Influence of Glyoxal on the Catalytic Oxidation of S(IV) in Acidic Aqueous Media

High Resolution Image Download MS PowerPoint Slide The role of glyoxal in S(IV) oxidation in acidic aqueous solutions catalyzed by iron in the form of aqueous Fe3+ ions and solid iron oxide was investigated under different experimental conditions. It is found that the rate of Fe3+(aqueous (aq)) ion-catalyzed S(IV) oxidation decreases in the presence of glyoxal. The results of mass spectral analysis and infrared spectra suggest that the trapping of SO4– radicals, as well as the formation of glyoxal–S(IV) adducts, are responsible for this inhibition effect. Interestingly, although sulfur oxidation is kinetically inhibited in the presence of glyoxal, S(IV) in the form of sulfite is over time completely converted to sulfate. Additionally, the inhibition effects of glyoxal can also be observed in the reaction of S(IV) catalyzed by iron oxide particles, albeit less than that catalyzed by dissolved Fe3+(aq). The observed inhibition effect for the iron oxide particles is proposed to be attributed to competitive surface adsorption on the iron oxide particle surface. Overall, these findings suggest that the effects of glyoxal on the catalytic oxidation of S(IV) are highly dependent on the mechanism, form of iron (dissolved vs solid), and the ambient conditions including pH and concentration