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

Elemental mercury (Hg-0) in flue gas can be efficiently captured by use of mercury chloride (HgCl2) solution. However, the ability of HgCl2 to absorb Hg-0 is severely reduced by high concentrations of sulfur dioxide (SO2) in the flue gas. Methods used to remove Hg-0 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 Hg-0 both occurred in HgCl2 solution in the presence of SO2. The reduced efficiency of Hg-0 removal was attributed to reduction of HgCl2 to Hg-0 by SO3 (2-) or HSO3 (-), formed from SO2. Moderate concentrations of Cl- and H2O2 had synergistic effects with low pH on Hg-0 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 Hg-0 and SO2, the latter of which is reclaimed by production of sulfuric acid after Hg-0 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 Hg-0 and lower concentrations of SO2, the latter of which is co-absorbed in the Hg-0 removal unit.