A defluoridation and hardness reduction system and method without the need for additional chemicals

Abstract

A defluorination and hardness reduction system and method without the need for external reagents is disclosed. A calcium fluoride crystallizer reacts with high-salt, fluoride-containing wastewater transported via a raw water pipeline to produce high-purity calcium fluoride, which is then used as seed crystals in the crystallizer. Hydrochloric acid effluent from a bipolar membrane device is introduced into a first sludge tank, where it reacts with calcium carbonate in the filter residue to produce calcium chloride solution and release carbon dioxide gas. The calcium chloride solution is then introduced into a calcium chloride crystallizer to obtain high-purity calcium chloride, which is reused in the calcium fluoride crystallizer. The carbon dioxide released during the hydrochloric acid dissolution of calcium carbonate is collected by a carbon dioxide collection device and then, together with sodium hydroxide effluent from the bipolar membrane device, is introduced into a sodium carbonate reaction device to produce sodium carbonate, which is used as a softener in the first high-density tank. Sulfuric acid effluent from the bipolar membrane device is used to adjust the pH of the softened wastewater in the second high-density tank. This invention eliminates reliance on external reagents, reducing investment and operating costs.

Description

Technical Field

[0001] This invention relates to a defluorination and hardness reduction system and method that does not require the addition of external chemicals, belonging to the field of water treatment technology. Background Technology

[0002] High-salt, fluoride-containing wastewater mainly originates from industrial sectors such as chemical, metallurgical, and mining. The water quality is often neutral to alkaline, with severely excessive salt content (>3.5wt%) and high concentrations of sodium. + Ca 2+ Mg 2+ Cl - SO4 2- Plasma. Fluoride concentrations in wastewater can reach over 1000 mg / L, posing a serious threat to the environment and human health. Due to its strong environmental pollution and difficulty in treatment, it is a pressing problem to be solved in the field of environmental governance. Current regulations require that the fluoride content in most industrial wastewater must be strictly controlled below 1 mg / L, while the salt content must not exceed 1000 mg / L.

[0003] Currently, the main methods for treating fluoride-containing wastewater include chemical precipitation, flocculation sedimentation, adsorption, and ion exchange. Lime precipitation is widely used due to its simplicity and relatively low cost, but it has significant limitations in practical applications. Theoretically, 1.47 mg of calcium oxide is needed to remove 1 mg of fluoride. However, in practice, due to interference from complex components in the wastewater, the low fluoride removal efficiency of lime slurry, and high suspended solids content, the amount of lime added often exceeds the theoretical value by 50%. This excessive addition not only significantly increases the cost of calcium hydroxide but also causes a surge in sludge production.

[0004] CN219950761U discloses a system for defluoridation and resource utilization of high-salt fluoride wastewater. This system utilizes a calcium fluoride destabilizing crystallizer to treat the high-salt fluoride wastewater after a primary and secondary membrane system. The addition of calcium fluoride seed crystals solves the problems of easy scaling and difficulty in resource utilization of calcium fluoride in the membrane modules. However, the entire treatment process still requires the external purchase of large quantities of calcium fluoride seed crystals, scale inhibitors, and softening agents, resulting in high system operating costs and low resource utilization.

[0005] Furthermore, the treatment of high-salt, fluoride-containing wastewater requires processes for calcium and magnesium ion removal and pH adjustment, which further increases the demand for acids, alkalis, and softening agents, thereby raising overall operating costs and increasing the system's treatment load. After softening treatment, the significant increase in salt content in the water also triggers additional costs for treating other salts and the need for salt separation and crystallization, all of which pose challenges to the economic viability of the process. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a defluorination and hardening system and method that does not require external reagents. The chemical products generated during the internal circulation of high-salt fluoride wastewater treatment are reused as defluorinating and softening agents in the system's defluorination and hardening treatment, eliminating dependence on external reagents, reducing investment and operating costs, and improving resource utilization and process economy.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a defluorination and hardening system that does not require the addition of external agents, comprising a calcium fluoride crystallizer, a first high-density tank, a second high-density tank, a filtration device, a flat sheet membrane device, a first ion exchanger, a second ion exchanger, a product water tank, a first concentrate tank, a second concentrate tank, a bipolar membrane device, a first sludge tank, a carbon dioxide collection device, a sodium carbonate reaction device, a calcium chloride crystallizer, and a calcium chloride collection device;

[0008] The inlet of the calcium fluoride crystallizer is connected to the raw water delivery pipeline, and the outlet of the calcium fluoride crystallizer is connected to the inlet of the first high-density tank; the calcium fluoride crystallizer is used to react with the high-salt fluoride wastewater delivered by the raw water delivery pipeline to generate calcium fluoride precipitate.

[0009] The outlet of the first high-density tank is connected to the inlet of the second high-density tank via a pipeline. The first high-density tank is used to remove calcium ions from the wastewater treated by the calcium fluoride crystallizer; the second high-density tank is used to remove magnesium ions from the wastewater treated by the first high-density tank.

[0010] The outlet of the second high-density tank is connected to the inlet of the filtration device through a conveying pipeline. The filtration device is used to filter and purify the wastewater treated by the second high-density tank.

[0011] The outlet of the filtration device is connected to the inlet of the flat sheet membrane equipment via a delivery pipeline. The flat sheet membrane equipment is used to concentrate the wastewater filtered and purified by the filtration device.

[0012] The first concentrate outlet of the flat sheet membrane device is connected to the first ion exchanger via a delivery pipeline. The first ion exchanger is used to remove calcium and magnesium ions from the sodium chloride concentrate delivered from the first concentrate outlet.

[0013] The second concentrate outlet of the flat sheet membrane device is connected to the second ion exchanger via a delivery pipeline. The second ion exchanger is used to remove calcium and magnesium ions from the sodium sulfate concentrate delivered from the second concentrate outlet.

[0014] The product water outlet of the flat sheet membrane equipment is connected to the product water tank through a delivery pipeline, the outlet of the first ion exchanger is connected to the first concentrate tank through a delivery pipeline, and the outlet of the second ion exchanger is connected to the second concentrate tank through a delivery pipeline.

[0015] The delivery pipelines from the outlet of the permeate tank and the outlet of the first concentrate tank converge and are connected to the inlet of the bipolar membrane device; the delivery pipelines from the outlet of the permeate tank and the outlet of the second concentrate tank converge and are connected to the inlet of the bipolar membrane device.

[0016] The first sludge tank is connected to the sediment outlet of the first high-density tank. The hydrochloric acid output pipeline of the bipolar membrane device is connected to the first sludge tank. The first sludge tank is connected to the calcium chloride crystallization device through a conveying pipeline. The calcium chloride crystallization device is connected to the calcium chloride collection device through a conveying pipeline. The calcium chloride collection device is connected to the calcium fluoride crystallizer through a conveying pipeline.

[0017] The first sludge tank is also connected to the carbon dioxide collection device via a conveying pipeline, and the sodium hydroxide output pipeline of the bipolar membrane device is connected to the carbon dioxide collection device; the outlet of the carbon dioxide collection device is connected to the sodium carbonate reaction device via a conveying pipeline, and the sodium carbonate reaction device is connected to the first high-density tank via a conveying pipeline.

[0018] As a preferred solution for a defluorination and hardening system that does not require the addition of external chemicals, a second sludge tank is also included. The sodium hydroxide output pipeline of the bipolar membrane device is also connected to the second high-density tank, and the sediment outlet of the second high-density tank is connected to the second sludge tank through a conveying pipeline.

[0019] As a preferred solution for a defluorination and hardness reduction system that does not require the addition of external chemicals, a product water return pipeline is provided between the first ion exchanger and the raw water delivery pipeline, and between the second ion exchanger and the raw water delivery pipeline.

[0020] As a preferred solution for a defluorination and hardening system that does not require the addition of external reagents, the sulfuric acid output pipeline of the bipolar membrane device is connected to the inlet of the second high-density tank.

[0021] This invention also provides a method for defluorination and hardening without the need for external reagents, comprising the following steps:

[0022] High-salt, fluoride-containing wastewater is transported to a calcium fluoride crystallizer that uses self-produced calcium fluoride as seed crystals, so that the high-salt, fluoride-containing wastewater forms calcium fluoride precipitate after contacting calcium chloride.

[0023] The wastewater after calcium fluoride crystallization is pretreated in two steps, passing through the first high-density tank and the second high-density tank to remove calcium and magnesium ions from the wastewater, respectively.

[0024] Wastewater that has undergone step-by-step pretreatment in the first high-density tank and the second high-density tank is transported to a filtration device for purification. The wastewater purified by the filtration device is then transported to a flat-sheet membrane module for concentration, resulting in sodium chloride concentrate and sodium sulfate concentrate, respectively.

[0025] After concentration by the flat sheet membrane module, sodium chloride concentrate and sodium sulfate concentrate are obtained and sent to the first ion exchanger and the second ion exchanger respectively. The calcium and magnesium ions remaining in the sodium chloride concentrate and sodium sulfate concentrate are removed by ion exchange.

[0026] The sodium chloride concentrate and sodium sulfate concentrate, after being treated by the first ion exchanger and the second ion exchanger, are respectively transported to the first concentrate tank and the second concentrate tank. They are diluted by the self-produced water in the product water tank configured with flat sheet membrane modules to reach the preset concentration, and then introduced into the inlet of the bipolar membrane equipment. The bipolar membrane equipment converts the sodium chloride concentrate and sodium sulfate concentrate into hydrochloric acid, sulfuric acid and sodium hydroxide.

[0027] The hydrochloric acid effluent from the bipolar membrane equipment is fed into the first sludge tank configured in the first high-density tank, so that the hydrochloric acid solution reacts with the calcium carbonate in the filter residue to generate calcium chloride solution and release carbon dioxide gas.

[0028] A calcium chloride solution is introduced into a calcium chloride crystallization device to obtain calcium chloride product, which is then reused in a calcium fluoride crystallizer.

[0029] The carbon dioxide released during the dissolution of calcium carbonate by hydrochloric acid is transported to a carbon dioxide collection device for enrichment. It is then fed into a sodium carbonate reaction device together with the sodium hydroxide effluent from the bipolar membrane device to generate sodium carbonate. The generated sodium carbonate is used as a softener in the first high-density tank and reacts with calcium ions in the wastewater to form calcium carbonate precipitate.

[0030] As a preferred method for defluorination and hardening without the need for external reagents, the waste liquid from the first high-density tank is treated to remove fluoride and calcium hardness before flowing into the second high-density tank, where it reacts with sodium hydroxide generated by the bipolar membrane equipment to produce magnesium hydroxide precipitate, thereby reducing the magnesium hardness of the waste liquid.

[0031] As a preferred method for defluorination and hardening without the need for external reagents, the sulfuric acid effluent from the bipolar membrane equipment and the softened waste liquid from the second high-density tank are mixed and the pH is adjusted.

[0032] As a preferred method for defluorination and hardness reduction without the need for external reagents, the reclaimed water produced by the first and second ion exchangers is recycled back to the raw water delivery pipeline.

[0033] The beneficial effects of this invention are as follows:

[0034] The calcium fluoride crystallizer utilizes a stable calcium fluoride seed reaction process, avoiding the problem of decreased treatment efficiency caused by fluctuations in reaction conditions or changes in fluoride content; it can maintain efficient and stable operation under different working conditions, enhancing the reliability of the entire water treatment system.

[0035] Through the chemical reactions that occur in the internal circulation, products such as calcium chloride, calcium fluoride and sodium carbonate are generated and reused in the system, maximizing resource utilization, eliminating dependence on external softening agents, significantly reducing operating costs, and realizing the added value of system by-products.

[0036] By using self-produced sodium carbonate and sodium hydroxide to remove calcium and magnesium ions respectively, the hardness of raw water is effectively controlled, ensuring that the hardness problem in the water treatment process is fully resolved, improving the operating efficiency of subsequent process equipment, and reducing the risk of scaling.

[0037] A large amount of surplus low-concentration acid and alkali products are directly supplied to other companies, reducing inventory costs; while the high-concentration products obtained after concentration can bring higher sales prices, further improving overall economic benefits. Attached Figure Description

[0038] 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.

[0039] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0040] Figure 1 This is a schematic diagram of a defluorination and hardening system that does not require the addition of external reagents, provided in an embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the defluorination and hardening method without the need for external reagents provided in the embodiments of the present invention.

[0042] In the diagram, 1. Calcium fluoride crystallizer; 2. First high-density tank; 3. Second high-density tank; 4. Filtration device; 5. Flat sheet membrane equipment; 6. First ion exchanger; 7. Second ion exchanger; 8. Product water tank; 9. First concentrate tank; 10. Second concentrate tank; 11. Bipolar membrane equipment; 12. First sludge tank; 13. Carbon dioxide collection device; 14. Sodium carbonate reaction device; 15. Calcium chloride crystallizer; 16. Calcium chloride collection device; 17. Raw water transmission pipeline; 18. Second sludge tank; 19. Hydrochloric acid output pipeline; 20. Sodium hydroxide output pipeline; 21. Sulfuric acid output pipeline. Detailed Implementation

[0043] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] See Figure 1 This invention provides a defluorination and hardening system that does not require the addition of external reagents, including a calcium fluoride crystallizer 1, a first high-density tank 2, a second high-density tank 3, a filtration device 4, a flat sheet membrane device 5, a first ion exchanger 6, a second ion exchanger 7, a product water tank 8, a first concentrate tank 9, a second concentrate tank 10, a bipolar membrane device 11, a first sludge tank 12, a carbon dioxide collection device 13, a sodium carbonate reaction device 14, a calcium chloride crystallizer 15, and a calcium chloride collection device 16;

[0046] The calcium fluoride crystallizer 1 has an inlet connected to a raw water delivery pipeline 17 and an outlet connected to the inlet of the first high-density tank 2. The inlet of the calcium fluoride crystallizer 1 is connected to the outlet of the calcium chloride collection device 16, which is used to react high-salt fluoride wastewater to generate calcium fluoride precipitate.

[0047] The outlet of the first high-density tank 2 is connected to the inlet of the second high-density tank 3 via a conveying pipeline. The first high-density tank 2 is used to remove calcium ions from the wastewater treated by the calcium fluoride crystallizer 1. The second high-density tank 3 is used to remove magnesium ions from the wastewater treated by the first high-density tank 2. The outlet of the second high-density tank 3 is connected to the inlet of the filter device 4 via a conveying pipeline. The filter device 4 is used to filter and purify the wastewater treated by the second high-density tank 3.

[0048] The outlet of the filter device 4 is connected to the inlet of the flat sheet membrane equipment 5 through a conveying pipeline. The flat sheet membrane equipment 5 is used to concentrate the wastewater filtered and purified by the filter device 4.

[0049] The first concentrate outlet of the flat sheet membrane device 5 is connected to the first ion exchanger 6 via a delivery pipeline. The first ion exchanger 6 is used to remove calcium and magnesium ions from the sodium chloride concentrate delivered from the first concentrate outlet. The second concentrate outlet of the flat sheet membrane device 5 is connected to the second ion exchanger 7 via a delivery pipeline. The second ion exchanger 7 is used to remove calcium and magnesium ions from the sodium sulfate concentrate delivered from the second concentrate outlet.

[0050] Among them, the product water outlet of the flat sheet membrane equipment 5 is connected to the product water tank 8 through a conveying pipeline, the outlet of the first ion exchanger 6 is connected to the first concentrate tank 9 through a conveying pipeline, and the outlet of the second ion exchanger 7 is connected to the second concentrate tank 10 through a conveying pipeline.

[0051] The pipelines connecting the outlet of the product water tank 8 and the outlet of the first concentrate tank 9 are connected to the inlet of the bipolar membrane device 11; the pipelines connecting the outlet of the product water tank 8 and the outlet of the second concentrate tank 10 are connected to the inlet of the bipolar membrane device 11.

[0052] The first sludge tank 12 is connected to the sediment outlet of the first high-density tank 2, the hydrochloric acid output pipeline 19 of the bipolar membrane device 11 is connected to the first sludge tank 12, the first sludge tank 12 is connected to the calcium chloride crystallization device 15 through the conveying pipeline, the calcium chloride crystallization device 15 is connected to the calcium chloride collection device 16 through the conveying pipeline, and the calcium chloride collection device 16 is connected to the calcium fluoride crystallizer 1 through the conveying pipeline.

[0053] The first sludge tank 12 is also connected to the carbon dioxide collection device 13 via a conveying pipeline, and the sodium hydroxide output pipeline 20 of the bipolar membrane device 11 is connected to the carbon dioxide collection device 13; the outlet of the carbon dioxide collection device 13 is connected to the sodium carbonate reaction device 14 via a conveying pipeline, and the sodium carbonate reaction device 14 is connected to the first high-density tank 2 via a conveying pipeline.

[0054] In this embodiment, a second sludge tank 18 is also included. The sodium hydroxide output pipeline 20 of the bipolar membrane device 11 is also connected to the second high-density tank 3. The sediment outlet of the second high-density tank 3 is connected to the second sludge tank 18 through a conveying pipeline. A product water return pipeline is provided between the first ion exchanger 6 and the raw water conveying pipeline 17, and between the second ion exchanger 7 and the raw water conveying pipeline 17. The sulfuric acid output pipeline 21 of the bipolar membrane device 11 is connected to the inlet of the second high-density tank 3.

[0055] See Figure 2 This invention also provides a method for defluorination and hardening without the need for external agents, comprising the following steps:

[0056] S1. High-salt fluoride wastewater is transported to calcium fluoride crystallizer 1, which uses self-produced calcium fluoride as seed crystals, so that calcium fluoride precipitate is formed after the high-salt fluoride wastewater comes into contact with calcium chloride.

[0057] S2. The wastewater after calcium fluoride crystallization is pretreated in two steps, passing through the first high-density tank 2 and the second high-density tank 3, to remove calcium and magnesium ions from the wastewater respectively.

[0058] S3. The wastewater that has been pretreated in the first high-density tank 2 and the second high-density tank 3 is transported to the filtration device 4 for purification. The wastewater after purification by the filtration device 4 is transported to the flat sheet membrane module for concentration, resulting in sodium chloride concentrate and sodium sulfate concentrate, respectively.

[0059] S4. After concentrating the flat sheet membrane module, sodium chloride concentrate and sodium sulfate concentrate are respectively sent to the first ion exchanger 6 and the second ion exchanger 7 to remove residual calcium and magnesium ions in the sodium chloride concentrate and sodium sulfate concentrate through ion exchange.

[0060] S5. The sodium chloride concentrate and sodium sulfate concentrate treated by the first ion exchanger 6 and the second ion exchanger 7 are respectively transported to the first concentrate tank 9 and the second concentrate tank 10. They are diluted by the self-produced water in the product water tank 8 configured with flat sheet membrane module. After reaching the preset concentration, they are introduced into the inlet of the bipolar membrane device 11. The bipolar membrane device 11 converts the sodium chloride concentrate and sodium sulfate concentrate into hydrochloric acid, sulfuric acid and sodium hydroxide.

[0061] S6. The hydrochloric acid effluent from the bipolar membrane device 11 is introduced into the first sludge tank 12 configured in the first high-density tank 2, so that the hydrochloric acid solution reacts with the calcium carbonate in the filter residue to generate calcium chloride solution and release carbon dioxide gas.

[0062] S7. The calcium chloride solution is introduced into the calcium chloride crystallization equipment 15 to obtain calcium chloride product, which is then recycled to the calcium fluoride crystallizer 1.

[0063] S8. The carbon dioxide released during the dissolution of calcium carbonate by hydrochloric acid is transported to the carbon dioxide collection device 13 for enrichment. It is then fed into the sodium carbonate reaction device 14 together with the sodium hydroxide effluent from the bipolar membrane device 11 to generate sodium carbonate. The generated sodium carbonate is used as a softener in the first high-density tank 2 and reacts with calcium ions in the wastewater to form calcium carbonate precipitate.

[0064] In this embodiment, calcium fluoride crystallizer 1 uses system-produced calcium fluoride as seed crystals to further promote the precipitation of calcium fluoride. The waste liquid from the first high-density tank 2, after fluoride and calcium hardness removal treatment, flows into the second high-density tank 3, where it reacts with sodium hydroxide generated by the bipolar membrane device 11 to form magnesium hydroxide precipitate, reducing the hardness of the waste liquid. The sulfuric acid effluent from the bipolar membrane device 11 and the waste liquid filtered by the filter device 4 are mixed for pH adjustment. The regenerated water produced by the first ion exchanger 6 and the second ion exchanger 7 is recycled back to the raw water delivery pipeline 17.

[0065] The operating principle of this invention is as follows:

[0066] High-salt, fluoride-containing wastewater first forms calcium fluoride precipitate after contacting calcium chloride in calcium fluoride crystallizer 1. However, when the fluoride content in the raw water is low, calcium fluoride crystallizer 1 is used to promote the formation of more calcium fluoride precipitates by using self-produced calcium fluoride seed crystals. Then, through stepwise pretreatment in the first high-density tank 2 and the second high-density tank 3, calcium and magnesium ions in the water are effectively removed. During this process, calcium carbonate and magnesium hydroxide sludge precipitates are formed in the first sludge tank 12 and the second sludge tank 18, respectively. Subsequently, through a filter press process, these precipitates are converted into solid sludge filter cake, achieving preliminary separation of impurities.

[0067] The pretreated high-salt, fluoride-containing wastewater exhibits significantly improved water quality and then flows through filtration device 4 for further purification. Subsequently, the wastewater enters a flat-sheet membrane module for concentration, yielding concentrated sodium chloride and sodium sulfate solutions. To meet the influent requirements of the bipolar membrane device 11, the concentrated sodium chloride and sodium sulfate solutions are fed into the first ion exchanger 6 and the second ion exchanger 7, respectively, where residual calcium and magnesium ions are deeply removed using ion exchange technology. The concentrated sodium chloride and sodium sulfate solutions, after treatment by the first and second ion exchangers 6 and 7, flow into the first concentrate tank 9 and the second concentrate tank 10, respectively. After dilution using self-produced water from the product water tank 8 to achieve suitable concentrations, they are introduced into the inlet of the bipolar membrane device 11. The concentrated water is directly converted into acid and alkali products such as hydrochloric acid, sulfuric acid, and sodium hydroxide.

[0068] The hydrochloric acid effluent from the bipolar membrane device 11 is fed into the first sludge tank 12, where it reacts with the calcium carbonate in the filter residue to produce a calcium chloride solution and release carbon dioxide gas. The calcium chloride solution is then introduced into the calcium chloride crystallization device 15 to obtain a high-purity calcium chloride product. This calcium chloride product can be reused for fluoride removal in the system. Specifically, in the calcium fluoride crystallizer 1, calcium fluoride precipitates form after the raw water contacts calcium chloride. However, when the fluoride content in the raw water is low, calcium fluoride seed crystals are used to promote the formation of more calcium fluoride precipitates. After drying, the precipitate yields the calcium fluoride product.

[0069] The carbon dioxide released during the dissolution of calcium carbonate with hydrochloric acid is enriched by the carbon dioxide collection device 13 and then fed into the sodium carbonate reaction device 14 along with the sodium hydroxide effluent from the bipolar membrane device 11 to generate sodium carbonate. The generated sodium carbonate is used as a softener in the first high-density tank 2, reacting with calcium ions in the water to form calcium carbonate precipitate, thus reducing the water's calcium hardness. The wastewater from the first high-density tank 2, after fluoride and calcium hardness removal treatment, flows into the second high-density tank 3, where it reacts with the sodium hydroxide generated by the bipolar membrane device 11 to form magnesium hydroxide precipitate, further reducing the raw water hardness. The sulfuric acid effluent from the bipolar membrane device 11 is used for system pH adjustment. The regenerated water produced by the first ion exchanger 6 and the second ion exchanger 7 is recycled back into the system.

[0070] In summary, the sodium chloride and sodium sulfate concentrates obtained by the flat-sheet membrane module are diluted using the membrane system's own produced water to reach a suitable concentration before being directly supplied to the inlet of different bipolar membrane devices 11, where they are converted into acidic and alkaline products such as hydrochloric acid, sulfuric acid, and sodium hydroxide. Given the high salinity of the wastewater, the bipolar membrane device 11 not only meets the internal process self-circulation consumption but also provides a surplus of acidic and alkaline products. The concentrations of these initially produced acidic and alkaline products are generally maintained in the range of 2 to 4 mol / L, possessing broad industrial application value. They can be directly supplied to partner companies, and the concentration can be increased through further concentration processes to meet market demand for high-purity acidic and alkaline products, promoting efficient resource recycling. After pretreatment in the first high-density tank 2 and the second high-density tank 3, the resulting precipitated sludge is filtered to form solid sludge filter cake. The hydrochloric acid solution generated by the bipolar membrane device 11 reacts chemically with the calcium carbonate in the filter cake, causing the calcium carbonate to redissolve into a calcium chloride solution, while simultaneously releasing carbon dioxide gas. Subsequently, the calcium chloride solution is introduced into the calcium chloride crystallization device 15 to ultimately obtain a high-purity calcium chloride product. This calcium chloride product can be reused in the process system, influencing the solubility balance of calcium fluoride in water through the common ion effect, reducing its solubility, and promoting the precipitation of more calcium fluoride. When the fluoride content in the raw water is low, seed crystal formation is difficult, making it difficult for calcium fluoride precipitate to form. In this case, using the calcium fluoride crystallizer 1 can further improve the efficiency of fluoride removal. Using the generated calcium fluoride precipitate as a seed crystal can effectively promote the formation of more calcium fluoride precipitate. The calcium fluoride seed crystals not only reduce the calcium ion concentration required to initiate the precipitation reaction but also reduce the fluoride concentration in the wastewater to a lower level. After treatment by the calcium fluoride crystallizer 1, the precipitate is dried to obtain the calcium fluoride product. Furthermore, the carbon dioxide released during the dissolution of calcium carbonate is also fully utilized. This gas is collected and introduced into the alkaline outlet of the bipolar membrane device 11, reacting with sodium hydroxide to generate sodium carbonate. This generated sodium carbonate can be used as a softener in the first high-density tank 2, reacting with calcium ions in the water to form calcium carbonate precipitate, thereby reducing water hardness. After defluorination and calcium hardness removal, the water flows into the second high-density tank 3. In this stage, it reacts with sodium hydroxide generated by the system to form magnesium hydroxide precipitate, further reducing the hardness of the raw water. The sulfuric acid product generated by the bipolar membrane equipment 11 can be used for pH adjustment in subsequent systems to ensure water quality stability. After pretreatment, the water passes sequentially through the filter device 4 and the flat sheet membrane module, ultimately producing water that meets the Class III standard of "GB3838-2002 Surface Water Environmental Quality Standard" or the standard of "GBT19923-2005 Urban Wastewater Reuse - Industrial Water Quality". Simultaneously, the concentrated water, after calcium and magnesium removal by an ion exchanger, is reused along with some of the permeate as raw material for the production of acid and alkali products in the bipolar membrane equipment.The regenerated water produced by the first ion exchanger 6 and the second ion exchanger 7 is recycled back into the system, which not only efficiently purifies high-salt, fluoride-containing wastewater but also maximizes resource utilization, resulting in good environmental and economic benefits. The calcium fluoride crystallizer 1 of this invention utilizes a stable calcium fluoride seed crystal reaction process, avoiding the problem of decreased treatment efficiency caused by fluctuations in reaction conditions or changes in fluoride content; it can maintain efficient and stable operation under different working conditions, enhancing the reliability of the entire water treatment system; through the chemical reaction occurring in the internal circulation, products such as calcium chloride, calcium fluoride, and sodium carbonate are generated and reused in the system, maximizing resource utilization, eliminating dependence on external softening agents, significantly reducing operating costs, and realizing the added value of system byproducts; using self-produced sodium carbonate and sodium hydroxide to remove calcium and magnesium ions respectively, it achieves effective control of raw water hardness, ensuring that the hardness problem in the water treatment process is fully resolved, improving the operating efficiency of subsequent process equipment, and reducing the risk of scaling; a large amount of surplus low-concentration acid and alkali products are directly supplied to other enterprises, reducing inventory costs; while the high-concentration products obtained after concentration can bring higher sales prices, further improving overall economic benefits.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A defluorination and hardening system that requires no external reagents, characterized in that, It includes a calcium fluoride crystallizer (1), a first high-density tank (2), a second high-density tank (3), a filtration device (4), a flat sheet membrane device (5), a first ion exchanger (6), a second ion exchanger (7), a product water tank (8), a first concentrate tank (9), a second concentrate tank (10), a bipolar membrane device (11), a first sludge tank (12), a carbon dioxide collection device (13), a sodium carbonate reaction device (14), a calcium chloride crystallizer (15), and a calcium chloride collection device (16). The inlet of the calcium fluoride crystallizer (1) is connected to the raw water conveying pipeline (17), and the outlet of the calcium fluoride crystallizer (1) is connected to the inlet of the first high-density tank (2). The calcium fluoride crystallizer (1) is used to react with the high-salt fluoride wastewater conveyed by the raw water conveying pipeline (17) to generate calcium fluoride precipitate. The outlet of the first high-density tank (2) is connected to the inlet of the second high-density tank (3) through a conveying pipeline. The first high-density tank (2) is used to remove calcium ions from the wastewater after treatment by the calcium fluoride crystallizer (1); the second high-density tank (3) is used to remove magnesium ions from the wastewater after treatment by the first high-density tank (2). The outlet of the second high-density tank (3) is connected to the inlet of the filter device (4) through a conveying pipeline. The filter device (4) is used to filter and purify the wastewater treated by the second high-density tank (3). The outlet of the filter device (4) is connected to the inlet of the flat sheet membrane device (5) through a conveying pipeline. The flat sheet membrane device (5) is used to concentrate the wastewater filtered and purified by the filter device (4). The first concentrate outlet of the flat sheet membrane device (5) is connected to the first ion exchanger (6) through a delivery pipeline. The first ion exchanger (6) is used to remove calcium and magnesium ions from the sodium chloride concentrate delivered by the first concentrate outlet. The second concentrate outlet of the flat sheet membrane device (5) is connected to the second ion exchanger (7) through a delivery pipeline. The second ion exchanger (7) is used to remove calcium and magnesium ions from the sodium sulfate concentrate delivered by the second concentrate outlet. The product water outlet of the flat sheet membrane device (5) is connected to the product water tank (8) through a conveying pipeline, the outlet of the first ion exchanger (6) is connected to the first concentrate tank (9) through a conveying pipeline, and the outlet of the second ion exchanger (7) is connected to the second concentrate tank (10) through a conveying pipeline. The delivery pipelines of the outlet of the product water tank (8) and the outlet of the first concentrate tank (9) are connected to the inlet of the bipolar membrane device (11); the delivery pipelines of the outlet of the product water tank (8) and the outlet of the second concentrate tank (10) are connected to the inlet of the bipolar membrane device (11). The first sludge tank (12) is connected to the sediment outlet of the first high-density tank (2), the hydrochloric acid output pipeline (19) of the bipolar membrane device (11) is connected to the first sludge tank (12), the first sludge tank (12) is connected to the calcium chloride crystallization device (15) through a conveying pipeline, the calcium chloride crystallization device (15) is connected to the calcium chloride collection device (16) through a conveying pipeline, and the calcium chloride collection device (16) is connected to the calcium fluoride crystallizer (1) through a conveying pipeline. The first sludge tank (12) is also connected to the carbon dioxide collection device (13) through a conveying pipeline, and the sodium hydroxide output pipeline (20) of the bipolar membrane device (11) is connected to the carbon dioxide collection device (13); the outlet of the carbon dioxide collection device (13) is connected to the sodium carbonate reaction device (14) through a conveying pipeline, and the sodium carbonate reaction device (14) is connected to the first high-density tank (2) through a conveying pipeline.

2. The defluorination and hardening system without the need for external reagents according to claim 1, characterized in that, It also includes a second sludge tank (18), and the sodium hydroxide output pipeline (20) of the bipolar membrane device (11) is also connected to the second high-density tank (3). The sediment outlet of the second high-density tank (3) is connected to the second sludge tank (18) through a conveying pipeline.

3. The defluorination and hardening system without the need for external reagents according to claim 1, characterized in that, A product water return pipeline is provided between the first ion exchanger (6) and the raw water delivery pipeline (17), and between the second ion exchanger (7) and the raw water delivery pipeline (17).

4. The defluorination and hardening system without the need for external reagents according to claim 1, characterized in that, The sulfuric acid output pipeline (21) of the bipolar membrane device (11) is connected to the inlet of the second high-density tank (3).

5. A method for defluorination and hardening without the need for external reagents, employing the defluorination and hardening system for defluorination and hardening without the need for external reagents as described in any one of claims 1 to 4, characterized in that, Includes the following steps: High-salt, fluoride-containing wastewater is transported to a calcium fluoride crystallizer that uses self-produced calcium fluoride as seed crystals, so that the high-salt, fluoride-containing wastewater forms calcium fluoride precipitate after contacting calcium chloride. The wastewater after calcium fluoride crystallization is pretreated in two steps, passing through the first high-density tank and the second high-density tank to remove calcium and magnesium ions from the wastewater, respectively. Wastewater that has undergone step-by-step pretreatment in the first high-density tank and the second high-density tank is transported to a filtration device for purification. The wastewater purified by the filtration device is then transported to a flat-sheet membrane module for concentration, resulting in sodium chloride concentrate and sodium sulfate concentrate, respectively. After concentration by the flat sheet membrane module, sodium chloride concentrate and sodium sulfate concentrate are obtained and sent to the first ion exchanger and the second ion exchanger respectively. The calcium and magnesium ions remaining in the sodium chloride concentrate and sodium sulfate concentrate are removed by ion exchange. The sodium chloride concentrate and sodium sulfate concentrate, after being treated by the first ion exchanger and the second ion exchanger, are respectively transported to the first concentrate tank and the second concentrate tank. They are diluted by the self-produced water in the product water tank configured with flat sheet membrane modules to reach the preset concentration, and then introduced into the inlet of the bipolar membrane equipment. The bipolar membrane equipment converts the sodium chloride concentrate and sodium sulfate concentrate into hydrochloric acid, sulfuric acid and sodium hydroxide. The hydrochloric acid effluent from the bipolar membrane equipment is fed into the first sludge tank configured in the first high-density tank, so that the hydrochloric acid solution reacts with the calcium carbonate in the filter residue to generate calcium chloride solution and release carbon dioxide gas. A calcium chloride solution is introduced into a calcium chloride crystallization device to obtain calcium chloride product, which is then reused in a calcium fluoride crystallizer. The carbon dioxide released during the dissolution of calcium carbonate by hydrochloric acid is transported to a carbon dioxide collection device for enrichment. It is then fed into a sodium carbonate reaction device together with the sodium hydroxide effluent from the bipolar membrane device to generate sodium carbonate. The generated sodium carbonate is used as a softener in the first high-density tank and reacts with calcium ions in the wastewater to form calcium carbonate precipitate.

6. The method for defluorination and hardening without the need for external reagents according to claim 5, characterized in that, After the waste liquid from the first high-density tank is treated to remove fluoride and calcium hardness, it flows into the second high-density tank, where it reacts with sodium hydroxide generated by the bipolar membrane equipment to produce magnesium hydroxide precipitate, thereby reducing the magnesium hardness of the waste liquid.

7. The method for defluorination and hardening without the need for external agents according to claim 5, characterized in that, The sulfuric acid effluent from the bipolar membrane equipment and the softened waste liquid from the second high-density tank are mixed for pH adjustment.

8. The method for defluorination and hardening without the need for external reagents according to claim 5, characterized in that, The reclaimed water produced by the first and second ion exchangers is recycled back to the raw water delivery pipeline.

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