Process for the recovery of ammonium components in the production of sodium bicarbonate from sodium sulfate

Abstract

This invention relates to a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate, belonging to the field of chemical production technology. The recovery method includes: pretreating a crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate, and diammonium carbonate, then mixing it with sodium sulfate and crystallizing to obtain a liquid-solid mixture; separating fine particles from coarse crystals in the liquid-solid mixture to obtain a coarse crystal slurry and a slurry containing fine particles, respectively; performing solid-liquid separation on the obtained coarse crystal slurry to obtain a double salt and a filtrate; and mixing the obtained double salt with a solution for washing to obtain solid sodium sulfate and a solution of ammonium sulfate. The recovery method provided by this invention has advantages such as a short process flow, simple operation, and no environmental pollution risk. This method not only avoids high-temperature ammonia stripping and low-temperature freezing processes, reducing investment and operating costs and energy consumption, but also improves the ammonia recovery rate and enhances raw material utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, specifically to a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate. Background Technology

[0002] Currently, there are still many problems to be solved in the technology of preparing sodium bicarbonate or sodium carbonate and ammonium sulfate from sodium sulfate. This is because the single-pass utilization rate of sodium in the metathesis reaction during the preparation process is only 50-60%. The main components of the sodium bicarbonate mother liquor after the reaction are sodium sulfate, ammonium sulfate, ammonium bicarbonate and a small amount of diammonium carbonate. It is impossible to obtain a relatively pure ammonium sulfate product in subsequent processes, whether by thermal or cold methods.

[0003] The traditional solution involves freezing the sodium bicarbonate mother liquor to -10°C to crystallize sodium sulfate, and then recovering ammonium bicarbonate by high-temperature ammonia stripping or distillation. The mother liquor from which ammonium bicarbonate is recovered is then subjected to evaporation, freezing, and evaporation processes to obtain ammonium sulfate. This route involves complex equipment, high energy consumption, and the risk of ammonia leakage. Furthermore, repeated freezing and heating result in a long process flow and high investment and operating costs. Therefore, sodium sulfate production of alkali has not been industrialized.

[0004] For example, CN116835833A discloses a method for the resource utilization of sodium sulfate wastewater containing heavy metals. To avoid the high energy consumption and long process flow caused by multiple freezing and evaporation processes, this method involves distilling the sodium bicarbonate crystallization mother liquor to recover ammonium bicarbonate, mixing it with the cooled mother liquor, and directly evaporating to crystallize ammonium sulfate. After cooling the mother liquor, a double salt is crystallized and returned to the metathesis reaction. Although this method achieves the separation of ammonium bicarbonate and recovered ammonium sulfate through a single ammonia stripping, single evaporation crystallization, and single cooling, the amount of ammonium bicarbonate input in the metathesis reaction process is more than twice the molar amount of sodium sulfate. Since the single-pass conversion rate of sodium sulfate is only 50-60%, this means that 75% of the ammonium bicarbonate remains unreacted and needs to be circulated within the system through distillation at temperatures above 100°C. This not only fails to reduce energy consumption but also increases ammonia loss. Furthermore, returning the cooled crystals to the metathesis reaction further reduces the single-pass conversion rate of sodium and can also result in the sodium bicarbonate product, leading to low product purity.

[0005] CN114455612A discloses a process for producing gypsum as a byproduct of soda ash production using sodium sulfate and carbon dioxide as raw materials. This process recovers ammonium bicarbonate from the sodium bicarbonate crystallization mother liquor using a traditional ammonia stripping process. However, the mother liquor after ammonium bicarbonate recovery is not further processed to obtain ammonium sulfate; instead, calcium carbonate is added and ammonia is stripped again to prepare gypsum. Although this process eliminates the need for a freezing step, the resulting gypsum product has low value, contains sodium sulfate and ammonium sulfate, resulting in low product quality. Furthermore, the multiple ammonia stripping processes increase the risk of ammonia leakage.

[0006] CN108975356A discloses a method for producing sodium bicarbonate and ammonium sulfate from sodium sulfate and / or sodium sulfate. The method involves distilling ammonia from the sodium bicarbonate crystallization mother liquor at 100-130°C, then dehydrating and crystallizing sodium sulfate at 80-100°C. The sodium sulfate crystallization mother liquor is then cooled to precipitate a double salt, and the cooled mother liquor is evaporated to crystallize ammonium sulfate. While this method reduces the amount of raw materials circulating in the system by increasing the sodium conversion rate and to some extent reduces the heat required for mother liquor treatment, it does not fundamentally solve the high energy consumption problem caused by high-temperature ammonia distillation and repeated heating and cooling processes.

[0007] In summary, existing technologies for ammonia removal struggle to eliminate the need for both high-temperature ammonia stripping and low-temperature freezing processes. High-temperature ammonia stripping requires a combination of equipment, including stripping towers, condensers, and gas-liquid separators, resulting in complex and diverse equipment with high steam consumption. Furthermore, the need for a low-temperature condensation process to separate ammonia and carbon dioxide from the condensate poses a risk of ammonia leakage into the environment. Low-temperature freezing requires refrigeration units and the freezing medium must be cooled to below zero degrees Celsius, placing extremely high demands on equipment and resulting in high energy consumption.

[0008] Therefore, developing a low-cost, safe, environmentally friendly, and efficient method for recovering ammonium components, which addresses the shortcomings of existing technologies, is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0009] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for recovering ammonium components in the process of producing sodium bicarbonate from sodium sulfate, so as to solve the problems of ineffective recovery of ammonium components and poor recovery efficiency in the existing recovery schemes.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] This invention provides a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate, the recovery method comprising:

[0012] The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate was pretreated and then mixed with sodium sulfate in the first stage and crystallized to obtain a liquid-solid mixture.

[0013] Fine particles and coarse crystals in a liquid-solid mixture are separated to obtain coarse crystal slurry and slurry containing fine particles, respectively.

[0014] The obtained coarse crystal slurry was subjected to solid-liquid separation to obtain a complex salt and filtrate;

[0015] The resulting double salt was mixed with the solution and washed to obtain sodium sulfate solid and ammonium sulfate solution; the obtained sodium sulfate solid was returned to the first mixture, and the obtained filtrate was returned to the first mixture.

[0016] The recycling method provided by this invention has the advantages of short process flow, simple operation, and no environmental pollution risk. This method can not only avoid the high-temperature ammonia stripping and low-temperature freezing process, reduce the large-scale equipment required for the sodium sulfate to sodium bicarbonate production process, reduce investment and operating costs, and reduce energy consumption, but also improve the ammonia recovery rate and improve the raw material utilization efficiency.

[0017] As a preferred technical solution of the present invention, the pretreatment method includes neutralizing bicarbonate ions with alkali to convert them into carbonate ions and / or heating to 50-80°C to decompose bicarbonate ions into carbonate ions.

[0018] Preferably, the endpoint of the pretreatment is to reduce the concentration of bicarbonate in the crystallization mother liquor to 40-75 g / L.

[0019] As a preferred technical solution of the present invention, the solid-liquid ratio (g / L) of sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate in the first mixture is (200-500):1.

[0020] Preferably, the sodium sulfate comprises commercially available sodium sulfate and / or solid sodium sulfate obtained by washing.

[0021] As a preferred technical solution of the present invention, the crystallization operation temperature is 10-40℃.

[0022] As a preferred embodiment of the present invention, the crystallization time is 1-12 hours.

[0023] As a preferred technical solution of the present invention, the method for separating fine particles and coarse crystals in a liquid-solid mixture includes one or a combination of at least two of gravity classification, hydrocyclone, centrifugal separation or sieving.

[0024] As a preferred embodiment of the present invention, the temperature of the liquid phase material in the washing process is 60-100℃.

[0025] As a preferred embodiment of the present invention, the washing dwell time is 30-240 min.

[0026] As a preferred embodiment of the present invention, the slurry containing fine particles enters the sodium bicarbonate production system.

[0027] As a preferred embodiment of the present invention, the washing medium used in the washing process includes water or a solution containing sodium sulfate and ammonium sulfate.

[0028] This invention uses a mild method to recover the ammonium component from the sodium bicarbonate crystallization mother liquor, and achieves efficient separation of sodium sulfate and ammonium sulfate through enhanced gradient crystallization. This overcomes the shortcomings of existing processes for preparing sodium bicarbonate and ammonium sulfate from sodium sulfate, such as high-temperature decomposition of ammonium bicarbonate, multiple low-temperature (below zero degrees Celsius) freezing, high energy consumption, complex processes, and high environmental risks.

[0029] Compared with existing technical solutions, the present invention has the following beneficial effects:

[0030] (1) This invention utilizes ammonia neutralization, heating, or a combination of both to convert a small amount of bicarbonate into carbonate, thereby reducing the bicarbonate content in the mother liquor. The entire process is simple to operate and has no environmental pollution risk caused by ammonia leakage. It eliminates the need for traditional ammonia stripping towers, condensers, and gas-liquid separators. It has low energy consumption, overcoming the shortcomings of high steam consumption caused by high-temperature ammonia stripping in existing methods. It has a high ammonia recovery rate, truly realizing the safe and low-cost recycling of ammonia media within the system.

[0031] (2) Based on the phase equilibrium law of the five-element water-salt system and the principle of salting out effect, this invention utilizes the differences in solubility, density and particle size of different substances at different temperatures. By adding sodium sulfate to the crystallization mother liquor after reducing bicarbonate, the invention simultaneously achieves the recycling of ammonia medium, the preparation of sodium sulfate saturated solution and the preliminary separation of ammonium sulfate. The whole process is carried out in a mild manner, with a short process, rapid reaction and no waste generated.

[0032] (3) This invention enhances the gradient crystallization of sodium sulfate and ammonium sulfate through the salting-out effect and the phase diagram law of the ternary water-salt system, thereby achieving efficient separation of sodium sulfate and ammonium sulfate in a short process and avoiding the problems of high energy consumption, high equipment damage rate and high operation difficulty caused by multiple freezing (below zero degrees) and heating in the existing methods.

[0033] (4) The fine particle slurry obtained by the present invention is used to prepare sodium bicarbonate (or sodium carbonate) through a metathesis reaction process, and ammonium sulfate is obtained by crystallization through an evaporation process using a hot solution of ammonium sulfate. This provides a low-cost, safe and environmentally friendly method for preparing sodium bicarbonate (or sodium carbonate) and ammonium sulfate from sodium sulfate. No waste gas, waste liquid and solid waste are generated throughout the process, and the environmental and economic benefits are significant. Attached Figure Description

[0034] Figure 1 This is a flowchart of a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate, as provided in an embodiment of the present invention.

[0035] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims. Detailed Implementation

[0036] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0037] This embodiment provides a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate, such as... Figure 1As shown, the recycling method includes:

[0038] The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is pretreated and then mixed with sodium sulfate for the first time and crystallized to obtain a liquid-solid mixture.

[0039] Fine particles and coarse crystals in a liquid-solid mixture are separated to obtain coarse crystal slurry and slurry containing fine particles, respectively.

[0040] The obtained coarse crystal slurry was subjected to solid-liquid separation to obtain a complex salt and filtrate;

[0041] The obtained double salt was washed to obtain sodium sulfate solid and ammonium sulfate solution;

[0042] The resulting sodium sulfate solid was returned to the first mixture, and the resulting filtrate was also returned to the first mixture.

[0043] In this invention, the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is the mother liquor obtained after the metathesis reaction during the production of sodium bicarbonate from sodium sulfate.

[0044] In this invention, the pretreatment method includes neutralizing bicarbonate ions with alkali to convert them into carbonate ions and / or heating to 50-80°C to decompose bicarbonate ions into carbonate ions.

[0045] In this invention, the alkali used in the pretreatment includes commonly used alkaline solutions in the art, such as ammonia water, sodium hydroxide solution, and potassium hydroxide solution.

[0046] In this invention, the mass percentage of nitrogen in the obtained double salt is 4-8.5%, for example, it can be 4%, 5%, 6%, 7%, 8% or 8.5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0047] Specifically, the endpoint of the pretreatment is to reduce the bicarbonate concentration in the crystallization mother liquor to 40-75 g / L, for example, it can be 40 g / L, 43 g / L, 45 g / L, 48 g / L, 50 g / L, 53 g / L, 55 g / L, 57 g / L, 60 g / L, 63 g / L, 65 g / L, 67 g / L, 70 g / L, 73 g / L or 75 g / L, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also acceptable.

[0048] In this invention, if the concentration of bicarbonate in the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate meets the limit, pretreatment is not required and subsequent processes can be carried out directly. Otherwise, the concentration of bicarbonate in the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is reduced / increased to the limit before being mixed with sodium sulfate.

[0049] Specifically, the solid-liquid ratio (g / L) of sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate, and diammonium carbonate in the first mixture is (200-500):1. For example, it can be 200:1, 220:1, 240:1, 260:1, 280:1, 300:1, 320:1, 340:1, 360:1, 380:1, 400:1, 420:1, 440:1, 460:1, 480:1, or 500:1, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0050] In this invention, the sodium sulfate used in the first mixture includes commercially available sodium sulfate and / or solid sodium sulfate obtained from washing, or sodium sulfate formed in other processes.

[0051] Specifically, the crystallization operation temperature is 10-40℃, for example, it can be 10℃, 13℃, 15℃, 18℃, 20℃, 23℃, 25℃, 27℃, 30℃, 32℃, 35℃, 38℃ or 40℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0052] Specifically, the crystallization time is 1-12 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 10 hours, 11 hours, or 12 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0053] In this invention, the liquid-solid mixture is separated to obtain a coarse-grained slurry and a slurry containing fine particles.

[0054] Specifically, the methods for separating fine particles from coarse crystals in a liquid-solid mixture include one or at least two combinations of gravity classification, hydrocyclone, centrifugal separation, or sieving.

[0055] In this invention, the temperature of the washing medium can be maintained by heat exchange or by direct heating.

[0056] Specifically, the temperature of the liquid phase material in the washing process is 60-100℃, for example, it can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0057] Specifically, the washing dwell time is 30-240 minutes, for example, it can be 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 130 minutes, 150 minutes, 170 minutes, 190 minutes, 210 minutes, 230 minutes or 240 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0058] Specifically, the ratio of liquid phase material to double salt in the washing process is such that the ammonium sulfate in the double salt is just completely dissolved. Specifically, the amount of liquid phase material can be determined according to the amount of ammonium sulfate based on the phase diagram of the ternary aqueous salt system.

[0059] In this invention, the washing medium used in the washing process includes water or a solution containing sodium sulfate and ammonium sulfate.

[0060] The washing effect of this invention can be achieved by selecting a solution containing sodium sulfate and ammonium sulfate where the mass concentrations of sodium sulfate and ammonium sulfate are less than or equal to the saturation concentration of the corresponding solutes.

[0061] In this invention, the sodium sulfate solid is returned to the first mixing reaction process for secondary utilization.

[0062] In this invention, the resulting slurry containing fine particles is fed into a sodium sulfate metathesis reaction system to produce sodium bicarbonate for the preparation of sodium bicarbonate or sodium carbonate, and the purity of the prepared sodium bicarbonate is ≥98.5%.

[0063] In this invention, the obtained ammonium sulfate solution is evaporated and crystallized to obtain the ammonium sulfate product.

[0064] In this invention, the solid-liquid separation method includes methods commonly used in the art to achieve solid-liquid separation, such as filtration, vacuum filtration, pressure filtration, centrifugation, etc.

[0065] In this invention, the solvents used in preparing the relevant solutions during the processing include water and other solvents commonly used in the art for preparing solutions. The water used can be industrial water, industrial water that meets the requirements, residential water, etc.

[0066] Furthermore, to illustrate the excellent recovery effect of the method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate provided by this invention, a practical example is used for explanation, as follows:

[0067] Example 1

[0068] This embodiment provides a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate. The recovery method includes:

[0069] The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate was pretreated to reduce the bicarbonate content to 50 g / L. Then it was mixed with sodium sulfate from the outside and sodium sulfate returned from washing with double salts and crystallized to obtain a liquid-solid mixture.

[0070] Fine particles and coarse crystals in the liquid-solid mixture are separated to obtain coarse crystal slurry and fine particle slurry, respectively. The fine particle slurry is then fed into the sodium bicarbonate production system.

[0071] The coarse crystal slurry was centrifuged to obtain the complex salt and filtrate;

[0072] The double salt was washed with water to obtain sodium sulfate solid and ammonium sulfate solution;

[0073] The crystallization temperature is 30°C; the crystallization time is 4 hours.

[0074] The solid-liquid ratio (g / L) of the sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is 400:1.

[0075] The temperature of the liquid phase material during washing is 100℃; the washing residence time is 30 minutes.

[0076] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0077] Example 2

[0078] This embodiment provides a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate. The recovery method includes:

[0079] The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate was pretreated to reduce the bicarbonate content to 60 g / L. Then it was mixed with sodium sulfate from the outside and sodium sulfate returned from washing with double salts and crystallized to obtain a liquid-solid mixture.

[0080] Fine particles and coarse crystals in the liquid-solid mixture are separated to obtain coarse crystal slurry and fine particle slurry, respectively. The fine particle slurry is then fed into the sodium bicarbonate production system.

[0081] The coarse crystal slurry was centrifuged to obtain the complex salt and filtrate;

[0082] The double salt was washed with a solution containing sodium sulfate and ammonium sulfate (the mass concentration of sodium sulfate in the solution was 20% and the mass concentration of ammonium sulfate was 10%) to obtain sodium sulfate solid and ammonium sulfate solution.

[0083] The crystallization temperature is 40℃; the crystallization time is 1 hour.

[0084] The solid-liquid ratio (g / L) of the sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is 500:1.

[0085] The temperature of the liquid phase material during washing is 90℃; the washing residence time is 90min.

[0086] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0087] Example 3

[0088] This embodiment provides a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate. The recovery method includes:

[0089] The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate was pretreated to reduce the bicarbonate content to 40 g / L. Then it was mixed with sodium sulfate from the outside and sodium sulfate returned from washing with double salts and crystallized to obtain a liquid-solid mixture.

[0090] Fine particles and coarse crystals in the liquid-solid mixture are separated to obtain coarse crystal slurry and fine particle slurry, respectively. The fine particle slurry is then fed into the sodium bicarbonate production system.

[0091] The coarse crystal slurry was centrifuged to obtain the complex salt and filtrate;

[0092] The double salt was washed with water to obtain sodium sulfate solid and ammonium sulfate solution;

[0093] The crystallization temperature is 20°C; the crystallization time is 8 hours.

[0094] The solid-liquid ratio (g / L) of the sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is 300:1.

[0095] The temperature of the liquid phase material during washing is 75°C; the washing residence time is 150 min.

[0096] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0097] Example 4

[0098] This embodiment provides a method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate. The recovery method includes:

[0099] The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate was pretreated to reduce the bicarbonate content to 75 g / L. Then it was mixed with sodium sulfate from the outside and sodium sulfate returned from washing with double salts and crystallized to obtain a liquid-solid mixture.

[0100] Fine particles and coarse crystals in the liquid-solid mixture are separated to obtain coarse crystal slurry and fine particle slurry, respectively. The fine particle slurry is then fed into the sodium bicarbonate production system.

[0101] The coarse crystal slurry was centrifuged to obtain the complex salt and filtrate;

[0102] The double salt was washed with water to obtain sodium sulfate solid and ammonium sulfate solution;

[0103] The crystallization temperature is 10℃; the crystallization time is 12h;

[0104] The solid-liquid ratio (g / L) of the sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is 200:1.

[0105] The temperature of the liquid phase material during washing is 60°C; the washing residence time is 240 min.

[0106] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0107] Comparative Example 1

[0108] The only difference from Example 1 is that the cooling crystallization time is 0.5h.

[0109] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0110] Comparative Example 2

[0111] The only difference from Example 1 is that the solid-liquid ratio (g / L) of sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is 700:1.

[0112] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0113] Comparative Example 3

[0114] The only difference from Example 1 is that the temperature of the liquid phase material during washing is 45°C.

[0115] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0116] Comparative Example 4

[0117] The only difference from Example 1 is that the endpoint of the pretreatment is to reduce the concentration of bicarbonate ions in the sodium bicarbonate crystallization mother liquor to 5 g / L.

[0118] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0119] Comparative Example 5

[0120] The only difference from Example 1 is that the endpoint of the pretreatment is to reduce the concentration of bicarbonate ions in the sodium bicarbonate crystallization mother liquor to 95 g / L.

[0121] The results of sodium content, nitrogen content of ammonium sulfate solution, and ammonia recovery rate of the obtained fine-particle slurry are detailed in Table 1.

[0122] The crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate used in the above examples has the following composition: sodium ion content of 50 g / L, ammonium ion content of 100 g / L, sulfate content of 305 g / L, bicarbonate content of 85 g / L and carbonate content of 10 g / L.

[0123] The ammonium sulfate solution obtained in the above example was evaporated and crystallized to obtain the ammonium sulfate product.

[0124] Table 1

[0125]

[0126]

[0127] In this invention, the formula for calculating the ammonia recovery rate is the ratio of the mass of total ammonium ions in the fine-particle slurry to the mass of total ammonium ions in the crystallization mother liquor.

[0128] The results shown in Table 1 lead to the following conclusions:

[0129] (1) The results of comparative examples 1-4 show that when the crystallization temperature drops from 40°C to 10°C, the recovery rate of ammonia medium gradually decreases, but is greater than 98%; the crystallization temperature, time and amount of sodium sulfate added will affect the sodium content of the slurry containing fine particles; when the double salt washing temperature drops from 100°C to 60°C, the nitrogen content of the ammonium sulfate hot solution gradually decreases, but is greater than 100 g / L.

[0130] (2) Comparing the results of Example 1 and Comparative Examples 1-3, it can be seen that the cooling crystallization time was too short (0.5h), which caused sodium sulfate to fail to dissolve into the solution in time. During solid-liquid separation, the undissolved sodium sulfate carried over the solution not only caused the loss of ammonia medium, but also reduced the sodium content of the fine particle slurry and reduced the washing effect of the double salt. When the solid-liquid ratio g / L of sodium sulfate to the crystallization mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate was too high at 700:1, although the sodium content of the fine particle slurry was not affected, a large amount of undissolved sodium sulfate would still be carried over the solution, resulting in a decrease in the recovery rate of ammonia medium. The washing temperature of the double salt was too low (45℃), which resulted in the nitrogen content of the ammonium sulfate hot solution being only 90g / L. The low nitrogen content of the ammonium sulfate hot solution would lead to a decrease in the quality of the ammonium sulfate produced during the evaporation crystallization process.

[0131] (3) Comparing the results of Example 1 and Comparative Examples 4-5, it can be seen that the endpoint of the pretreatment is to reduce the concentration of bicarbonate in the sodium bicarbonate crystallization mother liquor to too high (95 g / L) or too low (5 g / L) without affecting the quality of ammonium sulfate. However, if the concentration of bicarbonate is too high, an excessive amount of fine slurry will be generated during the cooling crystallization process. When the excessive fine slurry enters the metathesis reaction section to prepare sodium bicarbonate, the purity of the sodium bicarbonate product will decrease sharply. If the concentration of bicarbonate is too low, the sodium content of the fine particle slurry will be low, which is not conducive to the preparation of sodium bicarbonate in the metathesis reaction section and increases the circulation volume and energy consumption.

[0132] The present invention is described in detail through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0133] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0134] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0135] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for recovering ammonium components during the production of sodium bicarbonate from sodium sulfate, characterized in that, The recycling method includes: The mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate is pretreated and then mixed with sodium sulfate in the first mixture and crystallized to obtain a liquid-solid mixture. The endpoint of the pretreatment is to reduce the concentration of bicarbonate in the mother liquor to 40-75 g / L. The solid-liquid ratio (g / L) of sodium sulfate to the mother liquor containing sodium sulfate, ammonium sulfate, ammonium bicarbonate and diammonium carbonate in the first mixture is (200-500):

1. Fine particles and coarse crystals in a liquid-solid mixture are separated to obtain coarse crystal slurry and slurry containing fine particles, respectively. The obtained coarse crystal slurry was subjected to solid-liquid separation to obtain a complex salt and filtrate; The obtained double salt was washed to obtain sodium sulfate solid and ammonium sulfate solution; The resulting sodium sulfate solid was returned to the first mixture, and the resulting filtrate was also returned to the first mixture.

2. The recycling method as described in claim 1, characterized in that, The pretreatment methods include neutralizing bicarbonate ions with alkali to convert them into carbonate ions and / or heating to 50-80°C to decompose bicarbonate ions into carbonate ions.

3. The recycling method as described in claim 1, characterized in that, The sodium sulfate includes commercially available sodium sulfate and / or solid sodium sulfate obtained from washing.

4. The recycling method as described in claim 1, characterized in that, The crystallization process is carried out at a temperature of 10-40℃.

5. The recycling method as described in claim 1, characterized in that, The crystallization time is 1-12 hours.

6. The recycling method as described in claim 1, characterized in that, The method for separating fine particles from coarse crystals in the liquid-solid mixture includes one or a combination of at least two of gravity classification, hydrocyclone, centrifugal separation, or sieving.

7. The recycling method as described in claim 1, characterized in that, The temperature of the liquid phase material during the washing process is 60-100℃.

8. The recycling method as described in claim 1, characterized in that, The washing dwell time is 30-240 minutes.

9. The recycling method as described in claim 1, characterized in that, The slurry containing fine particles enters the sodium bicarbonate production system.

10. The recycling method as described in claim 1, characterized in that, The washing medium used in the washing process includes water or a solution containing sodium sulfate and ammonium sulfate.

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