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Thermodynamic study of the complexation of humic acid by calorimetry

熱量滴定法によるフミン酸錯生成の熱力学研究

紀室 辰伍; 桐島 陽*; 北辻 章浩; 宮川 和也 ; 秋山 大輔*; 佐藤 修彰*

Kimuro, Shingo; Kirishima, Akira*; Kitatsuji, Yoshihiro; Miyakawa, Kazuya; Akiyama, Daisuke*; Sato, Nobuaki*

幌延深部地下水から抽出したフミン酸及び一般的なフミン酸と、銅(II)イオン及びウラニル(VI)イオンとの錯生成反応に対して熱量滴定法を適用し、ギブス自由エネルギー,反応エンタルピー及び反応エントロピーを決定した。一般的なフミン酸の錯生成反応が高分子電解質性と組成不均質性によって特徴付けられるのに対し、幌延深部地下水フミン酸の錯生成反応ではどちらの影響も確認されなかった。反応熱力学量を正確に決定することから、深部地下水フミン酸の特徴的な反応機構が明らかになった。

A combination of potentiometry and calorimetry was used for the determination of the thermodynamic quantities of complexation of generic and groundwater humic acid (HA), which was isolated from deep groundwater at Horonobe, Hokkaido, Japan, with copper (II) ions and uranyl (VI) ions. The apparent complexation constant of Horonobe HA was independent of the pH, whereas that of generic HA was dependent on the pH. This observation indicates that the polyelectrolyte effect of Horonobe HA is negligible because of its small molecular size. In addition, the effect of the heterogeneity of Horonobe HA was not significant. Moreover, the complexation enthalpy of Horonobe HA was consistent with that of homogeneous poly(acrylic acid), which means the complexation of Horonobe HA was not affected by the functional group heterogeneity . Consequently, the characteristic complexation mechanism of Horonobe HA was revealed based on the determined thermodynamic quantities.

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