Sorption of Cs+ and Eu3+ ions onto sedimentary rock in the presence of gamma-irradiated humic acid

Qi Zhao; Takeshi Saito; Kazuya Miyakawa; Hiroshi Sasamoto; Taishi Kobayashi; Takayuki Sasaki

doi:10.1016/j.jhazmat.2021.128211

Sorption of Cs⁺ and Eu³⁺ ions onto sedimentary rock in the presence of gamma-irradiated humic acid

J Hazard Mater. 2022 Apr 15:428:128211. doi: 10.1016/j.jhazmat.2021.128211. Epub 2022 Jan 6.

Authors

Qi Zhao¹, Takeshi Saito², Kazuya Miyakawa³, Hiroshi Sasamoto³, Taishi Kobayashi¹, Takayuki Sasaki⁴

Affiliations

¹ Department of Nuclear Engineering, Kyoto University, Kyoto, Japan.
² Institute for Integrated Radiation and Nuclear Science (KURNS), Kyoto University, Osaka, Japan.
³ Horonobe Underground Research Center, Japan Atomic Energy Agency (JAEA), Hokkaido, Japan.
⁴ Department of Nuclear Engineering, Kyoto University, Kyoto, Japan. Electronic address: sasaki.takayuki.2a@kyoto-u.ac.jp.

PMID: 35032954
DOI: 10.1016/j.jhazmat.2021.128211

Abstract

The influence of humic acid (HA) and its radiological degradation on the sorption of Cs⁺ and Eu³⁺ by sedimentary rock (obtained from the Horonobe Underground Research Laboratory in Japan) was investigated to understand the sorption process of metal ions and humic substances. Aldrich HA solution was gamma-irradiated assuming a strong radiation from a highly radioactive waste to be disposed of in deep geological formations. Batch sorption experiments were performed to evaluate the effect of gamma-irradiated HA on the sorption of Cs⁺ and Eu³⁺ ions. The addition of non-irradiated HA weakened the Eu sorption because of the lower sorption of the negatively charged Eu-HA complexes compared with free Eu ions. The sorption of Cs ions was barely affected by the presence of HA and its gamma irradiation. The concentration ratio of metal complexed and non-complexed species in the solid and liquid phases was evaluated by sequential filtration and chemical equilibrium calculations. The ratios were low in both phases for Cs and supported the minimal contribution of HA to Cs sorption. However, the concentration ratio for Eu³⁺ in the liquid phase was high, indicating that the complexing ability of HA to Eu³⁺ was higher than that of HA to Cs⁺.

Keywords: Gamma irradiation; Humic acid; Metal complexation; Sedimentary rock; Sorption coefficient.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adsorption
Europium*
Humic Substances* / analysis
Hydrogen-Ion Concentration
Ions
Metals

Substances

Humic Substances
Ions
Metals
Europium