Method for preparing potassium carbonate

Abstract

The invention provides a method for preparing potassium carbonate. The method comprises the following steps: controlling the mass concentration of a potassium chloride aqueous solution to be 18-50% and the pressure of CO2 gas to be 2-6Mpa; inorganic magnesium salt, a potassium chloride aqueous solution and carbon dioxide efficiently form a low-solubility Enger double salt of potassium bicarbonate, and a potassium carbonate product is prepared through decomposition of the Enger double salt and multiple separation operations. By improving the concentration of the potassium chloride aqueous solution in the preparation process and reducing the pressure of the introduced CO2 gas, the preparation capacity of potassium carbonate is improved, the preparation energy consumption is reduced, the preparation efficiency of potassium carbonate is effectively improved, and the production cost of potassium carbonate is reduced. In addition, according to the method, the filtrate separated in the separation process is recycled, the use amount of water in the preparation process is reduced, pollution can be reduced, and the cost caused by wastewater treatment can be reduced. The method also has the advantages of simple process flow and low equipment investment cost, and is suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the field of chemical industry, and in particular to a method for preparing potassium carbonate. Background Art

[0002] Potassium carbonate (Potassium Carbonate), an important inorganic chemical substance, has applications in many fields that cannot be underestimated. In industry, as a flux for glass manufacturing, it can effectively reduce the melting temperature, which not only improves production efficiency, but also enhances the stability and strength of glass, laying the foundation for the high-quality production of modern building materials. In the printing and dyeing industry, potassium carbonate plays the role of a color fixative and detergent, significantly improving the dyeing effect, effectively removing stains on fabrics, and meeting the high requirements for textile quality. The chemical industry uses it as a basic raw material for the manufacture of potassium salts, which is widely used in fertilizers, pharmaceuticals and other industries. Its importance is self-evident. In the food field, potassium carbonate is used as a loosening agent in pasta products. It can not only adjust the pH of food, but also plays a key role in the production of monosodium glutamate, affecting the taste and quality of food. In addition, potassium carbonate has irreplaceable applications in many fields such as the electronics industry, analytical chemistry, and fire extinguishing agent manufacturing, and its market demand is stable and showing a sustained growth momentum.

[0003] At present, the preparation methods of potassium carbonate mainly include ion membrane-fluidized bed process, electrolysis and ion exchange. Among them, the ion membrane-fluidized bed process is favored for its high-quality products and relatively simple operation process. However, the high equipment investment, limited membrane life and greater environmental pressure limit its application in a wider range, especially in China. In view of cost and environmental factors, this method has not become mainstream. Electrolysis and ion exchange have therefore become the preferred processes for domestic production of potassium carbonate. The electrolysis method prepares potassium carbonate by electrolyzing a solution containing potassium compounds, reducing potassium ions at the cathode to generate metallic potassium, which then reacts with water to generate potassium hydroxide, and finally potassium hydroxide reacts with carbon dioxide to obtain potassium carbonate. The process is easy to obtain raw materials, has a high utilization rate of potassium, and does not produce wastewater, waste gas, waste residue and other three waste problems, but due to high power consumption and strict maintenance requirements for the electrolytic cell (including regular replacement of electrodes and diaphragms, etc.), the production cost is pushed up, and the improper treatment of the by-product chlorine gas poses a potential threat to the environment. The ion exchange method uses the selective adsorption and exchange characteristics of ion exchange resins in solution to prepare potassium carbonate. This method is known for its high product purity, simple operation, environmental protection and energy saving, but is limited by the high cost of resin regeneration, low production efficiency and short resin life. For example, patent CN115448332 discloses a method for preparing potassium carbonate by fixed bed continuous ion exchange. Although the product yield is improved by optimizing the resin washing process, the complex process flow, high equipment cost and low potassium bicarbonate solution concentration result in a large amount of water evaporation and a significant increase in energy consumption.

[0004] CN1166453 discloses a method for the combined production of potassium carbonate and light magnesium carbonate. Although this method achieves a higher potassium carbonate yield under specific conditions, it is limited by the insufficient potassium chloride concentration (less than 10%) and the excessively high reaction pressure (10-20 MPa), resulting in limited production capacity, huge energy consumption, and high production and preparation costs.

[0005] In summary, the prior art has certain limitations in the preparation of potassium carbonate, either due to investment cost problems, environmental pollution problems, or low production efficiency. In view of the idle status of a large number of salt lake tailings in the process of salt lake resource utilization in my country, it is one of the key issues to be solved in the chemical industry to develop a potassium carbonate preparation process with low investment cost, simple process flow, low energy consumption, low pollution, high efficiency, and the ability to realize resource utilization of salt lake tailings and stable large-scale production. Therefore, the present invention is specially proposed. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for preparing potassium carbonate, so as to solve the problems of complicated preparation process, high energy consumption, low efficiency, high investment and production cost, and excessive waste of energy caused by the use of water in the preparation process in the prior art, which are particularly prominent in the large-scale production of potassium carbonate. Therefore, developing a potassium carbonate preparation process with low cost, high efficiency, environmental friendliness, simple operation and large-scale stable production has become one of the key issues to be solved in the chemical industry.

[0007] The invention provides a method for preparing potassium carbonate, which comprises the following steps: S1: mixing an inorganic magnesium salt and a potassium chloride aqueous solution, introducing CO2 gas to carry out a first reaction, and obtaining a first mixed slurry; separating the mixed slurry to obtain a first filter residue and a first filtrate; wherein the mass concentration of the potassium chloride aqueous solution is 18-50%; the pressure of the CO2 gas is 2-6Mpa; the pressure of the first reaction is the same as the pressure of the CO2 gas; S2: performing a first washing on the first filter residue with a first water to obtain a second filter residue and a second filtrate; returning the second filtrate to the system of the first reaction in step S1; S3: adding a second water to the second filter residue, heating it to carry out A second reaction is performed to obtain a second mixed slurry; the second mixed slurry is separated to obtain a third filter residue and a third filtrate; S4: the third filtrate is returned to S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 30-40%, thereby obtaining a third mixed slurry; S5: the third mixed slurry is separated to obtain a fourth filter residue and a fourth filtrate; the fourth filtrate is successively concentrated and cooled to obtain a fourth mixed slurry; S6: the fourth mixed slurry is separated to obtain a fifth filter residue and a fifth filtrate, and the fifth filter residue is first dried to obtain a potassium carbonate product; the fifth filtrate is returned to step S4 as at least part of the second water.

[0008] Furthermore, the preparation method also includes: after mixing the third filter residue and the fourth filter residue, adding the third water thereto, performing heating and slurry washing to obtain a fifth mixed slurry; separating the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; performing a second drying on the sixth filter residue to obtain basic magnesium carbonate; returning the sixth filtrate to step S3 as at least part of the second water; preferably, the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue is (1 to 3): 1; preferably, the temperature of the heating and slurry washing is 60 to 90° C., and the time of the heating and slurry washing is 30 to 60 min; preferably, the temperature of the second drying is 110 to 150° C., and the time of the second drying is 3 to 5 h.

[0009] Furthermore, when the mass concentration of the potassium chloride aqueous solution is less than 30%, the pressure of the CO2 gas is 2 to 4 MPa; or, when the mass concentration of the potassium chloride aqueous solution is 30 to 50%, the pressure of the CO2 gas is 4 to 6 MPa; preferably, the temperature of the first reaction is 18 to 35°C, and the time of the first reaction is 2 to 8 hours; further preferably, the temperature of the first reaction is 20 to 25°C, and the time of the first reaction is 3 to 6 hours.

[0010] Furthermore, the temperature of the second reaction is 60-90°C, and the time of the second reaction is 30-120 min; preferably, the temperature of the second reaction is 80-90°C.

[0011] Furthermore, the inorganic magnesium salt includes one or more of magnesium carbonate, basic magnesium carbonate, magnesium chloride, magnesium sulfate and magnesium hydroxide; preferably, the inorganic magnesium salt is prepared from salt lake tailings; preferably, potassium chloride is prepared from salt lake brine.

[0012] Furthermore, the Mg in the inorganic magnesium salt 2+ and potassium chloride aqueous solution K + The molar ratio of Mg in the inorganic magnesium salt is 1.2 to 1.6; preferably, the Mg in the inorganic magnesium salt 2+ and potassium chloride aqueous solution K + The molar ratio is 1.4 to 1.5.

[0013] Furthermore, the first washing further comprises: mixing and stirring the first water and the first filter residue, and then separating the solid and the liquid to obtain a second filter residue and a second filtrate; preferably, the stirring temperature is 0°C to 30°C; and the stirring time is 15 to 60 minutes.

[0014] Furthermore, in the step of concentrating the fourth filtrate in step S5, water in the fourth filtrate is evaporated to 70-90% of the original volume; in the cooling operation step, the concentrated fourth filtrate is cooled to 0-35°C to obtain a fourth mixed slurry; preferably, the concentrated fourth filtrate is cooled to 15-25°C to obtain a fourth mixed slurry.

[0015] Furthermore, the mass ratio of the first filter residue to the first water is (1-3):1; preferably, the mass ratio of the first filter residue to the first water is (1.5-2):1; preferably, the mass ratio of the second filter residue to the second water is 1:(3-10); further preferably, the mass ratio of the second filter residue to the second water is 1:(5-7).

[0016] Furthermore, the temperature of the first drying is 200-300° C.; preferably, the time of the first drying is 3-5 hours.

[0017] The present invention proposes a method for preparing potassium carbonate, which is formed by an inorganic magnesium salt and a potassium chloride aqueous solution with carbon dioxide into an Engel's double salt of potassium bicarbonate with low solubility, and then the Engel's double salt is decomposed, and a potassium carbonate product is prepared by multiple separation operations. The present invention improves the potassium carbonate preparation capacity and reduces the preparation energy consumption by increasing the concentration of the potassium chloride aqueous solution in the preparation process and reducing the pressure of the CO2 gas introduced, effectively improving the efficiency of potassium carbonate production and reducing its production cost. In addition, the preparation method further reuses the filtrate generated in the separation process, reduces the amount of water used in the preparation process, and can also reduce pollution and reduce the cost of treating wastewater. The method has the advantages of a simple process flow, and the preparation method has low investment cost for equipment, which is of great significance especially for the large-scale production of potassium carbonate. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0019] As described in the background technology section, the existing technology has certain limitations in the preparation of potassium carbonate due to cost issues, environmental pressures, or low efficiency. In view of the fact that a large number of salt lake tailings are idle in the process of utilizing salt lake resources in my country, it has become one of the key issues to be solved in the chemical industry to develop a potassium carbonate preparation process that has simple process flow, low energy consumption, low pollution, high efficiency, low cost, can realize the resource utilization of idle salt lake tailings resources, and can achieve stable large-scale production.

[0020] In order to solve the above problems, the present invention proposes a method for preparing potassium carbonate, which comprises: firstly mixing an inorganic magnesium salt and a potassium chloride aqueous solution, introducing CO2 gas to carry out a first reaction, and obtaining a first mixed slurry; then separating the mixed slurry to obtain a first filter residue and a first filtrate; wherein the mass concentration of the potassium chloride aqueous solution is 18-50%; the pressure of the CO2 gas is 2-6Mpa; the pressure of the first reaction is the same as the pressure of the CO2 gas; S2: washing the first filter residue with a first water to obtain a second filter residue and a second filtrate; returning the second filtrate to the first filter residue; Return to the system of the first reaction of step S1; S3: add second water to the second filter residue, heat to carry out a second reaction, and obtain a second mixed slurry; separate the second mixed slurry to obtain a third filter residue and a third filtrate; S4: return the third filtrate to S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 30-40%, and obtain a third mixed slurry; S5: separate the third mixed slurry to obtain a fourth filter residue and a fourth filtrate; concentrate and cool the fourth filtrate in sequence to obtain a fourth mixed slurry;

[0021] S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate, perform a first drying on the fifth filter residue to obtain a potassium carbonate product; return the fifth filtrate to step S4 as at least part of the second water.

[0022] Specifically, the preparation method first mixes an inorganic magnesium salt and a potassium chloride aqueous solution, and introduces CO2 gas therein to react the magnesium salt and potassium chloride therein to generate Engel's double salt (KHCO3·MgCO3·4H2O) containing potassium bicarbonate. Since the Engel's double salt has a low solubility, it can be precipitated from the reaction system, and the first filter residue of the Engel's double salt (containing a small amount of magnesium carbonate trihydrate) whose main component is potassium bicarbonate and the first filtrate containing soluble salts such as potassium chloride and magnesium chloride can be obtained by filtering and separating it. In particular, the inventor creatively found through a large number of experiments that controlling the mass concentration of the potassium chloride aqueous solution in the process to 18-50%, and controlling the pressure of the CO2 gas introduced in the first reaction process to 2-6Mpa, can make the generation of the Engel's double salt faster and the conversion rate higher, thereby effectively improving the preparation efficiency of potassium carbonate. It is speculated that it may be due to the following reasons: First, the increase in the solubility of carbon dioxide in the system caused by the salt effect: When the concentration of potassium chloride increases, the ionic strength in the solution increases accordingly, which may change the chemical equilibrium and reaction rate of the reaction system, so that the reaction can still be carried out effectively at a lower pressure. The salt effect can affect the chemical equilibrium between the reactants, causing more CO2 to dissolve in the solution, fully contact and react with potassium chloride, which is conducive to the formation of potassium carbonate. Second, the reaction kinetics change: The increase in potassium chloride concentration may change the kinetic path of the reaction, making the reaction mechanism more efficient. At high concentrations, the probability of collision between reactants increases, which may form a more effective reaction path, thereby achieving a good conversion rate at a lower pressure. Third, the chemical equilibrium moves: According to Le Chatelier's principle, increasing the concentration of reactants will cause the chemical equilibrium to move in the direction of the product. Therefore, increasing the concentration of potassium chloride may cause the equilibrium to move in the direction of potassium carbonate, which can promote the formation of potassium carbonate even at a lower pressure.

[0023] In addition, controlling the mass concentration of the potassium chloride aqueous solution in the first reaction process to a higher range of 18 to 50% can effectively increase the production capacity in the potassium carbonate preparation process. Controlling the pressure of the CO2 gas introduced in the first reaction process to a lower pressure of 2 to 6Mpa can reduce the energy consumption in the preparation process. At the same time, the pressure of the first reaction is the same as the pressure of the CO2 gas, both within a lower range, which can further reduce the energy consumption in the preparation of potassium carbonate. The optimization of the above reaction conditions has obvious effects on increasing production capacity and reducing energy consumption, especially in the large-scale production of potassium carbonate, the above favorable effects are of great significance. The reaction equation involved in the above process is:

[0024] Mg 2+ +2CO2+3H2O→MgCO3·3H2O;

[0025] 2KCl+3(MgCO3·3H2O)+CO2=2(KHCO3·MgCO3·4H2O)+MgCl2.

[0026] Further, the first filter residue is washed with the first water, and the soluble salts such as potassium chloride and magnesium chloride carried on the surface of the Engel's double salt containing a small amount of magnesium carbonate trihydrate are washed away to obtain a cleaner Engel's double salt containing a small amount of magnesium carbonate trihydrate, and the obtained second filtrate is a dilute solution containing potassium chloride and magnesium chloride, so it can continue to return to the system of the first reaction in step S1 for further recycling. Secondly, the second water is added to the washed second filter residue with the Engel's double salt as the main component, and then heated to carry out the second reaction. This process can decompose the Engel's double salt to obtain a third filter residue with basic magnesium carbonate and magnesium carbonate trihydrate as the main components and a third filtrate dissolved with potassium bicarbonate and potassium carbonate. The third filtrate is returned to S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated new third filtrate is 30-40%, and a third mixed slurry is obtained. This operation step is mainly to further enrich the third filtrate containing potassium bicarbonate and potassium carbonate to obtain a high concentration of a mixed solution containing potassium bicarbonate and potassium carbonate. The third mixed slurry is separated to obtain a fourth filter residue and a fourth filtrate, wherein the fourth filter residue is mainly composed of basic magnesium carbonate and magnesium carbonate trihydrate, and the fourth filtrate is a mixed solution of potassium bicarbonate and potassium carbonate at a high concentration after enrichment. The fourth filtrate is sequentially concentrated and cooled to obtain a fourth mixed slurry, and the process can precipitate potassium bicarbonate and potassium carbonate after concentration and cooling. The fourth mixed slurry is separated to obtain a fifth filter residue and a fifth filtrate, wherein the fifth filter residue is the potassium bicarbonate and potassium carbonate precipitated after concentration and cooling, and the fifth filtrate is a saturated potassium bicarbonate solution. The fifth filter residue is dried to obtain a potassium carbonate product, and the fifth filtrate is returned to step S4 as at least part of the second water. The above process can not only obtain potassium carbonate products that meet quality requirements, but also further utilize the filtrate generated during the separation process, reduce the amount of water used in the preparation process, and avoid water pollution problems and increased preparation costs caused by treating large amounts of wastewater. The reaction equation involved in this process is:

[0027] KHCO3·MgCO3·4H2O=KHCO3+MgCO3·3H2O+H2O;

[0028] 5[MgCO3·3H2O]→4MgCO3·Mg(OH)2·4H2O+10H2O+CO2.

[0029] In summary, in the above-mentioned preparation method, by increasing the mass concentration of potassium chloride aqueous solution in the first reaction process, and reducing the pressure of the CO2 gas passed in, while making the potassium carbonate product have a higher yield, it is also possible to improve the preparation capacity, reduce the preparation energy consumption, and effectively improve the efficiency of potassium carbonate production and preparation. In addition, the filtrate produced in the separation process is further utilized in the preparation process, reducing the amount of water used in the preparation process, and can also reduce pollution, reducing the cost caused by treating wastewater. The above-mentioned preparation method has the advantages of simple process flow, high efficiency, low energy consumption, etc., which is of great significance for the large-scale production of potassium carbonate.

[0030] In a preferred embodiment, the preparation method further comprises: after mixing the third filter residue and the fourth filter residue, adding the third water thereto, performing heating and slurry washing, and obtaining a fifth mixed slurry; separating the fifth mixed slurry, obtaining a sixth filter residue and a sixth filtrate; performing a second drying on the sixth filter residue, obtaining basic magnesium carbonate; and returning the sixth filtrate to step S3 as at least part of the second water. The main components of the third filter residue and the fourth filter residue are basic magnesium carbonate and magnesium carbonate trihydrate, and some soluble salts, such as potassium bicarbonate and potassium carbonate, may remain on the surface. Mixing the third filter residue and the fourth filter residue and adding water for heating and slurry washing can convert all magnesium salts in the solid sample into basic magnesium carbonate, and wash the soluble salts such as potassium bicarbonate and potassium carbonate attached to the surface of the mixture of the third filter residue and the fourth filter residue and dissolve them in the system. The fifth mixed slurry is separated to obtain a sixth filter residue and a sixth filtrate, wherein the sixth filter residue is basic magnesium carbonate, and the sixth filtrate is a dilute solution of potassium bicarbonate and potassium carbonate, and the sixth filter residue is subjected to a second drying to obtain basic magnesium carbonate; the sixth filtrate is returned to step S3 as at least part of the second water. The above-mentioned preparation and separation operation can further obtain basic magnesium carbonate in the process of preparing potassium carbonate, further improving the value of the additives produced in the process of preparing potassium carbonate.

[0031] Preferably, the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue is (1-3):1; preferably, the temperature of the heating pulp washing is 60-90°C, and the time of the heating pulp washing is 30-60 minutes; by controlling the amount of the third water added and the temperature of the heating pulp washing within the above range, a higher purity basic magnesium carbonate can be obtained, and the amount of the third water added and the sixth filtrate can be accurately controlled to further reduce costs and be more environmentally friendly. Preferably, the temperature of the second drying is 110-150°C, and the time of the second drying is 3-5 hours.

[0032] In a preferred embodiment, when the mass concentration of the potassium chloride aqueous solution is less than 30%, the pressure of the CO2 gas is 2 to 4Mpa; or, when the mass concentration of the potassium chloride aqueous solution is 30 to 50%, the pressure of the CO2 gas is 4 to 6Mpa. Controlling the mass concentration of the potassium chloride aqueous solution and the pressure of the CO2 gas within the above-mentioned more preferred range, and matching them accordingly, can make the yield of the prepared potassium carbonate higher, and further reduce energy consumption while increasing production capacity. Preferably, the temperature of the first reaction is 18 to 35°C, and the time of the first reaction is 2 to 8h; the above reaction temperature range is usually almost in the room temperature range, and the temperature of the first reaction is controlled within the above range, and the reaction can be achieved without additional heating. It is precisely because the present application strictly controls the mass concentration of the potassium chloride aqueous solution and the pressure of the CO2 gas that the reaction can be carried out in the above mild state, which is conducive to further reducing energy consumption. Further preferably, the temperature of the first reaction is 20 to 25°C, and the time of the first reaction is 3 to 6h. The above reaction conditions can make the overall reaction effect better.

[0033] In a preferred embodiment, the temperature of the second reaction is 60-90°C, and the time of the second reaction is 30-120 minutes; the second reaction process is to promote the decomposition reaction of Engel's double salt, and the temperature and time of the second reaction are controlled within the above range to completely decompose the Engel's double salt to produce potassium bicarbonate, basic magnesium carbonate and magnesium carbonate trihydrate. Preferably, the temperature of the second reaction is 80-90°C.

[0034] In a preferred embodiment, the inorganic magnesium salt includes one or more of magnesium carbonate, basic magnesium carbonate, magnesium chloride, magnesium sulfate and magnesium hydroxide. Preferably, the inorganic magnesium salt is prepared from salt lake tailings; preferably, potassium chloride is prepared from salt lake brine. my country is rich in salt lake resources. After potassium chloride is prepared from salt lake brine, a large amount of salt lake tailings halide magnesium ore solution will remain idle. The method for preparing potassium carbonate described in the present invention can further utilize the salt lake tailings. The potassium chloride and inorganic magnesium salt raw materials used are widely available and easy to obtain. While the salt lake tailings solution is utilized as a resource, the production cost of potassium carbonate and the difficulty of obtaining raw material inorganic magnesium salt resources can be greatly reduced. In addition, the preparation method is simple to operate, especially its preparation does not require further purchase of expensive equipment, the investment cost is low, and it is easier to implement. The preparation method proposed in the present invention has good practicality, especially for areas with rich salt lake tailings resources. In addition, in the process of preparing potassium carbonate using salt lake tailings resources, it is also possible to further enrich elements such as lithium, bromine, and boron contained in the salt lake tailings resources, which is more conducive to later extraction and further improves the added value of the preparation process.

[0035] In a preferred embodiment, the Mg in the inorganic magnesium salt 2+ and potassium chloride aqueous solution K+ The molar ratio of Mg in the inorganic magnesium salt is 1.2 to 1.6; 2+ and potassium chloride aqueous solution K + The addition ratio of Mg in the inorganic magnesium salt is controlled within the above range, which can make the reaction more complete and help improve production efficiency. 2+ and potassium chloride aqueous solution K + The molar ratio is 1.4 to 1.5.

[0036] In a preferred embodiment, the first water and the first filter residue are mixed and stirred, and then the solid and liquid are separated to obtain the second filter residue and the second filtrate; preferably, the stirring temperature is 0°C to 30°C; the stirring time is 15 to 60 minutes. During the first washing process, the operation under the above conditions can make the washing more complete and the first filter residue and the first filtrate more completely separated.

[0037] In a preferred embodiment, in the step of concentrating the fourth filtrate in step S5, the water in the fourth filtrate is evaporated to 70-90% of the original volume; in the cooling operation step, the concentrated fourth filtrate is cooled to 0-35°C to obtain a fourth mixed slurry; preferably, the concentrated fourth filtrate is cooled to 15-25°C to obtain a fourth mixed slurry. After evaporating and concentrating the water in the fourth filtrate and then further cooling it, more components in the fourth mixed slurry can be converted into potassium carbonate and potassium bicarbonate, which is conducive to further improving the yield.

[0038] In a preferred embodiment, the mass ratio of the first filter residue to the first water is (1-3):1; preferably, the mass ratio of the second filter residue to the second water is 1:(3-10); controlling the addition ratio of the first filter residue to the first water during the first reaction and the addition ratio of the second filter residue to the second water during the second reaction within the above range can reduce the amount of water used, energy consumption and cost while allowing the reaction to proceed smoothly. Preferably, the mass ratio of the first filter residue to the first water is (1.5-2):1; further preferably, the mass ratio of the second filter residue to the second water is 1:(5-7).

[0039] In a preferred embodiment, the temperature of the first drying is 200-300°C; preferably, the time of the first drying is 3-5 hours. Controlling the drying conditions within the above range can make the quality of the prepared potassium carbonate product better.

[0040] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0041] Example 1

[0042] S1: Prepare a 30% potassium chloride aqueous solution, mix it and place it in a high-pressure reactor, add magnesium carbonate trihydrate into it, so that the Mg content of the solution is 2+ and K + The molar ratio is 1.5. A high-pressure CO2 gas of 4 MPa is introduced into the autoclave, and the reaction is stirred at 25°C for 4 hours to obtain a first mixed slurry, and the first mixed slurry is separated to obtain a first filter residue and a first filtrate; the pressure of the first reaction is 4 MPa;

[0043] S2: Mix the first filter residue and the first water at a mass ratio of 1.5:1, stir at 25°C for 30 minutes, and separate to obtain a second filter residue and a second filtrate. Return the second filtrate to the first reaction system in step S1.

[0044] S3: Mix the second filter residue and the second water in a mass ratio of 1:5, and stir at 80°C for 30 minutes to obtain a second mixed slurry. Separate the second mixed slurry to obtain a third filter residue and a third filtrate;

[0045] S4: returning the third filtrate to step S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 35%, thereby obtaining a third mixed slurry.

[0046] S5: Separating the third mixed slurry to obtain a fourth filter residue and a fourth filtrate, evaporating the fourth filtrate to 80% of the original volume, and then cooling it to 25° C. to obtain a fourth mixed slurry.

[0047] S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate. Return the fifth filtrate to step S4 as at least part of the second water; dry the fifth filter residue at 250° C. for 4 hours to obtain a potassium carbonate product;

[0048] S7: After mixing the third filter residue and the fourth filter residue, add the third water thereto, wash at 80°C for 45 minutes to obtain a fifth mixed slurry; separate the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; dry the sixth filter residue at 120°C for 4 hours to obtain basic magnesium carbonate; return the sixth filtrate to step S3 as at least part of the second water, and the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue in this process is 2:1.

[0049] Example 2

[0050] S1: Prepare a 30% potassium chloride aqueous solution, mix it and place it in a high-pressure reactor, add magnesium carbonate trihydrate into it, so that the Mg content of the solution is 2+ and K +The molar ratio is 1.2. 4Mpa high-pressure CO2 gas is introduced into the autoclave, and the reaction is stirred at 35°C for 2 hours to obtain a first mixed slurry, and the first mixed slurry is separated to obtain a first filter residue and a first filtrate; the pressure of the first reaction is 4MPa;

[0051] S2: Mix the first filter residue and the first water in a mass ratio of 1:1, stir at 0°C for 60 minutes, and separate to obtain a second filter residue and a second filtrate. Return the second filtrate to the first reaction system of step S1.

[0052] S3: Mix the second filter residue and the second water in a mass ratio of 1:10, and stir at 60°C for 120 minutes to obtain a second mixed slurry. Separate the second mixed slurry to obtain a third filter residue and a third filtrate;

[0053] S4: returning the third filtrate to step S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 30%, thereby obtaining a third mixed slurry.

[0054] S5: separating the third mixed slurry to obtain a fourth filter residue and a fourth filtrate, evaporating the fourth filtrate to 70% of the original volume, and then cooling it to 0° C. to obtain a fourth mixed slurry.

[0055] S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate. Return the fifth filtrate to step S4 as at least part of the second water; dry the fifth filter residue at 200° C. for 5 hours to obtain a potassium carbonate product;

[0056] S7: After mixing the third filter residue and the fourth filter residue, add the third water thereto, wash at 60°C for 60 minutes to obtain a fifth mixed slurry; separate the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; dry the sixth filter residue at 110°C for 5 hours to obtain basic magnesium carbonate; return the sixth filtrate to step S3 as at least part of the second water, and the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue in this process is 1:1.

[0057] Example 3

[0058] S1: Prepare a 30% potassium chloride aqueous solution, mix it and place it in a high-pressure reactor, add magnesium carbonate trihydrate into it, so that the Mg content of the solution is 2+ and K + The molar ratio is 1.6. A high-pressure CO2 gas of 4 MPa is introduced into the autoclave, and the reaction is stirred at 18°C ​​for 8 hours to obtain a first mixed slurry, and the first mixed slurry is separated to obtain a first filter residue and a first filtrate; the pressure of the first reaction is 4 MPa;

[0059] S2: Mix the first filter residue and the first water in a mass ratio of 3:1, stir at 30°C for 15 minutes, and separate to obtain a second filter residue and a second filtrate. Return the second filtrate to the first reaction system of step S1.

[0060] S3: Mix the second filter residue and the second water in a mass ratio of 1:3, and stir at 90°C for 30 minutes to obtain a second mixed slurry. Separate the second mixed slurry to obtain a third filter residue and a third filtrate;

[0061] S4: returning the third filtrate to step S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 40%, thereby obtaining a third mixed slurry.

[0062] S5: Separating the third mixed slurry to obtain a fourth filter residue and a fourth filtrate, evaporating the fourth filtrate to 90% of the original volume, and then cooling it to 35° C. to obtain a fourth mixed slurry.

[0063] S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate. Return the fifth filtrate to step S4 as at least part of the second water; dry the fifth filter residue at 300° C. for 3 hours to obtain a potassium carbonate product;

[0064] S7: After mixing the third filter residue and the fourth filter residue, add the third water thereto, wash at 90°C for 30 minutes to obtain a fifth mixed slurry; separate the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; dry the sixth filter residue at 150°C for 3 hours to obtain basic magnesium carbonate; return the sixth filtrate to step S3 as at least part of the second water, and the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue in this process is 3:1.

[0065] Example 4

[0066] S1: Prepare a 30% potassium chloride aqueous solution, mix it and place it in a high-pressure reactor, add magnesium carbonate trihydrate into it, so that the Mg content of the solution is 2+ and K + The molar ratio is 1.4. A high-pressure CO2 gas of 4 MPa is introduced into the autoclave, and the reaction is stirred at 20°C for 3 hours to obtain a first mixed slurry, and the first mixed slurry is separated to obtain a first filter residue and a first filtrate; the pressure of the first reaction is 4 MPa;

[0067] S2: Mix the first filter residue and the first water at a mass ratio of 1.5:1, stir at 25°C for 45 minutes, and separate to obtain a second filter residue and a second filtrate. Return the second filtrate to the system used as the first reaction in step S1.

[0068] S3: Mix the second filter residue and the second water in a mass ratio of 1:5, and stir at 80°C for 60 minutes to obtain a second mixed slurry. Separate the second mixed slurry to obtain a third filter residue and a third filtrate;

[0069] S4: returning the third filtrate to step S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 35%, thereby obtaining a third mixed slurry.

[0070] S5: Separating the third mixed slurry to obtain a fourth filter residue and a fourth filtrate, evaporating the fourth filtrate to 80% of the original volume, and then cooling it to 15° C. to obtain a fourth mixed slurry.

[0071] S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate. Return the fifth filtrate to step S4 as at least part of the second water; dry the fifth filter residue at 250° C. for 4 hours to obtain a potassium carbonate product;

[0072] S7: After mixing the third filter residue and the fourth filter residue, add the third water thereto, wash at 80°C for 45 minutes to obtain a fifth mixed slurry; separate the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; dry the sixth filter residue at 120°C for 4 hours to obtain basic magnesium carbonate; return the sixth filtrate to step S3 as at least part of the second water, and the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue in this process is 2:1.

[0073] Example 5

[0074] S1: Prepare a 30% potassium chloride aqueous solution, mix it and place it in a high-pressure reactor, add magnesium carbonate trihydrate into it, so that the Mg content of the solution is 2+ and K + The molar ratio is 1.5. A high-pressure CO2 gas of 4 MPa is introduced into the autoclave, and the reaction is stirred at 25°C for 6 hours to obtain a first mixed slurry, and the first mixed slurry is separated to obtain a first filter residue and a first filtrate; the pressure of the first reaction is 4 MPa;

[0075] S2: Mix the first filter residue and the first water in a mass ratio of 2:1, stir at 25°C for 45 minutes, and separate to obtain a second filter residue and a second filtrate. Return the second filtrate to the first reaction system of step S1.

[0076] S3: Mix the second filter residue and the second water in a mass ratio of 1:7, and stir at 90°C for 60 minutes to obtain a second mixed slurry. Separate the second mixed slurry to obtain a third filter residue and a third filtrate;

[0077] S4: returning the third filtrate to step S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 35%, thereby obtaining a third mixed slurry.

[0078] S5: Separating the third mixed slurry to obtain a fourth filter residue and a fourth filtrate, evaporating the fourth filtrate to 80% of the original volume, and then cooling it to 25° C. to obtain a fourth mixed slurry.

[0079] S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate. Return the fifth filtrate to step S4 as at least part of the second water; dry the fifth filter residue at 250° C. for 4 hours to obtain a potassium carbonate product;

[0080] S7: After mixing the third filter residue and the fourth filter residue, add the third water thereto, wash at 80°C for 45 minutes to obtain a fifth mixed slurry; separate the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; dry the sixth filter residue at 120°C for 4 hours to obtain basic magnesium carbonate; return the sixth filtrate to step S3 as at least part of the second water, and the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue in this process is 2:1.

[0081] Example 6

[0082] The difference between Example 6 and Example 1 is that the concentration of the potassium chloride aqueous solution is 18% and the pressure of the CO2 gas is 2 MPa.

[0083] Example 7

[0084] The difference between Example 7 and Example 1 is that the concentration of the potassium chloride aqueous solution is 25%, and the pressure of the CO2 gas is 3.5 MPa.

[0085] Example 8

[0086] The difference between Example 8 and Example 1 is that the concentration of the potassium chloride aqueous solution is 50% and the pressure of the CO2 gas is 6 MPa.

[0087] Example 9

[0088] The difference between Example 9 and Example 1 is that the concentration of the potassium chloride aqueous solution is 18% and the pressure of the CO2 gas is 6 MPa.

[0089] Example 10

[0090] The difference between Example 10 and Example 1 is:

[0091] S3: Mix the second filter residue and the second water in a mass ratio of 1:2, and stir at 50°C for 30 minutes to obtain a second mixed slurry. Separate the second mixed slurry to obtain a third filter residue and a third filtrate;

[0092] S4: returning the third filtrate to step S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 20%, thereby obtaining a third mixed slurry.

[0093] Comparative Example 1

[0094] The difference between Comparative Example 1 and Example 1 is that the mass concentration of the potassium chloride aqueous solution is 10%, and the pressure of the CO2 gas is 4 MPa.

[0095] Comparative Example 2

[0096] The difference between Comparative Example 2 and Example 1 is that the mass concentration of the potassium chloride aqueous solution is 10%, and the pressure of the CO2 gas is 20 MPa.

[0097] The preparation results of Examples 1 to 10 and Comparative Examples 1 and 2 are shown in Table 1. The test methods involved include:

[0098] Determination of potassium carbonate purity: Since the impurities present in the prepared potassium carbonate product are Na + Mg 2+ In the process of testing its purity, ICP-OES was used to determine the Na + , ICP-OES analysis was used to determine the K + Mg was determined by ICP-OES supplemented with EDTA analysis. 2+ , the CO3 was determined by acid-base titration 2- , so as to comprehensively determine the purity of potassium carbonate in the product;

[0099] Potassium carbonate yield: K in potassium carbonate product + Molar amount / K in the KCl feed + molar amount × 100%;

[0100] Daily production capacity of potassium carbonate: In both the examples and comparative examples, a 50 L high-pressure reactor was used for the first reaction during the experiment, and the daily production capacity of potassium carbonate was calculated based on this as a unified measure.

[0101] Table 1

[0102]

[0103] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0104] Embodiments 1 to 10 are methods for preparing potassium carbonate provided by the present invention. The preparation process controls the mass concentration of potassium chloride aqueous solution to 18-50%; controls the pressure of CO2 gas to 2-6Mpa, and the prepared potassium carbonate has a higher purity and yield. In addition, increasing the concentration of potassium chloride and reducing the pressure of CO2 gas can effectively reduce the energy consumption in the process of preparing potassium carbonate and increase the production capacity in the process of preparing potassium carbonate. In particular, when the mass concentration of potassium chloride aqueous solution is less than 30%, the pressure of CO2 gas is 2-4Mpa; or, when the mass concentration of potassium chloride aqueous solution is 30-50%, the pressure of CO2 gas is 4-6Mpa, not only potassium carbonate has a higher purity and yield, but also can further save energy consumption.

[0105] In Comparative Example 1, the mass concentration of the potassium chloride aqueous solution is 10%, and the pressure of CO2 gas is 4MPa. The concentration of potassium chloride is relatively low, and the yield of potassium carbonate prepared is relatively low, and its daily production capacity is also relatively low compared with the embodiment of the present invention. In Comparative Example 2, the mass concentration of the potassium chloride aqueous solution is 10%, and the pressure of CO2 gas is 20MPa. The concentration of potassium chloride is relatively low. Although the pressure of CO2 gas is increased, the yield and daily production capacity of potassium carbonate are still relatively large compared with those in the embodiment of the present invention.

[0106] In summary, by utilizing the method for preparing potassium carbonate of the present invention, the mass concentration of the potassium chloride aqueous solution is controlled to be 18-50%; and the pressure of the CO2 gas is controlled to be 2-6Mpa, which can effectively improve the yield and production capacity of potassium carbonate, not only improve the production efficiency of potassium carbonate, but also further reduce the cost.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing potassium carbonate, characterized in that: The preparation method comprises the following steps: S1: Mixing an inorganic magnesium salt and a potassium chloride aqueous solution, introducing CO2 gas to carry out a first reaction, and obtaining a first mixed slurry; separating the mixed slurry to obtain a first filter residue and a first filtrate; wherein the mass concentration of the potassium chloride aqueous solution is 18-50%; the pressure of the CO2 gas is 2-6Mpa; the pressure of the first reaction is the same as the pressure of the CO2 gas; S2: washing the first filter residue with first water to obtain a second filter residue and a second filtrate; returning the second filtrate to the first reaction system of step S1; S3: adding second water to the second filter residue, heating to perform a second reaction, and obtaining a second mixed slurry; separating the second mixed slurry to obtain a third filter residue and a third filtrate; S4: returning the third filtrate to S3 as at least part of the second water to repeat the operation of step S3 until the mass concentration of KHCO3 in the separated third filtrate is 30-40%, thereby obtaining a third mixed slurry; S5: separating the third mixed slurry to obtain a fourth filter residue and a fourth filtrate; concentrating and cooling the fourth filtrate in sequence to obtain a fourth mixed slurry; S6: Separate the fourth mixed slurry to obtain a fifth filter residue and a fifth filtrate, perform a first drying on the fifth filter residue to obtain a potassium carbonate product; return the fifth filtrate to step S4 as at least part of the second water.

2. The method for preparing potassium carbonate according to claim 1, wherein The preparation method further comprises: After the third filter residue and the fourth filter residue are mixed, the third water is added thereto, and heating and slurry washing are performed to obtain a fifth mixed slurry; Separating the fifth mixed slurry to obtain a sixth filter residue and a sixth filtrate; performing a second drying on the sixth filter residue to obtain basic magnesium carbonate; returning the sixth filtrate to step S3 as at least part of the second water; Preferably, the weight ratio of the third water to the total amount of the third filter residue and the fourth filter residue is (1-3):1; Preferably, the temperature of the heated pulping is 60 to 90° C., and the time of the heated pulping is 30 to 60 minutes; Preferably, the temperature of the second drying is 110-150° C., and the time of the second drying is 3-5 hours.

3. The method for preparing potassium carbonate according to claim 1, characterized in that When the mass concentration of the potassium chloride aqueous solution is below 30%, the pressure of the CO2 gas is 2-4 MPa; or When the mass concentration of the potassium chloride aqueous solution is 30-50%, the pressure of the CO2 gas is 4-6Mpa; Preferably, the temperature of the first reaction is 18 to 35° C., and the time of the first reaction is 2 to 8 hours; More preferably, the temperature of the first reaction is 20-25° C., and the time of the first reaction is 3-6 hours.

4. The method for preparing potassium carbonate according to any one of claims 1 to 3, characterized in that The temperature of the second reaction is 60 to 90° C., and the time of the second reaction is 30 to 120 min; Preferably, the temperature of the second reaction is 80-90°C.

5. The method for preparing potassium carbonate according to any one of claims 1 to 3, characterized in that The inorganic magnesium salt includes one or more of magnesium carbonate, basic magnesium carbonate, magnesium chloride, magnesium sulfate and magnesium hydroxide; Preferably, the inorganic magnesium salt is prepared from salt lake tailings; Preferably, the potassium chloride is prepared from salt lake brine.

6. The method for preparing potassium carbonate according to any one of claims 1 to 5, characterized in that The Mg in the inorganic magnesium salt 2+ and K in the potassium chloride aqueous solution + The molar ratio is 1.2 to 1.6; Preferably, the Mg in the inorganic magnesium salt is 2+ and K in the potassium chloride aqueous solution + The molar ratio is 1.4 to 1.

5.

7. The method for preparing potassium carbonate according to any one of claims 1 to 5, characterized in that The first washing further comprises: mixing and stirring the first water and the first filter residue, and then separating the solid and the liquid to obtain the second filter residue and the second filtrate; preferably, the stirring temperature is 0°C to 30°C; and the stirring time is 15 to 60 minutes.

8. The method for preparing potassium carbonate according to any one of claims 1 to 5, characterized in that In step S5, in the step of concentrating the fourth filtrate, water in the fourth filtrate is evaporated to 70-90% of the original volume; in the cooling operation step, the concentrated fourth filtrate is cooled to 0-35° C. to obtain the fourth mixed slurry; Preferably, the fourth filtrate after concentration is cooled to 15-25° C. to obtain the fourth mixed slurry.

9. The method for preparing potassium carbonate according to any one of claims 1 to 5, characterized in that The mass ratio of the first filter residue to the first water is (1-3):1; preferably, the mass ratio of the first filter residue to the first water is (1.5-2):1; Preferably, the mass ratio of the second filter residue to the second water is 1:(3-10); Further preferably, the mass ratio of the second filter residue to the second water is 1:(5-7).

10. The method for preparing potassium carbonate according to any one of claims 1 to 5, characterized in that The first drying temperature is 200-300°C; Preferably, the first drying time is 3 to 5 hours.

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