Solubility in the LaCl3-LnCl3-HCl-H2O (Ln = Pr, Nd) systems at 25°C

Article abstract of DOI:10.1134/S0036023612040122

The solubility in the quaternary water-salt systems LaCl ₃-NdCl₃-HCl-H₂O (1) and LaCl₃- PrCl₃-HCl-H₂O (2) at 25°C was studied in the section of 40 wt % hydrochloric acid, a system with a eutonic discontinuity. The composition at the point of discontinuity for the eutonic solution is the following. In system 1: 4.67 wt % LaCl₃ · 7H₂O, 0.37 wt % PrCl₃ · 7H₂O, 37.98 wt % HCl, and 56.98 wt % H₂O; in system 2: 4.37 wt % LaCl₃ · 7H ₂O, 0.93 wt % NdCl₃ · 6H₂O, 37.88 wt % HCl, and 56.82 wt % H₂O.

Full text of DOI:10.1134/S0036023612040122

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 4, pp. 592–595. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.I. Knyazeva, G.S. Skiba, N.V. Serba, 2012, published in Zhurnal Neorganicheskoi Khimii, 2012, Vol. 57, No. 4, pp. 657–660.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Solubility in the LaCl3–LnCl3–HCl–H2O (Ln = Pr, Nd)
Systems at 25°C
A. I. Knyazeva, G. S. Skiba, and N. V. Serba
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Research Center,
Russian Academy of Sciences, Akademgorodok 26a, Apatity, Murmansk oblast, 184209 Russia
Received February 25, 2010
Abstract—The solubility in the quaternary water–salt systems LaCl3–NdCl3–HCl–H2O (
PrCl3–HCl–H2O ( at 25 was studied in the section of 40 wt % hydrochloric acid, a system with a eutonic
discontinuity. The composition at the point of discontinuity for the eutonic solution is the following. In sysꢀ
tem : 4.67 wt % LaCl3 7H2O, 0.37 wt % PrCl3 7H2O, 37.98 wt % HCl, and 56.98 wt % H2O; in system
4.37 wt % LaCl3 7H2O, 0.93 wt % NdCl3 6H2O, 37.88 wt % HCl, and 56.82 wt % H2O
1) and LaCl3–
2
)
°C
1
⋅
⋅
2:
⋅
⋅
.
DOI: 10.1134/S0036023612040122
In this work, we continue our study of the interactions LaCl3
⋅
7H2O and NdCl3 6H2O and the point correꢀ
⋅
of rareꢀearth element chlorides in strong (40 wt %)
hydrochloric acid solutions [1, 2].
sponding to 40 wt % HCl. When studying the system,
the solvent content in the section 90 wt % (HCl +
H2O) of the equilibrium liquid phases was sought. For
this purpose, the equilibrium liquid phases were evapꢀ
orated to a constant weight at a temperature of no
The solubility in the systems was studied by deterꢀ
mining the dependence of the solvent content (in the
system LaCl3–NdCl3–HCl–H2O (
tration of rareꢀearth element salts (in the system
LaCl3–PrCl3–HCl–H2O ( ) in the equilibrium liqꢀ
1)) or the concenꢀ
more than 40 С because, at higher temperature, the
°
2)
crystalline hydrates of lanthanum and praseodymium
chlorides begin to lose crystallization water and it is
uid phases on the salt composition of the initial mixꢀ
tures in a section with a constant concentration of a
component [3–5].
(HCl + H2O), wt %
EXPERIMENTAL
The initial reactants were lanthanum chloride
(chemically pure) and praseodymium and neodyꢀ
mium chlorides obtained as follows. To a solution of a
chemically pure rareꢀearth element nitrate, an oxalic
acid solution was added with a 50% excess relative to
the stoichiometry. The precipitate of oxalates was
washed with distilled water, filtered off, dried, and calꢀ
99
98
96
94
cined at 950 С for 2 h. The forming oxide was disꢀ
°
solved in hydrochloric acid. The rareꢀearth element
chloride was dried to a constant weight at a temperaꢀ
ture that ruled out crystallization water loss. The crysꢀ
tallization water content was determined from the
weight loss after calcination of the produced crystalꢀ
line hydrates to oxychlorides at 500 and 380
PrCl3 7H2O and SmCl3 6H2O, respectively.
An isothermal medium was created in a TZhꢀTSꢀ
01 water thermostat with an accuracy of 0.1 . Therꢀ
°
С for
LaCl3 · 7H2O 20
40
wt %
60
80 NdCl3 · 6H2O
⋅
⋅
°
С
modynamic equilibrium in the continuously stirred
system is reached in 4 h.
Fig. 1. Dependence of the (HCl + H O) content of the
2
equilibrium liquid phases of system
tion of the initial mixtures in the section of 90 wt %
at 25
1 on the salt composiꢀ
System
1 was studied in the section passing through
the representative points of the crystalline hydrates
°С.
H O + HCl
2
∑
592

SOLUBILITY IN THE LaCl3–LnCl3–HCl–H2O
593
100
80
60
40
20
LaCl3 · 7H2O
(equil. liquid phases),
wt %
4
2
LaCl3 · 7H2O 20
40
60
80 PrCl3 · 7H2O
20
40
60
80
wt %
[LaCl3 · 7H2O] (solid phase), wt %
Fig. 3. Dependence of the lanthanum content of the equiꢀ
librium liquid phases of system on the salt composition of
the initial mixtures in the section of 90 wt
at 25
2
%
Fig. 2.Distribution curve for system
tion of 40 wt % HCl.
1 at 25°С in the secꢀ
°С.
(H O + HCl)
∑
2
impossible to obtain a solid phase of a definite compoꢀ
The compositions of the solid phases were found
sition [6]. The equilibrium liquid phases were also using the equation of the tie line passing through the
analyzed by atomic emission spectroscopy with a Shiꢀ
madzu ICPE 9000 spectrometer for finding the lanꢀ
thanum and neodymium contents.
points representing the initial composition and the
compositions of the liquid and solid phases that are in
equilibrium with the initial composition.
Figure 1 shows the functional curves for the solvent
content versus the salt composition of the initial mixꢀ
tures. The shapes of these curves and also the distribuꢀ
xsolid − xliquid ysolid − yliquid zsolid − zliquid
=
=
,
xinit − xliquid yinit − yliquid
zinit − zliquid
tion curve (Fig. 2) suggest that system 1 is of type IV of
where and z are the concentrations of the correꢀ
x
,
y
,
solid solutions (with a eutonic discontinuity).
sponding components.
Table 1. Compositions of the equilibrium phases in system 1 at 25°C
Liquidꢀphase composition, wt %
Solidꢀphase composition, wt %
LaCl 7H O NdCl 6H O
K
La/Nd
LaCl
⋅
7H O NdCl
⋅
6H O
HCl
H O
⋅
⋅
3
3
2
3
2
2
3
2
2
4.5
0
38.20
37.89
37.86
37.84
37.93
38.46
38.70
39.03
39.45
57.30
56.84
56.80
56.77
56.89
57.69
58.06
58.54
59.17
100
0
4.83
4.56
4.39
4.17
2.69
1.96
1.06
0
0.44
0.78
1.00
1.01
1.16
1.28
1.37
1.38
98.33
94.78
57.90
20.50
7.56
2.53
0.33
0
1.67
5.22
0.19
0.32
3.19
42.10
79.50
92.44
97.47
99.67
16.01
28.36
58.99
233.69
100
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

594
KNYAZEVA et al.
100
PrCl3 · 7H2O
(equil. liquid phases),
wt %
80
60
40
20
3
2
1
LaCl3 · 7H2O 20
40
60
80 PrCl3 · 7H2O
0
20
40
60
80
100
wt %
[LaCl3 · 7H2O] (solid phase), wt %
Fig. 4. Dependence of the praseodymium content of the
equilibrium liquid phases of system on the salt composiꢀ
tion of the initial mixtures in the section of 90 wt %
at 25
2
Fig. 5. Distribution curve for system 2 at 25°С in the secꢀ
tion of 40 wt % HCl.
°С.
(H O + HCl)
∑
2
where the variance is 1.29
×
10–1,
is the NdCl3 ⋅
x
is the LaCl3
6H2O concentraꢀ
⋅ 7H2O
The averaged composition at the point of discontiꢀ
nuity is 4.37 wt % LaCl3 · 7H2O, 0.93 wt % NdCl3 ·
6H2O, 37.88 wt % HCl, and 56.82 wt % H2O. Table 1
presents the compositions of the equilibrium phases
and the separation factors for system 1, and Fig. 2
shows the distribution curve at 25°C in the section of
40 wt % HCl.
concentration, and
tion.
y
System 2 was studied in the section passing through
the representative points of the crystal hydrates LaCl3 ·
7H2O and PrCl3 · 7H2O and the point corresponding
to 40 wt % HCl. The equilibrium liquid phases were
analyzed by atomic emission spectroscopy with a Shiꢀ
madzu ICPE 9000 spectrometer for finding the lanꢀ
thanum and praseodymium contents.
The line of saturated solutions was approximated
by least squares by the secondꢀdegree polynomial
3598.5669
x
2 + 8.1417
×
104
– 633.8311
y
2 + 2.6451
+ 1 = 0,
×
104xy
Figures 3 and 4 show the functional curves of the
lanthanum and praseodymium content versus the salt
– 130.6725
x
y
Table 2. Compositions of the equilibrium phases in system 2 at 25°C
Liquidꢀphase composition, wt %
Solidꢀphase composition, wt %
LaCl 7H O PrCl 7H O
K
La/Pr
LaCl
⋅
7H O
PrCl
⋅
7H O
HCl
H O
⋅
⋅
3
3
2
3
2
2
3
2
2
4.09
4.28
3.73
3.05
3.00
2.95
2.79
1.23
0
0
38.36
37.95
37.94
38.02
38.00
38.03
38.07
38.48
38.86
57.55
56.93
56.92
57.02
57.00
57.04
57.11
57.73
58.28
100
0
0.84
1.41
1.91
2.00
1.98
2.03
2.56
2.86
93.84
85.25
73.56
60.00
22.64
6.70
0
6.16
14.75
26.44
40.00
77.36
93.30
0.33
0.46
0.57
1
5.09
19.14
100
100
0
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

SOLUBILITY IN THE LaCl3–LnCl3–HCl–H2O
595
composition of the initial mixtures located in the secꢀ approximated, and the obtained equations can be used
tion with the constant content
σ
(HCl + H O)
for investigating systems comprising more compoꢀ
nents.
2
.
The shapes of these curves and also the distribution
curve (Fig. 5) suggest that system 2 is of type IV of solid
solutions (with a eutonic discontinuity).
The averaged composition at the point of discontiꢀ
nuity is 2.95 wt % LaCl3 ⋅ 7H2O, 1.98 wt % PrCl3 ·
7H2O, 38.03 wt % HCl, and 57.04 wt % H2O.
Table 2 presents the compositions of the equilibꢀ
rium phases and the separation factors for system 2,
REFERENCES
1. A. I. Knyazeva, G. S. Skiba, and N. B. Voskoboinikov,
Zh. Neorg. Khim. (in press).
2. A. I. Knyazeva, G. S. Skiba, and N. B. Voskoboinikov,
Zh. Neorg. Khim. (in press).
3. N. B. Voskoboinikov and G. S. Skiba, Mathematical
Modeling of Phase Equilibria in Water–Salt Systems
(KNTs RAN, Apatity, 1994) [in Russian].
and Fig. 5 shows the distribution curve at 25°С in the
section of 40 wt % HCl.
Thus, we studied phase equilibria in the systems
LaCl3–NdCl3–HCl–H2O and LaCl3–PrCl3–HCl–
H2O. The compositions at the points of discontinuity
for the studied systems were determined. The separaꢀ
tion factors for the lanthanum/neodymium and lanꢀ
thanum/praseodymium pairs were calculated. Based
on experimental data, the solubility branches were
4. N. B. Voskoboinikov and G. S. Skiba, Zh. Neorg.
Khim. 45, 542 (2000).
5. N. B. Voskoboinikov and G. S. Skiba, Zh. Neorg.
Khim. 35, 1349 (1990).
6. Gmelin Handbook of Inorganic Chemistry. Sc, Y, La–Lu
Rare Earth Elements, Part C 4b: Data on Individual
Chlorides (Springer, Berlin, 1982), p. 68.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012