A METHOD FOR PRODUCING SODIUM SULPHATE FROM MIRABILITE BY THEIR DISSOLVING AND THE BRANCH OF THE INSOLVENT BALANCE AND ITS ECONOMIC CHARACTERISTICS

A method is known for the production of sodium sulfate by dissolving it, separating the insoluble precipitate by filtration and evaporating the filtrate, in which 50-100 % of the solution is subjected to evaporation, and salting out with the uterine solution of the evaporation process [1].

In this method, before dissolution, the mirabilite is frozen to 0° C, and the mirabilite is dissolved by melting it.

The closest to the technical essence and achieved effect to the proposed is the method of obtaining sodium sulfate from mirabilite by dissolving it at a temperature of 30-70° C, separating the undissolved precipitate by filtration and evaporating the filtrate into two stages, separating the sodium sulfate crystals by filtration, drying and evaporating the uterine solution after the first step to a solution with a concentration of 75-85 % and drying [2].

The stated problem is solved by the fact that in the process for producing sodium sulfate from mirabilite by dissolving it and separating the insoluble residue at a temperature of 30-70° C, evaporating the solution in the first stage to a concentration of 45-60 %, filtering and drying, evaporation of the uterine solution in the second stage to concentration of 75-85 % and drying dissolving mirabilite conduct condensate of juice vapors from the stage of evaporation.

Another difference is that dissolution of the mirabilite is carried out simultaneously with the introduction of sodium carbonate at a ratio of CaO: CO₂ = 1: (1-1.05) based on CaO in solution and sodium hydroxide in the amount of 100-105% from stoichiometry to the formation of hydroxide magnesium (pH of the medium is 10-12).

In addition, the evaporation is carried out in one stage to a concentration of sodium sulfate of 60-65 %, and the uterine solution is returned to the stage of dissolution of the mirabilite.

The use of juice vapor at the stage of dissolving the condensate from the evaporation stage and uterine solution allows maintaining the dissolution temperature above 50° C, which makes it possible to obtain saturated solutions of sodium sulfate in a short (4-6 minutes) time interval, and the calcium sulfate contained in mirabilite due to its poor solubility on achieves the maximum solubility.

This makes it possible to obtain saturated solutions of sodium sulfate by dissolving mirabilite without the use of heat from outside. There is no need to heat water for dissolution up to 50-70° C, which saves energy. The return of the uterine solution from the evaporation stage not only maintains the temperature, but also itself is purified of impurities.

The introduction of carbonate and sodium hydroxide, allows to purify saturated solutions of sodium sulfate from impurities of calcium and magnesium salts.

The lower limit of the amount of sodium carbonate introduced at the ratio CaO: CO₂ = 1: 1 is due to the fact that with a smaller amount of sodium carbonate, the degree of precipitation of calcium ions in the form of CaCO₃ decreases due to the shortage of CO₂ ions, which ultimately leads to contamination of the final product.

Filtration of saturated solution allows us to separate not only water-insoluble residues, but also calcium carbonate and magnesium hydroxide, and obtain practically pure solutions of sodium sulfate.

The uterine solutionof filtration after separation of the sodium sulfate crystals are returned to the stage of dissolution of the mirabilite. Elimination of the second stage of evaporation, in addition to obtaining high purity sodium sulphate, not only simplifies the technological process, but also facilitates the return of the uterine solution, with an increased content of impurities, to the stage of its purification while maintaining the thermal balance of the dissolution process. Return of the uterine solution to the dissolution stage increases the degree of sodium sulfate transition from mirabilite to the desired product to 99-100 %.

The implementation of the proposed method for the production of sodium sulfate allows:

• exclude heating at the stage of dissolving mirabilite;
• exclude the second stage of the process of uterine solution evaporation and drying of sodium sulfate;
• increase the yield of pure high quality sodium sulphate to 100 %;
• to increase the extraction of sodium sulfate from mirabilite to 99-100 %.

Dissolving mirabilite in the condensate of juice vapors in the presence of uterine solution and eliminating the second stage of evaporation and drying allows saving energy.

The main chemical exporting products of Uzbekistan are the followings [1]:

• Ammonium nitrate
• Urea
• Ammonium sulfate
• Ammonium Sulfate phosphate
• Suprephos
• Nitric-phosphoric fertilizers
• Superphosphat
• Ammoniac
• Nytron fiber
• Acetic threads
• Acetic acid
• Fluid chlorine
• Sodium chlorine
• Chlorine magnesium defoliant
• Diacetate of cellulose
• Cellulose
• Plastic pipes
• Polyethylene film
• Methanol
• Sodium metallic
• Formalin
• Concentrated nitric acid
• Non concentrated nitric acid
• Ammoniac water
• Methyl acrylate
• Nytril acrylic acid
• Polyacrylamide

Picture 1. The main exporting products of chemical industry in Uzbekistan

According to State Joint Stock Company O’zkimyosanoat, In January-September 2012, enterprises of chemical industry of Uzbekistan produced industrial products to the amount of 1965.6 billion soums that exceeds indicators of relevant period of the last year by 4.7 %. Also there is rise in production of such products as carboxymethyl cellulose (by 2.1 times.), nitric acid strong (by 2.0 times), salt technical (by 2.0 times), acetaldehyde (162.5 %), synthetic detergents (149.4 %), ammonium sulfate (117.7 %), sodium cyanide (113.8 %), hydrochloric acid (112.1 %), sulfuric acid (104.4 %), synthetic ammonia (106.5 %), caustic soda (103.2 %) and others [4].

Used literatures:

1. Авт. свид. SU № 644732.
2. Патент РУз № IAP 04470, Опубл. Бюл. № 2, 2012.
3. Х.Ч. Мирзакулов, Г.Х. Джураева. Производство сульфата натрия. – Ташкент, 2014. – 224 с.
4. www.uzkimyosanoat.uz.