Catalytic effects of cations on selenium conversion and distribution by peroxydisulfate in FGD slurry: A combined study.

Abstract

The toxic trace element of selenium, emitted from coal combustion in power plants and enriched in flue gas desulfurization (FGD) slurry, is easily purified in the liquid phase. In order to make as much selenium gathered in the liquid phase of FGD slurry as possible, it is necessary to investigate how peroxydisulfate, the key oxidant in FGD slurry, affects conversion and distribution of selenium with active cations involved. Experiments on the simulated FGD slurry find that Cu²⁺ & Fe²⁺ have positive effects on oxidation of selenite to selenate by peroxydisulfate via different routes, Co²⁺ presents nearly neutral effects and Mn²⁺ shows negative effects. Density functional theory (DFT) calculations verify the experimental results by comparing dissociation energy change of peroxydisulfate with different cations added. With the laboratory experiments and DFT calculations combined, selenium distribution in the real FGD slurry sample with peroxydisulfate and copper ion added shows that selenite adsorbed in the gypsum can be quickly oxidized to selenate by the additives and then sent back to the liquid phase without causing damage to the gypsum. This study supplies adequate mechanism explanation and direct technical guidance for selenium purification in FGD slurry.