Insight into the Unique Oxidation Chemistry of Elemental Mercury by Chlorine-Containing Species: Experiment and Simulation

This work investigated the oxidation chemistry of elemental mercury (Hg0) by chlorine-containing species produced indirectly through the gas-to-solid phase reaction between NO x gases and NaClO2 powder (NaClO2(s)), where both experiment and simulation results were compared to clarify which species are responsible for the oxidation of Hg0. At first, we introduced 30 ppm of NO2 into the pack-bed reactor containing NaClO2(s) to produce OClO species and then injected NO and Hg0 (260 μg/Nm3) to Mixer, where the concentration of NO was varied up to 180 ppm and the reaction temperature was set to 130 °C. We observed for the first time that the degree of Hg0 oxidation is completely controlled by the introduced concentration of NO: for example, the oxidation efficiency of Hg0 is drastically increased to become 100% at near 7 ppm NO, but further increasing NO concentration results in the oxidation efficiency of Hg0 being gradually decreased. The simulation results indicated that such a propensity of Hg0 oxidation efficiency to NO concentration can be attributed to the NO concentration-dependent Cl, ClO, and Cl2 formation which plays a critical role in the oxidation of Hg0.