RemovalofnanoparticlesfromCMPwastewaterbymagnetic

TechnicalNoteRemovalofnanoparticlesfromCMPwastewaterbymagneticseedingaggregationChing-JuMonicaChin*,Pei-WenChen,Li-JenWangGraduateInstituteofEnvironmentalEngineering,NationalCentralUniversity,300JungdaRoad,JungliCity,Taoyuan320,Taiwan,ROCReceived21March2005;receivedinrevisedform19September2005;accepted22September2005Availableonline9November2005AbstractCMPwastewatershavehighsolidscontentresultedfromabrasivenanoparticles.TremendousamountofultrapurewaterconsumptionalsomakestheremovalofnanoparticlesfromCMPwastewatersanimportantissue.Magneticseed-ingaggregationofsilicananoparticlesfromtheoxideCMPwastewaterisstudiedinthiswork.Magnetitenanoparticlesweresynthesizedandusedasseedingparticles.TheturbidityoftheCMPwastewaterwasreducedfrom110NTUto7NTUwhensolutionpHwas6andnoadditionofsalt.Thisisbecausesilicaandmagnetitenanoparticleswerehighlyoppositelychargedandtheaggregationbetweensilicaandmagnetitenanoparticleswasachievedbyelectrostaticattrac-tions.Whentheseededwastewaterwasplacedinamagneticfieldstrengthhigherthan800G,theturbidityoftheCMPwastewaterwasreducedto1NTU,whichwasclearerthantheCMPwastewatertreatedbymanyothertechnologies.2005ElsevierLtd.Allrightsreserved.Keywords:CMPwastewater;Nano-magnetite;Magneticseedingaggregation1.IntroductionNanoparticleshavefascinatedindustriesandresearchersfortheirbroadapplicationsinelectronicsdevices,biomedicines,andseparationprocesses.Itcanbeforeseenthattherewillbemoreandmorenanoparti-clesmanufacturedanddischargedtonaturalwaterenvi-ronments.Silicananoparticlesinchemicalmechanicalpolishing(CMP)wastewatersfromthesemiconductorindustry,forinstance,havebecomeamajorsourceofnanoscalewaste.SilicananoparticlesarecommonlyusedasabrasiveinCMPslurries,inwhichparticlesarehighlychargedtoavoidaggregationsbetweenparti-clesandparticlesorparticlesandwafersurfaces.There-fore,theCMPwastewaterhasveryhighsolidscontentandtheremovalofthosesolidshasreceivedgreatattentions.ConventionalchemicalcoagulationismostlyusedtoremovesilicananoparticlesfromtheCMPwastewater;however,ithasbeennotoriousfortremendousproduc-tionofsludge.Also,dramaticvariationsintheturbidityoftheCMPwastewater(65–400NTU)alwaysleadtodifficultiesincontrolsofcoagulantdosage.Alternativetreatmentprocesses,suchaselectrocoagulation,flota-tion,andmembranefiltration,havebeendevelopedtoremovenanoparticlesfromCMPwastewaters(Goldenetal.,2000;Lien,2001;Huangetal.,2004;LaiandLin,2004).Theremovalefficienciesofnanoparticlesby0045-6535/$-seefrontmatter2005ElsevierLtd.Allrightsreserved.doi:10.1016/j.chemosphere.2005.09.035*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](C.-J.M.Chin).Chemosphere63(2006)1809–1813ffectedbythequalityoftheCMPwastewaters.Astherearemoreandmoreapplicationsofnano-materialsinwastewatertreatments,separationofnano-materialsfromaqueousstreamsbecomesanimportantissue.Recently,magneticseparationattractsgreatatten-tionsbecausemagneticforceisalong-rangeattraction;thus,separationsofnanoparticlescanbeenhanced.Non-magneticmaterialscanbecomemagneticviamag-neticseedingaggregation,whichcanbeeasilyadoptedinvariousprocesses.Magneticseedingaggregationhasbeenusedtoimprovethesludgecharacteristicsinacti-vatedsludgesystems(Sakaietal.,1997).ThesludgeagewasincreasedandtheremovalefficiencyofCODwasimproved.Magneticseedingaggregationsandsepa-rationscanalsoremovedissolvedmoleculeseffectively.Fengetal.(2000)magnetizedmetal-ions-sorbedzeoliteparticlesbymagneticseedingaggregationandfoundthattheremovalefficiencyofleadionswasalmost100%.Wuetal.(2004)studiedtheremovalofazodyeAcidRedBbymagneticCuFe2O4powder.ItwasfoundthatCuFe2O4powderactedasanadsorbentaswellasacatalystandtheremovalefficiencyofAcidRedBcouldbeenhancedto95%.Magneticseedingaggregationhasalsobeenusedintheremediationofoilspill(ChunandPark,2001).Itisfoundthatover90%ofcrudeoilcouldbeadsorbedbymaghemiteparticles.Theobjectiveofthisstudyistodevelopanalterna-tivetreatmentprocesstoremovesilicananoparticlesfromtheoxideCMPwastewater.Toensuresufficientcollisionsbetweenmagnetiteandsilicananoparticlesperunitmassofmagnetiteseedingparticles,magnetitenanoparticlesweresynthesizedandthenusedintheaggregationexperiments.InfluencesofsolutionpH,additionofsalt,andtypesofmagnetiteseedingparticlesontheremovalofturbiditywereexamined.Sedimenta-tionsofaggregatesindifferentmagneticfieldstrengthswerealsoobserved.2.MaterialsandmethodsMagnetitenanoparticlesweresynthesizedbychemi-calco-precipitationofFeCl2andFeCl3inNaOHsolu-tions.Topreventtheaggregationbetweenmagnetitenanoparticlesduetotheremnantmagnetizationandtoavoidthedifficultiesincapturingnanoparticles,thesizeofmagnetitenanoparticleswascontrolledto100nmbytheadditionofsodiumdodecylsulfate(SDS).Synthe-sizedparticleswerewashedbydeionizedwater.Moredetailedsyntheticprocedurescanbefoundinourprevi-ouswork(Chinetal.,2005).TheoxideCMPwastewaterwasobtainedfromasemiconductorplant.ThequalityofthewastewaterisgiveninTable1.Particlesizesandzetapotentialsofsynthesizedmagnetiteandsilicanano-particlesfromCMPwastewa