawn from
the data obtained in this study:
• Elemental identifications by ESCA are
reproducible for major components
(>5 percent atomic), but minor ele-
ments are often misidentified as noise
or vice versa.
• Quantification by ESCA is fairly precise
(15 percent RSD) for most elements
present as major components or for
which ESCA has high sensitivity. This
precision holds only for homogeneous
samples or samples for which repre-
sentative aliquots can be mounted on
ESCA substrates. Elements producing
low photoelectron counts show much
greater variation in quantification
which is attributable to subjective
decisions by the analyst.
• The material used as substrates to
mount samples in the ESCA appears to
introduce no consistent bias in the
concentrations of elements measured
in the samples.
• The Level 1 aqueous leaching pro-
cedure has a rather low extraction
efficiency for many species found in
process waste samples. It also suffers
from poor precision when inhomogen-
eous samples or nonrepresentative
aliquots are analyzed.
• ESCA can be used to speciate chrom-
ium, lead, and zinc when these ele-
ments are present in fairly high con-
centrations. At the detection limit,
they do not produce sharp enough
peaks for the analyst to determine a
precise binding energy for the element.
As learned from previous ESCA work,
it is also possible to speciate sulfur and
carbon in samples of this type.
• The ESCA/leachate analytical scheme
can be used to detect changes in
sample composition caused by aque-
ous leaching. As expected, water
soluble components are easily extract-
ed from the sample while metals show
an apparent increase in concentration
after leaching. This is primarily due to
the removal of the soluble surface
components. The species of metals
present in the samples did not seem to
change after leaching.
Recommendations
The following recommendations are
based on the results of this experimental
program:
• The combined ESCA/leachate analyt-
ical scheme should probably not be
pursued as a means for determining
the degree of hazard associated with
.^disposal of process wastes. The com-
bined procedure requires a great deal
of analytical time, and the benefits of
post-leaching ESCA analyses appear
minimal based on the samples used in
this study. Although other samples
may behave differently, it must be
recognized that these samples (con-
taining metals at concentrations de-
tectable by ESCA) were extremely
difficult to obtain and will probably not
be routinely encountered in practice.
The use of ESCA alone to predict
aqueous leachability has advantages.
Its focussing on the surface of partic-
ulate matter and its ability to detect
elements and species of high aqueous
solubility recommend it for this pur-
pose. This statement, supported by the
literature, is based on the supposition
that, under the conditions of the Level
1 leaching procedure, only small a-
mounts of trace metals will be leach-
able from the waste.
The use of ESCA to determine trace
metal oxidation states could be useful
in a study to correlate the metal
compounds formed during incineration
with combustion conditions and the
type of waste. Similar work has been
performed using metal compound vola-
tility to predict if the metal will ac-
cumulate in flyash, bottom ash, or
scrubber slurry, or be emitted from the
stack. Adding the speciation capability
of ESCA to this evaluation could prove
quite interesting.
Barbara M. Myatt is with GCA, Technology Division, Bedford, MA 01730.
Frank £. Briden is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of an ESC A/Leachate Analytical
Scheme to Characterize Process Stream Wastes,"(Order No. PB 85-116 192;
Cost: $14.50, 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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
•tt U.S. GOVERNMENT PRINTING OFFICE; 1984 — 559-016/7847
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