Confounding Effects of Aqueous-Phase Impinger Chemistry on Apparent Oxidation of Mercury in Flue Gases

Brydger Cauch, Geoffrey D. Silcox, JoAnn S. Lighty, Jost O.L. Wendt, Andrew Fry, Constance L. Senior

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

Gas- phase  reactions between elemental  mercury  and chlorine are a possible pathway to producing oxidized  mercury  species such as  mercuric  chloride in combustion systems. This study examines the effect of the  chemistry  of a commonly used sample conditioning system on  apparent  and actual levels of  mercury   oxidation  in a methane-fired, 0.3 kW, quartz-lined reactor in which gas composition (HCl, Cl<sub> 2</sub> , NO<sub> X</sub> , SO<sub> 2</sub> ) and quench rate were varied. The sample conditioning system included two impingers in parallel: one containing an  aqueous  solution of KCl to trap HgCl<sub> 2</sub> , and one containing an  aqueous  solution of SnCl<sub> 2</sub>  to reduce HgCl<sub> 2</sub>  to elemental  mercury  (Hg<sup> 0</sup> ). Gas- phase  concentrations of Cl<sub> 2</sub> as low as 1.5 ppmv were sufficient to oxidize a significant fraction of the elemental  mercury  in the KCl  impinger  via the hypochlorite ion. Furthermore, these low, but interfering levels of Cl<sub> 2</sub> appeared to persist in  flue   gases  from several doped rapidly mixed flames with varied post flame temperature quench rates. The addition of 0.5 wt% sodium thiosulfate to the KCl solution completely prevented the  oxidation  from occurring in the  impinger . The addition of thiosulfate did not inhibit the KCl  impinger’s  ability to capture HgCl<sub> 2</sub> . The effectiveness of the thiosulfate was unchanged by NO or SO<sub> 2</sub> . These results bring into question laboratory scale experimental data on  mercury   oxidation  where wet  chemistry was used to partition metallic and oxidized  mercury  without the presence of sufficient levels of SO<sub> 2</sub> .
Original languageAmerican English
JournalEnvironmental Science & Technology
Volume42
Issue number7
DOIs
StatePublished - 1 Apr 2008
Externally publishedYes

EGS Disciplines

  • Chemical Engineering

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