Method for treating metal pollutants by using nano zero-valent iron and hydrogen nanobubbles in cooperation

Abstract

The application provides a method for treating metal pollutants by using nanometer zero-valent iron and hydrogen nanobubbles, and belongs to the technical field of wastewater and groundwater treatment. The method comprises the following steps: adding nanometer zero-valent iron particles into polluted water under anoxic conditions, and introducing hydrogen nanobubbles to remove metal pollutants in the polluted water. The nanometer zero-valent iron has a particle size of 20-200 nm, is in a spherical core-shell structure, and has a core of Fe 0 7 8 The average particle size of the hydrogen nanobubbles is 100-300 nm, and the bubble particle number is 10-10 7 8 The application can strengthen the reducing property of the system and promote the pollutant treatment capacity of nanometer zero-valent iron by using the synergistic effect of nanometer zero-valent iron and hydrogen nanobubbles in the anoxic groundwater environment. The preparation method is simple and easy to implement, no other harmful substances are generated, and the method is clean and safe, can quickly participate in the removal of groundwater metal pollutants, and has high removal efficiency.

Description

Technical Field

[0001] This invention relates to the field of wastewater and groundwater treatment technology, and in particular to a method for the synergistic treatment of metallic pollutants using nano-zero valent iron and hydrogen nanobubbles. Background Technology

[0002] In the increasingly complex and evolving landscape of water pollution control, hundreds of water treatment technologies have been implemented. Water purification is primarily based on physicochemical processes, such as particle aggregation, pollutant mitigation, disinfection and chemical oxidation, adsorption, or biotransformation. Among these technologies, nano-zero-valent iron is a highly attractive nanomaterial due to its environmental friendliness, large specific surface area, and low cost, making it a promising candidate for environmental remediation. However, nano-zero-valent iron readily settles in water and readily reacts with water, causing corrosion. Therefore, surface modification or alteration of external conditions is necessary to enhance its pollutant removal efficiency.

[0003] The unique properties of nanobubble technology in water treatment have attracted significant attention for generating fewer byproducts and achieving safer water treatment. Nanobubbles are defined as bubbles with a diameter of less than 1000 nm, and their numerous superior properties have led to their widespread application in water treatment, such as ultra-high stability, high mass transfer efficiency, high Zeta (ζ) potential, and unique biological effects.

[0004] There are various methods for generating nanobubbles, including chemical reactions, ultrasonic cavitation, periodic pressure changes, water-solvent mixing, nanomembrane filtration, gas compression / decompression, electrolysis, fluid oscillation, vibration, and electric fields. Among these, hydrogen nanobubbles have been reported to have important applications in the treatment of metal pollution and can exist stably in water. According to Henry's Law, the solubility of hydrogen in water at room temperature and pressure is 0.8 mM (1.6 mg / L, w / v), while using nanobubble technology, the solubility of hydrogen can be increased to 2.0 mg / L, and even after 8 to 13 months of storage, approximately 0.5% of the bubbles remain. Hydrogen nanobubble technology is now increasingly being applied in environmental fields such as pollutant removal.

[0005] The technology of combining hydrogen nanobubbles with nano-zero valent iron shows significant promise in improving the reducing properties of oxygen-deficient groundwater environments, promoting charge transfer of nano-zero valent iron, improving sedimentation, and synergistically participating in processes such as chemical adsorption. This technology is expected to reduce capital costs and the use of chemicals, and will not produce secondary pollution, making it cleaner and more efficient. Summary of the Invention

[0006] To develop a simple and effective technology for the removal of metallic pollutants from groundwater, this invention provides a method for the synergistic treatment of metallic pollutants using nano-zero-valent iron and hydrogen nanobubbles. This invention can enhance the reducibility of the system and improve the ability of nano-zero-valent iron to treat pollutants in anoxic groundwater environments by utilizing the synergistic effect of nano-zero-valent iron and hydrogen nanobubbles.

[0007] The technical solution of the present invention is as follows:

[0008] A method for synergistic treatment of metallic pollutants using nano-zero valent iron and hydrogen nanobubbles, wherein the method involves adding nano-zero valent iron particles to polluted water under anaerobic conditions and introducing hydrogen nanobubbles to remove metallic pollutants from the polluted water.

[0009] The nano-sized zero-valent iron has a particle size of 20-200 nm, a spherical core-shell structure, and a core of Fe. 0 The outer layer is coated with iron oxide;

[0010] The hydrogen nanobubbles have an average particle size of 100-300 nm and a particle number of 10. 7 -10 8 per mL.

[0011] Preferably, the mass-to-volume ratio of the nano-zero-valent iron particles to the polluted water is 0.5-1.0 g / L.

[0012] Preferably, the treatment time for metal pollutants by the synergistic treatment of nano-zero valent iron and hydrogen nanobubbles is 1-60 min.

[0013] Preferably, the nano-zero-valent iron is prepared by sodium borohydride liquid-phase reduction method.

[0014] More preferably, the sodium borohydride liquid-phase reduction method includes the following steps:

[0015] (1) Prepare equal volumes of ferric chloride (FeCl3) solution and sodium borohydride (NaBH4) solution, wherein the molar ratio of NaBH4 to FeCl3 is not less than 4:1;

[0016] (2) Under nitrogen purging conditions, NaBH4 solution is slowly added dropwise to FeCl3 solution at a rate of 2-10 mL / min, and mechanically stirred to mix thoroughly; preferably, the nitrogen purity is >99.9%;

[0017] (3) After the NaBH4 solution was added dropwise, the obtained nZVI was collected by vacuum filtration, washed repeatedly with a large amount of deionized water and anhydrous ethanol, and then stored in anhydrous ethanol at 4℃ for later use.

[0018] Preferably, the preparation method of the hydrogen nanobubbles includes, but is not limited to: micro / nanobubble machine method, pressure reduction method, electrolysis method, or microporous medium method.

[0019] Preferably, the reaction temperature for the synergistic treatment of metal pollutants by nano-zero valent iron and hydrogen nanobubbles is 20-30℃, and the system pressure is 1 atm.

[0020] The method described in this invention can treat at least one of the following metallic pollutants: Mn, Cr, Cu, As, Se, Cd, Sb, and Pb; and it is universally applicable to other pollutants with oxidizing properties.

[0021] The method described in this invention can treat polluted water bodies, including groundwater, and further including groundwater in mining areas.

[0022] This invention can also treat water bodies containing metal pollutants in other environments.

[0023] The beneficial technical effects of this invention are as follows:

[0024] 1. This invention involves adding a certain amount of nano-zero-valent iron particles to polluted groundwater and introducing hydrogen nanobubbles. Under anaerobic conditions, these bubbles enhance the reducing power of the groundwater system, thereby strengthening the removal capacity of the nano-zero-valent iron for metallic pollutants. Because hydrogen nanobubbles have strong reducing properties, their presence, in addition to promoting the removal of Fe... 0 In addition to chemical reduction, it also promotes the removal of pollutants from anaerobic polluted water bodies.

[0025] 2. This invention requires only a certain amount of nano-zero-valent iron particles and hydrogen nanobubbles. Its preparation method is simple and easy to implement, and no other harmful substances are generated. It is clean and safe, and can quickly participate in the removal of metal pollutants in groundwater with high removal efficiency.

[0026] 3. This invention can rapidly remove groundwater pollutants without any catalyst, and the removal efficiency is high. The technology combining nano-zero-valent iron with hydrogen nanobubbles is expected to improve the reducing properties of oxygen-deficient groundwater environments. The hydrogen nanobubbles, in conjunction with nano-zero-valent iron, participate in processes such as chemical adsorption, potentially reducing capital costs and the use of chemicals, and effectively preventing the sedimentation of nano-zero-valent iron, thus improving removal efficiency.

[0027] 4. The anaerobic environmental conditions required by this invention are perfectly suited to anaerobic groundwater environments. This invention produces no corrosive solutions and no other harmful substances, thus meeting environmental safety principles and making it suitable for groundwater treatment. Attached Figure Description

[0028] Figure 1 This is the experimental procedure for treating polluted water bodies according to the present invention.

[0029] Figure 2 The physical properties and stability of the hydrogen nanobubbles prepared in Example 1 are as follows: (a) the relationship between the number density of hydrogen nanobubbles and the hydrogen content (the embedding diagrams are dynamic light scattering spot diagrams of each system); (b) the particle size distribution of hydrogen nanobubbles; and (c) the average particle size of hydrogen nanobubbles.

[0030] Figure 3 The graph shows the change in As removal rate over time in Example 3.

[0031] Figure 4 The graph shows the change in Se removal rate over time in Example 4.

[0032] Figure 5 The graph shows the change in Fe ion concentration over time in Example 4. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] The chemical reagents used in the following examples include FeCl3·6H2O, NaBH4, and Na2SeO3 (AR, Sigma Aldrich (Shanghai) Trading Co., Ltd.). Deionized water was prepared using an ultrapure water system (Smart, Heal Force Biomedical Technology Holding Co., Ltd.). High-purity nitrogen (≥99.9% purity) was used for deoxygenation of the solution and as a vacuum protective gas for various characterization instruments. The particle size and number density of hydrogen nanobubbles were determined using a nanoparticle tracking analyzer (NTA, ZetaView, ParticleMetrix, Germany).

[0035] To prevent oxidation of nano-zero ferric iron, it is generally stored in an ethanol solution at 4°C. Before adding nano-zero ferric iron, the nano-zero ferric iron ethanol suspension should be sonicated in an ice bath for 30 minutes to better disperse any aggregated particles. The actual particle concentration of the nano-zero ferric iron ethanol suspension is determined by constant weight method.

[0036] Due to the extremely low solubility of hydrogen in water, this invention requires a certain oxygen-deficient or anaerobic environment in order to effectively generate and stably exist hydrogen nanobubbles.

[0037] The reaction system in the following examples was placed in a constant-temperature shaker at 25°C and 180 rpm throughout the entire process to ensure complete mixing and full reaction. The instrument operation was as follows: Figure 1 As shown.

[0038] Example 1: Preparation and Measurement of the Properties of Hydrogen Nanobubble Water

[0039] High-purity hydrogen gas (H2, ≥99.999%, Bentong (Shanghai) Chemical Products Sales Co., Ltd.) was introduced into ultrapure water using a micro-nano bubble device (OXYDEEP-TABLE-0.3, Nanjing Bona Scientific Instruments Co., Ltd.). The pump speed was 2300 r / min, the gas flow rate was 100 mL / min, the pump outlet pressure was 0.5 MPa, and the instrument running time was 30 min.

[0040] During operation, the solution appears milky white because it contains a large number of micron-sized air bubbles, which are invisible to the naked eye. After operation, the solution is left to stand for 1 minute, and the micron-sized air bubbles gradually disappear from bottom to top, turning the solution from milky white to clear and transparent.

[0041] The number density and particle size distribution of the prepared hydrogen nanobubble water were determined using a nanoparticle tracking analyzer (25℃, Sensitivity: 65, Shutter: 150). The total hydrogen content in the solution was determined using headspace gas chromatography. The sample concentration was measured again after deep degassing (complete freezing at -20℃, followed by degassing at 0.1 atm for 10 h, and then freezing again to eliminate bubble particles in the solution). Deep degassing removes most of the gas from the system, including dissolved gases and gases encapsulated in nanobubbles. The changes in sample particle concentration before and after degassing were compared. The test results are as follows: Figure 2 As shown.

[0042] from Figure 2 It can be seen that three degassing processes can reduce the number density of hydrogen nanobubbles in water from 3.8 × 10⁻⁶ to 10⁻⁶. 8 The number of cells / mL decreased to 6.7 × 10⁻⁶ 6 The number of particles per mL is close to the particle number density in ultrapure water (1.5-5.5×10⁻⁶). 6 (Number of nanobubbles / mL). A small amount of hydrogen gas was detected in the solution after two degassing cycles, while three degassing cycles completely removed the hydrogen gas from the water. This indicates that the hydrogen nanobubble water prepared by this device is relatively stable, and at least three freeze-vacuum degassing cycles are required to completely remove the hydrogen nanobubbles from the solution. The dynamic light scattering spot of the nanobubbles in the solution, measured by the nanoparticle tracking analyzer, is shown below. Figure 2 The embedded diagram is shown in a.

[0043] Figure 2 b indicates that the nanoparticles in the freshly prepared hydrogen nanobubble water are concentrated in the range of 50-250 nm. Although the particle size after degassing is also within this range, the number of particles is significantly reduced, and the particle size distribution becomes more dispersed with the increase of degassing times.

[0044] The average particle size also varies with different degassing cycles. Figure 2 c) The particle size of freshly prepared hydrogen nanobubbles was 144.6 ± 88.9 nm, while the average particle size after degassing was around 250 nm. This indicates that degassing has a significant impact on the hydrogen nanobubble water system, not only reducing the number of bubbles but also increasing the bubble size. Therefore, the particle size and number density of hydrogen nanobubbles will change to some extent in practical applications, but these changes have little impact on the removal of metal contaminants.

[0045] Example 2: Preparation of nano-zero valent iron

[0046] The nano-zero-valent iron was prepared by sodium borohydride liquid-phase reduction method, and the specific steps are as follows:

[0047] (1) Prepare a 0.05M ferric chloride (FeCl3) solution and an equal volume of a 0.2M sodium borohydride (NaBH4) solution;

[0048] (2) Under the condition of nitrogen (N2, purity >99.9%) purging, slowly add NaBH4 solution to FeCl3 solution at a rate of 2-10 mL / min and mix thoroughly by mechanical stirring;

[0049] (3) After the NaBH4 solution is added dropwise, the obtained nZVI is collected by vacuum filtration, washed repeatedly with a large amount of deionized water and anhydrous ethanol, and then stored in anhydrous ethanol at 4℃ for later use. Before use, the nano-zero ferric ethanol suspension should be sonicated in an ice bath for 30 minutes to prevent aggregation.

[0050] The nano-zero-valent iron prepared by this invention has a spherical core-shell structure, with Fe as the core. 0 The outer layer is coated with iron oxide, with a particle size ranging from 20 to 200 nm.

[0051] Example 3: Synergistic treatment of As with nano-zero valent iron and hydrogen nanobubbles 3+ Metal pollutants

[0052] Formulating As 3+ 100 mg / L sodium selenite solution was placed in an Erlenmeyer flask, and after adjusting the pH to 5.00, 1.0 g / L of nano-zero ferric ethanol suspension was added. The flask was then quickly sealed with a rubber stopper and placed in a constant temperature shaker at 25°C for 2 hours.

[0053] Formulating As 3+ The solvent used in the sodium selenite solution was the hydrogen nanobubble water in Example 1 before degassing, which was called the experimental group; the control group used deionized water as the solvent and aerated the deionized water with high-purity nitrogen in advance to simulate the oxygen-deficient groundwater environment, and then carried out deep degassing to eliminate bubble particles in the system.

[0054] Samples were taken in segments at reaction times of 0, 1, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min. The samples were filtered through a 0.22 μm filter membrane, acidified with 4% ultra-high purity HNO3, and then diluted to 10 mL with deionized water. The total soluble As ions were determined using inductively coupled plasma atomic emission spectrometry (ICP, Agilent 720ES, USA). Figure 3 ).

[0055] from Figure 3 As can be seen, compared with the control group, the presence of hydrogen nanobubbles significantly improved the removal rate of As ions, and the removal was basically completed after 10 minutes. This indicates that the presence of hydrogen nanobubbles accelerated the removal of As in the early stage of the reaction.

[0056] Example 4: Synergistic treatment of Se with nano-zero valent iron and hydrogen nanobubbles 4+ Metal pollutants

[0057] Formulating Se 4+ 100 mg / L sodium selenite solution was placed in an Erlenmeyer flask, and after adjusting the pH to 5.00, 1.0 g / L of nano-zero ferric ethanol suspension was added. The flask was then quickly sealed with a rubber stopper and placed in a constant temperature shaker at 25°C for 2 hours.

[0058] Formulating Se 4+ The sodium selenite solution used hydrogen nanobubble water as the solvent, which was called the experimental group; the control group used deionized water as the solvent, and the deionized water was aerated with high-purity nitrogen beforehand to deoxygenate, in order to simulate the oxygen-deficient groundwater environment, and then deep degassing was carried out to eliminate bubble particles in the system.

[0059] Samples were taken in segments at reaction times of 0, 1, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min. The samples were filtered through a 0.22 μm filter membrane, acidified with 4% ultra-high purity HNO3, and then diluted to 10 mL with deionized water. The total soluble Se ions were determined using inductively coupled plasma atomic emission spectrometry (ICP, Agilent 720ES, USA). Figure 4 ).

[0060] from Figure 4 As can be seen, compared with the control group, the presence of hydrogen nanobubbles can significantly improve the removal rate of Se ions, and Se in the solution can be completely removed within 10 minutes, which is consistent with the effect in Example 2. This indicates that hydrogen nanobubbles have the same promoting effect on the removal of Se by nano-zero valent iron as in the As system.

[0061] Figure 5 This represents the change in Fe ion concentration over time during the experiment. Figure 5It can be seen that the presence of hydrogen nanobubbles slows down the precipitation rate of Fe ions and reduces the concentration of Fe ions in the solution. This indicates that hydrogen nanobubbles have strong reducing properties and can reduce free Fe ions to Fe2+. 0 It can then participate in the reaction again, a characteristic that is highly compatible with anaerobic groundwater environments.

[0062] The above experiments demonstrate that this technology can effectively remove metallic pollutants from groundwater and is universally applicable to other pollutants with oxidizing properties.

[0063] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, and for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for synergistic treatment of metallic pollutants using nano-zero-valent iron and hydrogen nanobubbles, characterized in that, The method involves adding nano-zero-valent iron particles to polluted water under anaerobic conditions and introducing hydrogen nanobubbles to remove metallic pollutants from the polluted water. The presence of hydrogen nanobubbles slows down the precipitation rate of iron ions and reduces the concentration of iron ions in the solution. Hydrogen nanobubbles also have strong reducing properties, capable of reducing free iron ions to Fe. 0 It then participates in the reaction again, adapting to the hypoxic environment; hydrogen nanobubbles, together with nano-zero valent iron, participate in the chemical adsorption process, which can effectively prevent the precipitation of nano-zero valent iron. The nano-sized zero-valent iron has a particle size of 20-200 nm, a spherical core-shell structure, and a core of Fe. 0 The outer layer is coated with iron oxide; The hydrogen nanobubbles have an average particle size of 100-300 nm and a particle number of 10. 7 -10 8 cells / mL; The mass-to-volume ratio of the nano-zero-valent iron particles to the polluted water is 0.5-1.0 g / L; The time for treating metal pollutants by synergistic treatment of nano-zero valent iron and hydrogen nanobubbles is 1-10 min. The reaction temperature for the synergistic treatment of metallic pollutants by nano-zero valent iron and hydrogen nanobubbles is 20-30 ℃, and the system pressure is 1 atm. The metallic contaminants include at least one of As and Se.

2. The method according to claim 1, characterized in that, The nano-zero-valent iron was prepared by sodium borohydride liquid-phase reduction.

3. The method according to claim 2, characterized in that, The sodium borohydride liquid-phase reduction method includes the following steps: (1) Prepare equal volumes of ferric chloride (FeCl3) solution and sodium borohydride (NaBH4) solution, wherein the molar ratio of NaBH4 to FeCl3 is not less than 4:1; (2) Under nitrogen purging conditions, slowly add NaBH4 solution to FeCl3 solution at a rate of 2-10 mL / min and mix thoroughly by mechanical stirring; (3) After the NaBH4 solution is added, the obtained nZVI is collected by vacuum filtration, washed repeatedly with a large amount of deionized water and anhydrous ethanol, and then stored in anhydrous ethanol at 4℃ for later use.

4. The method according to claim 1, characterized in that, The methods for preparing hydrogen nanobubbles include, but are not limited to: micro / nanobubble machine method, pressure reduction method, electrolysis method, or microporous medium method.

5. The method according to claim 1, characterized in that, The polluted water bodies include groundwater.

6. The method according to claim 1, characterized in that, The polluted water body includes groundwater in the mining area.

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