Surface composition and catalytic activity of an iron mining residue for simultaneous degradation of sulfonamide antibiotics

Iron mining residue was evaluated as a potential catalyst for heterogeneous Fenton/photo-Fenton degradation of sulfonamide antibiotics. The residue contained 25% Fe2O3 and 8% CeO2, as determined by X-ray fluorescence spectroscopy, as well as other minor phases such as P2O5, SiO2, and TiO2. X-ray photoelectron spectroscopy analysis revealed a lower content of iron oxides on the surface, which restricted interaction of the residue with H2O2. Despite this limitation and the relatively low specific surface area (26 m(2) g(-1)) of the crude iron mining residue (without any pretreatment), the material presented high catalytic activity for Fenton degradation of sulfonamide antibiotics. The degradation was strongly dependent on the initial pH, showing the highest efficiency at pH 2.5. For this condition, a concentration of sulfathiazole below the detection limit was obtained within 30 min, under black light irradiation and using 0.3 g L-1 residue, with low H2O2 consumption (0.2 mmol L-1). The residue also provided highly efficient sulfathiazole degradation in the dark, with the concentration of the antibiotic decreasing to an undetectable level after 45 min. Simultaneous degradation of two sulfonamide antibiotics revealed higher recalcitrance of sulfamethazine, compared to sulfathiazole, but the levels of both antibiotics decreased to below the detection limit after 45 min. The residue was very stable, since no significant concentration of soluble iron was detected after the degradation process. Furthermore, high catalytic activity was maintained during up to five cycles, showing the potential of this material for use as a low-cost and environmentally compliant catalyst in Fenton processes.