EDTA, oxalate, and phosphate ions enhanced reactive oxygen species generation and sulfamethazine removal by...

The activation rate of oxygen by zero-valent iron (Fe°) was very low. In this study, ethylenediaminetetraacetic acid (EDTA), oxalate (Ox), and phosphate ions (Na₂HPO₄) were used to enhance the oxygen activation by Fe° for sulfamethazine (SMT) removal. The addition of these ligands could significantly enhance the SMT degradation. SMT removal was improved from 10.5 % in the Fe° system (360 min) to 70.3 %, 85.2 % and 77.8 % in the Fe°/EDTA (60 min), Fe°/Ox (180 min) and Fe°/phosphate (360 min) systems, respectively. Scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier transform infrared reflection (FTIR), contact angle and X-ray photoelectron spectra (XPS) of Fe° in different systems were recorded. The presence of chelating agents hydroxylated Fe°, inhibited the iron oxide formation on the Fe° surface and promoted iron ion release from the solid. Moreover, the agents improved the recovery of surface Fe²⁺ which could subsequently enhance the activation of O₂ to produce more H₂O₂ and reactive oxygen radicals for SMT removal. OH radical produced mainly through H₂O₂ decomposition was primarily responsible for removing SMT in all three systems. The Fe° system added with chelating agents is a new and promising approach for treating wastewaters containing ligands.