Coal minor elements

Minor elements contribute >1 wt % to the ash trace elements contribute <0.1 wt %. The degree of de-ashing achievable by physical cleaning depends on the distribution of mineral matter in the coal. In some cases, a considerable amount of the mineral matter can be removed in other cases, especially where the mineral matter is distributed throughout the coal as microscopic particles, deashing by physical cleaning is not practical. 

Kuhn, J.K., F.L. Fiene, R.A. Cahill, HJ. Gluskoter, and N.F. Shimp. 1980. Abundance of trace and minor elements in organic and mineral fractions of coal. Environ. Geol. Notes 88. Illinois State Geol. Surv. Div., Urbana, IL. 67 pp. 

Titanium in Plants and Animals. In 1896 C. E. Wait found large amounts of titanium in the ashes of bituminous and anthracite coals, oak wood, and apple and pear wood (23, 57). L. G. Willis, in his bibliography on the minor elements in plant and animal nutrition, gave several references to the presence of small amounts of titanium in soils, in plants, and in the human body (58). 

Table 7. Concentrations (in mg/kg) of minor elements in solid coal combustion residues and natural sediments...

Zubovic, P., Stadnichenko, T. Sheffey, N.B. 1960. The Association of Minor Elements with Organic and Inorganic Phases of Coal. US Geological Survey Professional Paper, 400-B, Washington, DC. 

Hower, J. C., Robertson, J. D. Roberts, J. M. 2001. Petrology and minor element chemistry of combustion by-products from the co-combustion of coal, tire-derived fuel, and petroleum coke at a western Kentucky cyclone-fired unit. Fuel Processing Technology, 74, 125-142. 

Simultaneously with the efforts to determine the origin of mineral matter in coal, systematic efforts were underway to estimate the quantitative distribution of trace and minor elements in American coals. The early analyses were performed on high-temperature ashes, and as a consequence, the investigators had to be content with determining the nonvolatile metallic oxides. However, with the advent of the low temperature asher and improvisations and advances in wet chemical, radiochemical, and instrumental analytical techniques, we not only can analyze nondecomposed mineral matter but also can study the composition of whole 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. 

Goldschmidt (32) also introduced the concept of a geochemical classification of elements, in which the elements are classified on the basis of their affinities and tendencies to occur in minerals of a single group. The chalcophile elements are those which commonly form sulfides. In addition to sulfur, they include Zn, Cd, Hg, Cu, Pb, As, Sb, Se, and others. When present in coals, these elements would be expected to occur, at least in part, in sulfide minerals. Sulfides other than pyrite and marcasite have been noted in coals, but, except in areas of local concentration, they occur in trace or minor amounts. 

Horton and Aubrey (34) handpicked pure vitrain samples from coals and separated them into five different specific gravity fractions. They then analyzed these for 16 minor elements. They concluded that for the three vitrains they studied, beryllium, germanium, vanadium, titanium, and boron were contributed almost entirely by the inherent (organically combined) mineral matter and that manganese, phosphorus, and tin were associated with the adventitious (inorganically combined) mineral matter. 

Averitt, Paul, Breger, I. A., Swanson, V. E., Zubovic, Peter, Gluskoter, H. J., Minor Elements in Coal—A Selected Bibliography, July 1972, Professional Paper 800-D, p. D-169-D-171, U.S. Geological Survey, 1972. 

Zubovic, P., Minor Element Content of Coal from Illinois Beds 5 and 6... 

Very little data have been reported on the analysis of elements in whole coal and mine dusts in particular. Kessler, Sharkey, and Friedel analyzed trace elements in coal from mines in 10 coal seams located in Pennsylvania, West Virginia, Virginia, Colorado, and Utah (5). Sixty-four elements ranging in concentration from 0.01 to 41,000 ppm wt were determined. Several surveys published previously have provided data on the concentration of minor elements in ashes from coals rather than a direct determination on the whole coals or mine dusts. Previous investigations include studies by Headlee and Hunter (6), Nunn, Lovell, and Wright (7), Abernethy, Peterson, and Gibson (8), and others (9, 10, 11,12). 

TJecent interest in the trace element content of coal has increased the need for rapid and accurate analytical methods for their determination. Because x-ray fluorescence analysis has demonstrated its usefulness in determining major, minor, and trace elements in numerous other types of materials, it was felt that this method could be extended to trace element determinations in whole coal. In the past, such analyses were seriously hampered by the lack of standard samples. However, research being conducted in our laboratories under the sponsorship of the U. S. Environmental Protection Agency produced a large number of coal samples for which trace elements had been determined by two or more independent analytical procedures, for example, optical emission, neutron activation, atomic absorption, and wet chemical methods. These coals were used as standards to develop an x-ray fluorescence method that would determine many trace and minor elements in pressed whole coal samples. 

Preliminary Investigation of Major and Minor Elements in Whole Coal and Coal Ash... 

The use of x-ray fluorescence was originally intended to obtain information about the major element matrix of coal ashes that were to be analyzed for trace elements by optical emission spectroscopy. Both low-temperature (<150°C) and high-temperature (450°C) coal ashes, prepared as described by Ruch et al. (I), were analyzed, and the method of Rose et al. (2) was adapted to determine the major and minor elements (Si, Ti, Al, Fe, Mg, Ca, K, and V). The instrumental parameters used for these elements are given in Table I. 

Because of these encouraging results and previous work on brown coals by Sweatman et al. (4) and Kiss (5), which indicated that major and minor elements could be determined in whole coal, a series of 25 coals was prepared for x-ray fluorescence analysis. For each coal, a low-temperature ash, a high-temperature ash, and the whole coal itself... 

The relative errors for all elements determined are given in Table IV. For completeness, data on minor elements in whole coal also are included in the trace element tables. These data indicate the precision obtained for the x-ray fluorescence analysis on replicates of 15 samples of whole coal ground to —325 mesh. 

It is apparent from Table IV that trace elements determined by the x-ray fluorescence method are limited to those occurring in whole coals at concentrations of at least a few parts per million. Elements such as selenium, mercury, and antimony, which are generally present in whole coal at levels below 1 ppm, cannot be determined by this method. The major elements in coal, hydrogen, carbon, oxygen, and nitrogen, cannot be determined by x-ray fluorescence, but this should not inhibit the use of the method for trace and minor element determinations. 

The results of the mass balance calculations for eight major elements and 22 minor elements for run 9 are given in Tables II and III, together with the corresponding concentrations in the coal, precipitator inlet and outlet fly ash, and in the slag tank solids. Complete tabulation of results for all three runs and some data for 57 elements is given in a project progress report (4). 

Physicochemical Properties of Certain Minor Elements as Controlling Factors in their Distribution in Coal... 

Analyses of float-sink separates of coal reveal a systematic variation of the minor elements with the organic matter which can be arranged into an organic affinity series. This series appears to be related to the chelating properties of the metals. Deviations in this series may be explained by the chemical nature of the depositional environment. 

Minor Element Distribution in Cool Samples of the Interior Coal Province... 

The samples of the Eastern Interior Region considered here are those shown in Figure 1 west of the dashed north-south line in Illinois. All these samples are from Illinois beds 5 and 6. This selection was made to obtain a series of samples located at increasing distances from the source area of the sediments. Because the sedimentary source for the Indiana and Kentucky coal areas are less certainly known (6), the samples from those areas are not considered here. Except for beryllium and vanadium, the minor element content of samples from those areas is comparable to samples from western Illinois. The beryllium content of all these coals was reported by Stadnichenko and others (8). The unusually high vanadium content of some of the southern coals of the Eastern Interior Region is discussed below. 

Distribution of the elements in coal beds of four areas is shown in Figures 2-8. Reading from left to right, the first column shows the minor element... 

It is suggested here that the greater insolubility of the humic fraction of coal may be the result, in part, of polymerization by complexing with metals, particularly aluminum and silicon. These elements are suggested because of their presumed greater availability. The minor elements also play a part, however, only in relation to their availability compared with major elements such as aluminum and silicon. 

The weathering of coal samples can produce anomalous minor-element concentrations. 

ASTM D-3682. Standard Test Method for Major and Minor Elements in Combustion Residues from Coal Utilization Processes. 

Major and minor elements in coal, having concentrations easily detectable by most modem analytical techniques, can be determined by a number of acceptable procedures. Various approaches, combining a. number of specific procedures, are frequently referenced in the literature. For example, the presently accepted procedure (ASTM D-2795) determines silicon, aluminum, iron, titanium, and phosphorus colorimetrically, calcium and magnesium chelatometrically, and sodium and potassium by flame photometry. This standard test method was withdrawn in 2001 but is still used in some laboratories. 

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