Thermodynamic stability of pentlandite and violarite and new EH-pH diagrams for the iron-nickel sulphur aqueous system

The role of pyrrhotite (Fe7S8) and the sample texture in the hydrothermal transformation of pentlandite ((Fe,Ni)9S8) to violarite ((Ni,Fe)3S4)

“…Reaction (8) indicates that the catalytic role of pyrrhotite in the pentlandite replacement reaction by violarite is due to the consumption of nickel ions by pyrrhotite, which favors the forward direction of reaction (7). Reactions (7) and (8) indicate that the transformation of 1 mole pentlandite consumes 0.33 mole of pyrrhotite.…”

“…Reactions (7) and (8) indicate that the transformation of 1 mole pentlandite consumes 0.33 mole of pyrrhotite. This contradicts our experimental observations; in our experiments involving pyrrhotite, the mass of pyrrhotite remained almost constant (undetectable change by XRD -less than 3% change).…”

“…Violarite is another economically important nickel sulfide mineral and thus has been the focus of a number of studies [5][6][7][8]. Secondary violarite that formed by alteration of pentlandite under mild hydrothermal conditions inherits the texture of the parent pentlandite and can thus be regarded as a pseudomorph.…”

Transformation of pentlandite to violarite under mild hydrothermal conditions

“…Available thermodynamic properties (Warner et al 1996) indicate that, under acidic conditions, the reaction happens under very reducing conditions (fH 2 (g) ca. 0.2 bars; Figure 4b).…”

“…Violarite is metastable relative to vaesite and polydymite, and these two minerals were not considered. Thermodynamic properties are from the Lawrence Livermore National Laboratory database (version 8, revision 6), except for the following species: first ionisation constant of H 2 S(aq) from Suleimenov & Seward (1997), violarite and pentlandite from Warner et al (1996).…”