Elucidation of the Mechanism of Reaction between S_2O_8~(2-), Selenite and Mn~ (2+) in Aqueous Solution and Limestone-Gypsum FGD Liquor

摘要

The mechanism of reaction between peroxodisulfate ion (S_2O_8~(2-)), selenite (Se(IV)O_3~(2-)) and Mn~(2+) as an inhibitor of selenite oxidation was studied using aqueous solutions composed of commercial reagents, as well as limestone-gypsum flue gas desuliurization (FGD) liquors sampled from coal fired power plants. The oxidation of selenite to selenate (Se(VI)O_4~(2-)) is promoted by the sulfate ion radical (SO_4~-) which results from decomposition of S_2O_8~(2-). In the presence of Mn~(2+), selenite oxidation was prevented due to the difference in rates of reaction with SO_4~-. The ratio of the oxidation rate constants of selenite and Mn~(2+) with SO_4~- was determined over a temperature range of 40-60 ℃, and was found to be little influenced by the various coexisting components in FGD liquors.