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.