J. van R. Smit
Nationol Chemical Research laboratories Pretoria, South Africa
II
Thorium-234 "COW"
In a paper entitled "A Thorium-234 'Cow' for Pa-234" in the October, 1959, issue of THIS JOURNAL, CarsweU and Lawrence (1) describe a new routine ion-exchange procedure for the separation of 24-day Th-234 from its parent U-238. While incorporating some new features their method strikes us as extraordinarily complicated. Except for large-scale work (2), ether extraction is still the simplest and quickest method of separating the Th-234 activity from uranium. When uranyl nitrate, UOZ(N03.)2.6HZO,is dissolved in ethyl ether, the water of crystallization gives rise to the formatioil of a small aqueous phase which contains essentially all the Th-234, together with a small amount of uranium. For the elimination of the latter several convenient methods are available: (a) solvent extraction with tributyl phosphate (1); (b) selective adsorption of Th-234 on a cation exchanger, removal of uranium by elution with hydrochloric acid, and recovery of the thorium activity with oxalic acid solution (2, 3); (c) selective adsorption of uranium on an anion-exchange resin from strong hydrochloric acid solution (4). Carswell and Lawrence (1) have attempted to apply t,he latter method, without prior enrichment, to the separation of Th-234 from GO g of uranium. In order to adsorb the major constituent quantitatively a large (600 ml) anion-exchanger bed was needed, but this was apparently still inadequate, yielding a product contaminated by traces of uranium. To overcome this difficulty they have inserted a 5-ml cation-exchange column in the elution cycle to absorb the Th-234. This immediately nullifies any advantage which may have accrued from the use of the anion-exchanger column, for the same result may be obtained by per-
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Journal of Chemical Education
colating an aqueous solution of the same amount of uranium salt through a column bed of cation exchanger (e.g., Dowex 50) as small as 2.0 ml in volume.' For the routine separation of Th-234 from amounts of uraninm up to a few hundred grams, the following simple procedure can be recommended. If crystalline uranyl nitrate is available, dissolve the salt in the minimum quantity of ethyl ether and collect the small aqueous phase. Evaporate to dryness, take up in l O A l HCL and pass the solution through a small column of "strong-base" anion exchanger in the chloride cycle. Wash with three to five column volumes of 10M HC1. Pure Th-234 is now obtained in the effluent. Alternatively, extract the traces of uranium with tributgl phosphate. For further milkings of the activity, extract the ethereal solution with 2-ml portions of distilled water, followed by ion-exchange or solvent-extraction purificatio~ias above. When the uranium is not available as the nitrate, or when the separation is to be performed on larger quantities, a cation-exchange separation procedure (93) is indicated. Literature Cited (1) CARSWELL, D. J.,
AND LAWRENCE, J. J., J. CHEM.EDUC.,36, 499 (1959). (2) SMIT,J. VAN R., REISACH, M., AND STRELOW, F. W. E., 2nd International Conference on Peaceful Uses of Atomic Energy, Paper 1119, 1958. (3) DYRSSEN, D., S w m k Kem. Tidskr., 62, 153 (1950). (4) KEAUS,K. A,, AND NELSON.F., 1st Internt~tionrtlConference on Peaceful Uses of Atomic Energy, Paper 837, 1955.
For instance, a. column bed of approximrttely one liter was used by Smit, et al., ( d ) for the quantitative separation of Th-234 from about 50 kg of uranium.
