A green and economical ball milling reduction of micro-nano zero-valent iron and its application

Abstract

The present invention relates to green and economical ball-milled reduced micro-nano zero-valent iron and its applications. Using industrial ferric oxide powder as raw material, the green and economical ball-milled reduced micro-nano zero-valent iron is obtained through ball milling, freeze-drying, and hydrogen reduction. The present invention uses zirconia ball milling beads with an average particle size of 1 mm, a Mohs hardness of 11, and easy-to-clean but non-contaminated properties to mill the ferric oxide powder. After freeze-drying and reduction, the green and economical ball-milled reduced micro-nano zero-valent iron prepared has a particle size of 400-800 nm and a zero-valent iron content of 78%. The preparation cost is 14% of that of commercial nZVI, making it economical and green. This material can efficiently fix Cd in farmland soil, transferring Cd from a bioavailable form to a non-bioavailable form, reducing the likelihood of Cd accumulation in plants. Furthermore, the material also has excellent Cd removal capabilities in aqueous solutions. The preparation method proposed in the present invention is simple, easy to operate, and has the potential for large-scale production. Its Cd fixation performance is comparable to commercially available nano-zero-valent iron, and it can be applied to the remediation of Cd-contaminated farmland soil and water bodies.

Description

Technical Field

[0001] The present invention belongs to the field of functional nanomaterials and technologies, and specifically relates to green and economical ball-milled reduced micro-nano zero-valent iron and its application. Background Art

[0002] Nanoscale zero-valent iron (nZVI) is widely used in groundwater and soil pollution control due to its large surface area, high activity, and effective treatment. However, the main obstacles to its widespread adoption are the high application volume and high cost. nZVI preparation methods can be categorized as top-down or bottom-up. The top-down method includes mechanical ball milling, while the bottom-up methods include gas-phase reduction and liquid-phase reduction. However, the liquid-phase reduction method faces challenges in industrialization due to its high cost and severe secondary pollution.

[0003] Industrialized methods for producing nZVI include vapor-phase reduction and mechanical ball milling. Hydrogen vapor-phase reduction can effectively preserve the original particle morphology, but the cost of preparing the dispersed spherical nano-ferric oxide used for reduction accounts for nearly 60% of the total cost (Caroline et al., J. Hazard. Mater., 2021). Mechanical ball milling has advantages such as ease of operation, environmental friendliness, and affordability, but also has disadvantages such as difficulty controlling particle morphology. Directly milling micronized iron powder results in nanometer-thick iron flakes due to the metal's ductility, which have a lower specific surface area and activity than spherical nano-zero-valent iron. Ferric oxide is more brittle than iron and is easier to grind into nearly spherical particles. Furthermore, the industrial preparation of ferric oxide is very mature and inexpensive. Therefore, in this patent, the step of preparing ferric oxide in the vapor phase reduction method is replaced by ball milling. By using harder and easier-to-clean zirconium oxide ball milling beads to ball mill ferric oxide to the nanoscale, and then reducing it, a green and economical ball-milled reduced micro-nano zero-valent iron material is prepared. The market price of zero-valent iron with a particle size of 50nm to 100nm ranges from 1,600 yuan / kg to 17,000 yuan / kg, while the preparation cost of this material is low, with the laboratory preparation cost being only 36.4 yuan / kg. It is green and environmentally friendly and has great prospects for industrialization. In addition, the performance of this material is close to or even better than that of commercial nano zero-valent iron. In short, this invention provides a new design concept and technical method reference for the preparation of nano zero-valent iron materials. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the existing technology and provide a green and economical ball-milled reduced micro-nano zero-valent iron and its application.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a green and economical ball-milled reduced micro-nano zero-valent iron, wherein the green and economical ball-milled reduced micro-nano zero-valent iron is prepared by the following method:

[0007] (1) taking ferric oxide powder, a zirconia ball milling bead combination, and a grinding aid and placing them in a ball mill jar, wherein the zirconia ball milling bead combination consists of zirconia ball milling bead A, zirconia ball milling bead B, and zirconia ball milling bead C, wherein the diameter of the zirconia ball milling bead A is 10.0-10.2 mm, the diameter of the zirconia ball milling bead B is 5.0-5.2 mm, the diameter of the zirconia ball milling bead C is 1.0-1.2 mm, and the mass ratio of the zirconia ball milling bead A, zirconia ball milling bead B, and zirconia ball milling bead C is 1:2.0-3.0:18.0-20.0; the mass ratio of the ferric oxide to the zirconia ball milling bead combination is 1:30.0-32.0;

[0008] (2) The ball mill is then placed on a planetary ball mill for ball milling, and after the ball milling is completed, the ground ferric oxide powder is washed with water to obtain the ground ferric oxide powder;

[0009] (3) freezing the ground ferric oxide powder obtained in step (2) at -20 to -45°C for 10 to 12 hours or rapidly stirring with liquid nitrogen to obtain a ferric oxide powder solid;

[0010] (4) placing the ferric oxide powder solidified in step (3) into a freeze dryer and freeze-drying for 8 h, and passing through a 200-mesh sieve to obtain a freeze-dried powder;

[0011] (5) Take 2.0-2.5 g of the freeze-dried powder obtained in step (4) and spread it evenly in a calcined boat, put it into a reduction furnace, and heat it to a reduction temperature of 600-650° C. in a pure hydrogen atmosphere; after heating to the reduction temperature, keep it at this temperature for 60-75 minutes; then switch to argon gas, cool it to room temperature in an argon atmosphere, turn off the argon gas and keep it warm for 10-12 hours or continue to keep it warm for 0.5 hours in a mixed gas atmosphere to obtain green and economical ball-milled reduced micro-nano zero-valent iron.

[0012] Furthermore, the particle diameter of the ferric oxide powder is 100 to 4000 nm.

[0013] Furthermore, the grinding aid is pure water.

[0014] Furthermore, in step (2), the ball milling parameters are set to 350-450 rpm for 8-10 hours.

[0015] Furthermore, in step (5), the mixed gas consists of air and nitrogen.

[0016] Furthermore, the volume fractions of the gases in the mixed gas are: air accounts for 9% to 15%, and nitrogen accounts for 85% to 91%.

[0017] In a second aspect, the present invention provides a green and economical application of ball milling reduction of micro-nano zero-valent iron for the fixation of Cd in Cd-contaminated soil.

[0018] Furthermore, the method specifically includes the following steps:

[0019] (a1) 1–1.5 g of Cd-contaminated farmland soil was air-dried, ground, sieved, and placed in a centrifuge tube.

[0020] (a2) 0.001-0.1 g of green and economical ball-milled reduced micro-nano zero-valent iron was placed in a centrifuge tube containing Cd-contaminated farmland soil, and then purified water was added to cover the soil by 2-3 cm;

[0021] (a3) The centrifuge tube was then placed in a constant temperature incubator for 7 days at a temperature of 23.5-25°C to immobilize the Cd in the Cd-contaminated soil.

[0022] Furthermore, the concentration of Cd in the Cd-contaminated farmland soil is 17.0-17.4 mg / kg.

[0023] Furthermore, the dosage of the green and economical ball milling reduced micro-nano zero-valent iron is 10 to 1000 mg.

[0024] The beneficial effects of the present invention are:

[0025] (1) The green and economical ball-milling reduction method for preparing micro-nano zero-valent iron material is to first ball-mill the relatively brittle ferric oxide powder to the nanoscale and then reduce it, which is simple and easy to operate;

[0026] (2) This preparation method can produce zero-valent iron materials with properties close to or even exceeding those of commercially available nano-zero-valent iron, and the preparation cost is only 14% of that of commercial nano-zero-valent iron, which has good industrial value and prospects;

[0027] (3) The preparation method has mild reaction conditions and no secondary pollution;

[0028] (4) This material can efficiently fix the heavy metal pollutant Cd in soil and water. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the test result diagram of zero-valent iron content;

[0030] Figure 2 This is a thermal field emission scanning electron microscope characterization image and particle size test experimental image of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3, wherein: Figure 2(a) is a thermal field emission scanning electron microscope characterization image of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3. Figure 2 (b) is a graph showing the particle size test of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3;

[0031] Figure 3 The thermal field emission scanning electron microscope characterization and particle size test experimental diagram of micron zero-valent iron without ball milling and direct reduction are shown. Figure 3 (a) is a thermal field emission scanning electron microscope characterization image of micronized zero-valent iron directly reduced without ball milling. Figure 3 (b) is a graph showing the particle size of micron zero-valent iron directly reduced without ball milling;

[0032] Figure 4 This is a thermal field emission scanning electron microscope characterization image and particle size test experimental image of ferric oxide before ball milling, where: Figure 4 (a) is a thermal field emission scanning electron microscope characterization image of ferric oxide before ball milling. Figure 4 (b) is the experimental diagram of the particle size test of ferric oxide before ball milling;

[0033] Figure 5 The thermal field emission scanning electron microscope characterization diagram and particle size test experimental diagram of ferric oxide after ball milling are shown in FIG. Figure 5 (a) is the thermal field emission scanning electron microscope characterization image of iron sesquioxide after ball milling. Figure 5 (b) is the particle size test experimental diagram of ferric oxide after ball milling;

[0034] Figure 6 X-ray diffraction patterns of the green and economical ball-milled reduced micron-nano zero-valent iron, the directly reduced micron-zero-valent iron without ball milling, and the ball-milled ferric oxide prepared in Example 3;

[0035] Figure 7 This is a comparison chart of the preparation costs of the green and economical ball-milled reduced micro-nano zero-valent iron and commercial nano zero-valent iron prepared in Example 3;

[0036] Figure 8 This is the distribution of Cd in soil;

[0037] Figure 9 This is a graph showing the change of Cd removal rate over time. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to illustrate the present invention, rather than to represent all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0039] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0040] The present invention provides a green and economical ball-milled reduced micro-nano zero-valent iron, which is prepared by the following method:

[0041] (1) Ferrous oxide powder, a zirconium oxide ball milling bead combination, and a grinding aid are placed in a ball mill jar. The zirconium oxide ball milling bead combination consists of zirconium oxide ball milling bead A, zirconium oxide ball milling bead B, and zirconium oxide ball milling bead C. The diameter of the zirconium oxide ball milling bead A is 10.0-10.2 mm, the diameter of the zirconium oxide ball milling bead B is 5.0-5.2 mm, and the diameter of the zirconium oxide ball milling bead C is 1.0-1.2 mm. The mass ratio of the zirconium oxide ball milling bead A, the zirconium oxide ball milling bead B, and the zirconium oxide ball milling bead C is 1:2.0-3.0:18.0-20.0; the mass ratio of the ferrous oxide to the zirconium oxide ball milling bead combination is 1:30.0-32.0. The particle diameter of the ferrous oxide powder is 100-4000 nm. The grinding aid is purified water.

[0042] The zirconia ball milling beads used in the present invention have an average particle size of 1 mm and a Mohs hardness of 11. The zirconia ball milling beads are easy to clean but not easily contaminated, so that the preparation process of green and economical ball milling reduction of micro-nano zero-valent iron produces less pollution.

[0043] (2) The ball mill is then placed on a planetary ball mill for ball milling. After the ball milling is completed, the ground ferric oxide powder is washed with water to obtain the ground ferric oxide powder. The ball milling parameters are set to 350-450 rpm and the ball milling is carried out for 8-10 hours.

[0044] (3) Freezing the ground ferric oxide powder obtained in step (2) at -20 to -45°C for 10 to 12 hours or rapidly stirring with liquid nitrogen to obtain a ferric oxide powder solid.

[0045] (4) The ferric oxide powder solidified in step (3) was placed in a freeze dryer and freeze-dried for 8 h, and passed through a 200-mesh sieve to obtain a freeze-dried powder.

[0046] (5) 2.0-2.5 g of the freeze-dried powder obtained in step (4) was spread evenly in a calcined boat, placed in a reduction furnace, and heated to a reduction temperature of 600-650° C. in a pure hydrogen atmosphere; after heating to the reduction temperature, the temperature was kept at this temperature for 60-75 minutes; then argon was switched on, and after cooling to room temperature under the argon atmosphere, the argon was turned off and kept warm for 10-12 hours or continued to be kept warm for 0.5 hours under a mixed gas atmosphere to obtain green and economical ball-milled reduced micro-nano zero-valent iron. The mixed gas consists of air and nitrogen; the volume fractions of each gas in the mixed gas are: air accounts for 9%-15%, and nitrogen accounts for 85%-91%.

[0047] Example 1: A green and economical method for preparing micro-nano zero-valent iron by ball milling reduction

[0048] (1) Take 1.43g of ferric oxide powder, 2.0g of zirconia ball milling beads A, 4.1g of zirconia ball milling beads B, 36.8g of zirconia ball milling beads C, and 1.5mL of pure water and place them in a ball mill jar. The pure water is a grinding aid. The diameter of the zirconia ball milling beads A is 10.0mm, the diameter of the zirconia ball milling beads B is 5.0mm, and the diameter of the zirconia ball milling beads C is 1.0mm.

[0049] (2) The ball mill jar was then placed on a planetary ball mill for ball milling at a rotation speed of 350 rpm for 10 h. After the ball milling was completed, the ground ferric oxide powder was washed with water to obtain the ground ferric oxide powder.

[0050] (3) Freezing the ground ferric oxide powder obtained in step (2) at -20°C for 12 hours to obtain a ferric oxide powder solid.

[0051] (4) The ferric oxide powder solidified in step (3) was placed in a freeze dryer and freeze-dried for 8 h, and passed through a 200-mesh sieve to obtain a freeze-dried powder.

[0052] (5) 2.0 g of the freeze-dried powder obtained in step (4) was spread flatly in a calcined boat, placed in a reduction furnace, and heated to a reduction temperature of 600°C under a pure hydrogen atmosphere at a heating rate of 5°C / min; after heating to the reduction temperature, it was kept at this temperature for 75 minutes; then argon was switched, and after cooling to room temperature under argon atmosphere, the rubber tube at the tail end of the tubular furnace was taken out of the water, the argon was slowly turned off, and the temperature was kept for 10 hours to obtain green and economical ball-milled reduced micro-nano zero-valent iron ( BM / RE ZVI).

[0053] Example 2: A green and economical method for preparing micro-nano zero-valent iron by ball milling reduction

[0054] (1) Take 1.43g of ferric oxide powder, 2.0g of zirconia ball milling beads A, 4.4g of zirconia ball milling beads B, 38.2g of zirconia ball milling beads C, and 1.5mL of pure water and place them in a ball mill jar. The pure water is a grinding aid. The diameter of the zirconia ball milling beads A is 10.0mm, the diameter of the zirconia ball milling beads B is 5.0mm, and the diameter of the zirconia ball milling beads C is 1.0mm.

[0055] (2) The ball mill jar was then placed on a planetary ball mill for ball milling at a rotation speed of 400 rpm for 10 h. After the ball milling was completed, the ground ferric oxide powder was washed with water to obtain the ground ferric oxide powder.

[0056] (3) The ground ferric oxide powder obtained in step (2) is rapidly stirred and condensed with liquid nitrogen to solidify the ferric oxide and water to obtain a ferric oxide powder solid.

[0057] (4) The ferric oxide powder solidified in step (3) was placed in a freeze dryer and freeze-dried for 8 h, and passed through a 200-mesh sieve to obtain a freeze-dried powder.

[0058] (5) Take 2.5g of the freeze-dried powder obtained in step (4) and spread it flatly in a calcined boat, put it into a reduction furnace, and heat it to the reduction temperature of 600℃ under a pure hydrogen atmosphere at a heating rate of 5℃ / min; after heating to the reduction temperature, keep it at this temperature for 60min; then switch to argon gas, cool it to room temperature under argon atmosphere, take the rubber tube at the tail end of the tube furnace out of the water, slowly turn off the argon gas, and continue to stand for 12h to obtain green and economical ball-milled reduced micro-nano zero-valent iron ( BM / RE ZVI).

[0059] Example 3: A green and economical method for preparing micro-nano zero-valent iron by ball milling reduction

[0060] (1) Take 1.43g of ferric oxide powder, 2.0g of zirconia ball milling beads A, 4.1g of zirconia ball milling beads B, 36.8g of zirconia ball milling beads C, and 1.5mL of pure water and place them in a ball mill jar. The pure water is a grinding aid. The diameter of the zirconia ball milling beads A is 10.0mm, the diameter of the zirconia ball milling beads B is 5.0mm, and the diameter of the zirconia ball milling beads C is 1.0mm.

[0061] (2) The ball mill jar was then placed on a planetary ball mill for ball milling at a rotation speed of 450 rpm for 8 h. After the ball milling was completed, the ground ferric oxide powder was washed with water to obtain the ground ferric oxide powder.

[0062] (3) The ground ferric oxide powder obtained in step (2) is rapidly stirred and condensed with liquid nitrogen to solidify the ferric oxide and water to obtain a ferric oxide powder solid.

[0063] (4) The ferric oxide powder solidified in step (3) was placed in a freeze dryer and freeze-dried for 8 h, and passed through a 200-mesh sieve to obtain a freeze-dried powder.

[0064] (5) 2.5 g of the freeze-dried powder obtained in step (4) was spread flat in a calcined boat, placed in a reduction furnace, and heated to a reduction temperature of 600°C under a pure hydrogen atmosphere at a heating rate of 5°C / min; after heating to the reduction temperature, it was kept at this temperature for 60 minutes; then argon was switched, and after cooling to room temperature under argon atmosphere, the rubber tube at the tail end of the tubular furnace was taken out of the water, the argon was slowly turned off, and the mixed gas was slowly introduced and kept warm for 0.5 hours to obtain green and economical ball-milled reduced micro-nano zero-valent iron ( BM / RE ZVI); the mixed gas consists of air and nitrogen, and the volume fractions of the gases in the mixed gas are: air accounts for 10% and nitrogen accounts for 90%.

[0065] Application Example 1: Zero-valent Iron Content Test Experiment

[0066] 0.1 g of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Examples 1 to 3 was respectively placed in different sample bottles, and the green and economical ball-milled reduced micro-nano zero-valent iron powder was sucked to the top of the bottle wall of the sample bottle with a magnet, and 10 mL of a 1 mol / L sulfuric acid solution was added respectively, being careful not to let the sulfuric acid solution touch the green and economical ball-milled reduced micro-nano zero-valent iron powder; after sealing the sample bottle, the magnet was removed, and the green and economical ball-milled reduced micro-nano zero-valent iron powder was placed down to react with the sulfuric acid solution; after the green and economical ball-milled reduced micro-nano zero-valent iron powder had completed the reaction, the amount of hydrogen in the headspace of the sample bottle was measured in triplicate, and the zero-valent iron content in the green and economical ball-milled reduced micro-nano zero-valent iron powder was calculated. The calculation results are as follows: Figure 1 shown.

[0067] from Figure 1 It can be seen that the zero-valent iron content of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Examples 1 to 3 is all above 73%, which is higher than the commercially available nZVI (commercial nano zero-valent iron). The zero-valent iron content of Example 3 reaches 78.5%, indicating that the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3 has the highest reduction rate. The introduction of mixed gas for oxidation and stabilization of the green and economical ball-milled reduced micro-nano zero-valent iron can not only shorten the slow oxidation time, but also ensure the activity of the zero-valent iron.

[0068] Application Example 2: Thermal Field Emission Scanning Electron Microscopy (SEM) Characterization and Particle Size Measurement Experiment

[0069] Since the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3 has the highest content of zero-valent iron and the strongest activity, only the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3 ( BM / REZVI) and micronized zero-valent iron ( RE mZVI), ferric oxide before ball milling (Fe2O3), ferric oxide after ball milling ( BM Fe2O3) was characterized by thermal field emission scanning electron microscopy. The specific steps are as follows: the powder to be tested was completely dispersed with anhydrous ethanol, dropped on a silicon wafer, air-dried and then sprayed with gold, and then characterized by thermal field emission scanning electron microscopy. The particle size distribution of the powder to be tested was then calculated using the software ImaginJ. The characterization and calculation results are shown in Figure 2. Figure 2-Figure 5 shown. Figure 2 This is a thermal field emission scanning electron microscope characterization image and particle size test experimental image of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3. Figure 3 This is a thermal field emission scanning electron microscope characterization image and particle size test experimental image of micron zero-valent iron directly reduced without ball milling. Figure 4 This is the thermal field emission scanning electron microscope characterization image and particle size test experimental image of ferric oxide before ball milling. Figure 5 These are thermal field emission scanning electron microscope characterization images and particle size test experimental images of ferric oxide after ball milling.

[0070] from Figure 2-Figure 5 As can be seen, the average particle size of the ferric oxide powder before ball milling was 331 nm, while the average particle size after ball milling was 80 nm, a 76% reduction compared to the unmilled state. The initial agglomeration became more dispersed, facilitating the subsequent reduction step. The average particle size of the directly reduced micronized zero-valent iron without ball milling was 0.9 μm, with a smooth, flat surface and an irregular, polyhedral shape. The average particle size of the green and economically ball-milled, reduced micronized zero-valent iron was 0.7 nm, with a rough surface and a mostly cubic shape. This represents a 22% reduction in particle size compared to the directly reduced micronized zero-valent iron without ball milling.

[0071] Application Example 3: X-ray Diffraction (XRD) Test Experiment

[0072] The green economic ball milling reduction micro-nano zero-valent iron ( BM / RE ZVI), micron zero-valent iron ( RE mZVI), ball-milled ferric oxide ( BM Fe2O3) was tested by X-ray diffraction, and the test results were as follows Figure 6 shown.

[0073] from Figure 6 It can be seen that after ball milling, the iron oxide ( BM Fe2O3) shows the characteristic peak of ferric oxide, and the micronized zero-valent iron ( RE mZVI) and ball-milled ferric oxide ( BMFe2O3) only Fe 0 The characteristic peaks indicate that the powder is fully reduced.

[0074] Application Example 4: Cost Settlement of Green Economic Ball Milling Reduction of Micro-Nano Zero-Valent Iron and Commercial Nano-Zero-Valent Iron

[0075] The green economic ball milling reduction micro-nano zero-valent iron ( BM / RE A cost survey was conducted on the green economic ball-milled reduced micro-nano zero-valent iron (ZVI) and commercial nano-zero-valent iron (nZVI). The method was to list the preparation steps of green economic ball-milled reduced micro-nano zero-valent iron and commercial nano-zero-valent iron, and divide the items into raw material cost, processing cost, and treatment cost according to the purpose. Among them, the raw material cost includes the chemicals and gases used in the preparation process, the processing cost includes energy consumption, and the treatment cost includes wastewater and tail gas treatment, etc. The same unit price was used for specific items. For example, the "energy consumption" item used the price of half of the industrial and commercial and other electricity consumption less than 1 kilovolt in the "Zhejiang Power Grid Sales Electricity Price Table" (0.6964 yuan / kWh). The survey results are as follows Figure 7 shown.

[0076] from Figure 7 As can be seen, the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3 has a raw material cost of 6.7 yuan / kg, a processing cost of 29.7 yuan / kg, and a disposal cost of 0 yuan / kg, for a total cost of 36.4 yuan / kg. The cost of commercial nano-zero-valent iron is 64.3 yuan / kg for raw materials, 192.0 yuan / kg for processing, and 0.2 yuan / kg for disposal, for a total cost of 36.4 yuan / kg. The total cost of ball-milled reduced micro-nano zero-valent iron is 14% of the cost of commercial nano-zero-valent iron prepared using the same method. Furthermore, the ball-milled reduced zero-valent iron preparation process produces no waste gas or wastewater, and the disposal cost is zero. Compared to commercial nano-zero-valent iron, the production is both economical and environmentally friendly, demonstrating its promising industrial prospects.

[0077] Application Example 5: Cd Fixation Experiment in Soil

[0078] The collected in situ Cd-contaminated farmland soil (N: 30°32136"E119346") was air-dried, ground, and sieved to obtain the treated Cd-contaminated farmland soil.

[0079] Blank group: 1.0 g of treated Cd-contaminated farmland soil was placed in a 50 mL centrifuge tube.

[0080] Experimental Group: 1.0 g of treated Cd-contaminated farmland soil was placed in three 50 mL centrifuge tubes, and 1 mL of the green and economical ball-milled reduced micro-nano zero-valent iron prepared in Example 3 was added at a concentration of 1000 mg / L (high), 100 mg / L (medium), or 10 mg / L (low), respectively. The initial concentrations of the green and economical ball-milled reduced micro-nano zero-valent iron were 1000 mg / kg (high), 100 mg / kg (medium), and 10 mg / kg (low).

[0081] Control group: 1.0 g of treated Cd-contaminated farmland soil was placed in three 50 mL centrifuge tubes, and 1 mL of commercial nano-zero-valent iron (1000 mg / L (high), 100 mg / L (medium), or 10 mg / L (low) was added to each tube, respectively, so that the initial concentrations of commercial nano-zero-valent iron were 1000 mg / kg (high), 100 mg / kg (medium), and 10 mg / kg (low).

[0082] Subsequently, deionized water was added to 7 centrifuge tubes until the soil was covered by 2 cm, and the tubes were left to stand at 25 ° C for 7 days. The different forms of Cd in the soil were extracted by Tessir extraction after 7 days, and the Cd content was detected by ICP-MS. The proportion of Cd forms in the soil was Figure 8 shown.

[0083] from Figure 8 As can be seen, the predominant Cd form in the soil is a residual form. Both commercial nano-ZVI and green economic ball-milled reduced micro-nano-ZVI at a high concentration of 1000 mg / kg exhibited excellent fixation of exchangeable Cd in the soil. The green economic ball-milled reduced micro-nano-ZVI at 1000 mg / kg reduced exchangeable Cd in the soil from 7% to 0% within 7 days, while increasing carbonate-bound Cd from 1% to 4%, iron-manganese-oxidized Cd from 5% to 25%, and organic Cd from 3% to 13%, significantly outperforming commercial nano-ZVI at the same concentration. This demonstrates that the application of green economic ball-milled reduced micro-nano-ZVI can promote the transformation of Cd in the soil from a highly bioavailable form to a less bioavailable form, fully demonstrating the practical application potential of green economic ball-milled reduced micro-nano-ZVI in the remediation of high-Cd-contaminated soils.

[0084] Application Example 6: Cd Removal Experiment in Water

[0085] 500 mg of commercial nano zero-valent iron (nZVI) and the green economic ball-milled reduced micro-nano zero-valent iron ( BM / RE ZV) in two 10mL centrifuge tubes, add 5mL of oxygen-deficient deionized water, shake slowly and obtain nZVI mother solution and BM / RE ZVI mother solution: Dissolve 0.0205 g of CdCl2 in a 25 mL constant volume tube to obtain a 500 mg / L Cd solution.

[0086] Measure 97 mL of anoxic deionized water, insert the glass tube below the liquid surface for 10 seconds to drive out the air, add 1 mL of nZVI mother solution and 2 mL of Cd solution, and seal it. This is the nZVI treatment group.

[0087] Measure 97 mL of anoxic deionized water, insert the glass tube below the liquid surface for 10 seconds to drive out the air, and add 1 mL BM / RE ZVI mother solution and 2mL Cd solution, sealed, BM / RE ZVI-treated group.

[0088] Measure 98 mL of anoxic deionized water, insert the glass tube below the liquid surface for 10 seconds to drive out the air, add 22 mL of Cd solution, and seal it to serve as the blank control group.

[0089] Each treatment group was run in triplicate. At the pre-set time points, 2 mL of solution was taken and filtered through a 0.22 μm aqueous polyethersulfone filter membrane. The residual Cd content in the solution was determined by ICP-MS. The change in Cd concentration over time during the reaction was shown in Figure 2. Figure 9 shown.

[0090] from Figure 9 As can be seen, compared to the blank control group, both commercial nano-ZVI and green economic ball-milled reduced micro-nano-ZVI removed Cd from the solution. The green economic ball-milled reduced micro-nano-ZVI achieved a Cd removal rate of 70% after 96 hours, significantly exceeding the 17% removal rate of commercial nano-ZVI over the same time period. This fully demonstrates the potential of green economic ball-milled reduced micro-nano-ZVI for the treatment of Cd-contaminated water.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A green and economical ball milling reduction of micro-nano zero-valent iron, characterized by: The green and economical ball-milled reduced micro-nano zero-valent iron is prepared by the following method: (1) Iron oxide powder, a zirconium oxide ball milling bead combination, and a grinding aid are placed in a ball mill jar, wherein the zirconium oxide ball milling bead combination consists of zirconium oxide ball milling bead A, zirconium oxide ball milling bead B, and zirconium oxide ball milling bead C, wherein the diameter of the zirconium oxide ball milling bead A is 10.0-10.2 mm, the diameter of the zirconium oxide ball milling bead B is 5.0-5.2 mm, the diameter of the zirconium oxide ball milling bead C is 1.0-1.2 mm, and the mass ratio of the zirconium oxide ball milling bead A, the zirconium oxide ball milling bead B, and the zirconium oxide ball milling bead C is 1:2.0-3.0:18.0-20.0; the mass ratio of the iron oxide to the zirconium oxide ball milling bead combination is 1:30.0-32.0; and the particle diameter of the iron oxide powder is 100-4000 nm; (2) The ball mill is then placed on a planetary ball mill for ball milling. After the ball milling is completed, the ground ferric oxide powder is obtained by washing with water; (3) freezing the ground ferric oxide powder obtained in step (2) at -20 to -45°C for 10 to 12 hours or rapidly stirring with liquid nitrogen to obtain a ferric oxide powder solid; (4) The ferric oxide powder solidified in step (3) was placed in a freeze dryer and freeze-dried for 8 h, and passed through a 200-mesh sieve to obtain a freeze-dried powder; (5) Take 2.0-2.5 g of the freeze-dried powder obtained in step (4) and spread it evenly in a calcined boat, put it into a reduction furnace, and heat it to a reduction temperature of 600-650°C in a pure hydrogen atmosphere; after heating to the reduction temperature, keep it at this temperature for 60-75 minutes; then switch to argon gas, cool it to room temperature in an argon atmosphere, turn off the argon gas and keep it warm for 10-12 hours or continue to keep it warm in a mixed gas atmosphere for 0.5 hours to obtain green and economical ball-milled reduced micro-nano zero-valent iron; the mixed gas consists of air and nitrogen; the volume fractions of each gas in the mixed gas are: air accounts for 9%-15%, and nitrogen accounts for 85%-91%.

2. The green and economical ball-milled reduced micro-nano zero-valent iron according to claim 1, characterized in that: The grinding aid is pure water.

3. The green and economical ball-milled reduced micro-nano zero-valent iron according to claim 1, characterized in that: In step (2), the ball milling parameters are set to 350-450 rpm for 8-10 h.

4. An application of the green and economical ball-milled reduced micro-nano zero-valent iron according to claim 1 for the fixation of Cd in Cd-contaminated soil.

5. The use according to claim 4, characterized in that The specific steps include: (a1) 1–1.5 g of Cd-contaminated farmland soil was air-dried, ground, sieved, and placed in a centrifuge tube; (a2) Place 0.001-0.1 g of green and economical ball-milled reduced micro-nano zero-valent iron into a centrifuge tube containing Cd-contaminated farmland soil, and then add pure water to cover the soil by 2-3 cm; (a3) The centrifuge tube was then placed in a constant temperature incubator for 7 days at a temperature of 23.5-25°C to fix the Cd in the Cd-contaminated soil.

6. The use according to claim 4, characterized in that The concentration of Cd in the Cd-contaminated farmland soil is 17.0-17.4 mg / kg.

7. The use according to claim 4, characterized in that The dosage of the green and economical ball milling reduction of micro-nano zero-valent iron is 10-1000 mg / L.

Images