锶、铯与典型层状黏土矿物表面位点的微观作用机制研究

As the high-yield fission products in spent fuel, strontium-90 and cesium-137 have drawn significant concerns, especially on environment protection as well as nuclear emergency. The transformation and migration of strontium and cesium in natural environmental media are significantly controlled by the sorption process on phyllosilicate minerals. The availability of different sorption sites is varying due to the discrepant interlayer expandability of phyllosilicates, whereas the investigations on strontium and cesium interaction with different sites of phyllosilicates are scarce. In this proposal, the immobilization of strontium and cesium on phyllosilicate minerals with different expandability (illite, vermiculite and montmorillonite) will be studied at molecular scales, the availability of different sorption sites to strontium/cesium immobilization will be explored by employing the extended X-ray absorption fine structure spectroscopy (EXAFS), and the effect of mineralogical structure and environmental factors on strontium/cesium sorption species will be demonstrated, the availability and contribution of surface sites to strontium/cesium sorption will be discussed. Moreover, a quantitative model basing on thermodynamic will be constructed to predict the geochemical behaviors of strontium/cesium in natural environment, and to understand the primary difference for strontium/cesium migration. The results will be expected to illustrate the immobilization and migration mechanism of strontium and cesium in phyllosilicates media at different conditions, which is of great importance to the nuclear environment safety as well as nuclear emergency. We hope the corresponding results can serve for the construction of ecological civilization and the construction of beautiful China.

作为产额较大的关键裂变产物，锶-90和铯-137是核环境安全和核应急需重点关注的核素，其环境行为受到典型环境介质——层状黏土矿物的显著影响。尽管人们已认识到矿物的结构差异会使矿物对锶铯的作用方式和作用效果产生较大的差异，但目前关于层状黏土矿物不同位点对锶铯环境行为的详细控制机制尚不明确。本项目拟从微观水平上研究锶-90和铯-137在典型层状硅酸盐矿物（伊利石、蛭石和蒙脱石）上的吸附作用，借助扩展边X射线吸收精细结构光谱（EXAFS）重点考察矿物结构和环境因素对锶铯吸附形态和精细结构的影响，深入探讨典型层状硅酸盐矿物不同位点对锶铯吸附的贡献和有效性，揭示锶铯微观形态与其迁移/滞留的关系，构建可量化描述和预测锶铯吸附行为的模型，从本质上认识锶和铯迁移能力差异的根本机制，为我国核环境安全和核应急提供重要的科学依据，为生态文明建设和美丽中国建设做出贡献。

作为产额较大的关键裂变产物，锶-90和铯-137是核环境安全和核应急需重点关注的核素，其环境行为受到典型环境介质——层状黏土矿物的显著影响。尽管人们已认识到矿物的结构差异会使矿物对锶铯的作用方式和作用效果产生较大的差异，但目前关于层状黏土矿物不同位点对锶铯环境行为的详细控制机制尚不明确。本项目针对锶和铯的环境行为，从分子水平上研究锶和铯在典型层状黏土矿物（坡缕石、伊利石、蛭石和蒙脱石）上的吸附作用，利用EXAFS光谱获取锶铯在不同膨胀性层状黏土矿物表面的微观结构信息，阐明了不同膨胀性层状黏土矿物的不同位点对锶铯吸附的有效性，揭示了矿物的结构差异对锶铯作用方式和作用效果产生较大差异的原因，阐明了锶铯微观形态与其迁移/滞留的关系，构建了可描述锶铯在层状黏土矿物介质中吸附行为的模型。项目成功纯化并转型了层状黏土矿物（坡缕石、伊利石、蛭石和蒙脱石），使不同膨胀性的层状黏土矿物发生不同程度的层间塌陷，进而改变层间位点和FES位点的可利用性。研究结果表明，铯由于其较低的水合能，易脱水以内层络合物的形式被FES吸附位点所吸附。锶则与之相反，其难以脱水，水合态锶难以进入层间位点和FES位点，水合态锶通过静电相互作用与带负电的位点结合，以外层络合物形式被吸附。由于锶较弱的吸附能力，锶在饱和多孔介质中的迁移能力显著强于铯，黏土矿物胶体对铯迁移的促进能力显著高于锶。项目相关研究结果，对评价锶铯的环境迁移风险具有重要的意义，可为我国核环境安全评价提供重要的科学依据。