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Report No.
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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.

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Category:Chemistry, Inorganic & Nuclear

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