Mercury speciation in urban landfill leachate by cold vapor generation atomic absorption spectrometry using ion exchange and amalgamation

Abstract

Foi desenvolvido um sistema em linha para a especiação de Hg orgânico (Hg org ) e Hg inorgânico (Hg inorg ) em chorume. Clorocomplexos produzidos a partir do Hg inorg são separados em uma coluna trocadora de ânions. O Hg retido na coluna é eluído com NaBH 4 na presença de HCl. O Hg 0 produzido é medido por espectrometria de absorção atômica com geração de vapor frio (CV AAS). O Hg org , que não fica retido na coluna, é misturado com NaBH 4 produzindo espécies voláteis de Hg, as quais são amalgamadas numa rede de Au/Pt. O Hg é removido desta coluna por aquecimento a 600 °C e medido por CV AAS. Para a especiação de Hg inorg e Hg org em chorume, as amostras são centrifugadas, filtradas e tratadas com HCl. Os limites de detecção (3 s) são 9 e 12 ng L -1 de Hg para Hg inorg e Hg org , respectivamente. A freqüência de análise é 22 h -1 .This work deals with on line speciation of organic Hg (Hg org ) and inorganic Hg (Hg inorg ) in urban landfill leachate. Chlorocomplexes of Hg inorg are produced in HCl medium and retained on an anion exchange column. The retained Hg is eluted with NaBH 4 in presence of HCl. Hg 0 is produced and then measured by cold vapor atomic absorption spectrometry (CV AAS). Hg org does not interact with the resin and is mixed with NaBH 4 at the exit of the column producing volatile species of Hg that are then amalgamated by a gauze of Au/Pt. Mercury is removed from the gauze by heating to 600 °C and subsequently measured by CV AAS. For Hg inorg and Hg org speciation in urban landfill leachate, the samples are centrifuged, filtered and treated with HCl. The detection limits (3 s) of Hg inorg and Hg org are 9 and 12 ng L -1 of Hg, respectively. The analysis frequency is 22 h -1 .Keywords: mercury speciation, landfill leachate; flow analysis, ion exchange, amalgamation, CVG AAS IntroductionIn several countries, the urban waste is usually discarded in landfills, producing toxic leachate and toxic gases. The rainwater percolation through the residues and its inherent aqueous fraction comprise the leachate, which is characterized by high concentration of organic matter, salts, suspended particles and toxic elements. 1,2 Mercury is one of the elements often present in landfill leachate and become an environmental problem. 3 Inorganic Hg (Hg inorg ), mainly as Hg 0 and Hg 2+ , is generally disposed in urban landfills, 4 where it can associate to colloidal particles, complex with organic matter and/or bind to sulfides. 5 Under anaerobic conditions a significant fraction of Hg is transformed into more toxic species. Inorganic mercury may be transformed to other toxic species in landfill, such as methyl mercury, ethyl mercury and phenyl mercury. 6 However, the concentrations of ethyl mercury and phenyl mercury are very low and usually not detected by conventional techniques. Despite the possibility of formation of many organic and inorganic compounds of Hg in the environment, methyl mercury is usually the most abundant Hg org species found in environmental samples, [7][8][9] whereas Hg 2+ is the main Hg ino...

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