Mercury Isotope Fractionation during Precipitation of Metacinnabar (β-HgS) and Montroydite (HgO)

Citations Over TimeTop 10% of 2015 papers

Abstract

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 ε(202)Hg(precipitate-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.

Related Papers

• → Mercury Stable Isotope Fractionation during Abiotic Dark Oxidation in the Presence of Thiols and Natural Organic Matter(2018)110 cited
• → Mercury Isotope Fractionation during Precipitation of Metacinnabar (β-HgS) and Montroydite (HgO)(2015)61 cited
• → Copper isotope fractionation by diffusion in a basaltic melt(2023)7 cited
• → Quantification of Isotope Fractionation in Experiments with Deuterium-Labeled Substrate(2002)27 cited
• → Pressure Effect on Isotope Fractionation Factor(2020)