Investigation of three-liquid-phase extraction systems for the separation of Ti(IV), Fe(III)

SeparationandPuri cationTechnology76 (2010) 191–197

ContentslistsavailableatScienceDirect

SeparationandPuri cation

Technology

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r

Investigationofthree-liquid-phaseextractionsystemsfortheseparationofTi(IV),Fe(III)andMg(II)

KengXiea,b,c,JunmeiZhaoa,LiangrongYanga,c,PinhuaYua,c,HuizhouLiua,

a

KeyLaboratoryofGreenProcessandEngineering,InstituteofProcessEngineering,ChineseAcademyofSciences,Beijing100190,ChinaNationalEngineeringLaboratoryforHydrometallurgicalCleanerProductionTechnology,Beijing100190,Chinac

GraduateUniversityoftheChineseAcademyofSciences,Beijing100039,China

b

articleinfoabstract

Three-liquid-phaseextractionsystem(TES)composedofanorganicsolvent-richtopphase,apolymer-richmiddlephaseandasalt-richbottomphasehasbeenconsideredtobeapromisingmethodofisolationandseparationofmulti-component.Inthispaper,wetriedtouseTEStotreatmulti-metalsolutionsincludingTi(IV),Fe(III)andMg(II)forthe rsttime.Differentcombinationsoforganicextractant–polymer–inorganicsaltwereevaluated.Andtheeffectsofsolutionacidity,complexingagentsandadditivesonthemetalionspartitioningwereinvestigated.TheresultsindicatedthatMg(II)wascon-centratedinthesalt-richbottomphase,whereasTi(IV)andFe(III)werequantitativelyextractedintothetrialkylphosphineoxide(TRPO)(ordi-2-ethyl-hexylphosphoricacid(D2EHPA))-richtopphase.Andtheadditionofethylenediaminetetraaceticacid(EDTA)enabledFe(III)todistributeintothepolyethyleneglycolwithmolecularmass2000(PEG2000)-richmiddlephase.ThetransferofFe(III)greatlyimprovedtheselectivityofthetopphaseforTi(IV)andmadeasigni cantimpactontheseparationofTi(IV),Fe(III)andMg(II).

© 2010 Elsevier B.V. All rights reserved.

Articlehistory:

Received31January2010

Receivedinrevisedform8October2010Accepted14October2010

Keywords:

Three-liquid-phaseextractionsystemSeparationTi(IV)Fe(III)Mg(II)

1.Introduction

Avastmajorityofindustrialef uentsandwastewater,suchasetchingorpickingbaths,electroplatingrinseliquors,leachingsolutiongeneratedduringhydrometallurgyminingwater,spentphotographicsolutionsandsoforthmaycarryiron,manganese,chromiumandahostofnon-ferrousmetalssuchascopper,nickel,zinc,titanium,magnesium,aluminum[1].Discardoftheseef u-entsmaycauseenvironmentalproblemsandeconomicloss.Thusitisnecessaryto ndoutsuitabletechniqueforextraction,sep-aration,andrecoveryofthesemetalsinconsiderationofwastetreatment,ualtechniquesfortheseparationandrecoveryofmetalsare,forexample,precipitation,liquid–liquidextraction,electroly-sisandionexchange.Amongthesetechniques,theliquid–liquidextractiontechniqueexhibitsasuperiorseparationperformancethanothers.Throughtheapplicationofdifferentdiluents,extrac-tants,andaqueousphaseconditions,thetechniquemaybeadaptedtohandleawidevarietyofsolutes.Extractionkineticsisoftenrapid,enablinghighthroughput,andthetechnologymaybeengineeredforselectivityandef ciencythroughtheuseofmultistagecontac-

Correspondingauthorat:No.1,BeiErTiao,ZhongGuanCun,HaidianDistrict,Beijing100190,China.Tel.:+861062554264;fax:+861062554264.

E-mailaddress:hzliu@(H.Liu).1383-5866/$–seefrontmatter© 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.seppur.2010.10.007

tors.However,itiscon nedtopurifyonemetalinonestepduetothemasstransferbetweenthetwophases.

Three-liquid-phaseextractionsystem(TES)composedofanorganicsolvent-richtopphase,apolymer-richmiddlephaseandasalt-richbottomphaseshowspossiblemuchhigherselectivitythantheusualwater–oilliquid–liquidsystemandaqueous-two-phasesystem(ATPS),providingphaseswithawiderangeofpolaritiesandchemicalpropertiestosuitdifferentpurposes[2].Inourlabo-ratory,Chenetal.[3]andShenetal.[4]havedevelopedsomeTESscontainingpolyethyleneglycol(PEG)orethyleneoxide–propyleneoxide(EOPO)randomcopolymersandusedthemforseparat-ingofglycyrrhizicacidandliquiritinfromglycyrrhizauralensis schextractaswellastreatingsimulatedwastewatercontainingp-nitrophenol(p-NP)andphenol.ResultsshowedthatTEScon-tainingethyleneoxide–propyleneoxiderandompolymers,butylacetateand(NH4)2SO4couldachievesatisfyingseparationyieldsatpH=9.3withabout80%phenolinthesolvent-richtopphaseand95%p-NPinthepolymer-richmiddlephase,respectively[5].Yuetal.[6]continuedtheresearchandselectedTESscontain-inghexanetotreatthemodelwastewatercontainingisomersofp-NPando-NP.About85wt.%o-NPand90wt.%p-NPcouldbesimultaneouslyextractedintothetopandmiddlephaseatpH=4.0,respectively.TESoffersapotentiallyattractivealternativetotreatmulti-componentef uentsinthatitcombinestheprocessofextractionandpuri cationofleasttwocomponentsinasingleunitoperation.

192K.Xieetal./SeparationandPuri cationTechnology76 (2010) 191–197

Inthepresentpaper,aninnovativeapplicationofTESintheseparationofthreemetalspecies,Ti(IV),Fe(III)andMg(II),whicharecommonlyassociatedinilmenite,titaniumslagandredmud,was rstreported.AccordingtothefactthatTi(IV)isextractedef cientlybytrialkylphosphineoxide(TRPO)[7–11],aTESwasinitiallycreatedusingTRPOandthemostfrequentlymadePEG2000–ammoniumsulfateATPS.PartitioningofTi(IV),Fe(III)andMg(II)amongthethreephaseswasstudiedwithsystematicchangesinthephasecomposition.Thechangeswereperformedbyalteringtheinitialacidityoftheaqueoussolution,thetypeandconcentrationofwatersolublecomplexingagentandPEG2000solubleadditive.Othercommonextractantsfortitaniumoriron,suchasdi-2-ethyl-hexylphosphoricacid(D2EHPA)[12–14],tri-n-butylphosphate(TBP)[15,16],C19–C23secondaryalkylprimaryamine(N1923)[17,18],trialkylamine(N235)[19],werealsotestedforformationofTESswithPEG2000–(NH4)2SO4ATPSandselectedbasedontheirabilitytoextractmetalions.Moreover,adiffer-entphase-formingsalt(Na2SO4)andaPEGwithmolecularweight(PEG10,000)wereevaluated.Bystudyingtheeffectivenessofthesolvent-richtopphaseandthepolymer-richmiddlephaseoftheTESsintheextractionofonemetalandrejectionofanothermetal,itishopedtogaininsightwhichcanbeutilizedinthedevelopmentofanappropriateTESforuseintheseparationofTi(IV),Fe(III)andMg(II).

2.Experimental

2.1.Reagentsandchemicals

Theorganicextractant,tri-n-butylphosphate(TBP),wassuppliedbyBeijingBeihuaFineChemicalReagentCo.,Ltd.Otherorganicextractantsused,includingtrialkylphosphineoxide(TRPO,93%),C19–C23secondaryalkylprimaryamine(N1923,98%),trialkylamine(N235,98%),di-2-ethyl-hexylphosphoricacid(D2EHPA,98%),werepurchasedfromShanghaiLaiyashiChem-icalCo.,Ltd.PEGwithaveragemolecularweightof2000(PEG2000)and10,000(PEG10,000)werepurchasedfromSinopharmChemicalReagentCo.,Ltd.,China.PluronicL62,L121andF127whicharedifunctionalblockcopolymersurfactantsterminatinginhydroxylgroupswerereceivedfromBASF.StocksolutionofTi(IV),Fe(III)andMg(II)sulfateswaspreparedwithdilutesulfuricacidfromreagentgrade(SinopharmChemicalReagentCo.,Ltd.)materials.TheconcentrationsofTi(IV),Fe(III)andMg(II)inthesolutionweremaintainedat6mmol/L,1mmol/Land3mmol/L,respectively.Stockcomplexingagentsolutionswerepreparedbydissolvingweighedamountsofdriedsolid(NH4SCN,NaF,NH4Cl,KBr,NaI,NaNO2,CH3COONH4,Na2H2EDTA,Urea,sul-fosalicylicacid)indeionizedwater.ThecommerciallyavailableN,N-dimethylformamide,N-methylpyrrolidideandethanolwereusedasaddictives.Allotherchemicalswereofanalyticalgrade.2.2.Three-liquid-phaseextraction

PrescribedvolumesofstocksolutionofTi(IV),Fe(III),Mg(II)andphase-formingcomponentswereplacedingraduatedcen-trifugetubes.Theselectedphase-formingreagentswerelistedinTable1.Acomplexingagentormodi erwasaddedwhenneces-Table1

Phase-formingcomponentsinTESs.Phase

Phase-formingcomponents

Percentrange(wt.%)Organicextractant(top)TRPO,TBP,N235,N1923,

20D2EHPA

Polymer(middle)PEG2000,PEG10,0007.5–15Inorganicsalt(bottom)(NH4)2SO4,Na2SO4

12–20

saryandthesystemswerepreparedwithaglobalweightabout25gatroomtemperature.ThepHvalueofaqueoussolutionwasadjustedbyaddingeitherdiluteNH4OHsolutionorconcentratedsulfuricacidandmeasuredbyapH211acidometer(Hanna,Italy).Then,theloadedtubeswereshakenfor40minonamechanicshakertoensurecompletemixing.Theseparationofeachphasewasenhancedbycentrifugationfor10minataspeedof4000rpm.

Afterseparation,phasevolumesweremeasuredandthecon-centrationsofTi(IV),Fe(III),Mg(II)inmiddleandbottomphasewereanalyzedbyanOPTIMA5300DVinductivelycoupledplasma-opticalemissionspectrometer(ICP-OES,PekinElmer,USA)atthewavelengthof335nm,238nmand285nm,respectively.Thecon-centrationofmetalionsinthetopphasewasdeterminedfrommaterialbalance.

2.3.Determinationofextractionabilityandseparationef ciencyToevaluatetheextractionofTi(IV),Fe(III)andMg(II)usingtheTESs,theextractionpercentages(E)ofmetalioninthetopandmid-dlephaseweredeterminedaccordingtothefollowingequation:Ei=

Ci·Vi

00

×100%

(1)

whereirepresentsthetop(t)ormiddle(m)phase.CiandViaretheconcentrationsofmetalionintheiphaseandthevolumeoftheiphase,respectively.C0istheoriginalconcentrationofthemetalioninthestocksolutionandV0isthevolumeofstocksolutionaddedtothesystem.

Distributionratio(D)wasalsoquotedasameasureofhowwell-extractedaspeciesis.Fromtheseconcentrationvaluesindifferentphases,thedistributionratiowascalculated.Speci cally,distribu-tionratiosofTi(IV),Fe(III)andMg(II)betweentwophasesintheTESareDM,t/m=CM,t(2)M,mDM,t/b=CM,t(3)M,bDM,t/b=

CM,m(4)

M,b

whereMrepresentsmetalions;CM,t,CM,mandCM,bareconcen-trationsofmetalionMinthetop,middleandbottomphase,respectively.

Furthermore,separationfactor(ˇ)betweentwometalionswascalculatedbytheratiooftheirdistributionratios.Theseparationfactorembodiesthepossibilityoftheseparationofthetwometalionsforaspecialsystem.Forinstance,theTi(IV)/Fe(III)separationfactorbetweentheuppertwophasesisde nedasˇDTi(IV),t/mTi(IV)/Fe(III),t/m=

(5)

Ti(IV),t/m

3.Resultsanddiscussion

3.1.TRPO–PEG2000–(NH4)2SO4TESwithoutacomplexingagentPreliminaryexperimentsoftheeffectofpHvalueontheforma-tionofTESindicatedthatitisnoteasyfor(NH4)2SO4andPEG2000toformtwoaqueousphasesatpH<0andhydrolysisoftitaniumionswouldhappenatpH>2.0.Therefore,thepHrange0–2wasusedunderthecurrentexperimentalconditions.

Fig.1(a)showsthepartitionbehaviorofTi(IV),Fe(III)andMg(II)intheTESscontaining25wt.%TRPO,15wt.%PEG2000and20wt.%(NH4)2SO4.ItisobservedthatthePEG2000-richmiddlephasesexhibitedlittleabilitytoextractTi(IV),Fe(III)andMg(II)andalmostallMg(II)remainedinthe(NH4)2SO4-richbottomphase.Inlightof

K.Xieetal./SeparationandPuri cationTechnology76 (2010) 191–197193

10090

80)

%(70 ega60tnec50rep 40noitc30artx20E100

0.6

0.81.01.21.41.61.82.0

pH value

88

776

6o

r

iot5tacr afn oni45t ouitbairrtas3piD4eS2130

0.60.81.01.21.41.61.82.0

2

pH value

Fig.1.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining25wt.%TRPO,15wt.%PEG2000and20wt.%(NH4)2SO4atdifferentpHvalues.

thefactsthatMg(II)iscommonlyusedtosalt-outPEG[20–22]andTRPOhasweakextractabilityfordivalentcations[23],itisreason-ablethatMg(II)preferthesalt-richphaseintheTESs.TheextremelylowextractabilityofTi(IV)andFe(III)inthePEG-richphasewerealsoobservedforthePEG-inorganicsaltaqueoustwo-phasesys-temsandcanbecorrelatedtotheions’largenegativeGibbsfreeenergiesofhydration[24].Sincethemiddlephaseseemeduselessinextractingmetalions,thefunctionoftheTESwascomparabletothatofaTRPO–waterliquid–liquidextractionsystem.

AscanbeseenfromFig.1(a),morethanhalfamountofTi(IV)andFe(III)weredistributedintotheTRPO-richtopphase.Ti(IV)extractionisbetterthanFe(III)asTi(IV)hasastrongercomplex-ationwithTRPO.ExtractionpercentageofTi(IV)bythetopphasewas71.85%atpH0.5andslightlydeceasedto64.8%atpH2.0,whilethatofFe(III)increasedfrom55%atpH0.5tonearly65%atpH2.0.Thebehavioragreeswiththereportedliterature[9]anditmaybeunderstoodthataqueousaciditycanaffectthephasemiscibil-ity,thechemicalpropertiesoftheextractantandparticularlythespeciationofmetalionsintheaqueousphase.Thesulfatedegreeoftitaniumwasenhancedbyincreasingthesulfuricconcentra-tion,thusformingmoreneutralspecies,whicharepreferentiallytransferredtotheTRPO-richtopphase.Fig.1(b)showsthedistri-butionratiosofTi(IV)andFe(III)betweenthetopphaseandthebottomphase,andtheseparationfactorˇTi(IV)/Fe(III),t/m.Themax-imumˇTi(IV)/Fe(III),t/misonly4.Hence,Ti(IV)andFe(III)couldnotbeseparatedfromeachotherdespitetheycouldbeseparatedfromMg(II).

10090

80)

%70( ega60tnec50rep n40oitca30rtxE2010

N235N

235+TRPO

D2EHPAEHPA+TRP

O

2PO

D

TROrganic solvent

Fig.2.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining15wt.%PEG

2000,20wt.%(NH4)2SO4and25wt.%organicextractantatpH0.5.TheextractantsareN235,D2EHPA,TRPO,amixtureofN235andTRPO(1:1,wt.%)andamixtureofD2EHPAandTRPO(1:1,wt.%).

3.2.PEG2000–(NH4)2SO4basedTESswithdifferentorganicextractants

Fourorganicextractants,whichwereN235,N1923,D2EHPAandTBP,wereusedassubstituteforTRPOintheformationofTESs.N1923ledtofullygelwhenitwasinvolvedinamixturecontain-ing15wt.%PEG2000and20wt.%(NH4)2SO4atpH0.5.IncaseofN235,D2EHPAandTBP,stableTESswereobtained.However,approximatelyone fthoftotalTBPenteredintothemiddlephaseoftheTEScontaining25wt.%TBP,15wt.%PEG2000,and20wt.%(NH4)2SO4.TheintersolubilityofTBPandPEG2000wouldmaketherecyclingofTBPandPEG2000aheavyproblem.Therefore,N235andD2EHPAwerepreferredasextractantsastheyprovidedbetterphaseseparationbehaviors.TheextractionpercentagesofTi(IV),Fe(III)andMg(II)inTESsusingN235,D2EHPA,N235–TRPO(1:1,wt.%),andD2EHPA–TRPO(1:1,wt.%)werecalculatedandcom-paredwiththatofTRPOatpH0.5.

TheresultsweregiveninFig.2.AscanbeseenfromFig.2,almostcompleteTi(IV)and70%ofFe(III)wereextractedintotheD2EHPAorganicphase,leavingMg(II)inthebottomaqueousphase.TheextractabilityofTi(IV)andFe(III)bydifferentextrac-tantsdecreasedfollowingtheorder:D2EHPA>TRPO>N235.Thiscouldbeconnectedwiththenatureofextractedmetalspeciesandtheextractionmechanism.TakingTi(IV)forexample,inthesulfatesolutions,Ti(IV)ispresentasmonomericdivalentcations,assumedtobeTiO2+[25],andformstwoweaktitanylsulfatocom-plexesTiOSO4andTiO(SO4)22 ,withTiOSO4predominating[26].Theequilibriumshavebeenwrittenas:TiO2++SO42 TiOSO4

(6)TiOSO4+SO42 TiO(SO4)22

(7)

ExtractionoftitaniumwithD2EHPAisprobablygovernedbyacationexchangemechanismwithD2EHPA(representedasthedimerH2A2)accordingtothereaction:TiO2+(a)+2H2A2(t) TiOH2A4(t)+2H+(a)

(8)

where(a)and(t)denotespeciesintheaqueousphasesandthetopphase,respectively.

Becausethestabilityconstantsassociatedwiththetwotitanylsulfatocomplexesaremuchsmallerthanthatofthetitanium–D2EHPAcomplex,theequilibria(6)and(7)shiftedtothe

194K.Xieetal./SeparationandPuri cationTechnology76 (2010) 191–197

Extraction percentage (%)

leftafterD2EHPAaddedtothesystem,andtheequilibrium(8)infavorofTiOH2A4prevailed.ThusmoreandmoreTiOH2A4canleadtothecompleteextractionofTi(IV).

TRPOisasolvatingreagent,andthereforefavorscomplexa-tionwithneutralTiOSO4,whiletheanionexchangerN235favorscomplexationwithTiO(SO4)22 .SoitisreasonablethatfairlypoorextractionofTi(IV)(<20%)wasachievedwithN235.ItisworthyofnotethatFe(III)couldbeextractedwithgoodselectivityoverTi(IV)whenN235wasusedastheextractant.3.3.TRPO–PEG2000–Na2SO4TESandTRPO–PEG10,000–(NH4)2SO4TES

SodiumsulfateandPEG10,000wereusedasphase-formingsubstances.TheyofferedaglimpseattheeffectofanotherinorganicsaltandPEGwithhighermolecularweight10,000onthephaseseparationbehaviorofTESandthepartitioningbehaviorofTi(IV),Fe(III)andMg(II).FourdifferentTESsweredesignedasfollows:(1)25wt.%TRPO–15wt.%PEG2000–20wt.%Na2SO4,(2)25wt.%TRPO–15wt.%PEG2000–12wt.%Na2SO4,(3)25wt.%TRPO–15wt.%PEG2000–20wt.%Na2SO4–20wt.%H2SO4,(4)25wt.%TRPO–15wt.%PEG10,000–12wt.%(NH4)2SO4.Amongthem(1),(2)and(4)wereconductedatpH0.5.

Itisobservedthatsubstitutionof(NH4)2SO4withNa2SO4resultedinarelativelymoreviscousPEG-richmiddlephase.Thiscoincideswiththesalting-outabilityofthesalts[27,28],whichisNa2SO4>(NH4)2SO4.Na2SO4showstobemoreeffectiveinphaseseparationandthusatagivenconcentration,Na2SO4inducesmoreincompatibilitybetweenthebottomphaseandtheuppertwophases.Itisclearfromtheliteraturethatincreasingtheincom-patibilitybetweentwophasesincreasestheaf nityofasoluteforaparticularphase[29].SinceTi(IV)andFe(III)preferthetopphase,theextractionpercentagesincreaseastheincompatibilityincreases.BycontrastingTestnumber1inFig.3withitscounter-partinFig.1,anincreaseof15%orsowasfoundat20wt.%saltconcentrationandpH0.5.Interestingly,atalowerconcentration(12wt.%,seeTestnumber2inFig.3)ofNa2SO4,ETi(IV),tandEFe(III),tmaintainedquantitativeratherthandecreasedinresponsetolessincompatibilitybetweenthetopphaseandthebottomphase.Itindicatesthatthesalt-outpowerofthesaltshasalimitedin u-enceonthetransferofmetalionstoorganicextracatantsandotherfactorssuchascoordinationbetweenammoniumandmetalionscanalsobeassumedtoplayarole.

Besides,compared(1)with20wt.%Na2SO4to(2)with12wt.%Na2SO4,(2)gavealargermiddlephasevolume.Similarresultswereobtainedundertheconditionofahigheracidity(20wt.%H2SO4,(3)inFig.3)orahigherPEGmolecularweight(PEG10,000(4)inFig.3).Decreasingsalinity,increasingaciditytogetherwithincreas-ingPEGmolecularweightdirectlyin uencestheequilibriumofthesystemsandfurtherlythemetalions’partitionparameters.Under

120

1101009080706050403020100

1

2

Test number

Fig.3.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining(1)25wt.%TRPO–15wt.%PEG2000–20wt.%Na2SO4,(2)25wt.%TRPO–15wt.%PEG2000–12wt.%Na2SO4,(3)25wt.%TRPO–15wt.%PEG2000–20wt.%Na2SO4–20wt.%H2SO4,(4)25wt.%TRPO–15wt.%PEG10,000–12wt.%(NH4)2SO4.Alltestsexcept(3)wereconductedatpH0.5.

34

suchconditions,morewaterwasincorporatedintothePEG-richmiddlephase.Metalsaccompaniedfreewatertothemiddlephase,hence,ETi(IV),m,EFe(III),mandEMg(II),mbecamehigher.However,thereisapracticallimitonthechoiceofthesalinityandacidityofaqueoussolutionandPEGmolecularmassbecauseofnotenoughofagainindistributionratioandseparationfactor.AndtheuseofhighermolecularweightPEGssufferincreasedviscosityandexpense.3.4.Modi cationofthemiddlephaseofTRPO–PEG2000–(NH4)2SO4TES

N,N-dimethylfomamide,N-methylpyrrolidone,L62,L121andF127weretriedasmiddlephasemodi ersbecausetheycouldbemisciblewithPEG2000andenrichedintothemiddlephase.ItwasprospectedthatN,N-dimethylfomamideandN-methylpyrroli-donecoordinatewithFe(III)viaamideligandandtransferFe(III)tothemiddlephase,andthesepluronicsurfactantsalterthehydrophilic–lipophilicbalanceofthemiddlephasesandsubse-quentlyfacilitatetheloadingofmetalions.Thechemicalstructuresofthesemodi ersareshowninFig.4.Thehydrophobicityofthepolymer-richmiddlephaseincreasedbypartiallyreplacingPEG2000withthetriblockcopolymerformedbyacertainamountofpropyleneoxidemonomer,whichisahydrophobicsegment.

ItisobservedthattheuppertwophasesturnedintoaviscousemulsioninthepresenceofasmallamountofL121orF127.ItismostprobablybecausethelonghydrophobicPPOblocksof

the

Fig.4.Chemicalstructuresof(a)N,N-dimethylfomamide,(b)N-methylpyrrolidone,(c)L62,(d)L121and(e)F127.

K.Xieetal./SeparationandPuri cationTechnology76 (2010) 191–197195

Extraction percentage (%)

twocopolymersarestronglyattractedtoTRPOandtheinteractionbetweenthehydrophilicblocksandPEG2000isalsointen-sive.TheTESscontaining25wt.%TRPO,20wt.%(NH4)2SO4and15wt.%mixtureofPEG2000andoneofN,N-dimethylfomamide,N-methylpyrrolidoneandL62ateitherpH0.5orpH1.0pre-sentedthreedistinctliquidlayersandtheirextractabilitiesforTi(IV),Fe(III)andMg(II)aredepictedinFig.5.Unfortunately,N,N-dimethylfomamide,N-methylpyrrolidoneandL62hadnoobviouseffectforincreasingtheextractionofmetalionsbyPEG2000phase.

1009080706050403020100

Test number

3.5.TRPO–PEG2000–(NH4)2SO4TESwithinorganiccomplexingagents

Theuseofcomplexingionsintheaqueousphaseforliquid–liquidextractionofmetalionshasevokedwideinterestinrecentyears.InordertoimprovetheselectivityofthethreemetalionsinthepresentTES,effectoftheadditionof5mmolinorganiccomplexingagentontheextractionofTi(IV),Fe(III)andMg(II)wasinvestigatedwithTEScontaining25wt.%TRPO,15wt.%PEG2000and20wt.%(NH4)2SO4atpH0.5and1.2.Wetriedtheinor-ganiccomplexingagentssuchasNH4SCN,NaF,NH4Cl,KBr,NaI,andNaNO2,whicharemostfrequentlyusedinextractions.

Unfortunately,theuseofNH4SCN,NaF,NH4Cl,KBr,NaI,andNaNO2intheTESswasmuchlesseffectivewiththeextractabilityofmetalswaslessthan5%inthemiddlephases,asshowninFig.6(a)and(c).Thisisdifferentfromtheirperformancesinaqueoustwo-phasesystems,wheretheuseofhalidesaltsorpseudohalidesaltscanproducemetalanioncomplexesthatareinclinedtotransfer

Fig.5.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining25wt.%TRPO,20wt.%(NH4)2SO4and15wt.%PEG2000-modi ermixtureateitherpH0.5or1.0.((1)PEG2000–N,N-dimethylfomamide2:1,wt.%,pH0.5;(2)PEG2000–N,N-dimethylfomamide1:1,wt.%,pH0.5;(3)PEG2000–N,N-dimethylfomamide1:1,wt.%,pH1.0;(4)PEG2000–N-methylpyrrolidone2:1,wt.%,pH0.5,(5)PEG2000–N-methylpyrrolidone1:1,wt.%,pH0.5;(6)PEG2000–N-methylpyrrolidone1:1,wt.%,pH1.0;(7)PEG2000–L627:1,wt.%,pH1.0).

tothePEG-richphase[24,30].Hydrophobicityofthemetalcom-plexesmayaccountforthedifferences.Intrinsichydrophobicityofphasesvariesfollowingtheorder:TRPO-richphase>PEG2000-richphase>salt-richphase.Therefore,thehighlyhydrophobic

metal

Fig.6.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining25wt.%TRPO,15wt.%PEG2000and20wt.%(NH4)2SO4with5mmolinorganiccomplexingagentorwithoutacomplexingagent(blank)at(a,b)pH0.5and(c,d)pH1.2.

196K.Xieetal./SeparationandPuri cationTechnology76 (2010) 191–197

)

%( e

gatn

ecrep noitcartxE

Amount of complexing agent (mmol)

Fig.7.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining25wt.%TRPO,15wt.%PEG2000and20wt.%(NH4)2SO4withvariedamountsof(a)NaF,(b)NaIand(c)NaNO2ascomplexingagentsatpH0.5(( )Ti(IV),t;( )Fe(III),t;( )Mg(II),t;( )Ti(IV),m;( )Fe(III),m;( )Mg(II),m).

complexesaredistributedintothemorehydrophobicPEG-richinATPS.WhereasforTES,thosehydrophobicmetalcomplexesareapttotransfertothemosthydrophobicTRPO-richphase.

ThoughtheinactivityofthePEG-richphaseinmetalextractionmakessingle-stepseparationofTi(IV),Fe(III)andMg(II)impossi-ble,analysisofthein uenceofcomplexingagentsonthepartitionbehaviorofmetalsmayenlightentheestablishmentoftheopti-mumconditionfortheextractionandseparationofTi(IV)andFe(III).ItcanbeclearlyseenfromFig.6(a)and(c)thattheadditionofNH4SCNpromotedTi(IV)andFe(III)transferfromthesalt-richbottomphasetotheTRPO-richtopphaseandanextractionofMg(II)increasewasobservedatthehigherpHvalue.Thehalide,NaF,seemedtoexertverylimitedin uenceontheextractionofTi(IV)andFe(III)inthetopphaseatpH0.5butledtosharpdecreaseofTi(IV)andFe(III)extractionatpH1.2.TheotherhalidesandnitritealsohadlittleeffectontheTi(IV)buttheyaffecteddiffer-ently.EFe(III),tincreasedwithNH4ClandNaNO2,especiallyatthelowerpHvalue,anddeclinedwithNaI.KBrhadnoobviouseffectonEFe(III),t.Thechangeofcationspartitioningbehaviorduetocomplex-ingagents’presencecanbeascribedtotheligand–metalinteractionandthehydrationpropertiesoftheligand–metalcomplex[31,32].ItisworthnotingthatincomparisonwithNH4SCN,NH4ClandKBr,thecomplexingagentsNaF,NaI,andNaNO2toarelativelargerdegreeaffectedthedistributionratioofTi(IV)andFe(III)andtheseparationfactorofTi(IV)andFe(III)betweentheuppertwophase,asshownintheFig.6(b)and(d).ThisledtotheinvestigationoftheamountofNaF,NaI,andNaNO2onthepartitioningbehaviorofthemetalsintheTES.

TheextractionpercentagesofTi(IV),Fe(III)andMg(II)weredis-playedasafunctionoftheamountofNaF,NaI,andNaNO2inFig.7.Nottoourexpect,thecomplexingagentsamountvaryingfrom5mmolto20mmoldidnotboostEM,m,whichwasstillnegligi-

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1

2

3

4

5

6

Test number

Fig.8.PartitioningofTi(IV),Fe(III)andMg(II)intheTESscontaining25wt.%TRPO,15wt.%PEG2000and20wt.%(NH4)2SO4withanorganiccomplexingagentoranaddictiveatdifferentpHvalues((1)5mmolCH3COONH4atpH0.5;(2)5mmolCH3COONH4atpH1.2;(3)1mmolsulfosalicylicacidatpH0.5;(4)1mmolureaatpH0.5;(5)1mlethanolatpH1.0;(6)10 molEDTAatpH1.0)).

ble.EventhoughETi(IV),tweremoreorlessaffectedbydifferentamountsofNaIandNaNO2andgreatlydecreasedwithincreas-ingNaFamount,theTESswiththeseinorganiccomplexingagentswereinaptforthesimultaneousseparationofTi(IV),Fe(III)andMg(II).

3.6.TRPO–PEG2000–(NH4)2SO4TESwithorganicadditives

Anotherreasonablewaytorecovermetalionsusingsolventextractiontechniqueistoapplyorganicmoleculesascomplexingagents,whichgiveametalionahydrophobicexterior.Extrac-tionofTi(IV),Fe(III)andMg(II)usingwatersolublecomplexingagentssuchasCH3COONH4,sulfosalicylicacid,ureaandEDTAwerecarriedout.Theseorganicreagentswerechosenbasedontheirgoodcomplexingabilitywithmetalions.Inaddition,ethanolwasemployedhereinaccordingtoareport[33]thatthepresenceofalcoholenhancesthedifferenceinmetalcomplexesstabili-tiesasaresultofpartialdehydrationofthecation.TheresultsobtainedusingthedifferentorganicadditiveswerepresentedinFig.8.

Obviously,EDTAshowedgoodbehaviorcomparedtoalltheotherorganicadditivesthroughliftingthemetalions’af nitytoPEG2000-richphase.Fe(III)–EDTAcomplexescouldbemoreeas-ilyextractedbyPEG2000.Nearly23%Fe(III)appearedinthemiddlephaseoftheTEScontaining25wt.%TRPO,15wt.%PEG2000,20wt.%(NH4)2SO4and10 molEDTAatpH1.0.Mean-while,acorrespondingdecreaseofFe(III)extractionwasdetectedinthetopphase,where70%Ti(IV)wasenriched,andalmostallMg(II)remainedinthesalt-richbottomphase.ˇTi(IV)/Fe(III),t/mcalculatedfromEq.(5)reached80.Thusitispossibletoreal-izetheselectiveseparationofTi(IV),Fe(III)andMg(II)fromoneanother.

Inregardtotheselectiveextractionofmetalions,appreciabledifferencesintheextractionpercentagesbythetopphaseforTi(IV)versusFe(III)wereobservedwhensulfosalicylicacidwasusedascomplexingagent,allowingTRPOtoselectiveseparationofthetwometals.Butsingle-stepseparationofTi(IV),Fe(III)andMg(II)couldnotberealizednotwithstandingduetolittleaf nityofthemetalionsforthemiddlephase.Forthesamereason,CH3COONH4,ureaandethanolwerealsonotcapabletofacilitatethesimultaneousseparationofTi(IV),Fe(III)andMg(II).

K.Xieetal./SeparationandPuri cationTechnology76 (2010) 191–197197

4.Conclusion

Differentorganicextractants,polymersandinorganicsaltswereemployedinpreliminaryscreeningtestscarriedouttodeterminewhichofthesechemicalscouldcombinetoformstableorganicextractant–polymer–salttriphasicsystems.TheutilityoftheTESsonpartitionofTi(IV),Fe(III)andMg(II)wereassessed.Fromtheresults,TRPOandD2EHPAareconsideredtobeexcellenttopphase-formingcandidatesowingtotheirgoodphysicochemicalproperties.TheselectivityofmetalionswasfoundtodependonthepHvalueoftheaqueoussolution,thevalenceofmetalions,thepresenceofcomplexingagents,thehydrophobicitydif-ferenceamongphases,theextractedmetalspeciesandextractionmechanism.Themostimportantobservationinthepresentworkistheimprovementinaf nityofFe(III)forthePEG-richphaseandˇTi(IV)/Fe(III),t/mwhenEDTAisusedasacomplexingagent.ˇTi(IV)/Fe(III),t/msigni cantlyincreasedfromanegligibleamountto80usingTRPO–PEG2000–(NH4)2SO4TESatpH0.5.WhileMg(II)showedanabsolutepreferenceforthesalt-richbottomphase.TheseresultssuggestanexcitingpotentialmeansofseparationofTi(IV),Fe(III)andMg(II).

FurtherresearchisunderwaytocontinueoursurveyofusingtheTRPO–PEG2000andD2EHPA–PEG2000basedTESswiththecomplexingagentEDTAtosimultaneouslyseparateTi(IV),Fe(III)andMg(II)atalargeextent.Acknowledgement

TheauthorsthanktheNationalBasicResearchProgramofChina(973project2007CB613507)for nancingthiswork.References

[1]J.S.Gill,H.Singh,C.K.Gupta,Studiesonsupportedliquidmembraneforsimul-taneousseparationofFe(III),Cu(II)andNi(II)fromdilutefeed,Hydrometallurgy55(2000)113–116.

[2]L.H.M.daSilva,W.Loh,Polymerinducedmultiphasegenerationin

water/organicsolventmixtures.Strategiestowardsthedesignoftriphasicandtetraphasicliquidsystems,mun.(1998)787–788.

[3]J.Chen,H.Z.Liu,B.Wang,Studyonthethree-phaseextractionofpenicillin

Gwithasinglestepmethod,in:ProceedingsoftheConferenceonSolventExtraction(ISEC2002),CapeTown,2002,pp.602–606.

[4]S.F.Shen,Z.D.Chang,J.Liu,Separationofglycyrrhizicacidandliquiritinfrom

glycyrrhizauralensisFischextractbythree-liquid-phaseextractionsystems,Sep.Purif.Technol.53(2007)216–223.

[5]S.F.Shen,Z.D.Chang,H.Z.Liu,Three-liquid-phaseextractionsystemsforsep-arationofphenolandp-nitrophenolfromwastewater,Sep.Purif.Technol.49(2006)217–222.

[6]P.H.Yu,Z.D.Chang,Y.C.Ma,Separationofp-nitrophenolando-nitrophenol

withthree-liquid-phaseextractionsystem,Sep.Purif.Technol.70(2009)199–206.

[7]P.N.Remya,M.L.Reddy,Solventextractionseparationoftitanium(IV)vana-dium(V)andiron(III)fromsimulatedwastechlorideliquorsoftitaniummineralsprocessingindustrybythetrialkyphosphineoxideCyanex923,J.Chem.Technol.Biotechnol.79(2004)734–741.

[8]K.C.Sole,Recoveryoftitaniumfromtheleachliquorsoftitaniferousmagnetites

bysolventextraction:Part1.Reviewoftheliteratureandaqueousthermody-namics,Hydrometallurgy51(1999)239–253.

[9]K.C.Sole,Recoveryoftitaniumfromtheleachliquorsoftitaniferousmagnetites

bysolventextraction:boratory-scalestudies,Hydrometallurgy51(1999)263–274.

[10]K.C.Sole,A.Feather,J.P.O’Connell,Recoveryoftitaniumfromtheleachliquors

oftitaniferousmagnetitesbysolventextraction:Part3.Continuousmini-planttrials,Hydrometallurgy51(1999)275–284.

[11]K.SajiJohn,J.Saji,M.L.P.Reddy,Solventextractionoftitanium(IV)fromacidic

chloridesolutionsbyCyanex923,Hydrometallurgy51(1999)9–18.

[12]R.K.Biswas,M.R.Zaman,M.N.Islam,ExtractionofTiO2+from1M(Na+,H+)

SO42 byD2EHPA,Hydrometallurgy63(2002)159–169.

[13]R.K.Biswas,D.A.Begum,KineticsofextractionandstrippingofTi(IV)in

HCl–D2EHPA–kerosenesystemusingthesingledroptechnique,Hydromet-allurgy55(2000)57–77.

[14]T.Sato,T.Nakamura,Theextractionoftitanium(IV)andaluminium(III)from

sulphuricacidsolutionsbydi-(2-ethylhexyl)-phosphoricacid,Anal.Chim.Acta76(1975)401–408.

[15]K.M.Allal,D.Hauchard,M.Stambouli,Solventextractionoftitaniumbytrib-utylphosphate,trioctylphosphineoxideanddecanolfromchloridemedia,Hydrometallurgy45(1997)113–128.

[16]Z.SHu,X.P.Hu,W.Cui,ThreephaseextractionstudyII

TBP–kerosene/H2SO4–TiOSO4systemandthepreparationofultra nepowderofTiO2,ColloidSurf.A155(1999)383–393.

[17]M.X.Meng,S.Yu,J.Chen,Kineticsofiron(III)extractionwithprimaryamine

andTBPusingamodi edrotatingdiffusioncell,Hydrometallurgy41(1996)55–70.

[18]J.Chen,S.Yu,H.Z.Liu,Newmixedsolventsystemsfortheextractionandsepa-rationofferricironinsulphatesolutions,Hydrometallurgy30(1992)401–416.[19]P.Mahi,N.T.Bailey,Theuseofcoalspoilsasfeedmaterialsforaluminarecovery

byacid-leachingroutes.4.Theextractionofironfromaluminiferoussolutionswithamines,inparticularalamine336,Hydrometallurgy13(1985)293–304.[20]J.P.Martins,J.S.dosReisCoimbra,F.C.deOliveira,Liquid–liquidequilibriaofan

aqueoustwo-phasesystemcontainingpoly(ethylene)glycol1500andsulfatesaltsatdifferenttemperatures,J.Chem.Eng.Data53(2008)238–241.

[21]A.Salabat,Thein uenceofsaltsonthephasecompositioninaqueoustwo-phasesystems:experimentsandpredictions,FluidPhaseEquilibr.187–188(2001)489–498.

[22]Y.Wu,Z.Zhu,D.Lin,Modelingofliquid–liquidequilibriumofpolyethylene

glycol-saltaqueoustwo-phasesystems—theeffectofpartialdissociationofthesalt,FluidPhaseEquilibr.154(1999)109–122.

[23]V.Kislik,A.Eyal,AcidityofdependenceofTi(IV)extraction:acriticalanalysis,

SolventExtr.Ion.Exc.11(1993)259–283.

[24]R.D.Rogers,A.H.Bond,C.B.Bauer,Metalionseparationsinpolyethyleneglycol-basedaqueousbiphasicsystems:correlationofpartitioningbehaviorwithavailablethermodynamichydrationdata,J.Chromatogr.B680(1996)221–229.[25]B.I.Nabivanets,Electromigrationoftitanium(IV)ionsinnitric,hydrochloric,

andsulphuricacids,Russ.J.Inorg.Chem.7(1962)210–212.

[26]I.Szilágyi,E.Königsberger,P.M.May,Characterizationofchemicalspeciationof

titanylsulfatesolutionsforproductionoftitaniumdioxideprecipitates,Inorg.Chem.48(2009)2200–2204.

[27]K.P.Ananthapadmanabhan,E.D.Goddard,Aqueousbiphaseformationin

polyethyleneoxide–inorganicsaltsystems,Langmuir3(1987)25–31.

[28]D.J.Shaw(Ed.),IntroductiontoColloidandSurfaceChemistry,4thed.,Butter-worths,London,1992.

[29]M.A.Eiteman,Temperature-dependentphaseinversionanditseffectonpar-titioninginthepoly(ethyleneglycol)–ammoniumsulfateaqueoustwo-phasesystem,J.Chromatogr.A668(1994)13–19.

[30]L.Bulgariu,D.Bulgariu,Extractionofmetalionsinaqueouspolyethyleneglycol-inorganicsalttwo-phasesystemsinthepresenceofinorganicextractants:correlationbetweenextractionbehaviourandstabilityconstantsofextractedspecies,J.Chromatogr.A1196–1197(2008)117–124.

[31]M.Shibukawa,N.Nakayama,T.Hayashi,Extractionbehaviourofmetalions

inaqueouspolyethyleneglycol-sodiumsulphatetwo-phasesystemsinthepresenceofiodideandthiocyanateions,Anal.Chim.Acta427(2001)293–300.[32]R.D.Rogers,S.Grif n,Partitioningofmercuryinaqueousbiphasicsystemsand

onABECTMresins,J.Chromatogr.B711(1998)277–283.

[33]L.NashKenneth,AqueousComplexesinf-ElementSeparationScience,

Metal–IonSeparationandPreconcentration.ACSSymposiumSeries,AmericanChemicalSociety,Washington,DC,2009,pp.52–78.

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