锕系羟基硅酸盐胶体在饱和花岗岩介质中的迁移特征

Beishan (Gansu province, China) is preliminarily selected as a site to build a high-level radioactive waste repository in China. The first underground research laboratory is constructing at Beishan site. Because the groundwater in Beishan area is weakly alkaline and contains high concentrations of dissolved silicates, actinide oxyhydroxy silicate colloids will occur once actinides break through some engineering barriers of deep geological repository and contact with the groundwater. The colloids will be as important carriers for actinides to migrate from the near field of the repository. In this project, Eu(III), U(IV) and U(VI) are used to mimic different oxidation states of actinides to study the transport characteristics of their oxyhydroxy silicate colloids in Beishan granite media (granite particle column and granite fracture column) saturated with aqueous solution. The effects of pH, ionic strength, the composition of background electrolytes and humic acid on colloids transport will be investigated by an asymmetric flow field-flow fractionation system and various spectroscopic methods. The findings will provide basic experimental data and scientific basis for the relevant evaluation and design of China’s high-level radioactive waste repository.

甘肃北山地区是我国高放废物地质处置库的重点预选场址，我国首座高放废物地下实验室也将在北山建设。由于北山地下水呈弱碱性且含有相对较高溶解态硅酸盐的特性，一旦锕系元素突破部分工程屏障接触到地下水，将产生锕系羟基硅酸盐胶体，这类胶体将成为锕系元素从处置库近场向外迁移的重要载体。本项目以Eu(III)、U(IV)和U(VI)的羟基硅酸盐胶体作为研究不同氧化态的锕系元素的模型胶体，研究其在水溶液饱和的北山花岗岩介质（花岗岩颗粒柱和花岗岩裂隙柱）中的迁移行为，考察溶液pH值、离子强度、背景电解质种类及浓度、胡敏酸浓度等因素对所研究胶体迁移的影响；结合非对称场流分馏系统与多种谱学手段，探究影响所研究胶体迁移的机理；为我国北山高放废物地质处置库的相关评价和设计提供基础实验数据和科学依据。

高价锕系离子与地下水中溶解态硅酸盐反应生成的锕系硅酸盐胶体是处置条件下的一类重要锕系胶体。该类胶体在花岗岩介质中的迁移特征还存在研究空白。本项目以Eu(III)和Th(IV)分别作为+3价和+4价锕系元素的代表，制备并表征了不同氧化态的锕系硅酸盐胶体，探究了胶体稳定性并考察了其在花岗岩单裂隙中的迁移特征。研究结果表明，Eu(III)/Th(IV)的硅酸盐胶体在弱碱性pH条件下（pH = 8.8—9.4）易生成；胶体的稳定性与胶体中Si/An摩尔比、pH、背景电解质、FA浓度等因素有关；不同离子强度下悬浮液中Eu和Si在花岗岩单裂隙中的运移产生了分化，胶体中Si/Eu比值较小的组分由于尺寸较大更容易被滞留在介质中。上述结果对于我国北山高放废物地质处置库的设计和相关评价具有重要意义。.本项目自2020年启动，截止2022年12月底，共发表SCI论文5篇（第一标注），指导完成博士毕业论文1篇，本科毕业论文2篇。