Production method of low-nitrite ultrapure potassium carbonate
Through a production method including dissolution, crystallization, oxidation, centrifugal separation and airflow drying, the problem of high nitrite content in the existing potassium carbonate process is solved, and the production of ultrapure hydrated potassium carbonate with high purity and low nitrite is achieved.
Patent Information
- Application Number
- CN202510279237.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-11
- Publication Date
- 2025-05-27
AI Technical Summary
In the existing potassium carbonate production process, the nitrite content is relatively high, which is difficult to meet the quality requirements of customers.
A method for producing ultrapure hydrated potassium carbonate with low nitrite is adopted, including using pure water or potassium carbonate centrifuging mother liquor as solvent, and obtaining ultrapure hydrated potassium carbonate with low nitrite through steps such as heating dissolution, cooling crystallization, hydrogen peroxide oxidation, centrifugal separation and vibrating fluidized bed airflow drying.
The nitrite content was achieved significantly lower, the potassium carbonate content of the product reached ≥99.9%, the iron ion content was ≤1ppm, the potassium chloride content was ≤10ppm, the potassium sulfate content was ≤10ppm, and the nitrite content was ≤1ppm, meeting the quality requirements of high purity.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the field of inorganic chemical industry, specifically relates to potassium carbonate production technology, and particularly relates to a production method of ultrapure hydrated potassium carbonate with low nitrite content. Background Art
[0002] The current mainstream production routes of potassium carbonate are the ion exchange method (light quality) and the ion-exchange membrane electrolysis potassium hydroxide fluidized bed synthesis method (heavy quality). Due to the differences in production processes and quality control, both processes have their advantages and disadvantages.
[0003] During the production process of the ion exchange method, in order to solve the problem of the outlet of production wastewater, the production wastewater needs to be recycled. However, during the recycling process, the accumulation of nitrite in the water is caused by the reproduction of nitrifying bacteria (the content of nitrite is generally 200 - 500 mg / L).
[0004] During the production process of heavy potassium carbonate, potassium hydroxide solution reacts with carbon dioxide at high temperature to obtain potassium carbonate. At the same time, nitrogen oxides also react with potassium hydroxide to obtain potassium nitrite and potassium nitrate. Therefore, the nitrite content of heavy potassium carbonate is significantly higher than that of potassium carbonate produced by the ion exchange method (the content of nitrite is generally 100 - 200 ppm).
[0005] Through the quality tracking and analysis of heavy potassium carbonate and light potassium carbonate at home and abroad, it is found that the content of nitrite (calculated as potassium nitrite) in heavy potassium carbonate is as high as more than 100 ppm. The heavy potassium carbonate produced by the ion-exchange membrane electrolysis fluidized bed process is obtained by reacting high-temperature carbon dioxide obtained from natural gas combustion with potassium hydroxide droplets during the synthesis of potassium carbonate, and the potassium carbonate product is formed in one step. Since a small amount of nitrogen oxides will also be produced during the combustion of natural gas under alkaline conditions. For light potassium carbonate, the content of general nitrite (calculated as potassium nitrite) is about 10 - 30 ppm. Although it is significantly lower than that of heavy potassium carbonate, it still cannot meet the quality requirements of customers. Summary of the Invention
[0006] The technical problem to be solved by the present invention is to provide a production method of ultrapure (potassium carbonate content ≥ 99.9%, based on dry basis) hydrated potassium carbonate with low nitrite content (the content of potassium nitrite ≤ 1 ppm).
[0007] To solve the above technical problem, the present invention provides a production method of ultrapure hydrated potassium carbonate with low nitrite content, including the following steps:
[0008] 1), Using production pure water or the potassium carbonate centrifugal mother liquor IV obtained in the subsequent step 4) as a solvent, when the solvent is heated to 90 ± 5 °C, raw material potassium carbonate is added under stirring conditions, and the temperature is increased while adding the raw material potassium carbonate until the temperature reaches 110 - 112 °C and the added raw material potassium carbonate is saturated to obtain potassium carbonate saturated solution I;
[0009] Note: This step can be carried out in a dissolution crystallizer; during the process of adding raw material potassium carbonate while heating up, ensure that the added raw material potassium carbonate is dissolved.
[0010] 2), At a cooling rate of 20 - 30 °C / h, lower the temperature of the potassium carbonate saturated solution I obtained in step 1) to 45 ± 5 °C, and the resulting solution is named potassium carbonate saturated solution II.
[0011] Note: The cooling in this step can be achieved by passing circulating cooling water into the jacket and internal coil of the dissolution crystallizer.
[0012] 3), At a cooling rate of 5 ± 1 °C / h, lower the temperature of the potassium carbonate saturated solution II obtained in step 2) to 20 ± 2 °C, and then add a hydrogen peroxide solution with a mass concentration of 19 - 21% (preferably 20%); the resulting solution is named potassium carbonate saturated solution III; the weight ratio of the hydrogen peroxide solution to the potassium carbonate saturated solution II is (0.1 ± 0.005)%.
[0013] Note: The cooling in this step can be achieved by passing low-temperature water into the jacket and internal coil of the dissolution crystallizer.
[0014] 4), Centrifuge the potassium carbonate saturated solution III described in step 3). During the centrifugation process, use pure production water as the eluent to obtain wet hydrated potassium carbonate and potassium carbonate centrifugation mother liquor IV respectively.
[0015] The potassium carbonate centrifugation mother liquor IV can be returned to step 1) for recycling.
[0016] 5), Dry the wet hydrated potassium carbonate obtained by centrifugation in step 4) (by vibrating fluidized bed carbon dioxide gas drying) to obtain ultrapure hydrated potassium carbonate with low nitrite.
[0017] Note: After drying, cool to room temperature and then screen (the mesh size can be selected according to customer requirements) and package.
[0018] As an improvement to the production method of ultrapure hydrated potassium carbonate with low nitrite of the present invention:
[0019] When the potassium carbonate centrifugation mother liquor IV obtained in step 4) simultaneously meets the following indicators, it can be returned to step 1) for recycling: sodium ion concentration is less than 11500 mg / L, potassium chloride concentration is less than 440 mg / L, potassium sulfate concentration is less than 380 mg / L, iron ion concentration is less than 28 mg / L, and nitrite (calculated as potassium nitrite) is less than 25 mg / L.
[0020] That is, the centrifugal mother liquor IV of potassium carbonate produced in step 4) is returned to step 1) for dissolving the raw material potassium carbonate, and the number of return applications is controlled by the centrifugal mother liquor IV of potassium carbonate produced in step 4) simultaneously meeting the above indicators; therefore, when any one of the indicators in the centrifugal mother liquor IV of potassium carbonate exceeds the above limit value, the return of the centrifugal mother liquor IV of potassium carbonate to step 1) for recycling is stopped.
[0021] The centrifugal mother liquor IV of potassium carbonate that is not recycled can be used to produce industrial-grade potassium bicarbonate or potassium carbonate (that is, transferred to the industrial-grade potassium bicarbonate or potassium carbonate production line).
[0022] As a further improvement of the production method of ultra-pure hydrated potassium carbonate with low nitrite of the present invention, the dosage of the eluent in step 4) is as follows:
[0023] When using production pure water as the solvent in step 1), control the eluent: the raw material potassium carbonate used in step 1) = 8 - 10% by mass ratio.
[0024] When using the centrifugal mother liquor IV of potassium carbonate obtained in subsequent step 4) as the solvent in step 1), control the eluent: the raw material potassium carbonate used in step 1) = 21.5 - 26% by mass ratio.
[0025] As a further improvement of the production method of ultra-pure hydrated potassium carbonate with low nitrite of the present invention:
[0026] The raw material potassium carbonate described in step 1) is required to simultaneously meet the following indicators: potassium carbonate content ≥ 99.0%, iron ion content ≤ 10 ppm, potassium chloride content ≤ 150 ppm, potassium sulfate content ≤ 100 ppm, nitrite (calculated as potassium nitrite) content ≤ 20 ppm, sodium content ≤ 4000 ppm.
[0027] As a further improvement of the production method of ultra-pure hydrated potassium carbonate with low nitrite of the present invention: the production pure water described in steps 1) and 4) is deionized water, which is required to simultaneously meet the following indicators: iron ion concentration < 0.01 mg / L, chloride ion concentration < 0.1 mg / L, sulfate ion concentration < 0.1 mg / L, sodium ion concentration < 0.1 mg / L, nitrite (calculated as potassium nitrite) < 0.1 mg / L, pH = 6.0 - 8.0, total organic carbon < 1 mg / L.
[0028] As a further improvement of the production method of ultra-pure hydrated potassium carbonate with low nitrite of the present invention: in step 5), the wet hydrated potassium carbonate obtained by centrifugal separation in step 4) is dried by vibrating fluidized bed carbon dioxide gas flow, and the dried material has a calcination weight loss between 15.0 - 17.0% at 300 °C.
[0029] As a further improvement to the production method of ultrapure potassium carbonate with low nitrite of the present invention: In the vibrating fluidized bed carbon dioxide gas drying in step 5), the inlet air temperature is 140 - 150 °C, the bed temperature is 105 - 120 °C, and the outlet air temperature is 80 - 90 °C.
[0030] Note:
[0031] The inlet air includes recycled air and supplementary carbon dioxide.
[0032] During the gas drying process, carbon dioxide leaked due to air leakage points such as the feed inlet and the discharge outlet can be introduced through the air make-up inlet (this is a conventional operation mode). The outlet air undergoes secondary air-cooled heat exchange and secondary water condensation, and after removing the moisture, it returns to the inlet of the vibrating fluidized bed gas drying system, achieving efficient utilization of carbon dioxide and energy.
[0033] The ultrapure potassium carbonate with low nitrite obtained after the final drying of the present invention meets the following quality standards: potassium carbonate content (dry basis) ≥ 99.8%, iron ion content ≤ 1 ppm, potassium chloride content ≤ 10 ppm, potassium sulfate content ≤ 10 ppm, nitrite (calculated as potassium nitrite) content ≤ 1 ppm, sodium content ≤ 500 ppm, and the weight loss on calcination at 300 °C is between 15.0 - 17.0%.
[0034] The present invention uses industrial potassium carbonate as the raw material, and through dissolution, cooling crystallization, hydrogen peroxide oxidation, centrifugal separation, and drying with a vibrating fluidized bed gas dryer (low-temperature drying under a carbon dioxide atmosphere), ultrapure potassium carbonate with low nitrite is obtained.
[0035] The present invention has the technical advantages of simple process, easy control, and excellent product quality. The obtained potassium carbonate has the advantage of low nitrite content, that is, the nitrite (calculated as potassium nitrite) content ≤ 1 ppm. Specific Embodiments
[0036] The following further describes the present invention in combination with specific embodiments, but the protection scope of the present invention is not limited thereto:
[0037] The stirring speed of the present invention is 50 - 60 rpm,
[0038] The rotation speed of centrifugal separation is 800 - 1200 rpm.
[0039] Example 1 - 1, A production method of ultrapure potassium carbonate with low nitrite (corresponding to the serial number 1 in Table 1),
[0040] The raw material potassium carbonate has the following quality indicators: potassium carbonate content 99.0%, iron ion content 10 ppm, potassium chloride content 150 ppm, potassium sulfate content 100 ppm, nitrite (calculated as potassium nitrite) content 15.8 ppm, sodium content 3996 ppm.
[0041] The deionized water used in production is deionized water, and its main quality indicators are as follows: iron ion concentration less than 0.01 mg / L, chloride ion concentration less than 0.1 mg / L, sulfate ion concentration less than 0.1 mg / L, sodium ion concentration less than 0.1 mg / L, nitrite (calculated as potassium nitrite) less than 0.1 mg / L, pH = 6.0 - 8.0, total organic carbon less than 1 mg / L.
[0042] For the first production, the following steps are carried out in sequence:
[0043] 1), Put 1502 kg of deionized water used in production as a solvent into the dissolution crystallizer, and open the steam valve to raise the temperature. When the temperature rises to 90 ± 5 °C, add the raw material potassium carbonate under stirring. While adding the raw material potassium carbonate, raise the temperature, and during the process of adding the raw material potassium carbonate and raising the temperature, ensure that the added raw material potassium carbonate is dissolved;
[0044] Until the temperature rises to 110 - 112 °C and after holding the temperature and stirring for 30 min when potassium carbonate is saturated; obtain saturated potassium carbonate solution I;
[0045] When producing for the first time, 2269 kg of raw material potassium carbonate is added.
[0046] In this step, the dissolution situation of the raw material potassium carbonate can be observed through the sight glass.
[0047] 2), Pass circulating cooling water into the jacket and inner coil of the dissolution crystallizer, and reduce the temperature of the saturated potassium carbonate solution I obtained in step 1) to 45 ± 5 °C at a cooling rate of 20 - 30 °C / h, and name it saturated potassium carbonate solution II;
[0048] 3), Pass low-temperature water into the jacket and inner coil of the dissolution crystallizer, and reduce the temperature of the saturated potassium carbonate solution II obtained in step 2) to 20 °C at a cooling rate of 5 °C / h, and then add hydrogen peroxide solution with a concentration of 20% (mass%) in a weight ratio of 0.1% of the saturated potassium carbonate solution II, and name it saturated potassium carbonate solution III;
[0049] 4), Centrifuge the saturated potassium carbonate solution III described in step 3). During the centrifugation process, use deionized water used in production as a rinsing liquid to obtain wet hydrated potassium carbonate and potassium carbonate centrifugation mother liquor IV; the dosage details are shown in Table 1 below.
[0050] The potassium carbonate centrifugation mother liquor IV can be returned to step 1) for recycling. The control method for the number of recycling times is as follows: The potassium carbonate centrifugation mother liquor IV obtained in step 4) simultaneously meets the following indicators:
[0051] The sodium ion concentration is less than 11500 mg / L, the potassium chloride concentration is less than 440 mg / L, the potassium sulfate concentration is less than 380 mg / L, the iron ion concentration is less than 28 mg / L, and the nitrite (calculated as potassium nitrite) is less than 25 mg / L.
[0052] Therefore, when any one of the indicators in the potassium carbonate centrifugation mother liquor IV exceeds the above limit, the recycling of the potassium carbonate centrifugation mother liquor IV to step 1) is stopped.
[0053] The potassium carbonate centrifugation mother liquor IV that is not recycled is used for the production of industrial-grade potassium bicarbonate or potassium carbonate (i.e., transferred to the industrial-grade potassium bicarbonate or potassium carbonate production line).
[0054] The obtained amount and impurity content of the hydrated potassium carbonate wet product and the potassium carbonate centrifugation mother liquor IV are as described in item 1 of Table 1 below.
[0055] Example 1-2: 2727.2 kg of the potassium carbonate centrifugation mother liquor IV obtained in step 4) of Example 1-1 was used as a solvent and put into a dissolution crystallizer. In this case, the feeding amount of the raw material potassium carbonate in step 1) was 806 kg, and the amount of production pure water (i.e., washing water) used for rinsing in step 4) was correspondingly controlled at 191 kg; the rest was the same as in Example 1-1. This was used as the first recycling (corresponding to item 2 in Table 1).
[0056] Examples 1-3 to 1-20: And so on, the second recycling (corresponding to item 3 in Table 1) to the nineteenth recycling (corresponding to item 20 in Table 1) were obtained; each time during recycling, the feeding amount of the raw material potassium carbonate in step 1) and the amount of production pure water (i.e., washing water) used for rinsing in step 4) are shown in detail in Table 1.
[0057] The obtained amount and impurity content of the hydrated potassium carbonate wet product and the potassium carbonate centrifugation mother liquor IV obtained each time of recycling are as described in Table 1 below.
[0058] Table 1. Influence of the number of mother liquor recycling times in Example 1 on quality
[0059]
[0060]
[0061] The present invention sets that when the sodium ion concentration is less than 11500 mg / L, the potassium chloride concentration is less than 440 mg / L, the potassium sulfate concentration is less than 380 mg / L, the iron ion concentration is less than 28 mg / L, and the nitrite (calculated as potassium nitrite) is less than 25 mg / L, the potassium carbonate centrifugal mother liquor IV can be returned to step 1) for recycling. When any one of the indicators in the potassium carbonate solution I exceeds the above limits, the return of the potassium carbonate centrifugal mother liquor IV to step 1) for recycling is stopped.
[0062] As can be seen from the data in Table 1 above, with the increase in the number of times the mother liquor is recycled, the impurities in the obtained hydrated potassium carbonate will also increase. The potassium carbonate centrifugal mother liquor IV obtained from the ninth recycling (serial number 10 in Table 1) no longer meets the above conditions, so it cannot be recycled anymore.
[0063] Example 2: The hydrated potassium carbonate wet product obtained by centrifugation in step 4) of Examples 1-1 to 1-20 was dried:
[0064] The hydrated potassium carbonate wet product obtained by centrifugal separation in step 4) was dried by vibrating fluidized bed carbon dioxide gas flow; the set parameters of the vibrating fluidized bed carbon dioxide gas flow drying were: inlet air temperature 140 - 150 °C, bed temperature 105 - 120 °C, outlet air temperature 80 - 90 °C, and drying until the obtained dried material met the following conditions: the calcination loss at 300 °C was between 15.0 - 17.0%.
[0065] After cooling, it was sieved (the sieve size can be selected according to customer requirements) and packaged to obtain ultrapure hydrated potassium carbonate with low nitrite (K 2 CO 3 ·1.5H 2 O).
[0066] Note:
[0067] The inlet air includes recycled air and supplemented carbon dioxide.
[0068] During the vibrating fluidized bed carbon dioxide gas flow drying process, carbon dioxide leaked due to air leakage points such as the feed inlet and the discharge outlet can be introduced through the air make-up port (this is a conventional operation mode, and the purpose is to ensure that the circulating air volume remains unchanged). The outlet air passes through secondary air-cooled heat exchange and secondary water condensation (the temperature can generally be reduced to 60 - 70 °C after secondary air cooling; the temperature can generally be reduced to 35 - 40 °C after secondary water cooling), and after removing the moisture, it returns to the inlet of the vibrating fluidized bed gas flow drying system to achieve efficient utilization of carbon dioxide and energy. The water generated by condensation can be uniformly flowed into the condensation water tank for collection.
[0069] From the comparison data before and after drying in Table 2, it can be seen that by using the vibrated fluidized bed carbon dioxide gas drying described in the present invention, the obtained product can meet the specified quality requirements, and the nitrite will not increase significantly during the drying process.
[0070] Table 2. Comparison of data before and after drying in Example 2
[0071]
[0072] Note: The potassium carbonate monohydrate obtained after drying in the above serial numbers 1 to 9 all meet the following potassium carbonate mass standards:
[0073] Potassium carbonate content (dry basis) ≥ 99.9%, iron ion content ≤ 1 ppm, potassium chloride content ≤ 10 ppm, potassium sulfate content ≤ 10 ppm, nitrite (calculated as potassium nitrite) content ≤ 1 ppm, sodium content ≤ 500 ppm, calcination loss at 300 °C is between 15.0 - 17.0%.
[0074] In summary, it can be known that the obtained product (potassium carbonate monohydrate) of the present invention has a low nitrite content.
[0075] Comparative Example 1. Influence of different dissolution temperatures on product quality and yield
[0076] 1), Put 1500 kg of pure water for production into the dissolution and crystallization vessel, and open the steam valve to heat up until the temperature reaches 90 ± 5 °C. While stirring, add the raw material potassium carbonate. While adding the raw material potassium carbonate, heat up. Set the end temperatures to 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, and 115 °C respectively. When the potassium carbonate is saturated, stop adding potassium carbonate and keep it warm at 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, and 115 °C for 30 min to obtain a saturated potassium carbonate solution I;
[0077] That is, the experimental mother liquor of Comparative Example 1 is not recycled, and only the dissolution and crystallization with pure water are compared.
[0078] The operations and raw materials in other steps are the same as those in Example 1-1.
[0079] From the data in Table 3, it can be seen that the dissolution temperature has a great influence on the yield of potassium carbonate monohydrate. When dissolved at 85 °C, 130.06 kg of potassium carbonate monohydrate is obtained, while when dissolved at 115 °C, 1008.79 kg of potassium carbonate monohydrate is obtained. However, the difference in the yield of potassium carbonate monohydrate when dissolved at 110 °C and 115 °C is not significant, which are 994.06 kg and 1008.79 kg respectively. Therefore, it is the optimal choice to dissolve at 110 - 112 °C in the present invention.
[0080] Table 3. Experimental data of Comparative Example 1
[0081]
[0082] Comparative Example 2. Influence of Different Crystallization Temperatures on Product Quality and Yield
[0083] 1), Put 1500 kg of pure water for production into the dissolution crystallizer, and open the steam valve to raise the temperature until the temperature reaches 90 ± 5 °C. While stirring, add the raw material potassium carbonate. While adding the raw material potassium carbonate, raise the temperature to 110 °C. When the potassium carbonate is saturated, stop adding potassium carbonate and keep it warm at 110 °C for 30 min to obtain saturated potassium carbonate solution I;
[0084] The experimental mother liquor of Comparative Example 2 is not recycled, and only the dissolution crystallization with pure water is compared.
[0085] 2), Pass circulating cooling water into the jacket and inner coil of the dissolution crystallizer. At a cooling rate of 20 - 30 °C / h, lower the temperature of the saturated potassium carbonate solution I obtained in step 1) to 50 °C to obtain saturated potassium carbonate solution II;
[0086] 3), Pass low-temperature water into the jacket and inner coil of the dissolution crystallizer. At a cooling rate of 5 °C / h, lower the temperature of the saturated potassium carbonate solution II obtained in step 2) to 10 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C respectively to obtain saturated potassium carbonate solution III;
[0087] Other operations and raw materials are the same as those in Example 1-1.
[0088] It can be seen from the data in Table 4 that the crystallization temperature has a very large influence on the yield of potassium carbonate monohydrate. When crystallizing at 10 °C, the batch of potassium carbonate monohydrate is 1009.85 kg, while when crystallizing at 40 °C, the batch of potassium carbonate monohydrate is 862.48 kg. However, there is little difference in the yield of potassium carbonate monohydrate between crystallization at 20 °C and 10 °C, which are 994.06 kg and 1009.85 kg respectively. Therefore, choosing to crystallize at 20 °C is the optimal choice.
[0089] Table 4. Experimental Data of Comparative Example 2
[0090]
[0091] For the series of Comparative Example 1, change the "20% hydrogen peroxide solution" in step 3) of Example 1-1 to "pure water for production", and keep the volume usage unchanged; other operations are the same as those in Example 1-1.
[0092] And corresponding first application to nineteenth application are carried out; the feeding amount of the raw material potassium carbonate in step 1) and the usage amount of the pure water for production (i.e., washing water) as the eluent in step 4) are shown in Table 5 in detail.
[0093] The amount of the hydrated potassium carbonate wet product, the amount of potassium carbonate centrifuged mother liquor IV and the impurity content obtained in each application are as described in the following Table 5.
[0094] From the comparison between the data in Table 5 and the examples, it can be seen that after step 3) without adding hydrogen peroxide, the nitrite content and the nitrite concentration in the mother liquor will increase, and the 6th time of the series of comparative example 1 (corresponding to sequence number 7 in Table 5) no longer meets the mother liquor circulation conditions, so the addition of hydrogen peroxide has a substantial effect on reducing nitrite.
[0095] Table 5, Comparative Example 1 Data
[0096]
[0097]
[0098] Comparative Example 2: The vibrating fluidized bed carbon dioxide airflow drying in Example 2 was changed to vibrating fluidized bed airflow drying, that is, the circulating air and the supplementary air were changed from carbon dioxide to air. The rest was the same as Example 2.
[0099] From the comparative data before and after drying in Table 6, it can be seen that the product obtained by using vibrating fluidized bed air flow drying cannot meet the specified quality requirements, mainly because the nitrite content increases significantly before and after drying.
[0100] Table 6, Comparative Example 2 Data Comparison Before and After Drying
[0101]
[0102]
[0103] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.
Claims
1. A method for producing ultrapure hydrated potassium carbonate with low nitrite, characterized in that The following steps are involved: 1) Using pure water for production or potassium carbonate centrifugal mother liquor IV obtained in the subsequent step 4) as a solvent, heating the solvent to 90±5° C., adding raw potassium carbonate under stirring conditions, and heating while adding raw potassium carbonate until the temperature reaches 110-112° C. and the raw potassium carbonate added is saturated, thereby obtaining a saturated potassium carbonate solution I; 2) The temperature of the saturated potassium carbonate solution I obtained in step 1) is reduced to 45±5°C at a cooling rate of 20-30°C / h, and the obtained solution is named as saturated potassium carbonate solution II; 3) According to the cooling rate of 5±1°C / h, the temperature of the saturated potassium carbonate solution II obtained in step 2) is reduced to 20±2°C, and then a hydrogen peroxide solution with a mass concentration of 19-21% is added, and the obtained solution is named as a saturated potassium carbonate solution III; the weight ratio of the hydrogen peroxide solution: the saturated potassium carbonate solution II = (0.1±0.005)%; 4) centrifugally separating the saturated potassium carbonate solution III described in step 3), and using pure water for production as eluent during the centrifugation process to obtain a hydrated potassium carbonate wet product and a potassium carbonate centrifuge mother liquor IV; The potassium carbonate centrifuged mother liquor IV can be returned to step 1) for recycling; 5) The wet potassium carbonate hydrate obtained by centrifugation in step 4) is dried to obtain ultrapure potassium carbonate hydrate with low nitrite.
2. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to claim 1, characterized in that: When the potassium carbonate centrifugal mother liquor IV obtained in step 4) meets the following indicators at the same time, it can be returned to step 1) for recycling: sodium ion concentration is less than 11500 mg / L, potassium chloride concentration is less than 440 mg / L, potassium sulfate concentration is less than 380 mg / L, iron ion concentration is less than 28 mg / L, and nitrite is less than 25 mg / L.
3. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to claim 2, characterized in that: The amount of the eluent in step 4) is: When pure water for production is used as the solvent in step 1), the eluent is controlled to have a mass ratio of 8 to 10% of the raw material potassium carbonate used in step 1); When the potassium carbonate centrifugal mother liquor IV obtained in the subsequent step 4) is used as the solvent in step 1), the mass ratio of the eluent: the raw material potassium carbonate used in step 1) is controlled to be 21.5-26%.
4. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to any one of claims 1 to 3, characterized in that: The raw material potassium carbonate described in step 1) is required to meet the following indicators at the same time: potassium carbonate content ≥99.0%, iron ion content ≤10ppm, potassium chloride content ≤150ppm, potassium sulfate content ≤100ppm, nitrite content ≤20ppm, sodium content ≤4000ppm.
5. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to claim 4, characterized in that: The pure water for production described in step 1) and step 4) is deionized water, which is required to meet the following indicators at the same time: iron ion concentration is less than 0.01 mg / L, chloride ion concentration is less than 0.1 mg / L, sulfate concentration is less than 0.1 mg / L, sodium ion concentration is less than 0.1 mg / L, nitrite is less than 0.1 mg / L, pH=6.0-8.0, and total organic carbon is less than 1 mg / L.
6. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to any one of claims 1 to 5, characterized in that In step 5), the wet potassium carbonate hydrate obtained by centrifugal separation in step 4) is dried by a carbon dioxide gas flow in a vibrating fluidized bed, and the calcination weight loss of the dried material at 300° C. is between 15.0 and 17.0%.
7. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to claim 6, characterized in that: The vibrating fluidized bed carbon dioxide airflow drying in step 5) has an air inlet temperature of 140-150°C, a bed temperature of 105-120°C, and an air outlet temperature of 80-90°C.
8. The method for producing ultrapure hydrated potassium carbonate with low nitrite according to any one of claims 1 to 7, characterized in that: In step 5), the quality standards of the ultrapure hydrated potassium carbonate obtained by drying are as follows: potassium carbonate content ≥99.9%, iron ion content ≤1ppm, potassium chloride content ≤10ppm, potassium sulfate content ≤10ppm, nitrite content ≤1ppm, sodium content ≤500ppm, and calcination weight loss at 300°C between 15.0 and 17.0%.