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Revista Brasileira de Ciência do Solo

versão On-line ISSN 1806-9657

Resumo

BALDOTTO, Marihus Altoé et al. Redox properties and functional groups of humic acids isolated from organic residues. Rev. Bras. Ciênc. Solo [online]. 2007, vol.31, n.3, pp.465-475. ISSN 1806-9657.  http://dx.doi.org/10.1590/S0100-06832007000300006.

According to the system conditions, humic acids act as oxidants or as reductants. In natural systems the electron flow is directly associated with humus content and quality. Electrode potential and oxidation capacity inform about the intensity and capacity of the redox systems. In previous studies it has been assumed that free radicals participate in humic acid redox reactions. In our study six humic acids isolated from composed organic residues were titrated with an oxidant (I2) in inert atmosphere and specified conditions. Humic acids presented similar standard formal electrode potentials, with values between 0.773 and 0.794 V, at 25 ºC. The oxidation capacity of humic acids varied from 3.88 to 4.39 molc kg-1 at pH 5.0 and from 5.35 to 7.89 molc kg-1 at pH 7.0. Positive and significant correlations were observed between the oxidation capacity and the concentrations of the phenolic, quinone and semiquinone functional groups in the humic acids.

Palavras-chave : soil chemistry; humic substances; redox potential; oxidation capacity; humification.

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