Abstract
Aqueous Cr(VI) removal using Fe(II) was studied in a natural water as a function of temperature and pH, in kinetic batch experiments and also in a pilot and a full scale study. Temperature and pH strongly influenced the reduction of Cr(VI) by Fe(II). The reaction rate was increased by increasing pH in the range between 6 and 8 commonly encountered in natural waters. At 25°C and pH values higher than 7, maximum Cr(VI) removal was achieved at a reaction time equal or less than 5 min. The reaction followed a second order rate equation {–d[Cr(VI)]/dt = k obs[Cr(VI)] [Fe(II)][Cr(VI)]} with k obs [Cr(VI)] ≥ 1×104 M–1s–1. Reaction rate was also increased by increasing temperature from 10°C to 40°C, confirming the endothermic character of the reaction. Dissolved oxygen strongly competed with Cr(VI) in Fe(II) oxidation and batch experiments showed an increase of the reaction ratio [Fe(II)]/[Cr(VI)] from the almost stoichiometric value 3.1 at pH 6 to 25 at pH 8. These reaction ratio values were also verified by the...
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