Graphene adsorption material-based advanced denitrification method for industrial wastewater

Abstract

The present application relates to industrial wastewater denitrification technical field, specifically, it is a kind of industrial wastewater advanced denitrification method based on graphene adsorption material, it includes the following steps: the industrial wastewater containing total nitrogen is introduced into adsorption reaction unit;By adjusting empty bed contact time, ammonia nitrogen and nitrate nitrogen in wastewater are removed;When adsorption material reaches saturation, regeneration is carried out to particle, and regeneration liquid is collected for nitrogen resource utilization.In the present application, the core-shell type dual-functional graphene adsorption particle is rich in amine group function on the inner core PEI chain, which can efficiently and specifically remove ammonia nitrogen by ion exchange, and the outer shell is composed of in-situ grown magnesium-aluminum hydrotalcite, the exchangeable anions between hydrotalcite layers can be ion exchanged with nitrate nitrogen to realize selective adsorption of nitrate nitrogen;The simultaneous advanced removal of ammonia nitrogen and nitrate nitrogen in industrial wastewater is realized, which greatly improves the treatment efficiency and simplifies the process.

Description

A deep denitrification method for industrial wastewater based on graphene adsorbent materials Technical Field

[0001] This invention relates to the field of industrial wastewater denitrification technology, and more specifically, to a method for deep denitrification of industrial wastewater based on graphene adsorption materials. Background Technology

[0002] Nitrogen pollution in industrial wastewater, especially the deep removal of ammonia nitrogen and nitrate nitrogen, is a difficult and key challenge in the field of water treatment. Existing biological denitrification processes are often inefficient and unstable in industrial wastewater with low C / N ratios, high salinity, or containing toxic substances. In contrast, adsorption methods have become a promising alternative technology for deep denitrification due to their simple operation, stable effect, and flexible design. In recent years, graphene-based adsorbent materials have attracted widespread attention due to their ultra-large specific surface area, rich surface chemical properties, and potential for functional modification. Chinese invention patent CN115010245B discloses a chemical wastewater treatment agent, its preparation method, and its application. The wastewater treatment agent prepared by this patent has good mechanical strength and chemical stability, strong adaptability, excellent bio-adsorption-bio-denitrification performance, and significant ammonia nitrogen removal effect. It can be applied to the treatment of synthetic ammonia process wastewater.

[0003] However, existing materials are mostly designed to adsorb single forms of nitrogen pollutants (only ammonia nitrogen or only nitrate), lacking bifunctional integrated structures that can simultaneously and deeply remove multiple nitrogen forms, which limits their practical application in complex industrial wastewater. In view of this, we propose a method for deep denitrification of industrial wastewater based on graphene adsorbent materials. Summary of the Invention

[0004] The purpose of this invention is to provide a method for deep denitrification of industrial wastewater based on graphene adsorption materials, in order to solve the problem mentioned in the background art that the design of existing materials mostly focuses on the adsorption of single-form nitrogen pollutants (only for ammonia nitrogen or only for nitrate), and lacks a dual-functional integrated structure that can simultaneously and deeply remove multiple nitrogen forms, thus limiting its practical application in complex industrial wastewater.

[0005] This invention provides a method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0006] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0007] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0008] S1.2. Ammonia nitrogen and nitrate nitrogen in wastewater are removed by adjusting the empty bed contact time;

[0009] S1.3 When the adsorbent material reaches saturation, the particles are regenerated, and the regenerated liquid is collected for nitrogen resource utilization.

[0010] Preferably, the preparation process of the core-shell bifunctional graphene adsorbent particles is as follows:

[0011] Iron salts were added to a graphene suspension with a solid content of 0.5-2.0% at a mass ratio of 1:5, and the mixture was reacted at 60-80℃ with a 0.1mol / L sodium hydroxide solution to maintain the pH at 9-10 for 1-2 hours to form a magnetite / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid was added. The mixture was then reduced at 60℃ for 1 hour to obtain magnetic magnetite-graphene.

[0012] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 1.0-3.0%, and stirred at 300-400 rpm for 2 hours at pH 6-8. Then glutaraldehyde was added and reacted at room temperature for 1-2 hours to obtain amination magnetic iron oxide-graphene.

[0013] Inorganic salts were added to an amination-magnetic iron oxide-graphene suspension at a mass ratio of 1:1, and the mixture was stirred at 200-300 rpm while adjusting the pH to 9-10 with 0.1 mol / L sodium hydroxide for 30-60 min. The mixture was then washed with deionized water and dried at 60°C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0014] Preferably, the iron salt comprises ferrous sulfate and ferric nitrate, and the molar ratio of ferrous sulfate to ferric nitrate is 1:2.

[0015] Preferably, the mass ratio of the branched polyethyleneimine to the magnetic iron tetroxide-graphene suspension is 3-5:1.

[0016] Preferably, the mass ratio of ascorbic acid to iron salt is 1.2:1.

[0017] Preferably, the molar ratio of glutaraldehyde to branched polyethyleneimine is 0.01-0.1:1.

[0018] Preferably, the inorganic salt includes magnesium chloride and aluminum chloride, and the molar ratio of magnesium chloride to aluminum chloride is 3:1.

[0019] Preferably, the solid content of the amination magnetic iron tetroxide-graphene suspension is 1.0-3.0%.

[0020] Preferably, in step S1.2, the empty bed contact time is adjusted to 10-60 minutes.

[0021] Preferably, in step S1.3, the regeneration of the adsorbed particles is carried out by desorption using a sodium chloride solution with a mass concentration of 2-5%.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] In this invention, a method for deep denitrification of industrial wastewater based on graphene adsorption materials is disclosed. The core of the core-shell bifunctional graphene adsorption particles is composed of magnetic graphene loaded with iron oxide and grafted with cross-linked polyethyleneimine (PEI). The abundant amine functional groups on the PEI chains can efficiently and specifically adsorb and remove ammonia nitrogen through ion exchange. The outer shell is composed of in-situ grown magnesium aluminum hydrotalcite. The exchangeable anions between the hydrotalcite layers can selectively adsorb nitrate nitrogen by exchanging ions with nitrate nitrogen. This core-shell division of labor mechanism enables the simultaneous deep removal of ammonia nitrogen and nitrate nitrogen from industrial wastewater, greatly improving treatment efficiency and simplifying the process. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] The graphene (CAS No.: 10343434-98-0) was purchased from Anhui Kerun Nanotechnology Co., Ltd.

[0026] Ascorbic acid (CAS No.: 50-81-7) was purchased from Zhengzhou Wanruida Chemical Products Co., Ltd.

[0027] Branched polyethyleneimine was purchased from Shandong Xiya Chemical Co., Ltd.

[0028] Ferrous sulfate (98% purity, CAS No.: 7720-78-7) was purchased from Zhengzhou Ruipu Bioengineering Co., Ltd.

[0029] Ferric nitrate (98% purity, CAS No.: 10421-48-4) was purchased from Sichuan Huanan Inorganic Salt Co., Ltd.

[0030] Glutaraldehyde (50% purity, CAS No.: 111-30-8) was purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0031] Magnesium chloride (99% purity, CAS No.: 7786-30-3) was purchased from Qingdao Yufengda Fine Chemical Co., Ltd.

[0032] Aluminum chloride (98% purity, CAS No.: 7446-70-0) was purchased from Jinan Century Tongda Chemical Co., Ltd.

[0033] The iron salts include ferrous sulfate and ferric nitrate, and the molar ratio of ferrous sulfate to ferric nitrate is 1:2.

[0034] The inorganic salts include magnesium chloride and aluminum chloride, and the molar ratio of magnesium chloride to aluminum chloride is 3:1.

[0035] Example 1: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0036] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0037] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0038] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0039] Iron salt was added to a graphene suspension with a solid content of 1.5% at a mass ratio of 1:5, and the mixture was reacted at 60°C for 2 hours under conditions where the pH was adjusted and maintained at 9 using a 0.1 mol / L sodium hydroxide solution to form an iron oxide / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 hour to obtain magnetic iron oxide-graphene.

[0040] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 2.0% (mass ratio of 3:1), stirred at 300 rpm for 2 h at pH 7, and then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.01:1) was added and reacted at room temperature for 2 h to obtain amination magnetic iron oxide-graphene.

[0041] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 2.0% at a mass ratio of 1:1. The mixture was stirred at 300 rpm while the pH was adjusted to 10 with 0.1 mol / L sodium hydroxide and maintained for 60 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0042] S1.2 By adjusting the empty bed contact time to 60 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0043] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 4% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0044] Example 2: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0045] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0046] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0047] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0048] Iron salt was added to a graphene suspension with a solid content of 1.5% at a mass ratio of 1:5, and the mixture was reacted at 60°C for 2 hours under conditions where the pH was adjusted and maintained at 9 using a 0.1 mol / L sodium hydroxide solution to form an iron oxide / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 hour to obtain magnetic iron oxide-graphene.

[0049] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 2.0% (mass ratio of 4:1), stirred at 300 rpm for 2 h at pH 7, and then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.01:1) was added and reacted at room temperature for 2 h to obtain amination magnetic iron oxide-graphene.

[0050] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 2.0% at a mass ratio of 1:1. The mixture was stirred at 300 rpm while the pH was adjusted to 10 with 0.1 mol / L sodium hydroxide and maintained for 60 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0051] S1.2 By adjusting the empty bed contact time to 60 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0052] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 4% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0053] Example 3: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0054] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0055] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0056] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0057] Iron salt was added to a graphene suspension with a solid content of 1.5% at a mass ratio of 1:5, and the mixture was reacted at 60°C for 2 hours under conditions where the pH was adjusted and maintained at 9 using a 0.1 mol / L sodium hydroxide solution to form an iron oxide / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 hour to obtain magnetic iron oxide-graphene.

[0058] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 2.0% (mass ratio of 5:1), stirred at 300 rpm for 2 h at pH 7, and then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.01:1) was added and reacted at room temperature for 2 h to obtain amination magnetic iron oxide-graphene.

[0059] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 2.0% at a mass ratio of 1:1. The mixture was stirred at 300 rpm while the pH was adjusted to 10 with 0.1 mol / L sodium hydroxide and maintained for 60 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0060] S1.2 By adjusting the empty bed contact time to 60 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0061] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 4% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0062] Example 4: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0063] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0064] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0065] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0066] Iron salt was added to a graphene suspension with a solid content of 1.5% at a mass ratio of 1:5, and the mixture was reacted at 60°C for 2 hours under conditions where the pH was adjusted and maintained at 9 using a 0.1 mol / L sodium hydroxide solution to form an iron oxide / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 hour to obtain magnetic iron oxide-graphene.

[0067] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 2.0% (mass ratio of 3:1), stirred at 300 rpm for 2 h at pH 7, and then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.05:1) was added and reacted at room temperature for 2 h to obtain amination magnetic iron oxide-graphene.

[0068] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 2.0% at a mass ratio of 1:1. The mixture was stirred at 300 rpm while the pH was adjusted to 10 with 0.1 mol / L sodium hydroxide and maintained for 60 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0069] S1.2 By adjusting the empty bed contact time to 60 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0070] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 4% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0071] Example 5: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0072] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0073] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0074] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0075] Iron salt was added to a graphene suspension with a solid content of 1.5% at a mass ratio of 1:5, and the mixture was reacted at 60°C for 2 hours under conditions where the pH was adjusted and maintained at 9 using a 0.1 mol / L sodium hydroxide solution to form an iron oxide / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 hour to obtain magnetic iron oxide-graphene.

[0076] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 2.0% (mass ratio of 3:1), stirred at 300 rpm for 2 h at pH 7, and then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.1:1) was added and reacted at room temperature for 2 h to obtain amination magnetic iron oxide-graphene.

[0077] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 2.0% at a mass ratio of 1:1. The mixture was stirred at 300 rpm while the pH was adjusted to 10 with 0.1 mol / L sodium hydroxide and maintained for 60 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0078] S1.2 By adjusting the empty bed contact time to 60 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0079] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 4% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0080] Example 6: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0081] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0082] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0083] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0084] Iron salt was added to a graphene suspension with a solid content of 0.5% at a mass ratio of 1:5, and the mixture was reacted at 70°C with a pH of 9.5 adjusted and maintained using a 0.1 mol / L sodium hydroxide solution for 1 h to form a magnetite / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 h to obtain magnetic magnetite-graphene.

[0085] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 1.0% (mass ratio of 3:1), and stirred at 350 rpm for 2 h at pH 6. Then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.01:1) was added and reacted at room temperature for 1 h to obtain amination magnetic iron oxide-graphene.

[0086] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 1.0% at a mass ratio of 1:1. The mixture was stirred at 200 rpm, and the pH was adjusted to 9 with 0.1 mol / L sodium hydroxide for 30 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0087] S1.2 By adjusting the empty bed contact time to 10 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0088] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 2% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0089] Example 7: A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, comprising the following steps:

[0090] S1.1. Introduce industrial wastewater containing total nitrogen into the adsorption reaction unit;

[0091] The adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite.

[0092] The preparation process of core-shell bifunctional graphene adsorbent particles is as follows:

[0093] Iron salt was added to a graphene suspension with a solid content of 2.0% at a mass ratio of 1:5, and the mixture was reacted at 80°C for 1.5 h under conditions where the pH was adjusted and maintained at 10 using a 0.1 mol / L sodium hydroxide solution to form an iron oxide / graphene composite. The composite was washed with deionized water until neutral, and then ascorbic acid with a mass ratio of 1.2:1 to the iron salt was added. The mixture was then reduced at 60°C for 1 h to obtain magnetic iron oxide-graphene.

[0094] Branched polyethyleneimine was added to a magnetic iron oxide-graphene suspension with a solid content of 3.0% (mass ratio of 3:1), and stirred at 400 rpm for 2 h at pH 8. Then glutaraldehyde (molar ratio of glutaraldehyde to branched polyethyleneimine was 0.01:1) was added and the mixture was reacted at room temperature for 1.5 h to obtain amination magnetic iron oxide-graphene.

[0095] Inorganic salts were added to an aminated magnetic iron oxide-graphene suspension with a solid content of 3.0% at a mass ratio of 1:1. The mixture was stirred at 250 rpm while the pH was adjusted to 9.5 with 0.1 mol / L sodium hydroxide and maintained for 40 min. The mixture was then washed with deionized water and dried at 60 °C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

[0096] S1.2 By adjusting the empty bed contact time to 40 min, ammonia nitrogen and nitrate nitrogen in the wastewater are removed;

[0097] S1.3 When the adsorbent material reaches saturation, the particles are regenerated using a 5% sodium chloride solution. The regenerated liquid is collected for nitrogen resource utilization.

[0098] Determination of nitrogen adsorption capacity: Prepare ammonium chloride solutions (for measuring ammonia nitrogen adsorption capacity) and sodium nitrate solutions (for measuring nitrate nitrogen adsorption capacity) with specific concentration gradients. Take a series of conical flasks and add a certain volume (V, L) of nitrogen solution with a known initial concentration (C0, mg / L) and accurately weighed (m, g) of dried adsorption particles. Place the conical flasks in a constant temperature shaker and shake at a predetermined temperature (e.g., 25℃) until adsorption equilibrium is reached (the time can be determined through a preliminary experiment, e.g., 24 h). After the reaction is complete, take a sample and filter it through a 0.45 μm filter membrane. Determine the residual ammonia nitrogen concentration in the filtrate using Nessler's reagent spectrophotometry and the residual nitrate nitrogen concentration in the filtrate using ultraviolet spectrophotometry to obtain the equilibrium concentration (C0, mg / L). e (mg / L); calculate the adsorption capacity Q according to the formula. e (mg / g)=(C0-C e )×V / m.

[0099] Determination of Cyclic Regeneration Performance: Perform the above batch adsorption experiment to determine the initial adsorption capacity (Q0); collect the saturated particles by filtration and place them in a regenerator of a certain concentration (e.g., 2-5% NaCl solution), shaking at room temperature for a certain time (e.g., 4 hours) for desorption; wash the desorbed particles with deionized water until neutral and dry them at 60℃ for the next adsorption cycle; repeat the adsorption-desorption-regeneration cycle experiment multiple times (usually more than 5 times); and calculate the adsorption capacity retention rate after the nth cycle: Retention rate (%) = (Q0 / (Q0)) n / Q0)×100%.

[0100] Selectivity determination: Prepare a mixture containing multiple competing anions (such as SO42-). 2- ,Cl - HCO3 - ) and cations (such as Ca) 2+ Mg 2+ ,K+ ) and target pollutant (NH4) + and NO3 - Simulated wastewater solution, with ion concentrations set according to actual wastewater background; competitive adsorption experiment: conduct batch adsorption experiments, and measure the concentration changes of each ion before and after adsorption; calculate partition coefficient and selectivity coefficient: first calculate the partition coefficient of the adsorbent for each ion i; then, with the target ion (e.g., NO3-)... - Using as a benchmark, calculate its selectivity coefficient for interfering ion j.

[0101] Table 1 Performance data of core-shell bifunctional graphene adsorbent particles

[0102] Ammonia nitrogen adsorption capacity, nitrate nitrogen adsorption capacity, ammonia nitrogen retention rate, nitrate nitrogen retention rate, selectivity coefficient. Example 1: 18.5 mg / g, 22.3 mg / g, 75%, 82%, 5.2; Example 2: 29.8 mg / g, 20.1 mg / g, 70%, 85%, 8.5; Example 3: 38.5 mg / g, 15.8 mg / g, 65%, 87%, 12.1; Example 4: 15.2 mg / g, 24.8 mg / g, 88%, 90%, 4.8; Example 5: 10.1 mg / g, 25.5 mg / g, 92%, 93%, 3.5. surface

[0103] Comparing Examples 1, 2, and 3, as the amount of PEI increased (from 3:1 to 5:1), the number of amine functional groups available for ammonia nitrogen adsorption increased significantly, thus the ammonia nitrogen adsorption capacity continued to increase substantially.

[0104] Because the core PEI layer is too thick, it partially hinders the contact between the outer layer hydrotalcite layer and nitrate nitrogen in the water, resulting in a slight decrease in its adsorption capacity. At the same time, the thicker positively charged PEI layer enhances the electrostatic attraction of the material to negatively charged nitrate ions, thus significantly improving the ion exchange selectivity (S value).

[0105] With low cross-linking degree, the excessively thick PEI layer is more likely to swell and be lost in water, resulting in poor cycling stability of ammonia nitrogen (retention rate drops from 75% to 65%); the outer shell hydrotalcite structure is relatively stable, so the retention rate of nitrate nitrogen does not change much.

[0106] Comparing Examples 1, 4, and 5, as the glutaraldehyde ratio increased (from 0.01:1 to 0.1:1), the degree of cross-linking between PEI molecules increased, a large number of free amine groups were fixed by the reaction, and the ammonia nitrogen adsorption capacity was severely sacrificed.

[0107] The high degree of cross-linking forms a more stable core network, providing a more robust substrate for the growth of the outer shell hydrotalcite, while reducing the loss of PEI during the regeneration process. Therefore, the adsorption capacity and cycling stability of nitrate nitrogen are both improved.

[0108] High cross-linking reduces the degree of amine protonation and weakens the positive charge, resulting in a decrease in selectivity for nitrate (S value).

[0109] Based on the above measurements, Example 4 is selected as the optimal example.

[0110] Comparative Example 1: This comparative example differs from Example 4 in that branched polyethyleneimine was not added.

[0111] Comparative Example 2: This comparative example differs from Example 4 in that no magnesium-aluminum hydrotalcite shell layer was added.

[0112] Comparative Example 3: The difference between this comparative example and Example 4 is that graphene was directly added.

[0113] Determination of nitrogen removal efficiency: Prepare a solution containing a specific initial concentration (e.g., CO(NH4)2) + )=50mg / L, CO(NO3) - Simulated industrial wastewater with ammonia nitrogen and nitrate nitrogen concentrations of 50 mg / L was used. A certain amount (e.g., 10 g / L) of adsorption particles was packed into an adsorption column. The simulated wastewater was continuously fed into the adsorption column at a constant temperature (e.g., 25 °C) and a set empty bed contact time (e.g., 30 min). After the effluent reached stability, effluent samples were collected at different time points. The ammonia nitrogen concentration in the effluent was determined using Nessler's reagent spectrophotometry, and the nitrate nitrogen concentration was determined using ultraviolet spectrophotometry to obtain the equilibrium concentration (C0). e (mg / L); calculate the removal efficiency η(%) for each pollutant = (1-C e / C0)×100%.

[0114] Treatment flux determination: Set a target total nitrogen concentration in the effluent (e.g., <15 mg / L); under the condition of fixed adsorbent loading, gradually increase the influent flow rate (i.e. shorten the empty bed contact time), and operate at each flow rate until the effluent stabilizes; analyze the effluent quality at each flow rate; treatment flux is defined as the maximum volume of wastewater that can be treated per unit time and per unit volume of adsorbent under the premise of meeting the critical effluent standard, and the unit is usually L / (h·L-bed).

[0115] Ammonia nitrogen retention rate and nitrate nitrogen retention rate refer to the retention of adsorption capacity of the adsorbent in multiple adsorption-desorption cycle experiments. The calculation formula is as follows: Retention rate (%) = (Q...) n / Q0)×100%, where Q0 is the adsorption capacity of the first cycle, Q n The adsorption capacity is the adsorption capacity in the nth cycle.

[0116] Removal efficiency and retention rate reflect the single-use effectiveness and long-term cycle stability of the adsorbent, respectively.

[0117] Table 2 Performance data of treated industrial wastewater

[0118] Ammonia nitrogen removal efficiency, nitrate nitrogen removal efficiency, ammonia nitrogen retention rate, nitrate nitrogen retention rate, treatment flux: Example 4: 98.5%, 96.2%, 88%, 90%, 2.0 L / (h·L-bed); Comparative Example 1: 15.3%, 95.1%, 92%, 92%, 0.5 L / (h·L-bed); Comparative Example 2: 97.8%, 18.5%, 60%, <50%, 0.8 L / (h·L-bed); Comparative Example 3: 22.7%, 25.4%, <50%, <50%, 0.3 L / (h·L-bed). surface

[0119] The ammonia nitrogen removal efficiency of Comparative Example 1 dropped sharply to 15.3%, but the nitrate nitrogen removal efficiency was comparable to that of Example 4, and its regeneration stability was even slightly higher.

[0120] This directly proves that the amination layer formed by branched polyethyleneimine (PEI) is the key to the adsorption and removal of ammonia nitrogen; without it, the material has almost no ability to remove ammonia nitrogen; the removal of nitrate nitrogen depends entirely on the outer shell hydrotalcite, thus the performance is preserved.

[0121] The nitrate nitrogen removal efficiency of Comparative Example 2 plummeted to 18.5%, and although the ammonia nitrogen efficiency was high at the beginning, the retention rate dropped significantly to 60% after 5 regenerations.

[0122] This proves that the magnesium aluminum hydrotalcite (LDH) shell is key to the adsorption of nitrate nitrogen, and it also acts as an armor to protect the internal amination layer and improve the overall stability of the material. Without this protection, the internal PEI is prone to swelling and loss during regeneration, resulting in poor cycle stability of ammonia nitrogen adsorption performance.

[0123] Comparative Example 3 showed very low removal efficiency (<25%) for both nitrogen species, extremely poor stability, and the lowest processing throughput.

[0124] Although unfunctionalized raw graphene has a certain specific surface area, it lacks highly selective active sites for specific ions, resulting in low denitrification efficiency and susceptibility to interference. Its performance is orders of magnitude different from that of the bifunctionalized material in Example 4, which strongly highlights the decisive significance of the functionalization modification process of this invention, rather than the simple application of graphene substrate.

[0125] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for deep denitrification of industrial wastewater based on graphene adsorbent materials, characterized in that, Includes the following steps: S1.

1. Industrial wastewater containing total nitrogen is introduced into the adsorption reaction unit; the adsorption reaction unit is filled with core-shell bifunctional graphene adsorption particles, including a core layer composed of magnetically reduced graphene oxide and cross-linked branched polyethyleneimine, and a shell layer composed of magnesium-aluminum hydrotalcite; S1.

2. Ammonia nitrogen and nitrate nitrogen in the wastewater are removed by adjusting the empty bed contact time; S1.

3. When the adsorption material reaches saturation, the particles are regenerated using a 2-5% (w / w) sodium chloride solution. Liquid collection is used for nitrogen resource utilization; the preparation process of core-shell bifunctional graphene adsorbent particles is as follows: Iron salts, including ferrous sulfate and ferric nitrate, are added to a graphene suspension with a solid content of 0.5-2.0% at a mass ratio of 1:

5. The molar ratio of ferrous sulfate to ferric nitrate is 1:

2. The mixture is reacted at 60-80℃ with a 0.1 mol / L sodium hydroxide solution, maintaining the pH at 9-10, for 1-2 hours to form an iron(III) oxide / graphene composite; the mixture is then treated with deionized water. Wash until neutral, then add ascorbic acid and reduce at 60℃ for 1 hour to obtain magnetic iron oxide-graphene. Add branched polyethyleneimine to a magnetic iron oxide-graphene suspension with a solid content of 1.0-3.0%, wherein the mass ratio of branched polyethyleneimine to magnetic iron oxide-graphene suspension is 3-5:

1. Stir at 300-400 rpm for 2 hours at pH 6-8, then add glutaraldehyde and react at room temperature for 1-2 hours, wherein the molar ratio of glutaraldehyde to branched polyethyleneimine is 0. Amination of magnetic iron oxide-graphene was obtained by mixing 0.05:

1. Inorganic salts, including magnesium chloride and aluminum chloride, were added to the amination magnetic iron oxide-graphene suspension at a mass ratio of 1:

1. The mixture was stirred at 200-300 rpm, and the pH was adjusted to 9-10 with 0.1 mol / L sodium hydroxide for 30-60 min. The mixture was washed with deionized water and dried at 60°C under normal pressure to obtain core-shell bifunctional graphene adsorbent particles.

2. The method for deep denitrification of industrial wastewater based on graphene adsorbent materials according to claim 1, characterized in that, The mass ratio of ascorbic acid to iron salt is 1.2:

1.

3. The method for deep denitrification of industrial wastewater based on graphene adsorption materials according to claim 1, characterized in that, The solid content of the amination-modified magnetic iron tetroxide-graphene suspension is 1.0-3.0%.

4. The method for deep denitrification of industrial wastewater based on graphene adsorbent materials according to claim 1, characterized in that, In step S1.2, the empty bed contact time is adjusted to 10-60 minutes.