Mercury Pollution
Mark Bentley
David Herr
NSF April 2011
Mercury Facts
• Very dense, silvery-white metal that is extremely
toxic
• Only metal that is liquid at room temperature
and pressure
• Used to be used thermometers and barometers
• Used currently today in fluorescent bulbs and
LCD screens
How mercury is released into the
environment
• The largest mercury emissions into the
atmosphere are from volcanoes,
accounting for half of the total global
emissions
• The next largest emission contributor is
from coal-fired power plants
• U.S. plants emit 48 tons of mercury
annually
What happens to mercury in the
environment?
• Mercury is released from the atmosphere
in rain and volcanic ash where it then
enters the water shed
• Bacteria then metabolize the Hg0 into
methylmercury (CH3Hg+), the most toxic
form of mercury
• CH3Hg+ then becomes concentrated in fish
and birds
Wildlife and Mercury
• Fish higher in the food chain, such as
sharks, swordfish, and tuna, have higher
concentrations of mercury than others
• Fish are not very efficient at purifying their
bodies, so they accumulate the mercury in
their bodies; This is known as
biomagnification
• This caused mercury poisoning in
Minamata, Japan; now called Minamata
disease
Efforts to Reduce Mercury
Emissions
• In March 2005, the EPA issued the Clean
Air Mercury Rule (CAMR) to cap mercury
emissions from power plants in two
phases
• The first phase lasts from 2010-2017 and
caps emissions at 38 tons per year
• The second phase will have a cap of 15
tons per year for 2018 and beyond
Mercury Removal Technology
• Mercury is mainly found as three species in flue gas
• Oxidized mercury, mainly in the form of HgCl2 or Hg2Cl2
• Particulate bound mercury, Hgp
• Elemental mercury, Hg0
• Oxidized mercury can currently be removed using flue
gas desulfurization units (FGDs) or electrostatic
precipitators (ESPs)
• Particulate bound mercury can be removed using fabric
filters (FFs)
• Elemental mercury is very challenging to remove
• Very high volatility
• Low solubility in water
Techniques of Hg0 Removal
• Current ideas are to oxidize the mercury and then
remove it in FGDs & ESPs or bind it to particulate matter
and remove it with FFs.
• A promising method is direct injection of solid adsorbent
into the flue gas
• Activated carbon (AC) has been historically known for its
excellent sorption qualities
• Modifying the surface of AC with anions can greatly
improve adsorption capacity
• This can simultaneously oxidize and bind the Hg0 even
further improving removal