Coprecipitation of Uranium(VI) with Calcite: XAFS, micro-XAS, and luminescence characterization
Coprecipitation of Uranium(VI) with Calcite: XAFS, micro-XAS, and luminescence characterization
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DOI：
10.1016/s0016-7037(01)00647-0
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发表时间：
2001-10
影响因子：
5
通讯作者：
R. Reeder;M. Nugent;C. Tait;D. E. Morris;S. Heald;K. Beck;W. Hess;A. Lanzirotti
中科院分区：
文献类型：
--
作者：
R. Reeder;M. Nugent;C. Tait;D. E. Morris;S. Heald;K. Beck;W. Hess;A. Lanzirotti
X射线吸收和发光光谱已被用来表征的本地结构和协调的铀（VI）物种与方解石（碳酸钙）从室温水溶液共沉淀。不同的解决方案的化学和pH值被发现在赤道协调的铀酰物种（UO 22+）纳入方解石中的差异，与多个协调环境的铀酰明显在一个样品。在赤道协调之间的水相铀酰物种和那些发现在方解石的差异表明，协调的变化发生在注册成立的至少一些物种。这与以前的研究结果相比，没有变化，在赤道协调铀酰纳入文石，并可能解释更大的掺入在这后一阶段。钙背散射体和明确的结构超出赤道壳的情况下是一致的与当地方解石结构的破坏与混乱。这可能表明铀酰单元无法在宿主方解石中呈现稳定的结构环境，这可能降低含铀酰方解石的稳定性。在含铀酰的溶液中生长的方解石单晶在由四个邻位面组成的（101 <$4）面上呈现出螺旋状的螺旋生长丘，与面对称性一致。微X射线荧光显示，铀是差异不等价的邻位表面之间的注册成立，反映了一步选择性注册成立的铀酰物种在生长过程中。微X-射线吸收近边结构光谱从不等价的邻位面未能揭示邻位之间的物种形成的任何差异，或可能占的存在下，由发光和X-射线吸收光谱确定的多个协调环境。
X-ray absorption and luminescence spectroscopies have been used to characterize the local structure and coordination of uranium(VI) species coprecipitated with calcite (CaCO3) from room-temperature aqueous solutions. Different solution chemistries and pHs are found to result in differences in the equatorial coordination of the uranyl species (UO22+) incorporated in the calcite, with multiple coordination environments of uranyl evident in one sample. Differences in the equatorial coordination between the aqueous uranyl species and those found in the calcite indicate that coordination changes occur during incorporation of at least some species. This contrasts with previous findings showing no change in equatorial coordination during uranyl incorporation into aragonite, and may explain the greater incorporation in this latter phase. The absence of calcium backscatterers and well defined structure beyond the equatorial shell is consistent with disorder associated with disruption of the local calcite structure. This may indicate an inability of the uranyl unit to assume a stable structural environment in the host calcite, which could decrease the stability of uranyl-containing calcite. Calcite single crystals grown in uranyl-containing solutions exhibit polygonized spiral growth hillocks on (101̄4) surfaces composed of four vicinal surfaces, consistent with face symmetry. Micro-X-ray fluorescence reveals that uranium is differentially incorporated between nonequivalent vicinal surfaces, reflecting step-selective incorporation of uranyl species during growth. Micro-X-ray absorption near-edge structure spectra from the nonequivalent vicinal faces fail to reveal any differences in speciation between the vicinals or that might account for the presence of the multiple coordination environments identified by luminescence and X-ray absorption spectroscopies.