Kinetics and Mechanism Investigation of Selective Arsenite Oxidation by Reactive Iodine Species in Hydrogen Peroxide and Iodide (H<sub>2</sub>O<sub>2</sub>/I<sup>–</sup>) System
Zhihao Chen, Jingyi Li, Kok Yuen Koh, Zhongrong Du, Choon Nam Ong, J. Paul Chen
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 H2O2 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, Cu2+ 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–, H2O2 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 I2 and I3– 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.