A method and system for regulating fluorine-containing groundwater defluorination

Abstract

The present application belongs to the technical field of fluorine-containing water treatment, and relates to a regulation method and a regulation system for defluorination of fluorine-containing underground water. The regulation method comprises the following steps: obtaining the fluorine ion concentration, alkalinity and magnesium ion concentration of the actual fluorine-containing underground water; preparing simulated fluorine-containing underground water and a phosphoric acid solution, first making the fluorine concentration of the simulated fluorine-containing water same as the fluorine ion concentration of the actual fluorine-containing underground water; then continuously increasing the alkalinity of the simulated fluorine-containing water until the alkalinity of the simulated fluorine-containing water is same as the alkalinity of the actual fluorine-containing underground water, and adding an acid agent into the phosphoric acid solution; on the basis of the alkalinity reaching the alkalinity of the actual fluorine-containing underground water, adding magnesium salt into the simulated fluorine-containing water so that the magnesium ion concentration of the simulated fluorine-containing water is same as the magnesium ion concentration of the actual fluorine-containing underground water; then, replacing the simulated fluorine-containing water with the actual fluorine-containing water, so that the fluorine concentration of the effluent can be reduced to below 1.0 mg / L. The problem that the fluorine calcium phosphate precipitation reaction is invalid when the fluorine calcium phosphate precipitation method is used to treat the actual fluorine-containing underground water is solved.

Description

Technical Field

[0001] This invention belongs to the field of fluoride-containing water treatment technology, specifically a control method and control system for defluoridation of fluoride-containing groundwater. Background Technology

[0002] According to the requirements of the "Standards for Drinking Water Quality (GB5749-2022)", the concentration of fluoride ions in drinking water should be lower than 1.0 mg / L.

[0003] Common defluoridation methods include adsorption, ion exchange, electrocoagulation, membrane separation, and chemical precipitation. Adsorbents and ion exchangers have high regeneration costs and rapid performance degradation. Electrocoagulation and membrane separation are complex and costly, limiting their large-scale application. Chemical precipitation is effective for treating high-concentration fluoride water, but the sedimentation tanks require a large area, and the sludge has a high water content, limiting its application.

[0004] Calcium fluoride precipitation can reduce fluoride levels in water from hundreds or thousands of milligrams per liter to 10-20 mg / L, making it suitable for defluoridation of industrial wastewater but not for groundwater. In the 1990s, calcium fluorophosphate precipitation emerged, achieving defluoridation with a high calcium to phosphorus molar ratio (tens of times) and a long reaction time (72-96 hours). However, this method has consistently only been effective for treating simulated fluoride-containing water (pure water + NaF), failing to treat actual fluoride-containing groundwater. Technical personnel in this field have been unable to determine the underlying cause.

[0005] Therefore, a new process is urgently needed to remove fluoride from fluoride-containing groundwater. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for defluoridation of fluoride-containing groundwater, and to solve the problem of calcium fluorophosphate precipitation reaction failure when treating actual fluoride-containing groundwater by the calcium fluorophosphate precipitation method.

[0007] This invention is achieved through the following technical solution:

[0008] On one hand, this invention discloses a method for regulating the removal of fluoride from fluoride-containing groundwater, comprising the following processes:

[0009] S1. Obtain the fluoride ion concentration, alkalinity, and magnesium ion concentration of the actual fluoride-containing groundwater to be treated;

[0010] S2. Prepare a simulated fluoride-containing water and phosphoric acid solution; the fluoride concentration of the simulated fluoride-containing water is the same as the fluoride ion concentration of the actual fluoride-containing groundwater;

[0011] Phosphoric acid solution was mixed with simulated fluoride-containing water, and after calcium precipitation reaction, the fluoride concentration in the effluent was reduced to less than 1.0 mg / L.

[0012] S3. Continuously increase the alkalinity of the simulated fluoride-containing water until the alkalinity of the simulated fluoride-containing water is the same as that of the actual fluoride-containing groundwater.

[0013] An acid is added to a phosphoric acid solution, and the acidified phosphoric acid solution is mixed with alkalized simulated fluoride-containing water. The pH of the mixed solution is controlled at 5.0-6.0. After calcium precipitation reaction treatment, the fluoride concentration in the effluent is reduced to less than 1.0 mg / L.

[0014] S4. Based on the alkalinity reaching that of actual fluoride-containing groundwater, magnesium salts are continuously added to the simulated fluoride-containing water according to the concentration characteristics of magnesium ions in the actual fluoride-containing groundwater, so that the magnesium ion concentration of the simulated fluoride-containing water is the same as that of the actual fluoride-containing groundwater.

[0015] The acidified phosphoric acid solution was mixed with simulated fluoride-containing water containing magnesium salt. The pH of the mixed solution was controlled at 5.0-6.0. After calcium precipitation treatment, the fluoride concentration in the effluent was less than 1.0 mg / L.

[0016] S5. Replace the simulated fluoride-containing water with the actual fluoride-containing groundwater to be treated. At this time, the fluoride concentration in the effluent can be guaranteed to drop to below 1.0 mg / L.

[0017] Furthermore, the calcium source required for the calcium precipitation reaction is provided by the waste seashell particles filling the reactor.

[0018] Furthermore, in S3, bicarbonate is added to increase the alkalinity of the simulated fluoride-containing water;

[0019] In S3, the acid used is hydrochloric acid or sulfuric acid;

[0020] In S4, the magnesium salt is either magnesium chloride or magnesium sulfate.

[0021] Furthermore, in S2, after the phosphoric acid solution is mixed with the simulated fluoride-containing water, the molar ratio of phosphate ions to fluoride ions in the mixed solution is (2.0~6.0):1.

[0022] Furthermore, in S3, after the acidified phosphoric acid solution is mixed with the alkalized simulated fluoride-containing water, the molar ratio of phosphate ions to fluoride ions in the mixed solution is (2.0~6.0):1.

[0023] Furthermore, in S4, the phosphoric acid solution after adding acid is mixed with the simulated fluoride-containing water after adding magnesium salt, and the molar ratio of phosphate to fluoride ions in the mixed solution is (2.0~6.0):1.

[0024] On the other hand, the present invention also discloses a control system based on the control method for defluoridation of fluoride-containing groundwater, including a raw water tank, a dosing tank, a first inlet pump, a dosing pump, a pipeline mixer, a mixing storage tank, a second inlet pump, a fixed bed reactor, and an outlet tank.

[0025] Both the simulated fluoride-containing water and the actual groundwater are stored in the raw water tank during operation;

[0026] The phosphoric acid solution and the acidified phosphoric acid solution were added to the dosing tank;

[0027] The raw water tank is connected to the No. 1 inlet pump, and the chemical dosing tank is connected to the chemical dosing pump.

[0028] Both the No. 1 inlet pump and the dosing pump are connected to the pipeline mixer, which is connected to the mixing storage tank.

[0029] The outlet of the mixing tank is connected to the fixed-bed reactor via a second inlet pump; the effluent from the fixed-bed reactor is connected to the effluent tank via a pipeline.

[0030] The raw water tank is equipped with a real-time fluoride ion concentration monitor and an alkalinity meter.

[0031] The mixing tank is equipped with a real-time pH monitoring meter.

[0032] The effluent tank is equipped with a No. 2 real-time pH monitoring meter and a No. 2 real-time fluoride ion concentration monitoring meter.

[0033] Furthermore, the fixed-bed reactor is filled with waste seashell particles with a particle size of 0.5-1 mm.

[0034] Furthermore, the fixed-bed reactor has an inlet at the bottom and an outlet at the top; the outlet of the mixing storage tank is connected to the inlet of the fixed-bed reactor via a second inlet pump; the effluent from the fixed-bed reactor is connected to the effluent tank via a pipeline through the outlet.

[0035] The raw water tank has an inlet on one side and an outlet on the other side;

[0036] The dosing tank has a drug inlet on one side and a drug outlet on the other side.

[0037] The mixing water storage tank has a mixing water inlet on one side and a mixing water outlet on the other side; the outlet tank has a drain outlet on one side and a water inlet at the top.

[0038] Furthermore, the fixed-bed reactor is also equipped with a post-inlet phase; a third inlet pump is installed between the fixed-bed reactor and the effluent tank;

[0039] When flushing the fixed-bed reactor, the effluent collected in the effluent tank is used as flushing water, and the effluent tank is connected to the influent of the fixed-bed reactor through the No. 3 influent pump.

[0040] Compared with the prior art, the present invention has the following beneficial technical effects:

[0041] This invention discloses a method for regulating the defluoridation of fluoride-containing groundwater. Based on the fluoride ion concentration, alkalinity, and magnesium ion concentration in the actual fluoride-containing water, simulated fluoride-containing water is prepared. The method is then used to regulate the start-up phase of the defluoridation system, determining the dosage of phosphoric acid and acidifier corresponding to the actual fluoride-containing groundwater. This method effectively addresses the coexistence of high alkalinity and high magnesium ion concentrations with fluoride ions in the water, ensuring that the effluent fluoride ion concentration is less than 1.0 mg / L after the actual groundwater passes through the system. The fluoride-containing water can be actual fluoride-containing groundwater or low-concentration actual fluoride-containing wastewater, with an influent fluoride concentration range of 1–20 mg / L, making it widely applicable.

[0042] First, simulated fluoride-containing water is prepared based on the fluoride ion concentration. The fluoride ion concentration of the influent is fed back by a real-time fluoride ion monitoring meter. Phosphoric acid solution is then prepared. The fluoride-containing water and phosphoric acid are mixed evenly in a pipeline mixer according to the ratio to ensure that the molar ratio of phosphate to fluoride ions in the mixed water storage tank is (2.0~6.0):1. After the mixed water is reacted in the reactor, the fluoride ion concentration of the effluent can be less than 1.0 mg / L.

[0043] Secondly, simulated fluoride-containing water is prepared based on the fluoride ion concentration and alkalinity, and the alkalinity is continuously increased to make its final alkalinity consistent with that of actual groundwater. After the fluoride ion concentration and alkalinity of the influent are fed back by a real-time fluoride ion monitor and an alkalinity meter, an acidified phosphoric acid solution is prepared. The fluoride-containing water and the acidified phosphoric acid solution are mixed evenly in a pipeline mixer according to a certain ratio to ensure that the molar ratio of phosphate to fluoride ions in the mixed water storage tank is (2.0~6.0):1, and the pH of the mixed water is between 5.0 and 6.0. After the mixed water is reacted in the reactor, the fluoride ion concentration of the effluent can be less than 1.0 mg / L.

[0044] Then, based on the final alkalinity mentioned above, fluoride-containing water with magnesium ions is prepared, and the magnesium ion concentration is continuously increased until the final magnesium ion concentration is consistent with the actual groundwater. After the fluoride ion concentration and alkalinity of the influent are fed back by the fluoride ion real-time monitoring meter and the alkalinity meter, an acidified phosphoric acid solution is prepared. The fluoride-containing water and the acidified phosphoric acid solution are mixed evenly in the pipeline mixer according to the ratio to ensure that the molar ratio of phosphate ions to fluoride ions in the mixed water storage tank is (2.0~6.0):1, and the pH of the mixed water is between 5.0 and 6.0. After the mixed water is reacted in the reactor, the fluoride ion concentration of the effluent can be less than 1.0 mg / L.

[0045] Finally, replace the simulated fluoride-containing water in the inlet tank with actual fluoride-containing water, and continue operating under the above conditions; the fluoride ion concentration in the effluent will then meet the standard.

[0046] This invention determines the dosage of phosphoric acid and acid agent added during the start-up period of the defluoridation system to correspond to the actual fluoride-containing groundwater. This can effectively address the high alkalinity and coexistence of high magnesium ions and fluoride ions in the water, resulting in an effluent fluoride concentration of less than 1.0 mg / L.

[0047] Furthermore, this invention increases the alkalinity of simulated fluoride-containing water by adding bicarbonate. Bicarbonate and hydrogen ions exist in the mixed water as carbonic acid and participate in the calcium dissolution process in the subsequent reactor, eliminating the need for an additional decarbonator.

[0048] Furthermore, this invention uses waste seashells as the reactor packing material; the seashell particles serve as both a calcium source and filter media, saving on investment and operating costs. The operation process of this technology involves a cyclical "contact filtration + water rinsing" process. Compared to existing adsorption methods for fluoride removal, it eliminates the need for a solid material regeneration process, further saving on investment and operating costs. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a control system for defluoridation of fluoride-containing groundwater according to the present invention;

[0050] The components include: 1. Raw water tank; 1-1. No. 1 real-time fluoride ion concentration monitoring meter; 1-2. Alkalinity meter; 2. Dosing tank; 3. No. 1 inlet pump; 4. Dosing pump; 5. Pipeline mixer; 6. Mixing storage tank; 6-1. No. 1 real-time pH monitoring meter; 7. No. 2 inlet pump; 8. Fixed bed reactor; 8-1. Inlet; 8-2. Outlet; 9. No. 3 inlet pump; 10. Outlet tank; 10-1. No. 2 real-time pH monitoring meter; 10-2. No. 2 real-time fluoride ion concentration monitoring meter.

[0051] Figure 2 The image shows the scanning electron microscope (SEM) morphology of the calcium fluorophosphate precipitate generated in the examples.

[0052] Figure 3 This is a comparison chart of the calcium fluorophosphate precipitate generated in the examples and the standard card. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0054] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0055] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0056] After investigation, it was finally discovered that the existing calcium fluorophosphate precipitation method fails to remove fluoride when high alkalinity and high magnesium ion concentration coexist with fluoride ions.

[0057] The main reason is that magnesium ions and alkalinity in the water hinder the precipitation reaction of calcium fluorophosphate. When only fluoride and alkalinity are present in the water (within the scope of this instruction manual, alkalinity unless otherwise specified is defined as HCO3-), the precipitation reaction will proceed. - When there are no other coexisting substances, the amount of precipitant added needs to be increased several times to achieve defluoridation. When only fluoride and magnesium ions are present in the water, without other coexisting substances, not only does the amount of precipitant added increase significantly, but the precipitate is also rapidly "poisoned," requiring frequent sludge removal to achieve continuous defluoridation. The alkalinity of fluoride-containing groundwater is usually above 100 mg / L, and in some areas it can even reach 1120 mg / L. The concentration of magnesium ions in fluoride-containing groundwater is usually above 10 mg / L, and in some areas it can reach 400 mg / L. Their presence severely hinders the defluoridation precipitation reaction, rendering the calcium fluorophosphate precipitation method ineffective for actual groundwater defluoridation.

[0058] This invention discloses a method for defluoridation of fluoride-containing groundwater, comprising the following steps:

[0059] S1. Obtain the fluoride ion concentration, alkalinity, and magnesium ion concentration of the actual fluoride-containing groundwater to be treated;

[0060] S2. Prepare a simulated fluoride-containing water and phosphoric acid solution; the fluoride concentration of the simulated fluoride-containing water is the same as the fluoride ion concentration of the actual fluoride-containing groundwater;

[0061] Phosphoric acid solution was mixed with simulated fluoride-containing water, and after calcium precipitation reaction, the fluoride concentration in the effluent was reduced to less than 1.0 mg / L.

[0062] S3. By adding bicarbonate, the alkalinity of the simulated fluoride-containing water is continuously increased until the alkalinity of the simulated fluoride-containing water is the same as that of the actual fluoride-containing groundwater.

[0063] An acid is added to a phosphoric acid solution, and the acidified phosphoric acid solution is mixed with alkalized simulated fluoride-containing water. The pH of the mixed solution is controlled at 5.0-6.0. After calcium precipitation reaction treatment, the fluoride concentration in the effluent is reduced to less than 1.0 mg / L.

[0064] S4. Based on the alkalinity reaching that of actual fluoride-containing groundwater, magnesium salts are continuously added to the simulated fluoride-containing water according to the concentration characteristics of magnesium ions in the actual fluoride-containing groundwater, so that the magnesium ion concentration of the simulated fluoride-containing water is the same as that of the actual fluoride-containing groundwater.

[0065] The acidified phosphoric acid solution was mixed with simulated fluoride-containing water containing magnesium salt. The pH of the mixed solution was controlled at 5.0-6.0. After calcium precipitation treatment, the fluoride concentration in the effluent was less than 1.0 mg / L.

[0066] S5. Replace the simulated fluoride-containing water with the actual fluoride-containing groundwater to be treated. At this time, the fluoride concentration in the effluent can be guaranteed to drop to below 1.0 mg / L.

[0067] In S3, hydrochloric acid or sulfuric acid is used as the acid; in S4, magnesium chloride or magnesium sulfate is used as the magnesium salt.

[0068] In S2-S4, the molar ratio of phosphate to fluoride ions in the mixed solution is (2.0–6.0):1. This can be calculated after obtaining the fluoride ion concentration.

[0069] The features and performance of the present invention will be further described in detail below with reference to specific verification examples.

[0070] The groundwater in a certain area has a fluoride concentration of 3.25 mg / L, an alkalinity of 615 mg / L, and a magnesium ion concentration of 25.5 mg / L. Detailed indicators are shown in Table 1. The control method and system described in this invention are used for fluoride removal.

[0071] Simulated fluoride-containing water was prepared using tap water with a fluoride concentration of 3.25 mg / L. The ratio of influent to chemical flow rate was set to 100:1. A phosphoric acid solution was prepared so that the molar ratio of phosphorus to fluoride after mixing the influent and chemical solution was 4.0:1. Under these conditions, the solution was continuously operated until the fluoride concentration in the effluent was below 1.0 mg / L.

[0072] The alkalinity of the simulated fluoride-containing water was increased to 600 mg / L using sodium bicarbonate. The ratio of influent to chemical flow rate was set to 100:1. A phosphoric acid solution was prepared so that the molar ratio of phosphorus to fluoride after mixing the chemical and influent was 4.0:1. Hydrochloric acid was added to the prepared phosphoric acid solution to ensure the pH of the mixture was between 5.0 and 6.0. The mixture was operated under these conditions until the fluoride concentration in the effluent was below 1.0 mg / L.

[0073] Magnesium salts were used to increase the magnesium ion concentration in the simulated fluoride-containing water to 25 mg / L. The ratio of influent to chemical flow rate was set to 100:1. A phosphoric acid solution was prepared so that after mixing the influent and chemical, the molar ratio of phosphorus to fluoride was 4.0:1. Hydrochloric acid was added to the prepared phosphoric acid solution to ensure the pH of the mixture was between 5.0 and 6.0. The mixture was operated under these conditions until the fluoride concentration in the effluent stabilized below 1.0 mg / L.

[0074] After operating under the above conditions until the effluent fluoride concentration is stably below 1.0 mg / L, use the actual groundwater in the area as the raw water inlet, and use the same chemical inlet conditions as the simulated fluoride-containing water. At this point, the effluent fluoride concentration can meet the standard.

[0075] Using the above control methods, the fluoride concentration in the effluent can be kept stable below 1.0 mg / L for a long period of time.

[0076] The relationship between the parameters of phosphoric acid and acid in the final dosing tank and the fluoride ion concentration, alkalinity and magnesium ion concentration of the actual fluoride-containing groundwater is shown in Table 2 after adjustment.

[0077] Table 1: Groundwater Quality Data for a Certain Region

[0078] Indicator (mg / L) actual groundwater <![CDATA[K + ]]> 17.1±0.5 <![CDATA[Na + ]]> 635.2±0.5 <![CDATA[Ca 2+ ]]> 20.6±0.5 <![CDATA[Mg 2+ ]]> 25.2±0.7 <![CDATA[F - ]]> 3.2±0.05 <![CDATA[Cl - ]]> 330.5±2 alkalinity 609.2±7.5 <![CDATA[SO4 2- ]]> 365.8±2 pH 8.23±0.5 TDS 1357±15

[0079] Table 2: Relationship between the parameters of phosphoric acid and acid in the dosing tank and the fluoride ion concentration, alkalinity, and magnesium ion concentration in actual fluoride-containing groundwater.

[0080]

[0081] The products generated by the fixed-bed reactor were scanned by electron microscopy to obtain the following results: Figure 2 The SEM image shown, after XRD testing, yielded the following results: Figure 3 The comparison chart shown is as follows. Figure 2 and Figure 3 All of these indicate that the reaction product of the present invention is calcium fluorophosphate precipitate.

[0082] like Figure 1 As shown, the present invention also designs a control system, which mainly includes a raw water tank 1, a dosing tank 2, a first inlet pump 3, a dosing pump 4, a pipeline mixer 5, a mixing storage tank 6, a second inlet pump 7, a fixed bed reactor 8, a third inlet pump 9, and an outlet tank 10.

[0083] The simulated fluoride-containing water and actual groundwater are added to the raw water tank 1; the phosphoric acid solution and the acidified phosphoric acid solution are added to the dosing tank 2.

[0084] Specifically, the raw water tank 1 and the dosing tank 2 are respectively connected to the first inlet pump 3 and the dosing pump 4 through pipelines, and valves are installed on the pipelines; the first inlet pump 3 and the dosing pump 4 are connected to the pipeline mixer 5 through pipelines, and the pipeline mixer 5 is connected to the mixing storage tank 6 through pipelines; the outlet of the mixing storage tank 6 is connected to the fixed bed reactor 8 through a pipeline and the second inlet pump 7, and valves are installed on the pipelines; the effluent after the reaction is connected to the effluent tank 10 through pipelines.

[0085] More preferably, when rinsing the reactor, the effluent collected in the effluent tank 10 after the reaction is used as the rinsing water, and the effluent tank 10 is connected to the inlet of the fixed bed reactor 8 through the No. 3 inlet pump 9.

[0086] The raw water tank 1, the mixing storage tank 6, and the outlet tank 10 need to be tested, as detailed below:

[0087] The raw water tank 1 is equipped with a real-time fluoride ion concentration monitoring meter 1-1 and an alkalinity meter 1-2. The real-time fluoride ion concentration monitoring meter 1-1 is used to monitor the fluoride concentration of the simulated fluoride-containing water, and the alkalinity meter 1-2 is used to monitor the alkalinity of the simulated fluoride-containing water.

[0088] A real-time pH monitoring meter 6-1 is installed in the mixing water storage tank 6 to monitor the pH of the mixing water storage tank 6;

[0089] The effluent tank 10 is equipped with a second real-time pH monitoring meter 10-1 and a second real-time fluoride ion concentration monitoring meter 10-2. The second real-time pH monitoring meter 10-1 is used to monitor the pH of the effluent, and the second real-time fluoride ion concentration monitoring meter 10-2 is used to monitor the fluoride concentration of the effluent.

[0090] The fixed bed reactor 8 has an inlet 8-1 at the bottom and an outlet 8-2 at the top; the outlet of the mixing storage tank 6 is connected to the inlet 8-1 of the fixed bed reactor 8 through a second inlet pump 7; the effluent after the reaction in the fixed bed reactor 8 is connected to the effluent tank 10 through the outlet 8-2 via a pipeline.

[0091] The raw water tank 1 has an inlet on one side and an outlet on the other side; the dosing tank 2 has a dosing inlet on one side and a dosing outlet on the other side; the mixing water storage tank 6 has a mixing water inlet on one side and a mixing water outlet on the other side; the outlet tank 10 has a drain outlet on one side and a water inlet at the top.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for regulating and controlling the defluoridation of fluoride-containing groundwater, characterized in that, Includes the following processes: S1. Obtain the fluoride ion concentration, alkalinity, and magnesium ion concentration of the actual fluoride-containing groundwater to be treated; S2. Prepare a simulated fluoride-containing water and phosphoric acid solution; the fluoride concentration of the simulated fluoride-containing water is the same as the fluoride ion concentration of the actual fluoride-containing groundwater; Phosphoric acid solution was mixed with simulated fluoride-containing water, and after calcium precipitation reaction, the fluoride concentration in the effluent was reduced to less than 1.0 mg / L. S3. Continuously increase the alkalinity of the simulated fluoride-containing water until the alkalinity of the simulated fluoride-containing water is the same as that of the actual fluoride-containing groundwater. An acid is added to a phosphoric acid solution, and the acidified phosphoric acid solution is mixed with alkalized simulated fluoride-containing water. The pH of the mixed solution is controlled at 5.0~6.

0. After calcium precipitation reaction treatment, the fluoride concentration in the effluent is reduced to less than 1.0 mg / L. In S3, the acid used is hydrochloric acid or sulfuric acid; S4. Based on the alkalinity reaching that of actual fluoride-containing groundwater, magnesium salts are continuously added to the simulated fluoride-containing water according to the concentration characteristics of magnesium ions in the actual fluoride-containing groundwater, so that the magnesium ion concentration of the simulated fluoride-containing water is the same as that of the actual fluoride-containing groundwater. The acidified phosphoric acid solution was mixed with simulated fluoride-containing water containing magnesium salt. The pH of the mixed solution was controlled at 5.0~6.

0. After calcium precipitation reaction treatment, the fluoride concentration in the effluent was less than 1.0 mg / L. S5. Replace the simulated fluoride-containing water with the actual fluoride-containing groundwater to be treated. The conditions for adding the acid to the phosphoric acid solution are the same as those for the simulated fluoride-containing water. At this time, the fluoride concentration in the effluent can be guaranteed to drop to below 1.0 mg / L. The calcium source required for the calcium precipitation reaction is provided by the waste seashell particles that fill the reactor.

2. The method for defluoridation of fluoride-containing groundwater according to claim 1, characterized in that, In S3, bicarbonate is added to increase the alkalinity of the simulated fluoride-containing water; In S4, the magnesium salt is either magnesium chloride or magnesium sulfate.

3. The method for defluoridation of fluoride-containing groundwater according to claim 1, characterized in that, In S2, after the phosphoric acid solution is mixed with simulated fluoride-containing water, the molar ratio of phosphate ions to fluoride ions in the mixed solution is (2.0~6.0):

1.

4. The method for defluoridation of fluoride-containing groundwater according to claim 1, characterized in that, In S3, after the acidified phosphoric acid solution is mixed with the alkalized simulated fluoride-containing water, the molar ratio of phosphate to fluoride ions in the mixed solution is (2.0~6.0):

1.

5. The method for defluoridation of fluoride-containing groundwater according to claim 1, characterized in that, In S4, the phosphoric acid solution after acidification is mixed with simulated fluoride-containing water after magnesium salt is added. The molar ratio of phosphate to fluoride ions in the mixed solution is (2.0~6.0):1.

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