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

Abstract

Removal of Hg⁰ 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 Hg⁰ removal. Mechanism and kinetics of Hg⁰ removal were also investigated. The results indicated that Hg⁰ 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 Hg⁰ and NO concentrations. Hg⁰ was oxidized by four pathways: (A) oxidized by SO₄–• and •OH that were produced from UV-light activation of S₂O₈²–; (B) removed by UV light–water excitation reaction; (C) oxidized by SO₄–• and •OH 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 Hg⁰, and the other pathways “B–D” only play a complementary role. When CS₂O₈₂– < 0.06 mol/L or UV radiation intensity < 78 μW/cm², the Hg⁰ removal process belongs to a moderate speed reaction. Hg⁰ removal can be enhanced by simultaneously increasing the mass transfer rate and chemical reaction rate. When CS₂O₈₂– ≥ 0.06 mol/L and UV radiation intensity ≥ 78 μW/cm², the Hg⁰ removal process belongs to a fast reaction. Hg⁰ removal can be further enhanced by improving mass transfer rate (e.g., increasing gas–liquid contact area and enhancing turbulence in reactor).