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Section 4. Ohemistry
Tursunova Dildora Abdusattorovna, Senior Lecturer, Tashkent Institute of Chemical Technology
Erkaev Aktam Ulashevich, Doctor of technical sciences, Professor, Tashkent Institute of Chemical Technology Kaipbergenov Atabek Tulepbergenovich, Doctor of technical sciences, Head of the Department of the Ajiniyaz Institute Begimkulova Kamola Gafurjanovna, Master of the Tashkent Institute of Chemical Technology Karajanova Shakhnoza Daryabaevna, Student of the Ajiniyaz Institute E-mail: atabek2004@mail.ru
STUDYING OF A MINERALOGICAL COMPOSITION OF DEPOSITS FORMED BY VAPORIZATION CAUSTIC SODA SOLUTION
Abstract. In this article, we obtained data on the possibility of obtaining caustic soda by the lime method from soda ash in the presence of sodium sulfate. On the basis of X-ray, thermographic and mineralogical methods of analysis, the mineral composition of sediments was determined. A microscopic analysis of the precipitation was made.
Keywords: soda ash, caustic soda, radiograph, thermogram, microscopic analysis, solution, mi-rabilite, burkeite, filtration, caustification.
At the beginning of the 19th century, the development of caustic soda (NaOH) production was closely associated with the development of soda ash production. This relationship was due to the fact that soda ash was the raw material for the chemical method of producing NaOH, which was caustified with lime milk in the form of soda solution.
Under existing conditions, the most acceptable is to obtain a solution of caustic soda by the lime method, when at this enterprise there are lime and soda ash, which are raw materials.
This production method is characterized by low energy expenditure and simple instrumentation.
In the lime process, as a result of caustification reaction and subsequent separation of the sludge, a dilute solution of sodium hydroxide with a concentration of up to 120-140 g/l is obtained, which is further subjected to evaporation.
Considering the above, organizing the production of caustic soda solution at soda factories, for example, in Uzbekistan, will allow for the production
of an import-substituting product, which will have a significant technical and economic effect.
However, the advantages of this method are the stages of filtration and evaporation.
It is known that the size of calcium sulfate crystalline hydrates, depending on the conditions of caustification, can be several times larger than calcium carbonates. This creates good conditions for accelerating the process of settling and filtering.
In order to intensify the filtration process, causti-fication was carried out with the addition of mirabil-ite. The bottom line is that during caustification two reactions proceed in parallel:
Na2C03(so1)+Ca(0H)2(soUd)-2Na0H(so1)+ +CaC03(so1id)+Q1
Na2S°4+Ca(°H)2(soM)~2Na°H(Sol)+
"2 4' "'2(solid)
+ CaS°4 • nH2 0 (solid) + Q4
As a result of these reactions, caustic soda and a significant amount of sodium carbonate and sodium sulphate remain in solution with precipitation of sulphate and calcium carbonate crystalline hydrates.
To establish the relationship between the phys-icochemical properties of one of the evaporated caustic soda and the degree of evaporation, the process was carried out slowly with measuring the weight of the reaction mass and observing the state of the system.
From the analysis of the system 2Na+, Ca2+/20H-C02-, S02- -H20 it follows that in increasing the Na0H content in the liquid phase, the solubility of sulfate and carbonate salts of sodium and calcium decreases with their transition to the solid phase.
Table 1.- The influence of technological
Analysis of the lateral part of three- and four-component systems: Na2C03 - Na2S04-H20; Na2S04--Na0H-H20; Na2C03-Na0H-H20; Na2C03--Na2S04-Na0H-H20 shows that from weak solutions of caustic soda containing the above salts, it is possible to obtain concentrated or even scaly sodium hydroxide. However, the evaporation process is carried out in stages with the separation of precipitated crystals during the evaporation. The number of stages and the degree of evaporation are determined in advance by theoretical analysis of the above systems. Analysis of systems Na2C03--Na0H-H20; Na2S04-Na0H-H20 revealed that by caustification of Na2C03 and Na2S04 with lime milk, caustic soda can be obtained with a concentration of 10-15% with a content of 2-5% calcium carbonate or sodium sulfate. At the first stage of evaporation at 100 °C, concentrated caustic soda will be obtained with the content, mass.%: 34.5034.3% Na0H, 0.52% - Na2C03 and 1.00% Na2S04 with precipitation of the solid phase Na2C03 • H20, Na2C03 and Na2S04, respectively.
From the analysis of the Na2C03-Na2S04-H20 and Na2C03-Na2S04-Na0H-H20 system, it follows that the conversion of carbonate-sulphate solutions with lime milk can also produce a 10-15% solution of caustic soda with a content of 2-5% carbonates and sodium and calcium sulphates.
At the first stage ofstripping at 100 °C, one stripped off solution will be obtained with content, mass %: Na0H • Na2S04-0.32 and Na2C03-0.28 with precipitation of Na2S04, Na2C03 of the burkeite composition and mNa2S04 • nNa2C03 in the solid phase.
parameters on the process of evaporation
№ Level of Filtration rate, Humidity, The ratio of L: S after
evaporation% kg/m2 • h evaporation
1. 40 5306.93 33.09 14.11 : 1
2. 50 4570.72 28.58 6.36 : 1
3. 60 4103.07 4.0 2.03 : 1
4. 70 295.30 47.52 1.71 : 1
At the second stage of the process after separation of the solid phase at the boiling point, the solution is sent to the stage of obtaining solid caustic soda. You can get a solid caustic soda with a content of 2.42% -Na2SO4, 1.60% - Na2CO3, 0.64% - Na2SO4 and 0.56% - Na2CO3 concurrently when using sulfate, sodium carbonate or a mixture of these. Thus, analysis of the above systems implies that caustic soda from a mixture of sulphate and sodium carbonate is more effective
Table 2.- The chemical composition of
in terms of the quality of the products, processability and technical and economic indicators. Therefore, we previously studied [1; 2] the process of caustification of soda ash in the presence of sodium sulphate and showed the possibility of evaporation of caustification products. In this paper, the physicochemical properties of one evaporated solutions and the composition of the precipitates formed are studied using modern physicochemical methods of analysis.
the evaporated solutions of caustic soda
Correspond to numbers in Tab.1 Content of components, mass%
SO2 4 OH- CO- Ca2+ Na+ Ratio SO2-/ CO32-
1 2.754 6.74 2.80 0.0146 12.71 0.98
3 0.50 11.80 2.24 0.0149 18.10 0.22
4 0. 32 14.50 2.99 0.0141 25.59 0.10
Table 3.- The chemical composition of the solid phase formed during the evaporation of the initial solutions
Correspond to numbers in Tab.1 Content of components, mass.%
SO2- 4 OH- CO 3- Ca2+ Na+ Ratio SO4/CO3
1 41.16 0.84 17.20 0.049 38.60 2.39
3 29.16 0.94 21.60 0.059 27.71 1.35
4 24.65 3.78 22.17 0.0594 34.12 1.11
As the original solution used caustic soda solution with content, wt.%: 0H-4.084; Na+ - 7.811; SO2-- 1.870, C02--1.988, obtained from a mixture of soda ash and sodium sulfate at a ratio of10:1. The original solution was evaporated to 40, 50, 60, 70 and 80% of the total mass, and the precipitation were separated by filtration. The obtained liquid and solid phases were analyzed for the main components by well-known methods [3; 4] with the determination of the following physicochemical properties of the liquid phase: density, viscosity, electrical conductivity, light refraction index [5; 6].
The mineralogical composition ofthe precipitation was determined using X-ray, differential-thermal [6] and microscopic analysis methods [7] (Tables 1-4).
From table 1 shows that with an increase in the degree of evaporation, the amount of the solid phase increases from 3.95 to 10.70% relative to the initial solution, and the ratio W: T decreases from 14.10 to 1.7. The filtration rate is very high and varies in the range 4103-5306 kg/m2g, however, with an increase in the degree of evaporation to more than 70%, it sharply decreases to 295.3 kg/m2, which is explained by the increase in viscosity of the liquid phase.
With an increase in the degree of evaporation, the SO4/ CO3 ratio decreases from 0.98 to 0.10 and 1.11, respectively, in the liquid and solid phases. It should be noted that with an increase in the degree of evaporation, the amount of sulfate and carbonate ions in the liquid phase decreases from 5.55 to 1.8%.
Table 4.- Physico-chemical properties of one evaporated off solutions
Correspond to numbers in Tab.1 Viscosity, cPz Density, kg/m3 Electrical conductivity, at 25 °C. ^S/cm Indicator light refraction, at 20 °C
20 °C 40 °C 60 °C 80 °C 20 °C 40 °C 60 °C 80 °C 43.11 140,1
1 433.89 96.96 38.95 22.97 1.265 1.259 1.254 1.241 42.80 139.5
2 526.54 89.44 40.41 35.07 1.272 1.263 1.254 1.245 28.91 141.5
3 1337.1 207.82 72.43 47.20 1.354 1.343 1.338 1.331 19.77 143.5
With an increase in the degree of evaporation more than 60% of the liquid mass becomes thicker. Even at 70% evaporation at 20-80 °C, the liquid phase thickens, and therefore, in Table 4, the physi-cochemical properties of the samples evaporated to 60% are given. In the studied intervals of variation of the degree of evaporation, viscosity, density, electrical conductivity, and refractive index vary in the intervals of 22.97-1337.10 cPz, 1241-1354 kg/m3, 19.77-43.4 ^S/cm) and 140.1-143.5, respectively. The degree of evaporation and temperature strongly
Standajrd\TKTI-Probal-40ft
File N ante Sample Name Date & lime Condition X—lay Tube Scan Range Count Time
Comment :
affect the viscosity of the samples. An increase in the degree of evaporation from 30 to 60% leads to a viscosity increase of more than 2 times at 20 °C, and an increase in temperature from 20 to 80 °C leads to a decrease from 18.9 to 28, viscosity 33 centipoise, respectively, at 40 and 60% of the evaporation.
According to the results of physicochemical analyzes, the mineralogical composition of the solid phase consists mainly of burkeite and sodium carbonates, the ratio (Na2CO3-Na2CO3-2Na2SO4) increases with increasing degree of evaporation.
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Figure 1. The X-ray diffraction pattern of precipitation formed during evaporation of weak caustic soda solutions. Sample numbers correspond to the numbers in Table 1.
On the equipment of radiographic, thermographic and mineralógica! methods of analysis the mineral composition of precipitation is determined. The X-ray diffraction patterns (Fig. 1) and the data show that table 5 at the beginning of the process and 40% precipitation evaporate the burkeite with a content of up to 12.5 tenardite, and with a 50% degree of evaporation, sodium carbonate appears in the precipitation. and calcium sulphate, and with more than 60% evaporation in the precipitate appears a small amount of calcium carbonate. In the case of more than 70% evaporation, the content of calcium salts decreases to less than 0.5%, and therefore their characteristic peaks disappear in the X-ray diffraction pattern.
Thermoanalysis data (Fig. 2.) indicate that mass loss in the temperature range of20-270 °C occurs in one stage at - 80-95 °C, in the same range there is
a loss of free water with a loss of 1.88% of the mass. Two endothermic peaks at 82.0 and 88.7 °C are indicated on the DSC curves. The process is endothermic with energy absorption - 60.35 J/g.
The data of thermal analysis (Fig. 2) of the second sample is similar to the previous one (sample 1): mass loss in the temperature range 20-27 °C occurs in one stage at 80-95 °C, and in the same range there is a loss of crystallization free water with a loss of 2.51% by mass. Here, DSC curves indicate two endothermic peaks at 82.9 and 89.0 °C. The process is endothermic with absorption - 86.62 J/g of energy.
It follows from the thermogram that the loss of mass in the sample does not exceed 1.88 and 2.51% and there is a double deep endo-effect corresponding to 82.9 and 88.7-89.0 °C characteristic of the modification transformation of burkeite.
"lenpBciLie/°C
"lënpBciLie/°C
Figure 2. Thermogram of precipitation formed during the recovery of weak caustic soda solutions. The number of samples correspond to the numbers in Table 1.
Table 5.- Mineralogical composition of precipitation formed during the recovery of weak solutions of caustic soda
The number of samples corresponds to the numbers of the tables Content of minerals, mass.%
Na2SO4 Na CO. 23 2Na2SO4- Na2CO3 CaSO 4 CaCO3
1 12.50 — 87.50 — —
2 7.30 26.90 50.20 15.60 —
3 10.70 24.60 52.05 11.80 0.85
4 6.81 60.07 33.12 - —
From the micrograph of precipitation it can be formed scaly is formed with a crumbly precipitate seen that when caustic soda is evaporated, an un- with dimensions of 0.2-2.0 mm.
jfk1
Therefore, the filtration rate of the evaporated caustic soda is more than 4000 kg/m2^.
Sample 1
Sample 2
Figure 3. Microscopic analysis of precipitation. Sample numbers correspond to the numbers in Table 1.
Thus, the data obtained showed the possibility salts of sodium, corresponding to the composi-
of obtaining caustic soda by the lime method of tion: mNa2SO4 • nNa2CO3. Sodium is circulated
soda ash in the presence of sodium sulfate. In the at the conversion stage or it can be used as an
future, the solution is stepped up to obtain liquid additive upon receipt of detergents and cleaning
and solid caustic soda and sulphate - carbonate products.
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