Local structure of Y and Ho in calcite and its relevance to Y fractionation from Ho in partitioning between calcite and aqueous solution
Local structure of Y and Ho in calcite and its relevance to Y fractionation from Ho in partitioning between calcite and aqueous solution
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DOI：
10.1016/j.chemgeo.2007.11.003
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发表时间：
2008-02
期刊：
影响因子：
3.9
通讯作者：
Kazuya Tanaka;Y. Takahashi;H. Shimizu
中科院分区：
文献类型：
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作者：
Kazuya Tanaka;Y. Takahashi;H. Shimizu
在稀土元素（ree）中，Y和Ho在大多数火成岩活动中的行为非常接近，因为它们的离子半径相似，而Y在海洋系统中从Ho分出。为了从结构化学的角度阐明海洋体系中观察到的Y - Ho分馏现象，我们对方解石-水溶液（Y - Ho分馏体系）和强酸阳离子交换树脂-水溶液（非Y - Ho分馏体系）两种分馏体系进行了Ho - LIII-edge和Y - K-edge EXAFS研究。EXAFS分析结果显示，在所有样品中，Ho和Y之间与最邻近O原子的原子间距离没有显着差异。然而，发现Y-Ho掺杂方解石中的第一壳层Ho-O和Y-O距离比水合离子中的要短。相比之下，Y-Ho掺杂树脂的第一壳层Ho-O和Y-O距离与水离子中的相似。以往的研究表明，镧系元素（Ln）由于4f轨道参与成键而比y更具共价。对各种Ln3+配合物的光谱研究表明，随着Ln3+离子与阴离子配体成键共价的增加，Ln3+离子中4f电子排斥力的Racah参数降低。因此，我们的EXAFS结果表明，分配中的Y - Ho分馏可能归因于Y和Ho之间与配体交换相关的共价变化的差异，我们已经观察到方解石和水溶液之间分配系数的差异。
Among rare earth elements (REEs), the behavior of Y and Ho in most igneous activities is very close due to the similarity in their ionic radii, while Y fractionates from Ho in marine systems. In this study, in order to elucidate Y–Ho fractionation observed in marine systems in terms of structural chemistry, we examined Ho LIII-edge and Y K-edge EXAFS study for two partitioning systems, namely, 1) calcite-aqueous solution (Y–Ho fractionation system) and 2) strong acid cation exchange resin-aqueous solution (non-Y–Ho fractionation system). The results of the EXAFS analysis did not show significant differences in interatomic distances to the most neighboring O atoms between Ho and Y for all the samples. However, it was found that the first shell Ho–O and Y–O distances in the Y–Ho doped calcite were shorter than those in the aqua ion. In contrast, the first shell Ho–O and Y–O distances in the Y–Ho doped resin were similar to those in the aqua ion. Previous studies have suggested that lanthanide (Ln) is more covalent due to 4f orbital participation in bonding relative to Y. Spectroscopic studies on various Ln3+complexes show that Racah parameters for 4f electron repulsion in Ln3+ions decrease with an increase in covalency of bonding of Ln3+ions with anionic ligands. Therefore, our EXAFS results suggest that Y–Ho fractionation in partitioning is possibly attributed to the difference of change in covalency associated with the ligand exchange between Y and Ho, which we have observed as differences in partition coefficients between calcite and aqueous solution.