Photochemical Oxidation Removal of Hg⁰ from Flue Gas Containing SO₂/NO by an Ultraviolet Irradiation/Hydrogen Peroxide (UV/H₂O₂) Process

Abstract

In the present study, the process of photochemical oxidation removal of Hg0 from a flue gas containing SO2/NO, using ultraviolet irradiation and hydrogen peroxide (UV/H2O2), was investigated in a photochemical gas–liquid reactor. The effects of some important parameters, such as H2O2 concentration, UV radiated power per unit solution, solution pH, Hg0 concentration, solution temperature, flue gas flow, SO2 concentration, NO concentration, and O2 concentration on the removal of Hg0 using the UV/H2O2 process were investigated. The simultaneous removal of Hg0, NO, and SO2 via the UV/H2O2 and UV/H2O2/Ca(OH)2 processes is studied preliminarily. In addition, the removal mechanism of Hg0 via the UV/H2O2 process is also proposed. The results show that O2 and UV radiation have a significant role in promoting the removal of Hg0. The removal of Hg0 is significantly promoted by adding a low concentration of H2O2, but it is inhibited by adding a high concentration of H2O2. The removal efficiency of Hg0 is significantly reduced as the Hg0 concentration, flue gas flow, or solution pH is increased, but it is only slightly reduced with increased solution temperature, SO2 concentration, or NO concentration. Hg0, NO, and SO2 can be simultaneously removed effectively using UV/H2O2/Ca(OH)2 processes. Hg2+ is the final reaction product of Hg0 removal, and Hg0 is mainly removed by the oxidations of H2O2, ·OH, ·O, and O3, as well as UV photoexcitation.