Solubility of selenium at high ionic strength under anoxic conditions
還元環境下における高イオン強度溶液中のセレンの溶解度
飯田 芳久 ; 山口 徹治 ; 田中 忠夫 ; 中山 真一
Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao; Nakayama, Shinichi
還元環境下において、高イオン強度溶液中のセレンの溶解度試験を実施した。支配的な溶存化学形はHSe(pH: 5-8), Se(pH: 9-13)であった。溶解度制限固相はSe(am)(pH: 5-8), Se(cr)(pH: 9-13)であった。溶解反応とその平衡定数は、Se(am)+H+2e=HSe, logK=-6.570.15, 4Se(cr)+2e=Se, logK=-16.670.03と決定された。また、イオン相互作用係数は(HSe, Na)=-0.010.10, (Se, Na)=-0.030.02と決定された。アモルファスセレンの生成自由エネルギーはG(Se(am))=6.02.2kJ mol、ポリセレナイド種についてはG(Se)=111.641.61kJ mol, G(Se)=98.681.02kJ mol及びG(Se)=95.140.17kJ molと求められた。
Solubility experiments for selenium were performed at high ionic strengths (1.0 and 2.0 M NaCl) under anoxic conditions. Dominant aqueous selenium species were identified as hydrogen selenide, HSe, at pH between 5 and 8, and polyselenide, Se at pH between 9 and 13. A solubility-limiting solid was determined to be amorphous selenium at pH between 5 and 8, and crystalline selenium at pH between 9 and 13. The equilibrium constants of Se(am) + H + 2e = HSe, logK = -6.570.15, 4Se(cr) + 2e = Se logK = -16.670.03 and ion interaction coefficients for HSe and Se versus Na, (HSe, Na) = -0.010.10 and (Se, Na) = -0.030.02, were determined by specific ion interaction theory. The standard molar free energy of formation of amorphous selenium and polyselenide species were determined to be G (Se(am)) = 6.02.2 kJ mol, G(Se) = 111.641.61 kJ mol, G(Se) = 98.681.02 kJ mol and G (Se) = 95.140.17 kJ mol, respectively.