Geologic Controls on Sulfur Content in Coal: ABSTRACT

Abstract

One of the principal factors controlling sulfur content of coal is the pH of the ancestral peat-forming environment. Coals derived from peats are believed to have formed under highly acidic conditions (pH <4.5) are low in sulfur (<1%), whereas sulfur content in coals derived from peats formed under elevated pH conditions (pH 4.5 to 7.5) tends to increase where pH was higher. Maximum bacterial activity occurs where conditions are neutral, or nearly so; such conditions favor sulfate reduction and peat degradation. This pH model is consistent with Schopf's suggestion that the sulfur content of a coal may give an indirect indication of the extent of anaerobic decay. Also, the common occurrence of pyrite in fusain bands may be related to pH conditions (neutral to slightly alkaline) in the pre-fusain layer caused by hydrolysis of alkali and alkaline earth metal ions, which were concentrated by burning. Regional and stratigraphic differences in sulfur contents End_Page 689------------------------------ of Appalachian basin coals are related to differences in pH conditions of the peat-forming paleoenvironments. High-sulfur coals (1) are associated with calcareous sedimentary sequences (marine, nonmarine, or both), (2) have elevated calcium carbonate content, and (3) have a low kaolinite to illite ratio. The converse is true for low-sulfur coals. Exploration for low-sulfur coal should focus on coal-bearing sequences contain a paucity of calcareous sediments. End_of_Article - Last_Page 690------------