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Effect of Chloride and Sulfate Ions on the Photoreduction Rate of Ferric Ion in UV Reactor Equipped with a Low Pressure Mercury Lamp

Abstract This study aims to demonstrate the effects of pH and of inorganic anions on the photoreduction of Fe(III). Effective quantum yields for the production of •OH radicals from iron(III) hydroxo species in pechlorate medium and in the present of chloride and sulfate anions were determined in the pH range 1-3. Experiments were carried out in batch at 25°C with a low-pressure mercury vapor lamp emitted at 253.7 nm. The method was based on measuring the pseudo-first-order rate constant of the photoreduction of Fe(III)-complexes in which tert-butanol scavenged the •OH at an identical rate. The results showed that the apparent quantum yield of photoreduction of Fe(III) increased when the pH increases, the values passed from 0.063 at pH 1 to 0.1 at pH 3 ([Fe(III)]0 = 1 mM and 3 mM). The effects of Cl- or SO42- on the photoreduction of Fe(III) depended on pH and on ion concentrations. The apparent quantum yield values increased in the present of anion Cl-, whereas those values decreased in the present of anion SO42-. For the Photo Fenton system, the effects of Cl- or SO42- were found to depend on pH, on the concentrations of the inorganic anions and to decrease the rate of decomposition of H2O2.