Transformations of Pyrite and Pyrrhotite in Supercritical Water

The interaction of pyrite (FeS₂) with water at the uniform heating (1.5 K/min) of the reaction mixture to 923 K and its subsequent cooling (about 3 K/min) to 423 K is studied. The reaction products are analyzed using the methods of mass-spectrometry, elemental and X-ray diffraction analyses, and scanning electron microscopy. It is established that H₂S, SO₂, and rhombic and hexagonal pyrrhotite (FeS) are formed while heating, and the subsequent cooling of the reaction system gives rise to the formation of H₂S, H₂, cubic pyrite, and monoclinic pyrrhotite exhibiting ferromagnetic properties. It is shown that the transformations FeS₂ → FeS → FeS_x (1 OpenSPiltSPi x ≤ 2) are accompanied by changes in the morphology and size of particles.