OCR Text |
Show 8 CCSEM included quartz, kaolinite, illite, and pyrite. Chemical fractionation was also performed on the coal in order to compare with the mineral results, for the purpose of discerning elemental modes of occurrence. Although this technique is more applicable for low-rank coals having significant amounts of organically associated elements, it has some merit for trying to determine the association of elements which do not appear to have obvious mineral associations. Results of the chemical fractionation analysis, displayed in Table 2, are presented as the percentage the element that was removed after the ammonium acetate extraction and the amount of the element that remained after the full extraction process. In general, the ammonium acetate extraction, which best represents extractions of organically bound inorganics, shows minor amounts of metals extracted, except for Se which shows 25% extracted. The water and hydrochloric acid extractions were very effective in removing most of the As, Cd, and Pb, while Cr, Ni, Hg, and Se all have significant levels remaining in the final residue. The fInal type of coal analysis that was performed was WDS analysis of individual pyrite and clay mineral grains. Table 3 gives the range of trace metal levels determined for several pyrite and clay mineral grains. Trace Metal Inorganic Associations Table 3 shows that Ni, As, Se, and Hg are at least partly associated with pyrite, probably as accessory sulfide mineral species that are interspersed with the iron sulfide material or as impurities or solid solution series within the ubiquitous pyrite mineralization. Cr showed associations with clay minerals, most likely as a Cr oxide accessory mineral in the clay structure or as cation replacement of the Al in the clay structure. The clay minerals were identified in Table 1 as primarily kaolinite and illite, which commonly contain heavy metal impurities such as Se and Cr. Although these results are based on only limited WDS analysis of Illinois No.6 minerals, some general associations most likely hold true. The trace metals |