Lanthanum-loaded fluorite ball seed crystal and method for treating fluorine-containing wastewater by using lanthanum-loaded fluorite ball seed crystal

Abstract

The invention provides a lanthanum-loaded fluorite ball seed crystal and a method for treating fluorine-containing wastewater by using the lanthanum-loaded fluorite ball seed crystal. The preparation method of the lanthanum-loaded fluorite ball seed crystal comprises the following steps: firstly, mixing sodium silicate and polyacrylamide, and ultrasonically and uniformly dispersing the mixture in an aqueous solution to obtain a composite binder; then calcium fluoride powder and a composite binder are evenly mixed and then put into a pelletizer to be pelletized, and fluorite ball particles are obtained after the mixture is taken out and dried; and finally, soaking the obtained fluorite ball particles in a lanthanum solution, and roasting to obtain the lanthanum-loaded fluorite ball seed crystal. When the lanthanum-loaded fluorite ball seed crystal is used for fluorine-containing wastewater treatment, the fluorite ball is used as the seed crystal to induce calcium fluoride to crystallize on the surface of the fluorite ball, and fluorine ions in a solution are effectively removed. According to the method, the fluorine removal rate is high, fluorite ball seed crystals after induced crystallization and calcium fluoride loaded on the surface of the fluorite ball seed crystals are high in purity and can be recycled for the second time, waste such as sludge is not generated in the reaction process, and therefore an additional foreign matter removing device is not needed.

Description

Technical Field

[0001] The invention relates to a method for preparing lanthanum-loaded fluorite spherical crystal seeds and a method for deep-treating fluorine-containing wastewater by filtering and crystallizing the lanthanum-loaded fluorite spherical crystal seeds, belonging to the technical field of industrial wastewater treatment. Background Art

[0002] Faced with the challenges of global climate change and resource scarcity, the recovery of high-value elements in wastewater has become a research hotspot in wastewater resource utilization. With the mining of fluoride ores and the discharge of fluoride-containing wastewater from industries such as electronics and printing and dyeing, the fluoride content in water bodies has increased significantly. The resource recovery of valuable substances in wastewater is of great significance for reducing wastewater treatment costs and improving the level of social circular economy. Furthermore, the discharge of large amounts of fluoride-containing wastewater poses a serious threat to human health. When the fluoride concentration in drinking water exceeds 3 mg / L, it can cause fluorosis (such as skeletal deformities and dental abnormalities), cognitive impairment, infertility, and pathological changes in organs such as the endocrine glands, thyroid gland, and kidneys. Therefore, the recovery and treatment of fluoride ions in wastewater has become a pressing environmental challenge.

[0003] At present, the fluoride removal technologies at home and abroad mainly include chemical precipitation, coagulation, adsorption, ion exchange, electrodialysis and reverse osmosis. Among them, the chemical precipitation method mainly adds calcium hydroxide or soluble calcium salt (such as calcium chloride) to the wastewater to make Ca 2+ With F - The reaction generates CaF2 precipitate, thereby removing fluorine. Due to its advantages of low cost, simple operation and high removal rate, chemical precipitation method is widely used in fluoride removal from wastewater. Based on this, some studies focus on the development of induced crystallization defluoridation. For example, patent CN 118666388 A proposes an integrated defluoridation method and system based on a fluidized bed, which includes two-stage defluoridation and porous adsorption filler treatment. The defluoridation efficiency is high, but the operation is relatively cumbersome and not suitable for practical engineering applications. In addition, CN116947179 A discloses a fluidized bed deep defluoridation device, including main equipment, piping system and automatic control system, etc. The device is cumbersome. This process uses flocculation method for deep defluoridation, which will produce waste of aluminum salts or iron salts in this process, and also produces a large amount of chemical sludge containing fluorine, aluminum or iron, causing secondary pollution.

[0004] As can be seen from the above, existing methods for treating fluoride-containing wastewater all have several problems. Fluidized bed induced crystallization technology, when used to treat fluoride-containing wastewater, produces effluent concentrations of 10-20 mg / L, which does not meet direct discharge requirements. Further treatment with defluoridation agents requires high dosages and produces large amounts of water-rich sludge. Due to the high water content and low quality of the sludge, it is difficult to effectively recycle for subsequent secondary applications, increasing operating costs.

[0005] Based on the above situation, how to deeply remove fluoride ions from water and recover economically profitable calcium fluoride is a technical problem that needs to be solved urgently in the field of industrial wastewater resource recovery. Summary of the Invention

[0006] In response to the deficiencies in the prior art, the present invention provides a lanthanum-loaded fluorite spherical crystal seed and a method for treating fluoride-containing wastewater using the same. Lanthanum-loaded fluorite spherical crystal seed is prepared, and the prepared lanthanum-loaded fluorite spherical crystal seed is filled into a PVC pipe to remove fluoride ions from the water while recovering calcium fluoride. Fluoride ions in fluoride-containing wastewater can be effectively removed without the need to add chemical reagents during the entire process, the operation is stable, and the recovered calcium fluoride has high purity, thereby achieving green and sustainable environmental benefits.

[0007] The technical solutions adopted to achieve the above-mentioned purpose of the present invention are: A method for preparing lanthanum-loaded fluorite spherical seed crystals comprises the following steps: (1) Sodium silicate and polyacrylamide are mixed and uniformly dispersed in an aqueous solution by ultrasonication to obtain a composite binder; (2) The calcium fluoride powder and the composite binder are uniformly mixed and put into a granulator for granulation, and then taken out and dried to obtain fluorite ball particles; (3) The obtained fluorite ball particles are immersed in a lanthanum solution and calcined to obtain lanthanum-loaded fluorite ball seed crystals.

[0008] Furthermore, in step (1), the mass ratio of sodium silicate to polyacrylamide is 0.5-1.2:1, and after the sodium silicate and polyacrylamide are ultrasonically dispersed in the aqueous solution, the pH is adjusted to 5.0-7.0.

[0009] Furthermore, the calcium fluoride powder in step (2) comes from photovoltaic wastewater recovery products, wherein the purity of calcium fluoride is above 92%.

[0010] Furthermore, in step (2), the content of sodium silicate and polyacrylamide in the mixture obtained by uniformly mixing the calcium fluoride powder and the composite binder is 3-5 wt %, and the water content is 10-20%.

[0011] Furthermore, the granulation step in step (2) is as follows: the calcium fluoride powder and the composite binder are stirred into a gypsum-like state and then put into a pelletizing machine to generate particles of uniform size, the particles are polished into spherical particles with a particle size of 0.6-1.2 cm, and then the particles are air-cooled in cold air at 20-30°C for 2-4 hours; the drying step is as follows: placing in an electric blast dryer at a temperature of 40-60°C and drying for 8-12 hours.

[0012] Furthermore, the lanthanum solution in step (3) is a lanthanum nitrate or lanthanum chloride solution with a concentration of 0.1-0.5 mol / L, and the soaking time is 0.5-2 h, and stirring is performed during soaking; the specific steps of the roasting are as follows: the roasting temperature is 200-400° C., and the roasting time is 2-5 h.

[0013] The lanthanum-loaded fluorite sphere seed crystals prepared by the present invention are used for treating fluoride-containing wastewater. The treatment method is as follows: filling the lanthanum-loaded fluorite sphere seed crystals into a PVC pipe, slowly injecting the fluoride-containing wastewater and a calcium chloride solution from both ends of the bottom of the PVC pipe, immersing the fluorite sphere seed crystals in a mixed solution, and allowing the mixed solution to stand for treatment. Calcium fluoride in the mixed solution crystallizes on the surface of the fluorite sphere seed crystals. After the treatment is completed, the treated liquid is discharged, and the fluoride ion removal rate in the treated liquid is greater than 92%.

[0014] Furthermore, the inner diameter of the PVC tube is 40-42 mm, the height is 48-52 cm, the filling amount of the fluorite sphere seeds loaded with lanthanum inside the PVC tube is 300-1200 g, and the filling height is 20-50 cm.

[0015] Furthermore, the concentration of fluoride ions in the fluoride-containing wastewater is 5-20 mg / L, and the molar ratio of fluoride ions to calcium chloride in the fluoride-containing wastewater is 1:0.5-0.6; the inlet flow rate of the fluoride-containing wastewater and the calcium chloride solution is 25-35 mL / min; during the static treatment, the constant temperature is maintained at 10-28°C, and the treatment time is 20-60 min.

[0016] Compared with the prior art, the lanthanum-loaded fluorite spherical seed crystals and the method for treating fluorine-containing wastewater provided by the present invention have the following advantages: (1) The PVC pipe of the present invention can provide appropriate water pressure to promote the attachment and crystallization of fluoride ions and calcium ions in the solution on the surface of the fluorite sphere seed crystals; the lanthanum ions loaded on the fluorite sphere seed crystals can adsorb the fluoride ions in the solution to generate lanthanum fluoride; the fluorite sphere seed crystals are doped with polyacrylamide, which is conducive to the flocculation and aggregation of fluoride ions and calcium ions on the surface of the seed crystals, promoting the induced calcium fluoride crystallization of the fluorite sphere seed crystals, and further promoting the removal of fluoride ions and resource recovery.

[0017] (2) The present invention does not add any chemicals during the sewage treatment process, which saves costs. No waste such as sludge is generated during the reaction process, so no additional foreign matter removal device is required. The treatment method can effectively remove fluoride ions in wastewater and recover calcium fluoride at the same time. It has stable operation and green and sustainable environmental benefits.

[0018] (3) The lanthanum-loaded fluorite spherical crystals prepared in the present invention and the calcium fluoride crystals generated after induced crystallization are of high purity and have good economic benefits. At the same time, the overall structure of the treatment equipment is simple and easy to operate during the sewage treatment process, which facilitates engineering promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a photo of the lanthanum-loaded fluorite spherical seed crystals prepared in Example 2; Figure 2 The scanning electron microscope images of the fluorite spherical seed crystals prepared in Example 2 before and after fluorine removal; Figure 3 XRD patterns of calcium fluoride raw material, AR calcium fluoride, and fluorite spherical seeds prepared in Examples 1-3 and Comparative Examples 1-2; Figure 4 This is a comparison chart of the purity of the calcium fluoride raw material and the calcium fluoride recovered in Examples 1-3 and Comparative Examples 1-2; Figure 5 This is a graph showing the treatment results of fluoride ions in wastewater at different hydraulic retention times in Examples 1-3 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited to the following embodiments. Example 1

[0021] A composite binder consisting of sodium silicate and polyacrylamide is prepared, adjusted to a pH of 6.5-7, and calcium fluoride recovered from wastewater is added and thoroughly stirred into a paste-like mixture. The sodium silicate and polyacrylamide are ultrasonically dispersed into the aqueous solution in a 1:1 weight ratio. The calcium fluoride powder is sourced from recycled photovoltaic wastewater and has a purity exceeding 92%. The composite binder accounts for 4wt% of the mixed raw materials, and the water content of the mixed raw materials is 10%.

[0022] The resulting mixture is fed into a pelletizer for granulation, then removed and dried to produce fluorite sphere seed crystals with a diameter of 0.6-1.2 cm. The granulation process is as follows: the raw materials are stirred into a gypsum-like consistency, then fed into a pelletizer to produce uniformly sized granules. The granules are then polished into spherical shapes with a diameter of 0.6-1.2 cm. The resulting fluorite spheres are then air-cooled at 23°C for 2.5 hours. The fluorite spheres are then dried in an electric forced air dryer at 45°C for 9 hours.

[0023] The obtained particles were placed in a 0.1 mol / L lanthanum nitrate solution, immersed and stirred for 1 hour, allowed to stand for 5 hours, and calcined at 300°C for 4 hours to obtain fluorite spherical crystal seeds.

[0024] The prepared fluorite sphere seed crystals were filled into a PVC tube to a height of 50 cm. The filter material filling amount was 1200 g. The main component of the PVC tube was polyvinyl chloride, the inner diameter of the tube was 42 mm, and the height was 52 cm.

[0025] Simulated industrial wastewater containing fluoride ions and calcium chloride solution are slowly injected into both ends of the bottom of the PVC pipe. When the solutions are mixed and immersed in the fluorite balls, the fluorite balls act as crystal seeds to induce calcium fluoride to crystallize on their surface, effectively removing the fluoride ions in the solution. - The concentration is 23.04 mg / L, and the molar ratio of fluoride ion to calcium chloride solution is 1:0.6. The fluoride-containing wastewater and calcium chloride solution must be injected into the PVC pipe simultaneously and mixed evenly. The inlet flow rate of the fluoride-containing wastewater and calcium chloride solution is 25 mL / min. Example 2

[0026] A composite binder consisting of sodium silicate and polyacrylamide is prepared, adjusted to a pH of 6.5-7, and calcium fluoride recovered from wastewater is added and thoroughly stirred into a paste-like mixture. The sodium silicate and polyacrylamide are ultrasonically dispersed into the aqueous solution in a 1:1 weight ratio. The calcium fluoride powder is sourced from recycled photovoltaic wastewater and has a purity exceeding 92%. The composite binder accounts for 3.5% by weight of the mixed raw materials, and the water content of the mixed raw materials is 10%.

[0027] The resulting mixture is fed into a granulator for granulation, then removed and dried to produce fluorite sphere seed crystals with a diameter of 0.6-1.2 cm. The granulation process is as follows: the raw materials are stirred into a gypsum-like consistency, then fed into a pelletizer to produce uniformly sized granules. The granules are then polished into spherical particles with a diameter of 0.6-1.2 cm. The resulting fluorite spheres are then air-cooled at 25°C for 3 hours. The fluorite spheres are then dried in an electric forced air dryer at 50°C for 10 hours.

[0028] The obtained particles were placed in a 0.2 mol / L lanthanum nitrate solution, immersed and stirred for 1 hour, allowed to stand for 5 hours, and calcined at 350° C. for 3 hours to obtain fluorite spherical crystal seeds.

[0029] The prepared fluorite balls were filled into a PVC tube to a height of 50 cm. The filter material filling amount was 1200 g. The main component of the PVC tube was polyvinyl chloride, the inner diameter of the tube was 42 mm, and the height was 52 cm.

[0030] Simulated industrial wastewater containing fluoride ions and calcium chloride solution are slowly injected into both ends of the bottom of the PVC pipe. When the solutions are mixed and immersed in the fluorite balls, the fluorite balls act as crystal seeds to induce calcium fluoride to crystallize on their surface, effectively removing the fluoride ions in the solution. - The concentration is 23.12 mg / L, and the molar ratio of fluoride ion to calcium chloride solution is 1:0.6. The fluoride-containing wastewater and calcium chloride solution must be injected into the PVC pipe simultaneously and mixed evenly. The inlet flow rate of the fluoride-containing wastewater and calcium chloride solution is 28 mL / min. Example 3

[0031] A composite binder consisting of sodium silicate and polyacrylamide is prepared, adjusted to a pH of 6.5-7, and calcium fluoride recovered from wastewater is added and thoroughly stirred into a paste-like mixture. The sodium silicate and polyacrylamide are ultrasonically dispersed into the aqueous solution in a 1:1 weight ratio. The calcium fluoride powder is sourced from recycled photovoltaic wastewater and has a purity exceeding 92%. The composite binder accounts for 4.5% by weight of the mixed raw materials, and the water content of the mixed raw materials is 15%.

[0032] The resulting mixture is fed into a granulator for granulation, then removed and dried to produce fluorite sphere seed crystals with a diameter of 0.6-1.2 cm. The granulation process is as follows: the raw materials are stirred into a gypsum-like state and then fed into a pelletizer to produce uniformly sized granules. The granules are then polished into spherical particles with a diameter of 0.6-1.2 cm. The resulting fluorite spheres are then air-cooled at 28°C for 3.5 hours. The fluorite spheres are then dried in an electric forced air dryer at 55°C for 11 hours.

[0033] The obtained particles were placed in a 0.3 mol / L lanthanum chloride solution and immersed and stirred for 1.5 h, allowed to stand for 5 h, and calcined at 250° C. for 4.5 h to obtain fluorite spherical crystal seeds.

[0034] The prepared fluorite sphere seed crystals were filled into a PVC tube to a height of 50 cm. The filter material filling amount was 1200 g. The main component of the PVC tube was polyvinyl chloride, the inner diameter of the tube was 42 mm, and the height was 52 cm.

[0035] Simulated industrial wastewater containing fluoride ions and calcium chloride solution are slowly injected into both ends of the bottom of the PVC pipe. When the solutions are mixed and immersed in the fluorite balls, the fluorite balls act as crystal seeds to induce calcium fluoride to crystallize on their surface, effectively removing the fluoride ions in the solution. - The concentration is 22.28 mg / L, and the molar ratio of fluoride ion to calcium chloride solution is 1:0.5. The fluoride-containing wastewater and calcium chloride solution must be injected into the PVC pipe simultaneously and mixed evenly. The inlet flow rate of the fluoride-containing wastewater and calcium chloride solution is 33 mL / min.

[0036] Comparative Example 1 Sodium silicate is evenly dispersed in an aqueous solution, adjusted to a pH of 6.5-7, and calcium fluoride recovered from wastewater is added and thoroughly stirred into a paste-like mixture. The calcium fluoride powder is derived from recycled photovoltaic wastewater and has a purity of over 92%. The sodium silicate accounts for 4wt% of the mixed raw material, and the water content of the mixed raw material is 10%.

[0037] The resulting mixture is fed into a granulator for granulation, then removed and dried to produce fluorite sphere seed crystals with a diameter of 0.6-1.2 cm. The granulation process is as follows: the raw materials are stirred into a gypsum-like consistency, then fed into a pelletizer to produce uniformly sized granules. The granules are then polished into spherical shapes with a diameter of 0.6-1.2 cm. The resulting fluorite spheres are then cooled in cold air at 20-30°C for 2-4 hours. The fluorite spheres are then dried in an electric forced air dryer at 40-60°C for 8-12 hours.

[0038] The prepared fluorite balls were filled into a PVC tube to a height of 50 cm. The filter material filling amount was 1200 g. The main component of the PVC tube was polyvinyl chloride, the inner diameter of the tube was 42 mm, and the height was 52 cm.

[0039] Simulated industrial wastewater containing fluoride ions and calcium chloride solution are slowly injected into both ends of the bottom of the PVC pipe. When the solutions are mixed and immersed in the fluorite balls, the fluorite balls act as crystal seeds to induce calcium fluoride to crystallize on their surface, effectively removing the fluoride ions in the solution. - The concentration is 21.67 mg / L, and the molar ratio of fluoride ion to calcium chloride solution is 1:0.6. The fluoride-containing wastewater and calcium chloride solution must be injected into the PVC pipe simultaneously and mixed evenly. The inlet flow rate of the fluoride-containing wastewater and calcium chloride solution is 25 mL / min.

[0040] Comparative Example 2 A composite binder consisting of sodium silicate and polyacrylamide is prepared, adjusted to a pH of 6.5-7, and calcium fluoride recovered from wastewater is added and thoroughly stirred into a paste-like mixture. The sodium silicate and polyacrylamide are ultrasonically dispersed into the aqueous solution in a 1:1 weight ratio. The calcium fluoride powder is sourced from recycled photovoltaic wastewater and has a purity exceeding 92%. The composite binder accounts for 4wt% of the mixed raw materials, and the water content of the mixed raw materials is 10%.

[0041] The resulting mixture is fed into a granulator for granulation, then removed and dried to produce fluorite sphere seed crystals with a diameter of 0.6-1.2 cm. The granulation process is as follows: the raw materials are stirred into a gypsum-like consistency, then fed into a pelletizer to produce uniformly sized granules. The granules are then polished into spherical shapes with a diameter of 0.6-1.2 cm. The resulting fluorite spheres are then cooled in cold air at 20-30°C for 2-4 hours. The fluorite spheres are then dried in an electric forced air dryer at 40-60°C for 8-12 hours.

[0042] The prepared fluorite balls were filled into a PVC tube to a height of 50 cm. The filter material filling amount was 1200 g. The main component of the PVC tube was polyvinyl chloride, the inner diameter of the tube was 42 mm, and the height was 52 cm.

[0043] Simulated industrial wastewater containing fluoride ions and calcium chloride solution are slowly injected into both ends of the bottom of the PVC pipe. When the solutions are mixed and immersed in the fluorite balls, the fluorite balls act as crystal seeds to induce calcium fluoride to crystallize on their surface, effectively removing the fluoride ions in the solution. - The concentration is 22.06 mg / L, and the molar ratio of fluoride ion to calcium chloride solution is 1:0.6. The fluoride-containing wastewater and calcium chloride solution must be injected into the PVC pipe simultaneously and mixed evenly. The inlet flow rate of the fluoride-containing wastewater and calcium chloride solution is 25 mL / min.

[0044] Comparative Example 3 No seed crystals were added in this comparative example. - The concentration is 21.17 mg / L, and the molar ratio of fluoride ion to calcium chloride solution is 1:0.6. The fluoride-containing wastewater and calcium chloride solution must be injected into the PVC pipe simultaneously and mixed evenly. The inlet flow rate of the fluoride-containing wastewater and calcium chloride solution is 25 mL / min.

[0045] Result Analysis The physical picture of the lanthanum-loaded fluorite sphere seed prepared in Example 2 is as follows: Figure 1 As shown, the prepared lanthanum-loaded fluorite sphere seed crystals mainly contain C, O, F, Ca, and La. Further testing shows that La accounts for 17.22% of the total elements. This result shows that Example 2 successfully synthesized lanthanum-loaded fluorite sphere seed crystals and that lanthanum was successfully loaded on the fluorite sphere seed crystals.

[0046] The scanning electron microscope images of the lanthanum-loaded fluorite sphere seed prepared in Example 2 before and after defluorination are as follows: Figure 2 As shown, (a), (b) and (c) are scanning electron micrographs of the lanthanum-loaded fluorite sphere seeds prepared in Example 2 before defluorination; (d), (e) and (f) are the corresponding scanning electron micrographs after induced defluorination of the seeds. As can be seen from the figure, there is no obvious change in the particles before and after the reaction, which indicates that compared with the CaF2 raw material, the purity of Example 2 after defluorination does not change much. The above results show that after induced defluorination of the lanthanum-loaded fluorite sphere seeds, the recovered calcium fluoride still has a high purity.

[0047] The XRD patterns of calcium fluoride raw material, AR calcium fluoride and fluorite spherical seeds prepared in Examples 1-3 and Comparative Examples 1-2 are as follows: Figure 3As shown, similar to AR CaF2, the raw material CaF2 and the fluorite sphere seeds prepared in Comparative Example 1-2 all have peaks corresponding to CaF2 in PDF#35-0816 at 28.2°, 47°, 55.7°, 68.6°, 75.8°, and 87.3°. This result shows that the fluorite sphere seeds were successfully prepared. However, as the loading amount of lanthanum gradually increased, the characteristic peak of CaF2 in the lanthanum-loaded fluorite sphere seeds prepared in Example 1-3 gradually weakened, while the characteristic peak of LaF3 began to appear. This result further confirms that lanthanum has been successfully loaded on the fluorite sphere seeds.

[0048] The purity comparison of the calcium fluoride raw material and the calcium fluoride recovered in Example 1-3 and Comparative Example 1-2 is shown in the figure below. Figure 4 As shown, compared with the CaF2 raw material, the purity of calcium fluoride after defluorination in Examples 1-3 and Comparative Examples 1-2 does not decrease significantly. Figure 2 and 4 It can be seen that the product obtained after the induced crystallization reaction of the lanthanum-loaded fluorite spherical seeds is mainly calcium fluoride crystals.

[0049] The results of treating fluoride ions in wastewater with different hydraulic retention times in Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 5 and the following table:

[0050] Depend on Figure 5 As can be seen from the above table, compared with Comparative Example 3, the fluorine removal rates of Comparative Examples 1-2 using fluorite spherical crystal seeds for fluorine removal are significantly improved, among which the fluorine removal rates of Comparative Example 2 are all above 90%. Furthermore, the fluorine removal rates of Examples 1-3 are significantly improved after the fluorite spherical crystal seeds are loaded with lanthanum elements, and can reach up to 96.99%.

Claims

1. A method for preparing lanthanum-loaded fluorite spherical seed crystals, characterized in that The following steps are involved: (1) Sodium silicate and polyacrylamide are mixed and uniformly dispersed in an aqueous solution by ultrasonication to obtain a composite binder; (2) The calcium fluoride powder and the composite binder are uniformly mixed and put into a granulator for granulation, and then taken out and dried to obtain fluorite ball particles; (3) The obtained fluorite ball particles are immersed in a lanthanum solution and calcined to obtain lanthanum-loaded fluorite ball seed crystals.

2. The method for preparing lanthanum-loaded fluorite spherical seed crystals according to claim 1, wherein: In step (1), the mass ratio of sodium silicate to polyacrylamide is 0.5-1.2:

1. After the sodium silicate and polyacrylamide are ultrasonically dispersed in the aqueous solution, the pH is adjusted to 5.0-7.

0.

3. The method for preparing lanthanum-loaded fluorite spherical seed crystals according to claim 1, wherein: The calcium fluoride powder in step (2) comes from photovoltaic wastewater recovery products, wherein the purity of calcium fluoride is above 92%.

4. The method for preparing lanthanum-loaded fluorite spherical seed crystals according to claim 1, wherein: In step (2), the calcium fluoride powder and the composite binder are uniformly mixed to obtain a mixture having a content of sodium silicate and polyacrylamide of 3-5 wt % and a water content of 10-20 %.

5. The method for preparing lanthanum-loaded fluorite spherical seed crystals according to claim 1, wherein: The granulation step in step (2) is as follows: the calcium fluoride powder and the composite binder are stirred into a gypsum-like state and then put into a pelletizing machine to generate particles of uniform size, the particles are polished into spherical particles with a particle size of 0.6-1.2 cm, and then the particles are air-cooled in cold air at 20-30°C for 2-4 hours; the drying step is as follows: placing in an electric blast dryer at a temperature of 40-60°C and drying for 8-12 hours.

6. The method for preparing lanthanum-loaded fluorite spherical seed crystals according to claim 1, wherein: The lanthanum solution in step (3) is a lanthanum nitrate or lanthanum chloride solution with a concentration of 0.1-0.5 mol / L, and the immersion time is 0.5-2 h, and stirring is performed during the immersion; the specific steps of the calcination are as follows: the calcination temperature is 200-400° C., and the calcination time is 2-5 h.

7. Use of the lanthanum-loaded fluorite spherical seed crystals according to claim 1 in treating fluorine-containing wastewater.

8. A method for treating fluorine-containing wastewater using lanthanum-loaded fluorite spherical seed crystals, characterized in that: The fluorite ball crystal seeds loaded with lanthanum are filled into a PVC pipe, and the fluoride-containing wastewater and calcium chloride solution are slowly injected from both ends of the bottom of the PVC pipe respectively. The mixed solution of the two is immersed in the fluorite ball crystal seeds and left to stand for treatment. The calcium fluoride in the mixed solution crystallizes on the surface of the fluorite ball crystal seeds. After the treatment is completed, the treated liquid is discharged. The fluoride ion removal rate in the treated liquid is greater than 92%.

9. The method for treating fluorine-containing wastewater using lanthanum-loaded fluorite spherical seed crystals according to claim 8, characterized in that: The inner diameter of the PVC tube is 40-42 mm, and the height is 48-52 cm. The filling amount of the fluorite sphere seed crystal loaded with lanthanum inside the PVC tube is 300-1200 g, and the filling height is 20-50 cm.

10. The method for treating fluorine-containing wastewater using lanthanum-loaded fluorite spherical seed crystals according to claim 8, characterized in that: The concentration of fluoride ions in the fluoride-containing wastewater is 5-20 mg / L, and the molar ratio of fluoride ions to calcium chloride in the fluoride-containing wastewater is 1:0.5-0.6; the inlet flow rate of the fluoride-containing wastewater and the calcium chloride solution is 25-35 mL / min; during the static treatment, the temperature is maintained at 10-28° C., and the treatment time is 20-60 min.

Images