A flow electrode capacitive deionization treatment process suitable for fluorine-containing wastewater in a photovoltaic industry

Abstract

The application belongs to the technical field of industrial wastewater treatment, and discloses a flow electrode capacitive deionization treatment process suitable for fluorine-containing wastewater in a photovoltaic industry. The application uses SnO2 / AC composite material as a flow electrode in a selective adsorption stage, and through three-step regulation, realizes selective fluorine removal by using the specific chemical adsorption of SnO2 / AC electrodes on F ‑ in a 0.8-1V low-voltage stage, after strengthening the selectivity in a zero-pressure stage, realizes the strengthened removal of NO3 ‑ in a 1.2-1.4V high-voltage stage. Under the working condition of photovoltaic wastewater, F ‑ and NO3 ‑ can be effectively separated, and the fluorine removal efficiency is improved. The whole treatment process is simple to operate, does not need to add a large amount of chemical agents, has a small sludge yield, can realize the recycling of fluorine, and can be further applied to the treatment of fluorine-containing wastewater in the electronic, semiconductor, coal chemical and other industries, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a flow electrode capacitor deionization process suitable for fluoride-containing wastewater in the photovoltaic industry. Background Technology

[0002] In the photovoltaic industry, the production of polycrystalline silicon wafers typically involves texturing and etching processes using nitric acid and hydrofluoric acid, followed by rinsing with high-purity water. This generates a large amount of fluoride-containing wastewater. Typical characteristics of this type of wastewater include: pH 2-4, F... - Concentration 200~500 mg / L, NO3 - The concentration is 800-1500 mg / L, and the COD is 300-800 mg / L. This type of wastewater is characterized by high fluoride and nitrate levels and low COD. Fluoride and nitrate ions are the main pollutants, while the organic matter concentration is relatively low and its biodegradability is poor. According to the "Integrated Wastewater Discharge Standard" (GB8978-1996), the maximum allowable discharge concentration of fluoride in wastewater shall not exceed 10 mg / L. Therefore, fluoride-containing wastewater from the photovoltaic industry must be effectively treated before it can be discharged or reused.

[0003] Currently, the main methods for treating fluoride-containing wastewater include chemical precipitation, coagulation and sedimentation, adsorption, ion exchange, membrane separation, and capacitive deionization technology.

[0004] Chemical precipitation and coagulation sedimentation are currently the most commonly used defluoridation methods in the photovoltaic industry. These methods involve adding calcium salts (such as lime and calcium chloride) to wastewater to generate calcium fluoride precipitate, thus removing fluoride ions. However, the dosage of calcium salts required is large, typically 3 to 4 times the theoretical value, resulting in high treatment costs. Furthermore, the process generates large amounts of fluoride-containing sludge with complex composition, making disposal difficult and prone to secondary pollution. The effluent fluoride concentration from chemical precipitation alone is often insufficient to meet discharge standards.

[0005] Adsorption and ion exchange methods are suitable for the advanced treatment of medium- and low-concentration fluoride-containing wastewater. However, when treating low-concentration fluoride-containing wastewater, the adsorbent has a small adsorption capacity, insufficient mass transfer driving force, and limited selectivity.

[0006] Membrane separation methods (such as reverse osmosis and nanofiltration) have a stable defluorination effect, but the equipment investment and operating energy consumption are high, and membrane fouling is a prominent problem.

[0007] Capacitive deionization (CDI) technology purifies water by applying a low voltage between two porous electrodes, causing anions and cations in the solution to migrate towards the electrodes under electrostatic forces and be adsorbed into the electric double layer. Flow electrode capacitive deionization (FCDI) technology introduces a flow electrode and ion exchange membrane into traditional CDI, enabling continuous operation. In recent years, research has applied FCDI technology to fluoride removal from photovoltaic wastewater. However, when NO3...- When the concentration doubles, F - The removal rate decreased from 96.2% to 87.3%. This indicates that in photovoltaic wastewater NO3... - Concentration much higher than F - Under actual operating conditions, competitive adsorption has a more severe negative impact on defluorination efficiency. Summary of the Invention

[0008] The purpose of this invention is to provide a flow electrode capacitor deionization process suitable for fluoride-containing wastewater in the photovoltaic industry, which solves the problems of competitive adsorption interference of high-concentration nitrate ions on fluoride ions in existing photovoltaic fluoride-containing wastewater treatment processes, as well as high cost, large sludge volume, and difficulty in deep treatment of defluorination methods.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a flow electrode capacitor deionization treatment process for fluoride-containing wastewater in the photovoltaic industry, comprising the following steps: S1. Adjust the pH of the fluoride-containing wastewater from the photovoltaic industry to 6-9 and filter it to obtain pretreated wastewater; S2. The pretreated wastewater described in step S1 is fed into the dual-flow electrode capacitor deionization unit for ion removal to obtain effluent and the adsorbed dual-flow electrode. S3. Detect the effluent from step S2. When the F in the effluent... - <10mg / L and NO3 - If the concentration is <40 mg / L, discharge shall be carried out in compliance with standards; otherwise, the effluent shall be returned to step S2 for ion removal again. S4. The adsorbed dual-flow electrode described in step S2 is regenerated to obtain a regenerated dual-flow electrode and a regeneration solution; the regenerated dual-flow electrode is returned to the dual-flow electrode capacitor deionization unit in step S2; the regeneration solution is used for resource recovery. In step S2, the dual-flow electrode capacitive deionization unit includes a first flow electrode and a second flow electrode; the first flow electrode includes a mixture of SnO2 / activated carbon composite material, carbon black, and NaNO3 electrolyte solution; the second flow electrode includes a mixture of activated carbon, carbon black, and NaNO3 electrolyte solution. Step S2, the ion removal sequentially includes: selective adsorption stage, zero-pressure desorption stage, and enhanced desalination stage; There is no restriction on the order of steps S3 and S4.

[0010] Furthermore, in the processing technology, in the first flowing electrode, the mass ratio of SnO2 / activated carbon composite material to carbon black is 85~90:10~15, the concentration of NaNO3 electrolyte solution is 0.5~1g / L, and the sum of the masses of SnO2 / activated carbon composite material and carbon black is 0.75~1.5% of the mass fraction of NaNO3 electrolyte solution.

[0011] Furthermore, in the processing technology, in the second flowing electrode, the mass ratio of activated carbon to carbon black is 75~80:20~25, the concentration of NaNO3 electrolyte solution is 0.5~1g / L, and the sum of the masses of activated carbon and carbon black is 2~3% of the mass fraction of NaNO3 electrolyte solution.

[0012] Furthermore, in the aforementioned processing technology, step S2, the ion removal sequentially includes the following processes: (1) Select the adsorption stage: apply voltage of 0.8~1V, treatment time of 20~60min, influent flow rate of 15~25mL / min, and flow electrode flow rate of 30~60mL / min; (2) Zero-pressure desorption stage: The applied voltage is 0V, and the treatment time is 3~5min; (3) Enhanced desalination stage: Replace with the first flow electrode that is not adsorbed, apply a reverse voltage of 1.2~1.4V, process for 40~80min, influent flow rate of 15~25mL / min, and flow electrode flow rate of 30~60mL / min.

[0013] Furthermore, in the processing technology, the regeneration method in step S4 is as follows: applying a reverse voltage of 1.2~1.5V for a duration of 5~8min.

[0014] Furthermore, in the processing technology, when the removal efficiency of the regenerated dual-flow electrode in step S4 decreases by ≥15%, the regenerated dual-flow electrode is activated; the activation treatment includes: sequentially performing ultrasonic-assisted regeneration and alkaline washing.

[0015] Furthermore, in the processing technology, the ultrasonic frequency of the ultrasonic-assisted regeneration is 40~80kHz, and the ultrasonic time is 10~15min; the pH of the alkaline solution is 9~10, and the alkaline solution is NaOH solution or KOH solution; the number of washing cycles is 1~5 times.

[0016] Furthermore, in the processing technology, the preparation method of the SnO2 / activated carbon composite material includes the following steps: 1) The activated carbon is subjected to acid activation treatment to obtain pretreated activated carbon; 2) Pretreated activated carbon, SnO2 nanoparticles and organic solvent are mixed and subjected to ultrasonic treatment to obtain loaded activated carbon; 3) Under a protective atmosphere, the loaded activated carbon is calcined to obtain a SnO2 / activated carbon composite material.

[0017] Furthermore, in the processing technology, the specific surface area of ​​the activated carbon in the SnO2 / activated carbon composite material is independently ≥1500m², which is different from that of the activated carbon in the second flowing electrode. 2 / g.

[0018] Furthermore, in the treatment process, the detection in step S3 also includes: detecting the pH of the effluent; if the pH is between 6 and 9, the effluent is discharged in compliance with standards; otherwise, the pH of the effluent is adjusted to between 6 and 9 before being discharged in compliance with standards.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, SnO2 / activated carbon composite material (SnO2 / AC) is used as the anolyte flow electrode in the selective adsorption stage. SnO2 has a high affinity for F - It has specific chemical adsorption capabilities and forms Sn-F bonds through ligand exchange reactions. Compared with existing FCDI defluorination materials such as Al2O3 / AC, SnO2 / AC has both higher chemical adsorption selectivity and better conductivity, and its preparation process is simple and low cost.

[0020] (2) This invention utilizes a three-step voltage regulation scheme to control F in the low voltage stage of 0.8~1V using SnO2 / AC electrodes. - The specific chemical adsorption achieves selective fluoride removal, and after further enhancing selectivity in the zero-pressure stage, NO3 is removed in the high-voltage stage of 1.2~1.4V. - Enhanced removal. Compared to the traditional constant voltage FCDI mode (1.2V throughout), under photovoltaic wastewater conditions, it can remove F... - NO3 - Effective separation, thereby improving defluorination efficiency.

[0021] (3) This invention combines reverse voltage regeneration with ultrasonic-assisted activation through gradient activation and regeneration, which effectively extends the service life of the electrode. The introduction of the ultrasonic field allows the flow electrode to accommodate more activated carbon without clogging, and combined with alkaline flushing, ensures the long-term stable operation of the system.

[0022] (4) The entire treatment process of this invention is simple to operate, requires no large amount of chemical reagents, produces little sludge, and can realize the resource recovery of fluoride, thus significantly reducing treatment costs. It is not only applicable to fluoride-containing wastewater in the photovoltaic industry, but can also be applied to the treatment of fluoride-containing wastewater in other industries such as electronics, semiconductors, and coal chemicals by changing the type of electrolyte according to the ions that need to be separated in the wastewater, and has broad application prospects. Detailed Implementation

[0023] This invention provides a flow electrode capacitor deionization treatment process for fluoride-containing wastewater in the photovoltaic industry, comprising the following steps: S1. Adjust the pH of the fluoride-containing wastewater from the photovoltaic industry to 6-9 and filter it to obtain pretreated wastewater; S2. The pretreated wastewater described in step S1 is fed into the dual-flow electrode capacitor deionization unit for ion removal to obtain effluent and the adsorbed dual-flow electrode. S3. Detect the effluent from step S2. When the F in the effluent... - <10mg / L and NO3 - If the concentration is <40 mg / L, discharge shall be carried out in compliance with standards; otherwise, the effluent shall be returned to step S2 for ion removal again. S4. The adsorbed dual-flow electrode described in step S2 is regenerated to obtain a regenerated dual-flow electrode and a regeneration solution; the regenerated dual-flow electrode is returned to the dual-flow electrode capacitor deionization unit in step S2; the regeneration solution is used for resource recovery. In step S2, the dual-flow electrode capacitive deionization unit includes a first flow electrode and a second flow electrode; the first flow electrode includes a mixture of SnO2 / activated carbon composite material, carbon black, and NaNO3 electrolyte solution; the second flow electrode includes a mixture of activated carbon, carbon black, and NaNO3 electrolyte solution. Step S2, the ion removal sequentially includes: selective adsorption stage, zero-pressure desorption stage, and enhanced desalination stage; There is no restriction on the order of steps S3 and S4.

[0024] In this invention, the fluoride-containing wastewater from the photovoltaic industry described in step S1 has a pH of 2-4 and a fluoride content of... - Concentration 200~500 mg / L, NO3 - The concentration should be 800~1500 mg / L, and the COD should be 300~800 mg / L. There are no specific restrictions on the source of fluoride-containing wastewater from the photovoltaic industry; as long as it originates from photovoltaic-related industries and meets the above water quality conditions, it is acceptable.

[0025] In this invention, the reagent used to adjust the pH to 6-9 in step S1 is not limited; any inorganic base well-known in the art can be used, provided that no impurities are introduced. Specifically, in this embodiment, NaOH solution is used to adjust the pH of fluoride-containing wastewater from the photovoltaic industry.

[0026] In this invention, the pH of step S1 is preferably 6.5 to 7.5, and more preferably 7.

[0027] The filtration described in step S1 is not specifically limited; any sand filter or microfiltration well-known in the art can be used to remove suspended solids and particulate impurities.

[0028] In this invention, the preparation method of the SnO2 / activated carbon composite material preferably includes the following steps: 1) The activated carbon is subjected to acid activation treatment to obtain pretreated activated carbon; 2) Pretreated activated carbon, SnO2 nanoparticles and organic solvent are mixed and subjected to ultrasonic treatment to obtain loaded activated carbon; 3) Under a protective atmosphere, the supported activated carbon is calcined to obtain a SnO2 / activated carbon composite material. The conditions for preparing the SnO2 / activated carbon composite material and the source of the SnO2 nanoparticles are not specifically limited; well-known methods or commercially available products can be used. The particle size of the SnO2 nanoparticles is 5~20 nm.

[0029] In this invention, the specific surface area of ​​the activated carbon in the SnO2 / activated carbon composite material is preferably ≥1500m², independent of that of the activated carbon in the second flow electrode. 2 / g.

[0030] In this invention, the particle size of the SnO2 / activated carbon composite material is preferably 10~50 μm. The method for obtaining this particle size is not limited; grinding followed by sieving, a method well-known in the art, is sufficient.

[0031] In this invention, the mass ratio of SnO2 / activated carbon composite material to carbon black in the first flow electrode is preferably 85~90:10~15, more preferably 87~89:11~13, and even more preferably 88:12. The concentration of the NaNO3 electrolyte solution is preferably 0.5~1 g / L, more preferably 0.7~0.9 g / L, and even more preferably 0.8 g / L; The sum of the mass of the SnO2 / activated carbon composite material and carbon black is preferably 0.75 to 1.5% of the mass fraction of the NaNO3 electrolyte solution, more preferably 1 to 1.2%, and even more preferably 1%.

[0032] In this invention, the mass ratio of activated carbon to carbon black in the second flow electrode is preferably 75~80:20~25, more preferably 77~79:21~23, and even more preferably 78:22; The concentration of the NaNO3 electrolyte solution is preferably 0.5~1 g / L, more preferably 0.7~0.9 g / L, and even more preferably 0.8 g / L; The sum of the masses of activated carbon and carbon black is preferably 2-3% of the mass fraction of the NaNO3 electrolyte solution, more preferably 2-2.5%, and even more preferably 2%.

[0033] In this invention, the mixing conditions for the first and second flowing electrodes during preparation are independent, including: a mixing speed preferably of 300-500 rpm, more preferably 350-450 rpm, and even more preferably 400 rpm; and a mixing time preferably of 24-72 h, more preferably 36-60 h, and even more preferably 48 h. Uniform mixing is achieved separately.

[0034] In this invention, the ion removal in step S2 sequentially includes the following processes: (1) Selection of adsorption stage: The applied voltage is preferably 0.8~1V, more preferably 0.8~0.9V, and more preferably 0.8V; the treatment time is preferably 20~60min, more preferably 40~60min, and more preferably 60min; the influent flow rate is preferably 15~25mL / min, more preferably 15~20mL / min, and more preferably 15mL / min; the flow electrode flow rate is preferably 30~60mL / min, more preferably 30~45mL / min, and more preferably 30mL / min; (2) Zero-pressure desorption stage: The applied voltage is preferably 0V; the processing time is preferably 3~5min, more preferably 4~5min, and even more preferably 5min; (3) Enhanced desalination stage: Replace with a non-adsorbed first flow electrode; the applied reverse voltage is preferably 1.2~1.4V, more preferably 1.2~1.3V, and more preferably 1.2V; the treatment time is preferably 40~80min, more preferably 60~80min, and more preferably 80min; the influent flow rate is preferably 15~25mL / min, more preferably 15~20mL / min, and more preferably 15mL / min; the flow electrode flow rate is preferably 30~60mL / min, more preferably 30~45mL / min, and more preferably 30mL / min.

[0035] During the selective adsorption stage, the electric driving force is mild, the first flow electrode is the anode, and the second flow electrode is the cathode. -NO3- is selectively captured via specific chemisorption on the SnO2 / AC electrode surface. During the zero-pressure desorption stage, the electric double layer on the electrode surface is reconstructed, and NO3-, which has weaker adsorption capacity, is captured. - Competition ions preferentially desorb and return to the solution, while chemisorbed F - The strong Sn-F bond is preserved. During the enhanced desalination stage, a reverse electric field is applied, with the first flow electrode as the cathode and the second flow electrode as the anode. This strengthens the electric field driving force, thus reducing NO3-. - Under the influence of a strong reverse electric field, it accelerates towards the second flow electrode and is adsorbed by the flow electrode.

[0036] In this invention, during the enhanced desalination stage, the method of replacing the first flow electrode with an unadsorbed first flow electrode includes: re-injecting the unadsorbed first flow electrode; or, connecting a second dual flow electrode capacitor deionization unit in series, wherein the second dual flow electrode capacitor deionization unit also includes an unadsorbed first flow electrode and an unadsorbed second flow electrode.

[0037] In this invention, the detection in step S3 further includes: detecting the pH of the effluent; if the pH is between 6 and 9, the effluent is discharged in compliance with standards; otherwise, the pH of the effluent is adjusted to between 6 and 9 before being discharged in compliance with standards. The reagent used to adjust the pH to between 6 and 9 is not limited; any inorganic acid or inorganic base well-known in the art, or a reagent with minimal environmental harm, such as nitric acid or NaOH, can be used.

[0038] In this invention, the regeneration method in step S4 is as follows: applying a reverse voltage preferably 1.2~1.5V, more preferably 1.2~1.3V, and more preferably 1.2V; the duration is preferably 5~8min, more preferably 6~8min, and more preferably 8min.

[0039] In this invention, when the removal efficiency of the regenerated dual-flow electrode in step S4 decreases by ≥15%, the regenerated dual-flow electrode is activated. A removal efficiency decrease of ≥15% means that after the regenerated dual-flow electrode is reused in the dual-flow electrode capacitor deionization unit of step S2, its removal efficiency for F... - Or NO3 - The removal efficiency is reduced by ≥15% compared to the first use of the dual-flow electrode; The activation process includes sequential ultrasonic-assisted regeneration and alkaline washing. The ultrasonic frequency of the ultrasonic-assisted regeneration is preferably 40~80kHz, more preferably 50~70kHz, and even more preferably 60kHz; the ultrasonic time is preferably 10~15min, more preferably 11~13min, and even more preferably 12min. The pH of the alkaline solution is preferably 9-10, more preferably 9.5; the alkaline solution is preferably NaOH solution or KOH solution, more preferably NaOH solution; the number of washing cycles is preferably 1-5 times, more preferably 2-4 times, and more preferably 3 times.

[0040] In this invention, the regenerated dual-flow electrode described in step S4 and the regenerated dual-flow electrode after activation treatment are returned to step S2 as the first flow electrode or the second flow electrode.

[0041] In this invention, the regenerated liquid in step S4 includes F. - Desorption liquid and NO3 - Desorption solution. The F - The desorption solution is further recycled for resource recovery, such as the preparation of products like calcium fluoride or cryolite. The NO3... - The desorption solution can be further recycled to produce nitrate products, or subjected to harmless treatment.

[0042] Unless otherwise stated, other parameters and conditions in the processing technology of this invention are not limited, and methods well known in the art can be used.

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0044] The wastewater treated in the examples and comparative cases was fluoride-containing wastewater generated by a photovoltaic company. The influent water quality was: pH=3.2, F - Concentration 350 mg / L, NO3 - Concentration 1200 mg / L, COD 600 mg / L.

[0045] The activated carbon used in Preparation Examples 1-2, Examples 1-3, and Comparative Examples 1-5 was purchased from Xiamen Aote Electronic Technology Co., Ltd. It was high-efficiency coconut shell activated carbon YP-50F with a specific surface area of ​​1600 m². 2 / g; Carbon black was purchased from Tianjin Youmeng Chemical Technology Co., Ltd., conductive carbon black.

[0046] Preparation Example 1

[0047] Preparation of SnO2 / AC composite materials: Coconut shell activated carbon was stirred in 1 mol / L HNO3 at 80℃ for 4 h, washed with water until neutral, and dried to obtain pretreated activated carbon. 10g of pretreated activated carbon, 0.8g of SnO2 nanoparticles with a particle size of 5-20nm, and 150mL of anhydrous ethanol were mixed, ultrasonically dispersed for 30min, filtered, dried at 80℃, calcined at 400℃ for 2h under N2 atmosphere, and ground and sieved to obtain SnO2 / AC composite material with a particle size of 10-50μm.

[0048] Preparation Example 2

[0049] Preparation of Al2O3 / AC composite materials: The SnO2 nanoparticles in Preparation Example 1 were replaced with an equal amount of nano-Al2O3, and the other methods were the same as in Preparation Example 1. The Al2O3 / AC composite material with a particle size of 10~50μm was obtained by grinding and sieving.

[0050] Example 1

[0051] This embodiment provides a flow electrode capacitor deionization treatment process suitable for fluoride-containing wastewater in the photovoltaic industry, including the following steps: S1. Adjust the pH of the wastewater to 7.0 with 1 mol / L NaOH solution, and then filter it through a sand filter to obtain pretreated wastewater; S2, First flow electrode: The SnO2 / AC composite material of Preparation Example 1 was mixed with carbon black at a mass ratio of 90:10 and added to a NaNO3 electrolyte solution with a concentration of 1 g / L. The total mass fraction of solids was 1.2%. The mixture was stirred at 400 rpm for 48 h to obtain a uniform slurry. Second flow electrode: Activated carbon and carbon black are mixed at a mass ratio of 80:20 and added to a 1 g / L NaNO3 solution, with a total solid mass fraction of 2.5%, and stirred at 400 rpm for 48 h; Ion removal procedure: (1) Selective adsorption stage: The first flow electrode is connected to the positive electrode, the second flow electrode is connected to the negative electrode, the applied voltage is 0.9V, the treatment time is 40min, the influent flow rate is 20mL / min, and the flow rate of the flow electrode is 45mL / min; (2) Zero-pressure desorption stage: The voltage is adjusted to 0V and maintained for 4 minutes, while keeping the influent and flow electrode flow rates constant; (3) Enhanced desalination stage: Discharge the first flow electrode that has been adsorbed and re-inject the first flow electrode that has not been adsorbed; apply a reverse voltage of 1.3V (the first flow electrode is connected to the negative electrode and the second flow electrode is connected to the positive electrode), the treatment time is 60min, the influent flow rate is 20mL / min, and the flow electrode flow rate is 45mL / min. S3, F in water - 2.5 mg / L, NO3 - 18mg / L, COD 120mg / L, pH 7.2, F - With NO3 -All emissions meet standards and can be discharged directly. S4. Select the first flow electrode after the adsorption stage (adsorption F) - ) and the second flow electrode after the enhanced desalination stage (adsorbing NO3) - Reverse voltage regeneration was performed separately: 1.3V was applied for 6 minutes, and F was collected separately. - Desorption liquid and NO3 - Desorption solution; F - In the desorption solution: F - 1820 mg / L, NO3 - 25 mg / L; NO3 - In the desorption solution: NO3 - 3450mg / L, F - 8 mg / L; The two desorption solutions exhibit low cross-contamination and excellent separation performance.

[0052] Example 2

[0053] This embodiment provides a flow electrode capacitor deionization treatment process suitable for fluoride-containing wastewater in the photovoltaic industry, including the following steps: S1. Adjust the pH of the wastewater to 7.5 with 1 mol / L NaOH solution, and then filter it through a sand filter to obtain pretreated wastewater; S2, First flow electrode: The SnO2 / AC composite material of Preparation Example 1 was mixed with carbon black at a mass ratio of 85:15 and added to a NaNO3 electrolyte solution with a concentration of 0.5 g / L. The total mass fraction of solids was 1.5%. The mixture was stirred at 300 rpm for 72 h to obtain a uniform slurry. Second flow electrode: Activated carbon and carbon black are mixed at a mass ratio of 75:25, added to a 0.5 g / L NaNO3 solution, with a total solid mass fraction of 3%, and stirred at 300 rpm for 72 h; Ion removal procedure: (1) Select the adsorption stage: the first flow electrode is connected to the positive electrode, the second flow electrode is connected to the negative electrode, the applied voltage is 1.0V, the treatment time is 20min, the influent flow rate is 25mL / min, and the flow rate of the flow electrode is 60mL / min; (2) Zero-pressure desorption stage: The voltage is adjusted to 0V and maintained for 3 minutes, while keeping the influent and flow electrode flow rates constant; (3) Enhanced desalination stage: Discharge the first flow electrode that has been adsorbed and re-inject the first flow electrode that has not been adsorbed; apply a reverse voltage of 1.4V (the first flow electrode is connected to the negative electrode and the second flow electrode is connected to the positive electrode), the treatment time is 40min, the influent flow rate is 25mL / min, and the flow electrode flow rate is 60mL / min. S3, F in water- 4.8 mg / L, NO3 - 28mg / L, COD 90mg / L, pH 7.5, F - With NO3 - All emissions meet standards and can be discharged directly. S4. Select the first flow electrode after the adsorption stage (adsorption F) - ) and the second flow electrode after the enhanced desalination stage (adsorbing NO3) - Reverse voltage regeneration was performed separately: 1.5V was applied for 5 minutes, and F was collected separately. - Desorption liquid and NO3 - Desorption solution; F - In the desorption solution: F - 1680 mg / L, NO3 - 32 mg / L; NO3 - In the desorption solution: NO3 - 2960mg / L, F - 12 mg / L; The two desorption solutions exhibit low cross-contamination and excellent separation performance.

[0054] Example 3

[0055] This embodiment provides a flow electrode capacitor deionization treatment process suitable for fluoride-containing wastewater in the photovoltaic industry, including the following steps: S1. Adjust the pH of the wastewater to 6.5 with 1 mol / L NaOH solution, and then filter it through a sand filter to obtain pretreated wastewater; S2, First flow electrode: The SnO2 / AC composite material of Preparation Example 1 was mixed with carbon black at a mass ratio of 88:12 and added to a NaNO3 electrolyte solution with a concentration of 0.8 g / L. The total mass fraction of solids was 1.0%. The mixture was stirred at 500 rpm for 24 h to obtain a uniform slurry. Second flow electrode: Activated carbon and carbon black are mixed at a mass ratio of 78:22, added to a 0.8 g / L NaNO3 solution, with a total solid mass fraction of 2%, and stirred at 500 rpm for 24 h; Ion removal procedure: (1) Select the adsorption stage: the first flow electrode is connected to the positive electrode, the second flow electrode is connected to the negative electrode, the applied voltage is 0.8V, the treatment time is 60min, the influent flow rate is 15mL / min, and the flow rate of the flow electrode is 30mL / min; (2) Zero-pressure desorption stage: Adjust the voltage to 0V and continue for 5 minutes, keeping the influent and flow electrode flow rates constant; (3) Enhanced desalination stage: Discharge the first flow electrode that has been adsorbed and re-inject the first flow electrode that has not been adsorbed; apply a reverse voltage of 1.2V (the first flow electrode is connected to the negative electrode and the second flow electrode is connected to the positive electrode), the treatment time is 80min, the influent flow rate is 15mL / min, and the flow electrode flow rate is 30mL / min. S3, F in water - 1.2 mg / L, NO3 - 12mg / L, COD 75mg / L, pH 7.0, F - With NO3 - All emissions meet standards and can be discharged directly. S4. Select the first flow electrode after the adsorption stage (adsorption F) - ) and the second flow electrode after the enhanced desalination stage (adsorbing NO3) - Reverse voltage regeneration was performed separately: 1.2V was applied for 8 minutes, and F was collected separately. - Desorption liquid and NO3 - Desorption solution; After seven cycles, the removal efficiency of the regenerated first and second flow electrodes decreased by 16%. Ultrasonic-assisted regeneration and alkaline washing were performed. The ultrasonic frequency was 60 kHz, and the ultrasonic treatment lasted for 10 min. The electrodes were then rinsed four times with NaOH solution at pH 9. F - In the desorption solution: F - 2050 mg / L, NO3 - 18 mg / L; NO3 - In the desorption solution: NO3 - 3780mg / L, F - 5 mg / L; The two desorption solutions exhibit low cross-contamination and excellent separation performance.

[0056] Comparative Example 1

[0057] The difference between Comparative Example 1 and Example 1 is as follows: In step S2, both the first and second flow electrodes are the second flow electrodes of Example 1; the ion removal program in step S2 is as follows: constant pressure 1.2V adsorption for 40 min → 0V zero pressure for 4 min → discharge of the adsorbed first flow electrode, constant pressure 1.2V adsorption for 60 min; The effluent from step S3 is: F - 18.5 mg / L, NO3 - 43mg / L, COD 155mg / L, pH 7.1; Step S4 F - In the desorption solution: F -1470 mg / L, NO3 - 2620 mg / L; NO3 - In the desorption solution: NO3 - 3430mg / L, F - 210 mg / L; poor separation effect.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 1 is as follows: In step S2, both the first flow electrode and the second flow electrode are the second flow electrodes of Example 1; The effluent from step S3 is: F - 20mg / L, NO3 - 32mg / L, COD 158mg / L, pH 7.2; Step S4 F - In the desorption solution: F - 1320 mg / L, NO3 - 1850 mg / L; NO3 - In the desorption solution: NO3 - 3650mg / L, F - 275 mg / L; poor separation effect.

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 1 is as follows: The ion removal program in step S2 is as follows: constant pressure 1.2V adsorption for 40 min → 0V zero pressure for 4 min → discharge of the adsorbed first flow electrode, and positive constant pressure 1.2V adsorption for 60 min; The effluent from step S3 is: F - 4.2 mg / L, NO3 - 57mg / L, COD 128mg / L, pH 7.0; Step S4 F - In the desorption solution: F - 1920 mg / L, NO3 - 230 mg / L; NO3 - In the desorption solution: NO3 - 2950mg / L, F - 145 mg / L; lack of reverse voltage-driven NO3 - Directed migration, relying solely on double-layer adsorption, NO3 - The residue was too high, and the separation effect was poor.

[0062] Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 1 is as follows: In step S2, the ion removal program removes 0V zero voltage for 4 minutes; The effluent from step S3 is: F - 3.5 mg / L, NO3 - 48mg / L, COD 105mg / L, pH 7.3; Step S4 F - In the desorption solution: F - 2150 mg / L, NO3 - 85 mg / L; NO3 - In the desorption solution: NO3 - 3310 mg / L, F - 365 mg / L; lacking zero-pressure pre-desorption, NO3 - Incomplete removal and NO3 - Desorption solution contains F - Significantly increased.

[0064] Comparative Example 5

[0065] The difference between Comparative Example 5 and Example 1 is as follows: In step S2, the SnO2 / AC composite material of Preparation Example 1 is replaced with the Al2O3 / AC composite material of Preparation Example 2 in the first flow electrode. The effluent from step S3 is: F - 11 mg / L, NO3 - 34mg / L, COD 142mg / L, pH 7.1; Step S4 F - In the desorption solution: F - 1520 mg / L, NO3 - 870 mg / L; NO3 - In the desorption solution: NO3 - 2970mg / L, F - 195 mg / L; Al2O3 against F - The chemical bonding force is weaker than that of SnO2, and the F in the zero-pressure stage - Partial desorption, separation effect and effluent compliance are not as good as SnO2 / AC.

[0066] Based on the influent water quality of the fluoride-containing wastewater, calculate the Fo of Examples 1-3 and Comparative Examples 1-5. - and NO3 - The removal rate was calculated, and the impurities in the desorbate were statistically analyzed. The results are shown in Table 1.

[0067] Table 1. Comparison of removal rates and impurity ions in Examples 1-3 and Comparative Examples 1-5

[0068] As can be seen from the examples, comparative examples, and the results in Table 1, the embodiments of the present invention achieve F through the synergistic effect of the SnO2 / AC composite electrode material and the three-stage process of selective adsorption-zero pressure desorption-enhanced desalination. - NO3 - It achieves efficient separation and removal of pollutants and meets emission standards, while the cross-contamination of the regenerated liquid is extremely low, and the separation effect is significantly better than all comparative examples.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flow electrode capacitor deionization treatment process suitable for fluoride-containing wastewater in the photovoltaic industry, characterized in that, Includes the following steps: S1. Adjust the pH of the fluoride-containing wastewater from the photovoltaic industry to 6-9 and filter it to obtain pretreated wastewater; S2. The pretreated wastewater described in step S1 is fed into the dual-flow electrode capacitor deionization unit for ion removal to obtain effluent and the adsorbed dual-flow electrode. S3. Detect the effluent from step S2. When the F in the effluent... - <10mg / L and NO3 - When the concentration is <40mg / L, emissions must meet the standards. Otherwise, the effluent return step S2 will perform ion removal again; S4. The adsorbed dual-flow electrode described in step S2 is regenerated to obtain a regenerated dual-flow electrode and a regeneration solution; the regenerated dual-flow electrode is returned to the dual-flow electrode capacitor deionization unit in step S2; the regeneration solution is used for resource recovery. In step S2, the dual-flow electrode capacitive deionization unit includes a first flow electrode and a second flow electrode; the first flow electrode includes a mixture of SnO2 / activated carbon composite material, carbon black, and NaNO3 electrolyte solution; the second flow electrode includes a mixture of activated carbon, carbon black, and NaNO3 electrolyte solution. Step S2, the ion removal sequentially includes: selective adsorption stage, zero-pressure desorption stage, and enhanced desalination stage; There is no restriction on the order of steps S3 and S4.

2. The processing technology according to claim 1, characterized in that, In the first flowing electrode, the mass ratio of SnO2 / activated carbon composite material to carbon black is 85~90:10~15, the concentration of NaNO3 electrolyte solution is 0.5~1g / L, and the sum of the masses of SnO2 / activated carbon composite material and carbon black is 0.75~1.5% of the mass fraction of NaNO3 electrolyte solution.

3. The processing technology according to claim 1 or 2, characterized in that, In the second flow electrode, the mass ratio of activated carbon to carbon black is 75~80:20~25, the concentration of NaNO3 electrolyte solution is 0.5~1g / L, and the sum of the masses of activated carbon and carbon black is 2~3% of the mass fraction of NaNO3 electrolyte solution.

4. The processing technology according to claim 3, characterized in that, The ion removal in step S2 is sequential The process includes the following: (1) Select the adsorption stage: apply voltage of 0.8~1V, treatment time of 20~60min, influent flow rate of 15~25mL / min, and flow electrode flow rate of 30~60mL / min; (2) Zero-pressure desorption stage: The applied voltage is 0V, and the treatment time is 3~5min; (3) Enhanced desalination stage: Replace with the first flow electrode that is not adsorbed, apply a reverse voltage of 1.2~1.4V, process for 40~80min, influent flow rate of 15~25mL / min, and flow electrode flow rate of 30~60mL / min.

5. The processing technology according to claim 1, characterized in that, The regeneration method described in step S4 is as follows: apply a reverse voltage of 1.2~1.5V for a duration of 5~8 minutes.

6. The processing method according to claim 1 or 5, characterized in that, When the removal efficiency of the regenerated dual-flow electrode decreases by ≥15% in step S4, the regenerated dual-flow electrode is activated; the activation process includes: sequential ultrasonic-assisted regeneration and alkaline washing.

7. The processing technology according to claim 6, characterized in that, The ultrasonic frequency for the ultrasonic-assisted regeneration is 40-80 kHz, and the ultrasonic time is 10-15 min; the pH of the alkaline solution is 9-10, and the alkaline solution is a NaOH solution or a KOH solution; the number of washing cycles is 1-5.

8. The processing technology according to claim 1 or 2, characterized in that, The preparation method of the SnO2 / activated carbon composite material includes the following steps: 1) The activated carbon is subjected to acid activation treatment to obtain pretreated activated carbon; 2) Pretreated activated carbon, SnO2 nanoparticles and organic solvent are mixed and subjected to ultrasonic treatment to obtain loaded activated carbon; 3) Under a protective atmosphere, the loaded activated carbon is calcined to obtain a SnO2 / activated carbon composite material.

9. The processing technology according to claim 8, characterized in that, The specific surface area of ​​the activated carbon in the SnO2 / activated carbon composite material is ≥1500m², which is independent of the specific surface area of ​​the activated carbon in the second flow electrode. 2 / g.

10. The processing method according to claim 1, characterized in that, The detection in step S3 further includes: detecting the pH of the effluent; if the pH is between 6 and 9, the effluent is discharged in compliance with standards; otherwise, the pH of the effluent is adjusted to between 6 and 9 before being discharged in compliance with standards.

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