Post on 19-Jun-2020
Microtrace
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microscopy ● microchemistry ● forensic consulting LLC
®
16 October 2019
Mr. Robert Wilkinson
CCR Techical Manager
TDEC
312 Rosa Parks Avenue
Nashville, TN 37243
RE: MT19-0298
Dear Mr. Wilkinson,
We have completed our analysis of six environmental samples, which were submitted to our
laboratory for the identification of coal ash. The results of our analysis were reported to you by
telephone on Thursday 10 October 2019. This report describes our analytical methods,
documents our results, and discusses the conclusions we have drawn from them.
Sample(s)
The following samples were received in our laboratory on 25 September 2019:
Sample 1: TDEC-BRF-001 (Figure 1)
Sample 2: TDEC-BRF-002 (Figure 2)
Sample 3: TDEC-BRF-003 (Figure 3)
Sample 4: TDEC-BRF-004 (Figure 4)
Sample 5: TDEC-BRF-005 (Figure 5)
Sample 6: TDEC-BRF-006 (Figure 6)
Task
Analyze the six samples for coal ash by SEM and PLM
Analytical Methods and Results
Preliminary Examination
The samples were documented, on receipt, in their original packaging. Because the quantities of
samples 2-6 were quite small, they were first examined in their original packaging with the
unaided eye and then by stereomicroscopy to locate the material and to devise methods for their
recovery. The isolated samples from each plastic bag as well as the bottle and swab are
illustrated in Figures 7-12. Examination under the stereomicroscope indicated that the majority
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of the samples appeared to consist of a mineral rich soil composed primarily clay and clay coated
fine sand and coarse silt. Based on this observation, representative samples of the six samples
were prepared as slides for petrographic microscopy.
Microscopical Examination of the Samples to Search for and Identify Coal Ash
Microscope slides were prepared from the six samples and examined for coal ash using the
methods described in the Particle Atlas1. The slides were searched by polarized light microcopy
using a petrographic microscope. The particles comprising the specimens were identified on the
basis of their microscopic morphology and optical crystallographic properties. The identity of
particles originating from combustion properties was confirmed by isolating examples of the
tentatively identified particle types from the slide preparations and washing them free of the
refractive index liquids. These combustion particles were then mounted on a polished beryllium
plate2 for examination and analysis by SEM-EDS
3 to more carefully examine their morphology
at high magnification and determine their elemental compositions.
The analytical results obtained from each sample are described below. All of the samples are
otherwise similar with respect to their major composition, with the exception of -BRF 006,
which consists in large part of particles of white paint film and plant matter with a few of the
reddish-brown soil clumps. Sample -BRF-001 is the only one found to contain coal ash.
Therefore, its composition is described in detail below to put the amount of combustion products
identified into quantitative perspective.
Analytical Results
TDEC-BRF-001. The general appearance of this dust is illustrated in Figures 13 and 14. It a
reddish-brown soil composed almost entirely of mineral grains, primarily quartz and feldspars,
coated with an oxidized iron stained clay. Figure 15 shows a round, colorless, glassy sphere
among the mineral grains in a selected field of view. Two glassy spheres from another area of
the preparation are illustrated in Figure 16. These particles are one of the most characteristic
features of high efficiency coal-fired utility boilers. They show evidence of their time-
temperature history as the carbon of the coal burns away, leaving only the silicates originally
trapped in the coal, which melt to spheres. The bubbles inside are trapped escaping combustion
gases.
Figures 17 and 19 are SEM micrographs of glassy flyash spheres isolated from the microscope
slide preparations. Figures 18 and 20 are EDS spectra that provide the elemental composition of
these two particles. Note that, as expected, they are alumino-silicates composed primarily of
aluminum (Al), silicon (Si) and oxygen (O). The potassium (K) and sodium (Na) indicate the
feldspar silicates trapped in the coal from which they originated were of a type known as alkali
1 Palenik, S.J., Microscopical Examination of Air Pollutants in McCrone, W.C., Delly, J.G. and Palenik, S.J, The
Particle Atlas, Volume V, Ann Arbor Science Publishers (1973-1979), pp. 1362-1368 2 The low atomic number of the polished beryllium metal (Z=4) provides an essentially zero background for EDS.
3 Scanning electron microscopy – energy dispersive x-ray spectroscopy
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feldspars. The exact elemental composition of coals can be used4 to compare coal ash from
different sources.
Other characteristics of combustion products are carbonaceous soots and chars. Because of the
high efficiency of coal fired utility boilers, soot is typically rare in their effluent. Chars, which
however in this case, are unburned coal may be present based on the efficiency of the unit (the
more efficient the boiler, the less char that remains in the ash). This sample contains
carbonaceous chars. Charred carbonaceous matter is black, opaque and brittle. Figure 21 shows
a black opaque particle; however, this particular particles is not brittle, but elastomeric, and is a
particle of black rubber produced by tire wear and not related to combustion.
Black, opaque, round, ferro-magnetic particles are also present, although rare, in this sample.
These spheres are composed of magnetite (Fe3O4) and are produced in much the same way as the
glassy flyash spheres, but do not result from feldspars and other silicates but from iron sulfides,
which is where most of the sulfur is locked up in coal. Figure 22 shows one of these rare spheres
in this sample.
Figures 23 and 24 show examples of another type of carbonaceous char called cenospheres.
Cenospheres can be found in coal ash but are more characteristic of oil-fired boilers. Examples
of the appearance of carbonaceous cenospheres from this sample were also examined by SEM-
EDS and examples of several are shown in Figures 25, 27, 29 and 31. Their accompanying EDS
spectra are illustrated in Figures 26, 28, 30 and 32. Note the lacey structure of the cenospheres
themselves. This characteristic structure is caused by vapor produced by the burning fuel
forming “blow-holes” as it liquifies and decomposes inside the particle as it is burning.
Examination of these EDS spectra show, as expected, that the particles consist almost entirely of
carbon (C). Note that the small peaks contain the elements as the glassy flyash spheres, with the
exception of sulfur (S), because in the char it has not yet burned off.
Figures 33-34 show another carbonaceous particle type that was observed in this sample. These
particles are black, opaque and rounded to egg shaped. When crushed the particle is brittle and
breaks into small, greenish pieces as illustrated in Figure 35. The interior emits green
fluorescence, when excited by blue light, as depicted in Figure 36. Additional particles of this
type were also isolated and prepared for SEM-EDS analysis. Figures 37 and 39 show two
examples of these particles as they appear in the SEM. Figures 38 and 40, respectively, show
their EDS spectra. Note that although they are carbonaceous, they also contain a relatively high
silicate (silicon and oxygen) content. The presence of phosphorous (P) and nitrogen (short
unmarked peak between the carbon and oxygen in Figures 38 and 40) is somewhat interesting
since neither of these elements is typically associated with fossil fuels. They are, however, often
found in the ash of plants. These particles are present in trace amounts. We do not recognize the
source of these black, ovular particles and have not encountered them in samples of power plant
flyash. However, the best way to determine if they could originate from the coal ash from the
power plant that is suspected to be the source of the coal ash traces in this sample would be to
microscopically examine samples of that ash from that power plant.
4 By means of a more highly refined application of the same general method to compare coal or combustion
products to known coal and coal ash to help establish their sources.
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An example of another carbonaceous particle type found in -BRF-001 is illustrated in Figure 41.
Particles with this morphology are typical of oil soot. A few of these particles were located but
they are rare.
TDEC-BRF-002-006. No glassy flyash spheres or carbonaceous char that could be associated
with coal were detected in any of the remaining samples. Sample -BRF-005 contained a few rare
oil soot spheres and some particles of wood char. The black and brown colors on one of the
paint chips comprising -BRF-006 are not soot but dark matter from an inner layer of the multi-
layer paint that shows through to the surface and stands out against the white paint by contrast.
Summary and Conclusions
Sample TDCE-BRF-001 was the only sample showing detectable levels of glassy spheres and
carbonaceous char that could be associated with coal ash. The quantities of coal ash detected
were too low to quantitate. They are present only in trace amounts in this sample when
considered either by number of weight percentage. The other five samples showed no detectable
amounts of coal ash. Most of all of the samples consist of a red-brown soil composed primarily
minerals and a small amount of humic matter. Sample TDEC-BRF-006 consists primarily of
pieces of paint, plant matter, and a small amount of the red-brown soil (of the type that
constitutes the majority of the other samples).
One type of oval-shaped carbonaceous particle (observed in TDCE-BRF-001) could not be
associated with a particular source.
In summary, sample TDCE-BRF-001 contains traces of coal ash. No coal ash was detected in
the other five samples, which are composed almost entirely of a soil containing very little
organic matter.
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This report shall not be reproduced except in full, without written approval of Microtrace. Analyses performed at Microtrace are accredited under ISO/IEC 17025.
See certificate #5106.01 issued by the A2LA accrediting body.
Microtrace
LLC
If you have any questions concerning this report, or if we may be of further assistance, please do
not hesitate to contact either of us directly. It is our policy to retain samples for 30 days after
completion of our report, at which time they will be discarded. If you would prefer to have the
samples archived or returned, please contact us to make these arrangements before then. Thank
you for consulting Microtrace.
Sincerely,
Skip Palenik
Senior Research Microscopist
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Figure 1. Sample BRF-001, as received.
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Figure 2. Sample BRF-002, as received.
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Figure 3. Sample BRF-003, as received.
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Figure 4. Sample BRF-004, as received.
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Figure 5. Sample BRF-005, as received.
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Figure 6. Sample BRF-006, as received.
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Figure 7. The contents of sample –BRF-001 after transfer to a small petri dish.
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Figure 8. The contents of sample –BRF-002 after transfer to a small petri dish.
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Figure 9. The contents of sample –BRF-003 after transfer to a small petri dish.
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Figure 10. The contents of sample –BRF-004 after transfer to a small petri dish.
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Figure 11. The contents of sample –BRF-004 after transfer to a small petri dish.
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Figure 12. The contents of sample –BRF-006 after transfer to a small petri dish. The yellow arrows depict the two larger particles of paint film.
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Figure 13. A representative field of view of –BRF-001 showing the relatively bimodal size distribution of the particles comprising this sample.
Note that the fine particles are almost all crystals of silicates (quartz & feldspars). The larger particles are primarily crystals of minerals also.
Some of these are single crystals (e.g., the quartz grain at the upper right of the figure) while others are either single large mineral grains or
agglomerates of small grains coated with ferruginous (i.e., iron stained) clays. Transmitted plane polarized light.
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Figure 14. Same as Figure 8 but between crossed polars, which demonstrates that the majority of the crystals are anisotropic with low order
interference colors. Mounted in 1.660 index of refraction liquid.
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Figure 15. A typical glassy flyash sphere among the mineral grains comprising the majority of –BRF-001. Transmitted plane polarized light.
Mounting in 1.660 index of refraction liquid.
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Figure 16. Two colorless glassy coal flyash spheres in –BRF-001. Transmitted plane polarized light. Mounting in 1.660 index of refraction liquid.
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Figure 17. Backscatter electron (BSE) image of Particle F1 as it appears in the SEM. The inserted image shows the combustion product particles
isolated from sample –BRF-001 after they were removed from the microscope slides and washed prior to mounting on the beryllium plate for SEM-
EDS analysis.
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Figure 18. EDS spectrum of glassy flyash sphere Particle F1.
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Figure 19. Backscatter electron (BSE) image of Particle F2 as it appears in the SEM. Note the hollow sphere-within-a-sphere structure quite often
observed in glassy flyash spheres from coal fired utility boilers and some high efficiency municipal incinerators.
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Figure 20. EDS spectrum of Particle F2.
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Figure 21. Black particle of abraded tire rubber from sample –BRF-001.
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Figure 22. Magnetite sphere from –BRF-001 as it appears by reflected darkfield illumination among the particles of mineral soil.
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Figure 23. Black carbonaceous cenosphere fragment in –BRF-001. Transmitted plane polarized light.
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Figure 24. Black carbonaceous cenosphere fragment in –BRF-001. Transmitted plane polarized light.
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Figure 25. Backscatter electron (BSE) image of Particle B3 as it appears in the SEM.
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Figure 26. EDS spectrum of Particle B3.
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Figure 27. Backscatter electron (BSE) image of Particle A2 as it appears in the SEM. Inset shows the particle after isolation from the microscope
slide.
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Figure 28. EDS spectrum of Particle A2.
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Figure 29. Backscatter electron (BSE) image of Particle A3 as it appears in the SEM. Inset shows the particle after isolation from the microscope
slide.
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Figure 30. EDS spectrum of Particle A3.
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Figure 31. Backscatter electron (BSE) image of Particle B1 as it appears in the SEM. Inset shows the particle after isolation from the microscope
slide.
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Figure 32. EDS spectrum of Particle B1.
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Figure 33. Carbonaceous oval shaped particle of unknown combustion product. Transmitted plane polarized light. Mounted in 1.660 liquid.
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Figure 34. Same particle illustrated in Figure 33 by reflected light.
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Figure 35. The same particle illustrated in Figures 33 and 34 after crushing. Transmitted plane polarized light. Mounted in 1.660 index of
refraction liquid.
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Figure 36. A portion of the crushed interior of the black particle shown in Figures 33-35 as it appears in the same preparation by blue light
excitation under a fluorescence microscope.
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Figure 37. Backscatter electron (BE) image of Particle D1 as it appears in the SEM. Inset shows the particle after isolation from the microscope
slide.
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Figure 38. EDS spectrum of Particle D1.
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Figure 39. Backscatter electron (BSE) image of Particle D3 as it appears in the SEM. Inset shows the particle after isolation from the microscope
slide.
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Figure 40. EDS spectrum of Particle D3.
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Figure 41. Carbonaceous particle of the type usually associated with oil soot. Note the smoothed surface and the “blow holes” that pock mark its
surface.
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