RU2161125C2 - Method of production of potassium sulfate - Google Patents

Abstract

FIELD: inorganic chemistry, chemical technology. SUBSTANCE: method involves interaction of sodium sulfate and potassium chloride with potassium sulfate mother liquor with formation of glaserite and glaserite mother liquor, conversion of glaserite with potassium chloride and water to potassium sulfate and potassium sulfate mother liquor, separation of potassium sulfate and recirculation of potassium sulfate mother liquor to the process of glaserite formation. Glaserite mother liquor in the molar ratio K₂ : SO₄ = (1.5-6.0) : 1 and content of potassium and sulfate ions in the limits K₂ = 20.0-38.0 mol. % and SO₄ = 13.4-6.3 mol.% is subjected for air-solar evaporation in reservoirs that results to isolation of mixture of glaserite and sodium and potassium chloride in solid phase. Mixture is separated from solution and potassium salts are isolated from solution by dissolving/crystallization and flotation followed by recirculation of potassium salts to the main cycle of potassium sulfate producing. EFFECT: simplified process, decreased energy consumption. 4 cl, 1 tbl, 4 ex

Description

The invention relates to techniques for producing potassium sulfate from potassium chloride and sodium sulfate,
There is a two-stage method for producing potassium sulfate from potassium chloride and sodium sulfate or mirabilite (Na ₂ SO ₄ • 10H ₂ O) to produce glaserite in the first stage, followed by its decomposition in the second stage with an aqueous solution of potassium chloride to potassium sulfate and the mother liquor is returned to the first stage (see. "A static model of the process of producing potassium sulfate", ed. Sokolov I.D. et al. Khim.prom., 1978 (6), 444-447).

 The paper considers in detail the processes of conversion and utilization of a glaserite solution by evaporation.

 The proposed methods for processing a glaserite solution are complex and require large energy consumption to remove all the water supplied to the conversion processes.

 A known method of producing potassium sulfate by converting sodium sulfate with potassium chloride, followed by separation of the resulting pulp into a mother liquor and glaserite, which is then fed to the second stage of conversion with potassium chloride, and the mother liquor is cooled, followed by isolation of mirabilite and evaporation of the cooled mother liquor to obtain sodium chloride, while the mother liquor after separation of sodium chloride is mixed with mirabilite and the resulting sulfate pulp is returned to the first stage of conversion (see AS USSR N 710945, class C 01 D 5/06, BI N 3, 01/25/80).

 The known method is difficult to implement, since it requires large energy consumption for cooling the glaserite solution and removing water supplied to the process by evaporation using expensive equipment.

A known method for the continuous production of potassium sulfate from sodium sulfate is a prototype (see Russian patent N 2107028, class C 01 D 5/06, 11.22.94, BI N 8 (part II), 1998) by the interaction of potassium chloride and sodium sulfate (glauber's salt or its mixture with sodium sulfate) with the mother liquor of potassium sulfate in the stage of crystallization of glaserite with the formation of glaserite, the separation of glaserite from the mother liquor of glaserite, the conversion of glaserite with potassium chloride and water to potassium sulfate and the mother liquor of potassium sulfate, separation of sulfate potassium and uterine recirculation solution of potassium sulfate in the crystallization process glaserite, and the evaporation of the mother liquor glaserite with crystallization of pure sodium chloride, and separation of sodium chloride, and the mother liquor composition glaserite set at a molar ratio of K _2: SO _4> 3: 1 to 5: 1 and Na ₂ : SO ₄ > 6: 1 to 11 to 1, from this mother liquor of glaserite, 29-42% of the water contained is removed at 75-115 ^° C by evaporation, the largest, however, so as to avoid precipitation of sulfates, especially glaserite, and obtained after separation of mountain sodium chloride a clear, crystal-free solution from evaporation after cooling to a temperature of 15-40 ^o directly in the form of a suspension containing KCl is used to obtain glaserite.

According to the proposed method, the molar ratio of K ₂ : SO ₄ in the glaserite solution is more than 4: 1 to 5: 1 is preferred.

The proposed method is difficult to implement, since it requires high energy consumption for the evaporation of all the water supplied to the process using expensive equipment, it provides for conducting glaserite crystallization process in a very narrow range of the molar ratio K ₂ : SO ₄ , which requires tight control over the dosage of reagents and flows, involves the use of a large volume of recycled one stripped off glaserite solution after the separation of sodium chloride from it, which leads to an increased consumption of electric energy rgii and the use of additional equipment.

The task of the invention is to simplify the process while reducing energy costs for its implementation. A positive effect is achieved in that, in contrast to the known method, including the interaction of sodium sulfate and potassium chloride with a mother liquor of potassium sulfate with the formation of glaserite and mother liquor of glaserite, the conversion of glaserite with potassium chloride and water to potassium sulfate and mother liquor of potassium sulfate, separation of sulfate potassium and recirculation of the mother liquor of potassium sulfate in the process of crystallization of glaserite, according to the proposed method, the mother liquor of glaserite with the composition of the solution in a molar ratio of K ₂ : SO ₄ (1 , 5-6.0): 1 and the content of potassium and sulfate ion in molar percent within the range of K ₂ = 20.0 - 38.0%, SO ₄ = 13.4-6.3% is subjected to air-solar evaporation in pools with the allocation of a mixture of glaserite and sodium and potassium chlorides into the solid phase, the mixture is separated from the solution and potassium salts are separated from them by dissolution-crystallization or flotation, followed by recirculation of potassium salts in the main cycle for the production of potassium sulfate.

 The difference of the method is also the allocation of potassium salts from a mixture of them with sodium chloride by hot dissolution of potassium salts in a recirculated solution, followed by separation from a suspension of sodium chloride, cooling the clarified solution under vacuum, followed by separation of the crystallizate - potassium salts and recycling them into the main cycle, heating the solution after crystallisate is recovered and recirculated for hot dissolution.

 Another difference of the method is the separation of potassium salts from their mixture with sodium chloride by flotation of potassium salts into a valuable product in the mother liquor of glaserite using flotation reagents, thickening and filtering potassium salts with their subsequent recirculation into the main cycle, the allocation of sodium chloride in the flotation sands with its subsequent by filtration.

 The difference is also the recirculation of potassium salts in the main cycle of potassium sulfate production by supplying them to convert glaserite to potassium sulfate or by supplying potassium salts or their part to the formation of glaserite.

 The essence of the method is as follows: in contrast to the known method according to the proposed method, the mother liquor of glaserite is subjected to air-solar evaporation in pools with the release of sodium chloride and potassium chlorides in the solid phase.

In the known method for removing sodium chloride from the technological cycle, all water introduced into the process is removed by evaporation of the glaserite solution in expensive, usually titanium evaporators, and 29-42% of water is removed in one cycle, which sharply increases the flow of liquid phases - the crystallization cycle of glaserite, its isolation from suspension, evaporation of the glaserite solution and its cooling. In this case, the bulk of the heat cost is accounted for by water evaporation (more than 600 kcal per kg of water). According to the proposed method, the mother liquor glaserite solution is subjected to air-solar evaporation in pools at ambient temperature with the allocation in the solid phase of a mixture of glaserite and sodium and potassium chlorides. In this case, potassium chloride precipitates in the solid phase at lower temperatures of the liquid phase in the pool with a molar ratio of K ₂ : SO _{4 of} more than 4.5, as well as during dehydration of a solution saturated with three salts: potassium chloride, glaserite and sodium chloride.

 The mixture of salts obtained in the pool is separated from the solution by known methods, and the solution is returned to the pool. Thus, the entire liquid phase gradually turns into a mixture of salts.

 For climatic regions where the volume of evaporated water significantly exceeds the amount of precipitation, the proposed method has clear advantages, since the cost of maintaining the pools is negligible.

 The selection of potassium salts and mixtures thereof with sodium chloride, followed by recirculation of salts in the main cycle of potassium sulfate production by the proposed method is carried out by dissolution-crystallization, or flotation.

 The choice of a method for processing a mixture of salts depends on the specific conditions for the production of potassium sulfate: requirements for the quality of sodium chloride obtained as a by-product, the volume of proposed investments, the availability of energy resources, etc.

A method of processing soda by dissolution-crystallization includes dissolving potassium salts in a recycled solution at a temperature of 98-105 ^o , the allocation of sodium chloride by thickening and filtering in suspension, cooling the clarified solution to 20-45 ^o C in a vacuum crystallization unit to obtain crystallized potassium salts: mixtures of potassium chloride and glaserite, the separation of crystallizate by thickening and filtration, and its recycling into the main cycle for the production of potassium sulfate, heating the mother liquor of the crystallizate and its recycling to dissolve potassium salts.

 The energy consumption for processing a mixture of salts is much lower than in the known method, since the proposed method has heating and cooling solutions as in the known method and there are no costs for evaporation of water. In addition, the proposed recycling in the main cycle of solid salts instead of returning one stripped off glaserite solution by a known method leads to a sharp decrease in flows in the glaserite crystallization cycle.

 The method of dissolution-crystallization allows to obtain high-quality sodium chloride as a by-product, but requires a relatively high investment and energy costs for heating and cooling solutions.

To reduce the volume of investment by 20-30% and energy consumption by 80%, the proposed method uses flotation to separate potassium salts from their mixture with sodium chloride. The flotation process is carried out from a mixture of salts of fractions of less than 1 mm at ambient temperature in standard flotation machines using potassium salt flotation agents, for example, primary aliphatic amines with the length of hydrocarbon radicals C ₁₆ , C ₁₈ .

 The mother liquor of glaserite saturated with halite, glaserite and potassium chloride is used as a reverse solution. Potassium salts are sent by foams to thickening and filtration, followed by their recycling to the main cycle, and flotation sands, sodium chloride mixed with potassium salts, are filtered and used for technical purposes.

In contrast to the known method according to the proposed method, the ratio of K ₂ : SO ₄ expanded to (1.5-6.0): 1, while the content of potassium and sulfate ion in the glaserite solution is in the range of K ₂ = 20.0 - 38 0; SO ₄ = 13.4 - 6.3, in molar percent.

When evaporating the solution by a known method, the crystallization region of sodium chloride is very narrow, as shown in the analogue - see the article in the HPLC, and taking into account nonequilibrium states, the ratio is even more limited and amounts to K ₂ : SO ₄ (4-5): 1, which and is reflected in paragraph 2 of the claims of the prototype. Violation of this ratio leads to contamination of sodium chloride, as well as to inlaid heating surfaces of the evaporator.

According to the proposed method, the interval of the molar ratio of K ₂ : SO _{4 is} significantly expanded, since with air-solar evaporation of the glaserite solution in the pool, a change in the molar ratio of K ₂ : SO ₄ in the glaserite solution only leads to an increase or decrease in the share of glaserite and potassium chloride in its mixture with halite and after the isolation of potassium salts and their recirculation into the main cycle for the production of potassium sulfate, the losses of solid and liquid phases in it change insignificantly. It should be noted that the extension of the range of the molar ratio of K ₂ : SO ₄ less than 1.5 and more than 6 is possible, but undesirable, since when the content in the ratio of K ₂ - 1.5 leads to crystallization along with glaserite sodium sulfate, which complicates the process of selection potassium salts from their mixture with sodium chloride, and when the content in the ratio of K ₂ > 6.0 leads to an increase in the content of potassium chloride in the mixture and to an increase in the internal flow of potassium salts.

 According to the proposed method, the recirculation of potassium salts is carried out by feeding them to convert glaserite to potassium sulfate, or by supplying part of the salts to form glaserite.

 The salt mixture is dissolved in water to obtain a solution containing chloride and potassium sulfate, while glaserite from potassium salt is converted to potassium sulfate.

 The resulting suspension is used to convert the main cycle glaserite with potassium chloride and water to potassium sulfate and the mother liquor of potassium sulfate.

 Our studies have shown that all of the potassium chloride needed to produce potassium sulfate can be fed to the second stage of conversion, or up to 30% of potassium chloride can be fed to the glaserite formation stage, and the rest to the stage of glaserite conversion to potassium sulfate. Therefore, recycled potassium salts or part thereof can be used instead of potassium chloride in the first stage of conversion.

The proposed method claims the content of potassium and sulfate ion in the glaserite solution in molar percent in the range of K ₂ : 20.0 - 38.0; SO ₄ : 13.4 - 6.3. The molar ratio of Na ₂ : SO ₄ rigidly binds the composition of the glaserite solution to the ratio of K ₂ : SO ₄ and does not take into account the temperature fluctuations of the solution, metastable states in its composition, kinetic regularities of the process, which can lead to disturbances in the evaporation process in the known method.

 When specifying the composition of the solution in molar percent, these difficulties are eliminated.

The table shows the equilibrium compositions of the glaserite solution at 25 ^o C in molar percent, the ratio of potassium and sulfate ion and the composition of the hard ore in the initial period of dehydration in the pool.

The method is as follows: sodium sulfate, glauber's salt or a mixture with sodium sulfate, potassium chloride and a mother liquor of potassium sulfate (in the start-up period, water is used instead of the mother liquor of potassium sulfate) at an ambient temperature is subjected to vigorous stirring for 20-60 minutes while the molar ratio of K ₂ : SO ₄ in the glaserite solution is (1.5 - 6.0): 1 and the content of potassium and sulfate ion in molar percent in the range of K ₂ : 20.0 - 38.0%; SO ₄ : 13.4 - 6.3% (see table).

 The resulting suspension, if necessary, is concentrated and filtered to obtain glaserite and mother liquor glaserite. Glaserite is converted to potassium sulfate by treating it in an aqueous medium at ambient temperature with recycled potassium salts and potassium chloride with vigorous stirring for 20-60 minutes. In the starting period, in the absence of potassium salts, they are replaced with potassium chloride.

 The resulting suspension, if necessary, is concentrated and filtered to obtain wet potassium sulfate, which, after drying, is the target product, and a mother liquor of potassium sulfate, which are recycled to the stage of formation of glaserite.

 The mother liquor of glaserite is subjected to air-solar evaporation in pools at ambient temperature with the release of a mixture of glaserite and sodium and potassium chlorides into the solid phase. The mixture of salts is separated from the mother liquor and the solution is returned to the pool.

 Potassium salts are separated from the mixture of salts by dissolving-crystallization or flotation, followed by their recycling to the stage of conversion of glaserite to potassium sulfate or to the stage of glaserite formation, and only a part of potassium salts can be fed to this stage.

When potassium salts are separated from the mixture by dissolution-crystallization, the mixture is crushed to a particle size of less than 5 mm and subjected to vigorous stirring in a circulating solution at a temperature of 98 - 105 ^o C, the resulting suspension is concentrated and filtered with evolution of sodium chloride, and the clarified solution is cooled in a vacuum crystallization unit to a temperature of 20-45 ^o C to obtain a suspension of crystallizate - potassium salts: a mixture of potassium chloride and glaserite in the mother liquor. The suspension is concentrated and filtered to give potassium salts, which are recycled to the main potassium sulfate production cycle. The mother liquor of the crystallizate is heated and recycled to dissolve the potassium salts.

When potassium salts are separated from the mixture by flotation, the mixture is crushed to a particle size of less than 1 mm, and then potassium salts are floated from it in a circulating solution into a valuable product at ambient temperature, but not less than 10 ^o C using flotation reagents. A glaserite solution saturated with glaserite, sodium and potassium chlorides is used as a reverse solution.

 Potassium salts in the foam product are concentrated and filtered, followed by their recycling to the main cycle, and the flotation sands - sodium chloride mixed with potassium salts, are filtered and used for technical purposes.

 The proposed method is carried out in continuous or batch mode.

Example 1
1000 c. hours / h of sodium sulfate according to GOST 6318-77 with a content of Na ₂ SO ₄ 98%, 757 hours / h of potassium chloride according to GOST 4568-83 with a KCl content of 96% and 4397 in. . h / h potassium sulfate solution composition mas.dol%: K ^{+ - 8,89, Na + - 2,50} , SO ₄ ^{- - 2,70, Cl - - 9,93} , H ₂ O -75. , 98 was subjected to vigorous stirring at a temperature of 20 ^o C in a horizontal apparatus with a mixing device, providing a residence time of the reaction mass in the apparatus for 45 minutes

The resulting suspension was separated by thickening and filtering on a belt vacuum filter to obtain 4932 parts per hour of glaserite mother liquor with a molar ratio of K ₂ : SO ₄ = 6: 1 with a K ₂ content of 38.0 and SO _{4 of} 6.3 in molar percent and 1377 parts by weight per hour of glaserite with a moisture content of 8%. Glaserite mother liquor was subjected to air-solar evaporation in the pool with a daily temperature fluctuation in the range of 10 - 35 ^o C to obtain 1525 parts by weight per hour of a mixture of salts with a composition of wt%: NaCl - 52.0, KCl - 39.6 , Na ₂ SO ₄ • 3K ₂ SO ₄ - 8.42.

The mixture was ground to a particle size of less than 5 mm and subjected to vigorous stirring in a horizontal solvent at a temperature of 100 ^o C in a circulating solution, preheated to 112 ^o C. The resulting suspension was thickened and 800 parts per hour NaCl of the composition wt. : NaCl - 97.7, KCl - 0.8, SO ₄ ^- - 0.95. After washing the salt with NaCl in it, it exceeded 99%.

The filtrate and clarified solution with a temperature of 95 ^o C were subjected to cooling to a temperature of 35 ^o C to obtain a suspension of crystallizate - potassium salts; mixtures of potassium chloride and glaserite mixed with sodium chloride in the mother liquor. The suspension was concentrated and filtered to obtain potassium salts, which were recycled to the second stage of conversion in the amount of 725 parts per hour of the following composition, wt. dale %: KCl - 79.6, glaserite - 16.9, NaCl - 3.5. At the same time, glaserite from the first stage, potassium chloride and water were supplied to the second stage of conversion to convert glaserite to potassium sulfate and the mother liquor of potassium sulfate. The resulting suspension was subjected to vigorous stirring at a temperature of 20 ^o C in a horizontal apparatus with a mixing device, providing a residence time of the reaction mass in the apparatus for 45 minutes The resulting suspension was separated by thickening and filtering on a belt vacuum filter to obtain a mother liquor of potassium sulfate and the target product.

As a result of the method obtained potassium sulfate composition wt. share%: K ₂ O - 50.8, Cl ₂ - 0.38.

 The technological degree of extraction (excluding mechanical losses - drainage of the system, spills, equipment flushing, etc.): for potassium - 99.7%, for sulfate - 99.5%.

Example 2
1000 c. parts per hour of sodium sulfate, 120 parts per hour of potassium chloride, 3262 parts per hour of potassium sulfate solution and 306 parts per hour of recirculated potassium salts of the composition, wt. dale %: KCl - 39.95, Na ₂ SO ₄ • 3K ₂ SO ₄ - 52.05, NaCl - 8.0 were treated in accordance with example 1 to obtain 3557 parts by weight per hour of mother liquor glaserite with a molar ratio of K ₂ : SO ₄ = 1.5-1.0 and a content of K _{2 of} 20.0, SO _{4 of} 13.4 molar percent. The mother liquor was subjected to air-solar evaporation in the pool at ambient temperature to obtain 1157.9 parts per hour of a mixture of salts of the following composition, wt%: NaCl - 70.73, KCl - 11.7, Na ₂ SO ₄ • 3K ₂ SO ₄ - 17.57. The mixture was ground to a particle size of less than 1 mm and then flotation was carried out at ambient temperature (18-20 ^o C) the allocation of potassium salts from it into the foam product.

The flotation of potassium salts from their mixture with halite was carried out in a working solution of the composition, wt%: K ₂ - 29.5, SO ₄ - 6.5, with a ratio of K ₂ : SO ₄ = 4.53, Na ₂ : SO ₄ = 10.84 using primary aliphatic amines with a hydrocarbon radical length of C ₁₆ , C ₁₈ as a flotation reagent. At a flow rate of 75 g / t of the initial mixture of salts.

 The resulting potassium salts were sent to a thickening using a working solution, and then the thickened product was filtered to obtain potassium salts, which were recycled to the first stage of conversion. The thickener drain and filtrate were returned to the flotation cycle.

Flotation sands in the amount of 849 parts per hour were listened and filtered on a vacuum filter to obtain sodium chloride of the following composition, wt%: NaCl - 93.92, KCl - 2.42, Na ₂ SO ₄ • 3K ₂ SO ₄ - 3.66. The quality of sodium chloride can be significantly improved by the washing process,
The recovery of KCl in the foam product from the mixture of pool salts was 90.8%.

As a result of the method, potassium sulfate of the composition K ₂ O was obtained — 50.5%, Cl — 0.51%, the technological degree of extraction for potassium 96.4%, for sulfate 96.9%.

Example 3
The method is carried out in accordance with example 1, but 75% of the recirculated potassium salts were fed to the first stage of conversion, and 25% to the second.

Example 4
The method is carried out in accordance with example 1, but instead of sodium sulfate, a glauber salt (Na ₂ SO ₄ • 10H ₂ O) or its mixture with sodium sulfate is used with adjustment of the water balance.

Claims (4)

1. A method for producing potassium sulfate by reacting sodium sulfate and potassium chloride with a mother liquor of potassium sulfate to form glaserite and a mother liquor of glaserite, converting glaserite with potassium chloride and water to potassium sulfate and a mother liquor of potassium sulfate, separating potassium sulfate and recycling the mother liquor of sulfate potassium in the formation of glaserite, characterized in that the mother liquor of glaserite at a molar ratio of K ₂ : SO ₄ = (1.5 - 6.0): 1 and the content of potassium and sulfate ion in the range of K ₂ = 20.0 - 38 , 0 mol%, SO ₄ = 1 3.4 - 6.3 mol.% Is subjected to air-solar evaporation in pools with the separation of the glaserite and sodium and potassium chlorides into the solid phase, the mixture is separated from the solution and potassium salts are separated from it by dissolution - crystallization or flotation, followed by recirculation of potassium salts in the main cycle for the production of potassium sulfate.  2. The method according to claim 1, characterized in that the selection of potassium salts from their mixture with sodium chloride is carried out by hot dissolution of potassium salts in a recycled solution, followed by separation from a suspension of sodium chloride, cooling the clarified solution under vacuum, followed by crystallisate - potassium salts and recirculating them into the main cycle, heating the solution after isolating the crystallizate and recirculating it for hot dissolution.  3. The method according to claim 1, characterized in that the allocation of potassium salts from them mixtures with sodium chloride are carried out by flotation of potassium salts into a foam product in the mother liquor of glaserite using flotation reagents, thickening and filtering potassium salts, followed by their recycling to the main cycle, the allocation of sodium chloride in the sands of flotation, followed by filtration.  4. The method according to claim 1, characterized in that the recirculation of potassium salts in the main cycle for the production of potassium sulfate is carried out by supplying them to convert glaserite to potassium sulfate or by supplying potassium salts or part of them to form glaserite.

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