6th Annual Summer Symposium-Less Familiar Elements
Solvent Extraction Separations of Zirconium and Niobium EDITH M. SCADDEN AND NATHAN E. BALLOU U . S. Naval Radiological Defense Laboratory, San Francisco 24, Calif.
counters which utilized 90% argon-10% carbon dioxide as the counting gas. p H and titration curves Rere measured with a Beckman Model G p H meter and glass electrode.
The extraction characteristics of a iariety of soherit systems hale been examined for the purpose of finding a method for quickly and efficiently isolating zirconium and niobiumfrom allother fission product elements. The mixed butyl phosphoric acids in di-nbutyl ether were found effective for this purpose. Conditions have been established for rapid11 and efficiently separating both macro and carrier-free concentrations of these t w o elements from each other and from nearly all other fission product elements. Application of the solvent sjstem to other separations is indicated. Conditions for simply separating the 3 ttrium from the lanthanum group rare earths have been found.
PRELIMIN4RY EXPERIXIEhTS
R
ADIOCHEMICXL procedures for determining zirconium and niobium in a mist,ure of fission product elements have been based mainly on precipitation reactions (1-3, 5 ) . Development of solvent extraction procedures specific for zirconium and niobium appeared worth while, as it seemed that significant improvement in speed and efficiency of determinations might well be attained by this type of separation. Because solvent estractions are frequently as efficacious for isolating elements at very low as well as at high concentrations, utilization of the results of t,hese studies in separating carrier-free concentrations-i.e., no added carrier-of zirconium and niobium also seemed a definite possibility. Consequently, extraction properties of zirconium and niobium in several organic solvents were investigated. Speed and simplicity of operation and application of results to separations of other elements were sought. APPARATUS AND MATERIALS
Radioisotopes of all but four of the elements studied (palladium, molybdenum, holmium, iodine) were employed as tracers. T h e radionuclides used are: Zrg5, Nbg5, Gea9, Ge“, As74, Se75, Sr59, y 9 1 , Ru106, RhIOZ, Aglll Cdl091 In114, Sn113 Sb125 Te127 Tel29 Cs137, La140, Ce144, and Ta152. They were either purchased from the Oak Ridge National Laboratory or isolated from the appropriate element irradiated with deuterons a t the 60-inch cyclotron of the Crocker Laboratory, University of California. I n each case carrier-free preparations were obtained either as the purchased item or b y special chemical separations on the irradiated material. The organic compounds used were of the best grade supplied by the Eastman Kodak Co., and all other chemicals were of reagent grade quality. The “butyl phosphoric acid” obtained commercially is a mixture of mono- and dihydrogen butyl phosphate. I n the commercial mixtures obtained, these two compounds were in the ratio of about 1 t o 1.5, as shown by titration with sodium hydroxide. A 70% solution ( v / v ) of the mixed acids in di-n-butyl ether was enriched in the di-n-butyl ester by water washings (6). Four such washings yielded an ether solution containing 4.5 moles of di-n-butyl ester to 1 mole of mono-n-butyl ester. This solution was then diluted with di-n-butyl ether to obtain either 0.6M or 0.06M solutions of the di-n-butyl ester. Beta- and gamma-ray counting was done on either standard commercially available Geiger-Muller counters or on proportional
A variety of compounds under various e~perimentalconditions was studied in search of an extractant for zirconium and niobium. The systems investigated are: acetylacetone; trin-butyl phosphate; trichloroacetic acid vith chloroform as the solvent phase; ammonium thiocyanate with ethyl ether; ammonium thiocyanate plus quinoline with ethyl acetate; 2-nitroso1-naphthol Mith ethSl acetate; mandelic acid a i t h ethyl ether, benzene, or amyl alcohol; rn-nitrobenzoic acid with isobutyl acetate amyl alcohol, or tri-n-butyl phosphate; and the mixed mono- and di-n-butyl phosphoiic acids in n-butyl ether. I n all e\;perinients the concentrations of zirconium and niobium were 1 mg. per ml unless otherwise stated. Acetylacetone did not extract either zirconium or niobium from a 0.7X hydrochloric acid solution. Equal volumes of the two phases were used and mixing was for 10 minutes. Neither zirconium nor niobium was extracted in 10 minutes by chloroform from an equal volume of aqueous solution 0.5M in trichloroacetic acid, 0.5M in sulfuric acid, and 2.11 in ammonium sulfate. Diethyl ether (presaturated with thiocyanic acid) did not extract zirconium from 5.0 &I ammonium thiocyanate solutions which were 1 to 4 JI in hydrochloric acid and 0.05N in oxalic acid; extraction as for 15 minutes and the volume ratio of organic to aqueous phase was 6 to 1. Under these conditions about 30% of the niobium was extracted; the extent of extraction of niobium has been shown to decrease as the niobium concentration increases ( 4 ) . It is quantitative at a concentration of about 1 y per ml. of niobium. Zirconium and niobium were not extracted by ethyl acetate from 0.25M quinoline-0.5M ammonium thiocyanate solutions a t hydrochloric acid concentrations of 0.1 to 6M. The mixing time was 10 minutes and equal volumes of the two phases were used.
Table I.
Extraction Properties of Zirconium and Niobium with Tri-n-but11 Phosphate
Conditions. Carrier-free concentrations of Zr and S b : aqueous phase. mixing time, 35 minutes: volume
0 . 0 0 2 ~ ooxalic acid, variable HSOa: ratio (org./aq.), 1 t o 1 Concn. of HNOl, S 1 2 24 40 Z r extracted, 7%
S b extracted. 7%
19
25
4 65
27
6 87
41
10 93 63
12
96 88
An ethyl acetate solution which was 0.01M in 2-nitroso-lnaphthol did not extract zirconium but extracted about 60% of the niobium from equal volumes of aqueous solutions 1 to 8M in hydrochloric acid; mixing time was 5 minutes. Mandelic acid was ineffective in extracting zirconium and niobium out of 0.5M sulfuric acid-1M ammonium sulfate solutions into amyl alcohol or out of 0.1M hydrochloric acid2M sodium chloride solutions into benzene or diethyl ether. The volume of organic phase was twice that of the aqueous phase
1602
V O L U M E 25, NO. 11, N O V E M B E R 1 9 5 3
1603
and mixing was for 10 minutes. There was, however, partial extraction b y amyl alcohol of both zirconium and niobium from an aqueous mandelic acid-0.002M oxalic acid solution a t a pH of 2. Neither zirconium nor niobium was extracted in 10 minutes by amyl alcohol or isobutrl acetate 0.2.V in m-nitrobenzoic acid from an equal volume of aqueous solution 0.1M in hydrochloric acid and 2M in sodium chloride. When tri-n-butyl phosphate was used as the solvent containing the m-nitrobenzoic acid, about 15 and 5y0 of zirconium and niobium, respectively, were extracted A series of measurements v a s made of the extraction of carrier-free concentrations of zirconium and niobium by tri-n-butyl phosphate from nitric and hydrochloric acid solutions of various concentrations. The extraction of both elements increased as the acid concentrations increased. The behavior was similar with both acids. Results of the studies with nitric acid solutions are given in Table I. Although moderately good extractions can be obtained a t the high acid concentrations, separation of the two elements is not feasible under the conditions investigated.
Table 11. Extraction of Niobium as a Function of Monorc-butyl Phosphoric Acid Concentration Conditions. Carrier-free Zr a n d K b ; aqueous phase, 1M "0s. 0.004M H1C204,with a n d without HzOz;, organic phase, 0.5.V DBPAa; volume ratio (org./aq.), 1:1 ; 5-minute mixing time
No Hz02 Concn. of Sb hIBPA b , extracted,
1M
7%
3% HzOz Concn. of
MBPA, b M 0.47 0.18 0.13 0.11 0.003
Sb extracted, 6 -
67 66
58 a?
21
Di-n-butyl phosphoric acid. b Mono-n-butyl phosphorir acld.
a
lo%, respectively, of the niobium; the degree of extraction of zirconium was not influenced by these variations in times. Addition of hydrogen peroxide reduced the extraction of niobium. From aqueous solutions 1M in nitric acid, 0.004M in oxalic acid, and 3% in hydrogen peroxide, less than 1% of the niobium was removed by the organic phase mith mixing periods up to 10 minutes. The behavior of zirconium was unaffected by the presence of hydrogen peroxide. Measurements of the extraction of carrier-free amounts of zirconium and niobium by 0.6M di-n-butyl phosphoric acid showed both of them to be efficiently removed. For example, 99% of the zirconium and 95% of the niobium were extracted by 0.6M di-n-butyl phosphoric arid from a 1M nitric acid- 0.00434 oxalic acid solution, the degree of extiaction of niobium w s cut to 60% by a ?.yoconcentration of h j drogen peroxide in the aqueous phase. 11-hen the zirconium and niobium were in a 1M sulfuric acid-2.5M ammonium sulfate-0.004M oxalic arid solution, 0.631 di-n-butyl phosphoric acid extracted 99 and 95% of them, respectivelv. Introduction into such a sulfate solution of hydrogen peroxide reduced the degree of niobium extraction but not that of zirconium; concentrations of 6% hydrogen peroxide reduced the niobium extractions to about 80%. Information on the role of mono-n-butyl phosphoric acid and di-n-butyl phosphoric acid in the extraction of zirconium and of niobium is of interest. A series of experiments x-as performed in which there was measured the degree of extraction of carrier-free niobium by an organic phase of constant di-n-butyl phosphoric acid concentration and of variable mono-n-butyl phosphoric acid concentrations. The determinations were made with 1M nitric acid-O.004M oxalic arid solutions both with and without 3% hydrogen peroxide; the organic solvent was 0.5M in di-n-butyl phosphoric acid, and the concentrations of mono-n-butyl phosphoric acid varied from 0 . 4 i N to 0.0006M. The extent of niobium extraction dropped smoothly from 96 to i 5 % in the absence of hydrogen peroxide and from about 67 to 20% in the presence of 3y0 hydrogen peroxide. These results are summarized in Table
11. The preliminary experiments TI ith the mixed mono- and di-nbutyl phosphoric acids indicatedgood solvent extraction properties for zirconium and niobium. Consequently, more extensive measurements were ni:ide. EXTR4CTIOVS BY nIIXED BUTYL PHOSPHORIC ACIDS
Carrier-Free Concentrations of Zirconium and Niobium, Concentrations of both 0.06 M and 0.6 M of di-n-butyl phosphoric acid in di-n-butyl ether were used in these studies. Unless otherwise stated, all experiments in which the concentration of only din-butyl phosphoric acid is given involved the use of a solution in which the mole ratio of di-n-butyl phosphoric acid to mono-nbutyl phosphoric acid was 4.5 to 1. All experiments mere performed a t room temperature; 5 ml. each of organic and aqueous phases were vigorously agitated with a platinum nire stirrer in a glass centrifuge cone. Phases were rapidly and cleanly separated by centrifugation. Mixtures containing known amounts of y-ray activity of zirconium-95 and of niobium-95 were used. The degree of extraction of each was determined by measuring the total y-ray activity of each phase and the 7-ray activity of zirconium isolated from the aqueous phase as barium fluozirconate (2).
Extraction of zirconium and niobium in carrier-free concentrations by 0.06Ji di-n-butyl phosphoric acid from aqueous solutions 1M in either nitric, hydrochloric, perchloric, or sulfuric acid and 0.004M in oxalic acid was first measured. -4single extraction removed at least 99% of the zirconium and left about 98% of the niobium in the aqueous phase. The effect of time of mixing was found to be of importance in the extraction of niobium but not of zirconium. I n the case of nitric acid solutions, mixing times of 1, 2, and 5 minutes resulted in extraction of 2, 5, and
A41thoughthe concentration of di-n-butyl phosphoric acid seems to be the major factor in the extraction of niobium, it can be seen that mono-n-butyl phosphoric acid also plays some part in its extraction. Similar experiments mere performed to study the effect of mono-n-butyl phosphoric acid concentrations on the extraction of zirconium. As is shown by Table 111, the role of mono-n-butyl phosphoric acid is minor in comparison to that of di-n-butyl phosphoric acid. Elucidation of the reactions occurring among the constituents of these syEtems mupt await more detailed studies.
Table 111. Effect of Mono-n-butyl Phosphoric Acid Concentration on Extraction of Zirconium Conditions. Carrier-frqe oxalic acid: volume ratio Concn. of DBPAa, 1lf 0.5 0.05 0.005 0,005
Zr and Nb; aqueous phase, 1 X HN08-0.004M (org./aq.), 1:l; 5-minute mixing time. Concn. of Zr b MIBPAb, Extracted, Extracted
M
07
70
0,003 0.0003 0.00003 0.0011
99 99
78
10
64 45
1 1 1
Di-n-butyl phosphoric acid. b Mono-n-butyl phosphoric acid.
a
Macro Concentrations of Zirconium and Niobium. The extraction of zirconium and niobium (1 mg. per ml. of each) by the mixed butyl phosphoric acids (mole ratio of di-n-butyl phosphoric acid to mono-n-butyl phosphoric acid 4.5 to 1) in di-n-butyl ether was measured. Exchange between carrier and tracer zirconium and niobium was accomplished by adding hydrofluoric acid (8);
ANALYTICAL CHEMISTRY
1604 sulfuric acid was added and heated to fuming to expel the hydrofluoric acid before the extractions. The solution was made 131 in sulfuric acid, 2.5M in ammonium sulfate, 6% in hydrogen peroxide, and about 0.004M in oxalic acid. A 1 6 m h u t e extraction of this solution by an equal volume of 0.06M di-n-butyl phosphoric acid resulted in more than 99% of the zirconium and 5% of the niobium going into the organic phase. The initial contact of the two phases produced a precipitate a t the interface which dissolved upon mixing; the organic phase was pale yellow and the aqueous phase clear. Extraction of niobium was reduced by decreasing the concentration of monon-butyl phosphoric acid. An organic phase 0.06M in di-nbutyl phosphoric acid and 0.0003M in mono-n-butyl phosphoric acid extracted 98% of the zirconium and less than 1% of the nicbium Kith a 15-minute mixing period. Both zirconium and niobium can be extracted with the more concentrated di-n-butyl phosphoric acid solutions. In the absence of hydrogen peroxide 98% of the niobium and more than 99% of the zirconium were removed by a 5-minute extraction. Six per cent hydrogen peroxide reduced the extraction of niobium to about 937& The organic phase was colored bright yellow in both the presence and absence of hydrogen peroxide; a white precipitate gradually formed in the organic phase as it stood for about an hour.
Table IV. Extraction Properties of Carrier-Free Concentrations of Fission Product Elements with Mixed Butyl Phosphoric Acids Conditions. Aqueous phase, liM HNO3,3% HzOz; 5-minute mixing; volume
di-n-butylphosphoric acid. In carrier concentrations yttrium and holmium are about 95% estracted, while lanthium and cerium are only about 2Q/, extracted. This is a rapid and effective separation method for these rare earths. Further investigations are in progress to determine the extent of separation of other rare earths by this procedure. .-lpplication to isolation of individual rare earth elements from all other rare earth elements by multistage extractions are sought.
Table V. Extraction Properties of blacro Quantities of Fission Product Elements with Mixed Butyl Phosphoric Acids Conditions. Aqueous phase, 1 mg. element per mi., 1M H K h , 2.5M (KH4)zSO4 0.004M oxalic acid 6 % Hz02. volume ratio (org./aq.) 1 to 1. mixing tin;e, 15 minutes with 0.06.V DBPA and 5 minutes wiih 0.6.1; DBPA Elements Extracted __ Concn. of DBPAa, >E%by Jf < 5 7 , by DBPA 5-95c/, by DBPA DBPA o 06 Cs, Sr, Y, La, Ce (1111, 8n (IV) l a % , I n Zr, Iz Ag, Cd, Ge, Se (IV), 85% T e (IV) Sb (1II)b Sb (V), As’ (V), Pd, ‘ R u , Rh, Mo, N b 0 G Cs, Sr, La, Ce ( I I I ) , Ag, Yn (IV) SO%, T a Zr, Nbb, T,Ho, Cd, Ge, Se (IV), T e 35% I n , I2 (IV), Sb (IIIIb, Sb ( V ) , As (V), Pd, Ru, Rh, .\Io a Di-n-butyl phosphoric acid solution in which mole ratio of di-n-butyl phosphoric acid to mono-n-butyl phosphoric acld is 4.5 to 1. b S o hydrogen perolude present. -
~
~
- -~ ______
-___
ratio (org./aq.), 1 t o 1 Elements Extracted Concn. of DBPAa,
M
4 6 % by DBPA
0.06
Cs, Sr, La, Ce ( I I I ) , Ag,b Cd. Ge, Se (IV) T e (IV) Sb ( I I I ) c , Sd (V), As (V), Pdb, Ru, R h .
5-95% b y DBPA
Y -1570, Sn (IV
aO%, Mob 1 5 d
*
>95% by DBPA Zr, I n
Nb Cs S r La i g b Cd Ge AIob23%, Nb 60%, Zr, Nbc, Y, In, Se tIV): -Te ’(IVj, Sd TaC 85% Sn (IV) b (III)C, Sb V), As (V), Pdb, Ru, R 6 a Di-n-butyl phosphoric acid solution in which mole ratio of di-n-butyl phos horic acid t o mono-n-butyl phosphoric acid is 4.5 to 1. b Sn, Pd, and Mo, not carrier-free; their concentrations were 0.5, 3, 8, and 8 y / d . , respectively. c No hydrogen peroxide present. 0.6
&, ~
~
~
~
Re-extraction of Zirconium and Niobium from Di-n-butyl Phosphoric Acid Solutions. Zirconium and niobium were readily removed in either carrier-free or macro amounts from the various di-n-butyl phosphoric acid solutions n ith 451 hydrofluoric acid. Saturated oxalic acid solutions gave very slow and incomplete extractions. 2 M ammonium hydroside removed zirconium and niobium satisfactorily, but acidification of the solution generated an organic phase R-hich held appreciable quantities of zirconium and niobium. Extraction Properties of Other Fission Product Elements with Di-n-butyl Phosphoric Acid. Studies were made of the extraction characteristics of carrier-free and of macro concentrations of other fission product elements with di-n-butyl phosphoric acid. Concentrations of 0.06M and 0.631 di-n-butyl phosphoric acid were used, and the conditions were those employed in isolating zirconium and niobium. Results of the measurements with carrier-free and macro concentrations are given in Table IV and V. It is apparent that zirconium and niobium can be isolated from each other and from nearly all other fission product elements by extractions with the mixed butyl phosphoric acids. Separations of Rare Earths with Di-n-butyl Phosphoric Acid. It is of considerable interest to note the separation of the yttrium group from the lanthanum group rare earths as effected by 0.631
Fractionation of Niobium and Tantalum with Di-n-butyl Phosphoric Acid. Macro concentrations of niobium were partially ieparated from tantalum with 0.6-Wdi-n-butyl phosphoric acid under the conditions indicated in Table V. The effect of concentrations of the several constituents of the system on the tlegree of separation is being studied in search of conditions for iniproved separations. SUMMARY
Of a number of solvent systems eumined, that of the miled butyl phosphoric acids in di-n-butyl ether was found most useful for separations of several of the fission product elements. Conditions for rapidly and efficiently isolating zirconium and niobium from each other and from nearly all other fission product elements have been established; both carrier-free and macro concentrations of the elements can be isolated. Elements of the yttrium group have been separated from elements of the lanthanum group rare earths with 0.6Al di-nbutyl phosphoric acid in di-it-butyl ether. Partial separation of niobium froin tantalum has been attained with 0.6M di-n-butyl phosphoric acid in di-n-butyl ether. LITERATURE CITED
(1) Brady, E . L., and Engelkemeier, D. W., National
(2) (3) (4) (5)
(6)
Nuclear
Energy Series, Div. IV, Vol. 9, “Radiochemical Studies. The Fission Products,” C. D. Coryell and N. Sugarman, eds., Paper 242, pp. 1491-4, 1951. Hume, D. N., Ibid., Paper 245, pp. 1499-503. Katcoff, S., Finkle, B., and Hoagland, E. J., Ibid., Poper 248, pp. 1510-11. .Jr., and Hume, D. N., Lauw-Zecha, A. €3. H., Lord, d. W,, .%SAL. CAEM.,24, 1169-73 (1952). Rteinberg, E. P., Sational Nuclear Energy Series. Dir. IV, Vol. 9, “Radiochemical Studies. The Fission Products,” C . D. Coryell and 9.Sugarman, eds., Paper 243, pp. 1495-7, 1951. Stewart, D. C., and Crandall, H. W.,6. Am. Chem. SOL,73, 1377 (1951).
RECEIVEDfor review July 6, 1953.
Accepted August 21. 1953.
