Method and system for recovering high-purity calcium fluoride from rare earth ore fluorine-containing raffinate

Abstract

The invention discloses a method and system for recovering high-purity calcium fluoride from rare earth ore fluorine-containing raffinate, the rare earth ore fluorine-containing raffinate enters a nanofiltration separation unit after suspended solids and organic impurities are removed in a pretreatment unit, sulfate ions are intercepted by a nanofiltration membrane to form a sulfate concentrated solution, and monovalent fluorine ions enter nanofiltration produced water through the nanofiltration membrane; carrying out induced crystallization reaction on the nanofiltration produced water and lime milk in a calcium fluoride crystallization reactor to generate calcium fluoride crystals; small-particle calcium fluoride crystals obtained by solid-liquid separation from the effluent of the calcium fluoride crystallization reactor are sent back to the calcium fluoride crystallization reactor to serve as calcium fluoride seed crystals, and the water obtained by solid-liquid separation is discharged after reaching the standard; according to the method, the purity of the calcium fluoride generated by the method is stabilized at 90% or above, sulfate by-products can be produced, resource recycling of fluorine and sulfate in the rare earth raffinate is achieved, and the disposal amount of hazardous waste is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method and system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue. Background Technology

[0002] In rare earth smelting, fluorine, as a major by-product element, ultimately enters the raffinate during mineral decomposition and extraction separation processes, forming fluoride-containing wastewater with complex composition and high treatment difficulty. This type of raffinate mainly falls into two systems: one is a mixed solution containing ammonium sulfate and ammonium fluoride produced using ammonia soap extractant; the other is a composite system containing sodium sulfate and sodium fluoride produced using sodium soap extractant. These raffinates not only contain high concentrations of sulfates and fluorides but also trace amounts of heavy metal ions and residual organic extractants, making them complex in composition and difficult to treat.

[0003] Currently, the industry mainly uses the following technologies to treat fluoride-containing extraction residues:

[0004] Membrane separation technology, including reverse osmosis and electrodialysis, can effectively remove dissolved ions and recover some high-quality water. However, it faces challenges such as low water recovery rate, high energy consumption, severe membrane fouling, and subsequent treatment of concentrate. In particular, this method cannot effectively recover fluoride from rare earth raffinate with complex composition.

[0005] Flocculation and precipitation method: Flocculants such as aluminum and iron salts are added to calcium salt precipitation to enhance the fluoride removal effect through adsorption and co-precipitation. However, this method introduces new metal ions, increases the volume of the precipitate, is ineffective for sulfate separation, and has low resource utilization value of the product.

[0006] Calcium salt precipitation method: This is the most commonly used traditional method, which involves adding lime or calcium chloride to cause fluoride ions to form calcium fluoride precipitate. However, the calcium fluoride crystals formed by conventional calcium salt precipitation method are small in size, have poor sedimentation performance, and low purity (usually only 20%-50%). The main reason is that when calcium is added to form calcium fluoride, calcium ions combine with sulfate ions in the raffinate to form calcium sulfate co-precipitate, which makes subsequent solid-liquid separation difficult and results in low product utilization value. Summary of the Invention

[0007] To overcome the above-mentioned defects, the present invention provides a method and system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue. This method and system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue has the advantages of high product purity and value, high separation efficiency, no need to add chemical reagents, and simple operation.

[0008] The technical solution adopted by this invention to solve its technical problem is as follows: a method for recovering high-purity calcium fluoride from fluorine-containing extraction residue of rare earth mines, characterized by the following specific steps:

[0009] Step 1: Send the fluorine-containing raffinate from the rare earth ore into the pretreatment unit to remove suspended solids and organic impurities, ensuring that the turbidity entering the nanofiltration unit is less than 1 NTU and COD < 20 mg / L;

[0010] Step 2: The effluent from the pretreatment unit enters the nanofiltration separation unit, whose core component is the nanofiltration membrane module. Special nanofiltration membranes with high retention rates for sulfate ions and high permeability for monovalent fluoride ions, such as the Dow NF270 nanofiltration membrane, are selected. The nanofiltration membrane retains sulfate ions, which enter the concentrate of the nanofiltration separation unit to form a sulfate concentrate. Monovalent fluoride ions permeate through the nanofiltration membrane into the nanofiltration permeate, thus achieving the separation of sulfate and fluoride. The nanofiltration membrane separation process is continuous and efficient, solving the problem of low efficiency in traditional precipitation methods.

[0011] Step 3: The nanofiltration permeate from the nanofiltration separation unit enters the calcium fluoride crystallization reactor of the induced crystallization unit. The crystallization reactor is designed as a fully mixed fluidized bed, filled with calcium fluoride seed crystals as crystallization nuclei. The dosing system of the induced crystallization unit adds lime slurry (Ca(OH)2 solution) to the calcium fluoride crystallization reactor through a precision dosing system. The amount of lime slurry added is controlled according to the calcium-fluoride molar ratio of 1.05 to 1.1. Fluoride ions and calcium ions react in the calcium fluoride crystallization reactor to generate calcium fluoride. The calcium fluoride grows on the surface of the pre-filled calcium fluoride seed crystals in the calcium fluoride crystallization reactor to form calcium fluoride crystals.

[0012] Step 4: The effluent from the calcium fluoride crystallization reactor in the induced crystallization unit enters the solid-liquid separation system. The solid-liquid separation system separates the small-particle calcium fluoride crystals from the water in the effluent from the calcium fluoride crystallization reactor. The small-particle calcium fluoride crystals separated by the solid-liquid separation system are sent back to the calcium fluoride crystallization reactor as calcium fluoride seed crystals, thereby realizing the recycling of calcium fluoride crystals. The water separated by the solid-liquid separation system is discharged in compliance with standards.

[0013] Step 5: The large calcium fluoride crystals inside the bottom of the calcium fluoride crystallization reactor are periodically discharged through the discharge port. After being dehydrated by the dehydration equipment, high-purity calcium fluoride products with a purity of over 90% are obtained.

[0014] The above process achieves a single-pass fluoride recovery rate of over 90% and an induced crystallization fluoride removal rate of over 98%. The entire system is highly integrated, enabling automated control and reducing manual operation and intervention.

[0015] As a further improvement of the present invention, after the rare earth ore fluorine-containing extraction liquid enters the pretreatment unit, it first undergoes multi-media filtration to remove tiny suspended solids and residual organic extractants, then activated carbon filtration adsorption to remove residual organic matter in the water, then PP cotton precision filtration to remove tiny suspended solids and a small amount of turbidity in the water, and finally ultrafiltration to remove large molecular organic matter in the water.

[0016] The aforementioned pretreatment unit can effectively remove suspended solids and organic impurities from wastewater, preventing clogging of the nanofiltration membrane.

[0017] As a further improvement of the present invention, the multi-media filter is filled with quartz sand, manganese sand and garnet, and other filter media can also be filled, depending on the type of impurities in the wastewater.

[0018] As a further improvement of the present invention, when the effluent from the pretreatment unit enters the nanofiltration separation unit, the nanofiltration operating pressure is controlled at 0.8-1.5 MPa, and the temperature is maintained at [temperature missing].

[0019] At 25-35℃, the nanofiltration membrane can achieve a rejection rate of over 98% for sodium sulfate / ammonium sulfate, while the permeability of sodium fluoride / ammonium fluoride exceeds 90%, thus achieving efficient separation of sulfates and fluorides.

[0020] As a further improvement of this invention, the sulfate concentrate formed by the nanofiltration separation unit is further processed to recover sodium sulfate or ammonium sulfate products. Nanofiltration membranes are used to separate sulfate and fluoride. Although the nanofiltration membrane system has certain investment costs, most of the operating costs can be offset by the recovery of sulfate byproducts and the production of high-value calcium fluoride products. Estimates show that the byproduct revenue can cover 60%-70% of the operating costs for each ton of fluoride-containing raffinate treated, which is far higher than the traditional simple treatment mode. Furthermore, this application pre-treats the wastewater before nanofiltration, extending the membrane cleaning cycle (up to once every 2-3 months) and reducing the consumption of chemical cleaning agents and the frequency of membrane replacement.

[0021] As a further improvement of the present invention, the seed bed in the calcium fluoride crystallization reactor is fluidized by mechanical stirring. The reaction temperature in the calcium fluoride crystallization reactor is maintained at 15-60°C, and the hydraulic residence time is about 45-180 minutes. The fluoride permeate from the nanofiltration membrane enters the crystallization reactor, and the seed bed is fluidized by mechanical stirring. Under the above reaction conditions, the seed bed combines with calcium ions to form calcium fluoride precipitate. The calcium fluoride crystallizes and grows directionally with the seed crystal as the core to form a granular product with uniform particle size.

[0022] As a further improvement of the present invention, the solid-liquid separation system is a sedimentation tank connected to the outlet of the calcium fluoride crystallization reactor. Small calcium fluoride crystals are precipitated in the sedimentation tank and returned to the calcium fluoride crystallization reactor. The effluent from the sedimentation tank is discharged in compliance with standards.

[0023] A system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue includes a rare earth ore fluoride extraction residue collection tank, a pretreatment unit, a nanofiltration separation unit, an induced crystallization unit, several booster pumps, and a control system. The induced crystallization unit includes a calcium fluoride crystallization reactor, a dosing system, a solid-liquid separation system, and dehydration equipment. The outlet of the rare earth ore fluoride extraction residue collection tank is connected to the inlet of the pretreatment unit via a pipeline. The booster pumps continuously pump the rare earth ore fluoride extraction residue from the collection tank into the pretreatment unit, which removes suspended solids and organic impurities. The outlet of the pretreatment unit is connected to the inlet of the nanofiltration separation unit via a pipeline, allowing the booster pumps to pump the effluent from the pretreatment unit into the nanofiltration separation unit. The nanofiltration separation unit is equipped with a nanofiltration membrane that traps sulfate ions in the effluent from the pretreatment unit to form a sulfate concentrate. The nanofiltration membrane allows monovalent fluoride ions to pass through and enter the permeate of the nanofiltration separation unit. The permeate of the nanofiltration separation unit is connected to the induced crystallization unit via a pipeline. The inlet of the calcium fluoride crystallization reactor in the crystallization unit is connected to a booster pump, which pumps the permeate from the nanofiltration separation unit into the calcium fluoride crystallization reactor. The dosing system of the induced crystallization unit can quantitatively add lime slurry into the calcium fluoride crystallization reactor to control the calcium-fluoride molar ratio of the mixed liquid in the calcium fluoride crystallization reactor to be 1.05-1.1. The outlet of the calcium fluoride crystallization reactor is connected to the inlet of the solid-liquid separation system. The solid-liquid separation system can dehydrate small-particle calcium fluoride crystals in the effluent of the calcium fluoride crystallization reactor. The small-particle calcium fluoride crystals dehydrated by the solid-liquid separation system can be pumped back into the calcium fluoride crystallization reactor by a booster pump. The crystal discharge port at the bottom of the calcium fluoride crystallization reactor can periodically discharge the large-particle calcium fluoride crystals inside and send them to the dehydration equipment. The dehydration equipment can dehydrate the large-particle calcium fluoride crystals to form a calcium fluoride product with a purity of over 90%. The control system controls the operation of each booster pump. The entire system is intelligently controlled by the control system and does not require manual intervention.

[0024] As a further improvement of the present invention, the pretreatment unit includes a multi-media filter for removing minute suspended solids and residual organic extractants from the rare earth ore fluoride extraction residue, an activated carbon filter tank for removing residual organic matter in the water, a PP cotton precision filter for removing minute suspended solids and a small amount of turbidity in the water, and an ultrafiltration membrane system for removing macromolecular organic matter in the water. The multi-media filter is filled with quartz sand, manganese sand, and garnet. The outlet of the multi-media filter is connected to the inlet of the activated carbon filter tank, the outlet of the activated carbon filter tank is connected to the inlet of the PP cotton precision filter, and the outlet of the PP cotton precision filter is connected to the ultrafiltration membrane system. The effluent from the PP cotton precision filter can be pumped into the ultrafiltration membrane system by a booster pump. The water produced by the ultrafiltration membrane system forms the effluent of the pretreatment unit. The solid-liquid separation system of the induced crystallization unit is a sedimentation tank.

[0025] As a further improvement of the present invention, the calcium fluoride crystallization reactor is further equipped with a stirrer, a first heating device, and a first temperature sensor. The stirrer can continuously stir the mixture in the calcium fluoride crystallization reactor, the first heating device can heat the wastewater in the calcium fluoride crystallization reactor, and the first temperature sensor can detect the temperature of the wastewater in the calcium fluoride crystallization reactor in real time and feed it back to the control system. The nanofiltration separation unit is equipped with a second heating device, a second temperature sensor, and a pressure sensor. The second heating device can heat the wastewater entering the nanofiltration separation unit, and the second temperature sensor and pressure sensor can respectively detect the temperature of the wastewater in the nanofiltration separation unit and the pressure of the wastewater on the nanofiltration membrane in real time. The second temperature sensor and pressure sensor can respectively feed back the detection data to the control system, and the control system can control the start and stop of the first and second heating devices and the flow rate of the booster pump supplying water to the nanofiltration separation unit. By using various sensors to detect the system operating conditions in real time, the control system can control the flow rate of the heating device and the booster pump, so that the operating conditions of the entire system meet the design requirements, thereby forming intelligent control.

[0026] The beneficial effects of this invention are as follows: This invention applies nanofiltration membrane separation technology to the separation of sulfate and fluoride in rare earth extraction residues. Utilizing the selective separation characteristics of nanofiltration membranes for divalent sulfate and monovalent fluoride ions, it solves the problem of impurity contamination at the source, providing a raw material basis for the subsequent preparation of high-purity calcium fluoride. Compared with traditional chemical separation methods, this technology has advantages such as high separation efficiency, no need to add chemical reagents, and simple operation. This invention also combines induced crystallization technology, introducing calcium fluoride seeds as crystallization nuclei during lime precipitation. By precisely controlling reaction conditions (calcium-fluoride ratio, temperature, hydraulic characteristics), calcium fluoride is guided to form granular crystals through a heterogeneous nucleation-directional growth mechanism, completely changing the morphology of traditional amorphous precipitates. This solves the problems of low purity and difficult separation of calcium fluoride. The purity of the generated calcium fluoride is consistently above 90%, reaching up to 95%, far exceeding the 60%-80% level of the traditional lime method. High-purity calcium fluoride can be used as a high-quality metallurgical flux or raw material for the fluorochemical industry, realizing the transformation from hazardous waste to high-value products. Granular calcium fluoride possesses excellent settling performance (settling speed 3-5 times faster than traditional methods) and dehydration performance (moisture content can be reduced to below 20%), significantly reducing subsequent processing costs. This invention organically integrates three units—pretreatment, nanofiltration separation, and induced crystallization—to form a highly efficient and compact processing system, enabling continuous production from rare earth raffinate to high-purity calcium fluoride. This integrated design not only improves processing efficiency but also achieves resource recovery of pollutants and process optimization through the synergistic effect of each unit. The nanofiltration membrane system of this invention can also produce sulfate byproducts, realizing the resource recovery of fluoride and sulfate in rare earth raffinate without secondary pollution, significantly reducing the amount of hazardous waste to be disposed of (reduction rate of over 95%). The process flow is a closed-loop cycle, and the wastewater meets reuse standards and can be returned to the production process, realizing water resource recycling and aligning with the concepts of green metallurgy and circular economy. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention;

[0028] Figure 2 This is a system schematic diagram of the present invention. Detailed Implementation

[0029] Example 1: The raffinate after ammonia soap extraction of a rare earth mineral mainly consists of ammonium sulfate (12.5 g / L) and ammonium fluoride (4.2 g / L), with a pH of 6.8, and contains a small amount of suspended solids and trace heavy metal ions.

[0030] The method for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue using the rare earth ore fluoride extraction residue of the present invention comprises the following specific steps:

[0031] 1. Pretreatment: The wastewater passes through a multi-media filtration system, activated carbon filtration system, PP cotton precision filtration system, and ultrafiltration membrane system in the pretreatment unit in sequence, so that the turbidity of the effluent is reduced to 0.8 NTU and the COD is less than 15 mg / L;

[0032] 2. Nanofiltration separation: The pretreated wastewater enters the nanofiltration separation unit, with an operating pressure of 1.2 MPa and a temperature of 18-30℃. The nanofiltration membrane has a retention rate of 98.5% for ammonium sulfate and a permeation rate of 92% for ammonium fluoride. After separation, the product water of the nanofiltration separation unit is an ammonium fluoride solution, and the concentration of ammonium sulfate in the product water of the nanofiltration separation unit is reduced to below 0.2 g / L.

[0033] 3. Induced crystallization: Ammonium fluoride solution (concentration 3.9 g / L) is introduced into the calcium fluoride crystallization reactor, which is pre-loaded with calcium fluoride seed crystals (particle size 0.05-0.09 mm). Lime slurry is added at a Ca / F molar ratio of 1.08:1. The reaction temperature is 25-40℃ and the hydraulic residence time is 60 minutes.

[0034] Results: The generated calcium fluoride product was in the form of regular granules with an average particle size of 0.12 mm, a purity of 92.5%, and a fluorine removal rate of 98.8%. XRD analysis confirmed that the product was mainly composed of calcium fluoride crystals, which met the industrial fluorite standard.

[0035] Example 2: The raffinate after sodium soap extraction of a rare earth ore mainly consists of sodium sulfate (15.8 g / L) and sodium fluoride (3.8 g / L), with a pH of 7.2 and containing a small amount of organic matter.

[0036] The method for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue using the rare earth ore fluoride extraction residue of the present invention comprises the following specific steps:

[0037] 1. Pretreatment: The process is the same as in Example 1. The turbidity of the ultrafiltration membrane system in the pretreatment unit is 0.6 NTU, and the COD is <12 mg / L.

[0038] 2. Nanofiltration Separation: The pretreated wastewater enters the nanofiltration separation unit. The nanofiltration membrane used is the Dow NF270 nanofiltration membrane. The operating pressure is 1.5 MPa, and the temperature is 28-42℃. The nanofiltration membrane has a sodium sulfate rejection rate of 99.0% and a sodium fluoride permeation rate of 91%. After separation, the product water of the nanofiltration separation unit is a sodium fluoride solution, and the sodium sulfate concentration in the product water of the nanofiltration separation unit is reduced to 0.16 g / L.

[0039] 3. Induced crystallization: Sodium fluoride solution (concentration 3.5 g / L) is introduced into the calcium fluoride crystallization reactor, and lime slurry is added at a Ca / F molar ratio of 1.06:1. The reaction temperature is 25-38℃ and the hydraulic residence time is 100 minutes.

[0040] Results: The solid particles discharged from the outlet of the calcium fluoride crystallization reactor were uniform granular calcium fluoride with an average particle size of 0.14 mm, a purity of 91.8%, and a fluoride removal rate of 99.2%.

Claims

1. A method for recovering high-purity calcium fluoride from fluorine-containing extraction residue of rare earth ores, characterized in that: The specific steps are as follows: Step 1: Send the fluorine-containing raffinate from the rare earth ore into the pretreatment unit to remove suspended solids and organic impurities; Step 2: The effluent from the pretreatment unit enters the nanofiltration separation unit, where sulfate ions are retained by the nanofiltration membrane. The sulfate ions enter the concentrate of the nanofiltration separation unit to form a sulfate concentrate, while monovalent fluoride ions pass through the nanofiltration membrane into the nanofiltration permeate. Step 3: The nanofiltration permeate from the nanofiltration separation unit enters the calcium fluoride crystallization reactor of the induced crystallization unit. The dosing system of the induced crystallization unit adds lime slurry to the calcium fluoride crystallization reactor. The amount of lime slurry added is controlled according to the calcium-fluoride molar ratio of 1.05 to 1.

1. Fluoride ions and calcium ions react in the calcium fluoride crystallization reactor to generate calcium fluoride. The calcium fluoride grows on the surface of the calcium fluoride seed crystals pre-filled inside the calcium fluoride crystallization reactor to form calcium fluoride crystals. Step 4: The effluent from the calcium fluoride crystallization reactor in the induced crystallization unit enters the solid-liquid separation system. The solid-liquid separation system separates the small-particle calcium fluoride crystals from the water in the effluent from the calcium fluoride crystallization reactor. The small-particle calcium fluoride crystals separated by the solid-liquid separation system are sent back to the calcium fluoride crystallization reactor as calcium fluoride seed crystals. The water separated by the solid-liquid separation system is discharged in compliance with standards. Step 5: The large calcium fluoride crystals inside the bottom of the calcium fluoride crystallization reactor are periodically discharged through the discharge port. After being dehydrated by the dehydration equipment, high-purity calcium fluoride products with a purity of over 90% are obtained.

2. The method for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue according to claim 1, characterized in that: After entering the pretreatment unit, the rare earth ore fluorine-containing extraction liquid first undergoes multi-media filtration to remove tiny suspended solids and residual organic extractants, then activated carbon filtration adsorption to remove residual organic matter in the water, followed by PP cotton precision filtration to remove tiny suspended solids and a small amount of turbidity in the water, and finally ultrafiltration to remove large molecular organic matter in the water.

3. The method for recovering high-purity calcium fluoride from fluorine-containing extraction liquor of rare earth ore according to claim 2, characterized in that: The multi-media filter is filled with quartz sand, manganese sand and garnet.

4. The method for recovering high-purity calcium fluoride from fluoride-containing extraction liquor of rare earth ore according to claim 1, characterized in that: When the effluent from the pretreatment unit enters the nanofiltration separation unit, the nanofiltration operating pressure is controlled at 0.8-1.5MPa and the temperature is maintained at 25-35℃.

5. The method for recovering high-purity calcium fluoride from fluoride-containing extraction liquor of rare earth ore according to claim 1, characterized in that: The sulfate concentrate formed by the nanofiltration separation unit is further processed to recover sodium sulfate or ammonium sulfate products.

6. The method for recovering high-purity calcium fluoride from fluoride-containing extraction liquor of rare earth ore according to claim 1, characterized in that: The seed bed in the calcium fluoride crystallization reactor is fluidized by mechanical stirring. The reaction temperature in the calcium fluoride crystallization reactor is maintained at 15-60℃, and the hydraulic residence time is about 45-180 minutes.

7. The method for recovering high-purity calcium fluoride from fluoride-containing extraction liquor of rare earth ores according to claim 1, characterized in that: The solid-liquid separation system is a sedimentation tank connected to the outlet of the calcium fluoride crystallization reactor.

8. A system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue as described in any one of claims 1-7, characterized in that: The system includes a rare earth ore fluoride extraction residue collection tank, a pretreatment unit, a nanofiltration separation unit, an induced crystallization unit, several booster pumps, and a control system. The induced crystallization unit includes a calcium fluoride crystallization reactor, a dosing system, a solid-liquid separation system, and dehydration equipment. The outlet of the rare earth ore fluoride extraction residue collection tank is connected to the inlet of the pretreatment unit via a pipeline. The booster pumps continuously pump the rare earth ore fluoride extraction residue from the collection tank into the pretreatment unit, which removes suspended solids and organic impurities. The outlet of the pretreatment unit is connected to the inlet of the nanofiltration separation unit via a pipeline, and the booster pumps pump the effluent from the pretreatment unit into the nanofiltration separation unit. The nanofiltration separation unit is equipped with a nanofiltration membrane that traps sulfate ions in the effluent from the pretreatment unit to form a sulfate concentrate. The nanofiltration membrane allows monovalent fluoride ions to pass through and enter the permeate of the nanofiltration separation unit. The permeate of the nanofiltration separation unit is then transported through a pipeline... The system is connected to the inlet of the calcium fluoride crystallization reactor in the induced crystallization unit. A booster pump can pump the permeate from the nanofiltration unit into the calcium fluoride crystallization reactor. The dosing system of the induced crystallization unit can quantitatively add lime slurry to the calcium fluoride crystallization reactor to control the calcium-fluoride molar ratio of the mixed solution within the reactor to be 1.05–1.

1. The outlet of the calcium fluoride crystallization reactor is connected to the inlet of the solid-liquid separation system. The solid-liquid separation system can dehydrate small-particle calcium fluoride crystals in the effluent from the calcium fluoride crystallization reactor. The dehydrated small-particle calcium fluoride crystals can be pumped back into the calcium fluoride crystallization reactor via a booster pump. The discharge outlet at the bottom of the calcium fluoride crystallization reactor can periodically discharge large-particle calcium fluoride crystals from its interior and send them to a dehydration device. The dehydration device can dehydrate the large-particle calcium fluoride crystals to form a calcium fluoride product with a purity higher than 90%. The control system controls the operation of each booster pump.

9. The system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue according to claim 8, characterized in that: The pretreatment unit includes a multi-media filter for removing minute suspended solids and residual organic extractants from the rare earth ore fluoride extraction residue, an activated carbon filter tank for removing residual organic matter in the water, a PP cotton precision filter for removing minute suspended solids and small amounts of turbidity in the water, and an ultrafiltration membrane system for removing macromolecular organic matter in the water. The multi-media filter is filled with quartz sand, manganese sand, and garnet. The outlet of the multi-media filter is connected to the inlet of the activated carbon filter tank, the outlet of the activated carbon filter tank is connected to the inlet of the PP cotton precision filter, and the outlet of the PP cotton precision filter is connected to the ultrafiltration membrane system. The effluent from the PP cotton precision filter can be pumped into the ultrafiltration membrane system via a booster pump. The water produced by the ultrafiltration membrane system forms the effluent of the pretreatment unit. The solid-liquid separation system of the induced crystallization unit is a sedimentation tank.

10. The system for recovering high-purity calcium fluoride from rare earth ore fluoride extraction residue according to claim 8, characterized in that: The calcium fluoride crystallization reactor is also equipped with a stirrer, a first heating device, and a first temperature sensor. The stirrer can continuously stir the mixture in the calcium fluoride crystallization reactor. The first heating device can heat the wastewater in the calcium fluoride crystallization reactor. The first temperature sensor can detect the temperature of the wastewater in the calcium fluoride crystallization reactor in real time and feed it back to the control system. The nanofiltration separation unit is equipped with a second heating device, a second temperature sensor, and a pressure sensor. The second heating device can heat the wastewater entering the nanofiltration separation unit. The second temperature sensor and the pressure sensor can respectively detect the temperature of the wastewater in the nanofiltration separation unit and the pressure of the wastewater on the nanofiltration membrane in real time. The second temperature sensor and the pressure sensor can respectively feed the detection data back to the control system. The control system can control the start and stop of the first heating device and the second heating device, as well as the flow rate of the booster pump supplying water to the nanofiltration separation unit.

Images