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Title: Oxidation of iron (II) nanomolar with H2O2 in seawater
Authors: González-Davila, Melchor 
Santana-Casiano, J. Magdalena 
Millero, Frank J.
UNESCO Clasification: 251002 Oceanografía química
230331 Química del agua
Keywords: Seawater
Hydrogen-ion concentration
Issue Date: 2005
Project: Efecto de Los Compuestos Catecolatos, Hidroxamatos y Porfirinas en El Comportamiento Qwuimico de Fe(Ii) en El Medio Marino. 
Journal: Geochimica et Cosmochimica Acta 
Abstract: The oxidation of Fe(II) with H2O2 at nanomolar levels in seawater have been studied using an UV-Vis spectrophotometric system equipped with a long liquid waveguide capillary flow cell. The effect of pH (6.5 to 8.2), H2O2 (7.2 × 10−8 M to 5.2 × 10−7 M), HCO3− (2.05 mM to 4.05 mM) and Fe(II) (5 nM to 500 nM) as a function of temperature (3 to 35 °C) on the oxidation of Fe(II) are presented. The oxidation rate is linearly related to the pH with a slope of 0.89 ± 0.01 independent of the concentration of HCO3−. A kinetic model for the reaction has been developed to consider the interactions of Fe(II) with the major ions in seawater. The model has been used to examine the effect of pH, concentrations of Fe(II), H2O2 and HCO3− as a function of temperature. FeOH+ is the most important contributing species to the overall rate of oxidation from pH 6 to pH 8. At a pH higher than 8, the Fe(OH)2 and Fe(CO3)22− species contribute over 20% to the rates. Model results show that when the concentration of O2 is two orders of magnitude higher than the concentration of H2O2, the oxidation with O2 also needs to be considered. The rate constants for the five most kinetically active species (Fe2+, FeOH+, Fe(OH)2, FeCO3, Fe(CO3)22−) in seawater as a function of temperature have been determined. The kinetic model is also valid in pure water with different concentrations of HCO3− and the conditions found in fresh waters.
ISSN: 0016-7037
DOI: 10.1016/j.gca.2004.05.043
Source: Geochimica et Cosmochimica Acta [ISSN 0016-7037], v. 69, p. 83-93
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