DISTRIBUTION AND MODE OF OCCURRENCES OF SULFUR AND TRACE ELEMENTS IN ILLINOIS COAL

Coal is a heterogeneous, complex mixture of organic and inorganic constituents. Inorganic constituents in coal have a significant effect on almost every aspect of coal utilization, as well as major impacts on the environment. The main objective of this research has been to better understand the mode of occurrence and the distribution of sulfur and other inorganic components present in Illinois coal. Sulfur in coal occurs in several forms, such as sulfides, organic sulfur, sulfates, and elemental sulfur. Sulfides, most commonly pyrite, and organic sulfur are the most abundant forms. The origin and distribution of sulfur in coal is of special significance, because of environmental problems associated with the combustion of coals.

In this study, we investigated samples from Murphysboro, Mt. Rorah, Springfield (No. 5), and Herrin (No. 6) coals. Mineralogical and petrographic investigations were conducted on all coal samples to determine (i) inorganic components of coal, and (ii) maceral composition. Additional information has been obtained by analyzing the Scanning Electron Microscope (SEM) images and x-ray fluorescence (XRF) spectra of different minerals. The main minerals identified are kaolinite, pyrite, quartz, and calcite, with trace amounts of illite and mixed-layer illite-kaolinite. Pyrite occurs in several morphologies: as massive, framboidal, isolated enhedral/anhedral, and euhedral forms.

To separate various inorganic and organic sulfur compounds from coal, we designed a novel sequential extraction scheme. The sequential extraction procedures use iterative selective chemical leaching protocols on coals in combination with a range of complementary techniques. Our preliminary data show that the coal samples analyzed in this study have variable total sulfur content. Samples from Murphysboro and Mt. Rorah coal seams have relatively low-sulfur content with a content range from 0.7% to 1.2%. In contrast, coal samples from both Springfield (No. 5) and Herrin (No. 6) have relatively high sulfur concentration, with a content range from 2.9% to 4.5%.The dominant sulfur fraction present in all samples is the disulfide (pyritic) sulfur. There are other sulfides present such as sphalerite or chalcopyrite. In Mt. Rorah coals, the water- and acid-soluble sulfate fractions are major.