Anatomy of a complex mineral replacement reaction: Role of aqueous redox, mineral nucleation, and ion transport properties revealed by an in-situ study of the replacement of chalcopyrite by copper sulfides

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dc.contributor.authorChaudhari, Aen_AU
dc.contributor.authorWebster, NASen_AU
dc.contributor.authorXia, Fen_AU
dc.contributor.authorFrierdich, AJen_AU
dc.contributor.authorRam, Ren_AU
dc.contributor.authorEtschmann, BEen_AU
dc.contributor.authorLiu, WHen_AU
dc.contributor.authorWykes, JLen_AU
dc.contributor.authorBrand, HEAen_AU
dc.contributor.authorBrugger, Jen_AU
dc.date.accessioned2021-10-29T03:55:43Zen_AU
dc.date.available2021-10-29T03:55:43Zen_AU
dc.date.issued2021-10-20en_AU
dc.date.statistics2021-10-21en_AU
dc.description.abstractThe fluid-driven transformation of chalcopyrite (CuFeS2) into Cu-rich sulfides (e.g., digenite, Cu1.8S; covellite, CuS; and chalcocite, Cu2S) is a complex mineral replacement reaction where the reaction pathway is controlled by the interplay between evolving mineral make-up, texture/porosity, and solution chemistry. This trans-formation was investigated in CuCl2 +H2SO4 solutions under mild hydrothermal conditions (180 to 300 ◦C); the reaction kinetics, nature of minerals formed, and oxidation states of aqueous Fe and Cu were followed in-situ in real-time using synchrotron powder X-ray diffraction (PXRD) and X-ray absorption spectroscopy (XAS). These results are corroborated by an analysis of the textures of reaction products from comparative ex-situ quench experiments. The in-situ and ex-situ experiments revealed that: (i) aqueous Cu2+quickly reduced to Cu+ during chalcopyrite replacement in all experiments, and Fe dissolved as Fe2+; (ii) covellite was the first mineral to form, followed by digenite-high with delayed nucleation; and (iii) a non-quenchable hydrated Fe sulfate mineral (szomolnokite, FeSO4.H2O) formed at 240 ◦C at relatively low concentrations of added CuCl2, which supressed the formation of digenite-high. The quantitative mineral phase evolution retrieved using in-situ PXRD was modelled using a novel dual power law (dual Avrami approach). Avrami exponents revealed that chalcopyrite replacement proceeded initially via a 3-dimensional growth mechanism, followed by diffusion-controlled growth. This is consistent with initial formation of a porous covellite rim around chalcopyrite, confirmed by the observation of the ex-situ reaction products, followed by a second reaction stage where the transport properties of aqueous Fe (released from the chalcopyrite) and aqueous Cu (added from the initial solution) to and from the reaction front become the rate-limiting step; and these two kinetic stages exist even where covellite was the only replacement product. The activation energies calculated for these two kinetic stages were 42.9 ±7.4 kJ mol −1 and 39.3 ± 13.1 kJ mol−1, respectively. We conclude that (i) the replacement of chalcopyrite by covellite and digenite proceeds via an interface coupled dissolution and reprecipitation mechanism; (ii) availabilities of aqueous Cu+ and of Fe2+ play a critical role in covellite nucleation and on the sequence of mineral precipitation during chalcopyrite replacement; the Cu+ to Cu2+ ratio is controlled by the kinetics of Cu2+ to Cu+ reduction, which increases with increasing temperature, and by the transport of Cu2+ through the daughter mineral to the reaction front, while Fe2+ availability is limited at high temperature by the formation of insoluble ferrous sulfate; and (iii) this reaction evolves from a bulk fluid-chemistry controlled reaction (initial formation of covellite) to an interface-controlled reaction (digenite-high or further transformation to covellite). The current findings highlight the complex feedback between Cu2+/Cu+ aqueous redox, mineral nucleation, and ion transport properties during replacement reactions, and the applicability of combined in-situ PXRD and XAS techniques in deciphering complex fluid-driven mineral replacement reactions. © 2021 Elsevier B.Ven_AU
dc.identifier.citationChaudhari, A., Webster, N. A. S., Xia, F., Frierdich, A., Ram, R., Etschmann, B., Liu, W., Wykes, J., Brand, H. E. A. & Brugger, J. (2021). Anatomy of a complex mineral replacement reaction: Role of aqueous redox, mineral nucleation, and ion transport properties revealed by an in-situ study of the replacement of chalcopyrite by copper sulfides. Chemical Geology, 120390. doi:10.1016/j.chemgeo.2021.120390en_AU
dc.identifier.issn0009-2541en_AU
dc.identifier.journaltitleChemical Geologyen_AU
dc.identifier.pagination120390en_AU
dc.identifier.urihttps://doi.org/10.1016/j.chemgeo.2021.120390en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/12175en_AU
dc.identifier.volume581en_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectMineralsen_AU
dc.subjectCopper sulfidesen_AU
dc.subjectChalcopyriteen_AU
dc.subjectSynchrotronsen_AU
dc.subjectReaction kineticsen_AU
dc.subjectX-ray diffractionen_AU
dc.subjectCharged-particle transporten_AU
dc.subjectNucleationen_AU
dc.titleAnatomy of a complex mineral replacement reaction: Role of aqueous redox, mineral nucleation, and ion transport properties revealed by an in-situ study of the replacement of chalcopyrite by copper sulfidesen_AU
dc.typeJournal Articleen_AU
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