Harfouche M, Wieland E, Dähn R, Fujita T, Tits J, Kunz D, Tsukamoto M
Paul Scherrer Institute, Nuclear Energy and Safety Research Department, Laboratory for Waste Management, 5232 Villigen PSI, Switzerland.
J Colloid Interface Sci. 2006 Nov 1;303(1):195-204. doi: 10.1016/j.jcis.2006.07.019. Epub 2006 Aug 22.
Among the different cement minerals, calcium silicate hydrates (C-S-H) are the prime candidates for heavy metal binding because of their abundance and appropriate structure. Immobilization processes of heavy metals by cementitious materials, and in particular C-S-H phases, thus play an important role in multibarrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. In this study, the uptake of U(VI) by C-S-H has been investigated using X-ray absorption fine structure (XAFS) spectroscopy. C-S-H phases were synthesized using two different procedures: One is based on the mixing of CaO and SiO2 solids ("direct reaction" method); for the other one starting solutions of Ca and Si are used ("solution reaction" method). XAFS investigations were carried out on samples doped with U(VI). U(VI) was either sorbed onto previously precipitated C-S-H phases (sorption samples) or added during C-S-H synthesis (coprecipitation samples). The coordination environment of U(VI) in the sorption samples was found to be independent of the procedure used for C-S-H synthesis. A split equatorial oxygen shell (Oeq1: R=2.23-2.27 A; Oeq2: R=2.36-2.45 A), neighboring silicon atoms at short (R=3.07-3.11 A) and long (R=3.71-3.77 A) distances, and neighboring Ca atoms (R=3.77-3.81 and 4.15-4.29 A) were observed for all the samples. The structural parameters resemble those reported for uranophane. The coordination environment of U(VI) in the coprecipitation samples depends on the method used for C-S-H synthesis, and further, the spectra differ from those determined for the sorption samples. UU backscattering contributions were observed in the samples prepared using the direct reaction method, whereas no split equatorial shell appeared in the samples prepared using the solution reaction method.
在不同的水泥矿物中，硅酸钙水合物（C-S-H）因其含量丰富且结构适宜，成为重金属结合的主要候选物。因此，胶凝材料，特别是C-S-H相，对重金属的固定过程在全球范围内为安全处置危险和放射性废物而开发的多重屏障概念中起着重要作用。在本研究中，使用X射线吸收精细结构（XAFS）光谱研究了C-S-H对U(VI)的吸收。C-S-H相通过两种不同的程序合成：一种基于CaO和SiO2固体的混合（“直接反应”法）；另一种使用Ca和Si的起始溶液（“溶液反应”法）。对掺杂U(VI)的样品进行了XAFS研究。U(VI)要么吸附到先前沉淀的C-S-H相上（吸附样品），要么在C-S-H合成过程中添加（共沉淀样品）。发现吸附样品中U(VI)的配位环境与用于C-S-H合成的程序无关。所有样品均观察到赤道氧壳层分裂（Oeq1：R = 2.23 - 2.27 Å；Oeq2：R = 2.36 - 2.45 Å），在短距离（R = 3.07 - 3.11 Å）和长距离（R = 3.71 - 3.77 Å）处有相邻的硅原子，以及相邻的Ca原子（R = 3.77 - 3.81和4.15 - 4.29 Å）。结构参数与报道的硅钙铀矿的参数相似。共沉淀样品中U(VI)的配位环境取决于用于C-S-H合成的方法，此外，光谱与吸附样品的光谱不同。在使用直接反应法制备的样品中观察到U-U背散射贡献，而在使用溶液反应法制备的样品中未出现赤道壳层分裂。
