放射性锶和铯在具有系列风化程度云母类矿物上的微观吸附机制研究

Radioactive strontium and cesium receive a growing concern for the environmental nuclear safety, and their migration and transformation are largely affected by the micaceous minerals inside soils and sediments. It demonstrated that weathering, an important geochemical phenomenon, has influenced the chemicals and structure of the micaceous minerals, but its impact on the sorption behavior of strontium and cesium is still unclear. Our previous work has reported that nuclide sorption is closely related to the weathering of phlogopite. Recent experimental results have shown that the weathering degree of micaceous minerals is directly relevant to their permanent charge and available sites. Depending on the type and weathering degrees of the micaceous minerals, the sorption behaviors of radioactive strontium and cesium are significantly different. These results indicate that weathering is crucial to the environmental behaviors of strontium and cesium. Here we propose to study the immobilization of strontium and cesium on muscovite and phlogopite at a molecular scale. The sorption species and mechanism of strontium and cesium, and the relationship with the weathering degrees of micaceous minerals will be investigated through the macroscopic experiments (weathering simulation, batch experiment, etc.), and the advanced spectroscopic and optical techniques (EXAFS and STEM). Moreover, the general adsorption model (GAM) will be applied to describe and predict the geochemical behaviors of strontium and cesium considering a factor of weathering. These findings are expected to provide the fundamental basis and technical support for the control and remediation of radioactive pollution, and benefit the nuclear environment safety as well as nuclear emergency. We hope the corresponding results can serve for the construction of healthy and beautiful China.

放射性锶和铯是核环境安全的重点关注对象，云母类矿物是影响其迁移转化的主要环境介质；然而，地表重要的地球化学现象——风化如何影响锶和铯的环境行为及其中的微观机制尚不明确。申请人已报道，核素吸附行为与金云母风化正相关；预实验结果显示，云母的结构电荷及有效位点受其种类和风化程度直接影响，同时锶和铯在云母类矿物上的吸附行为差异显著，上述结果均表明风化对锶和铯的环境行为有重要作用。本项目拟选取白云母和金云母为研究对象，结合宏观实验（风化模拟、批式实验等）和广义吸附模型计算，基于先进谱学和光学技术（EXAFS和STEM）从分子水平上研究锶和铯在具有系列风化程度云母上的微观赋存状态、其中的吸附-解吸机理，探索锶和铯吸附行为与云母风化程度的关联，应用模型量化描述及预测锶和铯的吸附行为，为放射性污染的迁移控制、修复治理提供理论基础和技术支持，为我国核安全与核应急提供科学依据，为建设健康美丽中国做出贡献。

本项目对风化作用引起的云母类矿物有效位点的时空演化为预测放射性锶和铯的赋存状态、生物有效性和地质积累提供了新的视角。云母及其次生矿物的物理化学性质表征说明，具有系列风化程度云母类矿物的阳离子交换容量与其晶格应变高度线性相关，这将直接控制放射性锶和铯的吸附容量。通过吸附实验发现，当风化程度较低时Ca显著抑制Sr(II)吸附，而Na则影响较弱；而当风化程度较高时Ca和Na均有促进作用，这是因为强风化增加了可用层间位点的容量，导致Sr(II)吸附不被Ca完全抑制。尽管云母类矿物破损边缘位点容量低于1×10-6 mol/g，共吸附时一旦其完全被Cs(I)占据后，Sr(II)的吸附容量将被强烈抑制。风化导致的层间位点容量演化及共吸附时的位点占据顺序，是控制云母类矿物阻滞锶和铯迁移的重要因素。本研究表明，吸附-风化耦合评价能真实地描述放射性锶和铯的环境行为和形态转化，从而准确地预测放射性锶和铯的归趋。放射性锶和铯的赋存状态和迁移是评价赋存状态环境风险的重要考虑因素，它们将随着风化而在时间尺度上演化。在后续工作中，项目组将采用更多的数据修正基于系列风化程度的方法量化描述预测放射性锶和铯的赋存状态和归趋。相关研究成果和认识为放射性污染的迁移控制、修复治理提供理论基础和技术支持，为我国核安全与核应急提供科学依据。