Chemical and structural control of the partitioning of Co, Ce, and Pb in marine ferromanganese oxides
Chemical and structural control of the partitioning of Co, Ce, and Pb in marine ferromanganese oxides
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DOI：
10.1016/j.gca.2006.11.016
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发表时间：
2007-02-15
影响因子：
5
通讯作者：
Usui, Akira
中科院分区：
文献类型：
--
作者：
Takahashi, Yoshio;Manceau, Alain;Usui, Akira
采用X射线吸收近边结构（XANES）和扩展X射线吸收精细结构（EXAFS）光谱和化学提取方法，研究了水成、成岩和热液成因海洋铁锰氧化物中Co、Ce和Pb的氧化态和矿物相组合。钴是三价的，只与锰氧化物组分（水钠锰矿）相关。铈在所有遗传型氧化物中都是四价的（Ce（III）的检测限类似于5at。%），包括水成氧化物的富铁区（水铁矿），主要与水硼镁石有关。因此，Cc异常的程度不会导致氧化还原条件的变化，但似乎是动力学控制，减少时，从水成岩热氧化物的生长速率增加。铅是二价的，以不同的比例与锰和铁的氧化物结合。根据EXAFS数据，铅主要吸附在铁氧化物的链末端的边缘位点和锰氧化物（ES复合物）的层边缘，以及锰氧化物（TCS复合物）的层间空位位点。连续浸出实验，光谱数据，和电化学的考虑表明，有利于锰氧化物组分的地球化学分区减少从钴铈铅，并取决于他们的氧化清除锰和铁的氧化物。(c)2006爱思唯尔公司All rights reserved.
The oxidation state and mineral phase association of Co, Ce, and Pb in hydrogenetic, diagenetic, and hydrothermal marine ferromanganese oxides were characterized by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. Cobalt is trivalent and associated exclusively with the Mn oxide component (vernadite). Cerium is tetravalent in all genetic-type oxides (detection limit for Ce(III) similar to 5 at. %), including Fe-rich areas (ferrihydrite) of hydrogenetic oxides, and is associated primarily with vernadite. Thus, the extent of a Cc anomaly does not result from variations in redox conditions, but appears to be kinetically controlled, decreasing when the growth rate increases from hydrogenetic to diagenetic to hydrothermal oxides. Lead is divalent and associated with Mn and Fe oxides in variable proportions. According to EXAFS data, Pb is mostly sorbed on edge sites at chain terminations in Fe oxide and at layer edges in Mn oxide (ES complex), and also on interlayer vacancy sites in Mn oxide (TCS complex). Sequential leaching experiments, spectroscopic data, and electrochemical considerations suggest that the geochemical partitioning in favor of the Mn oxide component decreases from Co to Ce to Pb, and depends on their oxidative scavenging by Mn and Fe oxides. (c) 2006 Elsevier Inc. All rights reserved.