Formation of iodinated organic compounds by oxidation of iodide-containing waters with Manganese Dioxide

Abstract

This study shows that iodinated organic compounds can be produced when iodide-containing waters are in contact with manganese oxide birnessite (d-MnO2) in the pH range of 5-7. In the absence of natural organic matter (NOM), iodide is oxidized to iodate that is also adsorbed onto d-MnO2. In thepresence of iodide and NOM, adsordable organic iodine compounds (AOI) are formed at pH<7 because of the oxidation of iodide to iodine by d-MnO2 and the reactions of iodine with NOM. In addition, iodoacetic acid and iodoform have been identified as specific iodinated byproducts. Formation ofiodoform is not observed for high NOM/d-MnO2 ratios due to inhibition of the catalytic effect of d-MnO2 by NOM poisoning. Experiments with model compounds such as resorcinol and 3,5- heptanedione confirmed that the d-MnO2/I- system is very effective for the formation of iodinated organic compounds.These results suggest that birnessite acts as a catalyst through the oxidation of iodide to iodine and the polarization of the iodine molecule, which then reacts with NOM moieties.