CHAPTER 5
The Origin and Distribution of HAPs Elements in Relation to Maceral Composition of the A1 Lignite Bed (Paleocene, Calvert Bluff Formation, Wilcox Group), Calvert Mine area, East-Central Texas
By Sharon S. Crowley, Peter D. Warwick, Leslie F. Ruppert, and James Pontolillo
U.S. Geological Survey, MS 956, Reston, VA 22092
The origin and distribution of twelve potentially Hazardous Air Pollutants (HAPs; As, Be, Cd, Cr, Co, Hg, Mn, Ni, Pb, Sb, Se, and U) identified in the 1990 Clean Air Act Amendments were examined in relation to the maceral composition of the A1 bed (Paleocene, Calvert Bluff Formation, Wilcox Group) of the Calvert mine in east-central Texas. The 3.2 m-thick A1 bed was divided into nine incremental channel samples (7 lignite samples and 2 shaley coal samples) on the basis of megascopic characteristics.
Results indicate that As, Cd, Cr, Ni, Pb, Sb, and U are strongly correlated with ash yield and are enriched in the shaley coal samples. We infer that these elements are associated with inorganic constituents in the coal bed and may be derived from a penecontemporaneous stream channel located several kilometers southeast of the mining block. Of the HAPs elements studied, Mn and Hg are the most poorly correlated to ash yield. We infer an organic association for Mn; Hg may be associated with pyrite. The rest of the trace elements (Be, Co, and Se) are weakly correlated with ash yield. Further analytical work is necessary to determine the mode of occurrence for these elements. Overall, concentrations of the HAPs elements are generally similar to or less than those reported in previous studies of lignites of the Wilcox Group, east-central region, Texas.
Petrographic analysis indicates the following ranges in composition for the seven lignite samples: liptinites (5-8 percent), huminites (88-95 percent), and inertinites (trace amounts to 7 percent). Samples from the middle portion of the A1 bed contain abundant crypto-eugelinite compared to the rest of the samples; this relationship suggests that the degradation of plant material was an important process during the development of the peat mire. With the exception of Hg and Mn, relatively low levels of the HAPs elements studied are found in the samples containing abundant crypto-eugelinite. We infer that the peat-forming environment for this portion of the coal bed was very wet with minimal detrital input.
Relatively high concentrations of crypto-humotelinite were found in samples from the top and base of the coal bed. The presence of abundant crypto-humotelinite in this part of the coal bed suggests the accumulation of wood-rich peat under conditions conducive to a high degree of tissue preservation in the peat mire. Although several of the trace elements (Be, Co, Ni, and Sb) exhibit enrichment in these samples, they are not necessarily chemically associated with humotelinite. We infer that these elements, with the exception of Be, are possibly associated with deposition of the roof and floor rock of the coal bed; however, further analytical work would be necessary to confirm this hypothesis. Be may have an organic origin.
The U.S. Clean Air Act Amendments of 1990
identified potentially Hazardous Air Pollutants (HAPs) that may
be released during the combustion of coal. HAPs elements include
As, Be, Cd, Cr, Co, Hg, Mn, Ni, Pb, Sb, Se, and radionuclides
(e.g., U). In this study, we examined the origin and distribution
of these elements in lignite and shaley coal samples taken from
the A1 lignite bed of the Calvert Mine, east-central Texas (fig. 1).
We also identified the predominant maceral varieties in lignite
samples taken from the A1 bed to determine the association
between the trace elements and coal petrographic facies.
GEOLOGIC BACKGROUND
The lignite beds of the Calvert mine are
stratigraphically located in the lower Calvert Bluff Formation of
the Wilcox Group and are late Paleocene in age (N.O. Frederiksen,
written commun., 1995; fig. 2). The Wilcox Group,
estimated to be 366 to 1067 m thick in east-central Texas,
represents a major progradational phase (Kaiser and others,
1980). The Calvert Bluff Formation, primarily composed of mud
with sands and lignites, ranges in thickness from 152 to 610 m in
east central Texas (Kaiser and others, 1980). Ayers and Lewis
(1985) related lignite occurrence in the formation to sand
geometry and reported that sand bodies are paleofluvial channel
complexes that encase extensive interchannel floodbasins which
are mud-rich and contain abundant lignite. The most striking
characteristics of the Calvert Bluff Formation within the mining
blocks of the Calvert mine are the cyclical deposition, lateral
persistence of the lithologic units, and the overall sand-poor
nature of the overburden (Middleton and Luppens, this volume).
Five major and two minor lignite beds are mined within the
Calvert Mine. The A1 bed is stratigraphically the lowest, major
minable bed in the Calvert mine and also the thickest and most
areally extensive lignite bed in the mine (Middleton and Luppens,
this volume). A large penecontemporaneous sandstone channel is
present in the A1 bed; the main body of the channel is located a
few kilometers southeast of the sample location and is oriented
elongate to the northeast.
PREVIOUS WORK
Tewalt (1986) provided a com-prehensive characterization of near surface lignites in the Wilcox Group for east-central, northeast, and eastern Texas. Reported data included a summary of mean concentrations for proximate data, forms of sulfur data, ultimate analyses, major oxide data, and trace element analyses (Tewalt, 1986). Other studies have been made to compare chemical characteristics of samples from several states in the Gulf Coast lignite region (Oman and Meissner, 1987), to relate chemical characteristics of Gulf Coast lignites to depositional environment (Tewalt, 1987), and to examine the lateral and vertical variation of inorganic constituents in a mine of the Wilcox Group of east central Texas (Finkelman and Bhuyan, 1987). Benson (1987) reported on inorganic constituents in lignites from the Martin Lake mine (Wilcox Group) of east Texas and compared results to lignites of North Dakota. The coal petrography of lignites in the Wilcox Group has been investigated in relation to coal geochemistry, regional geology, hydrocarbon generation, and peat-forming environments in samples from outcrop, near-surface mines, and boreholes (Mukhopadhyay, 1987 and 1989). As a part of these studies, the petrographic composition of channel and lithotype samples collected from two mines (Sandow and Big Brown mines) located within 160 km of the Calvert mine is described (Mukhopadhyay, 1989). Other petrographic work has been completed on Texas lignites, however, the focus of these studies has been primarily to characterize liquefaction behavior (Spackman and others, 1976; Parkash and others, 1984).
The authors would like to thank Mark Middleton of the Walnut Creek Mining Company and Jim Luppens of the Phillips Coal Company for permission to collect samples in the Calvert mine and for facilitating our work in the mine.
DESCRIPTION OF SAMPLES
Nine incremental channel samples (seven lignite
samples and two shaley coal samples; fig. 3) were collected on the
basis of megascopic characteristics from a mine highwall in the
A1 bed of the Calvert mine near Bremond, Texas in April, 1993
(Block A, Cut 23, Pit A). Approximate location of the sample site
is 31o 05' 77" N, 96o 39' 19"W.
Incremental channel samples were collected in order to determine
the vertical variability of physical and chemical characteristics
of the coal bed. Because the mine highwall had been exposed for
about one month, samples were collected only after 30 cm of
lignite were removed from the face of the coal bed. The A1 bed
was divided into three sections: A1.1 lignite samples (a total of
192 cm thick), A1.P shaley coal samples (a total of 31 cm thick),
and A1.2 lignite samples (a total of 92 cm thick). Samples A1.P1
and A1.P2 are referred to as "shaley coal" samples in
this study because their megascopic characteristics were distinct
from the rest of the lignite samples in the A1 bed; samples A1.P1
and A1.P2 have an ash yield of 29.2 and 40.6 percent (air-dried
basis), respectively. Because the ash yields of the shaley coal
samples are less than 50 percent, we have assumed that they are
part of the minable lignite in this study.
CHEMICAL ANALYSIS
American Society for Testing and Materials standard proximate and sulfur form analyses were obtained for all lignite samples (ASTM, 1985). Elemental chemistry for 60 elements of the lignite and shaley coal samples were determined using inductively coupled plasma atomic emission spectroscopy (Na2O, SiO2, Al2O3, CaO, MgO, K2O, Fe2O3, TiO2, P2O5, B, Ba, Be, Co, Cr, Cu, Li, Mn, Ni, Sc, Sr, Th, V, Y, Zn, Zr), inductively coupled plasma mass spectroscopy (Ag, As, Au, Bi, Cd, Ce, Cs, Dy, Er, Eu, Ga, Gd, Ge, Hf, Ho, La, Mo, Nb, Nd, Pb, Pr, Rb, Sb, Sm, Sn, Ta, Tb, Te, Tl, Tm, U, Yb ), atomic absorption spectroscopy graphite furnace (Hg), X-ray fluorescence analysis (P), and hydride generation atomic absorption spectroscopy (Se). In this paper, all data are presented on a whole-coal basis (table 1). The distribution of the HAPs trace elements is depicted graphically in figure 4 for both lignite and shaley coal samples.
R-mode cluster analysis was applied to chemical data (60 elements, sulfur forms, and ash yield), on a whole-coal basis, for the seven lignite samples and the two shaley coal samples to identify groups of elements that were positively intercorrelated and to aid in the interpretation of their genetic groupings. The dendrogram produced by cluster analysis is displayed in figure 5. All chemical data were standardized (standardized to the same scale new variables with a mean=0 and standard deviation=1) before being used in cluster analysis. Standardization removes scale attributes within each set of data, and it equalizes the influence of variables with small variation to those with large variation (Massart and Kaufman, 1983). The clustering method used was the unweighted pair-group average with the squared euclidean distances measure. The unweighted pair group average method defines the distance between two clusters as the average of the distances between all pairs of cases in which one member of the pair is from each of the clusters (SPSS/PC, Inc., 1988). This method is preferred to the single and complete linkage methods because it uses information about all pairs of distances, not just the nearest or furthest (SPSS/PC, Inc., 1988). The centroid method was not used because it calculates the distance between two clusters as the distance between their means for all of the variables; a disadvantage of this method is that the distance at which clusters are combined can actually decrease from one step to the next. Since clusters merged at later stages are more dissimilar than those merged at early stages, this is an undesirable property (SPSS/PC, Inc., 1988).
Correlation coefficients were also calculated
between each of the HAPS elements and ash yield using the Pearson
Product-Moment Correlation Coefficient, to determine
relationships between concentrations of elements and ash yield (table 2). The value of the correlation coefficient does not
depend on the specific measurement units used and represents the
linear relationship between two variables (StatSoft Inc., 1994).
The sig-nificance level, or p-level, calculated for correlations
is an estimated measure of the degree to which the correlation is
repre-sentative of the population (StatSoft Inc., 1994). The
p-level for correlation coefficients in this study is .05, which
indicates that there is a 5% probability that the relation
between the variables found in the sample set are not valid.
MACERAL ANALYSIS
Seven lignite samples were analyzed for maceral composition. All petrographic data are presented in table 3. Maceral composition was determined by point counting standard polished pellets made from splits of each sample (ASTM, 1985). A total of 22 maceral varieties were counted. Huminite maceral varieties were counted using reflected white light on the etched surfaces of polished pellets. Etching the pellets with a potassium permanganate and sulfuric acid solution (Stach and others, 1982) permitted a detailed subdivision of the huminite group. Because etching methods were used in the identification of huminite maceral varieties, the prefix "crypto" was added to huminite varieties in this paper as suggested by Stach and others (1982). Inertinite maceral varieties were counted using reflected white light on non-etched surfaces of pellets, and liptinite maceral varieties were counted using blue-light fluorescence on non-etched surfaces of pellets. Two pellets made from each split were counted, yielding 2000 counts per sample. In this paper, all maceral percentages cited are mean volume percentages on a mineral-free basis. The distribution of maceral varieties (crypto-humotelinite, crypto-eugelinite, and crypto-poricorpohuminite in crypto-telinite) that showed the greatest variation throughout the channeled section is depicted graphically (fig. 6).
CHEMICAL ANALYSIS
Two major groups of elements were formed by R-mode cluster analysis of the chemical data from the nine samples (fig. 5). Cluster A contains two of the HAPS elements (Mn and Hg) in addition to Fe2O3, SO3, CaO, and Sr. Cluster A correlates very poorly to ash yield. This relationship is further demonstrated by negative correlation coefficients for Mn and Hg to ash yield (table 2). Cluster B consists of 54 elements and ash yield. Ten of the HAPS elements are included in cluster B: Be, Co, Se, Ni, Sb, U, Th, Pb, Cd, Cr, and As. Cluster B contains three subset clusters (I, II, and III). Cluster I comprises many of the heavy rare earth elements in addition to Be and Co. Cluster I correlates weakly with ash yield, as correlation coefficients of less than 0.32 also demonstrate (table 2). Cluster II contains many of the light rare earth elements in addition to Ni and Sb. Cluster II correlates somewhat more strongly than Cluster I to ash yield as indicated by the dendrogram and correlation coefficients (table 2). Cluster III contains five HAPS elements (As, Cd, Cr, Pb, and U) which correlate strongly with ash yield. Correlation coefficients for these elements and ash yield are greater than or equal to 0.85 (table 2).
The correlation between the HAPS elements and
ash yield is also apparent in the graphs of elemental
distribution (fig. 4). As, Cd, Cr, Pb, and U are enriched in the shaley coal
samples (A1.P1 and A1.P2). In contrast, Mn decreases in abundance
in the shaley coal samples and Hg concentrations show a poor
relationship to ash yield. Low levels of Be are found in the
shaley coal samples, in comparison with the rest of the coal bed.
Co, Ni, and Sb show enrichment in the shaley coal samples in
addition to samples at the roof and base of the coal bed. Se
increases in abundance in the shaley coal samples; however, it is
also abundant in low-ash lignite samples of the coal bed.
MACERAL ANALYSIS
Petrographic analysis indicates the following ranges in composition for the seven lignite samples: liptinites (5-8 percent), huminites (88-95 percent), and inertinites (trace amounts to 7 percent). Graphs show the distribution of the maceral varieties (crypto-humotelinite, crypto-eugelinite, and crypto-poricorpohuminite) having the greatest variation in concentration throughout the channeled section of the A1 bed (fig. 6). Petrographic analysis indicates that samples from the top (A1.1.1 and A1.1.2) and base (A1.2.2 and A1.2.3) of the coal bed contain higher concentrations of crypto-humotelinite (22-28 percent) than samples from the middle part of the coal bed (13-17 percent). These samples also contain lower levels of crypto-eugelinite (53-65 percent) than samples from the middle portion (A1.1.3, A1.1.4, and A1.2.1) of the coal bed (69-72 percent). Sample A1.2.2 contains the highest level of crypto-poricorpohuminite (8 percent).
CHEMICAL ANALYSIS
Graphs of elemental distribution indicate that As, Cd, Cr, Ni, Pb, Sb, and U are enriched in the shaley coal samples compared to most of the lignite samples in the channeled section (fig. 4). R-mode cluster analysis and correlation coefficients further demonstrate a strong correlation (correlation coefficients greater than 0.56) between these elements and ash yield (fig. 5, table 2). We infer that these elements are associated with inorganic constituents in the coal bed and are probably derived from the penecontemporaneous stream channel located several kilometers southeast of the mining block. Previous work supports the occurrence of As, Cd, Pb, Sb, and U as inorganic constituents in coal; however, evidence indicates that substantial amounts of Ni in coal may be organically bound (Finkelman, 1994). There are insufficient data to specify the mode of occurrence of Cr in coal (Finkelman, 1994).
Of the HAPs elements studied, Mn and Hg are the most poorly correlated to ash yield. Cluster analysis, correlation coefficients, and graphs of the distribution of Mn and Hg in the channeled section are consistent with this observation. We infer an organic association for Mn; previous work also suggests an organic association for Mn in low-rank coals (Swaine, 1990). Although both organic and inorganic associations for Hg have been noted in the literature, much of the Hg in coal appears to be in solid solution in pyrite (Finkelman, 1994). The distribution of pyritic sulfur (table 1) and R-mode cluster analysis of chemical data for the A1 bed also indicate the association of Hg with pyrite. The concentration of pyritic sulfur is generally very low for most samples in the A1 bed; however, sample A1.1.3 contains 2.09 percent pyritic sulfur.
Co and Se cluster weakly with ash yield (clusters B, I, and II; fig. 5). These elements may have an organic association, as suggested in previous studies (Finkelman, 1981; Finkelman, 1994). In particular, abundant evidence in the literature supports a dominant organic association for Se (Dreher and Finkelman, 1992; Finkelman, 1994). However, further analytical work would be necessary to definitely determine the modes of occurrence for Co and Se.
Concentrations of ten of the HAPs elements (using weighted averages repre-senting the entire thickness of the A1 lignite bed) are generally similar to or less than geometric means reported by Tewalt (1986) for lignites of the Wilcox Group in the east-central region of Texas (table 4). Exceptions include Mn, which occurs at a level of 148 ppm in the A1 lignite bed, compared to a mean average of 92 ppm for the lignites of the Wilcox Group. Se also occurs in elevated concentrations in the A1 bed (9 ppm) compared to the geometric mean for the Wilcox Group (4.3 ppm). Additional sampling in the Calvert mine would provide information on the local lateral variability of the A1 bed.
The Calvert mine provides feedstock for the
Texas-New Mexico Power Company (TNP) fluidized bed boiler. One
advantage of the circulating fluid bed combustor is that it can
efficiently burn coals with high sulfur and high ash contents;
scrubbers are not needed in this system to reduce sulfur
emissions (TNP, 1995). In the future, if emissions of any of the
potentially hazardous elements are found to exceed recommended
limits, perhaps selective mining of the A1 bed to eliminate or
dilute layers enriched in these elements would reduce emissions
to acceptable levels.
MACERAL ANALYSIS
Ranges in composition for the seven lignite samples of the A1 bed ( huminites: 88-95 percent; inertinites: trace amounts to 7 percent; and liptinites: 5-8 percent;) are in sharp contrast to those reported for samples of lignite from the Sandow and Big Brown mines of east-central Texas: huminites (53-79 percent), inertinites (2-14 percent), and liptinites (18-38 percent) (Mukhopadhyay, 1989). The contrast in petrographic compositions can perhaps be attributed to different sampling methods used in each study. Some of the samples analyzed by Mukhopadhyay were channel samples representing thicknesses of the coal bed (1.8 m or more) that were greater than those used in the present study (sample thicknesses of 0.6 m or less). Sample thickness data are not available for some of the samples described in Mukhopadhyay (1989).
Analysis of the distribution of maceral varieties in the A1 bed indicates that coal samples in the middle portion of the coal bed contain a higher percentage of crypto-eugelinite (55-70 percent) than samples from the top or base of the coal bed (fig. 6). The samples are from areas directly above and below the shaley coal samples (samples A1.P1 and A1.P2), which have a total thickness of 31 cm. Crypto-eugelinite represents a humic gel that results mainly from strongly decomposed plant parts originally low in lignin and rich in cellulose (Stach and others, 1982). The presence of crypto-eugelinite in the middle portion of the coal bed suggests that the peat-forming environment was conducive to biogenic or chemical conditions that enabled the degradation of plant material into matrix gels. Humic colloidal solutions or gels, which are precursors to crypto-eugelinite, form preferentially through oxidation of peat and brown coal in the presence of abundant water (Stach and others, 1982). Crypto-eugelinite has also been found to be particularly abundant above clay partings which dam up water (Stach and others, 1982; Crowley and others, 1994). We infer that the peat-forming environment for the middle portion of the A1 coal bed was very wet.
The highest percentages of crypto-humotelinite (22-27%) were found in samples from the top and base of the coal bed (fig. 6). The uppermost sample in the coal bed (A1.1.1) contained compressed wood logs up to 7 cm thick and 50 cm wide (fig. 3). Concentrations of crypto-humotelinite probably result from the accumulation of wood-rich peat under conditions conducive to a high degree of tissue preservation. These conditions may have been related to a low pH environment (Cecil and others, 1985) or differential decay of certain plants or plant parts (Thiessen, 1925; Teichmüller and Teichmüller, 1968). The presence of abundant crypto-poricorpohuminite in crypto-humotelinite at the base of the coal bed (sample A1.2.2) is also a good indicator of tissue preservation.
The distribution of maceral varieties in the A1
coal bed is similar to that of the thick (>30 m),
subbituminous Wyodak-Anderson coal bed of the Powder River Basin,
Wyoming. Warwick and Stanton (1988) report that the upper and
lower parts of the Wyodak-Anderson coal bed are rich in preserved
wood remains whereas the middle part of the bed contains
comparatively larger amounts of material that resulted from
degradation and comminution of the peat (e.g.,
crypto-eugelinite).
COMPARISON OF THE DISTRIBUTION OF HAPS ELEMENTS TO PETROGRAPHIC FACIES
Examination of the distribution of the HAPs elements (fig. 4) indicates that relatively low levels of the HAPs trace elements, with the exception of Mn and Hg, occur in samples taken from the middle portion of the coal bed (A1.1.3, A1.1.4, and A1.2.1), in areas adjacent to the 31 cm-thick shaley coal samples. As discussed previously, these samples contain the highest levels of crypto-eugelinite in the channeled section (fig. 6) and the peat-forming environment for this portion of the coal bed was probably very wet. Because these samples have the lowest ash yields of the entire coal bed (9-12 percent) and contain relatively low levels of the trace elements studied, we infer that the peat had a lower level of detrital input than at other stages in the development of the peat.
Several HAPs elements (Be, Co, Ni, and Sb) exhibit enrichment in samples taken from the top and base of the coal bed (A1.1.1 and A1.2.3), although not necessarily to the degree of enrichment found in the shaley coal samples (e.g. Ni and Sb). Samples from the top and base of the coal bed have high concentrations of crypto-humotelinite compared to the rest of the coal bed and ash yields that range from 15.2 to 30.0 percent. We infer that these elements are also associated with detrital input, possibly associated with deposition of the roof and floor rock of the coal bed; however, further analytical work would be necessary to make this determination. Nutrients derived from sediment input may have promoted the growth of plants containing woody tissue. With the exception of Be, these elements are probably not chemically associated with woody plant material. Because evidence in the literature suggests an organic affinity for Be (Finkelman, 1994), it is possible that Be is derived from crypto-humotelinite in the A1 bed. However, additional analytical work would be necessary to confirm this hypothesis.
Examination of the origin and distribution of potentially hazardous trace elements of the A1 bed of the Calvert mine indicates:
REFERENCES CITED
American Society for Testing and Materials (ASTM), 1985, Annual Book of ASTM Standards - Petroleum Products, Lubricants and Fossil Fuels, v. 5.05 Gaseous Fuels; Coal and Coke, 572 p.
Ayers, W.B. and Lewis, A.H., 1985, The Wilcox Group and Carrizo Sand (Paleocene) in East-Central Texas: Depositional Systems and Deep Basin Lignite: The University of Texas at Austin, Bureau of Economic Geology, 19 p.
Benson, S.A., 1987, Inorganic constituents in selected Texas and North Dakota lignites, in Finkelman, R.B., Casagrande, D.J., and Benson, S.A., eds., Gulf Coast Lignite Geology, Reston, Va., Environmental and Coal Associates, p. 224-230.
Cecil, C.B., Stanton, R.W., Neuzil, S.G., Dulong, F.T., Ruppert, L.F., and Pierce, B.S., 1985, Paleoclimate controls on late Paleozoic sedimentation and peat formation in the Central Appalachian Basin (U.S.A.): International Journal of Coal Geology, v. 5, p. 195-230.
Crowley, S.S., Dufek, D.A., Stanton, R.W., Ryer, T.A., 1994, The effects of volcanic ash disturbances on a peat-forming environment: Environmental disruption and taphonomic consequences: PALAIOS, v. 9, p. 158-174.
Dreher, G.B. and Finkelman, R.B., 1992, Selenium mobilization in a surface coal mine, Powder River basin, Wyoming, USA: Environmental Geology and Water Sciences, v. 19, no. 3, p. 155-167.
Finkelman, R.B., 1981, Modes of occurrence of trace elements in coal., U.S. Geological Survey Open-File Report, 81-99, 312 pp.
Finkelman, R.B., and Bhuyan, K., 1987, Inorganic geochemistry of a Texas lignite, in Finkelman, R.B., Casagrande, D.J., and Benson, S.A., eds., Gulf Coast Lignite Geology, Reston, Va., Environmental and Coal Associates, p. 231-241.
Finkelman, R.B., 1994, Modes of occurrence of potentially hazardous elements in coal: Levels of confidence: Fuel Processing Technology: v. 39, p.21-34.
Kaiser, W.R., Ayers, W.B., Jr., and La Brie, L.W., 1980, Lignite resources in Texas: The University of Texas at Austin, Bureau of Economic Geology Report of Investigations 104, 52 p.
Massart, D.L., and Kaufman, L., 1983, The interpretation of analytical chemical data by the use of cluster analysis., New York, Wiley.
Mukhopadhyay, P.K., 1987, Petrography of selected Wilcox and Jackson Group lignites from the Tertiary of Texas, in Finkelman, R.B., Casagrande, D.J., and Benson, S.A., eds., Gulf Coast Lignite Geology, Reston, Va., Environmental and Coal Associates, p. 140-159.
Mukhopadhyay, P.K., 1989, Organic petrography and organic geochemistry of Texas Tertiary coals in relation to depositional environment and hydrocarbon generation: The University of Texas at Austin, Bureau of Economic Geology Report of Investigations 188, 118 p.
Oman, C.L., and Meissner, C.R., Jr., 1987 Chemical analysis of Gulf Coast lignites samples with significant comparisons and interpretations of results, in Finkelman, R.B., Casagrande, D.J., and Benson, S.A., eds., Gulf Coast Lignite Geology, Reston, Va., Environmental and Coal Associates, p. 211-223.
Parkash, S., DuPlessis, M.P., Camerson, A.R., and Kalkreuth, W., 1984, Petrography of low-rank coals with reference to liquefaction potential: International Journal of Coal Geology, v. 4, no. 3, p. 209-234.
Spackman, W., Davis, A., and Mitchell, G.D., 1976, The fluorescence of liptinite macerals: Brigham Young University Geological Studies, v. 22, p. 59-75.
SPSS/PC Inc., 1988, Advanced Statistics for the IBM PC/XT/AT.
Stach, E., Mackowsky, M.-Th., Teichmüller, M., Taylor, G.H., Chandra, D., and Teichmüller, R., 1982, Stach's Textbook of Coal Petrology, Third Edition, Gebrüder Borntraeger, Berlin, 535 pp.
StatSoft, Inc., 1994, Statistica for Windows, v. I, General Conventions and Statistics I, p. 1001-1718.
Swaine, D.J., 1990, Trace Elements in Coal, London, Butterworths, 278 p.
Teichmüller, M., and Teichmüller, R., 1968, Cainozoic and Mesozoic coal deposits of Germany, in Murchison, D.G., and Westoll, T.S., eds., Coal and Coal-Bearing Strata, Edinburgh, Oliver and Boyd, p. 347-377.
Tewalt, S. J., 1986, Chemical Characterization of Texas Lignite: The University of Texas at Austin, Bureau of Economic Geology Geological Circular 86-1, 54 p.
Tewalt, S.J., 1987, Chemical characteristics of Gulf Coast Lignites, in Finkelman, R.B., Casagrande, D.J., and Benson, S.A., eds., Gulf Coast Lignite Geology, Reston, Va., Environmental and Coal Associates, p. 201-210.
TNP (Texas New Mexico Power Company), 1995, General description of TNP1 fluidized bed boiler, 12 p.
Thiessen, R., 1925, The constitution of coal: Transactions of the American Institute Mining, and Metallurgical Engineers, v. 1438, p. 1-50.
Warwick, P.D., and Stanton, R.W., 1988, Petrographic characteristics of the Wyodak-Anderson coal bed (Paleocene), Powder River Basin, Wyoming, U.S.A.: Organic Geochemistry, v. 12, no. 4, p. 389-399.
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