The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO₃ salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 ± 0.17‰). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5‰. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the δ⁶⁰Ni values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry.

在大氧事件期间，太古代海洋中的含水镍浓度急剧下降，这在当时的带状铁层（BIF）中固相镍浓度下降中很明显。已经进行了一些实验来确定Ni从海水中去除到BIFs中的主要机理，由此表明Ni在铁酸盐上的吸附是一种有效的方法。Ni同位素测量显示在此过程中同位素分数有限，但是，大多数实验是在简单溶液中进行的，其中包含不同比例的溶解的Fe和Ni作为NO ₃与在海水中占主导地位的Cl盐相反。此外，从硅质真核生物到来之前，太古代海洋很可能被非晶硅饱和，如在BIF的夹层石层中所见。尽管显示出Si极大地影响Ni元素在水铁矿固体上的分配，但是尚未对Si对Ni同位素分馏的影响进行研究。在这里，我们报告了多个共沉淀实验的结果，其中三水铁矿在与Ni和Si的混合溶液中沉淀。对于固定浓度为0、0.67或2.2 mM的Si，实验中的Ni浓度范围为200至4000 nM。结果表明，这些浓度的Si对亚铁水合物共沉淀过程中Ni同位素分馏的影响有限。在0.67 mM时，方石英的饱和浓度 沉淀的固体与实验流体之间的同位素分馏因子与不含硅的实验相同（0.34±0.17‰）。然而，在2.2 mM Si和无定形二氧化硅的饱和浓度下，铁水合物固体的Ni同位素组成会偏向更多的负值，并且与低或无Si时相比变化更大，并且一些样品的分馏率最高为0.5‰。 。尽管分馏行为看似更加不稳定，但综合结果表明，即使在高达2.2 mM的Si浓度下，Si的分馏行为仍会降低。亚铁酸盐固体的Ni同位素组成偏向更大的负值，并且与低或无Si时相比具有更大的变化，并且一些样品的分馏率高达0.5‰。尽管分馏行为看似更加不稳定，但综合结果表明，即使在高达2.2 mM的Si浓度下，Si的分馏行为仍会降低。亚铁酸盐固体的Ni同位素组成偏向更大的负值，并且与低或无Si时相比具有更大的变化，并且一些样品的分馏率高达0.5‰。尽管分馏行为看似更加不稳定，但综合结果表明，即使在高达2.2 mM的Si浓度下，Si的分馏行为仍会降低。δ ^60个形成ferrihydrites倪值并没有太大变化。我们的研究结果表明，Si可能不是分离稳定的Ni同位素的主要因素，这将使解释未来的BIF记录和重建太古代海洋化学更加容易。