Niu Zhiwei, Wei Xiaoyan, Qiang Shirong, Wu Hanyu, Pan Duoqiang, Wu Wangsuo, Fan Qiaohui
Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China.
Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China; Key Laboratory of Petroleum Resources, Gansu Province, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
Chemosphere. 2019 Apr;220:1100-1107. doi: 10.1016/j.chemosphere.2019.01.010. Epub 2019 Jan 4.
In this study, the incorporation of U(VI) into CaCO under 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 CaCO showed 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 CaCO might 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 CaCO can 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.
在本研究中，通过结合批量实验、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）方法，研究了在不同老化时间和U(VI)浓度下U(VI)在碳酸钙中的掺入情况。批量吸附实验表明，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)吸附，这可能是由于带正电的方解石与带负电的铀酰三碳酸盐物种之间的静电吸引。XRD图谱显示，在pH约为10.0时，方解石的[104]晶面朝向低角度移动，这表明U(VI)的铀酰三碳酸盐物种可能通过取代Ca原子扩散到方解石晶格中，进而导致方解石晶胞膨胀。U(VI)在碳酸钙中的掺入表明，U(VI)的摄取在前200小时内逐渐减少，然后随着老化时间的增加而显著增加。U(VI)掺入碳酸钙可能经历球霰石、从球霰石到方解石的转变以及方解石阶段，这通过XRD、ATR-FTIR和X射线吸收近边结构（XANES）光谱得到证实。随着U(VI)浓度的增加，从球霰石到方解石的转变时间相应增加，表明U(VI)掺入碳酸钙可以稳定球霰石相。EXAFS分析表明，在掺入过程中铀酰部分的局部结构在发生变化，掺入球霰石中的U(VI)物种类似于碳酸铀酰，但确实不同于方解石中存在的铀酰三碳酸盐物种。
