Negative Ce anomalies in Mn oxides: The role of Ce4+ mobility during water–mineral interaction
Negative Ce anomalies in Mn oxides: The role of Ce4+ mobility during water–mineral interaction
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DOI：
10.1016/j.gca.2012.03.017
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发表时间：
2012-06
影响因子：
5
通讯作者：
A. Loges;T. Wagner;M. Barth;M. Bau;Susanne Göb;G. Markl
中科院分区：
文献类型：
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作者：
A. Loges;T. Wagner;M. Barth;M. Bau;Susanne Göb;G. Markl
我们提出了一个非常罕见的自然的例子，非常负的Ce异常（高达4个数量级）的锰氧化物，由较高的流动性Ce 4+相比，REE 3+在水生环境中。在热液萤石脉中，年轻的次生锰氧化物在水-矿物相互作用过程中与萤石和针铁矿一起形成。我们的研究结果是相反的氧化清除铈，这是常见的锰氧化物。现代矿山沃茨与原生和次生矿物的稀土元素模式的比较表明，这不能仅仅被解释为一个源相关的功能或固定的Ce，但必须至少部分是优先动员的结果Ce 4+相比，RE 3+。我们建议，这种非常不寻常的行为是由于强大的络合Ce 4+，最有可能的铁载体或类似的有机分子，根据公布的复合物形成常数。溶解有机碳（DOC）的存在下，即使在最深的矿井水平流出的水样支持这个模型。最近的实验研究也表明，负Ce异常开发生物锰氧化物，但这种效果尚未报道，从自然环境。我们的研究结果强调自然系统的实验结果的相关性，并有相当大的影响，在地球表面环境或潜在的高级别永久性处置库的四价锕系元素（特别是Pu 4+）的流动性的评估。
We present one of the very rare natural examples of extremely negative Ce anomalies (up to 4 orders of magnitude) in manganese oxides, caused by higher mobility of Ce4+compared to REE3+in an aquatic environment. The young secondary Mn oxides formed together with fluorites and goethites during water–mineral interaction in a hydrothermal fluorite vein. Our findings are in contrast to the oxidative scavenging of Ce, which is commonly observed in Mn oxides. Comparison of REE patterns from modern mine waters with primary and secondary minerals demonstrates that this cannot be solely explained as a source-related feature or by immobilization of Ce, but must at least partially be the result of preferential mobilization of Ce4+compared to REE3+. We propose that this very unusual behavior is due to strong complexation of Ce4+, most likely by siderophores or similar organic molecules, based on published complex formation constants. The presence of dissolved organic carbon (DOC) even in water samples outflowing at the deepest mine level lends support to this model. Recent experimental studies have also demonstrated that negative Ce anomalies develop in biogenic Mn oxides, but this effect has not yet been reported from a natural environment. Our findings emphasize the relevance of experimental results for natural systems and have considerable implications for the assessment of the mobility of tetravalent actinide elements (especially Pu4+) in earth surface environments or potential high-level permanent repositories.