Study On Degradation Of Dye Wastewater Orange ? With Peroxymonosulfate Activated By MnFe₂O₄ Supported On Activated Carbon

Dye wastewater has characteristics of high organic content,poor biodegradability and strong toxicity.If it is untreated or not treated completely,it will cause serious pollution to food and water and then pose a threat to human survival and health.While being exposed to light radiation or acted by certain enzymes in human body,most azo dyes in dye wastewater will produce some carcinogenic aromatic amine compounds,which are difficult to be degraded.Therefore,it is of great significance to develop economical and efficient degradation technology for dye wastewater.Activated persulfate advanced oxidation technology has advantages of strong oxidation and high efficiency in the degradation of organic dyes and has attracted more and more attention in scientific research and practical application.According to the research progress of degradation technology and persulfate activation technology for dye wastewater in common use,combined with the catalytic activation of MnFe₂O₄ and activated carbon and the excellent characteristics of activated carbon as a cheap and easy-to-obtain carbonaceous material commonly used as the adsorption material and carrier matrix,the heterogeneous peroxymonosulfate?PMS?activator MnFe₂O₄supported on activated carbon?AC/MnFe₂O₄?with simple preparation process,separable recovery and high repeatability was synthesized by the coprecipitation method and was applied to the degradation study of azo dye Orange II.In the experiment,the preparation parameters of AC/MnFe₂O₄ were optimized to investigate the degradation of activated PMS on the orange II and optimum reaction conditions and the degradation mechanism of Orange II as well as the microscopic surface morphology,phase structure and structural stability of the material were evaluated comprehensively.The main conclusions are as follows:?1?Optimum preparation parameters of AC/MnFe₂O₄ are?the dosage of FeCl₃·6H₂O as 9.25 mM fixed for synthesis?:N₂ protected and water bath temperature is 90?,the pH value of synthetic mixed solution is 9,the dosage of AC is 5 g/L,molar mass ratio of iron/manganese is 2:1 and the stirring time is 30 min.?2?The catalytic activation ability of AC/MnFe₂O₄ on PMS is better than that of persulfacte?PS?and H₂O₂,and AC and MnFe₂O₄ in AC/MnFe₂O₄ synergistically promotes the activation effect on PMS.In the Orange II?100 mg/L?degradation experiment,the better dosage of AC/MnFe₂O₄ is 0.9 g/L and the better PMS concentration is 2 mM.The reaction system has a wide range of adaptability to the initial pH of the reaction solution.When the pH value is 11,the Orange II degradation rate is fast due to the synergistic activation of AC/MnFe₂O₄ and strong alkaline conditions,where the removal rate could be 97%after reaction for 2 min.Temperature and coexisting substances have little effect on the degradation of Orange II.It was found by the study that the reaction system has a good ability to degrade various dyes,the degradation rate for some common dyes from fast to slow is:Methyl orange>Malachite green>Orange II>Congo red>Methylene blue>Rhodamine B.?3?The degradation process of PMS activated by AC/MnFe₂O₄ on Orange II conforms to the pseudo-first order reaction kinetic model.The degradation mechanism is as follows:under the condition that the pH of the original reaction solution ranges from 3 to 9,a large amount of ¹O₂,SO₄^-·and·OH bound on the material surface is generated to degrade Orange II during the activation process;under the strong alkaline condition with the pH of the original reaction solution is 11,Orange II is degraded by a large amount O₂^-as well as SO₄^-·and·OH bound on the surface of the material.In the degradation process,chromophores of Orange II are rapidly destroyed with the cyclic transformation of redox couple between Fe?III?/Fe?II?and Mn?II?/Mn?III?and the conjugated system of naphthalene ring and benzene ring in the Orange II molecular structure is destroyed.Orange II is finally degraded into organic matter that is relatively stable and not easy to be further degraded,CO₂ and H₂O.?4?The SEM,TEM,BET,XRD and XPS of AC/MnFe₂O₄ showed that MnFe₂O₄are successfully loaded on the surface of activated carbon.Main mateiral components included in the AC/MnFe₂O₄ are SiO₂ and MnFe₂O₄.Compared with AC,the specific surface area of AC/MnFe₂O₄ is increased by about 11 times and the pore structure is mostly micropore and mesopore.AC/MnFe₂O₄ has larger specific surface area and porous structure,which can provide more activation sites.?5?The surface morphology and phase structure of AC/MnFe₂O₄ were not changed basically before and after the reaction.After 6 times of recycling,the degradation efficiency and removal rate of activated PMS on Orange II didn't decrease and the removal rate could be 99.3%.The concentration of Fe and Mn in the reaction solution after recycling reaction could be ignored which demonstrated AC/MnFe₂O₄has strong structural stability.This research explored a low-cost,simple and efficient Orange II dye simulated wastewater treatment technology,which avoids the problems that existing in the traditional Fenton oxidation degradation system.Besides,the activation and degradation mechanism was analyzed preliminarily to provide a certain experimental support for the theoretical development of persulfate activation technology and also offer certain theoretical reference for industrial application.It makes feeble performance to the development of dyeing wastewater treatment technology.