Key words: pyrite, pyrrhotite, supercritical water, hydrogen sulphide, sulfur
The interaction of pyrite (FeS2) with water at programmed heating (1.5 K/min) to 923 K and subsequent cooling (∼3 K/min) of the reactants to 423 K is studied. Reaction products are analyzed by means of mass-spectrometry, scanning electron microscopy, elemental and X-ray diffraction analyses. In the course of heating, H2S, SO2, rhombic and hexagonal pyrrhotite (FeS) are formed. The subsequent cooling of the reaction system results in the formation of monoclinic pyrrhotite with ferromagnetic properties, cubic pyrite, H2S, and H2. It is shown that the FeS2 → FeS → FeSx (1 < x ≤ 2) transformations are accompanied by changes in the morphology and the size of particles.