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Título: Reduction of mercury(II) by tropical river humic substances (Rio Negro) - Part II Influence of structural features (molecular size, aromaticity, phonolic groups, organically bound sulfur).
Autor(es): Julio Cesar Rocha
Ézio Sargentini Junior
Luiz Fabricio Zara
André Henrique Rosa
Ademir dos Santos
Peter Burba
Assunto: substâncias húmicas aquáticas
ISSN: 0039-9140
Revista: Talanta (Oxford)
Resumo: The influence of structural features of tropical river humic substances (HS) on their capability to reduce mercury(II) in aqueous solutions was studied. The HS investigated were conventionally isolated from Rio Negro water-Amazonas State/Brazil by means of the collector XAD 8. In addition, the isolated HS were on-line fractionated by tangential-flow multistage ultrafiltration (nominal molecular-weight cut-offs: 100, 50, 30, 10, 5 kDa) and characterized by potentiometry and UV/VIS spectroscopy. The reduction of Hg(II) ions to elemental Hg by size-fractions of Rio Negro HS was assessed by cold-vapor AAS (CVAAS). UV/VIS spectrometry revealed that the fractions of high molecular-size (F(1)>100 kDa and F(2): 50-100 kDa) have a higher aromaticity compared to the fractions of small molecular-size (F(5): 5-10 kDa, F(6): <5 kDa). In contrast, the potentiometric study showed different concentration of functional groups in the studied HS fractions. The reduction of Hg(II) by aquatic HS fractions at pH 5 proceeded in two steps (I, II) of slow first order kinetics (t(1/2) of I: 160 min, t(1/2) of II: 300 min) weakly influenced by the molecular-size, in contrast to the differing degree of Hg(II) reduction (F(5)>F(2)>>F(1)>F(3)>F(4)>>F(6)). Accordingly, Hg(II) ions were preferably reduced by HS molecules having a relatively high ratio of phenolic/carboxylic groups and a small concentration of sulfur. From these results a complex 'competition' between reduction and complexation of mercury(II) by aquatic HS occurring in tropical rivers such as the Rio Negro can be suggested.
ISSN: 0039-9140
Local de publicação: Estados Unidos
Aparece nas coleções:Coordenação de Dinâmica Ambiental (CDAM)

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