(364c) Gas-Phase Oxidation of Elemental Mercury and the Effects of Aqueous-Phase Impinger Chemistry on Apparent Levels of Oxidation

Cauch, B., University of Utah
Silcox, G., University of Utah
Wendt, J. O. L., University of Utah

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 effects of quench
rate, NO, SO2, HCl, and the chemistry of the sample conditioning
system on apparent and actual levels of oxidation in a methane-fired (293 W or
1000 Btu/h), quartz-lined reactor.  The sample conditioning system included two
impingers in parallel: one containing an aqueous solution of KCl to trap HgCl2,
and one containing an aqueous solution of SnCl2 to reduce HgCl2
to elemental mercury (Hg0).  Gas-phase concentrations of Cl2
as low as 1.5 ppmv were sufficient to oxidize a significant fraction of the
elemental mercury in the KCl impinger via hypochlorite ion.  The addition of
0.5% sodium thiosulfate to the KCl solution completely prevented the impinger
oxidation from occurring.  The measured homogeneous mercury oxidation levels
with the sodium thiosulfate additive ranged from 2 to 8% at reactor chlorine
levels of 100 to 500 ppmv (as HCl).  This is in contrast to oxidation levels
approaching 95% in the absence of sodium thiosulfate.  Quench rates ranging
from 440 to 210 K/s had little effect on the extent of oxidation.  Extents of
oxidation were also insensitive to SO2 and NO at concentrations of
400 and 500 ppmv.  The addition of thiosulfate did not inhibit the KCl
impinger's ability to capture HgCl2 and the effectiveness was not
affected by NO or SO2