Deciphering the Impact of Halogen Ions on the Oxidative Dynamics and Halogenated Byproduct Transformation in the Ferrate(VI)-Periodate Combined System

Abstract

Ferrate (Fe(VI)) and periodate (PI) are powerful oxidizing agents that have emerged as significant contributors to advanced wastewater treatment methods. Their synergistic interaction has been recognized for its enhanced oxidative capabilities. However, the presence of organic and inorganic ions, particularly halide ions such as chloride (Cl^–), bromide (Br^–), and iodide (I^–), can significantly influence oxidation kinetics and the transformation of organic pollutants. This study systematically investigated the oxidation mechanisms of the Fe(VI)–PI system and its performance in the presence of these halide ions. Dynamic experiments showed that halide ions markedly affected the activity of the Fe(VI)–PI system. Specifically, in the presence of Cl^–, the degradation efficiency of sulfamethoxazole (SMX) increased by 4.8% at pH 7.0 and 22.2% at pH 8.0. Similarly, Br^– enhanced the degradation efficiency by 12.5% at pH 7.0 and 26.2% at pH 8.0. In contrast, I^– completely inhibited the degradation process, likely due to their interaction with the oxidant. Additional removal experiments, detection tests, and electron spin resonance (ESR) analyses revealed that introducing halide ions significantly altered the composition of reactive species. Cl^– and Br^– promoted the formation of ^•OH and facilitated the reduction of Fe(VI) to Fe(IV)/Fe(V) species. This effect was strongly dependent on pH, which in turn influenced the degradation pathway. Product analysis and toxicity assessments further indicated that halide ions might lead to the formation of halogenated byproducts in the Fe(VI)–PI system, with pH playing a crucial role in regulating this process. This study provides a deeper understanding of the influence of halide ions on oxidation reactions and highlights their role in controlling the degradation of micropollutants and the formation of disinfection byproducts in water treatment.