Transformation of iodide by Fe(II) activated peroxydisulfate

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 center dot- 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 IO(3)(-)is favored by lower pH and higher temperature, due to the greater SO4 center dot- production by the reaction of Fe(II) with PDS under these conditions. Humic acid, as a representative natural organic matter, scavenges the formed HOT 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.