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Strontium Uptake by Cementitious Materials

机译：胶结材料对锶的吸收

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Wet chemistry experiments and X-ray absorption fine structure (XAFS) measurements were carried out to investigate the immobilization of nonradioactive Sr and ~(85)Sr in calcite-free and calcite-containing Portland cement. The partitioning of pristine Sr between hardened cement paste (HCP) and pore solution, and the uptake of ~(85)Sr and nonradioactive Sr were investigated in batch-type sorption/desorption experiments. Sr uptake by HCP was found to be fast and nearly linear for both cements, indicating that differences in the compositions of the two cements have no influence on Sr binding. The partitioning of pristine Sr bound in the cement matrix and ~(85)Sr between HCP and pore solution could be modeled in terms of a reversible sorption process using similar K_d values. These findings allow ~(85) Sr uptake to be interpreted in terms of an isotopic exchange process with pristine Sr. Sr K-edge EXAFS measurements on Sr doped HCP and calcium silicate hydrate (C-S-H) samples reveal no significant differences in the local coordination environments of pristine Sr and Sr bound to the cement matrix upon sorption. The first coordination sphere consists of five to six oxygen atoms located at a distance of about 2.6 A, which corresponds to Sr-0 distances in the hydration sphere of Sr~(2+) in alkaline solution. Sr binds to the cement matrix via two bridging oxygen atoms located at a distance of about 3.6 A. No further neighboring atoms could be detected, indicating that Sr is taken up as a partially hydrated species by HCP. Wet chemistry and spectroscopic data further indicate that Sr binding to C-S-H phases is likely to be the controlling uptake mechanism in the cement matrix, which allows Sr uptake by HCP to be predicted based on a Ca-Sr ion exchange model previously developed for Sr binding to C-S-H phases. The latter finding suggests that long-term predictions of Sr immobilization in the cementitious near field of repositories for radioactive waste can be based on a simplified sorption model with C-S-H phases.
机译：进行了湿化学实验和X射线吸收精细结构（XAFS）测量，以研究非放射性Sr和〜（85）Sr在无方解石和含方解石的硅酸盐水泥中的固定化。在间歇式吸附/解吸实验中研究了原始Sr在硬化水泥浆（HCP）和孔溶液之间的分配以及〜（85）Sr和非放射性Sr的吸收。对于两种水泥，HCP对Sr的吸收均很快且几乎呈线性，这表明两种水泥的成分差异对Sr的结合没有影响。结合在水泥基质中的原始Sr和HCP和孔隙溶液之间〜（85）Sr的分配可以使用相似的K_d值以可逆吸附过程建模。这些发现使得〜（85）Sr的吸收可以通过与原始Sr.Sr K-edge EXAFS的同位素交换过程来解释，该测量结果显示了Sr掺杂的HCP和水合硅酸钙（CSH）样品在局部配位环境中无显着差异吸附后，原始Sr和Sr结合到水泥基体上。第一配位球由五到六个氧原子组成，它们之间的距离约为2.6 A，这对应于碱性溶液中Sr〜（2+）水化球中的Sr-0距离。 Sr通过位于约3.6 A处的两个桥接氧原子与水泥基质结合。无法检测到其他邻近原子，这表明Sr被HCP吸收为部分水合物质。湿化学和光谱数据进一步表明，Sr与CSH相的结合可能是水泥基质中的控制吸收机制，这使得HCP可以根据先前为Sr与Sr结合而开发的Ca-Sr离子交换模型预测HCP对Sr的吸收。 CSH阶段。后一个发现表明，放射性废物处置库胶结近场中Sr固定化的长期预测可以基于具有C-S-H相的简化吸附模型。

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