Kinetics and Mechanism Investigation of Selective Arsenite Oxidation by Reactive Iodine Species in Hydrogen Peroxide and Iodide (H₂O₂/I^–) System

Abstract

Pretreatment of arsenite (As(III)) to arsenate (As(V)) is crucial in remediation of As(III)-contaminated waterbodies. Hydroxyl or sulfate radicals-based advanced oxidation processes are effective; however, the efficiency becomes low as radicals can be quenched by coexisting matters besides As(III). Both I − and As(III) coexist in several types of contaminated water such as shale gas flowback water. Herein, we proposed using H 2 O 2 to react with I − so as to generate reactive iodine species (RIS) for effective oxidation of As(III). The presence of commonly existing anions, methanol, tert-butanol, 2-propanol, formic acid, humic acid, phenol, and benzoquinone did not affect the oxidation performance. Chromate, Cu 2+ or divalent/trivalent irons would enhance the oxidation. Only hydroquinone (>0.3 mM) had an inhibition effect on the oxidation. Unlike peroxymonosulfate and peroxydisulfate that are reactive to Cl − or Br − , H 2 O 2 only showed a solely selective reactivity for the I − to form the RIS. Our experimental and kinetic simulation results confirmed the most significant reaction pathway and suggested that I 2 and I 3 − were the main responsible intermediates. Our study demonstrated that the RIS possessed a higher selectivity to As(III) compared with other coexisting matters. Therefore, the application of RIS is very promising in the redox conversion mediation.

A Simplified and Affordable Arsenic Filter to Prevent Arsenic Poisoning: Lab-Scale Study and Pilot Experiment

“…On the basis of the above existing state-of-the-art, it is apparent that water filters that have been developed are mostly composed of iron-based adsorbent media. Although these iron-based materials possess arsenic sequestration properties, their affinity toward the nonionic As­(III) is less and kinetically slower than As­(V). − In most of the technologies, oxidation of As­(III) is carried out either by dissolved oxygen or by some oxidants like ozone, chlorine, hypochlorite, potassium permanganate, hydrogen peroxide, and Fenton’s reagent (H 2 O 2 /Fe 2+ ). − However, the oxidation carried out by the dissolved oxygen is a very slow process that may take 2–3 days for complete oxidation of As­(III) to As­(V), and using the oxidants increases the risk of production of hazardous byproducts (i.e., arsenic-bearing residue) and also causes operational difficulty; hence, the overall process becomes more complex and expensive. Some filters are also dependent upon the photo-oxidation for the removal of As­(III), but such a method may not be feasible when the sunlight is scarce.…”

Synchronous Moderate Oxidation and Adsorption on the Surface of γ-MnO2 for Efficient Iodide Removal from Water

“…In weakly alkaline and reductive groundwater, iodide (I – ) is the main iodine species and accounts for over 95% of the total iodine content. The concentrations of other species, that is, iodate (IO 3 – ), iodine-containing organic matter, and active iodine species (I 2 /HOI), are usually low. , However, long-term exposure to excessive iodine via drinking water can cause health issues such as hypothyroidism and thyroid autoimmunity in local residents . According to the World Health Organization (WHO) guidelines, a daily iodine intake of 150 μg/day is recommended for adolescents and adults .…”