Method and device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater

Abstract

The present invention provides a method and device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. According to the phase equilibrium law of a multi-component water-salt system, through the regulation of crystallization kinetics and supersaturation, the sodium-based wastewater does not need to be evaporated and crystallized to produce sodium sulfate solid. Instead, the wastewater after simple pretreatment is directly treated to achieve gradient crystallization separation of sodium sulfate, ammonium sulfate and sodium bicarbonate, thereby obtaining high-quality sodium bicarbonate, sodium carbonate and ammonium sulfate products.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical treatment, and relates to a method and device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Background Art

[0002] With the rapid development of industrialization in my country, sodium-based wastewater is increasingly generated in industrial processes, such as those in the chemical, metallurgical, textile and dyeing, pharmaceutical, mining, and petroleum industries. This sodium-based wastewater, primarily composed of sodium sulfate, also contains impurities such as heavy metals, organic matter, fluorine, and silicon. Its complex composition and difficulty in treatment make direct discharge of the wastewater a serious environmental and ecological risk.

[0003] Currently, sodium sulfate products are primarily produced from sodium sulfate-containing wastewater using methods such as evaporative crystallization, freeze crystallization, membrane separation, ion exchange, and electrodialysis. These processes are not only lengthy, difficult to control, require significant equipment investment, consume significant energy, and have high operating costs, but also have limited market capacity and low value. The treatment and resource utilization of sodium sulfate-containing wastewater presents a dual challenge for both industrial pollution control and resource recovery. There is an urgent need to overcome the limitations of single technologies, promote high-value utilization, and ultimately achieve synergistic improvements in environmental and economic benefits.

[0004] CN118929994A discloses a method for resource-based treatment of sodium sulfate wastewater from tungsten smelting. This method uses sodium sulfate and barium hydroxide to produce sodium sulfide. However, it has disadvantages such as a long process flow, the requirement for harsh conditions such as high temperature and high pressure, high production costs, and a low market value for sodium sulfide. Furthermore, the high-temperature roasting of barium sulfate and hydrogen produces sulfur-containing gases, resulting in relatively low environmental and economic benefits.

[0005] CN117682539A discloses a method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials. While this method produces sodium sulfate as the bulk soda ash, it also produces gypsum as a byproduct, which is difficult to absorb in the market. Furthermore, the entire process requires multiple high-temperature steps, resulting in high costs and the risk of ammonia leakage.

[0006] CN117902610A discloses a method for recycling sodium sulfate high-salt wastewater. This method uses sodium sulfate and quicklime as raw materials to produce sodium bicarbonate, caustic soda, gypsum, and calcium carbonate. While achieving high-value sodium sulfate utilization, this method also produces new, low-value products that are difficult to absorb in the market.

[0007] In summary, the current approach to high-value utilization of sodium-based wastewater containing sodium sulfate is to produce sodium bicarbonate products. However, this process is plagued by long processes, high energy consumption, low conversion rates, easy leakage of polluting gases, low economic value of byproducts, and poor market absorption capacity. Therefore, there is an urgent need to develop a method and device system for harmless and high-value utilization of sodium-based wastewater. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method and device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, thereby achieving the harmless and high-value utilization of sodium-based wastewater, preparing large-particle, high-quality sodium bicarbonate and ammonium sulfate products, and overcoming the difficulties of the existing process for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, such as the need for high-temperature decomposition of ammonium bicarbonate, repeated low-temperature freezing and high-temperature evaporation, resulting in high energy consumption, large equipment investment, complex process, high environmental risks, and fine particles of sodium bicarbonate and ammonium sulfate products.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, the method comprising the following steps:

[0011] (1) Pre-treating the sodium-based wastewater, and then mixing the pre-treated sodium-based wastewater with double salt and acid solution to separate sodium and ammonium to obtain ammonium sulfate solution and sodium sulfate;

[0012] (2) evaporating and crystallizing the ammonium sulfate solution obtained in step (1) to obtain a mixed slurry of sodium sulfate and ammonium sulfate, and then subjecting the mixed slurry to particle size classification to obtain ammonium sulfate mother liquor, wet ammonium sulfate and sodium sulfate, and subjecting the wet ammonium sulfate to a first drying to obtain an ammonium sulfate product;

[0013] Wherein, the ammonium sulfate mother liquor is reused in the evaporation crystallization of step (2);

[0014] (3) mixing the sodium sulfate obtained in step (1) and the sodium sulfate obtained in step (2) with a sodium bicarbonate mother liquor, and performing a salting-out crystallization reaction to obtain a double salt and a salting-out mother liquor after a first separation, and then mixing the salting-out mother liquor with ammonia water or ammonia gas, and performing a calcium, magnesium and insoluble matter removal reaction to obtain a salting-out clear liquid and a calcium and magnesium slag;

[0015] Wherein, the double salt is reused in step (1) sodium-ammonium separation;

[0016] (4) mixing the salting-out clear solution obtained in step (3) with ammonium bicarbonate and carbon dioxide, and performing a double decomposition reaction to obtain a sodium bicarbonate slurry, and then performing a second separation on the sodium bicarbonate slurry to obtain wet sodium bicarbonate and a sodium bicarbonate mother liquor, and then performing a second drying or calcining on the wet sodium bicarbonate to obtain a sodium bicarbonate product or a sodium carbonate product;

[0017] The sodium bicarbonate mother liquor is recycled to the salting-out crystallization reaction in step (3).

[0018] The method provided by the present invention, based on the phase equilibrium law of a multi-element water-salt system, through the regulation of crystallization kinetics and supersaturation, eliminates the need for evaporating and crystallizing sodium sulfate solid from sodium-based wastewater. Instead, the wastewater that has undergone simple pretreatment is directly treated, thereby achieving gradient crystallization separation of sodium sulfate, ammonium sulfate and sodium bicarbonate, and obtaining high-quality sodium bicarbonate, sodium carbonate and ammonium sulfate products.

[0019] It should be noted that the sodium-ammonium separation is based on the phase equilibrium law of the ternary water-salt system and the principle that the solubility of ammonium sulfate is far greater than that of sodium sulfate at the co-saturation point. It also eliminates the process of evaporating sodium sulfate wastewater to crystallize sodium sulfate, shortens the process flow and reduces equipment investment. By evaporating and crystallizing the ammonium sulfate solution and regulating the crystal growth dynamics during evaporation and crystallization, such as solution pH and crystal residence time, a mixed slurry of large-particle ammonium sulfate and fine sodium sulfate is obtained, and then the ammonium sulfate mother liquor, wet ammonium sulfate and sodium sulfate are separated by particle size classification.

[0020] It should also be noted that by carrying out a salting-out crystallization reaction between sodium sulfate and sodium bicarbonate mother liquor, the recycling of ammonium carbonate is achieved, and the obtained double salt can be reused in the evaporation and crystallization of the ammonium sulfate solution. The obtained salting-out mother liquor can be used to prepare high-quality baking soda or soda ash products after impurities are removed; finally, by adding ammonium bicarbonate and carbon dioxide to the salting-out clear liquor for a double decomposition reaction, it not only helps to improve the sodium bicarbonate conversion rate, but also helps to increase the particle size of the sodium bicarbonate, thereby producing a high-quality sodium bicarbonate product.

[0021] As a preferred technical solution of the present invention, the pretreatment in step (1) includes purification, impurity removal and hardness removal performed in sequence.

[0022] In the present invention, after pre-treating the sodium-based wastewater, wastewater with higher purity and lower hardness can be obtained.

[0023] Preferably, the purification and impurity removal method comprises: adding a coagulant and a flocculant to the sodium-based wastewater in sequence, performing a purification and impurity removal reaction, and obtaining a clean liquid and clean residue.

[0024] In the present invention, after the purification and impurity removal reaction is completed, the material enters the liquid-solid separation device for clarification, the obtained impurity-removed clear liquid is used for subsequent hardness removal, and the obtained impurity-removed residue is removed to the outside.

[0025] In the present invention, the sodium-based wastewater includes sodium sulfate wastewater, sodium chloride wastewater, mixed wastewater of sodium sulfate and sodium chloride, or mixed wastewater of sodium sulfate and magnesium sulfate, etc. The sodium-based wastewater may also include insoluble inorganic matter, insoluble organic matter, or soluble organic matter, etc.

[0026] Preferably, the coagulant includes any one of polyaluminium chloride, polyaluminium sulfate, aluminium chloride or aluminium sulfate, or a combination of at least two thereof.

[0027] Preferably, the flocculant includes any one of anionic flocculant, cationic flocculant or amphoteric flocculant, or a combination of at least two of them.

[0028] In the present invention, the flocculant needs to be prepared into a solution with a mass concentration of 0.01% to 0.5%.

[0029] Preferably, the mass ratio of the coagulant to the insoluble matter in the sodium-based wastewater is (1~6):1, for example, it can be 2:1, 3:1, 4:1 or 5:1, etc.; the mass ratio of the coagulant to the flocculant is (50~500):1, for example, it can be 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1 or 450:1, etc.

[0030] In the present invention, the amount of coagulant added is determined based on the content of insoluble matter and fluoride ions in the sodium-based wastewater, preferably the higher of the two. The mass ratio of the coagulant to the fluoride ions in the sodium-based wastewater is (3-6):1.

[0031] Preferably, the interval between adding the coagulant and the flocculant is ≥15 min, for example, it can be 16 min, 18 min, 20 min, 22 min, 25 min, 28 min or 30 min.

[0032] Preferably, the pH of the purification and impurity removal reaction is 6 to 8, for example, 6.2, 6.5, 6.6, 6.8, 7, 7.2, 7.5, 7.6 or 7.8; the temperature is 30 to 80°C, for example, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C or 75°C; the time is 60 to 360 min, for example, 80 min, 100 min, 120 min, 150 min, 200 min, 250 min, 300 min or 350 min, etc.

[0033] Preferably, the hardness removal method comprises: adjusting the pH value of the impurity removal clear solution to be alkaline, and then adding sodium carbonate thereto to carry out a hardness removal reaction to obtain calcium magnesium slag and a hardness removal clear solution.

[0034] Preferably, the pH value of the impurity-removing supernatant is adjusted to 9-12, for example, it can be 9.2, 9.5, 9.6, 9.8, 10, 10.2, 10.5, 10.6, 10.8, 11, 11.2, 11.5, 11.6 or 11.8.

[0035] In the present invention, an alkali solution may be used to adjust the pH of the impurity removal clear solution, wherein the alkali solution comprises sodium hydroxide.

[0036] Preferably, the molar ratio of the sodium carbonate to the calcium and magnesium ions in the impurity removal clear solution is (1-3):1, for example, it can be 1.2:1, 1.5:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1 or 2.8:1, etc.

[0037] Preferably, the temperature of the hardness removal reaction is 30~80℃, for example, it can be 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃ or 75℃; the time is 30~180min, for example, it can be 50min, 60min, 80min, 100min, 120min, 150min or 160min.

[0038] As a preferred technical solution of the present invention, before performing the mixing in step (1), the method further includes: detecting the COD content of the pretreated sodium-based wastewater and performing different treatments according to the COD content; if the COD content of the pretreated sodium-based wastewater is less than 100 ppm, the wastewater is directly used for sodium-ammonium separation; if the COD content of the pretreated sodium-based wastewater is ≥100 ppm, a strong oxidant is added during the sodium-ammonium separation.

[0039] In the present invention, the heat generated in the sodium ammonium separation process or the ammonium sulfate preparation process is used to activate the strong oxidant, and the system pH value of 3-6 is the optimal acidity range for degrading COD, thereby promoting the generation of free radicals and the degradation of COD.

[0040] Preferably, the strong oxidant includes any one or a combination of at least two of ammonium sulfate, ammonium persulfate, disodium persulfate, sodium persulfate, hydrogen peroxide, ozone or oxygen.

[0041] Preferably, the mass ratio of the strong oxidant to the COD in the pretreated sodium-based wastewater is (4-10):1, for example, it can be 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1 or 9.5:1, etc.

[0042] Preferably, the double salt in step (1) comprises a composite salt formed by sodium sulfate and ammonium sulfate.

[0043] In the present invention, the chemical formula of the double salt includes but is not limited to Na2SO4·(NH4)2SO4·4H2O, (NaNH4)SO4·2H2O, or (NH4Na)SO4·2H2O. The double salt may further contain an alkaline substance with a mass content of ≤5%, and the alkaline substance includes any one of ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, ammonia water, or sodium hydroxide, or a combination of at least two thereof.

[0044] Preferably, the amount of sodium-based wastewater added after the pretreatment in step (1) is such that the ammonium sulfate in the double salt is completely dissolved.

[0045] It should be noted that by utilizing the difference in solubility of different substances at different temperatures, the ratio of sodium-based wastewater and double salt is controlled, so that all the ammonium sulfate in the double salt is dissolved, thereby achieving the enrichment of ammonium sulfate and direct crystallization of sodium sulfate from the wastewater, saving the evaporator required for the evaporation and crystallization of sodium sulfate wastewater, reducing equipment investment, and shortening the process flow.

[0046] Preferably, the amount of acid added in step (1) is such that the pH value of the mixed solution is 3 to 5, for example, 3.2, 3.5, 3.6, 3.8, 4, 4.2, 4.5, 4.6 or 4.8.

[0047] In the present invention, the acid solution comprises sulfuric acid with a mass concentration of ≥70%, preferably 98%.

[0048] Preferably, the temperature for sodium-ammonium separation in step (1) is 70-110° C., for example, 75° C., 80° C., 85° C., 90° C., 100° C., or 105° C., etc.; and the time is 30-240 min, for example, 50 min, 60 min, 100 min, 120 min, 150 min, 160 min, 200 min, or 220 min, etc.

[0049] It should be noted that controlling the temperature range of sodium-ammonium separation is beneficial to improving the separation effect. If the temperature is low, the amount of dissolved ammonium sulfate is small, and even complex salt crystals are precipitated, which not only reduces efficiency but also increases energy consumption. If the temperature is high, there is no obvious improvement in improving efficiency, which increases costs.

[0050] Preferably, the solid content of the ammonium sulfate solution in step (1) is ≤10 g / L, for example, it can be 9 g / L, 8 g / L, 7 g / L, 6 g / L, 5 g / L or 4 g / L, etc., preferably ≤5 g / L.

[0051] It should be noted that the temperature of the ammonium sulfate solution obtained in step (1) is ≥ the temperature of the evaporation crystallization in step (2), and the temperature of the ammonium sulfate solution is achieved by controlling the sodium-ammonium separation temperature in step (1).

[0052] Preferably, the N-NH4 in the sodium sulfate in step (1) + The content is ≤3%, for example, it can be 2.8%, 2.5%, 2.2%, 2%, 1.8%, 1.5% or 1%, etc., preferably ≤1.5%.

[0053] As a preferred technical solution of the present invention, during the evaporation crystallization in step (2), an acid solution is used to regulate the pH value of the ammonium sulfate solution to 2-6, for example, it can be 2.5, 3, 3.2, 3.5, 3.6, 3.8, 4, 4.5, 5 or 5.5, preferably 3-4.

[0054] It should be noted that regulating the pH value of the ammonium sulfate solution and the residence time of the evaporation crystallization within a specific range before evaporation crystallization is beneficial for increasing the size difference between ammonium sulfate and sodium sulfate particles through crystallization kinetics. If the pH value of the ammonium sulfate solution is low, it will lead to high equipment requirements and some indicators of the ammonium sulfate product being too high. If the pH value of the ammonium sulfate solution is high, the difference between sodium sulfate and ammonium sulfate particles will be reduced, resulting in a decrease in the quality of the ammonium sulfate product obtained by particle classification.

[0055] Preferably, the temperature of the evaporation crystallization in step (2) is 70-110°C, for example, 75°C, 80°C, 85°C, 90°C, 100°C or 105°C; the residence time is 120-300 min, for example, 150 min, 160 min, 180 min, 200 min, 220 min, 250 min, 260 min or 280 min.

[0056] It should be noted that, compared with the traditional method, the ammonium sulfate solution obtained by the separation of sodium and ammonium in step (1) is the raw material for preparing ammonium sulfate. In the process of preparing ammonium sulfate, cooling crystallization is not required. The temperature of the feed material for evaporation and crystallization is greater than or equal to the evaporation temperature, and the material does not need to be heated. In addition, the amount of water evaporated during the production of 1 t of ammonium sulfate product is 1.2 t. The entire process eliminates the need for devices and processes such as the cooling crystallization device, the material preheating device, and the ammonium sulfate drying device. The process is simpler, the system power consumption and steam consumption are lower, the operating cost is greatly reduced, and the economic advantage is obvious.

[0057] Preferably, in step (2), more than 95% of the ammonium sulfate in the mixed slurry has a particle size of ≥500 μm, for example, it can be 550 μm, 600 μm, 650 μm, 700 μm, 750 μm or 800 μm, etc.; more than 95% of the sodium sulfate has a particle size of ≤100 μm, for example, it can be 90 μm, 80 μm, 70 μm, 60 μm, 50 μm or 40 μm, etc.

[0058] In the present invention, the solid content of the mixed slurry is 20% to 40%, and the particle size difference between sodium sulfate and ammonium sulfate in the mixed slurry is relatively large, and the two can be separated by physical separation. The separated material can be thickened in a thickener.

[0059] Preferably, the particle size classification in step (2) includes any one of sedimentation separation, fluidization separation, screening separation or hydrocyclone separation, or a combination of at least two of them.

[0060] Preferably, during the sedimentation separation, the sedimentation rate of sodium sulfate in the mixed slurry is controlled to be ≤0.01 m / s; the sedimentation rate of ammonium sulfate is controlled to be ≥0.05 m / s.

[0061] Preferably, during the fluidized separation, the flow rate of the mixed slurry is controlled to be greater than 0.01 m / s, for example, 0.02 m / s, 0.03 m / s, 0.04 m / s or 0.05 m / s.

[0062] Preferably, the screening separation includes a first screening and a second screening performed sequentially; the pore size of the first screening is 40~80 mesh, for example, it can be 45 mesh, 50 mesh, 55 mesh, 60 mesh, 65 mesh, 70 mesh or 75 mesh, etc.; the pore size of the second screening is 80~120 mesh, excluding 80 mesh, for example, it can be 85 mesh, 90 mesh, 95 mesh, 100 mesh, 105 mesh, 110 mesh or 115 mesh, etc.

[0063] Preferably, in the hydrocyclone separation, the cone angle of the hydrocyclone is 10~30°, for example, it can be 12°, 15°, 18°, 20°, 22°, 25° or 28°; the diameter is 100~650 mm, for example, it can be 150 mm, 200 mm, 300 mm, 400 mm, 500 mm or 600 mm; the material feed flow rate is 1.5~3 m / s, for example, it can be 1.6 m / s, 1.8 m / s, 2 m / s, 2.2 m / s, 2.5 m / s, 2.6 m / s or 2.8 m / s.

[0064] Preferably, the mass content of sodium sulfate in the ammonium sulfate mother liquor in step (2) is ≤17%, for example, it can be 16%, 15%, 12%, 10%, 8% or 5%, etc.; the mass content of ammonium sulfate is ≤39%, for example, it can be 38%, 36%, 35%, 32%, 30% or 28%, etc.

[0065] Preferably, the average particle size of the ammonium sulfate product in step (2) is greater than 1000 μm, for example, it can be 1050 μm, 1100 μm, 1150 μm, 1200 μm, 1250 μm or 1300 μm, etc.

[0066] Preferably, the N-NH4 in the ammonium sulfate product in step (2) + The content is ≥20.5%, for example, it can be 38%, 36%, 35%, 32%, 30% or 28%.

[0067] Preferably, the water content in the ammonium sulfate product in step (2) is ≤0.5%, for example, it can be 0.4%, 0.3%, 0.2% or 0.1%.

[0068] As a preferred technical solution of the present invention, after the particle size classification in step (2), the method further comprises: detecting the COD content in the obtained ammonium sulfate mother liquor and performing different treatments according to the COD content; if the COD content is less than 300 ppm, the ammonium sulfate mother liquor is recycled to the evaporation crystallization in step (2); if the COD content is ≥300 ppm, a portion of the ammonium sulfate mother liquor is refluxed to the sodium-ammonium separation in step (1), and a strong oxidant is added thereto, and the remaining ammonium sulfate mother liquor is recycled to the evaporation crystallization in step (2); wherein the mass flow rate of the ammonium sulfate mother liquor recycled to the sodium-ammonium separation is 10% to 50% of the mass flow rate of the ammonium sulfate solution feed.

[0069] In the present invention, if the COD content in the ammonium sulfate mother liquor is too high, it can directly enter the sodium ammonium separation for coupled oxidation treatment, thereby achieving zero discharge of waste liquid without increasing energy consumption and equipment investment, and significantly improving economic and environmental performance.

[0070] In the present invention, the solid content of the ammonium sulfate mother liquor is preferably ≤5 g / L.

[0071] Preferably, the mass ratio of the strong oxidant to the COD in the refluxing ammonium sulfate mother liquor is (4-10):1, for example, it can be 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1 or 9.5:1, etc.

[0072] Preferably, after the particle size classification in step (2), the process further comprises: detecting the fluoride ion content in the obtained ammonium sulfate mother liquor, and performing different treatments according to the fluoride ion content; if the fluoride ion content is less than 15 ppm, the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2); if the fluoride ion content is ≥15 ppm, a portion of the ammonium sulfate mother liquor is refluxed to the purification and impurity removal reaction, and a coagulant is added thereto, and the remaining ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2); wherein the mass flow rate of the ammonium sulfate mother liquor refluxed to the purification and impurity removal reaction is 10% to 50% of the mass flow rate of the ammonium sulfate solution feed.

[0073] Preferably, the mass ratio of the added coagulant to the fluoride ions in the refluxed ammonium sulfate mother liquor is (3-6):1, for example, it can be 3.5:1, 4:1, 4.5:1, 5:1 or 5.5:1.

[0074] As a preferred technical solution of the present invention, the mass volume ratio of the total mass of the sodium sulfate described in step (3) to the sodium bicarbonate mother liquor is (180-400):1 g / L, for example, it can be 200:1 g / L, 220:1 g / L, 250:1 g / L, 280:1 g / L, 300:1 g / L, 320:1 g / L, 350:1 g / L or 380:1 g / L, etc.

[0075] Preferably, in step (3), the material temperature of the sodium sulfate is 10-20°C, for example, it can be 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C ​​or 19°C.

[0076] Preferably, the material temperature of the sodium bicarbonate mother liquor in step (3) is 25-35°C, for example, it can be 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C or 34°C.

[0077] In the present invention, the heat generated in the salting-out crystallization reaction process can be neutralized by controlling the material temperature range of sodium sulfate and sodium bicarbonate mother liquor, ensuring that the salting-out crystallization reaction is maintained in the range of 27-35° C., so that the crystallization device eliminates the need for an external cooler for cooling the temperature and a circulating pump and a circulating water auxiliary pump matched with the external cooler, thereby reducing equipment investment, power consumption, heat energy input caused by electrical energy and mechanical energy, and significantly reducing circulating water consumption, thereby achieving obvious economic advantages.

[0078] Preferably, the temperature of the salting-out crystallization reaction in step (3) is 25-35°C, for example, it can be 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C or 34°C, etc., preferably 27-35°C.

[0079] Preferably, the salting-out crystallization reaction time in step (3) is 3 to 11 hours, for example, it can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0080] Preferably, the molar ratio of the ammonia water or ammonia gas to the bicarbonate substance in the salting-out mother liquor in step (3) is 1:(0.8-1), for example, it can be 1:0.82, 1:0.85, 1:0.86, 1:0.88, 1:0.9, 1:0.92, 1:0.95, 1:0.96 or 1:0.98, etc.

[0081] Preferably, the mass concentration of the ammonia water is 8% to 25%, for example, it can be 10%, 12%, 15%, 16%, 18%, 20%, 22% or 24%; the mass concentration of the ammonia gas is 30% to 100%, for example, it can be 40%, 50%, 60%, 70%, 80% or 90%.

[0082] Preferably, the temperature of the calcium, magnesium and insoluble matter removal reaction in step (3) is 25-35°C, for example, it can be 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C or 34°C.

[0083] In the present invention, calcium, magnesium and insoluble matter removal reactions can remove substances such as calcium and magnesium in the salting-out clear solution that affect the quality of baking soda or soda ash, thereby improving the quality of baking soda or soda ash products.

[0084] As a preferred technical solution of the present invention, the mass ratio of the ammonium bicarbonate in step (4) to the effective amount of sodium sulfate in the salting-out clear solution is (1.2-1.4):1, for example, it can be 1.22:1, 1.25:1, 1.26:1, 1.28:1, 1.3:1, 1.32:1, 1.35:1, 1.36:1 or 1.38:1, etc.

[0085] In the present invention, the effective amount of sodium sulfate in the salting-out clear liquid refers to the mass of sodium sulfate corresponding to the remaining sodium ions converted into sodium sulfate after removing the sodium ions corresponding to bicarbonate in the salting-out clear liquid. For example, if the sodium ions in the salting-out clear liquid are 100 g / L and the bicarbonate is 61 g / L, the remaining sodium ions can be calculated to be 77 g / L, and the corresponding sodium sulfate is 237.7 g / L, that is, the effective mass of sodium sulfate is 237.7 g / L.

[0086] In the present invention, the volume mass ratio of the sodium bicarbonate slurry to the ammonium bicarbonate is (3-5):1.

[0087] Preferably, the ammonium bicarbonate is added in step (4) by slurrying with salting-out clear liquid, and 1-5 level feeding is adopted, for example, it can be level 1, level 2, level 3, level 4 or level 5, preferably level 2-3.

[0088] It should be noted that the addition of ammonium bicarbonate adopts salting-out clear liquid beating and graded addition, which can reduce the supersaturation of sodium bicarbonate crystals, inhibit explosive nucleation, promote crystal growth, and obtain large-particle sodium bicarbonate; if the feed level of ammonium bicarbonate is too low, it will cause the sodium bicarbonate particles to become finer, the water content to increase, and the product purity to decrease. If the feed level of ammonium bicarbonate is too high, it will increase equipment investment and operating costs, and there will be no obvious improvement on the size of sodium bicarbonate particles.

[0089] Preferably, the amount of carbon dioxide added in step (4) is such that the carbonate concentration in the mixed solution is 0-10 g / L, for example, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L or 9 g / L.

[0090] Preferably, the mass concentration of the carbon dioxide in step (4) is 40% to 100%, for example, 50%, 60%, 70%, 80% or 90%, etc.; the introduction temperature is 20 to 45°C, for example, 22°C, 25°C, 26°C, 28°C, 30°C, 32°C, 35°C, 36°C or 38°C, etc.

[0091] Preferably, the temperature of the metathesis reaction in step (4) is 30-45°C, for example, 32°C, 34°C, 35°C, 36°C, 38°C, 40°C, 42°C or 44°C, etc.; and the time is 2-6 h, for example, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h or 5.5 h, etc.

[0092] Preferably, after the double decomposition reaction in step (4), the average particle size of the sodium bicarbonate in the obtained sodium bicarbonate slurry is ≥300 μm, for example, it can be 320 μm, 350 μm, 360 μm, 380 μm, 400 μm, 450 μm or 500 μm.

[0093] Preferably, the water content of the wet sodium bicarbonate in step (4) is 5% to 8%, for example, it can be 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.6% or 7.8%.

[0094] It should be noted that the average particle size of sodium bicarbonate is larger and the water content of wet sodium bicarbonate is lower. When subsequently dried or calcined to prepare baking soda or soda ash products, the energy consumption is reduced by more than 50% compared with traditional double decomposition reactions, and the economic advantage is obvious.

[0095] Preferably, the total alkali content of the sodium bicarbonate product in step (4) is ≥99.5%, for example, it can be 99.6%, 99.7%, 99.8% or 99.9%.

[0096] In the present invention, the obtained sodium bicarbonate product meets the requirements of Class III products and above specified in the national standard GB / T 1606-2008.

[0097] Preferably, the average particle size of the sodium bicarbonate product in step (4) is ≥300 μm, for example, it can be 310 μm, 320 μm, 330 μm, 340 μm, 350 μm, 360 μm, 380 μm or 400 μm, etc.

[0098] Preferably, the purity of the sodium carbonate product in step (4) is ≥99.2%, for example, it can be 99.3%, 99.4%, 99.5%, 99.6%, 99.7% or 99.8%.

[0099] In the present invention, the obtained sodium carbonate product meets the requirements of Class II (general industrial soda ash) superior products in the national standard GB / T 210-2022.

[0100] As a preferred technical solution of the present invention, the method further includes step (5):

[0101] If the sodium-based wastewater contains chloride ions and the chloride ions in the ammonium sulfate mother liquor obtained in step (2) are saturated, part of the ammonium sulfate mother liquor is cooled and crystallized to obtain ammonium chloride product and ammonium chloride mother liquor, and the ammonium chloride mother liquor is reused in the sodium-ammonium separation in step (1).

[0102] In the present invention, the solid content of the ammonium sulfate mother liquor is preferably ≤5 g / L.

[0103] It should be noted that this step is designed for chlorine-containing, high-salt, sodium-based wastewater. There is no need for salt separation and change of technical route. Only an ammonium chloride preparation device needs to be added to the original technical route to realize the resource utilization of chlorine-containing, high-salt, sodium-based wastewater. Compared with the traditional salt separation process, the process is simple and energy consumption is low. In addition, compared with the traditional salt separation process, the by-product sodium chloride cannot be exported, while the by-product ammonium chloride obtained is a typical nitrogen fertilizer, which has huge market demand and is more economical.

[0104] It should also be noted that the preparation process of ammonium chloride does not require double decomposition reaction, repeated cooling and heating and other processes. Ammonium chloride can be obtained by directly cooling and crystallizing the ammonium sulfate mother liquor, eliminating the input of ammonium sulfate raw materials and having no requirements for chloride ion and water content. The process is simpler, energy consumption is lower, and raw material adaptability is stronger.

[0105] Preferably, the chloride ion in the ammonium sulfate mother liquor is in a saturated state, that is, the mass content of ammonium chloride in the ammonium sulfate mother liquor is 20% to 27%, for example, it can be 21%, 22%, 23%, 24%, 25% or 26%.

[0106] Preferably, the mass flow rate of the ammonium sulfate mother liquor used for cooling crystallization is 5% to 80% of the mass flow rate of the ammonium sulfate solution feed, for example, it can be 10%, 15%, 20%, 30%, 40%, 50%, 60% or 70%.

[0107] Preferably, the temperature of the cooling crystallization is 30-35°C, for example, 31°C, 32°C, 33°C or 34°C.

[0108] Preferably, the N-NH4 of the ammonium chloride product + The content is ≥23.5%, for example, it can be 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0109] Preferably, the solid content of the ammonium chloride mother liquor is ≤5 g / L, for example, it can be 4.5 g / L, 4 g / L, 3.5 g / L, 3 g / L, 2.5 g / L or 2 g / L.

[0110] In a second aspect, the present invention provides a device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, the device system comprising a pretreatment unit, a sodium-ammonium separation unit, an ammonium sulfate preparation unit, a carbonate-ammonium circulation unit, a calcium, magnesium and insoluble matter removal unit, a double decomposition reaction unit and a sodium bicarbonate treatment unit;

[0111] The wastewater outlet of the pretreatment unit is connected to the inlet of the sodium-ammonium separation device;

[0112] The ammonium sulfate preparation unit includes an evaporation crystallization device, a sodium sulfate and ammonium sulfate separation device, and a first drying device connected in sequence; the sodium sulfate and ammonium sulfate separation device includes any one of a sedimentation separation device, a fluidized separation device, a screening device, or a hydrocyclone separation device, or a combination of at least two thereof;

[0113] The ammonium sulfate liquid phase outlet of the sodium ammonium sulfate separation device is connected to the inlet of the evaporation crystallization device; the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device is connected to the inlet of the evaporation crystallization device; the wet ammonium sulfate outlet of the sodium sulfate and ammonium sulfate separation device is connected to the inlet of the first drying device; the first drying device is provided with an ammonium sulfate product outlet;

[0114] The ammonium carbonate circulation unit includes a pre-cooling unit, a salting-out crystallization device and a double salt separation device connected in sequence; the pre-cooling unit includes a sodium bicarbonate pre-cooling device and a sodium sulfate pre-cooling device arranged in parallel;

[0115] The sodium sulfate outlet of the sodium-ammonium separation device and the sodium sulfate outlet of the sodium sulfate and ammonium sulfate separation device are independently connected to the inlet of the sodium sulfate precooling device; the outlet of the sodium bicarbonate precooling device and the outlet of the sodium sulfate precooling device are independently connected to the inlet of the salting-out crystallization device;

[0116] The salting-out mother liquor outlet of the double salt separation device is connected to the inlet of the calcium, magnesium and insoluble matter removal device; the double salt outlet of the double salt separation device is connected to the inlet of the sodium-ammonium separation device;

[0117] The salting-out clear liquid outlet of the calcium, magnesium and insoluble matter removal device is connected to the inlet of the double decomposition reaction device;

[0118] The sodium bicarbonate processing unit includes a sodium bicarbonate separation device, a second drying device and a calcining device;

[0119] The sodium bicarbonate slurry outlet of the double decomposition reaction device is connected to the inlet of the sodium bicarbonate separation device; the sodium bicarbonate mother liquor outlet of the sodium bicarbonate separation device is connected to the inlet of the sodium bicarbonate precooling device; the wet sodium bicarbonate outlet of the sodium bicarbonate separation device is independently connected to the second drying device and the calcining device; the second drying device is provided with a sodium bicarbonate product outlet; and the calcining device is provided with a sodium carbonate product outlet.

[0120] In the present invention, the main function of setting up the sodium sulfate precooling device is to lower the temperature of the sodium sulfate from the sodium-ammonium separation device and the ammonium sulfate preparation device, reduce the heat entering the salting-out crystallization device, and alleviate its cooling load.

[0121] As a preferred technical solution of the present invention, the pretreatment unit includes a purification and impurity removal device and a hardness removal unit connected in sequence.

[0122] Preferably, the de-hardening unit comprises a pH regulating device, a fluidization induced crystallization device and a calcium-magnesium separation device which are connected in sequence.

[0123] Preferably, the outlet of the purification and impurity removal device is connected to the inlet of the pH adjustment device; the outlet of the hardness-removed clear liquid of the calcium-magnesium separation device is connected to the inlet of the sodium-ammonium separation device.

[0124] In the present invention, the seed amount of the fluidization induced crystallization device is 10% to 60% of the total volume of the fluidization induced crystallization device, for example, it can be 20%, 30%, 40%, 50% or 55%; the temperature of the fluidization induced crystallization device is 30 to 80°C, for example, it can be 35°C, 40°C, 45°C, 50°C, 60°C or 70°C; the liquid flow rate in the bed area of ​​the fluidization induced crystallization device is 0.002 to 0.1 m / s, for example, it can be 0.005 m / s, 0.008 m / s, 0.01 m / s, 0.03 m / s, 0.05 m / s, 0.06 m / s or 0.08 m / s.

[0125] Preferably, the evaporation crystallization device includes an MVR evaporator and / or a multiple-effect evaporator.

[0126] Preferably, the first drying device comprises any one of a thickening device with steam heating, a centrifugal device, or a screw conveying device with steam heating, or a combination of at least two of them.

[0127] In the present invention, the temperature of the heating steam of the thickening device is ≥120°C, and the temperature of the material in the thickening device is ≥90°C; the centrifugal device is a horizontal spiral unloading centrifuge, and the screen of the centrifuge is 60-100 mesh; the temperature of the wet ammonium sulfate obtained after the mixed slurry is subjected to particle size classification is ≥85°C, and the wet ammonium sulfate evaporates part of its water by its own residual heat; the wet ammonium sulfate that has evaporated part of its water enters a spiral conveying device containing steam heating, and the spiral conveying device supplements heat to the wet ammonium sulfate to further evaporate part of the water in the wet ammonium sulfate, and the rotating spiral stirs the ammonium sulfate to enhance heat exchange and water volatilization; after the water in the wet ammonium sulfate is volatilized twice, it can meet the requirements of Class I products in the national standard GB / T 535-2020.

[0128] It should be noted that the first drying unit (ammonium sulfate drying unit) leverages the advantages of a thickener and centrifuge to enhance solid-liquid separation, minimizing the water content of wet ammonium sulfate. A steam-heated screw conveyor provides additional heat and agitation to further volatilize the wet ammonium sulfate, ultimately ensuring that the moisture content of the ammonium sulfate product meets the requirements for Class I products in the national standard GB / T 535-2020. By utilizing waste heat and enhanced liquid-solid separation technology during the material separation and conveying process, the wet ammonium sulfate is dried. This shortens the drying process, reduces equipment investment and footprint, eliminates the energy consumption of steam and various equipment, lowers operating costs, simplifies operation and maintenance, and reduces overall operating costs by 90%.

[0129] Preferably, the metathesis reaction device comprises a fluidization induced crystallization device.

[0130] Preferably, the double salt separation device and the sodium bicarbonate separation device both include a thickening device and a centrifugal device connected in sequence.

[0131] Preferably, the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device is also connected to the inlet of the sodium-ammonium separation device and the inlet of the purification and impurity removal device, respectively.

[0132] Preferably, the device system also includes an ammonium chloride preparation device; the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device is connected to the inlet of the ammonium chloride preparation device; the ammonium chloride liquid phase outlet of the ammonium chloride preparation device is connected to the inlet of the sodium-ammonium separation device; the ammonium chloride preparation device is also provided with an ammonium chloride product outlet.

[0133] As a further preferred technical solution, the preparation method provided in the first aspect is carried out in the device system provided in the second aspect.

[0134] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0135] Compared with the prior art, the present invention has the following beneficial effects:

[0136] (1) The method provided by the present invention realizes gradient crystallization separation of sodium sulfate and ammonium sulfate according to the phase equilibrium law of multi-element water-salt system and the difference in solubility of different substances at different temperatures, thereby eliminating the evaporator required for the traditional sodium sulfate wastewater evaporation crystallization, shortening the process flow, reducing equipment investment, and avoiding the repeated heating and freezing process required for the traditional separation of sodium sulfate and ammonium sulfate, thereby greatly reducing energy consumption; then, a mixed slurry of large-particle ammonium sulfate and fine sodium sulfate is obtained by regulating the crystal growth kinetics, and then the ammonium sulfate mother liquor, wet ammonium sulfate and sodium sulfate are separated by particle size classification; wherein, the N-NH4 + Content ≥ 20.5%, average particle size > 1000μm;

[0137] (2) The method provided by the present invention realizes the recycling of ammonium carbonate by salting out and crystallizing sodium sulfate with sodium bicarbonate mother liquor. The obtained double salt can be reused in the evaporation and crystallization of ammonium sulfate solution. The obtained salting out mother liquor can be used to prepare high-quality baking soda or soda ash products after impurities are removed. Then, by adding ammonium bicarbonate and carbon dioxide to the salting out clear liquor for double decomposition reaction, it is not only helpful to improve the sodium bicarbonate conversion rate, but also to increase the particle size of sodium bicarbonate. The total alkali content of the obtained sodium bicarbonate product is ≥99.5%, and the average particle size is ≥300 μm. The purity of the obtained sodium carbonate product is ≥99.2%;

[0138] (3) The method provided by the present invention can directly cool and crystallize the ammonium sulfate mother liquor to obtain ammonium chloride for chlorine-containing high-salt sodium-based wastewater, eliminating the need for the input of ammonium sulfate raw materials and having no requirements for chloride ion and water content. The process is simpler, energy consumption is lower, and raw material adaptability is stronger; wherein, the N-NH4 + Content ≥23.5%;

[0139] (4) The device system provided by the present invention has low equipment investment, low energy consumption in the process of preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate, greatly reduced water consumption, and greatly reduced operating costs, with obvious economic advantages. At the same time, the product produced is of high quality, achieving the harmless and high-value utilization of sodium-based wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0140] Figure 1 This is a schematic structural diagram of a device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater provided by the present invention;

[0141] Among them, 1-purification and impurity removal device, 2-pH adjustment device, 3-fluidization induced crystallization device, 4-calcium and magnesium separation device, 5-sodium and ammonium separation device, 6-evaporation crystallization device, 7-sodium sulfate and ammonium sulfate separation device, 8-first drying device, 9-sodium bicarbonate precooling device, 10-sodium sulfate precooling device, 11-salting out crystallization device, 12-double salt separation device, 13-calcium, magnesium and insoluble matter removal device, 14-double decomposition reaction device, 15-sodium bicarbonate separation device, 16-second drying device, 17-calcination device, 18-ammonium chloride preparation device;

[0142] 100-pretreatment unit, 200-ammonium sulfate preparation unit, 300-ammonium carbonate circulation unit, 400-sodium bicarbonate treatment unit. DETAILED DESCRIPTION

[0143] It should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "disposed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0144] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples 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 shall be subject to the claims.

[0145] The specific embodiment of the present invention provides a device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater (such as Figure 1 As shown), the device system includes a pretreatment unit 100, a sodium ammonium separation device 5, an ammonium sulfate preparation unit 200, an ammonium carbonate circulation unit 300, a calcium, magnesium and insoluble matter removal device 13, a double decomposition reaction device 14 and a sodium bicarbonate treatment unit 400;

[0146] The pretreatment unit 100 includes a purification and impurity removal device 1 and a de-hardening unit connected in sequence; the de-hardening unit includes a pH adjustment device 2, a fluidization induced crystallization device 3 and a calcium-magnesium separation device 4 connected in sequence;

[0147] The outlet of the purification and impurity removal device 1 is connected to the inlet of the pH adjustment device 2; the outlet of the hardness-removed supernatant of the calcium-magnesium separation device 4 is connected to the inlet of the sodium-ammonium separation device 5;

[0148] The ammonium sulfate preparation unit 200 includes an evaporation crystallization device 6, a sodium sulfate and ammonium sulfate separation device 7, and a first drying device 8 connected in sequence; the sodium sulfate and ammonium sulfate separation device 7 includes any one of a sedimentation separation device, a fluidized separation device, a screening device, or a hydrocyclone separation device, or a combination of at least two thereof;

[0149] The ammonium sulfate liquid phase outlet of the sodium ammonium separation device 5 is connected to the inlet of the evaporation crystallization device 6; the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device 7 is connected to the inlet of the evaporation crystallization device 6; the wet ammonium sulfate outlet of the sodium sulfate and ammonium sulfate separation device 7 is connected to the inlet of the first drying device 8; the first drying device 8 is provided with an ammonium sulfate product outlet;

[0150] The ammonium carbonate circulation unit 300 includes a pre-cooling unit, a salting-out crystallization device 11 and a double salt separation device 12 connected in sequence; the pre-cooling unit includes a sodium bicarbonate pre-cooling device 9 and a sodium sulfate pre-cooling device 10 arranged in parallel;

[0151] The sodium sulfate outlet of the sodium-ammonium separation device 5 and the sodium sulfate outlet of the sodium sulfate and ammonium sulfate separation device 7 are independently connected to the inlet of the sodium sulfate precooling device 10; the outlet of the sodium bicarbonate precooling device 9 and the outlet of the sodium sulfate precooling device 10 are independently connected to the inlet of the salting-out crystallization device 11;

[0152] The salting-out mother liquor outlet of the double salt separation device 12 is connected to the inlet of the calcium, magnesium and insoluble matter removal device 13; the double salt outlet of the double salt separation device 12 is connected to the inlet of the sodium-ammonium separation device 5;

[0153] The salting-out clear liquid outlet of the calcium, magnesium and insoluble matter removal device 13 is connected to the inlet of the double decomposition reaction device 14;

[0154] The sodium bicarbonate processing unit 400 includes a sodium bicarbonate separation device 15, a second drying device 16 and a calcining device 17;

[0155] The sodium bicarbonate slurry outlet of the double decomposition reaction device 14 is connected to the inlet of the sodium bicarbonate separation device 15; the sodium bicarbonate mother liquor outlet of the sodium bicarbonate separation device 15 is connected to the inlet of the sodium bicarbonate precooling device 9; the wet sodium bicarbonate outlet of the sodium bicarbonate separation device 15 is independently connected to the second drying device 16 and the calcining device 17; the second drying device 16 is provided with a sodium bicarbonate product outlet; the calcining device 17 is provided with a sodium carbonate product outlet;

[0156] The device system also includes an ammonium chloride preparation device 18; the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device 7 is connected to the inlet of the ammonium chloride preparation device 18; the ammonium chloride liquid phase outlet of the ammonium chloride preparation device 18 is connected to the inlet of the sodium-ammonium separation device 5; the ammonium chloride preparation device 18 is also provided with an ammonium chloride product outlet.

[0157] When the above-mentioned device system is used to prepare sodium carbonate and / or sodium bicarbonate and co-produce ammonium sulfate and ammonium chloride from sodium-based wastewater, the following steps are included:

[0158] (a) sodium-based wastewater is purified and impurities removed in a purification and impurity removal device 1 to obtain a cleaned supernatant, the pH of the cleaned supernatant is adjusted to alkaline in a pH adjustment device 2, and then transferred to a fluidized bed induced crystallization device 3, and sodium carbonate is added thereto to remove hardness. After separation in a calcium-magnesium separation device 4, calcium-magnesium slag and a hardness-removed supernatant are obtained. The hardness-removed supernatant is then mixed with a double salt and an acid solution, and sodium-ammonium separation is performed in a sodium-ammonium separation device 5 to obtain an ammonium sulfate solution and sodium sulfate;

[0159] (b) subjecting the ammonium sulfate solution obtained in step (a) to evaporation crystallization in an evaporation crystallization device 6 to obtain a mixed slurry of sodium sulfate and ammonium sulfate, and then subjecting the mixed slurry to particle size classification in a sodium sulfate and ammonium sulfate separation device 7 to obtain an ammonium sulfate mother liquor, wet ammonium sulfate, and sodium sulfate, and subjecting the wet ammonium sulfate to a first drying in a first drying device 8 to obtain an ammonium sulfate product;

[0160] Wherein, the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (b);

[0161] (c) mixing the sodium sulfate obtained in step (a) after being precooled by a sodium sulfate precooling device 10 and the sodium sulfate obtained in step (b) with a sodium bicarbonate mother liquor precooled by a sodium bicarbonate precooling device 9, performing a salting-out crystallization reaction in a salting-out crystallization device 11, performing a first separation in a double salt separation device 12 to obtain a double salt and a salting-out mother liquor, and then mixing the salting-out mother liquor with ammonia water or ammonia gas, performing a calcium, magnesium and insoluble matter removal reaction in a calcium, magnesium and insoluble matter removal device 13 to obtain a salting-out clear liquid and a calcium, magnesium and insoluble matter slag;

[0162] wherein the double salt is reused in step (a) sodium-ammonium separation;

[0163] (d) mixing the salted-out clear solution obtained in step (c) with ammonium bicarbonate and carbon dioxide, performing a double decomposition reaction in a double decomposition reaction unit 14 to obtain a sodium bicarbonate slurry, and then performing a second separation on the sodium bicarbonate slurry in a sodium bicarbonate separation unit 15 to obtain wet sodium bicarbonate and a sodium bicarbonate mother liquor, and then performing a second drying in a second drying unit 16 or calcining in a calcining unit 17 to obtain a sodium bicarbonate product or a sodium carbonate product;

[0164] Wherein, the sodium bicarbonate mother liquor is reused in the salting-out crystallization reaction in step (c);

[0165] (e) if the sodium-based wastewater contains chloride ions and the ammonium sulfate mother liquor obtained in step (b) is saturated with chloride ions, a portion of the ammonium sulfate mother liquor is cooled and crystallized in the ammonium chloride preparation device 18 to obtain an ammonium chloride product and an ammonium chloride mother liquor;

[0166] The ammonium chloride mother liquor is recycled to the sodium-ammonium separation in step (a).

[0167] In the following examples and comparative examples, the pretreatment of the sodium-based wastewater was carried out according to the following method:

[0168] (A) adding polyaluminium chloride to sodium-based wastewater having a pH of 7, coagulating the wastewater at 60°C for 30 minutes, then adding anionic polyacrylamide at a mass concentration of 0.1% to the wastewater, coagulating the wastewater at 60°C for 30 minutes, and clarifying the reaction mass for 60 minutes to obtain a purified liquid and purified residue;

[0169] Wherein, the mass ratio of the polyaluminium chloride to the insoluble matter in the sodium-based wastewater is 4:1; the mass ratio of the polyaluminium chloride to the anionic polyacrylamide is 300:1;

[0170] (B) adjusting the pH value of the impurity-removed clear solution obtained in step (1) to 10 using sodium hydroxide, and then adding sodium carbonate thereto to carry out a hardness removal reaction at a temperature of 60° C. for 120 minutes to obtain calcium-magnesium slag and a hardness-removed clear solution;

[0171] The molar ratio of the sodium carbonate to the calcium and magnesium ions in the impurity removal clear solution is 2:1.

[0172] Example 1

[0173] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, the method comprising the following steps:

[0174] (1) Mix the de-hardening supernatant with double salt and 80% sulfuric acid, and perform sodium-ammonium separation at 80°C for 100 minutes to obtain ammonium sulfate solution and sodium sulfate;

[0175] Before the mixing, the COD content in the de-hardening supernatant is detected and different treatments are performed according to the COD content. If the COD content of the de-hardening supernatant is less than 100 ppm, it is directly used for sodium-ammonium separation; if the COD content of the de-hardening supernatant is ≥100 ppm, ammonium persulfate is added during the sodium-ammonium separation; the mass ratio of the ammonium persulfate to the COD in the de-hardening supernatant is 8:1;

[0176] The amount of the de-hardening supernatant added is such that the ammonium sulfate in the double salt is completely dissolved; the amount of sulfuric acid is such that the pH value of the mixed solution is 4;

[0177] The solid content of the ammonium sulfate solution is 4 g / L; the N-NH4 + The content is 1.5%;

[0178] (2) adjusting the pH value of the ammonium sulfate solution obtained in step (1) to 3 using sulfuric acid having a mass concentration of 80%, and then performing evaporation crystallization at a temperature of 80° C. for 200 min to obtain a mixed slurry of sodium sulfate and ammonium sulfate, and then subjecting the mixed slurry to particle size classification to obtain ammonium sulfate mother liquor, wet ammonium sulfate and sodium sulfate, and the wet ammonium sulfate is first dried to obtain an ammonium sulfate product;

[0179] Wherein, more than 95% of the ammonium sulfate in the mixed slurry has a particle size of 800 μm, and more than 95% of the sodium sulfate has a particle size of 100 μm;

[0180] The particle size classification method is screening separation, and the screening separation includes a first screening and a second screening performed in sequence; the aperture of the first screening is 60 mesh; the aperture of the second screening is 100 mesh;

[0181] The mass content of sodium sulfate in the ammonium sulfate mother liquor is 16.44%, and the mass content of ammonium sulfate is 38.76%; the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2);

[0182] (3) mixing the sodium sulfate obtained in step (1) and the sodium sulfate obtained in step (2) with the sodium bicarbonate mother liquor, and performing a salting-out crystallization reaction at a temperature of 30° C. for 6 hours, obtaining a double salt and a salting-out mother liquor after a first separation, and then mixing the salting-out mother liquor with aqueous ammonia, and performing a calcium, magnesium and insoluble matter removal reaction at a temperature of 30° C. to obtain a salting-out clear liquid and a calcium and magnesium slag;

[0183] The mass volume ratio of the total mass of the sodium sulfate to the sodium bicarbonate mother liquor is 300:1 g / L; the material temperature of the sodium sulfate is 15° C.; the material temperature of the sodium bicarbonate mother liquor is 30° C.;

[0184] The double salt is reused in step (1) sodium-ammonium separation;

[0185] The molar ratio of the ammonia water to the bicarbonate substance in the salting-out mother liquor is 1:0.9; the mass concentration of the ammonia water is 12%;

[0186] (4) The salting-out clear solution obtained in step (3) is mixed with ammonium bicarbonate and carbon dioxide, and subjected to a double decomposition reaction at 35° C. for 4 h to obtain a sodium bicarbonate slurry, and the sodium bicarbonate slurry is then subjected to a second separation to obtain wet sodium bicarbonate with a water content of 6% and a sodium bicarbonate mother liquor, and the wet sodium bicarbonate is then subjected to a second drying to obtain a sodium bicarbonate product;

[0187] The mass ratio of the ammonium bicarbonate to the effective amount of sodium sulfate in the salting-out clear solution is 1.3:1; the ammonium bicarbonate is added by slurrying the salting-out clear solution and adopting a three-stage feeding method; the amount of carbon dioxide added is such that the carbonate concentration in the mixed solution is 5 g / L; the mass concentration of the carbon dioxide is 70%, and the introduction temperature is 30°C;

[0188] After the double decomposition reaction, the average particle size of the sodium bicarbonate in the obtained sodium bicarbonate slurry is 300 μm;

[0189] The sodium bicarbonate mother liquor is reused in the salting-out crystallization reaction in step (3).

[0190] Example 2

[0191] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, the method comprising the following steps:

[0192] (1) Mix the de-hardening supernatant with double salt and 98% sulfuric acid, and perform sodium-ammonium separation at 90°C for 60 minutes to obtain ammonium sulfate solution and sodium sulfate;

[0193] Before the mixing, the COD content in the de-hardening supernatant is detected and different treatments are performed according to the COD content. If the COD content of the de-hardening supernatant is less than 100 ppm, it is directly used for sodium-ammonium separation; if the COD content of the de-hardening supernatant is ≥100 ppm, ammonium persulfate is added during the sodium-ammonium separation; the mass ratio of the ammonium persulfate to the COD in the de-hardening supernatant is 6:1;

[0194] The amount of the de-hardening supernatant added is such that the ammonium sulfate in the double salt is completely dissolved; the amount of sulfuric acid added is such that the pH value of the mixed solution is 4;

[0195] The solid content of the ammonium sulfate solution is 3g / L; the N-NH4 + The content is 1%;

[0196] (2) adjusting the pH value of the ammonium sulfate solution obtained in step (1) to 3.5 using sulfuric acid having a mass concentration of 98%, and then performing evaporation crystallization at a temperature of 90° C. for 180 minutes to obtain a mixed slurry of sodium sulfate and ammonium sulfate, and then subjecting the mixed slurry to particle size classification to obtain ammonium sulfate mother liquor, wet ammonium sulfate and sodium sulfate, and the wet ammonium sulfate is first dried to obtain an ammonium sulfate product;

[0197] wherein, more than 95% of the ammonium sulfate in the mixed slurry has a particle size of 850 μm, and more than 95% of the sodium sulfate has a particle size of 80 μm;

[0198] The particle size classification method is fluidized separation, and the flow rate of the mixed slurry during the fluidized separation process is controlled to be 0.03m / s;

[0199] The mass content of sodium sulfate in the ammonium sulfate mother liquor is 16.3%, and the mass content of ammonium sulfate is 38.8%; the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2);

[0200] (3) mixing the sodium sulfate obtained in step (1) and the sodium sulfate obtained in step (2) with the sodium bicarbonate mother liquor, and performing a salting-out crystallization reaction at a temperature of 27° C. for 10 hours, obtaining a double salt and a salting-out mother liquor after a first separation, and then mixing the salting-out mother liquor with ammonia gas, and performing a calcium, magnesium and insoluble matter removal reaction at a temperature of 27° C. to obtain a salting-out clear liquid and a calcium and magnesium slag;

[0201] The mass volume ratio of the total mass of the sodium sulfate to the sodium bicarbonate mother liquor is 220:1 g / L; the material temperature of the sodium sulfate is 10° C.; the material temperature of the sodium bicarbonate mother liquor is 26° C.;

[0202] The double salt is reused in step (1) sodium-ammonium separation;

[0203] The molar ratio of the ammonia gas to the bicarbonate substance in the salting-out mother liquor is 1:0.8; the mass concentration of the ammonia gas is 60%;

[0204] (4) The salting-out clear solution obtained in step (3) is mixed with ammonium bicarbonate and carbon dioxide, and subjected to a double decomposition reaction at a temperature of 45° C. for 3 h to obtain a sodium bicarbonate slurry, and then the sodium bicarbonate slurry is subjected to a second separation to obtain wet sodium bicarbonate with a water content of 5% and a sodium bicarbonate mother liquor, and then the wet sodium bicarbonate is subjected to a second drying to obtain a sodium bicarbonate product;

[0205] The mass ratio of the ammonium bicarbonate to the effective amount of sodium sulfate in the salting-out clear solution is 1.2:1; the ammonium bicarbonate is added by slurrying the salting-out clear solution and adopting a two-stage feeding method; the amount of carbon dioxide added is such that the carbonate concentration in the mixed solution is 2 g / L; the mass concentration of the carbon dioxide is 50%, and the introduction temperature is 45°C;

[0206] After the double decomposition reaction, the average particle size of the sodium bicarbonate in the obtained sodium bicarbonate slurry is 320 μm;

[0207] The sodium bicarbonate mother liquor is reused in the salting-out crystallization reaction in step (3).

[0208] Example 3

[0209] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Based on Example 1, the following steps are also performed:

[0210] The COD content in the ammonium sulfate mother liquor obtained in step (2) is detected, and different treatments are performed according to the COD content. If the COD content is less than 300 ppm, the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2); if the COD content is ≥300 ppm, part of the ammonium sulfate mother liquor is refluxed to the sodium-ammonium separation in step (1), and ammonium persulfate is added thereto, and the remaining ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2);

[0211] The mass flow rate of the ammonium sulfate mother liquor refluxed to the sodium-ammonium separation is 30% of the mass flow rate of the ammonium sulfate solution feed; the mass ratio of the ammonium persulfate to the COD in the refluxed ammonium sulfate mother liquor is 7:1;

[0212] At the same time, the fluoride ion content in the ammonium sulfate mother liquor obtained in step (2) is detected, and different treatments are performed according to the fluoride ion content. If the fluoride ion content is less than 15 ppm, the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2); if the fluoride ion content is ≥15 ppm, part of the ammonium sulfate mother liquor is refluxed to the purification and impurity removal reaction, and polyaluminum chloride is added thereto, and the remaining ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2);

[0213] The mass flow rate of the ammonium sulfate mother liquor refluxed to the purification and impurity removal reaction is 30% of the mass flow rate of the ammonium sulfate solution feed; the mass ratio of the added polyaluminum chloride to the fluoride ions in the refluxed ammonium sulfate mother liquor is 4:1.

[0214] Example 4

[0215] In this embodiment, the initial sodium-based wastewater contains chloride ions with a mass concentration of 2%.

[0216] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate and ammonium chloride from sodium-based wastewater. Based on Example 1, the following steps are also performed:

[0217] When the chloride ions in the ammonium sulfate mother liquor obtained in step (2) are saturated, a portion of the ammonium sulfate mother liquor is cooled and crystallized at a temperature of 32° C. to obtain an ammonium chloride product and an ammonium chloride mother liquor;

[0218] The saturation state of chloride ions in the ammonium sulfate mother liquor is that the mass content of ammonium chloride in the ammonium sulfate mother liquor is 23%; the mass flow rate of the ammonium sulfate mother liquor used for cooling crystallization is 40% of the mass flow rate of the ammonium sulfate solution feed;

[0219] The solid content of the ammonium chloride mother liquor is 3 g / L; the ammonium chloride mother liquor is reused in the sodium-ammonium separation in step (1).

[0220] In this embodiment, the N-NH4 + The content is 25.5%.

[0221] Example 5

[0222] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that in step (4), wet sodium bicarbonate is calcined to produce a sodium carbonate product, other conditions are the same as those in Example 1.

[0223] In this embodiment, the purity of the obtained sodium carbonate product is 99.5%.

[0224] Example 6

[0225] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the temperature for separating sodium and ammonium in step (1) is 50°C, other conditions are the same as those in Example 1.

[0226] Example 7

[0227] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the temperature for separating sodium and ammonium in step (1) is 150° C., other conditions are the same as those in Example 1.

[0228] Example 8

[0229] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except for adjusting the pH value of the ammonium sulfate solution to 1 in step (2), other conditions are the same as those in Example 1.

[0230] Example 9

[0231] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except for adjusting the pH value of the ammonium sulfate solution to 7 in step (2), other conditions are the same as those in Example 1.

[0232] Example 10

[0233] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the evaporation and crystallization time in step (2) is 60 minutes, other conditions are the same as those in Example 1.

[0234] Example 11

[0235] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the evaporation and crystallization time in step (2) is 400 minutes, other conditions are the same as those in Example 1.

[0236] Example 12

[0237] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that only the first screening is performed in the screening separation in step (2), other conditions are the same as those in Example 1.

[0238] Example 13

[0239] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that only the second screening is performed in the screening separation in step (2), other conditions are the same as those in Example 1.

[0240] Example 14

[0241] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the material temperature of sodium sulfate and sodium bicarbonate mother liquor in step (3) is both 25°C, other conditions are the same as those in Example 1.

[0242] Example 15

[0243] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the ammonium bicarbonate in step (4) is fed as a first-grade feed, other conditions are the same as those in Example 1.

[0244] Example 16

[0245] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the temperature of the double decomposition reaction in step (4) is 20°C, other conditions are the same as those in Example 1.

[0246] Example 17

[0247] This embodiment provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that the temperature of the double decomposition reaction in step (4) is 60°C, other conditions are the same as those in Example 1.

[0248] Comparative Example 1

[0249] This comparative example provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that calcium, magnesium and insoluble matter removal reactions are not performed in step (3), other conditions are the same as those in Example 1.

[0250] Comparative Example 2

[0251] This comparative example provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater. Except that no ammonia water and carbon dioxide are added in step (3) and step (4), the other conditions are the same as those in Example 1.

[0252] The total alkali content, average particle size of the sodium bicarbonate product obtained in the above examples and comparative examples and the N-NH4 of the ammonium sulfate product + The content, average particle size and water content were tested, and the above results are shown in Table 1.

[0253] Table 1

[0254]

[0255] From Table 1 we can see that:

[0256] (1) The method provided in Examples 1-3 of the present invention, according to the phase equilibrium law of the multi-element water-salt system, through the regulation of crystallization kinetics and supersaturation, does not require evaporation and crystallization of sodium sulfate solid from sodium-based wastewater. The wastewater after simple pretreatment is directly fed into the treatment system, thereby achieving gradient crystallization separation of sodium sulfate, ammonium sulfate and sodium bicarbonate, and obtaining high-quality sodium bicarbonate and ammonium sulfate products; wherein, the total alkali content of the sodium bicarbonate product is as high as 99.8%, the average particle size is ≥300 μm, and the sodium bicarbonate product meets the requirements of Class II in industrial sodium bicarbonate in GB / T 1606-2008; the nitrogen content of the ammonium sulfate product is as high as 20.5%, the water content is as low as 0.3%, and the average particle size is greater than 1000 μm, and the ammonium sulfate product meets the requirements of Type I in fertilizer-grade ammonium sulfate in GB / T 535-2020.

[0257] (2) A comprehensive comparison of Example 1 and Examples 6-7 shows that if the temperature of sodium ammonium separation in step (1) is too low, the double salt cannot dissociate, so the solid obtained after liquid-solid separation is still a double salt. After returning to the carbon ammonium cycle, it does not participate in the reaction but participates in the cycle, increasing the system circulation volume, pushing up the operating energy consumption and equipment investment cost; the concentrations of sodium sulfate and ammonium sulfate in the ammonium sulfate solution separated after evaporation and crystallization are 19.82% and 26.9%, respectively, and the water content is 53.28%. The ratio of ammonium sulfate to water is 1:1.98. The raw material feed concentration is low, the evaporation amount of water increases, and the system operating energy consumption increases; at the same time, due to the low raw material concentration, the material residence time is reduced under the same conditions, the ammonium sulfate particles become smaller, and the mass ratio of ammonium sulfate to sodium sulfate is reduced. Therefore, it is difficult to separate ammonium sulfate and sodium sulfate, and the separation depth is poor. The nitrogen content of the ammonium sulfate product is reduced to 19.1%, and the water content is increased to 0.8%. If the temperature of sodium-ammonium separation in step (1) is too high, although it has no significant effect on product quality, the excessively high reaction temperature requires a large amount of energy input, increasing energy costs; a reaction temperature of 150°C requires pressure equipment and higher materials to meet the requirements, increasing equipment investment and operating difficulty.

[0258] (3) From the comparison between Example 1 and Examples 8-9, it can be seen that if the pH value of the ammonium sulfate solution is regulated too low in step (2), a portion of the acid enters the ammonium sulfate product during the evaporation and crystallization process, and the sodium sulfate particles become finer and adhere to the surface of the ammonium sulfate, resulting in a high free acid content in the ammonium sulfate product, and a decrease in both purity and average particle size. If the pH value of the ammonium sulfate solution is regulated too high in step (2), the difference between the particles of sodium sulfate and ammonium sulfate becomes smaller during the evaporation and crystallization process, resulting in a decrease in the average particle size of the ammonium sulfate product.

[0259] (4) From the comparison between Example 1 and Examples 10-11, it can be seen that if the evaporation crystallization time in step (2) is too short, the ammonium sulfate crystals grow and the fine particles will adhere to the sodium sulfate, reducing the nitrogen content of the ammonium sulfate product and causing the average particle size of the ammonium sulfate product to decrease; if the evaporation crystallization time in step (2) is too long, although it will not affect the product quality, it will cause the solid content of the system to increase, making material transportation difficult and affecting the stable operation of the system.

[0260] (5) A comparison of Example 1 and Examples 12-13 shows that if only the first screening is performed for particle size classification in step (2), a certain amount of ammonium sulfate will be entrained in the sodium sulfate because ammonium sulfate and sodium sulfate cannot be completely separated. On the one hand, this will increase the system circulation volume, reduce the single ammonium sulfate output, and increase the system operation energy consumption. On the other hand, a large amount of water will be brought out during the salting out process, thereby causing a large amount of fine sodium bicarbonate to be produced during the salting out process. After the fine sodium bicarbonate enters the double decomposition reaction, the sodium bicarbonate particles are less than 100 μm and the quality is lower than 99%. At the same time, because there is no fine ammonium sulfate obtained by secondary screening as a seed crystal in the evaporation crystallization system, the particles of the ammonium sulfate product become smaller, the nitrogen content in the ammonium sulfate is reduced to 19.7%, and the water content is increased to 0.77%. If only the second screening is performed in step (2), the fine sodium sulfate will be entrained into the ammonium sulfate, which will ultimately affect the quality of the ammonium sulfate. The nitrogen content in the ammonium sulfate is reduced to 20.2%, the water content is increased to 0.9%, and the particle size of the ammonium sulfate product will also decrease.

[0261] (6) A comparison between Example 1 and Example 14 shows that if the material temperature of sodium sulfate in step (3) is too high, the heat generated by the salting-out crystallization reaction process cannot be neutralized, resulting in unstable temperature of the salting-out crystallization process and low sodium ion concentration in the salting-out clear liquid. Therefore, there is insufficient sodium sulfate to participate in the crystallization reaction during the double decomposition reaction, which ultimately leads to the particle size of the sodium bicarbonate product being reduced to 85 μm, the water content being increased, and the product quality being as low as 97.6%. A comparison between Example 1 and Example 15 shows that if ammonium bicarbonate in step (4) is fed only with level 1, sodium bicarbonate will precipitate out explosively due to excessive supersaturation during the double decomposition reaction, which ultimately leads to finer sodium bicarbonate particles, increased water content, and decreased product purity.

[0262] (7) A comprehensive comparison of Example 1 and Examples 16-17 shows that if the temperature of the double decomposition reaction in step (4) is too low, the sodium bicarbonate supersaturation is too high, causing the sodium bicarbonate to burst out and wash out, ultimately resulting in fine particles of the sodium bicarbonate product, increased water content, and decreased product purity; if the temperature of the double decomposition reaction in step (4) is too high, although it does not affect the product quality, it will lead to increased energy consumption and higher equipment requirements.

[0263] (8) From the comparison between Example 1 and Comparative Example 1, it can be seen that if the step (3) of removing calcium, magnesium and insoluble matter is not carried out, the quality of the sodium bicarbonate product will be affected, resulting in a decrease in the purity of the product.

[0264] (9) From the comparison between Example 1 and Comparative Example 2, it can be seen that if ammonia water and carbon dioxide are not added in step (3) and step (4), respectively, sodium bicarbonate will precipitate out during the salting out process and eventually enter the double decomposition reaction system, which will result in fine particles of the sodium bicarbonate product and reduced product purity.

[0265] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, characterized in that: The method comprises the following steps: (1) Pre-treating the sodium-based wastewater, and then mixing the pre-treated sodium-based wastewater with double salt and acid solution to separate sodium and ammonium to obtain ammonium sulfate solution and sodium sulfate; (2) evaporating and crystallizing the ammonium sulfate solution obtained in step (1) to obtain a mixed slurry of sodium sulfate and ammonium sulfate, and then subjecting the mixed slurry to particle size classification to obtain ammonium sulfate mother liquor, wet ammonium sulfate and sodium sulfate, and subjecting the wet ammonium sulfate to a first drying to obtain an ammonium sulfate product; Wherein, the ammonium sulfate mother liquor is reused in the evaporation crystallization of step (2); (3) mixing the sodium sulfate obtained in step (1) and the sodium sulfate obtained in step (2) with a sodium bicarbonate mother liquor, and performing a salting-out crystallization reaction to obtain a double salt and a salting-out mother liquor after a first separation, and then mixing the salting-out mother liquor with ammonia water or ammonia gas, and performing a calcium, magnesium and insoluble matter removal reaction to obtain a salting-out clear liquid and a calcium and magnesium slag; Wherein, the double salt is reused in step (1) sodium-ammonium separation; (4) mixing the salting-out clear solution obtained in step (3) with ammonium bicarbonate and carbon dioxide, and performing a double decomposition reaction to obtain a sodium bicarbonate slurry, and then performing a second separation on the sodium bicarbonate slurry to obtain wet sodium bicarbonate and a sodium bicarbonate mother liquor, and then performing a second drying or calcining on the wet sodium bicarbonate to obtain a sodium bicarbonate product or a sodium carbonate product; The sodium bicarbonate mother liquor is recycled to the salting-out crystallization reaction in step (3).

2. The method according to claim 1, characterized in that The pretreatment in step (1) includes purification, impurity removal and hardness removal performed in sequence; The purification and impurity removal method comprises: adding a coagulant and a flocculant to sodium-based wastewater in sequence to perform purification and impurity removal reactions to obtain a clean impurity-removed liquid and clean impurity-removed residue; The coagulant includes any one of polyaluminium chloride, polyaluminium sulfate, aluminium chloride or aluminium sulfate, or a combination of at least two thereof; The flocculant includes any one of anionic flocculant, cationic flocculant or amphoteric flocculant or a combination of at least two; The mass ratio of the coagulant to the insoluble matter in the sodium-based wastewater is (1-6):1; the mass ratio of the coagulant to the flocculant is (50-500):1; The interval between the addition of the coagulant and the flocculant is ≥15 min; The purification and impurity removal reaction has a pH of 6-8, a temperature of 30-80°C, and a time of 60-360 minutes; The hardness removal method comprises: adjusting the pH value of the impurity removal clear solution to be alkaline, and then adding sodium carbonate thereto to carry out a hardness removal reaction to obtain calcium magnesium slag and a hardness removal clear solution; Adjusting the pH value of the impurity-removing clear solution to 9-12; The molar ratio of the sodium carbonate to the calcium and magnesium ions in the impurity removal clear solution is (1-3):1; The temperature of the hardness removal reaction is 30-80° C. and the time is 30-180 min.

3. The method according to claim 1, characterized in that Before performing the mixing in step (1), the method further includes: detecting the COD content of the pretreated sodium-based wastewater and performing different treatments according to the COD content; if the COD content of the pretreated sodium-based wastewater is less than 100 ppm, the wastewater is directly used for sodium-ammonium separation; if the COD content of the pretreated sodium-based wastewater is greater than or equal to 100 ppm, a strong oxidant is added during the sodium-ammonium separation; The strong oxidant includes any one or a combination of at least two of ammonium sulfate, ammonium persulfate, disodium persulfate, sodium persulfate, hydrogen peroxide, ozone or oxygen; The mass ratio of the strong oxidant to the COD in the pretreated sodium-based wastewater is (4-10):1; The double salt in step (1) comprises a double salt formed by sodium sulfate and ammonium sulfate; The amount of sodium-based wastewater added after the pretreatment in step (1) is such that the ammonium sulfate in the double salt is completely dissolved; The amount of the acid solution added in step (1) is such that the pH value of the mixed solution is 3-5; The temperature of the sodium-ammonium separation in step (1) is 70-110° C. and the time is 30-240 min; The solid content of the ammonium sulfate solution in step (1) is ≤10 g / L; N-NH4 in the sodium sulfate in step (1) + Content ≤3%.

4. The method according to claim 1, wherein During the evaporation crystallization in step (2), an acid solution is used to adjust the pH value of the ammonium sulfate solution to 2-6; The evaporation crystallization temperature in step (2) is 70-110° C. and the residence time is 120-300 min; In step (2), more than 95% of the ammonium sulfate in the mixed slurry has a particle size of ≥500 μm, and more than 95% of the sodium sulfate has a particle size of ≤100 μm; The particle size classification in step (2) includes any one of sedimentation separation, fluidization separation, screening separation or hydrocyclone separation, or a combination of at least two thereof; During the sedimentation separation, the sedimentation rate of sodium sulfate in the mixed slurry is controlled to be ≤0.01 m / s, and the sedimentation rate of ammonium sulfate is controlled to be ≥0.05 m / s; During the fluidized separation, the flow rate of the mixed slurry is controlled to be greater than 0.01 m / s; The screening separation includes a first screening and a second screening performed in sequence; the aperture of the first screening is 40-80 mesh; the aperture of the second screening is 80-120 mesh, excluding 80 mesh; In the hydrocyclone separation, the cone angle of the hydrocyclone is 10-30°, the diameter is 100-650 mm, and the material feed flow rate is 1.5-3 m / s; The mass content of sodium sulfate in the ammonium sulfate mother liquor in step (2) is ≤17%, and the mass content of ammonium sulfate is ≤39%; The average particle size of the ammonium sulfate product in step (2) is greater than 1000 μm; N-NH4 in the ammonium sulfate product of step (2) + Content ≥20.5%; The water content in the ammonium sulfate product in step (2) is ≤0.5%.

5. The method according to claim 1, wherein After the particle size classification in step (2), the method further comprises: detecting the COD content in the obtained ammonium sulfate mother liquor and performing different treatments according to the COD content; if the COD content is less than 300 ppm, the ammonium sulfate mother liquor is recycled to the evaporation crystallization in step (2); if the COD content is greater than or equal to 300 ppm, a portion of the ammonium sulfate mother liquor is refluxed to the sodium-ammonium separation in step (1), and a strong oxidant is added thereto, and the remaining ammonium sulfate mother liquor is recycled to the evaporation crystallization in step (2); wherein the mass flow rate of the ammonium sulfate mother liquor recycled to the sodium-ammonium separation is 10% to 50% of the mass flow rate of the ammonium sulfate solution feed; The mass ratio of the strong oxidant to the COD in the refluxed ammonium sulfate mother liquor is (4-10):1; After the particle size classification in step (2), the method further comprises: detecting the fluoride ion content in the obtained ammonium sulfate mother liquor and performing different treatments according to the fluoride ion content; if the fluoride ion content is less than 15 ppm, the ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2); if the fluoride ion content is ≥15 ppm, a portion of the ammonium sulfate mother liquor is refluxed to the purification and impurity removal reaction, and a coagulant is added thereto, and the remaining ammonium sulfate mother liquor is reused in the evaporation crystallization in step (2); wherein the mass flow rate of the ammonium sulfate mother liquor refluxed to the purification and impurity removal reaction is 10% to 50% of the mass flow rate of the ammonium sulfate solution feed; The mass ratio of the added coagulant to the fluoride ions in the refluxed ammonium sulfate mother liquor is (3-6):

1.

6. The method according to claim 1, characterized in that The mass volume ratio of the total mass of the sodium sulfate in step (3) to the sodium bicarbonate mother liquor is (180-400): 1 g / L; In step (3), the material temperature of the sodium sulfate is 10-20°C; The material temperature of the sodium bicarbonate mother liquor in step (3) is 25-35°C; The temperature of the salting-out crystallization reaction in step (3) is 25-35°C; The time of the salting-out crystallization reaction in step (3) is 3 to 11 hours; The molar ratio of the ammonia water or ammonia gas to the bicarbonate substance in the salting-out mother liquor in step (3) is 1:(0.8-1); The mass concentration of the ammonia water is 8% to 25%; the mass concentration of the ammonia gas is 30% to 100%; The temperature of the calcium, magnesium and insoluble matter removal reaction in step (3) is 25-35°C.

7. The method according to claim 1, characterized in that The mass ratio of the ammonium bicarbonate in step (4) to the effective amount of sodium sulfate in the salting-out clear solution is (1.2-1.4):1; The ammonium bicarbonate is added in step (4) by salting out the clear liquid and beating, and 1-5 levels of feed are used; The amount of carbon dioxide added in step (4) is such that the carbonate concentration in the mixed solution is 0-10 g / L; The mass concentration of the carbon dioxide in step (4) is 40% to 100%, and the introduction temperature is 20 to 45°C; The temperature of the metathesis reaction in step (4) is 30-45°C and the time is 2-6 hours; After the double decomposition reaction in step (4), the average particle size of the sodium bicarbonate in the obtained sodium bicarbonate slurry is ≥300 μm; The water content of the wet sodium bicarbonate in step (4) is 5% to 8%; The total alkali content of the sodium bicarbonate product in step (4) is ≥99.5%; The average particle size of the sodium bicarbonate product in step (4) is ≥300 μm; The purity of the sodium carbonate product in step (4) is ≥99.2%.

8. The method according to claim 1, characterized in that The method further comprises step (5): If the sodium-based wastewater contains chloride ions, and the chloride ions in the ammonium sulfate mother liquor obtained in step (2) are saturated, part of the ammonium sulfate mother liquor is cooled and crystallized to obtain an ammonium chloride product and an ammonium chloride mother liquor, and the ammonium chloride mother liquor is reused in the sodium-ammonium separation in step (1); The chloride ion in the ammonium sulfate mother liquor is in a saturated state, that is, the mass content of ammonium chloride in the ammonium sulfate mother liquor is 20% to 27%; The mass flow rate of the ammonium sulfate mother liquor used for cooling crystallization is 5% to 80% of the mass flow rate of the ammonium sulfate solution feed; The temperature of the cooling crystallization is 30-35°C; The N-NH4 of the ammonium chloride product + Content ≥23.5%; The solid content of the ammonium chloride mother liquor is ≤5g / L.

9. A device system for preparing sodium carbonate and / or sodium bicarbonate and co-producing ammonium sulfate from sodium-based wastewater, characterized in that: The device system includes a pretreatment unit, a sodium-ammonium separation unit, an ammonium sulfate preparation unit, an ammonium carbonate circulation unit, a calcium, magnesium and insoluble matter removal unit, a double decomposition reaction unit and a sodium bicarbonate treatment unit; The wastewater outlet of the pretreatment unit is connected to the inlet of the sodium-ammonium separation device; The ammonium sulfate preparation unit includes an evaporation crystallization device, a sodium sulfate and ammonium sulfate separation device, and a first drying device connected in sequence; the sodium sulfate and ammonium sulfate separation device includes any one of a sedimentation separation device, a fluidized separation device, a screening device, or a hydrocyclone separation device, or a combination of at least two thereof; The ammonium sulfate liquid phase outlet of the sodium ammonium sulfate separation device is connected to the inlet of the evaporation crystallization device; the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device is connected to the inlet of the evaporation crystallization device; the wet ammonium sulfate outlet of the sodium sulfate and ammonium sulfate separation device is connected to the inlet of the first drying device; the first drying device is provided with an ammonium sulfate product outlet; The ammonium carbonate circulation unit includes a pre-cooling unit, a salting-out crystallization device and a double salt separation device connected in sequence; the pre-cooling unit includes a sodium bicarbonate pre-cooling device and a sodium sulfate pre-cooling device arranged in parallel; The sodium sulfate outlet of the sodium-ammonium separation device and the sodium sulfate outlet of the sodium sulfate and ammonium sulfate separation device are independently connected to the inlet of the sodium sulfate precooling device; the outlet of the sodium bicarbonate precooling device and the outlet of the sodium sulfate precooling device are independently connected to the inlet of the salting-out crystallization device; The salting-out mother liquor outlet of the double salt separation device is connected to the inlet of the calcium, magnesium and insoluble matter removal device; the double salt outlet of the double salt separation device is connected to the inlet of the sodium-ammonium separation device; The salting-out clear liquid outlet of the calcium, magnesium and insoluble matter removal device is connected to the inlet of the double decomposition reaction device; The sodium bicarbonate processing unit includes a sodium bicarbonate separation device, a second drying device and a calcining device; The sodium bicarbonate slurry outlet of the double decomposition reaction device is connected to the inlet of the sodium bicarbonate separation device; the sodium bicarbonate mother liquor outlet of the sodium bicarbonate separation device is connected to the inlet of the sodium bicarbonate precooling device; the wet sodium bicarbonate outlet of the sodium bicarbonate separation device is independently connected to the second drying device and the calcining device; the second drying device is provided with a sodium bicarbonate product outlet; and the calcining device is provided with a sodium carbonate product outlet.

10. The device system according to claim 9, characterized in that: The pretreatment unit includes a purification and impurity removal device and a de-hardening unit connected in sequence; The de-hardening unit includes a pH regulating device, a fluidization induced crystallization device and a calcium-magnesium separation device connected in sequence; The outlet of the purification and impurity removal device is connected to the inlet of the pH adjustment device; the outlet of the hardness-removed clear liquid of the calcium-magnesium separation device is connected to the inlet of the sodium-ammonium separation device; The evaporation crystallization device includes an MVR evaporator and / or a multiple-effect evaporator; The first drying device comprises any one or a combination of at least two of a thickening device with steam heating, a centrifugal device, or a screw conveying device with steam heating; The double decomposition reaction device includes a fluidization induced crystallization device; The double salt separation device and the sodium bicarbonate separation device both include a thickening device and a centrifugal device connected in sequence; The ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device is also connected to the inlet of the sodium-ammonium separation device and the inlet of the purification and impurity removal device respectively; The device system also includes an ammonium chloride preparation device; the ammonium sulfate liquid phase outlet of the sodium sulfate and ammonium sulfate separation device is connected to the inlet of the ammonium chloride preparation device; the ammonium chloride liquid phase outlet of the ammonium chloride preparation device is connected to the inlet of the sodium-ammonium separation device; the ammonium chloride preparation device is also provided with an ammonium chloride product outlet.

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