Mercury Re-emission Behaviors in Magnesium-Based Wet Flue Gas Desulfurization Process: The Effects of Oxidation Inhibitors

Abstract

The effects of four oxidation inhibitors (including ascorbic acid, formaldehyde, hydroquinone, and sodium thiosulfate) on mercury re-emission in simulated magnesium-based wet flue gas desulfurization solution were evaluated. Experimental results demonstrated that the addition of ascorbic acid significantly increased the mercury re-emission, whereas the formaldehyde and hydroquinone could slightly enhance this process at pH 6. Sodium thiosulfate was found to somewhat inhibit the bivalent mercury reduction owing to the strong binding between mercury and thiosulfate ions. pH variation showed dramatic effects on elemental mercury re-emission in the solution containing ascorbic acid or hydroquinone, and the mercury emission amount in 30 min increased about seven- and two-fold, respectively, when pH was adjusted from 6 to 8. These findings indicated that the ascorbic acid was an important reducer of mercury re-emission under acidic condition besides the sulfite ions, whereas it was the main reducer of mercury reduction under alkaline condition. In addition, the investigation on the effects of temperature and the presence of Cl– ions suggested that the mercury re-emission would be accelerated at elevated temperatures and could be suppressed in the presence of Cl– ions.