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. Hg0 re-emission occurs when the dissolved Hg(II) is converted to a volatile form (i.e., Hg0) that can be subsequently emitted into the ambient air from WFGD wastewater aeration basins. Others have shown that Hg0 re-emission depends on pH, temperature, ligands (Cl, Br, I, F, SO32-, SO42-, NO3-, SCN-, and ClO-), O2, minerals (Se and As), and metals (Fe and Cu) in WFGD wastewater. Still others have shown Hg0 re-emission restriction via inhibitor addition (adsorbents and precipitators). This is the first review that summarizes the complex and inconsistently reported Hg0 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 Hg0 formation and release. ? 2021 Elsevier B.V.