New Insight into the Characteristics and Mechanism of Hg⁰ Removal by NaClO₂ in Limestone Slurry

Abstract

In this study, the Hg0 removal characteristics of NaClO2 in limestone slurry were investigated in a bubbling reactor. The effects of slurry conditions (pH, temperature, and Cl– concentration) and flue gas components (NO, SO2, HCl, etc.) on Hg0 removal activity and efficient Hg0 removal duration were explored. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the solid products prepared under different conditions. It was found that NaClO2 exhibited superior Hg0 removal activity when both SO2 and NO were present in the flue gas, while the Hg0 removal efficiency reduced significantly in the absence of SO2 and/or NO. The Hg0 removal activity of NaClO2 decreased significantly with the increase of pH value. The slurry temperature had no obvious effect on Hg0 removal activity, while higher temperature could enhance the Hg0 re-emission at a later stage. However, the presence of Cl– in limestone slurry could notably inhibit the Hg0 re-emission. The characterization results showed that the presence of SO2 and NO promoted the formation of HgCl2, Hg­(NO3)2, and HgSO4, thus significantly enhancing the Hg0 removal activity of NaClO2 in limestone slurry.

Synergetic NOx Removal and Hg0 Oxidation over V2O5–WO3/TiO2 Catalysts in a Simulated Fast SCR Atmosphere: Catalytic Performance and Hg0 Oxidation Mechanism

“…36,39 Our previous study also found that the chemisorbed oxygen species was responsible for Hg 0 oxidation. 32,40 However, the O α ratio increased when the catalyst was pretreated in the presence of NO. This might be because the gaseous NO could adsorb on the catalyst surface to form adsorbed NO or other substance containing O species, thus increasing the chemisorbed oxygen species.…”

Oxidation Absorption of Hg0 in the Gas Phase Using a Double Catalyzers–Double Oxidants Coactivation Technology

“…In the past ten years, multifarious wet free-radical AOTs, which mainly comprises photochemical oxidation, electrochemical oxidation, metal ion-activated peroxide oxidation, thermal activation peroxide oxidation, metal oxide-activated peroxide oxidation, and so forth have been developed widely for oxidizing Hg 0 in flue gas. − Among these potential candidates, these Fenton oxidation technique demonstrates a good development and industrial application prospect due to a simpler system and smaller device requirement. ,, However, the traditional Fenton oxidation technique has low yield in free radicals owing to a low Fe 2+ /Fe 3+ cycle rate, severe side reactions, and low utilization rate in free radicals, thereby causing low pollutant treatment capacity and high reagent consumption cost. ,− Thus, exploring a new, simple, and effective method to improve these shortcomings in the traditional Fenton activation system is highly desired in this area.…”