电絮凝Complexingagentandheavymetalremovalsfrom

JournalofHazardousMaterials165(2009)838–845ContentslistsavailableatScienceDirectJournalofHazardousMaterialsjournalhomepage:fluentbyelectrocoagulationwithstainlesssteelelectrodesIs¸ıkKabdas¸lı∗,TülinArslan,Tu˘gbaÖlmez-Hancı,IdilArslan-Alaton,OlcayTünayIstanbulTechnicalUniversity,CivilEngineeringFaculty,EnvironmentalEngineeringDepartment,34469Maslak,Istanbul,TurkeyarticleinfoArticlehistory:Received8August2008Receivedinrevisedform15October2008Accepted16October2008Availableonline1November2008Keywords:MetalplatingeffluentComplexedmetaltreatmentElectrocoagulationwithstainlesssteelelectrodesOrganiccomplexformerremovalNickelandzincremovalabstractInthepresentstudy,thetreatabilityofametalplatingwastewatercontainingcomplexedmetalsorigi-natingfromthenickelandzincplatingprocessbyelectrocoagulationusingstainlesssteelelectrodeswasexperimentallyinvestigated.Thestudyfocusedontheeffectofimportantoperationparametersonelec-trocoagulationprocessperformanceintermsoforganiccomplexformer,nickelandzincremovalsaswellassludgeproductionandspecificenergyconsumption.Theresultsindicatedthatincreasingtheappliedcurrentdensityfrom2.25to9.0mA/cm2appreciablyenhancedTOCremovalefficiencyfrom20%to66%,butafurtherincreaseintheappliedcurrentdensityto56.25mA/cm2didnotaccelerateTOCremovalrates.ElectrolyteconcentrationdidnotaffecttheprocessperformancesignificantlyandthehighestTOCreduction(66%)accompaniedwithcompleteheavymetalremovalswereachievedattheoriginalchloridecontent(≈1500mgCl/L)ofthewastewatersample.NickelremovalperformancewasadverselyaffectedbythedecreaseofinitialpHfromitsoriginalvalueof6.Optimumworkingconditionsforelectrocoagu-lationofmetalplatingeffluentwereestablishedasfollows:anappliedcurrentdensityof9mA/cm2,theeffluent’soriginalelectrolyteconcentrationandpHofthecompositesample.TOCremovalratesobtainedforallelectrocoagulationrunsfittedpseudo-first-orderkineticsverywell(R292–99).©2008ElsevierB.V.Allrightsreserved.1.IntroductionTheincreasingdemandforthecontroloftoxicmetalsbeingreleasedfromindustrialactivitieshasledtothesearchofmoreeffectivetreatmentmethodsforheavymetalabatement.Conven-tionaltreatmentmethodshaveproventobesatisfactoryinmeetingthedischargeconsents.Amongthem,metalhydroxideprecipita-tionisthemostcommontreatmentmethodemployedforthemetalfinishingeffluents[1].Ontheotherhand,complexedmetalscannotbeefficientlyremovedbythismethodunderconventionaltreat-mentconditions.Complexedmetalsaretheformofmetalswhichareboundtostrongcomplexingagents(complexformer)keepingtheminsolution.Inthemetalfinishingindustry,electrolessplat-ingandimmersionplatingaretwomajorsourcesofwastewaterbearingcomplexedmetals[1].Modifiedhydroxideprecipitationorpretreatment(suchasoxidationandreduction)precedinghydrox-ideprecipitationareapplicabletreatmentmethodstocomplexedmetaleffluents.Modifiedhydroxideprecipitationisbasedontheadditionofcalciumtowhichcomplexingagentspreferentiallybind,allowingfreedmetalionstoprecipitateeffectively[1–4].Themain∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](I.Kabdas¸lı).obstacleofthisprocessisthatcomplexingagentswhichmaybeharmfulinmanywaysaresimultaneouslyreleasedintotheenvi-ronment.Viaapplicationofpretreatmentthecomplexingagentcanbecompletelydestroyedorconvertedintoaformthatdoesnotinterferewithconventionalprecipitation.Reductionandoxi-dationprocessesemployedaspretreatmentmethodshaveseveraldisadvantagessuchasthehighcostandtoxicityofthechemi-calsemployed[1–5].Hence,thedevelopmentofnewtreatmentmethodsforeffluentsbearingcomplexedmetalsisanurgentissue.Amongthemethodsthathaverecentlybeenstudied,electroco-agulation(EC)isdeemedapromisingoneasitprovedtobeveryefficientinremovingpollutantssuchasorganicandinorganicmat-tersfromtheindustrialwastewaters[6–17].Inaddition,anumberofscientificworkshaveindicatedthatheavymetalsinthefreeformcanbesuccessfullyremovedbyECusingaluminum,ironandcastironelectrodes[18–24].Adhoumetal.[18]experimentallyinvestigatedthetreatabilityofsyntheticsamplesfortheelectroplatingwastewatercontain-ingcopper,zincandhexavalentchromiumbyECwithaluminumelectrodes.Theirstudydemonstratedthattheincreaseofcurrentdensitythatrangedbetween8and48mA/cm2enhancedthetreat-mentrateandhighestremovalefficienciescouldbeachievedwhenthepHwaskeptbetween4and8.LaiandLin[19]experimen-tallyexploredtheECapplicationtochemicalmechanicalpolishing0304-3894/$–seefrontmatter©2008ElsevierB.V.Allrightsreserved.doi:10.1016/j.jhazmat.2008.10.065I.Kabdas¸lıetal./JournalofHazardousMaterials165(2009)838–845839(CMP)wastewaterfromsemiconductorfabricationusingcastiron,aluminumandtitaniumplatesindifferentcombinationsastheanode/cathodepairs.Theirresultsrevealedthataluminum/castiron(anode/cathode)wasagoodelectrodepairandwasabletoachieve99%copperremoval,96.5%turbidityreductionand75%CODremovalinlessthan100min.InotherstudiespublishedbyLaiandLin[20,21],sludgecharacteristicsofCMPtreatedbyECwereinvestigatedanditwasemphasizedthattheECprocessgen-eratesasignificantamountofsludgeth