Heterogeneous Fenton oxidation of paracetamol in aqueous solution using iron slag as a catalyst: Degradation mechanisms and kinetics

In this study, a catalyst derived from iron slag (Fe-S) was used for heterogeneous Fenton oxidation (H2O2/Fe-S) of paracetamol in aqueous solution; the conventional homogeneous Fenton reaction (H2O2/Fe2＋) was run in parallel for comparison. Degradation of paracetamol, in terms of chemical oxygen demand (COD) removal, was found strongly dependent on the solution pH, with the maximum efficiency obtained at pH 3 for both H2O2/Fe-S and H2O2/Fe2＋ systems. The efficacy of paracetamol degradation was also affected by the ratio (w/w) of hydrogen peroxide to iron, as the maxima degradation was observed at ratios of 1:2 and 2:1 for the heterogeneous and homogeneous Fenton, respectively. In addition, the degradation efficiency decreased when the initial paracetamol concentration increased from 100 mg/L to 500 mg/L. Kinetic experiments showed that degradation of paracetamol fitted a pseudo-first-order kinetic model well, as evidenced by the Kd values of the pseudo-first-order kinetic model that followed the same sequence as the degradation efficiency of paracetamol. Processes involved in the degradation of paracetamol by H2O2/Fe-S mainly included adsorption and oxidation; for latter, the presence of FeO, ZnO, and SiO2 in Fe-S constituent might enhance the decomposition of H2O2 and generate more *OH radicals. The *OH radical-mediated oxidation was confirmed by significant declines in the elimination of paracetamol when the system was subject to various radical-scavengers including t-butanol, chloride, and carbonate species. [Display omitted] •Fe2＋ and Fe-S were used as catalysts for homogeneous and heterogeneous Fenton.•The paracetamol degradation by H2O2/Fe2＋ and H2O2/Fe-S reached the highest at pH 3.•The Fe2＋ ions released from Fe-S enhanced the formation of *OH radicals.•The paracetamol degradation followed pseudo-first order kinetic model.•The paracetamol degradation mechanism in H2O2/Fe-S system involved both adsorption and oxidation.