In-situ high temperature XRD study of pyrite

Pyrite is the most common sulphide mineral on the earth and is present in almost all rock types in varying amounts. In majority of operations in mineral industries, presence of pyrite poses certain problems due to its chemical and physical properties. These problems can vary from minor to major, depending on the process. For example, pyrite is a major source of sulphur in shale oil. Understanding the reactions and changes in pyrite under different environmental conditions is essential in solving these problems. In this work, results from in-situ high-temperature X-ray diffraction (HTXRD) analyses on selected natural pyrite samples under different atmospheric conditions are presented and discussed. Samples were analysed in low-pressure, air, nitrogen, argon and carbon dioxide atmospheres. In some cases, not only the rate, but also the type and extent of decomposition reactions and individual peak intensities change considerably with the atmosphere. In non-oxidative environments pyrrhotite is the major product, while magnetite and hematite are dominating in oxidative environments. It was also observed that pyrite has a strong tendency to react with carbon dioxide to form magnetite through an intermediate step of non-stoichiometric pyrrhotite. Possible reaction pathways including self dissociation of carbon dioxide are proposed.