Ferrates(FeVI, FeV, and FeIV) oxidation of iodide: Formation of triiodide

Abstract

The presence of iodide (I(-)) in water during disinfection and oxidative treatment of water is a potential health concern because of the formation of iodinated disinfection by-products (DBPs), which may be more toxic than chlorinated DBPs. The kinetics of the oxidation of I(-) by a greener oxidant, ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) was determined as a function of pH. The second-order rate constants (k, M(-1) s(-1)) decreased from 3.9 × 10(4) M(-1) s(-1) at pH 5.0 to 1.2 × 10(1) M(-1) s(-1) at pH 10.3. The kinetics results could be described by the reactivity of monoprotonated species of Fe(VI) (HFe(VI)O4(-)) with I(-). In excess I(-) concentration, triiodide (I3(-)) was formed and the stoichiometry of ∼1:1 ([Fe(VI)]:[I3(-)]) was found in both acidic and basic pH. Ferrate(V) (Fe(V)O4(3-), Fe(V)) and ferrate(IV) (Fe(VI)O4(4-), Fe(IV)) also showed the formation of I3(-) in presence of excess I(-). A mechanism of the formation of I3(-) is proposed, which is consistent with the observed stoichiometry of 1:1. The oxidative treatment of I(-) in water will be rapid (t1/2 = 0.6 s at pH 7.0 using 10 mg L(-1) K2FeO4). The implications of the results and their comparison with the oxidation of I(-) by conventional disinfectants/oxidants in water treatment are briefly discussed.

Accelerated Oxidation of Organic Contaminants by Ferrate(VI): The Overlooked Role of Reducing Additives

“…A formation of I 3 − in the reaction of Fe VI with I– has been observed, which produced through initial one-electron transfer step (Fe VI + I − → Fe V + I • ) (SI Text S1). (20) The generated Fe V may react with TMP to enhance the oxidation of TMP. However, a recent study proposed oxygen-atom transfer step that gave Fe IV species in initial step (Fe VI + I − → Fe IV + HOI/OI − ) (SI Text S1).…”

“…This paper presents a systematic innovative strategy to tune the chemistry of Fe VI by selectively adding one-electron (S(IV)) and two-electron (or oxygen-atom transfer) reducing agents (hydroxylamine (NH 2 OH), arsenite (AsO 3 3− ), selenite (SeO 3 2− ), phosphite (PO 3 3− ), nitrite (NO 2 − ), iodide (I − ), and thiosulfate (S 2 O 3 2− )) (see Supporting Information (SI) Text S1)(20–25) that initially generate the short-lived Fe V and Fe IV species, respectively (i.e., R (1) (i.e., Fe VI → Fe V ),(26) and R (2) (i.e., Fe VI → Fe IV )). (27) Fe V and Fe IV have 2–5 orders of reactivity higher than that of Fe VI with reactivity order of Fe V > Fe IV > Fe VI .…”

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

“…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).…”

“…species accompanied with the formation of I 2 , both of which may react with residue organics yielding I-DBPs (Kralchevska et al, 2016b;Wang et al, 2018a). The reaction between Fe(VI) and Ican be presented by Eq.…”

Study of the oxidation kinetics of nitrite ions by potassium ferrate(VI)

“…The products, nitrate ion and molecular oxygen, were determined as a function of original solution composition. A set of six reactions at pH 9.3 with initial nitrite concentration of 3.3 mM and initial ferrate(VI) concentrations from 0.12-0.27 mM resulted in an average amount of nitrate produced being 59.7±1.2 %, the theoretical amount based on ferrate based on equation (4) and the average amount of oxygen corresponding to 46.9±3.8 %, the amount of ferrate based on equation (5). Moles of nitrite which disappears and moles of nitrate formed in the reaction were shown by ion chromatography to be equal and to increase and approach a limiting value of ca.…”