Phase complex of the system Na,Ca||SO4,CO3,HCO3-H2O at 100 oC

The article discusses the results of determining the possible phase equilibria in geometric images of a five-component reciprocal water-salt system of sulfates, carbonates, sodium bicarbonates and calcium at 100 °C with subsequent construction of its phase complex diagram. The laws that determine the structure of the phase complex diagram of this system are needed to be obtained for the production of scientific data used both as a reference material and also to create the optimal conditions for the recycling of liquid waste industrial production of aluminum-containing sulfate carbonate and bicarbonate salts of sodium and calcium. It was established that the system under study at 100 °C is characterized by the presence of 31 divariant double saturation fields, 25 monovariant trisaturation curves and 14 invariant points.


Introduction
The phase diagrams for the complex systems are not only of scientific interest, but also necessary for creating optimal conditions for the galurgic processing of natural mineral raw materials and industrial wastes containing sulfates, carbon-ates, sodium and calcium bicarbonates [1]. The Na,Ca||SO 4 ,CO 3 ,HCO 3 -H 2 O system has not been studied yet at 100 °C. Earlier we studied phase equilibria in this system by the translation method at temperatures of 0 and 50 °C [2,3].

Methods
We have deduced phase equilibria in the Na,Ca||SO 4 ,CO 3 ,HCO 3 -H 2 O system at 100 °C using translation methods [4,5] which follows from the principle of compatibility of structural elements of n and n + 1 component systems in one diagram [6,7]. According to the translation method, the addition of one more component to the n-component system and its transition to the n + 1 component state is accompanied by transformation of the geometric image of the n-component system. The transformed geometric images are translated to the n + 1 level according to their topological property in accordance with the Gibbs phase rule, forming correspondent geometric images (fields, curves, points) in the n + 1 component system. The application of translation methods for predicting and constructing phase diagram for multicomponent water-salt systems was considered in more details in our previous work [4]. Earlier this method was successfully used for other multicomponent systems [8,9].
The f ive-comp onent system Na,Ca||SO 4 ,CO 3 [1,10] and by the translational method [11][12][13][14][15]. Coexisted equilibrium solid phases inside the invariant four-component systems are listed in Table 1. Phase composi-tion of these non-variant points was used to predict the phase equilibria and for construction of phase complex of the studied system by the translation method.
In Table 1 and further E denotes the invariant point, where the upper index indicates its multiplicity (the number of system's component), and the lower index indicates its serial number. The following notations for solid phases that were formed in the system were used:

Results and discussion
Based on the data listed in Table 1 the phase diagram (phase complex) for the Na,Ca||SO 4 ,CO 3 ,HCO 3 -H 2 O system was constructed at 100 °C at the level of four component composition of the salt part, which is shown in the figure as projection of tetrahedral faces.
A unification of the salt part of the phase diagram (combining of identical crystallization fields of various constituent four-component systems), we obtain a schematic diagram for the phase equilibria in the Na,Ca||SO 4 , CO 3  The thin solid lines in Figure 3 indicate the monovariant curves at the level of four-component composition. The equilibrium solid phases that are correspondent to these curves were presented above.
Dash lines with arrows (in Table 2) indicate monovariant curves at the level of five-component composition, They are formed as a result of translation therefore the equilibrium phases corresponded to these monovariant curves are identical to the equilibrium solid phases of the invariant points of the corresponding quaternary systems.

Equilibrium solid phases of fields
Field contours in the diagram (Fig. 3)

Equilibrium solid phases of fields
Field contours in the diagram (Fig. 3 The decrease in the number of invariant points from 20 at the level of fourcomponent composition to 14 at the level of five-component composition is due to the mutual combination (from mathematical approach) of quadruple invariant points, or mutual intersection of monovariant curves (within the graphical approach) formed during the transformation and subsequent translation of these quadruple invariant points to the level of five-component composition and the formation of quintuple invariant points. The increase in the number of monovariant curves from 30 at the level of four-component composition up to 33 at the level of five-component composition is due to the fact that 20 of them are formed as a result of translation and quadruple invariant points, and another 13 connected five invariant points. The raise of components' number by unity from four to five leads to the increase of divariant fields' number from 13 at the level of four-component composition to 31 at the level of five-component composition. It was shown that 30 of them were formed in a course of translation procedure of monovariant curves of the level of fourcomponent composition and one more was obtained as a result of the surface contouring in the system with five invariant points and monovariant curves connecting these points.