Investigation of three-liquid-phase extraction systems for t(2)

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