Mutual solubility between hexane and tri-n-butyl phosphate solvates of lanthanide(III) and thorium(IV) nitrates at various temperatures

Article abstract of DOI:10.1134/S0036023607070261

The phase diagrams of binary liquid systems consisting of hexane and a tri-n-butyl phosphate (TBP) solvate of an Ln(III) (Ln = Nd, Gd, Y, Yb, Lu) or Th(IV) nitrate at various temperatures are considered. The diagrams show a field of homogeneous solutions and a two-phase field in which phase I is hexane-rich and phase II is rich in [Ln(NO₃)₃(TBP)₃] or [Th(NO₃)₄(TBP)₂]. The miscibility gap in the binary systems narrows with increasing temperature.

Full text of DOI:10.1134/S0036023607070261

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 7, pp. 1144–1146. © Pleiades Publishing, Inc., 2007.
Original Russian Text © V.A. Keskinov, V.V. Lishchuk, A.K. Pyartman, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1222–1224.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Mutual Solubility between Hexane and Tri-n-Butyl Phosphate
Solvates of Lanthanide(III) and Thorium(IV) Nitrates
at Various Temperatures
V. A. Keskinov, V. V. Lishchuk, and A. K. Pyartman
St. Petersburg Technological Institute (Technical University), Moskovskii pr. 26, St. Petersburg, 198013 Russia
Received July 25, 2006
Abstract—The phase diagrams of binary liquid systems consisting of hexane and a tri-n-butyl phosphate
(TBP) solvate of an Ln(III) (Ln = Nd, Gd, Y, Yb, Lu) or Th(IV) nitrate at various temperatures are considered.
The diagrams show a field of homogeneous solutions and a two-phase field in which phase I is hexane-rich and
phase II is rich in [Ln(NO3)3(TBP)3] or [Th(NO3)4(TBP)2]. The miscibility gap in the binary systems narrows
with increasing temperature.
DOI: 10.1134/S0036023607070261
Earlier [1, 2], we studied the diagrams of binary liq- and organic phases were determined chelatometrically
uid systems consisting of tetradecane (decane) and a [3, 7]. The compositions of coexisting organic phases
tri-n-butyl phosphate (TBP) solvate of an Ln(III) (Ln = (tie lines) were determined by a procedure reported in our
Nd, Sm, Gd,Y, Lu) nitrate at T = 273.15–373.15 K. The earlier works [1, 2]. The formation of a heterogeneous
diagrams of these systems consist of a homogeneous mixture was additionally verified by nephelometry using a
field and a two-phase field. In the latter, phase I is rich Kernco Model 966 R turbidimeter and a λ = 850 nm filter.
in tetradecane (decane) and phase II is rich in The error in the weight fractions of components did not
[Ln(NO3)3(TBP)3] (Ln = Nd, Sm, Gd,Y, Lu). The upper exceed (0.001–0.002), and the temperature error was
no larger than 0.2 K. Binodal curves were fitted to
third-order polynomials, and upper critical tempera-
tures were refined by the numerical differentiation of
the binodal curves using the graphing and digitizing
program Origin v. 6.0. The error in critical-point com-
position (weight fraction) data was (0.01–0.02).
critical mixing points were estimated and were found to
depend on Ln(III).
Here, we report the composition–temperature dia-
grams of binary liquid systems consisting of hexane
and a TBP solvate of Ln(III) (Ln = Md, Sm, Gd, Y, Lu)
or Th(IV) nitrate.
RESULTS AND DISCUSSION
EXPERIMENTAL
The
diagrams
of
the
binary
systems
The density of phases was measured with a picnom-
eter. The starting Ln(III) nitrate solutions were pre-
pared by dissolving respective oxides (special-purity
grade) in nitric acid (special-purity grade). TBP was
vacuum-distilled (ρ = 0.9727 g/cm3), and hexane
(reagent grade; ρ = 0.6548 g/cm3 at T = 298.15 K) was
used as-received. The coordination solvates
[Ln(NO3)3(TBP)3] (Ln = Nd, Gd, Y, Yb, Lu) and
[Th(NO3)4(TBP)2] were obtained by thrice reacting
TBP with a saturated aqueous solution of Ln(III) or
Th(IV) nitrate [1–3]. The [Ln(NO3)3(TBP)3] concentra-
[Ln(NO3)3(TBP)3]–C6H14 (Ln = Nd, Gd,Y,Yb, Lu) and
[Th(NO3)4(TBP)2]–C6H14 (Figs. 1–6) indicate an incom-
plete miscibility of the components and have a two-
phase region in which phase I is C6H14-rich and phase II
is rich in [Ln(NO3)3(TBP)3] or [Th(NO3)4(TBP)2]. As
the temperature is raised, the miscibility gap narrows
and, accordingly, the mutual solubility of the compo-
nents increases (Figs. 1–6). The thorium and neody-
mium systems have an upper critical mixing point. For
the Th(IV) solvate, the critical point occurs at Tcr =
337.85 0.25 K and a [Th(NO3)4(TBP)2] weight frac-
tion was 1.10 0.02 mol/L (ρ = 1.275 0.001 g/cm3, tion of 0.53; for the Nd(III) solvate, at Tcr = 316.15
and the [Th(NO3)4(TBP)2] concentration was 1.80
0.25 K and an [Nd(NO3)3(TBP)3] weight fraction of
0.59. The upper critical points for the other
[Ln(NO3)3(TBP)3]–C6H14 systems could not be
located, because they fell beyond the temperature limit
0.01 mol/L (ρ = 1.702 0.01 g/cm3). Binodal curves
were obtained by Alekseev’s visual polythermal
method [4−6]. The Ln(III) and Th(IV) concentrations
in the starting solutions and in the equilibrium aqueous set by the hexane boiling point (341.9 K [8]). Exceed-
1144

MUTUAL SOLUBILITY BETWEEN HEXANE AND TRI-n-BUTYL PHOSPHATE SOLVATES
1145
T, K
T, K
320
360
350
316
312
308
304
300
296
5
340
330
320
310
300
4
3
A
B
4
3
A
B
2
1
2
1
C
D
C
D
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[Gd(NO ) (TBP) ] weight fraction
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[Nd(NO ) (TBP) ] weight fraction
3 3
3
3 3
3
Fig. 1. Effect of temperature on liquid–liquid phase separa-
tion in the [Nd(NO ) (TBP) ]–C H system: (Ä) two-
Fig. 2. Effect of temperature on liquid–liquid phase separa-
tion in the [Cd(NO ) (TBP) ]–C H system. The designa-
3 3
3
6
14
3 3
3
6 14
phase field, (Ç) field of homogeneous solutions, (CD) bin-
odal curve, and (1–5) tie lines. The arrow points to the upper
critical mixing point.
tions are the same as in Fig. 1. The arrow points to the hypo-
thetical upper critical mixing point. The hexane bp
(341.90 K) is indicated by a dashed line.
T, K
360
T, K
350
350
340
5
4
340
330
4
330
3
3
320
B
320
A
2
B
2
310
310
300
A
1
1
C
D
300
C
D
0
0.2
0.4
3 3
0.6
0.8
1.0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[Yb(NO ) (TBP) ] weight fraction
[Y(NO ) (TBP) ] weight fraction
3
3 3
3
Fig. 3. Effect of temperature on liquid–liquid phase separa-
tion in the [Y(NO ) (TBP) ]–C H system. For the leg-
Fig. 4. Effect of temperature on liquid–liquid phase separa-
tion in the [Yb(NO ) (TBP) ]–C H system. For the leg-
3 3
3
6
14
3 3
3
6 14
end, see Fig. 2.
end, see Fig. 2.
ing this temperature limit caused hexane evaporation
The left- and right-hand side branches of the binodal
from the liquid phase rather than the homogenization of curve for the [Ln(NO3)3(TBP)3]–C6H14 systems
the system (in Figs. 2–5, the hexane bp is indicated by
a dashed line). For this reason, the Tcr values for these
systems were estimated by simultaneously fitting the reported in our previous publications [1, 2] demon-
left- and right-hand branches of the binodal curve to strates that Tcr increases and the solubility of the hydro-
(Figs. 1–5) depend considerably on Ln(III). Compari-
son between the results of this study and the data
third-order polynomials followed by numerical differ-
entiation of the curve. For the Gd(III), Y(III), and
Yb(III) solvates, Tcr ≈ 350 K; for the Lu(III) solvate,
carbon in the Ln(III) solvate solution decreases on
passing from hexane to decane and then tetradecane.
The critical temperature is much lower for the
Tcr ≈ 356 K. All of these temperatures are well above [Th(NO3)4(TBP)2]–C6H14 system than for the
the hexane bp [8]. For these solvates, the [Th(NO3)4(TBP)2]–C10H22 system. For the system
[Ln(NO3)3(TBP)3] weight fractions at Tcr are similar
and are approximately equal to 0.59.
involving decane, the hypothetical upper critical tem-
perature exceeds the decane boiling point, and this is
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 7 2007

1146
T, K
KESKINOV et al.
T, K
360
340
330
320
310
300
290
4
3
350
340
330
320
310
300
5
4
3
2
1
A
B
A
B
2
C
D
C
1
D
0
0.2
0.4
0.6
0.8
1.0
0
0.2
0.4
0.6
0.8
1.0
[Th(NO ) (TBP) ] weight fraction
3 4
2
[Lu(NO ) (TBP) ] weight fraction
3 3
3
Fig. 5. Effect of temperature on liquid–liquid phase separa-
tion in the [Lu(NO ) (TBP) ]–C H system. For the leg-
Fig. 6. Effect of temperature on liquid–liquid phase separa-
tion in the [Th(NO ) (TBP) ]–C H system. For the leg-
3 3
3
6
14
3 4
2
6 14
end, see Fig. 2.
end, see Fig. 1.
5. R. Traybal, Liquid Extraction (McGraw-Hill, N. Y.,
the reason why the decane solubility in the Th(IV) sol-
vate solution [9] is higher than the hexane solubility.
1963; Khimiya, Moscow, 1966).
6. A. V. Nikolaev and I. I. Yakovlev, Clathrate Formation
and Physicochemical Analysis of Extraction Systems
(Nauka, Novosibirsk, 1975) [in Russian].
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 7 2007