The role of pyrrhotite (Fe 7 S 8 ) and the sample texture in the hydrothermal transformation of pentlandite ((Fe,Ni) 9 S 8 ) to violarite ((Ni,Fe) 3 S 4 )

The catalytic role of pyrrhotite (Fe7S8) in the reaction kinetics of the hydrothermal transformation of pentlandite ((Fe,Ni)9S8) to violarite ((FeNi2S4) was found to depend on the physical form of pyrrhotite. Pyrrhotite in fine scale intergrown with pentlandite boosts the reaction, whereas in a mechanical mixture of pyrrhotite and pentlandite, it plays the opposite role. This phenomenon was interpreted as result of dissolution of pyrrhotite under reaction conditions.