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Transformation of iodide by Fe(II) activated peroxydisulfate

Dong, Zijun, Jiang, Chengchun, Yang, Jingxin, Zhang, Xi, Dai, Weili, Cai, Pengwei
Journal of hazardous materials 2019 v.373 pp. 519-526
byproducts, disinfection, humic acids, iodates, iodine, iron, oxidation, pH, temperature
This work investigates the transformation of iodide (I−) by Fe(II)-activated peroxydisulfate (PDS). The transformation of I− into iodate (IO3−) is a two-step process, involving reactive iodine species, such as hypoiodous acid (HOI), as a key intermediate, and IO3− as the final product. In the first step, SO4•- produced by Fe(II)-activated PDS is mainly responsible for the transformation of I− into HOI. In the second step, Fe(IV) formed by the reaction of Fe(III) with PDS is required, to facilitate the further oxidation of HOI to IO3−. The disproportionation of HOI and the oxidation by PDS alone contribute negligibly to IO3− formation. The IO3− yield increases to a maximum, before decreasing gradually, with increased PDS and Fe(II) dosages. The transformation of I− into IO3− is favored by lower pH and higher temperature, due to the greater SO4•- production by the reaction of Fe(II) with PDS under these conditions. Humic acid, as a representative natural organic matter, scavenges the formed HOI to form iodinated disinfection byproducts, which largely inhibit the transformation of I− into IO3−. In addition, the transformation of I− into IO3− and iodinated disinfection byproducts by Fe(II) activated PDS was confirmed in the natural waters.