between resin and solvent phases have been measured to be 5000 for ethanol/HCl and 20 for water/HCl solutions when the HC1 concentration is maintained above 2 M (13).The retention of U is unaffected by small changes in experimental conditions (elution rate, acid molarity, and ethanol/HCl ratio). Second, significant amounts of the U can be eluted from the column during the washing cycle when a water-based mixture is employed. No U release has been observed for U sample concentrations of up to 2 ppm when the ethanol-based mixture is used. Decontamination factors are shown in Table I11 for common short-lived activation products which interfere with the measurement of the low energy 239Uy-ray. These were determined by comparison of y-ray spectra from the ion exchange columns with corresponding spectra from unseparated, irradiated water samples counted in similar geometries. The column retains approximately 5% of the Br, Mn, Mg, and V; approximately 2% of the Cl, Al, and Ca; and approximately 1%of the Na and K. For t,he water samples studied, this degree of decontamination results in a peak-to-Compton background ratio of 1:l for 0.1 ppb U. The use of a Low Energy Photon Counting System would further eliminate much of the Compton background in the 74-keV region. This neutron activatiodanion exchange technique exhibits the same detection limits and precision as direct fluorometric analysis of water samples. The principal advantage is its insensitivity to unknown levels of chromophors (e.g., Fe, Cr, and Cu) which quench the U fluorescence and cause substantial underestimation of U concentrations by direct fluorometry. This activation method is rapid and requires considerably less laboratory preparation of samples or resins than an anion exchange/fluorometric technique described by Korkisch and Godl (9) or a Chelex lOO/x-ray fluorescence method recently reported by Hathaway and James (10).
Table 111. Decontamination Factors for Anion Exchange Separation of U Element I Br
v
Mn Mg
DF 3 16 16 20 24
Element A1 Ca
c1
Na K
DF 34
36 38 70 > 100
ACKNOWLEDGMENT The authors thank Priscilla Jose for her assistance with the fluorometric analysis; David Curtis and Ken Apt for their critical comment on the manuscript; and the staff of the Omega West Reactor for their assistance. LITERATURE CITED (1) U S Energy Research and Development Admin., A National Plan for Energy Research, Development and Demonstration: Creating Energy Choices for the Future, USERDA Rep., ERDA-48, June 1975. (2) H. Fauth. "Uranium Exploration Methods", International Atomic Energy Agency, Vienna, 1972, pp 209-218. (3) W. Dyck and E. M. Cameron, Geol. Surv. Can. Pap., 75-1, Part A., pp 209-212. (4) A. A. Saukoff, Proc. UNlnt. Conf. At. hergy, Geneva, 6, 756-759 (1955). (5)J. Plant, Trans. Sect. 8,lnst. Min. Metall., 80, London, 1971. (6) A. Y. Smith and J. J. Lynch, Geol. Surv. Can. Pap., 69-40, 1969. (7) S.Amiel, Anal. Chem., 34, 1683 (1962). (8) L. L. Thatcher and F. B. Barker, Anal. Chem., 29, 1575 (1957). (9) J. Korkisch and L. Godl, Anal. Chim. Acta, 71, 113 (1974). (10) L. R. Hathaway and G. W. James, Anal. Chem., 47, 2035 (1975). (1 1) G. R. Price, R. J. Ferretti, and S . Schwartz, Anal. Chem., 25, 322 (1953). (12) D. A. Becker, National Bureau of Standards, private communication, 1976. (13) J. Korkisch. P. Antal, and F. Hecht, J. lnorg. Nucl. Chem., 14, 247 (1960).
RECEIVEDfor review December 5,1975. Accepted February 23, 1976. This work was supported by the US.Energy Research and Development Administration.
Selective Foam Fractionation of Chloride Complexes of Zinc(ll), Cadmium(H), Mercury(ll), and Gold(111) Wladyslaw Walkowiak,' Dibakar Bhattacharyya, and R. B. Grieves* DepaHmentof Chemical Engineering, The University of Kentucky, Lexington, Ky. 40506
An experimental investigation is presented of the batch foam fractionation of the chloride complex anions of Zn( II), Cd(ll), Hg(ll), and Au(lll) from 1.0 X M (metal concentration) acidic aqueous solutions with the cationic surfactant hexadecyltrimethylammonium chloride. The effect on metal separation is established of the presence of CI- over the concentration range 0.01 to 3.0 M, both for solutions containing a single metal and for solutions equimolar in the four metals. At a 0.01 M concentration of chloride, Au(lll) can be efficiently foam-fractionated from the other three metals and, at a 0.5 M concentration of chloride, Au(lll) and Hg( II) can be efficiently foam-fractionated from Cd( II) and Zn( 11).
The effectiveness of a physicochemical method of concentration and separation is principally determined by its selectivity. Foam fractionation relies on the interactions of an Present address, Institute of Inorganic Chemistry and Metallurgy of Rare Elements,Technical University of Wroclaw, Wroclaw, Poland.
ionogenic surfactant with oppositely-charged ions in solution and a t solution-gas bubble interfaces to produce a most significant enrichment of selected ions in a foam formed above an aqueous bulk solution. The foam fractionation selectivity of cationic surfactants for inorganic anions has been studied in several recent investigations (1-9). The ionic structure of a solution of complex compounds depends on the stability, solubility, and other physicochemical properties of the solution components. The type of complexation process utilized to convert metallic cations into anions primarily determines the resultant ionic charge. Complexation with simple ligands such as C1-, CN-, SCN-, or S ~ 0 3 ~ is readily achieved, and transition metal complexes with these ligands are remarkably stable and can be obtained easily, both in the laboratory and on a larger scale. The enrichment and separation of metal complexes by foam fractionation has considerable promise. Jacobelli-Turi et al. (10) have utilized the fact that ThflV), unlike U(VI), does not form chloride complexes and were able to separate the metals in 8 M HCl medium with a cationic surfactant of the R4N+ type. The same type of surfactant ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
975
I
B 100c
E
9
80-
I
I
initial Z n U X Concentration I 0x10'5 M
-
0
,
-i
'0
1.0
2.0
3.0
Cl-, M
Figure 3. Maximum percent flotation at foam cease and percent formation of chloride complex anions of Hg(ll) vs. chloride ion concentration =looP
I I I Initial Cd(II) Concentration 10x10-5 M
.
I
I
I
1
I 2.0
I
-
n 0
-0A-201 '. r l '0
1 1.0
j
3.0
Cl-, M
Figure 4. Maximum percent flotation at foam cease and percent formation of chloride complex anions of Au(lll) vs. chloride ion concentration enabled the foam separation of U(V1) from V(V) in carbonate solutions due to the formation of [ U O Z ( C O ~ ) (11). ~ ] ~ -Lusher and Sebba (12) have separated A1 from Be by the ion flotation of oxalate complexes with an RNHs+ surfactant; the more stable Al(CZO4)- complexes predominated a t the experimental conditions, and Al(II1) was floated, leaving Be(I1) in the residual solution. Karger et al. (13, 14),by using the stability differences of Fe(II1) and Hg(I1) chloride complexes, have determined selective flotation conditions for mixed solutions of these metals with HC1 and an R4Nf surfactant. The complex anions HgC1d2- formed a t 0.5 M HCl, with Fe(II1) still existing as the cation; 8 M HC1 was necessary for the formation of FeC14-. The objective of this investigation is the selective separation of Zn(II), Cd(II), Hg(II), and Au(II1) by foam fractionation from acidic chloride solutions, using the cationic surfactant hexadecyltrimethylammonium chloride. Flotation results are discussed in terms of the stability constants of chloride complexes of these metals.
fractionated. It is possible that equilibrium was established sooner, but the 24-h period ensured experimental reproducibility. T h e surfactant, hexadecyltrimethylammonium chloride (HTMA-Cl), 99% active on a chloride basis and ~ 9 7 % active on a carbon basis, was utilized as 0.02 M standard solution in Analytical Reagent Grade methanol. The surfactant concentration in the initial solutions was maintained at 1.0 X M throughout this investigation. The y-radioactive isotopes 65Zn, lo9Cd, 203Hg,and lgSAuwere in the form of ZnCl2, CdC12, Hg(N03)2, and HAuC14 compounds that were water soluble. They were either carrier-free (65Znand lo9Cd)or of sufficiently low specific activity to neglect the effect of carrier concentration (*03Hg:7Ci/g; 19*Au:46Ci/g). The time dependence of the concentration of each metal in the bulk solution (zt) was recorded continuously during each foam fractionation by means of radioactive, analytical tracers, and y-radiation spectrometry, foliowing a procedure described previously (15). A single-channel, y-radiation spectrometer (RIDL Model 50-1) was used as the detector of radiation intensity of specified energy. The z t vs. time curves enabled the calculation of the maximum percent flotation, (1 - z,/zi)lOO, in which z, is the metal concentration in the residual solution a t foam cease. The separation coefficients of the chloride complex ions were calculated according to the relation:
EXPERIMENTAL The foam fractionation was carried out in a Pyrex column 45.7 cm in height and 2.4 cm in diameter. Air was saturated with water and the flow rate was maintained at 0.02 l./min (at 25 O C and 760 mm Hg) through a sintered glass sparger of 20-30 pm nominal porosity. The volume of each initial solution, prior to foam fractionation, was 0.10 l., and the temperature was maintained at 22.5 f 1.5 "C. The initial solutions were prepared with double distilled water of conductivity 6 pmho/cm at 25 OC and the salts ZnC12, CdC12, Hg(NOs)z,NaAuC14, and NaCl (Analytical Reagent Grade). To prevent the hydrolysis of metal ions, 0.1 ml of 1.0 M "03 was added to 100 ml of each initial solution. The p H of the initial solutions was in the range 2.8-3.0. To establish ionic equilibrium, the initial solutions, after chloride ion addition, were aged for 24 h before being foam976
ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
in which zf, the concentration of metal in the foam, was approximated by (zi - z,)Vi/Vf. The initial solution volume, Vi, was always 0.1 1. and Vf is the foam volume, collapsed, as liquid. In these experiments,zil = zi2: the initial solutions which contained all four metals were equimolar.
RESULTS AND DISCUSSION The initial solutions which were foam-fractionated in the first series of experiments contained only one metal each and were 1.0 X 10-5 M in Zn(II), Cd(II), Hg(II), or Au(II1). The chloride concentration was varied from 0.01 to 3.0 M (note
log61
+ +
Zn(I1) C1Cd(I1) C1Hg(I1) + C1Au(II1) + C1-
1qgPn 0.49 2.22 13.22 16.57
0.72
1.32 6.74 8.51
log P 3 -0.19 2.31 14.07 23.57
loo
1% P 4
+
+ [ZnClz] + [ZnCls-] + [ZnC142-] (1)
T h e percent formation of ZnC1d2- was calculated as: =
1 + pl[cl-]
P4[C1-I4
+ /32[C1-]2 + /33[C1-]3 + p‘Jc1-14
(100)
(2) in which [Cl-] is the equilibrium concentration of noncomplexed chloride and the p’s are the stability constants of the various chloride complexes of Zn(I1). Numerical values of the p’s are given in Table I. The sum of the percent formation of ZnCl3- ZnC142- was calculated as:
+
CY3
+
CY4
=
P3[C1-13
1
+ P4[C1-I4
+ /31[Cl-] + pZ[c1-]2 + /33[C1-]3 + P4[C1-]4 (100)
(3)
Similar expressions were used to compute the cy’s for Cd(II), Hg(II), and Au(III), utilizing the proper 6’s from Table I. The maximum percent flotation of Zn(I1) did not exceed 15%. As the chloride concentration was increased from 1.5 to 3.0 M, the percent formation of ZnC1d2- increased from 30 to 66%, and that of ZnCl3ZnC142- from 38 to 76%. This should have resulted in increased flotation of Zn(I1); however, chloride ions competed with the chloride complex anions of the metal for the surfactant cations, and the high concentrations of chloride (15 000-30 000-fold excess over the metal) effectively destroyed the surfactant’s selectivity for the chloride complex anions of Zn(I1). For Cd(II), from Figure 2, the efficiency of metal foam fractionation was higher due to the higher percent formation of CdC13CdC142- a t the lower chloride concentrations. Above 1.0 M C1- (a 100 000-fold excess or more), the surfactant’s selectivity for the anionic chloride complexes of Cd(1I) began to decline. For Hg(II), from Figure 3 a t 0.5 M chloride, HgC142-, and the percent flotation was 94% is as HgC1393%. Higher chloride concentrations provided more C1- to compete with the chloride complex anions of Hg(I1) for the surfactant cations. In the case of Au(II1) (Figure 4), a t a chloride concentration as low as 0.01 M, Au(II1) exists as AuC14-. Increases in the chloride concentration did not have much effect on the surfactant’s selectivity for AuC14- because of the monovalent complex anion’s strong affinity for the surfactant. The high affinity of Au(CN)4- for a cationic surfactant was also observed (8).Ion exchange studies with strong base resins with HC1 solutions of Zn(II), Cd(II),Hg(II), and Au(II1) reported
+
+
+
1
I
M
I
-1
1.86 15.07 29.64
+
CY4
-
0.18
that the surfactant concentration was always 1.0 X M). Results are presented in Figures 1-4 for Zn(II), Cd(II), Hg(II), and Au(III),respectively. In these figures, in addition to the maximum percent flotation, the calculated percent of the various chloride complex anions of each metal that should have been formed is shown. In Figure 1 (for Zn(II)), the percent formation of ZnC142is indicated by the u4 dashed curve and that of ZnCl3ZnC1d2- is indicated by the 013 u4 dashed curve. The total concentration of Zn(I1) is:
zi = [Zn2+]+ [ZnC1+]
I I~-=--\*.
Initial Metal Concentration 4 Oxlo-: ( I O X I O - ~ Min each metal)
Table I. Stability Constants of Chloride Complexes of Zn(II), Cd(II), Hg(II), and Au(II1) ( 2 6 )
Figure 5. Maximum percent flotation at foam cease of chloride complex anions of Zn(ll), Cd(ll), Hg(ll), and Au(lll) from equimolar solution of the four metals vs. chloride ion concentration
much higher distribution coefficients for gold and mercury than for cadmium and zinc ( 1 7 ) . I t should be noted that the predicted equilibrium percent formation of the various chloride complexes is based on concentrations that existed a t the beginning of each foam fractionation experiment and in the absence of surfactant. The equilibria would be shifted during the course of any given experiment as certain chloride complexes were preferentially floated and also, to some extent, by surfactant cation-complex anion interactions. Therefore, stability constant predictions can be used only to approximate the separation obtained by foam fractionation. Figures 1-4 suggest that it should be possible to effect a partial separation of the four metals by foam fractionation. Figure 5 presents results for solutions equimolar in Zn(II), Cd(II), Hg(II), and Au(II1). The total metal concentration was 4.0 X 10-5 M. A t each initial chloride concentration, four replicate foam fractionations were carried out: in each replicate, the initial solution was identical but a different metal concentration was monitored. The selectivity sequence is identical to that indicated in Figures 1-4, showing that single component foam fractionation experiments may be used to establish selectivity sequences for multicomponent mixtures. The relative separation of the anionic chloride complexes of the metals can be established from the experimental data in terms of the selectivity coefficient, &/2, effectively the ratio of the metal concentrations in the foam (4112 = 1.0 indicates no separation and values of 4112 substantially greater than unity indicate an efficient separation). Values of this coefficient are related to the initial chloride concentration in Figures 6 and 7. From Figure 6, a good separation of Au(II1) from Zn(I1) was achieved over 0.01 to 0.5 M chloride and of Au(II1) from Cd(I1) over 0.01 to 0.1 M chloride. Au(II1) could be separated from Hg(I1) only a t a very low chloride concentration of 0.01 M. From Figure 7, Hg(I1) could be effectively separated from Zn(I1) a t 0.5 M chloride. The maximum selectivity coefficients for Hg(I1) from Cd(I1) and for Cd(I1) from Zn(I1) were significantly lower than for the other metal combinations. Figures 8 and 9 present an additional method of describing the separation that was achieved by the foam fractionation of the equimolar, four metal solutions. Figure 9 relates the mole fraction of each metal in the residual solution after foam fractionation to the initial chloride concentration (sum of the four mole fractions = 1.0).Figure 10 relates the mole fraction of each metal in the foam to the initial chloride concentration. The logarithmic abscissa scales are used simply to give a clearer indication of the separation obtained a t the lower chloride concentrations. For an initial chloride concentration less than 0.5 M, the residual solution contained primarily Zn(II), Cd(II), and Hg(I1): most of the Au(II1) was fractionANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
*
977
301T
I
I
1
I
I
I
VAu/Zn 0 Au/Cd AAdHg
\
2
, N
-8
Figure 9. Effect of chloride ion concentration on the mole fraction of each of the four metal complexes in the foam after foam fractionation of equimolar solution
Cl-, M
Flgure 6. Separation coefficients Zn(ll), Cd(ll), Hg(ll), and Au(lll)
30
t
of chloride complex anions of Initial Metal Concentration 4 0 X IO-' M ' (iOx10-5M in each metal1 Initial CI- Concentration 0 50 M
i
oHg/Zn VHa/Cd
1
08
, N
-8
I 10
Au
1
20
30
Time, minute
Figure 10. Rate curves of metal concentration vs. time for equimolar solution of the four metals Bt initial chloride ion concentration of 0.5 M
C I-, M
Figure 7. Separation coefficients
of chloride complex anions of
Zn(ll), Cd(ll), and Hg(ll)
I
I
I O k
$m 4
B
ii
I I 1 I 1 1 i 1 I I I I i Initial Metal Concentration 4 0 ~ 0 M- ~ ( I OX10-5 M in each meyal)
1
08
06
LL
g
I
l l l l
v
1
00%
'
.
'
" " ' "
I
,
,,,
.L
I .o
0.1
"
v
fAu
3.0
GI-, M
Figure 8. Effect of chloride ion concentration on the mole fraction of each of the four metal complexes in the residual solution after foam fractionation of equimolar solution ated into the foam. At an initial chloride concentration of 0.01 M, the mole fraction of Au(II1) in the faam was 0.9. The optimum chloride concentration for the separation of Au(II1) and Hg(I1) from Cd(I1) and Zn(I1) was 0.5 M: the sum of the mole fractions of Au(II1) and Hg(I1) in the foam was 0.84 and the sum of the mole fractions of Cd(I1) and Zn(I1) in the residual solution was 0.88. 978
I t is possible to improve the selective separation of one or more of the metals by careful control of the foam fractionation time. All data presented above were at foam cease, coinciding with maximum flotation of all four metals. Figure 10 presents flotation curves a t an initial chloride concentration of 0.5 M. No data points are plotted, because the curves are continuous recorder traces of residual solution concentration vs. time. Each curve represents a different replicate experiment, with all conditions the same and an equimolar initial solution, but with a different metal concentration being monitored. Figure 10 can be used to compute $1/2 a t different foam fractionation times. At a time of 8 min, $Cd/Zn was 13, compared to 9.3 a t foam cease; $A"/z" was 90, compared to 32 a t foam cease. Throughout the foam fractionation experiments, the total volume of solution that was carried into the foam a t foam cease was less than 1ml, or less than 1%of the initial solution volume. Thus, foams very concentrated in the chloride complex anions were consistently obtained.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
ACKNOWLEDGMENT The authors acknowledge gratefully the assistance of William Ehmann, Professor and Chairman of the Chemistry Department a t the University of Kentucky, through the use of his radiochemistry laboratory and equipment. LITERATURE CITED W. Charewicz and W. Walkowiak, Sep. Sci., 7,631 (1972). R. 6.Grieves, D. Bhattacharyya, and P. J. W. The, Can. J. Chem. Eng., 51,
173 (1973). R. B. Grieves and P.J. W. The, J. Inorg. Nucl. Chem., 36, 1391 (1974). W. Charewicz and R. B. Grieves, Anal. Lett., 7,233 (1974). W. Charewicz and R. 6.Grieves, J. lnorg. Nucl. Chem., 36, 2371 (1974).
R. B. Grieves, W. Charewicz, and P. J. W. The, Sep. Sci., I O , 77 (1975). R. B. Grieves, R. L. Drahushuk, W. Walkowiak, and D. Bhattacharyya,Sep. Sci., in press. W. Walkowiak and R. B. Grieves, J. lnorg. Nucl. Chem., in press. , R. B. Grieves, Chem. Eng. J. (Lausanne),9, 93 (1975). (10)C. Jacobelli-Turi, S.Terenzi, and M. Palmera, ind. Eng. Chem., Process I
Des. Dev., 6,163 (1967). (11) C. Jacobelli-Turi, S. Terenzi, and M. Palmera, lnd. Eng. Chem., Process Des. Dev., 6,161 (1967). (12)J. A. Lusher and F. Sebba, J. Appi. Chem. Biotechnol., 15,577(1965);16, 129 (1966).
(13)8. L. Karger, R. P. Poncha, and M. M. Miller, Anal. Lett., 1, 437 (1968). (14)B. L. Karger and M. M. Miller, Anal. Chim. Acta, 48,273 (1969). (15) W. Charewicz and J. Niemiec, Nukleonika, 14, 17 (1969). (16)"Stability Constants", Spec. Pub/. No. 17, The Chemical Society, London, 1964. (17)K. A. Kraus and F. Nelson, Proc. First lnt. Conf. Peaceful Uses At. Energy, Geneva, 7, 113 (1956).
RECEIVEDfor review October 20, 1975. Accepted February 18, 1976.
Solvent-Solvent Extraction of Rhodium- 103m from Ruthenium103 Employing a Sulfate-Carbon Tetrachloride Medium Claude E. Epperson,' Robert R. Landolt," and Wayne V. Kessler Bionucleonics Department, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Ind. 47907
103mRhin equilibrium with parent lo3Ruwas separated in yields of 94% of those theoretically possible. lo3Ruchloride was first converted to the tetroxide which was then extracted from an aqueous solution of the equilibrium mixture with carbon tetrachloride.
Large quantities of 1°3Ru are available in nuclear fuel wastes. This radionuclide with a half-life of 39.8 days decays to loBmRh(tlj2 = 57 min). Some uses have already been found for 103mRhin the field of nuclear medicine ( I ) and, if this nuclide were readily available, additional uses would undoubtedly be found. Furthermore, the decay of IoBmRhleads to stable rhodium, an important metal. Estimates (2) indicate that the annual yield of rhodium from nuclear fuel wastes may equal the consumption level. Consequently, a practical method for separating loBmRh,either alone or in combination with stable Io3Rh,from the stable and radioactive ruthenium isotopes present in nuclear fuel wastes would be desirable. A survey of the literature revealed that no satisfactory, fast, and simple radiochemical separation of loBmRhfrom lo3Ruhas been reported. Ion exchange separations have been generally unsatisfactory (3-5), because of considerable amounts of Io3Ru contamination. .Extensive column chromatography studies in the authors' laboratory have produced similar unsatisfactory results. Published reports devoted solely to the separation of stable rhodium from ruthenium are few in number (6-9). Almost invariably, ruthenium is separated from other platinum metals by distilling off ruthenium as the volatile R u 0 4 from concentrated perchloric acid or another oxidizing material. Although many of the separations are ingenious, the time required to complete them is lengthy considering the short half-life of IoBmRh.In addition, the separations are usually nonrepetitive and tend to leave the separated rhodium in a form too complicated for immediate usage. In some instances, Ru04 has been separated from other platinum metals using solvent extraction techniques. The determination of submicrogram quantities of ruthenium (10) and purification of milligram quantities of ruthenium and rhodium (11,12)have utilized this method. These techniques (10-12) have been adapted and modified for this study. The basic separatory procedure is: 1) fume (evaporate) a Present address, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, Ark.
sample of Io3Ruchloride in equilibrium with the chlorides of loBmRhand Io3Rh in 1:l sulfuric acid for a period of time to convert Io3Ruto its sulfate form and to remove chloride, 2) add ceric sulfate in sulfuric acid to convert Io3Rusulfate to Io3Ru tetroxide, 3) remove Io3Ru tetroxide from the aqueous acid phase by extracting it into carbon tetrachloride, 4) recover the aqueous acid phase containing loBmRhwhich is not extractable in carbon tetrachloride, and 5) recover Io3Ru for later reuse from the organic phase with an aqueous.reducing extraction.
EXPERIMENTAL Apparatus. Radioactivity measurements were made with a sodium iodide well crystal and a multichannel analyzer. Reagents. Ceric Sulfate Reagent. A 0.2 N solution was prepared by dissolving ceric ammonium sulfate dihydrate (G. Frederick Smith) in 2 M H2SO4. This solution was allowed to stand undisturbed for 2 weeks and was then filtered through a fine grade sintered glass filter. Carbon Tetrachloride. SpectrAR (Mallinckrodt) was used as the organic extractant. Radioactiue Ruthenium. lo3Ru in equilibrium with loSmRhwas obtained from Amersham/Searle as ruthenium trichloride in 3 N HCl. The specific activity was approximately 5 mCi/mg of ruthenium. A stock solution was prepared to contain about 10 fig (50 fiCi)/ml in 2 N HC1. The radionuclidic purity was determined by y-ray spectrometry and half-life verification. Extraction Procedure. A 100-filaliquot ( 5 pCi) of the stock solution was added to 5 ml of 1:l HzS04 in a 20-ml glass beaker. The beaker was heated at a medium heat on a hot plate until white sulfuric anhydride fumes appeared. Heating was continued for 80 min following onset of the white fumes. The beaker was then cooled to room temperature and evaporation losses were replaced with water to make 5 ml of solution. Five milliliters of ceric sulfate reagent was added and the beaker was covered with a watch glass and allowed to stand for 10 min. The contents were then poured into 10 ml of carbon tetrachloride contained in a 60-ml separatory funnel equipped with a Teflon stopcock and a ground glass stopper. Three 1-min carbon tetrachloride extractions of 10 ml each were performed. The carbon tetrachloride extracts were combined and stored for subsequent recovery of Io3Ruif desired. An aliquot of the aqueous phase containing the loBmRhwas removed by pipet, placed in a plastic vial, and assayed immediately for IoBmRhand Io3Rucontent by y-ray spectrometry. For accurate determination of the 10BmRhyield, the elapsed time from separation to assay was considered by measuring from the start of the first extraction to the beginning of the assay. Reclamation of Extracted lo3Ru.T o determine if reclaimed lo3Ru could be reused, the carbon tetrachloride extracts (30 ml) were added to 10 ml of 2 M HzS04 containing 1mg of sodium sulfite in a separatory funnel. The two phases were shaken for 90 min on a wrist action shaker. The organic phase was then found to be entirely free of radioactivity. After aging the aqueous phase overnight to allow loBmRh ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
979
