Recycling of Fenton sludge containing Ni as an efficient catalyst for tetracycline degradation through peroxymonosulfate activation

Fe sludge containing heavy metal Ni was used as a catalyst to activate potassium peroxymonosulfate (PMS) after thermal treatment. The crystal structures of recycled Fe sludge samples occur in the form of alpha-Fe2O3 and gamma-Fe2O3. The existence of Ni had minimal effect on the crystal structure, but it changed the surface morphology and the internal chemical bond. X-ray photoelectron spectroscopy result proved that Ni existed as Fe-O-Ni. Influencing factors, such as the Ni content, PMS dosage, pH level, and the structural characteristics of the recycled products were explored. All the recycled Fe sludge products with and without Ni possessed catalytic activity in the removal of antibiotic tetracycline from the water for PMS activation. The optimal application conditions and possible mechanisms were proposed in accordance with the physicochemical properties of recycled products and the experimental results. Electron spin resonance spectra showed that Ni-containing Fe sludge could activate more OH center dot and SO4 center dot- than the product without Ni. OH center dot and SO4 center dot- are probably the critical free radicals in tetracycline degradation, but Ni did not significantly affect the catalytic degradation of tetracycline. Based on the findings of this study, the new idea and direction for the utilization of Fenton sludge can provide reference for heavy metal sludge recycling. (c) 2020 Elsevier Ltd. All rights reserved.