A system for recovering high-purity fluorite from fluorine-containing wastewater

Abstract

The application discloses a system for recovering high-purity fluorite from fluorine-containing wastewater, comprising a fluidized bed, wherein a water distribution area, an induced crystallization area and a precipitation area are sequentially arranged in the fluidized bed; the system further comprises a pretreatment device, a crystallization agent storage tank and a collection tank; the water distribution area is located at the bottom of the fluidized bed; a water distributor connected with a water inlet of the fluidized bed is arranged in the water distribution area, and a polytetrafluoroethylene ball layer is stacked on the water distributor; at least three layers of medicine distributors are arranged in the induced crystallization area at equal intervals, and the at least three layers of medicine distributors are arranged above the polytetrafluoroethylene ball layer and connected with medicine inlets in the side wall of the fluidized bed respectively; a crystallization separation device is arranged above the uppermost medicine distributor. The system can treat the fluorine-containing wastewater with a fluorine content of 200-800 mg / L commonly seen in the electronic industry, and simultaneously generate high-purity fluorite crystals, so that the fluorine can be recycled and reused.

Description

TECHNICAL FIELD

[0001] The present application relates to a system for recovering high-purity fluorite from fluorine-containing wastewater. BACKGROUND

[0002] A large amount of fluorine-containing wastewater is generated in the production processes of semiconductor, photovoltaic, rare earth smelting and other industries. At present, the treatment methods of fluorine-containing wastewater include chemical precipitation method, electrocoagulation method, reverse osmosis method, ion exchange method, membrane separation method and adsorption method. These methods have good removal effect, but a large amount of inorganic fluorine-containing sludge is generated, causing serious solid waste pollution and waste of fluorine resources.

[0003] Compared with the common chemical precipitation or coagulation precipitation method for treating fluorine-containing wastewater, the induced crystallization fluidized bed is used for fluorine resource recovery of fluorine-containing wastewater, which not only solves the problem of fluorine-containing sludge disposal, but also produces fluorite with low water content and high value (fluorite, also known as fluorite, is the main raw material for producing hydrofluoric acid, and the main component is calcium fluoride, chemical formula: CaF2).

[0004] However, sulfate, silicon, phosphate and other substances contained in wastewater are easy to react with the crystallizing agent to form precipitates, which interfere with the removal of fluorine ions, and also reduce the crystallization quality of calcium fluoride and cryolite, and increase the suspended solids content in the effluent. For 200-800 mg / L of medium and low concentration fluorine-containing wastewater, calcium salt can be added for induced crystallization; while for high concentration fluorine-containing wastewater exceeding 800 mg / L, it is difficult to be treated by fluorite crystallization technology. In addition, the current fluidized bed reactor cannot control the size of the discharged crystals, and the reactor needs to be stopped when the crystals are discharged, and the operation process is very complex. The above shortcomings limit the promotion of fluidized bed induced crystallization technology in the field of fluorine resource recovery. SUMMARY

[0005] The purpose of the present application is to provide a system for recovering high-purity fluorite from fluorine-containing wastewater, which can treat 200-800 mg / L of fluorine-containing wastewater commonly used in the electronic industry and simultaneously generate high-purity fluorite crystals, realizing the resource recovery of fluorine.

[0006] Technical solution: The system for recovering high-purity fluorite from fluorine-containing wastewater provided by the application comprises a fluidized bed, a water distribution zone, an induced crystallization zone and a precipitation zone arranged in the fluidized bed in sequence, a pretreatment device, a crystallization agent storage tank and a collection tank; the water distribution zone is located at the bottom of the fluidized bed; a water distributor connected with a water inlet of the fluidized bed is arranged in the water distribution zone, and a layer of polytetrafluoroethylene beads is stacked on the water distributor; at least three layers of medicine distributors are arranged in the induced crystallization zone at equal intervals, and the at least three layers of medicine distributors are arranged above the layer of polytetrafluoroethylene beads and connected with medicine inlets in the side walls of the fluidized bed; a crystallization separation device is arranged above the uppermost layer of medicine distributors; modified activated carbon particles are filled in the pretreatment device, and fluorine-containing wastewater treated by the pretreatment device enters the water distributor from a water inlet; the calcium-based crystallization agent is sent into each layer of medicine distributors through a medicine inlet of the crystallization agent storage tank; F - is removed from the fluorine-containing wastewater in the form of CaF2 in the calcium-based crystallization agent + CaF2 crystalline particles are generated in the induced crystallization zone of the fluidized bed, and the crystallization separation device is in an open state under the action of the upward water flow during the fluorine removal process of the fluidized bed; the calcium fluoride crystalline particles with small particle sizes pass through the crystallization separation device under the action of the water flow, and the calcium fluoride crystalline particles with large particle sizes fall into the induced crystallization zone; the fluidized bed is provided with a crystallization discharge port on the corresponding side wall of the induced crystallization zone; when the crystallization discharge port is opened, the upward water flow power is reduced, and at this time, the crystallization separation device is in a closed state; the calcium fluoride crystalline particles in the induced crystallization zone are discharged from the fluidized bed; the water outlet of the fluidized bed flows into the collection tank for subsequent deep fluorine removal.

[0007] The modified activated carbon particles are prepared by the following method: 50 g of activated carbon is uniformly dispersed in 1 L of HNO3 solution with a concentration of 1 mol / L, and heated at 50 DEG C for 6 hours; the activated carbon pretreated by HNO3 has a larger specific surface area; after being continuously washed with deionized water for 10 min, it is dried at 60 DEG C for 4 h; 50 g of the pretreated activated carbon is added to 500 mL of BaCl2 solution with a concentration of 0.5 mol / L, stirred at 120 r / min for 1 h at 25 DEG C, and then ultrasonic for 2 h; the activated carbon after ultrasonic is filtered and washed with deionized water for 3 times, dried at 60 DEG C for 4 h, and then calcined at 500 DEG C for 6 hours to obtain activated carbon particles loaded with barium ions on the surface. When the fluorine-containing wastewater is pretreated, the barium ions loaded on the surface of the activated carbon can remove impurities such as sulfate and phosphate under acidic conditions, and the generated small molecule barium sulfate and barium phosphate precipitates are adsorbed on the surface of the activated carbon.

[0008] The water distributor is placed at the bottom of the fluidized bed and communicates with the external water inlet pipe. A porous baffle I is placed above the water outlet of the water distributor. The diameter of the porous baffle I is equivalent to the diameter of the fluidized bed. A plurality of through holes with a diameter of 4 mm are uniformly distributed on the porous baffle I. A layer of polytetrafluoroethylene beads with a height of 10-15 cm is uniformly placed above the porous baffle. The diameter of the polytetrafluoroethylene beads is 5 mm. A porous baffle II is further placed at a position 2-3 cm above the layer of polytetrafluoroethylene beads. The porous baffle I and the porous baffle II are used for fixing the polytetrafluoroethylene beads. The diameter of the porous baffle II is equivalent to the diameter of the fluidized bed. A plurality of through holes with a diameter of 4 mm are also uniformly distributed on the porous baffle II. The water inlet is uniformly dispersed after passing through the water distributor and the layer of polytetrafluoroethylene beads. The polytetrafluoroethylene beads are solid beads. The polytetrafluoroethylene beads serve as a support layer for the crystalline particles, so as to avoid the blockage of the water outlet of the water distributor by the crystalline particles. A first layer of medicine distributor is installed at a position 2-3 cm above the porous baffle II. The first layer of medicine distributor is provided with an opening (medicine outlet) every 2 cm in the horizontal direction, so as to realize the sufficient reaction of the medicine with the uniformly dispersed fluorine-containing wastewater.

[0009] The medicine feeding pipe inside the fluidized bed adopts multi-layer three-dimensional water distribution, so that the calcium-based crystallization agent is fully mixed with the fluorine-containing wastewater, and the uniform growth of the crystal seeds is ensured. The backflow supernatant in the precipitation zone of the fluidized bed is transported to the bottom of the fluidized bed by a circulating pump, so as to ensure that the fluorine concentration of the fluorine-containing wastewater in the fluidized bed is 200-300 mg / L.

[0010] The crystallization separation device comprises a support layer, a filter screen and a triangular blade. The support layer is used for separating small size calcium fluoride crystal particles when the crystals are discharged. The support layer is a circular ring made of 304 carbon steel, the diameter of which is slightly smaller than the diameter of the fluidized bed body, and the edge of the circular ring is fixed on the fluidized bed body. The bottom of the support layer is provided with a support rod. The center point of the upper end surface of the support rod coincides with the center point of the circular ring. The inside of the circular ring is equally divided into eight parts by eight horizontal rods made of 304 carbon steel. A stainless steel support rod with a diameter of 4 cm and a height of 1.2 m is placed at the bottom of the circular ring, and the bottom of the support rod is fixed on the bottom of the fluidized bed for fixing the whole support layer. One end point of each horizontal rod is fixed at the center point of the upper end surface of the support rod, and the other end point of each horizontal rod is fixed on the edge of the circular ring (the length of the horizontal rod is equal to the radius of the circular ring). The triangular blade is an isosceles triangle (the included angle of adjacent horizontal rods is consistent with the top angle of the isosceles triangle), the length of the long side is equal to the radius of the circular ring, the long side is fixed on the horizontal rod by a rotating shaft and rotates relative to the horizontal rod, and the other two sides are not fixed. The filter screen is used for intercepting small particle calcium fluoride crystal particles when the crystals are discharged, and at the same time, the wastewater can pass through the filter screen. The pore size of the filter screen is 60 meshes. The filter screen is installed in the gap between the short side of the triangular blade and the circular ring. A sludge concentration meter is arranged 15 cm above the support layer for monitoring the growth of the fluorite in the fluidized bed. In the initial stage of induced crystallization, the fluorite seeds are uniformly dispersed in the induced crystallization zone under the action of the upward water flow. At this time, the index of the sludge concentration meter is the initial sludge concentration index (the wet fluorite seeds with a particle size of about 100 meshes are put into the top of the fluidized bed before the reactor is operated, and the data collected by the sludge concentration meter at this time is the initial concentration index of the fluorite). With the continuous growth of the particle size of the fluorite seed, the fluorite seed gradually deposits, and the sludge concentration index also increases with the increase of the particle size of the fluorite crystal. When the sludge concentration index is twice the initial addition index of the fluorite, the crystallization is discharged.

[0011] The crystallization separation device uses eight fan leaves to reduce the weight of each fan leaf, thereby reducing the flow rate of the water flow required for opening the fan leaf, and reducing the operating energy consumption and the loss to the pump. By adjusting the water inlet flow, the upward flow rate of the water flow can be controlled to be 10-20 m / h, so that the crystallization separation device can operate normally. Under this flow rate condition, the shearing action of the water flow on the seeds is reduced, so that the Ca 2+ , F - is more likely to crystallize on the calcium fluoride seed, thereby improving the efficiency of the induced crystallization of the calcium fluoride.

[0012] The three layers of the drug distributor are arranged at equal intervals in the induced crystallization zone. Ca 2+ and F -The mixing reaction is usually completed within 1 minute, so the water flow rising height for 1 minute is used as the interval of the distributor, the second layer of distributor is installed 25 cm above the first layer of distributor, and the third layer of distributor is installed 50 cm above the first layer of distributor, so that the calcium fluoride crystal particles are synchronously grown; the third layer of distributor is located 30 cm below the crystallization separation device.

[0013] The PLC control box, the sludge concentration meter and the valve on the crystallization discharge port are connected with the PLC control box respectively; when the fluorite concentration index collected by the sludge concentration meter is 2 times of the initial fluorite concentration index, the PLC control box drives the valve to open, and the crystallization discharge port discharges the crystals.

[0014] The working process of the system is as follows: the fluorine-containing wastewater is placed in the wastewater pool and is transported to the pretreatment device by the lifting pump I at a flow rate of 2 m 3 / h; in the pretreatment device, the sulfate, phosphate and silicate ions in the fluorine-containing wastewater are reacted with Ba 2+ to generate precipitates under the acidic condition and are effectively removed by being adsorbed on the activated carbon; the pretreated fluorine-containing wastewater is transported into the fluidized bed under the action of the lifting pump II, the fluorine-containing wastewater is uniformly dispersed under the action of the polytetrafluoroethylene ball layer, the calcium-based crystallization agent is sent into the fluidized bed by the metering pump, the dosing pipeline in the fluidized bed adopts the multi-layer three-dimensional water distribution mode, the calcium-based crystallization agent is fully mixed with the fluorine-containing wastewater, and the uniform growth of the crystal seeds is ensured; the fluorite induced crystallization is greatly affected by the reaction concentration, the crystallization growth of the fluorite is affected when the reaction concentration is greater than 300 mg / L, the reaction process needs to be controlled in a low supersaturation state, the supernatant in the precipitation zone of the fluidized bed is transported to the bottom of the fluidized bed by the circulating pump at a reflux ratio of 3-4:1, and the fluorine-containing wastewater concentration in the bed body is ensured to be 200-300 mg / L; the effluent of the fluidized bed flows into the collection pool for subsequent deep fluorine removal; during the fluorine removal process of the fluidized bed, the crystallization separation device is in the open state under the action of the rising water flow, the calcium fluoride crystal particles with small particle size pass through the crystallization separation device under the action of the water flow, the calcium fluoride crystal particles with large particle size are located in the induced crystallization zone, the fluidized bed is provided with a crystallization discharge port on the corresponding side wall of the induced crystallization zone, the rising water flow is reduced when the crystallization discharge port is opened, at this time, the crystallization separation device is in the closed state (i.e., the triangular blades of the crystallization separation device are automatically closed due to the insufficient thrust of the rising water flow), and the calcium fluoride crystal particles in the induced crystallization zone are discharged from the fluidized bed (the crystallization separation device automatically separates the crystal particles with small particle size above, and the crystal particles with large particle size below are discharged from the fluidized bed along with the crystallization discharge port); after the crystallization discharge is completed, the crystallization discharge port is closed, and the crystallization separation device is in the open state again under the action of the rising water flow.

[0015] Advantages: Compared with the prior art, the present application has the following remarkable effects:

[0016] (1) In the fluorine resource recovery by using induced crystallization technology, the sulfate, phosphate, silicate ions in the fluorine-containing wastewater can react with Ca 2+ , calcium phosphate, calcium silicate and other impurities to adhere to the surface of the crystal seed, thereby affecting the purity of fluorite; in addition, the presence of sulfate, phosphate, silicate ions also increases the use amount of the crystallizing agent, causing the increase of the cost of the reagent; the fluorine-containing wastewater itself is acidic, under acidic conditions, barium salt can precipitate sulfate, phosphate and other impurities, while under acidic conditions, HF exists in the form of molecules and does not react with Ba 2+ ; the modified activated carbon is used for pretreatment of the fluorine-containing wastewater, the barium ions loaded on the surface of the activated carbon can remove the impurities such as sulfate and phosphate under acidic conditions, and the generated small molecule barium sulfate and barium phosphate precipitate can be adsorbed on the surface of the activated carbon, without causing the problem of increasing suspended solids in the wastewater, after the pretreatment of the fluorine-containing wastewater by the barium ion modified activated carbon, the purity of the recovered fluorite can be greater than 95%;

[0017] (2) The present application can accurately determine the discharge timing of crystallization through the crystallization separation device and the sludge concentration meter, when the initial stage of induced crystallization, the fluorite crystal seeds are uniformly dispersed in the induced crystallization zone under the action of the upward water flow, at this time, it is the initial sludge concentration meter index, with the reaction, the fluorite crystal seeds grow continuously, and gradually deposit, when the sludge concentration meter index increases to 2 times the initial concentration index of fluorite crystal seeds, the crystallization is discharged, the crystallization separation device is automatically closed during the crystallization discharge process, and different particle sizes of the crystallization are automatically separated, so that the crystallization with relatively uniform particle size is discharged;

[0018] (3) The reaction of induced crystallization process is usually completed within 1 min, the multilayer dispersion water distribution device of the present application is installed at the bottom of the fluidized bed, and a layer of polytetrafluoroethylene solid ball which can prevent fluorine corrosion is placed above the water distributor, and the water inlet is further uniformly dispersed through the gap of each layer of polytetrafluoroethylene ball; in addition, the polytetrafluoroethylene ball can be used as a support layer for the crystal seed to avoid the blockage of the water outlet of the water distributor; Ca 2+ reacts rapidly with F - ion, and single-layer drug distribution can make the crystallization grow only in the bottom layer of fluorite crystal seeds; through the multi-layer drug distribution of the multilayer dispersion drug distribution device, the drug can be uniformly distributed, Ca 2+ reacts with F - in multi-layer reaction, the synchronous growth of the crystal seeds is realized, and the uniformity of the crystal grain size is promoted. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 is the system principle diagram of the system of the present application;

[0020] Fig. 2 is the schematic diagram of the opening state of the crystallization separation device;

[0021] Fig. 3 This is a schematic diagram of the crystallization separation device in the closed state. Detailed Implementation

[0022] like Figs. 1-3 As shown, the system for recovering high-purity fluorite from fluoride-containing wastewater according to the present invention includes a fluidized bed 9, which is sequentially provided with a water distribution zone, an induced crystallization zone, and a sedimentation zone; it also includes a pretreatment device 3, a crystallizing agent storage tank 5, and a collection tank 13; the water distribution zone is located at the bottom of the fluidized bed 9; a water distributor 14 connected to the fluidized bed inlet is provided in the water distribution zone, and a layer of polytetrafluoroethylene (PTFE) microspheres 15 is stacked on the water distributor 14; at least three layers of equidistantly arranged dosing devices 16 are provided in the induced crystallization zone, and the at least three layers of dosing devices 16 are arranged above the PTFE microspheres 15, with each layer of dosing devices 16 connected to the dosing inlet on the side wall of the fluidized bed; a crystallization separation device 10 is provided above the uppermost dosing device 16; the pretreatment device 3 is filled with modified activated carbon particles, and the fluoride-containing wastewater treated by the pretreatment device 3 is then treated with the fluoride-containing wastewater. Fluorine wastewater enters the distributor 14 through the inlet; the crystallizing agent storage tank 5 delivers calcium-based crystallizing agent into each layer of distributor 16 through the inlet; the fluorine-containing wastewater and calcium-based crystallizing agent mix in the induced crystallization zone to generate calcium fluoride crystal particles. During the fluidized bed defluorination process, the crystallization separation device 10 is in the open state under the action of the rising water flow. Small calcium fluoride crystal particles are carried through the crystallization separation device 10 by the water flow, while large calcium fluoride crystal particles fall into the induced crystallization zone. The fluidized bed has a crystallization discharge port 12 on the corresponding side wall of the induced crystallization zone. When the crystallization discharge port 12 is opened, the rising water flow power decreases, and the crystallization separation device 10 is in the closed state. The calcium fluoride crystal particles located in the induced crystallization zone are discharged from the fluidized bed; the effluent from the fluidized bed flows into the collection tank 13 for subsequent deep defluorination.

[0023] The modified activated carbon particles were prepared by the following method: 50g of activated carbon was uniformly dispersed in 1L of 1mol / L HNO3 solution and heated at 50℃ for 6 hours. The activated carbon pretreated with HNO3 was continuously rinsed with deionized water for 10 minutes and then dried at 60℃ for 4 hours. 50g of the pretreated activated carbon was added to 500mL of 0.5mol / L BaCl2 solution and stirred at 120r / min at 25℃ for 1 hour. Then, it was sonicated for 2 hours. The sonicated activated carbon was filtered and washed three times with deionized water. After drying at 60℃ for 4 hours, it was calcined at 500℃ for 6 hours to obtain activated carbon particles with barium ions loaded on the surface.

[0024] The water distributor 14 is placed at the bottom of the fluidized bed 9 and communicates with the external water inlet pipe. A porous baffle I is placed above the water outlet of the water distributor 14. The diameter of the porous baffle I is equivalent to the diameter of the fluidized bed 9. A plurality of through holes with a diameter of 4 mm are uniformly distributed on the porous baffle I. A layer of polytetrafluoroethylene balls 15 with a height of 10-15 cm is uniformly placed above the porous baffle. The diameter of the polytetrafluoroethylene balls is 5 mm. A porous baffle II is further placed at a position 2-3 cm above the layer of polytetrafluoroethylene balls 15. The porous baffle II is used to fix the polytetrafluoroethylene balls. The diameter of the porous baffle II is equivalent to the diameter of the fluidized bed 9. A plurality of through holes with a diameter of 4 mm are uniformly distributed on the porous baffle II. The water inlet is uniformly dispersed after passing through the water distributor 14 and the layer of polytetrafluoroethylene balls 15. The polytetrafluoroethylene balls are solid balls. The polytetrafluoroethylene balls serve as a support layer for the crystalline particles to avoid the blockage of the water outlet of the water distributor 14 by the crystalline particles. A first layer of medicine distributor 16 is installed at a position 2-3 cm above the porous baffle II. The first layer of medicine distributor 16 is provided with a medicine outlet every 2 cm in the horizontal direction to realize the full reaction of the medicine with the uniformly dispersed fluorine-containing wastewater.

[0025] The multi-layer three-dimensional water distribution is adopted for the medicine inlet pipe inside the fluidized bed, so that the calcium-based crystallization agent is fully mixed with the fluorine-containing wastewater, and the uniform growth of the seed crystals is ensured. The backflow supernatant in the precipitation zone of the fluidized bed is transported to the bottom of the fluidized bed 9 by the circulating pump 7 to ensure that the fluorine concentration of the fluorine-containing wastewater in the fluidized bed is 200-300 mg / L.

[0026] The crystallization and separation device 10 includes a support layer 101, a filter screen 102, and a triangular blade 103. The support layer 101 is a circular ring made of 304 carbon steel. The diameter of the circular ring is slightly smaller than the diameter of the bed body of the fluidized bed 9. The edge of the circular ring is fixed on the bed body of the fluidized bed 9. A stainless steel support rod 104 with a diameter of 4 cm and a height of 1.2 m is placed at the bottom of the support layer 101 for fixing the support layer 101. The center point of the upper end surface of the support rod 104 coincides with the center point of the circular ring. The inside of the circular ring is evenly divided into eight parts by eight horizontal rods made of 304 carbon steel. One end point of each horizontal rod is fixed at the center point of the upper end surface of the support rod 104, and the other end point of each horizontal rod is fixed on the edge of the circular ring (the length of the horizontal rod is equal to the radius of the circular ring). The triangular blade 103 is an isosceles triangle (the included angle of adjacent horizontal rods is consistent with the top angle of the isosceles triangle). The length of the long side is equal to the radius of the circular ring. The long side is fixed on the horizontal rod by a rotating shaft and rotates relative to the horizontal rod. The other two sides are not fixed. The filter screen 102 is used to intercept small calcium fluoride crystal particles when the crystals are discharged and allows the wastewater to pass through the filter screen 102. The pore size of the filter screen 102 is 60 mesh. The filter screen 102 is installed in the gap between the short side of the triangular blade and the circular ring. A sludge concentration meter 8 is arranged at a position 15 cm above the support layer.

[0027] The three layers of medicine distributors 16 are arranged equidistantly in the induced crystallization area, the interval of the medicine distributors is the rising height of water flow in 1 minute, the second layer of medicine distributors 16 is installed 25 cm above the first layer of medicine distributors 16, the third layer of medicine distributors 16 is installed 50 cm above the first layer of medicine distributors 16, so that the calcium fluoride crystalline particles can grow synchronously; the third layer of medicine distributors is located 30 cm below the crystallization separation device.

[0028] The system of the application further comprises a PLC control box, the valve on the sludge concentration meter 8 and the crystallization discharge port 12 is connected with the PLC control box respectively; when the fluorite concentration index collected by the sludge concentration meter is 2 times of the initial fluorite concentration index, the PLC control box drives the valve to open, and the crystallization discharge port 12 discharges the crystallization.

[0029] The working process of the system of the application is as follows: the fluorine-containing wastewater is placed in the wastewater pool 1, and is transported to the pretreatment device 3 by the lifting pump I 2 at a flow rate of 2 m 3 / s, in the pretreatment device 3, the impurity ions such as sulfate, phosphate and silicate in the fluorine-containing wastewater react with Ba 2+ under the acidic condition to generate precipitates and are effectively removed by being adsorbed on the activated carbon; the pretreated fluorine-containing wastewater is transported into the fluidized bed 9 under the action of the lifting pump II 4, the fluorine-containing wastewater is uniformly dispersed under the action of the polytetrafluoroethylene small ball layer 15, the calcium-based crystallization agent is sent into the fluidized bed 9 by the metering pump 6, the medicine feeding pipeline in the fluidized bed is arranged in a multi-layer three-dimensional water distribution mode, so that the calcium-based crystallization agent is fully mixed with the fluorine-containing wastewater, and the uniform growth of the crystal seeds is ensured; the backflow supernatant in the precipitation area of the fluidized bed 9 is transported to the bottom of the fluidized bed by the circulating pump 7, so that the concentration of the fluorine-containing wastewater in the bed body is kept at 200-300 mg / L; the effluent of the fluidized bed 9 flows into the collection pool 13 for subsequent deep fluorine removal; during the fluorine removal process of the fluidized bed, the crystallization separation device 10 is in the open state under the action of the rising water flow, the calcium fluoride crystalline particles with small particle size are driven by the water flow to pass through the crystallization separation device 10, the calcium fluoride crystalline particles with large particle size (the calcium fluoride crystalline particles with a mesh number not less than 60 are the calcium fluoride crystalline particles with large particle size) are located in the induced crystallization area, the fluidized bed is provided with a crystallization discharge port 12 on the corresponding side wall of the induced crystallization area, when the crystallization discharge port 12 is opened, the rising water flow power is reduced, at this time, the crystallization separation device 10 is in the closed state (that is, the triangular blades of the crystallization separation device 10 are automatically closed due to the insufficient thrust of the rising water flow), the calcium fluoride crystalline particles located in the induced crystallization area are discharged from the fluidized bed 9 (the crystallization separation device 10 automatically separates the crystalline particles with small particle size above, and the crystalline particles with large particle size below are discharged from the fluidized bed along with the crystallization discharge port); after the crystallization discharge is completed, the crystallization discharge port 12 is closed, and the crystallization separation device 10 is again in the open state under the action of the rising water flow.

[0030] The system of the application is applied to the treatment of the following fluorine-containing wastewater, specifically:

[0031] A certain photovoltaic factory waste acid cleaning solution in Hebei Province: fluoride ion concentration of 800 mg / L, pH 1.3, silicon concentration of 85 mg / L, ammonia nitrogen concentration of 20.7 mg / L, chloride ion concentration of 7.2 mg / L, sulfate ion concentration of 115 mg / L, water volume of 2 m 3 / h, running time 24 h;

[0032] (1) The calcium chloride and calcium hydroxide mixed with a molar fraction of 2:1 calcium-based crystallization agent is loaded into the reagent storage tank 5; before the reactor is operated, wet fluorite seed crystals with a particle size of about 100 mesh are added from the top of the fluidized bed 9, and the packing height of the fluorite seed crystals on the polytetrafluoroethylene small balls is 10 cm;

[0033] (2) The wastewater in the wastewater tank 1 is transported to the pretreatment device 3 at a flow rate of 2 m 3 / h under the action of the lifting pump I2, and the pretreatment device 3 removes sulfate, phosphate and silicon and other impurity ions in the fluorine-containing wastewater;

[0034] (3) Start the metering pump 6 to transport the calcium-based crystallization agent to the medicine inlet at a flow rate of 15 L / h, mix it with the fluorine-containing wastewater, and reduce the fluorine concentration to below 20 mg / L after reaction; the crystallization separation device 10 is automatically opened under the action of the rising water flow, the seed crystals are in a fluidized bed state, and after passing through the crystallization separation device 10, they rise to the settling zone for settling; when the crystalline particle size grows to 60 mesh, it can be precipitated below the crystallization separation device 10(induced crystallization zone), and the fluidized bed 9 outlet water is discharged into the collection tank 13;

[0035] (4) Monitor the sludge concentration meter index, when the sludge concentration meter index is raised to 2 times the initial fluorite addition index, open the crystallization discharge port 12 of the fluidized bed 9, the rising water flow slows down, the crystallization separation device 10 is automatically closed, the crystallization with smaller particle size is intercepted above the crystallization separation device 10, and the crystallization with larger particle size is discharged from the fluidized bed 9.

Claims

1. A system for recovering high purity fluorite from fluorine-containing wastewater, characterized by: The application relates to a fluidized bed defluorination device, which comprises a fluidized bed (9), a pretreatment device (3), a crystallization agent storage tank (5) and a collecting pool (13), wherein the fluidized bed (9) is sequentially provided with a water distribution area, an induced crystallization area and a precipitation area; the water distribution area is located at the bottom of the fluidized bed (9); a water distributor (14) connected with a water inlet of the fluidized bed is arranged in the water distribution area, and a polytetrafluoroethylene ball layer (15) is stacked on the water distributor (14); at least three layers of medicine distributors (16) are arranged in the induced crystallization area and are equidistantly arranged, the at least three layers of medicine distributors (16) are arranged above the polytetrafluoroethylene ball layer (15), and each layer of medicine distributors (16) is connected with a medicine inlet of the side wall of the fluidized bed; a crystallization separation device (10) is arranged above the uppermost layer of medicine distributors (16); the pretreatment device (3) is filled with modified activated carbon particles, fluorine-containing wastewater treated by the pretreatment device (3) enters the water distributor (14) from a water inlet; the crystallization agent storage tank (5) sends a calcium-based crystallization agent into each layer of medicine distributors (16) through a medicine inlet; F - is separated from Ca 2+ In the induced crystallization area of the fluidized bed, CaF2crystalline particles are generated, in the defluorination process of the fluidized bed, the crystallization separation device (10) is in an open state under the action of the upward water flow, the calcium fluoride crystalline particles with small particle sizes are driven by the water flow to pass through the crystallization separation device (10), the calcium fluoride crystalline particles with large particle sizes fall into the induced crystallization area, the fluidized bed is provided with a crystallization discharge port (12) on the corresponding side wall of the induced crystallization area, when the crystallization discharge port (12) is opened, the upward water flow power is reduced, at this moment, the crystallization separation device (10) is in a closed state, the calcium fluoride crystalline particles in the induced crystallization area are discharged from the fluidized bed; the water outlet of the fluidized bed flows into the collecting pool (13) to carry out subsequent deep defluorination. The modified activated carbon particles are prepared by the following method: uniformly dispersing activated carbon in HNO3 solution, washing with deionized water after heating, and then drying; adding the pretreated activated carbon into BaCl2 solution, and ultrasonic stirring; filtering and washing the activated carbon with deionized water after ultrasonic treatment, drying, and calcining to obtain activated carbon particles with barium ions loaded on the surface.

2. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 1, characterized in that: The calcium fluoride crystal particles with a particle size of not less than 60 mesh.

3. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 1, characterized in that: The water distributor (14) is arranged at the bottom of the fluidized bed (9) and communicates with the external water inlet pipeline. A porous baffle I is arranged above the water outlet of the water distributor (14), and the diameter of the porous baffle I is equivalent to the diameter of the fluidized bed (9). A plurality of through holes with a diameter smaller than the diameter of the polytetrafluoroethylene small ball are uniformly distributed on the porous baffle I. A polytetrafluoroethylene small ball layer (15) with a height of 10-15 cm is uniformly arranged above the porous baffle I. A porous baffle II is further arranged above the polytetrafluoroethylene small ball layer (15), and the diameter of the porous baffle II is equivalent to the diameter of the fluidized bed (9). A plurality of through holes with a diameter smaller than the diameter of the polytetrafluoroethylene small ball are also uniformly distributed on the porous baffle II.

4. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 1, characterized in that: The backflow supernatant of the fluidized bed precipitation zone is delivered to the bottom of the fluidized bed (9) through the circulating pump (7), and the supernatant of the fluidized bed precipitation zone is delivered to the bottom of the fluidized bed at a backflow ratio of 3-4:

1.

5. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 1, characterized in that: The crystallization separation device (10) comprises a support layer (101), a filter screen (102), and a triangular blade (103). The support layer (101) has a circular ring structure, and a support rod (104) is arranged at the bottom of the support layer (101). The center point of the upper end surface of the support rod (104) coincides with the center point of the circular ring. The edge of the circular ring is fixed on the bed body of the fluidized bed. The circular ring is evenly divided into eight equal parts by eight horizontal rods. One end point of each horizontal rod is fixed at the center point of the upper end surface of the support rod (104), and the other end point of each horizontal rod is fixed on the edge of the circular ring. The length of the horizontal rod is equal to the radius of the circular ring. The triangular blade (103) is an isosceles triangle. The included angle of adjacent horizontal rods is consistent with the top angle of the isosceles triangle. The length of the long side of the isosceles triangle is equal to the radius of the circular ring. The long side of the isosceles triangle is fixed on the horizontal rod by a rotating shaft and rotates relative to the horizontal rod. The filter screen (102) is installed in the gap between the short side of the triangular blade and the circular ring.

6. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 5, characterized in that: A sludge concentration meter (8) is arranged 12-15 cm above the support layer (101) to monitor the growth of fluorite in the fluidized bed.

7. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 1, characterized in that: Three layers of drug distributors (16) are arranged at equal intervals in the induction crystallization zone.

8. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 7, characterized in that: A first layer of drug distributors (16) is installed 2-3 cm above the porous baffle II. An opening is arranged every 2 cm in the horizontal direction of the first layer of drug distributors (16). A second layer of drug distributors (16) is installed 25 cm above the first layer of drug distributors (16), and a third layer of drug distributors (16) is installed 50 cm above the first layer of drug distributors (16). The third layer of drug distributors (16) is located 30 cm below the crystallization separation device (10).

9. The system for recovering high purity fluorite from fluorine-containing wastewater according to claim 1, characterized in that: Also include PLC control box, sludge concentration meter (8) and the valve on the crystallization discharge port (12) are connected with PLC control box respectively; when the fluorite concentration index collected by sludge concentration meter is 2 times of fluorite initial concentration index, PLC control box drives the valve to open, and the crystallization discharge port (12) carries out crystallization discharge.

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