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U.S. Geological Survey Bulletin 1823

Edited by D.W. Golightly and F.O. Simon

Methods for Sampling and Inorganic Analysis of Coal - Introduction

By D.W. Golightly and F.O. Simon


Methods used by the U.S. Geological Survey for the sampling, comminution, and inorganic analysis of coal are summarized in this bulletin. Details, capabilities, and limitations of the methods are presented.


The large body of chemical information (for example, see Averitt and Lopez, 1972; O'Gorman and Walker, 1972; Zubovic and others, 1980) available to the modern coal scientist has been provided by diverse instrumental and chemical methods of analysis. The methods used in U.S. Geological Survey laboratories (Golightly and others, 1986; Simon and Huffman, 1978; Swanson and Huffman, 1976) change with the requirements for investigations of coal composition and with refinements in the instrumentation and approaches to chemical analysis. Detailed descriptions of most of the methods routinely used in U.S. Geological Survey laboratories for determining the inorganic composition of coal are provided in this bulletin. In addition to the descriptions of methods, one section is dedicated to the important topic of coal sampling and another treats the comminution of field samples prior to analysis.

Concentrations of more than 70 elements important to investigations of coal are determined by diverse methods established for the chemical and instrumental analysis of both whole coal and coal ash. This diversity results from the different capabilities of the individual methods, the quality of information sought, and the cost of this information. The measurement techniques used for the determination of major, minor, and trace elements in coal and coal ash include atomic emission spectrography (AES), atomic absorption spectrometry (AAS), X-ray fluorescence (XRF) spectrometry, instrumental neutron activation analysis (INAA), and ion-selective electrode (ISE). The conventional routing of samples and types of analyses are illustrated by the chart in figure 1.

For the routine quantitative analysis of coal ash (ashing temperature of 525 oC), the elements Cd, Cu, Li, Mg, Mn, Na, Pb, and Zn are determined by AAS, and Al, Ca, Fe, K, Mg, Mn, Na, P, S, Si, and Ti are determined by XRF spectrometry. Rapid chemical methods, described in this bulletin, offer an alternative approach for measurements of the same elements determined by XRF spectrometry. After a special ashing procedure and fusion of the resulting ash with NaOH, fluorine concentrations are measured by ISE. An automated, semiquantitative direct-current (dc) arc AES method is applied to the analysis of all coal ashes for the determination of 64 elements. Lower determination limits for the methods used for the analysis of coal ash are listed in table 1.

For the routine quantitative analysis of whole coal, Hg is determined by cold-vapor AAS; Cl and P are measured by XRF spectrometry; and As, Ba, Br, Ce, Co, Cr, Cs, Eu, Fe, Hf, Hg, K, La, Lu, Na, Nd, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, U, W, Yb, and Zn are determined by INAA. Total sulfur and sulfur species (forms of sulfur) are determined by gas-phase infrared absorption spectrometry that is combined with chemical separation methods. Lower determination limits for these methods are summarized in table 1.

In addition to analyzing coal for the elements indicated in table 1, the U.S. Geological Survey routinely analyzes coals by methods recommended by the American Society for Testing and Materials (ASTM) for calorific value, proximate analysis (moisture, ash, volatile matter, and fixed carbon), ultimate analysis (C, H, N, O, and S), and physical parameters, such as Hardgrove grindability, ash-fusion temperature, specific gravity, and free-swelling index. Equilibrium moisture is determined on selected samples. The "1984 Annual Book of ASTM Standards" (ASTM, 1984) provides detailed descriptions of the standard procedures used. A list of the pertinent ASTM methods appears in table 2.

All data for coals and associated rocks analyzed by the U.S. Geological Survey reside in the National Coal Resources Data System (NCRDS) (Carter and others, 1981). The NCRDS is an interactive computerized storage, retrieval, and display system created to assess the quantity and quality of the nation's coal resources. Currently, the NCRDS USCHEM data bases contain analytical data on approximately 10,000 point-located coal and associated rock samples from all coal regions of the United States. Other data bases contain information on approximately 50,000 samples that are area located. In addition, the geochemical data bases contain geologic and geographic data for each sample. A total of 128 parameters, including the analytical data, can be stored for each sample. The geologic and geographic data include State, county, latitude, longitude, coal province, region, coal field, district, formation, group, coal bed, member, zone, series, location name, quadrangle, collector, point identification, date, estimated rank, calculated rank, laboratory identification number, and sample type.

The accuracy of analysis by the U.S. Geological Survey methods, each of which is the topic of a section of this bulletin, is ultimately linked to a standard reference material (Uriano and Gravatt, 1977). These standard coals and coal ashes are provided by various agencies, such as the National Bureau of Standards, and commercial laboratories, such as Alpha Resources, Inc. Representative materials are described in the appendix to this bulletin, where the addresses of suppliers are also given. A significant new development is underway at the Argonne National Laboratory where eight premium coal standards are being prepared (see the appendix).

In addition to this bulletin, a large body of information on the chemical and physical characterizations of coal is available to the coal scientist. The general methodologies used for inorganic analysis of coal, critically reviewed recently by Swaine (1985) for bituminous coal, are described in various journal articles and books. Valkovic (1983) has provided a comprehensive review of both the chemistry and the methodology used for the characterization of coal. Mills and Belcher (1981) surveyed atomic spectrometric methods for the analysis of coal, coke, ash, and mineral matter. The "1984 Annual Book of ASTM Standards" (ASTM, 1984) provides detailed descriptions of standard procedures for sampling, grinding, and analyzing coal and coke. Volumes edited by Babu (1975) and Karr(1978) describe numerous instrumental and chemical methods for the characterization of coal. Mineral matter and trace-element associations are treated in these two books and in a recently published book by Vorres (1986).


American Society for Testing and Materials (ASTM), 1984, annual book of ASTM standards, petroleum products, lubricants, and fossil fuels, sect. 5 of v. 05.05: Gaseous fuels, coal, and coke: Philadelphia, ASTM, p. 207-523.

Averitt, Paul, and Lopez, Lorreda, 1972, Bibliography and index of U.S. Geological Survey publications relating to coal, 1882-1970: U.S. Geological Survey Bulletin 1377, 173 p.

Babu, S.P., ed., 1975, Trace elements in fuel, in Advances in chemistry series 141: Washington, D.C., American Chemical Society, 216 p.

Carter, M.D., Medlin, A.L., and Krohn, K.K., 1981, The national coal resources data system: a status report: Geological Society of America Bulletin, v. 92, pt. 1, p. 563-573.

Golightly, D.W., Dorrzapf, A.F., Jr., Larson, R.R., Aruscavage, P.J., and Palmer, C.A., 1986, Current analytical methods for determining the inorganic composition of coal, in Garbini, Susan, and Schweinfurth, S.P., eds., A National Agenda for Coal-Quality Research, April 9-11, 1985 Symposium Proceedings: U.S. Geological Survey Circular 979, p. 232.

Karr, Clarence, ed., 1978, Analytical methods for coal and coke products, v. 1-3: New York, Academic Press.

Mills, J.C., and Belcher, C.B., 1981, Analysis of coal, coke, ash, and mineral matter by atomic spectroscopy: Progress in Analytical Atomic Spectroscopy, v. 4, p. 49-80.

O'Gorman, J.V., and Walker, P.L., 1972, Mineral matter and trace elements in U.S. coals: Washington, D.C., U.S. Government Printing Office, 183 p.

Simon, F.O., and Huffman, Claude, Jr., 1978, Analytical methods used by the U.S. Geological Survey for determining the composition of coal: Paper no. 82, Meeting of the American Chemical Society, 173rd, New Orleans, March 20-25.

Swaine, D.J., 1985, Modern methods in bituminous coal analysis: Trace elements: CRC Critical Reviews in Analytical Chemistry, v. 15, no. 4, p. 315-346.

Swanson, V.E., and Huffman, Claude, Jr., 1976, Guidelines for sample collecting and analytical methods used in the U.S. Geological Survey for determining chemical composition of coal: U.S. Geological Survey Circular 735, 11 p.

Uriano, G.A., and Gravatt, C.C., 1977, The role of reference materials and reference methods in chemical analysis: CRC Critical Reviews in Analytical Chemistry, v. 6, p. 361-411.

Valkovic, Vlado, 1983, Trace elements in coal, v. 1, II: CRC Press, Boca Raton, Florida, 491 p.

Vorres, K.S., ed., 1986, Mineral matter and ash in coal, in American Chemical Society symposium series no. 301: Washington, D.C., American Chemical Society, p. 538.

Zubovic, Peter, Oman, C.L., Bragg, L.J., Coleman, S.L., Rega, N.H., Lemaster, M.E., Rose, H.J., Golightly, D.W., and Puskas, John, 1980, Chemical analysis of 659 coal samples from the eastern United States: U.S. Geological Survey Open-File Report 80-2003, 513 p.

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