Spectroscopic studies on U(VI) incorporation into CaCO3: Effects of aging time and U(VI) concentration.
Spectroscopic studies on U(VI) incorporation into CaCO3: Effects of aging time and U(VI) concentration.
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DOI：
10.1016/j.chemosphere.2019.01.010
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发表时间：
2019-04
期刊：
影响因子：
8.8
通讯作者：
Zhiwei Niu;Xiaoyan Wei;Shirong Qiang;Hanyu Wu;D. Pan;Wang-suo Wu;Q. Fan
中科院分区：
文献类型：
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作者：
Zhiwei Niu;Xiaoyan Wei;Shirong Qiang;Hanyu Wu;D. Pan;Wang-suo Wu;Q. Fan
采用间歇实验、X射线衍射（XRD）、衰减全反射傅里叶变换红外光谱（ATR-FTIR）和扩展X射线吸收精细结构（EXAFS）等方法，研究了不同老化时间和不同U（VI）浓度下U（VI）在CaCO 3中的掺入情况。静态吸附实验表明，U（VI）在方解石上的吸附具有很强的pH依赖性，高pH有利于U（VI）的吸附，这可能是由于带正电荷的方解石与带负电荷的三碳酸铀酰物种之间的静电吸引作用。XRD分析表明，在pH = 10.0时，方解石的[104]晶面向低角度方向移动，表明U（VI）的三碳酸铀酰物种可能通过置换Ca原子扩散到方解石晶格中，导致方解石晶胞膨胀。U（VI）掺入CaCO 3的结果表明，随着老化时间的延长，CaCO 3对U（VI）的吸收在前200 h内逐渐减少，而后显著增加。通过XRD、ATR-FTIR和XANES光谱分析，证实了U（VI）在CaCO 3中的掺入可能经历了球文石、球文石向方解石的转变和方解石的生成阶段。随着U（VI）浓度的增加，球文石向方解石的转变时间相应增加，表明U（VI）掺入CaCO 3中可以稳定球文石相。EXAFS分析表明，U（VI）在球文石中的掺入过程中，其局域结构发生了变化，其掺入形态与碳酸铀酰相似，但与方解石中的三碳酸铀酰不同。
In this study, the incorporation of U(VI) into CaCO3under different aging times and U(VI) concentrations was studied by combining batch experiments, X-ray diffraction (XRD), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), and extended X-ray absorption fine structure (EXAFS) approaches. Batch sorption experiments showed that the sorption of U(VI) on calcite was strong pH-dependence, and high pH was beneficial for U(VI) sorption possibly due to the electrostatic attraction between positively charged calcite and negatively charged uranyl tri-carbonate species. XRD patterns showed that the [104] facet of calcite shifted toward low angle at pH ∼10.0, which indicated that the uranyl tri-carbonate species of U(VI) possibly diffused into calcite lattice by replacing Ca atoms, and then induced the expansion of calcite crystal cell. The incorporation of U(VI) into CaCO3showed that the uptake of U(VI) gradually decreased within the first 200 h, and then significantly increased with the increasing aging time. U(VI) incorporation into CaCO3might experience vaterite, transition from vaterite to calcite, and calcite stages, which were confirmed by XRD, ATR-FTIR, and X-ray absorption near-edge structure (XANES) spectroscopy. As the U(VI) concentration increased, the transition time from vaterite to calcite correspondingly increased, indicating that U(VI) incorporation into CaCO3can stabilize vaterite phase. EXAFS analyses suggested that the local structure of uranyl moiety was changing during the incorporation process, and the species of U(VI) incorporation into vaterite was similar to uranyl carbonates, however indeed different from the species of uranyl tri-carbonate presented in calcite.