Method for purifying fluorine-containing sludge and increasing granularity of calcium fluoride

Abstract

The invention belongs to the technical field of solid waste treatment and resource recovery, and particularly relates to a method for purifying fluorine-containing sludge and increasing the granularity of calcium fluoride. The method comprises the following steps: carrying out hydrothermal reaction on fluorine-containing sludge and a sodium hydroxide solution at 120-150 DEG C to obtain a solid phase without silicon dioxide impurities and a liquid phase containing sodium silicate; reacting the obtained solid phase with a dilute sulphuric acid solution to obtain a solid phase without calcium carbonate impurities and a liquid phase containing calcium sulfate; mixing the liquid phase containing calcium sulfate with the liquid phase containing sodium silicate for reaction, and recycling calcium silicate and sodium sulfate; and dynamically calcining the obtained solid phase at 600-800 DEG C for upgrading to obtain a CaF2 product of which the particle size is increased and the S impurity is removed. According to the method disclosed by the invention, impurities in the fluorine-containing sludge are efficiently removed by combining hydrothermal treatment with dynamic calcination, the particle size of calcium fluoride is increased, and efficient resource recycling treatment of other impurities is realized. The method has the advantages of environmental friendliness and wide application range.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste treatment and resource recovery, and specifically relates to a method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride. Background Art

[0002] Fluoride-containing sludge is produced during industrial production. The calcium fluoride in it is usually amorphous or weakly crystalline with very fine particle size, which makes it difficult to handle and utilize in the future. In addition, impurities such as calcium carbonate, silicon dioxide, and sulfur in fluoride-containing sludge will also affect the crystallization growth process of calcium fluoride and the purity of the product. Fine-grained calcium fluoride is difficult to separate and recycle, and there are also problems in the stabilization and harmless treatment of sludge. Therefore, developing an effective method to effectively remove impurities in fluoride-containing sludge and increase the particle size of calcium fluoride is of great significance for improving the recovery rate of fluorine resources and protecting the environment.

[0003] At present, the main methods to solve the problem of fine particle size and difficult separation of calcium fluoride in fluoride-containing sludge are chemical precipitation, flocculation precipitation, mechanical dehydration, heat treatment, ultrasonic treatment, biological treatment and membrane separation technology. Chemical precipitation requires a large amount of chemical reagents, which may increase the treatment cost, and the post-treatment and disposal of the precipitate is also a problem. The addition of flocculants in the flocculation precipitation method may affect the stability of the sludge, and has limited effect on very fine particles. The mechanical dehydration method has high energy consumption and limited effect on increasing the particle size of calcium fluoride. The thermal treatment method has very high energy consumption and may cause secondary pollution. The ultrasonic treatment method has high equipment cost and operating cost, and has strict requirements on operating conditions. The biological treatment method has a long treatment cycle, is greatly affected by environmental conditions, and has unstable effects. The pollution and cleaning of the membrane in membrane separation technology are technical difficulties, and the operating cost is high.

[0004] Patent CN 105601066A discloses a method for refining calcium fluoride using fluorine-containing sludge, and different grades of calcium fluoride products are obtained by sequentially performing acidification, fluoridation and alkalization operations on the fluorine-containing sludge, but the acidification operation has limited purification effect on calcium fluoride, and the fluoridation operation requires the additional introduction of highly corrosive hydrofluoric acid, which increases consumption and increases the requirements for equipment. And the above treatment method has limited effect on the particle size growth of the obtained calcium fluoride. Patent CN 107235502 A discloses a method for preparing a finished calcium fluoride product using calcium fluoride-containing sludge, by using alkaline solution or / and alkaline wastewater to react with fluorine-containing sludge to remove silicon dioxide, and then using hydrofluoric acid or / and hydrofluoric acid-containing wastewater to react with calcium hydroxide in the precipitate to form calcium fluoride, thereby obtaining a finished calcium fluoride product. However, it also introduces highly corrosive hydrofluoric acid, and it is difficult to achieve effective separation and resource utilization of the liquid phase, and the above treatment method has limited effect on the particle size growth of the obtained calcium fluoride. Summary of the invention

[0005] In view of the shortcomings and deficiencies of the above prior art, the purpose of the present invention is to provide a method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride. The method of the present invention uses hydrothermal combined with dynamic calcination to efficiently remove impurities in fluorine-containing sludge, increase the particle size of calcium fluoride and realize resource recovery of other components.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for purifying fluoride-containing sludge and increasing the particle size of calcium fluoride comprises the following steps:

[0008] (1) The fluorine-containing sludge and the sodium hydroxide solution are stirred and mixed uniformly, and then heated to 120-150° C. in a closed hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the solid and liquid are separated to obtain a solid phase with silicon dioxide impurities removed and a liquid phase containing sodium silicate;

[0009] (2) adding a dilute sulfuric acid solution to the solid phase obtained in step (1) to react, separating the solid and the liquid to obtain a solid phase from which calcium carbonate impurities have been removed and a liquid phase containing calcium sulfate; adding the obtained liquid phase containing calcium sulfate to the liquid phase containing sodium silicate obtained in step (1) to carry out a mixed reaction, and the obtained precipitate is recycled as calcium silicate, and the remaining liquid phase is dried and crystallized to obtain sodium sulfate for resource recovery;

[0010] (3) The solid phase obtained in step (2) from which the calcium carbonate impurities have been removed is dried and placed in a rotary tube furnace and heated to 600-800° C. for dynamic calcination and quality improvement to obtain a CaF2 product with an enlarged particle size and the S impurities removed.

[0011] Furthermore, the mass concentration of the sodium hydroxide solution in step (1) is 15-25%; and the mass ratio of the fluorine-containing sludge to the sodium hydroxide solution is 1:4-6.

[0012] Furthermore, the stirring speed of the hydrothermal reaction in step (1) is 100-300 r / min, and the reaction time is 10-60 min.

[0013] Furthermore, the solid-liquid separation in steps (1) and (2) refers to vacuum filtration solid-liquid separation under a vacuum degree of 0.01-0.1 MPa.

[0014] Furthermore, the mass concentration of the dilute sulfuric acid solution in step (2) is 15-25%; and the mass ratio of the solid phase to the dilute sulfuric acid solution is 1:4-6.

[0015] Furthermore, the liquid phase containing calcium sulfate and the liquid phase containing sodium silicate in step (2) are mixed and reacted until the pH value of the system is neutral (pH value is 6.5-7.5).

[0016] Furthermore, the drying in step (3) refers to drying in an oven at 100-120°C.

[0017] Furthermore, the time for dynamic calcination and upgrading in step (3) is 30-180 minutes.

[0018] Furthermore, the dynamic calcination and upgrading in step (3) is carried out under the condition of introducing air, and the rotation speed is 30-50r / min.

[0019] Furthermore, the gas generated during the dynamic calcination and upgrading reaction process in step (3) is collected and processed through a gas pipe.

[0020] The principle of the present invention is: by reacting the fluorine-containing sludge with the sodium hydroxide solution under hydrothermal conditions, at a relatively high temperature, the sodium hydroxide solution will react with the silicon dioxide in the fluorine-containing sludge to generate sodium silicate (Na2SiO3) which is transferred to the liquid phase. The specific reaction formula is as follows:

[0021] SiO2(s)+2NaOH(aq)=Na2SiO3(aq)+H2O(aq).

[0022] Through solid-liquid separation, the solid phase after separation mainly retains samples with high CaF2 content (containing calcium carbonate impurities), and then dilute sulfuric acid solution is added for reaction. The calcium carbonate (CaCO3) impurities contained in the solid phase will react with the dilute sulfuric acid solution (H2SO4) to generate calcium sulfate (CaSO4) and transfer to the liquid phase. The liquid phase containing calcium sulfate is then mixed with the liquid phase containing sodium silicate to generate calcium silicate precipitate (CaSiO3) for resource recovery, and the remaining liquid phase is dried and crystallized to obtain sodium sulfate for resource recovery. The specific reaction formula is as follows:

[0023] CaCO3(s)+H2SO4=CaSO4(aq)+H2O(aq)+CO2(g);

[0024] CaSO4(aq)+Na2SiO3(aq)=CaSiO3(s)+Na2SO4(aq).

[0025] Finally, the CaF2 solid phase after impurities removal is subjected to ventilation dynamic calcination to further increase the particle size of the calcium fluoride product, and the S in the fluoride-containing sludge reacts with O2 in the air to generate SO2, which is removed to obtain a high-quality calcium fluoride product.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The method of the present invention can effectively remove impurities such as calcium carbonate, silicon dioxide and sulfur in fluorine-containing sludge, improve the purity of the product calcium fluoride and promote the crystallization growth process of calcium fluoride; by further dynamic calcination and quality improvement, the particle size and purity of calcium fluoride in fluorine-containing sludge can be improved, which is convenient for resource utilization.

[0028] (2) The method of the present invention can treat fluorine-containing sludge of various impurity types by adjusting the reaction parameters, and is suitable for large-scale industrial applications; and the reaction products are recycled without generating secondary pollution, thus meeting environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow chart of a method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride in an embodiment of the present invention.

[0030] Figure 2 The SEM spectra of the fluoride-containing sludge before treatment in Example 1 and the high-quality calcium fluoride product obtained after treatment.

[0031] Figure 3 This is a physical picture of the fluorine-containing sludge after drying before treatment in Example 1 and the high-quality calcium fluoride product obtained after treatment. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0033] Example 1

[0034] A method for purifying fluoride-containing sludge and increasing the particle size of calcium fluoride, the process flow chart is as follows Figure 1 As shown, the following steps are included:

[0035] (1) Pretreatment and hydrothermal impurity removal: Sodium hydroxide and water are mixed in a mass ratio of 1:5 to prepare a sodium hydroxide solution, and then the fluorine-containing sludge and the sodium hydroxide solution are added to a mixing crusher in a mass ratio of 1:5. Under the stirring action, large pieces of fluorine-containing sludge are broken and fully mixed. The pretreated sample is sent to a hydrothermal reactor and reacted for 30 minutes at a temperature of 130°C and a stirrer speed of 200r / min. The sample after hydrothermal treatment is sent to the filtering device of a vacuum filter and solid-liquid separation is performed under a vacuum degree of 0.095MPa to obtain a CaF2 solid phase with silicon dioxide impurities removed and a liquid phase containing Na2SiO3.

[0036] (2) Solid phase dissolution and impurity removal and liquid phase precipitation separation treatment: sulfuric acid and water are prepared into a dilute sulfuric acid solution at a mass ratio of 1:5, and then the solid phase obtained in step (1) and the dilute sulfuric acid solution are added to a blender at a mass ratio of 1:5 for mixed reaction to dissolve the residual CaCO3 impurities therein. The mixed solution is then sent to the filtering device of a vacuum filter, solid-liquid separation is performed under a vacuum degree of 0.095 MPa, and a CaF2 solid phase with calcium carbonate impurities removed and a liquid phase containing CaSO4 are obtained. The liquid phase containing CaSO4 is added to the liquid phase containing Na2SiO3 obtained in step (1) for mixed reaction until the pH value of the system is neutral (pH value is 6.5-7.5), and the Na2SiO3 in the solution reacts with CaSO4 to generate CaSiO3 precipitation for resource recovery, and the remaining liquid phase is dried and crystallized to obtain sodium sulfate for resource recovery.

[0037] (3) Calcination and quality improvement: The CaF2 solid phase separated in step (2) is dried in an oven at 105°C, and then placed in a rotary tube furnace for calcination and quality improvement. The reaction conditions are set as follows: air is introduced, the rotation speed is 40r / min, the reaction temperature is 700°C, and the reaction time is 90min. The particle size of the calcium fluoride product is further increased by dynamic calcination, and the SO2 generated by the reaction of S in the fluorine-containing sludge with O2 in the air is removed to obtain a high-quality calcium fluoride product. The gas generated during the reaction process is collected and treated through a gas pipe.

[0038] The SEM spectra of the fluoride-containing sludge before treatment and the high-quality calcium fluoride product obtained after treatment in this example are shown in the figure below: Figure 2 The actual picture of the fluoride-containing sludge after drying before treatment and the high-quality calcium fluoride product obtained after treatment is shown in Figure 3 As shown. The calcium fluoride or calcium carbonate in the fluoride-containing sludge is mainly nano-scale agglomerates or dispersed particles, while the calcium fluoride in the treated product grows into large crystals with a size of about 50 microns. The particle size of the treated product on the 325 mesh sieve accounts for about 90%. The particle size of the calcium fluoride product obtained after treatment increases significantly.

[0039] The main components of the fluoride-containing sludge before treatment and the high-quality calcium fluoride product obtained after treatment in this embodiment are shown in Table 1. The calcium fluoride content of the product after treatment in the present invention is 98.22%, wherein the content of sulfur and phosphorus are both less than 0.05%, and the removal rate of Si also reaches 99.25%.

[0040] Table 1

[0041] Ingredients <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO S Si P Fluoride-containing sludge (wt.%) 68.866 21.362 / 1.394 7.641 0.009 Treated product (wt.%) 98.223 / 1.291 0.036 0.057 0.005

[0042] Example 2

[0043] A method for purifying fluoride-containing sludge and increasing the particle size of calcium fluoride, the process flow chart is as follows Figure 1As shown, the following steps are included:

[0044] (1) Pretreatment and hydrothermal impurity removal: Sodium hydroxide and water are mixed in a mass ratio of 1:3 to prepare a sodium hydroxide solution, and then the fluorine-containing sludge and the sodium hydroxide solution are added to a mixing crusher in a mass ratio of 1:4. Under the stirring action, large pieces of fluorine-containing sludge are broken and fully mixed. The pretreated sample is sent to a hydrothermal reactor and reacted for 60 minutes at a temperature of 120°C and a stirrer speed of 200r / min. The sample after hydrothermal treatment is sent to the filtration device of a vacuum filter and solid-liquid separation is performed under a vacuum degree of 0.095MPa to obtain a CaF2 solid phase with silicon dioxide impurities removed and a liquid phase containing Na2SiO3.

[0045] (2) Solid phase dissolution and impurity removal and liquid phase precipitation separation treatment: sulfuric acid and water are prepared into a dilute sulfuric acid solution at a mass ratio of 1:3, and then the solid phase obtained in step (1) and the dilute sulfuric acid solution are added to a blender at a mass ratio of 1:4 for mixed reaction to dissolve the residual CaCO3 impurities therein. The mixed solution is then sent to the filtering device of a vacuum filter, solid-liquid separation is performed under a vacuum degree of 0.095 MPa, and a CaF2 solid phase with calcium carbonate impurities removed and a liquid phase containing CaSO4 are obtained. The liquid phase containing CaSO4 is added to the liquid phase containing Na2SiO3 obtained in step (1) for mixed reaction until the pH value of the system is neutral (pH value is 6.5-7.5), and the Na2SiO3 in the solution reacts with CaSO4 to generate CaSiO3 precipitation for resource recovery, and the remaining liquid phase is dried and crystallized to obtain sodium sulfate for resource recovery.

[0046] (3) Calcination and quality improvement: The CaF2 solid phase separated in step (2) is dried in an oven at 105°C to remove moisture, and then placed in a rotary tube furnace for calcination and quality improvement. The reaction conditions are set as follows: air is introduced, the rotation speed is 30r / min, the reaction temperature is 600°C, and the reaction time is 60min. The particle size of the calcium fluoride product is further increased by dynamic calcination, and the SO2 generated by the reaction of S in the fluorine-containing sludge with O2 in the air is removed to obtain a high-quality calcium fluoride product. The gas generated during the reaction process is collected and treated through a gas pipe.

[0047] The main components of the fluoride-containing sludge before treatment and the high-quality calcium fluoride product obtained after treatment in this embodiment are shown in Table 2. The calcium fluoride content of the product after treatment in the present invention is 97.87%, wherein the content of sulfur and phosphorus are both less than 0.05%, and the removal rate of Si also reaches 99.43%.

[0048] Table 2

[0049] element <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO S Si P Fluoride-containing sludge (wt.%) 68.866 21.362 / 1.394 7.641 0.009 Treated product (wt.%) 97.872 / 1.437 0.027 0.043 0.005

[0050] Example 3

[0051] A method for purifying fluoride-containing sludge and increasing the particle size of calcium fluoride, the process flow chart is as follows Figure 1 As shown, the following steps are included:

[0052] (1) Pretreatment and hydrothermal impurity removal: Sodium hydroxide and water are mixed in a mass ratio of 1:4 to prepare a sodium hydroxide solution, and then the fluorine-containing sludge and the sodium hydroxide solution are added to a mixing crusher in a mass ratio of 1:6. Under the stirring action, large pieces of fluorine-containing sludge are broken and fully mixed. The pretreated sample is sent to a hydrothermal reactor and reacted for 15 minutes at a temperature of 150°C and a stirrer speed of 200r / min. The sample after hydrothermal treatment is sent to the filtration device of a vacuum filter and solid-liquid separation is performed under a vacuum degree of 0.095MPa to obtain a CaF2 solid phase with silicon dioxide impurities removed and a liquid phase containing Na2SiO3.

[0053] (2) Solid phase dissolution and impurity removal and liquid phase precipitation separation treatment: sulfuric acid and water are prepared into a dilute sulfuric acid solution at a mass ratio of 1:4, and then the solid phase obtained in step (1) and the dilute sulfuric acid solution are added to a blender at a mass ratio of 1:6 for mixed reaction to dissolve the residual CaCO3 impurities therein. The mixed solution is then sent to the filtering device of a vacuum filter, solid-liquid separation is performed under a vacuum degree of 0.095 MPa, and a CaF2 solid phase with calcium carbonate impurities removed and a liquid phase containing CaSO4 are obtained. The liquid phase containing CaSO4 is added to the liquid phase containing Na2SiO3 obtained in step (1) for mixed reaction until the pH value of the system is neutral (pH value is 6.5-7.5), and the Na2SiO3 in the solution reacts with CaSO4 to generate CaSiO3 precipitation for resource recovery, and the remaining liquid phase is dried and crystallized to obtain sodium sulfate for resource recovery.

[0054] (3) Calcination and quality improvement: The CaF2 solid phase separated in step (2) is dried in an oven at 105°C, and then placed in a rotary tube furnace for calcination and quality improvement. The reaction conditions are set as follows: air is introduced, the rotation speed is 50r / min, the reaction temperature is 800°C, and the reaction time is 120min. The particle size of the calcium fluoride product is further increased by dynamic calcination, and the SO2 generated by the reaction of S in the fluorine-containing sludge with O2 in the air is removed to obtain a high-quality calcium fluoride product. The gas generated during the reaction process is collected and treated through a gas pipe.

[0055] The main components of the fluoride-containing sludge before treatment and the high-quality calcium fluoride product obtained after treatment in this embodiment are shown in Table 3. The calcium fluoride content of the product after treatment in the present invention is 99.17%, wherein the content of sulfur and phosphorus are both less than 0.05%, and the removal rate of Si also reaches 99.75%.

[0056] Table 3

[0057] element <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO S Si P Fluoride-containing sludge (wt.%) 68.866 21.362 / 1.394 7.641 0.009 Treated product (wt.%) 99.168 / 0.085 0.034 0.019 0.004

[0058] Comparative Example 1

[0059] Compared with Example 1, in this comparative example, only dynamic calcination is performed on the fluorine-containing sludge (directly performing step (3) of Example 1), and no hydrothermal impurity removal, solid phase dissolution impurity removal and liquid phase precipitation separation treatment processes are performed.

[0060] The main components of the fluorine-containing sludge before treatment and the calcium fluoride product obtained after treatment in this comparative example are shown in Table 4. The calcium fluoride content of the treated product is only 73.20%, of which the contents of sulfur and phosphorus are both less than 0.05%, but due to the lack of hydrothermal impurity removal and solid phase dissolution impurity removal processes, the removal rate of Si is only 11.20%. In addition, the CaCO3 impurity in the fluorine-containing sludge cannot be effectively removed, resulting in the conversion of CaCO3 into CaO (18.29%) during the dynamic calcination stage and mixing in the calcium fluoride product as an impurity.

[0061] Table 4

[0062] element <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO S Si P Fluoride-containing sludge (wt.%) 68.866 21.362 / 1.394 7.641 0.009 Treated product (wt.%) 73.198 / 18.291 0.048 6.785 0.005

[0063] Comparative Example 2

[0064] Compared with Example 1, in this comparative example, only solid phase dissolution and impurity removal, liquid phase precipitation separation, and calcination and quality improvement treatment are performed on the fluorine-containing sludge (directly performing steps (2) and (3) of Example 1), and no hydrothermal impurity removal process is performed.

[0065] The main components of the fluoride-containing sludge before treatment and the calcium fluoride product obtained after treatment in this comparative example are shown in Table 5. The calcium fluoride content of the treated product is only 88.42%, of which the sulfur and phosphorus contents are both less than 0.05%, but due to the lack of hydrothermal impurity removal process, the removal rate of Si is only 5.56%.

[0066] Table 5

[0067] element <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO S Si P Fluoride-containing sludge (wt.%) 68.866 21.362 / 1.394 7.641 0.009 Treated product (wt.%) 88.422 / 2.071 0.019 7.216 0.002

[0068] Comparative Example 3

[0069] Compared with Example 1, in this comparative example, only the fluorine-containing sludge is subjected to hydrothermal impurity removal and calcination upgrading treatment (steps (1) and (3) of Example 1), and no solid phase dissolution impurity removal and liquid phase precipitation separation treatment process is performed.

[0070] The main components of the fluorine-containing sludge before treatment and the calcium fluoride product obtained after treatment in this comparative example are shown in Table 6 below. The calcium fluoride content of the treated product is only 78.49%, of which the content of sulfur and phosphorus are both less than 0.05%, and the removal rate of Si is 99.60%. However, due to the lack of solid phase dissolution and impurity removal process, the CaCO3 impurity in the fluorine-containing sludge cannot be effectively removed, resulting in the conversion of CaCO3 into CaO (19.37) in the dynamic calcination stage and mixing in the calcium fluoride product as an impurity.

[0071] Table 6

[0072] element <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO S Si P Fluoride-containing sludge (wt.%) 68.866 21.362 / 1.394 7.641 0.009 Treated product (wt.%) 78.492 / 19.374 0.022 0.031 0.003

[0073] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for purifying fluoride-containing sludge and increasing the particle size of calcium fluoride, characterized in that: The steps include: (1) The fluorine-containing sludge and the sodium hydroxide solution are stirred and mixed uniformly, and then heated to 120-150° C. in a closed hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the solid and liquid are separated to obtain a solid phase with silicon dioxide impurities removed and a liquid phase containing sodium silicate; (2) adding a dilute sulfuric acid solution to the solid phase obtained in step (1) to react, separating the solid and the liquid to obtain a solid phase from which calcium carbonate impurities have been removed and a liquid phase containing calcium sulfate; adding the obtained liquid phase containing calcium sulfate to the liquid phase containing sodium silicate obtained in step (1) to carry out a mixed reaction, and the obtained precipitate is recycled as calcium silicate, and the remaining liquid phase is dried and crystallized to obtain sodium sulfate for resource recovery; (3) The solid phase obtained in step (2) from which the calcium carbonate impurities have been removed is dried and placed in a rotary tube furnace and heated to 600-800° C. for dynamic calcination and quality improvement to obtain a CaF2 product with an enlarged particle size and the S impurities removed.

2. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The mass concentration of the sodium hydroxide solution in step (1) is 15-25%; the mass ratio of the fluorine-containing sludge to the sodium hydroxide solution is 1:4-6.

3. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The stirring speed of the hydrothermal reaction in step (1) is 100-300 r / min, and the reaction time is 10-60 min.

4. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The solid-liquid separation in steps (1) and (2) refers to vacuum filtration solid-liquid separation under a vacuum degree of 0.01-0.1 MPa.

5. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The mass concentration of the dilute sulfuric acid solution in step (2) is 15-25%; the mass ratio of the solid phase to the dilute sulfuric acid solution is 1:4-6.

6. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: In step (2), the liquid phase containing calcium sulfate and the liquid phase containing sodium silicate are mixed and reacted until the pH value of the system is neutral.

7. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The drying in step (3) refers to drying in an oven at 100-120°C.

8. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The time for dynamic calcination and upgrading in step (3) is 30-180 minutes.

9. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The dynamic calcination and upgrading in step (3) is carried out under air conditions at a rotation speed of 30-50 r / min.

10. The method for purifying fluorine-containing sludge and increasing the particle size of calcium fluoride according to claim 1, characterized in that: The gas generated during the dynamic calcination and upgrading reaction in step (3) is collected and processed through a gas pipe.

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