Investigation of three-liquid-phase extraction systems for t(5)

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.