Effect of oxidizing agents on selenate formation in a wet FGD

In a coal combustion process, a considerable amount of selenium is captured in the wet FGD, where it is oxidized from selenite ( Se ( IV ) O 3 2 - ) to selenate ( Se ( VI ) O 4 2 - ) , which is difficult to remove. Diethyl-p-phenylene-diammonium (DPD) absorptiometric analysis and ion chromatography identified peroxodisulfate ion ( S 2 O 8 2 - ) as the dominant oxidizing agent in the FGD liquor. Selenite was easily oxidized to selenate in the presence of S 2 O 8 2 - and the oxidation was accelerated as the temperature increased. Addition of Mn2+ ion was found to be effective in controlling selenate formation. When Mn2+ ion was added, S 2 O 8 2 - oxidized not selenite to selenate but rather Mn2+ to MnO2, which captured some dissolved selenite.