We examined Hg stable isotope fractionation after the partial reduction of Hg(II) to Hg(0) by the siderite and green rust of ferrous iron minerals. The fractionation of Hg isotopes in closed-system experiments followed an equilibrium fractionation model, with Hg(II) enriched in heavier isotopes. The results indicated isotopic fractionation (δ²⁰²Hg^II–δ²⁰²Hg⁰) of 2.43 ± 0.38 and 2.28 ± 0.40‰ for the siderite and green rust experiments, respectively. Experiments were also performed to determine if the rapid attainment of isotopic equilibrium was attributed to isotopic exchange between Hg(II) and Hg(0). In the absence of other redox-active species, we observed that the δ²⁰²Hg values of both Hg(0) and Hg(II) shifted substantially toward equilibrium within minutes and evolved to constant δ²⁰²Hg differences between the Hg(II) and Hg(0) pools. Mixing experiments conducted in water and 10 mM NaCl yielded δ²⁰²Hg^II–δ²⁰²Hg⁰ differences of 2.63 ± 0.37 and 2.77 ± 0.70‰, respectively. The ¹⁹⁹Hg/¹⁹⁸Hg and ²⁰¹Hg/¹⁹⁸Hg results were consistent with previously published experimental and computational studies indicating the involvement of nuclear volume effects in the observed fractionations between the mercury species. Together, these findings suggest that rapid Hg isotopic exchange can facilitate Hg stable isotope fractionation in Hg(II)–Hg(0) redox systems and overprint isotopic fractionation caused by kinetic processes.

中文翻译：

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亚铁矿物还原汞后快速达到同位素平衡以及 Hg(II) 和 Hg(0) 之间的同位素交换

我们研究了亚铁矿物的菱铁矿和绿锈将 Hg(II) 部分还原为 Hg(0) 后的 Hg 稳定同位素分馏。封闭系统实验中 Hg 同位素的分馏遵循平衡分馏模型，其中 Hg(II) 富含较重的同位素。结果表明菱铁矿和绿锈实验的同位素分馏(δ ²⁰² Hg ^II –δ ²⁰² Hg ⁰ ) 分别为2.43 ± 0.38 和2.28 ± 0.40‰。还进行了实验以确定快速达到同位素平衡是否归因于 Hg(II) 和 Hg(0) 之间的同位素交换。在没有其他氧化还原活性物质的情况下，我们观察到 δ ²⁰²Hg(0) 和 Hg(II) 的 Hg 值在几分钟内显着转向平衡，并演变为Hg(II) 和 Hg(0) 池之间恒定的 δ ²⁰² Hg 差异。在水和 10 mM NaCl 中进行的混合实验产生 δ ²⁰² Hg ^II –δ ²⁰² Hg ⁰差异分别为 2.63 ± 0.37 和 2.77 ± 0.70‰。在¹⁹⁹汞/ ¹⁹⁸ Hg和²⁰¹汞/ ¹⁹⁸汞结果与先前发表的实验和计算研究一致，表明核体积效应涉及观察到的汞物种之间的分馏。总之，这些发现表明，快速的 Hg 同位素交换可以促进 Hg(II)–Hg(0) 氧化还原系统中的 Hg 稳定同位素分馏和由动力学过程引起的同位素分馏。