A method for desulfate removal and recovery of ammonium chloride and sodium chloride from a multi-effect evaporation crystallization separated deaminated mother liquor

Abstract

This invention discloses a method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride through multi-effect evaporation crystallization separation, comprising the following steps: 1) collecting deammoniation mother liquor; 2) primary cold precipitation: the deammoniation mother liquor is transferred to an ammonium precipitation vessel at room temperature, cooled to 25-28℃ for cold precipitation crystallization, centrifuged to obtain agricultural ammonium chloride and mother liquor one; 3) secondary cold precipitation: mother liquor one is transferred to a cold precipitation crystallization vessel, sodium chloride is added, cooled to 20-23℃ for cold precipitation crystallization, centrifuged to obtain agricultural ammonium chloride and mother liquor two; 4) tertiary cold precipitation: mother liquor two is transferred to a strong cold precipitation vessel, cooled to 0-5℃ to crystallize sodium sulfate decahydrate, centrifuged to obtain sodium sulfate decahydrate and sodium chloride mother liquor; 5) the sodium chloride mother liquor is returned to the multi-effect evaporation system to recover sodium chloride. This invention uses a three-stage cold crystallization method to treat the deammoniation mother liquor, instead of directly returning it to the multi-effect evaporation system for recycling. This effectively avoids the vicious cycle of sulfate accumulation caused by the high sulfate content in the deammoniation mother liquor and repeated recycling, which leads to excessive sulfate content in the salt. This ensures that the sulfate content in the recovered industrial salt meets the standard of GB / T 5462-2015 for industrial salt, thus improving the product quality of industrial salt.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of treatment of the deamination mother liquor separated from the ammonium chloride recovered from the baking soda mother liquor, and particularly relates to a method for desulfate and recovery of ammonium chloride and sodium chloride through multi-effect evaporation crystallization separation. BACKGROUND

[0002] The baking soda mother liquor is obtained through washing and dehydration separation of baking soda in the process of preparing baking soda through double decomposition reaction of brine and ammonium bicarbonate, and contains a large amount of ammonium chloride, sodium chloride and ammonium bicarbonate. Therefore, recycling of ammonium chloride and sodium chloride from the mother liquor can turn waste into treasure and protect the environment.

[0003] At present, the method for recycling ammonium chloride from the baking soda mother liquor first removes ammonium through an ammonia evaporation tower, and then uses the method of multi-effect evaporation cooling crystallization. For example, patent application No. CN200910068695.6 discloses a process for recycling ammonium chloride and sodium chloride from wastewater containing ammonium chloride and sodium chloride. The process uses the mother liquor containing ammonium chloride and sodium chloride generated in the process of producing baking soda through natural brine double decomposition reaction as raw material to produce ammonium chloride and sodium chloride. The process uses evaporation, crystallization and separation process. The evaporation uses multi-effect, heat pump and vacuum evaporation process, selects falling film evaporator and forced circulation evaporator, three-effect mixed flow process, and crystallizes sodium chloride in the evaporation, and crystallizes ammonium chloride after cooling.

[0004] The process recycles ammonium chloride from the baking soda mother liquor by using the method of multi-effect evaporation to first extract the salt in the mother liquor after removing ammonium from the baking soda mother liquor, and then uses the flash vacuum cooling method to crystallize ammonium chloride from the mother liquor after recycling the salt, and obtains agricultural ammonium chloride and deamination mother liquor after centrifugal separation, and the deamination mother liquor is returned to the multi-effect evaporation system for recycling.

[0005] However, in the actual application process, it is found that when the deamination mother liquor is returned to the multi-effect evaporation system for repeated recycling, the content of SO4 2- will continuously accumulate, and the content of SO4 2- will increase by 10-15 times after 10 times of repeated recycling. The reason for the increase of SO4 2- is that in order to avoid too much Na2SO4 entering the ammonium chloride and causing the ammonium chloride to not meet the standard of agricultural ammonium chloride, the sodium sulfate is separated from the ammonium chloride and the ammonium chloride is crystallized and precipitated by using the characteristic that the solubility of sodium sulfate is the largest at 40-45℃ in the process of vacuum cooling crystallization. A large amount of sodium sulfate returns to the evaporation system with the mother liquor, and SO4 2- accumulates to the saturation of Na2SO4, and Na2SO4 and NaCl are co-precipitated, which is brought into the recycled salt, resulting in SO4 2-The content exceeds the standard and fails to meet the GB / T5462-2015 standard for industrial salt, which seriously reduces the quality of industrial salt. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a simple process that can effectively reduce the sulfate content by using multi-effect evaporation crystallization to separate the deammoniation mother liquor, remove sulfate, and recover ammonium chloride and sodium chloride.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride through multi-effect evaporation crystallization separation, comprising the following steps: 1) collecting deammoniation mother liquor; 2) primary cold precipitation: the deammoniation mother liquor is transported to an ammonium precipitation vessel at room temperature, cooled to 25-28℃ for cold precipitation crystallization, centrifuged to obtain agricultural ammonium chloride and mother liquor one; 3) secondary cold precipitation: mother liquor one is transported to a cold precipitation crystallization vessel, sodium chloride is added, cooled to 20-23℃ for cold precipitation crystallization, centrifuged to obtain agricultural ammonium chloride and mother liquor two; 4) tertiary cold precipitation: mother liquor two is transported to a strong cold precipitation vessel, cooled to 0-5℃ to crystallize sodium sulfate decahydrate, centrifuged to obtain sodium sulfate decahydrate and sodium chloride mother liquor; 5) the sodium chloride mother liquor is returned to the multi-effect evaporation system to recover sodium chloride.

[0008] Furthermore, the mother liquor for deammoniation in step 1) is obtained by first deammonizing by distillation, then extracting sodium chloride from the mother liquor after deammoniation by multi-effect evaporation, and finally precipitating ammonium chloride by flash evaporation and vacuum cooling and centrifuging to dehydrate and separate the mother liquor.

[0009] Furthermore, in step 2), the cold crystallization time after the deammoniation mother liquor is cooled to 25-28℃ is 4-6 hours.

[0010] Furthermore, in step 3), the time for cold crystallization after the mother liquor is cooled to 20-23°C is 2-4 hours.

[0011] Furthermore, the amount of sodium chloride added is equal to the content of ammonium chloride in the mother liquor × 0.6.

[0012] Furthermore, in step 4), the time for cold crystallization after the mother liquor is cooled to 0-5℃ is 2-4 hours.

[0013] Furthermore, the ambient temperature ammonium precipitation vessel, the cold precipitation crystallization vessel, and the strong cold precipitation vessel are all equipped with jackets, and cooling water is injected into the jackets to reduce the temperature of the solution inside the vessel.

[0014] The beneficial effects of this invention's method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride through multi-effect evaporation crystallization separation are as follows: The process of this invention is simple and highly operable. It treats the deammoniation mother liquor obtained during the recovery of ammonium chloride and sodium chloride from sodium bicarbonate mother liquor using multi-effect evaporation and flash evaporation vacuum cooling crystallization methods with a three-stage cold precipitation crystallization process. The resulting sodium chloride mother liquor is then returned to the multi-effect evaporation system for recycling, rather than being directly returned. The first two cold precipitation crystallization processes gradually crystallize ammonium chloride, yielding qualified agricultural-grade ammonium chloride. Furthermore, the crystallization process also removes sulfate ions from the ammonium chloride. Partially removing sulfate ions gradually reduces the sulfate content in the mother liquor. A final strong cold crystallization treatment precipitates the sulfate ions in the mother liquor as sodium sulfate decahydrate, yielding sodium chloride mother liquor, which significantly reduces the sulfate content. The three-stage cold crystallization treatment method described in this invention is applied to the deammoniation mother liquor before each recycling to the multi-effect evaporation system. This effectively avoids the vicious cycle of sulfate accumulation caused by high sulfate content in the deammoniation mother liquor and repeated recycling, which can lead to excessive sulfate content in the salt. This ensures that the sulfate content in the recovered industrial salt after recycling the sodium chloride mother liquor to the multi-effect evaporation system meets the GB / T 5462-2015 standard for industrial salt, greatly improving the product quality of industrial salt. Attached Figure Description

[0015] Figure 1 A comparison diagram of the process flow for treating deammoniation mother liquor using existing technologies and the method of this invention. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, but these specific embodiments do not limit the scope of protection of the present invention in any way.

[0017] Example 1

[0018] A method for removing sulfate and recovering ammonium chloride and sodium chloride from ammonia removal mother liquor obtained through multi-effect evaporation and crystallization separation includes the following steps:

[0019] 1) Collection of deammoniation mother liquor: The sodium bicarbonate mother liquor is fed into a reboiler and treated at 80-100℃ for 1 hour. It is then pumped into a deammoniation tower for circulation to remove sublimated ammonia and carbon dioxide, followed by cooling and carbonation in a carbonization tower to produce ammonium bicarbonate. After cooling to 38-42℃, the crystals are precipitated and centrifuged to obtain ammonium bicarbonate, which is then returned to sodium bicarbonate production. The deammoniation mother liquor obtained from centrifugation is then fed into a multi-effect evaporator to precipitate sodium chloride at 106℃. The sodium chloride is centrifuged to obtain solid sodium chloride. The mother liquor obtained from centrifugation is fed into a vacuum crystallizer, where the temperature is controlled at 50-55℃. Ammonium chloride crystals precipitate and is centrifuged to obtain ammonium chloride. The mother liquor obtained from centrifugation is the deammoniation mother liquor, with a total volume of 16m³. 3 / h, where the content of each component is: NaCl 80g / L, NH4Cl 350g / L, SO4 2- 75g / L;

[0020] 2) First-stage cold precipitation: The deammoniation mother liquor is pumped into an ambient temperature ammonium precipitation reactor. This reactor is equipped with a jacket, and cooling water is injected into the jacket to cool the solution inside the reactor to 25-28℃ (26℃ in this embodiment) for cold precipitation crystallization for 4-6 hours (5 hours in this embodiment). After centrifugation, qualified agricultural ammonium chloride with a nitrogen content of 26% and mother liquor 1 are obtained. After testing, all components of the agricultural ammonium chloride meet the standard of superior grade agricultural ammonium chloride in GB / T 2946-2008. The component content of mother liquor 1 is: NaCl 120g / L, NH4Cl 200g / L, SO4 2- 52.5g / L;

[0021] SO4 in deammoniation mother liquor 2- It mainly exists in the form of sulfates (Na2SO4, (NH4)2SO4). During a single cooling process, the solubility of Na2SO4 and (NH4)2SO4 is low at this temperature, causing (NH4)2SO4 and Na2SO4 to crystallize out. Furthermore, Na2SO4 will also be converted to (NH4)2SO4 under the influence of common ions, with the reaction equation: Na2SO4 + 2NH4Cl = (NH4)2SO4 + 2NaCl. This increases the (NH4)2SO4 content in the solution. Under the common ion effect, the increased (NH4)2SO4 content reduces the solubility of NH4Cl. With the (NH4)2SO4 intermediate salt promoting crystallization, NH4Cl will rapidly crystallize out at 25-28℃. (NH4)2SO4 will also undergo rapid co-precipitation with NH4Cl. This process not only yields qualified agricultural ammonium chloride but also reduces the SO4 content in the solution. 2- The content of SO4 in the mother liquor... 2- The content was only 52.5 g / L, based on the deammoniation mother liquor, SO4 2-The content decreased by 30%;

[0022] 3) Secondary Cold Separation: Mother liquor 1 is pumped into a cold separation crystallization kettle, and sodium chloride is added. The amount of sodium chloride added = the content of ammonium chloride in mother liquor 2 × 0.6 = 200 × 0.6 = 20g. The temperature is lowered to 20-23℃ (specifically 22℃ in this example) for cold separation crystallization for 2-4 hours (specifically 2 hours in this example). After centrifugation, agricultural ammonium chloride and mother liquor 2 are obtained. After testing, all components in the agricultural ammonium chloride meet the standard of superior grade agricultural ammonium chloride in GB / T 2946-2008. The component contents of mother liquor 2 are: NaCl 120g / L, NH4Cl 30g / L, SO42-20g / L. 2- 22.5g / L;

[0023] SO4 in Mother Liquor 2- It mainly exists in the form of sulfates (Na₂SO₄, (NH₄)₂SO₄). During the secondary cooling process, adding NaCl at 20-23℃ can rapidly dissolve NaCl, increasing the concentration of Cl₂ in the solution. - The concentration of [specific ion] will promote the rapid crystallization and precipitation of NH4Cl under the common ion effect. Simultaneously, (NH4)2SO4 will also undergo vigorous co-precipitation with NH4Cl, resulting in not only qualified agricultural ammonium chloride (tested to meet the standards for superior grade agricultural ammonium chloride in GB / T 2946-2008), but also a reduction in SO42- content in the solution. 2- The content of SO4 in the mother liquor is reduced. 2- The SO4 content was only 22.5 g / L, based on the mother liquor. 2- The content decreased by 57.1%;

[0024] 4) Three-stage cold precipitation: The second mother liquor is transferred to a strong cold precipitation reactor and cooled to 0-5℃ (3℃ in this embodiment), and cold precipitated for 2-4 hours (2 hours in this embodiment) to allow sodium sulfate decahydrate to crystallize out. After centrifugation, sodium sulfate decahydrate and sodium chloride mother liquor are obtained. The content of each component in the sodium chloride mother liquor is: NaCl 180g / L, NH4Cl 30g / L, SO42- 2- 6.2g / L;

[0025] SO4 in Mother Liquor II 2- It mainly exists in the form of sulfates (Na2SO4, (NH4)2SO4). During the three-stage cooling process, Na2SO4·10H2O will crystallize out at 0-5℃, further reducing the SO4 content in the solution. 2- The content of SO4 in the sodium chloride mother liquor 2- The content was only 6.2 g / L, based on the second mother liquor, SO4 2-The content of SO4 decreased by 87.3%. 2- The SO4 content in the mother liquor decreased by 72.4% compared to the deammoniation mother liquor; after three cold precipitation treatments, the SO4 content in the mother liquor was reduced. 2- The SO4 content decreased from 75 g / L in the deammoniation mother liquor to 6.2 g / L, a reduction of 91.7%, indicating that three cold precipitation treatments can effectively reduce SO4 in the mother liquor. 2- The content;

[0026] 5) The sodium chloride mother liquor is returned to the multi-effect evaporation system to recover sodium chloride. After ten cycles, the yield of recovered sodium chloride product is as follows: the sodium chloride product contains 99.8 g / 100g of sodium chloride, 0.07 g / 100g of moisture, 0.01 g / 100g of water-insoluble matter, 0.02 g / 100g of total calcium and magnesium ions, and 0.1 g / 100g of sulfate ions, which meets the standard of superior grade industrial dry salt in GB / T5462-2015.

[0027] See Figure 1 In existing technologies, the deammoniation mother liquor obtained after multi-effect evaporation and flash evaporation vacuum cooling of sodium bicarbonate mother liquor is directly returned to the multi-effect evaporation system for recycling (see...). Figure 1 (The dotted line in the text indicates that the deammoniation mother liquor contains a large amount of SO4.) 2- When it circulates to the multi-effect evaporation system to recover salt, it gradually accumulates in the salt. After repeated circulation, the SO4 content in the recovered salt will increase. 2- The content exceeded the standard, causing the prepared industrial salt to fail to meet the GB / T 5462-2015 standard for industrial salt;

[0028] The inventor discovered SO4 in the recovered salt. 2- The content exceeded the standard, and SO4 was identified. 2- The reason for the excessive content is that the mother liquor, which needs to be returned to the multi-effect evaporation system for recycling, undergoes the three-stage cold precipitation treatment of this invention (see [reference]). Figure 1 The process of using a large rectangular frame significantly reduces SO4 in the sodium chloride mother liquor after three cold precipitation treatments. 2- The content of SO42- is controlled, and the deammoniation mother liquor produced in each cycle undergoes three cold precipitation treatments before being returned to the multi-effect evaporation system, thus avoiding SO42-. 2- This vicious cycle accumulates in the recovered industrial salt, causing SO4 levels in the prepared industrial salt (which belongs to refined industrial salt and industrial dry salt) to rise. 2- The content is all below 0.3g / 100g, which meets the standard of superior grade industrial dry salt in GB / T 5462-2015, greatly improving the quality of the recovered salt.

[0029] Comparative Example 1

[0030] The difference between this comparative example and Example 1 is that the existing method for treating deammoniation mother liquor is used to directly return the deammoniation mother liquor to the multi-effect evaporation system to recover salt.

[0031] Comparative Example 2

[0032] The difference between this comparative example and Example 1 is that steps 3) and 4) are removed, and the mother liquor is directly recycled to the multi-effect evaporation system to recover salt.

[0033] Comparative Example 3

[0034] The difference between this comparative example and Example 1 is that step 4) is removed, and the mother liquor is directly recycled to the multi-effect evaporation system to recover salt.

[0035] Comparative Example 4

[0036] The difference between this comparative example and Example 1 is that step 3) is removed, and the mother liquor is directly transported to the strong cooling precipitation vessel in step 4) for processing. Then, the mother liquor after treatment in the strong cooling precipitation vessel is returned to the multi-effect evaporation crystallization system to recover salt.

[0037] Comparative Example 5

[0038] The difference between this comparative example and Example 1 is that step 2) is removed, and the deammoniation mother liquor is directly transported to the cold crystallization kettle in step 3) for processing, and then the mother liquor after processing in the cold crystallization kettle is transported to the strong cold crystallization kettle in step 4) for processing.

[0039] Comparative Example 6

[0040] The difference between this comparative example and Example 1 is that steps 2) and 4) are removed, and the deammoniation mother liquor is directly transported to the cold crystallization kettle of step 3) for processing. Then, the mother liquor after processing in the cold crystallization kettle is returned to the multi-effect evaporation crystallization system to recover salt.

[0041] Comparative Example 7

[0042] The difference between this comparative example and Example 1 is that steps 2) and 3) are removed, and the deammoniation mother liquor is directly transported to the strong cooling precipitation vessel in step 4) for processing. Then, the mother liquor after treatment in the strong cooling precipitation vessel is returned to the multi-effect evaporation crystallization system to recover salt.

[0043] Table 1. Differences between the methods used in Example 1 and Comparative Examples 1-7 for treating deammoniation mother liquor.

[0044]

[0045]

[0046] Note: In the table, "√" indicates that the process step has been performed, and "×" indicates that the process step has not been performed.

[0047] Table 1 shows the differences between the methods used in Example 1 and Comparative Examples 1-7 for treating the deammoniation mother liquor. The present invention also addresses the yield of sodium chloride product recovered from the deammoniation mother liquor treated using the methods of Example 1 and Comparative Examples 1-7, as well as the sodium chloride and SO4 content. 2- The content of [specific component] was determined, and the results are shown in Table 2:

[0048] Table 2. Yields of sodium chloride products recovered from the deammoniation mother liquor in Examples 1 and Comparative Examples 1-7, and the sodium chloride and SO4 content. 2- content

[0049] Yield (g / m 3 Deamination mother liquor) Sodium chloride (g / 100 g) SO4 2- (g / 100g) Example 1 180 99.8 0.1 Comparative Example 1 140 90 3.1 Comparative Example 2 142 92 2.1 Comparative Example 3 155 95 2 Comparative Example 4 146 93 1.95 Comparative Example 5 152 94 1.71 Comparative Example 6 150 93.5 2.2 Comparative Example 7 142 92 2.3

[0050] As shown in the table above, compared with Comparative Examples 1-7, the method for treating the deammoniation mother liquor in this invention (Example 1) can not only significantly increase the yield of sodium chloride product, but also effectively increase the sodium chloride content in the sodium chloride product, while significantly reducing the SO4 content in the sodium chloride product. 2- The content of [specific element] ensures that the prepared industrial sodium chloride meets the standard of GB / T 5462-2015 for superior grade industrial salt.

[0051] Furthermore, Comparative Examples 2-7 respectively employed one or a combination of two of the following methods to treat the deammoniation mother liquor: single-stage cold precipitation, double-stage cold precipitation, and triple-stage cold precipitation. Compared to Example 1, none of these methods simultaneously improved sodium chloride yield, purity, or SO4 removal as effectively as when all three methods are used together. 2- The technical effect demonstrates that the primary, secondary, and tertiary cold precipitation steps in this invention interact with each other, jointly reducing SO4 in the deammoniation mother liquor. 2- The absence of any one or two of these steps will affect the function of SO4. 2- The removal rate is significantly affected because: after one cold precipitation, SO4 2- The SO4 in the mother liquor is carried away by the crystallization of ammonium chloride; after a second cold precipitation, the SO4 in the mother liquor is removed. 2 - It is further carried away as ammonium chloride crystals precipitate; then it undergoes three cold precipitation processes. The mother liquor during the three cold precipitation processes is saturated brine, containing SO4. 2- The saturated brine is cooled to 0-5°C, and sodium sulfate is removed using sodium sulfate decahydrate (Na₂SO₄·10H₂O); finally, SO₄²⁻ is removed. 2- The sodium chloride mother liquor is returned to multi-effect evaporation, preventing sulfate ions from accumulating in sodium chloride and affecting the quality of industrial sodium chloride.

[0052] The present invention also determined the yield of agricultural ammonium chloride recovered from the deammoniation mother liquor treated by the methods of Example 1 and Comparative Examples 1-7, and the results are shown in Table 3:

[0053] Table 3. Yields of agricultural ammonium chloride recovered from the deammoniation mother liquor in Examples 1 and Comparative Examples 1-7

[0054] Agricultural ammonium chloride production (t / m 3 Deamination mother liquor) Example 1 0.45 Comparative Example 1 0.25 Comparative Example 2 0.28 Comparative Example 3 0.29 Comparative Example 4 0.35 Comparative Example 5 0.31 Comparative Example 6 0.315 Comparative Example 7 0.322

[0055] As can be seen from the table above, the method for treating the deammoniation mother liquor in this invention (Example 1) can further significantly increase the yield of ammonium chloride compared with Comparative Examples 1-7. The reason is that ammonium chloride in the mother liquor is precipitated by cold precipitation during both primary and secondary cold precipitation treatments, thereby further increasing the yield of ammonium chloride.

[0056] The changes in the above technical features can be understood and implemented by those skilled in the art through textual description, therefore no further drawings are required.

[0057] It should be noted that this article uses the terms "first," "second," "first," "second," "third," "fourth," etc., to describe various components, but these components should not be limited by these terms. These terms are only used to distinguish one component from another.

[0058] The terms "up," "down," "left," "right," "front," "back," "vertical," "inner," and "outer" used in this document to describe orientation or position are for ease of explanation and are based on the orientation or positional relationships shown in the accompanying drawings. In actual devices, these orientations may vary depending on the arrangement of the devices. They are only used to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride through multi-effect evaporation crystallization separation, characterized in that, Includes the following steps: 1) Collect the deammoniation mother liquor; 2) First cold precipitation: Transfer the deammoniation mother liquor to the ambient temperature ammonium precipitation kettle, cool it to 25-28℃ for cold precipitation crystallization, centrifuge to obtain agricultural ammonium chloride and mother liquor one; 3) Second cold precipitation: Transfer mother liquor one to the cold precipitation crystallization kettle, add sodium chloride, cool it to 20-23℃ for cold precipitation crystallization, centrifuge to obtain agricultural ammonium chloride and mother liquor two; 4) Third cold precipitation: Transfer mother liquor two to the strong cold precipitation kettle, cool it to 0-5℃ to crystallize sodium sulfate decahydrate, centrifuge to obtain sodium sulfate decahydrate and sodium chloride mother liquor; 5) Return the sodium chloride mother liquor to the multi-effect evaporation system to recover sodium chloride.

2. The method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride in multi-effect evaporation crystallization separation as described in claim 1, characterized in that, The deammoniation mother liquor in step 1) is obtained by first deammonizing by distillation, then extracting sodium chloride from the mother liquor by multi-effect evaporation, and finally precipitating ammonium chloride by flash evaporation and vacuum cooling, followed by centrifugation and dehydration.

3. The method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride in multi-effect evaporation crystallization separation as described in claim 1, characterized in that: In step 2), the time for cold crystallization after the deammoniation mother liquor is cooled to 25-28℃ is 4-6 hours.

4. The method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride in multi-effect evaporation crystallization separation as described in claim 1, characterized in that: In step 3), the time for cold crystallization after the mother liquor is cooled to 20-23℃ is 2-4 hours.

5. The method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride in multi-effect evaporation crystallization separation as described in claim 1, characterized in that: The amount of sodium chloride added is equal to the content of ammonium chloride in the mother liquor × 0.

6.

6. The method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride in multi-effect evaporation crystallization separation as described in claim 1, characterized in that: In step 4), the time for cold crystallization after the mother liquor is cooled to 0-5℃ is 2-4 hours.

7. The method for removing sulfate from deammoniation mother liquor and recovering ammonium chloride and sodium chloride from multi-effect evaporation crystallization separation as described in any one of claims 1-6, characterized in that: The ambient temperature ammonium precipitation vessel, the cold precipitation crystallization vessel, and the strong cold precipitation vessel are all equipped with jackets, and cooling water is injected into the jackets to reduce the temperature of the solution inside the vessel.

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