Trace elements in coal

Trace Elements in Coal—An Intedaboratory Study of Analytical Techniques,", Technical Bulletin ConsoHdation Coal Co., Oct. 1987. 

Von Lehmden DJ, Jungers RH, and Lee Jr RE (1974) Determination of trace elements in coal, fly ash, fuel oil, and gasoline - a preliminary comparison of selected analytical techniques. 

Coal contains detrital minerals that were deposited along with the plant material, and authigenic minerals that were formed during coalification. The abundance of mineral matter in coal varies considerably with its source, and is reported to range between 9.05 and 32.26 wt% (Valkovic 1983). Minerals found in coal include (Table 2) aluminosilicates, mainly clay minerals carbonates, such as, calcite, ankerite, siderite, and dolomite sulphides, mainly pyrite (FeS2) chlorides and silicates, principally quartz. Trace elements in coal are commonly associated with one or more of these minerals (see Table 2). 

As a result of the well-documented environmental concerns posed by coal combustion, and the disposal of CCPs, a large body of research has focused on characterizing the mechanisms of mobilization and attenuation of trace elements in coal and its ash. Based on their reported distribution in the solid phases of both source coals and coal ash, knowledge of the thermal transformations that occur to major mineral constituents during coal combustion, and a limited number of studies that have identified discrete solid phases of trace elements, a conceptual model of the chemical and mineralogical characteristics of trace elements in coal ash has been developed. 

Valkovic, V. 1983. Trace Elements in Coal Volumes I and II. CRC Press, Inc. Boca Raton, FL. 

Wu, E. J. Chen, K. Y. 1987. Chemical Form and Leachability of Inorganic Trace Elements in Coal Ash. Electric Power Research Institute Report, EA-5115, Palo Alto, CA. 

Wang, J., Sharma, A. Tomita, A. 2003. Determination of the modes of occurrence of trace elements in coal by leaching coal and coal ashes. Energy and Fuels, 17, 29-37. 

Carras, J. N. 1995. The transport and dispersion of plumes from tall stacks. In Swaine, D. J. Goodarzi, F. (eds) Environmental Aspects of Trace Elements in Coal. Kluwer Academic Publishers, Dordrecht, 146-177. 

Davidson, R. M. 2000. Modes of Occurrence of Trace Elements in Coal. IEA Coal Research, London, pp. 36. 

Sloss, L. L. Davidson, R. M. 2001. Pardoning of potentially hazardous trace elements in coal combustion. Proceedings of 18th Annual International Pittsburgh Coal Conference. CD Rom. 

Swaine, D. J. 1990. Trace Elements in Coal. Butter-worths, London, 294 pp. 

An analytical procedure for the determination of about 20 trace elements in coal samples after microwave digestion is described by Wang et al.15 It was found that high temperature digestion with HN03 alone (250 °C, 7.5 MPa) led to an extensive decomposition of the organic matrix and clay in coal, whereby solid carbon remained in the final solution after evaporation. Most of the trace elements were quantitatively dissolved in three standard coals. A lost of Hg was observed during the evaporation step. 

Chemical Analyses of Mineral Matter and Trace Elements in Coal... 

The minor and trace elements in coals are currently determined by several techniques, the most popular of which are optical emission and atomic absorption spectroscopy. Neutron activation analysis is also an excellent technique for determining many elements, but it requires a neutron source, usually an atomic reactor. In addition, x-ray fluorescence spectroscopy, electron spectroscopy for chemical analyses (ESCA), and spark source mass spectroscopy have been successfully applied to the analyses of some minor and trace elements in coal. 

Until recently, chemical analyses of coals were done on ash produced from the coal at relatively high temperatures. This was the standard approach for many years, and analyses of trace elements in coals do have a long history. An early article on an element as rare as cadmium in coal was published 125 yrs ago (28). One limitation of high-temperature ash sample is that volatile elements may be lost during combustion and will not be detected. Another problem which applies especially to analyses for trace and minor elements is that there have not been any coal standards available until very recently. 

A detailed review of the world literature concerned with mineral matter and trace elements in coal is well beyond the scope of this chap-... 

The modern investigations of trace elements in coals were pioneered by Goldschmidt, who developed the technique of quantitative chemical analysis by optical emission spectroscopy and applied it to coal ash. In these earliest works, Goldschmidt (31) was concerned with the chemical combinations of the trace elements in coals. In addition to identifying trace elements in inorganic combinations with the minerals in coal, he postulated the presence of metal organic complexes and attributed the observed concentrations of vanadium, molybdenum, and nickel to the presence of such complexes in coal. 

Many data on trace elements in coal are included in the chapter. The emphasis is on the geochemistry of the trace elements, with discussions of the concentration levels of trace elements in coals, the organic (or inorganic) affinities of the trace elements, and the geochemical controls of associations of elements. This and the following significant review article are contained within a single volume. 

The data on sulfur, nitrogen, and trace elements in coal and in oil are summarized. Emphasis is placed on the geographic and geologic distribution of the trace elements. 

This circular reviews the occurrence of 34 trace elements in coal and the occurrence and distribution of chlorine, phosphorus, titanium, and manganese, which are not considered rare in coal. Separate chapters are devoted to germanium, gallium, and uranium in coal. 

This bibliography lists 65 selected references to articles on trace elements in coals. Most articles cited are in English and are concerned with North American coals. 

This review contains sections on the occurrence of 13 trace elements in coals and a summary of trace element distribution in coals. 

The coal service laboratory, which in the past was concerned with determining the ASTM Procedures for Ultimate and Proximate Analysis, is now responsible for analyzing trace elements in coal. With this sort of facility and technical skill in mind, our own wet chemical laboratory devised relatively routine procedures for determining trace elements in coal that could have an undesirable environmental impact including Hg, Be, Se, As, Cd, Pb, F, Cu, Ni, Zn, Cr, Te, Ge, Mn, Sn, B, Bi, Sb, V, Li, Co, and Ag. 

Trace Elements in Coal by Optical Emission Spectroscopy... 

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