Effect of sulfite on divalent mercury reduction and re-emission in a simulated desulfurization aqueous solution

Wet flue gas desulfurization (WFGD) systems have several benefits, including SO2 removal and Hg pollution control. However, the absorbed ionic mercury may be transformed into insoluble elemental mercury because of the chemical interaction with the aqueous scrubbing solution, which causes mercury re-emission and reduces the mercury capture efficiency of the scrubber. This study investigates the effects of operating temperatures, pH, and O2 and SO42 − concentrations on the reduction of Hg2 + in the presence of SO32 − in a simulated desulfurization aqueous solution. The results indicate that excess SO32 − inhibits Hg2 + reduction due to the formation of the stable Hg(SO3)22 − complex, whereas a low SO32 − concentration (< 2 mM) leads to enhanced mercury re-emission due to the formation of more redox-unstable HgSO3. The Hg0 release increases from 18.6% to 59.6% when the operating temperature increases from 45 °C to 55 °C. A pH decrease in the slurry from 5 to 3 causes a significant increase in the Hg0 emission from 6.9 to 127.9 μg/m3 in a simulated desulfurization slurry. In addition, O2 caused a secondary emission of Hg0 by damaging the stable redox complexes of Hg2 + and SO32 −. In the presence of oxygen, the Hg0 emission decreases; subsequently, a HgSO3SO42 − complex is formed. Sulfate (HgSO4 and HgSO3SO42 −) inhibit the emission of Hg0.