Method for short-range macro-quantity preparation of high-stability micro-nano active material by shearing zero-valent iron with silicic acid

Abstract

The invention relates to the technical field of industrial production, in particular to a method for preparing a high-stability micro-nano active material from silicic acid shearing zero-valent iron in a short-range and macro manner. The invention develops a macro ball milling system to help to obtain a high-stability micro-nano active material, the system can realize autonomous internal circulation, manual control is not needed during packaging from feeding to discharging, smooth operation can be realized, and the industrialization efficiency is extremely high. Besides, according to the high-stability micro-nano active material provided by the invention, oxygen-free water is introduced to be subjected to ball milling with zero-valent iron and sodium silicate, a silicon dioxide protective shell is generated on the surface of the zero-valent iron, and the silicon dioxide protective shell has certain passivation resistance and can help to realize efficient dechlorination without damaging the high-stability micro-nano active material.

Description

Technical Field

[0001] This invention relates to the field of industrial production technology, specifically to a method for short-range, large-scale preparation of highly stable micro / nano active materials by shearing zero-valent iron from silicate. Background Technology

[0002] Micro- and nano-sized zero-valent iron, with its high specific surface area, strong reducing properties, and environmental friendliness, has shown broad application prospects in fields such as groundwater pollution remediation, soil heavy metal treatment, and wastewater treatment. Its preparation methods are mainly divided into top-down and bottom-up methods, among which thermal reduction methods (including gas-phase reduction and carbothermal reduction) and chemical reduction methods (including liquid-phase reduction) are currently the mainstream technologies for industrial mass production.

[0003] Thermal reduction prepares micro / nano zero-valent iron through a reduction reaction under high-temperature conditions. Gas-phase reduction preserves the original morphology of the particles, while carbothermal reduction can prepare composite functional materials; however, both require stringent reaction conditions. Chemical reduction involves the reaction of a reducing agent with iron ions in a liquid phase to generate products. It is relatively simple to operate and allows for easy control of particle size, making it a common method for laboratory and small-scale preparation.

[0004] With the increasing demand for environmental protection, the market demand for micro-nano zero-valent iron continues to grow, and the economy and practicality of mass production technology have become the core bottleneck for its promotion and application. As a top-down preparation technology, ball milling achieves the micro-nanoization of raw materials through mechanical force. It has advantages such as simple operation and green environmental protection, and has gradually become a research hotspot for low-cost mass production. However, traditional ball milling still has problems such as difficulty in controlling particle morphology and insufficient product stability, and its performance needs to be further improved through modification and optimization. Traditional ball milling has inherent shortcomings: (1) Poor particle performance. When directly ball milling micron iron powder, due to the ductility of metal, it is easy to form nanoscale flakes, and the specific surface area and reactivity are significantly lower than those of spherical particles. When using oxides as raw materials, the particle size distribution is wide and the morphology is difficult to control accurately. (2) Lack of product stability. Unmodified ball milling products are prone to agglomeration and oxidation. The activity loss is serious when stored in wet conditions, which limits its application scenarios.

[0005] Existing ball milling modification technologies mostly focus on optimizing a single performance, lacking an integrated solution that can simultaneously achieve micro-nanoization, stabilization, and high activity, making it difficult to balance large-scale preparation with product quality. Therefore, there is an urgent need for a novel process to obtain highly stable and highly active micro-nano-scale zero-valent iron materials. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of existing zero-valent iron ball milling processes that cannot simultaneously achieve micro / nano, high stability, and high activity, and provides a method for short-range, large-scale preparation of highly stable micro / nano active materials by shearing zero-valent iron with silica to overcome the above-mentioned shortcomings.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for short-range, large-scale preparation of highly stable micro / nano active materials by shearing sodium silicate with zero-valent iron. The method is performed within a large-scale ball milling system, which includes a high-speed mixing unit, a ball milling shearing unit, and an air supply unit arranged sequentially along the feed direction. The air supply unit is connected to the ball milling shearing unit, which is also connected to a solid-liquid separation unit and a particle size classification unit. The solid-liquid separation unit is sequentially connected to a particle size classification unit and an encapsulation unit along the discharge direction. Within the high-speed mixing unit, sodium silicate powder and reduced iron powder are mixed to obtain an iron-silicon composite material. The inert gas generated by the gas supply unit enters the ball mill shearing unit. In the flowing inert gas environment, the iron-silicon composite material is ball-milled with oxygen-free water in the ball mill shearing unit to obtain a ball mill slurry. Subsequently, the ball mill slurry enters the solid-liquid separation unit to separate the ball milling beads from the slurry. The ball milling beads are recycled back into the ball mill shearing unit, and the slurry enters the particle size classification unit to classify the particles into substandard and standard particles. The substandard particles enter the ball mill shearing unit for further ball milling, while the standard particles enter the encapsulation unit for encapsulation to obtain a highly stable micro-nano active material.

[0009] Preferably, the ball mill shearing unit is equipped with a jacketed cooling structure, which stores circulating cooling water at 28~32℃, and can stabilize the temperature inside the ball mill shearing unit at 25~32℃.

[0010] Preferably, the mass ball mill system further includes a dust removal unit and an exhaust fan unit disposed between the ball mill shearing unit and the air supply unit.

[0011] When the ball mill shearing unit starts feeding, the air supply unit is not turned on. The iron-silicon composite material is allowed to complete dust removal in the dust removal unit and light impurities are removed in the induced draft unit before entering the air supply unit. Then the air supply unit is turned on, and the iron-silicon composite material flows back into the ball mill shearing unit under the action of airflow. The outlet to the dust removal unit and the induced draft unit is closed, and ball milling begins in the ball mill shearing unit.

[0012] Preferably, sodium silicate powder and reduced iron powder are mixed at a silicon to iron molar ratio of 0.01 to 0.1; and / or, the sodium silicate powder is anhydrous sodium silicate powder with a purity ≥99%; and / or, the solid-liquid ratio of the iron-silicon composite material to oxygen-free water is 2 to 5 g / L.

[0013] Preferably, the inert gas inflow rate is 1~8 m³ / h. 3 / h.

[0014] Preferably, the mixing conditions are stirring at 600~1000 rpm for 10~30 min; and / or, the ball milling conditions are ball milling at 400~800 rpm for 4~20 h; and / or, during ball milling, the mass ratio of the grinding balls to the iron-silicon composite material is (3~20):1; and / or, the grinding balls are zirconia grinding balls with a diameter of 6~10 mm.

[0015] The mixing parameters should satisfy the requirement that the coefficient of variation of silicon element distribution in the mixed iron-silicon composite material is ≤5%.

[0016] Preferably, the grading standard is as follows: particles with D50 ≤ 0.5 μm are considered to meet the standard, and particles with D50 > 0.5 μm are considered to fail to meet the standard.

[0017] Preferably, the reduced iron powder contains ≥99.5 wt% zero-valent iron and has a particle size of 100~200 μm; and / or, the reduced iron powder is subjected to impurity removal treatment, and its dispersity is ≥90% after the impurity removal treatment.

[0018] The present invention also provides a highly stable micro / nano active material, which is a zero-valent iron core and a silicate protective layer wrapped around the zero-valent iron core, wherein Si-O-Fe bonds are formed between the silicate protective layer and the zero-valent iron core; the silicate coating includes a hydroxyl-bonded silica polymer and a multilayer silica structure.

[0019] In mechanochemical processes, silicate anions replace some surface hydroxyl groups on zero-valent iron, leading to the formation of Si-O-Fe bonds.

[0020] Silicate coating in ZVI@SiO x The formation mechanism involves the hydrolysis of Si-O bonds under mechanical force in the presence of water, initiating the formation of Si(OH)4. Si(OH)4 exhibits a high affinity for iron / iron oxide surfaces. These monomers then participate in a condensation reaction to form hydroxyl-bonded silica polymers and multilayer silica structures, ultimately growing into a silicate coating encapsulating ZVI.

[0021] The present invention also provides a dechlorination agent comprising highly stable micro / nano active materials.

[0022] Highly stable micro-nano active materials have good degradation effects on a variety of different chlorinated hydrocarbons, proving that they can be used as dechlorinating agents to address chlorine pollution problems in real-world environments.

[0023] Therefore, this invention has the following beneficial effects: This invention develops a large-scale ball milling system to help obtain highly stable micro / nano active materials. This system can achieve autonomous internal circulation, and from feeding to discharging and packaging, no manual control is required. It can operate smoothly and has extremely high industrial efficiency. Furthermore, the highly stable micro / nano active materials provided by this invention, through ball milling with oxygen-free water, zero-valent iron, and sodium silicate, generate a silica protective shell on the surface of the zero-valent iron. This silica protective shell has a certain degree of passivation resistance, which helps to achieve efficient dechlorination without damaging the highly stable micro / nano active materials. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a mass ball mill system.

[0025] Figure 2 The results represent the microstructure characterization, where a is ZVI@SiO x HAADF-STEM element mapping series diagrams, b is ZVI@SiO x HAADF-STEM linear scan image, c is ZVI@SiO x XPS combined with ion sputtering depth profile analysis results, d is the relative content of OH- in the O1s XPS spectrum, e is the FTIR spectrum, f is the XRD pattern, g is the ZVI@SiO x The mechanism diagram.

[0026] Figure 3 This is a graph showing the TCE degradation effect, where a is the TCE degradation curve and b is the K value. M，TCE and k SA，TCE Value, c is HER activity, d is the electronic efficiency of TCE dechlorination, e is ZVI@SiO x Continuous dechlorination results, f represents the concentration of chlorinated compounds in H2O and D2O based on ZVI, Si-ZVI, and ZVI@SiO2. x KIE values ​​calculated from the TCE dechlorination kinetics in the presence of 0.5 g, representing the effect of M ET on TCE degradation, and h representing the effect of different concentrations of TBA on ZVI@SiO₂. x The influence of i is the TCE degradation mechanism.

[0027] Figure 4 ZVI@SiO x The degradation effects of the material on different chlorinated hydrocarbons, where a, b, c, and d correspond to cis-DCE, trans-DCE, CF, and PCE, respectively; reaction conditions: Fe: 10 g·L⁻¹ -1 CHCs: 100 μM, 50 mM HEPES, pH=7, hypoxia, T=25℃.

[0028] The codes in the diagram are as follows: High-speed mixing unit 100; Ball mill shearing unit 200; Jacket cooling structure 210; Dust removal unit 300; Exhaust fan unit 400; Air supply unit 500; Solid-liquid separation unit 600; Particle size classification unit 700; Packaging unit 800. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0030]

Example

[0031] In this section, all examples / comparative examples were performed independently within the mass ball milling system provided by this invention. For example... Figure 1 As shown, the mass production ball mill system includes a high-speed mixing unit 100, a ball mill shearing unit 200, and an air supply unit 500 arranged sequentially along the feed direction. The air supply unit 500 is connected to the ball mill shearing unit 200, which is connected to a solid-liquid separation unit 600 and a particle size classification unit 700. The solid-liquid separation unit 600 is connected sequentially along the discharge direction to the particle size classification unit 700 and a packaging unit 800. The mass production ball mill system also includes a dust removal unit 300 and an induced draft unit 400 disposed between the ball mill shearing unit 200 and the air supply unit 500. The ball mill shearing unit 200 is equipped with a jacketed cooling structure 210, which stores circulating cooling water at 30°C, stabilizing the temperature inside the ball mill shearing unit 200 at 28~32°C. The entire mass production ball mill system operates under an inert atmosphere provided by the air supply unit 500.

[0032] Example 1

[0033] 1. Raw material pretreatment

[0034] Reduced iron powder (Fe) was processed using a 100-mesh vibrating screen. 0 The reduced iron powder (99.6% purity, particle size distribution 100-180 μm) was screened to remove impurities and agglomerates, resulting in a dispersion of over 95%. Reduced iron powder and anhydrous sodium silicate powder (99.2% purity) were weighed according to a silicon / iron molar ratio of 0.01 and added together to a 100L high-speed mixing unit 100 (i.e., a high-speed mixer). The mixture was stirred at 800 rpm for 12 min to obtain a homogeneous iron-silicon composite material. The iron-silicon composite material was then tested for mixing uniformity to ensure that the coefficient of variation of silicon distribution in the iron-silicon composite material was ≤3%. The iron-silicon composite material that met the requirements was then removed from the mixing and set aside for later use.

[0035] 2. Construction and Parameter Setting of Large-Scale Ball Mill System

[0036] The ball mill shearing unit 200 has an effective volume of 3.6 m³. 3 The continuous vertical ball mill is equipped with a PSA-50 nitrogen generator (nitrogen purity ≥ 99.999%) for gas supply unit 500. Zirconia grinding balls with a diameter of 6 mm are added to the continuous vertical ball mill, and iron-silicon composite material is added in stages, controlling the mass ratio of zirconia grinding balls to iron-silicon composite material to be 20:1.

[0037] When the continuous vertical ball mill is initially fed, the nitrogen generator is not turned on. The iron-silicon composite material undergoes dust removal in the dust removal unit 300 and light impurities removal in the induced draft unit 400 before entering the nitrogen generator. The feed inlet of the continuous vertical ball mill is then closed, and the nitrogen generator is started. The iron-silicon composite material flows back into the continuous vertical ball mill under the action of the nitrogen gas flow. The outlets to the dust removal unit 300 and the induced draft unit 400 are then closed. At this time, the nitrogen generator introduces high-purity nitrogen into the continuous vertical ball mill, maintaining a nitrogen flow rate of 5 m³ / s each time it is purged. 3 After purging 3 times per hour, the gas inside the tank was tested with an oxygen content detector to confirm that the oxygen content had dropped to 0.08% (≤0.1%), and then the mill tank was sealed.

[0038] Oxygen-free deionized water was added to the sealed continuous vertical ball mill using a metering pump, maintaining a liquid-to-solid ratio of 1:3. The continuous vertical ball mill was restarted, with the speed set to 400 rpm, using unidirectional rotation mode, and the milling time set to 5 hours. During the milling process, nitrogen gas (flow rate 2 m³ / s) was continuously introduced into the milling chamber of the continuous vertical ball mill via a nitrogen generator. 3 ( / h), while simultaneously turning on the jacketed cooling device and introducing 30℃ circulating cooling water, and monitoring the temperature inside the continuous vertical ball mill in real time to ensure that the ball mill temperature is stable within the range of 28~32℃.

[0039] 3. Product post-processing

[0040] After ball milling, open the discharge valve of the continuous vertical ball mill to discharge the milled slurry (containing zirconia grinding beads and ZVI@SiO2). x The particles and water are conveyed to the solid-liquid separation unit 600 (i.e., a plate and frame vacuum filter), where a vacuum of -0.08 MPa is set and the filtration time is 30 min to separate the zirconia grinding beads from the slurry. After separation, the zirconia grinding beads are purged with high-pressure air to remove residual powder and then returned to the continuous vertical ball mill for recycling via a return pipeline. The filtered ZVI@SiO₂... x Wet material (moisture content approximately 40%) is fed into particle size classification unit 700 (i.e., ultrasonic grading sieve, 0.1 μm mesh size), with a sieving frequency of 25 kHz and a classification time of 20 min. Particles meeting the size standard (D50 ≤ 0.42 μm) are screened out, while coarse particles (D50 > 0.5 μm) are returned to the continuous vertical ball mill for re-ball milling via a return pipe. The final collected particles are silica-grafted micro / nano zero-valent iron (denoted as ZVI@SiO). x )powder.

[0041] 4. Finished product packaging and quality inspection

[0042] ZVI@SiO after meeting the standards xThe powder is conveyed to a sealing unit 800 (i.e., a sealed sealing chamber) filled with nitrogen (oxygen content ≤0.1%), and packaged using a fully automatic vacuum packaging machine. The packaging material is a PET / AL / PE barrier composite film (oxygen permeability ≤0.1 cm). 3 / (m 2 (24h·atm), each bag is packaged in 25 kg bags, and the vacuum degree is controlled at -0.09MPa after packaging.

[0043] Example 2

[0044] 1. Raw material pretreatment

[0045] Reduced iron powder (Fe) was processed using a 100-mesh vibrating screen. 0 The reduced iron powder (99.5% purity, particle size distribution 150-200 μm) was screened to remove impurities and agglomerates, resulting in a dispersion of over 94%. Reduced iron powder and anhydrous sodium silicate powder (99.1% purity) were weighed according to a silicon / iron molar ratio of 0.1 and added together to a 100L high-speed mixing unit 100 (i.e., a high-speed mixer). The mixture was stirred at 900 rpm for 15 min to obtain a homogeneous iron-silicon composite material. The iron-silicon composite material was then tested for mixing uniformity to ensure that the coefficient of variation of silicon distribution in the iron-silicon composite material was ≤4%. The iron-silicon composite material that met the requirements was then removed from the mixing and set aside for later use.

[0046] 2. Construction and Parameter Setting of Large-Scale Ball Mill System

[0047] The ball mill shearing unit 200 has an effective volume of 3.6 m³. 3 The continuous vertical ball mill is equipped with a PSA-50 nitrogen generator (nitrogen purity ≥ 99.999%) for gas supply unit 500. Zirconia grinding balls with a diameter of 6 mm are added to the continuous vertical ball mill, and iron-silicon composite material is added in stages, controlling the mass ratio of zirconia grinding balls to iron-silicon composite material to be 3:1.

[0048] When the continuous vertical ball mill is initially fed, the nitrogen generator is not turned on. The iron-silicon composite material undergoes dust removal in the dust removal unit 300 and light impurities removal in the induced draft unit 400 before entering the nitrogen generator. The feed inlet of the continuous vertical ball mill is then closed, and the nitrogen generator is started. The iron-silicon composite material flows back into the continuous vertical ball mill under the action of the nitrogen gas flow. The outlets to the dust removal unit 300 and the induced draft unit 400 are then closed. At this time, the nitrogen generator introduces high-purity nitrogen into the continuous vertical ball mill, maintaining a nitrogen flow rate of 4 m³ / s during each purging. 3 After purging 3 times per hour, the gas inside the tank was tested with an oxygen content detector to confirm that the oxygen content had dropped to 0.09% (≤0.1%), and then the mill tank was sealed.

[0049] Oxygen-free deionized water was added to the sealed continuous vertical ball mill using a metering pump, maintaining a liquid-to-solid ratio of 1:3. The continuous vertical ball mill was restarted, with the speed set to 400 rpm, using unidirectional rotation mode, and the milling time set to 5 hours. During the milling process, nitrogen gas (flow rate 1.8 m³ / s) was continuously introduced into the milling chamber of the continuous vertical ball mill via a nitrogen generator. 3 ( / h), while simultaneously turning on the jacketed cooling device and introducing 28℃ circulating cooling water, and monitoring the temperature inside the continuous vertical ball mill in real time to ensure that the ball mill temperature is stable within the range of 25~28℃.

[0050] 3. Product post-processing

[0051] After ball milling, open the discharge valve of the continuous vertical ball mill to discharge the milled slurry (containing zirconia grinding beads and ZVI@SiO2). x The particles and water are conveyed to the solid-liquid separation unit 600 (i.e., a plate and frame vacuum filter), where a vacuum of -0.07 MPa is set and the filtration time is 25 min to separate the zirconia grinding beads from the slurry. After separation, the zirconia grinding beads are purged with high-pressure air to remove residual powder and then returned to the continuous vertical ball mill for recycling via a return pipeline. The filtered ZVI@SiO₂... x The wet material (moisture content approximately 35%) is fed into the particle size classification unit 700 (i.e., an ultrasonic grading sieve with a mesh size of 0.1 μm). The sieving frequency is set to 22 kHz, and the classification time is 25 min. Particles meeting the size standard (D50 of 0.48 μm, ≤0.5 μm) are screened out. Coarse particles that do not meet the standard (D50 >0.5 μm) are returned to the continuous vertical ball mill for re-ball milling via a return pipe. Finally, the qualified particles are collected, which is the silica-grafted micro / nano zero-valent iron powder.

[0052] 4. Finished product packaging and quality inspection

[0053] ZVI@SiO after meeting the standards x The powder is conveyed to a sealing unit 800 (i.e., a sealed sealing chamber) filled with nitrogen (oxygen content ≤0.1%), and packaged using a fully automatic vacuum packaging machine. The packaging material is a PET / AL / PE barrier composite film (oxygen permeability ≤0.1 cm). 3 / (m 2 (24h·atm), each bag is packaged in 25 kg bags, and the vacuum degree is controlled at -0.085MPa after packaging.

[0054] Comparative Example 1

[0055] This comparative example is basically the same as Example 1, except that no oxygen-free water and anhydrous sodium silicate powder are added, and the resulting material is denoted as ZVI.

[0056] Comparative Example 2

[0057] This comparative example is basically the same as Example 1, except that anhydrous sodium silicate powder is not added, and the resulting material is denoted as ZVI. H2O .

[0058] Comparative Example 3

[0059] This comparative example is basically the same as Example 1, except that no oxygen-free water is added, and the resulting material is denoted as Si-ZVI.

[0060] [Performance Testing]

[0061] 1. Industrial testing

[0062] In Example 1, three bags of finished product were randomly selected for quality testing. The test results are as follows: D50 was 0.40~0.43μm, meeting the requirement of D50≤0.5μm. XRD results showed a characteristic Fe0 diffraction peak at 2θ=44.7°, confirming Fe... 0 The crystal structure is intact. XPS results showed the presence of Si-O-Fe bond characteristic peaks (binding energy 531.2 eV) in the O 1s spectrum, proving the successful grafting of silica. TCE degradation experiments (52 mL serum bottle, initial TCE concentration 100 μM, dosage of high-stability micro / nano active material from Example 1 10 g / L, 25 °C) showed a TCE degradation rate of 96.5% within 24 h, ≥95%.

[0063] In Example 2, three bags of finished product were randomly selected for quality testing. The test results are as follows: D50 was 0.46~0.49μm, meeting the requirement of D50≤0.5μm. XRD results showed characteristic Fe0 diffraction peaks, confirming the integrity of the Fe0 crystal phase structure. XPS results showed characteristic peaks of Si-O-Fe bonds, proving the successful grafting of silica. The TCE degradation experiment (52mL serum bottle, initial TCE concentration 100μM, dosage of high-stability micro-nano active material in Example 2 10g / L, 25℃) showed that the TCE degradation rate was 95.2% within 24 h, ≥95%.

[0064] 2. Microstructure Research

[0065] To clarify the mechanism of action of highly stable micro / nano active materials, the ZVI@SiO2 prepared in Example 1 was used... x The ZVI powder, ZVIH2O prepared in Comparative Example 1, ZVIH2O prepared in Comparative Example 2, and Si-ZVI prepared in Comparative Example 3 were characterized in a series of ways.

[0066] Figure 2 a is ZVI@SiO x The HAADF-STEM images show that the zero-valent iron (ZVI) surface is coated with a silicate coating. Figure 2b is ZVI@SiO x HAADF-STEM line scan analysis showed that silicon dominated the zero-valent iron surface, while iron signals were extremely scarce; this is consistent with... Figure 2 The result is consistent with a. Figure 2 c represents ZVI@SiO x XPS combined with ion sputtering depth profile analysis results show that with the increase of sputtering time and depth, ZVI@SiO x The oxygen content decreases with depth, while the Fe content increases. The significant decrease in silicon content and [Si / Fe] ratio with depth highlights the non-uniform distribution of silicon within the structure. Overall, both STEM and XPS characterization clearly show a silicon-oxygen shell encapsulation phenomenon.

[0067] Figure 2 e represents the FTIR results, which reveal the interaction between sodium silicate and ZVI, manifested as an asymmetric tensile vibration peak at 1035 cm⁻¹ in the Si-O-Si region. -1 The characteristic peak of oriented Si-O-Fe is at 1083 cm⁻¹ -1 The offset at that point indicates the formation of Si-O-Fe bonds. Furthermore, prior to sputtering, Figure 2 O1s XPS analysis of d showed that, compared with ZVI H2O Compared to ZVI, ZVI@SiO x Surface hydroxyl groups (OH) - The contents of ) decreased by 24% and 10%, respectively. In the mechanochemical process, silicate anions replaced some surface hydroxyl groups on ZVI, leading to the formation of Si-O-Fe bonds.

[0068] Silicate coating in ZVI@SiO x The formation mechanism involves the hydrolysis of Si-O bonds under mechanical force in the presence of water, initiating the formation of Si(OH)4, such as... Figure 2 As shown in g, Si(OH)4 exhibits a high affinity for iron / iron oxide surfaces. These monomers then participate in a condensation reaction to form hydroxyl-bonded silica polymers and multilayer silica structures, ultimately growing into a silicate coating encapsulating ZVI.

[0069] 3. Dechlorination performance and mechanism

[0070] Figure 3 a is ZVI@SiO x Si-ZVI, ZVI H2O The TCE dechlorination results for ZVIs show that all four curves follow pseudo-first-order kinetics, and the obtained mass-normalized rate constant (k) M，TCE ) and the surface area normalization constant (k) of ZVI particles with normalized specific surface area. SA，TCE ),like Figure 3 as shown in b. ZVI@SiO x k values of M，TCE are 36, 22.9, and 22.9 times those of Si-ZVI, ZVI H2O and ZVI, respectively. In addition, the k x values of ZVI@SiO SA，TCE are 11.2, 71.2, and 12.6 times those of Si-ZVI, ZVI H2O and ZVI, respectively.

[0071] Figure 3 Figure c shows the results of the hydrogen evolution reaction. As Figure 3 shown in c, ZVI@SiO x inhibits the release of hydrogen within 24 h and then continues to produce hydrogen. This indicates that the ZVI@SiO x material is not passivated during the TCE degradation process, and the silicate coating exhibits certain anti-passivation properties. The electron efficiency (ε x ) of ZVI@SiO e , Si-ZVI, and ZVI after reacting for 10 h was calculated, and the results are as Figure 3 shown in d. The electron efficiency of TCE on ZVI@SiO x is 5.6 times that of Si-ZVI and 6.83 times that of ZVI. This shows that silicate doping does not significantly improve the electron efficiency of the material for degrading pollutants. However, the formation of a silica shell structure through deionized water assistance and silicate doping can significantly improve the electron efficiency of ZVI@SiO x for degrading TCE.

[0072] To verify the stability of the material, a cyclic experiment of 5 cycles was carried out, and the results were recorded in Figure 3 e. After running for 7 days, it was found that the dechlorination performance of the ZVI@SiO x material did not significantly decrease, proving that ZVI@SiO x has excellent structural stability.

[0073] To further clarify the role of proton transfer in the kinetics of TCE dechlorination, the KIE values of the prepared ZVIs for TCE dechlorination were analyzed, and the results were recorded in Figure 3 f. Figure 3 Figure f reveals that proton transfer is the rate-limiting step in the reaction. The unmodified ZVI exhibits a high KIE value of 3.6, confirming that proton transfer is the main mechanism in its dechlorination process. For ZVI@SiO x (KIE = 1.75) and Si-ZVI (KIE = 2.5), the observed KIE values indicate that proton transfer is still crucial. ZVI@SiO xEnhance TCE degradation by lowering the energy barrier of these reactions.

[0074] To determine ZVI@SiO x The dechlorination mechanism involves adding 0.5 M ectoine (ET) to disrupt the hydrogen bond network necessary for efficient proton transfer, with the following results: Figure 3 As shown in g. Figure 3 In g, ZVI@SiO x The dechlorination activity was significantly inhibited; however, the effect on ZVI and Si-ZVI was relatively small, with only a slight decrease in the rate constant. Furthermore, different concentrations of tert-butanol (TBA) were used as quenchers to evaluate key active groups in TCE degradation. Figure 3 As shown in h, 0.4 M TBA does not inhibit ZVI@SiO x The activity of ZVI@SiO2-mediated TCE dechlorination was slightly reduced, while that of 0.8 M TBA was slightly decreased. Both concentrations had a slight inhibitory effect on the degradation of TCE by ZVI and Si-ZVI, indicating that hydrogen atoms (•H) do not play a dominant role, and proton transfer is still the dominant process in ZVI@SiO2. x The main mechanism of TCE dechlorination. These results highlight the crucial role of proton transfer in the efficient dechlorination of TCEs via an interface hydrogen bonding network optimized by silicate coatings, such as... Figure 3 As shown in i.

[0075] 4. Degradation of various chlorinated hydrocarbons

[0076] To further study ZVI@SiO x The universality of the material in dechlorination was investigated using four different chlorinating compounds (cis-DCE, trans-DCE, PCE, and CF), and the results are recorded in [document name missing]. Figure 4 In the middle. Observation Figure 4 Discover ZVI@SiO x The material exhibits good dechlorination efficiency for all four chloride compounds; among them, ZVI@SiO x The degradation rates of cis-DCE, trans-DCE, PCE, and CF were 60.35, 55.56, 10, and 25.5 times that of ZVI, respectively. These results indicate that ZVI@SiO₂... x The material exhibits excellent performance and wide applicability in the dechlorination process.

Claims

1. A method for short-range, large-scale preparation of highly stable micro / nano active materials by shearing zero-valent iron from silicate, characterized in that, The process is completed within a mass ball milling system, which includes a high-speed mixing unit, a ball milling shearing unit, and an air supply unit arranged sequentially along the feeding direction. The air supply unit is connected to the ball milling shearing unit, and the ball milling shearing unit is connected to the solid-liquid separation unit and the particle size classification unit. The solid-liquid separation unit is connected sequentially to the particle size classification unit and the packaging unit along the discharge direction. In the high-speed mixing unit, sodium silicate powder and reduced iron powder are mixed to obtain an iron-silicon composite material. The inert gas generated by the gas supply unit enters the ball milling and shearing unit. Under the flowing inert gas environment, the iron-silicon composite material is ball-milled with oxygen-free water in the ball milling and shearing unit to obtain a ball milling slurry. Subsequently, the ball milling slurry enters the solid-liquid separation unit to separate the ball milling beads from the slurry. The ball milling beads are recycled back into the ball milling and shearing unit, and the slurry enters the particle size classification unit to classify the particles into substandard and standard particles. The substandard particles enter the ball milling and shearing unit for further ball milling, while the standard particles enter the encapsulation unit for encapsulation to obtain a highly stable micro-nano active material.

2. The method as described in claim 1, characterized in that, The ball mill shearing unit is equipped with a jacketed cooling structure, which stores circulating cooling water at 28~32℃, and can stabilize the temperature inside the ball mill shearing unit at 25~32℃.

3. The method as described in claim 1 or 2, characterized in that, The mass ball mill system also includes a dust removal unit and an exhaust fan unit located between the ball mill shearing unit and the air supply unit.

4. The method as described in claim 1, characterized in that, Sodium silicate powder and reduced iron powder are mixed at a silicon to iron molar ratio of 0.01 to 0.1; and / or, the sodium silicate powder is anhydrous sodium silicate powder with a purity ≥99%; and / or, the solid-liquid ratio of the iron-silicon composite material to oxygen-free water is 2 to 5 g / L.

5. The method as described in claim 1 or 4, characterized in that, The inert gas inlet flow rate is 1~8 m³ / h. 3 / h.

6. The method as described in claim 1 or 4, characterized in that, The mixing conditions are stirring at 600~1000 rpm for 10~30 min; and / or, the ball milling conditions are ball milling at 400~800 rpm for 4~20 h; and / or, during ball milling, the mass ratio of the ball milling beads to the iron-silicon composite material is (3~20):1; and / or, the ball milling beads are zirconia ball milling beads with a diameter of 6~10 mm.

7. The method as described in claim 1, characterized in that, The grading standard is as follows: particles with D50 ≤ 0.5 μm are considered to meet the standard, and particles with D50 > 0.5 μm are considered to fail to meet the standard.

8. The method as described in claim 1, characterized in that, The reduced iron powder contains ≥99.5 wt% zero-valent iron and has a particle size of 100~200 μm; and / or the reduced iron powder is treated to remove impurities, and its dispersibility is ≥90% after the impurity removal treatment.

9. The highly stable micro / nano active material prepared by the method according to any one of claims 1 to 8, characterized in that, The highly stable micro-nano active material consists of a zero-valent iron core and a silicate protective layer encapsulating the zero-valent iron core. Si-O-Fe bonds are formed between the silicate protective layer and the zero-valent iron core. The silicate coating includes hydroxyl-bonded silica polymers and multilayer silica structures.

10. A dechlorination agent, characterized in that, Including the highly stable micro / nano active materials as described in claim 9.

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