Control of Se~(6+) Formation in a Wet FGD Using Mn~(2+)

摘要

In a coal combustion process, a part of the selenium in coal is captured in a limestone-gypsum wet FGD. In the FGD liquor, it is oxidized from selenite (Se(IV)O_3~(2-)) to selenate (Se(VI)O_4~(2+)), which is difficult to remove by a conventional wastewater treatment such as coagulation-sedimentation. In the present work, the effect of Mn~(2+) on the prevention of selenium oxidation by peroxidisulfate ion (S_2O_8~2), which is the dominant oxidizing agent in the FGD liquor, has been investigated using reagents and a FGD facility. Selenite, S_2O_8~(2-) and Mn~(2 +) were dissolved in a solution at various concentrations, and were kept at 50 °C for several tens of hours. Selenium oxidation from selenite to selenate by S2O_8~(2-) was decelerated in the presence of Mn~(2+) because S2O_8~(2-) reacted with Mn~(2+) instead of selenite. Mn~(2+) prevented selenium oxidation in the FGD liquor and did not affect desulfurization efficiency.