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 (IO 3 − ) is a two-step process, involving reactive iodine species, such as hypoiodous acid (HOI), as a key intermediate, and IO 3 − as the final product. In the first step, SO 4 •- 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 IO 3 − . The disproportionation of HOI and the oxidation by PDS alone contribute negligibly to IO 3 − formation. The IO 3 − 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 SO 4 •- 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 IO 3 − . In addition, the transformation of I − into IO 3 − and iodinated disinfection byproducts by Fe(II) activated PDS was confirmed in the natural waters.