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Mercury Pollution

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

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Mercury Pollution

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  1. Mercury Pollution Mark Bentley David Herr NSF April 2011

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

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