Monday, November 5, 2007

The Characterization and Capture of Mercury from Broken Fluorescent Light Bulbs

Natalie C. Johnson, Chemical Engineering, Brown University, Box 2002, Brown University, Providence, RI 02912 and Robert H. Hurt, Engineering Division, Brown University, 182 Hope street, Providence, RI 02912.

In 2004, approximately 514 million mercury-containing lamps entered the solid waste stream, leaking as much as 2-4 metric tons of mercury into the environment either as a vapor or dissolved in groundwater. This study seeks to understand the evaporation behavior of mercury from broken, unused compact fluorescent bulbs (CFL's), and to engineer a solution to permanently capture the released mercury. The release was characterized by placing a CFL (made by n:vison, containing 5 mg of mercury) in a flow system and analyzing the nitrogen coming out of the bulb-containing chamber. It was found that nitrogen flow rate over the broken bulb had little effect on the evaporation rate, implying that evaporation is limited by some internal resistance. A commercial sulfur-impregnated activated carbon (HgR) shows promise as an effective sorbent, with a mercury capacity as high as 13 weight percent in a saturated environment. Breaking a single CFL in the presence of 1 gram of HgR and sealing the system in a Teflon bag for 24 hours reduces the initial mercury release rate by a factor of 10, and reduces the evaporation rate 10 hours after atmospheric exposure by 73%.