Cai Fangfei, Ma Funing, Zhang Xiaoying, Reimus Paul, Qi Linlin, Wang Yu, Lu Di, Thanh Hung Vo, Dai Zhenxue
College of Construction Engineering, Jilin University, Changchun 130026, China.
College of Construction Engineering, Jilin University, Changchun 130026, China.
Sci Total Environ. 2023 Nov 20;900:165819. doi: 10.1016/j.scitotenv.2023.165819. Epub 2023 Jul 26.
The disposal of high-level radioactive waste in deep geological repositories is a critical environmental issue. The presence of bentonite colloids generated in the engineering barrier can significantly impact the transport of radionuclides, but their effect on radionuclide sorption in granite remains poorly understood. This study aimed to investigate the sorption characteristics of strontium (Sr) on granite as well as on the coexistence system of granite and colloids under various hydrogeochemical conditions, through batch experiments. Fourier transform infrared spectroscopy was employed to analyze the sorption forms of Sr on granite before and after sorption. Several hydrogeochemical factors were examined, including contact time, pH, ionic strength, coexisting ions, and bentonite and humic acid colloid concentration. Among these factors, the concentration of bentonite colloids exhibited a significant effect on Sr sorption. Within a specific range of colloid concentration, the sorption of Sr on the solid system increased linearly with the bentonite colloid concentration. pH and ionic strength were also found to play crucial roles in the sorption process. At low pH, Sr sorption primarily occurred through the outer sphere's surface complexation and Na/H ion exchange. However, at high pH, inner sphere surface complexation dominated the process. As the ionic strength increased, electrostatic repulsion gradually increased, resulting in fewer binding sites for particle aggregation and Sr sorption on bentonite colloids. The results also indicate that with increasing pH, the predominant forms of Sr in the solution transitioned from SrHCO and SrCl to SrCO and SrCl. This was mainly due to the ion exchange of Ca/Mg in plagioclase and biotite, forming SrCO precipitation. These findings provide valuable insights into the transport behavior of radionuclides in the subsurface environment of the repository and highlight the importance of considering bentonite colloids and other hydrogeochemical factors when assessing the environmental impact of high-level radioactive waste disposal.
在深部地质处置库中处置高放废物是一个关键的环境问题。工程屏障中产生的膨润土胶体的存在会显著影响放射性核素的迁移，但它们对花岗岩中放射性核素吸附的影响仍知之甚少。本研究旨在通过批量实验，研究锶（Sr）在花岗岩以及花岗岩与胶体共存体系在各种水文地球化学条件下的吸附特性。采用傅里叶变换红外光谱分析吸附前后Sr在花岗岩上的吸附形态。研究了几个水文地球化学因素，包括接触时间、pH值、离子强度、共存离子以及膨润土和腐殖酸胶体浓度。在这些因素中，膨润土胶体浓度对Sr吸附有显著影响。在特定的胶体浓度范围内，Sr在固体体系上的吸附量随膨润土胶体浓度呈线性增加。pH值和离子强度在吸附过程中也起着关键作用。在低pH值下，Sr的吸附主要通过外层表面络合和Na/H离子交换发生。然而，在高pH值下，内层表面络合占主导地位。随着离子强度的增加，静电排斥逐渐增强，导致颗粒聚集和Sr在膨润土胶体上吸附的结合位点减少。结果还表明，随着pH值的升高，溶液中Sr的主要形态从SrHCO和SrCl转变为SrCO和SrCl。这主要是由于斜长石和黑云母中Ca/Mg的离子交换，形成了SrCO沉淀。这些发现为放射性核素在处置库地下环境中的迁移行为提供了有价值的见解，并突出了在评估高放废物处置的环境影响时考虑膨润土胶体和其他水文地球化学因素的重要性。
