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CHEMISTRY
Corresponding Member of the USSR Academy of Sciences A. V. NIKOLAEV, Yu. A. AFANAS’EV,
A. I. RYABININ
INVESTIGATION OF THE EXTRACTION SYSTEM
Th(NO₃)₄—HNO₃—H₂O—(C₄H₉O)₃PO AT 25°C BY THE METHOD OF EXTRACTION RAYS
Studies of extraction systems containing an actinide or lanthanide nitrate, nitric acid, water, and tributyl phosphate (TBP) are of considerable theoretical and practical interest. To date, the following systems have been studied and published: UO₂(NO₃)₂—HNO₃—H₂O—(C₄H₉O)₃PO (¹), La(NO₃)₃—HNO₃—H₂O—(C₄H₉O)₃PO, Ce(NO₃)₄—HNO₃—H₂O—(C₄H₉O)₃PO (²). We have studied the analogous system with thorium nitrate, namely Th(NO₃)₄—HNO₃—H₂O—(C₄H₉O)₃PO.
Fig. 1. Extraction rays and isolines of \(K_{\mathrm{distr}}\) for \( \mathrm{Th(NO_3)_4} \) in the system
\( \mathrm{Th(NO_3)_4}—\mathrm{HNO_3}—\mathrm{H_2O}—(\mathrm{C_4H_9O})_3\mathrm{PO} \) at 25°. Bold curves are saturation lines of the aqueous phase; dashed lines with dots are isolines of \(K_{\mathrm{distr}}\) for \( \mathrm{Th(NO_3)_4}\);
I–VII are extraction rays; a, b, c are Schreinemakers rays.
Extraction was carried out in graduated test tubes at \(25 \pm 0.05^\circ\mathrm{C}\). Before use, TBP was distilled twice in vacuum. Thorium was determined by titration with Trilon B using xylenol orange \((^3)\); nitric acid, by potentiometric titration with a solution of caustic potash in the presence of ammonium oxalate.
Table 1
Composition (mol/l) and specific gravities (g/cm\(^3\)) of the equilibrium phases
| Rays | Aqueous phase: Th(NO\(_3\))\(_4\) | Aqueous phase: HNO\(_3\) | Aqueous phase: sp. gr. | Organic phase: Th(NO\(_3\))\(_4\) | Organic phase: HNO\(_3\) | Organic phase: H\(_2\)O | Organic phase: TBP* | Organic phase: sp. gr.** | \(K_{\mathrm{calc.}}^{\mathrm{Th(NO_3)_4}}\)*** | \(K_{\mathrm{calc.}}^{\mathrm{HNO_3}}\)*** |
|---|---|---|---|---|---|---|---|---|---|---|
| I | 2.56 | 1.24 | 1.960 | 1.25 | 0.25 | — | 2.9 | 1.410 | 0.49 | 0.21 |
| I | 2.12 | 1.24 | 1.821 | 1.19 | 0.24 | — | 3.1 | 1.396 | 0.56 | 0.20 |
| I | 1.02 | 1.20 | 1.422 | 1.04 | 0.26 | — | 3.1 | 1.352 | 1.02 | 0.21 |
| I | 0.35 | 0.74 | 1.150 | 0.76 | 0.26 | — | 3.1 | 1.248 | 2.17 | 0.35 |
| I | 0.28 | 0.38 | 1.113 | 0.60 | 0.25 | — | 3.1 | 1.197 | 2.14 | 0.64 |
| I | 0.27 | 0.27 | 1.106 | 0.51 | 0.19 | — | 3.2 | 1.163 | 1.91 | 0.67 |
| II | 2.44 | 3.11 | 1.978 | 1.26 | 0.64 | — | 3.0 | 1.447 | 0.51 | 0.20 |
| II | 2.11 | 3.16 | 1.853 | 1.24 | 0.52 | — | 2.9 | 1.397 | 0.59 | 0.16 |
| II | 0.57 | 3.16 | 1.317 | 1.02 | 0.44 | — | 2.9 | 1.346 | 1.78 | 0.14 |
| II | 0.31 | 2.57 | 1.202 | 0.89 | 0.56 | — | 3.0 | 1.321 | 2.82 | 0.22 |
| II | 0.21 | 1.82 | 1.136 | 0.72 | 0.61 | — | 3.1 | 1.239 | 3.49 | 0.33 |
| II | 0.16 | 0.65 | 1.085 | 0.39 | 0.46 | — | 3.2 | 1.141 | 2.42 | 0.71 |
| III | 1.63 | 4.57 | 1.740 | 1.09 | 0.58 | 0.50 | 3.0 | 1.361 | 0.66 | 0.13 |
| III | 1.15 | 4.57 | 1.581 | 1.08 | 0.70 | 0.60 | 3.0 | 1.373 | 0.94 | 0.15 |
| III | 0.65 | 4.52 | 1.397 | 1.02 | 0.67 | 0.51 | 3.0 | 1.350 | 1.57 | 0.15 |
| III | 0.30 | 4.46 | 1.258 | 0.90 | 0.76 | 0.49 | 3.1 | 1.317 | 3.03 | 0.17 |
| III | 0.12 | 3.60 | 1.173 | 0.73 | 0.96 | 0.68 | 3.1 | 1.254 | 6.07 | 0.27 |
| III | 0.07 | 2.11 | 1.113 | 0.44 | 1.51 | 1.32 | 3.2 | 1.162 | 6.05 | 0.72 |
| IV | 1.77 | 6.60 | 1.806 | 1.08 | 1.58 | — | 2.9 | 1.389 | 0.61 | 0.24 |
| IV | 1.00 | 6.87 | 1.563 | 1.02 | 1.23 | — | 2.9 | 1.362 | 1.02 | 0.18 |
| IV | 0.43 | 6.87 | 1.362 | 0.95 | 1.15 | — | 3.0 | 1.330 | 2.21 | 0.17 |
| IV | 0.17 | 6.26 | 1.250 | 0.81 | 1.23 | — | 2.9 | 1.296 | 4.79 | 0.20 |
| IV | 0.05 | 4.24 | 1.150 | 0.58 | 1.31 | — | 3.1 | 1.218 | 10.70 | 0.31 |
| V | 1.48 | 9.07 | 1.763 | 1.01 | 2.29 | — | 2.8 | 1.374 | 0.68 | 0.25 |
| V | 0.66 | 9.11 | 1.493 | 0.88 | 1.95 | — | 2.8 | 1.336 | 1.33 | 0.21 |
| V | 0.36 | 9.17 | 1.393 | 0.83 | 1.92 | — | 2.9 | 1.307 | 2.30 | 0.21 |
| V | 0.26 | 8.88 | 1.357 | 0.80 | 1.86 | — | 2.9 | 1.298 | 3.10 | 0.21 |
| V | 0.048 | 7.56 | 1.248 | 0.61 | 1.96 | — | 2.8 | 1.234 | 12.6 | 0.26 |
| VI | 1.13 | 11.50 | 1.700 | 0.90 | 3.16 | — | 2.5 | 1.360 | 0.79 | 0.27 |
| VI | 0.83 | 11.76 | 1.611 | 0.81 | 3.21 | 1.33 | 2.7 | 1.335 | 0.97 | 0.27 |
| VI | 0.59 | 11.86 | 1.541 | 0.78 | 2.91 | 1.28 | 2.75 | 1.313 | 1.32 | 0.25 |
| VI | 0.22 | 11.30 | 1.394 | 0.69 | 2.74 | — | 2.8 | 1.276 | 3.18 | 0.24 |
| VI | 0.14 | 11.10 | 1.365 | 0.66 | 2.77 | — | 2.8 | 1.266 | 4.80 | 0.25 |
| VI | 0.047 | 10.50 | 1.334 | 0.54 | 2.78 | 1.10 | 2.9 | 1.229 | 11.50 | 0.26 |
| VI | 0.038 | 9.96 | 1.305 | 0.53 | 2.69 | — | 3.0 | 1.222 | 13.9 | 0.27 |
| VII | 0.85 | 14.4 | 1.662 | 0.85 | 4.57 | — | 2.4 | 1.363 | 1.0 | 0.32 |
| VII | 0.81 | 14.3 | 1.639 | 0.82 | 4.39 | — | 2.5 | 1.360 | 1.0 | 0.31 |
| VII | 0.59 | 14.4 | 1.576 | 0.78 | 4.21 | — | 2.5 | 1.340 | 1.32 | 0.29 |
| VII | 0.23 | 14.4 | 1.458 | 0.66 | 3.89 | — | 2.7 | 1.288 | 2.84 | 0.27 |
| VII | 0.052 | 13.5 | 1.381 | 0.51 | 3.72 | — | 2.8 | 1.238 | 9.85 | 0.27 |
* The concentration of TBP was found by calculation.
* On rays I–IV phase inversion is observed.
** In the calculation, the concentration for both phases was expressed in moles per 1 liter.
The experimental data are presented in Fig. 1 and in Table 1. The extraction rays in this system, as in the preceding one \((^2)\), were constructed by carrying out a series of extractions from the same initial solution at different phase ratios. The curve \(ABC\) in Fig. 1 is the solubility curve in the system Th(NO\(_3\))\(_4\)—HNO\(_3\)—H\(_2\)O according to the data of \((^4)\): solutions corresponding to branch \(AB\) are saturated with thorium nitrate pentahydrate, and solutions of branch \(BC\) with tetrahydrate Th(NO\(_3\))\(_4\cdot 4\)H\(_2\)O. We obtained
the solubility curve corresponding to line \(CBD\) was plotted. Independently of the acidity, the solid phase was thorium nitrate tetrahydrate, as was established by the Schreinemakers residue method. Figure 1 shows three Schreinemakers rays \((a, b, c)\), connecting the liquid phases at different portions of the solubility curve with the equilibrium solid phase (point \(E\)), containing 87% \(\mathrm{Th}(\mathrm{NO}_3)_4\) or \(\mathrm{Th}(\mathrm{NO}_3)_4 \cdot 4\mathrm{H}_2\mathrm{O}\). According to our data, the tetrahydrate proved to be stable also at low acidities.
The extraction rays \(I\)—\(VII\) (Fig. 1) are curvilinear over a considerable part of the field of unsaturated aqueous solutions of the system, which distinguishes this system from systems with uranyl nitrate and cerium(IV) nitrate \((^{1,2})\). This is apparently explained by the fact that, at a 15–20% concentration of thorium nitrate, nitric acid becomes a serious competitor in the struggle for the extractant. The extraction rays do not converge at any definite point, and none of them passes through the point corresponding to \(\mathrm{Th}(\mathrm{NO}_3)_4\). This also indicates the simultaneous extraction of thorium nitrate and nitric acid even when the content of the latter in the aqueous phase is low. At higher concentrations of thorium nitrate, good linearity of the rays is observed, and their curvature begins at the lower \(\mathrm{Th}(\mathrm{NO}_3)_4\) concentration the higher the acidity.
As can be seen from Fig. 1 and Table 1, the distribution coefficients of thorium nitrate increase along the rays, with the exception of rays \(I\) and \(II\), where, at a \(\mathrm{Th}(\mathrm{NO}_3)_4\) concentration in the aqueous phase of 7–12%, \(K_{\mathrm{distr}}\) for \(\mathrm{Th}(\mathrm{NO}_3)_4\) passes through a maximum. The rays themselves sharply change direction—falling toward the abscissa axis—which is associated with the predominant transfer of acid into the extract. At a \(\mathrm{Th}(\mathrm{NO}_3)_4\) concentration \(\geq 20\%\), with increasing acidity, a small change in \(K_{\mathrm{distr}}\) for \(\mathrm{Th}(\mathrm{NO}_3)_4\) is observed, almost the same for all its concentrations up to saturation. \(K_{\mathrm{distr}}^{\mathrm{HNO}_3}\) for rays \(IV\)—\(VII\) are practically constant (0.2–0.3), which indicates the small influence of thorium nitrate on the distribution of nitric acid. However, in this concentration region \(K_{\mathrm{distr}}\) in the presence of \(\mathrm{Th}(\mathrm{NO}_3)_4\) is smaller than that of \(\mathrm{HNO}_3\) alone, i.e., salting-out of the latter from the organic phase takes place. At low concentrations of thorium nitrate and \(\mathrm{HNO}_3\), \(K_{\mathrm{distr}}\) of the acid increases to a value of 0.67–0.71 (rays \(I\) and \(II\)); consequently, under these conditions the presence of thorium does not affect the extraction of nitric acid.
Analysis of the composition of the organic phases shows (Table 1) that nitric acid, apparently, either can dissolve in the solvate of thorium nitrate with TBP, without forming its own solvate, or extraction occurs here with the formation of two solvates (with \(\mathrm{Th}(\mathrm{NO}_3)_4\) and \(\mathrm{HNO}_3\)); but in both cases the rays obtained are the geometric sum of two rays with two composition poles \((^5)\). For rays \(III\) and \(VI\), water in the organic phase was determined by Fischer’s method. As can be seen from the data obtained, the water content on the rectilinear portion of the ray is practically constant, while on the curved portion it changes (increases). Thorium nitrate is extracted in an anhydrous form.
Thus, three regions can be distinguished on the extraction ray: 1) predominant extraction of thorium (the content of water and nitric acid is constant, the course of the ray is rectilinear), 2) comparable extraction of \(\mathrm{Th}(\mathrm{NO}_3)_4\) and \(\mathrm{HNO}_3\)—the ray begins to curve, 3) predominant extraction of \(\mathrm{HNO}_3\)—a steep downward deviation of the ray.
Institute of Inorganic Chemistry
Siberian Branch of the Academy of Sciences of the USSR
Received
15 VII 1963
CITED LITERATURE
- A. V. Nikolaev, I. I. Yakovlev, DAN, 145, 5, 1064 (1962).
- A. V. Nikolaev, A. I. Ryabinin, Yu. A. Afanas’ev, DAN, 150, 4, 820 (1963).
- Yu. A. Chernikhov, V. F. Luk’yanov, A. B. Kozlov, Zav. lab., 26, 8, 921 (1960).
- I. R. Ferraro, L. I. Katzin, G. I. Gibson, Am. Chem. Soc., 76, 909–910 (1954).
- A. V. Nikolaev, Collection of Proceedings of the Conference on Extraction in Analytical Chemistry, Publishing House of the USSR Academy of Sciences (1962).