Consideration on modeling of Nb sorption onto clay minerals

Yamaguchi, Tetsuji ; Ohira, Saki ; Hemmi, Ko ; Barr, L.; Shimada, Asako ; Maeda, Toshikatsu; Iida, Yoshihisa

Sorption distribution coefficient (Kd) of niobium-94 on minerals are an important parameter in safety assessment of intermediate-depth disposal of waste from core internals etc. The Kd of Nb on clay minerals in Ca(ClO $_{4}$ ) $_{2}$ solutions were, however, not successfully modeled in a previous study. The high distribution coefficients of Nb on illite in Ca(ClO $_{4}$ ) $_{2}$ solutions were successfully reproduced by taking Ca-Nb-OH surface species into account. Solubility of Nb was studied in Ca(ClO $_{4}$ ) $_{2}$ solutions and the results were reproduced by taking an aqueous Ca-Nb-OH complex species, CaNb(OH) $_{6}$ $^{+}$ , into account in addition to previously reported Nb(OH) $_{6}$ $^{-}$ and Nb(OH) $_{7}$ $^{2-}$ . Based on this aqueous speciation model, the Ca-Nb-OH surface species responsible for the sorption of Nb on illite in Ca(ClO $_{4}$ ) $_{2}$ solutions was presumed to be X_OCaNb(OH) $_{6}$ . Although uncertainties exist in the speciation of aqueous Ca-Nb-OH species, the result of this study proposed a possible mechanism for high distribution coefficient of Nb on illite in Ca(ClO $_{4}$ ) $_{2}$ solutions. The mechanism includes Ca-Nb-OH complex formation in aqueous, solid and surface phases.

Language	:	English
Journal	:	Radiochimica Acta
Volume	:	108
Number	:	11
Pages	:	p.873 - 877
Publication Year/Month	:	2020/11
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Paper URL	:	https://doi.org/10.1515/ract-2020-0006
DOI for research data	:	Link to research data related to this paper/report.
Keywords	:	sorption model; niobium; clay; distribution coefficient; solubility; complexation; sorption mechanism
Research Facility	:	環境シミュレーション試験棟 ;BECKY(バックエンド研究施設)
Press Release	:
Article of JAEA R&D Review	:	Migration of Radionuclides from Radioactive Wastes of Reactor Core Structures in Underground Environments; Modeling Niobium Sorption onto Clay Minerals in the Presence of Calcium[/]
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Registration No. : AA20190593
JAEA Abstracts No. : 49000058
Paper Submission No. : 23687

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