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Studies on the solvent extraction of some cadmium chelates
IZXTRACTION
OF
Hg BY DITHIZONE
ON SILlCA
GEL
567
REFERENCES
1 I,. C. CRAIG in Trace Analysis, 1957. 2 T. l3.
An&.
PIRRCI?.
edited by T. H. YOE ASD
Chirn. AC/U. 24 (fg6r)
I-i. J.
Koclr,
John Wiley,
New .York,
146.
PIERCE AND P. I;. PECK, J. ChYo?tlnfo&'.. 6 (1961) 248. J ‘I’. B. PIERCE AND P. 1:. bZCK. AnfllYSl. 86 (IQbt~ 580. _. .5 I-1.IRVING AND 13. J. 1’. \vlLLlAnlS, J. C/rent. Sac:,-(1949) 1841. fl S. S. COOPER ASD .\I. I-. SULLIVA.N, Anal. Cketn.. 23 (1951) 613. 7 H. IRVING AND c. F. DELL, J. Ckenz. Sot., (1953) 3538.
3 1'. 1%
fi S. AHRLAND, I. GRENTEIE AND B. NORM, Acla Clrew. Scntui., 14 (19Go) x0.59. u Y. MARCUS, Acfa C/rem. Scund., I I (1957) 599. 10 G. IWANTSCIIEFF, I>as I>iCirito?lzrnd seim A?awendrrtrg i)z dcr Mikro- 16ntl.?pfrrcnannlysc!. Vcrl.?g Clicmie, Wcinlwim, i 958. ‘I ‘J’. B. PIERCE AND P. F. PECK, in prCprat.iOn. 12 31. &I. HARDING, J. C/rent. Sot., (19513) 4130. 13 J. 1:. I~UNCAN AND 1;. G. 'lhoaf~s, J. C/mu. Sot.. (~c)Go)zHr.#. A riftI. C/rim. AC/U, 2G (rg6r)
STUDIES
ON THE
SOLVENT
EXTKACTION
OF SOME
557-567
CAI)lMIUM
CHELATES
Pveviol~s
cadmium extractions
Little detailed work has been clone concerning the solvent estraction behavior of cadmium chelates. Although qualitative observations of the extraction behavior of cadmium with various chelating agents are available in the literature, the quantitative data necessary for a useful interpretation and utilization of these observations are in most instances undetermined. Rather detailed studies of the solvent extraction of cadmium using dithizone and 2-(o-hydroxyphenyl)-benzosazole have been rcportcd by SCHWEITZEI~ AND DYI:R~ and such
DEVOE
AND MEINKE~,
diverse
tobenzothiazole,
Extraction
reagents and
respectively.
In addition,
as thenoyltrifluoroacetone, other
reagents
have
been
observations
of extractions
isonitrosoacetophenone,
using
z-mercap-
reported.3
equations
Consider a system made up of an aclueous phase and a non-aqueous phase of equal volume in contact. The aqueous phase, which has been pre-equilibrated with the nonaqueous solvent, contains cadmium(H) ion as the perchlorate, hydrogen ion as the perchlorate, and is made up to an ionic strength’ of, 0.1 with sodium perchlorate. Its Aqaal. Chim. Ada,
26 (x962) 567-57~
568
G. K. SCHWEITZER,
D. R. RANDOLPH
is adjusted by the addition of small amounts of sodium hydroxide and perchloric acid solutions. The non-aqueous phase, which has been pm-equilibrated with 0.1 M sodium perchlorate solution, contains a chelating agent HR with one acidic group and one neutral coordinating group. The chelating agent HR partitions between the two phases with an organic : aqueous partition coefficient Pr and ionizes in the aqueous phase with an association constant I<,. If one assumes’the cstracting species to be CdR2, then it will partition between the two phases with an organic: aqueous partition coefficient P, and will ionize in the aqueous phase with.an association constant Kc. Upon further assuming there to be no metal species other than Cd+” present in significant amount in the aclueous phase and assuming there to be no metal specks other than CdRz in the non-aqueous phase, the major extraction reaction may be written as PH
where Cd+2 and H+ are in the aqueous phase and HR and CdRz are preclominantly in the non-aqueous phase. I3y proper combination of relations plus the assumption that PC is quite large, the orginic : aqueous clistribution ratio E of the metal may be esprcsscd as follows : (1) In this expression (HR)o rcpreseuts the concentration of HR in the non-aqueous phase, (H) symbolizes the concentration of H+ in the aqueous phase, ancl K = I’&&/ Yr”Kr2. If the dominant extracting species is CclRz(HR),,,, then the major estraction equation might be espressccl as <:d+” + (,,I -I-2)1-fl7
r=i CtlR~(l-II<),,, -t_ .LH+
(2)
and (I) could be altered to read” PCf~,(Hlz)1:”
E=-
I<( l-llq~+z
P,“’ ~~fr’,(l-1)”
=
(3)
--y-I)”
The constant P, now represents the organic : aqueous distribution coefficient of the species CclRz(HR) ,,, and Kc represents its association constant. When the logarithm of relstion (3) is taken, and it is remcmbcred that equal phase volumes are being employed, the following esprcssion may be shown to hold when E = I, which is the condition at which 500/Oextraction of the metal has occurred log
I<
=
2pH1p
-
(m
-f- 2) log (I-IR)o
(4)
In this equation PHI/Z represents the PH value at which 50% extraction is observed. Thus, if m, PHI 12, and (HR)o are known for an extraction system, K can be estimated. Then if three of the four constants comprising I( arc found, the remaining constant can be estimated by calculation. This provides a means for estimating I<, in a number of cases. The estraction of a metal ion from an aqueous solution into an organic solvent using a chelating agent is an increasingly useful analytical operation. The extent to which a given chelating agent can be used effectively in such an operation is deterdud.
C/liwl. .4&a,
26
(1962)
567-571.v.
SOLVENT
EXTRACTION
OF SOME
Cd CHELATES
569
mined largely by two factors, the values of PHI/:! and P,. If the PHI/~ of the nonmasked extraction is low, considerable variation may be effected through the use of masking agents which form water-soluble complexes.3 This could allow selective extractions of several metals at different PH values, If the value of PC is high, practically quantitative extractions can be effected in a one-step operation. present problem In this present work, a study was made of the estraction of cadmium ion from aqueous solutions into chloroform containing a known amount of a chelating agent. Values of Pr and K, were obtained from the literature or were determined as a part of this study. From proper extraction esperiments, values of ~~‘12, PC, and K were found. From these data, it is possible to suggest which of the eighteen chelating agents should be most effective as reagents for cadmium estractions.
Tire
The chemicals, apparatus, and general procedures were essentially the same as clescribed in previous worksr.6. lo-ml portions of the aqueous phase were stirred with xo-ml portions of the chloroform phase for 12 h at 30” & 0.5”. In all cases the original labellecl cadmium concentration was approsimatcly IO --5-l M and was radioactively with 1i‘Wd to facilitate measurement of the extraction. All aqueous phases were maintained at constant ionic strength of 0.1 by the adclition of sodium perchlorate. At least 20 individual determinations were made in orclcr to characterize each of the systems listed in Table I.
_.-
___.. -
.
. _..._-... - .---.
----
SySlL#?’
_._..._
-...
I\‘t?/~ClIl (‘O,IC,,.
----__--..-.-__-._-. I
2 3 4 2 : 9 IO
II 12
‘3 14 ‘5 16
‘7 18
_-_._-
__..____...__ __~.___._ log
piill.
_._-.-.. .._____ ____.___._._.
2-mcrcaptobcnzot~~iaaolc g,7-dichlorooxinc oxinc isonitrosoacctoplicnonc 5,7-dibromooxinc thcnoyltrifluoroacctonc dibcnzoylmcthenc lwnzoylacctonc cinnamic acid snlicylaldoximc z-mcthyloxinc acctylacctonc quinine o-mcthoxylbcnzoic acid salicylic acid N-phcnylbcnzohydroxamic 3.5-dinitrobentoic acid anthranilic acid ---
_ ___
. . .._._.. --..--...
i\‘rugo,l
10-‘M
3.9
10-2
4.6
.-..-... --
a Irregular curves obtained : see text. b No extraction in pit range 2.0 to ‘2.0. 0 C. DYRSSHN, M. DYRSSIXN AND E. JOHANSSON, * R. E. CONNICK AND W. H. .McVeu,J. Am. = See rcfcrcnce 6. ’ J. STARY AND N. P. RUDENKO, Nauck Doklady
I’,
lnc
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4. ’ 3.8
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2.
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1.1
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10-I
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Acta.
Cirern.
Sot.,
-
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Chem.
K.
‘;.;”
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.
log
_.._- _.____.
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acid
. - . .._.___ --_~-----I’.
Scatrd., IO (rg5Gj 341, 71 (1949) 3x82.
VysslreiSlahoty,
Kliim.‘i Anal.
Khim.Tekhnol.,
Chkn.
Acta,
I
(x958) (i24.
26 (1962)
567-57x
570
G. K.ScHWEITZDR,
D. R. RANDOJZH
Determinations
of the values of Pr and Zcr followed the procedure as outlined by a zo-ml. MOTTERN .fi Values of PC were found by equilibrating portion of chloroform containing the cadmium chelate with I 1 of 10-l M sodium pet-chlorate solution at a proper PH value. After equilibration, alicluots of each phase were cvaporatccl to dryness, counted, and the P, value was calculated. Each value represents the average of at least three determinations. SCHWEITZER
AND
I summarizes the results of this study along with some values obtained from the literature. All values cncloscd in parcnthcses have been clcrivccl from previous works. No attempt is made to proviclc Pr and Kr values for those systems which sl~owccl irregular or no extraction (systems ro-x8). Curves of per cent metal estractccl into the organic phase vcyslfs the final p,r of the ;qucous phase for systems x-8 gave tlic theoretically-prcdictcd sigtnoid pattern 115o/ shown by regular systems of this type,’ having a slope of approsimntely units per pH unit at the PHI/~. However, systems 7 and 8 approached a maximum at about 90% metal extracted instead of the regular x000/~. System 9 gave an approximately linear curve having a slope of 17’/~ per pH unit between a pH of 6.0 (5’y0 cstraction) ant1 one of 1x.0 (92(x, estraction). System 10 gave extraction behavior which may bc characterizccl by the following points: ~1%ot 6.7 (I’/,, cxtractcd), 7.3 (I%), 7.4 (3”h)t 7.7 (Ifi%), 8.2 (Is%), 8.6 @I%), 9.x (17%), 10.0 (2O/,).System II also gave an irregular curve best characterized by the following points: pgr of 6.3 (7”/” cxtractccl), 0.7 (23’%,), 7.2 (ztJO/,), 7.4 (27%), 8.2 (2@{,), 9.2 (42o/o), II.6 (44(x,). Systems 12 mcl 13 cshibitcrl non-rcprocluciblc cstraction behavior. ‘1’1~ remainder of the systems, 14-18, sl~owctl no estraction in the pH range 2.0-12.0.
‘fnblc
J)ISCUSSION
From the results of this stucly, the potential usefulness of scvcral 01 the reagents stucliccl is apparent. For esamplc, 2-mercaptobcnzothiazolc, by virtue of the high Z’= and the low p1tll-, is an escellcnt reagent. ‘I’hc same is true for g,7-clichlorooxine, osinc, and, to a lcsscr cstent, 5,7-tlil~romoosinc. The low values of P, for tlic caclmium chelates of isonitrosoacetophcnone and tl~et~oyltrifluoroacctone indicate that the extractions with these reagents would not 1~ as quantitntivc as might be clesircd. The other reagents, by virtue of either high PHI/~ values or low PC values or no cstraction, could not bc employccl to estract cadmium cffcctively. On the other hand, these reagents might bc used to separate one or more mctnls from cadmium if the cstraction were more favorable with respect to these other metals. In these espcriments, the esact nature of the cstracting species in each case has not been dctcrmincd. Consequently, the value of no.cannot bc assigned with any dcgrec of assurance. From the data prescntecl in this study, however, equations 3 and 4 can be used to calculate possible values of K and ZC, assuming various values for ~8. This is clone as follows: Choosing from Table I system 3, osinc, Pr is 100.~1,ZCr is x00*7, I’, is 10‘*.0, p~l/z is 5.2, and (HR)” is ro- 1 M. If the cstracting species is Cdl&, then 7~ is 2 and ?lt is o. Thus equations 3 and 4 may be used to give K equal to IO-~*~ and ICC cqualto IO 12.2 . If tile species is CclRn.HR, then values of Zr’ equal to IO-~*~ and I I<, equal to 10 lG.8 result. If the species is CclRc.2HR, Zi turns out to be 10-(1*4and Kc ~Jmzl.Claim.ilcin,zG (x9&) 567-571
SOLVENT
to be
xois-4.
HELLWEGE
oxinate
that
the extracting
AND
are
knowledge
of the character
applicable
must
such determinations.
OF SOME Cd CHELATES
SCHWEITZE~~
species
paragraph await
the
EXTRACTION
ones. of the
have
is CdRzazHR, In
no other
extracting
found
thus case,
species.
in
the last however, Thus
571
the
case
values
of
cadmium
in the previous
is there
calculations
unequivocal of Ir’ and
&
SUMMARY Eighteen different chelating agents have been invcstigatcd as possible extractants for radiolabcllcd 10-6.1 M cadmium from aqueous solutions into chloroform. The cxpcrimcntally-dctcrmind extraction data have been analyzed thcorctically by mcnsurcmcnt of metal chclatc and chelating agent association constants and distribution constants.
Ixs autcurs ont cffectd unc rcchcrchc cadmium cn solution aqucusc.
13cschrcibung cincr Untcrsuchung form ILUSw%srigcn Liisungcn.
sur I’cxtraction
par Ic chloroformc
iibcr tlic 13xtrahicrlarkcit
dc qudqucs
von Cntllniumchclatcn
ch6latcs dc
mit Chloro-
REFERENCES G. I<. SCHWI?ITZI:H AND 1:. 1;. DYEH. A uul. Chim. Acfa. 22 (rgGo) 172. J. I<. DKVOIZ AXE3 \\‘. \k-. >IEINKE, .df II&. ~/~ern.. 31 (1959) 1,128. G. i4. hlOHRlSOS AND H. ~7RElSI~R. SoheM f%~frucliorr in nndyfical Che,nislry, John \vilcy ant1 Sons. New York, 1957. pp. 157-180. r\. 31. I’OSKAXZER ASD H. hl. ~:ORi:MAN. Jr., J. fn0Yg. &‘NffCf. Chmz.. Ic) (ICjGI) 323. G. I<. ~CIlWIIIT%l’.H AND G. I<. CoR, .-1 rraf. c/rim. /I c/n, 2‘) (lcJ61) 3I I* G. 1;. SCHWI’ITZRH AND J. L. ~IOTTERN, .*IIIN~. Cirinf. .*fclo. 2G (136~) I 20. For cx;~rnplc. SW k-1. .-1. LAITXSI:N. Clrcmical A rrafysis, XlcCraw-Hill Hook Co., New York. 1g60, PP. 247-275. H. I-IELLW~GE ASD Ci. Ii. SCHWEITZER, A naf.Chinr. ,dct~, to bc published. .*l#ial. Cl~inr.Ada.
20 (19G2) 5G7-571
OF
Hg BY DITHIZONE
ON SILlCA
GEL
567
REFERENCES
1 I,. C. CRAIG in Trace Analysis, 1957. 2 T. l3.
An&.
PIRRCI?.
edited by T. H. YOE ASD
Chirn. AC/U. 24 (fg6r)
I-i. J.
Koclr,
John Wiley,
New .York,
146.
PIERCE AND P. I;. PECK, J. ChYo?tlnfo&'.. 6 (1961) 248. J ‘I’. B. PIERCE AND P. 1:. bZCK. AnfllYSl. 86 (IQbt~ 580. _. .5 I-1.IRVING AND 13. J. 1’. \vlLLlAnlS, J. C/rent. Sac:,-(1949) 1841. fl S. S. COOPER ASD .\I. I-. SULLIVA.N, Anal. Cketn.. 23 (1951) 613. 7 H. IRVING AND c. F. DELL, J. Ckenz. Sot., (1953) 3538.
3 1'. 1%
fi S. AHRLAND, I. GRENTEIE AND B. NORM, Acla Clrew. Scntui., 14 (19Go) x0.59. u Y. MARCUS, Acfa C/rem. Scund., I I (1957) 599. 10 G. IWANTSCIIEFF, I>as I>iCirito?lzrnd seim A?awendrrtrg i)z dcr Mikro- 16ntl.?pfrrcnannlysc!. Vcrl.?g Clicmie, Wcinlwim, i 958. ‘I ‘J’. B. PIERCE AND P. F. PECK, in prCprat.iOn. 12 31. &I. HARDING, J. C/rent. Sot., (19513) 4130. 13 J. 1:. I~UNCAN AND 1;. G. 'lhoaf~s, J. C/mu. Sot.. (~c)Go)zHr.#. A riftI. C/rim. AC/U, 2G (rg6r)
STUDIES
ON THE
SOLVENT
EXTKACTION
OF SOME
557-567
CAI)lMIUM
CHELATES
Pveviol~s
cadmium extractions
Little detailed work has been clone concerning the solvent estraction behavior of cadmium chelates. Although qualitative observations of the extraction behavior of cadmium with various chelating agents are available in the literature, the quantitative data necessary for a useful interpretation and utilization of these observations are in most instances undetermined. Rather detailed studies of the solvent extraction of cadmium using dithizone and 2-(o-hydroxyphenyl)-benzosazole have been rcportcd by SCHWEITZEI~ AND DYI:R~ and such
DEVOE
AND MEINKE~,
diverse
tobenzothiazole,
Extraction
reagents and
respectively.
In addition,
as thenoyltrifluoroacetone, other
reagents
have
been
observations
of extractions
isonitrosoacetophenone,
using
z-mercap-
reported.3
equations
Consider a system made up of an aclueous phase and a non-aqueous phase of equal volume in contact. The aqueous phase, which has been pre-equilibrated with the nonaqueous solvent, contains cadmium(H) ion as the perchlorate, hydrogen ion as the perchlorate, and is made up to an ionic strength’ of, 0.1 with sodium perchlorate. Its Aqaal. Chim. Ada,
26 (x962) 567-57~
568
G. K. SCHWEITZER,
D. R. RANDOLPH
is adjusted by the addition of small amounts of sodium hydroxide and perchloric acid solutions. The non-aqueous phase, which has been pm-equilibrated with 0.1 M sodium perchlorate solution, contains a chelating agent HR with one acidic group and one neutral coordinating group. The chelating agent HR partitions between the two phases with an organic : aqueous partition coefficient Pr and ionizes in the aqueous phase with an association constant I<,. If one assumes’the cstracting species to be CdR2, then it will partition between the two phases with an organic: aqueous partition coefficient P, and will ionize in the aqueous phase with.an association constant Kc. Upon further assuming there to be no metal species other than Cd+” present in significant amount in the aclueous phase and assuming there to be no metal specks other than CdRz in the non-aqueous phase, the major extraction reaction may be written as PH
where Cd+2 and H+ are in the aqueous phase and HR and CdRz are preclominantly in the non-aqueous phase. I3y proper combination of relations plus the assumption that PC is quite large, the orginic : aqueous clistribution ratio E of the metal may be esprcsscd as follows : (1) In this expression (HR)o rcpreseuts the concentration of HR in the non-aqueous phase, (H) symbolizes the concentration of H+ in the aqueous phase, ancl K = I’&&/ Yr”Kr2. If the dominant extracting species is CclRz(HR),,,, then the major estraction equation might be espressccl as <:d+” + (,,I -I-2)1-fl7
r=i CtlR~(l-II<),,, -t_ .LH+
(2)
and (I) could be altered to read” PCf~,(Hlz)1:”
E=-
I<( l-llq~+z
P,“’ ~~fr’,(l-1)”
=
(3)
--y-I)”
The constant P, now represents the organic : aqueous distribution coefficient of the species CclRz(HR) ,,, and Kc represents its association constant. When the logarithm of relstion (3) is taken, and it is remcmbcred that equal phase volumes are being employed, the following esprcssion may be shown to hold when E = I, which is the condition at which 500/Oextraction of the metal has occurred log
I<
=
2pH1p
-
(m
-f- 2) log (I-IR)o
(4)
In this equation PHI/Z represents the PH value at which 50% extraction is observed. Thus, if m, PHI 12, and (HR)o are known for an extraction system, K can be estimated. Then if three of the four constants comprising I( arc found, the remaining constant can be estimated by calculation. This provides a means for estimating I<, in a number of cases. The estraction of a metal ion from an aqueous solution into an organic solvent using a chelating agent is an increasingly useful analytical operation. The extent to which a given chelating agent can be used effectively in such an operation is deterdud.
C/liwl. .4&a,
26
(1962)
567-571.v.
SOLVENT
EXTRACTION
OF SOME
Cd CHELATES
569
mined largely by two factors, the values of PHI/:! and P,. If the PHI/~ of the nonmasked extraction is low, considerable variation may be effected through the use of masking agents which form water-soluble complexes.3 This could allow selective extractions of several metals at different PH values, If the value of PC is high, practically quantitative extractions can be effected in a one-step operation. present problem In this present work, a study was made of the estraction of cadmium ion from aqueous solutions into chloroform containing a known amount of a chelating agent. Values of Pr and K, were obtained from the literature or were determined as a part of this study. From proper extraction esperiments, values of ~~‘12, PC, and K were found. From these data, it is possible to suggest which of the eighteen chelating agents should be most effective as reagents for cadmium estractions.
Tire
The chemicals, apparatus, and general procedures were essentially the same as clescribed in previous worksr.6. lo-ml portions of the aqueous phase were stirred with xo-ml portions of the chloroform phase for 12 h at 30” & 0.5”. In all cases the original labellecl cadmium concentration was approsimatcly IO --5-l M and was radioactively with 1i‘Wd to facilitate measurement of the extraction. All aqueous phases were maintained at constant ionic strength of 0.1 by the adclition of sodium perchlorate. At least 20 individual determinations were made in orclcr to characterize each of the systems listed in Table I.
_.-
___.. -
.
. _..._-... - .---.
----
SySlL#?’
_._..._
-...
I\‘t?/~ClIl (‘O,IC,,.
----__--..-.-__-._-. I
2 3 4 2 : 9 IO
II 12
‘3 14 ‘5 16
‘7 18
_-_._-
__..____...__ __~.___._ log
piill.
_._-.-.. .._____ ____.___._._.
2-mcrcaptobcnzot~~iaaolc g,7-dichlorooxinc oxinc isonitrosoacctoplicnonc 5,7-dibromooxinc thcnoyltrifluoroacctonc dibcnzoylmcthenc lwnzoylacctonc cinnamic acid snlicylaldoximc z-mcthyloxinc acctylacctonc quinine o-mcthoxylbcnzoic acid salicylic acid N-phcnylbcnzohydroxamic 3.5-dinitrobentoic acid anthranilic acid ---
_ ___
. . .._._.. --..--...
i\‘rugo,l
10-‘M
3.9
10-2
4.6
.-..-... --
a Irregular curves obtained : see text. b No extraction in pit range 2.0 to ‘2.0. 0 C. DYRSSHN, M. DYRSSIXN AND E. JOHANSSON, * R. E. CONNICK AND W. H. .McVeu,J. Am. = See rcfcrcnce 6. ’ J. STARY AND N. P. RUDENKO, Nauck Doklady
I’,
lnc
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2.2
4. ’ 3.8
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;:I:
I.6
10-Z
G. I
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Acta.
Cirern.
Sot.,
-
_-_-..
_--__---..--
Chem.
K.
‘;.;”
‘I.0
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.
log
_.._- _.____.
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acid
. - . .._.___ --_~-----I’.
Scatrd., IO (rg5Gj 341, 71 (1949) 3x82.
VysslreiSlahoty,
Kliim.‘i Anal.
Khim.Tekhnol.,
Chkn.
Acta,
I
(x958) (i24.
26 (1962)
567-57x
570
G. K.ScHWEITZDR,
D. R. RANDOJZH
Determinations
of the values of Pr and Zcr followed the procedure as outlined by a zo-ml. MOTTERN .fi Values of PC were found by equilibrating portion of chloroform containing the cadmium chelate with I 1 of 10-l M sodium pet-chlorate solution at a proper PH value. After equilibration, alicluots of each phase were cvaporatccl to dryness, counted, and the P, value was calculated. Each value represents the average of at least three determinations. SCHWEITZER
AND
I summarizes the results of this study along with some values obtained from the literature. All values cncloscd in parcnthcses have been clcrivccl from previous works. No attempt is made to proviclc Pr and Kr values for those systems which sl~owccl irregular or no extraction (systems ro-x8). Curves of per cent metal estractccl into the organic phase vcyslfs the final p,r of the ;qucous phase for systems x-8 gave tlic theoretically-prcdictcd sigtnoid pattern 115o/ shown by regular systems of this type,’ having a slope of approsimntely units per pH unit at the PHI/~. However, systems 7 and 8 approached a maximum at about 90% metal extracted instead of the regular x000/~. System 9 gave an approximately linear curve having a slope of 17’/~ per pH unit between a pH of 6.0 (5’y0 cstraction) ant1 one of 1x.0 (92(x, estraction). System 10 gave extraction behavior which may bc characterizccl by the following points: ~1%ot 6.7 (I’/,, cxtractcd), 7.3 (I%), 7.4 (3”h)t 7.7 (Ifi%), 8.2 (Is%), 8.6 @I%), 9.x (17%), 10.0 (2O/,).System II also gave an irregular curve best characterized by the following points: pgr of 6.3 (7”/” cxtractccl), 0.7 (23’%,), 7.2 (ztJO/,), 7.4 (27%), 8.2 (2@{,), 9.2 (42o/o), II.6 (44(x,). Systems 12 mcl 13 cshibitcrl non-rcprocluciblc cstraction behavior. ‘1’1~ remainder of the systems, 14-18, sl~owctl no estraction in the pH range 2.0-12.0.
‘fnblc
J)ISCUSSION
From the results of this stucly, the potential usefulness of scvcral 01 the reagents stucliccl is apparent. For esamplc, 2-mercaptobcnzothiazolc, by virtue of the high Z’= and the low p1tll-, is an escellcnt reagent. ‘I’hc same is true for g,7-clichlorooxine, osinc, and, to a lcsscr cstent, 5,7-tlil~romoosinc. The low values of P, for tlic caclmium chelates of isonitrosoacetophcnone and tl~et~oyltrifluoroacctone indicate that the extractions with these reagents would not 1~ as quantitntivc as might be clesircd. The other reagents, by virtue of either high PHI/~ values or low PC values or no cstraction, could not bc employccl to estract cadmium cffcctively. On the other hand, these reagents might bc used to separate one or more mctnls from cadmium if the cstraction were more favorable with respect to these other metals. In these espcriments, the esact nature of the cstracting species in each case has not been dctcrmincd. Consequently, the value of no.cannot bc assigned with any dcgrec of assurance. From the data prescntecl in this study, however, equations 3 and 4 can be used to calculate possible values of K and ZC, assuming various values for ~8. This is clone as follows: Choosing from Table I system 3, osinc, Pr is 100.~1,ZCr is x00*7, I’, is 10‘*.0, p~l/z is 5.2, and (HR)” is ro- 1 M. If the cstracting species is Cdl&, then 7~ is 2 and ?lt is o. Thus equations 3 and 4 may be used to give K equal to IO-~*~ and ICC cqualto IO 12.2 . If tile species is CclRn.HR, then values of Zr’ equal to IO-~*~ and I I<, equal to 10 lG.8 result. If the species is CclRc.2HR, Zi turns out to be 10-(1*4and Kc ~Jmzl.Claim.ilcin,zG (x9&) 567-571
SOLVENT
to be
xois-4.
HELLWEGE
oxinate
that
the extracting
AND
are
knowledge
of the character
applicable
must
such determinations.
OF SOME Cd CHELATES
SCHWEITZE~~
species
paragraph await
the
EXTRACTION
ones. of the
have
is CdRzazHR, In
no other
extracting
found
thus case,
species.
in
the last however, Thus
571
the
case
values
of
cadmium
in the previous
is there
calculations
unequivocal of Ir’ and
&
SUMMARY Eighteen different chelating agents have been invcstigatcd as possible extractants for radiolabcllcd 10-6.1 M cadmium from aqueous solutions into chloroform. The cxpcrimcntally-dctcrmind extraction data have been analyzed thcorctically by mcnsurcmcnt of metal chclatc and chelating agent association constants and distribution constants.
Ixs autcurs ont cffectd unc rcchcrchc cadmium cn solution aqucusc.
13cschrcibung cincr Untcrsuchung form ILUSw%srigcn Liisungcn.
sur I’cxtraction
par Ic chloroformc
iibcr tlic 13xtrahicrlarkcit
dc qudqucs
von Cntllniumchclatcn
ch6latcs dc
mit Chloro-
REFERENCES G. I<. SCHWI?ITZI:H AND 1:. 1;. DYEH. A uul. Chim. Acfa. 22 (rgGo) 172. J. I<. DKVOIZ AXE3 \\‘. \k-. >IEINKE, .df II&. ~/~ern.. 31 (1959) 1,128. G. i4. hlOHRlSOS AND H. ~7RElSI~R. SoheM f%~frucliorr in nndyfical Che,nislry, John \vilcy ant1 Sons. New York, 1957. pp. 157-180. r\. 31. I’OSKAXZER ASD H. hl. ~:ORi:MAN. Jr., J. fn0Yg. &‘NffCf. Chmz.. Ic) (ICjGI) 323. G. I<. ~CIlWIIIT%l’.H AND G. I<. CoR, .-1 rraf. c/rim. /I c/n, 2‘) (lcJ61) 3I I* G. 1;. SCHWI’ITZRH AND J. L. ~IOTTERN, .*IIIN~. Cirinf. .*fclo. 2G (136~) I 20. For cx;~rnplc. SW k-1. .-1. LAITXSI:N. Clrcmical A rrafysis, XlcCraw-Hill Hook Co., New York. 1g60, PP. 247-275. H. I-IELLW~GE ASD Ci. Ii. SCHWEITZER, A naf.Chinr. ,dct~, to bc published. .*l#ial. Cl~inr.Ada.
20 (19G2) 5G7-571