Mo isotope fractionation during adsorption to Fe (oxyhydr)oxides
Mo isotope fractionation during adsorption to Fe (oxyhydr)oxides
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DOI：
10.1016/j.gca.2009.08.004
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发表时间：
2009-11-01
影响因子：
5
通讯作者：
Poulton, Simon W.
中科院分区：
文献类型：
--
作者：
Goldberg, Tatiana;Archer, Corey;Poulton, Simon W.
钼（Mo）同位素作为古氧化还原指示剂具有很大的潜力，但这种潜力目前受到对关键（生物）地球化学过程中发生的同位素分馏的不完全理解的限制。为了解决这样一个不确定性，我们已经调查了钼的同位素分馏吸附过程中的一系列的铁（oxyhydr）氧化物，在可变的钼/铁矿物比和pH值。我们的数据证实，铁（oxyhydr）氧化物可以很容易地吸附钼，突出了潜在的重要性，这种去除途径的全球钼循环。此外，吸附钼铁（oxyhydr）氧化物与优先吸收的较轻的钼同位素。固相和溶解相之间的分级（Δ Mo-98）在较高pH下增加，并且也随矿物学而变化，按磁铁矿的顺序递增（Δ Mo-98 = 0.83 +/- 0.60份/千份）（Delta Mo-98 = 1.11 +/-0.15份/千）<针铁矿（Delta Mo-98 = 1.40 +/-0.48份/千）<赤铁矿（Delta Mo-98 = 2.19 +/-0.54份/千）。同位素分馏的小差异也被认为是在不同的钼/铁矿物比个别矿物。所观察到的同位素行为是一致的分馏过程中吸附到矿物表面（振动能的函数）和吸附不同的钼物种/结构从溶液中。不同的分馏系数确定不同的铁（oxyhydr）氧化物表明，这些矿物可能施加一个主要的控制观察到的天然钼同位素组成的沉积物沉积过程中，通过缺氧（但非硫化物）底部沃茨。我们的研究结果证实，钼同位素可以提供重要的信息，不同的古氧化还原条件的空间范围，提供它们与其他技术相结合，用于评估当地的氧化还原环境和沉积沉积物的矿物学。（C）2009 Elsevier Ltd.保留所有权利。
Molybdenum (Mo) isotopes have great potential as a paleoredox indicator, but this potential is currently restricted by an incomplete understanding of isotope fractionations occurring during key (bio) geochemical processes. To address one such uncertainty we have investigated the isotopic fractionation of Mo during adsorption to a range of Fe (oxyhydr)oxides, under variable Mo/Fe-mineral ratios and pH. Our data confirm that Fe (oxyhydr)oxides can readily adsorb Mo, highlighting the potential importance of this removal pathway for the global Mo cycle. Furthermore, adsorption of Mo to Fe (oxyhydr)oxides is associated with preferential uptake of the lighter Mo isotopes. Fractionations between the solid and dissolved phase(Delta Mo-98) increase at higher pH, and also vary with mineralogy, increasing in the order magnetite (Delta Mo-98 = 0.83 +/- 0.60 parts per thousand) < ferrihydrite (Delta Mo-98 = 1.11 +/- 0.15 parts per thousand) < goethite (Delta Mo-98 = 1.40 +/- 0.48 parts per thousand) < hematite (Delta Mo-98 = 2.19 +/- 0.54 parts per thousand). Small differences in isotopic fractionation are also seen at varying Mo/Fe-mineral ratios for individual minerals. The observed isotopic behaviour is consistent with both fractionation during adsorption to the mineral surface (a function of vibrational energy) and adsorption of different Mo species/structures from solution. The different fractionation factors determined for different Fe (oxyhydr)oxides suggests that these minerals likely exert a major control on observed natural Mo isotope compositions during sediment deposition beneath suboxic through to anoxic (but non-sulfidic)bottom waters. Our results confirm that Mo isotopes can provide important information on the spatial extent of different paleoredox conditions, providing they are used in combination with other techniques for evaluating the local redox environment and the mineralogy of the depositing sediments. (C)2009 Elsevier Ltd. All rights reserved.