distinguishing ''new'' from ''old'' organic carbon on reclaimed coal mine ...

0038-075X/07/17204-292–301 Soil Science Copyright * 2007 by Lippincott Williams & Wilkins, Inc.

April 2007 Vol. 172, No. 4 Printed in U.S.A.

DISTINGUISHING ‘‘NEW’’ FROM ‘‘OLD’’ ORGANIC CARBON ON RECLAIMED COAL MINE SITES USING THERMOGRAVIMETRY: I. METHOD DEVELOPMENT Sally Maharaj1, Christopher D. Barton1, Tasos A. D. Karathanasis2, Harry D. Rowe3, and Susan M. Rimmer3 Reclaimed coal mine sites represent a potential terrestrial carbon (C) sink. However, there is currently no cost-effective, rapid, and reliable method to quantify soil organic matter accumulation in soils containing appreciable quantities of coal and carbonate media. The derivative thermogravimetry method was evaluated as a potential analytical tool for differentiating C in spoils that may contain both recently derived (Bnew^) and ancient (Bold^) C fractions. Grass litter and coal were used to represent Bnew^ and Bold^ organic C, respectively, and limestone to represent the carbonate fraction. Analysis was carried out using a temperature ramp of 20 -C minj1 and a nitrogen flow rate of 20 mL minj1 on a TG analyzer. Derivative thermogravimetry curves showed pyrolysis peaks at distinctively different temperatures: grass litter, 270 to 395 -C; coal, 415 to 520 -C; limestone, 700 to 785 -C. Recoveries from mixtures of these three components at the 95% confidence interval were found to be 94.49% T 4.23% (coal), 93.67% T 2.11% (litter), and 108.88% T 2.88% (limestone). Petrographic analysis was used to validate derivative thermogravimetry findings. Duplicate point count analyses (300 points) of a 1:1:1 mixture of grass litter, coal, and limestone yielded 39.2% T 1.2% of Bnew^ organic C, 35.0% T 2.4% of coal, and 25.9 T 1.2% of minerals (in this case, limestone). These results indicate that organic petrography can be a useful approximation of Bnew^ organic C, but particle density differences and time constraints might limit it. Thermogravimetry appears to be the superior of the two methods as it proved to be a more cost-effective, rapid, and direct method for differentiating and quantifying C. (Soil Science 2007;172:292–301) Key words: carbon sequestration, thermogravimetry, coal, carbonates, mine land reforestation.

ROJECTED climate change resulting from elevated atmospheric carbon dioxide (CO2) has given rise to various strategies designed to sequester C in terrestrial ecosystems. Reclaimed coal mine soils represent one such potential C sink. However, quantifying Bnew^ organic C

(organic matter that has been added to soil through recent biological processes, such as plant root exudates and detrital matter) in reclaimed mine soils has proven to be difficult because of the presence of carbonate minerals and coal particles in the reclaimed coal mine spoils. Larger, visible coal particles can be removed, but smaller, indiscernible coal fragments and dust particles may be difficult to isolate as they have similar coloration to the parent materials. Methods to determine organic C in mine spoils are problematic because they do not distinguish between Bold^ organic C (such as, fossilized plant matter, limestone, and coal fragments) and

P

1Department

of Forestry, University of Kentucky, Lexington, KY 40546. Dr. Barton is corresponding author. E-mail: [email protected]

2Department

of Agronomy, University of Kentucky, Lexington, KY 40506.

3Department

of Geology, University of Kentucky, Lexington, KY 40506.

Received Aug. 16, 2006; accepted Dec. 11, 2006. DOI: 10.1097/SS.0b013e31803146e8

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VOL. 172 ~ NO. 4 USE OF THERMOGRAVIMETRY IN DISTINGUISHING ORGANIC CARBON 293 TABLE 1 Total C and N content from LECO analysis for standard and reference samples %C

Sample Grass litter (n = 20) Coal (n = 20) Limestone (n = 20) Apple leaves (NIST). (n = 10) Cellulose. (n = 10) Lignin. (n = 10) Mixture (35:45:20 litter/coal/limestone) (n = 20) Standard samples. .

%N

Mean

S.D.

Mean

S.D.

43.42 71.60 13.74 47.99 43.11 59.58 50.17

0.14 0.52 0.30 0.10 0.08 0.16 0.34

1.94 1.42 0.29 2.34 0.05 0.25 1.43

0.02 0.04 0.01 0.01 0.01 0.02 0.03

Reference samples EDTA (LECO standard) recoveries ranged from 99.4% to 100.6% for C and from 98.5% to 100.7% for N.

Bnew^ organic C. Some researchers have tried simple techniques such as flotation to physically separate the coal particles, but this has proven to be unsuccessful (Akala and Lal, 2001). Other techniques such as diffuse reflectance infrared Fourier transform spectroscopy and 13C-CPMAS NMR spectroscopy (Rumpel et al., 2000) have been suggested but are expensive and instrument availability is limited. Methods employing rapid dichromate oxidation techniques (Nelson and Sommers, 1996) have also been found to be inappropriate as these methods cannot discriminate between C in carbonized materials and C in soil organic matter. This is because of the variation in organic C recovery with the type of carbonized material and time, temperature, and hazardous nature of heating the chromic acid mixture (Nelson and Sommers, 1996). Wet and dry combustion techniques have been used to remove inorganic C by acid dissolution and use evolved CO2 to quantify organic C or use the difference between total C and quantified inorganic C to estimate organic C (Allison, 1960; Nommik, 1971). However, researchers have found acid dissolution to be ineffective in removing all carbonate C (Midwood and Boutton, 1998). A correction factor to account for unoxidized inorganic C may be used, but its utility depends upon the type of soil and

soil horizon, indicating that there is no appropriate correction factor for all soils (Nelson and Sommers, 1996). Thermal analysis techniques, which allow for measurement of a physical property of a substance (mass, temperature, enthalpy) while it is subjected to a controlled temperature program (Wendlandt, 1986), may provide the avenue for monitoring soil organic matter changes in soil containing coal and carbonate phases. For instance, differential scanning calorimetry (DSC) is commonly used to provide quantitative data for minerals in soil (Karathanasis and Harris, 1994). Differential scanning calorimetry has also been used to characterize soil organic carbon (C), monitor changes in organic matter associated with clays, and evaluate organic matter maturation during the composting process (Dell’Abate et al., 2000; Lopez-Capel et al., 2005; Pietro and Paola, 2004; Plante et al., 2005). Another thermal analysis technique, thermogravimetry (TG), was suggested for rapid, reliable and simultaneous screening of soil components such as organic C, nitrogen (N), clay, and carbonates (Siewert, 2004). The first derivative of the TG, derivative thermogravimetry (DTG), is obtained simultaneously. Subtle inflections on the TG are represented by discrete peaks on the DTG curve that allow for interpretation and resolution of thermal events. Thermogravimetry has been

TABLE 2 Thermogravimetry and derivative thermogravimetry pyrolysis data for standards (n = 5) Sample Grass litter Coal Limestone Cellulose Lignin

Weight loss (%) 270–400 -C

415–520 -C

9700 -C

58.6 T 1.1 ND ND 83.2 T 1.2 35.8 T 1.1

ND 23.7 T 0.1 ND ND ND

ND ND 39.8 T 0.7 ND ND

ND = not determined.


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organic matter, whereas weight loss above 600 -C can be attributed to calcium carbonate minerals (Dagounaki et al., 2004; Dell’Abate et al., 2000; Lopez-Capel et al., 2005; Piotrowski, 1999; Siewert, 2004). Thus, TG/DTG may be useful as a simple and direct method for quantifying Bnew^ C in spoils of mixed materials at coal mine sites. A standard procedure for measuring C sequestration in soil and geologic media is needed. Thus, a study was initiated to evaluate TG/ DTG as a potential cost-effective, rapid, and simple method for quantifying and differentiating Bnew^ organic C from carbonates and coal. Differential scanning calorimetry was used to confirm TG/DTG results, and petrographic analysis was used as a standard method for validating the TG results. MATERIALS AND METHODS

Fig. 1. Representative TG (I) and DTG (II) patterns for (A) grass liter, (B) coal, and (C) limestone.

used to study coal and carbonate rocks (Avid et al., 2002; Dagounaki et al., 2004; Warne, 1985, 1996; Khraisha and Shabib, 2002; Levy and Kramer, 1988; Varey et al., 1996), oil shales (Khraisha and Shabib, 2002; Levy and Kramer, 1988), soil minerals (Karathanasis and Harris, 1994), and organic matter fractions (Dell’Abate et al., 2000; Leinweber et al., 1992; Pietro and Paola, 2004; Plante et al., 2005). Although the type of reaction and temperature region for weight loss varies widely between soil minerals (Karathanasis and Harris, 1994), general weight losses at temperatures lower than 200 -C can be attributed to the loss of crystalline lattice H2O and hygroscopic H2O in salts and organic matter, those between 250 and 450 -C are attributed to

Preparation of Standard Samples/Mixtures Samples of coal were collected from the Lewis Fork Mine in Perry County, Kentucky, in August 2004, washed with deionized H2O and air-dried. They were subsequently ground using a SPEX Certiprep 8000 Mixer Ball Mill (SPEX Certiprep, Metuchen, NJ) and sieved (G1 mm). Limestone (Southern States Pelleted Lexington, KY) was used to standardize test runs with a known carbonate value. Grass litter, ground and sieved (G1 mm), was used as the Bnew^ organic matter matrix. In addition to individual samples consisting of air-dried grass litter, limestone, and coal, mixtures containing all three components were created for analysis. Expected C concentrations in the mixtures were calculated on a dry weight mass to mass basis using baseline C concentrations from the

Fig. 2. Representative TG (I) and DTG (II) for a laboratory mixture of grass litter (OM), coal, and limestone.


VOL. 172 ~ NO. 4 USE OF THERMOGRAVIMETRY IN DISTINGUISHING ORGANIC CARBON 295 TABLE 3 Thermogravimetry and derivative thermogravimetry pyrolysis data for mixtures of litter, coal, and limestone Temperature interval Sample

1 2 3 4 5 6 7 8 9 10 Mean

Mixture composition (mg)

3.8:2.9:3.3 4.8:2.9:2.2 5.0:2.0:3.0 2.9:4.5:2.6 4.3:2.3:3.4 2.8:4.4:2.8 3.0:4.7:2.3 1.4:6.2:2.4 3.8:3.9:2.0 3.9:3.7:2.8

270–400 -C

415–520 -C

9700-

Weight loss (%)

Recovery (%)

Weight loss (%)

Recovery (%)

Weight loss (%)

Recovery (%)

19.3 26.0 27.3 16.2 23.5 16.0 16.2 8.1 21.1 21.6

86.8 91.7 94.0 94.0 94.3 98.1 91.8 99.1 98.4 94.0 94.2

6.7 7.0 4.6 9.2 5.4 8.8 11.4 12.4 9.5 8.7

96.2 101.1 95.7 86.2 98.2 84.0 101.9 84.8 92.9 98.4 93.9

14.7 10.4 12.2 10.8 14.9 12.4 10.0 10.0 9.5 10.3

111.5 116.0 100.9 105.5 108.8 110.9 109.4 103.3 114.0 108.5 108.9

Mixture composition are given by weight in the following order: litter/coal/limestone.

individual samples. Different types of organic matter including cellulose (Sigma Aldrich, St. Louis, MO), apple leaves (NIST, Washington, DC), and extracted lignin (van Soest, 1994) from wood shavings, were used as reference materials for correlation purposes. Total C and N Content Total C (organic and inorganic) and N contents were determined by dry combustion using a LECO CHN 2000 analyzer (St. Joseph, MI). No more than 0.2000 g of sample was placed in a tin foil capsule and combusted in a resistance furnace at 950 -C using O2 as a carrier gas. The resulting gases were equilibrated in a ballast chamber followed by infrared detection of CO2 and H2O. N2 was determined using a thermal conductivity detector after reduction of N oxides and removal of CO2 and H2O. Calibration curves were validated on a daily basis by using a LECO standard (EDTA-C10H16N2O8; LECO), and quality control was assured by running an EDTA standard for every 10 samples. Organic C Characterization Differential Scanning Calorimetry Differential scanning calorimetry is a technique that measures the thermal response of an unknown specimen as compared with a standard when the two are heated uniformly at a constant rate (Karathanasis and Harris, 1994). Samples were scanned using the Dupont Instrument 910 DSC (Wilmington, DE) that uses a heat-flow principle of operation. Thermocouple junctions were connected directly to two thermally con-

ducting bases with the sample (in an alumina pan) resting on one of the conducting bases and the reference (an empty, covered alumina pan) on the other base. Approximately 10 mg of sample were used with a temperature ramp of 10 -C minj1 up to 600 -C and an N flow rate of 10 mL minj1. Heat-flow DSC provides a signal that is essentially independent of the thermal properties of the sample (Karathanasis and Harris, 1994). Thermogravimetric Analysis Derivative thermogravimetry was carried out with a Dupont 951 Thermogravimetric Analyzer using a platinum pan sample holder. Mass changes with incremental temperature increases were evaluated by means of the Thermal Analyst 2000 TA Instrument (New Castle, DE) program. Weight loss was monitored by heating approximately 10 mg of sample from an initial TG analysis temperature of 25 -C up to final temperature of 1000 -C. Optimum results (representative weight loss per sample and the best thermal curve with minimum overlapping of peaks) were obtained using a temperature ramp of 20 -C minj1 and an N flow rate of 20 mL minj1. Each component for the standard mixture was individually added to the platinum pan, mixed to ensure homogeneity, and then analyzed on the TG analysis. This was to ensure that the mixture contained known amounts of each component as opposed to a general mixture where the chances of density differences may have interfered with the calculated and actual TG recoveries of the components.


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Quantitative determinations were based on weight loss and theoretical compositions of the standards. This method was then used to quantify the Bnew^ or recent organic C on reclaimed coal mine sites. Petrographic Analysis Approximately 4 to 5 g of 20-mesh sample (1.5 g of each component for the 1:1:1 mixture of grass litter, coal, and limestone) were mixed with a small amount of epoxy resin, poured into 2.5-cm-diameter phenolic ring molds and vacuum impregnated before being allowed to cure. Petrographic analysis was conducted on plugs of the standard and samples that had been polished according to standard procedures (Pontolillo and Stanton, 1994). A Zeiss Universal reflected light microscope, using a 40 oil immersion lens and a total magnification of 500, was used for all petrographic analyses. Duplicate point-count petrographic analyses were performed under both reflected white and blue light (450–490 nm). Analysis of 300 points on two separate pellets was sufficient to produce an acceptable precision of T2% to 3% (Taylor et al., 1998a). Petrographic composition of each sample was summarized as Bnew^ organic matter, coal, and minerals.

SOIL SCIENCE

showed pyrolysis peaks at distinctively different temperatures with the peak for litter occurring at 270 to 395 -C, for coal at 415 to 520 -C, and for limestone at 700 to 785 -C. Several factors were used to ensure peak identification. Use of N as the carrier gas instead of air and a temperature ramp of 20 -C minj1 instead of 10 -C minj1 minimized baseline noise. In addition, it was also found that an N flow rate of 20 versus 10 mL minj1 greatly enhanced peak definition. Laboratory mixtures of the litter, coal, and limestone show distinct peaks for each component. The fact that there is no peak overlap greatly

Statistical Analysis Total C and N are given as mean values resulting from multiple analyses (standard samples, n = 20; reference samples, n = 10). Student t tests were used to determine differences between expected C (from LECO) and actual C from TG analyses at ! = 0.05. RESULTS AND DISCUSSION Initial C and N Content (Total) Results for C and N fractions of Bold^ (coal and limestone), Bnew^ (grass litter), and reference samples are presented in Table 1. Expected C and N for the laboratory mixture was 50.17% and 1.43%, respectively. Actual C and N results on replicate samples of the mixture (n = 20) yielded recoveries of 95% (for C) and 104% (for N). Thermogravimetric Analysis The data analysis system plotted weight loss (percentage) and first derivative as a function of temperature. Weight loss for each component is shown in Table 2. Representative TG/DTG patterns for the Bold^ and Bnew^ C fractions (grass litter, coal, and limestone) are shown in Fig. 1. Differential thermogravimetry curves

Fig. 3. Representative TG (I) and DTG (II) patterns for (A) cellulose, (B) NIST apple leaves, and (C) lignin.


VOL. 172 ~ NO. 4 USE OF THERMOGRAVIMETRY IN DISTINGUISHING ORGANIC CARBON 297

Fig. 4. Expected C (%) versus TG (%) for (A) grass litter, (B) coal, (C) limestone fractions from mixtures (n = 10) and relationship between actual recoveries and a theoretical perfect linear regression line, 1:1 (- - - -).

enhances the ability to Bisolate^ the different C fractions. Pyrolysis results are shown in Table 3. Different component ratios were used to check peak detectability and temperature intervals were selected based on the major DTG peaks for the individual components. Average recoveries of C for each component in the mixtures were 93.9% T 4.2% for coal, 94.2 T 2.1% for litter, and 108.9 T 2.9% for limestone (n = 10). Thermogravimetry and derivative thermogravimetry thermographs for the mixtures showed a weight loss ranging from 50 to 150 -C, indicative of dehydration reactions (Fig. 2) (Pietro and Paola, 2004). The weight loss in the 270 to 375 -C region is characteristic of Bnew^ organic matter as indicated in the thermographs of grass litter (Fig. 1A), cellulose (Fig. 3A), and apple leaves (NIST) (Fig. 3B). This also correlates well with other studies that report combustion of carbohydrates, decarboxylation of acidic groups, and dehydration of hydroxylate aliphatic structures in the 200 to 350 -C range (Francioso et al., 2005; Pietro and Paola 2004; Schulten and Leinweber, 1999). In addition, lignin decomposition occurs between 375 and 430 -C (Lopez-Capel et al., 2005; Sheppard and

Forgeron, 1987) and is characterized by a single broad peak (Fig. 3C). The NIST apple leaves (Fig. 3B) show overlapping peaks for both cellulose and lignin. Weight loss for the coal fraction occurs between 415 and 520 -C and is attributed to the splitting of phenol hydroxyl groups, breaking of —C—C bonds, and partial transition of coal matter into a plastic state (Hodzˇic and Paxic, 1985; Markova et al., 1985; Morgan et al., 1987). The peak temperature for coal pyrolysis may shift depending on coal maturity or rank (Markova et al., 1985). As coal rank increases, so too does its aromaticity (Francioso et al., 2005; Taylor et al., 1998b), which may result in a higher pyrolysis temperature. For instance, peak temperatures of 420 and 513 -C were found for high- and low-volatility coals, respectively (Biagini et al., 2002), whereas peak temperatures higher than 400 -C were found for highly decomposed peat or lignite (Sheppard and Forgeron, 1987). This confirms that the Bnew^ organic matter peak will not be masked by that of the coal. Weight loss in the 650 to 750 -C range (Fig. 2) is attributed to carbonate thermal degradation (Bhargava et al., 2005; Pietro and


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Paola, 2004; Schnitzer and Hoffman, 1966; Siewert, 2004). Comparing TG and LECO results, linear relationships are observed for each component in the mixtures (n = 10) containing grass litter, coal, and limestone (Fig. 4A–C). There are no significant differences between the experimental data and the 1:1 model (Fig. 4) based on P values at ! = 0.05. This is supported by high linear regression values (90.9) for each component. However, TG analysis tends to provide consistently higher estimates of C in the limestone fraction than are obtained using the LECO analyzer. This observation may be because of incomplete combustion in the LECO. Temperature ranges suggested by literature are lower than 580 -C for siderite, 580 to 690 -C for magnesite, 690 to 800 -C for magnesite from dolomite, and more than 950 -C for calcite (Karathanasis and Harris, 1994) Calcite may have decomposed to a greater extent using the TG because the temperature maximum used was 1000 -C as opposed to a maximum temper-

SOIL SCIENCE

ature of 950 -C with the LECO. Another possibility may be because of density differences when using a whole mixture (for the LECO samples) as opposed to weighing out the individual components to make up a mixture for each sample before TG analysis. Differential Scanning Calorimetry Analysis Differential scanning calorimetry patterns show inflections between 270 and 382 -C for the grass litter. A sharp endothermic peak occurs between 291 to 355 -C for cellulose, a broader exothermic peak between 287 and 390 -C for lignin, followed by an exothermic peak between 420 and 525 -C for coal (Fig. 5). These temperature ranges support those found using the TG/DTG for the organic matter and coal fractions. However, identification of the carbonate peaks is not possible due to the lower temperature maximum of the DSC (600 versus 1000 -C for the TG analysis). Differential scanning calorimetry may enable separation of the cellulose and lignin peaks, as well as used to differentiate mineral types.

Fig. 5. Representative DSC patterns for (A) grass litter, (B) cellulose, (C) lignin, and (D) coal.


VOL. 172 ~ NO. 4 USE OF THERMOGRAVIMETRY IN DISTINGUISHING ORGANIC CARBON 299 Petrographic Analysis Optical microscopy revealed that Bnew^ organic matter, grass litter, and sycamore leaves exhibit strong fluorescence (yellow, green, red, and brown) under blue-light illumination and also distinctive cell morphology (Fig. 6A and B). BOld^ organic matter, coal, and limestone are very different in their morphological structure and appearance in reflected white and blue light. Limestone appears massive and highly reflective under white light (Fig. 6C). Most of the coal appears as angular macerals including vitrinite (coalified woody material) and inertinite (e.g., preserved fragments of fossil charcoal) that show no fluorescence under blue light and are characterized by gray to light gray or white in white light (Fig. 6D). These variations in petrographic composition make it possible to differentiate between the different C fractions in the mixture. Duplicate point-count analyses of a

1:1:1 mixture of grass litter, coal, and limestone yielded 39.2% T 1.2% Bnew^ organic matter, 35.0% T 2.4% coal, and 25.9% T 1.2% minerals (in this case, limestone). These results may suggest that particle density differences led to some separation during vacuum impregnation. The least dense fraction, litter, was pulled to the top, yielding a higher recovery than expected followed by the coal fraction. Recovery of limestone, the most dense of the three fractions, was below the expected value (33.3%). This separation could probably be avoided by using less epoxy in the initial impregnation, thus providing a thicker mixture that would minimize any density differences. CONCLUSIONS Thermogravimetry and derivative thermogravimetry has the potential to differentiate and quantify Bnew^ organic C in soils containing coal

Fig. 6. Representative photomicrographs of (A) grass litter, (B) sycamore leaves, (C) limestone, and (D) coal. All photomicrographs were taken under oil immersion; A–C, under blue-light illumination; D, under reflected whitelight illumination.


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and carbonate minerals and has the distinct advantage of analyzing whole samples without pretreatment. The TG/DTG technique is rapid (1–2 hours for complete analysis) and easy to use, giving repeatable results. However, potential pitfalls of using TG/DTG may include interference from impurities such as high mineral content (pyrite, 400–550 -C; goethite, 300–400 -C) and clay (kaolinite, 400–600 -C) in soil samples. Similarly, mineral matter dispersed throughout the coal (clays, carbonates, and pyrite) may produce peaks during pyrolysis. Carbonates such as siderite may decompose at temperatures lower than 580 -C and could potentially overlap with the peak for coal. Presence of some of these minerals may be problematic for identification and quantification of Bnew^ organic matter (between 250 and 450 -C). Elemental analyses and X-ray diffraction data may help to account for such interferences. Larger sample weights (915 mg) and larger particle size (91 mm) may also limit reproducibility of thermal curves. However, potential overlapping weight-loss temperature regions may be minimized and resolution enhanced by the use of different carrier gases and varying temperature. Petrographic analysis takes several days for sample preparation and analysis. Particle density differences may limit the use of petrography, because, in this study, they overestimated the organic matter fraction and underestimated the carbonate fraction (118% and 78%, respectively) compared with thermogravimetry, which provided a more accurate measure for these fractions (litter, 94.2%; carbonate, 108.9%). Organic petrography, however, may be useful in helping to decipher the TG/DTG curves as rank (and possible maceral content) may influence the location of peaks (Morgan et al., 1987). These results suggest that petrographic analysis can be used as a proxy for detection of Bnew^ organic C. However, thermogravimetry appears to be the superior of the two because it provides a cost-effective, rapid, direct, and simple method to differentiate and quantify Bnew^ organic C in soil media containing coal and carbonate minerals. Further work is required to validate this method on actual field samples from reclaimed coal mine sites. ACKNOWLEDGMENTS Research was supported by the U.S. Department of Energy grant and the American Association of Petroleum Geologists grants-in-aid (2005).

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The authors thank Yvonne Thompson of the University of Kentucky, who provided assistance in thermogravimetry and derivative thermogravimetry analyses. REFERENCES Akala, V. A., and R. Lal. 2001. Soil organic carbon pools and sequestration rates in minesoils in Ohio. J. Environ. Qual. 30:2098–2104. Allison, L. E. 1960. Wet-combustion apparatus and procedure for organic and inorganic carbon in soil. Soil Sci. Soc. Am. J. 24:36–40. Avid, B., B. Purevsuren, M. Born, J. Dugarjav, Y. Davaajav, and A. Tuvshinjargal. 2002. Pyrolysis and TG analysis of Shivee Ovoo coal from Mongolia. J. Therm. Anal. Calorim. 68:877–885. Bhargava, S., F. Awaja, and N. D. Subasinghe. 2005. Characterization of some Australian oil shale using thermal, X-ray and IR techniques. Fuel 84: 707–715. Biagini, E., F. Lippi, L. Petarca, and L. Tognotti. 2002. Devolatilization rate of biomasses and coalbiomass blends: An experimental investigation. Fuel 81:1041–1050. Dagounaki, C., K. Chrissafis, A. Kassoli-Fournaraki, A. Tsirambides, C. Sikalidis, and K. M. Paraskevopoulos. 2004. Thermal characterization of carbonate rocks. Kozani area, north-western Macedonia, Greece. J. Therm. Anal. Calorim. 78:295–306. Dell’Abate, M. T., A. Benedetti, and P. Sequi. 2000. Thermal methods of organic matter maturation monitoring during a composting process. J. Therm. Anal. Calorim. 61:389–396. Francioso, O., D. Montecchio, P. Gioacchini, and C. Ciavatta. 2005. Thermal analysis (TG-DTA) and isotopic characterization (13C-15N) of humic acids from different origins. Appl. Geochem. 20: 37–544. Hodzˇic, E., and Z. Paxic. 1985. Differential thermal analysis of ashes of some Yugoslav brown coals. Thermochim. Acta 93:365–368. Karathanasis, A. D., and W. G. Harris. 1994. Quantitative thermal analysis of soil materials. In: Quantitative Methods in Soil Mineralogy. J. E. Amonette and J. W. Stucki (eds.). SSSA Miscellaneous Publication, Madison, WI, pp. 360–411. Khraisha, Y. H., and I. M. Shabib. 2002. Thermal analysis of shale oil using thermogravimetry and differential scanning calorimetry. Energy Conv. Manage. 43:229–239. Leinweber, P., H. R. Schulten, and C. Horte. 1992. Differential thermal analysis, thermogravimetry and pyrolysis-field ionization mass spectrometry of soil organic matter in particle-size fractions and bulk soil samples. Thermochim. Acta 194: 175–187. Levy, M., and R. Kramer. 1988. Comparative TGA and DSC studies of oil shales. Thermochim. Acta 134:327–331.


VOL. 172 ~ NO. 4 USE OF THERMOGRAVIMETRY IN DISTINGUISHING ORGANIC CARBON 301 Lopez-Capel, E., S. P. Sohi, J. L. Gaunt, and D. A. C. Manning. 2005. Use of thermogravimetry– differential scanning calorimetry to characterize modelable soil organic matter fractions. Soil Sci. Soc. Am. J. 69:136–140. Markova, H. I., S. P. Valceva, and R. P. Petrova. 1985. DTA and TGA of coals and bituminous rocks. Thermochim. Acta 93:385–388. Midwood, A. J., and T. W. Boutton. 1998. Soil carbonate decomposition by acid has little effect on %13C of organic matter. Soil Biol. Biochem. 30:1301–1307. Morgan, P. A., S. D. Robertson, and J. F. Unsworth. 1987. Combustion studies by thermogravimetric analysis. Fuel 66:210–215. Nelson, D. W., and L. E. Sommers. 1996. Total carbon, organic carbon, and organic matter. In: Methods of Soil Analysis, Part 3. Chemical Methods. D. L. Sparks (ed.). SSSA Book Series 5. SSSA, Madison, WI, pp. 961–1010. Nommik, H. 1971. A modified procedure for determination of organic carbon in soils by wet combustion. Soil Sci. 11:300–336. Pietro, M., and C. Paola. 2004. Thermal analysis for the evaluation of the organic matter evolution during municipal solid waste aerobic composting process. Thermochim. Acta 413:209–214. Piotrowski, S. 1999. Examination of contemporary lake sediments by means of thermal analysis. J. Therm. Anal. Calorim. 57:527–540. Plante, A. F., M. Pernes, and C. Chenu. 2005. Changes in clay-associated organic matter quality in a C depletion sequence as measured by differential thermal analyses. Geoderma 129:186–199. Pontolillo, J., and R. W. Stanton. 1994. Coal Petrographic Laboratory Procedures and Safety Manual, II. U.S. Geology Survey Open-File Report, pp. 94–631. Rumpel, C., I. Kogel-Knabner and H. Knicke. 2000. Composition and distribution of organic mat-

ter in physical fractions of a rehabilitated mine soil rich in lignite-derived carbon. Geoderma 98: 177–192. Schnitzer, M., and I. A. Hoffman. 1966. A thermogravimetric approach to the classification of organic soils. Soil Sci. Soc. Am. Proc. 30:63–66. Schulten, H. R., and P. Leinweber. 1999. Thermal stability and composition of mineral-bound organic matter in density fraction of soil. Eur. J. Soil Sci. 50:237–248. Sheppard, J. D., and D. W. Forgeron. 1987. Differential thermogravimetry of peat fractions. Fuel 66: 232–236. Siewert, C. 2004. Rapid screening of soil properties using thermogravimetry. Soil Sci. Soc. Am. J. 68: 1656–1661. Taylor, G. H., M. Teichmu¨ller, A. Davis, C. F. K Diessel, R. Littke, and P. Robert. 1998a. Methods and procedures. In: Organic Petrology. Borntraeger, Berlin, pp. 335–450. Taylor, G. H., M. Teichmu¨ller, A. Davis, C. F. K Diessel, R. Littke, and P. Robert. 1998a. Methods and procedures. In: Organic Petrology. Borntraeger, Berlin, pp. 86–174. Van Soest, P. J. 1994. Lignin. In: Nutritional Ecology of the Ruminant. Cornell University Press, Ithaca, NY, pp. 177–195. Varey, J. E., C. J. Hindmarsh, and K. M. Thomas. 1996. The detection of reactive intermediates in the combustion and pyrolysis of coals, chars and macerals. Fuel 75:164–176. Warne, S. St. J. 1985. The assessment of the coal-organic matter contents of geological materials by differential thermal analysis. Thermochim. Acta 86:337–342. Warne, S. St. J. 1996. Thermal analysis and coal assessment: An overview with new developments. Thermochim. Acta 272:1–9. Wendlandt, W. W. 1986. In: Thermal Analysis, 3rd Ed. Wiley-Interscience, New York, pp. 832.
