Table 111.
Contaminative radioisotope SI‘86
Zr96-N bo5 Rulo3 Ba138
Results of Decontamination Studies Involving Important FissionProduct Radioisotopes
Initial 1.96 X 1.64 X 5.95 x 4.46 X
IO6 lo6 108
lo6
Radioactivitv. c.~.m.O After Zr(IO& After CszSnClcpptn. and Fe(IOs:)I scavenge 1st 2nd 15 None 5 . 7 2 X 106 191 None 1 . 1 9 x 104 2 . 5 3 x 104 Noneb 3 . 9 6 X IO6 None 3.61 X lo6 None
All c.p.m. values corrected for background count. A drop of Ru+Jholdback solution added to sample just prior to second precipitation of CskhC16. a
technique t h a t eliminates t h e hazards associated with perchloric acid or costly reagents such as chloroplatinic acid. It is d f i c u l t to eliminate ruthenium activity in samples that are aqueous extracts of soil and in which the ruthenium activity is lo5 to IOe times greater than the cesium activity. In such a case, ruthenium can be removed by oxidation to ruthenium tetroxide, Ru04, followed by volatilization of the Ru04, before the procedure described is carried out (6). LITERATURE CITED
(1) Finston, H. L., Xinsley, M. T., eds.,
method, the special reagent used must be refrigerated to prevent its decomposition. Removal of Contaminative Radioisotopes. The chlorostannate method was also checked for stepwise and over-all effectiveness in decontamination with respect t o specific important radioisotopes usually present in large quantities in fission-product mixtures. T h e results are shown in Table 111. Decontamination factors 2 lo6were also obtained for radioisotopes of cerium, protactinium, the rare-earth elements, iodine, and molybdenum. Sodium and potassium, each present in quantities as large as 200 mg. per test portion, do not interfere in the determination of cesium (6). Samples known to contain am-
monium ions require preteatment, which consists in the addition of concentrated HN’Oa to the solution of sample and carrier until the solution becomes slightly acid. The solution, contained in a small beaker, is then evaporated slowly. Heat is applied to the side of the beaker t o volatilize any ammonium salts that may have adhered to the glass. The residue is dissolved in a few milliliters of hot water and transferred to a centrifuge tube; then the procedure as given can be carried out. Applicability of Method, The method is applicable t o a variety of samples, although most of t h e studies were made o n fission-product mixtures. It gives t h e radiochemist another choice of a precipitation
Natl. Acad. Sei.-Natl. Research Council Rept. NAS-NS-3035 (1961). (2) Glendenin, L. E., Nelson, C. M., Paper 283, Natl. Nuclear Energy Series. Div. IV. Vol. 9. Book 3. 1942-5
(195ij. (3) Handley, T. H., Burros, C. L., ANAL. CHEM.31,332 (1959). (4) Moser, L., Ritschel, E., 2. Anal. Chem. 70, 184 (1927). (5) Strominger, D., Hollander, J. M., Seaborg, G. T., Revs. Modern Phys. 30, No. 2, Part 11, 585 (1958); esp. pp. 714, 715, 718. (6) Wyatt, E. I., Ghann, C. L., “Cesium
Activity in Aqueoy,s Solutions, Chlorostannate Method, Method 2 21195 (3-7-61), “ORNL Master Analytical Manual,” U. S. At. Energy Comm. Rept. TID-7015, Suppl. 4 (1961).
RECEIVEDfor review April 1, 1963. Accepted June 14, 1963. Southeastern Regional Meeting, ACS, Gatlinburg, Tenn., November 1962.
Radioche mica1 Separation of Bismuth by Amalgam Exchange F. E. ORBE’, I. H. QURESH12, and W. W. MEINKE Department o f Chemistry, University of Michigan, Ann Arbor, Mich.
b Radiochemical separation of bismuth by amalgam exchange in an aqueous sulfuric acid system has been critically evaluated. The bismuth amalgam exchange step is followed by a back-extraction with saturated cupric sulfate in 1.ON nitric acid for selective removal of bismuth from the mercury phase. Bismuth yields of 97.5% were obtained with less than 0.1 % contamination from most typical elements. Mineral acids below 2.OM do not affect the exchange. At room temperature the over-all separation requires about 10 minutes; at higher temperatures, about 4 to 5 minutes.
T
HE PRINCIPAL methods used to isolate minute quantities of bismuth are precipitation with hydrogen sulfide and solvent extraction from basic
1436
ANALYTICAL CHEMISTRY
citrate solution with carbon tetrachloride-dithizone (11). Novey and coworkers (7) have used a chemical deposition method in which bismuth deposits on nickel powder from a 0.5.M hydrochloric acid solution, while a very reliable method for the separation of bismuth is a n anion exchange column technique using Dowex-1 (9). However, since bismuth has a great tendency to be contaminated by other elements there are very few selective separations available. The principle of isotopic exchange between cadmium ion and a dilute amalgam of that metal has been explored by Fronaeus (4, 6). A preliminary communication from this laboratory (1) indicated t h a t this principle could he used for radiochemical separation and could be applied to metals other than cadmium. This
early work has been confirmed and amplified by our recent studies on the radiochemical separation of cadmium (S), indium (IO), and strontium (8) employing the amalgam exchange principle. For these elements a simple 10-minute procedure gives excellent decontamination, far better than that obtained with the best standard procedures previously available. The separation technique for bismuth involves two isotopic exchange steps. I n the first, radioactive bismuth exchanges m-ith inactive bismuth in the amalgam. This exchange can be represented by the following reaction: Bi(Hg)
+ Bi*+3Fi Bi*(Hg) f Bifa
1 Present address, National Polytechnic University, Quito, Ecuador. a Present address, Pakistan Atomic Energy Commission, Karachi, Pakistan.
the amalgam to another bottle, wash twice with Zml. portions of 0.1N nitric acid and then transfer to a third bottle containing 2 ml. of saturated cupric sulfate solution in 1N nitric acid. Cap this bottle and shake mechanically for 5 minutes. Take a 100-pl. aliquot of aqueous layer containing separated bismuth isotopes and count. Total time for the separation is about 10 minutes.
SEPARATION BY A M A L G A M EXCHANGE
RADIOCHI!MICAL
7
SEPARATIOI'I BETTER THAN MEASURAEILE LOWER LIMIT
DISCUSSION AND RESULTS
~
;
I
'
Cs E a - L o Sr Ce-Pr Zr-NbZn Cd
I
In
TI
l Co
l
1
Sn
Sb
A number of preliminary experiments were performed to determine the optimum separation procedure. Carrier-free bismuth-210 obtained as a decay product of lead-210 was used as a tracer in these experiments. The bismuth-210 was separated from accompanying lead-210 and polonium-210 activities with Dowex-1 resin (9). In addition to sulfuric acid, several other exchange media were also investigated such as nitric, hydrochloric, perchloric, hydrofluoric, and phosphoric acids, potassium chloride, potassium iodide, ammonium nitrate, and sodium sulfate. In general, these media, in concentrations of from 0.5 to 2.OM, are favorable for the exchange and give yields of about 96-98%, although halogen acids in low concentrations can not be used because of the formation of bismuth oxyhalide precipitates. Nitric acid above 2N concentration tends to dissolve the amalgam. Studies with different concentrations of sulfuric acid gave yields of 98.5, 98.5, and 98.6% for procedures using 0.5N, 2N, and concentrated sulfuric acid, respectively. Sulfuric acid solution of 0.5N was used for the standard procedure to keep the total cation concentration low. Employing the general procedure with 1.4% bismuth amalgam, studies were made with varying amounts of amalgam. The exchange increases as the amount of amalgam increases and begins to level off a t 200 pl. Yields of 86, 95.2, 98, and 98% were obtained with 50, 100, 200, and 300 p L of the amalgam, respectively. Aliquots of 200 pl. of the amalgam were used in the standard procedure. Failure to purge the air above the system with nitrogen gas leads to a
I
I BI Ru-Rh Se
Hg
If
Figure 1. Comparison of decontamination obtained for strontium, cadmium, indium, and bismuth in radiochemical separations by amalgam technique
where the asterisk denotes a radioisotope of bismuth. The concentration of bismuth in the smalgam must be much greater than that in the aqueous phase for effective separation. In the second step, the radioactive bismuth is selectively back-extracted into the aqueous phase by contact with saturated copper sulfate solution. Radioactive tracers were used to determine the degree of separation and the yield of bismuth. EXPERlMlfNTAL
Apparatus. T h e separations were made in a 1/2-ounce Boston round bottle with polyethylene insert screw cap (Plax Corp., Bioomfield, Conn.). T h e bottle was c1,tmped in a mechanical shaker (Model 33, Burrell Corp., Pittsburgh, Pa.), t o which a n extension a r m of 12 inches was connected for added racial action. Gamma-ray measurements were made in the Nuclear-Chic ago Model DS-3 scintillation well counter described previously (1.9). Reagents. Bismuth metal sticks, c.P., Amend Chemicrtl Co., New York 10, N. Y. Saturated cupric sulfate solution in 1 N nitric acid, Baker analyzed reagent. Mercury, Baker and Adamson, triple distilled, analytical reagent, further p u r s e d by washing with dilute nitric acid, followed by rinsing with distilled water. Nitrogen gas, 98%, Liquid Carbonic co. All other nonradioactive reagents were of C.P. or analyz.sd reagent grade.
Radioactive tracers used in this work have been described previously [Table I1 (1.9) and Table I (@I. Preparation of Bismuth Amalgam.
Add the appropriate weight (1.4% b y weight is the solubility of bismuth in mercury at room temperature) of bismuth metal t o the mercury stored under 0.5N nitric acid in a beaker. H e a t the system and agitate i t for a short time to amalgamate the bismuth completely. Amalgam
Exchange
Procedure.
Place in a bottle 2 ml. of 0.5N sulfuric acid solution containing tracers of contaminating ions plus 10 pg. of bismuth. Use inactive bismuth for contamination studies-radioactive bismuth and nonradioactive interfering substances for yield determinations, Mix well. Add 200 ~ 1 .(-2.7 grams by weight) of 1.4% bismuth amalgam (-37.8 mg. of bismuth). Purge the system with nitrogen gas for 1 minute. Quickly cap the bottle and shake mechanically for 2 minutes. Remove the aqueous phase by suction, transfer
Table 1.
Agitation time, extraction step, minutes 0.5 1 1.25 0.25 0.5
... ...
Temperature Dependence of Separation on Agitation Time
Exchange,
%
84.3 95.8 97.5 91.1 98.0
... ...
Temperature,
c.
52 52 52 90 90 90 90
Agitation time, back extraction, minutes 0.5 1 2 0.25 1 1.5 2
Yield, % (total) 70 87.3 88 69.2 90.6 94.8 96.7
VOL. 35, NO. 10, SEPTEMBER 1963
1437
Table II. Separation of Bismuth and Contarninants
Amalgam Exchange Procedure“ Separated, % Reductiond potential, Exchange Elution Total volts separated Weightc step step 0.17 35.8 0.06 C.F. e I 0.09 < O . 003 1 mg. f -2.92
