Reinvestigation of Ferrate(VI) Oxidation of Bisphenol A over a Wide pH Range

Abstract

Ferrate (Fe(VI), K2FeO4) has attracted much attention in water treatment for its high redox potential, especially under acidic conditions. Although interests have been arising in the performance of Fe(VI) at pH below 7.0, a contradicting trend of second order reaction rates (kapp) was observed at acidic conditions, and the reactive species (i.e., high-valent iron species or hydroxyl radicals (HO•)) of Fe(VI) oxidation at acidic pH remains unclear. Thus, the kinetics of Fe(VI) oxidizing bisphenol A (BPA) under a wide pH range was reinvestigated. The kapp value of Fe(VI) with BPA strongly depends on pH, which increased from 7.31 × 101 to 2.44 × 103 M–1 s–1 with pH decreasing from 10.0 to 3.0. Moreover, high-valent iron species were identified as the reactive species, i.e., Fe(VI), Fe(V), and Fe(IV), in both alkaline and acidic solutions, while HO• was identified as the secondary reactive species at acidic conditions with negligible contribution. Theoretical calculation was used to predict the reactive sites, and similar degradation products of BPA were identified under both acidic and alkaline conditions, ascribed to the similar reactive species. Toxicity assessment based on the Toxicity Estimation Software Tool suggested that Fe(VI) can alleviate the bioaccumulation toxicity efficiently. Humic acid (0.2–2.0 mgC L–1) and ubiquitous anions (1.0 mM) showed no obvious adverse effect on Fe(VI) oxidation while 1.0 mM Fe3+ or Cu2+ could accelerate it, and Fe(VI) showed a promising performance for the abatement of BPA in real waters.