Coal gangue-based composite fluorine removal agent, preparation method and application thereof

Abstract

The application discloses a coal gangue-based composite fluorine removal agent and a preparation method and application thereof, and belongs to the technical field of fluorine removal materials. The preparation method comprises the following steps: mixing coal gangue and an alkali metal chloride aqueous solution to obtain a suspension, adding a soluble aluminum salt solution at 50 DEG C-95 DEG C, controlling the pH value to be 8-11, and generating a coprecipitation reaction to obtain a coal gangue-based composite fluorine removal agent with boehmite loaded on the coal gangue. In the preparation, the coal gangue is used as a carrier, and the boehmite is loaded on the surface of the coal gangue through a simple coprecipitation method, so that the coal gangue-based composite fluorine removal agent is obtained. According to the preparation method, the problem that the fluorine removal cost is high and the aluminum (hydrogen) oxide is prone to agglomeration when the aluminum (hydrogen) oxide is used as an adsorbent alone is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of defluorination materials technology, specifically relating to a coal gangue-based composite defluorinating agent, its preparation method, and its application. Background Technology

[0002] Fluorine is a trace element. Drinking water with a fluoride content of 0.4-0.6 mg / L is harmless and beneficial to the human body. However, long-term consumption of water with a fluoride content greater than 1.5 mg / L can have adverse effects on the human body, and in severe cases, can cause dental fluorosis and skeletal fluorosis. With the rapid development of emerging industries such as semiconductors and solar energy, the discharge of fluoride-containing wastewater is increasing year by year, posing a serious challenge to human survival and safety. Therefore, it is essential to treat fluoride-containing wastewater.

[0003] Currently, the main technology for removing high-concentration fluoride ions in practical applications is the chemical method, but it typically only reduces fluoride ions to around 10 mg / L, far exceeding the WHO's drinking water standard of 1.5 mg / L. To obtain low-fluoride water, further deep defluorination is needed after chemical pretreatment. Among various methods, adsorption is of great interest due to its simple process, convenient operation, and low cost. Developing efficient and low-cost fluoride ion adsorption materials is crucial for achieving deep defluorination.

[0004] Aluminum (hydrogen) oxides such as boehmite (AlOOH) and γ-alumina have high specific surface area and good defluorination performance, and are often used as defluorination materials. However, their high synthesis cost and easy agglomeration limit their practical application. Summary of the Invention

[0005] To address the above problems, this invention provides a coal gangue-based composite defluorinating agent and its preparation method. This invention uses coal gangue as a carrier, and loads boehmite onto the surface of the coal gangue using a simple co-precipitation method. After drying, the coal gangue-based composite defluorinating agent is obtained. This effectively solves the problems of high cost and easy agglomeration when using aluminum (hydrogen) oxides alone as adsorbents for defluorination.

[0006] The first objective of this invention is to provide a method for preparing a coal gangue-based deep defluorination agent, characterized by comprising the following steps:

[0007] A suspension is obtained by mixing coal gangue with an aqueous solution of alkali metal chloride salts. A soluble aluminum salt solution is added at 50℃~95℃, and the pH value is controlled at 8~11 to induce a co-precipitation reaction, thereby obtaining a coal gangue-based composite defluorinating agent with boehmite loaded on the coal gangue.

[0008] When adding soluble salts, the temperature can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, etc., but is not limited to the listed values; other unlisted values ​​within the above range also apply. Furthermore, the temperature is 80℃.

[0009] The pH value can be 8, 9, 10, 11, etc., but is not limited to the listed values; other unlisted values ​​within the above range also apply. If the alkalinity is too strong, boehmite will form independently before loading, which is not conducive to loading onto coal gangue.

[0010] In a preferred embodiment, the concentration of the alkali metal chloride aqueous solution is 0.01 g / ml to 0.2 g / ml. For example, the concentration of the alkali metal chloride aqueous solution is 0.01 g / ml, 0.02 g / ml, 0.04 g / ml, 0.06 g / ml, 0.08 g / ml, 0.1 g / ml, 0.12 g / ml, 0.14 g / ml, 0.16 g / ml, 0.18 g / ml, 0.2 g / ml, etc., but is not limited to the listed values; other unlisted values ​​within the above range are also applicable. Further, the concentration of the alkali metal chloride aqueous solution is 0.2 g / ml.

[0011] In a preferred embodiment, the solid-liquid ratio of coal gangue to the alkali metal chloride aqueous solution is (0.2g~5g):30ml. For example, the solid-liquid ratios of coal gangue to the alkali metal chloride aqueous solution are 0.2g:30ml, 0.8g:30ml, 1.4g:30ml, 2g:30ml, 2.6g:30ml, 3.2g:30ml, 3.8g:30ml, 4.4g:30ml, 5g:30ml, etc., but are not limited to the listed values; other unlisted values ​​within the above range are also applicable. Further, the solid-liquid ratio of coal gangue to the alkali metal chloride aqueous solution is 1g:30ml.

[0012] In a preferred embodiment, the concentration of aluminum ions in the soluble aluminum salt solution is between 10 mmol / L and 100 mmol / L. For example, the concentration of aluminum ions in the soluble aluminum salt solution can be 10 mmol / L, 20 mmol / L, 30 mmol / L, 40 mmol / L, 50 mmol / L, 60 mmol / L, 70 mmol / L, 80 mmol / L, 90 mmol / L, 100 mmol / L, etc., but is not limited to the listed values; other unlisted values ​​within the above range are also applicable. Further, the concentration of aluminum ions in the soluble aluminum salt solution is 40 mmol / L.

[0013] In a preferred embodiment, the volume ratio of the alkali metal chloride aqueous solution to the soluble aluminum salt solution is 1:1.

[0014] In a preferred embodiment, the coprecipitation reaction time is 10 min to 4 h. For example, the coprecipitation reaction time is 10 min, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, or 4 h, but it is not limited to the listed values; other unlisted values ​​within the above range are also applicable. Furthermore, the coprecipitation reaction time is 2 h.

[0015] In a preferred embodiment, the soluble aluminum salt is one or more of aluminum sulfate, aluminum nitrate, aluminum chloride, and alum.

[0016] In a preferred embodiment, the alkali metal chloride salt is one of potassium chloride, sodium chloride, and lithium chloride.

[0017] The second objective of this invention is to provide a coal gangue-based composite defluorinating agent prepared by the above-described preparation method.

[0018] The third objective of this invention is to provide the application of the above-mentioned coal gangue-based composite defluorinating agent in the treatment of fluoride-containing wastewater, characterized in that the concentration of fluoride ions in the fluoride-containing wastewater is 1.5 mg / L to 10 mg / L, and the amount of coal gangue-based composite defluorinating agent added is 0.5 g / L to 1 g / L.

[0019] In a preferred embodiment, the pH value of the fluoride-containing water is 3 to 3.5.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention provides a method for preparing a coal gangue-based composite defluorinating agent, which uses only conventional soluble aluminum salts, alkali metal chloride salts and coal gangue solid waste as reaction reagents and raw materials, without using other expensive reagents and artificially synthesized carriers. The preparation method is simple, requires no special equipment, and effectively reduces production costs. During the preparation process, the pH of the system is controlled at 8~11 to induce a co-precipitation reaction, which is beneficial to the reaction of chloride ions with Al. 3+ The boehmite precursor, [AlCl4], is preferentially formed. - The ligands slowly hydrolyze to form boehmite, which facilitates migration to the surface of coal gangue to form a load. On the other hand, a system pH of 8-11 increases solution viscosity, reduces boehmite continuity, and promotes the formation of multi-layered nanostructures, increasing the number of adsorption active sites. Therefore, using coal gangue as a carrier can effectively improve the dispersibility of boehmite and reduce agglomeration. Compared with pure boehmite, the amount of boehmite in the coal gangue-based composite defluorinator is reduced, thus lowering the price per unit mass of defluorinator.

[0022] (2) The present invention provides a coal gangue-based composite defluorinating agent, which uses solid waste coal gangue as a carrier, which can effectively improve the dispersibility of boehmite particles and improve their defluorination efficiency; the loaded boehmite is in a multi-layered network, which is conducive to improving the adsorption capacity; in addition, small-sized boehmite is anchored on the surface of large-sized coal gangue particles, which greatly improves recyclability.

[0023] (3) The coal gangue-based composite defluorinating agent provided by the present invention can defluorinate fluoride-containing wastewater with a fluoride ion concentration of less than 10 mg / L to less than 1 mg / L; it is less affected by coexisting anions such as nitrate, carbonate, bicarbonate and sulfate during the defluorination process, and has excellent selectivity; in addition, the defluorinating agent causes little additional pollution when used in practice, and the Pb content in the aqueous solution after defluorination is lower than the minimum limit of the national standard. Attached Figure Description

[0024] Figure 1 The X-ray diffraction patterns of the coal gangue-based composite defluorinating agent, coal gangue, and boehmite prepared in Example 1 are shown below.

[0025] Figure 2 Scanning electron microscope (SEM) images of coal gangue and the coal gangue-based composite defluorinating agent prepared in Example 1. In the images, a represents coal gangue at a scale bar of 5 μm, b represents coal gangue at a scale bar of 500 nm, c represents the coal gangue-based composite defluorinating agent at a scale bar of 5 μm, and d represents the coal gangue-based composite defluorinating agent at a scale bar of 500 nm.

[0026] Figure 3 Scanning electron microscope (SEM) images and corresponding energy dispersive spectroscopy (EDS) results of coal gangue and the coal gangue-based composite defluorinating agent prepared in Example 1 are shown. In the image, a represents the local scanning morphology of coal gangue and the elemental distribution percentage corresponding to the rectangular sampling frame, while b represents the local scanning morphology of the coal gangue-based composite defluorinating agent and the elemental distribution percentage corresponding to the rectangular sampling frame.

[0027] Figure 4 The graph shows a comparison of the defluorination efficiency of the coal gangue-based composite defluorinating agent prepared in Example 1 and coal gangue at different addition amounts.

[0028] Figure 5 This is a comparison chart of the defluorination efficiency of the coal gangue-based composite defluorinating agent prepared in Example 1 of the present invention and coal gangue at different pH values.

[0029] Figure 6 The defluorination efficiency and equilibrium adsorption capacity of the coal gangue-based composite defluorinating agent prepared in Example 1 at different addition amounts are shown.

[0030] Figure 7 The graph shows the effect of coexisting anions on the defluorination efficiency of the coal gangue-based composite defluorinator prepared in Example 1.

[0031] Figure 8The defluorination efficiency and the content of loaded aluminum (hydrogen) oxides of the defluorinating agents prepared for different embodiments and comparative examples. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention provides a method for preparing a coal gangue-based composite defluorinating agent, comprising the following steps:

[0034] A suspension is obtained by mixing coal gangue with an aqueous solution of alkali metal chloride salts. A soluble aluminum salt solution is added at 50-95℃, and the pH value is controlled at 8-11 to induce a co-precipitation reaction, thereby obtaining a coal gangue-based composite defluorinating agent with boehmite loaded on the coal gangue.

[0035] Coal gangue, acting as a carrier, utilizes its surface structure to facilitate the reaction of chloride ions from alkali metal chloride salts with aluminum ions from soluble aluminum salts in an alkaline environment, forming [AlCl4]. - The ligands generate boehmite on the surface of coal gangue. The nucleated and grown boehmite on the coal gangue surface forms a multi-layered nanostructure, increasing the number of adsorption active sites and thus improving the adsorption efficiency of surface-loaded boehmite. Therefore, the coal gangue-based composite defluorinator provided by this invention achieves the effects of pure boehmite and commercial alumina using only a small amount of surface-loaded boehmite.

[0036] The amount of each raw material added and the preparation parameters can affect the boehmite loading and distribution morphology. If there is too little boehmite on the surface of the coal gangue, there will be few adsorption sites; if there is too much boehmite on the surface of the coal gangue, the boehmite near the surface of the coal gangue will not be effective. In addition, the amount of each raw material added and the preparation parameters can also affect whether the coal gangue-based composite defluorinating agent forms a multi-level nanostructure, which will affect the activity to a certain extent.

[0037] The present invention does not impose any particular restrictions on the selection of the soluble aluminum salt, and any conventional soluble aluminum salt well known to those skilled in the art can be used. Those skilled in the art can select and adjust the salt according to the actual application, product quality and product performance. Preferably, the soluble aluminum salt used in the present invention is one or more of aluminum sulfate, aluminum nitrate, aluminum chloride and alum.

[0038] The present invention does not impose any particular restrictions on the selection of the alkali metal chloride salt, and any conventional alkali metal chloride salt known to those skilled in the art is acceptable. Those skilled in the art can select and adjust the alkali metal chloride salt according to the actual application, product quality and product performance. The alkali metal chloride salt is one of potassium chloride, sodium chloride and lithium chloride.

[0039] The coal gangue used in this invention comes from Huainan, Anhui Province. Its mineral composition is shown in Table 1. When used, the particle size of the coal gangue is 800 mesh.

[0040] Table 1. Main mineral composition of coal gangue

[0041]

[0042] The coal gangue-based composite defluorinating agent prepared by this invention can be used to treat fluoride-containing wastewater.

[0043] Example 1

[0044] Preparation of coal gangue-based composite defluorinating agent:

[0045] A suspension was prepared by mixing 5g of coal gangue with 150ml of a 0.02g / ml sodium chloride aqueous solution and heating the solution to 80℃. 150ml of a 20mmol / L aluminum nitrate solution was added dropwise to the suspension, while maintaining the pH at 8, and a co-precipitation reaction was carried out for 2 hours. After centrifugation, washing, and drying, a coal gangue-based composite defluorinating agent was obtained, denoted as GA8.

[0046] Example 2

[0047] A suspension was prepared by mixing 5g of coal gangue with 150ml of a 0.01g / ml sodium chloride aqueous solution and heating it to 50℃; 150ml of a 5mmol / L aluminum sulfate solution (Al) was then added. 3+ A 10 mmol / L concentration was added dropwise to the suspension, while the pH was controlled at 8, and a co-precipitation reaction was carried out for 4 hours. After centrifugation, washing, and drying, a coal gangue-based composite defluorinating agent was obtained.

[0048] Example 3

[0049] A suspension was prepared by mixing 25g of coal gangue with 150ml of a 0.2g / ml potassium chloride aqueous solution and heating it to 95℃; 150ml of a 100mmol / L alum solution (Al) was added. 3+ A 100 mmol / L concentration was added dropwise to the suspension, while the pH was controlled at 11, and a co-precipitation reaction was carried out for 10 minutes. After centrifugation, washing, and drying, a coal gangue-based composite defluorinating agent was obtained.

[0050] Comparative Example 1

[0051] A suspension was prepared by mixing 150 ml of 0.02 g / ml sodium chloride aqueous solution and heating it to 80 °C. 150 ml of 20 mmol / L aluminum nitrate solution was added dropwise to the suspension while controlling the pH value to 8, and a co-precipitation reaction was carried out for 2 h. After centrifugation, washing and drying, boehmite was obtained and denoted as A8.

[0052] Figure 1 The X-ray diffraction (XRD) patterns of the coal gangue-based composite defluorinating agent (GA8), coal gangue (G), and boehmite (A8) prepared in Example 1 are shown. The synthesis conditions for boehmite were the same as for GA8, but without the addition of coal gangue. It can be seen that the coal gangue mainly consists of kaolinite (K) and small amounts of quartz (Q) and muscovite (M) impurities. The XRD diffraction pattern of the coal gangue-based composite defluorinating agent (GA8) shows a new peak around 27.6° compared to pure coal gangue, corresponding to boehmite, but the weak peak intensity indicates a lower loading. The reference sample without added coal gangue exhibits typical boehmite (A8) characteristics, with all major diffraction peaks clearly distinguishable. Since coal gangue is insoluble and only acts as a matrix, the XRD results demonstrate that in GA8 obtained in Example 1, if aluminum can be loaded onto the coal gangue, it exists in the form of boehmite.

[0053] Figure 2 Scanning electron microscope (SEM) images of coal gangue (G) and the coal gangue-based composite defluorinating agent (GA8) prepared in Example 1. (The images are obtained through...) Figure 2 As can be seen from 'a' and 'b', coal gangue mainly exhibits a smooth, flaky morphology; through... Figure 2 Figures c and d clearly show that a multi-layered network structure has been added to the surface of the coal gangue. The appearance of this structure is beneficial to improving the adsorption capacity.

[0054] Figure 3 Scanning electron microscope (SEM) images and corresponding energy dispersive spectroscopy (EDS) results of coal gangue (G) and the coal gangue-based composite defluorinating agent (GA8) prepared in Example 1 are shown. Interference from conductive adhesive and residual atmosphere (C and O) is disregarded, and Si in the coal gangue is used as a reference. Figure 3 In sample b, the Al / Si atomic ratio in the composite defluorinating agent for coal gangue was found to be 1.44, significantly higher than the 0.83 in coal gangue. Figure 3 a) This indicates that the newly added multi-layered network material on the surface of coal gangue is an aluminum-containing compound, combined with Figure 1 The XRD results confirmed that it is boehmite.

[0055] To further demonstrate the defluorination efficiency of the coal gangue-based composite defluorinator (GA8) in this invention, a defluorination test was conducted on the coal gangue-based composite defluorinator prepared in Example 1.

[0056] Fluoride-containing wastewater was treated as follows: a 10 mg / L NaF aqueous solution was prepared, and the pH was adjusted by adding 1M NaOH or 1M HCl solution. Then, a coal gangue-based composite defluorinating agent was added for adsorption experiments. The adsorption capacity of the defluorinating agent was investigated by varying the dosage of the coal gangue-based composite defluorinating agent, the pH of the fluoride-containing wastewater, and the concentration of acid anions added. After the adsorption experiments, the supernatant was centrifuged, separated, and the concentration of remaining fluoride ions in the solution was measured using a fluoride ion meter.

[0057] First, under the conditions of 6 hours of defluorination time, 30°C, initial fluoride ion solution concentration CO of 10 mg / L, and pH of 3.5, the dosage of the coal gangue-based composite defluorinating agent was varied to investigate its effect on defluorination efficiency. Figure 4 As shown, the defluorination rate of GA8 is much higher than that of coal gangue at different addition amounts.

[0058] Under the conditions of 0.5 g / L defluorinating agent, 6 h defluorination time, 30 °C temperature, and initial fluoride ion concentration (CO) of 10 mg / L, the pH value of the fluoride-containing wastewater was changed to investigate the effect of pH on defluorination efficiency. Figure 5 As shown, the adsorption rate of fluoride ions is highest at pH=3. Since excessively high adsorption rates are not conducive to studying the influence of various factors on the sample's adsorption performance, pH=3.5 was chosen when studying the effects of other factors, and pH=3 was chosen when studying the optimal adsorption performance.

[0059] Under the conditions of 6 hours of defluorination time, 30°C, initial fluoride ion solution concentration CO of 10 mg / L, and pH of 3.5, the defluorination efficiency and equilibrium adsorption capacity at different amounts of defluorinating agent are as follows: Figure 6 As shown, the defluorination efficiency is lowest at the minimum dosage of 0.125 g / L for the coal gangue-based composite defluorinating agent. The defluorination efficiency increases with increasing dosage to 1 g / L, mainly because the number of adsorption active sites increases with the dosage. However, when the dosage is further increased to 3 g / L, the adsorption efficiency gradually decreases, possibly due to increased particle overlap caused by excessive defluorinating agent. (Equilibrium adsorption capacity) q e The adsorption capacity gradually decreases, mainly because the number of active sites increases with the increase of the defluorinating agent, but the concentration of fluoride ions in the solution remains constant, thus the equilibrium adsorption capacity gradually decreases. In studying the influence of other factors, to simultaneously consider the fluoride ion removal rate and the equilibrium adsorption capacity, a dosage of 0.5 mg / L was selected for the coal gangue-based composite defluorinating agent; while in studying the optimal adsorption rate, a dosage of 1 mg / L was selected.

[0060] Under the conditions of 0.5 g / L defluorinating agent, 6 h defluorination time, 30 °C, initial fluoride ion solution concentration CO of 10 mg / L, and pH of 3.5, different concentrations of anions were added to study the effect of coexisting anions on the defluorination efficiency of the coal gangue-based composite defluorinating agent (GA8) prepared in Example 1. Figure 7 As shown, the effects of several anions on the performance of the coal gangue-based composite defluorinating agent are not significant, indicating good adsorption selectivity.

[0061] Figure 8 The defluorination rates of the coal gangue-based composite defluorinating agent (GA8), boehmite (A8), and commercially available activated alumina prepared in Example 1 were compared under optimal adsorption conditions: a defluorinating agent dosage of 1 g / L, a defluorination time of 6 h, a temperature of 30 ℃, an initial fluoride ion solution concentration (C0) of 10 mg / L, and a pH of 3. Combined with the comparison of the residual fluoride ion concentration and the aluminum (hydrogen) oxide content in different samples, it was found that the defluorination rate of GA8 was slightly lower than that of pure boehmite but slightly higher than that of commercially available activated alumina. However, coal gangue only has about 7.2% boehmite loaded on it, thus exhibiting a significant cost advantage. Furthermore, the fluoride ion concentration in the solution after defluorination with GA8 was 0.24 mg / L, lower than 1 mg / L, meeting the national drinking water standard GB 5749-2022.

[0062] Coal gangue is affected by various factors during mining, washing, and processing, resulting in high levels of heavy metal ions such as lead, mercury, cadmium, and chromium. These pose potential risks to human health and the environment. Therefore, the additional environmental impacts caused by the release of these heavy metal ions must be considered when utilizing coal gangue as a resource. Elemental analysis using X-ray fluorescence spectrometry showed that the coal gangue-based composite defluorinating agent (GA8) prepared in Example 1 contained only lead, a hazardous element specified in the national standard GB 5749-2022.

[0063] Table 2 compares the concentrations of lead ions in the solution before and after adsorption of the coal gangue-based composite defluorinating agent (GA8) prepared in Example 1, under the following conditions: defluorinating agent dosage of 1 g / L, defluorination time of 6 h, temperature of 30 °C, initial concentration of fluoride ion solution CO of 10 mg / L, and pH of 3. It can be seen that the Pb content in the aqueous solution after adsorption is 0.0073 mg / L, which meets the requirement of GB 5749-2022 of less than 0.01 mg / L.

[0064] Table 2. Concentration of lead ions in fluoride-containing wastewater before and after adsorption.

[0065]

[0066] In practical application testing, the dosage of the defluorinating agent was adjusted from 0.5 g / L to 1 g / L, and the initial solution pH was adjusted to 3, which has the optimal adsorption performance, while other parameters remained unchanged.

[0067] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for preparing a coal gangue-based composite defluorinating agent, characterized in that, Includes the following steps: A suspension was obtained by mixing coal gangue with an aqueous solution of alkali metal chloride. A soluble aluminum salt solution was added at 50℃~95℃, and the pH was controlled at 8~11 to induce a co-precipitation reaction, resulting in a coal gangue-based composite defluorinating agent with boehmite loaded on the coal gangue. The concentration of the alkali metal chloride aqueous solution was 0.01g / mL~0.2g / mL, the solid-liquid ratio of coal gangue to alkali metal chloride aqueous solution was 0.2g~5g:30mL, the concentration of aluminum ions in the soluble aluminum salt solution was 10mmol / L~100mmol / L, and the volume ratio of the alkali metal chloride aqueous solution to the soluble aluminum salt solution was 1:

1.

2. The preparation method of the coal gangue-based composite defluorinating agent according to claim 1, characterized in that, The coprecipitation reaction time is 10 min to 4 h.

3. The preparation method of the coal gangue-based composite defluorinating agent according to claim 1, characterized in that, Soluble aluminum salts are one or more of aluminum sulfate, aluminum nitrate, aluminum chloride, and alum.

4. The preparation method of the coal gangue-based composite defluorinating agent according to claim 1, characterized in that, Alkali metal chloride salts are one of potassium chloride, sodium chloride, and lithium chloride.

5. A coal gangue-based composite defluorinating agent prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the coal gangue-based composite defluorinating agent according to claim 5 in the treatment of fluoride-containing wastewater, characterized in that, The concentration of fluoride ions in the fluoride-containing wastewater is 1.5 mg / L to 10 mg / L, and the dosage of the coal gangue-based composite defluorinating agent is 0.5 g / L to 1 g / L.

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