A nitrogen-modified micron zero-valent iron material and its preparation method and application

Abstract

The present invention relates to a nitrogen-modified micron zero-valent iron material and a preparation method and application thereof, which specifically comprises: in an anaerobic sealed system, a nitrogen source is added after oscillating an iron source for 10 minutes, and after constant temperature flip oscillation for a certain period of time, N-ZVI can be obtained by filtering and freeze drying. The nitrogen source is ammonium chloride, ammonium bromide, and ammonium iodide, and the nitrogen-iron molar ratio is 0.028-0.07:1. The present invention applies the obtained material to the treatment of chromium-containing wastewater. Compared with micron zero-valent iron, the pseudo-first-order reaction kinetic constant (k) of nitrogen-modified micron zero-valent iron for chromium removal is obs ) increased by 23.85-41.62 times, and the best nitrogen-iron ratio (0.056) obs Up to 0.328min ‑1 The material modifies the main material zero-valent iron by nitrogen species, realizes the effective regulation of the surface of the zero-valent iron material, and improves the overall electronic conductivity of the material. Therefore, the present invention is of great significance for the development of modified zero-valent iron materials with high activity and high stability, as well as the treatment of heavy metal-contaminated wastewater.

Description

Technical field:

[0001] The invention belongs to the field of environmental material preparation and water treatment, and specifically relates to a nitrogen-modified micron zero-valent iron material and a preparation method thereof, as well as an application in efficiently removing hexavalent chromium from water. Background technology:

[0002] Heavy metals are a type of pollutant that is highly soluble, easy to migrate, and difficult to degrade. Untreated heavy metal wastewater will pollute lakes, rivers, and groundwater to varying degrees, seriously endangering the survival of organisms and human health. Hexavalent chromium (Cr(VI)), which is 100 times more toxic than trivalent chromium, can cause nasal ulcers and perforations, asthma, changes in lung function, skin ulcers, stomach, liver, and kidney damage, and damage to the immune system. Therefore, seeking feasible ways to remove hexavalent chromium (CrVI) from water bodies is of great significance for environmental pollution control. In recent years, zero-valent iron (ZVI) has been widely used in heavy metal wastewater treatment due to its strong reducing ability, low cost, easy availability, and environmental friendliness.

[0003] Although zero-valent iron has high reduction activity and can efficiently remove a variety of heavy metals and organic matter from water, its disadvantages such as easy aggregation, low electron utilization, poor electron selectivity, and easy passivation during transportation and reaction have always restricted its large-scale application in industrial treatment. Therefore, the modification research of zero-valent iron materials needs to be promoted. In recent years, scholars at home and abroad have proposed many methods for modifying or modifying zero-valent iron. Among them, the most widely studied are (1) bimetallic method [Pd-Fe nanoparticles stabilized by chitosan derivatives for perchloroethene dechlorination. Environ Int, 37 (2011) 1044.] This method accelerates the reaction of zero-valent iron by introducing a second metal under the action of the primary cell, but the synthesis and production of bimetallic materials are relatively difficult, and the manufacture of bimetallic materials will bring certain material consumption, such as the metal used as the cathode material cannot be recovered after the reaction. (2) Sulfidation has attracted extensive attention as a new modification method for stabilizing ZVI [Effects of Sulfidation, Magnetization, and Oxygenation on Azo Dye Reduction by Zerovalent Iron. Environ Sci Technol, 50 (2016) 11879]. However, the release of sulfides during the sulfidation process will affect the environment and human health. Therefore, it is necessary to further explore green and environmentally friendly zero-valent iron modification methods to achieve the widespread application of zero-valent iron materials in future industrial wastewater treatment. Summary of the invention:

[0004] In view of the shortcomings of the prior art, especially the low electron utilization rate of zero-valent iron, easy passivation, easy agglomeration, and the need for improvement in zero-valent iron modification technology, the present invention provides a nitrogen-modified zero-valent iron material and a method for quickly removing hexavalent chromium from water. Micronized zero-valent iron and ammonium salts (ammonium chloride, ammonium bromide, ammonium iodide) are used as iron source and nitrogen source respectively, and nitrogen species are successfully introduced into the surface of zero-valent iron through constant temperature flip oscillation, so as to achieve effective regulation of the surface of zero-valent iron, thereby achieving the purpose of efficiently treating chromium-containing wastewater. The raw materials of this material are cheap and easy to obtain, and the preparation method is simple and low in energy consumption. In the future, it can be widely used in industry to a certain extent. Summary of the invention:

[0006] In the present invention, a nitrogen source (ammonium salt) is added to the micron zero-valent iron after being pickled with a buffer solution, and after reacting with the ammonium salt for a certain period of time, a nitrogen-modified micron zero-valent iron material is formed, which is not only easy to operate, but also realizes effective regulation of the surface of the micron zero-valent iron, greatly improving the electron transfer capacity of the material. The material is added to chromium-containing wastewater and mechanically stirred to efficiently remove chromium pollutants in the water, providing certain theoretical support for the modification of zero-valent iron materials and industrial wastewater treatment. Detailed description of the invention:

[0008] The technical solution adopted by the present invention is as follows:

[0009] A nitrogen-modified micron zero-valent iron material, wherein nitrogen species are introduced into the surface of zero-valent iron, and effective bonding between Fe and N exists, and the molar ratio of nitrogen to iron is (0.028-0.07):1.

[0010] According to the present invention, preferably, the molar ratio of nitrogen to iron is (0.04-0.06):1, and most preferably 0.056:1.

[0011] According to the present invention, preferably, the nitrogen species in the material is NH4 + It exists in the form of and NH3(aq).

[0012] According to the present invention, preferably, the nitrogen source used for nitrogen modification is an ammonium halide salt, more preferably ammonium chloride, ammonium bromide or ammonium iodide.

[0013] According to the present invention, the method for preparing the above-mentioned nitrogen-modified micron zero-valent iron material comprises:

[0014] In an acetic acid-sodium acetate buffer solution, the micron zero-valent iron is oscillated at a constant temperature under anaerobic conditions to remove the passivation layer film on the surface of the zero-valent iron. Then, ammonium salt is added to the system, and the reaction is reversed and vibrated at a constant temperature. After filtration and freeze-drying, the nitrogen-modified micron zero-valent iron material is obtained. The material is sealed and stored for future use.

[0015] According to the present invention, preferably, the anaerobic condition is to introduce high-purity nitrogen into the preparation system until the dissolved oxygen is zero.

[0016] According to the present invention, preferably, the particle size of the micron zero-valent iron particles is 70-80 μm, most preferably 75 μm.

[0017] According to the present invention, preferably, the ammonium salt is an ammonium halide salt, more preferably ammonium chloride, ammonium bromide or ammonium iodide, and the concentration of the ammonium salt is 1 mol / L.

[0018] According to the present invention, preferably, the pH of the acetic acid-sodium acetate buffer solution is 6±0.05, and the concentration is 0.2 mol / L.

[0019] According to the present invention, preferably, the molar ratio of zero-valent iron to ammonium salt is 1:(0.028-0.07), further preferably 1:(0.04-0.06), and most preferably 1:0.056.

[0020] According to the present invention, preferably, the micronized zero-valent iron is oscillated under anaerobic conditions for 10 minutes.

[0021] According to the present invention, preferably, the reaction time with the ammonium salt (nitrogen modification) in the above reaction system is 10 hours.

[0022] According to the present invention, the above-mentioned nitrogen-modified micron zero-valent iron material is used to treat chromium-containing wastewater.

[0023] According to the present invention, a method for rapidly treating chromium-containing wastewater using the nitrogen-modified micron zero-valent iron material is also provided, comprising the following steps:

[0024] Nitrogen-modified micron zero-valent iron material is added to the chromium-containing wastewater to react under mechanical stirring, thereby achieving rapid treatment of the chromium-containing wastewater.

[0025] According to the method for treating chromium-containing wastewater of the present invention, preferably, the mechanical stirring paddle is a polytetrafluoroethylene stirring rod paddle.

[0026] According to the method for treating chromium-containing wastewater of the present invention, preferably, the dosage of the nitrogen-modified micron zero-valent iron material is 0.4 g / L.

[0027] According to the method for treating chromium-containing wastewater of the present invention, preferably, the concentration of Cr(VI) in the wastewater is 5 mg / L.

[0028] According to the method for treating chromium-containing wastewater of the present invention, preferably, the reaction system is an acetic acid-sodium acetate buffer solution with a pH of 5 and a concentration of 0.2 mol / L.

[0029] According to the method for treating chromium-containing wastewater of the present invention, preferably, the rotation speed of the stirring reaction is 400±10r / min, and the chromium removal time of N-ZVI is 10-20min.

[0030] According to the method for treating chromium-containing wastewater of the present invention, preferably, the reaction system is a 500 mL beaker system.

[0031] According to the method for treating chromium-containing wastewater of the present invention, preferably, the reaction system is carried out under aerobic conditions (exposed to air).

[0032] The present invention successfully introduces nitrogen species on the original micron zero-valent iron and proves the effective bonding between Fe and N. Therefore, the introduction of nitrogen species effectively modifies the zero-valent iron, on the one hand, provides more reactive sites, which is beneficial to the adsorption of pollutants; on the other hand, it destroys the passivation layer on the surface of the original zero-valent iron, improves the electron utilization rate of the material, and accelerates the reduction and removal of pollutants.

[0033] Beneficial effects of the present invention:

[0034] (1) In the present invention, after the iron source (micron zero-valent iron) is pickled for 10 minutes, a nitrogen source (ammonium chloride, ammonium bromide, ammonium iodide) is added to the preparation system, and the nitrogen species are successfully modified on the zero-valent iron surface by tumbling oscillation. Among them, the nitrogen species is NH4 + and The SEM and XPS test images of the material directly confirmed the stable existence of nitrogen species, and the nitrogen element was evenly distributed on the surface of zero-valent iron, achieving the successful modification of zero-valent iron materials.

[0035] (2) The present invention studies the treatment of chromium-containing wastewater by nitrogen-modified micron zero-valent iron materials. Compared with the removal rate of 54.82% of the original zero-valent iron within 120 minutes, the nitrogen-modified micron zero-valent iron with the best nitrogen source and nitrogen-iron ratio can achieve complete removal of Cr(VI) within 12 minutes. The chromium removal curves of N-ZVI with different nitrogen-iron ratios were fitted with pseudo-first-order kinetics, and it was easily obtained that the chromium removal reaction rate constants of N-ZVI under the conditions of nitrogen-iron ratios of 0.028, 0.042, 0.056, 0.070, and 0.084 were 27.01, 26.75, 41.62, 23.85, and 1.65 times that of ZVI, respectively. In addition, the chromium removal reaction rate constants of N-ZVI (N / Fe=0.056) with ammonium bromide and ammonium iodide as nitrogen sources were 34.52 and 26.74 times that of ZVI, respectively.

[0036] (3) Using cheap and readily available ammonium chloride, ammonium bromide, and ammonium iodide as nitrogen sources, we successfully prepared nitrogen-modified micronized zero-valent iron materials with rapid chromium removal effects. No toxic or harmful substances were introduced during the material preparation or pollutant removal process, which is a green and environmentally friendly new material development and application. Description of the drawings:

[0037] Figure 1These are the scanning electron microscope images and element mapping images of the micron zero-valent iron material in Example 1.

[0038] Figure 2 These are the scanning electron microscope images and element mapping images of the nitrogen-modified micron zero-valent iron material in Example 1.

[0039] Figure 3 This is the XPS (X-ray photoelectron spectroscopy) graph of nitrogen in the nitrogen-modified micron zero-valent iron material in Example 1.

[0040] Figure 4 This is a graph showing the removal of the pollutant Cr(VI) by the nitrogen-modified micron zero-valent iron (N / Fe=0.028) material and zero-valent iron in Experimental Example 1.

[0041] Figure 5 This is a graph showing the removal of the pollutant Cr(VI) by the nitrogen-modified micron zero-valent iron (N / Fe=0.042) material and zero-valent iron in Experimental Example 1.

[0042] Figure 6 This is a graph showing the removal of the pollutant Cr(VI) by the nitrogen-modified micron zero-valent iron (N / Fe=0.056) material and zero-valent iron in Experimental Example 1.

[0043] Figure 7 This is a graph showing the removal of the pollutant Cr(VI) by the nitrogen-modified micron zero-valent iron (N / Fe=0.070) material and zero-valent iron in Experimental Example 1.

[0044] Figure 8 This is a curve diagram of the removal of the pollutant Cr(VI) by the nitrogen-modified micron zero-valent iron (N / Fe=0.084) material and zero-valent iron in Experimental Example 1.

[0045] Fig. 9 This is a comparison chart of reaction rate constants obtained by pseudo-first-order kinetic fitting of the treatment process of heavy metal chromium by the material in Experimental Example 2.

[0046] Fig.10 This is a graph showing the removal of the pollutant Cr(VI) by the micronized zero-valent iron (N / Fe=0.056) material modified with different nitrogen sources and zero-valent iron in Experimental Example 3.

[0047] Fig.11 This is a comparison chart of reaction rate constants obtained by pseudo-first-order kinetic fitting of the treatment process of heavy metal chromium by micron zero-valent iron materials modified with different nitrogen sources in Experimental Example 4. Specific implementation method:

[0048] The specific implementation of the present invention is further described below in conjunction with implementation cases and drawings, but the scope of protection claimed by the present invention is not limited thereto.

[0049] Embodiment 1:

[0050] A nitrogen-modified micron zero-valent iron material is prepared according to the following method:

[0051] Prepare 250mL of 0.2M acetic acid-sodium acetate buffer solution with a pH of 6.0±0.05, and transfer it to a 250mL serum bottle, and continue to pass high-purity nitrogen for 30min (to create an oxygen-free environment). Accurately weigh 1g of zero-valent iron powder, quickly add it to the serum bottle, seal it with a polyethylene stopper, and place it in a constant temperature oscillator for oscillation. Set the temperature to 25±0.2℃ and the speed to 120r / min. Stop stirring after 10min. At this time, the Fe(II) concentration in the solution is about 50mg / L. Use a microsyringe to inject 1mL of ammonium chloride (1M) into the serum bottle, and then flip and oscillate for 10h under the above conditions. Wash and filter the obtained N-ZVI suspension with a suction filtration device, and freeze-dry the filtered solid particles in a freeze dryer for 2-3h, and the drying temperature is about -50℃.

[0052] The molar ratio of zero-valent iron to ammonium chloride in this embodiment is 1:0.056. The scanning electron microscope image and element mapping image of the nitrogen-modified micron zero-valent iron material prepared in this embodiment are shown in FIG. Figure 2 As shown, combined Figure 1 Analysis shows that compared with zero-valent iron, the surface of nitrogen-modified micronized zero-valent iron material becomes loose and porous due to the appearance of flake-like substances. Combined with the element mapping image comparison, it can be seen that the nitrogen element is successfully introduced and evenly distributed on the surface of zero-valent iron, which also shows the successful preparation of nitrogen-modified zero-valent iron material.

[0053] The XPS image of the nitrogen-modified micronized zero-valent iron material prepared in this example is shown in FIG. Figure 3 , nitrogen species were successfully introduced into the surface of zero-valent iron, and there was an effective bonding between Fe and N, revealing that nitrogen species not only existed on the surface of zero-valent iron, but also interacted with zero-valent iron, further confirming the feasibility of the N-ZVI preparation method described in this invention.

[0054] Example 2

[0055] A method for rapidly treating chromium-containing wastewater using nitrogen-modified micron zero-valent iron material, wherein the chromium concentration of the wastewater is 5 mg / L, and the reaction system is an acetic acid-sodium acetate buffer system with a pH of 5.

[0056] The steps include:

[0057] Prepare 500mL of acetic acid-sodium acetate buffer solution with pH=5 in a volumetric flask and transfer it to a 500mL open beaker after ultrasound. The mechanical stirring speed is 400±10r / min. After the pH of the reaction system is stable, add 1mL of Cr(VI) stock solution (2500mg / L). Draw about 4mL of sample with a syringe, filter the sample through a 0.22μm water filter membrane and transfer it to a 5mL centrifuge tube. Then add 0.2g of material and regularly sample the reaction solution with a syringe (0min, 2min, 5min, 7min, 10min, 15min, 20min, 30min, 45min, 60min, 90min, 120min), and promptly determine the concentration of Cr(VI) by spectrophotometry.

[0058] Example 3

[0059] A nitrogen-modified micron zero-valent iron material is prepared according to the following method:

[0060] Prepare 250mL of 0.2M acetic acid-sodium acetate buffer solution with a pH of 6.0±0.05, and transfer it to a 250mL serum bottle, and continue to pass high-purity nitrogen for 30min (to create an oxygen-free environment). Accurately weigh 1g of zero-valent iron powder, quickly add it to the serum bottle, seal it with a polyethylene stopper, and place it in a constant temperature oscillator for oscillation. Set the temperature to 25±0.2℃ and the speed to 120r / min. Stop stirring after 10min. At this time, the Fe(II) concentration in the solution is about 50mg / L. Use a microsyringe to inject 1mL of ammonium bromide (1M) into the serum bottle, and then flip and oscillate for 10h under the above conditions. Wash and filter the obtained N-ZVI suspension with a suction filtration device, and freeze-dry the filtered solid particles in a freeze dryer for 2-3h, and the drying temperature is about -50℃.

[0061] 0.2 g of nitrogen-modified micron zero-valent iron material was added to a beaker containing 500 mL of acetic acid-sodium acetate buffer solution at pH = 5. The experimental conditions were controlled as follows: water bath temperature was controlled at 25° C., and the mechanical stirring rate was 400±10 r / min.

[0062] Example 4

[0063] A nitrogen-modified micron zero-valent iron material is prepared according to the following method:

[0064] Prepare 250mL of 0.2M acetic acid-sodium acetate buffer solution with a pH of 6.0±0.05, and transfer it to a 250mL serum bottle, and continue to pass high-purity nitrogen for 30min (to create an oxygen-free environment). Accurately weigh 1g of zero-valent iron powder, quickly add it to the serum bottle, seal it with a polyethylene stopper, and place it in a constant temperature oscillator for oscillation. Set the temperature to 25±0.2℃ and the speed to 120r / min. Stop stirring after 10min. At this time, the Fe(II) concentration in the solution is about 50mg / L. Use a microsyringe to inject 1mL of ammonium iodide (1M) into the serum bottle, and then flip and oscillate for 10h under the above conditions. Wash and filter the obtained N-ZVI suspension with a suction filtration device, and freeze-dry the filtered solid particles in a freeze dryer for 2-3h, and the drying temperature is about -50℃.

[0065] 0.2 g of nitrogen-modified micron zero-valent iron material was added to a beaker containing 500 mL of acetic acid-sodium acetate buffer solution at pH = 5. The experimental conditions were controlled as follows: water bath temperature was controlled at 25° C., and the mechanical stirring rate was 400±10 r / min.

[0066] Example 5

[0067] As described in Example 1, except that:

[0068] The amount of ammonium chloride added to the preparation system was 0.5 mL, so that N / Fe=0.028.

[0069] Example 6

[0070] As described in Example 1, except that:

[0071] The amount of ammonium chloride added to the preparation system was 0.75 mL, resulting in N / Fe=0.042.

[0072] Example 7

[0073] As described in Example 1, except that:

[0074] The amount of ammonium chloride added to the preparation system was 1.25 mL so that N / Fe=0.070.

[0075] Comparative Example 1

[0076] As described in Example 2, except that:

[0077] The micron zero-valent iron material after pickling is used to remove the pollutant chromium in the wastewater. The preparation method is as follows:

[0078] 250 mL of acetic acid-sodium acetate buffer solution with a pH of 6.0 was placed in a 250 mL serum bottle, nitrogen was passed until the dissolved oxygen was zero (about 30 minutes), and then 1 g of zero-valent iron (Fe / FeO) was quickly added to seal the bottle and rotated in a constant temperature oscillator (25±0.2°C) at a speed of 120 r / min, and reversed and oscillated for 10 minutes. The mixture in the bottle was filtered with a sand core filter device, washed with pure water and anhydrous ethanol for 3 times each, and finally vacuum-freeze-dried for 2 hours to obtain the material.

[0079] Comparative Example 2

[0080] As described in Example 1, except that:

[0081] The amount of ammonium chloride added to the preparation system was 1.5 mL, so that N / Fe=0.084.

[0082] Test Example 1

[0083] The removal process of the pollutant chromium in Example 2, Examples 5-7 and Comparative Examples 1-2 is plotted as follows: Figure 4-8 shown.

[0084] pass Figure 6 It can be seen that compared with the Cr(VI) removal rate of ZVI within 120 min, which is 54.82%, N-ZVI with N / Fe=0.056 can achieve complete removal of Cr(VI) within 12 min. Figure 4 , 5 , 7, 8 corresponding to N / Fe = 0.028, 0.042, 0.070, 0.084 N-ZVI in 30, 15, 20, 90 minutes respectively for Cr (VI) removal rate of 99.99%. Figure 4-8 From the above data analysis, it can be seen that the N-ZVI with N / Fe=0.056 used in Example 2 has the best chromium removal effect, which also reflects that the amount of nitrogen source introduced needs to be appropriate to achieve effective regulation of zero-valent iron.

[0085] Test Example 2

[0086] The chromium removal curves of Example 2, Examples 5-7 and Comparative Examples 1-2 were fitted with pseudo-first-order kinetics, and the formula is as follows:

[0087]

[0088] Where C and C0 represent the concentration of Cr(VI) in the reaction system at t min and 0 min, respectively, and k obs It is the apparent rate constant when the pollutant is removed. It is mainly used to describe the rate of the reaction process and is obtained by calculating the slope of the functional relationship between -ln(C / C0) and time t.

[0089] pass Fig. 9 The bar chart of is easy to obtain. The nitrogen-modified zero-valent iron material (N-ZVI, N / Fe=0.056) of Example 2 has the largest chromium removal reaction rate constant, which is 41.62 times that of Comparative Example 1 and 25.18 times that of Comparative Example 2. In addition, the reaction rate constants of Examples 5-7 are 27.01, 26.75, and 23.85 times that of Comparative Example 1, respectively. Figure 8 , 9 From the above data analysis, it can be seen that on the one hand, the introduction of nitrogen species can effectively modify zero-valent iron and achieve efficient removal of Cr(VI); on the other hand, it also shows that the amount of nitrogen source added during the preparation of N-ZVI materials and the chromium removal effect are in a "peak" shape, with an optimal nitrogen-to-iron ratio range.

[0090] It can be seen that the dosage of ammonium chloride in the preparation system set by the present invention, that is, the nitrogen-iron ratio is optimal. The pseudo-first-order kinetic constant of chromium removal in comparative example 2 with too high nitrogen-iron ratio is poor, so the nitrogen-iron ratio set by the present invention (N / Fe=(0.028-0.07): 1) can achieve efficient treatment of chromium-containing wastewater.

[0091] Test Example 3

[0092] The removal process of the pollutant chromium in Examples 2, 3, 4 and Comparative Example 1 is plotted as follows: Fig.10 shown.

[0093] Depend on Fig.10 It can be seen that, whether it is ammonium chloride, ammonium bromide or ammonium iodide, the introduction of nitrogen source has an obvious effect on modifying zero-valent iron and thus improving the chromium removal rate. Compared with the ZVI in Comparative Example 1, which has a Cr(VI) removal rate of 14.97% within 15 minutes, the N-ZVI used in Examples 2-4 can achieve a chromium removal efficiency of 99.99% within 10-15 minutes. It can be seen that in Examples 2-4, ammonium salts as nitrogen sources can effectively modify zero-valent iron, and the effects of anions (halogen ions) of different nitrogen sources can be ignored.

[0094] Test Example 4

[0095] The chromium removal curves of Examples 2, 3, 4 and Comparative Example 1 were fitted with pseudo-first-order kinetics, as shown in Fig.11 shown.

[0096] Depend on Fig.11 It can be seen that the chromium removal reaction rate constants of N-ZVI used in Examples 2, 3, and 4 are much higher than that of zero-valent iron in the comparative example, which are 41.62, 34.52, and 26.74 times that of comparative example 1, respectively.

[0097] In summary, although there is a certain gap in the chromium removal effect of zero-valent iron modified with different nitrogen sources (within the error range), the effects of effectively modifying zero-valent iron and improving the chromium removal effect of zero-valent iron are very significant.

Claims

1. A nitrogen-modified micron zero-valent iron material, characterized in that: The material is a nitrogen species introduced into the surface of zero-valent iron, and there is an effective bond between Fe and N, with a nitrogen-iron molar ratio of (0.028-0.07):1; the nitrogen species in the material is NH4 + It exists in the form of NH3(aq), and the nitrogen source used for nitrogen modification is ammonium halide; The preparation steps of the nitrogen-modified micron zero-valent iron material are as follows: In an acetic acid-sodium acetate buffer solution, micron zero-valent iron is oscillated at a constant temperature under anaerobic conditions to remove the passivation layer film on the surface of the zero-valent iron. Ammonium salt is then added and the reaction is reversed and vibrated at a constant temperature. After filtration and freeze-drying, nitrogen-modified micron zero-valent iron material is obtained.

2. The nitrogen-modified micron zero-valent iron material according to claim 1, characterized in that: The molar ratio of nitrogen to iron is (0.04-0.06):1, and the nitrogen source is ammonium chloride, ammonium bromide or ammonium iodide.

3. The method for preparing the nitrogen-modified micron zero-valent iron material according to claim 1, characterized in that: The preparation steps are: In an acetic acid-sodium acetate buffer solution, micron zero-valent iron is oscillated at a constant temperature under anaerobic conditions to remove the passivation layer film on the surface of the zero-valent iron. Ammonium salt is then added and the reaction is reversed and vibrated at a constant temperature. After filtration and freeze-drying, nitrogen-modified micron zero-valent iron material is obtained.

4. The method for preparing the nitrogen-modified micron zero-valent iron material according to claim 3, characterized in that: The anaerobic condition is to introduce high-purity nitrogen into the preparation system until the dissolved oxygen is zero.

5. The method for preparing the nitrogen-modified micron zero-valent iron material according to claim 3, characterized in that: The particle size of the micron zero-valent iron particles is 70-80 μm; the ammonium salt is ammonium chloride, ammonium bromide or ammonium iodide, and the ammonium salt concentration is 1 mol / L.

6. The method for preparing the nitrogen-modified micron zero-valent iron material according to claim 3, characterized in that: The pH of the acetic acid-sodium acetate buffer solution is 6±0.05, the concentration is 0.2 mol / L, and the molar ratio of zero-valent iron to ammonium salt is 1:(0.028-0.07).

7. The method for preparing the nitrogen-modified micron zero-valent iron material according to claim 3, characterized in that: The oscillation time of the micron zero-valent iron under anaerobic conditions is 10 min, and the reaction time with the ammonium salt in the reaction system is 10 h.

8. Use of the nitrogen-modified micron zero-valent iron material according to claim 1 in treating chromium-containing wastewater.

9. A method for rapidly treating chromium-containing wastewater, comprising using the nitrogen-modified micron zero-valent iron material of claim 1, comprising the following steps: Nitrogen-modified micron zero-valent iron material is added to the chromium-containing wastewater to react under mechanical stirring, thereby achieving rapid treatment of the chromium-containing wastewater.

10. The method for rapidly treating chromium-containing wastewater according to claim 9, characterized in that: The dosage of nitrogen-modified micron zero-valent iron material was 0.4 g / L, and the concentration of Cr(VI) in the wastewater was 5 mg / L.

11. The method for rapidly treating chromium-containing wastewater according to claim 9, characterized in that: The reaction system was an acetic acid-sodium acetate buffer system with a pH of 5 and a concentration of 0.2 mol / L.

12. The method for rapidly treating chromium-containing wastewater according to claim 9, characterized in that: The speed of the stirring reaction is 400±10 r / min, the chromium removal time of N-ZVI is 10-20 min, and the reaction is carried out under aerobic conditions.

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