Preparation method and application of Fe-Ni-C ternary three-dimensional electrode

Abstract

The invention discloses a preparation method and application of a Fe-Ni-C ternary three-dimensional electrode, the preparation method comprises the following steps: firstly, treating a landfill leachate membrane concentrated solution through a three-dimensional electro-Fenton technology, introducing a Fe-Ni-C ternary electrode to construct a three-dimensional electro-Fenton system, and removing refractory organic pollutants in the concentrated solution by anodic oxidation and in-situ Fenton reaction to obtain the Fe-Ni-C ternary three-dimensional electrode. Then, the electrochemical reduction technology is used for treating three-dimensional electro-Fenton effluent, a cathode is used for reducing nitrogen pollutants mainly containing NO3 <->-N, the landfill leachate membrane concentrated solution is treated through the two-stage combined treatment process of three-dimensional electro-Fenton combined electrochemical reduction, and finally efficient treatment of organic matter and nitrogen pollutants in the membrane concentrated solution is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of landfill leachate treatment, and in particular to a preparation method of a Fe-Ni-C ternary three-dimensional electrode and applications thereof. Background Art

[0002] Landfill leachate refers to a high-concentration, highly polluting organic wastewater that seeps out of the landfill layer during the landfill process due to the combined effects of moisture generated by the biodegradation of the garbage itself, infiltration of external precipitation (rainwater, snowmelt, etc.), and water retention within the garbage. "Biochemical treatment-membrane deep treatment," centered around reverse osmosis (RO) and nanofiltration (NF) technologies, is the current mainstream technology in the field of landfill leachate treatment. However, as a physical separation process, membrane treatment causes persistent accumulation and enrichment of refractory organic matter on the membrane retention side, producing a secondary product, landfill leachate membrane concentrate, which is more difficult to treat. Landfill leachate membrane concentrate has a complex composition, contains high concentrations of refractory organic pollutants, has high chroma and total nitrogen content, and has poor biodegradability. Treatment technology is difficult and the cost is high, making it a challenge in environmental governance.

[0003] Three-dimensional electro-Fenton technology is a highly efficient advanced oxidation water treatment technology. It improves the removal efficiency of organic pollutants by introducing particle electrodes (such as activated carbon, metal oxide-loaded catalysts, etc.) into the traditional two-dimensional electro-Fenton system to form a three-dimensional reaction system. When the three-dimensional electro-Fenton system treats membrane concentrate, on the one hand, the organic pollutants in the membrane concentrate are directly degraded by oxidation reaction on the anode surface; on the other hand, the cathode and the polarized three-dimensional electrodes, combined with the oxygen delivered by the aeration device and the H + Generate H2O2, while the Fe sites carried by the three-dimensional electrodes used in the existing technology can release Fe in situ 2+ , catalyzing H2O2 to produce Fenton reaction to produce free radicals mainly composed of ·OH to degrade organic matter. Although the three-dimensional electro-Fenton technology has a high effect on the degradation of organic matter, the existing three-dimensional electro-Fenton technology has a low degradation effect on nitrate nitrogen (NO3 - -N) is limited in removal effect, and the three-dimensional electrode has problems such as excessive iron ion leaching and low effective utilization rate. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a preparation method and application of an Fe-Ni-C ternary three-dimensional electrode to achieve effective treatment of organic matter and nitrogen pollutants in membrane concentrate, thereby solving the problems in the prior art of limited nitrogen pollutant removal effect of three-dimensional electro-Fenton technology, excessive iron ion leaching and low effective utilization rate of the three-dimensional electrodes used.

[0005] In the first aspect, in order to solve the above technical problems, the present invention provides a method for preparing a Fe-Ni-C ternary three-dimensional electrode, the specific steps of which are as follows:

[0006] Step 1: Evenly mix biochar, conductive carbon black, and polytetrafluoroethylene to obtain electrode slurry;

[0007] Step 2: Immerse the Fe-Ni foam in the electrode slurry prepared in step 1, so that the electrode slurry evenly covers the Fe-Ni foam, and then dry it;

[0008] Step 3: Place the product treated in step 2 in an inert atmosphere and calcine at 600°C-800°C for 1h-3h, and obtain a Fe-Ni-C ternary three-dimensional electrode after cooling.

[0009] Preferably, the biochar is prepared by calcining bamboo as raw material.

[0010] Preferably, the mass ratio of polytetrafluoroethylene:conductive carbon black:biochar is (8-10):(0.5-1):1.

[0011] Preferably, the average pore size of the foamed Fe-Ni is 0.7 mm to 1 mm.

[0012] In a second aspect, the present invention provides an application of a Fe-Ni-C ternary three-dimensional electrode. The Fe-Ni-C ternary three-dimensional electrode prepared by the above preparation method is used to treat landfill leachate membrane concentrate to remove organic matter in the concentrate.

[0013] Preferably, the Fe-Ni-C ternary three-dimensional electrode is installed in a device for treating landfill leachate membrane concentrate by a three-dimensional electro-Fenton-electrochemical reduction combination; wherein the device comprises an electrolytic cell, the electrolytic cell being divided into a three-dimensional electro-Fenton reaction zone and an electrochemical reduction reaction zone by a central partition; the three-dimensional electro-Fenton reaction zone and the electrochemical reduction reaction zone are fluidically connected via a water pump;

[0014] A first cathode electrode and a first anode electrode are provided in the three-dimensional electro-Fenton reaction zone, the first anode electrode is connected to the anode of a first direct current power supply, and the first cathode electrode is connected to the cathode of the first direct current power supply. A Fe-Ni-C ternary three-dimensional electrode is placed in the three-dimensional electro-Fenton reaction zone without contacting the first cathode electrode and the first anode electrode; the first anode electrode is a titanium-iridium-ruthenium coated electrode plate, and the first cathode electrode is one of foamed nickel and activated carbon fiber felt;

[0015] A second cathode electrode and a second anode electrode are provided in the electrochemical reduction reaction zone. The second anode electrode is connected to the anode of the second DC power supply, and the second cathode electrode is connected to the cathode of the second DC power supply. The second anode electrode is a titanium-iridium-ruthenium coated electrode plate, and the second cathode electrode is foam copper.

[0016] Preferably, a water pump pumps the supernatant in the three-dimensional electro-Fenton reaction zone into the electrochemical reduction reaction zone; a porous partition is also provided in the three-dimensional electro-Fenton reaction zone, and the porous partition is located below the first cathode electrode and the first anode electrode; an aeration device is also provided in the three-dimensional electro-Fenton reaction zone, and the aeration device is located above the porous partition and close to the cathode electrode; a mud discharge hole is provided below the porous partition, and a water outlet is provided at the bottom of the electrochemical reduction reaction zone.

[0017] In a third aspect, the present invention further provides a method for treating landfill leachate concentrate, using the device in the above application to treat the landfill leachate concentrate through the following steps:

[0018] S1: transport the membrane concentrate to the three-dimensional electro-Fenton reaction zone of the device, adjust the pH value of the membrane concentrate to 3-4, turn on the first DC power supply and the aeration device, control the plate spacing between the first cathode electrode and the first anode electrode to be 2 cm, and the electrolysis current density to be 20-25 mA / cm 2 The dosage of Fe-Ni-C ternary three-dimensional electrode is 10-15 g / L, and the aeration intensity is 0.05 m 3 / m 3 h for electrolysis reaction for 3-5 hours, and organic pollutants are effectively degraded through anodic oxidation and Fenton reaction in the three-dimensional electro-Fenton reaction zone;

[0019] S2: After the electrolysis reaction in S1 is completed, the first DC power supply and the aeration device are turned off, and the pH value of the water in the three-dimensional electro-Fenton reaction zone is adjusted to 9-10 to produce iron sludge, which is allowed to stand for at least 30 minutes for precipitation, and then the sludge and water are separated;

[0020] S3: The supernatant after S2 treatment is pumped into the electrochemical reduction reaction zone, the pH value of the supernatant is adjusted to 6.5-7.5, the second DC power supply is turned on for electrolysis reaction, the distance between the second cathode electrode and the second anode electrode is controlled to be 2 cm, and the current density is 20-25 mA / cm 2 The supernatant is denitrified in the electrochemical reduction reaction zone. After 3-5 hours of electrolysis, the electrolysis is completed and the treated water is discharged through the outlet.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention unexpectedly prepared a three-dimensional electrode with high catalytic efficiency and high stability. The composite structure of Fe-Ni alloy and carbon matrix forms a three-dimensional conductive network, which can significantly improve the catalytic activity of the three-dimensional electrode. By utilizing the synergistic effect between Fe and Ni, Fe promotes electron transfer and releases Fe in situ. 2+Ni can increase the generation of H2O2, thereby accelerating the generation of hydroxyl radicals in the electro-Fenton reaction, enabling it to degrade organic matter more efficiently; at the same time, the biochar coating reduces the leaching of Fe / Ni ions through physical isolation, thereby extending the life of the three-dimensional electrode.

[0023] 2. The present invention found that the three-dimensional porous structure of the Fe-Ni foam (pore size 0.7mm-1mm) provides a large specific surface area, which promotes the contact between the reactants and the active sites; the porous characteristics of the biochar further enhance the adsorption capacity, and cooperate with the electrochemical reaction to achieve the enrichment and degradation of pollutants; moreover, the calcination process can promote the formation of a stable interface between carbon and Fe-Ni. On the one hand, ultra-dispersed Fe-Ni nanoparticles are embedded, forming a micro-electrolytic cell group under electric field polarization, so that the reaction area extends from the electrode surface to the entire three-dimensional space; on the other hand, the carbon layer acts as an electron transport network, promoting the in-situ generation of H2O2 at the cathode, and reacting with Fe 2+ The Fenton reaction is continuously triggered without the need to add additional Fenton reagents.

[0024] 3. The present invention also combines the design of three-dimensional electro-Fenton with electrochemical reduction. Through the step-by-step treatment of degrading organic matter under acidic conditions, separating iron sludge by alkaline precipitation, and reducing nitrate under neutral conditions, it can achieve the simultaneous removal of organic matter and nitrogen pollutants. At the same time, the iron sludge can be recycled to avoid secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of the device for treating landfill leachate membrane concentrate using a three-dimensional electro-Fenton-electrochemical reduction combination as described in the present invention.

[0026] Figure 2 The three-dimensional fluorescence spectra of the landfill leachate membrane concentrate before and after treatment of the present invention; wherein a is the membrane concentrate stock solution, b is the effluent from the three-dimensional electro-Fenton reaction zone, and c is the effluent from the electrochemical reduction reaction zone.

[0027] Figure 3 The GC-MS total ion current chromatograms of the landfill leachate membrane concentrate before and after treatment of the present invention; wherein a is the original membrane concentrate solution, b is the effluent from the three-dimensional electro-Fenton reaction zone, and c is the effluent from the electrochemical reduction reaction zone.

[0028] In the figure: three-dimensional electro-Fenton reaction zone 1, first DC power supply 101, first anode electrode 102, first cathode electrode 103, Fe-Ni-C ternary three-dimensional electrode 104, porous partition 105, aeration pump 106, rotor flowmeter 107, aeration disk 108, mud discharge hole 109, electrochemical reduction reaction zone 2, second DC power supply 201, second anode electrode 202, second cathode electrode 203, water pump 204, water outlet 205. DETAILED DESCRIPTION

[0029] The present invention will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the present invention are within the scope of protection of the present invention.

[0030] Unless otherwise indicated in specific cases, the numerical ranges listed herein include the upper and lower limits, and all integers and fractions within the range, and are not limited to the specific values ​​listed when defining the range.

[0031] 1. Preparation method of Fe-Ni-C ternary three-dimensional electrode

[0032] Step 1: Evenly mix biochar, conductive carbon black, and polytetrafluoroethylene to obtain electrode slurry;

[0033] Step 2: Immerse the Fe-Ni foam in the electrode slurry prepared in step 1, so that the electrode slurry evenly covers the Fe-Ni foam, and then dry it;

[0034] Step 3: Place the product treated in step 2 in an inert atmosphere and calcine at 600°C-800°C for 1h-3h, and obtain a Fe-Ni-C ternary three-dimensional electrode after cooling.

[0035] The present invention found that there are bottlenecks in the traditional landfill leachate treatment. The traditional electro-Fenton electrode has a high iron dissolution rate, which leads to the loss of active components and the generation of secondary pollution (iron mud); the composition of the landfill leachate membrane concentrate is complex (high COD, high salt, nitrogen-containing pollutants), and a single process is difficult to simultaneously remove organic matter and nitrate nitrogen; the conductivity, catalytic activity and structural stability of the three-dimensional electrode are difficult to balance. Based on this, the present invention conceived the preparation of a new three-dimensional electrode. For this purpose, foamed Fe-Ni is selected as the substrate and bimetallic synergistic catalysis is utilized; it is coated with a composite slurry of bamboo-sourced biochar and conductive carbon black, and the amount of raw materials is optimized to balance bonding strength and conductivity; the biochar is then graphitized by high-temperature calcination to improve conductivity, and a carbon layer is formed to encapsulate metal particles to inhibit iron dissolution; finally, electro-Fenton (acidic degradation of organic matter) and electrochemical reduction (neutral denitrification) are combined and regulated in stages to avoid reaction interference and achieve the treatment of complex membrane concentrate.

[0036] To this end, the present invention found that the prepared Fe-Ni-C ternary three-dimensional electrode has excellent electrochemical properties and can enhance mass transfer and reaction efficiency. The foamed Fe-Ni substrate provides a large specific surface area and a hierarchical pore structure, which greatly improves the mass transfer rate of the reactants. Bamboo-derived biochar and conductive carbon black are calcined in a high-temperature inert atmosphere to form a carbon coating layer. On the one hand, the Fe-Ni-C ternary three-dimensional electrode forms a micro-electrolytic cell group under electric field polarization, so that the reaction area extends from the electrode surface to the entire three-dimensional space. On the other hand, the carbon layer acts as an electron transport network to promote the in-situ generation of H2O2 (O2+2H + +2e - →H2O2), and with Fe 2+ The Fenton reaction (·OH radical mineralization of organic matter) is continuously triggered. This process can continuously provide sufficient H2O2, and it also makes it completely unnecessary to add any Fenton reagent during the membrane concentrate treatment process. The Fenton reaction can still proceed normally and continuously. Biochar also plays a synergistic catalytic role. After high-temperature pyrolysis, the specific surface area of ​​Zhuyuan biochar increases significantly. Its microporous structure enriches pollutants through the molecular sieve effect, and the mesopores / macroporous structures accelerate ion diffusion. At the same time, the oxygen-containing functional groups (such as carboxyl and carbonyl) on the surface of biochar induce pseudocapacitive behavior, enhancing the charge transfer capacity of the electrode interface. Ultimately, the chemical structure of the total macromolecular organic matter in the difficult-to-degrade membrane concentrate is effectively destroyed through strong oxidation, and it is decomposed into small molecular weight organic matter, thereby achieving an overall decrease in the molecular weight of the organic matter, which is more conducive to subsequent electrochemical reduction treatment, making it easier for electrochemical reduction treatment to degrade pollutants in water bodies and achieve harmless treatment of membrane concentrate.

[0037] In some embodiments of the present invention, the biochar is prepared by calcining bamboo as a raw material and then carbonizing it.

[0038] In some embodiments of the present invention, the mass ratio of polytetrafluoroethylene: conductive carbon black: biochar is (8-10): (0.5-1): 1. Polytetrafluoroethylene acts as a binder. A ratio that is too low (below the range) will result in insufficient bonding strength, and the carbon material will easily fall off the foamed Fe-Ni. A ratio that is too high (exceeding the range) will reduce the porosity, block the pores of the foamed Fe-Ni, significantly reduce the effective specific surface area of ​​the electrode, and hinder the contact between pollutants and active sites. Conductive carbon black is used to connect the biochar particles and the foamed Fe-Ni, reducing the contact resistance and the overall electrode resistance. A ratio that is too low (below the range) will increase the internal resistance of the electrode, and a ratio that is too high (exceeding the range) will occupy the space of the biochar and weaken the overall reaction activity of the electrode.

[0039] In some embodiments of the present invention, the average pore size of the Fe-Ni foam is 0.7 mm to 1 mm. If the pore size of the Fe-Ni foam is too small, the electrode pores are easily blocked by the electrode slurry, significantly reducing the effective specific surface area of ​​the electrode. If the pore size is too large, the mechanical strength and structural stability of the prepared Fe-Ni-C electrode material will be reduced.

[0040] 2. Application of a Fe-Ni-C ternary three-dimensional electrode

[0041] In the present invention, the Fe-Ni-C ternary three-dimensional electrode prepared by the above preparation method is used to treat landfill leachate concentrate to remove organic matter in the concentrate.

[0042] Specifically, the Fe-Ni-C ternary three-dimensional electrode is installed in a device for treating landfill leachate membrane concentrate using a combined three-dimensional electro-Fenton and electrochemical reduction process. The device includes an electrolytic cell, which is divided into two independent regions by a central partition: a three-dimensional electro-Fenton reaction zone 1 and an electrochemical reduction reaction zone 2. The three-dimensional electro-Fenton reaction zone 1 and the electrochemical reduction reaction zone 2 are fluidically connected via a water pump 204, which pumps the supernatant from the three-dimensional electro-Fenton reaction zone to the electrochemical reduction reaction zone for further processing.

[0043] A first cathode electrode 103 and a first anode electrode 102 are provided in the three-dimensional electro-Fenton reaction zone 1. The first anode electrode 102 is connected to the anode of the first DC power supply 101, and the first cathode electrode 103 is connected to the cathode of the first DC power supply 101. The Fe-Ni-C ternary three-dimensional electrode 104 is placed in the three-dimensional electro-Fenton reaction zone, and it is ensured that it does not contact the first cathode electrode 103 and the first anode electrode 102; the first anode electrode 102 is a titanium-iridium-ruthenium coated electrode plate, and the first cathode electrode 103 is one of foamed nickel and activated carbon fiber felt.

[0044] A second cathode electrode 203 and a second anode electrode 202 are provided in the electrochemical reduction reaction zone 2. The second anode electrode 202 is connected to the anode of the second DC power supply 201, and the second cathode electrode 203 is connected to the cathode of the second DC power supply 201. The second anode electrode 202 is a titanium-iridium-ruthenium coated electrode plate, and the second cathode electrode 203 is foam copper.

[0045] Preferably, a water pump pumps the supernatant from the three-dimensional electro-Fenton reaction zone into the electrochemical reduction reaction zone. A porous partition 105 is also provided within the three-dimensional electro-Fenton reaction zone 1. The porous partition 105 is located below the first cathode electrode 103 and the first anode electrode 102, and the edges of the porous partition are fixedly connected to the inner sidewall of the three-dimensional electro-Fenton reaction zone. The porous partition acts as a physical barrier, separating the precipitation zone from the electrolysis reaction zone, allowing the iron sludge to sink to the bottom without touching the electrode plates. An aeration device is also provided within the three-dimensional electro-Fenton reaction zone. The aeration device is located above the porous partition and near the first cathode electrode 103. The aeration device includes an aeration pump 106, a rotor flowmeter 107, and an aeration disk 108. The aeration disk 108 is placed above the porous partition 105 and near the first cathode electrode 102. The aeration device continuously provides sufficient oxygen to the first cathode electrode. A mud discharge hole 109 is provided below the porous partition 105, through which the iron sludge generated during the treatment process can be discharged, facilitating its recovery. A water outlet 205 is provided at the bottom of the electrochemical reduction reaction zone 2, through which the treated water flows out of the electrochemical reduction reaction zone 2.

[0046] 3. A method for treating landfill leachate concentrate

[0047] The present invention uses the device in the above application to treat the landfill leachate concentrate through the following steps:

[0048] S1: transport the membrane concentrate to the three-dimensional electro-Fenton reaction zone of the device, adjust the pH value of the membrane concentrate to 3-4, turn on the first DC power supply and the aeration device, control the plate spacing between the first cathode electrode and the first anode electrode to be 2 cm, and the electrolysis current density to be 20-25 mA / cm 2 The dosage of Fe-Ni-C ternary three-dimensional electrode is 10-15 g / L, and the aeration intensity is 0.05 m 3 / m 3 h for electrolysis reaction for 3-5 hours, and organic pollutants are effectively degraded through anodic oxidation and Fenton reaction in the three-dimensional electro-Fenton reaction zone;

[0049] S2: After the electrolysis reaction in S1 is completed, the first DC power supply and the aeration device are turned off, and the pH value of the water in the three-dimensional electro-Fenton reaction zone is adjusted to 9-10 to produce iron sludge, which is allowed to stand for at least 30 minutes for precipitation, and then the sludge and water are separated;

[0050] S3: The supernatant after S2 treatment is pumped into the electrochemical reduction reaction zone, the pH value of the supernatant is adjusted to 6.5-7.5, the second DC power supply is turned on for electrolysis reaction, the distance between the second cathode electrode and the second anode electrode is controlled to be 2 cm, and the current density is 20-25 mA / cm 2The supernatant is denitrified in the electrochemical reduction reaction zone. After 3-5 hours of electrolysis, the electrolysis is completed and the treated water is discharged through the outlet.

[0051] The present invention combines the prepared Fe-Ni-C ternary three-dimensional electrode with a treatment device, and after treating the membrane concentrate, it is unexpectedly found that the carbon coating layer protects the Fe-Ni active sites, so that the ternary three-dimensional electrode can maintain high catalytic activity in a relatively wide pH environment (acidic pH 3-4); at the same time, after the Fenton reaction, the generated iron mud can be separated and recovered by alkali adjustment treatment, thereby reducing the cost of solid waste treatment; the pyrolytic carbon layer can significantly inhibit the leaching of Fe ions, thereby extending the service life of the ternary three-dimensional electrode and making the electrode long-lasting; and there is no need to add Fenton reagent during the treatment process, because the core of the electro-Fenton reaction is to generate H2O2 (O2+2H + +2e - →H2O2), this process requires continuous replenishment of H2O2 reagent and Fe 2+ Iron salt (commonly used ferrous sulfate). In the present invention, the three-dimensional electro-Fenton reaction zone adopts Fe-Ni-C ternary three-dimensional electrode. The large pore size (0.7mm-1mm) of the Fe-Ni foam and the carbon coating (biochar + conductive carbon black) can significantly increase the specific surface area and active sites, enhance the O2 adsorption and electron transfer efficiency, and achieve efficient and continuous H2O2 in-situ synthesis; the aeration device is also set near the cathode motor to continuously provide it with an O2 source and maintain the generation rate of H2O2; at the same time, in the present invention, Fe 2+ There is a stable self-circulation and slow-release mechanism. The Fe-Ni-C ternary three-dimensional electrode has a heterogeneous catalytic effect. The carbon coating formed by high-temperature calcination (600-800℃) is embedded in the Fe-Ni nanoparticles. Under the electric field polarization, the surface Fe 0 / Fe 2+ The active sites directly catalyze the decomposition of H2O2 into ·OH(Fe 2+ +H2O2→Fe 3+ +·OH+OH - ), the first cathode electrode reduces and regenerates Fe 2+ (Fe 3+ +e - →Fe 2+), forming a closed-loop iron cycle; the carbon coating layer acts as a physical barrier to control the leaching of Fe ions and avoid catalyst loss. Ultimately, through the design of the ternary three-dimensional electrode of the present invention, the oxygen-containing functional groups (carboxyl, carbonyl) of the carbon layer enhance the interfacial charge transfer, so that it can maintain high activity in the pH range of 3-4, and can also adjust the pH to 9-10 after the Fenton reaction to precipitate iron sludge (Fe(OH)3) to complete the iron sludge recovery. At the same time, the ternary three-dimensional electrode can still maintain structural stability in an alkaline environment due to carbon protection; at the same time, the present invention combines the back-end electrochemical reduction technology, the front-end three-dimensional electro-Fenton system uses anodic oxidation and in-situ Fenton reaction to remove difficult-to-degrade organic pollutants in the concentrate, and the back-end electrochemical reduction technology uses cathode reduction to remove NO3 - -N was the main nitrogen pollutant, and the landfill leachate membrane concentrate was treated using a two-stage combined treatment process of three-dimensional electro-Fenton combined with electrochemical reduction, ultimately achieving efficient treatment of organic matter and nitrogen pollutants in the membrane concentrate.

[0052] 4. Examples and Comparative Examples

[0053] 1. Preparation of Fe-Ni-C ternary three-dimensional electrode

[0054] Example 1

[0055] Step 1: sort, dry, and crush the biochar, and pass it through a 100-mesh sieve to obtain biochar powder for later use. Then, mix the biochar with conductive carbon black and polytetrafluoroethylene to obtain an electrode slurry. The mass ratio of biochar to conductive carbon black and polytetrafluoroethylene is 10:1:1.

[0056] Step 2: Immerse the Fe-Ni foam in the electrode slurry prepared in step 1, so that the electrode slurry evenly covers the Fe-Ni foam, and then place it in an electric oven at 105° C. and dry it for 1 hour.

[0057] Step 3: Place the product treated in step 2 in an inert atmosphere of N2, heat it to 600°C at a heating rate of 5°C / min, calcine it for 2h, and obtain a Fe-Ni-C ternary three-dimensional electrode after cooling.

[0058] Step 4: The membrane concentrate of landfill leachate was used as the treatment object. The water quality of the membrane concentrate was as follows: pH = 7.4-8.3, COD = 721.71 mg / L. The membrane concentrate was pumped from the water collection tank into the three-dimensional electro-Fenton reaction zone (1). Acid was added to adjust the pH value of the membrane concentrate to 4. The DC power supply and aeration device were turned on. The distance between the anode and cathode plates was controlled to 2 cm. The electrolysis current density was controlled to 20 mA / cm 2 , the dosage of Fe-Ni-C three-dimensional electrode is 10g / L, and the aeration intensity is 0.05m 3 / m 3·h for electrolysis reaction. After 5h of electrolysis, turn off the power supply and aeration device, add alkali to adjust the water quality to 10 to produce iron mud, let it stand for 30min for precipitation, and then separate the mud and water. After treatment, the COD of the supernatant is reduced to 120.85mg / L.

[0059] Example 2

[0060] This improvement was made based on Example 1, differing in that the mass ratio of biochar to conductive carbon black to polytetrafluoroethylene was 8:1:1. All other steps were identical to those in Example 1. After treatment, the COD content of the landfill leachate membrane concentrate was reduced to 151.24 mg / L.

[0061] Example 3

[0062] This improvement was made based on Example 1, differing in that the mass ratio of biochar to conductive carbon black to polytetrafluoroethylene was 10:0.5:1. All other steps were identical to those in Example 1. After treatment, the COD content of the landfill leachate membrane concentrate was reduced to 144.71 mg / L.

[0063] Example 4

[0064] An improvement was made based on Example 1, except that the calcination temperature was 700° C. The other steps were identical to those of Example 1. After treatment, the COD of the landfill leachate membrane concentrate was reduced to 167.29 mg / L.

[0065] Example 5

[0066] An improvement was made based on Example 1, except that the calcination temperature was 800° C. The other steps were identical to those of Example 1. After treatment, the COD of the landfill leachate membrane concentrate was reduced to 173.80 mg / L.

[0067] 2. Membrane concentrate of leachate from a landfill

[0068] The landfill leachate membrane concentrate was used as the treatment object. The water quality of the membrane concentrate was as follows: pH = 7.4 ~ 8.3, COD = 721.71 mg / L, TN = 239.76 mg / L, NH4 + -N=6.64mg / L,NO3 - -N=186.05mg / L.

[0069] Example 6

[0070] Taking Example 1 as an example, first, wastewater is pumped from the water collection tank into the three-dimensional electro-Fenton reaction zone (1) through a water pump, acid is added to adjust the pH value of the membrane concentrate to 4, the DC power supply and the aeration device are turned on, the distance between the anode and cathode plates is controlled to 2 cm, and the electrolysis current density is controlled to 24.93 mA / cm 2, the dosage of Fe-Ni-C three-dimensional electrode is 13.20g / L, and the aeration intensity is 0.05m 3 / m 3 ·h for electrolysis reaction. After 3h of electrolysis, turn off the power supply and aeration device, add alkali to adjust the water quality to 10 to produce iron mud, let it stand for 30min for precipitation, and then separate the mud and water. After treatment, the COD of the supernatant is reduced to 154.5mg / L, TN is reduced to 201.79mg / L, and NH4 + -N dropped to 0.2mg / L, NO3 - -N dropped to 166.54 mg / L.

[0071] The supernatant after the mud-water separation was then pumped into the electrochemical reduction reaction zone (2). The water pH was adjusted to 7, and the DC power supply was turned on for electrolysis. The distance between the anode and cathode plates was controlled to be 2 cm, and the current density was 22.10 mA / cm 2 After 3 hours of electrolysis, the power supply was turned off and the water was discharged through the outlet. The COD of the effluent dropped to 91.02 mg / L, TN dropped to 27.42 mg / L, and NH4 + -N is 0.4mg / L, NO3 - -N dropped to 22.49mg / L, effluent COD, NH4 + -N and TN both meet the emission limits in Table 2 of the "Pollution Control Standard for Municipal Waste Landfills" (GB 16889-2024).

[0072] Example 7

[0073] The method was adjusted based on Example 6, except that the electrolysis time of the three-dimensional electro-Fenton reaction zone was set to 5 h, and the electrolysis time of the electrochemical reduction reaction zone was set to 5 h. The other steps were exactly the same as those in Example 6. After the treatment in the three-dimensional electro-Fenton reaction zone, the COD of the supernatant was reduced to 105.67 mg / L, the TN was reduced to 161.89 mg / L, and the NH4 + -N dropped to 0.92mg / L, NO3 - -N dropped to 159.17mg / L. After treatment in the electrochemical reduction reaction zone, the final effluent COD dropped to 37.98mg / L, TN dropped to 22.44mg / L, and NH4 + -N is 0.32mg / L, NO3 - -N dropped to 6.51mg / L, effluent COD, NH4 + -N and TN both meet the emission limits in Table 2 of the "Pollution Control Standard for Municipal Waste Landfills" (GB 16889-2024).

[0074] Comparative Example 1

[0075] The membrane concentrate of landfill leachate was used as the treatment object. The water quality of the membrane concentrate was as follows: pH = 7.4-8.3, COD = 721.71 mg / L. Using Fe-Ni foam as a three-dimensional electrode, the membrane concentrate was pumped from the water collection tank to the three-dimensional electro-Fenton reaction zone (1). Acid was added to adjust the pH value of the membrane concentrate to 4. The DC power supply and aeration device were turned on. The distance between the anode and cathode plates was controlled to 2 cm, and the electrolysis current density was controlled to 20 mA / cm. 2 The dosage of foamed Fe-Ni three-dimensional electrode is 10g / L, and the aeration intensity is 0.05m 3 / m 3 ·h for electrolysis reaction. After 5h of electrolysis, turn off the power supply and aeration device, add alkali to adjust the water quality to 10 to produce iron mud, let it stand for 30min for precipitation, and then separate the mud and water. After treatment, the COD of the supernatant is reduced to 239.46mg / L.

[0076] Comparative Example 2

[0077] This improvement was made based on Comparative Example 1, differing in that foamed Fe was used as the three-dimensional electrode. All other steps were identical to Comparative Example 1. After treatment, the COD content of the landfill leachate membrane concentrate was reduced to 257.09 mg / L.

[0078] Comparative Example 3

[0079] This improvement was made based on Comparative Example 1, differing from it in that biochar was used as the three-dimensional electrode. All other steps were identical to Comparative Example 1. After treatment, the COD content of the landfill leachate membrane concentrate was reduced to 349.63 mg / L.

[0080] Further analysis of Example 6 is performed. Figure 2 The three-dimensional fluorescence spectra of the membrane concentrate stock solution (a), the three-dimensional electro-Fenton effluent (b) and the electrochemical reduction effluent (c) are shown. The three-dimensional fluorescence spectrum analysis technology can identify the characteristic fluorescence signals of different organic matter in the water body through the combination of excitation wavelength and emission wavelength, thereby achieving a refined analysis of the types and contents of organic pollutants. According to the similarity of the pollutant types, similar organic pollutants can be divided into five two-dimensional fluorescence regions (I, II, III, IV, V) according to specific fluorescence peaks, where region I represents protein-like organic matter such as tyrosine, region II represents protein-like organic matter such as tryptophan, region III represents fulvic acid-like organic matter, region IV represents soluble microbial metabolic byproducts, and region V represents humic acid-like organic matter. From Figure 2 It can be seen that the organic matter in the initial membrane concentrate is mainly humic acid and fulvic acid. After the membrane concentrate is treated by the three-dimensional electro-Fenton system, the content of humic substances is greatly reduced. After the electrochemical reduction system, the organic matter content is further reduced, indicating that the combined process can effectively remove the difficult-to-degrade organic matter in the membrane concentrate.

[0081] Figure 3 GC-MS total ion current chromatograms of membrane concentrate (a), three-dimensional electro-Fenton effluent (b) and electrochemical reduction effluent (c). Figure 3 As can be seen from the figure, the organic composition of the initial membrane concentrate is quite complex. After 3D electro-Fenton electrolysis, the overall abundance of organic matter in the water sample decreases, and the peak heights of the characteristic peaks of the substances are significantly reduced. This indicates that the 3D electro-Fenton technology effectively destroys the chemical structure of the recalcitrant macromolecular organic matter through strong oxidation, decomposing it into small molecular weight organic matter, thereby achieving an overall reduction in the molecular weight of the organic matter. After electrochemical reduction treatment, the peak areas of various organic matter species are further reduced, and most organic pollutants are effectively degraded. This demonstrates that the 3D electro-Fenton combined with electrochemical reduction process can effectively remove pollutants from membrane concentrate, achieving harmless treatment of the membrane concentrate.

[0082] The Fe ions leached from the concentrated solution after treatment in Example 1 and Comparative Example 1 were measured. After the reaction, the Fe 2+ 、Fe 3+ and total Fe ion concentrations were 48.87 mg / L, 29.83 mg / L and 78.70 mg / L, respectively. The Fe 2+ 、Fe 3+ The concentrations of Fe ions and total Fe ions were 14.55 mg / L, 25.74 mg / L, and 40.29 mg / L, respectively. 2+ 、Fe 3+ The total Fe ion concentrations were 3.36 times, 1.16 times and 1.95 times that of the Fe-Ni-C leaching concentrations at 600℃, respectively, proving that Fe-Ni-C can generate Fe in situ at 600℃. 2+ At the same time, it can alleviate the leaching of Fe ions, avoid excessive waste of Fe ions, and reduce the generation of iron sludge.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present invention that do not depart from the purpose and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a Fe-Ni-C ternary three-dimensional electrode, characterized in that: The specific steps are as follows: Step 1: Evenly mix biochar, conductive carbon black, and polytetrafluoroethylene to obtain electrode slurry; Step 2: Immerse the Fe-Ni foam in the electrode slurry prepared in step 1, so that the electrode slurry evenly covers the Fe-Ni foam, and then dry it; Step 3: Place the product treated in step 2 in an inert atmosphere and calcine at 600°C-800°C for 1h-3h, and obtain a Fe-Ni-C ternary three-dimensional electrode after cooling.

2. The preparation method according to claim 1, characterized in that The biochar is prepared by calcining bamboo as a raw material.

3. The preparation method according to claim 1, characterized in that the mass ratio of polytetrafluoroethylene: conductive carbon black: biochar is (8-10): (0.5-1):

1.

4. The preparation method according to claim 1, characterized in that The average pore size of the Fe-Ni foam is 0.7mm-1mm.

5. An application of a Fe-Ni-C ternary three-dimensional electrode, characterized in that: The Fe-Ni-C ternary three-dimensional electrode prepared by the preparation method of any one of claims 1 to 4 is used to treat landfill leachate concentrate to remove organic matter from the concentrate.

6. The application according to claim 5, characterized in that The Fe-Ni-C ternary three-dimensional electrode is installed in a device for treating landfill leachate membrane concentrate by a three-dimensional electro-Fenton-electrochemical reduction combination; wherein the device comprises an electrolytic cell, the electrolytic cell being divided into a three-dimensional electro-Fenton reaction zone (1) and an electrochemical reduction reaction zone (2) by a middle partition; the three-dimensional electro-Fenton reaction zone and the electrochemical reduction reaction zone are fluidically connected via a water pump (204); A first cathode electrode (103) and a first anode electrode (102) are provided in a three-dimensional electro-Fenton reaction zone, the first anode electrode (102) is connected to the anode of a first DC power supply (101), and the first cathode electrode (103) is connected to the cathode of the first DC power supply (101); a Fe-Ni-C ternary three-dimensional electrode (104) is placed in the three-dimensional electro-Fenton reaction zone and is not in contact with the first cathode electrode (103) and the first anode electrode (102); the first anode electrode is a titanium-iridium-ruthenium coated electrode plate, and the first cathode electrode is one of foamed nickel and activated carbon fiber felt; A second cathode electrode (203) and a second anode electrode (202) are provided in the electrochemical reduction reaction zone. The second anode electrode (202) is connected to the anode of a second DC power supply (201), and the second cathode electrode (203) is connected to the cathode of the second DC power supply (201). The second anode electrode is a titanium-iridium-ruthenium coated electrode plate, and the second cathode electrode is foam copper.

7. The application according to claim 6, characterized in that A water pump pumps the supernatant in the three-dimensional electro-Fenton reaction zone into the electrochemical reduction reaction zone; a porous partition (105) is also provided in the three-dimensional electro-Fenton reaction zone, and the porous partition is located below the first cathode electrode (103) and the first anode electrode (102); an aeration device is also provided in the three-dimensional electro-Fenton reaction zone, and the aeration device is located above the porous partition and close to the first cathode electrode; a mud discharge hole (109) is provided below the porous partition, and a water outlet (205) is provided at the bottom of the electrochemical reduction reaction zone.

8. A method for treating landfill leachate concentrate, characterized in that: The device according to any one of claims 6 to 7 is used to treat landfill leachate concentrate by the following steps: S1: transport the membrane concentrate to the three-dimensional electro-Fenton reaction zone of the device, adjust the pH value of the membrane concentrate to 3-4, turn on the first DC power supply and the aeration device, control the plate spacing between the first cathode electrode and the first anode electrode to be 2 cm, and the electrolysis current density to be 20-25 mA / cm 2 The dosage of Fe-Ni-C ternary three-dimensional electrode is 10-15 g / L, and the aeration intensity is 0.05 m 3 / m 3 h for electrolysis reaction for 3-5 hours, and organic pollutants are effectively degraded through anodic oxidation and Fenton reaction in the three-dimensional electro-Fenton reaction zone; S2: After the electrolysis reaction in S1 is completed, the first DC power supply and the aeration device are turned off, and the pH value of the water in the three-dimensional electro-Fenton reaction zone is adjusted to 9-10 to produce iron sludge, which is allowed to stand for at least 30 minutes for precipitation, and then the sludge and water are separated; S3: The supernatant after S2 treatment is pumped into the electrochemical reduction reaction zone, the pH value of the supernatant is adjusted to 6.5-7.5, the second DC power supply is turned on for electrolysis reaction, the distance between the second cathode electrode and the second anode electrode is controlled to be 2 cm, and the current density is 20-25 mA / cm 2 The supernatant is denitrified in the electrochemical reduction reaction zone. After 3-5 hours of electrolysis, the electrolysis is completed and the treated water is discharged through the outlet.

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