Nickel accelerates pyrite nucleation at ambient temperature

Abstract

Chemical and isotopic compositions of pyrites are used as biogeochemical tracers in Archean to modern sediments. Moreover, pyrite formation from monosulphide precursors has been proposed to be involved in prebiotic chemistry. However, the factors controlling pyrite formation and distribution in the sedimentary record are incompletely understood. Here, we show that Ni 2+ ions accelerate ~5 times the nucleation of pyrite at ambient temperature. Using Fe and Ni K-edge EXAFS and TEM-EDXS we demonstrate that Ni(II) is directly involved in the nucleation of pyrite synthesised by reacting Fe(III) with Na 2 S in the presence of aqueous Ni(II) impurity. Initial formation of a Ni-enriched pyrite core is followed by overgrowth of a Ni-depleted pyrite shell, leading to compositional zoning of the Fe 1-x Ni x S 2 nanocrystals (x = 0.05 to 0.0004). The molar Ni/Fe ratio in the final aqueous solution was then 2000 times lower than the starting ratio of 0.01. This enhanced and accelerated trapping of Ni by pyrite could be of prime importance in controlling Ni concentration in the ocean during early diagenesis of marine sediments, and could thus have important implications for interpreting abundances of Ni and pyrite in the sedimentary record. In addition, acceleration of pyrite nucleation in the presence of nickel could help understanding the role of Fe-Ni sulphides in catalysing potential prebiotic reactions.

Experimental redox transformations of uranium phosphate minerals and mononuclear species in a contaminated wetland

“…In order to quantitatively determine the fractions of U(VI) and U(IV), U-L III edge XANES spectra were least-squares fit by linear combinations (LCF) of pure U(IV) and U(VI) model compounds XANES spectra, using a home-built code [10,19,26]. The chosen model compounds were a U(IV) humus sample and a synthetic U(VI)-humic acid model compound [10].…”

“…The chosen model compounds were a U(IV) humus sample and a synthetic U(VI)-humic acid model compound [10]. Uranium L III -edge EXAFS spectra of the incubated samples were least-squares fit by linear combinations (LCF) of model compounds EXAFS spectra using a home-built code [10,19,26]. The model compounds chosen for this procedure were already used by Stetten et al.…”

Organic and Inorganic Geochemical and Mineralogical Assessments of the Silurian Akkas Formation, Western Iraq

“…High Ni/ Co values are therefore typical of reducing conditions in which organic matter accumulates (Morford and Emerson, 1999). Nickel is dominantly delivered to the sediments in association with the organic matter; but it is released through organic matter decay and can be trapped by pyrite under sulphate-reducing conditions (Morin et al, 2017). Nickel and cobalt (Co) are enriched mainly under sulphate-reducing conditions alone and their abundance can serve as a marker of a relatively high organic matter flux (e.g.…”

“…Ce-anomaly (Akkas-1 well only): The susceptibility of Ce to redox conditions in the ocean, in contrast to other REEs, makes it suitable as a palaeo-redox indicator in a sedimentary rock (German and Elderfield, 1990). Whole rock Ce-anomaly values are calculated according to Murray et al (1990) as: Ce anomaly = Ce/Ce* = CeSN/(0.5LaSN + 0.5PrSN)…”

Facile Hydrothermal Synthesis of Nanocubic Pyrite Crystals Using Greigite Fe3S4 and Thiourea as Precursors

“…Specifically, the diffraction peaks agreed well with hexagonal scalenohedral hematite (JCPDS no. 33 214), and (300) planes of hematite, respectively. This phenomenon suggests that a low concentration of thiourea was not sufficient to completely convert the greigite into pyrite.…”