of neptunium with 1.5M HDEHP in toluene from lhf HC1 followed by an acidity adjustment and the regular procedure. Although americium and curium were not tested in these studies, it is quite certain that they would follow the rare earths quantitatively under the conditions used. However, since they are alpha emitters with only low energy gammas associated, their interference in both beta and gamma counting can be prevented. Yield. T h a t no yield determination is required in this method was ascertained by carrying 10 aliquots of cerium-144 tracer solution through the entire procedure and counting aliquots of the 8M hydrochloric acid etrip solution. The average recovery was 98.3% with a coefficient of variation of 1%. RESULTS
Samples of irradiated uranium alloya and of spent fuel elements were analyaed
for total rare earths by the described extraction method and by the standard precipitation method. The results obtained on duplicates by the two methods are given in Table XI. I n each extraction the final aqueous etrip solutions mere checked for radiochcmical purity with a gamma-ray epectrorneter. Less than 1% of the gamma activity was due to fission products other than rare earthe. The precieion of the method was checked by carrying out 10 replicate analyses on an irradiated uranium5% fimium alloy. The coefficient of variation waa 2.4%.
chanan, R. F., ANAL. CHEM.32, 186673, (1960). (3) Bunney L. R., Freilin E. C., McIsaac, L. b., Scndden, E. Nucleonics 15, 81-3 1957). (4) Hume N., Martens, R. I., “Radiochemical Studiea of the Fiasion Producta,” Ci D. Corvell and N. Sugarman, ede., National fluclear Ener Seriea, Div. IV, Vol. 9, pp. 1732-6,%cGrawHill, New York, 1951. (5) Peppard, D. F., Faris J. P., Gray, P. R., Mason, G. W., j . Phys. C h m . 57, 294 (1953). (6) Pep ard, D. F., Mason, G. W., Moline, w., J . inorg. ~ u c ~ e Chem. ar 5, 141-6 (1957). (7) Petrow, H. G., ANAL.CAEM.26, 1614 (1954). (8) Scadden, E. M., Ballou, N. E., lbid., 25, 1602 1953). (9) Weat, (r S., Melallurgia 53, 186 (1956). (10) Wilkinson, G., Grummitt, W. E., Nucleonics 9, 52-62 (1951).
k,
b.
8.
.
LITERATURE CITED
(1) Ballou N. E. “Radiochemical gtudtea
of the Fkxiion f’roducta,” C. D. Corvell
and N. Sugarman, de., National Huclear Energy %ries, Div. IV, Vol. 9, pp. 1673-91, McGraw-Hill, New York, 1951. (2) Blaedel, W. J., Olsen, E. D., Bu-
RECEIVED for review October 21, 1960. Accepted April 14,1961. Work erformed under the auspices of the U. Atomic Energy Commission under contract W-31109-eng-38.
1.
Selective Dissolution of Uranium from UraniumUranium Oxide Mixtures by Bromine-Ethyl Acetate G. F. BRUNZIE,l T. R. JOHNSON, and R. K. STEUNENBERG Chemical Engineering Division, Argonnr National Laborafory, Argonne, 111. b A method is described whereby uranium is separated from its oxides by selectively dissolving the uranium in a 4M solution of bromine in ethyl acetate. Acids produced in side reactions of bromine with the solvent are neutralized by magnesium oxide, permitting a n extension of the dissolution period.
F
if any, suitable methods for the selective dissolution of uranium metal in the presence of uranium oxides have been reported in the literature. Phosphoric acid and solutions of hydrogen chloride in organic solvents have been mentioned by Larsen (9) as possibilities for this separation. Restrictive conditions, solvent attack, and solubility problems, however, have limited the usefulness of such reagents. Selective dissolution in liquid metals such as zinc or cadmium has also been used for this purpose in this laboratory, but the method is cumbersome and limited in its application. Solutions of bromine in ethyl acetate EW,
Present addreea, state University of
Iowa, Iowa City, Iowa
have been used previously for the dissolution of uranium and its alloys (3). A similar reagent, bromine in methanol, haa been used by Eberle and Lerner ( 1 ) to dissolve uranium in a procedure for the determination of boron. With the completion of preliminary experiments indicating that uranium oxides are insoluble in bromineethyl acetate solutions (4, it became apparent that this reagent might be useful for the selective dissolution of uranium in mixtures of the metal and oxides.
excessive decomposition. The presence of water must be minimized. Although ethyl acetate with a maximum water content of 0.20% as specified by the manufacturer proved as satisfactory tu material with 0.01% maximum water content, the results of these studies, aa well as those of Eberle and Lerner (8), indicate that the presence of water htu a large influence on the dissolution of oxides. The metallic uranium used in the experiments was in the form of 100- to 200-mesh shot. Where magnesium oxide was used in the experiments, analytical grade material was employed.
EXPERIMENTAL
The dissolution apparatus consisted primarily of a round-bottomed flask equipped with a reflux condenser. Addition of the bromine-ethyl acetate to the flask from a calibrated reservoir was controlled by a stopcock at the base of the reservoir. The ground joints were lubricated with ethyl acetate and the stopcock with Dow-Corning silicone grease. The ethyl acetate solution approximately 4M in bromine was prepared by mixing 50 ml. of analytical grade bromine with 200 ml. of ethyl acetate. The prepared re ent can be stored in a glass-stoppered ttle for about 3 weeks at room temperature without
%
PROCEDURE
The sample of uranium-uranium oxide mixture, about 20 ml. of ethyl acetate, and 0.1 to 1.0 gram of magnesium oxide are added to the dry flask and heated almost to boilin (about 65’ C.). The function of t e ma nesium oxide is to neutralize aci s formed by reaction of bromine with the solvent. Samples containing more than about 1 gram of uranium require approximately 0.5 gram of magnesium oxide per hour of dissolution time. For smaller samples, about 0.3 gram per hour is sufficient. The bromineethyl acetate solution is added to the flask a t E rate sufficient to sustain
$
VOL. 33, NO. 8, JULY 1961
f-
lo05
continuous boiling during most of the dissolution. The total quantity of reagent added should be at least 1.5 to 2.0 times tohestoichiometric amount required t o convert the metallic uranium to uranium(1V) bromide (3). If necessary, bromine may be added during the reaction to increase the dissolution rate. The rraction can be stopped at any time by immersing the flask in ice water. Whcn the dissolution is complete, the contents of thc flask are transferred to a fine-porosity sintered-glass filtering crucible and the insoluble uranium oxide is filtercd from the ethyl acetate solution. The residrial solids are washed with ethyl acctate until the bromine color is no longer evident in the washings, then with 10 to 15 ml. of distilled water. The filtrate and all washings are transferred to a separatory funnel, shaken briefly, and the aqueous phase removed. The ethyl acetate solution is extracted three additional timcs using 10- to 15-1nl. portions of water. The combined aqueous solution is then heated to oxidize the uranium to the (VI) state. The solution is extracted with three 5-ml. portions of carbon tetrachloride to remove any residual ethyl acetate and bromine. The resulting solution, after dilution to volume, is analyzed by any of the conventional methods for uranium in aqueous solution. In this work the uranium was determined by reduction in a lead reductor and titration with standard cerium(1V) solution (6). RESULTS
In experiments both with untreated uranium shot and with shot cleaned in dilute nitric acid quantitative uranium recoveries were obtained, indicating that no losses occur in the extraction steps. The effects of various materials on the reaction are indicated in Table I. Quantitative recoveries were obtained with matwive metallic uranium, as
well as with the shot. Uranium oxides added in amounts equal to and ten times the quantity of metallic uranium present had no effect on the results when the dissolution time was short. When the dissolution time was increased and no magnesium oxide was present, however, high results were obtained, probably as a result of attack on the uranium oxide by acids formed in a side reaction of bromine with the ethyl acetate. The addition of a small amount of water caused some dissolution of the uranium oxide, producing a high result. Although small amounts of magnesium oxide added to the system are effective in scavenging acids produced in the bromine-solvent side reaction, the quantity should be limited. Large amounts not only make the filtration more difficult; they are not any more effective in counteracting the effect of water in the system than are smaller amounts. When the method was applied to process samples consisting mainly of uranium oxides, but containing some metallic uranium, i t was possible to conduct dissolutions of more than 2 hours' duration without appreciable dissolution of the uranium oxides. In general, dissolution times of at least 1, and preferably 2 hours are recommended for samples of 1 to 3 grams. In two experiments the undissolved uranium oxide was recovered quantitatively by collecting the solid residue on a filter and leaching it with acetic acid to remove magnesium oxide. The amount of uranium oxide was determined by weight and i t was characterized by x-ray diffraction. A few results were obtained on samples of uranium along with other metals in the presence of oxides.
Magnesium, aluminum, and 7inc are dissolved by the bromine-ethyl acetate reagent, but the rates are variable. Although systematic studies of these systems were not made, it appears that the techniqqe may prove useful for the analysis of alloys and mixtures of uranium with other metals in the presence of their oxides. DISCUSSION
The usual safety precautions observed in handling elemental bromine are appropriate. The vapor pressure of bromine over the ethyl acetate solution is somewhat lower than that of liquid bromine. While minor spills of the freshly prepared reagent evaporate completely, solutions stored longer than 2 or 3 weeks appear to contain a less volatile component, excessive quantities of which cause difficulty in the exttaction step. The reaction with metallic uranium is vigorous enough to sustain a refluxing condition until the dissolution is nearly complete. Magnesium metal dissolves at a high rate initially, but requires a longer time for complete dissolution. The method is limited only by the dimensions of the sample. The dissolution reaction can be stopped, the flask drained, and more reagent added. With the proper amount of magnesium oxide present, the procedure can be repeated until all the metal is dissolved. When the uranium solutions obtained from the extraction are to be stored for more than an hour or so, the preferred procedure is to oxidize the uranium to the (VI) state by heating prior to the scrubbing step. Otherwise, black precipitates have a tendency to form in the uranium(1V) bromide solution on standing I
ACKNOWLEDGMENT
Table 1.
Effects of Various Constituents on Uranium Recovery
Reflux in 8N bromine-ethyl acetate solution followed by filtration, washing, and extraction with water Uranium M- -e-t-. d -.
MgO
... ... ...
...
... *..
1000
1000 825
1000 1207
...
Constituents Added (mg.) H20 U02 UsOl
...
...
... ... ... ...
100 2062
...
1000 42
...
... ...
... ., .
... ...
100
...
...
...
...
100
... ... ... ...
106 1163
... ...
1242 39 794
...
U metal 243.9* 211.5 106.2 109.1 115.1 187.3 100.4 200.8 178.2 204.4 133.2 100.8
Reflux Time (mh.) 30 30 60 120 60 60 60 60 60 60 120 30
lk~nd" (mg.) (%I 244 212 109.0 117.0 116.4 191.0 100.2 200.0 178.9 201.0 135.0 111.2
100 100 103 107 101 102 100
looc 100 98 101 110
".Uranium determined by reduction in a lead reductor and titration with standard ceric ion, precision (lo) = f0.5%((6). 'Massive uranium metal. Uranium oxide recovery after leaching with acetic acid to remove magnesium oxide: 101% by weighing. dUranium oxide recovery after acetic acid leaching: 103% by weighing; 987'0 by dissolution in hydrochloric acid and determination of uranium in solution.
The authors are indebted to R. P. Larsen, R. J. Meyer, and L. E. ROSS for thcir helpful advice, comments, and cooperation in providing uranium determinations. LITERATURE CITED
(1) Eberle, A. R., Lerner, M. W., ANAL. CHEW32,146 (1960). (2) Eberle, A. R., Lerner, M. W., MetalZurgza 59,49 (1959). (3) Larsen, R. P., ANAL. CHEM. 31, 545 (1959). (4) Larsen, R. P., Argonne National Laboratorv. Araonne, com- , Ill.,. Drivate -
municktion.
(5) Sill, C. W., Peterson, H. E., ANAL. CHEM. 24,1175 (1952).
8
1006
ANALYTICAL CHEMISTRY
RECEIVED for review December 12, 1960. Accepted April 10, 1961. Work performed under the auspices of the U. S. Atomic Energy Commission.
