A method for recovering fluorides in large-scale production of photoresist bottles

Abstract

The application relates to the technical field of waste resource processing, and discloses a fluorine compound recovery method special for large-scale production of photoresist bottles, which comprises the following steps: waste hydrofluoric acid stock solution and reflux liquid are subjected to vacuum membrane concentration after ultrafiltration, the concentrated liquid is purified in a double-tower rectification system with nitrogen, and the residual liquid is closed-loop refluxed; fluorine-containing wastewater is adjusted and then enters a quartz seed induced fluidized bed for crystallization, the fluidized bed effluent is subjected to fluorine removal by fluorine-selective chelating resin and then is subjected to multistage desalination and reuse, and the resin regeneration liquid is refluxed; the crystal slurry discharged from the fluidized bed is subjected to concentration, pressure filtration and dewatering, is mixed with a stabilizer containing quicklime, slag powder and an organic chelating agent, and is cured and maintained, and the solidified body is subjected to slurry mixing and flotation to obtain fluorite concentrate. The application breaks the constant boiling limit of the mixture, introduces a heterogeneous induced crystallization and dynamic parameter regulation mechanism, realizes high-purity recovery of waste acid, deep fluorine removal and reuse of waste water, and harmless treatment and resource utilization of fluorine-containing sludge.

Description

Technical Field

[0001] This invention relates to the field of waste resource utilization technology, specifically a method for recycling fluorides used in the large-scale production of photoresist bottles. Background Technology

[0002] In the large-scale production of photoresist bottles, processes such as ultra-high purity silica leaching and washing generate large amounts of high-concentration waste hydrofluoric acid and fluoride-containing wastewater containing impurities such as complexed fluorides and heavy metals. These fluoride-containing wastes have complex compositions, and if not effectively treated, they will not only cause environmental pollution but also lead to a waste of fluorine resources. Currently, there are still technical limitations in the treatment and recycling processes for such fluoride-containing waste liquids and derived solid wastes.

[0003] In the recovery process of waste hydrofluoric acid, the azeotropic relationship between hydrofluoric acid and water at atmospheric pressure is fixed, making it difficult for conventional atmospheric distillation processes to overcome this limitation, thus restricting the concentration of the recovered product. Conventional recovery processes do not effectively isolate free oxygen during heating and vaporization, allowing trace transition metal impurities to easily oxidize and form volatile oxides that mix into the product. This makes it difficult for the recovered acid to meet electronic-grade purity standards, and the process lacks a closed-loop material handling design, resulting in a low overall resource recovery rate.

[0004] In the defluoridation process of fluoride-containing wastewater, existing technologies mostly employ direct addition of calcium salts for chemical precipitation. Direct addition of chemicals in high-concentration fluoride environments easily triggers homogeneous nucleation, generating a large number of amorphous fine colloidal flocs. These colloids have extremely poor settling properties, not only leading to excessive suspended solids in the effluent but also flowing into subsequent multi-stage desalination systems, where they adhere to the surfaces of ultrafiltration and reverse osmosis membranes, forming irreversible gel polarization layers and causing severe physical fouling. Conventional treatment systems, when faced with high-concentration impurity loads on the production line, typically use fixed operating parameters, lacking dynamic response mechanisms tailored to hydraulic and chemical reaction kinetics. This easily leads to separation load imbalances and subsequent resin adsorption components being damaged by high concentrations of free fluoride.

[0005] The large amount of fluoride-containing sludge generated at the end of the wastewater sedimentation process is another challenge restricting the resource utilization of the entire system. Conventional sludge disposal methods mostly involve direct landfilling after dewatering, resulting in unstable internal crystal structure and physicochemical properties. Under the impact of external acidic leaching environments, the free fluoride ions and heavy metals physically encapsulated within the sludge are prone to secondary leaching, posing a long-term environmental pollution hazard. Existing methods have failed to stabilize the sludge structure through effective chemical mineralization mechanisms and lack supporting processes for further separation and purification into high-purity resource products, thus limiting the economic recovery value of fluoride-containing solid waste. Summary of the Invention

[0006] The technical problem addressed by this invention lies in the low resource recovery rate of high-concentration waste hydrofluoric acid and fluoride-containing wastewater generated from the large-scale production of photoresist bottles using conventional treatment methods. Direct distillation recovery is limited by the azeotropic point of hydrofluoric acid and water, making it difficult to obtain high-purity products. Direct addition of calcium salts during wastewater defluorination easily leads to homogeneous nucleation and the formation of fine colloids, causing physical clogging of filter components. Furthermore, the unstable microstructure of the end-of-pipe fluoride-containing sludge poses a risk of secondary leaching of fluoride and heavy metals, resulting in environmental pollution.

[0007] To address the above problems, the present invention provides the following technical solution: This invention provides a method for recovering fluorides specifically for the large-scale production of photoresist bottles, employing the following technical solution: A method for recovering fluorides used in the large-scale production of photoresist bottles includes the following steps: Waste hydrofluoric acid stock solution, along with residual liquid and regenerated liquid from subsequent processes, are introduced into a homogenizing tank and stirred for homogenization. The solution is then subjected to coarse filtration via a filter cartridge and fine filtration via a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane. The permeate is then concentrated under controlled feed temperature and vacuum conditions using a perfluoro spiral wound membrane module, separating it into a concentrate and a membrane concentrate permeate. The concentrate is then introduced into a dual-tower distillation system, with high-purity nitrogen gas introduced into the bottom of each tower for distillation purification to obtain the final product. The residue from the distillation tower bottom is entirely recycled back to the homogenizing tank. The membrane concentrate permeate and fluorine-containing wastewater are then collected in an equalization tank, where calcium hydroxide emulsion is added and stirred. The final pH should be adjusted; after conditioning, the wastewater enters a two-stage quartz seed-induced fluidized bed, and the fluidized bed effluent enters an adsorption column filled with D402 fluoride selective chelating resin for defluorination. After saturation, it is regenerated with dilute hydrofluoric acid, and the regenerated liquid is returned to the homogenizing tank; the adsorption effluent is fully reused after membrane desalination; the crystal slurry discharged from the two-stage quartz seed-induced fluidized bed is concentrated and then filtered by a fluoride-resistant plate and frame filter press. The dewatered sludge is mixed with a composite solidification stabilizer and cured at room temperature; after the solidified body is crushed and slurry is adjusted, it is floated, and sodium oleate, pine oil, and water glass are added to finally obtain fluorite concentrate product.

[0008] The specific reaction mechanism and innovative points of this invention, based on the above technical solution, are described as follows: Waste acid concentration and purification mechanism: Hydrofluoric acid and water form an azeotrope of fixed concentration under normal pressure. This solution uses a perfluorinated spiral wound membrane module to control a specific negative pressure vacuum condition, changing the total pressure of the gas-liquid equilibrium system, causing a shift in the azeotropic point of the mixture, promoting preferential transmembrane vaporization of water, breaking the azeotropic limitation and achieving pre-concentration. In the dual-tower distillation stage, high-purity nitrogen is continuously introduced into the reboiler, using a slight positive pressure to replace and isolate residual free oxygen molecules inside the equipment. This cuts off the path for trace transition metal impurities to undergo oxidation reactions to generate high-valence volatile metal oxides, preventing metal oxides from entering the product end with the hydrofluoric acid azeotrope, thus ensuring the purity of the semiconductor-grade product.

[0009] Wastewater crystallization mechanism: Fluoride-containing wastewater contains complexed fluorosilicic acid. Adjusting the pH promotes the dissociation reaction of fluorosilicic acid. After the release of free fluoride ions, calcium ions in the fluidized bed react with fluoride ions to crystallize and form calcium fluoride. Without seed crystals, the above reaction easily induces homogeneous nucleation, forming amorphous fine colloidal flocs. This solution provides quartz sand of a specified particle size as a heterogeneous crystallization interface to reduce the activation energy of crystal nucleation. Calcium and fluoride ions in the liquid phase adhere to the surface of the quartz sand and undergo ordered lattice growth, forming dense crystalline particles with high density and easy settling, avoiding gel polarization layer fouling of subsequent membrane desalination components.

[0010] Selective adsorption mechanism of resin: Trace amounts of fluoride ions and high concentrations of conventional anions remain in the fluidized bed effluent. The central zirconium atom supported on the resin framework exhibits extremely hard acid characteristics, while fluoride ions in the water exhibit extremely hard base characteristics. When these two meet at the solid-liquid interface, an inner coordination layer substitution reaction occurs, where fluoride ions replace coordinated water molecules to form highly stable coordination bonds. Conventional background anions cannot enter the inner coordination layer to compete for space due to low electron orbital overlap and steric hindrance from polyamine groups. This mechanism eliminates interference from high-salt background, achieving deep fluoride removal.

[0011] Sludge solidification and material closed-loop mechanism: Dewatered sludge undergoes a hydration reaction after mixing with a composite solidification stabilizer. Quicklime provides alkaline activation conditions, prompting slag powder to release active silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra, generating amorphous calcium silicate hydrate. Fluoride ions enter the calcium silicate hydrate lattice through isomorphic substitution, completing chemical mineralization. Free heavy metal ions combine with organic chelating agents through multi-base toothed coordination to form insoluble chelates. Simultaneously, the process flow fully recirculates distillation residue and resin desorption regeneration liquid to the system front end, retaining free fluoride components and improving the overall closed-loop recovery rate of resources.

[0012] Preferably, in the step of sequential coarse filtration via a filter element and fine filtration via a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane: the coarse filtration uses a 5μm PTFE filter element; in the step of vacuum membrane concentration by controlling the feed temperature and vacuum: the vacuum membrane concentration controls the feed temperature to 42 to 46°C, and maintains the vacuum at -0.068 to -0.072 MPa under normal operating conditions, automatically lowering the vacuum to -0.078 to -0.080 MPa when the DCS detects a load impact; in the step of the concentrate entering a dual-tower distillation system, with high-purity nitrogen gas introduced into the reboiler, and the product obtained through distillation purification: the dual-tower distillation system includes one tower and two towers; under normal operating conditions, the reflux ratio of the first tower is 1.8 to 2.2, and the reflux ratio of the second tower is 1.2 to 1.5; under impact conditions, the DCS automatically switches the reflux ratio of the first tower to 2.5 and the reflux ratio of the second tower to 1.6.

[0013] By adopting the above technical solution, a dynamic control response logic for fluctuations in the influent load was constructed. When a sudden increase in the concentration and viscosity of impurities in the influent leads to an imbalance in the system's separation load, lowering the vacuum level can increase the vaporization driving force of the concentration process and alleviate physical fouling caused by concentration polarization at the membrane surface. Simultaneously, increasing the reflux ratio of the distillation column increases the gas-liquid two-phase mass transfer contact time and the number of reflux cuts within the column, ensuring the accuracy of component separation.

[0014] Preferably, the preparation method of the modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane includes: dissolving 12% to 18% by weight of polyvinylidene fluoride-hexafluoropropylene copolymer, 1% to 3% by weight of polytetrafluoroethylene nanoparticles with a particle size of 30 to 50 nm, and 5% by weight of polyvinylpyrrolidone in 74% to 82% by weight of N,N-dimethylacetamide solvent; preparing a casting solution by mechanically stirring at 50 to 70°C for 10 to 15 hours; after vacuum degassing the casting solution for 24 hours, using a dry-wet spinning process, extruding the core liquid and casting solution with a water to N,N-dimethylacetamide volume ratio of 7:3 through an annular spinneret; after passing through a 10 cm air section, immersing the extrudate in a pure water coagulation bath at 15 to 35°C to undergo phase inversion and form a membrane; and washing in pure water at 60°C for 24 hours.

[0015] By adopting the above technical solution, and by introducing copolymers containing hexafluoropropylene segments in combination with polytetrafluoroethylene nanoparticles, the molecular structure defect of conventional polymer molecular chains being prone to defluorination and hydrogen degradation in strongly acidic complexed fluoride water bodies is overcome, the three-dimensional network skeleton of the membrane pore size is maintained and the membrane fibers are prevented from breaking and losing their retention capacity.

[0016] Preferably, in the step of adjusting the final pH of the stirring reaction: the final pH is adjusted to 7.8 to 8.2; in the step of the conditioned wastewater entering the two-stage quartz seed-induced fluidized bed: the two-stage quartz seed-induced fluidized bed includes a primary fluidized bed and a secondary fluidized bed, the reaction temperature is controlled at 25 to 35°C, and the upward flow velocity is 22 to 25 m / h; the primary fluidized bed is filled with 0.3 to 0.6 mm quartz sand seeds, and the secondary fluidized bed is filled with 0.15 to 0.3 mm quartz sand; under normal operating conditions, the primary fluidized bed controls the calcium-fluorine molar ratio to be 0.60 to 0.65, and the hydraulic retention time is 40 min; when encountering load shock, the auxiliary calcium source is automatically added to increase the calcium-fluorine molar ratio to 0.80, and at the same time extend the hydraulic retention time to 50 min; the hydraulic retention time of the secondary fluidized bed is maintained at 50 min.

[0017] By adopting the above technical solution, a dynamic matching mechanism between liquid-phase chemical reaction kinetics and hydraulic parameters was established. When high concentrations of fluoride ions cause water quality shocks, the system automatically increases the calcium-fluoride ratio to supplement the micro-supersaturation driving force required for the crystallization process, increases the hydraulic residence time to ensure the crystal development cycle, and prevents high concentrations of ions from not completely precipitating and entering the next stage with the overflow liquid, causing resin penetration.

[0018] Preferably, the preparation method of the D402 fluorine selective chelating resin includes: using macroporous cross-linked styrene-divinylbenzene copolymer white spheres as the backbone material, adding chloromethyl ether reagent and anhydrous zinc chloride catalyst, and reacting at 40 to 50°C for 6 to 10 hours to obtain chloromethylated cross-linked polystyrene; reacting the chloromethylated cross-linked polystyrene with excess ethylenediamine at 70 to 90°C under reflux for 8 to 12 hours, washing and drying to obtain a polyamine-type anion exchange resin; impregnating the polyamine-type anion exchange resin in an acidic solution of zirconium oxychloride with a concentration of 0.3 to 0.7 mol / L, and reacting at a constant temperature of 50 to 70°C with shaking for 18 to 30 hours; and washing with deionized water until neutral.

[0019] By employing the above-mentioned technical solution, macroporous cross-linked polystyrene is used as the matrix, and polyamine groups are introduced through chloromethylation and amination reactions. The polyamine groups possess multidentate coordination characteristics, enabling them to effectively complex and fix zirconium atoms in an acidic impregnation environment. The immobilized zirconium atoms constitute high-charge-density adsorption active centers, laying the material foundation for selective coordination substitution reactions in subsequent water treatment processes.

[0020] Preferably, in the steps of the crystal slurry discharged from the two-stage quartz seed-induced fluidized bed being concentrated and then filtered by a fluorine-resistant plate and frame filter press, the dewatered sludge is mixed with the composite solidification stabilizer and cured at room temperature: under normal operating conditions, the filtration cycle is 4 hours per batch; under impact operating conditions, it is shortened to 3 hours per batch; the dewatered sludge is cured at room temperature for 72 hours under conditions of 15 to 30°C and 60% to 80% humidity.

[0021] By adopting the above technical solution and setting a room temperature curing time boundary of 72 hours, sufficient time is provided for the growth, cross-linking and internal lattice rearrangement of the aforementioned amorphous calcium silicate hydrate gel network, ensuring that fluoride ions deeply enter the lattice to complete the mineralization process and preventing the risk of secondary dissolution caused by incomplete crystal structure stability.

[0022] Preferably, the total dosage ratio of the composite solidifying stabilizer is as follows: under normal operating conditions, the total solidifying agent ratio is 17.5%, accounting for the dry sludge mass, including 10% quicklime, 6% slag powder, and 1.5% organic chelating agent; under impact operating conditions, the total solidifying agent ratio is increased to 20.5%, accounting for the dry sludge mass, including 12% quicklime, 7% slag powder, and 1.5% organic chelating agent.

[0023] By adopting the above technical solution, alkaline activators and gel precursors are distributed in stages under different sludge loads to match the concentration of residual free pollutants in the waste residue, thus maintaining a balance between the economic efficiency of stabilizer consumption and the depth of harmless treatment.

[0024] Preferably, the method for preparing the organic chelating agent includes: weighing disodium ethylenediaminetetraacetate and sodium diethyldithiocarbamate, mixing them in a mass ratio of 0.8 to 1.2:1, and mechanically dry mixing at room temperature for 30 minutes to obtain a powdered organic chelating agent.

[0025] By adopting the above technical solution, two broad-spectrum complexing agents are dry-mixed in a specific ratio. The difference in affinity of the two groups for transition metals of different valence states is utilized to generate a synergistic effect, thereby improving the range of capture and complexation of the agent for multi-component heavy metal residue systems.

[0026] Preferably, in the step of adding sodium oleate, pine oil, and water glass after the solidified body is crushed and slurried to a concentration of 25% to 28%, the solidified body is crushed and slurried to a concentration of 25% to 28% and then floated. The amounts of sodium oleate, pine oil, and water glass added are 600 g / t of sodium oleate, 40 g / t of pine oil, and 300 g / t of water glass, respectively.

[0027] By employing the above technical solution, the colloidal molecules generated by the hydrolysis of sodium silicate selectively adsorb onto the gangue surface, maintaining hydrophilicity and allowing it to settle in the slurry. The polar head of sodium oleate chemically bonds with calcium ions on the mineral surface, while the nonpolar hydrocarbon tail faces the aqueous phase, increasing the contact angle of the solid particles and achieving surface hydrophobicity. The hydrophobic particles, combined with the microbubbles generated by pine oil, float and separate, transforming the harmless solidified body into a high-purity resource.

[0028] Preferably, in the step of regenerating with dilute hydrofluoric acid after saturation: the saturation is regenerated with dilute hydrofluoric acid of concentration 4%.

[0029] By adopting the above technical solution, the resin desorption is achieved by using the common ion effect to break the coordination bonds, avoiding the destruction of the active group structure of the resin caused by the use of conventional alkaline regenerators, and maintaining the long-term cycle life of the adsorption material.

[0030] This invention provides a method for recovering fluorides specifically for large-scale production of photoresist bottles. It has the following beneficial effects: 1. This invention uses a membrane module to control the vacuum level for reduced pressure concentration, and combines it with a dual-tower distillation process to introduce high-purity nitrogen gas. At the same time, the distillation residue and resin regeneration liquid are fully refluxed to the front-end homogenizer. This design changes the gas-liquid phase equilibrium to break the azeotropic limit of hydrofluoric acid and water, cuts off the oxidation and volatilization path of trace metal impurities, and improves the product purity of hydrofluoric acid and the overall system recovery rate of fluoride without increasing additional raw material consumption. 2. This invention introduces quartz sand as a heterogeneous crystallization interface in the wastewater defluorination process, combined with fluoride selective chelating resin, and constructs a dynamic control mechanism based on influent load fluctuations. This scheme avoids the physical fouling of subsequent desalination membrane components by homogeneous fine colloids generated by direct chemical addition. At the same time, by adaptively adjusting the system vacuum degree, calcium-fluoride molar ratio and hydraulic residence time, the separation load and chemical reaction kinetics are rematched, ensuring the stable operation of the system and the deep defluorination effect under high load impurity impact. 3. This invention uses a composite solidification stabilizer containing quicklime, slag powder and organic chelating agent to mix and cure fluoride-containing sludge, and then separates it through slurry conditioning and closed-circuit flotation. This process utilizes the isomorphic substitution and multi-dental coordination of the hydrated gel network to lock free fluorine and heavy metals inside the crystal lattice, blocking the secondary leaching path of pollutants. Finally, the harmless solidified body is purified into fluorite concentrate product, realizing the safe disposal and economic resource utilization of solid waste. Attached Figure Description

[0031] Figure 1 This is a graph showing the normalized membrane flux versus time under different process conditions of the present invention when the system responds to high load impacts. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, preparation examples, embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Example 1: This preparation example provides a method for preparing a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane (material A1), a D402 fluorine selective chelating resin (material B1), and a sludge solidification organic chelating agent (material C1), including the following steps: (1) Preparation of material A1: 12% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 1% polytetrafluoroethylene (PTFE) nanoparticles (particle size 30-50nm), and 5% polyvinylpyrrolidone (PVP) were dissolved in 82% N,N-dimethylacetamide (DMAc) solvent. The casting solution was prepared by mechanical stirring at 50℃ for 10 hours until homogeneous. After vacuum degassing of the casting solution for 24 hours, the core solution (water to DMAc volume ratio of 7:3) and the casting solution were extruded through an annular spinneret using a dry-wet spinning process. After passing through a 10cm air section, the extrudate is immersed in a 15°C pure water coagulation bath to undergo phase transformation and form a film; finally, it is washed in 60°C pure water for 24 hours to remove pore-forming agents and solvents, thus obtaining the final product.

[0034] (2) Preparation of material B1: Chloromethylated crosslinked polystyrene was prepared by using macroporous crosslinked styrene-divinylbenzene copolymer white spheres as the backbone material, chloromethyl ether as the reagent, and anhydrous ZnCl2 as the catalyst, and reacting at 40℃ for 6 h. The obtained product was refluxed with excess ethylenediamine at 70°C for 8 hours, and then washed and dried to obtain a polyamine anion exchange resin. The above-mentioned amination resin was impregnated in an acidic solution of zirconium oxychloride (ZrOCl2) with a concentration of 0.3 mol / L and reacted at a constant temperature of 50°C with shaking for 18 h; finally, it was washed with deionized water until neutral to obtain the final product.

[0035] (3) Preparation of material C1: Weigh out disodium ethylenediaminetetraacetate (EDTA-2Na) and sodium diethyldithiocarbamate (DDTC), mix them in a mass ratio of 0.8:1, and mechanically dry mix them at room temperature for 30 minutes to obtain a powdered organic chelating agent.

[0036] Preparation Example 2: This preparation example provides a method for preparing a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane (material A2), a D402 fluorine selective chelating resin (material B2), and a sludge solidification organic chelating agent (material C2), including the following steps: (1) Preparation of material A2: 15% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 2% polytetrafluoroethylene (PTFE) nanoparticles (particle size 30-50nm), and 5% polyvinylpyrrolidone (PVP) were dissolved in 78% N,N-dimethylacetamide (DMAc) solvent. The casting solution was prepared by mechanical stirring at 60℃ for 12 hours until homogeneous. After vacuum degassing of the casting solution for 24 hours, the core solution (water to DMAc volume ratio of 7:3) and the casting solution were extruded through an annular spinneret using a dry-wet spinning process. After passing through a 10cm air section, the extrudate is immersed in a 25°C pure water coagulation bath to undergo phase transformation and form a film. Finally, wash in pure water at 60℃ for 24 hours to remove pore-forming agents and solvents, and the product is obtained.

[0037] (2) Preparation of material B2: Chloromethylated crosslinked polystyrene was prepared by using macroporous crosslinked styrene-divinylbenzene copolymer white spheres as the backbone material, chloromethyl ether as the reagent, and anhydrous ZnCl2 as the catalyst, and reacting at 45℃ for 8 h. The obtained product was refluxed with excess ethylenediamine at 80°C for 10 h, and then washed and dried to obtain a polyamine anion exchange resin. The above-mentioned amination resin was impregnated in an acidic solution of zirconium oxychloride (ZrOCl2) with a concentration of 0.5 mol / L and reacted at a constant temperature of 60°C with shaking for 24 h. Finally, wash with deionized water until neutral to obtain the final product.

[0038] (3) Preparation of material C2: Weigh out disodium ethylenediaminetetraacetate (EDTA-2Na) and sodium diethyldithiocarbamate (DDTC), mix them in a 1:1 mass ratio, and mechanically dry mix at room temperature for 30 minutes to obtain a powdered organic chelating agent.

[0039] Preparation Example 3: This preparation example provides a method for preparing a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane (material A3), a D402 fluorine selective chelating resin (material B3), and a sludge solidification organic chelating agent (material C3), including the following steps: (1) Preparation of material A3: 18% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 3% polytetrafluoroethylene (PTFE) nanoparticles (particle size 30-50nm), and 5% polyvinylpyrrolidone (PVP) were dissolved in 74% N,N-dimethylacetamide (DMAc) solvent. The casting solution was prepared by mechanical stirring at 70℃ for 15 hours until homogeneous. After vacuum degassing of the casting solution for 24 hours, the core solution (water to DMAc volume ratio of 7:3) and the casting solution were extruded through an annular spinneret using a dry-wet spinning process. After passing through a 10cm air section, the extrudate is immersed in a 35°C pure water coagulation bath to undergo phase transformation and form a film. Finally, wash in pure water at 60℃ for 24 hours to remove pore-forming agents and solvents, and the product is obtained.

[0040] (2) Preparation of material B3: Using macroporous cross-linked styrene-divinylbenzene copolymer white spheres as the backbone material, chloromethyl ether as the reagent, and anhydrous ZnCl2 as the catalyst, the reaction was carried out at 50℃ for 10 h to obtain chloromethylated cross-linked polystyrene; the obtained product was reacted with excess ethylenediamine under reflux at 90℃ for 12 h, and then washed and dried to obtain a polyamine-type anion exchange resin. The above-mentioned amination resin was impregnated in an acidic solution of zirconium oxychloride (ZrOCl2) with a concentration of 0.7 mol / L and reacted at a constant temperature of 70°C with shaking for 30 h. Finally, wash with deionized water until neutral to obtain the final product.

[0041] (3) Preparation of material C3: Weigh out disodium ethylenediaminetetraacetate (EDTA-2Na) and sodium diethyldithiocarbamate (DDTC), mix them in a mass ratio of 1.2:1, and mechanically dry mix them at room temperature for 30 minutes to obtain a powdered organic chelating agent.

[0042] Example 1: This example provides a method for recovering fluorides used in the large-scale production of photoresist bottles, including the following steps: (1) Closed-loop recycling of waste hydrofluoric acid: Waste hydrofluoric acid stock solution, residual liquid from subsequent processes, and regenerated liquid were poured into a homogenizing tank and homogenized at 20°C for 35 min. Subsequently, the solution was subjected to coarse filtration through a 5 μm PTFE filter cartridge and fine filtration through material A1 (modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane) provided in Preparation Example 1. The permeate entered a perfluorinated spiral wound membrane module, and vacuum membrane concentration was performed under reduced pressure while maintaining the feed temperature at 42°C and a vacuum of -0.068 MPa. The concentrate entered a dual-tower distillation system, with a bottom flow rate of 3 Nm³. 3 High-purity nitrogen gas is used for protection; the temperature at the top of the first distillation column is controlled at 105℃ and the bottom at 120℃, while the temperature at the top of the second distillation column is 98℃; the reflux ratio is set to the lower limit: R=1.8 for the first column and R=1.2 for the second column. All the residue in the distillation column bottom is refluxed to the homogenizer.

[0043] (2) Zero-discharge treatment of fluoride-containing wastewater: Fluoride-containing wastewater, including membrane concentrate permeate, is collected in an equalization tank. A 20% Ca(OH)₂ emulsion is added, and the reaction is stirred until the final pH is adjusted to 7.8. After conditioning, the wastewater enters a two-stage quartz seed-induced fluidized bed. The reaction temperature is controlled at 25℃, and the upward flow velocity is 22 m / h. The primary fluidized bed is filled with 0.3-0.6 mm quartz sand seeds. The Ca / F molar ratio in the reaction system is controlled at 0.60 according to stoichiometry, and the hydraulic retention time (HRT) is controlled to the lower limit of 40 min. The secondary fluidized bed is filled with 0.15-0.3 mm quartz sand, and the HRT is 50 min. The effluent from the fluidized bed enters an adsorption column filled with material B1 (D402 fluoride selective chelating resin) provided in Preparation Example 1 for deep defluorination. After saturation, it is regenerated with 4% dilute HF, and the regenerated liquid is refluxed back to the homogenizer in a closed loop. The adsorbed water is completely reused after being desalinated by a membrane.

[0044] (3) Harmlessness and resource utilization of fluoride-containing sludge: The concentrated slurry discharged from the fluidized bed is then fed into a fluorine-resistant plate and frame filter press, with a filtration cycle of 4 hours per batch. The dewatered sludge is mixed with a composite solidifying stabilizer at 15°C and 60% humidity. The total solidifying agent dosage is set at the lower limit of 17.5% (based on the dry sludge mass, including 10% quicklime, 6% slag powder, and 1.5% organic chelating agent provided in Preparation Example 1), and cured at room temperature for 72 hours. After the solidified body is crushed and adjusted to a concentration of 25%, flotation is performed, adding 600 g / t sodium oleate, 40 g / t pine oil, and 300 g / t water glass to finally obtain fluorite concentrate.

[0045] Example 2: This example provides a method for recovering fluorides used in the large-scale production of photoresist bottles, including the following steps: (1) Closed-loop recovery of waste hydrofluoric acid: After homogenization at 25°C for 35 min, the material is finely filtered through a 5 μm filter element and material A2 provided in Preparation Example 2. After entering the membrane module, the feed temperature is controlled at 44°C and the vacuum degree is -0.072 MPa under normal operating conditions; When the DCS detects a load impact from high-impurity quartz ore, it automatically lowers the vacuum to -0.078 MPa to improve evaporation efficiency. The concentrated liquid enters the distillation system, through which 4Nm³ of gas is introduced. 3 / h nitrogen; Under normal operating conditions, the reflux ratio is 2.0 for the first tower and 1.35 for the second tower. Under shock conditions, the DCS automatically switches the reflux ratio to 2.5 for the first tower and 1.6 for the second tower to ensure the purity of the electronic-grade product. The bottom liquid is refluxed in a closed loop.

[0046] (2) Zero-discharge treatment of fluoride-containing wastewater: The wastewater was treated with Ca(OH)₂ to adjust the final pH to 8.0. It then entered a fluidized bed (temperature 30℃, flow rate 23.5 m / h). Under normal operating conditions, the Ca / F molar ratio was controlled at 0.65 in the primary fluidized bed, and the HRT was 40 min. When subjected to high load shocks, the system automatically increases the dosage of auxiliary calcium source to raise the Ca / F molar ratio to 0.80, while extending the HRT to 50 min to ensure complete crystallization of high-concentration fluoride ions. The HRT of the secondary fluidized bed is maintained at 50 min. The effluent enters an adsorption column filled with material B2 provided in Preparation Example 2 for deep fluoride removal. After saturation, it is regenerated with 4% dilute HF and refluxed in a closed loop.

[0047] (3) Harmlessness and resource utilization of fluoride-containing sludge: After the discharged crystal slurry is concentrated, it is filtered by pressure. Under normal operating conditions, the filtration cycle is 4 hours per batch. Under impact conditions, the time per batch is shortened to 3 hours for rapid sludge removal. Dewatered sludge is solidified at 25℃ and 70% humidity. Under normal conditions, the total solidifying agent ratio is 17.5% (10% quicklime, 6% slag powder, and 1.5% material C2); under impact conditions, a high-ratio adaptive state is adopted, increasing the total solidifying agent ratio to 20.5% (12% quicklime, 7% slag powder, and 1.5% material C2). After 72 hours of curing, the slurry is crushed and adjusted (concentration 26.5%), and flotation reagents are added for resource-based separation.

[0048] Example 3: This example provides a method for recovering fluorides used in the large-scale production of photoresist bottles, including the following steps: (1) Closed-loop recycling of waste hydrofluoric acid: After homogenization at 30°C for 35 min, the material was finely filtered through a 5 μm filter cartridge and material A3 provided in Preparation Example 3. Upon entering the membrane module, the feed temperature was controlled at the upper limit of 46°C. To prevent membrane bubbling damage caused by exceeding the equipment design limits, the vacuum level was set to the safe upper limit of -0.080 MPa. The concentrate then entered the distillation system with a flow rate of the upper limit of 5 Nm³. 3 Nitrogen gas per hour; control the temperature of the first column top to 110℃ and the column bottom to 125℃, and the temperature of the second column top to 102℃; The rectification reflux ratio is set to the upper limit of the conventional value: The first column has a pressure of R=2.2, and the second column has a pressure of R=1.5. All the residual liquid in the column bottoms is refluxed to the homogenizer.

[0049] (2) Zero-discharge treatment of fluoride-containing wastewater: The wastewater was treated with Ca(OH)₂ to adjust the final pH to the upper limit of 8.2. It then entered a fluidized bed, with the reaction temperature controlled at the upper limit of 35℃ and the upflow velocity at 25 m / h. The Ca / F molar ratio was controlled at 0.80 in the primary fluidized bed, and the hydraulic retention time (HRT) was controlled at the upper limit of 50 min. The HRT of the secondary fluidized bed is 50 min. The effluent enters an adsorption column filled with material B3 provided in Preparation Example 3 for deep fluoride removal. After saturation, it is regenerated with 4% dilute HF, and the regenerated solution is returned to the homogenizing tank. The adsorbed effluent is desalinated by a membrane system and then reused.

[0050] (3) Harmlessness and resource utilization of fluoride-containing sludge: The slurry discharged from the fluidized bed was concentrated and then filtered by pressure, with a filtration cycle of 4 hours per batch. The dewatered sludge was mixed with a composite solidifying stabilizer at 30°C and 80% humidity, with the total solidifying agent dosage set at the upper limit of 20.5% (12% quicklime, 7% slag powder, and 1.5% C3 material provided in Preparation Example 3), and cured at room temperature for 72 hours. The solidified body was crushed and adjusted to the upper limit concentration of 28% before flotation. Sodium oleate (600 g / t), pine oil (40 g / t), and water glass (300 g / t) were added to finally obtain fluorite concentrate.

[0051] Comparative Example 1: The difference compared to Example 2 is as follows: The secondary fine filtration uses a commercially available PVDF ultrafiltration membrane instead of a modified fluorine-resistant PVDF ultrafiltration membrane, and the deep adsorption unit uses a commercially available polyamine anion exchange resin instead of a D402 fluorine selective chelating resin; all other components are the same.

[0052] Comparative Example 2: The difference compared to Example 2 is as follows: The vacuum level of the vacuum membrane concentration was changed to atmospheric pressure (0 MPa), the feed temperature was increased to 55°C, and the high-purity nitrogen protection in the distillation process was removed; all other aspects remained the same.

[0053] Comparative Example 3: The difference compared to Example 2 is as follows: The fluidized bed reactor was not filled with high-purity quartz sand seeds, and the pH of the wastewater was adjusted to 6.0 at the end of the conditioning process; all other parameters were the same.

[0054] Comparative Example 4: The difference compared to Example 2 is as follows: The residual liquid produced in the distillation column bottom and the 4% dilute HF regenerated liquid produced in the resin deep adsorption unit are directly discharged to the plant waste liquid treatment station and are not returned to the waste acid homogenizing tank. All other aspects are the same.

[0055] Comparative Example 5: The difference compared to Example 2 is as follows: When the system encounters high-load mixed quartz ore impact conditions, it does not perform DCS automatic interlocking dynamic parameter adjustment, but maintains the conventional operating parameters (i.e., vacuum degree -0.072MPa, distillation column R=2.0, fluidized bed Ca / F molar ratio 0.65 and HRT 40min, total solidifying agent ratio 17.5%), and all other parameters remain the same.

[0056] Comparative Example 6: The difference compared to Example 2 is as follows: The composite curing stabilizer does not contain any organic chelating agent (material C2 in Preparation Example 2), and the natural static curing time at room temperature is shortened to 24 hours, while the rest are the same.

[0057] Test Example 1: Accurately weigh 15.0 g of the D402 fluorine selective chelating resin obtained in Preparation Example 2 under dry weight condition. After fully swelling with deionized water, it is wet-packed into a glass chromatography column with an inner diameter of 15 mm and a constant temperature jacket. The resin bed height is maintained at about 120 mm, and the resin bed volume (BV) is recorded.

[0058] A mixed simulated water sample was prepared using analytical grade sodium fluoride, sodium chloride, and anhydrous sodium sulfate. Offline analysis revealed that the initial fluoride ion concentration (F...) in this simulated water sample... - The concentration was 21.4 mg / L, and the chloride ion concentration was 21.4 mg / L. - The concentration was 1053.2 mg / L, and the sulfate ion concentration (SO4) was... 2- The concentration was 1018.7 mg / L, used to simulate a high-salt background interference environment.

[0059] Turn on the circulating water in the thermostatic jacket of the chromatography column to control the temperature of the adsorption system at 25±1℃. Start the peristaltic pump and pump the prepared mixed simulated water sample into the resin column from bottom to top in a countercurrent manner, controlling the operating flow rate at 8 BV / h.

[0060] An automatic fraction collector is installed at the effluent end of the chromatography column to continuously sample at regular intervals using resin bed volume (BV) as the unit of measurement.

[0061] After filtration through a 0.22 μm microporous membrane, the sample solution was injected into an ion chromatograph (IC) to determine the F in the effluent at different breakthrough volumes. - Cl - and SO4 2- The concentration of each ion was determined. After the test, the peak areas were integrated, and the penetration rate of each ion and the saturated adsorption capacity of the resin were calculated.

[0062] .

[0063] in conclusion: According to the data in Table 1, the D402 fluorine-selective chelating resin exhibits specific adsorption and retention capacity for fluoride ions in an environment where chloride and sulfate ions coexist at concentrations nearly 100 times its own. When the system reaches 10 BV, Cl... - and SO4 2- The effluent concentrations reached 985.41 mg / L and 942.33 mg / L, respectively, and subsequently reached the same level as the influent concentration at 50 BV, indicating that conventional background anions did not undergo chemical adsorption within the resin bed, but only directly penetrated via physical fluid mass transfer. The F in the effluent... - The concentration was maintained below 0.86 mg / L before reaching 300 BV, achieving deep defluorination. This separation behavior is consistent with the soft and hard acid-base theory and the mechanism of coordination field strength.

[0064] The Zr(Ⅳ) central atom immobilized on the resin framework exhibits extremely hard acid properties, and the F in the water... - Exhibiting extremely hard base properties, the two undergo an internal coordination layer substitution reaction upon contact at the solid-liquid interface, F - It replaced the original coordinated water molecules to form stable [Zr-F] coordination bonds. Cl coexisting in the water body - and SO42- These substances, belonging to the boundary base and the weaker base respectively, have low overlap with the electron orbitals of Zr(Ⅳ) atoms and are unable to compete for space within the inner coordination ring of Zr(Ⅳ) due to the steric hindrance effect of the polyamine groups. Test results show that the resin material, relying on the sieving effect of the coordination field strength of the central metal atom, eliminates the competitive adsorption interference of conventional high-concentration anions, ensuring the efficiency of the defluorination process in high-salt systems. From a patent examination and protection perspective, the data in the table fully supports the objectivity of this technology's effectiveness, requiring no additional accompanying drawings.

[0065] Test Example 2: Four identical acrylic fluidized bed reactors were constructed, each with an inner diameter of 50 mm and an effective height of 1500 mm. These four reactors were labeled Experimental Group A, Experimental Group B, Experimental Group C, and Experimental Group D.

[0066] Experimental group A was not filled with seed crystals; experimental groups B, C, and D were filled with high-purity quartz sand with a particle size range of 0.3-0.6 mm as seed crystals, and the static filling height was controlled at 1.2 m.

[0067] The fluoride-containing permeate produced in the membrane concentration section is collected as raw water, and the initial fluoride ion concentration is measured. Calcium chloride solution is added to the raw water at a Ca / F molar ratio of 0.65, and the mixture is then used as the unified feed water.

[0068] Start the inlet pump and set the upward flow rate of each fluidized bed reactor to 22 m / h, while maintaining the reaction environment temperature at 25°C.

[0069] Sodium hydroxide or hydrochloric acid solution was added in parallel to the inlet pipe using a metering pump to stabilize the pH value of the system in experimental groups A and C at 8.0, the pH value of the system in experimental group B at 6.0, and the pH value of the system in experimental group D at 9.5.

[0070] After the fluidized bed reaches hydraulic equilibrium and the running time reaches 40 minutes, water samples are continuously taken from the overflow weir at the top of the reactor for continuous operation.

[0071] After the sample solution was allowed to stand for 10 minutes, the supernatant was extracted and the turbidity (NTU) of the water sample was measured using a scattering light turbidimeter; a separate quantitative homogeneous water sample was taken and the concentration of suspended solids (SS) in the water sample was determined by gravimetric method.

[0072] .

[0073] in conclusion: According to the data in Table 2, the effluent turbidity of experimental group C was 12.4 NTU, and the suspended solids concentration was 18.7 mg / L. In contrast, experimental group A, under the same pH conditions but without the addition of quartz sand seed crystals, underwent a homogeneous nucleation reaction, producing extremely difficult-to-settle fine colloidal flocs, resulting in an effluent turbidity as high as 845.7 NTU, with a large amount of unretained suspended solids overflowing with the water flow. Filling with quartz sand provides a physical interface for heterogeneous crystallization, lowers the activation energy for crystal nucleation, and allows calcium and fluoride ions in the liquid phase to adhere to the surface of the seed crystals, undergoing lattice growth and forming denser crystalline particles that settle and are retained inside the reactor, thus avoiding colloid formation.

[0074] Comparing the pH conditions of experimental groups B, C, and D, experimental group B, under weakly acidic conditions at pH 6.0, exhibited higher effluent turbidity and suspended solids (SS). In this pH environment, the fluorosilicic acid in the wastewater did not completely dissociate, fluoride ions were in a complexed and masked state, the crystallization reaction rate was inhibited, crystal development was incomplete, and fine particulate debris was produced. In experimental group D, under alkaline conditions at pH 9.5, side reactions occurred within the system, generating loose calcium hydroxide or calcium carbonate precipitates, leading to deterioration of the overflow water quality. Experimental group C, with pH controlled at 8.0, eliminated the interference of acidic complexation masking and alkaline side reactions, resulting in complete dissociation of fluorosilicic acid, thorough heterogeneous induced crystallization, and optimal effluent quality indicators.

[0075] Test Example 3: Based on the process parameters and connection relationships of Examples 1 to 3 and Comparative Examples 2 and 4, corresponding waste acid treatment and distillation recovery systems were constructed.

[0076] Waste hydrofluoric acid from the photoresist bottle production line was used as the raw material. Offline testing revealed that the HF mass fraction in this raw material was 8.45%, and the total metal impurity concentration was 12450 ppb. The raw material was then pumped into the homogenization tanks of each system group.

[0077] Start each group of systems and run them continuously for 72 hours according to the operating conditions set in each embodiment and comparative example, so that the material circulation and gas-liquid mass transfer inside the system reach a steady state.

[0078] During steady-state operation, the hydrofluoric acid product condensed from the top of the second distillation column is continuously collected. The HF mass fraction in the product is determined by acid-base neutralization titration. The total weight of the feed liquid and the total weight of the product are measured over 72 hours, and the overall HF recovery rate of each system is calculated based on the absolute mass of HF in the feed and output materials.

[0079] A sample of the finished hydrofluoric acid product was extracted from the sampling port in a dust-free environment and sent to an inductively coupled plasma mass spectrometer (ICP-MS) to determine the total concentration of metal impurities in the sample.

[0080] .

[0081] in conclusion: According to the data in Table 3, the overall HF recovery rate of Comparative Example 4 was only 62.37%, lower than that of Examples 1 to 3. Comparative Example 4 disrupted the material loop of the system, with the high-concentration residual liquid accumulated at the bottom of the distillation column and the dilute HF regenerated liquid generated by the resin adsorption unit being discharged into the waste liquid network, resulting in a large amount of recoverable fluorides leaving the main process flow. In the examples, the residual liquid and regenerated liquid were recycled back to the homogenizing tank for further processing. Without increasing the consumption of additional fresh raw materials, this method retained the free fluorine components in the system, maintaining the overall HF recovery rate above 85%.

[0082] The HF mass fraction of the finished product in Comparative Example 2 was 36.82%, and the total metal impurity concentration reached 3142 ppb. Hydrofluoric acid and water form an azeotrope with a concentration limit of approximately 38.2% under normal pressure. Comparative Example 2 used atmospheric pressure membrane concentration, which did not change the gas-liquid phase equilibrium. Water could not overcome the azeotropic limitation to achieve transmembrane vaporization, leading to the failure of the pre-concentration process and resulting in a substandard product concentration. The combination of vacuum degree (-0.068 to -0.082 MPa) and low temperature conditions set in the example changed the total system pressure, causing a shift in the azeotropic point of the mixture and ensuring that the finished product concentration reached over 40%. In Comparative Example 2, the high-purity nitrogen protection was omitted during the distillation process. Residual oxygen molecules inside the equipment participated in the oxidation reaction of trace heavy metal impurities, generating high-valence volatile metal oxides that azeotropically mixed with HF, causing a decrease in purity. In this embodiment, high-purity nitrogen gas under slight positive pressure is introduced into the distillation column reboiler to replace and isolate free oxygen, thus cutting off the oxidation pathway of transition metals and controlling the metal impurities in the product below 400 ppb. The discrete numerical indicators shown in Table 3 directly reflect the negative impact of deviations in system connectivity and physical parameters on the terminal recovery efficiency, providing complete persuasiveness in demonstrating the effectiveness of the patented technology, without the need for additional illustrations in the accompanying drawings.

[0083] Test Example 4: Four processing systems were built according to the process parameters and hardware configurations set in Example 2, Comparative Example 1, Comparative Example 3 and Comparative Example 5.

[0084] The system was started with routine production wastewater and membrane concentrate permeate from the plant for the first phase of routine operating condition testing. The system ran continuously for 360 hours. At the beginning of the system startup and at the end of the 360-hour period, standard pure water was used to test the flux of modified or ordinary ultrafiltration membrane modules. The values ​​were recorded and the operating flux decay rate was calculated. Simultaneously, the resistivity of the ultrapure water produced by the desalination process at the end of each group of systems was continuously measured and averaged.

[0085] After the routine operating condition test was completed, the system entered the second stage of high-load impact condition test without shutting down. A mixed waste liquid containing high concentrations of free fluoride and silicate powder was continuously and quantitatively injected into the water inlet of each system through a dosing pump to simulate the load impact generated by the washing of high-impurity quartz ore in the production line.

[0086] At the start of the impact, the DCS control system of Example 2 triggered an interlock, automatically lowering the vacuum to -0.078 MPa, adjusting the fluidized bed Ca / F molar ratio to 0.80, and extending the HRT to 50 min. Comparative Examples 1, 3, and 5 maintained their original operating conditions.

[0087] During the 24-hour period of continuous impact conditions, the permeate flux of the ultrafiltration membrane module was monitored in real time using an online flow meter, and the flux decrease at the 24-hour mark was calculated. At the 24-hour mark, the effluent from the resin adsorption unit was extracted, and the fluoride concentration in the effluent was determined using an ion chromatograph.

[0088] .

[0089] in conclusion: refer to Figure 1 As shown in the figure, the horizontal axis represents the duration of high-load quartz ore impact waste injection, in hours (h); the vertical axis represents the normalized membrane flux, which is the ratio of real-time membrane flux J to the initial stable membrane flux J0 of the system.

[0090] According to the data in Table 4, the ultrafiltration membrane in Comparative Example 1 experienced a flux decline rate of 35.12%, and the resistivity of the recycled water was only 9.43 MΩ·cm. Comparative Example 1 used a commercially available PVDF membrane and a common polyamine anion exchange resin. In acidic water containing complexed fluorides, the molecular chains of the common PVDF membrane undergo defluorination degradation, leading to damage to the membrane pore structure and loss of retention capacity. The common resin lacks an internal coordination binding mechanism for fluoride ions, causing impurities leaking from the front end and fluoride ions to enter the desalination system, increasing the ion load on the reverse osmosis and EDI units, resulting in the product water resistivity failing to meet the electronic-grade reuse standard of 16 MΩ·cm.

[0091] During normal operation, the indicators of Comparative Example 5 are similar to those of Example 2. However, when encountering high load shocks, the results, combined with the data in Table 4, show... Figure 1 The three data evolution curves, represented by different line types, show that: The third curve (black dotted line), representing the operating state of Comparative Example 3, shows a precipitous drop within the first 5 hours after the impact, with flux rapidly decreasing to below 0.2 and remaining at its lowest point for a long period. The membrane flux decrease at the end of 24 hours under impact conditions reached as high as 81.04%, and the overall flux decay rate was as high as 68.45%. In a fluidized bed environment without quartz seed crystals and with a slightly acidic pH adjustment, the reaction between fluorine and calcium is dominated by homogeneous nucleation, producing a large number of amorphous fine colloidal flocs. The lack of high-purity quartz seed crystals in the fluidized bed leads to homogeneous burst nucleation. The generated fine amorphous colloids rapidly deposit on the membrane surface as they flow through the ultrafiltration module, creating an extremely dense and irreversible gel polarization layer covering the membrane pores, causing severe membrane fouling and loss of permeability.

[0092] The second curve (black dashed line), representing the operating status of Comparative Example 5, shows a near-linear downward trend from the initial impact point, dropping below 0.44 by the end of 24 hours. Membrane flux decreased by 56.12%, and the effluent fluoride concentration soared to 19.64 mg / L. Comparative Example 5 lacked a dynamic parameter adjustment mechanism; fixed operating parameters could not cope with the sudden increase in feedwater load. The sudden increase in feedwater concentration and viscosity led to an imbalance in the system's separation load. Failure to lower the vacuum level exacerbated concentration polarization at the membrane surface, causing a sharp decline in flux and continuous physical fouling accumulation on the membrane surface. The failure to simultaneously increase the Ca / F molar ratio of the fluidized bed to enhance crystallization supersaturation and the failure to extend the hydraulic retention time to ensure crystal development resulted in high-concentration fluoride ions entering the next stage before complete crystallization and precipitation. The excessive free fluoride ions overwhelmed the resin's exchange capacity, leading to a complete system collapse.

[0093] The first curve (solid black line), representing the operating status of Example 2, experienced a slight decrease in the initial stage of impact, then quickly leveled off and formed a stable horizontal asymptote of approximately 0.87. At the end of 24 hours, the membrane flux decreased by only 12.35%, and the effluent fluoride concentration stabilized at 0.42 mg / L. Example 2 relied on the DCS system's automatic adjustment based on the influent load. With the intervention of the interlocking mechanism, the vacuum degree was dynamically reduced to enhance the gasification driving force, and the fluidized bed dosing and flow rate parameters were simultaneously adjusted to increase the residence time of the crystallization reaction, thus re-matching the hydraulic and chemical reaction kinetics.

[0094] The differences in the curve shapes and the data in the table clearly demonstrate that this dynamic parameter adjustment mechanism effectively rebalances the separation load of the system, curbs membrane concentration polarization and high-pressure fouling, and ensures the stability of the adsorbed water quality. The heterogeneous induced crystallization mechanism and DCS dynamic interlocking parameter adjustment scheme integrated in this application possess core technical effects in ensuring long-term stable system operation and resisting overload water quality shocks.

[0095] Test Example 5: The crystal slurry dewatering sludge generated under normal operating conditions in Examples 1 to 3 and Comparative Example 6 was extracted, and sludge solidified samples were prepared according to the solidifying agent formulation and curing conditions set for each group. Examples 1 to 3 were supplemented with the organic chelating agent provided in the preparation example and cured at room temperature for 72 hours; Comparative Example 6 was not supplemented with organic chelating agent, and the room temperature curing time was shortened to 24 hours.

[0096] According to the TCLP standard procedure for toxicity characterization leaching, the solidified samples of each group were crushed and passed through a standard sieve with a 9.5 mm aperture. 100 g of the solidified sample that passed through the sieve was weighed and placed in an extraction bottle, and an extraction solution adjusted to pH 2.88 with glacial acetic acid was added at a liquid-to-solid ratio of 1:20.

[0097] After sealing the extraction bottle, it was fixed on a tilting shaker and continuously tilted and shaken at 30 r / min for 18 h at room temperature. After shaking, the solid-liquid mixture was vacuum filtered through a 0.6 μm glass fiber filter membrane, and the leachate was collected.

[0098] Take a sample of the leachate and determine the fluoride ions (F) in it using ion chromatography. - The concentrations of lead (Pb) and chromium (Cr) in the leachate were determined using inductively coupled plasma mass spectrometry (ICP-MS) to evaluate the curing stability of heavy metals and fluorine.

[0099] The remaining solidified samples from each group were further crushed to a particle size ≤5mm, and the liquid-to-solid ratio was adjusted to a pulp concentration between 25% and 28%. Sodium oleate, pine oil, and water glass were added, and the mixture was fed into a mechanically stirred flotation machine to perform a closed-circuit flotation process consisting of one roughing, one cleaning, and one scavenging stage.

[0100] Collect the concentrate froth products generated from each group of flotation, filter and dry them, and then use EDTA complexometric titration to determine the mass fraction of calcium fluoride (CaF2) in the concentrate products and calculate the product purity.

[0101] .

[0102] in conclusion: According to the data in Table 5, the F- concentration in the leachate of Comparative Example 6 reached 24.63 mg / L, and the concentrations of Pb and Cr reached 3.85 mg / L and 4.12 mg / L, respectively, indicating a significant risk of secondary leaching. In Examples 1 to 3, the F- leaching concentration was controlled below 2.2 mg / L, the heavy metal concentration was below 0.15 mg / L, and the purity of the fluorite concentrate was above 85%. The sludge solidification process relies on a solid solution mineralization mechanism. Lime-activated slag powder releases active [SiO4] and [AlO4] tetrahedra, which subsequently combine with Ca2+ to form amorphous calcium silicate hydrate (CSH) and hydrated calcium aluminate crystals. This hydration reaction requires a sufficient time period to construct a complete gel network. The curing time in Comparative Example 6 was shortened to 24 h, resulting in incomplete hydration; fluoride ions failed to enter the CSH crystal structure through isomorphous substitution to achieve deep chemical mineralization. In Comparative Example 6, the formulation did not contain the organic chelating agent EDTA-2Na and DDTC compound, resulting in the loss of coordination locking of free transition metal ions due to the absence of multi-dentate chelation. Under the acidic extraction environment of the TCLP test, the physical microencapsulations formed solely by the incomplete gel network ruptured, leading to the significant release of free fluorine and heavy metals into the liquid phase.

[0103] The example employed a combination of 72-hour room temperature curing and the addition of 1.5% organic chelating agent to achieve lattice solidification and chelation locking of contaminants. During the flotation purification stage, the solidified structure in this example remained stable. The gangue components dissociated in the aqueous solution maintained hydrophilic sedimentation under the action of sodium silicate inhibitor. The calcium fluoride microcrystals released from the solidified body underwent interfacial hydrophobicization under the chemical adsorption of sodium oleate collector and adhered to bubbles, resulting in a fluorite concentrate with a purity higher than 85%. In Comparative Example 6, due to incomplete mineralization of the crystal structure in the early stage, some incompletely hydrated gangue flocs carried hydrophilic impurities and floated together during the strong mechanical slurry preparation and flotation process, leading to a decrease in the purity of the concentrate product to 79.46%. Test data proves that the set composite solidification stabilizer formulation and its curing parameters are necessary process conditions to block the secondary leaching path of contaminants and ensure the quality of subsequent resource-based products.

Claims

1. A method for recovering fluorides specifically for large-scale production of photoresist bottles, characterized in that, Includes the following steps: Waste hydrofluoric acid stock solution and residual liquid and regenerated liquid returned from subsequent processes are introduced into a homogenizing tank, stirred and homogenized, and then subjected to coarse filtration through a filter element and fine filtration through a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane. The permeate enters the perfluorinated spiral wound membrane module to control the feed temperature and vacuum degree for vacuum membrane concentration. The concentrate enters the dual-tower distillation system. High-purity nitrogen is introduced into the bottom of the tower for distillation and purification to obtain the finished product. The residual liquid in the bottom of the distillation tower is completely refluxed to the homogenizer. The membrane concentrate permeate and fluoride-containing wastewater are collected in an equalization tank, calcium hydroxide emulsion is added, and the reaction is stirred to adjust the final pH. After conditioning, the wastewater enters a two-stage quartz seed-induced fluidized bed. The effluent from the fluidized bed enters an adsorption column filled with D402 fluorine selective chelating resin for defluorination. After saturation, it is regenerated with dilute hydrofluoric acid, and the regenerated liquid is returned to the homogenizing tank. The adsorbed water is completely reused after membrane desalination. The crystal slurry discharged from the two-stage quartz seed-induced fluidized bed is concentrated and then filtered by a fluorine-resistant plate and frame filter press. The dewatered sludge is mixed with a composite solidification stabilizer and cured at room temperature. After the solidified body is crushed and slurry is prepared, it is subjected to flotation, and sodium oleate, pine oil and water glass are added to finally obtain fluorite concentrate product.

2. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, In the step of sequential coarse filtration by a filter element and fine filtration by a modified fluorine-resistant PVDF hollow fiber ultrafiltration membrane: The coarse filter uses a 5μm PTFE filter element; In the step of controlling the feed temperature and vacuum degree for vacuum membrane concentration: The vacuum membrane concentration controls the feed temperature to 42 to 46°C, and the vacuum degree is maintained at -0.068 to -0.072 MPa under normal operating conditions. When the DCS detects a load impact, it automatically lowers the vacuum degree to -0.078 to -0.080 MPa. In the step where the concentrated liquid enters the dual-tower distillation system, high-purity nitrogen is introduced into the reboiler, and the product is obtained through distillation and purification: The dual-tower distillation system includes one tower and two towers; Under normal operating conditions, the reflux ratio of a single tower is 1.8 to 2.2, and the reflux ratio of two towers is 1.2 to 1.

5. Under impact conditions, the DCS automatically switches the reflux ratio of the first tower to 2.5 and the reflux ratio of the second tower to 1.

6.

3. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, The preparation methods of modified fluorine-resistant PVDF hollow fiber ultrafiltration membranes include: 12% to 18% by weight of polyvinylidene fluoride-hexafluoropropylene copolymer, 1% to 3% by weight of polytetrafluoroethylene nanoparticles with a particle size of 30 to 50 nm, and 5% by weight of polyvinylpyrrolidone are dissolved in 74% to 82% by weight of N,N-dimethylacetamide solvent. The casting solution is prepared by mechanical stirring at 50 to 70°C for 10 to 15 hours. After vacuum degassing the casting solution for 24 hours, a dry-wet spinning process was used to extrude the core solution and casting solution with a volume ratio of water to N,N-dimethylacetamide of 7:3 through an annular spinneret. After passing through a 10cm air section, the extrudate is immersed in a pure water coagulation bath at 15 to 35°C to undergo phase transformation and form a film. Wash in 60℃ pure water for 24 hours.

4. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, In the step of adjusting the final pH of the stirred reaction: The final pH value for adjustment is 7.8 to 8.2; In the step where the conditioned wastewater enters the two-stage quartz seed-induced fluidized bed: The two-stage quartz seed-induced fluidized bed includes a primary fluidized bed and a secondary fluidized bed, with the reaction temperature controlled at 25 to 35°C and the upward flow rate at 22 to 25 m / h; The primary fluidized bed is filled with 0.3 to 0.6 mm quartz sand seed crystals, and the secondary fluidized bed is filled with 0.15 to 0.3 mm quartz sand. Under normal operating conditions, the calcium-fluorine molar ratio of the primary fluidized bed is controlled at 0.60 to 0.65, and the hydraulic retention time is 40 min. When encountering load shocks, the system automatically increases the dosage of auxiliary calcium source to raise the calcium-fluorine molar ratio to 0.80, while extending the hydraulic residence time to 50 minutes. The hydraulic retention time in the secondary fluidized bed is maintained at 50 minutes.

5. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, The preparation methods of D402 fluorine selective chelating resin include: Using macroporous cross-linked styrene-divinylbenzene copolymer white spheres as the backbone material, chloromethyl ether reagent and anhydrous zinc chloride catalyst were added, and the reaction was carried out at 40 to 50 °C for 6 to 10 hours to obtain chloromethylated cross-linked polystyrene. Chloromethylated crosslinked polystyrene was refluxed with excess ethylenediamine at 70 to 90 °C for 8 to 12 h, and then washed and dried to obtain a polyamine anion exchange resin. The polyamine-type anion exchange resin was impregnated in an acidic solution of zirconium oxychloride with a concentration of 0.3 to 0.7 mol / L and reacted at a constant temperature of 50 to 70 °C with shaking for 18 to 30 hours. Wash with deionized water until neutral.

6. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, In the process of the crystal slurry discharged from the two-stage quartz seed-induced fluidized bed being concentrated and then filtered by a fluorine-resistant plate and frame filter press, the dewatered sludge is mixed with a composite solidification stabilizer and cured at room temperature: Under normal operating conditions, the filter press cycle is 4 hours per batch. Under impact conditions, the time per batch can be shortened to 3 hours. The dewatered sludge is cured at room temperature for 72 hours under conditions of 15 to 30°C and 60% to 80% humidity.

7. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, The total dosage ratio of the composite curing stabilizer is: The total proportion of solidifying agent under normal operating conditions is 17.5%, accounting for 10% of the dry sludge mass, including 10% quicklime, 6% slag powder, and 1.5% organic chelating agent. Under impact conditions, the total proportion of solidifying agent is increased to 20.5%, accounting for 12% of the dry sludge mass, including quicklime 12%, slag powder 7%, and organic chelating agent 1.5%.

8. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 7, characterized in that, Methods for preparing organic chelating agents include: Weigh out disodium ethylenediaminetetraacetate and sodium diethyldithiocarbamate, mix them in a mass ratio of 0.8 to 1.2:1, and mechanically dry mix at room temperature for 30 minutes to obtain a powdered organic chelating agent.

9. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, In the step of adding sodium oleate, pine oil, and water glass during flotation after the solidified body is crushed and slurried: The solidified body is crushed and slurryed to a concentration of 25% to 28% before flotation. The amounts of sodium oleate, pine oil, and water glass added are as follows: Add 600g / t sodium oleate, 40g / t pine oil, and 300g / t water glass.

10. The method for recovering fluoride from photoresist bottles for large-scale production according to claim 1, characterized in that, In the step of regenerating with dilute hydrofluoric acid after saturation: After saturation, it is regenerated with 4% dilute hydrofluoric acid.

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