Selenium capture using sorbent powders: Mechanism of sorption by hydrated lime

This study investigates the potential of mineral sorbents to capture selenium which is sufficiently volatile to occur in the flue gas in vapor state. The sorption studies are conducted in a high-temperature reactor using SeO2 as the source of selenium. In both high (800-1000 degrees C) and medium-temperature (400-700 degrees C) range, hydrated lime exhibits superior selenium sorption capability compared to other sorbent powders. The results show that the mechanism of capture by Ca(OH)(2) is not a simple physical adsorption process but seems to involve a chemical reaction between CaO and SeO2. The medium temperature range of 400-600 degrees C is favorable for the reaction to occur and leads to high selenium sorption. At higher temperatures, thermodynamic equilibrium aids dissociation of the reaction product, and the amount of metal capture reduces drastically with increasing temperature. XRD studies further confirm that calcium selenite is the dominant reaction product.