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

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.