Formation Mechanism Of High-valent Iron（Ⅳ）-oxo Complex And Free Radicals In Fe（Ⅲ）/Sulfite Advanced Oxidation System

In recent years,sulfate radical(SO₄^·-)has attracted extensive attention in the field of environmental pollution control because of its high redox potential,long semi-decay period and selective oxidation of organic pollutants.The iron-catalyzed sulfite auto-oxidation process is one of the main methods to generate SO₄^·-.In this process,the production of persulfate（PS）and the activation of PS by iron ions are considered to be important pathways for the production of SO₄^·-and its secondary radicals（hydroxyl radicals,^·OH）.However,recent studies have found that Fe（Ⅳ）rather than SO₄^·-is the main active species in the Fe（II）/PS system.To address this issue,micropollutants are selected as the probe to identify the types of non-free radicals and free radical in the Fe（III）/sulfite system.By using a variety of active component research methods,the relative yields and generation rules of Fe（Ⅳ）and free radicals in the Fe（III）/sulfite system were further explored.It provides theoretical support for the practical application of Fe（III）activated sulfite pollution removal technology.The main research contents and results are as follows:（1）Using high performance liquid chromatography-triple quadrupole mass spectrometry（HPLC-MS/MS）,the oxidation products of atrazine（ATZ）by Fe（Ⅳ）,SO₄^·-and^·OH were analyzed.It was found that the yield ratios of[DEA]/[DIA])degraded by Fe（Ⅳ）,SO₄^·-and^·OH,which were 7.5,10 and 2,respectively.The yield ratios of[CDIT]/[DEA]were 0.6,2and 0.7,respectively,by Fe（Ⅳ）,SO₄^·-and^·OH.That is,the yield ratio of ATZ characteristic products has an indicative effect on the types of active components.Further using ATZ as probe compound,it was found that the values of[DEA]/[DIA]and[CDIT]/[DEA]decreased gradually during reaction,and increased with the increase of Fe（III）and sulfite initial concentration in the Fe（III）/sulfite system.It shows that Fe（Ⅳ）increases gradually with the progress of reaction and the initial concentration of the reactants.（2）Methyl phenyl sulfoxide（PMSO）was transformed into its oxygen transfer product methyl phenyl sulfone（PMSO₂）by Fe（Ⅳ）,markedly differing from their biphenyl compounds and^·OH-induced products.Using PMSO as a probe,it was found that PMSO₂ was generated in the Fe（III）/sulfite system,indicating the formation of Fe（Ⅳ）.Further the results of EPR and alcohol inhibitor experiments confirmed the formation of SO₄^·-and a small amount of^·OH in the system.The yield of PMSO₂（η（PMSO₂））was analyzed.It was found that theη（PMSO₂）increased gradually with the Fe（III）-sulfite reaction,and increased with the increase of Fe（III）and sulfite initial concentration,with an upper limit of 80%～90%.It shows that the relative yield of Fe（Ⅳ）increases gradually with the progress of the reaction and the increase of initial concentration of reactants.This is consistent with the conclusion of ATZ probe.（3）Based on the generation and decay of Fe（Ⅳ）and free radicals(SO₄^·-/^·OH),a kinetic model of Fe（III）activated sulfite was established.The model accurately simulated the conversion of PMSO and the consumption of dissolved oxygen in the Fe（III）/sulfite system.Moreover,it revealed the evolution of Fe（Ⅳ）and SO₄^·-/^·OH in the system,and deeply analyzed the decontamination process and active component formation mechanism of Fe（III）/sulfite system.