(2) found that the complex formed in alkali hydroxide medi t and extractable into isoamyl alcohol iii red in color and exhibits a $ingle abzorption peak a t 550 mp. The composition of this complex was found t3 be three molecules of oxime for each atom of iron when an excess of oxime was present. When the concentration of oxime was less than three times that of iroli, another species was apparently present.
where: M = E a , K, Li; the cation necessary for complete charge neutralization is readily available from the alkali hydroxide media empl3yed. In ethylene amine media the 2 : l complex that is formed is a neutral
entity. However, if the stereochemical arrangement is octahedral, two sites remain open for coordination. With a neutral 1,a-diamine species available, a complex of the following structure is possible:
The extraction step in the present procedure is of special significance since it was observed that only the colored complex is extracted and any extraneous color originally present in the amine is left behind in the aqueous phase. ACKNOWLEDGMENT
The authors express their sincere appreciation to J. F. Fisher, Union Carbide Corp., Chemicals Division, South Charleston, W. Va., for evaluating the phenyl-2-pyridyl ketoxime method us. other unpublished methods. where: R = IT, --CH2CH2KH2, etc. The specific ethylene amine medium in which the ferrous complex is formed does not affect the absorption characteristics to any great degree. This is evidenced by the identical visible absorption patterns obtained with three maxima a t 588, 509, and 405 mp. The molar absorptivities, a t the former wavelength, are all of the order of lo4.
LITERATURE CITED
(1) Diehl, H., Smith, G. F., “The Iron
Reagents” (Monograph), G. Frederick Smith Chemical Co., Columbus, Ohio, 1960.
( 2 ) -Trusell, F., Diehl, H., ANAL. CHEM. 31,
1978 (1959).
(3) Yoe, J. H., Jones, A. L., IND.ENO. CHEM.,ANAL.ED. 16, 111 (1944).
RECEIVED for review X’ovember 22, 1963. Accepted February 7, 1964.
Separation of Rare Earths from Other Metal Ions by Anion Exchange JAMES S. FRITZ and RICHARD G. GREENE Institute for Atomic Research and Department o f Chemistry, Iowa State University, Ames, Iowa
b Elements of the rare earth group are retained by a nitrate-form anion exchange column from dilute nitric acid solutions in water-isopropyl alcohol. Elution with ‘I .5M nitric acid in 85y0 isopropyl alcohol allows many less sorbable elements to be separated from the rare earths. The higher rare earths can be eluted from the column using lower percentages of isopropyl alcohol and separated from bismuth (Ill), lead(ll), and thorium(lV), which remain on the column.
P
research ( I , 6, 6) has shown that the rare earths can be sorbed onto anion exchangers from nitric acid-alcohol systems. Korkisch and Tera (6) separated thorium from other metal ions using nitric acidmethanol as the medium, and from their data it appeared that the rare earths could be separai,ed from various other metal ions. Korkisch, Hazan, and Arrhenius in a rwent article (6) suggested, on the basi3 of distribution coefficients that the rare earths could be separated from some less sorbable elements using variouc, aqueous nitric acid-alcohol systems, REVIOUS
An anion exchange separat,ion of calcium and magnesium developed in our laboratory (3) uaing 0.5M nitric acid in a 90% isopropyl alcohol-lO~o aqueous solvent system led us to try B similar system for the separation of rare earths as a group from other metal ions. In the present study, rare earths have been separatd from other metal ions using Amberlyst XN-1002 resin and 1.5M nitric acid in 85% isopropyl alcohol as a sample and as an eluting medium. Up to 0.25 mmole of rare earths can be separated using a 1.2 x 12 cm. or 1.2 X 16 cm. column, and the method is selective for the rare earth group. EXPERIMENTAL
Apparatus. Conventional 12-mm. i.d. glass columns with coarse glass frits were used for the ion exchange separations. Resin. Amberlyst Xpi-1002 (Rohm and Haas Co.) anion exchange resin was used. It was ground to 60- to 100-mesh size for use in both the batch and column experiments. The resin was converted t o the nitrate form with nitric acid and then air-dried. Dowex 1-X8, 100- to 200-mesh, was also used in some comparison experiments.
For column experiments the airdried resin was soaked in the eluting solution prior to its addition of the column. The ion exchange column was also prepared by adding the resin to the column from an aqueous solution and then passing from 2 to 3 column volumes of the eluting solution through the column. Reagents. Stock solutions of the elements used were prepared 0.05M in metal ion, mostly from their nitrate salts in dilute nitric acid. Titanium(IV) and vanadium(1V) solutions were made up in sulfuric acid solution. Zirconium(1V) was used in a perchloric acid solution. The eluting solution was made up by adding concentrated nitric acid and water to the approximate amount of isopropyl alcohol needed and then diluting to the mark in a volumetric flask with isopropyl alcohol. Procedure. For the determination of batch distribution coefficients, aqueous solutions containing 0.1 mmole of metal ion were evaporated just barely to dryness in a 10-ml. beaker. Then 3 to 4 drops of dilute nitric acid were added to bring the residue into solution. This was then washed into a 50-ml. volumetric flask and diluted to volume with the medium of interest. The resulting VOL. 36, NO. 6, MAY 1964
1095
pzz- 1 AMBERLYST XN-1002
- - - - -- - -
0.80 070
[MJt=SORBED AMOUNT OF METAL AT TIME t
b = S O R B E D AMOUNT OF METAL AT EOUlLlBRlUM
0.201 0
I
1.01
0.5
I
1.0 1.5 MOLARITY OF NITRIC ACID
I
20
ANALYTICAL CHEMISTRY
I 80
I
solution was added to 1 gram of resin in a 125-ml. ground-glass-stoppered flask and shaken mechanically for a t least 4 hours to ensure equilibrium. In the column experiments from 0.05 t ? 0.25 mmole of an element was used. The metal ion solution was evaporated to dryness and brought back into solut i m as described above. Three to 5 ml. of the eluting solution was added to the beaker and this was poured onto the top of the ion exchange column. The beaker was then washed thoroughly with additional eluting solution to give a total volume in the reservoir of the column of about 10 to 12 ml. A resin height of 12 or 16 cm. was used in the column. A flow rate of approximately 0.5 ml. per minute was employed to sorb the metals onto the column and also in the elution step. A flow rate of up to 0.9 ml. per minute was used to elute some metals easily separated from t?ie rare earths. After the weakly sorbed metal ion was eluted from the column, the remaining element or elements were stripped off with approximately 100 ml. of dilute aqueous nitric acid. Both solutions were then titrated with EDTA. Because of the high alcohol and nitric acid content in the solution containing the metal ion eluted first, best results wvtre obtained in these analyses when beak-titrations were performed. In both the distribution and column experiments all elements were determined with 0.005 to 0.05M EDTA, depending on the amount of metal ion present. In the separation of vanadium(IV), after the sulfate solution had been evaporated to near dryness and 3 to 4 drops of dilute nitric acid had been added, some solid ascorbic acid was added to make sure vanadium was in the quadrivalent state. Loading experiments were performed by determining batch distribution coefficients as a function of the amount of 0
I 60
I 100
I 140
I 120
I
160
I 180
I I 200 220
I
240
I
TIME (MIN.)
2.0
Figure 2.
Figure 1. Variation of distribution coefficient with concentration of nitric acid
1096
I
40
Sorption rate experiment
1.5 M HN03-85%
metal ion present, and also by determining breakthrough points on a column using different amounts of metal ion. The breakthrough point was taken as the place in the elution where a t least 0.1% of the total metal ion present had appeared in the effluent. A sorption rate experiment comparing Dowex 1-X8 with Amberlyst XN1002 was performed in a manner described by Fritz and Waki (3). The ytterbium(II1) used was determined by the spectrophotometric method of Fritz, Richard, and Lane (2). RESULTS
Preliminary experiments showed that the rare earths are more strongly sorbed onto an anion exchange column (nitrate form) from aqueous isopropyl alcohol solutions containing nitric acid than from solutions containing a lower alcohol. Using 0.5M nitric acid in 90% isopropyl alcohol, it was found that the higher rare earths are not sorbed strongly enough to allow good column separations. However, a plot of the logarithm of the batch distribution coefficient against the concentration of nitric acid showed a linear increase of log D with acid concentration (see Figure 1). It was found that all of the rare earths tested are taken up by a nitrate-form anion exchange column from 1.5M nitric a ~ i d - 8 5 7 isopropyl ~ alcohol. I n the anion exchange separation of magnesium(I1) and calcium(I1) (3) using a nitrate system, the highly porous anion exchange resin h b e r l y s t XN-1002 proved to have an advantage over a conventional resin. As shown in Figure 2, equilibrium is also attained more quickly in the present system using the Amberlyst resin. In column separations there is less tailing with this
isopropyl alcohol
I
IOL
0.01
I
0.10 METAL LOAD,MMOLES YMDIhg,RESIN
Figure 3. Variation of distribution coefficients with load using 0.5M nitric acid-95% isopropyl alcohol
resin than with other anion exchange resins. In agreement with previous work (1, 6),we found that the batch distribution coefficient decreases with increasing atomic number of the rare earths. The lower rare earths are tightly held by an anion exchange column, but in some experiments the higher rare earths showed a tendency to break through before a column separation was complete. On checking, it was found that the sorbability of a t least the higher rare earths is strongly affected by the degree of loading. This effect for yttrium(II1) is shown by the batch distribution coefficients (Figure 3) and by the breakthrough volume in column elutions (Table I). Thus a successful separation of rare earths from other metal ions is facilitated by selection of sample size so that a rather small amount of the higher rare earths is present. Data for the batch distribution coefficients and the volume required for column elution of the elements
studied are summarized in Table 11. Using a 1.2 X 16 cm. column, any element having a batch distribution coefficient of 10 or less can be quantitatively separated from 0.25 mmole or less of the higher rare earths and probably from a somewhat larger quantity of the lower rare earths. The only exception in 'Table I1 is the titanium(1V) peroxide complex, which appears to tail. Ccpper(I1) (D=14) can be separated from 0.1 mmole of
Table 111.
Comparison of Isopropyl Alcohol-Nitric Acid-Amberlyst System with Acetic Acid-Nitric Acid-Dowex System
(Flow rate 0.5 ml./min. 15-cm. column) Metal ion eluted mmole co(11)0.25
Yb( 111) 0.0057
Elution conditions 1.5M "03-8570 isopropyl, Amberlyst column 0 . 5 M HXOa-9Oyo acetic acid, Dowex column 1.5M HNO3-85% isopropyl, Amberlyst column 0.5M HNOs-907G acetic acid, Doivex column
Breakthrough volume, ml.
Elution volume, ml.
... ...
100
350
...
210
...
90
Table I. Column LolIding Experiment Using 1.5M HN03-85% Isopropyl Alcohol
Colunin 16-cm.
12-cm.
8-cm.
Nilliniole ytterbiurn(II1) 0.0057 0.10 0.20 0.25 0.30 0.35 0.10 0.25 mmole La(II1)
Breakth-ough volume, ml.
360 310 230 200
130 120 215 >200
Table II. Distributiori Coefficients and Elution Volumes in 1 S M HN03-85%. Isopropyl Alcohol or1 Amberlyst XN-,
1 oo;!
Metal ion hlg(I1) Ca(11) Sr(I1) Sc(II1) Y(I1I) Zr(IT) Ti( I \') with
Distributim coefficien ;, 0 . 1 mmole/ 50-ml. load 2.3 56 187 22 85 16 9.9
H202
Ti(1T) with
9.9
Elution volume, ml., on 16-cm.
column, 0.25-mmole load 75
... ... ... ...
NO' ii2-cm.
column) 220
H202
5'(11) T'(W
Rln(1I) Fe(II1) Fe(II1) Co(I1) Ki(I1) Cu(1I) Zn(I1) Cd(I1) HgW)
-4g( 1)
Al(II1)
(:a( I11)
In(II1) Pb(I1) Bi(II1) Yb(II1) Dy(1II) Sm(II1) Sd(II1) La(II1)
6.7 15
6.7 3.3
3.3
5.8 5.4 14
3.2 65 228 17 2.6 3.8
9.1 1100 1300
85 180 866 2200 5900
100
>200 130 120 (12-cni. column) 140 110 110 175 (12-cm. column) 110
... ... ...
120 130
150
...
... ...
... ... *..
...
ytterbium(II1) using a 1.2 X 12 em. column. A shorter column was used, to minimize the volume of eluent needed to elute all the copper(I1) from the column. Because ytterbium(II1) has the lowest batch distribution coefficient of the rare earths studied, most of the quantitative separations were carried out using ytterbium(II1) to represent the rare earths. It was reasoned that ytterbium (111) is the most difficult case [except for lutetium(III)] and that any lower rare earth would be separated more easily from other metal ions. Using a 1.2 X 16 cm. column and 1.5M nitric acid in 85% isopropyl alcohol as the eluting medium, quantitative separations of ytterbium(II1) from each of the following metal ions were achieved: aluminum(III), cobalt(II), gallium(III), indium(III), iron(III), magnesium(II), manganese(II), nickel(I1), vanadium (IV), and zinc(I1). A 1.2 X 12 em. column gave quantitative separations of ytterbium(II1) from copper(I1) and iron(II1). The amount of ytterbium (111) and the other metal ion in the sample each ranged from 0.05 to 0.25 mmole. For separation and analysis of 21 two-component samples (42 individual analyses), the average recovery was 99.9% with a standard deviation of zt0.3%. From the high distribution coefficients of thorium(IV), lead(II), and bi>muth (111),it would seem that these metal ions could be separated from some of the rare earths by finding conditions such that the rare earths would be eluted first. It was found that 0.05 mmole of lead(I1) and 0.25 mmole of bismuth (111) could be separated from 0.25 mmole of samarium(II1) by first eluting the samarium(II1) with 1.5M nitric acid-55% isopropyl alcohol. Also 0.10 mmole of bismuth(II1) was separated from 0.10 mmole of neodymium(II1) by eluting the neodymium(II1) first with 1.5M nitric acid45% isopropyl alcohol. The average recovery here was 99.9% with a standard deviation of 3=0.25%. -4ttempts to separate
milligram aniouiits of titaaium(1V) as its peroxide complex were unsuccessful because a precipitate formed in the eluting solution when titanium was mixed with a rare earth. DISCUSSION
When our work was essentially complete, a method of Korkisch and Arrhenius (4) came to our attention. These workers separated rare earths as a group from several other metal ions by anion exchange, using 0.531 nitric acid in a 90% acetic acid-lOyo aqueous solvent system. While this system works a t the very low loadings suggested by Korkisch and Arrhenius, we found that amounts of ytterbium(II1) greater than about 10 mg. break through too soon to permit a quantitative column separation. Comparison of the acetic acid and the isopropyl alcohol system proposed in our present paper shows that 1-mg. (0.0057-mmole) portiom of ytterbium(II1) break through considerably sooner with the acetic acid system than with the isopropyl alcohol system, while a typical bivalent metal [cobalt(II)] is completely eluted in about the same volume in the two systems (see Table 111). Our experiments also show that the nitric acid-methanol system earlier recommended for separation of rare earths from other metal ions is limited to very small amounts, when the heavier rare earths are used. LITERATURE CITED
(1) Faris, J. P., Warton, J. W,, AXAI,. CHEX34, 1077 (1962). (2) Fritz, J. S., Richard, AT. J., Lane, \V. J., Ibid., 30, 1776 (1958).
(3) Fritz, J. S.,\%7alri,H., Zbid., 35, 1079 (1963). (4)Korkisch, J., Arrhenius, G., Ibid., 3 6 , 850 (1964). (5) Korkisch, J., Hazan, I., Arrheiiius, G , Talanta 10,565 (1963). (6) Iiorkisch, J., Tera, F., ANIL.CHEM. 33, 1264 (1961). RECEIVEDfor review January 2, 1964. Accepted March 12, 1964. Work performed in the Ames Laboratory of the U. S. Atomic Energy Commission. VOL 36, NO. 6, MAY 1964
1097
