M. N. Yakimov, A. A. Grigorieva, E. I. Kuminova.

Isothermal Evaporation of Water from the Brines of Lakes Ebeity and Kulundinskoye

The present study is a continuation of the investigation of the mineral raw materials of the Kulunda steppe.

In the preceding work, “Isothermal Evaporation of Water from the Brine of Lake B. Yarovoye,” we presented exhaustive data concerning Lake B. Yarovoye.

Similarly, the study of Lakes Ebeity and Kulundinskoye had as its chief aim to trace the change in the salt composition of the natural brines of these lakes during the evaporation of water from them at a temperature of \(25^\circ\mathrm{C}\).

As the basis for our investigations we used the theoretical equilibrium diagram of the reciprocal system \(2\mathrm{NaCl} + \mathrm{MgSO}_4 \rightleftarrows \mathrm{Na}_2\mathrm{SO}_4 + \mathrm{MgCl}_2\), repeatedly studied by many investigators and making it possible to follow the course of the crystallization ray during the evaporation of marine and lake brines, and also, using the method of graphical calculations, to determine approximately the points at which one or another phase begins to appear.

I. Descriptive Part

Lake Ebeity is situated in the eastern part of the Irtysh steppe, 140 kilometers southwest of the city of Omsk, 20 kilometers from the Southern Main Line of the Siberian Railway. The lake is 10 km long, 8.25 km wide, and 0.70 meter deep. The climate is hot and dry. The mean annual temperature is \(+10^\circ\); the maximum summer temperature is \(+35^\circ\). The lake belongs to the saline-sulfate group; its brine has a high concentration, reaching \(31^\circ\) Baumé in summer.

The sulfate reserves, according to data of the Western Siberian Geological Administration, are about 1,650,000 tons; in addition, the reserves of common salt are about 3 million tons.

Lake Kulundinskoye is located near the well-known Lake Kuchuk, in the central part of the interfluvial area between the Ob and Irtysh. The lake is enormous in size: it is 40 km long and 25 km wide.

The concentration of the brine is very low, on average \(4\text{–}5^\circ\) Baumé. The lake has no immediate industrial significance as such, and may be regarded as a reserve basin for regulating the regime of the sulfate Lake Kuchuk, which possesses enormous raw-material resources of sulfate, common salt, and magnesium salts.

For carrying out experiments on the evaporation of brine from the above-mentioned lakes under laboratory conditions, we used the same apparatus and methodology as in the study of Lake B. Yarovoe¹.

In the calculations only the following ions were taken into account: \(Na^\cdot\), \(Mg^{\cdot\cdot}\), \(SO_4^{\prime\prime}\), \(Cl^\prime\), which combined into salts. The ions \(HCO_3^\prime\), \(CO_3^{\prime\prime}\), \(Br^\prime\), \(Ca^{\cdot\cdot}\), \(K^\cdot\) were omitted from the calculations, since their insignificant presence has no noticeable influence on the equilibrium of the system. Thus the system was reduced to a 4-component one.

II. Results.

At our disposal was a sample taken from Lake Ebeity in July 1931. At the bottom of the bottle there was a precipitate of crystalline sulfate. After dissolution of the latter, the brine showed a specific gravity equal to 1.222, or \(26.2^\circ\) Baumé, with the following chemical composition in weight percent per 100 grams of brine.

The tables given below (1 and 2) show the course of evaporation of the brine and the change in its salt composition.

The data, after the corresponding calculation into the number of moles per 1000 molecules of water, were plotted on the horizontal projection of the equilibrium diagram of N. S. Kurnakov, supplemented by the recent work of V. P. Nikolaev², who established the labile crystallization fields of epsomite and common salt, which is extremely essential for the study of natural brines characterized by labile equilibria; in addition, the composition is given of the triple astrakhanite point obtained by him from synthetic solutions. Finding and determining the composition of the latter in natural brines is of very profound scientific and practical interest, making it possible to approach the solution of the question of the formation and composition of astrakhanite under natural conditions, which for the lakes of the Kulunda steppe has not yet been studied by anyone.

In addition, to clarify the very concept of lability and labile states, and their relation to the so-called stable state, which can be achieved only on the basis of the study

labile equilibria, so widespread in nature.” (V. I. Nikolaev), see Table 1, Figure 1.

Conclusions.

In the evaporation of water from the brine of Lake Ebeity at 25° C we have:

1. At 30.4° Baumé the precipitation of two salts, NaCl and Na₂SO₄·10H₂O, begins. The joint precipitation of these salts continues up to 31.4° Baumé (points 1, 2, 3, 4, Fig. 1).

2. At 32° Baumé we have the precipitation of common salt and astrakhanite (Fig. 1, point 5). The crystallization ray intersects a labile region in the field of astrakhanite. At point 5 one can observe the formation of astrakhanite from the components MgSO₄·7H₂O and Na₂SO₄·10H₂O simultaneously with the separating NaCl.

3. At 32.4° Baumé the crystallization ray intersects the most interesting triple point (point 6, Fig. 1) of simultaneous precipitation of three salts: NaCl, astrakhanite, and MgSO₄·7H₂O. The obtained triple point and its composition give us the possibility of establishing the labile fields of crystallization of common salt and epsomite for Lake Ebeity—and, to some extent, of prejudging the question of the possibility of obtaining, and the composition of, astrakhanite from the lake brine. The composition of the point obtained is close to the composition of the analogous triple point obtained by V. I. Nikolaev from synthetic brines¹).

The boundaries of the labile fields of crystallization of common salt and epsomite are outlined approximately along the same lines.

1. The precipitation of three salts is replaced by crystallization of two salts, NaCl and MgSO₄·7H₂O (points 7, 8, 9, 10, 11, 12, 13). The crystallization ray follows the boundary separating the labile fields of NaCl and epsomite, then passes to the boundary separating the stable fields of the same salts. We do not have precipitation of astrakhanite here, which once again confirms that NaCl, outside its limits in the field of astrakhanite, is characterized by metastable solutions and, evidently, always occurs in all cases in the presence of brines with a high coefficient of metamorphization. The vapor pressure of the solution is higher than the vapor pressure of the true, stable one corresponding to the crystallization of astrakhanite.

2. The precipitation of these two salts, NaCl and MgSO₄·7H₂O, continues approximately up to 35° Baumé and is replaced by the precipitation of NaCl and MgSO₄·6H₂O (points 14, 15, Fig. 1). By this moment the liquid phase becomes very enriched in magnesium chloride, which acts in a dehydrating manner on the crystallizing magnesium sulfate. The latter, in turn, entrains a considerable amount of mother brine, which explains the contamination of the solid phase by magnesium chloride.

III. Lake Kulundinskoye.

A sample of brine was taken on 2/V—1932 on the southern shore, 15 meters from the shore, from a depth of 0.3 m, Baumé 4°, with the following chemical composition in weight percent per 100 grams of brine.

¹) On the question of the composition of astrakhanite. Labile fields of crystallization of common salt and epsomite. Zh. Prikl. Khim., vol. 5, No. 6–7.

The data obtained as a result of isothermal evaporation are set forth in Table 2, graphical drawing 2.

IV. Results.

Lake Kulundinskoye, in its chemical composition, is analogous to Lake Ebeyty; it differs from it only in its initial concentration and, as a result of isothermal evaporation at 25° C, reached very similar results with respect to the character and sequence in the crystallization of salts as Lake Ebeyty. This made it possible for us to compare the results obtained, almost completely transferring our reasoning concerning Lake Ebeyty to Lake Kulundinskoye (see drawing 2, table 2).

Conclusions.

1. After removal, first of all, from the brine of Lake Kulundinskoye during isothermal evaporation at 25° C, of the basic magnesium carbonates and calcium sulfate, we have mainly the deposition of two salts, $\mathrm{NaCl}$ and $\mathrm{Na_2SO_4 \cdot 10H_2O}$; the deposition of these salts begins at 29° Baumé and continues approximately to 32° Baumé (drawing 2, point 1).

2. At 32.4° Baumé we have the deposition of common salt and astrakhanite. The crystallization ray enters the labile portion of the astrakhanite field. (Drawing 2, point 2).

3. At 32.6° Baumé the deposition of common salt and astrakhanite is replaced by the crystallization of three salts: $\mathrm{NaCl}$, astrakhanite, $\mathrm{MgSO_4 \cdot 7H_2O}$ (drawing 2, point 3), i.e., similarly to Lake Ebeyty, we here also observe a triple astrakhanite point, establishing the labile fields of crystallization of common salt and epsomite for Lake Kulundinskoye. The composition of the liquid phase corresponding to this point is almost identical with the composition of the similar point cited by Nikolaev in his work, namely:

Composition of the astrakhanite triple point.

1. Beginning at 32.6° Baumé, common salt and $\mathrm{MgSO_4\cdot 7H_2O}$ crystallize together (points 4, 5, 6, Fig. 2). No precipitation of astrakhanite is observed. The crystallization ray, as in Lake Ebeity, follows the boundary separating the labile and stable fields of NaCl and epsomite.

2. The solution dries out at 33° Baumé, having NaCl and magnesium sulfate in the liquid phase (point 7), and in the solid phase also common salt, $\mathrm{MgSO_4\cdot 6H_2O}$, and, in a very insignificant amount, magnesium chloride entrained by crystals of hexahydrate.

Note: Information on the occurrence, dimensions, and reserves of salts in the lakes is taken from the report of engineer M. I. Kuchin, “Raw-Material Resources of the Salts of the Kulunda Steppe and Ways of Their Industrial Utilization.”

Proceedings of the 1st enlarged plenum of the Regional Committee for the Chemization of Narkhozzapsibkrai.

Table No. 1

Composition of liquid phases of the 25° C isotherm

Table No. 2

Liquid phases of Kulunda Lake during isothermal evaporation at 25°C

Table No. 3

Specific gravities obtained as a result of testing the brine of Lake Ebeity.

1. See the paper “Evaporation of the brine of Lake B. Yarovoe.” ↩

2. On the question of the origin and composition of astrakhanite. Labile fields, crystallization of epsomite and common salt. Journal of Applied Chemistry, vol. 5, no. 6–7. ↩