Development of the fluorescent lamp crushing unit for mercury removal

Abstract

This research aimed to develop a prototype of the fluorescent lamp crushing unit with mercury emission control. The used fluorescent lamp has been classified as hazardous waste containing mercury which is a persistent and bio accumulative toxin. Mercury vapor could be released into the atmosphere and other forms of mercury in the lamp residue could be leached into environments when a fluorescent lamp is broken or crushed. Mercury emission control was made by spraying sodium sulfide on the crushed lamp and stabilizing/solidifying with cement of the mercury containing lamp residue. The crushing unit was constructed as the drum of 230 liters equipped with the auger blade crusher and the feeder chute on the top. This crushing unit could accommodate for a total number of 1,300-1,400 tubes with the crushing rate at 4-6 of 4-ft lamps per minute. Firstly, the mercury content of the vapor, lamp residue were determined by crushing the lamp without sodium sulfide spraying. Averagely, the volume of each fluorescent lamp after crushing could be decreased to approximately 80 percent. The concentrations of mercury vapor emitted from the crushed lamp were in the range of 1.26 to 8.22 mg/m3. The average mercury concentration of lamp residue was 26 pg/g of lamp residue. Then, the average mercury content could be calculated as 5.1 mg per lamp of 1-inch diameter size. The mercury concentrations leached from lamp residue were in range of 18-78 µg/l. The experiments were set up for emission control by spraying with sodium sulfide after crushing the lamps. The results revealed that the amount of mercury vapor could be reduced by 77.4-97.3 percent. With the leachability tests, the results indicated that the mercury from the solidified lamp residues with all studied ratios of waste/cement (0.5, 0.75, and 1.00) met the criterion for leachate extraction procedure.