Despite substantial kinetic investigations on Fe(VI) oxidation of emerging organic contaminants (EOCs), few attentions have been paid to the inherent relation of reactive iron intermediates in-situ generated, i.e. Fe(V) and Fe(IV), with different kinetic behaviors of EOCs degradation during Fe(VI) oxidation. This study showed that kapp of six selected EOCs oxidation by Fe(VI) increased, remained, or declined with time, with a strong reliance on [EOC]0/[Fe(VI)]0, pH, and EOCs species. The experiments with excess caffeine as the quenching reagents for Fe(V) and Fe(IV) showed that Fe(V)/Fe(IV) contributed to 20–30% of degradation of phenol and bisphenol F and the contributions of Fe(V)/Fe(IV) remained nearly constant with time under all the tested conditions. However, the contributions of Fe(V)/Fe(IV) accounted for over 50% during the oxidation of sulfamethoxazole, bisphenol S, and iohexol by Fe(VI), while the variation trends of kapp with time coincided with those of the contributions of Fe(V)/Fe(IV) with time. Results from the quenching experiments were further validated through simulating the kinetic oxidation data of phenyl sulfoxide by Fe(VI). The kinetic modelling results revealed that the variation trends of kapp with time were significantly determined by the change of molar ratio of Fe(V) to Fe(VI) with time, highlighting the key role of Fe(V) in the oxidative process. This study provides comprehensive and insightful information regarding the role of intermediate Fe(V)/Fe(IV) during EOCs oxidation by Fe(VI), which may serve as a basis for more efficient application of Fe(VI) to EOCs control in water and wastewater treatment industries.

New insights into the role of reactive intermediate Fe species during the oxidation of emerging organic contaminants by Fe(VI)

ACS Fall 2021

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