Removal of Hg0 from Simulated Flue Gas by Ultraviolet Light/Heat/Persulfate Process in an UV-Impinging Stream Reactor

Removal of Hg-0 from simulated flue gas by ultraviolet light (UV)/heat/ammonium persulfate process in an UV-impinging stream reactor was investigated for the first time. Experiments were conducted to evaluate the effects of several parameters and gas composition on Hg-0 removal. Mechanism and kinetics of Hg-0 removal were also investigated. The results indicated that Hg-0 removal efficiency was increased by increasing UV radiation intensity, activation temperature, persulfate concentration, and solution circulation rate; was decreased by increasing solution pH and SO2 concentration; and was not obviously affected by Hg-0 and NO concentrations. Hg-0 was oxidized by four pathways: (A) oxidized by SO4-center dot and (OH)-O-center dot that were produced from UV-light activation of S2O82-; (B) removed by UV light-water excitation reaction; (C) oxidized by SO4-center dot and (OH)-O-center dot that were produced from heat activation of S2O82-; (D) oxidized by S2O82-. In the four pathways, the A pathway plays a major role in the removal of Hg-0, and the other pathways B-D only play a complementary role. When C-S2O8(2-) < 0.06 mol/L or UV radiation intensity < 78 mu W/cm(2), the Hg-0 removal process belongs to a moderate speed reaction. Hg-0 removal can be enhanced by simultaneously increasing the mass transfer rate and chemical reaction rate. When C-S2O8(2-) >= 0.06 mol/L and UV radiation intensity >= 78 mu W/cm(2), the Hg-0 removal process belongs to a fast reaction. Hg-0 removal can be further enhanced by improving mass transfer rate (e.g., increasing gas-liquid contact area and enhancing turbulence in reactor).