ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 1, pp. 125–127. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.I. Knyazeva, G.S. Skiba, N.B. Voskoboinikov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 1, pp. 126–128.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Solubility in the PrCl3–SmCl3–HCl–H2O System at 25°C
A. I. Knyazevaa, G. S. Skibab, and N. B. Voskoboinikovb
a Murmansk State Technical University, ul. Sportivnaya 13, Murmansk, 183010 Russia
b Institute of Rare Element and Mineral Chemistry and Technology, Kola Research Center, Russian Academy of Sciences,
ul. Fersmana 14, Apatity, Murmansk oblast, 184200 Russia
Received July 27, 2007
Abstract—The solubility in the PrCl3–SmCl3–HCl– H2O quaternary water–salt system was studied at 25°C along
the 40% hydrochloric acid section (a system with solid solutions and discontinuity). The composition of the discon-
tinuity point was as follows: PrCl3 · 7H2O, 2.33; SmCl3 · 6H2O, 0.11; HCl, 40.05; and H2O, 57.51 wt %.
DOI: 10.1134/S0036023609010203
This work continues our studies of phase equilibria
The system was studied along the section passing
in Lnël3–Ln'ël3–HCl–H2O systems [1, 2]. The differ- through the figurative points of PrCl3 · 7H2O and SmCl3 ·
ence between the solubilities of individual rare-earth 6H2O and the point corresponding to 40 wt % HCl.
metal chlorides increases with the hydrochloric acid
concentration [3]. The ion radius and crystal structure
of the salt (dimer, monomer) also affect the solubility of
lanthanide chlorides [4]. Solubility was studied in the
PrCl3–SmCl3–H2O system including lanthanide chlo-
rides with similar ion radii and different crystal struc-
tures [5]. We studied solubility in the PrCl3–SmCl3–
HCl–H2O system at 25°ë along the 40% HCl section to
evaluate the influence of the hydrochloric acid concen-
tration on the character of the evolved phases.
PrCl3 · 7H2O and SmCl3 · 6H2O begin to lose water of
crystallization at 40 and 70°ë, respectively [9]. Based
on this fact, equilibrium liquid phases were brought to
a constant weight at a temperature not higher than 40°ë
to retain the constant composition of the praseodymium
and samarium crystal hydrates.
The solvent in the equilibrium liquid phases was
determined along the 90 and 95 wt % (HCl + H2O) sec-
tions. The functional curves showing the dependence of
the solvent percentage in the equilibrium liquid phases
on the salt composition of the initial mixtures arranged
along sections with the constant Σ(HCl + H2O) content
are presented in Fig. 1. The shape of these curves and
EXPERIMENTAL
Solubility was studied by the method described in
[6–8], determining the solvent concentration in equilib-
rium liquid phases as a function of the salt composition
of initial mixtures lying on the sections with a constant
percentage of some component.
(HCl + H O), wt %
2
99.5
99.0
98.5
Praseodymium and samarium chlorides were syn-
thesized as follows. A solution of oxalic acid was added
in a 50% excess over stoichiometry to a solution of a
rare-earth metal nitrate (chemically pure grade). The
oxalate precipitate was washed with distilled water, fil-
tered off, dried, and calcined at 950°ë for 2 h. The
resulting oxide was dissolved in hydrochloric acid. The
rare-earth metal chloride was dried to a constant weight
at a temperature that excluded the loss of water of crys-
tallization. The water of crystallization was determined
by the weight loss on the ignition of PrCl3 · 7H2O and
SmCl3 · 6H2O to oxychlorides at 500 and 380°ë, respec-
tively.
98.0
97.5
1
2
PrCl · 7H O 20
40
wt %
60
80 SmCl · 6H O
3 2
3
2
The isothermic medium was maintained in a TZh-
TS-01 water thermostat with an accuracy of 0.1°ë.
Thermodynamic equilibrium in the system was estab-
lished in 4 h with continuous stirring.
Fig. 1. HCl + H O content in equilibrium liquid phases vs.
2
the salt composition of the initial mixtures along the (1) 90
and (2) 95 wt % Σ(H O + HCl) sections at 25°C.
2
125
Knyazeva
