the half lives are 77 hours for tellurium132 and lf33 hours for uranium-237, it is possible to let the former decay so that the latter can be counted. This decay method is practical only if the initial uranium activity is greater than or equal to the technecium activity. The uranium-237 in sample 7 was determined in this manner. An anion exchange separation of tellurium from uranium is now being investigated. Molybdenum. T h e molybdenum99-technecium-99 pair contained no significant y-ray impurity and in most cases was still in equilibrium immediately after elution with 12N nitric acid. Therefore, a n initial y-ray count in the scintillation well counter was sufficient. I n one or two samples a few per cent of the technecium daughter was not in this fraction, and it was necessary to wait 24 hours for the equilibrium measurement.
for sample 6. The precision in the direct method compares favorably with the other results. The uranium-237 determinations by the two methods are within 2%. The zjrconium-95 and niobium-95 counting rates show a precision to about 2y0 for the triplicate values.
ACKNOWLEDGMENT
The author is indebted t o E. C. Freiling and N. E. Ballou for competent advice and Edith Scadden for performing the radiochemical molybdenum analyses.
SUMMARY
The direct sequential elution procedure gives quantitative yields for molybdenum, zirconium, niobium, neptunium, and uranium activities in complex radionuclide mixtures from neutron bombardments of uranium. The y-ray purity of the molybdenum and neptunium is greater than 99%, whereas the contaminants found in the zirconium and niobium fractions can be tolerated by using y-ray spectrometry. The uranium activity is mixed with the tellurium-132-iodine-132 pair and usually requires further purification. The main advantage of the method is reduction in time due to elimination of tracer and carrier addition, pre-ionexchange chemistry, subsequent yield determination, and decay measurements. If a flow rate of 1 ml. per 3 to 5 minutes is maintained, several samples in concentrated hydrochloric acid can be analyzed in about 6 hours. A large fraction of this time can be spent in other work, as the columns require very little attention. Many other fission elements are adsorbed in Dowex 2 from concentrated hydrochloric acid solutions ( 4 ) ; some of these will be investigated for inclusion in the sequential elution procedure.
COMPARISON WITH STANDARD PROCEDURES
The analytical results are given in Table 11. The direct elution data were obtained in triplicate. For comparison the molybdenum-99, uranium-237, and most of the neptunium-239 activities were determined on similar aliquota by standard radiochemical procedures. The zirconium-95 and niobium-% counting rates were obtained by adding the pulses in the channels under the peak in the y-ray spectrum obtained from the 256-channel spectrometer. For neptunium-239 and moIybdenum99 the average relative activities from both procedures agree within l%,except for a 5% difference in the molybdenum
LITERATURE CITED
( I ) Bunney, L. R., Ballou, N. E., Pascual, J., Foti, S. C., A s . 4 ~ .CHEV. 31, 324 (1959). (2) Connally, R. E., Zbid., 28, 1847(1956). (3) Hague, J. L., Broir-n, E. D., Bright, H. A., J . Research Nntl. Bur. Standards 53,261 (1954). (4) Hicks, H. G., Gilbert, R. S., Stevenson, P. C., Hutchin, W. H., Livermore Research Laboratory, Rept. LRL-65 (1953). (5) Huffman, E. H., Lilly, R. C., J . -4m. Chem. SOC.71, 4141 (1949). (6) Ibzd., 73, 2902 (1951). (7) Huffman, E. H., Osnalt, R. L., 'h7illiams, L. A., J . Inorg. & ,I-uclear Chem. 3, 49 (1956). (8) Kraus, K. A., Moore, G. E., J . Am. Chem. SOC.71, 3855 (1949). (9) Zbid., 73, 9 (1951). (10) Ibid., p. 13. (11) ZbLd., p. 2900. (12) Zbid., 77, 1383 (1955). (13) Kraus, K. A., Nelson, F., Moore G. E., Ibad., 77,3972 (1955). (14) PIIeloche, V. E., Preues, -4. F., ANAL.CHEM. 26, 1911 (1954). (15) Wish, L., Rowell, XI., L'. 8. Xaval
Radiological Defense Laboratory, Tech Rept. USNRDL-TR-117 (1956).
RECEIVEDfor review May 12, 1958. Accepted December 15, 1958. Division of Analytical Chemistry, Symposium on Radiochemical .4nalysis, 133rd Meeting, ACS, San Francisco, Calif., -4pril 1958.
Qua nt it at ive Rad io c hemicaI An a lysis by 1on Excha nge Anion Exchange Equilibrations in Phosphoric Acid Solutions E. C. FREILING, JUAN PASCUAL, and A. A. DELUCCHI'
U. S. Naval Radiological Defense laboratory, b The applicability of phosphoric acid solutions to the quantitative anion exchange separation of tellurium from uranium and neptunium has been investigated. The equilibrium distribution coefficients of cesium, strontium, cerium(lll), zirconium(IV), teIIurium(IV), cerium(lV), neptunium(lV), niobium(\/), molybdenum(VI), and uranium(V1) between Dowex 2 resin in the phosphate form and various strengths of phosphoric acid solutions have been determined. These elements fall into three groups. The first, cesium and tellurium(lV), does not favor the resin
330
ANALYTICAL CHEMISTRY
Son Francisco 24, Calif.
phase even a t 0.1N phosphoric acid. The group composed of strontium, cerium(lll), and cerium(lV) is weakly adsorbed a t low phosphoric acid conKd < l o ) ; the recentrations (4 maining elements are strongly ad1000). The adsorption sorbed ( K d of all elements studied decreases monotonically with increasing phosphoric acid concentrations. Dilute phosphoric eluents therefore show promise for incorporating tellurium in the sequential scheme of quantitative radiochemical analysis developed by
Wish.
I
YEIRS anion exchange resin equilibration studies in pure and mixed hydrochloric, hydrofluoric, nitric, and sulfuric acids have been fruitful sources of potential and actual radiochemical separations ( I , 2, 4 ) . Kraus and ?\Telson (2) point out the relatively little attention given to phosphate media, although Marcus has described studies of the Do\Vex 1-XlO-uranyl phosphate system (3). This conimuni-
x RECEST
I Present address, Department of Chemistry, Vniversity of California, Berkeley 4,
Calif.
cation reports the results of equiiibration studies in phosphoric acid solutions with cesium, strontium, cerium(lII), cerium(IT), neptunium(IV), zirconium(IV), tellurium(IV), niobium(V), molybdenum(VI), and uranium(V1). The applicability of phosphoric acid eluents to the incorporation of tellurium in the radiochemical scheme of Kish ( 4 ) was determined from gamma pulse height distributions of fractions obtained by the stepn ise elution of mixed fission products from Dowex 2 with phosphoric acid solution. Similar experiments on the selective retention of fission products by anion exchange resins in noncompiexing media are in progress. EXPERIMENTAL
Reagents. Analytical grade, 200 to 400 mesh Donex 2-X8, purchased from BioRad Laboratories, was used in all equilibrations. The resin was converted from the chloride to the phosphate form by repeated treatments with approximately 1O S phosphoric acid, then washed with distilled water until the effluent was free from detectable chloride and phosphate ions. The resin was air-dried for approximately 2 weeks, a t which time no further progressive weight loss due to drying could be detwted. Solutions were prepared from Baker's analyzed reagent grade phosphoric acid. Tracer quantities of radioisotopes were used in all equilibrations. The molybdenum-99, uranium-237, and neptunium-239 were obtained from neutron bombardments of uranium-235, The -236, and -238, respectively. products were purified by the method described by Kish (4) and checked for purity by y-ray pulse height distribution and decay measurements. The radionuclides strontium-89, zirconium95, niobium-95, tellurium-132, and cerium-144 were purchased from Oak Ridge Kational Laboratories. Equilibration Procedure. Stock solutions of tracers were prepared as dilute phosphoric acid. T h e zirconium-95 was purified from the niobium95 daughter just prior t o use. Equilibrations were carried out in 30-ml. polyethylene, screw-cap bottles, using 15 ml. of solution. I n the cases of cesium, strontium, cerium(III), and cerium(IV), 5 grams of resin were used and equilibration lasted 18 hours. I n all other cases a preliminary run was made using 1 gram of resin and a 4-hour equilibration. This preliminary run was used to calculate the amount of resin required to give maximum accuracy-Le., a n even distribution of activity between the resin and liquid phases-in subsequent experiments which were carried out for 18 hours. All equilibrations were made by shaking a t room temperature (25" i 2" C.). After equilibration, the resin and liquid phases were separated by filtration through sintered-glass filters. Except for zirconium-95, sufficient time for daughter activities to come to equilibrium with their parents was allowed when necessary. Resin ad-
sorption was determined by comparing the activity of a 5-ml. aliquot of this filtrate with that of 5-ml. aliquots of control solutions. Activity measurements were made using a crystal welltype scintillation gamma counter. EQUILIBRATION RESULTS AND DISCUSSION
The equilibration results were calculated as Kd, the activity per gram of resin divided by the activity per milliliter of solution, and corrected for preferential solvent absorption (Figure 1). The species studied fall into three groups. The first group, consisting of cesium(1) and tellurium(VI), does not favor the resin phase to any great extentdown to a concentration of 0.lN phosphoric acid. The second group, consisting of strontium, cerium(III), and cerium(IV), is weakly adsorbed a t low phosphoric acid concentrations (4 < Kd < 10). The third group, consisting of all the other elements studied, adsorbs strongly on the resin (Kd > lo3) in 0.1S phosphoric acid. The adsorption of all species studied decreases monotonically with increasing phosphoric acid concentration. The data obtained with neptunium are presented as two curves. The upper curve n-as obtained with neptunium which had been back-extracted from a thenoyltrifluoroacetone solution into phosphoric acid, and probably best represents the behavior of neptunium(1T'). The lower curve was obtained by reducing neptunium with hydroxylamine hydrochloride, and the discrepancy is probably due to perturbing the system by the introduction of small quantities of this reagent along with the added activity. Xeptunium(1V) obtained by reduction of the neptunium stock solution with sulfur dioxide follows the thenoyltrifluoroacetone curve above 61V phosphoric acid, but below this concentration the results differ widely and erratically. A fourth method of producing neptunium(IT-) consisted of boiling stock neptunium solution in 6A' phosphoric acid to remove other anions and convert the neptunium to neptunium(1V) through stabilization of the IV state by phosphate complex formation. Points obtained by this method do not deviate appreciably from the thenoyltrifluoroacetone curve until the phosphoric acid concentration drops to 3iy. The shape of the uranium(1V) curve is similar to that obtained by hIarcus using Dowex 1-X10. However, his distribution coefficients are lower by factors of 2 a t 0.1M phosphoric acid to 50 a t 3111 phosphoric acid. It is evident from the number of points for a given element shown in Figure 1 that much greater care was exercised in determining Kd for the more strongly adsorbed species. The curves for cesium, strontium, cerium(III), and cerium(1V) bear checking before being applied to problems other than analytical separations. The designation cerium(1V) refers to the initial state of the cerium. The addition of reagents to ensure the preservation of the IV state would so alter the experimental conditions that the behavior of other oxidiz-
,o" 10-1
I
I
,
,
'
I
h
,
0 *.PO1
Figure 1. Equilibrium distribution of fission products, uranium, and neptunium between Dowex 2 and phosphoric acid solutions
able species in this environment would have to be redetermined in order to obtain a firm basis for predicting separations. The applicability of this system to the radiochemical separation of tellurium is evident from the curves shown in Figure 1. Incorporation of this system into the sequential separation scheme of Wish (4) and the details of separations made with this eluent will be described in a forthcoming communication. ACKNOWLEDGMENT
The authors are grateful to K. E. Ballou, of this laboratory, for continued encouragement, and Frederick Nelson, Oak Ridge Sational Laboratory for valuable comments. LITERATURE CITED
(1) Bunney, L. R., Ballou, X. E., Pascual, J., Foti, S. C., AKAL. CHEM.31, 324 (1959). (2) Kraus, K. A., Nelson, Frederick, .4nn. Rev. Nuclear Sci. 7, 31, 1957. (3) Marcus, Y., 2nd United Nations International Conference on Peaceful Uses of Atomic Energy, Session A-15, P/1605, Geneva, Switzerland, 1958. (4)Wish, L., ANAL.CHEJI.31,326 (1959). RECEIVEDfor review May 23, 1988. Accepted December 15, 1958. Division of Analytical Chemistry, Symposium on
Radiochemical Analysis, 133rd Meeting, ACS, San Francisco, Calif., April 1958. VOL. 31, NO. 3, MARCH 1959
331
