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Report No.

Thermodynamic study of complexation of deep groundwater humic acid by calorimetry

Kimuro, Shingo   ; Terashima, Motoki  ; Tachi, Yukio  ; Kitatsuji, Yoshihiro  ; Miyakawa, Kazuya   ; Akiyama, Daisuke*; Sato, Nobuaki*; Kirishima, Akira*

Humic acid is confirmed to be present even in deep underground where radioactive wastes are planned to be disposed. Although the characteristic properties and reaction mechanism of humic acid are strongly affected by its origin, the reaction enthalpy and entropy for groundwater humic acid complexation are only estimated values obtained from the equilibrium constants at different temperature despite these thermodynamic quantities is necessary for the discussion of reaction thermodynamics. In this study, the thermodynamic quantities of the complexation of deep groundwater humic acid at Horonobe, Hokkaido, Japan with copper (II) and uranyl (VI) ion were determined by the combination of the potentiometry and calorimetry to cultivate a better understanding of the reaction mechanism. By the comparison of thermodynamic quantities with typical humic acid and simple organic acid, the characteristic reaction mechanism of Horonobe humic acid was revealed. In addition, thermodynamic equilibrium calculations based on the determined thermodynamic quantities were performed for the discussion of the impact of humic acid complexation and the origin of humic acid in the migration of radionuclide.



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