INTRODUCTION
U.S. Environemental Protection Agency (EPA) investigation into health risks associated with
mercury emissions from utility steam generators, municipal waste combustion units, and other
sources was mandated by the Clean Air Act Amendments (CAAA) of 1990. In anticipation of
mercury emission regulation, attention has been focused on quantification of mercury emissions,
which require verifiable sampling and analytical techniques. Several sampling and analytical
methods are currently under the final stages of development as well as a variety of emission control
methods. In particular, wet scrubber systems designed for Sq control in coal-fired utilities have
been targeted for mercury control. Conventional wet-scrubbers remove mercury in a variety of
soluble oxidized forms. Oxidized mercury is highly water-soluble and can be removed by scrubber
slurry, theoretically limited only by gas-film mass transfer. However, since some oxidized mercury
forms such as HgC1, are both soluble and volatile, the final fate of mercury trapped in scrubber
solutions is unclear. Elemental mercury is not water-soluble, remaining in the vapor state at
temperatures through pollution control devices and exiting the stack into the environment.
However, notable exceptions to this rule exist. Depending on the type of mercury-sampling method
used, an increase of I 10% in elemental mercury concentrations across wet scrubbers has been
measured but is yet unconfirmed. Also, significant amounts of elemental mercury (metallic form)
have been removed during wet scrubber maintenance. In addition, questions concerning
1) the initial speciation between oxidized and elemental forms of mercury in flue gas from coal-
fired boilers and 2) the effects of scrubber slurry composition and pH on the mercury species have
been raised