Kinetic and Mechanistic Aspects of the Reactions of Iodide and Hypoiodous Acid with Permanganate: Oxidation and Disproportionation.

Environmental science & technology

PubMedID: 27003721

Zhao X, Salhi E, Liu H, Ma J, von Gunten U. Kinetic and Mechanistic Aspects of the Reactions of Iodide and Hypoiodous Acid with Permanganate: Oxidation and Disproportionation. Environ Sci Technol. 2016;.
Oxidation kinetics of iodide and HOI/OI(-) by permanganate were studied in the pH range of 5. 0-10. 0. Iodide oxidation and iodate formation were faster at lower pH. The apparent second-order rate constants (kobs) for iodide oxidation by permanganate decrease with increasing pH from 29 M(-1) s(-1) at pH 5. 0 and 6. 9 M(-1) s(-1) at pH 7. 0 to 2. 7 M(-1) s(-1) at pH 10. 0. kobs for HOI abatement are 56 M(-1) s(-1) at pH 5. 0, 2. 5 M(-1) s(-1) at pH 7. 0, and 173 M(-1) s(-1) at pH 10. 0. Iodate yields over HOI abatement decrease from 98% at pH 6. 0 to 33% for pH = 9. 5, demonstrating that HOI disproportionation dominates HOI transformation by permanganate at pH = 8. 0. MnO2 formed as a product from permanganate reduction, oxidizes HOI to iodate for pH < 8. 0, and promotes HOI disproportionation for pH = 8. 0. The rate of HOI oxidation or disproportionation induced by MnO2 is much lower than for permanganate. During treatment of iodide-containing waters, the potential for iodinated disinfection byproducts (I-DBPs) formation is highest at pH 7. 0-8. 0 due to the long lifetime of HOI. For pH < 6. 0, HOI/I2 is quickly oxidized by permanganate to iodate, whereas for pH = 8. 0, HOI/OI(-) undergoes a fast permanganate-mediated disproportionation.