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http://dx.doi.org/10.31618/ESU.2413-9335.2019.2.66.304
UDC 541.123.6
Usmonov Muhammadsalim Bozorovich
PhD, Associate Professor Tajik State Pedagogical University
PHASE EQUILIBRIA IN THE NA, CA// SO4, F- H2O SYSTEM AT 75°C
Abstract. The phase equilibria in the Na, Ca //SO4, F - H2O system at 75°C were investigated by the translation method. The closed phase diagram for the system was constructed based on the obtained data.
Keywords: translation method - phase equilibria - component -geometric images.
Knowledge of the laws of phase equilibria of the Na, Ca // SO4, F - H2O system is necessary to establish optimal conditions for the separation of sulfate and fluoride salts of sodium and calcium from natural and technological solutions containing these salts.
As an analysis of the literature [1] shows, this system has not been investigated so far. We studied it using the translation method, which follows from the principle of compatibility of structural elements n and (n + 1) component systems in one diagram [2]. According to the translation method, structural elements of the diagrams of n-component systems increase their dimension by one unit and translated to the (n + 1) component composition in a transformed form when the next component is added to them (at constant temperature and pressure),. For example, in this case, invariant points of n - component systems at the (n + 1) component level turn into monovariant curves, and monovariant curves into divariant fields, etc. Transformed geometric images, according to their topological properties, at the level of (n + 1) component
composition, intersecting each other (observing the Gibbs phase rule) form geometric images of the system at this component level. Thus, the translation method will make it possible to predict the possible phase equilibria of multicomponent systems (when moving from the n-component level to the (n + 1) component level) and theoretically construct their closed phase diagrams. A more detailed application of the translation method for predicting the structure of the phase equilibrium diagram in multicomponent water - salt systems was considered in literature [3-4].
The studied four-component system includes the following three-component systems: Na2SO4 - CaSO4 - H2O, NaF - CaF2 - H2O, NaF - Na2SO4 - H2O and CaF2 - CaSO4 - H2O.
There are 3, 1, 2 and 1 invaraint points in the Na2SO4 - CaSO4 - H2O, NaF - CaF2 - H2O, NaF -Na2SO4 - H2O and CaF2 - CaSO4 - H2O systems at 75°C respectively according to literature [5]. Table 1 gives the list and equilibrium solid phases at the ternary invariant points of the listed systems.
Table 1
Phase equilibria in the invariant points of the Na, Ca// SO4,F-H2O system
Invariant point Solid phase composition Invariant point Solid phase composition
Na2SO4 - NaF -H2O system NaF - CaF2 - H2O system
Е3 Wo+Shr Е3 Е4 Wo+Fo
Е2 Shr+Te Na2SO4 - CaSO4 - H2O system
CaF2 - CaSO4 -H2O system Е5 Те+Gb
Ез Fo+ Gp Е6 Gb+ 5Ca№3
Е7 5Ca№3+ Gp
Letter E in Table 1 and further denotes an invariant point with an superscript indicating the multiplicity of the point (system complexity) and subscript indicating the serial number of the point. Following notations were used: Te-tenarditis Na2SO4, Gb - glauberite
Na2SO4- CaSO4, Gp - gypsum CaSO4-2H2O, Wo -willomite NaF, Fo - fluorite CaF2, Shr - sheireritis Na2SO4-NaF, 5Ca-Na-3 - 5CaSO4-Na2SO4-3H2O.
Figure 1 shows phase equilibria diagram of the Na, Ca//SO4, F - H2O system at 75° C. Unfolded pyramid
.....—— Wschodnioeuropejskie Czasopismo Naukowe (East European Scientific Journal) #3(55), 2020
in Figure 1 which is constructed based of the data in Table 1 shows the ternary composition of the system.
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Figure 1. Phase equilibria diagram of the Na, Ca// SO4, F - H2O system at 75oC at the ternary composition shown in the form of an unfolded pyramid.
The translation of invariant points of ternary composition to the quaternary composition leads to the formation of the following quaternary points with equilibrium solid phases:
E? + E4 E4 = Wo +JShr + Fo; E? + E? E2 = Fe 5Ca-Na-3;
E2 + E? E? = -Shr-+-Te+ Gb; EH + Shr E4 =-Shn+ Gb + 5Ca-Na-3.
The phase equilibria diagram of the Na, Ca// SO4, F-H2O system at 75°C constructed on this basis of data
at a four-component composition level shows that the divariant fields Gb, 5Ca-Na-3, Fo are not closed. For their closure, we found the fourth E| invariant point with the (Shr + 5Ca-Na-3 + Fo) equilibrium solid phases using the "intermediate" translation method [3,4].
Fig. 2. Schematic phase equilibria diagram constructed by the translation method for Na, Ca//SO4, F - H2O system at 75°C
Figure 2 shows the final version of schematic phase equilibria diagram [6] of 75 °C isotherm of the Na, Ca// SO4, F-H2O system at the four-component composition. The presented diagram combines elements of the structure of the system at the levels of three- and four-component compositions. In particular,
the sides of the diagram are the coordinate cores of the diagram of the three-component systems that make up this four-component system. On them are schematically plotted (projected) the positions of the corresponding invariant points. When translating to the level of four-component composition, they turn into
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monovariant curves (in the figure, these monovariant curves are shown as dashed lines, and the arrow indicates the directions of translation). The phase composition of the precipitation of these curves is identical to the phase composition of the translated triple invariant points. The monovariant curves formed during the translation of triple invariant points at the level of four-component composition mutually
intersecting (following the Gibbs phase rule) form quadruple invariant points, the phase composition of the precipitation of which is given above.
Between the invariant level points of the four-component composition, monovariant curves pass, which are characterized by the following phase composition of precipitation:
Table 2
Equilibrium solid phases and contours of divariant fields in the diagram
of the Na, Ca// SO4, F-H2O system at 75°C
The equilibrium solid phase of the fields The contours of the fields in the diagram (Fig. 2) The equilibrium solid phase of the fields The contours of the fields in the diagram (Fig. 2)
Wo N STaF F3 1 1 1 V E4------------> 14 Gb E4<------------ E 1 E4 <------------E "3 '5 '3 '6
Shr E3 E2 - - - -> E4 1 i4_ 4 _ 1 E4 E5 E4 5Ca-Na-3 E5-E4 «----E 1 E2 <------------E 73 J6 17
Fo p3 —- p4 -"4 E1 ^5 CaF2 E? - - - - >E2 Gp E2 <"-----------E A 1 1 1 E?-CaSO 73 J7 )4
Te E2 Na2SO4 1 1 1 * E4 -------------E5
E? E| = Fo + Shr; E| Ef = 5Ca-Na-3 + ®o;
— E| = Shr + Gb; E| — Ef = Shr + 5Ca-Na-3.
The system under study at the level of the four- presence of six (6) divariant fields, the contours of component composition is characterized by the which are presented in Table. 2.
The structure of the system under study at 75° C shows that the crystallization fields of fluorite, sheirerite and 5Ca-Na-3 border 5 of the 7 fields of crystallization of other phases. This indicates that, due to their low solubility, these salts occupy a significant part of the studied system under the given conditions.
References
1. Experimental data on the solubility of multicomponent water - salt systems Handbook. V. II., B. 1-2. St. Petersburg: Khimizdat, 2004, 1247 P.
2. Goroshchenko Ya. G. Masscentric image method of multicomponent systems. - Kiev: Naukova Dumka, 1982, 264 P.
3. Soliev L. Prediction of the structure of phase equilibrium diagrams of multicomponent water - salt systems by the translation method. M., 1987, 283. Dep. VINITI, USSR Academy of Sciences, 20.20.87, № 8990 - B87.
4. Soliev L. Prediction of phase equilibria in a multicomponent system of the marine type by the translation method (book 1). Dushanbe. TSPU. 2000, 247P.
5. Experimental data on the solubility of multicomponent water - salt systems (reference). V. 1., book. 1-2. SPb: Khimizdat, 2003, 1151 P.
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