The oxidation of Fe(II) has been studied as a function of pH (5 to 9), temperature (5 to 45°C), and salinity (0 to 35). The pseudo-first-order rate constant, k1, -d[Fe(II)] dt = k1[Fe(II)] in water and seawater was found to be a second degree function of pH over the pH range of 7.5 to 8.5 at 5°C and 6.0 to 8.0 at 25°C. The overall rate constant (k) -d[Fe(II)] dt = k[Fe(II)][O2][OH-]2 was determined from 5 to 45°C and S = 0 to 35. The results have been fit to an equation of the form (T = 273.15 + t°C) log k = log k0 - 3.29I 1 2 + 1.52I where log k0 = 21.56-1545/T with a standard error = 0.09. The energy of activation for the overall rate constant in water and seawater was 29 ± 2 kJ mol-1. The values of the rate constant for pure water (k0) are in good agreement with literature data. The half times for seawater from some previous studies at a pH = 8.0 were slower than our results for Gulf Stream waters. Measurements on Biscayne Bay waters also yield slower half times apparently due to the presence of organic ligands that can complex Fe(II).
ASJC Scopus subject areas
- Geochemistry and Petrology