Magneticseedingofnonmagneticadsorbentpowders

Magneticseedingofnon-magneticadsorbentpowdersbycoagulationusingferricchlorideandmagnetiteC.C.BorghiandM.FabbriABSTRACTAmagneticmodificationofconventionaladsorbentpowderstoremovethemrapidlyfromwaterisinvestigated.Inthispaperwestudythepossibilityofusinganon-magneticadsorbentpowdermixedwithmagnetiteandacoagulantsuchasferricchlorideaddedaftertheadsorptiontocreatemagneticflocsthatcanbemagneticallyseparated(magneticseeding).AnaturalzeoliteandNa-activatedzeolitemixedwithmagnetiteandferricchloridearetested.Thecombinationofsedimentation(withcoagulant)followedbymagneticfiltrationisfromsixto30timesfasterthanonlysedimentation(withcoagulant)inattainingthesamefinalturbidity.Also,amagneticactivatedcarbon(MAC)powderwithandwithouttheadditionofferricchlorideistested.Theprocessconditionsthatleadtoaresidualturbiditylessthan10%after5–10minofmagneticseparationaredefinedforallthepowders.ThetestsonMn(II)adsorptiononNa-activatedzeolite–magnetitemixturesshowthattheadsorptionimprovementduetoactivationisnotaffectedbytheadditionofthecoagulant.Moreover,adsorptionofthetestedcationicsurfactantsonMACisupto30%higherbyaddingferricchloride.NegligibleconcentrationsofFe(III)arefoundinalltreatedsamples.Thistechniquecanpotentiallybeappliedtoanynon-magneticadsorbentpowderand/ortoanyexistingcoagulation/flocculationtreatment.C.C.Borghi(correspondingauthor)M.FabbriDepartmentofElectric,ElectronicandInformationEngineering‘GuglielmoMarconi’(DEI),UniversityofBologna,VialeRisorgimento2,40136Bologna,ItalyE-mail:[e-mail]|adsorbentpowders,coagulation,magneticseeding,magneticseparation,watertreatmentINTRODUCTIONThemagneticseparationofpollutantsfromwaterisnotanewprocess(Svoboda;Nishijima&Takeda;Tangetal.).Amagneticfilterexploitsthemagneticforceactingonamagnetizableparticleinanexternallyappliedfluxdensityfieldwithaspatialgradient(Abbasov;Marianietal.).InMarianietal.(),Borghietal.(,)andBorghi&Fabbri()acontinuous-flowmagneticsystemusingsteelwoolorsteelspheresasthefilteringelementisanalysedtoremovemagneticpow-dersthatcanadsorbpollutantsfromwater.Themagneticseparationofpollutantsfromwaterconsistsoftwophases:first,thepollutantisadsorbedonapowderandsecond,thepowderisremovedbypassingthroughamag-neticfilter.Theefficiencyoftheprocesscriticallydependsonbothsteps:theoptimalprocessrequiresapowderwithbothgoodadsorbanceandmagneticproperties.Usually,tofulfilltheserequirements,powderswithgoodadsorbentpropertiesortailoredforspecificpollutants(zeolites,acti-vatedcarbons,polymers,etc.)aremagneticallymodifiedinthelaboratoryusingdifferenttechniques(Oliveiraetal.;Nakahiraetal.;Gangetal.;Nethajietal.).Theuseofthesemagneticpowdershaseconomicandenvironmentalcostsintermsofchemicalsandenergyrequiredintheirsynthesis.Asimpleralternativecanbetheuseofanon-magneticadsorbentpowdertogetherwithamagneticnon-adsorbentpowderbondedbyacoagulantaddedafterthepollutantadsorptionphase.Thus,thiskindofmagneticseeding(Svoboda)canbeappliedtoanytreatmentinvolvingconventionaladsorbentpow-ders.Thiswouldallowallthesurfaceoftheadsorbent728©IWAPublishing2014WaterScience&Technology:WaterSupply|14.5|2014doi:10.2166/ws.2014.009powdertobeavailableforadsorption.Theadditionofacoagulantisnotaconcernfortheapplicationinwatertreatmentplantssinceitisalreadywidelyusedtoclarifysuspensions.Usually,theseparationofthesuspendedsolidfractioniscarriedoutbyintroducingacoagulantduringrapidmixingtodestabilizethesuspensionandgen-erateaggregates(flocs)removedthroughsedimentationfollowedbysandormembranefiltration(Kawamura;Metcalf&Eddy;Amirtharajah&CaseyJones).However,ifthecoagulationalsoinvolvesamagneticfraction,thereisthepossibilitytoremovethegeneratedaggregatesusingfastmagneticfiltration.Besidesalltheadvantagesofusinganalready-knownadsorbentpowder,avoidingthenecessityofanewcharacterization,thissolutioncanbeappliedtoanynon-magneticadsorbentpowderand/oranyexistingcoagulation/flocculationtreatmentinordertoreducethespaceandtimerequirements.Theaimofthispaperistoinvestigatethepossibleapplicationoftheproposedprocesstoaconventionaladsorbentpowder.Inparticular,theadditionofferricchloride(FeCl3·6H2O)toamixtureofnaturalzeolite(mainlychabazite:(Na0.14K1.03Ca1.00Mg0.17)[Al3.46Si8.53-O24]9.7H2O)andmagnetite(Fe3O4)powdersafterthepollutantadsorptionisanalyzed.Moreover,thesamecoagulantisalsoappliedtoacommercialmagneticallymodifiedactivatedcarbon(MAC)powder.First,theimpor-tanceofthecoagulantadditiontothemagneticfiltrationefficiencyisanalyzed.Second,apossibleproblemrelatedtotheadditionofthecoagulant,thatis,itseffectsonthepollutantsadsorption,isinvestigated.Consideringthezeo-lite–magnetitemixtures,theadsorptionefficiencyofMn(II)isstudiedasinTaffarel&Rubio()inordertotestwhethertheadsorptionimprovementduetoNa-activationisaffectedbytheadditionofthecoagulant.TocarryoutthesetestsMn(II)ischosenbecausezeolitesarewidelyusedtoremovecations.ConsideringtheMACpowder,theresidualconcentrationsofpollutantsafterthetreat-ment,withandwithouttheadditionofthecoagulantduringtheprocess,aremeasuredtocheckthe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