Air Oxidation of Aqueous Ferrous Sulfate Solution in the Alkaline Region

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The air oxidation of an aqueous FeSO4 solution was Studied in an alkaline region by blowing air from a horizontal nozzle into the solution. The pH value of the solution was maintained at ca. 10 by adding Na2CO3 in the solution. No catalytic action of Cu2+ ion was observed. The rate of oxidation was not virtually affected by the temperature, but increased with the rise of the flow rate of air. A zero order rate equation was found. From the presumption that the reaction is composed of the sequential steps of dissolution of gaseous oxygen at the surface of rising air bubbles and the oxidation of Fe2+ ion and Fe(OH)2 precipitate by the dissolved oxygen, it was revealed that the rate determining step of the overall reaction is the step of oxygen dissolution. From the rate constant of the rate equation, the liquid-film mass transfer coefficient of dissolved oxygen in the liquid boundary layer at the bubble surface was estimated, and it was fairly well coincident with the directly measured values. The rise of the rate of oxidation with the flow rate of air stream was interpreted in terms of the increase in the surface area of rising air bubbles.
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