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 Hg 0 into methylmercury (CH 3 Hg + ), the most toxic form of mercury CH 3 Hg + 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 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 HgCl 2 or Hg 2 Cl 2 Particulate bound mercury, Hg p Elemental mercury, Hg 0 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 Hg 0 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 Hg 0 even further improving removal