Gaseous mercury re-emission from wet flue gas desulfurization wastewater aeration basins: A review

Wet flue gas desulfurization (WFGD) simultaneously removes Hg and SO2 from coal-fired power plant flue gas streams. Hg-0 re-emission occurs when the dissolved Hg(II) is converted to a volatile form (i.e., Hg-0) that can be subsequently emitted into the ambient air from WFGD wastewater aeration basins. Others have shown that Hg-0 re-emission depends on pH, temperature, ligands (Cl, Br, I, F, SO32-, SO42-, NO3-, SCN-, and ClO-), O-2, minerals (Se and As), and metals (Fe and Cu) in WFGD wastewater. Still others have shown Hg-0 re-emission restriction via inhibitor addition (adsorbents and precipitators). This is the first review that summarizes the complex and inconsistently reported Hg-0 re-emission mechanisms, updates misconceptions related to Hg(II) complexation and reduction, and reviews applications of inhibitors that convert aqueous Hg(II) into stable solid forms to prevent gaseous Hg-0 formation and release.

Automated summary

Studies have shown that Hg-0 re-emission is influenced by various factors and can be restricted through the addition of inhibitors. This review summarizes the mechanisms of Hg-0 re-emission, updates misconceptions, and reviews the application of inhibitors.