Enhanced Hg 2+ removal and Hg 0 re-emission control from wet fuel gas desulfurization liquors with additives

Abstract

Secondary atmospheric pollutions may result from wet flue gas desulfurization (FGD) systems caused by the reduction of Hg 2+ to Hg 0. The present study employed three agents: Na 2S, 2,4,6-trimercaptotiazine, trisodium salt nonahydrate (TMT) and sodium dithiocarbamate (DTCR) to precipitate aqueous Hg 2+ in simulated desulfurization solutions. The effects of the precipitator’s dosing quantity, the initial pH value, the reaction temperature, the concentrations of Cl − and other metal ions (e.g. Cu 2+ and Pb 2+) on Hg 2+ removal were studied. A linear relationship was observed between Hg 2+ removal efficiency and the increasing precipitator’s doses along with initial pH. The addition of chloride and metal ions impaired the Hg 2+ removal from solutions due to the complexation of Cl − and Hg 2+ as well as the chelating competition between Hg 2+ and other metal ions. Based on a comprehensive comparison of the treatment effects, DTCR was found to be the most effective precipitating agent. Moreover, all the precipitating agents were potent enough to inhibit Hg 2+ reduction as well as Hg 0 re-emission from FGD liquors. More than 90% Hg 2+ was captured by precipitating agents while Hg 2+ reduction efficiency decreased from 54% to just less than 3%. The additives could efficiently control the secondary Hg 0 pollution from FGD liquors.