Safe treatment of antibiotics requires efficient removal of both antibiotics and their degraded intermediates. In this study, we demonstrate that FeC₂O₄•2H₂O enables the more sustainable conversion of H₂O₂ to ^•OH than commonly used FeSO₄•7H₂O, promoting the detoxification of a typical antibiotic sulfadimidine. It was found that the FeC₂O₄/H₂O₂ system could completely degrade 250 mg L⁻¹ of sulfadimidine within 40 min at pH 3.0, along with decreasing the contents of chemical oxygen demand and total organic carbon by 295.0 and 33.5 mg L⁻¹, respectively, more efficient than those in a classical Fenton system (FeSO₄/H₂O₂). Analysis of sulfadimidine degraded intermediates and toxicity evaluation suggested that the FeC₂O₄/H₂O₂ treatment could more effectively decrease the overall toxicity of the sulfadimidine solution than the FeSO₄/H₂O₂ counterpart. The sustainability of FeC₂O₄•2H₂O in H₂O₂ conversion to ^•OH was attributed to its controlled release of Fe²⁺ into the solution to prevent the quenching of ^•OH by excessive Fe²⁺, as well as the simultaneous release of C₂O₄²⁻ to complex with Fe²⁺ and Fe³⁺, which could inhibit iron sludge formation and accelerate Fe³⁺/Fe²⁺ redox cycle. This study provides a promising Fenton system for the safe treatment of antibiotics and sheds light on the potential of FeC₂O₄•2H₂O in environmental remediation.