光触媒によるセレン酸イオン除去反応に及ぼす硫酸イオンの影響

Abstract

The reduction reaction of selenate ion by TiO2 photocatalyst in the presence of sulfate ion was studied. Sodium selenate solution was used in the experiments. The selenium concentration of this solution was 10 to 100 ppm as selenium (1.27×10-1 to 1.27 mmol / dm3), and 1.27 to 1.27×10 mmol / dm3 of sodium sulfate and 2.5×10 mmol / dm3 of formic acid were added to it.The rate of the reduction reaction of selenate ion by the TiO2 photocatalyst became smaller by the presence of the sulfate ion. However, the reduction reaction of selenate ion proceeded until the remaining total selenium concentration became under 0.1 ppm. Reduced selenate ion became hydrogen selenide via amorphous selenium, and trapped by the CuSO4 solution gas trap. On the contrary, sulfate ion was not reduced by the TiO2 photocatalyst. The rate of the reduction reaction of selenate ion to amorphous selenium depended on the amount of adsorbed selenate ion (CSeA) and was expressed as a dimensional function of CSeA. The amount of adsorbed selenate ion on the TiO2 photocatalyst was decreased with increase of the amount of sulfate ion, and was expressed as the competitive Langumuir isotherm. This is the reason why the rate of the reduction of selenate ion becomes smaller by the presence of sulfate ion.