added to the HC1-"0s system. The result was that mercurous ion began t o tail, owing to its strong interaction with methyl alcohol. When methyl alcohol was replaced by isobutyl alcohol, the system became less polar and Hg2+z gave a compact spot. Three ions gave R/ values significantly different from those of Hg,+z and Hg+2. With isopropyl alcohol, which is intermediate in polarity between methyl alcohol and isobutyl alcohol, the system became fast, selective, and efficient. A reference to Table I shows that Sbf3 and Sb+O have different R, values in a number of organic solvents-i.e., acetic, propionic, and butyric acids; dioxane, acetone, ethyl methyl ketone, methyl alcohol, and isopropyl ether. And, therefore, a number of excellent separations are possible with slight modifications in these solvents. All efforts to separate Sbf3 and Sbf6 using individual organic solvents failed because most of them were not, sufficiently polar. Acetic acid gave an elongated spot owing to its low ionization. The addition of water increased the ionization of acetic acid sufficiently to give compact spots. Because of the high polarity of the system, however, ARf was very small. The addition of
ethyl acetate decreased the polarity of the system to such an extent that A R, became signi6cant. It was noticed in this study that the higher valence state almost always had the higher R f value. This is easily understood because the higher valence state has a greater covalent character and therefore a greater complexing power. Of the solvents we studied only formic acid appears to be an exception t o this trend. The R f of Sb+6 in formic acid is smaller than that of Sb+3. In the homologous series of fatty acids studied, the R, values decreased with an increase in molecular weight owing to a decrease in the polarity of the system. In this case also formic acid is an exception. The R/ value of Sb+6 in formic acid is less than in acetic acid. We are making a more complete study of the behavior of formic acid and the findings will be reported later. The importance of time of separation in such cases has been emphasized earlier. To incorporate it in paper chromatography we suggest that the time required for a 1-cm. separation between spot boundaries should be mentioned where necessary along with other data. A paper chromatographic separation may be classified as fast,
rapid, normal, slow, or extra slow according as this time ( t ) is 0 to 30 minutes, 30 minutes to 1 hour, 1 to 6 hours, 6 to 24 hours, or more than 24 hours, respectively. Time for the Hg2+z-Hg+2 separation with 8 3 and 8 1 is 10 minutes, and for the Sb+" Sbf6 separation with Sa is 20 minutes. Hence, both these separations may be classified as fast. ACKNOWLEDGMENT
The authors are grateful to A. R. Kidwai, Head of the Department of Chemistry, for his interest and encouragement. LITERATURE CITED
lOS! ___
(3) Q1 34,1341(1962). (4) Qureshi, M., Khan, M. A., J. Chromatog. 8,276 (1962).
RECEIVEDfor review July 30, 1962. Accepted July 8, 1963. One of UB (M. A. K.) thanks C.S.I.R., India, for financial assistance.
Separation of Technetium from Mixed Fission Products by Solvent Extrac tio n with Tributyl Phosphate MILTON H. CAMPBELL Chemical Processing Deportment, General Electric Co., Richland, Wash.
b A new liquid-liquid separation technique is described for quantitatively extracting technetium-99(V11) into a tributyl phosphate phase from a sulfuric acid solution of mixed fission products, Technetium(VI1) distribution ratios are presented as a function of hydrogen ion molarity and tributyl phosphate concentration. Sodium flvoride is used to provide the necessary zirconium-niobium decontamination and a cation exchange column ensures decontamination from metallic ions such as uranium. Decontamination factors for zirconium-niobium and ruthenium are 2 X lo4 and 1 X lo4, respectively. Technetium yields of 92% were obtained with a standard deviation of *0.8%.
T
the first man-made element (9), does not occur naturally (6). The most substantial source of this element is irradiated uranium fuel (1) which contains the long-lived radioisotope technetium-99. ECHNETIUM,
2052
ANALYTICAL CHEMISTRY
Since these fuel elements are processed chemically for recovery of uranium, plutonium, and some fission products, raffinate solutions containing significant quantities of the pertechnetate ion are available for recovery. Technetium-99 is normally found as the pertechnetate ion in dissolved fuel element solutions and the subsequent raffinate. An analytical method capable of separating pertechnetate from gross quantities of fission products with a minimum elapsed time would be required to support a recovery process. Analytically, the pertechnetate ion has been separated from most fission products by a variety of methods including precipitation and distillation (8), extraction (10,1B, IS), and anion exchange resin (7). Radioassay, the most sensitive measurement for technetium-99, was used in most methods. This isotope has a low beta energy of 0.29 m.e.v., hence the presence of other radioactive material on the mount would create serious interference. Of all analytical methods reviewed, only the distillation technique
provided satisfactory decontamination from radioactive ruthenium isotopes. Solvent extraction techniques for separating pertechnetate from radioactive wastes have been widely studied. Boyd and Larson (2) reviewed pertechnetate separation by 34 organic solvents and determined that tertiary amines or quaternary ammonium salts had the best partition coefficients. Gerlit (S), in studying this ion's extraction characteristics into 21 different organic solutions from various acidic, basic, and neutral media, found that tributyl phosphate-sulfuric acid was a potential extraction system. Siddall (11)suggested the extraction mechanism of pertechnetate in a 30% tributyl phosphate-nitric acid system using n-dodecane as a diluent. Kertes and Beck (6) found a different mechanism for the same system using carbon tetrachloride as diluent, and additionally, defined the nitric acid-dibutyl phosphate system. These works lead t o the generalization that the pertechnetate ion can be extracted into organic
solvents containing oxygen, phosphorus, or nitrogen. Since trihutyl phosphate provides excellent decontamination from ruthenium in the Purex process (4), potential use as an analytical reagent was investigated. EXPERIMENTAL
Reagents and Equipment. Potassium pertechnetate (KTcg90d) was obtained from Oak Ridge National Laboratory as a 3.4 grams per liter solution in a 1.OM a,mmonium hvdroxide matrix. Tributyl phosphate (TBP) of C.P. -grade was diluted to the desired concentration with a kerosine diluent (Soltrol). All dilutions were prepared on a volume basis. After dilution, T B P degradation products were removed by washing with m equal volume of three per cent sodium carbonate. Prior to use the TBP-k erosine mixture was equilibrated with an equal volume of sulfuric acid a t the s:ime molarity to be used in the experiment. The cation exchange resin used was Dowex-50x8, 100- to 200-mesh, in the hydrogen ion form and of an analytical grade. The resin was gravity loaded in a 5-cm. long, 3-mm. i.d. column until a bed height of 1.5 cm. was attained. All extractions were performed in flat-bottomed 15-ml. vials on a magnetic stirrer using glass covered stir bars. These contacts were performed a t room temperature. Radioactive sample aliquots were mounted and dried on 1-inch diameber stainless steel dishes, 1/8-inch deep. Beta activities were counted in a gas flow beta proportional counter, and beta energy spectra were obtained using a terphenyl crystal detector and a multichannel analyzer. Procedure. The sariple, calculated t o provide a good counting rate, was diluted to 2 ml. with &so4 and N a F to yield a final concentration of 1 M H2S04and 0.025M NaF. One drop of 30% H202 was added to ensure that all technetium was present as pertechnetate, and the solution was stirred for several minutes. Exactly 4 ml. of 45y0 T B P was then added, and the mixture was stirred a t a complete emulsion for 5 minutes. Phases were separated by centrifuging and 3.0 ml. of the organic was transferred to a vial containing 1.5 ml. of 1M sulfuric acid-0.025M sodium fluoride-0.2M Hz02 scrub solution. Thizi mixture was stirred for 2 minutes and again centrifuged to separate thi: phases. Onehalf milliliter of the organic phase was transferred to a stripping solution consisting of 10 ml. of distilled water. This mixture was stirred at a complete emulsion for 8 minutes, then centrifuged. A half milliliter of the aqueous phase was transferred to a cation exchange column and allowed to flow through it onto a inounting dish. Three 0.2-ml. water wtshes were also passed through the column and accumulated on the mounting d sh. The mount was dried under an infrared lamp, cooled, covered with a thin layer of
collodion, and counted in a gas flow beta proportional counter. The analysis was completed within 45 minutes. RESULTS AND DISCUSSION
Extraction of pertechnetate was first studied as a function of acid molarity with a 45% T B P solvent. Both nitric and sulfuric acid matrices were tried for the aqueous phase. At first, distribution ratios checked neither those available in the literature (3, 11) nor the second equilibration between the pertechnetate laden organic and a virgin acid scrub solution. However, on adding a drop of 3oy0hydrogen peroxide to the aqueous phase just prior to extraction, distribution ratios consistent with literature were found. Subsequent analyses of plant samples also showed a consistently higher pertechnetate value when the sample was pretreated with hydrogen peroxide. Pertechnetate distribution ratios in these two acids are presented in Table I. All further work was performed with a 1 M solution of sulfuric acid which provided a much better distribution ratio than was possible from a nitric acid solution. [Pertechnetate distribution ratios for nitric acid were in good agreement with the work of Kertes and Beck (6).] This particular molarity was selected to reduce pertechnetate losses during the organic extraction and stripping cycle. Since the method requires two volumes of organic per volume of aqueous, increased acid concentration would enhance the pertechnetate extraction only slightly (96.47, at 1 M us. 96.9y0 a t 2iM), but the acid in the extractant would increase markedly. Presence of excess acid in the solvent would have the negative effect of reducing the stripping efficiency for pertechnetate. A test t o find the minimum equilibration time for the above experiments showed that equilibrium was achieved within 3 minutes. To find the variation in the pertechnetate distribution ratio as a function of the TBP concentration, a l d f sulfuric acid phase was contacted with TBP concentrations between 0 and 60 volume yo. Table I1 contains these distribution ratios. A T B P concentration of 45 volume yo was selected for the analysis. This distribution ratio was very close to the maximum observation and, additionally, the solvent a t 45% TUP was less viscous than a t SO%, thus permitting better phase separations and more accuratr volumetric transfers. In considering a stripping solution for removing pertechnetate from the organic phase, distilled water was selected. As previously mentioned, sulfuric acid would also be stripped into the water. For an organic to aqueous
Table 1. Distribution of Pertechnetate between Nitric Acid or Sulfuric Acid and 45% TBP as Function of Hydrogen Ion Concentration
Hydrogen ion, rnoles/l. 0.0 (pH 6 . 7 ) 0.5 1.0 1.5 2.0 3.0 4.0 a
Distribution ratio, Do HNOs 0.0
HzSOa 0.0
1.36 1.16 0.91 0.65 0.30 0.09
3.1 4.5 iti.9 13.3 14.2 15.7
Distribution ratio, D, is defined as
(c./m./mnl. in organic phase)/(c./m./ml. in aqueous phase). These data were
calculated from duplicate analyses having material balances 295%.
Table II. Distribution of Pertechnetate between 2.ON Sulfuric Acid and Solvent as Function of TBP Concentration
TBP concn., vol. %
Distribution ratio, D
0 15 30 45
0.0 0.66 1.47 13.3 14.8
60
ratio of 1:20, a D of 0.11 was found when the solvent had first been contacted with a 1M sulfuric acid solution. h'eglecting any variation in acidity due to change of the water volume, the best stripping ratio was calculated to be 1:20. In this case less than o.5yOof the pertechnetate would be retained in the organic phase. The cation exchange resin was used to remove radioactive ions such as uranium or plutonium-i.e., decontamination factor was >lo6-which could follow the solvent cycle purification of pertechnetate. Material balance across the exchanger revealed no pertechnetate loss. Decontamination for pertechnetate from other fission products was very good. The major radioisotopes present in the sample solutions were Zrg5-Nb'6, Rul03-106 7 Ce144-Pr144, Ce141, C ~ l 2 7 , Srgo-Yg0, and SrE9. Of these, the rare earths, cesium, strontium, and yttrium were notably inextractable in TBP. Both zirconium-niobium and ruthenium were extractable to a limited extent. To reduce zirconium-niobium carried by the organic, the aqueous phase for the initial extraction was made 0.025M in sodium fluoride. In some highly radioactive samples it was necessary to add a scrub step in which the pertechnetate laden organic was scrubbed with a 1144 HZS04-0.025M NaF-0.2M H,On solution a t a 2 :1organic to aqueous ratio. Only one such scrub should be used since there is a pertechnetate loss (D = 13.3) of 4% in this step. Decontamination in the extraction step VOL. 35, NO. 13, DECEMBER 1963
2053
105
104
OI I
3
.-c
I
I
103
i
L
0 a
n c c
a 0
V
I
0
O
U
0 1 0.2
0 3
+
0.4
'
!
0 8
'
'
I 2
'
'
1.6
'
I
2 0
EiMevl
Figure 2. analysis I
t 0
I
I
I
I
I
I
0 2
0.3
0.4
0.5
0.6
0.7
Beta decontamination profile of pertechnetate
O S
€(MeV1
Figure 1 . Gamma decontamination profile of pertechnetate analysis
was 83 for zirconium-niobium and 311 for ruthenium. Decontamination gained by the scrub was 82 for zirconium-niobium and 6 for the ruthenium. Difference in ruthenium decontamination for the extraction and scrub steps showed it was present in more than one ionic form, one or more of which was not extractable in TBP. The above decontaminations as well as those for the remaining steps are illustrated in Figure l. All the gamma spectra have been normalized to represent the quantity of pertechnetate mounted at the end of the analyses. The remainder of the method, consisting of the aqueous strip and the cation exchange purification, yielded decontamination factors of 3 for zirconium-niobium and 6 for ruthenium.
Table 111.
Determination of Pertechnetate AV.
No. of c./rn. T o g g Atiitlysl sxniples takon R
6
b
4 4
a b
2
%>I40 35,140
17,570 17,570
Standard dev.: *0.8% ~~
2054
~
ANALYTICAL CHEMISTRY
yo
Tcgg
found 92.5 91.6 91.6 92.7
The overall decontamination was 2 X 104 for zirconium-niobium and 1 X lo4 for ruthenium. These factors are based on actual stream samples, not on prepared tracers which for the most part would not contain the same mixture of ionic species found in plant solutions. 4 beta energy profile for the analysis: is shown in Figure 2. There is a scale change between 0.3 and 0.4 m.e.v. to distinguish low energy spectra and still present the full spectra obtained (curve shape does not change in the break). As previously mentioned, these spectra were obtained using a terphenyl crystal and a multichannel analyzer. The top curve showing the sample spectra has its ordinate to the right. A high continuum above 0.4 m.e.v. was due to Y90 and Pr144. The second and third curves showed the decontamination gained by extraction and scrubbing. In this case, the high energy portion is due to The final spectra demonstrates purity of the mount. Note the maximum energy of 0.30 m.e.v. correlates closely with that of Tc99. Results of aualrses performed on a pertechnetate standard are shown in Table 111. The reader should note that all waste solutions of interest originated from fuel elements with a t least a 200day cooling period after irradiation. This analysis would not be specific for
Tcg9 in extremely short cooled fuels which could contain a variety of technetium isotopes depending on fuel type and irradiation history. LITERATURE CITED
(1) Boyd, G. E., J . Chem. Educ. 36, 2 (19591. (2)' Boyd, G. E., Larson, Q. V., U . S . At. Energy Comm. Document ORNL-2159, 1956. (3) Gerlit, J. B., Proc. of the Intern. Conf. Peaceful Use At. Energy 7, 1952 (1955). (4) Irish, E. R., Reas, W. H., U . S. At. Energy Comm. Document HW-49483A, 1957. (5) Katcoff, S., Phys. Rev. 111,575 (1958). ( 6 ) Kertes, A. S., Beck, A., Proc. 7th
Intern. Cong. Clin. Chem., Stockholm,
pp. 352-4 (1962). (7) Miller, H. H., U. S.At. Energu Comm. Document ORNL 1880 (Rev.), 2 (1955). (8) Nelson, C. RI., Cobble, J. W., Boyd, G. E., Smith, W. T., Jr., U . S. At. Energy Comm. Document ORNL 1116 (declassified), 30 (1951). (9) Perrier, C., SegrO, E., Nature 159, 24 (1947). (IO) Salaria, G. B. S., Rulfs, C. L., Elving, P. J., ANAL. CHEV. 35, 983 (1963). (11) Siddall, T. H., 111, U . S. At. Energy Comm. Document DP-364 (declassified), 1959. (12). Smith, F. M., General Electric Co.,
Richland, Wash., private communication. (13) Tribalat, S., Beydon, J., Aiwl. Chim. Acta 8 , 2 2 (1958).
RECEIVEDfor review May 6, 1963.
Accepted September 9, 1963. Division of Analytical Chemistry, 144th Meeting ACS, Lou Angeles, Calif., April 1963. Work performed under contract No. AT(45-1)1350 between the Atomic Energy Commission and General Electric Co.
