Carbonate Radical Anion (CO₃^•-) in Carbonated Water: Generation and Importance in Environmental Processes

Reactions of ferrous iron (Fe(II)) with oxidants (O₂, H₂O₂, and persulfate) in the presence of bicarbonate affect the Fenton and Fenton-like reactions in water treatment at neutral pH through the formation of the carbonate radical anion (CO₃^•-) rather than only the usually accepted hydroxyl radical (HO^•) or sulfate radical anion (SO₄^•-). Mechanisms of such a direct formation of CO₃^•- in reactions of low-valent iron with oxidants are presented. The reactivity of ferrate (Fe(VI)) enhanced the oxidation of pollutants in carbonate-rich water, and herein, the role of carbonate in high-valent iron-based oxidations is discussed. Advanced oxidation methods, based on HO^• treatments and reactions occurring in natural waters and water-containing aerosol particles, should consider these overlooked reactions in inorganic carbon-containing environments.