Preparation of zero-valent iron-based composite catalyst with red mud and scrap tire as starting materials for Fenton-like degradation of methyl blue

Red mud (RM) is an attractive catalyst precursor due to its valuable components. In this study, we successfully synthesized a zero-valent iron-based composite catalyst by carbothermal reduction of RM with carbon black obtained by pyrolysis of the scrap tire as the reductant for the first time and evaluated the catalytic performance of the as-prepared catalyst for activating H 2 O 2 to degrade methylene blue (MB) in an aqueous solution. The characterization results signified that a gradual transformation of iron-related species, i.e. Fe 2 O 3  → Fe 3 O 4  → FeO → Fe 0 , might occur by varying the carbothermal reduction temperature. The Fe@RM catalyst reduced at 900 °C exhibited much higher MB degradation efficiency than those reduced at 850 °C and below, proving that the stabilized zero-valent iron nanoparticles are more effective than iron oxides in the heterogeneous Fenton-like processes. The response surface methodology (RSM) based on Central composite design (CCD) was employed to design and optimize individual and interactive effects of the independent parameters. Chemical quenching tests ascertained the contributions of free radicals (•OH and O 2 − • ) and singlet oxygen ( 1 O 2 ) reactive oxygen species to MB decomposition in the Fenton-like process. The present results demonstrate the promising reutilization of RM and scrap tires as low-cost raw materials for preparing zero-valent iron heterogeneous catalysts being active for the Fenton-like oxidation of organic pollutants in wastewater.