Study On Ascorbic Acid Improving The Effect Of Rare Earth Catalyzed Fenton-like System In Degrading Printing And Dyeing Wastewater

Due to its complex composition and difficult biochemical degradation,the secondary biological treatment of printing and dyeing wastewater has been unable to meet my country’s discharge requirements.Therefore,feasible advanced treatment has become an inevitable choice for printing and dyeing wastewater treatment.The advanced oxidation technology represented by the traditional Fenton reaction is hindered in practical application due to its high chemical cost,narrow pH applicable range,large amount of iron sludge and low recycling rate.Fenton-like oxidation technology is developed on the basis of traditional Fenton oxidation technology.The current research on Fenton-like can be roughly divided into two types:（1）activating H₂O₂ by introducing additional energy into the system;（2）developing new catalytic materials that can exist in solid form in the system.Compared with traditional Fenton,the Fenton-like system generally has a wider pH range,and the use of solid iron-based catalytic materials can also effectively improve the problems of iron sludge and reuse.However,in practical applications,Fenton-like systems still have many problems such as slow reduction of Fe³⁺to Fe²⁺and low catalytic reaction efficiency.Aiming at the problems existing in the Fenton-like system,this study,based on the rare earth catalytic composite RE-Fe₃O₄-CD developed in the previous research,discussed the method to effectively promote the Fe³⁺to Fe²⁺and improve the catalytic efficiency of the Fenton-like reaction.An improved scheme is proposed:ascorbic acid（AA）is used as an activator for rare earth catalytic composites,or as a promoter for rare earth catalytic Fenton systems.A heterogeneous Fenton-like system was established,and the cationic blue X-GRL dye was used as the target pollutant to explore the catalytic degradation principle and synergistic mechanism of AA and rare earth elements.The main content and results were outlined as follows:（1）Usingβ-cyclodextrin（β-CD）,ferric oxide and rare earth lanthanum（La）or cerium（Ce）as raw materials,RE-Fe₃O₄-CD catalytic composites were prepared by hydrothermal method.Two rare earth catalytic composites were activated by ascorbic acid to obtain AA-RE-Fe₃O₄-CD.The morphology and structure of the material were characterized by SEM,TEM,XPS and FTIR,and the properties of the material were analyzed.From the SEM and TEM tests,it can be seen that the RE-Fe₃O₄-CD prepared by the hydrothermal method has loose structure and dispersed particles,and the overall structure of the material becomes compact after activation by AA;it can be seen from the FTIR test results that AA is also successfully loaded on the surface of the material after activation;From the XPS test results,it can be seen that after the material is activated by AA,the Fe²⁺and Ce³⁺contents on the surface of AA-RE-Fe₃O₄-CD are increased.（2）First,the effect of AA on the Fenton-like reaction was studied by using Fe₃O₄-CD,a composite material not doped with rare earth elements,as a catalyst.The experimental results show that the participation of AA can increase the dye removal rate from 31.1%.to 73.0%.Then the composite material RE-Fe₃O₄-CD was used as a catalyst to conduct experiments to explore the promoting effect of rare earth elements in the system,and compared two different ways of utilizing AA:（1）The AA/RE-Fe₃O₄-CD/H₂O₂ system formed by directly adding AA during the Fenton-like reaction;（2）In the process of material preparation,AA-RE-Fe₃O₄-CD catalytic composite was obtained by AA activation,and the AA-RE-Fe₃O₄-CD/H₂O₂ system was formed by Fenton-like reaction.Through the experimental comparison,it is found that the AA/La-Fe₃O₄-CD/H₂O₂,AA/Ce-Fe₃O₄-CD/H₂O₂,AA-La-Fe₃O₄-CD/H₂O₂ and AA-Ce-Fe₃O₄-CD/H₂O₂ systems are in the best reaction conditions After 30 min of reaction,the degradation rates of cationic blue X-GRL in each system were 96.0%,96.7%,98.3%and 98.7%,respectively,and the AA-RE-Fe₃O₄-CD/H₂O₂system contained more AA and H₂O₂.less,and less iron ion precipitation.The analysis of degradation kinetics shows that the degradation process of cationic blue X-GRL conforms to the first-order reaction in AA/RE-Fe₃O₄-CD/H₂O₂ and AA-RE-Fe₃O₄-CD/H₂O₂ systems.The degradation rate constants of dyes were higher in the AA-RE-Fe₃O₄-CD/H₂O₂ system.Cyclic degradation experiments show that the rare earth catalytic composites activated by AA have good reusability.（3）The mechanism of AA-RE-Fe₃O₄-CD/H₂O₂ system catalyzed degradation of dyes was explored through radical quenching experiment and ESR radical identification experiment.It can be seen from the experimental results that the AA-RE-Fe₃O₄-CD/H₂O₂ system mainly removes pollutants through Fenton-like oxidation,and·OH plays a major role in the system.The strong reducibility of AA can effectively reduce Fe³⁺and Ce⁴⁺in the system,and at the same time,its chelation greatly reduces the redox potential of Fe³⁺/Fe²⁺and Ce⁴⁺/Ce³⁺cycles,thereby enhancing the reaction of H₂O₂ with both cycles.（4）Select the more efficient and economical AA-RE-Fe₃O₄-CD/H₂O₂ system for the application research of printing and dyeing wastewater.The AA-RE-Fe₃O₄-CD/H₂O₂ system showed good degradation effect on rhodamine B,acid red and polyvinyl alcohol（PVA）,and the mineralization rate of terephthalic acid（PTA）at 30 min could reach above 50%.The AA-Ce-Fe₃O₄-CD/H₂O₂ system was reacted for 90 min under the conditions of pH 3,the dosage of the catalytic composite material was 0.2 g/L,and the dosage of H₂O₂ was 10 m M,and the mineralization rate of the simulated printing and dyeing wastewater was 83.3%.The experimental results show that the AA-RE-Fe₃O₄-CD/H₂O₂ system has practical significance in the application of advanced treatment of printing and dyeing wastewater.In this study,a series of systems have been developed to realize the organic combination of AA,rare earth elements and Fenton-like reaction,which can effectively improve the low efficiency of Fe³⁺reduction to Fe²⁺in Fenton-like reaction,and is expected to provide a new way for advanced treatment of printing and dyeing wastewater.