Mechanism study of oxytetracycline hydrochloride degradation through activating sulfite by Fe2+/Mn2+
Oxytetracycline hydrochloride is often used in the treatment of livestock and poultry diseases,however,it cannot be completely metabolized.The residual oxytetracycline hydrochloride entering water poses a threat to the health of water environment.Bivalent iron and bivalent manganese,as common transition metals,can usually activate sulfides to degrade organic pollutants.Its reaction conditions are mild and the operation is simple.However,the redox potential of single divalent iron and single divalent manganese is low,and the performance of activating sulfide is poor.In this experiment,Fe2+/Mn2+ coactivating Na2 SO3 was used to degrade oxytetracycline hydrochloride in water.The effects of reagent dosage,pH,dissolved oxygen,chloride ion,carbonate ions and humic acid on the degradation of oxytetracycline hydrochloride in the Fe2+/Mn2+/Na2 SO3 system were investigated.The oxidizing active substances in the Fe2+/Mn2+/Na2 SO3 system were analyzed using pyrophosphate test,free radical quenching test and EPR experiment.The changes of functional groups and degradation intermediates of oxytetracycline hydrochloride were identified by UV-Vis spectroscopy,Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry,and the degradation pathway of oxytetracycline hydrochloride was inferred.The results showed that when the concentration ratio of Fe2+/Mn2+/Na2 SO3 was 1∶4∶20(the concentrations were 0.1,0.4 and 2 mmol/L,respectively),the reaction time was 45 min and the pH was 9.0,removal efficiency and mineralization rate of oxytetracycline hydrochloride were the highest,and up to 94%and 49%,respectively.When dissolved oxygen decreased from 9 mg/L to 1.89 mg/L,removal efficiency of oxytetracycline hydrochloride decreased from 94%to 17%.Chlorine ions,humic acids and carbonate ions all had inhibitory effects on the degradation of oxytetracycline hydrochloride.Mn(Ⅲ)and SO·-4 were main active oxidants for the degradation of oxytetracycline hydrochloride,and the degradation underwent the processes of electron transfer,ring opening and acylation.
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