Froth flotation was used to separate the pyrite sulfur and ash from pulverized coal samples of Illinois No. 6, Pittsburgh, and Middle Kittanning seams. In order to depress the coal pyrite in the flotation process, the coal samples were conditioned in "bacterial liquor." Iron oxidizing bacteria Thiobacillus ferrooxidans was used to cause the superficial oxidation of the coal pyrite. A number of chemical substances known as pyrite depressants were used to suppress pyrite in the flotation process. The results of the tests with the bacteria and the pyrite depressants were then compared. The effects of flotation reagents, variations of flotation pulp pH, and mean temperature of the flotation pulp were studied. Also the effectiveness of the freshly made "bacterial liquor," recycled "bacterial liquor," and old "bacterial liquor" was tested. The retention time studies of coal in "bacterial liquor" showed that for a five hour retention time, the maximum sulfur removal from Illinois No. 6 coal seam was accomplished. The effect of increasing the ratio of coal to "bacterial liquor" in the conditioning tank was studied. It was concluded that the sulfur removal increases as the pulp density increased. Illinois No. 6 coal seam samples were examined optically by binocular, reflected light, and scanning electron microscopes. The degree of dissemination of pyrite in the coal matrix was observed. Washability studies of Illinois No. 6, Pittsburgh, and Middle Kittanning coal seam samples were performed. The washability curves of these coals are presented. / Master of Science