Preparation Of Fe(Ⅲ)-Oxalate/Attapulgite Heterogeneous Catalyst And Its Application In The Treatment Of Refractory Organic Wastewater

With the rapid development of agricultural modernization and industrialization,a large number of persistent and hard-to-degrade organic pollutants（ROS）have been released into the environment,causing great harm to human life and the ecological environment.Therefore,it is necessary to develop an efficient and environmentally friendly method for the removal of organic pollutants.It is well known that the heterogeneous Fenton technology is one of the advanced oxidation methods,which is widely used in the treatment of refractory organic wastewater by virtue of its wide p H range of reaction,high catalyst reusability and good stability.Therefore,the development and preparation of heterogeneous catalysts have become the focus of current research in the field of heterogeneous Fenton technology.Attapulgite（APT）is a natural water-rich magnesium-aluminum silicate clay mineral.Due to its rich pore structure and large specific surface area as well as its wide distribution and low price,it has become an ideal choice as a carrier for heterogeneous catalysts.In this study,Fe（III）-Oxalate/Attapulgite（FOA）heterogeneous catalysts were prepared by loading oxalate（OX）and Fe Cl₃with APT as a carrier.Tetracycline（TC）and methylene blue（MB）were selected as the target pollutants to investigate the catalytic degradation of the refractory organic pollutants in the FOA/H₂O₂heterogeneous Fenton system.The main research results are as follows below:（1）FOA heterogeneous catalyst was prepared by hydrothermal synthesis using attapulgite as carrier and ferric oxalate as support.Through the test and analysis of X-ray diffraction（XRD）,Fourier Transform Infrared Spectroscopy（FTIR）,Scanning Electron Microscopy（SEM）and Energy Dispersive X-ray Spectroscopy（EDS）,the catalyst not only retained the crystal diffraction peak and functional group of attapulgite,but also detected the crystal diffraction peak and characteristic functional group of ferric oxalate,which indicated that ferric oxalate was successfully supported on the surface of attapulgite.The micro-morphology analysis shows that a large number of ferric oxalate nanoparticles are uniformly deposited on the surface of attapulgite,and the aggregation between rod bundles becomes more uniform and loose.（2）The experimental study on the degradation of tetracycline（TC）as the target pollutant showed that under the experimental conditions of FOA=0.9g/L,H₂O₂=5mmol/L,p H=4,T=75min,the degradation rate of TC solution of 50mg/L could reach 94.28%,and the ideal TC removal effect could be achieved in the range of p H=4～8.Response surface model（RSM）based on BBD optimizes the experimental condition of TC degradation:the removal efficiency of FOA=0.6g/L,H₂O₂=4mmol/L,p H=4,TC can reach 98.86%.In the heterogeneous Fenton system of FOA/H₂O₂,·OH_adsplays a leading role in the oxidative degradation of TC.According to the detection of the intermediate products of TC degradation by LC-IM-QTOF,it is concluded that TC is mainly degraded by three ways dominated by demethylation.（3）Taking methylene blue（MB）as the target pollutant,the effects of FOA dosage,H₂O₂concentration,p H and MB initial concentration on the degradation efficiency were investigated.On the basis of single factor experiments,the response surface method was used to optimize the degradation of MB.Under the best combination conditions（FOA=1g/L,H₂O₂=10mmol/L,p H=4）,the degradation rate of MB solution of 100mg/L can reach 97.34%,which is consistent with the predicted value.The quadratic polynomial fitting of the experimental results showed that the order of factors affecting MB removal was as follows:initial p H value>FOA dosage>H₂O₂concentration.In addition,the catalytic activity of the catalyst in FOA/H₂O₂system has strong anti-interference to many kinds of inorganic anions(Cl^-,NO₃^-,HCO₃^-,HPO₄^2-)in water.Similarly,the efficient degradation of MB is attributed to the attack of the aromatic ring of MB by strong oxidizing active groups dominated by·OH_ads.