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