Effect of Some Metal Chlorides on the Transformation of Pyrite to Pyrrhotite

摘要

Samples of the iron-sulfide mineral pyrrhotite were prepared using a procedure designed to closely model the pyrite-to-pyrrhotite conversion that occurs during coal-conversion processing. Pyrite mixed with graphite converts to mixtures of monoclinic and hexagonal pyrrhotite when heated at 500C for 4.5 hours, and an iron-rich pyrrhotite (Fe10S11) forms at 600 to 700C. In addition to temperature effects, the pyrrhotites formed from pyrite in graphite are also dependent on additives or impurities in the form of metal salts. The pyrrhotites used in this study were prepared in the presence of selected transition metal chlorides: PdCl2, NiCl2, CoCl2, ZnCl2, MoCl5, and ZrCl4. When these metal salts were used, pyrrhotites with an increased number of iron vacancies were produced. For example, in the presence of ZrCl4 at temperatures as high as 700C, a pyrrhotite was produced that exhibited Moessbauer magnetic-splitting values characteristic of pyrrhotite with a high number of iron vacancies (iron-poor). These pyrrhotites were then converted to troilite at 400C in the presence of CO and H2; and this troilite is an active catalyst for the Fischer-Tropsch synthesis, alkene hydrogenation, the Boudouard reaction, the water-gas shift reaction, and the hydrodesulfurization of organic sulfur compounds.