XANES Spectroscopic Characterization of Selected Elements in Deep-Cleaned Fractions of Kentucky No. 9 Coal

Abstract

The mode of occurrence of various elements in Kentucky No. 9 coal has been examined by XAFS spectroscopic characterization of the elements in float and tailings fractions generated by different flotation tests and chemical leaching methods on the finely ground coal. PIXE spectroscopy was used to determine the elemental concentrations in the same fractions. In this investigation, the elements examined include the lithophile elements, K, Ca, Ti, V, Cr, and Mn, and the predominantly chalcophile elements, Fe and As. The lithophile elements, except for K, exist in two distinct forms: an organically associated form that contributes as much as 50% of the occurrence of Ti, V, and Cr in the coal and a mineralogical form consisting of either illite (K, Ti, V, Cr) or calcite (Ca, Mn). In contrast, the two chalcophile elements examined are associated almost exclusively with pyrite and its oxidation products. Evidence is presented for arsenic as arsenate being incorporated in the major pyrite oxidation product, jarosite. There is a useful synergy in such studies because the more fractions examined with XAFS spectroscopy the better the mode of occurrence is determined, and conversely, the better the mode of occurrence is determined, the better the behavior of elements in flotation and leaching tests can be explained.

Xanes Spectroscopy of Sulfur in Earth Materials

“…Differential reduction of organic S compounds to H 2 S does not identify the organic functional groups or the intermediate oxidation states of S. The pyrolysis -gas chromatography -mass spectrometry approach is used for coal, kerogens and aquatic humic substances, but is limited to speciation of thermally stable forms of S. Within this context, S K-and L-edge XANES spectroscopy are proving to be invaluable, non-destructive, and in some cases in situ, techniques for characterizing the S functional groups in natural organic matter. The method has been applied to coals (e.g., Hussain et al 1982, Spiro et al 1984, Huffman et al 1991, George et al 1991, Brown et al 1992, Kasrai et al 1990, 1996b, Olivella et al 2002, Huggins et al 1997, heavy petroleum asphalts (bitumens) and asphaltenes (George & Gorbaty 1989, Gorbaty et al 1991, Waldo et al 1991, Kasrai et al 1994, Vairavamurthy et al 1994, Sarret et al 1999, kerogens , Sarret et al 2002 and sediments, soils and humus (Vairavamurthy et al 1994, 1997, Morra et al 1997, Olivella et al 2002, Qian et al 2002, Beauchemin et al 2002, Solomon et al 2003, Jokic et al 2003. FIG.…”

“…Both the content and chemical form of S vary considerably with provenance and rank of the coal. The presence of organically bound S, which cannot be removed by physical coal-cleaning methods, is a major obstacle in the use of high-S coals: the inorganic-S content, which is principally in the form of pyrite and sulfate minerals, is readily removed by physical methods (e.g., Huggins et al 1997). The potential applications of S K-edge XANES spectroscopy for fi ngerprinting and quantifying S in coal was explored by Hussain et al (1982), who showed that the absorption at the S K edge is qualitatively in proportion to the amount of S present in lignite (1.1 wt.% S), semanthracite (0.6 wt.% S), subbituminous coal (0.4 wt.…”

“…% S) and a bituminous (high volatile content) coal (3.6 wt.% S). The S K-edge XANES method was used to characterize and quantify organic S species in a number of subsequent studies (George & Gorbaty 1989, George et al 1991, Huffman et al 1991, Huggins et al 1997. The different functional S groups were resolved by least-squares fi tting by Huffman et al (1991) and third-derivative analysis by George et al (1991).…”

Toxic Substances From Coal Combustion-a Comprehensive Assessment

“…Note that count rates for Cd, Sb, and As are all similar, even though arsenic in pyrite is generally more abundant than the other two elements. This suggests that relative sensitivity factors (RSF's) for these elements in pyrite are like those in silicate matrices, in which RSF's for Cd and Sb are similar, and the RSF for As is lower [54].…”

Continuation of Crosscutting Technology Development at Cast

“…For all three elements, the correlations with illite are highly significant (R 2 > 0.99). Evidence from previous XAFS investigations into the mode of occurrence of V and Cr in various Illinois basin coals indicates that both of these elements are likely to be distributed between illite and macerals (Maylotte et al, 1981;Huggins et al, 1997Huggins et al, , 2000Huggins and Huffman, 2004); however, less is established regarding the mode of occurrence of Ni and other mineral occurrences are certainly possible Finkelman, 1994). Based on the assumption that these three elements are distributed only between illite and the macerals in this coal, the average contents of these elements in illite are 400 ppm V, 625 ppm Cr, and 280 ppm Ni, while their contents in the macerals would average 21 ppm, 7 ppm, and 6 ppm, respectively.…”