Removal of sulfachloropyridazine by ferrate(VI): Kinetics, reaction pathways, biodegradation, and toxicity evaluation

Sulfachloropyridazine (SCP) is a broad-spectrum sulfonamide antibiotic and has been detected in cattle farming and fishpond water samples. This paper presents the kinetics and removal of SCP by ferrate(VI) (FeO42-, Fe-VI) in the acidic to basic pH range. The species-specific rate constant (k, M-1 s(-1)) of protonated FeVI species (HFeO4-) is higher than that of the FeO42- species. This describes the decrease in k with increase in pH. The identified organic oxidized products (OPs) of reaction between Fe-VI and SCP suggest an extrusion of SO2 from the sulfonamide group and hydroxylation of the aniline moiety of SCP. The peak areas of the OPs at different molar ratios of Fe-VI to SCP (2.0-15.0) and the formation of sulfate ion are used to give a plausible mechanism for the transformation of SCP to different OPs. In the proposed mechanisms, the major pathway involves a single-electron transfer that leads to Fe-V and a radical cation intermediate resulting in SO2 extrusion. A secondary minor pathway, which does not lead to SO2 extrusion, involves the hydroxylation of the aniline moiety of SCP, which likely occurs via an oxygen-atom transfer step. The sulfate ion was formed as a result of SO2 (or sulfite ion) oxidation by Fe-VI, which could also generate the Fe-V species. The generated Fe-V species also participate in the overall oxidation of SCP by Fe-VI. Biodegradation and toxicity tests of the OPs were performed. Treatment results in river waters demonstrated that more than 90% of SCP was removed by Fe-VI.