Research On Chlorine Removal Performance And Recycling Of Bismuth Ferrite Type Chlorine Remover From Wastewater

Chloride ions(Cl^-)in wastewater are harmful,but conventional removal methods have disadvantages such as high cost and low removal efficiency.To reduce the cost in the process of Cl^-removal and improve the removal efficiency,the precipitation method has become a research hotspot in recent years.In this paper,based on the precipitation method,bismuth ferrite was selected as the precipitation removal agent,and the characteristics of BiOCl precipitation generated by the combination of bismuth ferrite and Cl^-were used to study the quality of the three components of BiFeO₃,Bi₂Fe₄O₉and Bi₂₅FeO₄₀in the bismuth ferrite samples under different preparation conditions.The effects of fraction and its relationship with Cl^-removal performance were studied.By analyzing and comparing the chlorine removal efficiency of the obtained samples,the soft bismuth ore type Bi₂₅FeO₄₀sample with the best Cl^-removal performance was searched out,and then its Cl^-removal efficiencies under different conditions were investigated.The dry method and wet method are used to regenerate the Cl^-removal product BiOCl,and Bi₂₅FeO₄₀is re-prepared from the regenerated raw materials to achieve the purpose of recycling Bi₂₅FeO₄₀for Cl^-removal at low consumption.The main research results are as follows:(1)The conditions of pH,calcination temperature,calcination time in the preparation process are important factors that affect the content sof BiFeO₃,Bi₂Fe₄O₉,and Bi₂₅FeO₄₀in the bismuth ferrite samples.Under the conditions of low pH,low calcination temperature,and short calcination time,BiFeO₃is easy to form,but it is difficult to obtain a pure phase.With the increase of co-precipitation pH,calcination temperature and calcination time,the large irregular morphology of Bi₂₅FeO₄₀is easily generated.Under the conditions of pH=11,calcination temperature of 650?,and calcination time of 4 h,the content of Bi₂₅FeO₄₀in the sample reached 85.1%,and the remaining 14.9%was Bi₂Fe₄O₉with small hexahedral shape.(2)The Cl^-removal performance of different components of bismuth ferrites is quite different.The Cl^-removal efficiency has a linear relationship with the content of Bi₂₅FeO₄₀in each sample,so Bi₂₅FeO₄₀is selected as the Cl^-removal agent.The mass fraction of Bi₂₅FeO₄₀in the best sample is 85.1%,and the chlorine removal efficiency is 88.8%.The chlorine removal product is mainly two-dimensional flake BiOCl with a thickness of 60 nm,and contains a small amount of Bi₂Fe₄O₉.Under these conditions,when the Bi₂₅FeO₄₀content is high,the Cl^-removal efficiency is high,so this condition is selected as the preparation condition of Bi₂₅FeO₄₀.(3)Adjusting the preparation conditions,and the obtained Bi₂₅FeO₄₀is a pure phase with an irregular block morphology.The sample has good Cl^-removal performance,and can convert chloride ions in wastewater into two-dimensional BiOCl with a thickness of 26 nm.Acidic conditions are conducive to the release of Bi in the Bi₂₅FeO₄₀sample.When the pH is0.5 during the Cl^-removal process,Bi₂₅FeO₄₀can exhibit the best removal performance.With the increase of the initial concentration of Cl^-in the wastewater,the removal rate of Bi₂₅FeO₄₀also increases.In the low Bi content system,the utilization rate of Bi is greatly improved.When the removal reaction is carried out for 8 h,the utilization rate of Bi can reach 98.4%.In a system with high Bi content,the time for the Cl^-removal reaction to reach the maximum removal efficiency is greatly shortened,and the Cl^-removal rate can reach within 0.5 h.(4)Both the dry method and the wet method can realize the conversion of the Cl^-removal product BiOCl to Bi₂O₃.Among them,the products obtained from dry regeneration are mainly Bi₂O₃,Bi Cl₃and Bi₂₄O₃₁Cl₁₀.At different calcination temperatures,the pure phase product cannot be obtained,so it is not suitable as a Bi source for Bi₂₅FeO₄₀regeneration.In wet regeneration,the Cl^-removal product BiOCl can be converted into Bi₂O₃after being treated with a certain concentration of NaOH.When the NaOH concentration reaches 1mol·L-1 or more,after 1 h of reaction,the reduced product is pure phase Bi₂O₃,which can be used as the Bi source for regeneration of Bi₂₅FeO₄₀.Bi₂O₃obtained by wet regeneration of BiOCl is used as the regenerated Bi source of Bi₂₅FeO₄₀,and the pure phase Bi₂₅FeO₄₀can be obtained again.The Cl^-removal experiment shows that the regenerated Bi₂₅FeO₄₀has similar Cl^-removal performance to the original Bi₂₅FeO₄₀.The flaky BiOCl can be obtained in two cycles of regeneration and Cl^-removal experiments,where both of the Cl^-removal efficiencies of 0.5 h can reach more than 80%,which further respectively increase to 96.1%and 94.9%after 8 h.