VOL 9, pp. 285 to 287. Pergamon Press Ltd. printed ia Northern Ireland
IMPROVED RADIOCHEMICAL DETERMINATION OF COBALT* S. FREDRLC [email protected]
and WILLIAM J. MAECK Phillips Petroleum Company, Atomic Energy Division, Idaho Falls, Idaho, U.S.A.
(Received20 October 1961. Accepted 8 November 1961) Summary--A shortened procedure for the radiochemical determination of cobalt is described. The precipitation of cobalt mercuryn thiocyanate for the tinal yield determination, proposed by Hahn and Smith,l has been verified. Decontamination from 5-hr cooled fission products and l-day cooled stainless steel activation products is complete.
RECENTLYHahn and Smith1 surveyed the then existing procedures for the radiochemical determination of cobalt. They concluded that the method of Burgus, with a changed yield determination, was best. The change in yield determination was from the electrodeposition of cobalt to precipitation as cobalt mercuryI thiocyanate,
WHgWN),I. At the time their article appeared, research in our laboratory had resulted in a method using this same precipitate. Our reasons for the selection of this precipitate are in complete agreement with those stated in the article. However, in our method the separation steps prior to the yield determination require only 45 min, resulting in a saving of over 1 hr in the overall procedure with no significant change in decontamination. Omitting the potassium cobaltinitrite and sulphide precipitations, two of the more tedious steps, accounts for most of the time saving. EXPERIMENTAL Procedure 1. Place an aliquot of sample in a 50-ml centrifuge containing 1 ml of cobalt carrier [lo mg/ml as Co(NO&]. Add sufficient sodium hydroxide to precipitate Co(OH), completely. Centrifuge and discard the supernatant solution. 2. Dissolve the precipitate in a minimum (cu. 2 drops) of cont. sulphuric acid. Heat, if necessary, until dissolution is complete and the cobalt red colour appears. Cool, add 2 ml of cont. ammonium hydroxide solution, and dilute to 10 ml with water. 3. Slowly add 10 drops of 10 mg/ml iron I* holdback while vigorously swirling the solution. Centrifuge and decant (or filter) into a 125~ml separatory funnel. 4. Add 2 ml of glacial acetic acid, 20 ml of 25 % ammonium thiocyanate solution (pH 7*0), and 10 ml of methyl isobutyl ketone. Extract for 1 mm. Discard the aqueous phase. 5. Add 20 ml of 25 % ammonium thiocyanate solution and scrub the organic phase for 1 min. Discard the aqueous phase. Repeat. 6. Strip the cobalt with 5 ml of water for 30 sec. Drain the aqueous phase into a clean 50-ml centrifuge tube. Repeat the strip with an additional 5 ml of water, combining the aqueous portions. Add 3 drops of cont. hydrochloric acid. 7. Heat nearly to boiling and add 2 ml of 1M ammonium mercuryu thiocyanate. Swirl until precipitation of the blue cobalt thiocyanate is complete, as evidenced by the lack of red colour in solution. 8. Cool in an ice bath and filter onto a tared filter. Wash with water, ethanol, and ether. Dry for 5 min in a vacuum desiccator and weigh as Co[Hg(SCN),I (11.98 % by weight cobalt). * Work performed under contract At(lO-l)-205 for the U.S. Atomic Energy Commission. 285
S. FRBDRICMARSHand WILLIAM J. MAECK
IO r Co [Hg(SCN&] I 0.50 I.00
Energy, FIG. 1.--Defiontamination
from !%hr cooled f&ion
Enwy. FIG. 2.-Decontamination
final product I 1.50
from l-day cooled stainless steel activation products.
The gamma ray spectra shown in Figs. 1 and 2 illustrate the decontamination of cobalt from 5-hrcooled fission products and I-day cooled stainless steel (Bureau of Standards Sample No. 123-A) activation products. Zwammenfawan$-Es wird ein gekmztes Verfahren zur radiochemischen Bestimmung von Kobalt beschrieben. Die Falhmg von Kobalt mercurirhodanid wird nach Hahn und Smith fti die endliche Bestimmung best;itigt. Die Entgiftung ist aus 5-Stunde-gektihlt Spaltprodukten und 1-Tag-gektihltNichtrostende-Stahl-Aktivierungsprodukten vollig. R&sum&T-s auteurs d&crivent une methode simplifies de dosage radiocbimique du cobalt. La precipitation du mercurithiocyanate de cobalt pour le dosage final, propos&e par Hahn et Smith, a ete v&ifiee. La decontamination des produits de fissions refroidis pendant 5 heures et des produits d’activation de I’acier inoxydable refroidis pendant 1 jour est complete. REFERENCES 1 R. B. Hahn and D. L. Smith, Talanfu, 1961,7,291. a W. H. Burgus, Collected Radiochemical Procedures, edited by J. Kleinberg. Rept. LA-1721 (Rev.), November 18, 1955, pp. 66-72.
Atomic Energy Comm.