A method and system for efficient fluoride removal using a combination of sulfate and phosphate

Abstract

The invention discloses a method and system for efficient fluorine removal by using sulfate and phosphate in combination, belonging to the field of water treatment technology. When fluorine-containing wastewater flows through a primary reaction tank and a primary sedimentation tank, a control system accurately controls the amount of sulfate added, and the sulfate is fully mixed in a pipeline mixer. After entering the primary reaction tank, calcium ions, fluoride ions and sulfate ions in the water react together, so that sulfate is doped in calcium fluoride particles, and calcium fluoride quickly agglomerates and sinks, so that the area of ​​the sedimentation tank is reduced by half of the original area. In order to achieve the purpose of deep fluorine removal, phosphate and calcium salt are added to the secondary defluorination system to generate more insoluble precipitates with fluoride ions, so that the fluoride ion concentration of the effluent water is reduced by less than 1 mg / L. The invention not only has a simple process flow and high automation, but also because the addition of sulfate promotes precipitation, the area of ​​the sedimentation tank is reduced, saving costs, and at the same time, because the addition of phosphate generates more insoluble precipitates, fluorine can be removed efficiently.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a method and system for efficiently removing fluorine by combining sulfate and phosphate. Background Art

[0002] Fluorine is a chemically active halogen element and an essential trace element for the human body. Excessive or insufficient intake from the outside will affect the health of the human body. Long-term drinking of water with a fluoride concentration of less than 1 mg / L is prone to dental caries, and long-term drinking of high-fluoride water is prone to fluorosis and skeletal fluorosis, and even damages the human nervous and reproductive systems. Excessive absorption of fluorine will produce toxic effects and affect the active transport of photosynthesis products across the membrane. Therefore, fluoride ions not only affect human health, but also affect the growth and development of plants.

[0003] Fluoride-containing wastewater generally comes from fluorine chemical industry, steel smelting, coal mining, battery manufacturing, semiconductor and other industries. Industrial wastewater is generally high-concentration fluoride-containing wastewater. Currently, the defluorination technologies with large-scale application are mainly chemical precipitation, coagulation precipitation and adsorption. Chemical precipitation + coagulation precipitation or chemical precipitation + adsorption are commonly used for treatment. However, these traditional methods are difficult to reduce the fluoride ion concentration to below 1 mg / L.

[0004] Calcium fluoride particles are fine, slightly soluble in solution, and not easy to settle, so the calcium salt precipitation method is difficult to meet the effluent standards; the coagulation sedimentation method is not suitable for treating high-concentration fluoride wastewater, and is often used in conjunction with the calcium salt precipitation method. Due to the fine calcium fluoride particles, a large amount of sludge will be produced during the coagulant addition process, which will increase the treatment cost. At the same time, the sedimentation tank occupies a large area due to slow sedimentation. The defluoridation agent used in the adsorption method is usually a powder. Although the contact between fluoride ions and the defluoridation agent increases, it is easy to lose and difficult to settle in actual projects.

[0005] Patent publication number CN 209428309 U discloses a wastewater chemical complexation defluorination treatment system with enhanced precipitation. The method connects the water storage area, defluorination reactor, flocculation area, and sedimentation area, and performs enhanced precipitation through a high-density sedimentation-aiding carrier addition system. However, after a shearing machine is set in the solid phase treatment area to shear and destroy the fluorine-containing flocs and the high-density sedimentation-aiding carrier, it not only increases the process flow, but also causes energy consumption.

[0006] Patent publication number CN 216687573 U discloses a fluoride ion treatment device for fluoride-containing wastewater. The fluoride removal effect is increased by improving the defluoridation agent and the online detection device. This patent designs a multi-stage sedimentation tank, which increases the land area, but the fluoride ion concentration of the effluent is only reduced to 20 mg / L, not below 1 mg / L, so it cannot meet the discharge standards.

[0007] Patent publication number CN 114890582 A discloses a system and method for efficient fluoride removal from sewage. By using a segmented device to remove fluoride in stages, the fluoride ion in sewage is reduced to below 1 mg / L. However, this method is a three-stage defluorination method, which lengthens the process flow, and the flocculation tank is set up to increase the floor space, and also increases the area of ​​the sedimentation tank, making the construction cost high. Summary of the invention

[0008] In order to solve the above technical problems, the present invention proposes a method and system for efficient fluorine removal by combining sulfate and phosphate. Calcium salt and sulfate are added to fluorine-containing wastewater during primary treatment to reduce the fluoride ion content in the wastewater to 10-20 mg / L; calcium salt and phosphate are added during secondary treatment to reduce the fluoride ion concentration in the effluent to below 1 mg / L.

[0009] To achieve the above-mentioned purpose, the present invention provides a method for efficiently removing fluorine by using sulfate and phosphate in combination, wherein sulfate and phosphate are added into the defluorination system in steps, specifically, in the process of treating fluorine-containing wastewater, calcium salt and sulfate are added in the primary treatment, and calcium salt and phosphate are added in the secondary treatment.

[0010] Furthermore, in the method for efficient fluoride removal using a combination of sulfate and phosphate, the molar ratio of calcium ions to fluoride ions in the calcium salt is (0.7-1):1, and the molar ratio of sulfate ions to fluoride ions in the sulfate is SO4 2- :F - =(1-30):1000; the molar ratio of calcium ions in calcium salts and phosphate ions to fluoride ions in phosphates is (10-20):(3-10):1.

[0011] Furthermore, in the method for efficient fluoride removal using a combination of sulfate and phosphate, the sulfate is sodium sulfate or potassium sulfate; the calcium salt is lime or calcium chloride; and the phosphate is sodium dihydrogen phosphate.

[0012] A system for efficient fluorine removal using a combination of sulfate and phosphate, using the above method, the system comprising a sulfate dosing box, a calcium salt dosing box, a primary reaction tank, a primary sedimentation tank, a secondary reaction tank, a phosphate dosing box, a secondary sedimentation tank outlet tank and a control system;

[0013] The primary reaction tank is connected to the primary sedimentation tank via a pipeline, the primary sedimentation tank is connected to the secondary reaction tank via a pipeline, the secondary reaction tank is connected to the secondary sedimentation tank via a pipeline, and the secondary sedimentation tank is connected to the effluent tank via a pipeline;

[0014] The primary reaction tank is connected to the sulfate dosing box through a first metering pump, the primary reaction tank is connected to the calcium salt dosing box through the second metering pump, the secondary reaction tank is connected to the phosphate dosing box through a third metering pump, and the secondary reaction tank is connected to the calcium salt dosing box through the second metering pump;

[0015] The control system is connected to the calcium salt dosing box through the second metering pump, the control system is connected to the sulfate dosing box through the first metering pump, the control system is connected to the phosphate dosing box through the third metering pump, and the control system is also connected to the primary reaction tank, the primary sedimentation tank, the secondary reaction tank, the secondary sedimentation tank and the effluent tank.

[0016] In the system and method of the present invention, when the fluoride-containing wastewater flows through the primary reaction tank, the fluoride ion concentration in the reaction tank is determined according to the online detection device (fluoride ion detection device), and is fed back to the dosing device through the computer control system, so that sulfate is added to the pipeline mixer in a certain proportion and fully mixed into uniform sulfate ions; the automatic detection device and the control system ensure that the molar ratio of sulfate ions to fluoride ions in the reaction tank is SO4 2- :F - =1~30:1000; at the same time, soluble calcium salt (calcium chloride or calcium hydroxide) is added into the primary reaction tank through the pipeline mixer. The stirring speed in the primary reaction tank is 200r / min and the stirring time is 30min. At this time, the sulfate ions and calcium ions in the solution react with the fluoride ions to form calcium fluoride precipitates doped with sulfate ions; after entering the primary sedimentation tank, the fine calcium fluoride particles can quickly agglomerate and become larger and settle quickly due to the doping of sulfate ions, and then the precipitates are discharged from the mud discharge hole, and the fluoride in the wastewater is removed. The principle of the secondary defluorination system is to use calcium salts and phosphates to generate more insoluble calcium fluorophosphate precipitates with fluorine. The wastewater after primary treatment enters the secondary reaction tank, and calcium salts and phosphates are added to the secondary reaction tank through the pipeline mixer. The dosage ratio can be added according to the molar ratio of calcium salt: phosphate: fluorine (10~20): (3~10): 1, and the pH range is controlled at 6~8.5. Subsequently, the wastewater enters the secondary sedimentation tank, and the effluent can meet the standards.

[0017] The method proposed by the present invention adds sulfate to the primary reaction tank, and the ratio of fluoride ions and sulfate ions in the reaction tank can be accurately regulated by the automatic detection system, so as to promote the rapid agglomeration and sedimentation of the generated fine calcium fluoride particles. The sedimentation time is shortened by 30% to 50%, the area of ​​the sedimentation tank can be reduced by half, and the turbidity of the effluent is reduced. If coagulation and sedimentation are subsequently adopted, the input of coagulant agents can be reduced, a large amount of coagulated sludge can be avoided, and the cost of sludge treatment can be saved; if the adsorption method is adopted, the addition of adsorbents can be reduced; if membrane treatment is subsequently performed, membrane pollution can also be mitigated. The automatic control system can save labor costs and improve automation and digitization. The method has the advantages of a wide range of applications and good economic benefits.

[0018] The purpose of adding sulfate in the primary defluorination system (including the primary reaction tank and the primary sedimentation tank) of the present invention is to overcome the shortcomings of the prior art. The addition of sulfate improves the properties of calcium fluoride sludge, promotes precipitation, and reduces calcium fluoride suspended matter. Calcium ions react with fluoride ions to generate calcium fluoride, and sulfate radicals after the sulfate is dissolved are adsorbed on the surface of fine calcium fluoride particles, reducing the surface zeta potential of calcium fluoride and the repulsive force between particles, and promoting agglomeration. The particle size of solid particles is increased to accelerate sedimentation, and suspended matter of particles is reduced. The sludge structure is also made more compact, and the sludge volume is smaller under the premise of the same sludge quality. At the same time, the fluoride ion concentration of the effluent can be controlled at 10-20 mg / L.

[0019] Since the present invention generates more insoluble calcium fluorophosphate in the secondary defluorination system, the fluoride ion concentration of the effluent can be reduced to less than 1 mg / L, and does not need to regenerate the adsorbent like the adsorption method, the process is simple and the treatment effect is good. In the treatment process, the primary reaction tank, the secondary sedimentation tank, the secondary reaction tank, the secondary sedimentation tank, and the effluent tank are connected in sequence according to the water inlet direction, and the process flow is simple and the automation is high. Two sections of pipeline mixers are set in the water inlet direction. The first pipeline mixer and the second pipeline mixer are connected in sequence, and the fluoride-containing wastewater first flows through the first pipeline mixer, and then flows through the second pipeline mixer to enter the primary reaction tank. The first pipeline mixer is connected to the sulfate dosing device (sulfate dosing box), and the second pipeline mixer is connected to the calcium salt dosing device (calcium salt dosing box). The sulfate dosage is controlled by the first metering pump, and after being added to the first pipeline mixer and fully mixed, it enters the second pipeline mixer with the wastewater and then enters the primary reaction tank. In this way, on the one hand, the reagent is fully mixed and diluted; on the other hand, it is ensured that there are sulfate radicals at the same time as calcium fluoride is generated, which promotes the agglomeration of calcium fluoride.

[0020] Furthermore, a first water inlet, a first PAM dosing port and a first pH dosing port are sequentially arranged at the bottom of one side of the primary reaction tank from bottom to top, and a first water outlet and a first mud discharge port are arranged on the other side; the water inlet is connected to a first pipeline mixer and a second pipeline mixer, the first pipeline mixer is connected to the sulfate dosing box through the first metering pump, the second pipeline mixer is connected to the calcium salt dosing box through the second metering pump, and the water inlet ends of the two pipeline mixers are connected to the metering pumps of the dosing device (referring to the sulfate dosing box or the calcium salt dosing box).

[0021] Furthermore, a second water inlet is provided on one side of the primary sedimentation tank, a first baffle and a first inclined tube are provided inside the primary sedimentation tank, a second water outlet is provided on the other side, and a sedimentation tank mud discharge port is provided at the bottom. After being blocked by the first baffle, the wastewater entering the primary sedimentation tank enters the first inclined tube from the bottom for sedimentation, flows out through the second water outlet after sedimentation, and enters the secondary defluorination treatment system (including the secondary reaction tank and the secondary sedimentation tank).

[0022] Furthermore, the bottom of one side of the secondary reaction tank is provided with a third water inlet, a third PAM dosing port and a third pH dosing port in sequence from bottom to top, and the other side is provided with a third water outlet and a second mud outlet, the third water inlet is connected to a third pipeline mixer and a fourth pipeline mixer, the third pipeline mixer is connected to the phosphate dosing box through the third metering pump, and the fourth pipeline mixer is connected to the second metering pump. The effluent of the primary sedimentation tank passes through two sections of pipeline mixers, the third pipeline mixer near one end of the water inlet is connected to the phosphate dosing device, the second section is the fourth pipeline mixer for adding calcium salt, and the calcium salt and phosphate are fully mixed and enter the secondary reaction tank.

[0023] Furthermore, the secondary sedimentation tank is provided with a fourth water inlet on one side, a second baffle and a second inclined tube are provided inside, and a fourth water outlet is provided on the other side, and the fourth water outlet is connected to the outlet tank through a pipeline. After being blocked by the second baffle, the wastewater entering the secondary sedimentation tank enters the second inclined tube from the bottom for sedimentation, and after sedimentation, flows out through the fourth water outlet and enters the outlet tank.

[0024] Furthermore, the primary reaction pool, the primary sedimentation pool, the secondary reaction pool, the secondary sedimentation pool and the outlet pool are all connected to a control system by a fluoride ion detection device, and the control system is controlled by a computer. The control system feeds back the fluoride ion concentration and sulfate concentration information to the metering pump to ensure accurate dosage, so that the sulfate can fully play its role and remove fluorine efficiently. The fluoride ion detection device connected to the primary reaction pool can detect the fluoride ion concentration in the primary reaction pool and transmit it to the control system. According to the molar ratio of sulfate ion to fluoride ion, SO4 2- :F -=(1-30):1000 to calculate the amount of sulfate that needs to be added, and control the sulfate dosing box to add the required amount of sulfate to the first pipeline mixer. The fluoride ion detection device connected to the secondary reaction tank can detect the fluoride ion concentration in the secondary reaction tank and transmit it to the control system, and calculate the amount of calcium salt and phosphate that need to be added according to the molar ratio of calcium salt: phosphate: fluorine (10-20):(3-10):1, and control the phosphate dosing box to add the required amount of phosphate to the third pipeline mixer, and the calcium salt dosing box adds the required calcium salt to the fourth pipeline mixer, and the calcium salt and phosphate are fully mixed and enter the secondary reaction tank.

[0025] Furthermore, the pH in the primary reaction tank is 9.5-12.5, the stirring speed is 200r / min, and the stirring time is 30min; the precipitation time in the primary precipitation tank is 30min;

[0026] The pH in the secondary reaction tank is 6-8.5, the stirring speed is 100 r / min, and the stirring time is 30 min; the precipitation time in the secondary precipitation tank is 60 min.

[0027] Furthermore, the agent for adjusting pH is hydrochloric acid or sodium hydroxide.

[0028] Furthermore, stirring paddles are arranged in the calcium salt dosing box, the sulfate dosing box, the phosphate dosing box, the primary reaction tank and the secondary reaction tank.

[0029] When the fluoride-containing wastewater flows through the primary reaction tank and the primary sedimentation tank, the control system accurately controls the amount of sulfate added. The sulfate is fully mixed in the pipeline mixer. After entering the primary reaction tank, the calcium ions, fluoride ions and sulfate ions in the water react together, so that the sulfate is doped in the calcium fluoride particles. Therefore, in the primary sedimentation tank, the calcium fluoride can quickly agglomerate and sink, so that the area of ​​the sedimentation tank is reduced by half of the original area. In order to achieve the purpose of deep defluorination, phosphate and calcium salt are added to the secondary defluorination system to generate more insoluble precipitates with fluoride ions, so that the fluoride ion concentration of the effluent is reduced by less than 1 mg / L. The present invention not only has a simple process flow and high automation, but also promotes precipitation due to the addition of sulfate, thereby reducing the area of ​​the sedimentation tank, saving the addition of coagulants and flocculants, and saving costs. At the same time, due to the addition of phosphate to generate more insoluble precipitates, fluorine can be removed efficiently.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] 1. The present invention adds sulfate and calcium fluoride particles, and can enter the secondary reaction tank without the need for additional coagulant (such as PAC), thereby reducing the floor space of the coagulation tank. The calcium fluoride particles become larger, which can increase the surface load of the sedimentation tank, reduce the area of ​​the sedimentation tank, and save investment costs.

[0032] 2. In the primary defluorination system, the addition of sulfate improves the properties of the sludge, and the structure of the sludge becomes tighter. If membrane treatment is carried out, membrane pollution can be slowed down; suspended solids are reduced, and if adsorption treatment is carried out later, the input of adsorbent can be reduced, thereby improving the defluorination effect.

[0033] 3. The secondary defluorination system uses calcium salt, phosphate and fluoride ion to generate calcium fluorophosphate, which can reduce the fluoride ion concentration of the effluent to 1 mg / L, achieving the purpose of deep and efficient fluoride removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0035] Figure 1 This is a comparison of the sedimentation effects of calcium fluoride particles generated after the solution without sulfate addition (left) and the solution with sulfate addition (right);

[0036] Figure 2 This is a comparison diagram of XRD of the precipitated product after adding sulfate to the solution in Example 5;

[0037] Figure 3 This is a scanning electron microscope morphology of the calcium fluoride precipitate after sulfate-promoted precipitation in Example 5;

[0038] Figure 4 This is a flow chart of the method for efficient fluorine removal using a combination of sulfate and phosphate according to the present invention;

[0039] Figure 5 The schematic diagram of the efficient fluorine removal system for combined use of sulfate and phosphate of the present invention, wherein 1, sulfate dosing box; 2-1, first metering pump; 2-2, second metering pump; 2-3, third metering pump; 3, calcium salt dosing box; 4-1, first pipeline mixer; 4-2, second pipeline mixer; 4-3, third pipeline mixer; 4-4, fourth pipeline mixer; 5, primary reaction tank; 6-1, first water inlet; 6-2, third water inlet; 7-1, first mud outlet; 7-2, second mud outlet; 8-1, first PAM dosing port; 8-2, third PAM dosing port; 9-1, first pH dosing port; 9-2, third pH dosing port; 10-1, first water outlet; 10-2, third water outlet; 11, first inclined pipe; 12, second water outlet; 13, first partition; 14, primary sedimentation tank; 15, sedimentation tank sludge outlet; 16, fluoride ion detection device; 17, secondary reaction tank; 18, phosphate dosing box; 19, secondary sedimentation tank; 20, control system; 21, water outlet tank. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0045] The process flow chart of the method for efficient fluorine removal by using sulfate and phosphate in combination according to the present invention is shown in Figure 4 The schematic diagram of the efficient fluorine removal system using sulfate and phosphate in combination is shown in Figure 5, where 1, sulfate dosing box; 2-1, first metering pump; 2-2, second metering pump; 2-3, third metering pump; 3, calcium salt dosing box; 4-1, first pipeline mixer; 4-2, second pipeline mixer; 4-3, third pipeline mixer; 4-4, fourth pipeline mixer; 5, primary reaction tank; 6-1, first water inlet; 6-2, third water inlet; 7-1, first mud outlet; 7-2, second mud outlet; 8-1, first PAM dosing port ; 8-2, the third PAM dosing port; 9-1, the first pH dosing port; 9-2, the third pH dosing port; 10-1, the first water outlet; 10-2, the third water outlet; 11, the first inclined pipe; 12, the second water outlet; 13, the first partition; 14, the primary sedimentation tank; 15, the sedimentation tank mud outlet; 16, the fluoride ion detection device; 17, the secondary reaction tank; 18, the phosphate dosing box; 19, the secondary sedimentation tank; 20, the control system; 21, the water outlet tank.

[0046] The embodiment of the present invention provides a method for efficiently removing fluorine by using sulfate and phosphate in combination, wherein sulfate and phosphate are added into the defluorine removal system in steps. Specifically, in the process of treating fluorine-containing wastewater, calcium salt and sulfate are added in the primary treatment, and calcium salt and phosphate are added in the secondary treatment.

[0047] In the embodiment of the present invention, the molar ratio of calcium ion to fluoride ion in the calcium salt is (0.7-1):1, and the molar ratio of sulfate ion to fluoride ion in the sulfate is SO4 2- :F - =(1-30):1000; the molar ratio of calcium ions in calcium salts and phosphate ions to fluoride ions in phosphates is (10-20):(3-10):1.

[0048] In an embodiment of the present invention, the sulfate is sodium sulfate or potassium sulfate; the calcium salt is lime or calcium chloride; and the phosphate is sodium dihydrogen phosphate.

[0049] In an embodiment of the present invention, a system for efficient fluoride removal using sulfate and phosphate in combination includes a sulfate dosing box 1, a calcium salt dosing box 3, a primary reaction tank 5, a primary sedimentation tank 14, a secondary reaction tank 17, a phosphate dosing box 18, a secondary sedimentation tank 19, a water outlet tank 21 and a control system 20;

[0050] The primary reaction tank 5 is connected to the primary sedimentation tank 14 through a pipeline, the primary sedimentation tank 14 is connected to the secondary reaction tank 17 through a pipeline, the secondary reaction tank 17 is connected to the secondary sedimentation tank 19 through a pipeline, and the secondary sedimentation tank 19 is connected to the effluent tank 21 through a pipeline;

[0051] The primary reaction tank 5 is connected to the sulfate dosing box 1 through the first metering pump 2-1, the primary reaction tank 5 is connected to the calcium salt dosing box 3 through the second metering pump 2-2, the secondary reaction tank 17 is connected to the phosphate dosing box 18 through the third metering pump 2-3, and the secondary reaction tank 17 is connected to the calcium salt dosing box 3 through the second metering pump 2-2;

[0052] The control system 20 is connected to the calcium salt dosing box 3 through the second metering pump 2-2, the control system 20 is connected to the sulfate dosing box 1 through the first metering pump 2-1, the control system 20 is connected to the phosphate dosing box 18 through the third metering pump 2-3, and the control system 20 is also connected to the primary reaction tank 5, the primary sedimentation tank 14, the secondary reaction tank 17, the secondary sedimentation tank 19 and the effluent tank 21.

[0053] In an embodiment of the present invention, a first water inlet 6-1, a first PAM dosing port 8-1 and a first pH dosing port 9-1 are sequentially arranged at the bottom of one side of the primary reaction tank 5 from bottom to top, and a first water outlet 10-1 and a first mud discharge port 7-1 are arranged on the other side; the water inlet 6 is connected to a first pipeline mixer 4-1 and a second pipeline mixer 4-2, the first pipeline mixer 4-1 is connected to the sulfate dosing box 1 through the first metering pump 2-1, and the second pipeline mixer 4-2 is connected to the calcium salt dosing box 3 through the second metering pump 2-2.

[0054] In an embodiment of the present invention, a second water inlet is provided on one side of the primary sedimentation tank 14, a first baffle 13 and a first inclined tube 11 are provided inside the primary sedimentation tank 14, a second water outlet 12 is provided on the other side, and a sedimentation tank mud discharge port 15 is provided at the bottom.

[0055] In an embodiment of the present invention, a third water inlet 6-2, a third PAM dosing port 8-2 and a third pH dosing port 9-2 are sequentially arranged at the bottom of one side of the secondary reaction tank 17 from bottom to top, and a third water outlet 10-2 and a second mud discharge port 7-2 are arranged on the other side. The third water inlet 6-2 is connected to the third pipeline mixer 4-3 and the fourth pipeline mixer 4-4. The third pipeline mixer 4-3 is connected to the phosphate dosing box 18 through the third metering pump 2-3, and the fourth pipeline mixer 4-4 is connected to the second metering pump 2-2.

[0056] In an embodiment of the present invention, a fourth water inlet is provided on one side of the secondary sedimentation tank 19, a second partition and a second inclined tube are provided inside, and a fourth water outlet is provided on the other side, and the fourth water outlet is connected to the water outlet tank 21 through a pipeline.

[0057] In an embodiment of the present invention, the primary reaction tank 5, the primary sedimentation tank 14, the secondary reaction tank 17, the secondary sedimentation tank 19 and the effluent tank 21 are all connected to a control system 20 via a fluoride ion detection device 16, and the control system 20 is controlled by a computer.

[0058] In the embodiment of the present invention, the pH in the primary reaction tank 5 is 9.5-12.5, the stirring speed is 200r / min, and the stirring time is 30min; the precipitation time in the primary precipitation tank 14 is 30min;

[0059] The pH in the secondary reaction tank 17 is 6-8.5, the rotation speed is 100 r / min, and the stirring time is 30 min; the precipitation time in the secondary precipitation tank 19 is 60 min.

[0060] In the embodiment of the present invention, the agent for adjusting pH is hydrochloric acid or sodium hydroxide. The calcium salt dosing box 3, the sulfate dosing box 1, the phosphate dosing box 8, the primary reaction tank 5, and the secondary reaction tank 17 are all provided with stirring paddles.

[0061] Example 1

[0062] Treat 30m3 of fluoride wastewater containing 2200mg / L of a battery disassembly liquid at one time 3 The wastewater enters the primary reaction tank 5 through the preceding process pipeline, passes through the fluoride ion concentration detection device 16, and is fed back to the sulfate dosing box 1 through the control system 20 to automatically add 0.5g of sodium sulfate in the form of a concentrated solution into the first pipeline mixer 4-1 for dilution and mixing and enters the primary reaction tank 5. 20wt% lime slurry is prepared in the calcium salt dosing box 3, and 0.92m 3 The lime slurry is used to make the calcium ion content in the mixed solution 5000 mg / L and the pH value 9.5. The solution is stirred at a stirring speed of 200 r / min for 30 minutes in the primary reaction tank 5. The mixed solution enters the primary sedimentation tank 14, and the bottom mud is discharged after sedimentation for 30 minutes. The fluoride ion concentration of the effluent from the primary sedimentation tank 14 is 19 mg / L. According to the same method as above, under the promotion of sulfate, the fluoride ion concentration of the effluent from the primary defluoridation at different pH values ​​(fluoride ion concentration of the effluent from the primary sedimentation tank 14) is shown in Table 1.

[0063] Table 1 Fluoride ion concentration in the effluent of primary defluoridation at different pH values ​​under the promotion of sulfate

[0064]

[0065] The supernatant in the primary sedimentation tank 14 enters the secondary defluorination system. In the secondary reaction tank 17, calcium salt and phosphate are added according to different molar ratios, and 1 mg / L of 0.1wt% PAM is added. After reacting at a speed of 100 r / min for 30 minutes in the secondary reaction tank 17, it enters the secondary sedimentation tank 19 for precipitation for 60 minutes. The fluoride ion concentration of the effluent after the secondary treatment is shown in Tables 2 and 3, and the discharge meets the standard.

[0066] Table 2 Fluoride ion concentration in effluent after secondary defluoridation with different molar ratios of calcium salt and phosphate

[0067]

[0068]

[0069] Table 3 Fluoride ion concentration in the effluent after secondary treatment and secondary defluorination at different pH in the secondary reaction tank (pH of the primary sedimentation tank is 9.5)

[0070]

[0071] Comparative Example 1

[0072] 21.3 mg of sodium sulfate was added to 50 mL of 1900 mg / L fluoride ion solution to dissolve. The molar ratio of sulfate ion to fluoride ion in the solution was SO4 2- :F - =3:100; add 1mL of 1mol / L calcium chloride solution to 50mL of fluoride ion solution, set the stirring speed to 200r / min, stir for 30min, and let it stand. And compare it with the experiment without adding sulfate ions under the same conditions. The comparison of the precipitation effect of calcium fluoride particles generated by the solution without adding sulfate (left) and the solution with adding sulfate (right) is shown in Figure 1 From the precipitation effect, it can be seen that after adding sulfate ions, the time for calcium fluoride particles in the solution to be completely precipitated is reduced by 30 minutes. The supernatant is clearer, which accelerates the sedimentation of calcium fluoride particles.

[0073] Example 2

[0074] 21.3 mg of sodium sulfate was added to 50 mL of 1900 mg / L fluoride ion solution to dissolve. The molar ratio of sulfate ion to fluoride ion in the solution was SO4 2- :F -=3:100; add 1mL of 1mol / L calcium chloride solution to 50mL of fluoride ion solution; place on a magnetic stirrer, stirring at a speed of 200r / min; take 5mL of the solution 2.0cm below the liquid surface and pour it into a cuvette, and use a nanoparticle size analyzer to measure the particle size of calcium fluoride. And compare it with the experiment without adding sulfate ions to the solution under the same conditions. The data shows that sulfate ions promote the increase of calcium fluoride particle size from 800nm ​​to 2400nm, promote the aggregation of calcium fluoride particles, and accelerate the precipitation of calcium fluoride.

[0075] Example 3

[0076] This example is the same as Example 2 in each step, except that the amount of sodium sulfate added is 7.1 mg. 7.1 mg of sodium sulfate is added to 50 mL of 1900 mg / L fluoride ion solution to dissolve. At this time, the molar ratio of sulfate ion to fluoride ion in the solution is SO4 2- :F - =1:100; add 1mL of 1mol / L calcium chloride solution to 50mL of fluoride ion solution; place on a magnetic stirrer, stirring at a speed of 200r / min; take 5mL of the solution 2.0cm below the liquid surface and pour it into a cuvette, and use a nanoparticle size analyzer to measure the particle size of calcium fluoride. And compare it with the experiment without adding sulfate ions to the solution under the same conditions. The data shows that sulfate ions promote the increase of the particle size of calcium fluoride particles from 800nm ​​to 1600nm, promote the aggregation of calcium fluoride particles, and accelerate the precipitation of calcium fluoride.

[0077] Example 4

[0078] This example is the same as Example 2 in each step, except that the amount of sodium sulfate added is 0.71 mg. 0.71 mg of sodium sulfate is added to 50 mL of 1900 mg / L fluoride ion solution to dissolve. At this time, the molar ratio of sulfate ion to fluoride ion in the solution is SO4 2- :F - =1:1000; add 1mL of 1mol / L calcium chloride solution to 50mL of fluoride ion solution; place on a magnetic stirrer, stirring at a speed of 200r / min; take 5mL of the solution 2.0cm below the liquid surface and pour it into a cuvette, and use a nanoparticle size analyzer to measure the particle size of calcium fluoride. And compare it with the experiment without adding sulfate ions to the solution under the same conditions. The data shows that sulfate ions promote the increase of the particle size of calcium fluoride particles from 800nm ​​to 1000nm, promote the aggregation of calcium fluoride particles, and accelerate the precipitation of calcium fluoride.

[0079] Example 5

[0080] 21.3 mg of sodium sulfate was added to 50 mL of 1900 mg / L fluoride ion solution to dissolve. The molar ratio of sulfate ion to fluoride ion in the solution was SO4 2- :F - =3:100; add 1mL of 1mol / L calcium chloride solution to 50mL of fluoride ion solution and let it stand for 30min. Use filter membrane to separate calcium fluoride solid precipitate from solution, dry in 65℃ oven for 6h, and measure XRD. Compare with the experiment without adding sulfate ion to solution under the same conditions. The XRD comparison diagram of the precipitate product after adding sulfate to the solution in this example is shown in Figure 2 The scanning electron microscope morphology of calcium fluoride precipitate after sulfate-promoted precipitation is shown in Figure 3 , indicating that the main crystal form of the precipitate is calcium fluoride. The incorporation of sulfate ions does not affect the main crystal form of calcium fluoride, but the peak intensity of the X-ray diffraction characteristic peak becomes significantly weaker with the incorporation of sulfate ions.

[0081] Example 6

[0082] Treat 30m3 of fluoride wastewater containing 2200mg / L of a battery disassembly liquid at one time 3 The wastewater enters the reaction tank through the previous process pipeline. After the fluoride ion concentration detection device, it is fed back to the dosing system through the control system and automatically adds 0.5g of sodium sulfate in the form of a concentrated solution into the pipeline mixing tank for dilution and mixing and then enters the reaction tank. 20wt% lime slurry is prepared in the soluble calcium salt dosing box, and 0.92m 3 Lime slurry is used to make the calcium ion content in the mixed solution 5000mg / L, and it is stirred in the reaction tank for 30 minutes; the mixture also enters the sedimentation tank, and the bottom mud is discharged after sedimentation for 30 minutes. The supernatant is then treated with aluminum salt coagulation process, with 800mg / L aluminum salt added and 0.1wt% PAM added, and then mixed and allowed to stand. The fluoride ion concentration of the supernatant in the sedimentation tank was measured to be 20mg / L, and the fluoride ion concentration of the effluent after deep treatment was 3.4mg / L, which meets the discharge standard. The amount of coagulant added is reduced by about 30% compared with the previous process.

[0083] The above Example 1 shows that by adding sulfate and phosphate step by step into the defluorination system, fluorine can be removed efficiently and deeply. Example 2, Example 3, and Example 4 show the method of defluorination by precipitation of sulfate. The increase in the addition of sulfate reduces the repulsive force between calcium fluoride particles, and the larger the particle size of calcium fluoride particles, the faster the sedimentation rate. Compared with no addition of inorganic ions, the precipitation rate is greatly improved. Example 6 shows that after adding sulfate, the system meets the requirements of subsequent coagulation treatment and reduces the input of coagulant.

[0084] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for reducing the fluorine concentration in fluoride-containing wastewater to below 1 mg / L, It is characterized in that Adding sulfate and phosphate into the defluorination system in steps, specifically, in the process of treating fluoride-containing wastewater, adding calcium salt and sulfate in the primary treatment, and adding calcium salt and phosphate in the secondary treatment; In the primary treatment, the molar ratio of calcium ion to fluoride ion in calcium salt is (0.7-1):1, and the molar ratio of sulfate ion to fluoride ion in sulfate is SO 4 2- :F - =(1-30):1000; in the secondary treatment, the molar ratio of calcium ions in calcium salts, phosphate ions in phosphates and fluoride ions is (10-20):(3-10):1; The sulfate is sodium sulfate or potassium sulfate; the calcium salt is lime or calcium chloride; and the phosphate is sodium dihydrogen phosphate.

2. A system for efficient fluoride removal using a combination of sulfate and phosphate, It is characterized in that The method according to claim 1 is adopted, wherein the system comprises a sulfate dosing box (1), a calcium salt dosing box (3), a primary reaction tank (5), a primary sedimentation tank (14), a secondary reaction tank (17), a phosphate dosing box (18), a secondary sedimentation tank (19), a water outlet tank (21) and a control system (20); The primary reaction tank (5) is connected to the primary sedimentation tank (14) via a pipeline, the primary sedimentation tank (14) is connected to the secondary reaction tank (17) via a pipeline, the secondary reaction tank (17) is connected to the secondary sedimentation tank (19) via a pipeline, and the secondary sedimentation tank (19) is connected to the effluent tank (21) via a pipeline; The primary reaction tank (5) is connected to the sulfate dosing box (1) via a first metering pump (2-1), the primary reaction tank (5) is connected to the calcium salt dosing box (3) via a second metering pump (2-2), the secondary reaction tank (17) is connected to the phosphate dosing box (18) via a third metering pump (2-3), and the secondary reaction tank (17) is connected to the calcium salt dosing box (3) via the second metering pump (2-2); The control system (20) is connected to the calcium salt dosing box (3) through the second metering pump (2-2), the control system (20) is connected to the sulfate dosing box (1) through the first metering pump (2-1), the control system (20) is connected to the phosphate dosing box (18) through the third metering pump (2-3), and the control system (20) is also connected to the primary reaction tank (5), the primary sedimentation tank (14), the secondary reaction tank (17), the secondary sedimentation tank (19) and the effluent tank (21).

3. A system for efficient fluorine removal using a combination of sulfate and phosphate according to claim 2, It is characterized in that A first water inlet (6-1), a first PAM dosing port (8-1) and a first pH dosing port (9-1) are sequentially arranged at the bottom of one side of the primary reaction tank (5) from bottom to top, and a first water outlet (10-1) and a first mud discharge port (7-1) are arranged at the other side; the water inlet (6) is connected to a first pipeline mixer (4-1) and a second pipeline mixer (4-2); the first pipeline mixer (4-1) is connected to the sulfate dosing box (1) via the first metering pump (2-1); and the second pipeline mixer (4-2) is connected to the calcium salt dosing box (3) via the second metering pump (2-2).

4. A system for efficient fluorine removal using a combination of sulfate and phosphate according to claim 2, It is characterized in that A second water inlet is arranged on one side of the primary sedimentation tank (14), a first baffle (13) and a first inclined tube (11) are arranged inside the primary sedimentation tank (14), and a second water outlet (12) is arranged on the other side.

5. A system for efficient fluorine removal using a combination of sulfate and phosphate according to claim 2, It is characterized in that A third water inlet (6-2), a third PAM dosing port (8-2) and a third pH dosing port (9-2) are sequentially arranged at the bottom of one side of the secondary reaction tank (17) from bottom to top, and a third water outlet (10-2) and a second mud discharge port (7-2) are arranged at the other side. The third water inlet (6-2) is connected to a third pipeline mixer (4-3) and a fourth pipeline mixer (4-4). The third pipeline mixer (4-3) is connected to the phosphate dosing box (18) via the third metering pump (2-3), and the fourth pipeline mixer (4-4) is connected to the second metering pump (2-2).

6. A system for efficient fluorine removal using a combination of sulfate and phosphate according to claim 2, It is characterized in that The secondary sedimentation tank (19) is provided with a fourth water inlet on one side, a second partition plate and a second inclined tube are provided inside, and a fourth water outlet is provided on the other side. The fourth water outlet is connected to the water outlet tank (21) through a pipeline.

7. A system for efficient fluorine removal using a combination of sulfate and phosphate according to claim 2, It is characterized in that The primary reaction tank (5), the primary sedimentation tank (14), the secondary reaction tank (17), the secondary sedimentation tank (19) and the effluent tank (21) are all connected to a control system (20) via a fluoride ion detection device (16), and the control system (20) is controlled by a computer.

8. A system for efficient fluorine removal using a combination of sulfate and phosphate according to claim 2, It is characterized in that The pH in the primary reaction tank (5) is 9.5-12.5, the stirring speed is 200 r / min, and the stirring time is 30 min; the precipitation time in the primary precipitation tank (14) is 30 min; The pH in the secondary reaction tank (17) is 6-8.5, the stirring speed is 100 r / min, and the stirring time is 30 min; the precipitation time in the secondary precipitation tank (19) is 60 min.

Images