Influence Of Manganese Ions On Bisphenol A Degradation By Potassium Ferrate And Its Mechanism

With more and more serious water resource shortage and environmental water pollution problems,ferrate has an extensive application for drinking water treatment and advanced wastewater treatment.However,when potassium ferrate oxidation was applied to wastewater to remove dissolved contamination,plenty of reduced components in wastewater would compete with micro-pollutants for oxidants,which would decrease the degradation of target micro-pollutants.This article particularly studied the influence and reaction mechanism of reduced manganese iron(such as Mn²⁺)on typical contamination degradation by potassium ferrate.In borate buffer,with the increase of the Mn/Fe molar ratios,Mn²⁺could significantly inhibit BPA degradation by K₂FeO₄,resulting from the consumption of K₂FeO₄ by Mn²⁺and the formation of insoluble iron-manganese oxide particles,hindering BPA degradation by K₂FeO₄.However,in phosphate buffer,when the Mn/Fe molar ratios were between 0.5 and 3.0,Mn²⁺could enhance BPA degradation by K₂FeO₄.Compared with the simple K₂FeO₄ oxidation system,the degradation efficiency of BPA in the Mn²⁺/K₂FeO₄ system was higher,but the degradation rate was not improved obviously.In order to expose the enhancement mechanism of Mn²⁺on ferrate oxidation in phosphate buffer,in this paper,the main active species in the Mn²⁺/K₂FeO₄ system were distinguished according to the difference of oxidation characteristics between active iron species and active manganese species.The results showed that the main active species in the Mn²⁺/K₂FeO₄ system were relevant to the Mn/Fe molar ratios.At low Mn/Fe molar ratios（up to～0.1）,the involvement of active iron species could not be negligible.When Mn/Fe molar ratios were close to 0.5,Mn（VII）contribution was primary during the degradation process of BPA.When the Mn/Fe molar ratios were between 0.5 and 3.0,Mn（III）was mainly involved in BPA degradation.Combined with the formation of H₂O₂in the Mn²⁺/K₂FeO₄ system,it was speculated that the strengthening influence of Mn²⁺on ferrate oxidation in phosphate buffer was related to the transfer of oxidation ability between active iron species and active manganese species.Whether Mn（VII）or Mn（III）played the major role,the system could adequately utilize the oxidation ability of K₂FeO₄to reduce the waste of oxidation ability caused by the self-decomposition of ferrate.In order to analyze the transfer of oxidation ability between K₂FeO₄ and active manganese species,the formation pathway of Mn（VII）and Mn（III）was explored by UV-Vis spectra of the Mn²⁺/K₂FeO₄/PP system.When the Mn/Fe molar ratios were lower than0.5,Mn²⁺and K₂FeO₄ would eventually generate stable Mn（VII）.When the Mn/Fe molar ratios were more than 4.0,Mn（VII）was primarily formed by Mn²⁺and K₂FeO₄,and Mn（VII）could only exist for a short time,then would form Mn（III）,but would not further transformed it into Mn（IV）.When the Mn/Fe molar ratios were between 1.0 and 3.0,the concentration of free Mn²⁺was relatively low,which was not enough to reduce all the in-situ generated Mn（VII）to Mn（III）,and Mn（VII）and Mn（III）could coexist for a while.However,with the extension of reaction time,Mn（VII）and Mn（III）would also react and eventually convert to Mn（IV）.