Uranium Immobilization and Nanofilm Formation on Magnesium-Rich Minerals.
Uranium Immobilization and Nanofilm Formation on Magnesium-Rich Minerals.
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DOI：
10.1021/acs.est.5b06041
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发表时间：
2016-03
影响因子：
11.4
通讯作者：
A. van Veelen;J. Bargar;G. Law;G. Brown;R. Wogelius
中科院分区：
文献类型：
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作者：
A. van Veelen;J. Bargar;G. Law;G. Brown;R. Wogelius
用偏振相关掠入射X射线吸收光谱(XAS)测量了在pH 8.3和常压(pCO2=10(-3.5))或二氧化碳分压(pCO2=10(-4.5))条件下，取向的菱镁矿[MgCO3]和水镁石[Mg(OH)2]分别与水合铀酰氯在水溶液中(500、50和5ppm)反应的偏振相关掠入射X射线吸收光谱(XAS)。X射线吸收近边结构(XANES)谱显示出明显的偏振相关性(χ分别为入射光束偏振面的0°和90°)，并一致地证明铀酰分子在与镁矿(10 1̅4)和水镁石(0 0 0 1)成大角度(6 0~80°)时，以同轴的U(VI)═同轴键优先取向。扩展X射线吸收精细结构(EXAFS)分析表明，U(VI)轴向氧的“有效”数是作为极化函数影响最大的拟合参数。此外，表面薄膜的轴向倾斜(厚度∼21？)与表面粗糙度[σ]相关。我们的结果表明，水合铀酰(-碳酸酯)络合物在我们所有的实验表面上都是聚合的，并且这个过程是由表面羟基化控制的。这些结果为铀酰络合物在环境意义重大的碳酸盐和氢氧化物矿物表面的预期成键构型提供了新的见解。
Polarization-dependent grazing incidence X-ray absorption spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO3] and brucite [Mg(OH)2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (PCO2 = 10(-3.5)) or reduced partial pressures of carbon dioxide (PCO2 = 10(-4.5)). X-ray absorption near edge structure (XANES) spectra show a striking polarization dependence (χ = 0° and 90° relative to the polarization plane of the incident beam) and consistently demonstrated that the uranyl molecule was preferentially oriented with its Oaxial═U(VI)═Oaxial linkage at high angles (60-80°) to both magnesite (101̅4) and brucite (0001). Extended X-ray absorption fine structure (EXAFS) analysis shows that the "effective" number of U(VI) axial oxygens is the most strongly affected fitting parameter as a function of polarization. Furthermore, axial tilt in the surface thin films (thickness ∼ 21 Å) is correlated with surface roughness [σ]. Our results show that hydrated uranyl(-carbonate) complexes polymerize on all of our experimental surfaces and that this process is controlled by surface hydroxylation. These results provide new insights into the bonding configuration expected for uranyl complexes on the environmentally significant carbonate and hydroxide mineral surfaces.