The distribution and conversion of selenite and selenate with the bubbling of simulated flue gas in simulated WFGD slurry

Highlights: • Identification of amorphous elemental selenium in SO₂ bubbled simulated WFGD slurry. • Reveal of the reduction of selenite by SO₂ and the influences of reaction conditions. • The mutual inhibition of oxidation effect of S₂O₈²⁻ and the reduction effect of SO₂. Selenium is one of the hazardous trace elements emitted from coal-fired power plants. The distribution of selenium in Wet Flue Gas Desulfurization (WFGD) process is still unclear and even in controversial, impeding the development of selenium removal technologies. This research has found that the selenite in simulated slurry could be reduced by SO₂ while selenate has not been affected. Characterization methods including X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to provide an evidence that the product of the reduction reaction is amorphous elemental selenium. Meanwhile, the influences of other gaseous components, pH, temperature and S₂O₈²⁻ in simulated slurry has also been considered in this research. It is found that with the increase of SO₂ concentration in flue gas, the reduction of selenite increased and the reduction reaction is an exothermic reaction. Meanwhile, the oxidation effect of S₂O₈²⁻ competes with the reduction effect of SO₂. This study introduced the influence of flue gas into the research of the conversion of selenium in FGD slurry and indicate the effect of flue gas on the potential emission treatment techniques of selenium in FGD slurry.