Abstract Marine ferromanganese crusts and nodules host high concentrations of many economically interesting metals such as platinum (Pt), with Pt concentrations in the range of 44 to 3207 ppb in 182 analyzed samples from various locations in the global ocean. Different mechanisms have been proposed to explain this strong enrichment in the MnFe oxide phases compared to seawater, including reduction of seawater Pt(II) to Pt(0) or oxidation to Pt(IV) and surface adsorption on the Fe-oxyhydroxide or Mn-oxide phases. To shed more light on the process of Pt enrichment in nodules and crusts, we applied a multi-method approach including bulk analyses, statistics (correlations and Q-mode factor analyses), sequential leaching, sorption experiments, and XANES and EXAFS measurements. Our analyses lend new support to the heterogeneous oxidation/sorption mechanism advanced by Maeno et al. (2016) to explain the initial Pt(II) enrichment on FeMn crusts, with Pt oxidation only taking place on the Mn-oxide phase but not on the Fe-oxyhydroxide phase of crusts. Nodules show lower concentrations and a lesser association of Pt with the Mn phase as the latter is partly of diagenetic origin while the origin of Pt is hydrogenetic. Our results also indicate that sorption of Pt2+(aq) to FeO(OH) is possible if Pt2+(aq) exists under conditions typical of nodule and crust growth in the oceans. Platinum concentrations are consistently highest in phosphatized FeMn crusts where they appear to be related to the occurrence of a 10 A manganate, so they are likely to be the best exploration target for Pt globally in marine FeMn crusts. However, further work is needed to understand the geochemical reactions that dominate mass transfer of Pt under conditions under which crusts are phosphatized and to identify the exact mineral type which hosts the Pt enrichment. The complex Pt geochemistry in marine FeMn crusts and nodules due to the different phase associations and enrichment processes on the different carrier phases make a straightforward interpretation of Pt data in specific samples difficult. Our findings suggest that only spatially resolved, species-specific methods available via synchrotron-based X-ray and modern electron-probe micro-analyzers (in development) could provide the combination of spatial resolution and species-specificity to determine which of several proposed mechanisms are actually responsible for Pt enrichment in FeMn crusts.

中文翻译：

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基于多方法方法的海相铁锰结壳和结核中铂的富集和相结合

摘要 海洋铁锰结壳和结核含有高浓度的许多具有经济意义的金属，例如铂 (Pt)，在来自全球海洋不同位置的 182 个分析样品中，铂浓度在 44 至 3207 ppb 的范围内。已经提出了不同的机制来解释与海水相比在 MnFe 氧化物相中的这种强烈富集，包括海水 Pt(II) 还原为 Pt(0) 或氧化为 Pt(IV) 以及 Fe-羟基氧化物或 Mn-的表面吸附氧化物相。为了更深入地了解结核和结壳中 Pt 的富集过程，我们采用了多方法方法，包括批量分析、统计（相关性和 Q 模式因子分析）、顺序浸出、吸附实验以及 XANES 和 EXAFS 测量。我们的分析为 Maeno 等人提出的异质氧化/吸附机制提供了新的支持。(2016) 解释了 FeMn 结壳上的初始 Pt(II) 富集，Pt 氧化仅发生在 Mn-氧化物相上，而不发生在结壳的 Fe-羟基氧化物相上。结核显示出较低的浓度和 Pt 与 Mn 相的较少关联，因为后者部分是成岩起源的，而 Pt 的起源是氢化的。我们的结果还表明，如果 Pt2+(aq) 在海洋中结核和地壳生长的典型条件下存在，则 Pt2+(aq) 吸附到 FeO(OH) 是可能的。磷化 FeMn 结壳中的铂浓度始终最高，它们似乎与 10 A 锰酸盐的存在有关，因此它们可能是全球海洋 FeMn 结壳中 Pt 的最佳勘探目标。然而，需要进一步的工作来了解在结壳磷化的条件下主导 Pt 传质的地球化学反应，并确定导致 Pt 富集的确切矿物类型。由于不同相结合和不同载体相上的富集过程，海洋 FeMn 结壳和结核中复杂的 Pt 地球化学使得对特定样品中 Pt 数据的直接解释变得困难。我们的研究结果表明，只有通过基于同步加速器的 X 射线和现代电子探针微分析仪（开发中）可用的空间分辨率、物种特异性方法才能提供空间分辨率和物种特异性的组合，以确定几种拟议机制中的哪一种实际上负责 FeMn 结皮中 Pt 的富集。