V O L U M E 25, NO. 10, O C T O B E R 1 9 5 3 (8) Linnig, F. J., Milliken, L. T., and Cohen, R. I., J . Research Natl. Bur. Standards, 47, 135-8 (1951). (9) hlaron, S. H., Llevitch, I. N., and Elder, M. E., ANAL.CHEM.,
24, 1068-70 (1952). (10) Moses, F. L., private communication to the Reconstruction
Finance Corp., Office of Synthetic Rubber. (11) Reconstruction Finance Corp., Office of Synthetic Rubber, “Specifications for Government Synthetic Rubbers” (Revised Edition, Oct. 1, 1952). (12) Tryon, M a x , J . Research Natl. Bur. Standards, 45, 362-6 (1951).
1517 (13) Tryon, Max, unpublished work. (14) Tryon, Max, and Arnold, Au&lia, private communication to the Reconstruction Finance Corp., Office of Synthetic Rubber. (15) Yanko, J. A,, J . PoEymm Sci., 3,576-600 (1948); Rubber Chem. and Technol., 22, 494-517 (1949). RBCEIVED for review February 14, 1953. Bccepted August 4, 1953. Presented in part a t the 61st Meeting of the Division of Rubber Chemistry of the AMERICANCHEMICAL SOCIETY, Buffalo, N.Y., October 1952.
Separation of Tantalum and Niobium by SoIvent Extraction PETER C. STEVENSON, Radiation Laboratory, University of California, Berkeley, Calif., AND
€LARRY G. HICKS, California Research and Development Co., Livermore, Calif. During a systematic investigation into methods of radiochemical purification of the less familiar elements, the need arose for separating niobium and tantalum from each other and from the remaining elements. The reported extractability of the fluoride complex of tantalum seemed a promising lead. The extractability of the fluoride complexes of tantalum and niobium by diisopropyl ketone was investigated from various mineral acid media as a function of conditions. Both complexes were found to extract, that of tantalum being much more readily extracted than that of niobium. The difference in
extractability was such that the two elements could readily be separated from each other, and the extraction of both elements from a sulfuric acid-hydrofluoric acid medium was found to be specific for the two elements. The rate of extraction was rapid. The fraction extracted under proper conditions was high enough so that the phenomenon should prove useful for a radiochemical analytical method for the two elements, with possible applications in quantitative separation. The process should be applicable to industrial separation and purification of tantalum and niobium elements.
T
ANTALUM and niobium have been found t o extract into certain polar organic solvents from aqueous solutions containing hydrofluoric and hydrochloric acid (1-3). The dependence of per cent extracted on extraction conditions has been studied t o investigate the possibility of a tantalum-niobium separation based on this phenomenon. Diisopropyl ketone was chosen as a solvent for examination, as it does not extract significant amounts of hydrochloric acid. Preliminary investigations indicated that a tantalum-niobium separation was indeed possible, tantalum being far more readily extracted than niobium. In addition to the system tantalumhydrochloric acid-hydrofluoric acid, the systems tantalumsulfuric acid-hydrofluoric acid, tantalum-nitric acid-hydrofluoric acid, and tantalum-perchloric acid-hydrofluoric acid were inves- ; tigated. The system sulfuric acid-hydrofluoric acid seemed t o offer the most nearly specific solvent-extraction separation and purification of tantalum and niobium. EXPERIMENTAL
Tantalum tracer was prepared by dissolving neutron-irradiated tantalum metal in nitric and hydrofluoric acids, adding a large volume of 6 M hydrochloric acid, and extracting twice into diisopropyl ketone. The ketone layers were combined and washed twice with an aqueous solution 6 M in hydrochloric acid and 1 M in hydrofluoric acid. The tantalum was then brought into aqueous medium by bringing the diieopropyl ketone twice into contact with water. The resultant clear aqueous solution had a p H of 1.5 and no tantalum precipitated upon standing 2 or 3 weeks in a glass centrifuge cone. Aliquots (50 PI.) of the above solution containing about 1 mg. of tantalum pentoxide were added t o measured amounts of standardized acids and the total volume was adjusted to 1 ml. in a glass centrifuge cone. One milliliter of Eastman technical grade diisopropyl ketone was added to the cone, and the mivture was stirred well with a platinum stirring wire for 1 minute and centrifuged briefly; then equal aliquots were taken from each phase for counting.
-----=-
e
2ov a
0.40YW
0
0.20M HF
A O.IOp? HF
0
0
LO
21)
3.0
4.0
5.0
6.0
HCI MOLARITY
Figure 1. Tantalum Extracted in System Hydrochloric Acid-Hydrofluoric Acid-Diisopropyl Ketone as a Function of Hydrochloric Acid Concentration
Care was taken to work rapidly and at room temperature to minimize the effects of the hydrofluoric acid on the glass. The rate of extraction was too rapid to measure. If the mineral acid was known t o extract appreciably into diisopropyl ketone, the ketone was pre-equilibrated with the same concentration of the mineral acid used in the extraction. Hydrochloric and sulfuric acids did not extract appreciably, while perchloric, hydrofluoric, and nitric acids did extract. For simplicity and ease of handling, results were based on initial concentration of the hydrofluoric acid in the aqueous phase because the hydrofluoric acid extracted appreciably into the ketone.
1518
ANALYTICAL CHEMISTRY
There was no attempt in this work t o keep ionic strength constant; hence no conclusion c c h d be made regarding species in solution. The liquid aliquots from the extraction were transferred to machined Teflon cups and the top was covered with pressuresensitive tape to prevent spilling The gamma radiation from the tantalum182tracer in these samplec; was counted by means of a single-channel scintillation pulse analyzer using a thalliumactivated sodium iodide crystal. Samples of the organic and aqueous phases of a given extraction were counted consecutively in the same geometry to minimize errors. The results are shown in Figures 1, 2, and 3. S o b i u m tracer was prepared by adding 15 nig. of niobium as the oxalate to a zirconiurn-95-niobi~m-~6 mixture containing inactive zirconium. The oxalate was destroyed with nitric acid and potassium chlorate: niobium pentoxide thereupon precipitated and was centrifuged, washed into a LuEteroid cone, and dissolved in 1 ml. of concentrated hydrofluoric acid. The solution was adjusted t o approximately 10 M in hydrofluoric acid and 6 M in hydrochloric acid, and transferred to a polyethylene bottle. This solution was extracted twice with equal volumes of diisopropyl ketone, the organic layers being combined and washed with a solution 6 A I in hydrochloric acid and 10 M in hydrofluoric acid. The niobium was extracted from the organic phase IT-ith water. The procedure was then the same as for the tantalum.
Table I.
Extraction of Tantalum and Niobium into Diisopropyl Ketone
HC1 HF HSOs HF HpSOi HE HC104
3 70 0 40 3 92 0 40 4 50
0 40
4 61 0 40
HF
Ta hrb Ta Nb Ta Nb Ta Nb
4 3 0 047
81
4 5 79 0 43 95
91
3 8 0 0013
880
19 0 12
11
160
9 0 0 031
90
3 0
290
I00
0 W
I-
$
80
K
c x
w
I
60
3 $
0 H C l - 0.40 M HF
9
A %SO,-O.4OM
2 40
be
HF
HNO,-0.40MHF
20
0
0 HCI0,-0.40
1.0
2.0
30
4.0
MHF
5.0
6.0
ACID MOLARITY
Figure 3. Tantalum Extracted in System Mineral Acid-Hydrofluoric Acid-Diisopropyl Ketone as a Function of Mineral Acid Concentration
o
0.10
0.20
a30
0.40
as0
0.60
0.x)
HF MOLARITY
Figure 2. Tantalum Extracted in System Hydrochloric Acid-Hydrofluoric Acid-Diisopropyl Ketone as a Function of Hydrofluoric Acid Concentration
Points were taken t o show the large differences in extraction coefficients of tantalum and niobium (Table I), under conditions where tantalum extracted well in the systems studied. I n all cases the amount of niobium estracted was small. Because accurate volume measurement with very high hydrofluoric acid concentrations did not seem feasible, the behavior of niobium under conditions where it extracted appreciably was not studied in detail. However, in a solution about 6 31' in sulfuric acid and 9 AI in hydrofluoric acid, 90% of the niobium extracted into an equal volume of ketone and from about 3 121sulfuric acid and 4.5 M hydrofluoric acid, 40% extracted. The ratios of extraction coefficients in Table I show that separation of tantalum and niobium by this method is possible. Best separation of tantalum from niobium is achieved in a nitric-hydrofluoric acid system.
Test of Separation. .4 mixture of 10 mg. (as metals) each of tantalum and niobium was put into 5 ml. of a solution adjusted to 3 M in hydrochloric acid and 0.4 M in hydrofluoric acid. This solution waa extracted with 5 ml. of diisopropyl ketone for 1 minute. The phases were separated, the aqueous phase was extracted again, and the organic phase was washed with 3 ,If hydrochloric acid and 0.4 M hydrofluoric acid. The washing and second extraction were discarded. Boric acid was added to the aqueous phase to complex any fluoride present. Then ammonium hydroxide was added to precipitate the hydrated oxides, which were washed with a dilute ammonium nitrate solution. The organic phase was brought in contact twice with water, the water layers were combined,
boric acid was added, and the hydrated oxides were precipitated with ammonium hydroxide and washed with a dilute ammonium nitrate solution. The precipitates were analyzed spectrographically. The composition of the precipitate from the aqueous layer was 98% niobium and 2% tantalum, and the composition of the precipitate from the organic layer was 99.5% tantalum and 0.5% niobium. The amounts of other elements estracted into the ketone were examined briefly. In the 6 111' hydrochloric acid-0.4 M hydrofluoric acid system elemental halogens, iron(III), gallium(III), antimony(V), arsenic(III), selenium(VI), and tellurium(F'1) apparently estract very well, and all but antimony(Y) back-extract into water. rlntimony(II1) extracts slightly and srsenic(V) and tellurium(1V) somewhat better, while selenium(1V) does not extract appreciably. I t is significant that silicon(IV), tin(1V) titanium(IV), manganese(II), zirconium(IV), and hafnium(1V) do not extract, as these elements commonly occur with niobium or tantalum. In the 6 M sulfuric acid-0.4 IIf hydrofluoric acid system, only elemental halogens, selenium(VI), and tellurium(V1) tend t o follow. The sulfuric-hydrofluoric acid system thlis appears best for the separationof tantalum and niobium from general chemical contamination, especially under slight15 reducing conditions. Radiochemical Application. -5. radiochemical separation procedure has been designed and tested for tantalum n-hich gives decontamination factors of a t least lo5 from all fission products. 1. Dissolve uranium target in hydrochloric acid and make a clear solution with hydrogen peroxide in a polyethylene cone (avoid contact between hydrofluoric acid solutions and glass). 2. Add tantalum in hydrochloric acid and hydrofluoric acid t o target 3olution and add a few milligrams of inert selenium and tellurium (add sufficient hydrofluoric acid t o make final solution a t least 0.6 .If in hydrofluoric acid: final volume is 15 ml.).
.
V O L U M E 2 5 , NO. 10, O C T O B E R 1 9 5 3 3. Extract three times for 5 minutes with 5 nil. of diisopropyl ketone (remove ketone with saran pipet). 4. Combine and wash organic layers in polyethylene three times with 5 ml. of a 3olution 6 -1.I in sulfuric acid and 0.4 M in hydrofluoric acid. 5. Back-extract tantalum three times for 1 minute with 5nil. portions of 6 -11 hydrochloric acid containing boric acid and combine in glass. 6. Wash aqueous phase once for 1 minute with 10 ml. of diiwpropyl ketone; discard organic phase. i . Add 1 drop of phenolphthalein t o aqueous phase, make basic. with ammonium hydroxide, add 1 drop of 2% aerosol, digest hot, and centrifuge. 8. Wash with ,slightly basic ammonium nitrate solution. 9. Waah twice with fuming nitric acid, digest, and rentrifuge. 10. Transfer to Lusteroid cone, and dissolve precipitate in a solution 6 31 i n sulfuric acid and 0.6 M in hydrofluoric acid. 1I . Tranqfer to polyethylene cone and repeat steps 3 through 9. 12. Transfer tantalum precipitate t o platinum crucible, ignite, and weigh a? TazOs.
A fission product separation procedure has been devised for niobium t o give decontamination factors of 1OBfor all other fission products. 1. Dissolve uranium target in concentrated hydrochloric< acid to which niobium carrier has been added in oxalate form (Lusteroid tube). 2 . ildd a drop of concentrated hydrofluoric acid, and clear solution n-ith a few drops of concentrated nitric acid and digestion. 3. Transfer t o polyethylene cone, adjust to 6 JI in hydrochloric acid, and extract three times with half volumes of diisopropyl ketone. Discard organic layer. 4. Add sufficient concentrated hydrochloric acid and hydrofluoric acid t o make the solution 6 .If in hvdrochloric acid and 9 j I i n hydrofluoric acid. 5 . Extract three times with half volumes of diisopropyl ketone, and combine ketone layers. 6 . Wash combined organic layers three times with a solution 6 .lI in sulfuric acid and 9 .II in hydrofluoric acid.
1519
T. Extract niobium from ketone three times with half volumes of water. Collect water layers in a tube containing iaturated boric acid solution. 8. lldd phenolphthalein, make just basic with ammonium hydroxide. and digest. 9. Wash niobium precipitate twice with slightly basic ammonium nitrate qolution, then twice with concentrated nitric acid. 10. Trander precipitate to polyethylene cone and dissolve in a wlution 6 Jf in d f u r i c acid and 9 'If in hydrofluoric acid. 11. Repeat steps 5 through 9. 12. Transfer precipitate to platinum crucible, ignite, and n-eigh as Sh20s. CONC LUSION s
Tantalum and niobium can be separated by preferential extraction of the tantalum into diisopropyl ketone from mineral acid-hydrofluoric acid aqueous systems. Siobium may also be separated from nearly all other elements by extraction from solutions suhstantiallg higher in acidity and hydrofluoric acid concentrat ion. ACKNOWLEDGBlENT
The authors wish t o thank R. S. Gilbert, IV. H. Hutchin, and Margaret Servik for their assistance in the experimental work. This n ork was done under the auspices of the U . S. Atomic Energy Commission. LITERATURE CITED
(1) Miher, G . W. P , , and Wood. -4.J., Ministry of Supply, Great Britain, Atoniic Energy Research Establishment, rnczassified Rept. C I R 895 (1952). (2) Servik, W. E., private communication. (3) Wood, G. A., Ministry of Supply, Great Britain, Chemical Research Laboratory, Cnclassified Rept. CRL/AE-62 (1960); obtainable from Technical Information Division, U. S. dtomic
Energy Commission, ORE, Oak Ridge, Tenn. RECEIVED f o r review .January 13, 1933. Accepted July 2 2 , 1953. Report 2009.
UCRL
Precipitation of Iodates from Homogeneous Solution Separation of Thorium Iodate C l W L E Y R . STIYEl
. ~ N DLOUIS
GORDOY
D e p a r t m e n t of C h e m i s t r y , Syracuse I.nicersity, Syracuse 10, 3..E'.
i method was desired for the synthesis of iodate ion in homogeneous solution to be used for the precipitation of dense insoluble iodates. Thoriunl iodate mal he precipitated from homogeneous solution in a dense and granular form with iodate produced by the reduction of periodate with ethjlene gljcol, which is slowl? produced by the h>drol>sisof 6h>drox>eth? 1 acetate. The precipitate thus obtained is easil! washed and filtered. With a single precipitation less contamination b> foreign ions is
T
HE use of the iodate ion as a precipitant has been limited,
although methods utilizing iodate in nitric acid solution have been described for thorium ( 9 ) , cerium(1V) (Z), and titanium ( I ). As the iodate ion can form insoluble compounds with several cations, other methods could be developed-zirconium iodate ( 1 6 )has been characterized as almost insoluble in nitric acid solution and precipitation of iron(II1) as the iodate (3)has been suggested as a separation from aluminum.
' Present address. E. I
d u Pont de Piemours & Co., Inc., Wilrnington, Del
encountered than in the conventional heterogeneous method. Upon a double precipitation, this method effects quantitative separation of thorium from large amounts of rare earths and phosphate. Because of increased efficiency of separation, an improved procedure is possible for the determination of thorium in monazite sand. As there are other insoluble iodates, this method also presents possibilities for improving the quantitative separation of other cations which normally form gelatinous iodates.
The eytremely gelatinous character and the concomitant coprecipitation b?- such iodates have perhaps been deterrent factors in the development of iodates as precipitation forms. The physical characteristics of such precipitates can be markedly improved b y precipitation from homogeneous solution ( 4 , 1 7 ) . This has already been accomplished with cerium (19 ) , thorium ( 5 ) ,and zirconium (8). Cerium(II1) does not form an insoluble iodate, but it can be slowly oxidized t o cerium(1V) in the presence of iodate to form a
