Ferrate Oxidation of Phenolic Compounds in Iodine-Containing Water: Control of Iodinated Aromatic Products

Abstract

Highly toxic iodinated products would form in oxidation and disinfection of iodine-containing water. Variation of iodinated aromatic products in ferrate [Fe­(VI)] oxidation of phenolic compounds (phenol, bisphenol A (BPA), and p-hydroxybenzoic acid (p-HBA)) in iodine-containing water was investigated. At pH 5.0, oxidation of phenolic compounds was inhibited by competitive reaction of ferrate with I–, and no formation of iodinated aromatic products was detected. Almost all I– was converted into nontoxic IO3 –. At pH 7.0, 8.0, and 9.0, HOI formed in ferrate oxidation of I– and further reacted with phenols, with the formation of iodinated aromatic products. Mass spectrometry analysis showed that both kinds and contents of iodinated aromatic products were raised with the increase in solution pH and the content of I–, and these iodinated aromatic products were further oxidized by ferrate. Ferrate deprived iodine from iodinated aromatic products and transferred highly toxic organic iodine into nontoxic IO3 –. An electron-donating substituent (alkyl) increased the reactivity of phenol with ferrate and HOI and facilitated ferrate oxidation of iodinated phenols. An electron-drawing substituent (carboxyl) decreased the reactivity of phenol with ferrate and HOI and hindered the further oxidation of iodinated aromatic products. A kinetic model about the variation of phenol, BPA, and p-HBA in reaction with ferrate in iodine-containing water was developed, and the oxidation profile of phenolic compounds could be satisfactorily predicted at various iodide concentrations.

Application of Fe(VI) in abating contaminants in water: State of art and knowledge gaps

“…pH (Wang et al, 2020). This was because the reactivity of Fe(VI) with HOI decreased with the increasing pH while the reactivity of HOI with BPA increased with elevating pH (Wang et al, 2020).…”

“…Fe (VI) can oxidize iodide (I -) to the highly reactive hypoiodous acid (HOI) through 2etransfer, which can be transformed to iodate (IO 3 -) swiftly by disproportionation or further oxidation by Fe(VI) (Shin et al, 2018). Unlike other commonly used oxidants such as O 3 , NH 2 Cl, KMnO 4 , and HOCl, the second-order rate constant of Fe (VI) with HOI (k app[Fe(VI)-HOI] = 1.03 Â 10 5 M -1 $s -1 at pH 7.2) is higher than that of Fe(VI) with I -(k app[Fe(VI)-I -]~2 .0 Â 10 4 M -1 $s -1 at pH 7.0) (Kralchevska et al, 2016b;Wang et al, 2018a;Wang et al, 2020). Therefore, the accumulation of the highly reactive HOI and the associated I-DBPs can be well inhibited (Wang et al, 2018a).…”

“…might increase the possibility of forming I-DBPs in iodine-containing water (Wang et al, 2020). Therefore, the potential of forming halogenated byproducts in real practice might be underestimated if phosphate is used as buffer.…”

“…The newly formed halogenated byproducts might be more toxic than the parent compounds. Therefore, if Fe(VI) is not enough to further degrade these halogenated byproducts and stabilize the inorganic halogen intermediates, the newly formed halogenated byproducts would pose a serious threat to the public health (Wang et al, 2020).…”

“…pH (Wang et al, 2020). This was because the reactivity of Fe(VI) with HOI decreased with the increasing pH while the reactivity of HOI with BPA increased with elevating pH (Wang et al, 2020). Furthermore, the newly formed iodinated byproducts could not be completely decomposed by Fe(VI) within a short time scale due to the low oxidation ability of Fe(VI) at high pH.…”