Selenium migration behaviors in wet flue gas desulfurization slurry and an in-situ treatment approach

Abstract

Excessive discharge of Se-containing wastewater from coal-fired power plants is a disaster for aquatic life, and it must be strictly controlled. However, conventional coagulation-precipitation technology cannot efficiently remove selenium from wastewater, owing to its complex species and high solubility. In this study, an innovative approach was proposed to realize the in-situ removal of selenium in desulfurization slurry, instead of treating it in wastewater. Firstly, the migration behaviors of selenium in slurry was studied. Among various ions, the ferric ion could significantly convert liquid selenite into solid phase by the formation insoluble ferric selenite. Then, several oxidizing factors were tested and the S2O82− showed obvious inhibition effect. A multi-component removal agent containing Fe3+/Mn2+ or Fe3+/Fe2+ successfully removed selenite from slurry in the presence of S2O82−, and the efficiency was as high as 96.5%. Furthermore, the in-situ removal agent was tested using a field slurry obtained from a full-scale coal-fired power plant, and the selenium concentration could be reduced to 38.4 μg/L. It is promising that the application of this technology in full-scale power plants will achieve better performance because the formation of troublesome selenate can be avoided. No complex system or process is needed for this in-situ selenium removal approach, and it can easily combine with other available advanced deep removal technologies, to build the double defense walls for controlling selenium discharge.