282 valent cations but less t h a n tri-, or tetra-valent cations investigated. The behaviour of the trivalent elements investigated is almost the same, a slight increase in the distribution ratio with increasing nitric acid concentration until a b o u t 5 ~ nitric acid where a rapid increase in D was achieved. I n these cases, a t 12 IV[ nitric acid concentration the percentage extracted is always more t h a n 900/0 and the sequence of such elements is I n > T m > E u > Ce (reverse sequence of the ionic radii), moreover, for the trivalent lanthanides investigated, the extraction ratio increases b y increasing the atomic number. Regarding tetravalent hafnium, it could be seen t h a t it is the element extracted best if compared to all the elements studied all over the nitric acid concentration range. The extraction behaviour of hafnium shows an increase in the D value till i$ reaches a m a x i m a at 7 M acid concentration followed b y a slight decrease in the extraction. I n order to evaluate the extraction capacity of DBDECP, it is found useful to make a rough comparison between the extraction data obtained with those of the well known monodendate e x t r a c t a n t tri-butyl phosphate (TBP). I n Fig. 1, the extractabilit y of some elements b y 250/0 T B P in CCl~ from nitric acid solution as obtained from reference [2] is given together with t h a t of DBDECP. I t is obvious t h a t for a l l the elements D B D E C P has higher extraction ability when compared with TBP. I n this respect, the increase in the D values obtained are between 50 fold for strontium and 3000 fold for silver when using D B D E C P system rather t h a n TBP. This shows t h a t D B D E C P is much stronger e x t r a c t a n t t h a n TBP. The enhancement in using D B D E C P could probably be explained on its bidendate nature. F r o m the data obtained in the present work, the system investigated could be suggested for radiochemical separation of certain fission products. The problem of separating the fission product silver from caesium is quite familiar. Using 20~ D B D E C P in carbon tetraehloride and 12 M H N O 3 solution, more t h a n 850/0 of silver will be extracted into the organic phase leaving more t h a n 98~ of Cs in the aqueous phase. Using a multi-extraction system, high radiochemical purity of Cs and Ag could be easily obtained. Moreover, generation of trivalent lanthanides and aetinides from fission waste could be achieved using the DBDECP-nitrie acid system. I n this respect more t h a n 90~ of the trivalent lanthanides in 12 M H N 0 3 solution will be generated in 200/0 D B D E C P organic phase. I n addition, the extracted lanthanides

Z. Anal. Chem., Band 258, Heft 4 (1972) will be decontaminated to different extent from different fission products.

Re/erences 1. Aly, H. F., Latimer, R. M.: J. Inorg. Nuel. Chem. 82, 3081 (1970). 2. Ishimori, T., Nakamura, E. : Japan Atomic Energy Res. Inst. Report, JAERI-1047 (1963). 3. Siddall, T. H. : J. Inorg. Nucl. Chem. 25, 883 (1963). 4. - - J. Inorg, Nuel. Chem. 26, 1991 (1964). Dr. H. F. Aly Nucl. Chem. Dept. Atomic Energy Establ., P. O. Box Cairo, Egypt/U.A.R.

Exchange Behaviour of Tin, Antimony and Uranium in Aqueous/Nonaqueous Media on the Cation-Exchanger Zirconium Phosphate Austauschverhalten yon Zinn, Antimon und Uran in w~llrig/ nichtw~llrigem Medium an Zirkoniumphosphat als Kationenaustauscher S. A. MAREI,H. F. ALY and N. ZAKAR~A Nuel. Chem. Dept., U.A.R. Atomic Energy Establishment, Egypt, U.A.R, Received October 7, 1971 I n the present work, the distribution of tin, antim o n y and uranium between aqueous-organic solvent media and zirconium phosphate is studied.

Experimental Materials. 1 M HC1 solution of tin-ll3 and antimony-124 and analytical grade uranyl nitrate is used. The zirconium phosphate is prepared according to the procedure given by Gal and Gal [1]. Distribution Coe//icient Measurements. A known volume of the liquid phase of known HC1 concentration containing the element under investigation (10-4--10-3 M)together with certain weight of the dried zirconium phosphate was brought to equilibrium by shaking in a test tube for 24 h. A known aliquot portion from the liquid phase was taken before the addition of zirconium phosphate (Co) and after equilibriation (C) and the concentration of the ion was determined. The distribution coefficient, D, was calculated according to

D=Co-_____~o.V where V and m are the volume of the liquid phase and the weigh8 of the zirconium phosphate, respectively.

Kurze t~Iitteilungen

The concentration of tin and antimony was determined radiometrically using NaI(TI) scintillation crystal connected to an ECKO counter. Uranium was determined colorimetrically using the peroxide method [2].

Results and Discussion In Table 1, the distribution coefficients of antimony, tin and uranium from hydrochloric acid solution of different molarities are given. The sequence for the D values is antimony ~ tin uranium. The effect of organic solvent addition on the exchange behaviour of the different cations has also been investigated. In case ofuraninm, the distribution coefficient shows an increase to a maximum by increasing the percent concentration of the solvent followed by a rapid decrease in D at high concentration. This behaviour is rather general for all the organic solvents used, nevertheless the position of the maximum varies from one solvent to another. The increase in D is most probably due to enhanced ion-pair formation between the uranyl ion and the fixed ions of zirconium phosphate. This is mainly caused by the decrease of the dielectric constant with increasing the percent of the organic solvent added. The decrease in the D value on the other hand, at high concentration could be attributed to the tendency of the uranyl ion to form with the chloride ion a neutral compound or a chloride complex at such low dielectric constant medium. Based on the assumption that the dielectric constant plays the main role in the behaviour of uranium observed, one should expect that the D values should be inversely proportional to the dielectric constant of the mixed aqueous-organic phase. The maximum values of D should be expected to take the sequence acetone > n-propanol > ethanol > iso-propanol > methanol according to their dielectric constant. However, the D sequence obtained is acetone > ethanol > methanol > n-propanol > iso-propanol. This shows that the dielectric constant is not the main factor governing the exchange phenomena for uranium. In the case of tin, the effect of organic solvent addition on the D values is less pronounced than in the case of uranium and antimony but the general behaviour is more or less similar to uranium. The distribution coefficient is constant or goes through a very small maximum followed by a slight decrease at high solvent concentration. The difference in the D values between different organic solvents is not very significant. Regarding antimony, the behaviour of D b y the addition of organic solvent is quite different. B y the

283 Table 1. Distribution coe//ioients o~antimony, tin and uranium between zirconium phosphate and hydrochloric acid solution

HC1 cone.

0.5 1.0 2.0 4.0

Distribution coefficient, D Sb Sn 135.0 104.5 40.2 3.3

22.5 12.5 3.6 1.3

U 6.8 3.0 1.2

addition of 10 ~ of any of the solvents investigatedthe D value obtained is decreased by more than 500/0. The sudden decrease is followed by a reverse proportionality of D with the amount of the solvent added. The amount of the decrease in the D obtained with different organic solvent goes from acetone (22) > n-propanol (23) > ethanol (26) > iso-propanel (27) > methanol (32). This decrease is fairly good inversely proportional to the dielectric constant of the solvents used and supports the concept that the decrease in the D values are mainly related to the enhanced formation of antimonyl chloride complexes with a decrease in the dielectric constant of the medium. For the chroma$ographiv separation of antimony from tin and/or uranium using zirconium phosphate column, the use of 1 M HC1 solution is recommended since it gives the highest separation factor (ca. 100 for Dsb/Dv and 10 for Dsn/Du). Adding organic solvent to the aqueous phase decreases the separation factor, nervertheless, the sequence for the uptake of uranium and antimony is reversed. Therefore the elution sequence of the elements is expected to be reversed, a condition recommended for the separation of antimony from uranium, since the fraction eluted first is always less contaminated than the following fractions. On the other hand, the separation factor between tin and uranium is increased speci. ally when the aqueous phase contains 40--50~ acetone, which increases the selective isolation of the two elements from each other.

Re]erences 1. Gal, I., Gal, O. S. : Proceeding of the second united nation international conference on peaceful uses of atomic energy, vol. 28, p. 24 (1958). 2. Sandell, E. B.: Colorimetric determination of traces of metals, second edit. New York: Intersei. Publ. 1959. Dr. H. F. Aly l~uel. Chem. Dept. Atomic Energy Establ., P. O. Box Cairo, Egypt/U.A.R.