524
Anal. Chem. 1980, 52, 524-527
Ion-Exchange Separation of Lithium from Large Amounts of Sodium, Calcium, and Other Elements by a Double Column of Dowex 50W-X8 and Crystalline Antimonic(V) Acid Mitsuo A b e , " Endang Asijati Achmad Ichsan,' and Kenji Hayashi Depadment of Chemistry, Faculty of Science, Tokyo Institute of Technology, 2- 12- I , Ookayama, Meguro-ku, Tokyo 152 Japan
The elution behavior of lithium and magnesium ions was studied with nitric acid solution on crystalllne antimonic(V) acid (CSbA) as a cation-exchanger. On the basis of the relevant distribution coefficients for various metal ions on the resin and C-SbA, an effective separation of llthium from large amounts of other metals can be performed quantitatively on the double column which consists of an upper column (14.0 cm long X 1.0 cm i.d.) of Dowex 50W-X8 and a lower column (2.2 cm long X 0.8 cm 1.d.) of C-SbA. The proposed method was employed to the determination of lithium in some standard rock samples.
Inorganic ion-exchangers have been of interest during the past two decades because of their higher ion-exchange selectivities for certain elements than those on organic ion-exchange resins (1-5). Among the various inorganic ion-exchangers, crystalline antimonic(V) acid (C-SbA) shows the unique order of selectivities; Li+ < K+ < Cs+ < Rb+ < Na+ for alkali metals (6, 7 ) ,Mg2+< Ba2+< Ca2+ < Sr2+for alkaline earth metals ( 8 ) , Ni2+ < Mn2+ < Zn2+< Co*+ < Cu2+ < Cd2+(9, 10) for transition metals. T h e mutual separations can be performed effectively for alkali metals (6, 7 ) and for various series of (Mg*+-Ba*+),(Mg2+-Cs+-Ba2+),(Mg*+-Cs+-Ca2+,Sr-") (81, a n d (Ni2+-Cu2+),(Zn2+-Cd2+)(9, 10) on the relatively small column of C-SbA. T h e chromatographic separation of lithium from sodium on sulfonated cation-exchange resins is not favorable because the separation factor is only about 1.5-2.0 in aqueous inorganic acid solutions (11). An improved separation factor (about 3-5) is obtained by eluting with a hydrochloric acid solution containing a large percentage of methanol or ethanol (12). The distribution coefficient (Kd)for sodium is rather low under these conditions a n d only small amounts of sodium can be separated satisfactorily (12, 13). More favorable conditions are obtained for the separation of 1 mg of lithium from 20 mg of sodium by using a column (8.0 cm long x 1.9 cm i d . ) of Bio-Rex 40 resin (100-200 mesh) which has functional phosphonate groups, by eluting with a 1.0 M hydrochloric acid solution containing 80% ethanol ( 1 4 ) . About 35 pg to 35 mg of lithium have been separated from as much as about 115 mg of sodium by the elution with 1 M nitric acid solution in 80% methanol on a column (19 cm long X 2.1 cm i.d.) of AG 50W-X8 sulfonated polystyrene cation-exchange resin (200-400 mesh) ( 1 5 ) . T h e addition of organic solvent brings a sufficiently large separation factor, but it has a disadvantage in t h a t a large effluent volume is needed before elution of lithium ions because of the increased distribution coefficient Present address: Department of Chemistry, Faculty of Mathematics and Natural Sciences, University of Indonesia, Jakarta, Indonesia.
0003-2700/80/0352-0524S01 O O / O
of lithium. Furthermore, t h e lithium fraction of several hundred milliliters, which eluted first, must be evaporated to dryness for the detection limit of lithium. This important factor is not only responsible for the increase of the selectivites between lithium and sodium on t h e ion-exchanger, but also for the selection of eluant and further procedures after the elution for more accurate and rapid determination of lithium. If atomic absorption spectrometry (AA) or flame photometry (FP) is carried out directly by the introduction of effluent of lithium fraction into its flame system without concentration or drying, the time required for the determination may be reduced markedly. Nitric acid was selected for this purpose because of much less interference for the determination of lithium by AA or FP (16),and also because of less tendency of the complex formation to iron, transition metals and other elements. The determination of lithium in environmental materials is complicated because of interference by the presence of alkali and alkaline earth metals at a relatively high concentration (16). More rapid separation of microamounts of lithium from a large amounts of alkali metals may be needed for the analytical purposes. An extremely high separation factor, cu(A/B), where A and B are alkali metals, was observed in the values of 2.6 X lo5 for cu(Na/Li) and 1.45 X lo3 for cu(K/Li) on C-SbA (17). I t is preferable for the separation of lithium from environmental elements that the Kd value of lithium on C-SbA be very small in inorganic acid solutions even a t relatively low concentration, while the values of sodium be extremely high in these solutions. On the basis of the elution behavior of lithium, magnesium, and sodium, an effective separation of microamounts of lithium from large quantities of other elements with a double column of Dowex 50W-X8 and C-SbA is proposed. This procedure was employed for the determination of lithium in some standard rock samples.
EXPERIMENTAL Reagents and Apparatus. Antimony pentachloride (Yotsuhata Chemical Co. Ltd. Japan) was used without further purification. The resin was Dowex 50W-X8 (100-200 mesh) sulfonated polystyrene cation-exchanger. The samples of JB-1 (titanaugite-olivine basalt, split No. 8) and JG-1 (porphyritic biotite granodiorite,split No. 9) were supplied from The Geological Survey of Japan. The other reagents used were all of analytical grade. A Varian Techtron 1100 atomic-absorption spectrometer was employed for the determination of the concentration of various metals. The C-SbA (100-200 mesh) was prepared as described previously (6, 18). The resin was conditioned by alternate treatment in the usual manner with 1 M HCl and 1 M NaOH solutions before use (19). Distribution Coefficients ( K d ) .Dry resin (0.250 g) in the H+ form was equilibrated with 25.0 mL of metal solution (1 X mol/L) containing nitric acid of desired concentration by shaking occasionally a t 30 "C. The Kd values for batch equilibration were calculated from C 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
Kd =
amount of the metal ions in exchanger X amount of the metal ions in solution mL of solution (1) g of exchanger
From the plate theory, the following correlation may be obtained between the K d and the peak elution volume (VmaX). V,, = I + M K , (2) where I and M are the total interstitial volume and the weight of exchanger in the column, respectively. The elution curve for lithium and magnesium was prepared with a column containing 1.26 g of C-SbA. The column was 5.0 cm long and 0.4 cm i.d. A nitrate salt solution (1.0 mL) of the metals was added on the top of the C-SbA column, and the column was then washed with a small portion of demineralized water. The adsorbed metal ions were eluted with a nitric acid solution at different concentrations at flow rate of 0.3 mL/min. The elution experiments were carried out a t different loading of the metal ions. The Kd values of Li+ and Mg2+on C-SbA were calculated from Equation 2 by finding the maximum peak of the elution curves. Separation of Lithium, Magnesium, and Sodium with the C-SbA Column. The C-SbA column, 5.0 cm long and 0.4 cm id., was pretreated with 0.05 M HN03 and 3 mL of a mixed solution containing 1.0 X mmol of each metal was then added on the top of the column. The adsorbed metal ions were eluted with various eluants at flow rate of 0.3 mL/min (Figure 3). Separation of Lithium, Magnesium, a n d Sodium w i t h a Double Column of Dowex 50W-X8 a n d C-SbA. The double column used to obtain the rapid separation of these metals consists of an upper column (14.0 cm long X1.0 cm i.d.) of Dowex 50W-X8 and a lower column (2.2 cm long X 0.8 cm i d . ) of C-SbA. A solution (3.0 mL) containing 1.0 X mmol of each of the metals was added on the top of the double column. The Li+ was eluted with 0.5 M HN03. The Na+ was retained by the C-SbA column and the Mg*+by the Dowex 5OW-X8 up to 100 mL of the injection of 0.5 M H N 0 3 solution. After removing the upper column, the Na+ adsorbed was eluted with 6 M ",NO3 solution as an eluant. and the Mg2+adsorbed was eluted with 2 M HNO,. Quantitative Separation of Lithium from Synthetic Mixture w i t h t h e Double Column. The synthetic mixtures were prepared by mixing the metal nitrate solutions in the ratio corresponding to the composition of JB-1 and JG-1, and the concentration of nitric acid was adjusted to 0.2 M. The C-SbA column was separated initially from the resin column in order to prevent adsorption of phosphate ions which are difficult to remove from the C-SbA column, even by concentrated nitric acid. Twenty milliliters of the mixed solution were added on the top of the resin column. The column was washed with about 30 mL of 0.05 M "OB. When the mixed solution contains an appreciable amount of phosphate ions and Fe3+,the column was washed with about 5 mL of 0.5 M HNO, before adding the solution of 0.05 M H N 0 3 in order to remove phosphate ions rapidly. After connecting the C-SbA column to lower end of the resin column. the adsorbed Li+ was eluted with 0.5 M "OB as an eluant. The first 40 mL of the lithium fraction was collected into measuring flask (50 mL). Determination of Lithium in the Standard Rock Samples. About 0.25 g of the rock sample was weighed out accurately and dissolved with a mixed solution of hydrofluoric acid and perchloric acid in a 100-mL Teflon beaker by heating on the hot plate regulated a t 200 "C. The solution was evaporated to dryness and a small portion of perchloric acid solution was then added in order to eliminate all of hydrofluoric acid. After adding 2 mL of 5 M "03, the solution was diluted t o 50 mL with demineralized water. The concentrations of the metals were found to be about 7.9 X l o 4 (Li), 4.5 X lo-, (Na), 1.53 X ( K ) , 9.6 X (Mg), 8.2 X (Ca), 1.42 X (All and 5.6 X (Fe) mol/L for JB-1, and 5.8 X (Li), 5.4 x (Na), 4.2 X lo-,( K ) , 0.91 x 10.' (Mg), 1.93 X (Ca),1.39 X lo-' (Al) and 1.36 X (Fe) mol/L for JG-1, respectively. Twenty milliliters of the sample solution were added on the top of the resin column pretreated with 0.2 M HNO,, and the column was than washed with 5 mL of 0.5 M HNO, and then 30 mL of 0.05 M HNOBin order to remove phosphate and perchlorate
525
a l
,
0 .lMHNO, 0.08M
.3 'T.iC?l^l
..u-.L.
r e
Figure 1. Elution curves of lithium and magnesium ions on C-SbA at various concentrations of nitric acid solution. (a) elution of lithium ions; (b) elution of magnesium ions. Column, 5.0 X 0.4 cm i.d.; flow rate, 0.3 mL/min; fraction, 1.95 mL (Li'), 1.3 mL (Mg"); loading, 1 X 1O-' mmol (Li') and 1 X mmol (Mg") ions. After connecting the C-SbA column to the lower end of the resin column, the elution of lithium ions was carried out by continuous injection of 0.5 M HN03. RESULTS AND DISCUSSION T h e results of TGA, DTA, and X-ray studies for C-SbA showed a good agreement with our earlier works (17, 20). E l u t i o n C u r v e s of L i t h i u m and M a g n e s i u m Ions on C-SbA. T h e elution was carried lout with the nitric acid solution a t different concentrations. T h e elution curve observed for Li+ showed a slightly sloping front and a sharp rear, and the curves for Mg2+ showed a sharp front and a tailing rear (Figure 1). I t has been known t h a t the peaks in the former are caused by ion-exchange reaction for anti-langmuir-type isotherms, and the latter by Langmuir isotherms (19). The values of V,, depend on the loading of the elements on t h e exchanger of the nonlinear isotherms; a t same concentration of nitric acid, the Kd value of Li+ increases with increasing the loading amounts on the C-SbA column, while the value for Mg2+decreases with increasing the loading. The calculated K d values are plotted against log [H+]in Figure 2, the values of other metal ions on C-SbA being included for comparison. T h e slopes of d log K,i/d log [H+]were found to be about -1 for Li+ and -2 for Mg2+,respectively, indicating the "ideal" 1:l and 1:2 ion-exchange reaction. It is evident from studies of the distribution coefficients on C-SbA t h a t selective separation is feasible for Li.+,Mg*+,and Na+ (Figure 2 ) . T h e adsorbed Li+ was eluted completely without tailing by 0.05 M H N 0 3 as an eluant. Unfortunately, very strong tailing was observed on the elution 'of Mg2+with 1 M H N 0 3 as an eluant, and a rapid elution was not performed even by increasing the concentration of nitric acid. The tailing effect may be due to the slow rate of adsorption and desorption of Mg*+ on C-SbA, as pointed out in the previous report (8). Adsorbed Na+ was easily eluted with 5 M ",NO3 solution.
526
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
Table I. Determination of Lithium in a Synthetic Mixture of Rock Sample
__AAb ~ _
amount of metalsu interfering elements
Li'
without Li' sepn
N a 2 . 0 mg Ca 6 . 6 mg Na, K , Mg, Ca, Fe, AI, P,O;'' N a 2 . 4 mg Ca 1 . 4 mg Na, K , Mg, Ca, Fe, AI, P,O,"
1.2 pg 1 . 2 iig 1 . 2 !Jg 8.1 !Jg 8.1 ~g 8.1i i g
I n 20 mL of solution. J B - 1 . ' t o JG-1.
Atomic absorption spectrometry
\ \\
\ \ \
~
109 110 114
108 104
109
' Flame
111
100
115 117 109 105 109
101
100 99 99 99
Composition ratio corresponding to
photometry.
I \
lithium found, 5% __-__-___ FPC _ after without Li' sepn Li' sepn
F0.05MHNO +5 M N HL NO,
3'
' \ \ isr \
Na
3 Figure 3. Separation of lithium, magnesium, and sodium ions on C-SbA column. Column, 5.0 X 0.4 cm i.d.; flow rate, 0.3 mL/min; fraction, 4.0 mL; loading, 1 X mmol of each of metals
Rb
t
t
K
' Mg,,
I -
I
I
I :o-l
1
13 [
I!XC
I
I
__
, 3 ?,
I
' Fe.AI A
1 IC1
'
Figure 2. Calculated distribution coefficient of lithium and magnesium ions from maximum elution volumes on CSbA at different concentrations of nitric acid solution. Numerical numbers; mmol of loading of the metal ions: (...) data from ref. 7, (-.-) data from ref 8
Separation of Lithium, Sodium, and Magnesium with a Double Column. If t h e C-SbA column is applied t o t h e separation of Li+ from the elements in t h e environmental sample containing a large amount of Mg2* a n d Ca'+, these elements can be separated in principle. B u t the separation is not effective because of long tailing of Mg" (Figure 3) and, furthermore, incomplete regeneration is observed for t h e C-SbA ion-exchanged with Ca2+even if a 14 M HNO:{is used as an eluant ( 2 2 ) . A comparative study for distribution coefficients indicates t h a t the separation of L i + / t h e other metal ions is extremely high on C-SbA and t h e Kd values of multivalent cation are much higher than those of Na+ and K+ on Dowex 50W-X8 u p t o 2 M HNO,j (Figures 2 and 4). T h e double column technique was then employed for t h e mutual separation of 1 2 , Na+, and Mg'+. T h e three elements were individually isolated by injection of a relatively small volume of 0.5 M "0,; Li+ in eluate, Na+ on the C-SbA column, and Mg2+ on t h e resin column. A quantitative separation was performed effectively with 99--1009'0 recovery for the elements
I
I
I
Figure 4. Batch distribution coefficients of metals on Dowex 50W-X8 and calculated distribution coefficients of lithium and magnesium ions on CSbA at various concentrations of nrtric acld solutlon ( ) on Dowex 50W-X8, (--) on C-SbA, loading on C-SbA. mmol of Li+ and MgZ+
for a relatively short time (Figure 5 ) . Quantitative Separation of Lithium from Synthetic Mixture. When the determination of lithium by atomic absorption spectrometry (AA) or flame photometry (FP) were carried out without its separation from the solution containing an appreciable amount of various metals, large interferences
b-6M ",NO,
k- 0 5M HN03 -
LDowex 5 0 W -X8
n I ; Na
k 2 M HNO,
D I
Li
from the double column within t h e limit of detection by emission spectrometry. T h e Na+ and K+ were retained by t h e C-SbA column by the injection of 0.5 M HNO, and were eluted with 5 M ",NO, as an eluant, after removing t h e resin column. T h e elements, such as Mg2+,Ca2+,A13+,Fe3+, and transition metal ions, were retained by t h e resin column and were eluted with 2 M HCl as an eluant. T h e C-SbA column treated with 5 M ",NO3 contains an appreciable amounts of ammonium ions. T h e adsorbed ammonium ions can be readily eluted with 1 M HN03. T h e C-SbA column can be therefore used repeatedly under the usual conditions of column operation. In a fivefold analysis of t h e standard rock samples, t h e lithium was determined by a mean value of 11.2 ppm with a standard deviation (S.D.) of 0.05 p p m and a coefficient of ..
Figure 5. Separation of lithium, sodium, and magnesium ions with double column. Dowex 50W-X8 column, 14.0 X 1.0 cm i.d.; C-SbA column, 2.2 X 0.8 cm i.d.; fraction, 5.3 mL; flow rate, 0.9 mL/min; loading, 1 X mmol of each of the metal ions
aI
-
L . 3
1.3
0.0 53
d
-03
I
4
1 . '7
0.3
respectively. T h e literature values for J B - 1 and J G - 1 were collected by Ando e t d.(23). T h e contents of lithium in JB-1 are between 7.67 and 16 ppm with a mean value of 11.4 ppm, which seems to be in mod aueement with the values obtained by the method descriYbed a b k e . The literature values in JG-1 are between 83 and 106 ppm with (a mean value of 94 ppm. T h e results obtained indicate the lowest value amone the literature values. Terashima gives a mean value of 96 ppm by means of a conventional method which can be determined by atomic absorption spectrometry after addition of calcium salt of equivalent amounts corresponding to the total amounts of metals in t h e rock samples ( 2 4 ) . A fivefold analysis described by Terashima gave a mean value of 80.8 p p m which seemed t o be in reasonably good agreement with t h e values obtained by t h e method proposed above. T h e lowest value obtained may be due t o the difference in the split of the JG-1 sample.
LA 1
2
0
I
I
A
ACKNOWLEDGMENT T h e authors are indebted t o A. Ando, Geological Survey of Japan, for provision of the standard rock samples and for helpful suggestions. LITERATURE CITED
1~2A10-3
K
(1) (2) (3) (4) (5) (6) (7)
(8) (9)
(IO) ( 1 1) I
Flgure 6. Separation of lithium from the solution of rock sample ( J B l ) with single column of Dowex 50W-X8 and double column. (a) Single column, 25.0 X 0.7 cm i.d. (Dowex 50W-X8) with flow rate of 0.4 mL/min. (b) Double column, 25.0 X 0.7 cm i.d. (Dowex 50W-X8) and 2.0 X 0.5 cm i.d. (C-SbA) with flow rate of 0.4 mL/min
were observed (Table I). After separation from these elements, t h e Li+ was determined quantitatively with t h e recovery of 99-101% as given in Table I. D e t e r m i n a t i o n of L i t h i u m in S t a n d a r d Rock Samples. A typical elution curve obtained was illustrated in Figure 6b, the elution curves observed on t h e single column of Dowex 50W-X8 being included for comparison (Figure 6a). Any other metal ions cannot be found in the lithium fraction eluted
(12) (13) (14) (15) (16) (17) (18) ( 19) (20) (21) (22) (23) (24)
Veselp, V.: PekBrek, V. Talanta 1972, 19, 219-262. PekLrek, V.; Veselj', V. Talanta 1972, 19, 1245-1283. Abe, M. Bunseki Kagaku 1974, 23, 1254-1283. Abe. M. Bunseki Kagaku 1974, 2 3 , 1561-1598. De, A. K.; Sen, A. K. Sep. Sci. Technol. 1978, 13, 517-540. Abe, M.; Ito, T. Bull. Chem. SOC.Jpn. 1967, 4 0 , 1013. Abe. M., Bull. Chem. SOC. Jpn. 1969, 4 2 , 2683-2685. Abe, M.; Uno, K.. Sep. Sci. Technoi. 1979, 1 4 . 355-366. Abe. M. Chem. Lett. 1979, 561-564 Abe. M.; Kasai K. Sep. Sci. Technol.. 1979, 14. 895-907. Strelow. F. W. E.; Rethemeyer, R.; Bothma, C. J. C. Anal. Chem. 1965, 37. 106-111. Okuno. H.: Honda. M.; Ishimori. T. Bunseki Kaaaku 1953, 2 , 428-432. Nevoral, V. Fresenius' Z . Anal. Chern. 1965, 195. 332-337. Strelow, F. W. E. Anal. Chim. Acta 1968, 43, 465-473. Strelow, F. W. E.; Weinert, C. H. S. W.; van der Walt, T. N. Anal. Chim. Acta 1974, 7 7 , 123-132. Abe, M.; Hayashi, K. Bunseki Kagaku 1979, 28, 700-702. Abe, M. Sep. Sci. Technol. 1978, 1 3 , 347-365. Abe, M.; Ito. T. Bull. Chem. Soc. Jpn. 1968, 4 1 . 333-342. Dorfner, K. "Ion Exchangers-Properties and Applications"; Ann Arbor Science Publishers: Ann Arbor, Mich., 1972: p 187. Abe, M. Kogyo Kagaku Zasshi 1967, 7 0 , 2226-2234. Dean J. A. "Chemical Separation Methods": Van Nostrand Reinhold: New York, 1969; p 66. Abe. M. Bull. Chem. Soc. Jpn. 1979, 52, 1378-1390 Ando, A.; Kurasawa, H.; Ohmori, T ; Tnrada, E Geochem J. 1974, 8 , 175- 192. Terashima, S. Bunseki Kagaku 1971, 2 0 , 321-326
RECEIVED for review August 8, 1979. Accepted November 26, 1979. Presented in part a t the 37th National meeting of the Japan Chemical Society, Tokyo, April 3, 1978.
