Articles
Indian Journal of Chemical Technology
Vol.lO, July 2003, pp. 391-395
Investigation on the equilibrium solubility of cesium chloride-hydrochloric
acid-water ternary system and the application
Yucheng Jianga·b, Mancheng Hub, Mei Mengb, Shiyang Gaoa,b• & Shuping Xiaa
"The Institute of Salt Lake, Chinese Academy of Sciences, Xi'an 710043 , P.R. China
bSchool of Chemi stry and Material Science, Shaanxi Normal University , Xi'an 710062, P.R. China
Received 29 May 2002; revised received 21 October 2002; accepted 24 February 2003
Equilibrium solubility of cesium chloride-hydrochloric acid-water system is measured in the temperature range of
-24 to 50°C. Based on this data and the solubility data of the cesium chloride-water system available in the literature, a simple and practical method for preparation and purification of cesium chloride is presented. A rapid and sensitive analytical
system employing atomic absorption spectrometry (AAS) convenient to monitor the quality of the products is also described.
Cesium is a rare and important element. Recent researches find that it has close relationship with health
of people1.2. In addition, it can be used as energy material in many fields, such as atomic energy industry,
automatic technology and aerospace industry 3 .
The research on cesium is attracting more interests
these years, and the demand for cesium compounds is
increasing rapidly. But cesium is very scarce in the
nature, and its compounds are limited and not so stable as compared to those of other alkali metals, and
moreover, cesium often exists together with other alkali metals. The preparation of high purity cesium
chloride is not easy.
A series of researches on the basic properties of cesium have been carried out recently, including the
studies on the equilibrium solubility, phase diagram
and thermodynamic parameters of the cesium compounds in some ternary , quarternary and quinary systems4-6. Based on these studies, preparation of high
purity cesium chloride and its purification from cesium carbonate by taking advantage of temperature
function on solubility and the salting-out effect of
hydrogen chloride on cesium chloride, has been reported here. The impurities can be removed effectively in this way.
The primary impurities in the products are Lt, Na+,
K+ and Rb+, which are determined by tlame atomic
absorption spectrometry (FAAS). The interference is
discussed and the optimum conditions are ascertained.
*For correspondence (E-mail : amao525 @hotmail.com)
Experimental Procedure
Equilibrium solubility of CsCl-HCl-HzO ternary
system
A micro-device, produced indigenously, was used
for the measurement of equilibrium solubility .
BP211D model electronic balance (Sartorius, Germany) was employed for the determination of
weights.
CsCl (G .R., China Medicine Group, Shanghai
Chemical Reagent Company), was dried for 2 h at
500°C, then stocked in a desiccator. Hydrochloric
acid of G.R. grade (36-38%) was used. NaOH (A.R),
calibrated by standard potassium biphthalate, was
made into 0.015 M solution . A 0 .1 M solution of
AgN0 3 (A.R.) was made. Fluorescein-3,6-dichloride
was used as indicator in titration of AgN0 3 . Deionized and doubly distilled water was used throughout
this work.
35 g CsCl was taken in 10 mL water and heated till
the solid was dissolved completely. This saturated
solution was filtered to remove the residue while still
hot. The solution was then sealed in a reaction bottle,
which was agitated by an electrical agitator.
Hydrogen chloride was introduced into the bottle
from another entrance. After equilibrium (about 4 h),
1 mL clear liquid was introduced into 100 mL water
as the analyte for chemical analysis. The mass
percentage of HCl was determined by titration of
NaOH while that of CsCl was confirmed through
titration of AgN0 3 .
Articles
Indian J. Chern. Techno!., July 2003
Preparation and purification of CsCI
In order to determine the suitable technological
procedure for the preparation and purification of
CsCI, the equilibrium solubility of CsCI-H20 binary
system is required. The equilibrium solubility of
CsCI-H20 binary system at different temperatures 7 is
shown in Fig. 1. It can be seen that the solubility of
cesium chloride is greatly influenced by variation in
temperature. It decreases rapidly with lowering of
temperature. Table 1 gives solubility-temperature coefficients at different temperature zone, which shows
that the solubility decreases gently with lowering of
temperature in higher temperature zone, but decreases
sharply in lower temperature zone.
Based on these results, the preparation and purification of cesium chloride was carried out in concentrated hydrogen chloride atmosphere and at lower
temperature by the following method:
Cesium carbonate (500 g) was taken in a 250 mL
beaker and gradualiy concentrated hydrochloric acid
was added to this beaker with constant stirring until
no carbon dioxide was given off. This is an exothermic reaction.
This cesium chloride saturated solution was filtered
through a 4# sand core fi lter to get rid of residue in it
while it was still hot. On cooling the solution to room
temperature (about I 0°C), colourless crystalline precipitate appeared. The solution was filtered again to
separate the crystals from solution, and washed with
anhydrous ethanol for three times. The ethanol washing was recollected. Solid cesium chloride was dried
for an hour at 80, I 00 and l20°C respectively till its
weight was constant. The yield of CsCI was 100.7 g
(product I) .
This solution was cooled at -24°C for about half an
hour when colourless crystals appeared again. The
crystals were filtered, washed and dried the same way
as above. It gave 77.7 g of cesium chloride (product II).
Hydrogen chloride gas was introduced at room
temperature, into the cesium chloride solution for
about 1.5 h till a solid appeared. This solution was
cooled to -24°C, when light yellow crystals separated
out. The crystals were filtered , washed and dried .
Yield of CsCI was found to be 101.6 g (product III).
The solution was heated and evaporated till it became saturated. On cooling the solution to room temperature, 60.1 g CsCI was obtained (product IV).
In the recollected ethanol solution, there was still
some cesium chloride powder, from which 39.4 g cesium chloride was obtained (product V).
The technological procedure for preparation and
purification of cesium chloride is presented in Fig. 3.
Analysis of the impurities in product
The main impurities in the products are chlorides
of lithium, sodium, potassium and rubidium. The purity of products depends on the content of these impurities. The content of alkali metal impurities was determined by flame atomic absorption spectrometry
(FAAS).
Results and Discussion
Equilibrium solubility of CsCl-HCl-H2 0 ternary
system at -24, -15, 0, 25 and 50°( respectively is obtained for the first time. The results are shown in Table 2 and Fig. 2.
Figure 2 shows the dependence of equilibrium
solubility of CsCI-HCI-H20 ternary system on the
amount of hydrogen chloride introduced and the temperature of system. It can be seen that HCl has powerful salting--out effect on CsCI. At the same temperature, higher concentration of hydrogen chloride is advanta~~rlUs to the salting-out of cesium chloride. On
the other hanJ, at the same concentration of HCI, the
74
72
70
~68
~66
u
u 64
"'
62
60
58
56
-40
-20
0
20
80
100
120
Fig. !-Equilibrium solubility-temperature curve for CsCI-H 20
binary system
Table !-Solubility-temperature coefficient of CsCI-H 20 system
~ec)
S-T coefficiem
-24--15
-15-o
0-10
10-20
20-30
30-40
0.19
0.33
0.19
0.15
0.13
0.11
-------------------------------------------------392
40-50
50-60
60-70
70-90
90-110
0.11
0.10
0.09
0.09
0.04
----------------------------------
Articles
Jiang et at.: Investigation on the equilibrium solubility of cesium chloride-hydrochloric acid-water ternary system
salting-out effect becomes stronger with lowering of
temperature, but the degree weakens gradually. This
study helps in the preparation and purification of cesium chloride.
The ionization potential of alkali metals is very
low 8 . It is very easy for them to ionize in the air70
65
•
60
~ 55
i13
-24°C
• -1s'c
o'c
"f'
50
25°C
so'c
Ill
u 45
40
35
30
25
20
0
5
10
15
20
30
25
HCI(W.%1
Fig. 2-Equilibrium solubility-temperat;Jre curves for CsCI-HCIH20 ternary system
acetylene flame. Ionization is the major interference
to the FAAS determination of Lt, Na+, K+ and Rb+.
Because the ioni zation potential of cesium is lower
than other alkali metal s, high concentrated cesium can
restrain the ionization interference effectively. Experimental results indicate that though the interference
is serious in air-acetylene flame, the absorbance can
increase obviously with introducing cesium chloride.
For 1 J.lg/mL Li+, Na+, K+ and Rb+, when the adding
of CsCl came up to 20, 20, 60 and 60 J.lgl mL respectively, the absorbance did not increase and was constant, which means the ionization interference can
completely be eliminated. As there is large a amount
of cesium chloride in the sample, it is unnecessary for
other regents to be added in the sample to eliminate
the ionization interference. But it is necessary for
CsCl to be added into the standard sol utions of Li+,
Na+, K+ and Rb+ according to these proportion to produce the corresponding linear calibration curve, so as
that the determination of linear calibration curve and
the sample analysis can be carried out in the same
condition.
As some hydrochloric acid is introduced in sample
during the process of the preparation, it is necessary
to study its influence. Experimental results show that
Concentrated HCI
C36%HCJ
_e::.::x:-".O:.:..:lh.::..:enn=ic'--~
Saturated CsCl solution
cso·c)
Cooled down to room temperature and been
separated
Washed by
~th ano l
and dried
[CSc1 product I
Cooled down to -24 "C and been separated
~:n ci)'~-------~L_____,<_w_e_t_s_o_li_d_)~
HCI was introduced in, then cooled
down to -24 "C and been separated
(wet solid)
Washed by eth ano l and dried
solution (3)
i
Washed by ethanol
and dried
[Cscl product II
Evaporated and concentrated, then cooled
down to -24 'C and been separated
solution ( 4)
Washed by
ethanol and dried
product IV
Fig. 3-Technological procedure for the preparation of high purity CsCI
393
Articles
Indian J. Chern. Techno!. , July 2003
Table 2-Equi librium solubility of CsCJ-HCI-H2'0 ternary system
-24°C (W%)
-l5°C (W%)
0°C (W%)
sooc (W%)
25 °C (W%)
HCI
CsCJ
HCJ
CsCI
HCI
CsCI
HCI
CsCI
HCI
CsCI
0
56.98
0
58.68
0
62.00
0
65.77
0
68 .95
0.62
54.00
3.24
50.40
3.20
56.53
3.21
59.68
0.2 1
67.72
5.10
43.90
4.50
47 .30
7.31
49 .07
4.15
57.88
0.54
66.68
12.70
35.00
8.80
39.70
9.92
48.00
6.92
53.57
1.02
66.64
16.00
31.60
11 .30
36.30
15.52
43.34
11.03
49.1 I
2.63
65.64
18.90
28.00
15.06
33.40
24.02
39.29
14.51
46.10
7.0 1
62.40
26.70
22. 10
21.50
28.90
15.44
45 .51
14.80
61.44
Table 3-Determination of impurity of the sample
Sample
Na+
CsC0 3
0.0041
Product I
Product II
Content of impurity (W %)*
K+
Rb+
CsCI Purity(%)
0.265
0.063
1.20
98.47
0.0003
0.00007
0.0052
99.9944
0.0013
0.00006
0.0046
99.9940
Product III
0.00001
0.0015
0.00013
0.0112
99.9871
Product IV
0.00001
0.015
0.00064
0.0110
99 .9733
Product V
0.00003
0.0080
0.00044
0.0023
99.9892
*Mean values for three determinations
Table 4- Recovery analysis for alkali metal ions
Metal ion added
()lglrnL)
0.5
0.5
0.5
0.5
Found (!lg/mL)
0.470
0.981
0.532
0.920
0.527
1.02
0.481
0.934
Recovery(%)
94.0
98. 1
106.4
92.0
105.4
102.0
96.2
93.4
when the concentration of hydrochloric acid is higher
than 2%, the absorbance begins to decrease. Concentration of hydrochloric acid in the products has been
found to be lower than 0.4%, on analys is by acid-base
titration. Hence the little amount of hydrochloric acid
in the sample will not interfere the FAAS determination.
According to the linear range of the curve, solutions are prepared by weighing a certain amount of
each kind of product at different preparation stages,
and determined by FAAS. The results are shown in
Table 3.
In order to examine the reliability of the presented
method, a certain amount of standard solutions are
added into the sample to carry out the recovery experiment. The results are shown in Table 4.
394
Conclusion
In this paper, the equilibrium solubility of CsClHCI-H20 ternary system as well as that of CsCI-H20
binary is studied. Based on the results, a method for
preparation and purification of cesium chloride is
presented, by which the purity of the products is
raised over 99.99% and the output rate comes up to
75.9%. The proposed method is simple, effective and
practical. In this laboratory, a large amount of high
purity cesium chloride has been prepared by thi s
method.
In addition, an FAAS analysis system for the alkali
metal impurities in products has been standardized.
The method is simple, sensitive and reliable, which
can be used to monitor the quality of the products
conveniently .
Jiang et al.: Investigation on the equilibrium solubility of cesium chloride-hydrochloric acid-water ternary system
Acknowledgements
The financial support from the National Natural
Science Foundation of China (20 171 032) is acknowledged.
4
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