Date of Award
Master of Science (MS)
A study of high- and low-sodium lignite of the Beulah-Zap bed sampled at the Indian Head Mine, Pit 11 and 12, respectively, in Mercer County, North Dakota and fly ash derived from utilization tests on the lignite, indicates the fly-ash composition and related utilization potential can be correlated to coal geochemistry.
Average lithotype abundances for each of the sampling sites were estimated to be vitrain 50%, attritus 45%, and fusain 5%. Attritus occurs more frequently in the upper part and vitrain in the middle and lower parts of the seam. Maceral groups, identified microscopically, were (in order of decreasing abundance): huminite, inertinite, and liptinite. The percentage of huminite macerals increased toward the bottom and inertinite macerals toward the top of the seam at each sampling location. Similar abundances and trends for l ithotypes and maceral groups between the high- and low-sodium lignites indicate similar depositional processes.
Scanning electron microscopy and electron microprobe analysis were used to determine the abundance and distribution of major elements in the lignite. Sodium concentrations were found to be an order of magnitude higher in Pit 11 than in Pit 12. Calcium and magnesium concentrations were also higher in Pit 11 and iron, sulfur, aluminum, and silicon concentrations were higher in Pit 12. A distinct correlation between iron and sulfur abundance was noted in Pit 11, consistent with high pyrite content as determined during field descriptions and microscopic evaluation of the samples.
The differences in sodium concentrations at the two sampling locations relate to a hydrogeochemical model presented in the literature. High-sodium coal corresponds with fine-textured overburden sediments. The source of the sodium in the high-sodium coal is believed to be sodium montmorillonite clays in the overburden at Pit 11.
Combustion tests at flue-gas temperatures of 1300°c and 1500°c were made on a composite lignite sample from each of the two sampling locations. Fly-ash samples were analyzed by point-count techniques with an electron microprobe and by energy-dispersive X-ray fluorescence analyses. The chemical composition of fly-ash particles was extremely variable indicating the complexity of reaction mechanisms involved in the formation of the fly ash. Average oxide concentrations of fly ash correlate with oxide concentrations in the lignite indicating that the fly-ash composition and utilization potential can be related directly to the lignite composition. The specific mineral and amorphous phases present in the fly ash are interpreted to be determined by the elemental composition of the 1 ignite and the temperature at which the fly-ash particles are formed.
Mayer, Gale G., "Characterization and utilization of high- and low-sodium lignite of the Beulah-Zap bed (Paleocene), Indian Head Mine, southwestern North Dakota" (1988). Theses and Dissertations. 192.