Radioc hemica I Determination of Ionium in Uranium Fluorination Ash FLETCHER 1. MOORE Oak Ridge National laboratory, Oak Ridge, Tenn.
b A carrier-free method for the determination of ionium (thorium-230) in process solutions of uranium fluorination ash i s described. Ionium is carried on lanthanum hydroxide and lanthanum fluoride and extracted with 0.5M 2-thenoyltrifluoroacetone-xylene to effect high selectivity. The technique gives satisfactory results when applied to process solutions. Yields average 97 i 3%. The method may be used to determine ionium in the presence of all other alpha emitters.
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detection (5) of ionium 8 X lo4 years, 4.68 m.e.v. alpha emitter) in process solutions of uranium “ash” from various gaseous diffusion processes necessitated a n analytical method for the determination of this radioactivity. Many of the process solutions contain aluminum, iron, stainless steel corrosion products, fluoride, uranium-234 and -238, neptunium237, and plutonium-239. The present method ( 1 ) for the radiochemical determination of the thorium isotope, thorium-234 (UXJ, in the presence of uranium and fission products is satisfactorv, as the gamma radioactivity may be counted efficiently in the presence of the thorium carrier prescribed. Hoiwver, a carrier-free method was desired for the determination of ionium to avoid self-absorption losses of the alpha particles. The method for UX1 does not provide for the separation of neptunium and plutonium. 4 method for the determination of ionium in coral limestone (4) appears rather lengthy, because both anion and cation exchange steps are necessary to eliminate the plutonium interference. The radiochemical method described gives satisfactory results on uranium ash process solutions. Nost interferences are eliminated by a combination of lanthanum hydroxide and fluoride precipitations which carry the ionium quantitatively. Uranium, neptunium, and plutonium are effectively eliminated by maintaining them in the fluoridesoluble sexivalent oxidation state. The lanthanum fluoride technique is an adaptation of the familiar method (3) of carrying plutonium(II1, 11’) in the presence of plutonium(V1). Iron(II1) forms a fluoride-soluble complex and is essentially eliminated in this step. A ECENT
1020
(tllz,
ANALYTICAL CHEMISTRY
final extraction ( 2 ) of the ionium with 0.5M 2-thenoyltrifluoroacetone-xylene eliminates the lanthanum carrier, increases the selectivity, and provides a solid-free plate for alpha counting. PROCEDURE
Pipet a suitable aliquot of the sample solution into a 5-nil. Pyrex Brand 8060 centrifuge cone. ildd 0.1 ml. of lanthanum carrier ( 5 my. per nil.) and mix well with a platinum stirrer. Add 1 ml. of 19M sodium hydroxide, mix well, and digest for 5 minutes a t room temperature. Centrifuge in a clinical centrifuge for 3 minutes. Remove the supernatant solution with mild suction. TT’ash the precipitate by stirring with 2 to 3 ml. of 0.05M sodium hydroyide. Centrifuge for 3 minutes, remove the supernatant solution, and repeat the wash step. Dissolve the precipitate in several drops of concentrated nitric acid and add 8 to 10 drops in excess. Add 0.3 ml. of 0.4M potassium dichromate, mix well, and digest for 10 minutes in a beaker of water a t approximately boiling temperature. Add 0.3 ml. of 27M hydrofluoric acid, niiu well, and digest at room temperature for 5 minutes. Centrifuge for 3 minutes. Add 0.05 ml. of lanthanum carrier and stir the supernatant solution, being careful not to disturb the precipitate. Digest for 5 minutes a t room temperature. Centrifuge for 3 minutes and carefully remove the supernatant solution, leaving about 1 drop. Wash the precipitate by stirring with 0.5 nil. of 1-11 hydrofluoric acid-1.M nitric acid containing 1 drop of 0.4M potassium dichromate. Centrifuge for 3 minutes, remove the supernatant solution, and wash the precipitate with 0.5 ml. of 1 M hydrofluoric acid1M nitric acid. Dissolve the lanthanum fluoride precipitate by adding 0.5 ml. of 2111 aluminum nitrate and several drops of 1M nitric acid. Carefully transfer the solution to a 10-ml. beaker using several distilled water washes. Adjust the p H t o 1.4 to 1.5 with a p H meter and extract for 10 minutes with a one-half volume portion of 0.5114 thenoyltrifluoroacetone-xylene. After centrifugation, evaporate an aliquot of the organic phase on a platinum or stainless steel disk, flame to a red heat, cool to room temperature, and count in a pioportional alpha counter. An alpha energy analyzer is useful for occasionally checking the disks, !Then small amounts of ionium are determined in the pres-
ence uf high levels of other alpha rndioactivities. If radium, piotactiiiiuni, americium, or curium is not prment, omit the final extraction step. Slurry the lanthanum fluoride prccipitatc n-ith several drops of 1;M nitric acid and transfer quantitatively to a platinum or stainless steel disk. Rinse the cone with three %drop portions of distilled wvnt’er, transferring the rinses to the disk. Dry undei an infrared heat lamp, flame to a red heat, and count the disk in a proportional alpha count,er. The initial hydroxide precipitation may be omitted if the sample solution does not contain aluminum or chromium. DISCUSSION
The procedure dmcribed yields 97
z
37, on process solutions. N o s t losses are in the p H adjustment prior to the final extraction. By rinsing the centrifuge cone n ith several distilled n.ater washes before p H adjustment and by using sereral portions of the organic phase to wash the beaker afterwards, essentially quantitative recovery of ionium can be effected. Quadruplicate analysis of a dilute nitric acid solution containing 1.4 X 105 alpha counts per minute per milliliter of ioniuni gave 99.4, 98.0, 98.1, and 99.57, recovery, R-hich is satisfactory for a carrier-free technique. The radiochemist niay desire to apply a yield correction for the ionium recovery, particularly if many chemical separations are performed. The beta, gamma emitter, thorium-234 (VX,), ir 1-ery useful in such cases. The niajor alpha radioactivity present in this particular process wis neptunium-23i along xith much smaller amounts of plutonium-239 and uranium234 and -238. Decontamination from these alpha emitters was satisfactory. d solution containing 2 X lo5alpha counts per minute per milliliter of neptunium237 and 5.6 X lo4 alpha counts per minute per milliliter of ionium was analyzed by the prescribed procedure. An alpha energy analysis of the final plate indicated pure ionium with no neptunium-237 detected. This analysis should be performed occasionally, if very low levels of ionium are being determined in the presence of high concentrations of other alpha emitters. Although radium, polonium, protactinium, americium, and curium were not
detected in solutions of this particular process, these elements are often present in uranium wastes. Radium will be eliminated in the hydroxide precipitation and traces that do carry will be eliminated very effectively in the final extraction of ionium ( 2 ) . Decontamination of ionium from polonium was excellent: 0.02, 0.03, 0, 0.03, and 0.02% in fire experiments. Solutions containing 7.6 X lo4 alplia counts per minute per milliliter of polonium-208 were analyzed using the ionium procedure. Analysis of the various separated fractions in the procedure indicated that essentially all of the polonium was in the oxidized supernatant solution from the lanthanum fluoride precipitation. Thus, polonium behaves like uranium, neptunium, and plutonium in the procedure. As quadrivalent polonium readily carries on lanthanum fluoride from nitric acid solution, the polonium may be in the sexivalent fluoride-soluble state in the presence of potassium dichromate. dpproximately 50% of the protactinium originally present remained in the supernatant solution as a fluoride soluble complex upon the precipitation of lanthanum fluoridc. If protnctiiiium-231 is pres-
ent, the ionium should be stripped from the 0.5M 2-thenoyltrifluoroacetone-xylene by stirring with an equal volume of 2M nitric acid for 5 minutes. Ionium strips quantitatively, leaving the protactinium in the organic phase. Typical decontamination data for protactinium in four experiments (including the final strip with Z M nitric acid) gave 0.03, 0.20, 0.07, and 0.05%. A 2iM nitric acid solution containing 6.5 X lo5 gamma counts per minute per milliliter of protactinium-233 mas analyzed in 1-ml. aliquots by the ionium procedure. The final 2M nitric acid strip solution was counted for protactinium-233 gamma radioactivity using a scintillation counter having a sodium iodide crystal. Although it is rarely necessary, the last traces of protactinium may be removed by re-extracting the 2M nitric acid strip solution with an equal volume of 0.5-$1 2-thenoyltrifluoroacetone-xylene for 5 minutes. Americium and curium are readily eliminated along with the lanthanum carrier when the ionium is extracted with this reagent. The method should prove useful in the carrier-free isolation of thorium isotopes. Although the procedure has been used specifically to determine
ionium in uranium fluorination ash, it should be useful for the determination of ionium in various waters and rocks. Ionium may be isolated from complex mixtures of elements by lanthanum hydroxide and fluoride carrying, followed by extraction with 2-thenoyltrifluoroacetone-xylene. I n analyzing materials containing natural thorium, a final alpha energy analysis should be performed t o differentiate ionium from other thorium isotopes. LITERATURE CITED
(1) Ballou, S . E., Hume, D. S . ,National Nuclear Energy Series, Division IV, Vol. 9, 1755-7, McGraw-Hill, New York, 1951. (2) Hagemann, F., J . Am. Cheni. SOC.,72, 768 (1950). ( 3 ) Koshland, D. E., Jr., Oak Ridge National Laboratory Unclassified Rept., CN-2041 (Jan. 8, 1945). (4) Potratz, H. A., Los Alamos Unclassified Rept., LA-1721 (Sept. 10, 1954). (5) Rickard, R. R., Oak Ridge National Laboratory, Oak .Ridge, Tenn., private communication. RECEIVEDfor review October 23, 1957. hccepted January 27, 1958. Oak Ridge National Laboratory is operated by the Union Carbide Nuclear Co. for the U.S. Atomic Energy Commission.
Detection of Thorium and Uranium JAMES S. FRITZ and EVELIN CARLSTON BRADFORD Institute for Afomic Research and Department of Chemistry, Iowa Sfate College, Ames, Iowa
b Simple qualitative tests for thorium(IV) and uranium(V1) are proposed, based on color reactions with the reagent arsenazo. EDTA is first added to mask foreign metal ions. Uranium(VI) is separated from thorium(lV) by extracting uranyl diethyldithiocarbamate into benzene.
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exkting methods for detecting thoriuni in aqueous solution are by it:, spectra, fluorescence, and color reactions with organic indicators. A test tube flame test has a sensitivity of 800 p.p.ni. ( 2 ) . Direct spectral analysis using t'he porous cup electrode technique achieves a sensitivity of 35 p.p.m. ( 2 1 ) . Flame photomet'ry a t its best wave lengbh requires a niininiuni thorium concentration of 100 p.p.ni. (21). The fluorescence of thorium with 1 - amino - 4 - hydroxyanthraquinone has been proposed as n qualitative test for thorium (18, 19). The sensitivity is good, but numerous ions interfere. The indicators, alizarin (17),3-alizarinsulfonic acid (9, IC), I-(0-nrsonophenylHE
3 - (2 - arsonophenj-lazo) - 4>5 - dihydroxy - 2,7 - naphthalenedisulfonic 1,8-dihydrox\--3,6-naphthalenedisulfonicacid (arsenazo) forms a violet color acid (4) give sensitive qualitative with thorium and a blue color with tests but are lacking in selectivity, uraniuni(T'1). If uranium(V1) is present especially n ith respect to zirconium. or is to be tested for, a preliminary exhIany qualitative tests for uranium traction of uranyl diethyldithiocarhave been proposed. The fluorescent bamate is carried out. The aqueous method involves observation of the layer is then tested for thorium, and unknown on a fused alkali fluoride the organic portion is tested for uraunder ultraviolet light (1, 10, 1 1 ) . nium(V1). This is a sensitive test, but some metals interfere. Extraction methods have THORIUM TEST increased the selectivity of qualitative tests for uranium in aqueous solution. In the p H range of 1.7 to 3.0. thoMost of these involve extraction of rium can be titrated quantitatively n-ith uranyl nitrate into ether (15) or uranyl EDTA using arsenazo indicator. At diethyldithiocarba~nate into chloroform higher pH values, the violet thorium(7, S), although several other schemes arsenazo complex remained even after have bpen used (13, 16, 20). A good a considerable excess of EDTA had summary of the chemical tests for been added. This was made the basis uranium is given by Kenger and Duckof the proposed qualitative test for ert (17). thorium. Sufficient EDTA is added The qualitative tests proposed for to complex all interfering metal ions thorium and uranium(T'1) are simple, present in the sample. The p H is sensitive. and selective. I n aqueous adjusted to approximately 8 and arsesolution containing (ethylenedri1inito)nazo solution is added. Only thorium tetraacetic acid (EDTA). the reagent and a fen- other metal ionc: give a
azo)-2-naphthol-3,6-disulfonic acid (3,6, 6, l a ) , and 2,7-bis(4-sulfonaphthylazo)-
VOL. 30, NO. 6, JUNE 1958
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