Elemental mercury removal by a novel advanced oxidation process of ultraviolet/chlorite-ammonia: Mechanism and kinetics.
JOURNAL OF HAZARDOUS MATERIALS 2019;
374:120-128. [PMID:
30986639 DOI:
10.1016/j.jhazmat.2019.03.134]
[Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Revised: 03/29/2019] [Accepted: 03/30/2019] [Indexed: 05/21/2023]
Abstract
A novel advanced oxidation process (AOP) of ultraviolet/chlorite-ammonia (UV/NaClO2-NH4OH) was developed to remove Hg0 from flue gas. The distribution of mercury concentration in three solutions of NaClO2-NH4OH, KCl, and H2SO4-KMnO4 was determined by cold atom fluorescence spectrometry (AFS). The role of NH4OH was to help NaClO2 preserving and/or stabilizing Hg2+ meanwhile inhibiting the photo-production of ClO2. In the absence of UV, decreasing pH promoted the release of Hg2+ from NaClO2-NH4OH; introducing NO, SO2, O2, Br-, Cl-, and HCO3- suppressed Hg0 oxidation. In the presence of UV, rising temperature accelerated the release of Hg2+ from NaClO2-NH4OH; while SO2, Br- and HCO3- facilitated Hg0 oxidation. In the absence and presence of UV, Hg0 oxidation was controlled by ClO2- and by ClO/Cl2O2/HO/ClO2, respectively. The formations of ClO/HO/ClO2 were confirmed by electron spin resonance (ESR). X-ray photoelectron spectroscopy (XPS) revealed that the products of Hg0 and ClO2- were HgCl2, and ClO2, Cl-, ClO3-, Cl2, and ClO4-, respectively. Analysis of kinetics showed that the Hatta numbers were 23-133 and 69-305 without and with UV, respectively, thus, the gas-film mass transfer was the rate-determining step. This paper gives a new insight in radical behavior in Hg0 oxidation.
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