Study On Oxidative Flocculation Characteristics Of Simultaneous Removal Of Copper,Cadmium And Phosphorus By Potassium Ferrate In Water

Sewage treatment plants are the ultimate barriers that block contaminants in the water from entering the natural environment.However,the removal effect of the biological treatment process on heavy metals and phosphorus is not obvious.The traditional coagulation advanced treatment process cannot remove heavy metals and phosphorus simultaneously,and the removal effect of heavy metals is not ideal.As a green water treatment agent,potassium ferrate has both oxidation and flocculation effects.It is of practical value to study the removal characteristics of potassium ferrate for heavy metals and phosphorus in the advanced treatment of sewage.In this experiment,the influencing factors of the self-decomposition characteristics of potassium ferrate?K₂FeO₄?in aqueous solution were studied.In this experiment,using the self-decomposition characteristics of K₂FeO₄,Cu???,Cd???and TP in water were used as the research objects.The effect of K₂FeO₄ removal of Cu???,Cd???and TP in water at the same time,the effect of Fe???and Fe???on the removal of Cu???,Cd???and TP by K₂FeO₄ were studied.At the same time,using SEM-EDS,FTIR,XRD,XPS and other technical means,preliminary analysis of K₂FeO₄self-decomposition characteristics,K₂FeO₄ removal mechanism of Cu???,Cd???and TP,Fe????Fe???promote K₂FeO₄ removal mechanism of Cu???,Cd???and TP.The experimental research results are as follows:?1?The self-decomposition of K₂FeO₄ in aqueous solution is significantly affected by the dosage and pH value.With the increase of K₂FeO₄ dosage,the higher the decomposition rate of K₂FeO₄ in water,the faster the self-decomposition rate.When the pH value was adjusted first,the self-decomposition rate of K₂FeO₄ in the solution was low.When K₂FeO₄ was added first and then the pH value was adjusted,under acidic and neutral conditions,K₂FeO₄ could rapidly decompose,and the highest decomposition rate under the condition of pH=7.02;Fe???and Fe???in the solution promoted the self-decomposition of K₂FeO₄ in the solution.When 80 mg/L Fe???and Fe???were added,the decomposition rate of K₂FeO₄ after decomposition was increased by 54.63%and 49.83%compared with those without Fe???and Fe???;SiO₃^2-in the solution inhibit the self-decomposition of K₂FeO₄ in the solution.As the dosage of SiO₃^2-increased,the self-decomposition rate of K₂FeO₄ decreased.?2?According to the SEM-EDS,XRD,FTIR,XPS characterization results of K₂FeO₄ self-decomposition products,K₂FeO₄ self-decomposition in water was the process of reduction from Fe???to Fe???.The self-decomposition products were round granular nanoparticles,which were iron oxides?Fe₂O₃?or hydroxides?FeOOH or Fe?OH?₃?,and had a flocculation effect.?3?The effect of K₂FeO₄ on the simultaneous removal of Cu???,Cd???and TP in water samples was greatly affected by the dosage,pH value,organic matter concentration and so on.With the increased of the dosage of K₂FeO₄,the removal effects of Cu???,Cd???and TP all increased rapidly and then remained basically unchanged.When 60 mg/L K₂FeO₄ was added,the removal rates of Cu???,Cd???and TP were 97.75%,90.53%and 99.50%respectively.When the pH was adjusted first,the removal rates of Cu???,Cd???and TP were lower than that of the post-adjustment pH.When the pH was adjusted later,when pH=7.02,Cu???,Cd???and TP had the highest removal rate;K₂FeO₄ preferentially removed TP and Cu???in water before removing Cd???;Choose humic acid concentration to represent the change of organic matter concentration in water.The removal effects of Cu???,Cd???and TP in the samples all showed a downward trend.The raw water was selected as the effluent from the secondary settling tank of the Zhongshui Station.With the increased of the dosage of K₂FeO₄,the removal efficiency of Cu???,Cd???and TP had continuously increased.When 150 mg/L K₂FeO₄ was added,the concentration of remaining Cu???,Cd???and TP in the solution meets the requirements of copper,cadmium and phosphorus in the first grade A effluent.The SEM-EDS,XRD,FTIR,XPS characterization results of the simultaneous removal of Cu???,Cd???and TP products by K₂FeO₄ can be obtained.The precipitation products of K₂FeO₄ after removing Cu???,Cd???and TP become balls gather together.And the presence of CuFe₂O₄ and CdFe₂O₄ in the product shows that K₂FeO₄ was decomposed in the solution to remove Cu???and Cd???in the water by decomposition product adsorption.P in the precipitate was in the form of KH₂PO₄ and FePO₄,indicating that the removal of phosphorus by K₂FeO₄ was partly through direct adsorption,partly through the formation of FePO₄ and then adsorbed and removed by the K₂FeO₄self-decomposition.?4?As the concentration of Fe???and Fe???in the solution increased,the removal rate of Cu???,Cd???and TP by K₂FeO₄ increased.When 40 mg/L Fe???was added to the solution,the removal rate of Cu???,Cd???and TP by K₂FeO₄ was increased by 71.8%,62.4%and 22.2%respectively when K₂FeO₄ was added alone.When 40 mg/L Fe???was added during dissolution,the removal rate of K₂FeO₄ to Cu???,Cd???and TP in the configuration water samples was increased by 69.3%and52.9%and 20.5%respectively when K₂FeO₄ was added.?5?According to the XRD analysis results,the diffraction peak of the precipitated product was not obvious compared with the absence of Fe???and Fe???.After adding Fe???and Fe???,the intensity of each characteristic peak of the infrared spectrum of the precipitated product decreased.A small shift occurs,indicated that the addition of Fe???and Fe???changed the electron transfer pathway during the conversion of Fe???to Fe???,and positively charged network can be formed through various electron transfer processes Fe-like intermediate valence products to achieve the adsorption and removal of heavy metals and FePO₄.