Investigating the role of Na-bentonite colloids in facilitating Sr transport in granite minerals through column experiments and modeling

Xiaoying Zhang; Fangfei Cai; Funing Ma; Paul Reimus; Linlin Qi; Di Lu; Mohamad Reza Soltanian; Zhenxue Dai

doi:10.1016/j.jhazmat.2023.132851

Investigating the role of Na-bentonite colloids in facilitating Sr transport in granite minerals through column experiments and modeling

J Hazard Mater. 2023 Oct 24:463:132851. doi: 10.1016/j.jhazmat.2023.132851. Online ahead of print.

Authors

Xiaoying Zhang¹, Fangfei Cai¹, Funing Ma², Paul Reimus³, Linlin Qi¹, Di Lu⁴, Mohamad Reza Soltanian⁵, Zhenxue Dai⁶

Affiliations

¹ College of Construction Engineering, Jilin University, Changchun 130026, China.
² School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266520, China. Electronic address: [email protected].
³ Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
⁴ Science and Technology Research Center of China Customs, Beijing, 100026, China.
⁵ Department of Geosciences, University of Cincinnati, Cincinnati, OH, USA; Department of Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA.
⁶ College of Construction Engineering, Jilin University, Changchun 130026, China; School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266520, China; Key Laboratory of Groundwater Resources and Environment, Jilin University, Ministry of Education, Changchun 130021, China. Electronic address: [email protected].

PMID: 39491990
DOI: 10.1016/j.jhazmat.2023.132851

Abstract

Colloids play a crucial role in influencing the mobility of radionuclides in high-level radioactive waste repositories. However, the co-transport behavior of radionuclides and colloids in geological media remains insufficiently understood. This study investigated the transport of Strontium (Sr) in four types of granite minerals (quartz, biotite, K-feldspar, and plagioclase) in the presence and absence of Na-bentonite colloids (Na-BC) using column experiments. Employing a stepwise modeling strategy, this study first determined the basic flow and transport parameters through breakthrough curve analysis of the conservative tracer (Br). Then, the experimental data of Sr in the colloid-free Sr transport experiments and Na-BC in the Sr-colloid co-transport experiments were quantitatively explained using a two-site sorption model and a two kinetic sites model, respectively. Finally, the co-transport behavior of Sr and Na-BC was fitted using the colloid-facilitated solute transport model. The stepwise modeling allowed quantification of the kinetics of Sr sorption onto mobile and immobile Na-BC and highlighted the role of straining in Na-BC retention. In the absence of Na-BC, Sr transport experienced the greatest retardation in biotite, followed by plagioclase, K-feldspar, and quartz, respectively, which positively correlated with the specific surface area of the minerals. Moreover, Na-BC enhanced Sr transport with the same retardation order in all tested minerals, with recovery rate increments of 68.61%, 19.21%, 6.67%, and 4.33%, respectively. The transport of Sr in K-feldspar was found to be less affected by Na-BC compared to the other tested minerals, likely due to the strong cation exchange capacity of K⁺ among the cation components of minerals, making hydrated K⁺ more likely to exchange with Sr²⁺ on K-feldspar surfaces. These findings hold significant implications for assessing the risks associated with the transport of radionuclides in deep geological repositories.

Keywords: Co-transport; Granite minerals; Na-bentonite colloids; Sorption; Sr(II).