Method for deep treatment and resource utilization of fluorine-containing wastewater

Abstract

The application discloses a kind of fluorine-containing wastewater advanced treatment resource utilization method, belong to wastewater treatment technical field, method includes the following steps: S1, fluorine-containing wastewater is introduced into reaction tank, adjusts pH value to be 4-6, adds activated seed to reaction tank and stirs 10-15min before adding precipitant, stirs under 30-40 DEG C and reacts 45-60min, then wastewater in reaction tank is introduced into sedimentation tank and carries out solid-liquid separation, sediment is dehydrated, dried, grinds, obtains cryolite product;Liquid is primary wastewater;S2, modified lanthanum class hydrotalcite is added to primary wastewater, stirs 3-5h under room temperature, then, solid-liquid separation is carried out after 12h, and the treatment step is completed, the whole process of the application has the advantages of simple operation, high processing efficiency, low running cost etc., both solves the problem of fluorine resource waste in traditional treatment method, and also guarantees the environmental safety of wastewater discharge through deep purification technology.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for the deep treatment and resource utilization of fluoride-containing wastewater. Background Technology

[0002] Industries such as metal smelting, electrolytic aluminum, fluorochemicals, fertilizers, pesticides, semiconductors, and photovoltaics discharge fluoride-containing wastewater with concentrations ranging from tens to tens of thousands of milligrams per liter during production processes. Direct discharge of this type of wastewater not only causes serious pollution to water bodies and soil but may also accumulate through the food chain, harming the ecological environment and human health. Therefore, its treatment has always been a key challenge in industrial wastewater management.

[0003] Currently, chemical precipitation is the most widely used method for treating fluoride-containing wastewater. This method involves adding calcium salts (such as calcium chloride and calcium hydroxide) to precipitate fluoride ions into calcium fluoride. It has the advantages of simple operation and low cost. However, the large amount of sludge produced is mainly composed of calcium fluoride. If it is only treated as solid waste, it will waste fluoride resources and increase the cost of solid waste treatment.

[0004] To achieve the recovery and utilization of fluoride resources, researchers have proposed a method for recovering fluoride ions in the form of cryolite (Na3AlF6). Cryolite, an important chemical raw material, is widely used in electrolytic aluminum fluxing agents, glass and enamel opacifiers, and other fields. Its solubility in water is extremely low. Theoretically, by adding sodium and aluminum salts to fluoride-containing wastewater, fluoride ions can precipitate out as cryolite, thus reducing the fluoride concentration in the wastewater and achieving the resource recovery of fluoride. However, the existing cryolite recovery process has a fluoride removal efficiency of only about 80%, which is relatively low, indicating significant room for optimization. Summary of the Invention

[0005] This invention provides a method for the deep treatment and resource utilization of fluoride-containing wastewater, which can solve the problem of low defluorination efficiency in the existing technology of treating fluoride-containing wastewater by cryolite recovery.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for the deep treatment and resource utilization of fluoride-containing wastewater includes the following steps:

[0008] S1. Introduce fluoride-containing wastewater into a reaction tank, adjust the pH to 4-6, add activated seed crystals to the reaction tank and stir for 10-15 minutes, then add precipitant, stir and react at 30-40℃ for 45-60 minutes, then introduce the wastewater from the reaction tank into a sedimentation tank for solid-liquid separation. The precipitate is dehydrated, dried and ground to obtain cryolite product; the liquid is primary wastewater.

[0009] S2. Add modified lanthanum-based hydrotalcite to the primary wastewater, stir at room temperature for 3-5 hours, let stand for 12 hours, and then separate the solid and liquid to complete the treatment step.

[0010] Furthermore, in S1, the precipitant is sodium chloride and sodium aluminate, the pH adjuster is sodium hydroxide, the molar ratio of F, Al, and Na in the reaction tank is controlled to be 6:1:3, and the amount of activated seed crystals added is 0.8-1.2 times the mass of sodium aluminate.

[0011] Furthermore, the activated seed crystal is plasma-treated cryolite.

[0012] Furthermore, the ratio of primary wastewater to modified lanthanum-based hydrotalcite is 1L:15-25mg.

[0013] Furthermore, the activated seed crystals are prepared through the following steps:

[0014] Cryolite is treated in a low-temperature plasma treatment instrument for 3-5 minutes. The frequency of the low-temperature plasma treatment instrument is 40-70kHz, the power is 50-80W, the pressure is 35-50Pa, and the atmosphere is oxygen. The plasma treatment increases the specific surface area of ​​the cryolite and introduces oxygen-containing groups on its surface. These groups can become more active crystal growth sites, promote the combination of fluoride ions, aluminum ions, and sodium ions, promote the crystallization process, help form cryolite with larger particle size, and achieve higher defluorination efficiency.

[0015] Furthermore, the raw materials for preparing the modified lanthanum-based hydrotalcite include the following components: itaconic acid-intercalated lanthanum-based hydrotalcite, allyl thiourea, and azobisisobutyronitrile.

[0016] Furthermore, the method for preparing the modified lanthanum-based hydrotalcite is as follows:

[0017] Itaconic acid-intercalated lanthanum-based hydrotalcite was added to anhydrous ethanol and stirred until homogeneous. Allyl thiourea was then added and the mixture was stirred and heated to 70-80°C. Azobisisobutyronitrile was then added and the reaction was maintained at this temperature for 12 hours. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain modified lanthanum-based hydrotalcite.

[0018] Under the initiation of azobisisobutyronitrile, itaconic acid-intercalated lanthanum-based hydrotalcite undergoes a polymerization reaction with allyl thiourea, introducing thiourea groups onto the surface of itaconic acid-intercalated lanthanum-based hydrotalcite to obtain modified lanthanum-based hydrotalcite.

[0019] Furthermore, the mass ratio of itaconic acid intercalated lanthanum hydrotalcite, allyl thiourea, and azobisisobutyronitrile is 10:1.5-3:0.01-0.03.

[0020] Furthermore, the itaconic acid-intercalated lanthanum-based hydrotalcite is prepared through the following steps:

[0021] Aluminum nitrate solution, zinc nitrate solution, and lanthanum nitrate solution were mixed evenly to obtain a nitrate solution. The nitrate solution was heated to 80°C, and then sodium hydroxide solution and sodium bicarbonate solution were added dropwise to the nitrate solution simultaneously. After the addition was complete, itaconic acid ethanol solution was added dropwise. After the addition was complete, the reaction was kept at the temperature for 24 hours. After the reaction was completed, the mixture was transferred to a high-pressure reactor for hydrothermal reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain itaconic acid intercalated lanthanum-based hydrotalcite.

[0022] Using aluminum nitrate, zinc nitrate, and lanthanum nitrate as metal ion sources and itaconic acid as an intercalating agent, itaconic acid-intercalated lanthanum-based layered double hydroxides were synthesized via co-precipitation-hydrothermal treatment. Through intercalation, itaconic acid forms covalent bonds with cations on the surface of the layered double hydroxide, which on the one hand expands the interlayer spacing of the layered double hydroxide. The increased interlayer spacing is beneficial to improving the contact area between the layered double hydroxide and wastewater, thereby exerting a good adsorption effect. On the other hand, carboxyl groups and unsaturated double bonds are introduced on the surface of the layered double hydroxide, laying the foundation for subsequent modification.

[0023] Furthermore, the hydrothermal reaction temperature is 175-185℃, and the hydrothermal reaction time is 8-16h.

[0024] Furthermore, the mass ratio of aluminum nitrate, zinc nitrate, lanthanum nitrate, sodium hydroxide, sodium bicarbonate, and itaconic acid is 18.76:49.09:2.86-3.57:17.6:9.24:7.0-7.5.

[0025] Furthermore, the dropping rate ratio of sodium hydroxide solution to sodium bicarbonate solution is 1.5:1.

[0026] The beneficial effects of this invention are:

[0027] 1. The method for deep treatment and resource utilization of fluoride-containing wastewater provided by this invention achieves efficient recovery of fluoride resources and compliant discharge of wastewater through a two-step synergistic process of "precipitation recovery + deep purification". In the first step, aluminum and sodium salts are added as precipitants to address the high fluoride ion concentration in the wastewater. These precipitants react with fluoride ions to form cryolite. After separation, a certain amount of fluoride ions remain in the wastewater, which is then purified by using modified lanthanum-based hydrotalcite as an adsorbent. The modified lanthanum-based hydrotalcite, through surface modification and interlayer structure optimization, significantly enhances its selective adsorption capacity for low-concentration fluoride ions. The entire process is characterized by simple operation, high treatment efficiency, and low operating costs. It solves the problem of fluoride resource waste in traditional treatment methods and ensures environmental safety of wastewater discharge through deep purification technology, providing a solution for the comprehensive treatment of fluoride-containing wastewater that combines economic and ecological benefits.

[0028] 2. In the cryolite precipitation process of this invention, activated seed crystals are introduced to provide growth sites for the deposition and crystallization of solute molecules, promoting the directional nucleation of solute molecules on the crystal surface, thereby reducing the energy barrier for the solution-to-solid phase transition. The activated seed crystals are plasma-treated cryolite, which achieves dual optimization through plasma treatment: on the one hand, it significantly increases the specific surface area, enhancing the physical carrier capacity for crystal growth; on the other hand, it introduces a large number of oxygen-containing groups on the surface. These groups serve as highly active crystal growth sites, efficiently adsorbing and promoting the directional binding of fluoride ions, aluminum ions, and sodium ions. These effects collectively accelerate the crystallization process, not only facilitating the formation of larger cryolite crystals but also significantly improving the defluorination efficiency.

[0029] 3. This invention employs modified lanthanum-based layered double hydroxides (LDHs) as a deep adsorbent for fluoride-containing wastewater. Its superior adsorption performance stems from the synergistic effect of multiple mechanisms, exhibiting significant advantages in the adsorption of fluoride and chloride ions. Specifically, the interlayer anions of the modified lanthanum-based LDH can undergo ion exchange reactions with fluoride and chloride ions in the wastewater, achieving rapid capture of target ions through dynamic adjustment of the interlayer structure. Simultaneously, the abundant lanthanum ions in its crystal lattice can form stable coordination bonds with fluoride and chloride ions, significantly enhancing adsorption selectivity and binding strength through chemical coordination. Furthermore, the amino, thiourea structures, and carboxyl groups of the modified lanthanum-based LDH can adsorb fluoride and chloride ions through hydrogen bonding or electrostatic attraction. This synergistic effect of ion exchange, chemical coordination, and surface functional group interactions enables the modified lanthanum-based LDH to achieve highly efficient removal of fluoride and chloride ions in fluoride-containing wastewater systems while maintaining excellent adsorption capacity and stability, significantly outperforming traditional adsorbent materials. Detailed Implementation

[0030] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0032] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0035] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0036] Preparation Example 1

[0037] This preparation example provides a modified lanthanum-based hydrotalcite, prepared by the following method:

[0038] 10g of itaconic acid-intercalated lanthanum-based hydrotalcite was added to 100mL of anhydrous ethanol and stirred until homogeneous. Then, 1.5g of allyl thiourea was added and the mixture was stirred and heated to 70℃. 0.01g of azobisisobutyronitrile was added and the mixture was kept at this temperature for 12h. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain modified lanthanum-based hydrotalcite.

[0039] The itaconic acid-intercalated lanthanum-based hydrotalcite is prepared through the following steps:

[0040] 18.76 g of aluminum nitrate was dissolved in 180 mL of deionized water to obtain an aluminum nitrate solution. 49.09 g of zinc nitrate was dissolved in 400 mL of deionized water to obtain a zinc nitrate solution. 2.86 g of lanthanum nitrate was dissolved in 30 mL of deionized water to obtain a lanthanum nitrate solution. The aluminum nitrate, zinc nitrate, and lanthanum nitrate solutions were mixed thoroughly to obtain a nitrate solution. The nitrate solution was heated to 80 °C. Then, sodium hydroxide and sodium bicarbonate solutions were added dropwise simultaneously. After the addition was complete, itaconic acid ethanol solution and sodium hydroxide were added dropwise. The solution consisted of 17.6 g sodium hydroxide and 150 mL deionized water, the sodium bicarbonate solution consisted of 9.24 g sodium bicarbonate and 100 mL deionized water, and the itaconic acid ethanol solution consisted of 7.0 g itaconic acid and 70 mL anhydrous ethanol. The sodium hydroxide was added at a rate of 3 drops per second, and the sodium bicarbonate solution was added at a rate of 2 drops per second. After the addition was complete, the mixture was kept at a constant temperature for 24 h. After the reaction was completed, the mixture was transferred to a high-pressure reactor for hydrothermal reaction at 175 °C for 16 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain itaconic acid-intercalated lanthanum-based hydrotalcite.

[0041] Preparation Example 2

[0042] This preparation example provides a modified lanthanum-based hydrotalcite, prepared by the following method:

[0043] 10g of itaconic acid-intercalated lanthanum-based hydrotalcite was added to 100mL of anhydrous ethanol and stirred until homogeneous. Then, 2g of allyl thiourea was added and the mixture was stirred and heated to 75℃. 0.02g of azobisisobutyronitrile was added and the mixture was kept at this temperature for 12h. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain modified lanthanum-based hydrotalcite.

[0044] The itaconic acid-intercalated lanthanum-based hydrotalcite is prepared through the following steps:

[0045] 18.76 g of aluminum nitrate was dissolved in 180 mL of deionized water to obtain an aluminum nitrate solution. 49.09 g of zinc nitrate was dissolved in 400 mL of deionized water to obtain a zinc nitrate solution. 3.0 g of lanthanum nitrate was dissolved in 30 mL of deionized water to obtain a lanthanum nitrate solution. The aluminum nitrate, zinc nitrate, and lanthanum nitrate solutions were mixed thoroughly to obtain a nitrate solution. The nitrate solution was heated to 80 °C. Then, sodium hydroxide and sodium bicarbonate solutions were added dropwise simultaneously. After the addition was complete, itaconic acid ethanol solution and sodium hydroxide were added dropwise. The solution consisted of 17.6 g sodium hydroxide and 150 mL deionized water, the sodium bicarbonate solution consisted of 9.24 g sodium bicarbonate and 100 mL deionized water, and the itaconic acid ethanol solution consisted of 7.3 g itaconic acid and 70 mL anhydrous ethanol. The sodium hydroxide was added at a rate of 3 drops per second, and the sodium bicarbonate solution was added at a rate of 2 drops per second. After the addition was complete, the mixture was kept at a constant temperature for 24 h. After the reaction was completed, the mixture was transferred to a high-pressure reactor for hydrothermal reaction at 180 °C for 10 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain itaconic acid-intercalated lanthanum-based hydrotalcite.

[0046] Preparation Example 3

[0047] This preparation example provides a modified lanthanum-based hydrotalcite, prepared by the following method:

[0048] 10g of itaconic acid-intercalated lanthanum-based hydrotalcite was added to 100mL of anhydrous ethanol and stirred until homogeneous. Then, 3g of allyl thiourea was added and the mixture was stirred and heated to 80℃. 0.03g of azobisisobutyronitrile was added and the mixture was kept at this temperature for 12h. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain modified lanthanum-based hydrotalcite.

[0049] The itaconic acid-intercalated lanthanum-based hydrotalcite is prepared through the following steps:

[0050] 18.76 g of aluminum nitrate was dissolved in 180 mL of deionized water to obtain an aluminum nitrate solution. 49.09 g of zinc nitrate was dissolved in 400 mL of deionized water to obtain a zinc nitrate solution. 3.57 g of lanthanum nitrate was dissolved in 30 mL of deionized water to obtain a lanthanum nitrate solution. The aluminum nitrate, zinc nitrate, and lanthanum nitrate solutions were mixed thoroughly to obtain a nitrate solution. The nitrate solution was heated to 80 °C. Then, sodium hydroxide and sodium bicarbonate solutions were added dropwise simultaneously. After the addition was complete, itaconic acid ethanol solution was added dropwise. The sodium solution consisted of 17.6 g sodium hydroxide and 150 mL deionized water, the sodium bicarbonate solution consisted of 9.24 g sodium bicarbonate and 100 mL deionized water, and the itaconic acid ethanol solution consisted of 7.5 g itaconic acid and 70 mL anhydrous ethanol. The sodium hydroxide was added at a rate of 3 drops per second, and the sodium bicarbonate solution was added at a rate of 2 drops per second. After the addition was complete, the mixture was kept at a constant temperature for 24 h. After the reaction was completed, the mixture was transferred to a high-pressure reactor for hydrothermal reaction at 185 °C for 8 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain itaconic acid-intercalated lanthanum-based hydrotalcite.

[0051] Compare with Example 1

[0052] This comparative example provides a modified lanthanum-based hydrotalcite, prepared by the following method:

[0053] 10g of itaconic acid-intercalated lanthanum-based hydrotalcite was added to 100mL of anhydrous ethanol and stirred until homogeneous. Then, 1.5g of allyl thiourea was added, and the mixture was stirred and heated to 70℃. The reaction was maintained at this temperature for 12h. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain modified lanthanum-based hydrotalcite.

[0054] Compare with Example 2

[0055] This comparative example is an itaconic acid-intercalated lanthanum-based hydrotalcite, and the preparation process of the itaconic acid-intercalated lanthanum-based hydrotalcite is the same as that of Preparation Example 1.

[0056] Example 1

[0057] A method for the deep treatment and resource utilization of fluoride-containing wastewater includes the following steps:

[0058] S1. Fluorine-containing wastewater is introduced into a reaction tank, and the pH is adjusted to 4 with sodium hydroxide. Activated seed crystals are added to the reaction tank and stirred for 10 minutes, followed by the addition of sodium chloride and sodium aluminate. The molar ratio of F, Al, and Na in the reaction tank is controlled at 6:1:3, and the amount of activated seed crystals added is 0.8 times the mass of sodium aluminate. The reaction is stirred at 30°C for 45 minutes. The wastewater in the reaction tank is then introduced into a sedimentation tank and allowed to stand for 2 hours. Solid-liquid separation is then performed. The precipitate is dehydrated, dried, and ground to obtain cryolite product; the liquid is primary wastewater.

[0059] S2. Add the modified lanthanum-based hydrotalcite from Preparation Example 1 to the primary wastewater. The ratio of primary wastewater to modified lanthanum-based hydrotalcite is 1L:15mg. Stir at room temperature for 3 hours, then let stand for 12 hours to separate the solid and liquid. The liquid is the water to be discharged, thus completing the treatment step.

[0060] The activated seed crystals are prepared through the following steps:

[0061] Cryolite (commercial cryolite, particle size 5-15um) was placed in a low-temperature plasma treatment instrument for 3 minutes. The low-temperature plasma treatment instrument had a frequency of 40kHz, a power of 50W, a pressure of 35Pa, and an oxygen atmosphere.

[0062] Example 2

[0063] A method for the deep treatment and resource utilization of fluoride-containing wastewater includes the following steps:

[0064] S1. Fluorine-containing wastewater is introduced into a reaction tank. The pH is adjusted to 5 with sodium hydroxide. Activated seed crystals are added to the reaction tank and stirred for 12 minutes. Then, sodium chloride and sodium aluminate are added. The molar ratio of F, Al, and Na in the reaction tank is controlled to be 6:1:3. The amount of activated seed crystals added is 1.0 times the mass of sodium aluminate. The reaction is stirred at 35°C for 50 minutes. The wastewater in the reaction tank is introduced into a sedimentation tank and allowed to stand for 3 hours. After solid-liquid separation, the precipitate is dehydrated, dried, and ground to obtain cryolite product. The liquid is primary wastewater.

[0065] S2. Add the modified lanthanum-based hydrotalcite from Preparation Example 1 to the primary wastewater. The ratio of primary wastewater to modified lanthanum-based hydrotalcite is 1L:20mg. Stir at room temperature for 4 hours, then let stand for 12 hours to separate the solid and liquid. The liquid is the water to be discharged, thus completing the treatment step.

[0066] The steps for preparing the activated seed crystals are the same as in Example 1.

[0067] Example 3

[0068] A method for the deep treatment and resource utilization of fluoride-containing wastewater includes the following steps:

[0069] S1. Fluorine-containing wastewater is introduced into a reaction tank, and the pH is adjusted to 6 with sodium hydroxide. Activated seed crystals are added to the reaction tank and stirred for 15 minutes, followed by the addition of sodium chloride and sodium aluminate. The molar ratio of F, Al, and Na in the reaction tank is controlled at 6:1:3, and the amount of activated seed crystals added is 1.2 times the mass of sodium aluminate. The reaction is stirred at 40°C for 60 minutes. The wastewater in the reaction tank is then introduced into a sedimentation tank and allowed to stand for 4 hours. Solid-liquid separation is then performed. The precipitate is dehydrated, dried, and ground to obtain cryolite product; the liquid is primary wastewater.

[0070] S2. Add the modified lanthanum-based hydrotalcite from Preparation Example 1 to the primary wastewater. The ratio of primary wastewater to modified lanthanum-based hydrotalcite is 1L:25mg. Stir at room temperature for 5 hours, then let stand for 12 hours to separate the solid and liquid. The liquid is the water to be discharged, thus completing the treatment step.

[0071] The steps for preparing the activated seed crystals are the same as in Example 1.

[0072] Example 4

[0073] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the modified lanthanum-based hydrotalcite in Example 1 is replaced with an equal mass of the product obtained in Preparation Example 2.

[0074] Example 5

[0075] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the modified lanthanum-based hydrotalcite in Example 1 is replaced with an equal mass of the product obtained in Preparation Example 3.

[0076] Example 6

[0077] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the activated seed preparation step is different. In this example, the activated seed is prepared through the following steps:

[0078] Cryolite (commercial cryolite, particle size 5-15um) was placed in a low-temperature plasma treatment instrument for 4 minutes. The low-temperature plasma treatment instrument had a frequency of 60kHz, a power of 70W, a pressure of 40Pa, and an oxygen atmosphere.

[0079] Example 7

[0080] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the activated seed preparation step is different. In this example, the activated seed is prepared through the following steps:

[0081] Cryolite (commercial cryolite, particle size 5-15um) was placed in a low-temperature plasma treatment instrument for 5 minutes. The low-temperature plasma treatment instrument had a frequency of 70kHz, a power of 80W, a pressure of 50Pa, and an oxygen atmosphere.

[0082] Example 8

[0083] A method for the deep treatment and resource utilization of fluoride-containing wastewater, compared with Example 3, differs in that the activated seed preparation step is different. In this example, the activated seed is prepared through the following steps:

[0084] Cryolite (commercial cryolite, particle size 5-15um) was placed in a low-temperature plasma treatment instrument for 4 minutes. The low-temperature plasma treatment instrument had a frequency of 60kHz, a power of 70W, a pressure of 40Pa, and an oxygen atmosphere.

[0085] Comparative Example 1

[0086] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the modified lanthanum-based hydrotalcite in Example 1 is replaced with the product obtained from Control Example 1 of equal mass.

[0087] Comparative Example 2

[0088] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the modified lanthanum-based hydrotalcite in Example 1 is replaced with the product obtained from Control Example 2 of equal mass.

[0089] Comparative Example 3

[0090] A method for the deep treatment and resource utilization of fluoride-containing wastewater, which differs from Example 1 in that the activated seed crystals in Example 1 are replaced with cryolite of equal mass (commercial cryolite, particle size 5-15um).

[0091] The resource utilization method for deep treatment of fluoride-containing wastewater provided in Examples 1-8 and Comparative Examples 1-3 was used to treat fluoride-containing wastewater generated by a photovoltaic industry in Anhui Province. The wastewater quality was as follows: pH 1.46, fluoride ion content 3265 mg / L, and chloride ion content 3500 mg / L. The particle size distribution of the precipitate obtained in step S1 was measured using a Malvern laser particle size analyzer. The fluoride ion concentration in the primary wastewater was detected. The fluoride and chloride ion contents of the liquid after solid-liquid separation in step S2 were also detected. The results are shown in Table 1.

[0092] Table 1

[0093]

[0094] As can be seen from the data recorded in Table 1, the average particle size of the precipitate obtained by the deep treatment and resource utilization method S1 for fluoride-containing wastewater provided in Examples 1-3 is 95.2-102.4 μm, the fluoride ion concentration in the primary wastewater is 417.8-454.3 mg / L, the fluoride ion concentration in the effluent to be discharged is 1.2-1.8 mg / L, and the chloride ion concentration in the effluent to be discharged is 134.2-156.4 mg / L, which meets the discharge standards. Among them, Example 3 has the best treatment effect.

[0095] The experimental results of Examples 1, 4 and 5 show that the modified lanthanum-based hydrotalcite provided in Preparation Examples 1, 2 and 3 have similar treatment effects on primary wastewater.

[0096] The experimental results of Examples 1, 6 and 7, and Examples 3 and 8 show that the particle size of cryolite precipitates induced by activated crystals obtained with different low-temperature plasma parameters is different, and the removal effect of fluoride ions in primary wastewater is also different.

[0097] The experimental results from Example 1, Comparative Example 1 and Comparative Example 2 show that the adsorbent material obtained by chemically bonding allyl thiourea with itaconic acid intercalated lanthanum-based hydrotalcite has a better adsorption effect on fluoride and chloride ions in wastewater.

[0098] The experimental results of Example 1 and Comparative Example 3 show that, compared with using untreated cryolite as seed crystals, the average particle size of the precipitate obtained by using activated seed crystals is larger, and the fluoride ion content in the primary wastewater is lower. This indicates that the application of activated seed crystals can obtain cryolite precipitates with larger average particle size, which are easier to dehydrate and thus obtain high-quality cryolite products, thereby playing a higher role in fluoride removal.

[0099] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for the deep treatment and resource utilization of fluoride-containing wastewater, characterized in that, Includes the following steps: S1. Introduce fluoride-containing wastewater into a reaction tank, adjust the pH to 4-6, add activated seed crystals to the reaction tank and stir for 10-15 minutes, then add precipitant, stir and react at 30-40℃ for 45-60 minutes, then introduce the wastewater from the reaction tank into a sedimentation tank for solid-liquid separation. The precipitate is dehydrated, dried and ground to obtain cryolite product; the liquid is primary wastewater. S2. Add modified lanthanum-based hydrotalcite to the primary wastewater, stir at room temperature for 3-5 hours, let stand for 12 hours, and then separate the solid and liquid to complete the treatment step. The activated seed crystal is plasma-treated cryolite; The precipitant in S1 is sodium chloride and sodium aluminate; The method for preparing the modified lanthanum-based hydrotalcite is as follows: Itaconic acid-intercalated lanthanum-based hydrotalcite was added to anhydrous ethanol and stirred until homogeneous. Allyl thiourea was then added and the mixture was stirred and heated to 70-80℃. Azobisisobutyronitrile was then added and the reaction was maintained at this temperature for 12 hours. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain modified lanthanum-based hydrotalcite. The itaconic acid-intercalated lanthanum-based hydrotalcite is prepared through the following steps: Aluminum nitrate solution, zinc nitrate solution, and lanthanum nitrate solution were mixed evenly to obtain a nitrate solution. The nitrate solution was heated to 80°C, and then sodium hydroxide solution and sodium bicarbonate solution were added dropwise to the nitrate solution simultaneously. After the addition was complete, itaconic acid ethanol solution was added dropwise. After the addition was complete, the reaction was kept at the temperature for 24 hours. After the reaction was completed, the mixture was transferred to a high-pressure reactor for hydrothermal reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain itaconic acid intercalated lanthanum-based hydrotalcite.

2. The method for deep treatment and resource utilization of fluoride-containing wastewater according to claim 1, characterized in that, The pH adjuster is sodium hydroxide, and the molar ratio of F, Al, and Na in the reaction tank is controlled at 6:1:

3. The amount of activated seed crystals added is 0.8-1.2 times the mass of sodium aluminate.

3. The method for deep treatment and resource utilization of fluoride-containing wastewater according to claim 1, characterized in that, The dosage ratio of primary wastewater to modified lanthanum-based hydrotalcite is 1L:15-25mg.

4. The method for deep treatment and resource utilization of fluoride-containing wastewater according to claim 1, characterized in that, The activated seed crystals are prepared through the following steps: Place the cryolite in a low-temperature plasma treatment instrument for 3-5 minutes. The frequency of the low-temperature plasma treatment instrument is 40-70kHz, the power is 50-80W, the pressure is 35-50Pa, and the atmosphere is oxygen.

5. The method for deep treatment and resource utilization of fluoride-containing wastewater according to claim 1, characterized in that, The mass ratio of itaconic acid intercalated lanthanum hydrotalcite, allyl thiourea, and azobisisobutyronitrile is 10:1.5-3:0.01-0.

03.

6. The method for deep treatment and resource utilization of fluoride-containing wastewater according to claim 1, characterized in that, The hydrothermal reaction temperature is 175-185℃, and the hydrothermal reaction time is 8-16h.

7. The method for deep treatment and resource utilization of fluoride-containing wastewater according to claim 1, characterized in that, The mass ratio of aluminum nitrate, zinc nitrate, lanthanum nitrate, sodium hydroxide, sodium bicarbonate, and itaconic acid is 18.76:49.09:2.86-3.57:17.6:9.24:7.0-7.5.

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