centrated aluminum nitrate salting agent t o get satisfactory yields in the ether extractions. Therefore, the ether extraction was replaced with the recently developed tri(iso-octy1)amine method (8) which does not require a solid salting agent. While the uranyl-hydroxylamine complex appears strong in alkaline solution, it is rendered ineffective upon the addition of concentrated hydrochloric acid solution prior to the extraction. One cycle of precipitation and extraction steps effected a good decontamination of the uranium-237 but mas erratic, in that small amounts of impurities were detected occasionally. Therefore, the procedure recommended involves two cycles; it yields a uranium-237 product of excellent radiochemical purity when tested on process solutions. Decay studies and gamma scintillation spectrometry were used to check the purity of the uranium oxide product. Typical decontamination data are shonm in Table 11. Gamma spectra of separated uranium-237 were studied to evaluate decontamination factors achieved in the analysis of three reactor samples. This was a precautionary measure to ensure that interference was not caused by some fission product occurring in a chemical state different from that in the tracer solutions described earlier (8).
The scintillation spectrometer employed consisted of a 3 X 3 inch sodium iodide crystal with associated electronic equipment including a 20-channel analyzer. From the spectra of the separated uranium-237, similar to that reported previously (5), the maximum disintegration rates of several fission products were estimated. These disintegration rates were compared with the radiochemical analyses of the samples and the minimum decontamination factors (Table 11) were calculated. Yields averaged 60 to 70 yo. The time required for analysis is approximately 2 hours. The technique previously described (7) of performing extractions in test tubes appeared to be as satisfactory as the conventional use of separatory funnels. The new method has the advantages of speed and elimination of the use of fluoride chemistry as compared with the present method (IO). It should find application in the separation and determination of other uranium isotopes. ACKNOWLEDGMENT
The authors acknowledge the capable assistance of D. K. Smith and P. S. Gouge in testing the procedure. LITERATURE CITED
(1) Bane, R. W., U.
S. Atomic Energy
Table II. Minimum Decontamination Factors Achieved on Actual Samples
Nuclide Mo-99
._ ._ .
Zr-Nb-95 Ru-103 1-131 CS-137 Ba-140 La-140 Ce-141
Decontamination Factors One cycle Two cycles 20 3 . 5 x 102 1 X 102 6 x 102 1 x 102 1 . 5 x 102 2 x 103 1 x 103 1 . 5 ’ X lo4 1 . 5 X lo4 1 x 102
x 102 x 104 x 104 1 x 104
3 2 2
Comm. Declassified Rept., CC-3336 (November 1945). ( 2 j Becker, A., Jannasch, P., Physik. 2. 12.I 1 I19lfi’i. ~
\ - - - -
(3)Brinton, P: H., Ellestad, R. B., J. Am. Chem. SOC.45, 395 (1923). (4) . , Bruce. F. R., Baldwin, W. H., U. S. -4tomic ‘ Energy Comm. Declassified R e d . MonT-199 (October 1946). (5) e e i t h , R. L., Zbid., Unclassified Rept., IDO-16408(July 1957 . (6) Hecht, F., Donau, ., “Anorganische Mikrogewichtsanalyse,”Julius Springer, Vienna, 1940. (7) Moore, F. L., ANAL. CHEN. 2 9 , 448 (1957). (8) Ihzd., 30, 908 (1958). (9) Rodden, C. J., “Analytical Chemistry of the Manhattan Project,” pp. 46-7, McGraw-Hill, New York, 1950. (10) Warren, B., U. S. Atomic Energy Comm. Unclassified ReDt., LA-1721. 244 (September 1954). RECEIVED for review October 6, 1958. Accepted January 7 , 1959.
1
Determination of Uranium and Beryllium in Fused Fluoride Systems N. E. ROGERS and W. D. PRATHER Mound laboratory, Miornisburg, Ohio
b A method is described for the quantitative separation and determination of uranium and beryllium in the presence of macro quantities of sodium in a ternary system of fused fluorides. The fluoride ion is volatilized as fluoboric acid during the dissolution of the dried, mixed salts with acids. Sexivalent uranium is separated from beryllium and sodium by the electrolytic deposition of the uranium as a hydrous oxide on a platinum electrode from a hot ammonium acetate solution a p H 4.0. The beryllium remains in the plating solution with the sodium, and is determined as the hydroxide. Both the uranium deposit and the beryllium hydroxide precipitate are ignited and weighed as their oxides. Sodium is determined by flame photometer or calculated as the difference between the combined weights of the uranium and beryllium fluorides and the original sample weight.
A
determination of the components in the fused salt ternary system, UF4-BeF2-NaF, was required in the determination of the phase relationships of the system. This report discusses a satisfactory analytical procedure which was developed for the quantitative determination of uranium and beryllium in the presence of macro quantities of sodium in such a fused salt system. Previously reported methods for the separation and determination of uranium from beryllium have been limited to a comparatively few gravimetric prccedures. Wunder and Wenger (9) reported the chemical separation of uranium from beryllium by doubleprecipitation of uranium with hydrogen peroxide in chloride solutions followed by the determination of beryllium as the hydroxide. Complexing the uranyl ion with ammonium carbonate ( I ) and determining the beryllium as a basic carbonate N BCCURATE
were tried unsuccessfully in this laboratory. In addition t o giving erratic results, the method was tedious and timeconsuming. Of the general separation techniques, electrolytic methods seemed to offer the most promise and were investigated more thoroughly than other methods. The determination of uranium by electrolysis has been known for many years. In 1880, uranium was reported to be quantitatively electroplated on platinum in a hot ammonium acetate solution ( 7 ) . Kollock and Smith ( 6 ) , in 1901, described the electrolytic separation of uranium from the alkaline earth elements, barium, calcium, magnesium, and zinc. I n spite of the excellent results reported in the early part of the century, additional data on the electrodeposition of uranium have been very scanty during the past 50 years ( 2 , 3). Although electrolysis had not been previously employed specifically for the VOL. 31, NO. 6, JUNE 1959
1081
separation of uranium from beryllium and sodium, preliminary experiments indicated it to be suit'able. The results obtained from subsequent experiments conducted under controlled conditions were excellent, with little or no interference from foreign substances in the plating solution. The procedure reported here, which involves electrodeposition of uranium from a hot ammonium acetate solution, precipitation of beryllium hydroxide, and determination of sodium with the flame photometer or by difference, gives consistent, quantitative results. PROCEDURE
Accurately weigh samples of the mixed fluoride salts in duplicate or triplicate in flat-bottomed platinum dishes. A convenient sample size is 200 mg., which should contain no less than 10 mg. of uranium or 4 to 5 mg. of beryllium for quantitative results. Sodium may be tolerated up to about one half of the tot'al sample Tveight without seriously affecting the beryllium determination. Dissolve the neighed fluoride samples with acids by treating the sample with approximately 10 nil. of concentrated nitric acid, 5 ml. of a saturated solution of boric acid, and 2 ml. of concentrated sulfuric acid. Digest the sample on a steam bat'h until it is entirely dissolved. The addition of more nitric acid may be necessary, particclarly if the sample is composed chiefl>- of uranium fluoride. Evaporate the sample until fumes of sulfur trioxide appear, transfer the platinum dish to a hot plate, and carefully evaporate the contents nearly to dryness. Fluoboric acid (HBFI) is completely volatilized from the sample during the hot acid treatment, and the uranium is oxidized to the plus-six valence state. The latt'er form is necessary for the electrodeposition. Add a little distilled water to the residue in the platinum dish, heat to effect solution, and transfer the solution quantitatively to a 400-ml. tall-form beaker with distilled water. The volume of the solution should be approximately 275 ml. Cool to room temperature and add 1 to 1 ammonium hydroxide dropwise to the solution, with stirring, until a permanent precipitate is formed (approximately p H 8.0). Immediately add acetic acid t o the mixture and adjust it to p H 4.0, using a p H meter. The solution is now ready for the plating of uranium. The platinum-gauze electrodes, 45mesh, are cylindrical in shape, 1.5 inches in diameter, and 1.5 inches high. The stem of the gauze electrode is a 16- to 18gage platinum wire, approximately 5 inches in length. A heavy platinum Ivire, shaped in the form of a conical helix, serves as the anode. Suspend a tared platinum gauze from the cathode on a n electroplating unit such as a Fisher Electroanalyzer. Connect the anode to the positive terminal, carefully centering it within the cathode. Place the 400-ml. beaker containing the buffered solution in a beaker-type elec1082
ANALYTICAL CHEMISTRY
tric heating mantle and raise the beaker until the solution around the gauze is within one or tm-o wire widths of the top of the gauze, adding more distilled water if necessary to obtain the correct solution level. Apply heat to the solution and start slow mechanical stirring. When the solution reaches the temperature of slow vaporization, turn on the plating current and adjust to about 0.25 ampere. This will usually require about 3 to 4 volts. Most of the uranium in solution \vi11 deposit on the gauze after 1 hour of plating. Continue the electrolysis, however, for 2 hours to assure complete deposition. During the course of electrolysis, maintain the temperature of the plating bath a t 80" to 85" C. Replace the solution lost by evaporation by dropwise addition of distilled miter throughout the plating period. At the end of 2 hours, stop the heating and mechanical stirring operations, and lower the beaker of hot solution carefully to a point just below the gauze. K i t h the current still on, thoroughly wash the electrodes and the stirring rod with a fine jet of distilled water, taking precautions to lose none of the solution. Filter the plating solution through a coarse paper to recover granules of the uranium deposit which might have fallen off during rinsing. Place the filter paper and gauze electrode in a wide-mouthed retaining cup. The purpose of this cup is t o prevent the loss of uranium during the ignition and weighing steps. The container, previously weighed with the gauze electrode, may be constructed of any material that will withstand the ignition temperature of 950" C. and maintain a constant weight. I n the present work, platinum cups, 2.5 inches in diameter and 2 inches high, were used. Start heating the electrode assembly in a muffle furnace and slowly raise the temperature by 25" stages until the paper is completely charred (450" to 500" C.).Finally raise the temperatureof the furnace to 950 "C.. and maintain i t a t that heat for a t least 4 hours to assure complete conversion of the uranium to ' L T 3 0 8 . Remove the gauze and its container from the furnace, cool to room temperature in a desiccator, and n-eigh. The gauze and container must be weighed quickly, as the ignited t T 3 0 8 absorbs moisture rapidly. A good practice is to have the approximate weights placed in the balance pan before the gauze is removed from the desiccator. The final weight of uranium as U 3 0 8 on the gauze may be converted to the weight as UF, by multiplying by the factor, 1.12. Heat the plating solution, which should be clear (a yellow tint indicates the incomplete removal of uranium) t o 65" C. and precipitate the beryllium as the hydroxide ( 4 ) b y the dropwise addition of 1 to 1 ammonium hydroxide solution to a slight excess ( p H 8 to 9). Heat the solution containing the precipitated beryllium hydroxide nearly to boiling to aid in the coagulation of the precipitate. Cover the beaker with a watch-glass and let i t stand for a t least 4 hours. or preferably, overnight.
Filter the beryllium hydroxide precipitate on a No. 40 K h a t m a n filter paper. Scrub the walls and bottom of the precipitation beaker thoroughly with a policeman, using small portions of a hot 2% ammonium nitrate as the washing solution. Wash the precipitate on the filter five or six times with the hot ammonium nitrate wash solution. T o obtain a purer product, a reprecipitation of the beryllium hydroxide may be carried out. I n performing the double precipitation, carefully dissolve the beryllium hydroxide precipitate in its filter paper with approximately 10 ml. of concentrated nitric acid from a dropping pipet. K a s h the filter paper several times with distilled water. Drain the dissolved beryllium and the washings from the filter into the original precipitation beaker. Dilute the contents of the beaker to about 275 ml., heat to 65" C., and precipitate with ammonium hydroxide as before. Ignite the beryllium hydroxide precipitate to constant weight in a tared platinum or porcelain crucible a t 950" C. [Data obtained after this nork was completed indicate that if the ignition temperatureisraised to 1050" to 1100°C. (8),a single hydroxide precipitation is adequate to produce quantitative results.] Cool in a desiccator and weigh to determine the weight of BeO. RIultiply this weight by 1.88 for conversion t o the weight of the fluoride, BeF2. Subtract the combined weights of the UF, and BeF2 from the sample )?-eight to calculate the K a F content of the sample. For more accurate sodium determinations, the filtrate from the beryllium precipitations may be analyzed n ith precision by use of the flame photometer (6). INTERFERENCES
The dissolved samples should be free of metallic ions that may be electroplated in an acidic solution and lead to contamination of the uranium deposit. bmong the many objectionable elements are Icad, copper, tin, bismuth, and silver. The alkaline earth and alkali metal elements may be present in moderate amounts. The chloride ion should be absent because of its attack on the platinum electrodes. Other elements, with the exception of uranium, that are precipitated by sodium hydroxide, must be absent in the sample solution in nhich beryllium is to be determined gravimetrically. DISCUSSION
Hot, 72'% perchloric acid, as well as concentrated nitric acid and sulfuric acid were tried as solvents for the fluoride samples. A mixture of boric (5 ml.), nitric (10 ml.), and sulfuric (2 ml.) acids, however, proved superior to the other solvents. Approximately 1.5 hours were needed to dissolve the sample, evaporate the sulfuric acid, and prepare an average mixed fluoride sample for analysis. Samples containing little
or no sodium and/or a large amount of uranium fluoride often required the addition of more acids to effect complete dissolution. Synthetic samples were used in all of the experimental work. These were prepared from known quantities of uranium, beryllium, and sodium fluoride salts accurately weighed in a flat-bottomed platinum dish. The dried fluoride salts were weighed separately or together in the platinum dish, depending on the nature of the experiments. Precautions were taken in handling beryllium salts, because the dust is very toxic. I n preliminary work, a large platinum dish of about 150-ml. capacity was used as the cathode in the electrolytic separation of uranium from beryllium. Hydrous uranium oxide deposited on the walls and bottom of the platinum dish and was conveniently ignited and weighed as CT308.This method of analysis was discontinued, however, because a small quantity of beryllium salts usually deposited on the upper walls of the container because of evaporation during electrolysis. This error was eliminated when the uranium was plated on platinum gauze and the volume of the plating solution was increased to about 275 to 300 ml. The effect of temperature upon the rate of plating was found to be an important factor. A minimum temperature of 80" to 85' C. is necessary to obtain quantitative yields. The percentage of uranium deposited drops off rapidly with a reduction of temperature. The deposition of uranium from a hot ammonium acetate solution buffered at a pH of 4.0 was not affected by either the presence of beryllium or a combination of beryllium and sodium. The results of eyperiments illustrating the quantitative separations of uranium from beryllium and sodium are presented in Tables I and 11. I n all the analyses presented in these tables, the solutions Tyere plated for 2 hours a t 0.28 ampere at 3 to 4 volts. It is apparent from the data that a n y contamination of the uranium deposit by these elements was present in trace amounts only. Beryllium was determined, after the deposition of uranium, by precipitation of beryllium hydroxide from the hot plating solution n-ith ammonium hydroxide. The beryllium content as BeF2 of the mixed ternary salts under investigation varied from 17 to 65 mg. per sample. Sodium fluoride was always present in larger amounts. Over the range studied, a standard deviation of +1.6 mg. was obtained with a single precipitation of beryllium as the hydroxide (Table 111). This deviation n-as reduced to zt0.3 mg. per sample b y reprecipitation of the hydroxide. Recent data obtained by coworkers indicate that quantitative results may
Table I. Electrodeposition of Uranium from an Acetate Solution"
UF, Taken,
a
UF4 Found, Error, Mg. Mg. Mg. 94.6 94.5 0.1 98.2 97 9 0.3 120.4 120.2 0.2 121.5 121.4 0.1 146.8 146.8 0.0 148.3 148.5 0.2 174.2 174.0 0.2 179.4 179.1 0.3 182.6 182 4 0.2 183.9 183.8 0.1 Standard deviation & O , 20 Hot solution, buffered at pH 4.0.
Table II. Separation of Uranium from Beryllium and Sodium by Electrolysis"
BeFZ, NaF Taken, Taken, UF47 Error, Mg. Mg. Taken Found Mg. 18.3 .. 101.7 101.6 0 . 1 19.7 .. 100.8 100,;i 0 . 3 .. 9 9 . 7 99.6 0 . 1 19.2 40.8 ,. 99.1 9 9 . 1 0 . 0 41.3 .. 98.3 98.1 0 . 2 .. 49.6 49.2 0 . 4 54.2 55.8 .. 46.2 4 6 . 3 0 . 1 55 9 99.4 46 9 46 7 0 . 2 98.2 49 1 49 1 0 . 0 5;i 8 571 979 451 4 4 8 0 3 562 975 475 477 0 2 541 983 464 464 0 0 567 970 524 522 0 2 40 8 62 2 99 1 99 1 0 . 0 62 9 101 3 101 0 0 3 41 5 42 1 63 0 102 1 101 7 0 4 35.7 6 6 . 4 102.5 102.7 0 . 2 39.1 63.1 100.1 100.0 0 . 1 39.6 6 2 . 0 101.6 101.3 0 . 3 17.5 82.8 9 9 . 1 98.7 0 . 4 17.9 81.9 100.6 100.4 0 . 2 17.2 83 0 98.8 98 8 0 . 0 174 842 972 969 0 3 217 822 993 990 0 3 19 5 81 5 100 7 100 5 0 2 Standard deviation 0.24 Hot solution, buffered at pH 4.0. 5
be obtained for the determination of beryllium by a single hydroxide precipitation if the ignition temperature is raised to 1050" to 1100' C. (8) for 1 hour. A number of evperiments were performed in an effort to determine the source of the small positive error obtained when only a single precipitation xyas made and ignited at 950" C. I t n.as found that B e 0 ignited a t this temperature did not contain sodium as a contaminant as might be expected. This fact was verified by flame photometer analyses. It is the authors' opinion, therefore, that this error is not due to a contaminating element but is the result of the incomplete conversion of the hydroxide to the oxide perhaps because of minute traces of mater. The elevated ignition temperature (1100" C.) seems to be required to obtain a pure B e 0 product.
Table Ill. Determination of Beryllium in the Presence of Sodium
NaF Taken,
Error,
Mg.
Xg.
BeFz, big. Taken Found Single Precipitation 19.4 82.8 17.5 81.9 19.6 19.9 79.0 17.8 18.2 81.7 18.8 21.1 81 9 17 9 18 8 80 4 18 7 20 1 23 2 82 2 21 7 21 8 22 4 83.1 42 9 62 2 40 8 41.5 43.2 62.9 61 442 1 42 7 ._ 41 9 66.4 39.7 39 1 38.5 63.1 39.9 62.0 39 6 56.6 55.9 99.4 57.1 58.1 97.9 101.1 62.9 63.2 56.6 97.5 56.2 55.8 58.3 98.2 53.7 55.5 98.1 56.5 58.7 95.0 59.4 97.0 56.7 55.3 55.6 99.1 Standard deviation Double Precipitation 56.6 94.4 56.6 56.9 57.0 98.4 56.6 57.1 101.2 56.9 57.0 98.4 40.5 40.6 62.7 43.1 43.4 64.3 18.0 18.6 82.6 18.4 18.2 80.1 Standard deviation
1.9 0.3 0.4 2.3 0.9 1.4 1.5 0.6 2.1 1.7 0.6 2.2 0.6 0.3 0.7
1.0 0.3 0.4 2.5 1.8 2.2 3.3 0.3 1.6
0.0
0.1 0.5 0.1 0.1 0.3 0.6 0.2
0.33
CONCLUSIONS
Uranium(V1) may be quantitatively separated from a hot ammonium acetate solution containing beryllium and sodium by electrodeposition on a platinum electrode. Uranium is deposited in the form of a greenish yellom oxide that is dense and coherent. The deposit adheres firmly to the gauze electrode with little or no loss of material either during electrolysis or at the end after repeated rinsings. Consistent quantitative determinations of uranium were obtained in the present work n-ith the ammonium acetate solution buffered a t a p H value of 4.0. This is contrary to most of the published reports (2, 3, 6, '7) which advocate a p H value of 5 to 7 in order to obtain quantitative results. Electroplating a t this lower p H value was compulsory because beryllium hydroxide, accompanied by some uranium, begins to precipitate from a hot solution at a p H of about 4.6 to 4.8. rlttempts to electroplate uranium in the presence of precipitated uranyl and beryllium salts always resulted in low yields of uranium. Quantitative results were obtained in the gravimetric determination of beryllium from the ternary mixture, UF4FeFz-KaF, with a single hydroxide VOL. 31, NO. 6, JUNE 1959
1083
precipitation with ignition to B e 0 a t 1050’ to 1100’ C. for 1 hour. Alternatively, a double precipitation followed by ignition a t 950’ C. may be made. ACKNOWLEDGMENT
The authors acknowledge the helpful suggestions of L. V. Jones, George Pish, and L. J. Wittenberg. LITERATURE CITED
(1) Brinten, P. H., Ellestad, R. B., J.Am. Chem. SOC.45, 395-8 (1923).
(2) Castro, C. C., in “National Nuclear Energy Series,” C. J. Rodden, ed., Vol. VIII-i; pp. 523-35, McGraw-Hill,’ Sew York, 1950. (3) . , Cook. 0. A.. in “National Kuclear Energy Series,”’ IV-l4B, G. T. Seaborg, J. J. Katz, W. Manning, eds., Part 1, pp. 147-61, McGraw-Hill, New York, 1949.
(4) Hillebrand, W. F., Lundell, G. E. F., “Applied Inorganic Analysis,” 2nd ed., p. 522, Wiley, New York, 1953. (5) Kollock, L. G., Smith, E. F., J . Am. Chem. SOC.23, 607-10 (1901).
(6) Porter, P., N7yld, G., ANAL.CKEM.27, 733-6 (1955). ( 7 ) Smith, E. F.,
