电絮凝Effectofanionsonremoving

JournalofHazardousMaterials189(2011)572–576ContentslistsavailableatScienceDirectJournalofHazardousMaterialsjournalhomepage:ÖzgeHanay,HalilHasar∗FiratUniversity,FacultyofEngineering,DepartmentofEnvironmentalEngineering,23119Elazig,TurkeyarticleinfoArticlehistory:Received4June2010Receivedinrevisedform20January2011Accepted23February2011Availableonline1March2011Keywords:HeavyMetalElectrocoagulationAluminumelectrodesAnionsabstractInthepresentstudy,theperformanceofelectrocoagulationprocesswithaluminumelectrodesinthetreatmentofCu2+,Zn2+andMn2+containingaqueoussolutionswasinvestigatedbydependingontypeofanioninsolution,consideringsomeoperatingconditionssuchasinitialmetalconcentrationandpH.Resultsobtainedfromsyntheticwastewatershowedthattypeofanioninsolutionshasasignificanteffectonthemetalremoval.TheinitialconcentrationofzincinfluencedsignificantlytheperformanceofelectrocoagulationprocessascomparedwiththeresultsobtainedfromMnandCumetals.AnionsstudieddidnotgenerateanimportantdifferencebetweenpHvariations.BestremovalsforthreemetalswereachievedwithincreasingthepHinthepresenceofbothanions.Totalremovalsofcopperandzincreachedalmost100%after5minatpHvalues7.Attheendoftheexperimentsfor35min,theMnremovalswere85and80%inthepresenceofsulfateandchlorideanions,respectively.©2011ElsevierB.V.Allrightsreserved.1.IntroductionAnumberoftheindustrialeffluentscontaintoxicmetalssuchasCd,Cr,Cu,NiandZn,whichareharmfultotheenvironmentwhentheyaredirectlydischarged.Theycanbeeasilyabsorbedbyfishesandvegetablesduetotheirhighsolubilityintheaquaticenviron-ments.Hencetheymayaccumulateinthehumanbodybymeansofthefoodchain[1–3].Toeliminatetheiradverseeffectsonhumanandecology,itisabsolutelynecessarytotreatwastewaterincludingthesemetalsbeforebeingdischarged.Uptonow,severaltech-niquessuchaschemicalprecipitation,coagulation–flocculation,flotation,ionexchange,membraneseparation,solventextrac-tion,adsorptionandelectrocoagulation(EC)havebeenappliedtoremoveheavymetalsfromindustrialeffluents[1].Amongthevarioustechniquesmentionedabove,electrocoagulationhasbeenfoundtobequiteinterestingbothforeconomicalandenvironmen-talreasons[4].EChasbeensuccessfullyappliedtoremovesolubleionicspeciesfromsolutions,particularlyheavymetals[3,5].Electrocoagulation(EC)isbasedontheinsituformationofthecoagulantasthesacrificialanodecorrodesduetoanappliedcur-rent,whilethesimultaneousevolutionofhydrogenatthecathodeallowsforpollutantremoval.Intheelectrocoagulationprocess,mainreactionsoccurringattheelectrodesare:Al↔Al3++3e−(anode)(1)∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:hhasar@firat.edu.tr(H.Hasar).3H2O+3e−↔(3/2)H2+3OH−(cathode)(2)Inaddition,Al3+andOH−ionsgeneratedatelectrodesurfacesreactinthebulkwastewatertoformaluminumhydroxide:Al3++3OH−↔Al(OH)3(3)Thealuminumhydroxideflocsactasadsorbentsand/ortrapsformetalionsandsoeliminatethemfromthesolution.Simulta-neously,thehydroxylionsproducedatthecathodeincreasethepHintheelectrolyteandmayinducecoprecipitationofmetalsintheformoftheirhydroxides[5–7].IthasbeenreportedthattheinitialpHhasaconsiderableinfluenceontheperformanceofelec-trocoagulationprocess[3,5,8].Inaddition,chemicaldissolutionofaluminumisstronglyinfluencedbythepH[9].ManystudiesontheeffectsofvariousparameterssuchaspH,initialconcentration,currentdensity,inter-electrodedistanceandconductivityhavebeenperformed;thereisalittleknowledgeabouttheanioneffectonmetalremovalduetolimitedstudiesintheliter-ature[10–14].Inthisstudy,theeffectofanionsonremovingCu,ZnandMnbyelectrocoagulationwasinvestigatedonsolutionscon-tainingthesulfateandchlorideatdifferentoperatingparameterssuchasinitialconcentration,operatingtimeandinitialpH.2.MaterialsandmethodsStocksolutionsof1000mg/LCu,ZnandMnwerepreparedwithsulfateandchloridesaltsofeachmetal.Experimentswereperformedintwostages.Inthefirststage,toexaminetheeffectofinitialmetalconcentrationsonthesystemperformance,six0304-3894/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.jhazmat.2011.02.073Ö.Hanay,H.Hasar/JournalofHazardousMaterials189(2011)572–576573Table1Characteristicsoftheexperiments.ThecodeofrunsTheconditionsofrunsThecodeofrunsTheconditionsofrunsThecodeofrunsTheconditionsofrunsCS1Cu=50mg/LSO42−=75.6mg/LZS1Zn=50mg/LSO42−=73.4mg/LMS1Mn=50mg/LSO42−=87.4mg/LCS2Cu=100mg/LSO42−=151.2mg/LZS2Zn=100mg/LSO42−=146.8mg/LMS2Mn=100mg/LSO42−=174.8mg/LCS3Cu=200mg/LSO42−=302.4mg/LZS3Zn=200mg/LSO42−=293.6mg/LMS3Mn=200mg/LSO42−=349.7mg/LCC1Cu=50mg/LCl−=56mg/LZC1Zn=50mg/LCl−=54.4mg/LMC1Mn=50mg/LCl−=64.8mg/LCC2Cu=100mg/LCl−=112mg/LZC2Zn=100mg/LCl−=108.8mg/LMC2Mn=100mg/LCl−=129.6mg/LCC3Cu=200mg/LCl−=224mg/LZC3Zn=200mg/LCl−=217.6mg/LMC3Mn=200mg/LCl−=259.2mg/Lsolutions,whichwerepreparedindividuallyfromCuSO4·5H2O,MnSO4·H2O,ZnSO4·7H2O,CuCl2,MnCl2·4H2OandZnCl2,wereusedintheECsetupatdifferentconcentrations(50–200mg/L)andaconstantpHvalue(pH=3).ThepHincreasedovertimeduringoper-ation.Inthesecondstage,theinfluenceofpHwasexaminedtoensureabetterel