Advanced treatment method for organic fluoride wastewater in electronic industry

Abstract

The invention discloses an advanced treatment method of organic fluoride wastewater in the electronic industry, which adopts a three-dimensional electrochemical process and a fluorine ion adsorbent to realize treatment of high-concentration organic fluoride-containing wastewater under low dosage (small dosage of the fluorine ion adsorbent), and can stably ensure that the concentration of fluoride in effluent is reduced to 1.0 mg / L or below. And therefore, the problem of up-to-standard discharge of the high-organic fluorine-containing wastewater in the electronic industry is fundamentally solved.

Description

TECHNICAL FIELD

[0001] The application relates to a deep treatment method for organic fluorine compound wastewater in the electronic industry. BACKGROUND

[0002] The rapid growth of the electronic industry leads to a sharp increase in the consumption of chemical drugs such as organic solvents, inorganic acids and bases, among which fluorine-containing compounds are important raw materials indispensable to the electronic industry due to their excellent performance. For example, hydrogen fluoride (HF) and ammonium fluoride (NH4F) are used to remove oxides on the surface of silicon and as etching agents to etch silicon or other materials in important processes such as pickling and wet etching. At the same time, perfluorinated compounds (PFCs) and perfluoropolyether (PFPE) are used as lubricants, cleaning agents or heat transfer media in the production process of electronic products. The above applications will result in a large amount of inorganic fluorine compounds and organic fluorine compounds in industrial wastewater.

[0003] The existing fluorine-containing wastewater in the electronic industry often adopts a multi-stage chemical precipitation technology, that is, calcium fluoride, aluminum fluoride and other precipitates are generated to remove free fluoride ions in the wastewater, but this method has a low removal rate of organic fluorine compounds such as PFCs in the water body and cannot meet the increasingly stringent emission index requirements. The existing electro-catalytic oxidation method can effectively destroy the C-F bond, but on the one hand, it cannot realize efficient mineralization of organic fluorine, and on the other hand, it will produce free fluoride ions to cause secondary pollution, so that the total fluorine concentration of the effluent cannot be stably reduced to below 1.0 mg / L. SUMMARY

[0004] The purpose of the application is to provide a deep treatment method for organic fluorine compound wastewater in the electronic industry, which can realize efficient mineralization of organic fluorine and synchronous adsorption and fixation of released fluoride ions, so that the fluorine concentration of the organic fluorine compound wastewater effluent can be stably reduced to below 1 mg / L.

[0005] Technical scheme: The deep treatment method for organic fluorine compound wastewater in the electronic industry provided by the application comprises the following steps: (1) The fluorine-containing wastewater in the electronic industry is sent to a homogenizing adjustment tank I to uniformly adjust the water quality and adjust the pH of the wastewater to 2-5 (the influent pH is controlled at 2-5 to improve the oxidation efficiency (more hydroxyl radicals are generated) and protect the electrode, because the active of the anode coating PbO2 is higher in an acidic environment and is easily passivated in an alkaline environment); the reaction time is 15-20 min (the hydraulic retention time is 15-20 min), and the pH, organic fluorine compound concentration and fluoride ion concentration of the wastewater are monitored during the process; (2) The effluent from the homogenization and conditioning tank I was sent to the three-dimensional electrochemical reactor. The anode of the three-dimensional electrochemical reactor was Ti / PbO2-graphene & Gd, the cathode was stainless steel, the particle electrode was Ni-Co / GBC, the applied voltage was set to 9.0 V, the electrolyte solution was 0.05 mol / L NaCl solution, the aeration rate of the external aeration pump was 1.5~2 L / min, and the reaction lasted for 40~60 min. On the one hand, the particle electrode Ni-Co / GBC can capture and attach organic fluoride molecules in the wastewater to its surface through physical and electro-adsorption (the huge specific surface area and rich pore structure of the particle electrode can capture and attach organic fluoride molecules in the wastewater to its surface through intermolecular forces (van der Waals forces), providing a high concentration of reactants for the subsequent catalytic oxidation reaction. On the other hand, the organic fluoride adsorbed on the surface of the particle electrode is reacted with the highly oxidizing ·OH and O2 generated by the electrode. - • Strong oxidizing substances are oxidized into small molecules and fluoride ions, which are then desorbed from the granular electrode. (After the original large-molecule organic fluoride is oxidized into small-molecule products (especially hydrophilic inorganic fluoride ions), the adsorption force between them and the granular electrode is greatly weakened, thus desorbing from the surface of the granular electrode and re-entering the water body.) As organic fluoride is continuously adsorbed, oxidized, and desorbed, the granular electrode continuously undergoes an adsorption-electrochemical regeneration cycle. (On the one hand, the granular electrode acts as an adsorbent, which can quickly adsorb and enrich organic fluoride. On the other hand, the free radicals generated by electrochemistry react with organic fluoride, decomposing it into small molecules (free fluoride). The small molecules desorb from the granular electrode, freeing up adsorption sites, and the granular electrode can then adsorb new organic fluoride in the water, and so on.) (3) Send the effluent from the three-dimensional electrochemical reactor to the homogenization and equalization tank II to homogenize the water quality and react for 15-20 min (hydraulic retention 15-30 min). Monitor the concentration of organic fluoride and fluoride ions in the wastewater. If the concentration of organic fluoride is greater than 0.5 mg / L, send the effluent back into the three-dimensional electrochemical reactor for electrocatalytic oxidation of organic fluoride again. If the concentration of organic fluoride is less than 0.5 mg / L, send the effluent into the adsorption tank. (4) Fluoride ion adsorbent is added to the adsorption tank and the pH of the wastewater in the adsorption tank is adjusted to weakly acidic (pH 6~7). Because the surface of the adsorbent carries a positive charge in this pH range, the fluoride ions can generate a strong interaction with the positively charged adsorbent. The adsorption is carried out for 40~60 min (hydraulic retention time 40~60 min) under rapid stirring (the average stirring speed is 20 r / min~70 r / min to allow the adsorbent and fluoride ions to react fully and accelerate the reaction efficiency). (5) Send the effluent from the adsorption tank to the flocculation tank, add PAM to it, and stir slowly (the average stirring speed is 5 r / min to 10 r / min. Slow stirring provides a gentle collision opportunity, which is conducive to the growth of flocs, while avoiding excessive shear force that will break the flocs that have been formed). React for 5 to 10 minutes (hydraulic retention 5 to 10 minutes). (6) Send the effluent from the flocculation tank to the sedimentation tank and monitor the fluoride ion concentration of the supernatant in the sedimentation tank. If the fluoride ion concentration is less than 1 mg / L, send the effluent to the next unit. If the fluoride ion concentration is greater than 1 mg / L, return the supernatant to the adsorption tank.

[0006] In step (2), the three-dimensional electrochemical reactor is a vertical flow continuous flow reactor. The main body consists of an inlet chamber, an electrochemical chamber, and an outlet chamber from bottom to top, and the chambers are separated by a porous insulating plate (made of plastic). The electrochemical chamber is equipped with a cathode, an anode, and a particle electrode filled in the electrochemical chamber. The cathode is set around the inert wall of the electrochemical chamber, the anode is located in the center of the electrochemical chamber, and the particle electrode is filled in the electrochemical chamber. The three-dimensional electrochemical reactor also includes a microporous aeration disc. The microporous aeration disc is set at the bottom of the electrochemical chamber and is supplied with air by an air pump. By aeration, the turbulence of the water body can be increased, thereby increasing the contact area between the particle electrode and the organic fluoride, thus accelerating the degradation reaction process. It can also effectively prevent the particle electrode from accumulating at the bottom, causing a current short circuit (the voltage between the anode (center) and the cathode (peripheral wall) is applied to the entire reaction chamber. If the conductive particles accumulated at the bottom contact the anode and the cathode at the same time, a low-resistance conductive bridge will be established between them, causing most of the current to not pass through the solution and the effective electrode interface, but directly through the particle short circuit). The anode is connected to the positive terminal of a DC regulated constant current power supply, and the cathode is connected to the negative terminal of the same power supply. After the three-dimensional electrochemical reactor is energized, a closed loop is formed: positive electrode-electrolyte-particle electrode-electrolyte-negative electrode. A large amount of effective current, i.e., reaction current, is generated within this closed loop. During this process, a series of electrochemical reactions occur at the main electrode, catalyzing the generation of highly oxidizing substances such as hydroxyl radicals and superoxide radicals, leading to the electrochemical oxidation and degradation of organofluorine compounds. Simultaneously, the particle electrodes filling the spaces between the main electrodes are polarized by an external electric field, forming a large number of charged bipolar microelectrodes. One side of each particle electrode is considered the anode, and the other side the cathode. Each particle can independently function as an electrolytic cell, catalyzing the generation of various types of strong oxidants to oxidize and decompose organofluorine compounds, similar to the surface of the main electrode.

[0007] The anode Ti / PbO2-graphene & Gd comprises a Ti matrix and a PbO2 layer doped with graphene and rare earth metal Cd supported on the Ti matrix. The preparation principle is as follows: in an acidic Pb-containing environment... 2+ Graphene oxide (GO) and Gd 3+In the electrodeposition solution, a pretreated solid titanium rod was used as the anode, and a constant current was applied. Pb deposition occurred on the anode surface. 2+ Electrochemical oxidation to PbO2 deposition, simultaneously, negatively charged GO sheets and Gd 3+ Under the influence of an electric field, the particles migrate to the anode surface and are embedded or adsorbed into the growing PbO2 lattice, forming a uniform composite coating.

[0008] It is prepared using the following method: (1.1) Pretreatment of titanium rod substrate: Solid titanium rods were mechanically polished, degreased by alkaline washing (10wt.% NaOH, 80℃, 30 min), activated by etching (boiling 10wt.% oxalic acid solution, 2 h, to increase micro-roughness) and washed with water. After washing with water, the rods were immediately stored in ethanol to prevent re-oxidation. (1.2) Preparation of electrodeposition solution: Prepare a mixed solution containing 0.3~0.5 M Pb(NO3)2 and 0.1~0.2 M Cu(NO3)2, adjust the pH of the mixed solution to 1.0~2.0 with HNO3, add graphene oxide to make the graphene oxide concentration 50~80 mg / L, sonicate for 30~60 min, and then add Gd(NO3)3 to make the concentration 0.5~2.0 mmol / L to form the electrodeposition solution; (1.3) Constant current electrodeposition: A three-electrode system was used, with a titanium rod as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode; during electrodeposition, the current density was 10~20 mA / cm². 2 The plating solution temperature is 65±5℃, the deposition time is 90~120 min, and the stirring speed of the electrodeposition solution is greater than 500 rpm to ensure uniform mass transfer and deposition. (1.4) Post-treatment: After deposition, the substrate was rinsed with deionized water and dried in an oven at 80°C for 1 hour to obtain a titanium substrate coated with a PbO2 layer doped with graphene and rare earth metal Cd.

[0009] Compared to conventional Ti / PbO2 electrodes, Ti / PbO2-graphene & Gd electrodes have a denser and smoother surface. Graphene sheets themselves possess extremely high mechanical strength and toughness. When PbO2 is deposited on and around the graphene surface, the graphene acts as a microscopic "steel mesh," supporting and connecting the PbO2 grains, filling voids, and effectively preventing microcracks and pores caused by internal stress or uneven growth. This results in a dense and smooth coating, effectively solving the problem of severe cavitation on the electrode surface and preventing electrolyte from easily seeping into the electrode coating and passivating it during electrolysis, thus significantly extending its service life. Furthermore, Gd doping improves the electrode's oxygen atom transfer capability and catalytic performance, further enhancing the electrode's electrochemical performance.

[0010] The particulate electrode is a Ni-Co bimetallic modified carbon-based material (graphene-biochar, GBC) Ni-Co / GBC. As a new electrode in the electrocatalytic reactor, it fills the space between the main cathode and the main anode and is polarized under the action of an electric field to form multiple microelectrodes. Compared with the traditional two-dimensional electrochemical system, the addition of the particulate electrode gives it a larger active electrode area, higher processing efficiency and lower energy consumption.

[0011] The Ni-Co / GBC particulate electrode possesses abundant electroactive functional groups and a well-developed porous structure, enabling the adsorption of organofluorine compounds within its pores and providing a high concentration of reactants for subsequent catalytic oxidation reactions. Simultaneously, Ni-Co / GBC exhibits excellent conductivity and electron transfer capabilities. On one hand, an electric field can facilitate the direct transfer of electrons from the organofluorine compounds to the particulate electrode, achieving initial conversion and degradation. On the other hand, the metal catalysts Ni and Co on Ni-Co / GBC can catalyze the generation of reactive oxygen species such as hydroxyl radicals and superoxide radicals from water or oxygen. These reactive oxygen species possess strong oxidizing power, capable of further attacking unsaturated bonds and aromatic rings in organofluorine molecule structures, causing oxidative decomposition and ultimately converting them into carbon dioxide, water, and fluoride ions.

[0012] The method for preparing the Ni-Co / GBC particulate electrode includes the following steps: (2.1) Boil the biomass pellets in deionized water for 30 min to remove pigments and some impurities, dry them, pulverize them, and sieve them to obtain 80-100 mesh powder. (2.2) Take 2~5 g of GO and add it to 1 L of deionized water. Stir vigorously and disperse by ultrasonication for 30 min to obtain GO dispersion. (2.3) Add 100 g of biomass particles and 0.6~1.5 g of solid citric acid to the GO dispersion in step (2.2) in sequence, disperse by ultrasonication for 1 h, freeze in an ultra-low temperature freezer at -80℃ for 6~8 h, and then dry in a freeze dryer for 36 h to obtain composite precursor GBC particles. (2.4) Take an appropriate amount of nickel salt and cobalt salt to prepare 1 L of impregnation solution with a total metal ion concentration of 0.5 mol / L (Ni:Co=2:1, molar ratio), add 96 g of citric acid to it, and stir at 60℃ until dissolved; (2.5) Determine the saturated water absorption rate of the GBC particles obtained in (2.3). Take the solution from step (2.4) with just the saturated water absorption volume and slowly add it dropwise to the GBC particle powder while stirring. After adding, let it stand at room temperature for 12 h. (2.6) The impregnated sample was placed in a tube furnace and heated to 300°C at 5°C / min under the protection of high-purity N2 (flow rate 200 sccm) and held at 1 h. Then the temperature was increased to 700°C at 5°C / min and held at 2 h. Subsequently, CO2 was pulsed into the N2 gas flow (flow rate 50 sccm, 5 min on, 5 min off, 5-8 cycles) to slightly etch and activate the material and increase the number of mesopores. (2.7) Cool the product from step (2.6) to room temperature, soak it in 0.1 M dilute nitric acid solution for 30 min, then rinse it three times each with deionized water and anhydrous ethanol, and dry it in an 85℃ dryer until constant weight. Select 0.5~2.0 mm particles by sieve as Ni-Co / GBC particle electrodes.

[0013] In step (2.2), the biomass pellets used are corn stalks, walnut shells or microalgae; in step (2.4), the nickel salt is nickel nitrate, nickel sulfate or nickel chloride; and the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride.

[0014] In step (4), the mass ratio of the amount of fluoride ion adsorbent added to the mass of fluoride ions in the wastewater is 120~150:1.

[0015] The fluoride ion adsorbent is prepared by the following method, with the specific steps as follows: (3.1) Wash 50-70 parts by weight of natural zeolite 3-5 times with deionized water to remove impurities on the surface of the zeolite, and then soak it in deionized water for more than 24 hours. (3.2) Place the rinsed zeolite in a muffle furnace and heat it to 300℃ at a rate of 3℃ / min, and calcine for 2 h; (3.3) Grind the heat-modified zeolite into 80-100 mesh powder; (3.4) Disperse the thermally modified zeolite powder in deionized water (solid-liquid ratio 1:10~20, g / mL), stir for 15~30 min, add 5~7 parts by mass of humic acid (HA), adjust the pH to 8~9 with 0.5 M NaOH solution, and stir until dissolved; (3.5) Introduce 5-7 parts by mass of aluminum salt into the solution of (3.4), stir evenly, and while stirring continuously, add glutaraldehyde aqueous solution (the amount of glutaraldehyde added is 30% of the mass of HA) and 0.5 M NaOH solution dropwise (control the endpoint pH to 7-8). (3.6) The solution was placed in a water bath at 60~70℃ for 6~8h. After cooling the solution to room temperature, it was filtered, washed several times, and then dried under vacuum at 60~80℃ to constant weight to obtain the fluoride ion adsorbent, namely the modified zeolite-Al2O3 composite.

[0016] The modified zeolite-Al2O3 composite has a specific surface area and pore size that are several times larger than those of the original natural zeolite, and also increases the number of active sites on the zeolite surface, which is beneficial to increasing the adsorption capacity and adsorption rate of the material.

[0017] In step (3.1), the natural zeolite has a mesh size of 80~100 mesh; in step (3.5), the C / N ratio of HA is 10~12:1 (within this range, HA has abundant carboxyl / hydroxyl groups and a moderate proportion of nitrogen-containing functional groups); in step (3.7), the aluminum salt is aluminum sulfate, aluminum chloride or aluminum nitrate.

[0018] In step (5), the dosage of PAM is 3~5 mg / L.

[0019] In step (6), 20% to 30% (by volume) of the sludge at the bottom of the sedimentation tank is returned to the adsorption tank via the sludge return pipe, where it is recycled. The remaining sludge in the sedimentation tank is discharged to the regeneration system. The regenerant used is a 0.1 M sodium hydroxide solution, and the regenerated adsorbent can be added back into the adsorption tank.

[0020] This invention employs a three-dimensional electrochemical process coupling adsorption and electrochemical oxidation to electrocatalytically oxidize organofluorine compounds in fluoride-containing wastewater. The positive electrode in this three-dimensional electrochemical process is a modified Ti / PbO2-graphene & Gd electrode, which has a denser and smoother surface than conventional Ti / PbO2 electrodes. This effectively solves the severe porosity problem on the electrode surface, preventing the electrolyte from easily penetrating into the electrode coating and causing passivation during the electrolysis reaction, thus effectively extending its service life. Furthermore, Gd doping improves the electrode's oxygen atom transfer capability and catalytic performance, further enhancing its electrochemical performance. The particulate electrode in this three-dimensional electrochemical process is Ni-Co / GBC. Compared to BC, GBC, as a dual-carbon support, possesses abundant electroactive functional groups, a well-developed porous structure, and excellent conductivity and electron transfer capabilities. Simultaneously, the bimetallic Ni and Co loaded on the GBC particles have unpaired electrons and unfilled empty orbitals in their outermost layers, which can act as a bridge for electron transport, improving the electron mobility of the particulate electrode and enhancing its conductivity. In addition, Ni and Co can be used as catalysts to effectively reduce the energy barrier required for the reaction. At the same time, the two work synergistically, and their structure can significantly hinder particle aggregation, promote the generation of more free radicals with strong oxidizing properties, enhance the oxidation capacity of the system, and achieve the decomposition and release of more than 95% of organofluorine compounds.

[0021] This invention incorporates an electrolyte, NaCl solution, into a three-dimensional electrochemical process. Charged ions in the NaCl solution migrate towards the opposite charge side of the particle electrode due to Coulomb forces, leading to electroadsorption. The combination of electroadsorption and electrooxidation effectively promotes the degradation of organofluorine compounds. Furthermore, the NaCl solution, upon contact with the particle electrode, can electrochemically oxidize and generate oxidizing substances such as ·OH and active chlorine, which can attack and decompose residual small-molecule organic matter adsorbed in the micropores of Ni-Co / GBC. This achieves in-situ electrochemical regeneration of Ni-Co / GBC, and no significant decrease in the removal rate of organofluorine compounds was observed in the regenerated Ni-Co / GBC particle electrode, with a reactivation rate of approximately 95%.

[0022] This invention involves the combined modification of zeolite. Thermal modification removes moisture and organic impurities from the zeolite channels, widens the pores, increases the specific surface area, and thus enhances its adsorption and ion exchange capabilities, particularly increasing the loading capacity of subsequent organic matter. HA contains abundant functional groups, which can form complexes with Al, enhancing the stability and reactivity of the composite material. The modified zeolite has a larger specific surface area and a greater number of ·OH groups. Through electrostatic attraction, ligand exchange, hydrogen bonding, and ion exchange, it adsorbs fluoride ions, resulting in a stable effluent fluoride concentration of less than 1 mg / L with a low dosing coefficient. Simultaneously, the adsorbent can be regenerated using an alkaline solution and reused up to 5 times with minimal change in its fluoride removal performance after regeneration. The dosing coefficient for effluent fluoride concentrations below 1 mg / L is 108% of that before regeneration, demonstrating excellent regeneration performance.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The process of the present invention adopts "three-dimensional electrochemical process + fluoride ion adsorbent", which can treat high-concentration organic fluoride wastewater with low dosage (small amount of adsorbent added), and can stably ensure that the fluoride concentration in the effluent is reduced to below 1.0 mg / L, meeting the discharge standards, and fundamentally solving the problem of meeting the discharge standards for high organic fluoride wastewater in the electronics industry. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the method of the present invention; Figure 2 This is a schematic diagram of the structure of the three-dimensional electrochemical reactor used in this invention. Detailed Implementation

[0025] Example 1 The anode of this invention is a modified Ti / PbO2-graphene & Gd, wherein a PbO2 layer doped with graphene and rare earth metal Cd is deposited on a Ti substrate. The specific preparation method is as follows: (1) Pretreatment of titanium rod substrate: Solid titanium rods were mechanically polished, degreased by alkaline washing (10wt.% NaOH, 80℃, 30 min), activated by etching (boiling 10wt.% oxalic acid solution, 2 h, to increase micro-roughness) and washed with water. After washing with water, the rods were immediately stored in ethanol to prevent re-oxidation. (2) Preparation of electrodeposition solution: Prepare a mixed solution containing 0.4 M Pb(NO3)2 and 0.15 M Cu(NO3)2, adjust the pH of the mixed solution to 1.5 with HNO3, add graphene oxide to make the graphene oxide concentration 60 mg / L, sonicate for 45 min, and then add Gd(NO3)3 to make the concentration 1.0 mmol / L to form the electrodeposition solution; (3) Constant current electrodeposition: A three-electrode system was used, with a titanium rod as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode; the current density during the deposition process was set to 15 mA / cm². 2 The plating bath temperature was 65±5℃, the deposition time was 110 min, and the stirring speed was greater than 500 rpm to ensure uniform mass transfer and deposition. (4) Post-treatment: After deposition, the substrate is rinsed with deionized water and dried in an oven at 80°C for 1 hour to obtain a titanium substrate coated with a PbO2 layer doped with graphene and rare earth metal Cd.

[0026] Example 2 The three-dimensional particulate electrode of the present invention uses GBC as a framework and loads transition metals Ni and Co on the framework to improve the adsorption and conductivity of the material, while providing more active sites that can interact with organofluorides. The specific steps for preparing the Ni-Co / GBC particulate electrode are as follows: (2.1) Boil the biomass pellets (walnut shells) in deionized water for 30 minutes to remove pigments and some impurities, dry them, pulverize them, and sieve them to obtain 80-100 mesh powder. (2.2) Take 5 g of GO and add it to 1 L of deionized water. Stir vigorously and disperse by ultrasonication for 30 min to obtain GO dispersion. (2.3) Add 100 g of biomass powder from step (2.1) and 0.6 g of solid citric acid to the GO dispersion in step (2.2) in sequence. After ultrasonic dispersion for 1 h, freeze in an ultra-low temperature freezer at -80℃ for 8 h, and then dry in a freeze dryer for 36 h to obtain composite precursor GBC particles. (2.4) Measure nickel nitrate and cobalt nitrate to prepare 1 L of impregnation solution with a total metal ion concentration of 0.5 mol / L (Ni:Co=2:1, molar ratio), add 96 g of citric acid to it, and stir at 60℃ until dissolved; (2.5) Determine that the saturated water absorption rate of the GBC particles obtained in step (2.3) is 80%. Take 80 mL of the solution in step (2.4) and slowly add it dropwise to the GBC particle powder while stirring. After adding, let it stand at room temperature for 12 h. (2.6) The impregnated sample was placed in a tube furnace and heated to 300°C at 5°C / min under the protection of high-purity N2 (flow rate 200 sccm) and held at 1 h. Then the temperature was increased to 700°C at 5°C / min and held at 2 h. Subsequently, CO2 was pulsed into the N2 gas flow (flow rate 50 sccm, 5 min on, 5 min off, 5 cycles) to slightly etch and activate the material and increase the number of mesopores. (2.7) Cool the product from step (2.6) to room temperature, soak it in 0.1 M dilute nitric acid solution for 30 min, then rinse it three times each with deionized water and anhydrous ethanol, and dry it in an 85℃ dryer until constant weight. Select 0.5~2.0 mm particles by sieve as Ni-Co / GBC particle electrodes.

[0027] Example 3 The fluoride ion adsorbent of this invention uses thermally modified zeolite as a framework, with HA loaded onto the framework to increase the electrostatic attraction and ion exchange capacity of the zeolite, thereby expanding the adsorption capacity of the modified zeolite. Modification of the organically loaded zeolite with Al further enhances the material's adsorption capacity and rate for fluoride ions through greater electrostatic attraction, ligand exchange, hydrogen bonding, and ion exchange. The fluoride ion adsorbent of this invention is prepared from components in the following mass ratio: natural zeolite: aluminum salt: HA = 10:1:1, wherein the natural zeolite is selected from 80-100 mesh, the aluminum salt is aluminum chloride, and the C / N ratio of HA is 12:1. The above-mentioned fluoride ion adsorbent is prepared by the following method, specifically including the following steps: (3.1) Wash 70 parts by weight of natural zeolite 5 times with deionized water to remove impurities on the surface of the zeolite, and then soak it in deionized water for more than 24 hours. (3.2) Place the rinsed zeolite in a muffle furnace and heat it to 300℃ at a rate of 3℃ / min, and calcine for 2 h; (3.3) Grind the heat-modified zeolite into 80-100 mesh powder; (3.4) Disperse the thermally modified zeolite powder in deionized water (solid-liquid ratio 1:10, g / mL), stir for 15 min, add 7 parts by mass of humic acid (HA), adjust the pH to 8-9 with 0.5 M NaOH solution, and stir until dissolved; (3.5) Add 7 parts by mass of aluminum chloride to the solution in step (3.4), stir evenly, and while stirring continuously, add glutaraldehyde aqueous solution (the amount of glutaraldehyde added is 30% of the mass of HA) and 0.5 M NaOH solution dropwise (control the endpoint pH to 7~8). (3.6) The solution was placed in a water bath at 70°C for 6 h. After cooling to room temperature, the solution was filtered, washed several times, and dried under vacuum at 80°C to constant weight to obtain the fluoride ion adsorbent, namely the modified zeolite-Al2O3 complex.

[0028] The modified zeolite-Al2O3 composite is a more porous material than natural zeolite. Its specific surface area and pore size are several times larger than those of the original natural zeolite, increasing the number of active sites on the zeolite surface, which is beneficial to increasing the adsorption capacity and adsorption rate of the material.

[0029] Example 4 The present invention provides a method for deep treatment of organofluorine compounds, comprising the following steps: (1) Fluorine-containing wastewater from the electronics industry was sent to equalization tank I to homogenize the water quality. 50wt.% H2SO4 and 30wt.% NaOH were added to adjust the pH of the wastewater to 2-3. The hydraulic retention time was 15 min. During the process, the pH value, organic fluoride concentration and fluoride ion concentration of the wastewater were monitored. (2) The effluent from the uniform pool was sent to the three-dimensional electrochemical reactor. The anode of the three-dimensional electrochemical reactor was Ti / PbO2-graphene & Gd (prepared in Example 1), the cathode was stainless steel, and the particle electrode was Ni-Co / GBC (prepared in Example 2). The applied voltage was set to 9.0 V, 0.05 mol / L NaCl solution was added, the external aeration pump flow rate was 2 L / min, and the hydraulic retention time was 40 min. During the process, the combined action of electroadsorption and electrooxidation effectively achieved the rapid degradation of organic fluorides and released fluoride ions from the organic fluorides. (3) The effluent from the three-dimensional electrochemical reactor is sent to the homogenization and equalization tank II to homogenize the water quality. The hydraulic retention time is 15 min. During the process, the concentration of organic fluoride and fluoride ions in the wastewater are monitored. The concentration of fluoride ions and total fluoride are determined by ion chromatography. The concentration of organic fluoride is equal to the total fluoride concentration minus the concentration of fluoride ions. If the concentration of organic fluoride is greater than 0.5 mg / L, the effluent is sent to the three-dimensional electrochemical reactor for electrocatalytic oxidation of organic fluoride again. If the concentration of organic fluoride is less than 0.5 mg / L, the effluent is sent to the adsorption tank. (4) Add appropriate fluoride ion adsorbent (prepared in Example 3) to the adsorption tank (the mass ratio of fluoride ion adsorbent to fluoride ion is 120:1), and adjust the pH of the wastewater to weakly acidic (pH 6~7) with 50wt.% H2SO4 and 30wt.% NaOH. Because the surface of the adsorbent is positively charged in this pH range, strong interaction occurs between the fluoride ions and the positively charged adsorbent surface. Stir quickly and the hydraulic retention time is 60 min. (5) Send the effluent from the adsorption tank to the flocculation tank, add 5 mg / L of PAM, stir slowly, and allow the hydraulic retention time to be 10 min. (6) The effluent from the flocculation tank is sent to the sedimentation tank. During the process, the fluoride concentration of the supernatant in the sedimentation tank is monitored. If the fluoride concentration is less than 1 mg / L, the effluent is sent to the next unit. If the fluoride concentration is greater than 1 mg / L, the supernatant is returned to the adsorption tank. 20% (by volume) of the sludge at the bottom of the sedimentation tank is returned to the adsorption tank through the sludge return pipe and recycled in the adsorption tank. The remaining sludge is discharged to the regeneration system.

[0030] The adsorbent is batch regenerated in a dedicated regeneration tank by soaking it in a 2 M sodium hydroxide solution (solid-liquid ratio of about 1:10, g / mL) for 4 h, filtering and drying to obtain an adsorbent with restored active sites. The regenerated adsorbent can be put back into the adsorption tank.

[0031] The water quality indicators before and after the three-dimensional electrochemical reaction are shown in Table 1 below: Table 1 Water quality indicators before and after the three-dimensional electrochemical reaction

[0032] The water quality indicators before and after the adsorption reaction are shown in Table 2 below: Table 2 Water quality indicators before and after the adsorption reaction

[0033] As shown in Table 1, the organic fluoride removal rate of fluoride-containing wastewater from the electronics industry after the three-dimensional electrochemical reaction process designed in this invention can reach 99.07%. Furthermore, as shown in Table 2, after treatment with a fluoride ion adsorbent (dosage of 120 g defluorinator / g fluoride ion), the fluoride ion concentration in the effluent is less than 1.0 mg / L.

[0034] Comparative Example 1 Compared to Example 4, the only difference in Comparative Example 1 is that the anode of the three-dimensional electrochemical reactor is Ti / PbO2. The water quality indicators before and after the three-dimensional electrochemical reaction using Ti / PbO2 as the anode are shown in Table 3 below: Table 3 Water quality indicators before and after the three-dimensional electrochemical reaction

[0035] As shown in Table 3, the concentration of organic fluoride in the fluoride-containing wastewater treated by the three-dimensional electrochemical reactor with Ti / PbO2 anode decreased from 3.22 mg / L to 0.52 mg / L, and the organic fluoride removal rate was 83.85%. Compared with the three-dimensional electrochemical reactor with Ti / PbO2-graphene & Gd anode, the organic fluoride removal rate decreased by 15.7 percentage points.

[0036] Comparative Example 2 Compared to Example 4, the only difference in Comparative Example 2 is that the particulate electrode in the three-dimensional electrochemical reactor is Ni-Co / BC. The water quality indicators before and after the three-dimensional electrochemical reaction using Ni-Co / BC as the particulate electrode are shown in Table 4 below: Table 4 Water quality indicators before and after the three-dimensional electrochemical reaction

[0037] As shown in Table 4, the concentration of organic fluoride in the fluoride-containing wastewater treated by the three-dimensional electrochemical reactor with Ni-Co / BC particulate electrode decreased from 3.22 mg / L to 0.49 mg / L, and the organic fluoride removal rate was 84.78%. Compared with the three-dimensional electrochemical reactor with Ni-Co / GBC particulate electrode, the organic fluoride removal rate decreased by 14.29 percentage points.

[0038] Comparative Example 3 Compared to Example 4, the only difference in Comparative Example 3 is that no particulate electrode was placed in the electrochemical reactor. The water quality indicators before and after the electrochemical reaction without the particulate electrode are shown in Table 5 below: Table 5 Water quality indicators before and after the electrochemical reaction

[0039] As shown in Table 5, the concentration of organic fluoride in the fluoride-containing wastewater treated by the electrochemical reactor without granular electrodes decreased from 3.22 mg / L to 0.96 mg / L, with an organic fluoride removal rate of 70.19%. Compared with the three-dimensional electrochemical reactor using granular electrodes Ni-Co / GBC, the organic fluoride removal rate decreased by 28.88 percentage points.

[0040] Comparative Example 4 Compared to Example 4, the only difference in Comparative Example 4 is that the fluoride ion adsorbent is natural zeolite. The water quality indicators before and after the adsorption reaction are shown in Table 6 below: Table 6 Water quality indicators before and after the adsorption reaction

[0041] As shown in Table 6, when the dosage is the same as that of the modified zeolite-Al2O3 composite, the fluoride ion concentration in the wastewater after treatment with natural zeolite is 7.87 mg / L, and the fluoride removal effect is much lower than that of the modified zeolite-Al2O3 composite.

Claims

1. A method for the advanced treatment of organofluorine wastewater from the electronics industry, characterized in that, Includes the following steps: (1) The fluoride-containing wastewater from the electronics industry is sent to equalization tank I to adjust the pH of the wastewater to 2-5; (2) The effluent from the homogenization conditioning tank I is sent to the three-dimensional electrochemical reactor. The anode of the three-dimensional electrochemical reactor is Ti / PbO2-graphene & Gd, the cathode is stainless steel, the particle electrode is Ni-Co / GBC, the applied voltage is set to 9.0~10 V, the electrolyte solution is 0.05~0.06 mol / L NaCl solution, the aeration rate of the external aeration pump is 1.5~2 L / min, and the reaction lasts for 40~60 min. (3) Send the effluent from the three-dimensional electrochemical reactor to the homogenization and equalization tank II, monitor the concentration of organic fluoride and fluoride ions in the wastewater. If the concentration of organic fluoride is greater than 0.5 mg / L, send the effluent back into the three-dimensional electrochemical reactor for electrocatalytic oxidation of organic fluoride again. If the concentration of organic fluoride is less than 0.5 mg / L, send the effluent into the adsorption tank. (4) Fluoride ion adsorbent is added to the adsorption tank, the pH of the wastewater in the adsorption tank is adjusted to weak acidity, and adsorption is carried out for 40~60 min under rapid stirring. (5) Send the effluent from the adsorption tank to the flocculation tank, add PAM into it, stir slowly, and react for 5~10 min. (6) Send the effluent from the flocculation tank to the sedimentation tank and monitor the fluoride ion concentration of the supernatant in the sedimentation tank. If the fluoride ion concentration is less than 1 mg / L, send the effluent to the next unit. If the fluoride ion concentration is greater than 1 mg / L, return the supernatant to the adsorption tank for recycling.

2. The depth processing method according to claim 1, characterized in that: In step (2), the three-dimensional electrochemical reactor is a vertical flow continuous flow reactor, which is mainly composed of an inlet chamber, an electrochemical chamber, and an outlet chamber from bottom to top, and the chambers are separated by a porous insulating plate. The electrochemical chamber is equipped with a cathode, an anode, and a particle electrode filled in the electrochemical chamber. The cathode is set around the inert wall of the electrochemical chamber, the anode is located in the center of the electrochemical chamber, and the particle electrode is filled in the electrochemical chamber. The three-dimensional electrochemical reactor also includes a microporous aeration disc, which is set at the bottom of the electrochemical chamber and is supplied with air by an air pump. Both the cathode and the anode are connected to an external DC regulated constant current power supply.

3. The depth processing method according to claim 2, characterized in that: The anode of the three-dimensional electrochemical reactor includes a Ti substrate and a PbO2 layer doped with graphene and rare earth metal Cd supported on the Ti substrate.

4. The depth processing method according to claim 3, characterized in that: The anode is specifically prepared by the following method: in an acidic environment containing Pb 2+ Graphene oxide and Gd 3+ In the electrodeposition solution, a pretreated solid titanium rod was used as the anode, and a constant current was applied to generate Pb on the anode surface. 2+ Electrochemical oxidation to PbO2 deposition yields a titanium substrate coated with a PbO2 layer doped with graphene and rare earth metal Cd.

5. The depth processing method according to claim 2, characterized in that: The particulate electrode of the three-dimensional electrochemical reactor is a Ni-Co / GBC particulate electrode, and the preparation method of the Ni-Co / GBC particulate electrode includes the following steps: (2.1) Boil the biomass pellets in deionized water for 30-40 minutes, dry them, pulverize them, and sieve them to obtain 80-100 mesh powder; (2.2) Take 2~5 g of GO and add it to 1 L of deionized water. After ultrasonic dispersion, a GO dispersion is obtained. (2.3) Add 100 g of biomass particles and 0.6~1.5 g of solid citric acid to the GO dispersion in step (2.2) in sequence. After ultrasonic dispersion, freeze at -80~-100℃ for 6~8 h and then dry in a freeze dryer for 36~38 h to obtain composite precursor GBC particles. (2.4) Prepare a 1 L impregnation solution with a total metal ion concentration of 0.5~0.6 mol / L by taking nickel salt and cobalt salt, add 96~98 g of citric acid to it, and stir at 60~80℃ until dissolved; (2.5) Determine the saturated water absorption rate of the GBC particles obtained in step (2.3). Take the solution from step (2.4) with just the saturated water absorption volume and slowly add it dropwise to the GBC particle powder while stirring. After adding, let it stand at room temperature for 12-14 h. (2.6) The impregnated sample was placed in a tube furnace and heated to 300-350°C at 5-6°C / min under N2 gas protection, and held at the temperature for 1-1.5 h. Then the temperature was increased to 700-750°C at 5-6°C / min and held at the temperature for 2-3 h. Subsequently, CO2 was pulsed into the N2 gas flow to etch and activate the material. (2.7) Cool the product from step (2.6) to room temperature, wash it with acid and water in sequence, and then dry it to obtain Ni-Co / GBC particle electrode.

6. The depth processing method according to claim 5, characterized in that: In step (2.1), the biomass pellets used are corn stalks, walnut shells or microalgae; in step (2.4), the nickel salt is nickel nitrate, nickel sulfate or nickel chloride; the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride.

7. The depth processing method according to claim 1, characterized in that: In step (4), the mass ratio of the amount of fluoride ion adsorbent added to the mass of fluoride ions in the wastewater is 120~150:

1.

8. The depth processing method according to claim 7, characterized in that: The fluoride ion adsorbent is prepared by the following method, with the specific steps as follows: (3.1) 50-70 parts by weight of cleaned natural zeolite are calcined at high temperature and then ground into 80-100 mesh powder. (3.2) Disperse the natural zeolite powder in deionized water at a solid-liquid ratio of 1g:10~20mL, add 5~7 parts by mass of humic acid, and adjust the pH of the solution to 8~9; (3.3) Introduce 5-7 parts by mass of aluminum salt into the solution of step (3.2), stir evenly, and add glutaraldehyde aqueous solution dropwise while stirring continuously. After adding, adjust the pH of the solution to 7-8. (3.4) The solution was placed in a water bath at 60-70℃ for 6-8 hours. After cooling the solution to room temperature, it was filtered, washed several times, and then dried under vacuum at 60-80℃ to constant weight to obtain the fluoride ion adsorbent.

9. The depth processing method according to claim 1, characterized in that: In step (5), the dosage of PAM is 3~5 mg / L.

10. The depth processing method according to claim 1, characterized in that: In step (6), 20% to 30% of the sludge at the bottom of the sedimentation tank is returned to the adsorption tank through the sludge return pipe.

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