电絮凝EvaluationofMn2andCo2removalbyelectro

ChemicalEngineeringandProcessing50(2011)1115–1121ContentslistsavailableatSciVerseScienceDirectChemicalEngineeringandProcessing:ProcessIntensificationjournalhomepage::AcasestudyAshrafShafaeia,b,∗,MaryamRezaieb,ManouchehrNikazarbaNationalPetrochemicalCompany,ResearchandTechnologyCo.,No.12,SarvAlley,ShiraziSouthStreet,MollaSadraAve.,POBox14358-84711,Tehran,IranbChemicalEngineeringDepartment,AmirkabirUniversity,No.424,HafezAve.,Tehran,IranarticleinfoArticlehistory:Received1June2011Receivedinrevisedform18September2011Accepted8October2011Availableonline20October2011Keywords:ElectrocoagulationprocessWastewatertreatmentHeavymetalsManganeseCobaltabstractInthispaper,removalofManganese(Mn2+)andCobalt(Co2+)ionsfromaqueoussolutionsarestudiedusingelectrocoagulation(EC)withaluminiumelectrodes.Theeffectofoperationalparameterssuchasinitialmetalconcentration,appliedcurrentdensity,chargeloadingandthepresenceofothermetalionsontheperformanceoftheECprocesswereinvestigated.TheexperimentalresultsrevealedthattheremovalrateofMn2+andCo2+decreasedbyincreasingtheinitialmetalconcentration.Increasingthecurrentdensityacceleratedthepollutantremovalrate.Also,itwasfoundthatCobaltionswereremovedtwicefasterthanManganeseionsunderthesameconditions.TheoptimumEC-postcontacttimewas15minandabout10%additionalremovalofMn2+andCo2+wasobserved.Inaddition,theobtainedresultsshowedthatMn2+andCo2+wereeffectivelyremovedfromanindustrialwastewateratoptimaloperatingconditions.©2011ElsevierB.V.Allrightsreserved.1.IntroductionWastewaterscontainingheavymetalslikeManganese(Mn)andCobalt(Co)pollutantscreateaseriousdischargeproblemduetotheirnon-biodegradability,hightoxicityandecologicalaspects.MnandCoasnaturalelementsareessentialforlifeintraceamounts.But,excessiveconcentrationsofthesemetalshavedetrimentaleffectsonthelivingorganisms.Therefore,beforedisposingindus-trialwastewaters,theirmetalcontentsshouldbeeliminated.Thereareseveralmethodsfortheremovalofthesemetalionsfromwaterandwastewater[1,2].Electrocoagulation(EC)isanelectrochemicalwastewatertreat-menttechnology.TheECprocessisbasedonthecontinuousinsituproductionofacoagulantbyanodicdissolutionand,subsequently,producesaluminiumorironhydroxidesinthecontaminatedwater.TheelectrochemicalreactionswithaluminiumelectrodeinanECcellmaybesummarizedasfollows:Abbreviations:EC,electrocoagulation;Mn2+,Manganeseion;Co2+,Cobaltion;C0,initialconcentrationofstudiedmetalions(mg/l);Ct,themetalionsconcentra-tionsattimet(mg/l);Kt,kineticconstant(min−1);CD,currentdensity(mA/cm2);CL,chargeloading(mAsl−1);TMRe,totalmetalremovalefficiency;COD,chemicaloxygendemand(mg/l).∗Correspondingauthorat:NationalPetrochemicalCompany,ResearchandTech-nologyCo.,No.12,SarvAlley,ShiraziSouthStreet,MollaSadraAve.,POBox14358-84711,Tehran,Iran.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail],[e-mail](A.Shafaei).a.Anodicreactions:Al→Al3++3e−(1)2H2O→O2(gas)+4H+(aq)+4e−(2)b.Cathodicreactions:2H2O+2e−→H2(gas)+2(OH)−(aq)(3)Furthermore,thehydroxideionsformedatthecathodeincreasethepHofthewastewater;therebyinducingtheprecipitationofmetalionsascorrespondinghydroxidesandco-precipitationwithaluminiumhydroxides[3]:Mn++nOH−→M(OH)n↓(4)ElectrolyticdissolutionofthealuminiumanodeproducescationicmonomericspeciessuchasAl3+andAl(OH)2+atlowpH,which,atappropriatepH-values,areinitiallytransformedintoAl(OH)3and,finally,polymerizedtoAln(OH)3n[4].Incomparisonwithtraditionalmethods,ECprocesshasmanyadvantageslikesimpleequipmentrequirement,easyoperation,nochemicaluserequirement,rapidsedimentationanddecreasedamountofsludge[4–6].Hence,ECisanefficient,credibleandlow-costmethodfortreatingalargevarietyofwastewatersuchasindustrialwastewater[7],phenolicwastewater[8,9],CODremoval[10],dyes[11–13],restaurantwastewater[14],oil–wateremul-sions[15],andheavymetal-containingsolutions[1–4,16–21].Inthepresentresearchers’previousstudies,Mn2+[1]andCo2+[2]removalfromsinglemetalionsolutionsthroughtheECprocesswasstudiedandtheeffectofseveraloperationalparametersonthe0255-2701/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.cep.2011.10.0031116A.Shafaeietal./ChemicalEngineeringandProcessing50(2011)1115–1121removalefficiencyofthesemetalionsfromsingle-metalsolutionswasinvestigated.TheresultsindicatedthattheinitialpHofsolutionhadasignificanteffectontheremovalefficiency,especiallyatlowpH,andtheoptimuminitialpHwasintherangeof4–8.Also,theremovalofmetalionswasnotinfluencedbythesolutionconduc-tivity;however,theelectricalenergyconsumptionofECdecreasedwithanincreaseinthesolutionconductivity.Theaimofthisstudyistoinvestigatetheeffectofinitialmetalconcentration,currentden-sityandchargeloadingontheremovalrateofMn2+andCo2+andtocomparetheremovalrateofthesemetalsfromsinglemetalsolu-tions.Inaddition,theremovalefficienciesofMn2+andCo2+frombinarymetalsolutionswithdifferentMn–Coconcentrationratiosarestudied.FinallyMn2+andCo2+removalfromarealwastewaterisgoingtobedetermined.2.Experiments2.1.MaterialsandmethodsManganeseS