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

Wet flue gas desulfurization (WFGD) simultaneously removes Hg and SO from coal-fired power plant flue gas streams. Hg re-emission occurs when the dissolved Hg(II) is converted to a volatile form (i.e., Hg) that can be subsequently emitted into the ambient air from WFGD wastewater aeration basins. Others have shown that Hg re-emission depends on pH, temperature, ligands (Cl, Br, I, F, SO, SO, NO, SCN, and ClO), O, minerals (Se and As), and metals (Fe and Cu) in WFGD wastewater. Still others have shown Hg re-emission restriction via inhibitor addition (adsorbents and precipitators). This is the first review that summarizes the complex and inconsistently reported Hg 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 formation and release.