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
=-6.57
0.15, 4Se(cr)+2e
=Se
, logK
=-16.67
0.03と決定された。また、イオン相互作用係数は
(HSe
, Na
)=-0.01
0.10,
(Se
, Na
)=-0.03
0.02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))=6.0
2.2kJ mol
、ポリセレナイド種については
G
(Se
)=111.64
1.61kJ mol
, 
G
(Se
)=98.68
1.02kJ mol
及び
G
(Se
)=95.14
0.17kJ 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
= -6.57
0.15, 4Se(cr) + 2e
= Se
logK
= -16.67
0.03 and ion interaction coefficients for HSe
and Se
versus Na
,
(HSe
, Na
) = -0.01
0.10 and
(Se
, Na
) = -0.03
0.02, 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)) = 6.0
2.2 kJ mol
, 
G
(Se
) = 111.64
1.61 kJ mol
, 
G
(Se
) = 98.68
1.02 kJ mol
and 
G
(Se
) = 95.14
0.17 kJ mol
, respectively.