aqueous是什么意思eous在线翻译读音例句

IndianJournalofChemicalTechnology

Vol.12,November2005,pp.713-718

Studiesonextractionofchromium(VI)fromacidicsolutionby

emulsionliquidmembrane

SekharChakraborty,SiddharthaDatta*&PinakiBhattacharya

DepartmentofChemicalEngineering,JadavpurUniversity,Kolkata700032,India

Received11November2004;revisedreceived15July2005;accepted2September2005

Highmolecularweightamines,epotentialofremovingheavymetalionsincludingthe

resentworkanattempthasbeenmadetoextractCr(VI)throughemulsionliquid

surfactantmemb云青青兮欲雨下一句 rane(or,emulsionliquidmembrane-ELM)fromit’sacidicsolutionusingalamine-336andcausticsodaas

97%extractionofCr(VI)fromaqueoussolutionsofpotassium

rucialtotheoverallsuccessoftheELMprocesses,

experimentsonemulsionstabilityhaveof

variousprocessparameterssuchasinitialsoluteconcentration,thatofpHon

extractionofchromiumhavebeeninvestigated.

Keywords:Emulsionliquidmembrane,alamine-336,simultaneousextractionandstripping,equilibriumconcentration,

ELM

IPCCode:C22B3/06;C22B34/32

Byvirtueofitslargesurfaceareaformasstransfer,

shortdiffusionpath,goodpermeability

characteristics,simultaneousextractionandstripping

inasingleunitetc.

liquidsurfactantmembranes(as

distinctfromSupportedliquidmembranes,Liquid

membranedropletcolumns,Hollowfiberliquid

membranes,Liquidmembranesinstirredcellsetc.)is

viewedasapotentiallyviabletechniqueforseparation

oforganicandinorganiccontaminantsfromwaste

waters,removalofheavymetalionsfromliquid

Li1inventedand

usedthetechniquetoseparatehydrocarbonswayback

in1968.

Emulsionliquidmembrane(ELM)ismadebyfirst

makingaprimaryemulsion(oil/waterorwater/oil)

andthendispersingthesameintoanotherphase,oilor

water(alsoreferredtoasthethirdorexternalphase

containingtheextractiblespecies)therebyforminga

multipleemulsionofthetypeO/W/OorW/O/

dispersedphaseusuallyhasadropletsizerangeof

0.5-10mwhilethatoftheemulsionglobules(

continuousphase)x

ofthediffusingspeciesthroughthemembranephase

asalsothecapacityofthereceivingphasecanbe

es

offacilitatedtransportmechanismsofELM(viz.

type-Iandtype-II)havebeenidentifiedby

Matulevicius&Li3.

Intype-Ithediffusingspecies,dissolvedinthe

membranephasereactswiththeinternalphase

reagenttoformmembraneinsolubleproductsthat

remainsencapsulatedwithintheinternalphaseviz.

hesoluteis

immediatelyremovedbyreactionwithinternal

reagent,theconcentrationdrivingforceformass

IIfacilitation,anoil

solublecarrier/extractantisincorporatedinthe

membranephasetocarrytheoilinsolubleextractible

speciesacrossthemembranebyformingcomplex.

Thecomplexreactswithinternalphasereagentatthe

membrane-internalphaseinterfacereleasingthe

carrierwhichdiffusesbacktothemembrane-external

phaseinterfaceforfurthercomplexationreactions

egree

ofseparationcanbeachievedbyusingonlyasmall

amountofcarriereventhoughthepartition

coefficientsbetweenextern厝火积薪的意思 alandmembranephases

tionofcopper

ionsbyELMtechnique7.

Liquidsurfactantmembranetechniquehasbeen

widelyappliedbyresearchersinvariousareasof

separationandextractionofwhichextractionofheavy

7,9,

cobalt10,zinc11,12,nickel13,molybdenum14etc.

______________

*Forcorrespondence(E-mail:sdatta_che@)

L.,NOVEMBER2005714

Chromiumhaswideapplicationsinindustriessuchas,

electroplating,tion

ofCr(VI)fromwastestreamsofindustriesbyliquid

membranetechniquehavebeenstudiedusing

differentamines,iers15,19.

Recoveryofextractedspeciesfromtheinternalphase

stumblingblockisdemulsificationoftheoil

membraneinwhichtheextractedspeciesis

r,useofstrongelectricfield,

electrostaticsplitter(energyconsumptionaround

4kwh/m3ofemulsion)enreportedtohave

beenappliedindemulsifyingoilemulsionfor

recoveryofextractedmaterial.

Inthepresentworkalamine-336,astraightchain

tri-alkylaminehasbeenusedtoremovehexavalent

chromium[(Cr

2

O

7

)2−]fromdiluteacidicsolutions

(50-100ppm/pH~2).

ExperimentalProcedure

Theconstituentmaterialsoftheliquidmembrane

usedinthisstudyareasfollows:keroseneoil(24g)

asthesolvent(locallyprocured,b.p−150-240C,

density–0.798g/mLandviscosity−11.710–4

kg/m/sec),surfactant.-span-80(3wt%)-sorbitan

monooleatetostabilizewater-in-oilemulsions(HLB

value4.3,Sigma),poly-butylsuccinimide(LZ-890,

2wt%)asmembranestrengtheningagent(Lubrizol,

India,.,0.93andviscosity,270cst.),alamine

336(Henkel,USA)asthecomplexingagent(0.25to

4wt%,astraightchaintri-alkylamine,density

–0.81g/mLat25C,.,392).Sincethe

successofLEMlargelydependsonitsstability,stable

emulsionformulationhasbeenfoundexperimentally.

Anemulsionpreparedwith3wt%span80and2wt%

LZ-890hasbeenfoundtobereasonablystable

throughoutthedurationoftheexperiments.

Batchextractionswereconductedinaspecially

designedglassmixer-settler(7′′dia.)fittedwith

baffles,astop-cockforeasysamplingandavariable

maryemulsion

(W/O)waspreparedbygraduallydrippingNaOH

solutionintotheoilphaseinabeakerbyhighspeed

stirring(REMI,India)ataround4000rpm

(Fig.1/Step1)ultantmilky

whiteemulsionwasthendispersed(at150rpm/Fig.1

Step2A)intheexternalaqueousphasecontaining

solutes(Cr6+=50-350ppmasfeedintheformof

potassiumdichromate)s

drawnatfixedintervals(Fig.1Step2B)werefiltered

beforeanalyzingforchromiumfoll籁的拼音 owingstandard

proceduresusingaUVspectrophotometer(Systronic

Instruments,USA).pHoftheexternalphasewas

othe

mixer-settler.

Equilibriumexperiments

Equilibriumexperimentshavebeencarriedoutin

separatingflaskswiththesoluteconcentration

varyingbetween25-100mg/LofCr(VI)takenin1:1

oil:brium

experimentsconductedinbothacidicandbasicpH

conditionsshowthatextractionofchromium(VI)

beenobservedthatatbasicpHrange(~7-9)extraction

parentthatinacidicpH

(~2)rangeonanaveragemorethan96%

chromium(VI)hasbeenextracted(Table1).

Distributioncoefficient

Atthemembrane-externalphaseinterfacethe

solutehasbeenconsideredtobeinequilibriumwith

asisof

Fig.1—Schematicdiagramofremovalofheavymetalionfrom

wastewaterbyliquidmembranetechnique

Table1—EquilibriumconcentrationofCr6+atlowpH

Expt.

no

Initialfeedcomposition

(Cr6+ppm)

%extractionofCr6+in

theoilphase

(atequilibrium)

110088

27593.22

35095

42597

CHAKRABORTYetal.:EXTRACTIONOFCr(VI)BYEMULSIONLIQUIDMEMBRANE715

experimentallydeterminedequilibriumsolute

concentrationsintheaqueousphase,distribution

coefficientsofthesolute[Cr(VI)]betweenorganic

andaqueousphaseshavebeencalculatedasfollows:

C

D

=(C

SA

−C

SE

/C

SE

)(V

aqueous

/V

organic

)

where,C

SA

=Initialsoluteconcentrationinaqueous

phase(mg/L),C

SE

=Equilibriumsoluteconcentration

inaqueousphase(mg/L),V

aqueous

,V

organic

=Volumeof

aqueousandorganicphasesrespectively(L).

Calculateddistributioncoefficienthasbeencorrelated

withequilibriumaqueousphasesoluteconcentration

bylinearregressionmethodandthefollowing

equationhasbeenobtainedC

D

=aC

S

–b,where,

constantsa=29.36202,b=−0.52462andcorrelation

coefficient,R2(forchromium)=.2shows

theplotofdistributioncoefficient(C

D

)versus

equilibriumaqueousphasesoluteconcentration(C

S

)

ofchromium(VI)atpH≈identthat

distributioncoefficientofthespeciesdecreaseswith

increasinginitialsoluteconcentration.

Emulsionstability–tracerexperiments

ItisimportanttodesignanELMwhichwillensure

tracerexperiment‘tracer’[0.5(N)HCl,30mL]was

encapsulatedintheinternalphaseofemulsionhaving

variouscompositionsoftheconstitutingmaterialsviz.

oilmembrane(kerosene=30mL),internalaqueous

phase(NaOH=30mL),surfactant(sorbitan

monooleateorSpan80,1.5-3wt%),membrane

strengtheningagents(LZ890-polybutylsuccinimide,

−0.5-2wt%)paredemulsion(60mL)was

dispersedindistilledwater(pH~7,900mL).From

timetotimepHoftheexternalaqueousphas西江月遣兴阅读答案 ewas

measuredbecausedecreasingpHoftheexternalphase

wouldmeanemulsionruptureduetoshearforces

sionhavingoil:

internalaquaeousphase=1:1byvol.,Span80=3.0

wt%andLZ890=2wt%wasfoundtobereasonably

stablewithminimumbreakageandwasused

throughoutthework(Figs3-5).

Fig.3—Span80=1.75wt%,Averagestirrerspeed=150rpm,

LZ890=2wt%(tracerexpt.1)

Fig.4—Span80=2.25wt%,Averagestirrerspeed=150rpm,

LZ-890=2.0wt%(tracerexpt.2)

Fig.5—Surfactant=3.0wt%,LZ890=2wt%,Stirrerspeed=150

rpm(tracerexpt.3)

Fig.2—Variationofdistributioncoefficient(Cd)ofCr6+with

equilibriumsoluteconcentration(Cs)intheexternalphase

p

H

o

f

e

x

t

e

m

al

a

q

u

e

o

u

s

p

h

a

s

e

L.,NOVEMBER2005716

ResultsandDiscussion

Intheextractionexperiments,unlessotherwise

mentioned,followingemulsion/systemcompositions

havebeenused:oilphase:kerosene=30mL,internal

reagentphase=0.75(N)NaOH,30mL,Span80=3.0

wt%,LZ890=2wt%andexternalaqueousphase=

110ppmofCr(VI)in900mLofwater(pH~2).

MechanismofCr(VI)extraction

Hexavalentchromiummayexistintheaqueous

phaseindifferentionicformsdependinguponthepH

nbasicor

mildlyacidicsolutionsCrO2−

4

dominates,(Cr

2

O

7

)2−

e

336complexeswellwiththeanionicspeciesof

chromiumasalsoofhostofothermetalsatlowpH

(VI)-alaminecomplexdissociatesupon

ultaneousextractionand

strippingreactionsinvolvingchromiuminLEMareas

follows:

[R

3

N]

org

+H+Cl−=[R

3

NH+Cl−]

org

…(1)

2[R

3

NH+Cl−]

org

+K

2

Cr

2

O

7

=[(R

3

NH+)

2

Cr

2

O

7

2−]

org

+[2KCl]

aq

…(2)

Extractionreaction(Eq.2)takesplaceatthe

interfacebetweentheexternalandmembranephase.

Thecomplexthendiffusesacrossmembranetothe

interfacebetweenthemembraneandtheinternal

phasewhereitbreaksdownduetoreactionwithabase

NaOH(stripping)whilethereactionproduct,being

oilinsolubleremainsintheinternalphase:

[(R

3

NH+)

2

Cr

2

O

7

2−]

org

+4[Na+OH-]=2(R

3

N)

org

+2[Na

2

CrO

4

]

aq

+3H

2

O…(3)

Attemptshavebeenmadeinthisworktoexplain

theseparationandpermeationmechanismswith

respecttothefollowingparameters:thepHofthe

system,externalphasesoluteconcentration,treat

ratio,concentrationofcomplexingagentandthatof

theinternalphasebyperformingbatchexperiments.

Figure6givesapictorialrepresentationofCr6+

extractionwithreactionstakingplaceatdifferent

interfaces.

EffectofpHofexternalaqueousphaseonextractionofCr(VI)

Theequilibriumexperimentsindicatedthatashift

towardsacidicpHrangefavouredgreaterextraction

ofCr(VI)ionfromaqueousphase(Table2).Thisis

an

Fig.6—SchematicdiagramshowingthemechanismofCr(VI)extractionandstrippingreactions

CHAKRABORTYetal.:EXTRACTIONOFCr(VI)BYEMULSIONLIQUIDMEMBRANE717

96%extraction(pH~2)starteddecreasingasthepH

oftheex梨花颂 ternalphasestartedincreasingas3.5

(95.83%),5(57.61%)and6(27.27%).

Effectofinternalreagentconcentrationontheextractionof

Cr(VI)

Theeffectoftheconcentrationofinternalreagent

(NaOH-0.25-1.0N)onextractionofchromiumis

identthatwiththeincreasein

NaOHconcentrationtheextractionrateofCr(VI)

duetothefactthat,withthe

moleculesavailableforreactionwithCr-alamine

complexa峰回路转的意思解释 ttheinternalphase-membranephase

interfacebecomefewerwithintheinternaldroplets.

Thisresultsinlongerpenetrationofthesolute

particlestoreachtheavailableNaOHmoleculedeep

ultofincreaseddiffusional

lengthmasstransferresistanceincreaseswhich

ultimatelydecreasestheextractionrate.

Effectofconcentrationofcomplexingagentonextractionof

Cr(VI)

Theexperimentalresults(Fig.9)indicatethatrate

ofpercentageextractionofchromium(VI)increases

withtheincreaseincomplexingagentconcentration

(3.01,4.16,6.23wt%).Increaseinconcentrationof

complexingagentmeansincreasedavailabilityof

aminemoleculeforcomplexformationwithsolute

moleculeatthemembranephase-externalphase

,thereisquickerdepletionofinternal

reagentasmoreamine-[Cr

2

O

7

]2−complexmolecules

resultthereisincreaseinextractionrate.

Effectofinitialsoluteconcentrationintheexternalaqueous

phaseonextractionofCr(VI)

ItappearsfromFig.10thatthefractionofsolute

extractedishigheratlowerinitialexternalphase

ybe

explainedinthefollowingmanner:thesolutemoves

towardstheemulsionglobulebytheprocessof

nitialsoluteconcentrationsincetheTable2—VariationofextractionofCr(VI)withchangein

externalphasepH

TimepH2pH3.5pH5pH6

0

264.910199.5298.26

447.7878893.9

634.672.277.3588

82456.1669.984

1013.5426681.4

126.631.264.8279.85

144.724.7163.779.84

16421.46479.85

203.121.3864.179.85

303.521.3864.379.85

Fig.7—EffectofpHoftheexternalaqueousphaseonextraction

ofCr(VI)

Fig.8—Effectofstrengthofinternalreagent(NaOH)onCr(VI)

extraction

Fig.9—Effectofvaryingconcentrationsofalamine336%on

extractionofCr6+

L.,NOVEMBER2005718

drivingforceformasstransferislow,themolecules

takelongertimetoreachtheemulsionglobule.

However,thisiscompensatedbyincreased

distributioncoefficientwithdecreasinginitialsolute

ore,thesolutesdissolvefasterin

theotherhand,althoughincreasedsolute

concentrationresultsinfasterdiffusiontowardsthe

emulsionglobule,buttheextractionratedecreases

duetodecreaseddistributioncoefficient.

Effectofvolumeratioofemulsiontoexternalaqueousphase

onextractionofCr(VI)

Figure11showstheeffectofchangeinvolume

ratioofemulsiontoexternalphaseonextractionrate

forthreeconditions:V

E

:V

Ext惯看秋月春风

=1:7(60:420),1:10.41

(60:625)and1:15(60:900mL).Withtheincreasein

thevolumeofexternalphase(seinV

E

:V

Ext

ratio)actualavailabilityofsolute(metalions)for

complexformationwithalamine336becomesfewer

(initialsoluteconcentrationintheexternalphase=

110ppminallcases).Asaresultrateofextraction

therhand,withincreaseinV

E

:V

Ext

ratioextractionbecomesfastersincerelativelymore

solutemoleculesareavailableforreaction.

Conclusion

Inthisworkanattempthasbeenmadetoexplain

theunderlyingmechanismofmasstransferin

emulsionliquidmembraneprocessbywayof

simultaneousextractionandstrippingofhexavalent

chromiumfromitsdiluteaqueoussolutionsatlow

processhasbeenexplainedintermsof

importantphysico-chemicalparametersthatgovern

eenseenthatmorethan96%

solutecouldbeseparatedandconcentratedinthe

internalphasewithinfifteenminutesofoperation.A

reasonablystableemulsioncompositionhasalsobeen

workedout.

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Fig.10—Effectofinitialsoluteconcentrationonextractionof

Cr(VI)

Fig.11—EffectofvariationofV

em

:V

ex

onextractionofCr(VI)