Fe-S-O-H System

The strategies used in studies of high temperature reactions of metals have been brought to bear on some of the problems associated with the direct liquefaction of coaL Many coals contain sulfur, combined in both organic and inorganic forms, in excess of amounts allowable under current combustion standards. In some coals much of the sulfur is in the form of pyrite, Fe 2> which may, paradoxically, serve as a catalyst or the precursor of a catalyst for the liquefaction process. The information available for the Fe-S-O-H system has been assembled in an attempt to provide a framework for interpreting experimental results, and to facilitate the planning of further experim ents. 

Two related graphical representations are detailed below. Both are variants of Pourbaix diagrams, which systematize and display the relationship between thermodynamic variables for multicomponent systems. General discussions of such diagrams have been published, by Pourbaix (6), by Garrels and Christ (7), and, in the second form used here, by Gulbransen and Jansson (8). This paper deals with the conclusions that may be drawn based on only the known and inferable thermodynamics of the Fe-S-O-H system, and does not depend on the details of the structures of pyrite or the pyrrhotites, nor on the mechanism of the conversion of pyrite to pyrrhotite. 

The thermochemical stability of solid phases, aqueous species and gaseous species in Fe-S-O-H system will be considered below. Solid phases of this system include Fe, FeO, Fe304, Fe203, FeS, and FeS2- Dominant aqueous species considered... 

Fig. 1.29 Log foz-pH diagram for Fe-S-O-H system at 200 °C. The K-mica-kaolinite curve is taken from Hemley et al. (1969) Log a is -1.25 (Barton 1984)...

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