A device and method for removing fluorine by non-homogeneous fluidized bed nested electrochemistry

Abstract

The application discloses a device and a method for removing fluorine by non-homogeneous fluidized bed nested electrochemistry, wherein the device comprises an electrochemical reaction module and a fluidized bed reaction module above the electrochemical reaction module; the device can realize continuous and stable operation of fluorine-containing wastewater by adding a small amount of zeolite as a fluidized bed carrier in the fluidized bed reaction module without additional aeration device, and the treatment cost is low, the operation process is green and secondary pollution-free, sludge dewatering is not needed, and the fluorine ion removal efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of water treatment defluoridation technology, and in particular to a defluoridation device and method using a heterogeneous fluidized bed nested electrochemical defluorination device. Background Technology

[0002] Fluorine is an essential trace element for the human body. However, when the concentration of fluoride in water exceeds 1 mg / L, it can cause dental fluorosis. If the concentration increases to 3-5 mg / L, it can pollute the water and cause skeletal fluorosis, posing a potential threat to the health of both organisms and humans.

[0003] Currently, the main methods for removing fluoride from water include precipitation, adsorption, ion exchange, and membrane separation. However, these methods are prone to generating large amounts of water-rich sludge, poor settling properties, increased costs due to large adsorbent dosages, and membrane fouling issues during membrane separation. CN 211497055U discusses the advantages and disadvantages of the above conventional processes and proposes a fluidized bed crystallization method for treating fluoride-containing wastewater, mainly using calcium-based defluorinating agents. CN 112047418 A discloses a fluidized bed-like cyclone defluorination device, which uses the addition of defluorinating agents and filter screens to stir the wastewater in the cyclone for a thorough reaction. CN201911138584.8 discloses a composite defluorination filter material prepared from cerium hydroxide, zeolite powder, and bentonite as raw materials, which has high adsorption efficiency.

[0004] The above-mentioned scheme still focuses on defluorinating agents and modified adsorbents, supplemented by fluidized bed or fluidized bed-like rotating bodies to reduce the amount of reagents added and increase the removal effect. However, it still does not solve the drawbacks of secondary sludge and large reagent dosage. Long-term application still has problems such as secondary pollution of reagents / sludge and large reagent consumption. Summary of the Invention

[0005] In view of this, this solution proposes a coupling approach between electrochemical technology and heterogeneous fluidized beds, and invents a heterogeneous fluidized bed nested electrochemical defluorination device and defluorination method to solve the problem that existing fluidized bed defluorination devices still rely on reagents such as calcium fluoride as the core treatment method, thus avoiding problems such as large reagent dosage and secondary pollution of calcium sludge.

[0006] To achieve one aspect of the above-mentioned objectives, the present invention adopts the following technical solution: A heterogeneous fluidized bed nested electrochemical defluorination device, the device comprising an electrochemical reaction module and a fluidized bed reaction module located above the electrochemical reaction module; wherein, The electrochemical reaction module includes a reaction shell and an annular electrode assembly disposed within the reaction shell. The annular electrode assembly includes annular iron mesh electrodes and annular aluminum mesh electrodes, which are arranged sequentially from the inside to the outside within the reaction shell at intervals, such that an aluminum mesh electrode is disposed between adjacent iron mesh electrodes and an iron mesh electrode is disposed between adjacent aluminum mesh electrodes. Each electrode in the annular electrode assembly is electrically connected to an external power source, such that an anode electrode is disposed between adjacent cathode electrodes and a cathode electrode is disposed between adjacent anode electrodes. The reaction shell is provided with an inlet at the bottom for introducing water to be treated and a connecting port at the top; The fluidized bed reaction module includes a fluidized bed cylinder and a multi-stage zeolite filter bed arranged axially at intervals within the fluidized bed cylinder. The zeolite filter bed includes a liner screen disposed within the fluidized bed cylinder and zeolite filter media filled on the liner screen. The bottom of the cylinder is connected to the reaction shell through the connecting port, and the top is provided with a water outlet to discharge purified water.

[0007] According to the device of the present invention, preferably, a fan disc is further provided in the communication port so that water from the reaction shell enters the fluidized bed body in a swirling motion after passing through the fan disc. By setting the fan disc, it is beneficial to make full use of the gas generated by the electrochemical reaction in the reaction shell to aerate the upper fluidized bed, so that the zeolite filter material is in a suspended state and fully mixed with water, thereby increasing the reaction efficiency.

[0008] According to the device of the present invention, preferably, the reaction shell is further provided with a rotating shaft passing through the annular electrode assembly, the lower end of the rotating shaft is connected to an external motor, and each electrode of the annular electrode assembly is fixedly connected to the rotating shaft by a fixing member so as to rotate with the rotating shaft.

[0009] According to the device of the present invention, preferably, the reaction shell is further provided with a rotating shaft passing through the annular electrode assembly, the lower end of the rotating shaft is connected to an external motor, and each electrode of the annular electrode assembly is fixedly connected to the rotating shaft by a fixing member so as to rotate with the rotating shaft; the communication port is further provided with a fan disc connected to the upper end of the rotating shaft so as to rotate with the rotating shaft, so that water from the reaction shell enters the fluidized bed body in a swirling flow after passing through the fan disc.

[0010] According to the device of the present invention, preferably, the reaction shell is further provided with an inner shell descaling scraper, which is fixedly connected to the rotating shaft by a fixing member so as to scrape off the scale on the inner side of the reaction shell as the rotating shaft rotates.

[0011] According to the apparatus of the present invention, preferably, the multi-stage zeolite filter bed is a first-stage zeolite filter bed, a second-stage zeolite filter bed and a third-stage zeolite filter bed arranged sequentially from bottom to top.

[0012] According to the apparatus of the present invention, preferably, the particle size of the zeolite filter media in the primary zeolite filter bed, the secondary zeolite filter bed and the tertiary zeolite filter bed decreases sequentially to form a stepped treatment; Preferably, the zeolite filter media of the primary zeolite filter bed has a particle size of 1.5~2.0 cm, more preferably 1.6~1.8 cm; the zeolite filter media of the secondary zeolite filter bed has a particle size of 0.8~1.2 cm, more preferably 0.9~1.0 cm; and the zeolite filter media of the tertiary zeolite filter bed has a particle size of 0.4~0.8 cm, more preferably 0.5~0.6 cm.

[0013] According to the apparatus of the present invention, preferably, the zeolite filter media is zeolite particles with iron oxides loaded on their surface; studies have found that, within a fluidized bed reaction module, the iron oxides loaded on the surface of the zeolite filter media can serve as a carrier to promote the precipitation of Fe in the water sample. 2+ To Fe 3+ Crystallization (reversible reaction), at the same time, Fe 3+ It will also precipitate on the zeolite surface through crystallization or precipitation (the process of fluidized bed crystallization and FeOOH reduction and dissolution), allowing the zeolite filter media to be reused. This not only increases its service life but also facilitates defluorination and water purification. Preferably, the iron content on the surface of the zeolite particles, as determined by energy dispersive spectroscopy analysis, is 20-50%, such as 30%-45%, 35%-45%, or 40%.

[0014] In one embodiment, the zeolite particles with surface-loaded iron oxide are obtained from zeolite particles through the following modification process: The raw zeolite particles are first soaked in the first sulfuric acid solution, then washed with deionized water, and then soaked a second time in the second sulfuric acid solution. Ferrous sulfate solution and hydrogen peroxide solution are added, and during the second soaking, an intermittent aeration reaction is carried out through an aeration device to form a brown precipitate on the surface of the zeolite particles. Then, the particles are dried to obtain zeolite particles with iron oxide loaded on the surface for later use. The first sulfuric acid solution has a mass fraction of 42-65%, preferably 45-55%, such as 50%; the second sulfuric acid solution has a mass fraction of 25-40%, preferably 30-38%, such as 32% or 36%; the ferrous sulfate concentration is 2-6 mmol / L, preferably 3-5 mmol / L, such as 3.8 mmol / L; the hydrogen peroxide molar concentration is 10-15 mmol / L, preferably 12-13 mmol / L, such as 12.5 mmol / L; the first soaking time is 24-36 h, preferably 28-32 h; the second soaking time is 10-15 d, preferably 12-13 d; and the aeration time is 7-11 h / d, preferably 8-10 h / d.

[0015] In the above modification process, by providing an acidic environment and hydrogen peroxide as a hydrogenation agent, and employing a circulating soaking-aeration method, iron oxides are loaded onto the surface of the zeolite filter media to form a heterogeneous fluidized bed system. Loading with iron oxides increases the chemisorption capacity of the zeolite, further increasing its adsorption capacity. When it comes into contact with F ions in the water sample, it can undergo complexation, further increasing the F removal capacity.

[0016] According to the device of the present invention, preferably, the top of the fluidized bed body is provided with a coaxially arranged cylindrical overflow weir, the diameter of the overflow weir being larger than that of the fluidized bed body, thereby forming an annular connection between the bottom of the overflow weir and the top of the fluidized bed body, and the outlet is provided on the annular connection to discharge purified water.

[0017] According to the device of the present invention, preferably, the top of the reaction shell is provided with an anode connection post connected to the anode in the annular electrode group, and a cathode connection post connected to the cathode in the annular electrode group, so as to facilitate connection.

[0018] According to the device of the present invention, preferably, the bottom of the reaction shell is also provided with a drain port so as to drain the waste when cleaning the reaction shell.

[0019] The present invention also provides a defluorination method for removing fluoride from water using the above-mentioned device; preferably, the anode and cathode are periodically swapped during the operation of the device to prevent passivation of a single electrode due to long-term use.

[0020] In this invention, unless otherwise specified, the percentage or percentage content refers to a mass percentage or mass content.

[0021] Compared with the prior art, the present invention has the following advantages: (1) By combining heterogeneous crystallization fluidized bed with electrochemistry, a multi-stage fluoride removal function is realized, which combines electrochemical degradation, physical adsorption and chemical adsorption. Through the creative coupling of electrochemistry and fluidized bed technology, various flocs and gases generated by electrochemistry are used as efficient fluoride removal and purification agents and aeration, thus avoiding the aeration and agent costs of traditional fluidized bed crystallizers. (2) A large amount of aluminum and iron flocs were generated through the electrochemical electrocoagulation process and rose with the water flow, bringing the gas generated by electrochemistry into the fluidized bed, which solved the problem of the aeration module of the traditional fluidized bed and reduced energy consumption. (3) Modified zeolite filter media has a large adsorption capacity and is simple to prepare and can be reused. In addition, the multi-stage zeolite filter media is fixed in the fluidized bed reactor. Under the action of fluidized bed water flow and bubble disturbance, the multi-stage filter media achieves a micro-suspension state, which further improves the quality of the effluent.

[0022] In summary, this invention removes F ions based on electrocoagulation and zeolite adsorption (physicochemical) as the core. Furthermore, the modified zeolite filter media, relying on surface iron oxides and device characteristics, can be reused, thereby improving the F ion removal rate, reducing the cost of use, and avoiding the drawbacks of secondary sludge pollution during use. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of one embodiment of the defluorination device of the present invention; Figure 2 for Figure 1 A schematic diagram of the central fan turntable; Figure 3 for Figure 1 Front view a and side view b of the reaction shell portion of the electrochemical reaction module; The markings in the diagram are explained as follows: Fluidized bed reaction module 1, fluidized bed cylinder 100, overflow weir 101, outlet 102, three-stage zeolite filter bed 103, two-stage zeolite filter bed 104, one-stage zeolite filter bed 105, zeolite filter media for the three-stage zeolite filter bed 106, zeolite filter media for the two-stage zeolite filter bed 107, zeolite filter media for the one-stage zeolite filter bed 108; Electrochemical reaction module 2, connecting port 200, anode connecting column 201, cathode connecting column 202, fan turntable 203, shell reinforcement module 204, reaction shell 205, water inlet 206, sewage outlet 207, external motor 208, support leg 209, rotating shaft 210, iron mesh electrode 211, aluminum mesh electrode 212, fixing component 213, descaling plate inside the shell 214. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments and accompanying drawings. However, the present invention is not limited to the listed embodiments, but should also include equivalent improvements and modifications to the technical solutions defined in the appended claims of the present invention.

[0025] like Figure 1As shown, the device of the present invention includes an electrochemical reaction module 2 and a fluidized bed reaction module 1 located above the electrochemical reaction module 2. The electrochemical reaction module 2 includes a reaction shell 205 and an annular electrode assembly disposed within the reaction shell 205. The annular electrode assembly includes annular iron mesh electrodes 211 and annular aluminum mesh electrodes 212, which are arranged sequentially from the inside to the outside within the reaction shell at intervals, such that an aluminum mesh electrode 212 is positioned between adjacent iron mesh electrodes 211 and an iron mesh electrode 211 is positioned between adjacent aluminum mesh electrodes 212. Each electrode in the annular electrode assembly is electrically connected to an external power source, such that an anode electrode is positioned between adjacent cathode electrodes and a cathode electrode is positioned between adjacent anode electrodes. In one embodiment, the distance between the cathode electrode and the adjacent anode electrode is set to 2-4 cm, for example, 2-3 cm.

[0026] In one embodiment, such as Figure 3 As shown, the ring-shaped motor assembly includes two sets of electrodes (one set of iron mesh electrodes and one set of aluminum mesh electrodes). Of course, those skilled in the art will understand that, depending on the available space, the iron and aluminum mesh electrodes can be further arranged in a cross-hatching pattern to fully utilize the iron and aluminum products for flocculation and precipitation, thereby improving the defluorination effect. Additionally, during use, the iron mesh electrodes and aluminum mesh electrodes can be periodically swapped as anode and cathode electrodes to prevent electrode passivation and increase service life and efficiency. In one embodiment, the reaction shell 205 is cylindrical, and each electrode is coaxially arranged with the reaction shell to ensure a better even distribution of the basic spacing. Of course, those skilled in the art will understand that the height of the electrodes can also be appropriately increased or decreased with the height of the reaction shell.

[0027] The reaction shell 205 has an inlet 206 at the bottom for introducing water to be treated and a connecting port 200 at the top. The fluidized bed reaction module 1 includes a fluidized bed cylinder 100 and a multi-stage zeolite filter bed arranged axially at intervals within the fluidized bed cylinder 100. The zeolite filter bed includes a liner screen disposed within the fluidized bed cylinder and zeolite filter media filled on the liner screen. The bottom of the fluidized bed cylinder is connected to the reaction shell 205 through the connecting port, and the top is provided with an outlet 102. Thus, the water to be treated first enters the reaction shell 205, and after treatment, it enters the fluidized bed cylinder through the connecting port and is further treated by the zeolite filter bed before being discharged as purified water.

[0028] In one implementation, such as Figure 3As shown, the reaction shell 205 is also provided with a rotating shaft 210 passing through the annular electrode assembly. The lower end of the rotating shaft 210 is connected to an external motor 208 to drive the rotating shaft 210 to rotate. Each electrode of the annular electrode assembly is fixedly connected to the rotating shaft by a fixing member 213 so that it rotates with the rotating shaft. The specific fixing method is well known in the art. For example, it can be fixed by a fixing rod perpendicular to the rotating shaft, with the middle part of the fixing rod fixed to the rotating shaft and both ends connected to the upper end of the annular electrode. Of course, it can also be fixed by other methods, which will not be described in detail here.

[0029] In one implementation, such as Figure 1 and 2 As shown, a fan disc 203 is also provided inside the communication port 200 so that the water from the reaction shell 205 is homogenized when it enters the fluidized bed cylinder 100 after passing through the fan disc, presenting a certain direction of uniform disturbance, reducing irregular surging, and on this basis, making better use of the gas generated by the electrochemical reaction in the reaction shell to aerate the upper fluidized bed and improve the defluorination efficiency.

[0030] In one embodiment, the fan disc 203 is connected to the upper end of the rotating shaft 210 to rotate with the rotating shaft, thereby enhancing the rotation of the fan disc and improving the defluorination efficiency.

[0031] The reaction shell may also be equipped with an inner descaling scraper 214, which is fixedly connected to the rotating shaft by a fixing member so as to scrape off the scale inside the reaction shell as the rotating shaft rotates. The bottom of the reaction shell may also be equipped with a drain port 207, which can be opened when needed to discharge the sludge formed after long-term operation.

[0032] The annular motor assembly includes multiple electrode pairs, each consisting of a cathode and a corresponding anode. In one embodiment, the top of the reaction shell may be provided with an anode connection post 201 connected to the anode in the annular electrode assembly, and a cathode connection post 202 connected to the cathode in the annular electrode assembly, so as to further connect to an external power source through the cathode connection post and the anode connection post.

[0033] The top of the fluidized bed cylinder 100 may also be provided with a coaxially arranged cylindrical overflow weir 101. The diameter of the overflow weir 101 is larger than that of the fluidized bed cylinder, so that an annular connection is formed between the bottom of the overflow weir and the top of the fluidized bed cylinder. The outlet 102 is provided on the annular connection, for example, multiple outlets 102 are evenly distributed on the annular connection to discharge purified water; at the same time, the overflow weir can form a reserve space to accommodate purified water that is not discharged in time.

[0034] The multi-stage zeolite filter bed can be a primary zeolite filter bed 105, a secondary zeolite filter bed 104, and a tertiary zeolite filter bed 103 arranged sequentially from bottom to top to further ensure the defluorination and purification effect. In one embodiment, the particle size of the zeolite filter media in the primary zeolite filter bed 105, the secondary zeolite filter bed 104, and the tertiary zeolite filter bed 103 decreases sequentially. As the particle size decreases, the specific surface area of ​​the material increases, and the adsorption efficiency increases, which can further adsorb small molecule pollutant F ions, forming a cascade filtration. In addition, setting the small-particle-size packing material last is also beneficial to avoid other large molecule organic matter or pollutants occupying adsorption sites, thereby interfering with the adsorption of F ions. In one embodiment, the zeolite filter media 108 of the primary zeolite filter bed has a particle size of 1.5~2.0 cm, preferably 1.6~1.8 cm, such as 1.7 cm; the zeolite filter media 107 of the secondary zeolite filter bed has a particle size of 0.8~1.2 cm, preferably 0.9~1.0 cm; and the zeolite filter media 106 of the tertiary zeolite filter bed has a particle size of 0.4~0.8 cm, preferably 0.5~0.6 cm, to form a stepped filtration effect.

[0035] When the device of the present invention is in operation, the wastewater to be treated first enters the electrochemical reaction module 2 through the bottom inlet 206. The anode and cathode of the annular electrode group inside the reaction shell are connected to an external DC power supply through the anode connecting post 201 and the cathode connecting post 202, respectively. The iron mesh electrode 211 and aluminum mesh electrode 212 inside the reaction shell 205 become two pairs of Al-Al and Fe-Fe electrochemical working electrodes, which are fixed to the rotating shaft 210 driven by the external motor 208 by the insulating fixing member 213. During operation, the self-rotating stirring function is achieved by driving the stirring motor 208. At this time, the electrode anode and cathode mesh undergo the following reactions: Anode reaction: Fe(s) → Fe 2+ (aq)+2e - Al(s) → Al 3+ (aq)=3e - Al 3+ (aq) + 3OH - →Al(OH)3(s) 2H₂O - 4e⁻ → O₂ + 4H + Fe 2+ (aq)+5H2O(l)+1 / 2O2(aq)→2Fe(OH)3(s)+4H + (aq) cathode reaction 2H₂O + 2e⁻ → H₂ + 2OH⁻ - Fluorine-containing wastewater reacts continuously in the electrochemical reaction module 2. As the influent volume increases, the aqueous solution is swirled into the fluidized bed reaction module 1 via the fan turntable 203. The fan turntable 203 is a design similar to the turbine blades of an electric fan. It is driven to rotate by the central rotating shaft 210, realizing the rotation of water flow from bottom to top and entraining the gas generated by the electrochemical reaction into the fluidized bed module, thus realizing the "micro-aeration" and "micro-suspension" functions of the fluidized bed.

[0036] The fluidized bed reaction module 1 has, from top to bottom, three zeolite filter bed liners 103, two zeolite filter bed liners 104, and one zeolite filter bed liners 105, respectively, filled with zeolite filter media, namely zeolite filter media 106 for the three zeolite filter bed, zeolite filter media 107 for the two zeolite filter bed, and zeolite filter media 108 for the one zeolite filter bed. The zeolite filter media will be micro-suspended under the conditions of water flow rotation and bubble disturbance, which will further adsorb and remove fluoride.

[0037] In summary, the water sample of this invention enters from the bottom and first undergoes electrocoagulation reaction through iron mesh electrode 211 and aluminum mesh electrode 212, generating charged Fe and Al flocs through electrochemical action. Subsequently, the water sample is rotated by the central rotating shaft 210 and the blades of the fan turntable 203 to form a turbine-type upward water flow. Specifically, in the electrochemical reaction module, hydrolyzed Fe(OH)3 and Al(OH)3 are generated under the electrolysis of iron and aluminum cathode and anode, forming positively charged colloidal groups in the water. Through sweeping and adsorption, SS, F ions and other ions in the water are aggregated into flocs and continuously aggregated. Under the influence of water flow and bubble disturbance, the flocs enter the fluidized bed reaction module.

[0038] The flocs and gas generated during the electrocoagulation process pass through the first, second and third zeolite filter beds, respectively, and the F ions in the water are removed again through physical adsorption and chemical complexation. Finally, the supernatant is discharged through the outlet 102 of the overflow weir 101. In addition, during operation, the iron mesh electrode 211 and aluminum mesh electrode 212 can be replaced periodically (e.g., once every 96 hours) to prevent passivation of a single electrode due to long-term use. Furthermore, the zeolite filter media of the device can be reused and cleaned periodically during repeated modification and preparation processes to ensure the stability of the surface loading of the zeolite filter media.

[0039] The present invention will be further described below with reference to embodiments and comparative examples. Example 1: Using natural zeolite from a certain manufacturer as raw material, zeolite raw materials with average diameters of 0.5 cm, 1.0 cm, and 1.8 cm were obtained after multi-stage particle size sieving. These raw materials were soaked in a 50% sulfuric acid solution for 28 h, then rinsed thoroughly with purified water. They were then soaked in a mixed solution of sulfuric acid (36%), ferrous sulfate (3.8 mmol / L), and hydrogen peroxide (12.5 mmol / L) for 12 days, during which time aeration was carried out every 3 hours for 1 h using an aeration pump. After 12 days, zeolite with surface-loaded iron oxides was obtained and used as modified zeolite for later use.

[0040] Test Example 1 Energy dispersive spectroscopy (EDS) analysis was performed on the modified zeolite filter media prepared in Example 1, and the results are shown in Table 1 below. It can be found that the zeolite surface was loaded with a large amount of Fe after cyclic soaking treatment.

[0041] Table 1. Energy dispersive spectroscopy analysis of modified zeolite surface

[0042] Test Example 2 To further evaluate the application stability of the modified zeolite prepared in Example 1, the prepared modified zeolite filter media was soaked in concentrated sulfuric acid for 24 h to dissolve all the surface-loaded Fe, and then the total iron content in the solution was measured. Equal masses and particle sizes of modified zeolite were also soaked in hydrochloric acid and sodium hydroxide (mixed) solutions at pH 3 to pH 11 for 24 h, and the iron concentration in the solutions was measured under different pH conditions. Nucleic acid analysis revealed that the Fe dissolution rates of the modified zeolite filter media prepared in this scheme were 16.8%, 13.5%, 12.4%, 7.8%, 4.2%, 9.5%, 13.3%, 19.9%, and 24.8% under pH conditions of 3, 4, 5, 6, 7, 8, 9, 10, and 11, respectively. It can be seen that the dissolution rate is low under neutral pH conditions, making it suitable for most environmental wastewater applications and demonstrating stable performance.

[0043] Application Example 1 The secondary effluent from a mine shaft in a certain mining area (COD: 52 mg / L, F: 3.8 mg / L) is pumped into the following system: Figure 1 The device of the present invention, shown, uses a bottom inlet 206 for the defluorination process described above. The parameters are: current density 12 mA / cm², hydraulic retention time 20 min, and rotating shaft speed 30 rpm. The effluent results are: COD 31 mg / L, F ions 0.4 mg / L. After five cycles, the COD effluent remains below 35 mg / L, and the F ion concentration remains stable below 0.65 mg / L.

[0044] Application Example 2 The sample was taken from the pretreated wastewater effluent of a factory (COD: 123 mg / L; F: 15.5 mg / L). The conditions were: current density 18 mA / cm2, hydraulic retention time 30 min, and rotating shaft speed 40 rpm. The effluent results were: COD: 46 mg / L, F ion: 1.5 mg / L.

[0045] Application Example 3 The difference from Application Example 1 is that the zeolite filter media used is the natural zeolite from Example 1; otherwise, they are the same. The effluent results were: COD: 40 mg / L, F ions: 2.7 mg / L.

[0046] Application Example 4 The difference from Application Example 1 is that a rotating shaft is not used; otherwise, they are the same. The effluent results were COD: 37 mg / L, F ion: 0.74 mg / L. After 5 cycles, the COD of the effluent was 41 mg / L, and the F ion concentration was approximately 1.15 mg / L, but significant scaling occurred inside the reaction tank.

[0047] All devices or components involved in this invention can be existing processing facilities, devices, or components with corresponding functions in the art, and will not be described in detail. Anything not specifically described herein is understood or known to those skilled in the art based on their prior knowledge, and will not be described in detail here.

[0048] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are within the spirit and scope of the present invention.

Claims

1. A device for heterogeneous fluidized bed nested electrochemical defluorination, characterized in that, The device includes an electrochemical reaction module and a fluidized bed reaction module located above the electrochemical reaction module; wherein, The electrochemical reaction module includes a reaction shell and an annular electrode assembly disposed within the reaction shell. The annular electrode assembly includes annular iron mesh electrodes and annular aluminum mesh electrodes, which are arranged sequentially from the inside to the outside within the reaction shell at intervals, such that an aluminum mesh electrode is disposed between adjacent iron mesh electrodes and an iron mesh electrode is disposed between adjacent aluminum mesh electrodes. Each electrode in the ring electrode group is electrically connected to an external power source, so that an anode electrode is provided between adjacent cathode electrodes and a cathode electrode is provided between adjacent anode electrodes; and the anode and cathode are periodically interchanged during the operation of the device. The reaction shell is provided with an inlet at the bottom for introducing water to be treated and a connecting port at the top; The fluidized bed reaction module includes a fluidized bed cylinder and a multi-stage zeolite filter bed arranged axially spaced within the fluidized bed cylinder. The zeolite filter bed includes a liner mesh disposed within the fluidized bed cylinder and zeolite filter media packed on the liner mesh. The zeolite filter media consists of zeolite particles with surface-loaded iron oxides. The zeolite filter media is obtained from the zeolite particles through the following modification process: The raw material zeolite particles are first soaked in a first sulfuric acid solution, then washed with deionized water, and then soaked a second time in a second sulfuric acid solution. Ferrous sulfate solution and hydrogen peroxide solution are added, and during the second soaking, intermittent aeration is carried out through an aeration device to form a brown precipitate on the surface of the zeolite particles. The particles are then dried to obtain zeolite particles with iron oxide loaded on the surface for later use. The bottom of the fluidized bed cylinder is connected to the reaction shell through the connecting port, and the top is provided with a water outlet to discharge purified water.

2. The apparatus according to claim 1, characterized in that, The communication port is also equipped with a fan disc, so that water from the reaction shell can be swirled into the fluidized bed body after passing through the fan disc.

3. The apparatus according to claim 1, characterized in that, The reaction shell is also provided with a rotating shaft passing through the annular electrode assembly. The lower end of the rotating shaft is connected to an external motor. Each electrode of the annular electrode assembly is fixedly connected to the rotating shaft by a fixing member so that it can rotate with the rotating shaft.

4. The apparatus according to claim 1, characterized in that, The reaction shell is also provided with a rotating shaft passing through the annular electrode assembly. The lower end of the rotating shaft is connected to an external motor. Each electrode of the annular electrode assembly is fixedly connected to the rotating shaft by a fixing member so that it can rotate with the rotating shaft. The communication port is also provided with a fan disc connected to the upper end of the rotating shaft so that it can rotate with the rotating shaft, so that water from the reaction shell can be swirled into the fluidized bed body after passing through the fan disc.

5. The apparatus according to claim 3 or 4, characterized in that, The reaction shell is also provided with an inner descaling scraper, which is fixedly connected to the rotating shaft by a fixing member so that it can scrape off the scale inside the reaction shell as the rotating shaft rotates.

6. The apparatus according to any one of claims 1-4, characterized in that, The multi-stage zeolite filter bed consists of a first-stage zeolite filter bed, a second-stage zeolite filter bed, and a third-stage zeolite filter bed arranged sequentially from bottom to top.

7. The apparatus according to claim 6, characterized in that, The particle size of the zeolite filter media in the primary, secondary, and tertiary zeolite filter beds decreases sequentially.

8. The apparatus according to claim 7, characterized in that, The zeolite filter media of the primary zeolite filter bed has a particle size of 1.5~2.0 cm; the zeolite filter media of the secondary zeolite filter bed has a particle size of 0.8~1.2 cm; and the zeolite filter media of the tertiary zeolite filter bed has a particle size of 0.4~0.8 cm.

9. The apparatus according to claim 8, characterized in that, The zeolite filter media of the first-stage zeolite filter bed has a particle size of 1.6~1.8 cm; the zeolite filter media of the second-stage zeolite filter bed has a particle size of 0.9~1.0 cm; and the zeolite filter media of the third-stage zeolite filter bed has a particle size of 0.5~0.6 cm.

10. The apparatus according to any one of claims 1-4, characterized in that, The iron content on the surface of the zeolite particles, as determined by energy dispersive spectroscopy analysis, is 20-50%.

11. The apparatus according to claim 10, characterized in that, The first sulfuric acid solution has a mass fraction of 42-65%; the second sulfuric acid solution has a mass fraction of 25-40%; the ferrous sulfate concentration is 2-6 mmol / L; the hydrogen peroxide molar concentration is 10-15 mmol / L; the first soaking time is 24-36 h; the second soaking time is 10-15 d; and the aeration time is 7-11 h / d.

12. The apparatus according to claim 11, characterized in that, The first sulfuric acid solution has a mass fraction of 45-55%; the second sulfuric acid solution has a mass fraction of 30-38%; the ferrous sulfate concentration is 3-5 mmol / L; the hydrogen peroxide molar concentration is 12-13 mmol / L; the first soaking time is 28-32 h; the second soaking time is 12-13 d; and the aeration time is 8-10 h / d.

13. The apparatus according to any one of claims 1-4, characterized in that, The top of the fluidized bed cylinder is provided with a coaxially arranged cylindrical overflow weir. The diameter of the overflow weir is larger than that of the fluidized bed cylinder, so that the bottom of the overflow weir and the top of the fluidized bed cylinder form an annular connection. The water outlet is provided on the annular connection to discharge purified water. The top of the reaction shell is provided with an anode connection column that is connected to the anode in the annular electrode group, and a cathode connection column that is connected to the cathode in the annular electrode group. The bottom of the reaction shell is also provided with a drain outlet.

14. A defluorination method for removing fluoride from water using the apparatus of claim 1.

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