Preparation method and application of ball-milled charcoal loaded boron modified zero-valent iron material

Abstract

The invention discloses a preparation method and application of a ball-milled charcoal loaded boron modified zero-valent iron material, and relates to the technical field of nano zero-valent iron preparation. The invention aims to solve the problem of low Cr (VI) removal efficiency caused by the defects that zero-valent iron is easy to agglomerate and easy to oxidize and inactivate at present, and electrons of a core-shell structure are not easy to release and the like. Some iron-boron compounds are formed on the surface of the nZVI through doping of boron, so that reduction of reaction activity caused by formation of oxides on the surface of the nZVI is prevented, and the removal capacity of the nZVI to Cr (VI) is enhanced; in a mechanical ball milling process, along with fracture of chemical bonds and formation of new chemical bonds, a B-B bond formed by the BnZVI-coated BCBM material in the ball milling process can promote Fe (III) / Fe (II) circulation, so that the material has excellent Cr (VI) removal capability. The preparation method and application of the ball-milled charcoal loaded boron modified zero-valent iron material can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of nanometer zero-valent iron preparation, and in particular to a preparation method and application of a ball-milled biochar-loaded boron-modified zero-valent iron material. Background Art

[0002] With the development of industry, the problem of chromium (Cr) pollution in soil in my country is becoming increasingly serious, mainly due to improper discharge of chromium-containing industrial wastewater, accumulation of chromium slag and other factors. Chromium, as a highly toxic heavy metal, is widely present in the environment. Among them, Cr(III) is relatively stable in the soil, with low mobility and bioavailability; on the contrary, Cr(VI) is extremely toxic to organisms, more than 100 times that of Cr(III), and can cause serious damage to the skin, functional organs, intestines and immune system after contact. Therefore, exploring efficient strategies for remediation of chromium (VI) contaminated soil is a key issue that needs to be urgently addressed in the current field of environmental remediation.

[0003] At present, the remediation technologies for Cr(VI) soil contamination mainly include guest soil method, electrokinetic remediation, microbial remediation and chemical reduction technology. Given that Cr(III) has lower biological toxicity than Cr(VI), chemical reduction is often used to reduce Cr(VI) in soil to Cr(III) as an effective way to remediate soil chromium contamination. Among many reducing agents, nano zero-valent iron (nZVI) is widely used to treat Cr(VI) contaminated soil due to its low electrode potential and strong reaction activity. Its mechanism of removing Cr(VI) includes reduction and co-precipitation. However, the original nano zero-valent iron has problems such as easy agglomeration, easy oxidation and inactivation, and easy side reactions with H2O and dissolved oxygen. In addition, due to the typical core-shell structure of nZVI, iron oxides are deposited on the surface of nZVI during the reaction, resulting in low electron release efficiency. Therefore, how to improve the efficiency of nano zero-valent iron in the remediation process of hexavalent chromium contaminated sites is an urgent problem to be solved.

[0004] Commonly used nZVI modification techniques include porous material loading, surface modification (introduction of surfactants, etc.) and boron modification. Among them, biochar is widely used in loading modification due to its large specific surface area, rich pores, low cost and rich oxygen-containing functional groups. The use of boron for surface modification can effectively inhibit the competition of oxygen for electrons in the process of zero-valent iron removing heavy metals, thereby improving the efficiency of zero-valent iron in removing heavy metals and the utilization rate of electrons; in addition, the addition of boron can accelerate the iron cycle and improve the performance of nZVI in removing Cr(VI). At present, the preparation methods of zero-valent iron include common liquid phase reduction method, carbon thermal reduction method and mechanical ball milling method. Different preparation methods and preparation conditions have a great influence on the reactivity and material properties of nZVI. Therefore, it is extremely important to find a modification preparation method that is convenient, environmentally friendly, and can improve the defects of nZVI and be used for the efficient removal of heavy metals. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of low Cr(VI) removal efficiency caused by the easy agglomeration and oxidation deactivation of zero-valent iron and the difficulty in releasing electrons due to the core-shell structure, and to provide a preparation method and application of ball-milled biochar-loaded boron-modified zero-valent iron material.

[0006] A method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material is carried out according to the following steps:

[0007] Step S1: Preparation of straw biochar;

[0008] The corn stalks are crushed, dried and sieved, placed in a tube furnace, and then heated to 300-500° C. in a nitrogen atmosphere, and fully pyrolyzed at a temperature of 300-500° C. to obtain biochar;

[0009] Step S2: preparation of ball-milled biochar-loaded boron-modified zero-valent iron material;

[0010] The first step is ball milling, placing the biochar and iron powder obtained in step S1 in a ball milling jar, and placing the ball milling jar in a ball mill, and after sufficient ball milling, obtaining ball milled biochar loaded with zero-valent iron; the mass ratio of the biochar to the iron powder is (0.15-0.03): (2.4-2.6);

[0011] The second step is ball milling, wherein the ball-milled biochar loaded with zero-valent iron and boron oxide are placed in a ball milling jar, and the ball milling jar is placed in a ball mill. After sufficient ball milling, the ball milling jar is finally ground and sieved to obtain a ball-milled biochar loaded with boron-modified zero-valent iron material; the mass ratio of the ball-milled biochar loaded with zero-valent iron to the boron oxide is (2.4-2.6): (0.64-1.88);

[0012] The grinding balls in the ball mill are composed of large balls, medium balls and small balls, and the number ratio of the large balls, medium balls and small balls is (1-3): (14-16): (15-17).

[0013] An application of a ball-milled biochar loaded with boron-modified zero-valent iron material, and an application of the ball-milled biochar loaded with boron-modified zero-valent iron material in the passivation of heavy metal chromium.

[0014] Principle of the present invention:

[0015] First, nZVI has a lower electrode potential (E 0 (Fe 2+ / Fe 0 )=-0.44eV), so nZVI can act as a reducing agent or electron donor to reduce Cr(VI) by direct electron transfer, and nZVI loses electrons to generate Fe 2+Cr(VI) can also be further reduced. However, the original nZVI is easy to agglomerate and oxidize, which leads to a reduction in its specific surface area and active sites, hindering the transfer of electrons from nZVI to Cr(VI). B doping can change the physical and chemical properties of the material, such as enhancing the hydrophobicity and electron transfer ability of the material. At the same time, biochar loaded with nano zero-valent iron can effectively disperse nZVI, prevent nZVI from agglomerating, and improve its reaction activity, thereby significantly improving the removal ability of nZVI for Cr(VI).

[0016] In addition, during the mechanical ball milling process, BnZVI@BCBM was broken into small particles by the kinetic energy and mechanical stress generated by high-speed motion, and chemical reactions, chemical bond breaking and new bond formation occurred during the process. In particular, the BB bond can promote the Fe(III) / Fe(II) cycle, so it has excellent ability to remove Cr(VI), but boron oxide cannot promote the transformation of Fe(III) to Fe(II), indicating that the BB bond is not inherent in boron oxide, but is unique to BnZVI@BCBM obtained after nitrogen doping and ball milling.

[0017] Beneficial effects of the present invention:

[0018] 1. The present invention prepares biochar-loaded boron-modified zero-valent iron by ball milling to repair soil heavy metal chromium, which has the advantages of simple synthesis, good repair effect and green environmental protection. Its main mechanism of action includes:

[0019] (1) By incorporating boron, some iron-boron compounds are formed on the surface of nZVI to prevent the formation of oxides on the surface of nZVI, which would lead to a decrease in the reaction activity and enhance its ability to remove Cr(VI);

[0020] (2) Due to the large specific surface area and rich surface groups of biochar, the modification of zero-valent iron with biochar-loaded boron can weaken the easy agglomeration defects caused by the magnetism of nZVI itself and enhance the reactivity of nZVI;

[0021] (3) The mechanical ball milling process is accompanied by the breaking of chemical bonds and the formation of new chemical bonds. The BB bonds formed in the BnZVI@BCBM material during the ball milling process can promote the Fe(III) / Fe(II) cycle, so the material has an excellent ability to remove Cr(VI).

[0022] Therefore, the ball-milled biochar loaded with boron-modified zero-valent iron prepared by the present invention realizes the efficient adsorption and reduction of heavy metal chromium in farmland, and promotes the development and application of heavy metal repair agents in soil.

[0023] 2. Among the many modification methods, ball milling technology is a simple, efficient and economical modification method. Ball milling technology can form BB bonds to promote Fe(III) / Fe(II) circulation and enhance the removal effect of zero-valent iron on Cr(VI). Ball milling has been proven to improve the dispersion of iron oxide on the surface of biochar, thereby doubling the Cr(VI) adsorption capacity. In addition, ball milling technology can achieve large-scale production to meet the needs of agricultural land.

[0024] 3. The present invention prepares biochar loaded with boron-modified zero-valent iron by ball milling, explores the passivation performance of biochar loaded with boron-modified zero-valent iron composite materials on soil Cr, and analyzes its related action mechanism.

[0025] The present invention can obtain a preparation method and application of a ball-milled biochar-loaded boron-modified zero-valent iron material. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 represents a scanning electron microscope image of BnZVI@BCBM prepared in Example 1;

[0027] Figure 2 Elemental energy spectrum analysis diagram of BnZVI@BCBM prepared in Example 1;

[0028] Figure 3 represents the X-ray diffraction patterns of the different materials prepared in Examples 1-4, Fe 0 ;

[0029] Figure 4 The electrochemical impedance spectroscopy (EIS) analysis diagrams of different materials prepared in Examples 1-4 are shown;

[0030] Figure 5 Tafel corrosion curves of different materials prepared in Examples 1-4 are shown;

[0031] Figure 6 The figures show the removal effects of different systems on Cr(VI) in water in Examples 1-4; 1 represents nZVIBM, 2 represents nZVI@BCBM, 3 represents BnZVIBM, and 4 represents BnZVI@BCBM;

[0032] Figure 7 A diagram showing the remediation effects of different remediation materials in Examples 1-4 on Cr(VI) in soil. DETAILED DESCRIPTION

[0033] Specific implementation method 1: This implementation method is a method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material, which is carried out according to the following steps:

[0034] Step S1: Preparation of straw biochar;

[0035] The corn stalks are crushed, dried and sieved, placed in a tube furnace, and then heated to 300-500° C. in a nitrogen atmosphere, and fully pyrolyzed at a temperature of 300-500° C. to obtain biochar;

[0036] Step S2: preparation of ball-milled biochar-loaded boron-modified zero-valent iron material;

[0037] The first step is ball milling, placing the biochar and iron powder obtained in step S1 in a ball milling jar, and placing the ball milling jar in a ball mill, and after sufficient ball milling, obtaining ball milled biochar loaded with zero-valent iron; the mass ratio of the biochar to the iron powder is (0.15-0.03): (2.4-2.6);

[0038] The second step is ball milling, wherein the ball-milled biochar loaded with zero-valent iron and boron oxide are placed in a ball milling jar, and the ball milling jar is placed in a ball mill. After sufficient ball milling, the ball milling jar is finally ground and sieved to obtain a ball-milled biochar loaded with boron-modified zero-valent iron material; the mass ratio of the ball-milled biochar loaded with zero-valent iron to the boron oxide is (2.4-2.6): (0.64-1.88);

[0039] The grinding balls in the ball mill are composed of large balls, medium balls and small balls, and the number ratio of the large balls, medium balls and small balls is (1-3): (14-16): (15-17).

[0040] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that the drying temperature in step S1 is 60-80°C.

[0041] The other steps are the same as those in the first specific implementation.

[0042] Specific implementation method three: The difference between this implementation method and specific implementation method one or two is that in step S1, the dried product is sieved through a 100-mesh screen.

[0043] The other steps are the same as those in the first or second embodiment.

[0044] Specific embodiment 4: The difference between this embodiment and specific embodiments 1 to 3 is that the heating temperature in step S1 is 300-400°C.

[0045] The other steps are the same as those in Specific Embodiments 1 to 3.

[0046] Specific embodiment 5: The difference between this embodiment and specific embodiments 1 to 4 is that the pyrolysis time in step S1 is 2 to 3 hours.

[0047] The other steps are the same as those in Specific Embodiments 1 to 4.

[0048] Specific implementation method 6: The difference between this implementation method and specific implementation methods 1 to 5 is that the grinding balls described in step S2 are zirconium dioxide balls.

[0049] The other steps are the same as those in Specific Embodiments 1 to 5.

[0050] Specific implementation method 7: The difference between this implementation method and specific implementation methods 1 to 6 is that the rotation speed of the first ball milling in step S2 is 300 to 500 rpm, and the ball milling time is 3 to 5 hours.

[0051] The other steps are the same as those in Specific Embodiments 1 to 6.

[0052] Specific implementation eight: This implementation differs from specific implementations one to seven in that: the rotation speed of the second ball milling in step S2 is 300 to 500 rpm, and the ball milling time is 2 to 3 hours.

[0053] The other steps are the same as those in Specific Embodiments 1 to 7.

[0054] Specific embodiment 9: The difference between this embodiment and specific embodiments 1 to 8 is that after the second ball milling in step S2, the final grinding and passing through a 100-mesh sieve are performed.

[0055] The other steps are the same as those in Specific Embodiments 1 to 8.

[0056] Specific implementation method ten: This implementation method is an application of ball-milled biochar loaded with boron-modified zero-valent iron material, and the application of the ball-milled biochar loaded with boron-modified zero-valent iron material in the passivation of heavy metal chromium.

[0057] The following examples are used to verify the beneficial effects of the present invention:

[0058] Example 1: A method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material, comprising the following steps:

[0059] Step S1: Preparation of straw biochar;

[0060] The corn stalks were crushed, dried at 80°C, passed through a 100-mesh sieve, placed in a tube furnace, and then heated to 300°C under a nitrogen atmosphere and pyrolyzed at 300°C for 2h to obtain biochar;

[0061] Step S2: preparation of ball-milled biochar-loaded boron-modified zero-valent iron material;

[0062] The first step is ball milling, placing 0.15 g of biochar obtained in step S1 and 2.5 g of reduced iron powder in a ball milling jar, and placing the ball milling jar in a ball mill, and ball milling at a speed of 500 rpm for 3 h to obtain ball-milled biochar loaded with zero-valent iron;

[0063] In the second step, 2.5 g of ball-milled biochar loaded with zero-valent iron and 1.88 g of boron oxide were placed in a ball mill jar, and the ball mill jar was placed in a ball mill. The ball mill was milled at a speed of 500 rpm for 2 h. After the ball milling, the material in the agate jar of the ball mill was taken out, and finally ground and passed through a 100-mesh sieve to obtain the ball-milled biochar loaded with boron modified zero-valent iron material;

[0064] The grinding balls in the ball mill are zirconium dioxide balls, which are composed of large balls, medium balls and small balls. The number ratio of the large balls, medium balls and small balls is 2:16:15.

[0065] Example 2: In this example, the nanometer zero-valent iron material nZVIBM was prepared by ball milling. Other experimental conditions were the same as those in Example 1.

[0066] Example 3: In this example, ball milling was used to prepare nano zero-valent iron-biochar material nZVI@BCBM. Other experimental conditions were the same as those in Example 1.

[0067] Example 4: In this example, ball milling was used to prepare boron-modified nano zero-valent iron material BnZVIBM. Other experimental conditions were the same as those in Example 1.

[0068] The ball-milled biochar-loaded boron-modified zero-valent iron material prepared in this embodiment was subjected to scanning electron microscopy, elemental energy spectrum analysis, X-ray diffraction, electrochemical impedance spectroscopy (EIS) analysis, Tafel curve characterization, and the material's chromium removal experiment in water phase and soil chromium remediation experiment. The specific conclusions are as follows:

[0069] 1. Characterization (scanning electron microscopy, elemental energy spectrum analysis, X-ray diffraction, electrochemical impedance spectroscopy (EIS) analysis, Tafel curve):

[0070] The surface morphology, elemental composition, and crystal structure of BnZVI@BCBM were determined by scanning electron microscopy, elemental energy spectrum analysis, and X-ray diffraction. BnZVI@BCBM was electrochemically characterized by electrochemical impedance spectroscopy (EIS) analysis and Tafel curves to explore its charge transfer resistance and self-corrosion potential.

[0071] Figure 1 The scanning electron microscope image of BnZVI@BCBM prepared in Example 1 is shown; Figure 1 As shown, BnZVI@BCBM appears as irregular particles with a rough surface and small particle size, and nZVI is evenly dispersed on the surface of biochar, indicating the strong dispersion ability of biochar.

[0072] Figure 2 Elemental energy spectrum analysis diagram of BnZVI@BCBM prepared in Example 1; Figure 2As shown in the figure, the iron element is distributed relatively evenly on the surface of BM-ZVI / BC, which indicates that the deformation and agglomeration of nZVI are significantly alleviated during the ball milling process.

[0073] Figure 3 represents the X-ray diffraction patterns of the different materials prepared in Examples 1-4, Fe 0 ;like Figure 3 As shown, nZVIBM, nZVI@BCBM, BnZVIBM and BnZVI@BCBM have obvious peaks at 44.6°, 65.0° and 82.3°, corresponding to Fe 0 The (110), (200) and (211) diffraction peaks of the nZVI crystal planes indicate that the crystal structure of the material has not changed during the ball milling process, and Fe0 is still the main phase.

[0074] Figure 4 The electrochemical impedance spectroscopy (EIS) analysis diagrams of different materials prepared in Examples 1-4 are shown; Figure 4 As shown, the electrochemical impedance spectroscopy (EIS) test results show that the charge transfer resistance of BnZVI@BCBM is the smallest, proving that boron doping and biochar loading reduce the charge transfer resistance of the material and are more conducive to electron transfer.

[0075] Figure 5 The Tafel corrosion curves of different materials prepared in Examples 1-4 are shown; Figure 5 As shown in Figure 2, the order of corrosion potential of different materials observed from the Tafel corrosion curve is nZVIBM (-0.52V) > nZVI@BCBM (-0.76V) > BnZVIBM (-1.02V) > BnZVI@BCBM (-1.07V). BnZVI@BCBM has the lowest corrosion potential, which means that BnZVI@BCBM has a faster electron release rate, which is beneficial to the reduction of Cr(VI) by the material.

[0076] 2. Effect of different materials on the removal of Cr(VI):

[0077] The adsorption process was as follows: 0.05 ± 0.005 g of different nZVIBM, nZVI@BCBM, BnZVIBM, and BnZVI@BCBM were weighed using a balance and added to a 150 mL conical flask, and then 100 mL of a 200 mg / L Cr(VI) solution was added to the conical flask, and the initial pH of the solution was adjusted to 2.0 ± 0.1 with 1 M HCl. After shaking at 200 rpm for 2 h, the concentration of Cr(VI) in the solution was measured, and the removal rate of the adsorbent material was calculated.

[0078] Figure 61 represents the removal effect of Cr(VI) in water by different systems in Examples 1-4; 1 represents nZVIBM, 2 represents nZVI@BCBM, 3 represents BnZVIBM, and 4 represents BnZVI@BCBM; Figure 6 As shown in the figure, the removal effect of nZVIBM on Cr(VI) is not obvious. After biochar loading, the removal rate of nZVI@BCBM on Cr(VI) increased. In addition, the effect of BnZVIBM on Cr(VI) after boron modification was further improved compared with nZVIBM. After the zero-valent iron loaded with biochar was doped with boron, BnZVI@BCBM almost achieved 100% removal of Cr(VI). The results show that boron doping and biochar loading are both beneficial to improve the removal of Cr(VI) by nZVI.

[0079] 3. Removal effect of ball-milled biochar loaded with boron-modified zero-valent iron material on soil Cr(VI):

[0080] Experimental conditions: Soil was collected from the campus of Northeast Agricultural University in Harbin, Heilongjiang Province. It is a typical black loam. 2 kg of sieved soil samples were placed in a plastic box. 500 mL of 2000 mg / L K2Cr2O7 solution was evenly sprayed on the soil with a spray bottle. After sufficient stirring, it was left to age for 30 days to obtain 1000 mg / L Cr(VI) contaminated soil. The soil moisture content was adjusted to 40% after passing through a 20-mesh sieve. In this study, three parallel samples were tested simultaneously for each treatment. In soil with a moisture content of 40%, 1% of different types of adsorbents (nZVIBM, nZVI@BCBM, BnZVIBM and BnZVI@BCBM) were applied for a 42-day remediation test. A certain amount of soil samples were taken using the five-point method on the 0th, 3rd, 7th, 14th, 21st, 28th, 35th and 42nd day of remediation, and the Cr(VI) concentration in the soil was determined by alkaline digestion.

[0081] Figure 7 The figure shows the repair effect of different repair materials on Cr(VI) in soil in Examples 1-4; Figure 7As shown, after 42 days of remediation of contaminated soil using nZVIBM, nZVI@BCBM, BnZVIBM and BnZVI@BCBM as passivators, the Cr(VI) concentrations in the soil decreased to varying degrees, decreasing to 503.12 mg / kg, 378.54 mg / kg, 216.73 mg / kg and 50.53 mg / kg, respectively. Comparing the passivation rates of four passivators on soil Cr(VI), nZVIBM has a passivation rate of 44.10%, which is because the individual iron particles tend to agglomerate after entering the soil, which inhibits its reduction performance of soil Cr(VI); while the modified BnZVI@BCBM has the highest passivation efficiency on soil Cr(VI), reaching 94.38%, which may be due to: on the one hand, BC has a strong dispersion effect on the material, inhibiting the agglomeration of the material after entering the soil; on the other hand, the mechanical ball milling process is accompanied by the breaking of chemical bonds and the formation of new chemical bonds. The BB bonds formed by the BnZVI@BCBM material during the ball milling process can promote the Fe(III) / Fe(II) cycle, so the material has excellent ability to remove Cr(VI). In summary, BnZVI@BCBM is an efficient soil heavy metal passivator.

Claims

1. A method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material, characterized in that The preparation method is carried out according to the following steps: Step S1: Preparation of straw biochar; The corn stalks are crushed, dried and sieved, placed in a tube furnace, and then heated to 300-500° C. in a nitrogen atmosphere, and fully pyrolyzed at a temperature of 300-500° C. to obtain biochar; Step S2: preparation of ball-milled biochar-loaded boron-modified zero-valent iron material; The first step is ball milling, placing the biochar and iron powder obtained in step S1 in a ball milling jar, and placing the ball milling jar in a ball mill, and after sufficient ball milling, obtaining ball milled biochar loaded with zero-valent iron; the mass ratio of the biochar to the iron powder is (0.15-0.03): (2.4-2.6); The second step is ball milling, wherein the ball-milled biochar loaded with zero-valent iron and boron oxide are placed in a ball milling jar, and the ball milling jar is placed in a ball mill. After sufficient ball milling, the ball milling jar is finally ground and sieved to obtain a ball-milled biochar loaded with boron-modified zero-valent iron material; the mass ratio of the ball-milled biochar loaded with zero-valent iron to the boron oxide is (2.4-2.6): (0.64-1.88); The grinding balls in the ball mill are composed of large balls, medium balls and small balls, and the number ratio of the large balls, medium balls and small balls is (1-3): (14-16): (15-17).

2. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that The drying temperature in step S1 is 60-80°C.

3. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that After drying in step S1, the product is sieved through a 100-mesh sieve.

4. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that The heating temperature in step S1 is 300-400°C.

5. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that The pyrolysis time in step S1 is 2 to 3 hours.

6. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that The grinding balls described in step S2 are zirconium dioxide balls.

7. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that In step S2, the rotation speed of the first ball milling is 300-500 rpm, and the ball milling time is 3-5 hours.

8. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that The rotation speed of the second ball milling in step S2 is 300-500 rpm, and the ball milling time is 2-3 hours.

9. The method for preparing a ball-milled biochar-loaded boron-modified zero-valent iron material according to claim 1, characterized in that After the second ball milling in step S2, the product is finally ground and passed through a 100-mesh sieve.

10. Use of a ball-milled biochar-loaded boron-modified zero-valent iron material prepared by the method according to any one of claims 1 to 9, characterized in that The application of the ball-milled biochar-loaded boron-modified zero-valent iron material in the passivation of heavy metal chromium.

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