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Interactions between anionic complex species of actinides and negatively charged mineral surfaces

Yamaguchi, Tetsuji ; Nakayama, Shinichi ; Yoshida, Takahiro

Adsorption of actinides onto negatively charged mineral surfaces was investigated under conditions that actinides were predominantly present as anionic complex species: Th(CO$$_{3}$$)$$_{5}$$$$^{6-}$$, Am(CO$$_{3}$$)$$_{3}$$$$^{3-}$$, Np(CO$$_{3}$$)$$_{2}$$(OH)$$_{2}$$$$^{2-}$$, UO$$_{2}$$(OH)$$_{4}$$$$^{2-}$$, NpO$$_{2}$$(OH)$$_{2}$$$$^{-}$$, Sn(OH)$$_{5}$$$$^{-}$$ and Pb(OH)$$_{3}$$$$^{-}$$. These solutions were left to stand for 2 days to confirm these elements stable in dissolved state, and then contacted with minerals, $$gamma$$-Al$$_{2}$$O$$_{3}$$ or SiO$$_{2}$$ (AEROSIL, specific surface area: 10$$^{5}$$ m$$^{2}$$ kg$$^{-1}$$). After desired contact time for 2 days or more, the solutions were ultra-filtered through 10$$^{4}$$-molecular-weight cutoff Millipore filters and the concentrations of the elements in the filtrates were determined. The sorption experiments were performed at room temperature (25$$^{circ}$$C) under Ar. Distribution coefficients decreased with the increasing pH and with increasing carbonate concentrations. The monotonous decrease in the distribution coefficients in the investigated pH range suggests that the electrostatic repulsion was a dominant interaction between anionic complex species of actinides and negatively charged mineral surfaces.



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Category:Chemistry, Inorganic & Nuclear



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