Removal Of Cu-EDTA And Cr(Ⅵ) From Wastewater By Persulfate/formate Oxidation-reduction Method

As electroplating,electroless plating and printing and dyeing industry fast development,in order to improve the activity of the surfactant,a large number of organic complexing agent such as ethylenediaminetetraacetic acid（EDTA）is widely used,so EDTA and heavy metal ions are very easy to discharge to the wastewater,and the EDTA is easily chelated with heavy metal ions in waste water to generate steady heavy metal complex.Compared with heavy metal ions,heavy metal complexes are more toxic to the environment and microorganisms,and have poor biodegradability.The removal effect of heavy metal complexes is not good by traditional water treatment methods.It is urgent to remove heavy metal complexes and heavy metal ions effectively from wastewater.In recent years,the application of persulfate（PS）oxidation technology in wastewater treatment has received widespread attention.However,the traditional persulfate activation method has the problems of adding additional chemical substances or consuming energy.An endogenously activated persulfate system for Cu-EDTA removal and a persulfate/sodium formate（FA）redox system for simultaneous removal of Cu-EDTA and Cr（Ⅵ）have been proposed.It mainly focuses on the degradation law of target pollutants,the identification and contribution analysis of radicals,the degradation mechanism and pathway of heavy metal complexes and heavy metal ions.The main work and conclusions of this study are as follows:（1）The endogenously activated persulfate was used to remove Cu-EDTA from wastewater.The degradation characteristics of Cu-EDTA were investigated by the dosage of sulfate,the initial Cu-EDTA concentration,the addition amount of Cu²⁺and EDTA,and the initial p H value of the solution.It was found that the endogenously activated persulfate system could efficiently degrade Cu-EDTA from wastewater.After 90 min of oxidation treatment,the remocal efficiency of Cu-EDTA can reach 90.98%.Increasing the PS content and adding extra Cu²⁺to the reaction system can promote the Cu-EDTA removal efficiency.Increasing the initial concentration of Cu-EDTA and adding extra EDTA to the reaction system are not conducive to the removal of Cu-EDTA.The removal effect of Cu-EDTA is better under acidic conditions.（2）The reactive oxygen species were identified by electron paramagnetic resonance spectrometer（EPR）,and the contribution of the active species was investigated by radicals quenching experiment.The Zeta potential and p H value of the solution were analyzed by electron laser particle size analyzer and p H meter.The intermediate products and by-products were identified by GC/MS and Ion Chromatography（IC）.The precipitates were investigated by energy dispersive X-ray（EDX）and X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）,respectively.The ability of Cu-EDTA intermediates on PS activation was verified.It was found that SO₄^·-,·OH,and ¹O₂played an important role in the removal of Cu-EDTA.The system is a persulfate activation system induced by Cu-EDTA and strengthened by intermediates.Under the action of reactive oxygen species,Cu-EDTA is gradually decomposed into small molecular acids,which release Cu²⁺and finally decompose into H₂O and CO₂.（3）Cu-EDTA and Cr（Ⅵ） can be simultaneously removed from wastewater by a PS/FA redox system.The removal property of Cu-EDTA and Cr（Ⅵ）in the reaction process were investigated through the solution temperature,the FA and PS content.When the dosage of PS and FA was 20 mmol L^-1and 10 mmol L^-1at 60℃,the removal efficiency of Cu-EDTA and Cr（Ⅵ）could reach 93%and 100%after 90 min treatment.Electron paramagnetic resonance spectrometer（EPR）was used to identify the radicals produced during the reaction process,and radicals quenching experiment was carried out to analyze the contribution of the radicals.UV-vis spectroscopy（UV-Vis）and FTIR were used to detect t structural changes of pollutants after treatment.GC-MS was used to identify the intermediate products during treatment.The precipitates were analyzed by XRD,FTIR and XPS.It was found that oxidizing radicals SO₄^·-,·OH,and ¹O₂played an important role in the removal of Cu-EDTA,while reducing radicals CO₂^·-was mainly responsible for the removal of Cr（Ⅵ）in the reaction solution.Cu-EDTA was oxidized and decomposed into small molecular acids,which were finally decomposed into H₂O and CO₂,and Cr（Ⅵ）is reduced to Cr³⁺.