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Empiricalcorrelationstoestimateagglomeratesizeanddepositionduringinjectionofapolyelectrolyte-modifiedFe0nanoparticleathighparticleconcentrationinsaturatedsandTanaponPhenrata,b,Hye-JinKima,FritjofFagerlundb,c,TissaIllangasekareb,GregoryV.Lowrya,⁎aCenterforEnvironmentalImplicationsofNanotechnology(CEINT),DepartmentofCivil&EnvironmentalEngineering,CarnegieMellonUniversity,Pittsburgh,PA15213-3890,USAbCenterforExperimentalStudyofSubsurfaceEnvironmentalProcessesatColoradoSchoolofMines,USAcDepartmentofEarthSciences,UppsalaUniversity,Villavägen16,75236Uppsala,SwedenarticleinfoabstractArticlehistory:Received22April2010Receivedinrevisedform19August2010Accepted1September2010Availableonline16September2010Controlledemplacementofpolyelectrolyte-modifiednanoscalezerovalentiron(NZVI)particlesathighparticleconcentration(1–10g/L)isneededforeffectiveinsitusubsurfaceremediationusingNZVI.Deepbedfiltrationtheorycannotbeusedtoestimatethetransportanddepositionofconcentratedpolyelectrolyte-modifiedNZVIdispersions(N0.03g/L)becauseparticlesagglomerateduringtransportwhichviolatesafundamentalassumptionofthetheory.Herewedeveloptwoempiricalcorrelationsforestimatingthedepositionandtransportofconcentratedpolyelectrolyte-modifiedNZVIdispersionsinsaturatedporousmediawhenNZVIagglomerationinporousmediaisassumedtoreachsteadystatequickly.ThefirstcorrelationdeterminestheapparentstableagglomeratesizeformedduringNZVItransportinporousmediaforafixedhydrogeochemicalcondition.Thesecondcorrelationestimatestheattachmentefficiency(stickingcoefficient)ofthestableagglomerates.Bothcorrelationsaredescribedusingdimensionlessnumbersderivedfromparametersaffectingdepositionandagglomerationinporousmedia.Theexponentsforthedimensionlessnumbersaredeterminedfromstatisticalanalysisofbreakthroughdataforpolyelectrolyte-modifiedNZVIdispersionscollectedinlaboratoryscalecolumnexperimentsforarangeofionicstrength(1,10,and50mMNa+and0.25,1,and1.25mMCa2+),approachvelocity(0.8to55×10−4m/s),averagecollectorsizes(d50=99μm,300μm,and880μm),andpolyelectrolytesurfacemodifierproperties.Attachmentefficiencydependedonapproachvelocityandwasinverselyrelatedtocollectorsize,whichiscontrarytothatpredictedfromclassicfiltrationmodels.Highionicstrength,thepresenceofdivalentcations,lowerextendedadsorbedpolyelectrolytelayerthickness,decreasedapproachvelocity,andalargercollectorsizepromotedNZVIagglomer-ationanddepositionandthuslimiteditsmobilityinporousmedia.Theseeffectsarecapturedquantitativelyinthetwocorrelationsdeveloped.TheapplicationandlimitationsofusingthecorrelationsforpreliminarydesignofinsituNZVIemplacementstrategiesisdiscussed.©2010ElsevierB.V.Allrightsreserved.Keywords:ZerovalentironnanoparticlesRemediationColloidaltransportSubsurfacedeliveryEmpiricalmodelDNAPLChlorinatedorganicsMetalsEnvironmentalnanotechnologyFateandtransportDLVOFiltrationmodelPorousmediaSubsurface1.IntroductionNanoscalezerovalentiron(NZVI)rapidlydechlorinateschlorinatedorganicsorimmobilizesheavymetalsfoundincontaminatedgroundwater(Liuetal.,2005,2007;Lowry,2007;Phenratetal.,2009b,2010a;Zhang,2003).Initialfielddemonstrationsassessingtheperformanceofthistechnologyarepromising(ElliottandZhang,2001;HennandWaddill,2006;Karnetal.,2009).BareNZVI,however,agglomeratesrapidly,makingsubsurfacedeliverydifficult(Phenratetal.,2007).SeveraltechniqueshavebeenusedtodecreaseJournalofContaminantHydrology118(2010)152–164⁎Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](G.V.Lowry).0169-7722/$–seefrontmatter©2010ElsevierB.V.Allrightsreserved.doi:10.1016/j.jconhyd.2010.09.002ContentslistsavailableatScienceDirectJournalofContaminantHydrologyjournalhomepage:fiedbyadsorbedpolymerafterNZVIsynthesis(Kimetal.,2009;Phenratetal.,2009a;2008;Salehetal.,2008;Sirketal.,2009).ThisenhancesbothNZVIdispersionstability(Phenratetal.,2008;Salehetal.,2005)anddeliverabilityinporousmedia(Phenratetal.,2009a;Salehetal.,2008,2007;Sirketal.,2009)duetoelectrostericrepulsionsaffordedbyadsorbedpolymerthatcountermagneticandvanderWaalsattractionsthatpromoteagglomerationanddeposition.ImprovedstabilityagainstagglomerationandenhancedtransportinporousmediacanalsoresultfrompolymericsurfacemodificationduringNZVIsynthesis(Heetal.,2009;Kaneletal.,2008).SubmicronporoussilicaorcarbonhasalsobeenusedasasupportforNZVI.ThissupportedNZVIhadenhancedtransportcomparedtounsupportedNZVI(Schricketal.,2004;Zhanetal.,2009,2008).ThesedifferentNZVImodificationapproachesyieldNZVIhavingdifferentphysicochemicalpropertiesandthere-foredifferentinteractionforcesgoverningtheiragglomera-tionandtransportinporousmedia.Inthisstudy,wefocusonpolymermodifiedNZVIwheresurfacemodificationoccurredpostNZVIsynthesis(Hydutskyetal.,2007;Johnsonetal.,2009;Phenratetal.,2009a,2008;Salehetal.,2005;Tiraferrietal.,2008;Vecchiaetal.,2009).SuccessofinsituremediationusingpolymermodifiedNZVIdependsontheabilitytodeliverNZVIdispersionathighparticleconcentration(1to20g/L)tocontaminatedareas.Althoughseveralresearchgroupshavestudiedtransportanddepositi