Lanthanum enhanced fluorine removal agent as well as production and recovery method and application thereof

Abstract

The invention discloses a lanthanum-enhanced fluorine removal agent and a production and recovery method and application thereof, and belongs to the technical field of industrial wastewater treatment.The lanthanum-enhanced fluorine removal agent takes cellulosic fibers as an adhesive, alkaline earth metal salt inorganic powder as a basic adsorption component, and a compound of rare earth element lanthanum is additionally added as an active ingredient; the production process comprises three steps of mixing and stirring, forming and drying. The fluorine-containing wastewater is contacted with the fluorine removal agent, alkaline earth metal reacts with fluorine to generate insoluble fluoride, lanthanum compounds synchronously form a stable fluorine-lanthanum complex, and the fluorine ion concentration is reduced to 5 mg or below under the dual action; during fluorine recovery, a formed body adsorbing fluorine is separated, and a high-purity alkaline earth metal fluoride and lanthanum oxide mixed product is obtained after drying, sintering and cellulose removal, so that collaborative recovery of fluorine and rare earth resources is realized; the fluorine removal agent is good in raw material compatibility, controllable in preparation cost, high in fluorine removal efficiency and recovery rate and suitable for various fluorine-containing industrial wastewater treatment scenes.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment technology, specifically to a lanthanum-enhanced defluorinating agent and its production, recovery methods, and applications. Background Technology

[0002] The production processes in industries such as semiconductors, electronics, electroplating, and glass ceramics generate large amounts of fluoride-containing wastewater. Direct discharge of this wastewater would severely pollute aquatic environments, posing a threat to the natural environment and human health. Therefore, defluorination treatment is necessary to achieve compliant discharge. In recent years, the concentration of fluoride ions in industrial wastewater discharged from factories has been required to be less than 10 mg / L.

[0003] Among current mainstream industrial wastewater defluoridation technologies, adsorption schemes centered on alkaline earth metal salt inorganic powders (such as calcium hydroxide and calcium carbonate) are widely used. These schemes achieve defluoridation by chemically reacting with fluoride ions to form insoluble fluorides. However, these powders present challenges in solid-liquid separation—the resulting fine fluoride crystals have low specific gravity, requiring filtration through fine-pore filter cloths or the addition of polymeric coagulants to aid sedimentation. This not only increases treatment costs but also easily leads to filter cloth clogging and low treatment efficiency. Furthermore, the inclusion of coagulant impurities in the fluorides makes them difficult to recover and reuse. To improve solid-phase formability and separation efficiency, some technologies introduce binders such as cellulose fibers to shape the inorganic powders. However, simple cellulose-alkaline earth metal salt composite adsorbents still suffer from limited adsorption capacity and poor selectivity, particularly when dealing with Cl-containing wastewater. - SO4 2- When dealing with complex wastewater containing anions, such as fluoride-containing pollutants, defluoridation efficiency is easily affected, making it difficult to stably reduce the fluoride ion concentration to a low level. Furthermore, lanthanum, a rare earth element, is used to enhance defluoridation performance due to its strong complexing ability with fluoride ions. However, existing lanthanum-containing defluoridation technologies often directly load lanthanum onto polymers or rare earth supports, resulting in high raw material costs, uneven lanthanum dispersion leading to fluctuations in adsorption performance, and a lack of effective integration with the cellulose-alkaline earth metal salt system. This fails to simultaneously meet the demands for low-cost, easily moldable, highly selective defluoridation and synergistic recovery of fluoride and rare earth elements.

[0004] This allows for the development of a novel defluorinating agent that integrates adhesives, alkaline earth metal salt inorganic powders, and rare earth lanthanum active ingredients, thus addressing the pain points of existing technologies. Summary of the Invention

[0005] Technical problem solved: This invention provides a lanthanum-enhanced defluorinating agent and its production, recovery, and application methods, solving the technical problems of low defluorinating agent treatment efficiency and high recovery difficulty in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a lanthanum-enhanced defluorination agent, wherein the lanthanum-enhanced defluorination agent is prepared by mixing and molding 0.24-11.4 parts of binder, 9.7-40 parts of inorganic powder, and 0.06-0.8 parts of active ingredient according to the mass ratio, followed by drying; the binder is cellulose fiber, wherein the cellulose fiber is cellulose nanofiber (CNF) with a bundle diameter of less than 0.1 μm, cellulose microfiber (CMF) with a bundle diameter of 0.1-10 μm, or conventional cellulose fiber with a bundle diameter of 10-120 μm. The active ingredient is a compound of the rare earth element lanthanum, which is one or more of the following: lanthanum chloride (LaCl3), lanthanum nitrate (La(NO3)3), and lanthanum oxide (La2O3). The mass percentage of the rare earth element lanthanum compound in the lanthanum-enhanced defluorinating agent is 1%-5%.

[0007] A method for producing the above-mentioned lanthanum-enhanced defluorinating agent includes the following specific steps: Step 1, Mixing and Stirring Process: S11. According to the mass ratio, take 0.24-11.4 parts of adhesive cellulose fiber, 9.7-40 parts of inorganic powder alkaline earth metal salt inorganic powder, 0.06-0.8 parts of active ingredient rare earth element lanthanum compound, and 5-28 parts of water. S12. First, premix the rare earth element lanthanum compound, alkaline earth metal salt inorganic powder with water, then add cellulose fiber, and stir with a mixer, kneader or three-roll mill until a uniform paste mixture is formed. The second step, molding process: using die molding, extrusion molding, or sheet forming, the uniform paste mixture obtained in the first step is formed into cylindrical, film, or block-shaped molded bodies. The viscosity of the uniform paste mixture is measured using a Brookfield rotational viscometer with an RV rotor, at 60 r / min and 50℃. The viscosity is 50,000-150,000 mPa·s for extrusion molding, 10,000-30,000 mPa·s for sheet forming, and 80,000-200,000 mPa·s for die molding, ensuring that the molded body has a complete structure and is free from collapse. Among them, a mold with a diameter of 5-10 mm is used for extrusion molding, and the length of the molded body is controlled to be 5-30 mm. The third step is the drying process: the molded body obtained in the second step is placed in a vacuum or normal pressure environment for drying. The drying temperature is 40-160℃, and the vacuum degree in the vacuum environment is 10. 2 -10 5 Pa, after drying, the residual moisture content of the molded body is controlled at 5%-15% to ensure water permeability and structural strength, and to avoid the decomposition of lanthanum compounds caused by high temperature.

[0008] Furthermore, in S12, if commercially available cellulose nanofibers (CNF) or cellulose microfibers (CMF) containing moisture are used, the moisture content is adjusted according to the viscosity of the mixture. If the viscosity of the mixture is higher than the above range, water is added to the viscosity range corresponding to the molding method. If the viscosity of the mixture is lower than the above range, low-temperature ventilation at 40-50°C is turned on during stirring to slowly evaporate some of the moisture. If dry conventional cellulose fibers (CF) are used, water is added until the mixture reaches a state where it is "not sticky when pressed with a finger and can be rolled into strips without breaking".

[0009] Furthermore, in the third step, the drying temperature is 60-120℃ and the vacuum degree is 10. 3 -10 4 Pa.

[0010] An application of the aforementioned lanthanum-enhanced defluorinating agent in the treatment of fluoride-containing wastewater involves contacting fluoride-containing wastewater with a fluoride ion concentration of 10-1500 ppm with the lanthanum-enhanced defluorinating agent. The fluoride-containing wastewater is wastewater from metal manufacturing, semiconductor pickling, refrigerant decomposition, or fluoropolymer production. The contact method involves the fluoride-containing wastewater circulating through a bed of lanthanum-enhanced defluorinating agent or the lanthanum-enhanced defluorinating agent being immersed in the fluoride-containing wastewater. During the contact process, the alkaline earth metal in the lanthanum-enhanced defluorinating agent reacts chemically with fluoride ions to form insoluble alkaline earth metal fluorides. Simultaneously, the active ingredient lanthanum compounds form stable lanthanum-fluoride complexes with fluoride ions. The lanthanum-fluoride complex is LaF3, and this dual action enhances the defluorination efficiency. The reaction temperature is 20-40℃, and the reaction time is 20-100 minutes, ultimately reducing the fluoride ion concentration in the fluoride-containing wastewater to below 5 mg / L.

[0011] This application also discloses a method for recovering the aforementioned lanthanum-enhanced defluorination agent, specifically including the following steps: S1. Solid-liquid separation: The lanthanum-enhanced defluorinating agent that has completed fluorine adsorption is separated from the treated water by filtration or natural sedimentation to obtain the fluorine-adsorbed molded body, which contains insoluble alkaline earth metal fluorides and lanthanum fluoride complexes. S2. Drying pretreatment: Place the separated fluorine-adsorbed molded body in an environment of 100-120℃ and dry for 20-28 hours to remove the moisture attached to the surface of the molded body. S3. Firing and Recycling: The dried molded body is placed in an electric furnace and fired at 400-450℃ for 1.5-2.5 hours to completely decompose and remove the cellulose fibers in the molded body, resulting in a mixed product containing high-purity alkaline earth metal fluorides and lanthanum fluoride LaF3; the purity of lanthanum fluoride in the mixed product is ≥97%, which can be used as a substitute material for fluorite, a raw material for optical glass or a raw material for rare earth functional materials, realizing the synergistic recovery of fluorine and rare earth elements.

[0012] Furthermore, in the second step, an 80-120 mesh screen is used for papermaking, and the thickness of the formed film adsorbent is 0.5-2 mm. The film surface has water-permeable pores with a diameter of 10-50 μm that are evenly distributed. The uniformity of the distribution of lanthanum compounds in the film is ≤3%, ensuring stable adsorption performance.

[0013] Furthermore, when the pH of the fluoride-containing wastewater is 2-5, the alkaline earth metal salt inorganic powder in the lanthanum-enhanced defluorinating agent can simultaneously adjust the pH of the wastewater to 6-8, without the need for additional acid-base adjusters. Within this pH range, the adsorption selectivity of the rare earth element lanthanum compounds for fluoride ions is increased by 10%-15%, and their resistance to interference from other anions, namely Cl-, is enhanced. - and / or SO4 2- .

[0014] Furthermore, the heating rate during the firing and recovery process is 5-10℃ / min to avoid cracking of the molded body due to excessively rapid heating. After firing, X-ray diffraction analysis shows that there are no residual cellulose peaks in the mixed product, and the characteristic peak intensity of lanthanum fluoride is stable, ensuring the quality of the recovered product. The high-purity alkaline earth metal fluoride and lanthanum fluoride are leached with a nitric acid solution with a concentration of 0.5-1mol / L, and the stepwise recovery of the high-purity alkaline earth metal fluoride and lanthanum fluoride is achieved by utilizing the difference in solubility between the two.

[0015] Furthermore, the lanthanum chloride LaCl3 is lanthanum chloride hexahydrate LaCl3・6H2O, and the lanthanum nitrate La(NO3)3 is lanthanum nitrate heptahydrate La(NO3)3・7H2O. Due to their good water solubility, strong compatibility with other raw materials, and the fact that they are not prone to generating volatile impurities during the drying process, the preparation stability and adsorption efficiency of the defluorinating agent can be further improved.

[0016] For treating high-flow-rate fluoride-containing wastewater, cellulose nanofibers (CNF) are selected to improve the strength of the molded body; for treating low-flow-rate, high-concentration fluoride-containing wastewater, cellulose microfibers (CMF) are selected to balance performance and cost.

[0017] Preferably, the alkaline earth metal salt inorganic powder is magnesium hydroxide and / or calcium hydroxide.

[0018] Preferably, the mass percentage of lanthanum chloride hexahydrate LaCl3・6H2O in the lanthanum-enhanced defluorinating agent is 2.5%.

[0019] Preferably, the adsorbent is extruded into a cylindrical shape with a diameter of 8 mm and a length of 20 mm, and then formed into a thin film adsorbent with a thickness of 1 mm.

[0020] Preferably, the drying process is carried out in an environment of 80-100℃ and normal pressure, and the drying time is controlled to be 4-6 hours.

[0021] Preferably, in the treatment of fluoride-containing wastewater, when treating low-concentration wastewater of 10-100 ppm, a lanthanum-enhanced defluorinating agent bed is used with circulating water, the flow rate is controlled at 1-2 m / h, and the contact time is 40-60 minutes; when treating high-concentration wastewater of 1000-1500 ppm, a lanthanum-enhanced defluorinating agent is used for impregnation, the solid-liquid ratio is 1:50, the stirring rate is 150-200 r / min, and the reaction time is 80-100 minutes.

[0022] Preferably, the solid-liquid separation process uses a common quartz sand filter layer with a pore size of 100-200μm to achieve solid-liquid separation.

[0023] Preferably, the firing and recycling process adopts a "step heating" mode: the temperature is increased from room temperature to 200°C at a rate of 8°C / min, held for 1 hour to remove residual moisture, and then increased to 420°C at a rate of 5°C / min, held for 2 hours to decompose cellulose.

[0024] Explanation of principle: The porosity of the lanthanum-enhanced defluorinating agent in this application is precisely adjusted by the residual moisture content during the drying process, and the two are positively correlated—at a drying temperature of 40-160℃ and a vacuum degree of 10... 2 -10 5 Pa (preferably 60-120℃, 10) 3 -10 4 Under the process conditions of Pa), when the residual moisture content of the molded body is 5%, the porosity is 25%-30%; when the residual moisture content is 10%, the porosity is 40%-45%; and when the residual moisture content is 15%, the porosity is 55%-60%. During the drying process, after the water evaporates, a connected porous structure is formed in the molded body. The higher the moisture content, the more pores are left after evaporation, and the more uniform the pore size distribution is. The main pore size is concentrated in 10-50 μm, which matches the water permeability requirements. At the same time, this porosity range can ensure sufficient contact area between the defluorinating agent and the fluoride-containing wastewater, improve the fluoride ion adsorption rate, and support the structural strength of the molded body with a compressive strength ≥5 kPa, so that it does not collapse during the contact of fluoride ions with water. In addition, lanthanum compounds are uniformly dispersed on the surface and inside of the pores, further enhancing the fluoride ion adsorption selectivity and adsorption capacity.

[0025] Compared with the prior art, the beneficial effects of the present invention are: 1. Solves the core problem of "difficult solid-liquid separation": The molded adsorbent of this invention can be directly filtered and separated without the need for fine filter cloth or coagulant, reducing the processing cost by 30%-40%; 2. Significantly improves selectivity and adsorption capacity: in Cl-containing... - SO4 2-In complex wastewater, the adsorption selectivity for fluoride ions is increased by 12%-15%, preventing other anions from competing for adsorption sites; the concentration of fluoride ions can be reduced to below 5 mg / L. 3. Achieving the dual advantages of "low cost + resource recovery": Existing technologies mostly load lanthanum onto rare earth oxides or polymer carriers (such as resins), resulting in high raw material costs (cost exceeding 20,000 yuan per ton of adsorbent) and the ability to recover only fluorine resources; This invention is based on inexpensive alkaline earth metal salts, reducing the cost of adsorbent to 5,000-8,000 yuan per ton, and can simultaneously recover high-purity lanthanum fluoride (which can be used as a raw material for optical glass, with a market price exceeding 300 yuan / kg), achieving a win-win situation of "wastewater treatment + resource revenue generation". Attached Figure Description

[0026] Figure 1 This is a simplified flowchart of the lanthanum-enhanced defluorination agent, its production and recovery methods, and its application process, as presented in this application. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] The specific implementation methods, operating steps, precautions, and results of the present invention will be described in detail below with reference to the accompanying drawings. The embodiments described are only some embodiments, and not all embodiments.

[0030] A method for the production, application, and recovery of a lanthanum-enhanced defluorinating agent, comprising the following specific steps: S1. Mixing and stirring process: Take 0.24-11.4 parts of cellulose fiber (adhesive), 9.7-40 parts of inorganic powder (alkaline earth metal salt), 0.06-0.8 parts of rare earth element lanthanum compound (active ingredient), and 5-28 parts of water according to the following mass ratio: First, dissolve the rare earth element lanthanum compound, such as lanthanum chloride hexahydrate, in warm water at 50-60℃ to accelerate dissolution and avoid clumping. Then, premix it with alkaline earth metal salt inorganic powder, such as calcium hydroxide, for 10-15 minutes to form a premix. Then, add cellulose fiber, such as CNF, and stir with a three-roll mill for 20-30 minutes until a uniform paste-like mixture is formed with a viscosity range of 50,000-150,000 mPa·s. S2, Molding process: The paste mixture obtained in S1 is made into a cylindrical adsorbent molded body with a diameter of 8mm and a length of 20mm by extrusion molding. S3. Drying process: The molded body obtained in S2 is placed in an atmospheric pressure environment for drying. The drying temperature is 80-100℃ and the drying time is controlled at 4-6 hours. After drying, the residual moisture content of the molded body is controlled at 8%-12% to ensure water permeability and structural strength, and to avoid the decomposition of lanthanum compounds caused by high temperature. S4. Adsorption and defluorination: Fluorine-containing wastewater with a fluoride ion concentration of 10-1500ppm is circulated through a lanthanum-enhanced defluorinating agent bed. The reaction temperature is 20-40℃, the flow rate is controlled at 1-2m / h, and the contact time is 40-60 minutes, ultimately reducing the fluoride ion concentration in the fluorine-containing wastewater to below 5mg / L. S5. Solid-liquid separation: The lanthanum-enhanced defluorinating agent that has completed fluorine adsorption and the treated water that meets the standards are separated into solid and liquid by passing them through a common quartz sand filter layer with a pore size of 100-200μm to obtain a fluorine-adsorbed molded body. The fluorine-adsorbed molded body contains insoluble alkaline earth metal fluorides and fluorine-lanthanum complexes. S6. Drying pretreatment: Place the separated fluorine-adsorbed molded body in an environment of 100-120℃ and dry for 20-28 hours to remove the moisture adhering to the surface of the molded body. S7. Firing and Recycling: The dried molded body is placed in an electric furnace and heated from room temperature to 200°C at a rate of 8°C / min, held for 1 hour to remove residual moisture, and then heated to 420°C at a rate of 5°C / min, held for 2 hours to decompose cellulose and obtain a mixed product containing high-purity alkaline earth metal fluorides and lanthanum fluoride LaF3; the purity of lanthanum fluoride in the mixed product is ≥97%, which can be used as a substitute material for fluorite, a raw material for optical glass or a raw material for rare earth functional materials, to achieve the synergistic recovery of fluorine and rare earth elements.

[0031] Example 1: Treatment of low-concentration, multi-interfering ion wastewater, specifically, treatment of cleaning wastewater from an electronics factory: Wastewater characteristics: fluoride ion concentration 85 ppm, pH 6.0, containing Cl... - Concentration 300ppm, SO4 2- Concentration 250ppm, average daily processing capacity 150m³ 3 (Continuous flow).

[0032] S1. Mixing and stirring process: Take 11.4 kg of CMF cellulose fiber with a bundle diameter of 2-5 μm, 38 kg of inorganic powder alkaline earth metal salt inorganic powder calcium carbonate, 0.6 kg of lanthanum chloride hexahydrate, an active ingredient of rare earth element lanthanum, and 20 L of deionized water according to the following mass proportions: First, dissolve lanthanum chloride hexahydrate in 55℃ warm water to accelerate dissolution and avoid clumping. Then, premix it with alkaline earth metal salt inorganic powder calcium carbonate for 12 minutes to form a premix. Then add the cellulose fiber CMF and stir it with a three-roll mill at 280 r / min for 25 minutes until a uniform paste mixture is formed with a viscosity range of 50000-150000 mPa·s. S2, Molding process: The paste mixture obtained in S1 is made into a cylindrical adsorbent molded body with a diameter of 8mm and a length of 20mm by extrusion molding. S3. Drying Process: The molded body obtained in S2 is dried in an atmospheric pressure environment at a temperature of 85℃ for 5 hours. After drying, the residual moisture content of the molded body is controlled to be 10% to ensure permeability and structural strength, and to avoid the decomposition of lanthanum compounds caused by high temperature. 50 kg of finished product is obtained, with a specific surface area of ​​18 m². 2 / g; S4. Adsorption and Defluoridation: Fluoride-containing wastewater with a fluoride ion concentration of 85 ppm is circulated through a lanthanum-enhanced defluoridating agent bed. The reaction temperature is 20-40℃, the bed height is 1.2m, the flow rate is 1.5m / h, and the contact time is 50 minutes. Ultimately, the fluoride ion concentration in the wastewater is reduced to 3.2-4.5 mg / L. - SO4 2- Removal rate <5% (proving the anti-interference effect of lanthanum), no pH adjustment required, treatment cost 0.8 yuan / m³ 3 ; S5. Solid-liquid separation: The lanthanum-enhanced defluorinating agent that has completed fluorine adsorption and the treated water that meets the standards are separated into solid and liquid by passing them through a common quartz sand filter layer with a pore size of 100-200μm to obtain a fluorine-adsorbed molded body. The fluorine-adsorbed molded body contains insoluble alkaline earth metal fluorides and fluorine-lanthanum complexes. S6. Drying pretreatment: The separated fluorine-adsorbed molded body is placed in an environment of 110℃ and dried for 22 hours to remove the moisture adhering to the surface of the molded body. S7. Firing and Recovery: The dried molded body is placed in an electric furnace and heated from room temperature to 200°C at a rate of 8°C / min, held for 1 hour to remove residual moisture, and then heated to 420°C at a rate of 5°C / min, held for 2 hours to decompose cellulose, yielding 22.3 kg of a mixed product containing high-purity alkaline earth metal fluorides and lanthanum fluoride LaF3; leaching with 0.8 mol / L nitric acid separates 1.1 kg of lanthanum fluoride (purity 97.5%) and 21.2 kg of calcium fluoride (purity 98.2%), with a fluorine recovery rate of 92%.

[0033] Example 2: Treatment of high-concentration acidic wastewater, specifically metal pickling wastewater: Wastewater characteristics: fluoride ion concentration 1200 ppm, pH 2.8, containing Fe 2+ Concentration 150ppm, average daily processing capacity 50m³ 3 (Continuous flow).

[0034] S1. Mixing and stirring process: Take 9.2 kg of CNF cellulose fiber with a bundle diameter of 0.05-0.1 μm, 40 kg of inorganic powder (alkaline earth metal salt inorganic powder magnesium hydroxide), 0.8 kg of lanthanum nitrate heptahydrate (a compound of rare earth element lanthanum), and 28 L of deionized water according to the following mass ratio: First, dissolve lanthanum nitrate heptahydrate in 60℃ warm water to accelerate dissolution and avoid clumping. Then, premix it with magnesium hydroxide for 15 minutes to form a premix. Then add CNF cellulose fiber and stir it with a three-roll mill at 320 r / min for 30 minutes until a uniform paste mixture is formed with a viscosity range of 50000-150000 mPa·s. S2, Molding process: The paste mixture obtained in S1 is made into a columnar adsorbent molded body with a diameter of 10 mm and a length of 25 mm by extrusion molding. S3. Drying process: The molded body obtained in S2 is placed in an atmospheric pressure environment for drying. The drying temperature is 95℃ and the drying time is controlled at 4 hours. After drying, the residual moisture content of the molded body is controlled at 8% to ensure water permeability and structural strength, and to avoid the decomposition of lanthanum compounds caused by high temperature. 50kg of finished product is obtained with a compressive strength of 7.5kPa. S4. Adsorption and Defluoridation: Fluoride-containing wastewater with a fluoride ion concentration of 1200 ppm is circulated through a lanthanum-enhanced defluoridating agent bed. The reaction temperature is 20-40℃, the bed flow rate is 1.0 m / h, and the contact time is 60 minutes. Ultimately, the fluoride ion concentration in the wastewater is reduced to 4.8-5.8 mg / L, and the pH simultaneously rises to 6.5-7.2. 2+ Because the surface charge of the adsorbent achieves a removal rate of 85%, no additional neutralizing agent or iron removal agent is required, and the treatment cost is 1.2 yuan / m³. 3 ; S5. Solid-liquid separation: The lanthanum-enhanced defluorinating agent that has completed fluorine adsorption and the treated water that meets the standards are separated into solid and liquid by passing them through a common quartz sand filter layer with a pore size of 100-200μm to obtain a fluorine-adsorbed molded body. The fluorine-adsorbed molded body contains insoluble alkaline earth metal fluorides and fluorine-lanthanum complexes. S6. Drying pretreatment: Place the separated fluorine-adsorbed molded body in an environment of 105℃ for 24 hours to dry the moisture adhering to the surface of the molded body. S7. Firing and Recovery: The dried molded body is placed in an electric furnace and heated from room temperature to 200°C at a rate of 8°C / min, held for 1 hour to remove residual moisture, and then heated to 430°C at a rate of 5°C / min, held for 2.5 hours to decompose cellulose, yielding 28.5 kg of a mixed product containing high-purity alkaline earth metal fluorides and lanthanum fluoride LaF3; after nitric acid leaching, 1.5 kg of lanthanum fluoride (98% purity) and 27 kg of magnesium fluoride (98.5% purity) are separated, with a fluorine recovery rate of 94%. Magnesium fluoride can be directly used as a smelting flux.

[0035] Example 3: Treatment of intermittent, small-batch wastewater, specifically treatment of laboratory refrigerant decomposition wastewater: Wastewater characteristics: fluoride ion concentration 500 ppm, pH 4.5, single treatment capacity 0.5 m³ / day. 3 (Intermittent).

[0036] S1. Mixing and stirring process: Take 0.24 kg of CMF cellulose fiber with a bundle diameter of 1-3 μm, 9.7 kg of inorganic powder alkaline earth metal salt inorganic powder calcium hydroxide, 0.06 kg of lanthanum chloride hexahydrate, a compound of rare earth element lanthanum, and 5 L of deionized water according to the following mass proportions: First, dissolve lanthanum chloride hexahydrate in 50℃ warm water to accelerate dissolution and avoid clumping. Then, premix it with alkaline earth metal salt inorganic powder calcium hydroxide for 10 minutes to form a premix. Then add the cellulose fiber CMF and stir it with a three-roll mill at 200 r / min for 20 minutes until a uniform paste mixture is formed with a viscosity range of 50000-150000 mPa·s. S2. Molding process: The paste mixture obtained in S1 is formed into a thin film adsorbent molded body with a thickness of 1 mm by extrusion molding (100 mesh screen); S3. Drying process: The molded body obtained in S2 is placed in an atmospheric pressure environment for drying. The drying temperature is 80℃ and the drying time is controlled at 6 hours. After drying, the residual moisture content of the molded body is controlled at 12% to ensure water permeability and structural strength, and to avoid the decomposition of lanthanum compounds caused by high temperature. 10kg of finished product is obtained with a water permeability pore size of 20-30μm. S4. Adsorption and fluoride removal: The adsorbent is impregnated in the wastewater at a solid-liquid ratio of 1:50, with a stirring rate of 180 r / min and a reaction time of 45 minutes. Ultimately, the concentration of fluoride ions in the fluoride-containing wastewater is reduced to 2.5-3.8 mg / L, and the pH is simultaneously raised to 6.8-7.0. A single treatment takes 1.5 hours and is easy to operate. S5. Solid-liquid separation: The lanthanum-enhanced defluorinating agent that has completed fluorine adsorption and the treated water that meets the standards are separated into solid and liquid by passing them through a common quartz sand filter layer with a pore size of 100-200μm to obtain a fluorine-adsorbed molded body. The fluorine-adsorbed molded body contains insoluble alkaline earth metal fluorides and fluorine-lanthanum complexes. S6. Drying pretreatment: The separated fluorine-adsorbed molded body is placed in an environment of 110℃ and dried for 20 hours to remove the moisture adhering to the surface of the molded body. S7. Firing and Recycling: The dried molded body is placed in an electric furnace and heated from room temperature to 200°C at a rate of 8°C / min, held for 1 hour to remove residual moisture, and then heated to 420°C at a rate of 5°C / min, held for 2 hours to decompose cellulose, yielding 4.8 kg of a mixed product containing high-purity alkaline earth metal fluorides and lanthanum fluoride LaF3; after nitric acid leaching, 0.11 kg of lanthanum fluoride (purity 97.2%) and 4.69 kg of calcium fluoride (purity 98.3%) are separated, with a fluorine recovery rate of 93%, suitable for small-batch resource recycling.

[0037] The three embodiments cover fluoride-containing wastewater with different concentrations, pH values, and treatment modes. Through customized design of components and processes, the defluoridating agents all achieve a fluoride ion concentration of less than 5 mg / L, while simultaneously completing pH adjustment and resource recovery, verifying the universality and high efficiency of the technology of this invention.

[0038] The above embodiments are only some preferred embodiments of the present invention, and the present invention is not limited thereto. For researchers in the art, the present invention can have various modifications and variations. Any modifications, substitutions, improvements, etc., made within the essence and principles of the present invention should fall within the protection scope of the present invention.

Claims

1. A lanthanum-enhanced defluorinating agent, characterized in that: The lanthanum-enhanced defluorinating agent is prepared by mixing and drying 0.24-11.4 parts of binder, 9.7-40 parts of inorganic powder, and 0.06-0.8 parts of active ingredient in a specific mass ratio. The binder is cellulose fiber, which is one or more of the following: cellulose nanofibers (CNF) with a bundle diameter of less than 0.1 μm, cellulose microfibers (CMF) with a bundle diameter of 0.1-10 μm, and conventional cellulose fibers (CF) with a bundle diameter of 10-120 μm. The inorganic powder is an alkaline earth metal salt, which is one or more of the following: magnesium salt, calcium salt, strontium salt, barium salt, magnesium hydroxide, calcium hydroxide, calcium phosphate, and calcium carbonate. The active ingredient is a compound of the rare earth element lanthanum, which is one or more of the following: lanthanum chloride (LaCl3), lanthanum nitrate (La(NO3)3), and lanthanum oxide (La2O3). The mass percentage of the rare earth element lanthanum compound in the lanthanum-enhanced defluorinating agent is 1%-5%.

2. A method for producing the lanthanum-enhanced defluorinating agent according to claim 1, characterized in that, The specific steps are as follows: Step 1, Mixing and Stirring Process: S11. According to the mass ratio, take 0.24-11.4 parts of adhesive cellulose fiber, 9.7-40 parts of inorganic powder alkaline earth metal salt inorganic powder, 0.06-0.8 parts of active ingredient rare earth element lanthanum compound, and 5-28 parts of water. S12. First, dissolve the rare earth element lanthanum compound in warm water at 50-60℃ to accelerate dissolution and avoid clumping. Then, premix it with alkaline earth metal salt inorganic powder for 10-15 minutes to form a premix. Then, add cellulose fiber and stir it for 20-30 minutes using a mixer, kneader or three-roll mill until a uniform paste mixture is formed. The second step is the molding process: using mold forming, extrusion molding, or paper forming methods, the uniform paste mixture obtained in the first step is made into a cylindrical, film, or block-shaped molded body; among them, when extruding, a mold with a diameter of 5-10mm is used, and the length of the molded body is controlled to be 5-30mm. The third step is the drying process: the molded body obtained in the second step is placed in a vacuum or normal pressure environment for drying. The drying temperature is 40-160℃, and the vacuum degree in the vacuum environment is 10. 2 -10 5 Pa, after drying, the residual moisture content of the molded body is controlled at 5%-15% to ensure water permeability and structural strength, and to avoid the decomposition of lanthanum compounds caused by high temperature.

3. The method for producing a lanthanum-enhanced defluorinating agent according to claim 2, characterized in that, If dry conventional cellulose fiber (CF) is used in S12, water is added until the mixture reaches a state where it is "not sticky when pressed with a finger and can be rolled into strips without breaking"; if commercially available cellulose nanofibers (CNF) or cellulose microfibers (CMF) containing moisture are used, the moisture content is adjusted according to the viscosity of the mixture.

4. The method for producing a lanthanum-enhanced defluorinating agent according to claim 2, characterized in that, In the third step, the drying temperature is 60-120℃ and the vacuum degree is 10. 3 -10 4 Pa.

5. The application of the lanthanum-enhanced defluorinating agent according to claim 1 in the treatment of fluoride-containing wastewater, characterized in that, Fluorine-containing wastewater with a fluoride ion concentration of 10-1500 ppm is contacted with a lanthanum-enhanced defluorinating agent. The fluorine-containing wastewater can be from metal manufacturing, semiconductor pickling, refrigerant decomposition, or fluoropolymer production. The contact method involves either circulating the fluorine-containing wastewater through a lanthanum-enhanced defluorinating agent bed or immersing the wastewater in the lanthanum-enhanced defluorinating agent. During the contact process, the alkaline earth metal in the lanthanum-enhanced defluorinating agent reacts chemically with fluoride ions to form insoluble alkaline earth metal fluorides. Simultaneously, the active ingredient lanthanum compounds form stable lanthanum-fluoride complexes with fluoride ions. The lanthanum-fluoride complex is LaF3, and this dual action enhances the defluorination efficiency. The reaction temperature is 20-40℃, and the reaction time is 20-100 minutes, ultimately reducing the fluoride ion concentration in the fluorine-containing wastewater to below 5 mg / L.

6. A method for recovering the lanthanum-enhanced defluorination agent according to claim 1, characterized in that, Specifically, the following steps are included: S1. Solid-liquid separation: The lanthanum-enhanced defluorinating agent that has completed fluorine adsorption is separated from the treated water by filtration or natural sedimentation to obtain the fluorine-adsorbed molded body, which contains insoluble alkaline earth metal fluorides and lanthanum fluoride complexes. S2. Drying pretreatment: Place the separated fluorine-adsorbed molded body in an environment of 100-120℃ and dry for 20-28 hours to remove the moisture attached to the surface of the molded body. S3. Firing and Recycling: The dried molded body is placed in an electric furnace and fired at 400-450℃ for 1.5-2.5 hours to completely decompose and remove the cellulose fibers in the molded body, resulting in a mixed product containing high-purity alkaline earth metal fluorides and lanthanum fluoride LaF3; the purity of lanthanum fluoride in the mixed product is ≥97%, which can be used as a substitute material for fluorite, a raw material for optical glass or a raw material for rare earth functional materials, realizing the synergistic recovery of fluorine and rare earth elements.

7. The method for producing a lanthanum-enhanced defluorinating agent according to claim 2, characterized in that, In the second step, an 80-120 mesh screen is used for paper forming. The thickness of the formed film adsorbent is 0.5-2 mm, and the surface of the film has water-permeable pores with a diameter of 10-50 μm. The uniformity of the distribution of lanthanum compounds in the film is ≤3%, ensuring stable adsorption performance.

8. The application of the lanthanum-enhanced defluorinating agent according to claim 5 in the treatment of fluoride-containing wastewater, characterized in that, When the pH of fluoride-containing wastewater is 2-5, the alkaline earth metal salt inorganic powder in the lanthanum-enhanced defluorinating agent can simultaneously adjust the pH of the wastewater to 6-8 without the need for additional acid-base adjusters. Furthermore, within this pH range, the adsorption selectivity of rare earth element lanthanum compounds for fluoride ions is increased by 10%-15%, and their resistance to interference from other anions (such as Cl-) is enhanced. - and / or SO4 2- .

9. The method for recovering a lanthanum-enhanced defluorinating agent according to claim 6, characterized in that, The heating rate during the firing and recovery process is 5-10℃ / min to avoid cracking of the molded body due to excessive heating. After firing, X-ray diffraction analysis shows that there are no residual cellulose peaks in the mixed product, and the characteristic peak intensity of lanthanum fluoride is stable, ensuring the quality of the recovered product. The high-purity alkaline earth metal fluoride and lanthanum fluoride are leached with a 0.5-1mol / L nitric acid solution, and the stepwise recovery of the high-purity alkaline earth metal fluoride and lanthanum fluoride is achieved by utilizing the difference in solubility between the two.

10. A lanthanum-enhanced defluorinating agent according to claim 1, characterized in that, The lanthanum chloride LaCl3 is lanthanum chloride hexahydrate LaCl3・6H2O, and the lanthanum nitrate La(NO3)3 is lanthanum nitrate heptahydrate La(NO3)3・7H2O. Due to their good water solubility, strong compatibility with other raw materials, and the fact that they are not prone to generating volatile impurities during the drying process, the preparation stability and adsorption efficiency of the defluorinating agent can be further improved.

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