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Fe(II) oxidation kinetics were studied in seawater and in seawater enriched with exudates excreted by Phaeodactylum tricornutum as an organic ligand model. The exudates produced after 2, 4, and 8 days of culture at 6.21 × 107, 2.29 × 108, and 4.98 × 108 cell L–1 were selected. The effects of pH (7.2–8.2), temperature (5–35 oC), and salinity (10–36.72) on the Fe(II) oxidation rate were studied. All the data were compared with the results for seawater without exudates (control). The Fe(II) rate constant decreased as a function of culture time and cell concentration in the culture at different pH, temperature, and salinity. All the experimental data obtained in this study were fitted to a polynomial function in order to quantify the fractional contribution of the organic exudates from the diatoms to the Fe(II) oxidation rate in natural seawater. Experimental results showed that the organic exudates excreted by P. tricornutum affect Fe(II) oxidation, increasing the lifetime of Fe(II) in seawater. A kinetic model approach was carried out to account for the speciation of each Fe(II) type together with its contribution to the overall rate.   Se estudio la cinetica de oxidacion del Fe(II) en agua de mar y en agua de mar enriquecida con exudados excretados por Phaeodactylum tricornutum como modelo de ligando organico. Se seleccionaron los exudados producidos despues de 2, 4 y 8 dias de cultivo, correspondientes a 6.21 × 107, 2.29 × 108 y 4.98 × 108 celulas L–1. Se estudio el efecto del pH (7.2–8.2), la temperatura (5–35 oC) y la salinidad (10–36.72) en la velocidad de oxidacion del Fe(II). Todos los datos se compararon con los resultados obtenidos en agua de mar sin exudados (control). La constante de velocidad de oxidacion del Fe(II) disminuyo en funcion del tiempo de cultivo y la concentracion de celulas a diferentes valores de pH, temperatura y salinidad. Todos los datos experimentales obtenidos en este estudio se ajustaron a una funcion polinomica con el objetivo de cuantificar la contribucion parcial de los exudados organicos de diatomeas a la velocidad de oxidacion del Fe(II) en agua de mar. Los resultados experimentales mostraron que los exudados organicos excretados por P. tricornutum afectan a la oxidacion del Fe(II) incrementando su tiempo de vida media en agua de mar. Se aplico un modelo cinetico para calcular la especiacion de Fe(II) y la contribucion de cada especie a la velocidad total del proceso de oxidacion.

Effect of organic exudates of Phaeodactylum tricornutum on the Fe(II) oxidation rate constant