花岗岩裂隙填充物胶体作用于核素Sr的化学形态变化及其吸附迁移机制研究

Geological disposal of radioactive waste may cause secondary pollution, such as the release and leaks of nuclear, has been garnered particular attention. Because of strontium with the characteristics of high toxicity and environmental activity, the improper disposal will rapidly cause long-term harm to human and biosphere. However, it is not yet clear at chemical species of strontium, sorption behavior, mechanism of the migration in fracture media with natural colloids. As the object of study, natural filler colloids of granite fracture in Beishan HLW disposal site were analyzed for the physical and chemical characteristics. Based on field survey, sampling analysis, grading filters, batch tests and dynamic column experiments, chemical species of strontium were calculated by thermodynamic calculations and software simulation analysis, and the adsorption and migration on fracture media was analyzed by mathematical statistics method. The correlation of different types of colloids and strontium was found, adsorption mechanism and influence factors of strontium under colloids in fracture medium were explored, the processes of strontium migration with the effect of colloid under the action of different flow rate in fracture media was revealed. This study could provide a scientific basis for the safe disposal of radioactive waste and environmental management.

由于放射性废物地质处置可能会引发核释放等二次污染而备受关注。放射性核素锶具有高毒性和高环境活性特征，若对处置不当将会以较快的速度造成对人类和生物圈的长期危害，但在胶体作用下，核素Sr在裂隙介质中的化学形态、吸附行为、迁移过程等作用机理尚不清晰。本申请拟以北山高放废物处置预选场花岗岩裂隙填充物胶体为研究对象，通过野外调查取样，分级过滤、室内静态批实验和动态柱实验等手段，在天然胶体理化特征分析基础上，采用热力学计算和软件模拟分析等方法，进行裂隙介质中不同胶体类型与Sr化学形态变化相关性分析，研究不同胶体作用下Sr吸附过程，不同流速和不同初始浓度作用下Sr迁移行为及影响因素研究，探索花岗岩裂隙填充介质对Sr的吸附机理，揭示胶体作用对Sr在裂隙介质中迁移过程的影响，系统阐明胶体对核素Sr的形态变化和迁移影响作用机制，为我国放射性废物处置安全和环境管理提供科学依据。

放射性核素在地质介质中的反应和迁移行为，是放射性污染防治的重要问题之一。为探究环境胶体作用下，关键核素Sr在典型孔隙和裂隙介质中的反应迁移过程，本研究通过室内柱迁移实验和批式静态反应实验，讨论了Sr在裂隙花岗岩和松散孔隙介质中的迁移与阻滞规律，并对比了常见环境胶体对Sr迁移过程的影响；同时，结合微观分析方法，深入研究了“Sr-胶体-介质”体系的反应和作用过程。研究结果表明，胶体对Sr在介质中的迁移均起到了促进作用，作用效果会在不同程度上受到胶体种类和环境条件的影响；连续时间随机游走模型（CTRW）能够很好地描述胶体存在时Sr在介质中的非费克行为和胶体促进迁移。Langmui和Freundlichr等温方程式均可以用于描述有无胶体条件下Sr在介质上的吸附过程，腐殖酸胶体由于平均粒径更小，因此能够促进Sr在介质上的吸附；且与针铁矿胶体混合时，可提高针铁矿胶体体系的吸附能力，原因是改变了胶体颗粒的表面官能团结构。采用90Sr代替反应体系中的稳定Sr时，吸附实验所体现的吸附过程和特征参数与稳定Sr同位素一致，且该过程同样符合Langmui和Freundlichr等温吸附模型。