A novel process for removal of Hg0 from flue gas using urea/persulfate activated by high temperature in a spray reactor

Urea-based wet flue gas desulfurization (Urea-WFGD) is a promising technology because of its simple process, high desulfurization efficiency, and recyclability of the products. However, it cannot effectively remove Hg0 from flue gas because of the low solubility of Hg0 in water. In this study, enhancement of the removal of Hg0 from flue gas in a urea-WFGD system using high-temperature-activated (NH4)2S2O8 was investigated for the first time in a spray reactor. Experiments were conducted to evaluate the effects of process parameters on Hg0 removal. Reaction products and key radicals were detected. The reaction mechanism and pathways were also revealed. Removal of Hg0 in urea-WFGD system was significantly enhanced by high-temperature-activated (NH4)2S2O8. The mechanism behind this effect is that an increase of reaction temperature significantly increases the concentration of (NH4)2S2O8 or liquid-gas ratio, thereby increasing Hg0 removal efficiency. However, an increase of solution pH or urea concentration significantly decreases the removal efficiency. Changing Hg0 or SO2 concentration has only a small effect on Hg0 removal. NH4+, SO42−, NO3−, and Hg2+ are found in solution, and S2O82−/OH/SO4− oxidations play an important role in the removal of Hg0. The results demonstrate that the feasibility of Hg0 removal in urea-WFGD system was enhanced by high-temperature-activated (NH4)2S2O8 in a spray reactor.