Method for preparing high-concentration and high-stability nanoscale zero-valent iron through microwave method and application

Abstract

The invention discloses a method for preparing high-concentration and high-stability nanoscale zero-valent iron through a microwave method and application. The method comprises the following steps that a, an iron ion solution is prepared; b) adding a dispersing agent and a surfactant; c) adding a reducing agent; d) microwave heating reaction; e) separating and purifying a product; and f) drying: drying the product at low temperature to obtain the nano zero-valent iron particles. The preparation method is easy and convenient to operate and short in reaction time, and the prepared nanoscale zero-valent iron particles are controllable in particle size, good in dispersity, environmentally friendly, capable of efficiently treating waste water containing nitrate radicals and heavy metal ions and suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial preparation, and in particular to a method for preparing high-concentration and high-stability nano zero-valent iron using a microwave method and its application. Background Art

[0002] Nanoscale zero-valent iron (nZVI) has garnered widespread attention in the field of environmental pollution control due to its high surface area and strong reducing properties. nZVI can effectively remove heavy metal ions, organic pollutants, and nitrates from water, and has promising application prospects.

[0003] Traditional nZVI preparation methods primarily include liquid-phase chemical reduction, thermal decomposition, microemulsion, and vapor deposition. However, these methods often suffer from drawbacks such as harsh reaction conditions, long reaction times, high energy consumption, complex equipment, and high production costs. Furthermore, the resulting nZVI particles are prone to aggregation, resulting in a reduction in specific surface area, which compromises their effectiveness in environmental remediation applications.

[0004] Microwave-assisted synthesis technology has been widely used in the preparation of nanomaterials due to its advantages such as uniform heating, fast reaction speed, low energy consumption, and strong selectivity. However, the application of microwave technology in the preparation of nZVI has not been deeply studied and applied.

[0005] Therefore, providing a simple, rapid, low-energy, and highly controllable microwave method for preparing nZVI is of great significance for promoting the application of nZVI in the environmental field. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method and its application.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method comprises the following steps:

[0009] a) preparing an iron ion solution: dissolving a soluble divalent iron salt in deionized water to obtain a divalent iron ion aqueous solution;

[0010] b) adding a dispersant and a surfactant: adding a dispersant and a surfactant to the divalent iron ion solution of step a) and stirring uniformly;

[0011] c) adding a reducing agent: adding a reducing agent to the mixed solution in proportion while stirring, and continuing to stir to form a uniform reaction mixture;

[0012] d) microwave heating reaction: transferring the reaction mixture of step c) into a microwave reaction vessel and heating;

[0013] e) Product separation and purification: After the reaction is completed, cool, centrifuge and separate the product, wash and remove impurities;

[0014] f) Drying: Drying the product at low temperature to obtain nanometer zero-valent iron particles.

[0015] Preferably, in step a), the soluble divalent iron salt is one or more of ferrous sulfate and ferrous chloride;

[0016] The concentration range of the ferrous sulfate is 0.1-0.4 mol / L, and the molecular weight is 278.02;

[0017] The concentration range of the ferrous chloride is 0.15-0.5 mol / L, and the molecular weight is 198.81;

[0018] The amount of the soluble divalent iron salt added is:

[0019] The nano-scale ferrous sulfate: 27.8 g / 500 mL deionized water;

[0020] The micron-grade ferrous chloride: 29.8 g / 500 mL deionized water.

[0021] Preferably, in step b), the dispersant and surfactant are one or more of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG); the dispersant also includes sodium dodecylbenzenesulfonate (SDBS) and gelatin;

[0022] The concentration of the polyvinylpyrrolidone PVP is 5-15g / L;

[0023] The concentration of the polyethylene glycol PEG is 5-20 g / L and the molecular weight is 400;

[0024] The concentration of the sodium dodecylbenzenesulfonate (SDBS) is 2-5 g / L;

[0025] The concentration of the gelatin is 3-8 g / L.

[0026] Preferably, in step c), the reducing agent is one or more of hydrazine hydrate and ethylene glycol;

[0027] The molar ratio of hydrazine hydrate to divalent iron ion is 2:1-5:1;

[0028] The concentration range of the hydrazine hydrate is 0.5-2.0 mol / L;

[0029] The volume ratio of the ethylene glycol to deionized water is 1:2-1:1.

[0030] Preferably, in step d), the microwave power is 300-800 W, the heating time under the microwave power is 1-10 minutes, and the microwave heating temperature is 60-100° C.

[0031] Preferably, in step e), the centrifugation conditions are:

[0032] Nanoscale: 8000-12000 rpm, 10-15 minutes;

[0033] Micron level: 6000-8000rpm, 5-10 minutes.

[0034] Preferably, in step e), washing is performed by repeatedly washing with deionized water and anhydrous ethanol three times to remove unreacted reagents and impurities.

[0035] Preferably, in step f), the vacuum drying temperature at low temperature is 40-60° C., and the drying time is 8-12 hours.

[0036] Preferably, in step f), the particle size of the obtained nano zero-valent iron particles is 40-100 nanometers.

[0037] A method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method is used in treating wastewater containing nitrate or heavy metal ions. The specific application method is as follows:

[0038] Nano-zero-valent iron particles are added to wastewater, stirred for reaction, and then the nano-zero-valent iron particles are separated to remove pollutants in the wastewater.

[0039] Compared with the prior art, the present invention has achieved the following technical effects:

[0040] (1) The method is simple and quick:

[0041] The present invention utilizes microwave heating, which has uniform heating and fast reaction speed, and can be completed in only 1-10 minutes, with high reduction efficiency;

[0042] (2) Controllable particle size and good dispersibility:

[0043] The present invention adjusts the reaction conditions and adds a dispersant to prepare nZVI particles with uniform particle size distributed in the range of 40-100 nm and good dispersibility;

[0044] (3) Green and environmentally friendly:

[0045] No harmful gases are emitted during the reaction process of the present invention, and the preparation process is safe, clean, and environmentally friendly;

[0046] (4) Efficient wastewater treatment:

[0047] The nZVI prepared by the present invention can effectively remove nitrate and heavy metal ions in wastewater, and the treatment process is fast and efficient;

[0048] (5) Suitable for industrial production:

[0049] The method of the invention has simple process, mild reaction conditions, is easy to scale up, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention provides a flow chart of a method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method and its application.

[0051] Figure 2 This is a method for preparing high-concentration and high-stability nano-zero-valent iron using a microwave method of the present invention and an SEM image of the carbon-coated nano-zero-valent iron used;

[0052] Among them, ab are SEM images of 4-8 μm carbon-coated nano-zero-valent iron; cd are SEM images of 6-10 μm carbon-coated nano-zero-valent iron; e is SEM-EDS image of 6-10 μm carbon-coated nano-zero-valent iron; fg are the element ratios of carbon-coated nano-zero-valent iron;

[0053] Figure 3 This is a TEM image of the nano-zero-valent iron prepared by a microwave method with high concentration and high stability;

[0054] Among them, a is the TEM image of 200-400nm nano-zero-valent iron; b is the TEM image of 100-300nm nano-zero-valent iron. DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0056] A method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method comprises the following steps:

[0057] a) preparing an iron ion solution: dissolving a soluble divalent iron salt in deionized water to obtain a divalent iron ion aqueous solution;

[0058] b) adding a dispersant and a surfactant: adding a dispersant and a surfactant to the divalent iron ion solution of step a) and stirring uniformly;

[0059] c) adding a reducing agent: adding a reducing agent to the mixed solution in proportion while stirring, and continuing to stir to form a uniform reaction mixture;

[0060] d) microwave heating reaction: transferring the reaction mixture of step c) into a microwave reaction vessel, heating the reaction mixture at a microwave power of 300-800 W for 1-10 minutes at a microwave heating temperature of 60-100° C.

[0061] e) Product separation and purification: After the reaction is completed, the product is cooled, centrifuged, and washed three times with deionized water and anhydrous ethanol to remove unreacted reagents and impurities;

[0062] f) Drying: The product is vacuum dried at a low temperature of 40-60° C. for 8-12 hours to obtain nano zero-valent iron particles.

[0063] In step a), the soluble divalent iron salt is one or more of ferrous sulfate and ferrous chloride;

[0064] The concentration range of ferrous sulfate is 0.1-0.4 mol / L, and the molecular weight is 278.02;

[0065] The concentration range of ferrous chloride is 0.15-0.5 mol / L, and the molecular weight is 198.81;

[0066] The amount of soluble divalent iron salt added is:

[0067] Ferrous sulfate nanoparticles: 27.8 g / 500 mL deionized water;

[0068] Ferrous chloride micron grade: 29.8g / 500mL deionized water.

[0069] In step b), the dispersant and surfactant are one or more of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG); the dispersant also includes sodium dodecylbenzene sulfonate (SDBS) and gelatin;

[0070] The concentration of polyvinylpyrrolidone PVP is 5-15g / L;

[0071] The concentration of polyethylene glycol PEG is 5-20 g / L and the molecular weight is 400;

[0072] The concentration of sodium dodecylbenzenesulfonate (SDBS) is 2-5 g / L;

[0073] The concentration of gelatin is 3-8g / L.

[0074] In step c), the reducing agent is one or more of hydrazine hydrate and ethylene glycol;

[0075] The molar ratio of hydrazine hydrate to divalent iron ion is 2:1-5:1;

[0076] The concentration range of hydrazine hydrate is 0.5-2.0 mol / L;

[0077] The volume ratio of ethylene glycol to deionized water is 1:2-1:1.

[0078] In step e), the centrifugal conditions are:

[0079] Nanoscale: 8000-12000 rpm, 10-15 minutes;

[0080] Micron level: 6000-8000rpm, 5-10 minutes.

[0081] In step f), the particle size of the obtained nano-zero-valent iron particles is 40-100 nanometers.

[0082] A method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method is used in treating wastewater containing nitrate or heavy metal ions. The specific application method is as follows:

[0083] Nano-zero-valent iron particles are added to wastewater, stirred for reaction, and then the nano-zero-valent iron particles are separated to remove pollutants in the wastewater.

[0084] Example 1: Preparation of Nano-Zero-Valent Iron Particles Using Microwave Method

[0085] 1. Reagents and Materials:

[0086] Iron salt: ferrous sulfate heptahydrate, analytical grade;

[0087] Reducing agent: hydrazine hydrate, analytical grade;

[0088] Dispersant: polyvinylpyrrolidone (PVP), analytical grade;

[0089] Solvent: deionized water.

[0090] 2. Preparation steps:

[0091] a) Prepare iron ion solution: Weigh 27.8 g of ferrous sulfate heptahydrate and dissolve it in 500 ml of deionized water to obtain 0.2 mol / L Fe 2+ solution;

[0092] b) adding a dispersant and a surfactant: adding 5 g of PVP to the divalent iron ion solution of step a) and stirring for 30 minutes until it is completely dissolved to form a uniform light green solution;

[0093] c) Adding a reducing agent: Slowly add 50 ml of 1 mol / L hydrazine hydrate solution to the mixed solution under stirring, continue stirring for 15 minutes, and the color of the solution gradually turns dark gray;

[0094] d) Microwave heating reaction: The reaction mixture of step c) was transferred to a microwave reaction vessel, placed in a microwave reactor, and the microwave power was set to 600 W, the reaction time was 5 minutes, and the temperature was controlled at 80° C.;

[0095] e) Product Isolation and Purification: After the reaction, the container was removed and cooled to room temperature. The solution was centrifuged at 8000 rpm for 10 minutes, the supernatant was discarded, and the precipitate was washed three times with deionized water and anhydrous ethanol to remove impurities.

[0096] f) Drying: The washed product was placed in a vacuum drying oven and dried at 40° C. for 12 hours to obtain black nano-zero-valent iron powder.

[0097] 3. Characterization of results:

[0098] Particle size analysis: Transmission electron microscopy (TEM) observation showed that the obtained nZVI particles were spherical with a particle size distribution of 50-80 nm;

[0099] Crystal structure: X-ray diffraction (XRD) tests show that the product is crystalline zero-valent iron;

[0100] Specific surface area: According to BET test, the specific surface area of nZVI is 35m 2 / g.

[0101] Example 2: Preparation of Nano Zero-Valent Iron Particles Using Ethylene Glycol as Reducing Agent

[0102] 1. Reagents and Materials:

[0103] Iron salt: ferrous chloride tetrahydrate, analytical grade;

[0104] Reducing agent: ethylene glycol, analytical grade;

[0105] Dispersant: polyethylene glycol (PEG-400), analytical grade;

[0106] Solvent: deionized water.

[0107] 2. Preparation steps:

[0108] a) Prepare iron ion solution: Weigh 19.8 g of ferrous chloride tetrahydrate and dissolve it in 500 ml of deionized water to obtain 0.2 mol / L Fe 2+ solution;

[0109] b) adding a dispersant and a surfactant: adding 3 g of PEG-400 to the divalent iron ion solution of step a) and stirring for 20 minutes to form a homogeneous solution;

[0110] c) Adding a reducing agent: Add 100 ml of ethylene glycol to the mixed solution while stirring, and continue stirring for 10 minutes;

[0111] d) Microwave heating reaction: The reaction mixture of step c) was transferred to a microwave reaction vessel, placed in a microwave reactor, and the microwave power was set to 700 W, the reaction time was 8 minutes, and the temperature was controlled at 90° C.;

[0112] e) Product separation and purification: After the reaction is completed, the product is cooled to room temperature, centrifuged, and washed three times with deionized water and anhydrous ethanol to remove impurities;

[0113] f) Drying: The product was placed in a vacuum drying oven at 50° C. and dried for 10 hours to obtain nanometer zero-valent iron powder.

[0114] 3. Characterization of results:

[0115] Particle size analysis: Scanning electron microscopy (SEM) observation showed that the particle size of nZVI particles was distributed in the range of 60-100 nm with uniform morphology.

[0116] Magnetic test: nZVI has good ferromagnetism as tested by vibrating sample magnetometer (VSM).

[0117] Example 3: Preparation of small particle size nZVI using low concentration iron salt

[0118] 1. Reagents and Materials:

[0119] Iron salt: ferrous sulfate heptahydrate, analytical grade;

[0120] Reducing agent: hydrazine hydrate, analytical grade;

[0121] Dispersant: polyvinylpyrrolidone (PVP), analytical grade;

[0122] Solvent: deionized water.

[0123] 2. Preparation steps:

[0124] a) Prepare iron ion solution: Weigh 13.9 g of ferrous sulfate heptahydrate and dissolve it in 500 ml of deionized water to obtain 0.1 mol / L Fe 2+ solution;

[0125] b) adding a dispersant and a surfactant: adding 2.5 g of PVP to the divalent iron ion solution of step a) and stirring for 30 minutes until it is completely dissolved to form a uniform light green solution;

[0126] c) Adding a reducing agent: Slowly add 50 ml of 0.5 mol / L hydrazine hydrate solution to the mixed solution under stirring, continue stirring for 15 minutes, and the color of the solution gradually turns dark gray;

[0127] d) Microwave heating reaction: The reaction mixture of step c) was transferred to a microwave reaction vessel, placed in a microwave reactor, set the microwave power to 500 W, the reaction time to 3 minutes, and the temperature to 70° C.;

[0128] e) Product Isolation and Purification: After the reaction, the container was removed and cooled to room temperature. The solution was centrifuged at 8000 rpm for 10 minutes, the supernatant was discarded, and the precipitate was washed three times with deionized water and anhydrous ethanol to remove impurities.

[0129] f) Drying: The washed product was placed in a vacuum drying oven and dried at 40° C. for 12 hours to obtain black nano-zero-valent iron powder.

[0130] 3. Characterization of results:

[0131] Particle size analysis: Transmission electron microscopy (TEM) observation showed that the particle size distribution was 40-60 nm.

[0132] Crystal structure: X-ray diffraction (XRD) tests show that the product has a face-centered cubic crystal structure of pure metallic platinum;

[0133] Specific surface area: According to BET test, the specific surface area of nZVI is 42m 2 / g;

[0134] Nitrate removal rate: 95%.

[0135] Example 4: Preparation of magnetic nZVI using high concentration ethylene glycol

[0136] 1. Reagents and Materials:

[0137] Iron salt: ferrous chloride tetrahydrate, analytical grade;

[0138] Reducing agent: ethylene glycol, analytical grade;

[0139] Dispersant: polyethylene glycol (PEG-400), analytical grade;

[0140] Solvent: deionized water.

[0141] 2. Preparation steps:

[0142] a) Prepare iron ion solution: weigh 39.6 g of ferrous chloride tetrahydrate and dissolve it in 500 ml of deionized water to obtain 0.4 mol / L Fe 2+ solution;

[0143] b) adding a dispersant and a surfactant: adding 10 g of PEG-400 to the divalent iron ion solution of step a) and stirring for 20 minutes to form a homogeneous solution;

[0144] c) Adding a reducing agent: Add 200 ml of ethylene glycol to the mixed solution while stirring, and continue stirring for 10 minutes;

[0145] d) Microwave heating reaction: The reaction mixture of step c) was transferred to a microwave reaction vessel, placed in a microwave reactor, and the microwave power was set to 800 W, the reaction time was 10 minutes, and the temperature was controlled at 95° C.;

[0146] e) Product separation and purification: After the reaction is completed, the product is cooled to room temperature, centrifuged, and washed three times with deionized water and anhydrous ethanol to remove impurities;

[0147] f) Drying: The product was placed in a vacuum drying oven at 50° C. and dried for 10 hours to obtain nanometer zero-valent iron powder.

[0148] 3. Characterization of results:

[0149] Particle size analysis: Scanning electron microscopy (SEM) observation showed that the particle size of nZVI particles was distributed in the range of 80-120 nm.

[0150] Magnetic test: tested using a vibrating sample magnetometer (VSM), the magnetization intensity is 85emu / g.

[0151] Cr 6+ Removal rate: 99.5%.

[0152] Among them, the effect of iron salt concentration on particle size is shown in Table 1;

[0153] Table 1:

[0154]

[0155] The reducing agent ratio and pollutant removal efficiency are shown in Table 2;

[0156] Table 2:

[0157]

[0158] SEM image of carbon-coated nano-zero-valent iron Figure 2 As shown;

[0159] Among them, ab are SEM images of 4-8μm carbon-coated nano-zero-valent iron; cd are SEM images of 6-10μm carbon-coated nano-zero-valent iron; e is SEM-EDS image of 6-10μm carbon-coated nano-zero-valent iron; fg are the element proportions of carbon-coated nano-zero-valent iron.

[0160] TEM image of nano-zero-valent iron Figure 3 As shown;

[0161] Among them, a is the TEM image of 200-400nm nano-zero-valent iron; b is the TEM image of 100-300nm nano-zero-valent iron.

[0162] Example 5: Treatment of nitrate-containing wastewater with nano-zero-valent iron

[0163] 1. Wastewater preparation:

[0164] A sodium nitrate solution with a concentration of 100 mg / L was prepared to simulate nitrate-containing wastewater.

[0165] 2. Processing process:

[0166] 0.2 g of nZVI prepared in Example 1 was added to 200 ml of simulated wastewater and ultrasonically dispersed for 10 minutes.

[0167] The reaction was stirred at room temperature for 1 hour;

[0168] After the reaction was completed, the solid matter was separated by centrifugation, and the supernatant was taken to determine the nitrate concentration.

[0169] 3. Results:

[0170] After treatment, the nitrate concentration dropped to 10 mg / L and the removal rate reached 90%.

[0171] Example 6: Treatment of wastewater containing heavy metal ions with nano-zero-valent iron

[0172] 1. Wastewater preparation:

[0173] A hexavalent chromium solution with a concentration of 50 mg / L was prepared to simulate heavy metal-containing wastewater.

[0174] 2. Processing process:

[0175] 0.1 g of nZVI prepared in Example 2 was added to 100 ml of simulated wastewater and ultrasonically dispersed for 5 minutes.

[0176] The reaction was stirred at room temperature for 2 hours;

[0177] After the reaction was completed, the solid matter was separated by centrifugation and the supernatant was taken to determine Cr 6+ concentration.

[0178] 3. Results:

[0179] After treatment, Cr 6+ The concentration dropped to 0.5 mg / L and the removal rate reached 99%.

[0180] The above description is merely a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method, characterized in that: The steps include: a) preparing an iron ion solution: dissolving a soluble divalent iron salt in deionized water to obtain a divalent iron ion aqueous solution; b) adding a dispersant and a surfactant: adding a dispersant and a surfactant to the divalent iron ion solution of step a) and stirring uniformly; c) adding a reducing agent: adding a reducing agent to the mixed solution in proportion while stirring, and continuing to stir to form a uniform reaction mixture; d) microwave heating reaction: transferring the reaction mixture of step c) into a microwave reaction vessel and heating; e) Product separation and purification: After the reaction is completed, cool, centrifuge and separate the product, wash and remove impurities; f) Drying: Drying the product at low temperature to obtain nanometer zero-valent iron particles.

2. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In step a), the soluble divalent iron salt is one or more of ferrous sulfate and ferrous chloride; The concentration range of the ferrous sulfate is 0.1-0.4 mol / L, and the molecular weight is 278.02; The concentration range of the ferrous chloride is 0.15-0.5 mol / L, and the molecular weight is 198.81; The amount of the soluble ferrous salt added is: The nano-scale ferrous sulfate: 27.8 g / 500 mL deionized water; The micron-grade ferrous chloride: 29.8 g / 500 mL deionized water.

3. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step b), the dispersant and surfactant are one or more of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG); the dispersant also includes sodium dodecylbenzene sulfonate (SDBS) and gelatin; The concentration of the polyvinylpyrrolidone PVP is 5-15g / L; The concentration of the polyethylene glycol PEG is 5-20 g / L and the molecular weight is 400; The concentration of the sodium dodecylbenzenesulfonate (SDBS) is 2-5 g / L; The concentration of the gelatin is 3-8 g / L.

4. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step c), the reducing agent is one or more of hydrazine hydrate and ethylene glycol; The molar ratio of hydrazine hydrate to divalent iron ion is 2:1-5:1; The concentration range of the hydrazine hydrate is 0.5-2.0 mol / L; The volume ratio of the ethylene glycol to deionized water is 1:2-1:

1.

5. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step d), the microwave power is 300-800W, the heating time under the microwave power is 1-10 minutes, and the microwave heating temperature is 60-100°C.

6. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step e), the centrifugation conditions are: Nanoscale: 8000-12000 rpm, 10-15 minutes; Micron level: 6000-8000rpm, 5-10 minutes.

7. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step e), washing is performed by repeatedly washing with deionized water and anhydrous ethanol three times to remove unreacted reagents and impurities.

8. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step f), the vacuum drying temperature is 40-60° C. and the drying time is 8-12 hours.

9. The method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claim 1, characterized in that: In the step f), the particle size of the obtained nano zero-valent iron particles is 40-100 nanometers.

10. Application of the method for preparing high-concentration and high-stability nano-zero-valent iron by microwave method according to claims 1-9 in treating wastewater containing nitrate or heavy metal ions, characterized in that: The specific application method is: Nano-zero-valent iron particles are added to wastewater, stirred for reaction, and then the nano-zero-valent iron particles are separated to remove pollutants in the wastewater.

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