tion rate is much more rapid in lilf alkali than in 6 M . SUMMARY
Table I summarizes the more common uranium alloys and the reagents which are used to dissolve them. The choice of reagent for the dissolution of a particular sample of uranium or uranium alloy will, of course, depend not only on the ability of the reagent to dissolve the sample but also on what analyses are to be performed on the solution. Many hours of analysis time can be saved if the sample is dissolved in the medium in which the analysis is to be run, rather than in aqua regia, for example, and t.hen converted to the desired medium by fuming.
LITERATURE CITED
(1) .411en, R., Beederman, M., Munnecke,
V. H., Radke, J., Vogel, R. C., Vogler, S., in Argonne National Laboratory Chem. Eng. Division Quart. Rept. ANL-4675, 31-8 (April-June 1951). (2) Banks, C. V., “Analysis of Certain Uranium Alloys,” U. S. Atomic Energy Comm. Rept. M-3056 (1941, declassified January 1956). (3) Beederman, M., Munnecke, V. H., Vogel, R. C., Vogler, S., in Argonne National Laboratory, Chem. Eng. Division Quart. Rept. ANL-4720, 18-20 (July-September 1951). (4) Feder, H. bl., Larsen, R. P., Beederman, M., Evans, H. E., Ibid., ANL5103,51-3 (April-June 1953). (5) Kate, J. J., Rabinomitch, E., “Chemistry of Uranium,” p. 164, McGrawHill, New York, 1951.
(6) Kittel, J. H., Greenberg, S., Paine, S. H., Draley, J. E., Nuclear Sci. and Eng. 2, 431-49 (1957). (7) Larsen, R. €’., Shor, R. S., Feder, H. M., Flikkema, D. S., “Study of
Explosive Proylerties of Uranium-Zirconium Alloys,” U. S. Atomic Energy Comm. Rept. ANL-5135 (July 1954). (8) Rodden, C. J., “Analytical Chemistry of the Manhattan Project,” p. 6, RicGrsw-Hill, New York, 19i59p. (9) Saller, H. S., Rough, F. A., Compilation of U. S. aid U. K. Uranium and Thorium Const .tutional Diagrams,” U. S. Atomic Energy Comm. Rept. BMI1000 (June 195,;). (10) Warf, J. C., Banks, C. V., U. S. Atomic Energy Comm. Rept. CC-2942 (July 1945). RECEIVED for review September 8, 1058. Accepted Novemher 28, 1958. Based on work performed under the auspices of the U. S. Atomic Enevgy Commission.
Separation of Rare Earths from Beryllium, Magnesium, Zirconium, Titanium, Uranium, and Stainless Steel M. W. LERNER and L. J. PINTO New Brunswick laborafory,
U. S.
Afomic Energy Commission, New Brunswick, N. J.
Certain rare earths possessing high thermal neutron absorption cross sections, when present in only trace quantities in metals used in nuclear technology, must be separated before a satisfactory spectrographic determination can be made. These rare earths are separated from beryllium and magnesium by precipitation as oxalates with added thorium as a carrier. The thorium is removed by an 8-quinolinol extraction leaving a residue suitable for spectrographic analysis. With zirconium, titanium, uranium, and stainless steel, a preliminary fluoride precipitation is made. At least 96% of the rare earths are consistently recovered.
T
concentration of elements possessing high thermal neutron cross sections in metals used in nuclear technology is important from the standpoint of neutron economy. Accordingly, the high cross sections of certain rare earths make essential the determination of even traces of these elements. The spectrographic determination of most rare earths in the lower microgram range requires their prior separat,ion. The classic precipitation procedures generally fail when only traces are present. For example, the fluoride precipitation method of Rodden and Vinci (6) for beryllium samples is inadequate for these trace quantities. The chemical similarity of the rare earths and thorium, together with the HE
recently developed 8-quinolinol extraction procedure for the separation of thorium and other elements from the rare earths (S), suggested the use of milligram quantities of thorium as a precipitation carrier for the rare earths. The (ethylenedinitri1o)tetraacetic acid (EDTA)-oxalate precipitation method of Gordon, Firsching, and Shaver (1) for concentrating the rare earths in thorium would not be as useful in this separation because the procedure, besides being slow, requires a fair amount of thorium to precipitate with the rare earths. Other elements uncomplexed by EDTA may also accompany the rare earths. With beryllium samples, an oxalate precipitation made with added thorium gives essentially complete recovery of rare earths possessing the highest cross sections: samarium, europium, gadolinium, dysprosium, and erbium. After removal of the thorium by the 8-quinolinol extraction, the rare earths are precipitated as oxinates with added lanthanum as a carrier and internal standard for the subsequent spectrographic determination (6). The same procedure is successful n-ith magnesium samples. Fluoride was used as the precipitating anion for zirconium and titanium samples because these metals are readily dissolved by hydrofluoric acid. Hettel and Fassel (2) have pointed out that traces of rare earths are not precipitated in hydrofluoric acid solutions of
zirconium despii,e the insolubility of the fluorides, although a precipitate of some nonrare earth may be contaminated with rare earths. In preliminary work this difficulty was confirmed. Despite the use of large quantities of carrier thorium, tracer europium-152154 was not quantitatively precipitated. I n an attempt to increase the tracer recovery, ammonium fluoride was added to the hydrofluoric acid solution of zirconium containing added thorium. A few minutes after the addition of the salt, the gela tinous thorium fluoride changed abruptly to a dense, white precipitate that could be easily filtered or centrifuged. This precipitate, believed to be ammonium thorium fluoride, carried the tracer completely. It is readily dissolved in a nitric-boric acid mixture. The oxalate separation and 8-quinolinol extrxtion can then be applied to the soluldon to obtain the rare earths. Essentially the same procedure is applicable to the analysis of stainless steel and uranium. REAGENTS AND APPARATUS
8-Quinolinol, Eastmaii Organic Chemicals Co. Europium-152- 1.54tracer, not carrierfree, prepared al, Oak Ridge National Laboratory by neutron irradiation of europium oxalat 3. Samarium, gadolinium, dysprosium, and erbium oxides of a t least 99.0% purity. Thorium nitrrtte tetrahydrate, anVOL. 31, NO. 4, APRIL 1959
* 549
alyticnl grade. treated to remove gamma-emitters and rare earths (3). Bakelite beakers. 150-nil.; Lusteroid centrifuge tubes, 50- and 100-ml. Gamma scintillntioii counter. PROCEDURES
BERYLLIUM a m ~ ~ z 4 G N E S I U & I .Dissolve a 10- to 4o-gram sample suspended in n-nter with sufficient concentrated hydrochloric acid io give a solution 0.25i11 in excess hydrochloric acid when made up to 300 to 800 ml. Digest beryllium solutions on a hot plate for a few minutes and filter through Whatman No. 42 paper to remove traces of undissolved oxide. Ignite the paper in a platinum crucible, fume the residue with a few drops of concentrated sulfuric acid, and add the dissolved residue to the main solution. Add 100 mg. of purified thorium nitrate tetrahydrate and stir until the salt dissolves. Continue stirring and add 3 grams of oxalic acid dissolved in 100 nil. of hot water. Heat on a hot plate to near boiling and cool for about 1 hour. Filter the oxalates with vacuum on a medium porosity fritted-glass filter crucible. Wash the crucible sides and precipitate with lY0 oxalic acid. Place the crucible in a 150-ml. beaker, add 15 ml. of concentrated nitric acid and 1 nil. of 70% perchloric acid, and heat on a hot plate until the precipitate dissolves. Wash and remove the crucible. Evaporate the solution to near dryness. Take up the residue in 2 nil. of Concentrated nitric acid and about 5 ml. of water. If the solution is not clear, iepeat the evaporation to near dryness after the addition of a few more drops of 70% perchloric acid. JS7hen the residue yields a clear solution with the dilute nitric acid, dilute the solution to about 100 ml. Reprecipitate the oxalates by adding 1 gram of oxalic acid in 30 ml. of hot water. After filtration and destruction of the oxalates as before, take up in 2 ml. of concentrated nitric acid and dilute to about 50 ml. Add 10 ml. of glacial acetic acid and adjust the p H with a meter to about 2.0 with concentrated ammonium hydroxide. Cool to room temperature, add 3 grams of 8-quinolinol, and adjust the pH to 4.20. Transfer to a 250-ml. separatory funnel. Extract with five 10-ml. portions of 5-quinolinol in chloroform, 10 grams per 50 ml., and wash with two 25-ml. portions of chloroforni. Transfer the solution to a 250-ml. beaker. Add 1.0 mg. of lanthanum as a solution of the nitrate. Add about 10% by volume of concentrated ammonium hydroxide and heat until the precipitate flocculates. Filter hot through Whatman No. 42 paper and ignite the precipitate in platinum to the oxides for the spectrographic determination. ZIRCONIUAf AKD TITA~;IUIL Dissolve a 5- to 10-grani sample suspended in water in a 15o-ni1. Bakelite beaker by adding 48% hydrofluoric acid in small increments. Add about 5 ml. of acid in excess. 550
c
ANALYTICAL CHEMISTRY
Add rapidly with stirring 200 mg. of purified tho1 ium nitrate tetrahydrate dissolved in 10 nil. of water. Add 3 grams of arinonium fluoride and stir until the silt dissolves. ST'hen the thorium precipitate becomes white and granular, tiaiisfer the suspension with washing to B Lusteroid centrifuge tube and centrifuge a t 2000 r.p.m. for about 5 minutes. Discard the supernatant liquid. m7ash the precipitate into the same Bakelite bea-:er with about 10 ml. of water. Add 1 gram of solid boric acid and 5 ml. oj' conceiitiated nitric acid. Stir until the t;olids dissolve completely, adding wate:. if necessary to dissolve the excess boric acid. Transfer to a 600-ml. beakix, dilute to about 300 ml., and add 1 grxm of oxalic acid dissolved in about 50 nil. of hot water. Heat t,he solution to n t m boiling, cool, and filter. Proceed wit11 the destruction of the oxalates, tht: 8-quinolinol extraction, and the raxe earth precipitation as for beryllium. UnANIux Dissolve a 5-gram sample in nitric acid (1 1) and evaporate to dryness on the steani bath. Dissolve the salt in 40 ml. of water and transfer to a 150-ml. Bakelite beaker. Add 5 nil. of 48% hydrofluoric acid. Proceed as with xircoiiium samples. STAINLESS ,I!TEEL. Dissolve a 5-gram sample in 30 ml. each of hot concentrated nitric : d d and hydrochloric acid. Cool, add 41) ml. of 70% perchloric acid, and heat. until red salts are visible. Cool and cari:fully add 50 nil. of mater. Filter th1oug.i Whatman No. 42 paper into a 150-ml. Bakelite beaker. Treat the residue m described for beryllium samples, but use a few drops of hydrofluoric acid in addition to the sulfuric acid. Add 1:) nil. of 48y0 hydrofluoric acid and pimeed as for zirconium samples.
+
EXPERIMENTAL
The optimum conditions for the oxalate precipitation and carrying of the rare eartlui in the presence of beryllium was studied using the eurpoium152-154 trace *. With 3-gram quantities of beryllium as the chloride in 150 to 400 ml. of 0.25M hydrochloric acid containing 100 mg. of freshly purified thorium nitrs te tetrahydrate, the tracer was completely carried when 1 gram of oxalic acid wr18 used. T17iththis quantity of oxalic acid, complete recovery of the tracer mas c btained when the excess acid concenimtion was as high as 1.0M. The iwovery decreased to 96% with 1.5M and to 92% with 2211 acid. The oxalatw can be rapidly destroyed prior t o the ibquinolinol extraction by heating with concentrated nitric acid plus a trace o.'permanganateas reported by Nietzel, Wessling, and DeSesa (4). The mangan 138, however, ends up in the final rare earth residue and is best avoided beca1lt;e of its complex spectrum. The recommz nded nitric-perchloric acid treatment so netimes requires multiple treatments nith 1 to 2 ml. of the acid
mixture. The oxalate is completely destroyed when all of the residue resulting from the evaporation of the acid to near dryness appears glassy. The compound obtained by the addition of ammonium fluoride to the thorium fluoride suspension mas investigated briefly. It gives a distinct x-ray pattern which could not be found in the published thorium literature. Analyses for nitrogen, thorium, fluoride, and water strongly suggest the compound NHdThFb. HzO, although precise agreement of the analyses with the calculated values was not obtained, presumably because a pure sample was not obtained. Any further characterization of this compound will be reported elsewhere. A similar uranium compound has been prepared recently by Tolley (7). Preliminary tests showed the inability of the thorium carrier to gather tracer europium-152-154 completely and consistently under the conditions of the simple fluoride or oxalate precipitation when the tracer was added to zirconium, titanium, uranium, or stainless steel solutions (Table I). However, the conditions leading to the formation of the double thorium salt led to essentially complete recovery with each type of sample. With the stainless steel samples it was necessary to oxidize the chromium(111) to (VI) because the insolubility of chromic fluoride interferes. Also, more hydrofluoric acid must be used for the thorium precipitation because of the presence of the ferric ion. Because appreciable amounts of the base metals might also be coprecipitated with thorium, the 8-quinolinol extraction of these metals was briefly studied. Under the conditions used for the extraction of the thorium, 50-mg. quantities of zirconium, titanium, iron, uranium, and nickel were extracted completely. Only 26% of chromium(111) was extracted. Thus, if coprecipitation of these metals occurred, only traces of chromium(III), resulting from reduction of the chromium(V1) in the stainless steel samples, mould survive the 8-quinolinol extraction. After the sample dissolution, the beryllium solutions may contain traces of undissolved oxide, the stainless steel solutions, traces of silica. These should be filtered to eliminate the possibility of their presence in the final rare earth concentrate. Although they probably contain only insignificant amounts of rare earths, they can be worked up as described. Other types of stainless steel may require additional treatment for the insolubles present. RESULTS
The rare earth recovery in the 8quinolinol extract'ion of the thorium
together with the precipitation of the rare earth oxinates with the lanthanum carrier is a t least 97% (3). Because the recovery in either the double oxalate or fluoride precipitation was essentially loo%, the over-all recovery of the rare earths should be about 97%. This value was checked bv analyzing duplicate 10-gram samples of beryllium to which was added europium-152-154 after dissolution. An average 98% recovery of the tracer activity was found in the final oxide residue. With larger 28-gram samples, the recovery was 96%. K i t h 40-gram samples of magnesium, the recovery was 96%. Tracer recovery testq were also carried out on duplicate &gram samples of zirconium, titanium, uranium, and stainless steel. In the case of uranium, the blank activity of any gammaemitters in the final residue was determined first by carrying an identical sample through the procedure without the tracer addition. The blank was small enough to be ignored. In each case, the recovery of the tracer in the final residues for the spectrographic analysis was a t least 97%. The separation was further checked by analyzing samples both with and ~ i t h o u the t addition of 25-y quantities of samarium, gadolinium, dysprosium, and erbium (Table 11). The rare earth residues generally n-eigh about 2 mg., which includes 1.2 mg. of linthanuni oxide. Traces of calcium, magnesium, aluminum, bergllium, silicon, and thorium are frequently found in addition to the rare earths. Further purification can be carried out if desired (3).
Table
I.
Recovery of Tracer under Various Conditions
Precipitat,ing Conditions Saniple Tho48% HF, C2H204, NHdF, rium(IV), Wt., Sample Grams ml . grams grams mg. 100 Zr 5 Excessa .. 100 5 Excessa 3 100 4’ . . Excessa 8.5 .. 50 Ti 4 Excessa 50 3 5 Excessa 100 U02(N03)2,6H20 10 5 .. 100 10 5 .* 3 100 Stainless steel 310 5 .. 3 5 10 100 .. 100 5 10 .. 3 a About 5 ml. in excess. b Identical result obtained in triplicate tests. Table 11.
Be Zr
10
U
5 5 5
7
Ti
Stainless steel 310
%
61, 66
99*
94 99b 92 995 43, 70 91, 98 99*
Recovery of Rare Earths Added to Metal Samples
Sample Wt., Grams
Sample
EuIs2-16‘ in Ppt.,
Sm 30 24 25 28 26
ACKNOWLEDGMENT
Acknowledgment is given to the New Brunswick Laboratory Spectrographic Analysis Section for the Spectrographic determinations. LITERATURE CITED
(1) Gordon, Louis, Firsching, F. H., Shaver, K. J., ANAL. CHEM.28, 1476 (1956). (2) Hettel, H. J., Fassel, V. A., Ibid., 27, 1311 (1955).
Rare Earth Recovered, y Gd DY 27 27 27 24 25 21 28 25 26 29
Er 25 23 25 27 25
(3) Lerner, h4. W.,Petretic, G. J., Ibid., 28, 227 (19561. (4) Nietzel, 0. TFressling, 1V.t
EtEEj,&,&
~g~,)Atomic (5) ~, Rodden. C. J.. Ibid.. TID-7003 (Del.) io8 ( i m j . (6) Rodden, C J., Vinci, F. A,, “The Metal Beryllium,’’ 13. TV. White, J. E. Burke. eds., p. 645, Am. SOC. Metals, Cleveland, Ohio, 1955. (7) Tolley, W. B., U. S. Atomic Energy Comm. HW-35814 (1955) (declassified 1957). RECEIVED for rsview September 11, 1958. Accepted December 5, 1958. .
