Multistage deep fluorine removal method and device for fluorine-containing wastewater

Abstract

The invention provides a multistage deep fluorine removal method and device for fluorine-containing wastewater, and the method comprises the following steps: S1, uniformly mixing the fluorine-containing wastewater with a calcium chloride solution to separate out calcium fluoride crystals; s2, uniformly mixing the supernate obtained after standing in the step S1 with an aluminum coagulant, reacting, adding a particle medium, and stirring and fully mixing; then adding a flocculating agent to promote coagulation to form alumen ustum and form a large-particle flocculating constituent; and S3, precipitating the wastewater reacted in the step S2 through a filler area, carrying out solid-liquid separation, and discharging the treated water. According to the technical scheme, the crystallization-adsorption-coordination-co-precipitation principle is utilized, fluorine is removed step by step, efficient and stable removal of fluoride is achieved, the fluoride in effluent of the system is stably lower than 1 mg / L, meanwhile, the sludge yield is reduced, and calcium fluoride crystals can be recycled.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly to a multi-stage deep defluorination method and device for fluoride-containing wastewater. Background Art

[0002] With the rapid development of industrialization, the problem of fluoride-containing wastewater pollution has become increasingly severe. Fluoride widely exists in industrial processes such as semiconductor manufacturing, photovoltaic industry, electroplating, and metallurgy. The wastewater discharged from these industries often contains high concentrations of fluoride ions (F-). Fluorine is one of the essential trace elements for the human body, but excessive intake can cause diseases such as dental fluorosis and skeletal fluorosis. The World Health Organization (WHO) stipulates that the limit value of fluoride ions in drinking water is 1.5 mg / L. Long-term drinking of high-fluoride water (>1.5 mg / L) can cause chronic diseases such as skeletal deformation and nervous system damage. If directly discharged without effective treatment, it will not only threaten human health but also damage the soil structure and water ecosystem, and even cause long-term environmental risks through food chain enrichment.

[0003] However, the concentration of fluoride in industrial wastewater often reaches dozens to hundreds of milligrams per liter. Enterprises generating fluoride-containing wastewater generally treat it to meet the industry standards according to environmental protection requirements (the indirect discharge requirement of "Discharge Standard of Water Pollutants for Electronic Industry" (GB 39731-2020) for fluoride is ≤20 mg / L, and the direct discharge requirement for fluoride is ≤20 mg / L; the fluoride concentration limit of "Integrated Wastewater Discharge Standard" (GB 8978-1996) is 10 mg / L), but often fails to meet the water environmental quality of the receiving water body. According to the "Surface Water Environmental Quality Standard" (GB3838-2002), the surface water class III standard requires fluoride ≤1.0 mg / L (the class IV standard requires fluoride ≤1.5 mg / L). Therefore, the tail water discharged by enterprises needs to be further treated deeply.

[0004] Currently, deep defluorination technologies include membrane separation, adsorption method, etc. For fluoride-containing wastewater with relatively low fluoride concentration (such as the tail water discharged by semiconductor enterprises with fluoride ≤20 mg / L), the traditional crystallization and coagulation processes have poor treatment efficiency and are difficult to meet the strict requirements of the surface water environmental quality standard for fluoride. Although membrane separation and resin adsorption technologies can achieve deep defluorination to meet the water quality target, they have problems such as membrane fouling, high energy consumption, low adsorption capacity, difficult regeneration, and high operating costs, and have limitations in large-scale applications. Summary of the Invention

[0005] In view of the above technical problems, the present invention discloses a multi-stage deep defluorination method and device for fluoride-containing wastewater, which utilizes the principle of crystallization-adsorption-coordination-coprecipitation to remove fluoride step by step, ultimately achieving deep defluorination of the wastewater, with the effluent fluoride ≤1.0 mg / L, while reducing the sludge production, having simple operation, and relatively low investment and operating costs.

[0006] For this, the technical solution adopted by the present invention is as follows:

[0007] A multi-stage deep defluorination method for fluorine-containing wastewater, comprising the following steps:

[0008] Step S1, mixing the fluorine-containing wastewater with a calcium chloride solution evenly to precipitate calcium fluoride crystals;

[0009] Step S2, evenly mixing the supernatant obtained after standing in Step S1 with an aluminum-based coagulant, reacting, and then adding a particulate medium and stirring thoroughly for uniform mixing; then adding a flocculant to promote coagulation to form flocs and form larger flocculates;

[0010] Step S3, passing the wastewater after the reaction in Step S2 through a packing area for precipitation, and after solid-liquid separation, discharging the treated water.

[0011] Adopting this technical solution, in Step S1, most of the fluoride ions are removed by mixing the fluorine-containing wastewater with a calcium chloride solution evenly to form calcium fluoride crystals, and the calcium fluoride crystals generated in this process can be recycled, thereby greatly reducing the process sludge yield. Then the supernatant is evenly mixed with an aluminum-based coagulant. The coagulant hydrolyzes to generate amorphous aluminum hydroxide flocs with a large specific surface area, which come into full contact with the fluoride ions in the wastewater, adsorb the fluoride ions or form Al-F complexes. Coupled with the added particulate medium, this particulate medium enhances the aggregation and sedimentation separation ability of the fluoride after coagulation. A flocculant is added in the flocculation area to promote coagulation to form flocs, which wrap the fluoride through the adsorption bridging effect to form larger flocculates. At the same time, the stirring rate in the reaction tank is controlled to prevent the flocs from being broken and forming precipitates in the reaction area. Further, the added coagulant is an aluminum-based coagulant, which hydrolyzes in water to generate various hydroxyaluminum complexes, can adsorb negatively charged fluoride ions, generate stable Al-F complexes with fluorine, and at the same time remove fluoride ions through electrostatic adsorption and enmeshment. Then, by adding a particulate medium, the aggregation and sedimentation separation ability of the fluoride after coagulation is enhanced. After adding the flocculant, the flocculant forms a network structure in water and captures fluoride and other suspended particles through adsorption bridging and enmeshment. The wastewater treated as above passes through the packing area for precipitation, and chemical reaction precipitation particles, coagulation reaction flocs, colloids, and particulate media are removed here, and finally the fluoride concentration of the effluent is lower than 1 mg / L. After the sludge in the sedimentation area is hydraulically separated, the particulate medium is recycled.

[0012] As a further improvement of the present invention, the particulate medium is fine sand with a particle size of 0.1 - 0.15 mm.

[0013] As a further improvement of the present invention, in step S1, calcium carbonate or hydroxyapatite seeds are added, and the particle size of the seeds is 0.1 - 0.2 mm. With this technical solution, after the fluoride ions are uniformly mixed with the calcium ions in the added calcium chloride solution, the interfacial energy can be reduced under the induction of the seeds, and the calcium ion supersaturation required for nucleation is reduced. The calcium ions and fluoride ions diffuse to the crystal surface through the solution. Under the conditions of concentration gradient and low-speed fluidization kinetics, the ions are adsorbed on the crystal surface, desolvated and embedded in the lattice, and continuously nucleate and crystallize in different directions, finally forming stable calcium fluoride crystals.

[0014] As a further improvement of the present invention, in step S1, the addition amount of the calcium chloride solution satisfies that the molar ratio of calcium ions to fluoride ions is 1.2 - 1.5:1. With this technical solution, the calcium ions and fluoride ions in the water quality are adsorbed on the crystal surface and embedded in the lattice under the conditions of concentration gradient and turbulent flow, continuously forming calcium fluoride crystals and growing continuously, and finally stable crystals can be formed.

[0015] As a further improvement of the present invention, in step S2, after adding the aluminum-based coagulant, sodium hydroxide lye is also added to adjust the pH of the solution to 6.5 - 6.8. With this technical solution, the solution is generally acidic after adding the coagulant, and adding sodium hydroxide lye can control the reaction conditions and make the reaction more complete.

[0016] As a further improvement of the present invention, in step S2, the dosage of the aluminum-based coagulant satisfies that the molar ratio of aluminum ions to fluoride ions is 1:2.5 - 4. Further, in step S2, the reaction time after adding the aluminum-based coagulant and the wastewater is 4 - 5 min.

[0017] As a further improvement of the present invention, in step S2, the dosage of the flocculant is 1 - 2 mg / L. The flocculant uses the flocculant of the existing technology.

[0018] As a further improvement of the present invention, in step S2, the reaction time after adding the flocculant is 15 - 20 min.

[0019] As a further improvement of the present invention, after the precipitate obtained by solid-liquid separation in step S3 is hydraulically separated, the particulate medium is recovered.

[0020] The present invention also discloses a multi-stage deep defluorination device for the multi-stage deep defluorination method of fluorine-containing wastewater as described above, which includes a crystallization tank, a coagulation tank, a coagulant aid tank, a flocculation tank, a sedimentation distribution tank, and a high-efficiency sedimentation tank connected in sequence; a wastewater inlet is provided at the lower part of the crystallization tank, and a supernatant outlet is provided at the upper part. A calcium chloride solution dosing pipe is provided in the crystallization tank, and dosing holes are evenly arranged on the calcium chloride solution dosing pipe; a first stirrer, a coagulant dosing pipe, and an alkali solution dosing pipe are provided in the coagulation tank; a second stirrer and a particulate medium dosing mechanism are provided in the coagulant aid tank; a draft tube is provided in the flocculation tank, and a flocculant dosing pipe is provided at the upper part of the draft tube; a plurality of inclined tubes filled with packing and a water outlet collecting tank are provided in the sedimentation distribution tank, and the outlet of the inclined tube is communicated with the water outlet collecting tank; a sludge hopper and a sludge scraper are provided at the bottom of the high-efficiency sedimentation tank, and the outlet of the sludge hopper is connected to a sludge discharge pipe.

[0021] As a further improvement of the present invention, calcium carbonate or hydroxyapatite crystal seeds are filled in the crystallization tank. Further, the particle size of the calcium carbonate or hydroxyapatite crystal seeds is 0.1-0.2 mm. Further, the filling volume of the calcium carbonate or hydroxyapatite crystal seeds accounts for 40-50% of the volume of the crystallization tank.

[0022] As a further improvement of the present invention, the calcium chloride solution dosing pipe includes a dosing pipe with an upper and lower double-layer annular structure. Further, the double-layer spacing of the calcium chloride solution dosing pipe is 0.8-1 m.

[0023] As a further improvement of the present invention, the dosing holes are evenly distributed on the inner and outer sides of the dosing pipe with an upper and lower double-layer annular structure, and the orifice of the dosing hole is inclined downward. Further, the orifice of the dosing hole is inclined downward at an angle of 45 degrees. Further, the diameter of the dosing hole is 5-10 mm. Further, the diameter of the dosing hole is 8 mm.

[0024] As a further improvement of the present invention, a water distribution plate is provided at the wastewater inlet of the crystallization tank.

[0025] As a further improvement of the present invention, the crystallization tank has a regular octagon structure.

[0026] As a further improvement of the present invention, the diameter of the upper and lower double-layer annular structure dosing pipe is 32 mm.

[0027] As a further improvement of the present invention, a triangular weir is provided at the supernatant outlet, the outlet of the triangular weir faces the annular collecting tank, and the water outlet hole of the annular collecting tank is communicated with the inlet of the coagulation tank.

[0028] As a further improvement of the present invention, the alkali solution dosing pipe is located above the coagulant dosing pipe.

[0029] As a further improvement of the present invention, the medicine outlet holes of the coagulant dosing pipe and the lye dosing pipe are arranged downward and evenly distributed. Further, the diameter of the medicine outlet holes of the coagulant dosing pipe and the lye dosing pipe is 10-20 mm, and more preferably 15 mm.

[0030] As a further improvement of the present invention, the upper part of the coagulant aid tank is provided with a water inlet, and the bottom is provided with a water outlet; the fine particle medium dosing mechanism is located in the middle of the coagulant aid tank.

[0031] As a further improvement of the present invention, the water outlet of the coagulant aid tank is connected to the bottom water inlet of the flocculation tank through a bottom connecting pipe, and the bottom water inlet of the flocculation tank is a flared opening and faces into the draft tube.

[0032] As a further improvement of the present invention, the flocculant dosing pipe is annular, and the medicine outlet holes of the flocculant dosing pipe are evenly arranged downward.

[0033] As a further improvement of the present invention, the draft tube is connected and supported to the inner wall of the flocculation tank through a support rod.

[0034] As a further improvement of the present invention, a water outlet weir is provided at the outlet of the inclined tube, and the water outlet weir faces the water collection tank.

[0035] As a further improvement of the present invention, the bottom of the high-efficiency sedimentation tank is an inclined plane, inclined towards the sludge hopper, and the outlet of the sludge hopper is connected to the sludge discharge pipe through a sludge pump.

[0036] As a further improvement of the present invention, the crystallization tank, the coagulation tank, the coagulant aid tank, the flocculation tank, the sedimentation water distribution tank and the high-efficiency sedimentation tank are integrally constructed by steel structure.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] Adopting the technical solution of the present invention, through the integration of crystallization, adsorption, complexation, coprecipitation and other effects, using the principle of crystallization-adsorption-coordination-coprecipitation, fluoride is removed step by step and step by step, realizing the efficient and stable removal of fluoride. The fluoride in the system effluent is stably lower than 1 mg / L, while reducing the sludge production. The calcium fluoride crystals can be recycled, which is environmentally friendly, has high fluoride removal efficiency, realizes the recycling of calcium fluoride resources, is easy to operate, has intensive land use and low treatment cost, and has great popularization and application value. Description of the Drawings

[0039] Figure 1 It is a schematic diagram of the partition structure of the multi-stage deep fluoride removal device according to the embodiment of the present invention.

[0040] Figure 2 It is a plan view of the lower layer of the multi-stage deep fluoride removal device according to the embodiment of the present invention.

[0041] Figure 3 It is the upper - layer plan view of the embodiment of the present invention.

[0042] Figure 4 It is Figure 3 the sectional view taken along the line A - A in

[0043] Figure 5 It is Figure 3 the sectional view taken along the line B - B in

[0044] Figure 6 It is Figure 3 the sectional view taken along the line C - C in

[0045] Figure 7 It is Figure 3 the sectional view taken along the line D - D in

[0046] Figure 8 It is Figure 3 the sectional view taken along the line E - E in

[0047] Figure 9 It is Figure 3 the sectional view taken along the line F - F in

[0048] Figure 10 It is the structural schematic diagram of the calcium chloride solution dosing pipeline and the reagent annular dosing pipe in the embodiment of the present invention; wherein, a) is the connection schematic diagram of the main reagent dosing pipe, the sub - reagent dosing pipes and the reagent annular dosing pipe, and b) is the structural schematic diagram of the reagent annular dosing pipe.

[0049] Figure 11 It is the structural schematic diagram of the flocculant dosing pipeline and the flocculant annular dosing pipe in the embodiment of the present invention; wherein, a) is the connection schematic diagram of the main flocculant dosing pipe, the sub - flocculant dosing pipes and the flocculant annular dosing pipe, and b) is the structural schematic diagram of the flocculant annular dosing pipe.

[0050] The reference numerals include:

[0051] 1 - crystallization tank, 2 - coagulation tank, 3 - coagulant aid tank, 4 - flocculation tank, 5 - sedimentation distribution water tank, 6 - high - efficiency sedimentation tank, 7 - effluent area, 8 - main inlet pipe, 9 - branch inlet pipe, 10 - emptying pipe, 11 - sludge pipe, 12 - main chemical dosing pipe, 13 - branch chemical dosing pipe, 14 - annular chemical dosing pipe, 15 - chemical outlet hole, 16 - coagulant dosing pipe, 17 - coagulant outlet hole, 18 - lye dosing pipe, 19 - lye outlet hole, 20 - main flocculant dosing pipe, 21 - branch flocculant dosing pipe, 22 - annular flocculant dosing pipe, 23 - flocculant outlet hole, 24 - draft tube, 25 - sludge scraper, 26 - sludge discharge pipe, 27 - sludge pump, 28 - water distribution plate, 29 - distributed water inlet holes, 30 - supernatant water outlet, 31 - confluent water outlet, 32 - rapid coagulation mixer, 33 - rapid coagulant aid mixer, 34 - slow flocculation mixer, 35 - bottom connection hole, 36 - bottom connection pipe, 37 - hydrocyclone, 38 - inclined tube packing, 39 - effluent triangular weir, 40 - outlet pipe, 41 - bell mouth, 42 - support rod, 43 - triangular weir, 44 - annular collecting tank, 45 - crystal nucleus packing, 46 - crystal discharge port, 47 - transparent observation window, 48 - effluent collecting tank. Detailed implementation manners

[0052] The following further elaborates on the preferred embodiments of the present invention.

[0053] Embodiment 1

[0054] A multi - stage deep defluorination method for fluoride - containing wastewater includes the following steps:

[0055] Step S1: Mix the fluoride - containing wastewater evenly with calcium chloride solution, and add calcium carbonate or hydroxyapatite crystal seeds to precipitate calcium fluoride.

[0056] Step S2: Uniformly mix the supernatant obtained after standing in Step S1 with an aluminum - based coagulant, react, and then add a particulate medium and stir thoroughly; then add a flocculant to promote aggregation to form flocs and form larger - sized flocculates; the flocculant used is a flocculant of the prior art.

[0057] Step S3: Pass the wastewater after the reaction in Step S2 through a packing area for sedimentation. After solid - liquid separation, discharge the treated water.

[0058] Among them, in Step S1, the particle size of the added calcium carbonate or hydroxyapatite crystal seeds is 0.1 - 0.2 mm; the addition amount of the calcium chloride solution satisfies a calcium ion to fluoride ion molar ratio of 1.2 - 1.5:1; after adding the aluminum - based coagulant, sodium hydroxide lye is also added to adjust the pH of the solution to 6.5 - 6.8; the dosage of the aluminum - based coagulant satisfies an aluminum ion to fluoride ion molar ratio of 1:2.5 - 4; the dosage of the flocculant is 1 - 2 mg / L.

[0059] In step S3, after the precipitate obtained by solid-liquid separation is hydraulically separated, the particulate medium is recovered.

[0060] Example 2

[0061] As Figures 1 to 11 shown, a multi-stage deep defluorination device, that is, the device used in the multi-stage deep defluorination method for fluorine-containing wastewater as described in Example 1, includes a frame and a crystallization tank 1, a coagulation tank 2, a coagulant aid tank 3, a flocculation tank 4, a sedimentation distribution tank 5, and a high-efficiency sedimentation tank 6 that are sequentially connected on the frame. The crystallization tank 1, the coagulation tank 2, the coagulant aid tank 3, the flocculation tank 4, the sedimentation distribution tank 5, and the high-efficiency sedimentation tank 6 are integrally constructed using steel structures.

[0062] A wastewater inlet is provided at the lower part of the crystallization tank 1, and a supernatant outlet is provided at the upper part. A pharmaceutical annular dosing pipe 14 for adding calcium chloride solution is provided in the crystallization tank 1, and pharmaceutical dosing holes 15 are evenly provided on the pharmaceutical annular dosing pipe 14; a first stirrer, a coagulant dosing pipe 16, and an alkali solution dosing pipe 18 are provided in the coagulation tank 2; a second stirrer and a particulate medium dosing mechanism, namely a hydrocyclone 37, are provided in the coagulant aid tank 3; a draft tube 24 is provided in the flocculation tank 4, and a flocculant annular dosing pipe 22 is provided at the upper part of the draft tube 24; a plurality of inclined tubes filled with fillers, namely inclined tube fillers 38, and a water outlet collecting tank are provided in the sedimentation distribution tank 5, and the outlets of the inclined tubes are communicated with the water outlet collecting tank; a sludge hopper and a sludge scraper 25 are provided at the bottom of the high-efficiency sedimentation tank 6, and the outlet of the sludge hopper is connected to a sludge discharge pipe 26.

[0063] The fluorine-containing wastewater first enters the crystallization tank 1. To avoid flow dead zones, the crystallization tank 1 is constructed as a regular octahedron, with an equivalent diameter range of 1.2 m - 2.5 m and a height of 4.5 - 6 m. The pressure-flow incoming water flows through the water inlet main pipe 8 and the water inlet branch pipe 9, and uniformly enters the fluidized crystallization tank 1 through the distributed water inlet holes 29 of the water distribution plate 28, with an upward flow velocity of 8 - 10 m / h.

[0064] The crystallization tank 1 is filled with crystal nucleus fillers 45, that is, calcium carbonate or hydroxyapatite crystal seeds, with a crystal seed particle size of 0.1 - 0.2 mm and a volume filling rate of 40 - 50%. The crystal seeds are recycled and regularly replenished. During the upward flow of the water, precipitation crystallization occurs with the added calcium chloride solution.

[0065] The calcium chloride solution is dosed using an upper and lower double-layer pharmaceutical annular dosing pipe 14, with a double-layer spacing of 0.8 - 1 m. The calcium chloride solution is connected from the pharmaceutical dosing main pipe 12 and the pharmaceutical dosing branch pipe 13 to the double-layer pharmaceutical annular dosing pipe 14. The diameter of the pharmaceutical annular dosing pipe 14 is 32 mm. The pharmaceutical dosing holes 15 are evenly distributed on the inner and outer sides of the octagonal pharmaceutical annular dosing pipe 14. Two holes are opened on the outer edge of each side of the octagon and one hole is opened on the inner edge, with the hole opening inclined downward at 45 degrees and a hole diameter of 8 mm.

[0066] The fluoride ions in the fluoride-containing wastewater are uniformly mixed with the calcium ions in the calcium chloride solution added through the chemical dosing hole 15. Under the induction of calcium carbonate crystal seeds, the calcium ion supersaturation required for nucleation is effectively reduced. The dosage of the calcium chloride solution is controlled according to the molar ratio of calcium ions to fluoride ions of 1.2 - 1.5:1. The calcium ions and fluoride ions in the water quality are adsorbed on the crystal surface and embedded in the crystal lattice under the conditions of concentration gradient and turbulence, continuously forming calcium fluoride crystals and growing continuously, and finally forming stable crystals. The crystallization tank 1 operates in two groups in parallel, and the crystals are regularly discharged through the crystal discharge port 46. The crystal seeds are supplemented by direct addition from the top, and the addition of crystal seeds and the fluidization of the water body and the formation of crystals during the operation period are observed and confirmed through the transparent observation window 47. When overhauling, the water body is emptied through the drain pipe 10.

[0067] The water discharged from the crystallization tank 1 converges to the annular collecting tank 44 through the triangular weir 43, and flows out from the two supernatant outlets 30 and converges to the outlet 31, and then enters the next stage. The fluoride concentration in the water discharged from the crystallization tank 1 is controlled at 5 - 8 mg / L.

[0068] The water in the crystallization tank 1 enters the coagulation tank 2. The coagulant is mixed with the wastewater through the coagulant dosing hole 17 of the coagulant dosing pipe 16. There are 8 holes vertically downward at the coagulant dosing hole 17, and the diameter of each hole is 15 mm. The coagulant and the fluoride-containing wastewater are fully mixed under the rapid stirring of the coagulation rapid mixer 32. The added coagulant is an aluminum-based coagulant, which hydrolyzes in water to generate various hydroxyaluminum complexes, which can adsorb negatively charged fluoride ions and produce stable Al-F complexes with fluoride. At the same time, fluoride ions are removed through electrostatic adsorption and net trapping. After the coagulant is added, the solution is generally acidic. To control the reaction conditions, sodium hydroxide lye is added through the lye dosing hole 19 of the lye dosing pipe 18 located above it. The lye dosing pipe 18 has 12 holes vertically downward along the length direction, which are evenly distributed, and the diameter of each hole is 10 mm. The optimal reaction pH of the mixed solution is adjusted to be between 6.5 - 6.8 by adding alkali. The molar ratio of aluminum ions to fluoride ions is controlled at 1:2.5 - 4, and the residence time in the coagulation reaction zone is 4 - 5 min. The effluent enters the coagulant aid tank 3 from bottom to top through the baffle.

[0069] The upper part of the coagulant aid tank 3 is provided with a water inlet, and the bottom is provided with a water outlet; the particulate medium dosing mechanism is located in the middle of the coagulant aid tank 3. The wastewater in the coagulant aid tank 3 enters from the upper layer and is fully mixed with the particulate medium added by the hydrocyclone 37 under the stirring of the coagulant aid rapid mixer 33. The particulate medium is fine sand with a particle size of 0.1 - 0.15 mm. By adding the particulate medium, the aggregation and sedimentation separation ability of fluoride after coagulation is enhanced. The residence time of the wastewater in the coagulant aid tank 3 is 4 - 5 min, and the effluent enters the flocculation tank 44 through the bottom connecting hole 35.

[0070] The bottom water inlet of the flocculation tank 4 is a flared opening 41, which faces into the draft tube 24. The flocculation tank 44 is filled with water through the bottom connecting pipe 36, and the incoming water upflow is diffused into the draft tube 24 through the flared opening 41.

[0071] The flocculant enters the annular flocculant dosing pipe 22 through the main flocculant dosing pipe 20 and the sub-flocculant dosing pipes 21, and is put in through the annular flocculant dosing pipe 22. There are 8 vertical downward openings for the flocculant dosing holes 23, which are evenly arranged, and the aperture is 15 mm. Inside the draft tube 24, the flocculant and the incoming water are fully mixed under the slow stirring of the slow flocculation mixer 34, and the water then slowly flows out from the upper edge of the draft tube 24. The diameter of the draft tube 24 is 0.9 - 1.2 m, and it is connected and supported to the four walls of the flocculation tank 4 through the support rods 42. The water residence time in the flocculation tank 4 is 15 - 20 min, the flocculant dosage is 1 - 2 mg / L, the flocculant forms a network structure in the water, and captures fluoride and other suspended particles through adsorption bridging and net trapping effects. The effluent enters the sedimentation and distribution tank 5 from the bottom.

[0072] The wastewater flows upward from the bottom of the sedimentation and distribution tank 5, precipitates in the inclined tube packing 38 of the sedimentation and distribution tank 5. After solid-liquid separation, it flows out through the effluent triangular weir 39 and is collected and converged into the effluent area 7 through the effluent collection tank 48. The sedimentation area of the high-efficiency sedimentation tank 66 is square, and the bottom sludge area is a circular sludge hopper with an inclined bottom that slopes towards the sludge hopper. A sludge scraper 25 is used to scrape the sludge into the sludge hopper, and then it is suctioned by the sludge pump 27 and discharged to the sludge pipe 11 through the sludge discharge pipe 26. The particulate medium in the sludge is separated by the hydrocyclone 37 and then added to the coagulant aid tank 3 for recycling, and the remaining fluoride-containing sludge is discharged for disposal. The effluent after the final deep fluoride removal of the system is discharged from the outlet pipe 40.

[0073] This multi-stage high-efficiency deep fluoride removal system of the patent utilizes the principles of crystallization - adsorption - coordination - coprecipitation, removes fluoride step by step in a ladder-like manner, and finally realizes the deep fluoride removal of wastewater. The fluoride concentration in the effluent is ≤ 1.0 mg / L, while reducing the sludge production, and obtaining CaF 2 crystalline product. The application scenario of this patent is the deep purification project of fluoride-containing tail water with ultra-low fluoride emission requirements.

[0074] Using the above device and method to treat the tail water discharged by a semiconductor integrated circuit enterprise, the fluoride ion concentration is 14.22 - 27.76 mg / L. The calcium chloride dosage of the system is based on the molar ratio of calcium to fluoride of 1.2:1, the coagulant dosage is based on the molar ratio of aluminum to fluoride of 1:2.8, and the flocculant dosage is 2 mg / L. After multi-stage purification, the fluoride ion concentration in the final effluent of the system is stably between 0.45 - 0.93 mg / L, which is lower than the concentration limit of 1.0 mg / L of fluoride in surface water class III standard.

[0075] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A multi-stage deep defluorination method for fluorine-containing wastewater, characterized in that: The steps include: Step S1, mixing the fluoride-containing wastewater and the calcium chloride solution evenly to allow calcium fluoride to crystallize and precipitate; Step S2, uniformly mixing the supernatant obtained after standing in step S1 with an aluminum-based coagulant, reacting, and then adding a particulate medium to stir and mix thoroughly; then adding a flocculant to promote agglomeration to form alum flocs, forming flocs with larger particles; Step S3, the wastewater after the reaction in step S2 is precipitated through the packing area, and after solid-liquid separation, the treated water is discharged.

2. The multi-stage deep defluorination method for fluorine-containing wastewater according to claim 1, characterized in that: In step S1, calcium carbonate or hydroxyapatite seed crystals are added, and the seed crystal particle size is 0.1-0.2 mm; In step S1, the amount of calcium chloride solution added satisfies the molar ratio of calcium ions to fluoride ions of 1.2-1.5:1; In step S2, after adding the aluminum coagulant, sodium hydroxide alkali solution is also added to adjust the pH of the solution to 6.5-6.8; the amount of the aluminum coagulant is such that the molar ratio of aluminum ions to fluoride ions is 1:2.5-4; In step S2, the dosage of the flocculant is 1-2 mg / L.

3. The multi-stage deep defluorination method for fluorine-containing wastewater according to claim 2, characterized in that: The precipitate obtained by the solid-liquid separation in step S3 is subjected to hydraulic separation to recover the particulate medium.

4. The multi-stage deep defluorination device used in the multi-stage deep defluorination method for fluorine-containing wastewater according to claim 1 is characterized in that: It comprises a crystallization tank, a coagulation tank, an auxiliary coagulant tank, a flocculation tank, a sedimentation water distribution tank and a high-efficiency sedimentation tank which are connected in sequence; the lower part of the crystallization tank is provided with a wastewater inlet, the upper part is provided with a supernatant outlet, the crystallization tank is provided with a calcium chloride solution dosing pipe, and the calcium chloride solution dosing pipe is evenly provided with discharge holes; the coagulation tank is provided with a first agitator, a coagulant dosing pipe and an alkali solution dosing pipe; the auxiliary coagulant tank is provided with a second agitator and a particulate medium dosing mechanism; the flocculation tank is provided with a guide tube, and the upper part of the guide tube is provided with a flocculant dosing pipe; the sedimentation water distribution tank is provided with a plurality of inclined tubes filled with fillers and a water outlet trough, and the outlet of the inclined tube is connected to the water outlet trough; the bottom of the high-efficiency sedimentation tank is provided with a mud hopper and a mud scraper, and the outlet of the mud hopper is connected to the mud discharge pipe.

5. The multi-stage deep defluorination device according to claim 4, characterized in that: The crystallization tank is filled with calcium carbonate or hydroxyapatite seeds, the particle size of the calcium carbonate or hydroxyapatite seeds is 0.1-0.2 mm, and the filling volume accounts for 40-50% of the volume of the crystallization tank.

6. The multi-stage deep defluorination device according to claim 5, characterized in that: The calcium chloride solution dosing pipe comprises a dosing pipe with an upper and lower double-layer annular structure; the drug outlet holes are evenly distributed on the inner and outer sides of the dosing pipe with an upper and lower double-layer annular structure, and the orifices of the drug outlet holes are arranged obliquely downward; a water distribution plate is provided at the wastewater inlet of the crystallization tank; and the crystallization tank is a regular octagonal structure.

7. The multi-stage deep defluorination device according to claim 4, characterized in that: The supernatant outlet is provided with a triangular weir, the outlet of the triangular weir faces the annular water collecting trough, and the water outlet hole of the annular water collecting trough is connected with the inlet of the coagulation tank; the alkali solution dosing pipe is located above the coagulant dosing pipe, and the coagulant dosing pipe and the alkali solution dosing pipe have the outlet holes arranged downward and evenly distributed.

8. The multi-stage deep defluorination device according to claim 4, characterized in that: The upper part of the coagulation-aiding tank is provided with a water inlet, and the bottom part is provided with a water outlet; the particle medium dosing mechanism is located in the middle part of the coagulation-aiding tank.

9. The multi-stage deep defluorination device according to claim 4, characterized in that: The water outlet of the coagulant aid tank is connected to the bottom water inlet of the flocculation tank through a bottom connecting pipe. The bottom water inlet of the flocculation tank is a bell-shaped mouth and faces the inside of the guide cylinder. The flocculant dosing pipe is annular, and the outlet holes of the flocculant dosing pipe are evenly arranged downward. The guide cylinder is connected and supported by the inner wall of the flocculation tank through a support rod.

10. The multi-stage deep defluorination device according to claim 4, characterized in that: The outlet of the inclined pipe is provided with a water outlet weir, which faces the water outlet sump; the bottom of the high-efficiency sedimentation tank is an inclined surface, which is inclined toward the mud bucket, and the outlet of the mud bucket is connected to the mud discharge pipe through a sludge pump.

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