Colloidal silica is a nanoparticulate material that could have a transformative effect on environmental risk management at nuclear legacy sites through their use in in situ installation of injectable hydraulic barriers. In order to utilize such nanoparticulate material as a barrier, we require detailed understanding of its impact on the geochemistry of radionuclides in the environment (e.g. fission products such as Sr and Cs). Here we show, through combining leaching experiments with XAS analyses, that colloidal silica induces several competing effects on the mobility of Sr and Cs. First, cations within the colloidal silica gel compete with Sr and Cs for surface complexation sites. Second, an increased number of surface complexation sites is provided by the silica nanoparticles and finally, the elevated pH within the colloidal silica increases the surface complexation to clay minerals and the silica nanoparticles. XAS analyses show that Sr and Cs complex predominantly with the clay mineral phases in the soil through inner-sphere surface complexes (Sr) and through complexation on the clay basal surfaces at Si vacancy sites (Cs). For binary soil – colloidal silica gel systems, a fraction of the Sr and Cs complexes with the amorphous silica-like surfaces through the formation of outer-sphere surface complexes. Importantly, the net effect of nanoparticulate colloidal silica gel is to increase the retention of Sr and Cs, when compared to untreated soil and waste materials. Our research opens the door to applications of colloidal silica gel to form barriers within risk management strategies at legacy nuclear sites.

中文翻译：

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地球化学证据表明纳米颗粒胶体硅胶可用于原位遏制遗留核废料

胶体二氧化硅是一种纳米颗粒材料，通过在原位安装可注射水力屏障的使用，可能会对核废料场址的环境风险管理产生变革性影响。为了利用这种纳米颗粒材料作为屏障，我们需要详细了解其对环境中放射性核素地球化学的影响（例如裂变产物，例如Sr和Cs）。在这里，我们通过结合XAS分析的浸出实验表明，胶体二氧化硅对Sr和Cs的迁移率具有多种竞争作用。首先，胶体硅胶中的阳离子与Sr和Cs竞争表面络合位点。第二，二氧化硅纳米颗粒提供了增加数量的表面络合位点，最后，胶态二氧化硅内的升高的pH增加了与粘土矿物和二氧化硅纳米颗粒的表面络合。XAS分析表明，Sr和Cs主要通过内球表面复合物（Sr）和硅空位（Cs）在粘土基面上的复合而与土壤中的粘土矿物相复合。对于二元土壤-胶体硅胶系统，通过形成外球表面配合物，一部分Sr和Cs与无定形二氧化硅样表面形成配合物。重要的是，与未经处理的土壤和废料相比，纳米微粒胶体硅胶的净效应是增加了Sr和Cs的保留。我们的研究为使用胶体硅胶在传统核电站的风险管理策略中形成障碍打开了大门。