Treatment of aniline wastewater with sponge iron/O ₂ : influencing factors and potential degradation mechanisms

Zero-valent iron (ZVI) serves not only as a reductive agent but also activates molecular oxygen to produce reactive oxygen species (ROS) for the oxidation of organic matter. This paper investigates the molecular oxygen activation with sponge iron (S-Fe) system and explores the key factors influencing ROS production. Response surface methodology (RSM) was employed to optimize the operating parameters to increase the production of ROS. Under the optimal conditions, the treatment effects and degradation pathway of aniline (AN) were investigated. It was confirmed that the quadratic equation model was accurate and reliable, the optimal operating parameters were obtained as follows: pH of 4, S-Fe dosage of 119 g/L, agitation speed of 114 rpm. The AN degradation process accords with zero-order reaction kinetics. Deamination occurs mainly at 36 h before the reaction, then the ring-opening rate of the benzene ring was greater than the deamination. A distinct iron corrosion product resembling Fe₂O₃, Fe₃O₄, and FeOOH formed on the surface of S-Fe. The S-Fe/O₂ system played a crucial role in AN degradation. These findings provide valuable insights for the further exploration and application of ZVI technology.