电絮凝Applicationoftheelectrocoagulationtechniqu

854†Towhomcorrespondenceshouldbeaddressed.E-mail:[e-mail].,27(3),854-861(2010)DOI:10.1007/s11814-010-0145-3RAPIDCOMMUNICATIONApplicationoftheelectrocoagulationtechniquefortreatingheavymetalscontainingwastewaterfromthepicklingprocessofabilletplantChaloempanPetsriprasit*,JirachayaNamboonmee**,andMaliHunsom*,**,†*DepartmentofChemicalTechnology,FacultyofScience,**CenterforPetroleum,Petrochemicals,andAdvancedMaterials,ChulalongkornUniversity,Bangkok10330,Thailand(Received9March2009•accepted13October2009)Abstract−Thisworkwascarriedouttostudytheremovalofvariousheavymetals,includingCu,Cr,PbandZn,frombilletindustrywastewaterbytheelectrocoagulationprocessinbothbatchandcontinuousexperimentsatala-boratoryscaleandambienttemperature(30oC).Inthebatchexperiment,theeffectofvariousparametersincludingthecurrentdensity,initialwastewaterpHandelectrolysistime,onthemetalremovalefficiencywasexamined.Optimalmetaliondepletionwasattainedwithacurrentdensityof98A/m2,aninitialwastewaterpHof5anda30minelec-trolysistime.Undertheseconditions,greaterthan99%ofCu,CrandZnwasremoved,whilsttheoutletwastewatercontainedCu,Cr,PbandZnatlessthan0.02,0.01,0.07and0.05mg/l,respectively.Forthecontinuousprocess,theresultsindicatedthatthetreatmentsystemreacheditssteadystateconditionwithin120min,andtheoptimumconditionforthecontinuoustreatmentwasfoundataninitialwastewaterpHof3andflowrateof55ml/min.Atthiscondition,acompleteremovalofCuandPbandgreaterthan99%removalofCrandZnwereachieved.Keywords:Electrocoagulation,MetalRemoval,CurrentEfficiency,PicklingProcessINTRODUCTIONThepicklingprocess,whichisusedtoremoveoxidescalesfromthesurfaceofrawmetalspecimenspriortoprocessing,isahydro-metallurgicalprocessthattypicallyuseshydrochloric,sulfuric,nitricandhydrofluoricacidsforthesurfaceetching[1].Effluentsfromthisprocessaretypicallycharacterizedbyhighlyconcentratedsolu-tionsofheavymetalionssuchaschromium(Cr),copper(Cu),nickel(Ni),zinc(Zn),etc.,andtheleachingacids,dependingonthepro-ductionprocess.Dischargingsuchwastewatertotheenvironmentwithoutproperremedialtreatmentisforbiddenduetoitshazard-ouspropertiestobothhumansandtheenvironment.Manyman-agementconceptsofsuchwastewaterhavebeencarriedout,suchasspentacidminimizationandspentacidrecovery[2-6].How-ever,duetothelargequantityofsuchwasteproductioneachyear,inthepastdecade,somenewapproacheshavebeeninvestigatedforthetreatmentofspentpicklingliquors,includingabsorption[7,8],chemicalprecipitation[9,10],extraction[11,12]andnanofiltration[13].However,alltheseschemesontheirownareeitherincom-plete,impracticalorunviable.Precipitation,forexample,requiresalargeamountofchemicaltreatmentandalsoproducesaconsider-ablevolumeoflow-densitysludge.Nanofiltrationisapressure-relatedprocessthatrequiresaspecificmembranetypeandhigh-pressurepumpleadingtohighinvestmentcosts.Inaddition,itrequiresthechemicalpre-treatmentofwastewatertopreventscalingandpre-cipitationofinsolublesolidsonthemembranesurface.Consideringtheeconomicsandscaleofwastewaterpurificationoperations,theelectrochemicalprocedurehasbeenfoundtobethemostsuitableprocess[14]duetoitsfastreactionrate,versatility,simplicityandeaseofoperation.Applicationofthisprocessfortreat-ingindustrialwastewatercanbeperformedindifferentways.Byemployingelectrooxidation,Vlyssidesetal.[15]demonstratedthatthetypesofanodeusedandthepresenceofanoxidizingagenthadasignificantinfluenceonthetreatmentprocess.Greaterthan92%ofthecolorfromadistilleryeffluentwasreducedbyusingtitaniumsubstrateinsolubleanodes(RuO2-Ti)[7],orbyusingavoluminouselectrodeorgraphite[16].Chouetal.[17]demonstratedanovelelectro-Fentonmethod,usinganappliedH2O2andelectrogeneratedferrousion,andreportedthatthiswasthemosteffectivemethodcomparedwithH2O2/Fe2+,H2O2/Fe3+anddirectelectrolysis.ForCODremoval,Zhangetal.[18]reportedthattheCODremovaleffi-ciencyincreasedasthecurrentdensity,ferrousionandhydrogenperoxidedosageswereincreased.However,further(extreme)in-creasesinanyofthesethreevariablesaboveanoptimallevelthenledtoasignificantdecreaseinthemetalremovalefficiency.Inaddi-tion,theyreportedthatthestepwiseorcontinuousadditionofhy-drogenperoxidewasmoreeffectivethanasinglestepaddition.Byusingtheelectro-Fentonsystemcontainingapolypyrrole/anthraquino-nedisulphonate(PPy/AQDS)compositefilmmodifiedgraphitecath-ode,Zhangetal.[19]showedthattheirsystemcandegradeama-ranthazodyeefficientlyinvariousacidicsolutionsandtheamountofdopingAQDSinPPymatrixdidnotsignificantlyinfluencethedyedecayrate.Amongthepossibleusesoftheelectrochemicalprocessforwaste-waterremediation,electrocoagulationhasrecentlyattractedconsid-erableattentionduetoitsvarietyofapplicationsforvariouskindsofindustrialwastewatercontainingbothorganicandinorganicsub-stances.Forwastewatercontainingheavymetalions,Adhoumetal.[20]reportedthatthemosteffectivemetalremovalcapacitywasApplicationoftheelectrocoagulationtechniquefortreatingheavymetalscontainingwastewaterfromthepicklingprocessofabilletplant855KoreanJ.Chem.Eng.(Vol.27,No.3)byusinganaluminumelectrodeinthepHrangebetween4and8,whereasbyusingaironelectr