Vespa M, Dähn R, Grolimund D, Wieland E, Scheidegger A M
Paul Scherrer Institute, Laboratory for Waste Management, 5232 Villigen PSI, Switzerland.
Environ Sci Technol. 2006 Apr 1;40(7):2275-82. doi: 10.1021/es052240q.
Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. Cement is used to condition and stabilize the waste materials and to construct the engineered barrier systems (container, backfill, and liner materials) of repositories for radioactive waste. In this study, Ni uptake by hardened cement paste has been investigated with the aim of improving our understanding of the immobilization process of heavy metals in cement on the molecular level. X-ray absorption spectroscopy (XAS) coupled with diffuse reflectance spectroscopy (DRS) techniques were used to determine the local environment of Ni in cement systems. The Ni-doped samples were prepared at two different water/cement ratios (0.4, 1.3) and different hydration times (1 hour to 1 year) using a sulfate-resisting Portland cement. The metal loadings and the metal salts added to the system were varied (50 up to 5000 mg/kg; NO3(-), SO4(2-), Cl-). The XAS study showed that for all investigated systems Ni(ll) is predominantly immobilized in a layered double hydroxide (LDH) phase, which was corroborated by DRS measurements. Only a minor extent of Ni(ll) precipitates as Ni-hydroxides (alpha-Ni(OH)2 and beta-Ni(OH)2). This finding suggests that Ni-Al LDH, rather than Ni-hydroxides, is the solubility-limiting phase in the Ni-doped cement system.
在全球为安全处置危险和放射性废物而开发的多屏障概念中，水泥基材料发挥着重要作用。水泥用于处理和稳定废料，并用于构建放射性废物储存库的工程屏障系统（容器、回填材料和衬垫材料）。在本研究中，对硬化水泥浆体对镍的吸收进行了研究，目的是在分子水平上增进我们对水泥中重金属固定化过程的理解。采用X射线吸收光谱（XAS）与漫反射光谱（DRS）联用技术来确定水泥体系中镍的局部环境。使用抗硫酸盐波特兰水泥，在两种不同的水灰比（0.4、1.3）和不同的水化时间（1小时至1年）下制备掺镍样品。改变添加到体系中的金属负载量和金属盐（50至5000mg/kg；NO3(-)、SO4(2-)、Cl-）。XAS研究表明，对于所有研究体系，Ni(II)主要固定在层状双氢氧化物（LDH）相中，DRS测量证实了这一点。只有少量的Ni(II)以氢氧化镍（α-Ni(OH)2和β-Ni(OH)2）的形式沉淀。这一发现表明，在掺镍水泥体系中Ni-Al LDH而非氢氧化镍是溶解度限制相。
