Elemental Mercury Removal by a Method of Ultraviolet-Heat Synergistically Catalysis of H2O2-Halide Complex.

A novel method of ultraviolet-heat synergistically catalyzing H2O2-X (X: NaCl, NaBr, HCl, and HBr) for removal of elemental mercury (Hg0) was developed. In terms of Hg0 removal efficiency and economy, HCl and HBr were the suitable additives. Hg0 removal efficiencies reached 93.6% for H2O2-HCl and 91.4% for H2O2-HBr, the concentrations of H2O2, HCl and HBr were 1 M, 4.2 mM and 0.5 mM. The doses of gaseous Cl and Br-oxidants were 6.27 and 0.75 ppm. The costs by using H2O2-HCl and H2O2-HBr were 1,180 USD/lb-Hg0 and 1,170 USD/lb-Hg0. The best temperature for heat catalysis was 413 K. Hg0 removal was enhanced by 500 mg/m3 SO2 and 300 mg/m3 NO due to the formation of sulfuric and NO2. Mercury distribution analyses indicated that 500 mg/m3 SO2, 300 mg/m3 NO, and 6% O2 favored KCl retaining Hg2+. When the H2O2 concentration was adjusted to 3 M, the simultaneous removal efficiencies of NO and Hg0 reached 83.7% and 99.2% for H2O2-HCl, and 82.8% and 98.8% for H2O2-HBr. Electron spin resonance demonstrated that ClOH•-/BrOH•- and Cl2•-/Br2•- played leading roles in Hg0 oxidation, besides Cl2/Br2. The mercury forms in spent KCl were HgCl2, HgBr2, and HgNO3, according to X-ray photoelectron spectroscopy.