Energy & Fuels 1992,6,120-125
120
ECUIGJ 20 18 16 Refined hydrotreatedpyrolysis oil Refined aromaticsfrom zeoliteS
14 12
Crude pyrolysis oil
Refined hydrotreatedpyrolysis oil Refined aromatics from zeolites
10 8
Crude pyrolysisoil
6 4 2
0 0
20
40
60
80
100
Feed cost, ECUR (daf)
Figure 9. Effect of feed cost on the cost of crude and upgraded pyrolysis oil (1ECU = $1.20).
ronmental, and other aspects is shown in Figure 10.
Conclusions The performance and cost estimates for both crude pyrolysis liquids and refined hydrocarbon products show that, while crude liquids can be economic at low feedstock
0
20
40 60 80 Feed Cost, ECUh (daf)
100
Figure 10. Effect of environmental and socioeconomiccredits at 3 ECUs/GJ on costs of crude and refined products (1ECU = $1.20).
costs, refined hydrocarbons are still not competitive without credits for low sulfur, environmental contributions, and socioeconomiccontributions. As feedstock cost is the major cost item, any process that can utilize waste materials with their low inherent cost will show economic viability in the short term.
Articles An Unusual Occurrence of Arsenic-Bearing Pyrite in the Upper Freeport Coal Bed, West-Central Pennsylvania Leslie F. Ruppert,” Jean A. Minkin, James J. McGee, and C. Blaine Cecil U.S. Geological Survey, 956, National Center, Reston, Virginia 22092 Received June 24,1991. Revised Manuscript Received January 7,1992 Scanning electron microscopy and electron microprobe analysis were used to identify a rare type of As-bearing pyrite in selected specific gravity separates from the Pennsylvanian age Upper Freeport coal bed, west-central Pennsylvania. Arsenic was detected mainly in cell-wall replacement pyrite where concentrations ranged from nondetectable to 1.9 wt % . Although the majority of arsenic-bearing pyrite in the Upper Freeport coal bed is concentrated in massive and late diagenetic pyrite morphologies, the rarer As-bearing cell-replacement pyrite was observed in both light and heavy gravity separates from the three coal facies examined. Arsenic was occasionally detected in cell-filling replacement pyrite, but this As appears to be an artifact produced by signals from underlying and/or adjacent As-bearing cell-wall replacement pyrite. It is postulated that some plants of the Upper Freeport paleoswamp may have biomethylated As, which later could have been converted to dimethylarsine or other volatile organoarsenic compounds by either biologically or chemically driven processes. Once liberated, the arsenic may have been incorporated into pyrite during pyritization of the cell walls. The As incorporation occurred early, before significantcompaction of the peat, because the pyritized cell walls are not compacted.
(1) Chapman, A. C. The Analyst 1901,26,139-159. (2) Simmersbach, 0. Stahl Eisen 1917,37, 502. (3) Valkovie, V. Trace Elements in Coal; CRC Press: Boca Raton, FL, 1983; 210 p. (4) National Research Council. Arsenic; Medical and biologic effects of environmental pollutants; National Academy of Sciences, 1977; 332 P.
(5) Gluskoter, H. J.; Ruch, R. R.; Miller, W. G.; Chill, R. A.; Dreher, G. B.; Kuhn, J. K. “Trace elements in coal: occurrences and distribution”; Illinois State Geological Survey Circular 499, 1977; 153 p. (6) Neavel, R. C., Sulfur in coal; its distribution in the seam and in mine products. Ph.D. Thesis, Pennsylvania State Univ., 322 p. (7) Altschuler, Z. S.; Schnepfe, M. M.; Silber, C. C.; Simon, F. 0. Science 1983,4607, 221-227.
This article not subject to US.Copyright. Published 1992 by the American Chemical Society
Arsenic-Bearing Pyrite Upper Freeport coal bed channel sample.
Facies 1
Facies 2
-
F l o a t 1.275
F l o a t 1.400
F l o a t 1.300
S l n k 1.800
Sink
1.800
Shale parting F l o a t 1.400
Slnk
1.800
Facies 3
Figure 1. The gravity separates examined in this study. They were obtained from the 8 X 100 mesh size fraction from a coal channel sample obtained from an interior part of the Upper Freeport coal bed, west-central Pennsylvania. The core was sampled by facies. The shale parting material was included in facies 3. For a detailed description of the facies, see Cecil and
other^.^
of As incorporation may be evaluated on the basis of recognition of specific As-bearing pyrite morphologies. The association of As with pyrite has been verified and documented in the Upper Freeport coal bed, west-central Pennsylvania.*12 Studies by Minkin and others1°J3 showed that certain pyrite forms, or morphologies, tend to contain As. Arsenic-bearing morphologies included massive, fractured, and/or mottled forms that are associated with fractures or cracks in the uppermost of the three coal facies (megascopically recognizable subunits in the coal) at the locations studied.13 These morphologies are considered to be epigenetic (formed after significant peat burial). Minkin and others13did find a single grain of As-bearing pyritelo in the two lower facies: that grain was framboidal in form. Framboidal pyrite, unlike the massive and fractured morphologies observed in the top facies, may form contemporaneously with the peat or very soon afterward. Its origin, therefore, is considered to be early to early-late syngenetic8 In electron microprobe (EMP) analyses of samples from the Upper Freeport coal bed, collected immediately adjacent to the samples studied by Minkin and others,1°-13another occurrence. of Asbearing pyrite was observed (Ruppert, 1983, unpublished data); the As was detected in pyritized plant cell walls. This type of As-bearing pyrite is rare and its origin is inferred to be ~yngenetic.~ On the basis of the EMP analyses, further study was initiated on the distribution of As in syngenetic pyrite morphologies, especially framboidal and cell-wall re(8) Querol, x.;Chinchon, s.;Lopez-Soler, A. Int. J. Coal Geol. 1989, 11, 171-189. (9) Cecil, C. B.; Stanton, R. W.; Dulong, F. T. "Geology of Contaminants in Coal: Phase I, Report of Investigations"; U.S. Geological Survey Open File Report 81-953-A; 92 p. (10) Minkin, J. A.; Finkleman, R. B.; Thompson, C. L.; Chao, E. C. T.; Ruppert, L. F.; Blank, H.; Cecil, C. B. Scanning Electron Microsc. 1984, 1515-1524. (11)Dulong, F. T.; Cecil, C. B.; Kilgroe, J. D. Elemental variability and characterization by physical coal cleaning-Arsenic, a case study. In Symposium Proceedings: A National Agenda for Coal-QualityResearch; Garbini, S., Schweinfurth, S. P., Eds.; U.S. Geological Survey Circular 979,1986; p 226. (12) Pierce, B. S.; Stanton, R. W. Pyritic sulfur and trace-element affinities in facies of the Upper Freeport coal bed, Allegheny Formation, west-central Pennsylvania. In USGS Research on Energy Resources1990 Program and Abstracts; Carter, L. M., Ed.; U.S. Geological Survey Circular 1060, 1990; p 64-65. (13) Minkin, J. A.; Finkelman, R. B.; Thompson, C. L.; Cecil, C. B.; Stanton, R. W.; Chao, E. C. T. Arsenic-bearing pyrite in the Upper Freeport coal, Indiana County, Pennsylvania. In Ninth International Congress of Carboniferous Stratigraphy and Geology, Abstracts of Papers, p 140-141.
Energy & Fuels, Vol. 6, No. 2, 1992 121 placement (CWR) forms. To do this, gravity separates from the three coal facies of the Upper Freeport coal bed present in the study area (Figure 1) were examined by EMP techniques. Although gravity separates offer the advantage of concentrating mineral matter for analysis, genetic or organic-mineral relationships are difficult to ascertain in the separates because the coal components are artificially separated and removed from their geologic context. Samples in the present study were chosen because extensive petrographic, chemical, and mineralogic data were a ~ a i l a b l e . ~ J ~These J ~ data show that the Upper Freeport is a medium-volatile bituminous coal (volatile matter = 29.4% (dry, ash-free basis)) with a Btu value of 15400. Ash and sulfur values are relatively low (11.7 and 2.11 wt % ,respectively) in the head sample, but variation among facies is ob~erved.~ For example, the ash content ranges from 8.2 wt % in facies 1to 21.3 wt % in facies 3 and total S ranges from 3.3 wt % in facies 1to 0.7 wt % in facies 2.9 Methods Petrographic pellets of the float 1.275,1.300,1.400,1.600, 1.800, and sink 1.800 gravity separates from each of the three facies were prepared according to ASTM standard procedures.16 The pellets were carbon-coated to prevent charging and examined for observable CWR pyrite with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray analyzer. The separates chosen for EMP analysis included the heaviest gravity fraction (sink 1.800) for facies 1, 2, and 3, the float 1.400 gravity fraction for facies 1and 3, and the floats 1.300 and 1.275 for facies 1. For As analyses, two EMPs were used, one for the quantitative measurement of pyrite compositions and the second for the qualitative determinations of As in traverses of pyrite grains. The quantitative measurements were made with an ARL-SEMQ electron microprobe and the traverses were made with an ARL EMX-SM microprobe. Both instruments were operated at 25 kV accelerating voltage and 150 nA beam (aperture) current. [Note: Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.] Initially, quantitative measurements consisted of determining s,Fe, As, Se, Hg, Cu, Ni, and Co concentrations in pyrite grains. Because Hg, Ni, Co, and Cu were not present in concentrations above the minimum detection limits (MDL) (approximately 0.04 wt %) in any of the grains analyzed and because there was no systematic variation in the concentration of Se with pyrite morphology, all of these elements were excluded from further analyses. Synthetic sulfide standards were used to calibrate the S, Fe, and As Ka!X-ray lines. Counting times of 120 s were used on the standards and the unknowns. The analyses were corrected for background and instrument drift, and deadtime and matrix correction procedures were applied by using the MAGIC IV correction r0utine.l' (14) Palmer, C. A.; Filby, R. H. Determination of the mode of occurrence of trace elements in the Upper Freeport coal bed using size and density separation procedures. In Proceedings of the 1983 International Conferenceon Coal Science; Pittsburgh Energy Technology Center, U.S. Department of the Interior: Pittsburgh, PA, 1983; p 365-368. (15) Dulong, F. T.; Cecil, C. B. Arsenic concentration variability and inorganic affinity for selected coal beds of Central Appalachian Basin. In Eastern Section American Association of Petroleum Geologists, Program with Abstracts, November 10-12,1985. (16) American Society for Testing and Materials. Standard method of preparing coal samples for microscopical analyses by reflected light: 1982 Annual Book of ASTM Standards, part 26,1982; p 373-377. (17) Colby, J. W. Adu. X-ray Anal. 1968, 11, 287-305.
122 Energy & Fuels, Vol. 6, No. 2, 1992
Ruppert et al.
Figure 2. SEM photomicrographs of the four analyzed pyrite morphologies. (A, upper left) Secondary electron (SE) image of framboids. (B, upper right) BSE image of a massive pyrite grain. (C, lower left) BSE image of CLR pyrite. Note that the cell walls are not replaced by pyrite. (D, lower right) BSE image of CWR pyrite with pyritized cell lumens (CL). Note that not all of the cell wall has been replaced by pyrite.
To assess total uncertainties in the analyses, the calibration was checked by analyzing an independent sulfide standard (C533) supplied by L. Cabri (1983, written communication). On the basis of 35 analyses of this standard, the MDL for As was determined to be approximately 0.02 w t %. Total estimated relative errors were less than 2% for Fe and S, and less than 10% for As. Qualitative traverses were made by peaking the microprobe spectrometers on the wavelengths for S Ka, Fe Ka, and As La. The samples were stepped across the electron beam at 5-pm increments, and counts were accumulated for 10 s at each step. Fifteen pyrite grains, some of which had been previously analyzed quantitatively and were determined to contain As, were traversed in this manner. The counts were compared with those for As-free pyrite standards of known composition to detect locations of As enrichment. Results A total of 39 pyrite grains, representing framboidal, massive, and cell-lumen replacement (CLR) and cell-wall replacement (CWR) pyrite morphologies were analyzed (Figure 2A-D). Only one or two of the observed framboidal and massive pyrite grains were analyzed in each sample; however, every observed CWR pyrite grain was analyzed. One hundred and seventy-four analyses were obtained on the analyzed grains (Table I). Arsenic was not detected in the few massive and framboidal grains that were examined in this study (Table I).
Figure 3. SEM-SE photomicrograph of CWR pyrite and contiguous CLR pyrite. Arsenic was detected in some CLR pyrite that was directly adjacent to As-bearing CWR pyrite, typically within 20 pm. Arsenic was not detected in the interior portions of CLR pyrite.
Arsenic was detected primarily in CWR and, more rarely, in CLR pyrite. Arsenic concentrations in CWR pyrite ranged from 0.06 to 1.87 w t %. Where arsenic was detected in CLR pyrite, the area analyzed was always in contact with As-bearing CWR pyrite; the As concentration was always highest adjacent to the As-bearing cell walls
Arsenic-Bearing Pyrite
Energy & Fuels, Vol. 6, No. 2, 1992 123
Table I. Quantitative Electron MicroDrobe Results for As in Pyrite from Gravity SeDarates of the UDwr FreeDort Coal" sample n freq, morph n(w/As) n(anal) wt % As range As % py sulfur ppm As notes float 1.275 0.13 0.06-0.21 0.17 2.0 no As in CLR pyrite facies 1 4 2,CWR 1 7 4 0 2, massive float 1.300 2 5 3,CWR 8 0.69 0.10-1.64 0.13 3.6 no As in CLR pyrite facies 1 1, framb 0 3 1, massive 0 2 float 1.400 2 2 2,CWR 20 0.68 0.21-1.18 0.54 25 facies 1 0.24 1 1, CLR 4 11 7, CWR facies 3 33 7.0 0.44 0.08-0.87 0.24 4 2, massive 0 2, framb 0 9 sink 1.800 5 29 0.55 0.10-1.87 2.54 670 facies 1 5 5,CWR 3 5 0.68 0.10-0.68 3, CLR 2 9 0.33 0.29-0.50 0.58 39 facies 2 4 3,CWR 0 18 1, framb 0 13 9 8 3,CWR facies 3 0 3, framb 10 2, massive 0 4 OAbbreviations: n = total number of grains analyzed; freq and morph = number of analyzed pyrite grains and morphology; n(w/As) = number of grains with As for each morphology; n(anal) = total number of analyses on individual morphologies; wt % As = mean weight percent As; As range = highest and lowest As value (in weight percent) determined in traverses across an individual grain; % py sulfur = weight percent pyrite in gravity separate (whole-codbasis); ppm As = parts per million As in gravity separate; CWR = cell-wall replacement pyrite; CLR = cell-lumen replacement pyrite; framb = framboid; wt % = weight percent.
and decreased to nondetectable levels toward the middle of the CLR pyrite (Figure 3). Where only CLR's were pyritized (Figure 2 0 , As was not detected. Most of the As-bearing pyrite grains were concentrated in the heaviest separates of facies 1 and 2, the facies that contained the highest pyritic sulfur and As concentrations (Table I). Of the 17 analyzed grains in the sink 1.800 fractions, seven CWR grains contained As. Detected As concentrations ranged from 0.1 to 1.87 wt %. Arsenic was not detected in pyrite from the sink 1.800gravity separate from facies 3. In analyses of the lighter gravity separates (Table I), in contrast to the sink 1.800 separate from facies 3, the float 1.400 separate from facies 3 yielded four CWR pyrite grains with As concentrations above the MDL. In the two lightest gravity separates, floats 1.300 and 1.275 from facies 1, three CWR pyrite grains contained detectable As. Comparison of electron microprobe traverses across massive, framboidal, CLR, and CWR pyrite grains from the various separates (Figure 4) indicate differences in As concentration. Arsenic concentrations remained at background levels for traverses across framboidal and massive pyrite grains (Figure 4, A and B). In traverses across grains where both the cell walls and the cell lumens were pyritized, when As was present in CWR pyrite, it was lacking in the interior portions of CLR pyrite. Although concentrations usually drop rapidly away from those pyritized cell walls that contain As (Figure 4C), occasionally a more gradual decrease in concentration is noted in the immediately adjacent cell lumens.
Discussion Detailed examination of CWR and CLR pyrite morphologies in the Upper Freeport coal bed shows that As appears to be incorporated in some of the analyzed grains. This is the first time As has been detected in CWR and CLR pyrite in the Upper Freeport coal. Although the mejority of Aa in the Upper Freeport coal bed is associated with massive, epigenetic pyrite forms (Minkin and othersl0J3),As was not detected in the massive grains that were examined in this study, probably because so few were analyzed.
Most of the As-bearing CWR pyrite is concentrated in facies 1, the upper facies, where pyritic sulfur and As concentrations are the highest; however, facies 2 and 3 also contain As-bearing CWR pyrite (Table I). Arsenic-bearing CWR pyrite was detected in the heaviest (sink 1.800) to the lightest (float 1.275) gravity separates. Lighter gravity separates rarely contain abundant accessory heavy mineral phases, but small fragments of As-bearingCWR and CLR pyrite were observed in the float 1.275. These small fragments, produced by grinding the coal during sample preparation, remain attached to organic particles that have been rafted into the lighter gravity separates. The As detected in some CLR pyrite grains may originate from adjacent and underlying As-bearing CWR pyrite and may therefore be an artifact of microprobe analysis. Arsenic was detected in only four CLR pyrite grains and only where they were adjacent to As-bearing CWR pyrite. Computer-generated Monte Carlo simulations18were used to mathematically predict the depth and width of X-ray generation in the microprobe analyses. For the operating conditions and target materials used in this study, an impinging electron beam measuring approximately 3-5 pm in diameter results in the analysis of a volume with a surface measuring approximately 9-11 pm in diameter. An analysis point of this diameter would have included adjacent As-bearing CWR pyrite. Arsenic was probably not detected in the centers of the pyritized cell lumens because the distance to the As-bearing CWR pyrite was greater than the excitation volume of the beam. From the microprobe data, we were unable to determine whether the As was present in pyrite in solid solution or as submicrometer inclusions of arsenopyrite. Because of the relatively small depth and width of penetration of the electron beam, randomly situated submicrometer inclusions of arsenopyrite could not be easily detected by differences in S and Fe concentrations because of the small size of inclusions in comparison to the electron beam. However, the back-scattered electron (BSE)mode of the (18) Joy, D. C.; Armstrong, J. MSPLOT-A Pascal program for Monte Carlo calculations of electron trajectories. Lehigh University Short Course in X-Ray Microanalyses.
Ruppert et al.
124 Energy & Fuels, Vol. 6, No. 2, 1992
aerobic environments of nonhydric soils, it commonly occurs as inorganic arsenate (Asv) bound to metal hydroxides. However, in anaerobic environments such as peat swamps, arsenite (As"') is the stable species.lg Arsenite is more toxic to plants than arsenate, but some plant species may have limited metabolic protection against arsenite (R.D. Wauchope, U.S. Department of Agriculture, 1990, oral communication). Small amounts of As in both valence states can be taken up by plant roots through the phosphate uptake system and transported to all active cells in the plant.Ig Once As is transported through the vascular system, plants metabolize small amounts of it by utilizing the biological detoxification process of biomethylation to reduce As to dimethylarsinic acid and other large organoarsenic AsV As"' (CH3)2AsOOH
MASSIVE PYRITE
4---4.cr.C*IrC.C)..Y*
100
le(
200
300
400
Traverse (microns) FRAMBOIDAL PYRITE
1200 1
- -
15
10
5
25
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El
REPLACEMENT PYRITE
1200 7
*
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100
150
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Organically bound As appears to be stable in plants22and may be encapsulated in the structural parts of the living plant20 or sequestered into cell walls (R. D. Wauchope, 1990, oral communication). However, sometime during the decay of the plant material, the organoarseniccompounds break down, through chemical degradation and/or biological processes that may be bacterially driven, into volatile arsines or other reactive As species. Although various organic and inorganic23reactions can occur to form these species, one possible biologically mitigated reaction helpful in understanding the formation of As-bearing CWR pyrite is a heterotrophic bacterial conversion of dimethylarsinic acid to dimethylarsine: (CHJzAsOOH (CHJ2AsH Methanogenic bacteria can catalyze this reaction24and sulfate-reducing bacteria may also do so (D. Lovely, U.S. Geological Survey, 1990, oral communication). If sulfate-reducing bacteria are active and Fez+is present when the degradation of As compounds occur, the As could be incorporated in sulfur c o m p o ~ n d ssome ,~~~ of~which may be precursors to pyrite.20 Alternatively, degradation of large organoarsenic compounds may not be necessary. For example, dimethylarsinic acid can react directly with S compounds by forming -S-AsMe2 derivative^.^^ Tolerance of plants to As is related to dosage and modifying parameters including plant species, soil types, and ~ l i m a t e .Although ~ the tolerance of As by Pennsylvanian age plants such as lycopods, tree ferns, and seed ferns cannot be known, modern ferns can contain up to 3.5 ppm As on a dry-weight basis.lg Tropical temperatures are known to increase As uptake in modern plants4 and may have done so in Pennsylvanian age plants. Certain Pennsylvanian plants may have had greater metabolic protection from As toxicity than others, and these plants
*I
I
i
250
300
Traverse (microns)
+
E Cell-lumen replacement pyMe (CLR) A = Cell-wall replacement pyrite (CWR)
Figure 4. Electron microprobe traverses across selected pyrite grains. Minimum detection limit for As was approximately 300 counta/s. Total errors in analysis are approximately 10%. (A) Traverse across a 550-rm-wide massive pyrite grain. Note the flat profile of the traverse at or around 300 counts/s indicative of the absence of detectable As. (B) Traverse across a framboidal pyrite grain. (C) Traverse across an As-bearing CWR pyrite grain with adjacent CLR (CL) pyrite. SEM is sensitive to differences in atomic number. If relatively large inclusions of arsenopyrite were present in the pyrite, they would show up as higher brightness areas. No differences were noted in As-bearing CWR pyrite in the SEM-BSE images. Cell-wall replacement pyrite in the Upper Freeport coal bed is probably formed during the peat stage of coal formation based on the lack of cell-wall and cell-lumen comp a ~ t i o n . Compactional ~ features are reported to form syngenetically, perhaps in two separate episodes, one very early and one somewhat later in the peat-forming stage.8 Because As appears to be consistently associated with CWR pyrite, it is likely, but speculative, that As was present in the cell walls of some of the peat-forming plants when they were growing. Therefore, we postulate the following organically-associatedsource for the As-bearing CWR pyrite. Arsenic is a natural trace component of marine and fresh waters and soils.4 However, the Upper Freeport coal bed is not associated with marine influence; it is strictly fresh-water. When As is present in the modern fresh-water
(19) Wauchope, R. D. Uptake, Translocation and Phytotoxicity of Arsenic in Plants. In Arsenic: Industrial, Biomedical, Environmental Perspectives, Proceedings of the Arsenic Symposium, Gaithersburg, Md; Lederer, W. H., Fersterheim, R. J., Eds.; Van Nostrand Reinhold: New York, 1982; p 348-377. (20) Andreae, M. 0.Biotransformation of Arsenic in the Marine Environment. In Arsenic: Industrial, Biomedical, Environmental Perspectives, Proceedings of the Arsenic Symposium, Gaithersburg, Md; Lederer, W. H., Fersterheim, R. J., Eds.; Van Nostrand Reinhold New York, 1982; pp 378-392. (21) Zingaro, R. A. Biochemistry of Arsenic: Recent Developments. In Arsenic: Industrial, Biomedical, Environmental Perspectives, Proceedings of the Arsenic Symposium, Gaithersburg, Md.; Van Nostrand Reinhold: New York, 1982; p 328-347. (22) Duble, R. L.; Holt, E. C.; Me%, G. C. J. Agric. Food Chem. 1969, 17,1237-1250. (23) Applegate, C. A.; Meyers, E. A.; Zingaro, R. A.; Merijanian, A. Phosphorus Sulfur 1988,35, 363-370. (24) McBride, B.; Wolfe, R. Biochemistry 1971, 10, 4312-4317.
Energy & Fuels 1992,6, 125-136 could have bioaccumulated methylated As in their tissues. Future work on the quantification of As in nonpyritized plant cell walls may lead to the identity of particular plant types that concentrated As. Cell-wall replacement pyrite is rare (less than 3% of the total pyriteg by volume) and As-bearing CWR pyrite is even rarer in facies samples of the Upper Freeport coal bed. This is to be expected as the toxicity of As precludes an organic association for all but a small amount of the substance. However, we do fiid it significant that some pyritized plant cell walls contain As. The Upper Freeport paleoswamp was probably similar to some other Pennsylvanian peat swamps, and because CWR pyrite is present in many Appalachian Basin Pennsylvanian age coals (W. Grady, 1990, personal communication) the postulated mechanism of As emplacement may apply to other
125
Pennsylvanian coal beds as well.
Conclusions Electron microprobe analyses of gravity separates from three facies of the Upper Freeport coal bed show that some CWR pyrite morphologies contain As. Arsenic values in CWR pyrite ranged from 0.06 to 1.87 w t %. Arsenicbearing CWR pyrite is most common in the uppermost facies of this coal bed. The As is postulated to have been present in the peat-forming environment where it may have been taken up by some of the plants and encapsulated in the cell walls through such processes as detoxification. Through chemical or biologic pathways, methylated organo-As compounds could have been released or volatilized and incorporated into cell walls during pyritization.
Chemical Structure of Bituminous Coal and Its Constituting Maceral Fractions As Revealed by Flash Pyrolysis+ Margriet Nip$ and Jan W. de Leeuw* Organic Geochemistry Unit, Faculty of Chemical Engineering and Materials Science, Delft University of Technology, De Vries van Heystplantsoen 2, 2628 RZ Delft, The Netherlands
John C. Crelling Coal Characterization Laboratory, Department of Geology, Southern Illinois University at Carbondale, Carbondale, Illinois 62901 Received December 10, 1990. Revised Manuscript Received November 25, 1991
To study the relationships between the chemical structures of coals, coal macerals, and their precursors (plant tissues), a high-volatile bituminous Upper Carboniferous coal and ita constituting maceral fractions, cutinite, resinite, sporinite, vitrinite, pseudovitrinite, semifusinite, and fusinite, were investigated by Curie point pyrolysis-gas chromatography and Curie point pyrolysis-gas chromatography-mass spectrometry. Single maceral fractions were isolated from the coal by density gradient centrifugation. In the pyrolysates of the density fractions similar types of pyrolysis products are observed; however, the relative contributions of these products vary considerably with the various density fractions. The variation in the distribution of the various pyrolysis products is sufficient to distinguish between the various maceral groups and to serve as a maceral “fingerprint”. The internal distribution patterns of the alkyl derivatives of some of these families of pyrolysis products are similar for all density fractions. This observation and the fact that all families of pyrolysis products occur in the pyrolysates of all density fractions probably indicate that on a chemical basis these fractions representing single macerals do not represent single chemical compounds. Despite this fact, it is still possible to relate the chemical nature of the most prominent types of pyrolysis products to structural elements present in the precursors of the macerals which are most dominantly present in the density fractions.
Introduction Coal is an extremely complex, heterogeneous material which consists mainly of a large variety of organic components derived from plant tissues. The biopolymers present in plant tissues and their chemical behavior upon coalification determine for the greater part the chemical structure of a coal. The organic components that constitute coal are called macerals. This term was originally ‘Delft Organic Geochemistry Unit, Contribution 139. Present address: Industrial Quimica del Nalon S. A., Apartado 8,33100 Trubia, Provincia de Oviedo, Spain.
*
introduced by Marie C. Stopes in 1935l in the following way: “I now propose the new word “Maceral ” (from the Latin macerare, to macerate) as a distinctive and comprehensive word tallying with the work “mineral”. Its derivation from the Latin word to “macerate” appears to make it peculiarly applicable to coal, for whatever the original nature of the coals, they now all consist of the macerated fragments of vegetation, accumulated under water. The concept behind the word “macerals”is that the complex of biological units (1)Stopes, M.C.h o c . R. SOC.,Ser. B lSlS,!W, 470.
0887-0624/92/2506-0125$03.00/00 1992 American Chemical Society
