Effect of Metal Ions on Oxidation of Micropollutants by Ferrate(VI): Enhancing Role of Fe IV Species.

This paper investigated the oxidation of recalcitrant micropollutants [i.e., atenolol (ATL), flumequine, aspartame, and diatrizoic acid] by combining ferrate(VI) (Fe ^VI O ₄ ^2- , Fe ^VI ) with a series of metal ions [i.e., Fe(III), Ca(II), Al(III), Sc(III), Co(II), and Ni(II)]. An addition of Fe(III) to Fe ^VI enhanced the oxidation of micropollutants compared solely to Fe ^VI . The enhanced oxidation of studied micropollutants increased with increasing [Fe(III)]/[Fe ^VI ] to 2.0. The complete conversion of phenyl methyl sulfoxide (PMSO), as a probe agent, to phenyl methyl sulfone (PMSO ₂ ) by the Fe ^VI -Fe(III) system suggested that the highly reactive intermediate Fe ^IV /Fe ^V species causes the increased oxidation of all four micropollutants. A kinetic modeling of the oxidation of ATL demonstrated that the major species causing the increase in ATL removal was Fe ^IV , which had an estimated rate constant as (6.3 ± 0.2) × 10 ⁴ M ^-1 s ^-1 , much higher than that of Fe ^VI [(5.0 ± 0.4) × 10 ^-1 M ^-1 s ^-1 ]. Mechanisms of the formed oxidation products of ATL by Fe ^IV , which included aromatic and/or benzylic oxidation, are delineated. The presence of natural organic matter significantly inhibited the removal of four pollutants by the Fe ^VI -Fe(III) system. The enhanced effect of the Fe ^VI -Fe(III) system was also seen in the oxidation of the micropollutants in river water and lake water.