Adsorption structures and bonding states of cesium and barium adsorbed on various sites of vermiculite

Akiko Yamaguchi; Masahiko Okumura; Naomi Kawamura; Yoshio Takahashi

doi:10.1016/j.scitotenv.2025.178585

Adsorption structures and bonding states of cesium and barium adsorbed on various sites of vermiculite

Sci Total Environ. 2025 Jan 24:964:178585. doi: 10.1016/j.scitotenv.2025.178585. Online ahead of print.

Authors

Akiko Yamaguchi¹, Masahiko Okumura², Naomi Kawamura³, Yoshio Takahashi⁴

Affiliations

¹ Center for Computational Science and e-Systems, Japan Atomic Energy Agency, Kashiwa, Chiba 277-0871, Japan; Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan. Electronic address: yamaguchi.akiko@jaea.go.jp.
² Center for Computational Science and e-Systems, Japan Atomic Energy Agency, Kashiwa, Chiba 277-0871, Japan. Electronic address: okumura.masahiko@jaea.go.jp.
³ Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo 679-5198, Japan. Electronic address: naochan@spring8.or.jp.
⁴ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan; Isotope Science Center, The University of Tokyo, Bunkyo, Tokyo 113-0032, Japan. Electronic address: ytakaha@eps.s.u-tokyo.ac.jp.

PMID: 39862504
DOI: 10.1016/j.scitotenv.2025.178585

Abstract

The adsorption reaction on clay minerals is crucial for understanding the environmental behavior of various cations, including cesium (Cs). However, its details remain unclear because of multiple adsorption sites of the clay minerals, a significant difference between concentrations in the atomic-scale experiments and the actual environment, and difficulties of evaluating bonding states of the adsorbed cations. It is expected that systematic experiments at the atomic-scale with a wide concentration range and application of density functional theory (DFT) calculations overcome the problems and bring crucial insights to link laboratory experiment results with environmental sample analysis. This study obtained adsorption isotherms and conducted X-ray diffraction and extended X-ray absorption fine structure (EXAFS) measurements at various concentrations of Cs⁺ or barium (Ba²⁺). Additionally, high-energy resolution fluorescence detection (HERFD) X-ray absorption near edge structure (XANES) measurements was performed for Cs⁺ to estimate its bonding state. To interpret the results, DFT calculations were also conducted. The results clarified the transition process of the adsorption site and local structures of adsorbed cations depending on the adsorption concentrations. Especially, the combination of EXAFS and DFT calculations succeeded in revealing the intermediate state between frayed edge site at a low concentration and collapsed interlayer site at a high concentration. Furthermore, HERFD-XANES and DFT calculations suggested the ionic bonding nature of Cs⁺, regardless of the adsorption sites.

Keywords: Adsorption isotherm; Clay minerals; DFT; EXAFS; HERFD–XANES.