J. Phys. Chem. 1982, 86, 1015-1018
of the similarity in slope of the experimental and theoretical curves and the magnitude of the ratios obtained we feel that the comparison of experimental and theoretical rates is best characterized by the mean values of the ratios for each initial temperature Ti and carrier gas. These values and the temperatures Texpin the measuring chamber at intermediate nucleation rates (Jexpt = 2 X lo7 cm-3 s-l) are given in Table I. Further reducing the data it can be stated that the experimental nucleation rates at 250 and 270 K are larger than the theoretical ones by factors of 5(f4) X 1013and 6(f3) X 108,respectively. Accordingly, it is found that the actual experimental nucleation rates in 1-pentanol vapor as well as their temperature dependence considerably deviate from classical nucleation theory. However, the comparatively small relative standard deviation u (see Table I) indicates good agreement between the slopes of experimental and theoretical curves. The
1015
results for other systems will be presented in due course.
Summary We found that homogeneous nucleation in 1-pentanol vapor is unchanged if different carrier gases (He, Ar, and N,) are chosen. These result.9 confirm the corresponding assumption made in the nucleation theories.a10 Furthermore they support experimental evidence given by some author^^-^ and contradict others.6 While the classical nucleation theory succeeds in predicting the slope of the experimental nucleation rate vs. supersaturation curve for 1-pentanol, the actual measured values and their temperature dependence considerably deviate from theory. Acknowledgment. This work was performed in the department of Professor Dr.M. Kahlweit. We thank him for the interest in and support of this work.
Raman Spectroscopic and Chromatographic Study of the Uranium Isotope Effect in Uranyl Acetate Complex Formation Y. Tanaka, Y. FuJIl,and M. Okamoto' Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Ookayama, MegureKu, Tokyo 152, Japan (Received June 24, 198 1; In Final Form: October 20, 198 1)
Raman spectra of aqueous solutions of uranyl acetate complexes were measured. The downward shift of the frequency for the totally symmetrical stretching vibration of the O==U=O bond was brought about by stepwise formation of uranyl acetate complexes. In order to predict the direction of the fractionation of uranium isotopes in complexes, the reduced partition function ratio for each uranyl acetate species was calculated by use of each assigned O=U=O stretching frequency. It was found that the lighter isotope 235Uis accumulated more preferentially in uranyl acetate species than in the hydrated uranyl ion. This trend is consistent with that obtained by cation-exchange chromatography of uranyl acetate solutions.
Introduction Uranium isotope fractionation in complexes formed in solution have been investigated for enrichment of uranium isotopes by chemical exchange methods.l+ In order to predict the magnitude and direction of the isotope fractionation, reduced partition function ratios for uranium isotopes have been theoretically calculated by use of Raman and infrared spectral data of According to these calculations the complexes should incorporate the heavier isotope 238Uin preference to the aquauranium ion
in uranyl systems? This trend is in accord with that observed in cation-exchange chromatography by CiriE3and by Sakuma et al.'O But the results obtained by Okamoto et a1.11J2 using uranyl acetate, tartarate, citrgte, and fluoride are the reverse of the results reported by CiriE and are not consistent with the theoretical calculations. Part of this inconsistency might be due to the fact that the spectral data measured in the solid state13-18 were employed in the calculations for solution systems because of the lack of data for solutions. In the present work, first,
(1)H.Kakihana, K. Kurieu, and M. Hosoe, Nippon Kagaku Zasshi, 84, 24 (1963). (2)H.Tomiyasu, H.Fukutomi, and H. Kakihana, J. Inorg. Nucl. Chem., 30 2501 (1968). (3)M.&E, Energ. Nucl. (Paris), 10,376 (1968). (4)H.Kakihana, Nippon Kagaku Zasshi, 89,734(1968). (5)J. Aaltonen and K. G. Heumann, 2.Naturforsch. B , 29,190(1974). (6)H.Kakihana, Sep. Sci. Technol., 15, 567 (1980). (7)Y. Yato and H. Kakihana, Bull. Tokyo Inst. Technol., No. 127.63 (1975). (8) Y. Yato and H. K a k i i a , Bull. Tokyo Inst. Technol., No. 127,71 (1975). (9)H.Kakihana and Y. Yato, Bull. Res. Lab. Nucl. React. (Tokyo Inst. Technol.), 1, 43 (1976).
(10)Y.Sakuma. M.Okamoto. and H. Kakihana. J. Nucl. Sci. Techno!:, 18, 9 (1981).' (11)M.Okamoto, R. Goda, A. Nakagawa, Y. Sakuma, and H. Kakihana, Isotopenpraxis, 16, 293 (1980). (12)Y. Tanaka, J. Fukuda, M. Okamoto, and M. Maeda, J. Inorg. Nucl. Chem., in press. (13)J. E.Newberry, Spectrochim. Acta, 25, 1699 (1969). (14)J. I. Bullock, J. Chem. SOC.A, 781 (1969). (15)A. Perrin, J. Inorg. Nucl. Chem., 39, 1169 (1977). (16)A. Perrin and J. Pright, Spectrochirn. Acta, Part A, 33, 781
0022-3854/82/2088-1015$01.25/0
(1977). (17)W.Scheuermann and A. Van Teta, J. Raman Spectrosc., 6, 100 (1977). (18)C. Caville, J.Raman Spectrosc., 6, 235 (1977).
@ 1982 American Chemical Society
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Tanaka et at.
The Journal of Physical Chemistry, Vol. 86, No. 6, 1982
TABLE I: Experimental Conditions for Cation-Exchange Chromatography and the Enriched Isotopes Found in Uranyl Acetate Complexes isotope enriched bed band in uranyl length, [CH,COONH,], velocity, temp, acetate run no. resin cm m ~ l d m - ~ pH cm h-l "C complexes remarks YA-1 YA-2 YA-3 YA-4 YA-5 YA-6
PK-1 PK-1 PK-1 PK-1 PK-1 PK-1
98.5 114.5 103.0 660.0 400.0 400.0
0.2 0.2 0.2 0.2 0.6 0.6
the direction of the fractionation of uranium isotopes was determined by cation-exchange chromatography of uranyl acetate solution under conditions different from those reported previously1' in order to confirm the previous results. Raman spectra of uranyl acetate solutions with differing concentrations of acetate ions were measured to observe the effect of formation of uranyl acetate complexes on the frequencies of the O=U=O totally symmetrical stretching vibration, which is the only Raman-active vibration of the three fundamental vibrations. By use of these frequencies the reduced partition function ratio for each uranyl acetate complex was calculated and the directions thus estimated were compared with those obtained by cation-exchange chromatography of uranyl acetate solutions.
Experimental Section Reagents. Uranyl nitrate was prepared by dissolving U308in nitric acid and was purified by solvent extraction and recrystallization. Uranyl perchlorate solution was prepared by eluting uranyl ions with barium perchlorate solution from a column of the cation-exchange resin in the uranyl form. The solution was evaporated to dryness under an infrared lamp, and the crystals were dissolved in water and deuterated water. Other reagents were analytical grade. Determination of the Direction of the Isotope Fractionation by Cation-Exchange Chromatography. In order to confirm the directions observed previously, isotope separation experiments were carried out by the following procedures. The column used had 1-cm diameter and 100-cm resin bed height and had a water jacket for temperature control (see Figure 1). For a long-migration experiment, two or more columns were connected in a series by thin poly(viny1 chloride) tubing. The resin used was a strongly acidic cation-exchange resin PK-1 supplied by Asahi Chemical Industry, 100-200 mesh, and was converted to the H+form by the usual way. A uranyl acetate absorbed band was formed in the top of the resin bed by feeding the uranyl acetate solution, and then the eluent solution was introduced into the column with a constant flow rate controlled by a peristaltic pump. Thus, the uranium band began to migrate, attained an equilibrium length, and then continued displacement migration with a constant velocity down to the bottom of the column as illustrated in Figure 1. The effluent from the bottom of the column was collected in fractions. For each fraction the uranium content and the uranium isotopic ratio were determined by a colorimetric method and by mass-spectrometric analysis, respectively. The experimental conditions are listed in Table I. More experimental details have been described in a previous paper.12 Raman Spectral Measurements. Raman spectral measurements were performed in a thermostated room at 25 f 1 "C on a R-2D laser Raman spectrophotometer (Shimazu Seisakusho) using the 5145-A beam of an argon
7.6 5.2 4.0 4.0 5.0 7.0
0.7 1.7 1.4 1.2 2.0 2.0
235U 23SU
25 25 25 25 25 25
this work this work this work this work ref 11 ref 11
1 3 5 ~
235U 235U 23SU
Elueit r i e l
W Per i s t o l t ! c Dump
To water thermostat
t h e rmos t c t
Uranium
+-
-
oana
Class beads
Froni wcte: I he r m s @: t
7 Frehectin; co 1 umn
From
+ water thermosto: TO f r a c t l i o n c o l l e c t o r
or next coluiln
Flgure 1. Column system used for chromatographic separation of
uranium isotopes. TABLE 11: Compositions of Sample Solutions for Raman Spectral Measurement components
R1-1
R1-2
[CH,COONH,], mol dm'3 1",NO 3 I mol dm'3 [UO,(NO,),], mol dm-3 PH
1.6
1.2
R1-3 R1-4 R1-5 0.8 0.4 0
0
0.4
0.8
1.2
1.6
0.49
0.49
0.49
0.49
0.49
1.58
1.58
1.58
1.58
1.76
I
ion laser (Spectra Physics Model 165). Sample solutions were held in small Pyrex tubes. The sample solutions were as follows: (a) uranyl perchlorate solution and deuterated solution, (b) mixed solution of uranyl perchlorate and ammonium benzenesulfonate, (c) uranyl acetate solutions with five different compositions, which are tabulated in Table 11.
Results and Discussion Determination of the Direction of the Isotope Fractionation by Cation-Exchange Chromatography. An ex-
Uranium Isotope Effect in Uranyl Acetate Complex
The Journal of Physlcel Chemlstty, Vol. 86, No. 6, 1982 1017
nqp
ann
464
398
zn
"43 RwY&
>d F
cr
Flguro 3. Raman spectra of uranyl perchlorate solution of H,O and DZO.
Effluent volume (ml)
Flguro 2. Chromatogram and isotopic ratios for uranyl acetate system (run no. YA-1).
ample of the results obtained by cation-exchange chromatography is shown in Figure 2. The reactions which occur in the ion-exchange column can be expressed as follows: (i) at the rear boundary of the uranium band
-
UOZ2++ nNH4++ nCH3COO- = nNH4++ U02(CH3C00),(2-n)+ (ii) at the frontal boundary of the uranium band - U02(CH3C00)n(2-n)+ + nH+ = U022++ nCH,COOH 900 700 500 330 I 10 where a bar denotes the resin phase. According to the RAMAR S H I F T icn-'' stability constants of the uranyl acetate complexes and the Flgure 4. Raman spectra of mixed solution of uranyl perchlorate and dissociation constant of acetic acid,l9the above two reacammonium benzenesulfonate. tions tend to proceed to the right. Thus, the uranyl acetate species should be eluted faster than the aquauranyl ion dm-3). It is seen that the band attributed to the uranyl preferentially absorbed on the cation-exchange resin. It ion is observed at the same position (881 cm-') as that for is obvious from the feature of isotopic ratios illustrated in the perchlorate solution. This means that the O=U=O Figure 2 that the lighter isotope is enriched in uranyl bond strength is not affected by interaction with the acetate complexes. The same tendency was observed in sulfonate ion; i.e., the uranyl ion in the resin phase may all other cases, the results being summerized in Table I, be taken to be the analogous situation to that in the together with those reported previously.12 The present perchlorate solution. This is because the functional group results suggest that the equilibrium constant of the folof the cation-exchange resin used was sulfonate ion bound lowing isotopic exchange reaction that takes place in the with the benzene ring of divinylbenzene, which was used uranium band should be larger than unity: as a cross-linking reagent. The shifts of the O=U=O peak positions for the uranyl acetate solutions with different 235UO22+ + 238UO2(CH3C00)n(2-n)+ = acetate ion concentrations are illustrated in Figure 5. The 23SU02(CH3C00),(2-n)+ + 238u022+ peak positions shift to the lower-frequency side with an In other words, the reduced partition function ratio of increase of the total concentration of acetate ion, which aquauranyl ion should be larger than those of uranyl indicates that the O=U=O bond reduces its strength with acetate complexes. stepwise formation of uranyl acetate complexes. The Analysis of Raman Spectra and Calculation of Reduced bands at around 850-900 cm-' may be overlapped by Partition Function Ratios. The Raman spectra of uranyl contributions from acetate, aquauranyl, and various uranyl perchlorate solutions but water and deuterated water are acetate species. The bands were, therefore, resolved on shown in Figure 3. It is apparent that the peaks appear the assumption that each band was represented by a at identical positions in both systems. The bands observed Lorentz-Gaussian curve. Base lines were approximated at arouhd 460, 625, and 930 cm-l are easily attributable by quadratic equations. The resolution of the spectra was to the C104-ion.m The band located at 881 cm-' should performed by use of a Model HITAC-M180 computer. An be assigned to the totally symmetrical stretching vibration example of the resolution is illustrated in Figure 6. The of the aquauranyl ion. Figure 4 shows the Raman specresolved peak positions and their assignments are sumtrum of the 1:l mixed solution of uranyl perchlorate (0.5 marized in Table 111. Using the frequencies assigned, we mol d m 9 and ammonium benzenesulfonate (1.0 mol calculated the reduced partition function ratio (s/s?f(238V/%U) for each complex on the basis of the well-known equation derived by Bigeleisen and Mayer21and Ishida et (19)D.D.Perrin, "Stability Constanta of Metal-Ion Complexes",Part B Pergamon Prese, Elmeford, NY, 1979. (20)M. H.Brooker, C. H.Huang, and J. Sylwestrowicz,J. Zmrg. Nucl. Chem., 42,1431(1980).
_ _ _ _ _ _ _ _ ~
~
(21)J. Bigeleisen and M. G. Mayer, J. Chem. Phys., 15, 261 (1947).
1018
The Journal of Physical Chemistty, Vol. 86, No.
6, 1982
Tanaka et ai.
"i""
.6
"
Flguro 6. Example of computer analysis of Raman spectra (sample solution R 1-2).
TABLE IV: Calculated Reduced Partition Function Ratios vi,obyij
species UO." UO;CH,COO+ UO,(CH,COO), UO2(CH3C0O),-
cm-
880 874 863 (850p
Calculated from RAMAN
SHIFT
(Cm-')
F W 5. Raman spectra of uranyl acetate sdutbns with different total concentrations of acetate ions.
TABLE 111: Frequencies for Resolved Raman Bands obsd wavenumber, cm" O = U = O in
uo *-
uo
R1-1 R1-2 R1-3 R1-4 R1-5
864 863
874 873 874 874
adopted value for calculation
863
874
sample no.
2-
(CH,COO), CH,COO' UO,z' CH,COO-
881 881 877 879 880 880
899 899 897
a1.,22 and it can be expressed for uranium isotopes as follows: In ( S / S ' ) ~ ( ~ ~ ~ = U/~~~U) (W/24)mlnl[(M238- M235)/(M2&235)1
vi2
where W is a modulation factor derived and tabulated by Ishida et ml is the mass of the liquid, nl is the number of the ligand, and M m are the masses of 238v and %U, respectively, s and s'are the symmetry numbers of isotopic molecules, f(238v/236U) is the partition function ratio, and Ui is the energy of the totally symmetrical stretching vibration. The calculated results are collected with the values of Vi and W in Table IV. vl, which should be assigned to the O=U=O of U02(CH3C00)3-ion, could (22) T.Ishida, W.Spindel, and J. Bigeleisen,Adu. Chern. Ser., No.89, 192 (1969).
vi 4.22 4.19 4.14 (4.08)
v 3 reported
w
f('"U/235U) (s/s' )*
0.877 1.001 12 0.879 1.001 10 0.881 1.001 08 (0.884) (1.00105)
by McGlynn.13
not be found under the present experimental conditions. Hence, v1 of this case was calculated from the v3 data reported by McGlynn and Smith.23 The differences among these ratios are small but sufficiently large to determine the direction of the isotope fractionation which should occur in the ion-exchange chromatographic process. In the present system, the reduced partition function ratio of the aquauranyl ion is larger than those of the complexes; thus, it can be said, when the isotopic exchange reaction occurs between aquauranyl ion and the uranyl acetate species, that 238U should be enriched in aquauranyl ion; i.e., 235Ushould be accumulated preferentially in uranyl acetate complexes. It may be concluded, therefore, that the direction of the isotope fractionation of uranium observed in the present ion-exchange chromatography is consistent with that estimated by the reduced partition function ratios calculated by using the shifts of the frequencies of the O=U=O stretching vibration measured in aqueous solutions of uranyl acetate complexes. The reduction of the O=U=O bond strength by complex formation may be a predominant factor for quantitative interpretation of the reversal of the direction of the isotope fractionation between uranyl and uranous complex formation reactions. In the latter case, 238Uwas enriched in uranous sulfate complex as reported by Sakuma et al.l0 The facts found by the present study are consistent with those found by the infrared spectroscopic study of the uranium isotope effect reported by us reviously; l2 however, the opposite results obtained by &riE cannot be explained. Acknowledgment. We heartily thank Associate Professor M. Maeda of the Nagoya Institute of Technology for his helpful discussions and encouragement, (23) S. P.McGlynn and J. K.Smith, J. Mol. Spectrosc., 6,164 (1961).
