Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria. ABSTRAC'I. The Pitzer ion-interaction model has been used for thermodynamic simulation of the ternary ...
22, No. 4, pp. 449-457, 1998 Science Ltd. All rights reserved 0364-5916/99/$ - see front matter
CalphadVol.
Pergamon
Q 1999 Elsevier
PII: SO364-5916(99)00004-8 THERMODYNAMIC
STUDY OF THE KC1 - KzS04 - K2Crz07 - Hz0 SYSTEM AT THE TEMPERATURE 298.15 K
Christomir Christov Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
ABSTRAC’I The Pitzer ion-interaction model has been used for thermodynamic simulation of the ternary solutions KCl-K,Cr&H,O, KBr-KaCraOr-Ha0 and KZS04-K2Cr207-Hz0 and the quaternary system KClKzS04-K2Crz07-Ha0 at T=298.15 K. The necessary thermodynamic functions (binary and ternary parameters of interionic interaction and thermodynamic solubility products) have been calculated and the theoretical solubility isotherms have been plotted. Good agreement between experimentally determined and calculated solubilities has been found. 1. Introduction
The purpos~e of the present pa er was a thermodynamic simulation, on the basis of Pitzer model, of the ternary systems KCl-Ka E raO,-HaO, KBr-K,CraO,-Ha0 and KaSO,-KaCr207-Ha0 and the quaternary system KCl-K,SO,-KaCr,O,-Ha0 at T=298.15 K. The study of the quaternary KCl-K2S04-KaCraOr-Ha0 system and the corresponding ternary subsystems is of great practical importance above all in association with the choice of optimum preparation conditions of potassium bichromate.For that reason, systems with the participation of KaCraO, have been the subject of many experimental investigations over a wide temperature range. Robertson (1) and Zhuravlev and Kudrashov (2) have studied the system KCl-K,Cr,O,-Ha0 at different temperatures and established a solubility isotherm consisting of a very narrow crystallization field of potassium bichromate and a broad field of potassium chloride. The rise of temperature from T = 298.15 K to T = 398.15 K leads to a slight broadening of the field of KaCraO,. Analogous results have been obtained by Bogojavlenskii (3) in his study on the system KBr-KaCraOr-Ha0 at temperatures T = 273.15 K, 283.15 K, 293.15 K, 303.15 K and 313.15 K. Data on the solubilities in the system at 298.15 K are given in (4). According to data available in the literature (5,6), the system K,SO,-K2Cr&H20 is also a simple eutonic type within the range from T= 273.15 K to T=371.15 K. Borovskih and Vilnjanskii (7) have established the composition of the invariant point in the quaternary s,ystem KCl-KzS04-KaCraO,-Hz0 at T = 298.15 K. In the literature we have found no data on the thermodynamic simulation of ternary and multicomponent solutions with the participation of bichromate sialts. The thermodynamic analysis of the potassium bichromate-containing systems investigated in the present work are of great practical and theoretical importance. The simulation was made in order to enable us to draw conclusions concerning (i) the applicability of Pitzer model to obtain a sufficiently precise description of the properties of ternary and multicomponent solutions with the participation of potassium bichromates, and (ii) the correctness of the experimental data on the solubilities available in the literature. 2. Solubility calculations In agreement with the aim formulated above, we used the Pitzer ion-interaction model (8-11) aliowing determination of the activity coefficients in saturated and unsaturated electrolyte solutions with an accuracy of 2 to 6 per cent (12). According to Pitzer model (8) the electrolytes are completely dissociated oiubilities in KBr-K2Cr,07-Hz0 system:experimental data: o, at T = 298.15 K from reference 4; ., at T = 293.15 K from reference 3; A, at T = 303.15 K from reference 3.
KCI-K$S04-K$r207-H20:
0
0.1
0.2
03
THERMODYNAMIC STUDY
ox 8
mK2S044mol-k
1
0.6
455
07
FIG. 3 Molality m’ solubilities in K2S04-K2Cr207-Hz0 system at T = 298.15 K: -, experimental data: o , from reference 5; l , from reference 7.
calculated values;
K2Cr207
FIG.4 Solubilities iin the quaternary
at T = 298.15 K: l , experimental quatematy invariant pofnt (Ref. 7);o, calculated ternary invariant points (Table 4). The values are plotted in terms of the mole percent of the component (KC& K2S04, or K2Cr20,) with respect to the total number of moles of KCI + K2S04 + K&O,. system KCl-K$O,-K&r,0rH20
C. CHRISTOV 2.3. Quaternary System The calculated thermodynamic functions (binary and ternary parameters of interionic interaction and thermodynamic solubility products) are used for plotting the theoretical solubility diagram of the system KCl - K,S04 - K2Crz07 - Hz0 at T = 298.15 K. The values of Pitzer ternary parameters for KCl-KzS04-Hz0 system were taken from the literature (18) (Table 3). The composition of the invariant point(KC1 + K,SO, + K2Cr207) was calculated as a point where the chemical potential of all three components is constant, i.e. the eutonic represents the solution of the system of equations (3), (4) and (6). The results obtained are given in Fig. 4 as a horizontal nonaqueous projection of the solubility diagram, presented as triangular prism (20). Table 4 shows the composition of the calculated and the experimentally determined [(Borovskih and Vilnjanskii(7)] eutonics. The results from the calculation agree very well with the experimental data.
TABLE 4 Experimental and Predicted Compositions of Invariant Points for the Quaternary System KC1 - &SO4 - K&&O, - Hz0 and for the Ternary Subsystems at T = 298.15 K.
*Reference 2; bReference 1; ‘Reference 5; ‘Reference 7. 3. Conclusion The theoretical solubility isotherms of the systems KCl-K,Cr20,-HzO, KBr-KzCrzO,-HzO, K2SOr KzCrzOTHzO and KCl-KzSO,-K.Q,O,-HzO at T=298.15 K have been plotted. The agreement with the experiment is very good. This permits conclusions about (i) the applicability of the thermodynamic approach used to obtain a sufficiently precise description of the properties of binary, ternary and multicomponent bichromate solutions, and (ii) the correctness of the thermodynamic functions calculated in this paper. Acknowledgements I am grateful to Professor W. Voigt for stimulating discussion. This work was supported by the Bulgarian Ministry of Science and Education, Project X-594.
KCI-K$30.,-K2Crz07-H20:
THERMODYNAMIC
STUDY
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References
J. Robertson, J. Sot. Chem. Znd 43,334 (1924). E. I!huravlev and S. Kudrashov, Russ. J. Znorg. Chem. 9, 1996 (1964). P. E;ogojavlenskii, Russ. J. General Chem. 19, 1987 (1949). Gmelins HandZx& der Anorganischen
Chemie, CHROM, Teil B, System Number 52, p. 601,
Verlag Chemie GMBH, 1962. 5.
P. Bogojavlenskii, Russ. J. General Chem. 22,551 (1952).
6.
A. Rakovskii, A. Babaewa, Trudy Znstitutu Chistqh. Himich. Reuktivov, 11, 15 (1931).
7.
L. Borovskih, J. Vilnjanskii, Trudy Konferenziipo hromovqh Zftoristqh solei, Goshimizdat,
Usovershenstvovaniy
Tehnologii Proizvodstva
1959, pp. 46-54
8.
K. Pitzer, .I. Phys. Chem. 77,268 (1973).
9.
K. Pitzer, J. Solution Chem. 4,249 (1975).
10.
K. Pitzer and G. Mayorga, J. Phys. Chem. 77,230O (1973).
11.
K. Pitzer and G. Mayorga, .I. Solution Chem 3,539 (1974).
12.
K. Pitzer and J. Kim, .I Am. Chem Sot. 96,5701(1974).
13.
V. Filippov, N. Charykov and N. Solechnik, Russ. J. Applied Chem 58,1966 (1985).
14.
C. Christov, J. Chem. Thermodynamics 26,1071(1994).
15.
C. Christov and S. Petrenko, Z. Physik. Chem. 194,43 (1996).
16.
C. Christov, Coil. Czech. Chem. Commun. 61,507 (1996).
17.
T. Ojkova, Chr. Christov and D. Mihov, 2. Physik. Chem. 203,87 (1997).
18.
C. Harvie and J. Weare, Geochim. Cosmochim. Acta 44,981(1980).
19.
R. Pabalan and K. Pitzer, Geochim. Cosmochim. Acta 51,2429 (1987).
20.
C. Christov, S. Petrenko, C. Balarew and V. Valyashko, Monatsh. Chem. 125,1371(1994).
21.
H. Kim and W. Frederick, J. Chem. Erg. Data 33,177 (1988).
22.
C. Christov, CALPZZAZI 20, 501 (1996).
23.
C. Balarew, C. Christov, V. Valyashko and S. Petrenko, J. Solution Chem. 22, 173 (1993).
24.
C. Christov, C. Balarew, S. Petrenko and V. Valyashko, J. Solution Chem. 23,595 (1994).
25.
C. Christov and C. Balarew, J. Solution Chem. 24, 1171 (1995).
26.
C. Christov, J. Chem. 77termodynamics 27, 1267 (1995).
27.
C. Christov, S. Petrenko, C. Balarew and V. Valyashko, J. Solution Chem. 23,795 (1994).
28.
R. Goldberg, J. Phys. Chem. Ref Data 10, 671 (1981).
29.
C. Christov, J. Chem. Thermodynamics
30.
D. St’oilova, C. Christov, T. Ojkova and D. Staneva, Monatsh. Chem. 126,535 (1995).
31.
C. Christov, Coil. Czech. Chem. Commun. 61, 1585 (1996).
32.
D. Wagman, W. Evans, V. Parker, R. Schumm, I. Halow, S. Bayler, K. Churney and R. Nutall, .I Phys. Chem. Ref Data
29, 481 (1997).
11 (1982) (Suppl.2).
