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

Abstract

The catalytic role of pyrrhotite (Fe 7 S 8 ) in the reaction kinetics of the hydrothermal transformation of pentlandite ((Fe,Ni) 9 S 8 ) to violarite ((FeNi 2 S 4 ) 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.

Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

“…Ni 3 S 4 ), heazlewoodite (Ni 3 S 2 ), and millerite (NiS) are all supersaturated as violarite forms.Yet, violarite was the only Ni-sulfide observed in hydrothermal experiments conducted over a wide range of temperatures (125 -210 ℃) and solution compositions(Tenailleau et al 2006;Xia et al 2007Xia et al , 2009a. In experiments conducted at similar temperature, but under dry conditions,Xia et al (2009a) observed a complex assemblage of phases, more consistent with the predictions from the thermodynamic model.…”

“…The local interfacial solution controls key processes such as volume change, nucleation rate, and growth mechanism; while in conjunction with the interfacial solution chemistry, the parent phase can act to stabilize metastable phases and/or compositions (Ruiz-Agudo et al 2014;Xia et al 2007Xia et al , 2008. Kinetic factors play a critical role in enabling the formation of metastable products.…”

Characterization of porosity in sulfide ore minerals: A USANS/SANS study

“…In all cases the product mineral showed evidence of reaction generated porosity. The ore-forming reactions that have been studied include the replacement of pentlandite by violarite (Tenailleau et al 2006;Xia et al 2009Xia et al , 2008Xia et al , 2007, pyrrhotite by marcasite and pyrite (Qian et al 2011;Xia et al 2010Xia et al , 2007, hematite by chalcopyrite (Zhao et al 2014b), chalcopyrite by bornite (Zhao et al 2014a), magnetite by pyrite (Qian et al 2010) and by arsenian-pyrite (Qian et al 2013), calaverite by gold (Zhao et al 2009, and sylvanite and krennerite by gold-silver alloy (Xu et al 2013;Zhao et al 2013). In all these replacement reactions, porosity was generated in the daughter minerals regardless whether the reaction involves volume contraction or expansion.…”

A Novel Route for the Synthesis of Mesoporous and Low-Thermal Stability Materials by Coupled Dissolution-Reprecipitation Reactions: Mimicking Hydrothermal Mineral Formation

“…Xia et al [9,18,19] found that the Fe/Ni ratio of (Ni,Fe) 3 S 4 could be adjusted by varying the reaction conditions, including temperature (125-145 ºC), pH (1 to 6), and precursor stoichiometry. Between pH 1 and 6 the reaction proceeds via an ICDR reaction, with a very sharp reaction front and porous (Ni,Fe) 3 S 4 product, as the dissolution of the pentlandite precursor is rate-limiting (Fig.…”