Removal of mercury from flue gas from nonferrous metal smelting, by use of mercury chloride solution, and mechanisms of inhibition by sulfur dioxide

Abstract

Elemental mercury (Hg0) in flue gas can be efficiently captured by use of mercury chloride (HgCl2) solution. However, the ability of HgCl2 to absorb Hg0 is severely reduced by high concentrations of sulfur dioxide (SO2) in the flue gas. Methods used to remove Hg0 by absorption in HgCl2 solution, and mechanisms by which these methods are inhibited by SO2, were studied in this work. Reduction of HgCl2 and absorption of Hg0 both occurred in HgCl2 solution in the presence of SO2. The reduced efficiency of Hg0 removal was attributed to reduction of HgCl2 to Hg0 by SO3 2− or HSO3 −, formed from SO2. Moderate concentrations of Cl− and H2O2 had synergistic effects with low pH on Hg0 removal by HgCl2 solution. A new composite absorption solution containing 7.36 mmol/L HgCl2 and 73.6 mmol/L Cl− at pH 0 was suitable for treatment of flue gas containing high concentrations of both Hg0 and SO2, the latter of which is reclaimed by production of sulfuric acid after Hg0 removal. Another new composite absorption solution containing 7.36 mmol/L HgCl2 and 1.0 % H2O2 at pH 0 was suitable for treatment of flue gas containing high concentrations of Hg0 and lower concentrations of SO2, the latter of which is co-absorbed in the Hg0 removal unit.