Novel UV-Strengthened Oxidative Decomplexation Processes And Mechanism For Efficient Treatment Of Cu-organic Complexes

Nowadays,advanced Treatment of Heavy Metals from Industrial Wastewater Has Been A Major Consideration Because of the Increasingly Stringent Emission Standards.Free Heavy Metals Ions Could Be Readily Removed by Traditional Processes,including Adsorption,precipitation,and Ion Exchange.however,due to the Complex Components and Variation of the Industrial Wastewaters,the Heavy Metals Therein Usually Strongly Interact with Ligands to Form Heavy Metals Complexes(HMCs).For Example,the Electroplating and Tanning Effluents Frequently Contain EDTA and Citrate,Which Could Complex with Most Heavy Metals.the HMCs Are Recalcitrant to Traditional Processes and Thus Become the Major Barrier to Meet the Emission Standards."oxidative Decomplexation/precipitation" Is the Common Strategy for Complexed Heavy Metals Removal.currently,hydroxyl Radical(OH)Based Advanced Oxidation Processes(AOPs)Has Been the Major Concern for HMCs Decomplexation.While There Are Still Some Drawbacks in These Processes,such as High H2O2 Dosage,Low Decomplexation Efficiency,and High Operation Cost.In This Dissertation,copper Complexes Were Selected as the Representative HMCs.Efficient Removal of Copper Complexes from Wastewater Was Achieved by the UV/persulfate(UV/PS)Process.then A Novel Combined Process of Fe(?)displacement/UV Photolysis/alkaline Precipitation(Abbreviated as Fe(?)/UV/OH)Was Proposed for the Removal of Several Kinds of Common Copper Complexes.The Results Showed That Both UV/PS and UV/H2O2 Processes Could Decomplex Cu(?)-EDTA,While UV/PS Exhibited Much Higher Efficiency with Broader Applicable pH Range in Comparison with the UV/H2O2 Process.moreover,the UV/PS Process Exhibited Better Performance in the Presence of Co-existing Substances,such as OH-,NO3-and Cl-.Similar Degradation Pathways of Cu(?)-EDTA Were Observed in Both Cases,indicating That Decarboxylation Is the Major Decomplexation Mechanism by Both ·OH and SO4·-.EPR Results Showed That Most Degradation Products Were Able to Activate PS and H2O2.Based on the Intensity of EPR Signals,the Consumption of Oxidants,and the Detection of Cu(?),the Active Species in the UV/PS Process Were Obviously Higher Than UV/H2O2.Finally,the Feasibility of UV/PS Process Was Further Demonstrated by Decomplexing Cu(?)-citrate,Cu(?)-NTA and Practical Electroplating Effluent.Despite UV/PS Has Showed Great Potential for Cu-complexes Decontamination,the Low Selectivity of Active Radicals Still Limits Its Efficiency in the Presence of Radical Quenchers at High Levels in Wastewaters.in This Dissertation,a Novel Combined Process of Fe(?)/UV/OH Was Proposed to Address the above Issue.the Combined Process Showed Satisfactory Performance in the Mitigation of Cu(?)-EDTA,Cu(?)-NTA,Cu(?)-citrate,Cu(?)-tartrate and Cu(?)-sorbate(From 19.2 Mg Cu/L to<1 Mg Cu/L).in Contrast,the precipitation,UV/precipitation and Fe(?)/precipitation Processes Exhibited Poor Copper Removal.based on above Results,cu(?)-citrate Was Selected as A Model Pollutant for Systematic Investigation.the Optimal Conditions for Cu(?)-citrate Treatment Were Found to Be at Initial pH 1.8-5.4,[Fe]:[Cu]=4:1,Irradiation Time 10 Min,and Precipitation pH 6.6-13.the Mechanism of Cu Removal from Cu(?)-citrate Was Disclosed as Follows:firstly,the Introduced Fe(?)Displaced Cu(?)from the Citrate Complex and Thus Fe(?)-citrate Was Formed.then,Fe(?)-citrate Was Degraded by Photolysis to Form 3-oxoglutarate and Acetoacetate.after 5 Min of Irradiation,citrate Was Almost Completely Removed with Only Small Amount of 3-oxoglutarate as the Degradation products.Finally,Cu(?)Was Removed by Fe(?)/Fe(?)Flocculation.an Electroplating Effluent Containing Complexed Cu(338 Mg Cu/L)Was Treated by the Proposed Combined Process,and the Final Cu Concentration Was Less Than 1 Mg Cu/L.Meanwhile,satisfactory Cu Removal Was Achieved with Solar Irradiation as the Light Source.In This Dissertation,distinct Decontamination Characteristics Were Observed between Cu(?)-carboxyl and Cu(?)-aminocarboxyl Complexes.to This end,Cu(?)-EDTA Was Selected as A Typical Cu(?)-aminocarboxyl Complex for Further Study.according to the Results,fe(?)Displacement and Photolytic Decarboxylation Were Regarded as the Major Mechanism of the First Two Steps,which Was Similar with the Case of Cu(?)-citrate.However,in the Case of Cu(?)-EDTA,decarboxylation Was No Longer An Important Mechanism for Cu(?)removal.Instead,Fe(?)Played An Essential Role in the Precipitation.the Degradation Products of EDTA,mostly Containing Amino Groups,Still Have Strong Interaction with Cu(?).Thus,the Fe(?)Generated during the Photolysis Could Complex with the Amino Groups and Thus Facilitate the Precipitation of Cu(?).Afterwards,Fe(?)Was Oxidized to Fe(?)by Dissolved Oxygen(DO),which Was Subsequently Removed via Co-precipitation.furthermore,the Concentration Evolutions of Cu(?),Fe(?)and DO during the Precipitation Were Measured to Rationalize the Optimal Fe(?)Dosage.finally,the Treatment of Cu(?)Aminocarboxyl Complexes Could Be Improved by Auxiliary Alcohols,which Was Ascribed to the Consumption of DO by the Fe(?)/alcohol/UV System.