Oxidative and Reductive Pathways in Iron-Ethylenediaminetetraacetic Acid–Activated Persulfate Systems

Abstract

The iron (II)-ethylenediaminetetraacetic acid (EDTA) and iron (III)-EDTA activation of persulfate was compared using reactant-specific probe compounds: the combined sulfate radical and hydroxyl radical probe anisole, the hydroxyl radical probe nitrobenzene, and the reductant/nucleophile probe hexachloroethane. Iron (II)-EDTA and iron (III)-EDTA were equally effective for activating persulfate decomposition and for generating reductants/nucleophiles at pH 5, while iron (III)-EDTA was a more effective activator than iron (II)-EDTA for generating oxidants. Use of the combined sulfate radical and hydroxyl radical scavenger isopropanol and the hydroxyl radical scavenger tert-butanol demonstrated that approximately 86 and 73% of the oxidation activity in iron (II)-EDTA and iron (III)-EDTA-activated persulfate systems, respectively, was attributable to hydroxyl radical activity. The generation of hydroxyl radical in iron-EDTA-activated persulfate systems at pH 5 was confirmed using electron spin resonance spectroscopy. The results of these pathway analyses, in conjunction with confirmation of the results using the common groundwater contaminant trichloroethylene (TCE), show that iron (II)-EDTA and iron (III)-EDTA-activated persulfate may be an effective system for the in situ remediation of contaminated groundwater.