Comment on “A non-mass-dependent isotopic fractionation effect” by F. Robert, J. Halbout and J. Baudon
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Mass-independent fractionation
Equilibrium fractionation
Equilibrium fractionation
Mass-independent fractionation
Kinetic isotope effect
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Equilibrium fractionation
Mass-independent fractionation
Isotopes of sulfur
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To utilize stable Hg isotopes as a tracer for Hg cycling and pollution sources in the environment, it is imperative that fractionation factors for important biogeochemical processes involving Hg are determined. Here, we report experimental results on Hg isotope fractionation during precipitation of metacinnabar (β-HgS) and montroydite (HgO). In both systems, we observed mass-dependent enrichments of light Hg isotopes in the precipitates relative to the dissolved Hg. Precipitation of β-HgS appeared to follow equilibrium isotope fractionation with an enrichment factor ε202Hgprecipitate–supernatant of −0.63‰. Precipitation of HgO resulted in kinetic isotope fractionation, which was described by a Rayleigh model with an enrichment factor of −0.32‰. Small mass-independent fractionation was observed in the HgS system, presumably related to nuclear volume fractionation. We propose that Hg isotope fractionation in the HgS system occurred in solution during the transition of O- to S-coordination of Hg(II), consistent with theoretical predictions. In the HgO system, fractionation was presumably caused by the faster precipitation of light Hg isotopes, and no isotopic exchange between solid and solution was observed on the timescale investigated. The results of this work emphasize the importance of Hg solution speciation and suggest that bonding partners of Hg in solution complexes may control the overall isotope fractionation. The determined fractionation factor and mechanistic insights will have implications for the interpretation of Hg isotope signatures and their use as an environmental tracer.
Equilibrium fractionation
Mass-independent fractionation
Enrichment factor
Mercury
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Equilibrium fractionation
Mass-independent fractionation
Isotopes of magnesium
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This chapter contains sections titled: Physical Chemistry Background Fractionation Factor α and Enrichment Factor ε Isotopic Fractionation in Rayleigh Processes Isotopic Fractionation Summary
Equilibrium fractionation
Mass-independent fractionation
Enrichment factor
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Mass-independent fractionation
Equilibrium fractionation
Isotope Analysis
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Equilibrium fractionation
Mass-independent fractionation
Cassiterite
Pegmatite
Isotope Geochemistry
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Minerals and rocks exhibit various isotope compositions depending on their origins and histories. In interpreting their isotopic variations, the equilibrium isotope fractionation factor is a key because it depends on the environment parameters such as temperature. Recent studies have shown that the effect of pressure on the isotope fractionation, which was considered negligible compared to temperature, is significant under the conditions of the Earth's interior. In this article we review recent advances in experimental studies to determine the isotope fractionation of iron and hydrogen at high pressure over several GPa, discussing their issues and future perspectives.
Equilibrium fractionation
Mass-independent fractionation
Hydrogen isotope
Kinetic isotope effect
Isotope Geochemistry
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Laboratory experiments demonstrate that iron isotopes can be chemically fractionated in the absence of biology. Isotopic variations comparable to those seen during microbially mediated reduction of ferrihydrite are observed. Fractionation may occur in aqueous solution during equilibration between inorganic iron complexes. These findings provide insight into the mechanisms of iron isotope fractionation and suggest that nonbiological processes may contribute to iron isotope variations observed in sediments.
Ferrihydrite
Equilibrium fractionation
Mass-independent fractionation
Iron Isotopes
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