Jurnal b.ing Distribusi

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Copyright 2004 by Taylor & Francis Group, LLC

4

Solvent Etraction E!uilibria

JAN RYDBERG* Chal"ers #niversity o$ Technology, Go% teborg,Se'en

GREGORY R. CHOPPIN* Flori'a State #niversity, Tallahassee, Flori'a,

#(S()(

CLAUDE MUSIKAS* Co""issariat a* l+Energie )to"i!ue, aris,

France

TATSUYA SEKINE

Science #niversity o$ To-yo, To-yo, .apan

4.1 INTRODUCTION

The ability o$ a solute /inorganic or organic to 'istribute itsel$ beteen an

a!ueous solution an' an i""iscible organic solvent has long been applie' to

separation an' puri$ication o$ solutes either by etraction into the organic phase,leaving un'esirable substances in the a!ueous phase1 or by etraction o$ the

un'esirable substances into the organic phase, leaving the 'esirable solute in the

a!ueous phase( The properties o$ the organic solvent, 'escribe' in Chapter 2,

re!uire that the 'issolve' species be electrically neutral( Species that pre$er the

organic phase /e(g(, "ost organic co"poun's are sai' to be lipophilic /li-ing

$at3 or hydrophobic /'isli-ing ater3, hile the species that pre$er ater

/e(g(, electrolytes are sai' to be hydrophilic /li-ing ater3, or lipophobic

/'isli-ing $at3( ecause o$ this, a hy'rophilic inorganic solute "ust be ren5

'ere' hy'rophobic an' lipophilic in or'er to enter the organic phase(6pti"i7ation o$ separation processes to pro'uce the purest possible pro'5

uct at the highest yiel' an' loest possible cost, an' un'er the "ost $avorable

environ"ental con'itions, re!uires 'etaile' -nole'ge about the solute reac5

tions in the a!ueous an' the organic phases( 8n Chapter 2 e 'escribe' physical

$actors that govern the solubility o$ a solute in a solvent phase1 an' in Chapter

9, e presente' the interactions in ater beteen "etal cations an' anions by

This chapter is a revise' an' epan'e' synthesis o$ Chapters 4 /by :y'berg an' Se-ine an' ; /by

)llar', Choppin,


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y B)

hich neutral "etal co"plees are $or"e'( This chapter 'iscusses the e!uations

that eplain the etraction 'ata $or inorganic as ell as organic co"plees in a

!uantitative "anner1 i(e(, the "easure' solute 'istribution ratio, Dsolute, to the

concentration o$ the reactants in the to phases( 8t presents che"ical "o'eling

o$ solvent etraction processes, particularly $or "etal co"plees, as ell as a

'escription o$ ho such "o'els can be teste' an' use' to obtain e!uilibriu"

constants(

The subDect o$ this chapter is broa' an' it is possible to 'iscuss only the

si"plerthough $un'a"entalaspects, using ea"ples that are representative(

The goal is to provi'e the rea'er ith the necessary insight to engage in solvent

etraction research an' process 'evelop"ent ith goo' hope o$ success(

4.1.1 The Distribution Law

The distribution law, 'erive' in => by ( Hernst, relates to the 'istributiono$ a solute in the organic an' in the a!ueous phases( For the e!uilibriu" reaction

) /a! ) /org

the Hernst 'istribution la is ritten

Concentration o$ Species ) in organic phase B)org

/4(=a

KA, ) = = /4(=b

Concentration o$ Species ) in a!ueous phase B)a!

here brac-ets re$er to concentrations1 E!( /4(= is the sa"e as E!s( /=(2 an'

/2(29( KA,) is the distribution constant /so"eti"es 'esignate' by P, e(g(, in

Chapter 21 see also )ppen'i C o$ the solute ) /so"eti"es re$erre' to as the

distribuend ( Strictly, this e!uation is vali' only ith pure solvents( 8n practice,

the solvents are alays saturate' ith "olecules o$ the other phase1 e(g(, ater

in the organic phase( Further, the solute ) "ay be 'i$$erently solvate' in the

to solvents( Hevertheless, E!( /4(= "ay be consi'ere' vali', i$ the "utual

solubilities o$ the solvents /see Table 2(2 are s"all, say


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li-e HaCl64( #n'er such con'itions the activity $actor ratio o$ E!( /4(2 is as5

su"e' to be constant, an'KA is use' as in E!( /4(= as con'itions are varie' at

a constant ionic strength value( 8n the $olloing 'erivations, e assu"e that the

activity $actors $or the solute in the a!ueous an' organic solvents are constant(

E$$ects 'ue to variations o$ activity $actors in the a!ueous phase are treate' in

Chapter ;, but no such si"ple treat"ent is available $or species in the organic

phase /see Chapter 2(

The assu"ption that the activity $actor ratio is constant has been $oun' to

be vali' over large solute concentration ranges $or so"e solutes even at high

total ionic strengths( For ea"ple, the 'istribution o$ ra'ioactively labele' GaCl9beteen 'iethyl ether an' ;< KCl as $oun' to be constant /KD,Ga = at all

Ga concentrations beteen =09

an' =0=2

< B=(

8n the $olloing relations, tables, an' $igures, the te"perature o$ the sys5

te"s is alays assu"e' to be 2JC, i$ not speci$ie' /te"perature e$$ects are'iscusse' in Chapters 9 an' ;, an' section 4(=9(;( e use org to 'e$ine speciesin the organic phase, an' no sy"bol $or species in the a!ueous phase /see )p5

pen'i C(

4.1.2 The Distribution Ratio

The 8#)C 'e$inition o$ the distribution ratio, D, is given in the intro'uction

to Chapter = an' in )ppen'i C( For a "etal species < it can be ritten

Concentration o$ all species containing

DM

=< in organicphase

Concentration o$ o$ all species containing

< in a!ueousphase

B


4/120Copyright 2004 by Taylor & Francis Group, LLC

J0

Fig. 4.1 Li!ui'5li!ui' 'istribution plots( /a The 'istribution ratiosD $or three 'i$$erentsubstances ), , an' C, plotte' against the variable Z o$ the a!ueous phase( Z "ay

represent pK, concentration o$ etractant in organic phase /BK)org, $ree ligan' ion con5

centration in the a!ueous phase /B), a!ueous salt concentration, etc( /b Sa"e syste"s

shoing percentage etraction IE as a $unction o$ Z( D an' Z are usually plotte' on

logarith"ic scale(

range o$ D is best "easure' $ro" about 0(==0, though ranges $ro" about

=0J=0

4can be "easure' ith special techni!ues /see section 4(=J(

8n "any practical situations, a plot li-e Fig( 4(=a is less in$or"ative than

one o$ percentage etraction, IE, hereM

IE ==00D N/=+D /4(4

Such a plot is shon in Fig( 4(=b $or the sa"e syste" as in Fig( 4(=a( ercentage

etraction curves are particularly use$ul $or 'esigning separation sche"es( )

series o$ such curves has alrea'y been presente' in Fig( =(9(

) convenient ay to characteri7e the S5shape' curves in Figs( =(9 or 4(=b,

here the etraction 'epen's on the variableZ, is to use the logZ value o$ J0Ietraction, e(g(, logBCl ( The pKJ05value in'icates logBK+ $or J0I etrac5

tion( This is shon in Fig( 4(= $or 'istribuen's ) an' (


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2

Oery e$$icient separations are o$ten nee'e' in in'ustry, an' a single e5

traction stage "ay be insu$$icient( The 'esire' purity, yiel', etc( can be achieve'

by "ultiple etractions, as 'iscusse' in Chapter P /see also section =(2( 8n

the 'esign o$ separation processes using "ultistage etractions, other etraction

'iagra"s are pre$erre'( 6nly single stage etraction is 'iscusse' in this chapter,

hile "ultistage etraction is 'iscusse' in the secon' part /Chapters P=4 o$

this boo-(

4.2 THERMODYNAMICS OF EXTRACTION SYSTEMS

Etraction $ro" a!ueous solutions into organic solvents can be achieve' through

'i$$erent che"ical reactions( So"e "ay see" very co"plicate', but usually oc5

cur through a nu"ber o$ rather si"ple steps1 e assu"e this in "a-ing a "o'el

o$ the syste"( The sub'ivision o$ an etraction reaction into its si"pler steps is

use$ul $or un'erstan'ing ho the 'istribution ratio varies as a $unction o$ the

type an' concentration o$ the reagents( 6$ten these "o'els allo e!uilibriu"

constants to be "easure'(

)s solute, e consi'er both nonelectrolytes /abbreviate' as ) or , or5

ganic or inorganic, an' electrolytes /e(g(, as "etal5organic co"plees, "etal

ions ren'ere' soluble in organic solvents through reactions ith organic anions

)

an' ith a''uct $or"ers ( The syste" o$ e!uations shon later is only

vali' as long as no species are $or"e' other than those given by the e!uations,

all concentrations re$er to thefree concentrations /i(e(, unco"plee', an' activ5ity $actors an' te"peratures are constant( Further, e assu"e that e!uilibriu"

has been establishe'( 8t "ay be note' that the use o$ e!uilibriu" reactions "ean

that the reactions ta-e place in the a!ueous phase, the organic phase or at the

inter$ace, as is illustrate' in the net ea"ples, but 'o not sho any inter"e'i5

ates $or"e'1 this in$or"ation can be obtaine' by -inetic stu'ies, as 'escribe' in

Chapter J, or by $ingerprinting3 techni!ues such as "olecular spectroscopy(

e$ore a 'etaile' analysis o$ the che"ical reactions that govern the 'istri5

bution o$ 'i$$erent solutes in solvent etraction syste"s, so"e representative

practical ea"ples are presente' to illustrate i"portant subprocesses assu"e' tobe essential steps in the overall etraction processes(

4.2.1 Case I: Extraction of ran!" #itrateb! $%%uct &ormation

This is a puri$ication process use' in the pro'uction o$ uraniu"( The overall

reaction is given by

#62Q+2 KH6

9+2 T/org#6

2/H6

9

2/T

2

/org

/4(J

here T stan's $or tributylphosphate( The organic solvent is co""only -ero5

sene( 8n Table 4(= this etraction process is 'escribe' in $our steps( 8n Table


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9

2 2 ;

i

e

e

Table 4.1 Sche"atic :epresentation o$ the Kypothetical Steps in #/O8

Etraction by T an' Their )ssociate Gi o$ :eaction

Secon'

First step step Thir' step Fourth step

6rganic phase T #62/T2/H692/T +'iluent

2+)!ueous solution 2 KH69 +#622+

#62/H692 +2T +/KH69 +#62

K26

+ #62/H692 +2K T #62/T2/H692#62/T2/H692

StartFinal G= >0 G2 >0 G9 0 G4 0Gex 9, is "ore basic than the reactive oygen o$ ater, T, hich

slightly 'issolves in ater /Step 2, replaces ater in the #62/K26;/H692 co"5ple to $or" the adduct complex #62/T2/H692( This reaction is assu"e' to

ta-e place in the a!ueous phase /Step 9( Adduct formation is one o$ the "ost

co""only use' reactions in solvent etraction o$ inorganic as ell as organic

co"poun's( /HoteM the ter" adduct is o$ten use' both $or the 'onor "olecule

an' $or its pro'uct ith the solute( The net process is the etraction o$ the

co"ple /Step 4( Even i$ the solubility o$ the a''uct $or"er T in the a!ueous

phase is !uite s"all /i(e(, DT very large, it is co""on to assu"e that the

replace"ent o$ hy'rate ater by the a''uct $or"er ta-es place in the a!ueous

phase, as shon in the thir' step o$ Table 4(=1 $urther, the solubility o$ the

a''uct #62/T2/H692 "ust be "uch larger in the organic than in the a!ueousphase /i(e(, D#6 /T /H6 =, to "a-e the process use$ul( 6ther inter"e'iate2 2 9 2reaction paths "ay be conte"plate', but this is o$ little signi$icance as G0

'epen's only on the starting an' $inal states o$ the syste"( The use o$ such a

ther"o'yna"ic representation 'epen's on the -nole'ge o$ the G0 values asthey are necessary $or vali' calculations o$ the process(

The relation beteen G0 an'Ke is given byo oGe

=Gi =RT lnK

e /4(;


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K =K = K

#

e

4

6"itting ater o$ hy'ration, the e!uilibriu" constant $or the net etraction pro5

cess in E!( /4(J isKe, here

[#62 /H69 2 /T2 ]orgKe

=

[#6

2Q

][KH6

]

2

[T]2

/4(P2 9 org

The extraction constant,Ke, can be epresse' as the pro'uct o$ several e!uilib5

riu" constants $or other assu"e' e!uilibria in the net reactionM

2e i 2,H69 A: 2,TP AC

/4(

here 2,H69 is the complex formation constant o$ #62/H692, an' 2,T the

$or"ation constant o$ the etractable #62/H692/T2 co"ple $ro" $ro"

#62/H692 an' T( KA: an' KAC are the distribution constants of the un!

charged species, the reagent an' the etractable co"ple, respectively(

Ke 'eter"ines the e$$iciency o$ an etraction process( 8t 'epen's on the

internal che"ical para"eters3 o$ the syste", i(e(, the che"ical reactions an'

the concentration o$ reactants o$ both phases( The latter 'eter"ine the nu"erical

value o$ the distribution factor for the solute, hich $or our ea"ple is

D =B#

tot,org

=#62 (H69 )2 (T)2org

/4(>a

B# 2Q 2n tot,a!#62 +#62 (H69 )n

2n8n the a!ueous phase e have inclu'e' the #62/H69n co"plees but eclu'e'

the #62/H692/T2 co"ple, because the concentration o$ the last co"ple

in the a!ueous phase is negligible co"pare' to the other to( 8n 'ilute solutions,2+the nitrate co"ple can be neglete' co"pare' to the $ree #62

8n the latter case the # 'istribution e!uals

= [KH6 ]2

[T]2

concentration(

/4(>bD# Ke 9 org

6$ the reaction steps, only the $irst three have values o$ G0

>01 hoever,the large negative value o$ the $ourth step "a-es the overall reaction G0 nega5tive, thus $avoring the etraction o$ the co"ple( The $irst step can be "easure'

by the 'eter"ination o$ the 'initrato co"ple in the a!ueous phase( The secon'

is relate' to the 'istribution constant KD,T in the solvent syste"( )lso, the

$or"ation constant o$ the a!ueous #62/H692/T2 can be "easure' /$or e5

a"ple by H


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chelate is a ea- organic aci'( For ea"ple, the uranyl ion can be neutrali7e'


9/120

by to TT)

/)ppen'i AMJe anions to $or" the neutral #6 /TT) /K 62 2 2 2co"ple( This co"ple is etractable into organic solvents, but only at high

concentrations o$ the TT) anion(

) large a''uct $or"ation constant increases the hy'rophobicity o$ the

"etal co"ple an' thus the 'istribution ratio o$ the "etal( This is co""only

re$erre' to as a synergistic effect( Figure 4(2 illustrates the etraction o$ the

#62/TT)2 co"ple $ro" 0(0= < KH69 into cycloheane( ecause the linear

6R#R6 group is believe' to have $ive to seven coor'ination sites, here only

Fig. 4.2 Synergistic etractionM Aistribution o$ #/O8 beteen 0(0= < KH69 an' "i5

tures o$ thenoyltri$luoroacetone /TT) an' tributylphosphate /T, or tributylphos5

phineoi'e /T6, at constant total "olarity /BTT)org plus BTorg or BT6org =0(02


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9

9

n

$our are occupie' in this co"ple, the uranyl group is coor'inativaly unsatu5

rate'( )t the le$t vertical aes o$ Fig( 4(2, the $ree coor'ination sites are occu5

pie' by ater an'Nor H6, only1 an' the #/O8 co"ple is poorly etracte', log

D# about =( hen T or T6 /tributylphosphine oi'e? Bboth in'icate'by are a''e' hile BKTT) +B is -ept constant, theD# value increases toabout ;0 $or T an' to about =000 $or T6( )t the pea- value, the co"ple

is assu"e' to be #62/TT)2= or 2( The 'ecrease o$D# at even higher B is 'ue

to the correspon'ing 'ecrease in BTT), so that at the right vertical aes o$

Fig( 4(2 no #/O8TT) co"ple is $or"e'( For this particular case, at "uch

higher nitrate concentrations, the #/O8 is co"plee' by H6

an' is etracte'

as an a''uct co"ple o$ the co"position #62/H692 =2, as 'iscusse' earlier

$or Case 8(

The pri"ary cause $or synergis" in solvent etraction is an increase in

hy'rophobic character o$ the etracte' "etal co"ple upon a''ition o$ the a'5'uct $or"er( Three "echanis"s have been propose' to eplain the synergis"

$or "etal +chelan'@ + a''uct $or"er( 8n the $irst suggeste' "echanis", thechelate rings 'o not coor'inately saturate the "etal ion, hich retains resi'ual

aters in the re"aining coor'ination sites an' these aters are replace' by other

a''uct5$or"ing "olecules( The secon' involves an opening o$ one or "ore o$

the chelate rings an' occupation by the a''uct $or"ers o$ the vacate' "etal

coor'ination sites( The thir' "echanis" involves an epansion o$ the coor'ina5

tion sphere o$ the "etal ion upon a''ition o$ a''uct $or"ers so no replace"ent

o$ aters is necessary to acco""o'ate the a''uct $or"er( )s pointe' out be$ore,it is not possible $ro" the etraction constants to choose beteen these alterna5

tive "echanis"s, but enthalpy an' entropy 'ata o$ the reactions can be use' to

provi'e "ore 'e$initive argu"ents(

The KTT) +T syste" can serve to illustrate the "ain points o$ ther5"o'yna"ics o$ synergis"( The o"erall extraction reaction is ritten asM

96, see )ppen'i A, ea"ple =;, at the en' o$ this boo-(@$heland or chelator is the chelating ligan'(


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9 =9

9 2 9 9 2 =2

The a''uct $or"ation reaction in the organic phase /the synergistic reaction3

is obtaine' by subtracting E!s( /4(=0b an' /4(=0c $ro" E!( /4(=0aM


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an' )n "ay go $ro" > to an', $inally, bac- to >( The last step re$lects the

operation o$ the thir' "echanis" propose' $or synergis"(

Th/TT)4 can be 'issolve' in 'ry ben7ene ithout hy'rate ater( The

values o$ the reaction o$ E!( /4(=2 in the syste" areM logK =J(4;, %o =9>(2


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-. "ol=

, T&o =(0 -. "ol

=

=( The negative entropy is un'erstan'able

as the net 'egrees o$ $ree'o" are 'ecrease' /to reactant "olecules co"bine

to $or" one pro'uct "olecule( Koever, the %o

value is "uch "ore negative(

These e!uations 'o not provi'e co"plete 'e$inition o$ the reactions that

"ay be o$ signi$icance in particular solvent etraction syste"s( For ea"ple,KTT) can eist as a -eto, an enol, an' a -eto5hy'rate species( The "etal co"5

bines ith the enol $or", hich usually is the 'o"inant one in organic solvents

/e(g(,K =BKTT)enolNBKTT)-eto = ; in et ben7ene( The -inetics o$ the -eto enol reaction are not $ast although it see"s to be cataly7e' by the

presence

o$ a reagent such as T or T66( Such reagents react ith the enol $or" in

'rier solvents but cannot co"pete ith ater in etter ones( KTT) T

an' T K26 species also are present in these synergistic syste"s(

Koever, i$ etraction into only one solvent /e(g(, ben7ene is consi'ere', thesee$$ects are constant an' nee' not be consi'ere' in a si"ple analysis(

8n section 4(=9(9 e return brie$ly to the ther"o'yna"ics o$ solvent e5

traction(

4.3 OVERVIEW OF EXTRACTION PROCESSES

J0


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Table 4.2 Sy"bolic Survey o$ Fun'a"ental Li!ui'5Li!ui' Aistribution rocessesa

Type (5A )onelectrolyte extractionb

Solute ) etracte' into organic phase /solvent)

/E!uilibriu" governe' by the Hernst 'istribution la

Solute is the nonelectrolyte ) in ater)

Type (5 )onelectrolyte adduct formation and extractionc

)''uct ) in organic phase /plus eventually

Solute ) an' a''uct $or"er /or etractant

Type ((5A Extraction of nonadduct organic acids

)ci' an' 'i"er /an' possible poly"ers in organic phase

)ci' 'issociation in a!ueous phase

)

/ ) +

)

K)K=U2K2)2+((

(

K)

K +)+

Type ((5 Extraction of acid as adduct

)ci' a''uct /an' aci' an' a''uct $or"er in organic phase K) / /+ K)

/ /)ci' 'issociation in a!ueous phase

K)

+ K)K++

)

Type(((5'

Extraction of saturated metal complex

Heutral, coor'inatively saturate' "etal co"ple in organic phase


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+7)

0 9J J; 9P =22

en7ene /5bon's 2(JP 2P JJ P 9J0Hitroben7ene 94( =4 2= 4= =P

&ourceM :e$( 4(

ligan' concentrations are "ore co"ple( So"e o$ these si"pli$ications are not

use' in later chapters(

4.4 EXTRACTION OF INERT MOECUES !TYPE I"A#

Kere, an' in later sections, e begin ith sa"e -in' o$ rectangular $igure to

in'icate the type o$ etractionM to the right e in'icate the 'istribution o$ the

solutes in a to5phase syste" /the organic phase is sha'e'1 the syste" is also

brie$ly 'escribe' by the tet to the le$t, an'o$ coursein 'etail in the "ain

tet(

SoluteA etracte' into organic phase /solvent A

/Hernst 'istribution la $or regular "itures an' solventsM The non5electrolyte soluteA in ater A

8$ the solute ) 'oes not un'ergo any reaction in the to solvents, ecept $or the

solubility cause' by the solvation3 'ue to the nonspeci$ic cohesive $orces in

the li!ui's, the 'istribution o$ the solute $ollos the Hernst 'istribution la, an'

the e!uilibriu" reaction can be 'escribe' either by a 'istribution constant KD,A,

or an /e!uilibriu" etraction constantKeM

)/a!)/org1

KA,)

=Ke

=B)org

NB)a! /4(=4

Ke alays re$ers to a to5phase syste"( The measured distribution ratio $orthe solute ),D), e!ualsKD,), an' is a constant in'epen'ent o$ the concentration

o$ ) in the syste"( 6nly eternal3 con'itions in$luence the KD,) value( 8n

eternal3 con'itions e inclu'e the organic solvent, in a''ition to physical

con'itions li-e te"perature an' pressure(

The noble gases an' the halogens belong to the sa"e type o$ stable "olec5

ular co"poun'sM :u64, 6s64, GeCl4, )sCl9, SbCl9, an' KgCl2( The si"plest

ea"ple is the 'istribution o$ the inert gases, as given in Table 4(9( The larger

Table 4.3 Aistribution :atios o$ So"e Gases eteen 6rganic Solvents

an' 0(0= < HaCl64 at 2JC

Solute


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:n is etracte' "ore easily than the s"aller Ve, because the or- to pro'uce a

cavity in the ater structure is larger $or the larger "olecule( The energy to

pro'uce a cavity in nonpolar solvents is "uch less, because o$ the ea-er inter5

actions beteen neighboring solvent "olecules( Energy is release' hen the

solute leaves the a!ueous phase, alloing the cavity to be $ille' by the hy'ro5

gen5bon'e' ater structure( Thus the 'istribution constant increases ith in5

creasing inertness o$ the solvent, hich is "easure' by the 'ielectric constant

/or relative per"ittivity( The halogens r2 an' 82 sho an opposite or'er 'ue

to so"e lo reactivity o$ halogens ith organic solvents( Oery inert solvents

ith lo per"ittivity, such as the pure hy'rocarbons, etract inert co"poun's

better than solvents o$ higher per"ittivity1 conversely, li!ui's o$ higher per"it5

tivity are better solvents $or less inert co"poun's(


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:eagent pKa logKA,K)

6ine >(P 2(P

25 9(9

J5)cetyloine P( 2(

4,P5Aichlorooine P(4 9(>

P,P5Aiio'ooine (0 4(2

J5Chloro5P5io'ooine P(> 9(>

a)!ueous phase 0(= < Ha

2JC(l641 organic phase chloro$or" at

&ourceM :e$s( a, b(

Fig. 4.4 Aistribution constantsKA,K) o$ $atty aci's as a $unction o$ the nu"ber n o$

carbon ato"s in the al-yl chain /$= is acetic aci' in the syste" 0(= < HaCl64Nben7ene(

/Fro" :e$( P(

Table 4.$ Aissociation,Ka, an' Aistribution,KD,%A,

Constants $or Substitute' 6inesa

C


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: is C CK C : W is thenoyl, K C SCXX XX

4

Table 4.% AissociationKa an' Aistribution ConstantsKA,K) $or 5Ai-etones1)!ueous hase 0(= < HaCl6

a

logKA:

:eagent /solute pKa C;K; CKCl9 CCl4

)cetylacetone, ))1 CK9 : CK9 (P; 0(P; =(9; 0(J=en7oylacetone, Y)1 CK9 : C;KJ (P4 9(=J 9(;0 2(=

Aiben7oyl"ethane, A(9J J(94 J(40 4(J=

Thenoyltri$luoroacetone, TT)1 ::CF9 ;(9 =(;= =(4 =(J4

6 6

a

6rganic phases 0(= < in solute1 2JC(&ourceM :e$( 4(

lea'ing to a re'uction in the 'istribution constant( Thus, either the si7e e$$ect

relate' to the ater structure or the presence o$ hy'rophilic groups in the solute

'eter"ines the general level o$ its 'istribution constant(

4.$ EXTRACTION OF ADDUCT"FORMIN&NONEECTROYTES !TYPE I"'#

)''uctA in organic phase /plus evt( A

/ Solute ) an' a''uct $or"er /etractant A +A

The etraction o$ a solute ) "ay be i"prove' by its reaction ith another

solute /etraction reagent3, or extractant, , $or"ing an adduct compound,)( This occurs through che"ical interaction beteen ) an' (

/org

) Q

)

KD,

=Borg

NB /4(=Ja

Kad

=B)NB) B /4(=Jb

hereKa' is the adduct formation constant /in the a!ueous phase

)

)/org KD,) =B)org NB) /4(=Jc

an'KD,) the a''uct 'istribution constant( The etraction constant $or the overall


25/120


reaction is


26/120


a'= org org org

0

o

)/a! Q /org

)/org

an' also

D)

=Ke

Borg

Ke

=B)org

NB)a!

Borg

=KD,)

Ka'K

D

,

/4(=J'

/4(=Je

For the etraction reaction it "ay su$$ice to rite the reaction o$ E!(

/4(=J', though it consists o$ a nu"ber o$ "ore or less hypothetical steps( )s

"entione', e!uilibriu" stu'ies o$ this syste" cannot 'e$ine the in'ivi'ual steps,

but supple"entary stu'ies by other techni!ues "ay reveal the vali' ones( E!ua5

tion /4(=J in'icates that the reaction ta-es place at the boun'ary /interface

beteen the a!ueous an' organic phases( Koever, it is co""on to assu"e that

a s"all a"ount o$ 'issolves in the a!ueous phase, an' the reaction ta-es place

in the steps

)/a! +/a!)/a!)/org

These e!uations allo 'e$inition o$ a 'istribution constant $or the species ),

KD,) Bsee E!( /4(=Jc( Aistribution constants can also be 'e$ine' $or each o$

the species ), an' ) /KD,), etc( but this is o$ little interest as the concentra5

tion o$ these species is relate' through Ke( ) largeKe $or the syste" in'icates

that large 'istribution ratios D) can be obtaine' in practice( )s shon in E!(

/4(=J, the concentration o$ in$luences the 'istribution ratioD)(Consi'er $irst the etraction o$ hea$luoroacetylacetone /KF) by T66

by Ea"ple =, an', secon', the etraction o$ nitric aci' by T /Ea"ple P(

The principles o$ volu"e an' ater5structure e$$ects, 'iscusse' $or the solute )

in section 4(4, are also i"portant in the 'istribution o$ the a''ucts(

Ea"ple =M Etraction o$ hea$luoroacetylacetone /KF) by trioctylphospine

oi'e /T66(

)bbreviating KF) /co"p( structure Je, )ppen'i A by K), an' T66

by , e can rite the relevant reactions

K)/a!K)/org K =BK) NBK) =D /4(=;a A org 0

K)/org +/orgK)/org

K Z BK) NBK) B /4(=;b

K)/org +2/orgK) /orgK

Z BK) NBK) B2

/4(=;c 2 a'2 2 org org org

assu"ing that 2 a''ucts are $or"e', K) an' K)2, the latter containing 2

T66 "olecules( E!uation /4(=;a 'enotes the 'istribution o$ unco"plee'

K)3 byDo( Co"bining these e!uations yiel's

D D= == +Ka'=B +Ka'2B

2/4(=;'

Figure 4(J shos the relative 'istribution, logD D=

, o$ hea$luoroace5


27/120


tylacetone as a $unction o$ the concentration o$ the a''uct $or"er T66( KF)


28/120

o

org org

Fig. 4.$ :elative increase, DNDo in etraction o$ hea$luoroacetylacetone /KF) into

heane $ro" 0(=< HaCl64 at pK =2, at 'i$$erent concentrations o$ the a''uct trioctyl5phosphine oi'e /T66 in the organic phase( The $itte' curve is DND == +=04(22

BT66 +=0P(J=BT662 ( /Fro" :e$( >(

is a "o'erately ea- aci', hile T66 associates strongly ith hy'rogen5

bon' 'onors in nonpolar solvents li-e heane( The constants ere 'eter"ine'

to log Ka'= = 4(22 an' log Ka'2 = P(J=( Thus even at "o'erately lo T66concentrations, the 'i"er a''uct3 'o"inates(

4.% EXTRACTION OF NONADDUCT OR&ANIC ACIDS!TYPE II"A#

)ci' an' 'i"er /an' possibly %A=U2 %2A2

+( ( ( poly"ers in organic phase )ci' 'issociation in a!ueous phase /%+A%

%A%++

A

/an' protonation

Tables 4(J4(P an' Fig( 4(; list organic aci's co""only use' as "etal

etractants( hen the aci's are not protonate', 'issociate', poly"eri7e', hy5

'rate', nor $or" a''ucts, the 'istribution ratio o$ the aci' K) is constant in a

given solvent etraction syste"M

K)/a!K)/org D,K) =BK)org NBK) =DK)

/4(=P

This is shon by the hori7ontal tren's in Fig( 4(;, $or hich E!( /4(=P is vali'1


29/120

i(e(, the 'istribution constantKD,K) e!uals the "easure' 'istribution ratio( hen


30/120

)ci' 'iluentb

S / 2(=

en7oyltri$luoroacetone /TF) CCl4 E ;(09 2(9>

Thenoyltri$luoroacetone /TT) en7ene J(2P ;(9 =(;

AMo Chloro$or" E =(4=5Hitroso525naphthol Chloro$or" =(9J P(; 2(>P

Ai/25ethylheylphosphoric aci'$

0I o$ the organic phase is acetylacetone /


31/120


Fig. 4.% Aistribution ratios calculate' by E!( /4(22 $or acetylacetone /K))1 ben7oyl5

acetone /K)1 be7oyltri$luoroacetone /KTF)1 an' oine /5hy'roy!uinoline,

K6[, in the syste" 0(= < HaCl64 NCCl4, using the $olloing constants( /Fro" :e$s(

a, b(

K)) K) KTF) K6[

logKA 0(J= 2(= 2(9> 2(=

logKa (;P (9> ;(09 >(;;

logKaK E E J(00

in'icates 'i$$erent interactions beteen the acetylacetone an' the to solvents(

8t is assu"e' that the polar CKCl9 interacts ith K), "a-ing it "ore soluble in

the organic phase1 it is also un'erstan'able hy the 'istribution o$ K) 'ecreasesith 'ecreasing concentration /"ole $raction o$ CKCl9( C;K; an' aro"atic sol5

vents 'o not behave as 'o "ost aliphatic solventsM in so"e cases the aro"atics

see" to be inert or even antagonistic to the etracte' organic species, hile in

other cases their pi5electrons interact in a $avorable ay ith the solute( For

acetylacetone, the interaction see"s to be very ea-( The salting5in e$$ect is

shon both in Figs( 4(Pa( an' 4(Pb(

4.).1 Dissociation

)ci's 'issociate in the a!ueous phase ith a 'issociation constantKa


32/120



33/120


) org

a

a

+

K)KQ +

)

K =BKQ B) NBK) /4(=

The 'istribution ratio incorporates theKa $or etraction o$ aci's, K), asM

D =BK) /BK)+B)

=

=KD,K)/=+

Ka

BKQ

=

/4(=>

8n'e ) in'icates that the 'istribution ratio re$ers to the concentration o$ all

species o$ ) in the organic an' in the a!ueous phase( 8n Fig( 4(; the 'istribution

o$ the 5'i-etones is constant in the higher hy'rogen ion concentration range/loer pK here they are un'issociate'( 8n the higher pK region, D)beco"es

inversely proportional to the hy'rogen ion concentration 'ue to increase in the

concentration o$ the 'issociate' $or" o$ the aci' ), in agree"ent ith E!(

/4(=>(The free ligand concentration, B)

, is an i"portant para"eter in the $or5

"ation o$ "etal co"plees /see Chapter 9 an' section 4(( 8n a solvent etrac5

tion syste" ith the volu"es , an' ,org o$ the a!ueous an' organic phases,

respectively, B) is calculate' $ro" the "aterial balanceM

here

log B) =logK logBK

Q

+log /mK),t

N ,org

log/

/4(20a

= Q =/ =KD

,K)

+, ,org

+Ka

BK ,

,org

/4(20b

mK),t is the total a"ount /in "oles o$ K) /reagent a''e' to the syste"( 6$ten= omK),t ,org is abbreviate' BK)org, in'icating the original concentration o$ K) in

the organic phase at the beginning o$ the eperi"ent /hen BK)a! =0( hen,org =, an' pK pKa, / == +KD,K)( Fro" E!( /4(20 it can be 'e'uce' thatB)

increases ith increasing pK, but ten's to beco"e constant as the pK value

approaches that o$ the pKa value( 8n the e!uations relating to the etraction o$

"etal co"plees, K) is o$ten i'entical ith reagent :1 the in'ees "ay be

change' accor'ingly, thus e(g(, KD,K) KA:( /HoteM Oarious authors use slightly'i$$erent no"enclature1 here e $ollo re$erence )ppen'i C(

4.).2 *rotonation

)t lo pK, so"e organic aci's accept an etra proton to $or" the K 2) co"5

ple( This lea's to a 'ecrease in theD) value at pK


34/120


beteen CKCl9 /upper curves or C;K; /loer curves an' a!ueous phase 0(= an' =(0

B)

0Cu 2 org AC 2

)t the highest )

concentrations a hori7ontal asy"ptote is approache'M

li" D =BCu) NBCu) =K /4(40B)

Cu 2 org 2 AC

The hori7ontal asy"ptote e!uals the 'istribution constant o$ Cu)2, i(e(, KAC(

Fro" the curvature beteen the to asy"ptotes, the stability constants = an'2 can be calculate'(

This ea"ple in'icates that in solvent etraction o$ "etal co"plees ith

aci'ic ligan's, it can be "ore a'vantageous to plot log D vs( logB), rather

than against pK, hich is the "ore co""on /an' easy techni!ue(

8n or'er to calculateD< $ro" E!( /4(9;, several e!uilibriu" constants as

ell as the concentration o$ $ree )

are nee'e'( Though "any re$erence or-s

report stability constants B=>, 20 an' 'istribution constants B4, 2=, $or practical

purposes it is si"pler to use the etraction constantKe $or the reactiona',b 2 b org 2 org org

8n the absence o$ any a''uct $or"er, DYn is given as a $unction o$ the $ree

ligan' concentration by E!( /4(9;, i(e(,0 the parentheses in E!( /4(4b e!uals

=1 'enoting thisDYn5value asDo, an' intro'ucing it into E!( /4(4 gives

/= B B2

L /4(J0D =D +Kad ,= org +Ka',2 org +

DYn /instea' o$ DYn in'icates that this epression is vali' only at constant

B), or, better, constant BK

+ an' BK)

=org Bsee E!s( /4(9; an' /4(4=c( 8n Fig(

4(=2, log DYnDo is plotte' as a $unction o$ log Borg( The 'istribution ratio

procee's $ro" al"ost 7ero, hen al"ost no a''uct is $or"e', toar's a li"it5

ing slope o$ 2, in'icating that the etracte' co"ple has a''e' to "oleculeso$ to $or" Yn)22( Fro" the curvature an' slope the Ka',b5values ere 'eter5

"ine' /see section 4(=0( The calculation o$ the e!uilibriu" constants is $urther

'iscusse' un'er Ea"ple =9(

Tables 4(==4(=9 presents a''uct $or"ation constants accor'ing to E!(

/4(4P( For the al-aline earths TT) co"plees in carbon tetrachlori'e in Table

4(==, the T "olecules bon' perpen'icular to the s!uare plane o$ the to TT)

rings, pro'ucing an octahe'ral co"ple( The higher the charge 'ensity o$ the

Table 4.11 )''uct For"ation Constants$or the :eaction


56/120

)''uct $or"ing

ligan' / logKa'= logKa'2 logKa'= logKa'2

TT)/sel$5a''uct 0(J; E >0(J Keone =(=; =(J2 =(P= 2(94

[uinoline 9(2> E 9(4 J(=;

T 9(;9 J(40 J(9; (>;T66 J(40 P(;0 P(4> =2(2;

&ourceM :e$( 4(

Table 4.12 )''uct For"ation Constants $or the :eaction Eu)9/org +bT/org V Eu)9/Tb/org, E!( /4(2;a, here org =CKCl9,an'%A Substitute' )cetylacetone Ligan's

Ligan' /A LogKa LogKa'= LogKa'2

)cetylacetone, )) (P; =(>0

en7oylacetone, Y) (P4 =(;0

Tri$luoroacetone, TF) E 9(92 4(;4

en7oyltri$luoroacetone, T) E 9(;4 J(2

25Furoyltri$luoroacetone, FT) E 9(J0 J(00

Thenoyltri$luoroacetone, TT) ;(9 9(94 J(2

&ourceM :e$( 4(

central ato", the stronger is the a''uct co"ple ith T( HoteM $hargedensity re$ers to the electrostatic interaction beteen ions o$ opposite charge

accor'ing to the orn e!uation Bsee /2(=9, an' /9(=9 /base' on the Coulo"b

interac5 tion( 8t is "ostly given as the ratio beteen the ionic charge, #+ /or

#+# an' the ionic ra'ius r+ /or r+r( Table 4(=2 co"pares the a''uct $or"ation

o$ the europiu" 5'i-etone co"plees ith T in chloro$or"( 8nEu/TT)9 the TT)s only occupy si o$ the eight coor'ination positions

available1 the to e"pty positions have been shon to be occupie' by ater(

Though the ten'ency is not strong, the stronger the aci' /i(e(, the larger its

electronegativity, the larger is the a''uct $or"ation constant( Table 4(=9

co"pares the a''uct $or"a5 tion ten'ency o$ the Eu/TT)9 co"ple ith

various a''uctants( The basicity o$ the 'onor oygen ato" increases in the

or'er as shon in Table 4(=9, as 'oes the a''uct $or"ation constant1 this is in

agree"ent ith the or'er o$ basicity in Table 4( an' the 'onor nu"bers o$

Table 9(91 see also section 4(2(

Table 4.13 Constants $or For"ation o$ Eu/TT)9b )''ucts)ccor'ing to E!( /4(2;a

Chloro$or" Carbon tetrachlori'e


57/120


4

9

4

The 'i$$erence beteen the to solvent syste"s is li-ely a result o$ CKCl9solvating the Eu co"ple to so"e etent, hile CCl4 is inert( This has to

e$$ectsM theKAC value increases 'ue to the solvation by CKCl9 /not shon in the

table, hile the a''uct $or"ation constantKa' 'ecreases as the solvation hin'ers

the a''uct $or"ation1 the "ore inert solvent CCl4 causes an opposite e$$ect, a

loerKAC an' a largerKa'(

4..2 (eta" Inorganic Com6"exes with rganic

$%%uct &ormers T!6e (8+7b

The etraction o$ "ineral salts is generally less co"plicate' than the etraction

o$ "ineral aci's(


58/120


4

D

Dn

Yn

Fig. 4.13 Aistribution ratio o$ Yn/88 hen etracte' $ro" = < Ha/SCH,Cl6

into

0(00= < T66 in heane, as a $unction o$ a!ueous SCH

concentration( The $olloingPe!uilibriu" constants ere obtaine' ith E!( /4(J9M = 9(P, 2 2=, 9 =J,Ke 2(J =0

b =2( /Fro" :e$( 2;($or

YnL +b /orgYnL /org

/4(J=

2 2 b

$or hich e "ay 'e$ine an e!uilibriu" constantKe,b(

ecause "ore than one solvate' species "ay be etracte', the 'istribution ratio

beco"es

BYnL +BYnL + L=2 org 2 2 org

BYn+BYnL+BYnL2+BYnL

9+

L

/4 J2

8nserting the partial e!uilibriu" constants Bsee E!( /4(4;,

BL K Bb

=2 2 e ,b org

Yn

=+BLn/4(J9

here both su""ations are ta-en $ro" =( The solvation nu"ber b can be 'eter5

"ine' $ro" the 'epen'ence o$ D on Borg hile BL is -ept constant( Fro" the

slope o$ the line in Fig( 4(=9 at lo SCH concentrations, it $ollos that b =21 thus only one a''uct co"ple is i'enti$ie'M Yn/SCH2/T662( The authors

ere able to calculate the $or"ation constants n $ro" the 'eviation o$ thecurve $ro" the straight the line at constant Borg, assu"ing b constant( ith


59/120

4

4

org

D"

these e!uilibriu" constants, the line through the points as calculate' ith E!(

/4(J9(

4..3 'e"f5$%%ucts T!6e ($+0,$b

Ky'ration only occurs in neutral co"plees that are coor'inatively unsaturate'by the organic ligan'( The hy'rate ater re'uces the etractability o$ the co"5

ple( 8n the absence o$ strong 'onor "olecules, hich can replace this hy'rate

ater, there is still a chance $or the un'issociate' aci' to replace the ater,

lea'ing to aself5adduct accor'ing to the reaction


60/120

hich is abbreviate', using the earlier relations, to


61/120


D3

Fig. 4.14 Etraction o$ "/888 by acetylacetone /K)a $ro" = < HaCl64 into ben5

7ene at three 'i$$erent original concentrations o$ K)a in the organic phase( p) =

logB)a

is calculate' accor'ing to E!( /4(20( The analysis o$ the syste" yiel'e' theconstants log = J(9J, log 2 >(20, log 9 =9(22, log 4 =4(0;, Ka'= P, Ka'2 9, an' KAC0(00, shon $orPm in Fig( 4(=J( /Fro" :e$s( 2Pa,b(

K B)9 /=+K BK) +K BK)2 +L

=AC 9 a '= o rg a '2 org

" B)n/4(JJb

here KAC re$ers to the 'istribution o$ uncharge' ")9 beteen the ben7ene

an' the a!ueous phase

KAC

=B")9

orgNB")

9 /4(J;

Ka',b is the e!uilibriu" constant $or the sel$5a''uct $or"ation in the organic

phase, i(e(,

") /org +b K)/org") /K)

/org/4(JPa

9 9 b

K =B") /K) B") = BK)b /4(JPba',b 9 b org 9 org org

For pe'agogic reasons e rerite E!( /4(JJb


62/120


D

4

n

K /=+K BK) +K BK)2 +L

=AC a ',= org a ',2 org

"

/B)9 = B)n

/4(J3 n

Hote that the 'eno"inator only re$ers to species in the a!ueous phase(

Thus at constant BK)org, the curvature o$ the etraction curve an' its position

along the B) aes is only cause' by varying B)

, i(e(, the a!ueous phase

co"pleation( The nu"erator re$ers to the organic phase species only, an' is

responsible $or the position o$ the etraction curve along the D5ais1 thus at

three 'i$$erent constants BK)org, three curves are epecte' to be obtaine', ith

eactly the sa"e curvatures, but higher up along the D5scale ith higher

BK)org concentration1 see Fig( 4(=4(

The asy"ptote ith the slope o$ 9 at high p) /i(e(, lo B), $its E!(

/4(J, hen "9+

'o"inates the 'eno"inator /i(e(, the a!ueous phase, hile

the asy"ptote ith slope o$ += $its the sa"e e!uation hen the a!ueous phase

is 'o"inate' by ")

( eteen these to li"iting slopes, the other three")n co"plees are $or"e' in varying concentrations( ) 'etaile' analysis o$

the curves yiel'e' all e!uilibriu" constants Ke,Kn, Ka',b an' KAC /see section

4(=4(9, hich are plotte' in Fig( 4(=J( The curves in Fig( 4(=4 have been

calculate' ith these constants(Kn is 'e$ine' by

n

=Kn

accor'ing to E!( /9(J(

/4(J>

The "ai"u" 'istribution ratio $or the "5K) syste" /D" about 0(=

is reache' in the pK range ;P( 8t is ell -non that the lanthani'es hy'roly7ein this pK region, but it can be shon that the concentration o$ hy'roly7e'

species is


63/120



64/120


Table 4.14 Constants $or the For"ation o$ So"e

La/888 )cetylacetone, )) C;K; 2(;

Eu/888 Thenoyltri$luoroacetone, TT) CKCl9 0(J;

Eu/888 Thenoyltri$luoroacetone, TT) CCl4 0(J

Eu/888 8sopropyltropolone, 8T CKCl9 2(=

Eu/888 8sopropyltropolone, 8T CCl4 2(0

#/O8 )cetylacetone, )) CKCl9 =(=;

#/O8 Thenoyltri$luoroacetone, TT) C;K; 0(J0

&ourceM :e$( 4(

reaction probably occurs in the organic phase( Table 4(=4 contains both very

inert /e(g(, CCl4, polar /CKCl9, an' pi5bon'ing solvents /C;K;(

4.1+ META EXTRACTION 'Y I,UID ANIONEXCHAN&ERS !TYPE III"D#

6rganic phase ith anion :HK+*

/:HK

+M*

pp n

echanger an' "etal co"ple )!ueous phaseM "etal ith M

#++nL

+p:HK

+*

/:HK

+


65/120

4

4 9


'iagra"1 hoever, here it su$$ices to use concentrations( )n interesting $eature

in Fig( =(9 is the 'i$$erences beteen "etals in various oi'ation state, notably

Fe/88 an' Fe/888, the latter being "uch "ore easily etracte' than the $or"er

because Fe/888 $or"s "uch stronger co"plees ith Cl

ions( The re!uire"ent

$or etraction o$ "etals by an a"ineli-e T6), or by its a"ine salt, T6)K+Cl

,

is the $or"ation o$ negatively charge' "etal chlori'e co"plees in the a!ueous

phase( The co"ple $or"ation $ro" 2 an' in the parapos5

ition, 9(>(

These general rules hol' rather ell $or the aci'ic organic etractants an'

can be use' to etrapolate $ro" relate' co"poun's to ne ones as ell as to

'evelop ne etractants( The e$$ect o$ various substituen's on pKa is etensively

'iscusse' in tetboo-s on organic che"istry Be(g(, =4, 94(

4.13.1.) The C'+,e- '/(i'! #'/ S(0i,i(%

C'!&(!( !Ke also increases ith increasing $or"ation constant o$ the uncharge' "etal

co"ple, 7( Ther"o'yna"ic $actors an' geo"etrical aspects that in$luence thesi7e o$ n are 'iscusse' in Chapter 9( So"e $urther observations $ollo(

To achieve the highest possibleD value, the concentration o$ the etracte'

uncharge' co"ple /


83/120

ever, at high pK the "etal "ay be hy'roly7e'( ) care$ul balance "ust be struc-

beteen 7,Ka, an' pK to achieve an opti"u" "ai"u" concentration o$ theuncharge' co"ple(

4.13.2 Effects of (o"ecu"ar ;o"ume an% ater'tructure 6on


84/120

=A ,

,

KAC values $or the lanthani'e acetylacetonates are the reverse $ro" that epecte'

$or the si7e e$$ect( The eplanation is li-ely that the neutral co"ple ith the

$or"ula Ln)9 is coor'inatively unsaturate', hich "eans that a hy'rate' co"5

ple eists in the a!ueous phase /possibly also in the organic phase( The "ore

coor'inatively unsaturate' lanthani'e co"plees /o$ the larger ions can acco"5

"o'ate "ore ater an' thus are "ore hy'rophilic( The result is a KAC several

or'ers o$ "agnitu'e loer $or the lightest, La, than $or the heaviest, Lu(

The tetravalent "etal acetylacetonates B9; have all coor'ination nu"bers

/CH or > in the neutral co"plees( For Th /ra'ius =0> p" at CH > there is

o$ten one "olecule o$ ater in Th)4, hereas $or the correspon'ing co"plees

o$ #/8O an' Hp/8O /ra'ius =00 an' > p", respectively, CH =, there see"sto be none( The "easure' 'istribution constants /log KAC are $or Th 2(JJ an'

$or # an' Hp 9(J2 an' 9(4J, respectively, in = < HaCl64Nben7ene( This agrees

ith the greater hy'rophilic nature o$ the Th)4 K26 co"ple(4.13.).) C'//e,(i'!& Be(2ee! KDR !" KDC[ualitatively, the 'istribution constants o$ the co"pleing reagent an' the corre5

spon'ing neutral "etal co"ple are relate' 'ue to their si"ilar outer sur$ace

toar' the solvents( Thus it is reasonable that there shoul' be goo' correlation

beteen KA: an' KAC $or ho"ologous series o$ reagents or co"plees( This is

in'ee' the case, as is seen hen KA,: is plotte' vs( KA,C, in Fig( 4(20 $or a

co"ple ith a variation o$ the solvent, an' in Fig( 4(2= $or co"plees o$

relate' reagents ith the sa"e solvent( This correlation can be relate' to thesolubility para"eter concept 'iscusse' later(

4.13.3 The 'o"ubi"it! *arameter

8n Chapter 2 e learne' that the cohesive $orces that -eep "olecules together

in a solution can be 'escribe' by

2 =/% RTN,

/2(=1 4(PJa

here 2 is the cohesi"e energy density, an' , the solubility parameter, ,, the

"olar volu"e an' %,, the "olar heat o$ vapori7ation( This hol's $or regularsolutions B9P that sho i'eal entropy e$$ects in "iing solute an' solvent, an'

no interactions occur besi'es the cohesive $orces beteen the solute an' solvent

"olecules( BHoteM :egular solutions ehibit heat changes hen "ie', hile $or

i'eal solutions, the heat o$ "iing is 7ero /see section 2(4(=( There is no

change o$ state in association or in orientation( Thus the or- re!uire' to pro5

'uce a cavity, Gcav, by the solute in the solvent is given by

Gcav 2cav

/2(=01 4(PJb

hereAcav is a proportionality $actor an' , is the "olar volu"e o$ the solute (


85/120

= + +

Fig. 4.2+ Aistribution constantsKAC $or uncharge' "etal co"plees ;0s B9a40c( Several revies on

the use o$ this theory $or to5phase 'istribution processes are also available

B4=,42( :ecently this theory has been re$ine' by the use o$ %ansen solubility

parameters B;,49,44, accor'ing to hich

2 2 2 2

total 'ispersion polar hy'rogen /4(PJchere interactions beteen the solute an' the solvent are 'escribe' by contribu5

tions $ro" the various types o$ cohesive $orces( 8n general, the 'ispersion /or

Lon'on $orces 'o"inate( 8n Fig( 4(22 the "easure' 'istribution ratios o$ an

a"ericiu" co"ple beteen an a!ueous nitrate solution an' various organic

solvent co"binations are co"pare' ith 'istribution ratios calculate' $ro" tabu5

late' Kansen para"eter values B4J(

Fe solubility para"eters are available $or the "etal5organic co"plees

'iscusse' in this chapter( )nother approach is then necessary( The 'istribution

constant $or the reagent /etractant, R, can be epresse' asM


86/120


Fig. 4.21 Aistribution constants,KAC, $or uncharge' "etal co"plees


87/120


org : : org a!

Fig. 4.22 Co"parison o$ "easure' an' calculate' 'istribution ratios D)" o$ a"erici5

u"/8885terpyri'ine5'ecanoic aci' co"plees beteen 0(0J < KH69 an' various organic

solvent co"binations( The calculate' values are obtaine' ith the Kansen partial solubil5

ity para"eters( /Fro" :e$( 4J(

RT lnKA:

=,:

B/a!

:2 /

2 Q RT , /=N , =N , /4(P;

hereKA: is given in ter"s o$ "ole $ractions( The solubility para"eter o$ ater

has to be e"pirically esti"ate'( The ther"o'yna"ic value is 4, but, since the

syste" "ay be sensitive to the choice o$ a!, it is better to select a re$erence a!3

in each set o$ eperi"ents, assu"ing constant values $or the a!ueous syste"s in

the to 'i$$erent to5phase syste"s(


88/120

Thus $ro" solubility para"eters, hich are speci$ic $or the various solutes

an' solvents, an' "olar volu"es, values $orKA: can be esti"ate', or 'eviations

$ro" regularity can be assesse'( These 'eviations can be esti"ate' !uantita5

tively an', in in'ivi'ual syste"s, can be ascribe' to speci$ic reactions in either

o$ the phases, e(g(, hy'ration, solvation, a''uct $or"ation, etc(

Fro" E!( /4(P; the relation

logKAC

=/,C

N ,:

logKA:

+const(

/4(P

can be 'erive'1 the subscript $ re$ers to the neutral "etal co"ple( The "olar

volu"e ratio is close to or s"aller than #, here # is the nu"ber o$ singly

charge' anionic species attache' to the central "etal ion org a! org org a!

shoul' yiel' a straight line ith slope ,: N RT ln=0( ) plot o$ this relation in

Fig( 4(29 'e"onstrates a satis$actory correlation beteen 'istribution constants

an' solvent para"eters, in'icating the use$ulness o$ the solubility para"eter

concept in pre'ictingKA: as ell asKAC values(

Fig. 4.23 )pplication o$ the regular solution theory $or correlation o$ 'istribution con5stants $or Yn)2 an' Cu)2 ith solvent properties /solubility para"eters1 the nu"bers

re$er to the solvents liste' in Table 4(=0( /Fro" :e$( 22(


89/120

4.13.4 Effects of the 'o"=ent 0Di"uent Com6osition

The co"position o$ the organic phase solvent /'iluent in$luences the 'istribu5

tion o$ both the neutral "etal organic co"ple


90/120

heane 0(>J, cycloheane =(09, ethylben7ene 9(9=, an' ben7ene J(>9 /a!ueous

phase = < HaCl64, the 'ecrease observe' in Fig( 4(24 "ay si"ply be an e$$ect

o$ the increasing aliphatic character o$ the solvents(

4.13.> Effects of the $ueous (e%ium

The e$$ect o$ the ater activity o$ the a!ueous phase, 'iscusse' in Chapters 2,

9, an' ;, is 'eter"ine' by the total concentration an' nature o$ the salts( Gener5

ally, the 'istribution constant $or a neutral "etal co"ple oul' increase ith

increasing ionic strength, as illustrate' in Fig( 4(2J( This salting5out effect is

o$ten ascribe' to a re'uction in $ree ater available $or hy'ration( 6n the other

han', the salt also brea-s 'on the ater structure, hich coul' re'uce the

energy to $or" a hole in the phase(

4.13.) Effects of the Tem6erature

The intro'uction o$ a neutral co"ple into a solution phase involves a nu"ber

o$ processes that can be associate' ith large changes in enthalpy /solvation

processes an' in entropy /solvent orientation an' restructuring, lea'ing to con5

si'erable te"perature e$$ects1 see Chapter 2( 8n general, the 'istribution o$ a

neutral "etal co"ple increases ith increasing te"perature $or co"plees ith

signi$icant hy'rophobic character( The "etal acetylacetonate syste"s in Fig(

4(2; illustrate this e$$ect( 8n these particular syste"s, the $ree energy o$ 'istribu5

tion beteen the organic an' a!ueous phases is 'o"inate' by the enthalpy ter"(

Fig. 4.2$ The 'istribution constantKAC $or 7inc 'iacetylacetonate, Yn)2, beteen ben57ene an' various concentrations o$ HaCl64 in the a!ueous phase1 2JC( /Fro" :e$( 9;(


91/120

Fig. 4.2% Aistribution constant KAC $or "etal 'iacetylacetonates,


92/120

T6) 0(00J J BJ0

T(9 P BJ0,J=

A 2 2 2 4 > 2 2 2 2A


93/120

a 7 a

in the sa"e or'er B2Pa2, see Fig( 4(=J1 i(e(, the stronger the co"ple, the

ea-er the a''uct(

The increase, by a''uct $or"ation, in the coor'ination nu"ber o$ the cen5

tral ato" is possible not only $or ea- but also $or strong chelates, provi'e'

their ligan' bites are relatively short( To "a-e roo" in the inner sphere o$ the

"etal ion $or another a''uct5$or"ing ligan', three chelating ligan's o$ s"all

bite angle can easily be shi$te' aay ithout signi$icant energy5consu"ing 'is5

tortion o$ the chelate rings BJ9a,b( The electronic structure o$ the central ato"

is also o$ -ey i"portance $or synergis", as illustrate' by the easy a''uct $or"a5

tion o$ "etal ions ith un$ille' or partially $ille' ' or $ orbitals, contrary to,

e(g(, p5bloc- ele"ents( 8nner5 an' outer5sphere co"pleation is $urther 'iscusse'

in the net to paragraphs an' in Chapter =;(

4.13..) D'!'/ Lig!" E66e$(&

Table 4(=P shos etraction constants $or so"e "etal ions ith three al-ylphosphates substitute' by 0, =, an' 2 sul$ur ato"s, but ith al"ost i'entical

aliphatic branchings( Section 9(9 'iscusses har' an' so$t aci's an' bases /KS)

theory( )ccor'ing to this theory, har' aci's $or" strong co"plees ith har'

bases, hile ea- aci's $or" strong co"plees ith ea- bases( 8n Table 4(=P,

the "etals are or'ere' in increasing har'ness, the sub 88(b group being rather

so$t /Table 9(2( resu"ably the Ke values re$lect this pattern, as they are pro5

portional to K7

an' ( 8n Table 4(=P, the aci'ity o$ the aci's increases /i(e(, Kincreases in or'er ' SSK (;

logKe $or'66K 2(20 =(0 =(20 2(J2 0(44 2(>logKe $or /C4K>62 6SK J(40 9(P0 0(P0 4(P 4(29 0(94logKe $or /C4K>62 SSK 4(40 9(4> 2(40 (2

aOalues esti"ate' $ro" :e$s( J, 20, J4, JJ, an' J;( : is /C K CK/C K CK 6 (4 > 2 J 2 2


94/120


2 2 ;

2 2 ; 9

4.13..3 I!!e/ !" O7(e/ S+he/e C''/"i!(i'!

The etractabilities o$ "etal5organic co"plees 'epen' on hether inner or

outer sphere co"plees are $or"e'( Case 8, section 4(2(=, the etraction o$ ura5

nyl nitrate by T, is a goo' ea"ple( The $ree uranyl ion is surroun'e' by

ater o$ hy'ration, $or"ing #6 /K 6

2+

, hich $ro" nitric aci' solutions can2+ 2be crystalli7e' out as the salt #62/K26; /H692 , though it co""only is ritten2+#62/H692/K26;( Thus, in solution as ell as in the soli' salt, the #62 is

surroun'e' by ; K26 in an inner coordination sphere( 8n the soli' nitrate salt,

the 'istance d#56/nitratebeteen the closest oygen ato"s o$ the nitrate anions,

/O2HO, an' the #5ato" is longer than the correspon'ing 'istance, d#56/ater,

to the ater "olecules, OK2, i(e(, d#56/nitrate >d#56/ater1 thus the nitrateanions are in an outer coordination sphere(

hen the a''uct $or"er T is a''e', the O/6C4K>9 groups are closer

to the #5ato"s than the OK2+s, d#56/T


95/120


Fig. 4.2( Structure o$ the #62/H692 2/C2KJ696( The uranyl oygens are situate'

perpen'icular to the plane shon aroun' the central ato"( /Fro" :e$( =2(


96/120


e 2

2

9 4

9 4

9 4

9 4

e

stu'ie' by "a-ing substitutions in the organic ligan', hich structurally inter5

$eres ith the $or"ation o$ the co"ple( For ea"ple, Ayrssen B substitute'

oines /5hy'roy!uinolinols, )ppen'i A(; in various positions, Table 4(J,

an' "easure' their 'istribution constants, KAC( )lthough the pKa an' KA,K) in

Table 4(J 'i' not vary "uch ith the substitution, theKAC $or the Th)4 co"ple

ith unsubstitute' oine as 42J, an' $or the J5"ethyl substitute' co"ple

aroun' =000, hile the 25"ethyl substitute' co"ple as not etractable( This

can be attribute' to the 25"ethyl group bloc-ing the co"ple $or"ation(

Table 4(= listsK values $or #62+

an' u4+

ith $our organophosphorous

etractants, T an' A6), an' Ti an' A6i), the iso5$or"s being "ore

branche'( The 'ata in the upper hal$ o$ the table shos little change inKe hen

T is replace' by Ti( Thus the branching has little e$$ect 'ue to the $ree

rotation o$ the substituents aroun' the phosphorous ato"( 8n the loer group,

the a"i'e A6), an' its branche' iso"er A6i), the nature o$ :, : an' :in ::HC6:is i"portant 'ue to the "olecular rigi'ity o$ the a"i'e group( The

branche' substituent strongly 'epresses the etraction constant, hich li-ely is

'ue to a "uch loer stability constant $or the branche' co"ple( This e$$ect is

"ore pronounce' $or u/8O than $or #62+

( 8n a search $or selective syste"s

$or separating trivalent actini'es $or" $ission lanthani'es, SpDuth et al( BJ> in5

vestigate' the etraction o$ trivalent ions $ro" a!ueous KH69 solutions contain5

ing 25bro"o'ecanoic aci' /KA) by "eans o$ terphenyl an' tria7ine 'eriva5

tives 'issolve' in the organic 'iluent tert5butylben7ene /T( Figure 4(2

shos the 'istribution ratio o$ the syste" as a $unction KA) in T ith an'ithout the terpyri'ine /$or"ula in Fig( 4(2>( This is an illustration o$ the

Table 4.1) Constants $or Etraction o$ )ctini'e Hitrate )''ucts ith

hosphoric )ci' Trial-ylesters /Free :otation o$ the P Substituents an'

ith),)5Aial-yla"i'es /:estricte' :otation )roun' the )"i'e


97/120


Fig. 4.2) Etraction o$ Eu/888 an' )"/888 $ro" ,KH69 ith 0(02 < oligopyri'ine

or tria7ine an' = < 25bro"o'ecanoic aci' in tert5butylben7ene( /Fro" :e$( J>(

necessity to achieve synergistic e$$ects by using a''uct $or"ers $or etraction

o$ "etal ions that otherise are too strongly hy'rate' to be etractable( The

structures o$ the terphenyls /a''uct $or"ers teste' are liste' in Fig( 4(2> ith

the 'istribution ratios achieve' $or )"/888, D)"( For ea"ple, in the syste"

ith A6A6V_,D)" is 4(2, hile ith T)ATY it is 9J>( The tria7ine T)A5

TY is "ore branche' /the terphenyl A6A6V_ "ore linear an' has a slightly

larger "olar volu"e, but the 'i$$erence "ay also be attribute' to the greater

basicity /i(e(, s"allerKa co"pare' to terphenyl( Koever, the =00 ti"es larger


98/120


Fig. 4.2* Structure o$ various oligopyri'ine an' tria7ine a''ucts, an' 'istribution ra5

tios /inserts $or )"/888 co"plees ith these oligopyri'ines /0(02


99/120


etraction by the tria7ine cannot be eplaine' by the KS) theory1 various

eplanations are suggeste' BJ>( Steric hin'rance can be pre'icte' by "o'eling

the "olecular structures an' che"ical reactions( )'vance' progra"s re!uire

"ain$ra"e co"puters, but use$ul progra"s are available $or 'es-top co"puters

B4>(

4.14 CACUATION OF E,UII'RIUM CONSTANTS

Earlier sections presente' che"ical "o'els $or the etraction o$ aci's an' "etals

into organic solvents, an' sho that these "o'els, epresse' "athe"atically,

agree ith eperi"ental 'ata at trace "etal concentrations an' at constant activ5

ity coe$$icients( These "o'els provi'e a rationale $or un'erstan'ing the che"i5

cal principles o$ solvent etraction(

Fro" plots o$ the 'istribution ratio against the variables o$ the syste"

B


100/120


2

This "etho' is use$ul hen only one species is etracte', but it has little

value $or the stu'y o$ solvent etraction syste"s that contain several co"ple

species(

4.14.1.) Lig!" N70e/ Me(h'"

This "etho' B;J;P is use$ul $or i'enti$ying the average co"position o$ the"etal species in the syste"( Consi'er E!( /4(9;a $or the etraction o$


101/120


n =n 0(J, logKn

log B)n /4(9

This "etho' o$ obtaining an esti"ate o$ the $or"ation constants as 'one as a

$irst step in the Th/8O5acetylacetone syste" in Fig 4(90, here in the loer


102/120


Fig. 4.3+ #pper curveM the 'istribution o$ Th/8O beteen ben7ene an' 0(= < HaCl64

as a $unction o$ a!ueous acetylacetonate ion concentration1 p) =logB)1 the asy"p5

totes have slopes 0 an' 4( Loer curveM The average nu"ber o$ ligan's per centralato", n7 , in sa"e syste", as obtaine' $ro" a 'erivation o$ the log D/p) curve(

#sing the ligan' nu"ber "etho', the $olloing e!uilibriu" constants ere esti"ate'/ith values $ro" graphical slope analysis ithin parenthesisM logK= (0 /P(J,

logK2 P(; /P(P, logK9 ;(4 /;(9, an' logK4 J(= /J(0( Log KA4 2(J0 is obtaine' $ro" the

hori7ontal asy"ptote( /Fro" :e$s( ;;a,b(

$igure, n7 is plotte' against log B), yiel'ing the preli"inary log

K

values

given in Fig( 4(9( 8n a si"ilar "anner, the a''uct $or"ation constants can be

'eter"ine'MEa"ple =9M The etraction o$ Yn/88 by 5'i-etones an' phosphoryl a''uct$or"ers /cont( o$ Ea"ple J(

Consi'er the $or"ation o$ a''ucts o$ the type


103/120


esti"ate' accor'ing to E!( /4(9(


104/120


2

4.14.2 ?ra6hic '"o6e $na"!sis

For a rational application o$ slope analysis it is i"portant to "easure the varia5

tion o$ the 'istribution ratioD ith one co"ponentx at a ti"e hile the others,

$, are -ept constant( The solvent etraction e!uation can then be epresse' in

the $or" o$ a si"ple polyno"ial o$ type

y =a0

+a=x +a

2

x

+L /4(J

here y is a $unction o$ the 'istribution ratio Dconst(C an' x a $unction o$ the

variable /e(g(, pK, the $ree ligan' ion concentration B), the concentration o$

$ree etractant K) or a''uct $or"er in the organic phase, etc((

4.14.).1 Li!e/ P,'(&

hen the 'istribution e!uation can be epresse' in the $or" y =a0 +a=x, $ro"a plot o$y vs(x the intercept on they ais yiel's the a0para"eter an' the slopethe a=para"eter( This treat"ent is re$erre' to as the limiting "alue method(

Ea"ple =4M The etraction o$ Cu/88 by KTT) /cont( $ro" Ea"ple 4(

Ea"ple 4 /Fig( 4(==a, is represente' by E!( /4(44, hich in logarith5

"ic $or" is ritten

logD =logK +2 log BK) +2 pK /4(;Cu e org

For constant BK)org /Fig( 4(==a, a plot o$ logDCu vs( pK yiel's a line o$ slope

2, hich intercepts pK =0 at logDCu =logKe +2log BK)org( )nother plot o$logDCu against log BK)org at constant pK yiel's a line that intercepts BK)org=0 at log DCu =log Ke +2pK /Fig( 4(==b( 8n either case, the KTT) syste"yiel's logKe ==(2J $or the CKCl9, an' =(0 $or the CCl4 syste"( The corre5spon'ing values $or the 8T syste" are =(;0 an' 0(>J, respectively(

Ea"ple =JM Etraction o$ Th/8O by acetylacetone /cont( $ro" Ea"ple =2(

8n Ea"ple =2, it as conclu'e' $ro" Fig( 4(90 that the a!ueous phase

containe' all Th)n5co"plees ith 0


105/120


= AC = 2 9


106/120


2 = = 2 9 4

H

is obtaine' $or hich there is no si"ple solution(

Ea"ple =;M Etraction o$ #/O8 by acetylacetone(

Fig( 4(9= shos the etraction o$ #/O8 by acetylacetone /%A $ro"

nitric aci' solutions, D#, as a $unction o$ p) =log B) at si 'i$$erent totalconcentrations o$ K)( ) co"parison ith Fig( 4(9 in'icates that e can epect

co"plees o$ the type


107/120



108/120


Fig. 4.31 Etraction o$ #/O8 by acetylacetone /K) $ro" 0(= < HaCl64 into chloro5

$or" as a $unction o$ pK at 'i$$erent total concentrations o$ K)( /Fro" :e$( ;>(


109/120


x

i 2

4.14.3 #umerica" (etho%s

The "ost co"plicate' e!uations presente' in this chapter are o$ the types shon

by E!( /4(>, here a series o$ co"plees are $or"e' in the organic phase an',

at the sa"e ti"e, one or a series o$ co"plees in the a!ueous phase( hen bothx an'y >0(8n practice, there$ore, one variable "ust be -ept constant /or 7ero, hile the

value o$ the other changes( This as 'escribe' $or Ea"ple =;( Thus, i$ x is

-ept constant, the 'ouble polyno"ial is re'uce' to a si"ple one

y =$x

iy

/$= =a

0+a

=x +a

2

x

+L /4(>0

here $ is a constant at constant x( The proble" is there$ore re'uce' to the

'eter"ination o$ the para"eters o$ a si"ple polyno"ial, to hich "any nu"eri5

cal "etho's have been applie' ith varying 'egrees o$ success( The "ain re5

!uire"ent is that all co"pute' para"eters shoul' be positive nu"bers /or 7ero(

8n or'er to solve an algebraic syste" o$ n para"eters, only n e!uations

are nee'e' /a "ini"u" ith no error esti"ates( hen the solvent etraction

reaction can be 'escribe' by E!( /4(>0, there are as "any e!uations as there

are eperi"ental points( Co""only, in solvent etraction =0J0 points are

nee'e' to cover the hole concentration range o$ interest, hile the nu"ber o$

un-non para"eters in si"ple cases is


110/120

i n i i i

2

ratioD( The least s!uare "etho' re!uires that & /the weighted s+uared residu!

als in epression E!( /4(>= is "ini"i7e'

* ) n & =wi /anxi yi

/4(>=

i== n=0 here ) += is the nu"ber o$ para"eters, an' * the nu"ber o$ eperi"entals

points1 ) +* = is re$erre' to as the nu"ber o$ 'egrees o$ $ree'o" o$ thesyste"1 each point has a valuexi N yi( ecause eperi"ents are carrie' out over

a large range o$ D, B) an'Nor B values, the points carry 'i$$erent algebraic

eight /e(g(, the value =000 obscures a value o$ 0(00=( There$ore, in or'er to

use the LS[ techni!ue properly, each point must be correctly weighted, wi( This

can be 'one in several ays, the "ost co""on being to eight it by yi, or by

2, or by a percentage value o$y 1 is the stan'ar' 'eviation in the "easure5i i in"ent o$yi( The 'i$$erence anxi yi /the residual is not 7ero, because the 'i$$er5

ence is to be ta-en beteen a "easure' value,yi /"eas(, an' the correspon'ing

calculate' value,y /calc(, by the a xn

$unction Bi(e(,y /calc( y /"eas(, usingthe actual an values at the ti"e o$ the operation(

The principle o$ the LS[ techni!ue is to co"pute the set o$ positive anvalues that give the s"allest su" o$ the resi'uals1 E!( /4(>= reaches the &"invalue( 8$ the resi'uals e!ual 7ero /hich rarely occurs in practice, &"in oul'

be 7ero, an' there oul' be a per$ect $it beteen the eperi"ental points an'

the calculate' curve(There are several "athe"atically 'i$$erent ays to con'uct the "ini"i7a5

tion o$ & Bsee :e$s( P0PJ( 1 reriting E!(

/4(JJb

3 =D B)n

N B)9

=K /=+

K

BK) +L /4(>2" n 9

hich can be sub'ivi'e' into

AC a'= org

3 =$ K /=+K

BK) +L /4(>9a


111/120

B) = AC a'= org


112/120

an'

3 =$ D B)n

N B)9

/4(>9bBK)org 2 " n 9

3BK)org contains the "easure'D", the B) values, an' the n values( 8t can thusin principle be treate' as an Ea"ple =; to yiel' the n values an' the $2 values/one $or each BK)org, re"e"bering that a0 ==( ecause 3B) N$= =3BK)orgN$2=3, a secon' plot o$ 3 against BK)org yiel's the KA9 an' Ka'b values( Theanalysis o$ the syste" yiel'e'KAC =0(00,Ka',= =P an'Ka',2 =9( 8n these cal5culations, a S8.1 'tirre% Ce"" 'emicontinuous Techniues

Each point5by5point eperi"ent re!uires a co"plete set o$ "iing, separation,

sa"pling, an' analysis( This usually lea's to scattere' results, though it "ay

not be critical, i$ theD values cover a li"ite' range $ro" 0(==0( Koever, the

"ore theD values 'eviate $ro" =, the "ore accurate "ust be the "easure"ents1

also the nu"ber o$ points re!uire' $or a reliable etraction curve usually in5

creases( To re'uce the uncertainty an' labor involve' ith the batch techni!ue,

the stirre' cell techni!ue has beco"e popular(

Figure 4(92 shos a typical ther"ostate' stirre' cell( The li!ui' volu"es

are co""only J0 + J0 "L( The stirrer "ay consist o$ a single pa''le at theinter$ace, or a 'ouble pa''le, one in the center o$ each phase( The cell "ay

contain ba$$les, etc(, to i"prove the "iing( Stirring "ay be violent, co"pletely'estroying the inter$ace an' pro'ucing very s"all / = "" 'roplets, or slo



Fig. 4.32 ) ther"ostate' 'ouble Dac-et /= cell $or solvent etraction stu'ies /heavier

phase , lighter phase > un'er nonoi'i7ing con'itions, using a hy'rogen gas inlet /;

to a '5blac- catalyst /==, pK glass electro'e /9, "agnetic stirrer /=0, connections $or

a''itions /J( )lternative constructions contain rotating pa''les an' $ie' pipings con5

necte' to the to phases $or $re!uent sa"ple ith'raals(

in or'er not to 'estroy the inter$ace( The stirring rate is opti"i7e' to the ti"e

$or reaching e!uilibriu" an' co"plete phase separation( The eperi"ents are

either carrie' out ith inter"ittent violent stirring, in hich case sa"ples are

ith'ran a$ter each co"plete phase separation, or ith "il' stirring 'uring

hich it is possible to continously ithra sa"ples( E!ual volu"es are sa"ple'

each ti"e, co""only ( This

is particulary a'vantageous $or -inetic eperi"ents an' is $urther 'escribe' in

Chapter J( The sa"pling o$ the stirre' cell can be auto"ate', so that at regular

intervals pK an' te"perature are recor'e', an' sa"ples ith'ran $or auto"atic

analysis o$ concentration o$ interesting species in "ore or less stan'ar' $ashion(

8t is also possible to use ion5sensitive probes in one o$ the phases instea' o$

sa"pling(

4.1>.2 Centrifuga" Extraction5'e6aration '!stems

) 'i$$erent approach to solvent etraction eperi"entation, re$erre' to as the

)#FOE principle, as 'evelope' in the =>;0s B0a'( The )#FOE is



illustrate' in Fig( 4(99( E$$icient "iing o$ the to phases an' their a''itions is

achieve' in the "iing vessel an' at the in$lo into the phase separator, hich

consists o$ a continuous flow centrifuge, hich in a special separation cha"ber

an' at very high rotational velocity /J,000J0,000 rotations per "inute sepa5

rates the "iture into to very pure phases, containing


115/120


Ti, or EE /polyether ether -etone to allo "easure"ents un'er very corro5

sive con'itions( The separate' phases pass )


116/120


site in an accelerator or a research reactor to the S8S) e!uip"ent via a gas5

Det transport syste"( The nucli'es are 'issolve' in an a!ueous phase that is $e'

into a centri$uge battery co"prising =4 solvent etraction steps( The pro'uct

solution leaving the last step is pu"pe', e(g(, to a nuclear ra'iation 'etection

syste"( The transport ti"e $ro" the target site to the 'etection syste" 'epen's

on the centri$uge si7e, nu"ber o$ centri$uge steps, an' $lo rate( For a one5step

che"istry, i(e(, 'issolution step an' a single centri$uge etraction, an' "ai"u"

$lo rates, the overall transport ti"e is aroun' 2(J s( This $ast transport has

alloe' 'etaile' 5spectroscopicstu'ies o$ ra'ionucli'es ith hal$5lives aroun'= s( :ecently the S8S) e!uip"ent as succes$ully applie' to stu'ies o$ the

heaviest ele"ents, an' solvent etraction 'ata ere obtaine' $or ele"ent =04 :$

BJ( Fast che"ical separation syste"s have been 'evelope' $or !uite a large

nu"ber o$ ele"ents B;(

Centri$ugal etractors have been 'esigne' $or a nu"ber o$ in'ustrial uses

/see succee'ing chapters( 8n so"e cases they have been scale' 'on to labora5

tory si7e but "ainly been use' $or 'eveloping in'ustrial "ultistage processes(

4.1>.3 Liui% *artition Chromatogra6h!

8n li!ui' partition chro"atography a solute 'istributes itsel$ beteen a "obile

li!ui' phase an' an i""obile solvent attache' to a soli' "atri /in the earliest

eperi"ents a clayli-e 0ieselguhr( 8t is outsi'e the scope o$ this chapter to

'iscuss this techni!ue, hich, hoever, is brie$ly 'escribe' in Chapter =J(

4.1% CONCUSION AND FINA COMMENTS

The solvent etraction process is usually 'escribe' by a single net reaction,

'e$ine' by the etraction constantKe( Oariations inKe cause' by "o'i$ications

o$ the solvent syste", such as changes in the te"perature or a!ueous ionic

strength, or by replacing one solvent by another, or "a-ing substitutions in the

etractant "olecule, "ay be eplaine' by care$ul consi'eration o$ the para"e5

ters o$ the syste"( Koever, such stu'ies are 'i$$icult an' not alays su$$icient

$or pre'icting ne syste"s( ) better $oun'ation $or un'erstan'ing the etractionprocess is to consi'er the steps in the process contributing to the net etraction

reaction, particularily hen these steps are governe' by regularities( nole'ge

o$ these regularities helps in interpreting syste"s as ell as in pre'icting ne

ones( Etension o$ these 'istribution 'ata to ther"o'yna"ic constants is li-ely

to give bene$its in increase' che"ical -nole'ge o$ the behavior o$ solutes in

'i$$erent solvent syste"s( )'vance' !uantu" che"istry calculations an' co"5

puter "o'eling o$ etraction processes can help us in 'esigning ne, selective

solvent etraction syste"s, as ell as in interpreting etraction pheno"ena /see

Chapter =;(


117/120


REFERENCES

=( Graha"e, A( C(1 Seaborg, G( T( 5(Am( $hem( &oc( 1938, 89M2J24(

2( 8rving, K( p( >=, (&E$688, &ol"ent Extraction $hemistry Ayrssen, A(1 LilDen7in,

.( 6(1 :y'berg, .( E's(1 Horth Kollan', )"ster'a" /=>;P(

9a( :y'berg, .(Ar0i" Kemi =>J4, :M=0=(9b( :y'berg, .('ec( Tra"( $him( 1956, ;;>(

;( arton, )( F( ( Se-ine, T( et al(ull( $hem( &oc(5ap( 1983, P9(

=9( .assi", T( ;(=4( P0(

=Pa( Harbutt, .(5((norg()ucl( $hem( 1981, @>M9949(

=Pb( Harbutt, .(5(Phys( $hem( 1991, C


118/120


29b( )llar', (1 .ohnsson, S(1 Harbutt, .1 Lun'!uist, :((&E$ ;;, $(M &pecial ,olume

?, =>PP(

24( Se-ine, T(1 8hara, H(ull( $hem( &oc(5ap( 1971, @@M2>42(

2J( Cecconie, T(1 Freiser, K(Anal( $hem( 1990, 8?M;22(

2;( ;P(

90a( Se-ine( T(1 Ayrssen, A(Anal( $him(Acta 1969, @P2(

99a( :y'berg, .('e"((norg( $hem( 1999, CM24J(

99b( :y'berg, .(Min(Pro(Ext(Met('e"( 2000, ?M=;P(

94( Carey, F( )(1 Sun'berg, :( .(Ad"anced =rganic $hemistry, Thir' E'ition, lenu"

ress, He _or-, =>>0(

9J( Fu-s, L(1


119/120


120/120

P;( M20JP(

P( E-berg, Ch( Bncertainties in Actinide &olubility $alculations (llustrated Bsing the

ThR=%RP=@ &ystem, Aiss( Chal"ers te-nis-a ho%gs-ola, Go%teborg,

=>>>(

P>( atari, K(1 Cunningha", L(1 Freiser, K(Anal( $hem( 1982, 0(0a( :einhar't, K(1 :y'berg,5( &ol"ent Extraction $hem( /(&E$ =>;;, Horth5Kollan'

ubl( Co( )"ster'a", ;=2 pp(

0b( :einhar't, K(1 :y'berg,5( $hem((nd( 1970, 4 pp(

0c( :y'berg, .(, et al(Acta $hem( &cand( 1969, ?>M;4P(

0'( :y'berg, .(, et al(,Acta $hem(, 1969, 2PP9, 2P=, 2P>P pp(

=(

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