Removal and recovery of mercury from used fluorescent lamp glass by pyrolysis

Abstract

Recovering mercury in metallic form from used fluorescent lamps is important for environmental safety and for its re-use in industry. Presently, pyrolysis has become a widely used thermal treatment technology for various wastes. Since it is performed under anaerobic conditions, the toxic metals are not oxidized and this minimizes their leaching from the treated material. This technology also reduces the risk of formation of toxic chloro-organic compounds such as dioxins. Therefore, in the study reported in this paper, pyrolysis was applied for the treatment of used fluorescent lamp glass, with special emphasis on mercury removal and recovery in metallic form. A laboratory scale pyrolyser was used for all the experiments. Pyrolysis was conducted at different temperatures using nitrogen as the carrier gas. A cold trap was attached to condense and recover metallic mercury from the flue gas. Results showed that a temperature of 600 oC is sufficient to achieve nearly 100% mercury removal. Around 20% of metallic mercury was recovered in the cold trap. The rest were trapped in the activated carbon filter and acid trap, showing that the process is able to completely prevent release of mercury to the environment.