CONCENTRATION AND DISTRIBUTION OF TRACE ELEMENTS IN COALS FROM ILLINOIS BASIN

Coal consumption is a significant cause for health, environmental, and technological hazards due to the presence of trace elements such as: S, Hg, Pb, Zn, Mo, Se, Cu, and Ti; which are common in coal of southern Illinois. It is very important to document the distribution, abundance, speciation, and modes of occurrence of trace elements and understand their mineralogical association with coal. The present study was undertaken to assess the geochemical controls of different trace elements in the Illinois coal. Samples were collected from four coal seams: (1) Herrin No. 6 and (2) Springfield No. 5 of Carbondale Formation and (3) Murphysboro and (4) Mt. Rorah of Spoon Formation. We used Proton-induced x-ray emission (PIXE) for measuring the concentration of trace elements and scanning electronic microscopy-energy dispersive spectroscopy (SEM-EDS) for characterizing the mineralogical associations in the coal samples.

Preliminary SEM observations show that the major inorganic constituents in our samples are sulfide minerals (e.g., pyrite, chalcopyrite, galena, and blenda), quartz, clays, and calcite. Murphysboro coals contain framboidal pyrites and Mt. Rorah coals contain gypsum. Preliminary PIXE results indicate that coal samples have total sulfur (S_t) concentrations in the range of 1% to 3.5%. The highest S_t concentrations were measured in Murphysboro coals and the lowest were measured in Herrin No. 6 coals. Silica content is much higher in the Springfield coal (3.37% to 6.32%) compare to the other coals. Springfield No. 5 (Ca_ave = 0.77%) and Herrin No. 6 (Ca_ave = 0.78%) coals are calcium rich. Al, Fe, S, Si, and Ti element are common in all coal samples. Except Sr, most of the trace elements are higher in concentration in Mt. Rorah and Murphysboro compare to Springfield No. 5 and Herring No. 6. Springfield No.5 coals show the presence of other trace elements such as Ga, Ge, Se, Rb, Zr, and Mo where as coals from other units do not contain these elements. Mt. Rorah (Hg_ave = 0.163 ppm) and Murphysboro (Hg_ave = 0.095 ppm) coal samples show Hg concentration among the analyzed samples from the Illinois Basin. The chalcophile (Pb, Cu, Zn, and Ga) and siderophile elements (Ni and Mn) correlate positively with Fe and suggest that these elements may be bound partly with pyrite or other sulphides and iron containing minerals.