CN113880119A - Method for preparing potassium sulfate from potassium chloride - Google Patents
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- C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
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- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
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Abstract
The invention provides a method for preparing potassium sulfate by potassium chloride, which takes the potassium chloride as a potassium source and soluble sulfate as a sulfur source, and can obtain the potassium sulfate, sodium chloride and calcium sulfate through a certain reaction, thereby overcoming the defect of preparing the potassium sulfate by a Mannheim method and improving the utilization rate of potassium; the method has the advantages of clean process, simple flow and low cost, the utilization rate of potassium reaches more than 95.1 percent, the purity of the potassium sulfate product is not less than 97 percent by weight, the requirement of qualified powdery crystalline potassium sulfate products in GB/T20406-.
Description
Technical Field
The invention belongs to the technical field of inorganic chemical industry, and particularly relates to a method for preparing potassium sulfate from potassium chloride.
Background
The potassium sulfate is an important chemical raw material, is an agricultural potassium fertilizer with wide application, and is also an important raw material for preparing other potassium fertilizers. The main varieties of the potash fertilizer comprise potassium chloride, potassium sulfate, potassium nitrate and the like, and because chlorine has certain harm to soil and partial crops, the potassium chloride cannot be directly applied under most conditions and needs to be converted into the potassium sulfate; potassium nitrate is expensive and dangerous chemical, and the application is greatly limited; the potassium sulfate is low in price, and the sulfur and the potassium are effective elements, so that the potassium sulfate is harmless to soil, and is particularly suitable for partial crops which are free from chlorine, and therefore, the market demand is huge.
At present, besides the direct preparation of potassium sulfate in a salt lake system, the domestic potassium sulfate preparation process mainly uses potassium chloride as a raw material to prepare the potassium sulfate by a certain conversion method, and the main method comprises the following steps: the Mannheim process, the sodium sulfate process, the ammonium sulfate process, and the associative process.
The Mannheim method is a mainstream method of the current potassium sulfate preparation process, the method takes sulfuric acid and potassium chloride as raw materials, the preparation of the potassium sulfate is realized through high-temperature double decomposition reaction, hydrogen chloride is a byproduct, the obtained potassium sulfate has high purity and good quality, but the equipment is seriously corroded, and the average service life of a Mannheim furnace is about 1 year.
A sodium sulfate method: the method is characterized in that sodium sulfate and potassium chloride are used as raw materials to prepare the glaserite through liquid-phase double decomposition reaction, and the glaserite reacts with the potassium chloride to obtain the potassium sulfate.
The ammonium sulfate method is divided into a fire method and a wet method: the pyrogenic process is characterized in that ammonium sulfate and potassium chloride are used as raw materials to form potassium sulfate and ammonium chloride through a high-temperature solid-phase double decomposition reaction, the ammonium chloride is decomposed and volatilized at high temperature and is separated from the potassium sulfate, the method is similar to the Mannheim process, equipment is seriously corroded, the cost is high, and no industrial application example exists at present; the wet method is to use ammonium sulfate and potassium chloride as raw materials, obtain ammonium sulfate and potassium sulfate double salt through liquid-phase double decomposition reaction, and further wash the ammonium sulfate and potassium chloride to obtain potassium sulfate, for example, CN1093680A discloses a method for preparing potassium sulfate by converting ammonium sulfate and potassium chloride.
Association method: the method is carried out at normal temperature, has low energy consumption and large corrosion on equipment, but the cost of the extractant is high, and the subsequent problem of failure of a large amount of extractants in the production process causes the integral operation cost to be increased, the product quality to be poor, and finally causes the production stop of a part of production lines.
In summary, the mannheim method is still the mainstream technology in the current methods for preparing potassium sulfate by using potassium chloride as a raw material, and no other effective technology exists. However, the Mannheim method has serious corrosion on equipment, high energy consumption, serious pollution, limited market absorption capacity of byproduct hydrochloric acid, and frequent production stoppage of most enterprises due to high stock of hydrochloric acid. Therefore, a novel technology for preparing potassium sulfate from potassium chloride is needed to supplement the technical deficiency of the current potassium sulfate market, solve the problems of the traditional Mannheim method and further promote the technical upgrading and sustainable development of the industry.
Disclosure of Invention
The potassium chloride is used as a potassium source, the soluble sulfate is used as a sulfur source, and the potassium sulfate, the sodium chloride and the calcium sulfate can be obtained through a certain reaction, so that the defect of preparing the potassium sulfate by adopting a Mannheim method is overcome, and the method is favorable for industrial production.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for preparing potassium sulfate by potassium chloride, which comprises the following steps:
(1) mixing potassium chloride and soluble sulfate with water, adjusting the pH value, mixing with a precipitator for reaction, and carrying out solid-liquid separation after the reaction to obtain a potassium-containing precipitate and a precipitate mother liquor;
(2) mixing the potassium-containing precipitate obtained in the step (1) with a dissociating agent and water to perform a first reaction, and then performing solid-liquid separation to obtain a precipitate solid and a potassium sulfate solution;
mixing the precipitation mother liquor obtained in the step (1) with an impurity removing agent, adjusting the pH value to perform a second reaction, and then performing solid-liquid separation to obtain a purified precipitate and a purified solution;
(3) cooling and crystallizing the potassium sulfate solution obtained in the step (2) to obtain a potassium sulfate product and a crystallization mother liquor; the crystallization mother liquor is returned to the step (2) to participate in the first reaction;
mixing the precipitate solid and the purified precipitate obtained in the step (2) with water, adjusting the pH value to react, and then carrying out solid-liquid separation to obtain calcium sulfate and a precipitant regeneration solution; the precipitant regeneration solution is returned to the step (1) for recycling;
evaporating and crystallizing the purified solution obtained in the step (2) to obtain sodium chloride and an evaporation mother liquor; and (3) returning the evaporation mother liquor to the step (1) for recycling.
According to the method, potassium chloride is used as a potassium source, soluble sulfate is used as a sulfur source, and a reaction network is designed, so that potassium sulfate, sodium chloride and calcium sulfate products can be simply and efficiently obtained, the defect of preparing potassium sulfate by adopting a Mannheim method is overcome, the utilization rate of potassium is improved, the quality of the obtained product is guaranteed, a certain use standard is compounded, industrial production is facilitated, and certain economic benefits are achieved.
The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.
In a preferred embodiment of the present invention, the soluble sulfate in step (1) includes sodium sulfate, and the mass ratio of the soluble sulfate to the potassium chloride is 1: 1.1-1: 1.3, for example, 1:1.1, 1:1.2, or 1: 1.3; the pH is adjusted to 0 to 2, for example, 0, 0.5, 1, 1.5 or 2, and the above-mentioned values are not limited to the listed values, and other values not listed in the respective numerical ranges are also applicable, and preferably 1:1.1 to 1: 1.2.
In the invention, the regulator used for regulating the pH value in the step (1) is sulfuric acid.
As the preferred technical scheme of the invention, the temperature of the reaction in the step (1) is 10-90 ℃, such as 10 ℃, 20 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃ or 90 ℃ and the like; the time is 30 to 120min, for example 30min, 60min, 90min or 120min, preferably 30 to 60min, and the above values are not limited to the listed values, and other values not listed in the respective ranges of values are also applicable.
As a preferred technical scheme of the invention, the precipitator in the step (1) comprises any one or a combination of at least two of aluminum sulfate, aluminum chloride, ferric sulfate or ferric chloride, and typical but non-limiting examples of the combination are as follows: a combination of aluminum sulfate and aluminum chloride, a combination of ferric sulfate and ferric chloride, and the like.
As a preferred embodiment of the present invention, the dissociation agent in step (2) comprises any one or a combination of at least two of calcium carbonate, calcium oxide or calcium hydroxide, and the combination is typically but not limited to: combinations of calcium carbonate and calcium oxide, calcium oxide and calcium hydroxide, and the like; the addition amount of the dissociation agent is 0.2 to 1 time, for example, 0.2 time, 0.4 time, 0.6 time, 0.8 time, or 1 time, of the total mass of the potassium-containing precipitate, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned value range are also applicable, and preferably 0.3 to 0.6 time.
As a preferred technical solution of the present invention, the impurity removing agent in step (2) includes any one or a combination of at least two of calcium oxide, calcium hydroxide, calcium carbonate, sodium bicarbonate or sodium hydroxide, and typical but non-limiting examples of the combination are: combinations of calcium oxide and calcium hydroxide, combinations of sodium carbonate and sodium bicarbonate, combinations of calcium hydroxide and sodium hydroxide, and the like.
As the preferable technical scheme of the invention, the temperature of the first reaction in the step (2) is 70-100 ℃, for example, 70 ℃, 80 ℃, 90 ℃ or 100 ℃, preferably 85-95 ℃; the time is 30 to 90min, for example 30min, 50min, 80min or 90min, or 30 to 60min, and the above values are not limited to the listed values, and other values not listed in the respective ranges of values are also applicable.
As a preferable technical scheme of the invention, the pH value in the step (2) is adjusted to 4-11, such as 4, 5, 6, 7, 8, 9, 10 or 11, preferably 6-8; the temperature of the second reaction is 60-90 ℃, such as 60 ℃, 70 ℃, 80 ℃ or 90 ℃, preferably 80-90 ℃; the time is 30 to 120min, for example 30min, 60min, 90min or 120min, preferably 30 to 60min, and the above values are not limited to the listed values, and other values not listed in the respective ranges of values are also applicable.
In the present invention, the temperature of the cooling crystallization in the step (3) is 20 to 50 ℃, for example, 20 ℃, 30 ℃, 40 ℃ or 50 ℃, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned value range are also applicable, and preferably 30 to 40 ℃.
In a preferred embodiment of the present invention, the pH in step (3) is adjusted to 0.5 to 1.5, for example, 0.5, 0.7, 0.9, 1.2, or 1.5, but not limited to the above-mentioned values, and other values within the above-mentioned range are also applicable, preferably 0.5 to 1.
As a preferred technical scheme of the invention, the temperature of the reaction in the step (3) is 60-90 ℃, such as 60 ℃, 70 ℃, 80 ℃ or 90 ℃, preferably 80-90 ℃; the time is 30 to 120min, for example 30min, 60min, 90min or 120min, preferably 30 to 60min, and the above values are not limited to the listed values, and other values not listed in the respective ranges of values are also applicable.
Compared with the prior art, the invention has the following beneficial effects:
(1) the method takes potassium chloride as a potassium source, soluble sulfate and sulfuric acid as sulfur sources, potassium sulfate, sodium chloride and calcium sulfate are obtained through a certain reaction, and by controlling conditions in the operation process, the comprehensive recovery rate of potassium is not less than 95.1%, the purity of a potassium sulfate product is not less than 97wt%, the requirement of qualified powdery crystalline potassium sulfate in GB/T20406-2017 is met, the purity of sodium chloride is not less than 98wt%, the requirement of first-class industrial dry salt in GB/T5462-2015 is met, and the purity of a calcium sulfate product is not less than 82.1wt%, so that the method can be used for building materials;
(2) the method has the advantages of clean process, short process section, low energy consumption and obvious economic benefit and environmental benefit.
Drawings
Fig. 1 is a process flow chart of a method for preparing potassium sulfate from potassium chloride according to an embodiment of the invention.
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.
The following are typical but non-limiting examples of the invention:
example 1:
the embodiment provides a method for preparing potassium sulfate by potassium chloride, the process flow of the method is shown in fig. 1, and the method comprises the following steps:
(1) mixing sodium sulfate and potassium chloride with water and evaporation mother liquor at 85 ℃ according to the mass ratio of 1:1.1, then adding sulfuric acid to adjust the pH value to 1.5, mixing with the recovered ferric sulfate solution (when the anhydrous ferric sulfate is used for the first time, the use amount of the anhydrous ferric sulfate is 3 times of the mass of the potassium chloride), then reacting for 60min at 95 ℃, and after the reaction is finished, carrying out solid-liquid separation to obtain jarosite and precipitation mother liquor;
(2) mixing calcium hydroxide and jarosite obtained in the step (1) with water and crystallization mother liquor according to the mass ratio of 0.4:1 to prepare pulp, reacting at 85 ℃ for 30min, and after the reaction is finished, carrying out solid-liquid separation to obtain a precipitate solid and a potassium sulfate solution;
mixing calcium oxide with the precipitation mother liquor obtained in the step (1) at 70 ℃, adjusting the pH value to 7, reacting for 60min, and carrying out solid-liquid separation to obtain a purified precipitate and a purified solution;
(3) cooling the potassium sulfate solution obtained in the step (2) to 30 ℃, crystallizing the potassium sulfate from the solution in the form of crystals, performing solid-liquid separation to obtain a crystallization mother liquor and the potassium sulfate, and returning the crystallization mother liquor to the step (2) to participate in the first reaction;
mixing the precipitated solid and the purified precipitate obtained in the step (2) with water, then adding sulfuric acid to adjust the pH value to 1, reacting for 60min at 90 ℃, carrying out solid-liquid separation after the reaction to obtain calcium sulfate and a precipitant regeneration solution (namely, a ferric sulfate solution), outputting the calcium sulfate as a product, and returning the precipitant regeneration solution to the step (1) for recycling;
and (3) carrying out evaporative crystallization on the purified solution obtained in the step (2) at the temperature of 90 ℃ to obtain sodium chloride and evaporation mother liquor, and returning the evaporation mother liquor to the step (1) for recycling.
Example 2:
the embodiment provides a method for preparing potassium sulfate by potassium chloride, which comprises the following steps:
(1) mixing sodium sulfate and potassium chloride with water and evaporation mother liquor at 85 ℃ according to the mass ratio of 1:1.1, then adding sulfuric acid to adjust the pH value to 1, mixing with the recovered aluminum sulfate solution (when the anhydrous aluminum sulfate is used for the first time, the use amount of the anhydrous aluminum sulfate is 2.4 times of the mass of the potassium chloride), then reacting for 60min at 20 ℃, and after the reaction is finished, carrying out solid-liquid separation to obtain potassium alum and precipitation mother liquor;
(2) mixing calcium oxide and potassium alum obtained in the step (1) with water and crystallization mother liquor according to the mass ratio of 0.3:1 to prepare pulp, reacting for 60min at 90 ℃, and after the reaction is finished, carrying out solid-liquid separation to obtain a precipitate solid and a potassium sulfate solution;
mixing calcium carbonate with the precipitation mother liquor obtained in the step (1) at 80 ℃, adjusting the pH value to 7, reacting for 60min, and carrying out solid-liquid separation to obtain a purified precipitate and a purified solution;
(3) cooling the potassium sulfate solution obtained in the step (2) to 35 ℃, crystallizing the potassium sulfate from the solution in the form of crystals, performing solid-liquid separation to obtain a crystallization mother liquor and the potassium sulfate, and returning the crystallization mother liquor to the step (2) to participate in the first reaction;
mixing the precipitate solid and the purified precipitate obtained in the step (2) with water, then adding sulfuric acid to adjust the pH value to 0.5, reacting for 60min at 80 ℃, carrying out solid-liquid separation after the reaction to obtain calcium sulfate and a precipitant regeneration solution (namely an aluminum sulfate solution), outputting the calcium sulfate as a product, and returning the precipitant regeneration solution to the step (1) for recycling;
and (3) carrying out evaporative crystallization on the purified solution obtained in the step (2) at the temperature of 95 ℃ to obtain sodium chloride and evaporation mother liquor, and returning the evaporation mother liquor to the step (1) for recycling.
Example 3:
the embodiment provides a method for preparing potassium sulfate by potassium chloride, which comprises the following steps:
(1) mixing sodium sulfate and potassium chloride with water and evaporation mother liquor at 90 ℃ according to the mass ratio of 1:1.2, then adding sulfuric acid to adjust the pH value to 1.5, mixing with the recovered aluminum chloride solution (when the first reaction is carried out, the use amount of aluminum chloride is 2.4 times of the mass of potassium chloride), then reacting for 60min at 20 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain potassium alum and precipitation mother liquor;
(2) mixing calcium carbonate and potassium alum obtained in the step (1) with water and crystallization mother liquor according to the mass ratio of 0.35:1 to prepare pulp, reacting for 60min at 90 ℃, and after the reaction is finished, carrying out solid-liquid separation to obtain a precipitate solid and a potassium sulfate solution;
mixing calcium oxide with the precipitation mother liquor obtained in the step (1) at 80 ℃, adjusting the pH value to 7, reacting for 60min, and carrying out solid-liquid separation to obtain a purified precipitate and a purified solution;
(3) cooling the potassium sulfate solution obtained in the step (2) to 40 ℃, crystallizing the potassium sulfate from the solution in the form of crystals, performing solid-liquid separation to obtain a crystallization mother liquor and the potassium sulfate, and returning the crystallization mother liquor to the step (2) to participate in the first reaction;
mixing the precipitated solid and the purified precipitate obtained in the step (2) with water, then adding sulfuric acid to adjust the pH value to 1, reacting at 90 ℃ for 60min, carrying out solid-liquid separation after the reaction to obtain calcium sulfate and a precipitant regeneration solution (namely an aluminum chloride solution), outputting the calcium sulfate as a product, and returning the precipitant regeneration solution to the step (1) for recycling;
and (3) carrying out evaporative crystallization on the purified solution obtained in the step (2) at the temperature of 95 ℃ to obtain sodium chloride and evaporation mother liquor, and returning the evaporation mother liquor to the step (1) for recycling.
Example 4:
the embodiment provides a method for preparing potassium sulfate by potassium chloride, which comprises the following steps:
(1) mixing sodium sulfate and potassium chloride with water and evaporation mother liquor at 90 ℃ according to the mass ratio of 1:1.2, then adding sulfuric acid to adjust the pH value to 1.3, mixing with the recycled ferric chloride solution (the use amount of ferric chloride is 2.4 times of the mass of potassium chloride in the first reaction), then reacting for 60min at 90 ℃, and after the reaction is finished, carrying out solid-liquid separation to obtain jarosite and precipitation mother liquor;
(2) mixing calcium carbonate and jarosite obtained in the step (1) with water and crystallization mother liquor according to the mass ratio of 0.35:1 to prepare slurry, reacting for 60min at 90 ℃, and after the reaction is finished, carrying out solid-liquid separation to obtain a precipitate solid and a potassium sulfate solution;
mixing sodium carbonate with the precipitation mother liquor obtained in the step (1) at 80 ℃, adjusting the pH value to 7, reacting for 60min, and carrying out solid-liquid separation to obtain a purified precipitate and a purified solution;
(3) cooling the potassium sulfate solution obtained in the step (2) to 40 ℃, crystallizing the potassium sulfate from the solution in the form of crystals, performing solid-liquid separation to obtain a crystallization mother liquor and the potassium sulfate, and returning the crystallization mother liquor to the step (2) to participate in the first reaction;
mixing the precipitated solid and the purified precipitate obtained in the step (2) with water, then adding sulfuric acid to adjust the pH value to 1, reacting at 90 ℃ for 60min, carrying out solid-liquid separation after the reaction to obtain calcium sulfate and a precipitator regeneration solution (namely, a ferric chloride solution), outputting the calcium sulfate as a product, and returning the precipitator regeneration solution to the step (1) for recycling;
and (3) carrying out evaporative crystallization on the purified solution obtained in the step (2) at the temperature of 95 ℃ to obtain sodium chloride and evaporation mother liquor, and returning the evaporation mother liquor to the step (1) for recycling.
Example 5:
this example provides a process for the preparation of potassium sulfate from potassium chloride with reference to the process of example 2, except that: in the step (2), the calcium oxide and the potassium alum obtained in the step (1) are mixed with water and crystallization mother liquor according to the mass ratio of 0.1:1 for pulping.
Example 6:
this example provides a process for the preparation of potassium sulfate from potassium chloride with reference to the process of example 1, except that: in the step (2), calcium hydroxide and jarosite obtained in the step (1) are mixed with water and crystallization mother liquor according to the mass ratio of 1.2:1 to prepare pulp.
Example 7:
this example provides a process for the preparation of potassium sulfate from potassium chloride with reference to the process of example 2, except that: in the step (3), the precipitated solid and the purified precipitate obtained in the step (2) are mixed with water, and then sulfuric acid is added to adjust the pH to 0.1.
Example 8:
this example provides a process for the preparation of potassium sulfate from potassium chloride with reference to the process of example 1, except that: in the step (3), the precipitated solid and the purified precipitate obtained in the step (2) are mixed with water, and then sulfuric acid is added to adjust the pH to 2.
The results of the tests on the products obtained in examples 1 to 8, including the potassium utilization, potassium sulfate product purity, sodium chloride product purity, and calcium sulfate product purity, are shown in table 1.
TABLE 1
As can be seen from table 1, in the first pulping process, the added amount of the dissociation agent in example 5 is too small, which results in incomplete dissociation of potassium-containing precipitate, low potassium recovery rate and low purity of calcium sulfate, and the added amount of the dissociation agent in example 6 results in residual dissociation agent in precipitated solid, too large yield of calcium sulfate and poor quality. Example 7 when the precipitant was recovered, the pH was too low, which affected the formation of potassium-containing precipitate in step (1), the potassium precipitation rate decreased, and the sodium chloride product quality was poor; example 8 when the precipitant was recovered, the pH was too high, resulting in incomplete recovery of the precipitant and the precipitant being entrained in the calcium sulfate.
It can be seen from the above embodiments that, in the method of the present invention, potassium chloride is used as a potassium source, soluble sulfate and sulfuric acid are used as a sulfur source, potassium sulfate, sodium chloride and calcium sulfate are obtained through a certain reaction, and conditions in the operation process are controlled, such that the comprehensive recovery rate of potassium is up to 95.1% or more, the purity of potassium sulfate product is not less than 97wt%, the requirement of qualified powdery crystalline potassium sulfate in GB/T20406-2017 is satisfied, the purity of sodium chloride is not less than 98wt%, the requirement of first-grade industrial dry salt in GB/T5462-2015 is satisfied, and the purity of calcium sulfate product is not less than 82.1wt%, and the method can be used for building materials; the method has the advantages of clean process, short process section, low energy consumption and obvious economic and environmental benefits.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It will be apparent to those skilled in the art that any modifications to the present invention, equivalents thereof, additions of additional operations, selection of specific ways, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. The method for preparing potassium sulfate from potassium chloride is characterized by comprising the following steps of:
(1) mixing potassium chloride and soluble sulfate with water, adjusting the pH value, mixing with a precipitator for reaction, and carrying out solid-liquid separation after the reaction to obtain a potassium-containing precipitate and a precipitate mother liquor;
(2) mixing the potassium-containing precipitate obtained in the step (1) with a dissociating agent and water to perform a first reaction, and then performing solid-liquid separation to obtain a precipitate solid and a potassium sulfate solution;
mixing the precipitation mother liquor obtained in the step (1) with an impurity removing agent, adjusting the pH value to perform a second reaction, and then performing solid-liquid separation to obtain a purified precipitate and a purified solution;
(3) cooling and crystallizing the potassium sulfate solution obtained in the step (2) to obtain a potassium sulfate product and a crystallization mother liquor; the crystallization mother liquor is returned to the step (2) to participate in the first reaction;
mixing the precipitate solid and the purified precipitate obtained in the step (2) with water, adjusting the pH value to react, and then carrying out solid-liquid separation to obtain calcium sulfate and a precipitant regeneration solution; the precipitant regeneration solution is returned to the step (1) for recycling;
evaporating and crystallizing the purified solution obtained in the step (2) to obtain sodium chloride and an evaporation mother liquor; and (3) returning the evaporation mother liquor to the step (1) for recycling.
2. The method according to claim 1, wherein the soluble sulfate in the step (1) comprises sodium sulfate, the mass ratio of the soluble sulfate to the potassium chloride is 1: 1.1-1: 1.3, and the pH is adjusted to 0-2.
3. The method of claim 1, wherein the reaction in step (1) is carried out at a temperature of 10 to 90 ℃ for 30 to 120 min.
4. The method of claim 1, wherein the precipitant of step (1) comprises any one of aluminum sulfate, aluminum chloride, ferric sulfate, or ferric chloride, or a combination of at least two thereof.
5. The method according to claim 1, wherein the dissociation agent in step (2) comprises any one or a combination of at least two of calcium carbonate, calcium oxide or calcium hydroxide, and the addition amount of the dissociation agent is 0.2-1 times of the total mass of the potassium-containing precipitate.
6. The method according to claim 1, wherein the impurity removing agent in the step (2) comprises any one or a combination of at least two of calcium oxide, calcium hydroxide, calcium carbonate, sodium bicarbonate or sodium hydroxide.
7. The method according to claim 1, wherein the temperature of the first reaction in the step (2) is 70 to 100 ℃ and the time is 30 to 90 min.
8. The method of claim 1, wherein the pH in the step (2) is adjusted to 4-11, and the temperature of the second reaction is 60-90 ℃ for 30-120 min.
9. The method according to claim 1, wherein the pH in the step (3) is adjusted to 0.5 to 1.5.
10. The method of claim 1, wherein the temperature of the reaction in step (3) is 60 to 90 ℃ and the time is 30 to 120 min.
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