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Report No.

Solubility measurement of iron-selenium compounds under reducing conditions

Kitamura, Akira  ; Shibata, Masahiro ; Kitao, Hideo*

Chemical behavior of selenium(Se), which was one of the important elements for performance assessment of geological disposal of high-level radioactive waste, was investigated under reducing and iron-containing conditions. A washing method for an iron diselenide(FeSe$$_{2}$$(cr)) reagent with acidic and basic solutions (0.1 and 1 M HCl and 1 M NaOH) was carried out for the purification of FeSe$$_{2}$$ reagent, which was considered to be a solubility limiting solid for Se under the geological disposal conditions. Furthermore, solubility of FeSe$$_{2}$$(cr) was measured in alkaline solution (pH: 11 - 13) under reducing conditions (E$$_{h}$$ vs SHE: -0.4 - O V), and thermodynamic data on equilibrium reactions between Se in solution and Se precipitate were obtained. The dependencies of solubility values on pH and redox potential (Eh: vs. standard hydrogen electrode) were best interpreted that the solubility limiting solid was not FeSe$$_{2}$$(cr) but Se(cr) and the aqueous species was SeO$$_{3}$$$$^{2-}$$ in the present experimental conditions. The equilibrium constant between Se(cr) and SeO$$_{3}$$$$^{2-}$$ at zero ionic strength was determined and compared with literature values. The chemical behavior of Se under geological disposal conditions was discussed.



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