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High speed separation of the light rare earths on centri-fugally accelerated ion-exchange paper
hNhLY’1’ICh
148
HIGH
CHf MICA
SPEED SEPARATION OF THE FUGALLY ACCELERATED CIARENCE
I-115CNINC;lSR,
Jhpurl~~ac~~t of CJumrisLry,
(lbxcivcd
LIGHT RARE EARTHS ON ION-EXCHANGE PAPER* L~ICRNK
JR. AND
St. Jolrtr
I:islrcr July
ACTA
College,
CENTRI-
M. I,hN%AI~hMIS+* l~ochcslcr,
N. Y. (U.S..4
.)
3rd. 19G3)
In an attempt todevclop a rapid, clean separation applicable to the lighter rare earths (La to Sm), the technique of high speed, centrifugal chromatography1 on ion-exchange papcra was investigated. was possible to separate completely the elements in any combination cxccpt the pair 1% and Nd. It was also possible to calculate from the data the average number of glycolate anions held in the resin-plus-paper phase per t-arc earth ion so held.
rt
The apparatus used was a Hi-Speed Chromatograph manufacturccl by Precision Scientific Company. In this apparatus, circular sheets of ion-exchange paper arc mount&l on the shaft of a variable speed motor (300-1500 rcv./min). Four metal spokes arc usccl to support the paper; the spokes arc best coated with a plastic tape in order to prevent attack of the metal by the cluant. The eluant is delivered under pressure in a fine stream through a o.I-mm diamctcr orifice in a stainless steel disk and directed onto the paper inside the point at which the ion mixture was applied. In our arrangement, the cluant was dclivcrccl from a roo-ml gas burct so that the flow rate could be dctcrminccl. The ion-exchange paper was Ambcrlitc W-2, which is a paper containing about 50% by weight of Ambcrlitc IR-IZO sulfonic acid resin in the Na+ form. The rare earth solutions wcrc made from oxides obtained from Lindsay Chemical Company ancl said to bc at least ~>g.gO/~ pure. The eluant solutions wcrc prepared from Fisher Scientific Company glycolic acid and brought to the dcsirecl PH by addition of ammonia. They were filtcrcd before use to eliminate clogging of tlic orifice The inclicator solution was 0.1% PAN (r-(z+pyridylazo)-2-naphthol from J. ‘1‘. Baker Chemical Company) by weight in ethyl alcohol. The paper was placed on the apparatus and washccl with cluant. ‘The rotation was stopped and the rare earth solutions wcrc spotted on the wet paper in a circle 4 cm from the center of rotation with a z-p1 pipct. The quantity of rare cartli ion applied was about 0.02 mg, which does not exccccl the exchange capacity of thcrcsin at the point of application. The statccl capacity is 0.025 mcq./cm”. + This rcsccrrch Wiis pClrtiillly YupIm~lcd I>y tllo U.S. Atomic Energy Commission. ** Prcscnt addrcus: Ihprrrtmcnt of Chemistry, University of 12ochcutcr, New York.
HIGH
SPEED
SEPARATION
OF
LIGHT
RARE
EARTHS
I49
The chromatogram was eluted for I to 12 min at 5 ml/min and x500 rev./min. The paper was then dried, sprayed with PAN solution, and exposed to ammonia vapor. Red spots appeared because of formation of a PAN-rare earth complex in ammoniacal medium. These fade on drying and therefore must be outlined in pencil. The distance traveled was measured from the point of application to the center of the spot. RF values could not be determined because the solvent front washed off ,L,the edge of the 3z-cm diameter paper circles. RESULTS
Obvious variables to be considered when developing a separation method using the
MOVEMISNT
GIycolic mid M 0.25
0.30
Qlr 4.0 4-o 4-S 3.50
GI’
soCtclion
QG0.84
0.84 o.G8 I.01
METAL
IONS
T i7nc (rrrin)
DURING
-.-I-n
4.0
4Q5
0.74
o.Go
Dislancc cc
3.25
I.28
I.07
3.75
4.0
0.74
o.Gz
SIII
1.5
2.0
2.0 5.I
3.0
5.6
7.0
3.1 9.1
0.2
0.4 0.5 I .o
0.5
0.6
I
2.2
I *5
3.0
.6
4.2 6.8
7.9
0.1
0.2
0.2
0.2
0 . ‘)
12
7.5
>
‘).G
I r.8
>I2
I2
>
I2
0.4 0.5
0.3 0.7 1.5 2.5 3.4
0.4
0.7
0.7
;:A 8.2 C).I
2:;
0.2
0.2 033
0.3
0.3 0.6 I .2
O..)
0.9
I.7
1.8
0.2
0.4 0.7 1.1
0.‘)
G-4 I.0 I.2
2.2
1.6
3.2
3.3 4.3
0.6 2.0 4.2 4.G
0.7 1.2
2.0
2.6
4.2
3.7
6.1
I .o 1,s
2.8
5.7
1.2
1.8
3.1
4.4 7.6
I.3 2.5 2.9
7.2 7.7 2.3
9.2
10.8
10
3.1 9.3
Z:i:
>I2
IO.5
AraaC. Ckiar.
1.0
it:;
2.2 5.8 10.4
> I2 > 17.
0.4 0.5
0.2
1.5
>
5*0 94 12
0.3 o-4
0.3 0.5 0.6
2:;
5.4 9.6
>
10.0
0.X
4.9
3~2
2:::
6.5 10.6 12
1.0
2.2
2.9
3-7
Z.CJ
24
0.9
2.2
2.6
3.6
1.2
0.8
4.4 5.1
G.0
I
11
2.1
! .o
-
3.3 4.8
3.5 4.1
2.3 34
>
1’
11.8
0.7 I.5 * *9
1.0
I.0
I .2
0.2
O.Y!,
Nd
1.5
0.
3.50
(cm)
I .8
6.7
3.0
iravelcd
Pr
.o
IILUTION
I
5.0
0.40
CHROMATOCHAPIIIC
I.1
0.4
3.75
SPY,EI>
0.6
0.2
0.86
HIGH
ACta,
30 (1964)
>I2
7.7 9.7 3.4 9.9
>I2 X48-154
150
C. HEININGER, JR., I;.
M.
LANZAFAME
technique described here arc eluant flow rate, amount of sample. speed of rotation, type of paper and ion-exchange resin, separation time, temperature, and identity, concentration, and pH of the eluant solution. The ion-exchange papers show good wet strength in addition to having the conventional ion-exchange properties. Because most ion-exchange separations of the rare earths have been made on strong acid cation exchanger@, the one commercially available paper of this type known to us was chosen for study. An eluant flow rate of 5 ml/min was chosen because greaterflowratesledtoexcessive . 1 1, tailing and smaller flow rates were difficult to achieve and reproduce. The maximum rotation speed, x500 rcv./min, was chosen in order togive the fastest possibleseparation. Preliminary runs using solutions of glycolic, lactic, a-hydroxyisobutyric, and citric acids of varying concentrations and PH suggested that glycolic acid would be most likely to give satisfactory separations. Determinations of the distance traveled by the elements La, Cc, Pr, Nd, Sm and Y were made for glycolic acid concentrations of 0.25 to 0.40 M, a PH range of 3.0 to 4.5, and running times of I to 12 min.Theglycolate anion concentration varied from 0.053 to 0.25 M. The results arc given in Table I. A typical plot of distance traveled as a function of elution time is shown in Fig. I. In general, it can be said that velocity is constant at the lower velocities and distances, but that the velocity decreases as time increases. In other words, as the ion approaches the edge of the paper, its velocity decreases. The best time intervals to be used for separations appear to be 3 to 6 min. The ions are able to move a good distance from their point of origin but in gcncral have not begun to bunch at the outside cdgc.
r
.---_ 1
___A
I
1-
----l---
1
7lme (tnin) Pig. I. Distnnco travolcd by the clomcnts IA; Co, Pr, Nd, Sm nnd Y as ;L function of timo of centrifugal olution. Tho solution WDS 0.40 M in glycolic acid nncl hnd a PH of 3.75. At CJmin, Y had washed off the papcr.
For a given running time, a plot of distance traveled as a function of PIX will suggest optimum conditions for a particular separation. Fig. 2 is a typical representation. Suggested conditions for each separation are given in Table II. With the glycolic acid eluant, we were able to separate any adjacent pair of the Amal. ChittI.ACta, 30 (1964))148454
~_a
HIGH
SPEED
SEPARATION
OF
LIGHT
RARE
EARTHS
151
elements considered with the exception of Nd-Pr and Sm-Y. -4 partial separation of Nd-Yr was achieved. Sm and Y can be separated with 0.4 M lactic acid at a pH of about 4.5. A good example of the appearance of a chromatogram after clution is shown in
r
___‘__‘____
_--_
--
1 Nd
Sm,Y
J
Pr
Ce 1 LO
-- ___/
01 _-_
3.5
L_ _~1~___‘.__~.&
Fig. 3. A typiciil clcvclopcd chromntogram :rftcr the color has faclcd shotviug only the pcncilccl outlines of tlrc spots ;intl the ccntcr points to which distance mcilsurcmcnts wcrc mdc. The numbers xc the mcusurcd distzmccs in cm. The outer circle if3 the cdgc of the 32-cm diamctcr disk. The inner circle dcscribcs the 4-cm radius on which the satnplcs \vcro originally ykrccd.
PH
IGg. z. Dintnncc truvclcrl by the clcmcnts La, Cc, IV, Nd. Sm ancl Y RS in function of cluont PH. Tfio solution wns 0.30 Af in glycolic acid. The running timo W(LR6 min. The Sm( X) and Y (+ ) did not scparrrtc.
TAIILE SI’ISCII’IC
CONI>ITIONS
I’OR
rI
SILI’ARATING
PARTICULAR
ItLWMlZNTS -
Is2trenls
La-CcNd La-Cc-l? partial Ncl -I%-
Time (tnin)
Clycolic acid concenlralion (M)
pIf
0.40
3.75
0.30
3.75
0.30
.) .oo
9
IA-Sm Cc-Sm
or Y or Y
3
Nd-Sm Pr-Sm
or Y or Y
6
.’
DISCUSSION
All the distance VS. time data wcrc plotted as in Fig. I and initial velocities were dctermined. Thcsc arc plotted in Fig. 4 as a function of PG, the negative logarithm of the glycolate ion concentration. In order to interpret the data shown in Fig. 4, we can consider that v, the velocity, is proportional to the amount of rare earth in solution and invcrscly proportional to the amount in the paper-plus-resin phase: v = I([MC”n-n]/{hIG+Ra-r} (1) Amd. Clrinr. Ada,
30 (1964)
148-154
C. HEININGER,
~52
‘0.06
-
0.04
-.
0.02
I 0.6
I 0.7
. &-GQ
.
lb,
JR.,
I;. M. LANZAFAME
I 0.6
0.02
1’1 .
I 0.7
I 0.8
PG
I 0.9
I 1.0
I
1.1
PG
Fig. 4. The logarithm of tlio initial velocity of the metal spccics ils a function of pc, the ncgntivc logrrrithin of tlic glycolatc anion concentration. *rhc error limits aru the cxporimcntnl uncertainty in rcirding the slop0 of tlio distance us. timo plots.
where M is a rare earth ion, G is the glycolate anion, R is a singly charged resin site, I< is a proportionality constant dependent on the kinetic forces involved, n is the average number of ligand glycolates in the solution phase per rare earth ion, and x is the avcragc number of ligand glycolate ions in the resin phase per rare earth ion. The [ 1 symbolize molarity units; ( ) symbolize moles. The expression for v and the subsequent analysis rccognizcs that the ratio of ligand to metal in the spccics most probably adsorbed on the resin is not necessarily the ratio prcdominnting in open solution. It is the metal ion species involved in the r-c-sin equilibrium whose outward movement is impeded with respect to the solvent flow. The equilibrium bctwccn solvent and resin phase can be written: RIG=:‘-= -t_ (3 -
By replacing mole fraction
x)
Nli.,Li+
activity with concentration in the resin phase, WC:have:
=
The equilibrium
=
{MGJ-b-r}
-
for the complex
phase ancl activity
with
-l- {N I-feR}
{N&R)
[Nlh.~] O--L {MCrR~-r} [MG~3-=-J
x) NH.,+
in the solution
{MG+Ra-I} Kr
-I- (3 -
{MG,Ib,}
[NH.,+]-= K,
MG+Ra_,
{N&R}
formation
if
-+ (N&R} {N&R}
is : Ma+ +
g
(MGIl~~-z}
it G- s
(2)
MG,,a-n
A rraz.ClrirU.AcCn,30 (rgG4) ‘48-154
HIGH
The appropriate
SPEED
stability
SEPARATION
constants
OF
LIGHT
RARE
EARTHS
153
are (3)
and (4) Insertion
of
(2)
and (3) in (I)
gives:
y =
Insertion
,~ h’n[hl3+] [G-l’8 [NI.I4’]3-.-’ --~---_ K,[MG2-‘1
{ NH4R)
(5)
of (4) in (5) gives: KK,,[G-In-r [NL14+]“-r t, == -fi,K, {h’l-1411)
&cause of the manner in which the eluant was prepared earth concentration is about one per cent of [G-J, [Xl&+] *
and because the total rare
[c-]
A log plot of Y VS. pc should have a negative slope equal to -(3+12--2x). Because both n and x will vary with pc, the line will probably not be straight (Fig. 4). SONESSON~ has studied the rare earth-glycolate system and has determined the stability constants for the species MG12+, MC;a+, MG3, MG4-, and MGa2-. His data, which unfortunately omit Y, can be used to calculate values of ?t in the pG range studied here. From these, values of x can bc calculated. The results are given in Table III. Both t.he values of n and of x decrease with increasing pc, as is to bc cxpcctccl. Similarly, tliere is a general incrcasc in n and x from La to Sm. But it is interesting to note that Nd and Pr tend to have essentially the same values of n and x in this 1~ region. SONESSON’S data show that tt for Nd is less than it for Pr at PG values less than x.00 and is greater at higher pc vcllucs. From the behavior of the other rare earths stuclied, only the latter behavior would be expected. Thus a crossover in relative stabilities of the glycolate complexes of Nd and Pr occurs just in the PG region most applicable to USC of the high speed chromatograph with strong acid ion-exchange paper. This essential indistinguishability of Pr and Nd is also seen in the comparison of x values. The fact that the :Y values generally lie between I and z shows that the species undergoing ion exchange are usually singly or doubly charged. This is true even though the PCvalues are close to 3, and there is thercforc a large fraction of uncharged metal species in solution. Although it seems possible to separate Nd and Pr by a properly chosen glycolic acid eluant, it would probably be easier to do this by using an eluant that forms Nd and Pr complexes which differ more in their stabilities.
c. HEININGER,
154
”
._
-~Anrx”iII AVlSHhGll
NUMDEI<
OIr
GLYCOLA’I-15
IONS
I’ISR
w
P. M. LANZAFAME
JR.,
RARE
-
RARTH
TIIIC HItSIN YfIASE --
IN
l-Ii11
SOLUTION
714
PC
La
o-7 (I.8 0.9 I .o
2.74
2.92
I.59
2.90 3.10
2.77 2.6:
3.4”
2.47
I*4d I .zG I .O.)
o-7 0.8 0.9 1.0
2.99 2.99 2.99 2.99
3.10
I *g>
2.93 2.77 2.GI
‘ 47 I.39 1.31
0.7 0.8
2.40
3.22 3.08
I.91 1.64
2.93 2.80
IS.57 r.3G
2 .OCJ
3.16
2.74 2.79 2.g-J
3.03 2.92 2.80
2.05 1 .G4 I.fjG I .,I2
x *97 2.49 2.09 2.82
3#30 3.17 3 *Od 2.02
c’c
1%
0.9 1.0
Sm
o-7 0.8 0.9 1.0
2.79 2.79 3-09
PHAS1.Z
02)
AND
IN
x
ixwacr1t
3-t-n
-2%
ION
(X)
2.IG X.8,~ I .G8 I.55
SUMMARY ‘I’hu separation of the rare onrthe, IA, Cc, X’r, Nd, Sm and Y on centrifugally accclcmtcd Amhcrlitc S&2 cation-cxchnngo pnpcr was studicd. All combinations of the clcmonts can bo complctcly sFparntcd cxcopt the Pr-Ncl pair by using as clurrnt glycolic acid of a properly-choecn conccntratlon (0.30 or 0.40 M) and pfr (3.0 to 4.5). T11c l’r-Nd pair can bo partially scptlmtcd. The avcrogo number of lignnd glycolnto ions per rare cnrtll ion in tliu rosin phase was tlctcrminod for each rnrc cart11 over thu pc range 0.7 to I .o.
Unc Jtuclc a dtJ cffcctudc sur la dparation clcs tcrros rams, La. Cc, I%-, Ncl, Sm ct Y, sur papicr dcliangcur do cations, hmborlitc Sh-2, nccdlc’rdc par ccntrifugntion. Chacun dc CCR dlbmcnts pcut &tro sdpard quantitntivcmcnt dos Itutrus (h l’cxccption do la prliro Pr-Ncl) CIIutilisrrnt commc 6luant I’uciclo glycoliquc. Pr-Nd Fcuvont &to dpnrds particllcmont. IAZ nombro moycn d’ions glycolatcs par ion mdtdliquu, clnnn la rdainc, R btd cldtcrminb pour clinquc tcrrc rilro. ZUSAMMENFASSUNG Die Trcnnung dcr Scltcncn Erclon Ia, Cc, Pr, Ncl, Sm und Y nut zcntrifugal bcschlcunigtom Iiationonaustausclicrpapior (hniborlitc W-2) wurdc untorsucht. Alla Kombinationon diosor Blcmcntc (ausscr Pr-Nd) Icl)nncn vclllig gutronnt worclcn boi Anwcnclung von 0.3 odor 0.4 M Glylcols!Luro und oinom ptr-Wurt von 3.0~4-5. Im pci-Bercich von 0.7-1 .o wurclo in clcr Harzphirso fllr jcdcs Elomont die durchsclinittlicho Zrrlil clcr Ligandcn bcsliinmt. REITRENCES in I?. I-IEFTRIANN, Cirro?,lcclogrnplry, Reinhold, Now Yorlc, 19G1, p. 140. KUNIN, in E. IIIWTMANN, Clrvoirrcctojircrpl~y, Reinhold. New York, WJGI, p. 325. 8 P. C. STISVENSON AND W. 15. NERVIK, Tlrc Rndiochemisfry of the Rare E’artlrs. Scandium, Yttriaon, atrd A clirrirrm, Subcommittoc cm Radiochcmistry, National Acndomy of Scicnccs - National Rcscarch Council, Wushington, 19Gr. 4 A. SONZSSON, Acla CIW~PJ. Scar&., 13 (1959) 1437. 1 Ii. a R.
MACEK,
Arlal.
Ciritn. Acm, 30 (x964)
148-154
148
HIGH
CHf MICA
SPEED SEPARATION OF THE FUGALLY ACCELERATED CIARENCE
I-115CNINC;lSR,
Jhpurl~~ac~~t of CJumrisLry,
(lbxcivcd
LIGHT RARE EARTHS ON ION-EXCHANGE PAPER* L~ICRNK
JR. AND
St. Jolrtr
I:islrcr July
ACTA
College,
CENTRI-
M. I,hN%AI~hMIS+* l~ochcslcr,
N. Y. (U.S..4
.)
3rd. 19G3)
In an attempt todevclop a rapid, clean separation applicable to the lighter rare earths (La to Sm), the technique of high speed, centrifugal chromatography1 on ion-exchange papcra was investigated. was possible to separate completely the elements in any combination cxccpt the pair 1% and Nd. It was also possible to calculate from the data the average number of glycolate anions held in the resin-plus-paper phase per t-arc earth ion so held.
rt
The apparatus used was a Hi-Speed Chromatograph manufacturccl by Precision Scientific Company. In this apparatus, circular sheets of ion-exchange paper arc mount&l on the shaft of a variable speed motor (300-1500 rcv./min). Four metal spokes arc usccl to support the paper; the spokes arc best coated with a plastic tape in order to prevent attack of the metal by the cluant. The eluant is delivered under pressure in a fine stream through a o.I-mm diamctcr orifice in a stainless steel disk and directed onto the paper inside the point at which the ion mixture was applied. In our arrangement, the cluant was dclivcrccl from a roo-ml gas burct so that the flow rate could be dctcrminccl. The ion-exchange paper was Ambcrlitc W-2, which is a paper containing about 50% by weight of Ambcrlitc IR-IZO sulfonic acid resin in the Na+ form. The rare earth solutions wcrc made from oxides obtained from Lindsay Chemical Company ancl said to bc at least ~>g.gO/~ pure. The eluant solutions wcrc prepared from Fisher Scientific Company glycolic acid and brought to the dcsirecl PH by addition of ammonia. They were filtcrcd before use to eliminate clogging of tlic orifice The inclicator solution was 0.1% PAN (r-(z+pyridylazo)-2-naphthol from J. ‘1‘. Baker Chemical Company) by weight in ethyl alcohol. The paper was placed on the apparatus and washccl with cluant. ‘The rotation was stopped and the rare earth solutions wcrc spotted on the wet paper in a circle 4 cm from the center of rotation with a z-p1 pipct. The quantity of rare cartli ion applied was about 0.02 mg, which does not exccccl the exchange capacity of thcrcsin at the point of application. The statccl capacity is 0.025 mcq./cm”. + This rcsccrrch Wiis pClrtiillly YupIm~lcd I>y tllo U.S. Atomic Energy Commission. ** Prcscnt addrcus: Ihprrrtmcnt of Chemistry, University of 12ochcutcr, New York.
HIGH
SPEED
SEPARATION
OF
LIGHT
RARE
EARTHS
I49
The chromatogram was eluted for I to 12 min at 5 ml/min and x500 rev./min. The paper was then dried, sprayed with PAN solution, and exposed to ammonia vapor. Red spots appeared because of formation of a PAN-rare earth complex in ammoniacal medium. These fade on drying and therefore must be outlined in pencil. The distance traveled was measured from the point of application to the center of the spot. RF values could not be determined because the solvent front washed off ,L,the edge of the 3z-cm diameter paper circles. RESULTS
Obvious variables to be considered when developing a separation method using the
MOVEMISNT
GIycolic mid M 0.25
0.30
Qlr 4.0 4-o 4-S 3.50
GI’
soCtclion
QG0.84
0.84 o.G8 I.01
METAL
IONS
T i7nc (rrrin)
DURING
-.-I-n
4.0
4Q5
0.74
o.Go
Dislancc cc
3.25
I.28
I.07
3.75
4.0
0.74
o.Gz
SIII
1.5
2.0
2.0 5.I
3.0
5.6
7.0
3.1 9.1
0.2
0.4 0.5 I .o
0.5
0.6
I
2.2
I *5
3.0
.6
4.2 6.8
7.9
0.1
0.2
0.2
0.2
0 . ‘)
12
7.5
>
‘).G
I r.8
>I2
I2
>
I2
0.4 0.5
0.3 0.7 1.5 2.5 3.4
0.4
0.7
0.7
;:A 8.2 C).I
2:;
0.2
0.2 033
0.3
0.3 0.6 I .2
O..)
0.9
I.7
1.8
0.2
0.4 0.7 1.1
0.‘)
G-4 I.0 I.2
2.2
1.6
3.2
3.3 4.3
0.6 2.0 4.2 4.G
0.7 1.2
2.0
2.6
4.2
3.7
6.1
I .o 1,s
2.8
5.7
1.2
1.8
3.1
4.4 7.6
I.3 2.5 2.9
7.2 7.7 2.3
9.2
10.8
10
3.1 9.3
Z:i:
>I2
IO.5
AraaC. Ckiar.
1.0
it:;
2.2 5.8 10.4
> I2 > 17.
0.4 0.5
0.2
1.5
>
5*0 94 12
0.3 o-4
0.3 0.5 0.6
2:;
5.4 9.6
>
10.0
0.X
4.9
3~2
2:::
6.5 10.6 12
1.0
2.2
2.9
3-7
Z.CJ
24
0.9
2.2
2.6
3.6
1.2
0.8
4.4 5.1
G.0
I
11
2.1
! .o
-
3.3 4.8
3.5 4.1
2.3 34
>
1’
11.8
0.7 I.5 * *9
1.0
I.0
I .2
0.2
O.Y!,
Nd
1.5
0.
3.50
(cm)
I .8
6.7
3.0
iravelcd
Pr
.o
IILUTION
I
5.0
0.40
CHROMATOCHAPIIIC
I.1
0.4
3.75
SPY,EI>
0.6
0.2
0.86
HIGH
ACta,
30 (1964)
>I2
7.7 9.7 3.4 9.9
>I2 X48-154
150
C. HEININGER, JR., I;.
M.
LANZAFAME
technique described here arc eluant flow rate, amount of sample. speed of rotation, type of paper and ion-exchange resin, separation time, temperature, and identity, concentration, and pH of the eluant solution. The ion-exchange papers show good wet strength in addition to having the conventional ion-exchange properties. Because most ion-exchange separations of the rare earths have been made on strong acid cation exchanger@, the one commercially available paper of this type known to us was chosen for study. An eluant flow rate of 5 ml/min was chosen because greaterflowratesledtoexcessive . 1 1, tailing and smaller flow rates were difficult to achieve and reproduce. The maximum rotation speed, x500 rcv./min, was chosen in order togive the fastest possibleseparation. Preliminary runs using solutions of glycolic, lactic, a-hydroxyisobutyric, and citric acids of varying concentrations and PH suggested that glycolic acid would be most likely to give satisfactory separations. Determinations of the distance traveled by the elements La, Cc, Pr, Nd, Sm and Y were made for glycolic acid concentrations of 0.25 to 0.40 M, a PH range of 3.0 to 4.5, and running times of I to 12 min.Theglycolate anion concentration varied from 0.053 to 0.25 M. The results arc given in Table I. A typical plot of distance traveled as a function of elution time is shown in Fig. I. In general, it can be said that velocity is constant at the lower velocities and distances, but that the velocity decreases as time increases. In other words, as the ion approaches the edge of the paper, its velocity decreases. The best time intervals to be used for separations appear to be 3 to 6 min. The ions are able to move a good distance from their point of origin but in gcncral have not begun to bunch at the outside cdgc.
r
.---_ 1
___A
I
1-
----l---
1
7lme (tnin) Pig. I. Distnnco travolcd by the clomcnts IA; Co, Pr, Nd, Sm nnd Y as ;L function of timo of centrifugal olution. Tho solution WDS 0.40 M in glycolic acid nncl hnd a PH of 3.75. At CJmin, Y had washed off the papcr.
For a given running time, a plot of distance traveled as a function of PIX will suggest optimum conditions for a particular separation. Fig. 2 is a typical representation. Suggested conditions for each separation are given in Table II. With the glycolic acid eluant, we were able to separate any adjacent pair of the Amal. ChittI.ACta, 30 (1964))148454
~_a
HIGH
SPEED
SEPARATION
OF
LIGHT
RARE
EARTHS
151
elements considered with the exception of Nd-Pr and Sm-Y. -4 partial separation of Nd-Yr was achieved. Sm and Y can be separated with 0.4 M lactic acid at a pH of about 4.5. A good example of the appearance of a chromatogram after clution is shown in
r
___‘__‘____
_--_
--
1 Nd
Sm,Y
J
Pr
Ce 1 LO
-- ___/
01 _-_
3.5
L_ _~1~___‘.__~.&
Fig. 3. A typiciil clcvclopcd chromntogram :rftcr the color has faclcd shotviug only the pcncilccl outlines of tlrc spots ;intl the ccntcr points to which distance mcilsurcmcnts wcrc mdc. The numbers xc the mcusurcd distzmccs in cm. The outer circle if3 the cdgc of the 32-cm diamctcr disk. The inner circle dcscribcs the 4-cm radius on which the satnplcs \vcro originally ykrccd.
PH
IGg. z. Dintnncc truvclcrl by the clcmcnts La, Cc, IV, Nd. Sm ancl Y RS in function of cluont PH. Tfio solution wns 0.30 Af in glycolic acid. The running timo W(LR6 min. The Sm( X) and Y (+ ) did not scparrrtc.
TAIILE SI’ISCII’IC
CONI>ITIONS
I’OR
rI
SILI’ARATING
PARTICULAR
ItLWMlZNTS -
Is2trenls
La-CcNd La-Cc-l? partial Ncl -I%-
Time (tnin)
Clycolic acid concenlralion (M)
pIf
0.40
3.75
0.30
3.75
0.30
.) .oo
9
IA-Sm Cc-Sm
or Y or Y
3
Nd-Sm Pr-Sm
or Y or Y
6
.’
DISCUSSION
All the distance VS. time data wcrc plotted as in Fig. I and initial velocities were dctermined. Thcsc arc plotted in Fig. 4 as a function of PG, the negative logarithm of the glycolate ion concentration. In order to interpret the data shown in Fig. 4, we can consider that v, the velocity, is proportional to the amount of rare earth in solution and invcrscly proportional to the amount in the paper-plus-resin phase: v = I([MC”n-n]/{hIG+Ra-r} (1) Amd. Clrinr. Ada,
30 (1964)
148-154
C. HEININGER,
~52
‘0.06
-
0.04
-.
0.02
I 0.6
I 0.7
. &-GQ
.
lb,
JR.,
I;. M. LANZAFAME
I 0.6
0.02
1’1 .
I 0.7
I 0.8
PG
I 0.9
I 1.0
I
1.1
PG
Fig. 4. The logarithm of tlio initial velocity of the metal spccics ils a function of pc, the ncgntivc logrrrithin of tlic glycolatc anion concentration. *rhc error limits aru the cxporimcntnl uncertainty in rcirding the slop0 of tlio distance us. timo plots.
where M is a rare earth ion, G is the glycolate anion, R is a singly charged resin site, I< is a proportionality constant dependent on the kinetic forces involved, n is the average number of ligand glycolates in the solution phase per rare earth ion, and x is the avcragc number of ligand glycolate ions in the resin phase per rare earth ion. The [ 1 symbolize molarity units; ( ) symbolize moles. The expression for v and the subsequent analysis rccognizcs that the ratio of ligand to metal in the spccics most probably adsorbed on the resin is not necessarily the ratio prcdominnting in open solution. It is the metal ion species involved in the r-c-sin equilibrium whose outward movement is impeded with respect to the solvent flow. The equilibrium bctwccn solvent and resin phase can be written: RIG=:‘-= -t_ (3 -
By replacing mole fraction
x)
Nli.,Li+
activity with concentration in the resin phase, WC:have:
=
The equilibrium
=
{MGJ-b-r}
-
for the complex
phase ancl activity
with
-l- {N I-feR}
{N&R)
[Nlh.~] O--L {MCrR~-r} [MG~3-=-J
x) NH.,+
in the solution
{MG+Ra-I} Kr
-I- (3 -
{MG,Ib,}
[NH.,+]-= K,
MG+Ra_,
{N&R}
formation
if
-+ (N&R} {N&R}
is : Ma+ +
g
(MGIl~~-z}
it G- s
(2)
MG,,a-n
A rraz.ClrirU.AcCn,30 (rgG4) ‘48-154
HIGH
The appropriate
SPEED
stability
SEPARATION
constants
OF
LIGHT
RARE
EARTHS
153
are (3)
and (4) Insertion
of
(2)
and (3) in (I)
gives:
y =
Insertion
,~ h’n[hl3+] [G-l’8 [NI.I4’]3-.-’ --~---_ K,[MG2-‘1
{ NH4R)
(5)
of (4) in (5) gives: KK,,[G-In-r [NL14+]“-r t, == -fi,K, {h’l-1411)
&cause of the manner in which the eluant was prepared earth concentration is about one per cent of [G-J, [Xl&+] *
and because the total rare
[c-]
A log plot of Y VS. pc should have a negative slope equal to -(3+12--2x). Because both n and x will vary with pc, the line will probably not be straight (Fig. 4). SONESSON~ has studied the rare earth-glycolate system and has determined the stability constants for the species MG12+, MC;a+, MG3, MG4-, and MGa2-. His data, which unfortunately omit Y, can be used to calculate values of ?t in the pG range studied here. From these, values of x can bc calculated. The results are given in Table III. Both t.he values of n and of x decrease with increasing pc, as is to bc cxpcctccl. Similarly, tliere is a general incrcasc in n and x from La to Sm. But it is interesting to note that Nd and Pr tend to have essentially the same values of n and x in this 1~ region. SONESSON’S data show that tt for Nd is less than it for Pr at PG values less than x.00 and is greater at higher pc vcllucs. From the behavior of the other rare earths stuclied, only the latter behavior would be expected. Thus a crossover in relative stabilities of the glycolate complexes of Nd and Pr occurs just in the PG region most applicable to USC of the high speed chromatograph with strong acid ion-exchange paper. This essential indistinguishability of Pr and Nd is also seen in the comparison of x values. The fact that the :Y values generally lie between I and z shows that the species undergoing ion exchange are usually singly or doubly charged. This is true even though the PCvalues are close to 3, and there is thercforc a large fraction of uncharged metal species in solution. Although it seems possible to separate Nd and Pr by a properly chosen glycolic acid eluant, it would probably be easier to do this by using an eluant that forms Nd and Pr complexes which differ more in their stabilities.
c. HEININGER,
154
”
._
-~Anrx”iII AVlSHhGll
NUMDEI<
OIr
GLYCOLA’I-15
IONS
I’ISR
w
P. M. LANZAFAME
JR.,
RARE
-
RARTH
TIIIC HItSIN YfIASE --
IN
l-Ii11
SOLUTION
714
PC
La
o-7 (I.8 0.9 I .o
2.74
2.92
I.59
2.90 3.10
2.77 2.6:
3.4”
2.47
I*4d I .zG I .O.)
o-7 0.8 0.9 1.0
2.99 2.99 2.99 2.99
3.10
I *g>
2.93 2.77 2.GI
‘ 47 I.39 1.31
0.7 0.8
2.40
3.22 3.08
I.91 1.64
2.93 2.80
IS.57 r.3G
2 .OCJ
3.16
2.74 2.79 2.g-J
3.03 2.92 2.80
2.05 1 .G4 I.fjG I .,I2
x *97 2.49 2.09 2.82
3#30 3.17 3 *Od 2.02
c’c
1%
0.9 1.0
Sm
o-7 0.8 0.9 1.0
2.79 2.79 3-09
PHAS1.Z
02)
AND
IN
x
ixwacr1t
3-t-n
-2%
ION
(X)
2.IG X.8,~ I .G8 I.55
SUMMARY ‘I’hu separation of the rare onrthe, IA, Cc, X’r, Nd, Sm and Y on centrifugally accclcmtcd Amhcrlitc S&2 cation-cxchnngo pnpcr was studicd. All combinations of the clcmonts can bo complctcly sFparntcd cxcopt the Pr-Ncl pair by using as clurrnt glycolic acid of a properly-choecn conccntratlon (0.30 or 0.40 M) and pfr (3.0 to 4.5). T11c l’r-Nd pair can bo partially scptlmtcd. The avcrogo number of lignnd glycolnto ions per rare cnrtll ion in tliu rosin phase was tlctcrminod for each rnrc cart11 over thu pc range 0.7 to I .o.
Unc Jtuclc a dtJ cffcctudc sur la dparation clcs tcrros rams, La. Cc, I%-, Ncl, Sm ct Y, sur papicr dcliangcur do cations, hmborlitc Sh-2, nccdlc’rdc par ccntrifugntion. Chacun dc CCR dlbmcnts pcut &tro sdpard quantitntivcmcnt dos Itutrus (h l’cxccption do la prliro Pr-Ncl) CIIutilisrrnt commc 6luant I’uciclo glycoliquc. Pr-Nd Fcuvont &to dpnrds particllcmont. IAZ nombro moycn d’ions glycolatcs par ion mdtdliquu, clnnn la rdainc, R btd cldtcrminb pour clinquc tcrrc rilro. ZUSAMMENFASSUNG Die Trcnnung dcr Scltcncn Erclon Ia, Cc, Pr, Ncl, Sm und Y nut zcntrifugal bcschlcunigtom Iiationonaustausclicrpapior (hniborlitc W-2) wurdc untorsucht. Alla Kombinationon diosor Blcmcntc (ausscr Pr-Nd) Icl)nncn vclllig gutronnt worclcn boi Anwcnclung von 0.3 odor 0.4 M Glylcols!Luro und oinom ptr-Wurt von 3.0~4-5. Im pci-Bercich von 0.7-1 .o wurclo in clcr Harzphirso fllr jcdcs Elomont die durchsclinittlicho Zrrlil clcr Ligandcn bcsliinmt. REITRENCES in I?. I-IEFTRIANN, Cirro?,lcclogrnplry, Reinhold, Now Yorlc, 19G1, p. 140. KUNIN, in E. IIIWTMANN, Clrvoirrcctojircrpl~y, Reinhold. New York, WJGI, p. 325. 8 P. C. STISVENSON AND W. 15. NERVIK, Tlrc Rndiochemisfry of the Rare E’artlrs. Scandium, Yttriaon, atrd A clirrirrm, Subcommittoc cm Radiochcmistry, National Acndomy of Scicnccs - National Rcscarch Council, Wushington, 19Gr. 4 A. SONZSSON, Acla CIW~PJ. Scar&., 13 (1959) 1437. 1 Ii. a R.
MACEK,
Arlal.
Ciritn. Acm, 30 (x964)
148-154