Abstract:

 The phase transition of pyrite to monoclinic pyrrhotite and monoclinic pyrrhotite to hexagonal pyrrhotite in the nitrogen atmosphere has been investigated. The study was performed using differential thermal analysis and thermo-gravimetric analyzer (DTA-TGA), X-ray powder diffractometer (XRD) and magnetic susceptibility meter. The decomposition of pyrite begins at the temperature of about 400℃. At the temperature below 500℃, there is no phase change. As temperature increases to 500-600℃, pyrite phase begins to transform to monoclinic pyrrhotite and the transformation rate rises as the temperature rises. And the magnetic susceptibility is also higher as a result of the existence of monoclinic pyrrhotite. The rate of pyrite transformation to monoclinic pyrrhotite is higher than the rate of monoclinic pyrrhotite transformation to hexagonal pyrrhotite. With the temperature elevating, the two rates increase as well. When the temperature is higher than 600℃, hexagonal pyrrhotite, even troilite (FeS), is the primary product. The rate of pyrite transformation to monoclinic pyrrhotite is lower than the rate of monoclinic pyrrhotite transformation to hexagonal pyrrhotite.

Key words:  pyrite, phase transition, monoclinic pyrrhotite, hexagonal pyrrhotite, magnetic susceptibility