Mössbauer study of transformations of pyrite under conditions of coal liquefaction

The Mössbauer effect is used to study in-situ transformations of pyrite under conditions of coal liquefaction based on Illinois No. 6 coal from St. Clair County. A marked reduction is observed at high temperatures in the isomer shift of the iron sulphides during coal liquefactions. By contrast the pure sulphides do not show such a strong effect in the presence of solvent and hydrogen. This reduction in the isomer shift may result from covalent bonding between the iron on the pyrrhotite surfaces and the coalderived liquid and gases. Marked broadening of the linewidth of Fe_{1 ? x}S occurs above 300 °C in the presence of solvent and hydrogen. The stoichiometries of the pyrrhotites formed in the different runs were determined and a correlation was observed between the total amount of sulphur in the coal and the iron deficiency in Fe_{1 ? x}S. Coal-derived liquids are more active in enhancing pyrite decomposition than tetralin. Both H₂S and Fe_{1 ? x}S seem to be actively involved in the liquefaction process.