52-paper-Mechanism of Removal and Recycling of Hea

MechanismofRemovalandRecyclingofHeavyMetalsfromCopperbyChlorinationReactionYangCUI,HiroyukiMATSUURA,TasukuHAMANOandFumitakaTSUKIHASHI(DepartmentofAdvancedMaterialsScience,GraduateSchoolofFrontierSciences,TheUniversityofTokyo,5-1-5,Kashiwanoha,Kashiwa,Chiba,277-8561,Japan)Abstract:Inordertomakecleartheremovalandrecyclingmechanismofiron,leadandantimonyfrommoltencopperscrapbychlorinationreaction,theremovalrateofthesemetalsbyCuCl-basedfluxeswasmeasuredfrom1423Kto1473K.TheconcentrationsofironandleadinliquidcopperdecreasedwithtimebyusingCuClfluxesat1473K,andreachedarelativelylowvalueafter60minutes.Apartofironandleadvaporizedfromthefluxasmetalchloride.TheremovalofantimonyfromliquidcopperwasdifficultbyCuClfluxat1423K.However,theadditionofCaOorNa2CO3toCuClfluxwaseffectivefortheremovalofantimony.ByusingCuCl-CaOorCuCl-Na2CO3fluxes,theconcentrationofantimonyincopperdecreasedwithtime,andreachedarelativelylowvalueafter15minutes,becauseoftherapidchlorinationreactionofantimonyoxide.Themechanismoftheoxidation-chlorinationreactionofantimonywasdiscussedbasedontheobservedmassbalanceofantimony.Keywords:Heavymetal;Copperscrap;Removal;Recycling;CuCl-basedFlux;Reactionrate1.IntroductionRecently,theremovalandrecyclingofheavymetalsfrommetalscrapbecomeveryimportantinordertouseeffectivelyresourcesandsolvetheenvironmentalissue.1,2)Sincethevaporpressureofheavymetalchloridesisgenerallyhigh,thechlorinationrefiningiseffectivetoremovetheheavymetalsfromscrapmetalsandrecycletheirchloridessuchastherecyclingofaluminumscrapandrefiningofcrudelead.Fromthethermodynamicviewpoint,itispossibletoremoveheavymetalsandrecycletheirchloridesasresourceintherecyclingprocessofcopperscrap.Inordertoimprovetherecyclingefficiencyofcopperscrap,itisnecessarytoinvestigateanddiscusstheremovalandrecyclingmechanismofheavymetalsfromcopperscrapbychlorinationreaction.ThepurposeofpresentstudyistomakeclearthemechanismofremovalandrecyclingofFe,PbandSbfromcopperscrapbychlorinationreaction.TheremovalrateofFe,PbandSbbyCuCl-basedfluxwasmeasuredfrom1423Kto1473K.2.ExperimentalproceduresFivegramsoffluxeswerepreparedbymixingthereagentgradeCuCl,Na2OandCaOthatwascalcinedfromCaCO3at1273K.SodiumcarbonateasNa2OwasdirectlyaddedtoCuClflux.TengramsofCu-1mass%FeandCu-1mass%PballoysandfivegramsofCu-1mass%Sballoywereused.Themetalandfluxsampleswerechargedinanaluminacrucible,andthensetinanelectricfurnacewithargonflowof150to400cm3/min.Allexperimentswerecarriedoutat1473Kexceptforantimonyat1423K.Aftertheexperimentaltime,thesamplewasquicklytakenoutandthenquenchedwithflushingargon.Themetalandfluxwereseparatedandsubjectedtochemicalanalysis.InductivelyCoupledPlasmaAtomicEmissionSpectroscopywasusedtoanalyzethecontentofCu,Fe,Pb,Sb,NaandCa.TheMohrmethodwasappliedforchlorineanalysis.TheLECOcombustionanalyzerwasusedfordeterminingthecontentofoxygeninmetal.3.Resultsanddiscussion3.1ThermodynamicanalysisThechlorinationreactionsandstandardGibbsfreeenergychangesforFe,PbandSbareshowninEqs.(1)to(10).2Cu(l)(l)FeCl2CuCl(l)Fe(l)fluxin2fluxinmetalin(1)3)01J/mol.91855500ΔTG(2)(g)FeCl(l)FeCl2fluxin2(3)3)03J/mol2.93122310ΔTG(4)2Cu(l)(l)PbCl2CuCl(l)Pb(l)fluxin2fluxinmetalin(5)3)05J/mol30.659000ΔTG(6)(g)PbCl(l)PbCl2fluxin2(7)3)07J/mol4.94114750ΔTG(8)3Cu(l)(g)SbCl3CuCl(l)Sb(l)3fluxinmetalin(9)4)09J/mol.80214120ΔTG(10)AssumingthattheactivitiesofCuandCuClareunity,therelationshipbetweentheconcentrationofFe,PborSbincopperandtheirpartialpressureofchloridecanbecalculated.TheactivitycoefficientsofFe,PbandSbrelativetopuremetalswereestimatedtobe5)0Fe21.5(1473K),6)0Pb5.61)K1473(,)70Sb0109.0(1423K))70Sb0139.0)K1473(,where0MistheRaoultianactivitycoefficientatinfinitedilution.ThepartialpressureofchlorideisshowninFig.1forFeandPbat1473K,andinFig.2forSbat1473Kand1423K.ThevaporizationofFeCl2andPbCl2fromfluxiseasy.However,thevaporpressureofSbCl3istoolowtoremovebychlorinationreaction.3.2RemovalrateofFe,PbandSbbyCuClfluxTheconcentrationchangesofFe,PbandSbofcopperwithtimeareshowninFig.3.ByusingCuClflux,theconcentrationsofFeandPbdecreaseveryfastwithtimeat1473K,whilethatofSbslightlydecreasesat1423K.Thesebehaviorsareinaccordwiththethermodynamiccalculation.Hattaetal.8)measuredthepartitionratiosofFeandPbbetweenCuCl-basedfluxandliquidcopperat1473K,andthehighpartitionratiosofFeandPbwereobtained.ThesefactsshowthatCuCl-basedfluxesareeffectivetoremoveFeandPbfromtheviewpointsofboththermodynamicsandkinetics.0.00.20.40.60.81.00.00.20.40.60.81.0[mass%Fe]or[mass%Pb]PPbCl2orPFeCl2(atm)PPbCl2PFeCl21473KFig.1Relationshipbetweenthepartialpressureofchlorideandconcentrationofmetalincopper.0.00.20.40.60.81.00.02.0x10-54.0x10-56.0x10-58.0x10-51.0x10-4[mass%Sb]PSbCl3(atm)1473K1423KFig.2RelationshipbetweenthepartialpressureofSbCl3andconcentrationofSbincopper.3.3EffectoftheadditionstoCuClfluxontheremovalrateofSbat1423KTheadditionofthebasicNa2CO3orCaOisrelativelyeffectivefortheremovalofSb.ByusingCuCl-Na2CO3orCuCl-CaOfluxes,theconcentrationofSbincopperdecreasesverymuchwithtime.Moreover,theconcentrationofSbalsodecreaseswithincreasingthecontent