Fluorine removal and hardness reduction system and method without adding medicament

Abstract

According to the fluorine removal and hardness reduction system and method without the addition of the chemical, a calcium fluoride crystallizer reacts with received high-salt fluorine-containing waste water conveyed by a raw water conveying pipeline to generate a high-purity calcium fluoride product, and the high-purity calcium fluoride product serves as a seed crystal to be reused in the calcium fluoride crystallizer; and introducing the hydrochloric acid effluent of the bipolar membrane equipment into a first sludge tank, so that the hydrochloric acid solution reacts with calcium carbonate in the filter residues to generate a calcium chloride solution and release carbon dioxide gas. The calcium chloride solution is introduced into calcium chloride crystallization equipment to obtain a high-purity calcium chloride product which is reused in a calcium fluoride crystallizer. Carbon dioxide released in the process of dissolving calcium carbonate by hydrochloric acid is enriched by the carbon dioxide collecting device and then is jointly introduced into the sodium carbonate reaction device together with sodium hydroxide effluent of the bipolar membrane equipment to generate sodium carbonate which is used as a softening agent in the first high-density tank. The sulfuric acid effluent of the bipolar membrane equipment is used for adjusting the pH value of the wastewater softened by the second high-density tank. The method gets rid of dependence on external chemicals, and the investment and operation cost is reduced.

Description

Technical Field

[0001] The invention relates to a fluorine removal and hardness reduction system and method without the need for external chemicals, belonging to the technical field of water treatment. Background Art

[0002] High-salt fluoride-containing wastewater mainly comes from industrial fields such as chemical, metallurgical and mining. The water quality is often neutral to alkaline, with a serious excess of salt content (>3.5wt%) and high concentration of Na + , Ca 2+ Mg 2+ , Cl - 、SO4 2- Plasma. The fluoride concentration in wastewater is as high as 1000mg / L, which poses a serious threat to the environment and human health. Due to its strong environmental pollution and difficulty in treatment, it is a difficult problem that needs to be overcome in the field of environmental governance. Current regulations require that the fluoride content in most industrial wastewater must be strictly controlled below 1mg / L, and the salt content must not exceed 1000mg / L.

[0003] At present, the main treatment methods for fluoride-containing wastewater are: chemical precipitation, flocculation precipitation, adsorption, ion exchange, etc. The lime precipitation method is widely used because of its simple operation and relatively low cost, but this method has obvious limitations in practical applications. Theoretically, 1.47 mg of calcium oxide is required to remove 1 mg of fluoride, but in actual operation, due to the interference of complex components in the wastewater, the low fluoride removal efficiency of lime milk, and the high content of suspended matter, the amount of lime added often needs to exceed 50% of the theoretical value. This excessive addition not only leads to a significant increase in the cost of calcium hydroxide, but also causes a surge in the amount of sludge.

[0004] CN219950761U discloses a high-salt fluorine-containing wastewater defluorination and resource utilization treatment system. The system uses a calcium fluoride destabilization crystallizer after the primary membrane system and the secondary membrane system to defluorinate the high-salt fluorine-containing wastewater. The problem of calcium fluoride scaling and difficulty in resource utilization in the membrane assembly is solved by adding calcium fluoride seeds. However, a large amount of calcium fluoride seeds, scale inhibitors and softening agents still need to be purchased during the entire treatment process, the system operation cost is high, and the resource utilization rate is low.

[0005] In addition, high-salinity fluoride-containing wastewater also requires processes for calcium and magnesium ion removal and pH adjustment during treatment, which further increases the demand for acid, alkali, and softening agents, thereby increasing the overall operating cost and the system's processing load. After softening treatment, the significant increase in salt content in the water will also trigger additional salt treatment costs and the need for salt separation and crystallization treatment, all of which pose a challenge to the economic feasibility of the process. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a fluorine removal and hardness reduction system and method that does not require the addition of external agents. The chemicals generated by the internal circulation of high-salt fluorine-containing wastewater treatment are reused as defluorinating agents and softening agents in the system's defluorinating and hardness reduction treatment, thus getting rid of the dependence on external agents, reducing investment and operating costs, and improving resource utilization and process economy.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: a fluorine removal and hardness reduction system without the need for external agents, comprising a calcium fluoride crystallizer, a first high-density tank, a second high-density tank, a filtering device, a flat membrane device, a first ion exchanger, a second ion exchanger, a water production tank, a first concentrated water tank, a second concentrated water tank, a bipolar membrane device, a first sludge tank, a carbon dioxide collection device, a sodium carbonate reaction device, a calcium chloride crystallization device and a calcium chloride collection device; The inlet of the calcium fluoride crystallizer is connected to a 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-salinity fluoride-containing wastewater delivered by the raw water delivery pipeline to generate calcium fluoride precipitate; The outlet of the first high-density tank is connected to the inlet of the second high-density tank through a conveying pipeline, and the first high-density tank is used to remove calcium ions in the wastewater treated by the calcium fluoride crystallizer; the second high-density tank is used to remove magnesium ions in the wastewater treated by the first high-density tank; The outlet of the second high-density tank is connected to the inlet of the filtering device through a delivery pipeline, and the filtering device is used to filter and purify the wastewater treated by the second high-density tank; The outlet of the filtering device is connected to the inlet of the flat membrane device through a delivery pipeline, and the flat membrane device is used to concentrate the wastewater filtered and purified by the filtering device; The first concentrated water outlet of the flat membrane device is connected to the first ion exchanger through a delivery pipeline, and the first ion exchanger is used to remove calcium and magnesium ions from the sodium chloride concentrated water delivered by the first concentrated water outlet; The second concentrated water outlet of the flat membrane device is connected to the second ion exchanger through a delivery pipeline, and the second ion exchanger is used to remove calcium and magnesium ions from the sodium sulfate concentrated water delivered by the second concentrated water outlet; The water outlet of the flat membrane device is connected to the water production tank through a delivery pipeline, the outlet of the first ion exchanger is connected to the first concentrated water tank through a delivery pipeline, and the outlet of the second ion exchanger is connected to the second concentrated water tank through a delivery pipeline; The delivery pipelines of the outlet of the water production pool and the outlet of the first concentrated water pool are connected to the inlet of the bipolar membrane device after being collected; the delivery pipelines of the outlet of the water production pool and the outlet of the second concentrated water pool are connected to the inlet of the bipolar membrane device after being collected; 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 delivery pipeline, the calcium chloride crystallization device is connected to the calcium chloride collection device through a delivery pipeline, and the calcium chloride collection device is connected to the calcium fluoride crystallizer through a delivery pipeline; The first sludge tank is also connected to the carbon dioxide collection device through a delivery pipeline, and the sodium hydroxide output pipeline of the bipolar membrane equipment is connected to the carbon dioxide collection device; the outlet of the carbon dioxide collection device is connected to the sodium carbonate reaction device through a delivery pipeline, and the sodium carbonate reaction device is connected to the first high-density tank through a delivery pipeline.

[0008] As a preferred solution for the fluorine removal and hardness reduction system without the need for external agents, it also includes a second sludge tank, 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.

[0009] As a preferred solution for the fluorine removal and hardness reduction system without the need for external chemicals, a produced 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.

[0010] As a preferred solution for the fluorine removal and hardness reduction system without the need for external reagents, the sulfuric acid output pipeline of the bipolar membrane device is connected to the inlet of the second high-density tank.

[0011] The present invention also provides a method for removing fluorine and reducing hardness without adding external agents, comprising the following steps: The high-salt fluoride-containing wastewater is transported to a calcium fluoride crystallizer using self-produced calcium fluoride as a seed crystal, so that the high-salt fluoride-containing wastewater contacts calcium chloride to form calcium fluoride precipitation; The wastewater after the calcium fluoride crystallization treatment is sequentially pre-treated in the first high-density tank and the second high-density tank to remove calcium and magnesium ions in the wastewater respectively; The wastewater pre-treated in the first high-density tank and the second high-density tank is transported to the filter device for purification, and the wastewater purified by the filter device is transported to the flat membrane module for concentration to obtain sodium chloride concentrated water and sodium sulfate concentrated water respectively; Concentrating the flat membrane assembly to obtain sodium chloride concentrated water and sodium sulfate concentrated water is transported to the first ion exchanger and the second ion exchanger respectively, and the residual calcium and magnesium ions in the sodium chloride concentrated water and the sodium sulfate concentrated water are removed by ion exchange; The sodium chloride concentrated water and the sodium sulfate concentrated water treated by the first ion exchanger and the second ion exchanger are respectively transported to the first concentrated water tank and the second concentrated water tank, and are diluted by the self-produced water in the water production tank configured by the flat membrane module. After reaching the preset concentration, they are respectively introduced into the water inlet of the bipolar membrane device, and the sodium chloride concentrated water and the sodium sulfate concentrated water are converted into hydrochloric acid, sulfuric acid and sodium hydroxide by the bipolar membrane device; The hydrochloric acid effluent of the bipolar membrane device is passed 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 a calcium chloride solution and release carbon dioxide gas; The calcium chloride solution is introduced into the calcium chloride crystallization equipment to obtain a calcium chloride product, and the calcium chloride product is recycled to the calcium fluoride crystallizer; The carbon dioxide released during the hydrochloric acid dissolving calcium carbonate is transported to the carbon dioxide collection device for enrichment, and then passed into the 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.

[0012] As a preferred solution for the method of removing fluorine and reducing hardness without adding external agents, the waste liquid from the first high-density tank is treated to remove fluorine and calcium hardness, and then flows into the second high-density tank to react with the sodium hydroxide generated by the bipolar membrane device to form magnesium hydroxide precipitate, thereby reducing the magnesium hardness of the waste liquid.

[0013] As a preferred solution for the method of removing fluorine and reducing hardness without adding external chemicals, the sulfuric acid effluent from the bipolar membrane device and the softened waste liquid from the second high-density tank are mixed to adjust the pH.

[0014] As a preferred solution for the method of removing fluorine and reducing hardness without adding external chemicals, the regenerated water produced by the first ion exchanger and the second ion exchanger is circulated back to the raw water delivery pipeline.

[0015] The beneficial effects of the present invention are as follows: The calcium fluoride crystallizer utilizes a stable calcium fluoride seed reaction process to avoid the problem of decreased treatment efficiency caused by fluctuations in reaction conditions or changes in fluorine 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 in the internal cycle, calcium chloride, calcium fluoride and sodium carbonate are generated and reused in the system, maximizing resource utilization, getting rid of the dependence on external softening agents, greatly reducing operating costs, and realizing the added value of system by-products; Self-produced sodium carbonate and sodium hydroxide are used to remove calcium and magnesium ions respectively, achieving effective control of raw water hardness, ensuring that the hardness problem in the water treatment process is fully solved, 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 companies, reducing inventory costs; and the high-concentration products obtained after concentration can bring higher sales prices, further improving the overall economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0017] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0018] Figure 1 A schematic diagram of a fluorine removal and hardness reduction system without the need for external agents provided in an embodiment of the present invention; Figure 2 This is a schematic flow chart of a method for removing fluorine and reducing hardness without adding external agents provided in an embodiment of the present invention.

[0019] In the figure, 1, calcium fluoride crystallizer; 2, first high-density tank; 3, second high-density tank; 4, filtering device; 5, flat membrane equipment; 6, first ion exchanger; 7, second ion exchanger; 8, water production tank; 9, first concentrated water tank; 10, second concentrated water tank; 11, bipolar membrane equipment; 12, first sludge tank; 13, carbon dioxide collection device; 14, sodium carbonate reaction device; 15, calcium chloride crystallization equipment; 16, calcium chloride collection equipment; 17, raw water delivery pipeline; 18, second sludge tank; 19, hydrochloric acid output pipeline; 20, sodium hydroxide output pipeline; 21, sulfuric acid output pipeline. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0022] See also Figure 1 The embodiment of the present invention provides a fluorine removal and hardness reduction system without the need for external agents, including a calcium fluoride crystallizer 1, a first high-density tank 2, a second high-density tank 3, a filtering device 4, a flat membrane device 5, a first ion exchanger 6, a second ion exchanger 7, a water production tank 8, a first concentrated water tank 9, a second concentrated water 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 crystallization device 15 and a calcium chloride collection device 16; The inlet of the calcium fluoride crystallizer 1 is connected to a raw water delivery pipeline 17, and the outlet of the calcium fluoride crystallizer 1 is connected to the inlet of the first high-density pool 2; the inlet of the calcium fluoride crystallizer 1 is connected to the outlet of a calcium chloride collection device 16, which is used for high-salinity fluoride-containing wastewater to react and generate calcium fluoride precipitation; Among them, the outlet of the first high-density pool 2 is connected to the inlet of the second high-density pool 3 through a conveying pipeline, and the first high-density pool 2 is used to remove calcium ions in the wastewater treated by the calcium fluoride crystallizer 1; the second high-density pool 3 is used to remove magnesium ions in the wastewater treated by the first high-density pool 2; the outlet of the second high-density pool 3 is connected to the inlet of the filter device 4 through a conveying pipeline, and the filter device 4 is used to filter and purify the wastewater treated by the second high-density pool 3; The outlet of the filter device 4 is connected to the inlet of the flat membrane device 5 through a delivery pipeline, and the flat membrane device 5 is used to concentrate the wastewater filtered and purified by the filter device 4; The first concentrated water outlet of the flat membrane device 5 is connected to the first ion exchanger 6 through a delivery pipeline, and the first ion exchanger 6 is used to remove calcium and magnesium ions from the sodium chloride concentrated water delivered by the first concentrated water outlet; the second concentrated water outlet of the flat membrane device 5 is connected to the second ion exchanger 7 through a delivery pipeline, and the second ion exchanger 7 is used to remove calcium and magnesium ions from the sodium sulfate concentrated water delivered by the second concentrated water outlet; The water outlet of the flat membrane device 5 is connected to the water production tank 8 through a delivery pipeline, the outlet of the first ion exchanger 6 is connected to the first concentrated water tank 9 through a delivery pipeline, and the outlet of the second ion exchanger 7 is connected to the second concentrated water tank 10 through a delivery pipeline; The delivery pipelines of the outlet of the water production pool 8 and the outlet of the first concentrated water pool 9 are connected to the inlet of the bipolar membrane device 11 after being collected; the delivery pipelines of the outlet of the water production pool 8 and the outlet of the second concentrated water pool 10 are connected to the inlet of the bipolar membrane device 11 after being collected; 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 delivery pipeline, the calcium chloride crystallization device 15 is connected to the calcium chloride collection device 16 through a delivery pipeline, and the calcium chloride collection device 16 is connected to the calcium fluoride crystallizer 1 through a delivery pipeline; Among them, the first sludge tank 12 is also connected to the carbon dioxide collection device 13 through a delivery pipeline, and the sodium hydroxide output pipeline 20 of the bipolar membrane equipment 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 delivery pipeline, and the sodium carbonate reaction device 14 is connected to the first high-density tank 2 through a delivery pipeline.

[0023] In this embodiment, a second sludge tank 18 is also included, and the sodium hydroxide output pipeline 20 of the bipolar membrane device 11 is also connected to the second high-density tank 3, and the sediment outlet of the second high-density tank 3 is connected to the second sludge tank 18 through a conveying pipeline; a produced 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.

[0024] See also Figure 2 The embodiment of the present invention also provides a method for removing fluorine and reducing hardness without adding external agents, comprising the following steps: S1, transporting the high-salt fluoride-containing wastewater to a calcium fluoride crystallizer 1 using self-produced calcium fluoride as a crystal seed, so that the high-salt fluoride-containing wastewater contacts calcium chloride to form calcium fluoride precipitation; S2, pre-treating the wastewater after calcium fluoride crystallization in the first high-density tank 2 and the second high-density tank 3 in order to remove calcium and magnesium ions in the wastewater respectively; S3, transporting the wastewater pre-treated in the first high-density tank 2 and the second high-density tank 3 to the filter device 4 for purification, and transporting the wastewater purified by the filter device 4 to the flat membrane module for concentration to obtain sodium chloride concentrated water and sodium sulfate concentrated water respectively; S4, concentrating the flat membrane assembly to obtain sodium chloride concentrated water and sodium sulfate concentrated water, respectively, and transporting them to the first ion exchanger 6 and the second ion exchanger 7, and removing residual calcium and magnesium ions in the sodium chloride concentrated water and the sodium sulfate concentrated water by ion exchange; S5, transporting the sodium chloride concentrated water and the sodium sulfate concentrated water treated by the first ion exchanger 6 and the second ion exchanger 7 to the first concentrated water tank 9 and the second concentrated water tank 10 respectively, diluting them by using the self-produced water in the water production tank 8 configured by the flat membrane assembly, and introducing them into the water inlet of the bipolar membrane device 11 after reaching a preset concentration, and converting the sodium chloride concentrated water and the sodium sulfate concentrated water into hydrochloric acid, sulfuric acid and sodium hydroxide through the bipolar membrane device 11; S6, passing the hydrochloric acid effluent from the bipolar membrane device 11 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 a calcium chloride solution and release carbon dioxide gas; S7, introducing the calcium chloride solution into the calcium chloride crystallization device 15 to obtain a calcium chloride product, and the calcium chloride product is recycled to the calcium fluoride crystallizer 1; S8. The carbon dioxide released during the hydrochloric acid dissolving calcium carbonate is transported to the carbon dioxide collecting device 13 for enrichment, and then passed together with the sodium hydroxide effluent from the bipolar membrane device 11 into the sodium carbonate reaction device 14 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 precipitation.

[0025] In this embodiment, a calcium fluoride crystallizer 1 is used to use the system's self-produced calcium fluoride as a seed crystal to further promote the formation of calcium fluoride precipitation. The waste liquid from the first high-density tank 2 is treated to remove fluorine and calcium hardness, and then flows into the second high-density tank 3 to react with the sodium hydroxide generated by the bipolar membrane device 11 to generate magnesium hydroxide precipitation, thereby 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 to adjust the pH. The regenerated water produced by the first ion exchanger 6 and the second ion exchanger 7 is circulated back to the raw water delivery pipeline 17.

[0026] The operating principle of the present invention is as follows: High-salt fluoride-containing wastewater first forms calcium fluoride precipitate after contacting calcium chloride in the calcium fluoride crystallizer 1. However, when the fluoride content in the raw water is low, the calcium fluoride crystallizer 1 is used to promote the formation of more calcium fluoride precipitate with self-produced calcium fluoride seeds. Then, after the step-by-step pretreatment in the first high-density tank 2 and the second high-density tank 3, the calcium and magnesium ions in the water are effectively removed. In this process, sludge precipitates of calcium carbonate and magnesium hydroxide are formed in the first sludge tank 12 and the second sludge tank 18, respectively. Subsequently, these precipitates are converted into solid sludge residues through the filter press process, achieving the initial separation of impurities.

[0027] The water quality of the high-salt fluoride-containing wastewater after pretreatment is significantly improved, and then it flows through the filter device 4 for further purification. Subsequently, the wastewater enters the flat membrane assembly for concentration, and sodium chloride concentrated water and sodium sulfate concentrated water are obtained respectively. In order to meet the water inlet requirements of the bipolar membrane device 11, the sodium chloride concentrated water and the sodium sulfate concentrated water are respectively sent to the first ion exchanger 6 and the second ion exchanger 7, and the residual calcium and magnesium ions therein are deeply removed by ion exchange technology. The sodium chloride concentrated water and the sodium sulfate concentrated water treated by the first ion exchanger 6 and the second ion exchanger 7 flow into the first concentrated water pool 9 and the second concentrated water pool 10 respectively, and are diluted by using the self-produced water in the water production pool 8. After reaching the appropriate concentration, they are introduced into the water inlet of the bipolar membrane device 11 respectively. The concentrated water is directly converted into acid and alkali products such as hydrochloric acid, sulfuric acid and sodium hydroxide.

[0028] The hydrochloric acid effluent of the bipolar membrane device 11 is passed into the first sludge tank 12, so that the hydrochloric acid solution reacts with the calcium carbonate in the filter residue to generate a calcium chloride solution and release carbon dioxide gas. The calcium chloride solution is introduced into the calcium chloride crystallization device 15 to obtain a high-purity calcium chloride product. The calcium chloride product can be reused for the removal of fluoride in the system. That is, in the calcium fluoride crystallizer 1, the raw water contacts the calcium chloride to form a calcium fluoride precipitate, but when the fluorine content in the raw water is low, the calcium fluoride seed is used to promote the formation of more calcium fluoride precipitation, and the calcium fluoride product is obtained after the precipitation is dried.

[0029] The carbon dioxide released during the hydrochloric acid dissolving calcium carbonate is enriched by the carbon dioxide collection device 13, and then passed into the sodium carbonate reaction device 14 together with the sodium hydroxide outlet of 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, thereby reducing the calcium hardness of the water. After the waste liquid of the first high-density tank 2 is treated to remove fluorine and calcium hardness, it flows into the second high-density tank 3, reacts with the sodium hydroxide generated by the bipolar membrane device 11 to generate magnesium hydroxide precipitate, further reducing the hardness of the raw water. The sulfuric acid outlet of the bipolar membrane device 11 is used to adjust the pH of the system. Among them, the regenerated water generated by the first ion exchanger 6 and the second ion exchanger 7 is circulated back into the system.

[0030] In summary, the sodium chloride concentrate and sodium sulfate concentrate concentrated by the flat membrane assembly of the present invention are diluted by using the self-produced water of the membrane system, and after reaching the appropriate concentration, they are directly transported to the water inlet of different bipolar membrane devices 11, and converted into acid and alkali products such as hydrochloric acid, sulfuric acid and sodium hydroxide. In view of the high salt characteristics of the wastewater, the bipolar membrane device 11 can not only meet the self-circulation consumption of the internal process, but also have a large surplus of acid and alkali products. The concentration of these initially produced acid and alkali products is generally maintained in the range of 2 to 4 mol / L, and has a wide range of industrial application value. Not only can it be directly supplied to cooperative enterprises, but also the product concentration can be increased by deepening the concentration process to meet the market demand for high-purity acid and alkali products and promote efficient recycling of resources. After the raw water is pre-treated by the first high-density tank 2 and the second high-density tank 3, the precipitated sludge produced is filtered to form a solid sludge filter residue. The hydrochloric acid solution generated by the bipolar membrane device 11 reacts chemically with the calcium carbonate in the filter residue to dissolve the calcium carbonate into a calcium chloride solution and release carbon dioxide gas at the same time. Subsequently, the calcium chloride solution is introduced into the calcium chloride crystallization device 15, and finally a high-purity calcium chloride product is obtained. These calcium chloride products can be reused in the process system, and the dissolution equilibrium of calcium fluoride in water is affected by the common ion effect, so as to reduce its solubility and promote more calcium fluoride precipitation. When the fluorine content in the raw water is low, the formation of seed crystals is more difficult, resulting in the difficulty in the formation of calcium fluoride precipitation. In this case, the use of the calcium fluoride crystallizer 1 can further improve the efficiency of fluorine removal. Using the generated calcium fluoride precipitation as a seed crystal can effectively promote the formation of more calcium fluoride precipitation. The calcium fluoride seed crystal can not only reduce the calcium ion concentration required to start the precipitation reaction, but also reduce the fluorine concentration in the wastewater to a lower level. After being treated by the calcium fluoride crystallizer 1, the calcium fluoride product can be obtained after the precipitation is dried. In addition, the carbon dioxide released by calcium carbonate during the dissolution process is also fully utilized. The gas is collected and introduced into the alkali solution outlet of the bipolar membrane device 11, and reacts with sodium hydroxide to form sodium carbonate. The generated sodium carbonate can be used as a softener for the first high-density pool 2, reacting with calcium ions in water to form calcium carbonate precipitation, thereby reducing the hardness of water. After the treatment of defluorination and calcium hardness removal, the water flows into the second high-density pool 3. At this stage, magnesium hydroxide precipitation is generated by reacting with the sodium hydroxide generated by the system, thereby further reducing the hardness of the raw water. The sulfuric acid product generated by the bipolar membrane device 11 can be used for pH adjustment in the subsequent system to ensure stable water quality. After pretreatment, the water passes through the filter device 4 and the flat membrane assembly in turn, and the final output water quality meets the Class III standard of "GB3838-2002 Surface Water Environmental Quality Standard" or the standard of "GBT19923-2005 Urban Wastewater Recycling-Industrial Water Quality". At the same time, after the concentrated water passes through the ion exchanger to remove calcium and magnesium, it is reused together with part of the produced water as the raw material for the production of acid and alkali products in the bipolar membrane device.The regenerated water produced by the first ion exchanger 6 and the second ion exchanger 7 is circulated back into the system, which not only efficiently purifies the high-salt fluoride-containing wastewater, but also maximizes the utilization of resources, with good environmental and economic benefits. The calcium fluoride crystallizer 1 of the present invention utilizes a stable calcium fluoride seed reaction process to avoid the problem of reduced treatment efficiency caused by fluctuations in reaction conditions or changes in fluorine 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 cycle, products such as calcium chloride, calcium fluoride and sodium carbonate are generated and reused in the system, maximizing resource utilization, getting rid of the dependence on external softening agents, greatly reducing operating costs, and realizing the value-added of system by-products; using self-produced sodium carbonate and sodium hydroxide to remove calcium and magnesium ions respectively, achieving effective control of raw water hardness, ensuring that the hardness problem in the water treatment process is fully solved, improving the operating efficiency of subsequent process equipment, and reducing the risk of scaling; a large amount of remaining low-concentration acid and alkali products are directly supplied to other companies, reducing inventory costs; and the high-concentration products obtained after concentration can bring higher sales prices, further improving the overall economic benefits.

[0031] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0032] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A fluorine removal and hardness reduction system without the need for external agents, characterized in that: It comprises a calcium fluoride crystallizer (1), a first high-density tank (2), a second high-density tank (3), a filtering device (4), a flat membrane device (5), a first ion exchanger (6), a second ion exchanger (7), a water production tank (8), a first concentrated water tank (9), a second concentrated water 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 crystallization device (15) and a calcium chloride collection device (16); The inlet of the calcium fluoride crystallizer (1) is connected to a raw water delivery 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-salinity fluoride-containing wastewater delivered by the raw water delivery 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 in the wastewater treated by the calcium fluoride crystallizer (1); the second high-density tank (3) is used to remove magnesium ions in 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 filtering device (4) through a delivery pipeline, and the filtering device (4) is used to filter and purify the wastewater treated by the second high-density tank (3); The outlet of the filtering device (4) is connected to the inlet of the flat membrane device (5) via a delivery pipeline, and the flat membrane device (5) is used to concentrate the wastewater filtered and purified by the filtering device (4); The first concentrated water outlet of the flat membrane device (5) is connected to the first ion exchanger (6) via a delivery pipeline, and the first ion exchanger (6) is used to remove calcium and magnesium ions from the sodium chloride concentrated water delivered by the first concentrated water outlet; The second concentrated water outlet of the flat membrane device (5) is connected to the second ion exchanger (7) via a delivery pipeline, and the second ion exchanger (7) is used to remove calcium and magnesium ions from the sodium sulfate concentrated water delivered by the second concentrated water outlet; The water production port of the flat membrane device (5) is connected to the water production pool (8) via a delivery pipeline, the outlet of the first ion exchanger (6) is connected to the first concentrated water pool (9) via a delivery pipeline, and the outlet of the second ion exchanger (7) is connected to the second concentrated water pool (10) via a delivery pipeline; The delivery pipelines of the outlet of the water production pool (8) and the outlet of the first concentrated water pool (9) are connected to the inlet of the bipolar membrane device (11); the delivery pipelines of the outlet of the water production pool (8) and the outlet of the second concentrated water pool (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) via a delivery pipeline; the calcium chloride crystallization device (15) is connected to the calcium chloride collection device (16) via a delivery pipeline; and the calcium chloride collection device (16) is connected to the calcium fluoride crystallizer (1) via a delivery pipeline; The first sludge tank (12) is also connected to the carbon dioxide collection device (13) via a delivery 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 delivery pipeline, and the sodium carbonate reaction device (14) is connected to the first high-density tank (2) via a delivery pipeline.

2. A defluorination and hardness reduction system without adding external agents according to claim 1, characterized in that: It also includes a second sludge tank (18), the sodium hydroxide output pipeline (20) of the bipolar membrane device (11) is also connected to the second high-density tank (3), and the sediment outlet of the second high-density tank (3) is connected to the second sludge tank (18) via a conveying pipeline.

3. A defluorination and hardness reduction system without adding external agents according to claim 1, characterized in that: A produced 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. A defluorination and hardness reduction system without adding external agents 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 removing fluorine and reducing hardness without adding external agents, characterized in that: The following steps are involved: The high-salt fluoride-containing wastewater is transported to a calcium fluoride crystallizer using self-produced calcium fluoride as a seed crystal, so that the high-salt fluoride-containing wastewater contacts calcium chloride to form calcium fluoride precipitation; The wastewater after the calcium fluoride crystallization treatment is sequentially pre-treated in the first high-density tank and the second high-density tank to remove calcium and magnesium ions in the wastewater respectively; The wastewater pre-treated in the first high-density tank and the second high-density tank is transported to the filter device for purification, and the wastewater purified by the filter device is transported to the flat membrane module for concentration to obtain sodium chloride concentrated water and sodium sulfate concentrated water respectively; Concentrating the flat membrane assembly to obtain sodium chloride concentrated water and sodium sulfate concentrated water is transported to the first ion exchanger and the second ion exchanger respectively, and the residual calcium and magnesium ions in the sodium chloride concentrated water and the sodium sulfate concentrated water are removed by ion exchange; The sodium chloride concentrated water and the sodium sulfate concentrated water treated by the first ion exchanger and the second ion exchanger are respectively transported to the first concentrated water tank and the second concentrated water tank, and are diluted by the self-produced water in the water production tank configured by the flat membrane module. After reaching the preset concentration, they are respectively introduced into the water inlet of the bipolar membrane device, and the sodium chloride concentrated water and the sodium sulfate concentrated water are converted into hydrochloric acid, sulfuric acid and sodium hydroxide by the bipolar membrane device; The hydrochloric acid effluent of the bipolar membrane device is passed 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 a calcium chloride solution and release carbon dioxide gas; The calcium chloride solution is introduced into the calcium chloride crystallization equipment to obtain a calcium chloride product, and the calcium chloride product is recycled to the calcium fluoride crystallizer; The carbon dioxide released during the hydrochloric acid dissolving calcium carbonate is transported to the carbon dioxide collection device for enrichment, and then passed into the 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. A method for removing fluorine and reducing hardness without adding external agents according to claim 5, characterized in that: After the waste liquid from the first high-density tank is treated to remove fluorine and calcium hardness, it flows into the second high-density tank and reacts with the sodium hydroxide generated by the bipolar membrane device to form magnesium hydroxide precipitate, thereby reducing the magnesium hardness of the waste liquid.

7. A method for removing fluorine and reducing hardness without adding external agents according to claim 5, characterized in that: The sulfuric acid effluent from the bipolar membrane device and the softened waste liquid from the second high-density tank are mixed to adjust the pH.

8. The method for removing fluorine and reducing hardness without adding external agents according to claim 5, characterized in that: The regenerated water produced by the first ion exchanger and the second ion exchanger is circulated back to the raw water delivery pipeline.

Images