Atomistic Simulations of Uranium Incorporation into Iron (Hydr)Oxides
Atomistic Simulations of Uranium Incorporation into Iron (Hydr)Oxides
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DOI：
10.1021/es1037639
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发表时间：
2011-04-01
影响因子：
11.4
通讯作者：
Ilton, Eugene S.
中科院分区：
文献类型：
--
作者：
Kerisit, Sebastien;Felmy, Andrew R.;Ilton, Eugene S.
原子模拟进行了表征的配位环境的U纳入三个Fe-（氢）氧化物矿物：针铁矿，磁铁矿，赤铁矿。这些模拟提供了关于U-O和U-Fe距离、配位数和掺入不同位点（例如，未被占据的位置对被占据的位置，八面体对四面体）作为U的氧化态和电荷补偿机制（即，去质子化、空位形成或Fe（III）还原成Fe（II））。对于针铁矿，去质子化的第一壳羟基使取代的U Fe（III）的晶格畸变量最小，而在未占用的八面体网站取代诱导明显的失真7倍协调，无论U的氧化态和电荷补偿机制。重要的是，类似于3.6埃的U-Fe距离与U的结构结合有关，不能被认为是针铁矿表面简单吸附的诊断。对于磁铁矿，八面体位置容纳U（V）或U（VI），晶格畸变很小。在大多数情况下，U取代赤铁矿中的Fe（III）保持八面体配位。在一般情况下，与现有的实验数据的模拟比较提供了进一步的证据，U在铁（氢）氧化物矿物的结构纳入。
Atomistic simulations were carried out to characterize the coordination environments of U incorporated in three Fe-(hydr)oxide minerals: goethite, magnetite, and hematite. The simulations provided information on U-O and U-Fe distances, coordination numbers, and lattice distortion for U incorporated in different sites (e.g., unoccupied versus occupied sites, octahedral versus tetrahedral) as a function of the oxidation state of U and charge compensation mechanisms (i.e., deprotonation, vacancy formation, or reduction of Fe(III) to Fe(II)). For goethite, deprotonation of first shell hydroxyls enables substitution of U for Fe(III) with a minimal amount of lattice distortion, whereas substitution in unoccupied octahedral sites induced appreciable distortion to 7-fold coordination regardless of U oxidation states and charge compensation mechanisms. Importantly, U-Fe distances of similar to 3.6 angstrom were associated with structural incorporation of U and cannot be considered diagnostic of simple adsorption to goethite surfaces. For magnetite, the octahedral site accommodates U(V) or U(VI) with little lattice distortion. U substituted for Fe(III) in hematite maintained octahedral coordination in most cases. In general, comparison of the simulations with available experimental data provides further evidence for the structural incorporation of U in iron (hydr)oxide minerals.