Co-transport and co-release of Eu(III) with bentonite colloids in saturated porous sand columns: Controlling factors and governing mechanisms

Zhen Xu; Duoqiang Pan; Qingfeng Tang; Xiaoyan Wei; Chunli Liu; Xiaolong Li; Ximeng Chen; Wangsuo Wu

doi:10.1016/j.envpol.2022.118842

Co-transport and co-release of Eu(III) with bentonite colloids in saturated porous sand columns: Controlling factors and governing mechanisms

Environ Pollut. 2022 Apr 1:298:118842. doi: 10.1016/j.envpol.2022.118842. Epub 2022 Jan 11.

Authors

Zhen Xu¹, Duoqiang Pan², Qingfeng Tang³, Xiaoyan Wei³, Chunli Liu⁴, Xiaolong Li⁵, Ximeng Chen¹, Wangsuo Wu¹

Affiliations

¹ Frontiers Science Center for Rare Isotopes, Lanzhou University, Lanzhou, 730000, China; School of Nuclear Science and Technology, Lanzhou University, Lanzhou, 730000, China.
² Frontiers Science Center for Rare Isotopes, Lanzhou University, Lanzhou, 730000, China; School of Nuclear Science and Technology, Lanzhou University, Lanzhou, 730000, China. Electronic address: panduoqiang@lzu.edu.cn.
³ School of Nuclear Science and Technology, Lanzhou University, Lanzhou, 730000, China.
⁴ Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry and Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.
⁵ China Academy of Engineering Physics, Mianyang, 621000, China.

PMID: 35031401
DOI: 10.1016/j.envpol.2022.118842

Abstract

Accurate prediction of the colloid-driven transport of radionuclides in porous media is critical for the long-term safety assessment of radioactive waste disposal repository. However, the co-transport and corelease process of radionuclides with colloids have not been well documented, the intrinsic mechanisms for colloids-driven retention/transport of radionuclides are still pending for further discussion. Thus the controlling factors and governing mechanisms of co-transport and co-release behavior of Eu(III) with bentonite colloids (BC) were discussed and quantified by combining laboratory-scale column experiments, colloid filtration theory and advection dispersion equation model. The results showed that the role of colloids in facilitating or retarding the Eu(III) transport in porous media varied with cations concentration, pH, and humic acid (HA). The transport of Eu(III) was facilitated by the dispersed colloids under the low ionic strength and high pH conditions, while was impeded by the aggregated colloids cluster. The enhancement of Eu(III) transport was not monotonically risen with the increase of colloids concentration, the most optimized colloids concentration in facilitating Eu(III) transport was approximately 150 mg L^-1. HA showed significant promotion on both Eu(III) and colloid transport because of not only its strong Eu(III) complexion ability but also the increased dispersion of HA-coated colloid particles. The HA and BC displayed a synergistic effect on Eu(III) transport, the co-transport occurred by forming the ternary BC-HA-Eu(III) hybrid. The transport patterns could be simulated well with a two-site model that used the advection dispersion equation by reflecting the blocking effect. The retarded Eu(III) on the stationary phase was released and remobilized by the introduction of colloids, or by a transient reduction in cation concentration. The findings are essential for predicting the geological fate and the migration risk of radionuclides in the repository environment.

Keywords: Bentonite colloids; Co-release; Co-transport; Eu(III); Humic acid.

MeSH terms

Bentonite*
Colloids
Humic Substances / analysis
Porosity
Sand*

Substances

Colloids
Humic Substances
Sand
Bentonite