SULFUR IN ILLINOIS COALS

This study presents results of our investigation on the distribution and modes of occurrences of sulfur in coal samples from the Illinois basin. The samples are from Springfield No. 5, Herrin 6, Murphysboro, and Mt. Rorah coal seams. The methods used in this study include: scanning electron microscopy (SEM-EDS), chemical sequential extractions, and sulfur isotopes analyses. SEM photomicrographs showed pyrite as the dominant sulfide mineral associated with Illinois coals. Framboidal pyrites were identified in Murphysboro coals and galena in Mt. Rorah coals. Additional fracture-filling minerals identified were quartz, calcite, iron sulfates and clay in Springfield No. 5 and calcite, clay and pyrite in Herrin 6 coals. The EDS spectra show various trace elements such as Zn, Pb, Cu, Cr, Hg, Se, Ti, As, Al and Mn associated mostly with inorganic phases in coal. The seven-step chemical sequential extractions of homogenized, powdered coal samples result in the characterization of the following sulfur species: water soluble, acid soluble (gypsum and carbonate bound sulfur), copper extractable (elemental sulfur), acid volatile (monosulfides), chrome-reducible (pyrite and other disulfides), humic acid sulfur and fulvic acid sulfur. The water soluble sulfur is the dominant sulfur fraction extracted followed by fulvic acid, acid soluble, chrome-reducible, and copper extractable sulfur. Sulfur isotope measurements of the different sulfur fractions were conducted to further establish the isotope composition of inorganic and organic phases in Illinois coals. Preliminary δ³⁴S values of sulfur fractions in the: (1) Springfield No. 5 coals range from -1.7 to -0.9‰ in water-soluble sulfur, and from +0.07 to +5.1‰ in chrome-reducible (disulfides) sulfur; (2) Murphysboro coals range from -2.5 to +4.6‰ in water-soluble sulfur, from -2.7 to +4.7‰ in acid soluble sulfur, from +6.5 to +10.8‰ in chrome-reducible (disulfides) sulfur and from -3.9 to +8.7‰ in copper extractable (elemental sulfur), (3) Mt. Rorah coals range from +4.4 to +14.1‰ in water-soluble sulfur, from -6.9 to +14.1‰ in acid soluble sulfur, from -0.8 to +18.1‰ in chrome-reducible (disulfides) sulfur, and from +10.8 to +21.9‰ in copper extractable (elemental sulfur). Interpretation of the sulfur isotopes values will be further discussed at the meeting.