Investigation of three-liquid-phase extraction systems for t(6)

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

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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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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).