Two advanced oxidation pathways of modified iron-shavings participation in ozonation

Abstract

In this study, the performance of ozonation, catalytic ozonation and activation of molecular oxygen (AMO) process was examined with oxalate as the target refractory organics. Modified iron-shavings was used as catalyst for catalytic ozonation in degradation of oxalate at ambient temperature (25 ± 2 °C). Under catalytic ozonation, the removal of oxalate was as high as 90%, which was much better than ozone alone. Initial pH was a key factor affecting the mechanisms of oxalate degradation. In AMO process, with the existence of Fe (II) there occurred an inner-Fenton reaction, hydrogen peroxide (H2O2) was produced at initial pH2.27 and its concentration ranged from 120 to 200 μmol/L. Heterogeneous catalytic ozonation occurred in alkaline solution with hydroxyl radicals (·OH) production, which was indirectly oxidation instead of inner-Fenton reaction. Carbonate would be produced in alkaline solution during catalytic ozonation of oxalate which would in turn inhibit the process. Lepidocrocite (γ-FeOOH) was formed through the dissolved iron ions precipitation and considered as the main component of catalyst, which was confirmed via field emission scanning electron microscope with energy-dispersive spectrometer (SEM-EDS), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Hydroxyl radicals produced via different paths were detected out by electron paramagnetic resonance (EPR) and were considered as strong oxidant in catalytic ozonation and AMO process.