Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK.
Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, UK.
Sci Rep. 2023 Feb 28;13(1):3374. doi: 10.1038/s41598-023-30024-0.
Portland cement-based grouts used for radioactive waste immobilisation contain a Ca- and Si-rich binder phase, known as calcium-silicate-hydrate (C-S-H). Depending on the blend of cement used, the Ca/Si ratio can vary considerably. A range of C-S-H minerals with Ca/Si ratios from 0.6 to 1.6 were synthesised and contacted with aqueous U(VI) at 0.5 mM and 10 mM concentrations. Solid-state Si MAS-NMR spectroscopy was applied to probe the Si coordination environment in U(VI)-contacted C-S-H minerals and, in conjunction with U L-edge X-ray absorption spectroscopy analysis, inferences of the fate of U(VI) in these systems were made. At moderate or high Ca/Si ratios, uranophane-type uranyl silicates or Ca-uranates dominated, while at the lowest Ca/Si ratios, the formation of a Ca-bearing uranyl silicate mineral, similar to haiweeite (Ca[(UO)SiO(OH)]·3HO) or Ca-bearing weeksite (Ca(UO)SiO·10HO) was identified. This study highlights the influence of Ca/Si ratio on uranyl sequestration, of interest in the development of post-closure safety models for U-bearing radioactive waste disposal.
用于放射性废物固化的基于波特兰水泥的灌浆料中含有一种富钙和硅的结合相，称为钙硅水合物（C-S-H）。根据所用水泥的混合比，Ca/Si 比可以有很大的变化。合成了一系列 Ca/Si 比从 0.6 到 1.6 的 C-S-H 矿物，并在 0.5 mM 和 10 mM 浓度下与含 U(VI)的水溶液接触。采用固态 Si MAS-NMR 光谱法探测 U(VI)接触的 C-S-H 矿物中的 Si 配位环境，并结合 U 边 X 射线吸收光谱分析，对这些体系中 U(VI)的归宿进行推断。在中等或高 Ca/Si 比下，水硅钙铀矿型的铀硅酸盐或钙铀酸盐占主导地位，而在最低 Ca/Si 比下，形成了一种类似于海维石（Ca[(UO)SiO(OH)]·3H2O）或含钙硅铀矿（Ca(UO)SiO·10H2O）的含 Ca 的铀硅酸盐矿物。这项研究强调了 Ca/Si 比对铀酰固定的影响，这对于开发含 U 放射性废物处置的闭库后安全模型具有重要意义。
