Reduction of Lead Oxide (PbO₂) by Iodide and Formation of Iodoform in the PbO₂/I⁻/NOM System

Abstract

Lead oxide (PbO2) can be an important form of lead mineral scale occurring in some water distribution systems. It is believed to be formed by the oxidation of lead-containing plumbing materials by free chlorine. Its reactivity in water, however, has not been well studied. Iodide is also found in source drinking waters, albeit at low concentrations. Consideration of thermodynamics suggests that iodide can be oxidized by PbO2. In this investigation, iodide ion was used as a probe compound to study the reduction of PbO2 and the formation of iodoform, which has been predicted to be a carcinogen, in the presence of natural organic matter (NOM). The reduction of PbO2 by iodide can be expressed as PbO2 + 31(-) + 4H+ --> Pb(2+) + I3(-) + 2H2O, and the reaction kinetics has been determined in this study. In the presence of NOM, I3- reacts with NOM to form iodoform and its concentration is proportional to the NOM concentration. Our results indicate that PbO2 is a very powerful oxidant and can possibly serve as an oxidant reservoir for the formation of iodinated disinfection byproduct through a novel reaction pathway.

The kinetics of iodide oxidation by the manganese oxide mineral birnessite

“…Anschutz et al (2000) proposed manganese oxides (MnO 2 ) and nitrate as possible electron acceptors in the oxidation of iodide to iodine and/or iodate based on the observed coupling of N, Mn, and I redox cycles in marine sediments. Lin et al (2008) also demonstrated that I À may be oxidized by lead oxide (PbO 2 ) in Pb-containing systems. From Fig.…”

Formation of iodinated disinfection by-products during oxidation of iodide-containing water with potassium permanganate

“…However, concentration of IF, IAA and TIAA kept increasing from 4 h to 3 days while HOI and I 2 concentration decreased from 1 h to the end of reaction (Fig. 1), which implied that other reaction mechanism played a significant role in the formation of IF, IAA and TIAA, such as reaction of I 3 − with NOM [16].…”

“…Many studies reported that formation of I-DBPs during oxidative treatment of iodide-containing waters using chlorine [5][6][7]12,13], chloramines [5,13,14], ozone [13], manganese dioxide [15] and lead oxide [16]. However, few literatures specifically addressed the formation of iodinated organic compounds when treating iodidecontaining waters with potassium permanganate (KMnO 4 ), which is an oxidizing agent widely used throughout water industries.…”

“…As reported, application of potassium permanganate resulted in the precipitation of manganese dioxide (MnO 2 ) [20], which can act as a catalyst in the electrophilic iodination of organic compounds through the activation of the iodine molecule and leads to the formation of iodinated organic compounds [15]. Moreover, potassium permanganate can oxidize I − to I 2 , HOI or I 3 − , which are reactive iodine species [12,16,21,22]. Therefore, the use of potassium permanganate in water treatment processes may have a great risk of forming iodinated organic compounds, resulting in not only taste and odor problems but also increased toxicity.…”

Kinetics of lead(IV) oxide (PbO2) reductive dissolution: Role of lead(II) adsorption and surface speciation

“…HOCl + OCl À ), a widely used disinfectant in distribution systems, provides a high ORP that favors PbO 2 formation [1,5,6]. The presence of reductants that include natural organic matter (NOM), Br À , I À , Mn 2+ , and Fe 2+ significantly enhanced the dissolution of PbO 2 [7][8][9][10][11][12][13]. The reductive dissolution of PbO 2 by water itself is even thermodynamically favorable [8,14].…”