Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
Environ Sci Technol. 2011 Apr 1;45(7):2770-6. doi: 10.1021/es1037639. Epub 2011 Mar 10.
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 ∼3.6 Å 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.
采用原子模拟方法研究了 U 在三种铁（氢）氧化物矿物中的配位环境：针铁矿、磁铁矿和赤铁矿。模拟结果提供了 U-O 和 U-Fe 距离、配位数以及 U 占据不同位置（如空位、八面体或四面体）时晶格畸变的信息，这与 U 的氧化态和电荷补偿机制（即去质子化、空位形成或 Fe(III)还原为 Fe(II)）有关。对于针铁矿，通过第一壳层羟基的去质子化，可以用最小的晶格畸变取代 U 取代 Fe(III)，而不管 U 的氧化态和电荷补偿机制如何，占据八面体位置的取代都会导致 7 配位的明显畸变。重要的是，~3.6 Å 的 U-Fe 距离与 U 的结构掺入有关，不能被认为是简单吸附到针铁矿表面的诊断标准。对于磁铁矿，八面体位置可以容纳 U(V)或 U(VI)，几乎没有晶格畸变。U 取代赤铁矿中的 Fe(III)时，大多数情况下仍保持八面体配位。总的来说，模拟结果与现有实验数据的比较进一步证明了 U 在铁（氢）氧化物矿物中的结构掺入。
