A method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine

Abstract

This invention relates to a method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype brine in salt lakes, comprising the following steps: S1, evaporating the original brine in a concentration tank until saturation; S2, introducing the saturated brine into a freezing tank for cold crystallization to precipitate mirabilite; S3, introducing the frozen mirabilite mother liquor into a sodium-magnesium mixed salt tank for evaporation to precipitate sodium-magnesium mixed salt; S4, introducing the brine into a carnallite tank for evaporation to precipitate carnallite mixed salt, with the remaining liquid phase stored in an old brine tank; S5, producing sodium sulfate from the mirabilite; S7, extracting potassium chloride from the carnallite mixed salt using a cold decomposition-flotation method. This invention first precipitates mirabilite through cold crystallization when the original brine in the salt lake reaches saturation, then evaporates the mother liquor to precipitate sodium-magnesium mixed salt. This process separates a large amount of sodium sulfate, reduces the sulfate content, and ensures that potassium crystallizes and precipitates in the form of carnallite, avoiding precipitation as potassium magnesium alum. This results in a lower potassium content being concentrated and enriched in carnallite for potassium chloride extraction.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical separation for the comprehensive utilization of salt lake brine resources, specifically relating to a method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine. Background Technology

[0002] Potassium is one of the three essential elements for crop growth and a vital resource for agricultural production and food security. Its importance is self-evident. Potassium fertilizer (potassium salt) is a raw material that cannot be replaced by other products. Therefore, efforts should be strengthened in potassium exploration and technological research to improve the security of potassium salt resources. Some sodium sulfate subtype salt lakes have brine whose main components are sodium, sulfate, chloride, and magnesium, while also containing a small amount of potassium (potassium content 2-3 g / L). Potassium recovery from such salt lake brines has not yet been developed, mainly because the separation and extraction of the large amount of sodium sulfate and the small amount of potassium chloride in these brines is difficult.

[0003] Against this backdrop, this application proposes a method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, aiming to extract sodium sulfate while simultaneously recovering scarce potassium fertilizer, revitalizing this type of low-potassium brine resource, and improving the security of potassium salt resources. Summary of the Invention

[0004] The purpose of this application is to provide a method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, so as to solve the technical problem of separating and extracting small amounts of potassium chloride and large amounts of sodium sulfate from sodium sulfate subtype salt lake brine, maximize the development and utilization value of this type of sodium sulfate subtype salt lake brine with low potassium quality, and comprehensively extract sodium sulfate and potassium chloride products.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, comprising:

[0007] Step S1: The original brine of the salt lake is evaporated in a concentration tank until it is saturated;

[0008] Step S2: The saturated brine obtained in step S1 is introduced into a freezing tank for cold crystallization treatment to precipitate mirabilite.

[0009] Step S3: The frozen nitrate mother liquor obtained in step S2 is introduced into a sodium-magnesium mixed salt tank for evaporation treatment to precipitate sodium-magnesium mixed salt.

[0010] Step S4: The brine obtained in step S3 is introduced into the carnallite pool for evaporation treatment to precipitate carnallite mixed salts, and the remaining liquid phase is stored in the old brine pool.

[0011] Step S5: The mirabilite obtained in step S3 is used to produce sodium sulfate by total dissolution evaporation and dehydration.

[0012] Step S7: Extract potassium chloride product from the carnallite mixed salt obtained in step S4 using a cold decomposition-flotation method.

[0013] In the above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, as a preferred embodiment, the evaporation treatment in step S1 is solar evaporation, that is, evaporation under open-air natural conditions.

[0014] In the above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, as a preferred embodiment, in step S2, the cold crystallization treatment is carried out by overwintering in a frozen nitrate pond at a temperature equal to the local winter air temperature of the salt lake, approximately -20℃ to 2℃.

[0015] In the above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, as a preferred embodiment, in step S3, when it is detected that carnallite is about to precipitate in the brine, the brine is introduced from the sodium-magnesium mixed salt pool into the carnallite pool; in step S4, when it is detected that hydrated magnesium chloride is about to precipitate in the carnallite pool, the brine is introduced from the carnallite pool into the old brine pool as old brine.

[0016] In the above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, as a preferred embodiment, in step S3, the sodium-magnesium mixed salt is mainly composed of sodium magnesium sulfate, esperidin, and rock salt, and the K content is controlled to be 0.2%–0.8%, sulfate content to be 32%–42%, Na content to be 11%–13%, Mg content to be 8.2%–9.6%, and Cl content to be 18%–24%.

[0017] In the above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, as a preferred embodiment, in step S4, the carnallite mixed salt is mainly composed of carnallite, esperidin, and halite, and the K content is controlled to be 5.0%–9.5%, sulfate content to be 11.1%–21.0%, Na content to be 1%–4%, Mg content to be 8.5%–10.6%, and Cl content to be 22%–32%.

[0018] The above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, as a preferred embodiment, further includes: step S6, dissolving the sodium-magnesium mixed salt precipitated in step S3 in the original brine and then cold crystallizing it in a freezing tank to recover mirabilite, and then processing it into sodium sulfate in step S5; more preferably, in step S6, the liquid-solid mass ratio of the original brine to the sodium-magnesium mixed salt is 1.4 to 1.6:1.

[0019] In a preferred embodiment of the above-mentioned method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, in step S7, the collector used for potassium chloride flotation is composed of octadecylamine hydrochloride, dodecylamine hydrochloride, and sodium dodecyl sulfate; more preferably, in the collector, by weight percentage, octadecylamine hydrochloride accounts for 60%-65%, dodecylamine hydrochloride accounts for 10%-20%, and sodium dodecyl sulfate accounts for 20%-30%.

[0020] Compared with the prior art, the solution of this application has the following beneficial effects:

[0021] (1) The local climate of the salt lake area is characterized by aridity, low rainfall, and high evaporation. By making full use of natural energy sources such as solar, wind, and cold energy, and adopting the salt field process for brine evaporation concentration and freezing crystallization, it is characterized by being adapted to local conditions, low carbon emissions, and energy saving. It is easy to operate and can be implemented industrially. From April to October, the temperature is relatively high, which is the peak evaporation season, and brine evaporation concentration is carried out. From November to March of the following year, the temperature is relatively low, and freezing crystallization is carried out.

[0022] (2) The process route was cleverly designed. On the one hand, when the original brine of the salt lake reached saturation, it was put into the frozen nitrate pool for overwintering and cold crystallization to precipitate mirabilite mainly composed of sodium sulfate decahydrate. On the other hand, the frozen nitrate mother liquor was evaporated by sunlight to precipitate sodium magnesium salt mainly composed of sodium magnesium alum. After the sodium magnesium salt was dissolved by the original brine, it was put into the frozen nitrate pool for overwintering and cold crystallization to precipitate mirabilite mainly composed of sodium sulfate decahydrate. Through these two methods, a large amount of sodium sulfate was separated from the brine and the content of sulfate in the brine in the later stage was reduced. This ensured that potassium was crystallized and precipitated in the form of carnallite in the subsequent evaporation and concentration, avoiding potassium from precipitating in the form of potassium salt magnesium alum. Thus, a low content of potassium was concentrated and enriched in carnallite and then potassium chloride was extracted.

[0023] (3) The carnallite mixed salt contains some estriate salt, and the presence of sulfate ions leads to a low yield of potassium chloride in the traditional octadecylamine hydrochloride flotation process. In this invention, a mixture of octadecylamine hydrochloride, dodecylamine hydrochloride, and sodium dodecyl sulfate is used as a collector in the cold decomposition-flotation process. This avoids the adverse effect of low potassium yield caused by the presence of sulfate ions, improves the flotation yield of potassium chloride, and improves the yield and economy of potassium extraction from sodium sulfate subtype brine.

[0024] In summary, this invention is suitable for treating sodium sulfate subtype brine from salt lakes with low potassium content. By adapting to local conditions and cleverly designing the process route, it solves the technical challenge of separating and extracting small amounts of potassium chloride and large amounts of sodium sulfate from sodium sulfate subtype salt lake brine, achieving comprehensive recovery of sodium sulfate and potassium chloride. This invention features a simple process, high separation efficiency, high recovery rate, and is easy to operate, facilitating large-scale industrial production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The present invention provides a process flow diagram of a method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, which is a preferred embodiment of the present invention. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, such as... Figure 1 As shown, a preferred embodiment of the method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype brine provided by the present invention includes the following steps:

[0028] (1) The original brine of the salt lake is evaporated by sunlight in the concentration tank, and the brine density is tested regularly until it is saturated.

[0029] (2) Saturated brine enters the freezing tank for overwintering, and mirabilite precipitates out through cold crystallization.

[0030] (3) The frozen nitrate mother liquor enters the sodium-magnesium mixed salt pool and is evaporated by sunlight to precipitate sodium-magnesium alum, espresso salt, rock salt and other sodium-magnesium mixed salts;

[0031] (4) After the sodium and magnesium mixed salts are precipitated, the brine is put into the carnallite pool for sun evaporation to precipitate carnallite, estriol salt and halite mixed salts, and the remaining liquid phase is stored in the old brine pool.

[0032] (5) The sodium sulfate precipitate obtained by freezing in step (2) is dehydrated by total dissolution evaporation to produce sodium sulfate;

[0033] (6) The sodium-magnesium mixed salt precipitated in step (3) is dissolved in the original brine (i.e., the original brine) and then cold crystallized in the freezing tank to recover the mirabilite, and then processed into sodium sulfate product in step (5).

[0034] (7) The carnallite mixed salt precipitated in step (4) is used to extract potassium chloride product by cold decomposition-flotation method.

[0035] In step (1), the evaporation caused by sunlight is evaporation under natural conditions in the open air.

[0036] In step (2), the overwintering temperature in the frozen nitrate pool is the local winter air temperature of the salt lake (approximately -20℃ to 2℃). The Na2SO4·10H2O content in the mirabilite obtained in step (2) is 70% to 95%.

[0037] In steps (3) and (4), it is necessary to control the starting and ending points of evaporation. Monitoring is conducted through density detection and composition analysis. In step (3), when it is detected that carnallite is about to precipitate from the brine, the brine is transferred from the sodium-magnesium mixed salt pool to the carnallite pool. In step (4), when it is detected that hydrated magnesium chloride is about to precipitate in the carnallite pool, the brine is transferred from the carnallite pool to the old brine pool as old brine. By controlling the brine transfer, it is ensured that the carnallite precipitation is concentrated and that the potassium grade is high.

[0038] Preferably, in step (3), the precipitated salt is a sodium-magnesium mixed salt mainly composed of sodium magnesium sulfate, esperidin and halite, and the brine is controlled to ensure that the K content is 0.2% to 0.8%, the sulfate content is 32% to 42%, the Na content is 11% to 13%, the Mg content is 8.2% to 9.6%, and the Cl content is 18% to 24%.

[0039] Preferably, in step (4), the precipitated salt is a mixed carnallite salt mainly composed of carnallite, esperidin, and halite. The brine is controlled to ensure that the K content is 5.0%–9.5%, the sulfate content is 11.1%–21.0%, the Na content is 1%–4%, the Mg content is 8.5%–10.6%, and the Cl content is 22%–32%.

[0040] In step (5), the total dissolution evaporation dehydration method involves dissolving mirabilite into a nearly saturated sodium sulfate solution, clarifying to remove water-insoluble matter and mechanical impurities, precipitating to remove small amounts of chemical impurities such as calcium and magnesium, and obtaining a clear mirabilite solution. After evaporation and dehydration, anhydrous sodium sulfate is obtained. This is a conventional method in the field and also the main production method of sodium sulfate.

[0041] Preferably, in step (6), the liquid-to-solid mass ratio of the original brine (i.e., the original brine) to the sodium-magnesium mixed salt is 1.4 to 1.6:1 (e.g., 1.45:1, 1.5:1, 1.55:1, etc.). Limiting the liquid-to-solid ratio to this range ensures that the sodium sulfate and magnesium sulfate are completely dissolved while maintaining a high concentration in the mother liquor, which is beneficial for subsequent freezing and condensation of nitrates.

[0042] In step (7), the cold decomposition-flotation method is one of the conventional methods for producing potassium chloride in this field. First, the carnallite mixed salt is crushed and mixed with water to carry out a cold decomposition reaction, dissolving magnesium chloride in the carnallite into the solution, while potassium chloride precipitates out in the solid phase; then, the cold-decomposed slurry is subjected to positive flotation, by adding appropriate reagents (generally using octadecylamine hydrochloride as a collector) and aerating and stirring, so that potassium chloride particles float up with the bubbles.

[0043] Preferably, in step (7), the collector used for potassium chloride flotation is composed of octadecylamine hydrochloride, dodecylamine hydrochloride, and sodium dodecyl sulfate. Using this mixed collector overcomes the adverse effect of low potassium yield caused by the presence of sulfate ions in carnallite mixed salts. More preferably, in the collector, by weight percentage, octadecylamine hydrochloride accounts for 60%-65%, dodecylamine hydrochloride accounts for 10%-20%, and sodium dodecyl sulfate accounts for 20%-30%.

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The scope of protection of the present invention includes, but is not limited to, the following embodiments.

[0045] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional steps or conditions described in the literature in this field.

[0046] Unless otherwise stated, all reagents and raw materials used in the examples are commercially available products.

[0047] Example 1

[0048] A certain sodium sulfate subtype salt lake brine has the following composition: Na 2.73%, K 0.23%, Mg 1.22%, SO42-. 2- 6.29%, Cl 3.43%.

[0049] (1) The raw brine from the salt lake is introduced into a concentration tank for natural sun evaporation. The brine density is tested periodically until saturation, at which point the brine density is 1.308 g / cm³. 3 ;

[0050] (2) Saturated brine is introduced into the freezing tank. The temperature of the freezing tank varies with the local winter temperature of the salt lake. The highest temperature is 2℃ and the lowest temperature is -20℃. After overwintering, mirabilite is precipitated by cold crystallization. The content of Na2SO4·10H2O in mirabilite is 88%.

[0051] (3) The frozen nitrate mother liquor was introduced into the sodium magnesium mixed salt pool and evaporated by sunlight to precipitate sodium magnesium alum, espresso salt, rock salt and other sodium magnesium mixed salts. The sodium magnesium mixed salts obtained contained K content of 0.37%, sulfate content of 42%, Na content of 12.9%, Mg content of 9.6% and Cl content of 18%.

[0052] (4) The brine after the sodium and magnesium mixed salts are precipitated is introduced into the carnallite pool for sun evaporation to precipitate carnallite, esperidin salt and halite mixed salts. The remaining liquid phase is stored in the old brine pool. The carnallite mixed salts contain 9.5% K, 11.1% sulfate, 4% Na, 8.5% Mg and 32% Cl.

[0053] (5) The sodium sulfate precipitated in step (2) is used to produce sodium sulfate by total dissolution evaporation and dehydration, with a sodium sulfate purity of 99.35%.

[0054] (6) The sodium-magnesium mixed salt precipitated in step (3) is dissolved with the original brine at a liquid-solid mass ratio of 1.6:1. The mother liquor is introduced into the freezing tank for cold crystallization to recover mirabilite, and then processed into sodium sulfate product in step (5).

[0055] (7) The carnallite mixed salt precipitated in step (4) was used to extract potassium chloride product by cold decomposition-flotation method. The flotation collector used was a mixture of 60% octadecylamine hydrochloride, 20% dodecylamine hydrochloride and 20% sodium dodecyl sulfate. The purity of the extracted potassium chloride product reached 95.6%.

[0056] Example 2

[0057] A certain sodium sulfate subtype salt lake brine has the following composition: Na 2.73%, K 0.23%, Mg 1.22%, SO42-. 2- 6.29%, Cl 3.43%.

[0058] (1) The raw brine from the salt lake is introduced into a concentration tank for natural sun evaporation. The brine density is tested periodically until saturation, at which point the brine density is 1.310 g / cm³. 3 ;

[0059] (2) Saturated brine is introduced into the freezing tank. The temperature of the freezing tank varies with the local winter temperature of the salt lake. The highest temperature is 2℃ and the lowest temperature is -20℃. After overwintering, mirabilite is precipitated by cold crystallization. The content of Na2SO4·10H2O in mirabilite is 70%.

[0060] (3) The frozen nitrate mother liquor was introduced into the sodium magnesium mixed salt pool and evaporated by sunlight to precipitate sodium magnesium alum, espresso salt, rock salt and other sodium magnesium mixed salts. The sodium magnesium mixed salts obtained contained K content of 0.8%, sulfate content of 32%, Na content of 13%, Mg content of 9.2% and Cl content of 24%.

[0061] (4) The brine after the sodium and magnesium mixed salts are precipitated is introduced into the carnallite pool for sun evaporation to precipitate carnallite, esperidin salt and halite mixed salts. The remaining liquid phase is stored in the old brine pool. The carnallite mixed salts contain 5.0% K, 21.0% sulfate, 1% Na, 10.6% Mg and 22% Cl.

[0062] (5) The sodium sulfate precipitated in step (2) is used to produce sodium sulfate by total dissolution evaporation and dehydration. The sodium sulfate purity is 99.17%.

[0063] (6) The sodium-magnesium mixed salt precipitated in step (3) is dissolved with the original brine at a liquid-solid mass ratio of 1.4:1. The mother liquor is introduced into the freezing tank for cold crystallization to recover mirabilite, and then processed into sodium sulfate product in step (5).

[0064] (7) The carnallite mixed salt precipitated in step (4) was used to extract potassium chloride product by cold decomposition-flotation method. The flotation collector used was a mixture of 60% octadecylamine hydrochloride, 10% dodecylamine hydrochloride and 30% sodium dodecyl sulfate. The purity of the extracted potassium chloride product reached 91.7%.

[0065] Example 3

[0066] A certain sodium sulfate subtype salt lake brine has the following composition: Na 2.73%, K 0.23%, Mg 1.22%, SO42-. 2- 6.29%, Cl 3.43%.

[0067] (1) The raw brine from the salt lake is introduced into a concentration tank for natural sun evaporation. The brine density is tested periodically until saturation, at which point the brine density is 1.305 g / cm³. 3 ;

[0068] (2) Saturated brine is introduced into the freezing tank. The temperature of the freezing tank varies with the local winter temperature of the salt lake. The highest temperature is 2℃ and the lowest temperature is -20℃. After overwintering, mirabilite is precipitated by cold crystallization. The content of Na2SO4·10H2O in mirabilite is 95%.

[0069] (3) The frozen nitrate mother liquor was introduced into the sodium magnesium mixed salt pool and evaporated by sunlight to precipitate sodium magnesium alum, espresso salt, rock salt and other sodium magnesium mixed salts. The sodium magnesium mixed salts obtained contained K content of 0.2%, sulfate content of 32.1%, Na content of 11%, Mg content of 8.2% and Cl content of 18.2%.

[0070] (4) The brine after the sodium and magnesium mixed salts are precipitated is introduced into the carnallite pool for sun evaporation to precipitate carnallite, esperidin salt and halite mixed salts. The remaining liquid phase is stored in the old brine pool. The carnallite mixed salts contain 6.58% K, 13.6% sulfate, 2.52% Na, 9.14% Mg and 26.9% Cl.

[0071] (5) The sodium sulfate precipitated in step (2) is used to produce sodium sulfate by total dissolution evaporation and dehydration, with a sodium sulfate purity of 99.57%.

[0072] (6) The sodium-magnesium mixed salt precipitated in step (3) is dissolved with the original brine at a liquid-solid mass ratio of 1.5:1. The mother liquor is introduced into the freezing tank for cold crystallization to recover mirabilite, and then processed into sodium sulfate product in step (5).

[0073] (7) The carnallite mixed salt precipitated in step (4) was used to extract potassium chloride product by cold decomposition-flotation method. The flotation collector used was a mixture of 65% octadecylamine hydrochloride, 10% dodecylamine hydrochloride and 25% sodium dodecyl sulfate. The purity of the extracted potassium chloride product reached 93.4%.

[0074] As can be seen from the above embodiments, the process route of the method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine provided by the present invention is mainly as follows: The raw brine of the salt lake first enters the concentration tank for evaporation and concentration to a saturated state, and then enters the freezing tank for overwintering and cold crystallization to precipitate mirabilite. The mirabilite is then dehydrated by total dissolution evaporation to produce sodium sulfate; the mother liquor of the freezing tank enters the sodium magnesium mixed salt tank, where it is evaporated and crystallized by sunlight to precipitate a mixed salt of sodium magnesium alum, esperidin, and halite. This sodium magnesium mixed salt is dissolved by the raw brine and cold crystallized in the freezing tank to recover mirabilite, and the mother liquor is returned to the sodium magnesium mixed salt tank; finally, the brine enters the carnallite tank for evaporation and crystallization to precipitate a mixed salt of carnallite, esperidin, and halite. This carnallite mixed salt is then recovered by cold decomposition-flotation. The present invention makes full use of natural energy sources such as solar energy, wind energy, and cold energy in the salt lake area, and adopts salt field technology for evaporation, concentration, and cold crystallization of brine. It has the characteristics of low carbon and energy saving, and the cleverly designed process route achieves efficient extraction and recovery of sodium sulfate and potassium chloride. It is easy to operate and implement.

[0075] It should be noted that, in this invention, unless otherwise understood in conjunction with the entire text, any expression "A / B" should be interpreted as any of the following three parallel situations: A; B; A and B.

[0076] It should also be noted that, in this invention, unless otherwise understood in conjunction with the entire text, the relevant terminology should be understood as follows: Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0077] Although the invention has been disclosed above through the description of specific embodiments, it should be understood that those skilled in the art can design various modifications, improvements, or equivalents to the invention within the spirit and scope of the appended embodiments. These modifications, improvements, or equivalents should also be considered to be included within the scope of protection claimed by the invention.

Claims

1. A method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine, characterized in that, include: Step S1: The original brine of the salt lake is evaporated in a concentration tank until it is saturated; Step S2: The saturated brine obtained in step S1 is introduced into a freezing tank for cold crystallization treatment to precipitate mirabilite. Step S3: The frozen nitrate mother liquor obtained in step S2 is introduced into a sodium-magnesium mixed salt tank for evaporation treatment to precipitate sodium-magnesium mixed salt; the sodium-magnesium mixed salt is mainly composed of sodium magnesium sulfate, esperidin salt and halite, and the K content is controlled at 0.2%~0.8%, sulfate content at 32%~42%, Na content at 11%~13%, Mg content at 8.2%~9.6%, and Cl content at 18%~24%; In step S4, when it is detected in step S3 that carnallite is about to precipitate from the brine in the sodium-magnesium mixed salt pool, the brine obtained in step S3 is introduced from the sodium-magnesium mixed salt pool into the carnallite pool for evaporation treatment to precipitate carnallite mixed salt. The remaining liquid phase is stored in the old brine pool. In step S4, when it is detected that hydrated magnesium chloride is about to precipitate from the carnallite pool, the brine is introduced from the carnallite pool into the old brine pool as old brine. The carnallite mixed salt is mainly composed of carnallite, esperidin, and halite, and the K content is controlled at 5.0%~9.5%, sulfate content at 11.1%~21.0%, Na content at 1%~4%, Mg content at 8.5%~10.6%, and Cl content at 22%~32%. Step S5: The mirabilite obtained in step S2 is used to produce sodium sulfate by total dissolution evaporation and dehydration. Step S6: The sodium-magnesium mixed salt precipitated in step S3 is dissolved in the original brine and then fed into the freezing tank for cold crystallization to recover mirabilite, which is then processed into sodium sulfate in step S5. Step S7: Extract potassium chloride product from the carnallite mixed salt obtained in step S4 using a cold decomposition-flotation method.

2. The method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine according to claim 1, characterized in that, In step S1, the evaporation process is solar evaporation.

3. The method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine according to claim 1 or 2, characterized in that, In step S2, the cold crystallization treatment is carried out by using the low winter temperature during the overwintering of the frozen nitrate pond, with the temperature being the local winter air temperature of the salt lake.

4. The method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine according to claim 1, characterized in that, In step S6, the liquid-solid mass ratio of the original brine to the sodium-magnesium mixed salt is 1.4~1.6:

1.

5. The method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine according to any one of claims 1-2 and 4, characterized in that, In step S7, the collector used for potassium chloride flotation consists of octadecylamine hydrochloride, dodecylamine hydrochloride, and sodium dodecyl sulfate.

6. The method for extracting sodium sulfate and potassium chloride from sodium sulfate subtype salt lake brine according to claim 5, characterized in that, In step S7, the collector comprises, by weight percentage, 60%-65% octadecylamine hydrochloride, 10%-20% dodecylamine hydrochloride, and 20%-30% sodium dodecyl sulfate.

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