A high-nitrate symbiotic natural soda ash development and processing system and process

Abstract

The application discloses a high-nitrate symbiotic natural soda exploitation and processing system and process and belongs to the technical field of natural soda ore exploitation and processing. The system comprises a solution mining unit, a refining unit, a membrane separation and concentration unit, a crystallization and drying unit and a causticization circulation unit; the process uses NaOH solution as a solution mining agent, pumps the NaOH solution into an ore bed through an injection well, and reacts with the ore to generate Na2CO3 solution; ‑ After muddy soda brine is refined and clarified, the muddy soda brine is sequentially separated and concentrated through a selective low-pressure reverse osmosis membrane system and a high-multiple-concentration flat membrane system; heavy-duty pure soda is obtained by crystallization and drying of concentrated soda liquor, NaOH is generated by causticization of concentrated water containing Na2SO4 and is reused, and gypsum is by-produced. The application simplifies a process, realizes high-value and clean development of high-nitrate natural soda, and solves problems of high energy consumption, high operation cost, a complex process and low added value of by-products existing in a traditional high-nitrate natural soda processing process.

Description

Technical Field

[0001] This invention relates to the field of natural alkali mining and processing technology, specifically to a high-nitrate symbiotic natural alkali development and processing system and process. Background Technology

[0002] Currently, for natural alkali minerals with high nitrate content, which are composed of alkali, salt, and nitrate symbiotic products, the traditional approach is a carbonation-evaporation-causticization co-production process. This process essentially involves high energy consumption and complex operations to convert low-value-added byproducts into chemicals with some market value, thereby achieving resource recovery. However, as green, low-carbon, and high-quality products become clear directions for industrial upgrading, the shortcomings of this process are becoming increasingly apparent: on the one hand, the continued high energy consumption and investment severely restrict its techno-economic viability; on the other hand, the market capacity and low added value of byproducts such as sodium sulfate further weaken the overall competitiveness of the process. Therefore, developing an alternative process with a simpler flow, controllable energy consumption, and optimized product structure has become a critical issue that the industry urgently needs to address.

[0003] In related technologies, CN112850753A discloses a natural soda ash production process, including steps such as leaching, pretreatment, stripping and concentration, crystallization and separation of sodium carbonate decahydrate, dissolution of sodium carbonate decahydrate, crystallization and separation of sodium carbonate monohydrate, and drying of sodium carbonate monohydrate, ultimately yielding heavy soda ash. This process can also utilize sodium carbonate decahydrate solution or concentrated brine to produce sodium bicarbonate through sodium bicarbonate crystallization, separation, and drying processes. Furthermore, this process causticizes and evaporates the effluent generated during sodium carbonate decahydrate crystallization to obtain a concentrated NaOH solution that is recycled back into the production system; the causticized sludge is calcined to recover quicklime and reintroduced into the production process. While this process is effective in reducing impurity content and wastewater discharge, it is only suitable for natural soda ash ores containing small amounts of sodium chloride / sodium sulfate and is difficult to effectively treat the mNa₂SO₄·nNa₂CO₃ type double salts present in high-nitrate natural soda ash ores, resulting in difficulty in guaranteeing the purity of the final product.

[0004] In summary, existing technologies for the development and processing of high-nitrate symbiotic natural alkali have problems such as high energy consumption, complex processes, difficulty in guaranteeing product purity, and poor economic efficiency. They cannot meet the industrial development direction of green, low-carbon, and high-quality products. There is an urgent need for a new process that can overcome the above limitations in order to achieve high-value and clean development of high-nitrate natural alkali mines. Summary of the Invention

[0005] Therefore, this invention provides a high-nitrate symbiotic natural alkali development and processing system and process, which solves the problems of high energy consumption, high operating costs, complex processes and low added value of by-products in traditional high-nitrate natural alkali processing technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a high-nitrate symbiotic natural alkali development and processing system, comprising a solvent extraction unit, a refining unit, a membrane separation and concentration unit, a crystallization and drying unit, and a causticization circulation unit;

[0007] The leaching and extraction unit includes an injection well and a brine extraction well. The injection well is used to deliver leaching agent to the high-nitrate symbiotic natural alkali mineral layer. The brine extraction well is used to extract the extracted turbid alkali brine.

[0008] The refining unit includes an alkaline brine refining device and a raw water tank. The alkaline brine refining device is connected to the brine outlet well to process turbid alkaline brine, and the raw water tank is used to temporarily store the clarified alkaline solution after being processed by the alkaline brine refining device.

[0009] The membrane separation and concentration unit includes a security filter I, a selective low-pressure reverse osmosis membrane system, a security filter II, a high-concentration flat sheet membrane system, a product water tank, a concentrate tank I, and a concentrate tank II. One end of the security filter I is connected to the raw water tank, and the other end of the security filter I is connected to the selective low-pressure reverse osmosis membrane system. The product water end of the selective low-pressure reverse osmosis membrane system is connected to the product water tank, and the concentrate end of the selective low-pressure reverse osmosis membrane system is connected to the concentrate tank II. One end of the security filter II is connected to the product water tank, and the other end of the security filter II is connected to the high-concentration flat sheet membrane system. The concentrate end of the high-concentration flat sheet membrane system is connected to the concentrate tank I.

[0010] The crystallization and drying unit includes a sodium carbonate monohydrate crystallization device, a centrifuge, and a drying device. The sodium carbonate monohydrate crystallization device is connected to the concentrated water tank I, and the centrifuge is connected to both the sodium carbonate monohydrate crystallization device and the drying device.

[0011] The causticization cycle unit includes a calcium sulfate crystallization device, a sludge tank, and a plate and frame filter press. The calcium sulfate crystallization device is connected to the concentrate tank II and the sludge tank, respectively. The plate and frame filter press is connected to the sludge tank. The NaOH outlet of the calcium sulfate crystallization device is connected to the injection well and the raw water tank.

[0012] As a preferred solution for the development and processing system of high-nitrate symbiotic natural alkali, the high-concentration flat sheet membrane system adopts a reflux design, the product water end of the high-concentration flat sheet membrane system is connected to the product water tank, and the mother liquor outlet of the sodium carbonate monohydrate crystallization device is connected to the product water tank.

[0013] This invention also provides a high-nitrate symbiotic natural alkali development and processing technology based on the above-mentioned high-nitrate symbiotic natural alkali development and processing system, comprising the following steps:

[0014] Step 1: In the leaching stage, the leaching agent is pumped into the high-nitrate symbiotic natural alkali mineral layer through the injection well. The OH- in the leaching agent reacts with NaHCO3 in the ore and natural alkali minerals to generate soluble Na2CO3, resulting in turbid alkali brine, which is then extracted through the brine well.

[0015] Step 2: Refining stage. The turbid alkaline brine from Step 1 is sent to the alkaline brine refining device to remove solid suspended matter. The resulting clear alkaline solution is temporarily stored in the raw water tank. According to the monitored alkalinity, an appropriate amount of NaOH is added to the raw water tank to completely convert the residual NaHCO3 into Na2CO3, resulting in a clear alkaline solution with Na2CO3 and Na2SO4 as the main components.

[0016] Step 3: Membrane separation and concentration stage. The clarified alkaline solution obtained in step 2 is filtered through security filter I and then sent to a selective low-pressure reverse osmosis membrane system to separate permeate containing Na2CO3 and concentrate containing Na2SO4. The concentrate is sent to concentrate tank II and the permeate is sent to permeate tank. The permeate in the permeate tank is pretreated by security filter II and then sent to a high-concentration flat sheet membrane system. The resulting concentrate is sent to concentrate tank I.

[0017] Step 4: Crystallization and drying stage. The concentrated water in the concentrated water tank I is sent to the sodium carbonate monohydrate crystallization device to crystallize and generate Na2CO3·H2O crystal slurry. After separation by centrifuge, the crystal slurry is sent to the drying device for drying to obtain heavy soda ash product.

[0018] Step 5: Causticization cycle stage. The Na2SO4-containing concentrated water in the concentrated water tank II is mixed with the filtrate from the plate and frame filter press to prepare a supersaturated Na2SO4 solution. This solution is then sent to the calcium sulfate crystallization device, where seed crystals and lime solution are added to carry out a causticization reaction, generating NaOH solution and calcium sulfate crystals. The calcium sulfate crystals are collected in the sludge tank and then sent to the plate and frame filter press for filtration to obtain gypsum by-product. The NaOH solution is returned to the injection well as a solvent for recycling.

[0019] As a preferred option for the development and processing of high-nitrate symbiotic natural alkali, the solvent in step 1 is a 3%-4% NaOH solution.

[0020] As a preferred option for the development and processing of high-nitrate symbiotic natural alkali, the clarified alkali solution obtained in step 2, with Na2CO3 and Na2SO4 as the main components, has a pH ≤ 10.5 and the contents of each component are 19.38wt% Na2CO3, 4.31wt% Na2SO4, 0.84wt% NaHCO3, and 0.23wt% NaCl. The system influent flow rate is 1000t / h.

[0021] As a preferred option for the development and processing of high-nitrate symbiotic natural alkali, the selective low-pressure reverse osmosis membrane system in step 3 has a recovery rate of 75% for SO4. 2-The rejection rate is 85-90%, and the Na2SO4 content in the Na2SO4 concentrate obtained by separation is 15.5wt%. The product water composition of the selective low-pressure reverse osmosis membrane system is 25.84wt% Na2CO3, 0.73wt% Na2SO4, and 0.31wt% NaCl, with a product water flow rate of 750t / h.

[0022] As a preferred option for the development and processing of high-nitrate symbiotic natural alkali, the concentrate flow rate generated by the high-concentration flat sheet membrane system in step 3 is 232.5 t / h, the Na2CO3 concentration is 32.01 wt%, the Na2CO3 concentration in the permeate of the high-concentration flat sheet membrane system is 23.61 wt%, and the permeate of the high-concentration flat sheet membrane system is returned to the permeate tank.

[0023] As a preferred option for the development and processing of high-nitrate symbiotic natural alkali, the selective low-pressure reverse osmosis membrane system in step 3 operates under normal temperature conditions, and the direct separation of Na2CO3 and Na2SO4 is achieved through normal temperature operation.

[0024] In step 3, the high-concentration flat sheet membrane system increases the osmotic pressure on the feed water side of the membrane to raise the concentration of alkaline solution on the permeate side, and gradually concentrates the alkaline solution to a crystallizable concentration.

[0025] As a preferred option for the development and processing of high-nitrate symbiotic natural soda ash, the crystallization temperature of the sodium carbonate monohydrate crystallization device in step 4 is 35℃-90℃, and the yield of heavy soda ash product obtained after treatment by centrifugation and drying devices is 57.64t / h; the mother liquor from the sodium carbonate monohydrate crystallization device is returned to the production water tank, and the content of each component in the mother liquor is 30-32wt% Na2CO3, 1-2.5wt% Na2SO4, and 0.6-1.3wt% NaCl.

[0026] As a preferred option for the development and processing of high-nitrate symbiotic natural alkali, the supersaturation degree of the supersaturated CaSO4 solution in step 5 is 400%-500%, the added seed crystal is CaSO4·2H2O seed crystal, the concentration of the NaOH solution generated by the causticization reaction is 3%-4%, and the calcium sulfate content in the gypsum by-product obtained by plate and frame filter press is not less than 75%.

[0027] The beneficial effects of this invention are as follows:

[0028] First, this invention effectively solves the problems of high energy consumption, high operating costs, complex processes, and low added value of by-products in traditional high-nitrate natural alkali processing. Compared with the traditional carbonation-evaporation-causticization co-production process, the technical path of caustic soda leaching and membrane separation significantly simplifies the process flow, avoids the energy-intensive evaporation stage in the traditional process, and avoids the drawbacks of limited market capacity and low added value of by-product sodium sulfate, thus significantly improving the competitiveness of the process.

[0029] Secondly, this invention employs a selective low-pressure reverse osmosis membrane system, which can achieve efficient separation of sodium carbonate and sodium sulfate under normal temperature conditions, with a sulfate rejection rate of 85-90%. It can effectively treat the mNa2SO4·nNa2CO3 type double salt present in high-nitrate natural soda ash ore, avoiding the impact of double salt on product purity. Subsequently, a high-concentration flat sheet membrane system concentrates the alkali solution to a crystallizable concentration. Finally, the heavy soda ash product obtained by crystallization and drying meets the Class II Grade I standard of "GB / T210—2022 Industrial Soda Carbonate", breaking through the limitations of existing technologies that are only applicable to low-nitrate natural soda ash ore and have difficulty in guaranteeing product purity.

[0030] Third, this invention uses a causticization recycling unit to mix the sodium sulfate concentrate and filtrate generated by the selective low-pressure reverse osmosis membrane system into a supersaturated sodium sulfate solution, which is then converted into a 3%-4% sodium hydroxide solution through a causticization reaction and reused in the front-end solvent extraction and conversion process, thus achieving closed-loop utilization of sodium hydroxide. At the same time, the by-product gypsum with a calcium sulfate content of not less than 75% can be sold as building materials, forming a resource-product-recycled resource recycling model, which reduces the procurement cost of solvent extraction agents and reduces solid waste emissions, meeting the needs of clean production.

[0031] Fourth, the comprehensive operating cost per ton of water for the membrane separation and concentration unit of this invention is only 6.5-9 yuan. Compared with the traditional process with triple-effect evaporation as the core, the membrane concentration section can reduce the equivalent energy consumption by about 85%. In terms of unit product energy consumption, the comprehensive energy consumption for producing each ton of heavy soda ash is reduced by 40-50% compared with the traditional process, which greatly reduces the energy consumption and operating cost of the process. Under the current background of green and low-carbon industrial upgrading, it has significant economic advantages and market competitiveness.

[0032] Fifth, this invention is designed specifically for the characteristics of high-nitrate alkali-salt symbiotic minerals. Through the synergistic effect of technologies such as sodium hydroxide dissolution and membrane separation concentration, it can effectively process natural alkali minerals with high nitrate content, breaking the dependence of traditional processes on low-nitrate natural alkali minerals. It provides a feasible technical path for the high-value development of high-nitrate natural alkali minerals, expands the scope of development and utilization of natural alkali resources, and is of great significance for promoting the efficient utilization of resources in the soda ash chemical industry. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of a high-nitrate symbiotic natural alkali development and processing system provided in an embodiment of the present invention;

[0035] Figure 2 This is a flowchart of the development and processing technology of high-nitrate symbiotic natural alkali provided in the embodiments of the present invention.

[0036] In the diagram, 1. Injection well; 2. Brine outlet well; 3. Alkaline brine refining unit; 4. Raw water tank; 5. Security filter I; 6. Selective low-pressure reverse osmosis membrane system; 7. Product water tank; 8. Security filter II; 9. High-concentration flat sheet membrane system; 10. Concentrate tank I; 11. Sodium carbonate monohydrate crystallization unit; 12. Centrifuge; 13. Drying unit; 14. Plate and frame filter press; 15. Sludge tank; 16. Concentrate tank II; 17. Calcium sulfate crystallization unit. Detailed Implementation

[0037] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] See Figure 1This invention provides a high-nitrate symbiotic natural alkali development and processing system, including a solvent extraction unit, a refining unit, a membrane separation and concentration unit, a crystallization and drying unit, and a causticization circulation unit. The solvent extraction unit includes an injection well 1 and a brine outlet well 2. The injection well 1 is used to deliver solvent to the high-nitrate symbiotic natural alkali deposit, and the brine outlet well 2 is used to extract the extracted turbid alkali brine. The refining unit includes an alkali brine refining device 3 and a raw water tank 4. The alkali brine refining device 3 is connected to the brine outlet well 2 to process the turbid alkali brine, and the raw water tank 4 is used to temporarily store the clarified alkali solution after treatment by the alkali brine refining device 3. The membrane separation and concentration unit includes a security filter I 5, a selective low-pressure reverse osmosis membrane system 6, a security filter II 8, a high-concentration flat sheet membrane system 9, a product water tank 7, a concentrate tank I 10, and a concentrate tank II 16. One end of the security filter I 5 is connected to the raw water tank 4, and the other end of the security filter I 5 is connected to the selective low-pressure reverse osmosis membrane system 6. The selective low-pressure reverse osmosis membrane system 6... The product water end is connected to the product water tank 7; the concentrate end of the selective low-pressure reverse osmosis membrane system 6 is connected to the concentrate tank II 16; one end of the security filter II 8 is connected to the product water tank 7; the other end of the security filter II 8 is connected to the high-concentration flat sheet membrane system 9; and the concentrate end of the high-concentration flat sheet membrane system 9 is connected to the concentrate tank I 10. The crystallization and drying unit includes a sodium carbonate monohydrate crystallization device 11, a centrifuge 12, and a drying device 13. The sodium carbonate monohydrate crystallization device 11 is connected to the concentrate tank I 10, and the centrifuge 12 is connected to both the sodium carbonate monohydrate crystallization device 11 and the drying device 13. The causticization circulation unit includes a calcium sulfate crystallization device 17, a sludge tank 15, and a plate and frame filter press 14. The calcium sulfate crystallization device 17 is connected to both the concentrate tank II 16 and the sludge tank 15, and the plate and frame filter press 14 is connected to the sludge tank 15. The NaOH outlet of the calcium sulfate crystallization device 17 is connected to the injection well 1.

[0039] The solution extraction unit serves as the raw material acquisition end, delivering the solvent through injection well 1 to react with the ore layer and achieve the dissolution of effective components. The brine extraction well 2 ensures the smooth export of the dissolved mixture. The refining unit receives the solution extraction products, using alkaline brine refining device 3 to remove suspended impurities and prevent clogging of subsequent membrane systems. The raw water tank 4 provides a stable raw material buffer for subsequent processes and removes residual bicarbonate ions. The membrane separation and concentration unit is the core purification and concentration stage. Security filters I 5 and II 8 further filter the liquids entering the selective low-pressure reverse osmosis membrane and high-concentration flat sheet membrane, respectively, with a filtration accuracy of 5-10 μm, protecting the membrane components. The selective low-pressure reverse osmosis membrane system 6 achieves the separation of key components, and the high-concentration flat sheet membrane system 9 completes the target separation. The process involves component concentration, with product water tank 7, concentrate tank I 10, and concentrate tank II 16 temporarily storing products from different stages to ensure continuous and stable operation. The crystallization and drying unit converts the concentrated target components into solid products. Sodium carbonate monohydrate crystallization device 11 generates stable crystals under controlled conditions, centrifuge 12 achieves solid-liquid separation, and drying device 13 removes moisture from the crystals to ensure product quality. The causticization recycling unit realizes the recovery of auxiliary materials and the resource utilization of by-products. Calcium sulfate crystallization device 17 converts intermediate products into reusable auxiliary materials and solid by-products. Sludge tank 15 temporarily stores solid by-products, plate and frame filter press 14 achieves solid dewatering, and finally, the reusable auxiliary materials are returned to the melting and extraction unit through injection well 1, forming a resource cycle of raw materials-products-auxiliary materials-raw materials, reducing energy consumption and costs.

[0040] In this embodiment, the high-concentration flat sheet membrane system 9 adopts a reflux design, the product water end of the high-concentration flat sheet membrane system 9 is connected to the product water tank 7, and the mother liquor outlet of the sodium carbonate monohydrate crystallization device 11 is connected to the product water tank 7.

[0041] Specifically, although the permeate from the high-concentration flat-sheet membrane system 9 has not reached the crystallization concentration, it still contains a certain amount of sodium carbonate. Returning it to the permeate tank 7 allows it to re-enter the concentration process, avoiding waste of the target component and improving raw material utilization. Similarly, the mother liquor from the sodium carbonate monohydrate crystallization unit 11 also contains incompletely crystallized sodium carbonate. Returning it to the permeate tank 7 allows it to participate in the concentration-crystallization process again, further improving product yield. At the same time, the returned material can regulate the concentration of the liquid in the permeate tank 7, preventing instability in the subsequent membrane system operation due to fluctuations in raw material concentration, ensuring the continuous and stable operation of the membrane separation and concentration unit, and indirectly reducing system energy consumption and operating costs.

[0042] See Figure 2 The present invention also provides a high-nitrate symbiotic natural alkali development and processing technology based on the high-nitrate symbiotic natural alkali development and processing system of the above embodiments, including the following steps:

[0043] Step 1: In the leaching stage, the leaching agent is pumped into the high-nitrate symbiotic natural alkali mineral layer through injection well 1. The OH- in the leaching agent reacts with NaHCO3 and natural alkali minerals in the ore to generate soluble Na2CO3. At the same time, the high concentration of Na in the leaching agent... + The dissolution of Na2SO4 and NaCl is suppressed by the common ion effect, resulting in turbid alkaline brine, which is then extracted through brine well 2.

[0044] In this process, the NaOH in the solvent reacts with the NaHCO3 in the ore: NaOH + NaHCO3 = Na2CO3 + H2O, and simultaneously reacts with the natural alkali mineral: Na2CO3·NaHCO3·2H2O + 2NaOH = 2Na2CO3 + 3H2O, achieving efficient dissolution of the target component; ultimately, a turbid alkali brine with Na2CO3 as the main dissolved component and a small amount of suspended impurities is obtained.

[0045] Step 2: Refining stage. The turbid alkaline brine from Step 1 is sent to the alkaline brine refining device 3 to remove solid suspended matter. The resulting clear alkaline solution is temporarily stored in the raw water tank 4. Based on the monitored alkalinity, an appropriate amount of NaOH is added to the raw water tank 4 to completely convert the residual NaHCO3 into Na2CO3, resulting in a clear alkaline solution with Na2CO3 and Na2SO4 as the main components.

[0046] If the solid suspended matter contained in the turbid alkaline brine enters the subsequent membrane system, it will clog the membrane pores and damage the membrane components. The alkaline brine refining unit 3 can physically remove these suspended matter to obtain a clear liquid. Since the reaction between the solvent and the ore in step 1 may be incomplete, a small amount of NaHCO3 may remain in the clear alkaline solution. According to the alkalinity monitoring, adding an appropriate amount of NaOH can cause the reaction: NaOH + NaHCO3 = 2Na2CO3 + H2O, which completely converts the residual NaHCO3 into the target component Na2CO3. This avoids the decrease in product purity due to the presence of NaHCO3 during the subsequent crystallization process, and finally obtains a clear alkaline solution with stable composition and low impurity content, which is beneficial for subsequent processing.

[0047] Step 3: Membrane separation and concentration stage. The clarified alkaline solution obtained in step 2 is filtered through security filter I5 and then sent to selective low-pressure reverse osmosis membrane system 6 to separate permeate containing Na2CO3 and concentrate containing Na2SO4. The concentrate is sent to concentrate tank II16 and the permeate is sent to permeate tank 7. The permeate in permeate tank 7 is pretreated by security filter II8 and then sent to high-concentration flat sheet membrane system 9. The resulting concentrate is sent to concentrate tank I10.

[0048] Among them, the security filter I5 uses a high-precision filter medium of 5-10μm to remove any tiny particles that may remain in the clarified alkaline solution, preventing them from entering the selective low-pressure reverse osmosis membrane system 6 and scratching the membrane surface or clogging the membrane pores, thus ensuring the separation performance and service life of the membrane system; the selective low-pressure reverse osmosis membrane system 6 utilizes the selective permeability of the membrane to allow Na+ to pass through under low-pressure conditions. + CO3 2- Water molecules pass through the membrane into the product water side, while SO4... 2- With a high rejection rate, Na2CO3 and Na2SO4 are separated, resulting in pre-concentrated Na2CO3 permeate and Na2SO4 concentrate. The function of security filter II8 is similar to that of security filter I5, further removing any minute impurities that may be present in the permeate and protecting the high-concentration flat sheet membrane module 9. Under constant operating pressure, the high-concentration flat sheet membrane system 9 increases the osmotic pressure of the water on the feed side of the membrane by increasing the osmotic pressure of the water on the permeate side, thereby increasing the salt content on the concentrate side and concentrating the Na2CO3 concentration to a level that meets the requirements for direct crystallization. This achieves efficient concentration of the target component, and the concentrated concentrate is finally sent to concentrate tank I10 to await crystallization.

[0049] Step 4: Crystallization and drying stage. The concentrated water in the concentrated water tank I10 is sent to the sodium carbonate monohydrate crystallization device 11 to crystallize and generate Na2CO3·H2O crystal slurry. The crystal slurry is separated by centrifuge 12 and then sent to drying device 13 to dry, to obtain heavy soda ash product.

[0050] In this process, the sodium carbonate monohydrate crystallization device 11 controls the temperature, concentration, and other process conditions to make the Na2CO3 in the concentrated solution reach a supersaturated state. According to the crystallization principle, the solute in the supersaturated solution will precipitate in the form of crystals, and Na2CO3 will combine with water molecules to form Na2CO3·H2O crystals, forming a solid-liquid mixed crystal slurry. The centrifuge 12 uses centrifugal force to quickly separate the solid crystals from the liquid in the crystal slurry, obtaining Na2CO3·H2O crystals. Then, the drying device 13 is used to remove the water of crystallization from the crystals, converting Na2CO3·H2O into anhydrous Na2CO3. At the same time, the drying conditions are controlled to ensure that the particle size and purity of the product meet the industrial standards, and finally a qualified solid product is obtained.

[0051] Step 5: Causticization and recycling stage. The Na2SO4-containing concentrated water in the concentrated water tank II 16 is mixed with the filtrate from the plate and frame filter press 14 to prepare a supersaturated Na2SO4 solution. This solution is then fed into the calcium sulfate crystallization device 17, where seed crystals and lime solution are added to carry out a causticization reaction, generating NaOH solution and calcium sulfate crystals. The calcium sulfate crystals are collected in the sludge tank 15 and then sent to the plate and frame filter press 14 for filtration to obtain gypsum by-product. The NaOH solution is returned to the injection well 1 as a solvent for recycling and is also returned to the raw water tank to remove residual NaHCO3.

[0052] The concentrated water in the concentrated water tank II 16 is rich in Na2SO4. When mixed with the filtrate (containing a small amount of Na2SO4) from the plate and frame filter press 14, it increases the Na2SO4 concentration in the solution, bringing it to a supersaturated state and providing sufficient raw materials for subsequent reactions. The CaSO4·2H2O seed crystals added to the calcium sulfate crystallization device 17 serve as the core for crystal growth, reducing the instability caused by excessive supersaturation of calcium sulfate and promoting uniform crystal growth. The lime solution undergoes a causticizing reaction with Na2SO4. The generated CaSO4 precipitates in crystal form; the calcium sulfate crystals are temporarily stored in sludge tank 15, and the water in the crystals is removed by the plate and frame filter press 14 through pressure to obtain gypsum by-product with high calcium sulfate content; the concentration of the generated NaOH solution meets the requirements of the solvent and is returned to injection well 1 for reuse as a solvent, realizing the recycling of NaOH and reducing the cost of auxiliary materials.

[0053] In this embodiment, the solvent in step 1 is a 3%-4% NaOH solution. At ambient temperature, a 3%-4% NaOH solution provides sufficient OH- to ensure efficient reaction with NaHCO3 and natural alkali minerals in the ore, achieving efficient dissolution of Na2CO3. If the NaOH concentration is too low (<3%), some NaHCO3 solid phase decomposes and forms a "barrier" preventing the dissolution of natural alkali, leaving approximately 8%-10% of the effective components in the solution cavity, reducing dissolution efficiency. If the NaOH concentration is too high (>5.5%), the extracted Na2CO3 does not show a significant increase; instead, it increases the causticizing load, resulting in low economic efficiency. When the caustic soda concentration is controlled at 3%-5.5%, an alkaline brine of 18%-24% Na2CO3 can be obtained, and the calcium sulfate crystallization device 17 generates 3%-4% sodium hydroxide to meet production needs without requiring external purchase.

[0054] In this embodiment, the clarified alkaline solution obtained in step 2, with Na2CO3 and Na2SO4 as the main components, has a pH ≤ 10.5 and the contents of each component are 19.38wt% Na2CO3, 4.31wt% Na2SO4, 0.84wt% NaHCO3, and 0.23wt% NaCl. The system influent flow rate is 1000t / h.

[0055] Specifically, controlling the pH value of this unit below 10.5 can ensure HCO3- - In OH - Under the influence of the action, it is almost completely converted into CO3 2- This condition effectively prevents HCO3 from being caused by insufficient pH. - This avoids the problem of excessive NaOH addition leading to excess OH residue in the solution. -This pH level can negatively impact subsequent crystallization and drying processes, as well as the final product quality of soda ash (Na2CO3). Furthermore, this pH condition is suitable for the long-term stable operation of the membrane system and does not negatively affect the performance and lifespan of the membrane materials. The content of each component is set based on the characteristics of the raw ore and the requirements of subsequent membrane separation: a Na2CO3 concentration of 19.38 wt% ensures the concentration efficiency of the subsequent membrane concentration unit while avoiding increased solution viscosity due to excessive concentration, which would affect the flux of the membrane system; the contents of Na2SO4 (4.31 wt%), NaHCO3 (0.84 wt%), and NaCl (0.23 wt%) are at low levels, allowing for effective separation or removal by the subsequent membrane system, ensuring the purity of the final product. A system feed water flow of 1000 t / h ensures stable operation of each unit under the design load, preventing process parameter loss due to water flow fluctuations and ensuring production continuity and product quality stability.

[0056] In this embodiment, the recovery rate of the selective low-pressure reverse osmosis membrane system 6 in step 3 is 75%, and the recovery rate of SO4 is... 2- The rejection rate is 85-90%, and the Na2SO4 content in the Na2SO4 concentrate obtained by separation is 15.5wt%. The product water composition of the selective low-pressure reverse osmosis membrane system 6 is 25.84wt% Na2CO3, 0.73wt% Na2SO4, and 0.31wt% NaCl, with a product water flow rate of 750t / h.

[0057] Specifically, a recovery rate of 75% means that 75% of the influent is converted into permeate, while the remaining 25% becomes concentrate. This value is an optimized result after comprehensively considering system operation and energy consumption: A recovery rate that is too high, while increasing permeate volume, will result in a low Na₂CO₃ concentration in the permeate, thus increasing the processing load on the subsequent high-concentration flat-sheet membrane system; conversely, a recovery rate that is too low will lead to an increased concentrate volume, making the NaOH concentration generated in the subsequent causticization process insufficient for reuse. Therefore, a recovery rate of 75% is the optimal choice to balance water volume, salinity, and operating energy consumption. 85-90% SO₄²⁻ 2- Retention rate can effectively remove most SO4 2-By retaining Na2SO4 in the concentrate, the Na2SO4 content in the product water is reduced to 0.73 wt%, ensuring the purity of the subsequent crystallized product. This retention rate is based on the selective permeation performance of the membrane material and the operating pressure setting. The 15.5 wt% Na2SO4 content in the Na2SO4-containing concentrate meets the feed concentration requirements of the subsequent causticization reaction while avoiding excessive concentration that could lead to solution crystallization and pipe blockage. The 25.84 wt% Na2CO3 concentration in the product water provides a suitable initial concentration for the subsequent high-concentration membrane system, reducing concentration energy consumption. The low Na2SO4 and NaCl contents of 0.73 wt% do not affect product purity. The product water flow rate of 750 t / h matches the system feed water flow rate of 1000 t / h and the recovery rate of 75%, ensuring stable operation of the membrane system and avoiding process disturbances caused by flow fluctuations.

[0058] In this embodiment, the concentrate flow rate of the high-concentration flat sheet membrane system 9 in step 3 is 232.5 t / h, the Na2CO3 concentration is 32.01 wt%, the Na2CO3 concentration in the permeate of the high-concentration flat sheet membrane system 9 is 23.61 wt%, and the permeate of the high-concentration flat sheet membrane system 9 is returned to the permeate tank 7.

[0059] Specifically, the 32.01 wt% Na₂CO₃ concentration is exactly the supersaturation concentration required for sodium carbonate monohydrate crystallization, eliminating the need for subsequent additional evaporation and concentration, thus significantly reducing energy consumption. The concentrate flow rate of 232.5 t / h is set according to the design capacity of the subsequent sodium carbonate monohydrate crystallization unit 11, ensuring stable operation of the crystallization unit within the load range and avoiding poor crystallization results due to fluctuations in feed rate. Although the 23.61 wt% Na₂CO₃ concentration in the permeate is not the crystallization concentration, it is still higher than the concentration before membrane separation. Returning it to the permeate tank 7 allows it to re-enter the high-concentration flat sheet membrane system 9 for secondary concentration, avoiding Na₂CO₃ waste and improving raw material utilization. At the same time, the returned permeate can adjust the concentration of the liquid in the permeate tank 7, keeping the liquid concentration entering the membrane system stable and avoiding changes in membrane system flux due to concentration fluctuations, thus ensuring the continuous and stable operation of the membrane concentration unit.

[0060] In this embodiment, the selective low-pressure reverse osmosis membrane system 6 in step 3 operates under normal temperature conditions, and achieves direct separation of Na2CO3 and Na2SO4 through normal temperature operation; the high-concentration flat sheet membrane system 9 in step 3 increases the concentration of alkaline solution on the concentrate side by adjusting the osmotic pressure of the water, and concentrates the alkaline solution to a crystallizable concentration.

[0061] Specifically, the selective low-pressure reverse osmosis membrane system 6 operates at room temperature without additional heating, significantly reducing energy consumption and avoiding damage to the membrane material from high temperatures, thus extending membrane lifespan. Furthermore, under room temperature conditions, the solubility difference between Na2CO3 and Na2SO4, as well as the membrane's selective permeability to both, can be stably utilized, achieving efficient direct separation. The high-concentration flat-sheet membrane system 9, under constant pressure, increases the osmotic pressure of the water on the feed side of the membrane element, thereby increasing the osmotic pressure of the water on the permeate side, achieving Na2CO3 concentration in the concentrate of the high-concentration flat-sheet membrane system. Through permeate reflux, the concentration of the system's concentrated alkaline solution is stably increased to a crystallizable concentration of 32.01 wt%, preventing excessive concentration from causing solute precipitation and clogging of the membrane pores. Simultaneously, it eliminates the need for the high-temperature, high-pressure conditions of traditional triple-effect evaporation, achieving low-energy concentration.

[0062] In this embodiment, the crystallization temperature of the sodium carbonate monohydrate crystallization device 11 in step 4 is 35-90℃, and the yield of heavy soda ash product obtained after treatment by the centrifugation device 12 and the drying device 13 is 57.64t / h; the mother liquor of the sodium carbonate monohydrate crystallization device 11 is returned to the product water tank 7, and the content of each component in the mother liquor is 30-32wt% Na2CO3, 1-2.5wt% Na2SO4, and 0.6-1.3wt% NaCl.

[0063] Specifically, the crystallization temperature of 35-90℃ falls within the stable region of the monohydrate, where the system free energy is lowest. Low-temperature crystallization yields sodium carbonate monohydrate slurry, which is then separated into solid and liquid components by centrifugation to remove a large amount of mother liquor. This results in low subsequent drying load, low energy consumption, and a stable and reliable process. Below this temperature, sodium carbonate decahydrate (Na₂CO₃·10H₂O) or sodium carbonate heptahydrate (Na₂CO₃·7H₂O) may be formed. These crystals have high water content, leading to high energy consumption for subsequent drying and poor crystal stability. Above this temperature, sodium carbonate monohydrate may dehydrate to form anhydrous sodium carbonate, resulting in high energy consumption and the product being hygroscopic. It requires sealing or cooling and packaging in a dry environment; otherwise, it will absorb moisture from the air and transform into monohydrate or even decahydrate. The product output of 57.64 t / h is the design output calculated based on the system's influent flow rate and the processing efficiency of each unit, matching the equipment's processing capacity to ensure a balance between production efficiency and product quality. The 30-32 wt% Na₂CO₃ concentration in the mother liquor is close to the crystallization concentration. Returning it to the permeate tank 7 allows it to re-enter the membrane concentration-crystallization process, reducing Na₂CO₃ loss and improving product yield. The 1-2.5 wt% Na₂SO₄ and 0.6-1.3 wt% NaCl in the mother liquor do not affect product purity within specified concentrations, and their reuse helps stabilize the concentration in the permeate tank. To address the risk of forming double salts (2Na₂SO₄·Na₂CO₄) when the Na₂SO₄ concentration exceeds 3%, the high-risk mother liquor can be temporarily transferred to the raw water tank for salt separation treatment, thereby fundamentally eliminating the potential impact of double salts on product purity.

[0064] In this embodiment, the supersaturation of the supersaturated CaSO4 solution in step 5 is 400%-500%, the added seed crystal is CaSO4·2H2O seed crystal, the concentration of the NaOH solution generated by the causticizing reaction is 3%-4%, and the calcium sulfate content in the gypsum by-product obtained by plate and frame filter press 14 is not less than 75%.

[0065] Specifically, a supersaturation of 400%-500% can significantly increase the crystallization rate of CaSO4 and improve the efficiency of generating high-concentration NaOH. If the supersaturation is too low, the reaction rate is slow, and the concentration of NaOH generated is low, which cannot meet the requirements for solvent recycling. If the supersaturation is too high, the amount of reagent used is large, resulting in low economic efficiency. Adding CaSO4·2H2O seed crystals can serve as the "core" for the growth of calcium sulfate crystals, guiding the calcium sulfate crystals to grow uniformly on the seed crystal surface, avoiding excessively small crystals or agglomeration. The settled crystals are periodically discharged through the bottom outlet, ensuring that the calcium sulfate concentration in the solution is always lower than the equilibrium solubility, continuously promoting the forward reaction, and stably preparing a NaOH solution with a concentration of 3%-4%.

[0066] The 3%-4% NaOH content meets the concentration requirements of the solvent and can be directly returned to injection well 1 as a solvent without additional dilution or concentration, thus reducing energy consumption and operational steps. The calcium sulfate content in the gypsum by-product is not less than 75%, which meets the quality requirements of the building materials industry for gypsum raw materials, realizes the resource utilization of by-products, reduces solid waste emissions, and conforms to the concept of green production.

[0067] The core of the operating cost of the process in this invention lies in the energy consumption and resource recycling efficiency of the two-stage membrane system. Calculations show that for treating a total of 1000 t / h of feed alkaline solution, the total installed power of the selective low-pressure reverse osmosis and high-concentration membrane system is approximately 8500 kW. Based on an industrial electricity price of 0.7 yuan / kWh, the direct electricity cost per ton of water treated is approximately 5.95 yuan. Adding membrane module depreciation, maintenance, and a small amount of chemical consumption, the comprehensive operating cost per ton of water for the membrane system remains stable in the range of 6.5–9 yuan. Compared to traditional processes using triple-effect evaporation as the core concentration method (evaporation requires 0.35–0.4 tons of steam per ton of water, equivalent to an electricity consumption of approximately 200–250 kWh), this invention, while achieving the same water concentration, can reduce the equivalent energy consumption by approximately 85% in the membrane concentration stage alone. When calculated per unit product, the membrane method significantly reduces steam consumption in the front-end concentration stage and incorporates NaOH recycling, resulting in a total energy consumption reduction of approximately 40-50% per ton of heavy soda ash compared to traditional processes, demonstrating significant economic and environmental advantages.

[0068] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A system for developing and processing high-nitrate symbiotic natural alkali, characterized in that, It includes a solution extraction unit, a purification unit, a membrane separation and concentration unit, a crystallization and drying unit, and a causticization circulation unit; The leaching and mining unit includes an injection well (1) and a brine outlet well (2). The injection well (1) is used to transport the leaching agent to the high-nitrate symbiotic natural alkali mineral layer, and the brine outlet well (2) is used to extract the mined turbid alkali brine. The refining unit includes an alkaline brine refining device (3) and a raw water tank (4). The alkaline brine refining device (3) is connected to the brine outlet well (2) to process turbid alkaline brine. The raw water tank (4) is used to temporarily store the clarified alkaline solution after being processed by the alkaline brine refining device (3). The membrane separation and concentration unit includes a security filter I (5), a selective low-pressure reverse osmosis membrane system (6), a security filter II (8), a high-concentration flat sheet membrane system (9), a product water tank (7), a concentrate tank I (10), and a concentrate tank II (16). One end of the security filter I (5) is connected to the raw water tank (4), and the other end of the security filter I (5) is connected to the selective low-pressure reverse osmosis membrane system (6). The product water end of the selective low-pressure reverse osmosis membrane system (6) is connected to the product water tank (7). The concentrate end of the selective low-pressure reverse osmosis membrane system (6) is connected to the concentrate tank II (16). One end of the security filter II (8) is connected to the product water tank (7), and the other end of the security filter II (8) is connected to the high-concentration flat sheet membrane system (9). The concentrate end of the high-concentration flat sheet membrane system (9) is connected to the concentrate tank I (10). The crystallization and drying unit includes a sodium carbonate monohydrate crystallization device (11), a centrifuge (12) and a drying device (13). The sodium carbonate monohydrate crystallization device (11) is connected to the concentrated water tank I (10), and the centrifuge (12) is connected to the sodium carbonate monohydrate crystallization device (11) and the drying device (13) respectively. The causticization cycle unit includes a calcium sulfate crystallization device (17), a sludge tank (15), and a plate and frame filter press (14). The calcium sulfate crystallization device (17) is connected to the concentrate tank II (16) and the sludge tank (15) respectively. The plate and frame filter press (14) is connected to the sludge tank (15). The NaOH outlet of the calcium sulfate crystallization device (17) is connected to the injection well (1).

2. The high-nitrate symbiotic natural alkali development and processing system according to claim 1, characterized in that, The high-concentration flat sheet membrane system (9) adopts a reflux design. The product water end of the high-concentration flat sheet membrane system (9) is connected to the product water tank (7), and the mother liquor outlet of the sodium carbonate monohydrate crystallization device (11) is connected to the product water tank (7).

3. A process for developing and processing high-nitrate symbiotic natural alkali based on the high-nitrate symbiotic natural alkali development and processing system according to any one of claims 1 to 2, characterized in that, Includes the following steps: Step 1: In the sintering stage, the sintering agent is pumped into the high-nitrate symbiotic natural alkali mineral layer through the injection well (1). The OH- in the sintering agent reacts with NaHCO3 in the ore and natural alkali minerals to generate soluble Na2CO3, and turbid alkali brine is obtained and drawn out through the brine well (2). Step 2: Refining stage, the turbid alkaline brine from step 1 is sent to the alkaline brine refining device (3) to remove solid suspended matter. The resulting clear alkaline solution is temporarily stored in the raw water tank (4). According to the monitored alkalinity, an appropriate amount of NaOH is added to the raw water tank (4) to completely convert the residual NaHCO3 into Na2CO3, and a clear alkaline solution with Na2CO3 and Na2SO4 as the main components is obtained. Step 3: Membrane separation and concentration stage. The clarified alkaline solution obtained in step 2 is filtered through security filter I (5) and then sent to selective low-pressure reverse osmosis membrane system (6) to separate the permeate containing Na2CO3 and the concentrate containing Na2SO4. The concentrate is sent to concentrate tank II (16) and the permeate is sent to permeate tank (7). The permeate in permeate tank (7) is pretreated by security filter II (8) and then sent to high-concentration flat sheet membrane system (9). The resulting concentrate is sent to concentrate tank I (10). Step 4: Crystallization and drying stage. The concentrated water in the concentrated water tank I (10) is sent to the sodium carbonate monohydrate crystallization device (11) to crystallize and generate Na2CO3·H2O crystal slurry. The crystal slurry is separated by centrifuge (12) and then sent to the drying device (13) for drying to obtain heavy soda ash product. Step 5: Causticization cycle stage. The Na2SO4-containing concentrated water in the concentrated water tank II (16) is mixed with the filtrate from the plate and frame filter press (14) to prepare a supersaturated Na2SO4 solution. This solution is then sent to the calcium sulfate crystallization device (17) and seed crystals are added to the lime solution for causticization reaction, generating NaOH solution and calcium sulfate crystals. The calcium sulfate crystals are collected in the sludge tank (15) and sent to the plate and frame filter press (14) for filtration to obtain gypsum by-product. The NaOH solution is returned to the injection well (1) as a solvent for recycling.

4. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, In step 1, the solvent is a 3%-4% NaOH solution.

5. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, The clarified alkaline solution obtained in step 2, with Na2CO3 and Na2SO4 as the main components, has a pH ≤ 10.5 and the contents of each component are 19.38wt% Na2CO3, 4.31wt% Na2SO4, 0.84wt% NaHCO3, and 0.23wt% NaCl. The system influent flow rate is 1000t / h.

6. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, In step 3, the selective low-pressure reverse osmosis membrane system (6) has a recovery rate of 75% and a SO42- rejection rate of 85-90%. The Na2SO4 content in the Na2SO4 concentrate obtained is 15.5 wt%. The product water composition of the selective low-pressure reverse osmosis membrane system (6) is 25.84 wt% Na2CO3, 0.73 wt% Na2SO4, and 0.31 wt% NaCl, with a product water flow rate of 750 t / h.

7. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, In step 3, the concentrate flow rate of the high-concentration flat sheet membrane system (9) is 232.5 t / h and the Na2CO3 concentration is 32.01 wt%. The Na2CO3 concentration in the permeate of the high-concentration flat sheet membrane system (9) is 23.61 wt%, and the permeate of the high-concentration flat sheet membrane system (9) is returned to the permeate tank (7).

8. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, In step 3, the selective low-pressure reverse osmosis membrane system (6) operates at room temperature, and the direct separation of Na2CO3 and Na2SO4 is achieved through room temperature operation; In step 3, the high-concentration flat sheet membrane system (9) increases the concentration of alkaline solution on the permeate side by increasing the osmotic pressure on the feed water side of the membrane, and gradually concentrates the alkaline solution to a crystallizable concentration.

9. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, In step 4, the crystallization temperature of the sodium carbonate monohydrate crystallization device (11) is 35℃-90℃. After being processed by the centrifuge device (12) and the drying device (13), the yield of heavy soda ash product is 57.64t / h. The mother liquor of the sodium carbonate monohydrate crystallization device (11) is returned to the production water tank (7). The content of each component in the mother liquor is 30-32wt% Na2CO3, 1-2.5wt% Na2SO4, and 0.6-1.3wt% NaCl.

10. The high-nitrate symbiotic natural alkali development and processing technology according to claim 3, characterized in that, In step 5, the supersaturation of the CaSO4 solution is 400%-500%, the added seed crystal is CaSO4·2H2O seed crystal, the concentration of the NaOH solution generated by the causticizing reaction is 3%-4%, and the calcium sulfate content in the gypsum by-product obtained by plate and frame filter press (14) is not less than 75%.

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