Abstract
Full Text
CHEMISTRY
Corresponding Member of the Academy of Sciences of the USSR A. V. NIKOLAEV, O. R. DYACHENKO,
Yu. A. AFANAS’EV
ON THE JOINT EXTRACTION OF URANYL NITRATE AND CERIUM(IV) NITRATE BY TRIBUTYL PHOSPHATE (TBP)
As was shown earlier \((^{1})\), the study of the joint extraction of two or more extractable compounds is of great theoretical and practical importance.
We have studied an isoconcentrate of the system
\[ \mathrm{UO_2(NO_3)_2 — Ce(NO_3)_4 — 1.5N\ HNO_3 — H_2O — TBP}. \]
The extraction was carried out in separatory funnels at a temperature of \(25^\circ\). Before use, the TBP was twice distilled in vacuum and saturated with water. Uranium was determined by Sakharov’s method \((^{2})\), cerium by oxidimetric titration \((^{3})\), and nitric acid by potentiometric titration with potassium hydroxide solution in the presence of ammonium oxalate.
The results obtained are collected in Table 1.
Table 1
| No. | Conc. in equilibrium aqueous phase, g/l: uranyl nitrate | Conc. in equilibrium aqueous phase, g/l: cerium(IV) nitrate | Distribution coefficient: \(K_U\) | Distribution coefficient: \(K_{\mathrm{Ce}}\) | No. | Conc. in equilibrium aqueous phase, g/l: uranyl nitrate | Conc. in equilibrium aqueous phase, g/l: cerium(IV) nitrate | Distribution coefficient: \(K_U\) | Distribution coefficient: \(K_{\mathrm{Ce}}\) |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 20.4 | — | 15.2 | — | 24 | 104 | 254 | 1.28 | 1.72 |
| 2 | 60.1 | — | 7.73 | — | 25 | 94.7 | 562 | 0.89 | 0.86 |
| 3 | 109.8 | — | 4.07 | — | 26 | 106 | 954 | 0.55 | 0.55 |
| 4 | 223 | — | 2.60 | — | 27 | 201 | 9.7 | 2.47 | 8.1 |
| 5 | 433 | — | 1.42 | — | 28 | 206 | 136 | 1.33 | 2.23 |
| 6 | 645 | — | 0.97 | — | 29 | 196 | 198 | 1.23 | 1.80 |
| 7 | 745 | — | 0.87 | — | 30 | 311 | 392 | 0.96 | 1.00 |
| 8 | — | 40.3 | — | 11.2 | 31 | 235 | 661 | 0.56 | 0.68 |
| 9 | — | 71.6 | — | 6.8 | 32 | 218 | 897 | 0.47 | 0.53 |
| 10 | — | 224 | — | 2.46 | 33 | 408 | 7.9 | 1.38 | 4.76 |
| 11 | — | 424 | — | 1.33 | 34 | 410 | 38.1 | 1.20 | 2.78 |
| 12 | — | 610 | — | 0.93 | 35 | 449 | 50.5 | 1.12 | 2.07 |
| 13 | — | 839 | — | 0.70 | 36 | 417 | 77.6 | 1.09 | 1.95 |
| 14 | — | 1020 | — | 0.57 | 37 | 449 | 204 | 0.91 | 1.05 |
| 15 | 19.9 | 20.4 | 3.98 | 18.6 | 38 | 447 | 299 | 0.79 | 0.83 |
| 16 | 27.3 | 55.3 | 2.91 | 7.66 | 39 | 397 | 375 | 0.79 | 0.81 |
| 17 | 21.1 | 834.0 | 0.62 | 0.67 | 40 | 656 | 31.5 | 0.85 | 1.76 |
| 18 | 69.6 | 105 | 1.83 | 3.84 | 41 | 670 | 44.6 | 0.83 | 1.39 |
| 19 | 62.1 | 306 | 1.25 | 1.61 | 42 | 640 | 95.0 | 0.81 | 1.33 |
| 20 | 56.0 | 373 | 1.25 | 1.33 | 43 | 631 | 154 | 0.76 | 1.02 |
| 21 | 59.6 | 586 | 0.88 | 0.89 | 44 | 31.0 | 983 | 0.49 | 0.57 |
| 22 | 112 | 75.6 | 2.02 | 3.94 | 45 | 184 | 970 | 0.43 | 0.51 |
| 23 | 100 | 100 | 1.71 | 3.34 | 46 | 233 | 953 | 0.45 | 0.50 |
Uranyl nitrate and cerium(IV) nitrate, as individual substances, are extracted by TBP approximately equally (since their molecular weights are 394 and 388, respectively, comparison may also be made when the concentration is expressed in grams per liter). In joint extraction, \(K_U\) and \(K_{\mathrm{Ce}}\) decrease. However, the effect of cerium(IV) nitrate on \(K_U\) is somewhat greater than that of uranyl nitrate on \(K_{\mathrm{Ce}}\), which is especially noticeable at concentrations of each component up to 200 g/l.
In this connection, for solutions with equal contents of both salts, \(K_{\mathrm{Ce}} > K_{\mathrm{U}}\). At concentrations above 200 g/liter, the indicated difference in mutual influence approaches zero; the distribution coefficients of uranyl nitrate and cerium(IV) nitrate become very close. Consequently, separation of U(VI) and Ce(IV) by fractional extraction is impossible.
As additional studies have shown, analogous regularities are also observed in extraction with TBP solutions in carbon tetrachloride. Such behavior of the compounds studied during joint extraction is explained by the fact that the stability of the solvate of cerium(IV) nitrate with TBP is only slightly greater than the stability of the uranyl nitrate solvate.
Thus, on the basis of an analysis of extraction systems, it is possible to make an approximate estimate of solvate stability. Comparing the data of the present work with the data of the preceding work \(^{4}\), it is evident that the stability of solvates formed by TBP with nitrates decreases in the series: Ce(IV), U(VI), Th(IV). Therefore it should be assumed that the influence of uranyl nitrate on the extraction of thorium nitrate is similar in character to that described in \(^{4}\). Nevertheless, the displacement of thorium from the organic phase into the aqueous phase by cerium(IV) should proceed better than the analogous displacement by uranyl nitrate.
These conclusions are in good agreement with the possibility of separating uranium and thorium nitrates by fractional extraction with a 5% TBP solution \(^{5}\).
Institute of Inorganic Chemistry
Siberian Branch of the Academy of Sciences of the USSR
Received
15 V 1962
References
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