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The solvent extraction of Thulium with aliphatic monocarboxylic acids
Amlytica Chimico Acla Elscvicr Publislling Company, Printed in TlwzNetherlands
Arnstcrdam
THE SOLVENT E~XTILK’I‘ION MONOCARBOXYl,XC ACIDS
OF
THULTU&I
WIT14
ATJPHATIC
Some simple carbosylic acid estractions of ram-earth ions have been carried out previously. It has been shown that mixed napllthenic acids in such organic media as ethyl ether, x-hexanol, and kcrosinc will extract rare-earth ions from aqueous solutions at appropriate l”I values 1. The slopes obtained for plots of the logarithm of the distribution (log D) against 1~1-1 and for plots of log D against the logarithm of the naphthcnic acid concentration in the organic phase (log [HR],,) are cu. 3. The value of log I> is dcpcndcnt upon PH, naphthcnic acid concentration. mole ratio of nnplithcnic acid to rare-earth ion, organic solvent, contact time,
In each distribution determination, a ao-ml bottle contained 8.00 ml of an aqueous phase and 8.00 ml of an organic phase. The aqueous phase was either IO-~.OM or x0-8-0 M in thulium perchlorate labelled with thulium-170, was made up to an and may have contained a given ionic strength of 0.10 with sodium perchlorate, concentration of a water-soluble acid such as formic, acetic, or propionic acid. The
G. K.
20
SCHWEITZER,
S. M.
SANGHVI
p'h~X COIwiStCCl either (Jf a. p_HX! CaIh.XyliC aXid or Of an OrganiC SOlVent WlliCh may hnvc contained a known concentration of 8 carboxylic acid. All aclueous phases and all organic phases were were pre-saturated with the proper organic plmse, pre-saturated witli a propi ac~u~:cms phase containing no thulium. The aqueous pH was adjusted wit11 sotliuni l~ydro,xicle ant1 percllloric acid solutions. After preparation, tl~c: m-nil bottles were rotated on a turning bar for 4 clays o ‘I’liis period of time was clcmonstratcd to 1~ quite sufficient for the attainment at 27 . ‘I‘hc httles wc’rc’ then centrifuged, the pH value of the aqueous pl~1,~2 of cquilil~rium. w;~s clctcrniinccl, the pl~ascs were snrnplcd with Ioo-/AI pipettes, the samples were and tile plancl~ets were count& wit11 conventional p-clctcction clricd on plnnclicts, apparatus. IIistribution coefficient (II) values were obtainccl by dividing the organic investigations lmcl clernonstratccl tliat no count by t11e aql.lcous ccJu11t. Previous self-absorption corrections were nccclccl for citlicr pl~nsc.
OrgalliC
l;igurc I presents data for tlic estraction of Io-A.o M tliulium into 1.0 M solutions of various carbosylic acids in 4-mcti~yl-z-pcntaIlone. Extractions wit11 I.0 M formic, ncctic, and propanoic acids and with pure 4-methyl-z-pcntanone gave no log 1) values greater than -3.00, and so they are not shown in the figure. Figure 2
3.0 2.
A - Eutanoic - Pentonoic 0 - Hexonoic 0 - Octanoic V - Nonanoic
acid acid acid acid acid
,*$Ll--
Cl-
CYJ m
l-
.
0 0 0 V
3 . 2
-
Pentanoic Hexanoic Octanoic Nonanoic econoic
acid acid acid acid acid
1
'7
A@4A
-2. B
’
-3.
234567
sir
Li ,.
’
I PH
I
2
3
4
PH
5
6
I
7
depicts the results obtained when cIlloroform was enil~loyccl as the organic phase. Again. x.0 1X! formic, acetic, and. propanoic acids as well as pure clilorofcmn gave log D values less than -3.00. Figure 3 shows tllc esperhental data arrived at when pure hesanoic acid and various concentrations of hesanoic acid in 4-methyl-z-yentanone were used for
SOLVENT
0 3 _ 0 A 0
ESTRACTIOS
-
Pure 3.0M l.OM 0.3 M
OF
TIT1
31
acid acid acid acid
32-
,‘A
l-
,’
F-l-2-3-
1 t
2
3
4
5
6
1
7
l:iK.
.f.
ICstmction
(of
1 o-~
i\f
thuliutli
c;ll CII~VCS (SW test.) ; (-.-.----)
- lo-“M
A
into
cspcritlIclit;tl
6
2
3
.~-~l~ctll~l-~-~~c~~t~~llc,llc cspcrinicntal
cllloroforin citrk’cs.
0 - Pum acid 0 - 3.0 M acid A - 1.0 M acid O-0.3M acid
/
I
PH l;iK:. 3. ‘I
cP-@.
,’
,’
O-
n
1 I’
4
PH
5
6 hcsanc,ic
colltitilli~l~
7 xcitl.
cllrvcs.
cont;~inirlF: Iics;ilIoic
xitl.
(--
) ‘I’lworcti-
Tm
2l(3 TO-1 -
fQ
et*
-2-3
d
I’
a
1 I
4
5
w
6
PH
Kxtrnctions of thulium I.0 M hcsanoic m5cl.
Fig.
5.
into
(a)
,I-nl”th~l-2-pCllt;LllOnC
ant1 (11) clllorofornl
containing
extraction of IO-**0 M thulium. Figure 4 shows the results obtained for similar systems with chloroform solutions of hexanoic acid. Figure 5 illustrates the effects of altering the thulium concentration. Results for both x0-4.0 and 10-8-o M thulium extracted into 1.0 M hexanoic acid in both 4-methyl-2-pentanone and chloroform are given. A?zal. Chi??r. Ada,
47 (19fi9)
19-25
c;.
22
I<.
SCHWELT%ER,
S.
31.
SAXGHVI
‘l;igures I ancl 2 il1IlslriLtc the generally cxpectcd tendency as larger and larger ‘I’hc slight differences cvidcncccl in the highermolccu1ar weight aCiCk arc cmp~oyccl. wcigllt acids are probably clue to variations in tlie organic-aqueous partition constants (1’) ailcl in tile organic climcrization constants (C). In the 4-methyl-2-pentanonc systems, which arc shown in Fig. 3, the llcxanoic acid is csscntially in the monomeric form in tlie organic phase as is reflcctecl by the negligil,le clirnerization constant (C) measured by SAWHNICYG. The total hcxanoic acid concentration [HR]t at any given pH value is given by [I-IRJr= [HRlo+ [HR] + [I<], where [FIR],, is the monomer concentration in tllc organic phase, [HJ<] is tile monomer concentration in the aqueous pliase, and [J<) is the hcxanoatc ion concentration in tllc ac]ucous pl1asc. Substituting a value of 104.Q for the association constant Ir’ of tlic acid”, and a, value of x01.” for tlic partition constant”, one obtains tllc relation:
Using this equation to calculate [HR]O a t various pw values, and fitting ‘Fig, 3 to the best mathematical expression, one arrives at I)-1 = x013.3 [I-IR]“-qH]3+
100.4
tlic clata. of
[I-IR].-~qH]~.
Tlic solid lines in Fig. 3 were obtained with this esprcssion. If it is assumccl that the predominant specks in the organic pllasc coulci Ix? rcprcscntecl as l’mRn(HR) 1,and that the prcclnminant species in the aqueous pllasc could bc rcprcscntcd as TmlC r(OH) I~,then D--l= [Tll~R~(OH)I,:][‘~mIt?(MI~)‘,]o-’. Making appropriate
substitutions,
one can write tllis csprcssion
as
where K is tllc acicl association constant, P is the organic-aqueous acid partition constant, C ,.I,is the aqueous association constant of TmR,.(OH)~,, W is the ion product ot water, KS,, is the association constant of TI~R~(HII)~,, and Pa,, is the organicaqueous partition constant of TniR3(HIC)a. When this theoretical expression is comparccl wit11 the equation clcrivecl from tllc curve fitting, the following may bc recognized: an organic species for tlic first and second tcrnis of ‘lYn~R3(HR), an aqueous spccics for the first term of Tm3+, an aqueous species for the second term of TmOH”+, an overall equation of
a log K31P31 value of Io7*“, and a log Co1 value of Iolo*oS Application of the esprcssion from the curve fitting to the pure hesanoic acid extraction produces a curve which dcviatcs consiclerably from the esperimental one. This is not surprising since the hexanoic acid probably exists as an acid-solvent adcluct in the +methyl-z-pentanone but as a climer in the pure acid. In addition, the extracting species in the 4-methyl-z-pentanone system is TmRs(HR) probably with several molecules of the solvent attached, whereas the cstracting species in the purcacid system is probably Tm&(IiR),, with an a value greater than unity. .47rctl.
Clrim.
nckz,
47
(1gGg)
19-25
Tm
SOLVESTEXTRACTIOFOF
23
In the chloroform systems, which are shown in Fig. 4, the hexanoic acid in the organic phase is predominantly in the dimeric form, as is indicated by the dimerization constant (C) of 101.~ as measured by SAWHNEYG. The total hesanoic acid concentration [HRlt at any given PH value is esprcssable as [HR] t = 2 [H&z], + [HR]” + [FIR:] + [RJ. where [H2R210 is the dimer concentration in the organic phase and the other symbols have their previous significances. With a value of IO ‘1.0for the acid association constant (Kc), x0 0.0 for the partition constant (Z’)5, and 101.0 for the dinlerization constant (C) 5, the following equation can be written: [HRlt.=2
[HzII~]o+(C-‘I”+C-LI”P-~+C-‘~“I~-’T-’-’[H]-’)
= 2 [HaRn]o+
(IO --R.fJ+IO-I.74
lo-"."[H]-1)
[HJ
[&&]J/",
This relation was used to calculate [H2I&], at various pH values. Then tile data of Fig, 4 were fitted to the best, mathematical espression which turned out to be D-1 = 101’.3[HzRz]o-~[H]3+
107~O[Ho_liz]o-~~[Ii~~.
Tile
solid lines in Fig. 4 were calcula.ted from this espression. If it is assumed that the predominant species in the organic phase could bc reprcscntecl as TmlG(HR) ,, and that the prevailing species in tllc aqueous phase could be represented as TmR r(OH) I,. then,
wliere the symbols are as previously stated. When this theoretical espression is comparecl with tile equation derived from the esperimental data, the following may be recognized: an organic species for the first and second terms of TmIQ(HR),=j, an aqueous species for the first term of Tni”+, an aqueous species for the second term of TmOH”+, and an overall equation of Z, -l=
Z<“Z=Z
[H)z,
with a 1<3#36 value of 107.0, and a Cot value of x00.7. When the expression derived from curve fitting of thcexpcritnental chloroformsystem data is applied to the pure hexanoic acid extraction, a curve which fits the pure hexanoic acid data very closely is obtained. This curve is shown by a solid line in Fig. 4. The fit probably indicates that tile species extracting into the pure acicl is similar to the species estracting into chloroform solutions of the acid, namely, Tn-&(HR) G.Such a formula evidences a coordination number of at least S. This is not unusual since rare-earth ions with coordination numbers of 8 and greater are now well knownO. The assumption has been made in all the above considerations that no polymerization of either the predominant aqueous or organic metal-bearing species is occurring. This supposition appears to be warranted in view of the lack of dependency of extraction upon the thulium concentration as shown in Fig. 5. The values for the first-hydrolysis constant of the thulium(II1) ion obtained in these two systems, x010.2 and 100.7, seem to be high in comparison with other rare-earth first-hydrolysis constants. Values7 for lanthanum(II1) range from 103.9 to 108.4 in various aqueous media, for cerium(II1) 1oG.0, for praseodymium(II1) xoG.G, and for lutetium(II1) 107.4. Values7 for scandium(II1) range from x08*0 to 1010.2 and i .;
Anal.
Chim.
Acta.
47 (rg6g)
1g-25
24
C.
K. SCHWEITZER,
S. M.
SANGHVI
for yttlium(III) from xofi.(Jto xo 7-('.At first, it miglJt be thought tllat the discrepancy could be assigned to sligllt errors in the constants I<, P, and C which are magnified by raising them to higher powers. However, this cannot be maintained since the constants in the first and second terms of the empirical equations cliffcr only by COlw causing everything else (for example, for tlie chloroform system K”I-‘“1<35-‘system K~P~I<~I-~Z?I~-~) to cancel out. Pns- ‘Cd and for the 4-metl~yl-2-pcntanonc Thus small errors in K, 23, and C should not affect the results. It is possible that the l)rescnce of organic solvent in the aqueous pha.%s could alter the constant COl, this being one of tile difficulties encountered in the use of solvent extraction for association ion-constant studies”. It is interesting to note tliat a Iligher CO1 vduc for scandium(III) was also obtained by a solvent extraction method”. Because of the several tlifficultics with extraction tccllniclucs, tile autllors tend to trust the potcntiometrically detcrminccl values more than tllose obtained by extraction.
The extraction of 10-4 and IO-” M tllulium(II1) into +mcthyl-2-pentanone and chloroform containing aliphatic monocarbosylic acids leas been studied witll formic through clccanoic acids. Estraction tends to increase wit11 acid molecular and pEr up to about 6. I)etailccl studies with lic.xanoic weight, acid concentration, acid indicate tllat tlic species extracting into 4-metllyl-2-pcntanone is TnlIZ3( I-11<) and tile spccics extracting into chloroform is TmR3(Hl<)rj. In both cases the prcdominant aqueous species are Tm3f and TmOH2+. From tile data first hydrolysis constants of Tm:J+ have been calculatecl to be 1010.2 and xou.7, thcsc values being larger than those cspectccl from previous rare-earth hydrolysis data.
Unc dtucle a dt6 cffectucc sur l’extraction clu thulium(II1) (IO-‘* et x0-H M) clans la m&hyl-+pentanone-2 et le chloroforrne, renfermant dcs acidcs aliphatiques monocarboxyliques. L’extraction tend h augmenter avec Ic poids mol&culairc des acides, la concentration en acicle et le PH jusqu’g environ 6. Avec l’acicle hexano’ique, on extrait Tm.R3(HR) dans la m&hyl-4-pentanone-2 ct Ttn&(HI?)a dans lc chlorofox-me. Dans les deus cas les particules prddominantes dans l’eau sont Tm3+ ct TmOH3+. Les constantes cl’hydrolyse clc Tm3-+ calculc!es sont 1010.z ct 100.7. Ces valeurs sont plus grancles clue pr6vues d’aprbs les valeurs d’hydrolyse cles terres rares. ZUSAMMENFASSUNG
mit 4-Methyl-2-pentanon Die Extraktion von IO-” und IO-” M Thulium(II1) and Cllloroform, das alipllatische Monocarbons#uren enth:ilt (Ameisen- bis Dekansliure), wurde untersucht. Die Estrnktion steigt mit dem Molekulnrgewicht der Sliure, cler ZXurekonzentration uncl dem pa-Wert bis zunl Wert 6. Genauere Untersuchungen mit Hexansiiure zeigen, dnss die Spezies, welche mit 4-Methyl-2-Pentanon extrahiert werden. TmRa(HR) und class die Species, welche rnit Chloroform extrahiert werden, TmR:~(HR)~ sind. In beiclen FBllen sind die bevorzugten wsssrigen Spezies Tm3+ und TmOH~+. Aus diesen Daten wurdcn die ersten Hyclrolyse-Konstanten des A,Jrnl.Cl&Jl. nctn, 47 (1969) x9-25
SOLVEST
ESTIZACTIOS
OF
Tm
2.5
Tm3+ zu x010.” und zu x00-7 bcrechnct. Diese Werte sincl griisser als diejenigen, welche aus friiheren Hyclrolysedaten Seltener Erclen errnittelt wurden.
Arnstcrdam
THE SOLVENT E~XTILK’I‘ION MONOCARBOXYl,XC ACIDS
OF
THULTU&I
WIT14
ATJPHATIC
Some simple carbosylic acid estractions of ram-earth ions have been carried out previously. It has been shown that mixed napllthenic acids in such organic media as ethyl ether, x-hexanol, and kcrosinc will extract rare-earth ions from aqueous solutions at appropriate l”I values 1. The slopes obtained for plots of the logarithm of the distribution (log D) against 1~1-1 and for plots of log D against the logarithm of the naphthcnic acid concentration in the organic phase (log [HR],,) are cu. 3. The value of log I> is dcpcndcnt upon PH, naphthcnic acid concentration. mole ratio of nnplithcnic acid to rare-earth ion, organic solvent, contact time,
In each distribution determination, a ao-ml bottle contained 8.00 ml of an aqueous phase and 8.00 ml of an organic phase. The aqueous phase was either IO-~.OM or x0-8-0 M in thulium perchlorate labelled with thulium-170, was made up to an and may have contained a given ionic strength of 0.10 with sodium perchlorate, concentration of a water-soluble acid such as formic, acetic, or propionic acid. The
G. K.
20
SCHWEITZER,
S. M.
SANGHVI
p'h~X COIwiStCCl either (Jf a. p_HX! CaIh.XyliC aXid or Of an OrganiC SOlVent WlliCh may hnvc contained a known concentration of 8 carboxylic acid. All aclueous phases and all organic phases were were pre-saturated with the proper organic plmse, pre-saturated witli a propi ac~u~:cms phase containing no thulium. The aqueous pH was adjusted wit11 sotliuni l~ydro,xicle ant1 percllloric acid solutions. After preparation, tl~c: m-nil bottles were rotated on a turning bar for 4 clays o ‘I’liis period of time was clcmonstratcd to 1~ quite sufficient for the attainment at 27 . ‘I‘hc httles wc’rc’ then centrifuged, the pH value of the aqueous pl~1,~2 of cquilil~rium. w;~s clctcrniinccl, the pl~ascs were snrnplcd with Ioo-/AI pipettes, the samples were and tile plancl~ets were count& wit11 conventional p-clctcction clricd on plnnclicts, apparatus. IIistribution coefficient (II) values were obtainccl by dividing the organic investigations lmcl clernonstratccl tliat no count by t11e aql.lcous ccJu11t. Previous self-absorption corrections were nccclccl for citlicr pl~nsc.
OrgalliC
l;igurc I presents data for tlic estraction of Io-A.o M tliulium into 1.0 M solutions of various carbosylic acids in 4-mcti~yl-z-pcntaIlone. Extractions wit11 I.0 M formic, ncctic, and propanoic acids and with pure 4-methyl-z-pcntanone gave no log 1) values greater than -3.00, and so they are not shown in the figure. Figure 2
3.0 2.
A - Eutanoic - Pentonoic 0 - Hexonoic 0 - Octanoic V - Nonanoic
acid acid acid acid acid
,*$Ll--
Cl-
CYJ m
l-
.
0 0 0 V
3 . 2
-
Pentanoic Hexanoic Octanoic Nonanoic econoic
acid acid acid acid acid
1
'7
A@4A
-2. B
’
-3.
234567
sir
Li ,.
’
I PH
I
2
3
4
PH
5
6
I
7
depicts the results obtained when cIlloroform was enil~loyccl as the organic phase. Again. x.0 1X! formic, acetic, and. propanoic acids as well as pure clilorofcmn gave log D values less than -3.00. Figure 3 shows tllc esperhental data arrived at when pure hesanoic acid and various concentrations of hesanoic acid in 4-methyl-z-yentanone were used for
SOLVENT
0 3 _ 0 A 0
ESTRACTIOS
-
Pure 3.0M l.OM 0.3 M
OF
TIT1
31
acid acid acid acid
32-
,‘A
l-
,’
F-l-2-3-
1 t
2
3
4
5
6
1
7
l:iK.
.f.
ICstmction
(of
1 o-~
i\f
thuliutli
c;ll CII~VCS (SW test.) ; (-.-.----)
- lo-“M
A
into
cspcritlIclit;tl
6
2
3
.~-~l~ctll~l-~-~~c~~t~~llc,llc cspcrinicntal
cllloroforin citrk’cs.
0 - Pum acid 0 - 3.0 M acid A - 1.0 M acid O-0.3M acid
/
I
PH l;iK:. 3. ‘I
cP-@.
,’
,’
O-
n
1 I’
4
PH
5
6 hcsanc,ic
colltitilli~l~
7 xcitl.
cllrvcs.
cont;~inirlF: Iics;ilIoic
xitl.
(--
) ‘I’lworcti-
Tm
2l(3 TO-1 -
fQ
et*
-2-3
d
I’
a
1 I
4
5
w
6
PH
Kxtrnctions of thulium I.0 M hcsanoic m5cl.
Fig.
5.
into
(a)
,I-nl”th~l-2-pCllt;LllOnC
ant1 (11) clllorofornl
containing
extraction of IO-**0 M thulium. Figure 4 shows the results obtained for similar systems with chloroform solutions of hexanoic acid. Figure 5 illustrates the effects of altering the thulium concentration. Results for both x0-4.0 and 10-8-o M thulium extracted into 1.0 M hexanoic acid in both 4-methyl-2-pentanone and chloroform are given. A?zal. Chi??r. Ada,
47 (19fi9)
19-25
c;.
22
I<.
SCHWELT%ER,
S.
31.
SAXGHVI
‘l;igures I ancl 2 il1IlslriLtc the generally cxpectcd tendency as larger and larger ‘I’hc slight differences cvidcncccl in the highermolccu1ar weight aCiCk arc cmp~oyccl. wcigllt acids are probably clue to variations in tlie organic-aqueous partition constants (1’) ailcl in tile organic climcrization constants (C). In the 4-methyl-2-pentanonc systems, which arc shown in Fig. 3, the llcxanoic acid is csscntially in the monomeric form in tlie organic phase as is reflcctecl by the negligil,le clirnerization constant (C) measured by SAWHNICYG. The total hcxanoic acid concentration [HR]t at any given pH value is given by [I-IRJr= [HRlo+ [HR] + [I<], where [FIR],, is the monomer concentration in tllc organic phase, [HJ<] is tile monomer concentration in the aqueous pliase, and [J<) is the hcxanoatc ion concentration in tllc ac]ucous pl1asc. Substituting a value of 104.Q for the association constant Ir’ of tlic acid”, and a, value of x01.” for tlic partition constant”, one obtains tllc relation:
Using this equation to calculate [HR]O a t various pw values, and fitting ‘Fig, 3 to the best mathematical expression, one arrives at I)-1 = x013.3 [I-IR]“-qH]3+
100.4
tlic clata. of
[I-IR].-~qH]~.
Tlic solid lines in Fig. 3 were obtained with this esprcssion. If it is assumccl that the predominant specks in the organic pllasc coulci Ix? rcprcscntecl as l’mRn(HR) 1,and that the prcclnminant species in the aqueous pllasc could bc rcprcscntcd as TmlC r(OH) I~,then D--l= [Tll~R~(OH)I,:][‘~mIt?(MI~)‘,]o-’. Making appropriate
substitutions,
one can write tllis csprcssion
as
where K is tllc acicl association constant, P is the organic-aqueous acid partition constant, C ,.I,is the aqueous association constant of TmR,.(OH)~,, W is the ion product ot water, KS,, is the association constant of TI~R~(HII)~,, and Pa,, is the organicaqueous partition constant of TniR3(HIC)a. When this theoretical expression is comparccl wit11 the equation clcrivecl from tllc curve fitting, the following may bc recognized: an organic species for tlic first and second tcrnis of ‘lYn~R3(HR), an aqueous spccics for the first term of Tm3+, an aqueous species for the second term of TmOH”+, an overall equation of
a log K31P31 value of Io7*“, and a log Co1 value of Iolo*oS Application of the esprcssion from the curve fitting to the pure hesanoic acid extraction produces a curve which dcviatcs consiclerably from the esperimental one. This is not surprising since the hexanoic acid probably exists as an acid-solvent adcluct in the +methyl-z-pentanone but as a climer in the pure acid. In addition, the extracting species in the 4-methyl-z-pentanone system is TmRs(HR) probably with several molecules of the solvent attached, whereas the cstracting species in the purcacid system is probably Tm&(IiR),, with an a value greater than unity. .47rctl.
Clrim.
nckz,
47
(1gGg)
19-25
Tm
SOLVESTEXTRACTIOFOF
23
In the chloroform systems, which are shown in Fig. 4, the hexanoic acid in the organic phase is predominantly in the dimeric form, as is indicated by the dimerization constant (C) of 101.~ as measured by SAWHNEYG. The total hesanoic acid concentration [HRlt at any given PH value is esprcssable as [HR] t = 2 [H&z], + [HR]” + [FIR:] + [RJ. where [H2R210 is the dimer concentration in the organic phase and the other symbols have their previous significances. With a value of IO ‘1.0for the acid association constant (Kc), x0 0.0 for the partition constant (Z’)5, and 101.0 for the dinlerization constant (C) 5, the following equation can be written: [HRlt.=2
[HzII~]o+(C-‘I”+C-LI”P-~+C-‘~“I~-’T-’-’[H]-’)
= 2 [HaRn]o+
(IO --R.fJ+IO-I.74
lo-"."[H]-1)
[HJ
[&&]J/",
This relation was used to calculate [H2I&], at various pH values. Then tile data of Fig, 4 were fitted to the best, mathematical espression which turned out to be D-1 = 101’.3[HzRz]o-~[H]3+
107~O[Ho_liz]o-~~[Ii~~.
Tile
solid lines in Fig. 4 were calcula.ted from this espression. If it is assumed that the predominant species in the organic phase could bc reprcscntecl as TmlG(HR) ,, and that the prevailing species in tllc aqueous phase could be represented as TmR r(OH) I,. then,
wliere the symbols are as previously stated. When this theoretical espression is comparecl with tile equation derived from the esperimental data, the following may be recognized: an organic species for the first and second terms of TmIQ(HR),=j, an aqueous species for the first term of Tni”+, an aqueous species for the second term of TmOH”+, and an overall equation of Z, -l=
Z<“Z=Z
[H)z,
with a 1<3#36 value of 107.0, and a Cot value of x00.7. When the expression derived from curve fitting of thcexpcritnental chloroformsystem data is applied to the pure hexanoic acid extraction, a curve which fits the pure hexanoic acid data very closely is obtained. This curve is shown by a solid line in Fig. 4. The fit probably indicates that tile species extracting into the pure acicl is similar to the species estracting into chloroform solutions of the acid, namely, Tn-&(HR) G.Such a formula evidences a coordination number of at least S. This is not unusual since rare-earth ions with coordination numbers of 8 and greater are now well knownO. The assumption has been made in all the above considerations that no polymerization of either the predominant aqueous or organic metal-bearing species is occurring. This supposition appears to be warranted in view of the lack of dependency of extraction upon the thulium concentration as shown in Fig. 5. The values for the first-hydrolysis constant of the thulium(II1) ion obtained in these two systems, x010.2 and 100.7, seem to be high in comparison with other rare-earth first-hydrolysis constants. Values7 for lanthanum(II1) range from 103.9 to 108.4 in various aqueous media, for cerium(II1) 1oG.0, for praseodymium(II1) xoG.G, and for lutetium(II1) 107.4. Values7 for scandium(II1) range from x08*0 to 1010.2 and i .;
Anal.
Chim.
Acta.
47 (rg6g)
1g-25
24
C.
K. SCHWEITZER,
S. M.
SANGHVI
for yttlium(III) from xofi.(Jto xo 7-('.At first, it miglJt be thought tllat the discrepancy could be assigned to sligllt errors in the constants I<, P, and C which are magnified by raising them to higher powers. However, this cannot be maintained since the constants in the first and second terms of the empirical equations cliffcr only by COlw causing everything else (for example, for tlie chloroform system K”I-‘“1<35-‘system K~P~I<~I-~Z?I~-~) to cancel out. Pns- ‘Cd and for the 4-metl~yl-2-pcntanonc Thus small errors in K, 23, and C should not affect the results. It is possible that the l)rescnce of organic solvent in the aqueous pha.%s could alter the constant COl, this being one of tile difficulties encountered in the use of solvent extraction for association ion-constant studies”. It is interesting to note tliat a Iligher CO1 vduc for scandium(III) was also obtained by a solvent extraction method”. Because of the several tlifficultics with extraction tccllniclucs, tile autllors tend to trust the potcntiometrically detcrminccl values more than tllose obtained by extraction.
The extraction of 10-4 and IO-” M tllulium(II1) into +mcthyl-2-pentanone and chloroform containing aliphatic monocarbosylic acids leas been studied witll formic through clccanoic acids. Estraction tends to increase wit11 acid molecular and pEr up to about 6. I)etailccl studies with lic.xanoic weight, acid concentration, acid indicate tllat tlic species extracting into 4-metllyl-2-pcntanone is TnlIZ3( I-11<) and tile spccics extracting into chloroform is TmR3(Hl<)rj. In both cases the prcdominant aqueous species are Tm3f and TmOH2+. From tile data first hydrolysis constants of Tm:J+ have been calculatecl to be 1010.2 and xou.7, thcsc values being larger than those cspectccl from previous rare-earth hydrolysis data.
Unc dtucle a dt6 cffectucc sur l’extraction clu thulium(II1) (IO-‘* et x0-H M) clans la m&hyl-+pentanone-2 et le chloroforrne, renfermant dcs acidcs aliphatiques monocarboxyliques. L’extraction tend h augmenter avec Ic poids mol&culairc des acides, la concentration en acicle et le PH jusqu’g environ 6. Avec l’acicle hexano’ique, on extrait Tm.R3(HR) dans la m&hyl-4-pentanone-2 ct Ttn&(HI?)a dans lc chlorofox-me. Dans les deus cas les particules prddominantes dans l’eau sont Tm3+ ct TmOH3+. Les constantes cl’hydrolyse clc Tm3-+ calculc!es sont 1010.z ct 100.7. Ces valeurs sont plus grancles clue pr6vues d’aprbs les valeurs d’hydrolyse cles terres rares. ZUSAMMENFASSUNG
mit 4-Methyl-2-pentanon Die Extraktion von IO-” und IO-” M Thulium(II1) and Cllloroform, das alipllatische Monocarbons#uren enth:ilt (Ameisen- bis Dekansliure), wurde untersucht. Die Estrnktion steigt mit dem Molekulnrgewicht der Sliure, cler ZXurekonzentration uncl dem pa-Wert bis zunl Wert 6. Genauere Untersuchungen mit Hexansiiure zeigen, dnss die Spezies, welche mit 4-Methyl-2-Pentanon extrahiert werden. TmRa(HR) und class die Species, welche rnit Chloroform extrahiert werden, TmR:~(HR)~ sind. In beiclen FBllen sind die bevorzugten wsssrigen Spezies Tm3+ und TmOH~+. Aus diesen Daten wurdcn die ersten Hyclrolyse-Konstanten des A,Jrnl.Cl&Jl. nctn, 47 (1969) x9-25
SOLVEST
ESTIZACTIOS
OF
Tm
2.5
Tm3+ zu x010.” und zu x00-7 bcrechnct. Diese Werte sincl griisser als diejenigen, welche aus friiheren Hyclrolysedaten Seltener Erclen errnittelt wurden.