Distribution Studies of Radium and Other Metallic Elements between Thenoyltrifluoroacetone in Methyl Isobutyl Ketone and Aqueous Solutions W. Morrison Jackson’ and Geoffrey I. Gleason Special Training Division, Oak Ridge Associated Universities, Oak Ridge, Tenn.
Using a standardized procedure previously reported, the distribution of radium and 13 other metallic elements were quantitatively compared, by distributing a radiotracer of the element of interest between an aqueous phase and an organic phase consisting of 0.1M TTA in MIBK. From the ratio of activity in the organic phase to activity in the aqueous phase, distribution coefficients were calculated as a function of pH (Atomic absorption was used for measuring the concentration of magnesium). Using radium-224, the extraction of radium by TTA in MIBK was successfully demonstrated to occur under almost identical pH conditions as previously reported for barium. In addition, distribution coefficients for reversible extractions into the TTA-MIBK phase from the aqueous phase were measured for magnesium, manganese, cobalt, nickel, copper, praseodymium, lead, and thorium. When the log D values were plotted YS. pH for iron, molybdenum, technetium, tungsten, and gold, the normal Sshaped curves were not obtained. From the data, pH conditions can be selected to allow the separation of the daughter elements, radium and lead, from thorium, as well as for many other element pairs.
The use of thenoyltrifluoroacetone (TTA) in methyl isobutyl ketone (MIBK) to study the distribution coefficients of 13 Group Il and Group I11 elements was reported in a previous paper ( I ) . Based upon the results of this work. it was the authors’ opinion that radium should be extracted by TTA, although Hageman (2) had earlier reported no extraction by 0.25M TTA in benzene. Smithson, Shea, and Tewksbury (3) in a more recent literature review, covering liquid-liquid extraction of nonferrous metals, reported only one example of the use of organic extractants for the separation of radium, which was the separation of barium and radium by precipitation from glacial acetic acid. This was in agreement with the authors’ own literature survey and only after completion of the work reported here, were two examples of the successful extraction of radium from aqueous solutions discovered. Keller and Mosdzelewsky ( 4 ) reported that radium was extracted by 8-hydroxyquinoline in CHClB within the pH range of 10 to 12, but that quantitative extraction was only possible a t the higher concentrations of 1-2M 8-hydroxyquinoline. Sekine and coworkers, ( 5 , 6) reported the extraction of raPresent address, Alabama Power Company, Birmingham, Ala. 35291. ( 1 ) W. M . Jackson, G . I . Gleason, and P. J . Hammons, Jr.. Anal. Chem., 42, 1242 ( 1 9 7 0 ) . ( 2 ) F. Hageman, J. Amer. Chem. SOC.,72, 768 ( 1 9 5 0 ) . ( 3 ) G . R . Smithson, Jr., J. F. Shea, and T. L. Tewksbury, J. Metals, 18, 1037 ( 1 9 6 6 ) . ( 4 ) C. Keller and K . Mosdzelewski, (5) T. Sekine. Y . Kawashima, T. Soc. J a p . , 41, 3013 ( 1 9 6 8 )
Radiochim. Acta, 7, 185 ( 1 9 6 7 ) Unnai, and M. Sakairi, Bull. Chem.
dium by a TTA-TBP adduct in CC14, but gave no extraction data for TTA alone. The objectives of these studies were to determine if radium could be extracted from aqueous solutions by TTA in MIBK and to extend the standardized distribution coefficient measurements to metallic elements outside Groups I1 and 111, so that the chemist should have a much enlarged group of elements pairs, which are feasible to separate using TTA in MIBK.
EXPERIMENTAL Apparatus. A Burrell “Wrist-Action Shaker,” Model BB, was used for equilibration of samples. After equilibration, the following were used for the measurement of relative concentrations in the aqueous and TTA-MIBK phases: Gamma Counting. A 2-inch SaI(T1) lead shielded detector was used in combination with a single channel analyzer for measurements when a single radioactive species was present. Where interferences were possible from other radioactive species, e . g . , radioisotopes in a decay series, a 3-inch NaI(T1) lead shielded detector was used in combination with a Technical Measurement Corp. multichannel analyzer ( T M C Gammascope 11) Model 102 and a Teletype printer. Alpha and Beta Counting. A Beckman Liquid Scintillation System, Model LS-100 was used. Atomic Absorption. For magnesium, a Beckman Spectrophotometer, Model DB-G was used in combination with a Beckman Atomic Absorption attachment, Model 1301. Reagents. Organic Solutions. Thenoyltrifluoroacetone (TTA) obtained from the Columbia Organic Chemicals Company was dissolved in methyl isobutyl ketone (MIBK) to make 0.1M solutions. Tracer Stock Solutions. The radioisotopes. C O C O , 59Fe(III), 54Mn. and 63Ni in HC1 solutions were obtained from the International Chemical and Nuclear Corporation (ICK). The radioisotopes, 64Cu. 76As, I9*Au, 99Mo, I4*Pr, and IS7W were obtained by neutron activation of the respective reagent grade stable salts, CuO, As203, AuC13, Moos, Pr203. and WOS in the Oak Ridge National Laboratory LITR reactor. Aqueous stock solutions were then prepared by dissolving the activated salts. The radioisotope 99mTc in saline solution was obtained from a Union Carbide Corp. 99Mo “cow.” The radioisotopes, *12Pb, 224Ra. and 228Th were separated from a 228Th nitrate solution in equilibrium with the daughter radioisotopes, that was obtained from ICY. Aqueous Tracer Solutions. For solutions of p H 1 or above, the tracer stock solutions were diluted with 0.1M HC1 and aqueous NH3 was added as required to give the desired pH. For solutions with a p H less than 1, the aqueous tracer solution pH’s were calculated from the molarity of the diluting HCI and solution volumes. The dilution of the stock tracer solutions was, where possible, adjusted to give count rates of 50.000 to 100.000 cpm for 2-ml gamma samples and 0.1-ml alpha or beta samples in a liquid scintillator. Aqueous Magnesium Solutions. The aqueous MgC12 solutions were prepared by dissolving weighed amounts of magnesium metal in HC1 solutions and then diluting to give concentration ranges from 0.05 to 5 ppm of Mg. Aqueous NH3 was used to increase the p H where desired. To avoid changes in p H during the Sekine and Y . Hasegawa, “Solvent Extraction Research.” A . S. Kertes and Y . Marcus, Ed.. Wiley-lnterscience, New York, N . Y . ,
( 6 ) T.
1969. p 2 8 9 .
A N A L Y T I C A L C H E M I S T R Y , VOL. 45, NO. 12, OCTOBER 1973
2125
extractions, 0.02M potassium acetate was added to form a pH buffer in the aqueous phase. Liquid Scintillation “Cocktail.” The liquid scintillator was prepared by dissolving 7 grams of 2,5-diphenyloxazole (PPO), 0.375 gram of 1,4 bis-2-(5-phenyloxazolyl)-benzene(POPOP), and 150 grams of napthalene in 1liter of dioxane. Procedure. The standardized procedure reported earlier ( I ) for obtaining comparable distribution coefficient data as a function of pH was used in these studies. Thus, only new procedures pertinent to the distribution studies reported here are described. The aqueous tracer solutions of 228Th, 224Ra, and 212Pb were prepared by equilibrating aqueous chloride solutions, containing 228Thand its decay products plus an approximate 0.02M ammonium acetate pH buffer, with 0.1M TTA in MIBK as follows: ( a ) 22sTh-The TTA-MIBK phase from an equilibration within the p H range, 1.6 to 1.8, was equilibrated with a fresh (no initial activity) aqueous chloride solution, also, within the same pH range. Thorium-228 for use in the distribution studies was then back extracted from the separated TTA-MIBK phase into aqueous solutions having the desired HCI concentration. ( b ) 224Ra-The aqueous phase from an equilibration within the pH range, 5.0 to 5.2, was equilibrated with a fresh TTA-MIBK solution. The separated aqueous phase was then used for the 224Ra distribution studies. (c) 212Pb-Two successive double extractions at different p H ranges were used. First, with the pH within the range, 2.6 to 2.8, the aqueous phase was equilibrated in succession with t w o fresh TTA-MIBK solutions. Second, the resulting separated aqueous phase was then adjusted to the pH range, 5.0 to 5.2, and equilibrated with a fresh TTA-MIBK solution. The separated TTA-MIBK phase was then equilibrated with a fresh aqueous chloride solution, also, within the pH range, 5.0 to 5.2. Lead-212 for distribution studies was then back extracted into a 0.1M HC1 solution. The following procedure was used to calculate the net count rates for the 0.241-MeV gammas from 224Ra in the presence of 0.239-MeV gammas from the daughter radioisotope, 21ZPb: First, the activity of a freshly separated 224Ra sample was measured and plotted as a function of time. A corresponding growth factor curve, that changed linearly from 1.0 a t t = 0 to 1.855 at t = 100 min, was then plotted us. time. Second, during the 2Z4Ra distribution studies, very careful records of the elapsed time were kept from the initial separation ( t = 0) of the 224Ra used until the distribution phase samples were counted. Third, the appropriate correction factors were applied to compute the net count rate from the Zz4Ra in each sample. In these calculations, the assumption was made that all 2lzPb buildup from t = 0 until the time at which equilibration of the phases stopped would be present in the TTA-MIBK phase. Thus, computation of the net count rate for 224Rain the TTA-MIBK phase involved a series of successive approximations, whereas the count rates of the aqueous samples required correction only for buildup of activity from the end of the equilibration until they were counted, and for only the 224Ra in the aqueous phase a t the end of the equilibration. The liquid scintillation samples for the measurement of alphas from 228Th were prepared by dissolving a 0.1-ml sample of either the aqueous or the TTA-MIBK phase in the liquid scintillation “cocktail.” Measurement of the activity from a freshly separated sample of 228Th in the P-32 window of the liquid scintillation counter resulted in a linear activity increase of 1.035 a t the end of a 100-minute period. As described above for 224Ra,the net count rates for 228Th in each phase were corrected for buildup of activity by careful recording of elapsed times and application of the appropriate factor. Here the assumption was made that all buildup of activity from t = 0 until the end of equilibration would remain in the aqueous phase. The concentration of magnesium was measured by atomic absorption. The magnesium concentrations were varied from 0.5 to 5 ppm for the aqueous samples and from 0.05 to 0.5 ppm for the TTA-MIBK samples in order to obtain reasonable readings at a wavelength of 285.2 nm. An estimated error of 15% was arbitarily applied to each distribution coefficient for magnesium, since counting statistics did not apply.
RESULTS AND DISCUSSION Thorium, Radium, and Lead. The distribution studies for these three elements involved two distinct phases: 2126
Separation of the radioisotope of interest from the other members of the 228Th decay chain, and distribution studies using the separated radioisotopes as tracers. In actuality, the two phases overlapped in that the pH conditions for the separation of radium were first determined and its distribution studies completed before moving to lead and finally to thorium. In all of this work, very extensive use of gamma spectroscopy was used not only to monitor the degree of separation from the other members of the 228Th decay chain, but also to monitor the growth of daughter radioisotopes after a separation. Because of the influence which even a very small amount of impurity activity can have when the distribution coefficients are less than 10-2 or greater than 102, successive double extractions were used in the separation of 228Th,224Ra,and 21zPb for use in the distribution studies. Although he showed radium as not extractable by T T A in benzene, Hageman’s ( 2 ) study of 227Ac and its decay products was quite useful in choosing the initial trial pH values for the separations reported here. Thorium. The separation procedure for 228Th and the correction curve to be applied for the growth of activity from daughter radioisotopes were experimentally determined. Also, the decision to use alpha liquid scintillation counting rather than counting of the 0.084 MeV gamma was based on comparative measurement of the relative activity in a series of samples. The counting data were more reproducible using liquid scintillation in which the sample was dissolved directly into the “cocktail.” Gentle evaporation of the sample prior to adding the cocktail resulted in very erratic results in contrast with that obtained when counting beta emitters. The distribution coefficient data for thorium are shown in Table I. When the log D values are plotted us. pH, and compared with Hageman’s (2) curve for the extraction of thorium by 0.25M TTA in benzene, the agreement is fairly good. Hageman’s curve has a slightly steeper slope so that the entire curve falls between the pH values of 0 and 1, whereas the curve from the data in Table I starts slightly below a pH of 0 and extends above 1. The point of equal distribution between phases occurs at a pH of about 0.1. Radium. A separation procedure for 2z4Ra from 228Th and its own daughter radioisotopes was the first experimental requirement. Also, because of the impossibility of separating the 0.241-MeV gammas of 224Ra from the 0.239-MeV gammas of its daughter, 212Pb, with the NaI detector used; a means of correcting the total counts under the photopeak for the contribution due to 212Pb was required in order to obtain the net counts from 224Ra. Both of these requirements were accomplished. The distribution coefficient data for radium are shown in Table I. When the log D values for radium are plotted u s pH and compared with plots of the earlier reported data for calcium, strontium, and barium ( I ) , the linear mid-portion of the plot is almost identical with that previously found for barium. For both, the point of equal distribution between phases falls a t a pH of 6.4, only a slight change in slope was noted which placed the lower end of the radium curve between strontium and barium and the upper end above barium. This good agreement was taken as a confirmation of the separation procedure used for 224Ra and the corrections applied t o the count rate data for build-up of ZlZPb. Also, the agreement between these data and Sekine and coworkers’ (5) data for the distribution of radium between 0.1M sodium perchlorate solutions and CC14 containing 0.1M TTA and 0.1M TBP is excellent with an estimated difference at the midpoint of only 0.1
A N A L Y T I C A L C H E M I S T R Y , V O L . 45, NO. 12, OCTOBER 1973
Table I. Distribution of Thorium, Lead, and Radium between Aqueous Chloride Solutions and 0.1M TTA in MlBK Lead
Thorium PH
-0.30 -0.18 -0.01 0.30 0.40 1.02 1.58
Dist. coeff., D
1 . 3 3 f 0.10 3.68 f 0.03 8.70 f 0.31 5.61 f 0.04 2.00 f 0.01 1.38 f 0.09 2.22 f 0.03
x 10-3 X lo-’ X lo-’ X loo
x 10’ X loz X lo2
Dist. coeff., D
PH
3.31 f 0.43 X 2.97 f 0.09 X 9.23 f 0.19 X 7.93 f 0.07 X 1.68 f 0.02 X 5.87 f 0.10 X 4.83 f 0.18 X 3.04 f 0.44 X 5.26 f 1.73 X
2.05 2.95 3.36 3.90 4.15 4.45 4.97 5.46 5.85
pH unit. The conclusion inferred in a later paper by Sekine and Hasegawa (6) that the successful extraction of radium was due to the synergistic enhancement of metal TTA chelate extraction by T B P would thus appear to be invalid, since TTA alone was used as the extractant in the present study. Neither are in agreement with Hageman’s ( 2 ) data showing no extraction by 0.25M TTA in benzene. The data in Table I show that radium can be completely extracted into the TTA-MIBK phase as the pH is increased. Lead. The procedure for the separation of 212Pb from *28Th and the other radioisotopes in its decay chain was experimentally determined, as the first step prior to determination of the distribution coefficients for lead, which are shown in Table I. When the log D values are plotted us. p H and compared with Hageman’s ( 2 ) curve for the distribution of lead between aqueous solutions and 0.25M TTA in benzene, there is agreement that the initial extraction into the TTA-organic phase starts between pH 2 and 3. However, Hageman’s curve has a steeper slope with extraction into the organic phase essentially complete a t a pH of 4. The slope of the curve from these data is not as steep and does not show complete extraction into the TTA-MIBK phase until a p H of 5. The point of equal distribution between the two phases occurs a t a p H of about 4.0. Magnesium. With the completion of the distribution studies for radium, only magnesium of the Group I1 elements remained to be studied. In the absence of an available radioisotope of magnesium, atomic absorption was chosen for measurement of the concentration of magnesium in the aqueous and TTA-MIBK phases because of its high sensitivity for magnesium. In setting up the calibration curves for magnesium, an enhancement of about 8 was noted for the TTA-MIBK solutions. This agrees well with the 10-fold emission intensity enhancement reported by Dean (7) for magnesium a t a wavelength of 285.2 nm. The distribution coefficient data for magnesium are shown in Table 11. When the log D values are plotted us. p H and compared with similar plots of data previously reported ( 1 ) for calcium, strontium, and barium, the curve for magnesium falls just slightly to the left (lower pH) of calcium as should be expected from its smaller ionic size. The point of equal distribution between the two phases occurs a t a p H of about 5.1. Praseodymium. The rare earth elements are generally reported to have chemical properties very similar to the Group I11 elements, yttrium and lanthanum. For a com(7) J . A. Dean, “Flame Photometry,” McGraw Hill, New York, N.Y., 1960, p 63.
Radium Dist. coeff., D
PH
IO-’ lo-’ 101 Oo loo 10’ 10’ 10’
5.05 5.46 5.88 5.98 6.25 6.58 7.08 7.15 7.47 7.78 8.08 8.68
1.06 f 0.10 X 1.95 f 0.12 X 1.05 f 0.02 X 2.22 f 0.03 X 6.14 f 0.06 X 1.42 f 0.01 X 1.61 f 0.03 X 1.90 f 0.04 X 4.43 f 0.24 X 1.30 f 0.08 X 1.59 f 0.11 X 7.99 f 1 . 9 8 X
lo-’ lo-’ lo-’ lo-’ lo-’ loo 10’ 10’ 10’ 10’ 10’ 10’
Table I I. Distribution of Praseodymium and Magnesium between Aqueous Chloride Solutions and 0.1M TTA in MlBK Praseodymium PH
2.02 2.33 2.62 2.90 3.04 3.16 3.32 3.42 3.57 3.82 4.26 4.40 4.90
Magnesium
Dist. coeff., D
9 . 5 f 3.6 X 6.67 f 0.60 X 3.39 f 0.12 X 1.94 f 0.03 X 2.98 f 0.04 X 1.10 f 0.01 X 1.88 f 0.02 X 3.20 f 0.05 X 5.57 f 0.10 X 2.90 f 0.10 X 3.08 f 0.49 X 6.81 f 1.86 X 2.89 f 3.12 X
lo-‘ lo-’ lo-’ loo loo loo loo
10’ 10’ 10’ lo3
PH
Dist. coeff., D
4.25 4.53 4.71 4.85 5.09 5.23 5.47 5.65 5.95 6.18 6.42 6.62 6.74
2.4 f 0.3 X l o - ‘ 6.4 f 0.8 X lo-’ 1 . 6 f 0.2 X l o - ’ 2.75 f 0.35 X 10-1 6.70 f 0.9 X l o - ’ 1.40 f 0.2 X l o o 3.10 f 0.4 X l o o 6.00 f 0.8 X l o o 2.10 f 0 . 3 X 10’ 6.80 f 0.9 X 10’ 1.75 f 0.2 X 10‘ 4.40 f 0.6 X 10’ 6.20 f 0.8 X 10’
parison of distribution coefficients, 142Prwas equilibrated between aqueous chloride solutions and 0.1M TTA-MIBK solutions with the results shown in Table 11. When the log D values are plotted us. p H and compared with similar curves for yttrium and lanthanum, the praseodymium curve falls between the two, but becomes identical with the lanthanum curve above the midpoint until the two separate again, as lanthanum starts to form the top of its S-shape before praseodymium. The point of equal distribution between the two phases occurs a t pH of about 3.2 for praseodymium. The chemical similarities of the three elements are verified to the extent that it would be impossible to separate the three unless many stages of extraction were employed. Iron, Cobalt, a n d Nickel. The distribution coefficients for iron, cobalt, and nickel as a function of p H are shown in Table 111. When the log D values are plotted us. pH, nickel and cobalt show the expected S-shaped distribution coefficient curves with the point of equal distribution between the phases occurring a t a p H of 3.3 for nickel and 3.8 for cobalt. The straight midsection of the nickel curve is quite long and breaks over quite sharply a t the upper end, probably an indication of the formation of a very stable chelate compound with the TTA. A plot of the log D values for iron L’S. pH produces an abnormal V-shaped curve with a minimum a t about a p H of 1.2. On either side of this pH value, extraction into the ’ITA-MIBK phase increases a t almost a linear rate, but with increasing pH starts to curve above a p H of 2. The portion of the curve a t pH values below 1.2 is attributed
A N A L Y T I C A L C H E M I S T R Y , VOL.
45, NO. 12, OCTOBER 1973
2127
Table 1 1 1 . Distribution of Iron, Cobalt, and Nickel between Aqueous Chloride Solutions and 0.1M TTA in MlBK Iron Dist. coeff.. D
PH
-0.60 -0.30 0.0 0.40 0.70 1.20 1.37 1.55 1.80 2.10 2.85 3.27 3.88 4.28
1.25 f 0.03 X 3.57 f 0.05 X 8.69 f 0.04 X 7.88 f 0.04 X 2.92 f 0.02 X 1.21 f 0.01 x 1.59 f 0.01 X 5.71 f 0.04 X 1.77 f 0.01 X 8 . 7 3 f 0.09 X 5.33 f 0.08 X 9.06 f 0.19 X 2.47 f 0.09 X 3.44 f 0.19 x
loo loo
10’ 10’ loz 10’
Dist. coeff., D
PH
10‘ 10’ loo lo-’ 10lo-’ 10-1 lo-’
1.91 2.30 2.70 2.78 3.10 3.20 3.61 3.76 4.03 4.21 4.35 4.61 4.95 5.35 5.77 6.71 7.80
5.76 f 0.13 X 6.31 f 0.13 X 1.21 f 0.02 x 1.62 f 0.02 X 7.76 f 0.06 X 1.05 f 0.01 X 5.31 f 0.04 X 1.32 f 0.01 X 3.02 f 0.02 X 6.08 f 0.04 X 1.32 f 0.02 X 3.83 f 0.04 X 6.92 f 0.08 X 1.14 f 0.01 X 1.65 f 0.03 X 2.91 f 0.07 X 4.86 f 0.15 X
Table I V . Distribution of Copper and Manganese between Aqueous Chloride Solutions and 0.1M TTA in MlBK Copper PH
0.22 0.45 1.03 1.35 1.60 1.79 2.21 2.40 3.00 3.51 4.28
10-3 lo-’ lo-’ lo-’ loo
10’ 10’ 10’ 10’ lo3
Dist. coeff., D
PH
1.61 2.74 3.26 3.66 3.96 4.35 4.52 4.70 4.80 4.92 5.10 5.37 5.58 5.87 6.50
3.7 f 0 . 2 x 10-4 4.11 f 0.06 X 1.70 f 0.01 X lo-’ 6.75 f 0.06 X 3.35 f 0.02 x l o - ’ 1.01 f O . O 1 x 100 3.01 f 0.02 X l o o 7.41 f 0.05 X l o o 1.29 f 0.01 X 10’ 2.95 f 0.02 X 10’ 7.23 f 0.07 X 10’ 1.98 f 0.03 X 1 0’ 5.92 f 0.17 X 10’ 1.63 f 0.09 x 103 2.93 f 0.26 X l o 3
1.18 1.31 1.86 2.71 3.50 4.55 5.1 1 5.75 6.20 6.37 6.83 7.20 8.30 9.25
Table V. Distribution of Molybdenum and Technetium between Aqueous Chloride Solutions and 0.1M TTA in MlBK PH
-0.90 -0.60 0.0 0.90 1.20 1.95 3.02 4.43 5.20 5.98 6.98 7.00 7.68
2128
Technetium
Dist. coeff., D
3.62 f 0.10 X 1.72 f 0 . 0 8 X 7.98 f 0.05 X 5.20 f 0.08 X 2.93 f 0.02 X 1.34 f 0.02 X 4.37 f 0.17 X 1.40 f 0.09 X 5.84 f 0.97 X 2.71 f 0.35 X 1.72 f 0.90 X 1.60 f 0.02 X 1.97 f 0.33 X
10’ 10’ lo-’ lo-’ lo-’ lo-’ lo-’
lo-’
PH
-0.60 -0.30 0.0 0.30 0.70 1.23 1.47 1.80 2.35 3.05 3.78 4.53 5.02 5.82 6.73 7.03 7.83
A N A L Y T I C A L C H E M I S T R Y , VOL.
Dist. coeff.. D
1.36 f 0.04 X 1 . 2 2 f 0.01 X 9.15 f 0.04 X 8 . 2 4 f 0.04 X 9 . 4 3 f 0.13 X 7.24 f 0.03 X 4.91 f 0.05 X 2.85 f 0.01 X 1.67 f 0.01 X 9.96 f 0.03 X 7.34 f 0.03 X 4.21 f 0.02 X 2.53 f 0.01 X 1.19 f 0.01 X 5.64 f 0.05 X 4.21 f 0.04 X 2.72 f 0 . 0 3 X
Dist. coeff., D
9.0 f 1 . 4 x 10-4 2.69 f 0.27 X 1.03 f 0.04 X lo-’ 3.78 f 0.08 X lo-’ 3.11 f 0.03 X l o - ’ 2.34 f 0.02 X l o o 5.43 f 0.05 X l o o 2.76 f 0.05 X 10’ 1.56 f 0.07 X 10’ 2.70 f 0.15 X 10’ 1.09 0.18 x 103 1.23 f 0.18 X l o 3 1.20 f 0.21 x 103
Gold
PH
Molybdenum
lo-’ lo-’ lo-’ lo-’ lo-’ 1 Oo loo loo 10’ 10’ 10’ 10’ 10’ 10’ 10’
PH
1.86 2.02 2.30 2.66 3.06 3.47 3.70 3.95 4.26 4.48 4.93 5.23 6.06
Table V I . Distribution of Gold and Tungsten between Aqueous Chloride Solutions and 0.1M TTA in MlBK
Manganese
Dist. coeff., D
1.91 0.12 x 5.33 f 0 . 2 3 X 4.85 f 0.04 X 2.57 f 0.02 X 8.52 f 0.05 X 2.76 f 0.02 X 1.61 f 0.02 X 5.23 f 0.08 X 2.74 f 0.07 X 8.60 f 0.52 X 3.60 f 0.74 X
Nickel
Cobalt
10’ 10’ loo loo loo loo
loo loo lo0 lo-’ lo-’ lo-’ lo-’ lo-’
lo-‘ lo-’ lo-‘
Tungsten
Dist. coeff.. D
9.86 f 0.44 X 5.74 f 0.17 X 1.07 f 0.02 X 4.13 f 0.04 X 2.54 f 0.02 X 2.36 f 0.02 X 2.28 f 0.02 X 1.40 f 0.01 X 5.92 f 0.04 X 2.59 f 0.01 X 1.17 f 0.01 X 7.11 f 0.02 X 6.69 f 0.03 X 5.23 f 0 . 0 3 X
10’ 10’ 10’ 10’ 10’ 10’ 10’ 10’ loo loo loo lo-’ 10-1 lo-’
PH
Dist. coeff., D
-0.78 -0.60 -0.30 2.40 5.05 7.14 9.19
4.92 f 0.05 X l o o 1.31 f 0.02 X 1Oo 8.95 f 0.07 X l o - ’ 7.96 f 0.07 X lo-‘ 4.12 f 0.05 X lo-’ 1.43 f 0.03 X lo-‘ 2.3 f 0 . 2 x 10-3
to the extraction of an iron(II1) chloride complex into the MIBK and the portion of the curve above a pH of 1.2 is considered to be extraction of iron(II1) as a TTA chelate. However, the nature of the chelate differs from that of nickel and cobalt, because it was not reversible when the pH of the aqueous phase was lowered. Thus, extraction of iron as a TTA chelate is useful only for the removal of iron from an aqueous solution. The two midpoints of equal distribution between the aqueous and organic phases are found a t pH values of about 0.5 and 1.7. Copper and Manganese. The distribution coefficients for copper and manganese as a function of p H are shown in Table IV. Both form the usual S-shaped curve when their log D values plotted us. pH. The point of equal distribution between the aqueous and TTA-MIBK phases occurs a t a pH of about 1.6 for copper and a t a pH of about 4.2 for manganese. Molybdenum and Technetium. The interest in measuring the distribution coefficients for these two elements stemmed primarily from the widespread use of 99Mo as a “cow” to supply 99mTc for medical purposes. It was recognized from the start that both elements did not exist as simple cations in aqueous solutions, but were surrounded with oxygen to give a net negative charge, and thus should behave as anions.’ The distribution coefficients as a func-
45, NO. 1 2 , OCTOBER 1973
Table V I I . Element Pairs with Single Stage Separation Factors of 1000 or Greater Element pair
Element pair PH
range
Aqueous phase
1.4-1.6
Indiuma
1.6-1.8 1.6-2.0 1.6-2.0
Nickel Lead Zinca
1.6-2.0
Y tt r i u ma
1.6-2.0 1.6-2.2
Praseod y m i u m Cobalt Lanthanuma Manganese Cadniiuma Magnesium ThalliumU Calciuma Strontiuma BariumU Radium Cobalt Nickel Lead Praseodymium Manganese Cobalt Manganese Lan than u ma Lead
1.6-2.2 1.6-2.4 1.6-3.4
1.6-3.6 1.6-3.8 1.6-4.0 1.6-4.4 1.6-4.6
1.6-4.6 2.0-2.2 2.0-2.2
2.0-2.2 2.0-2,2 2.2-2.4
2.6-2.8 2.6-3.0 2.8-3.0 2.8-3.0
Previously published distribution data ( 7 ) .
TTA-M I BK
PH range
Aqueous phase
Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Thorium Scandiuma Scandiuma Scandiuma Scandiuma Scandiuma Copper Copper Copper Copper
3.0-3.2 3.0-3.8 3.0-4.6 3.6-3.8
Zinca Magnesium Radium Thal I i u mU Magnesium Cadmiuma Magnesium Calciuma StrontiumU Bar i urna Nickel Thalliu ma Radium Calciuma Strontiuma Bariuma Radium Radium Radium Radium Radium Radium Radium Radium
phase
3.6-4.0
3.8-4.0 3.8-4.0 3.8-4.2 3.8-4.2 3.8-4.6 4.0-4.2 4.0-4.2 4.0-4.8 4.2-4.4 4.2-4.4 4.2-4.6
4.2-4.6 4.4-4.6 4.8-5.0
4.8-5.0 4.8-5.0
4.8-5.0 4.8-5.0 5.0-5.2
TTA-MIBK
Copper Scandiuma Scandiuma Copper Copper Copper I ronb Copper Copper Copper Cad miuma Praseodymium Copper 1 ronb I ronb I ronb I ronb
phase
Yttriuma Indiuma
Cobalt Nickel Lan t h an u ma Praseodymium Lead
Irreversibly extracted into T T A - M I B K phase
tion of p H are shown in Table V. As expected, the extractions obtained did not correspond to that typical of a TTA metal chelate. In fact, for both elements it was just the opposite with the highest D values a t low pH's and then decreasing in a somewhat irregular manner with increasing pH, as seen when the log D values are plotted L'S pH. The midpoints of equal distribution between the aqueous and TTA-MIBK phases occurred at a p H of about 0 for molybdenum and a t a p H of about 3.0 for technetium. From a practical standpoint, this system would not be suitable for the separation of technetium from molybdenum. Gold, Tungsten, and Arsenic. The elements gold, tungsten, and arsenic, like molybdenum and technetium above, did not form metal chelates with TTA. The distribution coefficient data as a function of pH for gold and tungsten are shown in Table VI. For arsenic, no extraction into the TTA-MIBK phase occurred a t any pH. When the log D values are plotted L'S. p H for gold and tungsten, curves similar t o t h a t for technetium and molybdenum are obtained. It is to be noted from the data t h a t gold favors the TTA-MIBK phase, whereas tungsten favors the aqueous phase. This could be of significance in making separations, particularly where gold is present. since extraction into the TTA-MIBK phase is essentially complete a t a pH of about 1.0. The points of equal distribution between the aqueous and TTA-MIBK phases occur a t a p H of about -0.4 for tungsten and a t a p H of about 6.9 for gold.
CONCLUSIONS Contrary to Hageman's (2) curves for the extraction of actinium and its daughter elements, which showed no extraction of radium from aqueous solutions into 0.25M TTA in benzene, these distribution studies show t h a t radium is extracted into 0.1M TTA in MIBK under p H conditions almost identical to that obtained earlier for bariu m ( 2 ) . This study also extends the comparative data for the distribution between aqueous and TTA-MIBK phases to many elements not included in the previous paper. Element pairs with single stage separation factors of 1000 or more are shown in Table VII, and include new combinations resulting from the comparison of distribution coefficient curves for each element reported here with those previously reported. With these collective data reported here and previously ( I j , the investigator interested in separating one or more metallic elements from a n aqueous solution should be able to quickly and accurately determine the suitability of TTA in MIBK for making the separation.
Received for review April 3, 1973. Accepted May 29, 1973. Presented at the 24th ACS Southeastern Regional Meeting, Birmingham, Ala., November 2-4. 1972. This work was supported by the U.S. Atomic Energy Commission under contract with Oak Ridge Associated Universities.
A N A L Y T I C A L C H E M I S T R Y , V O L . 45. NO. 1 2 , OCTOBER 1973
2129
