A fluorine-containing wastewater resource utilization system and method

Abstract

This application relates to a system and method for the resource utilization of fluoride-containing wastewater. The system includes: a pretreatment unit for removing impurities and filtering fluoride-containing waste acid; a silicon source addition unit connected to the pretreatment unit for adding a silicon source to convert hydrofluoric acid in the fluoride-containing waste acid into fluorosilicic acid to obtain a pretreatment solution; an acid-base adjustment unit connected to the pretreatment unit for adjusting the pH value of the pretreatment solution by adding waste alkali to obtain a concentrated solution; a multi-stage evaporation, concentration, and crystallization unit connected to the acid-base adjustment unit for multi-stage evaporation, concentration, and crystallization of the concentrated solution to obtain a silicate sol; and a crystallization and drying unit connected to the multi-stage evaporation, concentration, and crystallization unit for cooling, crystallizing, and drying the silicate sol to obtain fluorosilicates. This system can achieve efficient and deep purification of fluoride-containing waste acid and synergistically utilize waste gas and waste alkali from the photovoltaic industry. Through multi-stage concentration and purification, it produces high-purity, low-moisture fluorosilicates, reducing energy consumption and reagent costs.

Description

Technical Field

[0001] This application belongs to the field of industrial wastewater treatment technology, and in particular relates to a system and method for the resource utilization of fluoride-containing wastewater. Background Technology

[0002] The photovoltaic industry (monocrystalline silicon solar cells and polycrystalline silicon solar cells) uses large amounts of hydrofluoric acid in its production process, resulting in industrial wastewater with high fluoride ion concentrations. This fluoride-containing wastewater is generated during processes such as pickling, surface texturing, and dephosphorized silicon glass production, and mainly consists of concentrated acid wastewater and dilute acid wastewater. In addition, the production processes of polycrystalline and monocrystalline silicon also discharge large amounts of concentrated alkaline wastewater and dilute alkaline wastewater.

[0003] The conventional treatment process for fluoride-containing wastewater involves adding calcium salts such as lime or calcium chloride to generate calcium fluoride precipitate. The CaF2 content in calcium fluoride sludge is only about 60% or less (dry basis), and it contains a large amount of silica, calcium carbonate, etc., which does not meet the standards for direct utilization. It can only be disposed of as solid waste through landfill, which leads to problems such as high disposal costs and resource waste.

[0004] Chinese invention patent CN115872406A proposes a system and method for the resource utilization of hydrogen fluoride wastewater from the photovoltaic industry. The system uses a fluorosilicic acid reaction device to precipitate fluorosilicic acid. After centrifugation, the fluorosilicate precipitated in the wastewater is washed and reused, while the supernatant from the wastewater enters a hydrofluoric acid refining device for hydrofluoric acid refining and recycling. While this existing technology can achieve the resource utilization of waste acid from photovoltaic industry wastewater to obtain fluorosilicates, it only recovers the effective components of the waste acid, such as fluorosilicic acid. An additional sodium salt precipitant is needed during the precipitation of fluorosilicic acid, and it does not comprehensively utilize the waste alkali and photovoltaic exhaust gases in the wastewater, resulting in a low overall recovery rate. Summary of the Invention

[0005] The purpose of this application is to provide a system and method for the resource utilization of fluoride-containing wastewater. This system can achieve efficient and in-depth purification of fluoride-containing waste acid and synergistically utilize waste gas and waste alkali generated in the photovoltaic industry. Through multi-stage concentration and purification processes, it can stably produce high-purity, low-moisture fluorosilicate products, significantly reducing energy consumption and reagent consumption costs in the wastewater treatment process, and achieving a higher overall recovery rate.

[0006] This application provides a system for the resource utilization of fluoride-containing wastewater, comprising: a pretreatment unit for removing impurities and filtering fluoride-containing waste acid; a silicon source addition unit connected to the pretreatment unit for adding a silicon source to convert hydrofluoric acid in the waste acid into fluorosilicic acid, thereby obtaining a pretreatment liquid; wherein the silicon source is silicon dioxide generated from the combustion of photovoltaic exhaust gas; an acid-base adjustment unit connected to the pretreatment unit for adjusting the pH value of the pretreatment liquid by adding waste alkali, thereby obtaining a concentrated liquid; a multi-stage evaporation, concentration, and crystallization unit connected to the acid-base adjustment unit for performing multi-stage evaporation, concentration, and crystallization on the concentrated liquid, thereby obtaining a silicate sol; and a crystallization and drying unit connected to the multi-stage evaporation, concentration, and crystallization unit for cooling, crystallizing, and drying the silicate sol, thereby obtaining a fluorosilicate product with a water content ≤0.1%.

[0007] In a further technical solution, the multi-stage evaporation concentration and crystallization unit includes a primary evaporation concentration and crystallization unit and a secondary evaporation purification and crystallization unit; the primary evaporation concentration and crystallization unit is connected to the acid-base adjustment unit and the secondary evaporation purification and crystallization unit, and is used to perform preliminary evaporation and crystallization on the liquid to be concentrated to obtain a primary silicate sol; the secondary evaporation purification and crystallization unit is connected to the primary evaporation concentration and crystallization unit and the crystallization drying unit, and is used to perform secondary evaporation and purification on the primary silicate sol to obtain a secondary silicate sol.

[0008] In a further technical solution, the primary evaporation concentration and crystallization unit includes a primary distillation column, a third collection pump, a first circulation pump, a first heat exchanger, and a first pure water supplier; the primary distillation column is connected to the upstream acid-base adjustment unit via a pipeline; the primary distillation column is connected to the downstream secondary evaporation purification and crystallization unit via a pipeline through the third collection pump; the primary distillation column and the first heat exchanger are connected to the first circulation pump via a pipeline; the first pure water supplier is connected to the primary distillation column via a pipeline for providing pure water spray.

[0009] In a further technical solution, the secondary purification and crystallization unit includes a secondary distillation column, a fourth outflow pump, a second circulation pump, a second heat exchanger, and a second pure water supplier; the secondary distillation column is connected to the third outflow pump of the primary evaporation, concentration, and crystallization unit at the front end via a pipeline; the secondary distillation column is connected to the crystallization and drying unit at the rear end via a pipeline through the fourth outflow pump; the second circulation pump is connected between the secondary distillation column and the second heat exchanger via a pipeline; the second pure water supplier is connected to the secondary distillation column via a pipeline for providing pure water spray.

[0010] In a further technical solution, the pretreatment unit includes a pretreatment tank, a first feed pump, a first filter, and a first outlet pump; the pretreatment tank is connected to a concentrated acid tank containing the fluorine-containing waste acid via a pipeline through the first feed pump; the pretreatment tank is connected to the downstream acid-base adjustment unit via a pipeline through the first filter and the first outlet pump; the pretreatment tank is connected to the silicon source addition unit via a pipeline to achieve silicon source addition; preferably, the pretreatment unit further includes a purification agent additive, which is connected to the pretreatment tank via a pipeline and is used to add carbonate to remove impurities from the fluorine-containing waste acid.

[0011] In a further technical solution, the acid-base adjustment unit includes a pH adjustment tank, a second feed pump, a second filter, and a second discharge pump; the pH adjustment tank is connected to the first discharge pump of the pretreatment unit at the front end via a pipeline; the pH adjustment tank is connected to a concentrated alkali tank containing the waste alkali via the second feed pump via a pipeline; the pH adjustment tank is connected to the multi-stage evaporation, concentration, and crystallization unit at the rear end via a pipeline via the second filter and the second discharge pump; preferably, the acid-base adjustment unit further includes a chemical alkali additive, which is connected to the pH adjustment tank via a pipeline and is used to add chemical alkali to provide metal ions and adjust the pH of the pretreatment solution.

[0012] In a further technical solution, the crystallization and drying unit includes a fluidized bed crystallizer, a fluidized bed dryer, and a heat source; the fluidized bed crystallizer is connected to the multi-stage evaporation and concentration crystallization unit at the front end via a pipeline, and is used to cool and crystallize the silicate sol to obtain wet fluorosilicate crystals; the fluidized bed dryer is connected to the fluidized bed crystallizer at the front end via a pipeline, and is used to dry the wet fluorosilicate crystals to obtain fluorosilicate products; the heat source is connected to the fluidized bed dryer via a pipeline, and is used to provide the heat required by the fluidized bed dryer.

[0013] This application also provides a method for the resource utilization of fluoride-containing wastewater, using the aforementioned fluoride-containing wastewater resource utilization system, comprising the following steps: S1. The fluorine-containing waste acid to be treated is introduced into the pretreatment unit for impurity removal. S2. Add a silicon source to the pretreatment unit using the silicon source addition unit to convert the hydrofluoric acid in the fluorine-containing waste acid into fluorosilicic acid to obtain a pretreatment solution. S3. The pretreated liquid is introduced into the acid-base adjustment unit, and the pH value of the mixture is controlled within a preset range by adding waste alkali to obtain the concentrated liquid. S4. The liquid to be concentrated is introduced into the multi-stage evaporation, concentration and crystallization unit to carry out multi-stage evaporation, concentration and crystallization to obtain silicate sol; S5. The silicate sol is introduced into the crystallization and drying unit for cooling, crystallization and drying to obtain a fluorosilicate product with a water content of ≤0.1%.

[0014] In a further technical solution, in S2; The silicon source is one or more of silicon dioxide generated from the combustion of photovoltaic waste gas, industrial-grade silicon dioxide, or sodium silicate, and the molar ratio of the amount of silicon source added to hydrofluoric acid in the fluorine-containing waste acid is 1:6 to 1:8. And / or, In S4; The multi-stage evaporation, concentration, and crystallization unit includes a primary evaporation, concentration, and crystallization unit and a secondary evaporation, purification, and crystallization unit. The liquid to be concentrated is pumped into the primary evaporation, concentration, and crystallization unit for preliminary evaporation and crystallization to obtain a primary silicate sol. The primary silicate sol is then pumped into the secondary evaporation, purification, and crystallization unit for secondary evaporation and purification to obtain a secondary silicate sol. And / or, In step S5, the crystallization and drying unit includes a fluidized bed crystallizer and a fluidized bed dryer. The cooling crystallization operation is as follows: the secondary silicate sol is pumped into the fluidized bed crystallizer and slowly cooled and crystallized at a cooling rate of 0.2~0.5℃ / min to obtain wet fluorosilicate crystals. The drying operation is as follows: the wet fluorosilicate crystals are fed into the fluidized bed dryer using a screw feeder and dried for 15~30 minutes under the conditions of an inlet air temperature of 110~130℃ and a fluidizing gas velocity of 0.4~0.7 m / s to obtain a fluorosilicate product with a water content ≤0.1%.

[0015] In a further technical solution, the preliminary evaporation and crystallization operation is as follows: the liquid to be concentrated is pumped into the first-stage evaporation and concentration crystallization unit, and evaporated for 60-120 minutes at a solution pH of 5-7 and a temperature of 80-90℃ to obtain a first-stage silicate sol; the secondary evaporation and purification operation is as follows: the first-stage silicate sol is pumped into the second-stage evaporation and purification crystallization unit with pure water at 60-70℃ at a solid-liquid ratio of 1:3 to 1:5, and dissolved for 20-30 minutes at a stirring temperature of 60-70℃ and 200-300 rpm to obtain a fluorosilicate solution; a complexing agent and a dispersant are added to the fluorosilicate solution for purification to obtain a clear solution; the clear solution is evaporated for 60-120 minutes at a solution pH of 5-7 and a temperature of 60-70℃ to obtain a second-stage silicate sol.

[0016] Compared with the prior art, the advantages of the present invention are as follows: This application innovatively utilizes fluorinated waste acid (providing a fluorine source and part of a silicon source), waste alkali (providing a metal ion source and used for pH adjustment), and process waste gas (providing a high-purity silicon source after combustion) from photovoltaic factories as raw materials for the production of fluorosilicates. This significantly reduces raw material costs, achieves high-value conversion of waste, alleviates end-of-pipe disposal pressure, and eliminates the need for expensive raw materials such as high-purity hydrofluoric acid required in traditional fluorosilicate production. By combining basic unit processes such as pretreatment and impurity removal of fluorinated waste acid, silicon source addition, pH adjustment and control, gradient crystallization, and product drying, high-quality fluorosilicate products (such as sodium fluorosilicate) with a purity ≥99.0% are obtained. This achieves comprehensive resource utilization of photovoltaic factory waste, rationally integrates water, heat, and materials for multi-dimensional reuse, reduces energy consumption and treatment costs, and reduces the generation of production waste and corresponding disposal costs from the source. Attached Figure Description

[0017] Figure 1 This diagram shows the connection diagram of each unit in the fluoride-containing wastewater resource utilization system in this embodiment; Figure 2 This diagram illustrates the process flow of the fluoride-containing wastewater resource utilization method in this embodiment.

[0018] Figure Labels 10. Pretreatment unit; 11. Pretreatment tank; 12. First feed pump; 13. First filter; 14. First outflow pump; 15. Impurity remover additive; 20. Silicon source addition unit; 30. Acid-base adjustment unit; 31. pH adjustment tank; 32. Second feed pump; 33. Second filter; 34. Second outflow pump; 35. Alkali additive; 40. First-stage evaporation, concentration, and crystallization unit; 41. First-stage distillation column; 42. Third outflow pump; 43. ... 44. First circulating pump; 45. First heat exchanger; 50. First pure water supplier; 51. Secondary evaporation purification and crystallization unit; 52. Secondary distillation column; 53. Fourth outflow pump; 54. Second circulating pump; 55. Second heat exchanger; 60. Second pure water supplier; 61. Crystallization drying unit; 62. Fluidized bed crystallizer; 63. Fluidized bed dryer; 70. Heat source; 80. Concentrated acid tank; 90. Concentrated alkali tank; 100. Collection unit; 110. Tail gas treatment unit. Detailed Implementation

[0019] The technical solutions of this application are further illustrated below through specific embodiments. These specific embodiments do not represent a limitation on the scope of protection of this application. Any non-essential modifications and adjustments made by others based on the concept of this application still fall within the scope of protection of this application.

[0020] Example 1 Please refer to Figure 1As shown, this embodiment provides a fluoride-containing wastewater resource utilization system, including a pretreatment unit 10, which is used to remove impurities and filter fluoride-containing waste acid; the pretreatment unit 10 is connected to a silicon source addition unit 20, which is used to add a silicon source to the pretreatment unit 10 to convert hydrofluoric acid in the fluoride-containing waste acid into fluorosilicic acid, obtaining a pretreated liquid. The silicon source is generated by high-purity SiO2 through high-temperature combustion (800~1000℃) of photovoltaic waste gas (SiH4 combustion tail gas); the rear end of the pretreatment unit 10 is connected to... The acid-base adjustment unit 30 is used to adjust the pH value of the pretreatment liquid by adding waste alkali to obtain the concentrated liquid. The rear end of the acid-base adjustment unit 30 is connected to a multi-stage evaporation, concentration and crystallization unit, which is used to perform multi-stage evaporation, concentration and crystallization on the concentrated liquid to obtain silicate sol. The rear end of the multi-stage evaporation, concentration and crystallization unit is connected to a crystallization and drying unit 60, which is used to cool, crystallize and dry the silicate sol to obtain a fluorosilicate product with a water content ≤0.1%.

[0021] Current technologies for the resource utilization of hydrogen fluoride wastewater only recover the effective components, such as fluorosilicic acid, from the waste acid. Sodium salt is added as a flocculant during the precipitation of fluorosilicic acid. However, there is no comprehensive resource utilization of the waste alkali and photovoltaic exhaust gas in the wastewater, resulting in a low overall recovery rate. Traditional fluorosilicate production requires high-purity hydrogen fluoride, silicon sources, and metal salts, which is costly. In contrast, photovoltaic factory wastewater typically contains fluorinated waste acid, waste alkali, and exhaust gas. The fluorinated waste acid contains fluoride ions and fluorosilicate ions required for fluorosilicate production and can serve as fluorine and silicon sources for fluorosilicate recycling. The waste alkali provides metal ions for fluorosilicate production and can be used to adjust the pH of the solution. Silicon tetrafluoride in the photovoltaic production exhaust gas is converted into silicon dioxide through combustion and can be used as a regulating silicon source for fluorosilicate production. Therefore, this embodiment innovatively utilizes fluorinated waste acid (providing a fluorine source and part of a silicon source), waste alkali (providing a metal ion source and used for pH adjustment), and photovoltaic exhaust gas (providing a high-purity silicon source after combustion) from photovoltaic plants as raw materials for the production of fluorosilicates. This achieves comprehensive resource utilization of fluorinated waste acid, waste alkali, and photovoltaic exhaust gas, while eliminating the need for expensive raw materials such as high-purity hydrofluoric acid required in traditional fluorosilicate production. This significantly reduces raw material costs, achieves high-value conversion of waste, avoids the high pollution, high cost, and high energy consumption defects of the traditional discharge-then-treatment method, and alleviates the pressure of end-of-pipe disposal. By combining unit processes including pretreatment and impurity removal of fluorinated waste acid, silicon source addition, pH adjustment and control, multi-stage evaporation, concentration, crystallization, and product drying, high-quality fluorosilicate products (such as sodium fluorosilicate) with a purity ≥99.0% can be obtained, enhancing the economic value of the product.

[0022] Please refer to Figure 1As shown, in a specific embodiment, the pretreatment unit 10 is a closed kettle-type structure, a tank-type structure, or a trough-type structure. The specific structure adopted is not limited in this embodiment and can be selected according to the actual situation.

[0023] The pretreatment unit 10 includes a pretreatment tank 11, a first feed pump 12, a first filter 13, a first outlet pump 14, and a decontaminant additive 15. The pretreatment tank 11 has a silicon source inlet and a decontaminant additive inlet at its top, a first feed inlet near the top on its side, and a first outlet at its bottom. The first feed inlet is connected to a concentrated acid tank 70 containing fluorinated waste acid via a pipeline through the first feed pump 12. The first outlet is connected to an acid-base adjustment unit 30 at the rear end via a pipeline through the first filter 13 and the first outlet pump 14. The silicon source inlet is connected to a silicon source addition unit 20 via a pipeline, and the decontaminant additive inlet is connected to the decontaminant additive 15 via a pipeline. In use, the fluorinated waste acid in the concentrated acid tank 70 is pumped into the pretreatment tank 11 through the first feed inlet by the first feed pump 12. The decontaminant additive 15 adds carbonate to the pretreatment tank 11 through the decontaminant additive inlet for decontamination, mainly removing Ca. 2+ and Mg 2+ Metal impurities are removed. The silicon source addition unit 20 adds silicon source to the pretreatment tank 11 through the silicon source addition port. The silicon source can convert hydrofluoric acid in the fluorine-containing waste acid into fluorosilicic acid. Finally, the pretreatment liquid in the pretreatment tank 11 is filtered by the first filter 13 through the first extraction pump 14 to remove suspended particulate matter and excess silicon source in the solution, and then pumped into the downstream acid-base adjustment unit 30.

[0024] Furthermore, if an additional silicon source needs to be added and its dosage controlled, silica particles with a particle size of less than 10 μm can be selected as the silicon source. If necessary, the particle size can be adjusted and refined through ball milling. Smaller particle size results in a larger specific surface area, which is more conducive to increasing the reaction contact area and improving the reaction rate. Alternatively, industrial-grade sodium silicate can also be selected as the silicon source, and the amount added can be adjusted by weighing.

[0025] The pH adjustment unit 30 includes a pH adjustment tank 31, a second feed pump 32, a second filter 33, a second outlet pump 34, and a alkali additive 35. The pH adjustment tank 31 has an alkali addition port at the top, a liquid inlet near the top on the side, and a second feed port and a second outlet at the bottom. The liquid inlet is connected to the first outlet pump 14 of the pretreatment unit 10 at the front end via a pipeline. The second feed port is connected to the concentrated alkali tank 80 containing waste alkali via the second feed pump 32 via a pipeline. The second outlet is connected to the multi-stage evaporation, concentration, and crystallization unit at the rear end via the second filter 33 and the second outlet pump 34 via a pipeline. The alkali additive 35 is connected to the alkali addition port of the pH adjustment tank 31 via a pipeline. In operation, the pretreatment liquid in the pretreatment tank 11 is pumped into the pH adjustment tank 31 through the inlet by the first extraction pump 14. Industrial waste alkali liquid (such as waste liquid containing 1%~30% NaOH or KOH) stored in the concentrated alkali tank 80 is pumped into the pretreatment tank 11 through the second feed pump 32, reacting with the fluorosilicic acid in the pretreatment liquid to generate corresponding fluorosilicates (such as Na2SiF6 or K2SiF6) and adjust the pH. The chemical alkali additive 35 can supplement the corresponding chemical alkali (such as KOH) according to the target product type (such as the need to produce fluorosilicates of specific metal ions) to provide specific metal ions and precisely control the final pH within the suitable crystallization range of 5~7. Simultaneously, mechanical stirring is used to ensure uniform mixing of the reactants, avoiding localized excessively high pH or the formation of flocculent matter or precipitation. Finally, the pH-adjusted concentrate in the pH adjustment tank 31 is pumped into the downstream multi-stage evaporation, concentration, and crystallization unit through the second extraction pump 34. It should be noted that the pH of the solution is controlled between 5 and 7 through waste alkali adjustment. If the system is too alkaline, precipitation is likely to occur, leading to the formation of fluorosilicates. Fluorosilicates are relatively stable in weakly acidic to neutral environments. Conversely, excessive acidity should be avoided to prevent the decomposition of fluorosilicic acid in such conditions.

[0026] Furthermore, the pH adjustment tank 31 can also be equipped with a detection port (not shown in the figure) for pH detection and sampling. Online pH detection is achieved through the detection port, and the feed rate of waste alkali is adjusted in real time based on the detection results to control the pH of the system within a suitable range. This prevents the decomposition of fluorosilicic acid to produce hydrogen fluoride and silicon tetrafluoride gases, thus preventing equipment corrosion and reduced yield.

[0027] In this embodiment, it should be noted that multi-stage evaporation concentration crystallization is adopted, specifically two-stage evaporation concentration crystallization, including a first-stage evaporation concentration crystallization unit 40 and a second-stage evaporation purification crystallization unit 50, which will be described below.

[0028] In one specific embodiment, in the primary evaporation, concentration, and crystallization unit 40, the liquid to be concentrated evaporates a large amount of water under heating conditions, causing the fluorosilicate concentration to continuously increase. Once supersaturation is reached, crystals begin to precipitate. The main purpose of this unit is to achieve preliminary concentration and crystallization, obtaining a primary silicate sol containing a large amount of crystals and mother liquor. During this process, some impurities with low solubility may co-precipitate with the crystals or be carried away by the mother liquor.

[0029] Please refer to Figure 1 As shown, the primary evaporation, concentration, and crystallization unit 40 further includes a primary distillation column 41, a third outflow pump 42, a first circulating pump 43, a first heat exchanger 44, and a first pure water supplier 45. The primary distillation column 41 is a packed column, and its internal components include a bottom baffle, a packing layer, a demister layer, and material inlets. The bottom baffle stabilizes the operating liquid level. The packing layer (usually using Pall rings or rectangular saddle rings) is 3-5 meters high, providing a large gas-liquid mass transfer surface. The demister layer (such as a wire mesh demister) is located at the top to remove droplets and microcrystals entrained in the vapor. The primary distillation column 41 is also equipped with a feeding device. During the evaporation process, NaOH alkaline solution is automatically added to precisely stabilize the pH value of the material between 5 and 7, preventing the decomposition of fluorosilicates (such as Na2SiF6) into toxic SiF4 gas due to excessively low pH, thus ensuring equipment safety and the operating environment. It should be noted that the distillation column is a relatively mature structure in this field, and will not be described in detail here.

[0030] Furthermore, the first-stage distillation column 41 has a third feed inlet in the middle section of the column bottom, a first pure water inlet in the upper middle section of the column bottom, a third outlet and a first circulation outlet at the bottom of the column bottom, and a first circulation inlet on the side of the column bottom near the top. The third feed inlet is connected to the second outlet pump 34 of the front-end acid-base adjustment unit 30 via a pipeline. The third outlet is connected to the rear-end secondary evaporation purification and crystallization unit 50 via a pipeline through the third outlet pump 42. The first circulation outlet is connected to the first circulation inlet via a pipeline through the first circulation pump 43 and the first heat exchanger 44. The first pure water provider 45 is connected to the first pure water inlet of the first-stage distillation column 41 via a pipeline to provide pure water for washing the steam. The core of this first-stage distillation column 41 is to remove most of the water through evaporation, allowing the concentrated liquid to undergo preliminary evaporation and crystallization to obtain a first-stage silicate sol, and producing condensate. In operation, the liquid to be concentrated is drawn from the pH adjustment tank 31 of the acid-base adjustment unit 30 via the second outflow pump 34 and enters the middle section of the bottom of the primary distillation column 41. The first circulation pump 43 draws the liquid from the bottom of the column through the first circulation outlet, heats it to 80-90°C via the first heat exchanger 44, and then returns it to the bottom of the column through the first circulation inlet, achieving forced circulation at a flow rate of ≥3 m / s. Under the condition that the first heat exchanger 44 provides the heat source, evaporation and concentration are carried out at 80-90°C and pH 5-7 for 60-120 minutes. The first pure water provider 45 can provide a small amount of pure water to spray and wash any mist that may be entrained in the column. As the water evaporates, the concentration of fluorosilicate increases, gradually forming a primary silicate sol (supersaturated solution). The first circulation pump 43 circulates the liquid between the column and the heat exchanger to ensure uniform heating. After being concentrated to a certain concentration, the primary silicate sol is collected by the third outflow pump 42 and pumped into the secondary evaporation purification and crystallization unit 50 at the rear end. It should be noted that heating to boiling allows for slow evaporation of water. However, if the heating temperature is too high, crystallization can easily occur, making it difficult to control. Therefore, heating to 80-90℃ is chosen to evaporate most of the water without producing excessive crystallization.

[0031] Furthermore, a steam outlet is provided at the top of the reboiler of the primary distillation column 41. The steam (approximately 85°C) generated by evaporation within the primary distillation column 41 is discharged from the steam outlet at the top of the column. The steam first passes through a gas-liquid separator to remove liquid phase entrainment and crystalline particles ≥10 µm in size. It then enters a condenser, where it is cooled to 30-40°C and condensed into liquid water to obtain low-fluoride condensate. The fluoride content of this low-fluoride condensate can be reduced to <15 mg / L. This condensate can also be used as process makeup water for the secondary evaporation purification and crystallization unit 50, or it can be treated to meet discharge standards.

[0032] It should be noted that by controlling the temperature of the first heat exchanger 44, the pressure inside the tower, and the material residence and evaporation time, and by appropriately adding alkali to control the pH of the material, acidity fluctuations and fluorosilicate decomposition can be avoided.

[0033] In one specific embodiment, the secondary evaporation purification crystallization unit 50 has the same structure as the primary evaporation concentration crystallization unit 40, but its function focuses on purification. It is mainly used to improve the purity of the product and obtain high-purity fluorosilicate products by controlling the crystallization conditions. The primary silicate sol is pumped into the secondary evaporation purification crystallization unit 50 and undergoes secondary evaporation purification in the secondary evaporation purification crystallization unit 50. The secondary silicate sol obtained in this stage has significantly improved crystal purity, particle size and color.

[0034] Please refer to Figure 1 As shown, the secondary evaporation purification and crystallization unit 50 further includes a secondary distillation column 51, a fourth outflow pump 52, a second circulation pump 53, a second heat exchanger 54, and a second pure water supplier 55. The top of the secondary distillation column 51 is equipped with a demister; the middle section of the column has a fourth feed inlet; the upper middle section of the column has a second pure water inlet; the bottom of the column has a fourth outflow outlet and a second circulation outlet; and the side of the column near the top has a second circulation inlet. The fourth feed inlet is connected to the third outflow pump 42 of the primary evaporation concentration and crystallization unit 40 via a pipeline. The fourth outflow outlet is connected to the rear crystallization drying unit 60 via a pipeline through the fourth outflow pump 52. The second circulation outlet is connected to the second circulation inlet via a pipeline through the second circulation pump 53 and the second heat exchanger 54. The second pure water supplier 55 is connected to the second pure water inlet of the secondary distillation column 51 via a pipeline to provide pure water for washing the steam. This pure water can be the condensate produced by the primary evaporation concentration and crystallization unit 40. In operation, the primary silicate sol from the primary evaporation concentration and crystallization unit 40 is first mixed and stirred with pure water at 60-70℃ in a tower at a certain solid-liquid ratio to form a relatively dilute fluorosilicate solution. Disodium EDTA (ethylenediaminetetraacetic acid disodium salt) is added to this solution as a complexing agent and sodium polyacrylate as a dispersant to complex residual trace metal ions and prevent impurities from co-crystallizing. Then, a secondary evaporation purification process is carried out under mild conditions of 60-70℃ and pH 5-7 (also using forced circulation) to obtain a secondary silicate sol with higher purity. This process effectively purifies the product. The second pure water supplier 55 functions the same as the first pure water supplier 45. The purified secondary silicate sol is then sent to the downstream crystallization and drying unit 60 by the fourth extraction pump 52.

[0035] Please refer to Figure 1As shown, in one specific embodiment, the crystallization drying unit 60 includes a fluidized bed crystallizer 61, a fluidized bed dryer 62, and a heat source 63. The fluidized bed crystallizer 61 is connected to the fourth outflow pump 52 of the front-end secondary evaporation purification crystallization unit 50 via pipeline, and is used to cool and crystallize the secondary silicate sol to obtain wet fluorosilicate crystals. The fluidized bed crystallizer 61 uses a screw feeder to transport the wet fluorosilicate crystals to the fluidized bed dryer 62, which is used to dry the wet fluorosilicate crystals to reduce the product moisture content to ≤0.1%, ultimately obtaining a qualified fluorosilicate product. The heat source 63 is connected to the fluidized bed dryer 62 via pipeline and is used to provide the heat required by the fluidized bed dryer 62. Alternatively, the fluidized bed crystallizer 61 can also be a crystallization kettle. In use, the secondary silicate sol enters the fluidized bed crystallizer 61, where it is cooled at a slow rate of 0.2~0.5℃ / min by controlling the cooling medium, inducing the uniform precipitation of fluorosilicate crystals to form uniformly sized wet fluorosilicate crystals. The wet crystals are then fed into the fluidized bed dryer 62 via a conveying device (such as a screw feeder). A heat source 63 (such as an electric heater or a steam heat exchanger) provides hot air at 110~130℃, which dries the crystals in a fluidized state for 15~30 minutes at a gas velocity of 0.4~0.7 m / s, efficiently removing moisture and ultimately obtaining a high-purity, free-flowing fluorosilicate product with a moisture content of no more than 0.1%, which can then be packaged and sold as a commercial product.

[0036] Furthermore, the key components and process parameters of the fluidized bed dryer 62 are described in detail below.

[0037] 1. Feeding method: A screw feeder with adjustable speed is used to ensure that the material enters the drying fluidized bed evenly, continuously, and stably. The feeding rate is designed to be strictly matched with the evaporation capacity of the drying host to avoid the bed being too thick or too thin, thus maintaining the stability of the fluidization state.

[0038] 2. Drying medium and hot air system: Heat source selection: Saturated steam (pressure range 0.6 - 0.8 MPa) is preferred as the heat source, indirectly heating the air through a heat exchanger. This solution uses a clean heat source, effectively preventing product contamination from fuel or direct electric heating elements. An electric heater can be used as an alternative.

[0039] Heater: Finned steam radiators are preferred to improve heat exchange efficiency. If electric heating is used, it must be ensured that the surface temperature of the heating element is uniform and does not react harmfully with the air.

[0040] Inlet air temperature: strictly controlled at 110-130℃.

[0041] Note: If the inlet air temperature is too low, the drying driving force will be insufficient, and the drying efficiency will be significantly reduced; if the inlet air temperature is too high (above 140℃), it may cause slight sintering on the surface of Na2SiF6 particles or trigger a thermal decomposition reaction, affecting the physical and chemical properties of the product.

[0042] Outlet air temperature: Strictly controlled at 50-60℃. This parameter is linked to inlet air temperature, feed rate, and material moisture content, and is one of the important indicators for judging whether the drying process has reached its endpoint.

[0043] Hot air quality: All air entering the heater and dryer must pass through a pre-filter and a medium-efficiency filter in sequence to remove dust and other impurities and prevent product contamination. In areas with extremely high humidity, pre-dehumidification of the fresh air may be considered.

[0044] 3. Fluidization and operating parameters: Fluidizing gas velocity: Control the gas velocity in the empty bed section within the range of 0.4 - 0.7 m / s.

[0045] Note: This velocity range has been precisely calculated and experimentally verified. It is higher than the minimum fluidization velocity of the Na2SiF6 material layer, but significantly lower than its average particle carry-out velocity. At this gas velocity, the material is in a stable "boiling" fluidization state, and the particles are fully mixed and in contact with the hot air, ensuring extremely high heat and mass transfer efficiency. At the same time, it effectively suppresses excessive entrainment of fine powder, reducing the load on the separation system and product loss.

[0046] Bed thickness: refers to the thickness of the stationary material accumulation on the distribution plate, controlled within 100-200 mm. This thickness range is conducive to the formation of a stable fluidized bed and ensures sufficient material throughput.

[0047] Material residence time: The average residence time of the material in the fluidized bed is controlled at 15-30 minutes.

[0048] Note: Sufficient residence time is a key process to ensure that the internal moisture of the material is completely removed, achieving the stringent requirement of deep drying to a moisture content of ≤0.1%. Too short a time will result in insufficient drying; too long a time may reduce the production capacity of the equipment.

[0049] Bed pressure drop: The pressure drop of the fluidized bed during system operation is maintained within the range of 1.0 - 2.5 kPa. Note: This pressure drop range is a combined reflection of the fluidizing gas velocity and bed thickness mentioned above. Too low a pressure drop may indicate uneven fluidization or an excessively thin bed; too high a pressure drop may indicate an excessively thick bed or a tendency for material agglomeration. Monitoring this parameter helps in assessing fluidization quality and equipment operating status.

[0050] Please refer to Figure 1As shown in this embodiment, it should also be noted that the fluoride-containing wastewater resource utilization system further includes a collection unit 90 and a tail gas treatment unit 100. The collection unit 90 is connected to the front-end fluidized bed dryer 62 for collecting fluorosilicate products. The collection unit 90 is like a cyclone collector, which collects the fluorosilicate products dried by the fluidized bed dryer 62. The cyclone collector is connected to a product collection device, which serves as the outlet for the product output. The tail gas treatment unit 100 is sequentially connected to the pretreatment unit 10, the acid-base adjustment unit 30, the primary evaporation concentration and crystallization unit 40, the secondary evaporation purification and crystallization unit 50, and the fluidized bed dryer 62 for collecting the emitted tail gas. The tail gas treatment unit 100 can be an existing gas absorption tank in the photovoltaic factory.

[0051] The implementation principle of this embodiment is as follows: This embodiment establishes a "waste-to-waste" process route, recovering and utilizing fluoride and fluorosilicate ions in fluoride-containing wastewater, and combining them with metallic sodium in photovoltaic waste gas and waste alkali. Through the combination of basic unit processes such as pretreatment unit 10, silicon source addition unit 20, acid-base adjustment unit 30, primary evaporation concentration and crystallization unit 40, secondary evaporation purification and crystallization unit 50, and crystallization drying unit 60, multi-stage concentration and purification are achieved to produce high-purity, low-moisture fluorosilicates. This eliminates the need for expensive raw materials such as high-purity hydrofluoric acid required for traditional fluorosilicate production, and can also significantly reduce energy consumption and reagent consumption costs in the wastewater treatment process. It realizes the resource-based recycling and utilization of photovoltaic wastewater and achieves standard discharge, thereby reducing costs and increasing efficiency for photovoltaic enterprises.

[0052] Example 2 Please refer to Figure 2 As shown, this embodiment provides a method for the resource utilization of fluoride-containing wastewater, using the above-mentioned fluoride-containing wastewater resource utilization system, including the following steps: S1. The fluorine-containing waste acid to be treated is introduced into the pretreatment unit 10 for impurity removal treatment; S2. Add a silicon source to the pretreatment unit 10 using the silicon source addition unit 20 to convert hydrofluoric acid in the fluorine-containing waste acid into fluorosilicic acid to obtain a pretreatment liquid. S3. The pretreatment liquid is introduced into the acid-base adjustment unit 30, and the pH value of the mixture is controlled within the preset range by adding waste alkali to obtain the concentrated liquid. S4. The liquid to be concentrated is introduced into a multi-stage evaporation, concentration and crystallization unit for multi-stage evaporation, concentration and crystallization to obtain silicate sol. S5. The silicate sol is introduced into the crystallization and drying unit 60 for cooling, crystallization and drying to obtain a fluorosilicate product with a water content of ≤0.1%.

[0053] In this embodiment, by establishing a "waste-to-waste" process route, fluorine and fluorosilicate ions in fluorine-containing waste acid are recycled and utilized. Combined with metal ions such as metallic sodium in waste alkali and SiO2 generated by high-temperature combustion of waste gas, high-purity, low-moisture fluorosilicate products are stably produced through multi-stage concentration and purification processes. This achieves comprehensive resource utilization of waste and ensures that photovoltaic wastewater meets discharge standards. At the same time, it eliminates the need for expensive raw materials such as high-purity hydrofluoric acid required for traditional fluorosilicate production, significantly reducing energy consumption and reagent costs in the wastewater treatment process, and resulting in a higher overall waste recycling rate.

[0054] In this embodiment, it should be noted that the above-mentioned process of "S1 first removes impurities → S2 adds silicon source → S3 finally adjusts pH" mainly removes polyvalent metal cations, especially calcium (Ca) from the fluorine-containing waste acid in the first step of "removing impurities". 2+ ) and magnesium (Mg 2+ If calcium and magnesium ions are present in the fluoride-containing waste acid, fluoride ions (F) will be encountered in subsequent steps. - ) or silicon fluoride ions (SiF6) 2- This can lead to the formation of extremely insoluble precipitates, such as calcium fluoride (CaF2) and magnesium fluoride (MgF2). Therefore, removing these metal ions in advance as carbonates (such as CaCO3 and MgCO3) creates a pure solution environment for the next crucial "fluorine fixation" reaction, avoiding unnecessary side reactions and precipitate loss.

[0055] In the second step, “adding a silicon source”, a silicon source (usually water glass Na2SiO3 or silicon dioxide SiO2) is used to react with free hydrofluoric acid (HF) to generate fluorosilicic acid (H2SiF6).

[0056] Simplified reaction formulas: 6HF + SiO2 → H2SiF6 + 2H2O or 8HF + Na2SiO3 → H2SiF6 + 2NaF + 3H2O; The silicon source is added after impurity removal and before pH adjustment, primarily because hydrofluoric acid is a weak acid, but extremely corrosive and toxic. Converting it into fluorosilicic acid (a stronger acid) "locks" the fluorine in the stable SiF6. 2- In complexed ions, this form of fluorine is very stable under acidic to neutral conditions and has high solubility, unlike free fluoride ions (F). -This ensures that fluorine can be controlled and removed or recovered in a dissolved state during subsequent treatment, as it readily precipitates with residual or subsequently added cations. Furthermore, the waste acid from the concentrated acid tank is itself a strongly acidic environment, which is the optimal condition for the reaction between the silicon source and HF. If the silicon source is added after adjusting the pH, the reaction efficiency will decrease, and the silicon source itself (such as sodium silicate) will form silicic acid gel under alkaline conditions, causing operational difficulties. Conversely, if the pH is adjusted first (especially to alkalinity), the fluorine in the solution... - It will immediately interact with any existing Ca. 2+ / Mg 2+ The formation of precipitates such as CaF2 not only consumes the defluorination agent, but also encapsulates fluoride ions, making it difficult for them to be fully contacted and converted by the silicon source, resulting in incomplete defluorination.

[0057] In the third step, "pH adjustment," after impurity removal and conversion, the main components of the pretreatment solution are fluorosilicic acid (H2SiF6) and excess amounts of other acids (such as H2SO4, HNO3, etc.). At this stage, the solution remains highly corrosive. Premature neutralization may lead to the formation of salt crystals or silica gel in the pretreatment tank or pipelines, causing blockages and wear. Maintaining an acidic state facilitates safe transport using acid-resistant pumps and pipelines. The purpose of the acid-base adjustment unit 30 (usually for adding alkaline solutions such as NaOH) is to set appropriate pH conditions for subsequent processes.

[0058] In one specific implementation, in S2, the silicon source is high-purity SiO2 generated by high-temperature combustion (800~1000℃) of photovoltaic process waste gas (SiH4 combustion tail gas). Alternatively, if additional addition is required, the silicon source is silicon dioxide particles with a particle size of less than 10µm. Industrial-grade sodium silicate can also be selected as the silicon source, and the amount added is adjusted by weighing.

[0059] Furthermore, the molar ratio of the silicon source added to the hydrofluoric acid in the fluorine-containing wastewater is 1:6 to 1:8. Under this ratio, it can be ensured that the hydrofluoric acid in the fluorine-containing waste acid is fully converted into fluorosilicic acid (H2SiF6).

[0060] Please refer to Figure 1 and Figure 2 As shown, in a specific embodiment, in S4, the multi-stage evaporation concentration and crystallization unit includes a primary evaporation concentration and crystallization unit 40 and a secondary evaporation purification and crystallization unit 50. In use, the liquid to be concentrated is drawn from the pH adjustment tank 31 of the acid-base adjustment unit 30 through the second outflow pump 34 and pumped into the primary distillation column 41 of the primary evaporation concentration and crystallization unit 40 for preliminary evaporation and crystallization to obtain primary silicate sol. Then, the primary silicate sol is pumped into the secondary distillation column 51 of the secondary evaporation purification and crystallization unit 50 through the third outflow pump 42 for secondary evaporation purification to obtain secondary silicate sol.

[0061] The specific operation of the preliminary evaporation and crystallization is as follows: the concentrated liquid is drawn out from the pH adjustment tank 31 of the acid-base adjustment unit 30 through the second extraction pump 34 and pumped into the first-stage distillation column 41 of the first-stage evaporation, concentration and crystallization unit 40, and evaporated and concentrated for 60 to 120 minutes under the conditions of solution pH 5~7 and temperature 80~90℃.

[0062] The specific operation of secondary evaporation purification is as follows: Primary silicate sol and pure water at 60-70℃ are pumped into the secondary distillation column 51 of the secondary evaporation purification crystallization unit 50 at a solid-liquid ratio of 1:3 to 1:5. The solution is dissolved for 20-30 minutes under stirring conditions of 60-70℃ and 200-300 rpm to obtain a relatively dilute solution, yielding a fluorosilicate solution. Subsequently, 0.1%-0.3% (relative to the dry basis mass of the material) of disodium EDTA is added to the fluorosilicate solution as a complexing agent to effectively complex Ca. 2+ ⁺、Mg 2+ Fe 3+ Metal impurity ions are removed, and 50-100 ppm of sodium polyacrylate is added as a dispersant for purification to prevent microcrystal aggregation in subsequent processes and ensure the uniformity of product particles, thus obtaining a clear solution. The clear solution is then concentrated by secondary evaporation at pH 5-7 and a temperature of 60-70℃ to obtain a secondary silicate sol with higher purity. It should be noted that using pure water at 60-70℃ can increase the dissolution temperature, and using a solid-liquid ratio of 1:3 to 1:5 allows for precise control of the amount of pure water added; too much or too little will increase energy consumption, while too little will result in incomplete dissolution. Simultaneously, through a two-stage gradient crystallization process of "preliminary evaporation crystallization + secondary evaporation purification," combined with purification methods such as EDTA complexation and dispersant addition, impurities such as metal ions are effectively removed.

[0063] Please refer to Figure 1 and Figure 2 As shown, in one specific embodiment, in S5, the crystallization drying unit 60 includes a fluidized bed crystallizer 61 and a fluidized bed dryer 62.

[0064] The specific operation of cooling crystallization is as follows: the secondary silicate sol is pumped into the fluidized bed crystallizer 61 and cooled slowly from about 65°C to room temperature of 20-25°C at a constant and slow cooling rate (0.2-0.5°C / min). This process takes about 2-4 hours, which promotes the orderly precipitation of high-purity fluorosilicate crystals and obtains high-purity fluorosilicate wet crystals (such as sodium fluorosilicate) with a purity greater than 99.0%.

[0065] The specific drying operation is as follows: a screw feeder is used to feed the wet fluorosilicate crystals into the fluidized bed dryer 62, and the dryer is dried for 15 to 30 minutes under the conditions of inlet air temperature of 110~130℃ and fluidizing gas velocity of 0.4~0.7 m / s to obtain a fluorosilicate product with a water content of ≤0.1%.

[0066] It is understood that this application has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this application. Furthermore, based on the teachings of this application, these features and embodiments can be modified to suit specific circumstances and materials without departing from the spirit and scope of this application. Therefore, this application is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this application.

Claims

1. A system for the resource utilization of fluoride-containing wastewater, characterized in that, include: A pretreatment unit (10) is used to remove impurities and filter fluorine-containing waste acid; A silicon source addition unit (20), which is connected to the pretreatment unit (10), is used to add a silicon source to convert hydrofluoric acid in the fluorine-containing waste acid into fluorosilicic acid to obtain a pretreatment liquid; the silicon source is silicon dioxide generated by the combustion of photovoltaic waste gas; An acid-base adjustment unit (30), which is connected to the pretreatment unit (10), is used to adjust the pH value of the pretreatment liquid by adding waste alkali to obtain the concentrated liquid; A multi-stage evaporation, concentration and crystallization unit, which is connected to the acid-base adjustment unit (30), is used to perform multi-stage evaporation, concentration and crystallization on the liquid to be concentrated to obtain silicate sol; A crystallization drying unit (60) is connected to the multi-stage evaporation concentration crystallization unit and is used to cool, crystallize and dry the silicate sol to obtain a fluorosilicate product with a water content of ≤0.1%.

2. The system according to claim 1, characterized in that, The multi-stage evaporation concentration and crystallization unit includes a primary evaporation concentration and crystallization unit (40) and a secondary evaporation purification and crystallization unit (50); The primary evaporation concentration and crystallization unit (40) is connected to the acid-base adjustment unit (30) and the secondary evaporation purification and crystallization unit (50), and is used to perform preliminary evaporation and crystallization on the liquid to be concentrated to obtain primary silicate sol; The secondary evaporation purification and crystallization unit (50) is connected to the primary evaporation concentration and crystallization unit (40) and the crystallization drying unit (60), and is used to perform secondary evaporation purification on the primary silicate sol to obtain secondary silicate sol.

3. The system according to claim 2, characterized in that, The primary evaporation concentration and crystallization unit (40) includes a primary distillation column (41), a third outflow pump (42), a first circulation pump (43), a first heat exchanger (44), and a first pure water supplier (45); The primary distillation column (41) is connected to the acid-base adjustment unit (30) at the front end via a pipeline; The primary distillation column (41) is connected to the secondary evaporation, purification and crystallization unit (50) at the rear end via a pipeline through the third extraction pump (42); The first-stage distillation column (41) and the first heat exchanger (44) are connected by a pipeline to the first circulating pump (43); The first pure water provider (45) is connected to the first-stage distillation column (41) via a pipeline and is used to provide pure water spray.

4. The system according to claim 3, characterized in that, The secondary evaporation purification and crystallization unit (50) includes a secondary distillation column (51), a fourth outflow pump (52), a second circulation pump (53), a second heat exchanger (54), and a second pure water supplier (55); The secondary distillation column (51) is connected to the third outflow pump (42) of the primary evaporation, concentration and crystallization unit (40) at the front end via a pipeline; The secondary distillation column (51) is connected to the crystallization drying unit (60) at the rear end via a pipeline through the fourth extraction pump (52); The second circulating pump (53) is connected to the second distillation column (51) and the second heat exchanger (54) via a pipeline; The second pure water supplier (55) is connected to the secondary distillation tower (51) via a pipeline and is used to provide pure water spray.

5. The system according to any one of claims 1-4, characterized in that, The pretreatment unit (10) includes a pretreatment tank (11), a first feed pump (12), a first filter (13), and a first extraction pump (14); The pretreatment tank (11) is connected to the concentrated acid tank (70) containing the fluorine-containing waste acid via a pipeline through the first feed pump (12); The pretreatment tank (11) is connected to the acid-base adjustment unit (30) at the rear end via pipelines through the first filter (13) and the first extraction pump (14); The pretreatment tank (11) is connected to the silicon source addition unit (20) through a pipeline to achieve silicon source addition; Preferably, the pretreatment unit (10) further includes a decontaminant adder (15), which is connected to the pretreatment tank (11) via a pipeline and is used to add carbonate to remove impurities from the fluorine-containing waste acid.

6. The system according to any one of claims 1-4, characterized in that, The acid-base adjustment unit (30) includes a pH adjustment tank (31), a second feed pump (32), a second filter (33), and a second extraction pump (34); The pH adjustment tank (31) is connected to the pretreatment unit (10) at the front end via a pipeline; The pH adjustment tank (31) is connected to the concentrated alkali tank (80) containing the waste alkali via a pipeline and the second feed pump (32); The pH adjustment tank (31) is connected to the multi-stage evaporation concentration and crystallization unit at the rear end via a pipeline through the second filter (33) and the second extraction pump (34); Preferably, the acid-base adjustment unit (30) further includes a alkali additive (35), which is connected to the pH adjustment tank (31) via a pipeline, for adding additional alkali to provide metal ions and adjusting the pH of the pretreatment solution.

7. The system according to any one of claims 1-4, characterized in that, The crystallization and drying unit (60) includes a fluidized bed crystallizer (61), a fluidized bed dryer (62), and a heat source (63); The fluidized bed crystallizer (61) is connected to the multi-stage evaporation concentration crystallization unit at the front end through a pipeline, and is used to cool and crystallize the silicate sol to obtain fluorosilicate wet crystals; The fluidized bed dryer (62) is connected to the fluidized bed crystallizer (61) at the front end through a pipeline, and is used to dry the wet fluorosilicate crystals to obtain fluorosilicate products; The heat source (63) is connected to the fluidized bed dryer (62) via a pipeline and is used to provide the heat required by the fluidized bed dryer (62).

8. A method for the resource utilization of fluoride-containing wastewater, characterized in that, The fluoride-containing wastewater resource utilization system according to any one of claims 1-7 includes the following steps: S1. The fluorine-containing waste acid to be treated is introduced into the pretreatment unit (10) for impurity removal treatment; S2. Add a silicon source to the pretreatment unit (10) using the silicon source addition unit (20) to convert the hydrofluoric acid in the fluorine-containing waste acid into fluorosilicic acid to obtain a pretreatment liquid. S3. The pretreatment liquid is introduced into the acid-base adjustment unit (30), and the pH value of the mixture is controlled within a preset range by adding waste alkali to obtain the concentrated liquid. S4. The liquid to be concentrated is introduced into the multi-stage evaporation, concentration and crystallization unit to carry out multi-stage evaporation, concentration and crystallization to obtain silicate sol; S5. The silicate sol is introduced into the crystallization and drying unit (60) for cooling, crystallization and drying to obtain a fluorosilicate product with a water content of ≤0.1%.

9. The method according to claim 8, characterized in that, In S2; The silicon source is one or more of silicon dioxide generated from the combustion of photovoltaic waste gas, industrial-grade silicon dioxide, or sodium silicate, and the molar ratio of the amount of silicon source added to hydrofluoric acid in the fluorine-containing waste acid is 1:6 to 1:

8. And / or, In S4; The multi-stage evaporation concentration and crystallization unit includes a primary evaporation concentration and crystallization unit (40) and a secondary evaporation purification and crystallization unit (50); The liquid to be concentrated is pumped into the primary evaporation concentration and crystallization unit (40) for preliminary evaporation and crystallization to obtain primary silicate sol; The primary silicate sol is pumped into the secondary evaporation purification and crystallization unit (50) for secondary evaporation purification to obtain the secondary silicate sol; And / or, In S5; the crystallization drying unit (60) includes a fluidized bed crystallizer (61) and a fluidized bed dryer (62); The cooling crystallization operation is as follows: the secondary silicate sol is pumped into the fluidized bed crystallizer (61) and slowly cooled and crystallized at a cooling rate of 0.2~0.5℃ / min to obtain wet fluorosilicate crystals; The drying process is as follows: the wet fluorosilicate crystals are fed into the fluidized bed dryer (62) using a screw feeder, and dried for 15 to 30 minutes under the conditions of inlet air temperature of 110~130℃ and fluidizing gas velocity of 0.4~0.7 m / s to obtain a fluorosilicate product with a water content of ≤0.1%.

10. The method according to claim 9, characterized in that, The preliminary evaporation and crystallization operation is as follows: the liquid to be concentrated is pumped into the first-stage evaporation, concentration and crystallization unit (40), and evaporated for 60 to 120 minutes under the conditions of solution pH 5~7 and temperature 80~90℃ to obtain a first-stage silicate sol; The secondary evaporation purification process is as follows: the primary silicate sol and pure water at 60-70℃ are pumped into the secondary evaporation purification crystallization unit (50) at a solid-liquid ratio of 1:3 to 1:5, and dissolved for 20-30 minutes under stirring conditions of 60-70℃ and 200-300 rpm to obtain a fluorosilicate solution; a complexing agent and a dispersant are added to the fluorosilicate solution for purification to obtain a clear solution; the clear solution is evaporated for 60-120 minutes at a solution pH of 5-7 and a temperature of 60-70℃ to obtain a secondary silicate sol.

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