RU2144500C1 - Method of preparing potassium sulfate - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: method comprises conversion of potash with sodium sulfate or mixture thereof with sodium carbonate for 3 or 4 h to obtain sodium oxide concentration of 60-105 g/l in solution after recovery of potassium sulfate and evaporation followed by separation of soda from mother liquor. Desired sodium oxide concentration is maintained preferably due to recycle of mother liquor for dissolution of sodium sulfate or mixture thereof with sodium carbonate. Feed rate of potash solution to be mixed with sodium sulfate pulp or mixture thereof with sodium carbonate is 0,5÷5•10³ moles of alkali salts per minute. Industrial water resulting from washing potassium sulfate is preferably used for discolution of potash, and temperature of water for washing potassium sulfate is 20-50 C. EFFECT: improved quality of potassium sulfate, reduced moisture content thereof and simplified preparation process. 4 cl, 3 ex, 3 tbl

Description

 The invention relates to the field of chemical technology, and in particular to methods for producing potassium sulfate.

A known method of producing potassium sulfate from potassium ores of the chloride-sulfate type, comprising treating the ore with a solution of sodium chloride, separating insoluble sediment, diluting with water, crystallizing Shenite K ₂ SO ₄ • MgSO ₄ • 6H ₂ O by cooling the solutions to 20 ^o C, decomposition of Shenit water at 50 ^o C to obtain potassium sulfate and mother liquor [Posin M.E. The technology of mineral fertilizers. L.: Chemistry. S. 288-291]. The disadvantages of the method are difficulties in the processing of raw materials, due to the presence and fluctuations in the composition of impurities of clay substances, the presence of a large number of working materials, the need for multiple dilution of technological solutions with water, the presence of chlorine impurities in the final product, which reduces its quality.

There is also known a method for producing potassium sulfate from alunite K ₂ SO ₄ • Al ₂ (SO ₄ ) ₃ • 4Al (OH) ₃ , comprising treating with a steam at 700 ^o C a mixture of alunite and potassium chloride [M.E. Posin. The technology of mineral fertilizers. L .: Chemistry. S. 292]. The disadvantages of the method are its high energy intensity and the need for disposal or use of the resulting large amount of hydrochloric acid.

A known method of producing potassium sulfate in the complex processing of alkaline aluminosilicate raw materials, including multi-stage evaporation of solutions after carbonization with the release of soda and potassium-sodium carbonate recycled, cooling potassium-enriched evaporated solution through a heat exchange surface with separation of the recycle potash solution. To highlight potassium sulfate in the form of a commercial product, a mixture of potassium and sulfate-containing solution and water is made, and the resulting mixture is cooled to 25-35 ^o C with separation of the precipitate K ₂ SO ₄ [ed. St. USSR N 243592, 1967]. The method has the following disadvantages:
- high additional heat consumption for the organization of the allocation of potassium sulfate, due, firstly, the need to evaporate the water introduced into the crystallization of potassium sulfate, and secondly, the inability to effectively use the heat of the cooled solution (devices with a heat exchange surface, providing a high degree of heat use, due to the tendency of the surface to overgrow, it turns out to be ineffective), thirdly, by the need to heat the mother liquor of potassium sulfate and evaporate the crista tion of water;
- high specific investment due to the high temperature difference of the solutions before and after cooling;
- low productivity of equipment at the redistribution of the allocation of potassium sulfate, which is due to the low removal of K ₂ SO ₄ with 1 m ^{3 of the} solution directed to the allocation of K ₂ SO ₄ and a low degree of allocation of K ₂ SO ₄ .

The prototype of the alleged invention is a method for producing potassium sulfate, including the conversion of potassium chloride to sodium sulfate. The implementation of the process in one stage leads to a low technological yield of the finished product, therefore, the conversion process is conducted through an intermediate product - glaserite Na ₂ SO ₄ • 3K ₂ SO ₄ . The process proceeds at 25 ^o C. The time required to complete the first stage is 1 hour, the second 30 minutes. According to the technological scheme of conversion, potassium chloride and sodium sulfate are fed to the conversion reactor. Mirabilite and one stripped off solution obtained at the stage of recycling recycled solutions also come here. Glaserite suspension thickens to a ratio of W: T = 0.7-1.2 and is subjected to centrifugation. Filtered glaserite for enrichment is treated with a solution obtained in the second stage of conversion. After separation of the enriched glaserite, the clarified solution is fed to the first stage of conversion, and the enriched glaserite is treated with a 28% potassium chloride solution. The filtered potassium sulfate is washed in a centrifuge with water (5% by weight of the precipitate) and sent for drying. Glaserite mother liquor is cooled to 0-5 ^o C and crystallizing mirabilite served in the first stage of conversion. In the conversion of potassium chloride to sodium sulfate receive potassium sulfate with a mass content,%: K ₂ SO ₄ - 84,22; Na ₂ SO ₄ - 8.37; KCl - 3.83; H ₂ O - 3,58% [Processing of natural salts and brines: Handbook / Ed. I.D. Sokolova - L .: Chemistry, 1985. S. 80-85].

The disadvantage of the prototype is the low quality of the products, due to the high content of chlorine and sodium impurities, high humidity, the bulkiness of the production scheme, the need to use expensive refrigerants for cooling technological solutions to 0-25 ^o C.

In the inventive method for producing potassium sulfate, including the conversion of sodium sulfate (or its mixture with sodium carbonate) with a potassium reagent and evaporation, followed by separation of soda from the mother liquor, potash is used as the potassium reagent, and the conversion process is carried out at 45-60 ^o C, within 2-12 hours from the calculation of obtaining a concentration of Na ₂ O in solution after the allocation of potassium sulfate 60-120 g / l, which leads to an improvement in the quality of potassium sulfate, simplifying the process of its production and reducing humidity.

 By maintaining the required concentration of sodium oxide for the conversion process, a simplification of the process is achieved by returning the mother liquor to dissolve the potash.

By maintaining the feed rate of the potash solution for mixing with a pulp of sodium sulfate or its mixture with sodium carbonate - 0.5-5 • 10 ³ - moles of alkaline salts per minute, a decrease in the moisture content of potassium sulfate is achieved.

The temperature of the water for washing potassium sulfate is - 20-50 ^o C.

The method is as follows. Sodium sulfate or a mixture of sodium sulfate with sodium carbonate or salt - berkeite is repulped with a soda solution or a mother liquor after separation of soda with a density of 1.35-1.50 g / cm ³ , based on obtaining a pulp density of 1.40-1.55 g / cm ³ and fed to the conversion. Potash is also fed into the conversion in the form of a solution in water and / or in the wash after washing the potassium sulfate. The feed rate of the potash solution is - 0.5-5 • 10 ³ moles of alkaline salts per minute, which allows you to get large easily filtered crystals of potassium sulfate. The conversion for 2-12 hours at 45-60 ^o C get potassium sulfate and a mother liquor with a density of 1.3-1.42 g / cm ³ containing 60-120 g / l sodium oxide and a mole fraction of potassium salts ( Jeneke's potassium index) 50-67 units.

Increasing the concentration of sodium oxide over 120 g / l can cause sodium contamination of the production potassium sulfate. After crystallization and sedimentation for 2-12 hours, the pulp is concentrated and the clarified solution is drained. The thickened pulp of potassium sulfate is centrifuged in centrifuges. Potassium sulfate is washed with water at a temperature of 20-50 ^o C. Promoter potassium sulfate and the solution from washing the nets is used to dissolve potash.

Potassium sulfate from centrifuges is conveyed by the conveyor for drying to a moisture content of less than 1% and filling to the consumer. The centrate and drain the thickeners evaporated with the release of soda and the mother liquor with a density of 1.47-1.50 g / cm ³ potassium index 56-72 units. The soda is dried and sent to the consumer, and the mother liquor after soda separation is used to repulpate sodium sulfate or its mixture with sodium carbonate and / or for chemical purposes.

At a conversion temperature below 45 ^o C, it is possible to isolate, in addition to potassium sulfate, complex sodium salts, which pollute the final product. At a conversion temperature above 60 ^° C., the yield of potassium sulfate in the finished product is reduced.

 Reducing the duration of the conversion below 2 hours, as well as the concentration of sodium oxide in the solution after the isolation of potassium sulfate below 60 g / l, leads to an incomplete conversion of potash to potassium sulfate and contamination of the finished product with gelatinite.

 An increase in the conversion duration over 12 hours does not lead to a noticeable increase in the yield of potassium sulfate in the finished product. When the rate of supply of potash solution for mixing with sulfate pulp is less than 0.5 and more than 5 moles / min, fine crystalline potassium sulfate is obtained, which, when separated by centrifuge, has increased humidity.

At a water temperature for washing potassium sulfate below 20 ^o C, washing of potassium sulfate from impurities is insufficient, and at a temperature above 50 ^o C, the rate of dissolution of potassium sulfate during washing sharply increases.

 Example 1

In 4.9 m ^{3 of the} mother liquor after separation of soda with a content of, g / l: Na ₂ O - 93.6; K ₂ O - 315.7; SO ₃ - 5.51, the Jenecke index 2K - 68.9 and a density d - 1.49 g / cm ^{3 were} repulped at 50 ^o C 1.22 tons of a mixture of sodium sulfate with sodium carbonate with a content, wt.%: Na ₂ SO ₄ - 65.3; Na ₂ CO ₃ - 24.7; H ₂ O - 10. As a result, 5.6 sulfate pulps with a density of d - 1.52 g / cm ³ , 1.06 tons of sesame and potash containing, wt.%: K ₂ CO ₃ - 65.3 were obtained; Na ₂ CO ₃ - 2.2; H ₂ O - 17.4 was dissolved at 50 ^° C in 3.3 m ^{3 of} water to obtain a 3.7 m ³ solution with a concentration of 237.8 g / l K ₂ O and a density of d - 1.19 g / cm ³ . The conversion with the release of potassium sulfate was carried out at 45 ^o C for 3 hours by mixing sulfate pulp with potash pulp. The rate of supply of potash for mixing with sulfate pulp was 2 • 10 ³ moles of alkaline salts per minute. The resulting precipitate of potassium sulfate after conversion was separated from the mother liquor by thickening and centrifugation, washed and dried to a moisture content of 0.5%. The water temperature for washing the sulfate was 30 ^o C. As a result, 1 ton of potassium sulfate was obtained with a content, wt.%: Na ₂ O - 2.9; K ₂ O - 50.4; CO ₂ - 1.3. In the mother liquor, with a volume of 8.9 m ³ , density d - 1.36 g / cm ³ contained, g / l: Na ₂ O - 100.6; K ₂ O - 177.5; SO ₃ - 3.56, Yeneke index 2K - 53.8. The mother liquor after separation of potassium sulfate was subjected to a single-case evaporation at 120 ^o C with the release of 3.6 tons of water into the gas phase. After evaporation and phase separation, a soda precipitate was obtained in an amount of 0.90 t (in terms of dry product) with a content, wt.%: Na ₂ CO ₃ - 96.7; K ₂ CO ₃ - 2.2; K ₂ SO ₄ - 1.1 and a mother liquor with a volume of 4.9 m ³ , density d - 1.49 g / cm ³ . The mother liquor after soda recovery was returned to the preparation of sulfate pulp.

 Example 2

In 5 m ³ soda solution of chemical production with the content, g / l: Na ₂ O - 125.0; K ₂ O — 250.0, a Jenecke index 2K — 56.8 and a density d — 1.47 g / cm ³ repulpated at 50 ^° C. 1.38 tons of a mixture of sodium sulfate and sodium carbonate. The result was 5.8 m ^{3 of} sulfate pulp with a density of d - 1.50 g / cm ³ . 1.1 tons of potash and water potash was dissolved at 50 ^° C in 2.0 m ^{3 of a} centrate after washing with potassium sulfate with a content of, g / l: Na ₂ O - 50.0; K ₂ O -120,0 to obtain a 2.6 m ³ solution concentration, g / l: Na ₂ O - 26.0; K ₂ O - 420.0 and a density d - 1.47 g / cm ³ .

The conversion with the release of potassium sulfate was carried out under the conditions given in table. 1, by mixing sulfate pulp with potash. The rate of supply of potash pulp for mixing with sulfate pulp was determined by the need to obtain a coarse-grained precipitate of potassium sulfate with low final moisture content after filtration in a centrifuge and washing (Table 2). The resulting potassium sulfate was dried to a moisture content of 0.5%. The temperature of the water for washing the potassium sulfate was 55 ^o C. As a result, 1 ton of potassium sulfate and a mother liquor containing Na ₂ O were obtained according to the table. 1. The resulting mother liquor of potassium sulfate was subjected to a single-case evaporation with the release of water into the gas phase, and soda precipitate, similarly to example 1.

 Example 3

0.92 tons of sodium sulfate with a moisture content of 10% were repulpated in 5.8 m ^{3 of the} mother liquor after separation of soda with a content of, g / l: Na ₂ O = 109.4; K ₂ O = 266.7; SO ₃ = 6.8; 2K index - 65.2 and density ρ = 1.48. As a result, 6.1 m ^{3 of} sulphate pulp with a density of ρ = 1.50 g / cm ^{3 was} obtained, 1.08 t of a half-potash potash was dissolved at 40 ^° C in 1.8 m ^{3 of a} centrate after washing potassium sulphate with a content of 47 g / l Na ₂ O and 84 g / l K ₂ O to give 2.3 m ^{3 of} potash solution. The conversion with the release of potassium sulfate was carried out at 50 ^o C for 4 hours by mixing sulfate pulp with potassium chloride solution in the calculation of the concentration of Na ₂ O in the mother liquor of 100 g / L. The feed rate of the potash solution for mixing with sulfate pulp was 0.4 mol / min alkaline salts per minute. The resulting potassium sulfate precipitate after conversion was separated from the mother liquor by thickening and centrifugation, and then washed with water. The temperature of the washing water was chosen based on the need for maximum washing from sodium impurities with a minimum dissolution of K ₂ SO ₄ in the promvod (Table 3).

After washing, potassium sulfate was dried to a moisture content of 0.7% to obtain 1 ton of marketable product. The mother liquor with a volume of 8 m ^{3 with a} density ρ = 1.32 g / cm ³ with a content of, g / l: Na ₂ O = 103; K ₂ O = 198; SO ₃ = 4.81, index 2K - 56.1 was subjected to a single-case evaporation at 116 ^° C with the release of 2.34 tons of water into the gas phase, and soda in the amount of 0.85 tons into the sediment. 5.1 m mother liquor ³ and a density ρ = 1.48 g / cm ³ containing, g / l: Na ₂ O = 118.4; K ₂ O = 244.7; SO ₃ = 6.4 was returned to dissolve sodium sulfate in the preparation of sulfate pulp.

Claims (4)

1. A method of producing potassium sulfate, including the conversion of sodium sulfate or a mixture thereof with sodium carbonate of a potassium-containing reagent and evaporation followed by separation of soda from the mother liquor, characterized in that potash is used as the potassium-containing reagent, and the rate of supply of potash to mix with sodium sulfate pulp or a mixture of sodium carbonate amounts to 0.5 - 5 • March ¹⁰ moles of alkaline salt per minute and the conversion process is carried out for 2 - 4 hours at the rate of a concentration of sodium oxide in the solution after apportionment Ia potassium sulfate 60 - 105 g / l.  2. The method according to claim 1, characterized in that the required concentration of sodium oxide is maintained by returning the mother liquor to dissolve sodium sulfate or a mixture thereof with sodium carbonate. 3. The method according to p. 1, characterized in that the temperature of the water for washing potassium sulfate is 20 - 50 ^o C.  4. The method according to p. 1, characterized in that the promo from washing potassium sulfate is used to dissolve potash.

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