Mercury vapor release from broken compact fluorescent lamps and in situ capture by new nanomaterial sorbents

Abstract

The projected increase in the use of compact fluorescent lamps (CFLs) motivates the development of methods to manage consumer exposure to mercury and its environmental release at the end of lamp life. This work characterizes the time-resolved release of mercury vapor from broken CFLs and from underlying substrates after removal of glass fragments to simulate cleanup. In new lamps, mercury vapor is released gradually in amounts that reach 1.3 mg or 30% of the total lamp inventory after four days. Similar time profiles but smaller amounts are released from spent lamps or from underlying substrates. Nanoscale formulations of S, Se, Cu, Ni, Zn, Ag, and WS2 are evaluated for capture of Hg vapor under these conditions and compared to conventional microscale formulations. Adsorption capacities range over 7 orders of magnitude, from 0.005 (Zn micropowder) to 188 000 microg/g (unstabilized nano-Se), depending on sorbent chemistry and particle size. Nanosynthesis offers clear advantages for most sorbent chemistries. Unstabilized nano-selenium in two forms (dry powder and impregnated cloth) was successfully used in a proof-of-principle test for the in situ, real-time suppression of Hg vapor escape following CFL fracture.

Figure 1

Mercury vapor release characteristics for two brands of compact fluorescent lamps following catastrophic fracture at room temperature. A: Hg-vapor concentrations and release rates in a 2 L PTFE enclosure purged with a 1 L/min flow. For comparison, the plot shows the evaporation rate from a free Hg° drop corrected for differences in the Hg mass between the drop and the bulb for two limiting cases: convective mass transfer at constant mass transfer coefficient (rate ≈ area ≈ mass^2/3) and diffusion dominated mass transfer from a drop (rate ≈ K × area ≈ mass^1/3). B: Mercury evaporation rate as a function of gas flow rate over the broken lamp showing a weak influence of convection.

Figure 2

Standard Hg adsorption capacities for elemental sulfur nanotubes and conventional sulfur powder as a function of adsorption reaction temperature. Image is SEM micrograph of template S-nanotubes.

Figure 3

Synthesis, particle size distributions, and Hg-uptake kinetics of competing forms of selenium. A: Colloidal synthesis of BSA-stabilized (left) and unstabilized (right) nano-Se. B: Particle-size distributions in aqueous media by dynamic light scattering (44). C: Hg-uptake kinetics under standard conditions (60 μg/m³).

Figure 4

Comparison of the sorbents in this study. Left axis: Standard Hg adsorption capacity. Right axis: Amount of sorbent required for capture of 1 mg of Hg vapor typical of the total release from a single CFL over a three-day period.

Figure 5

Effect of sorbents applied in situ on mercury vapor release following catastrophic fracture of a CFL at room temperature. Top curve: No sorbent. Bottom curves: Same CFL broken in presence of sulfur-impregnated activated carbon (1 g of HgR) and unstabilized nano-selenium (10 mg) either as dry nanopowder or impregnated cloth. The integrated mercury released over the course of this experiment is 113 (untreated lamp), 20 (1 g of HgR treatment), 1.6 (Se in vials), and 1.2 μg (Se-impregnated cloth).