A continuous resource recovery system and method for photovoltaic fluoride-containing wastewater

Abstract

This invention belongs to the field of chemical raw material recovery and discloses a continuous resource-based treatment system and method for photovoltaic fluoride-containing wastewater. The system includes a primary fluoride removal unit, a secondary fluoride removal unit, and a silicon removal unit. This invention recovers fluoride in the form of high-purity calcium fluoride with a purity >95%, while avoiding the consumption of fresh sodium hydroxide solution, achieving the goal of treating waste with waste, and reducing the residual fluoride in the system effluent to <5 mg / L.

Description

Technical Field

[0001] This invention belongs to the field of chemical raw material recycling, and more specifically, relates to a continuous resource-based treatment system and method for photovoltaic fluoride-containing wastewater. Background Technology

[0002] The photovoltaic industry utilizes the photovoltaic effect, where sunlight shining on silicon materials generates electricity directly. It's a photoelectric conversion industry developed through the application of silicon materials, encompassing the production of high-purity polycrystalline silicon raw materials, solar cells, solar cell modules, and related production equipment. The production process includes texturing, alkaline washing, water washing, and acid washing. The alkaline washing step uses sodium hydroxide solution, generating a large amount of alkaline silicon-containing wastewater. The acid washing step uses hydrochloric acid and hydrofluoric acid etching, producing a large amount of acidic fluoride-containing wastewater. Existing wastewater defluorination methods include distillation, adsorption, ultraviolet light, lime methods, and calcium chloride methods, but these are difficult to industrialize due to various limitations.

[0003] Application No. 201610799160.6 proposes a method of evaporation followed by distillation to recover hydrofluoric acid. However, since hydrofluoric acid forms an azeotrope with water, its recovery requires almost complete evaporation of all water, resulting in enormous energy consumption. Application No. 202311206292.X proposes a method of flocculation and adsorption, but the adsorbents have small adsorption capacity, short lifespan, high cost, and generate a large amount of solid waste. Application No. 202410014006.8 proposes an online ultraviolet (UV) fluoride removal method, but UV light sources are expensive, and the UV method has low fluoride removal efficiency, making it difficult to meet effluent standards. Application No. 201610197407.7 proposes a lime method for fluoride removal, but the low solubility of lime leads to a time-consuming process, high operational difficulty, and low purity of recovered calcium fluoride. Application No. 201610463012.7 proposed using sodium hydroxide and calcium chloride to jointly remove fluoride and recover calcium fluoride. The calcium chloride method has a fast reaction rate and recovers calcium fluoride with high purity. However, after calcium chloride reacts with hydrofluoric acid to produce hydrochloric acid, the wastewater becomes more acidic with a pH < 1. At this pH value, the solubility of fluoride ions is high, making it difficult to precipitate completely, resulting in a low calcium fluoride yield. At the same time, a large amount of sodium hydroxide is required for neutralization, leading to a loss and making it difficult to realize industrialization.

[0004] In view of this, there is an urgent need to propose a continuous resource-based treatment system and method for photovoltaic fluoride-containing wastewater in order to solve the technical problem that existing defluorination technologies and processes are difficult to industrialize. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a continuous resource recovery system and method for photovoltaic fluoride-containing wastewater. This invention recovers fluoride in the form of high-purity calcium fluoride with a purity >95%, while avoiding the consumption of fresh sodium hydroxide solution, achieving the goal of treating waste with waste, and reducing the residual fluoride in the system effluent to <5 mg / L.

[0006] To achieve the above objectives, the present invention provides a continuous resource recovery system for photovoltaic fluoride-containing wastewater, the system comprising a primary fluoride removal unit, a secondary fluoride removal unit, and a silicon removal unit;

[0007] Each defluorination unit includes a reaction flocculant, a sedimentation discharge device, and a solid-liquid separator;

[0008] The upper and middle parts of the primary reactive flocculant are equipped with photovoltaic acidic fluoride wastewater inlet, calcium chloride aqueous solution inlet, primary lime slurry inlet and primary polyacrylamide aqueous solution inlet, and the bottom is equipped with primary reactive flocculant outlet.

[0009] The upper and middle parts of the secondary reactive flocculant are equipped with the inlet of the primary defluorination clear liquid mixture, the inlet of the desiliconization filtrate, and the inlet of the secondary polyacrylamide aqueous solution, while the bottom is equipped with the outlet of the secondary reactive flocculant.

[0010] Each stage of the sedimentation discharge device is equipped with a bottom inlet, an upper clear liquid overflow outlet, and a sedimentation outlet; each stage of the solid-liquid separator is equipped with a solid-liquid inlet, a filter cake outlet, and a filtrate outlet;

[0011] The discharge ports of the primary and secondary reaction flocculation devices are connected to the bottom inlets of their respective sedimentation discharge devices; the sedimentation outlets of each stage sedimentation discharge device are connected to the solid-liquid inlets of their respective solid-liquid separators; the upper clear liquid overflow port of the primary sedimentation discharge device and the filtrate outlet of the primary solid-liquid separator merge and are then connected to the inlet of the primary defluorination clear liquid mixture; the upper clear liquid overflow port of the secondary sedimentation discharge device and the filtrate outlet of the secondary solid-liquid separator merge and are then connected to the outside of the boundary.

[0012] The silicon removal unit includes a silicon removal reactor and a silicon removal solid-liquid separator. The upper and middle parts of the silicon removal reactor are provided with a photovoltaic alkaline silicon-containing wastewater inlet and a silicon removal lime slurry inlet, and the bottom is provided with a slurry outlet. The silicon removal solid-liquid separator is provided with a slurry inlet, a silicon-containing filter cake outlet and a silicon removal filtrate outlet. The slurry outlet of the silicon removal reactor is connected to the slurry inlet of the silicon removal solid-liquid separator. The silicon removal filtrate outlet of the silicon removal solid-liquid separator is connected to the silicon removal filtrate inlet of the secondary reaction flocculant.

[0013] According to the present invention, preferably, each of the primary reaction flocculant, the secondary reaction flocculant, and the desiliconization reactor is independently equipped with a stirrer.

[0014] According to the present invention, preferably, the filter cake outlet of each stage of the solid-liquid separator and the silica-containing filter cake outlet of the silica-removing solid-liquid separator are each independently connected to the outside.

[0015] According to the present invention, preferably, the system further includes a lime slurry high-level tank, a photovoltaic acidic fluoride-containing wastewater feed pump, a photovoltaic alkaline silicon-containing wastewater feed pump, a calcium chloride aqueous solution feed pump, and a polyacrylamide aqueous solution feed pump.

[0016] According to the present invention, preferably, a discharge control valve is provided at the discharge port of the lime slurry high-level tank, and the discharge port of the lime slurry high-level tank is divided into two paths, one path being connected to the primary lime slurry inlet and the other path being connected to the silica-removing lime slurry inlet; the lime slurry high-level tank is used to realize continuous feeding of lime slurry; and an agitator is provided inside the lime slurry high-level tank.

[0017] According to the present invention, preferably, the outlet of the photovoltaic acidic fluoride-containing wastewater feed pump is connected to the inlet of the photovoltaic acidic fluoride-containing wastewater; the photovoltaic acidic fluoride-containing wastewater feed pump is used to realize the continuous feeding of photovoltaic acidic fluoride-containing wastewater.

[0018] According to the present invention, preferably, the outlet of the calcium chloride aqueous solution feed pump is connected to the inlet of the calcium chloride aqueous solution; the calcium chloride aqueous solution feed pump is used to realize the continuous feeding of calcium chloride aqueous solution.

[0019] According to the present invention, preferably, the outlet of the polyacrylamide aqueous solution feed pump is divided into two paths, one path being connected to the primary polyacrylamide aqueous solution inlet and the other path being connected to the secondary polyacrylamide aqueous solution inlet; the polyacrylamide aqueous solution feed pump is used to realize the continuous feeding of polyacrylamide aqueous solution.

[0020] According to the present invention, preferably, the outlet of the photovoltaic alkaline silicon-containing wastewater feed pump is connected to the inlet of the photovoltaic alkaline silicon-containing wastewater; the photovoltaic alkaline silicon-containing wastewater feed pump is used to realize the continuous feeding of photovoltaic alkaline silicon-containing wastewater.

[0021] According to the present invention, preferably, the settling discharge device at each stage includes a settling discharge device, a washing leg and a screw discharge device connected in sequence from top to bottom;

[0022] The settling discharge device is equipped with a bottom inlet and an upper clear liquid overflow outlet;

[0023] The screw discharge device is equipped with the settling outlet.

[0024] According to the present invention, preferably, the top of the body of each stage of the reaction flocculant (excluding the height of the motor of the agitator) is set on the same horizontal plane as the top of the body of the corresponding stage of the settling discharge device.

[0025] According to the present invention, preferably, the height-to-diameter ratio of the primary reactive flocculant and the secondary reactive flocculant is independently 0.5-3:1.

[0026] According to the present invention, preferably, the diameter ratio of the primary sedimentation discharge device to the primary reactive flocculant is 1:1-5.

[0027] According to the present invention, preferably, the diameter ratio of the secondary sedimentation discharge device to the secondary reactive flocculant is 1:1-5.

[0028] According to the present invention, preferably, the diameter of the washing leg is 1 / 2 to 1 / 5 of the diameter of the settling discharge device.

[0029] In this invention, the pipes and equipment in the primary defluorination unit are all made of corrosion-resistant materials, or the pipes and equipment are lined with PTFE or enamel material.

[0030] Another aspect of the present invention provides a continuous resource recovery treatment method for photovoltaic fluoride-containing wastewater, the method employing the above-described system and comprising the following steps:

[0031] S1: Photovoltaic acidic fluoride-containing wastewater, calcium chloride aqueous solution, polyacrylamide aqueous solution, and lime slurry are continuously fed into the primary reactive flocculant from the upper middle part to obtain primary reactive materials; the primary reactive materials are sent to the primary sedimentation discharge device for flocculation and sedimentation to obtain primary clear liquid and primary sediment; the primary sediment is sent to the primary solid-liquid separator for filtration to obtain primary filtrate and calcium fluoride filter cake with a purity >95%;

[0032] S2: Photovoltaic alkaline silicon-containing wastewater and lime slurry are continuously fed into the silicon removal reactor from the middle and upper part to maintain a constant liquid level in the silicon removal reactor, thereby obtaining a silicon removal reaction slurry; the silicon removal reaction slurry is then fed into the silicon removal solid-liquid separator for filtration to obtain calcium silicate sludge filter cake and silicon removal alkaline filtrate.

[0033] S3: Mix the primary clear liquid and primary filtrate obtained in step S1 to form a primary defluorination clear liquid mixture; feed the primary defluorination clear liquid mixture, the desiliconized alkaline filtrate, and the polyacrylamide aqueous solution into the secondary reaction flocculant from the upper middle part of the secondary reaction flocculant to obtain secondary reaction materials; send the secondary reaction materials into the secondary sedimentation discharge device for flocculation and sedimentation to obtain secondary clear liquid and secondary sediment; send the secondary sediment into the secondary solid-liquid separator for filtration to obtain secondary filtrate and calcium fluoride filter cake with a purity >80%; mix the secondary clear liquid and secondary filtrate and discharge them outside the boundary.

[0034] According to the present invention, preferably, the lime slurry is provided by a lime slurry high-level tank, and the hydrated lime used to prepare the lime slurry contains >90% calcium hydroxide.

[0035] According to the present invention, preferably, the polyacrylamide in the aqueous polyacrylamide solution is cationic polyacrylamide; the mass fraction of the aqueous polyacrylamide solution is 0.08-0.12%; and the amount of polyacrylamide added in the primary reaction flocculant and the secondary reaction flocculant is determined independently according to the concentration of polyacrylamide in the photovoltaic acidic fluoride-containing wastewater being 1-50 ppm.

[0036] According to the present invention, preferably, the reactions in the primary reaction flocculant, the secondary reaction flocculant, and the desiliconization reactor are all carried out under stirring.

[0037] According to the present invention, preferably, the method further includes independently discharging the calcium fluoride filter cake with a purity >95%, the calcium silicate sludge filter cake, and the calcium fluoride filter cake with a purity >80% to the outside.

[0038] According to the present invention, preferably, the material residence time in the primary reaction flocculant and the secondary reaction flocculant is 5-60 min, more preferably 10-40 min;

[0039] According to the present invention, preferably, in the primary reactive flocculant, the ratio of the total number of moles of calcium ions in the calcium chloride aqueous solution and lime slurry to the number of moles of fluoride ions in the photovoltaic acidic fluoride-containing wastewater is 0.5-0.6:1; and in the primary reactive flocculant, the ratio of the number of moles of calcium chloride aqueous solution and lime slurry is 0.5-2:1.

[0040] According to the present invention, preferably, the silicon content in the silicon-removing alkaline filtrate is <20 mg / L.

[0041] According to the present invention, preferably, the pH of the reactants in the secondary reaction flocculant is 6-9, resulting in the formation of new calcium fluoride precipitate.

[0042] According to the present invention, preferably, the fluoride ion content in the liquid after mixing the secondary clear liquid and the secondary filtrate is <5 mg / L.

[0043] According to the present invention, preferably, the clear liquids at each stage (primary clear liquid, secondary clear liquid) are obtained by overflowing the clear liquids from the upper middle part of the sedimentation dischargers at each stage; the sediments at each stage (primary sediments, secondary sediments) are obtained by flocculating and settling the solid precipitates from the reactants at each stage into the washing legs at each stage for thickening, and then discharging them through the screw dischargers at each stage.

[0044] The beneficial effects of the technical solution of the present invention are as follows:

[0045] This invention employs continuous operation, ensuring stable system operation and enabling continuous treatment of fluoride-containing wastewater from the photovoltaic industry. It can recover fluoride ions as high-purity calcium fluoride with a purity of ≥95%, while reducing the fluoride ion concentration in the system effluent to <5mg / L.

[0046] This invention utilizes alkaline silicon-containing wastewater from photovoltaic plants to adjust the pH value of acidic fluoride-containing wastewater, treating waste with waste, avoiding the consumption of fresh sodium hydroxide solution, and reducing the treatment cost of acidic fluoride-containing wastewater.

[0047] This invention designs a clear liquid overflow port and a washing leg in both stages of sedimentation discharge device, which can realize the clear liquid and recovered calcium fluoride from different positions. The clear liquid overflows from the upper part of the sedimentation discharge device, and the calcium fluoride is collected after flocculation and thickened in the washing leg, which greatly reduces the workload and difficulty of the solid-liquid separator.

[0048] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0049] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0050] Figure 1 A schematic diagram of a continuous resource recovery system for photovoltaic fluoride-containing wastewater provided in Embodiment 1 of the present invention is shown.

[0051] Figure 2 This diagram illustrates a primary fluoride removal unit in a continuous resource recovery system for photovoltaic fluoride-containing wastewater provided in Embodiment 2 of the present invention.

[0052] The annotations in the attached figures are explained as follows:

[0053] 101-Photovoltaic acidic fluoride wastewater feed pump; 102-Calcium chloride aqueous solution feed pump; 103-Polyacrylamide aqueous solution feed pump; 104-Lime slurry high-level tank; 105-Primary reaction flocculant; 106-Primary sedimentation discharge device; 107-Primary washing leg; 108-Primary screw discharge device; 109-Primary solid-liquid separator; 110-Primary filter cake outlet; 111-Primary filtrate outlet; 112-Primary upper clear liquid overflow port;

[0054] 201-Photovoltaic alkaline silicon-containing wastewater feed pump; 202-Silicon removal reactor; 203-Silicon removal solid-liquid separator; 204-Silicon-containing filter cake outlet; 205-Silicon removal filtrate outlet;

[0055] 301 - Secondary reactive flocculant; 302 - Secondary sedimentation discharge device; 303 - Secondary washing leg; 304 - Secondary screw discharge device; 305 - Secondary solid-liquid separator; 306 - Secondary filter cake outlet; 307 - Upper clear liquid overflow port; 308 - Secondary filtrate outlet; 309 - Mixed wastewater discharged after fluoride removal;

[0056] 401-Photovoltaic acidic fluoride-containing wastewater feeding device; 402-Photovoltaic alkaline silicon-containing wastewater feeding device; 403-Calcium chloride aqueous solution feeding pump device; 404-Polyacrylamide aqueous solution feeding device. Detailed Implementation

[0057] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0058] The following are examples and comparative examples:

[0059] The study used acidic fluoride-containing wastewater and alkaline silicon-containing wastewater from a photovoltaic company's production site in Anhui Province. Ca 2+ The detection method used was EDTA titration, F - The detection methods adopted were ion-selective electrode method, the detection method for soluble SiO2 was silicomolybdenum yellow spectrophotometry, the pH value was measured using a pH meter, and the purity of calcium fluoride was measured in accordance with the national standard GB / T 27804-2011.

[0060] The compositions of the photovoltaic acidic fluoride-containing wastewater and photovoltaic alkaline silicon-containing wastewater used are shown in Table 1.

[0061] The calcium chloride solution used (Ca) 2+ The concentration was 161126 mg / L, and the lime slurry concentration was 2 mol / L.

[0062] Table 1

[0063] name <![CDATA[Cl - mg / L]]> <![CDATA[F - mg / L]]> <![CDATA[SiO2 (soluble) mg / L]]> pH Photovoltaic acidic fluoride wastewater 277 17591 14 3.0 Photovoltaic alkaline silicon-containing wastewater 11 43 7194 13.3

[0064] Example 1

[0065] This embodiment provides a continuous resource recovery system for photovoltaic fluoride-containing wastewater, such as... Figure 1 As shown, the system includes a primary defluorination unit, a secondary defluorination unit, a silicon removal unit, a lime slurry high-level tank 104, a photovoltaic acidic fluoride-containing wastewater feed pump 101, a photovoltaic alkaline silicon-containing wastewater feed pump 201, a calcium chloride aqueous solution feed pump 102, and a polyacrylamide aqueous solution feed pump 103.

[0066] Each defluorination unit includes a reaction flocculant, a sedimentation discharge device, and a solid-liquid separator;

[0067] The upper and middle parts of the primary reactive flocculant 105 are equipped with photovoltaic acidic fluoride wastewater inlet, calcium chloride aqueous solution inlet, primary lime slurry inlet and primary polyacrylamide aqueous solution inlet, and the bottom is equipped with primary reactive flocculant outlet.

[0068] The upper and middle parts of the secondary reaction flocculant 301 are provided with the inlet of the primary defluorination clear liquid mixture, the inlet of the desiliconization filtrate and the inlet of the secondary polyacrylamide aqueous solution, and the outlet of the secondary reaction flocculation is provided at the bottom;

[0069] The settling discharge device at each stage includes a settling discharge device, a washing leg, and a screw discharge device connected in sequence from top to bottom; the settling discharge device is provided with a bottom inlet and an upper clear liquid overflow outlet; the screw discharge device is provided with the settling outlet;

[0070] Each stage of the solid-liquid separator is equipped with a solid-liquid inlet, a filter cake outlet, and a filtrate outlet;

[0071] The top of each stage of the reactive flocculant is set on the same horizontal plane as the top of the corresponding stage of the sedimentation discharge device;

[0072] The primary and secondary reaction flocculation outlets are connected to the bottom inlet of the corresponding sedimentation discharge devices, respectively; the sedimentation outlets of each stage sedimentation discharge device are connected to the solid-liquid inlet of the corresponding stage solid-liquid separator; the primary upper clear liquid overflow port 112 of the primary sedimentation discharge device and the primary filtrate outlet 111 of the primary solid-liquid separator merge and are connected to the primary defluorination clear liquid mixture inlet; the secondary upper clear liquid overflow port 307 of the secondary sedimentation discharge device and the secondary filtrate outlet 308 of the secondary solid-liquid separator merge and are connected to the outside.

[0073] The silicon removal unit includes a silicon removal reactor 202 and a silicon removal solid-liquid separator 203. The upper and middle parts of the silicon removal reactor 202 are provided with a photovoltaic alkaline silicon-containing wastewater inlet and a silicon removal lime slurry inlet, and the bottom is provided with a slurry outlet. The silicon removal solid-liquid separator 203 is provided with a slurry inlet, a silicon-containing filter cake outlet 204, and a silicon removal filtrate outlet 205. The slurry outlet of the silicon removal reactor is connected to the slurry inlet of the silicon removal solid-liquid separator. The silicon removal filtrate outlet 205 of the silicon removal solid-liquid separator is connected to the silicon removal filtrate inlet of the secondary reaction flocculant.

[0074] The filter cake outlets of each stage of the solid-liquid separator and the silica-containing filter cake outlet of the silica removal solid-liquid separator are each independently connected to the outside.

[0075] Each of the primary reaction flocculant 105, the secondary reaction flocculant 301, and the desiliconization reactor 202 is independently equipped with a stirrer.

[0076] The high-level lime slurry tank 104 is equipped with a discharge control valve at its outlet, and the outlet of the high-level lime slurry tank 104 is divided into two paths, one of which is connected to the primary lime slurry inlet and the other of which is connected to the silica-removing lime slurry inlet; the high-level lime slurry tank 104 is used to realize continuous feeding of lime slurry; the high-level lime slurry tank 104 is equipped with an agitator.

[0077] The outlet of the photovoltaic acidic fluoride-containing wastewater feed pump 101 is connected to the inlet of the photovoltaic acidic fluoride-containing wastewater; the photovoltaic acidic fluoride-containing wastewater feed pump 101 is used to realize the continuous feeding of photovoltaic acidic fluoride-containing wastewater.

[0078] The outlet of the calcium chloride aqueous solution feed pump 102 is connected to the calcium chloride aqueous solution inlet; the calcium chloride aqueous solution feed pump 102 is used to realize the continuous feeding of calcium chloride aqueous solution;

[0079] The outlet of the polyacrylamide aqueous solution feed pump 103 is divided into two paths: one path is connected to the primary polyacrylamide aqueous solution inlet, and the other path is connected to the secondary polyacrylamide aqueous solution inlet; the polyacrylamide aqueous solution feed pump 103 is used to realize the continuous feeding of polyacrylamide aqueous solution.

[0080] The outlet of the photovoltaic alkaline silicon-containing wastewater feed pump 201 is connected to the inlet of the photovoltaic alkaline silicon-containing wastewater; the photovoltaic alkaline silicon-containing wastewater feed pump 201 is used to realize the continuous feeding of photovoltaic alkaline silicon-containing wastewater.

[0081] The diameters of the primary sedimentation discharge device 106, the primary reactive flocculant 105, the secondary sedimentation discharge device 302, and the secondary reactive flocculant 301 are all 200 mm, and the height-to-diameter ratio is 2:1.

[0082] Both Grade 1 Wash Leg 107 and Grade 2 Wash Leg 303 have a diameter of 80mm and a height-to-diameter ratio of 3:1.

[0083] This embodiment also provides a continuous resource recovery treatment method for photovoltaic fluoride-containing wastewater. The method uses the above-described system and includes the following steps:

[0084] S1: Turn on the agitator of the primary reaction flocculant 105, and feed 20L / h of photovoltaic acidic fluoride wastewater (feed rate), 1.2L / h of calcium chloride aqueous solution, 1L / h of polyacrylamide aqueous solution (mass fraction of 0.1%) and 2.2L / h of lime slurry into the primary reaction flocculant 105 continuously from the middle and upper part of the primary reaction flocculant 105 according to the material residence time of the primary reaction flocculant 105 of 30min. The feed temperature is 25℃, and the primary reaction material is obtained.

[0085] The primary reactants are fed into a primary settling discharge device. The solid precipitate in the primary reactants is flocculated and settled from the primary settling discharge device 106 into the primary washing leg 107 for thickening, and then discharged through the primary screw discharge device 108 to obtain primary sediment. The clear liquid in the primary reactants overflows from the middle and upper part of the primary settling discharge device 106 to obtain primary clear liquid. The primary sediment is fed into a primary solid-liquid separator 109 for filtration to obtain primary filtrate and primary calcium fluoride filter cake (primary calcium fluoride filter cake: 620 g / h, purity 95.4%, yield 90.3%).

[0086] S2: Turn on the stirrer of the silicon removal reactor 202, and continuously feed 22.2 L / h of photovoltaic alkaline silicon-containing wastewater and 3 L / h of lime slurry into the silicon removal reactor 202 from the middle and upper part of the reactor, keeping the liquid level in the reactor 202 constant, to obtain a silicon removal reaction slurry; send the silicon removal reaction slurry into the silicon removal solid-liquid separator 203 for filtration to obtain 460 g / h of calcium silicate sludge filter cake and a silicon removal alkaline filtrate (the concentration of soluble SiO2 in the silicon removal alkaline filtrate is 12.7 mg / L);

[0087] S3: Mix the primary clarified liquid and primary filtrate obtained in step S1 to form a primary defluoridated clarified liquid mixture (wherein, Ca... 2+ Concentration 1691 mg / L, F - (Concentration 1547 mg / L); Turn on the agitator of the secondary reaction flocculant 301, and according to the material residence time of the secondary reaction flocculant 301 of 20 min, feed the primary defluorination clear liquid mixture of 15.1 L / h, the desiliconization alkaline filtrate of 22.2 L / h and the polyacrylamide aqueous solution of 0.25 L / h into the secondary reaction flocculant 301 from the middle and upper part of the secondary reaction flocculant. The pH of the reaction material in the secondary reaction flocculant 301 is 6.5, and the secondary reaction material is obtained.

[0088] The secondary reactants are fed into a secondary sedimentation discharge device. The solid precipitates in the secondary reactants are flocculated and settled from the secondary sedimentation discharge device 302 into the secondary washing leg 303 for thickening, and then discharged through the secondary screw discharge device 304 to obtain secondary sediments. The clear liquid in the secondary reactants overflows from the middle and upper part of the secondary sedimentation discharge device 302 to obtain secondary clear liquid. The secondary sediments are sent to a secondary solid-liquid separator 305 for filtration to obtain secondary filtrate and secondary calcium fluoride filter cake (secondary calcium fluoride filter cake: 51 g / h, purity 82.3%).

[0089] The secondary clarified liquid and the secondary filtrate are mixed and then discharged outside the boundary. The liquid resulting from the mixture of the secondary clarified liquid and the secondary filtrate contains Ca. 2+ Concentration 0 mg / L, F - Concentration 4.6 mg / L.

[0090] Example 2

[0091] This embodiment provides a continuous resource recovery system for photovoltaic fluoride-containing wastewater, such as... Figure 2 As shown, the only difference between this embodiment and Embodiment 1 is that:

[0092] The diameters of the primary reactive flocculant 105, the secondary sedimentation discharge device 302, and the secondary reactive flocculant 301 are all 200 mm, and the height-to-diameter ratio is 2:1.

[0093] The diameter of the primary settling discharge device 106 is 100mm, and the height-to-diameter ratio is 4:1.

[0094] The diameter of the first-grade washed leg 107 is 40mm, and the height-to-diameter ratio is 3:1;

[0095] The diameter of the 303 secondary washing leg is 80mm, and the height-to-diameter ratio is 3:1.

[0096] This embodiment also provides a continuous resource recovery treatment method for photovoltaic fluoride-containing wastewater. The only difference between this method and Embodiment 1 is that:

[0097] Primary calcium fluoride filter cake: 616 g / h, purity 95.6%, yield 90%;

[0098] In the primary defluorination solution mixture, Ca 2+ Concentration 1702 mg / L, F - Concentration 1589 mg / L;

[0099] Secondary calcium fluoride filter cake: 52 g / h, purity 82.1%;

[0100] The liquid obtained by mixing the secondary clear liquid and the secondary filtrate contains Ca. 2+ Concentration 0 mg / L, F - Concentration 4.5 mg / L.

[0101] Comparative Example 1

[0102] This comparative example provides a continuous treatment method for photovoltaic fluoride-containing wastewater. The only difference between this comparative example and Example 1 is that this comparative example does not use the method of adjusting the pH after removing silicon from photovoltaic alkaline silicon-containing wastewater, but uses a 30% sodium hydroxide solution for secondary fluoride removal. Specifically:

[0103] Step S1 in Comparative Example 1 is the same as step S1 in Example 1;

[0104] This comparative example 1 omits step S2 of example 1;

[0105] Step S3 of Comparative Example 1: Mix the primary clarified liquid and primary filtrate obtained in step S1 to form a primary defluorinated clarified liquid mixture (wherein, Ca... 2+Concentration 1691 mg / L, F - (Concentration 1547 mg / L); Turn on the agitator of the secondary reaction flocculant 301, and feed the primary defluorination solution mixture (33.3 L / h), 30% sodium hydroxide aqueous solution (4 L / h), and polyacrylamide aqueous solution (0.55 L / h) into the secondary reaction flocculant 301 from the upper middle part of the secondary reaction flocculant 301 according to the material residence time of the secondary reaction flocculant 301 (20 min). The pH of the reaction material in the secondary reaction flocculant 301 is 6.5, and the secondary reaction material is obtained.

[0106] The secondary reactants are fed into a secondary sedimentation discharge device. The solid precipitates in the secondary reactants are flocculated and settled from the secondary sedimentation discharge device 302 into the secondary washing leg 303 for thickening, and then discharged through the secondary screw discharge device 304 to obtain secondary sediments. The clear liquid in the secondary reactants overflows from the middle and upper part of the secondary sedimentation discharge device 302 to obtain secondary clear liquid. The secondary sediments are sent to a secondary solid-liquid separator 305 for filtration to obtain secondary filtrate and secondary calcium fluoride filter cake (secondary calcium fluoride filter cake: 112 g / h, purity 81.6%).

[0107] The secondary clarified liquid and the secondary filtrate are mixed and then discharged outside the boundary. The liquid resulting from the mixture of the secondary clarified liquid and the secondary filtrate contains Ca. 2+ Concentration 0 mg / L, F - Concentration 4.8 mg / L.

[0108] This comparative example uses a 30% sodium hydroxide aqueous solution for a two-stage defluorination reaction. Treating one ton of acidic fluoride-containing photovoltaic wastewater requires 120 kg of fresh 30% sodium hydroxide solution, which greatly increases the cost.

[0109] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for continuous resourceful treatment of photovoltaic fluorine-containing wastewater using a continuous resourceful treatment system for photovoltaic fluorine-containing wastewater, characterized by, The system comprises a first fluorine removal unit, a second fluorine removal unit and a silicon removal unit; Each fluorine removal unit comprises a reaction flocculator, a sedimentation discharge device and a solid-liquid separator; The upper middle part of the first reaction flocculator is provided with a photovoltaic acidic fluorine-containing wastewater inlet, a calcium chloride aqueous solution inlet, a first lime milk inlet and a first polyacrylamide aqueous solution inlet, and the bottom part is provided with a first reaction flocculation discharge port; The upper middle part of the second reaction flocculator is provided with a first fluorine removal clear liquid mixture inlet, a silicon removal filtrate inlet and a second polyacrylamide aqueous solution inlet, and the bottom part is provided with a second reaction flocculation discharge port; Each sedimentation discharge device is provided with a bottom inlet, an upper clear liquid overflow port and a sedimentation outlet; each solid-liquid separator is provided with a solid-liquid inlet, a filter cake outlet and a filtrate outlet; The first reaction flocculation discharge port and the second reaction flocculation discharge port are respectively connected with the bottom inlet of the corresponding sedimentation discharge device; the sedimentation outlet of each sedimentation discharge device is connected with the solid-liquid inlet of the corresponding solid-liquid separator; the upper clear liquid overflow port of the first sedimentation discharge device and the filtrate outlet of the first solid-liquid separator are connected with the first fluorine removal clear liquid mixture inlet after being combined; the upper clear liquid overflow port of the second sedimentation discharge device and the filtrate outlet of the second solid-liquid separator are connected to the out-of-boundary after being combined; The silicon removal unit comprises a silicon removal reactor and a silicon removal solid-liquid separator; the upper middle part of the silicon removal reactor is provided with a photovoltaic alkaline silicon-containing wastewater inlet and a silicon removal lime milk inlet, and the bottom part is provided with a slurry outlet; the silicon removal solid-liquid separator is provided with a slurry inlet, a silicon-containing filter cake outlet and a silicon removal filtrate outlet; the slurry outlet of the silicon removal reactor is connected with the slurry inlet of the silicon removal solid-liquid separator; the silicon removal filtrate outlet of the silicon removal solid-liquid separator is connected with the silicon removal filtrate inlet of the second reaction flocculator; The method comprises the following steps: S1: continuously feeding photovoltaic acidic fluorine-containing wastewater, calcium chloride aqueous solution, polyacrylamide aqueous solution and lime milk into the first reaction flocculator from the upper middle part of the first reaction flocculator to obtain a first reaction material; feeding the first reaction material into the first sedimentation discharge device for flocculation and sedimentation to obtain a first clear liquid and a first sediment; feeding the first sediment into the first solid-liquid separator for filtration to obtain a first filtrate and a calcium fluoride filter cake with a purity of >95%; S2: continuously feeding photovoltaic alkaline silicon-containing wastewater and lime milk into the silicon removal reactor from the upper middle part of the silicon removal reactor to maintain the liquid level in the silicon removal reactor constant to obtain a silicon removal reaction slurry; feeding the silicon removal reaction slurry into the silicon removal solid-liquid separator for filtration to obtain a calcium silicate sludge filter cake and a silicon removal alkaline filtrate; S3: mixing the first clear liquid and the first filtrate obtained in step S1 into a first fluorine removal clear liquid mixture; feeding the first fluorine removal clear liquid mixture, the silicon removal alkaline filtrate and polyacrylamide aqueous solution into the second reaction flocculator from the upper middle part of the second reaction flocculator to obtain a second reaction material; feeding the second reaction material into the second sedimentation discharge device for flocculation and sedimentation to obtain a second clear liquid and a second sediment; feeding the second sediment into the second solid-liquid separator for filtration to obtain a second filtrate and a calcium fluoride filter cake with a purity of >80%; The secondary clear liquid and the secondary filtrate are mixed and discharged to the outside.

2. The continuous resourceful treatment method of photovoltaic fluorine-containing wastewater according to claim 1, characterized in that, Each of the primary reaction flocculator, the secondary reaction flocculator and the silicon removal reactor is independently provided with a stirrer; The filter cake outlet of each stage of the solid-liquid separator and the silicon-containing filter cake outlet of the silicon removal solid-liquid separator are independently connected to the outside.

3. The continuous re-sourc ing process for photovoltaic fluorochemical wastewater according to claim 1, characterized in that, The system further comprises a lime milk high tank, a photovoltaic acidic fluorine-containing wastewater feed pump, a photovoltaic alkaline silicon-containing wastewater feed pump, a calcium chloride aqueous solution feed pump and a polyacrylamide aqueous solution feed pump; The outlet of the lime milk high tank is provided with an outlet control valve, and the outlet of the lime milk high tank is divided into two routes, one of which is connected with the primary lime milk inlet, and the other of which is connected with the silicon removal lime milk inlet; the lime milk high tank is used to realize the continuous feeding of lime milk; a stirrer is arranged in the lime milk high tank; The outlet of the photovoltaic acidic fluorine-containing wastewater feed pump is connected with the photovoltaic acidic fluorine-containing wastewater inlet; the photovoltaic acidic fluorine-containing wastewater feed pump is used to realize the continuous feeding of photovoltaic acidic fluorine-containing wastewater; The outlet of the calcium chloride aqueous solution feed pump is connected with the calcium chloride aqueous solution inlet; the calcium chloride aqueous solution feed pump is used to realize the continuous feeding of calcium chloride aqueous solution; The outlet of the polyacrylamide aqueous solution feed pump is divided into two routes, one of which is connected with the primary polyacrylamide aqueous solution inlet, and the other of which is connected with the secondary polyacrylamide aqueous solution inlet; the polyacrylamide aqueous solution feed pump is used to realize the continuous feeding of polyacrylamide aqueous solution; The outlet of the photovoltaic alkaline silicon-containing wastewater feed pump is connected with the photovoltaic alkaline silicon-containing wastewater inlet; the photovoltaic alkaline silicon-containing wastewater feed pump is used to realize the continuous feeding of photovoltaic alkaline silicon-containing wastewater.

4. The continuous resourceful treatment method of photovoltaic fluorine-containing wastewater according to claim 1, characterized in that, Each stage of the sedimentation discharge device comprises a sedimentation discharger, an elutriation leg and a screw discharger connected in sequence from top to bottom; The sedimentation discharger is provided with the bottom inlet and an upper clear liquid overflow port; The screw discharger is provided with the sedimentation outlet.

5. The continuous resourceful treatment method of photovoltaic fluorine-containing wastewater according to claim 4, characterized in that, The top of the body of each stage of the reaction flocculator and the top of the body of the corresponding stage of the sedimentation discharger are arranged on the same horizontal plane.

6. The continuous resourceful treatment method of photovoltaic fluorine-containing wastewater according to claim 4, characterized in that, The height-diameter ratio of the primary reaction flocculator and the secondary reaction flocculator is independently 0.5-3:1; The diameter ratio of the primary sedimentation discharger and the primary reaction flocculator is 1:1-5; The diameter ratio of the secondary sedimentation discharger and the secondary reaction flocculator is 1:1-5; The diameter of the elutriation leg is 1 / 2 to 1 / 5 of the diameter of the sedimentation discharger.

7. The continuous resourceful treatment method of photovoltaic fluorine-containing wastewater according to claim 1, characterized in that, The lime milk is provided by a lime milk high tank, and the calcium hydroxide content in the slaked lime for preparing the lime milk is >90%. The polyacrylamide in the polyacrylamide aqueous solution is cationic polyacrylamide; the mass fraction of the polyacrylamide aqueous solution is 0.08-0.12%; the adding amount of the polyacrylamide in the primary reaction flocculator and the secondary reaction flocculator is independently determined according to the concentration of the polyacrylamide in the photovoltaic acidic fluorine-containing wastewater, which is 1-50 ppm.

8. The continuous resource processing method of photovoltaic fluorine-containing wastewater according to claim 1, characterized in that, The reactions in the primary reaction flocculator, the secondary reaction flocculator and the silicon removal reactor are all carried out under stirring; The method further comprises independently discharging the calcium fluoride filter cake with a purity of >95%, the calcium silicate sludge filter cake and the calcium fluoride filter cake with a purity of >80% to the outside; The residence time of the materials in the primary reaction flocculator and the secondary reaction flocculator is 5-60 min; In the primary reaction flocculator, the ratio of the total moles of calcium ions in the calcium chloride aqueous solution and the lime milk to the moles of fluorine ions in the photovoltaic acidic fluorine-containing wastewater is 0.5-0.6:1; in the primary reaction flocculator, the ratio of the moles of the calcium chloride aqueous solution to the moles of the lime milk is 0.5-2:1; The silicon content in the silicon removal alkaline filtrate is <20 mg / L; The pH of the reaction material in the secondary reaction flocculator is 6-9; The fluorine ion content in the liquid after mixing the secondary clear liquid and the secondary filtrate is <5 mg / L.

9. The continuous re-sourc ing process for photovoltaic fluorochemical wastewater according to claim 1, characterized in that, The clear liquid of each stage is obtained by overflow from the middle upper part of each stage of the settling discharger; the settled material of each stage is obtained by flocculating and settling the solid precipitate in the reaction material of each stage to be thick in each stage of the elutriation leg, and then discharged by each stage of the screw discharger. The polyacrylamide in the polyacrylamide aqueous solution is cationic polyacrylamide; the mass fraction of the polyacrylamide aqueous solution is 0.08-0.12%; the adding amount of the polyacrylamide in the primary reaction flocculator and the secondary reaction flocculator is independently determined according to the concentration of the polyacrylamide in the photovoltaic acidic fluorine-containing wastewater, which is 1-50 ppm.

Images